Muscle carnitine deficiency associated with zidovudine-induced mitochondrial myopathy

Carnitine in Human Immunodeficiency Virus Type 1 Infection/Acquired Immune Deficiency Syndrome

There is an increasing body of evidence that subgroups of patients infected with human immunodeficiency virus type 1 possess carnitine deficiency. Secondary carnitine deficiencies in these individuals may result from nutritional deficiencies, gastrointestinal disturbances, renal losses, or shifts in metabolic pathways. However, tissue depletion precipitated by drug toxicities, particularly zidovudine, is a major etiology and concern. Carnitine deficiency may impact on energy and lipid metabolism, causing mitochondrial and immune dysfunction. There are convincing laboratory data showing the in vitro ameliorative effects of L-carnitine supplementation on zidovudine-induced myopathies and lymphocyte function. Studies measuring the impact of L-carnitine supplementation on clinical characteristics are ongoing. (J Child Neurol 1995; 10(Suppl):2540-2544).

L-carnitine supplementation as a potential antioxidant therapy for inherited neurometabolic disorders

In recent years increasing evidence has emerged suggesting that oxidative stress is involved in the pathophysiology of a number of inherited metabolic disorders. However the clinical use of classical antioxidants in these diseases has been poorly evaluated and so far no benefit has been demonstrated. l-Carnitine is an endogenous substance that acts as a carrier for fatty acids across the inner mitochondrial membrane necessary for subsequent beta-oxidation and ATP production. Besides its important role in the metabolism of lipids, l-carnitine is also a potent antioxidant (free radical scavenger) and thus may protect tissues from oxidative damage. This review addresses recent findings obtained from patients with some inherited neurometabolic diseases showing that l-carnitine may be involved in the reduction of oxidative damage observed in these disorders. For some of these diseases, reduced concentrations of l-carnitine may occur due to the combination of this compound to the accumulating toxic metabolites, especially organic acids, or as a result of protein restricted diets. Thus, l-carnitine supplementation may be useful not only to prevent tissue deficiency of this element, but also to avoid oxidative damage secondary to increased production of reactive species in these diseases. Considering the ability of l-carnitine to easily cross the blood-brain barrier, l-carnitine supplementation may also be beneficial in preventing neurological damage derived from oxidative injury. However further studies are required to better explore this potential.

Low serum carnitine in HIV-infected children on antiretroviral treatment

OBJECTIVE

HIV-infection and antiretroviral therapies are associated with energy dysfunction and lipid metabolism in adults. Our aim was to detect a possible carnitine deficiency in HIV-infected children on antiretroviral treatments. We analysed the relation among serum carnitine, its amino-acid precursors (methionine and lysine), clinical evaluation and antiretroviral therapy.

DESIGN AND SETTING

Cross-sectional study performed in a tertiary care hospital.

SUBJECTS

A total of 79 HIV-infected children on antiretroviral therapy, monitored prospectively in our hospital.

INTERVENTIONS

Antiretroviral therapy included nucleoside analogues plus protease inhibitors and/or non-nucleoside analogues. Carnitine was analysed by an enzymatic-spectrometric procedure, and amino acids by ion exchange chromatography. Reference values of carnitine and amino acids were established in apparently healthy children who underwent presurgical analysis for minor surgery.

RESULTS

Serum free and total carnitine, acylcarnitines, methionine and lysine were significantly lower in HIV-infected children compared with our reference values for similar ages (P<0.0001; Student's t-test). Low carnitine values were observed in 37% of our HIV-infected children. A significantly positive correlation was observed between serum total carnitine and methionine or lysine (P<0.0001 and P=0.005, respectively; Pearson test). No relation was observed between serum carnitine and clinical stage of HIV infection, immunological or nutritional status or lipodystrophy. Free and total carnitine were significantly lower (P=0.002 and 0.033, respectively) in HIV-infected patients on protease inhibitors (N=56) compared with those on other treatments (N=23).

CONCLUSIONS

Low serum carnitine concentration was observed in 37% of our HIV-infected children on antiretroviral therapy. Malabsorption or defective synthesis may also account for the low serum carnitine values detected in these patients.