Nicotine-quercetin combination alleviate ulcerative colitis via PI3K/AKT and NF-κB pathway inhibition

Ulcerative colitis (UC), a chronic, idiopathic inflammatory bowel disease (IBD) confined to the colonic mucosa, has been classified as one of the refractory diseases due to its protracted course, limited existing treatment options and high recurrence rate. Although therapeutic options have expanded, UC remains incurable. It is currently managed primarily through pharmacologic agents—aminosalicylates, glucocorticoids, immunosuppressants and biologics—each burdened by substantial toxicity, protracted administration and high relapse rates after cessation. Consequently, discovering safe and efficient UC therapeutics is an urgent clinical priority. The etiology and pathogenesis of UC are multifaceted and still under investigation. Researchers posit that damaged intestinal barrier, intestinal microbiota, and immune dysregulation all contribute to UC development. Epidemiological studies have revealed a negative correlation between smoking and the incidence of UC. Tobacco is a traditional Chinese medicine with a long history and considered for its antioxidant, anti-inflammatory, as well as immune-modulatory impacts. Nicotine (NIC), the main active component of tobacco, has shown potential in the treatment of UC in many studies. However, for non-smokers, its application is often limited due to intolerance. To maximise the effect of nicotine and minimise side effects, the dose needs to be controlled, and co-administration is a good way to do it. Consequently, through preliminary bioinformatics screening, quercetin (QUE)—a type of flavonol in tobacco and positive allosteric modulator of the α7 nicotinic acetylcholine receptor—has been identified as a potential candidate drug capable of synergizing with NIC and potentially mitigating its adverse effects. Based on these findings, this study proposed the following hypothesis: the combination of half-dose NIC and half-dose QUE may enhance therapeutic efficacy. Using a DSS-induced murine colitis model, we comprehensively evaluated clinical symptoms (body weight, disease activity index [DAI], colon length, and histopathology), gut microenvironment (microbiota composition, short-chain fatty acids [SCFAs], and barrier integrity), and inflammatory mechanisms (cytokines and signaling pathways). The NIC-QUE combination at half-doses consistently outperformed individual treatments across all parameters, including body weight recovery, DAI reduction, colon length preservation, and histological improvement. Mechanistically, this synergy originated from early remodeling of the dysbiotic gut microbiota, significantly enriching beneficial taxa such as Clostridia and Eubacterium, while suppressing pro-inflammatory Erysipelotrichia. This microbial reconfiguration led to restored SCFAs levels, specifically acetate acid, butyrate acid, propionate acid, and valerate acid. These metabolic improvements converged on suppression of the PI3K/AKT and NF-κB pathway, as evidenced by transcriptomic profiling (RNA-seq), validation of gene and protein expression (Western blot), and pathway-specific rescue experiments using agonists to confirm mechanistic necessity. In summary, this is the first study to demonstrate that combining half-dose nicotine and half-dose quercetin is an effective new strategy for treating ulcerative colitis. Its treatment mechanism mainly involves inhibiting the PI3K/AKT and NF-κB signaling pathways.