Lactic acidosis caused by repressed lactate dehydrogenase subunit B expression down-regulates mitochondrial oxidative phosphorylation via the pyruvate dehydrogenase (PDH)-PDH kinase axis.

Aerobic glycolysis and mitochondrial dysfunction are key metabolic features of cancer cells, but their interplay during cancer development remains unclear. We previously reported that human hepatoma cells with mitochondrial defects exhibit down-regulated lactate dehydrogenase subunit B (LDHB) expression. Here, using several molecular and biochemical assays and informatics analyses, we investigated how LDHB suppression regulates mitochondrial respiratory activity and contributes to liver cancer progression. We found that transcriptional LDHB down-regulation is an upstream event during suppressed oxidative phosphorylation. We also observed that LDHB knockdown increases inhibitory phosphorylation of pyruvate dehydrogenase (PDH) via lactate-mediated PDH kinase (PDK) activation and thereby attenuates oxidative phosphorylation activity. Interestingly, monocarboxylate transporter 1 was the major lactate transporter in hepatoma cells, and its expression was essential for PDH phosphorylation by modulating intracellular lactate levels. Finally, bioinformatics analysis of the hepatocellular carcinoma cohort from The Cancer Genome Atlas revealed that a low LDHB/LDHA ratio is statistically significantly associated with poor prognostic outcomes. A low ratio was also associated with a significant enrichment in glycolysis genes and negatively correlated with PDK1 and 2 expression, supporting a close link between LDHB suppression and the PDK-PDH axis. These results suggest that LDHB suppression is a key mechanism that enhances glycolysis and is critically involved in the maintenance and propagation of mitochondrial dysfunction via lactate release in liver cancer progression.

Targeting Oxygen-Sensing Prolyl Hydroxylase for Metformin-Associated Lactic Acidosis Treatment.

Metformin is one of the most widely used therapeutics for type 2 diabetes mellitus and also has anticancer and antiaging properties. However, it is known to induce metformin-associated lactic acidosis (MALA), a severe medical condition with poor prognosis, especially in individuals with renal dysfunction. Inhibition of prolyl hydroxylase (PHD) is known to activate the transcription factor hypoxia-inducible factor (HIF) that increases lactate efflux as a result of enhanced glycolysis, but it also enhances gluconeogenesis from lactate in the liver that contributes to reducing circulating lactate levels. Here, we investigated the outcome of pharmaceutical inhibition of PHD in mice with MALA induced through the administration of metformin per os and an intraperitoneal injection of lactic acid. We found that the PHD inhibitors significantly increased the expression levels of genes involved in gluconeogenesis in the liver and the kidney and significantly improved the survival of mice with MALA. Furthermore, the PHD inhibitor also improved the rate of survival of MALA induced in mice with chronic kidney disease (CKD). Thus, PHD represents a new therapeutic target for MALA, which is a critical complication of metformin therapy.

Mutations in the accessory subunit NDUFB10 result in isolated complex I deficiency and illustrate the critical role of intermembrane space import for complex I holoenzyme assembly.

An infant presented with fatal infantile lactic acidosis and cardiomyopathy, and was found to have profoundly decreased activity of respiratory chain complex I in muscle, heart and liver. Exome sequencing revealed compound heterozygous mutations in NDUFB10, which encodes an accessory subunit located within the PD part of complex I. One mutation resulted in a premature stop codon and absent protein, while the second mutation replaced the highly conserved cysteine 107 with a serine residue. Protein expression of NDUFB10 was decreased in muscle and heart, and less so in the liver and fibroblasts, resulting in the perturbed assembly of the holoenzyme at the 830 kDa stage. NDUFB10 was identified together with three other complex I subunits as a substrate of the intermembrane space oxidoreductase CHCHD4 (also known as Mia40). We found that during its mitochondrial import and maturation NDUFB10 transiently interacts with CHCHD4 and acquires disulfide bonds. The mutation of cysteine residue 107 in NDUFB10 impaired oxidation and efficient mitochondrial accumulation of the protein and resulted in degradation of non-imported precursors. Our findings indicate that mutations in NDUFB10 are a novel cause of complex I deficiency associated with a late stage assembly defect and emphasize the role of intermembrane space proteins for the efficient assembly of complex I.

Normal muscle respiratory chain enzymes can complicate mitochondrial disease diagnosis.

This report presents a case of mitochondrial respiratory chain deficiency in a neonate with elevated plasma lactate, hypotonia, developmental delay, and dysmorphic features. The initial biochemical analyses of muscle tissue for mitochondrial function were normal. Additional testing on skin fibroblasts performed owing to a high clinical suspicion of a possible mitochondrial disorder indicated a deficiency of mitochondrial complex I. Western blotting of samples obtained both from muscle and fibroblast tissues also revealed an extensive defect in mitochondrial respiratory chain complex I, confirming the diagnosis. These observations underscore the fact that both enzymatic and immunological assays should be undertaken in alternate tissues when muscle biopsies are inconclusive in highly suspected cases.

Opposing and hierarchical roles of leukotrienes in local innate immune versus vascular responses in a model of sepsis.

The 5-lipoxygenase (5-LO)-derived leukotrienes (LTs) influence both local innate immunity and vascular responses, but the relative importance of effects on these two processes in sepsis is unknown. In a cecal ligation and puncture model of peritonitis with severe sepsis, 5-LO(-/-) mice showed a reduction in peritoneal neutrophil accumulation and an increase in the number of bacteria in the peritoneal cavity. Despite this impairment of local innate immunity, the null mice exhibited a marked improvement in survival, and this protection was also seen in wild-type animals treated with the LT synthesis inhibitor MK 886. A survival advantage in severe sepsis was also observed in mice treated with the cysteinyl-LT receptor antagonist MK 571, but not with the LTB(4) receptor antagonist CP 105, 696. Protection in the 5-LO(-/-) mice was associated with reduced vascular leak and serum lactate levels. Moreover, wild-type mice treated with MK 571 exhibited less sepsis-induced hypotension. These data demonstrate opposing effects of cysteinyl-LTs on innate immune vs hemodynamic responses, demonstrating protective effects on local immunity and deleterious effects on the vasculature. They also suggest the possible therapeutic utility of targeting vascular events in sepsis with cysteinyl-LT blockade.

Lactic acidosis and developmental delay due to deficiency of E3 binding protein (protein X) of the pyruvate dehydrogenase complex.

Pyruvate dehydrogenase deficiency is an important cause of primary lactic acidosis. Most cases occur as a result of mutations in the gene for the E1 alpha subunit of the complex, with a small number resulting from mutations in genes for other components, most commonly the E3 and E3-binding protein subunits. We describe pyruvate dehydrogenase E3-binding protein deficiency in two siblings in each of two unrelated families from Kuwait. The index patient in each family had reduced pyruvate dehydrogenase activity in cultured fibroblasts and no detectable immunoreactive E3-binding protein. Both were homozygous for nonsense mutations in the E3-binding protein gene, one involving the codon for glutamine 266, the other the codon for tryptophan 5.

A new case of pyruvate dehydrogenase deficiency due to a novel mutation in the PDX1 gene.

We report a case of neonatal congenital lactic acidosis associated with pyruvate dehydrogenase E3-binding protein deficiency in a newborn girl. She had a severe encephalopathy, and magnetic resonance imaging of the brain showed large subependymal cysts and no basal ganglia lesions. She died 35 days after birth. We detected a novel homozygous deletion (620delC) in the PDX1 gene, which encodes for the E3BP subunit of the pyruvate dehydrogenase complex.

Suppression of sodium pump activity and an increase in the intracellular Ca2+ concentration by dexamethasone in acidotic mouse brain.

The effects of dexamethasone on adenosine 5'-triphosphatase (ATPase) activity and the intracellular Ca(2+) concentration ([Ca(2+)](i)) were investigated in acidotic mouse brain. Dexamethasone (3 mg/kg, i.p.) or vehicle was administered 3 h before decapitation ischemia, and the brain concentration of adenosine 5'-triphosphate (ATP) was determined 0.5-2 min after ischemia. The effects of dexamethasone (0.3-3 mg/kg, i.p.) on Na(+),K(+)-activated ATPase (Na(+),K(+)-ATPase) and Ca(2+)-ATPase activities were evaluated at pH 7.4 and 6.8. Changes in [Ca(2+)](i) in an acidic medium were determined in hippocampal slices by microfluorometry using rhod-2 acetoxymethyl ester as a Ca(2+) marker, and the effects of dexamethasone (240 microg/l) was evaluated. Decapitation ischemia for 0.5 and 1 min reduced the brain ATP contents to 32% and 16% of the basal level, respectively. Dexamethasone slightly suppressed the extent of the decrease in the ATP level. Although dexamethasone did not affect Na(+),K(+)-ATPase activity at pH 7.4, the activity was suppressed by dexamethasone (3 mg/kg) to 68% at pH 6.8. The activity of Ca(2+)-ATPase was not affected by dexamethasone at either pH 7.4 or pH 6.8. When the pH of the medium of the brain slices was changed from 7.4 to 6.8, almost no increase in [Ca(2+)](i) was observed in the control group. The dexamethasone treatment increased [Ca(2+)](i) in the CA1 field and dentate gyrus immediately after induction of the acidic medium, the effect being significant after 150 s. Because anaerobic glucose metabolism in the early stage of ischemia enhances intracellular lactic acidosis, the findings may suggest a mechanism for the aggravation of ischemic neuronal damage by glucocorticoids.

A novel deficiency of mitochondrial ATPase of nuclear origin.

We report a new type of fatal mitochondrial disorder caused by selective deficiency of mitochondrial ATP synthase (ATPase). A hypotrophic newborn from a consanguineous marriage presented severe lactic acidosis, cardiomegaly and hepatomegaly and died from heart failure after 2 days. The activity of oligomycin-sensitive ATPase was only 31-34% of the control, both in muscle and heart, but the activities of cytochrome c oxidase, citrate synthase and pyruvate dehydrogenase were normal. Electrophoretic and western blot analysis revealed selective reduction of ATPase complex but normal levels of the respiratory chain complexes I, III and IV. The same selective deficiency of ATPase was found in cultured skin fibroblasts which showed similar decreases in ATPase content, ATPase hydrolytic activity and level of substrate-dependent ATP synthesis (20-25, 18 and 29-33% of the control, respectively). Pulse-chase labelling of patient fibroblasts revealed low incorporation of [(35)S]methionine into assembled ATPase complexes, but increased incorporation into immunoprecipitated ATPase subunit beta, which had a very short half-life. In contrast, no difference was found in the size and subunit composition of the assembled and newly produced ATPase complex. Transmitochondrial cybrids prepared from enucleated fibroblasts of the patient and rho degrees cells derived from 143B. TK(-)human osteosarcoma cells fully restored the ATPase activity, ATP synthesis and ATPase content, when compared with control cybrids. Likewise, the pattern of [(35)S]methionine labelling of ATPase was found to be normal in patient cybrids. We conclude that the generalized deficiency of mitochondrial ATPase described is of nuclear origin and is caused by altered biosynthesis of the enzyme.

Delayed posthypoxic demyelination. Association with arylsulfatase A deficiency and lactic acidosis on proton MR spectroscopy.

Delayed demyelination is a rare and poorly understood complication of hypoxic brain injury. A previous case report has suggested an association with mild-to-moderate deficiency of arylsulfatase A. We describe a 36-year-old man who recovered completely from an episode of hypoxia related to drug overdose, and 2 weeks later progressed from a confusional state to deep coma. MRI showed diffuse white matter signal changes, and brain biopsy demonstrated a noninflammatory demyelinating process. Proton magnetic resonance spectroscopy revealed elevated choline and lactate and reduced N-acetyl aspartate signal in the affected white matter, consistent with demyelination and a shift to anaerobic metabolism. Arylsulfatase A activity from peripheral leukocytes was approximately 50% of normal, consistent with a "pseudodeficiency" phenotype. These findings confirm the hypothesis that relative arylsulfatase A deficiency predisposes susceptible individuals to delayed posthypoxic leukoencephalopathy and implicates lactic acidosis in the pathogenesis of this disorder.

Effects of tyrphostins and genistein on the circulatory failure and organ dysfunction caused by endotoxin in the rat: a possible role for protein tyrosine kinase.

1 Here we compared the effects of various inhibitors of the activity of protein tyrosine kinase on (i) the expression of the activity of the inducible isoform of nitric oxide (NO) synthase (iNOS) caused by endotoxin (lipopolysaccharide, LPS) in cultured macrophages, (ii) the induction of iNOS and cyclooxygenase 2 (COX-2) protein and activity in rats with endotoxaemia, and (iii) the circulatory failure and organ dysfunction caused by LPS in the anesthetized rat. 2 Activation of murine cultured macrophages with LPS (1 microgram ml-1) resulted, within 24 h, in a significant increase in nitrite (an indicator of the formation of NO) in the cell supernatant. This increase in nitrate was attenuated by the tyrphostins AG126, AG556, AG490 or AG1641 or by genistein in a dose-dependent fashion (IC50: approximately 15 microM). In contrast, tyrphostin A1 (an analogue of tyrphostin AG126) or daidzein (an analogue of genistein) had no effect on the rise in nitrite caused by LPS. 3 Administration of LPS (E. coli, 10 mg kg-1, i.v.) caused hypotension and a reduction of the pressor responses elicited by noradrenaline (NA, 1 microgram kg-1, i.v.). Pretreatment of rats with the tyrphostins AG126, AG490, AG556, AG1641 or A1 attenuated the circulatory failure caused by LPS. Although genistein attenuated the vascular hyporeactivity to NA, it did not affect the hypotension caused by LPS. Daidzein did not affect the circulatory failure caused by LPS. 4 Endotoxaemia for 360 min resulted in rises in the serum levels of (i) urea and creatinine (indicators of renal failure), (ii) alanine aminotransferase (ALT), aspartate aminotransferase (AST), bilirubin and gamma-glutamyl transferase (gamma GT) (indicators of liver injury/dysfunction), lipase (an indicator of pancreatic injury) as well as lactate (an indicator of tissue hypoxia). None of the tyrosine kinase inhibitors tested had a significant effect on the rise i the serum levels of urea, but the tyrphostins AG126, AG556 or A1 significantly attenuated the rises in the serum level of creatinine caused by LPS. In addition, all tyrphostins and genistein attenuated the liver injury/failure, the pancreatic injury, the hypoglycaemia and the lactic acidosis caused by LPS. In contrast, daidzein did not reduce the organ injury/dysfunction or the lactic acidosis caused by LPS. 5 Injection of LPS resulted (within 90 min) in a substantial increase in the serum level of tumor necrosis factor alpha (TNF alpha), which was attenuated by pretreatment of LPS-rats with any of the tyrphostins used. Genistein, but not daidzein, also reduced the rise in the serum levels of TNF alpha caused by LPS. Endotoxaemia for 6 h also resulted in a substantial increase in the expression of iNOS and COX-2 protein and activity in the lung, which was attenuated by pretreatment of LPS-rats with the tyrphostins AG126, AG556 or genistein, but not by daidzein. 6 Thus, tyrphostins (AG126, AG556, AG1641 or A1) and genistein, but not daidzein (inactive analogue of genistein), prevent the (i) circulatory failure, (ii) the multiple organ dysfunction (liver and pancreatic dysfunction/injury lactacidosis, hypoglycaemia), as well as (iii) the induction of iNOS and COX-2 protein and activity in rats with endotoxic shock.

Morphological studies of skeletal muscle in lactic acidosis.

This paper underscores the contribution of routine morphological examination of skeletal muscle in patients with lactic acidosis. Mitochondrial disorders are by far the most common causes of primary lactic acidosis, in which muscle biopsy analysis helps in diagnosis and in the search for the molecular anomalies. Thus, we focus our attention on one particular point: the contribution of the morphological study of muscle biopsy in primary lactic acidosis due to mitochondrial disorders, especially mitochondrial respiratory-chain diseases.

Bilateral infantile cataractogenesis in a patient with deficiency of complex I, a mitochondrial electron transport chain enzyme.

Progressive bilateral cataracts developed in infancy in a 5-month-old girl with deficiency of complex I, a mitochondrial electron transport chain enzyme. In the newborn period, she had severe lactic acidosis and the diagnosis of complex I deficiency was confirmed by mitochondrial respiratory chain assay on muscle biopsy. By 5 months, she had completely opaque nuclear sclerotic cataracts, with loss of fixation and the red reflex. She underwent bilateral, sequential cataract extraction. The lens aspirate was submitted for cytologic analysis and electron microscopy, which revealed increased intracellular glycogen and swollen mitochondria. To our knowledge the association of complex I deficiency with cataracts in infancy has not been reported previously. The diagnosis of a respiratory chain enzyme defect in infancy is an indication for early ophthalmic evaluation to identify cataracts that may result in visual loss. Conversely, the recognition of cataracts in infants with unexplained neurologic disease or metabolic acidosis may necessitate further evaluation for metabolic etiologies, including mitochondrial disorders.

Evaluation of patients with lactic acidosis using microphotometric mitochondrial enzyme assay in single muscle fibers.

Microphotometric enzyme assay in single muscle fibers was performed on two patients with lactic acidosis. Neither case showed ragged red fibers upon histochemical evaluation. Biochemical analysis of mitochondrial enzymes demonstrated low normal cytochrome c oxidase (COX) activity in Case 1 and deficient COX in Case 2. Quantitative single muscle fiber analysis in patients showed marked variation in COX activity in Case 1, reflecting mosaic distribution of fibers with near-normal COX activity and with defective COX activity. These data suggest that this microphotometric assay may be valuable for elucidating the significance of 'partial enzyme deficiency'. In addition, this assay method may be applied to needle biopsy specimens.

Vitamin-responsive complex I deficiency in a myopathic patient with increased activity of the terminal respiratory chain and lactic acidosis.

An 11-year-old girl with exercise intolerance, fatiguability from early childhood, had high blood lactate levels. Histochemistry showed increased activity of succinate dehydrogenase at the periphery of the muscle fibres, whereas aggregates of mitochondria were seen by electron microscopy. Biochemical investigation of isolated mitochondria and homogenate from muscle showed evidence of a severe complex I deficiency. In contrast, succinate dehydrogenase, complex II+III and complex IV were increased in activity. Therapy with biotin, riboflavin, nicotinamide, carnitine and amino acids resulted in an improvement of her endurance. 31P NMR spectroscopy of her forearm muscle showed a decreased ratio of phosphocreatine (PCr) over ATP. After exercise the PCr recovery rate was 26% of the average rate in 20 healthy untrained controls. When the therapy was suspended the PCr/ATP ratio at rest decreased from 2.60 to 2.34, and the PCr recovery rate after exercise decreased to 21% of the average control rate. The therapy was reinstituted but only riboflavin and carnitine were given. The PCr/ATP ratio increased to 2.60 and the PCr recovery rate increased to 32% of the control rate. Improvement of the energy metabolism in patients with defects in the oxidative phosphorylation may add to the quality of life; 31P NMR spectroscopy can measure these improvements.

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS): a correlative study of the clinical features and mitochondrial DNA mutation.

We studied 40 MELAS patients (21 male and 19 female) to characterize the clinical features and biochemical and muscle biopsy findings related to the mtDNA mutation at the nucleotide position of 3,243, the most common genetic defect in MELAS. The most frequent symptom was episodic sudden headache with vomiting and convulsions, which commonly affected patients aged 5 to 15 years (80%). Biochemical defects in the muscle were variable; 13 patients had complex I, seven complex IV, and four complexes I + IV deficiencies. In four muscle biopsies without ragged-red fibers or any enzyme defect, we based the diagnosis on the identification of strongly SDH-reactive blood vessels, which occurred in 87.5% of the biopsies. The mtDNA mutation was present in 32 of 40 patients (80%). We conclude that there are no clinical and pathologic differences between the patients with and without this mtDNA mutation.

Defects of the mitochondrial respiratory chain complexes in three pediatric cases with hypotonia and cardiac involvement.

Three children displaying hypotonia, cardiac involvement and defects of the mitochondrial respiratory chain complexes are reported. The first case showed severe neonatal hypotonia, failure to thrive, hepatomegaly, dilation of the right cardiac cavities, profound lactic acidosis and amino aciduria. The boy died at the age of 7 weeks. In the second case hypotonia, severe cardiomyopathy, cyclic neutropenia, lactic acidosis and 3-methylglutaconic aciduria occurred. The boy died at the age of 27 months. The third case presented at the age of 16 months as an acute hypokinetic hypertrophic cardiomyopathy with transient hypotonia and mild lactic acidosis. Spontaneous clinical remission occurred. In all cases muscle biopsy was performed. Morphological studies failed to show ragged-red fibers but there was lipid storage myopathy and decreased cytochrome c oxidase activity. Biochemical studies confirmed the cytochrome c oxidase deficiency in muscle in all cases. It was associated with complex I III deficiency in case 1 and with severe deficits of all respiratory chain complexes in case 2. Post-mortem studies in case 1 indicated that complex IV was reduced in the liver but not in the heart and quantitative analysis of mtDNA revealed a depletion in muscle. Cases 1 and 2 shared some clinical features with fatal infantile myopathy associated with cytochrome c oxidase deficiency, while case 3 displayed a very unusual clinical presentation. The histochemical enzyme reaction of cytochrome c oxidase is useful for the diagnosis of mitochondrial myopathy because ragged-red fibers may be lacking. Finally, biochemical measurement of the different mitochondrial respiratory chain complexes is required because multiple defects are frequent and occasionally related to mtDNA depletion.

Defects in the E2 lipoyl transacetylase and the X-lipoyl containing component of the pyruvate dehydrogenase complex in patients with lactic acidemia.

Three patients with chronic lacticacidemia and deficiency of the pyruvate dehydrogenase complex demonstrated in cultured skin fibroblasts showed abnormalities on Western blotting with anti-pyruvate dehydrogenase complex antiserum which were not located in the E1 (alpha and beta) component of the complex. One of these patients had an enzymatically demonstrable deficiency in the E2 dihydrolipoyl transacetylase segment of the complex and very low observable E2 protein component on Western blotting of fibroblast proteins. The other two patients had abnormalities observable in the X component but no observable reduction in either E1, E2, or E3 enzymatic activities. One patient appeared to have a missing X component while the other had two distinct bands where X should be on Western blotting of fibroblast proteins. All three patients appeared to have severe clinical sequelae resulting from these defects. This is the first time that defects in either the E2 or the X component of the pyruvate dehydrogenase complex have been observed in the human population.

A case of mitochondrial myopathy, encephalopathy and lactic acidosis due to cytochrome c oxidase deficiency with neurogenic muscular changes.

An 18-year-old male with mitochondrial myopathy, encephalopathy and lactic acidosis was studied by electromyography (EMG) along with histological and biochemical studies on his biopsied muscle. Mitochondrial cytochrome c oxidase deficiency with a decrease in the amounts of the subunits 2, 6, and 7 was discovered. Although no apparent symptoms of peripheral neuropathy were present, EMG revealed high-amplitude motor unit action potentials with a reduced interference pattern and the histochemical study revealed fiber type grouping without grouped atrophy. These findings indicated lower motor neuron damage, probably due to the mitochondrial disorder, followed by reinnervation. Coenzyme Q10 administration was effective in reducing both the lactate and pyruvate levels and for recovering the muscle atrophy.