Role of platelets and neutrophils in regulating trypsinogen activation and tissue damage in acute pancreatitis

Acute pancreatitis is an inflammatory disease characterized by a diverse spectrum of clinical presentations ranging from a mild and self-limiting to a severe and systemic disorder. The relationship between inflammation and proteolytic activation in pancreatitis is an elusive issue. The aim of this thesis was to define the influence of platelets and neutrophils as well as their interrelations in relation to trypsinogen activation and tissue damage in pancreatitis. For this purpose, three different experimental models of acute pancreatitis were used in mice. Pancreatitis was induced by retrograde infusion of taurocholate into the pancreatic duct, by intraperitoneal administration of caerulein or L-arginine. Severity of pancreatitis was evaluated by morphological examination of the pancreas as well as serum and pancreatic biochemical markers. Intravital fluorescence microscopy was used to study leukocyte-endothelial interactions in the pancreatic microcirculation. Flowcytometry was used to quantify platelet-neutrophil aggregates and adhesive molecule expression on cells. Induction of pancreatitis provoked a clear cut tissue damage characterized by increased neutrophil infiltration, myeloperoxidase and macrophage inflammatory protein-2 levels, trypsinogen activation peptide, acinar cell necrosis, oedema formation and haemorrhage in the pancreas, as well as elevated serum amylase activity. Depletion of platelets and neutrophils reduced pancreatic tissue damage, neutrophil accumulation and macrophage inflammatory protein-2 formation as well as amylase levels. Also, it was found that initial trypsinogen activation is independent of neutrophils, whereas later activation is dependent on neutrophils and mediated by neutrophil-derived matrix metalloproteinase-9 in the pancreas. Platelets were found to regulate neutrophil recruitment in to the pancreas via upregulating P-selectin on pancreatic microvasculature. Depletion of platelets and inhibition of P-selectin not only reduced leukocyte rolling but also tissue damage in acute pancreatitis. Thus, targeting both neutrophil and platelet functions may be a useful strategy in the management of acute pancreatitis.