Lysozyme, a mediator of sepsis that intrinsically generates hydrogen peroxide to cause cardiovascular dysfunction

Abstract

In septic shock, cardiovascular collapse is caused by the release of inflammatory mediators. We previously found that lysozyme (Lzm-S), released from leukocytes, contributed to the myocardial depression and arterial vasodilation that develop in canine models of septic shock. To cause vasodilation, Lzm-S generates hydrogen peroxide (H(2)O(2)) that activates the smooth muscle soluble guanylate cyclase (sGC) pathway, although the mechanism of H(2)O(2) generation is not known. To cause myocardial depression, Lzm-S binds to the endocardial endothelium, resulting in the formation of nitric oxide (NO) and subsequent activation of myocardial sGC, although the initial signaling event is not clear. In this study, we examined whether the myocardial depression produced by Lzm-S was also caused by the generation of H(2)O(2) and whether Lzm-S could intrinsically generate H(2)O(2) as has been described for other protein types. In a canine ventricular trabecular preparation, we found that the peroxidizing agent Aspergillus niger catalase, that would breakdown H(2)O(2), prevented Lzm-S- induced decrease in contraction. We also found that compound I, a species of catalase formed during H(2)O(2) metabolism, could contribute to the NO generation caused by Lzm-S. In tissue-free experiments, we used a fluorometric assay (Ultra Amplex red H(2)O(2) assay) and electrochemical sensor techniques, respectively, to measure H(2)O(2) generation. We found that Lzm-S could generate H(2)O(2) and, furthermore, that this generation could be attenuated by the singlet oxygen quencher sodium azide. This study shows that Lzm-S, a mediator of sepsis, is able to intrinsically generate H(2)O(2). Moreover, this generation may activate H(2)O(2)-dependent pathways leading to cardiovascular collapse in septic shock.

Mechanisms of systemic vasodilation by lysozyme-c in septic shock

“…Wentworth and colleagues (29 -31) recently demonstrated that proteins can intrinsically generate H 2 O 2 from singlet oxygen ( 1 O 2 *). Based on the investigations of Wentworth and colleagues, we were able to show that Lzm-S was capable of intrinsically generating H 2 O 2 in this manner (20). Furthermore, we found that this generation of H 2 O 2 by Lzm-S led to activation of pathways that resulted in vasodilation and myocardial depression in ventricular trabecular and carotid artery preparations, respectively (20,23).…”

“…We previously delineated the pathways by which Lzm-S could cause cardiovascular dysfunction in this condition. In organ bath preparations, we found that these pathways were ultimately dependent on hydrogen peroxide (H 2 O 2 ) signaling (20,23). Although H 2 O 2 is a well-described reactive oxygen species that is known for its cytotoxic effects associated with tissue injury, H 2 O 2 has recently been established as an important signaling molecule, as well (6).…”

“…To cause myocardial depression, Lzm-S first binds to a glycoprotein moiety on the endocardial endothelium (EE), in particular to the mannose-␤(1-4)-N-acetylglucosamine (␤1-4)-N-acetylglucosamine moiety of high-mannose/hybrid and triantennary glycan subtypes, where generation of H 2 O 2 by Lzm-S subsequently occurs (15,20). Once H 2 O 2 is generated at this site, H 2 O 2 reacts with endogenous catalase in the EE to form compound I, which is an oxidized species of catalase (4,5,20). Compound I is a potent oxidant, and we found that compound I could stimulate the production of nitric oxide (NO) in the EE (20).…”

“…Once H 2 O 2 is generated at this site, H 2 O 2 reacts with endogenous catalase in the EE to form compound I, which is an oxidized species of catalase (4,5,20). Compound I is a potent oxidant, and we found that compound I could stimulate the production of nitric oxide (NO) in the EE (20). After NO is produced, NO diffuses to adjacent myocytes, resulting in an increase in guanosine 3=,5=monophosphate (cGMP), which depresses contraction via activation of cGMP-dependent protein kinase (PKG), a known effector of myocardial depression (17,18).…”

Immune defence mechanisms of barramundi (Lates calcarifer) peripheral blood against Streptococci

“…As well as directly degrading bacterial walls, lysozyme has also been reported to be involved in promotion of sepsis and toxic shock by generating hydrogen peroxide, which acts on muscle tissue activating the guanylate cyclase pathway, in turn resulting in vasodilation, and finally leading to cardiovascular collapse (Mink et al, 2009). A second mechanism of action determined lysozyme could also act directly on smooth muscle tissue, with the same end result (Gotes et al, 2012).…”