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Background: Biotinidase is the enzyme responsible for liberating the vitamin biotin from biocytin and dietary protein-bound vitamin. Individuals lacking biotinidase activity become biotin deficient. Because the liver is the major source of plasma biotinidase, chronic liver diseases can lead to decreased serum biotinidase activity and biotin deficiency. The aim of this study is to determine serum biotinidase activity values in children with chronic liver disease and to investigate the relation among enzyme activity, certain liver function tests, and degree of liver damage., Method: In this study, using a spectrophotometric method, biotinidase activity was determined in sera from 62 children with chronic liver diseases (median age, 9.73 years; range, 8 months to 18 years) and from 27 healthy controls. Diagnoses of the patient group were as follows: noncirrhotic chronic hepatitis B virus infection (n = 12), metabolic liver diseases (n = 16), autoimmune hepatitis (n = 6), intrahepatic and extrahepatic cholestasis (n = 14), fulminant hepatitis (n = 5), cryptogenic cirrhosis n = 5), prehepatic portal hypertension (n = 4). Meanwhile, serum albumin, total bilirubin, alkaline phosphatase, alanine aminotransferase, and gamma-glutamyltransferase concentrations and prothrombine time were determined for each patient and the results were correlated with serum biotinidase activity., Results: There was significant difference between mean enzyme activity of the controls (7.6 +/- 1.2 nmol x min(-1) x mL(-1)) and of all patients with chronic liver disease (6.3 +/- 2.5 nmol x min(-1) x mL(-1)) ( P < 0.05). Serum biotinidase activity in patients with noncirrhotic chronic liver diseases (chronic viral hepatitis, prehepatic portal hypertension, glycogen storage disease, Gaucher disease) was within the normal ranges. However, serum biotinidase activity in patients with cirrhosis and Wilson disease was significantly less than that of the control group ( P < 0.05). The lowest enzyme activities were detected in patients with fulminant hepatitis., Conclusion: In this study, serum biotinidase activity was significantly lower in patients with cirrhosis, particularly in the patients with decompensated cirrhosis and fulminant hepatitis who exhibited no clinical symptoms related to biotin deficiency. The decreased serum biotinidase activity in chronic liver diseases was associated with severe impairment of hepatocellular function.

Biotinidase deficiency is an autosomal-recessive disorder of biotin recycling. Children with profound biotinidase deficiency usually have neurological and cutaneous symptoms in early childhood, but they may not develop symptoms until adolescence. We now report on a man and a woman with profound biotinidase deficiency who are asymptomatic and who were diagnosed only because their biotinidase-deficient children were identified by newborn screening. These adults have never exhibited symptoms of the disorder and are homozygous for two different mutations resulting in different aberrant enzymes. There is no evidence of an increased dietary intake of biotin to explain why they have remained asymptomatic. Although these adults may still be at risk for developing symptoms, they could represent a small group of individuals with profound biotinidase deficiency who will never develop clinical problems. Their lack of symptoms suggests that there are probably epigenetic factors that protect some enzyme-deficient individuals from developing symptoms. These individuals broaden the spectrum of expression of biotinidase deficiency.

To investigate whether biotinidase deficiency may occur in liver disease, we determined biotinidase activity, biotin levels, and organic acids in patients with liver disease. Serum biotinidase activity in patients with liver disease (2.63 +/- 1.40 nmol/min/ml) was significantly lower than in the control group (5.43 +/- 1.06 nmol/min/ml). Serum biotinidase activity in decompensated liver cirrhosis (LC) and hepatoma was significantly lower than in acute viral hepatitis (AVH), chronic viral hepatitis (CVH), and compensated LC. The mean serum level of biotin in decompensated LC (1.8 +/- 0.6 microgram/ml) and hepatoma (1.7 +/- 0.8 microgram/ml) was significantly lower than in the control group (2.5 +/- 1.0 microgram/ml), and urinary excretion of biotin was increased in patients with liver disease, particularly in decompensated LC. Biotinidase activity correlated positively with serum biotin level and correlated negatively with urinary biotin level. Moreover, in four of five patients with severe liver disease the excretion of propionate, lactate, and 3-hydroxybutyrate decreased after biotin supplementation. The data for patients with severe liver disease so resembled those for late-onset multiple carboxylase deficiency that biotinidase deficiency is likely in patients with severe liver disease.

Lipoamidase, as determined by lipoyl-p-aminobenzoic acid (L-pABA) hydrolyzing activity, and biotinidase in human serum have similar pH profiles, molecular weights, thermostabilities, and are similarly inhibited by p-hydroxymercuribenzoate and not inhibited by phenylmethylsulfonylfluoride. A monospecific polyclonal antibody prepared against biotinidase immunoprecipitated greater than 95% of serum L-pABA hydrolyzing activity and an identical proportion of biotinidase activity. In addition, children with profound biotinidase deficiency (less than 10% normal serum activity) have greatly reduced levels of L-pABA hydrolyzing activity in serum (less than 15% of mean normal activity) and obligate heterozygotes have activities intermediate between that of normal and profoundly deficient individuals. These results indicate that most, if not all, of the L-pABA hydrolyzing activity in human serum is due to biotinidase. Moreover, since the Km of L-pABA hydrolysis by serum is high, it is unlikely that lipoic acid is recycled in the serum by biotinidase.

In order to evaluate the clinical significance of serum biotin and biotinidase in liver disease, serum biotin levels and biotinidase activities were determined in 83 patients with various liver diseases and 10 healthy controls. Serum biotin levels and biotinidase activities were determined by a simplified lactobacillus plantarum bioassay and liquid chromatography with fluorimetric detection respectively. Serum biotin levels in decompensated liver cirrhosis, hepatoma and fulminant hepatitis were found to be significant low compared with healthy controls, while it was significant high in autoimmune hepatitis. There was no significant difference between serum biotin levels in the other liver diseases and healthy controls. In various liver diseases except for both acute hepatitis and alcoholic liver disease biotinidase activities were significantly reduced than in healthy controls. Serum biotinidase activities were correlated with serum albumin, prothrombin time, ChE and total cholesterol respectively, suggesting that biotinidase activities may reflect the degree of liver damage. These results seem that biotin deficiency may occur in some cases of severe liver diseases.

Seventeen partially biotinidase-deficient patients detected by neonatal screening or family studies were compared with four patients with classical biotinidase deficiency. Using a sensitive HPLC method for biotinidase in plasma (substrate: biocytin) the patients could be divided into two groups: one with residual biotinidase activity, and the second with undetectable biotinidase activity (0-activity). Biocytin excretion, characteristically elevated in 0-activity patients, decreased rapidly with increasing residual biotinidase activity and was almost normal when residual activity exceeded 2-3% of mean normal. In one patient with classical disease (0-activity) biotin deficiency, typical organic aciduria and multiple carboxylase deficiency were found as early as at the second week of life. In contrast, 13 infants with residual activities from 1.2% to 23% had no remarkable clinical or biochemical abnormalities. However, in three 5-, 14- and 15-year-old healthy siblings with residual biotinidase activities between 2.3% and 4.2%, biotin deficiency was proven by decreased activities of the mitochondrial carboxylases in lymphocytes (30-57% of mean normal) and, in the older siblings, also by subnormal plasma biotin concentrations. In biotinidase deficiency, biotin depletion presumably occurs earlier in the brain than in other tissues and may thus first affect the central nervous system. For this reason and because of discrete biochemical abnormalities found in a patient with residual biotinidase activity of 8%, we suggest that at least all patients with residual activities below 10% should be treated with biotin.

Purified biotinidase (enriched 24,000-fold) from fresh human plasma exhibited reduced catalytic activity when incubated with heat-inactivated dialyzed plasma. The polypeptide fractions separated from the heat-inactivated dialyzed plasma using streptavidin-Sepharose resin showed the same effect on purified biotinidase. These inhibitory effects on biotinidase were partial (25-45%) rather than complete. The polypeptide fraction from streptavidin-Sepharose resin was analyzed by SDS-PAGE in the Laemmli system and by various types of HPLC. Analyses by ion-exchange and reversed-phase HPLC revealed the existence of three relatively small mol. wt polypeptides. Each of these peak fractions exhibited similar inhibitory effects on biotinidase activity. SDS-PAGE analysis indicated that the streptavidin affinity resin fraction was composed of four major polypeptides whose mol. wts were 120,000, 76,000, 53,000 and 27,000. The two bands of 120,000 and 76,000 corresponded to the mol. wts of the biotinyl subunit of pyruvate carboxylase, beta-methyl-crotonyl-CoA and/or propionyl-CoA carboxylase respectively. However, the polypeptides of mol. wts 53,000 and 27,000 were found to be two unique biotinyl-peptides present in human plasma. These bands on the gels were transblotted and exhibited a fluorescent activity after incubated with a FITC-avidin. These findings strongly suggest the existence of circulating plasma biotinyl-polypeptides as inhibitory factor(s) on human plasma biotinidase.

New solid-phase assays for the determination of biotin in plasma and urine and the determination of biocytin/biotinyl peptides in urine are described. These assays were used to demonstrate that patients with biotinidase deficiency excrete increased amounts of biocytin/biotinyl peptides.