Abstract: BACKGROUND: Auricular acne is an infection of hair follicles or sebaceous glands, primarily manifesting as skin itching, redness, swelling, pain, and scarring. In severe cases, it can even lead to intracranial infection and facial paralysis. Isorhamnetin is a flavonoid compound with pharmacological activities including anti-inflammatory, antioxidant, cardioprotective, antitumor, and immunomodulatory effects, and may also play an important role in the treatment of skin inflammation-related diseases.
OBJECTIVE: To investigate the effect of isorhamnetin on skin lesions and the transforming growth factor β1 (TGF-β1)/mothers against DPP homolog 3(Drosophila) (Smad3) signaling pathway in a rat model of auricular acne. 
METHODS: A rat model of auricular acne was established. Successfully modeled rats were randomly divided into model group, low-dose isorhamnetin group, high-dose isorhamnetin group, and high-dose isorhamnetin+SRI-011381 (TGF-β1/Smad3 pathway activator) group. Another normal healthy rats served as the control group. After the intervention, skin lesion severity was scored, and the auricular swelling rate was calculated. Serum levels of inflammatory factors were detected by ELISA. Histopathological changes and fibrosis of auricular tissue were observed using hematoxylin-eosin and Masson staining. Expression of α-smooth muscle actin and type I collagen was detected by immunohistochemistry. Expression of TGF-β1/Smad3 pathway-related proteins was detected by western blot.
RESULTS AND CONCLUSION: Compared with the control group, the model group showed local cartilage disruption, skin tissue thickening, epidermal spinous cell proliferation, sebaceous gland hyperplasia, enlarged hair follicle openings, loose dermal structure with visible edema and necrotic foci, marked inflammatory cell infiltration, increased blue collagen fiber deposition, and enlarged fibrotic area in the auricular tissue. Additionally, the model group exhibited significantly higher skin lesion severity scores, auricular swelling rates, levels of tumor necrosis factor α, interleukin 6, interleukin 1β, and interleukin 18, as well as increased expression of α-smooth muscle actin, type I collagen, TGF-β1, and phosphorylated Smad3/Smad3, while interleukin 10 levels were significantly decreased (P < 0.05). Compared with the model group, the low- and high-dose isorhamnetin groups showed varying degrees of improvement in auricular tissue pathological changes, reduced blue collagen fiber deposition, decreased fibrotic area, lower skin lesion severity scores, auricular swelling rates, levels of tumor necrosis factor α, interleukin 6, interleukin 1β, and interleukin 18, and reduced expression of α-smooth muscle actin, type I collagen, TGF-β1, and phosphorylated Smad3/Smad3, along with increased interleukin 10 levels (P < 0.05). The high-dose isorhamnetin+SRI-011381 group reversed the improvements in auricular tissue pathological damage, skin lesion severity scores, auricular swelling rates, inflammatory factors, and fibrosis observed with high-dose isorhamnetin alone. To conclude, these findings indicate that isorhamnetin can ameliorate skin lesions in a rat model of auricular acne, and this effect may be related to inhibition of the TGF-β1/Smad3 signaling pathway.

Key words: isorhamnetin, TGF-β1/Smad3 pathway, auricular acne, skin lesions, inflammatory factors, rats