This study was reviewed and approved by the Animal Ethics Committee of China-Japan Friendship Hospital (Approval No: zryhyy21-22-08-10) and conducted following institutional guidelines for the ethical care and use of laboratory animals.
Prediction and Screening of TFRD-related and GA-associated Targets
The chemical constituents of Rhizoma Drynariae were retrieved from the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) using “Rhizoma Drynariae” as the search term29. Screening for potentially bioactive constituents was performed based on the criteria of oral bioavailability (OB) ≥ 30% and drug-likeness (DL) ≥ 0.1830,31,32. From the resulting pool of compounds, flavonoid components were subsequently identified and selected according to their chemical structures. These flavonoid components, hereafter referred to as the total flavonoids of Rhizoma Drynariae (TFRD), were incorporated in downstream analysis. Upon retrieving the target genes associated with TFRD from the TCMSP database, their corresponding standardized gene symbols were annotated using the UniProt database33. Using “gout” as a search term, disease-related targets were retrieved from the GeneCards database to establish a set of candidate genes34.
Establishment of compound-target network
The intersection between TFRD-associated targets and GA-related targets was identified and defined as the key therapeutic targets mediating TFRD's anti-GA effects, and the overlapping set was visualized using a Venn diagram. Furthermore, a regulatory network of “TFRD - targets - GA” was constructed and analyzed using Cytoscape software35.
Protein-protein interaction network
The key therapeutic targets of TFRD against GA were imported into an online database to generate a protein-protein interaction (PPI) network, with the minimum required interaction score set to “high confidence (0.700)”36. The PPI network was optimized using Cytoscape software, and the top 30 core targets ranked by degree centrality were selected to generate a bar plot37,38.
KEGG pathway enrichment analysis
KEGG pathway enrichment analysis was performed on these core targets using R software and the Bioconductor database38,39. Pathways with a p-value < 0.05 were considered statistically significant. After excluding disease- and metabolism-related pathways, a pathway-target interaction network was visualized in Cytoscape. Among these pathways, the top 20 pathways ranked by ascending P value were presented in a bar plot.
Drug preparation
For the preparation of a monosodium urate (MSU) crystal suspension, 500 mg of MSU crystals were weighed using an analytical balance, dispersed in 10 mL of normal saline and 2 mL of Tween 80, and heated while stirring magnetically. The mixture was then adjusted to a final volume of 20 mL with normal saline to obtain a 25 mg/mL suspension. After autoclaving, the suspension was stored at 4 °C until use. The common clinical dosage for TFRD is 750 mg per day for a 70 kg adult, corresponding to a rat dose of 67.5 mg/kg body weight per day. TFRD was dissolved in distilled water to a concentration of 6.75 mg/mL and stored at 4 °C for later use. According to the body surface area normalization method, the equivalent oral dose of colchicine (the positive drug) in rats converted from the clinical human dose (0.6 mg/60 kg) is 0.062 mg/kg. A colchicine solution was prepared in distilled water at a concentration of 0.0062 mg/mL and stored at 4 °C for later use.
Animals
A total of 36 six-week-old male Sprague–Dawley (SD) rats (220 ± 10 g) were used in this study (animal license No. SCXK [Jing] 2025-0008). Animals were housed at the Laboratory Animal Center of China-Japan Friendship Hospital under standard diet conditions at a temperature of 22–24 °C and humidity of 50–70%.
Model establishment and intervention
Following one week of acclimation, rats were randomly divided into four groups (n = 9 each): control, model, TFRD, and positive drug. Randomization was performed using a random number table. Data collection and analysis were conducted under blinded conditions. All treatments were given once daily by oral gavage. All interventions were administered once daily by oral gavage at 08:00 for seven consecutive days. The blank control and model groups received normal saline (10 mL/kg), while the TFRD and the positive drug groups were given their respective drug suspensions at an equivalent volume (10 mL/kg). On the fourth day of the interventions, the blank control group received an intra-articular injection of sterile normal saline, while rats in the model, TFRD, and the positive drug groups were injected with an MSU crystal suspension to induce acute gouty arthritis. Prior to injection, rats were anesthetized using an isoflurane anesthesia system. Each rat in the model, TFRD, and the positive drug groups received 200 µL of the MSU suspension into the left ankle joint cavity. Following needle withdrawal, gentle pressure was applied at the injection site with a sterile cotton swab for several seconds to prevent leakage.
Sample collection and processing
72 h after model induction, rats were anesthetized and positioned supine. Following abdominal disinfection, the peritoneal cavity was opened, and the intestines were gently retracted to expose the abdominal aorta. A blood collection needle was inserted parallel to the vessel to draw abdominal aortic blood, which was immediately transferred into heparinized tubes pre-chilled in an ice water bath. Samples were centrifuged at 3000 × g for 10 min at 4 °C to obtain serum, which was aliquoted and stored at -80 °C for subsequent metabolomic profiling. Animals were then euthanized via CO₂ asphyxiation. The fur around the left ankle joint was shaved, and the surrounding skin and muscle were carefully removed to expose the intact joint structure. Synovial tissue, appearing as a thin whitish membrane lining the joint capsule, was gently isolated from adjacent fascia using fine forceps. The collected joint samples were fixed in 4% paraformaldehyde at 4 °C for 72 h. Then, part of the joint tissue was decalcified in EDTA decalcification solution, with the solution refreshed weekly for 8 weeks. Complete decalcification was confirmed by needle puncture testing: if resistance was encountered, decalcification was continued until the tissue was fully penetrable.
Following decalcification, ankle joints were sagittally sectioned, placed in processing cassettes, and subjected to gradient ethanol dehydration. Tissues were cleared in xylene, infiltrated with paraffin, and embedded in paraffin blocks. Sections of 6 µm thickness were cut using an automated microtome, floated on a 40 °C water bath, and mounted onto adhesive slides. After drying at 60 °C for 30 min, sections were deparaffinized, stained with hematoxylin and eosin (H&E) according to standard protocols, and finally coverslipped with neutral balsam. Whole slide images were acquired using a digital slide scanner.
Serum metabolomics analysis
Serum samples from the model and TFRD groups were thawed at 4 °C prior to processing. For each sample, 100 µL of serum was transferred into a microcentrifuge tube and combined with 400 µL of precooled extraction solvent (methanol: acetonitrile, 1:1, v/v) containing internal standards. The mixture was vortexed for 1 min, followed by sonication in an ice-water bath for 10 min. It was then incubated at -40 °C for 1 h to facilitate protein precipitation and subsequently centrifuged at 12,000 × g for 15 min at 4 °C. The supernatant obtained after centrifugation was carefully collected and transferred into autosampler vials for UHPLC–MS analysis. In addition, equal volumes of supernatant from each sample within the same group were pooled to generate quality control (QC) samples.
Following metabolite detection in serum samples from the two groups, the raw mass spectrometry data were processed by dedicated software for automated peak detection, extraction, alignment, and integration, yielding a structured data matrix of ion spectral features. The detected spectral features were matched against established metabolomics spectral libraries to identify metabolites derived from TFRD that had entered systemic circulation. Unidentified features and those containing excessive missing values were removed from the dataset. The curated dataset was re-indexed and structured into a standardized format40.
The differential expression of metabolites between the two groups was evaluated by calculating both fold change (FC, expressed as the inter-group ratio) and statistical significance (p-value). Metabolites meeting the threshold of |log₂FC| ≥ 1 and P < 0.05 were defined as differentially expressed metabolites (DEMs). The screening results were visually summarized using methods such as volcano plots. The screened differential metabolites were subsequently imported into the PubChem database to obtain their canonical identifiers (CIDs)41. The corresponding KEGG IDs were then obtained based on the CIDs. Finally, the KEGG IDs were imported into a metabolomics analysis platform to perform metabolic pathway enrichment analysis and identify the signaling pathways significantly associated with the DEMs.
ELISA
Synovial tissue samples were flash-frozen in liquid nitrogen and pulverized into a fine powder. Approximately 100 mg of the powder was weighed using an electronic precision balance, mixed with 1 mL of ice-cold PBS, and homogenized on ice using a glass homogenizer. The homogenate was centrifuged at 10,000 × g for 5 min at 4 °C, and the supernatant was collected for subsequent ELISA detection. Prior to analysis, the ELISA kit was allowed to equilibrate to room temperature for 30 min. All reagents, including serially diluted standards, wash buffer, biotin-labeled antibody working solution, and enzyme conjugate solution, were prepared in accordance with the manufacturer’s instructions. Subsequently, 100 µL of standards at different concentrations and samples were added to the designated wells of the pre-coated microplate. The plate was sealed and incubated at 37 °C for 90 min. After incubation, the contents were discarded, and the wells were washed four times. Then, 100 µL of biotinylated antibody working solution was added to each well, followed by incubation at 37 °C for 60 min and another washing step. Next, 100 µL of enzyme conjugate working solution was introduced, and the plate was incubated at 37 °C for 30 min, followed by additional washing. A chromogenic substrate was then added, and the plate was incubated in the dark at 37 °C for 10 min. The reaction was terminated by adding 100 µL of stop solution, and absorbance was measured at 450 nm using a microplate reader. A standard curve was constructed by fitting the optical density (OD) values of the standards against their corresponding concentrations, and sample concentrations were calculated accordingly.
Western blot
Synovial tissues were rapidly frozen and mechanically ground into a fine powder. A measured portion of the powder was lysed in an appropriate volume of ice-cold RIPA buffer supplemented with protease and phosphatase inhibitors (1:100, v/v), followed by incubation on ice for 30 min. The lysates were then centrifuged at 10,000 × g for 5 min at 4 °C, and the supernatants were carefully collected. Protein concentrations were quantified using a BCA assay, and all samples were adjusted to equal concentrations with RIPA buffer. Proteins were separated via SDS-PAGE and transferred onto PVDF membranes. Membranes were blocked and then incubated with primary antibodies (1:1000 dilution), followed by secondary antibodies (1:5000 dilution). Protein signals were visualized using an ECL detection system, and band intensities were quantified using Image Lab software (Version 5.2.1). The relative expression levels were normalized against β-actin.
Statistical analysis
Statistical analyses were performed using SPSS software (version 20.0). Data are presented as mean ± standard deviation (SD). For comparisons among multiple groups, one-way analysis of variance (ANOVA) was used when the assumption of homogeneity of variance was satisfied, followed by the LSD test for post hoc pairwise comparisons. If variance homogeneity was not met, Welch’s ANOVA was performed, followed by Dunnett's T3 test for multiple comparisons. A p-value < 0.05 was considered statistically significant.