Study on the therapeutic effects of Qinghuang ointment in a mouse model of imiquimod-induced psoriasis and its underlying mechanisms

[Objective] To study the therapeutic effects of Qinghuang ointment on psoriasis and its underlying mechanisms in a mouse model. [Methods] Twenty-five mice were randomly assigned to the following groups: blank control group, model group, Qinghuang ointment group, positive control group, and vehicle control group, with 5 mice per group. Except for the blank controls, all mice were treated topically with 5% imiquimod cream once daily for seven days to establish a psoriasis model. The Qinghuang ointment group and the positive control group were topically treated with Qinghuang ointment and clobetasol propionate urea cream, respectively, for 7 days, while mice treated with vehicle alone served as vehicle controls. The mice were observed daily for changes in erythema, scaling, and skin thickness on their backs, and PASI scores were recorded. On day 8, the stratum corneum hydration (SC), transepidermal water loss rates (TEWL), and pH value on the back skin were measured. Hematoxylin and eosin (HE) staining was performed to examine histopathological changes in the back skin. The spleen index was calculated. The mRNA expression levels of cytokines, TNF-α, IL-6, IL-17, IL-23 and IFN-γ, in skin tissues were measured by quantitative real-time PCR (qPCR). [Results] Starting from day 2, all groups except the blank control group began to develop erythema, scaling, and thickened skin lesions on their backs. The severity in the Qinghuang ointment group was reduced compared to the model group. The histopathological examination showed that compared to the model group, the Qinghuang ointment group reduced epidermal thickening, and decreased hyperkeratosis, parakeratosis, and inflammatory cells. Compared with the model and vehicle groups, mice in the Qinghuang ointment group showed significant reductions in PASI scores, reaching levels comparable to those in the positive control group. Moreover, Qinghuang ointment increased SC, decreased TEWL and the spleen index, while downregulating the mRNA expression levels of TNF-α, IL-6, IL-17, and IL-23 (all P<0.05 vs. model group). There were no significant differences in the expression levels of TNF-α、IL-17, and IL-23 mRNA between the positive group and the Qinghuang ointment group. There were no significant differences in either pH (F=1.22, P=0.335) or IFN-γ mRNA expression (F=2.49, P=0.088) among the five groups. [Conclusions] Qinghuang ointment has a good therapeutic effect on psoriasis in mice, and its mechanism may be related to improving skin barrier function, modulating immune responses, and inhibiting Th1/Th17 cell-mediated inflammatory response.