Treatment with antioxidants ameliorates oxidative damage in a mouse model of propionic acidemia.

Oxidative stress contributes to the pathogenesis of propionic acidemia (PA), a life threatening disease caused by the deficiency of propionyl CoA-carboxylase, in the catabolic pathway of branched-chain amino acids, odd-number chain fatty acids and cholesterol. Patients develop multisystemic complications including seizures, extrapyramidal symptoms, basal ganglia deterioration, pancreatitis and cardiomyopathy. The accumulation of toxic metabolites results in mitochondrial dysfunction, increased reactive oxygen species and oxidative damage, all of which have been documented in patients' samples and in a hypomorphic mouse model. Here we set out to investigate whether treatment with a mitochondria-targeted antioxidant, MitoQ, or with the natural polyphenol resveratrol, which is reported to have antioxidant and mitochondrial activation properties, could ameliorate the altered redox status and its functional consequences in the PA mouse model. The results show that oral treatment with MitoQ or resveratrol decreases lipid peroxidation and the expression levels of DNA repair enzyme OGG1 in PA mouse liver, as well as inducing tissue-specific changes in the expression of antioxidant enzymes. Notably, treatment decreased the cardiac hypertrophy marker BNP that is found upregulated in the PA mouse heart. Overall, the results provide in vivo evidence to justify more in depth investigations of antioxidants as adjuvant therapy in PA.

Anaplerotic therapy in propionic acidemia.

BACKGROUND: Propionic acidemia is a rare metabolic disorder caused by a deficiency of propionyl- CoA carboxylase, the enzyme converting propionyl-CoA to methylmalonyl-CoA that subsequently enters the citric acid cycle as succinyl-CoA. Patients with propionic acidemia cannot metabolize propionic acid, which combines with oxaloacetate to form methylcitric acid. This, with the defective supply of succinyl-CoA, may lead to a deficiency in citric acid cycle intermediates. PURPOSE: The objective of this study was to determine whether supplements with glutamine (400mg/kg per day), citrate (7.5mEq/kg per day), or ornithine α-ketoglutarate (400mg/kg per day) (anaplerotic agents that could fill up the citric acid cycle) would affect plasma levels of glutamine and ammonia, the urinary excretion of Krebs cycle intermediates, and the clinical outcome in 3 patients with propionic acidemia. METHODS: Each supplement was administered daily for four weeks with a two week washout period between supplements. The supplement that produced the most favorable changes was supplemented for 30 weeks following the initial study period and then for a 2 year extension. RESULTS: The urinary excretion of the Krebs cycle intermediates, α-ketoglutarate, succinate, and fumarate increased significantly compared to baseline during citrate supplementation, but not with the other two supplements. For this reason, citrate supplements were continued in the second part of the study. The urinary excretion of methylcitric acid and 3-hydroxypropionic acid did not change with any intervention. No significant changes in ammonia or glutamine levels were observed with any supplement. However, supplementation with any anaplerotic agents normalized the physiological buffering of ammonia by glutamate, with plasma glutamate and alanine levels significantly increasing, rather than decreasing with increasing ammonia levels. No significant side effects were observed with any therapy and safety labs (blood counts, chemistry and thyroid profile) remained unchanged. Motor and cognitive development was severely delayed before the trial and did not change significantly with therapy. Hospitalizations per year did not change during the trial period, but decreased significantly (p<0.05) in the 2years following the study (when citrate was continued) compared to the 2years before and during the study. CONCLUSIONS: These results indicate that citrate entered the Krebs cycle providing successful anaplerotic therapy by increasing levels of the downstream intermediates of the Krebs cycle: α-ketoglutarate, succinate and fumarate. Citrate supplements were safe and might have contributed to reduce hospitalizations in patients with propionic acidemia.

Successful reversal of propionic acidaemia associated cardiomyopathy: evidence for low myocardial coenzyme Q10 status and secondary mitochondrial dysfunction as an underlying pathophysiological mechanism.

Dilated cardiomyopathy is a rare complication in propionic acidaemia (PA). Underlying pathophysiological mechanisms are poorly understood. We present a child of Pakistani consanguineous parents, diagnosed with late-onset PA at 18months of age. He presented a mild phenotype, showed no severe further decompensations, normal growth and psychomotor development on a low protein diet and carnitine supplementation. At 15years, a mildly dilated left ventricle was noticed. At 17years he presented after a 2-3month history of lethargy and weight loss with severe decompensated dilated cardiomyopathy. He was stabilised on inotropic support and continuous haemofiltration; a Berlin Heart biventricular assist device was implanted. He received d,l-hydroxybutyrate 200mg/kg/day, riboflavin and thiamine 200mg/day each and coenzyme Q10 (CoQ10). Myocardial biopsy showed endocardial fibrosis, enlarged mitochondria, with atypical cristae and slightly low respiratory chain (RC) complex IV activity relative to citrate synthase (0.012, reference range 0.014-0.034). Myocardial CoQ10 was markedly decreased (224pmol/mg, reference range 942-2738), with a marginally decreased white blood cell level (34pmol/mg reference range 37-133). The dose of CoQ10 was increased from 1.5 to 25mg/kg/day. Cardiomyopathy slowly improved allowing removal of the external mechanical cardiac support after 67days. We demonstrate for the first time low myocardial CoQ10 in cardiomyopathy in PA, highlighting secondary mitochondrial impairment as a relevant causative mechanism. According to these findings, a high-dose CoQ10 supplementation could be a potential adjuvant therapeutic to be considered in PA-related cardiomyopathy.

Disruption of mitochondrial homeostasis in organic acidurias: insights from human and animal studies.

Organic acidurias or organic acidemias constitute a group of inherited disorders caused by deficient activity of specific enzymes of amino acids, carbohydrates or lipids catabolism, leading to large accumulation and excretion of one or more carboxylic (organic) acids. Affected patients usually present neurologic symptoms and abnormalities, sometimes accompanied by cardiac and skeletal muscle alterations, whose pathogenesis is poorly known. However, in recent years growing evidence has emerged indicating that mitochondrial dysfunction is directly or indirectly involved in the pathology of various organic acidemias. Mitochondrial impairment in some of these diseases are generally due to mutations in nuclear genes of the tricarboxylic acid cycle or oxidative phosphorylation, while in others it seems to result from toxic influences of the endogenous organic acids to the mitochondrion. In this minireview, we will briefly summarize the present knowledge obtained from human and animal studies showing that disruption of mitochondrial homeostasis may represent a relevant pathomechanism of tissue damage in selective organic acidemias. The discussion will focus on mitochondrial alterations found in patients affected by organic acidemias and by the deleterious effects of the accumulating organic acids on mitochondrial pathways that are crucial for ATP formation and transfer. The elucidation of the mechanisms of toxicity of these acidic compounds offers new perspectives for potential novel adjuvant therapeutic strategies in selected disorders of this group.