Leptin in peritoneal dialysate from continuous ambulatory peritoneal dialysis patients

The adipocyte-derived hormone leptin is the 16-kd product of the ob gene that regulates food intake and body weight. Plasma leptin level is elevated in patients with chronic renal failure, partly because of impaired clearance through the kidney. In this study, we examined whether leptin is cleared into peritoneal dialysate in patients with end-stage renal disease treated by continuous ambulatory peritoneal dialysis (CAPD). The subjects were 46 CAPD patients and 67 age- and gender-matched healthy subjects. Leptin concentration in peritoneal dialysate from CAPD patients was measurable by a sensitive enzyme-linked immunosorbent assay (ELISA), and the daily loss of leptin by the peritoneal route was estimated to correspond to the amount contained in approximately 2 L plasma. Dialysate leptin concentration correlated positively with plasma leptin level and with percent body fat measured by dual-energy X-ray absorptiometry. The dialysate-to-plasma (D/P) ratio of leptin concentration was twice higher than expected from its molecular weight. D/P ratios of beta2-microglobulin, albumin, and transferrin showed strong correlations with each other (r = 0.768 to 0.801), whereas the correlation between D/P ratios of leptin and beta2-microglobulin was less impressive (r = 0.378). This was also the case with the relationship between apparent peritoneal clearances of these macromolecules, suggesting that dialysate leptin had some origins other than passive transport of plasma leptin. To test the hypothesis that abdominal visceral fat may contribute to the unexpectedly raised peritoneal dialysate leptin concentration, multiple regression analysis was performed. Leptin concentration in peritoneal dialysate showed significant association with plasma leptin level and D/P ratio of beta2-microglobulin, and it also showed an independent association with abdominal visceral fat but not with subcutaneous fat assessed by ultrasonography. These results showed that peritoneal dialysate from CAPD patients contained a significant amount of leptin, which derived presumably from both plasma and local visceral fat tissue.