The Synergistic Effect of Low-Frequency Ultrasound Combined with Spironolactone for Reduction of Fibrosis after Myocardial Infarction in Rats

Background: Myocardial infarction (MI) is a major cause of myocardial collagen deposition leading to left ventricular remodeling and heart failure. The renin-angiotensin-aldosterone system (RAAS) plays a major role in ventricular remodeling. Post MI, spironolactone attenuates cardiac remodeling and subsequent fibrosis. We hypothesized that non-invasive transcutaneous therapeutic ultrasound (TUS) at a frequency of 1 MHz and intensity of 0.5 W/cm² with the addition of an aldosterone inhibitor may affect collagen deposition early after MI.

Methods: After echocardiographic evaluation rats underwent MI induction procedure. Subsequently rats were treated either by daily spironolactone, TUS (3 times a week) or their combination. Control rats were not treated. We re-evaluated cardiac function two weeks after treatment initiation and at the end of the experiments (4 weeks). We performed histological and biochemical evaluation of fibrosis after sacrifice.

Results: The basal ejection fraction (EF, 70±2%) deteriorated following MI induction to 36±3% (Pvs. baseline). TUS treatment alone did not significantly improve EF 4 weeks after MI (45±3%). Spironolactone alone increased the EF to 50±2%, (Pvs. control). A synergistic effect was observed in the dual treatment as EF increased to 54±3% (Pvs. control). On histology, we found a significant reduction in collagen deposition (Pvs. control) following spironolactone or the dual treatment (Pvs. control).

Conclusions: This study demonstrates a positive effect of spironolactone on myocardial collagen content post MI, as well as a synergistic effect of spironolactone with transcutaneous TUS.

Figure 1: Representative histological specimens of cardiac muscles stained with Tri-chrome Masson`s (first and third rows), and Picro-Sirius red stain (second and fourth rows). Specimens in the first 2 rows were taken from scar areas, and the lower 2 rows were taken from remote areas. Each column represents the designated treatment. (X10 magnification).

Figure 2: Quantification of collagen volume fraction in specimens taken from (A) Remote areas and (B) Scar areas. Left panel quantification from Tri-chrome Masson`s stained specimens. Right panel quantification from Picro-sirius red stained specimens. * Pvs. control, ** Pvs. control, *** Pvs. control.