The role of phospholipase A in gallstone formation.

CHOLESTEROL IS THE MAIN COMPONENT of human gallstones. It is held in solution in bile by mixed micelles of lecithin and bile salts [l]. Presence of both lecithin and bile salts are ersential for the solubilization of cholesterol in bile [2]. Normal human gallbladder bile is almost saturated with cholesterol [3]. Therefore, a small change in lecithin concentration might disturb the micellar solubility of cholesterol. Bacterial degradation of lecithin lowers the solubility of cholesterol in bile [4]. The conversion of lecithin to lysolecithin and fatty acids may be catalyzed by the enzyme phospholipase A. This enzyme is a normal component of pancreatic secretion, and the presence of this enzyme has been demonstrated in duodenal contents of man [5]. It has also been demonstrated in vitro that if the fatty acids liberated by the action of phospholipase A are removed from the micellar mixture, lysolecithin alone would not be able to hold the cholesterol in solution and hence the latter will be precipitated [6]. The absorption of fatty acids, liberated by the hydrolysis of lecithin in vitro, by the gallbladder has been demonstrated with the guinea pig gallbladder [7]. The presence of phospholipase A activity of human gallbladder bile from patients with gallstones and chronic cholecystitis has not been determined.