Coenzyme Q10

Deficiency and toxicity

There are two major factors that lead to deficiency of CoQ₁₀ in humans: reduced biosynthesis, and increased use by the body. Biosynthesis is the major source of CoQ₁₀. Biosynthesis requires at least 12 genes, and mutations in many of them cause CoQ deficiency. CoQ₁₀ levels also may be affected by other genetic defects (such as mutations of mitochondrial DNA, ETFDH, APTX, FXN, and BRAF, genes that are not directly related to the CoQ₁₀ biosynthetic process). The role of statins in deficiencies is controversial. Some chronic disease conditions (cancer, heart disease, etc.) also are thought to reduce the biosynthesis of and increase the demand for CoQ₁₀ in the body, but there are no definite data to support these claims.

Usually, toxicity is not observed with high doses of CoQ₁₀. A daily dosage up to 3600 mg was found to be tolerated by healthy as well as unhealthy persons. Some adverse effects, however, largely gastrointestinal, are reported with very high intakes. The observed safe level (OSL) risk assessment method indicated that the evidence of safety is strong at intakes up to 1200 mg/day, and this level is identified as the OSL.

Clinical assessment

Although CoQ₁₀ may be measured in blood plasma, these measurements reflect dietary intake rather than tissue status. Currently, most clinical centers measure CoQ₁₀ levels in cultured skin fibroblasts, muscle biopsies, and blood mononuclear cells. Culture fibroblasts can be used also to evaluate the rate of endogenous CoQ₁₀ biosynthesis, by measuring the uptake of ¹⁴C-labelled p-hydroxybenzoate.

Inhibition by statins and beta blockers

CoQ₁₀ shares a biosynthetic pathway with cholesterol. The synthesis of an intermediary precursor of CoQ₁₀, mevalonate, is inhibited by some beta blockers, blood pressure-lowering medication, and statins, a class of cholesterol-lowering drugs. Statins can reduce serum levels of CoQ₁₀ by up to 40%.

Supplementation

CoQ₁₀ is not approved by the U.S. Food and Drug Administration (FDA) for the treatment of any medical condition. It is sold as a dietary supplement. In the U.S., supplements are not regulated as drugs, but as foods. How CoQ₁₀ is manufactured is not regulated and different batches and brands may vary significantly.

A 2004 laboratory analysis by ConsumerLab.com of CoQ₁₀ supplements on the market found that some did not contain the quantity identified on the product label. Amounts varied from "no detectable CoQ₁₀", to 75% of stated dose, and up to a 75% excess.

Generally, CoQ₁₀ is well tolerated. The most common side effects are gastrointestinal symptoms (nausea, vomiting, appetite suppression, and stomachaches), rashes, and headaches.

Heart disease

A 2014 Cochrane Collaboration meta-analysis found "no convincing evidence to support or refute" the use of CoQ₁₀ for the treatment of heart failure. Evidence with respect to preventing heart disease in those who are otherwise healthy is also poor.

Another 2014 study of 420 patients in 17 patient centers over 7 years found that it "improves symptoms, and reduces major adverse cardiovascular events" after 106 weeks.

A 2016 Cochrane review concluded that studies looking at the effects of CoQ₁₀ on blood pressure provided moderately strong evidence that coenzyme Q₁₀ does not lower blood pressure.

Huntington's disease

Available evidence suggests that "CoQ₁₀ is likely ineffective in moderately improving" the chorea associated with Huntington's disease.

Male infertility

While CoQ₁₀ can improve some measurements regarding sperm quality, there is no evidence that CoQ₁₀ increases live births or pregnancy rates.

Migraine headaches

Supplementation of CoQ₁₀ has been found to have a beneficial effect on the condition of some sufferers of migraine. An explanation for this is the theory that migraines are a mitochondrial disorder, and that mitochondrial dysfunction can be improved with CoQ₁₀. The Canadian Headache Society guideline for migraine prophylaxis recommends, based on low-quality evidence, that 300 mg of CoQ₁₀ be offered as a choice for prophylaxis.

Statin myopathy

CoQ₁₀ has been routinely used to treat muscle breakdown associated as a side effect of use of statin medications. However, evidence from randomized controlled trials does not appear to support the idea that CoQ₁₀ is an effective treatment for statin myopathy.

Cancer

No large well-designed clinical trials of CoQ₁₀ in cancer treatment have been done. The National Cancer Institute identified issues with the few, small studies that have been done stating, "the way the studies were done and the amount of information reported made it unclear if benefits were caused by the CoQ₁₀ or by something else". The American Cancer Society has concluded, "CoQ₁₀ may reduce the effectiveness of chemo and radiation therapy, so most oncologists would recommend avoiding it during cancer treatment."

Dental disease

A review study has shown that there is no clinical benefit to the use of CoQ₁₀ in the treatment of periodontal disease. Most of the studies suggesting otherwise were outdated, focused on in vitro tests, had too few test subjects and/or erroneous statistical methodology and trial setup, or were sponsored by a manufacturer of the product.

Parkinson's disease

A 2011 review by the Cochrane Collaboration suggesting CoQ₁₀ supplementation might benefit people with Parkinson's disease was subsequently withdrawn from publication following a review by independent editors.

Drug interactions

Coenzyme Q₁₀ has potential to inhibit the effects of warfarin (Coumadin), a potent anticoagulant, by reducing the INR. The structure of coenzyme Q₁₀ is very much similar to the structure of vitamin K, which competes with and counteracts warfarin's anticoagulation effects. Coenzyme Q₁₀ should be avoided in patients currently taking warfarin due to the increased risk of clotting.

Chemical properties

The oxidized structure of CoQ₁₀ is shown on the top-right. The various kinds of Coenzyme Q may be distinguished by the number of isoprenoid subunits in their side-chains. The most common Coenzyme Q in human mitochondria is CoQ₁₀. Q refers to the quinone head and 10 refers to the number of isoprene repeats in the tail. The molecule below has three isoprenoid units and would be called Q₃.

Biochemical role

CoQ₁₀ is found in the membranes of many organelles. Since its primary function in cells is in generating energy, the highest concentration is found on the inner membrane of the mitochondrion. Some other organelles that contain CoQ₁₀ include endoplasmic reticulum, peroxisomes, lysosomes, and vesicles.

CoQ10 and electron transport chain

CoQ₁₀ is fat-soluble and is therefore mobile in cellular membranes; it plays a unique role in the electron transport chain (ETC). In the inner mitochondrial membrane, electrons from NADH and succinate pass through the ETC to oxygen, which is reduced to water. The transfer of electrons through ETC results in the pumping of H⁺ across the membrane creating a proton gradient across the membrane, which is used by ATP synthase (located on the membrane) to generate ATP. CoQ₁₀ functions as an electron carrier from enzyme complex I and enzyme complex II to complex III in this process. This is crucial in the process, since no other molecule can perform this function. (Recent research now establishes that Vitamin K₂ co-performs this role with CoQ₁₀.) Thus, CoQ₁₀ functions in every cell of the body to synthesize energy.

Antioxidant (reductant) function of CoQ10

The antioxidant nature of CoQ₁₀ derives from its energy carrier function. As an energy carrier, the CoQ₁₀ molecule continuously goes through an oxidation–reduction cycle. As it accepts electrons, it becomes reduced. As it gives up electrons, it becomes oxidized. In its reduced form, the CoQ₁₀ molecule holds electrons rather loosely, so this CoQ molecule will give up one or both electrons quite easily and, thus, act as an antioxidant. CoQ₁₀ inhibits lipid peroxidation by preventing the production of lipid peroxyl radicals (LOO). Moreover, CoQH₂ reduces the initial perferryl radical and singlet oxygen, with concomitant formation of ubisemiquinone and H₂O₂. This quenching of the initiating perferryl radicals, which prevent propagation of lipid peroxidation, protects not only lipids but also proteins from oxidation. In addition, the reduced form of CoQ effectively regenerates vitamin E from the α-tocopheroxyl radical, thereby interfering with the propagation step. Furthermore, during oxidative stress, interaction of H₂O₂ with metal ions bound to DNA generates hydroxyl radicals, and CoQ efficiently prevents the oxidation of bases, in particular, in mitochondrial DNA. In contrast to other antioxidants, this compound inhibits both the initiation and the propagation of lipid and protein oxidation. It also regenerates other antioxidants such as vitamin E. The circulating CoQ₁₀ in LDL prevents oxidation of low-density lipoprotein (LDL), which may provide benefit in cardiovascular diseases.

Biosynthesis

Biosynthesis occurs in most human tissue. There are three major steps:

1. Creation of the benzoquinone structure (using phenylalanine or tyrosine)
2. Creation of the isoprene side chain (using acetyl-CoA)
3. The joining or condensation of the above two structures

The initial two reactions occur in mitochondria, the endoplasmic reticulum, and peroxisomes, indicating multiple sites of synthesis in animal cells.

An important enzyme in this pathway is HMG-CoA reductase, usually a target for intervention in cardiovascular complications. The "statin" family of cholesterol-reducing medications inhibits HMG-CoA reductase. One possible side effect of statins is decreased production of CoQ₁₀, which may be connected to the development of myopathy and rhabdomyolysis.

Genes involved include PDSS1, PDSS2, COQ2, and ADCK3 (COQ8, CABC1).

Increasing the endogenous biosynthesis of CoQ₁₀ has gained attention in recent years as a strategy to fight CoQ₁₀ deficiency.

Absorption

CoQ₁₀ is a crystalline powder insoluble in water. Absorption follows the same process as that of lipids; the uptake mechanism appears to be similar to that of vitamin E, another lipid-soluble nutrient. This process in the human body involves secretion into the small intestine of pancreatic enzymes and bile, which facilitates emulsification and micelle formation required for absorption of lipophilic substances. Food intake (and the presence of lipids) stimulates bodily biliary excretion of bile acids and greatly enhances absorption of CoQ₁₀. Exogenous CoQ₁₀ is absorbed from the small intestine and is best absorbed if taken with a meal. Serum concentration of CoQ₁₀ in fed condition is higher than in fasting conditions.

Metabolism

Data on the metabolism of CoQ₁₀ in animals and humans are limited. A study with ¹⁴C-labeled CoQ₁₀ in rats showed most of the radioactivity in the liver two hours after oral administration when the peak plasma radioactivity was observed, but it should be noted that CoQ₉ (with only 9 isoprenyl units) is the predominant form of coenzyme Q in rats. It appears that CoQ₁₀ is metabolised in all tissues, while a major route for its elimination is biliary and fecal excretion. After the withdrawal of CoQ₁₀ supplementation, the levels return to normal within a few days, irrespective of the type of formulation used.

Pharmacokinetics

Some reports have been published on the pharmacokinetics of CoQ₁₀. The plasma peak can be observed 2–6 hours after oral administration, depending mainly on the design of the study. In some studies, a second plasma peak also was observed at approximately 24 hours after administration, probably due to both enterohepatic recycling and redistribution from the liver to circulation. Tomono et al. used deuterium-labeled crystalline CoQ₁₀ to investigate pharmacokinetics in humans and determined an elimination half-time of 33 hours.

Improving the bioavailability of CoQ10

The importance of how drugs are formulated for bioavailability is well known. In order to find a principle to boost the bioavailability of CoQ₁₀ after oral administration, several new approaches have been taken; different formulations and forms have been developed and tested on animals and humans.

Reduction of particle size

An obvious strategy is reduction of particle size to as low as the micro- and nanoscale. Nanoparticles have been explored as a delivery system for various drugs; an improvement of the oral bioavailability of drugs with poor absorption characteristics has been reported; pathways of absorption and efficiency were affected by reduction of particle size. So far, this protocol has not proved to be very successful with CoQ₁₀, although reports have differed widely. The use of aqueous suspension of finely powdered CoQ₁₀ in pure water also reveals only a minor effect.

Soft-gel capsules with CoQ10 in oil suspension

A successful approach was to use the emulsion system to facilitate absorption from the gastrointestinal tract and to improve bioavailability. Emulsions of soybean oil (lipid microspheres) could be stabilised very effectively by lecithin and were used in the preparation of soft gelatin capsules. In one of the first such attempts, Ozawa et al. performed a pharmacokinetic study on beagles in which the emulsion of CoQ₁₀ in soybean oil was investigated; about twice the plasma CoQ₁₀ level than that of the control tablet preparation was determined during administration of a lipid microsphere. Although an almost negligible improvement of bioavailability was observed by Kommuru et al. with oil-based softgel capsules in a later study on dogs, the significantly increased bioavailability of CoQ₁₀ was confirmed for several oil-based formulations in most other studies.

Novel forms of CoQ10 with increased water-solubility

Facilitating drug absorption by increasing its solubility in water is a common pharmaceutical strategy and also has been shown to be successful for CoQ₁₀. Various approaches have been developed to achieve this goal, with many of them producing significantly better results over oil-based softgel capsules in spite of the many attempts to optimize their composition. Examples of such approaches are use of the aqueous dispersion of solid CoQ₁₀ with the polymer tyloxapol, formulations based on various solubilising agents, such as hydrogenated lecithin, and complexation with cyclodextrins; among the latter, the complex with β-cyclodextrin has been found to have highly increased bioavailability. and also is used in pharmaceutical and food industries for CoQ₁₀-fortification. Also some other novel carrier systems, such as liposomes, nanoparticles or dendrimers, may be used to increase the bioavailability of CoQ₁₀.

History

CoQ₁₀ was first discovered by Fredrick L. Crane and colleagues at the University of Wisconsin–Madison Enzyme Institute in 1957. In 1958, its chemical structure was reported by Karl Folkers and coworkers at Merck. In the early 1970s Gian Paolo Littarru and Karl Folkers observed that a deficiency of CoQ₁₀ was associated with human heart disease. The 1980s witnessed a steep rise in the number of clinical trials due to the availability of large quantities of pure CoQ₁₀ and methods to measure plasma and blood CoQ₁₀ concentrations. The redox functions of CoQ in cellular energy production and antioxidant protection are based on the ability to exchange two electrons in a redox cycle between ubiquinol (reduced CoQ) and ubiquinone (oxidized CoQ). The antioxidant role of the molecule as a free radical scavenger was widely studied by Lars Ernster. Numerous scientists around the globe started studies on this molecule since then in relation to various diseases including cardiovascular diseases and cancer.

Dietary concentrations

Detailed reviews on occurrence of CoQ₁₀ and dietary intake were published in 2010. Besides the endogenous synthesis within organisms, CoQ₁₀ also is supplied to the organism by various foods. Despite the scientific community's great interest in this compound, however, a very limited number of studies have been performed to determine the contents of CoQ₁₀ in dietary components. The first reports on this aspect were published in 1959, but the sensitivity and selectivity of the analytical methods at that time did not allow reliable analyses, especially for products with low concentrations. Since then, developments in analytical chemistry have enabled a more reliable determination of CoQ₁₀ concentrations in various foods:

Meat and fish are the richest sources of dietary CoQ₁₀; levels over 50 mg/kg may be found in beef, pork, chicken heart, and chicken liver. Dairy products are much poorer sources of CoQ₁₀ compared to animal tissues. Vegetable oils also are quite rich in CoQ₁₀. Within vegetables, parsley and perilla are the richest CoQ₁₀ sources, but significant differences in their CoQ₁₀ levels may be found in the literature. Broccoli, grapes, and cauliflower are modest sources of CoQ₁₀. Most fruit and berries represent a poor to very poor source of CoQ₁₀, with the exception of avocados, which have a relatively high CoQ₁₀ content.

Intake

In the developed world, the estimated daily intake of CoQ₁₀ has been determined at 3–6 mg per day, derived primarily from meat.

Effect of heat and processing

Cooking by frying reduces CoQ₁₀ content by 14–32%.