Drugs, toxins and dietary amino acids affecting vitamin B12 or folic acid absorption or utilization

Renal Glycoprotein: Glycosyl Transferase Activities after Administration of Folic Acid

“…Similar in vitro results were obtained with methotrexate, but not with 5-formyl tetrahydrofolic acid. These findings are not explicable in terms of the known co-factor functions of folic acid [18,19,24] or the action of methotrexate as a folic acid antagonist [10]. Inasmuch as methotrexate, which does not precipitate in tubules [9,22] was ineffective in vivo in stimu lating glycoprotein : glycosyl transferase activity, it is concluded that the enzyme changes related to folic acid administration reported here are attribu table primarily to membrane injury rather than to any direct stimulation of the transferase enzymes.…”

Megaloblastic Anemia due to Folic Acid Deficiency in a Young Woman on Oral Contraceptives

“…Inhibition of Bc-conjugase must then be admitted [1]. The same mechanism has been evidenced with diphenyl-hydantoin [2,5,14].…”

“…A few cases of ane mia have even been described in this situation [11]; this type of anemia responded either to oral folic acid, or to a simple discontinuation of the contraceptive medication. Hormonal contraceptives seem to have the same action as diphenylhydantoin on the intestinal enzyme responsible for the deconjugation of food folates [1,12,14] and thus inhibit their absorption. However, it seems unlikely that this mechanism should be alone responsible for the development of this type of anemia.…”

Folate Deficiency in Humans

“…It has been suggested by various authors that protein binding of food folate may limit its absorption (Tamura and Stokstad, 1973;Butterworth and Krumdieck, 1975;Rosenberg, 1976), but no evidence for this hypothesis has been documented. Although it is possible that excess dietary glycine and methionine may interfere with folate absorption, their megaloblastic effects are probably attributable to impairment of its utilization (Waxman et al, 1970).…”