Original Article

Studies of the metabolism of -tocopherol stereoisomers in rats using [5-methyl-¹⁴C]SRR- and RRR--tocopherol

Correspondence to: Chikako Kiyose

We investigated the distribution and metabolism of SRR--tocopherol (SRR--Toc), synthetic -Toc compared with RRR--Toc, in rats after a single oral administration of 2 mg (20 µCi) SRR- and RRR--[5-methyl-¹⁴C]Toc. In the liver, there was no difference in the recovery of radioactivity until 12 h after administration, and it reached a maximum of 4.4% of the dose after 12 h, but in other tissues, radioactivity derived from RRR--Toc was clearly higher than that derived from SRR--Toc after 12 h. For 96 h after administration, urinary excretions of SRR--Toc were 7.8% of the dose and significantly greater than that of RRR--Toc, which was 1.3% of the dose. On the other hand, total fecal excretions of SRR- and RRR--Toc were 87.6% and 83.0%, respectively. Therefore, radioactivity in the urine was assumed to have transferred out of the liver. Furthermore, the urine samples were hydrolyzed with 3 N methanolic HCl and analyzed by high performance liquid chromatography (HPLC) and liquid chromatography/mass spectrometry.

The results showed that about 73% of the total radioactivity injected into HPLC was found to be 2,5,7,8-tetramethyl-2-(2'-carboxyethyl)-6-hydroxy chroman (-CEHC), as well as RRR--Toc. Thus, there is no difference between SRR--Toc and RRR--Toc in metabolic pathways, and it is suggested that SRR--Toc discriminated in the liver is rapidly metabolized by the liver and excreted as the conjugate of -CEHC in the urine.—Kaneko, K., C. Kiyose, T. Ueda, H. Ichikawa, and O. Igarishi. Studies of the metabolism of -tocopherol stereoisomers in rats using [5-methy1-¹⁴C]SRR- and RRR--tocopherol. J. Lipid Res. 2000. 41: 357;–367.

Supplementary key words: RRR--tocopherol, SRR--tocopherol, RRR--[5-methyl-¹⁴C]tocopherol, SRR--[5-methyl-¹⁴C]tocopherol, -CEHC, -tocopherol metabolism in vivo, distribution of radioactivity in rat, detection of LC-MS, urine metabolites

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