l-Carnitine is an osmotic agent suitable for peritoneal dialysis

Excessive intraperitoneal absorption of glucose during peritoneal dialysis has both local cytotoxic and systemic metabolic effects. Here we evaluate peritoneal dialysis solutions containing l-carnitine, an osmotically active compound that induces fluid flow across the peritoneum. In rats, l-carnitine in the peritoneal cavity had a dose-dependent osmotic effect similar to glucose. Analogous ultrafiltration and small solute transport characteristics were found for dialysates containing 3.86% glucose, equimolar l-carnitine, or combinations of both osmotic agents in mice. About half of the ultrafiltration generated by l-carnitine reflected facilitated water transport by aquaporin-1 (AQP1) water channels of endothelial cells. Nocturnal exchanges with 1.5% glucose and 0.25% l-carnitine in four patients receiving continuous ambulatory peritoneal dialysis were well tolerated and associated with higher net ultrafiltration than that achieved with 2.5% glucose solutions, despite the lower osmolarity of the carnitine-containing solution. Addition of l-carnitine to endothelial cells in culture increased the expression of AQP1, significantly improved viability, and prevented glucose-induced apoptosis. In a standard toxicity test, the addition of l-carnitine to peritoneal dialysis solution improved the viability of L929 fibroblasts. Thus, our studies support the use of l-carnitine as an alternative osmotic agent in peritoneal dialysis.