Abstract
Objectives
Saturated branched chain fatty acids (BCFA) terminating with either an isopropyl or sec-butyl group, are common bioactive food components consumed from beef, fish, and dairy products. Little is known about their endogenous metabolism and the enzymes mediating their interconversion. Our main objective was to test the substrate specificity of the fatty acid elongases (ELOVL1–7) towards elongation of representative BCFA, anteiso-15:0 and iso-18:0. We also assessed competition between BCFA and normal saturated fatty acid (n-SFA).
Methods
MCF7 human breast cancer cells are used for functional studies. PcDNA3.1 expression vector was used to clone seven open reading frames of ELOVL transcripts (ELOVL1–7). MCF7 cells were transiently transfected with specific ELOVL1–7 transgene vector or empty vector (control). After 24 h incubation, the transfected MCF7 cells were treated with BSA-bound substrates. After additional 24 h incubation, cells were harvested by trypsinization, fatty acid methyl esters prepared and analyzed quantitatively by GC-FID. Fatty acid composition was characterized by gas chromatography (GC) –electron ionization mass spectrometry (EIMS) and EIMS/MS for branched carbon chain.
Results
Transient transfection of ELOVL1–7 into MCF7 cells show that ELOVL6 had highest activity towards elongation of anteiso-15:0→anteiso-17:0, followed by ELOVL5 which showed moderate activity. ELOVL3 was found to be most active ELOVL mediating elongation of iso-18:0→iso-20:0. Our competition results show in ELOVL6 cells anteiso-15:0 competes with n-SFA n-16:0, whereas, in ELOVL3 cells iso-18:0 competes with n-18:0.
Conclusions
The elongation of anteiso-15:0 and iso-18:0 BCFA is predominantly operated by the ELOVL6 and ELOVL3, respectively that are well known to operate on normal saturated fatty acids, rather than the ELOVL2 and ELOVL5 which operate on lower-melting polyunsaturated fatty acids. The competition between BCFA and n-SFA for ELOVL1–7 mediated elongation may have implications in the skin, sebaceous, and meibomian glands where both normal and BCFA are present at comparable levels.
Funding Sources
NIH grant R01 AT007003.