Cannabinoids

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History of Marijuana and Introduction to Cannabinoids

Marijuana, also referred to as cannabis, is the most widely used illegal drug in Western societies. Apart from this, this drug has the longest recorded history of self-indulgent human use. This recreational drug is popular due to the effects it illicits on individuals consuming or smoking it. Such effects include alteration of sensory perception and causing elation and euphoria.

However, apart from being a recreational drug, cannabis also has medicinal properties. In fact, Chinese texts dating back to the third millennium BC, describe that extracts of the hemp plant (Cannabis sativa) are able to cause a variety of medicinal effects which are unrelated to its psychoactive properties (its ability to alter mood, perception, behaviour, consciousness or cognition). These Chinese texts state that extracts from Cannabis sativa are useful in the relief of pain and cramps.

The use of marijuana has also been recorded more than 3000 years ago in ancient India. In this case, marijuana, or bhang bhang (the Indian term for marijuana ingested as food) was used to reduce anxiety.

The 19th century saw the use of this psychoactive drug reaching Europe and the Americas through the Arab world. During this period, the use of cannabis extracts for sexual medicinal purposes had also become popular. However, such use was halted in 1937 due to the banning of marijuana in the United States for further medicinal use. The use of marijuana was banned due to concerns that the use of such extracts may lead to abuse.

Recently, there has been a resurgence of interest in the medicinal properties of this plant especially due to the discovery of the endocannabinoid system. The discovery of the endocannabinoid system has not only shed light on the mechanisms underlying therapeutic actions of cannabinoids, but it has also shed light on new possible molecular targets for pharmacotherapy.

References:

Pacher, Batkai, & Kunos. (2006). The endocannabinoid system as an emerging target of pharmacotherapy. Pharmacological Reviews, 58(3), 389-462. doi:10.1124/pr.58.3.2

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Types of Cannabinoids

Cannabinoids are known to be aryl-substituted meroterpenes which are unique to the plant genus Cannabis. There are three types of different cannabinoids based on their origins, these are: Phytocannabinoids, endocannabinoids and synthetic cannabinoids.

There is still a lot of unknown properties of cannabinoids with regards to pharmacology, though the most potent psychoactive agent Δ9-tetrahydrocannabinol (THC) has been isolated and synthesized to allow for a number of studies to be done. THC along with other synthetic analogs can be used therapeutically (Chilakapati & Farris, 2014).

Phytocannabinoids, which are also known as exogenous cannabinoids are derived from plants. The ancient Cannabis sativa plant is very well-known and has caught the eye of many scientific researchers throughout the past 50 years. This has been used both recreationally, and also has been used medicinally throughout thousands of years. This plant is formed out of around 100 phytocannabinoids. Today, the most studied phytocannabinoids are Δ9- tetrahydrocannabinol (Δ9-THC), Δ9-tetrahydrocannabivarin (Δ9-THCV), cannabinol (CBN), cannabidiol (CBD), cannabidivarin (CBDV), cannabigerol (CBG), and cannabichromene (CBC) (Bielawiec et al., 2020).

Endocannabinoids (ECs) are endogenous ligands of cannabinoid receptors - CB1 and CB2. These show a large amount of evidence regarding the roles of the endocannabinoid system through the regulation of a number of physiological conditions and numerous diseases (Piscitelli, 2015).

Synthetic cannabinoids (SCs) are available commercially using the names old spice and K2. These are man-made compounds binding the G protein-coupled cannabinoid receptors. The structural features of many SCs have demonstrated to show higher binding affinities to CB1 and CB2 receptors in comparison with THC. This is one of the largest groups of psychoactive substances and were originally made for experimentation (Alipour et al., 2019).

References:

Alipour, A., Patel, P. B., Shabbir, Z., & Gabrielson, S. (2019). Review of the many faces of synthetic cannabinoid toxicities. Mental Health Clinician, 9(2), 93–99. https://doi.org/10.9740/mhc.2019.03.093
Bielawiec, P., Harasim-Symbor, E., & Chabowski, A. (2020). Phytocannabinoids: Useful Drugs for the Treatment of Obesity? Special Focus on Cannabidiol. In Frontiers in Endocrinology (Vol. 11, p. 114). Frontiers Media S.A. https://doi.org/10.3389/fendo.2020.00114
Chilakapati, J., & Farris, F. F. (2014). Cannabinoids. In Encyclopedia of Toxicology: Third Edition (pp. 649–654). Elsevier. https://doi.org/10.1016/B978-0-12-386454-3.00267-0
Piscitelli, F. (2015). Endocannabinoidomics: “Omics” Approaches Applied to Endocannabinoids and Endocannabinoid-Like Mediators. In The Endocannabinoidome: The World of Endocannabinoids and Related Mediators (pp. 137–152). Elsevier Inc. https://doi.org/10.1016/B978-0-12-420126-2.00009-2

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Figure 1 - Types of Cannabinoids

Figure 2 - Structures of Cannabinoids

Endocannabinoid System

The Endocannabinoid System Physiology

Over the last twenty-five years, the endocannabinoid system (ECS) has evolved as a significant neuromodulatory system. The endocannabinoid system (ECS) is a widely distributed neuromodulatory system that is involved in CNS development, synaptic plasticity, and response to endogenous and environmental insults. In humans, this mechanism also regulates energy homeostasis and has a strong effect on the role of the central nervous system's food intake centers and gastrointestinal tract function (Komorowski & Stepień, 2007; Lu & Mackie, 2016).

Endogenous cannabinoids (endocannabinoids), cannabinoid receptors, and enzymes make up the ECS. Cannabinoid receptors are activated by endogenous cannabinoids, which are lipids. Anandamide and 2-arachidonoyl glycerol( 2-AG) were the first endocannabinoids to be identified and studied. Endocannabinoids are released into the extracellular space after being liberated in one or two rapid enzymatic stages. Classic neurotransmitters, on the other hand, are synthesized ahead of time and deposited in synaptic vesicles. Both CB1 and CB2 receptors have a high efficacy agonist in 2-AG (Lu & Mackie, 2016).

CB1 and CB2 cannabinoid receptors are largely responsible for the effects of endocannabinoids. The G protein-coupled receptors (GPCRs) CB1 and CB2 are G protein-coupled receptors (GPCRs) that primarily couple to G proteins of the Gi and Go classes. As a result of their activation, adenylyl cyclases and some voltage-dependent calcium channels are inhibited, while other MAP kinases and inwardly rectifying potassium channels are activated, with certain differences depending on the cell type. As a result, activating CB1 or CB2 receptors has a variety of effects on cellular physiology, such as synaptic control, gene transcription, cell motility, and so on (Lu & Mackie, 2016).

CB1 receptors are often found on axon terminals and pre-terminal axon branches. They are abundant in both the dorsal and ventral striatum's medium spiny neurons. Expression is particularly high on the direct pathway axons as they enter the globus pallidus heading towards the substantia nigra. The direct pathway axons entering the globus pallidus on their way to the substantia nigra have an especially high level of expression (Lu & Mackie, 2016).

In comparison to CB1, CB2 receptors are expressed at much lower levels in the CNS. Microglia and vascular components are the main sources of this receptor. CB2, on the other hand, appears to be expressed by certain neurons, especially in pathological situations. CB2 receptors tend to be highly inducible, with CB2 expression rising up to 100 fold in response to tissue damage or inflammation (Lu & Mackie, 2016).

Endocannabinoids in the Reward and Reinforcement System

The endocannabinoid system (eCB) is involved in both reward and affirmation mediation. Exogenous cannabinoid drugs' capacity to induce hedonia and sustain self-administration in both human and animal subjects demonstrates this. Via interactions with the mesolimbic dopamine (DA) and endogenous opioid systems, eCBs also promote reward-motivated behaviours. Indeed, eCB signaling in the ventral tegmental area facilitates dopamine release in terminal regions such as the nucleus accumbens by activating midbrain DA cells (NAc). Motivation, reward salience, and cost-benefit considerations are all mediated by DA transmission in reinforced actions. To promote reward, eCBs and their receptors interact with opioid systems within the NAc, most likely by augmenting dopamine release (Wenzel & Cheer, 2018).

Interestingly, both DAergic and opioid systems are highly influenced by endocannabinoid (eCB) signaling and mounting evidence indicates that the eCB system is critical in DAergic and opioid control of reinforcement and reward. Exogenous CBs, such as 9-tetrahydrocannabinol (THC), the most psychoactive component of marijuana, raise extracellular DA levels in the ventral striatum.

CBs increase extracellular DA concentrations in the NAc by increasing the baseline firing rate and burst duration of midbrain DA neurons in a CB1-dependent manner, according to single-unit recording studies. Recent research indicates that eCBs, such as 2-AG, can increase DA neuron excitability by interacting directly with ion channels (Wenzel & Cheer, 2018).

CB1 receptors are not expressed in midbrain DA neurons, implying that CBs would implicitly excite VTA DA cells. The VTA is mostly made up of DA neurons (60%), with a limited population of GABA cells (30%) and even less glutamate neurons (3%) (Wenzel & Cheer, 2018).

References:

Komorowski, J., & Stepień, H. (2007). [The role of the endocannabinoid system in the regulation of endocrine function and in the control of energy balance in humans]. Postepy Higieny I Medycyny Doswiadczalnej (Online), 61, 99-105.
Lu, H., & Mackie, K. (2016a). An introduction to the endogenous cannabinoid system. Biological Psychiatry, 79(7), 516-525. doi:10.1016/j.biopsych.2015.07.028
Lu, H., & Mackie, K. (2016b). An introduction to the endogenous cannabinoid system. Biological Psychiatry, 79(7), 516-525. doi:10.1016/j.biopsych.2015.07.028
Wenzel, J. M., & Cheer, J. F. (2018). Endocannabinoid regulation of reward and reinforcement through interaction with dopamine and endogenous opioid signaling. Neuropsychopharmacology, 43(1), 103-115. doi:10.1038/npp.2017.126

Figure 3 - Endocannabinoid Synthesis and Degradation Pathways

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Endocannabinoid System in Pathology

Various studies have mapped the localization of cannabinoid receptors in tissues and at a subcellular level, and these have been critical to our understanding of the effects of cannabinoids in disease.

Endocannabinoids in Neurodegenerative Diseases

There has been anecdotal and preliminary scientific evidence of cannabis affording symptomatic relief in diverse neurodegenerative disorders. These include multiple sclerosis, Huntington's, Parkinson's and Alzheimer's diseases, and amyotrophic lateral sclerosis. This evidence implied that hypofunction or dysregulation of the endocannabinoid system may be responsible for some of the symptomatology of these diseases (Scotter et al., 2010).

Huntington's Disease

One of the first detectable signs of cellular dysfunction in human HD brains is the loss of CB1 from GABAergic efferent terminals and somata. In Huntington's Disease (HD) patients with early symptoms but without gross neuropathology, there is a significant decrease in CB1 density in the internal and external globus pallidus and substantia nigra (Scotter et al., 2010). The question of whether CB1 activation may be therapeutic in HD has been explored in various rodent lesion models; however, reports are conflicting as to whether CB1 agonism is neuroprotective, exacerbatory, or is more useful in the treatment of HD symptoms (Scotter et al., 2010).

Epilepsy

A tightly regulated balance between excitatory and inhibitory neurotransmission is required for proper functioning of the brain in the long term. Although a strong excitatory drive is necessary for processes such as learning and memory, exaggerated levels of excitation may lead to the neuronal system getting out of control, possibly leading to pathological processes. They may range from epileptiform seizures to neurodegenerative disorders, finally resulting in a massive neuronal cell death. The endocannabinoid system works to maintain the balance between excitation and inhibition ion the brain. The system can be exploited for as a target against epilepsy. If excessive synchronized bursts of activities take place in cortical, hippocampal and thalamocortical networks, respectively, epileptiform seizures may occur and the development of epilepsy (Monory & Lutz, 2008).

In neurons, the typical intracellular effects after binding of agonists to CB1 receptors are (1) inhibition of adenylyl cyclase, leading to decreased levels of intracellular cAMP, (2) stimulation of potassium channels (A-type and inwardly rectifying potassium channels), leading to an increased efflux of potassium ions, and (3) inhibition of voltage-dependent calcium channels (N- and P/Q-type), leading to a decreased calcium ion influx. Collectively, CB1 receptor agonists render neurons less excitable. The activation of CB1 receptors at the presynaptic site leads to a transient decrease of neurotransmitter release from the presynaptic site (Monory & Lutz, 2008).

It has been established that CB1 receptors are present both on inhibitory synapses (i.e. GABAergic terminals) as well as on excitatory synapses (i.e. glutamate-containing terminals). Activation of CB1 receptors on glutamatergic neurons should be anti-convulsive, while the activation of CB1 receptors on GABAergic neurons should be pro-convulsive. The specific loss of receptors on glutamatergic terminals was shown to lead to an increased excitability of hippocampal glutamatergic neurons. Loss of CB1 receptors on glutamatergic terminals led to a significant increase of kainic acid-induced seizures. however, deleting CB1 receptor from GABAergic cells did not lead to any changes in seizure behavior (Monory & Lutz, 2008).

Further studies revealed changes in the endocannabinoid system as a possible mechanism underlying the observed alterations of inhibitory neurotransmission. Increased levels of CB1 receptors were found on presynaptic terminals of GABAergic interneurons in the hippocampus, leading to an increase in CB1 receptor-mediated suppression of GABA transmission. Recent investigations revealed that targeting different elements of the endocannabinoid system might be a promising direction towards the development of novel therapeutic approaches for seizure-related pathologies (Monory & Lutz, 2008).

Alzheimer's Disease

The disruptive effects of Δ9-THC on memory are well documented and have recently been more fully characterized at the molecular level. Alzheimer's disease (AD), a disease with major impact on memory systems, has therefore been investigated for evidence of dysfunction of the endocannabinoid system resulting from, or contributing to, disease pathophysiology. Studies have found CB1 expression on neurons to be reduced or unchanged in human AD brain. Remaining CB1 protein was shown to be excessively nitrated and to have decreased efficacy of G-protein coupling. In contrast, CB2 expression is dramatically up-regulated, particularly in the microglial cells surrounding β-amyloid plaques in human AD brain (Scotter et al., 2010).

References:

Monory K., Lutz B. (2008) The Endocannabinoid System as a Therapeutic Target in Epilepsy. In: Köfalvi A. (eds) Cannabinoids and the Brain. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-74349-3_20
Scotter, E. L., Abood, M. E., & Glass, M. (2010). The endocannabinoid system as a target for the treatment of neurodegenerative disease. British Journal of Pharmacology, 160(3), 480-498. doi:10.1111/j.1476-5381.2010.00735.x

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LAWS OF MALTA - REGULATIONS FOR ACQUIRING A LICENSE TO RESEARCH WITH CANNABINOIDS

According to this Act, there can be no cultivation, importation or processing of cannabis or any related products in the intention for medicinal and/or purposes for research in Malta before the appropriate and regulatory approvals, authorisations, licences and permits are obtained as is by or under all applicable laws including this Act and any regulations subsidiary to it:

If the above mentioned approvals and so on are obtained, the cannabis/related products may only have an intended use in research or for medicinal treatment,
The cultivation of cannabis may not be carried out so for the production of medicinal products and/or research purposes as is expressly prohibited.

(2) Any or all persons set to carry the activities enlisted in sub-article (1) are required to:

Comply with such provisions provided by this Act,
After the application of a prescribed form, a letter of intent is to be obtained form the Malta Enterprise (these ensure that the activity being carried out is solely a process of production).
Comply with all set regulations, including international obligations resulting from a treaty to which Malta may from time to time be a party, as may be applicable;
Comply with all regulations relating to the production and quality standards of products for medicinal and, or research purposes, as the case may be, as applicable under the Medicines Act and with any other relevant regulations;
Have obtained a letter from the regulatory authority,
Comply with any other relevant regulations as shall, from time to time, be promulgated under this Act or any other applicable law.

Obtained from: https://legislation.mt/eli/cap/578/eng/pdf

The above information is pertaining to the current legislation for cannabis use in Malta. However, as of March 2021, a white paper was proposed by the government. The following describes the new proposed legislation.

1) Adults must be in possession of 7 grams or less if this is to be considered for personal use only. This is not subjected to any fines or punishment.

2) Up to four plants can be grown in one's household, where it is not visible to the public. Additionally, any home-grown cannabis cannot be sold.

3) Previous crimes regarding possession of Cannabis should be legally removed from one's conduct certificate. In this manner, past crimes should not lead to punishment or loss of opportunities.

4) The government proposed that only CBD would be considered a legal substance since it is not psychoactive and has medicinal properties. THC on the other hand, is a psychoactive substance and therefore will remain considered as illegal. CBD can be used as a potential treatment for Epilepsy, as an analgesic, as a cancer treatment, and to reduce anxiety and depression symptoms.

5) Public smoking of Cannabis should still remain illegal, with a fine of 233.33 euro.

6) The government proposed that minors who are caught in possession of Cannabis should be subjected to administrative and not criminal penalties. This approach will be adopted for minors (under 18 years of age) rather than criminal punishment in order to distance minors from its use and potential harmful effects.

7) A government authority is being proposed to be specifically responsible for dealing with all matters related to this new legislation, including proposing more guidelines and improving on the legislation.

8) The government would like to conduct educational activities to inform the public on matters regarding the risks and benefits of Cannabis use, removing the stigma on Cannabis use, as well as promoting research and open discussions on the matter. This provides more opporunities for researchers and students to study the use of Cannabis for medicinal purposes and even further characterise any potential benefits or harm.

The above information was taken from the recently proposed White paper - https://meae.gov.mt/en/Public_Consultations/MJEG/PublishingImages/Pages/Consultations/TowardstheStrengtheningoftheLegalFrameworkontheResponsibleUseofCannabis/CANNABIS%20ENG.pdf

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