Long-term endurance training increases serum cathepsin S levels in healthy female subjects

Circulating cathepsin S (CS) has been associated with a lower risk for breast cancer in a large Swedish cohort. Long-term physical activity has been shown to have beneficial effects on the development of various cancer subtypes, in particular breast and colorectal cancers. The aim of this study was to investigate the effect of long-term endurance sport on CS levels in females. Thirty-six of 40 subjects completed the study. Subjects were told to increase their activity pensum for 8 months reaching 150 min/week moderate or 75 min/week intense exercise. Ergometries were performed at the beginning and the end of the study to prove/quantify the performance gain. Blood samples were drawn at baseline and every 2 months. Serum CS levels were measured by ELISA. To analyse the change and the progression of CS, Wilcoxon rank sum and Friedman tests were used. The sportive group (performance gain by > 4.9%) showed a significant increase of CS levels from 3.32/2.73/4.09 to 4.00/3.09/5.04 ng/ml (p = 0.008) corresponding to an increase of 20.5%. We could show a significant increase of circulating CS levels in healthy female subjects induced by long-term physical activity. CS, occurring in the tumour microenvironment, is well-known to promote tumour growth, e.g. by ameliorating angiogenesis. However, the role of circulating CS in cancer growth is not clear. As physical activity is known as preventive intervention, in particular concerning breast and colorectal cancers, and long-term physical activity leads to an increase of CS levels in female subjects, circulating CS might even be involved in this protective effect. Clinical trial registration: NCT02097199