Effects of phospholipase A(2), free fatty acids and 2-lysolecithin on the crystallization of cholesterol in gallbladder bile

Background Phospholipase A(2) (PLA(2)) and its enzymatic products free fatt y acids (FFAs) and 2-lysolecithin are physiological constituents of bile. T heir role in the crystallization of cholesterol in gallbladder bile of pati ents with cholesterol gallstones is still controversial. Design To clarify this issue we evaluated the activity of PLA(2) and the co ncentration and pattern of FFAs in the gallbladder bile of cholesterol ston e patients. We furthermore added PLA(2), FFAs and 2-lysolecithin to isotrop ic gallbladder bile, determined the crystal observation time (COT) and coun ted the cholesterol crystals in a crystal growth assay for up to 21 days. Results A PLA(2) activity of 1.8 +/- 1.2 U L-1 and total FFA concentrations of 1.32 +/- 0.71 mmol L-1 were determined. After incubation of bile for 24 h at 37 degrees C total FFAs increased to 2.72 +/- 1.29 mmol L-1 (P<0.005) . Biliary saturated and unsaturated FFAs were found in equal proportions be fore and after incubation, pointing to an additional presence of lipases ot her than PLA(2). A COT of 1 day was observed in all gallbladder biles and i ncreased to 1.7 +/- 0.5 days after addition of 5 U L-1 of PLA(2) (P<0.01). An even higher COT of 2.5 +/- 0.8 days was seen after addition of 5 mmol L- 1 of a 'biliary' mixture of FFAs (P<0.005) but the COT remained unchanged a fter addition of 5 mmol L-1 of 2-lysolecithin. However, in the crystal grow th assay in gallbladder bile addition of 5 U L-1 of PLA(2), of 5 mmol L-1 o f 'biliary' FFAs and of 5 mmol L-1 of 2-lysolecithin decreased significantl y the number of cholesterol crystals formed during follow-up. Conclusion An elevated activity of PLA(2) in gallbladder bile may counterac t the formation of cholesterol crystals through increased formation of FFAs and 2-lysolecithin. However, regarding the comparatively low activity of P LA(2) in gallbladder bile PLA(2) seems to be of only minor pathophysiologic al importance in the formation of cholesterol gallstones.