Presence of low-grade inflammation in old rats does not worsen skeletal muscle loss under an endotoxemic and dietary stress

The study aimed to determine if age-associated low-grade inflammation aggravates the response to a stress, especially regarding to sarcopenia. Initial inflammatory status in 22-month-old rats was based on plasma α₂-macroglobulin and fibrinogen concentrations. The stress applied was a single intra-peritoneal injection of lipopolysaccharide followed by a 23-day period of malnutrition, i.e. a 4% casein diet distributed in quantity limited to 50% of spontaneous food intake. The response to the stress was analyzed in non-inflamed and low-grade inflamed rats and compared to non-inflamed and low-grade inflamed rats, which received the control treatment (i.e. no lipopolysaccharide injection and an 18% casein diet). The stress-induced body weight loss was higher in inflamed than non-inflamed rats, but the decrease in muscle weight was not worsened. Muscle protein turnover was not affected by the stress. Plasma α₂-macroglobulin levels increased after the stress, whatever the initial inflammatory status. However, fibrinogen levels decreased more in inflamed than non-inflamed rats and albumin levels were not affected by the stress. Independently of the initial inflammatory status, the liver glutathione content was strongly depleted by the stress. These results extend and support our previous findings by demonstrating that age-associated low-grade inflammation does not aggravate sarcopenia in old rats.