Exogenous coenzyme Q (coq) fails to increase coq in skeletal muscle of two patients with mitochondrial myopathies

Secondary coenzyme Q deficiency in neurological disorders

Coenzyme Q (CoQ) is a ubiquitous lipid serving essential cellular functions. It is the only component of the mitochondrial respiratory chain that can be exogenously absorbed. Here, we provide an overview of current knowledge, controversies, and open questions about CoQ intracellular and tissue distribution, in particular in brain and skeletal muscle. We discuss human neurological diseases and mouse models associated with secondary CoQ deficiency in these tissues and highlight pharmacokinetic and anatomical challenges in exogenous CoQ biodistribution, recent improvements in CoQ formulations and imaging, as well as alternative therapeutical strategies to CoQ supplementation. The last section proposes possible mechanisms underlying secondary CoQ deficiency in human diseases with emphasis on neurological and neuromuscular disorders.

Histological characterization and biochemical analysis of paraspinal muscles in neuromuscularly healthy subjects

INTRODUCTION

There are no generally accepted histopathological reference values in paraspinal skeletal muscle biopsies.

METHODS

We examined multifidii muscle biopsies from 20 neuromuscularly healthy subjects using routine histological stains and biochemical analyses of respiratory chain enzymes.

RESULTS

Staining showed incomplete myopathic features, such as increased variability in fiber size, type 1 hypertrophy, rounded fiber shape, endomysial fibrosis, and replacement by adipose tissue. Acid phosphatase reaction was positive in up to 35% of the selected muscle fibers. Mitochondrial changes were obvious but revealed no selective age dependence. Reduced complex I, cytochrome c oxidase (COX), and citrate synthase (CS) could be observed.

CONCLUSIONS

Because the increased variability in morphological details can easily be misinterpreted as myopathic changes, analysis of paraspinal muscles should take into consideration that incomplete myopathic features and reduced oxidative enzyme activities for complex I, COX, and CS are normal variations at this location.

Mitochondrial changes in skeletal muscle in amyotrophic lateral sclerosis and other neurogenic atrophies

Previous findings suggested specific mitochondrial dysfunction in skeletal muscle of patients with amyotrophic lateral sclerosis (ALS). To answer the question of whether the dysfunction is specific, we investigated the histochemical distribution of mitochondrial marker activities, the ratio of mitochondrial (mt) versus nuclear (n) DNA, and the activities of citrate synthase (CS) and respiratory chain enzymes in muscle biopsies of 24 patients with sporadic ALS. The data were compared with those in 23 patients with other neurogenic atrophies (NAs), and 21 healthy controls. Muscle histology revealed similar signs of focally diminished mitochondrial oxidation activity in muscle fibres in both diseased groups. There was only minimal decline of mt/nDNA ratios in ALS and NA patients in comparison with healthy controls. The specific activities of mitochondrial markers CS and succinate dehydrogenase were significantly increased in both ALS and NA patients. The specific activities of respiratory chain enzymes were not significantly different in all three groups. It is concluded that the histochemical, biochemical and molecular mitochondrial changes in muscle are not specific for ALS, but accompany other NAs as well.

Coenzyme Q 10 Improves Lactic Acidosis, Strokelike Episodes, and Epilepsy in a Patient With MELAS (Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Strokelike episodes)

Mitochondrial encephalomyopathies encompass a group of disorders that have impaired oxidative metabolism in skeletal muscles and central nervous system. Many compounds have been used in clinical trials on mitochondrial diseases, but the outcomes have been variable. It remains controversial whether treatment of mitochondrial diseases with coenzyme Q 10 is effective. This paper describes a case of mitochondrial myopathy, encephalopathy, lactic acidosis, strokelike episodes, and exercise intolerance successfully treated with coenzyme Q 10. Efficacy of this therapy in this patient is correlated to control of lactic acidosis and serum creatine kinase levels. Disappointingly, larger studies with coenzyme Q 10 failed to demonstrate a clear beneficial effect on the entire study population with regard to clinical improvement or several parameters of the oxidative metabolism. They suggest that the use of coenzyme Q in treatment of mitochondrial diseases should be confined to protocols. There is a confounding variation in phenotype and genotype, and the natural history of the disorders in individual patients is not accurately predictable. The unpredictable a priori efficacy of therapy suggests that a long-term trial of oral coenzyme Q may be warranted.

Nutritional and exercise-based therapies in the treatment of mitochondrial disease

PURPOSE OF REVIEW

This review will critically summarize the nutritional and exercise-based interventions that have been used to treat mitochondrial disease, with a focus on the biochemical or molecular rationale for their use as well as recent advances in the field.

RECENT FINDINGS

Many nutritional-based treatment strategies have been used in an attempt to target energy impairment and its sequelae. Recently, coenzyme Q10, idebenone and triacylglycerol have been shown to bypass defective respiratory enzymes or scavenge free radicals, whereas creatine monohydrate has provided an alternative energy source. Thiamine has been used to decrease lactate levels and increase flux through aerobic metabolism, and riboflavin has been used as a precursor to complexes I and II. Several therapies employing various antioxidants in combination with other supplements have been effective at targeting several of the final common pathways of mitochondrial disease. Miscellaneous supplements, such as L-arginine and uridine, have also had recent success. However, although positive responses have been reported with these agents, many reports have shown no benefit, and there is widespread disparity in the literature. An alternative approach to treatment is exercise training. Both resistance and endurance exercise training have had positive outcomes in patients with mitochondrial disease, although several questions remain to be answered.

SUMMARY

There is no currently recognized treatment for mitochondrial disease. Future clinical trials are needed, as well as research into the potential for in-vitro screening of various compounds within affected cells from patients. Until this time, an accurate diagnosis will facilitate treatment on a case-by-case basis.

Mitochondrial respiratory rates and activities of respiratory chain complexes correlate linearly with heteroplasmy of deleted mtDNA without threshold and independently of deletion size

To clarify the importance of deleted protein and tRNA genes on the impairment of mitochondrial function, we performed a quantitative analysis of biochemical, genetic and morphological findings in skeletal muscles of 16 patients with single deletions and 5 patients with multiple deletions of mtDNA. Clinically, all patients showed chronic progressive external ophthalmoplegia (CPEO). The size of deletions varied between 2.5 and 9 kb, and heteroplasmy between 31% and 94%. In patients with single deletions, the citrate synthase (CS) activity was nearly doubled. Decreased ratios of pyruvate- and succinate-dependent respiration were detected in fibers of all patients in comparison to controls. Inverse and linear correlations without thresholds were established between heteroplasmy and (i) CS referenced activities of the complexes of respiratory chain, (ii) CS referenced maximal respiratory rates, (iii) and cytochrome-c-oxidase (COX) negative fibers. In patients with single and multiple deletions, all respiratory chain complexes as well as the respiratory rates were decreased to a similar extent. All changes detected in patients with single deletions were independent of deletion size. In one patient, only genes of ND5, ND4L as well as tRNA(Leu(CUN)), tRNA(Ser(AGY)), and tRNA(His) were deleted. The pronounced decrease in COX activity in this patient points to the high pathological impact of these missing tRNA genes. The activity of nuclear encoded SDH was also significantly decreased in patients, but to a lesser extent. This is an indication of secondary disturbances of mitochondria at CPEO. In conclusion, we have shown that different deletions cause mitochondrial impairments of the same phenotype correlating with heteroplasmy. The missing threshold at the level of mitochondrial function seems to be characteristic for large-scale deletions were tRNA and protein genes are deleted.

Plasma phenylalanine is associated with decreased serum ubiquinone-10 concentrations in phenylketonuria

Decreased serum ubiquinone-10 concentrations is a common condition in patients with phenylketonuria (PKU) under dietary treatment. Our aim was to investigate the implication of the metabolic abnormalities of PKU (low concentrations of tyrosine and high concentrations of phenylalanine) and the effect of treatment with phenylalanine-restricted diets in decreased ubiquinone-10 concentrations in PKU patients. We studied 30 PKU patients (age range 5 months to 35 years; median age 7 years) under dietary treatment. Correlation between plasma tyrosine or phenylalanine and serum ubiquinone-10 concentrations was investigated. Daily cholesterol intake was calculated from the data obtained through a dietary questionnaire. The index of dietary control (IDC) was calculated as the average of the medians of plasma phenylalanine concentrations obtained every 6 months in the metabolic control of patients. Negative correlations were observed between serum ubiquinone and the IDC (r=-0.46; p<0.01) in PKU patients. No correlation was observed between tyrosine or daily cholesterol intake and serum ubiquinone concentrations. After adjustment for daily cholesterol intake by multiple linear regression analysis, for each 113 units of increase in IDC values serum ubiquinone decreased 0.1 micromol/L. According to our results, the main factor associated with the decreased serum ubiquinone concentrations was high plasma phenylalanine values. Although daily cholesterol intake seems to be associated with ubiquinone concentrations, it may not be relevant if we take into account the low intake of cholesterol in treated PKU patients.

Decreased serum ubiquinone-10 concentrations in phenylketonuria

BACKGROUND

Ubiquinone-10 is a lipid with important metabolic functions that may be decreased in phenylketonuria (PKU) because patients with PKU consume diets restricted in natural proteins.

OBJECTIVE

We studied serum ubiquinone-10 concentrations in PKU patients.

DESIGN

This was a retrospective, transversal study in which we compared serum ubiquinone-10, plasma cholesterol, plasma tyrosine, and plasma phenylalanine concentrations in 43 PKU patients with concentrations in a reference population (n = 102). Serum ubiquinone-10 concentrations were analyzed by HPLC with ultraviolet detection. Plasma tyrosine and phenylalanine were measured by ion-exchange chromatography.

RESULTS

Serum ubiquinone-10 concentrations in PKU patients were significantly lower than in the reference population (P < 0.01 for patients aged 1 mo to <8 y and P < 0.00005 for patients aged 8-33 y). Moreover, 5 of 18 PKU patients (28%) in the younger age group and 10 of 23 (43%) in the older age group had serum ubiquinone-10 concentrations below the reference interval.

CONCLUSIONS

Serum ubiquinone-10 deficiency appears to be related to the restricted diet of PKU patients. Because serum ubiquinone-10 plays a major antioxidant role in the protection of circulating lipoproteins, the correction of ubiquinone-10 concentrations should be considered in PKU patients. Further investigation seems advisable to elucidate whether the deficiency in serum ubiquinone-10 status is clinically significant.

Improved brain and muscle mitochondrial respiration with CoQ. An in vivo study by 31P-MR spectroscopy in patients with mitochondrial cytopathies

We used in vivo phosphorus magnetic resonance spectroscopy (31P-MRS) to study the effect of CoQ10 on the efficiency of brain and skeletal muscle mitochondrial respiration in ten patients with mitochondrial cytopathies. Before CoQ, brain [PCr] was remarkably lower in patients than in controls, while [Pi] and [ADP] were higher. Brain cytosolic free [Mg2+] and delta G of ATP hydrolysis were also abnormal in all patients. MRS also revealed abnormal mitochondrial function in the skeletal muscles of all patients, as shown by a decreased rate of PCr recovery from exercise. After six-months of treatment with CoQ (150 mg/day), all brain MRS-measurable variables as well as the rate of muscle mitochondrial respiration were remarkably improved in all patients. These in vivo findings show that treatment with CoQ in patients with mitochondrial cytopathies improves mitochondrial respiration in both brain and skeletal muscles, and are consistent with Lenaz's view that increased CoQ concentration in the mitochondrial membrane increases the efficiency of oxidative phosphorylation independently of enzyme deficit.

Biochemical monitoring of the treatment in paediatric patients with mitochondrial disease

Treatment strategies in mitochondrial diseases consist of several drugs that diminish the deleterious effects of the abnormal respiratory chain function, reduce the presence of toxic agents or correct deficiencies in essential cofactors. In this study we evaluated the monitoring of tocopherol, carnitine and ubiquinone concentrations in a group of paediatric patients during a follow-up period of 18 months and the response to treatment of these patients by means of the determination of blood lactate, plasma alanine and oxygen consumption by lymphocytes in relation to the clinical status of the patients. Tocopherol, carnitine and ubiquinone concentrations were easily corrected with therapy. Blood lactate proved the best biochemical tool to assess the response to treatment in paediatric patients. According to our results, improvement or stabilization of the clinical course seems to be more related to the biochemical or molecular defect than to the effectiveness of the treatment.

Effects of oral supplementation of coenzyme Q10 on 31P-NMR detected skeletal muscle energy metabolism in middle-aged post-polio subjects and normal volunteers

The effects of oral supplementation of 100 mg coenzyme Q10 (CoQ10) for 6 months on muscle energy metabolism during exercise and recovery were evaluated in middle-aged post-polio (n = 3) and healthy subjects (n = 4) by the use of phosphorus-31 nuclear magnetic resonance spectroscopy. The metabolic response to isometric plantar flexion at 60% of maximal voluntary contraction force (MVC) for 1.5 min was determined in gastrocnemius muscles before, after 3- (3MO) and 6-month (6MO) of CoQ10 supplementation. The MVC of plantar flexion was unchanged following CoQ10 supplementation. The resting Pi/PCr ratio in gastrocnemius muscles of all subjects decreased after 3MO- and 6MO-CoQ10 (P < 0.05). The post-polio individuals showed a progressive decrease in this ratio, while less pronounced changes were observed in the control subjects. Similarly, the post-polio individuals showed a lower Pi/PCr ratio at the end of 60% MVC in both 3MO- and 6MO-CoQ10, whereas no change in the ratio was observed in the control subjects. A less pronounced decrease in muscle pH was observed at the end of 60% MVC in both 3MO- and 6MO-CoQ10 in the post-polio individuals, but not in the control subjects. No systematic difference in end-exercise ATP was observed between the three phases in both groups. The half-time of recovery for PCr decreased in all subjects after 6MO-CoQ10 supplementation (P < 0.05). The results suggest that CoQ10 supplementation affects muscle energy metabolism in post-polio individuals to a greater extent than in control subjects. The mechanism for this effect is not clear, but may involve an effect of CoQ10 on peripheral circulation in the calf muscles, its action in mitochondrial oxidative phosphorylation and/or its antioxidant potential.

Coenzyme Q10 in the central nervous system and its potential usefulness in the treatment of neurodegenerative diseases

Coenzyme Q10 is an essential cofactor of the electron transport chain and is an antioxidant. We examined the effects of oral feeding with coenzyme Q10 in young animals on brain concentrations. Feeding with coenzyme Q10 at a dose of 200 mg/kg for 1-2 months in young rats resulted in significant increases in liver concentrations, however, there was no significant increase in brain concentrations of either reduced- or total coenzyme Q10 levels. Nevertheless there was a reduction in malonate-induced increases in 2,5 dihydroxybenzoic acid to salicylate, consistent with an antioxidant effect. In other studies we found that oral administration of coenzyme Q10 significantly reduced increased concentrations of lactate in the occipital cortex of Huntington's disease patients. These findings suggest that coenzyme Q10 might be useful in treating neurodegenerative diseases.

Muscle fatigue, lactate, and pyruvate in mitochondrial myopathy with progressive external ophthalmoplegia

We studied muscle fatigue and serum lactate and pyruvate levels in 20 patients with mitochondrial myopathy with progressive external ophthalmoplegia (PEO). Fatigue was assessed in the adductor pollicis muscle (AP) using a low-intensity exercise protocol (20 min). Forces (TFs) and relaxation times of ulnar nerve evoked twitches, compound muscle action potentials (CMAPs), and maximal voluntary contractions (MVCs) were monitored. Serum lactate and pyruvate levels were independently measured at rest and after exercise on a bicycle (15 min, 30 W). Most patients showed abnormal fatigue of the AP with a reduction of TFs and MVCs and normal CMAPs. The reduced TFs were significantly correlated with lactate levels at rest (r= - 0.60, P<0.05) and less so with those after exercise (r=- 0.47,P<0.05). Pyruvate levels revealed a similar correlation although they were widely scattered. We conclude that abnormal fatigue in PEO is metabolic, is localized beyond the muscle fiber membrane, and involves the electrome-chanical coupling and the contractile apparatus. Serum lactate levels at rest are good predictors of fatigue in PEO.

The influence of Coenzyme Q10 on total serum calcium concentration in two patients with Kearns-Sayre Syndrome and hypoparathyroidism

Two patients with Kearns-Sayre Syndrome and hypoparathyroidism were treated with alfacalcidol (1a-OH D3) and total serum calcium concentration remained within normal range for a long period. After two months of combined therapy with Coenzyme Q10 (CoQ10), hypercalcemia was noticed and as a result, 1a-OHD3 was gradually discontinued. Normal total serum calcium concentration was obtained with CoQ10 monotherapy while the replacement of CoQ10 with placebo led to hypocalcemia. The mechanism of action of CoQ10 is difficult to explain. Since the parathormone level remained unchanged during CoQ10 or placebo therapy, we speculate that the capacity of producing an active form of vitamin D in mitochondria of proximal tubules was restored by CoQ10 therapy.

The therapy of respiratory chain encephalomyopathy: a critical review of the past and current perspective

The mitochondrial respiratory chain encephalomyopathies represent an important group of multisystem disorders. No curative treatment is currently available. A number of measures have been reported to have a theoretical potential to improve respiratory function. These treatment strategies have variable scientific support, many reports being anecdotal. We critically review the various therapeutic measures employed and suggest future treatment directions.

Riboflavin-responsive complex I deficiency

Three patients from a large consanguineous family, and one unrelated patient had exercise intolerance since early childhood and improved by supplementation with a high dosage of riboflavin. This was confirmed by higher endurance power in exercise testing. Riboflavin had been given because complex I, which contains riboflavin in FMN, one of its prosthetic groups, had a very low activity in muscle. Histochemistry showed an increase of subsarcolemmal mitochondria. The low complex I activity contrasted with an increase of the activities of succinate dehydrogenase, succinate-cytochrome c oxidoreductase and cytochrome c oxidase. Isolated mitochondria from these muscle specimens proved deficient in oxidizing pyruvate plus malate and other NAD(+)-linked substrates, but oxidized succinate and ascorbate at equal or higher levels than controls. Two years later a second biopsy was taken in one of the patients, and the activity of complex I had increased from 16% to 47% of the average activity in controls. In the four biopsies, cytochrome c oxidase activity correlated negatively with age. We suspect that this is due to reactive oxygen species generated by the proliferating mitochondria and peroxidizing unsaturated fatty acids of cardiolipin. Three of the four patients had low blood carnitine, and all were found to have hypocarnitinemic family members.

Mitochondrial myopathy with anemia, cardiomyopathy, and lactic acidosis: a distinct late onset mitochondrial disorder

A 40-year-old woman presented with profound muscle weakness resulting in failure to wean from a ventilator and persistent lactic acidosis after having recovered from a pneumonia complicated by adult respiratory distress syndrome, myocardial infarction, renal failure and shock. She had a 28 year history of chronic anemia and exercise intolerance. Anemia and thrombocytopenia persisted after admission. Nonobstructive hypertrophic cardiomyopathy was present. A stroke-like episode occurred. A mitochondrial myopathy with deficiencies in complexes IV and II was demonstrated, but no DNA defect has yet been found. This patient represents a distinct clinical presentation of a mitochondrial disorder characterized by late onset mitochondrial myopathy, chronic anemia, cardiomyopathy, and lactic acidosis.

Myopathy in long-term AZT therapy: clinical, electrophysiological and biopsy study in 67 HIV+ subjects

The occurrence of muscular pathologies in AZT treated subjects has been evaluated in 67 HIV seropositive outpatients (56 AZT-treated and 11 untreated controls) in a neurological clinical and paraclinical follow-up study. Standard electromyographic and electrodiagnostic examinations, together with muscle enzyme determination, were performed in every subject, and periodically repeated at fixed intervals; in 11 patients a muscle biopsy sample was also obtained. An AZT-related myopathy was diagnosed in 8 biopsied cases; 9 more patients were considered to have AZT myopathy on clinical, EMG and ex juvantibus criteria. Statistical analysis showed that treatment duration was more relevant to the development of the myopathy than AZT dosage, though an individual predisposition could not be excluded, at least in a small number of cases. The risk of developing a toxic myopathy will therefore have to be considered when evaluating long-term effects of AZT therapy.