Hepatic microsomal and peroxisomal docosahexaenoate biosynthesis during piglet development
The roles of peroxisomes and microsomes on the biosynthetic pathway for docosahexaenoic acid (DHA) from [Alpha]-linolenic acid (ALA) were investigated. Microsomes and peroxisomes were prepared from livers of fetal and neonatal piglets by a combination of differential and gradient layer centrifugation. Microsomes, peroxisomes and combined cell fractions were incubated with [13C-U]-18:3n-3. The [M] and [M+18] isotopomers of the fatty acids in the LCPUFA n-3 pathway were detected by gas chromatograph-mass spectrometer (GC-MS). The quantity of each fatty acid was detemiined by gas chromatograph-flame ionization detector (GC-FID) and synthesis of each fatty acid was calculated for a 30-minute period. Synthesis of DHA was not detected in fetal liver. The data suggests that DHA in the fetus is probably supplied from maternal sources through the placenta. In either singly incubated microsomal or peroxisomal preparations from neonatal livers, no DHA synthesis was detected. After combination of the microsomal and peroxisomal fractions, DHA synthesis was evident and increased rapidly between birth and 2 week of age. This is the first demonstration of the entire biosynthetic LCPUFA n-3 pathway in sub-cellular organelles starting from isotopically labeled ALA to the final product, DHA, with all the intermediates present and isotopically labeled. The primary importance of the data is that it unequivocally demonstrates that peroxisomes are required for biosynthesis of DHA from ALA.
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