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Epimedii folium (EF) is the dried leaves of Epimedium brevicornu Maxim., Epimedium sagittatum (Sieb. et Zucc.) Maxim., Epimedium pubescens Maxim., or Epimedium koreanum Nakai. EF can be used to treat osteoporosis, menopausal syndrome, breast lumps, hypertension, coronary heart disease, and other diseases1. As a traditional Chinese medicine (TCM), EF has a history in medicine and food of more than 2,000 years. Due to its low price and remarkable effect of tonifying the kidneys, it is widely used in medicines and health foods. EF is processed by stir-frying it with mutton oil, a process first described in Lei Gong Processing Theory written by Lei Xiao in the Liu Song period2. The efficacies of crude EF and stir-fried EF are quite different. Crude EF mainly dispels rheumatism, whereas the stir-fried EF warms the kidneys to reinforce yang3. At present, EF is widely used as a raw material in drugs and health foods; there are 399 listed Chinese patent medicines, nine imported health foods, and 455 domestic health foods with EF as a raw material4. This medicinal material has great application prospects. However, in recent years, there have been increasing reports of adverse reactions and human liver injury caused by health foods and Chinese patent medicines using EF as a raw material, and related toxicity studies5,6,7 have reported that EF as a raw material has potential safety risks.
Chinese medicinal processing refers to pharmaceutical techniques that can effectively reduce or eliminate the toxicity and improve the safety of TCMs. The traditional processing method of EF is stir-frying with mutton oil, which reduces the toxicity of EF and enhances its effect of warming the kidneys and promoting yang8. This processing method is included in the Chinese Pharmacopoeia and various processing specifications1. The process of EF is only specified as follows: for every 100 kg of EF, 20 kg amniotic oil (refined) is added, and it is mild-fired until uniform and shiny1. There are no strict EF processing method parameters in the above standards, so local processing specifications have not been unified to provide consistency. Therefore, it would be useful to conduct a systematic study of the EF process. In this paper, the Box-Behnken experimental design-response surface method was used to optimize the processing technology of EF.
The Box-Behnken experimental design is a method typically used to optimize the factors in a process. The extraction parameters can be optimized by establishing the functional relationship between multiple regression equation-fitting factors and effect values. Recently, this method has been widely used to study TCM extraction5,6,7 and processing9,10,11. Various studies have reported TCM preparation methods involving salt processing, wine processing, and stir-frying following a Box-Behnken design, such as for salt-processed Psoraleae fructus12, wine-processed Cnidii fructus13, and roasted Cinnamomi ramulus14. This method has reduced test time, high test accuracy, and is suitable for multi-factor and multi-level tests. The method is simpler than the orthogonal design test method and more comprehensive than the uniform design method15. The obtained relationships can determine the predicted value of any test point within the test range, which is a great advantage. A zebrafish model can be used to test whether EF is less toxic after processing.
In TCM toxicity studies, the zebrafish model has the dual advantages of the high throughput of cell experiments and the similarities with rodent experiments16. This model is characterized by its small size, high spawning rate, short reproduction cycle, and ease of breeding. The model can be used in large-scale synchronous experiments in cell culture plates, and the experimental drug dosage is small, the experimental cycle is short, the cost is low, and the whole experimental process is easy to observe and operate17. Zebrafish embryos are transparent and develop rapidly. Therefore, the toxicity and teratogenic effects of drugs on visceral tissues at different developmental stages can be directly observed under a microscope18. The gene homology between zebrafish and humans is as high as 85%18. The signal transduction pathway of zebrafish is similar to that of humans18. The biological structure and physiological function of zebrafish are highly similar to those of mammals18. Therefore, a zebrafish model for drug testing can provide experimental animals that are reliable and fully applicable to humans19.
In this study, we used the Box-Behnken design-response surface methodology to optimize the amount and temperature of mutton oil and the frying temperature used in the EF processing technology, with the contents of icariin, epimedin A, epimedin B, epimedin C, and baohuoside I as the evaluation indexes. The zebrafish model was used to preliminarily explore the effect of an EF water extract on zebrafish embryonic development before and after processing to evaluate the attenuation effect of processing on EF.