Interactions between ubiquinones and vitamins in membranes and cells

Vitamin E/Coenzyme Q-Dependent "Free Radical Reductases": Redox Regulators in Ferroptosis

Significance: Lipid peroxidation and its products, oxygenated polyunsaturated lipids, act as essential signals coordinating metabolism and physiology and can be deleterious to membranes when they accumulate in excessive amounts. Recent Advances: There is an emerging understanding that regulation of polyunsaturated fatty acid (PUFA) phospholipid peroxidation, particularly of PUFA-phosphatidylethanolamine, is important in a newly discovered type of regulated cell death, ferroptosis. Among the most recently described regulatory mechanisms is the ferroptosis suppressor protein, which controls the peroxidation process due to its ability to reduce coenzyme Q (CoQ). Critical Issues: In this study, we reviewed the most recent data in the context of the concept of free radical reductases formulated in the 1980-1990s and focused on enzymatic mechanisms of CoQ reduction in different membranes (e.g., mitochondrial, endoplasmic reticulum, and plasma membrane electron transporters) as well as TCA cycle components and cytosolic reductases capable of recycling the high antioxidant efficiency of the CoQ/vitamin E system. Future Directions: We highlight the importance of individual components of the free radical reductase network in regulating the ferroptotic program and defining the sensitivity/tolerance of cells to ferroptotic death. Complete deciphering of the interactive complexity of this system may be important for designing effective antiferroptotic modalities. Antioxid. Redox Signal. 40, 317-328.

Trolox aids coenzyme Q10 in neuroprotection against NMDA induced damage via upregulation of VEGF in rat model of glutamate excitotoxicity

Glutamate induced damage to retinal ganglion cells (RGCs) requires tight physiological regulation of the N-methyl-D-aspartate (NMDA) receptors. Previously, studies have demonstrated the neuroprotective abilities of antioxidants like coenzyme Q10 (CoQ10) and vitamin E analogs like α-tocopherol against neuropathies resulting from NMDA insult, but have failed to shed light on the effect of CoQ10 and trolox, a hydrophilic analog of vitamin E, on glaucomatous neurodegeneration. In the current study, we wanted to investigate whether the combined effect of trolox with CoQ10 could alleviate NMDA-induced death of retinal cells while also trying to elucidate the underlying mechanism in relation to the yet unexplained role of vascular endothelial growth factor (VEGF) in NMDA-mediated excitotoxicity. After successful NMDA-induced degeneration, we followed it up with the treatment of combination of Trolox and CoQ10. The structural damage by NMDA was repaired significantly and retina retained structural integrity comparable to levels of control in the treatment group of Trolox and CoQ10. Detection of ROS generation after NMDA insult showed that together, Trolox and CoQ10 could significantly bring down the high levels of free radicals while also rescuing mitochondrial membrane potential (MMP). A significant increase in NMDA receptor Grin2A by CoQ10 alone as well as by CoQ10 and trolox was accompanied by a lowered Grin2B receptor expression, suggesting neuroprotective action of Trolox and CoQ10. Subsequently, lowered VEGFR1 and VEGFR2 receptor expression by NMDA treatment also recovered when subjected to combined treatment of Trolox and CoQ10. Western blot analyses also indicated the same whereby Trolox and CoQ10 could increase the diminished levels of phosphorylated VEGFR2. Immunofluorescence studies also indicated a positive correlation between recovered VEGFR2 and NMDAR2A levels and diminished levels of NMDAR2D, confirming the results obtained by RT-PCR analysis. This is the first report in our knowledge that demonstrates the efficacy of trolox in combination with CoQ10 highlighting the importance of maintaining VEGF levels that are lowered in ocular diseases due to NMDA-related toxicities.

Effect of Statin Therapy on the Plasma Concentrations of Retinol, Alpha-Tocopherol and Coenzyme Q10 in Children with Familial Hypercholesterolemia

Purpose

Familial hypercholesterolemia (FH) requires early treatment. However, statins, which are regarded the first-line therapy, have an influence on redox balance. Antioxidant vitamins are important for many metabolic processes in the developing body. There are few data available on the long-term safety of statin use in children. The aim of this study was to evaluate the influence of statin treatment in children with FH on plasma concentrations of antioxidant vitamins: retinol, alpha-tocopherol and coenzyme Q10.

Methods

The first study group consisted of 13 children aged 10–18 years treated with simvastatin for at least 6 months, and the second group comprised 13 age- and sex-matched children with hypercholesterolemia, in whom pharmacological treatment had not been applied yet. Analyses were performed using a high-performance liquid chromatograph coupled with a MS detector.

Results

The analysis did not reveal significant differences in the concentration of retinol, alpha-tocopherol or coenzyme Q10 between the studied groups. The adjustment of the concentrations of the vitamins to the cholesterol level also indicated no significant differences. We found no deficits in antioxidant vitamins in patients treated with statins, or any risk of adverse effects associated with an increase in their concentration.

Conclusion

There is no rationale for additional supplementation using antioxidant vitamins or modification of low-fat and low-cholesterol diet in pediatric patients treated with statins.

Electronic supplementary material

The online version of this article (10.1007/s10557-020-07091-w) contains supplementary material, which is available to authorized users.

Topical Coenzyme Q10 demonstrates mitochondrial-mediated neuroprotection in a rodent model of ocular hypertension

Coenzyme Q10 (CoQ10) is a mitochondrial-targeted antioxidant with known neuroprotective activity. Its ocular effects when co-solubilised with α-tocopherol polyethylene glycol succinate (TPGS) were evaluated. In vitro studies confirmed that CoQ10 was significantly protective in different retinal ganglion cell (RGC) models. In vivo studies in Adult Dark Agouti (DA) rats with unilateral surgically-induced ocular hypertension (OHT) treated with either CoQ10/TPGS micelles or TPGS vehicle twice daily for three weeks were performed, following which retinal cell health was assessed in vivo using DARC (Detection of Apoptotic Retinal Cells) and post-mortem with Brn3a histological assessment on whole retinal mounts. CoQ10/TPGS showed a significant neuroprotective effect compared to control with DARC (p<0.05) and Brn3 (p<0.01). Topical CoQ10 appears an effective therapy preventing RGC apoptosis and loss in glaucoma-related models.

Important roles for membrane lipids in haloarchaeal bioenergetics

Recent advances in lipidomic analysis in combination with various physiological experiments set the stage for deciphering the structure-function of haloarchaeal membrane lipids. Here we focused primarily on changes in lipid composition of Haloferax volcanii, but also performed a comparative analysis with four other haloarchaeal species (Halobacterium salinarum, Halorubrum lacusprofundi, Halorubrum sodomense and Haloplanus natans) all representing distinctive cell morphologies and behaviors (i.e., rod shape vs. pleomorphic behavior). Common to all five haloarchaea, our data reveal an extraordinary high level of menaquinone, reaching up to 72% of the total lipids. This ubiquity suggests that menaquinones may function beyond their ordinary role as electron and proton transporter, acting simultaneously as ion permeability barriers and as powerful shield against oxidative stress. In addition, we aimed at understanding the role of cations interacting with the characteristic negatively charged surface of haloarchaeal membranes. We propose for instance that by bridging the negative charges of adjacent anionic phospholipids, Mg²⁺ acts as surrogate for cardiolipin, a molecule that is known to control curvature stress of membranes. This study further provides a bioenergetic perspective as to how haloarchaea evolved following oxygenation of Earth's atmosphere. The success of the aerobic lifestyle of haloarchaea includes multiple membrane-based strategies that successfully balance the need for a robust bilayer structure with the need for high rates of electron transport - collectively representing the molecular basis to inhabit hypersaline water bodies around the planet.

Coenzyme Q10 for Prevention of Anthracycline-Induced Cardiotoxicity

Preclinical and clinical studies suggest that anthracycline-induced cardiotoxicity can be prevented by administering coenzyme Q10 during cancer chemotherapy that includes drugs such as doxorubicin and daunorubicin. Studies further suggest that coenzyme Q10 does not interfere with the antineoplastic action of anthracyclines and might even enhance their anticancer effects. Preventing cardiotoxicity might allow for escalation of the anthracycline dose, which would further enhance the anticancer effects. Based on clinical investigation, although limited, a cumulative dose of doxorubicin of up to 900 mg/m2, and possibly higher, can be administered safely during chemotherapy as long as coenzyme Q10 is administered concurrently. The etiology of the dose-limiting cardiomyopathy that is induced by anthracyclines can be explained by irreversible damage to heart cell mitochondria, which differ from mitochondria of other cells in that they possess a unique enzyme on the inner mitochondrial membrane. This enzyme reduces anthracyclines to their semiquinones, resulting in severe oxidative stress, disruption of mitochondrial energetics, and irreversible damage to mitochondrial DNA. Damage to mitochondrial DNA blocks the regenerative capability of the organelle and ultimately leads to apoptosis or necrosis of myocytes. Coenzyme Q10, an essential component of the electron transport system and a potent intracellular antioxidant, appears to prevent damage to the mitochondria of the heart, thus preventing the development of anthracycline-induced cardiomyopathy.

Mitochondria: a new therapeutic target in chronic kidney disease

Cellular metabolic changes during chronic kidney disease (CKD) may induce higher production of oxygen radicals that play a significant role in the progression of renal damage and in the onset of important comorbidities. This condition seems to be in part related to dysfunctional mitochondria that cause an increased electron "leakage" from the respiratory chain during oxidative phosphorylation with a consequent generation of reactive oxygen species (ROS). ROS are highly active molecules that may oxidize proteins, lipids and nucleic acids with a consequent damage of cells and tissues. To mitigate this mitochondria-related functional impairment, a variety of agents (including endogenous and food derived antioxidants, natural plants extracts, mitochondria-targeted molecules) combined with conventional therapies could be employed. However, although the anti-oxidant properties of these substances are well known, their use in clinical practice has been only partially investigated. Additionally, for their correct utilization is extremely important to understand their effects, to identify the correct target of intervention and to minimize adverse effects. Therefore, in this manuscript, we reviewed the characteristics of the available mitochondria-targeted anti-oxidant compounds that could be employed routinely in our nephrology, internal medicine and renal transplant centers. Nevertheless, large clinical trials are needed to provide more definitive information about their use and to assess their overall efficacy or toxicity.

Coenzyme Q10 remarkably improves the bio-energetic function of rat liver mitochondria treated with statins

CoQ10 shares a biosynthetic pathway with cholesterol therefore it can be a potential target of the widely available lipid-lowering agents such as statins. Statins are the most widely prescribed cholesterol-lowering drugs with the ability to inhibit HMG-CoA (3-hydroxy-3-methylglutaryl-coenzyme A) reductase. Preclinical and clinical safety data have shown that statins do not cause serious adverse effects in humans. However, their long-term administration is associated with a variety of myopatic complaints. The aim of this study was to investigate whether CoQ10 supplementation of animals under high fat diet (HFD) treated with statins is able to bypass the mitochondrial metabolic defects or not? Animals were divided into 7 groups and fed with either regular (RD) or HFD during experiments. The first group considered as regular control and fed with a RD. Groups 2-7 including HFD control, CoQ10 (10mg/kg), simvastatin (30mg/kg), atorvastatin (30mg/kg), simvastatin+CoQ10 or atorvastatin+CoQ10 treated orally for 30 days and fed with HFD. At the end of treatments, the animals were killed and blood samples were collected for biochemical examinations. The rat liver mitochondria were isolated and several mitochondrial indices including succinate dehydrogenase activity (SDA), ATP levels, mitochondrial membrane potential (MMP) and mitochondrial permeability transition pore (MPP) were determined. We found that triglyceride (Tg), cholesterol (Chol) and low-density lipoprotein (LDL) were augmented with HFD compared to RD and treatment with statins remarkably lowered the Tg, Chol and LDL levels. Mitochondrial parameters including, SDA, ATP levels, MMP and MPP were reduced with statin treatment and improved by co-administration with CoQ10.

Effects of coenzyme Q10 supplementation (300 mg/day) on antioxidation and anti-inflammation in coronary artery disease patients during statins therapy: a randomized, placebo-controlled trial

Background

High oxidative stress and chronic inflammation can contribute to the pathogenesis of coronary artery disease (CAD). Coenzyme Q10 is an endogenous lipid-soluble antioxidant. Statins therapy can reduce the biosynthesis of coenzyme Q10. The purpose of this study was to investigate the effects of a coenzyme Q10 supplement (300 mg/d; 150 mg/b.i.d) on antioxidation and anti-inflammation in patients who have CAD during statins therapy.

Methods

Patients who were identified by cardiac catheterization as having at least 50% stenosis of one major coronary artery and who were treated with statins for at least one month were enrolled in this study. The subjects (n = 51) were randomly assigned to the placebo (n = 24) and coenzyme Q10 groups (Q10-300 group, n = 27). The intervention was administered for 12 weeks. The concentrations of coenzyme Q10, vitamin E, antioxidant enzymes activities (superoxide dismutase, catalase, and glutathione peroxidase), and inflammatory markers [C-reactive protein (CRP), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6)] were measured in the 42 subjects (placebo, n = 19; Q10-300, n = 23) who completed the study.

Results

The levels of the plasma coenzyme Q10 (P < 0.001) and antioxidant enzymes activities (P < 0.05) were significantly higher after coenzyme Q10 supplementation. The levels of inflammatory markers (TNF-α, P = 0.039) were significantly lower after coenzyme Q10 supplementation. The subjects in the Q10-300 group had significantly higher vitamin E (P = 0.043) and the antioxidant enzymes activities (P < 0.05) than the placebo group at week 12. The level of plasma coenzyme Q10 was significantly positively correlated with vitamin E (P = 0.008) and antioxidant enzymes activities (P < 0.05) and was negatively correlated with TNF-α (P = 0.034) and IL-6 (P = 0.027) after coenzyme Q10 supplementation.

Conclusion

Coenzyme Q10 supplementation at 300 mg/d significantly enhances antioxidant enzymes activities and lowers inflammation in patients who have CAD during statins therapy.

Trial registration

Clinical Trials.gov Identifier: NCT01424761.

Effects of widely used drugs on micronutrients: a story rarely told

Vitamins and trace elements are essential to the body, however, deficiencies are frequently observed in the general population. Diet is mostly responsible for these deficiencies but drugs also may play a significant role by influencing their metabolism. These effects are rarely assessed in clinical practice, in part because of limited data available in the literature. Drug-induced micronutrient depletions, however, may be the origin of otherwise unexplained symptoms that might sometimes influence medication compliance. We present various examples of widely prescribed drugs that can precipitate micronutrient deficiencies. This review aims at sensitizing physicians on drug-micronutrient interactions. High-risk population groups also are presented and supplementation protocols are suggested.

Inflammatory biomarkers for predicting cardiovascular disease

The pathology of cardiovascular disease (CVD) is complex; multiple biological pathways have been implicated, including, but not limited to, inflammation and oxidative stress. Biomarkers of inflammation and oxidative stress may serve to help identify patients at risk for CVD, to monitor the efficacy of treatments, and to develop new pharmacological tools. However, due to the complexities of CVD pathogenesis there is no single biomarker available to estimate absolute risk of future cardiovascular events. Furthermore, not all biomarkers are equal; the functions of many biomarkers overlap, some offer better prognostic information than others, and some are better suited to identify/predict the pathogenesis of particular cardiovascular events. The identification of the most appropriate set of biomarkers can provide a detailed picture of the specific nature of the cardiovascular event. The following review provides an overview of existing and emerging inflammatory biomarkers, pro-inflammatory cytokines, anti-inflammatory cytokines, chemokines, oxidative stress biomarkers, and antioxidant biomarkers. The functions of each biomarker are discussed, and prognostic data are provided where available.

Plasma vitamin E and coenzyme Q10 are not associated with a lower risk of acute myocardial infarction in Singapore Chinese adults

Vitamin E and coenzyme Q10 (CoQ10) have antioxidant effects that may benefit cardiovascular health. Meta-analyses of randomized controlled trials have not shown a protective effect of supplementation with the vitamin E isomer α-tocopherol on the risk of acute myocardial infarction (AMI), but data on other isomers and CoQ10 are limited. Our objective was to examine the association of the plasma concentrations of vitamin E isomers (α-, γ-, and δ-tocopherol and α-, γ-, and δ-tocotrienol) and CoQ10 (ubiquinol and ubiquinone) with the incidence of AMI. We conducted a nested case-control study with 233 cases of incident AMI and 466 matched controls selected from the Singapore Chinese Health Study, aged 45-74 y at the time of recruitment and free of cardiovascular disease at the time of blood collection. We used conditional logistic regression to examine the association between vitamin E and CoQ10 and the risk of AMI adjusted for other risk factors. In the basic model, higher δ-tocopherol and ubiquinone concentrations were significantly associated with a higher risk of AMI, whereas there were no significant associations for the other vitamin E and CoQ10 isomers. After adjusting for lifestyle and other risk factors, only the association between δ-tocopherol and AMI risk remained significant [OR = 3.09 (95% CI: 1.53, 6.25) highest vs. lowest quintile; P-trend = 0.028]. We did not observe an inverse association between plasma concentrations of vitamin E isomers or CoQ10 and risk of AMI in Singapore Chinese. In contrast, plasma δ-tocopherol concentrations were associated with a higher risk of AMI. Our findings do not support a role of higher vitamin E or CoQ10 intakes in the prevention of AMI.

Mitochondrial dysfunction in diabetes: from molecular mechanisms to functional significance and therapeutic opportunities

Given their essential function in aerobic metabolism, mitochondria are intuitively of interest in regard to the pathophysiology of diabetes. Qualitative, quantitative, and functional perturbations in mitochondria have been identified and affect the cause and complications of diabetes. Moreover, as a consequence of fuel oxidation, mitochondria generate considerable reactive oxygen species (ROS). Evidence is accumulating that these radicals per se are important in the pathophysiology of diabetes and its complications. In this review, we first present basic concepts underlying mitochondrial physiology. We then address mitochondrial function and ROS as related to diabetes. We consider different forms of diabetes and address both insulin secretion and insulin sensitivity. We also address the role of mitochondrial uncoupling and coenzyme Q. Finally, we address the potential for targeting mitochondria in the therapy of diabetes.

Recent developments in the treatment of atherosclerosis

Atherosclerosis is one of the most frequent causes of cardiac arrest. The major cause of this disease is high concentrations of lipid in the blood. Medicinal agents so far have been quite successful in the management of hyperlipidemia. Among the several widely used drugs, (fibrates, statins and niacin) statins are the most frequently prescribed in many forms of hyperlipidemia. Recently, statins have been found to produce serious toxicities, which are rare but can be potentially harmful and are noise concern for the immediate need to develop some new chemical entities in this category. This review is primarily concerned with recent developments in atherosclerotic drug discovery including novel inhibitors of cholesterol biosynthesis, cholesterol absorption inhibitors and antioxidants. The review also focuses on possible future targets including gene therapy.

Coenzyme Q10 protects retinal cells against oxidative stress in vitro and in vivo

PURPOSE

To investigate the neuroprotective effects of coenzyme Q10 and/or a vitamin E analogue on retinal damage both in vitro and in vivo.

METHODS

We employed cultured retinal ganglion cells (RGC-5, a rat ganglion cell-line transformed using E1A virus) in vitro. Cell damage was induced by 24-h hydrogen peroxide (H2O2) exposure, and cell viability was measured using tetrazolium salt (WST-8). To examine the retinal damage induced by intravitreal N-methyl-d-aspartate (NMDA) injection in mice in vivo, coenzyme Q10 at 10 mg/kg with or without alpha-tocopherol at 10 mg/kg was administered orally (p.o.) each day for 14 days, with NMDA being intravitreally injected on day 7 of this course.

RESULTS

In RGC-5, a combination of coenzyme Q10 and trolox, a water-soluble vitamin E analogue (a derivative of alpha-tocopherol), prevented cell damage more effectively than either agent alone. Coenzyme Q10 and alpha-tocopherol (separately or together) reduced the retinal damage, number of TUNEL-positive cells in the ganglion cell layer (GCL), and 4-hydroxyl-2-nonenal (4-HNE) expression induced by NMDA in mice in vivo.

CONCLUSIONS

Coenzyme Q10 and/or these vitamin E analogues exert neuroprotective effects against retinal damage both in vitro and in vivo.

Fluorescence studies of the interactions of ubiquinol-10 with liposomes

Ubiquinone-10 plays a central role in energy production and its reduced form, ubiquinol-10 is also capable of acting as a potent radical scavenging antioxidant against membrane lipid peroxidation. Efficiency of this protection depends mostly on its localization in lipid bilayer. The intrinsic fluorescence of ubiquinol-10 and of the exogenous probe, Laurdan, has been used to determine the location of ubiquinol-10 in unilamellar liposomes of egg phosphatidylcholine (EggPC) and dimyristoyl phosphatidylcholine. Laurdan fluorescence moiety is positioned at the hydrophilic-hydrophobic interface of the phospholipid bilayer and its parameters reflect the membrane polarity and microheterogeneity, which we have used to explore the coexistence of microdomains with distinct physical properties. In liquid-crystalline bilayers ubiquinol has a short fluorescence lifetime (0.4 ns) and a high steady-state anisotropy. In a concentration-dependent manner, ubiquinol-10 influences the Laurdan excitation, emission and generalized polarization measurements. In EggPC liposomes ubiquinol-10 induces a decrease in membrane water mobility near the probe, while in dimyristoyl liposomes a decrease in the membrane water content was found. Moreover the presence of ubiquinol results in the formation of coexisting phospholipid domains of gel and liquid-crystalline phases. The results indicate that ubiquinol-10 molecules are mainly located at the polar-lipid interface, inducing changes in the physico-chemical properties of the bilayer microenvironment.

The role of coenzyme Q10 in statin-associated myopathy: a systematic review

Statins (3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors) are currently the most effective medications for reducing low-density lipoprotein cholesterol concentrations. Although generally safe, they have been associated with a variety of myopathic complaints. Statins block production of farnesyl pyrophosphate, an intermediate in the synthesis of ubiquinone or coenzyme Q10 (CoQ10). This fact, plus the role of CoQ10 in mitochondrial energy production, has prompted the hypothesis that statin-induced CoQ10 deficiency is involved in the pathogenesis of statin myopathy. We identified English language articles relating statin treatment and CoQ10 levels via a PubMed search through August 2006. Abstracts were reviewed and articles addressing the relationship between statin treatment and CoQ10 levels were examined in detail. Statin treatment reduces circulating levels of CoQ10. The effect of statin therapy on intramuscular levels of CoQ10 is not clear, and data on intramuscular CoQ10 levels in symptomatic patients with statin-associated myopathy are scarce. Mitochondrial function may be impaired by statin therapy, and this effect may be exacerbated by exercise. Supplementation can raise the circulating levels of CoQ10, but data on the effect of CoQ10 supplementation on myopathic symptoms are scarce and contradictory. We conclude that there is insufficient evidence to prove the etiologic role of CoQ10 deficiency in statin-associated myopathy and that large, well-designed clinical trials are required to address this issue. The routine use of CoQ10 cannot be recommended in statin-treated patients. Nevertheless, there are no known risks to this supplement and there is some anecdotal and preliminary trial evidence of its effectiveness. Consequently, CoQ10 can be tested in patients requiring statin treatment, who develop statin myalgia, and who cannot be satisfactorily treated with other agents. Some patients may respond, if only via a placebo effect.

The importance of plasma membrane coenzyme Q in aging and stress responses

The plasma membrane of eukaryotic cells is the limit to interact with the environment. This position implies receiving stress signals that affects its components such as phospholipids. Inserted inside these components is coenzyme Q that is a redox compound acting as antioxidant. Coenzyme Q is reduced by diverse dehydrogenase enzymes mainly NADH-cytochrome b(5) reductase and NAD(P)H:quinone reductase 1. Reduced coenzyme Q can prevent lipid peroxidation chain reaction by itself or by reducing other antioxidants such as alpha-tocopherol and ascorbate. The group formed by antioxidants and the enzymes able to reduce coenzyme Q constitutes a plasma membrane redox system that is regulated by conditions that induce oxidative stress. Growth factor removal, ethidium bromide-induced rho degrees cells, and vitamin E deficiency are some of the conditions where both coenzyme Q and its reductases are increased in the plasma membrane. This antioxidant system in the plasma membrane has been observed to participate in the healthy aging induced by calorie restriction. Furthermore, coenzyme Q regulates the release of ceramide from sphingomyelin, which is concentrated in the plasma membrane. This results from the non-competitive inhibition of the neutral sphingomyelinase by coenzyme Q particularly by its reduced form. Coenzyme Q in the plasma membrane is then the center of a complex antioxidant system preventing the accumulation of oxidative damage and regulating the externally initiated ceramide signaling pathway.

Coenzyme Q10 in phenylketonuria and mevalonic aciduria

Mevalonic aciduria (MVA) and phenylketonuria (PKU) are inborn errors of metabolism caused by deficiencies in the enzymes mevalonate kinase and phenylalanine 4-hydroxylase, respectively. Despite numerous studies the factors responsible for the pathogenicity of these disorders remain to be fully characterised. In common with MVA, a deficit in coenzyme Q10 (CoQ10) concentration has been implicated in the pathophysiology of PKU. In MVA the decrease in CoQ10 concentration may be attributed to a deficiency in mevalonate kinase, an enzyme common to both CoQ10 and cholesterol synthesis. However, although dietary sources of cholesterol cannot be excluded, the low/normal cholesterol levels in MVA patients suggests that some other factor may also be contributing to the decrease in CoQ10.The main factor associated with the low CoQ10 level of PKU patients is purported to be the elevated phenylalanine level. Phenylalanine has been shown to inhibit the activities of both 3-hydroxy-3-methylglutaryl-CoA reductase and mevalonate-5-pyrophosphate decarboxylase, enzymes common to both cholesterol and CoQ10 biosynthesis. Although evidence of a lowered plasma/serum CoQ10 level has been reported in MVA and PKU, few studies have assessed the intracellular CoQ10 concentration of patients. Plasma/serum CoQ10 is influenced by dietary intake as well as its lipoprotein content and therefore may be limited as a means of assessing intracellular CoQ10 concentration. Whether the pathogenesis of MVA and PKU are related to a loss of CoQ10 has yet to be established and further studies are required to assess the intracellular CoQ10 concentration of patients before this relationship can be confirmed or refuted.

Coenzyme Q10 in cardiovascular disease

In this review we summarise the current state of knowledge of the therapeutic efficacy and mechanisms of action of CoQ(10) in cardiovascular disease. Our conclusions are: 1. There is promising evidence of a beneficial effect of CoQ(10) when given alone or in addition to standard therapies in hypertension and in heart failure, but less extensive evidence in ischemic heart disease. 2. Large scale multi-centre prospective randomised trials are indicated in all these areas but there are difficulties in funding such trials. 3. Presently, due to the notable absence of clinically significant side effects and likely therapeutic benefit, CoQ(10) can be considered a safe adjunct to standard therapies in cardiovascular disease.

Decreased coenzyme Q10 concentration in plasma of children with cystic fibrosis

OBJECTIVES

Coenzyme Q10 (CoQ10) is an effective lipophilic antioxidant and protects against lipid peroxidation by scavenging radicals. Patients with cystic fibrosis generally have fat malabsorption; thus, we hypothesized that overall plasma CoQ10 concentration in pediatric patients with cystic fibrosis might be diminished. Because these patients have increased oxidative stress due to chronic pulmonary inflammation, we also assumed that the oxidized form of CoQ10 might be relatively increased.

PATIENTS AND METHODS

The total plasma CoQ10 levels and the oxidized and reduced form were measured by high-performance liquid chromatography in 30 children with cystic fibrosis (mean FEV1 % predicted = 88.5% +/- 18.7%) and 30 age-matched controls.

RESULTS

Total plasma CoQ10 levels were significantly lower in the cystic fibrosis group as compared with the control group (0.87 +/- 0.42 micromol/L and 1.35 +/- 0.39 micromol/L, respectively; P < 0.001). When correcting for the lower serum cholesterol level in patients with cystic fibrosis, this difference remained significant: the CoQ10/cholesterol ratio (micromol/mol) was 268.8 +/- 136.7 and 334.0 +/- 102.9 in patients and controls, respectively (P < 0.05). However, the CoQ10 redox status was identical in patients and controls (86.4% +/- 7.1% and 85.4% +/- 7.3%, respectively).

CONCLUSIONS

We found that the overall plasma CoQ10 concentration is lower in patients with cystic fibrosis, probably because of fat malabsorption. The CoQ10 redox status was not disturbed, indicating that CoQ10 could still be adequately regenerated in this group of patients with cystic fibrosis with mild-to-moderate pulmonary disease.

Coenzyme Q-dependent functions of plasma membrane in the aging process

Coenzyme Q (Q) is reduced in plasma membrane and mitochondria by NAD(P)H-dependent reductases providing reducing equivalents to maintain both respiratory chain and antioxidant protection. Reactive oxygen species (ROS) are accumulated in the aging process originating mainly in mitochondria but also in other membranes, such as plasma membrane partially by the loss of electrons from the semiquinone. The reduction of Q by NAD(P)H-dependent reductases in plasma membrane is responsible for providing its antioxidant capacity, preventing both the lipid peroxidation chain and the activation of the ceramide-dependent apoptosis pathway. Both Q content and its reductases are decreased in plasma membrane of aging mammals. Calorie restriction, which extends mammal life span, increases the content of Q in the plasma membrane and also activates Q reductases in this membrane. Both lipid peroxidation and ceramide production are decreased in the plasma membrane in calorie-restricted animals. Plasma membrane is, then, an important cellular component to control the aging process through its concentration and redox state of Q.

Active oxygen chemistry within the liposomal bilayer. Part III: Locating Vitamin E, ubiquinol and ubiquinone and their derivatives in the lipid bilayer

We have previously shown that the location and orientation of compounds intercalated within the lipid bilayer can be qualitatively determined using an NMR chemical shift-polarity correlation. We describe herein the results of our application of this method to analogs of Vitamin E, ubiquinol and ubiquinone. The results indicate that tocopherol--and presumably the corresponding tocopheroxyl radical--reside adjacent to the interface, and can, therefore, abstract a hydrogen atom from ascorbic acid. On the other hand, the decaprenyl substituted ubiquinol and ubiquinone lie substantially deeper within the lipid membrane. Yet, contrary to the prevailing literature, their location is far from being the same. Ubiquinone-10 is situated above the long-chain fatty acid "slab". Ubiquinol-10 dwells well within the lipid slab, presumably out of "striking range" of Vitamin C. Nevertheless, ubiquinol can act as an antioxidant by reducing C- or O-centered lipid radicals or by recycling the lipid-resident tocopheroxyl radical.

The Effect of HMG-CoA Reductase Inhibitors on Coenzyme Q10

The HMG-CoA reductase inhibitors, also known as statins, have an enviable safety profile; however, myotoxicity and to a lesser extent hepatotoxicity have been noted in some patients following treatment. Statins target several tissues, depending upon their lipophilicity, where they competitively inhibit HMG-CoA reductase, the rate-limiting enzyme for mevalonic acid synthesis and subsequently cholesterol biosynthesis. HMG-CoA reductase is also the first committed rate-limiting step for the synthesis of a range of other compounds including steroid hormones and ubidecarenone (ubiquinone), otherwise known as coenzyme Q(10) (CoQ(10)). Recent interest has focused on the possible role CoQ(10) deficiency may have in the pathophysiology of the rare adverse effects of statin treatment. Currently, there is insufficient evidence from human studies to link statin therapy unequivocally to pathologically significantly decreased tissue CoQ(10) levels. Although statin treatment has been reported to lower plasma/serum CoQ(10) status, few human studies have assessed tissue CoQ(10) status. The plasma/serum CoQ(10) level is influenced by a number of physiological factors and, therefore, has limited value as a means of assessing intracellular CoQ(10) status. In those limited studies that have assessed the effect of statin treatment upon tissue CoQ(10) levels, none have shown evidence of a fall in CoQ(10) levels. This may reflect the doses of statins used, since many appear to have been used at doses below those recommended for their maximum therapeutic effects. Moreover, the poor bioavailability in those peripheral tissues tested may not reflect the effects the agents are having in liver and muscle, the tissues commonly affected in those patients who do not tolerate statins. This article reviews the biochemistry of CoQ(10), its role in cellular metabolism and the available evidence linking possible CoQ(10) deficiency to statin therapy.

Pilot trial of high dosages of coenzyme Q10 in patients with Parkinson's disease

The safety and tolerability of high dosages of coenzyme Q10 were studied in 17 patients with Parkinson's disease (PD) in an open label study. The subjects received an escalating dosage of coenzyme Q10--1200, 1800, 2400, and 3000 mg/day with a stable dosage of vitamin E (alpha-tocopherol) 1200 IU/day. The plasma level of coenzyme Q10 was measured at each dosage. Thirteen of the subjects achieved the maximal dosage, and adverse events were typically considered to be unrelated to coenzyme Q10. The plasma level reached a plateau at the 2400 mg/day dosage and did not increase further at the 3000 mg/day dosage. Our data suggest that in future studies of coenzyme Q10 in PD, a dosage of 2400 mg/day (with vitamin E/alpha-tocopherol 1200 IU/day) is an appropriate highest dosage to be studied.

Anisotropy measurements of intrinsic fluorescence of prenyllipids reveal much higher mobility of plastoquinol than alpha-tocopherol in model membranes

As an alternative to a fluorescent probe approach, the intrinsic fluorescence of reduced forms of prenylquinones has been exploited, which offers a convenient means of determining directly motional properties of these molecules. The steady-state fluorescence anisotropy measurements of plastoquinols (PQH(2)) and alpha-tocopherol (alpha-Toc) incorporated into phospholipid liposomes have been performed. The effect of prenyllipid concentration, PQH(2) side chain length and the composition of the membranes has been studied. For the data interpretation, the fundamental anisotropy of alpha-Toc, PQH(2), ubiquinol-10 and alpha-tocopherolquinol, as well as the angles between the absorption and emission transition moments have been also determined. It was concluded that alpha-Toc shows very low mobility in the lipid bilayer, whereas PQH(2)-9 displays significant motional freedom in dipalmitoylphosphatidylcholine vesicles and even higher in egg yolk lecithin membranes.

Hydrogen peroxide- and cell-density-regulated expression of NADH-cytochrome b5 reductase in HeLa cells

Environmental conditions regulate the expression of different antioxidant enzymes in cell culture. We have studied the effect of cell density and hydrogen peroxide on the expression of NADH-cytochrome b5 reductase in HeLa cells. Polypeptide levels of the NADH-cytochrome b5 reductase increased about three fold in confluent HeLa cells compared to sparse cells. Addition of H2O2 to HeLa cells altered expression levels of the NADH-cytochrome b5 reducatase in a concentration-dependent way, being sparse cells more sensitive to H2O2 addition than confluent cells. The presence of pyruvate, a H2O2 scavenger, produced a significant increment (200%) in the levels of NADH-cytochrome b5 reductase in sparse cells, but less increase (25%) in confluent cells, suggesting that generation of endogenous H2O2 could repress NADH-cytochrome b5 reductase expression, particularly in sparse cultures. Accordingly, confluent HeLa cells showed significantly lower levels of reactive oxygen species than cells in sparse cultures. Addition of tert-butylhydroquinone, a compound which generates reactive oxygen species through redox cycling, also reduced expression of the NADH-cytochrome b5 reductase. Increments in several antioxidant enzymes taking place during confluency could participate in the increase of NADH-cytochrome b5 reductase expression by reducing reactive oxygen species levels in cells. Overall, our results support that acute oxidative stress caused by H2O2 inhibits the expression levels of NADH-cytochrome b5 reductase, most likely due to inhibition of SP1 transcriptional activity. On the other hand, adaptation to H2O2 involved increased expression of the cytochrome b5 reductase, supporting the existence of additional regulatory mechanisms.

The clinical use of HMG CoA-reductase inhibitors and the associated depletion of coenzyme Q10. A review of animal and human publications

The depletion of the essential nutrient CoQ10 by the increasingly popular cholesterol lowering drugs, HMG CoA reductase inhibitors (statins), has grown from a level of concern to one of alarm. With ever higher statin potencies and dosages, and with a steadily shrinking target LDL cholesterol, the prevalence and severity of CoQ10 deficiency is increasing noticeably. An estimated 36 million Americans are now candidates for statin drug therapy. Statin-induced CoQ10 depletion is well documented in animal and human studies with detrimental cardiac consequences in both animal models and human trials. This drug-induced nutrient deficiency is dose related and more notable in settings of pre-existing CoQ10 deficiency such as in the elderly and in heart failure. Statin-induced CoQ10 deficiency is completely preventable with supplemental CoQ10 with no adverse impact on the cholesterol lowering or anti-inflammatory properties of the statin drugs. We are currently in the midst of a congestive heart failure epidemic in the United States, the cause or causes of which are unclear. As physicians, it is our duty to be absolutely certain that we are not inadvertently doing harm to our patients by creating a wide-spread deficiency of a nutrient critically important for normal heart function.

A novel plasma membrane quinone reductase and NAD(P)H:quinone oxidoreductase 1 are upregulated by serum withdrawal in human promyelocytic HL-60 cells

We have studied changes in plasma membrane NAD(P)H:quinone oxidoreductases of HL-60 cells under serum withdrawal conditions, as a model to analyze cell responses to oxidative stress. Highly enriched plasma membrane fractions were obtained from cell homogenates. A major part of NADH-quinone oxidoreductase in the plasma membrane was insensitive to micromolar concentrations of dicumarol, a specific inhibitor of the NAD(P)H:quinone oxidoreductase 1 (NQOI, DT-diaphorase), and only a minor portion was characterized as DT-diaphorase. An enzyme with properties of a cytochrome b5 reductase accounted for most dicumarol-resistant quinone reductase activity in HL-60 plasma membranes. The enzyme used mainly NADH as donor, it reduced coenzyme Q0 through a one-electron mechanism with generation of superoxide, and its inhibition profile by p-hydroxymercuribenzoate was similar to that of authentic cytochrome b5 reductase. Both NQO1 and a novel dicumarol-insensitive quinone reductase that was not accounted by a cytochrome b5 reductase were significantly increased in plasma membranes after serum deprivation, showing a peak at 32 h of treatment. The reductase was specific for NADH, did not generate superoxide during quinone reduction, and was significantly resistant to p-hydroxymercuribenzoate. The function of this novel quinone reductase remains to be elucidated whereas dicumarol inhibition of NQO1 strongly potentiated growth arrest and decreased viability of HL-60 cells in the absence of serum. Our results demonstrate that upregulation of two-electron quinone reductases at the plasma membrane is a mechanism evoked by cells for defense against oxidative stress caused by serum withdrawal.

The influence of structure and redox state of prenylquinones on thermotropic phase behaviour of phospholipids in model membranes

Our study was aimed to investigate the significance of the isoprenoid side chain size as well as redox state of the quinone ring for interaction of two main classes of prenylquinones: plastoquinones (PQ) and ubiquinones (UQ) with lipid bilayers. By use of differential scanning calorimetry (DSC) we have followed the thermotropic behaviour of multilamellar vesicles prepared from dipalmitoylphosphatidylcholine (DPPC) upon incorporation of increasing amount (1.3-12 mol%) of quinone (quinol) molecules. Our studies reveal that as the side chain is shorter (from 9 to 2 isoprenoid units) the height of the calorimetric profiles is reduced and the temperature of the main transition of DPPC (T(m)) decreases (T(m)=39.4 degrees C for a sample with 12 mol% of PQ-2), and then increases up to 39.8 degrees C for PQ-1. For the samples containing quinols the effect is more pronounced even at lower concentration. The greater influence of the added prenylquinones on the pretransition demonstrates a stronger distortion of the DPPC packing in the gel state. It seems that this is the isoprenoid side chain length rather than the redox state of prenylquinones that determines their effectiveness in perturbation of thermotropic properties of lipid bilayer.

Biomarkers of oxidative stress: an analytical approach

Oxidative stress is implicated in many pathological processes and results from a disruption of the prooxidant/antioxidant balance. This review will focus on noninvasive biomarkers of radical-induced damage in biological fluids and particularly in blood. Special attention will be addressed to new analytical methods for the measurement of radical-mediated alterations in the integrity of lipids, proteins and DNA.

Plasma membrane redox system in the control of stress-induced apoptosis

The plasma membrane of animal cells contains an electron transport system based on coenzyme Q (CoQ) reductases. Cytochrome b5 reductase is NADH-specific and reduces CoQ through a one-electron reaction mechanism. DT-diaphorase also reduces CoQ, although through a two-electron reaction mechanism using both NADH and NADPH, which may be particularly important under oxidative stress conditions. Because reduced CoQ protects membranes against peroxidations, and also maintains the reduced forms of exogenous antioxidants such as alpha-tocopherol and ascorbate, this molecule can be considered a central component of the plasma membrane antioxidant system. Stress-induced apoptosis is mediated by the activation of plasma membrane-bound neutral sphingomyelinase, which releases ceramide to the cytosol. Ceramide-dependent caspase activation is part of the apoptosis pathway. The reduced components of the plasma membrane antioxidant system, mainly CoQ, prevent both lipid peroxidation and sphingomyelinase activation. This results in the prevention of ceramide accumulation and caspase 3 activation and, as consequence, apoptosis is inhibited. We propose the hypothesis that antioxidant protective function of the plasma membrane redox system can be enough to protect cells against the externally induced mild oxidative stress. If this system is overwhelmed, intracellular mechanisms of protection are required to avoid activation of the apoptosis pathway.

The interaction of coenzyme Q with phosphatidylethanolamine membranes

Coenzyme Q (CoQ) is a component of the mitochondrial respiratory chain which carries out additional membrane functions, such as acting as an antioxidant. The location of CoQ in the membrane and the interaction with the phospholipid bilayer is still a subject of debate. The interaction of CoQ in the oxidized (ubiquinone-10) and reduced (ubiquinol-10) state with membrane model systems of 1,2-dielaidoyl-sn-glycero-3-phosphoethanolamine (Ela2Gro-P-Etn) has been studied by means of differential scanning calorimetry (DSC), 31P-nuclear magnetic resonance (31P-NMR) and small angle X-ray diffraction (SAXD). Ubiquinone-10 did not visibly affect the lamellar gel to lamellar liquid-crystalline phase transition of Ela2Gro-P-Etn, but it clearly perturbed the multicomponent lamellar liquid-crystalline to lamellar gel phase transition of the phospholipid. The perturbation of both transitions was more effective in the presence of ubiquinol-10. A location of CoQ forming head to head aggregates in the center of the Ela2Gro-P-Etn bilayer with the polar rings protruding toward the phospholipid acyl chains is suggested. The formation of such aggregates are compatible with the strong hexagonal HII phase promotion ability found for CoQ. This ability was evidenced by the shifting of the lamellar to hexagonal HII phase transition to lower temperatures and by the appearance of the characteristic hexagonal HII 31P-NMR resonance and SAXD pattern at temperatures at which the pure Ela2Gro-P-Etn is still organized in extended bilayer structures. The influence of CoQ on the thermotropic properties and phase behavior of Ela2Gro-P-Etn is discussed in relation to the role of CoQ in the membrane.

Role of plasma membrane coenzyme Q on the regulation of apoptosis

Serum withdrawal is a model to study the mechanisms involved in the induction of apoptosis caused by mild oxidative stress. Apoptosis induced by growth factors removal was prevented by the external addition of antioxidants such as ascorbate, alpha-tocopherol and coenzyme Q (CoQ). CoQ is a lipophilic antioxidant which prevents oxidative stress and participates in the regeneration of alpha-tocopherol and ascorbate in the plasma membrane. We have found an inverse relationship between CoQ content in plasma membrane and lipid peroxidation rates in leukaemic cells. CoQ10 addition to serum-free culture media prevented both lipid peroxidation and cell death. Also, CoQ10 addition decreased ceramide release after serum withdrawal by inhibition of magnesium-dependent plasma membrane neutral-sphingomyelinase. Moreover, CoQ10 addition partially blocked activation of CPP32/caspase-3. These results suggest CoQ of the plasma membrane as a regulator of initiation phase of oxidative stress-mediated serum withdrawal-induced apoptosis.

Overview of the use of CoQ10 in cardiovascular disease

The clinical experience in cardiology with CoQ10 includes studies on congestive heart failure, ischemic heart disease, hypertensive heart disease, diastolic dysfunction of the left ventricle, and reperfusion injury as it relates to coronary artery bypass graft surgery. The CoQ10-lowering effect of HMG-CoA reductase inhibitors and the potential adverse consequences are of growing concern. Supplemental CoQ10 alters the natural history of cardiovascular illnesses and has the potential for prevention of cardiovascular disease through the inhibition of LDL cholesterol oxidation and by the maintenance of optimal cellular and mitochondrial function throughout the ravages of time and internal and external stresses. The attainment of higher blood levels of CoQ10 (> 3.5 micrograms/ml) with the use of higher doses of CoQ10 appears to enhance both the magnitude and rate of clinical improvement. In this communication, 34 controlled trials and several open-label and long-term studies on the clinical effects of CoQ10 in cardiovascular diseases are reviewed.

Protective role of ubiquinone in vitamin E and selenium-deficient plasma membranes

We have studied the effects of dietary depletion of vitamin E and selenium on endogenous ubiquinone-dependent antioxidant system. Deficiency induced an increase in both coenzyme Q9 and Q10 in liver tissue, reaching a maximum between 4 and 7 weeks of deficient diet consumption. Cytochrome b5 reductase polypeptide was also enriched in membranes after 5 weeks of deficient diet consumption. Substantial DT-diaphorase activity was found in deficient, but not in control plasma membranes. Deficient membranes were very sensitive to lipid peroxidation, although a great protection was observed after incubation with NAD(P)H. Our results show that liver cells can boost endogenous ubiquinone-dependent protective mechanisms in response to deficiency in vitamin E and selenium.

Vitamin E and selenium deficiency induces expression of the ubiquinone-dependent antioxidant system at the plasma membrane

We have used a model of dietary deficiency that leads to a chronic oxidative stress to evaluate responses that are adaptations invoked to boost cellular defense systems. Long-Evans hooded rats were fed with a diet lacking vitamin E (E) and selenium (Se) for 7 wk from weaning leading to animals deficient in both nutrients (-E -Se). In the absence of an electron donor, liver plasma membranes from these rats were more sensitive to lipid peroxidation, although they contained 40% greater amounts of ubiquinone than the plasma membranes from rats consuming diets with sufficient vitamin E and Se (+E +Se). The incubation of plasma membranes with NAD(P)H resulted in protection against peroxidation, and this effect was more pronounced in -E -Se membranes. Deficiency was accompanied by a twofold increase in redox activities associated with trans plasma membrane electron transport such as ubiquinone reductase and ascorbate free radical reductase. Staining with a polyclonal antibody against pig liver cytochrome b5 reductase, which acts as one ubiquinone reductase in the plasma membrane, showed an increased expression of the enzyme in membranes from -E -Se rats. Little DT-diaphorase activity was measured in +E +Se plasma membranes, but this activity was dramatically increased in -E -Se plasma membranes. No such increase was found in liver cytosols, which contained elevated activity of calcium-independent phospholipase A2. Thus, ubiquinone-dependent antioxidant protection in +E +Se plasma membranes is based primarily on NADH-cytochrome b5 reductase, whereas additional protection needed in -E -Se plasma membranes is supported by the increase of ubiquinone levels, increased expression of the cytochrome b5 reductase, and translocation of soluble DT-diaphorase to the plasma membrane. Our results indicate that, in the absence of vitamin E and Se, enhancement of ubiquinone-dependent reductase systems can fulfill the membrane antioxidant protection.

Oxidative stress and the pathogenesis of heart failure

There is strong evidence for an adverse role of oxidative stress in CHF in both animals and humans. Antioxidant supplement have been very effective in the treatment of animal paradigms; however, the data for the possible benefits of treatment for patients with CHF is either retrospective or inferential. Such information is important and should be the subject of prospective randomized trials.

The diversity of coenzyme Q function

Coenzyme Q is uniquely designed as an electron and proton carrier within the lipid phase of membranes. It now appears that this unique chemistry has diverse application to important functions in all cellular membranes. The first function of coenzyme Q was defined in the energy transduction process in mitochondria. New studies show that the presence of coenzyme Q in other cellular membranes has dynamic rather than passive significance. Coenzyme Q functions in the plasma membrane electron transport involved in activation of signalling protein kinases related to gene activation for cellular proliferation. Furthermore, the antioxidant potential of the reduced coenzyme Q is now taken on a new significance in the evidence that the reduced quinone can act to maintain tocopherol in the reduced state in membranes and ascorbate reduced both inside and outside the cell.