SRM-based measurements of proprotein convertase subtilisin/kexin type 9 and lipoprotein(a) kinetics in nonhuman primate serum

Aim: PCSK9 and Lp(a) have been identified as potential biomarkers for cardiovascular disease. The ability to measure protein turnover rates will provide insights into the dynamic properties of these proteins and lead to better understanding of their biological roles. We aimed to implement the stable isotope-labeled tracers ([2H3]-leucine) and develop a novel LC-selected reaction monitoring (SRM) mass spectrometry (MS) method to study the kinetics of PCSK9 and Lp(a). Results: A sensitive method using immunoaffinity enrichment coupled with LC-SRM MS was developed to measure the production and degradation rates of PCSK9 and Lp(a) in naive nonhuman primate serum. Comparable results were obtained from two different routes of tracer administration. Conclusion: Immunoaffinity enrichment coupled with LC-SRM MS demonstrated success in in vivo kinetic measurements of proteins with relatively slow turnover rate (Lp[a]) or low abundance (PCSK9) in serum.