Serum based fluorescent assay for evaluating dipeptidyl peptidase I activity in collagen induced arthritis rat model

- Successfully modified and developed a synthetic route of a fluorescent probe GF-AFC, specifically targeting DPPI domain.
- The substrate GF-AFC was firstly applied to evaluate DPPI activity in serum or tissue homogenates of CIA rats.
- The DPPI activity level was correlated to the severity development during arthritis progress in CIA rats.
- A serum based DPPI assay has been firstly established and validated, providing a possible mean for medical research.

Dipeptidyl peptidase I (DPPI) is a lysosomal cysteine protease and derived from immune granule cells. It has been suggested playing an important role in the development of rheumatoid arthritis. In this study, a coumarin based fluorescent probe (GF-AFC) was designed and synthesized to evaluate DPPI activity in serum or tissue homogenates of collagen-induced arthritis (CIA) rats, an inflammatory arthropathy model. It was revealed that the fluorescent intensity was significantly increased in a very short time after specific substrate GF-AFC reacted with the DPPI. The fluorophore (AFC) was released to shine after the cleavage reaction which was examined by 19F NMR spectroscopy. It has been shown that DPPI hydrolyzed the GF-AFC in a robust, linear, and time dependent manner at a significant high rate. A serum-based DPPI activity assay was validated by spiking and gradient dilution methods, there were no interferences or auto-fluorescence observed. The Coefficient of Variance calculated for serum-based DPPI activity assays indicates the good reproducibility. The good correlation has been seen between serum DPPI levels and the severity of arthritis during RA development in CIA rats. Our study has demonstrated a new serum based diagnostic assay for detecting DPPI activity using coumarin conjugated fluorescent (GF-AFC) as a substrate. The successful implementation of the case would provide beneficial experience in rheumatoid arthritis research.