Thermosensitive microemulsion gel incorporating nano-ZnO and black soybean tar improves treatment adherence and alleviates psoriasis-like skin disease.

Tar has been used as a natural product in the treatment of psoriasis for thousands of years and has achieved good clinical therapeutic effects. This study aimed to develop black soybean tar (BST)-zinc oxide (ZnO) composite thermosensitive microemulsion gels (BST-ZnO-MBGs) to improve the properties of BST, increase patient compliance, and enhance drug treatment effects. BST-ZnO20/500/3000-MBGs containing different sizes of ZnO were prepared by high pressure homogenization technology, and the rheology, zinc ion release and transdermal mechanism of the gels were studied. The pruritus model of guinea pigs and the psoriasis-like model of mice were used to evaluate the therapeutic effect. The addition of 20 nm ZnO ensured the best mechanical properties and therapeutic effect. It could increase the itching threshold of guinea pigs by more than 15 times and reduce the epidermal thickness of psoriatic mice by 75.45 % compared with the marketed BST ointment, and also had a strong anti-inflammatory effect. BST-ZnO-MBGs could significantly relieve psoriasis skin lesions and itching with fewer side effects. A promising approach for natural products of psoriasis was presented, and this study also provided new possibilities for the application of microemulsion gels to other skin diseases.