5-6-7-8-tetrahydrofolic-acid and Choline-Deficiency

Topics: Animals; Antibody Formation; Carcinogens; Choline; Choline Deficiency; Diet; DNA; Folic Acid; Folic Acid Deficiency; Humans; Immunity, Cellular; Lipotropic Agents; Liver; Liver Neoplasms; Methionine; Methylation; Neoplasms; Neoplasms, Experimental; Pharmaceutical Preparations; Risk; Tetrahydrofolates; Vitamin B 12; Vitamin B 12 Deficiency

We examined the effects of feeding rats a choline deficient diet, of treating rats with low doses of methotrexate (MTX, 0.1 mg/kg, daily), and of combined choline deficiency and MTX treatment upon the content and distribution of folates in liver. We used a newly devised technique for analysis of folates which utilized affinity chromatography followed by high pressure liquid chromatography. Compared to control rats, total hepatic folate content decreased by 31% in the choline deficient rats, by 48% in the MTX treated rats, and by 60% in rats which were both choline deficient and treated with MTX. In extracts of livers from control rats, folates were present predominantly as penta (35%) and hexaglutamyl (52%) derivatives. The pteridine ring structure distribution of these folates was as follows: 48% 5-methyltetrahydrofolate, 14% formylated tetrahydrofolate, and 39% tetrahydrofolate. In choline deficient animals, there was a decrease in the relative concentration of pentaglutamyl folates and an increase in the relative concentration of heptaglutamyl folates. In livers from MTX treated animals, MTX-polyglutamates with 2-5 glutamate residues accumulated. The consequences of MTX treatment were: a) an elongation of the glutamate chains of the folates as the proportion of hepta- and octaglutamyl derivatives was increased relative to penta- and hexaglutamyl folates; b) the occurrence of unreduced folic acid; c) a decrease in the relative concentration of 5-methyltetrahydrofolate and an increase in the relative concentration of formylated tetrahydrofolate, and d) no change in the relative concentrations of tetrahydrofolate. In livers from animals that were both choline deficient and treated with MTX, the tetrahydrofolate concentrations were 50% of control while formylated tetrahydrofolate concentrations increased 3-fold. These data are discussed from the standpoint of the current understanding of mechanisms that regulate the elongation of the glutamic acid chains of folates and those that regulate folate dependent synthesis and utilization of one carbon unit.

Topics: Animals; Choline Deficiency; Chromatography, High Pressure Liquid; Folic Acid; Liver; Methotrexate; Pteroylpolyglutamic Acids; Rats; Rats, Inbred Strains; Tetrahydrofolates

The carcinogenic effects of methyl-deficient, amino acid-defined diets have been attributed to alterations in cellular methylation reactions. These diets contain no choline, and methionine is replaced by homocysteine. Hence, all methyl groups needed for methionine biosynthesis with subsequent formation of S-adenosylmethionine and polyamines must be formed de novo utilizing folate-dependent reduction of one-carbon units. In rats fed the methyl-deficient diet, there was a marked decrease in total liver folate levels. This decrease was apparent in the levels of the individual forms of folate: 10-HCO-H4folate, 5-HCO-H4folate, 5-CH3-H4folate and H4folate. The percent of the total folate pool made up by 5-CH3-H4folate did not change, however, until after the rats had been fed the methyl-deficient diet for 4 wk, and then an increase was seen. After the methyl-deficient rats were switched to a nutritionally adequate control diet containing methionine and choline, all values rapidly reversed. Increased use of folate for methyl group biosynthesis may be responsible for the loss of folates from the liver.

Topics: Amino Acids; Animals; Choline Deficiency; Chromatography, High Pressure Liquid; Diet; Folic Acid; Leucovorin; Liver; Male; Methionine; Methylation; Rats; Rats, Inbred F344; Tetrahydrofolates