Antioxidant supplementation had positive effects in old rat muscle, but through better oxidative status in other organs

Journal Title (Medline/Pubmed accepted abbreviation): Nutrition
Year: 2010
Volume: 26
Number: 11-12
Page numbers: 1157-1162
doi: 10.1016/j.nut.2009.09.016

Summary of Background and Research Design

Background: Sarcopenia (age-related muscle mass loss) is a major public health problem affecting individuals in the rapidly increasing elderly population. One of the mechanisms proposed for the development of sarcopenia is an oxidative stress-mediated imbalance between protein synthesis and degradation in muscles. Previous data showed that supplementation of an antioxidant mixture to 20-month-old rats had a beneficial effect on muscle protein synthesis by improving the anabolic response of old muscle to leucine.

Hypothesis/purpose of study:To determine whether the positive effects of antioxidant supplementation on muscle protein synthesis is attributable to improvement of local muscle oxidative status or related to systemic induction of antioxidant defenses.

Subjects:Thirty-two 20-month-old Wistar male rats. Twenty rats (10 in each group) survived until the experiment end and were included in the data analysis.

Experimental design: An experimental, randomized study in an animal model.

Treatments and protocol:Rats were equally randomized to one of two diets for 7 weeks: a basal diet or basal diet + antioxidant mixture. All animals were housed in a climate controlled room (2 per cage) with food and water provided ad libitum. The antioxidant mixture contained rutin (5 g/kg diet) and elevated concentrations of vitamin E (300 IU/kg diet), vitamin A (8000 IU/kg diet), zinc (30 mg/kg diet), and selenium (2 mg/kg diet). Food intake and animal body weight was monitored once a week during the entire experiment. Assessment of oxidative status included quantification of liver glutathione, liver and spleen γ-keto-aldehyde (γ-KA), muscle superoxide-dismutase (SOD) activity, total antioxidant capacity, and heart thiobarbituric acid-reactive substances (TBARS). Muscle oxidative damage was evaluated by measurement of myofibrillar protein carbonyl content.

Summary of research findings:
  • At 7 weeks, there was no significant difference in body weight, food intake, or muscle mass compared with baseline in either dietary group.
  • Muscle antioxidant capacity, total muscle SOD activity and oxidative damage were unaffected by antioxidant supplementation.
  • Total glutathione content measured in liver was greater with antioxidant treatment compared with basal diet (P = .08).
    • Effects were unrelated to liver weight and protein content or glutathione metabolism.
  • Protein γ-KA content (oxidative damage marker) in liver and spleen significantly decreased in response to the antioxidant treatment compared with basal diet (P < .05 for both).
  • Heart TBARS were significantly lower with antioxidant treatment compared with basal diet (40.2 nmol/g vs 73.2 nmol/g, respectively; P < .05).

Interpretation of findings/Key practice applications:

The results demonstrate that the beneficial effect of antioxidant supplementation is likely related to an increase of systemic antioxidant defense mechanisms rather than local muscular oxidative status. One drawback of this study approach was housing animals 2 per cage, which made it difficult to measure accurate food intake and dosage for individual animals. Additionally, the cause of death of 12 animals out of 36 total (33%) was undisclosed. Further research is necessary to determine which, if any, components of the antioxidant mixture are more important and if there are any synergistic effects between the antioxidant components.
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