Relation of short-term pyridoxine-HCI supplementation to plasma vitamin B−6 vitamers and amino acid concentrations in young women

Abstract

Pyridoxal 5'-phosphate (PLP) is a coenzyme in many metabolic transformations of amino acids and may play a role in their absorption and transport. This investigation analyzed the effects of large oral doses (27 mg/d) of pyridoxine (PN)-HCl over 2 wk on plasma PLP and amino acid concentrations in 10 young women. Plasma PLP was 45 +/- 2 nmol/L (means +/- SE) initially and reached 377 +/- 12 nmol/L after 7 d of supplementation. A steady-state PLP concentration remained as long as daily PN-HCl supplementation was continued. Plasma glutamic acid concentration was significantly lower after 7 and 14 d of supplementation whereas alpha-amino-N-butyric acid, alanine, cysteine, arginine, phosphoserine, and urea concentrations were significantly higher, particularly alpha-amino-N-butyric acid and cysteine. Altered plasma amino acid profiles and increased plasma urea concentrations in response to supplementation suggested accelerated protein and/or amino acid metabolism.

Effect of Phosphate on Stability of Pyridoxal in the Presence of Lysine

“…Interestingly, in vivo formation of similar cyclic compounds was reported from L-dopa and PLP or PL in the liver and blood of rats (15) and from histamine and PLP or PL in the tissues and urine of mice ( 16) when large quantities of L-dopa or histamine were given to the animal. Although plasma PLP was as low as 45 ( 2 nmol/L initially, it reached 377 ( 12 nmol/L after 7 days of supplementation (17). The possibility for the interaction between L-lysine and PLP to proceed in vivo increases as the concentration of L-lysine increases in blood when excess L-lysine is given the animals in the lysine-fortified cereal foods.…”