Alpha1-antitrypsin counteracts heme-induced endothelial cell inflammatory activation, autophagy dysfunction and death

Abstract

Free heme toxicity in the vascular endothelium is critical for the pathogenesis of hemolytic disorders including sickle cell disease. In the current study, it is demonstrated that human alpha1-antitrypsin (A1AT), a serine protease inhibitor with high binding-affinity for heme, rescues endothelial cell (EC) injury caused by free heme. A1AT provided endothelial protection against free heme toxicity via a pathway that differs from human serum albumin and hemopexin, two prototypical heme-binding proteins. A1AT inhibited heme-mediated pro-inflammatory activation and death of ECs, but did not affect the increase in intracellular heme levels and up-regulation of the heme-inducible enzyme heme oxygenase-1. Moreover, A1AT reduced heme-mediated generation of mitochondrial reactive oxygen species. Extracellular free heme led to an increased up-take of A1AT by ECs, which was detected in lysosomes and was found to reduce heme-dependent alkalization of these organelles. Finally, A1AT was able to restore heme-dependent dysfunctional autophagy in ECs. Taken together, our findings show that A1AT rescues ECs from free heme-mediated pro-inflammatory activation, cell death and dysfunctional autophagy. Hence, A1AT therapy may be useful in the treatment of hemolytic disorders such as sickle cell disease.

Alpha1-antitrypsin improves survival in murine abdominal sepsis model by decreasing inflammation and sequestration of free heme

“…However, plasma albumin levels in severe septic patients also decrease when compared to those in non-septic patients ( 54 ). We and other researchers have shown that AAT, similarly to albumin, binds free heme and neutralizes its cytotoxic effects ( 11 , 55 , 56 ). In this study, we demonstrate that a strong accumulation of free heme in the peritoneal cavity of septic mice was significantly reduced by AAT treatment.…”

“…It is important to point out that AAT not only interacts with target proteases and inhibits their activity but also binds and neutralizes various inflammatory substances such as free radicals, chemokines [interleukin 8 (CXCL8) and leukotriene B4 (LTB4)], cytokines [tumor necrosis factor (TNF)], and complement factors. Like albumin, AAT also interacts with free heme and neutralizes its toxicity ( 10 , 11 ). The fact that the half-life of circulating AAT is prolonged during bacteremia suggests that AAT is an important protection against organ damage ( 12 ).…”

Heme-Inducing Endothelial Pyroptosis Plays a Key Role in Radiofrequency Ablation of Hepatic Hemangioma Leading to Systemic Inflammatory Response Syndrome

“…Heme, a typical damage-associated molecular pattern (DAMP), recognizes receptors through patterns such as Toll-like receptors, induces autoimmune or immune tolerance, and plays an important role in the development of inflammation. [7][8][9][10] Heme can induce lipid peroxidation and mediate TNF-α-mediated programmed cell death. 11 In endothelial cells, heme not only activates NLRP3 inflammatory bodies, leading to inflammation but also induces endothelial barrier disturbance through the MKK3/p38MAPK axis, leading to impaired lung function.…”

Indirect effect of alpha-1-antitrypsin on endotoxin-induced IL-1β secretion from human PBMCs

“…AAT also interacts with chemoattractants, such as IL-8 and leukotriene B4 (LTB4), and thus modulates neutrophil adhesion and chemotaxis (Mcelvaney et al, 2020). The interaction between AAT and free heme neutralizes the cytotoxic effects of heme (Madyaningrana et al, 2021). These various interactions between AAT and its binding partners might dependent on the glycosylation and/or the hydrophilic/hydrophobic surface charges of the AAT (Mcelvaney et al, 2020).…”