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Metabolic Fate of Long-Chain Unsaturated Fatty Acids and Their Effects on Palmitic Acid Metabolism and Gluconeogenesis in Bovine Hepatocytes

Department of Dairy Science University of Wisconsin, Madison 53706

Corresponding author:
Ric R. Grummer; e-mail:
grummer{at}calshp.cals.wisc.edu.

The objectives were to determine the metabolic fate of different long-chain fatty acids, and their effects on palmitic acid metabolism and gluconeogenesis in bovine hepatocytes. Hepatocytes were isolated from four ruminating calves and exposed in suspension for 3 h to one of the following treatments: 1 mM palmitic acid (1C16), 2 mM palmitic acid (2C16), or 1 mM palmitic acid plus either 1 mM oleic (C18:1), linoleic (C18:2), linolenic (C18:3), eicosapentaenoic (C20:5), or docosahexaenoic acid (C22:6). Oxidation of [1-¹⁴C]palmitic acid or one of the [1-¹⁴C]-labeled treatment fatty acids to CO₂ or incorporation into cellular triglycerides (TG), phospholipids, cholesterol, and cholesterol esters were measured. Rates of oxidation to CO₂ were 3- to 4-fold higher for C22:6 than for other fatty acids, with the exception of C20:5, which had intermediate rates of oxidation to CO₂. In general, treatments 2C16 and C18:1 yielded the highest rates of incorporation into most cellular lipids, whereas the polyunsaturated fatty acids were poor substrates for incorporation into cellular lipids. The most pronounced change was a large reduction of polyunsaturated fatty acid incorporation into cellular TG compared to 1C16, 2C16, and C18:1. The unsaturated fatty acids also influenced palmitic acid metabolism. The addition of C20:5 yielded the highest rates of palmitic acid oxidation to CO₂ followed by addition of C18:1 and C22:6. Treatments containing polyunsaturated fatty acids decreased palmitic acid metabolism to TG and total cellular lipids compared with treatments 2C16 and C18:1. Rates of gluconeogenesis from propionate were significantly higher for the treatment containing C18:1. Long-chain fatty acids vary in their routes of metabolism and influence palmitic acid metabolism and gluconeogenesis in bovine hepatocytes.

Abbreviation key: ASP = acid-soluble products, CPT-1 = carnitine palmitoyltransferase-I, DGAT = diacylglycerol acyltransferase, PUFA = polyunsaturated fatty acids, TG = triglyceride

Key Words: fatty acids • hepatic metabolism • gluconeogenesis

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