[Expression of receptors for advanced glycation end products at surface of peripheral blood monocytes and relationship thereof to plasma proinflammatory cytokines in patients undergoing hemodialysis]

Abstract

Objective: To elucidate the relationship between the expression of receptors for AGE (RAGE) at the surface of monocyte and the plasma levels of tumor necrosis factor alpha (TNFalpha) and interleukin-1beta (IL-1beta), proinflammatory cytokines in patients with chronic renal failure (CRF) undergoing hemodialysis (HD).

Methods: Human serum albumin modified with AGE (AGE-HSA) was prepared in vitro and was radiolabeled with (125)I. Human peripheral blood monocytes were isolated from 59 CRF patients (37 of which underwent hemodialysis) and 30 normal volunteers by Ficoll-hypaque centrifugation technique. Specific binding of AGE-HSA to monocytes was analyzed by radioactive ligand-receptor binding assay. The degradation to AGE-HSA by monocytes was measured by trichloroacetic acid precipitation method. The expression of REGE in monocytes was determined by flow cytometry. The levels of TNFalpha and IL-1beta were detected by a sandwich enzyme immunoassay.

Results: The specific binding of (125)I-AGE-HSA to monocytes was 41.4 fmol/10(5) cells +/- 2.2 fmol/10(5) cells, significantly higher than that in normal controls (31.6 fmol/10(5) cells +/- 4.1 fmol/10(5) cells, P < 0.05). The number of AGE conjugated protein at the monocytes' surface of CRF patients undergoing HD was 2.42 +/- 0.21 x 10(5)/cells, significantly higher than that in normal controls (1.74 +/- 0.29 x 10(5)/cells, P < 0.001), and the affinity constant (Kd) of the monocytes of CRF patients undergoing HD was 228 nmol/L +/- 100 nmol/L, not significantly different from that in normal controls (262 nmol/L +/- 108 nmol/L, P > 0.05). The degration rate of AGE-HAS by monocytes in CRF patients undergoing HD was 25.24% +/- 4.35%, significantly higher than that in normal controls (18% +/- 0.6%, P < 0.05). The fluorescent intensity of RAGE at the surface of monocytes in CRF patients undergoing HD was 3.68 +/- 0.42, significantly higher than that in normal controls (1.09 +/- 0.37, P < 0.05), When the monocytes were incubated in vitro with 50 microgram/ml of AGE-HSA, the levels of TNFalpha and IL-1beta in the supernatants of CRF patients undergoing HD were 197 +/- 98 ng/L and 357.0 +/- 140.1 ng/L respectively, both significantly higher than those in the normal controls (111 +/- 77 ng/L and 184 +/- 118 ng/L respectively, both P < 0.05). The secretion of proinflammatory cytokines was inhibited when the monocytes were preincubated with anti-RAGE. Increased RAGE level was accompanied by higher plasma levels of TNFalpha and IL-1beta.

Conclusion: The expression of AGE receptors in monocytes is up-regulated in patients with CRF. This may contribute to the enhanced plasma level of proinflammatory cytokines seen in HD patients.