Nutritional folate deficiency augments the in vivo mutagenic and lymphocytotoxic activities of alkylating agents

Abstract

To investigate the interaction of folate deficiency and alkylating agents in vivo, weanling Fischer 344 rats were maintained for 5 weeks on a folate replete, moderately folate deficient, or a severely folate deficient diet. Mutant frequencies at the HPRT locus in splenic lymphocytes were 1.2 ± 0.6, 1.9 ±1.1, and 6.4 ± 4.0 × 10−6, respectively (P < 0.01). N‐nitroso‐N‐ethylurea (ENU), 100 mg/kg body weight, was much more mutagenic with progressive folate deficiency (5.0 ± 2.4 vs. 16.2 ± 7.3 vs. 39.2 ± 21.0 × 10−6), suggesting a synergistic interaction (P ≪ 0.01). Neither moderate nor severe folate deficiency significantly enhanced the mutagenic effects of cyclophosphamide, 50 mg/kgbody weight (18.0 ± 7.9 vs. 6.0 ± 2.8 vs. 28.5 ± 28.2 × 10−6). The number of cloning cells/spleen were reduced 68% in moderately folate deficient rats and by 87% in severely deficient animals (P < 0.05). The combination of folate deficiency and cyclophosphamide reduced the total number of cloning cells further, but ENU alone, or in combination with folate deficiency, did not. These findings indicate that folate deficiency increases the risk of somatic mutations and is lymphocytotoxic in rats. Folate deficiency enhances the mutagenic but not the lymphotoxic effects of ENU, while it increases the lymphotoxic but not the mutagenic activity of cyclophosphamide. Correction of folate deficiency may decrease the immunologic and genetic damage caused by some alkylating agents. Environ. Mol. Mutagen. 32:33–38, 1998 © 1998 Wiley‐Liss, Inc.

Imbalanced Base Excision Repair in Response to Folate Deficiency Is Accelerated by Polymerase β Haploinsufficiency

“…We have clearly shown that reduced BER capacity in response to ␤-pol haploinsufficiency (17) and in response to aging (50) reduces the threshold of DNA damage tolerance. Folate deficiency likewise reduces tolerance to DNA damage (7)(8)(9)(10)(11), further support that BER deficiency is responsible for the phenotype expressed by folate deficiency. Additionally, a genetic defect in ␤-pol intensifies the effects of folate deficiency, demonstrating that ␤-pol haploinsufficiency and folate deficiency interact to increase cancer risk.…”

“…The accumulation of strand breaks, mutations, and chromosomal instability observed in response to folate deficiency all suggest that DNA repair capacity is inhibited. In support of this, folate-deficient cells and animals inefficiently repair alkylation damage (7). Folate deficiency acts synergistically with ethane methyl sulfonate in Chinese hamster ovary cells (8), suggesting an inability to repair ethane methyl sulfonate-induced damage.…”

“…Mice with gene-targeted disruptions in the rate-limiting step of BER exhibit a dysregulation in this coordination and accumulate DNA single strand breaks both spontaneously and in response to carcinogen exposure, have a reduced DNA damage threshold, and exhibit genomic instability in the forms of both mutation induction and chromosomal damage (17). The phenotype of folate deficiency includes accumulation of strand breaks (9,10,15,18,19), reduced tolerance to DNA-damaging agents, increased mutation induction (7,8,20), and chromosomal instability (21, 22) (i.e. folate deficiency induces a phenotype identical to BER deficiency).…”

Effect of Folate on the Efficacy and Toxicity of Cancer Chemotherapy

“…The mutational spectrum after alkyator treatment in CHO cells probably is not representative of many other mammalian cell types because CHO cells lack alkyl transferase [40,41]. Therefore, studies of the effect of folate deficiency on the mutational spectrum in lymphocytes from rats treated with alkylating agents [30] and in human lymphocytes are planned. Studies in human cells may be useful both to provide additional insights into the synergy between folate deficiency and mutation induction and for molecular epidemiologic approaches to elucidate the relationship between dietary components such as folic acid and environmental mutagens or carcinogens.…”

“…[28,29]). In addition, our laboratory has shown that deficiency of this vitamin acts synergistically with alkylating agents to increase DNA strand breaks and mutant frequencies at the hprt locus both in vitro and in vivo [21,30]. To elucidate the mechanism underlying this synergy, we performed molecular analyses of hprt mutant CHO cells that were treated with EMS or AT-nitroso-TY-ethylurea (ENU).…”