Role of endogenous hydrogen sulfide synthesised by cystathionine-gamma-lyase in the inflammatory response in acute pancreatitis

Abstract

Mammals have the ability to synthesise endogenous hydrogen sulfide via desulfhydration enzymes though the physiological effects are still relatively unclear particularly in the inflammatory response. Endogenous hydrogen sulfide has been shown to be both pro and anti-inflammatory in numerous models of disease in animals. Common aspects of these studies are the reported dysregulation of tissue cystathionine-gamma-lyase (CSE) expression (the major hydrogen sulfide producing enzyme in the periphery) and the use of D,L-propargylglycine (PAG) to inhibit CSE activity. However, PAG is not a specific inhibitor and very few studies have correlated CSE dysregulation with changes in endogenous tissue hydrogen sulfide levels. Therefore the aims of this thesis were to investigate pancreatic and macrophage CSE dysregulation in acute pancreatitis, to correlate this dysregulation with changes in endogenous hydrogen sulfide levels/ hydrogen sulfide modified proteins and to determine the effect of CSE gene deletion on disease severity and the inflammatory response. Results in this thesis show that acute pancreatitis directly mediated upregulation in pancreatic CSE expression which was a gap in the existing body of knowledge. I have also found novel evidence of acute pancreatitis induced upregulation of CSE in macrophages with in vitro studies using plasma from pancreatitic mice and elucidated the molecular mechanisms involved. CSE gene deletion resulted in an amelioration of acute pancreatitis with reduced plasma amylase levels, pancreatic and lung neutrophil infiltration, oedema as well as acinar cell damage. There was also a reduction in pancreatic pro-inflammatory mediators, MCP-1, MIP-2alpha, IL-6, and PGE2 as well as NFkappaB activation. Similar findings were found in vitro using isolated primary pancreatic acini. The results of this thesis incontrovertibly show that CSE exerts pro-inflammatory effects in acute pancreatitis and corroborates with previous studies using PAG. It also shows upregulation of CSE in stimulated macrophages thus suggesting a role for endogenous hydrogen sulfide in the modulation of macrophage activation.