Abstract Body (Do not enter title and authors here): Background/Introduction:
Microvascular obstruction (MVO), due to damage to the coronary microvasculature, is a key determinant of infarct size, heart failure and poor outcomes following acute myocardial infarction, and there is currently no treatment for preventing MVO. Real-time in vivo imaging of MVO in the beating rodent heart is challenging due to the limited spatial and temporal resolution from movement artifacts. Here, we apply, for the first time, fiber-optic confocal laser endomicroscopy (CLM) for real-time imaging of the microvasculature in a beating murine heart with acute ischemia/reperfusion injury (IRI), and then monitoring the development of MVO.
Methods:
An in vivo murine acute myocardial IRI model (45 min ligation of left coronary artery (LCA) and 30 min reperfusion) was applied. At 10 min prior to ischaemia, 150 µl Dextran-FITC (150 kDa, 10 mg/ml) was injected retro-orbitally, and then CLM imaging with a flexible miniprobe (ProFlex S-1500 with CellVizio system) was applied to the epicardial surface at multiple sites at 5 min post-injection (baseline), 30 min post-ischemia and 30 min post-reperfusion. A nitric oxide donor(NO) nanoparticle (NONP) was synthesized and IV bolus injected into IRI mice 5min prior to reperfusion to prevent MVO.
Results:
We confirmed visualization of the macro- and microvasculature at various sites on the epicardial surface of the beating heart. Next, we observed reduced microvasculature blood flow below LCA ligature as evidenced by reduced or even totally absence of FITC within the vessels at 30min post-ischemia. The microvasculature at the non-ischemic myocardium was unaffected. Furthermore, at 30 min post-reperfusion, we visualised patchy areas of reduced FITC signal suggesting MVO, and damaged microvasculature as evidenced by leakage of FITC outside the vessel. Interestingly, NONP treatment preserved the microvascular network and prevented MVO at 30 min post-reperfusion with even greater FITC, suggesting increased microvascular blood flow and penetration into cardiac tissue because of the vasodilatory effect of NO in the ischemic area.
Conclusion:
With CellVizio CLM system, we have demonstrated the MVO development during IRI, and damage to the microvasculature with leakage of dye from vessels into cardiac interstitium, thereby providing a pre-clinical platform to test novel therapeutic agents for preventing MVO. Importantly, we have shown an effective MVO prevention with NO-donor nanoparticle following IRI in mice.