Effect of Low-Level Laser Irradiation on Oxygen Free Radicals and Ventricular Remodeling in the Infarcted Rat Heart

OBJECTIVE: The purpose of this study was to assess the effects of low-level laser irradiation (LLLI) on the expression of oxygen free radicals (OFR) and ventricular remodeling (VR) in the model of rat myocardial infarction (RMMI). BACKGROUND DATA: LLLI reduces the infarct size and formation of scar tissue in the rat heart after myocardial infarction (MI). However, the exact mechanism has not been demonstrated so far. METHODS: RMMI was induced by ligating the left anterior descending coronary artery (LAD). After 3 weeks, LLLI (635 nm, 6 mW laser, 7.64 mW/cm(2), 125 sec, 0.96 J/cm(2)) was applied to the surface of heart directly. Four to six rats were euthanized at 1 h, 24 h, 48 h, 72 h, and 1 week after LLLI, and the infarcted myocardia were excised for the measurement of the activity of superoxide dismutase (SOD) and the content of malondialdehyde (MDA). At the end of 4 weeks after MI, the hearts were harvested for histological analysis. RESULTS: Myocardial SOD activity with LLLI was lower compared with control (p<0.05), and myocardial MDA content with LLLI was higher compared with control (p<0.05), at all the time points. In all rats, the activity of SOD was down to the minimum and the content of MDA was up to the peak at 48 h after laser irradiation. The infarct size was reduced (35±10% vs. 18±9%, p<0.05), the left ventricular wall thickness was increased (0.31±0.03 vs. 0.84±0.02 mm, p<0.05) and the percentage of collagen fibers in the infarcted area was attenuated (64.34±2.20% vs. 30.97±2.60%) by LLLI. CONCLUSIONS: LLLI could cause OFR accumulation, reduce infarct size, increase ventricular wall thickness, and attenuate the formation of collagen fibers, suggesting the beneficial effects of LLLI on improvement of VR after MI.