Marginal maternal biotin deficiency in CD-1 mice reduces fetal mass of biotin-dependent carboxylases

Novel multimodal molecular imaging of Vitamin H (Biotin) transporter activity in the murine placenta

Vitamin H (biotin) is delivered to the fetus transplacentally by an active biotin-transport mechanism and is critical for fetal development. Our objective was to develop a comprehensive MRI technique for mapping biotin transporter activity in the murine placenta. Visualization of transporter activity can employ MRI's unique T₂*-dependent signal 'off-switch', which is triggered by transporter mediated aggregation of biotinylated contrast agent (b-BSA-Gd-DTPA). MRI data were collected from pregnant mice after administration of b-BSA-Gd-DTPA and analyzed using a new sub-voxel biophysical signal model. Validation experiments included competition with native biotin, comparative tests using PET, histology, and ICPMS. MRI signal was governed by binding, aggregation, and clearance of biotin (confirmed by histology). Signal dynamics reflected the placenta's perfusion pattern modulated by biotin transporter activity and trophoblast mediated retention, and were in congruence with a three-compartment sub-voxel model. Pre-saturation of the transporters with free biotin suppressed b-BSA-Gd-DTPA uptake. The results were confirmed by PET, histology and ICPMS. The presented MRI-based platform allows to track activity of essential molecular transporters in the placenta, reflecting a transporter-mediated uptake, followed by retention and aggregation, and recycling associated with the large b-BSA-Gd-DTPA conjugate. The presented DCE-MRI technique can furthermore be used to map and characterize microstructural compartmentation and transporter activity without exposing the fetus to contrast media.

Biotin: From Nutrition to Therapeutics

Although frank symptomatic biotin deficiency is rare, some evidence suggests that marginal biotin deficiency occurs spontaneously in a substantial proportion of women during normal human pregnancy and might confer an increased risk of birth defects. Herein I review 1) advances in assessing biotin status, including the relation between acylcarnitine excretion and biotin status; 2) recent studies of biotin status in pregnancy; 3) advances in understanding the role of biotin in gene expression and the potential roles of biotinylated proteins that are neither histones nor carboxylases; and 4) novel large-dose biotin supplementation as therapy for multiple sclerosis. The review concludes with a summary of recent studies that have reported potentially dangerous erroneous results in individuals consuming large amounts of biotin for measurements of various plasma hormones for common clinical assays that use streptavidin-biotin technology.

Effects of Biotin Deficiency on Biotinylated Proteins and Biotin-Related Genes in the Rat Brain

Biotin is a water-soluble vitamin that functions as a cofactor for biotin-dependent carboxylases. The biochemical and physiological roles of biotin in brain regions have not yet been investigated sufficiently in vivo. Thus, in order to clarify the function of biotin in the brain, we herein examined biotin contents, biotinylated protein expression (e.g. holocarboxylases), and biotin-related gene expression in the brain of biotin-deficient rats. Three-week-old male Wistar rats were divided into a control group, biotin-deficient group, and pair-fed group. Rats were fed experimental diets from 3 wk old for 8 wk, and the cortex, hippocampus, striatum, hypothalamus, and cerebellum were then collected. In the biotin-deficient group, the maintenance of total biotin and holocarboxylases, increases in the bound form of biotin and biotinidase activity, and the expression of an unknown biotinylated protein were observed in the cortex. In other regions, total and free biotin contents decreased, holocarboxylase expression was maintained, and bound biotin and biotinidase activity remained unchanged. Biotin-related gene (pyruvate carboxylase, sodium-dependent multivitamin transporter, holocarboxylase synthetase, and biotinidase) expression in the cortex and hippocampus also remained unchanged among the dietary groups. These results suggest that biotin may be related to cortex functions by binding protein, and the effects of a biotin deficiency and the importance of biotin differ among the different brain regions.

In HepG2 cells, coexisting carnitine deficiency masks important indicators of marginal biotin deficiency

BACKGROUND

A large number of birth defects are related to nutrient deficiencies; concern that biotin deficiency is teratogenic in humans is reasonable. Surprisingly, studies indicate that increased urinary 3-hydroxyisovalerylcarnitine (3HIAc), a previously validated marker of biotin deficiency, is not a valid biomarker in pregnancy.

OBJECTIVE

In this study we hypothesized that coexisting carnitine deficiency can prevent the increase in 3HIAc due to biotin deficiency.

METHODS

We used a 2-factor nutrient depletion design to induce isolated and combined biotin and carnitine deficiency in HepG2 cells and then repleted cells with carnitine. To elucidate the metabolic pathogenesis, we quantitated intracellular and extracellular free carnitine, acylcarnitines, and acylcarnitine ratios using liquid chromatography-tandem mass spectrometry.

RESULTS

Relative to biotin-sufficient, carnitine-sufficient cells, intracellular acetylcarnitine increased by 90%, propionylcarnitine more than doubled, and 3HIAc increased by >10-fold in biotin-deficient, carnitine-sufficient (BDCS) cells, consistent with a defensive mechanism in which biotin-deficient cells transesterify the acyl-coenzyme A (acyl-CoA) substrates of the biotin-dependent carboxylases to the related acylcarnitines. Likewise, in BDCS cells, the ratio of acetylcarnitine to malonylcarnitine and the ratio of propionylcarnitine to methylmalonylcarnitine both more than tripled, and the ratio of 3HIAc to 3-methylglutarylcarnitine (MGc) increased by >10-fold. In biotin-deficient, carnitine-deficient (BDCD) cells, the 3 substrate-derived acylcarnitines changed little, but the substrate:product ratios were masked to a lesser extent. Moreover, carnitine repletion unmasked biotin deficiency in BDCD cells as shown by increases in acetylcarnitine, propionylcarnitine, and 3HIAc (each increased by >50-fold). Likewise, ratios of acetylcarnitine:malonylcarnitine, propionylcarnitine:methylmalonylcarnitine, and 3HIAc:MGc all increased by >8-fold.

CONCLUSIONS

Our findings provide strong evidence that coexisting carnitine deficiency masks some indicators of biotin deficiency and support the potential importance of the ratios of acylcarnitines arising from the acyl-CoA substrates and products for biotin-dependent carboxylases in detecting the biotin deficiency that is masked by coexisting carnitine deficiency.

Conditional knockout of the Slc5a6 gene in mouse intestine impairs biotin absorption

The Slc5a6 gene expresses a plasma membrane protein involved in the transport of the water-soluble vitamin biotin; the transporter is commonly referred to as the sodium-dependent multivitamin transporter (SMVT) because it also transports pantothenic acid and lipoic acid. The relative contribution of the SMVT system toward carrier-mediated biotin uptake in the native intestine in vivo has not been established. We used a Cre/lox technology to generate an intestine-specific (conditional) SMVT knockout (KO) mouse model to address this issue. The KO mice exhibited absence of expression of SMVT in the intestine compared with sex-matched littermates as well as the expected normal SMVT expression in other tissues. About two-thirds of the KO mice died prematurely between the age of 6 and 10 wk. Growth retardation, decreased bone density, decreased bone length, and decreased biotin status were observed in the KO mice. Microscopic analysis showed histological abnormalities in the small bowel (shortened villi, dysplasia) and cecum (chronic active inflammation, dysplasia) of the KO mice. In vivo (and in vitro) transport studies showed complete inhibition in carrier-mediated biotin uptake in the intestine of the KO mice compared with their control littermates. These studies provide the first in vivo confirmation in native intestine that SMVT is solely responsible for intestinal biotin uptake. These studies also provide evidence for a casual association between SMVT function and normal intestinal health.

Measurement of acylcarnitine substrate to product ratios specific to biotin-dependent carboxylases offers a combination of indicators of biotin status in humans

This work describes a novel liquid chromatography tandem MS (LC-MS/MS) method for the determination of ratios of acylcarnitines arising from acyl-CoA substrates and products that reflect metabolic disturbances caused by marginal biotin deficiency. The urinary ratios reflecting reduced activities of biotin-dependent enzymes include the following: 1) the ratio of 3-hydroxyisovalerylcarnitine : 3-methylglutarylcarnitine (3HIAc : MGc) for methylcrotonyl-CoA carboxylase; 2) the ratio of propionylcarnitine:methylmalonylcarnitine (Pc : MMc) for propionyl-CoA carboxylase (PCC); and 3) the ratio of acetylcarnitine : malonylcarnitine (Ac : Mc) for acetyl-CoA carboxylase. To demonstrate the suitability of the LC-MS/MS method for biomonitoring, we measured the 3 ratios for 7 healthy adults at various time points (d 0, 14, and 28) during the induction of marginal biotin through the consumption of egg white. The mean change in the Pc : MMc ratio relative to d 0 was 5.3-fold by d 14 (P = 0.0049) and 8.5-fold by d 28 (P = 0.0042). The mean change in the 3HIAc : MGc ratio was 2.8-fold by d 14 (P = 0.0022) and 3.8-fold by d 28 (P = 0.0001). The mean change in the Ac : Mc ratio was 2.9-fold by d 14 (P = 0.03) and 4.7-fold by d 28 (P = 0.02). The results suggest that simultaneous assessment of ratios of multiple biotin-dependent pathways offers insight into the complex metabolic disturbances caused by marginal biotin deficiency. We hypothesize that one or a combination of the ratios might be more sensitive or robust with respect to other nutrient deficiencies or confounding metabolic processes.

Tissue-specific mRNA expression patterns reveal a coordinated metabolic response associated with genetic selection for milk production in cows

The molecular mechanisms regulating the physiological adaptation of tissues important for nutrient partitioning and metabolism in lactating cows are still not completely understood. The aim of our study was to identify tissue-specific regulatory mechanisms necessary to accommodate metabolic changes associated with different genetic potential for milk performance. For this purpose, we analyzed mRNA expression of genes involved in energy metabolism of segregating F(2) beef type cows with a combined genetic dairy and beef background (Charolais × German Holstein cross, CH×GH) in contrast to purebred German Holstein (GH) dairy cows. Three groups of cows differing in milk performance were examined using quantitative real-time PCR in liver, mammary gland, and skeletal muscle. Our results describe substantial tissue-specific differences in mRNA transcription profiles between cow groups in relation to their genetic potential for milk performance and highlight genes exhibiting specific, partially yet-unknown functions in dairy and beef type cows, e.g., upregulation of PCK2 transcripts in the mammary gland and FBP2 transcripts in skeletal muscle of dairy cows. Noticeably, PCCA and PPARGC1A mRNA abundance varied significantly across experimental groups in all three tissues, pointing to potential key gene functions in the metabolic adaptation relative to divergent milk production performance. Correlations of mRNA expression levels to milk performance traits indicate that gene transcriptional processes may play a regulatory role in liver, mammary gland, and skeletal muscle to enable cows with different genetic potential for milk performance to cope with metabolic lactation-associated challenges.

Urinary excretion of 3-hydroxyisovaleric acid and 3-hydroxyisovaleryl carnitine increases in response to a leucine challenge in marginally biotin-deficient humans

Experimentally increasing metabolic flux in a pathway in which an essential step is catalyzed by a vitamin-dependent enzyme (a challenge test) has been used in assessing functional vitamin status and elucidating common and alternate metabolic pathways. Conversion of 3-methylcrotonyl CoA to 3-methylglutaconyl CoA in the leucine catabolic pathway is catalyzed by the biotin-dependent enzyme methylcrotonyl-CoA carboxylase (MCC). Marginal biotin deficiency reduces MCC activity and increases urinary excretion of 3-hydroxyisovaleric acid (3HIA) and 3-hydroxyisovaleryl carnitine (3HIA-carnitine) measured in 24-h urine collections. We assessed urinary excretion of 3HIA and 3HIA-carnitine in response to a leucine challenge in humans made progressively biotin deficient by egg white consumption. In 2 cohorts of healthy adults (Study 1: n = 5; Study 2: n = 7) rendered biotin deficient over 28 d, urinary excretion of 3HIA and 3HIA-carnitine in response to a leucine challenge was quantitated weekly for 3 or 4 wk, respectively. In both studies, mean urinary excretion of both 3HIA and 3HIA-carnitine increased >2-fold by d 14 (P < 0.002 for both indicators for both studies). Diagnostically, both indicators were highly sensitive, but diagnostic sensitivities were not superior to those of 24-h excretion of 3HIA and 3HIA-carnitine. These studies provide evidence that urinary excretions of 3HIA and 3HIA-carnitine in response to an oral leucine challenge are early and sensitive indicators of marginal biotin deficiency in humans. The variability of the proportion of leucine catabolites excreted as 3HIA suggests substantial population heterogeneity in the metabolic capacity of the 3HIA-carnitine detoxification pathway.

Urinary excretion of 3-hydroxyisovaleryl carnitine is an early and sensitive indicator of marginal biotin deficiency in humans

Mounting evidence indicates that marginal biotin deficiency is not rare, contrary to previous assumptions. Accordingly, robust indicators of biotin status would be useful. In a study of 10 healthy adults, we recently provided evidence that abnormally increased plasma concentration of 3-hydroxyisovaleryl carnitine (3HIA-carnitine) is a sensitive indicator of marginal biotin deficiency. We sought to determine whether urinary excretion of 3HIA-carnitine (expressed as the ratio to urinary creatinine) significantly increases in marginal biotin deficiency. Marginal, asymptomatic biotin deficiency was induced experimentally in the same 10 healthy adults (8 women) by feeding undenatured egg white with meals for 28 d. Biotin status was repleted by a mixed general diet plus biotin supplementation. Urinary excretion of 3HIA-carnitine was determined by liquid chromatography-tandem MS on d 0, 14, and 28 (depletion) and on d 35 and 50 (repletion). Mean urinary 3HIA-carnitine concentration increased with depletion (P < 0.0001; d 0 vs. 28) and decreased with repletion (P = 0.0002; d 28 vs. 50). Urinary 3HIA-carnitine excretion was greater than the upper limit of normal in 9 of 10 participants by d 14 and decreased to within normal limits by d 50 in all participants. This study provides evidence that urinary excretion of 3HIA-carnitine is an early and sensitive indicator of marginal biotin deficiency. The ease of collection of untimed urine samples and application of a new analytical method with simplified sample preparation suggest that urinary 3HIA-carnitine is likely to be a useful indicator for large population studies.

Plasma concentration of 3-hydroxyisovaleryl carnitine is an early and sensitive indicator of marginal biotin deficiency in humans

BACKGROUND

Blood-based indicators of biotin status in humans were shown to be useful tools in several clinical situations, including pregnancy. We previously validated the activity of the biotin-dependent enzyme propionyl-coenzyme A carboxylase (PCC) in lymphocytes as a sensitive and specific blood-based indicator of marginal degrees of biotin deficiency. However, the measurement of PCC activity in population studies presents substantial analytic challenges. 3-Hydroxyisovaleryl carnitine (3HIA-carnitine) increases in response to the decreased activity of the biotin-dependent enzyme methylcrotonyl-coenzyme A carboxylase and might reflect biotin status.

OBJECTIVE

We sought to determine whether the plasma concentration of 3HIA-carnitine increases significantly in marginal biotin deficiency.

DESIGN

We experimentally induced marginal, asymptomatic biotin deficiency in 10 healthy adults (8 women) by having the subjects consume undenatured egg white for 28 d; biotin status was then repleted. Plasma concentrations of 3HIA-carnitine were measured on days 0, 14, 28, 35, and 50 by liquid chromatography-mass spectroscopy.

RESULTS

The mean plasma 3HIA-carnitine concentration increased with depletion (P < 0.0001) and decreased with repletion (P < 0.0001). Plasma 3HIA-carnitine concentrations were greater than the upper limit of normal concentrations in 7 of 10 subjects by day 14 and in 9 of 10 subjects by day 28 and decreased to within normal limits in 9 of 10 subjects by day 50.

CONCLUSIONS

These studies provide evidence that 3HIA-carnitine is an early and sensitive indicator of marginal biotin deficiency. The ease of sample collection, small sample volume requirement, and stability of 3HIA-carnitine during storage suggest that plasma 3HIA-carnitine concentration is likely to be a useful indicator of marginal biotin deficiency for larger population studies.

Quantitative measurement of urinary excretion of 3-hydroxyisovaleryl carnitine by LC-MS/MS as an indicator of biotin status in humans

Abnormally increased urinary excretion of 3-hydroxyisovaleryl carnitine (3HIA-carnitine) results from impairment in leucine catabolism caused by reduced activity of the biotin-dependent enzyme 3-methylcrotonyl-CoA carboxylase. Accordingly, urinary 3HIA-carnitine might reflect biotin status. Here, we describe an LC-MS/MS method for accurately quantitating the urinary concentration of 3HIA-carnitine at concentrations that are typical for excretion rates that are normal or only modestly increased. This method allows for high sample throughput and does not require solid-phase extraction. We used this method to provide evidence validating urinary 3HIA-carnitine as a biomarker of biotin deficiency in humans. Four healthy adult subjects were successfully made marginally biotin deficient by feeding a 30% egg white diet for 28 days. From study day 0 to 28, the mean urinary excretion of 3HIA-carnitine increased 3.5-fold (p = 0.026). These preliminary results indicate that urinary excretion of 3HIA-carnitine increases with marginal biotin deficiency. If these results are confirmed in studies involving larger numbers of subjects, urinary excretion of 3HIA-carnitine may potentially be a clinically useful indicator of biotin status.

Quantitative measurement of plasma 3-hydroxyisovaleryl carnitine by LC-MS/MS as a novel biomarker of biotin status in humans

An increased plasma concentration of 3-hydroxyisovaleryl carnitine (3HIA-carnitine) results from impairment in the leucine catabolic pathway at the conversion of 3-methylcrotonyl-CoA to 3-methylglutaconyl-CoA. The impairment is caused by reduced activity of the biotin-dependent enzyme 3-methylcrotonyl-CoA carboxylase. Here, we describe an LC-MS/MS method for the quantitation of 3HIA-carnitine in plasma and present preliminary evidence validating plasma 3HIA-carnitine as a novel biomarker of biotin deficiency in humans. Three healthy adult subjects were successfully made marginally biotin deficient by feeding of a 30% egg-white diet for 28 days. For each subject, the plasma 3HIA-carnitine increased approximately 3-fold from Study Day 0 to Study Day 28 (p = 0.027). These results indicate that plasma 3HIA-carnitine concentration increases with biotin deficiency. If these results are confirmed in larger studies, plasma 3HIA-carnitine is likely to be an important indicator of biotin status in a variety of clinical circumstances because quantitation of 3HIA-carnitine by this method has several technical advantages over existing validated indicators of biotin status in humans.

Biochemical alterations in the palatal processes in fetuses of biotin-deficient mice

To clarify the role of biotin in palatal formation, we investigated the effects of biotin deficiency on the development of palatal processes in mouse fetuses at midgestation. We also investigated protein expressions in the palatal processes. Pregnant mice were given either a biotin-deficient diet or a biotin-supplemented (control) diet from day 0 of gestation (dg 0). Some dams in the biotin-deficient group were changed to a biotin-supplemented diet on dg 12, 13 or 14. On dg 15, the palatal processes were dissected from these fetuses and their peptides were characterized using two-dimensional electrophoresis and liquid chromatography/tandem mass spectrometry (LC-MS/MS) system. Regarding Trasler's stage for the growth of the palatal processes in mouse fetuses on dg 15, the average stage of palatal development was 5.83 +/- 0.39 in the biotin-supplemented group, 5.39 +/- 0.66 in the dg 13-supplemented group, and 4.64 +/- 0.90 in the biotin-deficient group. The development of the palatal processes significantly increased in relation to the earlier day of biotin supplementation. In a protein analysis of palatal processes by isoelectro focusing (IEF) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), a 19-kDa spot was confirmed around position at pI 6-7 in the biotin-supplemented group, but this protein was not present in either the biotin-deficient group or the dg 13-supplemented group. From the MS/MS database of peptides, adenosine diphosphate (ADP)-ribosylation factor 2 (arf2) and alpha-crystallin were detected in the mesenchyme of the palatal processes. It is suggested that the expression of these proteins may be downregulated by biotin deficiency, inducing the inhibited development of palatal processes.

Biotin

Biotin is a water-soluble vitamin and serves as a coenzyme for five carboxylases in humans. Biotin is also covalently attached to distinct lysine residues in histones, affecting chromatin structure and mediating gene regulation. This review describes mammalian biotin metabolism, biotin analysis, markers of biotin status, and biological functions of biotin. Proteins such as holocarboxylase synthetase, biotinidase, and the biotin transporters SMVT and MCT1 play crucial roles in biotin homeostasis, and these roles are reviewed here. Possible effects of inadequate biotin intake, drug interactions, and inborn errors of metabolism are discussed, including putative effects on birth defects.

Marginal biotin deficiency is common in normal human pregnancy and is highly teratogenic in mice

In studies of marginal biotin deficiency induced experimentally in adults, increased urinary excretion of 3-hydroxyisovaleric acid (3HIA), which likely reflects decreased activity of the biotin-dependent enzyme beta-methylcrotonyl-CoA carboxylase, and decreased activity of the biotin-dependent enzyme propionyl-CoA carboxylase (PCC) in peripheral blood lymphocytes have been validated as indices of biotin status. About half of pregnant women excrete increased amounts of urinary 3HIA. However, interpretation of urinary 3HIA excretion rates is problematic, because renal function is altered by pregnancy per se. In a recent pilot study, activity of PCC in peripheral blood lymphocytes was decreased in 18 of 22 pregnant women. In 4 of 4 pregnant women with decreased PCC activity, biotin supplementation caused increased PCC activity by a mean of 95%. Taken together, such studies provide evidence that a substantial proportion of pregnant women are marginally biotin deficient. In mice, degrees of biotin deficiency that are metabolically similar to those seen in pregnant women are very teratogenic. Moreover, in mice, a marginal degree of biotin deficiency in the dam causes a much more severe degree of deficiency in the fetus. These observations further raise concerns that biotin deficiency does occur and does cause human birth defects.

Biotin and biotinidase deficiency

Biotin is a water-soluble vitamin that serves as an essential coenzyme for five carboxylases in mammals. Biotin-dependent carboxylases catalyze the fixation of bicarbonate in organic acids and play crucial roles in the metabolism of fatty acids, amino acids and glucose. Carboxylase activities decrease substantially in response to biotin deficiency. Biotin is also covalently attached to histones; biotinylated histones are enriched in repeat regions in the human genome and appear to play a role in transcriptional repression of genes and genome stability. Biotin deficiency may be caused by insufficient dietary uptake of biotin, drug-vitamin interactions and, perhaps, by increased biotin catabolism during pregnancy and in smokers. Biotin deficiency can also be precipitated by decreased activities of the following proteins that play critical roles in biotin homeostasis: the vitamin transporters sodium-dependent multivitamin transporter and monocarboxylate transporter 1, which mediate biotin transport in the intestine, liver and peripheral tissues, and renal reabsorption; holocarboxylase synthetase, which mediates the binding of biotin to carboxylases and histones; and biotinidase, which plays a central role in the intestinal absorption of biotin, the transport of biotin in plasma and the regulation of histone biotinylation. Symptoms of biotin deficiency include seizures, hypotonia, ataxia, dermatitis, hair loss, mental retardation, ketolactic acidosis, organic aciduria and also fetal malformations. This review focuses on the deficiencies of both biotin and biotinidase, and the medical management of such cases.

Biotin deficiency affects the proliferation of human embryonic palatal mesenchymal cells in culture

It has recently been demonstrated that pregnancy in women may cause mild biotin deficiency without any clinical signs. However, the teratogenicity of biotin deficiency in humans has not been well investigated. On the other hand, our previous studies have shown that maternal biotin deficiency induces many kinds of malformations, such as cleft palate, micrognathia, and micromelia, in all animal fetuses. However the mechanism for cleft palate induction under biotin-deficient conditions is unknown. Therefore, to investigate the possible mechanisms for cleft palate induction in embryos, we investigated the effects of biotin deficiency on human embryonic palatal mesenchymal (HEPM) cells in culture in this study. HEPM cells were cultured in biotin-deficient and biotin-physiological (control) media for 5 wk. The proliferative availabilities of HEPM cells in the biotin-deficient state were significantly lower after wk 2 of culture (41.3% of the control). Biotin concentrations in biotin-deficient cells were drastically lower after wk 1 of culture, whereas those in the control cells remained at almost the same level. Biotinidase activities were also lower in biotin-deficient cells. Holocarboxylases in biotin-deficient cells were fewer after the first week of culture and were almost undetectable after wk 2. The amount of biotinylated histones in the nuclei of biotin-deficient cells was lower than in the control cells. This suppressed proliferation of mesenchymal cells may delay or inhibit the growth of palatal processes in embryos and thus it may partially contribute to the mechanisms for cleft palate induction.

Effect of Biotin on Activity and Gene Expression of Biotin-Dependent Carboxylases in the Liver of Dairy Cows

Biotin is a cofactor of the gluconeogenic enzymes pyruvate carboxylase (PC) and propionyl-coenzyme A carboxylase (PCC). We hypothesized that biotin supplementation increases the activity and gene expression of PC and PCC and the gene expression of phosphoenol-pyruvate carboxykinase (PEPCK) in the liver of lactating dairy cows. Eight multiparous Holstein cows (40 +/- 2 kg/d of milk yield and 162 +/- 35 d in milk) were randomly assigned to 1 of 2 diet sequences in a crossover design with two 22-d periods. Treatments consisted of a basal diet (60% concentrate) containing 0 or 0.96 mg/kg of supplemental biotin. On d 21 of each period, liver tissue was collected by percutaneous liver biopsy. Activities of PC and PCC were determined by measuring the fixation of [14C]O2 in liver homogenates. Abundance of mRNA for PCC, PC, and PEPCK was determined by quantitative reverse-transcription PCR. Biotin supplementation did not affect milk production or composition. Biotin supplementation increased the activity of PC but had no effect on PCC activity. Biotin supplementation did not affect the gene expression of PC, PCC, and PEPCK. The increased activity of PC without changes in mRNA abundance may have been caused by increased activation of the apoenzymes by holocarboxylase synthetase. In conclusion, biotin supplementation affected the activity of PC in the liver of lactating dairy cows, but whether biotin supplementation increases glucose production in the liver remains to be determined.

Lymphocyte propionyl-CoA carboxylase and its activation by biotin are sensitive indicators of marginal biotin deficiency in humans

BACKGROUND

Marginal biotin deficiency may be a human teratogen. A biotin status indicator that is not dependent on renal function may be useful in studies of biotin status during pregnancy. A previous study of experimental biotin deficiency suggested that propionyl-coenzyme A carboxylase (PCC) activity in peripheral blood lymphocytes (PBLs) is a sensitive indicator of biotin status.

OBJECTIVE

We examined the utility of measuring PCC activity and the activation of PCC by biotin in detecting marginal biotin deficiency.

DESIGN

Marginal biotin deficiency was induced in 7 adults (3 women) by egg-white feeding for 28 d. Blood and urine were obtained on days 0, 14, and 28 (depletion phase) and 44 and 65 (repletion phase). PBLs were incubated with (activated) or without (control) biotin before PCC assay. The activation coefficient of PCC is the ratio of PCC activity in activated PBLs to that in control PBLs. The significance of differences for all measurements was tested by repeated-measures analysis of variance with Fisher's post hoc test and Bonferroni correction.

RESULTS

Changes in the urinary excretion of biotin and of 3-hydroxyisovaleric acid confirmed that marginal biotin deficiency was successfully induced. By day 14, PCC activity had decreased (P < 0.0001) to below the lower limit of normal in all subjects. By day 28, the activation coefficient of PCC had increased significantly (P = 0.003) and was above the upper limit of normal in 6 of 7 subjects.

CONCLUSION

PCC activity is the most sensitive indicator of biotin status tested to date. In future pregnancy studies, the use of lymphocyte PCC activity data should prove valuable in the assessment of biotin status.

Marginal biotin deficiency is teratogenic in mice and perhaps humans: a review of biotin deficiency during human pregnancy and effects of biotin deficiency on gene expression and enzyme activities in mouse dam and fetus

Recent studies of biotin status during pregnancy provide evidence that a marginal degree of biotin deficiency develops in a substantial proportion of women during normal pregnancy. Several lines of evidence suggest that although the degree of biotin deficiency is not severe enough to produce the classic cutaneous and behavioral manifestations of biotin deficiency, the deficiency is severe enough to produce metabolic derangements in women and may be teratogenic. In studies of mice, a similar degree of biotin deficiency induces characteristic fetal malformations at a high rate. Fetal hepatic biotin content and PCC activity decrease indicating that the fetuses also become biotin deficient. Fetal hepatic acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase and beta-methylcrotonyl-CoA carboxylase abundances determined by Western blotting decreased more than the dam holocarboxylase abundances (10% of sufficient vs. 50% of sufficient); however, hepatic mRNA for the carboxylases and for HCS did not change significantly in either dams or fetuses. These observations suggest that maternal biotin deficiency results in a lack of adequate biotin to biotinylate apocarboxylases in the fetus despite the normal expression of genes coding for the apocarboxylases and holocarboxylase synthetase.