Role of peroxisomal fatty acyl-CoA β-oxidation in phospholipid biosynthesis

We have already reported that peroxisomal β-oxidation has an anabolic function, supplying acetyl-CoA for bile acid biosynthesis [ H. Hayashi and A. Miwa, 1989, Arch. Biochem. Biophys. 274, 582–589]. The anabolic significance of peroxisomal β-oxidation was further investigated in the present study by using clofibrate, a peroxisome proliferator, as an experimental tool. Clofibrate suppressed 3-hydroxymethylglutaryl-CoA reductase activity (the key enzyme of cholesterol synthesis) and enhanced fatty acyl-CoA oxidase activity (the rate-limiting enzyme of β-oxidation). Rats were fed a chow containing 0.25% clofibrate for 2 weeks, and then a bile duct fistula was implanted. [1- 14C]lignoceric acid, which is degraded exclusively by peroxisomal FAOS, was injected into the rats 24 h after the operation. By this time, the secondary bile acids and pooled cholesterol which would normally be secreted into the bile are considered to have been exhausted from the liver. Clofibrate significantly decreased the incorporations of radioactivity into biliary bile acid (40% of the control) and cholesterol (50%), but did not affect biliary lipid contents. [ 14C]Acetyl-CoA formed by peroxisomal β-oxidation of [1- 14C]lignoceric acid was preferentially utilized for syntheses of long-chain fatty acids and phospholipids rather than synthesis of cholesterol or triglyceride. The radioactivities incorporated into the former two lipids were increased 2-fold over the control by administration of clofibrate, while the incorporation into triglyceride was decreased to approximately half. In particular, the incorporation into phosphotydylethanolamine was increased as much as 3.5-fold over the control. The contents of these lipids in the liver were not affected by clofibrate. The results suggest that peroxisomal β-oxidation plays an important role in the biosynthesis of functional lipids such as phospholipids (this work), in addition to bile acids and cholesterol (previous report) by supplying acetyl-CoA.