In vivo characterization of the absorption and biotransformation of pteroylmonoglutamic acid in man: a model for future studies.
HPLC-EC has been used to measure the appearance of 5-CH3-H4 folic acid in human plasma following oral administration of folic acid. The process was found to be saturable in accordance with Michaelis-Menten kinetics. The apparent Km for this enzyme system indicates that low doses of oral folic acid are rapidly converted into 5-CH3-H4 folic acid, an observation consistent with the needs of intestinal absorption of essential trace nutrients. The appearance of L. casei active folate in plasma was not rate-limited and showed a biphasic relationship to dose. Preparative HPLC combined with L. casei bioassay demonstrated that most of the L. casei active folate appearing in plasma following a 20,000-micrograms dose of folic acid was due to the unmodified vitamin, only 5.6% being due to 5-CH3-H4 folic acid and with no detectable contribution from 5-CHO-H4 folic acid. The absorption characteristics of the system seem consistent between and within subject(s). No relationship could be demonstrated between predose levels of plasma 5-CH3-H4 folic acid and total folate in erythrocytes, which reflect the status of transport and storage forms of the vitamin, respectively.
Lucock
M D
MD
University of Leeds, Department of Pediatrics and Child Health, United Kingdom.
Wild
J
J
Smithells
R W
RW
Hartley
R
R
D000042:Absorption; D000284:Administration, Oral; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D005260:Female; D005492:Folic Acid / Q000097:blood / Q000493:pharmacokinetics*; D006801:Humans; D007780:Lacticaseibacillus casei / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008954:Models, Biological
D005492:Folic Acid