ALTERATIONS IN NUCLEOTIDE POOLS IN RATS FED DIETS DEFICIENT IN CHOLINE, METHIONINE AND OR FOLIC-ACID

The fidelity of DNA synthesis is critically dependent on the correct balance and availability of the deoxynucleoside triphosphate (dNTP) percursors for the polymerases involved in replication and repair. Since folate-derived one-carbon groups are essential for the de novo synthesis of both purines and pyrimidines, the purpose of the present investigation was to determine whether diet-induced depletion of folates would alter intracellular dNTP pools. Fischer 344 rats were fed one of four semi-purified diets for a period of 8 weeks: (i) supplemented control; (ii) deficient in folic acid; (iii) deficient in methionine and choline; and (iv) deficient in methionine, choline and folic acid. In contrast to natural diets, semi-purified diets are nucleotide-free and consequently lack substrates for salvage pathway synthesis. This omission may place unusual stress on folate-dependent de novo nucleotide synthesis especially under conditions of dietary methyl-donor deficiency. Reversed-phase HPLC analysis of dNTP in spleen cell extracts indicated that both the thymidylate monophosphate and thymidylate triphosphate pools were decreased in spleen cells from the deficient rats consistent with a decrease in folate-dependent de novo synthesis. In addition, purine biosynthesis appeared to be negatively affect by methyl-donor deficiency as evidenced by a reduction in dGTP and dATP pools. These data indicate that deoxynucleotide pool imbalance, well known to produce cytogenetic and mutagenic events in vitro, can also be induced in this in vivo model of diet-induced carcinogenesis.