Exercise, but Not Metformin Prevents Loss of Muscle Function Due to Doxorubicin in Mice Using an In Situ Method.

Though effective in treating various types of cancer, the chemotherapeutic doxorubicin (DOX) is associated with skeletal muscle wasting and fatigue. The purpose of this study was to assess muscle function in situ following DOX administration in mice. Furthermore, pre-treatments with exercise (EX) or metformin (MET) were used in an attempt to preserve muscle function following DOX. Mice were assigned to the following groups: control, DOX, DOX + EX, or DOX + MET, and were given a single injection of DOX (15 mg/kg) or saline 3 days prior to sacrifice. Preceding the DOX injection, DOX + EX mice performed 60 min/day of running for 5 days, while DOX + MET mice received 5 daily oral doses of 500 mg/kg MET. Gastrocnemius-plantaris-soleus complex function was assessed in situ via direct stimulation of the sciatic nerve. DOX treatment increased time to half-relaxation following contractions, indicating impaired recovery (p < 0.05). Interestingly, EX prevented any increase in half-relaxation time, while MET did not. An impaired relaxation rate was associated with a reduction in SERCA1 protein content (p = 0.07) and AMPK phosphorylation (p < 0.05). There were no differences between groups in force production or mitochondrial respiration. These results suggest that EX, but not MET may be an effective strategy for the prevention of muscle fatigue following DOX administration in mice.

Nutrient Sensing and the Oxidative Stress Response.

The simplicity and effectiveness of calorie restriction (CR) in lifespan and healthspan extension have fascinated generations searching for the Fountain of Youth. CR reduces levels of oxidative stress and damage, which have been postulated in the free radical theory of aging as a major cause of aging and diseases of aging. This reduction has long been viewed as a result of passive slowing of metabolism. Recent advances in nutrient sensing have provided molecular insights into the oxidative stress response and suggest that CR triggers an active defense program involving a cascade of molecular regulators to reduce oxidative stress. Physiological studies have provided strong support for oxidative stress in the development of aging-associated conditions and diseases but have also revealed the surprising requirement for oxidative stress to support normal physiological functions and, in some contexts, even slow aging and prevent the progression of cancer. Deciphering the molecular mechanisms and physiological implications of the oxidative stress response during CR will increase our understanding of the basic biology of aging and pave the way for the design of CR mimetics to improve healthspan.