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Objectives: To describe the spectrum of movement disorders and cerebrospinal fluid (CSF) neurotransmitter profiles in paediatric patients with POLG disease., Methods: We identified children with genetically confirmed POLG disease, in whom CSF neurotransmitter analysis had been undertaken. Clinical data were collected retrospectively. CSF neurotransmitter levels were compared to both standardised age-related reference ranges and to non-POLG patients presenting with status epilepticus., Results: Forty-one patients with POLG disease were identified. Almost 50% of the patients had documented evidence of a movement disorder, including non-epileptic myoclonus, choreoathetosis and ataxia. CSF neurotransmitter analysis was undertaken in 15 cases and abnormalities were seen in the majority (87%) of cases tested. In many patients, distinctive patterns were evident, including raised neopterin, homovanillic acid and 5-hydroxyindoleacetic acid levels., Conclusions: Children with POLG mutations can manifest with a wide spectrum of abnormal movements, which are often prominent features of the clinical syndrome. Underlying pathophysiology is probably multifactorial, and aberrant monoamine metabolism is likely to play a role.

Cellular folate metabolism is highly compartmentalized, with mitochondria folate transport and metabolism being distinct from the well-known cytosolic folate metabolism. There is evidence supporting the association between low folate status and mitochondrial DNA (mtDNA) instability, and cerebral folate deficiency is relatively frequent in mitochondrial disorders. Furthermore, folinic acid supplementation has been reported to be beneficial not only in some patients with mitochondrial disease, but also in patients with relatively common diseases where folate deficiency might be an important pathophysiological factor. In this review, we focus on the evidence that supports the potential involvement of impaired folate metabolism in the pathophysiology of mitochondrial disorders., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Whole exome sequencing was used to investigate the genetic cause of mitochondrial disease in two siblings with a syndrome of congenital lamellar cataracts associated with nephrocalcinosis, medullary cysts and 3-methylglutaconic aciduria. Autosomal recessive inheritance in a gene encoding a mitochondrially targeted protein was assumed; the only variants which satisfied these criteria were c.1882C>T (p.Arg628Cys) and c.1915G>A (p.Glu639Lys) in the CLPB gene, encoding a heat shock protein/chaperonin responsible for disaggregating mitochondrial and cytosolic proteins. Functional studies, including quantitative PCR (qPCR) and Western blot, support pathogenicity of these mutations. Furthermore, molecular modelling suggests that the mutations disrupt interactions between subunits so that the CLPB hexamer cannot form or is unstable, thus impairing its role as a protein disaggregase. We conclude that accumulation of protein aggregates underlies the development of cataracts and nephrocalcinosis in CLPB deficiency, which is a novel genetic cause of 3-methylglutaconic aciduria. A common mitochondrial cause for 3-methylglutaconic aciduria appears to be disruption of the architecture of the mitochondrial membranes, as in Barth syndrome (tafazzin deficiency), Sengers syndrome (acylglycerol kinase deficiency) and MEGDEL syndrome (impaired remodelling of the mitochondrial membrane lipids because of SERAC1 mutations). We now propose that perturbation of the mitochondrial membranes by abnormal protein aggregates leads to 3-methylglutaconic aciduria in CLPB deficiency.

Primary Coenzyme Q10 (CoQ10) deficiency is an autosomal recessive disorder with a heterogeneous clinical presentation. Common presenting features include both muscle and neurological dysfunction. Muscle abnormalities can improve, both clinically and biochemically following CoQ10 supplementation, however neurological symptoms are only partially ameliorated. At present, the reasons for the refractory nature of the neurological dysfunction remain unknown. In order to investigate this at the biochemical level we evaluated the effect of CoQ10 treatment upon a previously established neuronal cell model of CoQ10 deficiency. This model was established by treatment of human SH-SY5Y neuronal cells with 1 mM para-aminobenzoic acid (PABA) which induced a 54% decrease in cellular CoQ10 status. CoQ10 treatment (2.5 μM) for 5 days significantly (p<0.0005) decreased the level of mitochondrial superoxide in the CoQ10 deficient neurons. In addition, CoQ10 treatment (5 μM) restored mitochondrial membrane potential to 90% of the control level. However, CoQ10 treatment (10 μM) was only partially effective at restoring mitochondrial electron transport chain (ETC) enzyme activities. ETC complexes II/III activity was significantly (p<0.05) increased to 82.5% of control levels. ETC complexes I and IV activities were restored to 71.1% and 77.7%, respectively of control levels. In conclusion, the results of this study have indicated that although mitochondrial oxidative stress can be attenuated in CoQ10 deficient neurons following CoQ10 supplementation, ETC enzyme activities appear partially refractory to treatment. Accordingly, treatment with >10 μM CoQ10 may be required to restore ETC enzyme activities to control level. Accordingly, these results have important implication for the treatment of the neurological presentations of CoQ10 deficiency and indicate that high doses of CoQ10 may be required to elicit therapeutic efficacy., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Mitochondrial diseases are an unusually genetically and phenotypically heterogeneous group of disorders, which are extremely challenging to treat. Currently, apart from supportive therapy, there are no effective treatments for the vast majority of mitochondrial diseases. Huge scientific effort, however, is being put into understanding the mechanisms underlying mitochondrial disease pathology and developing potential treatments. To date, a variety of treatments have been evaluated by randomized clinical trials, but unfortunately, none of these has delivered breakthrough results. Increased understanding of mitochondrial pathways and the development of many animal models, some of which are accurate phenocopies of human diseases, are facilitating the discovery and evaluation of novel prospective treatments. Targeting reactive oxygen species has been a treatment of interest for many years; however, only in recent years has it been possible to direct antioxidant delivery specifically into the mitochondria. Increasing mitochondrial biogenesis, whether by pharmacological approaches, dietary manipulation or exercise therapy, is also currently an active area of research. Modulating mitochondrial dynamics and mitophagy and the mitochondrial membrane lipid milieu have also emerged as possible treatment strategies. Recent technological advances in gene therapy, including allotopic and transkingdom gene expression and mitochondrially targeted transcription activator-like nucleases, have led to promising results in cell and animal models of mitochondrial diseases, but most of these techniques are still far from clinical application., (© 2013 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of The British Pharmacological Society.)

The pathogenesis of mitochondrial disorders has largely focused on the impairment of cellular energy metabolism. However, mitochondrial dysfunction has also been implicated as a factor in the initiation of apoptosis due to the translocation of cytochrome c, from mitochondria to the cytosol, and the subsequent cleavage of pro-caspase 3. In this study, we determined the cytochrome c content of cytosols (skeletal muscle) prepared from 22 patients with evidence of compromised mitochondrial electron transport chain enzyme activity and 26 disease controls. The cytochrome c content of the mitochondrial electron transport chain-deficient group was found to be significantly (p < 0.02) elevated when compared with the control group (63.7 +/- 15.5 versus 27.7 +/- 2.5 ng/mg protein). Furthermore, a relationship between the cytosolic cytochrome c content of skeletal muscle and complex I and complex IV activities was demonstrated. Such data raise the possibility that mitochondrial cytochrome c release may be a feature of mitochondrial disorders, particularly for those patients with marked deficiencies of respiratory chain enzymes. Whether initiation of apoptosis occurs as a direct consequence of this cytochrome c release has not been fully evaluated here. However, for one patient with the greatest documented cytosolic cytochrome c content, caspase 3 could be demonstrated in the cytosolic preparation. Further work is required in order to establish whether a relationship also exists between caspase 3 formation and the magnitude of respiratory chain deficiency.

Glutathione (GSH) is a key intracellular antioxidant. With regard to mitochondrial function, loss of GSH is associated with impairment of the electron transport chain (ETC). Since GSH biosynthesis is an energy-dependent process, we postulated that in patients with ETC defects GSH status becomes compromised, leading to further loss of ETC activity. We performed electrochemical HPLC analysis to determine the GSH concentration of 24 skeletal muscle biopsies from patients with defined ETC defects compared to 15 age-matched disease controls. Comparison of these groups revealed a significant (p < 0.001) decrease in GSH concentration in the ETC-deficient group: 7.7 +/- 0.9 vs 12.3 +/- 0.6 nmol/mg protein in the control group. Further analysis of the data revealed that patients with multiple defects of the ETC had the most marked GSH deficiency: 4.1 +/- 0.9 nmol/mg protein (n = 4, p < 0.05) when compared to the control group. These findings suggest that a deficiency in skeletal muscle GSH concentration is associated with an ETC defect, possibly as a consequence of diminished ATP availability or increased oxidative stress. The decreased ability to combat oxidative stress could therefore cause further loss of ETC activity and hence be a contributing factor in the progressive nature of this group of disorders. Furthermore, restoration of cellular GSH status could prove to be of therapeutic benefit in patients with a GSH deficiency associated with their ETC defects.

Coenzyme Q10 (CoQ10) serves as an electron carrier within the mitochondrial respiratory chain (MRC), where it is integrally involved in oxidative phosphorylation and consequently ATP production. It has recently been suggested that phenylketonuria (PKU) patients may be susceptible to a CoQ10 deficiency as a consequence of their phenylalanine-restricted diet, which avoids foods rich in CoQ10 and its precursors. Furthermore, the high phenylalanine level in PKU patients not on dietary restriction may also result in impaired endogenous CoQ10 production, as previous studies have suggested an inhibitory effect of phenylalanine on HMG-CoA reductase, the rate-controlling enzyme in CoQ10 biosynthesis. We investigated the effect of both dietary restriction and elevated plasma phenylalanine concentration on blood mononuclear cell CoQ10 concentration and the activity of MRC complex II + III (succinate:cytochrome-c reductase; an enzyme that relies on endogenous CoQ10) in a PKU patient population. The concentrations of CoQ10 and MRC complex II + III activity were not found to be significantly different between the PKU patients on dietary restriction, PKU patients off dietary restriction and the control group, although plasma phenylalanine levels were markedly different. The results from this investigation suggest that dietary restriction and the elevated plasma phenylalanine levels of PKU patients do not effect mononuclear cell CoQ10 concentration and consequently the activity of complex II + III of the MRC.

Background: Sepsis-induced multiple organ failure is the major cause of mortality and morbidity in critically ill patients. However, the precise mechanisms by which this dysfunction is caused remain to be elucidated. We and others have shown raised tissue oxygen tensions in septic animals and human beings, suggesting reduced ability of the organs to use oxygen. Because ATP production by mitochondrial oxidative phosphorylation accounts for more than 90% of total oxygen consumption, we postulated that mitochondrial dysfunction results in organ failure, possibly due to nitric oxide, which is known to inhibit mitochondrial respiration in vitro and is produced in excess in sepsis., Methods: We did skeletal muscle biopsies on 28 critically ill septic patients within 24 h of admission to intensive care, and on nine control patients undergoing elective hip surgery. The biopsy samples were analysed for respiratory-chain activity (complexes I-IV), ATP concentration, reduced glutathione (an intracellular antioxidant) concentration, and nitrite/nitrate concentrations (a marker of nitric oxide production)., Findings: Skeletal muscle ATP concentrations were significantly lower in the 12 patients with sepsis who subsequently died than in the 16 septic patients who survived (p=0.0003) and in controls (p=0.05). Complex I activity had a significant inverse correlation with norepinephrine requirements (a proxy for shock severity, p=0.0003) and nitrite/nitrate concentrations (p=0.0004), and a significant positive correlation with concentrations of reduced glutathione (p=0.006) and ATP (p=0.03)., Interpretation: In septic patients, we found an association between nitric oxide overproduction, antioxidant depletion, mitochondrial dysfunction, and decreased ATP concentrations that relate to organ failure and eventual outcome. These data implicate bioenergetic failure as an important pathophysiological mechanism underlying multiorgan dysfunction.