Novel urinary metabolite of d-& tocopherol in rats

A novel metabolite of d-&tocopherol was isolated from the urine of rats given d-3,4-[sH2]-6-tocopherol intravenously. The metabolite was collected from the urine of rats given d-&tocopherol in the same manner as that of the labeled compound. It was found that the metabolites consisted of sulfate conjugates. The portion of the major metabolite released with sulfatase was determined to be 2,8-dimethyI-2-(2‘-carboxyethyl)6-chromanol by infrared spectra, nuclear magnetic resonance spectra, and mass spectra. The proposed structure was confirmed by comparing the analytical results with those of a synthetically derived compound. As a result of the structural elucidation of this novel metabolite, a pathway for the biological transformation of &tocopherol is proposed which is different from that of atocopherol. A characteristic feature of the pathway is the absence of any opening of the chroman ring throughout the sequence.Chiku, S. , K. Hamamura, and T. Nakamura. Novel urinary metabolite of d-&tocopherol in rats. ]. Lipid Res. 1984. 25: 4048. Supplementary key words d-a-tocopherol d-3,4-[ ’H2]-6-tocopherol d-5-methyl-[14C]-cu-tocopherol urinary metabolites conjugates of sulfuric acid Tocopherol homologues are distributed widely in nature and occur mainly in a variety of plants. &Tocopherol is the most abundant of these homologues occurring naturally. The antioxidative activity of b-tocopherol is greater than that of a-tocopherol in vitro (1-4), but has less biological activity in vivo (5-9). &Tocopherol differs from a-tocopherol in that the former lacks two methyl groups in the aromatic ring of the chroman nucleus. Although studies on the biological transformation of a-tocopherol have been conducted (1 0-1 7), investigations into the transformation of b-tocopherol have not been reported. Simon et al. (1 8, 19) characterized two metabolites from the urine of rabbits and humans given large doses of atocopherol. After hydrolysis these metabolites were identified as a hydroxy acid and its lactone. The isolation of these metabolites provided a basis by which a possible metabolic pathway for tocopherol homologues could be constructed (Fig. 1). Watanabe et al. (20) later characterized minor urinary metabolites in the transformation of a-tocopherol and proposed a modification to the metabolic pathway described by Simon et al. (18, 19). The modified sequence proceeds as follows. a-Tocopheronic acid, formed by the w-oxidation of a-tocopherol, is in part converted to atocopheronolactone and in part dehydrated so that an unsaturated, coenzyme A derivative (E acid-I-CoA) is formed. By &oxidation and simultaneous reduction of E acid-I, two carbon units are removed to form E acid-11CoA. Thus, these metabolites are converted to their corresponding hydroquinones and excreted as conjugates. Urinary metabolites are excreted either as monoor diconjugates of glucuronic acid or sulfuric acid, or both. In the present study we describe the separation of a major metabolite of b-tocopherol from the urine of rats given b-tocopherol intravenously and the unambiguous determination of the structure of this metabolite. It is suggested that the metabolic pathway of b-tocopherol is different from that of a-tocopherol. MATERIALS AND METHODS