SUN-171 PRETREATMENT WITH LOW DOSE LIPOPOLYSACCHARIDE PREVENTS ISCHEMIA-REPERFUSION INDUCED RENAL VASCULAR CONGESTION IN WKY RATS.

Abstract

Our lab has previously shown red blood cell (RBC) congestion in the renal outer medulla is critical in determining the recovery of renal function following ischemia-reperfusion (IR). While pre-conditioning with lipopolysaccharide (LPS) has been reported to provide protection against IR-induced tubular injury, the effect of low dose LPS on renal medullary congestion has not been directly examined. We hypothesized prior exposure to low dose LPS would induce mild inflammation, promote rouleaux and increase RBC congestion following IR. Study 1: LPS dose response in 10wk old male Wistar-kyoto rats (WKY). Rats were injected (i.p.) with either 10 (n=3), 100 (n=3), 1000 (n=6) ug/kg LPS or saline (n=5) once daily for 7 days prior to IR. Low dose LPS concentrations are less than 1/10th of the dose reported to cause hemodynamic dysfunction. Study 2: Preconditioning vs acute low dose LPS in male WKY. Rats were treated with either 1) 1 injection (i.p) of LPS (1000ug/kg, n=3) or saline (n=3) 24h prior to IR, 2) daily injection of LPS (1000ug/kg, n=4) or saline (n=4) for 3 days prior to IR, or 3) daily injections of LPS (1000ug/kg, n=5) or saline (n=4) for 7 days prior to IR. Following pretreatment, all animals were anesthetized for 30min (Study 1) or 45min (Study 2) ischemia with 24h reperfusion, and humanely sacrificed. Kidneys were collected for histological analysis of RBC congestion (blinded scoring scale 0-5) and tubular injury (blinded, 0-100%). Blood was collected at baseline, pre-IR, and sacrifice for measurement of C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), blood urea nitrogen (BUN), and serum creatinine (SCr). Study 1: CRP and ESR measurements indicated modest inflammation and rouleaux formation in LPS (1000 ug/kg) pretreated animals (ESR: 5.9mm±1.2) compared to control (ESR: 3.2mm±1.4). Most striking, medullary peritubular congestion showed LPS pretreatment dose dependently attenuated congestion when compared to saline treated controls (Fig. 1). Study 2: Preconditioning with low dose LPS (1 injection daily for 3 or 7days) induced mild inflammation and reduced RBC congestion in the renal medulla (7 day congestion score: LPS 1.3±0.94, control 3.5±0.54). In these same animals, tubular injury showed no difference between LPS and control groups (p= 0.397). In contrast, a single, acute injection of low dose LPS 24h prior to IR demonstrated similar renal medullary RBC congestion as saline injected animals (Congestion score: LPS 3.2±0.83, control 2.2±1.09). We conclude that despite promoting inflammation, and rouleaux, 3-7days of pretreatment with low dose LPS attenuates RBC congestion in the renal medulla following IR. The effect appears to be largely independent of tubular injury, suggesting the phenomenon is not secondary to reduced parenchymal damage. As sustained congestion and hypoxia following IR may lead to progressive renal injury in the medulla after renal blood flow and GFR returns towards normal, understanding the mechanisms by which low dose LPS prevents renal congestion may lead to novel therapeutic approaches to improve recovery from ischemic acute kidney injury.