Phosphatidylinositol 3-kinase-dependent activation of trypsinogen modulates the severity of acute pancreatitis

Intra-acinar cell activation of digestive enzyme zymogens including trypsinogen is generally believed to be an early and critical event in acute pancreatitis. We have found that the phosphatidylinositol 3-kinase inhibitor wortmannin can reduce the intrapancreatic activation of trypsinogen that occurs during two dissimilar experimental models of rodent acute pancreatitis, secretagogue- and duct injection-induced pancreatitis. The severity of both models was also reduced by wortmannin administration. In contrast, the NF-kappa B activation that occurs during the early stages of secretagogue-induced pancreatitis is not altered by administration of wortmannin. Ex vivo, caerulein-induced trypsinogen activation is inhibited by wortmannin and LY294002. However, the cytoskeletal changes induced by caerulein were not affected by wortmannin. Concentrations of caerulein that induced ex vivo trypsinogen activation do not significantly increase phosphatidylinositol-3,4-bisphosphate or phosphatidylinositol 3,4,5-trisphosphate levels or induce phosphorylation of Akt/PKB, suggesting that class I phosphatidylinositol 3-kinases are not involved. The concentration of wortmannin that inhibits trypsinogen activation causes a 75% decrease in phosphatidylinositol 3-phosphate, which is implicated in vesicle trafficking and fusion. We conclude that a wortmannin-inhibitable phosphatidylinositol 3-kinase is necessary for intrapancreatic activation of trypsinogen and regulating the severity of acute pancreatitis. Our observations suggest that phosphatidylinositol 3-kinase inhibition might be of benefit in preventing acute pancreatitis.

Water immersion stress prevents caerulein-induced pancreatic acinar cell nf-kappa b activation by attenuating caerulein-induced intracellular Ca2+ changes

Prior stress ameliorates caerulein-induced pancreatitis in rats. NF-kappaB is a proinflammatory transcription factor activated during caerulein pancreatitis. However, the effects of prior stress on pancreatic NF-kappaB activation are unknown. In the current study, the effect of prior water immersion stress on caerulein and tumor necrosis factor-alpha (TNF-alpha)-induced NF-kappaB activation in the pancreas was evaluated. Water immersion of rats for up to 6 h prevents supramaximal caerulein-induced pancreatic IkappaB-alpha degradation and NF-kappaB activation in vivo. NF-kappaB activity is also inhibited in vitro in pancreatic acini prepared from water-immersed animals. TNF-alpha-induced NF-kappaB activation in pancreas or in pancreatic acini is unaffected by prior water immersion. Chelation of intracellular Ca(2+) by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate/acetoxymethyl ester has similar effects to water immersion in preventing caerulein but not TNF-alpha-induced NF-kappaB activation in pancreas. Both the spike response and the sustained rise in [Ca(2+)](i) in response to supramaximal caerulein stimulation are reduced markedly in acini prepared from water-immersed animals as compared with normal animals. Our findings indicate that, in addition to Ca(2+)-dependent mechanisms, Ca(2+)-independent signaling events also may lead to NF-kappaB activation in pancreatic acinar cells. Water immersion stress prevents supramaximal caerulein-induced NF-kappaB activation in pancreas in vivo and in vitro by affecting intracellular Ca(2+) homeostasis.