Tempol Improves Renal Autoregulation and Kidney Function Following Ischemia‐Reperfusion Injury in Rats

Abstract

Renal ischemia‐reperfusion (IR) induced acute kidney injury is characterized by inflammation, oxidative stress, increased renal vascular resistance, and reduced glomerular filtration rate. Our previous study revealed that renal autoregulation was impaired in IR, but restored with acute exposure to ROS scavengers or NADPH oxidase inhibitor. Accordingly, we postulated that chronic treatment with the superoxide dismutase mimetic Tempol would improve renal autoregulatory capacity and kidney function following kidney IR. IR was induced by 60‐minute bilateral renal artery occlusion. IR rats were treated with or without Tempol (25 mg/kg/day) in drinking water over a 7‐day period following surgery. Afferent arteriole autoregulatory behavior was assessed in vitro using blood‐perfused juxtamedullary nephrons (n = 6–7/each groups). Afferent arterioles from sham‐operated rats exhibited pressure‐dependent vasoreactivity. Baseline diameter averaged 13.4 ± 0.5 μm at a renal perfusion pressure (RPP) of 100 mmHg and increased to 117 ± 4% of baseline at RPP of 65 mmHg and decreased to 69 ± 2% at RPP of 170 mmHg, respectively. Afferent arterioles from IR rats however, only increased to 104 ± 2% and decreased to just 91 ± 5% of baseline (11.7 ± 0.6 μm) at 65 and 170 mmHg, respectively (P < 0.05 vs sham), indicating persistently impaired autoregulatory capacity. In contrast, Tempol‐treated IR rats exhibited normal autoregulatory function as the pressure‐diameter profile was similar to the shams. Afferent arterioles diameter increased to 109 ± 2% of baseline (13.3 ± 0.9 μm) and decreased to 69 ± 4% at RPP of 65 and 170 mmHg, respectively (P > 0.05 vs. sham). Preglomerular microvessels (PGMV) were collected from one set of sham, IR and IR+Tempol rats (n = 8 rats/group) on day 7 following IR. Steady‐state mRNA of NADPH oxidase subunits, MCP‐1 and TGF‐β in these PGMV were markedly elevated in IR compared to sham rats. The NADPH oxidase subunits, p67phox and p47phox but not p22phox, were increased by 4.5 and 3‐fold respectively in IR vs. sham (P < 0.05). MCP‐1 mRNA increased 6.7‐fold and TGF‐β 4–fold compared to sham (P < 0.05). Tempol treatment significantly suppressed the IR‐induced increase in mRNA expression of all measured markers. Glomerular filtration rate (GFR) was assessed in conscious rats using a transdermal non‐invasive clearance device with intravenous injection of FITC‐sinistrin on day 0 and day 7. GFR remained constant (1.0–1.4 mL/min/100g, n=6) in sham. On day 7 after IR, GFR was 0.27 ± 0.17 mL/min/100g (n=6, P < 0.05 vs sham) in untreated rats, and was 0.60 ± 0.12 mL/min/100g in Tempol‐treated IR rats (n=4, P > 0.05 vs sham). Tempol treatment also significantly reduced albuminuria. These results demonstrated that chronic Tempol treatment ameliorated IR‐induced chronic impairment of autoregulatory capacity and associated increases in expression of NADPH oxidase, MCP‐1 and TGF‐β in PGMV. We conclude that oxidative stress in the renal microvasculature contributed to a persistent lack of functional recovery from severe IR injury.Support or Funding InformationThis study was supported by NIH grants (DK106500 to ZG, and DK044628 and HL095499 to EWI).