Low levels of pyridoxal 5'-phosphate in patients with cystic fibrosis.

To determine the effect of cystic fibrosis on the regulation of plasma pyridoxal 5'-phosphate (PLP), the biologically active form of vitamin B6, we measured this compound in plasma from 56 patients with cystic fibrosis. The concentration of PLP in plasma was assayed by a radioenzymatic technique. The results of this study showed that PLP concentration was decreased significantly (6.44 +/- 5.20 ng/mL, mean +/- SD; median 4.45 ng/mL) in patients with cystic fibrosis as compared with a group of hospitalized children with neither cystic fibrosis nor hepatic disease serving as a control group (13.2 +/- 5.04 ng/mL, mean +/- SD; median 12.5 ng/mL). Additionally, 25% of the population with cystic fibrosis exhibited exceedingly low plasma PLP level (less than 2.75 ng/mL). In patients with cystic fibrosis, significant inverse linear associations were found between plasma PLP and serum levels of SGOT and SGPT (PLP v SGOT: r = -.60, P less than .03; PLP v SGPT: r = -.50, P less than .03). This study demonstrated that a deficiency of plasma PLP is a common abnormality in cystic fibrosis and that the low PLP level may be a reflection of impaired vitamin B6 metabolism associated with this disorder.