Biotin deficiency induces changes in subpopulations of spleen lymphocytes in mice

Biotin deficiency is known to affect immune function in both humans and experimental animals. In this study, we determined the effect of biotin deficiency on 4-wk-old Balb/cAnN mice during 20 wk of experimentation. The growth rate of mice slowed significantly during the first 6 wk of consumption of a diet designed to induce biotin deficiency; thereafter, from weeks 7 to 20 there was progressive weight loss in the mice receiving the biotin-deficient diet. In the livers of biotin-deficient mice, the specific activities of two biotin-dependent enzymes--pyruvate carboxylase and propionyl-CoA carboxylase--decreased by as much as 75% and 80%, respectively, and in spleen lymphocytes the specific activities of these two enzymes decreased by 63% and 75%, respectively. With respect to the effects of biotin deficiency on the immune system, we observed statistically significant changes in both the absolute number of spleen cells and in the proportions of spleen cells carrying different phenotypic markers: after 16 wk the percentage of cells expressing surface immunoglobulin (sIg) decreased from 47% (control and supplemented) to 27% (deficient) and CD3+ cells increased from 42% (control and supplemented) to 54% (deficient). The mitogen-induced proliferation of spleen cells from deficient mice was lower than that of spleen cells from the control mice. These findings suggest that biotin could have an important role in lymphocyte maturation and responsiveness to stimulation, and consequently in the capacity of the immune system to respond to an antigenic challenge.

Biotin status and its correlation with other biochemical parameters in the elderly people of Japan

OBJECTIVE

Biotin plays important roles in carbohydrate and lipid metabolism as well as in the decarboxylation of amino acids. In this study, to determine the biotin status in elderly people, we determined the levels of biotin and other biochemical variables in their serum.

METHODS

Blood was collected from 685 elderly people aged 65 years and over (284 men and 401 women) and from 2,004 reference people. Biotin levels in the serum were microbiologically quantified by the agar plate method and other biochemical variables were recorded using the autoanalyzer.

RESULTS

The serum biotin level in elderly people was 10.2 +/- 7.20 pmol/ml (2.5 +/- 1.76 ng/ml), the distribution of which was skewed to the right compared to the reference group (9.4 +/- 1.43 pmol/ml) (2.3 +/- 0.35 ng/ml). However, serum biotin levels did not change with age in the elderly people and no sex-related differences were detected. On the basis of the correlation coefficients among the biochemical variables in the serum, biotin levels were correlated positively with the total cholesterol level. A negative correlation was found between the biotin level and the serum albumin, triiodothyronine, phosphate, and calcium levels. On the other hand, 5.8% of the elderly people had biotinyl IgG in their serum, which did not differ from the percentage in the reference group (4.1%). However, in the elderly people the level of biotinyl IgG positivity was significantly lower in women than in men (4.1% vs. 8.1%). In the biotinyl IgG positive elderly, the levels of parathyroid hormone and total cholesterol were lower, whereas the uric acid level was higher compared to the biotinyl IgG negative elderly.

CONCLUSIONS

Although serum biotin levels are not affected by aging, the serum biotin levels of elderly people vary greatly.

Reduced blood accumulation of biotinylated monoclonal antibody A7 after the subsequent administration of avidin

Clear immunoscintigraphy with radiolabeled monoclonal antibodies (MAbs) requires a high tumor tissue/blood ratio of radioactivity. In this study, we attempted to obtain a high tumor tissue/blood ratio by the active removal of radiolabeled MAb from the circulation, using the avidin-biotin system. Biotinylated 125I-labeled MAb A7 was injected intravenously into nude mice bearing a human colon cancer (WiDr) xenograft. Avidin was injected 24 h later. The tumor tissue/blood ratio of radioactivity was almost four times that of controls. These results suggest that biotinylated 125I-labeled MAb A7 and avidin are potentially useful for the rapid immunodetection of human colon cancer.

Profound biotinidase deficiency in two asymptomatic adults

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.

Biotin catabolism is accelerated in adults receiving long-term therapy with anticonvulsants

Using serum biotin concentration as the indicator, a previous study reported biotin deficiency resulting from long-term anticonvulsant therapy. However, serum biotin may not be a good indicator of tissue biotin status. Using better indicators of biotin status in anticonvulsant-treated subjects, we found increased urinary excretion of biotin catabolites and 3-hydroxyisovaleric acid, an organic acid produced in greater quantities secondary to reduced activity of a biotin-dependent carboxylase. We conclude that anticonvulsant treatment led to increased biotin catabolism and probably to reduced biotin status.

Biliary excretion of biotin and biotin metabolites is quantitatively minor in rats and pigs

We sought to determine whether the biliary excretion of biotin contributes substantially to the overall excretion of the vitamin in mammals, and hence, whether metabolism by gut microorganisms could account for some metabolism of biotin administered parenterally. [carbonyl-14C]Biotin was injected intravenously into six rats; bile and urine were collected for 24 h after injection. In a study of five pigs, serum and bile were analyzed for endogenous biotin and metabolites. In rat bile and urine, biotin, bisnorbiotin, biotin-d,l-sulfoxide, bisnorbiotin methyl ketone and two unidentified compounds were quantitated. In bile, these six compounds accounted for only 1.9 +/- 0.2% of the administered 14C, but in urine they accounted for 60.6 +/- 4.1%. The metabolite and time profiles in bile were also strikingly different from those in urine. Only biotin, bisnorbiotin and biotin-d,l-sulfoxide were quantitated in pig bile and serum. The concentrations of biotin, bisnorbiotin and biotin-d,l-sulfoxide in bile were 6.9-14.7 times the concentrations in serum. However, the bile to serum ratios of biotin and metabolites were >99% less than those of bilirubin, which is actively excreted. These data provide evidence that the biliary excretion of biotin and metabolites is quantitatively negligible.

Biotin administration improves the impaired glucose tolerance of streptozotocin-induced diabetic Wistar rats

The effect of biotin administration on the glucose tolerance of streptozotocin (STZ)-induced diabetic Wistar rats was investigated. STZ-induced diabetes was induced by intraperitoneal injection of streptozotocin (45 mg/kg body weight as a single dose). The impaired glucose tolerance in response to an oral glucose load (1.8g per kg body weight) in STZ-induced diabetic rats (STZ-rat) was partially improved by intraperitoneal administration of biotin for 15 days (100 micrograms/rat/day). However, a recovery in the STZ-rat's insulin secretion was not found after biotin administration. To help clarify the mechanism underlying the improvement in glucose tolerance seen with biotin treatment, glucokinase and hexokinase activities were determined in the liver and pancreas. In STZ-rats that had received biotin (STZ-biotin rats), glucokinase activity was higher by 3.4-fold in liver and by 2.4-fold in pancreas than in the STZ-rats. The biotin level of STZ-rats was significantly lower in the liver and pancreas than that of the control rats (no STZ administration); but in STZ-biotin rats, the level in these organs recovered to the control level. These results demonstrate that injected biotin can improve glucose handling without increasing insulin secretion in STZ-rats.

Biotin status assessed longitudinally in pregnant women

This study assessed biotin nutritional status longitudinally during pregnancy as judged by urinary excretion of biotin and biotin metabolites and by serum concentration of biotin. 3-Hydroxyisovaleric acid excretion was also assessed because increased excretion of that acid reflects decreased tissue activity of the biotin-dependent enzyme, methylcrotonyl-CoA carboxylase. Thirteen women provided untimed urine samples during both early and late pregnancy. Twelve nonpregnant women served as controls. Biotin and metabolites were determined by a combined HPLC/avidin-binding assay. 3-Hydroxyisovaleric acid was determined by gas chromatography/mass spectrophotometry. Significance of changes from early to late pregnancy was tested by paired t test; to compare nonpregnant controls with early and late pregnancy, ANOVA was used. During early pregnancy, biotin excretion was not significantly different than controls; however, 3-hydroxyisovaleric acid excretion was significantly increased relative to controls (P < 0.0001) and was greater than the upper limit of normal in 9 of 13 women. From early to late pregnancy, biotin excretion decreased in 10 of 13 women (P < 0.01); by late pregnancy, biotin excretion was less than normal in six women. During late pregnancy, 3-hydroxyisovaleric acid remained significantly increased relative to controls (P < 0.0001). Serum concentrations of biotin were significantly greater than those of controls during early pregnancy (P < 0.0001) and decreased in each woman from early to late pregnancy (P < 0.0001). These data provide evidence that biotin status decreases during pregnancy.

Effect of endogenous biotin on the applications of streptavidin and biotin in mice

The use of streptavidin-conjugated antibody to pretarget tumors in animals and patients, prior to administration of radiolabeled biotin, has provided encouraging results, in part because of the high affinity of biotin for streptavidin and the rapid whole-body clearance of biotin. However, binding of endogenous biotin to streptavidin may interfere with the clinical potential of this approach. This report evaluates the effect of endogenous biotin on an antibody-streptavidin conjugate in a mouse tumor model. Tumored nude mice were depleted of endogenous biotin by sequential intraperitoneal injections of streptavidin. The assay of serum biotin levels indicated less than 0.5 ng of biotin per mL of serum in treated mice versus 4 ng per mL in untreated animals. Flow cytometric analysis was used on single-cell suspensions of tumor from animals receiving streptavidin-conjugated IgG to detect the presence of the antibody on the cell membrane (with fluoroisothiocyanate-conjugated goat anti-mouse antibody), and to detect biotin binding sites on streptavidin (with biotin-phycoerythrin). Both treated and untreated mice demonstrated the presence of antibody on tumor cells through 48 h postadministration, but only in treated animals were biotin binding sites observed. These results in the mouse model suggest that the small concentration of streptavidin delivered to a tumor via a specific antibody may be saturated with endogenous biotin and therefore not able to be targeted subsequently with radiolabeled biotin.

Increased urinary excretion of 3-hydroxyisovaleric acid and decreased urinary excretion of biotin are sensitive early indicators of decreased biotin status in experimental biotin deficiency

To assess the utility of various indicators of biotin status, marginal biotin deficiency was induced experimentally in normal adults. Ten subjects consumed a diet that contained enough avidin to bind seven times more biotin than that in the diet. Blood and 24-h urine samples were collected before the diet began and twice weekly thereafter for 20 d. The urinary excretion and serum concentration of biotin and its two principal inactive metabolites bisnorbiotin and biotin sulfoxide were determined after HPLC separation with an avidin-binding assay. The urinary concentration of 3-hydroxyisovaleric acid, an indicator of reduced activity of a biotin-dependent enzyme, was quantitated by gas chromatography-mass spectrometry. The urinary excretion of 3-hydroxyisovaleric acid increased significantly (P < 0.0001). For all subjects, the urinary excretion of both biotin and bisnorbiotin decreased significantly (P < 0.0001 for each). In contrast, the mean serum concentration of biotin did not decrease significantly (P = 0.06). These data provide evidence that the urinary excretion of 3-hydroxyisovaleric acid and the urinary excretion of biotin are early and sensitive indicators of biotin deficiency and that the serum concentration of biotin is not.

Serum concentrations of bisnorbiotin and biotin sulfoxide increase during both acute and chronic biotin supplementation

In addition to the pharmacokinetic interest, serum concentrations of biotin and biotin metabolites are important because biotin in serum might interfere with assays that use avidin-biotin detection systems. With acute and chronic oral administration of biotin the serum concentration of biotin increases. Because of limited specificity of bioassays or avidin-binding assays used in previous studies, the proportion of the increase attributable to biotin metabolites (if any) remains unknown. To address these questions 15 adults consumed 1,200 microg biotin daily for 14 days. Blood samples were obtained before biotin ingestion and at 3 hours after biotin ingestion on the first day ("acute supplementation") and the fourteenth day ("chronic supplementation"). Biotin, bisnorbiotin, and biotin sulfoxide were measured with a chemically specific high-pressure liquid chromatography/avidin-binding assay. Serum concentrations of biotin, bisnorbiotin, and biotin sulfoxide increased approximately fiftyfold with acute supplementation of biotin; each increased further with chronic supplementation. With acute supplementation the proportion of the total attributable to metabolites did not decrease significantly, suggesting that pathways for biotin catabolism are not easily saturated. With chronic supplementation the proportion of the total attributable to metabolites did not increase significantly, suggesting that biotin catabolism was not substantially induced. We conclude that on a mole basis the contribution of biotin metabolites is important, and we provide an estimate of the biotin and biotin metabolite concentration that might be encountered in individuals who self-select large biotin supplements.

Indirect enzyme-linked method for determining biotin in human serum

An indirect enzyme-linked assay was developed for quantifying biotin concentrations in human sera. Biotin standard solutions or unknown samples are preincubated with streptavidin-conjugated horseradish peroxidase (streptavidin-HRP) and added to plates coated with biotinylated bovine IgG (B-IgGb). The concentration of the streptavidin-HRP is such that the streptavidin binding sites are sufficient to bind apparently all the biotin present in samples, whereas, the remaining sites are inversely proportional to the amount of biotin in analysed sample. These sites could subsequently interact with the immobilized B-IgGb providing signal. The assay demonstrated dynamic range 5 to 640 ng/L, detection limit 2 ng/L, intra- and interassay C.V., 1.6-3.9% and 3.7-7.2% respectively, recovery 100-114% and linear recovery 90-117%. Serum biotin determined: healthy individuals 66 to 600 ng/L, pregnant women (> or = 36 weeks) 60 to 360 ng/L, and patients under chronic haemodialysis 0.56 to 1.62 micrograms/L. The method described is among those few which have been experimentally evaluated for their capabilitity of assessing biotin in human sera.

Preparation and biological evaluation of an astatine-211 labeled biotin conjugate: biotinyl-3-[211 At]astatoanilide

Biotinyl-3-[211 At]astatoanilide ([211 At]AtBA) was prepared in more than 80% yield by destannylation. In vitro, [211 At]AtBA exhibited a high affinity for streptavidin, and was stable after incubation in human serum, cerebrospinal fluid and distilled water, whereas it was rapidly degraded in mouse serum. HPLC analysis showed that the main degradation pathway in mouse serum was the cleavage of [211 At]astatoaniline. In mice, [211 At]AtBA and its 125I-labeled analogue cleared rapidly from most tissues; however, there was some evidence for dehalogenation of both tracers.

The vitamin status of young British adults

Using biochemical indices thiamin, riboflavin, pyridoxine, ascorbic acid, retinol, alpha-tocopherol, folic acid, cyanocobalanin, carotene and biotin status were assessed in a sample of 243 young British adults. Using conventional definitions the number of individuals whose vitamin status can be described as adequate, marginal or deficient was determined. Vitamin status was related to alcohol intake and smoking. The status of ascorbic acid, cyanocobalamin, alpha-tocopherol, folic acid and in males retinol, was adequate in the majority of cases. In the cases of riboflavin and pyridoxine the status of a substantial minority was either borderline or deficient. The thiamin and biotin status of a minority of both sexes, and retinol in the females, was marginal. In males alcohol was associated with better retinol, ascorbic acid, alpha-tocopherol and pyridoxine status and lower levels of biotin. Lower carotene values were associated with drinking alcohol. In both sexes those who smoked had lower ascorbic acid, folic acid and carotene values. In males smoking was additionally associated with lower riboflavin and biotin; in females cyanocobalamin and alpha-tocopherol were lower. As all the subjects were students volunteers, care should be taken in generalizing the data to other groups.

A high biotin diet improves the impaired glucose tolerance of long-term spontaneously hyperglycemic rats with non-insulin-dependent diabetes mellitus

The Otsuka Long-Evans Tokushima Fatty (OLETF) rat, serving as a spontaneously diabetic model with non-insulin-dependent diabetes mellitus (NIDDM), exhibits impaired glucose tolerance (IGT) at about 16 weeks of age. In this study, we investigated whether or not biotin, a water-soluble vitamin, improved the IGT of OLETF rats. To this end, we administered diets containing one of three levels of biotin, a high-biotin diet (BH), a normal-biotin diet (BN) and a basal-biotin diet (BB), to OLETF rats up to 24 weeks of age. An oral glucose tolerance test (OGTT) was performed four times between 13 and 22 weeks of age. The administration of a BH corrected the IGT of OLETF rats. Upon further investigation, we found that insulin secretion in the OLETF-BH rats was decreased to a significant extent, signaling that the hyperinsulinemia typical to the OLETF-BH rats had clearly improved. Body weights were significantly lower in the OLETF-BH group than in the other OLETF groups, even though the OLETF-BH rats showed a significantly higher average daily food intake. The body weight gain of the OLETF-BH rats followed the same tendency as the control-LETO (Long Evans Tokushima Otsuka) rats (LETO-BB and LETO-BN). These results demonstrate that a high-level biotin diet can improve the glucose handicap in NIDDM rats.

[A quantitative of serum biotin with microplate-assay using affinity streptavidin]

We modified Bayer's method of micro-plate assay for quantitation of biotin concentration. Biotin concentration in the solution and serum which cannot be quantitated directly by a microorganism assay (bio-assay), was easily determined by this method, which showed a high affinity of streptavidin for biotin this method and had a wide measurement range (0.9-60,000 pg/ml). We measured the concentration of biotin in 150 sera from 44 patients (21 males and 23 females) with active hepatitis (high level of both GOT and GPT, over 100 IU/l), 15 patients (7 males and 8 females) with inactive hepatitis (positive HCV-Ab but within normal limits of both GOT and GPT level), 17 patients (8 males and 9 females) with hepatoma and liver cirrhosis and 71 healthy persons (34 males and 37 females). The biotin concentration of sera in the healthy persons was 243.5 +/- 184.6 pg/ml, there being no sex difference. The biotin concentration in sera was higher in the patients than in healthy persons. It was high in the hepatoma and cirrhosis group (4,394.0 +/- 6,176.3), the active hepatitis group (2,397.4 +/- 2,785.5), and the inactive hepatitis group (1,873.2 +/- 1,523.7). These findings suggest that the biotin concentration is not significantly correlated with an escape enzyme such as GOT and GPT. These findings suggest that a high biotin concentration reflects other mechanisms such as escape from damaged liver cells.

Extracorporeal immunoadsorption from whole blood based on the avidin-biotin concept. Evaluation of a new method

This study of 36 rats with rat colon adenocarcinoma transplants was carried out to investigate the efficacy of a new method of whole blood immunoadsorption (WBIA) in removing biotinylated monoclonal antibodies (MAbs) directly from unseparated blood, in order to increase 'the tumor/normal-tissue uptake ratio', as compared with extracorporeal immunoadsorption (ECIA) of antibodies from plasma. Compared with the ECIA system, the overall volume of the WBIA system (comprising only a pump, an adsorption column, a drop-chamber and tubings) was less (3.6 vs. 6.2 ml), and procedure duration 2 h less. The 17 rats undergoing the WBIA procedure, started 12 h after i.v. injection of 4.0-4.5 MBq 125I-BR96-biotin, manifested neither hemolysis nor any other complication; no signs of organ edema were found at dissection; whole body and blood radioactivity values were reduced by 51% and 89.5%, respectively. The WBIA method was as effective as ECIA, but technically simpler, safer and more reliable.

Methodologic considerations for the use of canine in vivo aged biotinylated erythrocytes to study RBC senescence

Biotinylation of erythrocytes has been developed in rabbits as a tool to retrieve labeled cells following various periods in circulation. This retrieval capability allows biochemical studies to be conducted on red blood cells (RBC) that have aged for desired times in vivo. However, because erythrocyte life span is much shorter in rabbits than in humans, and because cell removal is measurably age-independent in rabbits, we have sought to validate the same protocol in dogs, whose cell life span and age-dependent removal characteristics are similar to humans'. Canine RBC were biotinylated in vivo by infusion of N-hydroxysuccinimidyl biotin dissolved in dimethylacetamide or dimethylsulfoxide. Cell life spans were evaluated using 14C-cyanate labeling followed by scintillation counting or avidin-FITC labeling followed by flow cytometry. Both methods gave identical results. The life span of the biotin-conjugated cells was found to be normal (approximately 110 days), and the stability of the biotin ligand was adequate for efficient retrieval of cells using avidin-coated magnetic beads (magnetic cell sorting [MACS]). From each isolation, approximately 20 microL of packed biotinylated cells of approximately 90% purity (i.e., 10% contamination by unlabeled cells) could be harvested. On average, approximately 60% of the biotinylated cells in any sample could be retrieved. Either multiple isolations or use of larger collection columns will facilitate collection of cell numbers sufficient for biochemical tests. After incorporating several modifications in the previous biotinylation protocol that were required for adaptation to the dog, the methodology can be used to study red cell senescence in an animal that has several pertinent similarities to humans.

Biotin deficiency decreases ornithine transcarbamylase activity and mRNA in rat liver

Biotin deficiency is well known as a cause of hyperammonemia, but there has been no report on the effect of biotin deficiency on hepatic ureagenesis. In this study, we examined the changes in the activities and gene expression of urea cycle enzymes using rats fed raw egg white as a model of biotin deficiency. All rats were made biotin-deficient by feeding them an avidin-containing diet for 6 wk. The rats were divided into two groups at the beginning of this experiment: biotin-deficient rats (BD rats) and biotin-supplemented rats (BS rats) which were treated with biotin once a day at a dose of 1 mg per rat intraperitoneally. The plasma ammonia concentration of the BD rats (92.8 +/- 12 mumol/L) was significantly higher than that of BS rats (63.9 +/- 16 mumol/L, P < 0.05). The activities of ornithine transcarbamylase (OTC) was significantly lower in the liver of the BD (110.2 +/- 5.5) rats than in the BS rats (154 +/- 3.8 U/mg protein, P < 0.01). Activities of the other urea cycle enzymes were not significantly different in the two groups. OTC gene expression in the liver of BD rats was 40% lower than in BS rats (P < 0.05). These data suggest that biotin deficiency decreases OTC activity and the amount of OTC mRNA.

Quantification and lowering of serum biotin

An enzyme-linked assay was developed to quantify serum biotin concentrations in experimental animals and humans. With this assay the effect on serum biotin concentration after intravenous injection of streptavidin or the addition of avidin to food was studied in rabbits and dogs. Intravenous injection of streptavidin reduced serum biotin values quickly but temporarily, in a dose-dependent manner in both species. Addition of avidin to the diet lowered biotin values approximately four- to fivefold in the rabbits, with resultant biotin concentrations similar to those of humans.

Homogeneous immunoassay of whole-blood samples

Proof of principle has been shown for a rapid, quantitative, homogeneous immunoassay capable of analyzing whole-blood samples. The assay was performed with test cards and a small instrument designed for use at the point of care. The immunoassay has an immunological "front end" combined with a coagulation cascade chemistry "back end" and is made possible by combining two patented technologies: (a) a serine protease inhibitor [Porter and Bruhnke, Photochem and Photobiol 1990; 51(1):37] and (b) paramagnetic iron oxide particles (PIOP) in a mixture of buffers and coagulation assay components supplied as a dry film in a test-card reaction chamber [Oberhardt et al., Clin Chem 1991;37:520]. A model steric-hindrance immunoassay based on these technologies was established for the measurement of biotin. The calibration curve was developed by measuring plasma samples supplemented with biotin. The reagents were inhibited biotinylated thrombin, anti-biotin monoclonal antibody, and PIOP.

Hoof horn abnormalities in Lipizzaner horses and the effect of dietary biotin on macroscopic aspects of hoof horn quality

This study involved a macroscopic evaluation of hoof quality in 152 Lipizzaner horses (130 from Austria and 22 from other countries) and a controlled double blind trial of the effects of biotin on hoof horn growth and quality over 19 months in 42 stallions from the Spanish Riding School (SRS) in Vienna. Using a grading system that incorporated evaluation of horn wall, white line, sole and frog, the macroscopic study revealed the following: 90% of the Austrian Lipizzaners had soft white lines and crumbling, fissured horn at the bearing border of the walls; 39% of the stallions of the SRS, > 4-years-old, had medium to severe hoof horn changes. Daily administration of 20 mg biotin to a test group of horses (n = 26) and a placebo to a control group (n = 16) showed that after 9 months the test group had significantly improved compared to the beginning of the trial and the placebo group (P < 0.01). In the test group, further improvement was observed during the following 5 months and, subsequently, the same good level of hoof condition was maintained over 3 further years of observation. Growth rate of the horn wall was equal in the biotin and placebo group, being 7 mm/28 days, giving a wall renewal period of 11 months. Mean plasma biotin level of untreated horses was 350 ng/l; plasma levels of biotin supplemented horses were > 1000 ng/l. It was concluded that continuous dietary supplementation with biotin at a daily dose of 20 mg is indicated to improve and maintain hoof horn quality in horses with less than optimum quality hoof.

Biotin accounts for only half of the total avidin-binding substances in human serum

In studies using an avidin-binding assay to measure the serum or plasma concentration of biotin, biotin is sometimes assumed to be equal to the avidin-binding substances detected. To provide a range of values for serum concentrations of biotin, bisnorbiotin, and biotin sulfoxide, HPLC was used to separate avidin-binding substances in human serum, and the chromatographic fractions were assayed for avidin-binding substances (biotin and biotin metabolites). In sera from 15 normal fasting adults, substantial concentrations of avidin-binding substances other than biotin were detected. Two of the principal substances were identified as bisnorbiotin and biotin sulfoxide based on their chromatographic properties. The serum concentrations of bisnorbiotin and biotin sulfoxide varied widely among the individuals. In three subjects, the concentration of bisnorbiotin exceeded that of biotin. The presence of avidin-binding substances in addition to biotin may have confounded previous measurements of the concentration of biotin in serum, plasma, and blood when avidin-binding assays were used. Because bioassay methods for biotin sometimes use organisms for which one or more of these biotin metabolites are growth factors, measurements of biotin in blood using some bioassays are likely to overestimate the concentrations of biotin.