Endocannabinoids and endocannabinoid-like compounds modulate hypoxia-induced permeability in CaCo-2 cells via CB1, TRPV1, and PPARα

Background and purpose: We have previously reported that endocannabinoids modulate permeability in Caco-2 cells under inflammatory conditions and hypothesised in the present study that endocannabinoids could also modulate permeability in ischemia/reperfusion. Experimental approach: Caco-2 cells were grown on cell culture inserts to confluence. Trans-epithelial electrical resistance (TEER) was used to measure permeability. To generate hypoxia (0% O-2), a GasPak (TM) EZ anaerobe pouch system was used. Endocannabinoids were applied to the apical or basolateral membrane in the presence or absence of receptor antagonists. Key results: Complete hypoxia decreased TEER (increased permeability) by similar to 35% after 4 h (recoverable) and similar to 50% after 6 h (non-recoverable). When applied either pre- or post-hypoxia, apical application of N-arachidonoyl-dopamine (NADA, via TRPV1), oleamide (OA, via TRPV1) and oleoylethanolamine (OEA, via TRPV1) inhibited the increase in permeability. Apical administration of anandamide (AEA) and 2-arachidonoylglycerol (2-AG) worsened the permeability effect of hypoxia (both via CB1). Basolateral application of NADA (via TRPV1), OA (via CB1 and TRPV1), noladin ether (NE, via PPAR alpha), and palmitoylethanolamine (PEA, via PPAR alpha) restored permeability after 4 h hypoxia, whereas OEA increased permeability (via PPAR alpha). After 6 h hypoxia, where permeability does not recover, only basolateral application PEA sustainably decreased permeability, and NE decreased permeability. Conclusions and implications: A variety of endocannabinoids and endocannabinoid-like compounds modulate Caco-2 permeability in hypoxia/reoxygenation, which involves multiple targets, depending on whether the compounds are applied to the basolateral or apical membrane. CB1 antagonism and TRPV1 or PPAR alpha agonism may represent novel therapeutic targets against several intestinal disorders associated with increased permeability.