Carnitine

Carnitine, also known as L-carnitine or levocarnitine, is a quaternary ammonium compound biosynthesized from the amino acids stereoisomer.

Production

Carnitine is biosynthesized within the body from the amino acids ascorbic acid) is essential to the synthesis of carnitine. It has been speculated that during growth or pregnancy the requirement of carnitine could exceed its natural production.

Role in fatty acid metabolism

Carnitine transports long-chain acyl groups from fatty acids into the mitochondrial matrix, so that they can be broken down through coenzyme A (CoA). This reaction is catalyzed by the enzyme fatty acyl-CoA synthetase and driven to completion by inorganic pyrophosphatase.

The acyl group on CoA can now be transferred to carnitine and the resulting acyl-carnitine transported into the mitochondrial matrix. This occurs via a series of similar steps:

1. Acyl-CoA is conjugated to carnitine by carnitine acyltransferase I (palmitoyltransferase) located on the outer mitochondrial membrane
2. Acyl-carnitine is shuttled inside by a carnitine-acylcarnitine translocase
3. Acyl-carnitine is converted to acyl-CoA by carnitine acyltransferase II (palmitoyltransferase) located on the inner mitochondrial membrane. The liberated carnitine returns to the cytosol.

Dysfunction of this process leads to the genetic disorders carnitine-acylcarnitine translocase deficiency.^[3]

Carnitine acyltransferase I undergoes malonyl-CoA, an intermediate in fatty acid biosynthesis, in order to prevent futile cycling between beta-oxidation and fatty acid synthesis.

Natural sources

The highest concentrations of carnitine are found in red meat and dairy products. Other natural sources of carnitine include nuts and seeds (e.g. pumpkin, corn, millet, oatmeal, rice bran, rye, whole wheat, wheat bran, wheat germ) and other 'health' foods (bee pollen, brewer's yeast, carob, and kale).

Other sources

Other sources may be found in over the counter vitamins, energy drinks and various other products. Products containing L-carnitine cannot be marketed as "natural health products" in Canada. L-Carnitine products and supplements are not allowed to be imported into Canada (Health Canada).^[4]

Effects on diabetes

L-Carnitine improved glucose disposal among 15 patients with type II diabetes and 20 healthy volunteers.^[5] Glucose storage increased between both groups, but glucose oxidation increased only in the diabetic group. Finally, glucose uptake increased about 8% for both.

See also

• Acetylcarnitine
• Primary carnitine deficiency

References

1. ^ Steiber A, Kerner J, Hoppel C (2004). "Carnitine: a nutritional, biosynthetic, and functional perspective". Mol. Aspects Med. 25 (5-6): 455-73. PMID 15363636.
2. ^ L-Carnitine. Retrieved on 2007-06-01.
3. ^ Olpin S (2005). "Fatty acid oxidation defects as a cause of neuromyopathic disease in infants and adults". Clin. Lab. 51 (5-6): 289-306. PMID 15991803.
4. ^ NHPD Monthly Communique, Vol. 1, Issue 1, September 2005. Retrieved on 2007-06-01.
5. ^ Geltrude Mingrone, Aldo V. Greco, Esmeralda Capristo, Giuseppe Benedetti, Annalisa Giancaterini, Andrea De Gaetano, and Giovanni Gasbarrini (1999). "L-Carnitine Improves Glucose Disposal in Type 2 Diabetic Patients". Journal of the American College of Nutrition 18 (1): 77-82.