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Carnitine

Carnitine, also known as L-carnitine is an amino acid responsible for transport of fatty acids into a cell's mitochondria. It is often sold as a nutritional supplement. more...

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Like all other proteinogenic amino acids natural carnitine is the L-stereoisomer. 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

Fatty acids must be activated before they can be carried into the mitochondria, where fatty acid oxidation occurs. This process occurs in two steps:

The formula for the above is:
RCOO- + CoA + ATP + H2O → RCO-CoA + AMP + PPi + 2H+
This reaction is reversible and its equilibrium lies near 1. However, pyrophosphate is hydrolized by a pyrophosphatase, which drives the reaction forward, and to completion.

Once activated, the acyl CoA is transported into the mitochondrial matrix. This occurs via a series of similar steps:

  1. Acyl CoA is conjugated to carnitine by carnitine acyltransferase I located on the outer mitochondrial membrane
  2. Acyl carnitine is shuttled inside by a translocase
  3. Acyl carnitine is converted to acyl CoA by carnitine acyltransferase II located on the inner mitochondrial membrane

It is important to note that carnitine acyltransferase I undergoes allosteric inhibition as a result of malonyl CoA, an intermediate in fatty acid biosynthesis.

Natural sources

The best source of natural carnitine is 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, kale).

Acetyl-L-carnitine

section references:

Acetyl-L-carnitine or ALCAR, is an acetylated form of L-carnitine. ALCAR is far superior to normal L-carnitine in terms of bioavailability in that it is absorbed by the gastrointestinal tract, enters cells and crosses the blood-brain barrier more readily than unacetylated carnitine.

ALCAR has a broad range of uses including combination with alpha lipoic acid to comprise a patented formulation that has been evidenced to "rejuvenate" the mitochondria of aging mice in studies conducted by Bruce Ames and others. Accordingly, acetyl-L-carnitine has potential as a life extension supplement probably capable of improving the quality and possibily also extending the average life-span of humans. Other attributed uses for ALCAR include using it as a treatment for depression (250 mg per day for several weeks) and for clearing plaque/fatty deposits out of the veins and arteries.

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Carnitine levels in valproic acid-treated psychiatric patients: a cross-sectional study
From Alternative Medicine Review, 9/1/05 by F.A. Moreno

Carnitine levels in valproic acid-treated psychiatric patients: a cross-sectional study. Moreno FA, Macey H, Schreiber B. J Clin Psychiatry 2005;66:555-558.

BACKGROUND: Carnitine facilitates the transport of long-chain fatty acids across the mitochondria for beta oxidation, and the removal of potentially toxic acylcoenzyme-A metabolites from the inner aspect of mitochondrion as acylcarnitines. Previous studies suggest a significant decrease in carnitine concentrations and changes in the ratio of acylcarnitine to free carnitine in seizure-disoriented patients treated with valproic acid (VPA), which may lead to clinical manifestations of carnitine deficiency. This study sought to explore whether the same decrease in plasma free carnitine and increase in acylcarnitines are seen when VPA is used in the treatment of patients with psychiatric disease. METHOD: Thirty psychiatric patients treated with VPA for at least six months were selected for the study and granted informed consent for participation. Exclusion criteria included liver disorder or pancreatitis, metabolic defects known to affect plasma carnitine levels, or noncompliance with VPA regimen. Plasma free carnitine, total carnitine, VPA, and amylase levels were determined, and liver function tests (LFFs) were performed. Pearson correlations were conducted between VPA levels, levels and ratios of carnitines, as well as LFTs and amylase levels. RESULTS: Plasma free and total carnitine levels were lower than the reported normal range for the laboratory performing the assay, and the ratio of acylcarnitine to free carnitine was increased. There was a significant positive correlation of VPA levels and acylcarnitine-free carnitine ratio, a trend toward significance between VPA levels and acylcarnitine levels, and a marginal negative correlation between VPA levels and free carnitine levels. VPA levels correlated also with several LFTs and acylcarnitine levels. Octanoyl carnitine and acylcarnitine levels, as well as acylcarnitine-free carnitine and octanoyl-free carnitine ratios, correlated significantly with amylase levels. CONCLUSION: Although the study was limited by a cross-sectional design without direct control comparison, the findings suggest that patients with various psychiatric conditions treated with polypharmacy that includes VPA may have lower plasma carnitine levels than would be expected in healthy controls.

COPYRIGHT 2005 Thorne Research Inc.
COPYRIGHT 2005 Gale Group

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