Understanding the complex pharmacology of cannabidiol: Mounting evidence suggests a common binding site with cholesterol

A cautionary tale of paradox and false positives in cannabidiol research

INTRODUCTION

Decades of research on cannabidiol (CBD) have identified thousands of purported cellular effects, and many of these have been proposed to correlate with a vast therapeutic potential. Yet despite the large volume of findings fueling broad optimism in this regard, few have translated into any demonstrable clinical benefit or even notable side effects. Therein resides the great paradox of CBD: a drug that appears to affect almost everything in vitro does not clearly do much of anything in a clinical setting.

AREAS COVERED

Comparative critical evaluation of literature searched in PubMed and Google Scholar discovers multiple instances of inconsistent and contradictory findings regarding the pharmacology and clinical effects of CBD, as well as several uncelebrated reports that suggest potential explanations for these observations. Many of those effects attributed to the ostensible pharmacologic activity of cannabidiol are almost certainly the product of false-positive experimental results and artifactual findings that are unlikely to be realized under physiologic conditions.

EXPERT OPINION

Concerns regarding the physiological relevance and translational potential of in vitro findings across the field of cannabinoid research are both far-reaching and demanding of attention in the form of appropriate experimental controls that remain almost universally absent.

Emerging medications and pharmacological treatment approaches for substance use disorders

Medications to treat substance use disorders remain suboptimal or, in the case of stimulants and cannabis, non-existent. Many factors have contributed to this paucity, including the biological complexity of addiction, regulatory challenges, and a historical lack of enthusiasm among pharmaceutical companies to commit resources to this disease space. Despite these headwinds, the recent opioid crisis has highlighted the devastating consequences of SUDs for both individuals and society, stimulating urgent efforts to identify novel treatment approaches. In addition, several neurobiological systems have been recently implicated in unique aspects of drug reward, opening the door to candidate medications with novel mechanisms of action. Here, we provide an overview of efforts to target several of these new systems, with a focus on those that are the subject of ongoing clinical trials as well as being areas of interest among the authors' research groups (MHJ, MTB, NAE). Specifically, we discuss new classes of medications targeting the serotonin 2 A receptor (i.e., psychedelics), glucagon-like peptide 1 receptor, cannabidiol, dynorphin/kappa opioid receptor, orexin/hypocretin, and oxytocin receptor systems, as well as emergent approaches for modulating the more canonical dopaminergic system via agonist therapies for stimulant use disorders. Collectively, innovations in this space give reason for optimism for an improved therapeutic landscape for substance use disorders in the near future.

Effects of CB1 receptor negative allosteric modulator Org27569 on oxycodone withdrawal symptoms in mice

RATIONALE/OBJECTIVES

Targeting cannabinoid receptor type 1 (CB1R) has shown promise for treating opioid withdrawal symptoms. This study aimed to investigate the efficacy of a specific CB1R negative allosteric modulator (NAM), Org27569, in reducing both naloxone-precipitated and protracted withdrawal symptoms in oxycodone-dependent mice.

METHODS

Mice received escalating doses of oxycodone (9-33 mg/kg IP) or saline twice daily for 9 days, followed by a final dose of oxycodone (33 mg/kg) or saline in the morning of day 9. In one cohort, the impact of Org27569 (3, 10, and 30 mg/kg) on naloxone (10 mg/kg IP) precipitated withdrawal symptoms was assessed. In another cohort, Org27569 (3 mg/kg) effects on the acquisition of conditioned place aversion to naloxone (0.6 mg/kg) precipitated opioid withdrawal, on behaviour following a 7-9-day abstinence period, and on naloxone (0.6 mg/kg) precipitated withdrawal-induced escape behaviour in a novel assay were assessed.

RESULTS

Although Org27569 decreased opioid withdrawal-induced jumping at doses of 10 and 30 mg/kg, these effects were confounded by reduced locomotion. At all doses tested, Org27569 had a modest inhibitory effect on gastrointestinal motility. At the lower dose of 3 mg/kg, which was not confounded by locomotor effects, Org27569 did not impact naloxone-precipitated withdrawal-induced jumping, acquisition of oxycodone withdrawal-induced conditioned place aversion, or naloxone-precipitated withdrawal-induced escape behaviour in a novel assay. A clear protracted opioid withdrawal phenotype was not observed in assays of anxiety-like or social behaviour.

CONCLUSIONS

Org27569 effects on negative affective-like symptoms were confounded by locomotor effects and effects on gastrointestinal motility were not opioid withdrawal specific. Further studies are needed in a model that produces a more pronounced protracted withdrawal syndrome.

Historical perspective on the therapeutic potential of cannabidiol

Cannabidiol (CBD) is one of over 200 cannabinoids present in the Cannabis plant. Unlike the plant's primary cannabinoid, delta-9-tetrahydrocannabinol (THC), CBD does not produce psychotomimetic effects nor induce dependence. Initially considered an inactive cannabinoid, interest in its pharmacological properties and therapeutic potential has grown exponentially over the last 20 years. Currently employed as a medication for certain epileptic syndromes, numerous pre-clinical and clinical studies support its potential use in various other disorders. In this chapter, we provide a brief historical overview of how this compound evolved from an "inactive substance" to a multifunctional clinical agent. Additionally, we discuss the current challenges in researching its potential therapeutic effects.

The NLRP3 Inflammasome in Stress Response: Another Target for the Promiscuous Cannabidiol

Many psychiatric patients do not respond to conventional therapy. There is a vast effort to investigate possible mechanisms involved in treatment resistance, trying to provide better treatment options, and several data points toward a possible involvement of inflammatory mechanisms. Microglia, glial, and resident immune cells are involved in complex responses in the brain, orchestrating homeostatic functions, such as synaptic pruning and maintaining neuronal activity. In contrast, microglia play a major role in neuroinflammation, neurodegeneration, and cell death. Increasing evidence implicate microglia dysfunction in neuropsychiatric disorders. The mechanisms are still unclear, but one pathway in microglia has received increased attention in the last 8 years, i.e., the NLRP3 inflammasome pathway. Stress response and inflammation, including microglia activation, can be attenuated by Cannabidiol (CBD). CBD has antidepressant, anti-stress, antipsychotic, anti-inflammatory, and other properties. CBD effects are mediated by direct or indirect modulation of many receptors, enzymes, and other targets. This review will highlight some findings for neuroinflammation and microglia involvement in stress-related psychiatric disorders, particularly addressing the NLRP3 inflammasome pathway. Moreover, we will discuss evidence and mechanisms for CBD effects in psychiatric disorders and animal models and address its potential effects on stress response via neuroinflammation and NLRP3 inflammasome modulation.

Effects of cannabinoids on ligand-gated ion channels

Phytocannabinoids such as Δ⁹-tetrahydrocannabinol and cannabidiol, endocannabinoids such as N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol, and synthetic cannabinoids such as CP47,497 and JWH-018 constitute major groups of structurally diverse cannabinoids. Along with these cannabinoids, CB1 and CB2 cannabinoid receptors and enzymes involved in synthesis and degradation of endocannabinoids comprise the major components of the cannabinoid system. Although, cannabinoid receptors are known to be involved in anti-convulsant, anti-nociceptive, anti-psychotic, anti-emetic, and anti-oxidant effects of cannabinoids, in recent years, an increasing number of studies suggest that, at pharmacologically relevant concentrations, these compounds interact with several molecular targets including G-protein coupled receptors, ion channels, and enzymes in a cannabinoid-receptor independent manner. In this report, the direct actions of endo-, phyto-, and synthetic cannabinoids on the functional properties of ligand-gated ion channels and the plausible mechanisms mediating these effects were reviewed and discussed.

Differential Interaction of Cannabidiol with Biomembranes Dependent on Cholesterol Concentration

Cannabidiol (CBD), the major nonpsychoactive component of plant-derived cannabinoids, has been reported to have a broad range of potential beneficial pharmacological effects on the central nervous system (CNS). In this study, the droplet interface bilayer, a model cell membrane, is used to examine the effects of CBD on passive water permeability, a fundamental membrane biophysical property. The presence of CBD decreases the water permeability of model lipid membranes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and at low concentrations of cholesterol (Chol) (20 mol %) in DOPC, whereas when higher concentrations of Chol are present (33 mol %), CBD has an opposing effect, increasing water permeability. The diametric effect in water permeability change upon addition of CBD to Chol-low and Chol-high bilayers signifies a variant interaction of CBD, depending on the initial state of bilayer packing and fluidity. Additionally, differential scanning calorimetry studies provide evidence that there are selective changes in thermotropic behavior for CBD with DOPC and with DOPC/Chol membranes, respectively, supportive of these varying membrane interactions of CBD dependent upon cholesterol. The intriguing ability of CBD to sensitively respond to membrane Chol concentrations in modifying physical properties highlights the significant impact that CBD can have on heterogeneous biomembranes including those of the CNS, the neurons of which are enriched in Chol to a point where up to a quarter of the body's total Chol is in the brain, and defective brain Chol homeostasis is implicated in neurodegenerative diseases.

Major Phytocannabinoids and Their Related Compounds: Should We Only Search for Drugs That Act on Cannabinoid Receptors?

The most important discoveries in pharmacology, such as certain classes of analgesics or chemotherapeutics, started from natural extracts which have been found to have effects in traditional medicine. Cannabis, traditionally used in Asia for the treatment of pain, nausea, spasms, sleep, depression, and low appetite, is still a good candidate for the development of new compounds. If initially all attention was directed to the endocannabinoid system, recent studies suggest that many of the clinically proven effects are based on an intrinsic chain of mechanisms that do not necessarily involve only cannabinoid receptors. Recent research has shown that major phytocannabinoids and their derivatives also interact with non-cannabinoid receptors such as vanilloid receptor 1, transient receptor ankyrin 1 potential, peroxisome proliferator-activated receptor-gamma or glitazone receptor, G55 protein-coupled receptor, and nuclear receptor, producing pharmacological effects in diseases such as Alzheimer's, epilepsy, depression, neuropathic pain, cancer, and diabetes. Nonetheless, further studies are needed to elucidate the precise mechanisms of these compounds. Structure modulation of phytocannabinoids, in order to improve pharmacological effects, should not be limited to the exploration of cannabinoid receptors, and it should target other courses of action discovered through recent research.

Agathadiol, a labdane diterpenoid from juniper berries, is a positive allosteric modulator of CB1R

The neutral fraction of a juniper (Juniperus communis L.) berries acetone extract could positively modulate the activity of type 1 - cannabinoid receptor (CB₁R). Bioactivity-directed fractionation identified the labdane diterpenoid agathadiol (4) as a positive allosteric modulator of CB₁R, while closely related analogues were inactive. Agathadiol (4) is a minor constituent of juniper, but could be more conveniently obtained by semisynthesis from agathic acid (8), a major constituent of Manila copal.