a(CHEBI:heme) CO inhibits Hb oxidation and subsequently heme release, thus blocking heme accumulation in serum and preventing heme from exerting its inflammatory effects in the course of malaria disease (Ferreira et al., 2011). PubMed:24904418
Within cells, heme is catabolized by the activity of heme oxygenases (inducible HO-1 and constitutive HO-2) into iron, carbon monoxide, and biliverdin. PubMed:26675351
Besides its physiological importance, heme has a potent oxidative capacity oxidizing lipids (Tappel, 1953, 1955; Vincent et al., 1988) and proteins (Aft and Mueller, 1984; Vincent, 1989), and damaging DNA (Aft and Mueller, 1983). PubMed:24904418
As shown in Figure 3, the level of heme degradation is highly correlated with the level of metHb in RBCs (R = 0.6233, p < 0.0177) supporting the hypothesis that the heme degradation product formed in PRDX2 knockout mice is associated with the un-scavenged H2O2 generated during Hb autoxidation. PubMed:23215741
Within cells, heme is catabolized by the activity of heme oxygenases (inducible HO-1 and constitutive HO-2) into iron, carbon monoxide, and biliverdin. PubMed:26675351
Under heme overload conditions, macrophages acquire an iron phenotype characterized by low intracellular iron and high ferroportin expression. PubMed:29212341
Pb treatment has been demonstrated to reduce heme availability for globin assembly.38 PubMed:25411909
The main mediator of these adverse effects is thought to be free haem via its effects on NO scavenging, pro-inflammatory cytokine responses, and reactive oxygen species (ROS) generation. PubMed:25307023
In fact, heme-induced LDL oxidation is highly cytotoxic for endothelial cells and LDL oxidation seems to be mediated by Fe (Jeney et al., 2002; Nagy et al., 2010). PubMed:24904418
Thus, the antioxidant, anticoagulant, anti-proliferative and vasodilating effects of the HMOX1 and biliverdin reductase systems probably compensate for the nitric oxide (NO) scavenging, vasoconstrictive, proliferative, inflammatory and pro-oxidant effects of circulating free haemoglobin, haem and haem-iron, which are discussed below (Rother et al, 2005). PubMed:25307023
Within cells, heme is catabolized by the activity of heme oxygenases (inducible HO-1 and constitutive HO-2) into iron, carbon monoxide, and biliverdin. PubMed:26675351
Hp bound metHb and prevented heme loss and hemopexin captures any free heme released from metHb during its denaturation. PubMed:24486321
In subsequent reactions, metHb or metHb-derived heme participates in redox chain reactions that lead to the accumulation of modified lipids and proteins, as well as to heme degradation and to the release of free iron.19,25 PubMed:29610666
The small increase in heme degradation in the absence of SOD1 may, however, be attributed to low levels of heme degradation products produced either by the increased levels of superoxide [17] or perhaps the peroxynitrite that forms due to the rapid reaction of superoxide with any NO present. PubMed:23215741
Figures 5A-5B, show that at d7, faster rates for nitrite oxidation in the lag phase were positively associated with higher concentrations of extracellular free heme at d7 and d35. PubMed:26202471
Ferryl heme and associated protein radicals with high redox potentials (~1.0 V) can induce a wide variety of oxidative reactions that affect the protein and nearby molecules [2]. PubMed:24486321
Figures 2A-F show changes in oxyhemoglobin, methemoglobin and free heme in both the intraerythrocytic and supernatant fractions in both d7 and d35 RBC. Significant storage-dependent increases for all species in the cell-free fraction were observed, with no storage-dependent differences observed in the erythrocyte. PubMed:26202471
More recently, we have also shown that free heme is also released during storage and may mediate further inflammation28 PubMed:26202471
Consistent with our previous studies [25,36], free oxyHb, metHb, and heme levels were increased after 14 d of RBC storage, being 930 ± 125 μM, 40.3 ± 8.8 μM, and 168 ± 44.7 μM, respectively (mean ± SEM, n = 7). PubMed:29522519
Fig 2 shows that free hemoglobin and free heme were higher 4 h after resuscitation with stored RBCs compared to fresh RBCs (n = 3±7 as indicated); NTBI level was also higher, but this difference did not reach statistical significance (p = 0.07). PubMed:29522519
The results reported here indicate that, once exposed to oxidized plaque material, erythrocytes are lysed, the liberated hemoglobin is oxidized and heme dissociates from the resultant ferrihemoglobin. PubMed:20378845
There is a clear need for, and medical benefit from, blood transfusions; nonetheless, administration of red blood cells (RBCs) does result in exposure to toxicants specific to hemoglobin (Hb) and its degradation components, hemin and iron. PubMed:30281034
Free heme has been proved possess pro-inflammatory activities, such as leukocyte activation, migration and infiltration, adhesion molecules activation, and cytokines and acute phase proteins induction [17, 18]. PubMed:24464629
Hemin induces expression of the adhesion molecules on endothelial cells [7, 8] and enables firm neutrophil attachment to the endothelium and initiation of an inflammatory response [9, 10]. PubMed:28716864
Based on the previous findings that hemin induces neutrophil adhesion to endothelial cells [8] and that A1AT protects endothelial cells from neutrophil adhesion induced by fMLP [27], we investigated whether A1AT, as a scavenger of hemin, can prevent hemin-induced neutrophil adhesion to HUVECs. As shown in Fig. 4, neutrophils treated with hemin or fMLP (used as a positive control) exhibited a 3-fold higher adhesion to HUVECs compared with controls. However, the adherence of neutrophils treated with hemin/A1AT did not differ from controls (Fig. 4). PubMed:28716864
However, at higher heme concentrations (20 and 40 μM), we observed a cytotoxic response with the irreversible breakdown of the epithelial barrier. PubMed:26794659
Accordingly, higher levels of lipid peroxide-protein adducts were detected in heme-treated Hmox1 (− /−) than in Hmox1 (+/+) MEF cells when the cells were heme exposed in the presence of an alkyne-tagged analog of linoleic acid, which is an unsaturated, heme-reactive fatty acid (Supplementary Figure 3). PubMed:25301065
The main mediator of these adverse effects is thought to be free haem via its effects on NO scavenging, pro-inflammatory cytokine responses, and reactive oxygen species (ROS) generation. PubMed:25307023
Toxicity of free hemoglobin is also caused by the release of cell-free heme, which produces lipid peroxidation and mitochondrial damage and increases the production of reactive oxygen species. PubMed:27515135
Heme is an amphipathic molecule that can promote the generation of reactive oxygen species (ROS) via Fenton chemistry, thereby leading to membrane damage. PubMed:27798618
As expected, incubation of neutrophils with hemin resulted in a significant number of cells producing ROS (Fig. 8A and B). PubMed:28716864
Free heme has been proved possess pro-inflammatory activities, such as leukocyte activation, migration and infiltration, adhesion molecules activation, and cytokines and acute phase proteins induction [17, 18]. PubMed:24464629
Upon degradation of RBCs in the erythrophagosome, heme is imported into the cytoplasm for degradation by the heme-degrading enzyme heme oxygenase-1 (HMOX1) [7]. PubMed:30248094
Like MetHb, ferrylHb is unstable and releases free heme to further increase oxLDL formation (Potor et al., 2013). PubMed:24904418
We quantified these changes by automatic image analysis and found that heme-induced cytoskeleton rearrangement led to a significant increase in cell area and perimeter, as well as a decrease in circularity (form factor) (Fig. 4d,e and Supplementary Fig. 3b–d), indicating that the heme-induced defective phagocytic response was likely tied to cytoskeleton rearrangements. PubMed:27798618
Taken sequentially, it appears that the release of heme under hemolytic conditions initiates the extrinsic pathway of coagulation through the upregulation of TF on endothelial cells and leukocytes, but subsequently blocks the propagation of coagulation by inhibiting FVIII and FV, and by inhibiting the conversion of fibrinogen into fibrin and fibrin clots. PubMed:26875449
These data, in addition to older biochemical studies that empirically used heme to inhibit proteasome function in biochemical assays, led us to the hypothesis that excessive intracellular heme could disrupt cellular protein homeostasis by an inhibitory action on the proteasome. PubMed:25301065
The proteasome is the principal pathway to remove senescent and damaged proteins, and intact proteasome function is essential to preserve and repair cellular homeostasis during oxidative stress, such as that triggered by heme exposure.27 PubMed:25301065
Free hemin is a cytotoxic molecule that mediates oxidative stress, endothelial activation, and inflammation, and it is implicated in malaria pathogenesis [40] and AKI, among others [41]. PubMed:28716864
In addition, we observed that heme treatment of RAW264.7 macrophages led to a dose-dependent inhibition of apoptotic cell uptake (Supplementary Fig. 2m). PubMed:27798618
These observations suggest that in any physiological scenario in which heme might be present in extracellular spaces as a component of a natural hemoprotein, the concentration of free or quasi-free heme can be expected to be very low, possibly below the minimum range required to trigger granulocyte activation and other innate immunity responses. PubMed:29610666
As a component of hemoglobin, free heme is released when hemolysis or extensive cell damage occur which results in inflammatory response. PubMed:24464629
Hemin induces expression of the adhesion molecules on endothelial cells [7, 8] and enables firm neutrophil attachment to the endothelium and initiation of an inflammatory response [9, 10]. PubMed:28716864
Free heme has been proved possess pro-inflammatory activities, such as leukocyte activation, migration and infiltration, adhesion molecules activation, and cytokines and acute phase proteins induction [17, 18]. PubMed:24464629
As a consequence, infused heme (hemin) has been demonstrated to enhance leukocyte adhesion to the vessel wall (17, 18), a finding confirmed in the current study. PubMed:19276082
Heme injection in mice leads to vascular permeability, leukocyte migration from the intravascular environment to tissues and increase of acute-phase proteins (Lyoumi et al., 1999; Wagener et al., 2001b), hallmarks of acute inflammation. PubMed:24904418
By modeling the equilibrium concentration in the experiments performed with heme-albumin we could show that the free heme is the active neutrophil-stimulating component, which is inactivated by protein association (Figure S2). PubMed:29610666
Besides its physiological importance, heme has a potent oxidative capacity oxidizing lipids (Tappel, 1953, 1955; Vincent et al., 1988) and proteins (Aft and Mueller, 1984; Vincent, 1989), and damaging DNA (Aft and Mueller, 1983). PubMed:24904418
Free heme is lipophilic and intercalates into the membrane of endothelial cells increasing vascular permeability and ICAM-1, VCAM-1, and E-selectin expression (19). PubMed:19276082
Heme injection in mice leads to vascular permeability, leukocyte migration from the intravascular environment to tissues and increase of acute-phase proteins (Lyoumi et al., 1999; Wagener et al., 2001b), hallmarks of acute inflammation. PubMed:24904418
For example, the in vitro appearance of strong reactivity towards phospholipids of antibodies from normal human plasma following exposure to heme suggests that heme, when released in vivo, may perturb coagulation processes indirectly via its effects on antibodies. PubMed:26875449
Following i.p. E. coli infection, we observed a significant increase in plasma heme levels in LysM-Cre+/−Hmox1fl/fl mice (Fig. 1e and Supplementary Fig. 1c), which was accompanied by increased bacterial numbers in blood and liver (Fig. 1f and Supplementary Fig. 1d) and impaired survival (Fig. 1g) when compared with LysM-Cre−/−Hmox1fl/fl controls. PubMed:27798618
Thus, enhanced levels of plasma heme, induced by either exogenous heme administration or a lack of HO-1 expression in macrophages, resulted in an increased susceptibility to E. coli sepsis. PubMed:27798618
Plasma heme amounts were comparable in mice pretreated with Fe3+ or PBS (Fig. 2d), and despite the similarly increased availability of iron in both heme- and Fe3+-treated mice (Fig. 2e), only heme-treated mice presented a significantly higher bacterial burden in the blood and liver compared with PBS- or Fe3+-treated mice (Fig. 2f). PubMed:27798618
These results indicate that increased heme concentrations directly lead to increased bacterial counts during sepsis and that bacterial iron requirements are met via heme-independent mechanisms. PubMed:27798618
Whereas at the doses of 3, 4, and 5 μM, heme significantly reduced the viability of cells, which was in agreement with an earlier study [1]. PubMed:30324533
Sickle cell disease (SCD) and malaria are paradigmatic hemolytic disorders, in which alteration in the structure of red blood cells (RBCs) leads to the release of Hb and heme into the circulation. PubMed:26675351
Previously we have shown that heme can enter the lipid moiety of LDL and induce iron-dependent lipid peroxidation.8 PubMed:20378845
Here we demonstrate that lipids isolated from human atheromatous lesions – which are already in an oxidized state – can be further oxidized in the presence of heme, whereas this effect is not observed using lipids isolated from normal vasculature. PubMed:20378845
Thus, it appears that these extracts oxidize ferrohemoglobin to ferrihemoglobin, thereby leading to heme instability and heme-mediated initiation of lipid peroxidation. PubMed:20378845
Besides its physiological importance, heme has a potent oxidative capacity oxidizing lipids (Tappel, 1953, 1955; Vincent et al., 1988) and proteins (Aft and Mueller, 1984; Vincent, 1989), and damaging DNA (Aft and Mueller, 1983). PubMed:24904418
Free heme is a potent trigger of lipid peroxidation and a promoter of inflammation.4–6 PubMed:26794659
Toxicity of free hemoglobin is also caused by the release of cell-free heme, which produces lipid peroxidation and mitochondrial damage and increases the production of reactive oxygen species. PubMed:27515135
Reduced glutathione (GSH) was also depleted after 4 h of heme exposure, indicating that heme induces oxidative stress in exposed cells (Figure 5c). PubMed:26794659
These data suggest that the estimated free heme concentrations that occur in the renal tubular system during severe intravascular hemolysis are in the range of heme concentrations that could trigger oxidative stress and cell damage to the renal epithelium. PubMed:26794659
Free hemin is a cytotoxic molecule that mediates oxidative stress, endothelial activation, and inflammation, and it is implicated in malaria pathogenesis [40] and AKI, among others [41]. PubMed:28716864
During hemolysis, hemoglobin and heme released from red blood cells promote oxidative stress, inflammation and thrombosis. PubMed:29694434
There are in vitro and animal model data linking increased free Hb, heme, and iron to inflammation, 6 infection,7 platelet (PLT) activation,8,9 vasculopathy, 10 and thrombosis. PubMed:29603246
Ultimately, we found that uncontrolled cellular heme levels can activate the response to unfolded proteins and associated apoptosis pathways in mouse embryonic fibroblast cells. PubMed:26794659
We focused on macrophage effector functions and found that heme pretreatment (15 min, 3–30 μM unless otherwise indicated) led to a strong, dose-dependent reduction of phagocytosis of E. coli by RAW264.7 macrophages compared with DMSO-treated controls (Fig. 3a,b and Supplementary Fig. 2a). PubMed:27798618
Induction of hemolysis with phenylhydrazine or addition of heme to whole blood at concentrations mimicking the physiological range of plasma heme in hemolytic patients (5–50 μM)6 led to a dose-dependent impairment of E. coli phagocytosis by neutrophils and monocytes, as compared with DMSO controls (Fig. 3g and Supplementary Fig. 2n,o), indicating that our mouse model was reflective of human hemolytic conditions. PubMed:27798618
In that study, heme was shown to specifically bind to endothelial Toll-like receptors (TLR4) and trigger a cascade of inflammatory responses, which could be attributed to oxidation and degradation of cell-free Hb [73]. PubMed:24486321
Hemolysis increases the concentration of Hb which, under oxidative stress, releases free heme. PubMed:24904418
Exposure to Hb and its oxidized products increases heme overload on the AT1 cells. Heme overload induces the expression of HO-1 and iron-sequestering proteins, such as ferritin. PubMed:26974230
Toxicity of free hemoglobin is also caused by the release of cell-free heme, which produces lipid peroxidation and mitochondrial damage and increases the production of reactive oxygen species. PubMed:27515135
Extracellular hemoglobin and its degradation products, free heme and iron, are highly toxic due to oxidative stress induction and decrease in nitric oxide availability. PubMed:28088643
For instance, earlier studies have demonstrated that neutrophil elastase degrades the hemoglobin liberating free hemin that induces ROS production. PubMed:28716864
Serum albumin (SA) can act as the heme scavenger by forming heme-SA complex [2, 4–8]. PubMed:30324533
This serum protein, present at remarkably high concentrations in plasma (≈1g/L), binds heme with extraordinary avidity (Kd less than 1 pmol/ L) and promotes its clearance. PubMed:20378845
Importantly, heme b interaction with heme oxygenase (HO; Lad et al., 2003), the enzyme responsible for heme intracellular catabolism, and hemopexin (Hx; Paoli et al., 1999), a plasmatic heme scavenger, is essential for the regulation of free heme availability and Fe recycling (Kovtunovych et al., 2010; Tolosano et al., 2010). PubMed:24904418
Based on clinical observations the Hb and heme scavenger proteins haptoglobin (Hp) and hemopexin (Hx) have been characterized as a sequential defense system with Hp as the primary protector and Hx as a backup when all Hp is depleted during more severe intravascular hemolysis. PubMed:26475040
Recently, we demonstrated that Hx controls hepatic heme uptake and thus limits heme accumulation in extrahepatic tissues, such as the vessel wall and the heart, preventing heme-induced toxicity and tissue injury. PubMed:26675351
Taken together, these data demonstrate that Hx limits macrophage heme overload and prevents the prooxidant and proinflammatory effects triggered by heme in cellular assays and in vivo. PubMed:26675351
Thus, the interactions of hemoglobin with haptoglobin, and of heme with hemopexin, ensure safe disposal of potentially dangerous molecules [6,7,15–19] PubMed:26875449
Heme released from cell-free hemoglobin on oxidation is bound by hemopexin and degraded by hepatocytes in the liver [12]. PubMed:29956069
Of the biological components known to bind hemin, Hpx is by far the most efficient with a dissociation constant (Kd) lower than 1 x 10–13 M; as a result, after binding, the transfer of hemin from Hpx to other proteins or lipids is not possible [24]. PubMed:30281034
On the extracellular level, within the circulation, haptoglobin (Hp) and hemopexin (Hpx) are two of the most prominent scavenger proteins, with antioxidative properties through their capacity to remove cell-free Hb (by Hp) and heme (by Hpx). PubMed:30505280
Therefore, we demonstrated that an active scavenging of heme by NEAT can reduce peroxidase activity of hemoglobin, whereas passive scavengers cannot. PubMed:28088643
Hp bound metHb and prevented heme loss and hemopexin captures any free heme released from metHb during its denaturation. PubMed:24486321
The increase in hemopexin was associated with decreased plasma heme levels (Figure 3I). PubMed:27515135
Hx-heme-treated CMs were protected from heme accumulation, compared to cells treated with albumin-heme or heme alone (Figure 1A), indicating that Hx prevents heme entry in cardiac cells. PubMed:28400318
Other studies demonstrated that heme can trigger the activation of Toll-like receptor 4 and inflammasomes, thus leading to inflammatory reactions.5,35–37 PubMed:26794659
Cell-free heme selectively triggers pro-inflammatory receptors such as TLR-4 and BACH-1, and activates proteasomes25. PubMed:27515135
The released heme can activate the innate immune pattern recognition receptor toll-like receptor 4 (TLR4) on inflammatory cells, platelets and endothelium, promoting a pro-inflammatory and pro-coagulant phenotype, ultimately leading to vaso-occlusion, ischemia-reperfusion physiology, tissue injury, and pain in murine models of SCD [5, 7±10]. PubMed:29694434
Resuscitation with SRBCs together with albumin did not alter plasma levels of hemoglobin, hemopexin, haptoglobin, or heme as compared to resuscitation with SRBCs alone (Figure 3C–E, I, Supplemental Material and Supplemental Figure II A–B). PubMed:27515135
These results demonstrate that transfusion with SRBCs and simultaneous infusion of exogenous hemopexin results in decreased levels of circulating cell-free heme. PubMed:27515135
It is seen in Fig. 2 that after incubation with NEAT-HP, Hb has decreased the heme content by 85%, which confirms heme removal ability of NEAT-HP construct. PubMed:28088643
First, addition of exogenous Hp both markedly inhibits heme loss and second, as a result of this inhibition, globin precipitation is prevented. PubMed:24486321
High ferroportin levels were measured in macrophages upon heme overload and erythrophagocytosis (12, 13, 31, 32, 37) and in hemolytic murine models of b-thalassemia and phenylhydrazineinduced hemolytic anemia (11, 22, 34). PubMed:29212341
These data suggested that during severe hemolysis, heme mediated ferroportin induction and low hepcidin in HbS mice (11) served to elevate systemic iron availability, required to sustain high erythropoietic demands in these mice. PubMed:29212341
Our in vivo observations could be recapitulated in isolated macrophages, which upon stimulation with heme (25 lM; 16 h) demonstrated increased ferroportin mRNA and protein expression (Fig. 4A, B) and a significant decrease in the intracellular iron pool (2.2-fold; p < 0.01) (Fig. 4C). PubMed:29212341
So far, our results established that in the conditions of acute and chronic heme overload, macrophages acquired high ferroportin expression and an efficient iron export. PubMed:29212341
Under heme overload conditions, macrophages acquire an iron phenotype characterized by low intracellular iron and high ferroportin expression. PubMed:29212341
These results indicate that heme degradation increases in RBCs of PRDX2 knockout mice in spite of the presence of catalase and GPx. PubMed:23215741
The expression of A1M is up-regulated by elevated levels of free Hb, heme and ROS [23]. PubMed:24489717
Furthermore, the plasmaand extravascular reductase and heme- and radical scavenger α1-microglobulin (A1M) binds and degrades free heme and can reduce metHb [28–30]. PubMed:26368565
Excess extracellular heme is weakly bound to albumin [22], /1-microglobulin (which can also degrade heme) [23] and, most likely, to other plasma proteins and lipoproteins; there is a dynamic nature to such interactions. PubMed:26875449
Expression and synthesis of A1M has been shown to be upregulated in cells after exposure to heme and ROS (Olsson et al., 2007, 2011). PubMed:30505280
This is consistent with our findings here that both heme and Hb were associated with increased levels of synovial fluid A1M. PubMed:30505280
Cell-free heme selectively triggers pro-inflammatory receptors such as TLR-4 and BACH-1, and activates proteasomes25. PubMed:27515135
Cells deficient on FtH are more susceptible to oxidative damage, while increased amounts of FtH protects cells from death induced by challenges such as Fe, tumor necrosis factor (TNF), heme, heme plus TNF, or oxidized low-density lipoprotein (LDL; Juckett et al., 1995; Pham et al., 2004; Gozzelino et al., 2012). PubMed:24904418
Free heme is a dangerous molecule which can be recognized and degenerated by stress-responsive enzyme oxygenase- 1 (HO-1) [16] which plays an essential role in host defense against heme. PubMed:24464629
Lysis of red blood cells with consequent increases in free heme most likely caused the increase in HO-1 activity responsible for increased COHb concentrations, which is similar to that observed with circulatory devices [6]. PubMed:24553061
Importantly, heme b interaction with heme oxygenase (HO; Lad et al., 2003), the enzyme responsible for heme intracellular catabolism, and hemopexin (Hx; Paoli et al., 1999), a plasmatic heme scavenger, is essential for the regulation of free heme availability and Fe recycling (Kovtunovych et al., 2010; Tolosano et al., 2010). PubMed:24904418
In the extravascular compartment, cellular heme oxygenase (HO) is the most essential heme degrading protein, converting heme to free iron, biliverdin and CO [26,27]. PubMed:26368565
Despite its damaging effects, heme induces the expression of HO-1, which degrades heme to anti-inflammatory, cytoprotective, and antioxidant products [25]. PubMed:26875449
CD163 mediated hemoglobin/hematoma clearance is involved in the induction of HO-1, a rate-limiting enzyme for heme degradation 26. PubMed:27125525
As predicted, HMOX1 expression levels (means 6 SD) in hemin-treated cells were much higher (7.25 6 5.02, n = 12; P , 0.001) than in nontreated controls (0.14 6 0.18, n = 9) or A1AT-treated cells (0.09 6 0.1, n = 9). PubMed:28716864
Upon degradation of RBCs in the erythrophagosome, heme is imported into the cytoplasm for degradation by the heme-degrading enzyme heme oxygenase-1 (HMOX1) [7]. PubMed:30248094
A major intracellular antioxidant is heme oxygenase-1 (HO-1) which, through its heme-degrading activity, plays a critical role in the protection of cells. PubMed:30505280
Mice lacking HO-1 (Hmox1−/−) are highly susceptible to pathologic conditions associated with increased serum heme concentration. PubMed:24904418
Normally, haemopexin safely transports haem away from the vessel wall to ligate LRP1 (also termed CD91) on hepatocytes and macrophages, where the haem–haemopexin complex is endocytosed and haem is degraded intracellularly (Hvidberg et al, 2005). PubMed:25307023
It has been reported that an increase in extracellular heme activates NLRP3 expression, triggering inflammasome activation [28]. PubMed:30248094
The consequences of heme toxicity can be appreciated in hemolytic diseases such as β-thalassemia, sickle-cell disease (SCD), ischemia-reperfusion (IR), and malaria (Katori et al., 2002; Pamplona et al., 2007;Vinchi et al., 2013). PubMed:24904418
Heme has been suggested to induce polyubiquitination and proteasome-dependent degradation of BACH1 (Zenke-Kawasaki et al., 2007; Tan et al., 2013). PubMed:24630724
Here we showed that Bach1 was a transcriptional repressor of Spic and that heme-induced proteasome-dependent degradation of BACH1 protein in monocytes led to Spic expression and promoted RPM and BMM development (Figure 7F). PubMed:24630724
Western blotting results showed that the p10 active form of caspase-1 was detected in macrophages incubated with heme for 12 h. PubMed:24464629
These results suggest that heme induces maturation and secretion of IL-1b in macrophages through activating caspase-1 (Fig. 2a). PubMed:24464629
Furthermore, free heme also induced extracellular release of HMGB1 from RMVECs compared to vehicle control (Fig 5B). PubMed:29522519
In summary, these results indicate that heme from resuscitation with stored RBCs increases extracellular release of HMGB1, which inhibits macrophage phagocytosis of P. aeruginosa, leading to increased mortality. PubMed:29522519
The results showed that enforced HO-1 could efficiently decline the heme level in the lysates of ligated kidneys, and inhibit kidney inflammation characterized by down-regulation of NLRP3-Caspase- 1-IL-1b axis. PubMed:24464629
The Hmox1 (− /− ) MEF cells expressed no functional Hmox1 mRNA (Figure 1a) and as a result accumulated more cell-associated heme during extracellular exposure compared with wild-type cells (Figure 1b). PubMed:25301065
Macrophages are crucial for the removal of excess heme resulting from hemolysis via the uptake and degradation of heme by HO-1 (ref. 23), encoded by Hmox1. PubMed:27798618
Free heme is lipophilic and intercalates into the membrane of endothelial cells increasing vascular permeability and ICAM-1, VCAM-1, and E-selectin expression (19). PubMed:19276082
These results demonstrate that free heme induces IL-1b through activating NLRP3 inflammasome via ASC and suggest that free heme plays an essential role in inflammation response as a dangerous signal. PubMed:24464629
These results strongly suggest that heme activates NLRP3 through P2X receptors, especially P2X4R and P2X7R. PubMed:24464629
These results strongly suggest that heme activates NLRP3 through P2X receptors, especially P2X4R and P2X7R. PubMed:24464629
Free heme is lipophilic and intercalates into the membrane of endothelial cells increasing vascular permeability and ICAM-1, VCAM-1, and E-selectin expression (19). PubMed:19276082
These results are consistent with our earlier observations that the presence of SOD1 does not significantly inhibit or accelerate the formation of heme degradation products during in vitro autoxidation of oxyHb [18].. PubMed:23215741
This result strongly supports that high cellular heme concentration impairs degradation of Sqstm1 by the homeostatic protein degradation pathways. PubMed:25301065
However, a weak TNF-alpha signal appeared in macrophages that were treated with the highest concentration of NaOH-dissolved heme (500 lmolL1). PubMed:29610666
Free heme is lipophilic and intercalates into the membrane of endothelial cells increasing vascular permeability and ICAM-1, VCAM-1, and E-selectin expression (19). PubMed:19276082
Cell-free heme selectively triggers pro-inflammatory receptors such as TLR-4 and BACH-1, and activates proteasomes25. PubMed:27515135
Endothelial injury may also be related to Free hemoglobin and its breakdown oxidative product heme, and MPs, which mediates direct proinflammatory, proliferative, and pro-oxidant effects on endothelial cells [22–24] both in PNH and congenital CD59 deficiency, but may be more pronounced in congenital CD59 deficiency and perhaps even more in the brain due to loss of CD59 in the endothelium of these patients. PubMed:29929138
The released heme can activate the innate immune pattern recognition receptor toll-like receptor 4 (TLR4) on inflammatory cells, platelets and endothelium, promoting a pro-inflammatory and pro-coagulant phenotype, ultimately leading to vaso-occlusion, ischemia-reperfusion physiology, tissue injury, and pain in murine models of SCD [5, 7±10]. PubMed:29694434
These data collectively indicate that heart free heme accumulating when Hx is lost is responsible for systolic dysfunction. PubMed:28400318
For example, infusion of haem into humans is associated with disturbances in coagulation assays and overt thrombophlebitis (Simionatto et al, 1988). PubMed:25307023
For example, infusion of haem into humans is associated with disturbances in coagulation assays and overt thrombophlebitis (Simionatto et al, 1988). PubMed:25307023
Altogether, our best interpretation of these data is that increased levels of cell-free Hb and heme in synovial fluid early after injury triggered an increase in the synovial fluid A1M concentration that appeared to be protective of oxidative damage. PubMed:30505280
These data indicate that the increased severity of bacterial lung injury secondary to massive resuscitation with stored RBCs is heme-dependent. PubMed:29522519
During heme exposure the Hmox1 (−/ −) cells show a dose-dependent decrease in mitochondrial function as indicated by decreased cellular ATP (Figure 1c) and parallel induction of caspase 3/7 activity (Figure 1d) as well as nuclear condensation (Figure 1e) that occurred at heme concentrations exceeding 10 μM. PubMed:25301065
In line with previously published studies [13,14] the extravascular heme- and radical scavenger A1M was significantly increased in plasma of women with PE. PubMed:26368565
The consequences of heme toxicity can be appreciated in hemolytic diseases such as β-thalassemia, sickle-cell disease (SCD), ischemia-reperfusion (IR), and malaria (Katori et al., 2002; Pamplona et al., 2007;Vinchi et al., 2013). PubMed:24904418
The released heme can activate the innate immune pattern recognition receptor toll-like receptor 4 (TLR4) on inflammatory cells, platelets and endothelium, promoting a pro-inflammatory and pro-coagulant phenotype, ultimately leading to vaso-occlusion, ischemia-reperfusion physiology, tissue injury, and pain in murine models of SCD [5, 7±10]. PubMed:29694434
There are in vitro and animal model data linking increased free Hb, heme, and iron to inflammation, 6 infection,7 platelet (PLT) activation,8,9 vasculopathy, 10 and thrombosis. PubMed:29603246
The consequences of heme toxicity can be appreciated in hemolytic diseases such as β-thalassemia, sickle-cell disease (SCD), ischemia-reperfusion (IR), and malaria (Katori et al., 2002; Pamplona et al., 2007;Vinchi et al., 2013). PubMed:24904418
Haemoglobin and haem levels increase in plasma and urine when haptoglobin and haemopexin scavenging mechanisms are saturated during acute or chronic haemolysis. PubMed:25307023
Free heme is generated by intra- and extra-vascular hemolysis or extensive cell damage [14, 15]. PubMed:24464629
Lysis of red blood cells with consequent increases in free heme most likely caused the increase in HO-1 activity responsible for increased COHb concentrations, which is similar to that observed with circulatory devices [6]. PubMed:24553061
The above-discussed findings provide strong in vivo evidence that high concentrations of ferric Hb(Fe3+) and free heme can accumulate in the renal cortex during hemolysis. PubMed:26794659
During hemolysis, hemoglobin and heme released from red blood cells promote oxidative stress, inflammation and thrombosis. PubMed:29694434
In infectious diseases, such as malaria and sepsis, high amounts of cell-free hemoglobin and heme were found [8], suggesting that hemolysis during sepsis and systemic inflammation is of pathophysiological relevance. PubMed:29956069
These results suggest that heme plays an essential role in kidney inflammation via regulating NLRP3-Caspase-1-IL-1b axis. PubMed:24464629
More recently, we have also shown that free heme is also released during storage and may mediate further inflammation28 PubMed:26202471
Free heme is a potent trigger of lipid peroxidation and a promoter of inflammation.4–6 PubMed:26794659
Free hemin is a cytotoxic molecule that mediates oxidative stress, endothelial activation, and inflammation, and it is implicated in malaria pathogenesis [40] and AKI, among others [41]. PubMed:28716864
There are in vitro and animal model data linking increased free Hb, heme, and iron to inflammation, 6 infection,7 platelet (PLT) activation,8,9 vasculopathy, 10 and thrombosis. PubMed:29603246
During hemolysis, hemoglobin and heme released from red blood cells promote oxidative stress, inflammation and thrombosis. PubMed:29694434
In infectious diseases, such as malaria and sepsis, high amounts of cell-free hemoglobin and heme were found [8], suggesting that hemolysis during sepsis and systemic inflammation is of pathophysiological relevance. PubMed:29956069
The consequences of heme toxicity can be appreciated in hemolytic diseases such as β-thalassemia, sickle-cell disease (SCD), ischemia-reperfusion (IR), and malaria (Katori et al., 2002; Pamplona et al., 2007;Vinchi et al., 2013). PubMed:24904418
The released heme can activate the innate immune pattern recognition receptor toll-like receptor 4 (TLR4) on inflammatory cells, platelets and endothelium, promoting a pro-inflammatory and pro-coagulant phenotype, ultimately leading to vaso-occlusion, ischemia-reperfusion physiology, tissue injury, and pain in murine models of SCD [5, 7±10]. PubMed:29694434
There are in vitro and animal model data linking increased free Hb, heme, and iron to inflammation, 6 infection,7 platelet (PLT) activation,8,9 vasculopathy, 10 and thrombosis. PubMed:29603246
During hemolysis, hemoglobin and heme released from red blood cells promote oxidative stress, inflammation and thrombosis. PubMed:29694434
Our in vivo observations could be recapitulated in isolated macrophages, which upon stimulation with heme (25 lM; 16 h) demonstrated increased ferroportin mRNA and protein expression (Fig. 4A, B) and a significant decrease in the intracellular iron pool (2.2-fold; p < 0.01) (Fig. 4C). PubMed:29212341
Heme activates neutrophils and endothelial cells, by ROS generation. PubMed:24904418
Extracellular hemoglobin and heme are pro-oxidative, proinflammatory, and cytotoxic [10–12], and can contribute to the pathology of hemolytic diseases. PubMed:26875449
Furthermore, haem-induced release of P-selectin and VWF is mediated by TLR4 and NFkB signalling. PubMed:25307023
. Heme activates macrophages inducing the production of TNF, KC (Figueiredo et al., 2007), IL-1β (unpublished), and LTB4 (Monteiro et al., 2011). PubMed:24904418
Moreover, heme amplifies MyD88- (TNF and IL-6) and TRIF-dependent (IP-10) cytokines. PubMed:24904418
Heme may be implicated and contribute to the development of (i) bp(MESH: PubMed:26875449
Heme may be implicated and contribute to the development of (i) bp(MESH: PubMed:26875449
Free heme is lipophilic and intercalates into the membrane of endothelial cells increasing vascular permeability and ICAM-1, VCAM-1, and E-selectin expression (19). PubMed:19276082
Heme injection in mice leads to vascular permeability, leukocyte migration from the intravascular environment to tissues and increase of acute-phase proteins (Lyoumi et al., 1999; Wagener et al., 2001b), hallmarks of acute inflammation. PubMed:24904418
Free heme is lipophilic and intercalates into the membrane of endothelial cells increasing vascular permeability and ICAM-1, VCAM-1, and E-selectin expression (19). PubMed:19276082
Heme activates endothelial cells inducing the expression of the adhesion molecules ICAM-1 (intercellular adhesion molecule 1), VCAM-1 (vascular cell adhesion molecule 1), E-selectin, Pselectin, and von Willebrand factor (VWF; Wagener et al., 1997; Belcher et al., 2014) and causes neutrophil migration (GraçaSouza et al., 2002; Porto et al., 2007). PubMed:24904418
Free heme is lipophilic and intercalates into the membrane of endothelial cells increasing vascular permeability and ICAM-1, VCAM-1, and E-selectin expression (19). PubMed:19276082
Heme activates endothelial cells inducing the expression of the adhesion molecules ICAM-1 (intercellular adhesion molecule 1), VCAM-1 (vascular cell adhesion molecule 1), E-selectin, Pselectin, and von Willebrand factor (VWF; Wagener et al., 1997; Belcher et al., 2014) and causes neutrophil migration (GraçaSouza et al., 2002; Porto et al., 2007). PubMed:24904418
Free heme is a potent trigger of lipid peroxidation and a promoter of inflammation.4–6 PubMed:26794659
Free heme is lipophilic and intercalates into the membrane of endothelial cells increasing vascular permeability and ICAM-1, VCAM-1, and E-selectin expression (19). PubMed:19276082
As a consequence, infused heme (hemin) has been demonstrated to enhance leukocyte adhesion to the vessel wall (17, 18), a finding confirmed in the current study. PubMed:19276082
Previously we have shown that heme can enter the lipid moiety of LDL and induce iron-dependent lipid peroxidation.8 PubMed:20378845
Here we demonstrate that lipids isolated from human atheromatous lesions – which are already in an oxidized state – can be further oxidized in the presence of heme, whereas this effect is not observed using lipids isolated from normal vasculature. PubMed:20378845
Thus, it appears that these extracts oxidize ferrohemoglobin to ferrihemoglobin, thereby leading to heme instability and heme-mediated initiation of lipid peroxidation. PubMed:20378845
Besides its physiological importance, heme has a potent oxidative capacity oxidizing lipids (Tappel, 1953, 1955; Vincent et al., 1988) and proteins (Aft and Mueller, 1984; Vincent, 1989), and damaging DNA (Aft and Mueller, 1983). PubMed:24904418
In contrast, at an equal antioxidant concentration, Trolox completely blocked heme-triggered lipid peroxidation (measured as production of thiobarbituric acid reactive substances (TBARS)) in soybean lecithin micelles (Figure 7g). PubMed:25301065
Toxicity of free hemoglobin is also caused by the release of cell-free heme, which produces lipid peroxidation and mitochondrial damage and increases the production of reactive oxygen species. PubMed:27515135
Consistently, we measured increased lipid peroxidation in both cells and tissues exposed to free heme, which can be rescued by α-tocopherol, an agent able to react with lipid radicals and interrupt the oxidation reaction. PubMed:28400318
As can be observed in Fig. 1, heme has a potent chemotactic activity on VSMC (Fig. 1A), and is also a potent inducer of VSMC proliferation (Fig. 1B). PubMed:22954673
Thus, the antioxidant, anticoagulant, anti-proliferative and vasodilating effects of the HMOX1 and biliverdin reductase systems probably compensate for the nitric oxide (NO) scavenging, vasoconstrictive, proliferative, inflammatory and pro-oxidant effects of circulating free haemoglobin, haem and haem-iron, which are discussed below (Rother et al, 2005). PubMed:25307023
Accordingly, Fig. 2A shows that heme (10 mM) induces a strong ROS production after 1 h of incubation with VSMC. PubMed:22954673
Corroborating recent studies that showed heme as an inductor of ROS generation via NADPHox in neutrophils, macrophages and in VSMC [7,8,19], the pretreatment of cells with DPI (10 mM), a NADPHox inhibitor [20], prevented heme-induced ROS production in A7r5 VSMC (Fig. 2A). PubMed:22954673
Furthermore, heme induces ROS generation dependent on enzymatic reactions. PubMed:24904418
Heme induces ROS generation independently of TLR4. PubMed:24904418
The main mediator of these adverse effects is thought to be free haem via its effects on NO scavenging, pro-inflammatory cytokine responses, and reactive oxygen species (ROS) generation. PubMed:25307023
In addition, we observed increased ROS production ( Figure 2I; supplemental Figure 2), as well as an enhanced expression of IL-6 and TNFα in cells treated with heme-albumin compared with heme-Hx (Figure 2J-K). PubMed:26675351
Toxicity of free hemoglobin is also caused by the release of cell-free heme, which produces lipid peroxidation and mitochondrial damage and increases the production of reactive oxygen species. PubMed:27515135
Heme is an amphipathic molecule that can promote the generation of reactive oxygen species (ROS) via Fenton chemistry, thereby leading to membrane damage. PubMed:27798618
Moreover, heme-derived ROS induce the proliferation of smooth muscle cells, that participate in vasculopathy associated with atherosclerosis and hypertension [15]. PubMed:28400318
Free heme upregulates heme oxygenase activity, generates reactive oxygen species, and activates endothelial cells and macrophages directly[65]. PubMed:28458720
As expected, incubation of neutrophils with hemin resulted in a significant number of cells producing ROS (Fig. 8A and B). PubMed:28716864
For instance, earlier studies have demonstrated that neutrophil elastase degrades the hemoglobin liberating free hemin that induces ROS production. PubMed:28716864
We show that heme, in a concentration range found during hemolytic episodes, increases intracellular ROS production and consequentially signals for ferroportin induction and subsequent iron export from the macrophages. PubMed:29212341
On the other hand, heme induced HO-1 expression in VSMC (Suppl. Fig. 2). PubMed:22954673
These results indicate that heme degradation increases in RBCs of PRDX2 knockout mice in spite of the presence of catalase and GPx. PubMed:23215741
The small increase in heme degradation in the absence of SOD1 may, however, be attributed to low levels of heme degradation products produced either by the increased levels of superoxide [17] or perhaps the peroxynitrite that forms due to the rapid reaction of superoxide with any NO present. PubMed:23215741
As shown in Figure 3, the level of heme degradation is highly correlated with the level of metHb in RBCs (R = 0.6233, p < 0.0177) supporting the hypothesis that the heme degradation product formed in PRDX2 knockout mice is associated with the un-scavenged H2O2 generated during Hb autoxidation. PubMed:23215741
As a component of hemoglobin, free heme is released when hemolysis or extensive cell damage occur which results in inflammatory response. PubMed:24464629
Hemin induces expression of the adhesion molecules on endothelial cells [7, 8] and enables firm neutrophil attachment to the endothelium and initiation of an inflammatory response [9, 10]. PubMed:28716864
These experiments confirm a number of earlier reports and support the idea that certain solutions derived from purified/crystalline heme have the potential to induce weak TLR4-mediated inflammatory responses in macrophages in the complete absence of plasma derived proteins. PubMed:29610666
Free heme is generated by intra- and extra-vascular hemolysis or extensive cell damage [14, 15]. PubMed:24464629
Lysis of red blood cells with consequent increases in free heme most likely caused the increase in HO-1 activity responsible for increased COHb concentrations, which is similar to that observed with circulatory devices [6]. PubMed:24553061
Haemoglobin and haem levels increase in plasma and urine when haptoglobin and haemopexin scavenging mechanisms are saturated during acute or chronic haemolysis. PubMed:25307023
The above-discussed findings provide strong in vivo evidence that high concentrations of ferric Hb(Fe3+) and free heme can accumulate in the renal cortex during hemolysis. PubMed:26794659
During hemolysis, hemoglobin and heme released from red blood cells promote oxidative stress, inflammation and thrombosis. PubMed:29694434
In infectious diseases, such as malaria and sepsis, high amounts of cell-free hemoglobin and heme were found [8], suggesting that hemolysis during sepsis and systemic inflammation is of pathophysiological relevance. PubMed:29956069
Free heme is a dangerous molecule which can be recognized and degenerated by stress-responsive enzyme oxygenase- 1 (HO-1) [16] which plays an essential role in host defense against heme. PubMed:24464629
Lysis of red blood cells with consequent increases in free heme most likely caused the increase in HO-1 activity responsible for increased COHb concentrations, which is similar to that observed with circulatory devices [6]. PubMed:24553061
Importantly, heme b interaction with heme oxygenase (HO; Lad et al., 2003), the enzyme responsible for heme intracellular catabolism, and hemopexin (Hx; Paoli et al., 1999), a plasmatic heme scavenger, is essential for the regulation of free heme availability and Fe recycling (Kovtunovych et al., 2010; Tolosano et al., 2010). PubMed:24904418
Consistently, CD11b cells (granulocytes and monocytes) and iron-rich cells (macrophages) isolated from heme-treated Hx-null mice show a higher heme content and increased mRNA and protein expression of HO-1, Lferritin, and Fpn (Figure 1B-G) and elevated mRNA levels of the proinflammatory cytokine IL-6 ( Figure 1H). PubMed:26675351
In agreement with the electrical cell–substrate impedance sensing data described above, the proteome changes triggered by 10 μM heme were indicative of an adaptive response with prominent induction of HMOX1 and ferritin light (FTL) and heavy (FTH1) chains (Figure 5d,left panel). PubMed:26794659
Despite its damaging effects, heme induces the expression of HO-1, which degrades heme to anti-inflammatory, cytoprotective, and antioxidant products [25]. PubMed:26875449
A recent Phase IIB clinical trial showed that preconditioning using hemin upregulated HO-1 in renal transplantation, launching further studies on clinical outcome [97]. PubMed:26875449
CD163 mediated hemoglobin/hematoma clearance is involved in the induction of HO-1, a rate-limiting enzyme for heme degradation 26. PubMed:27125525
As predicted, HMOX1 expression levels (means 6 SD) in hemin-treated cells were much higher (7.25 6 5.02, n = 12; P , 0.001) than in nontreated controls (0.14 6 0.18, n = 9) or A1AT-treated cells (0.09 6 0.1, n = 9). PubMed:28716864
Free heme has been proved possess pro-inflammatory activities, such as leukocyte activation, migration and infiltration, adhesion molecules activation, and cytokines and acute phase proteins induction [17, 18]. PubMed:24464629
Free heme has been proved possess pro-inflammatory activities, such as leukocyte activation, migration and infiltration, adhesion molecules activation, and cytokines and acute phase proteins induction [17, 18]. PubMed:24464629
Heme promotes endothelial dysfunction by inducing the expression of adhesion molecules and reducing nitric oxide (NO) availability, which causes vasoconstriction [9-14]. PubMed:28400318
Hemin induces expression of the adhesion molecules on endothelial cells [7, 8] and enables firm neutrophil attachment to the endothelium and initiation of an inflammatory response [9, 10]. PubMed:28716864
Based on the previous findings that hemin induces neutrophil adhesion to endothelial cells [8] and that A1AT protects endothelial cells from neutrophil adhesion induced by fMLP [27], we investigated whether A1AT, as a scavenger of hemin, can prevent hemin-induced neutrophil adhesion to HUVECs. As shown in Fig. 4, neutrophils treated with hemin or fMLP (used as a positive control) exhibited a 3-fold higher adhesion to HUVECs compared with controls. However, the adherence of neutrophils treated with hemin/A1AT did not differ from controls (Fig. 4). PubMed:28716864
Free heme has been proved possess pro-inflammatory activities, such as leukocyte activation, migration and infiltration, adhesion molecules activation, and cytokines and acute phase proteins induction [17, 18]. PubMed:24464629
Heme amplifies cytokines induced by cell surface receptors (TLR2, TLR4, TLR5), endosome receptors (TLR3, TLR9), and cytosolic receptors (NOD1 and NOD2). PubMed:24904418
ELISA analysis displayed that the concentration of IL-1b in culture supernatants was significantly enhanced after stimulated by heme and PPIX. PubMed:24464629
The effect of heme on IL-1b production initiated as early as 4 h after stimulation and displayed strict time- and dose-dependent manner (Fig. 1a– d). PubMed:24464629
These results demonstrate that heme could efficiently induce maturation and secretion of IL-1b in macrophages and primarily suggested that heme participates in immune response. PubMed:24464629
Western blotting results showed that the p10 active form of caspase-1 was detected in macrophages incubated with heme for 12 h. PubMed:24464629
These results suggest that heme induces maturation and secretion of IL-1b in macrophages through activating caspase-1 (Fig. 2a). PubMed:24464629
These results demonstrate that free heme induces IL-1b through activating NLRP3 inflammasome via ASC and suggest that free heme plays an essential role in inflammation response as a dangerous signal. PubMed:24464629
These results strongly suggest that heme activates NLRP3 through P2X receptors, especially P2X4R and P2X7R. PubMed:24464629
These results strongly suggest that heme activates NLRP3 through P2X receptors, especially P2X4R and P2X7R. PubMed:24464629
The results showed that enforced HO-1 could efficiently decline the heme level in the lysates of ligated kidneys, and inhibit kidney inflammation characterized by down-regulation of NLRP3-Caspase- 1-IL-1b axis. PubMed:24464629
Heme induced the expression of Ho1 and Blvrb as well as Slc40a1, which encodes the mammalian iron exporter (Figure 5A), in agreement with previous reports (Delaby et al., 2008). PubMed:24630724
The Hmox1 (− /− ) MEF cells expressed no functional Hmox1 mRNA (Figure 1a) and as a result accumulated more cell-associated heme during extracellular exposure compared with wild-type cells (Figure 1b). PubMed:25301065
Exposure to Hb and its oxidized products increases heme overload on the AT1 cells. Heme overload induces the expression of HO-1 and iron-sequestering proteins, such as ferritin. PubMed:26974230
These results suggest that heme plays an essential role in kidney inflammation via regulating NLRP3-Caspase-1-IL-1b axis. PubMed:24464629
CO inhibits Hb oxidation and subsequently heme release, thus blocking heme accumulation in serum and preventing heme from exerting its inflammatory effects in the course of malaria disease (Ferreira et al., 2011). PubMed:24904418
During intravascular hemolysis the serum proteins responsible for removing heme get saturated and heme can exert its inflammatory effects. PubMed:24904418
Thus, the antioxidant, anticoagulant, anti-proliferative and vasodilating effects of the HMOX1 and biliverdin reductase systems probably compensate for the nitric oxide (NO) scavenging, vasoconstrictive, proliferative, inflammatory and pro-oxidant effects of circulating free haemoglobin, haem and haem-iron, which are discussed below (Rother et al, 2005). PubMed:25307023
Free plasma haemoglobin and haem also scavenge NO and have multiple pro-inflammatory and pro-oxidant properties that mediate many of the adverse effects of haemolysis. PubMed:25307023
More recently, we have also shown that free heme is also released during storage and may mediate further inflammation28 PubMed:26202471
Free heme is a potent trigger of lipid peroxidation and a promoter of inflammation.4–6 PubMed:26794659
Increased plasma concentrations of cell-free heme, the breakdown product of 390 hemoglobin, promote activation and inflammation of endothelial cells and enhance 391 oxidative stress and vascular permeability (22). PubMed:28314763
Free hemin is a cytotoxic molecule that mediates oxidative stress, endothelial activation, and inflammation, and it is implicated in malaria pathogenesis [40] and AKI, among others [41]. PubMed:28716864
There are in vitro and animal model data linking increased free Hb, heme, and iron to inflammation, 6 infection,7 platelet (PLT) activation,8,9 vasculopathy, 10 and thrombosis. PubMed:29603246
During hemolysis, hemoglobin and heme released from red blood cells promote oxidative stress, inflammation and thrombosis. PubMed:29694434
Administration of heme in healthy volunteers caused thrombophlebitis, demonstrating that it can cause vascular inflammation followed by vascular obstruction [18]. PubMed:29929138
In infectious diseases, such as malaria and sepsis, high amounts of cell-free hemoglobin and heme were found [8], suggesting that hemolysis during sepsis and systemic inflammation is of pathophysiological relevance. PubMed:29956069
In mice, this response was attenuated after administration of the TLR-4 inhibitor, TAK-242, suggesting hemin potentiates pulmonary macrophage activation and inflammation through hemin-induced TLR-4 receptor binding [27]. PubMed:30281034
Ferryl heme and associated protein radicals with high redox potentials (~1.0 V) can induce a wide variety of oxidative reactions that affect the protein and nearby molecules [2]. PubMed:24486321
Extracellular hemoglobin and heme are pro-oxidative, proinflammatory, and cytotoxic [10–12], and can contribute to the pathology of hemolytic diseases. PubMed:26875449
First, addition of exogenous Hp both markedly inhibits heme loss and second, as a result of this inhibition, globin precipitation is prevented. PubMed:24486321
The expression of A1M is up-regulated by elevated levels of free Hb, heme and ROS [23]. PubMed:24489717
Expression and synthesis of A1M has been shown to be upregulated in cells after exposure to heme and ROS (Olsson et al., 2007, 2011). PubMed:30505280
This is consistent with our findings here that both heme and Hb were associated with increased levels of synovial fluid A1M. PubMed:30505280
Heme-induced Spic expression was confirmed by reverse transcription PCR and was dose-dependent (Figure 2C). PubMed:24630724
In addition, Spic was induced as expected, as was Treml4, which can be used as a marker for RPM (Figure 5A). PubMed:24630724
Heme induced the expression of Ho1 and Blvrb as well as Slc40a1, which encodes the mammalian iron exporter (Figure 5A), in agreement with previous reports (Delaby et al., 2008). PubMed:24630724
Heme induced the expression of Ho1 and Blvrb as well as Slc40a1, which encodes the mammalian iron exporter (Figure 5A), in agreement with previous reports (Delaby et al., 2008). PubMed:24630724
High ferroportin levels were measured in macrophages upon heme overload and erythrophagocytosis (12, 13, 31, 32, 37) and in hemolytic murine models of b-thalassemia and phenylhydrazineinduced hemolytic anemia (11, 22, 34). PubMed:29212341
These data suggested that during severe hemolysis, heme mediated ferroportin induction and low hepcidin in HbS mice (11) served to elevate systemic iron availability, required to sustain high erythropoietic demands in these mice. PubMed:29212341
Our in vivo observations could be recapitulated in isolated macrophages, which upon stimulation with heme (25 lM; 16 h) demonstrated increased ferroportin mRNA and protein expression (Fig. 4A, B) and a significant decrease in the intracellular iron pool (2.2-fold; p < 0.01) (Fig. 4C). PubMed:29212341
So far, our results established that in the conditions of acute and chronic heme overload, macrophages acquired high ferroportin expression and an efficient iron export. PubMed:29212341
Under heme overload conditions, macrophages acquire an iron phenotype characterized by low intracellular iron and high ferroportin expression. PubMed:29212341
In addition, Spic was induced as expected, as was Treml4, which can be used as a marker for RPM (Figure 5A). PubMed:24630724
Heme has been suggested to induce polyubiquitination and proteasome-dependent degradation of BACH1 (Zenke-Kawasaki et al., 2007; Tan et al., 2013). PubMed:24630724
Here we showed that Bach1 was a transcriptional repressor of Spic and that heme-induced proteasome-dependent degradation of BACH1 protein in monocytes led to Spic expression and promoted RPM and BMM development (Figure 7F). PubMed:24630724
Besides its physiological importance, heme has a potent oxidative capacity oxidizing lipids (Tappel, 1953, 1955; Vincent et al., 1988) and proteins (Aft and Mueller, 1984; Vincent, 1989), and damaging DNA (Aft and Mueller, 1983). PubMed:24904418
Besides its physiological importance, heme has a potent oxidative capacity oxidizing lipids (Tappel, 1953, 1955; Vincent et al., 1988) and proteins (Aft and Mueller, 1984; Vincent, 1989), and damaging DNA (Aft and Mueller, 1983). PubMed:24904418
The consequences of heme toxicity can be appreciated in hemolytic diseases such as β-thalassemia, sickle-cell disease (SCD), ischemia-reperfusion (IR), and malaria (Katori et al., 2002; Pamplona et al., 2007;Vinchi et al., 2013). PubMed:24904418
The consequences of heme toxicity can be appreciated in hemolytic diseases such as β-thalassemia, sickle-cell disease (SCD), ischemia-reperfusion (IR), and malaria (Katori et al., 2002; Pamplona et al., 2007;Vinchi et al., 2013). PubMed:24904418
The consequences of heme toxicity can be appreciated in hemolytic diseases such as β-thalassemia, sickle-cell disease (SCD), ischemia-reperfusion (IR), and malaria (Katori et al., 2002; Pamplona et al., 2007;Vinchi et al., 2013). PubMed:24904418
The released heme can activate the innate immune pattern recognition receptor toll-like receptor 4 (TLR4) on inflammatory cells, platelets and endothelium, promoting a pro-inflammatory and pro-coagulant phenotype, ultimately leading to vaso-occlusion, ischemia-reperfusion physiology, tissue injury, and pain in murine models of SCD [5, 7±10]. PubMed:29694434
The consequences of heme toxicity can be appreciated in hemolytic diseases such as β-thalassemia, sickle-cell disease (SCD), ischemia-reperfusion (IR), and malaria (Katori et al., 2002; Pamplona et al., 2007;Vinchi et al., 2013). PubMed:24904418
. Heme can destabilize biological membranes increasing its permeability and the chance of lysis (Schmitt et al., 1993), as it happens with erythrocytes (Chiu and Lubin, 1989). PubMed:24904418
Once intercalated into cellular plasma membranes heme amplifies cellular susceptibility to oxidative-mediated injury by oxidants such as H2O2 or those derived from activated inflammatory cells (Balla et al., 1991a,b, 1993). PubMed:24904418
Alternatively, heme induced formation of radical species relies on the conversion of low-reactive organic hydroperoxides (ROOH) into highly reactive alkoxyl (RO•) and peroxyl (ROO•) radicals (Tappel, 1953, 1955; Van der Zee et al., 1996). PubMed:24904418
Heme injection in mice leads to vascular permeability, leukocyte migration from the intravascular environment to tissues and increase of acute-phase proteins (Lyoumi et al., 1999; Wagener et al., 2001b), hallmarks of acute inflammation. PubMed:24904418
Heme activates endothelial cells inducing the expression of the adhesion molecules ICAM-1 (intercellular adhesion molecule 1), VCAM-1 (vascular cell adhesion molecule 1), E-selectin, Pselectin, and von Willebrand factor (VWF; Wagener et al., 1997; Belcher et al., 2014) and causes neutrophil migration (GraçaSouza et al., 2002; Porto et al., 2007). PubMed:24904418
Heme is one of the factors capable of inducing stimulation and damage of endothelium, promoting the recruitment of neutrophils and sickle-cell erythro- cytes, and subsequently prompting a vaso-occlusive crisis. PubMed:26875449
Increased plasma concentrations of cell-free heme, the breakdown product of 390 hemoglobin, promote activation and inflammation of endothelial cells and enhance 391 oxidative stress and vascular permeability (22). PubMed:28314763
Free heme upregulates heme oxygenase activity, generates reactive oxygen species, and activates endothelial cells and macrophages directly[65]. PubMed:28458720
Free hemin is a cytotoxic molecule that mediates oxidative stress, endothelial activation, and inflammation, and it is implicated in malaria pathogenesis [40] and AKI, among others [41]. PubMed:28716864
Heme activates endothelial cells inducing the expression of the adhesion molecules ICAM-1 (intercellular adhesion molecule 1), VCAM-1 (vascular cell adhesion molecule 1), E-selectin, Pselectin, and von Willebrand factor (VWF; Wagener et al., 1997; Belcher et al., 2014) and causes neutrophil migration (GraçaSouza et al., 2002; Porto et al., 2007). PubMed:24904418
Heme also induces the expression of the adhesion molecules ICAM-1, VCAM-1, and E-selectins. PubMed:24904418
In addition, haem activates endothelial cell expression of intracellular adhesion molecule 1 (ICAM1), vascular cell adhesion molecule (VCAM1), and E-selectin (Wagener et al, 1997). PubMed:25307023
Heme activates endothelial cells inducing the expression of the adhesion molecules ICAM-1 (intercellular adhesion molecule 1), VCAM-1 (vascular cell adhesion molecule 1), E-selectin, Pselectin, and von Willebrand factor (VWF; Wagener et al., 1997; Belcher et al., 2014) and causes neutrophil migration (GraçaSouza et al., 2002; Porto et al., 2007). PubMed:24904418
In endothelial cells, heme induces TLR4-dependent degranulation of Weibel–Palade bodies and P-selectins and VWF release. PubMed:24904418
For example, haem stimulates expression of P-selectin and von Willebrand Factor (VWF) ‘strings’ on endothelial cells in vitro and on the vessel walls of both normal and SCD mice (Belcher et al, 2014). PubMed:25307023
Heme activates endothelial cells inducing the expression of the adhesion molecules ICAM-1 (intercellular adhesion molecule 1), VCAM-1 (vascular cell adhesion molecule 1), E-selectin, Pselectin, and von Willebrand factor (VWF; Wagener et al., 1997; Belcher et al., 2014) and causes neutrophil migration (GraçaSouza et al., 2002; Porto et al., 2007). PubMed:24904418
Heme activates endothelial cells inducing the expression of the adhesion molecules ICAM-1 (intercellular adhesion molecule 1), VCAM-1 (vascular cell adhesion molecule 1), E-selectin, Pselectin, and von Willebrand factor (VWF; Wagener et al., 1997; Belcher et al., 2014) and causes neutrophil migration (GraçaSouza et al., 2002; Porto et al., 2007). PubMed:24904418
A seminal study demonstrated that the ability of heme to activate neutrophils depend on protein kinase C (PKC) activation and ROS generation, inducing the expression of adhesion molecules and modifying actin cytoskeleton dynamics, necessary features for neutrophils migration (Graça-Souza et al., 2002). PubMed:24904418
As described before, LTB4 has an important function regulating heme-induced neutrophils migration (Monteiro et al., 2011). PubMed:24904418
With the triggering of the oxidative burst and modification of actin cytoskeleton dynamics, hemin also induces neutrophil migration [10] PubMed:28716864
Heme-induced neutrophils activation leads to extracellular traps (NETs) release through a mechanism dependent on ROS generation (Chen et al., 2014). PubMed:24904418
Heme is one of the factors capable of inducing stimulation and damage of endothelium, promoting the recruitment of neutrophils and sickle-cell erythro- cytes, and subsequently prompting a vaso-occlusive crisis. PubMed:26875449
By modeling the equilibrium concentration in the experiments performed with heme-albumin we could show that the free heme is the active neutrophil-stimulating component, which is inactivated by protein association (Figure S2). PubMed:29610666
In this context, heme inhibits neutrophils apoptosis, increasing their longevity, and possibly enhancing harmful stimuli from these cells (Arruda et al., 2004, 2006). PubMed:24904418
. Heme activates macrophages inducing the production of TNF, KC (Figueiredo et al., 2007), IL-1β (unpublished), and LTB4 (Monteiro et al., 2011). PubMed:24904418
On the other hand, TNF secretion induced by heme is essential for the activation of the programed necrotic cell death pathway, which is denominated necroptosis (Fortes et al., 2012). PubMed:24904418
Moreover, heme amplifies MyD88- (TNF and IL-6) and TRIF-dependent (IP-10) cytokines. PubMed:24904418
Haem also induces tumour necrosis factor (TNF) secretion in monocyte/macrophages through TLR4 and the adaptor molecule, MYD88 (Figueiredo et al, 2007). PubMed:25307023
In addition, we observed increased ROS production ( Figure 2I; supplemental Figure 2), as well as an enhanced expression of IL-6 and TNFα in cells treated with heme-albumin compared with heme-Hx (Figure 2J-K). PubMed:26675351
Taken sequentially, it appears that the release of heme under hemolytic conditions initiates the extrinsic pathway of coagulation through the upregulation of TF on endothelial cells and leukocytes, but subsequently blocks the propagation of coagulation by inhibiting FVIII and FV, and by inhibiting the conversion of fibrinogen into fibrin and fibrin clots. PubMed:26875449
Likewise, heme and FeNTA treatment causes the induction of the M1 markers MHCII, CD86, CD14, TNFα, IL-6, and IL1β and a decrease in the M2 markers CD206, IL-10, and Arginase-1 (the last with FeNTA only) in M0 BMDMs (Figure 3A; supplemental Figures 5, 6A, and 7). PubMed:26675351
. Heme activates macrophages inducing the production of TNF, KC (Figueiredo et al., 2007), IL-1β (unpublished), and LTB4 (Monteiro et al., 2011). PubMed:24904418
Highly purified heme free of endotoxin contamination was used, as well as polymyxin B, anti-TLR4/MD2, and lipid A antagonist, all of which inhibited the effects of LPS but did not interfere with the induction of TNF by heme. PubMed:24904418
The TLR4 activates two distinct pathways: MyD88 and TRIF. In macrophages, heme induces a biased MyD88 activation and the secretion of the pro-inflammatory cytokines TNF and KC. PubMed:24904418
Moreover, human embryonic kidney (HEK) cells transfected with human TLR4 secretes IL-8 upon stimulation with heme (Piazza et al., 2011). PubMed:24904418
Heme amplifies cytokines induced by cell surface receptors (TLR2, TLR4, TLR5), endosome receptors (TLR3, TLR9), and cytosolic receptors (NOD1 and NOD2). PubMed:24904418
In fact, TLR4 is involved in intracerebral hemorrhage (ICH) induced by heme (Lin et al., 2012). PubMed:24904418
Other studies demonstrated that heme can trigger the activation of Toll-like receptor 4 and inflammasomes, thus leading to inflammatory reactions.5,35–37 PubMed:26794659
Most studies concerning the pathophysiological roles of heme have focused on the protective effect of the heme-degrading enzyme, heme oxygenase 1 (HO-1) [25] (Box 2), and on the effect of this danger-associated molecule on cells, leading to oxidative stress, TLR4 signaling [26,27], and NLRP3 inflammasome activation [28] (Box 4). PubMed:26875449
Cell-free heme selectively triggers pro-inflammatory receptors such as TLR-4 and BACH-1, and activates proteasomes25. PubMed:27515135
Purified heme was found to be an activator of TLR4 8,11,27 in some studies and of the inflammasome 9 in others, and these activities were considered to be the molecular mechanism behind the coexistence of inflammation and hemolysis. PubMed:29610666
Only under protein-free conditions did we observe a limited heme-induced TNF-alpha response in cultured macrophages, which was triggered via signaling of the classical TLR4–MyD88–TRIF pathway of NF-kB activation.28 PubMed:29610666
The released heme can activate the innate immune pattern recognition receptor toll-like receptor 4 (TLR4) on inflammatory cells, platelets and endothelium, promoting a pro-inflammatory and pro-coagulant phenotype, ultimately leading to vaso-occlusion, ischemia-reperfusion physiology, tissue injury, and pain in murine models of SCD [5, 7±10]. PubMed:29694434
Heme released from cell-free hemoglobin has been described to be an activator of TLR-4 [39, 41, 42]. PubMed:29956069
Heme/TLR-4 signaling, moreover, was found to activate NF-κB and trigger vaso-occlusion [42]. PubMed:29956069
In addition, haem activates endothelial cell expression of intracellular adhesion molecule 1 (ICAM1), vascular cell adhesion molecule (VCAM1), and E-selectin (Wagener et al, 1997). PubMed:25307023
In mice, this response was attenuated after administration of the TLR-4 inhibitor, TAK-242, suggesting hemin potentiates pulmonary macrophage activation and inflammation through hemin-induced TLR-4 receptor binding [27]. PubMed:30281034