Correction to: Spectrum of movement disorders and neurotransmitter abnormalities in paediatric POLG disease.

Due to a typesetting error the wrong Table 2 was used. The correct Table 2 is shown here.

Spectrum of movement disorders and neurotransmitter abnormalities in paediatric POLG disease.

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.

Clinical features and pharmacotherapy of childhood monoamine neurotransmitter disorders.

Childhood neurotransmitter disorders are increasingly recognised as an expanding group of inherited neurometabolic syndromes. They are caused by disturbance in synthesis, metabolism, and homeostasis of the monoamine neurotransmitters, including the catecholamines (dopamine, norepinephrine, and epinephrine) and serotonin. Disturbances in monoamine neurotransmission will lead to neurological symptoms that often overlap with clinical features of other childhood neurological disorders (such as hypoxic ischaemic encephalopathy, cerebral palsy, other movement disorders, and paroxysmal conditions); consequently, neurotransmitter disorders are frequently misdiagnosed. The diagnosis of neurotransmitter disorders is made through detailed clinical assessment, analysis of cerebrospinal fluid neurotransmitters, and further supportive diagnostic investigations. Early and accurate diagnosis of neurotransmitter disorders is important, as many are amenable to therapeutic intervention. The principles of treatment for monoamine neurotransmitter disorders are mainly directly derived from understanding these metabolic pathways. In disorders characterized by enzyme deficiency, we aim to increase monoamine substrate availability, boost enzyme co-factor levels, reduce monoamine breakdown, and replace depleted levels of monoamines with pharmacological analogs as clinically indicated. Most monoamine neurotransmitter disorders lead to reduced levels of central dopamine and/or serotonin. Complete amelioration of motor symptoms is achievable in some disorders, such as Segawa's syndrome, and, in other conditions, significant improvement in quality of life can be attained with pharmacotherapy. In this review, we provide an overview of the clinical features and current treatment strategies for childhood monoamine neurotransmitter disorders.

Effect of Coenzyme Q10 supplementation on mitochondrial electron transport chain activity and mitochondrial oxidative stress in Coenzyme Q10 deficient human neuronal cells.

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.

Altered skeletal muscle insulin signaling and mitochondrial complex II-III linked activity in adult offspring of obese mice.

We recently reported insulin resistance in adult offspring of obese C57BL/6J mice. We have now evaluated whether parameters of skeletal muscle structure and function may play a role in insulin resistance in this model of developmental programming. Obesity was induced in female mice by feeding a highly palatable sugar and fat-rich diet for 6 wk prior to pregnancy, and during pregnancy and lactation. Offspring of obese dams were weaned onto standard laboratory chow. At 3 mo of age, skeletal muscle insulin signaling protein expression, mitochondrial electron transport chain activity (ETC), muscle fiber type, fiber density, and fiber cross-sectional area were compared with that of offspring of control dams weaned onto the chow diet. Female offspring of obese dams demonstrated decreased skeletal muscle expression of p110beta, the catalytic subunit of PI3K (P < 0.01), as well as reduced Akt phosphorylation at Serine residue 473 compared with control offspring. Male offspring of obese dams demonstrated increased skeletal muscle Akt2 and PKCzeta expression (P < 0.01; P < 0.001, respectively). A decrease in mitochondrial-linked complex II-III was observed in male offspring of obese dams (P < 0.01), which was unrelated to CoQ deficiency. This was not observed in females. There were no differences in muscle fiber density between offspring of obese dams and control offspring in either sex. Sex-related alterations in key insulin-signaling proteins and in mitochondrial ETC may contribute to a state of insulin resistance in offspring of obese mice.

Mitochondrial cytochrome c release: a factor to consider in mitochondrial disease?

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.

Nitric oxide accelerates the degradation of tetrahydrobiopterin but not total neopterin in cerebrospinal fluid; potential implications for the assessment of tetrahydrobiopterin metabolism.

Assessment of total neopterin and tetrahydrobioterin (BH4) concentrations in cerebrospinal fluid (CSF) can be used to identify potential disorders of BH4 biosynthesis. In this study, we demonstrate that exposure of CSF to nitric oxide leads to an accelerated degradation of BH4 but does not affect the total neopterin concentration. These data suggest that in those conditions associated with increased nitric oxide formation, perturbation of the total neopterin to BH4 ratio could occur. Under such circumstances a putative diagnosis of a defect in BH4 biosynthesis may erroneously be proposed. Assessment of central nitric oxide generation may therefore be a useful adjunct to the determination of CSF pterin status.

Inhibition of mitochondrial complex IV leads to secondary loss complex II-III activity: implications for the pathogenesis and treatment of mitochondrial encephalomyopathies.

Mitochondrial encephalomyopathies, arising from deficiencies of the electron transport chain (ETC) give rise to a wide clinical spectrum of presentation and are often progressive in nature. The aetiology of mitochondrial encephalomyopathies have yet to be fully elucidated, however, a successive loss of ETC function may contribute to the progressive nature of these disorders. The possibility arises that as a consequence of a primary impairment of ETC activity, secondary damage to the ETC may occur. In order to investigate this hypothesis, we established a model of cytochrome oxidase (Complex IV) deficiency in cultured human astrocytoma 1321N cells. Potassium cyanide (KCN, 1mM) resulted in a sustained 50% (p<0.01) loss of complex IV. At 24h activities of the other ETC complexes were unaffected. However, at 72h significant loss of succinate-cytochrome c reductase (complex II-III) activity expressed as a ratio to the mitochondrial marker, citrate synthase was observed. (KCN treated; 0.065+/-0.011 vs controls; 0.118+/-0.017 mean+/-SEM, n=8, p<0.05). These results provide a possible mechanism for the progressive nature of ETC defects and why in some patients multiple patterns of ETC deficiencies can be demonstrated.

Tetrahydrobiopterin availability, nitric oxide metabolism and glutathione status in the hph-1 mouse; implications for the pathogenesis and treatment of tetrahydrobiopterin deficiency states.

Tetrahydrobiopterin (BH4) is an essential cofactor for all isoforms of nitric oxide synthase. While it is well established that BH4 deficiency states are associated with impairment of dopamine, serotonin and phenylalanine metabolism, less is known with regard to the effects of deficiency of the cofactor upon nitric oxide (NO) metabolism. In this study, we have evaluated the effects of partial BH4 deficiency upon (a) tissue availability of the antioxidant glutathione, (b) basal NO production and (c) NO generation following exposure to lipopolysaccharide (LPS), which is known to increase expression of the inducible form of nitric oxide synthase. Using the hph-1 mouse, which displays a partial BH4 deficiency owing to impaired activity of GTP cyclohydrolase, we report decreased levels of glutathione in brain and kidney and evidence for decreased basal generation of nitric oxide in the periphery (as judged by the plasma nitrate plus nitrite concentration). Following LPS administration, peripheral NO generation increases. However, the concentration of plasma nitrate plus nitrite achieved was significantly decreased in the hph-1 mouse. Furthermore, LPS administration caused loss of glutathione in both wild-type and hph-1 liver and kidney. It is concluded that cofactor replacement, sufficient to fully correct a cellular BH4 deficiency, may be of benefit to patients with inborn errors of BH4 metabolism.

Glutathione deficiency in patients with mitochondrial disease: implications for pathogenesis and treatment.

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.

Co-culture of neurones with glutathione deficient astrocytes leads to increased neuronal susceptibility to nitric oxide and increased glutamate-cysteine ligase activity.

The antioxidant glutathione (GSH) plays an important role in protecting the mitochondrial electron transport chain (ETC) from damage by oxidative stress in astrocytes and neurones. Neurones co-cultured with astrocytes have greater GSH levels, compared to neurones cultured alone, leading to the hypothesis that astrocytes play a key role in brain GSH metabolism by supplying essential GSH precursors to neurones. A previous study has postulated that damage to the ETC following exposure to reactive nitrogen species (RNS) is less in co-cultured neurones, compared to neurones cultured alone, because of the greater GSH levels in the former cells. To investigate this further, primary culture rat neurones were co-cultured with either rat astrocytes activated with IFN-gamma and LPS to produce NO, or NO-generating astrocytes that had been depleted of intracellular GSH by 87% following incubation with the GSH synthesis inhibitor L-buthionine-S,R-sulfoximine (L-BSO). Neurones incubated with NO-generating astrocytes depleted of GSH were unable to elevate GSH levels, unlike neurones co-cultured with NO-generating astrocytes. Complexes II + III and IV of the neuronal ETC were significantly inhibited following exposure to NO-generating astrocytes depleted of GSH. No ETC damage was observed in neurones co-cultured with NO-generating astrocytes. Although neurones co-cultured with GSH depleted astrocytes did not increase cellular GSH levels, the activity of glutamate cysteine ligase (GCL), the rate-limiting enzyme of GSH synthesis, was increased by 218%, compared to neurones cultured with control astrocytes. This suggests that neuronal GCL activity could be modulated when GSH metabolism is inhibited in neighboring astrocytes.

Alterations in expression of dopamine receptors and neuropeptides in the striatum of GTP cyclohydrolase-deficient mice.

The hph-1 mice have defective tetrahydrobiopterin biosynthesis and share many neurochemical similarities with l-dopa-responsive dystonia (DRD) in humans. In both, there are deficiencies in GTP cyclohydrolase I and low brain levels of dopamine (DA). Striatal tyrosine hydroxylase (TH) levels are decreased while the number of DA neurones in substantia nigra (SN) appears normal. The hph-1 mouse is therefore a useful model in which to investigate the biochemical mechanisms underlying dystonia in DRD. In the present study, the density of striatal DA terminals and DA receptors and the expression of D-1, D-2, and D-3 receptors, preproenkephalin (PPE-A), preprotachykinin (PPT), and nitric oxide synthase (NOS) mRNAs in the striatum and nucleus accumbens and nigral TH mRNA expression were examined. Striatal DA terminal density as judged by specific [3H]mazindol binding was not altered while the levels of TH mRNA were elevated in the SN of hph-1 mice compared to control (C57BL) mice. Total and subregional analysis of the striatum and nucleus accumbens showed that D-2 receptor ([3H]spiperone) binding density was increased while D-1 receptor ([3H]SCH 23390) and D-3 receptor ([3H]7-OH-DPAT) binding density was not altered. In the striatum and nucleus accumbens, expression of PPT mRNA was elevated but PPE-A mRNA, D-1, D-2 receptor, and nNOS mRNA were not changed in hph-1 mice compared to controls. These findings suggest that an imbalance between the direct strionigral and indirect striopallidal output pathways may be relevant to the genesis of DRD. However, the pattern of changes observed is not that expected as a result of striatal dopamine deficiency and suggests that other effects of GTP cyclohydrolase I deficiency may be involved.

Infantile Parkinsonism-dystonia and elevated dopamine metabolites in CSF.

Two girls and one boy are described, with severe infantile parkinsonism-dystonia. This syndrome is usually caused by endogenous dopamine deficiency but in these patients was associated with elevated dopamine metabolites in CSF and an unusual eye movement disorder: ocular flutter together with saccade initiation failure. Pyramidal tract signs also emerged in the course of the disease in two patients. This combination of symptoms and biochemical findings suggests a unique pathogenic mechanism.

Primary pyruvate dehydrogenase E3 binding protein deficiency with mild hyperlactataemia and hyperalaninaemia.

A case of pyruvate dehydrogenase E3 binding protein deficiency is reported in a 24-year-old male with encephalomyopathy. Blood lactate was only minimally elevated, as was alanine.

Differential effect of nitric oxide on glutathione metabolism and mitochondrial function in astrocytes and neurones: implications for neuroprotection/neurodegeneration?

Primary culture rat astrocytes exposed to the long acting nitric oxide donor (Z)-1-[2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NO) for 24 h approximately double their concentration of glutathione (GSH) and show no sign of cell death. In contrast, GSH was depleted by 48%, and significant loss of mitochondrial respiratory chain complex activity and cell death were observed in primary culture rat neurones subjected to DETA-NO for 18 h. Northern blot analysis suggested that mRNA amounts of both subunits of glutamate-cysteine ligase (GCL), the rate-limiting enzyme in GSH synthesis, were elevated in astrocytes following nitric oxide (NO) exposure. This correlated with an increase in astrocytic GCL activity. Neurones on the other hand did not exhibit increased GCL activity when exposed to NO. In addition, the rate of GSH efflux was doubled and gamma-glutamyltranspeptidase (gamma-GT) activity was increased by 42% in astrocytes treated with NO for 24 h. These results suggest that astrocytes, but not neurones, up-regulate GSH synthesis as a defence mechanism against excess NO. It is possible that the increased rate of GSH release and activity of gamma-GT in astrocytes may have important implications for neuroprotection in vivo by optimizing the supply of GSH precursors to neurones in close proximity.

N-acetylcysteine and Unverricht-Lundborg disease: variable response and possible side effects.

Serum glutathione levels were assessed in a patient with genetically proven Unverricht-Lundborg disease (ULD) before and during treatment with the antioxidant N-acetylcysteine (NAC). Glutathione levels were low before treatment, and increased during treatment. This increase was mirrored by an improvement in seizures, but not in myoclonus or ataxia. Three other patients with clinically determined ULD showed a variable response and some notable side effects during treatment with NAC.

Diagnostic value of succinate ubiquinone reductase activity in the identification of patients with mitochondrial DNA depletion.

Mitochondrial DNA (mtDNA) depletion syndrome (McKusick 251880) is characterized by a progressive quantitative loss of mtDNA resulting in severe mitochondrial dysfunction. A diagnosis of mtDNA depletion can only be confirmed after Southern blot analysis of affected tissue. Only a limited number of centres have the facilities to offer this service, and this is frequently on an irregular basis. There is therefore a need for a test that can refine sample selection as well as complementing the molecular analysis. In this study we compared the activities of the nuclear-encoded succinate ubiquinone reductase (complex II) to the activities of the combined mitochondrial and nuclear-encoded mitochondrial electron transport chain (ETC) complexes; NADH:ubiquinone reductase (complex I), ubiquinol-cytochrome-c reductase (complex III), and cytochrome-c oxidase (complex IV), in skeletal muscle biopsies from 7 patients with confirmed mtDNA depletion. In one patient there was no evidence of an ETC defect. However, the remaining 6 patients exhibited reduced complex I and IV activities. Five of these patients also displayed reduced complex II-III (succinate:cytochrome-c reductase) activity. Individual measurement of complex II and complex III activities demonstrated normal levels of complex II activity compared to complex III, which was reduced in the 5 biopsies assayed. These findings suggest a possible diagnostic value for the detection of normal levels of complex II activity in conjunction with reduced complex I, III and IV activity in the identification of likely candidates for mtDNA depletion syndrome

Nitric oxide-dependent damage to neuronal mitochondria involves the NMDA receptor.

Cytokine-stimulated astrocytes produce nitric oxide, which can inhibit components of the mitochondrial respiratory chain. We have previously demonstrated that prolonged exposure (48 h) to rat astrocytic nitric oxide damages complexes II--III and IV of neighbouring rat neurons in coculture, resulting in neuronal death. Expanding on these observations, we have now shown that the NMDA receptor antagonist, MK-801, prevents this damage, suggesting involvement of glutamate. We postulate that astrocyte-derived nitric oxide stimulates release of neuronal glutamate. Indeed we demonstrate that neurons incubated with nitric oxide-generating astrocytes display enhanced glutamate release. Furthermore, direct exposure to the nitric oxide donor, DETA-NONOate resulted in a loss of activity of all the neuronal mitochondrial complexes, which was again prevented by MK-801. Thus, nitric oxide, generated by both cytokine-stimulated astrocytes and by a nitric oxide donor, causes activation of the NMDA receptor leading to damage to the neuronal mitochondrial respiratory chain. Glutamate exposure is known to damage the neuronal mitochondrial respiratory chain via neuronal nitric oxide synthase. Therefore, we propose that astrocyte-derived nitric oxide is capable of eliciting neuronal glutamate release, which in turn activates the neuronal NMDA receptor and stimulates further formation of reactive nitrogen species via neuronal nitric oxide synthases, leading to mitochondrial damage and neuronal death. Our findings support the hypothesis that glutamate, reactive nitrogen species and mitochondrial dysfunction may have a role in the neurodegenerative process.

Blood mononuclear cell coenzyme Q10 concentration and mitochondrial respiratory chain succinate cytochrome-c reductase activity in phenylketonuric patients.

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.