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

Abstract

Abstract: We investigated the distribution and metabolism of SRR-α-tocopherol (SRR-α-Toc), synthetic α-Toc compared with RRR-α-Toc, in rats after a single oral administration of 2 mg (20 μCi) SRR- and RRR-α-[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-α-Toc was clearly higher than that derived from SRR-α-Toc after 12 h. For 96 h after administration, urinary excretions of SRR-α-Toc were 7.8% of the dose and significantly greater than that of RRR-α-Toc, which was 1.3% of the dose. On the other hand, total fecal excretions of SRR- and RRR-α-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 (α-CEHC), as well as RRR-α-Toc. Thus, there is no difference between SRR-α-Toc and RRR-α-Toc in metabolic pathways, and it is suggested that SRR-α-Toc discriminated in the liver is rapidly metabolized by the liver and excreted as the conjugate of α-CEHC in the urine. —Kaneko, K., C. Kiyose, T. Ueda, H. Ichikawa, and O. Igarishi. Studies of the metabolism of α-tocopherol stereoisomers in rats using [5-methy1-14C]SRR- and RRR-α-tocopherol. J. Lipid Res. 2000. 41: 357–367.

Keywords

• RRR-α-tocopherol
• SRR-α-tocopherol
• RRR-α-[5-methyl-14C]tocopherol
• SRR-α-[5-methyl-14C]tocopherol
• α-CEHC
• α-tocopherol metabolism in vivo