T.P.4 Treatment with oral metformin improves muscle function in mdx mice

Abstract

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease caused by an absence of dystrophin. DMD is caused by out of frame mutations in the dystrophin gene and is characterised by muscle inflammation, necrosis and eventual loss of function of cardiac and skeletal muscle. Slow, oxidative fibres appear to be relatively protected compared to fast, glycolytic fibres. Evidence from transgenic animals suggests that driving muscle into a more aerobic phenotype by upregulating PPAR gamma coactivator 1-alpha (PGC1α) may be beneficial in mdx mice, the murine genetic homologue of DMD. PGC1α is a downstream target of AMP-activated protein kinase (AMPK). Metformin (N,N-dimethylbiguanide) hydrochloride is an AMPK agonist and a commonly prescribed antidiabetic drug used as a first-line treatment for type II diabetes. We hypothesised that metformin would improve skeletal muscle function in mdx mice. Mdx mice were treated for 10weeks from 14weeks of age with metformin at 2mg/ml in their drinking water. Age-matched controls received drinking water alone and all mice were weighed twice a week. The effect of treatment on muscle function was assessed using a standardised in vivo exercise test on the Tibialis Anterior (TA) muscle in situ. The test comprised a warm up, measurement of the force–frequency relationship and a series of eccentric contractions with a 10% stretch. Mice were then euthanised and their muscles’ collected for sectioning and histological analysis. Treatment with metformin at 2mg/ml in drinking water reduced the magnitude and speed of the force drop associated with 10 eccentric contractions compared to untreated controls, thereby improving the muscle’s resistance to contraction induced injury. There was no significant effect of metformin treatment on body weight. Further work is ongoing to assess the effect of metformin treatment on muscle histopathology, free radical content, fibre type distribution, and downstream targets (by western-blotting).