Evaluation of effectiveness of antiarthritic treatment by in situ ratiometric fluorescence imaging of the endoplasmic reticulum pH

Rheumatoid arthritis (RA) is a chronic inflammatory disease that can cause extreme joint pain. However, current therapies cannot provide symptomatic relief for a large proportion of patients with RA. Thus, the development of novel therapeutic drugs constitutes a major challenge for RA treatment. Endoplasmic reticulum (ER) stress is reportedly involved in RA pathogenesis. Notably, abnormal ER pH is often closely related to ER stress. Therefore, ER pH has the potential to become a new evaluation parameter for RA. In this study, we demonstrated that a novel ratiometric fluorescence probe, herein called pH-ER, could be used in imaging ER pH in cells in situ within the range of 6.02–9.57. This probe was successfully applied in the evaluation of the joints of mice with RA of different severity. The novel probe developed herein can be used to evaluate the efficacy of drugs for RA treatment.