Progressive muscle injury and weakness are hallmarks of Duchenne muscular dystrophy. We showed previously that quercetin (Q) partially protected dystrophic limb muscles from disease-related injury. As quercetin activates PGC-1α through Sirtuin-1, an NAD+-dependent deacetylase, the depleted NAD+ in dystrophic skeletal muscle may limit quercetin efficacy; hence, supplementation with the NAD+ donor, nicotinamide riboside (NR), may facilitate quercetin efficacy. Lisinopril (Lis) protects skeletal muscle and improves cardiac function in dystrophin-deficient mice; therefore, it was included in this study to evaluate the effects of lisinopril used with quercetin and NR. Our purpose was to determine the extent to which Q, NR, and Lis decreased dystrophic injury. We hypothesized that Q, NR, or Lis alone would improve muscle function and decrease histological injury and when used in combination would have additive effects. Muscle function of 11-mo-old DBA (healthy), D2-mdx (dystrophin-deficient), and D2-mdx mice was assessed after treatment with Q, NR, and/or Lis for 7 mo. To mimic typical pharmacology of patients with Duchenne muscular dystrophy, a group was treated with prednisolone (Pred) in combination with Q, NR, and Lis. At 11 mo of age, dystrophin deficiency decreased specific tension and tetanic force in the soleus and extensor digitorum longus muscles and was not corrected by any treatment. Dystrophic muscle was more sensitive to contraction-induced injury, which was partially offset in the QNRLisPred group, whereas fatigue was similar between all groups. Treatments did not decrease histological damage. These data suggest that treatment with Q, NR, Lis, and Pred failed to adequately maintain dystrophic limb muscle function or decrease histological damage. NEW & NOTEWORTHY Despite a compelling rationale and previous evidence to the contrary in short-term investigations, quercetin, nicotinamide riboside, or Lisinopril, alone or in combination, failed to restore muscle function or decrease histological injury in dystrophic limb muscle from D2-mdx mice after long-term administration. Importantly, we also found that in the D2-mdx model, an emerging and relatively understudied model of Duchenne muscular dystrophy dystrophin deficiency caused profound muscle dysfunction and histopathology in skeletal muscle.
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