CARNITINE

'Carnitine', also known as 'L-carnitine' (levocarnitine) is a quaternary ammonium compound synthesized from the amino acids lysine and methionine primarily in the liver and kidneys.^[1] It helps in the consumption and disposal of fat in the body because it is responsible for the transport of fatty acids from the cytosol into the mitochondria. It is often sold as a nutritional supplement. Originally found as a growth factor for mealworms and labeled vitamin Bt.
Natural carnitine is the L-stereoisomer.

Contents

Production

Role in fatty acid metabolism

Natural sources

Effects on diabetes

Health supplements

See also

References

Footnotes

External links

Production

It can be synthesised within the body from the amino acids lysine or methionine. Vitamin C (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 beta-oxidation to acetate to obtain usable energy via the citric acid cycle, or in some organisms such as fungi, to use actetate in the glyoxylate cycle to enter gluconeogenesis for the formation of carbohydrates. Fatty acids must be activated before binding to the carnitine molecule to form 'acyl-carnitine'. The free fatty acid in the cytosol is attached with a thioester bond to 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:
# Acyl-CoA is conjugated to carnitine by ''carnitine acyltransferase I'' (palmitoyltransferase) located on the outer mitochondrial membrane
# Acyl-carnitine is shuttled inside by a ''carnitine-acylcarnitine translocase''
# 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 primary carnitine deficiency, carnitine palmitoyltransferase I deficiency, carnitine palmitoyltransferase II deficiency, and carnitine-acylcarnitine translocase deficiency.
It is important to note that ''carnitine acyltransferase I'' undergoes allosteric inhibition as a result of malonyl-CoA, an intermediate in fatty acid biosynthesis, in order to prevent futile cycling between beta-oxidation and fatty acid synthesis.

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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, sunflower, sesame), legumes or pulses (beans, peas, lentils, peanuts), vegetables (artichokes, asparagus, beet greens, broccoli, brussels sprouts, collard greens, garlic, mustard greens, okra, parsley), fruits (apricots, bananas), cereals (buckwheat, corn, millet, oatmeal, rice bran, rye, whole wheat, wheat bran, wheat germ) and other 'health' foods (bee pollen, brewer's yeast, carob, and kale).

'Product'	'Quantity'	'Carnitine'
Beef Steak	3.5 oz	95 mg
Ground Beef	3.5 oz	94 mg
Pork	3.5 oz	27.7 mg
Bacon	3.5 oz	23.3 mg
Cod Fish	3.5 oz	5.6 mg
Chicken Breast	3.5 oz	3.9 mg
American Cheese	3.5 oz	3.7 mg
Ice Cream	3.5 fl oz	3.7 mg
Whole Milk	3.5 fl oz	3.3 mg
Cottage Cheese	3.5 fl oz	1.1 mg
Whole Wheat Bread	3.5 oz	0.36 mg
Asparagus	3.5 oz	0.195 mg
White Bread	3.5 oz	0.147 mg
Macaroni	3.5 oz	0.126 mg
Peanut Butter	3.5 oz	0.083 mg
Rice (cooked)	3.5 oz	0.0449 mg
Eggs	3.5 oz	0.0121 mg
Orange Juice	3.5 fl oz	0.0019 mg

Effects on diabetes

L-Carnitine improved glucose disposal among 15 patients with Type II Diabetes and 20 healthy volunteers.^[2] Glucose storage increased between both groups, but glucose oxidation increased only in the diabetic group. Finally, glucose uptake increased about 8% for both.

Health supplements

★ Products containing L-carnitine cannot be marketed as "natural health products" in Canada, since L-carnitine is not considered a natural ingredient. L-carnitine products and supplements are not allowed to be imported into the country (Health Canada).^[3]

See also

★ Acetylcarnitine

★ Primary carnitine deficiency

References

★ Fatty acid oxidation defects as a cause of neuromyopathic disease in infants and adults, Olpin S, , , Clin. Lab., 2005

★ Carnitine: a nutritional, biosynthetic, and functional perspective, Steiber A, Kerner J, Hoppel C, , , Mol. Aspects Med., 2004

Footnotes

1. L-Carnitine
2. L-Carnitine Improves Glucose Disposal in Type 2 Diabetic Patients, Geltrude Mingrone, Aldo V. Greco, Esmeralda Capristo, Giuseppe Benedetti, Annalisa Giancaterini, Andrea De Gaetano, and Giovanni Gasbarrini, , , Journal of the American College of Nutrition, 1999
3. NHPD Monthly Communique, Vol. 1, Issue 1, September 2005

External links

★ article on Carnitine at University of Maryland Medical Center

★ Molecule of the Month at University of Bristol

★ Carnitine Team at University of Florida