The elongation of very long-chain fatty acid 6 gene product catalyses elongation of n-13 : 0 and n-15 : 0 odd-chain SFA in human cells

Normal odd-chain SFA (OCSFA), particularly tridecanoic acid ( n -13 : 0), pentadecanoic acid ( n -15 : 0) and heptadecanoic acid ( n -17 : 0), are normal components of dairy products, beef and seafood. The ratio of n -15 : 0: n -17 : 0 in ruminant foods (dairy products and beef) is 2:1, while in seafood and human tissues it is 1:2, and their appearance in plasma is often used as a marker for ruminant fat intake. Human elongases encoded by elongation of very long-chain fatty acid (ELOVL)1, ELOVL3, ELOVL6 and ELOVL7 catalyse biosynthesis of the dominant even-chain SFA; however, there are no reports of elongase function on OCSFA. ELOVL transfected MCF7 cells were treated with n -13 : 0, n -15 : 0 or n -17 : 0 (80 µ m ) and products analysed. ELOVL6 catalysed elongation of n -13 : 0→ n -15 : 0 and n -15 : 0→ n -17 : 0; and ELOVL7 had modest activity toward n -15 : 0 ( n -15 : 0→ n -17 : 0). No elongation activity was detected for n -17 : 0→ n -19 : 0. Our data expand ELOVL specificity to OCSFA, providing the first molecular evidence demonstrating ELOVL6 as the major elongase acting on OCSFA n -13 : 0 and n -15 : 0 fatty acids. Studies of food intake relying on OCSFA as a biomarker should consider endogenous human metabolism when relying on OCSFA ratios to indicate specific food intake.