Ulcerative colitis (UC) is one of non-specific chronic intestinal inflammation which is characterized by continuous inflammatory areas occurring in mucosal surface (Krugliak Cleveland et al., 2022). The current treatments of UC mainly are 5-amino salicylic acids, immunosuppressants, glucocorticoids and biological agents, etc., which have positive short-term effects. However, the long-term usage of them associates with different side events, such as high recurrence rate after withdrawal of therapy and cumulative damage to other organs (Chapman et al., 2020). The pathogenesis of UC are widely thought to be mediated by genetic susceptibility, life style, diet, environmental factors and dysfunctional gut barrier (Shouval and Rufo, 2017). The weakened gut barrier results in translocation and invasion of pathogens to intestinal lamina propria, driving abnormal immune response and uncontrolled inflammation (de Souza et al., 2017).

UC is commonly recognized as aseptic inflammation combined with mucosal injury. Immersion of immune cells and cytokines storm within the intestinal lamina propria have been proposed as key drivers of colonic mucosal injuries. Macrophages, with remarkable plasticity, are polarized into classically activated (M1) macrophages and alternatively activated (M2) macrophages in response to immune microenvironment (Mantovani et al., 2005; Mosser and Edwards, 2008). M1 cells massively secreted pro-inflammatory cytokines IL-6, IL-1β and TNF-α. IL-1β and TNF-α increased intestinal permeability in an MLCK-dependent manner (Al-Sadi et al., 2012; Su et al., 2013). IL-6 undermined integrity and function of gut barrier by inducing the expression of claudin-2, which is related to intestinal permeability (Suzuki et al., 2011). IFN-γ-producing Th1 cells and IL-17A-producing Th17 cells massively infiltrated in the inflamed intestine, amplifying inflammatory response (Fuss, 2008; Galvez, 2014). So, regulation of immune cell crosstalk and regeneration of injured tissue might be available therapeutic strategies for UC.

Due to modest effects or drug resistance, single TCM herb or active compound may fail to achieve satisfactory therapeutic effects for UC (Zhao et al., 2010). Researchers offer alternative therapeutic paradigm for UC, from one-target drug to multiple-targets drug combination such as cocktail therapies (Zhang et al., 2015). TCM formula is comprised of multiple herbs following the guidance of herbal property (cold, hot, warm and cool) and the compatibility (peiwu) principle (monarch, minister, assistant, and guide) instead of simple aggregation of medicinal herbs or compounds (Luan et al., 2020). Compatibility is the fundamental mechanism to determine the clinical efficacy of formula, and the compatibility study is also the core task of formula research.

Huanglian Ganjiang decoction (HGD) was first recorded in Beiji Qianjin Yao Fang (Invaluable Prescriptions for Ready Reference) in the Tang Dynasty without specific name. HGD is named according to main herbs Coptis chinensis Franch. (Huanglian) and Zingiber officinale Roscoe (Ganjiang) in the prescription. In accordance with theory of herbal property and compatibility, HGD consists of cold-natured medicines: Coptis chinensis Franch. and Phellodendron chinense C.K.Schneid.; hot-natured medicines: Zingiber officinale Roscoe and Angelica sinensis (Oliv.) Diels; astringent medicine: Sanguisorba officinalis L., Punica granatum L. and Equus asinm L. (Asini Corii Colla) with a mass ratio of 2:4:3:4:4:3:2. HGD was derived from a classic TCM formula Wu-Mei-Wan rooted in the “Treatise on Cold Damage Diseases”, which was found to effectively attenuate UC (Yan et al., 2022). Another TCM prescription Zhu-Che-Wan, with similar herb combination to HGD, also improved UC patients (Zou et al., 2015). Besides, HGD and the single herb in it were clinically used for cold, distension and pain in abdomen, diarrhea and hematochezia, which are similar to clinical symptoms of UC (Xiong et al., 2016; Zhang and Zhou, 2015). For example, Sanguisorba officinalis L. water extract can reduce intestinal inflammation in UC rats (Zhao et al., 2011). Punica granatum L. extract can also ameliorate UC rats through anti-oxidation and relief of inflammatory reaction (Ai et al., 2007). Our previous studies also suggested that HGD attenuated colitis-associated symptoms and reduced inflammation (Wei et al., 2020). The compatibility between cold-natured medicine Coptis chinensis Franch. plus Phellodendron chinense C.K.Schneid. (CP) and hot-natured medicine Angelica sinensis (Oliv.) Diels plus Zingiber officinale Roscoe (AZ) is the main compatibility in HGD.

Therefore, in this study, we will investigate different effects and compatibility theory-based synergistic effect between cold-natured medicine CP and hot-natured medicine AZ in HGD on colitis mice.