Lipoic acid metabolism in the rat |
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Authors: | Joseph T Spence Donald B McCormick |
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Institution: | Division of Nutritional Sciences and the Section of Biochemistry, Molecular and Cell Biology, Cornell University, Savage Hall, Ithaca, New York 14853 USA |
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Abstract: | dl-1,6-14C]Lipoic acid was administered by intraperitoneal injection to rats at the level of 0.5 mg/100 g body weight. Approximately 56% of the radioactivity was recovered in the urine. When acidified and extracted with benzene, 92% of the radioactivity remained in the aqueous phase. Gel-filtration and paper chromatography were used to identify three of the compounds in the benzene extract as lipoic, bisnorlipoic and tetranorlipoic acids. In addition, a keto compound appears to be present. The aqueous phase contained several radioactive components separable by ion-exchange and paper chromatographies. Two of these compounds were identified as lipoate and β-hydroxybisnorlipoate. No evidence for oxidation of the dithiolane ring of lipoic acid was observed. dl-7,8-14C]Lipoic acid was administered to rats under the same conditions. The urine contained 81% of the radioactivity, 72% of which remained in the aqueous phase and 28% was extracted into benzene. In contrast to over 30% of the label from dl-(1,6-14C] lipoate being expired as 14CO2, a negligible amount of 14CO2 was produced by rats injected with dl-7,8-14C]lipoate. The catabolites identified were the same as those found using the 1,6-labeled lipoate. Another dithiolane-intact compound was also isolated. It appears that the rat, similar to Pseudomonas putida LP, metabolizes lipoate mainly via β-oxidation of the valeric acid side chain. |
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