Serum levels of procollagen type IIA N-terminal propeptide (sPIIANP) and type-II collagen helical peptide (sHELIXII) biomarkers were evaluated for variation diurnally and with physical activity and food in participants with osteoarthritis (OA) of the knee.
Forty participants with OA of at least one knee were admitted overnight to the General Clinical Research Center for serial serum sampling. Samples were obtained on the evening (6-8 pm) of Day 1 (T3, n=40); prior to rising (8 am) from bed (T0, n=40); 1 h after rising (9 am) without food consumption (T1a, n=20); 1-2 h after rising (9-10 am) with food consumption (T1, n=40); and additionally at noon, 4 h after rising (T2, n=20). sPIIANP and sHELIXII were measured by enzyme-linked immunosorbent assay. Results were analyzed using non-parametric Freidman's test with Dunn's post-hoc multiple comparison test.
Normalized mean concentrations for sPIIANP and sHELIXII increased significantly from T0 to T1 (P<0.05).
This is the first study to demonstrate diurnal variation of these collagen-II biomarkers in individuals with knee OA. These results suggest that serum sampling for these markers should be standardized for purposes of clinical trials.