OXIDATIVE INJURY TO ISOLATED RAT PANCREATIC ACINAR-CELLS VS ISOLATED ZYMOGEN GRANULES

This study compares the susceptibility of pancreatic acinar cells and zymogen granules against oxidative injury and analyzes the mechanisms involved. Zymogen granules and acinar cells, isolated from rat pancrea s, were exposed to a reaction mixture containing xanthine oxidase, hyp oxanthine, and chelated iron. Cell function and viability were assesse d by various techniques. Trypsin activation was quantified by an Elisa for trypsinogen activating peptide. Integrity of granules was determi ned by release of amylase. The reaction mixture rapidly generated radi cals as assessed by deoxyribose and luminol assays. This oxidative str ess caused lysis of granules in a matter of minutes but significant ce ll death only after some hours. Nevertheless, radicals initiated intra cellular vacuolization, morphological damage to zymogen granules and m itochondria, increase in trypsinogen activating peptide, and decrease in ATP already after 5-30 min. Supramaximal caerulein concentrations a lso caused rapid trypsin activation. Addition of cells but not of gran ules reduced deoxyribose oxidation, suggesting that intact cells act a s scavengers. Caerulein pretreatment only slightly increased the susce ptibility of cells but markedly that of granules. In conclusion, isola ted zymogen granules are markedly more susceptible to oxidative injury than intact acinar cells, in particular, in early stages of caerulein pancreatitis. The results show that oxidative stress causes a rapid t rypsin activation that may contribute to cell damage by triggering aut odigestion. Zymogen granules and mitochondria appear to be important t argets of oxidative damage inside acinar cells. The series of intracel lular events initiated by oxidative stress was similar to changes seen in early stages of pancreatitis.