Exogenous Coenzyme Q Research Articles

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.

Genes and lipids that impact uptake and assimilation of exogenous coenzyme Q in Saccharomyces cerevisiae

Coenzyme Q (CoQ) is an essential player in the respiratory electron transport chain and is the only lipid-soluble antioxidant synthesized endogenously in mammalian and yeast cells. In humans, genetic mutations, pathologies, certain medical treatments, and aging, result in CoQ deficiencies, which are linked to mitochondrial, cardiovascular, and neurodegenerative diseases. The only strategy available for these patients is CoQ supplementation. CoQ supplements benefit a small subset of patients, but the poor solubility of CoQ greatly limits treatment efficacy. Consequently, the efficient delivery of CoQ to the mitochondria and restoration of respiratory function remains a major challenge. A better understanding of CoQ uptake and mitochondrial delivery is crucial to make this molecule a more efficient and effective therapeutic tool. In this study, we investigated the mechanism of CoQ uptake and distribution using the yeast Saccharomyces cerevisiae as a model organism. The addition of exogenous CoQ was tested for the ability to restore growth on non-fermentable medium in several strains that lack CoQ synthesis (coq mutants). Surprisingly, we discovered that the presence of CoQ biosynthetic intermediates impairs assimilation of CoQ into a functional respiratory chain in yeast cells. Moreover, a screen of 40 gene deletions considered to be candidates to prevent exogenous CoQ from rescuing growth of the CoQ-less coq2Δ mutant, identified six novel genes (CDC10, RTS1, RVS161, RVS167, VPS1, and NAT3) as necessary for efficient trafficking of CoQ to mitochondria. The proteins encoded by these genes represent essential steps in the pathways responsible for transport of exogenously supplied CoQ to its functional sites in the cell, and definitively associate CoQ distribution with endocytosis and intracellular vesicular trafficking pathways conserved from yeast to human cells.

Vanillic Acid Restores Coenzyme Q Biosynthesis and ATP Production in Human Cells Lacking COQ6.

Coenzyme Q (CoQ), a redox-active lipid, is comprised of a quinone group and a polyisoprenoid tail. It is an electron carrier in the mitochondrial respiratory chain, a cofactor of other mitochondrial dehydrogenases, and an essential antioxidant. CoQ requires a large set of enzymes for its biosynthesis; mutations in genes encoding these proteins cause primary CoQ deficiency, a clinically and genetically heterogeneous group of diseases. Patients with CoQ deficiency often respond to oral CoQ10 supplementation. Treatment is however problematic because of the low bioavailability of CoQ10 and the poor tissue delivery. In recent years, bypass therapy using analogues of the precursor of the aromatic ring of CoQ has been proposed as a promising alternative. We have previously shown using a yeast model that vanillic acid (VA) can bypass mutations of COQ6, a monooxygenase required for the hydroxylation of the C5 carbon of the ring. In this work, we have generated a human cell line lacking functional COQ6 using CRISPR/Cas9 technology. We show that these cells cannot synthesize CoQ and display severe ATP deficiency. Treatment with VA can recover CoQ biosynthesis and ATP production. Moreover, these cells display increased ROS production, which is only partially corrected by exogenous CoQ, while VA restores ROS to normal levels. Furthermore, we show that these cells accumulate 3-decaprenyl-1,4-benzoquinone, suggesting that in mammals, the decarboxylation and C1 hydroxylation reactions occur before or independently of the C5 hydroxylation. Finally, we show that COQ6 isoform c (transcript NM_182480) does not encode an active enzyme. VA can be produced in the liver by the oxidation of vanillin, a nontoxic compound commonly used as a food additive, and crosses the blood-brain barrier. These characteristics make it a promising compound for the treatment of patients with CoQ deficiency due to COQ6 mutations.

Age-related decline of neural activities in the motor cortex is ameliorated by coenzyme Q<sub>10</sub>.

Not only neurological disease but also physiological aging affects brain function. Takahashi et al (2016) found that histological and motor functional alterations were associated with age-related decline of brain mitochondrial function. Aged mice (15-month-old) displayed significant reductions in mitochondrial oxygen consumption rate, coenzyme Q (CoQ) content, vesicular glutamate transporter 1 level in the motor cortex, and motor function compared to young mice (6-month-old). CoQ is a coenzyme, and present in the mitochondria. It is an electron transporter in the respiratory chain involved in ATP production. However, age-related electrophysiological impairments of the motor cortex were poorly understood. In this talk, I will describe how physiological aging affects electrophysiological activities in the motor cortex of mice, and present data to show how exogenous CoQ treatment affects the age-related alteration in the aged mice. I will also discuss the influence of exogenous CoQ treatment on the age-related decline of electrophysiological activities in the motor cortex. Takahashi and our studies suggested that the age-related alterations were ameliorated by exogenous CoQ treatment. Although the relation between central nervous system and age-related motor decline remain to be elucidated, our results may serve as the basis for developing therapy of age-related motor impairment.

β‐RA reduces DMQ/CoQ ratio and rescues the encephalopathic phenotype in Coq9R239X mice

Coenzyme Q (CoQ) deficiency has been associated with primary defects in the CoQ biosynthetic pathway or to secondary events. In some cases, the exogenous CoQ supplementation has limited efficacy. In the Coq9R239X mouse model with fatal mitochondrial encephalopathy due to CoQ deficiency, we have tested the therapeutic potential of β‐resorcylic acid (β‐RA), a structural analog of the CoQ precursor 4‐hydroxybenzoic acid and the anti‐inflammatory salicylic acid. β‐RA noticeably rescued the phenotypic, morphological, and histopathological signs of the encephalopathy, leading to a significant increase in the survival. Those effects were due to the decrease of the levels of demethoxyubiquinone‐9 (DMQ9) and the increase of mitochondrial bioenergetics in peripheral tissues. However, neither CoQ biosynthesis nor mitochondrial function changed in the brain after the therapy, suggesting that some endocrine interactions may induce the reduction of the astrogliosis, spongiosis, and the secondary down‐regulation of astrocytes‐related neuroinflammatory genes. Because the therapeutic outcomes of β‐RA administration were superior to those after CoQ10 supplementation, its use in the clinic should be considered in CoQ deficiencies.

Effects of reduced graphene oxide on the activities of anammox biomass and key enzymes

In this study, effects of reduced graphene oxide (RGO) on the activities of anammox biomass and key enzymes were investigated, which was the first time to relate the enzymes activities and RGO together. The batch experimental results demonstrated that the optimal dose grapheme oxide (GO) with 100mg/L could enhance the total nitrogen (TN) removal rate of 17.2%. Besides, the hydrazine dehydrogenase (HDH), nitrite reductase (NIR), and nitrate reductase (NAR) activities were enhanced with different dose RGO addition, about 0.70–2.75 folds compared to the control experiments. Moreover, the restoration of HDH activity with exogenous coenzyme Q (CoQ) and RGO addition proved that RGO was much more efficient than exogenous CoQ to recover the HDH activity in the extracted CoQ system. Therefore, it could infer that RGO had much better electron transfer ability compared to CoQ, which would be the root reason for the effects of the RGO on anammox process.

Dependence of Brown Adipose Tissue Function on CD36-Mediated Coenzyme Q Uptake

Brown adipose tissue (BAT) possesses the inherent ability to dissipate metabolic energy as heat through uncoupled mitochondrial respiration. An essential component of the mitochondrial electron transport chain is coenzyme Q (CoQ). While cells synthesize CoQ mostly endogenously, exogenous supplementation with CoQ has been successful as a therapy for patients with CoQ deficiency. However, which tissues depend on exogenous CoQ uptake as well as the mechanism by which CoQ is taken up by cells and the role of this process in BAT function are not well understood. Here, we report that the scavenger receptor CD36 drives the uptake of CoQ by BAT and is required for normal BAT function. BAT from mice lacking CD36 displays CoQ deficiency, impaired CoQ uptake, hypertrophy, altered lipid metabolism, mitochondrial dysfunction, and defective nonshivering thermogenesis. Together, these data reveal an important new role for the systemic transport of CoQ to BAT and its function in thermogenesis.

Exogenous administration of coenzyme Q10 restores mitochondrial oxygen consumption in the aged mouse brain

The level of coenzyme Q (CoQ) has been shown to decrease in an age-dependent manner in several types of animals. However, whether CoQ-dependent mitochondrial function decreases with aging remains unclear. In this study, we found that mitochondrial complexes I and II exhibited significantly reduced oxygen consumption in the brains of aged male mice relative to young male mice, although this decrease in oxygen consumption was not accompanied by a change in the CoQ9 or CoQ10 content. Nevertheless, the administration of exogenous CoQ10 significantly increased the content of CoQ10 and CoQ9 in the brain mitochondria of aged male mice and restored complex I- and II-mediated oxygen consumption to levels comparable to those observed in young mice. These results indicate that mitochondrial oxygen consumption in the brain decreases in aged male mice. Furthermore, these results suggest that exogenous CoQ10 restores mitochondrial oxygen use to levels equivalent to those observed in young mice.

Restoration of the behavioral rates and lifespan in clk-1 mutant nematodes in response to exogenous coenzyme Q10

The clk-1 gene encodes demethoxyubiquinone mono-oxygenase that is necessary for the biosynthesis of coenzyme Q (CoQ), which is an electron transporter in the respiratory chain of mitochondria. Therefore, clk-1 mutant nematodes that have loss-of-function mutations in the clk-1 gene lack endogenous CoQ9 and exhibit slowed behavioral rates and an extended lifespan compared with wild-type animals when they are fed standard bacteria containing endogenous CoQ8. This finding suggests that clk-1 regulates behavioral rates and the lifespan through CoQ in nematodes; however, the effects of exogenous CoQ on the regulation of these biological processes have been incompletely evaluated. In this study, we found that adding 10μM water-soluble CoQ10 to the culture medium of clk-1 mutant nematodes that were fed a diet of standard bacteria restored the pharyngeal pumping, defecation and the lifespan to levels that were comparable to those of wild-type animals. The results indicate that both behavioral rates and lifespan are regulated by the clk-1 gene through the action of CoQ in nematodes.

Complementation of coenzyme Q‐deficient yeast by coenzyme Q analogues requires the isoprenoid side chain

The ubiquinone coenzyme Q (CoQ) is synthesized in mitochondria with a large, hydrophobic isoprenoid side chain. It functions in mitochondrial respiration as well as protecting membranes from oxidative damage. Yeast that cannot synthesize CoQ (DeltaCoQ) are viable, but cannot grow on nonfermentable carbon sources, unless supplied with ubiquinone. Previously we demonstrated that the isoprenoid side chain of the exogenous ubiquinone was important for growth of a DeltaCoQ strain on the nonfermentable substrate glycerol [James AM et al. (2005) J Biol Chem280, 21295-21312]. In the present study we investigated the structural requirements of exogenously supplied CoQ(2) for growth on glycerol and found that the first double bond of the initial isoprenoid unit is essential for utilization of respiratory substrates. As CoQ(2) analogues that did not complement growth on glycerol supported respiration in isolated mitochondria, discrimination does not occur via the respiratory chain complexes. The endogenous form of CoQ in yeast (CoQ(6)) is extremely hydrophobic and transported to mitochondria via the endocytic pathway when supplied exogenously. We found that CoQ(2) does not require this pathway when supplied exogenously and the pathway is unlikely to be responsible for the structural discrimination observed. Interestingly, decylQ, an analogue unable to support growth on glycerol, is not toxic, but antagonizes growth of DeltaCoQ yeast in the presence of exogenous CoQ(2). Using a DeltaCoQ double-knockout library we identified a number of genes that decrease the ability of yeast to grow on exogenous CoQ. Here we suggest that CoQ or its redox state may be a signal for growth during the shift to respiration.

Evaluation of Coenzyme Q as an Antioxidant Strategy for Alzheimer's Disease

Increasing evidence suggests that Alzheimer's disease (AD) is associated with oxidative damage that is caused in part by mitochondrial dysfunction. Here we investigated the feasibility of modifying Alzheimer pathology with the mitochondrial antioxidant coenzyme Q (CoQ). Exogenous CoQ protected MC65 neuroblastoma cells from amyloid-beta protein precursor C-terminal fragment (APP CTF)-induced neurotoxicity in a concentration dependent manner, with concentrations of 6.25 microM and higher providing near complete protection. Dietary supplementation with CoQ at a dose of 10 g/kg diet to C65/Bl6 mice for one month significantly suppressed brain protein carbonyl levels, which are markers of oxidative damage. Treatment for one month with 2 g lovastatin/kg diet, which interferes with CoQ synthesis, resulted in a significant lowering of brain CoQ10 levels. Mitochondrial energetics (brain ATP levels and mitochondrial membrane potential) were unaffected by either CoQ or lovastatin treatment. Our results suggest that oral CoQ may be a viable antioxidant strategy for neurodegenerative disease. Our data supports a trial of CoQ in an animal model of AD in order to determine whether a clinical trial is warranted.

Coenzyme Q Intake Elevates the Mitochondrial and Tissue Levels of Coenzyme Q and α-Tocopherol in Young Mice

The main objective of this study was to resolve the issue of whether the amounts of Coenzyme Q (CoQ), which is endogenously synthesized in cells, can be elevated in tissues and mitochondria of young mice by dietary supplementation with CoQ10. The prevalent view is that the uptake of exogenous CoQ by tissues other than plasma and liver either does not occur or is quite minimal. Mice, 6 mo of age, were fed 0, 148 or 654 mg CoQ10/(kg body x d) in their diets for 11 wk. CoQ10 intake enhanced both CoQ9 and CoQ10 homologues in the plasma, and in homogenates and mitochondria of liver, heart and skeletal muscle. CoQ was elevated in brain mitochondria, but not in the brain homogenate. The uptake of exogenous CoQ was higher in mitochondria of heart and skeletal muscle than those in liver. CoQ10 administration also elevated the alpha-tocopherol concentration in tissue homogenates and their mitochondria, thereby providing an in vivo indication of the "sparing" effect of CoQ on alpha-tocopherol. Results of this study demonstrate that, contrary to the historical view, both total and mitochondrial CoQ concentrations in the heart and skeletal muscle and in the mitochondria of brain of young mice can be augmented by dietary supplementation. Furthermore, CoQ intake enhances the antioxidative potential of tissues by elevating the endogenous amounts of alpha-tocopherol.

Coenzyme Q releases the inhibitory effect of free fatty acids on mitochondrial glycerophosphate dehydrogenase.

Data presented in this paper show that the size of the endogenous coenzyme Q (CoQ) pool is not a limiting factor in the activation of mitochondrial glycerophosphate-dependent respiration by exogenous CoQ(3), since successive additions of succinate and NADH to brown adipose tissue mitochondria further increase the rate of oxygen uptake. Because the inhibition of glycerophosphate-dependent respiration by oleate was eliminated by added CoQ(3), our data indicate that the activating effect of CoQ(3) is related to the release of the inhibitory effect of endogenous free fatty acids (FFA). Both the inhibitory effect of FFA and the activating effect of CoQ(3) could be demonstrated only for glycerophosphate-dependent respiration, while succinate- or NADH-dependent respiration was not affected. The presented data suggest differences between mitochondrial glycerophosphate dehydrogenase and succinate or NADH dehydrogenases in the transfer of reducing equivalents to the CoQ pool.

Coenzyme Q releases the inhibitory effect of free fatty acids on mitochondrial glycerophosphate dehydrogenase.

Data presented in this paper show that the size of the endogenous coenzyme Q (CoQ) pool is not a limiting factor in the activation of mitochondrial glycerophosphate-dependent respiration by exogenous CoQ(3), since successive additions of succinate and NADH to brown adipose tissue mitochondria further increase the rate of oxygen uptake. Because the inhibition of glycerophosphate-dependent respiration by oleate was eliminated by added CoQ(3), our data indicate that the activating effect of CoQ(3) is related to the release of the inhibitory effect of endogenous free fatty acids (FFA). Both the inhibitory effect of FFA and the activating effect of CoQ(3) could be demonstrated only for glycerophosphate-dependent respiration, while succinate- or NADH-dependent respiration was not affected. The presented data suggest differences between mitochondrial glycerophosphate dehydrogenase and succinate or NADH dehydrogenases in the transfer of reducing equivalents to the CoQ pool.

Mitochondrial production of oxygen radical species and the role of Coenzyme Q as an antioxidant.

The mitochondrial respiratory chain is a powerful source of reactive oxygen species (ROS), which is considered as the pathogenic agent of many diseases and of aging. We have investigated the role of complex I in superoxide radical production and found by the combined use of specific inhibitors of complex I that the one-electron donor to oxygen in the complex is a redox center located prior to the sites where three different types of Coenzyme Q (CoQ) competitors bind, to be identified with an Fe-S cluster, most probably N2, or possibly an ubisemiquinone intermediate insensitive to all the above inhibitors. Short-chain Coenzyme Q analogs enhance superoxide formation, presumably by mediating electron transfer from N2 to oxygen. The clinically used CoQ analog, idebenone, is particularly effective, raising doubts on its safety as a drug. Cells counteract oxidative stress by antioxidants. CoQ is the only lipophilic antioxidant to be biosynthesized. Exogenous CoQ, however, protects cells from oxidative stress by conversion into its reduced antioxidant form by cellular reductases. The plasma membrane oxidoreductase and DT-diaphorase are two such systems, likewise, they are overexpressed under oxidative stress conditions.

Role of mitochondria in oxidative stress and aging.

The mitochondrial respiratory chain is a powerful source of reactive oxygen species (ROS), considered as the pathogenic agent of many diseases and of aging. We have investigated the role of Complex I in superoxide radical production and found by combined use of specific inhibitors of Complex I that the one-electron donor in the Complex to oxygen is a redox center located prior to the sites where three different types of coenzyme Q (CoQ) competitors bind, to be identified with an Fe-S cluster, most probably N2, or possibly an ubisemiquinone intermediate insensitive to all the above inhibitors. Short-chain coenzyme Q analogues enhance superoxide formation, presumably by mediating electron transfer from N2 to oxygen. The clinically used CoQ analogue idebenone is particularly effective, raising doubts about its safety as a drug. The mitochondrial theory of aging considers somatic mutations of mitochondrial DNA induced by ROS as the primary cause of energy decline; in rat liver mitochondria, Complex I appears to be most affected by aging and to become strongly rate limiting for electron transfer. Mitochondrial energetics is also deranged in human platelets upon aging, as demonstrated by the decreased Pasteur effect (enhancement of lactate production by respiratory inhibitors). Cells counteract oxidative stress by antioxidants: CoQ is the only lipophilic antioxidant to be biosynthesized. Exogenous CoQ, however, protects cells from oxidative stress by conversion into its reduced antioxidant form by cellular reductases. The plasma membrane oxidoreductase and DT-diaphorase are two such systems: likewise, they are overexpressed under oxidative stress conditions.

Ubiquinol and a Coenzyme Q Reducing System Protect Platelet Mitochondrial Function of Transfusional Buffy Coats from Oxidative Stress

The conditions under which Coenzyme Q (CoQ) may protect platelet mitochondrial function of transfusional buffy coats from aging and from induced oxidative stress were investigated. The Pasteur effect, i.e. the enhancement of lactate production after inhibition of mitochondrial respiratory chain, was exploited as a marker of mitochondrial function as it allows to calculate the ratio of mitochondrial ATP to glycolytic ATP. Reduced CoQ 10 improves platelet mitochondrial function of transfusional buffy coats and protects the cells from induced oxidative stress. Oxidized CoQ is usually less effective, despite the presence, shown for the first time in this study, of quinone reductase activities in the platelet plasma membranes. The addition of a CoQ reducing system to platelets is effective in enhancing the protection of platelet mitochondrial function from the oxidative stress. The results support on one hand a possibility of protection of mitochondrial function in aging by exogenous CoQ intake, on the other a possible application in protection of transfusional buffy coats from storage conditions and oxidative deterioration.

Effects of ethanol, lovastatin and Coenzyme Q 10 treatment on antioxidants and TBA reactive material in liver of rats

Alcohol metabolism may result in oxidant stress and free radical injury through a variety of mechanisms. Lovastatin may also produce oxidant stress by reducing levels of an endogenous antioxidant, coenzyme Q (CoQ). The separate and combined effects of ethanol, 20 EN% in a total liquid diet, and lovastatin, 67 mg/kg diet, on α-tocopherol, retinol palmitate, CoQ 9 and thiobarbituric acid reactive (TBAR) material in liver from rats were determined. The effect of exogenous CoQ 10 on these treatment groups was also determined. Food consumption, weight gain, liver lipid and TBAR material were similar between treatment groups. Compared to control animals, ethanol reduced retinol palmitate significantly, from 143 to 90 μg/g wet weight. Lovastatin had no effect on retinal palmitate nor did it act additively with ethanol. Ethanol decreased liver α-tocopherol from 28 to 12 μg/g wet weight and lovastatin diminished it to 12 μg; no additive effect was evident. Ethanol had no effect, but lovastatin decreased CoQ 9 from 83 to 55 μg/g wet weight. Supplementation with CoQ 10 did not modulate the effect of ethanol on retianl palmitate, but it did reverse the effect of lovastatin on CoQ 9. Supplementary CoQ 10 did not alter control levels of α-tocopherol, but it appeared to reverse most of the decrease in α-tocopherol attributable to ethanol or lovastatin separately. It only partially reversed the effect of ethanol and lovastatin combined on α-tocopherol, however. As expected, lovastatin had no effect on CoQ 10 levels in supplemented animals. Ethanol, either separately or in combination with lovastatin, diminished liver stores of CoQ 10 by almost 40%. We conclude that 20 EN% ethanol given in a liquid diet for 5 weeks is sufficient to lower retinol palmitate and that lovastatin reduces CoQ 9. Both diminish α-tocopherol, an effect largely overcome by CoQ 10 supplementation with either drug alone, but not with the combination. Since many individuals chronically consume the levels of ethanol represented by this experiment, and since a certain number of those also take lovastatin, further research into the possible clinical significance of these observations is warranted.

Saturation kinetics of coenzyme Q in NADH and succinate oxidation in beef heart mitochondria

The saturation kinetics of NADH and succinate oxidation for Coenzyme Q (CoQ) has been re-investigated in pentane-extracted lyophilized beef heart mitochondria reconstituted with exogenous CoQ 10. The apparent ‘ K m’ for CoQ 10 was one order of magnitude lower in succinate cytochrome c reductase than in NADH cytochrome c reductase. The K m value in NADH oxidation approaches the natural CoQ content of beef heart mitochondria, whereas that in succinate oxidation is close to the content of respiratory chain enzymes.

Free radical scavenging activity of coenzyme Q measured by a chemiluminescent assay

Involvement of coenzyme Q (CoQ) in anti-oxidant activities, in addition to its major redox role, has frequently been suggested in recent years. In order to elucidate if CoQ could really be engaged in scavenging free radicals produced endogenously in a biological system, an experimental system was developed in which beef heart mitochondria in the presence of a saturating NADH concentration and of rotenone produce free radicals. The presence of oxygen-reactive forms was easily detected by a luminol-dependent chemiluminescence process. The chemiluminescence assay showed that short-chain CoQ homologues can act as pro-oxidants, enhancing free radical effects, while exogenous coenzyme Q 10 could scavenge free radicals, especially at very low concentration. In this system, exogenous CoQ 10 was more effective than α-tocopherol at the same concentration in scavenging free radicals. The molecular mechanism that leads to this ability is still nuclear, but these results are of biochemical and biomedical importance because they indicate that CoQ may act as an anti-oxidant in situations mimicking physiopathological conditions. This direct chemiluminescent method is promising for studies of biochemical processes which involve active oxygen species.