Membrane sealant Poloxamer P188 protects against isoproterenol induced cardiomyopathy in dystrophin deficient mice

Abstract

Background: Cardiomyopathy in Duchenne muscular dystrophy (DMD) is an increasing cause of death in patients. The absence of dystrophin leads to loss of membrane integrity, cell death and fibrosis in cardiac muscle. Treatment of cardiomyocyte membrane instability could help prevent cardiomyopathy.

Methods: Three month old female mdx mice were exposed to the β(1) receptor agonist isoproterenol subcutaneously and treated with the non-ionic tri-block copolymer Poloxamer P188 (P188) (460 mg/kg/dose i.p. daily). Cardiac function was assessed using high frequency echocardiography. Tissue was evaluated with Evans Blue Dye (EBD) and picrosirius red staining.

Results: BL10 control mice tolerated 30 mg/kg/day of isoproterenol for 4 weeks while death occurred in mdx mice at 30, 15, 10, 5 and 1 mg/kg/day within 24 hours. Mdx mice tolerated a low dose of 0.5 mg/kg/day. Isoproterenol exposed mdx mice showed significantly increased heart rates (p < 0.02) and cardiac fibrosis (p < 0.01) over 4 weeks compared to unexposed controls. P188 treatment of mdx mice significantly increased heart rate (median 593 vs. 667 bpm; p < 0.001) after 2 weeks and prevented a decrease in cardiac function in isoproterenol exposed mice (Shortening Fraction = 46 ± 6% vs. 35 ± 6%; p = 0.007) after 4 weeks. P188 treated mdx mice did not show significant differences in cardiac fibrosis, but demonstrated significantly increased EBD positive fibers.

Conclusions: This model suggests that chronic intermittent intraperitoneal P188 treatment can prevent isoproterenol induced cardiomyopathy in dystrophin deficient mdx mice.

Figure 1

P188 treated, isoproterenol exposed and isoproterenol exposed mdx mice show significantly increased percent shortening fraction (%SF) compared to untreated mdx controls after 2 weeks of therapy.

Figure 2

P188 treated, isoproterenol exposed mdx mice show significantly increased percent shortening fraction (%SF) compared to isoproterenol exposed mdx mice and untreated controls after 4 weeks of therapy.

Figure 3

Representative cross-sectional tissue slices of hearts stained with picrosirius red show minimal fibrosis in untreated mdx hearts (mean 1% collagen; Panel A) and significantly increased fibrosis in mdx hearts exposed to 0.5 mg/kg/day isoproterenol for 4 weeks (mean 3.0% collagen; Panel B) and in mdx hearts exposed to 0.5 mg/kg/day isoproterenol and treated with P188 for 4 weeks (mean 2.9% collagen; Panel C). Staining is consistent with patchy fibrosis patterns seen in older mdx mice