Indirect enzyme-linked method for determining biotin in human serum

Biotin Auxotrophy and Biotin Enhanced Germ Tube Formation in Candida albicans

Due to the increased number of immunocompromised patients, infections with the pathogen Candida albicans have significantly increased in recent years. C. albicans transition from yeast to germ tubes is one of the essential factors for virulence. In this study we noted that Lee's medium, commonly used to induce filamentation, contained 500-fold more biotin than needed for growth and 40-fold more biotin than is typically added to growth media. Thus, we investigated the effects of excess biotin on growth rate and filamentation by C. albicans in different media. At 37 °C, excess biotin (4 µM) enhanced germ tube formation (GTF) ca. 10-fold in both Lee's medium and a defined glucose-proline medium, and ca. 4-fold in 1% serum. Two biotin precursors, desthiobiotin and 7-keto-8-aminopelargonic acid (KAPA), also stimulated GTF. During these studies we also noted an inverse correlation between the number of times the inoculum had been washed and the concentration of serum needed to stimulate GTF. C. albicans cells that had been washed eight times achieved 80% GTF with only 0.1% sheep serum. The mechanism by which 1-4 µM biotin enhances GTF is still unknown except to note that equivalent levels of biotin are needed to create an internal supply of stored biotin and biotinylated histones. Biotin did not restore filamentation for any of the four known filamentation defective mutants tested. C. albicans is auxotrophic for biotin and this biotin auxotrophy was fulfilled by biotin, desthiobiotin, or KAPA. However, biotin auxotrophy is not temperature dependent or influenced by the presence of 5% CO₂. Biotin starvation upregulated the biotin biosynthetic genes BIO2, BIO3, and BIO4 by 11-, 1500-, and 150-fold, respectively, and BIO2p is predicted to be mitochondrion-localized. Based on our findings, we suggest that biotin has two roles in the physiology of C. albicans, one as an enzymatic cofactor and another as a morphological regulator. Finally, we found no evidence supporting prior claims that C. albicans only forms hyphae at very low biotin (0.1 nM) growth conditions.

Analytical techniques for determining biotin

Biotin is a vitamin of the B-complex, which plays an important biochemical role in every living cell. In the recent years, the interest in this vitamin has been rekindled, mainly due to its association with serious human disorders, such as the inherited syndrome multiple carboxylase deficiency, which can be successfully treated with biotin administration. Diagnosis of biotin deficiency as well as monitoring of biotin levels in biological fluids of patients receiving biotin treatment is crucial. Equally important is the determination of biotin levels in pharmaceutical preparations as well as in food and food supplement products, which constitute the main source of biotin in humans. Several analytical methods for measuring biotin in various samples, e.g. human fluids, pharmaceutical formulations, food material etc., have been reported in the literature. In this review, the most representative of these methods are presented, and their characteristics are evaluated.

Biotin recycling impairment in phenylketonuric children with seborrheic dermatitis

OBJECTIVE

To investigate the effect of a therapeutic diet on serum biotin levels and to explain the seborrheic dermatitis in phenylketonuric (PKU) patients on a "loose" diet.

DESIGN

Forty-seven patients were divided into two groups: group A (n=21) demonstrated good compliance to a special diet and group B (n=26) were on a "loose" diet. Most of the patients in group B (20/26), who suffered from mild seborrheic dermatitis, were requested to return to phenylalanine (Phe)-restricted diet for at least 15 days. Seventy-nine healthy children of comparable age were used as controls. Biotin serum levels and plasma biotinidase activity were measured in patients as well as controls. In addition, biotinidase activity was evaluated in vitro after incubation with various concentrations of Phe.

RESULTS

Biotin levels in group A patients (636+/-118 ng/L) were statistically significantly elevated (P < 0.01) compared with those of group B patients before (412+/-184 ng/L) and after (501+/-160 ng/L) 15 days on a Phe-restricted diet, as well as with those of controls (337+/-290 ng/L). Furthermore, biotinidase activities were decreased in group B patients (4.2+/-1.68 nmol/min/L) compared with those of group A patients (6.4+/-0.7 nmol/min/L) and controls (6.10+/-0.8 nmol/min/L). Additionally, biotinidase activities in the patients of group B were restored to normal (5.78+/-0.81 nmol/min/L), with a simultaneous remission of their skin lesions, after 15 days on a Phe-restricted diet. Moreover, the in vitro findings showed a 51% inhibition of biotinidase activity when incubated with Phe (20 mg/dL).

CONCLUSIONS

It is suggested that the high biotin levels in group A patients reflect the intake of water-soluble biotin of vegetable origin. In contrast, the low biotinidase activity in group B patients may be attributed to their high Phe plasma levels, which acts as an enzyme inhibitor, as shown by the in vivo and in vitro results. Consequently, the observed seborrheic dermatitis in PKU children (group B) is associated with an impairment of biotin recycling.