Losartan decreases cardiac muscle fibrosis and improves cardiac function in dystrophin-deficient mdx mice

Abstract

Recent studies showed that chronic administration of losartan, an angiotensin II type I receptor antagonist, improved skeletal muscle function in dystrophin-deficient mdx mice. In this study, C57BL/10ScSn-Dmd(mdx)/J female mice were either untreated or treated with losartan (n = 15) in the drinking water at a dose of 600 mg/L over a 6-month period. Cardiac function was assessed via in vivo high frequency echocardiography and skeletal muscle function was assessed using grip strength testing, Digiscan monitoring, Rotarod timing, and in vitro force testing. Fibrosis was assessed using picrosirius red staining and Image J analysis. Gene expression was evaluated using real-time polymerized chain reaction (RT-PCR). Percentage shortening fraction was significantly decreased in untreated (26.9% ± 3.5%) mice compared to losartan-treated (32.2% ± 4.2%; P < .01) mice. Systolic blood pressure was significantly reduced in losartan-treated mice (56 ± 6 vs 69 ± 7 mm Hg; P < .0005). Percentage cardiac fibrosis was significantly reduced in losartan-treated hearts (P < .05) along with diaphragm (P < .01), extensor digitorum longus (P < .05), and gastrocnemius (P < .05) muscles compared to untreated mdx mice. There were no significant differences in skeletal muscle function between treated and untreated groups. Chronic treatment with losartan decreases cardiac and skeletal muscle fibrosis and improves cardiac systolic function in dystrophin-deficient mdx mice.

Figure 1

Significantly decreased fibrosis and myocyte cross-sectional area in the hearts of losartan-treated mdx mice compared to untreated mdx mice. Panel A shows a cross-section of an untreated mdx heart with the left ventricle (LV) and right ventricle (RV) labeled. The section is stained with picrosirus red, which colors collagen red. The image corresponds to 12.5% fibrosis (not log transformed data). Panel B shows a cross-section of a losartan-treated mdx heart at a similar level to Panel A. The image corresponds to 5.6% fibrosis (not log transformed data). Panel C is a representative image of untreated mdx left ventricular tissue with WGA staining. Measurement of the myocyte cross-sectional area (representative cells marked with *) shows increased area compared to losartan-treated mdx left ventricular tissue (Panel D).

Figure 2

High frequency echocardiography M-mode images of untreated (A) and losartan-treated (B) hearts. The arrows on the left in each panel show the left ventricular internal diameter (LVID) in diastole and the arrow on the right shows the LVID in systole. Panel A corresponds to a percentage shortening fraction (%SF) of 24% and panel B corresponds to a %SF of 31% (%SF = LVID diastole – LVID systole/LVID diastole).