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Coenzyme Q
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Coenzyme Q10 (also known as ubiquinone, ubidecarenone, coenzyme Q, and abbreviated at times to CoQ10, CoQ, Q10, or simply Q) is a benzoquinone, where Q refers to the quinone chemical group, and 10 refers to the isoprenyl chemical subunits.
This oil-soluble vitamin-like substance is present in most eukaryotic cells, primarily in the mitochondria.
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Encyclopedia
Coenzyme Q10 (also known as ubiquinone, ubidecarenone, coenzyme Q, and abbreviated at times to CoQ10, CoQ, Q10, or simply Q) is a benzoquinone, where Q refers to the quinone chemical group, and 10 refers to the isoprenyl chemical subunits.
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. Therefore, those organs with the highest energy requirements—such as the heart and the liver—have the highest CoQ10 concentrations.
History
Coenzyme Q was first discovered by professor Fred L. Crane and colleagues at the University of Wisconsin-Madison Enzyme Institute in 1957. In 1958, its chemical structure was reported by Professor Karl Folkers and coworkers at Merck.
Chemical properties
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 side-chains they have. The most common CoQ in human mitochondria is Q10. The 10 refers to the number of isoprene repeats. The image below has three isoprenoid units and would be called Q3.
If Coenzyme Q is reduced by one equivalent, the following structure results, a ubisemiquinone, and is denoted QH. Note the free-radical on one of the ring oxygens (either oxygen may become a free-radical, in this case the top oxygen is shown as such).
Biochemical role
CoQ 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.
Supplementation
Because of its ability to transfer electrons and therefore act as an antioxidant, Coenzyme Q is used as a dietary supplement.
According to the Mayo Clinic "CoQ10 has been used, recommended, or studied for numerous conditions, but remains controversial as a treatment in many areas." Further clinical results are needed to determine whether the supplementation with Coenzyme Q10 is beneficial for healthy people.
Mitochondrial disorders
Supplementation of Coenzyme Q10 is a treatment for some of the very rare and serious mitochondrial disorders and other metabolic disorders, where patients are not capable of producing enough coenzyme Q10 because of their disorder. Coenzyme Q10 is then prescribed by a physician.
Heart Failure
There is some clinical evidence that supplementation with Coenzyme Q10 is beneficial treatment of patients with congestive heart failure. However, The American College of Cardiology recently published an expert consensus document concluding that the value of coenzyme Q10 in cardiovascular disease has not been clearly established. The Mayo clinic says that there is not enough scientific evidence to recommend for or against the use of CoQ10 in patients with coronary heart disease.
Migraine headaches
Supplementation of Coenzyme Q10 has been found to have a beneficial effect on the condition of some sufferers of migraine headaches. So far, three studies have been done, of which two were small, did not have a placebo group, were not randomized, and were open-label, and one was a double-blind, randomized, placebo-controlled trial, which found statistically significant results despite its small sample size of 42 patients. Dosages were 150 to 300 mg/day.
Cancer
It is also being investigated as a treatment for cancer, and as relief from cancer treatment side-effects.
Cardiac arrest
Another recent study shows a survival benefit after cardiac arrest if coenzyme Q10 is administered in addition to commencing active cooling (to 32–34 degrees Celsius).
Blood pressure
There are several reports concerning the effect of CoQ10 on blood pressure in human studies.
In a recent meta-analysis of the clinical trials of CoQ10 for hypertension, a research group led by Professor Frank Rosenfeldt (Director, Cardiac Surgical Research Unit, Alfred Hospital, Melbourne, Australia) reviewed all published trials of Coenzyme Q10 for hypertension, and assessed overall efficacy, consistency of therapeutic action, and side-effect incidence. Meta-analysis was performed in 12 clinical trials (362 patients) comprising three randomized controlled trials, one crossover study, and eight open-label studies.
The research group concluded that coenzyme Q10 has the potential in hypertensive patients to lower systolic blood pressure by up to 17 mm Hg and diastolic blood pressure by up to 10 mm Hg without significant side-effects.
Biosynthesis
The benzoquinone portion of Coenzyme Q10 is synthesized from tyrosine, whereas the isoprene sidechain is synthesized from acetyl-CoA through the mevalonate pathway. The mevalonate pathway is also used for the first steps of cholesterol biosynthesis.
Inhibition by statins and beta blockers
Coenzyme Q10 shares a common biosynthetic pathway with cholesterol. The synthesis of an intermediary precursor of Coenzyme Q10, 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 coenzyme Q10 by up to 40%. Some research suggests the logical option of supplementation with coenzyme Q10 as a routine adjunct to any treatment that may reduce endogenous production of coenzyme Q10, based on a balance of likely benefit against very small risk.
Absorption and metabolism
CoQ10 is a crystalline powder that is insoluble in water due to its low polarity. It has a relatively high molecular weight (863 g/mol) and its solubility in lipids is also limited so it is very poorly absorbed in the gastrointestinal tract., 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. Emulsification and micelle formation is required for the absorption of fats. For CoQ10, this process is chiefly facilitated by secretions from the pancreas and bile salts in the small intestine. A general rule is that the higher the dose orally administered, the lower the percent of the dose absorbed.
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 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. 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 their normal levels within a few days, irrespective of the type of formulation used.
Pharmacokinetics and bioavailability
Some reports have been published on the pharmacokinetics of CoQ10. The plasma peak can be observed 2-6 hours after oral administration, mainly depending 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. Tomono et al. used deuterium-labelled crystalline CoQ10 to investigate pharmacokinetics in human and determined an elimination half-time of 33 hours.
Bioavailability is the degree to which a drug or other substance becomes available to the target tissue after administration. By definition, intravenously administered drugs have 100% bioavailability while decreased bioavailability can be observed when medication is administered via other routes. When orally administered, the substance has to pass the intestinal wall and then travels to the liver through portal circulation. These processes form part of the 1st pass metabolism and allow a drug to achieve systemic circulation. Insufficient time for absorption in the gastrointestinal tract is usually reflected in low bioavailability This is very common for orally administered compounds with poor water-solubility, such as Coenzyme Q10. High inter- and intra-individual variations of bioavailability can often be observed in such cases. Several physiological factors influence the bioavailability of drugs, such as sex, age, genetic phenotype, physical activity, health of the gastrointestinal tract and various disorders, type of administration (fed or fasted state), interactions with food etc. Relative bioavailability is one of the measurement tools used to assess the bioequivalence between two formulations of the same drug and is usually calculated as a test vs. reference ratio of the area under the curve (AUC), derived by the integration of the plasma concentration–time relationship after a single oral dose.
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 and different formulations and forms have been developed and tested on animals or humans.
Reduction of particle size
The 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; 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., The use of the aqueous suspension of finely powdered CoQ10 in pure water has also only revealed 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 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. 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, 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 has also been shown to be successful for Coenzyme Q10. Different 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. Examples of such approaches are use of the aqueous dispersion of solid CoQ10 with tyloxapol polymer, formulations based on various solubilising agents, i.e. hydrogenated lecithin, and complexation with cyclodextrins; among the latter, complex with ß-cyclodextrin has been found to have highly increased bioavailability. and is also used in pharmaceutical and food industry for CoQ10-fortification.
Also some other novel carrier systems like liposomes, nanoparticles, dendrimers etc can be used to increase the bioavailability of Coenzyme Q10.
Occurrence in nature
CoQ10 occurs in mackerel and herring fresh heart tissue in concentrations of 105-148 µg/g. In fresh mackerel "red and white tissue," CoQ10 concentrations of 67 and 15 µg/g, respectively, have been reported. In fresh herring tissue, an amount of 15–24 µg/g of CoQ10 has been reported.
Cooking by frying reduces Q10 content from 14-32%.
See also
- Idebenone - synthetic analog with reduced oxidant generating properties
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