Up-regulation of HO-1 attenuates left ventricular remodeling post myocardial infarction in rats
Tee, Rebecca E.
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Background/Objective: Reperfusion injury is a serious consequence of blood flow reestablishment after myocardial infarction (MI) mediated by reactive oxygen species and neutrophilic cellular damage. Following MI, the left ventricle (LV) undergoes remodeling characterized by progressive wall thinning and cavity dilatation. Heme-Oxygenase-1 (HO-1) dependent decrease in oxidative stress may attenuate injury in part by inhibiting transcription factor NFκB-mediated inflammation. Hypothesis: I hypothesized that upregulation of HO-1 by hemin administration confers acute and chronic cardioprotection against I/R injury in rats and attenuates LV remodeling post-MI. I proposed the HO-1-dependent decrease in oxidative stress attenuates post-ischemic myocardial injury in part by inhibiting NFκB-mediated inflammation. Methods: Six week old male Wistar rats were randomly assigned to sham, vehicle, or hemin-treated groups. Vehicle and hemin were administered intraperitoneally once daily for 3 consecutive days prior to left anterior descending (LAD) coronary artery occlusion. Administration resumed 48 hours post-operatively and continued once every 3 days. Infarct size was determined by H&E histological analysis and fibrosis was quantified by Masson’s Trichrome staining. Transthoracic echocardiography was used to assess LV parameters and wall motion. Results: Hemin increased HO-1 expression, decreased infarct size and fibrosis, and attenuated LV remodeling in the short-term (4 days post-infarction). The decrease in infarct size and area of fibrosis in the hemin group was accompanied by a decrease in NFκB activity. No significant difference in infarct size and area of fibrosis between hemin and vehicle-treated groups was observed at 3 months. LV diameter and cardiac function did not differ significantly between the two groups at 3 months despite an attenuation of anterior wall thinning in the hemin group. Conclusion: HO-1 upregulation by hemin administration conferred acute cardioprotection and attenuated LV remodeling, possibly by inhibiting NFκB-mediated inflammation. However, chronic treatment with hemin did not prevent long-term post-infarction LV remodeling. It is possible that cardioprotection afforded by HO-1 upregulation is strong enough to curtail inflammation post-reperfusion and prevent LV remodeling acutely, but is not robust enough to protect the myocardium to the same degree in the long-term. Future research should focus on optimal HO-1 upregulation to attenuate long-term LV remodeling due to reperfusion injury.