Carnitine deficiency and supplementation do not affect the gene expression of carnitine biosynthetic enzymes in rats

The effects of exercise training on γ-butyrobetaine hydroxylase and novel organic cation transporter-2 gene expression in the rat

The concentration of carnitine in plasma is generally increased with exercise training, suggesting that either carnitine biosynthesis is stimulated or renal reabsorption of carnitine is enhanced, or both. Carnitine, an essential cofactor in the oxidation of fatty acids, is released into the plasma following hydroxylation by γ-butyrobetaine hydroxylase (BBH), the final enzyme in the biosynthetic pathway found primarily in the liver. The organic cation transporter (OCTN2), the carnitine transporter found in kidney, is important in the distribution of carnitine by facilitating its renal reabsorption from urine. In this study, we tested the hypothesis that exercise training increases gene and protein expression of BBH and OCTN2, resulting in enhanced plasma carnitine levels. Male Wistar rats were subjected to 2 daily exercise sessions of treadmill running, 5 days per week, for a 10-week period. The concentration of total carnitine in plasma was significantly increased in trained rats compared with sedentary rats. In trained rats, mRNA and protein expression of BBH were increased in liver, whereas only BBH mRNA expression was increased in kidney. Liver of trained rats demonstrated increased mRNA and protein expression of OCTN2 compared with sedentary rats. In kidney of trained rats, however, only an increase in mRNA expression of OCTN2 was observed. Our results suggest that the improved plasma carnitine status in the trained rat is associated with increased carnitine biosynthesis in liver and kidney. The observation that OCTN2 expression was increased in kidney suggests a potential role of the kidney in the reabsorption of carnitine from the urine.

L-carnitine supplementation and physical exercise restore age-associated decline in some mitochondrial functions in the rat

In mammals, during the aging process, an atrophy of the muscle fibers, an increase in body fat mass, and a decrease in skeletal muscle oxidative capacities occur. Compounds and activities that interact with lipid oxidative metabolism may be useful in limiting damages that occur in aging muscle. In this study, we evaluated the effect of L-carnitine and physical exercise on several parameters related to muscle physiology. We described that supplementing old rats with L-carnitine at 30 mg/kg body weight for 12 weeks (a) allowed the restoration of L-carnitine level in muscle cells, (b) restored muscle oxidative activity in the soleus, and (c) induced positive changes in body composition: a decrease in abdominal fat mass and an increase in muscle capabilities without any change in food intake. Moderate physical exercise was also effective in (a) limiting fat mass gain and (b) inducing an increase in the capacities of the soleus to oxidize fatty acids.

A moderate excess of dietary lysine lowers plasma and tissue carnitine concentrations in pigs

This study was performed to investigate whether dietary lysine concentration influences the carnitine status of pigs. Therefore, an experiment with twenty young pigs with an average body weight of 21 kg was performed which were fed either a control diet (9.7 g lysine/kg) or a diet with a moderate excess of lysine (16.8 g lysine/kg). Concentrations of all the other amino acids did not differ between the diets. Pigs fed the high-lysine diet had lower concentrations of free and total carnitine in plasma, liver, kidney and skeletal muscle than control pigs (P<0.05). Pigs fed the high-lysine diet moreover had an increased concentration of trimethyllysine (TML), a reduced mRNA abundance of TML dioxygenase and reduced concentrations of gamma-butyrobetaine (BB) in muscle, indicating that the conversion of TML into BB in muscle was impaired. Concentrations of BB, the metabolic precursor of carnitine, in plasma, liver and kidney were also reduced in pigs fed the high-lysine diet while the activity of BB dioxygenase in kidney was not different and that in liver was even increased compared to control pigs (P<0.05). In conclusion, this study shows that a moderate dietary excess of lysine lowers plasma and tissue carnitine concentrations in pigs. Reduced concentrations of BB in liver and kidney suggest that the depressed carnitine status was likely caused by a decreased rate of carnitine synthesis due to a diminished availability of carnitine precursor, probably mainly as a result of an impaired BB formation in muscle.

Pivalate lowers litter sizes and weights in female rats independent of its effect on carnitine status

The present study investigated whether treatment of female rats with pivalate affects their reproductive function. Therefore, two experiments with female rats were performed. The first experiment included two groups of rats which received drinking water without (control) or with 20 mmol pivalate/L. The second experiment included a control group (which received drinking water without pivalate and a diet without added carnitine) and four groups which received drinking water with 20 mmol/L pivalate and diets without or with 1, 3 or 5 g added carnitine/kg, respectively. In both experiments, rats treated with pivalate had a lower number of pups born alive and, as a consequence of this, lower litter weights than control rats (p<0.05); pup weights were not altered by pivalate treatment. Supplementation of dietary carnitine in Experiment 2 increased plasma and tissue carnitine concentration even in excess of those in control rats but did not restore normal litter sizes. This study shows for the first time that pivalate affects the reproductive function in female rats independent of its effect on the carnitine status.

Changes in l-carnitine content of fish and meat during domestic cooking

Human adults store around 20g of l-carnitine. In the human body, l-carnitine is not metabolized but excreted through the kidney. Lost l-carnitine has to be replenished either by a biosynthetic mechanism or by the consumption of foods containing l-carnitine. Today, there is no "official" recommended daily allowance for l-carnitine but the daily need for l-carnitine intake has been estimated in the wide range of 2-12μmol/day/kg body weight for an adult human. In this study we evaluated the effect of freezing and of different cooking methods on the l-carnitine content of red meat and fish. l-carnitine was abundantly present in all beef products analyzed. The amounts in the various cuts were similar and our data showed that freezing or cooking did not modify l-carnitine content. Salmon contained about 12 times less l-carnitine than beef but except in smoked salmon, cooking or freezing did not alter l-carnitine content. This study confirms the important role that meet products play for providing adequate amount of l-carnitine to the human body.