The effects of phospholipase A2, free fatty acids and lysophosphatidylcholine on the crystalization of cholesterol in gallbladder bile

Abstract

Free fatty acids (FFAs) and lysophosphatidylcholine (LPC) in bile are mainly generated by endogenous lipases. Their effect on the crystal observation time (COT) of cholesterol in bile is discussed controversially. We therefore incubated bile with increasing amounts of either phospholipase A 2 (PLA2), FFAs or LPC and compared the COTs of cholesterol to those of native bile. METHODS: Bile was obtained from cholesterol gallstone patients (n=5) during laparoscopic cholecystectomy by puncture of the gallbladder. Bile was immediately ultracentrifugated at 100.000 g for 1 hour. Ten aliquots of isotropic bile were incubated at 37°C. Butylated hydroxytoluene was added as an antioxidant. Sample l: native isotropic bile; samples 2-4: addition of 5, 10, 20 U/1 PLA2; samples 5-7: addition of 5, 10, 20 mmol/1 of a physiologic mixture of biliary FFAs (palmitic acid 46 %, linoleic acid 37 %, oleic acid 4 %, stearic acid 8 % and arachidonic acid 5 %); samples 8-10: addition of 5, 10 and 20 mmol/l LPC (Fig. l). We examined the COT of cholesterol up to 21 days. RESULTS: Cholesterol in native biles nucleated on the first day whereas addition of increasing amounts of PLA 2 or FFAs prolonged the COT of cholesterol significantly to 1.8 -+ 0.44 and 2.4 +_ 0.89 days (mean -+ SD) even at the lowest concentration (* = p<0.01, ** = p<0.005). Increasing amounts of LPC had no effect on the COT of cholesterol (Fig. 1).