Orally Administered Self-Microemulsifying Celastrol Alleviates Rheumatoid Arthritis by Modulating the Expression of TNF-α

Objective: This study aimed to develop an oral celastrol-loaded self-microemulsifying drug delivery system (Cel-SMEDDS) to enhance the therapeutic efficacy against rheumatoid arthritis and reduce toxicity. Methods: The optimal Cel-SMEDDS formulation, identified through solubility screening, excipient compatibility assays, and pseudo-ternary phase diagram analysis, was characterized by particle size, PDI, zeta potential, in vitro release, and stability. In vitro anti-inflammatory activity was evaluated in LPS-induced RAW264.7 macrophages, while in vivo anti-RA efficacy was assessed in CIA mice via paw swelling, clinical scoring, serum TNF-α, and joint histopathology. Preliminary safety was examined by hematological, serum biochemical, and histopathological analyses in mice. Results: The optimal Cel-SMEDDS formulation consisted of LABRAFIL M 1944 CS-Kolliphor RH40-CAPRYOL 90 (0.2:0.48:0.32, w/w/w) with a drug loading of 1.5% (w/w). It spontaneously formed uniform microemulsions with a mean particle size of 26.70 nm, PDI of 0.067, and zeta potential of −2.87 mV. In vitro, Cel-SMEDDS showed enhanced cytotoxicity against M1-type macrophages (IC50 = 0.1753 μg/mL vs. 0.2684 μg/mL for free Cel), significantly suppressed pro-inflammatory TNF-α and IL-1β expression, and upregulated anti-inflammatory IL-10. In CIA mice, oral Cel-SMEDDS reduced paw swelling by 37.42% (vs. 22.79% for free Cel), markedly decreased serum and intra-articular TNF-α levels, and alleviated articular cartilage damage. Preliminary safety evaluation demonstrated no significant abnormalities in hematological parameters, liver/kidney function, or major organ histology. Conclusions: The optimized oral Cel-SMEDDS effectively inhibits the expression of pro-inflammatory cytokine TNF-α both in vitro and in vivo, exhibits superior anti-RA activity compared to free Cel, and possesses favorable safety. This formulation addresses the key limitations of celastrol and shows promising potential for clinical translation in RA treatment.