Ulcerative colitis (UC) is a chronic idiopathic inflammatory disease that affects the colon, characterized by recurrence and remission of mucosal inflammation. Mucosal inflammation begins in the rectum and continues proximally to the colon [1]. The morbidity of UC is increasing in developing countries, thereby constituting a major public health problem [2]. Irritable Bowel Syndrome (IBS) is one of the most prevalent functional gastrointestinal disorders [3]. It affects approximately 10%∼ 25% of adults worldwide and occurs primarily in women [4, 5]. IBS typically manifests as a chronic and relapsing condition, characterized by several intestinal symptoms including abdominal pain, bloating, a sensation of incomplete evacuation, and altered bowel habits [5, 6]. It has become a healthcare burden on society due to severe psychological state and quality of life (QoL) damage [7]. UC and IBS appear to be quite separate entities, but they do share similarities in clinical symptoms and pathogenesis, even for treatment. Common etiology includes altered gut permeability, gut microbiota dysbiosis, mucosal immune responses, psychological factors, and abnormalities of enteric nerve structure and function [8–10]. Evidence has revealed that around 36% of UC patients have persistent IBS-like symptoms containing abnormalities of sensation, motility, and gut microbiota [11]. Current treatments for IBS include tachykinin, histamine receptor antagonists, and dietary therapy [12]. Therapeutic options for UC include 5-aminosalicylic acid, corticosteroids, anti-TNF agents, and JAK inhibitors [13]. Due to the similarity in pathogenesis, the same treatment may be used for IBS and mild UC patients, including Mesalazine, microecological preparations, and dietary therapy. With the prolongation of western medicine treatment time, distinct degrees of side effects will occur to affect adherence to the treatment process and thus reduce efficacy.

Traditional Chinese medicine (TCM) has been considered an alternative therapy for UC and IBS. TCM is known for its mild nature and has fewer side effects than western medicines. Rhubarb peony decoction (RPD) is a well-known TCM formula, first described in the “Golden Chamber Synopsis” written by the Chinese physician Zhongjing Zhang in the Chinese Eastern Han dynasty, and has more than 2000 years of clinical application history in China. RPD is composed of five herbs: da huang (Rhei Radix et Rhizoma), tao ren (Persicae semen), dong gua zi (Benincasae semen), dan pi (Moutan Cortex), and Mirabilite (a mineral substance, Na₂SO₄·10H₂O). RPD is widely used to treat intestinal carbuncle in China. So far, its novel and effective pharmacological effects on UC have been repeatedly discovered. Luo et al. confirmed that RPD could significantly alleviate the pathological damage in the colon of UC mice by reducing the proportion of Thl7 cells and inflammatory cytokine mediators [14]. Moreover, its major active ingredient, 6-methyl-1,3,8-trihydroxyanthraquinone with the commercial name of Emodin appears to have multiple health benefits in the treatment of a host of diseases, such as immune-inflammatory abnormality, bacterial infections, and tumor progression [15].

Consistent with UC, spleen deficiency and liver stagnation are the root causes of IBS. We speculate that RPD can not only exert significant effects on UC but also IBS. There is a lack of study on the common biological mechanism of RPD in treating IBS and UC. The explanation of the scientific connotation of “the same treatment of different diseases” is one of the significant contents of TCM modernization. Therefore, this study attempted to undertake network pharmacology to further explore the underlying core targets and pathways of the overall treatment effect of RPD against both IBS and UC (Figure 1). Further, this study aimed to provide a reliable reference value for subsequent research including experimental verification and new drug development, as well as for new clinical application.

Although the significant difference between UC and IBS is the endoscopic manifestation, more than 30% of quiescent UC patients report IBS-like symptoms, irrespective of whether they are accompanied by low-grade inflammation or not. UC concurrent IBS tends toward more severe psychological symptoms and worse quality of life, so proper intervention is warranted [25, 26]. Despite various established treatments for UC or IBS, promising feasible therapies for the overlapping symptoms remains a challenge. It still represents a therapeutic conundrum in the clinic because of the lack of comprehensive guidelines. As chronic intestinal inflammation exerts multi-system effects with heterogeneous symptoms and numerous complications, long-term western medicine treatment facesd problems such as gradual reduction of efficacy and many side effects, and more drug targets need to be explored.

Guided by a holistic view and syndrome differentiation, TCM achieves multi-target and multi-pathway efficacy through prescription and prescription coordination and interaction. Network pharmacology is an excellent tool to construct a drug-target network and reveal the underlying mechanisms of TCM. Spleen deficiency was regarded as the original cause of UC based on TCM theory [27]. Additionally, spleen deficiency and liver stagnation are the root causes of IBS [28, 29]. There is a certain internal relationship between the constitution and the syndrome, so the same treatment can be adopted. Nowadays, RPD has extensively been used for UC in previous studies, and its specific effectiveness was acknowledged in improving intestinal mucous lesions, modifying gut microbiota dysbiosis, and reducing inflammatory response [14, 30]. However, there is a lack of holistic and systematic understanding of the material basis and molecular pharmacological mechanism of its efficacy. Therefore, we performed a multi-level network to further clarify the underlying regulatory mechanism of RPD in the process of UC and IBS, thus enabling the provision ofadequate recommendations regarding potential treatment options.

By integrating all the targets of RPD and disease, 126 relative targets were identified, and top targets such as JUN, TP53, MAPK1, RELA, MYC, and ESR1 in the PPI network were considered as hub genes. Meanwhile, the GO and KEGG analysis revealed that inflammation, oxidative stress, immunity, oncogenicity, and gut microbiota dysbiosis are significantly involved in the pathological mechanisms of UC and IBS. BP enrichment results indicated that a variety of genes were associated with oxidative stress, including “response to oxidative stress,” “response to xenobiotic stimulus,” and “cellular response to chemical stress.” Emerging evidence has made great strides in clarifying that oxidative stress plays a crucial role in the development of colitis [31]. During inflammatory episodes, diffusive inflammatory cell infiltration and small intestinal mucosal crypt abscesses in colitis trigger the over-production of reactive oxygen species (ROS), followed by intestinal cell layer damage via free radical-dependent apoptosis. These pathological states lead to pathogen invasion and exaggeration of inflammatory cell infiltration as well as inflammatory damage [32], which ultimately promotes the initiation and progression of UC. Furthermore, several studies associate mild inflammation with IBS, and oxidative stress may be a crucial pathological factor since tissue damage due to oxidative attack is currently associated with inflammation [33, 34]. Moreover, an extensive study reported shreds of evidence of immune activation and epithelial barrier dysfunction in IBS patients with no other features of overt inflammation, containing intraepithelial lymphocyte aggregation and proinflammatory cytokine expression [35]. Therefore, ROS-targeted treatment and antioxidant prevention were proposed to be potential measures for alleviating UC and IBS [36].

Furthermore, the molecular docking results indicate that MAPK1, RELA, TP53, JUN, MYC, and ESR1, have superior affinities to the five core compounds quercetin, kaempferol, aloe-emodin, beta-sitosterol and (+)-catechin, which verified that colon damage may be repaired by improving inflammation, and reducing oxidative stress. Quercetin is a natural polyphenolic compound belonging to the flavonoid family. It is considered the most effective reactive oxygen species (ROS) scavenger by upregulating proinflammatory factors. Multiple animal models have confirmed quercetin exerts antioxidant and anti-inflammatory effects [37] by appearing to be mediated via interference in signal transduction pathways including the NF-κB and kinase systems [38]. Quercetin could offer dose-dependent protection for colitis mice through an antioxidant-like effect [39]. It is congruent with the fact that inflammatory responses are the important pathological mechanism of UC and IBS. Kaempferol is also a flavonoid with anti-inflammatory effects and has potential effects on alleviating murine experimental colitis by inhibiting the LPS-TLR4-NF-κB Axis and altering gut microbiota [40].

Likewise, aloe-emodin (a bioactive component of rhubarb), with a higher degree value in the PPI network, exerted an anti-inflammatory role by suppressing the secretion of inflammatory factors, downregulating the cascade reaction of NF-κB, MAPK, and PI3K pathways [41]. Aloe vera improved UC by enhancing colon mucus barrier functions in addition to reducing inflammation [42]. Increasing experimental and clinical evidence demonstrated that emodin exerted multi-targeting therapeutic mechanisms, involving anti-inflammatory, immunomodulatory, anti-fibrosis, and anti-tumor properties [15]. Catechins-flavanols attributes to flavonoids with diverse biological functions. They could exert potent antioxidant effects by inducing apoptosis, arresting cell-cycle, inhibiting NF-κB, and suppressing COX-2 overexpression in vitro and animal experiments [43]. β-Sitosterol is a phytosterol in plants that may play an anti-inflammatory role by reducing the production of proinflammatory cytokine and ROS [44]. Kang et al. found that novel effects of β-Sitosterol contributed to improving UC by exerting antimicrobial activity [45]. Taken together, the bioactive ingredients screened from RPD played significant roles in anti-inflammatory properties. These pharmacological activities indicated the interaction between “multiply compounds,” “multiply targets,” and “multiply pathways” of RPD.

KEGG analysis results demonstrated that the mechanism of RPD in the treatment of UC and IBS was mainly related to the following pathways indicating multiple targets and multiple pathways: “AGE-RAGE signaling pathway in diabetic complications,” “Inflammatory bowel disease,” “NF-κB signaling pathway,” “MAPK signaling pathway” and “Tp53 signaling pathway.” AGE-RAGE signaling pathway was involved in and mediated various signaling pathways by activating the PI3K-Akt and MAPK as well as the NF-κB signaling pathway, to induce ROS production and lead to inflammatory responses. NF-κB is acknowledged as a sign and the central pathway of inflammatory response, mediating various signaling pathways of inflammatory response [46]. The transcription factor NF-κB initiates expression of proinflammatory cytokines including IL-6, TNF-α, and IFN-γ [47]. The polymorphism of NFKB1A is associated with an increased risk of UC [48]. RELA is also a crucial member of the NF-κB family. Saito et. al claimed that compared to the resting proximal colon, a higher methylation level of ESR1 was detected in the actively inflamed colon [49]. Advanced glycosylation end products (AGE) and IL-17 can also be used as mediators for NF-κB pathway activation [50, 51]. Higher RAGE levels and RAGE polymorphisms have been found in UC patients correlated with the nuclear expression of pro-inflammatory, pro-oxidant, and pro-oncogenic genes [52], thus these pathways may be the potential inhibition point of intestinal symptoms and the progression to colorectal cancer (CRC) [47].

It is well-known that CRC is associated with the inflammation–dysplasia sequence, which poses a major threat to the prognosis of UC and IBS. The incidence of UC-related colon cancers was 1.6∼3.7%, accounting for 5.4% in all colon types [53, 54]. Chronic inflammation, the increased turnover of epithelial cells, and ROS production are thought to contribute to the development of dysplastic lesions, which may then transform into CRC [55]. JUN is a proto-oncogene that can induce oncogenic transformation [56]. The mutation of the p53 gene is a critical genetic change, involved in the early stages of UC-associated carcinogenesis of the colorectum. It is also used as a biomarker in predicting the risk of evolution toward malignancy [57].

Gut microbiota alternation is one of the underlying factors in perpetuating IBS symptoms [58]. Both our study and another study confirmed that the action mechanism of RPD is related to microbiota [14]. RPD could restore α diversity by enhancing Firmicutes and Actinobacteria and reducing Proteobacteria and Bacteroidetes [14]. Furthermore, quercetin was verified to exert a therapeutic effect in UC by altering the composition of gut microbiota [59]. The abundance of Bifidobacterium, Bacteroides, and Lactobacillus increased significantly while Fusobacterium and Enterococcus decreased totally. These findings indicate that RPD has the comprehensive ability to modify gut microbiota and suppress pro-inflammatory cytokines. Therefore, our results indicate that RPD may also have a role in regulating intestinal microbiota.

UC is a chronic recurrent intestinal inflammatory disease, whereas IBS is a functional intestinal disorder. The current clinical treatments for them are different, as IBS requires mainly symptomatic treatments. And the goal of UC treatment is to achieve clinical or endoscopic remission. It is challenging to tell the difference between IBS patients and UC in remission due to the numerous similarities between the two. Timely and accurate identification is key to avoiding overtreatment of IBS or delayed diagnosis of UC. When the two conditions are difficult to distinguish, Chinese medicine may be a proper option. However, the present study has several limitations. Firstly, absorption pathways, effective sites, and dose-effect outcomes, markedly effective components of bioactives in RPD, should be studied in depth. Secondly, the complex interaction between gut microbiota and herbal compounds needs more exploration. Moreover, any single certain bioactive detected in RPD is not sufficient to stand in completely for RPD. Thus, more experiments are required to further explore the potential molecular mechanism of RPD in the treatment of UC-IBS in vitro and in vivo.

In conclusion, both network pharmacology and molecular docking were applied to predict the common mechanism of RPD for the treatment of UC and IBS. The GO and KEGG pathways significantly enriched several signaling pathways involved in inflammation, oxidative stress, immunity, oncogenicity, and gut microbiota dysbiosis. Meanwhile, molecular docking results further verified that all the key active ingredients exhibited superior affinities to their core targets. RPD has revealed synergistic therapeutic effects in the treatment of UC and IBS partly by regulating multi-component, multi-target, and multi-pathway effects, which coincide with the biological mechanism of “treating different diseases with the same treatment.” This study offers novel insights into the effective therapeutic and management strategies for patients overlapping between UC and IBS, proposing future directions for research in this stimulating field.