B. A. Potz1, L. A. Scrimgeour1, R. T. Clements1, F. W. Sellke1 1Brown University School Of Medicine,Cardiothoracic Surgery Research,Providence, RI, USA
Introduction: Calpain is an intracellular calcium depedent protease whose activity gets overexpressed in cells during times of stress. Calpain overexpression has been linked to myocardial ischemic disease and organ dysfunction in patients with metabolic syndrome. Calpain overexpression is implicated in mitochondrial damage leading to tissue oxidative stress. The purpose of this study was to investigate the potential ability of calpain inhibition on mitochondrial impairment and oxidative stress in a swine model of chronic coronary ischemia in the setting of metabolic syndrome.
Methods: Yorkshire swine were divided into 3 groups, fed a high cholesterol diet for 4 weeks, then underwent surgical placement of an ameroid constrictor to their left circumflex artery. Three weeks later animals received either: no drug, high cholesterol control group (CON; n= 8); a low dose calpain inhibitor (0.12 mg/kg; LCI, n= 9); or high dose calpain inhibitor (0.25 mg/kg; HCI, n= 8). The diets and CI was continued for 5 weeks then the heart was harvested for analysis. OxyBlot which measures protein carbonyl content (Billerica, MA) was used to determine oxidative stress. Western Blot was used to identify protein expression (all data was normalized to GAPDH for loading control).
Results: Calpain inhibition was associated with decreased oxidative stress compared to the control group in the ischemic tissue. There was no change in oxidative stress between groups in the nonischemic tissue. [Figure 1A] In the ischemic myocardial tissue, calpain inhibition was associated with increased expression of the following mitochondrial proteins compared to the control group: the mitochondrial antioxidant protein superoxide dismutase 1; the electron transport chain protein succinate:quinone oxidoreductase; and the citric acid cycle protein pyruvate dehydrogenase. There was no change in expression between groups prohibitin 1 (p=0.13) and cytochrome c (p=0.15). [Figure 1B]
Conclusions: In the setting of metabolic syndrome, CI improved oxidative stress in the ischemic myocardial tissue and was associated with increased expression of mitochondrial proteins involved in 1) reducing superoxide radicals and 2) promoting the citric acid cycle and the electron transport chain. Calpain inhibition had no effect on oxidative stress in the non-ischemic myocardium. The results of the present study demonstrate the potential ability of calpain inhibition to improve myocardial oxidative stress and suggests that the mechanism through which this beneficial effect is taking place is through the mitochondria.
