A comparison of the metabolism of eighteen-carbon

Altered use of different dietary fatty acids may contribute to several chronic diseases, including obesity, noninsulin-dependent diabetes mellitus, and cardiovascular disease. However, few comparative data are available to support this link, so the goal of the present study was to compare the metabolism of [ 13 C]oleate, [ 13 C] -linolenate, [ 13 C]elaidate, and [ 13 C]linoleate through oxidation and incorporation into plasma lipid fractions and adipose tissue. Each tracer was given as a single oral bolus to six healthy women. Samples were collected over 8 days, and 13 C was analyzed using isotope ratio mass spectrometry. At 9 h postdose, cumulative oxidation was similar for [ 13 C]elaidate, [ 13 C]oleate, and [ 13 C] -linolenate (19 1%, 20 4%, and 19 3% dose, respectively). Significantly lower oxidation of [ 13 C]linoleate (12 4% dose; P 0.05) was accompanied by its higher incorporation into plasma phospholipids and cholesteryl esters. Abdominal adipose tissue was enriched with [ 13 C] -linolenate, [ 13 C]elaidate, or [ 13 C]linoleate within 6 h. The percentage linoleate in plasma phospholipids correlated positively with [ 13 C]linoleate and [ 13 C]elaidate oxidation, indicating a potential role of background diet. Conversion of [ 13 C]linoleate and [ 13 C] -linolenate to longer chain polyunsaturates was a quantitatively minor route of utilization.— McCloy, U., M. A. Ryan, P. B. Pencharz, R. J. Ross, and S. C. Cunnane. A comparison of the metabolism of eighteen-carbon 13 C-unsaturated fatty acids in healthy women. J. Lipid Res. 2004. 45: 474–485. Supplementary key words linoleic acid • -linolenic acid • elaidic acid • oleic acid • long chain polyunsaturated fatty acid • body fat • blood lipids • adipose tissue • fatty acid oxidation • dietary fat Linoleate (18:2n-6) and oleate ( cis -18:1n-9) are the two predominant unsaturated fatty acids in the diet and are associated with several health benefits (1). -Linolenate ( cis 18:3n-3) is much less common in the diet but also has well-known health benefits, particularly against coronary artery disease and mortality (2–5). Elaidate, the main trans -isomer of oleate ( trans -18:1n 9), which is mainly formed by food industry hydrogenation of vegetable oils, is associated with health concerns, particularly an increased risk of hypercholesterolemia (6–8). Despite their different abundances in the diet and different health implications, structurally, these four fatty acids are broadly similar in having 18 carbons and one to three double bonds. Nevertheless, comprehensive, comparative information is lacking about their metabolism that could help account for their differing health attributes in humans. This could be especially helpful in identifying potential reasons why trans -fatty acids may be hypercholesterolemic. The overall objective of this study was to gain insight into the differential health effects of these four common 18-carbon dietary unsaturated fatty acids by tracing their metabolism in healthy women using uniformly carbon-13 labeled (U13 C) stable isotope tracers. This was a crossover study in which free-living healthy subjects consuming a self-selected diet orally ingested a tracer dose of [U13 C]oleate, [U13 C]elaidate, [U13 C]linoleate, and [U13 C] -linolenate in random sequential order with washout periods between each tracer. 13 C was measured in breath ( -oxidation), plasma fatty acids, and adipose tissue (storage) by high-precision gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Thus, the amount of each tracer used for energy, esterified to different lipid classes in plasma, desaturated and chain-elongated to long-chain PUFAs or stored in adipose tissue, was measured over a period of 8 days. MRI was used to quantify adipose tissue volumes to obtain pool size. Relationships between abdominal subcutaneous fat volume, blood lipids, plasma fatty acid profiles, and the metabolism of these tracers were also determined to identify conAbbreviations: AP, atom percent; APE, atom percent excess; AUC, area under the curve; CE, cholesteryl ester; GC-C-IRMS, gas chromatography-combustion-isotope ratio mass spectrometry; PL, phospholipid; U13 C, uniformly carbon-13 labeled. 1 To whom correspondence should be addressed. e-mail: [email protected] Manuscript received 9 July 2003 and in revised form 2 December 2003. Published, JLR Papers in Press, December 16, 2003. DOI 10.1194/jlr.M300304-JLR200 by gest, on N ovem er 7, 2017 w w w .j.org D ow nladed fom