The effects of novel phytocannabinoids and their combinations on blood brain barrier permeability

Introduction
The blood-brain barrier (BBB) is formed by brain endothelial cells that line the cerebral microvasculature, capillary basement membranes and astrocyte end feet, which surround 99% of the BBB endothelia and play an important role in maintaining BBB integrity. Tight junctions restrict the paracellular pathway for diffusion of hydrophilic solutes, allowing the body to control which substances can gain access to the brain (Abbott, 2002). The endocannabinoid system (ECS) is comprised of cannabinoid receptors (CB1 and CB2), endogenous lipid ligands (the endocannabinoids) and enzymes that synthesise and degrade these compounds (Pertwee et al., 2010). Anandamide (AEA) and 2-arachidonoylglycerol (2-AG) are the best studied endocannabinoids, but other, chemically similar, compounds have been discovered over the last 15 years. In a recent PhD studentship, we demonstrated that several endocannabinoids decrease BBB permeability in vitro with roles for CB2, TRPV1, CGRP and PPAR activation (Hind et al., 2015a). We also showed that a phytocannabinoid, cannabidiol (CBD) decreases BBB permeability when given either before or after oxygen glucose deprivation (a cellular model of stroke), involving activation of PPAR and 5-HT1A, and associated with reductions in cell damage and VCAM-1, and increases in VEGF (Hind et al., 2015b in press). CBD is already available clinically; a CBD/THC combination (1:1 ratio, Sativex/Nabiximols, GW Pharmaceuticals, UK) is currently licensed internationally in more than 20 countries for the treatment of spasticity in multiple sclerosis, and a CBD alone product (Epidiolex, GW Pharmaceuticals, UK) has entered an expanded access program in children with intractable epilepsies. CBD has also received orphan designation status in treating newborn children with neonatal hypoxic-ischaemic encephalopathy. While CBD is a compound of significant interest, the Cannabis Sativa plant yields more than 80 chemicals with distinct pharmacological properties, many of which remain to be discovered and exploited. The primary aim of this project will be to explore a range of novel phytocannabinoids on BBB permeability, and to establish their mechanisms of action. These will be supplied by our industrial partner and include (but not limited to) tetrahydrocannabivarin, cannabidivarin, cannabichromene, cannabigerol and cannabinol. None of these compounds have been well characterised pharmacologically.
Aims& Milestones
1-10 month: Develop the BBB protocol to include additional cell types and flow over the endothelial cells
10-15 month: Screen a range of phytocannabinoids for their potential role on BBB permeability.
15-20 months: Probe the mechanisms of action of active phytocannabinoids and cannabinoid receptors.
20-24 months: Establish any potential benefits of coadministration of compounds and their interactions with medications such as thrombolytics.
Impact and translation:
Phytocannabinoids possess various properties that may lead to therapeutic benefit in a number of vascular and inflammatory conditions, including ischaemic stroke. This includes their potential to reduce inflammation and apoptosis, reducing cerebral oedema by maintaining blood-brain-barrier integrity, inducing a chemical hypothermia, and a vasodilatory effect that could benefit ischaemic organs by improving collateral blood flow. There have been multiple compounds tested in the setting of stroke that have failed to make it to the bedside, often blamed on inadequate understanding and research in the pre-clinical phases; it is therefore of vital importance to explore in greater detail the mechanisms of action of compounds to enhance the chances of finding a drug that improves patient outcomes after stroke.