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

α-Lipoic Acid Reduces Ceramide Synthesis and Neuroinflammation in the Hypothalamus of Insulin-Resistant Rats, While in the Cerebral Cortex Diminishes the β-Amyloid Accumulation

Background

Oxidative stress underlies metabolic diseases and cognitive impairment; thus, the use of antioxidants may improve brain function in insulin-resistant conditions. We are the first to evaluate the effects of α-lipoic acid (ALA) on redox homeostasis, sphingolipid metabolism, neuroinflammation, apoptosis, and β-amyloid accumulation in the cerebral cortex and hypothalamus of insulin-resistant rats.

Methods

The experiment was conducted on male cmdb/outbred Wistar rats fed a high-fat diet (HFD) for 10 weeks with intragastric administration of ALA (30 mg/kg body weight) for 4 weeks. Pro-oxidant and pro-inflammatory enzymes, oxidative stress, sphingolipid metabolism, neuroinflammation, apoptosis, and β-amyloid level were assessed in the hypothalamus and cerebral cortex using colorimetric, fluorimetric, ELISA, and HPLC methods. Statistical analysis was performed using three-way ANOVA followed by the Tukey HSD test.

Results

ALA normalizes body weight, food intake, glycemia, insulinemia, and systemic insulin sensitivity in HFD-fed rats. ALA treatment reduces nicotinamide adenine dinucleotide phosphate (NADPH) and xanthine oxidase activity, increases ferric-reducing antioxidant power (FRAP) and thiol levels in the hypothalamus of insulin-resistant rats. In addition, it decreases myeloperoxidase, glucuronidase, and metalloproteinase-2 activity and pro-inflammatory cytokines (IL-1β, IL-6) levels, while in the cerebral cortex ALA reduces β-amyloid accumulation. In both brain structures, ALA diminishes ceramide synthesis and caspase-3 activity. ALA improves systemic oxidative status and reduces insulin-resistant rats’ serum cytokines, chemokines, and growth factors.

Conclusion

ALA normalizes lipid and carbohydrate metabolism in insulin-resistant rats. At the brain level, ALA primarily affects hypothalamic metabolism. ALA improves redox homeostasis by decreasing the activity of pro-oxidant enzymes, enhancing total antioxidant potential, and reducing protein and lipid oxidative damage in the hypothalamus of HFD-fed rats. ALA also reduces hypothalamic inflammation and metalloproteinases activity, and cortical β-amyloid accumulation. In both brain structures, ALA diminishes ceramide synthesis and neuronal apoptosis. Although further study is needed, ALA may be a potential treatment for patients with cerebral complications of insulin resistance.

Antioxidant supplementation partially rescues accelerated ovarian follicle loss, but not oocyte quality, of glutathione-deficient mice†

The tripeptide thiol antioxidant glutathione (GSH) has multiple physiological functions. Female mice lacking the modifier subunit of glutamate cysteine ligase (GCLM), the rate-limiting enzyme in GSH synthesis, have decreased GSH concentrations, ovarian oxidative stress, preimplantation embryonic mortality, and accelerated age-related decline in ovarian follicles. We hypothesized that supplementation with thiol antioxidants, N-acetyl cysteine (NAC), or α-lipoic acid (ALA) will rescue this phenotype. Gclm-/- and Gclm+/+ females received 0 or 80 mM NAC in drinking water from postnatal day (PND) 21-30; follicle growth was induced with equine chorionic gonadotropin (eCG) on PND 27, followed by an ovulatory dose of human CG and mating with a wild type male on PND 29 and zygote harvest 20 h after hCG. N-acetyl cysteine supplementation failed to rescue the low rate of second pronucleus formation in zygotes from Gclm-/- versus Gclm+/+ females. In the second study, Gclm-/- and Gclm+/+ females received diet containing 0, 150, or 600 mg/kg ALA beginning at weaning and were mated with wild type males from 8 to 20 weeks of age. α-Lipoic acid failed to rescue the decreased offspring production of Gclm-/- females. However, 150 mg/kg diet ALA partially rescued the accelerated decline in primordial follicles, as well as the increased recruitment of follicles into the growing pool and the increased percentages of follicles with γH2AX positive oocytes or granulosa cells of Gclm-/- females. We conclude that ovarian oxidative stress is the cause of accelerated primordial follicle decline, while GSH deficiency per se may be responsible for preimplantation embryonic mortality in Gclm-/- females.

The neuroprotective effects of alpha-lipoic acid on an experimental model of Alzheimer's disease in PC12 cells

With the growth of the aging population, the prevalence of Alzheimer's disease (AD) has increased and influenced the work and daily life of AD patients, imposing a heavy burden on society and the patients' families. AD is a progressive disease with a long duration, and the pathogenesis is very complicated. Here, we found that alpha-lipoic acid (LA), an endogenous, naturally synthesized compound, could attenuate amyloid beta fragment (Aβ_25-35 )-induced PC12 cell toxicity. Aβ_25-35 treatment largely decreased the viability of PC12 cells, increased reactive oxygen species (ROS) levels, and increased the percentage of apoptotic cells, which were accompanied by changes in the expression of the apoptosis-related genes. Further, the Wnt pathway was inactivated, and the expression of Wnt pathway-related proteins such as Frizzled2, GSK3β, and phosphorylated GSK3β were dysregulated after Aβ_25-35 treatment. LA efficiently attenuated Aβ_25-35 -induced PC12 cell apoptosis and downregulated the phosphorylation-mediated degradation of β-catenin as well as GSK3β. Our results demonstrate that LA rescues Aβ_25-35 -induced neurocytotoxicity through the Wnt-β-catenin pathway.

Mitochondrial medicine therapies: rationale, evidence, and dosing guidelines

PURPOSE OF REVIEW

Primary mitochondrial disease is a highly heterogeneous but collectively common inherited metabolic disorder, affecting at least one in 4300 individuals. Therapeutic management of mitochondrial disease typically involves empiric prescription of enzymatic cofactors, antioxidants, and amino acid and other nutrient supplements, based on biochemical reasoning, historical experience, and consensus expert opinion. As the field continues to rapidly advance, we review here the preclinical and clinical evidence, and specific dosing guidelines, for common mitochondrial medicine therapies to guide practitioners in their prescribing practices.

RECENT FINDINGS

Since publication of Mitochondrial Medicine Society guidelines for mitochondrial medicine therapies management in 2009, data has emerged to support consideration for using additional therapeutic agents and discontinuation of several previously used agents. Preclinical animal modeling data have indicated a lack of efficacy for vitamin C as an antioxidant for primary mitochondrial disease, but provided strong evidence for vitamin E and N-acetylcysteine. Clinical data have suggested L-carnitine may accelerate atherosclerotic disease. Long-term follow up on L-arginine use as prophylaxis against or acute treatment for metabolic strokes has provided more data supporting its clinical use in individuals with mitochondrial encephalopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome and Leigh syndrome. Further, several precision therapies have been developed for specific molecular causes and/or shared clinical phenotypes of primary mitochondrial disease.

SUMMARY

We provide a comprehensive update on mitochondrial medicine therapies based on current evidence and our single-center clinical experience to support or refute their use, and provide detailed dosing guidelines, for the clinical management of mitochondrial disease. The overarching goal of empiric mitochondrial medicines is to utilize therapies with favorable benefit-to-risk profiles that may stabilize and enhance residual metabolic function to improve cellular resiliency and slow clinical disease progression and/or prevent acute decompensation.

Unified theory of Alzheimer's disease (UTAD): implications for prevention and curative therapy

The aim of this review is to propose a Unified Theory of Alzheimer's disease (UTAD) that integrates all key behavioural, genetic and environmental risk factors in a causal chain of etiological and pathogenetic events. It is based on three concepts that emanate from human's evolutionary history: (1) The grandmother-hypothesis (GMH), which explains human longevity due to an evolutionary advantage in reproduction by trans-generational transfer of acquired knowledge. Consequently it is argued that mental health at old-age must be the default pathway of humans' genetic program and not development of AD. (2) Therefore, mechanism like neuronal rejuvenation (NRJ) and adult hippocampal neurogenesis (AHN) that still function efficiently even at old age provide the required lifelong ability to memorize personal experiences important for survival. Cumulative evidence from a multitude of experimental and epidemiological studies indicate that behavioural and environmental risk factors, which impair productive AHN, result in reduced episodic memory performance and in reduced psychological resilience. This leads to avoidance of novelty, dysregulation of the hypothalamic-pituitary-adrenal (HPA)-axis and cortisol hypersecretion, which drives key pathogenic mechanisms of AD like the accumulation and oligomerization of synaptotoxic amyloid beta, chronic neuroinflammation and neuronal insulin resistance. (3) By applying to AHN the law of the minimum (LOM), which defines the basic requirements of biological growth processes, the UTAD explains why and how different lifestyle deficiencies initiate the AD process by impairing AHN and causing dysregulation of the HPA-axis, and how environmental and genetic risk factors such as toxins or ApoE4, respectively, turn into disease accelerators under these unnatural conditions. Consequently, the UTAD provides a rational strategy for the prevention of mental decline and a system-biological approach for the causal treatment of AD, which might even be curative if the systemic intervention is initiated early enough in the disease process. Hence an individualized system-biological treatment of patients with early AD is proposed as a test for the validity of UTAD and outlined in this review.

Lipoic acid biosynthesis defects

Lipoate is a covalently bound cofactor essential for five redox reactions in humans: in four 2-oxoacid dehydrogenases and the glycine cleavage system (GCS). Two enzymes are from the energy metabolism, α-ketoglutarate dehydrogenase and pyruvate dehydrogenase; and three are from the amino acid metabolism, branched-chain ketoacid dehydrogenase, 2-oxoadipate dehydrogenase, and the GCS. All these enzymes consist of multiple subunits and share a similar architecture. Lipoate synthesis in mitochondria involves mitochondrial fatty acid synthesis up to octanoyl-acyl-carrier protein; and three lipoate-specific steps, including octanoic acid transfer to glycine cleavage H protein by lipoyl(octanoyl) transferase 2 (putative) (LIPT2), lipoate synthesis by lipoic acid synthetase (LIAS), and lipoate transfer by lipoyltransferase 1 (LIPT1), which is necessary to lipoylate the E2 subunits of the 2-oxoacid dehydrogenases. The reduced form dihydrolipoate is reactivated by dihydrolipoyl dehydrogenase (DLD). Mutations in LIAS have been identified that result in a variant form of nonketotic hyperglycinemia with early-onset convulsions combined with a defect in mitochondrial energy metabolism with encephalopathy and cardiomyopathy. LIPT1 deficiency spares the GCS, and resulted in a combined 2-oxoacid dehydrogenase deficiency and early death in one patient and in a less severely affected individual with a Leigh-like phenotype. As LIAS is an iron-sulphur-cluster-dependent enzyme, a number of recently identified defects in mitochondrial iron-sulphur cluster synthesis, including NFU1, BOLA3, IBA57, GLRX5 presented with deficiency of LIAS and a LIAS-like phenotype. As in DLD deficiency, a broader clinical spectrum can be anticipated for lipoate synthesis defects depending on which of the affected enzymes is most rate limiting.

Identification and assessment of markers of biotin status in healthy adults

Human biotin requirements are unknown and the identification of reliable markers of biotin status is necessary to fill this knowledge gap. Here, we used an outpatient feeding protocol to create states of biotin deficiency, sufficiency and supplementation in sixteen healthy men and women. A total of twenty possible markers of biotin status were assessed, including the abundance of biotinylated carboxylases in lymphocytes, the expression of genes from biotin metabolism and the urinary excretion of biotin and organic acids. Only the abundance of biotinylated 3-methylcrotonyl-CoA carboxylase (holo-MCC) and propionyl-CoA carboxylase (holo-PCC) allowed for distinguishing biotin-deficient and biotin-sufficient individuals. The urinary excretion of biotin reliably identified biotin-supplemented subjects, but did not distinguish between biotin-depleted and biotin-sufficient individuals. The urinary excretion of 3-hydroxyisovaleric acid detected some biotin-deficient subjects, but produced a meaningful number of false-negative results and did not distinguish between biotin-sufficient and biotin-supplemented individuals. None of the other organic acids that were tested were useful markers of biotin status. Likewise, the abundance of mRNA coding for biotin transporters, holocarboxylase synthetase and biotin-dependent carboxylases in lymphocytes were not different among the treatment groups. Generally, datasets were characterised by variations that exceeded those seen in studies in cell cultures. We conclude that holo-MCC and holo-PCC are the most reliable, single markers of biotin status tested in the present study.

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.

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.

A combination of nutriments improves mitochondrial biogenesis and function in skeletal muscle of type 2 diabetic Goto-Kakizaki rats

Background

Recent evidence indicates that insulin resistance in skeletal muscle may be related to reduce mitochondrial number and oxidation capacity. However, it is not known whether increasing mitochondrial number and function improves insulin resistance. In the present study, we investigated the effects of a combination of nutrients on insulin resistance and mitochondrial biogenesis/function in skeletal muscle of type 2 diabetic Goto–Kakizaki rats.

Methodology/Principal Findings

We demonstrated that defect of glucose and lipid metabolism is associated with low mitochondrial content and reduced mitochondrial enzyme activity in skeletal muscle of the diabetic Goto-Kakizaki rats. The treatment of combination of R-α-lipoic acid, acetyl-L-carnitine, nicotinamide, and biotin effectively improved glucose tolerance, decreased the basal insulin secretion and the level of circulating free fatty acid (FFA), and prevented the reduction of mitochondrial biogenesis in skeletal muscle. The nutrients treatment also significantly increased mRNA levels of genes involved in lipid metabolism, including peroxisome proliferator–activated receptor-α (Pparα), peroxisome proliferator–activated receptor-δ (Pparδ), and carnitine palmitoyl transferase-1 (Mcpt-1) and activity of mitochondrial complex I and II in skeletal muscle. All of these effects of mitochondrial nutrients are comparable to that of the antidiabetic drug, pioglitazone. In addition, the treatment with nutrients, unlike pioglitazone, did not cause body weight gain.

Conclusions/Significance

These data suggest that a combination of mitochondrial targeting nutrients may improve skeletal mitochondrial dysfunction and exert hypoglycemic effects, without causing weight gain.

Use of synthetic peptides for identifying biotinylation sites in human histones

Posttranslational modifications of histones play an important role in the regulation of chromatin structure and, hence, gene regulation. Recently, we have identified a novel modification of histones: binding of the vitamin biotin to lysine residues in histones H2A, H3, and H4. Here, we describe a procedure to identify those amino acids that are targets for biotinylation in histones. Briefly, the following analytical sequence is used to identify biotinylation sites: (i) short peptides (<20 amino acids in length) are synthesized chemically; amino acid sequences in the peptides are based on the sequence in a given region of a given histone; (ii) peptides are incubated with biotinidase or holocarboxylase synthetase to conduct enzymatic biotinylation; and (iii) biotin in peptides are probed using streptavidin peroxidase. Amino acid substitutions (e.g., lysine-to-alanine substitutions) in synthetic peptides can be used to corroborate identification of biotinylation sites.

Susceptibility to heat stress and aberrant gene expression patterns in holocarboxylase synthetase-deficient Drosophila melanogaster are caused by decreased biotinylation of histones, not of carboxylases

Previously, we discovered that holocarboxylase synthetase (HCS) is a chromatin-associated protein in Drosophila melanogaster and that HCS deficiency alters chromatin structure and gene expression patterns, leading to decreased heat tolerance. The effects of HCS deficiency were attributed to decreased biotinylation of histones. However, HCS is known to mediate biotinylation of carboxylases in cytoplasm and mitochondria in addition to mediating biotinylation of histones. A challenge posed by the genetic analysis of HCS is to distinguish between the effects of decreased biotinylation of carboxylases from the effects of decreased histone biotinylation in the gene expression patterns and phenotypes observed in HCS-deficient flies. Here, we tested whether 3-methylcrotonyl-CoA carboxylase (MCC) mutant flies exhibit gene expression patterns and heat susceptibility similar to that in HCS-deficient Drosophila. Biotin transporter [sodium-dependent multivitamin transporter (SMVT)] mutants were used to investigate effects of cellular biotin depletion on gene expression and heat susceptibility. Deficiencies of MCC and SMVT in mutant flies were confirmed by real-time PCR, streptavidin blotting of holocarboxylases, and analysis of MCC activities; expression of HCS and biotinylation of histones were not altered in MCC and SMVT mutants. Gene expression patterns in MCC and SMVT mutants were different from that seen with HCS-deficient flies, as judged by the abundance of mRNA coding for defective chorion 1, chitin-binding peritrophin-A, dopamine receptor 2, and yolk protein 2. MCC mutants exhibited increased resistance to heat stress compared with wild-type flies. We conclude that gene expression patterns and phenotypes in HCS-deficient flies in previous studies are caused by decreased biotinylation of histones rather than MCC.

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.

Lipoic acid as a novel treatment for Alzheimer's disease and related dementias

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that destroys patient memory and cognition, communication ability with the social environment and the ability to carry out daily activities. Despite extensive research into the pathogenesis of AD, a neuroprotective treatment - particularly for the early stages of disease - remains unavailable for clinical use. In this review, we advance the suggestion that lipoic acid (LA) may fulfil this therapeutic need. A naturally occurring precursor of an essential cofactor for mitochondrial enzymes, including pyruvate dehydrogenase (PDH) and alpha-ketoglutarate dehydrogenase (KGDH), LA has been shown to have a variety of properties which can interfere with pathogenic principles of AD. For example, LA increases acetylcholine (ACh) production by activation of choline acetyltransferase and increases glucose uptake, thus supplying more acetyl-CoA for the production of ACh. LA chelates redox-active transition metals, thus inhibiting the formation of hydroxyl radicals and also scavenges reactive oxygen species (ROS), thereby increasing the levels of reduced glutathione. Via the same mechanisms, downregulation redox-sensitive inflammatory processes is also achieved. Furthermore, LA can scavenge lipid peroxidation products such as hydroxynonenal and acrolein. The reduced form of LA, dihydrolipoic acid (DHLA), is the active compound responsible for most of these beneficial effects. R-alpha-LA can be applied instead of DHLA, as it is reduced by mitochondrial lipoamide dehydrogenase, a part of the PDH complex. In this review, the properties of LA are explored with particular emphasis on how this agent, particularly the R-alpha-enantiomer, may be effective to treat AD and related dementias.

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.

Biotin deficiency decreases life span and fertility but increases stress resistance in Drosophila melanogaster

Biotin deficiency is associated with fetal malformations and activation of cell survival pathways in mammals. In this study we determined whether biotin status affects life span, stress resistance, and fertility in the fruit fly Drosophila melanogaster. Male and female flies of the Canton-S strain had free access to diets containing 6.0 (control), 4.8, 2.5, or 0 pmol biotin/100 mg. Biotin concentrations in diets correlated with activities of biotin-dependent propionyl-CoA carboxylase and biotin concentrations in fly homogenates, but not with biotinylation of histones (DNA-binding proteins). Propionyl-CoA carboxylase activities and biotin concentrations were lower in males than in females fed diets low in biotin. The life span of biotin-deficient males and females was up to 30% shorter compared to biotin-sufficient controls. Exposure to oxidative stress reversed the effects of biotin status on survival in male flies: survival times increased by 40% in biotin-deficient males compared to biotin-sufficient controls. Biotin status did not affect survival of females exposed to oxidative stress. Exposure of flies to cold, heat, and oxidative stress was associated with mobilization of biotin from yet unknown sources. Biotin deficiency decreased fertility of flies. When biotin-deficient males and females were mated, the hatching rate (larvae hatched per egg) decreased by about 28% compared to biotin-sufficient controls. These findings are consistent with the hypothesis that biotin affects life span, stress resistance, and fertility in fruit flies.

Biotin biochemistry and human requirements

Human biotin turnover and requirements can be estimated on the basis of (1) concentrations of biotin and metabolites in body fluids, (2) activities of biotin-dependent carboxylases, and (3) the urinary excretion of organic acids that are formed at increased rates if carboxylase activities are reduced. Recent studies suggest that the urinary excretions of biotin and its metabolite bisnorbiotin, activities of propionyl-CoA carboxylase and beta-methylcrotonyl-CoA carboxylase in lymphocytes, and urinary excretion of 3-hydroxyisovaleric acid are good indicators of marginal biotin deficiency. On the basis of studies using these indicators of biotin deficiency, an adequate intake of 30 microg (123 nmoles) of biotin per day is currently recommended for adults. The dietary biotin intake in Western populations has been estimated to be 35 to 70 microg/d (143-287 nmol/d). Recent studies suggest that humans absorb biotin nearly completely. Conditions that may increase biotin requirements in humans include pregnancy, lactation, and therapy with anticonvulsants or lipoic acid.

Biotin deficiency reduces expression of SLC19A3, a potential biotin transporter, in leukocytes from human blood

In evaluating potential indicators of biotin status, we quantitated the expression of biotin-related genes in leukocytes from human blood of normal subjects before and after inducing marginal biotin deficiency. Biotin deficiency was induced experimentally by feeding an egg-white diet for 28 d. Gene expression was quantitated for the following biotin-related proteins: methylcrotonyl-CoA carboxylase chains A (MCCA) and B (MCCB); propionyl-CoA carboxylase chains A (PCCA) and B (PCCB); pyruvate carboxylase (PC); acetyl-CoA carboxylase isoforms A (ACCA) and B (ACCB); holocarboxylase synthetase (HCS); biotinidase; and 2 potential biotin transporters: sodium-dependent multivitamin transporter (SMVT) and solute carrier family 19 member 3 (SLC19A3). For 7 subjects who successfully completed the study, the abundance of the specific mRNAs was determined by quantitative real-time RT-PCR at d 0 and 28. At d 28, SLC19A3 expression had decreased to 33% of d 0 (P < 0.02 by two-tailed, paired t test). Expression of MCCA, PCCA, PC, ACCA, ACCB, HCS, biotinidase, and SMVT decreased to approximately 80% of d 0 (P < 0.05). Expression of the MCCB and PCCB chains that do not carry the biotin-binding motif did not change significantly; we speculate that expression of the biotin-binding chains of biotin-dependent carboxylases is more responsive to biotin status changes. These data provide evidence that expression of SLC19A3 is a relatively sensitive indicator of marginal biotin deficiency.

Marginal biotin deficiency is teratogenic in ICR mice

The incidence of marginal biotin deficiency in normal human gestation is approximately one in three. In ICR mice, maternal biotin deficiency results in cleft palate, micrognathia, microglossia and limb hypoplasia. However, the relationships among the severity of maternal biotin deficiency, fetal biotin status and malformations have not been reported. This study utilized validated indices of biotin status to investigate the relationships among maternal biotin status, fetal biotin status and the rate of fetal malformations in ICR mice. Biotin status was controlled by feeding diets with varying egg white concentration. In dams and fetuses, biotin status was assessed by hepatic biotin content and hepatic activity of the biotin-dependent enzyme propionyl-CoA carboxylase; in dams, status was also assessed by urinary excretion of biotin and 3-hydroxyisovaleric acid. Malformations were assessed morphologically. Biotin was measured by HPLC/avidin-binding assay. Propionyl-CoA carboxylase (PCC) activity was determined by H(14)CO(3) incorporation. 3-Hydroxyisovaleric acid concentration was determined by GC/MS. Although no overt signs of deficiency appeared, metabolic disturbances caused by biotin deficiency were detectable in dams and fetuses. These disturbances increased with increasing egg white. Fetal biotin status correlated significantly with maternal biotin status (fetal vs. dam hepatic biotin, r = 0.671; fetal vs. dam PCC activity, r = 0.70). The incidences of malformations were strikingly dependent on egg white concentration. We conclude that in ICR mice, marginal maternal biotin deficiency causes fetal biotin deficiency. We speculate that the fetal malformations are primarily the consequence of fetal biotin deficiency. Because murine malformations appeared at degrees of biotin deficiency that are similar to those in human gestation, we speculate that some human fetal malformations may be caused by biotin deficiency.

Diaminobiotin and desthiobiotin have biotin-like activities in Jurkat cells

In mammals, biotin serves as a coenzyme for carboxylases such as propionyl-CoA carboxylase. The expression of genes encoding interleukin-2 (IL-2) and IL-2 receptor (IL-2R)gamma also depends on biotin. Biotin metabolites are structurally similar to biotin, and their concentrations in tissues are quantitatively important. Here, the hypothesis was tested that biotin metabolites can mimic the effects of biotin on gene expression and thus have biotin-like activities. A human T-cell line (Jurkat cells) was used to model effects of biotin and synthetic metabolites (diaminobiotin and desthiobiotin) on the expression of genes encoding IL-2 and IL-2Rgamma. Cells were cultured in biotin-deficient medium (0.025 nmol/L biotin) for 35 d; controls were cultured in medium containing 10 nmol/L biotin. The biotin-deficient medium was supplemented with 10 nmol/L of diaminobiotin, desthiobiotin, biotin or no biotin 24 h before gene expression analyses. Transcriptional activities of genes encoding IL-2 and IL-2Rgamma were increased up to 43% in cells supplemented with diaminobiotin, desthiobiotin or biotin compared with biotin-deficient cells, as judged by luciferase activities after transfection with reporter-gene constructs. These findings are consistent with the hypothesis that diaminobiotin and desthiobiotin mimic the effects of biotin on gene expression and thus have biotin-like activities. Supplementation of cells with diaminobiotin and desthiobiotin did not affect abundances of holocarboxylases and activities of propionyl-CoA carboxylase, suggesting that effects of synthetic biotin metabolites on gene expression are not mediated by carboxylase-dependent pathways. It is not known whether naturally occurring biotin metabolites also have biotin-like activities.

Interleukin-2 receptor-gamma -dependent endocytosis depends on biotin in Jurkat cells

Biotin has been credited with having beneficial effects on immune function despite observations that biotin supplementation causes decreased secretion of interleukin-2. Here this paradox was addressed by determining whether receptor-dependent internalization of interleukin-2 by immune cells depends on biotin. Theoretically, this would be consistent with both decreased net secretion of interleukin-2 by biotin-supplemented cells (causing increased endocytosis) and beneficial effects of biotin on immune function (causing increased receptor signaling). Jurkat cells were cultured in biotin-defined media (25, 250, or 10,000 pM). Secretion of interleukin-2 correlated negatively with biotin supply, but transcriptional activity of the interleukin-2 gene correlated positively with biotin supply, suggesting that decreased secretion of interleukin-2 by biotin-supplemented cells was not caused by decreased gene expression. Expression of the interleukin-2 receptor-gamma gene was greater at 10,000 pM than 25 pM biotin, mediating increased endocytosis of interleukin-2 in biotin-supplemented medium. Inhibition of endocytosis by genistein and overexpression of interleukin-2 receptor-gamma abolished the effect of biotin. These findings suggest that endocytosis of interleukin-2 depends on biotin.

Exposure to UV light causes increased biotinylation of histones in Jurkat cells

Biotin in breakdown products of biotinylated carboxylases serves as substrate for biotinylation of histones by biotinidase. Here we determined whether biotinylation of histones might play a role in repair of damaged DNA and in apoptosis. Jurkat cells were exposed to UV light to induce DNA damage. Abundance of thymine dimers increased about three times in response to UV exposure, consistent with DNA damage. Biotin-containing carboxylases were degraded in response to UV exposure, as judged by Western blot analysis and carboxylase activities. Mitochondrial integrity decreased in response to UV exposure (as judged by confocal microscopy), facilitating the release of breakdown products of carboxylases from mitochondria. Biotinylation of histones increased in response to UV exposure; biotinylation of histones did not occur specifically at sites of newly repaired DNA. UV exposure triggered apoptosis, as judged by caspase-3 activity and analysis by confocal microscopy. In summary, this study provided evidence that increased biotinylation of histones in DNA-damaged cells might either be a side product of carboxylase degradation or a step during apoptosis.

Lymphocyte propionyl-CoA carboxylase and accumulation of odd-chain fatty acid in plasma and erythrocytes are useful indicators of marginal biotin deficiency small star, filled

BACKGROUND: Recent studies indicate marginal biotin deficiency is more common than previously thought. That conclusion's validity rests on two indicators of biotin status that depend on renal function.OBJECTIVE: Assessing the validity of two indicators of biotin status that do not depend upon renal function: 1) activity of the biotin-dependent enzyme propionyl-CoA carboxylase (PCC) in lymphocytes and 2) accumulation of odd-chain fatty acids in the lipids of plasma and erythrocytes.DESIGN: Marginal biotin deficiency was induced in 11 healthy adults by egg-white feeding for 28 days. Blood and 24-h urine samples were collected before commencing the diet and twice weekly thereafter. After depletion, biotin status was restored with a general diet with or without 80 &mgr;g/day or 328 nmol/day biotin supplement. Activity of PCC was determined by an optimized NaH 14CO(3) incorporation assay. Fatty acid composition was determined by gas chromatography.RESULTS: With time on the egg-white diet, lymphocyte PCC activity decreased significantly (P <0.0001); C15:0 and C17:0 content increased significantly in the lipids of plasma and erythrocytes (P <0.015). In eight of 11 subjects, lymphocyte PCC activity returned to normal within three weeks of resuming general diets with or without biotin supplement. With repletion, C15:0 and C17:0 in plasma lipids decreased (P <0.02), but odd-chain content of erythrocytes did not decrease significantly.CONCLUSIONS: Lymphocyte PCC activity is an early and sensitive indicator of marginal biotin deficiency. Odd-chain fatty acids accumulate in blood lipids more gradually during marginal deficiency and return to normal more gradually after biotin repletion.

Biotin uptake into human peripheral blood mononuclear cells increases early in the cell cycle, increasing carboxylase activities

Cells respond to proliferation with increased accumulation of biotin, suggesting that proliferation enhances biotin demand. Here we determined whether peripheral blood mononuclear cells (PBMC) increase biotin uptake at specific phases of the cell cycle, and whether biotin is utilized to increase biotinylation of carboxylases. Biotin uptake was quantified in human PBMC that were arrested chemically at specific phases of the cell cycle, i.e., biotin uptake increased in the G1 phase of the cycle [658 +/- 574 amol biotin/(10(6) cells x 30 min)] and remained increased during phases S, G2, and M compared with quiescent controls [200 +/- 62 amol biotin/(10(6) cells x 30 min)]. The abundance of the sodium-dependent multivitamin transporter (SMVT, which transports biotin) was similar at all phases of the cell cycle, suggesting that transporters other than SMVT or splicing variants of SMVT may account for the increased biotin uptake observed in proliferating cells. Activities of biotin-dependent 3-methylcrotonyl-CoA carboxylase and propionyl-CoA carboxylase were up to two times greater in proliferating PBMC compared with controls. The abundance of mRNA encoding 3-methylcrotonyl-CoA carboxylase and propionyl-CoA carboxylase paralleled carboxylase activities, suggesting that PBMC respond to proliferation with increased expression of genes encoding carboxylases. Similarly, expression of the gene encoding holocarboxylase synthetase (which catalyzes binding of biotin to carboxylases) increased in response to proliferation, suggesting that cellular capacity to biotinylate carboxylases was increased. In summary, these findings suggest that PBMC respond to proliferation with increased biotin uptake early in the cell cycle, and that biotin is utilized to increase activities of two of the four biotin-requiring carboxylases.

Lymphocyte propionyl-CoA carboxylase is an early and sensitive indicator of biotin deficiency in rats, but urinary excretion of 3-hydroxypropionic acid is not

Recent clinical studies have provided evidence that marginal biotin deficiency is more common than previously thought. The validity of that conclusion rests on two indicators of biotin status that depend on renal function. Our goal was to develop and assess the usefulness of two additional indicators in detecting marginal biotin status in a rat model, i.e., 1) activity of the biotin-dependent enzyme propionyl-CoA carboxylase in lymphocytes; and 2) urinary excretion of 3-hydroxypropionic acid, an organic acid that reflects decreased activity of propionyl-CoA carboxylase. Marginal-to-moderate biotin deficiency was induced experimentally by an egg-white diet (deficient rats); the biotin-supplemented rats were fed the egg-white diet plus supplemental biotin. Propionyl-CoA carboxylase activity was determined by an optimized H(14)CO(3)(-) incorporation assay. Urinary organic acids were determined by gas chromatography/mass spectrometry. Lymphocyte propionyl-CoA carboxylase activity decreased dramatically and in parallel with hepatic propionyl-CoA carboxylase activity. By d 7, lymphocyte propionyl-CoA carboxylase activity in each rat in the deficient group had decreased to less than the lowest value of any rat on d 0. By two-way ANOVA, the effects of diet (P < 0.0001), time (P < 0.005) and their interaction (P < 0.0001) were all significant. The urinary excretion of 3-hydroxypropionic acid did not differ between the two groups. Lymphocyte propionyl-CoA carboxylase activity is an early and sensitive indicator of marginal biotin deficiency, whereas the urinary excretion of 3-hydroxypropionic acid is not.

Biotin supply affects expression of biotin transporters, biotinylation of carboxylases and metabolism of interleukin-2 in Jurkat cells

Biotin supply may affect transcription of genes and biotinylation of proteins in cells. In this study, Jurkat cells were used to model effects of biotin supply on biotin homeostasis and interleukin-2 metabolism in immune cells. Cells were cultured in media containing deficient (25 pmol/L), physiologic (250 pmol/L), or pharmacologic concentrations (10,000 pmol/L) of biotin for 4 wk. Activities of the biotin-dependent enzyme propionyl-CoA carboxylase paralleled the biotin concentrations in media [pmol bicarbonate fixed/(min x 10(6) cells)]: 1.9 +/- 0.7 (25 pmol/L biotin) vs. 19 +/- 1.2 (250 pmol/L biotin) vs. 40 +/- 2.0 (10,000 pmol/L biotin). Cells responded to biotin deficiency with increased expression of biotin transporter genes. Biotin-deficient cells maintained normal biotinylation of histones but contained reduced levels of biotinylated carboxylases, suggesting compartmentalization of intracellular biotin distribution. Rates of cell proliferation and activities of the apoptotic enzyme caspase-3 were similar among treatment groups, suggesting that net proliferation was not affected by biotin status. Net secretion of interleukin-2 by Jurkat cells was inversely associated with the biotin concentration in media [kU/(L x 24 h x 10(6) cells)]: 21 +/- 1.8 (25 pmol/L biotin) vs. 15 +/- 5.4 (250 pmol/L biotin) vs. 6.1 +/- 1.8 (10,000 pmol/L biotin), suggesting increased secretion or decreased internalization of interleukin-2 by biotin-deficient cells. This study provides evidence that biotin supply affects biotinylation of proteins, gene expression and metabolism of interleukin-2 in Jurkat cells. The physiological significance of effects of biotin status on metabolism of interleukin-2 remains to be elaborated.

Utilization of biotin in proliferating human lymphocytes

Lymphocytes are part of the immune system and respond to antigenic stimulation with proliferation. We sought to determine whether mitogen-stimulated, proliferating lymphocytes increase the cellular uptake of biotin and, if so, to identify mechanisms that mediate the increase. Lymphocytes were isolated from human peripheral blood; proliferation of lymphocytes was induced by incubation with pokeweed lectin, concanavalin A or phytohemagglutinin. Biotin uptake was quantitated by determination of [3H] uptake into the lymphocytes during incubation with [3H]biotin after establishing that [3H]biotin is not metabolized within the lymphocytes during the incubation period (<5%). Biotin uptake into proliferating lymphocytes increased to 278-722% of the control values for nonproliferating lymphocytes. Kinetic analysis of biotin transport provided evidence that the increase is mediated by an increased number of transporters on the cell surface rather than by an increase in transporter affinity. Cycloheximide, an inhibitor of protein synthesis, completely suppressed the mitogen-stimulated increase in biotin transport. This observation is consistent with the hypothesis that proliferating lymphocytes increase biotin uptake by increasing the synthesis of new transporters. Biotin affinity and structural specificity were similar in proliferating and nonproliferating lymphocytes, suggesting that mitogens induced an increase in the number of the same transporter molecule that mediates transport in unstimulated lymphocytes. Mitogen-stimulated lymphocytes exhibited 2.5 times greater activities of biotin-dependent beta-methylcrotonyl-CoA carboxylase compared with time 0 (at 72 h after addition of mitogen). This observation is consistent with the hypothesis that proliferating lymphocytes increase biotin uptake at least in part to provide adequate coenzyme for biotin-dependent carboxylases.

Biotin protein ligase from Saccharomyces cerevisiae. The N-terminal domain is required for complete activity

Catalytically active biotin protein ligase from Saccharomyces cerevisiae (EC 6.3.4.15) was overexpressed in Escherichia coli and purified to near homogeneity in three steps. Kinetic analysis demonstrated that the substrates ATP, biotin, and the biotin-accepting protein bind in an ordered manner in the reaction mechanism. Treatment with any of three proteases of differing specificity in vitro revealed that the sequence between residues 240 and 260 was extremely sensitive to proteolysis, suggesting that it forms an exposed linker between an N-terminal 27-kDa domain and the C-terminal 50-kDa domain containing the active site. The protease susceptibility of this linker region was considerably reduced in the presence of ATP and biotin. A second protease-sensitive sequence, located in the presumptive catalytic site, was protected against digestion by the substrates. Expression of N-terminally truncated variants of the yeast enzyme failed to complement E. coli strains defective in biotin protein ligase activity. In vitro assays performed with purified N-terminally truncated enzyme revealed that removal of the N-terminal domain reduced BPL activity by greater than 3500-fold. Our data indicate that both the N-terminal domain and the C-terminal domain containing the active site are necessary for complete catalytic function.

The effect of alpha-lipoic acid on the neurovascular reflex arc in patients with diabetic neuropathy assessed by capillary microscopy

Patients with diabetic polyneuropathy are known to have an impaired neurovascular reflex arc compared to healthy controls. This is seen in a delayed decrease in microcirculation of the ipsilateral hand after cooling of the contralateral hand. The aim of this pilot study was to investigate whether intravenous alpha-lipoic acid (ALA) (Thioctacid, Asta Medica) therapy might be able to improve this impaired neurovascular reflex arc in patients with diabetic neuropathy. In addition, clinical effects were evaluated with the aid of the neuropathy symptom score (NSS) and the neuropathy disability score (NDS). Ten patients with diabetes mellitus and polyneuropathy (5 females, 5 males, 2 smokers, 5 IDDM, 5 NIDDM, body mass index 26.1 +/- 1.0 kg/m2, age 58.3 +/- 9.5 years, diabetes duration 15.7 +/- 11.2 years, Hb A1c 6.8 +/- 0.3%) were investigated by nail-fold capillaroscopy after contralateral cooling before and after intravenous therapy with 600 mg alpha-lipoic acid per day over 3 weeks. Cardiac autonomic neuropathy was excluded by beat-to-beat variation analysis. Symptoms of diabetic neuropathy were evaluated before and after therapy with the aid of the NSS and NDS. Capillary blood cell velocity (CBV) of the hand was determined before, during, and for the following 30 min after cooling (3 min at 15 degrees C) of the contralateral hand. Blood pressure, heart rate, and local skin temperature were monitored at 2-min intervals. ALA therapy resulted in a significant improvement of the microcirculatory response to cooling, as seen by an immediate decrease in CBV of 12. 3% (P < 0.02 vs before treatment), which was absent before therapy. Blood pressure, heart rate, and local skin temperature were not different between investigations. There was a significant improvement of the NSS after therapy (5.4 +/- 1.1 vs 8.6 +/- 1.1 points, P < 0.01). These results demonstrate that intravenous therapy with ALA has a positive influence on the impaired neurovascular reflex arc in patients with diabetic neuropathy.

Structure, function and regulation of pyruvate carboxylase

Pyruvate carboxylase (PC; EC 6.4.1.1), a member of the biotin-dependent enzyme family, catalyses the ATP-dependent carboxylation of pyruvate to oxaloacetate. PC has been found in a wide variety of prokaryotes and eukaryotes. In mammals, PC plays a crucial role in gluconeogenesis and lipogenesis, in the biosynthesis of neurotransmitter substances, and in glucose-induced insulin secretion by pancreatic islets. The reaction catalysed by PC and the physical properties of the enzyme have been studied extensively. Although no high-resolution three-dimensional structure has yet been determined by X-ray crystallography, structural studies of PC have been conducted by electron microscopy, by limited proteolysis, and by cloning and sequencing of genes and cDNA encoding the enzyme. Most well characterized forms of active PC consist of four identical subunits arranged in a tetrahedron-like structure. Each subunit contains three functional domains: the biotin carboxylation domain, the transcarboxylation domain and the biotin carboxyl carrier domain. Different physiological conditions, including diabetes, hyperthyroidism, genetic obesity and postnatal development, increase the level of PC expression through transcriptional and translational mechanisms, whereas insulin inhibits PC expression. Glucocorticoids, glucagon and catecholamines cause an increase in PC activity or in the rate of pyruvate carboxylation in the short term. Molecular defects of PC in humans have recently been associated with four point mutations within the structural region of the PC gene, namely Val145-->Ala, Arg451-->Cys, Ala610-->Thr and Met743-->Thr.