Is a role of phospholipase A(2) in cholesterol gallstone formation phospholipid species-dependent?

Phospholipase A(2) plays a role in cholesterol gallstone formation by hydro lyzing bile phospholipids into lysolecithin and free fatty acids. This stud y investigated its effects on cholesterol crystallization in model bile sys tems. Supersaturated model bile solutions with different cholesterol satura tion indexes (1.2, 1.4, and 1.6) were prepared using cholesterol, taurochol ate, and egg yolk phosphatidylcholine, soybean phosphatidylcholine, palmito yl-oleoyl phosphatidylcholine, or palmitoyl-linoleoyl phosphatidylcholine. Then the effect of digestion of phosphatidylcholine by phospholipase A(2) o n bile metastability was assessed by spectrophotometry and video-enhanced d ifferential contrast microscopy. Addition of phospholipase A(2) caused the release of free fatty acids in a time-dependent manner. Cholesterol crystal lization was enhanced by an increased crystal growth rate in model bile con taining hydrophilic species such as soybean or palmitoyl-linoleoyl phosphat idylcholine, consisting predominantly of polyunsaturated fatty acids. Becau se phospholipase A(2) enhanced cholesterol crystallization in bile containi ng hydrophilic phosphatidylcholine species, but not hydrophobic phosphatidy lcholine species, release of polyunsaturated fatty acids by hydrolysis may be responsible for such enhancement. Therefore, the role of phospholipase A (2) in cholesterol gallstone formation depends on the phospholipid species present in bile, so that phospholipid species selection during hepatic excr etion is, in part, crucial to the cholesterol stone formation. (C) 2001 Els evier Science B.V. All rights reserved.