The Absorbability of Free and Esterified Eicosapentaenoic Acid

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Although the antithrombotic and hypolipidemic effects of certain fish oils containing -3 fatty acids are extensively documented, little is known regarding the digestibility, absorption, lipoprotein transport, and chylomicron clearance of lipids containing these acids. Systematic studies have now been conducted to demonstrate the following: the rate and extent of absorption of unesterified eicosapentaenoic acid (EPA) into thoracic duct lymph of rats are comparable to that of oleic and arachidonic acids; the same is true with respect to recovery of eicosapentaenoic, oleic, and arachidonic acids as chylomicron triglycerides. However, based on lymphatic recoveries of salmon oil fatty acids, the digestibility of triglycerides containing EPA is significantly less efficient than for corn oil, which is enriched in oleic and linoleic acids. In order to determine aspects of lipoprotein triglyceride clearance, mesenteric lymph chylomicrons, enriched in eicosapentaenoic or oleic acids, were prepared. In order to assess the activity of peripheral lipoprotein lipase (LPL) on these chylomicrons, the nonworking rat heart model was used for recirculating perfusion. With this membrane-supported LPL system, clearance rates of chylomicron triglycerides enriched with either EPA or oleic acid were identical. Furthermore, oxidation of the extracted fatty acids and incorporation into mycocardial esterified lipids, with the exception of phospholipid, were comparable for the two fatty acids. Finally, overall clearance rates of chylomicron triglycerides enriched with EPA or oleic acid were compared following intravenous injection into rats. Although initial clearances rates (2–10 min) were comparable for chylomicrons containing either fatty acid, the clearance of EPA-enriched chylomicrons was significantly slower at 25–90 min (P < 0.05). Nevertheless, at each time point, the distributions of the remaining oleate and EPA among circulating lipoproteins were comparable. These studies suggest that except for less efficient intestinal digestibility of EPA-containing fish oils, the subsequent absorption, transport, and clearance of EPA in the rat are typical of other more common fatty acids.