To the Editor:
We would like to thank Domínguez-Rodríguez et al for their interest in our article,1 in which we point to metalloproteinases (MMP) 9 and 10 as promising biomarkers of cardiovascular risk. In their letter, these authors make an important observation by highlighting the relevance of circadian variations in circulating MMP-9 concentrations, based on their previous data showing diurnal variations in MMP-9 serum concentration in patients with acute coronary syndrome2 not observed in healthy volunteers.3 The information provided reinforces our opinion on the adequate validation of new candidates for biomarkers, and the need to demonstrate reliability, stability, low variability, and standardization of such markers in the methodology used to measure them.1,4
Furthermore, the information provided by Domínguez-Rodríguez et al has led us to consider the possibility that circadian variations may affect circulating MMP-10 concentrations, a question we are currently investigating.