Biosynthesis of folate polyglutamates in the rat

Abstract

The biosynthesis of folate polyglutamates and the disposition of the folate monoglutamate pool have been investigated in the tissues of normal and tumour-bearing rats following the oral administration of radio labelled folic acid. The principal folate monoglutamates detected were identified as 5-methyltetrahydrofolate (SCH, THF) and unmetabolised folic acid (FA). These species were found in the liver and intestine of normal and host rats and in the tumour tissue, showed maximal levels between 2-6 hours after folic acid administration and were not detected at 24 or 48 hours. A progressive synthesis of folate polyglutamates was demonstrated in all tissues; these derivatives representing 85+10% (mean * SD) (n=20) of the total radio labelled folate at 24 hours after administration. DEAE-cellulose chromatography revealed three principal folate polyglutamates; folate polyglutamates A, B and C. Preliminary identification indicated these to be 10-formylfolic acid tetraglutamate (10CHOFA(glu) ,), 5-methyltetrahydrofolatetriglutamate (SCH, THF (glu) ) and a tetrahydrofolate polyglutamate (THF (glu) _) respectively. Tumour induced effects on the disposition of the hepatic folate pool were suggested. Between 2-6 hours after folic acid administration, the cumulative levels of SCH, THF were higher in rats bearing the sarcoma Mc103B or the Walker 256 carcosarcoma, than the corresponding normal rats. The biosynthesis of folate polyglutamates in the host liver was unaffected in rats bearing the sarcoma Mc103B, but reduced in rats bearing the Walker 256 carcosarcoma, compared to the normal rats. High performance liquid chromatography (HPLC) has been developed for the analysis of folate polyglutamates. Under suitable conditions, folate polyglutamates were rapidly resolved from folate monoglutamates and in most cases, from each other. This procedure offers considerable advantages over more conventional methods of folate analysis. Under conditions of gradient elution,a good linear relationship was observed between the retention time and the number of glutamate residues of three classes of folate polyglutamates. This observation may allow an effective theoretical approach to the identification of these species. HPLC analysis of tissue extracts revealed certain difficulties.