Fluorescence spectroscopy and imaging of myocardial apoptosis

Abstract

Fluorometry is used to detect intrinsic flavoprotein (FP) and nicotinamide adenine dinucleotide (NADH) signals in an open-chest rabbit model of myocardial ischemia-reperfusion injury. Myocyte apoptosis has been shown clinically to contribute to infarct size following reperfusion of ischemic myocardium. A noninvasive means of assessing apoptosis in this setting would aid in the treatment of subsequent ventricular remodeling. We show that in vivo fluorometry can be useful in apoptosis detection in open-chest surgeries. Specific changes in myocardial redox states have been shown to indicate the presence of apoptosis. Two main mitochondrial intrinsic fluorophores, NADH and FP signals, were measured during normoxia, ischemia, and reperfusion experimental protocol. Ischemia was induced by occlusion of the largest branch of the circumflex coronary artery and fluorescence signals are collected by applying two different fluorescence techniques: in vivo fluorometry and postmortem cryoimaging. The first technique was employed to detect FP and NADH signals in vivo and the latter technique uses freeze trapping and low-temperature fluorescence imaging. The heart is snap frozen while still in the chest cavity to make a "snapshot" of the metabolic state of the tissue. After freezing, the ischemic area and its surrounding border zone were excised and the sample was embedded in a frozen buffer for cryoscanning. These two data sets, in vivo fluorometry and low-temperature redox scanning, show consistent extreme oxidation of the mitochondrial redox states (higher redox ratio) suggesting the initiation of apoptosis following reperfusion. This represents the first attempt to assess myocyte apoptosis in the beating heart.