Purified and Recombinant Hemopexin: Protease Activity and Effect on Neutrophil Chemotaxis

Genomic organization and gene evolution of two warm temperature acclimation proteins (Wap65s) of Micropterus salmoides and their responses to temperature and bacterial/viral infections

Warm temperature acclimation-related 65-kDa proteins (Wap65s) are fish plasma acute-phase glycoproteins homologous to hemopexin with high affinity and clearance for heme. The study characterized Mswap65-1 and Mswap65-2 genes in Micropterus salmoides. Structural analysis showed MsWap65s contained conserved heme-binding sites. MsWap65-1 had a chloride-binding site similar to hemopexin, while MsWap65-2 had an additional calcium-binding site. Phylogenetic and Ka/Ks analysis showed that fish Wap65s were evolutionarily conserved and underwent strong purifying selection. Functional divergence analysis indicated that fish Wap65-2 retained the putative function of ancestral Wap65, while Wap65-1 underwent neofunctional differentiation. QPCR showed Mswap65s were predominantly expressed in liver, but prolonged hyperthermy inhibited Mswap65-2 expression. Mswap65-2 expression was up-regulated in liver and spleen after Nocardia seriolae infection, while Mswap65-1 was down-regulated. MsWap65-2 may be associated with pathogenesis and play potential role in pathogen resistance. LMBV infection resulted in both significant downregulation of Mswap65s were both significantly down-regulated, with differences observed between sexes. We speculated the immune system might suppress expression after viral infection. Exogenous rMsWap65s were prepared, and injection of rMsWap65s alleviated phenylhydrazine-induced hemolysis and inhibited increases in heme, complement C3 and inflammatory symptoms. Our results contribute to an advanced understanding of the functions and mechanisms of MsWap65s in stress resistance.

Deferoxamine therapy reduces brain hemin accumulation after intracerebral hemorrhage in piglets

Hemopexin (Hpx) is critical for hemin scavenging after the erythrocyte lysis that occurs following intracerebral hemorrhage (ICH). Low-density lipoprotein receptor-related protein-1 (LRP1, also called CD91) is an important receptor through which the hemin-Hpx complex can undergo endocytosis. This study investigated changes in the hemin-Hpx-CD91 axis in both hematoma and perihematomal tissue in a large animal ICH model. The effect of deferoxamine (DFX) on hemin-Hpx-CD91 was also examined. The study consisted of two parts. First, piglets had an injection of autologous blood into the right frontal lobe of brain and were euthanized from day 1 to day 7. Hematoma and perihematomal tissue of brains were used for hemin assay, immunohistochemistry, and immunofluorescence. Second, piglets with ICH were treated with deferoxamine or vehicle, and were euthanized for hemin measurement and Hpx and CD91 immunohistochemistry. We found that there was an increase of hemin levels within the hematoma and perihematomal brain tissue after ICH. Hpx and CD91-positive cells were present in the clot and perihematomal tissue from day 1. Hpx and CD91 positive cells were Iba1 positive. After DFX therapy, hemin dropped markedly in the hematoma and perihematomal brain tissue. Furthermore, DFX treatment decreased the number of Hpx and CD91 positive cells in and around the hematoma. In conclusion, hemin accumulation occurs in and around the hematoma. Increases in Hpx and CD91 may be important in scavenging that hemin. DFX treatment decreased hemin release from the hematoma and reduced the expression of Hpx and CD91.

Phosgene inhalation causes hemolysis and acute lung injury

Phosgene (Carbonyl Chloride, COCl₂) remains an important chemical intermediate in many industrial processes such as combustion of chlorinated hydrocarbons and synthesis of solvents (degreasers, cleaners). It is a sweet smelling gas, and therefore does not prompt escape by the victim upon exposure. Supplemental oxygen and ventilation are the only available management strategies. This study was aimed to delineate the pathogenesis and identify novel biomarkers of acute lung injury post exposure to COCl₂ gas. Adult male and female C57BL/6 mice (20-25 g), exposed to COCl₂ gas (10 or 20 ppm) for 10 min in environmental chambers, had a dose dependent reduction in P_aO₂ and an increase in P_aCO₂, 1 day post exposure. However, mortality increased only in mice exposed to 20 ppm of COCl₂ for 10 min. Correspondingly, these mice (20 ppm) also had severe acute lung injury as indicated by an increase in lung wet to dry weight ratio, extravasation of plasma proteins and neutrophils into the bronchoalveolar lavage fluid, and an increase in total lung resistance. The increase in acute lung injury parameters in COCl₂ (20 ppm, 10 min) exposed mice correlated with simultaneous increase in oxidation of red blood cells (RBC) membrane, RBC fragility, and plasma levels of cell-free heme. In addition, these mice had decreased plasmalogen levels (plasmenylethanolamine) and elevated levels of their breakdown product, polyunsaturated lysophosphatidylethanolamine, in the circulation suggesting damage to cellular plasma membranes. This study highlights the importance of free heme in the pathogenesis of COCl₂ lung injury and identifies plasma membrane breakdown product as potential biomarkers of COCl₂ toxicity.

Heme as a Target for Therapeutic Interventions

Heme is a complex of iron and the tetrapyrrole protoporphyrin IX with essential functions in aerobic organisms. Heme is the prosthetic group of hemoproteins such as hemoglobin and myoglobin, which are crucial for reversible oxygen binding and transport. By contrast, high levels of free heme, which may occur in various pathophysiological conditions, are toxic via pro-oxidant, pro-inflammatory and cytotoxic effects. The toxicity of heme plays a major role for the pathogenesis of prototypical hemolytic disorders including sickle cell disease and malaria. Moreover, there is increasing appreciation that detrimental effects of heme may also be critically involved in diseases, which usually are not associated with hemolysis such as severe sepsis and atherosclerosis. In mammalians homeostasis of heme and its potential toxicity are primarily controlled by two physiological systems. First, the scavenger protein hemopexin (Hx) non-covalently binds extracellular free heme with high affinity and attenuates toxicity of heme in plasma. Second, heme oxygenases (HOs), in particular the inducible HO isozyme, HO-1, can provide antioxidant cytoprotection via enzymatic degradation of intracellular heme. This review summarizes current knowledge on the pathophysiological role of heme for various diseases as demonstrated in experimental animal models and in humans. The functional significance of Hx and HOs for the regulation of heme homeostasis is highlighted. Finally, the therapeutic potential of pharmacological strategies that apply Hx and HO-1 in various clinical settings is discussed.