Formation and inhibition of lysolecithin in human gallbladder bile

Homogenized human gallbladder epithelium was incubated at 37 degrees C with 14C-lecithin in diluted gallbladder bile. During the incubation, lecithin was transformed to lysolecithin. The reaction rate was higher at pH 4.5 than at pH 7.0. No degradation of lecithin occurred if the reaction mixture did not contain the homogenate. Lysolecithin was mixed with red blood cells in (a) diluted human gallbladder bile and (b) 0.15 M saline. The surface activity in the different systems was then assessed from the amount of hemoglobin recovered in the red cell pellet after centrifugation. In human bile, 500 mug lysolecithin/ml did not affect the amount of hemoglobin recovered whereas in saline, concentrations exceeding 25-30 mug/ml affected the red blood cells such that no hemoglobin was pelleted by the centrifugation. Lysolecithin was further studied for effect upon lecithin-3H-cholesterol-dicetylphosphate liposomes containing 14C-glucose. The surface activity of lysolecithin was assessed from the distribution of 3H- and 14C-activity after centrifugation. Although 500 mug lysolecithin/ml increased the non-sedimented 14C-activity, 5000 mug lysolecithin/ml was necessary to decrease significantly the amount of sedimented 3H-activity. The results are interpreted such that phospholipase A activity from the gallbladder epithelium, if released into the gallbladder bile, may generate lysolecithin from lecithin. However, the surface activity and, thus, the inflammatory mediating activity of lysolecithin is inhibited by components in the gallbladder bile, possibly lecithin.