Effect of remote ischemic preconditioning on LPS-induced pulmonary inflammation in mice
So Jung Choi, University of Toronto; Ori Rotstein, St. Michael's Hospital
Remote ischemic preconditioning (RIPC) is an intervention that involves application of multiple cycles of ischemia/reperfusion to an extremity. It prevents pulmonary inflammation when applied prior to hemorrhagic shock and resuscitation. The protective effect of RIPC in part comes from the release of a humoral factor(s) that reduces neutrophil migration to the site of injury. As an effective intervention, RIPC may not be limited to ischemia/reperfusion injury, but also exert its protective effects on other inflammatory diseases such as acute lung injury (ALI).Hypothesis:
RIPC treatment is expected to have a protective effect against lipopolysaccharide (LPS)-induced pulmonary inflammation and injury.Methods:
Male C57BL/6 mice (9-12-week-old) were anesthetized via intraperitoneal injection of sodium pentobarbital (70 mg/kg) and subjected to RIPC or sham treatment. RIPC involved 4 cycles of 5-minute ischemia and 5-minute reperfusion being applied to the right hind limb using a tourniquet. Following the intervention or sham treatment, 50 μL of LPS (800 μg/kg) or phosphate-buffered saline was administered intratracheally. Mice were sacrificed and bronchoalveolar lavage (BAL) was performed at 4 hours post‐injection. BAL fluid (BALF) was assessed for quantification of immune cell populations and protein content.Results:
Intratracheal LPS administration caused massive neutrophil infiltration into the alveolar space by 4 hours. BALF neutrophil count was significantly reduced in mice that were conditioned prior to LPS administration (R-LPS=1.52*105 cells/mL, n=8) compared to that of LPS-only mice (LPS=3.79*105 cells/mL, n=8, P<0.05). It was decreased by 25% in the RIPC-LPS group relative to LPS-only group (R-LPS=49%, LPS=74%, n=8, P<0.05). Total leukocyte counts did not differ significantly between groups (sham=4.13*105, LPS=4.90*105, R-LPS=2.83*105, n=4-8, P>0.05). LPS treatment caused a modest increase in BALF protein content in both groups at 4 hours. Although it did not differ significantly between RIPC-LPS (R-LPS=0.095 µg/µl, n=8) and LPS-only (LPS=0.124 µg/µl, n=8, P=0.48) groups, the results exhibited a trend consistent with the hypothesis.Conclusions:
RIPC significantly reduced pulmonary inflammation following challenge with LPS at 4 hours post-injection. Its protective effect may allow application of RIPC as an intervention for the treatment and prevention of ALI as well as other conditions involving inflammation.