Phospholipase A2 isoforms in acute pancreatitis

Objective: To assess phospholipase A2 isoforms during human and experimental acute necrotizing pancreatitis. Phospholipase A2 isoforms (group I, II, and IV) were examined in acute pancreatitis tissues in humans and rats to determine whether the exocrine pancreas itself is a source of these mediators. Summary Background Data: Phospholipase A2 has important regulatory functions, especially in inflammation. Methods: Using Northern blot analysis and immunohistochemistry, the expression and localization of phospholipase A2 isoforms were analyzed in pancreatic tissue obtained from 21 patients with acute necrotizing pancreatitis and in pancreatic tissues of rats with acute edematous and necrotizing pancreatitis. Rat samples were examined daily for 1 week. Results: In human acute pancreatitis, phospholipase A2-1 mRNA expression was 8.9-fold decreased. By contrast, phospholipase A2-II (7.8-fold) and phospholipase A2-IV (8.1-fold) mRNA levels were increased. By in situ hybridization, phospholipase A2-IV was found to be expressed in remaining acinar and ductal cells adjacent to the necrotic areas. Immunostaining revealed moderate to intense phospholipase A2-II immunoreactivity in remaining acinar and ductal cells next to the necrosis. In rat pancreatitis, phospholipase A2-II mRNA levels in the pancreas were unchanged in the early phase (8 hours) but markedly increased after 24 hours, with a fluctuating pattern until day 7. Conclusions: Enhanced expression of phospholipase A2-II and A2-IV isoenzymes in human and experimental acute pancreatitis suggests that these enzymes play a role in modulating the inflammatory reaction in the pancreas. Because phospholipase A2-II and A2-IV mRNA was strongly present in remaining viable pancreatic acinar and ductal cells, the pancreas itself seems to be at least partly a source and a regulator of phospholipase A2-II- and A2-IV-dependent inflammatory reactions in acute pancreatitis.