Correlation between lactate dehydrogenase/pyruvate dehydrogenase activities ratio and tissue pH in the perfused mouse heart: A potential noninvasive indicator of cardiac pH provided by hyperpolarized magnetic resonance

Cardiovascular diseases account for more than 30% of all deaths worldwide and many could be ameliorated with early diagnosis. Current cardiac imaging modalities can assess blood flow, heart anatomy and mechanical function. However, for early diagnosis and improved treatment, further functional biomarkers are needed. One such functional biomarker could be the myocardium pH. Although tissue pH is already determinable via MR techniques, and has been since the early 1990s, it remains elusive to use practically. The objective of this study was to explore the possibility to evaluate cardiac pH noninvasively, using in-cell enzymatic rates of hyperpolarized [1-¹³ C]pyruvate metabolism (ie, moles of product produced per unit time) determined directly in real time using magnetic resonance spectroscopy in a perfused mouse heart model. As a gold standard for tissue pH we used ³¹ P spectroscopy and the chemical shift of the inorganic phosphate (Pi) signal. The nonhomogenous pH distribution of the perfused heart was analyzed using a multi-parametric analysis of this signal, thus taking into account the heterogeneous nature of this characteristic. As opposed to the signal ratio of hyperpolarized [¹³ C]bicarbonate to [¹³ CO₂ ], which has shown correlation to pH in other studies, we investigated here the ratio of two intracellular enzymatic rates: lactate dehydrogenase (LDH) and pyruvate dehydrogenase (PDH), by way of determining the production rates of [1-¹³ C]lactate and [¹³ C]bicarbonate, respectively. The enzyme activities determined here are intracellular, while the pH determined using the Pi signal may contain an extracellular component, which could not be ruled out. Nevertheless, we report a strong correlation between the tissue pH and the LDH/PDH activities ratio. This work may pave the way for using the LDH/PDH activities ratio as an indicator of cardiac intracellular pH in vivo, in an MRI examination.

Combining metabolic flux analysis tools and 13C NMR to estimate intracellular fluxes of cultured astrocytes

In this work, brain cell metabolism was investigated by (13)C NMR spectroscopy and metabolic flux analysis (MFA). Monotypic cultures of astrocytes were incubated with labeled glucose for 38 h, and the distribution of the label was analyzed by (13)C NMR spectroscopy. The analysis of the spectra reveals two distinct physiological states characterized by different ratios of pyruvate carboxylase to pyruvate dehydrogenase activities (PC/PDH). Intracellular flux distributions for both metabolic states were estimated by MFA using the isotopic information and extracellular rate measurements as constraints. The model was subsequently checked with the consistency index method. From a biological point of view, the occurrence of the two physiological states appears to be correlated with the presence or absence of extracellular glutamate. Concerning the model, it can be stated that the metabolic network and the set of constraints adopted provide a consistent and robust characterization of the astrocytic metabolism, allowing for the calculation of central intracellular fluxes such as pyruvate recycling, the anaplerotic flux mediated by pyruvate carboxylase, and the glutamine formation through glutamine synthetase.

Assay of the pyruvate dehydrogenase complex by coupling with recombinant chicken liver arylamine N-acetyltransferase

The activity of the pyruvate dehydrogenase complex has long been determined in some laboratories by coupling the production of acetyl-coenzyme A (acetyl-CoA) to the acetylation of 4-aminoazobenzene-4'-sulfonic acid by arylamine N-acetyltransferase. The assay has some advantages, but its use has been limited by the need for large amounts of arylamine N-acetyltransferase. Here we report production of recombinant chicken liver arylamine N-acetyltransferase and optimization of its use in miniaturized assays for the pyruvate dehydrogenase complex and its kinase.

Effect of short-term sprint interval training on human skeletal muscle carbohydrate metabolism during exercise and time-trial performance

Our laboratory recently showed that six sessions of sprint interval training (SIT) over 2 wk increased muscle oxidative potential and cycle endurance capacity (Burgomaster KA, Hughes SC, Heigenhauser GJF, Bradwell SN, and Gibala MJ. J Appl Physiol 98: 1895–1900, 2005). The present study tested the hypothesis that short-term SIT would reduce skeletal muscle glycogenolysis and lactate accumulation during exercise and increase the capacity for pyruvate oxidation via pyruvate dehydrogenase (PDH). Eight men [peak oxygen uptake (V̇o2 peak) = 3.8 ± 0.2 l/min] performed six sessions of SIT (4–7 × 30-s “all-out” cycling with 4 min of recovery) over 2 wk. Before and after SIT, biopsies (vastus lateralis) were obtained at rest and after each stage of a two-stage cycling test that consisted of 10 min at ∼60% followed by 10 min at ∼90% of V̇o2 peak. Subjects also performed a 250-kJ time trial (TT) before and after SIT to assess changes in cycling performance. SIT increased muscle glycogen content by ∼50% (main effect, P = 0.04) and the maximal activity of citrate synthase (posttraining: 7.8 ± 0.4 vs. pretraining: 7.0 ± 0.4 mol·kg protein −1·h−1; P = 0.04), but the maximal activity of 3-hydroxyacyl-CoA dehydrogenase was unchanged (posttraining: 5.1 ± 0.7 vs. pretraining: 4.9 ± 0.6 mol·kg protein −1·h−1; P = 0.76). The active form of PDH was higher after training (main effect, P = 0.04), and net muscle glycogenolysis (posttraining: 100 ± 16 vs. pretraining: 139 ± 11 mmol/kg dry wt; P = 0.03) and lactate accumulation (posttraining: 55 ± 2 vs. pretraining: 63 ± 1 mmol/kg dry wt; P = 0.03) during exercise were reduced. TT performance improved by 9.6% after training (posttraining: 15.5 ± 0.5 vs. pretraining: 17.2 ± 1.0 min; P = 0.006), and a control group ( n = 8, V̇o2 peak = 3.9 ± 0.2 l/min) showed no change in performance when tested 2 wk apart without SIT (posttraining: 18.8 ± 1.2 vs. pretraining: 18.9 ± 1.2 min; P = 0.74). We conclude that short-term SIT improved cycling TT performance and resulted in a closer matching of glycogenolytic flux and pyruvate oxidation during submaximal exercise.

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.

Mitochondrial tRNA gene mutations in patients having mitochondrial disease with lactic acidosis

Lactic acidosis has been associated with a variety of clinical conditions and can be due to mutation in nuclear or mitochondrial genes. We performed mutations screening of all mitochondrial tRNA genes in 44 patients who referred as hyperlactic acidosis. Patients showed heterogeneous phenotypes including Leigh disease in four, MELAS in six, unclassified mitochondrial myopathy in 10, cardiomyopathy in five, MERRF in one, pure lactic acidosis in six, and others in 12 including facio-scaplo-femoral muscular dystrophy (FSFD), familial cerebellar ataxia, recurrent Reye syndrome, cerebral palsy with mental retardation. We measured enzymatic activities of pyruvate dehydrogenase complex, and respiratory chain enzymes. All mitochondrial tRNA genes and known mutation of ATPase 6 were studied by single strand conformation polymorphism (SSCP), automated DNA sequence and PCR-RFLP methods. We have found one patient with PDHC deficiency and six patients with Complex I+IV deficiency, though the most of the patients showed subnormal to deficient state of respiratory chain enzyme activities. We have identified one of the nucleotide changes in 29 patients. Single nucleotide changes in mitochondrial tRNA genes are found in 27 patients and one in ATPase 6 gene in two patients. One of four pathogenic point mutations (A3243G, C3303T, A8348G, and T8993G) was identified in 12 patients who showed the phenotype of Leigh syndrome, MELAS, cardimyopathy and cerebral palsy with epilepsy. Seventeen patients have one of the normal polymorphisms in the mitochondrial tRNA gene reported before. SSCP and PCR-RFLP could detect the heteroplasmic condition when the percentage of mutant up to 5, however, it cannot be observed by direct sequencing method. It is important to screen the mtDNA mutation not only by direct sequence but also by PCR-RFLP and the other sensitive methods to detect the heroplasmy when lactic acidosis has been documented in the patients who are not fulfilled the criteria of mitochondrial disorders.

Carbohydrate metabolism during prolonged exercise and recovery: interactions between pyruvate dehydrogenase, fatty acids, and amino acids

During prolonged exercise, carbohydrate oxidation may result from decreased pyruvate production and increased fatty acid supply and ultimately lead to reduced pyruvate dehydrogenase (PDH) activity. Pyruvate also interacts with the amino acids alanine, glutamine, and glutamate, whereby the decline in pyruvate production could affect tricarboxycylic acid cycle flux as well as gluconeogenesis. To enhance our understanding of these interactions, we studied the time course of changes in substrate utilization in six men who cycled at 44+/-1% peak oxygen consumption (mean+/-SE) until exhaustion (exhaustion at 3 h 23 min+/-11 min). Femoral arterial and venous blood, blood flow measurements, and muscle samples were obtained hourly during exercise and recovery (3 h). Carbohydrate oxidation peaked at 30 min of exercise and subsequently decreased for the remainder of the exercise bout (P<0.05). PDH activity peaked at 2 h of exercise, whereas pyruvate production peaked at 1 h of exercise and was reduced (approximately 30%) thereafter, suggesting that pyruvate availability primarily accounted for reduced carbohydrate oxidation. Increased free fatty acid uptake (P<0.05) was also associated with decreasing PDH activity (P<0.05) and increased PDH kinase 4 mRNA (P<0.05) during exercise and recovery. At 1 h of exercise, pyruvate production was greatest and was closely linked to glutamate, which was the predominant amino acid taken up during exercise and recovery. Alanine and glutamine were also associated with pyruvate metabolism, and they comprised approximately 68% of total amino-acid release during exercise and recovery. Thus reduced pyruvate production was primarily associated with reduced carbohydrate oxidation, whereas the greatest production of pyruvate was related to glutamate, glutamine, and alanine metabolism in early exercise.

Focused proteomics: towards a high throughput monoclonal antibody-based resolution of proteins for diagnosis of mitochondrial diseases

The availability of monoclonal antibodies (mAbs) against the proteins of the oxidative phosphorylation chain (OXPHOS) and other mitochondrial components facilitates the analysis and ultimately the diagnosis of mitochondrially related diseases. mAbs against each of the five complexes and pyruvate dehydrogenase (PDH) are the basis of a rapid and simple immunocytochemical approach [Hanson, B.J., Capaldi, R.A., Marusich, M.F. and Sherwood, S.W., J. Histochem. Cytochem. 50 (2002) 1281-1288]. This approach can be used to detect if complexes have altered assembly in mitochondrial disease due to mutations in nuclear encoded genes, such as in Leigh's disease, or in mitochondrially encoded genes, e.g., MELAS. Other mAbs have recently been obtained that can immunocapture each of the five OXPHOS complexes, PDH and the adenine nucleotide translocase (ANT) from very small amounts of tissue such as that obtained from cell culture or needle biopsies from patients. When adapted to a 96-well plate format, these mAbs allow measurement of the specific activity of each of the mitochondrial components individually and analysis of their subunit composition and state of posttranslational modification. The immunocapture protocol should be useful not only in the analysis of genetic mitochondrial diseases but also in evaluating and ultimately diagnosing late-onset mitochondrial disorders including Parkinson's disease, Alzheimer's disease, and late-onset diabetes, which are thought to result from accumulated oxidative damage to mitochondrial proteins such as the OXPHOS chain.

Transmission and prenatal diagnosis of the T9176C mitochondrial DNA mutation

A family presented with three affected children with Leigh syndrome, a progressive neurodegenerative disorder. Analysis of the OXPHOS complexes in muscle of two affected patients showed an increase in activity of pyruvate dehydrogenase and a decrease of complex V activity. Mutation analysis revealed the T9176C mutation in the mtATPase 6 gene (OMIM 516060) and the mutation load was above 90% in the patients. Unaffected maternal relatives were tested for carrier-ship and one of them, with a mutation load of 55% in blood, was pregnant with her first child. The possibility of prenatal diagnosis was evaluated. The main problem was the lack of data on genotype-phenotype associations for the T9176C mutation and on variation of the mutation percentage in tissues and in time. Therefore, multiple tissues of affected and unaffected carriers were analysed. Eventually, prenatal diagnosis was offered with understanding by the couple that there could be considerable uncertainty in the interpretation of the results. Prenatal diagnosis was carried out twice on cultured and uncultured chorion villi and amniotic fluid cells. The result was a mutation percentage just below the assumed threshold of expression (90%). The couple decided to continue the pregnancy and an apparently healthy child was born with an as yet unclear prognosis. This is the first prenatal diagnosis for a carrier of the T9176C mutation. Prenatal diagnosis for this mutation is technically reliable, but the prognostic predictions are not straightforward.

Extensive homology between the major immunodominant mitochondrial antigen in primary biliary cirrhosis and Helicobacter pylori does not lead to immunological cross-reactivity

BACKGROUND

Primary biliary cirrhosis (PBC) is an immune-mediated chronic cholestatic disease characterized by the presence of antibodies directed predominantly against the E2 subunit of the pyruvate dehydrogenase complex (PDC-E2). What provokes tolerance breakdown in PBC remains to be established, though there is evidence to indicate that microbes may induce anti-mitochondrial antibodies (AMA) through a mechanism of molecular mimicry.

METHODS

Having found that urease beta (UREB)(22-36) antigen of Helicobacter pylori (HELPY) shares extensive (87%) similarity with PDC-E2(212-226), the major mitochondrial autoepitope, it was hypothesized that this would also lead to cross-reactivity. The UREB/PDC-E2 mimics were thus constructed and tested by ELISA in 112 PBC patients and 114 controls.

RESULTS

Reactivity to PDC-E2(212-226) was found in 104 patients but to UREB(22-36) in only 2. In these two patients, the double reactivity was not cross-reactive. The lack of surface antibody accessibility to UREB(22-36), as demonstrated through three-dimensional model prediction analysis, may explain this unexpected finding. There was some speculation on whether HELPY UREB(22-36) might act as a cross-reactive CD4 T-cell epitope. All seven PBC patients, tested in a standard proliferation assay against PDC-E2(212-226), gave a positive response. All seven were unresponsive to HELPY UREB(22-36). The pattern of reactivity to HELPY antigens by immunoblot was similar between anti-PDC-E2-positive and negative PBC cases, as well as between PBC patients and controls.

CONCLUSION

Contrary to common belief, extensive sequence homology (molecular mimicry) between self and microbe does not necessarily result in cross-reactivity. It is therefore likely that, when present, cross-reactivity between self and microbes is of biological importance.

Apoptosis as a mechanism for cell surface expression of the autoantigen pyruvate dehydrogenase complex

A number of antigens implicated in the pathogenesis of autoimmune diseases including Sjogren's syndrome and systemic lupus erythematosus (SLE) are expressed aberrantly by apoptotic cells. It is also known that apoptogenic proteins are released from the mitochondrial intermembrane space at an early stage during the induction and development of apoptosis. Combination of this evidence led us to test the hypothesis that apoptotic mechanisms provide an explanation for the abnormal expression of the inner mitochondrial enzyme, pyruvate dehydrogenase complex (PDC), observed on the surface of some cells in patients with the autoimmune liver disease primary biliary cirrhosis (PBC). Using one murine and two human cell lines it was found that the induction of apoptosis led to early detection of PDC within the cytoplasm. However, cytochrome c oxidase subunit 4 (COX 4), which is also present on the inner surface of the inner mitochondrial membrane, remained within the mitochondria. Immunoreactive PDC was also detected on the outer surface of the intact plasma membrane of cells sampled after the induction of apoptosis. Serial release of PDC to the cytoplasm and then onto the external surface of the plasma membrane provides direct evidence that the antigen on the cell surface is of mitochondrial origin. Immunoreactivity specific for PDC is strongly implicated in the pathogenesis of PBC, but this autoantigen is normally concealed from the immune system by three membrane systems. Release of PDC onto the cell surface during apoptosis provides a possible route for recognition of this antigen by the immune system which could contribute to both afferent and efferent phases of the disease process.

[Cloning and expressing the E2 subunit of pyruvate dehydrogenase complex]

OBJECTIVES

To construct the expression vector of the pyruvate dehydrogenase complex E2 subunit gene (PDC-E2).

METHODS

The PDC-E2 gene was amplified from human lymphocytes with RT-PCR, and was cloned into pExSecI vector to induce the PDC-E2 expression. The products were identified with western blot and ELISA.

RESULTS

The expression vector pExSecI/PDC-E2 was successfully constructed. The products could be identified by the specific self-antibodies in the sera from the primary biliary cirrhosis patients.

CONCLUSION

High efficient expression vector of PDC-E2 lays the foundation for serum assay of primary biliary cirrhosis patients with prokaryotic expressing PDC-E2.

Thiamine deficiency results in downregulation of the GLAST glutamate transporter in cultured astrocytes

Pyrithiamine-induced thiamine deficiency (TD) is a well-established model of Wernicke's encephalopathy in which a glutamate-mediated excitotoxic mechanism may play an important role in determining selective vulnerability. In order to examine this possibility, cultured astrocytes were exposed to TD and effects on glutamate transport and metabolic function were studied. TD led to decreases in cellular levels of thiamine and thiamine diphosphate (TDP) after 24 h of treatment and decreased activities of the TDP-dependent enzymes alpha-ketoglutarate dehydrogenase and transketolase after 4 and 7 days, respectively. TD treatment for 10 days led to a reversible decrease in the uptake of [(3)H]-D-aspartate, a nonmetabolizable analogue of glutamate. Kinetic analysis revealed that the uptake inhibition was caused by a 47% decrease in the V(max) for uptake of [(3)H]-D-aspartate, with no change in the K(m) value. Immunoblotting showed that this decrease in uptake was due to an 81% downregulation of the astrocyte-specific GLAST glutamate transporter. Loss of uptake activity and GLAST protein were blocked by treatment with the protein kinase C inhibitor H7, while exposure to DCG IV, a group II metabotropic glutamate receptor (mGluR) agonist, resulted in improvement of [(3)H]-D-aspartate uptake and a partial reversal of transporter downregulation. These results are consistent with our recent in vivo findings of a loss of astrocytic glutamate transporters in TD and provide evidence that TD conditions may increase phosphorylation of GLAST, contributing to its downregulation. In addition, manipulation of group II mGluR activity may provide an important strategy in the treatment of this disorder.

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.

Correlation between histopathological findings of the liver and IgA class antibodies to 2-oxo-acid dehydrogenase complex in primary biliary cirrhosis

Although anti-mitochondrial antibody (AMA) is the characteristic serological feature of primary biliary cirrhosis (PBC), its pathogenetic role remains unclear. We tested sera from 72 Japanese patients with histologically confirmed PBC for AMA by indirect immunofluorescence, anti-pyruvate dehydrogenase complex (PDC) by enzyme inhibition assay, immunoglobulin (Ig) G class anti-PDC by ELISA, and IgG, IgM, and IgA class anti-2-oxo-acid dehydrogenase complex (2-OADC) by immunoblotting. Of the 72 sera, 60 (83%), 50 (69%), 42 (58%), and 71 (99%) were positive for AMA by immunofluorescence, enzyme inhibition assay, ELISA, and immunoblotting, respectively. There was no significant correlation between histological stages and AMA by immunofluorescence, PDC inhibitory antibodies by enzyme inhibition assay, IgG class anti-PDC antibodies by ELISA, or IgG and IgM class anti-2-OADC by immunoblotting. IgA class anti-2-OADC by immunoblotting was more frequent in stages 2-4 than in stage 1 (P = 0.0083). Of the IgA class anti-2-OADC, anti-PDC-E2 (74 kDa) and anti-E3BP (52 kDa) were more frequent in stages 2-4 than in stage 1 (P = 0.0253 and 0.0042, respectively). Further examination of histopathological findings in 53 of 72 liver biopsy specimens showed that IgA class anti-PDC-E2 and IgA class anti-E3BP were associated with bile duct loss, and IgA class anti-PDC-E2 was also associated with interface hepatitis and atypical ductular proliferation. IgA is known to be secreted into the bile through biliary epithelial cells, implying that IgA class anti-PDC-E2 and E3BP may have a specific pathogenetic role during their transport into the bile by binding to their target antigen(s) in biliary epithelial cells, and this may be followed by dysfunction and finally destruction of biliary epithelial cells. Our present results suggest that these autoantibodies against 2-OADC detected by immunoblotting may be associated with the pathogenesis and pathologic progression of PBC.

Apparent mitochondrial asymmetry in Xenopus eggs

Cell polarity is manifest along the animal/vegetal axis in eggs of the frog, Xenopus laevis. Along this axis, maternal cytoplasmic components are asymmetrically distributed and are thought to underlie specification of distinct cell fates. To ascertain the molecular identities of such cytoplasmic components, we have used a monoclonal antibody that specifically stains the vegetal hemisphere of Xenopus eggs. The antigenic protein Vp67 (vegetal protein of 67 kDa) was identified through purification and cloning as a Xenopus homolog of the mitochondrial protein dihydrolipoamide acetyltransferase, a component of the pyruvate dehydrogenase complex. The identification of Vp67 as a mitochondrial protein could indicate that populations of mitochondria are asymmetrically distributed in Xenopus eggs.

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.

Molecular cloning, and characterization and expression of dihydrolipoamide acetyltransferase component of murine pyruvate dehydrogenase complex in bile duct cancer cells

BACKGROUND

The association between the dihydrolipoamide acetyltransferase component (E2) of pyruvate dehydrogenase complex (PDC) and primary biliary cirrhosis (PBC) is clinically established. However, the detailed pathological function of the PDC-E2 gene is as yet unclear. In order to study the gene function in knockout and transgenic mouse models, we cloned and characterized the mouse PDC-E2 (mPDC-E2) gene. Because the expression level of PDC-E2 was elevated in PBC bile duct cells, we tried to construct a bile duct carcinoma cell line that overexpressed PDC-E2 as a PBC cell model.

METHODS

The mPDC-E2 cDNA was obtained by the 3'Race method. We overexpressed this gene in KMBC cells, using a retrovirus vector. The transcript and translated protein of mPDC-E2 were detected by Northern blot and Western blot, respectively.

RESULTS

The deduced amino-acid sequence from the cloned cDNA indicated that the fully mature protein consisted of 557 amino-acid residues, with a calculated molecular mass of 59kD. This mature protein was highly consistent with those of previously reported rat and human PDC-E2, which possessed three structurally identifiable regions: the lipoyl-bearing domain, the E3-binding site, and the catalytic domain. Mouse fibroblast NIH3T3 cells expressed one species of mPDC-E2 mRNA, 3.5kb in length. We also successfully constructed a stable KMBC cell line overexpressing the PDC-E2.

CONCLUSIONS

This is the first report of the mPDC-E2 sequence and is valuable for further investigation of PDC-E2 gene function in transgenic or knockout mouse models. The PDC-E2 overexpressing KMBC cell line can be used to study alterations in signal transduction or gene expression profiles in PBC bile duct.

Thiamine-responsive pyruvate dehydrogenase deficiency in two patients caused by a point mutation (F205L and L216F) within the thiamine pyrophosphate binding region

The human pyruvate dehydrogenase complex (PDHC) catalyzes the thiamine-dependent decarboxylation of pyruvate. Thiamine treatment is very effective for some patients with PDHC deficiency. Among these patients, five mutations of the pyruvate dehydrogenase (E1)alpha subunit have been reported previously: H44R, R88S, G89S, R263G, and V389fs. All five mutations are in a region outside the thiamine pyrophosphate (TPP)-binding region of the E1alpha subunit. We report the biochemical and molecular analysis of two patients with clinically thiamine-responsive lactic acidemia. The PDHC activity was assayed using two different concentrations of TPP. These two patients displayed very low PDHC activity in the presence of a low (1 x 10(-4) mM) TPP concentration, but their PDHC activity significantly increased at a high (0.4 mM) TPP concentration. Therefore, the PDHC deficiency in these two patients was due to a decreased affinity of PDHC for TPP. Treatment of both patients with thiamine resulted in a reduction in the serum lactate concentration and clinical improvement, suggesting that these two patients have a thiamine-responsive PDHC deficiency. The DNA sequence of these two male patients' X-linked E1alpha subunit revealed a point mutation (F205L and L216F) within the TPP-binding region in exon 7.

Bcl-2-dependent oxidation of pyruvate dehydrogenase-E2, a primary biliary cirrhosis autoantigen, during apoptosis

The close association between autoantibodies against pyruvate dehydrogenase-E2 (PDC-E2), a ubiquitous mitochondrial protein, and primary biliary cirrhosis (PBC) is unexplained. Many autoantigens are selectively modified during apoptosis, which has focused attention on apoptotic cells as a potential source of "neo-antigens" responsible for activating autoreactive lymphocytes. Since increased apoptosis of bile duct epithelial cells (cholangiocytes) is evident in patients with PBC, we evaluated the effect of apoptosis on PDC-E2. Autoantibody recognition of PDC-E2 by immunofluorescence persisted in apoptotic cholangiocytes and appeared unchanged by immunoblot analysis. PDC-E2 was neither cleaved by caspases nor concentrated into surface blebs in apoptotic cells. In other cell types, autoantibody recognition of PDC-E2, as assessed by immunofluorescence, was abrogated after apoptosis, although expression levels of PDC-E2 appeared unchanged when examined by immunoblot analysis. Both overexpression of Bcl-2 and depletion of glutathione before inducing apoptosis prevented this loss of autoantibody recognition, suggesting that glutathiolation, rather than degradation or loss, of PDC-E2 was responsible for the loss of immunofluorescence signal. We postulate that apoptotic cholangiocytes, unlike other apoptotic cell types, are a potential source of immunogenic PDC-E2 in patients with PBC.

Neuronal subclass-selective loss of pyruvate dehydrogenase immunoreactivity following canine cardiac arrest and resuscitation

Chronic impairment of aerobic energy metabolism accompanies global cerebral ischemia and reperfusion and likely contributes to delayed neuronal cell death. Reperfusion-dependent inhibition of pyruvate dehydrogenase complex (PDHC) enzyme activity has been described and proposed to be at least partially responsible for this metabolic abnormality. This study tested the hypothesis that global cerebral ischemia and reperfusion results in the loss of pyruvate dehydrogenase immunoreactivity and that such loss is associated with selective neuronal vulnerability to transient ischemia. Following 10 min canine cardiac arrest, resuscitation, and 2 or 24 h of restoration of spontaneous circulation, brains were either perfusion fixed for immunohistochemical analyses or biopsy samples were removed for Western immunoblot analyses of PDHC immunoreactivity. A significant decrease in immunoreactivity was observed in frontal cortex homogenates from both 2 and 24 h reperfused animals compared to samples from nonischemic control animals. These results were supported by confocal microscopic immunohistochemical determinations of pyruvate dehydrogenase immunoreactivity in the neuronal cell bodies located within different layers of the frontal cortex. Loss of immunoreactivity was greatest for pyramidal neurons located in layer V compared to neurons in layers IIIc/IV, which correlates with a greater vulnerability of layer V neurons to delayed death caused by transient global cerebral ischemia.

Outcome of thiamine treatment in a child with Leigh disease due to thiamine-responsive pyruvate dehydrogenase deficiency

We describe a child with severe psychomotor retardation, peripheral neuropathy and bilateral abnormal signal in basal ganglia on magnetic resonance imaging, consistent with Leigh disease. Fibroblast pyruvate dehydrogenase assayed with routine method was normal. However, because of neurological improvement after treatment with thiamine, pyruvate dehydrogenase activity was studied again with thiamine pyrophosphate concentration adjusted to the normal human tissue level and found to be deficient. We report here on diagnostic difficulties and clinical follow-up of this patient.

Primary biliary cirrhosis an epithelitis: evidence of abnormal salivary gland immunohistochemistry

Primary biliary cirrhosis (PBC) is an autoimmune liver disease of unknown etiology. Nearly 93% of patients with PBC exhibit evidence of focal sialoadenitis. In an earlier study, we reported evidence of aberrant expression of PDC-E2, or a mimeotope, in the salivary glands of patients with PBC that had Sjogren's syndrome. At the time of the previous study, data was not yet available regarding patients with PBC without sicca complaints. Therefore, to investigate the extent of salivary gland involvement in PBC, we collected lip biopsy sections from 9 PBC patients diagnosed as PBC by liver biopsy, without clinical or histologic features of Sjogren's syndrome and 9 PBC patients with established Sjogren's syndrome. Using immunohistochemical staining with both a murine monoclonal antibody. C355.1, and a human combinatorial antibody, SP4, we examined the ducts of these salivary glands for the presence of the characteristic aberrant staining pattern found in patients with PBC. We report that 6/9 PBC patients fulfilling established Sjogren's syndrome criteria and 6/9 PBC patients lacking features of Sjogren's syndrome showed intense staining of the ductal epithelial cells of the salivary gland. These data suggest that the PBC-specific antigen recognized by C355.1 and SP4 in bile duct epithelial cells is expressed aberrantly in the salivary gland in 66% of patients with PBC, independent of Sjogren's syndrome. This finding suggests a common disease process in these two tissues. Further, expression of this molecule may be an early marker of salivary gland involvement in patients with PBC.

Pyruvate dehydrogenase complex deficiency and absence of subunit X

The pyruvate dehydrogenase complex (PDHc) is a multienzyme complex consisting of three catalytic and two regulatory enzymes, as well as a less well defined subunit called protein X. PDHc deficiency is a common cause of congenital lactic acidosis. Most patients with PDH deficiency have a mutation in the alpha chain of the PDH E1 enzyme. Very few patients have been described in whom the basic defect of a PDH deficiency is situated in the X protein. We studied a boy with severe lactic acidosis and developmental delay in whom a deficiency of PDH activity led to further investigations. Immunochemical analysis with anti-PDHc antibodies demonstrated an absence of the X component. This report is the fourth family in which an abnormal protein X has been found. In cases with PDH deficiency where no mutation of the PDHE1 alpha gene is found, further investigations by means of immunoblotting with specific antibodies against the different subunits should be performed.

Immunohistochemical evidence of disease recurrence after liver transplantation for primary biliary cirrhosis

Whether primary biliary cirrhosis (PBC) recurs after liver transplantation has remained an interesting and controversial issue; rejection, viral hepatitis, and drug effects all may mimic recurrent PBC histologically and biochemically. Furthermore, reliable clinical criteria for PBC recurrence are lacking. In this study, the issue of disease recurrence using a well-characterized monoclonal antibody (MAb), C355.1, that reacts with the immunodominant mitochondrial autoantigen of PBC (pyruvate dehydrogenase complex [PDC-E2]) was addressed. When used in an immunohistochemical assay, C355.1 produces intense apical staining of bile duct epithelium specifically in liver sections of patients with PBC and may be the earliest known marker of PBC. Immunohistochemical and histological analysis of serial liver biopsy specimens of 67 patients pre- and post-orthotopic liver transplantation (OLT), including 38 patients with PBC and 29 non-PBC liver disease controls, was performed. Sections were stained with MAb C355.1 or the control MAb C315 and analyzed to determine whether there was a recurrence of apical reactivity in the bile ducts of the posttransplantation biopsy specimens. The immunohistochemical staining was correlated with the histological findings and serum biochemistries at the time of the biopsy. Our data indicate that a significant number of patients who underwent transplantation for PBC (28 of 38) but not controls (0 of 29) develop a staining pattern of liver bile duct epithelium with MAb C355.1 that is indistinguishable from the pretransplantation pattern. Of the 28 patients with this apical staining pattern, 8 were characterized histologically as possible recurrent PBC, 2 as chronic rejection, 2 as acute rejection, 9 as nonspecific changes, 4 as normal or near normal, and 3 had other histological changes. Only 50% of the patients with apical C355.1 staining had liver enzyme levels suggestive of cholestasis. Thus, there appears to be immunohistochemical evidence that supports the concept of recurrence of PBC after OLT. The appearance of biliary epithelial abnormalities before the clinical appearance of disease is important not only for liver transplantation but also for understanding the natural history of PBC.

Different distribution of dihydrolipoamide succinyltransferase, dihydrolipoamide acetyltransferase and ATP synthase beta-subunit in monkey brain

The distribution of three mitochondrial enzymes: dihydrolipoamide succinyltransferase, dihydrolipoamide acetyltransferase, and beta-subunit of ATP synthase, were examined in the nucleus basalis of Meynert, substantia nigra, locus coeruleus, hippocampus, and cerebral cortex of monkey brain by immunocytochemical staining. Dihydrolipoamide succinyltransferase and dihydrolipoamide acetyltransferase had parallel distribution in the substantia nigra, but dihydrolipoamide acetyltransferase was rich in the locus coeruleus, nucleus basalis of Meynert, and especially in the hippocampus in comparison with dihydrolipoamide succinyltransferase. The ATP synthase beta-subunit was strikingly rich in many neurons of the locus coeruleus and cerebral cortex in comparison with dihydrolipoamide acetyltransferase and dihydrolipoamide succinyltransferase. These results show that these mitochondrial enzymes are not expressed synchronously in the neurons of brain, suggesting the differential regulation of mitochondrial enzymes and the heterogeneity of mitochondria.

The effects of the inhibition of fatty acid oxidation on pyruvate dehydrogenase complex activity in tissues of lean and obese mice

OBJECTIVE

To investigate the effects of an acute dose of the fatty acid oxidation inhibitor, Etomoxir, on the activity of the pyruvate dehydrogenase complex (PDHC) in different tissues in lean and obese mice.

DESIGN

An acute dose of Etomoxir was given to mice in which obesity had been induced by an injection of gold thioglucose and to age-matched controls. The effects of time, dose and nutritional state were studied.

MEASUREMENTS

PDHC activity in heart, quadricaps muscle, liver and white adipose tissue, glycogen content of liver and quadricaps muscle, serum glucose and insulin were measured in fed and fasted animals and in fasted animals after the ingestion of a glucose load.

RESULTS

Etomoxir caused an increase in the activity of the active form of the PDHC (PDHCa) in the heart, liver and WAT of fed lean mice and in the heart and liver of fed obese mice. In fasted mice, increased PDHCa was seen in the heart of lean mice and in the liver of obese mice. Etomoxir increased the PDHC response to an oral glucose challenge in the liver and WAT of lean mice and in the liver of obese mice. Etomoxir had no effect on PDHCa in quadricaps muscle. Serum glucose levels were decreased in fasted mice with no change in the fed mice. Etomoxir decreased liver glycogen content in both fed and fasted animals and inhibited the accumulation of muscle glycogen following the glucose load.

CONCLUSIONS

Acute inhibition of fatty acid oxidation results in tissue specific increases in PDHCa. Improvements in glucose oxidation in tissues other than skeletal muscle may contribute to the improved glucose tolerance seen following acute Etomoxir administration.

Deficiency of respiratory chain complex I is a common cause of Leigh disease

We reviewed the clinical features and etiologies of Leigh disease in 66 patients from 60 pedigrees. Biochemical or molecular defects were identified in 50% of all pedigrees, and in 74% of the 19 pedigrees with pathologically proved Leigh disease. Isolated deficiency of respiratory chain complex I was found in 7 patients, though the complex was only assayed in 25 patients, making this the second most common biochemical abnormality after complex IV deficiency. Mutations at residue 8993 of mitochondrial DNA were found in only 2 patients. No correlation was found between the clinical features and etiologies. No defects were identified in the 8 patients with normal lactate concentrations in the cerebrospinal fluid.

Pyruvate dehydrogenase activity and malonyl CoA levels in normal and ischemic swine myocardium: effects of dichloroacetate

The purposes of this study were to: (1) assess myocardial pyruvate dehydrogenase (PDH) activity and substrate exchange under well-perfused and ischemic conditions; (2) determine the metabolic effects of an intra-coronary infusion of the PDH activator, dichloroacetate (DCA); and (3) measure the effects of ischemia and DCA on malonyl CoA levels. Experiments were performed in anesthetised open-chest swine under non-ischemic conditions, followed by 40 min with a 60% reduction in left anterior descending coronary artery (LAD) blood flow. Myocardial needle biopsies for measurement of PDH activity were taken after an intracoronary infusion of either saline or DCA (1 mM in LAD blood) under aerobic conditions, and after 37 min of ischemia. Pyruvate dehydrogenase activity was measured with and without maximal activation by swine PDH phosphatase. Malonyl CoA and acetyl CoA were measured after 40 min of LAD ischemia in myocardium from the ischemic DCA- or saline-treated LAD bed, and the non-ischemic untreated left circumflex coronary artery (CFX) perfusion bed. Net glucose, lactate and free fatty acid (FFA) uptakes were measured across the LAD perfusion bed throughout the study. Dichloroacetate treatment increased the amount of active dephosphorylated PDH to 88% of the total activity under aerobic conditions, compared to 55% with saline (P < 0.01). Ischemia did not significantly change PDH activation state in either group. Acetyl CoA and malonyl CoA contents were significantly elevated in ischemic DCA-treated myocardium compared to saline-treated ischemic myocardium. Dichloroacetate treatment significantly lowered rates of myocardial FFA uptake under both aerobic and ischemic conditions, but did not effect glucose uptake or lactate exchange. Free fatty acid uptake was negatively correlated to malonyl CoA levels (r = -0.68) during ischemia. It is proposed that the inhibition of FFA uptake observed with DCA in ischemic myocardium is due to malonyl CoA inhibition of carnitine palmitoyl transferase I.

Genetic and physiological characterization of a Rhizobium etli mutant strain unable to synthesize poly-beta-hydroxybutyrate

Rhizobium etli accumulates poly-beta-hydroxybutyrate (PHB) in symbiosis and in free life. PHB is a reserve material that serves as a carbon and/or electron sink when optimal growth conditions are not met. It has been suggested that in symbiosis PHB can prolong nitrogen fixation until the last stages of seed development, but experiments to test this proposition have not been done until now. To address these questions in a direct way, we constructed an R. etli PHB-negative mutant by the insertion of an Omega-Km interposon within the PHB synthase structural gene (phaC). The identification and sequence of the R. etli phaC gene are also reported here. Physiological studies showed that the PHB-negative mutant strain was unable to synthesize PHB and excreted more lactate, acetate, pyruvate, beta-hydroxybutyrate, fumarate, and malate than the wild-type strain. The NAD+/NADH ratio in the mutant strain was lower than that in the parent strain. The oxidative capacity of the PHB-negative mutant was reduced. Accordingly, the ability to grow in minimal medium supplemented with glucose or pyruvate was severely diminished in the mutant strain. We propose that in free life PHB synthesis sequesters reductive power, allowing the tricarboxylic acid cycle to proceed under conditions in which oxygen is a limiting factor. In symbiosis with Phaseolus vulgaris, the PHB-negative mutant induced nodules that prolonged the capacity to fix nitrogen.

Pyruvate and hepatic pyruvate dehydrogenase levels in rat strains sensitive and resistant to dietary obesity

This study compared the effects of exogenous pyruvate and lactate on the serum levels of pyruvate, lactate, glucose, alanine, and insulin, as well as the activity of hepatic pyruvate dehydrogenase (PDH) in strains of rat that were either sensitive [Osborne-Mendel (OM)] or resistant (S5B/Pl) to high-fat diet-induced obesity. Serum pyruvate and lactate were significantly higher and glucose lower in ad libitum-fed OM rats, but these differences disappeared after an 18-h fast. The increase in pyruvate and lactate after exogenous pyruvate administration was significantly greater in S5B/Pl rats than OM rats. There were no differences in serum alanine with strain or diet. The total PDH activity was similar across strains and diets but the proportion of PDH in its activated form (PDHa) was decreased in ad libitum-fed S5B/Pl rats. Pyruvate injection increased insulin and hepatic PDHa activity in OM rats fed both high- and low-fat diets, but these responses were greatly attenuated or absent in S5B/Pl rats. The data are consistent with the hypothesis that modulation of carbohydrate oxidation by PDH may be related to susceptibility to obesity when rats are fed a high-fat diet.

Glycine decarboxylase and pyruvate dehydrogenase complexes share the same dihydrolipoamide dehydrogenase in pea leaf mitochondria: evidence from mass spectrometry and primary-structure analysis

In order to compare the dihydrolipoamide dehydrogenase associated with the pyruvate dehydrogenase complex (E3) with that associated with the glycine decarboxylase complex (L-protein), we report for the first time the purification and characterization of the E3 component from pea leaf mitochondria. The first 30 amino acids of the N-terminal sequence of the mature E3 protein are identical with those of the mature L-protein of the glycine decarboxylase complex. Electrospray ionization-mass spectrometric analysis of E3 and the L-protein gave exactly the same molecular mass of 49,753 +/- 5 Da. We have also confirmed the primary structure of the L-protein, in particular the C-terminal sequence, deduced from the cDNA published by Bourguignon, Macherel, Neuburger and Douce [(1992) Eur. J. Biochem. 204, 865-873]. Western-blot analysis shows that specific polyclonal antibodies raised against the L-protein recognize specifically both E3 and L-protein but not the porcine dihydrolipoamide dehydrogenase. We conclude that, in pea leaf mitochondria, the pyruvate dehydrogenase and glycine decarboxylase complexes share the same dihydrolipoamide dehydrogenase. We have also confirmed by MS analysis that the FAD is not covalently bound to the enzyme.

Low-carbohydrate diet alters intracellular glucose metabolism but not overall glucose disposal in exercise-trained subjects

Dietary composition has been strongly implicated as an important determinant of in vivo insulin sensitivity. However, the metabolic alterations associated with extreme changes in diet have not been well described. We compared glucose metabolism after a standard diet ([STD] 35% fat, 51% carbohydrate, and 14% protein) with the effects of a 3-week adaptation to a low-carbohydrate, high-fat diet ([LCD] 75% fat, 8% carbohydrate, and 17% protein). Ten healthy men were studied using the euglycemic clamp technique, indirect calorimetry, and percutaneous vastus lateralis muscle biopsies for analysis of glycogen synthase (GS) and pyruvate dehydrogenase (PDH) activities in the basal and insulin-stimulated states. Insulin-stimulated glucose disposal was unchanged (STD 46.1 +/- 4.3 v LCD 46.0 +/- 4.3 mumol/kg.min, P = NS), but marked alterations in the routes of glucose disposal were noted. Insulin-stimulated glucose oxidation (Gox) was markedly reduced following LCD (STD 18.6 +/- 1.9 v LCD 8.23 +/- 1.9 mumol/kg.min, P = .0001), and nonoxidative glucose metabolism (Gnox) was enhanced by LCD (STD 24.9 +/- 0.9 v LCD 38.9 +/- 4.3 mumol/kg.min, P = .03). Following LCD, both the total and active forms of PDH (PDHt and PDHa) were significantly depressed. After LCD, GS activates (FV0.1, %I, and A0.5) were unaffected in the basal state, but were greater than for STD (P = .004) after insulin stimulation. The apparent increase in the sensitivity of GS to activation by insulin following LCD correlated strongly with maximal O2 consumption ([VO2max] r = .97, P = .001), suggesting that physical conditioning interacted with the metabolic impact of LCD. In summary, LCD did not induce changes in net glucose disposal.(ABSTRACT TRUNCATED AT 250 WORDS)

An improved spectrophotometric assay of pyruvate dehydrogenase in lactate dehydrogenase contaminated mitochondrial preparations from human skeletal muscle

In mitochondria-enriched preparations of human skeletal muscle, the measurement of pyruvate dehydrogenase activity, as determined by conventional spectrophotometric assay of NADH accumulation, is underestimated due to the oxidizing activity of the contaminating lactate dehydrogenase. Using a model reaction system consisting of varying mixtures of purified lactate and pyruvate dehydrogenases, we found that the presence of oxamate, a competitive inhibitor of the lactate dehydrogenase, allowed the measurement of a linear rate of pyruvate dehydrogenase activity without interference from lactate dehydrogenase. In the presence of 25 mM oxamate, this holds true up to a ratio of 30:1 for lactate to pyruvate dehydrogenases, respectively. A similar result was obtained when using human skeletal muscle mitochondria contaminated by lactate dehydrogenase. Rates of pyruvate dehydrogenase activity ranging from 50 to 120 nmol/min/mg protein could be routinely measured in such mitochondrial fractions. We concluded that the use of oxamate allows a spectrophotometric assay for pyruvate dehydrogenase activity to be utilized when screening for pyruvate dehydrogenase deficiency in mitochondria-enriched preparations of human skeletal muscle.

Immunohistochemical analysis of adhesion molecules in the micro-environment of portal tracts in relation to aberrant expression of PDC-E2 and HLA-DR on the bile ducts in primary biliary cirrhosis

We have examined immunohistochemically the expression of adhesion molecules in the micro-environment of portal tracts and their relationship to the expression of the pyruvate dehydrogenase E2 complex (PDC-E2) and HLA-DR in liver biopsy specimens. Ten cases of primary biliary cirrhosis (PBC) and 19 controls were examined, including four cases of extrahepatic biliary obstruction, six of chronic viral hepatitis, and nine normal livers. In PBC, the damaged small bile ducts demonstrated an increased expression of PDC-E2 and an aberrant expression of HLA-DR; about half of these damaged bile ducts also expressed intercellular adhesion molecules (ICAM)-1 and a few expressed vascular adhesion molecule (VCAM)-1. In addition, lymphocyte function-associated antigen (LFA)-1 and very late antigen (VLA)-4 were expressed on infiltrating lymphocytes around these bile ducts. In contrast, in control livers, these alterations in antigen expression on the bile ducts were either not observed or were only focal and weak, when present. These findings suggest that ICAM-1/LFA-1 and also VCAM-1/VLA-4 linkages between the damaged bile ducts and lymphocytes may facilitate antigen-specific reactions such as the presentation of antigens, possibly PDC-E2, to the periductal lymphocytes in PBC. ICAM-1, VCAM-1, and E-selectin were strongly expressed on the endothelial cells of some vessels in the portal tracts in PBC, suggesting the facilitation of the recruitment of lymphocytes around the bile ducts of PBC. VCAM-1, a member of the immunoglobulin superfamily, has not hitherto been reported on bile ducts.

Homogeneity of the pyruvate dehydrogenase multienzyme complex from Bacillus stearothermophilus

The pyruvate dehydrogenase multienzyme complex was purified from Bacillus stearothermophilus by means of six gel-filtration column chromatographies; once on Cellulofine GCL-2000, twice on Sepharose CL-2B, and three times on Sephacryl S-500HR. The molecular size distribution of the complex was examined in detail by gel-filtration chromatography, analytical and sucrose-density ultracentrifugations, and dynamic light scattering. The complex was found to be homogeneous; a dimeric complex was undetectable even with a high concentration of protein (below 6.8 mg/ml).

Hepatitic bile duct injuries in chronic hepatitis C: histopathologic and immunohistochemical studies

Interlobular bile ducts are reported to be damaged in viral hepatitis. Such damages are called hepatitic duct injuries and mimic chronic nonsuppurative destructive cholangitis of primary biliary cirrhosis. In this study, hepatitic bile duct injuries were evaluated histopathologically and immunohistochemically in 149 needle liver biopsy specimens from patients with chronic hepatitis C and compared immunohistochemically with primary biliary cirrhosis. Fifty-one of the needle biopsies from patients with chronic hepatitis C (34.2%) showed hepatitic bile duct injuries which were distributed focally in the liver and showed variable epithelial damages such as cytoplasmic swelling, vacuolation and acidophilia, nuclear pleomorphism, and loss of nuclear polarity. Some of the injured bile ducts were embedded within lymphoid aggregates, whereas others were surrounded by lymphocytes as well as other inflammatory cells to varied degrees. The majority of lymphoid cells around hepatitic bile duct injury were B- and T-cells mixed in various proportions, and activated T-cells were occasionally found within the biliary epithelial layer. Histopathologic and serial section studies disclosed that bile duct loss was rare in chronic hepatitis C. Statistical analysis revealed that advancement of chronic hepatitis and the degree of necroinflammatory processes of the liver, particularly in the portal tracts, were positively correlated with the occurrence of hepatitic bile duct injuries. Immunohistochemical studies demonstrated that, whereas strong ectopic expression of HLA-DR and enhanced expression of HLA-A,B,C, and pyruvate dehydrogenase E2-complex in biliary epithelial cells were frequently observed in chronic nonsuppurative destructive cholangitis of primary biliary cirrhosis, such unusual expressions were generally absent or mild, even if present, in bile duct injuries in chronic hepatitis C.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonsuppurative cholangitis is induced in neonatally thymectomized mice: a possible animal model for primary biliary cirrhosis

Neonatally thymectomized mice are unique in that they are prone to organ-specific autoimmune diseases. We investigated whether autoimmune cholangitis could be induced in these mice when they were immunized with biliary antigens. Neonatally thymectomized A/J mice were immunized with porcine intrahepatic bile duct epithelial cells (group 1), porcine gallbladder epithelial cells (group 2), porcine splenocytes (group 3) or Freund's adjuvant (group 4). Nonthymectomized mice were immunized with bile duct epithelial cells (group 5) or Freund's adjuvant (group 6). The cell suspensions were injected intraperitoneally with Freund's adjuvant once a week for 8 wk. In group 1 varying amounts of mononuclear cells infiltrated around the bile duct in 14 of 22 mice, whereas little or no accumulation was noted in other groups. Ultrastructural observations revealed that the inflammatory cells consisted of lymphocytes, plasma cells and macrophages. The bile duct showed degenerative changes and some lymphocytes infiltrated between bile duct epithelial cells. An immunohistochemical study showed that the accumulated lymphocytes consisted of CD4+ and CD8+ T cells, as well as B cells. Both major histocompatibility complex class I and class II antigens were expressed on bile duct epithelial cells. Antimitochondrial antibody was demonstrated in some mice in groups 1 (9 of 17), 2 (2 of 3) and 5 (4 of 5) by immunofluorescence; the antibody reacted with the 68, 52 and 47 kD polypeptides of the pyruvate dehydrogenase complex on Western blotting. These findings suggest that autoimmune cholangitis can be induced in neonatally thymectomized mice stimulated with biliary antigens and that these mice could be a suitable animal model for primary biliary cirrhosis.

Distribution of pyruvate dehydrogenase dihydrolipoamide acetyltransferase (PDC-E2) and another mitochondrial marker in salivary gland and biliary epithelium from patients with primary biliary cirrhosis

Previous studies in which quantitative immunofluorescence was used have shown that certain biliary epithelial cells in liver with primary biliary cirrhosis show increased levels of pyruvate dehydrogenase dihydrolipoamide acetyltransferase compared with controls. This study was designed to determine whether the increase in intensity of pyruvate dehydrogenase dihydrolipoamide acetyltransferase in biliary epithelial cells is accounted for by an increase in the number of mitochondria in the same cells. A double-antibody staining technique was used with antibodies specific for pyruvate dehydrogenase dihydrolipoamide acetyltransferase and another mitochondrial inner membrane marker, recognized by the mouse monoclonal antibody MCA151A. Distribution of the antigens was studied in sections of liver and salivary gland, an additional site that is frequently involved in primary biliary cirrhosis. Confocal microscopy was used to quantify the intensity of fluorescence resulting from binding of fluorochrome-labeled antibody. In both liver and salivary glands MCA151A binding was similar in normal and sections with primary biliary cirrhosis and corresponded to the predicted distribution of mitochondria in these tissues. In the liver staining was less intense in biliary epithelial cells than in hepatocytes. In salivary gland binding of both antibodies was predominantly localized to duct cells, with those forming striated ducts, known to be rich in mitochondria, being most intensely stained. There was high coincidence of the two antigens in salivary glands (p < 0.01) and in biliary epithelial cells from normal liver (p = 0.01). However, in liver with primary biliary cirrhosis, despite high coincidence between the antigens on hepatocytes, biliary epithelial cells showed high intensity of pyruvate dehydrogenase dihydrolipoamide acetyltransferase but not MCA151A.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose-fatty acid cycle operates in humans at the levels of both whole body and skeletal muscle during low and high physiological plasma insulin concentrations

Plasma non-esterified fatty acid concentrations were elevated acutely (Intralipid+heparin infusion) in 14 normal humans in order to study the effects of fatty acids on whole-body basal and insulin-stimulated glucose metabolism, and on activities of skeletal muscle key enzymes. Whole-body glucose metabolism was assessed using [3-3H]glucose and indirect calorimetry. Biopsies were taken from the vastus lateralis muscle during basal and insulin-stimulated (3 h, 40 mU.m-2.min-1) steady-state periods. Total peripheral glucose uptake was unaffected by Intralipid infusion in the basal state, whereas it decreased during Intralipid infusion in the hyperinsulinemic state (10.7 +/- 0.7 vs 8.7 +/- 0.8 mg.kg-1 fat-free mass.min-1, p < 0.02). Intralipid infusion decreased whole-body glucose oxidation in the basal state (1.3 +/- 0.2 vs 0.8 +/- 0.1 mg.kg-1 fat-free mass.min-1, p < 0.001) and during hyperinsulinemia (3.6 +/- 0.2 vs 1.7 +/- 0.2 mg.kg-1 fat-free mass.min-1 p < 0.001). Whole-body nonoxidative glucose uptake increased during Intralipid infusion in the basal state and was unaffected in the hyperinsulinemic state. The skeletal muscle pyruvate dehydrogenase activity ratio decreased in the basal state during Intralipid infusion (55 +/- 6 vs 43 +/- 5%, p < 0.05), whereas no statistical significant decrease in the pyruvate dehydrogenase activity ratio was observed during insulin infusion (57 +/- 8 vs 47 +/- 5%, NS). Insulin increased the activity of the active form of pyruvate dehydrogenase on the control day, but not during Intralipid infusion. Activities of phosphofructokinase and glycogen synthase were unaffected by Intralipid infusion. Plasma glucose concentrations were similar during Intralipid infusion and on the control day, whereas Intralipid infusion increased the muscle glucose content in the basal state (1.36 +/- 0.09 vs 1.77 +/- 0.12 mmol/kg dry wt, p < 0.05) and in the hyperinsulinemic state (1.23 +/- 0.09 vs 1.82 +/- 0.16 mmol/kg dry wt, p < 0.05). Insulin increased the muscle lactate content on the control day (6.50 +/- 0.95 vs 8.65 +/- 0.77 mmol/kg dry wt, p < 0.05), but not during Intralipid infusion. In conclusion, the glucose-fatty acid cycle operates in humans in vivo at the levels of both whole body and skeletal muscle during both low and high physiological insulin concentrations.

Defect in the lipoyl-bearing protein X subunit of the pyruvate dehydrogenase complex in two patients with encephalomyelopathy

Among the many metabolic encephalomyelopathies caused by deficiencies in the pyruvate dehydrogenase complex (PDHC), nearly all involve its E1 subunit. We describe two new familial cases of PDHC deficiency with encephalomyelopathy, chronic lactic acidemia, and a normal E1 subunit of PDHC but deficiency in another component. Activity of PDHC was measured in cultured skin fibroblasts and skeletal muscle, and immunoblot studies were performed on mitochondrial extracts from skin fibroblasts. Spectra of muscle tissue, obtained in vivo with phosphorus 31 nuclear magnetic resonance, were recorded both at rest and with exercise. The PDHC activity was markedly reduced to 10% to 20% of normal values in both cultured skin fibroblasts and skeletal muscle. Immunoblotting of skin fibroblast mitochondrial extracts showed a specific deficiency in the protein X component of PDHC but normal E1, E2, and E3 components. Spectra obtained with 31P nuclear magnetic resonance showed alterations compatible with those found in mitochondrial myopathies. This is the second description of an encephalomyelopathy associated with a specific absence of the lipoyl-containing protein X component, which has a structural role in the formation of a functional PDHC.

Proton spectroscopy in five patients with Leigh's disease and mitochondrial enzyme deficiency

Five children with Leigh's disease and progressive neurological symptoms were compared with 14 control children. In all patients, MRI showed bilateral lesions of the putamina and caudate heads. Serum lactate was normal for four of the children, and CSF lactate slightly elevated for three. Volume-selective proton MR spectroscopy (1H-MRS) of the basal ganglia in the Leigh patients revealed elevated lactate, giving further evidence for a defect of energy metabolism in the brain. 1H-MRS is an important tool for non-invasive brain tissue analysis in Leigh's disease, particularly in the absence of peripheral lactate elevation.

Intracellular glucose metabolism after long term metabolic control with glyburide: improved glucose oxidation with unchanged glycogen synthase activity

To determine whether improved metabolic control with long term glyburide treatment alters intracellular glucose metabolism independent of effects on glucose uptake (GU), we studied eight obese patients with noninsulin-dependent diabetes mellitus before and 7 months after glyburide therapy. Indirect calorimetry and skeletal muscle biopsies were performed in the basal state and during 300 pmol/m2.min insulin infusions, with glucose turnover rates determined by [3-3H]glucose turnover. During the glucose clamps, rates of GU were matched before and after treatment using equivalent hyperinsulinemia and variable levels of hyperglycemia. After glyburide treatment, rates of GU were decreased in the basal state [4.16 +/- 0.57 vs. 3.29 +/- 0.37 mg/kg fat free mass (FFM)/min; P < 0.05], but similar during glucose clamps (11.53 +/- 1.42 vs. 11.93 +/- 1.32 mg/kg FFM.min; P = NS) according to study design. In both the basal state and during glucose clamps after glyburide therapy, rates of glucose oxidative metabolism (Gox) increased by 68-78% [1.21 +/- 0.16 vs. 2.03 +/- 0.31 mg/kg FFM.min (P < 0.05) and 3.13 +/- 0.51 vs. 5.58 +/- 0.55 mg/kg FFM.min (P < 0.05), respectively], and rates of nonoxidative glucose metabolism decreased [2.96 +/- 0.68 vs. 1.25 +/- 0.21 mg/kg FFM.min (P < 0.05) and 8.40 +/- 1.50 to 6.30 +/- 1.40 mg/kg FFM.min (P < 0.01), respectively]. Circulating plasma FFA levels and rates of fat oxidation (Fox) remained unchanged in both the basal state and during clamp studies. Skeletal muscle glycogen synthase (GS) activity, expressed as fractional velocity, was unchanged by glyburide therapy (2.2 +/- 0.8 vs. 2.7 +/- 0.3% in the basal state and 7.3 +/- 1.8 vs. 6.1 +/- 0.9% during clamps; both P = NS). In summary, at both matched (during clamp studies) and unmatched (during basal studies) rates of GU, improved metabolic control with glyburide therapy resulted in marked improvement of Gox independent of the effects on GU. The improvement in Gox was not associated with changes in Fox, circulating FFA, or muscle GS activity. These data indicate that long term metabolic control achieved by glyburide therapy markedly improves Gox, but not skeletal muscle GS activity, in noninsulin-dependent diabetes mellitus independent of GU and Fox.

Autoreactive liver-infiltrating T cells in primary biliary cirrhosis recognize inner mitochondrial epitopes and the pyruvate dehydrogenase complex

Primary biliary cirrhosis (PBC) is characterized by lymphoid infiltrates in the portal tracts of the liver and the occurrence of antimitochondrial autoantibodies in serum directed against components of the pyruvate dehydrogenase complex and the other alpha-keto acid dehydrogenase complexes. These enzymes are located on the inner mitochondrial membrane. The destruction of the biliary tract in PBC is thought to be mediated by autoreactive liver-infiltrating T cells exerting cytotoxic activity or releasing certain lymphokines. In this study the reactivity of liver infiltrating T cells was shown to a bovine pyruvate dehydrogenase complex (PDH), a purified E2 subunit (PDH-E2) and a crude preparation of human liver mitoplasts (HLM), i.e. mitochondria depleted of their outer membranes. Peripheral blood lymphocytes (PBL) from 11 of 15 patients (73.3%) with PBC showed a HLA class II-restricted proliferative response to the PDH complex whereas PBL from patients with chronic viral hepatitis, autoimmune hepatitis or extrahepatic cholestatic icterus (n = 20) and healthy controls (n = 5) did not. In addition 13 of 15 PBL from patients with PBC (86.6%) and three of nine PBL from patients with autoimmune hepatitis (33.3%) reacted with the crude HLM preparation whereas no reactivity was found with PBL from eight patients with chronic viral hepatitis, three patients with extrahepatic cholestasis or five healthy controls. Clonal analysis of 115 liver-infiltrating T cells derived from two diagnostic liver biopsies of patients with PBC revealed a predominance of activated CD4+CD8- T helper cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of totally activated pyruvate dehydrogenase complex activity in human muscle: evaluation of a useful assay

A sensitive radiochemical method for the determination of the pyruvate dehydrogenase complex (PDHC) activity in skeletal muscle tissue, based on the decarboxylation of [1-14C]-pyruvate to 14CO2, is described. Measurements can be carried out either in muscle homogenate or in 600-g supernatant, both obtainable from a small muscle biopsy specimen (20 mg). In addition to NAD+, thiamine pyrophosphate and coenzyme A in the incubation mixture, a preparation of NADH:cytochrome c reductase (NADHCR) together with cytochrome c has a stimulating effect on the PDHC activity. NADHCR constitutes an oxidation system for NADH to prevent feedback inhibition. Addition of L-carnitine also results in stimulation of PDHC by trapping the produced acetyl-CoA as acetylcarnitine. Special care for radioactive pyruvate, with freeze drying and storage at -20 degrees C under nitrogen, and determination of the purity during every PDHC assay, is required. In the presented assay a Km value of 0.084 mmol/l was found for pyruvate. Nonsigmoidal kinetics was found with a Hill coefficient of 1.63. With the described method, a totally Mg2+,Ca(2+)-stimulated PDHC activity is measured. Addition of a purified specific pyruvate dehydrogenase phosphatase did not yield a higher PDHC activity. Finally, comparison of total PDHC activity with [1-14C]-pyruvate oxidation rates, both measured in the supernatant prepared from fresh muscle, shows an equimolar correlation, indicating that total PDHC activity is rate limiting in the assay for the pyruvate oxidation rate. Neonatal muscle exhibits five to ten times lower PDHC activities and pyruvate oxidation rates than controls (age > 3 years).

Studies on the rapid stimulation of mitochondrial respiration by thyroid hormones

Injection of L-3,5-diiodothyronine (T2) into rats made hypothyroid by 6-n-propyl-2-thiouracil (PTU) increased the respiration rates of subsequently isolated liver mitochondria; this stimulation of respiration by T2 occurred in the presence of cycloheximide and is therefore independent of protein synthesis on cytoplasmic ribosomes. Injection of T3 into PTU-treated rats had a lesser effect than T2 on the respiration rates of subsequently isolated mitochondria; as PTU is an inhibitor of 5'-iodothyronine deiodinases, which convert T3 into T2 in vivo, the rapid stimulation of mitochondrial respiration by T3, which has been shown in a range of systems, may not be due directly to T3 itself, but may be mediated by its deiodination product T2. Injection of T2, or T3, into hypothyroid or euthyroid rats had no effect on the percentage activity of mitochondrial pyruvate hydrogenase assayed 30 min later. The amount of active pyruvate dehydrogenase is regulated by changes in mitochondrial calcium concentration and matrix ATP/ADP ratio; therefore these parameters are not persistently affected by treatment with T3 or T2. In addition, the total amount of pyruvate dehydrogenase present was the same in euthyroid and hypothyroid rats, indicating that the expression of this enzyme is not stringently controlled by thyroid hormone status.