Effect of Low-Frequency Non-Invasive Therapeutic Ultrasound on Attenuation of Cardiac Fibrosis Early After Myocardial Infarction in Rats

Abstract

Background: Myocardial infarction (MI) results in collagen deposition leading to left ventricular dysfunction. Therapeutic ultrasound (TUS) has proven anti-fibrotic effects on various tissues. We hypothesized that non-invasive TUS will attenuate fibrosis by downregulation of the transforming growth factor β1 (TGF-β1)/ small mother against decapentaplegic 3 (smad3) pathway in a rat model of MI. Methods: Rats underwent MI induction procedure after performing baseline cardiac echocardiography. Subsequently, we treated the rats with either daily spironolactone (a known anti-fibrotic agent), TUS (at 1 MHz frequency and 0.5 W/cm2 intensity, 3 times a week) or their combination (spironolactone + TUS). Control rats were not treated. We re-evaluated cardiac function at 2 and 4 weeks after treatment initiation (before sacrifice), then performed histological and biochemical evaluation of fibrosis. Results: Any treatment combination attenuated fibrosis, as seen in histology and by chemical analysis, and reduced TGF-β1 expression. Specifically, collagen volume fractions were 16.0±9.6%, 5.0±3.2%, 7.2±1.0% and 1.6±0.9%, and TGF-β1 expression were 3.34±0.36%, 0.77±0.37%, 0.59±0.25% and 0.39±0.16%, in the control (untreated group), spironolactone. TUS and spironolactone + TUS groups, respectively (P<0.05 vs. control for all). Yet, only spironolactone treatments affected also smad3 expression, and cardiac physiology, i.e., final ejection fraction were 36.0±2.5%, 50.1±2.3%, 45.2±2.5% and 54.0±2.7% in the control (untreated group), spironolactone. TUS and spironolactone + TUS groups, respectively (P<0.05 vs. control for spironolactone and spironolactone + TUS only). Conclusion: Post MI, TUS reduces myocardial collagen, fibrosis and TGF-β1 content. Only with the addition of spironolactone cardiac function was preserved. Further research is needed in order to refine and upgrade TUS to affect cardiac physiology early post MI.