Determination of plasma glucose enrichment in human subjects after primed, constant infusions of 13C‐glycine before and after dietary vitamin B‐6 restriction

Abstract

Pyridoxal 5′‐phosphate (PLP) is involved in the production of glucogenic substrates via its role as a coenzyme for transamination reactions. A deficiency of vitamin B‐6 leads to impaired availability of glucogenic amino acids in rats and may affect glucose synthesis rates. This study aims to assess the impact of marginal vitamin B‐6 deficiency (plasma PLP 20 ‐30 nM) on gluconeogenesis from glycine in humans. We report here the feasibility of determining the rate and extent of glucose synthesis from an infused precursor. Thirteen healthy men and women received primed, constant infusions of 9.26 µmol/(kg*h) [1,2‐13C2]glycine before and after a 28‐d dietary vitamin B‐6 restriction. Plasma glucose was analyzed by positive chemical ionization gas chromatography‐mass spectrometry following preparation of glucose aldonitrile pentaacetate derivatives. This infusion protocol yields glycine M+2 enrichment of 5.2 mole % excess (MPE), with serine M+1 and serine M+2 enrichment of 0.7 and 1.4 MPE, respectively. Plasma glucose M+1 enrichment in this protocol was approximately 0.4 MPE. Investigation is underway to determine glucose synthesis rates and evaluate the effect of vitamin B‐6 status on gluconeogenesis. Supported by NIH grant DK072398 and GCRC grant M01‐RR00082.Grant Funding SourceNIH