## 4 Discussion  
In this study, we used in vitro and in vivo colitis models to demonstrate that the combined administration of TA and LC exerted anti-inflammatory effects by modulating the AhR axis and influencing gut microbiota composition. Our study hypothesized that the synergistic effect of TA and LC fermentation metabolite uptake demonstrates that AhR regulates the gut microbiota through the basal axis, providing potent anti-inflammatory and protective effects on intestinal tight junctions, which was partially validated. In this study, extracting TA from _E. bicyclis_ using ethyl acetate after the initial methanol extraction increased the dieckol yield by 2.4 times, demonstrating the efficacy of this method for selectively isolating TA [38]. Fermenting the TA with LC resulted in the disappearance of the polymerized phlorotannin, dieckol, and the emergence of low-molecular-weight substances like phloroglucinol. Recognized for its excellent functional properties [39], phloroglucinol demonstrated anti-inflammatory effects in various experiments [40]. Since pure phloroglucinol might be absorbed in the small intestine and not effectively reach the colon when consumed directly or fermented externally before intake, we explored separately administering TA and LC. Another study indicated that high-molecular-weight phlorotannins potentially exert a stronger beneficial effect in the colon [41]. Notably, phlorotannin fermented with different Lactobacillus strains exhibited varying anti-inflammatory efficacy, suggesting variations in tannase enzyme production required for tannin degradation depending on the types of Lactobacillus strains [42]. It was reported that symbiotic administration facilitates probiotic colonization of the gastrointestinal tract, while prebiotics optimize the proliferation of specific probiotics, enhancing their production of active metabolites in the intestine and providing superior intestinal protection [43]. In this in vitro study, TA fermented with LC demonstrated the most remarkable anti-inflammatory effect. In vivo PCR analysis confirmed an increase in _L. casei_ abundance in the gut after consumption, indicating that phlorotannins, upon reaching the intestine, might undergo degradation, leading to increased metabolite production, including phloroglucinol, by augmented lactic bacteria. Phloroglucinol has been recently considered as one of the ligands that regulate AhR axis [25], a significant pathway involved in immune regulation within the intestines [44]. The synergistic effect of TA and LC may enhance the production of phloroglucinol from TA by LC when ingested simultaneously, thereby activating AhR to bolster immunity and repair tight junctions. The DSS-induced colitis model, which is commonly used to induce acute and chronic UC, was used in this study because of its simplicity and similarity to human UC [31]. The DSS-induced control group showed characteristics of colitis such as neutrophil infiltration, barrier damage, disruption of tight junctions, inflammation, and dysbiosis of the gut microbiome. However, mice treated with the combination of TA and LC showed significant alleviation of the disease and improved treatment effects. Phlorotannins isolated from _E. Stolonifera_ have previously demonstrated anti-inflammatory effects by inhibiting IL-1\(\beta\), IL-6, and TNF-\(\alpha\), along with a reduction in NF-\(\kappa\)B expression [45; 46]. In the current study, the synergistic combination of TA and LC reduced inflammation, particularly in parameters such as spleen enlargement and lipocalin 2, Cox2, Occludin, and STAT3 mRNA expression, which are involved in inflammatory modulation and tight junction regulation. The aryl hydrocarbon receptor (AhR) is a nuclear receptor that is pivotal in xenobiotic detoxification, immune regulation, and inflammation control. AhR activation results in the induction of cytochrome P450 1A1 (CYP1A1) and induces anti-inflammatory responses [47].