Anti-Psoriatic Potential of Rhinacanthus nasutus in HaCaT Keratinocytes and Imiquimod-Induced Psoriasis Model

Psoriasis is a long-standing inflammatory skin disease that is associated with the uncontrolled increase in the number of keratinocytes and immune system malfunction. The present study evaluated the anti-psoriatic effects of Rhinacanthus nasutus (RN), which has a history of use in the field of dermatology, and utilized both in vitro and in vivo studies. The cytotoxicity of RN solvent extracts (hexane, chloroform, ethyl acetate, and ethanol) was assessed on the HaCaT keratinocytes using the sulforhodamine B (SRB) assay at 12.5 to 200 µg/mL. A significant dose-dependent decrease in HaCaT cell viability was observed, with ethyl acetate (IC₅₀=41.5 µg/mL) and chloroform (IC₅₀ = 43.8 µg/mL) extracts being the most potent. The anti-psoriatic effect was studied in vivo using an imiquimod (IMQ)-induced psoriasis-like animal model in BALB/c mice, in which RN extracts were administered topically and orally. The psoriasis-like manifestations were significantly improved with treatment as indicated by a lower Psoriasis area severity index (PASI) score, reduced ear thickness, less epidermal hyperplasia, reduced spleen index, and histopathologic changes. There was a significant reduction in post-RN treatment IMQ-induced hematologic disturbances and elevated concentrations of pro-inflammatory cytokines (TNF-α, IL-17A, and IL-23). The ethyl acetate fraction exhibited the strongest therapeutic action compared to all the extracts with a maximum PASI score reduction of 63%, followed by the chloroform extract. Overall, Rhinacanthus nasutus has demonstrated a high anti-psoriatic effect by inhibiting hyperproliferation of the keratinocytes and modulating the inflammatory processes.