Abstract 299: Blockade of Toll-like Receptor 4 During Acute Lipopolysaccharide Treatment Preserves Afferent Arteriolar Autoregulatory Behavior.

Abstract

Lipopolysaccharide (LPS), a component of the bacterial wall of gram-negative bacteria is a ligand for toll-like receptor 4 (TLR4). Immune system activation and generation of reactive oxygen species (ROS) is linked to blunted renal autoregulatory behavior. Accordingly, we hypothesize that blockade of TLR4 during acute LPS treatment preserves afferent arteriolar autoregulatory behavior. Rats received a bolus injection of LPS (1 mg/kg i.p.) and were treated with either anti-TLR4 antibody (1μg; i.p.) or TLR4 receptor antagonist (LPS-RS; 5mg; i.p.). Kidneys were harvested 4 hours later for juxtamedullary nephron studies. Autoregulatory behavior was assessed in these groups by increasing perfusion pressure in 15 mmHg increments from 65 to 170 mmHg. In control kidneys, afferent arteriolar diameter decreased by 29 ± 5% when perfusion pressure was increased from 65 to 170 mmHg. LPS alone (4 hrs.) significantly blunted the autoregulatory response such that afferent arteriolar diameter remains essentially unchanged between 65 (12.4 ± 0.9 μm) and 170 mmHg (12.7 ± 1.2 μm). In kidneys co-treated with LPS and anti-TLR4 antibody, afferent arteriolar diameter decreased by 26 ± 6% (P < 0.05; n=6) during increments in perfusion pressure from 65 to 170mmHg. In kidneys co-treated with LPS and the TLR4 receptor antagonist, LPS-RS, afferent arteriolar diameter decreased by 24 ± 5% (P < 0.05; n=4) over the same pressure range, indicating preservation of pressure-induced vasoconstriction. Reactive oxygen species play a role in blunting rat afferent arteriolar autoregulatory resistance adjustments. Therefore, we assessed autoregulatory behavior in LPS treated kidneys during acute exposure to the superoxide dismutase mimetic, Tempol (10-6 mol/L). In these kidneys, afferent arteriolar diameter decreased by 28 ± 3% (P < 0.05; n=6) indicating restoration of autoregulatory capability. These data indicate that LPS treatment induces TLR4 activation, and stimulates ROS generation. Blocking TLR4 with anti-TLR4 antibody or LPS-RS or scavenging ROS with Tempol preserves and restores afferent arteriolar autoregulatory behavior suggesting that blockade of TLR4 may open novel therapeutic targets for inflammatory kidney disease.