Enhanced susceptibility to pancreatitis in severe hypertriglyceridaemic lipoprotein lipase-deficient mice and agonist-like function of pancreatic lipase in pancreatic cells

Background and aims: Recurrent pancreatitis is a common complication of severe hypertriglyceridaemia in patients with various gene mutations in lipoprotein lipase (LPL) or apolipoprotein CII. However, the exact pathogenetic mechanism has not yet been defined. Methods: Susceptibility to pancreatitis in LPL-deficient mice was compared with that of wild-type mice after intraperitoneal injections of caerulein by determination of amylase release and pancreatic pathological scores. The effect of chylomicrons and fatty acids on enzyme release, Ca2+ signalling and cell injury in isolated pancreatic acinar cells from wild-type and LPL-deficient mice was investigated. Results: Caerulein induced higher levels of serum amylase and more severe inflammation in the pancreas of LPL-deficient mice than in wild-type mice. Addition of free fatty acids or chylomicrons to isolated pancreatic acinar cells led to the release of amylase and caused cell injury at higher concentrations. The effect of chylomicrons was partially blocked by orlistat, an inhibitor of pancreatic lipase. These results suggest that increased concentrations of free fatty acids from chylomicron hydrolysis by pancreatic lipase can induce acinar cell injury. Surprisingly, pancreatic lipase, whether in its active or inactive state could act like an agonist by inducing amylase secretion without cell injury. It caused an increase in cGMP levels and conversion of cell-damaging sustained elevations of [Ca2+] to normal Ca2+ oscillations. Conclusions: LPL-deficient mice with severe hypertriglyceridaemia display enhanced susceptibility to acute pancreatitis. High levels of chylomicrons and free fatty acids result in pancreatic cell injury. Pancreatic lipase has a dual effect: generating free fatty acids from chylomicrons and preventing Ca2+ overload in pancreatic acinar cells.