The anti-catabolic effect of a couple of grams of L-carnitine

Supplementation with a few grams of L-carnitine daily may inhibit the molecular demolition machinery that breaks down your muscles. This is suggested in an animal study published by scientists at Justus-Liebig University, Giessen, Germany in Nutrition & Metabolism.

Supplementation with a few grams of L-carnitine daily may inhibit the molecular demolition machinery that breaks down your muscles. This is suggested in an animal study published by scientists at Justus-Liebig University, Giessen, Germany in Nutrition & Metabolism.

Under conditions of extreme hunger, serious illness and other forms of physical stress, the body starts to sacrifice muscle tissue. The ubiquitin-proteasome system is activated in muscle cells and this breaks down muscle proteins. The catabolic proteins that play an important role in this demolition process are MuRF1 and atrogin-1.

The German scientists are doing research on the effects of adding small quantities of L-carnitine to piglets’ food, in the hope that this amino acid will have a growth-enhancing effect. In 2011 and 2012 they published studies which show that L-carnitine supplementation reduces the functioning of the catabolic ubiquitin-proteasome system in the muscle cells of piglets. [Mol Nutr Food Res. 2011 Mar;55(3):419-29.] [Animal. 2012 Jan;6(1):70-8.]

In 2013 the same researchers published the results of a study in which they gave L-carnitine to rats in an attempt to elucidate more precisely how the anti-catabolic effect of L-carnitine works. The experimental group in the study consisted of four-week-old rats that were given 1250 mg L-carnitine per kg bodyweight. The human equivalent of this dose would be in the region of 1-3 g L-carnitine per day. The control group was given standard food.

During the four weeks that the experiment lasted, the rats built up a little more muscle protein and the amount of fat in their muscle tissue decreased.

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Part of the muscle-strengthening effect is explained in the figure above. L-Carnitine supplementation boosted the concentration of IGF-1 in the rats’ blood [above right]. The gene for IGF-1 started to work harder in the rats’ liver [above left]. [Hmm… Might that mean that growth-hormone users would grow faster if they took L-carnitine?]

L-Carnitine reduced the production and concentration of the catabolic proteins MuRF1 and atrogin-1 in the muscle cells. In addition, the researchers observed that fewer proteins were being broken down by the ubiquitin-proteasome system [far right in the figure below].

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In the muscle cells, L-carnitine boosted the activity of anabolic signal molecules such as Akt and mTOR. The number of phosphorylated Akt and mTOR molecules increased.

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The activation of the anabolic signal molecules probably also caused an increase in the number of phosphorylated FoxO1 molecules. FoxO1 is a catabolic signal molecule. When not phosphorylated it tells the cell nucleus – and therefore also muscle proteins – to convert molecules into glycogen. FoxO1 is also responsible for the production of the catabolic MuRF1. But when phosphorylated, FoxO1 is broken down more quickly.

“Probably, the suppression of the ubiquitin-proteasome system by carnitine with respect to muscle protein degradation might be more pronounced and more relevant under condition of negative N balance, chronic diseases and denervation or under unloading conditions”, the researchers write. “Under such conditions, the ubiquitin-proteasome system is strongly up-regulated leading to muscle atrophy and a reduction of the mass of skeletal muscles.”

Supplementation of carnitine leads to an activation of the IGF-1/PI3K/Akt signalling pathway and down regulates the E3 ligase MuRF1 in skeletal muscle of rats.

Keller J, Couturier A, Haferkamp M, Most E, Eder K.

Source

Institute of Animal Nutrition and Nutritional Physiology, Justus-Liebig-University, Heinrich-Buff-Ring 26-32, Giessen, 35392, Germany. Klaus.Eder@ernaehrung.uni-giessen.de.

Abstract

BACKGROUND:

Recently, it has been shown that carnitine down-regulates genes involved in the ubiquitin-proteasome system (UPS) in muscle of pigs and rats. The mechanisms underlying this observation are yet unknown. Based on the previous finding that carnitine increases plasma IGF-1 concentration, we investigated the hypothesis that carnitine down-regulates genes of the UPS by modulation of the of the IGF-1/PI3K/Akt signalling pathway which is an important regulator of UPS activity in muscle.

METHODS:

Male Sprague-Dawley rats, aged four weeks, were fed either a control diet with a low native carnitine concentration or the same diet supplemented with carnitine (1250 mg/kg diet) for four weeks. Components of the UPS and IGF-1/PI3K/Akt signalling pathway in skeletal muscle were examined.

RESULTS:

Rats fed the diet supplemented with carnitine had lower mRNA and protein levels of MuRF1, the most important E3 ubiquitin ligase in muscle, decreased concentrations of ubiquitin-protein conjugates in skeletal muscle and higher IGF-1 concentration in plasma than control rats (P < 0.05). Moreover, in skeletal muscle of rats fed the diet supplemented with carnitine there was an activation of the PI3K/Akt signalling pathway, as indicated by increased protein levels of phosphorylated (activated) Akt1 (P < 0.05). CONCLUSION: The present study shows that supplementation of carnitine markedly decreases the expression of MuRF1 and concentrations of ubiquitinated proteins in skeletal muscle of rats, indicating a diminished degradation of myofibrillar proteins by the UPS. The study moreover shows that supplementation of carnitine leads to an activation of the IGF-1/PI3K/Akt signalling pathway which in turn might contribute to the observed down-regulation of MuRF1 and muscle protein ubiquitination. PMID: 23497226 [PubMed] PMCID: PMC3631133 Source: http://www.ncbi.nlm.nih.gov/pubmed/23497226

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