Debate Forum: Levocarnitine Therapy Is Rational and Justified in Selected Dialysis Patients

Carnitine is a metabolic cofactor which is essential for normal fatty acid metabolism. Patients with chronic kidney disease on dialysis have been shown both to suffer from disordered fatty acid metabolism and to have a significant deficiency in plasma and tissue carnitine. Aberrant fatty acid metabolism has been associated with a number of cellular abnormalities such as increased mitochondrial permeability (a promoter of apoptosis), insulin resistance, and enhanced generation of free radicals. These cellular abnormalities have, in turn, been correlated with pathological clinical conditions common in dialysis patients including cardiomyopathy with attendant hypotension and resistance to the therapeutic effect of recombinant human erythropoietin (EPO). In 1999, the Food and Drug Administration approved levocarnitine injection for the prevention and treatment of carnitine deficiency in patients on dialysis based on documentation of free plasma carnitine levels in dialysis patients similar to other serious carnitine deficiency states for which treatment was required. Data analysis performed by expert panels convened by both the American Association of Kidney Patients and, subsequently, the National Kidney Foundation recommended a trial of levocarnitine therapy for specific subsets of dialysis patients including those with EPO resistance, dialysis-related hypotension, cardiomyopathy and muscle weakness. In 2003, the Centers for Medicare and Medicaid services convened a Medical Advisory Committee which established reimbursement on a national level for carnitine-deficient dialysis patients who had either dialysis-related hypotension or EPO resistance. Recently, a correlation between reductions in hospitalization rates of dialysis patients receiving levocarnitine therapy has been demonstrated in a large retrospective study. Despite data-based recommendations and national reimbursement, only a small minority of dialysis patients have been prescribed a therapeutic trial of levocarnitine. Whereas the reasons for the reluctance of nephrologists to prescribe this therapeutic trial are unclear, possible explanations include a lack of appreciation of the pivotal role played by carnitine in cellular metabolism and the strength of evidence for a substantial deficiency of carnitine in dialysis patients, an underestimation of the prognostic import of EPO resistance and dialysis-related hypotension, inadequate dissemination of the clinical trial data supporting the use of levocarnitine in dialysis patients, and the heterogeneous clinical response of dialysis patients to levocarnitine therapy. Difficulties in documenting both initial eligibility and evidence of improvement as a result of therapy may also be a contributing factor. This paper discusses the biological role of carnitine and its particular relevance to dialysis patients. Clinical trial data concerning an effect of therapy on EPO resistance and dialysis-related hypotension are summarized along with a discussion of the logic behind the use of levocarnitine in dialysis. Finally, the difficulties posed by a reimbursement policy based on clinical as opposed to laboratory endpoints and a heterogeneous response to therapy are addressed.

Congestive heart failure in patients with chronic kidney disease and on dialysis

CHF is highly prevalent in ESRD and is a leading cause of death in such patients. Hypertension, renal anemia, and comorbid conditions such as coronary artery disease are particularly important risk factors for CHF in ESRD. Dialysis hypotension may be a marker of poor prognosis in such persons. Recent studies suggest that lipid peroxidation and L-carnitine deficiency may contribute to CHF in some patients with ESRD. All forms of renal replacement therapy are capable of ameliorating symptoms of CHF, but their effect on cardiovascular mortality has not been firmly established. Drug therapy, particularly angiotensin-converting enzyme inhibitors and beta-adrenergic receptor blockers, is under-used in patients with ESRD and CHF. Heart/kidney transplantation may be a viable option for some patients with advanced CHF and ESRD.

Insulin-like growth factor-1 stimulates production of mesangial cell matrix components

Diabetic nephropathy is characterized by mesangial cell proliferation and expansion of the mesangial matrix. Insulin-like growth factor-1 (IGF-1) increases in the kidney early in experimental diabetes. The effect of IGF-1 on mesangial cell proliferation and synthesis of extracellular matrix (ECM) proteins was examined to test the hypothesis that IGF-1 stimulates mesangial cells to synthesize ECM proteins. ECM proteins were measured by immunoprecipitation after metabolic labeling of rat mesangial cells in culture. IGF-1 caused a 2.4-fold increase in mesangial cell proliferation as measured by 3H-thymidine incorporation. IGF-1 caused an increase in cellular laminin, fibronectin and type IV collagen, 46.8 +/- 15.4%, 31.3 +/- 11.4%, and 27.7 +/- 12.6% increase respectively compared to control cells. IGF-1 did not effect cellular type 1 collagen, decrease of 8.2 +/- 8.7%. There was a trend toward increased total protein synthesis by IGF-1, 36.5 +/- 2.5%. In summary, IGF-1 stimulates ECM component production by mesangial cells. Thus, IGF-1 has the capacity to mediate the histologic changes characteristic of diabetic nephropathy.