A PPARγ agonist reduces proinflammatory cytokine immunoreactivity and infarct size following transient focal ischemia in rats
Inflammation plays a critical role in the generation of ischemic injury. Ischemic insult results in the activation of microglia and secretion of proinflammatory products including the cytokines interleukin-1β and tumor necrosis factor-α. Both of these cytokines exacerbate ischemic injury. Microglial proinflammatory gene expression is regulated by the transcription factor peroxisome proliferator activated receptor (PPAR). PPARγ is a member of the nuclear hormone receptor family and upon binding of agonist acts to inhibit proinflammatory gene expression. We hypothesized that PPARγ agonists reduce the inflammatory reaction seen following stroke and limit infarction size. We utilized a reversible model of middle cerebral artery occlusion to induce two hours of ischemia in rats to test our hypothesis. Blood pressure, blood gases and temperature were monitored and maintained within normal ranges throughout the procedure. Vehicle (DMSO) or troglitazone, a PPARγ agonist previously approved by the FDA, was administered to rats twenty-four hours before and again at the time of occlusion in doses of 35, 70 or 100 mg/kg in DMSO. Twenty-four hours after occlusion animals were euthanized. Infarct volume was calculated from fixed frozen sections and additional sections were processed for immunocytochemistry. Results show over sixty percent reduction in infarct volume in rats treated with 35 mg/kg and 70 mg/kg troglitazone. These data were statistically significant (n≥5;p<0.05). Interestingly the 100 mg/kg dose of troglitazone did not protect against ischemia. Immunoreactivity against the proinflammatory cytokines Il-1β and TNFα was reduced in the peri-infarct region of troglitazone treated rats. Furthermore, immunoreactivity against other markers of inflammation, intracellular adhesion molecule, major histocompatibility complex antigen I and cyclooxygenase-2 was also reduced in troglitazone treated animals compared with vehicle treated animals. These data indicate that the PPARγ agonist, troglitazone, reduces infarct size following cerebral ischemia likely due to the drug’s anti-inflammatory properties.