Molecular composition of adiponectin in urine is a useful biomarker for detecting early stage of diabetic kidney disease

We previously developed two immune complex transfer enzyme immunoassays (ICT-EIA) to measure total adiponectin (T-AN) and high molecular weight adiponectin (H-AN) in urine and have verified their usefulness as biomarkers for diabetic kidney disease. In this study, we developed T-AN and H-AN assays using the sandwich EIA (Sand-EIA). The reactivities of Sand-EIAs were compared with ICT-EIAs by measuring size exclusion chromatography (SEC) fractions of urine and adiponectin standard. As a result, ICT-EIAs showed higher macromolecular specificity. We then analyzed the molecular profile of adiponectin in the urine of 5 patients with different eGFR stages by measuring SEC fractions of urine. The results showed that smaller adiponectin correlated relatively well with eGFR stage. Finally, because SEC is time-consuming, we investigated that the ratio of T-ANs by Sand-EIA and ICT-EIA could be a good indicator of the monomer adiponectin. The ratio was evaluated using 77 urine samples from patients with diabetes and showed a significant decrease at an earlier stage compared with other biomarkers. In conclusion, we demonstrated a new index to estimate monomer adiponectin in urine by using Sand-EIA and ICT-EIA, and urinary monomer adiponectin can be a good early indicator of deterioration of renal function in diabetic patients.