Activity of delta8- and delta9-tetrahydrocannabinol and related compounds in the mouse

An emerging trend in Novel Psychoactive Substances (NPSs): designer THC

Since its discovery as one of the main components of cannabis and its affinity towards the cannabinoid receptor CB1, serving as a means to exert its psychoactivity, Δ9-tetrahydrocannabinol (Δ9-THC) has inspired medicinal chemists throughout history to create more potent derivatives. Initially, the goal was to synthesize chemical probes for investigating the molecular mechanisms behind the pharmacology of Δ9-THC and finding potential medical applications. The unintended consequence of this noble intent has been the proliferation of these compounds for recreational use. This review comprehensively covers the most exhaustive number of THC-like cannabinoids circulating on the recreational market. It provides information on the chemistry, synthesis, pharmacology, analytical assessment, and experiences related to the psychoactive effects reported by recreational users on online forums. Some of these compounds can be found in natural cannabis, albeit in trace amounts, while others are entirely artificial. Moreover, to circumvent legal issues, many manufacturers resort to semi-synthetic processes starting from legal products extracted from hemp, such as cannabidiol (CBD). Despite the aim to encompass all known THC-like molecules, new species emerge on the drug users' pipeline each month. Beyond posing a significantly high public health risk due to unpredictable and unknown side effects, scientific research consistently lags behind the rapidly evolving recreational market.

Cannabis and Pregnancy: A Review

Importance

Prenatal cannabis use is rising and is a major public health issue. Cannabis use in pregnancy and during lactation has been associated with increased maternal and offspring morbidity and mortality.

Objective

This review aims to summarize the existing literature and current recommendations for cannabis use during pregnancy or lactation.

Evidence Acquisition

A PubMed, Cochrane Library, and Google Scholar literature search using the following terms was performed to gather relevant data: "cannabis," "cannabinoid," "delta-9-tetrahydrocannabinol," "THC," "cannabidiol," "fetal outcomes," "perinatal outcomes," "pregnancy," and "lactation."

Results

Available studies on cannabis use in pregnancy and during lactation were reviewed and support an association with increased risk of preterm birth, neonatal intensive care unit admission, low birth weight, and small-for-gestational-age infants.

Conclusion and Relevance

There is a critical need for research on the effects of cannabis use in pregnancy and during lactation. This is a necessary first step before furthering patient education, developing interventions, and targeting antenatal surveillance to ameliorate the adverse impacts on maternal and fetal health.

Cannabinoids and the placenta: Receptors, signaling and outcomes

Cannabis use during pregnancy is increasing. The improvement of pregnancy-related symptoms including morning sickness and management of mood and stress are among the most reported reasons for its use. Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) are the most abundant cannabinoids found within the cannabis flower. The concentration of these components has drastically increased in the past 20 years. Additionally, many edibles contain only one cannabinoid and are marketed to achieve a specific goal, meaning there are an increasing number of pregnancies that are exposed to isolated cannabinoids. Both Δ9-THC and CBD cross the placenta and can impact the fetus directly, but the receptors through which cannabinoids act are also expressed throughout the placenta, suggesting that the effects of in-utero cannabinoid exposure may include indirect effects from the placenta. In-utero cannabis research focuses on short and long-term fetal health and development; however, these studies include little to no placenta analysis. Prenatal cannabinoid exposure is linked to small for gestational age and fetal growth-restricted babies. Compromised placental development is also associated with fetal growth restriction and the few studies (clinical and animal models) that included placental analysis, identify changes in placental vasculature and function in these cannabinoid-exposed pregnancies. In vitro studies further support cannabinoid impact on cell function in the different populations that comprise the placenta. In this article, we aim to summarize how phytocannabinoids can impact placental development and function. Specifically, the cannabinoids and their actions at the different receptors are described, with receptor localization throughout the human and murine placenta discussed. Findings from studies that included placental analysis and how cannabinoid signaling may modulate critical developmental processing including cell proliferation, angiogenesis and migration are described. Considering the current research, prenatal cannabinoid exposure may significantly impact placental development, and, as such, identifying windows of placental vulnerability for each cannabinoid will be critical to elucidate the etiology of fetal outcome studies.

Nasal accumulation and metabolism of Δ9-tetrahydrocannabinol following aerosol ('vaping') administration in an adolescent rat model

Passive aerosol exposure to Δ9-tetrahydrocannabinol (THC) in laboratory animals results in faster onset of action and less extensive liver metabolism compared to most other administration routes and might thus provide an ecologically relevant model of human cannabis inhalation. Previous studies have, however, overlooked the possibility that rodents, as obligate nose breathers, may accumulate aerosolized THC in the nasal cavity, from where the drug might directly diffuse to the brain. To test this, we administered THC (ten 5-s puffs of 100 mg/mL of THC) to adolescent (31-day-old) Sprague-Dawley rats of both sexes. We used liquid chromatography/tandem mass spectrometry to quantify the drug and its first-pass metabolites - 11-hydroxy-Δ9-THC (11-OH-THC) and 11-nor-9-carboxy-Δ9-THC (11-COOH-THC) - in nasal mucosa, lungs, plasma, and brain (olfactory bulb and cerebellum) at various time points after exposure. Apparent maximal THC concentration and area under the curve were ∼5 times higher in nasal mucosa than in lungs and 50-80 times higher than in plasma. Concentrations of 11-OH-THC were also greater in nasal mucosa and lungs than other tissues, whereas 11-COOH-THC was consistently undetectable. Experiments with microsomal preparations confirmed local metabolism of THC into 11-OH-THC (not 11-COOH-THC) in nasal mucosa and lungs. Finally, whole-body exposure to THC deposited substantial amounts of THC (∼150 mg/g) on fur but suppressed post-exposure grooming in rats of both sexes. The results indicate that THC absorption and metabolism in nasal mucosa and lungs, but probably not gastrointestinal tract, contribute to the pharmacological effects of aerosolized THC in male and female rats.

Review of delta-8-tetrahydrocannabinol (Δ8 -THC): Comparative pharmacology with Δ9 -THC

The use of the intoxicating cannabinoid delta-8-tetrahydrocannabinol (Δ⁸ -THC) has grown rapidly over the last several years. There have been dozens of Δ⁸ -THC studies dating back over many decades, yet no review articles have comprehensively covered these findings. In this review, we summarize the pharmacological studies of Δ⁸ -THC, including receptor binding, cell signalling, in vivo cannabimimetic activity, clinical activity and pharmacokinetics. We give special focus to studies that directly compared Δ⁸ -THC to its more commonly studied isomer, Δ⁹ -THC. Overall, the pharmacokinetics and pharmacodynamics of Δ⁸ -THC and Δ⁹ -THC are very similar. Δ⁸ -THC is a partial agonist of the cannabinoid CB₁ receptor and has cannabimimetic activity in both animals and humans. The reduced potency of Δ⁸ -THC in clinical studies compared with Δ⁹ -THC can be explained by weaker cannabinoid CB₁ receptor affinity, although there are other plausible mechanisms that may contribute. We highlight the gaps in our knowledge of Δ⁸ -THC pharmacology where further studies are needed, particularly in humans.

Understanding the Placental Biology of Tobacco Smoke, Nicotine, and Marijuana (THC) Exposures During Pregnancy

Widespread public health campaigns have reduces the prevalence of tobacco and nicotine exposures during pregnancy in the United States. However, tobacco and nicotine exposures during pregnancy persist as a common modifiable perinatal risk exposure. Furthermore, declines in tobacco use have been accompanied by parallel rises in both the prevalence and incidence of marijuana use in pregnancy. This is worrisome, as the macromolecules which comprise tobacco and marijuana smoke affect placental function. In this chapter we summarize the decades of evidence contributing to our understanding of the placental molecular pathophysiology accompanying these chemical exposures, thereby rendering risk of adverse perinatal outcomes.

Cannabis for Medical Use: Versatile Plant Rather Than a Single Drug

Medical Cannabis and its major cannabinoids (−)-trans-Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD) are gaining momentum for various medical purposes as their therapeutic qualities are becoming better established. However, studies regarding their efficacy are oftentimes inconclusive. This is chiefly because Cannabis is a versatile plant rather than a single drug and its effects do not depend only on the amount of THC and CBD. Hundreds of Cannabis cultivars and hybrids exist worldwide, each with a unique and distinct chemical profile. Most studies focus on THC and CBD, but these are just two of over 140 phytocannabinoids found in the plant in addition to a milieu of terpenoids, flavonoids and other compounds with potential therapeutic activities. Different plants contain a very different array of these metabolites in varying relative ratios, and it is the interplay between these molecules from the plant and the endocannabinoid system in the body that determines the ultimate therapeutic response and associated adverse effects. Here, we discuss how phytocannabinoid profiles differ between plants depending on the chemovar types, review the major factors that affect secondary metabolite accumulation in the plant including the genotype, growth conditions, processing, storage and the delivery route; and highlight how these factors make Cannabis treatment highly complex.

Sedation and Acute Encephalopathy in a Pediatric Patient Following Ingestion of Delta-8-Tetrahydrocannabinol Gummies

Patient: Female, 2-year-old

Final Diagnosis: Acute encephalopathy, resolved • poisoning by delta-8-THC symptoms • altered mental status • respiratory failure

Symptoms: Acute encephalopathy • altered mental status • respiratory failure

Medication: —

Clinical Procedure: —

Specialty: Pediatrics and Neonatology • Toxicology

Molecular Targets of Cannabinoids Associated with Depression

Novel therapeutic strategies are needed to address depression, a major neurological disorder affecting hundreds of millions of people worldwide. Cannabinoids and their synthetic derivatives have demonstrated numerous neurological activities and may potentially be developed into new treatments for depression. This review highlights cannabinoid (CB) receptors, monoamine oxidase (MAO), N-methyl-D-aspartate (NMDA) receptor, gamma-aminobutyric acid (GABA) receptor, and cholecystokinin (CCK) receptor as key molecular targets of cannabinoids that are associated with depression. The anti-depressant activity of cannabinoids and their binding modes with cannabinoid receptors are discussed, providing insights into rational design and discovery of new cannabinoids or cannabimimetic agents with improved druggable properties.

Adverse effects of Δ9-tetrahydrocannabinol on neuronal bioenergetics during postnatal development

Ongoing societal changes in views on the medical and recreational roles of cannabis increased the use of concentrated plant extracts with a Δ⁹-tetrahydrocannabinol (THC) content of more than 90%. Even though prenatal THC exposure is widely considered adverse for neuronal development, equivalent experimental data for young age cohorts are largely lacking. Here, we administered plant-derived THC (1 or 5 mg/kg) to mice daily during P5–P16 and P5–P35 and monitored its effects on hippocampal neuronal survival and specification by high-resolution imaging and iTRAQ proteomics, respectively. We found that THC indiscriminately affects pyramidal cells and both cannabinoid receptor 1⁺ (CB₁R)⁺ and CB₁R^– interneurons by P16. THC particularly disrupted the expression of mitochondrial proteins (complexes I–IV), a change that had persisted even 4 months after the end of drug exposure. This was reflected by a THC-induced loss of membrane integrity occluding mitochondrial respiration and could be partially or completely rescued by pH stabilization, antioxidants, bypassed glycolysis, and targeting either mitochondrial soluble adenylyl cyclase or the mitochondrial voltage-dependent anion channel. Overall, THC exposure during infancy induces significant and long-lasting reorganization of neuronal circuits through mechanisms that, in large part, render cellular bioenergetics insufficient to sustain key developmental processes in otherwise healthy neurons.

Repeated THC exposure in juvenile mice compromises the limbic circuitry, with life-long impairment to the respiration of neurons.

[Central Effect of Components of Cannabis: Utility and Risk]

Cannabis contains over 700 known cannabinoids, terpenoids, flavonoids, and so on; however, the roles and importance of these components have yet to be fully understood. Δ⁹-Tetrahydrocannabinol (THC) is believed the most psychoactive component in cannabis, whereas cannabidiol (CBD), cannabinol, and cannabigerol are the most well-known non-psychoactive components. THC, but not CBD, has been shown to produce abnormal behavior in animals; these effects are caused, at least in part, by binding to cannabinoid receptor type 1 (CB₁) in the brain. Regarding the risks associated with cannabis use, acute effects of THC, such as a "high", cognitive deficits, and irritability, are considered more important than potential dependence. On the other hand, CBD has shown anticonvulsant, anti-inflammatory, immunosuppressive, analgesic, and anticancer effects. However, CBD has very low affinity (in the micromolar range) for the CB₁ receptor, as well as for the CB₂ receptor, and its underlying mechanism remains obscure. In this review, we demonstrate that THC induces abnormal behavior such as catalepsy-like immobilization, spatial memory impairment, and high and low sensitivity to ultrasonic vocalization after an aversive air-puff stimulus. Moreover, we demonstrate that THC and CBD improve brain injury in middle cerebral artery occlusion in a mouse model through different mechanisms. These findings suggest the need to discuss the recent development of "THC and CBD pharmacology" in animal studies, as well as the utility and risk of various cannabis components in humans.

Comparative Pharmacokinetics of Δ9-Tetrahydrocannabinol in Adolescent and Adult Male Mice

We investigated the pharmacokinetic properties of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the main psychoactive constituent of cannabis, in adolescent and adult male mice. The drug was administered at logarithmically ascending doses (0.5, 1.6, and 5 mg/kg, i.p.) to pubertal adolescent (37-day-old) and adult (70-day-old) mice. Δ⁹-THC and its first-pass metabolites-11-hydroxy-Δ⁹-THC and 11-nor-9-carboxy-Δ⁹-THC (11-COOH-THC)-were quantified in plasma, brain, and white adipose tissue (WAT) using a validated isotope-dilution liquid chromatography/tandem mass spectrometry assay. Δ⁹-THC (5 mg/kg) reached 50% higher circulating concentration in adolescent mice than in adult mice. A similar age-dependent difference was observed in WAT. Conversely, 40%-60% lower brain concentrations and brain-to-plasma ratios for Δ⁹-THC and 50%-70% higher brain concentrations for Δ⁹-THC metabolites were measured in adolescent animals relative to adult animals. Liver microsomes from adolescent mice converted Δ⁹-THC into 11-COOH-THC twice as fast as adult microsomes. Moreover, the brains of adolescent mice contained higher mRNA levels of the multidrug transporter breast cancer resistance protein, which may extrude Δ⁹-THC from the brain, and higher mRNA levels of claudin-5, a protein that contributes to blood-brain barrier integrity. Finally, administration of Δ⁹-THC (5 mg/kg) reduced spontaneous locomotor activity in adult, but not adolescent, animals. The results reveal the existence of multiple differences in the distribution and metabolism of Δ⁹-THC between adolescent and adult male mice, which might influence the pharmacological response to the drug. SIGNIFICANCE STATEMENT: Animal studies suggest that adolescent exposure to Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the intoxicating constituent of cannabis, causes persistent changes in brain function. These studies generally overlook the impact that age-dependent changes in the distribution and metabolism of the drug might exert on its pharmacological effects. This report provides a comparative analysis of the pharmacokinetic properties of Δ⁹-THC in adolescent and adult male mice and outlines multiple functionally significant dissimilarities in the distribution and metabolism of Δ⁹-THC between these two age groups.

Marijuana Use in Pregnancy: A Review

Importance

Marijuana is the most commonly used dependent substance in pregnancy. The main active chemical of marijuana (delta-9-tetrahydrocannabinol [THC]) readily crosses the placenta, and cannabinoid receptors have been identified in fetal brain and placenta. As a result, prenatal marijuana use could potentially have detrimental impact on fetal development.

Objective

This review aims to summarize the existing literature and current recommendations for marijuana use while pregnant or lactating.

Evidence Acquisition

A PubMed literature search using the following terms was performed to gather relevant data: "cannabis," "cannabinoids," "marijuana," "fetal outcomes," "perinatal outcomes," "pregnancy," "lactation."

Results

Available studies on marijuana exposure in pregnancy were reviewed and support some degree of developmental disruption, including an increased risk of fetal growth restriction and adverse neurodevelopmental consequences. However, much of the existing prenatal marijuana research was performed in the 1980s, when quantities of THC were lower and the frequency of use was less. Additionally, most human studies are also limited and conflicting as most studies have been observational or retrospective, relying primarily on patient self-report and confounded by polysubstance abuse and small sample sizes, precluding determination of a causal effect specific for marijuana. Given the paucity of evidence, it is currently recommended to avoid using marijuana while pregnant or when breastfeeding.

Conclusion and Relevance

There is a critical need for research on effects in pregnancy using present-day THC doses. Once the adverse perinatal effects of marijuana exposure are identified and well characterized, patient education and antenatal surveillance can be developed to predict and mitigate its impact on maternal and fetal health.

Relating Observed Psychoactive Effects to the Plasma Concentrations of Delta-9-Tetrahydrocannabinol and Its Active Metabolite: An Effect-Compartment Modeling Approach

The medical use of marijuana is increasing, yet little is known about the exposure-response relationship for its psychoactive effects. It is well known that the plasma concentrations of the principal psychoactive component of marijuana, Δ⁹-tetrahydrocannabinol (THC), do not directly correlate to the observed psychoactive effects. The purpose of this research was to use an effect-compartment modeling approach to predict and relate the concentrations of the psychoactive components (THC and its active metabolite) in the "hypothetical" effect-site compartment to the observed psychoactive effects. A "hypothetical" effect-compartment model was developed using literature data to characterize the observed delay in peak "highness" ratings compared with plasma concentrations of the psychoactive agents following intravenous administration of THC. A direct relationship was established between the reported psychoactive effects ("highness" or intoxication) and the predicted effect-site concentrations of THC. The differences between estimated equilibration half-lives for THC and THC-OH in the effect-compartment model indicated the differential equilibration of parent drug and the active metabolite between plasma and the effect-site. These models contribute to the understanding of the pharmacokinetic-pharmacodynamic relationships associated with marijuana use and are important steps in the prediction of pharmacodynamic effects related to the psychoactive components in marijuana.

Cannabis use during pregnancy: Pharmacokinetics and effects on child development

The broad-based legalization of cannabis use has created a strong need to understand its impact on human health and behavior. The risks that may be associated with cannabis use, particularly for sensitive subgroups such as pregnant women, are difficult to define because of a paucity of dose-response data and the recent increase in cannabis potency. Although there is a large body of evidence detailing the mode of action of Δ⁹-tetrahydrocannabinol (THC) in adults, little work has focused on understanding how cannabis use during pregnancy may impact the development of the fetal nervous system and whether additional plant-derived cannabinoids might participate. This manuscript presents an overview of the historical and contemporary literature focused on the mode of action of THC in the developing brain, comparative pharmacokinetics in both pregnant and nonpregnant model systems and neurodevelopmental outcomes in exposed offspring. Despite growing public health significance, pharmacokinetic studies of THC have focused on nonpregnant adult subjects and there are few published reports on disposition parameters during pregnancy. Data from preclinical species show that THC readily crosses the placenta although fetal exposures appear lower than maternal exposures. The neurodevelopmental data in humans and animals suggest that prenatal exposure to THC may lead to subtle, persistent changes in targeted aspects of higher-level cognition and psychological well-being. There is an urgent need for well-controlled studies in humans and preclinical models on THC as a developmental neurotoxicant. Until more information is available, pregnant women should not assume that using cannabis during pregnancy is safe.

Metabolomics of Δ9-tetrahydrocannabinol: implications in toxicity

Cannabis sativa is the most commonly used recreational drug, Δ(9)-tetrahydrocannabinol (Δ(9)-THC) being the main addictive compound. Biotransformation of cannabinoids is an important field of xenobiochemistry and toxicology and the study of the metabolism can lead to the discovery of new compounds, unknown metabolites with unique structures and new therapeutic effects. The pharmacokinetics of Δ(9)-THC is dependent on multiple factors such as physical/chemical form, route of administration, genetics, and concurrent consumption of alcohol. This review aims to discuss metabolomics of Δ(9)-THC, namely by presenting all known metabolites of Δ(9)-THC described both in vitro and in vivo, and their roles in the Δ(9)-THC-mediated toxic effects. Since medicinal use is increasing, metabolomics of Δ(9)-THC will also be discussed in order to uncover potential active metabolites that can be made available for this purpose.

Comparative effects of pulmonary and parenteral Δ⁹-tetrahydrocannabinol exposure on extinction of opiate-induced conditioned aversion in rats

RATIONALE

Evidence suggesting that the endogenous cannabinoid (eCB) system can be manipulated to facilitate or impair extinction of learned behaviours has important consequences for opiate withdrawal and abstinence. We demonstrated that the fatty acid amide hydrolase (FAAH) inhibitor URB597, which increases eCB levels, facilitates extinction of a naloxone-precipitated morphine withdrawal-induced conditioned place aversion (CPA).

OBJECTIVES

The potential of the exogenous CB1 ligand, Δ(9)-tetrahydrocannabinol (Δ(9)-THC), to facilitate extinction of this CPA was tested. Effects of both pulmonary and parenteral Δ(9)-THC exposure were evaluated using comparable doses previously determined.

METHODS

Rats trained to associate a naloxone-precipitated morphine withdrawal with a floor cue were administered Δ(9)-THC-pulmonary (1, 5, 10 mg vapour inhalation) or parenteral (0.5, 1.0, 1.5 mg/kg intraperitoneal injection)-prior to each of 20 to 28 extinction/testing trials.

RESULTS

Vapourized Δ(9)-THC facilitated extinction of the CPA in a dose- and time-dependent manner: 5 and 10 mg facilitated extinction compared to vehicle and 1 mg Δ(9)-THC. Injected Δ(9)-THC significantly impaired extinction only for the 1.0-mg/kg dose: it prolonged the CPA fourfold longer than the vehicle and 0.5- and 1.5-mg/kg doses.

CONCLUSIONS

These data suggest that both dose and route of Δ(9)-THC administration have important consequences for its pharmacokinetic and behavioural effects; specifically, pulmonary exposure at higher doses facilitates, whereas pulmonary and parenteral exposure at lower doses impairs, rates of extinction learning for CPA. Pulmonary-administered Δ(9)-THC may prove beneficial for potentiation of extinction learning for aversive memories, such as those supporting drug-craving/seeking in opiate withdrawal syndrome, and other causes of conditioned aversions, such as illness and stress.

Differential signalling in human cannabinoid CB1 receptors and their splice variants in autaptic hippocampal neurones

BACKGROUND AND PURPOSE

Cannabinoids such as Δ(9) - tetrahydrocannabinol, the major psychoactive component of marijuana and hashish, primarily act via cannabinoid CB(1) and CB(2) receptors to produce characteristic behavioural effects in humans. Due to the tractability of rodent models for electrophysiological and behavioural studies, most of the studies of cannabinoid receptor action have used rodent cannabinoid receptors. While CB(1) receptors are relatively well-conserved among mammals, human CB(1) (hCB(1) ) differs from rCB(1) and mCB(1) receptors at 13 residues, which may result in differential signalling. In addition, two hCB(1) splice variants (hCB(1a) and hCB(1b) ) have been reported, diverging in their amino-termini relative to hCB(1) receptors. In this study, we have examined hCB(1) signalling in neurones.

EXPERIMENTAL APPROACH

hCB(1) , hCB(1a) hCB(1b) or rCB(1) receptors were expressed in autaptic cultured hippocampal neurones from CB(1) (-/-) mice. Such cells express a complete endogenous cannabinoid signalling system. Electrophysiological techniques were used to assess CB(1) receptor-mediated signalling. KEY RESULTS Expressed in autaptic hippocampal neurones cultured from CB(1) (-/-) mice, hCB(1) , hCB(1a) and hCB(1b) signal differentially from one another and from rodent CB(1) receptors. Specifically, hCB(1) receptors inhibit synaptic transmission less effectively than rCB(1) receptors.

CONCLUSIONS AND IMPLICATIONS

Our results suggest that cannabinoid receptor signalling in humans is quantitatively very different from that in rodents. As the problems of marijuana and hashish abuse occur in humans, our results highlight the importance of studying hCB(1) receptors. They also suggest further study of the distribution and function of hCB(1) receptor splice variants, given their differential signalling and potential impact on human health.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids in Biology and Medicine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-8. To view Part I of Cannabinoids in Biology and Medicine visit http://dx.doi.org/10.1111/bph.2011.163.issue-7.

Δ9-tetrahydrocannabinol and its major metabolite Δ9-tetrahydrocannabinol-11-oic acid as 15-lipoxygenase inhibitors

15-Lipoxygenase (15-LOX) is one of the key enzymes responsible for the formation of oxidized low-density lipoprotein, a major causal factor for atherosclerosis. Δ(9)-Tetrahydrocannabinol (Δ(9)-THC), a major component of marijuana, has suggested to suppress atherosclerosis. Although Δ(9)-THC seems to be attractive for the prevention of atherosclerosis, there is no information about whether or not 15-LOX isoform can be inhibited by Δ(9)-THC. In the present study, Δ(9)-THC was found to be a direct inhibitor for 15-LOX with an IC(50) (50% inhibition concentration) value of 2.42 μM. Furthermore, Δ(9)-THC-11-oic acid, a major and nonpsychoactive metabolite of Δ(9) -THC, but not another Δ(9)-THC metabolite 11-OH-Δ(9)-THC (psychoactive), was revealed to inhibit 15-LOX. Taken together, it is suggested that Δ(9) -THC can abrogate atherosclerosis via direct inhibition of 15-LOX, and that Δ(9)-THC-11-oic acid is shown to be an "active metabolite" of Δ(9) -THC in this case.

Examining the roles of cannabinoids in pain and other therapeutic indications: a review

IMPORTANCE OF THE FIELD

In recent times, our knowledge of cannabinoids and the endocannabinoid system has greatly advanced. With expanding knowledge, synthetic cannabinoids - including nabilone, dronabinol and a combination of synthetic Delta9-THC and cannabidiol - have been developed and tested for benefit in a variety of therapeutic indications.

AREAS COVERED IN THIS REVIEW

The aim of this article is to provide a summative review of the vast amount of clinical trial data now available on these agents.

WHAT THE READER WILL GAIN

To locate clinical trials for review, a literature search was performed using PubMed between the dates of 25 May and 30 June 2009. Search parameters were set to isolate only human randomized controlled trials (RCTs) published between 1990 and 2009. Keywords consistently used for each search include: cannabinoids, marijuana, THC, nabilone and dronabinol. Preferential selection was given to the best-designed trials, focusing on placebo-controlled, double-blind RCTs with the largest patient populations, if available.

TAKE HOME MESSAGE

As efficacy and tolerability of these agents remain questionable, it is important that cannabinoids not be considered 'first-line' therapies for conditions for which there are more supported and better-tolerated agents. Instead, these agents could be considered in a situation of treatment failure with standard therapies or as adjunctive agents where appropriate.

Physiochemical and pharmacological characterization of a Delta(9)-THC aerosol generated by a metered dose inhaler

The goal of the present study was to formulate a Delta(9)-tetrahydrocannabinol (Delta(9)-THC) metered-dose inhaler (MDI) that can be used to provide a systemic dose of Delta(9)-THC via inhalation. Following physiochemical characterization and accelerated stability testing of the aerosol, mice were exposed to the aerosol and evaluated for pharmacological effects indicative of cannabinoid activity, including hypomotilìty, antinociception, catalepsy, and hypothermia. The fine particle dose of Delta(9)-THC was 0.22 +/- 0.03 mg (mean +/- S.D.) or 25% of the emitted dose and was not affected by accelerated stability testing. A 10-min exposure to aerosolized Delta(9)-THC elicited hypomotility, antinociception, catalepsy, and hypothermia. Additionally, Delta(9)-THC concentrations in blood and brain at the antinociceptive ED(50) dose were similar for both inhalation and intravenous routes of administration. Finally, pretreatment with the CB(1) receptor antagonist SR 141716A (10 mg/kg, i.p.) significantly antagonized all of the Delta(9)-THC-induced effects. These results indicate that an MDI is a viable method to deliver a systemic dose of Delta(9)-THC that elicits a full spectrum of cannabinoid pharmacological effects in mice that is mediated via a CB(1) receptor mechanism of action. Further development of a Delta(9)-THC MDI could provide an appropriate delivery device for the therapeutic use of cannabinoids, thereby reducing the need for medicinal marijuana.

Effect of repeated administration of delta 9-tetrahydrocannabinol on delayed matching-to-sample performance in rats

In the present study we examined the effect of repeated exposure to delta 9-tetrahydrocannabinol (THC) at a dose of 10 mg/kg (once a day for 4 days) 24 h after administration, on delayed matching-to-sample (DMTS) performance in rats using a three-lever operant apparatus. Although DMTS performance was not changed on the 1st day, it was impaired on the 2nd day. The impairment was potentiated in dependence of repeated administration. After withdrawal of THC, the impairment of DMTS performance gradually disappeared. On the 10th day after withdrawal, readministration of 10 mg/kg THC resulted in marked impairment of DMTS performance at 24 h after administration. Furthermore, a single administration of 1.0 mg/kg THC 30 min prior to the session, the dose at which a single administration did not cause impairment of DMTS performance in vehicle-treated rats, significantly decreased the number of reinforcements in the test trial. In conclusion, the present study demonstrated that repeated THC administration impaired DMTS performance under the condition of 24 h after administration, and that behavioral sensitization to this impairment developed. Furthermore, the suppressive state of lever-pressing induced by repeated THC administration may be a useful animal model for amotivational syndrome in humans.

Stereochemical effects of 11-OH-delta 8-tetrahydrocannabinol-dimethylheptyl to inhibit adenylate cyclase and bind to the cannabinoid receptor

The recent preparation of the enantiomers of 11-OH-delta 8-tetrahydrocannabinol-dimethylheptyl (THC-DMH), recrystallized to absolute enantiomeric purity, has made it possible to examine the requirement for stereospecificity for the interaction of this component with the cannabinoid receptor, defined by the binding of [3H]CP-55,940 and the adenylate cyclase enzyme. The enantiomer (-)11-OH-delta 8-THC-DMH exhibited a fully efficacious and potent (IC50 = 1.8 nM) inhibition of the accumulation of cAMP in intact N18TG2 cells. The (-)enantiomer was as efficacious and potent (Kinh = 7.2 nM) as desacetyllevonantradol in inhibiting adenylate cyclase activity in membrane preparations. The (-)enantiomer was able to compete fully for the specific binding of [3H]CP-55,940 to membranes from the brain of the rat in homologous displacement studies (Ki = 234 pM). The potency ratios exhibited by the (-) to (+)enantiomers of 11-OH-delta 8-THC-DMH exceeded 1000 for each of these activities.

Pharmacological evaluation of water soluble cannabinoids and related analogs

The two water-soluble cannabinoids 1-[(4-morpholino) butyryloxy]-delta 8-tetrahydro-cannabinol (MB-delta 8-THC) and 5'-trimethylammonium (TMA)-delta 8-THC, as well as structurally similar compounds, were evaluated for cannabimimetic activity in the mouse (locomotor activity, tail-flick antinociception, rectal temperature, and ring-immobility) and dog (static-ataxia) procedures. MB-delta 8-THC possesses full cannabimimetic activity and is approximately equipotent to delta 8-THC. 5'-TMA-delta 8-THC only possesses partial cannabimimetic activity in that it is inactive in the ring-immobility and static-ataxia procedures. However, this analog is potent in other respects. All alterations at the 5' position do not necessarily produce this spectrum of effects, as evidenced by the pharmacological activity of 5'-bromo-delta 8-THC, 5'-OH-delta 8-THC acetate, and 5'-N-dimethyl-delta 8-THC.

Altered hepatic microsomal function and elevated protooncogene expression as residual effects in rats exposed to delta-9-tetrahydrocannabinol

The microsomal activation of the potent hepatocarcinogen aflatoxin B1 (AFB1) and the expression of selected protooncogenes were investigated in the livers of rats exposed to delta 9-tetrahydrocannabinol (THC). At equimolar levels of cytochrome P-450, the microsome-mediated binding of AFB1 to DNA was significantly lower (56% of the controls) in preparations from drug exposed rats. Hepatic expression of the c-k-ras protooncogene was 3-fold higher in THC exposed animals. These results suggest the possible occurrence of long lasting residual effects in the rats exposed to THC.

Brain microsomal oxidation of delta 8- and delta 9-tetrahydrocannabinol

Brain microsomes of mice, rats, guinea pigs and rabbits catalyzed the oxidation of delta 8- and delta 9-tetrahydrocannabinol to their monohydroxylated metabolites. The most prominent metabolite was the 4'-hydroxylated metabolite on the pentyl side chain of the cannabinoids in all species tested, except that the 5'-hydroxylation of delta 9-tetrahydrocannabinol was most abundant in the guinea pig. These results are quite different from the metabolic profile of the cannabinoids with hepatic microsomes.

Oxygenation mechanism in the oxidation of xenobiotic aldehyde to carboxylic acid by mouse hepatic microsomes

11-Oxo-delta 8-tetrahydrocannabinol was oxidized to delta 8-tetrahydrocannabinol-11-oic acid by mouse hepatic microsomes. The oxygenation mechanism in the reaction was confirmed by the incorporation of oxygen-18 from molecular oxygen into delta 8-tetrahydrocannabinol-11-oic acid. The oxygenation of aldehyde to carboxylic acid represents a novel mechanism in biological oxidation of aldehyde to carboxylic acid.

Cross-tolerance development to the prolongation of pentobarbitone-induced sleep by delta 8-tetrahydrocannabinol and 11-hydroxy-delta 8-tetrahydrocannabinol in mice

Repeated administration (5 mg kg-1 day-1 i.v.) of delta 8-tetrahydrocannabinol and its active metabolite, 11-hydroxy-delta 8-tetrahydrocannabinol caused tolerance to develop to their prolonging effect on pentobarbitone-induced sleep in mice. Reciprocal cross-tolerance also developed after seven daily doses of these cannabinoids. The magnitude of the tolerance developed by the metabolite was greater than that by delta 8-tetrahydrocannabinol. The results suggest that 11-hydroxy-delta 8-tetrahydrocannabinol plays an important role both in the sleep-prolonging effect of delta 8-tetrahydrocannabinol and its tolerance development.

Self-catalyzed inactivation of cytochrome P-450 during microsomal metabolism of cannabidiol

When cannabidiol (CBD) was incubated with hepatic microsomes of mice in the presence of an NADPH-generating system, a significant decrease of cytochrome P-450 content was observed by measuring its carbon monoxide difference spectra. The decrease of cytochrome P-450 by CBD required NADPH and molecular oxygen. The effect was partially inhibited by SKF 525-A but not by various scavengers of active oxygen species, superoxide anion, hydroxyl radical and singlet oxygen. The incubation of CBD with hepatic microsomes did not affect total heme but decreased significantly free sulfhydryl contents in the microsomes. The derivatives of CBD modified in the resorcinol moiety, CBD-monomethyl- and dimethylethers, almost lost the effect on cytochrome P-450, whereas those modified in the terpene moiety, 8,9-dihydro- and 1,2,8,9-tetrahydro-CBDs exhibited some potency to inactivate cytochrome P-450. The inactivation of cytochrome P-450 by CBD and related compounds led to the inhibition of hepatic microsomal p-nitroanisole O-demethylase and aniline hydroxylase activities. These results suggest that the resorcinol moiety of CBD plays some role in the inactivation of cytochrome P-450 by the cannabinoid.

Cannabinoid inhibition of adenylate cyclase: relative activity of constituents and metabolites of marihuana

delta 9Tetrahydrocannabinol (THC) has been shown to inhibit the activity of adenylate cyclase in the N18TG2 clone of murine neuroblastoma cells. The concentration of delta 9THC exhibiting half-maximal inhibition was 500 nM. delta 8Tetrahydrocannabinol was less active, and cannabinol was only partially active. Cannabidiol, cannabigerol, cannabichromene, olivetol and compounds having a reduced length of the C3 alkyl side chain were inactive. The metabolites of delta 8THC and delta 9THC hydroxylated at the C11 position were more potent than the parent drugs. However, hydroxylation at the C8 position of the terpenoid ring resulted in loss of activity. Compounds hydroxylated along the C3 alkyl side chain were equally efficacious but less potent than delta 9THC. These findings are compared to the pharmacology of cannabinoids reported for psychological effects in humans and behavioral effects in a variety of animal models.

Enhancement of the hypothermic response of mice to delta-9-tetrahydrocannabinol by subhypothermic doses of chlorpromazine and phentolamine

Pretreatment with subhypothermic doses of chlorpromazine, given directly into the IIIrd cerebral ventricle via a chronically implanted cannula (50 micrograms) or subcutaneously (0.75 mg/kg), was found to enhance the hypothermic response to delta-9-tetrahydrocannabinol (THC: 5 20 mg/kg i.p.) in unrestrained adult male MF1 mice, kept at 22 degrees C. Subcutaneous pretreatment with a subhypothermic dose of phentolamine (30 mg/kg) had a similar effect, whereas pretreatment with desipramine (10 mg/kg s.c.), mepyramine (2.3 and 11.5 mg/kg s.c.), methysergide (2 mg/kg s.c.), pimozide (1 and 5 mg/kg s.c.) or lignocaine (50 mg/kg s.c.), had no effect. Intracerebroventricular pretreatment with phentolamine was also without effect and it is concluded that this drug interacts with THC at some site located outside the brain. Since, in mg/kg terms, chlorpromazine was more potent in enhancing THC-induced hypothermia when given subcutaneously than when injected into the IIIrd ventricle, it too may interact with THC at a peripheral site. Indeed, chlorpromazine and phentolamine may both increase the hypothermic response to THC by antagonizing alpha-adrenoceptors on cutaneous blood vessels, thereby decreasing the capacity of animals to minimise peripheral blood flow by vasoconstriction. Alternatively, since the distribution of chlorpromazine within the brain may well have been less efficient after intraventricular than after subcutaneous injection, the possibility remains that chlorpromazine interacted centrally with THC.

Cannabimimetic activity of cannabinol in rats and pigeons

The present experiments examined the cannabimimetic potential of cannabinol on its own as well as its interaction with delta 9-tetrahydrocannabinol (delta 9-THC) in vivo. Thus, cannabinol, as evaluated by repeated test procedures using drug-discrimination methodology (Hiltunen and Järbe, 1986; Järbe, Swedberg and Mechoulam, 1981) was found to substitute for the stimulus effects induced by delta 9-THC in both rats (delta 9-THC cue = 3 mg/kg) and pigeons (delta 9-THC cue = 0.56 mg/kg), though, relatively larger doses were required in the latter species (ED50 for cannabinol being 8.4 mg/kg, and 14.1 mg/kg at the time of maximum effect in rats and pigeons, respectively). When administered together, cannabinol added to the cue effects of delta 9-THC as shown by an increase in the percentage of responding appropriate to the drug, the effect appearing more pronounced in rats than in pigeons; no apparent change in the duration of the effect was indicated by the results obtained. Unconditioned effects of drug, as defined by rectal temperature recordings and open-field activity (ambulation, rearing, latency, circling, grooming, defecation and urination), as well as assessment of vocalization in rats were in keeping with the suggestion that the pharmacological profile of cannabinol is similar, though not necessarily identical, to that of tetrahydrocannabinols, such as delta 9-THC.

The pharmacological activity of the fatty acid conjugate 11-palmitoyloxy-delta 9-tetrahydrocannabinol

A long-retained cannabinoid metabolite has been detected in rat tissue after intravenous administration of delta 9-tetrahydrocannabinol (THC) and has been identified as a fatty acid conjugate of psychoactive 11-hydroxy-delta 9-tetrahydrocannabinol (11-OH-delta 9-THC) and palmitic acid. The objective of these studies was to determine if this compound, 11-palmitoyloxy-delta 9-tetrahydrocannabinol (11-palm-delta 9-THC) is pharmacologically active. Intravenously injected 11-palm-delta 9-THC decreased thermal sensitivity and induced catalepsy in rats, responses similar to those produced by 11-OH-delta 9-THC, but less pronounced and more delayed. To further characterize the response, animals were intracisternally injected with 11-OH-delta 9-THC or 11-palm-delta 9-THC. Catalepsy and decreased thermal sensitivity were seen in the 11-OH-delta 9-THC and 11-palm-delta 9-THC groups, and again, 11-OH-delta 9-THC appeared to be the more potent of the two cannabinoids. In contrast to the intravenous study, 11-palm-delta 9-THC-induced effects were seen soon after treatment and appeared to be fully developed by the first test time (15 min). The intracisternal results suggest that 11-palm-delta 9-THC itself is active; however, since it is known that the fatty acid conjugate is hydrolyzed in vivo to 11-OH-delta 9-THC in the rat, the possibility remains that the effects of 11-palm-delta 9-THC are due to metabolic conversion to 11-OH-delta 9-THC.

Cross-tolerance to the hypothermic effect of delta 8-tetrahydrocannabinol 11-hydroxy-delta 8-tetrahydrocannabinol and chlorpromazine in the mouse

When a 5 mg/kg i.v. dose of delta 8-tetrahydrocannabinol (delta 8-THC) and 11-hydroxy-delta 8-tetrahydrocannabinol (11-OH-delta 8-THC) was administered daily to mice, tolerance to their hypothermic effects developed quickly. Cross-tolerance to the hypothermic effect also developed between delta 8-THC and 11-OH-delta 8-THC. Tolerance development was dose-dependent and dose-effect experiments indicated that the magnitude of the tolerance developed to 11-OH-delta 8-THC was greater than that to delta 8-THC. Both cannabinoids were cross-tolerant to chlorpromazine in the hypothermic effect, but not to morphine, pentobarbital and reserpine under the conditions used. The present results suggest that 11-OH-delta 8-THC has some role in the development of tolerance to the hypothermic effect of delta 8-THC in mice.

Changes in body temperature and oxygen consumption rate of conscious mice produced by intrahypothalamic and intracerebroventricular injections of delta 9-tetrahydrocannabinol

delta 9-Tetrahydrocannabinol (delta 9-THC) was injected into the preoptic area of the anterior hypothalamus or into the third or fourth cerebral ventricle of the conscious mouse through a chronically implanted cannula and the effects on body temperature and oxygen consumption rate were measured. At an ambient temperature of 22 degrees C, injections of delta 9-THC into the fourth ventricle (5 and 10 microgram) produced dose-dependent falls in rectal temperature. Hypothermia was also observed after injections of the drug into the hypothalamus (5 and 10 microgram) or into the third ventricle (10 microgram). The hypothermia produced by delta 9-THC was associated with a fall in oxygen consumption rate. Falls in rectal temperature and in oxygen consumption rate were significantly greater after injection of delta 9-THC than after injection of the drug vehicle, Tween 80. The falls in rectal temperature and oxygen consumption rate produced by injection of delta 9-THC into the fourth ventricle were abolished by elevation of the ambient temperature from 22 to 32 degrees C. A pretreatment that consisted of subcutaneous injections of delta 9-THC (20 mg/kg) given once daily for three days produced tolerance to the hypothermic effect of the drug when injected on day 4 either into the fourth ventricle (10 microgram) or into a lateral tail vein (2.0 mg/kg). The results suggest that delta 9-THC acts centrally to alter thermoregulation in mice not only when it is injected directly into the hypothalamus or cerebral ventricles but also when it is given intravenously. After intraventricular or intravenous administration the drug may act at extrahypothalamic as well as at hypothalamic sites. The data also support the hypothesis that in mice, tolerance to the hypothermic effect of A9-THC is pharmacodynamic and does not depend on changes in metabolism or distribution of the drug.

Evidence for a caudal brainstem site of action for cannabinoid induced hypothermia

delta 9-Tetrahydrocannabinol (THC), 11-hydroxy delta 9-tetrahydrocannabinol (11-OH-THC) and the synthetic dimethylheptyl analogue of THC (DMHP) were injected intracerebrally into proven chemosensitive sites in the hypothalamus of unanesthetized cats with implanted microinjection guide tubes. 100 micrograms of each compound was administered in a volume of 8 microliters. Chemosensitivity of all injection sites was established by microinjection of carbamylcholine to induce hyperthermia and tetrodotoxin to induce hypothermia. THC or its analogues produced no significant change in body temperature when injected intracerebrally. However, in the same animals, parenteral administration of THC, 11-OH-THC or DMHP (0.5 to 2.0 mg/kg) induced hypothermic responses ranging from -2.0 to -7.0 degrees C. Intravenous administration of THC was effective in blocking shivering induced by cooling the preoptic region in unanesthetized cats with implanted thermodes. In cats with mid-pontine transections, cooling of the spinal cord by perfusion with an epidural double wall cannula at temperatures of 30, 20, 10 and 0 degrees C produced graded shivering which was recorded electromyographically. Intravenous THC, (0.25-2.0 mg/kg) produced a dose-dependent attenuation of spinal cord induced shivering. These data plus results of prior studies suggest that the tetrahydrocannabinols produce their hypothermic effect at sites in the caudal brainstem. Suppression of shivering at the ponto medullary or spinal cord level may represent an important mechanism which contributes to the lowering of body temperature.

Plasma and brain levels of delta 6-THC and seven monooxygenated metabolites correlated to the cataleptic effect in the mouse

The brain and plasma levels of unchanged delta 6-tetrahydrocannabinol (delta 6-THC), 7-hydroxy-delta 6-THC, the five side-chain hydroxylated delta 6-THC derivatives and 1 alpha, 2 alpha-epoxyhexahydrocannabinol (EHHC) were correlated to the cataleptic effect in the mouse up to 60 min. after intravenous administration of radiolabelled compounds in the range 1.3 to 12.4 mg/kg. All cannabinoids except delta 6-THC and 1"-hydroxy-delta 6-THC showed a very good correlation between brain/plasma concentrations and cataleptic effect. 4"-Hydroxy-and "1-hydroxy-delta 6-THC reached the highest concentration in the brain but the most potent cannabinoids were delta 6-THC, 7-hydroxy-, 3"-hydroxy-delta 6-THC, and EHHC followed by 5"-hydroxy-, 4"-hydroxy-, 2"-hydroxy-, and 1"-hydroxy-delta 6-THC in decreasing order. It was concluded that structural rather than pharmacokinetic features are most important in determining the psychoactivity of the various cannabinoid metabolites of THC.

3H-delta 9-Tetrahydrocannabinol, 3H-cannabinol and 3H-cannabidiol: penetration and regional distribution in rat brain

3H-delta 9-Tetrahydrocannabinol (3H-delta 9-THC), 3H-cannabidiol (3H-CBD) and 3H-cannabinol (3H-CBN) were administered (1 mg/kg) to male rats which were decapitated either 0.5, 1, 15, 30 or 90 min later. The plasma concentration was similar for all cannabinoids throughout the time course. After 5 min greater than 80% of the plasma radioactivity in each treatment was due to metabolites. Radioactivity rapidly entered brain after the administration of 3H-CBD, 3H-CBN, and 3H-delta 9-THC. The concentrations of unchanged 3H-CBD aand 3H-CBN in whole brain were higher than that of 3H-delta 9-THC 5 min after administration. Regional distribution of radioactivity in the brain after 5 min was similar for all three cannabinoids, the only significant difference being in hypothalamus. Coadministration of 3H-delta 9-THC with a five-fold excess of either CBD or delta 9-THC did not produce any significant alteration in the levels of radioactivity in brain or plasma 5 min after their injection. The difference in behavioral activity of delta 9-THC, CBD and CBN cannot be explained by penetrability or regional distribution in the brain.