Lymphocyte propionyl-CoA carboxylase is an early and sensitive indicator of biotin deficiency in rats, but urinary excretion of 3-hydroxypropionic acid is not.

Recent clinical studies have provided evidence that marginal biotin deficiency is more common than previously thought. The validity of that conclusion rests on two indicators of biotin status that depend on renal function. Our goal was to develop and assess the usefulness of two additional indicators in detecting marginal biotin status in a rat model, i.e., 1) activity of the biotin-dependent enzyme propionyl-CoA carboxylase in lymphocytes; and 2) urinary excretion of 3-hydroxypropionic acid, an organic acid that reflects decreased activity of propionyl-CoA carboxylase. Marginal-to-moderate biotin deficiency was induced experimentally by an egg-white diet (deficient rats); the biotin-supplemented rats were fed the egg-white diet plus supplemental biotin. Propionyl-CoA carboxylase activity was determined by an optimized H(14)CO(3)(-) incorporation assay. Urinary organic acids were determined by gas chromatography/mass spectrometry. Lymphocyte propionyl-CoA carboxylase activity decreased dramatically and in parallel with hepatic propionyl-CoA carboxylase activity. By d 7, lymphocyte propionyl-CoA carboxylase activity in each rat in the deficient group had decreased to less than the lowest value of any rat on d 0. By two-way ANOVA, the effects of diet (P < 0.0001), time (P < 0.005) and their interaction (P < 0.0001) were all significant. The urinary excretion of 3-hydroxypropionic acid did not differ between the two groups. Lymphocyte propionyl-CoA carboxylase activity is an early and sensitive indicator of marginal biotin deficiency, whereas the urinary excretion of 3-hydroxypropionic acid is not.