Nanoparticle delivery of AMPK activator 991 prevents its toxicity and improves muscle homeostasis in Duchenne muscular dystrophy

Muscular dystrophies, such as Duchenne muscular dystrophy (DMD), are caused by permanent muscle injuries leading to chronic inflammation, with macrophages harboring an altered inflammatory profile contributing to fibrosis through the secretion of transforming growth factor β1 (TGF-β1). We previously showed that AMP-activated protein kinase (AMPK) activation reduces TGF-β1 secretion by macrophages and improves muscle homeostasis and muscle force in a DMD mouse model. However, direct AMPK activators like compound 991 show strong adverse effects in vivo. To overcome this toxicity, we encapsulated 991 into biodegradable polymeric poly(lactic-co-glycolic) acid (PLGA) nanoparticles for in vivo delivery. We show that 991-loaded PLGA nanoparticles retained drug activity on fibrotic macrophages in vitro and in vivo. In the D2-mdx DMD mouse model, intravenously injected PLGA nanoparticles reached macrophages in gastrocnemius and diaphragm muscles, two severely affected muscles in this model, but not in heart and quadriceps. Chronic intravenous injections of 991-loaded PLGA nanoparticles decreased inflammation in both gastrocnemius and diaphragm, which was associated with TGF-β1 level and fibrosis reduction and increase in myofiber size and muscle mass in the gastrocnemius, without toxicity. These results demonstrate that nanomedicine is an efficient strategy to deliver AMPK activators in vivo to target inflammation and improve the dystrophic muscle phenotype in the gastrocnemius.