Vitamin B6 deficiency in chronic liver disease--evidence for increased degradation of pyridoxal-5'-phosphate.

Plasma levels of pyridoxal-5'-phosphate (PLP), the active coenzyme form of vitamin B6, were found to be significantly lower than normal in 22 out of 31 patients with decompensated cirrhosis or subacute hepatic necrosis. There was no significant difference in plasma PLP levels between those with liver disease due to alcohol and those with other varieties. When intravenous supplements with pyridoxine hydrochloride were given only 33% responded with an increase in plasma PLP. In contrast, all patients given PLP responded, although peak plasma levels were variable, the response being significantly less than that found in normal control subjects. After supplementation with pyridoxine hydrochloride, and with PLP, the urinary excretion of 4-pyridoxic acid, which is derived from the degradation of PLP, was higher in patients who showed the least increase in plasma PLP levels. Although impaired phosphorylation of pyridoxine hydrochloride may be one factor, the most likely explanation for these findings is an increased rate of PLP degradation which may be important in the pathogenesis of vitamin B6 deficiency in patients with severe liver disease.