PubMed · 8450776
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G M Shenfield. 1993-02-01. Slow-release overdose.. https://doi.org/10.5694/j.1326-5377.1993.tb121689.x
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The metabolic role of 5-formyltetrahydrofolate is not known; however, it is an inhibitor of several folate-dependent enzymes including serine hydroxymethyltransferase. Methenyltetrahydrofolate synthetase (MTHFS) is the only enzyme known to metabolize 5-formyltetrahydrofolate and catalyzes the conversion of 5-formyltetrahydrofolate to 5,10-methenyltetrahydrofolate. In order to address the function of 5-formyltetrahydrofolate in mammalian cells, intracellular 5-formyltetrahydrofolate levels were depleted in human 5Y neuroblastoma by overexpressing the human cDNA encoding MTHFS (5YMTHFS cells). When cultured with 2 mM exogenous glycine, the intracellular serine and glycine concentrations in 5YMTHFS cells are elevated approximately 3-fold relative to 5Y cells; 5YMTHFS cells do not contain measurable levels of free methionine and display a 30-40% decrease in cell proliferation rates compared with 5Y cells. Medium supplemented with pharmacological levels of exogenous folinate or methionine ameliorated the glycine induced growth inhibition. Analysis of the folate derivatives demonstrated that 5-methyltetrahydrofolate accounts for 30% of total cellular folate in 5Y cells when cultured with 5 mM exogenous glycine. 5YMTHFS cells do not contain detectable levels of 5-methyltetrahydrofolate under the same culture conditions. These results suggest that 5-formyltetrahydrofolate inhibits serine hydroxymethyltransferase activity in vivo and that serine synthesis and homocysteine remethylation compete for one-carbon units in the cytoplasm.
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Hospital pharmacies in Massachusetts were surveyed to determine their patterns of stocking antidotes. Mailed questionnaires were completed by hospital pharmacy directors at 82 of 93 acute care institutions (87% response rate). Results confirmed great variability in on-site accessibility of antidotes. Only 8 of the 82 hospitals (9.8%) stocked all of 14 common antidotes inventoried by the survey. Even fewer hospital pharmacies stocked specific antidotes (eg, Crotalid anti-venin, digoxin-specific Fab antibodies, pyridoxine) in an adequate quantity to treat one poisoned adult. Larger hospitals and those with a 24-hour pharmacy were more likely to have certain antidotes than smaller institutions. We conclude that Massachusetts hospitals do not carry complete inventories of 14 common antidotes. It is important that poisoned patients be referred to medical centers with adequate toxicological care. Improved guidelines for the accessibility of antidotes need to be developed and made available to hospital pharmacies and emergency departments.