Anti-inflammatory effects of PPAR-γ agonists directly correlate with PPAR-γ expression during acute pancreatitis

Peroxisome proliferator-activated receptors (PPARs) are ligand-inducible transcription factors that regulate cellular energy and lipid metabolism. PPAR-γ agonists also have potent anti-inflammatory properties through down-regulation of early inflammatory response genes. The role of PPAR-γ in acute pancreatitis has not been adequately examined. In this study, we determined the effect of PPAR-γ agonists on the severity of pancreatitis and sought to correlate PPAR-γ expression in pancreatic acinar cells and the severity of acute pancreatitis in vivo. Acute pancreatitis was induced in mice by hyperstimulation with the cholecystokinin analog, cerulein. PPAR-γ agonists were administered by intraperitoneal injection 15–30 minutes before induction of pancreatitis (pretreatment) or at various times after induction of pancreatitis (treatment). Pancreata and serum were harvested over the course of 24 hours. Serum amylase activity and glucose levels were measured. Pancreata were used for histological evaluation as well as protein and mRNA analysis. Pretreatment of mice with the PPAR-γ agonists 15-deoxy-Δ12, 14-prostaglandin J2, or troglitazone significantly reduced the severity of pancreatitis in a dose-dependent manner. This reduction was indicated by reduced serum amylase activity and histological damage (leukocyte infiltration, vacuolization, and necrosis). Although cerulein decreased PPAR-γ expression in the pancreas, pretreatment with agonists maintained PPAR-γ expression early in acute pancreatitis. The expression of PPAR-γ inversely correlated with pancreatitis severity and expression of the proinflammatory cytokines, interleukin-6, and tumor necrosis factor-α. Treatment with troglitazone after the induction of pancreatitis reduced serum amylase activity. The results suggest that PPAR-γ plays a direct role in the inflammatory cascade during the early events of acute pancreatitis. Our data are the first to demonstrate that PPAR-γ agonists represent a promising therapeutic strategy for acute pancreatitis.