Inflammatory bowel disease (IBD), a chronic, recurrent disorder of the gastrointestinal tract that includes ulcerative colitis (UC) and Crohn's disease (CD), is characterized by inflammation and impairment of the mucosal barrier (1). There has been a notable increase in the incidence of IBD in recent years. Over 1 million individuals in the USA and 2.5 million in Europe are considered to have IBD, with significant costs for healthcare (2). In Southeast Asia, the prevalence of IBD has risen alongside its economic development and urbanization during the last two decades (3). Although the exact cause of IBD remains unknown, it is considered to be the result of a complex interaction of genetic, environmental and immunological factors (4). IBD treatment continually develops, with studies exploring new medications to enhance patient results. Numerous medications and treatment approaches have been developed, including targeted therapies (5), personalized medicine (6), stem cell therapies (7) and fecal microbiota transplantation (8). Conventional treatments, such as anti-inflammatory medications, immunosuppressants and biologics, typically aim to control symptoms rather than target the root causes of the disease, and they can also involve considerable side effects (9).

In recent years, innovative biological therapeutics targeting molecular pathways associated with intestinal homeostasis have emerged as feasible alternatives. Among these pathways, the farnesoid X receptor (FXR), a nuclear receptor known for regulating bile acid (BA) homeostasis, has attracted considerable attention due to its role in modulating inflammation and maintaining intestinal health (10). FXR plays a crucial role in BA metabolism, and its activation has been shown to defend and lessen inflammation in the intestinal lining. Impaired FXR signaling is associated with the onset of IBD, indicating that targeting this pathway may offer a potential treatment approach (10). Notwithstanding this potential, the direct activation of FXR with synthetic agonists has encountered obstacles, including inadequate efficacy and off-target consequences (11). Therefore, alternative methods for modulating FXR, primarily through endogenous biological agents, are currently under investigation.

Exosomes, nanosized extracellular vesicles released by nearly all cell types, have emerged as essential mediators in intercellular communication and possess significant potential for therapeutic applications (12). Exosomes contain a variety of bioactive molecules, including proteins, lipids and nucleic acids, which facilitate the modulation of specific signaling pathways in target cells (13). Exosomes are primarily derived from the multi-vesicles formed by the invagination of lysosomal particles in cells, and they are released into the extracellular matrix following fusion between the multi-vesicle outer membrane and the cell membrane (14). Exosomes are naturally present in multiple bodily fluids, such as blood, saliva, urine, cerebrospinal fluid and milk. The exact molecular mechanisms governing their secretion, absorption, composition and associated functions have emerged as a novel area of study interest (15). Exosomes are recognized as membrane vesicles specially secreted and involved in intercellular communication.

There is increasing interest in investigating exosomes, both to understand their functions and to explore their potential uses in developing less invasive diagnostic methods in treating and diagnosing diseases. Research has shown that exosomes obtained from certain cell types possess therapeutic benefits in regulating FXR and mitigating intestinal inflammation in IBD. Specifically, a recent study revealed that exosomes from well-defined cells, such as mesenchymal stem cells (MSCs), can influence FXR signaling to reduce IBD-related symptoms, positioning them as a promising treatment option for the disease (16). In the same way, a recent study has further demonstrated that exosomes derived from human umbilical cord MSCs (hucMSC-Ex) can mitigate IBD by triggering the SIRT1-FXR pathway in macrophages. This process decreases FXR acetylation and suppresses NLRP3 inflammasome activation (17). The distinctive ability of exosomes to transport specific therapeutic agents to inflamed tissues presents an effective approach to addressing the difficulties linked to direct FXR modulation. The present review examines the molecular mechanisms underlying FXR regulation through exosomes, their therapeutic potential, and the increasing preclinical and clinical evidence supporting their use in IBD treatment. Leveraging exosome-driven FXR modulation could lead to novel, targeted therapies that enhance outcomes for patients with IBD, providing a safer and more effective option compared with conventional treatments.

Exosomes are nanoscale extracellular vesicles (EVs) (30-150 nm) formed by the plasma membrane's inward budding, which also produces early endosomes (18). Exosomes, the smallest category of EVs, are generated within the endosomal system through the maturation process from early to late endosomes (Fig. 1). The early endosome is formed by the inward budding of the cell membrane, which progresses to form multivesicular bodies (MVBs), which are characterized by the presence of intraluminal vesicles (ILVs). MVBs release ILVs into the extracellular space as exosomes upon fusion with the plasma membrane (19). The MVB may either merge with lysosomes or autophagosomes for degradation or fuse with the plasma membrane to release the internal ILVs as exosomes (20). The key components involved in exosome biogenesis consist of ceramide and various lipid-associated proteins, the endosomal sorting complex required for transport (ESCRT) machinery that facilitates the sorting of proteins into ILVs, and tetraspanins including CD63, CD9 and CD81, which are present on the surfaces of exosomes and play a significant role in their formation and release (21). The inhibition of ALIX proteins also modulates the release of exosomes (22). The mechanism of cargo sorting is not fully understood; still, it has been revealed that the ESCRT-dependent endo-lysosomal pathway plays a crucial role in exosome formation and cargo sorting involving the syndecan-syntenin-ALIX axis (23). The released exosomes are taken up by the recipient cells via receptor-mediated endocytosis or the receptor-ligand fusion process (24). It is worth mentioning that exosomes can be released by various cell types, including B cells (25), T cells (26), mast cells (27), MSCs (28), reticulocytes (29) and neurons (30), in both normal and pathological states. They are also widespread in body fluids, food, IECs, tumors, immune cells, and stem cells (31).

Exosomes primarily function as vehicles for intercellular communication, influencing recipient cells through the transfer of their cargo (32). In a disease context, exosomes can have both beneficial and detrimental effects. Tumor-derived exosomes can promote metastasis in cancer by preparing pre-metastatic niches and suppressing immune responses, thereby facilitating tumor growth and distribution (33). In neurodegenerative diseases such as Alzheimer's and Parkinson's, exosomes are considered to contribute to the spread of pathogenic proteins across neural networks and worsen the disease progression (34). By contrast, exosomes also possess therapeutic potential due to their ability to carry and deliver drugs or genetic material directly to specific cells, thereby reducing off-target effects and improving treatment efficacy. The cardiovascular system depends on exosomes for proper functioning. In addition, exosomes are involved in cardiovascular diseases by influencing processes such as angiogenesis and inflammation, as previously documented (35). Interestingly, exosome functional effects have been extensively explored in a variety of clinical and non-pathological conditions, including stroke (36), rheumatoid arthritis (37), diabetic cardiomyopathy (38), cardiac diseases (39), respiratory viral diseases (40), skin wound healing (41) and embryo implantation (42), among others. These findings highlight the increasing interest in utilizing exosomes for therapeutic applications, especially in the development of non-invasive diagnostic tools and novel treatment strategies.

Furthermore, exosomes are composed of diverse biological substances, such as proteins, nucleic acids and lipids. Research on exosomes derived from various sources suggests they possess shared exosomal components. Currently, there are 41,860 reported exosomal proteins, over 7,540 exosomal RNA molecules and 1,116 exosomal lipid molecules derived from more than 286 exosome-based studies, all annotated according to the International Society for EVs minimal experimental requirements for defining EVs (43). The standard proteins found in exosomes include tetraspanins (CD9, CD63 and CD81), heat shock proteins (HSP70 and HSP90), and proteins involved in membrane transport and fusion (44). These proteins are integral to exosome formation and functions. Exosomes also carry various RNA species, including mRNA, microRNA (miRNA or miR), and long non-coding RNA (45). These nucleic acids can modulate gene expression in recipient cells, influencing various biological processes. Moreover, apart from protein and nucleic acid, the lipid composition of exosomes is distinct and includes phosphatidylserine, sphingomyelin, cholesterol, arachidonic acid and prostaglandins, which contribute to their structural integrity and facilitate membrane fusion events of exosomes (46). Importantly, these compounds are associated with the physiological role or pathological alterations in the original cells and also reflect the original cell types.

IBD is a chronic, non-specific intestinal inflammatory condition encompassing UC, CD and unidentified colitis. The exact etiology and pathophysiology remain unclear, but studies suggest that IBD arises from a combination of genetic predisposition, environmental factors, immune dysregulation, intestinal barrier dysfunction and gut microbiota imbalance, leading to symptoms such as chronic abdominal pain, diarrhea and recurrent mucus-filled pus discharge (47). Treatments generally depend on anti-inflammatory medications, immunosuppressive medicines, purine analogs and anti-TNF monoclonal antibodies; nonetheless, the therapeutic efficacy remains suboptimal. Several studies indicate that the pathogenesis of IBD is associated with intestinal mucosal innate immunity and acquired immunodeficiency or atypical responses (48,49). The imbalance of intestinal anti-inflammatory and inflammatory substances is a major cause of IBD pathogenesis. Research has shown that exosomes derived or released from macrophages, hucMSCs, dendritic cells (DCs), bone marrow MSCs (bmMSCs), human mast cells-1 (HMCs-1) and adipose-derived MSCs, among others, have a role in both the pathogenesis and diagnosis of IBD. A summary of the studies on IBD exosomes using various cells or tissues is presented in Table I. Macrophages play a substantial role in the inflammatory response. Macrophages are categorized into M1 and M2 subtypes based on their activation status (Fig. 2). M1 macrophages release proinflammatory mediators including TNF-α, IL-1α, IL-1β, IL-6, CXCL9 and CXCL10. M2 macrophages synthesize anti-inflammatory mediators such as IL-10, TGF-β, C-C motif chemokine ligand 1 (CCL1), CCL17, CCL18 and CCL22 (50,51). Macrophage-derived exosome activation is critical for IBD pathogenesis (52). M2 macrophage-derived exosomes enhance regulatory T (Treg) cell levels and IL-4 production while decreasing the synthesis of pro-inflammatory cytokines IL-1β, IL-6 and IL-17A. These exosomes mitigate the severity of dextran sodium sulphate (DSS)-induced colitis in mice and provide a protective effect in colitis (53). Copper chaperone antioxidant-1 (Atox1) promotes M1 polarization and enhances the production of pro-inflammatory cytokines through the reactive oxygen species-NOD-like receptor protein 3 (NLRP3) inflammasome pathway, suggesting its potential as a therapeutic target in IBD treatments. This indicates a crucial link between Atox1 activity and the exacerbation of inflammatory responses in IBD through macrophage-derived exosomes influencing M1 polarization. Similarly, tofacitinib, a Janus kinase inhibitor, modulates the production of pro-inflammatory cytokines in M1-like macrophages. It significantly hinders the development of the M2-like phenotype, as evidenced by decreased IL-10 levels and reduced CD206 expression. Consequently, these effects influence the study outcomes concerning macrophage function in inflammation and immune response modulation (54).

Moreover, exosomes released by hucMSCs have been shown to alleviate DSS-induced IBD by modulating enzyme 15-LOX-1 gene expression in macrophages, reducing inflammatory responses, and inhibiting STAT3 activation in affected tissues, thereby relieving the inflammatory response (55). Correspondingly, it was previously revealed that hucMSCs-exosome reduced the expression of the pro-inflammatory cytokines TNF-α, IL-1β and IL-6 in the colon in IBD mice, increasing the expression of the anti-inflammatory cytokine IL-10 and attenuating the inflammatory response, thus lessening DSS-induced colitis in mice (56). In addition, a recent study revealed that hucMSCs-exosome also alleviates IBD in mice by enhancing M2-type macrophage polarization via the METTL3-Slc37a2-YTHDF1 axis (57). Besides, hucMSCs-exosome specifically shuttle miR-129-5p, which plays a key role in IBD by targeting the key enzyme, ACSL4, to inhibit ferroptosis and lipid peroxidation in intestinal epithelial cells (58). This finding suggests a novel therapeutic pathway for IBD treatment through the modulation of ferroptosis.

Exosomes derived from DCs (DCs-exosomes) regulate the immune response and inhibit the onset of autoimmune disorders (59). DCs-exosomes have been used to encapsulate triptolide (TP), resulting in reduced systemic toxicity and enhanced immunosuppressive effects in models of UC and rheumatoid arthritis (60). Combining TP with DCs-exosomes enhanced targeted delivery to DCs while transforming the immune landscape by influencing T-cell differentiation and suppressing the activation of DCs. These findings highlight the capability of DCs-exosomes-TP to offer a targeted therapeutic strategy that reduces side effects and encourages immune control. Notably, DCs-exosomes treated with staphylococcus enterotoxin A were found to lower the levels of pro-inflammatory cytokines, including TNF-α, IFN-γ, IL-17A, IL-12 and IL-22, in mice with acute DSS-induced colitis (61). In the same way, the increased expression of the anti-inflammatory cytokine TGF-β not only reduced intestinal inflammation but also contributed to the unique role of DCs-exosomes in reprogramming immune cells responsible for alveolar bone loss (62). Several subtypes of DCs-exosomes were investigated, including immuno-regulatory (regDC-EXO), immune stimulatory and immune 'null' immature. The regDC EXO, which contained the TGFB1 gene and IL-10, had a high affinity for inflamed areas and was effective in inhibiting the maturation of recipient DCs and Th17 effectors while increasing Treg cell recruitment. This resulted in a decrease in bone resorption cytokines and osteoclastic bone loss, presenting a unique therapy option for degenerative alveolar bone disease. In addition, numerous studies have shown the considerate effects of exosomes derived from bone marrow MSCs (bmMSCs-exosomes) in IBD treatment. The administration of bmMSCs-exosomes in patients with CD can aid in curing perianal fistula in CD (63). This reveals that bmMSC-exosomes therapy is a safe option, with sustained fistula closure observed in a significant proportion of patients with CD. Another study reported that bmMSCs-exosomes reveal higher efficacy in reducing leukocyte infiltration and neuronal loss in the myenteric plexus compared with adipose tissue-derived MSCs (64). Although both cell types ameliorated general symptoms of IBD, such as body weight loss and morphological damage to the colon, bmMSCs-exosomes were particularly effective in targeting enteric neuropathy, highlighting their potential as a more targeted treatment option for the neural aspects of IBD. In addition, a recent animal study also revealed that NLRP3 plays a critical role in modulating the function of bmMSCs by promoting glycolysis and increasing IL-10 production (65). Notably, the study found that bmMSCs-exosome lacking NLRP3 exhibited decreased IL-10 levels and diminished protective effects against colitis. Conversely, overexpression of NLRP3 in bmMSCs-exosomes significantly improved therapeutic outcomes, highlighting the crucial role of NLRP3 in enhancing the efficacy of bmMSCs-exosomes.

Furthermore, it is worth mentioning that exosomes derived from HMCs-1 significantly disrupt intestinal barrier function by transferring functional miRNAs to intestinal epithelial cells, leading to decreased expression of tight junction proteins (TJP) (66). Notably, exosomal miR-223 from HMCs-1 was shown to inhibit the expression of claudin 8 (CLDN8), thereby impairing intestinal barrier integrity. This suggests potential new therapeutic targets for IBD treatment. The HMCs-1 enhances intestinal epithelial permeability by delivering miRNAs that downregulate TJP, notably through miR-223 targeting CLDN8. The inhibition of CLDN8 disrupts intestinal barrier integrity, suggesting potential therapeutic targets for IBD management. In the same way, HMCs-1 derived from exosomes also upregulate intestinal epithelial permeability and destroy intestinal barrier function, which is attributed to the exosome-mediated transfer of functional miRNAs from HMCs-1 (67). These transferred miRNAs also decrease the expression of TJP, including CLDN8, TJP1 and occludin (OCLN). By contrast, adipose-derived MSCs release exosomes (adMSC-exosomes), which influence the pathogenic alterations of IBD. For example, a previous study showed that intraperitoneal administration of adMSC-exosomes on acute DSS-induced colitis in mice reduces levels of TNF-α, IFN-γ, IL-12 and IL-17 while enhancing levels of IL-4, TGF-β and IL-10 in the lymph nodes and spleen (68). Intraperitoneal administration of AdMSCs and MSC-CM improves symptoms and histopathology in a mouse model of chronic colitis (69). Yet again, intraperitoneal administration of adMSC-exosomes elevates the proportions of CD4⁺ CD25⁺ Foxp3⁺ Treg cells in the lymph nodes and spleen of mice (70).

Exosomes play a role not only in disease development but also in diagnosis and prognosis. In IBD, numerous studies highlight the role of exosomes in the diagnosis and prognosis of the disease. For instance, serum exosomal microRNA-144-3p, a non-invasive biomarker for diagnosing and monitoring CD, proves its reliability in detecting mucosal inflammation and predicting postoperative recurrence with greater accuracy than conventional CRP testing (71). Serum exosomes from patients with CD also exacerbate colitis by activating macrophages and disrupting epithelial barrier function, with altered exosomal microRNA profiles, particularly the let-7b-5p/TLR4 pathway, playing a critical role in these processes and suggesting potential diagnostic and therapeutic applications (72). MiRNAs exhibit differential expression patterns in UC and contribute to the regulation of inflammatory processes. Research has revealed multiple miRNAs with significantly altered expression levels in UC tissues when compared with healthy controls (73). A study conducted miRNA microarray analysis on peripheral blood samples from patients with CD, UC and healthy controls, comparing the miRNA expression patterns of exosomes among these three groups, and discovered that miRNA expression varied between patients with IBD and healthy controls (74). Notably, miRNA expression varied between patients with CD and UC (75). This finding suggests that miRNAs in blood could be valuable diagnostic tools for IBD. Further research is needed to distinguish between different types of IBD. On the other hand, DSS-induced colitis in mice models revealed that proteomics analysis identified 56 differentially expressed proteins, most of which were acute phase proteins and immunoglobulins, suggesting that specific exosomal proteins are potential inflammatory markers of IBD (76). According to a recent review (77), MSC-derived EVs reveal their diagnostic potential in IBD, highlighting their capacity to mimic parental cell functions, which could enhance diagnostic precision by evaluating their bioactive cargoes through transcriptomic, proteomic and lipidomic analyses. Also, exosomes derived from the saliva of patients with active IBD may exacerbate colitis by influencing macrophage activity, disrupting intestinal epithelial function, and altering the gut microbiome, potentially highlighting a diagnostic role of salivary exosomes in reflecting IBD activity. Similarly, salivary exosomes from both patients with IBD and healthy controls were examined, showing that PSMA7 expression was higher in the oral epithelium of the IBD group, consistent with its expression in the colonic tissues of the same cohort (78). The findings indicate that salivary exosomal PSMA7 serves as a significant protein biomarker for IBD, potentially functioning as a diagnostic instrument for this condition.

FXR is a ligand-activated transcription factor that regulates BA production and enterohepatic circulation. It is predominantly expressed in the liver, intestines, kidneys and adipose tissue (79). FXR is encoded by the NR1H4 gene and acts as a transcription factor, regulating the expression of numerous genes involved in various metabolic processes (Fig. 3) (80). FXR is composed of two members: FXRα and FXRβ. FXRβ is a pseudogene in humans and primates; however, it encodes a functioning receptor in other animals. The FXRα gene encodes four isoforms, FXRα1-α4 (81). The four isoforms (α1, α2, α3, α4) exhibit distinct tissue distribution and roles. FXRα1 and FXRα2 are mainly found in the liver, kidney and intestine, whereas FXRα3 and FXRα4 are more highly expressed in the ileum (82). The overall structure of FXR comprises an n-terminal DNA binding domain, a distinctive ligand binding domain facilitating receptor dimerization, AF1, and a c-terminal Activation domain (AF2) for interactions with co-regulators (83). AF1 and AF2 are the domains of FXR molecules that engage with regulatory proteins. Ligand-activated FXR binds to FXR response elements in target genes and can function as heterodimers with retinoid X receptor (RXR) or as monomers to control metabolism (84). Recent explorations of FXR agonists have produced positive results attributable to their role as a ligand-activated transcription factor (85).

The key physiological functions of FXR include BA metabolism, lipid and glucose homeostasis, and inflammatory responses. FXR is crucial for regulating BA metabolism and sustaining metabolic homeostasis. BA is synthesized by the liver and reabsorbed in the small intestine via enterohepatic circulation, with ~95% of BA being reabsorbed in the small intestine (86). FXR is primarily stimulated by BA, especially chenodeoxycholic acid (CDCA), recognized as the most effective natural activator of FXR (87). Other BA, such as lithocholic acid (LCA) and deoxycholic acid (DCA), can activate FXR but with less affinity relative to CDCA (88). In response to BA stimulation, FXR functions as an essential regulator of numerous physiological processes. It regulates the production of BA by inhibiting key enzymes such as cholesterol 7α-hydroxylase (CYP7A1) and sterol 12α-hydroxylase (CYP8B1), which are essential for the conversion of cholesterol into BA (89). FXR regulates BA metabolism mainly through the hepatic FXR/small heterodimer partner (SHP) axis and the ileal fibroblast growth factor 15/19 (FGF15/19)/hepatic FGF receptor 4 axis, hence it may reduce CYP7A1 activity, therefore inhibiting BA production (90). This regulation is essential for the maintenance of BA homeostasis. FXR also affects BA transport and secretion by promoting the expression of proteins such as the bile salt export pump (BSEP) and the intestinal BA binding protein (IBABP), which aid in the transfer of BA into bile and their later reabsorption in the intestine (91). A previous study revealed that the protein level of BSEP in hyperoside-treated rats is 1.44-fold greater than that in the model group, indicating that BSEP overexpression in mice diminishes hepatic steatosis when subjected to a lithogenic or methionine choline-deficient diet, likely due to FXR activation (92). Numerous studies indicate that FXR modulates a network of genes involved in hepatic BA synthesis, biliary BA secretion, intestinal BA absorption and hepatic BA uptake, thus playing a crucial role in the regulation of BA homeostasis (93-95).

The FXR activation influences not only BA metabolism but also the regulation of lipid and glucose metabolism. Targeted modulation of FXR may effectively address obesity-related metabolic disorders. Research using mice with FXR gene deletion or the administration of FXR agonists revealed critical insights into the pivotal role of FXR in lipid homeostasis. FXR regulates the production and secretion of lipoproteins and triglycerides (96). The activation of FXR can lead to a decrease in the production and secretion of very low-density lipoprotein (VLDL) from the liver. This effect is mediated by the regulation of genes involved in triglyceride synthesis, such as phosphatidate phosphohydrolase, resulting in a marked reduction in triglyceride levels. For instance, FXR regulates serum triglyceride (TG) levels, with FXR activation through CDCA or agonist (GW4064) significantly reducing the expression of PLA2G12B in HepG2 cells. By inhibiting the expression of hepatic phospholipase PLA2G12B, the secretion of TG-rich VLDL is decreased subsequently (97). FXR also positively affects high-density lipoprotein cholesterol (HDL-C) levels by enhancing the expression of apolipoprotein C-II and reducing the expression of apolipoprotein C-III, thus improving overall lipid profiles (98). A previous study revealed that FXR activation with the agonist GSK2324 regulates hepatic lipids through both reduced absorption and selective decreases in fatty acid synthesis, with distinct pathways controlled by hepatic and intestinal FXR; hence, its activation protects against non-alcoholic fatty liver disease (NAFLD) via BA-dependent reductions in lipid absorption (99). Notably, calsyntenin-3 (Clstn3), a transmembrane protein, also improves lipid metabolism disorders in NAFLD models, with its effects potentially mediated through the FXR, offering a novel therapeutic approach for NAFLD treatment (100). Interestingly, a recent study on the humanized dyslipidemia mice model revealed that fecal microbiota transplantation from donors with dyslipidemia reshapes the gut microbiota in mice, leading to alterations in BA synthesis and cholesterol accumulation through the hepatic FXR-SHP axis, while a high-fat diet reduces Muribaculum, affecting lipid absorption via the intestinal FXR-FGF19 axis, highlighting the role of intestinal FXR in regulating lipid metabolism in diet-induced dyslipidemia mediated by gut microbiota BA crosstalk (101).

Moreover, FXR also plays a significant role in glucose homeostasis, which aids in the management of type 2 diabetes (102). FXR can inhibit gluconeogenesis, the process of producing glucose from non-carbohydrate sources in the liver, by decreasing the expression of essential gluconeogenic enzymes such as phosphoenolpyruvate carboxy-kinase and glucose-6-phosphatase (103). This action reduces fasting blood glucose levels. The generation and phenotypic analysis of Fxr^−/− mice validate this crucial function in the regulation of lipid metabolism and glucose homeostasis. In early studies, Fxr^−/− mice have increased blood concentrations of free fatty acids, triglycerides and HDL-C (104,105); a previous study further showed that PPARα activation can mitigate some of these effects, by providing a potential therapeutic strategy for conditions such as NAFLD and atherosclerosis in FXR-deficient states (106). Moreover, although previous research (107,108) has indicated insulin resistance marked by hyperglycemia, impaired glucose tolerance, and significantly reduced insulin signaling in the liver and muscle, a more recent study revealed that Mebhydrolin, an FXR antagonist, enhances glucose regulation in type 2 diabetic mice. This improvement occurs by inhibiting hepatic gluconeogenesis through the FXR/miR-22-3p/PI3K/AKT/FoxO1 pathway and stimulating glycogen synthesis via the FXR/miR-22-3p/PI3K/AKT/GSK3β pathway (109).

Numerous studies show that FXR contributes to enhanced insulin sensitivity through its impact on lipid and glucose metabolism, thereby reinforcing its role in the regulation of glucose homeostasis (96,103). According to a recent study, BA-activated FXR in glucose homeostasis and inflammation in white adipose tissue (WAT) was investigated using both whole-body and adipocyte-specific FXR-deficient mice (FXR^−/− and Ad-FXR^−/−) (110). The results revealed that FXR deficiency in adipocytes reduced WAT pro-inflammatory macrophage infiltration and inflammation, leading to improved systemic glucose tolerance, insulin sensitivity and oxidative stress. Transcriptomic analysis identified the antioxidant enzyme Gsta4 as the most upregulated gene in Ad-FXR^−/− adipocytes, suggesting that FXR regulates glucose metabolism through the modulation of oxidative stress and inflammation (110). Also, notoginsenoside Ft1 (Ft1), a potent agonist of the BA receptors membrane-bound G protein-coupled receptor (TGR5) and FXR, boosts hepatic BA production and serum BA levels, which in turn activates TGR5 in adipose tissues to alleviate high-fat diet-induced obesity and insulin resistance in mice (111). The study utilized diet-induced obese mice to investigate these effects. These findings indicate that Ft1 could be a dual-target compound for treating obesity and insulin resistance. A similar study also revealed that activation of intestinal FXR by the agonist fexaramine (FEX) modulates the gut microbiota to induce LCA-producing bacteria, which activate TGR5 and stimulate GLP-1 secretion. This signaling pathway improves hepatic glucose and insulin sensitivity, enhances lipid metabolism, and promotes white adipose tissue browning in mice, suggesting that FXR plays a crucial role in regulating glucose homeostasis and metabolic diseases through its interaction with the gut microbiota (112).

On the other hand, FXR possesses anti-inflammatory properties that may diminish the expression of pro-inflammatory cytokines. It has emerged as a significant modulator of inflammatory responses in various tissues, notably the liver and intestines. It has been documented in both animal models (MDR2^−/− mice and diethoxycarbonyl-1,4-dihydrocollidine-induced SC) and patient-derived mononuclear cells that systemic activation of FXR reduces BA synthesis and suppressed pro-inflammatory cytokines, including IL1β and TNFα, through the inhibition of hepatic macrophage activity and TH1/TH17 lymphocyte polarization (113). The result indicates that the deletion of FXR in myeloid cells led to resistance to the anti-inflammatory and liver-protective effects of FXR agonists, highlighting the importance of FXR in regulating immune responses and disease progression in disease such as sclerosing cholangitis (SC). Yet again, in the Mdr2/Abcb4 knockout (-/-) mouse model of SC, cilofexor (also known as GS-9674), a non-steroidal FXR agonist, improved liver function by normalizing serum biomarkers such as aspartate aminotransferase and alkaline phosphatase, reducing hepatic fibrosis, and lowering intrahepatic BA concentrations (114). The aforementioned study suggests that cilofexor's action through FXR activation may attenuate liver inflammation and fibrosis by modulating BA synthesis and signaling, mainly through the FGF15 pathway. In addition, FXR influences inflammatory responses by maintaining the integrity of the intestinal barrier. For example, activation of the FXR in the intestine has been shown to play a protective role in inflammation-driven models of IBD by regulating the intestinal barrier and inflammatory responses, mainly through the modulation of innate lymphoid cells (ILCs) and the reduction of pro-inflammatory cytokines such as IL17, highlighting FXR as a potential therapeutic target for inflammatory intestinal diseases (115). In the same way, a study using a mouse CAC model showed that inflammation-induced epithelial damage disrupts FXR signaling, altering BA profiles, while FXR activation in gut macrophages detects abnormal BA, releasing pro-inflammatory cytokines, promoting intestinal stem cell proliferation, and reducing intestinal inflammation and tumor growth by modulating macrophage recruitment, polarization and Th17 cell interactions (116).

Furthermore, FXR also interacts with significant inflammatory signaling pathways. NF-κB activation reduces FXR activity, likely through NF-κB-dependent tethering, highlighting a potential vicious cycle where reduced FXR activation contributes to the development of chronic intestinal inflammation (117). It is worth mentioning that FXR also has significant effects on cardiovascular inflammation. Atherosclerosis has a potential therapeutic target via the intestinal FXR/SMPD3 axis (118). The aforementioned study highlights the relationship between intestinal FXR, ceramide metabolism and atherosclerosis, and reveals that inhibition of FXR or SMPD3 reduces atherosclerosis and ceramide levels in ApoE^−/− mice. Hence, FXR serves as a key relationship between metabolic processes and immunological responses. Its activation exhibits significant anti-inflammatory effects across multiple organs, establishing it as a prospective therapeutic target for inflammatory diseases associated with metabolic dysfunction.

IBD, which includes UC and CD, are chronic diseases that cause inflammation in the gastrointestinal system (119). Despite extensive investigation into IBD, the precise pathogenetic pathways remain inadequately clarified. Currently, IBD is generally considered to arise from disruptions in gut microbiota balance, impaired intestinal barrier function, and an irregular immune response in the mucosal lining (120). Research shows that FXR activation helps modulate immune responses, promote healthy gut microbiota, decrease inflammatory processes, and strengthen the intestinal epithelial barrier. These effects are achieved through multiple pathways, such as controlling inflammatory signals, maintaining the structure and function of the gut barrier, and preventing the movement of bacteria within the digestive system (Fig. 4) (121).

Exosomes are EVs carrying nucleic acids, lipids and proteins, playing pivotal roles in IBD pathogenesis and repair. They modulate immune responses, gut barrier integrity, and microbiota homeostasis, influencing key IBD-associated pathways (161). Their therapeutic potential stems from their ability to shift macrophages toward the anti-inflammatory M2 phenotype, suppress pro-inflammatory cytokines, and deliver regenerative cargo to damaged tissues (162). Their ability to regulate immune cells, gut microbiota and barrier function emphasizes their potential as diagnostic tools, drug carriers and therapeutics.

The interplay between exosomes and FXR is crucial for intestinal repair. FXR activation is impaired in IBD, exacerbating inflammation and dysbiosis (163). Exosomes derived from MSCs, or other sources enhance FXR activity by delivering anti-inflammatory cargo, modulating miRNAs, and targeting gut microbiota. For example, MSC-exosomes reduce pro-inflammatory cytokines (for example, IL-1β and IL-6) and elevate IL-10, rebalancing gut immunity (50). The aforementioned study revealed that MSC exosomes act as natural anti-inflammatory delivery vehicles, reprogramming immune cells in the gut to suppress harmful inflammation while promoting healing. Their ability to target specific pathways (IL-10 induction) makes them a promising therapeutic strategy for inflammatory gut diseases. Interestingly, research has shown that exosomes modulate and facilitate cell-to-cell communication by transporting miRNAs, which regulate various IBD-associated processes, including barrier function and immune responses (19). These exosomal miRNAs modulate oxidative stress pathways in colitis-associated cancer and interact with the gut microbiome and metabolites to mitigate colitis (164). MiRNAs play a vital role in regulating intestinal tight junction barrier function, with defects in this barrier implicated in IBD pathogenesis (165). Besides, exosomes also play a crucial role in mediating communication between the gut microbiota and host cells, potentially FXR signaling and metabolic homeostasis. MSC-derived exosomes mitigate colitis by altering gut metagenomics and metabolomics profiles, increasing colonic FXR expression, and restoring microbial diversity (16). In the same way, exosomal microRNA-181a also plays a crucial role in these protective effects, influencing gut microbiota composition and immune responses (166). Yet again, a recent study demonstrated that exosomes influence gut microbiota composition and promote intestinal barrier integrity, which is essential for maintaining microbiota and preventing exacerbations of IBD (167). This interaction between exosomes, gut microbiota and FXR is crucial, as it suggests exosomes as mediators of the microbiota-FXR axis in IBD. As aforementioned, exosomes also play a key role in barrier repair of IBD by modulating FXR signaling, as explored in numerous studies. FXR activation protects the intestinal barrier, reduces inflammation, and regulates immune cell function (138). Peroxiredoxin 3 deficiency exacerbates colitis by increasing exosomal miR-1260b, which disrupts the intestinal barrier and activates pro-inflammatory signaling, highlighting the interplay between mitochondrial dysfunction, exosome-mediated miRNA transfer and IBD pathogenesis, a mechanism potentially modulated by FXR, given its role in gut barrier integrity and inflammation regulation (168). Macrophage-derived exosomal miR-223 also contributes to intestinal barrier dysfunction in IBD by inhibiting TMIGD1 (169).

Furthermore, the mechanistic interaction between exosomes and FXR is characterized by bidirectional regulation, where FXR activation induces the release of anti-inflammatory exosomes, demonstrating their intertwined roles in modulating inflammation. For example, FXR activation in epithelial cells triggers the release of miRNA-enriched exosomes, creating a feedback loop that amplifies anti-inflammatory effects (10). A recent study further elucidated this interplay, demonstrating that hucMSC-Ex alleviates IBD by activating the SIRT1-FXR pathway in macrophages, leading to reduced FXR acetylation and subsequent suppression of NLRP3 inflammasome activation (17). The hucMSC-Ex administration upregulates SIRT1 in macrophages, leading to FXR deacetylation. Deacetylated FXR becomes more stable, suppressing pro-inflammatory pathways. Normally, acetylated FXR promotes NLRP3 inflammasome activation, worsening IBD inflammation. The hucMSC-Ex-induced FXR deacetylation blocks NLRP3, reducing IL-1β and IL-18. FXR regulates BA metabolism and gut immunity; its dysfunction in IBD disrupts barrier integrity. By activating SIRT1-FXR, hucMSC-Ex restores anti-inflammatory macrophages and gut homeostasis. Inhibiting SIRT1 (EX 527) reversed these benefits, confirming the pathway's role. The treatment of hucMSC-Ex in mice showed higher SIRT1/FXR, lower FXR acetylation, reduced NLRP3 activity and improved colitis symptoms. Thus, hucMSC-Ex modulates SIRT1-FXR to suppress NLRP3, offering a novel IBD therapy. In the same way, a recent study also highlighted the potential of miRNA-mediated mechanisms, such as the NEAT1/miR-34a-5p/PEA15 axis, as critical therapeutic targets for reducing IBD-associated CRC progression (170). Macrophage-derived exosomes enriched with NEAT1 promote CRC development by acting as a sponge for miR-34a-5p, which subsequently restores PEA15 expression and enhances tumor stemness. Given that FXR, a key regulator of BA metabolism and inflammation, is known to modulate miRNA expression in IBD and CRC, these findings highlight the importance of targeting such pathways to mitigate CRC progression in IBD.

Moreover, research has shown that exosome-mediated delivery enables the targeted transport of FXR modulators to inflamed tissues, enhancing therapeutic precision (171). For instance, studies revealed that exosomes can deliver miRNAs such as miR-155 and miR-146a to regulate inflammatory responses (172,173). Targeting the FXR-exosome axis offers promising therapeutic strategies, including combinatorial FXR agonist-exosome therapies and engineered exosomes for enhanced mucosal repair (98). It has been well-documented that a modified exosome approach carrying FXR-regulating miRNAs or proteins (for example, hucMSC-Ex) may accelerate mucosal healing (174). This exosome's regenerative ability, along with its anti-inflammatory effects, makes it a dual-action treatment option for IBD. Besides, the therapeutic potential of exosomes is reinforced by their capacity to target specific tissues, such as the inflamed gut. Administering exosomes can migrate to the intestinal mucosa, improving their effectiveness in delivering therapeutic agents directly to the site of inflammation (175). This targeted delivery is particularly advantageous in the treatment of IBD, as it helps reduce systemic side effects and enhance therapeutic results by focusing treatment on the affected area.

In summary, targeting the FXR-exosome axis shows promise for IBD therapy through potential strategies such as FXR agonists to enhance FXR activation and promote therapeutic exosome release, exosome-based therapies using engineered exosomes to deliver FXR-regulated miRNAs or proteins for targeted anti-inflammatory and regenerative effects, and combination therapies that integrate FXR agonists with exosome-based treatments to improve mucosal healing and reduce inflammation in IBD. While preclinical evidence is compelling, clinical trials are needed to validate these mechanisms and optimize delivery systems for human applications.

Recent developments in exosome-based therapies for IBD have attracted considerable interest because of their potential to transform treatment strategies. Exosomes, tiny EVs, are key players in intercellular communication and have emerged as promising carriers for targeted drug delivery, especially in the case of IBD.

Exosome-based treatments offer significant potential in regenerative medicine, targeted drug delivery, and immunotherapy owing to their natural ability to facilitate intercellular signaling. However, their broad clinical use faces hurdles due to several challenges and risks such as exosome heterogeneity, pro-tumorigenic effects, immune-related side effects, and stability issues.

Exosomes exhibit significant heterogeneity in their biophysical properties, molecular composition and biological functions (184). This heterogeneity arises from variations in cellular origin, biogenesis pathways and selective cargo enrichment (185). Different types of exosomes have been discovered, each with unique protein and RNA compositions, and they influence target cells in varying ways. The variety of molecules within exosomes, such as proteins, lipids and different types of RNA, enables their multifaceted functions in cell-to-cell signaling and the development of diseases (186). In cancer, exosomes released by tumors affect the spread of cancer cells and the development of pre-metastatic environments by delivering cancer-promoting molecules (187). Understanding exosome heterogeneity is vital for developing effective exosome-based therapeutics and diagnostics.

Moreover, tumor-derived exosomes (TDEs) significantly influence cancer growth and metastasis. They aid in establishing pre-metastatic conditions by modifying stromal cells and encouraging the recruitment of macrophages that suppress immune responses (188,189). TDEs support cancer progression by aiding cell dispersal, blood vessel growth, and dormant states via communication between cells and the transfer of biological materials. They regulate every stage of tumor metastasis, including the initial mechanisms, pre-metastatic niche formation, immunosuppression and angiogenesis (190). TDEs can also suppress the immune system by affecting various tumor-associated immune cells, such as natural killer cells, DCs, T and B lymphocytes, and myeloid-derived suppressor cells (191). Comprehending the function of TDEs in cancer development is crucial for developing targeted therapies and diagnostic tools.

Interestingly, exosomes have superior biocompatibility, but they also face challenges compared with synthetic nanoparticles (192). Despite their strengths in targeting and biocompatibility, exosomes have drawbacks, including low drug-loading efficiency, scalability issues and batch variability (193). Clinical use is also hindered by stability challenges, such as the need for specific storage conditions and quick removal from the bloodstream (194). To address these limitations, researchers are exploring hybrid exosomes, combining natural and synthetic components.

Furthermore, while EVs, including exosomes, hold potential as therapeutic tools and drug delivery vehicles, they may also cause immune-related adverse effects (195). Factors influencing EV or exosome immunogenicity include surface proteins, cargo and cell source. A previous study revealed minimal toxicity and immunogenicity of HEK293T-derived EVs in mice (196). Dendritic cell-derived exosomes can stimulate immune responses and have been explored for cancer immunotherapy (197). Strategies to enhance or mitigate immune responses involve optimizing antigen loading, exosome composition, and in vivo trafficking. For mRNA delivery, exosomes offer advantages over synthetic carriers due to reduced immunogenicity (198). Despite progress, engineering exosomes for optimal delivery and minimizing immune activation remains challenging. Further investigation is essential to fully understand and control the immunogenicity of EVs in therapy. It should be noted that exosomes also present challenges in terms of long-term stability and preservation (199). These challenges include sensitivity to temperature fluctuations, proteolytic degradation and oxidative stress (200). Temperature fluctuations between freezing and thawing can promote particle aggregation and decreased potency, though cryoprotective agents such as sucrose and trehalose enhance stability (201). The aforementioned recent study shows that freeze-drying has proven effective for extended storage, with research indicating that lyophilized cow's milk exosomes maintained stability for up to 3 months at 50°C and up to 2 years when stored at 2-8°C (202). However, the effectiveness of lyophilization can vary based on the origin of the exosomes and the procedures used. Existing storage techniques typically demand extremely low temperatures, which reduces their feasibility in clinical settings. Ongoing research aims to improve methods for isolating, characterizing, and storing exosomes to address these challenges and enhance their use in clinical settings.

The complex relationship between exosomes and FXR in the regulation of IBD presents a promising frontier for novel therapeutic interventions. The evidence discussed in the present review highlights exosomes as key mediators of intercellular communication, capable of modulating FXR signaling to alleviate intestinal inflammation, restore gut microbiota balance, and enhance intestinal barrier function. By serving as natural carriers of bioactive molecules, exosomes offer a unique strategy for targeted drug delivery, minimizing systemic side effects while maximizing therapeutic efficacy in IBD treatment. Moreover, the potential of exosome-based therapies extends beyond FXR regulation, opening avenues for personalized and precision medicine in managing chronic gastrointestinal diseases.

Notwithstanding the hopeful findings, several challenges must be addressed before exosome-based FXR therapies can be widely adopted in clinical settings. One of the primary limitations is the standardization of exosome isolation, purification and characterization methods. Current techniques often yield heterogeneous exosome populations, leading to variability in therapeutic outcomes. Additionally, the stability and scalability of exosome production for large-scale clinical applications remain significant hurdles. Further research is needed to refine engineering approaches that enhance exosomal targeting, cargo loading and delivery efficiency to inflamed intestinal tissues. Another critical challenge lies in the complexity of FXR signaling. While FXR activation has demonstrated protective effects against intestinal inflammation, its role is context-dependent, and excessive FXR stimulation may have unintended metabolic consequences. Understanding the precise mechanisms by which exosomes influence FXR in different pathological states of IBD is essential for optimizing therapeutic strategies. Moreover, the immunomodulatory effects of exosomes necessitate rigorous safety evaluations to ensure they do not trigger adverse immune responses or contribute to disease exacerbation. Future research should focus on conducting well-designed preclinical and clinical studies to validate the efficacy and safety of exosome-based FXR modulation in IBD. The integration of cutting-edge technologies, such as single-cell RNA sequencing and proteomics, will provide deeper insights into exosomal cargo composition and its impact on FXR signaling.

In summary, exosome-mediated FXR regulation represents a promising therapeutic avenue for IBD, offering targeted, minimally invasive and potentially long-lasting benefits. Addressing the current limitations through innovative research and technological advancements will be crucial in translating these findings into viable clinical applications. As the field continues to evolve, exosome-based therapies hold the potential to revolutionize IBD treatment, improving patient outcomes and quality of life.