Coenzyme Q10

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Coenzyme Q10
Unibuinone.svg
Identifiers
CAS number 303-98-0 YesY
PubChem 5281915
ChemSpider 4445197 YesY
UNII EJ27X76M46 YesY
ChEBI CHEBI:46245 YesY
ChEMBL CHEMBL454801 YesY
ATC code C01EB09
Jmol-3D images Image 1
Properties
Molecular formula C59H90O4
Molar mass 863.34 g mol−1
Related compounds
Related quinones 1,4-Benzoquinone
Plastoquinone
Ubiquinol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Coenzyme Q10, also known as ubiquinone, ubidecarenone, coenzyme Q, and abbreviated at times to CoQ10 /ˌk ˌkjuː ˈtɛn/, CoQ, or Q10 is a 1,4-benzoquinone, where Q refers to the quinone chemical group, and 10 refers to the number of isoprenyl chemical subunits in its tail.

This oil-soluble, vitamin-like substance is present in most eukaryotic cells, primarily in the mitochondria. It is a component of the electron transport chain and participates in aerobic cellular respiration, generating energy in the form of ATP. Ninety-five percent of the human body’s energy is generated this way.[1][2] Therefore, those organs with the highest energy requirements—such as the heart, liver and kidney—have the highest CoQ10 concentrations.[3][4][5] There are three redox states of CoQ10: fully oxidized (ubiquinone), semiquinone (ubisemiquinone), and fully reduced (ubiquinol). The capacity of this molecule to exist in a completely oxidized form and a completely reduced form enables it to perform its functions in the electron transport chain, and as an antioxidant, respectively.

Discovery and history[edit]

CoQ10 was first discovered by Professor Fredrick L. Crane and colleagues at the University of Wisconsin–Madison Enzyme Institute in 1957.[6][7] In 1958, its chemical structure was reported by Dr. Karl Folkers and coworkers at Merck. In 1961 Peter Mitchell proposed the electron transport chain (which includes the vital protonmotive role of CoQ10) and he received a Nobel prize for the same in 1978. In 1972, Gian Paolo Littarru and Karl Folkers separately demonstrated a deficiency of CoQ10 in 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).[8][9] 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.

Chemical properties[edit]

The oxidized structure of CoQ10 is shown on the top-right. The various kinds of Coenzyme Q can 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 image below has three isoprenoid units and would be called Q3.

Unibuinone3.svg

Biochemical role[edit]

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[edit]

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 (Note: recent research now establishes that Vitamin K2 co-performs this role with CoQ10[10]). Thus, CoQ10 functions in every cell of the body to synthesize energy.

Antioxidant function of CoQ10[edit]

The antioxidant nature of CoQ10 derives from its energy carrier function. As an energy carrier, the CoQ10 molecule continuously goes through 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 quite easily give up one or both electrons and, thus, act as an antioxidant.[11] 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 a-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.[11] 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 LDL, which may provide benefit in cardiovascular diseases.

Biosynthesis[edit]

Biosynthesis occurs in most human tissue. There are 3 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 2 structures

The initial two reactions occur in mitochondria, endoplasmic reticulum and peroxisomes, indicating multiple sites of synthesis in animal cells.[12]

An important enzyme in this pathway is HMG Co-A reductase, which is usually a target for intervention in cardiovascular complications. The "statin" family of cholesterol-reducing medications inhibit HMG Co-A reductase. Side effect of statins is decreased production of CoQ-10, which leads to myopathy and rhabdomyolysis. CoQ10 supplementation prevents myopathy and rhabdomyolysis caused by statins.

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

Genes involved include PDSS1, PDSS2, COQ2, and COQ8/CABC1.[13]

Absorption and metabolism[edit]

Absorption[edit]

CoQ10 is a crystalline powder that is insoluble in water. Absorption follows the same process as that of lipids and the uptake mechanism appears to be similar to that of vitamin E, another lipid-soluble nutrient. This process in the human body involves the secretion into the small intestines of pancreatic enzymes and bile that facilitate emulsification and micelle formation that is required for the absorption of lipophilic substances.[14] Food intake (and the presence of lipids) stimulates bodily biliary excretion of bile acids and greatly enhances the absorption of CoQ10. Exogenous CoQ10 is absorbed from the small intestinal tract and is best absorbed if it is taken with a meal. Serum concentration of CoQ10 in fed condition is higher than in fasting conditions.[15][16]

Metabolism[edit]

Data on the metabolism of CoQ10 in animals and humans are limited.[17] A study with 14C-labeled CoQ10 in rats showed most of the radioactivity in the liver 2 hours after oral administration when the peak plasma radioactivity was observed, but it should be noted that CoQ9 is the predominant form of coenzyme Q in rats.[18] 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.[19]

CoQ10 deficiency and toxicity[edit]

There are two major factors that lead to deficiency of CoQ10 in humans: reduced biosynthesis, and increased utilization 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 can also be affected by other genetic defects (such as mutations of mitochondrial DNA, ETFDH, APTX and BRAF, genes that are not directly related to the CoQ10 biosynthetic process) while the role of statins is controversial.[20] Some chronic disease conditions (cancer, heart disease, etc.) are also thought to reduce the biosynthesis and increase the demand for CoQ10 in the body, but there are no definite data to support these claims.

Toxicity is not usually 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.[21] However, some adverse effects, 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.[22]

Clinical assessment techniques[edit]

Although CoQ10 can be measured in 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.[20] Culture fibroblasts can be used also to evaluate the rate of endogenous CoQ10 biosynthesis, by measuring the uptake of 14C-labelled p-hydroxybenzoate.[23]

Inhibition by statins and beta blockers[edit]

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,[24] and statins, a class of cholesterol-lowering drugs.[25] Statins can reduce serum levels of CoQ10 by up to 40%.[26] Some research suggests the logical option of supplementation with CoQ10 as a routine adjunct to any treatment that may reduce endogenous production of CoQ10, based on a balance of likely benefit against very small risk.[27][28]

Pharmacokinetics[edit]

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 was also observed at about 24 hours after administration, probably due to both enterohepatic recycling and redistribution from the liver to circulation.[14] Tomono et al. used deuterium-labelled crystalline CoQ10 to investigate pharmacokinetics in human and determined an elimination half-time of 33 hours.[29]

Improving the bioavailability of CoQ10[edit]

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 or humans.[17]

Reduction of particle size[edit]

An obvious strategy is reduction of the particle size to as low as the micro- and nano-scale. Nanoparticles have been explored as a delivery system for various drugs and an improvement of the oral bioavailability of drugs with poor absorption characteristics has been reported;[30] the pathways of absorption and the efficiency were affected by reduction of particle size. This protocol has so far not proved to be very successful with CoQ10, although reports have differed widely.[31][32] The use of the aqueous suspension of finely powdered CoQ10 in pure water has also revealed only a minor effect.[19]

Soft-gel capsules with CoQ10 in oil suspension[edit]

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 utilised in the preparation of soft gelatine capsules. In one of the first such attempts, Ozawa et al. performed a pharmacokinetic study on beagle dogs in which the emulsion of CoQ10 in soybean oil was investigated; about two times higher plasma CoQ10 level than that of the control tablet preparation was determined during administration of a lipid microsphere.[19] Although an almost negligible improvement of bioavailability was observed by Kommuru et al. with oil-based soft-gel capsules in a later study on dogs,[33] the significantly increased bioavailability of CoQ10 was confirmed for several oil-based formulations in most other studies.[34]

Novel forms of CoQ10 with increased water-solubility[edit]

Facilitating drug absorption by increasing its solubility in water is a common pharmaceutical strategy and has also 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 soft-gel capsules in spite of the many attempts to optimize their composition.[17] Examples of such approaches are use of the aqueous dispersion of solid CoQ10 with tyloxapol polymer,[35] formulations based on various solubilising agents, i.e., hydrogenated lecithin,[36] and complexation with cyclodextrins; among the latter, complex with β-cyclodextrin has been found to have highly increased bioavailability.[37][38] and is also used in pharmaceutical and food industry for CoQ10-fortification.[17] Also some other novel carrier systems like liposomes, nanoparticles, dendrimers, etc. can be used to increase the bioavailability of CoQ10.[citation needed]

Supplementation effects[edit]

Coenzyme Q10 is not approved by the US Food and Drug Administration (FDA) for the treatment of any medical condition.[39] It is sold as a dietary supplement, in the US supplements are not regulated as drugs but as foods. How CoQ10 is manufactured is not regulated and different batches and brands may vary significantly.[39]

A 2004 laboratory analysis by ConsumerLab.com found CoQ10 supplements on the market did not all contain the quantity identified on the product label. Amounts varied from "no detectable CoQ10" to 75% of stated dose up to a 75% excess. Tod Cooperman president of ConsumerLab.com stated, "When a patient can go from zero dose to 175% of dose just by switching brands, there is potential for a real problem..."[40]

Heart failure[edit]

A 2014 Cochrane Collaboration meta-analysis found "no convincing evidence to support or refute" the use of CoQ10 for the treatment of heart failure. The analysis identified seven studies that met criteria but identified problems with possible bias, applicability to the general population and failure to identify clinically meaningful outcomes in these studies. The authors concluded, "Until further evidence emerges to support the use of coenzyme Q10 in heart failure, there might be a need to re-evaluate whether further trials testing coenzyme Q10 in heart failure are desirable."[41]

Huntington disease[edit]

Available evidence suggests that "Coenzyme Q10 is likely ineffective in moderately improving" Huntington disease chorea.[42]

Male infertility[edit]

While CoQ10 can improve some measurements regarding sperm quality, there is no evidence that CoQ10 increases live births or pregnancy rates.[43]

Migraine headaches[edit]

Supplementation of CoQ10 has been found to have a beneficial effect on the condition of some sufferers of migraine headaches based on one study. 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.[44]

Statin myopathy[edit]

CoQ10 has been routinely used to treat muscle breakdown associated as a side effect of use of statin medications. However, there is little rigorous evidence from clinical trials supporting its use for this purpose.[45]

Cancer[edit]

No large well designed clinical trials of CoQ10 in cancer treatment have been done.[39] 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."[39] 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."[46]

Blood pressure[edit]

A 2009 Cochrane review concluded that studies looking at the effects of coenzyme Q10 on blood pressure were unreliable, and therefore no conclusions could be made regarding its effectiveness in lower blood pressure.[47]

Periodontal disease[edit]

A review study has shown that there is no clinical benefit to the use of CoQ10 in the treatment of periodontal disease.[48] Most of the studies suggesting otherwise were outdated, focused on in-vitro tests,[49][50][51] had too few test subjects and/or erroneous statistical methodology and trial set-up,[52][53] or were sponsored by a manufacturer of the product.[54]

Parkinson's disease[edit]

A 2011 review by the Cochrane Collaboration suggesting coenzyme Q10 supplementation might benefit people with Parkinson's disease was subsequently withdrawn from publication following a review by independent editors.[55]

CoQ10 concentrations in foods and dietary intake[edit]

Detailed reviews on occurrence of CoQ10 and dietary intake were published in 2010.[56] Besides endogenous synthesis, CoQ10 is also supplied to the organism by various foods. However, despite the scientific community’s great interest in this compound, a very limited number of studies have been performed to determine the contents of CoQ10 in dietary components. The first reports on this issue 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.[56] Developments in analytical chemistry have since enabled a more reliable determination of CoQ10 concentrations in various foods (table below).

CoQ10 levels in selected foods[56]
Food CoQ10 concentration [mg/kg]
Beef
heart 113
liver 39–50
muscle 26–40
Pork
heart 11.8–128.2
liver 22.7–54.0
muscle 13.8–45.0
Chicken
heart 116.2–132.2
Fish
sardine 5–64
mackerel
red flesh 43–67
white flesh 11–16
salmon 4–8
tuna 5
Oils
soybean 54–280
olive 4–160
grapeseed 64–73
sunflower 4–15
rice bran /
coconut
Nuts
peanuts 27
walnuts 19
sesame seeds 18–23
pistachio nuts 20
hazelnuts 17
almond 5–14
Vegetables
parsley 8–26
broccoli 6–9
cauliflower 2–7
spinach up to 10
grape 6–7
Chinese cabbage 2–5
Fruit
avocado 10
blackcurrant 3
strawberry 1
orange 1–2
grapefruit 1
apple 1

Meat and fish are the richest source of dietary CoQ10 and levels over 50 mg/kg can be found in beef, pork, chicken heart, and chicken liver. Dairy products are much poorer sources of CoQ10 compared to animal tissues. Vegetable oils are also quite rich in CoQ10. Within vegetables, parsley and perilla are the richest CoQ10 sources, but significant differences in their CoQ10 levels can be found in the literature. Broccoli, grape, and cauliflower are modest sources of CoQ10. Most fruit and berries represent a poor to very poor source of CoQ10, with the exception of avocado, with a relatively high CoQ10 content.[56]

Intake[edit]

In the developed world, the estimated daily intake of CoQ10 has been determined at 3–6 mg per day, derived primarily from meat.[56]

Effect of heat and processing[edit]

Cooking by frying reduces CoQ10 content by 14–32%.[57]

See also[edit]

  • Idebenone – synthetic analog with reduced oxidant generating properties

References[edit]

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