Acute administration of metformin prior to cardiac ischemia/reperfusion injury protects brain injury

Myocardial ischemia is the malperfusion of cardiac tissue due to a blockage in a coronary artery. Subsequent return of blood flow to the ischemic area of the heart, results in ischemia/reperfusion (I/R) injury in the heart and other organs, including the brain. Besides the cardioprotective effects of metformin on the heart against cardiac I/R injury, metformin also reduced neuronal injury in a stroke model. However, the effects of metformin on the brain following cardiac I/R injury has not yet been investigated. Therefore, we hypothesize that metformin reduces brain damage via decreasing brain mitochondrial dysfunction, microglial hyperactivity, and Alzheimer's proteins in rats after cardiac I/R injury. Rats (n = 50) received either a sham operation (n = 10) or cardiac I/R (n = 40). Cardiac I/R was induced by 30 min of cardiac ischemia, followed by 120 min of reperfusion. Rats in cardiac I/R group were divided into 4 groups (n = 10/group); vehicle, metformin 100 mg/kg, metformin 200 mg/kg, and metformin 400 mg/kg. Metformin was given via femoral vein at 15 min prior to cardiac ischemia. At the end of reperfusion, brains were removed to determine dendritic spine density, brain mitochondrial function, microglial morphology, and amyloid beta formation. Cardiac I/R injury led to brain mitochondrial dysfunction, microglial hyperactivation, amyloid beta formation, Tau hyperphosphorylation, and reduced dendritic spine density with an increase in AMPK activation. All doses of metformin improved brain pathologies in rats with cardiac I/R injury possibly via activating cerebral AMPK. In summary, pre-treatment with metformin offers neuroprotection against the brain damages caused by cardiac I/R injury.