Systemic and intraperitoneal interleukin-6 system during the first year of peritoneal dialysis

Abstract

◆ Objective: To investigate if intraperitoneal and systemic interleukin-6 (IL-6) and soluble IL-6 receptor (sIL-6R) are related to each other and to peritoneal solute transport rate (PSTR). ◆ Design: Longitudinal study in retrospectively selected patients. ◆ Setting: Peritoneal dialysis (PD) unit of a university-based hospital. ◆ Patients and Methods: 31 PD patients on treatment with conventional glucose-based solutions participated in a longitudinal study. IL-6 and sIL-6R were measured in plasma and overnight effluent, both at baseline and after 12 ± 2 months on PD. C-reactive protein (CRP) and serum albumin were used as surrogate markers of inflammation. PSTR of small solutes was evaluated using the dialysate-to-plasma ratio (D/P) of creatinine after a 4-hour dwell; PSTR of large solutes was evaluated using the 24-hour D/P ratio of albumin. ◆ Results: D/P creat increased over time (0.67 ± 0.15 vs 0.80 ± 0.11, p < 0.0001) and correlated to D/P albumin only at the baseline evaluation. Patients with plasma IL-6 ≥ median had higher (p < 0.005) D/ P creat at baseline [0.74 (0.62 - 0.87)] compared to patients with IL-6 < median [0.57 (0.47 - 0.66)]. Dialysate IL-6 at baseline was also higher (p < 0.05) in patients with plasma IL-6 ≥ median [24.7 (16.5 - 38.5) pg/mL] compared to patients with IL-6 < 0.0001) at baseline, but not at 1 year. In contrast, there was a significant correlation between D/P creat and dialysate sIL-6R (rho = 0.39, p < 0.05) at 1 year, but not at baseline. At 1 year, 17 patients with increasing PSTR had higher increases in dialysate IL-6 (28 ± 26 vs -21 ± 78 pg/mL, p < 0.05) and levels of dialysate sIL-6R (693 ± 392 vs 394 ± 274 pg/mL, p = 0.05) compared to patients with stable PSTR (n = 11). Patients who had peritonitis presented higher baseline serum IL-6 concentration (6.8 ± 1.0 pg/mL) compared with patients without peritonitis (4.0 ± 0.6 pg/mL, p < 0.05). Finally, both at baseline and after 1 year, there were significant correlations between plasma and dialysate IL-6 (rho = 0.46, p < 0.05, and rho = 0.40, p < 0.05) respectively. ◆ Conclusions: These findings indicate that, (1) intraperitoneal and systemic inflammation increase in PD patients during the first year of therapy; (2) intraperitoneal and systemic inflammation may be interrelated and the IL-6 system may be the Link; (3) the IL-6 system (both intraperitoneal and systemic) is associated with PSTR, particularly in the early phase of PD treatment, in which small and large solute transport are linked. Signs of a transition between acute and chronic inflammation were observed in the follow-up evaluation. Inflammation may, at least in part, be responsible for the development of a high PSTR, and this could be one reason for the high mortality in patients with high PSTR. Copyright © 2006 International Society for Peritoneal Dialysis.