Uremic toxins have been suggested to promote progression of chronic renal failure by damaging tubular cells. Previous in vitro studies have indicated that some uremic toxins induce oxidative stress and activate NF-ĸB to upregulate plasminogen activator inhibitor-1 in tubular cells. These mechanisms may promote tubulointerstitial fibrosis. The present study examined whether uremic toxins induce glomerular and tubulointerstitial damage in vivo. Two uremic toxins, hippuric acid (HA) or indoleacetic acid (IAA), were tested in two independent experiments (HA-treated rats vs. non-HA-treated controls, IAA-treated rats vs. non-IAA-treated controls). The uremic toxins were administered to subtotally nephrectomized rats. Renal functions were measured periodically and glomerular sclerosis and interstitial fibrosis were examined at the end of the experimental period (18 and 24 weeks, respectively, after subtotal nephrectomy for HA and IAA treatments). Glomerular filtration rate (inulin clearance) at the end of the study period was significantly lower in uremic toxin-treated rats than in control rats (HA-treated rats: 0.090 ± 0.004 ml/min/100 g body weight vs. non-HA-treated controls: 0.125 ± 0.013, IAA-treated rats: 0.068 ± 0.006 versus non-IAA-treated controls: 0.100 ± 0.013; both p < 0.05). Beta-N-acetyl-glucoseamidase excretion was significantly higher in uremic toxin-treated rats than in control rats (HA-treated: 0.55 ± 0.05 U/day vs. control: 0.39 ± 0.04 at week 18, IAA-treated: 0.35 ± 0.02 vs. control: 0.26 ± 0.07 at week 16; both p < 0.05). Glomerular sclerosis index was significantly higher in uremic toxin-treated rats than in control rats (HA-treated: 0.85 ± 0.16 versus control: 0.48 ± 0.10, IAA-treated: 1.13 ± 0.25 vs. control: 0.57 ± 0.10; both p < 0.05). Significant enlargement of interstitial fibrosis was observed in indoleacetic acid-treated rats. These results indicate that overload of uremic toxins accelerates the loss of kidney function, glomerular sclerosis and tubulointerstitial injury in a rat model of chronic renal failure. The present study suggests the potential benefit of early intervention to remove various uremic toxins in delaying the onset of end-stage renal failure in patients with progressive renal disease.
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