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[Inhibitors of folic acid metabolism (author's transl)].

In contrast to antibiotic research, the study of folic acid metabolism and folic acid antagonists is conducted in the classical tradition of chemotherapy established by Paul Ehrlich. The elucidation of the mechanism of action of sulphonamides created an important prerequisite for the understanding of the biosynthesis of folic acid. The synthesis of inhibitors of dihydrofolate-reductase was guided on the one hand by the structure of dihydrofolate itself, and on the other hand by the fact that this substnce is essential for the growth of certain bacteria. Both approaches led to the synthesis of compounds which were effective and could be used therapeutically. The mechanism of selectivity of folic acid antagonists is described. A short account of the biochemical and genetic basis of resistance to folic acid antagonists is also given. The study of folic acid metabolism and folic acid antagonists provides a good example of the successful interaction of mechanistically inspired biochemical and chemical methods on the one hand, and an empirical approach characterised by the study of more complex biological phenomena on the other hand.

Folic Acid↗

Whole-body autoradiographic disposition and plasma pharmacokinetics of 5,10-dideazatetrahydrofolic acid in mice fed folic acid-deficient or regular diets.

The effect of folic acid depletion on the tissue distribution and plasma pharmacokinetics of the oncolytic agent 5,10-dideazatetrahydrofolic acid (DDATHF) was evaluated in mice fed either folic acid-deficient or regular diets. Mice were maintained on diets for 2 weeks prior to receiving a single i.v. 30 mg/kg dose of [14C]DDATHF (tissue distribution) or DDATHF (plasma pharmacokinetics). Whole-body autoradiographic evaluation and plasma analysis for DDATHF were conducted in mice at 5 min and 6, 24, 48, 96, 120, and 168 h postdose. Radiocarbon associated with [14C]DDATHF was readily distributed to all tissues in both diet groups at the early time points and was rapidly cleared from most tissues at 24 h postdose. At the later time points, substantial amounts of radioactivity remained in liver from mice fed either diet. However, levels of radiocarbon in liver from mice fed the folic acid-deficient diet were approximately 2.5-4.2-fold the radiocarbon levels in liver from mice fed the regular diet. Similarly, plasma pharmacokinetics indicated that mice fed the folic acid-deficient diet had sustained plasma concentrations of DDATHF compared to plasma concentrations in mice fed the regular diet. These data indicated that a deficiency in dietary folic acid in mice caused increased hepatic retention of radioactivity and sustained plasma concentrations of DDATHF which are probably responsible for the observed toxicity of DDATHF in mice.

Animals↗

Folate antagonism following teratogenic exposure to diphenylhydantoin.

Previous studies have reported indirect evidence for the mediation of folate antagonism in the induction of malformations by diphenylhydantion. We have demonstrated that a teratogenic regimen of folate-deficiency and antagonism using 9-methyl PGA in the rat produces significantly decreased rates of oxygen consumption in the maldeveloping embryos. The present study reports similar reductions in oxygen uptake by mouse embryos from mothers treated with teratogenic doses of diphenylhydantoin, and documents a significant depression of the actual folate levels in such embryos. The differences are less significant with lower doses of diphenylhydantoin, and do not occur with a nonteratogenic dose.

Abnormalities, Drug-Induced↗

Folic acid.

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Animals↗