Abstract P082: Exposure To Excess Albumin Causes Inflammatory Activation Of The Proximal Tubule.

In previous studies, we used chronic servo control experiments to show that renal inflammation is a secondary event in salt-sensitive hypertension, with pressure amplifying renal immune cell infiltration in Dahl salt-sensitive (SS) rats. In contrast, albuminuria occurs early in the development of hypertension and facilitates its progression. In this study, we tested the hypothesis that albuminuria causes release of pro-inflammatory cytokines in the proximal tubule, which in turn may initiate renal inflammation.We exposed the apical membrane of human proximal tubule cell monolayers (RPTEC-TERT1) to human serum albumin (HSA, 10 mg/ml, n=8) for 24 and 48hrs. Control cells were kept in standard media without HSA (n=8). The concentrations of 47 cytokines were measured in the basolateral (BM) and apical (AM) media using Luminex assays. After 24hrs we found that 18 cytokines were significantly higher in the BM and 14 in the AM relative to controls. At 48hrs, 17 cytokines were significantly higher in the BM and 15 in the AM. Notably, we found significant increases in basolateral release of several chemokines, including CCL2 (24hrs: 6.1±0.9 vs. 40.6±8.9, 48hrs: 20.1±4.5 vs. 85.8±15.6 pg/mg), CXCL1 (24hrs: 1.3±0.3 vs. 39.5±12.2, 48hrs: 3.4±1.1 vs. 94.2±41.4 pg/mg), and IL-8 (24hrs: 1.3±0.4 vs. 11.6±3.7, 48hrs: 2.1±0.5 vs. 10.1±3 pg/mg). We propose that HSA-induced chemokine secretion facilitates immune cell recruitment and the initiation of renal inflammation. To track the progression of albuminuria and proximal tubule injury in SS rats we performed daily urine collections in rats fed either a high-salt (HS, 4.0% NaCl, n=6) or a control-salt (CS, 0.4% NaCl, n=5) diet for 7-days. In SS rats fed HS, albuminuria preceded proximal tubule injury. Urinary albumin was elevated after 2-days of HS (22.6±6.5 vs. 61.1±18.7 mg/day) whereas Kidney Injury Molecule-1 (KIM-1) was increased after 5-days of HS (15.5±1.5 vs. 31.3±5.6 ng/day).To conclude, in vitro exposure to excess albumin causes significant increases in the levels of multiple cytokines involved in the initiation of inflammation. In SS rats fed HS, albuminuria precedes proximal tubule injury. Together these data suggest that albuminuria may facilitate hypertension through the initiation of renal inflammation.