Coenzyme Q₁₀

Description

Coenzyme Q₁₀ is a fat-soluble nutrient also known as CoQ₁₀, vitamin Q₁₀, ubidecarenone, or ubiquinone. It is a natural product of the human body that is primarily found in the mitochondria, which are the cellular organelles that produce energy. It occurs in most tissues of the human body; however, the highest concentrations are found in the heart, liver, kidneys, and pancreas. Ubiquinone takes its name from a combination of the word ubiquitous, meaning something that is found everywhere, and quinone 10. Quinones are substances found in all plants and animals. The variety found in humans has a 10-unit side chain in its molecular structure. Apart from the important process that provides energy, CoQ₁₀ also stabilizes cell membranes and acts as an antioxidant. In this capacity, it destroys free radicals, which are unstable molecules that can damage normal cells.

General use

CoQ₁₀ is used extensively in Canada, Western Europe, Japan, and Russia to treat congestive heart failure. It is available as a prescription medication almost everywhere it is sold, although it is sold over-the-counter as a nutritional supplement in the United States. Some studies have shown it to be effective for as many as 70% of patients with congestive heart failure. It appears to improve patient health and wellbeing, and to increase cardiac efficiency. The dosage generally recommended for this condition is 100–300 mg a day, preferably in divided doses. According to Dr. Karl Folkers in Prevention's Healing with Vitamins, it takes one to three months to achieve desired results from supplementation, and as long as six months to attain maximum benefit.

CoQ₁₀ may also help people with some forms of cardiomyopathy. Patients should consult their physician about the possible benefits of supplementation for this condition.

The usefulness of CoQ₁₀ in lowering blood pressure is not well documented. One study suggests that the supplement is helpful for hypertension , but the results are in question as it was not a double-blind, controlled research project. The dose recommended is 200–250 mg a day, with results taking several months to appear. It is possible that some patients with essential hypertension who are initially low in CoQ₁₀ may eventually be able to decrease the amount of their other blood pressure medications. This must be done under the care of a health care provider.

Oral supplementation of CoQ₁₀ has been shown to improve periodontal disease, as it decreases the size of abnormally deep pockets in the gums, and also reduces the extent of bacterial contamination. Other possible benefits of CoQ₁₀ are to decrease angina symptoms, improve immune function in patients with AIDS and other immune deficiencies, improve control of blood sugar, lower cholesterol , improve physical stamina, and help people with muscular dystrophy and Huntington's disease. A group of researchers at the University of California at San Diego reported in 2002 that coenzyme Q₁₀ appears to slow the progress of Parkinson's disease , Friedreich's ataxia, and other conditions marked by degeneration of the central nervous system. The supplement can also reduce the toxicity of some types of chemotherapy. Doxorubicin, a chemotherapeutic agent, is known to sometimes damage the heart. Concomitant supplementation seems to reduce this toxic effect. The possible benefits of CoQ₁₀ should be discussed with a nutritionally-oriented health care provider.

Since 1961, when it was first noticed that cancer patients in Sweden and the United States had low levels of the enzyme, coenzyme Q₁₀ has been studied as a possible cancer treatment. Researchers believe that coenzyme Q₁₀ may protect against cancer by stimulating the immune system, and functioning as an antioxidant. Although animal studies have been conducted, as of early 2004 no report of a randomized clinical trial involving human subjects whose survival times were lengthened by using coenzyme Q₁₀ in addition to a traditional cancer treatment has been reported in a peer-reviewed medical journal.

Deficiency

Patients with certain conditions tend to have lower levels of CoQ₁₀, and may benefit from supplements. Some diseases that are associated with decreased amounts of this nutrient are AIDS, chronic fatigue , congestive heart failure, cardiomyopathy, and inflammatory gum disease . Levels of CoQ₁₀ tend to decrease with age; tests for its presence in the body are not widely available. Adverse effects from this supplement are rare and mild, so anyone suffering from one of the listed conditions should consider discussing supplementation with a health care provider.

Preparations

Natural sources

Food products are a good source of CoQ₁₀, and provide approximately half of the body's requirement. Cold-water fish such as mackerel, salmon, sardines, and tuna are particularly high in CoQ₁₀. Vegetable oils and meats also provide good sources. The liver manufactures adequate amounts to fulfill the need not met in the diet. People who are deficient in B vitamins, selenium, vitamin C , and vitamin E may not be able to make as much CoQ₁₀ as they need because these nutrients are required for production. Consumption of foods rich in CoQ₁₀ and production of the nutrient in the liver will not provide the amounts needed to treat heart failure and other conditions that may contribute to a deficiency of this nutrient. In those cases, supplements are required.

Supplemental sources

Supplements of CoQ₁₀ are widely available; however, its cost varies considerably. As of 2004, it is available in the United States, ranging in price from $7.79 for a bottle of 40 30-mg capsules to $38.95 for a bottle of 60 100-mg capsules. It is found in various forms including capsules, gelcaps, liquids, and tablets. The latter may be the best choice, as this form generally includes a source of fat that improves absorption. Vitamin E is a helpful stabilizing additive as well. Most of the CoQ₁₀ products currently available on the market are manufactured in Japan. Like other supplements, Co₁₀ is best kept in a cool, dry place, out of direct light, and out of the reach of children.

Precautions

As of 2004, the safety of CoQ₁₀ for pregnant or breast-feeding women has not been established, and its use is not recommended under these conditions. It is also not recommended for young children. People diagnosed with heart failure, diabetes, kidney problems, or liver disease should use particular care with this supplement, as the dosage of other medications may require adjustment. These individuals should consult a physician before taking coenzyme Q₁₀.

Side effects

Reported adverse effects related to supplemental CoQ₁₀ use include diarrhea , irritation of the stomach, poor appetite, and nausea . These effects are rarely reported and are mild. CoQ₁₀ is considered extremely safe for most people. If doses over 300 mg per day are taken, liver enzyme levels may be affected, and may need monitoring.

Interactions

It is possible that CoQ₁₀ decreases the action of sodium warfarin (known by the brand name, Coumadin), which is prescribed to prevent the formation of blood clots in patients at risk of heart attack or stroke . Some oral diabetes medications may also interfere with the action of CoQ₁₀. Cholesterol-lowering drugs in the statin group may have this effect as well.

Resources

BOOKS

Bratman, Steven, and David Kroll. Natural Health Bible. Roseville, CA: Prima Publishing, 2000.

Griffith, H. Winter. Vitamins, Herbs, Minerals & Supplements: The Complete Guide. Tucson, AZ: Fisher Books, 2000.

Pressman, Alan H., and Sheila Buff. The Complete Idiot's Guide to Vitamins and Minerals., 2nd ed. Indianapolis: Macmillan General Reference, 2000.

Therapeutic Research Faculty Staff. Natural Medicines Comprehensive Database. Stockton, CA: Therapeutic Research Faculty, 1999.

PERIODICALS

Baker, S. K., and M. A. Tarnopolsky. "Targeting Cellular Energy Production in Neurological Disorders." Expert Opinion on Investigational Drugs 12 (October 2003): 1655–79.

Naini, A., V., J. Lewis, M. Hirano, and S. DiMauro. "Primary Coenzyme Q₁₀ and the Brain." Biofactors 18 (2003): 145–52.

Shults, C. W. "Coenzyme Q₁₀ in Neurodegenerative Diseases." Current Medical Chemistry 10 (October 2003): 1917–21.

Shults, C. W., D. Oakes, K. Kieburtz, et al. "Effects of Coenzyme Q₁₀ in Early Parkinson's Disease: Evidence of Slowing of the Functional Decline." Archives of Neurology 59 (October 2002): 1541–50.

Vedanarayanan, V. V. "Mitochondrial Disorders and Ataxia." Seminars in Pediatric Neurology 10 (September 2003): 200–9.

ORGANIZATIONS

Food and Drug Administration (FDA). 5600 Fishers Lane, Rockville, MD 20857. (888) 463-6332. <http://www.fda.gov>.

National Cancer Institute (NCI). <http://www.nci.nih.gov>.

National Center for Complementary and Alternative Medicine (NCCAM) Clearinghouse. P. O. Box 7923, Gaithersburg, MD 20898-7923. (888) 644-6226. Fax: (866) 464-3615. <http://nccam.nih.gov>.

OTHER

National Cancer Institute (NCI). Complementary and Alternative Medicine (CAM) Information Summary: Coenzyme Q₁₀. Bethesda, MD: NCI, 2003. [cited June 3, 2004]. <http:/www.nci.nih.gov/cancerinfo/pdq/cam/coenzymeQ10>.

National Institute of Neurological Disorders and Stroke (NINDS). "Study Suggests Coenzyme Q₁₀ Slows Functional Decline in Parkinson's Disease." NINDS press release, 14 October 2002. [cited June 3, 2004]. <http://www.ninds.nih.gov/news_and_events/pressrelease_parkinsons_coenzymeq10_10140>.

Rebecca J. Frey, PhD

Coenzyme

Coenzymes are small organic molecules that link to enzymes and whose presence is essential to the activity of those enzymes. Coenzymes belong to the larger group called cofactors, which also includes metal ions; cofactor is the more general term for small molecules required for the activity of their associated enzymes. The relationship between these two terms is as follows

I. Cofactors

• Essential ions
• Loosely bound (forming metal-activated enzymes)
• Tightly bound (forming metalloenzymes
• Coenzymes
• Tightly bound prosthetic groups
• 2 Loosely bound cosubstrates

Many coenzymes are derived from vitamins . Table 1 lists vitamins, the coenzymes derived from them, the type of reactions in which they participate, and the class of coenzyme.

Prosthetic groups are tightly bound to enzymes and participate in the catalytic cycles of enzymes. Like any catalyst , an enzyme–prosthetic group complex undergoes changes during the reaction, but before it can catalyze another reaction, it must return to its original state.

Flavin adenine dinucleotide (FAD) is a prosthetic group that participates in several intracellular oxidation -reduction reactions. During the catalytic cycle of the enzyme succinate dehydrogenase, FAD accepts two electrons from succinate, yielding fumarate as a product. Because FAD is tightly bound to the enzyme, the reaction is sometimes shown this way

succinate + E–FAD → fumarate + E–FADH₂

where E–FAD stands for the enzyme tightly bound to the FAD prosthetic group. In this reaction the coenzyme FAD is reduced to FADH₂ and remains tightly bound to the enzyme throughout. Before the enzyme can catalyze the oxidation of another succinate molecule, the two electrons now belonging to E–FADH₂ must be transferred to another electron acceptor, ubiquinone. The regenerated E–FAD complex can then oxidize another succinate molecule.

Cosubstrates are loosely bound coenzymes that are required in stoichiometric amounts by enzymes. The molecule nicotinamide adenine dinucleotide (NAD) acts as a cosubstrate in the oxidation-reduction reaction that is catalyzed by malate dehydrogenase, one of the enzymes of the citric acid cycle.

malate + NAD⁺ → oxaloacetate + NADH

In this reaction, malate and NAD⁺ diffuse into the active site of malate dehydrogenase. Here NAD⁺ accepts two electrons from malate; oxaloacetate and NADH then diffuse out of the active site. The reduced NADH must then be returned to its NAD⁺ form. For each catalytic cycle, a "new" NAD⁺ molecule is needed if the reaction is to occur; thus, stoichiometric quantities of the cosubstrate are needed. The reduced form of this coenzyme (NADH) is converted back to the oxidized form (NAD⁺) via a number of simultaneously occurring processes in the cell, and the regenerated NAD⁺ can then participate in another round of catalysis.

Coenzymes, then, are a type of cofactor. They are small organic molecules that bind tightly (prosthetic groups) or loosely (cosubstrates) to enzymes as they participate in catalysis.

see also Active Site; Cofactor; Enzymes.

Paul A. Craig

Bibliography

Berg, Jeremy M.; Tymoczko, John L.; and Stryer, Lubert (2002). Biochemistry, 5th edition. New York: W. H. Freeman.

Horton, H. Robert; Moran, Laurence A.; Ochs, Raymond S.; Rawn, David J.; and Scrimgeour, K. Gray (2002). Principles of Biochemistry, 3rd edition. Upper Saddle River, NJ: Prentice Hall.

Voet, Donald; Voet, Judith G.; and Pratt, Charlotte (1999). Fundamentals of Biochemistry. New York: Wiley.

coenzymes Organic compounds required for the activity of some enzymes; most are derived from vitamins. Coenzymes that remain tightly bound to the enzyme at all times are sometimes known as prosthetic groups; non‐protein components of the enzyme molecule. Other coenzymes act to transfer groups from one enzyme to another, e.g. coenzyme A transfers acetyl groups between enzymes, NAD transfers hydrogen between enzymes in oxidation and reduction reactions.

An enzyme that requires a tightly bound coenzyme is inactive in the absence of its coenzyme; this can be exploited to assess vitamin B1, B2, and B6 nutritional status, by measuring the activity of enzymes that require coenzymes derived from these vitamins (see enzyme activation Assays).

Coenzyme A (CoA) is derived from the vitamin pantothenic acid; it is required for the transfer and metabolism of acetyl groups (and other fatty acyl groups). Coenzyme Q is ubiquinone.

coenzyme A (CoA) A complex organic compound that acts in conjunction with enzymes involved in various biochemical reactions, notably the oxidation of pyruvate via the Krebs cycle and fatty-acid oxidation and synthesis (see acetyl coenzyme A). It comprises principally the B vitamin pantothenic acid, the nucleotide adenine, and a ribose–phosphate group (see formula).

succinyl coenzyme A An intermediate compound in the conversion of alpha-ketoglutaric acid to succinic acid during the citric acid cycle, a process linked to the formation of the energy-rich guanosine triphosphate (GTP). Succinate is not always the final product, as the succinyl coenzyme A may be employed for acylation reactions or to initiate porphyrin synthesis.