Peritoneal clearance of leptin in continuous ambulatory peritoneal dialysis

Leptin is a 16-kd protein that increases energy expenditure and limits food intake. Serum leptin (S-leptin) is elevated in dialysis patients, and little data have been reported on leptin clearance (Cl) during dialysis. We analyzed the peritoneal dialysis (PD) Cl of leptin in 15 continuous ambulatory peritoneal dialysis (CAPD) patients and compared the results to beta(2)-microglobulin (beta(2)-m), urea, and creatinine PD Cl. S-leptin was significantly elevated (Kruskal-Wallis, P < 0.005) in CAPD women (58.4 +/- 42.4 [SE] microg/L, n = 5) as compared with CAPD men (13.9 +/- 7.1, n = 10) and with healthy women (11.0 +/- 1.4, n = 13) and men (5.1 +/- 0. 9, n = 14). Correlations were found between percent of fat mass and S-leptin (P < 0.05); between S-leptin and the 24-hour PD leptin (P < 0.05); and between dialysate-to-plasma (D/P) beta(2)-m and D/P leptin (P < 0.01). PD leptin Cl (1.80 +/- 0.43 mL/min/1.73 m(2)) was higher than beta(2)-m Cl (1.22 +/- 0.31) (P < 0.01), but reduced as compared with urea Cl (8.84 +/- 1.20) (P < 0.005) and creatinine Cl (7.71 +/- 0.99) (P < 0.005). These results indicate that leptin is eliminated through the peritoneum membrane. However, peritoneal leptin clearance, as beta(2)-m, appears to be clearly restricted as compared with peritoneal transport of smaller molecules. Hence, leptin could use the same diffusion transport pathway as beta(2)-m. In addition, leptin, which has a higher molecular weight than beta(2)-m, was significantly more eliminated into the peritoneal dialysate. More studies are necessary to clarify whether this is an active leptin elimination process by peritoneal secretion or by a different restriction coefficient of diffusion through the peritoneum membrane.