Anti-arthritic activities of cross-linked hyaluronic acid-dexamethasone hydrogel in a rat model of gouty arthritis.

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Background: Gouty arthritis (GA) is a type of inflammatory joint disease in which the deposition of monosodium urate (MSU) crystals inside the joints leads to severe inflammatory reactions, such as synovitis. Cross-linked hyaluronic acid hydrogel (cHA gel) has been shown to have a chondroprotective effect, while dexamethasone (Dex) is an anti-inflammatory drug; both have been used in clinical practice to a certain extent. This study was designed to compare the therapeutic effects of cHA gel pre-mixed with Dex (cHA-Dex gel) or without Dex (cHA gel alone) in a rat model of GA.Methods: In this study, 2-month-old male Sprague-Dawley (SD) rats were used. The GA model was established by intra-articular injection of a solution containing 40 mg/mL MSU crystals and 0.1 mg/mL lipopolysaccharide (LPS) dissolved in saline, and this procedure was repeated every 2 weeks. The rats were subsequently randomly allocated into four groups (n = 8 per group): the MSU/LPS + saline group, the MSU/LPS + cHA gel group, the MSU/LPS + cHA gel containing 0.5 mg/mL Dex (cHA-Dex gel) group, and a negative control group. One day after MSU/LPS injection, the designated treatments were administered via intra-articular injection only once. Various examinations were performed 1 day after the fifth MSU/LPS induction. Behavioral indicators included the degree of knee joint swelling, the capacity of the limb to bear weight, grip strength, mechanical pain threshold, acetone test results, and the gait scoring. Imaging and histological assessments included micro X-ray, Indian ink staining, safranin O-fast green staining, immunohistochemistry, and synovial hematoxylin-eosin (HE) staining. Biochemical and molecular biological markers were evaluated by serum enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (RT-qPCR). The detected targets included interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-10 (IL-10), tumor necrosis factor α (TNF-α), matrix metalloproteinase-3 (MMP-3), and matrix metalloproteinase-9 (MMP-9) expression levels. Eight rats per group (n = 8) were used for all assays, with cartilage from two rats pooled to yield four biological replicates per group (n = 4) for RT-qPCR.Results: The findings showed that the deposition of intra-articular MSU/LPS led to pathological changes, including inflammation and cartilage damage. Micro X-ray scans showed that the knee joint structure treated with cHA-Dex gel had a much better level of integrity than the MSU/LPS + saline and MSU/LPS + cHA gel groups. In the MSU/LPS + cHA-Dex gel group, Indian ink staining was less, and safranin O-fast green staining showed an increase in proteoglycan (PG) content and a decrease in the extent of cartilage damage. Histological quantitative analysis showed statistically significant differences in the relevant scores (p < 0.05). Immunohistochemical staining indicated strong positive staining for type II collagen (COL II), while expression levels of MMP-3 and MMP-9 were downregulated. HE staining of synovial tissue showed that the synovial lining cell layer became thinner, with fewer infiltrating inflammatory cells. Analysis of serum and cartilage tissues showed that cHA-Dex gel significantly lowered the level of inflammatory factors.Conclusion: Altogether, the cHA gel combined with Dex demonstrated superior therapeutic outcomes in comparison to cHA gel alone in a rat model of GA. The presented work provides preclinical evidence for a localized cHA-Dex gel delivery strategy that may complement existing clinical treatments for GA, with further validation required for translational application.