Antoni L. Andreu

Exercise Intolerance Due to Mutations in the Cytochrome b Gene of Mitochondrial DNA

BACKGROUND The mitochondrial myopathies typically affect many organ systems and are associated with mutations in mitochondrial DNA (mtDNA) that are maternally inherited. However, there is also a sporadic form of mitochondrial myopathy in which exercise intolerance is the predominant symptom. We studied the biochemical and molecular characteristics of this sporadic myopathy. METHODS We sequenced the mtDNA cytochrome b gene in blood and muscle specimens from five patients with severe exercise intolerance, lactic acidosis in the resting state (in four patients), and biochemical evidence of complex III deficiency. We compared the clinical and molecular features of these patients with those previously described in four other patients with mutations in the cytochrome b gene. RESULTS We found a total of three different nonsense mutations (G15084A, G15168A, and G15723A), one missense mutation (G14846A), and a 24-bp deletion (from nucleotide 15498 to 15521) in the cytochrome b gene in the five patients. Each of these mutations impairs the enzymatic function of the cytochrome b protein. In these patients and those previously described, the clinical manifestations included progressive exercise intolerance, proximal limb weakness, and in some cases, attacks of myoglobinuria. There was no maternal inheritance and there were no mutations in tissues other than muscle. The absence of these findings suggests that the disorder is due to somatic mutations in myogenic stem cells after germ-layer differentiation. All the point mutations involved the substitution of adenine for guanine, but all were in different locations. CONCLUSIONS The sporadic form of mitochondrial myopathy is associated with somatic mutations in the cytochrome b gene of mtDNA. This myopathy is one cause of the common and often elusive syndrome of exercise intolerance.

A Stop-Codon Mutation in the Human mtDNA Cytochrome c Oxidase I Gene Disrupts the Functional Structure of Complex IV

We have identified a novel stop-codon mutation in the mtDNA of a young woman with a multisystem mitochondrial disorder. Histochemical analysis of a muscle-biopsy sample showed virtually absent cytochrome c oxidase (COX) stain, and biochemical studies confirmed an isolated reduction of COX activity. Sequence analysis of the mitochondrial-encoded COX-subunit genes identified a heteroplasmic G-->A transition at nucleotide position 6930 in the gene for subunit I (COX I). The mutation changes a glycine codon to a stop codon, resulting in a predicted loss of the last 170 amino acids (33%) of the polypeptide. The mutation was present in the patients muscle, myoblasts, and blood and was not detected in normal or disease controls. It was not detected in mtDNA from leukocytes of the patients mother, sister, and four maternal aunts. We studied the genetic, biochemical, and morphological characteristics of transmitochondrial cybrid cell lines, obtained by fusing of platelets from the patient with human cells lacking endogenous mtDNA (rho0 cells). There was a direct relationship between the proportion of mutant mtDNA and the biochemical defect. We also observed that the threshold for the phenotypic expression of this mutation was lower than that reported in mutations involving tRNA genes. We suggest that the G6930A mutation causes a disruption in the assembly of the respiratory-chain complex IV.

A Missense Mutation in the Mitochondrial Cytochrome b Gene in a Revisited Case with Histiocytoid Cardiomyopathy

We describe a pathogenic mutation in the mitochondrial cytochrome b gene in a patient with a multisystem disorder presenting as histiocytoid cardiomyopathy in whom a defect of ubiquinol cytochrome c oxidoreductase of the electron transport chain had been documented biochemically. The mutation, a G to A transition at nucleotide 15498, results in the substitution of glycine with aspartic acid at amino acid position 251.The mutation, which is heteroplasmic and fulfills all accepted criteria for pathogenicity, is likely to impair the function of the holoenzyme as deduced from its effects on the crystal structure of ubiquinol cytochrome c oxidoreductase. This is the first molecular defect associated with histiocytoid cardiomyopathy.

Cerebellar ataxia with coenzyme Q10 deficiency: diagnosis and follow-up after coenzyme Q10 supplementation.

UNLABELLED Our aim was to report a new case with cerebellar ataxia associated with coenzyme Q10 (CoQ) deficiency, the biochemical findings caused by this deficiency and the response to CoQ supplementation. PATIENT A 12-year-old girl presenting ataxia and cerebellar atrophy. BIOCHEMICAL STUDIES: Coenzyme Q10 in muscle was analysed by HPLC with electrochemical detection and mitochondrial respiratory chain (MRC) enzyme activities by spectrophotometric methods. CoQ biosynthesis in fibroblasts was assayed by studying the incorporation of radiolabeled 4-hydroxy[U 14C] benzoic acid by HPLC with radiometric detection. RESULTS Mitochondrial respiratory chain enzyme analysis showed a decrease in complex I + III and complex II + III activities. CoQ concentration in muscle was decreased (56 nmol/g of protein: reference values: 157-488 nmol/g protein). A reduced incorporation of radiolabeled 4-hydroxy[U- 14C] benzoic acid was observed in the patient (19% of incorporation respect to the median control values). After 16 months of CoQ supplementation, the patient is now able to walk unaided and cerebellar signs have disappeared. CONCLUSIONS Cerebellar ataxia associated with CoQ deficiency in our case might be allocated in the transprenylation pathway or in the metabolic steps after condensation of 4-hydroxybenzoate and the prenyl side chain of CoQ. Clinical improvement after CoQ supplementation was remarkable, supporting the importance of an early diagnosis of this kind of disorders.

Molecular heterogeneity of myophosphorylase deficiency (McArdle's disease): a genotype-phenotype correlation study.

We report on 54 Spanish patients with McArdles disease from 40 unrelated families. Molecular analysis revealed that the most common R49X mutation was present in 70% of patients and 55% of alleles. The G204S mutation was less frequent and found in 14.8% of patients and 9% of mutant alleles. The W797R mutation was observed in 16.5% of patients, accounting for 13.7% of mutant alleles. Moreover, 78% of mutant alleles among Spanish patients can be identified by using polymerase chain reaction‐restriction fragment length polymorphism analysis for the R49X, G204S, and W797R mutations, which makes noninvasive diagnosis possible through molecular genetic analysis of blood DNA. Six novel mutations were found. Three were missense mutations, E348K, R601W, and A703V; two nonsense mutations, E124X and Q754X; and one single base pair deletion, 533 delA. No clear genotype‐phenotype correlation emerges from our study. Most of the mutations of uncharged and solvent inaccessible residues and the truncations must disrupt the basic structure of the protein. The mutations of charged residues would be expected to interfere with internal hydrogen bonding networks, introducing severe incompatible partnering that is caused by poor packing or electrostatic repulsions.

Favorable responses to acute and chronic exercise in McArdle patients.

Objective:This study reports acute exercise responses in a large (N = 46) series of patients with McArdle disease and responses to exercise training in a smaller (n = 9) set of patients. Design:Patients were studied during both incremental and steady-state cycle ergometer exercise, using cardiopulmonary testing, and the patients were compared with age- and gender-matched controls. Setting:The study was performed in a university setting (clinical exercise physiology laboratory). Participants:The 46 patients showed common features of McArdle disease. They were definitively diagnosed by histochemistry, biochemistry, and/or molecular genetic analysis. The 46 controls were healthy, sedentary individuals. Intervention:Nine patients were studied before and after an 8-month supervised aerobic exercise training program (including five weekly sessions of walking and/or cycling exercise with a duration no greater than 60 minutes). Main Outcome Measurements:The main indicators of exercise capacity that we measured were peak power output, peak oxygen uptake (VO2peak), and ventilatory threshold (VT). Results:Exercise capacity (peak power output, 35% control; VO2peak, 44% control; VT, 66% control) was markedly depressed in the patients. The patients who trained improved peak power output (25%), VO2peak (44%), and VT (27%), with no evidence of negative outcomes from training. Although not achieving normal values, the response to training put the patients into the lower limit of normal controls. Conclusions:Under carefully controlled conditions, patients with McArdle disease may perform acute exercise safely, and they may respond favorably to training. This may offer an additional therapeutic option to help normalize the lifestyles of these patients.

Lack of paternal inheritance of muscle mitochondrial DNA in sporadic mitochondrial myopathies.

In 2002, paternal inheritance of muscle mitochondrial DNA (mtDNA) was reported in a patient with exercise intolerance and a mitochondrial DNA (mtDNA) mutation restricted to skeletal muscle. To evaluate whether paternal inheritance is a common phenomenon, we studied 10 sporadic patients with skeletal muscle‐restricted mtDNA mutations: five harbored mtDNA point mutations in protein‐coding genes and five had single mtDNA deletions. We performed haplotype analysis and direct sequencing of the hypervariable regions 1 and 2 of the D‐loop in muscle and blood from the patients and, when available, in blood from their parents. We did not observe paternal inheritance in any of our patients.

Oxidative Damage Compromises Energy Metabolism in the Axonal Degeneration Mouse Model of X-Adrenoleukodystrophy

AIMS Chronic metabolic impairment and oxidative stress are associated with the pathogenesis of axonal dysfunction in a growing number of neurodegenerative conditions. To investigate the intertwining of both noxious factors, we have chosen the mouse model of adrenoleukodystrophy (X-ALD), which exhibits axonal degeneration in spinal cords and motor disability. The disease is caused by loss of function of the ABCD1 transporter, involved in the import and degradation of very long-chain fatty acids (VLCFA) in peroxisomes. Oxidative stress due to VLCFA excess appears early in the neurodegenerative cascade. RESULTS In this study, we demonstrate by redox proteomics that oxidative damage to proteins specifically affects five key enzymes of glycolysis and TCA (Tricarboxylic acid) cycle in spinal cords of Abcd1(-) mice and pyruvate kinase in human X-ALD fibroblasts. We also show that NADH and ATP levels are significantly diminished in these samples, together with decrease of pyruvate kinase activities and GSH levels, and increase of NADPH. INNOVATION Treating Abcd1(-) mice with the antioxidants N-acetylcysteine and α-lipoic acid (LA) prevents protein oxidation; preserves NADH, NADPH, ATP, and GSH levels; and normalizes pyruvate kinase activity, which implies that oxidative stress provoked by VLCFA results in bioenergetic dysfunction, at a presymptomatic stage. CONCLUSION Our results provide mechanistic insight into the beneficial effects of antioxidants and enhance the rationale for translation into clinical trials for X-adrenoleukodystrophy.

Oxidative stress modulates mitochondrial failure and cyclophilin D function in X-linked adrenoleukodystrophy

A common process associated with oxidative stress and severe mitochondrial impairment is the opening of the mitochondrial permeability transition pore, as described in many neurodegenerative diseases. Thus, inhibition of mitochondrial permeability transition pore opening represents a potential target for inhibiting mitochondrial-driven cell death. Among the mitochondrial permeability transition pore components, cyclophilin D is the most studied and has been found increased under pathological conditions. Here, we have used in vitro and in vivo models of X-linked adrenoleukodystrophy to investigate the relationship between the mitochondrial permeability transition pore opening and redox homeostasis. X-linked adrenoleukodystrophy is a neurodegenerative condition caused by loss of function of the peroxisomal ABCD1 transporter, in which oxidative stress plays a pivotal role. In this study, we provide evidence of impaired mitochondrial metabolism in a peroxisomal disease, as fibroblasts in patients with X-linked adrenoleukodystrophy cannot survive when forced to rely on mitochondrial energy production, i.e. on incubation in galactose. Oxidative stress induced under galactose conditions leads to mitochondrial damage in the form of mitochondrial inner membrane potential dissipation, ATP drop and necrotic cell death, together with increased levels of oxidative modifications in cyclophilin D protein. Moreover, we show increased expression levels of cyclophilin D in the affected zones of brains in patients with adrenomyeloneuropathy, in spinal cord of a mouse model of X-linked adrenoleukodystrophy (Abcd1-null mice) and in fibroblasts from patients with X-linked adrenoleukodystrophy. Notably, treatment with antioxidants rescues mitochondrial damage markers in fibroblasts from patients with X-linked adrenoleukodystrophy, including cyclophilin D oxidative modifications, and reverses cyclophilin D induction in vitro and in vivo. These findings provide mechanistic insight into the beneficial effects of antioxidants in neurodegenerative and non-neurodegenerative cyclophilin D-dependent disorders.

Safety Profile of Tissue Plasminogen Activator Treatment Among Stroke Patients Carrying a Common Polymorphism (C-1562T) in the Promoter Region of the Matrix Metalloproteinase-9 Gene

Background and Purpose— Matrix metalloproteinase-9 (MMP-9) expression, related to blood-brain barrier disruption, has been implicated in the appearance of hemorrhagic transformation (HT) after tissue plasminogen activator (tPA) treatment in stroke patients. Because an in vitro functional polymorphism of the promoter region of MMP-9 gene (C-1562T) has been described, we hypothesize that patients carrying this mutation might have higher MMP-9 levels and greater susceptibility to developing HT when receiving tPA. Methods— We studied strokes involving the middle cerebral artery territory of 61 patients who received tPA <3 hours after stroke onset. Blood samples were obtained before tPA administration. Plasmatic MMP-9 determinations were performed (enzyme-linked immunosorbent assay, ng/mL), and C-1562T genotype was determined by polymerase chain reaction. Healthy age-matched control subjects were used to study allele distribution (n=59). Hemorrhagic events were classified according to CT criteria (petechial hemorrhagic infarctions [HI,1 to 2] and large parenchymal hemorrhages [PH,1 to 2]). Results— Allele distribution was similar in patients and control subjects (CC/CT/TT: 72.3/27.7/0% versus 79.7/20.3/0%, respectively; P =0.37). Among patients, mutation carriers (CT/TT alleles) had similar rates of HT and PH than noncarriers (HT: 23.1% versus 38.2%, P =0.49; PH: 15.4% versus 17.6%, P =1.0). Although the highest MMP-9 level corresponded to patients who later developed a PH (PH, 191.4 ng/mL; non-PH, 68.05 ng/mL; P =0.022), no relation between MMP-9 mutation presence and plasmatic levels was found (CC, 127.12 ng/mL; CT/TT, 46.31 ng/mL; P =0.11). Conclusions— Although MMP-9 level predicts PH appearance after tPA treatment, no relationship exists with the C-1562T polymorphism, probably because this mutation is not functional in response to cerebral ischemia in vivo.