Nataliya Povalko

L-arginine improves the symptoms of strokelike episodes in MELAS.

Based on the hypothesis that mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS) are caused by impaired vasodilation in an intracerebral artery, the authors evaluated the effects of administering l-arginine, a nitric oxide precursor. Patients were administered l-arginine intravenously at the acute phase or orally at the interictal phase. l-Arginine infusions significantly improved all strokelike symptoms, suggesting that oral administration within 30 minutes of a stroke significantly decreased frequency and severity of strokelike episodes.

Endothelial dysfunction in MELAS improved by l-arginine supplementation

The authors evaluated endothelial function in patients with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke) by flow-mediated vasodilation (FMD) and found a significant decrease vs controls. Two years of supplementation with oral l-arginine, a nitric oxide precursor, significantly improved endothelial function to control levels and was harmonized with the normalized plasma levels of l-arginine in patients. l-Arginine therapy improved endothelial dysfunction and showed promise in treating strokelike episodes in MELAS.

MELAS and l-arginine therapy: pathophysiology of stroke-like episodes

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke‐like episodes (MELAS) is a maternally inherited multisystem mitochondrial disorder. Although many molecular and cellular mechanisms have been discovered leading to mitochondrial cytopathy, the pathogenic mechanism of stroke‐like episodes seen in MELAS has not been clarified yet. According to the muscle and brain pathology and vascular physiology, mitochondrial angiopathy, or endothelial dysfunction, were proposed to play an important role for developing stroke‐like episodes. Based on a hypothesis of mitochondrial angiopathy theory, we use l‐arginine in MELAS patients and report its usefulness. This review aims to give a general idea on the actual knowledge about the possible pathogenic mechanism of stroke‐like episodes, including clinical symptoms that lead to stroke‐like episodes, muscle, or brain pathology, molecular cellular functions, neuroimagings including MRI, MRS, and SPECT, and the proposed site of action of l‐arginine therapy on MELAS patients. Currently, l‐arginine therapy may be the most promising for the treatment of stroke‐like episodes in MELAS.

MELAS: A nationwide prospective cohort study of 96 patients in Japan

BACKGROUND MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) (OMIM 540000) is the most dominant subtype of mitochondrial myopathy. The aim of this study was to determine the prevalence, natural course, and severity of MELAS. METHODS A prospective cohort study of 96 Japanese patients with MELAS was followed between June 2003 and April 2008. Patients with MELAS were identified and enrolled based on questionnaires administered to neurologists in Japan. MELAS was defined using the Japanese diagnostic criteria for MELAS. Two follow-up questionnaires were administered to neurologists managing MELAS patients at an interval of 5years. RESULTS A prevalence of at least 0.58 (95% confidential interval (CI), 0.54-0.62)/100,000 was calculated for mitochondrial myopathy, whereas the prevalence of MELAS was 0.18 (95%CI, 0.02-0.34)/100,000 in the total population. MELAS patients were divided into two sub-groups: juvenile form and adult form. Stroke-like episodes, seizure and headache were the most frequent symptoms seen in both forms of MELAS. Short stature was significantly more frequent in the juvenile form, whereas hearing loss, cortical blindness and diabetes mellitus were significantly more frequent in the adult form. According to the Japanese mitochondrial disease rating scale, MELAS patients showed rapidly increasing scores (mean±standard deviation, 12.8±8.7) within 5years from onset of the disease. According to a Kaplan-Meier analysis, the juvenile form was associated with a higher risk of death than the adult form (hazard ratio, 3.29; 95%CI, 1.32-8.20; p=0.0105). CONCLUSIONS AND GENERAL SIGNIFICANCE We confirmed that MELAS shows a rapid degenerative progression within a 5-year interval and that this occurs in both the juvenile and the adult forms of MELAS and follows different natural courses. This article is part of a Special Issue entitled: Biochemistry of Mitochondria.

Molecular pathology of MELAS and L-arginine effects.

BACKGROUND The pathogenic mechanism of stroke-like episodes seen in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) has not been clarified yet. About 80% of MELAS patients have an A3243G mutation in the mitochondrial tRNA(Leu(UUR)) gene, which is the base change at position 14 in the consensus structure of tRNA(Leu(UUR)) gene. SCOPE OF REVIEW This review aims to give an overview on the actual knowledge about the pathogenic mechanism of mitochondrial cytopathy at the molecular levels, the possible pathogenic mechanism of mitochondrial angiopathy to cause stroke-like episodes at the clinical and pathophysiological levels, and the proposed site of action of l-arginine therapy on MELAS. MAJOR CONCLUSIONS Molecular pathogenesis is mainly demonstrated using ρ(0) cybrid system. The mutation creates the protein synthesis defects caused by 1) decreased life span of steady state amount of tRNA(Leu(UUR)) molecules; 2) decreased ratio of aminoacyl-tRNA(Leu(UUR)) versus uncharged tRNA(Leu(UUR)) molecules; 3) the accumulation of aminoacylation with leucine without any misacylation; 4) accumulation of processing intermediates such as RNA 19, 5) wobble modification defects. All of these loss of function abnormalities are created by the threshold effects of cell or organ to the mitochondrial energy requirement when they establish the phenotype. Mitochondrial angiopathy demonstrated by muscle or brain pathology, as SSV (SDH strongly stained vessels), and by vascular physiology using FMD (flow mediated dilation). MELAS patients show decreased capacity of NO dependent vasodilation because of the low plasma levels of l-arginine and/or of respiratory chain dysfunction. Although the underlying mechanisms are not completely understood in stroke-like episodes in MELAS, l-arginine therapy improved endothelial dysfunction. GENERAL SIGNIFICANCE Though the molecular pathogenesis of an A3243G or T3271C mutation of mitochondrial tRNA(Leu(UUR)) gene has been clarified as a mitochondrial cytopathy, the underlying mechanisms of stroke-like episodes in MELAS are not completely understood. At this point, l-arginine therapy showed promise in treating of the stroke-like episodes in MELAS. This article is part of a Special Issue entitled Biochemistry of Mitochondria.

Beneficial effect of pyruvate therapy on Leigh syndrome due to a novel mutation in PDH E1α gene

Leigh syndrome (LS) is a progressive untreatable degenerating mitochondrial disorder caused by either mitochondrial or nuclear DNA mutations. A patient was a second child of unconsanguineous parents. On the third day of birth, he was transferred to neonatal intensive care units because of severe lactic acidosis. Since he was showing continuous lactic acidosis, the oral supplementation of dichloroacetate (DCA) was introduced on 31st day of birth at initial dose of 50 mg/kg, followed by maintenance dose of 25 mg/kg/every 12 h. The patient was diagnosed with LS due to a point mutation of an A-C at nucleotide 599 in exon 6 in the pyruvate dehydrogenase E1α gene, resulting in the substitution of aspartate for threonine at position 200 (N200T). Although the concentrations of lactate and pyruvate in blood were slightly decreased, his clinical conditions were deteriorating progressively. In order to overcome the mitochondrial or cytosolic energy crisis indicated by lactic acidosis as well as clinical symptoms, we terminated the DCA and administered 0.5 g/kg/day TID of sodium pyruvate orally. We analyzed the therapeutic effects of DCA or sodium pyruvate in the patient, and found that pyruvate therapy significantly decreased lactate, pyruvate and alanine levels, showed no adverse effects such as severe neuropathy seen in DCA, and had better clinical response on development and epilepsy. Though the efficacy of pyruvate on LS will be evaluated by randomized double-blind placebo-controlled study design in future, pyruvate therapy is a possible candidate for therapeutic choice for currently incurable mitochondrial disorders such as LS.

Effect of l-arginine on synaptosomal mitochondrial function

OBJECTIVE Specific aim of this study is to elucidate the direct effects of L-arginine on the synaptosomal neurotransmission related to the mitochondrial respiratory function. METHODS Using isolated endbrains from wild-type mice (ICR), crude synaptosome was analyzed for their concentration of gamma-aminobutyric acid (GABA) and glutamate (Glu) with/without addition of L-arginine. We analyzed the contents of releasing amino acids evoked by high potassium condition and uptake of them in three separated fractions (cytosol, vesicles, and intact mitochondria). The oxygen consumption was also measured by oxygen electrode. RESULTS The entire uptakes of GABA and Glu were inhibited by rotenone (about 30 nmol/mg protein) with dose-dependent manner and showed a plateau at about 70% of total uptake. L-arginine inhibited the uptake of Glu logarithmically, however it showed no change in uptake of GABA. The contents of GABA and Glu in synaptosome were decreased in the presence of L-arginine. L-arginine enhanced the respiration of state II by succinate on synaptosomal respiration, although the respiration of synaptosomal mitochondrial fraction and the respiratory chains enzyme activities were almost unaffected by L-arginine. In the presence of rotenone, L-arginine decreased the uptake of Glu without changing the uptake of GABA, increased the releasing of GABA, and may modulate the excitability of neuronal state on the cytosol, cytomembrane, and/or organelles except for mitochondria. CONCLUSIONS L-arginine may modulate excitation by neurotransmitters at nerve endings, in relation to potentiated respiratory metabolism of succinate in synaptosomes. Such effects might contribute to alleviation of stroke-like symptoms in MELAS.

New TRPM6 mutation and management of hypomagnesaemia with secondary hypocalcaemia

BACKGROUND TRPM6 gene mutation has been reported to cause hypomagnesemia with secondary hypocalcemia (HSH). However, the genotype-phenotype correlation for TRPM6 gene mutations has not been clarified. OBJECTIVE To elucidate the factors underlying the severe neurological complications in HSH and evaluate the potential association between the location of TRPM6 gene mutations and clinical data of HSH. METHODS A Japanese patient diagnosed with HSH at 10 weeks of age exhibited neurological damage and failed to thrive. Magnesium supplements were therefore started at 12 weeks of age. Mutational analysis of the TRPM6 gene was performed using a direct sequencing method to determine the position and type of mutation. Using the data of 29 HSH patients reported in the literature, linear regression analysis was also performed to examine the association between TRPM6 gene mutation location and HSH onset age, initial serum magnesium and calcium concentrations, and dose of oral magnesium. RESULTS A novel stop-codon homozygous mutation [c.4190 G>A] W1397X was identified in exon 26 of the patients TRPM6 gene. No statistical correlation was found between the location of mutations in the TRPM6 gene and the clinical data for 4 clinical indicators of HSH. CONCLUSIONS We identified the first Japanese HSH patient with a novel nonsense mutation in the TRPM6 gene. Regression analysis of mutation locations in the protein-coding region of TRPM6 and the reported clinical data for 4 clinical indicators of HSH in 30 HSH patients did not detect a genotype-phenotype correlation.