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.

Engineering mutually orthogonal PylRS/tRNA pairs for dual encoding of functional histidine analogues

The availability of an expanded genetic code opens exciting new opportunities in enzyme design and engineering. In this regard histidine analogues have proven particularly versatile, serving as ligands to augment metalloenzyme function and as catalytic nucleophiles in designed enzymes. The ability to genetically encode multiple functional residues could greatly expand the range of chemistry accessible within enzyme active sites. Here, we develop mutually orthogonal translation components to selectively encode two structurally similar histidine analogues. Transplanting known mutations from a promiscuous Methanosarcina mazei pyrrolysyl-tRNA synthetase (MmPylRSIFGFF ) into a single domain PylRS from Methanomethylophilus alvus (MaPylRSIFGFF ) provided a variant with improved efficiency and specificity for 3-methyl-L-histidine (MeHis) incorporation. The MaPylRSIFGFF clone was further characterized using in vitro biochemical assays and x-ray crystallography. We subsequently engineered the orthogonal MmPylRS for activity and selectivity for 3-(3-pyridyl)-L-alanine (3-Pyr), which was used in combination with MaPylRSIFGFF to produce proteins containing both 3-Pyr and MeHis. Given the versatile roles played by histidine in enzyme mechanisms, we anticipate that the tools developed within this study will underpin the development of enzymes with new and enhanced functions.