Urinary excretion of folate catabolites responds to changes in folate intake more slowly than plasma folate and homocysteine concentrations and lymphocyte DNA methylation in postmenopausal women

Folate turnover involves urinary excretion, fecal excretion, and catabolism that involves cleavage of the C9-N10 bond to yield pterins and para-aminob enzoylglutamate (pABG). Little is known about the relationship between the function of folate pools and their rates of catabolism. We report here an i nvestigation of excretion of urinary pABG and its primary excretory form, p ara-acetamldobenzoyiglutamete (ApABG) in samples collected during a previou sly published study of postmenopausal women. Ten women (49-63 y) were fed a low folate diet (56 mug/d) supplemented with folio acid to yield total fol ate intakes of 195 mug/d (d 1-5), 56 mug/d (d 6-41), 111 mug/d (d 42-69), 2 85 mug/d (d 70-80) and 516 mug/d (d 81-91). This caused changes in plasma f olate, plasma homocysteine and global methylation of lymphocyte DNA. For ea ch subject, a 7-d pooled urine sample was collected over d 1-7, 36-42, 64-7 0 and 85-91. ApABG constituted >85% of total catabolite excretion, and fola te intake did not significantly influence ApABG or pABG excretion. The mola r ratio of total catabolite excretion/folate intake varied significantly, w ith ratios of 1.0 +/- 0.17 (d 1-7), 3.0 +/- 0.55 (d 36-42), 1.1 +/- 0.18 (d 64-70) and 0.33 +/- 0.054 (d 85-91). These observations indicate that the rate of folate catabolite excretion is related mainly to masses of slow-tur nover folate pools governed by long-term folate intake. Folate pools functi oning in some forms of methyl group metabolism respond to dietary changes i n folate intake much more rapidly.