Cofactor treatment improves ATP synthetic capacity in patients with oxidative phosphorylation disorders
Introduction
Oxidative phosphorylation (OXPHOS) disorders are being increasingly identified and are characterized by a decline in the ability to supply cellular energy requirements. OXPHOS is unique because it is the only metabolic pathway controlled by both the nuclear and mitochondrial genomes, which may contribute to the vast clinical and genetic heterogeneity seen in associated disorders. Characteristics of the mitochondrial genome, such as replicative segregation, contribute to the broad spectrum of clinical presentations associated with defects in OXPHOS. Clinical features may include a combination of neuromuscular and non-neuromuscular symptoms with a progressive course and involvement of seemingly unrelated tissues. In fact, an OXPHOS disorder can give rise to any symptom, in any organ or tissue, at any age, and with any mode of inheritance [1]. Regardless of the specific defect, most OXPHOS disorders are marked by a decline in ATP synthetic capacity, a key product of mitochondrial metabolism. The goal of nutritional cofactor therapy in OXPHOS disease is to increase mitochondrial ATP production and slow or arrest the progression of clinical symptoms. The accumulation of toxic metabolites and concomitant reduction of respiratory activities has lead to the use of antioxidants, electron transfer mediators (which bypass the defective site), and enzyme cofactors in treatment modalities. Coenzyme Q10 (CoQ10), other antioxidants such as ascorbic acid and vitamin E, riboflavin, thiamine, niacin, vitamin K (phylloquinone and menadione), and carnitine have all been utilized in the treatment of OXPHOS disorders.
CoQ10 is the most widely used supplement in the treatment of mitochondrial disorders. A number of reports describe improvements in physical performance [2], enhanced exercise tolerance [3], [4], [5], [6], decreased muscle weakness [7], [8] or improvement in neurological function [3]. Other studies have not demonstrated a significant improvement in either biochemical parameters or clinical symptoms upon CoQ10 treatment [9], [10].
Most of the reports on the effect of cofactor treatment have been based on case studies with limited patient numbers and the lack of objective measurements has made the interpretation of results difficult. There have been few controlled clinical trials with sufficient patient numbers to evaluate effectiveness of therapy and larger trials have been unable to confirm that the treatment significantly improved oxidative metabolism [11], [12]. In most of the studies, the treatment period may also have been too short for beneficial effects to become evident.
The present study was designed to test the hypothesis that there will be an increase in cellular ATP production after cofactor administration. To assess the effectiveness of a combined cofactor therapy, ATP synthesis in lymphocytes from mitochondrial disease patients was evaluated over a 12-month period. We have previously shown that isolated lymphocytes are an effective tool for detecting and monitoring OXPHOS dysfunction [13]. In this study, we evaluated 12 patients with proven OXPHOS defects and show that ATP synthetic capacity in lymphocytes improves after cofactor treatment. To further assess the effects of individual cofactors on mitochondrial ATP synthetic capacity, we supplemented isolated lymphocytes from control subjects with each cofactor individually. Our data demonstrate that there is an increase in ATP synthesis for control lymphocytes incubated with CoQ10 incubation and suggest that CoQ10 may be the active ingredient in the current treatment protocol.
Section snippets
Subjects
Patients with a clearly identified mitochondrial defect were recruited for this study after obtaining informed consent. The purpose and requirements of the study were fully explained to each subject before they gave consent to participate. The study was approved by the Health Research Ethics Board, Department of Medicine, University of Alberta. Twelve patients (Table 1) were evaluated in this study, representing five distinct mitochondrial disorders: Leber hereditary optic neuropathy (LHON
Clinical evaluation
The clinical evaluation and management of patients with OXPHOS disorders is difficult due to the broad spectrum of the disease and its unpredictable clinical course. The patients in this study, ranging in age from 9 to 58 years, were assessed by metabolic physicians in the Medical Genetics Clinic at the University of Alberta. The management of these patients (in addition to cofactor treatment) included medications to treat symptoms (seizures, neuropathic pain, cardiac dysfunction), prompt
Discussion
In the present study, we have been able to demonstrate for the first time that there is an increase in ATP synthetic capacity in lymphocytes from mitochondrial disease patients undergoing cofactor treatment, although our patients did not experience an improvement in clinical symptoms. Reliance on clinical observation to assess the effectiveness of treatment in an open study such as this is difficult. The mitochondrial disorders in this study represent a variety of disease states ranging from
Acknowledgements
We thank the patients and control subjects for participating in this study, and Leanne Vicen-Wyhony and Elizabeth Dickinson for technical assistance. This work was supported by grants from the Canadian Institutes of Health Research (CIHR) (to D.M.G.) and Natural Sciences and Engineering Research Council (NSERC) (to M.T.C.). B.J.M. was the recipient of an Alberta Heritage Foundation for Medical Research (AHFMR) Studentship and a Province of Alberta Graduate Fellowship. D.M.G. is an AHFMR Senior
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