## 5 Effects of Cannabinoids on Intestinal Barrier Permeability
### Effects of Phytocannabinoids on Intestinal Barrier Permeability  
THC and CBD are the two phytocannabinoids with the largest number of studies describing their impact on intestinal permeability. In Caco-2 cell lines, THC and CBD sped up recovery of normal permeability, as measured by TEER, after disruption by EDTA. This was the case with both apical and basolateral administration and was mediated via CB1 receptors. After treatment with THC or CBD, there was significant upregulation of mRNA expression for the TJ protein ZO-I. This effect was also abolished by the CB1 receptor antagonist AM251 [86]. Apical incubation of Caco-2 cells with THC or CBD for 24 (but not 48) h after exposure to IFNg and TNFa accelerated the recovery of normal permeability (as measured by TEER) after the increase in permeability induced by cytokines. Administration of THC or CBD apically at the same time as IFNg and TNFa caused complete inhibition of the cytokine-induced fall in TEER and prevented increased FD4 flux. This effect was inhibited by the CB1 antagonist AM251, but not by CB2, GPR18, GPR55, TRPV1, PPARa, or PPARy antagonists. Interestingly, the CB1 antagonist AM251 also significantly decreased the fall in TEER when co-administered with the cytokines but had no effect when given 24 h after IFNg and TNFa [87]. A study found no difference between synthetic and plant-derived CBD in their effect on changes in intestinal permeability caused by inflammatory cytokines. Both types of CBD facilitated the return to baseline TEER values in Caco-2 cell monolayers incubated with TNFa and IFNg via CB1 [93]. THC decreased permeability in Caco-2 cell cultures with TEER decreases due to transfection with the inflammation-induced microRNA molecules miR-130a and miR-212. This effect was due to upregulation of PPARy receptor expression induced by THC [94]. Figure 6: **Intestinal barrier and elements involved in the influence of cannabinoids on its permeability. ** The effect of cannabinoids on intestinal permeability is achieved mainly through the CB1, TRPV1, MAPK, and adenylate cyclase signaling pathways, but also through the activation of PPARa. Cannabinoids may also cause changes in the synthesis of tight junction proteins (zonula occludens, claudin, occludin,), which play a significant role in regulating the integrity of the intestinal barrier. The figure was created with BioRendercom, accessed on 29 April 2024. CBD inhibited cytotoxicity and apoptosis induced by _Clostridium difficile_ toxin A (TcdA) in Caco-2 cell lines and reversed the decreased gene expression for the TJ proteins ZO-1 and occludin. The above protective effects were mediated by CB1 receptors [95]. In vitro, CBD decreased FD4 and FD10 flux in Caco-2 cell cultures exposed to IFNg and TNFa. This effect was blocked by CB1 antagonism, as well as antagonism of PKA, MAPK, and adenylyl cyclase signaling. CBD also decreased AQP3 gene expression and increased TRPV1 expression, which were respectively increased and decreased due to inflammation [92]. Another in vitro study conducted on Caco-2 cell lines found that CBD did not significantly reverse cytokine-induced hyperpermeability [96]. In contrast, a later study showed a significant protective effect of CBD on Caco-2 membrane permeability exposed to inflammatory and oxidative insults. Pretreatment of membranes with CBD ameliorated the drop in TEER induced by exposure to hydrogen peroxide, and was able to almost entirely prevent the fall in TEER caused by incubation of membranes with INF\(\gamma\) and TNF\(\alpha\). In addition, CBD was able to prevent changes in tight junction morphology caused by INF\(\gamma\) and TNF\(\alpha\) administration, as observed by confocal microscopy [97]. In human colonic tissue preparations, CBD counteracted the inflammation-induced decrease in claudin-5 mRNA. In the same study, healthy humans given mannitol, lactose, and high-dose aspirin experienced a decrease in the ratio of lactulose to mannitol in the urine after treatment with CBD, as compared to the group not given CBD.