The effect of long-term oral L-carnitine administration on insulin sensitivity, glucose disposal, plasma concentrations of leptin and acylcarnitines, and urinary acylcarnitine excretion in warmblood horses

BACKGROUND: Insulin resistance in horses is an emerging field of interest as it is thought to be a contributing factor in the pathogenesis of many equine conditions.

OBJECTIVES: The objectives of the present study were to determine the effects of long-term oral administration of L-carnitine on insulin sensitivity, glucose disposal, plasma leptin concentrations and acylcarnitine spectrum both in plasma and urine.

ANIMALS AND METHODS: Six 3-year-old healthy warmblood geldings were used. In a double blind 2 × 2 Latin square design at a dosage of 100 mg/kg body weight (BW)/day for 28 days the effects of oral supplementation of L-carnitine (as fumarate) were assessed. Glucose disposal and insulin sensitivity were measured by means of the euglycemic-hyperinsulinemic clamp technique. Radioimmunoassays were used to determine plasma leptin and insulin concentrations. Electrospray tandem mass spectrometry was used to assess acylcarnitines both in plasma and urine. Statistical analysis was performed using a linear mixed-effects model and P values <0.05 were considered significant.

RESULTS: Long-term L-carnitine administration did not affect insulin sensitivity. Plasma leptin and free carnitine concentrations in plasma and urine increased significantly (P = 0.047 and 0.000, respectively) following L-carnitine administration as well as short-chain acylcarnitines in plasma and urinary excretion of short- and medium-chain acylcarnitines.

CONCLUSION AND CLINICAL RELEVANCE: Given the effects of oral administration of L-carnitine further clinical study is necessary in order to assess the potential beneficial effects in equine patients suffering from metabolic myopathies such as acquired multiple acyl-CoA dehydrogenase deficiency.

IMPACT FOR HUMAN MEDICINE: The current study supports the treatment rationale of short-chain acyl-CoA dehydrogenase deficiency in humans with L-carnitine at an oral dosage of 100 mg/kg BW/day.