Insulin Protects Pancreatic Acinar Cells from Palmitoleic Acid-induced Cellular Injury

Background: Palmitoleic acid is a major pancreatitis-inducing agent. Results: Insulin protected cells from palmitoleic acid (POA)-induced ATP depletion, inhibition of the plasma membrane calcium pump (PMCA), cytotoxic Ca2+ overload and necrosis. Conclusion: Insulin protects against acinar cell injury induced by pancreatitis-inducing agents. Significance: This provides an important therapeutic strategy for treating pancreatitis with insulin therapy. Acute pancreatitis is a serious and sometimes fatal inflammatory disease where the pancreas digests itself. The non-oxidative ethanol metabolites palmitoleic acid (POA) and POA-ethylester (POAEE) are reported to induce pancreatitis caused by impaired mitochondrial metabolism, cytosolic Ca2+ ([Ca2+](i)) overload and necrosis of pancreatic acinar cells. Metabolism and [Ca2+](i) are linked critically by the ATP-driven plasma membrane Ca2+-ATPase (PMCA) important for maintaining low resting [Ca2+](i). The aim of the current study was to test the protective effects of insulin on cellular injury induced by the pancreatitis-inducing agents, ethanol, POA, and POAEE. Rat pancreatic acinar cells were isolated by collagenase digestion and [Ca2+](i) was measured by fura-2 imaging. An in situ [Ca2+](i) clearance assay was used to assess PMCA activity. Magnesium green (MgGreen) and a luciferase-based ATP kit were used to assess cellular ATP depletion. Ethanol (100 mm) and POAEE (100 m) induced a small but irreversible Ca2+ overload response but had no significant effect on PMCA activity. POA (50-100 m) induced a robust Ca2+ overload, ATP depletion, inhibited PMCA activity, and consequently induced necrosis. Insulin pretreatment (100 nm for 30 min) prevented the POA-induced Ca2+ overload, ATP depletion, inhibition of the PMCA, and necrosis. Moreover, the insulin-mediated protection of the POA-induced Ca2+ overload was partially prevented by the phosphoinositide-3-kinase (PI3K) inhibitor, LY294002. These data provide the first evidence that insulin directly protects pancreatic acinar cell injury induced by bona fide pancreatitis-inducing agents, such as POA. This may have important therapeutic implications for the treatment of pancreatitis.