Experimental carnitine depletion in rats

Carnitine Supplementation Fails to Maximize Fat Mass Loss Induced by Endurance Training in Rats

BACKGROUND/AIMS

Carnitine is a co-factor of the enzymatic system involved in long chain fatty acid transport across the mitochondrial membrane. This physiological role of carnitine raised the hypothesis that this compound could act as a 'fat burner' by optimizing fat oxidation and consequently reducing its availability for storage. Our aim was to verify whether carnitine supplementation could maximize fat mass loss in trained rats.

METHODS

Male Wistar rats (200 g) were divided into four groups: control (C), sedentary supplemented (S), trained (T) and trained supplemented (TS). The training protocol consisted of bouts of swimming exercise (60 min x day(-1)) for 6 weeks. During the last 14 days, before sacrifice, the supplemented groups received a daily dose of 28 mg x kg(-1) of L-carnitine. Carcass fat content, weight and fat content of adipose tissues were evaluated in all experimental groups.

RESULTS

Our results indicate that carnitine feeding, per se, failed to promote fat mass loss. Endurance training successfully induced a decrease in the fat content in the carcass (28%) and the weight of adipose tissues (retroperitoneal and mesenteric depots by 41 and 20%, respectively) in comparison to C. Despite the augmented carnitine content in the soleus mitochondria (2-fold) observed in TS, the higher content did not maximize the fat loss induced by endurance training.

CONCLUSIONS

Our data strongly suggest that endurance training, rather than carnitine content, is the major factor involved in fat mass loss.

Canine hereditary ceroid-lipofuscinosis: evidence for a defect in the carnitine biosynthetic pathway

The ceroid-lipofuscinoses are a group of autosomal-recessive hereditary lysosomal storage diseases that have been characterized in humans and other mammalian species. In a canine model for the juvenile form of the human disease, a major constituent of the storage bodies is the subunit c protein of mitochondrial ATP synthase that contains an epsilon-N-trimethyllysine (TML) residue. TML is a precursor in carnitine biosynthesis. To determine whether accumulation of the TML-containing protein could result from a defect in the carnitine biosynthetic pathway, plasma carnitine and trimethyllysine levels were measured in homozygous affected, heterozygous carriers, and in normal dogs. When compared top normal animals, mean carnitine levels were reduced by 67% in affected and 50% in carrier dogs. Mean plasma TML levels were elevated almost 50% above control levels in the carriers, but were decreased by approximately 25% in the affected animals. The changes in plasma carnitine and TML levels in the carriers are consistent with the possibility that the disease involves a defect in the carnitine biosynthetic pathway. Secondary effects of the disease process may account for the apparently contradictory decrease in plasma TML levels in affected animals.

Late onset primary systemic carnitine deficiency exacerbated by carnitine-free parenteral nutrition

We describe a 21-year-old male with previously normal plasma total and free carnitine levels who developed a deficiency manifest by decreased plasma and muscle total and free carnitine, decreased urine carnitine, severe hepatic steatosis, mediastinal lipomatosis, progressively impaired triglyceride clearance, myopathy and intermittent hypoglycemia. This case demonstrates that systemic carnitine deficiency may occur in some patients receiving long term carnitine-free TPN. Carnitine may be an essential element of the diet in this patient population.

Effect of carnitine loading on long-chain fatty acid oxidation, maximal exercise capacity, and nitrogen balance

Carnitine has a potential effect on exercise capacity due to its role in the transport of long-chain fatty acids into the mitochondria for beta-oxidation, the export of acyl-coenzyme A compounds from mitochondria and the activation of branched-chain amino acid oxidation in the muscle. We studied the effect of carnitine supplementation on palmitate oxidation, maximal exercise capacity and nitrogen balance in rats. Daily carnitine supplementation (500 mg.kg-1 body mass for 6 weeks) was given to 30 rats, 15 of which were on an otherwise carnitine-free diet (group I) and 15 pair-fed with a conventional pellet diet (group II). A control group (group III, n = 6) was fed ad libitum the pellet diet. Palmitate oxidation was measured by collecting 14CO2 after an intraperitoneal injection of [1-14C]palmitate and exercise capacity by swimming to exhaustion. After carnitine supplementation carnitine concentrations in serum were supranormal [group I, total 150.8 (SD 48.5), free 78.9 (SD 18.4); group II, total 170.9 (SD 27.9), free 115.8 (SD 24.6) mumol.l-1] and liver carnitine concentrations were normal in both groups [group I, total 1.6 (SD 0.3), free 1.2 (SD 0.2); group II, total 1.3 (SD 0.3), free 0.9 (SD 0.2) mumol.g-1 dry mass]. In muscle carnitine concentrations were normal in group I [total 3.8 (SD 1.2), free 3.2 (SD 1.0) mumol.g-1 dry mass] and increased in group II [total 6.6 (SD 0.5), free 4.9 (SD 0.9) mumol.g-1 dry mass].(ABSTRACT TRUNCATED AT 250 WORDS)