Dietary fish oil effects on biliary lipid secretion and cholesterol gallstone formation in the African green monkey

Abstract

We studied two groups of adult male African green monkeys to assess the effects of dietary fish oil on biliary lipid secretion and cholesterol gallstone formation. One group was fed 0.8 mg cholesterol/kcal and 42% of calories as fat with half of the fat calories derived from lard; the other group was fed a similar diet except for the isocaloric substitution of menhaden oil for lard. After 21/2 to 3 yr, necropsies were performed and the presence of gallstones was determined. Gallbladder bile specimens were analyzed for cholesterol saturation index, as well as for bile acid species and biliary phospholipid fatty acid composition. Our results showed that 67% of animals fed the lard diet had cholesterol gallstones compared with only 22% of animals in the group fed the fish oil diet (p = 0.08). The cholesterol saturation index of gallbladder bile also tended to be higher in the lard-fed group (1.15 ± 0.11) compared with the fish oil-fed group (0.86 ± 0.09, p = 0.06). No differences between the two dietary groups were noted in the percentages of the various types of bile acids. However, a greater percentage of ω-3 fatty acids and a lesser percentage of 18:1, 18:2 and 20:4 fatty acids were found in the biliary phospholipids from the fish oil-fed group compared with the lard-fed group. Biliary lipid secretion rates were then measured during isolated recirculating liver perfusion performed with a constant sodium taurocholate infusion. A significantly greater biliary phospholipid secretion rate was noted in the fish oil-fed animals compared with the lard-fed animals, whereas bile acid and cholesterol secretion rates were similar between the diet groups. We conclude that the increased biliary phospholipid secretion observed in the fish oil-fed group produced a less lithogenic gallbladder bile, which in turn resulted in a less frequent occurrence of gallstones in that group. In addition the increased phospholipid secretion was probably favored by the enrichment of biliary phospholipids with relatively less hydrophobic ω-3 fatty acids. (Hepatology 1991;14:679-684.)