T. Malmezat

Gas chromatographic-mass spectrometric analysis of stable isotopes of cysteine and glutathione in biological samples.

A gas chromatographic-mass spectrometric (GC-MS) procedure for the determination of stable isotope labelled glutathione has been applied to animal and human samples. The method, based on preparation of the N,S-ethoxycarbonyl methyl ester derivative of the intact peptide, is rapid and requires little or minor tissue treatment. The same method was applied to cysteine. The method was found to be reliable in terms of within-day and between-day precision, accuracy and linearity. The procedure was applied in humans and animals to determine in vivo the glutathione fractional synthesis rate using labelled cysteine infusion. The glutathione fractional synthesis rate was found to be 22.5%/day in blood from a healthy volunteer and 337+/-29%/day in rat liver.

Lower recovery of muscle protein lost during starvation in old rats despite a stimulation of protein synthesis

Sarcopenia could result from the inability of an older individual to recover muscle lost during catabolic periods. To test this hypothesis, we compared the capacity of 5-day-refed 12- and 24-mo-old rats to recover muscle mass lost after 10 days without food. We measured gastrocnemius and liver protein synthesis with the flooding-dose method and also measured nitrogen balance, 3-methylhistidine excretion, and the gene expression of components of proteolytic pathways in muscle comparing fed, starved, and refed rats at each age. We show that 24-mo-old rats had an altered capacity to recover muscle proteins. Muscle protein synthesis, inhibited during starvation, returned to control values during refeeding in both age groups. The lower recovery in 24-mo-old rats was related to a lack of inhibition of muscle proteolysis during refeeding. The level of gene expression of components of the proteolytic pathways did not account for the variations in muscle proteolysis at both ages. In conclusion, this study highlights the role of muscle proteolysis in the lower recovery of muscle protein mass lost during catabolic periods.