The dual roles of natural cannabidiol in combating oxidative stress and inflammation: A potential intestinal guardian.

1
Introduction
Plant cannabinoids (phyto-CB) derived from Cannabis sativa, including cannabidiol (CBD) and tetrahydrocannabinol (THC), share similar chemical structures [1]. Among these compounds, CBD has attracted growing attention due to its non-psychoactive characteristics and diverse pharmacological activities. As the second most abundant active component in cannabis, CBD exerts neuroprotective, anxiolytic, antidepressant, anti-tumor, antioxidant, and anti-inflammatory effects [2]. These effects largely arise from its interactions with the endocannabinoid system (ECS), a regulatory network involved in numerous physiological processes through biological signaling [3]. Acting as either an agonist or antagonist at multiple ECS receptors, CBD modulates redox homeostasis and immune responses via receptor-mediated pathways [4], thereby conferring therapeutic potential in oxidative stress–related inflammatory diseases, as demonstrated in vivo in models of colitis [5], liver injury induced by chronic alcohol intake combined with a high-fat, high-cholesterol diet [6], and autoimmune encephalomyelitis [7].
Recent evidence has expanded understanding of CBD's bioactivities within the gastrointestinal system, revealing prominent antioxidant and anti-inflammatory effects [8,9]. In vitro studies using hydrogen peroxide (H2O2)-stimulated Caco-2 cells—human colorectal adenocarcinoma-derived intestinal epithelial cells [10]—and tumor necrosis factor-alpha (TNF-α)-stimulated IPEC-J2 cells, a porcine small intestinal epithelial cell line [11], demonstrate CBD's capacity to preserve intestinal barrier integrity. In parallel, murine colitis models show that CBD ameliorates inflammatory manifestations such as body weight loss, fecal bleeding, and colonic injury [12]. Beyond these direct actions, emerging preclinical data indicate that CBD modulates gut microbiota composition and associated metabolites, particularly short-chain fatty acids (SCFAs)—including butyrate, acetate and propionate—which serve as essential energy substrates for colonic epithelial cells and contribute to intestinal development, villus proliferation, barrier maintenance, redox homeostasis, and immune regulation [13]. Consistent with these roles, oral CBD administration elevates serum SCFA levels, such as increased butyrate in collagen-induced arthritis rats (35 mg/kg for 21 days) [14] and elevated acetate and propionate in mice treated with CBD (30 mg/kg/day for 4 weeks) [15]. These metabolic shifts correspond with CBD-induced enrichment of SCFA-producing taxa including Lachnospiraceae_NK4A136, Allobaculum, and Veillonella [16,17].
Given the bidirectional communication between the gut and distal organs via the gut–brain axis [18] and gut–liver axis [19], alterations in gut microbiota and intestinal homeostasis can influence systemic physiology and contribute to extra-intestinal disorders. Dysbiosis is increasingly implicated in neuroinflammatory diseases (e.g., Parkinson's disease, multiple sclerosis [MS], Alzheimer's disease [AD]) and hepatic inflammatory conditions such as non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) [20]. Consequently, CBD's capacity to restore barrier function, modulate microbial communities, and enhance SCFA production may extend its pharmacological effects to these distal organs through gut–organ axes [21]. This review therefore synthesizes current knowledge on CBD's antioxidant and anti-inflammatory activities and its receptor-mediated interactions within the ECS, while critically evaluating its roles in gastrointestinal protection, microbiota regulation, and therapeutic potential in inflammatory bowel disease (IBD) and colorectal cancer (CRC). Moreover, the review explores how CBD's gut-mediated actions may influence systemic health through gut–brain and gut–liver communication pathways, providing a theoretical foundation for advancing its translational application in intestinal and related systemic diseases.

2
CBD: a plant component that maintains redox homeostasis
Reactive oxygen species (ROS) are unavoidable by-products of oxygen metabolism essential for mammalian cell survival. Among them, the gastrointestinal tract is a major source of ROS production [22]. The major intracellular ROS—hydroxyl radicals (•OH), H2O2, and superoxide (O2−•)—originate primarily from single-electron reduction of molecular oxygen due to electron leakage from the mitochondrial electron transport chain (ETC), or through direct catalysis by oxidases such as NADPH oxidase (NOX) and xanthine oxidase (XO) [23,24]. Superoxide dismutase (SOD) converts ETC-derived O2−• into H2O2, which is subsequently metabolized by catalase (CAT) into H2O and O2; in the presence of transition metals (e.g., Fe2+, Cu2+), H2O2 readily undergoes Fenton chemistry to generate highly reactive •OH [25]. Excess ROS overwhelm detoxification and repair mechanisms, causing indiscriminate oxidative damage to DNA, RNA, proteins, and lipids, and contributing to intestinal oxidative stress. CBD, a terpenophenolic compound with intrinsic antioxidant capacity, mitigates ROS accumulation through multiple mechanisms [[26], [27], [28]]: (a) direct radical scavenging via electron-donating methyl and hydroxyl groups; (b) chelation of redox-active transition metals to block Fenton-driven •OH formation; and (c) inhibition of ROS-generating oxidases such as XO and NOX. Through these direct chemical and enzymatic mechanisms, CBD effectively suppresses ROS formation and exerts immediate antioxidant protection.
Beyond its direct antioxidative actions, CBD also activates redox-regulated signaling—most prominently the nuclear factor erythroid 2–related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1)/antioxidant response element (ARE) pathway [29]. Under basal conditions, Keap1 forms a Cullin-3 (Cul3)–based E3 ligase complex that ubiquitinates Nrf2; oxidative modification of Keap1 cysteines (cys) permits Nrf2 nuclear translocation and induction of cytoprotective genes [30,31]. CBD functions as a key upstream activator of this antioxidant program: in L-02 hepatocytes, CBD (5 μM, 24 h) suppresses α-amanitin–induced ROS and upregulates Nrf2 and antioxidant enzymes—including CAT, SOD, and glutathione (GSH) [32]. In 5-fluorouracil–injured oral keratinocytes, CBD (5 μM, 12 h) similarly increases Nrf2 while elevating heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1) [33]. Mechanistic studies implicate the AMP-activated protein kinase (AMPK)/Sirtuin-3 (SIRT3) axis in CBD-induced Nrf2 activation. Caco-2 cells, also known as cancer-coli-2 cells, acquire intestinal epithelial cell-like characteristics, such as the formation of tight junctions and a rich array of microvilli, after differentiation, making them widely used as an in vitro model to study intestinal function and diseases [34]. CBD (10 μM, 24 h) increases Nrf2 abundance, enhances AMPK phosphorylation, and elevates SIRT3, a mitochondrial deacetylase required for optimal Nrf2 activation in Caco-2 cells [35]. Consistent co-activation of AMPK, SIRT3, and Nrf2 is also observed in high-glucose–damaged Schwann cells treated with CBD (3.65 μM, 24 h) and β-caryophyllene (75 μM) [36]. Moreover, in UVA/UVB-irradiated human keratinocytes, CBD (1 μM, 24 h) forms covalent adducts with Keap1 Cys288 and Cys151—residues essential for Keap1 conformation, Nrf2 binding, and Cul3-mediated ubiquitination—thereby disrupting Keap1 repression of Nrf2 [37]. Collectively, these convergent mechanisms establish Nrf2 pathway modulation as a principal, signal-regulated component of CBD's antioxidant defense. (Fig. 1)

3
Anti-inflammatory mechanisms of CBD: NF-κB and NLRP3 inflammasome signaling under redox regulation
Beyond its role in redox regulation, suppression of inflammation constitutes a major mechanism of CBD action, largely through inhibition of the nuclear factor κB (NF-κB) pathway [38]. NF-κB is a dimeric transcription factor composed of subunits such as p50, p52, p65 (RelA), RelB, and c-Rel, which are sequestered in the cytoplasm by inhibitor IκBα [39]. Pro-inflammatory stimuli—including TNF-α, interleukin-1 alpha (IL-1α), and lipopolysaccharide (LPS)—activate the IκB kinase (IKK) complex (IKKα/IKKβ/IKKγ), which phosphorylates IκBα and targets it for ubiquitin-proteasome degradation [40]. Released NF-κB translocates to the nucleus and induces transcription of inflammatory mediators such as interleukin-1 beta (IL-1β), interleukin-6 (IL-6), TNF-α, and interferon-gamma (IFN-γ) [41]. CBD attenuates this pathway across multiple systems. In high-fat/high-cholesterol diet–fed mice, CBD (5 mg/kg, 8 weeks) reduced hepatic IL-1β and TNF-α, along with phosphorylated IκBα (p-IκBα) and nuclear p65 [42]. In glucose oxidase–treated HSC-T6 and LX-2 stellate cells, CBD (5 μM, 24 h) similarly reduced p-IκBα and p65 [43]. In UVA/UVB-irradiated keratinocytes, CBD (4 μM, 24 h) lowered TNF-α expression and IKK complex abundance [44]. Mechanistic studies highlight FK506-binding protein 5 (FKBP5) as a critical target: CBD forms a stabilizing hydrogen bond with Tyr113, disrupting IKKα/IKKβ/IKKγ recruitment and LPS-induced cytokine production in BV-2 microglia (5 μM, 1 h); this effect is lost with FKBP5–Y113 mutation [45,46]. Another regulatory node involves protein kinase C (PKC): in human glioblastoma stem-like cells, CBD (10 μM, 16 h) downregulates PKC, preventing Ser311 phosphorylation of p65 and thereby limiting its transactivation capacity despite continued nuclear localization [47].
In addition to inhibiting NF-κB, CBD suppresses activation of the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, a key NF-κB–dependent effector implicated in diverse inflammatory diseases [48]. The inflammasome consists of the sensor NLRP3, the adaptor apoptosis-associated speck-like protein containing a CARD (ASC), and pro-caspase-1 [38]. NF-κB nuclear translocation initiates the priming step, inducing transcription of NLRP3, pro-caspase-1, pro-IL-1β, and pro-IL-18. The activation step is triggered by cellular stress signals—K+ efflux, Ca2+ influx, Cl− efflux, lysosomal rupture, or ROS accumulation—which promote NLRP3 oligomerization via NEK7 and assembly of the active NLRP3–ASC–caspase-1 complex [42]. Activated caspase-1 cleaves pro-IL-1β and pro-IL-18, generating mature cytokines that drive inflammatory amplification [38]. CBD inhibits both steps of this process. In high-fat/high-cholesterol diet–induced liver injury and in LPS-stimulated macrophages, CBD (5 mg/kg, 8 weeks; 5 μM, 2 h) reduced p-IκBα and p65 nuclear translocation, thereby downregulating NLRP3 and ASC expression and blocking the priming step [6]. Beyond suppressing the priming phase, CBD also interferes with inflammasome activation through a distinct upstream mechanism. In LPS- and nigericin-stimulated THP-1 cells, CBD treatment (10 μM, 30 min) markedly reduced K+ efflux and lowered NLRP3-dependent IL-1β production across a 0.1–10 μM, 24-h range [49]. Molecular docking analysis further demonstrated that CBD forms a stabilizing hydrogen bond with Glu172 of the P2X7 receptor, a key ion channel whose activation drives P2X7-mediated K+ efflux—one of the principal triggers for NLRP3 inflammasome assembly [49,50]. By dampening this ion flux signal, CBD effectively constrains the activation step of the NLRP3 inflammasome.
Notably, the activation of NF-κB signaling and the NLRP3 inflammasome relies on precise redox regulation, where Cys residues in key proteins undergo oxidative modifications in response to ROS, particularly H2O2, and antioxidant systems like GSH, thereby modulating protein function [51]. Within the NF-κB pathway, ROS-induced disulfide bond formation involving Cys54 and Cys347 of IKKγ (NEMO) promotes NEMO homodimerization and stabilizes the IKK complex, ultimately facilitating NF-κB activation [52]. In addition, S-glutathionylation represents a key redox modification that negatively regulates NF-κB signaling: glutathionylation of Cys62 in the p50 subunit impairs its DNA-binding capacity, whereas glutathionylation of Cys179 in IKKβ suppresses its kinase activity [53]. Similar redox-dependent regulatory mechanisms also operate in the NLRP3 inflammasome. ROS modulate inflammasome assembly by enhancing NEK7 phosphorylation and promoting its interaction with NLRP3, a process that critically depends on deglutathionylation of Cys253 in NEK7 [54]. In summary, the NF-κB–NLRP3 signaling axis is controlled at the molecular level by cys-dependent redox modifications (Fig. 2). Given the redox-regulatory properties of CBD, including suppression of ROS production and enhancement of GSH levels, CBD may exert its anti-inflammatory effects by modulating these redox modifications. However, whether CBD directly regulates oxidative modifications of specific redox-sensitive residues to mediate its anti-inflammatory actions remains to be further elucidated.

4
The ECS: a pharmacological target of CBD
As classical regulators of redox and immune homeostasis, Nrf2 activation and NF-κB inhibition are widely regarded as core molecular mechanisms underpinning the antioxidant and anti-inflammatory effects of CBD. Yet these pathways alone do not fully account for CBD's broad pharmacological profile. As a phyto-cannabinoid, CBD also exerts its actions through the ECS—a multidimensional regulatory network whose signaling architecture provides critical insight into CBD's intracellular mechanisms [55,56]. Given the high abundance of ECS components within the gut, CBD may influence intestinal redox balance and immune regulation, potentially contributing to its diverse pharmacological effects [57].
4.1
Composition of the ECS
Cannabinoid receptors 1 (CB1) and 2 (CB2) are well-characterized G-protein-coupled receptors (GPCRs), with CB1 predominantly expressed in the central nervous system (CNS), particularly in regions such as the pre-salient area, and CB2 found mainly in immune cells, microglia, blood vessels, and the peripheral nervous system [8]. Endocannabinoids, including anandamide (AEA) and 2-arachidonoylglycerol (2-AG), are lipid-derived molecules synthesized from membrane phospholipids, acting as endogenous ligands for CB1 and CB2 receptors [58]. Unlike typical neurotransmitters and hormones, endocannabinoids are not stored or transported in vesicles due to their hydrophobic properties. Instead, they are synthesized and released on-demand from membrane lipids in response to specific extracellular signals [59]. AEA is synthesized via NAPE-specific phospholipase D-like hydrolase (NAPE-PLD), which cleaves the phospholipid precursor N-arachidonic phosphatidyl ethanolamine (NAPE) [60]. Conversely, 2-AG is synthesized through the phosphatidylinositol 4,5-bisphosphate (PIP2) by phospholipase C (PLC), followed by conversion to 2-AG by diacylglycerol lipase α (DAGLα). Endocannabinoids synthesized in the postsynaptic membrane act retrogradely on CB1 receptors in the presynaptic membrane, inhibiting calcium ion channels and activating potassium ion channels, thereby suppressing neurotransmitter release [61]. Degradation of endocannabinoids is facilitated by fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), with cyclooxygenase-2 (COX-2) also playing a role in oxidizing 2-AG to produce the biologically active prostaglandin glyceryl esters (PGEs), which contributes to inflammatory regulation [62] (Fig. 3).

4.2
Regulatory function of the ECS in the gut
The components of the ECS are present in the intestinal epithelium and endocrine cells, where they play a critical role in maintaining gut homeostasis. They regulate essential gastrointestinal functions, including motility, permeability, hormone secretion, nutrient absorption, and the inflammatory response [63]. CB1 receptors are localized in the enteric nervous system (ENS), particularly in cholinergic neurons that contain acetylcholine, and are also found in afferent vagal neurons, modulating neurotransmitter release [64]. CB2 receptors are expressed in intestinal immune cells and epithelial cells of the intestinal mucosa, where they influence ileal contractility and are involved in immune function [65]. Both CB1 and CB2 receptors also play a role in regulating intestinal inflammation, a topic that will be discussed in detail later.
Changes in endocannabinoid levels, particularly in AEA, have been closely associated with intestinal immune status. Studies show that children with Crohn's disease (CD) exhibit lower blood levels of AEA throughout the course of the disease compared to healthy individuals, while 2-AG levels remain stable [66]. In patients with IBD, a study showed that AEA content is significantly lower in inflamed regions of the intestinal mucosa compared to non-inflamed areas, while 2-AG levels remain unchanged [67]. Additionally, this study observed a decrease in the activity of the AEA-synthesizing enzyme NAPE-PLD, coupled with an increase in FAAH activity, which degrades AEA [67]. Notably, inhibitors of enzymes responsible for endocannabinoid degradation, such as FAAH and MAGL, have demonstrated beneficial effects in alleviating intestinal inflammation symptoms [68]. FAAH inhibitors have been shown to reverse weight loss in murine colitis models by suppressing activated T cells, reducing inflammatory immune cells, and modulating pro-inflammatory cytokine-associated microRNA expression [69]. Collectively, these findings indicate that inhibiting the degradation of endocannabinoids within the gut to elevate their levels represents a potential therapeutic strategy for intestinal inflammation.

4.3
Interaction of CBD with receptors in the ECS
In addition to CB1 and CB2, the ECS includes several other receptors responsive to endogenous cannabinoids, often referred to as cannabinoid-like receptors, which are increasingly recognized as integral components of ECS signaling [8]. These receptors—such as peroxisome proliferator-activated receptor gamma (PPARγ), transient receptor potential vanilloid 1 (TRPV1), G protein-coupled receptor 55 (GPR55), 5-hydroxytryptamine 1A receptor (5-HT1A), and adenosine A2A receptor (A2A) [61]—participate in diverse physiological processes, including inflammatory regulation and redox homeostasis. All of them are expressed within the intestinal system, where they contribute to essential aspects of gut physiology [9] (Fig. 4). Considering the gut-modulating properties of the ECS and CBD's ability to interact with multiple ECS components, understanding how CBD engages these receptors is critical for elucidating its regulatory influence on intestinal function.
4.3.1
Cannabinoid receptors
Cannabinoid receptors CB1 and CB2 primarily signal through Gi/o-coupled pathways, inhibiting adenylate cyclase (AC), reducing cyclic adenosine monophosphate (cAMP) levels, and suppressing protein kinase A (PKA) activity [70]. Both receptors also interact with the mitogen-activated protein kinase (MAPK) cascade, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and phosphorylated p38 (p-p38), with p38 playing a central role in pro-inflammatory gene expression [71]. However, the influence of CB1/CB2 activation on p38 is highly context-dependent. In dextran sulfate sodium (DSS)-induced colitis, dual CB1/CB2 agonism reduces p-p38 and exerts strong anti-inflammatory effects [72]. Conversely, in murine macrophages, CB1 activation promotes inflammation via ROS production and p38 activation, an effect that is counteracted by CB2 activation of ras-related protein 1 (Rap1), which negatively regulates the pro-inflammatory effects induced by CB1 [73]. In acute pancreatitis, CB2 agonism alleviates disease but paradoxically increases p38 phosphorylation [74]. Despite these model-specific discrepancies, the activation of CB1/CB2 demonstrated a relatively consistent protective effect in the studies on experimental colitis, with CB2 promoting regulatory T-cell expansion [75] and CB1 or CB2 deficiency enhancing inflammation [[76], [77], [78]]. These divergent outcomes underscore the need for more mechanistic work to reconcile receptor-specific and tissue-specific signaling biases.
CBD further complicates this network through its multifaceted interactions with CB receptors. CBD acts as a negative allosteric modulator (NAM) at both CB1 and CB2, altering receptor activity without directly activating them [61]. For CB1, CBD engages allosteric sites within its unusually long N-terminal domain, attenuating orthosteric ligand-induced activation (e.g., by THC and 2-AG) [79,80]. At CB2, CBD exhibits dual behavior, acting as a NAM when present at low-nanomolar concentrations, but serving as a partial agonist at higher micromolar concentrations [81]. CBD also indirectly enhances CB1/CB2 signaling by inhibiting FAAH, increasing AEA and 2-AG levels; due to its low receptor affinity, this indirect mechanism likely underlies much of CBD's pharmacological effects [61]. These multimodal actions suggest that CBD's pharmacological profile arises more from network-level modulation than from classical receptor binding, an area requiring further mechanistic exploration.

4.3.2
GPR55 receptor
GPR55 is widely expressed throughout the gastrointestinal tract [82], where it regulates intestinal motility by suppressing neurogenic contractions [83]. In intestinal inflammation models, GPR55-deficient mice show milder colitis symptoms compared to wild-type controls, and GPR55 inhibitors reduce intestinal inflammation by limiting macrophage migration in the colon [84]. GPR55 is notably expressed in small intestinal intraepithelial lymphocytes (IELs), which play key roles in epithelial defense and immune surveillance. GPR55 limits IEL-epithelial cell association and negatively regulates T cell homing to the small intestine. In GPR55-deficient mice, increased IEL-epithelial interaction enhances resistance to indomethacin-induced intestinal barrier injury, improving small intestinal epithelial integrity [85]. As a result, GPR55 antagonists show promise in treating intestinal inflammation. CBD has been identified as a GPR55 antagonist [86]. Studies have demonstrated its efficacy in alleviating LPS-induced small intestinal mucosal edema and submucosal inflammatory infiltration in rats (CBD 1 mg/kg) [82]. Additionally, the study observed that CBD reversed LPS-induced inhibition of upper gastrointestinal transit, improved small intestinal electrical activity, restored intestinal contractile dysfunction, and reduced LPS-induced upregulation of GPR55 mRNA expression in intestinal tissue [87]. In line with this, intraperitoneal injection of a GPR55 agonist in mice slowed overall intestinal transit and colonic excretion; these effects were reversed by CBD (0.5 mg/kg) [88]. These findings collectively suggest that the regulatory effects of CBD on intestinal motility and inflammatory responses are associated with the GPR55 pathway.
The downstream signaling initiated by GPR55 involves an increase in intracellular Ca2+ and activation of ERK, a component of the MAPK signaling cascade [89]. Upon activation, the Gα subunit dissociates and activates members of the RhoA and Rho-associated protein kinase (ROCK), further triggering the PLC pathway and increasing intracellular Ca2+ concentration [90]. The inhibition of GPR55 and its downstream MAPK signaling pathway by CBD may be a key molecular mechanism underlying its anti-cancer effects. In colon cancer cells, treatment with CBD (2.5 μM, 1 h) or a GPR55 antagonist significantly inhibited cell migration [91]. In hepatocellular carcinoma (HCC), CBD treatment (100 nM, 24 h) suppressed cancer cell growth and metastasis by downregulating GPR55 expression and blocking the activation of the MAPK signaling pathway [82]. Similarly, in head and neck squamous cell carcinoma (HNSCC), the inhibitory effects of CBD on the GPR55/MAPK pathway and its tumor-suppressive efficacy were also reported [92]. In summary, by acting on GPR55, CBD is involved not only in immune function modulation but also demonstrates significant anti-cancer activity.

4.3.3
PPARγ receptor
PPARγ is highly expressed in colonic epithelial cells and immune cells of the gut mucosa, and is considered a promising therapeutic target for IBD [93]. In patients with ulcerative colitis (UC), PPARγ gene expression is reduced in the intestines and correlates inversely with inflammation severity [94]. CBD has been shown to reduce intestinal oxidative stress and inflammation via the PPARγ signaling pathway. Specifically, in the Caco-2 cell model, CBD (10−9 - 10−7 M, 24h) prevents SARS-CoV-2 spike protein-induced epithelial damage and inhibits the NLRP3 inflammasome pathway [95]. Similarly, in the rectal mucosa of UC patients, CBD (10−6 M, 24h) mitigates inflammation by suppressing enteric glial cell activation and reducing inducible nitric oxide synthase (iNOS) expression [96]. It is noteworthy that, in the aforementioned studies, the anti-inflammatory effects of CBD were significantly reversed upon administration of a PPARγ inhibitor. In addition, CBD (1 μM, 24h), through activation of PPARγ, reduces mitochondrial ROS levels and increases GSH in fibroblasts derived from Leigh syndrome (LS) patients, suggesting its potential for treating mitochondrial dysfunction-related disorders [97]. Notably, nitric oxide (•NO) produced by iNOS readily reacts with O2•- generated by NOX to form the highly reactive peroxynitrite (ONOO−) [98]. This NOX-NOS cross-talk dysregulation amplifies redox imbalance and cellular oxidative damage. In BV2 microglial cells, CBD (1 μM, 30 min) reduced LPS-induced iNOS expression and intracellular NO levels, an effect that was blocked by a PPARγ inhibitor [99]. Furthermore, activation of PPARγ in primary cortical neurons from mice inhibited NOX1 by reducing the expression of p22phox, a regulatory subunit of NOX that is responsible for anchoring and integrating NOX and its cofactors into the plasma membrane [100]. These findings suggest that CBD inhibits NOX-NOS cross-talk to some extent through the activation of PPARγ.
As a nuclear receptor, PPARγ modulates gene transcription by forming a heterodimer with the retinoid X receptor (RXR). This complex binds to peroxisome proliferator response elements (PPREs) in the nucleus, regulating the expression of genes involved in inflammation and oxidative stress response [101]. PPARγ directly controls redox genes such as HO-1, CAT, and GST, which are also regulated by Nrf2 [102]. Evidence indicates a positive feedback loop between Nrf2 and PPARγ, where Nrf2 enhances PPARγ expression and vice versa, promoting the expression of antioxidant genes [103]. The synergistic relationship between Nrf2 and PPARγ plays a key role in regulating inflammation through the NF-κB pathway. PPARγ inhibits NF-κB activity by forming repressor complexes at the promoters of NF-κB target genes or directly binding to NF-κB [104]. In parallel, Keap1, a negative regulator in the Nrf2 pathway, not only binds and degrades Nrf2 in the cytoplasm but also contributes to the attenuation of NF-κB signaling. This is achieved by facilitating the proteasomal degradation of the IKK complex, reducing the expression of downstream pro-inflammatory genes [105]. Thus, PPARγ plays a critical role in mediating CBD's antioxidant and anti-inflammatory effects by modulating both Nrf2 and NF-κB pathways.

4.3.4
A2A receptor
The A2A receptor is a key member of the adenosine receptor family, playing a crucial role in limiting inflammatory damage. Its activation is triggered by a rapid increase in adenosine levels under pathological conditions, such as hypoxia, ischemia, inflammation, and trauma [106]. Like other GPCRs, A2A activation influences the cAMP-PKA pathway, which has been implicated in the migration of gastric cancer cells [107,108]. In a rabbit model of immune colitis, A2A agonists inhibited leukocyte infiltration in the intestinal mucosa and reduced tissue necrosis [109]. In an oxazolone-induced rat model of colitis, the A2A selective agonist exerted anti-inflammatory effects by inhibiting interleukin 12 (IL-12) and IFN-γ production by monocytes and lymphocytes [110]. Moreover, A2A receptor activation prevented inflammation-induced intestinal motility dysfunction, a regulatory effect linked to the inhibition of neurotransmitter release [111,112]. These findings underscore the A2A receptor's association with intestinal inflammatory responses, highlighting its potential as a therapeutic target for IBD. In rat retinal microglial cells, CBD (0.5 μM, 30 min) enhances adenosine signaling by competitively inhibiting equilibrative nucleoside transporter 1 (ENT1), thereby increasing extracellular adenosine levels and suppressing LPS-induced TNF-α production [113]. In the Theiler's virus-induced murine model of MS, CBD (5 mg/kg, 7 days) exerted anti-inflammatory effects by downregulating Vascular Cell Adhesion Molecule-1 (VCAM-1), chemokines (CCL2 and CCL5), and IL-1β expression. However, these anti-inflammatory effects were partially blocked by an A2A receptor antagonist [114]. These findings suggest that CBD may modulate inflammation in an A2A-dependent manner.

4.3.5
TRPV1 receptor
The TRPV1 receptor is an ion channel that mediates various physiological effects, including muscle contraction, neuronal activity, neurotransmitter release, and the regulation of body temperature and pain through Ca2+ influx [115]. It is expressed in several organs, including the gastrointestinal tract and adipose tissue, playing a key role in metabolism, energy homeostasis, appetite control, body weight regulation, and pancreatic function [8]. Emerging evidence shows that TRPV1 interacts with appetite-regulating hormones like ghrelin, leptin, and glucagon-like peptide-1 (GLP-1) [116]. Additionally, activation of spinal sensory neurons expressing TRPV1 modulates immune responses, inducing innate lymphoid cells and macrophages while reducing the transcription factor retinoic acid-related orphan receptor gamma (RORγ)-expressing regulatory T cells in the colon and cecum, highlighting communication between TRPV1 and intestinal immune cells [117]. CBD can directly activate TRPV1 and indirectly enhance its activity by increasing endogenous ligands like AEA [118]. By activating TRPV1 receptors rather than CB1 or CB2 receptors, CBD (5 μM, 26h) enhances Nrf2 levels while concurrently reducing iNOS, Toll-like receptor 4 (TLR4), and NF-κB levels, thereby demonstrating a protective effect in LPS-stimulated murine macrophage cells [119].

4.3.6
5-HT1A receptor
The 5-HT1A receptor is one of the most prevalent serotonin (5-HT) receptors in the brain, regulating key physiological processes such as mood, sleep, pain perception, and cognition. It is widely regarded as a therapeutic target for mental health disorders, particularly anxiety and depression [120]. Notably, the 5-HT1A receptor is also expressed in intestinal epithelial cells, with approximately 90 % of the body's serotonin synthesized in the gut. Certain bacterial strains, including Lactococcus lactis subsp. cremoris, L. lactis subsp. lactis, and Streptococcus thermophilus, are capable of serotonin production [121], suggesting a potential link between serotonin signaling and disorders associated with gut microbial (GM) dysbiosis. In DSS-induced and CD4+ T cell transfer colitis mouse models, the topical administration of a 5-HT1A receptor agonist significantly mitigated mucosal damage, reduced inflammatory cell infiltration, and promoted the restoration of tight junctions [122]. CBD exerts pharmacological effects by activating the 5-HT1A receptor: it activates the 5-HT1A receptor in a concentration-dependent manner in Chinese hamster ovary (CHO) cells [123]. Moreover, the 5-HT1A receptor antagonist can inhibit the antidepressant-like effects of CBD in a mouse model of depression, as well as the increases in cortical 5-HT and glutamate levels [124]. However, the precise role of CBD-mediated 5-HT1A activation in the gut remains underexplored, warranting further investigation to fully assess its therapeutic potential in gastrointestinal disorders.

5
The potential role of CBD in the intestine
The intestine is a central organ for nutrient digestion and absorption, where the intestinal epithelium breaks down dietary components and transports essential nutrients to meet systemic physiological demands [125]. Beyond its metabolic roles, the gut also functions as a major immune organ and contains all core elements of the ECS [126]. Through its interactions with intestinal ECS components, CBD can modulate key aspects of gut physiology, including epithelial barrier integrity and GM composition (Fig. 5). These regulatory properties highlight the potential of CBD as a bioactive phytochemical capable of supporting intestinal homeostasis, with possible applications in nutritional or adjunctive dietary strategies [127]. Moreover, CBD-induced shifts in GM composition may exert broader physiological effects, influencing the function and health of distal organs throughout the body [21].
5.1
Intestinal function
5.1.1
Intestinal barrier
The intestinal barrier is essential for maintaining gut homeostasis and consists of four major components: the mechanical barrier formed by intestinal epithelial cells (IECs) and tight junctions; the immune barrier comprising immune cells and cytokines; the chemical barrier of mucus and antimicrobial peptides; and the microbial barrier mediated by the GM [128]. Together, these systems prevent harmful luminal substances—such as pathogens and toxins—from translocating into peripheral tissues.
When the intestinal barrier is compromised, intestinal permeability increases [129], allowing luminal antigens to enter the lamina propria, triggering intestinal inflammation, and in severe cases, potentially entering the systemic circulation and damaging distant organs [130]. Assessment of barrier integrity commonly involves transepithelial electrical resistance (TEER) measurements, paracellular flux assays using mannitol, inulin, dextran, PEG 4000, or fluorescein, and evaluation of tight junction proteins such as claudins, junctional adhesion molecules (JAMs), zonula occludens (ZOs), and occludin [131,132].
ROS in the gut are closely linked to barrier function. Moderate ROS levels are part of the antioxidant defense system, acting as signaling molecules that play a crucial role in intestinal inflammation and immune responses [23]. NOX1, a member of the NOX family, is highly expressed in intestinal epithelial cells and neutrophils, where it contributes to immune defense and inflammatory processes, maintaining the intestinal immune barrier's function [133]. This means that ROS, including O2•- and its derivatives like H2O2 and •NO, produced by NADPH oxidase, are essential for intestinal immune function [134]. However, excessive inflammation, such as large amounts of O2•-, H2O2, and •NO, can cause oxidative modifications of macromolecules, resulting in oxidative stress and intestinal mucosal dysfunction [135]. Lipid peroxidation is a major mechanism of intestinal barrier damage. Polyunsaturated fatty acids and cholesterol, key components of cell membranes, undergo peroxidation, disrupting lipid homeostasis and membrane function [136]. Additionally, ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) are prone to oxidative modifications, forming electrophilic aldehydes (α- and β-unsaturated aldehydes) that interact with proteins and nucleic acids, altering their structure and function, and disrupting cell signaling, thus compromising intestinal barrier integrity [137]. Therefore, using antioxidants and anti-inflammatory agents to control oxidative damage may help maintain intestinal barrier function.
Accumulating evidence indicates that CBD modulates barrier integrity across in vivo and in vitro systems, involving antioxidant effects and immune regulation. In SAMP8 Alzheimer's model mice, CBD (20 mg/kg/day i.p., 14 days) restored tight junction structure and reduced colonic permeability [138], while in Clostridioides difficile–infected chickens (15 mg/kg/day, 15 days), CBD enhanced barrier function by upregulating ZO-1 and JAM-2 [139]. In vitro, CBD protects epithelial monolayers by attenuating oxidative and inflammatory injury. In Caco-2 cells, CBD (10 μM, 48 h) improves mitochondrial function, suppresses basal and H2O2-induced ROS, activates the Nrf2 antioxidant pathway (HO-1, SOD, NQO1), and increases ZO-1 expression [10]. CBD also prevents reductions in TEER, paracellular flux, and tight junction proteins (occludin, ZO-1) induced by H2O2 or IFNγ+TNFα (1 μg/mL, 24 h) [140]. Similar barrier-protective effects are observed in IPEC-J2 cells, where CBD (40 μM, 48 h) blocks TNF-α–mediated TEER decline and claudin-1 loss [11], and at 5 μM (24 h) mitigates deoxynivalenol-induced injury via restoration of claudin-1, occludin, ZO-1, and CAT/SOD activity [141]. Collectively, these findings show that CBD protects the intestinal barrier partly through antioxidant and anti-inflammatory actions. Mechanistically, emerging data implicate the ECS. CBD elevates inflammation-suppressed claudin-5 in cytokine-exposed Caco-2 cells (10 μM, 24 h), an effect abolished by CB1 antagonism [142,143]. CBD also accelerates recovery after Ethylenediaminetetraacetic acid (EDTA)-induced permeabilization and increases ZO-1 expression in Caco-2 monolayers (10 μM, 72 h), again blocked by CB1 inhibitors [144]. These findings highlight CB1-dependent ECS signaling as a key pathway through which CBD maintains epithelial tight junction integrity and mitigates barrier dysfunction.

5.1.2
Gut microorganism
Disruption of GM composition is a major driver of IBD and numerous metabolic disorders. Accordingly, maintaining or restoring GM balance has emerged as a critical therapeutic strategy for gastrointestinal diseases [145,146]. Growing preclinical evidence suggests that CBD modulates gut microbial communities and associated metabolites, particularly SCFAs. In a collagen-induced arthritis (CIA) rat model, oral CBD (35 mg/kg, 21 days) significantly increased serum butyrate, accompanied by elevated abundance of Allobaculum, a genus involved in butyrate recycling via enhanced utilization of simple carbohydrates and acetate [14]. SCFAs, particularly butyrate, exhibit a wide range of biological activities. These include stimulating intestinal development to promote mucosal growth and enhance nutrient absorption, as well as alleviating oxidative stress and mitigating inflammation [147]. Similarly, in a pulmonary fibrosis rat model, oral CBD (108 mg/kg, 28 days) enriched Lachnospiraceae_NK4A136, a butyrate-producing genus [16]. This finding was reinforced in Clostridium sporogenes–colonized mice given CBD (50 mg/kg, 4 weeks), where CBD increased both Lachnospiraceae_NK4A136 and the Firmicutes-to-Bacteroidetes (F/B) ratio—a recognized indicator of GM health linked to SCFA production and various pathological states [148,149]. In contrast, in mice receiving intraperitoneal CBD (0.2 mg/kg, 28 days), the relative abundances of Firmicutes and Lachnospiraceae_NK4A136_group were reduced, suggesting that CBD's microbiota-modulating effects may depend on the route of administration [17].
Translation to humans remains limited. In a breast cancer survivor, CBD (300 mg/day, 2 months) altered GM composition, reducing the F/B ratio while enriching SCFA-producing genera such as Veillonella (propionate), Bacteroides, Lachnospiraceae CAG-56, and Turicibacter (butyrate), corresponding with improvement in chemotherapy-induced neuropathy [150]. However, short-term low-dose CBD (60 mg/day for several weeks) did not alter GM composition, glucose tolerance, or inflammatory markers in overweight adults [151], and escalating doses (up to 800 mg/day, 12 weeks) showed no significant microbiome changes in individuals with HIV on antiretroviral therapy [152]. Collectively, these findings indicate that CBD's effects on the GM–SCFA axis are highly context-dependent, influenced by dose, administration route, duration, microbiome baseline, and disease state.
While these observations suggest that CBD modulates the GM, a direct causal link remains unproven. One plausible mechanism involves the preservation of intestinal redox homeostasis: the colonic lumen's anaerobic environment sustains SCFA-producing strict anaerobes, whereas oxidative stress elevates oxygen tension, driving a shift from these keystone taxa toward aerotolerant or facultative species—a hallmark of dysbiosis that compromises SCFA synthesis [153,154]. Given its antioxidant properties, CBD may help stabilize this redox balance and thereby limit dysbiosis. Additionally, the role of NOX, especially NOX1 in epithelial cells, is crucial for maintaining microbiota balance under redox conditions and should be considered. Under normal conditions, O2•-/H2O2, acting as secondary messengers for NOX1, trigger immune signaling and disrupt bacterial pathogenicity signaling, reducing intestinal pathogen virulence [23]. However, excessive ROS production by certain pathogens can cause cellular damage. Escherichia coli expresses CAT, which breaks down H2O2 produced by NOX1, allowing the bacterium to survive in the anaerobic gut. The CNF1 toxin from Escherichia coli activates host NOX precursor Rac1, increasing intracellular ROS and causing cellular damage [155]. CBD's potential to inhibit NADPH reductases has been shown in animal models: CBD suppressed NOX1 and NOX4 in endometriosis lesion tissues (10 mg/kg, oral, 7 days) [156] and inhibited NOX2 in a mouse model of alcohol-induced liver injury (5 or 10 mg/kg, intraperitoneal, 11 days) [157]. However, further studies are needed to confirm CBD's effects on gut NOX enzymes and its regulation of the microbiota. In parallel, emerging data indicate direct endocannabinoid–bacterial crosstalk: the endocannabinoid 2-AG antagonizes the Enterobacteriaceae histidine kinase QseC, reducing disease severity in infection models [158,159]. Although no current evidence demonstrates that CBD—or other endocannabinoids such as AEA—engages analogous bacterial receptors, the structural and functional similarity between CBD and endogenous cannabinoids raises the intriguing possibility that CBD might be directly sensed by gut microbes, influencing bacterial behavior and host–microbe interactions.

5.2
Intestinal diseases
5.2.1
Inflammatory bowel disease
IBD, comprising UC and CD, is a chronic idiopathic disorder characterized by persistent intestinal inflammation, impaired epithelial integrity, macrophage infiltration, and a relapsing–remitting course that increases colorectal cancer risk [160]. Dysregulated immunity, GM imbalance, oxidative stress, and barrier dysfunction are key pathogenic drivers [161], while the limited tolerability of current therapies, such as aminosalicylates, has prompted growing interest in safer adjunctive strategies with integrated antioxidant, anti-inflammatory, and barrier-protective effects. In vitro studies demonstrate that CBD protects intestinal epithelial integrity. In Caco-2 cells, CBD (1 μM, 24 h) reduces basal and H2O2-induced ROS and maintains tight junction integrity [162], whereas higher-dose (10 μM, 72 h) accelerates recovery of EDTA-disrupted monolayers, increasing TEER and tight junction protein expression [144].Consistent with these findings, in DSS-induced colitis models, dietary CBD (200 mg/kg, 5 weeks) alleviated body weight loss, fecal bleeding, and colonic tissue damage, reduced macrophage infiltration, promoted mucosal repair, and suppressed NLRP3 inflammasome activation [12]. Intragastric CBD (60 mg/kg, 50 days) similarly attenuated colonic inflammation and fibrosis and inhibited NF-κB p65, phosphorylated IκBα, and pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β); these effects were largely abolished by Nrf2 inhibition, implicating Nrf2–NF-κB–mediated redox–inflammation coupling in CBD's intestinal protection [163]. Moreover, oral administration of nanoformulated CBD (100 mg/kg, 21 days) improved DSS-induced colitis by suppressing oxidative stress and inflammation, upregulating the tight junction protein ZO-1, restoring barrier function and permeability, inhibiting colonic NF-κB signaling, and reshaping the gut microbiota, including increased abundance of the SCFA-producing genus Lachnospiraceae_NK4A136 and elevated acetate, propionate, and butyrate levels [164]. Collectively, these findings indicate that CBD exerts multifaceted therapeutic effects in IBD by integrating antioxidant and anti-inflammatory actions with preservation of epithelial barrier integrity and modulation of the GM.
Beyond monotherapy, recent preclinical studies highlight the involvement of the ECS in CBD-mediated intestinal immune regulation and support cannabinoid-based combination strategies. In DSS-induced colitis, sub-therapeutic THC (2.5 mg/kg) alone was ineffective, whereas co-administration with CBD (10 mg/kg) or the CB1 receptor allosteric modulator ZCZ011 significantly improved disease activity indices, inflammatory mediators, and colonic integrity, indicating that CBD can potentiate THC efficacy in a partially CB1-dependent manner [165]. Similarly, a CBD–cannabidivarin (CBDV) combination (10 mg/kg and 0.6 mg/kg, intraperitoneal) markedly attenuated DSS-induced colitis via a CB2-dependent mechanism [166], underscoring complementary roles of CB1 and CB2 receptors in intestinal protection. In addition, low-dose CBD (10 mg/kg) enhanced the efficacy of standard IBD therapies, including olsalazine and cyclosporine, in both acute and chronic DSS-induced colitis models [167]. Cannabinoid-based combinations also appear particularly beneficial for symptom control, especially pain. In DSS-induced visceral hypersensitivity, CBD (10 mg/kg) reduced visceral pain responses [168], while oral administration of CBD (31 mg/kg) combined with cannabigerol (CBG; 30 mg/kg) similarly reduced epithelial damage and pain-related behaviors [169]. Consistent with these findings, observational studies in IBD patients report moderate improvement in gastrointestinal symptoms, including abdominal pain, anxiety, nausea/vomiting, as well as improvements in disease-related pain, appetite, and quality of life among CBD users [170,171]. Overall, while clinical evidence remains limited, available preclinical and observational data support cannabidiol-based monotherapy and combination strategies for symptom management in IBD, with combined approaches potentially offering safer and more effective therapeutic benefits.

5.2.2
Colorectal cancer
CRC is among the most common malignancies worldwide, ranking third in men and second in women [172]. Standard treatment relies on surgery followed by oxaliplatin- and 5-fluorouracil–based chemotherapy, but drug resistance is frequent, emphasizing the need for new therapeutic strategies [3]. Preclinical data indicate that CBD exerts direct anticancer effects on CRC cells. CBD (0–8 μM, 24 h) inhibits CRC cell growth and induces apoptosis in a dose-dependent manner [173], and CBD (5–20 μM, 12–48 h) reduces CRC cell viability and suppresses xenograft tumor growth in mice (20 mg/kg, intraperitoneal, 5 weeks) [174]. In both studies, growth inhibition was accompanied by excessive ROS accumulation, consistent with ROS-driven mitochondrial dysfunction and endoplasmic reticulum (ER) stress leading to cell-cycle arrest and apoptosis [175]. At the same time, CBD has been reported to enhance antioxidant defenses, suggesting context-dependent redox modulation. Notably, CBD (5–20 μM, 48 h) inhibited proliferation and induced ER stress in CRC cells but not in normal colonic epithelial cells [176]. This dichotomy highlights the need to clarify how CBD engages the Nrf2–ARE axis in cancer, given that Nrf2 activation can be cytoprotective in normal tissue yet, when hyperactivated, may promote tumor survival [175].
In addition to regulating the proliferation of cancer cells, CBD also affects the metastatic process of cancer cells. Metastasis of colorectal cancer cells, especially to the liver, is a major cause of mortality in CRC patients [177]. Activation of GPR55 promotes cancer dissemination via G12/13 signaling [178]. As a GPR55 antagonist, CBD (1 μM, 1 h) reduces CRC cell adhesion and migration in vitro and, at 5 mg/kg intraperitoneally, lowers hepatic trapping of colon carcinoma cells in a murine metastasis model [91]. In a separate mouse CRC model, CBD (5 mg/kg, three times weekly for 7 weeks, intraperitoneally) exerted antitumor and antimetastatic effects partly by downregulating vascular endothelial growth factor (VEGF) and thereby suppressing angiogenesis [179]. Together, these findings position CBD as a mechanistically multifaceted candidate for CRC therapy, though evidence remains largely preclinical and its complex redox and signaling effects require rigorous mechanistic and clinical evaluation.

5.3
Gut-organs axis
The relationship between the host and the GM is fundamental not only for intestinal health but also for the function of distant organs [160]. Dysbiosis can influence extraintestinal tissues via immune, metabolic, endocrine, and neural pathways—collectively termed gut–organ axes (e.g., gut–brain, gut–liver) [19,180]. Within this framework, CBD's actions on intestinal barrier integrity, redox balance, inflammation, and GM composition may propagate along these axes, providing an indirect route by which CBD modulates systemic physiology and disease.
5.3.1
Gut-brain axis
The gut–brain axis refers to the bidirectional communication network between the gastrointestinal tract and the CNS, mediated by the circulatory system, the vagus nerve, the immune system, the CNS, and the ENS [18]. This highly integrated system involves a range of neuroactive substances, including classical neurotransmitters, gut-derived hormones, and metabolites produced by the GM [181]. The GM is a key mediator within this axis: dysbiosis and loss of microbial diversity can impair brain function and contribute to neurological damage [182]. Multiple bacterial taxa synthesize and release neurotransmitters such as γ-aminobutyric acid, glutamate, acetylcholine, dopamine, and norepinephrine, thereby directly influencing CNS activity and mental state [183]. Consequently, the GM has emerged as a potential therapeutic target for central nervous system disorders.
CBD has attracted attention as a putative modulator of the gut–brain axis, acting at the level of GM composition, microbial metabolites, intestinal inflammation, and barrier integrity, with downstream consequences for neurodegenerative and neuroinflammatory diseases such as AD, epilepsy, and MS. In AD, dysbiosis characterized by expansion of amyloid- and LPS-producing bacteria is associated with increased gut permeability, microglial activation, and immune-mediated neuroinflammation—hallmarks of neurodegeneration [184]. In SAMP8 Alzheimer's model mice, intraperitoneal CBD (20 mg/kg per day, 14 days) attenuated microglial activation, lowered circulating LPS, decreased Bacteroides, and increased Firmicutes, a phylum enriched in SCFA producers that support barrier function [138]. In lithium–pilocarpine–induced epileptic rats, oral CBD (20 or 100 mg/kg, 7 days) reduced seizure severity and neuroinflammation by decreasing IL-1β, IL-6, and TNF-α, while restoring the SCFA-producing genus Prevotella_9_ucg-001 [185]. In a murine model of MS, experimental autoimmune encephalomyelitis (EAE), intraperitoneal injection of 10 mg/kg THC/CBD (1:1 ratio) increased colonic SCFA levels and decreased the abundance of Akkermansia, a genus associated with mucus erosion and barrier disruption [7]. More recently, advanced CBD formulations—such as 3D-printed rectal suppositories and lipid nanoparticles—have been shown in rodent models to further improve GM composition, enhance SCFA production, strengthen intestinal barrier integrity, and alleviate anxiety-like behavior [186,187]. Collectively, these preclinical data suggest that CBD may ameliorate neurological disease partly by rebalancing the microbiota, dampening gut inflammation, and reinforcing the intestinal barrier; however, the current evidence is largely preclinical, heterogeneous in models and dosing, and thus insufficient to support definitive clinical conclusions.

5.3.2
Gut-liver axis
The gut-liver axis is a bidirectional communication network between the gut, microbiota, and liver, primarily mediated via the portal vein. Bile acids (BAs) metabolism and the GM play critical roles in maintaining this axis' function [188]. The liver synthesizes primary BAs, released into the small intestine, where they are converted to secondary BAs by the GM through dehydroxylation [189]. Approximately 95 % of BAs are reabsorbed in the ileum and transported back to the liver through the portal circulation, forming the enterohepatic circulation of BAs. Disruptions in the GM are linked to liver diseases, such as NAFLD and NASH [190]. In addition to BAs, the gut absorbs LPS and other bacterial products, which are transported to the liver, activating the TLR4–NF-κB pathway and promoting inflammation [191].
CBD has been evaluated for its potential to improve inflammation-related liver diseases, including NAFLD, liver fibrosis, hepatocellular carcinoma, and chemical-induced liver damage [192]. However, direct studies on CBD's effects within the gut-liver axis remain scarce. Some preclinical models have demonstrated CBD's ability to modulate liver inflammation, bile acid composition, and gut microbiota. In a NAFLD mouse model, intragastric CBD (1 mg/kg, 14 days) reduced inflammatory markers such as iNOS and TNF-α, alleviating liver inflammation [5]. Although CBD did not significantly improve hepatic steatosis in this model, it notably increased the abundance of Ruminococcus, a genus known for its anti-inflammatory properties and typically reduced in NAFLD patients [193]. Additionally, dysregulation of GM alters the composition of bile acids, which is one of the key mechanisms of liver injury. For example, CBD (25 mg/kg, oral) alleviates intestinal inflammation and the reduction in tight junction protein levels caused by estrogen deficiency in ovariectomized mice, and an increase in the number of Lactobacillus was observed following CBD treatment [194]. Lactobacillus converts primary BAs into secondary BAs, activating the farnesoid X receptor (FXR), which inhibits hepatic triglyceride synthesis and reduces liver inflammation by suppressing NF-κB [195]. Similar effects of Lactobacillus increase and primary bile acid reduction were observed in pancreatic ductal adenocarcinoma (PDAC) mice treated with CBD (100 mg/kg, intraperitoneally) [196]. These findings suggest that CBD may regulate the gut-liver axis through modulation of bile acid composition and microbiota-dependent bile acid metabolism. However, direct evidence for CBD's role in bile acid homeostasis is lacking, highlighting the need for further research into its regulatory mechanisms within the gut-liver axis.

6
Conclusion and future perspective
CBD, as a non-psychoactive phyto-CB, has demonstrated substantial therapeutic potential for gastrointestinal health. By modulating the ECS, CBD enhances intestinal barrier integrity, regulates GM composition, and mitigates oxidative stress and inflammation. These effects contribute to its promising role in treating oxidative stress-related gastrointestinal conditions and maintaining intestinal homeostasis. Moreover, CBD's interaction with gut-organ axes, including the gut-brain and gut-liver axes, presents exciting opportunities for broader systemic therapeutic applications. While current research highlights the potential of CBD as a gut health modulator, much remains to be explored regarding its mechanistic pathways, particularly in regulating microbial metabolic networks and its impact on microbiota composition.
Looking ahead, CBD's therapeutic potential in gastrointestinal diseases and systemic health is vast, yet its clinical translation requires more rigorous investigation. A key area of future research is the identification of specific molecular pathways through which CBD modulates GM and microbial metabolism, particularly in relation to its impact on gut-brain and gut-liver interactions. Advances in metagenomics, single-cell sequencing, and multi-omics integration offer valuable tools for deeper insights into these complex mechanisms. Specifically, amplifying and sequencing the DNA encoding 16S rRNA is a rapid, reliable, and cost-effective approach, and it has become the preferred method for investigating the composition and structure of microbial communities. However, as CBD is increasingly considered for clinical use, its safety profile remains a critical consideration. While short-term clinical studies indicate that CBD is generally well-tolerated, with minor side effects such as fatigue, diarrhea, and headache, concerns about its long-term safety, particularly at higher doses, need addressing. Given that CBD may modulate intestinal barrier integrity and the composition of the GM, it is essential to elucidate whether these effects are related to the diarrhea observed in clinical practice. Meanwhile, considering that the intestines of teenagers are still in the process of development, the potential effects of CBD on gut maturation and microbiota homeostasis should be accorded high priority in future investigations. Moreover, the possible pharmacological interactions between CBD and other medications must be carefully studied to avoid adverse effects. To move forward, defining the optimal dosage, delivery methods, and understanding CBD's impact on specific tissues and organs will be essential for its successful clinical application.

Disclosure statement
The authors have no conflict of interest to declare. All the figures in this article were created using Adobe Illustrator.

Funding
This research was funded by the 10.13039/501100001809National Natural Science Foundation of China (32102594), Science and Technology Innovation Program of Hunan Province (2022RC1160, 2024RC8154), the Hunan Provincial University Key Laboratory of the Regional Characteristic Traditional Chinese Medicine Resources and Ecological Agriculture, the 10.13039/501100004735Natural Science Foundation of Hunan Province (2023JJ50332, 2024JJ7622), the Yuelu Young Talent Program of the Institute of Bast Fiber Crops, 10.13039/501100005196Chinese Academy of Agricultural Sciences (IBFC-YLQN-202401), the Hunan Agriculture Research System (HARS-06) and the Agricultural Science and Technology Innovation Project Fund of Chinese Academy of Agricultural Sciences.

CRediT authorship contribution statement
Biguang Lv: Writing – original draft, Writing – review & editing. Jieyi He: Writing – original draft. Sha Zhan: Writing – original draft. Ke Jin: Writing – review & editing. Xinyu Lei: Writing – review & editing. Xuan Cheng: Conceptualization, Visualization. Zonghao Lv: Investigation, Writing – original draft. Fengming Chen: Writing – review & editing. Yuying Li: Conceptualization, Funding acquisition, Investigation, Writing – review & editing. Jun Lu: Conceptualization, Writing – review & editing. Qian Lin: Conceptualization, Funding acquisition, Investigation, Supervision, Writing – review & editing.

Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.