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Cannabinoids are a class of diverse chemical compounds that activate cannabinoid receptors on cells that repress neurotransmitter release in the brain. These receptor proteins include the endocannabinoids (produced naturally in the body by humans and animals), the phytocannabinoids (found in cannabis and some other plants), and synthetic cannabinoids (produced chemically by humans). The most notable cannabinoid is the phytocannabinoid ∆-tetrahydrocannabinol (THC), the primary psychoactive compound of cannabis. However, there are known to exist numerous other cannabinoids with varied effects.

Synthetic cannabinoids encompass a variety of distinct chemical classes: the classical cannabinoids structurally related to THC, the nonclassical cannabinoids (cannabimimetics) including the aminoalkylindoles, 1,5-diarylpyrazoles, quinolines, and arylsulphonamides, as well as eicosanoids related to the endocannabinoids.

Cannabinoid receptors

Before the 1980s, it was often speculated that cannabinoids produced their physiological and behavioral effects via nonspecific interaction with cell membranes, instead of interacting with specific membrane-bound receptors. The discovery of the first cannabinoid receptors in the 1980s helped to resolve this debate. These receptors are common in animals, and have been found in mammals, birds, fish, and reptiles. At present, there are two known types of cannabinoid receptors, termed CB₁ and CB₂, with mounting evidence of more. The human brain has more cannabinoid receptors than any other G protein-coupled receptor (GPCR) type.

Cannabinoid receptor type 1

CB₁ receptors are found primarily in the brain, to be specific in the basal ganglia and in the limbic system, including the hippocampus. They are also found in the cerebellum and in both male and female reproductive systems. CB₁ receptors are absent in the medulla oblongata, the part of the brain stem responsible for respiratory and cardiovascular functions. Thus, there is not the risk of respiratory or cardiovascular failure that can be produced by some drugs. CB₁ receptors appear to be responsible for the euphoric and anticonvulsive effects of cannabis.

Cannabinoid receptor type 2

CB₂ receptors are predominantly found in the immune system, or immune-derived cells with the greatest density in the spleen. While found only in the peripheral nervous system, a report does indicate that CB₂ is expressed by a subpopulation of microglia in the human cerebellum . CB₂ receptors appear to be responsible for the anti-inflammatory and possibly other therapeutic effects of cannabis.

Phytocannabinoids

Type	Skeleton	Cyclization
Cannabigerol-type CBG
Cannabichromene-type CBC
Cannabidiol-type CBD
Tetrahydrocannabinol- and Cannabinol-type THC, CBN
Cannabielsoin-type CBE
iso- Tetrahydrocannabinol- type iso-THC
Cannabicyclol-type CBL
Cannabicitran-type CBT
Main classes of natural cannabinoids

Phytocannabinoids (also called natural cannabinoids, herbal cannabinoids, and classical cannabinoids) are known to occur in several different plant species. These include Cannabis sativa, Cannabis indica, Cannabis ruderalis, Echinacea purpurea, Echinacea angustifolia, Echinacea pallida, Acmella oleracea, Helichrysum umbraculigerum, and Radula marginata. The best known herbal cannabinoids are Δ9-tetrahydrocannabinol (THC) from Cannabis and the lipophilic alkamides (alkylamides) from Echinacea species.

At least 85 different cannabinoids have been isolated from the Cannabis plant and 25 different cannabinoids from Echinacea species. In Cannabis, these cannabinoids are concentrated in a viscous resin produced in structures known as glandular trichomes. In Echinacea species, cannabinoids are found throughout the plant structure, but are most concentrated in the roots and stems. Tea (Camellia sinensis) catechins have an affinity for human cannabinoid receptors.

Phytocannabinoids are nearly insoluble in water but are soluble in lipids, alcohols, and other non-polar organic solvents. However, as phenols, they form more water-soluble phenolate salts under strongly alkaline conditions.

All-natural cannabinoids are derived from their respective 2-carboxylic acids (2-COOH) by decarboxylation (catalyzed by heat, light, or alkaline conditions).

Cannabis-derived cannabinoids

Types

To the right, the main classes of cannabinoids from Cannabis are shown. All classes derive from cannabigerol-type compounds and differ mainly in the way this precursor is cyclized.

Tetrahydrocannabinol (THC), cannabidiol (CBD), cannabinol (CBN) (derived from Cannabis); and dodeca-2E,4E,8Z,10E/Z-tetraenoic-acid-isobutylamides (the main bioactive constituents from Echinacea species) are the most prevalent natural cannabinoids and have received the most study.

• CBG (Cannabigerol)
• CBC (Cannabichromene)
• CBL (Cannabicyclol)
• CBV (Cannabivarin)
• THCV (Tetrahydrocannabivarin)
• CBDV (Cannabidivarin)
• CBCV (Cannabichromevarin)
• CBGV (Cannabigerovarin)
• CBGM (Cannabigerol Monomethyl Ether)

Tetrahydrocannabinol

Tetrahydrocannabinol (THC) is the primary psychoactive component of the Cannabis plant. Delta-9-tetrahydrocannabinol (Δ-THC, THC) and delta-8-tetrahydrocannabinol (Δ-THC), mimic the action of anandamide, a neurotransmitter produced naturally in the body. These two THC's produce the effects associated with cannabis by binding to the CB₁ cannabinoid receptors in the brain. THC appears to ease moderate pain (analgesic) and to be neuroprotective. Studies show THC reduces neuroinflammation and stimulates neurogenesis. THC has approximately equal affinity for the CB₁ and CB₂ receptors.

Cannabidiol

Cannabidiol (CBD) is not psychoactive, and was thought not to affect the psychoactivity of THC. However, recent evidence shows that smokers of cannabis with a higher CBD/THC ratio were less likely to experience schizophrenia-like symptoms. This is supported by psychological tests, in which participants experience less intense psychotic-like effects when intravenous THC was co-administered with CBD (as measured with a PANSS test). Cannabidiol has little affinity for CB₁ and CB₂ receptors but acts as an indirect antagonist of cannabinoid agonists. Recently it was found to be an antagonist at the putative new cannabinoid receptor, GPR55, a GPCR expressed in the caudate nucleus and putamen. Cannabidiol has also been shown to act as a 5-HT_1A receptor agonist, an action that is involved in its antidepressant, anxiolytic, and neuroprotective effects.

It appears to relieve convulsion, inflammation, anxiety, and nausea. CBD has a greater affinity for the CB₂ receptor than for the CB₁ receptor.

CBD shares a precursor with THC and is the main cannabinoid in low-THC Cannabis strains. CBD apparently plays a role in preventing the short-term memory loss associated with THC in mammals.

Some research suggests that the antipsychotic effects of cannabidiol potentially represent a novel mechanism in the treatment of schizophrenia.

Researchers at California Pacific Medical Center discovered CBD's ability to "turn off" the activity of ID1, the gene responsible for metastasis in breast and other types of cancers, including the particularly aggressive triple negative breast cancer. The researchers hope to start human trials soon.

Cannabinol

Cannabinol (CBN) is the primary product of THC degradation, and there is usually little of it in a fresh plant. CBN content increases as THC degrades in storage, and with exposure to light and air. It is only mildly psychoactive. Its affinity to the CB₂ receptor is higher than for the CB₁ receptor.

Cannabigerol

Cannabigerol (CBG) is non-psychotomimetic but still affects the overall effects of Cannabis. It acts as an α₂-adrenergic receptor agonist, 5-HT_1A receptor antagonist, and CB₁ receptor antagonist. It also binds to the CB₂ receptor.

Tetrahydrocannabivarin

Tetrahydrocannabivarin (THCV) is prevalent in certain central Asian and southern African strains of Cannabis. It is an antagonist of THC at CB₁ receptors and attenuates the psychoactive effects of THC.

Cannabidivarin

Although cannabidivarin (CBDV) is usually a minor constituent of the cannabinoid profile, enhanced levels of CBDV have been reported in feral cannabis plants from the northwest Himalayas, and in hashish from Nepal.

Cannabichromene

Cannabichromene (CBC) is non-psychoactive and does not affect the psychoactivity of THC .

Double bond position

In addition, each of the compounds above may be in different forms depending on the position of the double bond in the alicyclic carbon ring. There is potential for confusion because there are different numbering systems used to describe the position of this double bond. Under the dibenzopyran numbering system widely used today, the major form of THC is called Δ-THC, while the minor form is called Δ-THC. Under the alternate terpene numbering system, these same compounds are called Δ-THC and Δ-THC, respectively.

Length

Most herbal cannabinoid compounds are 21-carbon compounds. However, some do not follow this rule, primarily because of variation in the length of the side-chain attached to the aromatic ring. In THC, CBD, and CBN, this side-chain is a pentyl (5-carbon) chain. In the most common homologue, the pentyl chain is replaced with a propyl (3-carbon) chain. Cannabinoids with the propyl side-chain are named using the suffix varin, and are designated, for example, THCV, CBDV, or CBNV.

Cannabis plant profile

Cannabis plants can exhibit wide variation in the quantity and type of cannabinoids they produce. The mixture of cannabinoids produced by a plant is known as the plant's cannabinoid profile. Selective breeding has been used to control the genetics of plants and modify the cannabinoid profile. For example, strains that are used as fiber (commonly called hemp) are bred such that they are low in psychoactive chemicals like THC. Strains used in medicine are often bred for high CBD content, and strains used for recreational purposes are usually bred for high THC content or for a specific chemical balance.

Quantitative analysis of a plant's cannabinoid profile is often determined by gas chromatography (GC), or more reliably by gas chromatography combined with mass spectrometry (GC/MS). Liquid chromatography (LC) techniques are also possible, and, unlike GC methods, can differentiate between the acid and neutral forms of the cannabinoids. There have been systematic attempts to monitor the cannabinoid profile of cannabis over time, but their accuracy is impeded by the illegal status of the plant in many countries.

Pharmacology

Cannabinoids can be administered by smoking, vaporizing, oral ingestion, transdermal patch, intravenous injection, sublingual absorption, or rectal suppository. Once in the body, most cannabinoids are metabolized in the liver, especially by cytochrome P450 mixed-function oxidases, mainly CYP 2C9. Thus supplementing with CYP 2C9 inhibitors leads to extended intoxication.

Some is also stored in fat in addition to being metabolized in liver. Δ-THC is metabolized to 11-hydroxy-Δ-THC, which is then metabolized to 9-carboxy-THC. Some cannabis metabolites can be detected in the body several weeks after administration. These metabolites are the chemicals recognized by common antibody-based "drug tests"; in the case of THC et al., these loads do not represent intoxication (compare to ethanol breath tests that measure instantaneous blood alcohol levels) but an integration of past consumption over an approximately month-long window.

Plant synthesis

Cannabinoid production starts when an enzyme causes geranyl pyrophosphate and olivetolic acid to combine and form CBG. Next, CBG is independently converted to either CBD or CBC by two separate synthase enzymes. CBD is then enzymatically cyclized to THC. For the propyl homologues (THCV, CBDV and CBNV), there is a similar pathway that is based on CBGV. Recent studies show that THC is not cyclized from CBD but rather directly from CBG. No experiment thus far has turned up an enzyme that converts CBD into THC, although it is still hypothesized.

Separation

Cannabinoids can be separated from the plant by extraction with organic solvents. Hydrocarbons and alcohols are often used as solvents. However, these solvents are flammable and many are toxic. Butane may be used, which evaporates extremely quickly. Supercritical solvent extraction with carbon dioxide is an alternative technique. Although this process requires high pressures (73 atmospheres or more), there is minimal risk of fire or toxicity, solvent removal is simple and efficient, and extract quality can be well controlled. Once extracted, cannabinoid blends can be separated into individual components using wiped film vacuum distillation or other distillation techniques. However, to produce high-purity cannabinoids, chemical synthesis or semisynthesis is generally required.

Natural occurrence

Cannabis indica may have a CBD:THC ratio 4–5 times that of Cannabis sativa.

History

Cannabinoids were first discovered in the 1940s, when CBD and CBN were identified. The structure of THC was first determined in 1964.

Due to molecular similarity and ease of synthetic conversion, CBD was originally believed to be a natural precursor to THC. However, it is now known that CBD and THC are produced independently in the cannabis plant from the precursor CBG.

Endocannabinoids

Endocannabinoids are substances produced from within the body that activate cannabinoid receptors. After the discovery of the first cannabinoid receptor in 1988, scientists began searching for an endogenous ligand for the receptor.

Types of endocannabinoid ligands

Arachidonoylethanolamine (Anandamide or AEA)

In 1992, in Raphael Mechoulam's lab, the first such compound was identified as arachidonoyl ethanolamine and named anandamide, a name derived from the Sanskrit word for bliss and -amide. Anandamide is derived from the essential fatty acid arachidonic acid. It has a pharmacology similar to THC, although its chemical structure is different. Anandamide binds to the central (CB₁) and, to a lesser extent, peripheral (CB₂) cannabinoid receptors, where it acts as a partial agonist. Anandamide is about as potent as THC at the CB₁ receptor. Anandamide is found in nearly all tissues in a wide range of animals. Anandamide has also been found in plants, including small amounts in chocolate.

Two analogs of anandamide, 7,10,13,16-docosatetraenoylethanolamide and homo-γ-linolenoylethanolamine, have similar pharmacology. All of these are members of a family of signalling lipids called N-acylethanolamines, which also includes the noncannabimimetic palmitoylethanolamide and oleoylethanolamide, which possess anti-inflammatory and orexigenic effects, respectively. Many N-acylethanolamines have also been identified in plant seeds and in molluscs.

2-arachidonoyl glycerol (2-AG)

Another endocannabinoid, 2-arachidonoyl glycerol, binds to both the CB₁ and CB₂ receptors with similar affinity, acting as a full agonist at both. 2-AG is present at significantly higher concentrations in the brain than anandamide, and there is some controversy over whether 2-AG rather than anandamide is chiefly responsible for endocannabinoid signalling in vivo. In particular, one in vitro study suggests that 2-AG is capable of stimulating higher G-protein activation than anandamide, although the physiological implications of this finding are not yet known.

2-arachidonyl glyceryl ether (noladin ether)

In 2001, a third, ether-type endocannabinoid, 2-arachidonyl glyceryl ether (noladin ether), was isolated from porcine brain. Prior to this discovery, it had been synthesized as a stable analog of 2-AG; indeed, some controversy remains over its classification as an endocannabinoid, as another group failed to detect the substance at "any appreciable amount" in the brains of several different mammalian species. It binds to the CB₁ cannabinoid receptor (K_i = 21.2 nmol/L) and causes sedation, hypothermia, intestinal immobility, and mild antinociception in mice. It binds primarily to the CB₁ receptor, and only weakly to the CB₂ receptor.

N-arachidonoyl-dopamine (NADA)

Discovered in 2000, NADA preferentially binds to the CB₁ receptor. Like anandamide, NADA is also an agonist for the vanilloid receptor subtype 1 (TRPV1), a member of the vanilloid receptor family.

Virodhamine (OAE)

A fifth endocannabinoid, virodhamine, or O-arachidonoyl-ethanolamine (OAE), was discovered in June 2002. Although it is a full agonist at CB₂ and a partial agonist at CB₁, it behaves as a CB₁ antagonist in vivo. In rats, virodhamine was found to be present at comparable or slightly lower concentrations than anandamide in the brain, but 2- to 9-fold higher concentrations peripherally.

Lysophosphatidylinositol (LPI)

Recent evidence has highlighted LPI as the endogenous ligand to novel endocannabinoid receptor GPR55, making it a strong contender as the sixth endocannabinoid.

Function

Endocannabinoids serve as intercellular 'lipid messengers', signaling molecules that are released from one cell and activating the cannabinoid receptors present on other nearby cells. Although in this intercellular signaling role they are similar to the well-known monoamine neurotransmitters, such as acetylcholine and dopamine, endocannabinoids differ in numerous ways from them. For instance, they are used in retrograde signaling between neurons. Furthermore, endocannabinoids are lipophilic molecules that are not very soluble in water. They are not stored in vesicles, and exist as integral constituents of the membrane bilayers that make up cells. They are believed to be synthesized 'on-demand' rather than made and stored for later use. The mechanisms and enzymes underlying the biosynthesis of endocannabinoids remain elusive and continue to be an area of active research.

The endocannabinoid 2-AG has been found in bovine and human maternal milk.

Retrograde signal

Conventional neurotransmitters are released from a ‘presynaptic’ cell and activate appropriate receptors on a ‘postsynaptic’ cell, where presynaptic and postsynaptic designate the sending and receiving sides of a synapse, respectively. Endocannabinoids, on the other hand, are described as retrograde transmitters because they most commonly travel ‘backward’ against the usual synaptic transmitter flow. They are, in effect, released from the postsynaptic cell and act on the presynaptic cell, where the target receptors are densely concentrated on axonal terminals in the zones from which conventional neurotransmitters are released. Activation of cannabinoid receptors temporarily reduces the amount of conventional neurotransmitter released. This endocannabinoid mediated system permits the postsynaptic cell to control its own incoming synaptic traffic. The ultimate effect on the endocannabinoid-releasing cell depends on the nature of the conventional transmitter being controlled. For instance, when the release of the inhibitory transmitter GABA is reduced, the net effect is an increase in the excitability of the endocannabinoid-releasing cell. On the converse, when release of the excitatory neurotransmitter glutamate is reduced, the net effect is a decrease in the excitability of the endocannabinoid-releasing cell.

Range

Endocannabinoids are hydrophobic molecules. They cannot travel unaided for long distances in the aqueous medium surrounding the cells from which they are released, and therefore act locally on nearby target cells. Hence, although emanating diffusely from their source cells, they have much more restricted spheres of influence than do hormones, which can affect cells throughout the body.

Synthetic cannabinoids

Historically, laboratory synthesis of cannabinoids were often based on the structure of herbal cannabinoids, and a large number of analogs have been produced and tested, especially in a group led by Roger Adams as early as 1941 and later in a group led by Raphael Mechoulam. Newer compounds are no longer related to natural cannabinoids or are based on the structure of the endogenous cannabinoids.

Synthetic cannabinoids are particularly useful in experiments to determine the relationship between the structure and activity of cannabinoid compounds, by making systematic, incremental modifications of cannabinoid molecules.

Medications containing natural or synthetic cannabinoids or cannabinoid analogs:

• Dronabinol (Marinol), is Δ-tetrahydrocannabinol (THC), used as an appetite stimulant, anti-emetic, and analgesic
• Nabilone (Cesamet), a synthetic cannabinoid and an analog of Marinol. It is Schedule II unlike Marinol, which is Schedule III
• Sativex, a cannabinoid extract oral spray containing THC, CBD, and other cannabinoids used for neuropathic pain and spasticity in 22 countries including England, Canada and Spain. Sativex develops whole-plant cannabinoid medicines
• Rimonabant (SR141716), a selective cannabinoid (CB₁) receptor inverse agonist used as an anti-obesity drug under the proprietary name Acomplia. It is also used for smoking cessation

Other notable synthetic cannabinoids include:

• JWH-018, a potent synthetic cannabinoid agonist discovered by Dr. John W. Huffman at Clemson University. It is being increasingly sold in legal smoke blends collectively known as "spice". Several countries and states have moved to ban it legally.
• JWH-073
• CP-55940, produced in 1974, this synthetic cannabinoid receptor agonist is many times more potent than THC.
• Dimethylheptylpyran
• HU-210, about 100 times as potent as THC
• HU-331 a potential anti-cancer drug derived from cannabidiol that specifically inhibits topoisomerase II.
• SR144528, a CB₂ receptor antagonist
• WIN 55,212-2, a potent cannabinoid receptor agonist
• JWH-133, a potent selective CB₂ receptor agonist
• Levonantradol (Nantrodolum), an anti-emetic and analgesic but not currently in use in medicine
• AM-2201, a potent cannabinoid receptor agonist.

See also

• Cannabinoid receptor antagonist

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Further reading

• Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 12586720, please use {{cite journal}} with |pmid=12586720 instead.

• Devane WA, Hanuš L, Breuer A; et al. (1992). "Isolation and structure of a brain constituent that binds to the cannabinoid receptor". Science. 258 (5090): 1946–9. doi:10.1126/science.1470919. PMID 1470919. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)

• Elsohly MA, Slade D (2005). "Chemical constituents of marijuana: the complex mixture of natural cannabinoids". Life Sci. 78 (5): 539–48. doi:10.1016/j.lfs.2005.09.011. PMID 16199061.

• Hanuš L, Gopher A, Almog S, Mechoulam R (1993). "Two new unsaturated fatty acid ethanolamides in brain that bind to the cannabinoid receptor". J. Med. Chem. 36 (20): 3032–4. doi:10.1021/jm00072a026. PMID 8411021.{{cite journal}}: CS1 maint: multiple names: authors list (link)

• Hanuš L (1987). "Biogenesis of cannabinoid substances in the plant". Acta Universitatis Palackianae Olomucensis Facultatis Medicae. 116: 47–53. PMID 2962461.

• Hanuš, L.; Krejčí, Z. (1975). "Isolation of two new cannabinoid acids from Cannabis sativa L. of Czechoslovak origin". Acta Univ. Olomuc., Fac. Med. 74: 161–166. {{cite journal}}: Cite has empty unknown parameter: |author-name-separator= (help); Unknown parameter |author-separator= ignored (help)

• Hanuš, L.; Krejčí, Z.; Hruban, L. (1975). "Isolation of cannabidiolic acid from Turkish variety of cannabis cultivated for fibre". Acta Univ. Olomuc., Fac. Med. 74: 167–172. {{cite journal}}: Cite has empty unknown parameter: |author-name-separator= (help); Unknown parameter |author-separator= ignored (help)

• Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1007/978-0-387-74349-3, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1007/978-0-387-74349-3 instead.

• Mechoulam R, Ben-Shabat S, Hanuš L; et al. (1995). "Identification of an endogenous 2-monoglyceride, present in canine gut, that binds to cannabinoid receptors". Biochem. Pharmacol. 50 (1): 83–90. doi:10.1016/0006-2952(95)00109-D. PMID 7605349. {{cite journal}}: Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)

• Nicoll RA, Alger BE (2004). "The brain's own marijuana". Sci. Am. 291 (6): 68–75. doi:10.1038/scientificamerican1204-68. PMID 15597982.

• Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 19005078, please use {{cite journal}} with |pmid=19005078 instead.

• Attention: This template ({{cite pmid}}) is deprecated. To cite the publication identified by PMID 19005077, please use {{cite journal}} with |pmid=19005077 instead.

• Turner, C. E.; Mole, M. L.; Hanuš, L.; ElSohly, H. N. (1981). "Constituents of Cannabis sativa L. XIX. Isolation and structure elucidation of cannabiglendol. A novel cannabinoid from an Indian variant" (PDF). J. Nat. Prod. 44 (1): 27–33. doi:10.1021/np50013a005. {{cite journal}}: Cite has empty unknown parameter: |author-name-separator= (help); Unknown parameter |author-separator= ignored (help)

External links

Cannabinoid information

• Bela Szabo: Pharmacology of Cannabinoid Receptors BIOTREND Reviews No. 02, February 2008
• Marijuana and Medicine - Assessing the Science Base (Institute of Medicine) - 1999 at National Academies Press
• House of Lords Report - Cannabis (United Kingdom) - 1998 at Parliament of the United Kingdom
• Cannabis: A Health Perspective and Research Agenda - 1997 at World Health Organization
• Chemical Ecology of Cannabis (J. Intl. Hemp Assn. - 1994)
• THC (tetrahydrocannabinol) accumulation in glands of Cannabis (Cannabaceae)
• Non-psychotropic plant cannabinoids: new therapeutic opportunities from an ancient herb (PDF)

Cannabinoid research organizations

• The International Cannabinoid Research Society
• The Canadian Consortium for the Investigation of Cannabinoids
• Therapeutic Potential in Spotlight at Cannabinoid Researchers' Meeting at California Cannabis Research Medical Group
• International Cannabinoid Research Society

• Analgesics
• Cannabinoids
• Cannabis
• Neurochemistry