Résumé
Growth hormone secretagogues (GHSs) exert multiple actions of interest in Duchenne muscular dystrophy (DMD), such as controlling inflammation and metabolism via GHS-R1a activation, enhancing GH/IGF-1 mediated myogenesis, and inhibiting angiotensin-converting enzyme (ACE). Our study aims to provide preclinical evidence for potential benefits of GHSs in DMD, via a multidisciplinary in vivo/ex vivo comparison of two ad hoc synthesized compounds with wide but different profile (EP80317 and JMV2894) in mdx mice, paralleled by in vitro assays on wild type (WT; H2K-2B4) and dystrophic (H2K-SF1) cell-lines. Four-week-old mdx mice were treated for 8 weeks (T0-T8) with EP80317 or JMV2894 (320 µg/kg/d, s.c.). WT and dystrophic myoblasts were treated with EP80317 or JMV2894 at increasing concentrations and analyzed at 12, 24, and 48-hour time points. In vivo, both GHSs increased mice forelimb force (recovery score toward WT value, RS: 20% for EP80317 and 32% for JMV2894 at T8), and reduced diaphragm (DIA) ultrasound echodensity (RS: 69% and 75%, respectively), whilst only EP80317 improved DIA amplitude (RS: 110%). Ex vivo, both drugs ameliorated DIA isometric contraction (e.g. RS: 40% for tetanic force), with EP80317 also partially preserving mdx DIA response to stretch. Both drugs, especially JMV2894, reduced collagen amount (%, measured via Masson's trichrome stain) in gastrocnemius muscle and mostly in DIA. Gene expression analyses are ongoing. Drug cytotoxicity was excluded by in vitro assays on both 2B4 and SF1 cell-lines. Preliminary qRT-PCR experiments showed a reduced SF1 commitment to myogenesis as revealed by a reduced time-dependent increase of Pax7, MyoD, myogenin and desmin levels. JMV2894 was the most effective in modulating these markers in differentiating SF1. Moreover, both drugs inhibited ACE activity. We confirmed the multiple actions of GHSs in dystrophic settings and disclosed an anti-fibrotic action of therapeutic interest.