Homocystinuria: the effect of pyridoxine supplementation on cultured skin fibroblasts.

Six skin fibroblast cultures, two derived from pyridoxine responsive homocystinurics, two from pyridoxine non-responsive homocystinurics, one from an obligate heterozygote and one from a normal control were grown for three passages in the presence of 9.7 mu mol/l, 243 mu mol/l and 486 mu mol/l of pyridoxine respectively. Cystathionine beta-synthase activity was stimulated in all four homocystinuric cell strains at 486 mu mol/l; aspartate and alanine aminotransferase activity was also increased, particularly in the pyridoxine responsive cell strains. There was, however, evidence of cytotoxicity at the pyridoxine levels of 243 mu mol/l and 486 mu mol/l.