Add time:07/12/2019         Source:sciencedirect.com

1.1. Urine samples from healthy humans have been analysed for branched shortchain dicarboxylic acids using combined gas-liquid chromatography-mass spectrometry.2.2. Methylsuccinic, 3-methylglutaric, 3-methylhexanedioic, 3-methylheptanedioic, and 3-methyloctanedioic acid were present in all urine samples examined. 3-Methylhexanedioic acid was excreted in amounts of 0.10–0.19 mmole in 24 h, the others in much smaller quantities (from traces to 0.03 mmole in 24 h).3.3. The amounts of branched short-chain dicarboxylic acids excreted in urine were not significantly influenced by a period of three days on a synthetic diet consisting of tripalmitin, triolein, sucrose, and water. Ketotic patients showed a normal or only a slightly raised urinary excretion of 3-methylhexanedioic acid, whereas the excretion of the straight-chained hexanedioic acid was markedly increased. Thus, neither the diet nor the fat depots seem to contain the precursors of the branched dicarboxylic acids.4.4. Since even trace amounts of 2,6-dimethyloctanedioic acid were lacking in the urine samples, 3-methylhexanedioic acid does probably not stem from the degradation of isoprenoid compounds. Feeding of 3-methylhexadecanoic acid to rats resulted in a slight increase of urinary 3-methylhexanedioic acid.5.5. It is suggested that the branched short-chain dicarboxylic acids are formed from 3-methyl-substituted or ante-iso medium- or long-chain fatty acids of even or uneven chain-length by a primary Ω-oxidation followed by β-oxidations. Microorganisms in the intestinal tract, which are known to produce monomethyl-substituted fatty acids, may possibly function as a precursor pool for the urinary branched dicarboxylic acids.

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