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The movement of a TRPV1 ligand (anandamide) across the human blood-brain barrier in vitro. Transient Receptor Potential Vanilloid 1 (TRPV1) receptors are intrinsically involved in pain and inflammation (Keeble et al., 2005). TRPV1 ligands appear to act on the intracellular side of the channel, in contrast to ligands of other ligand-gated ion channels. This suggests that ligands need to pass through the cell membrane in order to access their binding site and for metabolism/excretion from cells, perhaps via passive diffusion due to their lipid solubility. However, it is also possible that TRPV1 ligands are transported by an efficient biological system. Indeed, a recent article in Nature Neuroscience identified a FAAH-1 variant as a driver for anandamide transport into neuronal cells (Fu et al., 2012). Using an in vitro model of the human blood-brain barrier (hCMEC/D3, cultured as described in Watson et al., 2012), we have examined the cellular accumulation of [3H]anandamide over a 30 minute time course. Cells were co-incubated in the presence of dexamethasone (200 μM), haloperidol (40 μM), the selective TRPV1 agonist, capsaicin (10 μM) or their vehicle (0.05% DMSO). In the presence of unlabelled anandamide there was a significant (P<0.05) increase in the accumulation of [3H]anandamide, which is suggestive of a saturable efflux process in these cells. Further experiments revealed that this process was sensitive to both dexamethasone (P-gp substrate) and haloperidol (P-gp inhibition). Interestingly capsaicin caused a significant (P<0.05) decrease in the accumulation of [3H]anandamide which is indicative of an influx transport mechanism. In conclusion our preliminary experiments show for the first time that anandamide, an endogenous TRPV1 agonist, is a P-glycoprotein (P-gp) efflux transporter substrate. 1. Fu et al. (2012). Nat Neurosci, 15(1): 64-69. 2. Keeble (2005). et al. Arthritis Rheumatism, 52(10): 3248-56. 3. Thomas (2012). Brain Res, 1436: 111. 4. Watson et al. (2012) Brain Res. 1436: 111-21.
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