Abstract: BACKGROUND: Previous studies have shown that Tougu Xiaotong Capsules can reduce the expression of chondrocyte inflammatory factors, reduce chondrocyte apoptosis, promote chondrocyte proliferation, and delay cartilage and subchondral bone degeneration, thereby alleviating the process of osteoarthritis and reducing inflammation responses. However, the mechanism of this prescription on synovial lesions is unclear.
OBJECTIVE: To further explore the mechanism of anti-inflammatory and anti-swelling effect of Tougu Xiaotong Capsule on early osteoarthritis with synovial edema based on the regulation of aquaporins. 
METHODS: Twenty-four Sprague-Dawley rats were randomly divided into three groups: blank group, model group and traditional Chinese medicine (TCM) group. Osteoarthritis animal models were made by papain injection. After 1 week, animals were gavaged respectively with Tougu Xiaotong Capsule in the TCM group or saline in the blank and model groups for 4 weeks. The morphology and structure of the knee joints were observed by MRI. Interleukin-1β and tumor necrosis factor α in serum and joint fluid were detected by radioimmunoassay. Synovial tissue microstructure was observed through paraffin section, and the ultrastructure of synovial cells observed by transmission electron microscope. Aquaporins 1 and 3 were quantified and located by immunohistochemical staining/fluorescence staining. The study protocol was approved by the Laboratory Animal Ethics Committee of Fujian University of Traditional Chinese Medicine (approval No. [2019]024).
RESULTS AND CONCLUSION: Compared with the model group, synovial lesion was alleviated and synovial secretion was decreased in the TCM group; the contents of interleukin-1β and tumor necrosis factor α in the serum and joint fluid were decreased significantly in the TCM group; synovial cell hyperplasia was alleviated, tissue fibrosis and vascular hyperplasia was significantly reduced in the TCM group; the number of rough endoplasmic reticula, Golgi apparatus, vesicles and lysosomes was decreased in synovial cells in the TCM group; and the expressions of aquaporin 1 and aquaporin 3 were significantly down-regulated, and they were scattered in the cell membrane and cytoplasm, without aggregation. To conclude, by decreasing aquaporin 1 and aquaporin 3 expression in synovial tissue, Tougu Xiaotong Capsule can reduce synovial secretion and alleviate joint edema, which may be one of the anti-inflammation and anti-swelling mechanisms of the prescription.

Key words: synovium, Chinese herb, osteoarthritis, synovitis, aquaporin, anti-inflammation and anti-swelling, ultrastructure, experiment