Relationship between Hydration Status and Muscle Catabolism in the Aged Population: A Cross-Sectional Study

BACKGROUND

The physiopathology of sarcopenia is still not completely understood.

AIM

To assess the relationship between dehydration and skeletal muscle catabolism, muscle mass, and sarcopenia in an aged population.

METHODS

Observational cross-sectional study of community-dwelling subjects aged 70 years and older. Dehydration was assessed by plasma osmolarity; bioimpedance analysis (BIA) was used to assess body composition and water content; sarcopenia was established according to the EWGSOP-2 criteria; and 3-methyl-histidine (3MH) was used as an indicator of muscle catabolism.

RESULTS

190 participants were recruited (77.4 years; 51.6% women). In total, 22.6% and 20.5% presented plasma osmolarity of 295-300 mOsm/L and >300 mOsm/L, respectively. Age was correlated with plasma osmolarity (rs = 0.439; p < 0.001). Plasma osmolarity was correlated with 3MH (rs = 0.360; p < 0.001) and showed an effect on 3MH levels, with an adjusted (by age, sex, and number of medications) beta of 0.283 (p < 0.001). BIA water content indicators showed no correlation with 3MH. Lower in sarcopenic compared to non-sarcopenic subjects were the intracellular water percentage (60.3 vs. 61.2%; p = 0.004) and intracellular water/free-fat mass ratio (44.3 vs. 45.0; p = 0.004).

CONCLUSIONS

Dehydration is a highly prevalent clinical condition in aged populations, increases with age, and is associated with muscle catabolism but not sarcopenia.

Nitric Oxide does not mediate Atrogin-1/MAFbx upregulation by inflammatory mediators

Accelerated proteolysis through the ubiquitin-proteasome system has been recognized as a major contributor to muscle wasting, a serious complication frequently associated with a number of inflammatory disorders. Muscle expression of atrogin-1/MAFbx, a rate-limiting ubiquitin ligase for muscle wasting, is upregulated in various inflammatory conditions, and is considered a therapeutic target for muscle wasting. As one of the free radicals whose production is elevated in inflammatory conditions, nitric oxide (NO) is implicated in the pathogenesis of muscle wasting. To understand how inflammatory mediators upregulate atrogin-1/MAFbx expression, we tested the hypothesis that NO mediates the upregulation of atrogin-1/MAFbx expression. C2C12 myotubes were incubated with a cocktail comprised of TNF-α, interferon γ and lipopolysaccharide (LPS), which stimulated NO production and atrogin-1/MAFbx expression. Pre-incubation of the myotubes with nitric oxide synthase (NOS) inhibitor L-NAME or S-ethylisothiourea (SETU) blocked the stimulation of NO production by the cocktail. However, the stimulation of atrogin-1/MAFbx expression was not disrupted. Intraperitoneal administration of LPS to mice resulted in elevated atrogin-1/MAFbx expression in gastrocnemius muscle. But, pretreatment of the mice with L-NAME did not alter LPS stimulation of atrogin-1/MAFbx expression. Therefore, NO does not mediate upregulation of atrogin-1/MAFb expression by inflammatory mediators.