Abstract

One of the most widely used methods of treating oncological patients is ionizing radiation therapy. Radiation beam causes damage to the cancer cells which can reduce cancerous mass and leads to recovery of the oncological patients. On the other hand irradiation of other nearby tissues like myocardium can cause some damage which can induce serious health problems leading to the heart ischemia and heart failure. The aim of this work was to study the morphological changes and changes in molecular markers six weeks after irradiation with a single dose of 25 Gy, applied to mediastinal region of Wistar male rats. Irradiated myocardium was examined for PPAR-alpha and miRNA gene expression levels. Changes in ventricular myocardium were studied using electron microscopy. CRP (C - reactive protein) levels were monitored from blood serum of irradiated and non-irradiated rats. Six weeks after chest irradiation, electron microscopy revealed increased left ventricular capillary density and oedema, activation and or degeneration of endothelial cells and presence of inflammatory cells. Surprisingly, CRP levels in irradiated rats were about 50% lower than in the healthy rats, although CRP plays a major role in acute phase inflammation. This finding suggests the existence of compensatory phase or defence mechanisms in subacute phase of irradiated rats. The irradiated rats exhibited lower expression of PPAR-alpha (Peroxisome Proliferator-activated Receptor alpha) than the control ones. This indicates a shift in substrate preferences from fatty acids to glucose. Expression of microRNA-15b in irradiated rat myocardium was significantly decreased compared with that in normal hearts. Therefore, it can be assumed that irradiated hearts were probably protected by activation of some adaptive mechanism. Despite deleterious effects of irradiation on the myocardium, the results indicate that protective mechanisms maintaining the physiological function are activated in early phase of radiation injury.

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