Introduction
The endocannabinoid system (ECS) can have a role in gut homeostasis, pain, intestinal inflammation and immune function. This system comprises two cannabinoid G-protein coupled receptors, CNR1 and CNR2 that are predominantly expressed in the brain and nervous system, but also in other peripheral tissues, including in the gut [1]. Both receptors have been shown to play a role in Inflammatory Bowel Disease (IBD). In particular CNR1 has been found more expressed at protein level in inflamed mucosa from ulcerative colitis (UC) and Crohn Disease (CD) patients compared with non-inflamed mucosa, whereas no changes in CNR2 have been detected so far [2]. Other ECS members have been found altered in the inflamed mucosa of UC and CD patients compared with healthy or non-inflamed mucosa. However, the results are conflicting and dependent on the technique used [2].
Aims & Methods
In this study we aimed to evaluate the gene expression profile of a panel of genes involved in ECS in the IBD colonic mucosa. Thirty patients with IBD were included in the study: 17 were diagnosed with UC and 13 with CD. For each patient inflamed mucosa (IM) and non-inflamed mucosa (NIM) was collected. Normal mucosa (NM) was collected from 17 non-IBD individuals (CTRL). The two groups of IBD patients and controls were age matched (p>0.05), but were different on sex distribution (p<0.05). The following disease parameters were considered: clinical disease status at the moment of sample collection (active/remission), age at onset, disease duration and therapeutic regimen. The expression of ten transcripts belonging to the ECS (CNR1, CNR2, DAGLA, DAGLB, FAAH, GPR18, GPR55, MGLL, PPARG, TRPV1 ) was analyzed by qRT-PCR in IM, NIM and CTRL specimens. The Ct values were normalized against the geometric mean of two selected housekeeping genes (HPRT1 and RPLP0). Differences among the groups were evaluated using Kruskal-Wallis Test followed by pairwise comparison, whereas Related samples Wilcoxon Signed Rank test was used to assess differences between paired tissues (IM vs NIM).
Results
The comparison between IM vs NIM in the entire IBD cohort identified the upregulation of CNR2 (p=0.005), whereas a downregulation of TRPV1 and GPR18 was observed (p=0.032, p=0.037, respectively). The analysis of the UC group confirmed the upregulation of CNR2 (p=0.009), and the downregulation of TRPV1 (p=0.028) in the IM compared to NIM and to CTRL (p=0.003). When analyzing the gene expression level in the mucosa of the 13 patients with CD only TRPV1 was identified as downregulated in IM vs CTRL (p=0.040). No changes in the expression of any genes were observed according to the therapeutic regimen and no difference was observed comparing patients in remission vs active disease. Moreover, no significant correlation between gene expression levels and disease duration in years was observed (p>0.05).
Conclusion
In this study we identified a general impairment of the expression of genes belonging to ECS in the mucosa of IBD patients. The gene expression dysregulation was more evident in patients with UC than those diagnosed with CD. Further studies on larger IBD cohorts are needed to validate the obtained preliminary results.
References
[1] Rea, K.; O’ Mahony, S.M.; Cryan, J.F. High and Mighty? Cannabinoids and the microbiome in pain. Neurobiol. pain (Cambridge, Mass.) 9, 100061, doi:10.1016/j.ynpai.2021.100061.
[2] Ambrose, T.; Simmons, A. Cannabis, Cannabinoids, and the Endocannabinoid System-Is there Therapeutic Potential for Inflammatory Bowel Disease? J. Crohns. Colitis 2019, 13, 525–535, doi:10.1093/ecco-jcc/jjy185.