Thiamine analogues featuring amino-oxetanes as potent and selective inhibitors of pyruvate dehydrogenase

Pyruvate dehydrogenase complex (PDHc) is suppressed in some cancer types but overexpressed in others. To understand its contrasting oncogenic roles, there is a need for selective PDHc inhibitors. Its E1-subunit (PDH E1) is a thiamine pyrophosphate (TPP)-dependent enzyme and catalyses the first and rate-limiting step of the complex. In a recent study, we reported a series of ester-based thiamine analogues as selective TPP-competitive PDH E1 inhibitors with low nanomolar affinity. However, when the ester linker was replaced with an amide for stability reasons, the binding affinity was significantly reduced. In this study, we show that an amino-oxetane bioisostere of the amide improves the affinity and maintains stability towards esterase-catalysed hydrolysis.

HUANGKUISIWUFANG inhibits pyruvate dehydrogenase to improve glomerular injury in anti-Thy1 nephritis model

ETHNOPHARMACOLOGICAL RELEVANCE

Huangkuisiwufang (HKSWF) is composed of Abelmoschus manihot (L.) Medik., Astragalus mongholicus, Polygonum cuspidatum, Curcuma longa L. Abelmoschus Manihot (L.) Medik. has been widely used for the treatment of chronic renal disease, oral ulcers and burn in China for centuries (Committee of the Pharmacopoeia of PR China, 2010). Abelmoschus manihot (L.) Medik., Polygonum cuspidatum, Curcuma longa L. have been mainly applied in folk medicine for their therapeutic effects on diabetes, cancer, heart disease and other diseases.

AIM OF THE STUDY

We aimed to investigate the renoprotective function of HKSWF in anti-Thy nephritis model and clarify the relevant mechanisms.

MATERIALS AND METHODS

One week after the model of glomerulonephritis created by injecting anti-thymocyte serum (ATS), rats were treated with Huangkui capsule, enalapril or HKSWF by gavage for a period of 8 weeks. The therapeutic effect was evaluated by detection of proteinuria, plasma creatine, blood urea nitrogen (BUN), podocyte injury, glomerular accumulation of extracellular matrix (ECM) and the markers of oxidative stress and renal fibrosis. RNA Sequencing (RNA-seq), KEGG and western blotting analysis were performed to indicate the signaling pathway involved in the therapeutic effect of HKSWF.

RESULTS

Nephritic rats presented the increase of BUN, serum creatinine (Scr), proteinuria, podocyte damage, glomerular fibrosis, Ang II type 1 receptor (AT1R), and the reduction of creatinine clearance (Ccr). In contrast, application of HKSWF to nephritic rats decreased the levels of BUN and proteinuria, promoted mesangial cell recovery and improved oxidative stress level and podocyte injury. KEGG analysis revealed that pyruvate metabolism was the most significantly upregulated pathway in rats treated with HKSWF compared to disease control group. Increased pyruvate dehydrogenase and PAI-1 caused by nephritis was inhibited by HKSWF interposition. Furthermore, dichloroacetate sodium (DCA), an agonist of pyruvate dehydrogenase, could stimulate PAI-1 expression, which was suppressed by HKSWF.

CONCLUSION

Chinese herbal preparation HKSWF has remarkable curative effects on glomerulonephritis animals. HKSWF attenuates pyruvate dehydrogenase to improve glomerular injury.

Acute activation of pyruvate dehydrogenase increases glucose oxidation in muscle without changing glucose uptake

Pyruvate dehydrogenase (PDH) activity is a key component of the glucose/fatty acid cycle hypothesis for the regulation of glucose uptake and metabolism. We have investigated whether acute activation of PDH in muscle can alleviate the insulin resistance caused by feeding animals a high-fat diet (HFD). The importance of PDH activity in muscle glucose disposal under insulin-stimulated conditions was determined by infusing the PDH kinase inhibitor dichloroacetate (DCA) into HFD-fed Wistar rats during a hyperinsulinemic-euglycemic clamp. Acute DCA infusion did not alter glucose infusion rate, glucose disappearance, or hepatic glucose production but did decrease plasma lactate levels. DCA substantially increased muscle PDH activity; however, this did not improve insulin-stimulated glucose uptake in insulin-resistant muscle of HFD rats. DCA infusion increased the flux of pyruvate to acetyl-CoA and reduced glucose incorporation into glycogen and alanine in muscle. Similarly, in isolated muscle, DCA treatment increased glucose oxidation and decreased glycogen synthesis without changing glucose uptake. These results suggest that, although PDH activity controls the conversion of pyruvate to acetyl-CoA for oxidation, this has little effect on glucose uptake into muscle under insulin-stimulated conditions.

Dual effects of fibroblast growth factor 21 on hepatic energy metabolism

The aim of this study was to investigate the mechanisms by which fibroblast growth factor 21 (FGF21) affects hepatic integration of carbohydrate and fat metabolism in Siberian hamsters, a natural model of adiposity. Twelve aged matched adult male Siberian hamsters maintained in their long-day fat state since birth were randomly assigned to one of two treatment groups and were continuously infused with either vehicle (saline; n=6) or recombinant human FGF21 protein (1 mg/kg per day; n=6) for 14 days. FGF21 administration caused a 40% suppression (P<0.05) of hepatic pyruvate dehydrogenase complex (PDC), the rate-limiting step in glucose oxidation, a 34% decrease (P<0.05) in hepatic acetylcarnitine accumulation, an index of reduced PDC flux, a 35% increase (P<0.05) in long-chain acylcarnitine content (an index of flux through β-oxidation) and a 47% reduction (P<0.05) in hepatic lipid content. These effects were underpinned by increased protein abundance of PD kinase-4 (PDK4, a negative regulator of PDC), the phosphorylated (inhibited) form of acetyl-CoA carboxylase (ACC, a negative regulator of delivery of fatty acids into the mitochondria) and the transcriptional co-regulators of energy metabolism peroxisome proliferator activated receptor gamma co-activator alpha (PGC1α) and sirtuin-1. These findings provide novel mechanistic basis to support the notion that FGF21 exerts profound metabolic benefits in the liver by modulating nutrient flux through both carbohydrate (mediated by a PDK4-mediated suppression of PDC activity) and fat (mediated by deactivation of ACC) metabolism, and therefore may be an attractive target for protection from increased hepatic lipid content and insulin resistance that frequently accompany obesity and diabetes.

Differential inhibition of PDKs by phenylbutyrate and enhancement of pyruvate dehydrogenase complex activity by combination with dichloroacetate

Pyruvate dehydrogenase complex (PDHC) is a key enzyme in metabolism linking glycolysis to tricarboxylic acid cycle and its activity is tightly regulated by phosphorylation catalyzed by four pyruvate dehydrogenase kinase (PDK) isoforms. PDKs are pharmacological targets for several human diseases including cancer, diabetes, obesity, heart failure, and inherited PDHC deficiency. We investigated the inhibitory activity of phenylbutyrate toward PDKs and found that PDK isoforms 1-to-3 are inhibited whereas PDK4 is unaffected. Moreover, docking studies revealed putative binding sites of phenylbutyrate on PDK2 and 3 that are located on different sites compared to dichloroacetate (DCA), a previously known PDK inhibitor. Based on these findings, we showed both in cells and in mice that phenylbutyrate combined to DCA results in greater increase of PDHC activity compared to each drug alone. These results suggest that therapeutic efficacy can be enhanced by combination of drugs increasing PDHC enzyme activity.

Dichloroacetate, the Pyruvate Dehydrogenase Complex and the Modulation of mESC Pluripotency

Introduction

The pyruvate dehydrogenase (PDH) complex is localized in the mitochondrial matrix catalyzing the irreversible decarboxylation of pyruvate to acetyl-CoA and NADH. For proper complex regulation the E1-α subunit functions as an on/off switch regulated by phosphorylation/dephosphorylation. In different cell types one of the four-pyruvate dehydrogenase kinase isoforms (PDHK1-4) can phosphorylate this subunit leading to PDH inactivation. Our previous results with human Embryonic Stem Cells (hESC), suggested that PDHK could be a key regulator in the metabolic profile of pluripotent cells, as it is upregulated in pluripotent stem cells. Therefore, we wondered if metabolic modulation, via inexpensive pharmacological inhibition of PDHK, could impact metabolism and pluripotency.

Methods/Results

In order to assess the importance of the PDH cycle in mouse Embryonic Stem Cells (mESC), we incubated cells with the PDHK inhibitor dichloroacetate (DCA) and observed that in its presence ESC started to differentiate. Changes in mitochondrial function and proliferation potential were also found and protein levels for PDH (both phosphorylated and non-phosphorylated) and PDHK1 were monitored. Interestingly, we were also able to describe a possible pathway that involves Hif-1α and p53 during DCA-induced loss of pluripotency. Results with ESCs treated with DCA were comparable to those obtained for cells grown without Leukemia Inhibitor Factor (LIF), used in this case as a positive control for differentiation.

Conclusions

DCA negatively affects ESC pluripotency by changing cell metabolism and elements related to the PDH cycle, suggesting that PDHK could function as a possible metabolic gatekeeper in ESC, and may be a good target to modulate metabolism and differentiation. Although further molecular biology-based experiments are required, our data suggests that inactive PDH favors pluripotency and that ESC have similar strategies as cancer cells to maintain a glycolytic profile, by using some of the signaling pathways found in the latter cells.

Inhibiting sperm pyruvate dehydrogenase complex and its E3 subunit, dihydrolipoamide dehydrogenase affects fertilization in Syrian hamsters

Background/Aims

The importance of sperm capacitation for mammalian fertilization has been confirmed in the present study via sperm metabolism. Involvement of the metabolic enzymes pyruvate dehydrogenase complex (PDHc) and its E3 subunit, dihydrolipoamide dehydrogenase (DLD) in hamster in vitro fertilization (IVF) via in vitro sperm capacitation is being proposed through regulation of sperm intracellular lactate, pH and calcium.

Methodology and Principal Findings

Capacitated hamster spermatozoa were allowed to fertilize hamster oocytes in vitro which were then assessed for fertilization, microscopically. PDHc/DLD was inhibited by the use of the specific DLD-inhibitor, MICA (5-methoxyindole-2-carboxylic acid). Oocytes fertilized with MICA-treated (MT) [and thus PDHc/DLD-inhibited] spermatozoa showed defective fertilization where 2^nd polar body release and pronuclei formation were not observed. Defective fertilization was attributable to capacitation failure owing to high lactate and low intracellular pH and calcium in MT-spermatozoa during capacitation. Moreover, this defect could be overcome by alkalinizing spermatozoa, before fertilization. Increasing intracellular calcium in spermatozoa pre-IVF and in defectively-fertilized oocytes, post-fertilization rescued the arrest seen, suggesting the role of intracellular calcium from either of the gametes in fertilization. Parallel experiments carried out with control spermatozoa capacitated in medium with low extracellular pH or high lactate substantiated the necessity of optimal sperm intracellular lactate levels, intracellular pH and calcium during sperm capacitation, for proper fertilization.

Conclusions

This study confirms the importance of pyruvate/lactate metabolism in capacitating spermatozoa for successful fertilization, besides revealing for the first time the importance of sperm PDHc/ DLD in fertilization, via the modulation of sperm intracellular lactate, pH and calcium during capacitation. In addition, the observations made in the IVF studies in hamsters suggest that capacitation failures could be a plausible cause of unsuccessful fertilization encountered during human assisted reproductive technologies, like IVF and ICSI. Our studies indicate a role of sperm capacitation in the post-penetration events during fertilization.

α-(Substituted-phenoxyacetoxy)-α-heterocyclylmethylphosphonates: synthesis, herbicidal activity, inhibition on pyruvate dehydrogenase complex (PDHc), and application as postemergent herbicide against broadleaf weeds

Pyruvate dehydrogenase complex (PDHc) is the site of action of a new class of herbicides. On the basis of the previous work for O,O'-dimethyl α-(substituted-phenoxyacetoxy)alkylphosphonates (I), further synthetic modifications were made by introducing a fural and a thienyl group to structure I. A series of α-(substituted-phenoxyacetoxy)-α-heterocyclylmethylphosphonate derivatives (II) were synthesized as potential inhibitors of PDHc. The postemergent activity of the title compounds II was evaluated in greenhouse experiments. The in vitro efficacy of II against PDHc was also examined. Compounds II with fural as R(3) and 2,4-dichloro as X and Y showed significant herbicidal activity and effective inhibition against PDHc from plants. O,O'-Dimethyl α-(2,4-dichlorophenoxyacetoxy)-α-(furan-2-yl)methylphosphonate II-17 had higher inhibitory potency against PDHc from Pisum sativum than against PDHc from Oryza sativa in vitro and was most effective against broadleaf weeds at 50 and 300 ai g/ha. II-17 was safe for maize and rice even at the dose of 900-1200 ai g/ha. Field trials at different regions in China showed that II-17 (HWS) could control a broad spectrum of broad-leaved and sedge weeds at the rate of 225-375 ai g/ha for postemergent applications in maize fields. II-17 (HWS) displayed potential utility as a selective herbicide.

Autophagy in premature senescent cells is activated via AMPK pathway

Autophagy is a highly regulated intracellular process involved in the turnover of most cellular constituents and in the maintenance of cellular homeostasis. In this study, we show that the activity of autophagy increases in H₂O₂ or RasV12-induced senescent fibroblasts. Inhibiting autophagy promotes cell apoptosis in senescent cells, suggesting that autophagy activation plays a cytoprotective role. Furthermore, our data indicate that the increase of autophagy in senescent cells is linked to the activation of transcription factor FoxO3A, which blocks ATP generation by transcriptionally up-regulating the expression of PDK4, an inhibitor of pyruvate dehydrogenase complex, thus leading to AMPK activation and mTOR inhibition. These findings suggest a novel mechanism by which FoxO3A factors can activate autophagy via metabolic alteration.

Studies of O,O-dimethyl α-(2,4-dichlorophenoxyacetoxy)ethylphosphonate (HW02) as a new herbicide. 1. Synthesis and herbicidal activity of HW02 and analogues as novel inhibitors of pyruvate dehydrogenase complex

On the basis of the previous work for optimization of O,O-diethyl α-(substituted phenoxyacetoxy)alkylphosphonates, further extensive synthetic modifications were made to the substituents in alkylphosphonate and phenoxy moieties of the title compounds. New O,O-dimethyl α-(substituted phenoxyacetoxy)alkylphosphonates were synthesized as potential inhibitors of pyruvate dehydorogenase complex (PDHc). Their herbicidal activity and efficacy in vitro against PDHc were examined. Some of these compounds exhibited significant herbicidal activity and were demonstrated to be effective inhibitors of PDHc from three different plants. The structure-activity relationships of these compounds including previously reported analogous compounds were studied by examining their herbicidal activities. Both inhibitory potency against PDHc and herbicidal activity of title compounds could be increased greatly by optimizing substituent groups of the title compounds. O,O-Dimethyl α-(2,4-dichlorophenoxyacetoxy)ethylphosphonate (I-5), which acted as a competitive inhibitor of PDHc with much higher inhibitory potency against PDHc from Pisum sativum and Phaseolus radiatus than from Oryza sativa , was found to be the most effective compound against broadleaf weeds and showed potential utility as herbicide.

Novel therapy for malignant pleural mesothelioma based on anti-energetic effect: an experimental study using 3-Bromopyruvate on nude mice

BACKGROUND

Most cancer cells exhibit increased anaerobic glycolysis and use this metabolic pathway for the generation of ATP as a main source of energy. This impaired metabolism of glucose, leading to the secretion of lactic acid even in the presence of oxygen, is named the Warburg effect. Because cancer cells are partly or mainly dependent on such a pathway to generate ATP, inhibition of glycolysis may slow down the proliferation or kill cells.

MATERIALS AND METHODS

The effect of 3-Bromopyruvate (3-BrPA) alone or associated to cisplatin on nude mice presenting intraperitoneal carcinomatosis developed after intraperitoneal injection of human mesothelioma cells (MSTO-211H) was investigated.

RESULTS

3-BrPA significantly prolonged survival of animals. Combined with cisplatin, it demonstrated significant benefit on survival whereas cisplatin alone had no or a mild effect.

CONCLUSION

3-BrPA may thus constitute an interesting novel anticancer drug that could be tested in humans.

Apoptosis-inducing antitumor efficacy of hexokinase II inhibitor in hepatocellular carcinoma

Hypoxia stimulates hepatocellular carcinoma (HCC) cell growth via hexokinase (HK) II induction, and alternatively, HK II inhibition induces apoptosis by activating mitochondrial signaling. This study was to investigate whether the induction of HK II by hypoxia is associated with enhanced mitochondrial stability and to confirm the apoptosis-inducing efficacy of HK II inhibitor in an in vivo model of HCC. Mitochondrial stability was examined by treating isolated mitochondria with deoxycholate, a permeability-enhancing agent. Alteration of permeability transition pore complex composition was analyzed by immunoprecipitation and immunoblotting. An in vivo model of HCC was established in C3H mice i.d. implanted with MH134 cells. The antitumor efficacy of i.p. given 3-bromopyruvate (3-BrPA), a HK II inhibitor, was evaluated by measuring tumor volumes and quantifying apoptosis using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining and (99m)Tc-hydrazinonicotinamide-Annexin V scans. Hypoxia enhanced mitochondrial stability, and this was inhibited by 3-BrPA treatment. In particular, HK II levels in permeability transition pore complex immunoprecipitates were reduced after 3-BrPA treatment. In mice treated with 3-BrPA, mean tumor volumes and tumor volume growth were found to be significantly reduced. Moreover, percentages of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive cells were significantly increased in 3-BrPA-treated mice, and this apoptosis-inducing efficacy was reflected in vivo by (99m)Tc-hydrazinonicotinamide-Annexin V imaging. Our results show that hypoxia enhances mitochondrial stability via HK II induction and that HK II inhibitor treatment exhibits an in vivo antitumor effect by inducing apoptosis. Therefore, HK II inhibitors may be therapeutically useful for the treatment of advanced infiltrative hypovascular HCCs, which are growing in a hypoxic environment.

FDG-PET for evaluating the antitumor effect of intraarterial 3-bromopyruvate administration in a rabbit VX2 liver tumor model

OBJECTIVE

We wanted to investigate the feasibility of using FDG-PET for evaluating the antitumor effect of intraarterial administration of a hexokinase II inhibitor, 3-bromopyruvate (3-BrPA), in a rabbit VX2 liver tumor model.

MATERIALS AND METHODS

VX2 carcinoma was grown in the livers of ten rabbits. Two weeks later, liver CT was performed to confirm appropriate tumor growth for the experiment. After tumor volume-matched grouping of the rabbits, transcatheter intraarterial administration of 3-BrPA was performed (1 mM and 5 mM in five animals each, respectively). FDG-PET scan was performed the day before, immediately after and a week after 3-BrPA administration. FDG uptake was semiquantified by measuring the standardized uptake value (SUV). A week after treatment, the experimental animals were sacrificed and the necrosis rates of the tumors were calculated based on the histopathology.

RESULTS

The SUV of the VX2 tumors before treatment (3.87+/-1.51 [mean+/-SD]) was significantly higher than that of nontumorous liver parenchyma (1.72+/-0.34) (p < 0.0001, Mann-Whitney U test). The SUV was significantly decreased immediately after 3-BrPA administration (2.05+/-1.21) (p = 0.002, Wilcoxon signed rank test). On the one-week follow up PET scan, the FDG uptake remained significantly lower (SUV 1.41+/-0.73) than that before treatment (p = 0.002), although three out of ten animals showed a slightly increasing tendency for the FDG uptake. The tumor necrosis rate ranged from 50.00% to 99.90% (85.48%+/-15.87). There was no significant correlation between the SUV or the SUV decrease rate and the tumor necrosis rate in that range.

CONCLUSION

Even though FDG-PET cannot exactly reflect the tumor necrosis rate, FDG-PET is a useful modality for the early assessment of the antitumor effect of intraarterial administration of 3-BrPA in VX2 liver tumor.

Intraarterial therapy with a new potent inhibitor of tumor metabolism (3-bromopyruvate): identification of therapeutic dose and method of injection in an animal model of liver cancer

PURPOSE

A potent new adenosine triphosphate inhibitor--3-bromopyruvate (3-BrPA)--has been shown to have antitumor effects when injected intraarterially in the hepatic artery of rabbits with VX-2 tumors. The authors performed a stepwise study in rabbits to determine the therapeutic dose and method of delivery of 3-BrPA.

MATERIALS AND METHODS

White New Zealand rabbits with VX-2 tumors were used for this study. Eight animals were examined to establish the maximum tolerated dose (2.5 or 5.0 mmol/L of 25-mL 3-BrPA) as a single bolus injection. The 2.5 mmol/L dose was then used to compare three methods of delivery: injection of one bolus, two 12.5-mL serial bolus injections administered 1 hour apart, and continuous infusion of 25 mL for 1 hour. Finally, dose-response analysis was performed by using 10 groups of three animals each, with 1-hour intraarterial infusions of 3-BrPA (25 mL) at incremental doses of 0.25 mmol/L (range, 0.5-2.5 mmol/L) with phosphate buffered saline used for control animals. All animals were sacrificed at 48 hours, and histopathologic analysis was performed. chi2 statistics were used to analyze the data.

RESULTS

The maximum tolerated dose of 3-BrPA was 2.5 mmol/L; however, it caused substantial peripheral liver necrosis. These effects were minimized when 3-BrPA was infused over 1 hour. Complete tumor necrosis was identified in all samples with at least 2.0 mmol/L of 3-BrPA. The 1.75 mmol/L concentration was identified as therapeutic because it caused complete tumor apoptosis and minimal toxicity (P < .001).

CONCLUSIONS

The results identified both the therapeutic dose (1.75 mmol/L) and the method of infusion (1 hour intraarterial infusion) of 3-BrPA. This potent new treatment may prove to be an effective way of treating liver cancer and may become part of a new class of anticancer drugs based on the inhibition of tumor metabolism.

Antiparasitic drug nitazoxanide inhibits the pyruvate oxidoreductases of Helicobacter pylori, selected anaerobic bacteria and parasites, and Campylobacter jejuni

Nitazoxanide (NTZ) exhibits broad-spectrum activity against anaerobic bacteria and parasites and the ulcer-causing pathogen Helicobacter pylori. Here we show that NTZ is a noncompetitive inhibitor (K(i), 2 to 10 microM) of the pyruvate:ferredoxin/flavodoxin oxidoreductases (PFORs) of Trichomonas vaginalis, Entamoeba histolytica, Giardia intestinalis, Clostridium difficile, Clostridium perfringens, H. pylori, and Campylobacter jejuni and is weakly active against the pyruvate dehydrogenase of Escherichia coli. To further mechanistic studies, the PFOR operon of H. pylori was cloned and overexpressed in E. coli, and the multisubunit complex was purified by ion-exchange chromatography. Pyruvate-dependent PFOR activity with NTZ, as measured by a decrease in absorbance at 418 nm (spectral shift from 418 to 351 nm), unlike the reduction of viologen dyes, did not result in the accumulation of products (acetyl coenzyme A and CO(2)) and pyruvate was not consumed in the reaction. NTZ did not displace the thiamine pyrophosphate (TPP) cofactor of PFOR, and the 351-nm absorbing form of NTZ was inactive. Optical scans and (1)H nuclear magnetic resonance analyses determined that the spectral shift (A(418) to A(351)) of NTZ was due to protonation of the anion (NTZ(-)) of the 2-amino group of the thiazole ring which could be generated with the pure compound under acidic solutions (pK(a) = 6.18). We propose that NTZ(-) intercepts PFOR at an early step in the formation of the lactyl-TPP transition intermediate, resulting in the reversal of pyruvate binding prior to decarboxylation and in coordination with proton transfer to NTZ. Thus, NTZ might be the first example of an antimicrobial that targets the "activated cofactor" of an enzymatic reaction rather than its substrate or catalytic sites, a novel mechanism that may escape mutation-based drug resistance.

Secondary mitochondrial dysfunction in propionic aciduria: a pathogenic role for endogenous mitochondrial toxins

Mitochondrial dysfunction during acute metabolic crises is considered an important pathomechanism in inherited disorders of propionate metabolism, i.e. propionic and methylmalonic acidurias. Biochemically, these disorders are characterized by accumulation of propionyl-CoA and metabolites of alternative propionate oxidation. In the present study, we demonstrate uncompetitive inhibition of PDHc (pyruvate dehydrogenase complex) by propionyl-CoA in purified porcine enzyme and in submitochondrial particles from bovine heart being in the same range as the inhibition induced by acetyl-CoA, the physiological product and known inhibitor of PDHc. Evaluation of similar monocarboxylic CoA esters showed a chain-length specificity for PDHc inhibition. In contrast with CoA esters, non-esterified fatty acids did not inhibit PDHc activity. In addition to PDHc inhibition, analysis of respiratory chain and tricarboxylic acid cycle enzymes also revealed an inhibition by propionyl-CoA on respiratory chain complex III and alpha-ketoglutarate dehydrogenase complex. To test whether impairment of mitochondrial energy metabolism is involved in the pathogenesis of propionic aciduria, we performed a thorough bioenergetic analysis in muscle biopsy specimens of two patients. In line with the in vitro results, oxidative phosphorylation was severely compromised in both patients. Furthermore, expression of respiratory chain complexes I-IV and the amount of mitochondrial DNA were strongly decreased, and ultrastructural mitochondrial abnormalities were found, highlighting severe mitochondrial dysfunction. In conclusion, our results favour the hypothesis that toxic metabolites, in particular propionyl-CoA, are involved in the pathogenesis of inherited disorders of propionate metabolism, sharing mechanistic similarities with propionate toxicity in micro-organisms.

Modulation of mitochondrial metabolic function by phorbol 12-myristate 13-acetate through increased mitochondrial translocation of protein kinase Calpha in C2C12 myocytes

Protein kinase C (PKC) agonists including phorbol 12-myristate 13-acetate (PMA) not only induce the redistribution of cytosolic PKC to various subcellular compartments but also activate the kinase domain of the protein. In the present study we have investigated the nature of mitochondrial PKC pool and its effects on mitochondrial function in cells treated with PMA. Treatment of C2C12 myoblasts, C6 glioma and COS7 cells with PMA resulted in a dramatic redistribution of intracellular PKCalpha pool, with large fraction of the protein pool sequestered in the mitochondrial compartment. We also observed mitochondrial PKCdelta accumulation in a cell restricted manner. The intramitochondrial localization was ascertained by using a combination of protection against protease treatment of isolated mitochondria and immunofluorescence microscopy. PMA-induced mitochondrial localization of PKCalpha was accompanied by increased mitochondrial PKC activity, altered cell morphology, disruption of mitochondrial membrane potential, decreased complex I and pyruvate dehydrogenase activities, and increased mitochondrial ROS production. All of these changes could be retarded by treatment with PKC inhibitors. These results show a direct role for PMA-mediated PKCalpha translocation to mitochondria in inducing mitochondrial toxicity.

Chronic effects of different non-esterified fatty acids on pancreatic islets of rats

AIMS

The aim of this study was to examine the chronic effects of different non-esterified fatty acids (NEFA) on insulin secretion by pancreatic islets of normal Wistar rats in vitro.

METHODS

Pancreatic islets were isolated from normal Wistar rats, and were incubated with 0.2, 0.4, or 0.8 mmol/L palmitate (C16:0), stearate (C18:0), oleate (C18:1), or linoleate (C18:2) for 24 h, then the insulin secretion and pyruvate dehydrogenase (PDH) activity were examined.

RESULTS

Neither islet insulin content nor islet DNA content differed among islets incubated with each kind of NEFA. Compared with control, linoleate significantly inhibited glucose-stimulated insulin secretion (GSIS) and PDH activity at each concentration (p < 0.05), while others inhibited GSIS and PDH activity significantly only at 0.4 and 0.8 mmol/L (p < 0.05). There was no significant difference in GSIS and PDH activity among islets pretreated by palmitate, stearate, and oleate at the same concentration (p > 0.05). However, linoleate decreased GSIS more than others at the same concentration (p < 0.05), while linoleate (0.4 or 0.8 mmol/L) inhibited PDH activity more than others at the same concentration (p < 0.05).

CONCLUSIONS

Elevation of palmitate, stearate, oleate or linoleate decreases the beta-cell secretory response to glucose, through inhibiting PDH activity. Linoleate exerts more negative effect on GSIS than other NEFA.

Enzyme inhibition assay for pyruvate dehydrogenase complex: Clinical utility for the diagnosis of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is usually diagnosed by the presence of characteristic histopathological features of the liver and/or antimitochondrial antibodies (AMA) in the serum traditionally detected by immunofluorescence. Recently, new and more accurate serological assays for the detection of AMA, such as enzyme-linked immunosorbent assay (ELISA), immunoblotting, and enzyme inhibition assay, have been developed. Of these, the enzyme inhibition assay for the detection of anti- pyruvate dehydrogenase complex (PDC) antibodies offers certain advantages such as objectivity, rapidity, simplicity, and low cost. Since this assay has almost 100% specificity, it may have particular applicability in screening the at-risk segment of the population in developing countries. Moreover, this assay could be also used for monitoring the disease course in PBC. Almost all sera of PBC-suspected patients can be confirmed for PBC or non-PBC by the combination results of immunoblotting and enzyme inhibition assay without histopathological examination. For the development of a “complete” or "gold standard" diagnostic assay for PBC, similar assays of the enzyme inhibition for anti-2-oxoglutarate dehydrogenase complex (OGDC) and anti-branched chain oxo-acid dehydrogenase complex (BCOADC) antibodies will be needed in future.

Reperfusion-induced translocation of deltaPKC to cardiac mitochondria prevents pyruvate dehydrogenase reactivation

Cardiac ischemia and reperfusion are associated with loss in the activity of the mitochondrial enzyme pyruvate dehydrogenase (PDH). Pharmacological stimulation of PDH activity improves recovery in contractile function during reperfusion. Signaling mechanisms that control inhibition and reactivation of PDH during reperfusion were therefore investigated. Using an isolated rat heart model, we observed ischemia-induced PDH inhibition with only partial recovery evident on reperfusion. Translocation of the redox-sensitive delta-isoform of protein kinase C (PKC) to the mitochondria occurred during reperfusion. Inhibition of this process resulted in full recovery of PDH activity. Infusion of the deltaPKC activator H2O2 during normoxic perfusion, to mimic one aspect of cardiac reperfusion, resulted in loss in PDH activity that was largely attributable to translocation of deltaPKC to the mitochondria. Evidence indicates that reperfusion-induced translocation of deltaPKC is associated with phosphorylation of the alphaE1 subunit of PDH. A potential mechanism is provided by in vitro data demonstrating that deltaPKC specifically interacts with and phosphorylates pyruvate dehydrogenase kinase (PDK)2. Importantly, this results in activation of PDK2, an enzyme capable of phosphorylating and inhibiting PDH. Thus, translocation of deltaPKC to the mitochondria during reperfusion likely results in activation of PDK2 and phosphorylation-dependent inhibition of PDH.

Optimized spectrophotometric assay for the completely activated pyruvate dehydrogenase complex in fibroblasts

BACKGROUND

Analysis of the pyruvate dehydrogenase complex (PDHc) activity in human skin fibroblasts is hampered by low enzyme activity in the cells. The most commonly used radiochemical method detects the formation of (14)CO(2), an endproduct of the E1 component of PDHc, from [1-(14)C]pyruvate.

METHODS

We report a spectrophotometric method for the analysis of PDHc activity in fibroblasts based on detection of NADH formation via a p-iodonitrotetrazolium violet (INT)-coupled system. We investigated in detail the specific requirements of this assay, such as cofactor requirements and the effects of suggested stimulatory compounds and different cell disruption procedures. The reliability of the optimized assay was studied by investigation of patients previously diagnosed with PDHc deficiency and by comparison with results from the radiochemical method.

RESULTS

Mean (SD) total PDHc activities were 136 (31) and 58 (21) mU/U of citrate synthase in fibroblast homogenates from 10 healthy volunteers and 7 PDHc-deficient patients, respectively, by the spectrophotometric assay. Similar results were obtained in a mitochondrial fraction. Dithiothreitol (DTT) increased the nonspecific inhibitor-insensitive rate with less pronounced effect on the specific rate of PDHc activity. Administration of DTT increased PDHc activity to 193 (3)% of control activity (without DTT), but decreased the inhibitor-sensitive rate from 99 (0.3)% (without DTT) to 69 (2)% (with 0.3 mmol/L DTT).

CONCLUSION

The simple, optimized spectrophotometric assay for PDHc analysis allows reliable investigation of the enzyme complex in human skin fibroblasts.

PPARα ligand protects during cisplatin-induced acute renal failure by preventing inhibition of renal FAO and PDC activity

Previous studies demonstrated that during cisplatin-induced acute renal failure, there is a significant reduction in proximal tubule fatty acid oxidation. We now report on the effects of peroxisome proliferator-activated receptor-α (PPARα) ligand Wy-14643 (WY) on the abnormalities of medium chain fatty acid oxidation and pyruvate dehydrogenase complex (PDC) activity in kidney tissue of cisplatin-treated mice. Cisplatin causes a significant reduction in mRNA levels and enzyme activity of mitochondrial medium chain acyl-CoA dehydrogenase (MCAD). PPARα ligand WY ameliorated cisplatin-induced acute renal failure and prevented cisplatin-induced reduction of mRNA levels and enzyme activity of MCAD. In contrast, in cisplatin-treated PPARα null mice, WY did not protect kidney function and did not reverse cisplatin-induced decreased expression of MCAD. Cisplatin inhibited renal PDC activity before the development of acute tubular necrosis, and PDC inhibition was reversed by pretreatment with PPARα agonist WY. Cisplatin also induced increased mRNA and protein levels of pyruvate dehydrogenase kinase-4 (PDK4), and PPARα ligand WY prevented cisplatin-induced increased expression of PDK4 protein levels in wild-type mice. We conclude that PPARα agonists have therapeutic potential for cisplatin-induced acute renal failure. Use of PPARα ligands prevents acute tubular necrosis by ameliorating cisplatin-induced inhibition of two distinct metabolic processes, MCAD-mediated fatty acid oxidation and PDC activity.

Pyruvate and acetate metabolism in termite mitochondria

Intact mitochondria have been successfully prepared from body tissues from the termites Nasutitermes walkeri and Coptotermes formosanus. This is the first report of the successful isolation of mitochondria from termites (Isoptera: Termitidae). Using an oxygen electrode, oxygen consumption by the mitochondria during the oxidation of various respiratory substrates was determined and their properties measured in terms of respiratory control index and ADP/O. ADP/O was as expected for substrates such as pyruvate, acetylcarnitine and acetyl-CoA and carnitine. Pyruvate and acetate were the major respiratory substrates in both species. The total activity of the pyruvate dehydrogenase complex (PDHc) in the mitochondria from N. walkeri and C. formosanus was determined to be 72.87+/-8.98 and 8.29+/-0.42 nmol/termite/h, respectively. Mitochondria isolated in the presence of inhibitors of PDHc interconversion were used to determine that about 60% of the PDHc was maintained in the active form in both N. walkeri and C. formosanus. The sufficient PDHc activity and high rate of pyruvate oxidation in mitochondria from N. walkeri suggest that pyruvate is rapidly metabolised, whereas the low mitochondrial PDHc activity of C. formosanus suggests that in this species more pyruvate is produced than can be oxidised in the termite tissues.

Evidence for rapid "metabolic switching" through lipoprotein lipase occupation of endothelial-binding sites

During diabetes, impaired glucose transport and utilization by the heart switches energy production to exclusive beta-oxidation of fatty acid (FA). In the current study, we examined the contribution of cardiac lipoprotein lipase (LPL) towards providing FA to the diabetic heart. Streptozotocin (STZ) caused an augmentation of LPL activity at the coronary lumen, an effect duplicated by diazoxide (DZ). With DZ, the amplification of LPL at the coronary luminal surface was determined to be exceptionally rapid. Interestingly, unlike DZ, the capability of hearts from STZ animals to maintain this amplified LPL activity was sustained in vitro. This increased enzyme in the hyperglycemic heart is likely unrelated to an increase in the number of capillary endothelial LPL-binding sites. Our data imply that binding sites for LPL in the control rat heart are only partly occupied by the enzyme and diabetes rapidly initiates filling of all of these sites. Phloridzin treatment of STZ animals normalized plasma glucose with no effect on luminal LPL suggesting that the effects of diabetes on LPL are also largely independent of changes in blood glucose. Both 2 and 8 U of insulin normalized plasma glucose in DZ-treated animals but only 8 U reversed DZ-induced augmentation of cardiac luminal LPL. Our data suggest that impaired intracellular glucose utilization allows rapid vectorial transfer of LPL to unoccupied binding sites to supply the diabetic heart with excess FA. The persistence of increased coronary luminal LPL even in a setting of normoglycemia may provide excessive FA to the diabetic heart with deleterious consequences over the long term.

Immunization with a xenobiotic 6-bromohexanoate bovine serum albumin conjugate induces antimitochondrial antibodies

The E2 subunit of pyruvate dehydrogenase complex (PDC-E2) is the major autoantigen recognized by antimitochondrial Abs (AMA) in primary biliary cirrhosis (PBC). Recently, we replaced the lipoic acid moiety of PDC-E2 with a battery of synthetic structures designed to mimic a xenobiotically modified lipoyl hapten on a 12-aa peptide that was found within the immunodominant autoepitope of PDC-E2 and demonstrated that AMA in PBC reacted against several organic modified mimotopes as well as, or sometimes significantly better than, the native lipoyl domain. Based on this data, we immunized rabbits with one such xenobiotic organic compound, 6-bromohexanoate, coupled to BSA. One hundred percent of immunized rabbits developed AMA that have each and every characteristic of human AMAs with reactivity against PDC-E2, E2 subunit of branched chain 2-oxo-acid dehydrogenase, and E2 subunit of 2-oxoglutarate dehydrogenase complex. The rabbit AMA also inhibited enzymatic function of PDC-E2 and, importantly, binds to peptide sequences not present in the xenobiotic carrier immunogen. In contrast, BSA-immunized controls did not produce such activity. Our observation that animals immunized with a xenobiotic BSA complex produce autoantibodies that react not only with the xenobiotic, but also with mitochondrial autoantigens recognized by autoimmune PBC sera, suggests that environmental xenobiotic agents can be a risk factor for the induction of PBC.

Reactive oxygen species are involved in arsenic trioxide inhibition of pyruvate dehydrogenase activity

Arsenite was shown to inhibit pyruvate dehydrogenase (PDH) activity through binding to vicinal dithiols in pure enzyme and tissue extract. However, no data are available on how arsenite inhibits PDH activity in human cells. The IC(50) values for arsenic trioxide (As(2)O(3)) to inhibit the PDH activity in porcine heart pure enzyme preparation and in human leukemia cell line HL60 cells were estimated to be 182 and 2 microM, respectively. Thus, As(2)O(3) inactivation of PDH activity was about 90 times more potent in HL60 cells than in purified enzyme preparation. The IC(50) values for As(2)O(3) and phenylarsine oxide to reduce the vicinal thiol content in HL60 cells were estimated to be 81.7 and 1.9 microM, respectively. Thus, As(2)O(3) is a potent PDH inhibitor but a weak vicinal thiol reacting agent in HL60 cells. Antioxidants but not dithiol compounds suppressed As(2)O(3) inhibition of PDH activity in HL60 cells. Conversely, dithiol compounds but not antioxidants suppressed the inhibition of PDH activity by phenylarsine oxide. As(2)O(3) increased H(2)O(2) level in HL60 cells, but this was not observed for phenylarsine oxide. Mitochondrial respiration inhibitors suppressed the As(2)O(3)-induced H(2)O(2) production and As(2)O(3) inhibition of PDH activity. Moreover, metal chelators ameliorated whereas Fenton metals aggravated As(2)O(3) inhibition of PDH activity. Treatment with H(2)O(2) plus Fenton metals also decreased the PDH activity in HL60 cells. Therefore, it seems that As(2)O(3) elevates H(2)O(2) production in mitochondria and this may produce hydroxyl through the Fenton reaction and result in oxidative damage to the protein of PDH. The present results suggest that arsenite may cause protein oxidation to inactivate an enzyme and this can occur at a much lower concentration than arsenite binding directly to the critical thiols.

Immunocapture and microplate-based activity measurement of mammalian pyruvate dehydrogenase complex

Altered pyruvate dehydrogenase (PDH) functioning occurs in primary PDH deficiencies and in diabetes, starvation, sepsis, and possibly Alzheimer's disease. Currently, the activity of the enzyme complex is difficult to measure in a rapid high-throughput format. Here we describe the use of a monoclonal antibody raised against the E2 subunit to immunocapture the intact PDH complex still active when bound to 96-well plates. Enzyme turnover was measured by following NADH production spectrophotometrically or by a fluorescence assay on mitochondrial protein preparations in the range of 0.4 to 5.0 micro g per well. Activity is sensitive to known PDH inhibitors and remains regulated by phosphorylation and dephosphorylation after immunopurification because of the presence of bound PDH kinase(s) and phosphatase(s). It is shown that the immunocapture assay can be used to detect PDH deficiency in cell extracts of cultured fibroblasts from patients, making it useful in patient screens, as well as in the high-throughput format for discovery of new modulators of PDH functioning.

Acrolein inhibits NADH-linked mitochondrial enzyme activity: implications for Alzheimer's disease

In Alzheimer's disease (AD) brain increased lipid peroxidation and decreased energy utilization are found. Mitochondria membranes contain a significant amount of arachidonic and linoleic acids, precursors of lipid peroxidation products, 4-hydroxynonenal (HNE) and 2-propen-1-al (acrolein), that are extremely reactive. Both alkenals are increased in AD brain. In this study, we examined the effects of nanomolar levels of acrolein on the activities of pyruvate dehydrogenase (PDH) and Alpha-ketoglutarate dehydrogenase (KGDH), both reduced nicotinamide adenine dinucleotide (NADH)-linked mitochondrial enzymes. Acrolein decreased PDH and KGDH activities significantly in a dose-dependent manner. Using high performance liquid chromatography coupled to mass spectrometry (HPLC-MS), acrolein was found to bind lipoic acid, a component in both the PDH and KGDH complexes, most likely explaining the loss of enzyme activity. Acrolein also interacted with oxidized nicotinamide adenine dinucleotide (NAD(+)) in such a way as to decrease the production of NADH. Acrolein, which is increased in AD brain, may be partially responsible for the dysfunction of mitochondria and loss of energy found in AD brain by inhibition of PDH and KGDH activities, potentially contributing to the neurodegeneration in this disorder.

Inhibition of the alpha-ketoglutarate dehydrogenase and pyruvate dehydrogenase complexes by a putative aberrant metabolite of serotonin, tryptamine-4,5-dione

A transient energy impairment with resultant release and subsequent reuptake of 5-hydroxytryptamine (5-HT) and NMDA receptor activation with consequent cytoplasmic superoxide (O(2)(-)(*)), nitric oxide (NO(*)), and peroxynitrite (ONOO(-)) generation have all been implicated in a neurotoxic cascade which ultimately leads to the degeneration of serotonergic neurons evoked by methamphetamine (MA) and 3,4-methylenedioxymethamphetamine (MDMA). Such observations raise the possibility that the O(2)(-)(*)/NO(*)/ONOO(-)-mediated oxidation of 5-HT, as it returns via the plasma membrane transporter to the cytoplasm of serotonergic neurons when the MA/MDMA-induced energy impairment begins to subside, may generate an endogenous neurotoxin. In vitro the O(2)(-)(*)/NO(*)/ONOO(-)-mediated oxidation of 5-HT forms tryptamine-4,5-dione (T-4,5-D). When incubated with intact rat brain mitochondria, T-4,5-D strongly inhibits state 3 respiration with pyruvate or alpha-ketoglutarate as substrates at concentrations which do not affect succinate-supported (complex II) respiration. Experiments with freeze-thawed rat brain mitochondria reveal that T-4,5-D inhibits the pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes. These and other properties of T-4,5-D raise the possibility that it may be an endogenously formed intraneuronal metabolite of 5-HT that contributes to the serotonergic neurotoxicity of MA and MDMA.

Inhibition effects of furfural on alcohol dehydrogenase, aldehyde dehydrogenase and pyruvate dehydrogenase

The kinetics of furfural inhibition of the enzymes alcohol dehydrogenase (ADH; EC 1.1.1.1), aldehyde dehydrogenase (AlDH; EC 1.2.1.5) and the pyruvate dehydrogenase (PDH) complex were studied in vitro. At a concentration of less than 2 mM furfural was found to decrease the activity of both PDH and AlDH by more than 90%, whereas the ADH activity decreased by less than 20% at the same concentration. Furfural inhibition of ADH and AlDH activities could be described well by a competitive inhibition model, whereas the inhibition of PDH was best described as non-competitive. The estimated K(m) value of AlDH for furfural was found to be about 5 microM, which was lower than that for acetaldehyde (10 microM). For ADH, however, the estimated K(m) value for furfural (1.2 mM) was higher than that for acetaldehyde (0.4 mM). The inhibition of the three enzymes by 5-hydroxymethylfurfural (HMF) was also measured. The inhibition caused by HMF of ADH was very similar to that caused by furfural. However, HMF did not inhibit either AlDH or PDH as severely as furfural. The inhibition effects on the three enzymes could well explain previously reported in vivo effects caused by furfural and HMF on the overall metabolism of Saccharomyces cerevisiae, suggesting a critical role of these enzymes in the observed inhibition.

Inhibition of the Escherichia coli pyruvate dehydrogenase complex E1 subunit and its tyrosine 177 variants by thiamin 2-thiazolone and thiamin 2-thiothiazolone diphosphates. Evidence for reversible tight-binding inhibition

Variants of the pyruvate dehydrogenase subunit (E1; EC ) of the Escherichia coli pyruvate dehydrogenase multienzyme complex with Y177A and Y177F substitutions were created. Both variants displayed pyruvate dehydrogenase multienzyme complex activity at levels of 11% (Y177A E1) and 7% (Y177F E1) of the parental enzyme. The K(m) values for thiamin diphosphate (ThDP) were 1.58 microm (parental E1) and 6.65 microm (Y177A E1), whereas the Y177F E1 variant was not saturated at 200 microm. According to fluorescence studies, binding of ThDP was unaffected by the Tyr(177) substitutions. The ThDP analogs thiamin 2-thiazolone diphosphate (ThTDP) and thiamin 2-thiothiazolone diphosphate (ThTTDP) behaved as tight-binding inhibitors of parental E1 (K(i) = 0.003 microm for ThTDP and K(i) = 0.064 microm for ThTTDP) and the Y177A and Y177F variants. This analysis revealed that ThTDP and ThTTDP bound to parental E1 via a two-step mechanism, but that ThTDP bound to the Y177A variant via a one-step mechanism. Binding of ThTDP was affected and that of ThTTDP was unaffected by substitutions at Tyr(177). Addition of ThDP or ThTDP to parental E1 resulted in similar CD spectral changes in the near-UV region. In contrast, binding of ThTTDP to either parental E1 or the Y177A and Y177F variants was accompanied by the appearance of a positive band at 330 nm, indicating that ThTTDP was bound in a chiral environment. In combination with x-ray structural evidence on the location of Tyr(177), the kinetic and spectroscopic data suggest that Tyr(177) has a role in stabilization of some transition state(s) in the reaction pathway, starting with the free enzyme and culminating with the first irreversible step (decarboxylation), as well as in reductive acetylation of the dihydrolipoamide acetyltransferase component.

Impairment of pyruvate dehydrogenase activity by acetaldehyde

The facial features that are characteristic of fetal alcohol syndrome (FAS) are strikingly similar to those seen in pyruvate dehydrogenase (PDH) deficiency. Furthermore, alcohol-induced central nervous system insult results in midline anomalies such as agenesis of the corpus callosum, which has also been described in several metabolic diseases, including PDH deficiency. The purpose of this work was to examine the effect of acetaldehyde on PDH in vitro. The activity of PDH was measured in the presence of acetaldehyde (10 microM-1 mM) by measuring the formation of the reduced form of nicotinamide-adenine dinucleotide at 340 nm. Pyruvate dehydrogenase was separated by using the sodium dodecyl sulfate-polyacrylamide gel electrophoresis technique after incubation with [1,2-(14)C]-acetaldehyde to detect the formation of covalent adducts autoradiographically. The effect of acetaldehyde on the phosphorylation of the complex was also determined autoradiographically after incubating of PDH with (32)P-adenosine triphosphate. The results of this study show that acetaldehyde impairs PDH activity by a mixed inhibition type mechanism (Kic=62.4+/-25.7 microM, Kiu=225+/-68 microM), which is not a result of the formation of covalent adducts with PDH, nor of a stimulation of phosphorylation or inactivation of the complex. Because PDH levels are low throughout development and that the competition between pyruvate and acetaldehyde may be enhanced due to ethanol-induced lowering of ambient pyruvate concentrations, we conclude that impairment of PDH may have a significant effect on the developing fetus.

Protection by thiols of the mitochondrial complexes from 4-hydroxy-2-nonenal

In the present study, the effects of 4-hydroxy-2-nonenal (HNE) on highly purified pyruvate dehydrogenase complex (PDC) and its catalytic components in vitro and on PDC, alpha-ketoglutarate dehydrogenase complex (KGDC), and the branched-chain alpha-keto acid dehydrogenase complex (BCKDC) activities in cultured human HepG2 cells were investigated. Among the PDC components, the activity of the dihydrolipoamide acetyltransferase-E3-binding protein subcomplex (E2-E3BP) only was decreased by HNE. Dihydrolipoamide dehydrogenase (E3) protected the E2-E3BP subcomplex from HNE inactivation in the absence of the substrates. In the presence of E3 and NADH, when lipoyl groups were reduced, higher inactivation of the E2-E3BP subcomplex by HNE was observed. Purified PDC was protected from HNE-induced inactivation by several thiol compounds including lipoic acid plus [LA-plus; 2-(N,N-dimethylamine)ethylamidolipoate(.)HCl]. Treatment of cultured HepG2 cells with HNE resulted in a significant reduction of PDC and KGDC activities, whereas BCKDC activity decreased to a lesser extent. Lipoyl compounds afforded protection from HNE-induced inhibition of PDC. This protection was higher in the presence of cysteine and reduced glutathione. Cysteine was able to restore PDC activity to some extent after HNE treatment. These findings show that thiols, including lipoic acid, provide protection against HNE-induced inactivation of lipoyl-containing complexes in the mitochondria.

Expression and regulation of pyruvate dehydrogenase kinase isoforms in the developing rat heart and in adulthood: role of thyroid hormone status and lipid supply

Activation of the pyruvate dehydrogenase (PDH) complex (PDHC) promotes glucose disposal, whereas inactivation conserves glucose. The PDH kinases (PDHKs) regulate glucose oxidation through inhibitory phosphorylation of PDHC. The adult rat heart contains three PDHK isoforms PDHK1, PDHK2 and PDHK4. Using Western-blot analysis, with specific antibodies raised against individual recombinant PDHK1, PDHK2 and PDHK4, the present study investigated PDHK isoform expression in the developing rat heart and adulthood. We identified clear differences in the patterns of protein expression of each of these PDHK isoforms during the first 3 weeks of post-natal development, with most marked up-regulation of isoforms PDHK1 and PDHK4. Distinctions between the three cardiac PDHK isoforms were also demonstrated with respect to post-neonatal maturational up-regulation; with greatest up-regulation of PDHK1 and least up-regulation of PDHK4 from the post-neonatal period until maturity. The study also examined the role of thyroid hormone status and lipid supply on PDHK isoform expression. We observed marked selective increases in the amount of PDHK4 protein present relative to total cardiac protein in both hyperthyroidism and high-fat feeding. Overall, our data identify PDHK isoform PDHK1 as being of more potential regulatory importance for glucose oxidation in the adult compared with the neonatal heart, and cardiac PDHK4 as a PDHK isoform whose expression is specifically responsive to changes in lipid supply, suggesting that its up-regulation during early post-natal life may be the perinatal switch to use fatty acids as the energy source. We also identify regulation of pyruvate sensitivity of cardiac PDHK as a physiological variable, a change in which requires factors in addition to a change in lipid supply.

Partitioning of pyruvate between oxidation and anaplerosis in swine hearts

The goal of this study was to measure flux through pyruvate carboxylation and decarboxylation in the heart in vivo. These rates were measured in the anterior wall of normal anesthetized swine hearts by infusing [U-(13)C(3)]lactate and/or [U-(13)C(3)] pyruvate into the left anterior descending (LAD) coronary artery. After 1 h, the tissue was freeze-clamped and analyzed by gas chromatography-mass spectrometry for the mass isotopomer distribution of citrate and its oxaloacetate moiety. LAD blood pyruvate and lactate enrichments and concentrations were constant after 15 min of infusion. Under near-normal physiological concentrations of lactate and pyruvate, pyruvate carboxylation and decarboxylation accounted for 4.7 +/- 0.3 and 41.5 +/- 2.0% of citrate formation, respectively. Similar relative fluxes were found when arterial pyruvate was raised from 0.2 to 1.1 mM. Addition of 1 mM octanoate to 1 mM pyruvate inhibited pyruvate decarboxylation by 93% without affecting carboxylation. The absence of M1 and M2 pyruvate demonstrated net irreversible pyruvate carboxylation. Under our experimental conditions we found that pyruvate carboxylation in the in vivo heart accounts for at least 3-6% of the citric acid cycle flux despite considerable variation in the flux through pyruvate decarboxylation.

Serial changes in enzyme inhibitory antibody to pyruvate dehydrogenase complex during the course of primary biliary cirrhosis

To assess the usefulness of enzyme inhibition assay for the diagnosis of primary biliary cirrhosis (PBC), we determined the serial changes in enzymatic inhibitory antibody to pyruvate dehydrogenase complex (PDC) in patients with PBC, and compared the results to those of immunofluorescence and immunoblotting. Forty-nine sera from 19 patients with PBC who were followed-up for at least 16 months were tested for antimitochondrial antibodies (AMA) by indirect immunofluorescence, immunoblotting on bovine heart mitochondria, and enzyme inhibition assay using commercially available TRACE Enzymatic Mitochondrial Antibody (M2) Assay (EMA) kit. Of the 49 sera, 39 (80%), 35 (71%), 38 (78%), 31 (63%), and 36 (73%) were positive for AMA by immunofluorescence, for immunoglobulin G (IgG), IgM, and IgA class antibody against E2 subunit of PDC (PDC-E2) by immunoblotting, and for enzymatic inhibitory antibody to PDC by EMA, respectively. AMA titers determined by immunofluorescence did not change in 9 patients (47%), increased in 4 (21%), decreased in 3 (16%), and fluctuated in 3 (16%) during follow-up. The number of anti-M2 bands by immunoblotting did not change in 9 (47%), increased in 6 (32%), decreased in 2 (11%), and fluctuated in 2 (11%). Units of PDC activity by EMA did not change markedly in 16 (84%), increased in 2 (11%), and fluctuated in 1 (5%). Positive EMA results were common in cases with high levels of serum alkaline phosphatase and IgM, and the units of PDC activity by EMA correlated significantly and inversely with AMA titers by immunofluorescence, and serum reactivity to PDC-E2 by immunoblotting, respectively. There was no correlation between serial changes in biochemical data and units of PDC activity by EMA. In three patients who showed a decrease in AMA titers, AMA titers correlated more with EMA results than immunoblotting. Moreover, in a patient with fluctuating AMA titers, the units of PDC activity by EMA paralleled AMA titers. Our results suggest that EMA is useful for the diagnosis of AMA-positive PBC, and also could be used for monitoring the disease course in PBC.

The cytotoxic lipid peroxidation product, 4-hydroxy-2-nonenal, specifically inhibits decarboxylating dehydrogenases in the matrix of plant mitochondria

4-Hydroxy-2-nonenal (HNE), a cytotoxic product of lipid peroxidation, inhibits O(2) consumption by potato tuber mitochondria. 2-Oxoglutarate dehydrogenase (OGDC), pyruvate dehydrogenase complex (PDC) (both 80% inhibited) and NAD-malic enzyme (50% inhibited) are its major targets. Mitochondrial proteins identified by reaction with antibodies raised to lipoic acid lost this antigenicity following HNE treatment. These proteins were identified as acetyltransferases of PDC (78 kDa and 55 kDa), succinyltransferases of OGDC (50 kDa and 48 kDa) and glycine decarboxylase H protein (17 kDa). The significance of the effect of these inhibitions on the impact of lipid peroxidation and plant respiratory functions is discussed.

Chloropicrin dechlorination in relation to toxic action

Chloropicrin (CCl3NO2) is a widely used soil fumigant with an unknown mechanism of acute toxicity. We investigated the possible involvement of dechlorination in CCl3NO2 toxicity by considering its metabolism, inhibition of pyruvate and succinate dehydrogenases, cytotoxicity in cultured cells, and interaction with hemoproteins. In a newly discovered pathway, CCl3NO2 is metabolized to thiophosgene, which is characterized as the cyclic cysteine adduct (raphanusamic acid) in the urine of mice. CCl3NO2 inhibits porcine heart pyruvate dehydrogenase complex (IC-50 4 microM) and mouse liver succinate dehydrogenase complex (IC-50 13 microM), whereas its dehalogenated metabolites (CHCl2NO2 and CH2ClNO2) are more than 10 times less effective. The inhibitory potency of CCl3NO2 for these dehydrogenase complexes is similar to that of captan, folpet, and dichlone fungicides (IC-50 2-6 microM). CCl3NO2 cytotoxicity with Hepa 1c1c7+ mouse hepatoma cells (IC-50 9 microM) is not correlated with glutathione depletion. Mice treated intraperitoneally with CCl3NO2 at 50 mg/kg but not with an equivalent dose of CHCl2NO2 show increased concentrations of oxyhemoglobin in liver. The acute toxicity of CCl3NO2 in mice is due to the parent compound or metabolites other than CHCl2NO2 or CH2ClNO2 and may be associated with inhibition of the pyruvate dehydrogenase complex and elevated oxyhemoglobin.

Automated enzymatic mitochondrial antibody assay for the diagnosis of primary biliary cirrhosis

Primary biliary cirrhosis is a progressive autoimmune disease that affects middle aged women, resulting in liver cirrhosis. We describe here an automated enzymatic mitochondrial antibody assay adapted for performance on laboratory analysers for the serological diagnosis of primary biliary cirrhosis. This assay detects the characteristic autoantibody directed against the 74kDa E2 subunit of the pyruvate dehydrogenase complex. Analysis of receiver operator characteristic curve data indicated that the automated enzymatic mitochondrial assay procedure discriminated clinically identified patients with primary biliary cirrhosis from normal subjects with a sensitivity of 83% and a specificity of 100%. This method compared favourably against a commercial ELISA method which had a sensitivity of 73% and a specificity of 100%. The automated enzymatic mitochondrial antibody assay is a high throughput assay of use for the routine diagnosis of patients with primary biliary cirrhosis with autoantibodies to the E2 subunit of the pyruvate dehydrogenase complex. The method is of potential value for economical and rapid screening to detect asymptomatic primary biliary cirrhosis in the at-risk segment of the population, namely middle aged women.

Comparative immunoreactivity of anti-trifluoroacetyl (TFA) antibody and anti-lipoic acid antibody in primary biliary cirrhosis: searching for a mimic

Previous studies documenting the existence of cross-reactivity between the lipoated (but not unlipoated) forms of the inner lipoyl domain (E2L2) of PDC-E2 [the major autoantigen in Primary biliary cirrhosis (PBC)] and trifluoroacetylated (TFA) proteins, led us to hypothesize that PBC may be due to an initial insult with an environmental agent that cross-reacts with TFA. Therefore, we performed a comparative study of the reactivity of rabbit anti-TFA antibody and anti-lipoic acid (LA) antibody against the mitochondrial autoantigens of human PBC and various TFA and LA conjugated proteins. Whereas both anti-TFA and anti-LA reacted with PDC-E2, the wild-type lipoated form of E2L2, OGDC-E2, E3-BP and LA-KLH, neither reacted with BCOADC-E2 or the non-lipoated form of E2L2. Of interest was that while anti-TFA reacted with PDC-E2, TFA-RSA and LA-KLH, it failed to inhibit PDC-E2 enzyme function. In contrast, anti-LA demonstrated cytoplasmic and mitochondrial staining, and inhibited PDC enzyme activity. Hence, although considerable cross reactivity exists between anti-TFA and anti-LA, the molecular nature of the interaction is clearly different. One of 14 PBC sera reacted weakly with TFA-albumin, whereas four of 14 PBC sera reacted with LA-KLH. Immunohistochemically, both anti-TFA and anti-LA antibodies reacted focally with periportal hepatocytes and bile ducts in both PBC and controls. However, anti-LA produced much stronger focalized staining of the bile ducts of diseased liver. This study suggests that while anti-TFA antibody recognizes lipoic acid-linked enzymes and proteins, the epitope recognized differs from that of anti-LA antibody and PBC autoantibodies. It is unlikely that a response to TFA is the triggering event in PBC. Anti-LA antibodies share a higher degree of similarity to PBC sera providing suggestive evidence that anti-LA antibodies or anti-LA like antibodies (mimotopes) may help define the initiator of the autoimmune response.

Oxidative metabolites of 5-S-cysteinylnorepinephrine are irreversible inhibitors of mitochondrial complex I and the alpha-ketoglutarate dehydrogenase and pyruvate dehydrogenase complexes: possible implications for neurodegenerative brain disorders

The major initial product of the oxidation of norepinephrine (NE) in the presence of L-cysteine is 5-S-cysteinylnorepinephrine which is then further easily oxidized to the dihydrobenzothiazine (DHBT) 7-(1-hydroxy-2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1, 4-benzothiazine-3-carboxylic acid (DHBT-NE-1). When incubated with intact rat brain mitochondria, DHBT-NE-1 evokes rapid inhibition of complex I respiration without affecting complex II respiration. DHBT-NE-1 also evokes time- and concentration-dependent irreversible inhibition of NADH-coenzyme Q(1) (CoQ(1)) reductase, the pyruvate dehydrogenase complex (PDHC), and alpha-ketoglutarate dehydrogenase (alpha-KGDH) when incubated with frozen and thawed rat brain mitochondria (mitochondrial membranes). The time dependence of the inhibition of NADH-CoQ(1) reductase, PDHC, and alpha-KGDH by DHBT-NE-1 appears to be related to its oxidation, catalyzed by an unknown component of the inner mitochondrial membrane, to electrophilic intermediates which bind covalently to active site cysteinyl residues of these enzyme complexes. The latter conclusion is based on the ability of glutathione to block inhibition of NADH-CoQ(1) reductase, PDHC, and alpha-KGDH by scavenging electrophilic intermediates, generated by the mitochondrial membrane-catalyzed oxidation of DHBT-NE-1, forming glutathionyl conjugates, several of which have been isolated and spectroscopically identified. The possible implications of these results to the degeneration of neuromelanin-pigmented noradrenergic neurons in the locus ceruleus in Parkinson's disease are discussed.

Substrates for endogenous metabolism by mature boar spermatozoa

Washed boar spermatozoa incubated in the absence of exogenous substrates maintained a high energy charge potential (ECP) for at least 10 h. Addition of bromopyruvate, an inhibitor of stage 2 of the glycolytic pathway, at any time during the incubation caused an immediate decrease in the ECP, indicating that the mobilization of endogenous compounds requires this section of the pathway for the production of lactate, the major mitochondrial substrate for ATP production. Some of the sources of the metabolic substrates have been identified, by NMR and metabolic studies, as di- or triglycerides, to produce glycerol, and membrane phospholipids for the production of glycerol 3-phosphate. Acetylcarnitine contributes acetyl groups early in the incubation; glycerylphosphorylcholine is degraded to glycerol 3-phosphate and choline after about 5 h, and acetate also accumulates after about 5 h. The presence of phosphorylcholine and phosphorylethanolamine later in the incubation indicates that phospholipids are also degraded to glycerol.

Prediction of the immunodominant epitope of the pyruvate dehydrogenase complex E2 in primary biliary cirrhosis using phage display

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by autoantibodies reactive with the pyruvate dehydrogenase complex. A conformational epitope has been mapped to aa 91-227 within the inner lipoyl domain of the E2 subunit (pyruvate dehydrogenase complex E2 (PDC-E2)). We have used phage display to further localize this epitope. A random heptapeptide library was screened using IgG from two patients with PBC, with negative selection using pooled normal IgG. Phage that contained peptide inserts (phagotopes) selected using PBC sera differed from those selected using IgG from patients with RA or polychondritis. Two motifs occurred only among the PBC-selected phagotopes; these were MH (13 sequences, 16 phagotopes) and FV (FVEHTRW, FVEIYSP, FVLPWRI). The phagotopes selected were tested for reactivity with anti-PDC-E2 affinity purified from four patients with PBC. Phagotopes that contained 1 of 15 different peptide sequences were reactive with one or more of these four anti-PDC-E2 preparations, whereas phagotopes that contained 1of the remaining 28 sequences were negative. The peptides (FVLPWRI, MHLNTPP, MHLTQSP) encoded by three phagotopes that were strongly reactive with all four preparations of anti-PDC-E2 were synthesized. Each of the selected peptides, but not an irrelevant peptide, inhibited the reactivity by ELISA of PBC serum with recombinant PDC-E2 and reduced the inhibition of the enzyme activity of PDC by a PBC serum. The peptide sequences, along with the known NMR structure of the inner lipoyl domain of PDC-E2, allow the prediction of nonsequential residues 131HM132 and 178FEV180 that contribute to a conformational epitope.

Systemic indicators of inorganic arsenic toxicity in four animal species

The effect of arsenic compounds depends on the chemical form and is specific for certain organs. The lack of specific biological indicators for the effects of each arsenic species makes it difficult to differentiate their toxicity. Five prospective biological indicators of systemic toxicity were examined at time points ranging from 15 min to 24 h using male Sprague-Dawley rats, B6C3F1 mice, Golden-Syrian hamsters, and Hartley guinea pigs, following intraperitoneal dosing with 0.1 and 1 mg/kg sodium arsenite. Rats and mice were also dosed with 1 mg/kg sodium arsenate. Total blood arsenic levels were determined in all animal species to show that exposure occurred and as an index of the severity of the change is an indicator of toxicity. Total blood arsenic levels were increased in all animal species. This increase was dose, arsenic species, and animal dependent. Renal pyruvate dehydrogenase activity was significantly decreased at early time points in mice, hamsters, and guinea pigs, and at later time points in rats dosed with arsenite. Rats and mice dosed with arsenate also exhibited PDH decrease at early time points. Blood hematocrit and glucose were increased in the rat and guinea pig, respectively, after arsenite administration. Creatinine and urea nitrogen were found to be unresponsive to arsenic in most animal species. Data suggested that the mouse and secondly the hamster appear to be the most appropriate animal models for the study of acute arsenic toxicity.

Enzyme inhibitory antibody to pyruvate dehydrogenase: diagnostic utility in primary biliary cirrhosis

In primary biliary cirrhosis, autoantibodies are produced to the family of 2-oxoacid dehydrogenase complexes. These 'anti-mitochondrial' antibodies are traditionally detected by immunofluorescence but this method of detection is subjective and labour-intensive. We assessed an enzymatic mitochondrial antibody (EMA) assay based on antibody inhibition of enzymatic activity of pyruvate dehydrogenase complex in wells of microtitre plates with a colorimetric read-out. We tested 48 Australian and 1947 Japanese patients with primary biliary cirrhosis, 306 normal subjects and 691 patients with various hepatic and non-hepatic diseases. The overall sensitivity of the EMA for the diagnosis of primary biliary cirrhosis, 82%, was slightly lower than that of immunofluorescence, 90% The advantages of the EMA test include high specificity, >99%, and semi-automated features facilitating objectivity, rapidity, simplicity and economy. The EMA test could be particularly applicable to population screening for early primary biliary cirrhosis.