Xanthurenic Acid

Because this pathway is heavily dependent on vitamin B6, elevations of xanthurenic acid can reflect a functional need for vitamin B6.

Kynurenine pathway metabolites may also become elevated when there are needs for vitamin B3.

Elevations in urinary xanthurenic acid are seen with increased intake of tryptophan, and in high estrogen states. Pregnancy and oral contraceptive use is associated with elevated levels of urinary xanthurenic acid where a functional nutrient need for B-vitamins is pronounced.

Abnormalities in the kynurenine pathway have been associated with many clinical conditions including immune suppression, cancer, and inflammatory conditions. Administration of vitamin B6 can decrease xanthurenic acid excretion.

Xanthurenic acid is produced as part of the kynurenine pathway of tryptophan catabolism, along with kynurenic and quinolinic acid.

From the breakdown of hydroxykynurenine via kynurenine aminotransferases (KAT) +B6

- Elevated xanthurenic acid has been noted with B6 deficiency.

- Elevated levels have been noted as more significant in oral contraceptive users in studies using a tryptophan load.

- In a mathematical model without a tryptophan load, a moderate vitamin B6 deficiency resulted in a slight increase in xanthurenic acid and a slight decrease in kynurenic acid and anthranilate.

- Without a tryptophan load, urine kynurenine and xanthurenic acid both increase in a pronounced B6 deficiency.

- Animal studies found a low urinary excretion ratio of xanthurenic acid/ kynurenic acid as a possible marker of niacin need, proposing that levels may increase with repletion.

- Niacin (vitamin B3) is a product of tryptophan degradation. In alcoholic pellagra patients, the tryptophanniacin pathway is inhibited after the 3-hydroxyanthranilate oxidase step, which can result in increased kynurenic acid, and decreased xanthurenic acid and quinolinic acid.