It is critically important to identify all factors that may play a role in the recent increase of the incidence of stroke among the young population. Considering the worldwide use of cannabinoids (cannabis and synthetic cannabinoids), the recent legalization of their consumption in some countries, and their supposed involvement in cardiovascular events, we evaluated their role in the occurrence of neurovascular complications among the young. Ninety-eight patients were described in the literature as having a cannabinoids-related stroke (85 after cannabis use and 13 after synthetic cannabinoids). The distribution by type of stroke was as follows: 4 patients with an undetermined type of stroke, 85 with an ischemic stroke and/or a transient ischemic attack, and 9 with a hemorrhagic stroke. The mean age of patients was 32.3±11.8years (range 15-63), and the majority of them were male with a sex ratio of 3.7:1. Cannabis was often smoked with tobacco in 66% of cases. Most of the patients with cannabinoids-related strokes were chronic cannabis users in 81% of cases, and for 18% of them, there was a recent increase of the amount of cannabis consumption during the days before the occurrence of stroke. Even if the prognosis of stroke was globally favorable in 46% of cases, with no or few sequelae, 5 patients died after the neurovascular event. One striking element reported in the majority of the reports was a temporal relationship between cannabinoids use, whether natural or synthetic, and the occurrence of stroke. However, a temporal correlation does not mean causation, and other factors may be involved. Cannabis may be considered as a risk factor of stroke until research shows evidence of an underlying mechanism that, alone or in association with others, contributes to the development of stroke. As of today, reversible cerebral vasoconstriction triggered by cannabinoids use may be a convincing mechanism of stroke in 27% of cases. Indeed, despite the widespread use of cannabinoids, the low frequency of neurovascular complications after their use may be due to a genetic predisposition to their neurovascular toxicity in some individuals. Further studies should focus on this point. More importantly however, this low frequency may be underestimated because the drug consumption may not be systematically researched, neither by questioning nor by laboratory screening. Besides this vascular role of cannabinoids in the occurrence of stroke, a cellular effect of cannabis on brain mitochondria was recently suggested in an experimental study. One of the mechanisms involved in young cannabis users with stroke may be the generation of reactive oxygen species leading to an oxidative stress, which is a known mechanism in stroke in humans. It is useful to inform the young population about the real potential risk of using cannabinoids. We suggest to systematically ask all young adults with stroke about their drug consumption including cannabinoids, to screen urine for cannabis or to include a specific diagnostic test to detect synthetic cannabinoids, and to obtain non-invasive intracranial arterial investigations (i.e. CT-angiography or cerebral MRA) in order to search for cerebral vasoconstriction. However, several questions remained unresolved and further research is still needed to assess the pathophysiological mechanisms involved in young cannabinoids users with stroke. This article is part of a Special Issue entitled “Cannabinoids and Epilepsy”.
Keywords: Cannabis; Marijuana; Reversible cerebral vasoconstriction syndrome; Spice; Stroke; Synthetic cannabinoids.
Leker and co-workers investigated the therapeutic time window of the synthetic CB1 receptor agonist, HU210 in rats subjected to permanent middle cerebral artery occlusion (PMCAO). They demonstrated that administration of HU-210 (45 μg/kg) at 1, 2, or 4 but not 6 hours after PMCAO resulted in reduced motor disability and infarct volumes compared with vehicle controls 72 hours after cerebral ischemia and thus, therapeutic time window appeared to extend to 4 hours after PMCAO and the salutary effects of HU-210 were only partially abolished by the CB1 receptor antagonist SR141716 and warming . They concluded that the neuroprotective effects of HU-210 were dependent on potent hypothermia via CB1 receptor dependent mechanism. Another research group noted that 40 min before the induction of global cerebral ischemia, treatment with R(+)-WIN55,212-2 (1 mg/kg), a synthetic aminoalkylindole cannabinoid CB1 receptor agonist, induced a dose-dependent increase in neuronal survival that reached maximal levels (56% of sham-operated controls) in a global cerebral ischemia model in rats. Treatment with R(+)-WIN55,212-2 (1 mg/kg) 30 min before ischemia, but not 60–120 min after ischemia, reduced the infarct size 24 hours after ischemic stroke onset , suggesting that pre-ischemic treatment with R(+)-WIN55,212-2 is protective in cerebral ischemia.
Cannabis contains over 60 different terpeno-phenol compounds that have been identified so far but the role and importance of many of these has yet to be fully understood. Select structures are shown in Figure 1 . Delta 9 -tetrahydrocannabinol (delta 9 -THC) is the most psychoactive component that was isolated in 1964 by Gaoni and Mechoulam at the Weizmann Institute in Rehovot (Israel). It has been demonstrated to produce hypothermia, learning and memory impairment, impairment of the prepulse inhibition of the startle reflex, catalepsy-like immobilisation, aggressive behaviour, analgesia, hypoactivity and enhancement of preference for high fat diet [1,2,3,4,5,6,84,85,86,87,88]. These effects are at least partly caused by binding to cannabinoid receptor type 1 (CB1) within the brain. So far, two types of cannabinoid receptors have been identified: type1 (CB1 receptor) and type2 (CB2 receptor). CB1 receptors are mainly expressed in the central and the peripheral nervous system. CB2 receptors are found in cells of the immune system, such as lymphocytes and neutrophils, as well as in resident inflammatory cells within the CNS [7,8,9].
Accumulating data now suggest that cannabinoid CB1 receptors contribute to neuroprotection through anti-excitotoxicity , the phosphatidylinositol-3 kinase/Akt pathway , and hypothermia . We have reported that the neuroprotective and hypothermic effects of delta 9 -THC were related to CB1 receptors . CBD has also been described as protective against global and focal ischemic injury [14,18]. Several groups have recently shown that CBD can interact with cannabinoid CB1 and CB2 receptors. Pertwee and Ross showed that CBD can antagonize the CB1 agonists such as WIN55,212 and CP55940 by acting at prejunctional sites that was unlikely to be cannabinoid CB1 or CB2 receptors . Castillo and coworkers recently demonstrated that CBD implicated the neuroprotective effect mediated by CB2 and adenosine receptors in an in vitro model of newborn hypoxic-ischemic brain damage in mice . In addition, Thomas and coworkers noted that CBD displayed unexpected high potency as an antagonist of CB1 and CB2 receptor agonists . Interestingly, the neuroprotective effect of CBD showed a dose dependent bell shaped curve in mice subjected to middle cerebral artery occlusion (MCAO) . Intraperitoneal injection of CBD 1 or 3 mg/kg but not 10 mg/kg during 4 h MCAO prevented cerebral infarction 24 hours after cerebral ischemia. Other groups have demonstrated that 5 mg/kg was the most effective CBD dose, and that there was a dose-dependent bell-shaped curve for CBD’s effects on the electroencephalographic flattening in gerbils subjected to cerebral ischemia . CBD has been also reported to inhibit anandamide amidase  and the reuptake of anandamide , suggesting CBD may induce an increase of anandamide signaling within the ischemic brain. Anandamide and other CB1 receptor agonists are known to reduce the release of a variety of neurotransmitters including glutamate via CB1 receptor [25,26,27,28,29]. In our previous study, delta 9 -THC significant reduced the release of glutamate during MCAO, but CBD did not affect glutamate release , suggesting that CBD might have other mechanism or stimulate other receptors besides the cannabinoid receptors. The mechanism of this biphasic effect of CBD is still unclear, but CBD may induce cerebroprotective effect through modulating endogenous cannabinoid system.
3.2. Synthetic CB1 Receptor Agonist, HU210 and R(+)-WIN55,212-2
Dexanabinol (HU-211) is a synthetic, nonpsychotropic cannabinoid . It has been shown to act as a noncompetitive N-methyl-D-aspartate receptor antagonist , as well as having antioxidant , anti-inflammatory effects [93,94]. The therapeutic time window of nonpsychotropic cannabinoid, HU-211 in closed head injury was first reported by Mechoulam’s research group in 1993 . HU-211 dissolved in middle-chain triglycerides (MCT) oil at a dose of 25 mg/kg was given intraperitoneally immediately and 1, 2, or 3 h after impact. The drug was found to be very effective in improving motor function recovery when given 2 h after the injury. In addition, Shohami and co-workers have shown the long-term effect of HU-211 on motor and memory functions after closed head injury in the rat . HU-211 (5 mg/kg) was administered intravenously at 4 or 6 h after closed head injury. Cognitive functions were evaluated using the Morris water maze, with rats trained either before or after closed head injury. The data showed that HU-211 was a potent cerebroprotective agent, with a therapeutic window of about 4 h. Moreover, this compound HU-211 was also used for cerebral ischemia. Belayev and co-workers have reported that HU-211 (4 mg/kg, i.v.) significantly improved neurological deficits and reduced brain damage 60 min after forebrain ischemia in rats, but neuroprotection was no longer significant after 3 h . Leker’s research group demonstrated that treatment with HU-211, dexanabinol (4.5 mg/kg) 1 h and 3 h but not 6 h after permanent middle cerebral artery occlusion in rats improved motor function and reduced infarct volume 24 h post ischemia .
Within seconds to minutes after an excitotoxic injury oxidative stress is evident and this in turn causes microvascular injury, blood-brain barrier dysfunction, and post-ischemic inflammation over the next 24 hours. Moreover, the initial ischemic event activates migroglia and astrocytes which react by secreting cytokines, chemokines, and matrix metalloproteases. These inflammatory mediators lead to an upregulation of intracellular adhesion molecule-1, E-selectin and P-selectin on endothelial cells, allowing blood derived inflammatory cells, mainly neutrophils, to infiltrate the ischemic brain area . Damaged brain can be surprisingly plastic, and crosstalk between various types of remodeling brain cells take place after brain injury [64,65,66]. GABA, adenosine, and KATP activation may contribute to anti-excitotoxicity in the ischemic early phase. Endogeneous interleukin-10 and erythropoietin may lead to anti-inflammation and anti-apoptosis. In the late phase after cerebral ischemia, the generation of new blood vessels facilitates highly coupled neurorestorative processes including neurogenesis and synaptogenesis [67,68]. In fact, neurogenesis after stroke has been demonstrated in the adult human brain . Thus, cerebral ischemia induces complex mechanisms progressively such as the processes of cell destruction and of cell protection/regeneration, which suggest that multifunctional molecule and compounds without interfering with beneficial endogenous mechanisms may become a candidate to prolong the therapeutic time window after ischemic stroke. In the search for therapies for stroke, to date over 1,026 drugs have been tested in animal models, of which 114 underwent further clinical evaluation . Recombinant tissue plasminogen activator (rt-PA) remains the only agent shown to improve stroke outcome in clinical trials. However, patients are eligible for thrombolysis by using rt-PA only if they come to medical attention within a short time (3 hours) after symptom onset. This restriction is considered necessary due to the risk of hemorrhage and potential damage caused by ischemia/reperfusion injury. Research is now underway to expand the therapeutic time window for the use of thrombolytic therapy after cerebral ischemia.
Therapeutic time window of CBD and delta 9 -THC in pre-clinical study.
2. Pharmacology of CBD in Ischemic Stroke
Cannabis contains the psychoactive component delta 9 -tetrahydrocannabinol (delta 9 -THC), and the non-psychoactive components cannabidiol (CBD), cannabinol, and cannabigerol. It is well-known that delta 9 -THC and other cannabinoid CB1 receptor agonists are neuroprotective during global and focal ischemic injury. Additionally, delta 9 -THC also mediates psychological effects through the activation of the CB1 receptor in the central nervous system. In addition to the CB1 receptor agonists, cannabis also contains therapeutically active components which are CB1 receptor independent. Of the CB1 receptor-independent cannabis, the most important is CBD. In the past five years, an increasing number of publications have focused on the discovery of the anti-inflammatory, anti-oxidant, and neuroprotective effects of CBD. In particular, CBD exerts positive pharmacological effects in ischemic stroke and other chronic diseases, including Parkinson’s disease, Alzheimer’s disease, and rheumatoid arthritis. The cerebroprotective action of CBD is CB1 receptor-independent, long-lasting, and has potent anti-oxidant activity. Importantly, CBD use does not lead to tolerance. In this review, we will discuss the therapeutic possibility of CBD as a cerebroprotective agent, highlighting recent pharmacological advances, novel mechanisms, and therapeutic time window of CBD in ischemic stroke.
We have previously reported that CBD (3 mg/kg) has a potent and long-lasting neuroprotective effect when administered both pre- and post-ischemia, whereas only pre-ischemic treatment with delta 9 -THC (10 mg/kg) reduced the infarction size when administered 24 hours after 4 h MCAo in mice. The neuroprotective effect of delta 9 -THC and other cannabinoids is related to the CB1 receptor-mediated inhibition of voltage-sensitive Ca 2+ channels, which reduces Ca 2+ influx, glutamate release, and excitotoxicity . In fact, delta 9 -THC inhibited the massive release of glutamate, but this neuroprotective effect of delta- 9 THC was inhibited by the CB1 receptor antagonist SR141716 , which suggest that delta 9 -THC is neuroprotective as a pre-ischemic treatment via inhibition of glutamate excitotoxicity. Actually, treatment with delta 9 -THC immediately after reperfusion did not prevent cerebral infarction. On the other hand, CBD was neuroprotective even when administered 6 hours after cerebral ischemia (2 hours after reperfusion). In addition, CBD significantly inhibited the myeloperoxidase activity of neutrophils at 1 hour and 20 hours after reperfusion and suppressed the decrease in CBF due to the failure of cerebral microcirculation after reperfusion. In addition, CBD decreased the number of Iba1- and GFAP-positive cells and improved neurological score and motor coordination at 3 days after cerebral ischemia. We concluded that the therapeutic time window of CBD was 6 hours after onset of ischemia in early treatment. CBD had a potent and long-lasting neuro- protective effect and prevented progressive post-ischemic injury . In a more recent study, we reported that repeated treatment with CBD from 1 day or 3 days after cerebral ischemia improved the functional deficits, such as neurological score and motor coordination, and survival rates. In addition, both groups did not increase the HMGB1 level in plasma, and decreased the number of Iba1 expressing HMGB1 positive cells and TUNEL positive cells, which suggest that CBD may be cerebroprotective not only during the early phase, but also during the chronic phase after ischemic stroke . However, treatment with CBD from Day 5 did not improve the functional outcome Day 14 after cerebral ischemia. As described above, CBD has a potent anti-inflammatory effect, such as inhibition of glial activation. Activated microglia and reactive astrocytes have also a role of beneficial in ischemic brain. For example, microglia can produce neurotorophic factors such as brain-derived neurotorophic factor, insulin-like growth factor 1 . And, reactive astrocytes can also release many growth factors such as nerve growth factor . Taken together, a treatment with CBD in ischemic early phase may implicate the neuroprotective action through inhibition of acute inflammatory reaction, whereas ischemic delayed treatment with CBD may interfere with beneficial endogenous mechanisms.