ObjectiveThis paper aims to observe the protective effect of Huamoyan granules on knee osteoarthritis （KOA） and explore whether its protective effect is oriented toward an anti-inflammatory direction by regulation of macrophage polarization， which can effectively inhibit the progression of pathological inflammatory response， reduce the release of inflammatory pain mediators， and downregulate the protein expression level of transient receptor potential vanilloid 1 （TRPV1）， so as to provide experimental evidence for its clinical application and investigate its action mechanism. MethodsAfter adaptive feeding， Sprague-Dawley （SD） rats were randomly divided into six groups： sham group， model group， celecoxib group， and high， medium， and low-dose synovitis granule groups （9.6， 4.8， 2.4 g·kg^-1）. The administration dose of celecoxib capsules was 20 mg·kg^-1. There were 10 rats in the sham group and 12 rats in the model group and each administration group. A KOA animal model was established by means of intra-articular injection of sodium iodoacetate into the knee joint. From the 10^th day of the experiment， each administration group was given intragastric administration at a dose of 10 mL·kg^-1 for 4 weeks. General conditions of rats in each group were assessed daily. The pressure pain threshold （PPT） to mechanical stimulation and joint diameter were recorded. X-ray examination was performed on the right knee joints of rats for imaging analysis. Enzyme linked immunosorbent assay （ELISA） was performed to detect the tumor necrosis factor-α （TNF-α）， serum interleukin-1β （IL-1β）， and other pro-inflammatory cytokines in rat serum samples， as well as the expression levels of neurogenic inflammatory mediators such as nerve growth factor （NGF） and calcitonin gene-related peptide （CGRP）. Histopathological changes in the knee joint synovial tissues were examined by hematoxylineosin （HE） staining. Safranin O-fast green staining was performed to observe and evaluate the degree of knee cartilage lesions. Western blot was employed to quantitatively analyze TRPV1， p38 mitogen-activated protein kinase （p38 MAPK）， and phosphorylated （p）-p38 MAPK in rat knee synovial tissues. Immunofluorescence （IF） was used to measure and assess M1/M2 macrophage polarization. ResultsCompared with those in the sham group， the circumference and joint diameter of the right knee were markedly enlarged in the model group （P<0.01）， while PPTs of rats showed a significant reduction （P<0.01）. The contents of IL-1β， TNF-α， CGRP， and NGF in rats' serum were significantly elevated （P<0.01）， and the synovial Krenn score was increased （P<0.01）. The Mankin score of cartilage tissue was increased （P<0.01）， and the protein expressions of TRPV1 and p-p38 MAPK/p38 MAPK were significantly upregulated （P<0.01）. The experimental intervention significantly reduced the proportion of pro-inflammatory M1 macrophages in the total macrophage population （P<0.01）， and the percentage of M2 macrophages was decreased （P<0.01）. The M1/M2 macrophage ratio was significantly elevated （P<0.01）. Knee joint diameters of all dose groups of Huamoyan granules and the celecoxib group were reduced （P<0.01） compared with those of the model group， and the PPT recovery speeds in the high and medium-dose groups of Huamoyan granules were more obvious （P<0.05）. The contents of IL-1β， CGRP， and NGF in the rats' serum in all administration groups were significantly reduced （P<0.05， P<0.01）， and the content of TNF-α in rats' serum was significantly reduced （P<0.01）. All dose groups of Huamoyan granules demonstrated significant reductions in both synovial Krenn score （P<0.05， P<0.01） and protein expression of TRPV1 and p-p38 MAPK/p38 MAPK in rats' synovial tissues （P<0.01）. The percentage of M1 macrophages in the synovial tissues of the celecoxib group and all dose groups of Huamoyan granules was decreased （P<0.01）. The percentage of M2 macrophages was increased （P<0.05）， and the M1/M2 ratio was decreased （P<0.01）. ConclusionHuamoyan granules can alleviate the inflammatory response of KOA， reduce the release of inflammatory pain mediators， and downregulate TRPV1 protein expression by regulating macrophage polarization. Its mechanism may be related to the TRPV1/p38 MAPK signaling pathway， thereby achieving the effect of improving peripheral pain hypersensitivity in KOA.