Raman Trapping Analysis for Calciprotein Particle Assessment for Patients with CKD

Background: Cardiovascular disease is the leading cause of mortality and morbidity in chronic kidney disease (CKD) patients, due to vascular calcification (VC). CKD patients experience supersaturation of calcium and phosphate in the blood, which binds to fetuin-A to form monomers that aggregate to form amorphous primary calciprotein particles (CPPs). These colloidal nanoparticles are naturally occurring and are filtered out under normal physiological conditions. In patients with poor kidney function, primary CPPs spontaneously transition to crystalline secondary CPPs, which can lead to VC. Currently, no technology exists to monitor or quantify VC in CKD patients noninvasively. We have developed Raman Trapping Analysis (RTA) as a new noninvasive, label-free optical technique to measure and quantify serum composition in healthy and uremic patients. Methods: Sera containing endogenous CPPs were collected from dialysis patients and healthy subjects. Serum samples were incubated in a calcium and phosphate solution for maturation. Stimulated CPPs were collected and washed in tris buffer solution. Particle size was measured using Dynamic Light Scattering (DLS) and confirmed using Nanoparticle Tracking Analysis (NTA). The RTA system was used to gain compositional understanding of the CPP maturation over time. Transmission electron microscopy (TEM) was used to verify morphology change from primary to secondary CPPs. A reported Osteosense assay was used to estimate CPP concentration. Results: The RTA system detected a change from amorphous to crystalline structure in both stimulated CPPs groups between 3 and 6 hours, which TEM and NTA support. DLS output further verified NTA with altered average particle size and polydispersity index. We validated that there are more stimulated CPPs than endogenous CPPs in both health and uremic patients. Osteosense confirmed an increase in endogenous CPPs in uremic patient serum compared to healthy patients. RTA spectra were used to quantify mineral content for statistical analysis. Conclusion: Our RTA system reliably measures CPPs in uremic and healthy sera. This technology may provide clinicians with a fast, noninvasive way to measure changes in VC in CKD patients and potentially prognosticate cardiovascular outcomes. Funding: Private Foundation Support