Substrate product ratios of enzymes in the kynurenine pathway measured in plasma as indicators of functional vitamin B-6 status

Tryptophan metabolism through the kynurenine pathway includes 2 vitamin B-6 [pyridoxal 5′-phosphate (PLP)]–dependent enzymes. We recently showed that plasma 3-hydroxykynurenine (HK) was elevated at low PLP concentrations. We further evaluated and characterized kynurenine-based indexes as possible markers of functional B-vitamin status in plasma. Cross-sectional and longitudinal data were derived from the Western Norway B-vitamin Intervention...