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Biomedical subjects

D M Mock

Publications and source records attributed to D M Mock.

At least 37 records · Page 2Linked to original sources
PubMed1999

Bioavailability of biotin given orally to humans in pharmacologic doses.

BACKGROUND: Patients with carboxylase deficiency are treated with pharmacologic doses of biotin. OBJECTIVE: We sought to determine the bioavailability of biotin at pharmacologic doses. DESIGN: Biotin was administered orally (2.1, 8.2, or 81.9 micromol) or intravenously (18.4 micromol) to 6 healthy adults in a crossover design with > or =2 wk between each biotin administration. Before and after each administration, timed 24-h urine samples were collected. Urinary biotin and biotin metabolites were analyzed by an HPLC avidin-binding assay. RESULTS: Urinary recoveries of biotin plus metabolites were similar (approximately 50%) after the 2 largest oral doses and the 1 intravenous dose, suggesting 100% bioavailability of the 2 largest oral doses. For unexplained reasons, the apparent recovery of the smallest oral dose was about twice that of the other doses. For all 4 doses, biotin accounted for >50% of the total of biotin and biotin metabolites in urine. Bisnorbiotin (13-23%), biotin-d,l-sulfoxide (5-13%), bisnorbiotin methyl ketone (3-9%), and biotin sulfone (1-3%) accounted for the remainder. The percentage excretion of biotin was greater when biotin was administered intravenously and for the largest oral dose than for the 2 smallest oral doses. CONCLUSION: Our data provide evidence that oral biotin is completely absorbed even when pharmacologic doses are administered. Biotin metabolites account for a substantial portion of total urinary excretion and must be considered in bioavailability studies. We speculate that renal losses of biotin (as a percentage of the dose administered) are moderately elevated when pharmacologic doses of biotin are administered.

Administration, Oral↗
PubMed1999

Advanced analysis of biotin metabolites in body fluids allows a more accurate measurement of biotin bioavailability and metabolism in humans.

In previous studies, the bioavailability of biotin in humans was estimated from the recovery of biotin in urine; urinary biotin was measured by microbial growth assays or assays of avidin-binding activity. These assays underestimate concentrations of biotin metabolites, which originate from beta-oxidation, sulfur oxidation or a combination. We have developed an HPLC/avidin-binding assay that is specific for biotin and its metabolites. With the use of the HPLC/avidin-binding assay, TLC and derivatization with p-dimethylaminocinnamaldehyde, we have identified and quantitated biotin and metabolites in urine from six healthy adults. Of that total, biotin accounted for 32+/-12%, bisnorbiotin for 52+/-15%, bisnorbiotin methyl ketone for 7.9+/-5.8%, biotin-d,l-sulfoxide for 4.0+/-3.2% and biotin sulfone for 3.6+/-1.9%. After intravenous administration of 18.4 micromol of biotin, the urinary excretion of biotin metabolites increased 21-130 times above baseline values. Because the biliary excretion of biotin is quantitatively minor (1.9+/-0.2% of an intravenous [14C]biotin dose in rats), intravenously administered biotin is not exposed to intestinal microorganisms. Thus we conclude that biotin metabolites in human urine originate from biotin catabolism in human tissues rather than biotin catabolism by intestinal microorganisms. With the use of the HPLC/avidin-binding assay, we estimated the bioavailability of biotin in adults from the urinary excretion of biotin and metabolites after ingestion of 2.1, 8.2 and 81.9 micromol of biotin. These data provide evidence that biotin is nearly completely absorbed.

Animals↗
PubMed1999

Biotin status: which are valid indicators and how do we know?

Although estimated average requirements for biotin have been proposed, the human requirements for biotin in specific populations and at various ages remain uncertain, in part because indicators of biotin status have not been validated. With the use of improved methods for measuring biotin and metabolites, a recent study indicated that decreased urinary excretion of biotin and bisnorbiotin is an early and sensitive indicator of biotin deficiency, but decreased serum concentration of biotin is not. Increased urinary excretion of 3-hydroxyisovaleric acid (3-HIA), a leucine metabolite that is excreted in increased quantities with deficiency of the biotin-dependent enzyme beta-methylcrotonyl-CoA carboxylase, is also an early and sensitive indicator of biotin deficiency. When these indicators were assessed longitudinally in 13 pregnant women, biotin excretion was not significantly decreased early in pregnancy but did decrease significantly from early to late pregnancy. Excretion of 3-HIA was abnormally increased in about three-fourths of the women studied in both early and late pregnancy. Thus, each indicator detected biotin deficiency late in pregnancy, but assessment of biotin status for the two indicators conflicted early in pregnancy. Preliminary results from a trial assessing response of 3-HIA excretion to biotin treatment indicate that biotin status is indeed impaired both early and late in pregnancy.

Animals↗
PubMed1999

Mitogen-induced proliferation increases biotin uptake into human peripheral blood mononuclear cells.

We sought to determine whether the proliferation of immune cells affects the cellular uptake of the vitamin biotin. Peripheral blood mononuclear cells (PBMC) were isolated from healthy adults. The proliferation of PBMC was induced by either pokeweed lectin, concanavalin A, or phytohemagglutinin. When the medium contained a physiological concentration of [3H]biotin, nonproliferating PBMC accumulated 406 +/- 201 amol [3H]biotin. 10(6) cells-1. 30 min-1. For proliferating PBMC, [3H]biotin uptake increased to between 330 and 722% of nonproliferating values. Maximal transport rates of [3H]biotin in proliferating PBMC were also about four times greater than those in nonproliferating PBMC, suggesting that proliferation was associated with an increase in the number of biotin transporters on the PBMC membrane. The biotin affinities and specificities of the transporter for proliferating and nonproliferating PBMC were similar, providing evidence that the same transporter mediates biotin uptake in both states. [14C]urea uptake values for proliferating and nonproliferating PBMC were similar, suggesting that the increased [3H]biotin uptake was not caused by a global upregulation of transporters during proliferation. We conclude that PBMC proliferation increases the cellular accumulation of biotin.

Adult↗
PubMed1998

Disturbances in biotin metabolism in children undergoing long-term anticonvulsant therapy.

BACKGROUND: In subjects undergoing long-term therapy with carbamazepine and/or phenytoin, reduced plasma concentrations of biotin have been reported. However, the diagnostic value of plasma biotin is unclear, in part because of the presence of significant plasma concentrations of biotin metabolites. Pathologic organic aciduria has also been reported with long-term anticonvulsant therapy, suggesting biotin deficiency, but no mechanism leading to deficiency has yet been determined. METHODS: In the current study, we sought to determine whether biotin catabolism was accelerated in children receiving long-term treatment with certain anticonvulsants and to assess biotin status as judged by urinary excretion of biotin and 3-hydroxyisovaleric acid, an organic acid that is an indicator of deficiency of a biotin-dependent enzyme. Seven children treated with carbamazepine and/or phenytoin and six treated with phenobarbital provided untimed urine samples. Sixteen healthy children receiving no anticonvulsants served as controls. Biotin and biotin metabolites were determined by high-performance liquid chromatography/avidin-binding assay. Urinary excretion of 3-hydroxyisovaleric acid was determined using gas chromatography/mass spectrometry. RESULTS: Bisnorbiotin excretion was increased significantly in the carbamazepine/phenytoin group and in the phenobarbital group. Biotin sulfoxide excretion was significantly increased in the carbamazepine/phenytoin group but not in the phenobarbital group. 3-Hydroxyisovaleric acid excretion was increased significantly in the carbamazepine/phenytoin group. However, only one child (carbamazepine/phenytoin group) had a decreased urinary excretion of biotin. CONCLUSION: These data provide evidence that long-term administration of some anticonvulsants can accelerate biotin catabolism, but the indicators of biotin status conflict.

Anticonvulsants↗
PubMed1998

Uptake and metabolism of biotin by human peripheral blood mononuclear cells.

We studied the uptake of biotin into human peripheral blood mononuclear cells (PBMC) using [3H]biotin and studied the catabolism of biotin in PBMC using [14C]biotin. Over 30 min, [3H]biotin uptake was greater at 37 degrees C than at 25 degrees C (KT = 2.6 +/- 0.4 nM, maximal velocity = 2.9 +/- 0.2 fmol . 10(6) cells-1 . 30 min-1). Ouabain reduced [3H]biotin uptake to 65% of control values, suggesting that biotin uptake is Na-K-ATPase dependent. Unlabeled biotin and biotin analogs reduced the uptake of [3H]biotin to 22-70% of control values, suggesting the presence of a competition for a structurally specific biotin transporter. When endocytosis by PBMC was stimulated by various acyl glycerols, [3H]biotin uptake was 40-73% of control values; these data are consistent with the hypothesis that stimulated endocytosis reduces biotin transporter density on the cell surface. During a 168-h incubation, PBMC did not catabolize [14C]biotin.

Ammonium Chloride↗
PubMed1997

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.

Adult↗
PubMed1997

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.

Adult↗
PubMed1997

Concentrations of biotin metabolites in human milk.

Because estimates of the biotin requirement for infants currently are based on the biotin concentration in human milk, we sought to determine whether inactive biotin metabolites are present. Samples were collected for 7 weeks post partum from 15 healthy women. Biotin and the inactive metabolites bisnorbiotin and biotin sulfoxide were measured by means of a high-performance liquid chromatography avidin-binding assay. At 8 days post partum the proportion of biotin was 44%, bisnorbiotin 48%, and biotin sulfoxide 8%. Although biotin content increased post partum (p < 0.003), the metabolites remained an important portion of the total providing evidence that accurate measurement of biotin in human milk requires an assay that is specific for biotin.

Adult↗
PubMed1997

Conflicting indicators of biotin status from a cross-sectional study of normal pregnancy.

OBJECTIVE: To assess biotin nutritional status during normal human gestation. METHODS: Urine samples were obtained in a cross-sectional design from 16 women in early pregnancy (17 +/- 1 weeks, mean +/- 1 SD) and from 13 women in late pregnancy (36 +/- 1 weeks). The urinary excretion of biotin, two metabolites bisnorbiotin (BNB) and biotin sulfoxide (BSO), and the organic acid 3-hydroxyisovaleric acid (3-HIA) were measured by HPLC/avidin-binding assay and GC/MS, respectively. Excretion rates were expressed as concentration ratios to urinary creatinine. RESULTS: In both early and late pregnancy, 3-HIA excretion was increased compared to controls (p < 0.0001), suggesting decreased activity of a biotin-dependent enzyme caused by tissue biotin depletion. In early pregnancy, urinary excretion of biotin was normal; in late pregnancy, excretion was increased (p < 0.0002), suggesting biotin status was not decreased. In late pregnancy, urinary excretion of BNB and BSO were increased (p < 0.009). CONCLUSION: The apparent conflict in the indices of biotin status is not explained by this study but could be resolved by two alternate explanations: 1) Pregnancy caused an impairment of renal reclamation of biotin, BNB, and BSO leading to a paradoxical increase in biotin excretion 2) Pregnancy caused metabolic or renal effects that increased 3-HIA excretion nonspecifically; hence, the increased 3-HIA excretion did not reflect biotin deficiency. We speculate that some of the women studied were marginally biotin deficient and that renal wasting and accelerated breakdown of biotin contributed to the deficiency.

Adult↗
PubMed1997

Identification of biotin sulfone, bisnorbiotin methyl ketone, and tetranorbiotin-l-sulfoxide in human urine.

In previous studies using the HPLC and avidin-binding assay, five unidentified avidin-binding substances were observed in human urine. The present study investigated the identity of these substances. Urine was collected before and after intravenous administration of 18.5 mumol biotin to healthy adults. Unknown substances 1 and 3 were initially identified as biotin sulfone and bisnorbiotin methyl ketone, respectively, by coelution with authentic standards on HPLC. Identities were confirmed by thin-layer chromatography and by derivatization with p-dimethyl-aminocinnamaldehyde. As expected for biotin metabolites, the urinary excretion of biotin sulfone and bisnorbiotin methyl ketone increased with biotin administration. The urinary excretion of biotin sulfone increased 21-fold from 0.2 nmol/h before to 4.2 nmol/h after administration; the excretion of bisnorbiotin methyl ketone increased 130-fold from 0.4 to 51.8 nmol/h. At presumed steady state in free-living subjects (n = 6), biotin sulfone and bisnorbiotin methyl ketone accounted for 3.6% and 7.9% of total biotin excretion, respectively. Traces of tetranorbiotin-l-sulfoxide were also identified by using thin-layer chromatography and derivatization with p-dimethylaminocinnamaldehyde. However, tetranorbiotin-l-sulfoxide was not detectable in urine by the HPLC and avidin-binding assay because this metabolite has weak avidin-binding affinity. We conclude that biotin sulfone and bisnorbiotin methyl ketone are present in measurable quantities in human urine; their quantitation should allow more accurate studies on human biotin metabolism and turnover.

Adult↗
PubMed1997

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.

Adult↗
PubMed1997

Biotin biotransformation to bisnorbiotin is accelerated by several peroxisome proliferators and steroid hormones in rats.

Bisnorbiotin and biotin sulfoxide are the major catabolites of biotin for humans, swine, and rats. Increased urinary excretion of bisnorbiotin, biotin sulfoxide, or both have been observed during pregnancy and in patients treated with certain anticonvulsants. We sought more insight into the sites and mechanisms of biotin catabolism by exposing rats in vivo to compounds known to induce classes of enzymes that were candidates to catalyze the biotransformations. Rats were treated with the anticonvulsants phenytoin, phenobarbital, and carbamazepine, the steroid hormones dexamethasone and dehydroepiandrosterone, and the peroxisome proliferators clofibrate and di(2-ethylhexyl)phthalate. [14C]Biotin was injected intraperitoneally at physiologic doses in treated rats and control rats; HPLC and radiometric flow detection were used to specifically identify and quantify [14C]biotin and its metabolites in urine. Treatment effects were assessed by the change in the urinary excretion of [14C]bisnorbiotin and [14C]biotin sulfoxide in response to administration of [14C]biotin. No significant changes resulted from treatment with any of the anticonvulsants. With the steroid hormones and the peroxisome proliferators, [14C]bisnorbiotin excretion increased significantly. These results indicate that biotin is converted into bisnorbiotin in the liver and that this conversion likely occurs in peroxisomes or mitochondria or both via beta-oxidative cleavage, and, in contrast to responses in humans, the enzymes responsible for the formation of biotin sulfoxide in rats are not induced by the anticonvulsants examined here.

Analysis of Variance↗
PubMed1997

The pig is an appropriate model for human biotin catabolism as judged by the urinary metabolite profile of radioisotope-labeled biotin.

Because the rat model of biotin deficiency and biotin metabolism has important limitations, we sought to determine whether the urinary profile of biotin and its metabolites in pigs is similar to that in humans. Biotin labeled with either 3H on the side chain or 14C on the ureido ring was administered intravenously to 2-mo-old male pigs. Biotin and its metabolites were identified and quantified by HPLC and radiometric flow detection. At tracer doses of [3H]biotin, 12 +/- 6% (mean +/- SD, n = 3) of total administered radioactivity was excreted within 72 h; at a physiologic dose of [14C]biotin, 47 +/- 2% (n = 5) of the administered radioactivity was excreted within 72 h. Biotin was the major form excreted, as it was in humans. Substantial amounts of bisnorbiotin and biotin sulfoxide, two known biotin metabolites, were also excreted. Bisnorbiotin methyl ketone and biotin sulfone, two biotin metabolites recently identified in human urine, were also present in pig urine. This study provides evidence that biotin metabolism in pigs resembles that in humans.

Animals↗
PubMed1997

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.

Adult↗
PubMed1997

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.

Animals↗
PubMed1997

Lipoic acid reduces the activities of biotin-dependent carboxylases in rat liver.

In the past, lipoic acid has been administered to patients and test animals as therapy for diabetic neuropathy and various intoxications. Lipoic acid and the vitamin biotin have structural similarities. We sought to determine whether the chronic administration of lipoic acid affects the activities of biotin-dependent carboxylases. For 28 d, rats received daily intraperitoneal injections of one of the following: 1) a small dose of lipoic acid [4.3 micromol/( kg.d)]; 2) a large dose of lipoic acid [15.6 micromol/(kg.d)]; or 3) a large dose of lipoic acid plus biotin [15.6 and 2.0 micromol/(kg.d), respectively]. Another group received n-hexanoic acid [14.5 micromol/(kg.d)], which has structural similarities to lipoic acid and biotin and thus served as a control for the specificity of lipoic acid. A fifth group received phosphatidylcholine in saline injections and served as the vehicle control. The rat livers were assayed for the activities of acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and beta-methylcrotonyl-CoA carboxylase. Urine was analyzed for lipoic acid; serum was analyzed for indicators of liver damage and metabolic aberrations. The mean activities of pyruvate carboxylase and beta-methylcrotonyl-CoA carboxylase were 28-36% lower in the lipoic acid-treated rats compared with vehicle controls (P < 0.05). Rats treated with lipoic acid plus biotin had normal carboxylase activities. Carboxylase activities in livers of n-hexanoic acid-treated rats were normal despite some evidence of liver injury. Propionyl-CoA carboxylase and acetyl-CoA carboxylase were not significantly affected by administration of lipoic acid. This study provides evidence consistent with the hypothesis that chronic administration of lipoic acid lowers the activities of pyruvate carboxylase and beta-methylcrotonyl-CoA carboxylase in vivo by competing with biotin.

Acetyl-CoA Carboxylase↗