L-Carnitine in the treatment of painful diabetic neuropathy and its effect on plasma β-endorphin levels

Abstract

Objective: We investigated the efficacy of l-carnitine (LC) in the treatment of painful diabetic neuropathy (DN) and its effects on levels of the endogenous peptide β-endorphin. Methods: The study group consisted of 7 diabetic patients with painful DN, 7 diabetic patients without DN, and 7 healthy control subjects. Blood samples were obtained from all participants for determination of basal β-endorphin levels. A 30-mg/kg intravenous bolus injection of LC was then administered. DN was diagnosed by electroneuromyography, and severity of pain was evaluated on a scale from 1 (transient, very mild pain) to 4 (severe pain). Results: Before treatment, the 7 patients with DN had pain scores of 1 (n = 1), 2 (n = 3), 3 (n = 2), and 4 (n = 1). After treatment, 3 patients had a score of 1, and 4 had a score of 2. Mean (± SD) basal β-endorphin levels were 22.6 ± 13.02 pg/mL in the 7 patients with DN, 26.01 ± 9.06 pg/mL in the 7 without DN, and 90.04 ± 29.11 pg/mL in the control group ( P < 0.05). In the patients with painful DN, β-endorphin levels at 3 hours and on day 15 were 31.97 ± 11.81 pg/mL and 28.73 ± 12.53 pg/mL, respectively. An acute rise in β-endorphin levels was noted at 3 hours ( P < 0.05), but patients' pain scores did not change correspondingly. The improvement in pain scores in patients with DN after 15 days of LC treatment was not associated with any significant change in β-endorphin levels. Conclusions: β-Endorphin levels are lower in diabetic patients than in the nondiabetic population. Treatment with LC is effective in treating painful DN, but this effect does not appear to be mediated by alterations in β-endorphin levels.