Coenzyme Q10 for Diabetes and Cardiovascular Disease: Useful or Useless?

INTRODUCTION: Diabetes mellitus (T2DM) and cardiovascular diseases (CVDs) have become some of the most urgent and prevalent health problems in recent decades, side by side with the growing obesity crisis. The close relationship between T2DM and CVD has become clear: endothelial dysfunction caused by oxidative stress and inflammation resulting from hyperglycaemia are the key factors in the development of vascular complications of T2DM, leading to CVD. Coenzyme Q10 (CoQ10) is a great candidate for the treatment of these diseases, acting precisely at the intersection between T2DM and CVD that is oxidative stress, due to its strong antioxidant activity and fundamental physiological role in mitochondrial bioenergetics. CoQ10 is a biologically active liposoluble compound comprising a quinone group and a side chain of 10 isoprenoid units, which is synthesized endogenously in the body from tyrosine and mevalonic acid. The main biochemical action of CoQ10 is as a cofactor in the electron transport chain that synthesizes adenosine triphosphate (ATP). As most cellular functions depend on an adequate supply of ATP, CoQ10 is essential for the health of virtually all human tissues and organs. CoQ10 supplementation has been used as an intensifier of mitochondrial function and an antioxidant with the aim of palliating or reducing oxidative damage that can worsen the physiological outcome of a wide range of diseases including T2DM and CVDs. CONCLUSION: Although there is not enough evidence to conclude it is effective for different therapeutic indications, CoQ10 supplementation is probably safe and well-tolerated, with few drug interactions and minor side effects. Many valuable advances have been made in the use of CoQ10 in clinical practice for patients with T2DM and a high risk of CVD. However, further research is needed to assess the real safety and benefit to indicate CoQ10 supplementation in patients with T2DM.

Antioxidant and Anti-Inflammatory Effects of Coenzyme Q10 Supplementation on Infectious Diseases.

With the appearance of new viruses and infectious diseases (ID) such as COVID-19 in 2019, as well as the lack of specific pharmacological tools for the management of patients with severe complications or comorbidities, it is important to search for adjuvant treatments that help improve the prognosis of infectious disease patients. It is also important that these treatments limit the oxidative and hyperinflammatory damage caused as a response to pathogenic agents, since, in some cases, an inflammatory syndrome may develop that worsens the patient's prognosis. The potential benefits of complementary nutrients and dietary interventions in the treatment of pathological processes in which oxidative stress and inflammation play a fundamental role have been widely evaluated. Coenzyme Q10 (CoQ10) is a supplement that has been shown to protect cells and be effective in cardiovascular diseases and obesity. Additionally, some studies have proposed it as a possible adjuvant treatment in viral infections. Preclinical and clinical studies have shown that CoQ10 has anti-inflammatory and antioxidant effects, and effects on mitochondrial dysfunction, which have been linked to the inflammatory response.

Coq3p relevant residues for protein activity and stability.

Coenzyme Q (CoQ) is an essential molecule that consists of a highly substituted benzene ring attached to a polyprenyl tail anchored in the inner mitochondrial membrane. CoQ transfers electrons from NADH dehydrogenase and succinate dehydrogenase complexes toward ubiquinol-cytochrome c reductase, and that allows aerobic growth of cells. In Saccharomyces cerevisiae, the synthesis of CoQ depends on fourteen proteins Coq1p-Co11p, Yah1p, Arh1p, and Hfd1p. Some of these proteins are components of CoQ synthome. Using ab initio molecular modeling and site-directed mutagenesis, we identified the functional residues of the O-methyltransferase Coq3p, which depends on S-adenosylmethionine for catalysis and is necessary for two O-methylation steps required for CoQ maturation. Conserved residues as well as those that coevolved in the protein structure were found to have important roles in respiratory growth, CoQ biosynthesis, and also in the stability of CoQ synthome proteins. Finally, a multiple sequence alignment showed that S. cerevisiae Coq3p has a 45 amino acid residues insertion that is poorly conserved or absent in oleaginous yeast, cells that can store up to 20% of their dry weight as lipids. These results point to the Coq3p structural determinants of its biological and catalytic function and could contribute to the development of lipid-producing yeast for biotechnology.

Genotoxic risk in humans and acute toxicity in rats of a novel oral high-dose coenzyme Q10 oleogel.

Coenzyme Q10 (CoQ10) supplementation has demonstrated to be safe and effective in primary and secondary CoQ10 deficiencies. Previously, we have designed a high-dose CoQ10 oleogel (1 g/disk) with excipients used in quantities that do not represent any toxic risk. However, it was necessary to demonstrate their safety in the final formulation. Following this purpose, an acute toxicity study of the oleogel in rats was performed. Furthermore, the genotoxic risk was evaluated in human volunteers after CoQ10 supplementation with oleogel and compared to the solid form (1 g/three 00-size-capsules). In addition, the general health status and possible biochemical changes of the participants were determined using serum parameters. Results suggested the absence of adverse effects caused by the interaction of the components in the oleogel formulation. Therefore, we conclude that the designed novel high-dose CoQ10 oleogel was safe for oral consumption.

Effect of COQ9 and STAT5A polymorphisms on reproductive performance in a Holstein cow herd in Mexico.

Coenzyme Q9 (COQ9), a coenzyme Q (CoQ) precursor, is an essential component of the mitochondrial electron transport chain that drives adenosine triphosphate production. COQ9 polymorphism 18:25527339 is characterized by substitution of guanine (allele G) for adenine (allele A), which modifies the function of the protein encoded by the gene. In Holsteins, allele A has been associated with better reproductive performance in terms of the conception rate, number of services per conception (SPC) and days open (DO). The signal transducer and activator of transcription (STAT) protein is a transcription factor activated in the presence of cytokines and growth factors. STAT5A polymorphism 19:42407732 in exon 8 has been associated with higher fertility and embryonic survival rates. The objective of this study was to determine the relationship of COQ9 and STAT5A polymorphisms with reproductive parameters [calving to first heat interval (CFHI), DO and SPC]. Blood samples were taken from 112 lactating Holstein from a herd in México for allele genotyping by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). To estimate the association between reproductive parameters and genotypes, a linear mixed-effect model was performed. The COQ9 AG genotype was associated significantly with lower SPC (P<0.05) but not with DO or CFHI. No significant association with any reproductive parameter was found for STAT5A. Our findings suggest that the COQ9 18:25527339 polymorphism is a useful molecular marker for improvement of reproductive performance in dairy herds.

Effect of COQ9 and STAT5A polymorphisms on reproductive performance in a Holstein cow herd in Mexico

Coenzyme Q9 (COQ9), a coenzyme Q (CoQ) precursor, is an essential component of the mitochondrial electron transport chain that drives adenosine triphosphate production. COQ9 polymorphism 18:25527339 is characterized by substitution of guanine (allele G) for adenine (allele A), which modifies the function of the protein encoded by the gene. In Holsteins, allele A has been associated with better reproductive performance in terms of the conception rate, number of services per conception (SPC) and days open (DO). The signal transducer and activator of transcription (STAT) protein is a transcription factor activated in the presence of cytokines and growth factors. STAT5A polymorphism 19:42407732 in exon 8 has been associated with higher fertility and embryonic survival rates. The objective of this study was to determine the relationship of COQ9 and STAT5A polymorphisms with reproductive parameters [calving to first heat interval (CFHI), DO and SPC]. Blood samples were taken from 112 lactating Holstein from a herd in México for allele genotyping by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). To estimate the association between reproductive parameters and genotypes, a linear mixed-effect model was performed. The COQ9 AG genotype was associated significantly with lower SPC (P<0.05) but not with DO or CFHI. No significant association with any reproductive parameter was found for STAT5A. Our findings suggest that the COQ9 18:25527339 polymorphism is a useful molecular marker for improvement of reproductive performance in dairy herds.(AU)

Effect of COQ9 and STAT5A polymorphisms on reproductive performance in a Holstein cow herd in Mexico

Coenzyme Q9 (COQ9), a coenzyme Q (CoQ) precursor, is an essential component of the mitochondrial electron transport chain that drives adenosine triphosphate production. COQ9 polymorphism 18:25527339 is characterized by substitution of guanine (allele G) for adenine (allele A), which modifies the function of the protein encoded by the gene. In Holsteins, allele A has been associated with better reproductive performance in terms of the conception rate, number of services per conception (SPC) and days open (DO). The signal transducer and activator of transcription (STAT) protein is a transcription factor activated in the presence of cytokines and growth factors. STAT5A polymorphism 19:42407732 in exon 8 has been associated with higher fertility and embryonic survival rates. The objective of this study was to determine the relationship of COQ9 and STAT5A polymorphisms with reproductive parameters [calving to first heat interval (CFHI), DO and SPC]. Blood samples were taken from 112 lactating Holstein from a herd in México for allele genotyping by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). To estimate the association between reproductive parameters and genotypes, a linear mixed-effect model was performed. The COQ9 AG genotype was associated significantly with lower SPC (P<0.05) but not with DO or CFHI. No significant association with any reproductive parameter was found for STAT5A. Our findings suggest that the COQ9 18:25527339 polymorphism is a useful molecular marker for improvement of reproductive performance in dairy herds.

Coenzyme Q10 supplementation acts as antioxidant on dystrophic muscle cells.

Increased oxidative stress is a frequent feature in Duchenne muscular dystrophy (DMD). High reactive oxygen species (ROS) levels, associated with altered enzyme antioxidant activity, have been reported in dystrophic patients and mdx mice, an experimental model of DMD. In this study, we investigated the effects of coenzyme Q10 (CoQ10) on oxidative stress marker levels and calcium concentration in primary cultures of dystrophic muscle cells from mdx mice. Primary cultures of skeletal muscle cells from C57BL/10 and mdx mice were treated with coenzyme Q10 (5 µM) for 24 h. The untreated mdx and C57BL/10 muscle cells were used as controls. The MTT and live/dead cell assays showed that CoQ10 presented no cytotoxic effect on normal and dystrophic muscle cells. Intracellular calcium concentration, H2O2 production, 4-HNE, and SOD-2 levels were higher in mdx muscle cells. No significant difference in the catalase, GPx, and Gr levels was found between experimental groups. This study demonstrated that CoQ10 treatment was able to reduce levels of oxidative stress markers, such as H2O2, acting as an antioxidant, as well as decreasing abnormal intracellular calcium influx in dystrophic muscles cells. This study demonstrated that CoQ10 treatment was able to reduce levels of oxidative stress markers, such as H2O2, acting as an antioxidant, as well as decreasing abnormal intracellular calcium influx in dystrophic muscles cells. Our findings also suggest that the decrease of oxidative stress reduces the need for upregulation of antioxidant pathways, such as SOD and GSH.

Overproduction of isoprenoids by Saccharomyces cerevisiae in a synthetic grape juice medium in the absence of plant genes.

The objective of this work is to demonstrate if the hexaprenyl pyrophosphate synthetase Coq1p might be involved in monoterpenes synthesis in Saccharomyces cerevisiae, although its currently known function in yeast is to catalyze the first step in ubiquinone biosynthesis. However, in a BY4743 laboratory strain, the presence of an empty plasmid in a chemically defined grape juice medium results in a statistically significant increase of linalool, (E)-nerolidol and (E,E)-farnesol. When COQ1 is overexpressed from a plasmid, the levels of the volatile isoprenoids are further increased. Furthermore, overexpression of COQ1 in the same genetic context but with a mutated farnesyl pyrophosphate synthetase (erg20 mutation K197E), results in statistically significant higher levels of linalool (above 750 µg/L), geraniol, α-terpineol, and the sesquiterpenes, farnesol and nerolidol (total concentration of volatile isoprenoids surpasses 1300 µg/L). We show that the levels of monoterpenes and sesquiterpenes that S. cerevisiae can produce, in the absence of plant genes, depend on the composition of the medium and the genetic context. To the best of our knowledge, this is the highest level of linalool produced by S. cerevisiae up to now. Further research will be needed for understanding how COQ1 and the medium composition might interact to increase flavor complexity of fermented beverages.

Assessing the influence of the carbon source on the abatement of industrial N2O emissions coupled with the synthesis of added-value bioproducts.

The continuous abatement of a synthetic N2O emission from a nitric acid plant coupled with the simultaneously production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) copolymer and the coenzyme Q10 (CoQ10) in a bubble column reactor (BCR) was tested using methanol, glycerol and a mixture of sodium acetate-acetic acid (Ac-HAc) as a carbon and electron donor source. The BCRs were inoculated with Paracoccus denitrificans and supplied with the carbon/electron donor at a loading rate of 139gCm-3d-1. High N2O removal efficiencies (81-91%) were achieved, with glycerol supporting the highest abatement. The PHBV cell content ranged from 25 to 53%, with highest accumulation in the culture obtained with methanol and Ac-HAc. However, the greatest PHBV productivities were observed in the BCRs operated with glycerol and Ac-HAc (21.7 and 33.5gPHBVm-3d-1, respectively). Glycerol supply induced the highest molar ratio (23%) of the homopolymer 3-hydroxyvalerate in the composition of PHBV. In addition, the specific cell content of CoQ10 ranged from 0.4 to 1mgg-1. This work constitutes, to the best of our knowledge, the first study combining N2O abatement with the simultaneous production of multiple bioproducts, which pave the way to the development of greenhouse gas biorefineries for climate change mitigation.

The Effects of Coenzyme Q10 on Inflammation Markers in Streptozotocin-Induced Diabetic Rats

Background: Coenzyme Q10 is a well-known cofactor in the mitochondrial electron transport chain required for ATP production. Coenzyme Q10 is recognized as an intracellular antioxidant that protects cell membrane phospholipids, mitochondrial membrane protein, and plasma low-density lipoprotein against oxidative damage caused by free radicals. Diabetes and its complications have been related to increased levels of free radicals and systemic proinflammatory cytokines and to an abnormal lipid profile. The aim of this study was to investigate the effects of coenzyme Q10 supplementation on some cytokine levels in streptozotocin-induced diabetic rats.Materials, Methods & Results: In this study, 38 healthy, adult male rats were used. The rats were divided into 5 groups. All animals were housed in separated cages during the four weeks. The animals in group 1 was fed standard rat pellets for 4 weeks. It was administered at 0.3 mL corn oil intraperitoneally daily for four weeks in group 2 animals. The animals in group 3 was injected intraperitoneally with 10 mg/kg CoQ10 daily for 4 weeks. Group 4 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose for two days and group 5 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose

The Effects of Coenzyme Q10 on Inflammation Markers in Streptozotocin-Induced Diabetic Rats

Background: Coenzyme Q10 is a well-known cofactor in the mitochondrial electron transport chain required for ATP production. Coenzyme Q10 is recognized as an intracellular antioxidant that protects cell membrane phospholipids, mitochondrial membrane protein, and plasma low-density lipoprotein against oxidative damage caused by free radicals. Diabetes and its complications have been related to increased levels of free radicals and systemic proinflammatory cytokines and to an abnormal lipid profile. The aim of this study was to investigate the effects of coenzyme Q10 supplementation on some cytokine levels in streptozotocin-induced diabetic rats.Materials, Methods & Results: In this study, 38 healthy, adult male rats were used. The rats were divided into 5 groups. All animals were housed in separated cages during the four weeks. The animals in group 1 was fed standard rat pellets for 4 weeks. It was administered at 0.3 mL corn oil intraperitoneally daily for four weeks in group 2 animals. The animals in group 3 was injected intraperitoneally with 10 mg/kg CoQ10 daily for 4 weeks. Group 4 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose for two days and group 5 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose

The Effects of Coenzyme Q10 on Inflammation Markers in Streptozotocin-Induced Diabetic Rats

Background: Coenzyme Q10 is a well-known cofactor in the mitochondrial electron transport chain required for ATP production. Coenzyme Q10 is recognized as an intracellular antioxidant that protects cell membrane phospholipids, mitochondrial membrane protein, and plasma low-density lipoprotein against oxidative damage caused by free radicals. Diabetes and its complications have been related to increased levels of free radicals and systemic proinflammatory cytokines and to an abnormal lipid profile. The aim of this study was to investigate the effects of coenzyme Q10 supplementation on some cytokine levels in streptozotocin-induced diabetic rats.Materials, Methods & Results: In this study, 38 healthy, adult male rats were used. The rats were divided into 5 groups. All animals were housed in separated cages during the four weeks. The animals in group 1 was fed standard rat pellets for 4 weeks. It was administered at 0.3 mL corn oil intraperitoneally daily for four weeks in group 2 animals. The animals in group 3 was injected intraperitoneally with 10 mg/kg CoQ10 daily for 4 weeks. Group 4 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose for two days and group 5 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose

The Effects of Coenzyme Q10 on Inflammation Markers in Streptozotocin-Induced Diabetic Rats

Background: Coenzyme Q10 is a well-known cofactor in the mitochondrial electron transport chain required for ATP production. Coenzyme Q10 is recognized as an intracellular antioxidant that protects cell membrane phospholipids, mitochondrial membrane protein, and plasma low-density lipoprotein against oxidative damage caused by free radicals. Diabetes and its complications have been related to increased levels of free radicals and systemic proinflammatory cytokines and to an abnormal lipid profile. The aim of this study was to investigate the effects of coenzyme Q10 supplementation on some cytokine levels in streptozotocin-induced diabetic rats.Materials, Methods & Results: In this study, 38 healthy, adult male rats were used. The rats were divided into 5 groups. All animals were housed in separated cages during the four weeks. The animals in group 1 was fed standard rat pellets for 4 weeks. It was administered at 0.3 mL corn oil intraperitoneally daily for four weeks in group 2 animals. The animals in group 3 was injected intraperitoneally with 10 mg/kg CoQ10 daily for 4 weeks. Group 4 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose for two days and group 5 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose

The Effects of Coenzyme Q10 on Inflammation Markers in Streptozotocin-Induced Diabetic Rats

Background: Coenzyme Q10 is a well-known cofactor in the mitochondrial electron transport chain required for ATP production. Coenzyme Q10 is recognized as an intracellular antioxidant that protects cell membrane phospholipids, mitochondrial membrane protein, and plasma low-density lipoprotein against oxidative damage caused by free radicals. Diabetes and its complications have been related to increased levels of free radicals and systemic proinflammatory cytokines and to an abnormal lipid profile. The aim of this study was to investigate the effects of coenzyme Q10 supplementation on some cytokine levels in streptozotocin-induced diabetic rats.Materials, Methods & Results: In this study, 38 healthy, adult male rats were used. The rats were divided into 5 groups. All animals were housed in separated cages during the four weeks. The animals in group 1 was fed standard rat pellets for 4 weeks. It was administered at 0.3 mL corn oil intraperitoneally daily for four weeks in group 2 animals. The animals in group 3 was injected intraperitoneally with 10 mg/kg CoQ10 daily for 4 weeks. Group 4 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose for two days and group 5 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose

The effects of coenzyme Q10 on inflammation markers in streptozotocin-induced diabetic rats

Background: Coenzyme Q10 is a well-known cofactor in the mitochondrial electron transport chain required for ATP production. Coenzyme Q10 is recognized as an intracellular antioxidant that protects cell membrane phospholipids, mitochondrial membrane protein, and plasma low-density lipoprotein against oxidative damage caused by free radicals. Diabetes and its complications have been related to increased levels of free radicals and systemic proinflammatory cytokines and to an abnormal lipid profile. The aim of this study was to investigate the effects of coenzyme Q10 supplementation on some cytokine levels in streptozotocin-induced diabetic rats. Materials, Methods & Results: In this study, 38 healthy, adult male rats were used. The rats were divided into 5 groups. All animals were housed in separated cages during the four weeks. The animals in group 1 was fed standard rat pellets for 4 weeks. It was administered at 0.3 mL corn oil intraperitoneally daily for four weeks in group 2 animals. The animals in group 3 was injected intraperitoneally with 10 mg/kg CoQ10 daily for 4 weeks. Group 4 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose for two days and group 5 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose [...]

The Effects of Coenzyme Q10 on Inflammation Markers in Streptozotocin-Induced Diabetic Rats

Background: Coenzyme Q10 is a well-known cofactor in the mitochondrial electron transport chain required for ATP production. Coenzyme Q10 is recognized as an intracellular antioxidant that protects cell membrane phospholipids, mitochondrial membrane protein, and plasma low-density lipoprotein against oxidative damage caused by free radicals. Diabetes and its complications have been related to increased levels of free radicals and systemic proinflammatory cytokines and to an abnormal lipid profile. The aim of this study was to investigate the effects of coenzyme Q10 supplementation on some cytokine levels in streptozotocin-induced diabetic rats.Materials, Methods & Results: In this study, 38 healthy, adult male rats were used. The rats were divided into 5 groups. All animals were housed in separated cages during the four weeks. The animals in group 1 was fed standard rat pellets for 4 weeks. It was administered at 0.3 mL corn oil intraperitoneally daily for four weeks in group 2 animals. The animals in group 3 was injected intraperitoneally with 10 mg/kg CoQ10 daily for 4 weeks. Group 4 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose for two days and group 5 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose

The effects of coenzyme Q10 on inflammation markers in streptozotocin-induced diabetic rats

Background: Coenzyme Q10 is a well-known cofactor in the mitochondrial electron transport chain required for ATP production. Coenzyme Q10 is recognized as an intracellular antioxidant that protects cell membrane phospholipids, mitochondrial membrane protein, and plasma low-density lipoprotein against oxidative damage caused by free radicals. Diabetes and its complications have been related to increased levels of free radicals and systemic proinflammatory cytokines and to an abnormal lipid profile. The aim of this study was to investigate the effects of coenzyme Q10 supplementation on some cytokine levels in streptozotocin-induced diabetic rats. Materials, Methods & Results: In this study, 38 healthy, adult male rats were used. The rats were divided into 5 groups. All animals were housed in separated cages during the four weeks. The animals in group 1 was fed standard rat pellets for 4 weeks. It was administered at 0.3 mL corn oil intraperitoneally daily for four weeks in group 2 animals. The animals in group 3 was injected intraperitoneally with 10 mg/kg CoQ10 daily for 4 weeks. Group 4 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose for two days and group 5 was made diabetic by subcutaneous injections of streptozotocin at dose of 40 mg/kg in 0.1 M citrate buffer (pH 4.5) single daily dose [...](AU)

Coenzyme Q10 defects may be associated with a deficiency of Q10-independent mitochondrial respiratory chain complexes

BACKGROUND: Coenzyme Q10 (CoQ10 or ubiquinone) deficiency can be due either to mutations in genes involved in CoQ10 biosynthesis pathway, or to mutations in genes unrelated to CoQ10 biosynthesis. CoQ10 defect is the only oxidative phosphorylation disorder that can be clinically improved after oral CoQ10 supplementation. Thus, early diagnosis, first evoked by mitochondrial respiratory chain (MRC) spectrophotometric analysis, then confirmed by direct measurement of CoQ10 levels, is of critical importance to prevent irreversible damage in organs such as the kidney and the central nervous system. It is widely reported that CoQ10 deficient patients present decreased quinone-dependent activities (segments I + III or G3P + III and II + III) while MRC activities of complexes I, II, III, IV and V are normal. We previously suggested that CoQ10 defect may be associated with a deficiency of CoQ10-independent MRC complexes. The aim of this study was to verify this hypothesis in order to improve the diagnosis of this disease. RESULTS: To determine whether CoQ10 defect could be associated with MRC deficiency, we quantified CoQ10 by LC-MSMS in a cohort of 18 patients presenting CoQ10-dependent deficiency associated with MRC defect. We found decreased levels of CoQ10 in eight patients out of 18 (45 %), thus confirming CoQ10 disease. CONCLUSIONS: Our study shows that CoQ10 defect can be associated with MRC deficiency. This could be of major importance in clinical practice for the diagnosis of a disease that can be improved by CoQ10 supplementation.