Identification of new biomarkers for sarcopenia and characterization of cathepsin D biomarker

Background
Sarcopenia is the progressive generalized loss of skeletal muscle mass, strength, and function that occurs with aging. This study was undertaken to identify new biomarkers of sarcopenia by proteomics analysis of female sera.

Methods
A case–control study was set up, for which 19 sarcopenic subjects and 20 control subjects, according to the European Working Group on Sarcopenia Older People criteria published in 2010 (EWGSOP1), were enrolled. All the subjects were at least 65 years old and in majority female. Biomarker screening was performed by a comparative mass spectrometry analysis. Protein expression levels between the two groups were compared. One of the identified biomarkers, cathepsin D, was measured by immunoassay on the serum of the full sample set (n = 39). Its diagnostic performance was evaluated with a receiver operating characteristic curve (ROC curve).

Results
Two biomarkers were identified: fructose-biphosphate aldolase A (P ≤ 0.05) and cathepsin D (P ≤ 0.05). The levels of all of them were higher in sarcopenic patients. It was confirmed by immunoassay that cathepsin D levels in serum were significantly higher in the sarcopenic group of patients (P = 0.038). An inverse correlation (−0.385) was observed between cathepsin D levels in serum and gait speed. The area under the ROC curve measurement (AUC = 0.696) demonstrated that cathepsin D levels could discriminate between sarcopenic and non-sarcopenic subjects. A predictive model including cathepsin D, age, and body mass index was established to improve the diagnostic performance (AUC = 0.908).

Conclusions
Cathepsin D has been identified as a diagnostic biomarker of sarcopenia.