Identification of the endogenous cannabinoid system through integrative pharmacological approaches

Pharmacokinetics and Tolerability of Δ9-THC-Hemisuccinate in a Suppository Formulation as an Alternative to Capsules for the Systemic Delivery of Δ9-THC

The objectives of this study were: (1) to assess the safety, tolerability, and pharmacokinetics of ascending doses of Δ⁹-tetrahydrocannabinol-hemisuccinate (THC-HS) after rectal administration as suppositories in male volunteers; and (2) to compare the pharmacokinetics of oral administration of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) with an equivalent amount of Δ⁹-THC delivered as THC-HS via the suppository formulation. In support of the pharmacokinetic evaluations, an analytical method was developed and validated for the determination of Δ⁹-THC and for its major circulating metabolites 11-hydroxy-Δ⁹-tetrahydrocannabinol (11-OH-THC) and 11-nor-Δ⁹-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) in human plasma. Δ⁹-THC, 11-OH-THC, and THC-COOH were extracted from plasma using solid phase extraction and analyzed by liquid chromatography-tandem mass spectrometry. The limits of detection and quantitation for all 3 analytes were 0.25 and 0.5 ng/mL, respectively. The method was validated over the range of 0.5-25 ng/mL. This method was used to quantify Δ⁹-THC and any THC-HS as Δ⁹-THC due to the inclusion of a hydrolysis step as part of the extraction procedure. Therefore, Δ⁹-THC measured was the total THC (free Δ⁹-THC plus Δ⁹-THC derived from THC-HS). The assay was reproducible for the measurement of all 3 analytes, with a variability of 7.2, 13.7, and 8.3%, respectively, at the 1 ng/mL level. The method was then used to assess the pharmacokinetics of Δ⁹-THC and metabolites from the suppository dosage form in doses equivalent to 1.25, 2.5, 5, 10, and 20 mg Δ⁹-THC per suppository as THC-HS. Systemic exposure to Δ⁹-THC, administered as THC-HS suppository, increased broadly dose proportionally. Systemic exposure and C_{max (obs)} estimates for 11-OH-THC and THC-COOH generally increased subproportionally. The pharmacokinetic profiles of Δ⁹-THC and metabolites were also compared after oral administration of 10 mg Δ⁹-THC (as dronabinol capsules) and after administration of 10 mg equivalents of Δ⁹-THC as THC-HS in suppository form. Total systemic exposure to Δ⁹-THC was considerably higher following rectal administration of THC-HS than after oral administration. The Δ⁹-THC area under the plasma concentration versus time curve (AUC_(0-∞)) for THC-HS was 2.44-fold higher (90% confidence interval: 1.78, 3.35) than for the capsule administration.

Cannabinoids stimulate fibroblastic colony formation by bone marrow cells indirectly via CB2 receptors

Recently, the cannabinoid receptors CB(1) and CB(2) were shown to modulate bone formation and resorption in vivo, although little is known of the mechanisms underlying this. The effects of cannabinoids on mesenchymal stem cell (MSC) recruitment in whole bone marrow were investigated using either the fibroblastic colony-forming unit (CFU-f) assay or high-density cultures of whole bone marrow. Levels of the CB(1) and CB(2) receptors were assessed by flow cytometry. Treatment of CFU-f cultures with the endocannabinoid 2-arachidonylglycerol (2-AG) dose-dependently increased fibroblastic and differentiated colony formation along with colony size. The nonspecific agonists CP 55,940 and WIN 55,212 both increased colony numbers, as did the CB(2) agonists BML190 and JWH015. The CB(1)-specific agonist ACEA had no effect, whereas the CB(2) antagonist AM630 blocked the effect of the natural cannabinoid tetrahydrocannabivarin, confirming mediation via the CB(2) receptor. Treatment of primary bone marrow cultures with 2-AG stimulated proliferation and collagen accumulation, whereas treatment of subcultures of MSC had no effect, suggesting that the target cell is not the MSC but an accessory cell present in bone marrow. Subcultures of MSCs were negative for CB(1) and CB(2) receptors as shown by flow cytometry, whereas whole bone marrow contained a small population of cells positive for both receptors. These data suggest that cannabinoids may stimulate the recruitment of MSCs from the bone marrow indirectly via an accessory cell and mediated via the CB(2) receptor. This recruitment may be one mechanism responsible for the increased bone formation seen after cannabinoid treatment in vivo.

Effects of endocannabinoid neurotransmission modulators on brain stimulation reward

RATIONALE

The endogenous cannabinoid system is responsive to the neurobiological actions of Delta9-tetrahydrocannabinol (THC) and other cannabinoid ligands. While numerous studies have focused on the behavioral and pharmacological effects of THC and cannabinoid agonists in experimental animals, most recent work focuses on compounds that modulate endocannabinoid neurotransmission. However, the relevant studies concerning the ability of endocannabinoid modulators to modify reward processes in experimental animals remain rather scarce.

OBJECTIVES

The present study examined the effects of drugs modulating endocannabinoid neurotransmission on brain reward function using the rate-frequency curve shift paradigm of intracranial self-stimulation (ICSS).

METHODS

Animals were implanted with electrodes into the medial forebrain bundle (MFB). After brain stimulation reward thresholds stabilized, rats received intraperitoneal injections of the fatty acid amide hydrolase (FAAH) inhibitors phenylmethylsulfonyl fluoride (PMSF) (0, 15, 30, and 60 mg/kg) and URB-597 (0, 0.3, 1, and 3 mg/kg) and the selective anandamide reuptake inhibitor OMDM-2 (0, 3, 10, and 30 mg/kg).

RESULTS

The highest dose of URB-597 and OMDM-2 significantly increased the threshold frequency required for MFB ICSS, while PMSF increased the threshold frequency in all doses tested. The cannabinoid 1 (CB1) receptor antagonist SR141716A reversed the actions of URB-597 and OMDM-2, but not PMSF, without affecting reward thresholds by itself.

CONCLUSIONS

These results indicate that under the present experimental conditions endocannabinoid modulators do not exhibit reinforcing properties, but rather have inhibitory influence on reward processes. The anhedonic effects of URB-597 and OMDM-2, but not PMSF, observed at the highest doses in this study are probably mediated through direct CB1 receptor stimulation.

Evaluation of the role of the arachidonic acid cascade in anandamide's in vivo effects in mice

The pharmacological profiles of the endocannabinoid anandamide and exogenous cannabinoids (e.g., Delta9-tetrahydrocannabinol) are similar, but not exactly the same. One notable difference is that anandamide's in vivo effects in mice are not blocked by the brain cannabinoid (CB1) receptor antagonist SR141716A. The degree to which the rapid metabolism of anandamide to arachidonic acid might be involved in this unexpected lack of effect was the focus of this study. Mice were tested in a tetrad of tests sensitive to cannabinoids, consisting of spontaneous locomotion, ring immobility, rectal temperature and tail flick nociception. Anandamide and arachidonic acid produced a similar profile of effects, but neither drug was blocked by SR141716A. When hydrolysis of anandamide was inhibited by an amidase inhibitor (phenylmethyl sulfonyl fluoride; PMSF), however, SR141716A significantly attenuated anandamide's effects but did not completely block them. Similarly, the effects of the metabolically stable anandamide analog O-1812 were attenuated by SR141716A. The role of oxidative metabolism in anandamide's effects in the tetrad was also investigated through pharmacological modulation of cyclooxygenase and lipoxygenase, two major classes of enzymes that degrade arachidonic acid. Whereas the non-selective cyclooxygenase inhibitor ibuprofen blocked the in vivo effects of arachidonic acid, it did not alter anandamide's effects. Other modulators of the cyclooxygenase and lipoxygenase pathways also failed to block anandamide's effects. Together, these results offer partial support for a pharmacokinetic explanation of the failure of SR141716A to antagonize the effects of anandamide; however, they also suggest that non-CB1, non-CB2 receptors may be involved in mediation of anandamide's in vivo actions, particularly at higher doses.

Cannabinoid tolerance and dependence

The use of marijuana for recreational and medicinal purposes has resulted in a large prevalence of chronic marijuana users. Consequences of chronic cannabinoid administration include profound behavioral tolerance and withdrawal symptoms upon drug cessation. A marijuana withdrawal syndrome is only recently gaining acceptance as being clinically significant. Similarly, laboratory animals exhibit both tolerance and dependence following chronic administration of cannabinoids. These animal models are being used to evaluate the high degree of plasticity that occurs at the molecular level in various brain regions following chronic cannabinoid exposure. In this review, we describe recent advances that have increased our understanding of the impact of chronic cannabinoid administration on cannabinoid receptors and their signal transduction pathways. Additionally, we discuss several potential pharmacotherapies that have been examined to treat marijuana dependence.

Chronic topical administration of WIN-55-212-2 maintains a reduction in IOP in a rat glaucoma model without adverse effects

Glaucoma, one of the leading causes of blindness, is associated with high intraocular pressure (IOP) as a risk factor. The aim of this study was to examine both local and systemic effects of chronic topical administration of the synthetic CB1/CB2 agonist, WIN-55-212-2 and its potential to sustain ocular hypotension. WIN-55-212-2 (0.5%) or Tocrisolve, the vehicle, was administered topically three times daily to rats with surgically created glaucoma for 4 weeks, followed by a 1-week washout period. IOP, blood pressure and heart rate were measured weekly along with confocal microscopy and slit lamp biomicroscopy to detect ocular toxicity. IOP decreased rapidly by up to 47% in the WIN-55-212-2 treated group from 14.1+/-0.7 to 6.6+/-0.2 mmHg. The decrease was maintained during the treatment period. After the washout period, IOP (12.3+/-0.2 mmHg) was not different from baseline. In the contralateral eye, IOP showed a downward trend. Tocrisolve alone had no effect on IOP. No changes in blood pressure, heart rate or indicators of ocular toxicity were noted within either group. Topical application of WIN-55-212-2 significantly deceased IOP for duration of treatment. The decrease was sustained without the development of tolerance. Following cessation of therapy, IOP rapidly returned to baseline. No significant cardiovascular effects or ocular toxicity were noted during chronic topical therapy with either drug or vehicle.

Solid-phase synthesis of anandamide analogues

The endocannabinoids are amides and esters of arachidonic acid that can mimic the pharmacological properties of Delta(9)-tetrahydrocannabinol (Delta(9)-THC). Anandamide, the most prominent of the endocannabinoids, has been implicated in both metabolic/physiological roles of the central nervous system, making it an attractive medicinal target. As such, we report the first solid-phase methodology that expedites access to various anandamide analogues. Our synthesis features a repetitive Cu-mediated coupling reaction between terminal alkynes and propargyl halides or allylic halides.

The anandamide membrane transporter. Structure–activity relationships of anandamide and oleoylethanolamine analogs with phenyl rings in the polar head group region

A new series of anandamide and N-oleoylethanolamine analogs, most of which with aromatic moieties in the head group region, has been synthesized and evaluated as inhibitors of anandamide uptake. Some of them efficaciously inhibit the uptake process with K(i) values in the low micromolar range (2.4-21.2microM). Strict structural requisites are needed to observe a significant inhibition and in no case inhibition of fatty acid amidohydrolase overlaps with inhibition of anandamide uptake.

Medicinal cannabis: is delta9-tetrahydrocannabinol necessary for all its effects?

Cannabis is under clinical investigation to assess its potential for medicinal use, but the question arises as to whether there is any advantage in using cannabis extracts compared with isolated Delta9-trans-tetrahydrocannabinol (Delta9THC), the major psychoactive component. We have compared the effect of a standardized cannabis extract (SCE) with pure Delta9THC, at matched concentrations of Delta9THC, and also with a Delta9THC-free extract (Delta9THC-free SCE), using two cannabinoid-sensitive models, a mouse model of multiple sclerosis (MS), and an in-vitro rat brain slice model of epilepsy. Whilst SCE inhibited spasticity in the mouse model of MS to a comparable level, it caused a more rapid onset of muscle relaxation, and a reduction in the time to maximum effect compared with Delta9THC alone. The Delta9THC-free extract or cannabidiol (CBD) caused no inhibition of spasticity. However, in the in-vitro epilepsy model, in which sustained epileptiform seizures were induced by the muscarinic receptor agonist oxotremorine-M in immature rat piriform cortical brain slices, SCE was a more potent and again more rapidly-acting anticonvulsant than isolated Delta9THC, but in this model, the Delta9THC-free extract also exhibited anticonvulsant activity. Cannabidiol did not inhibit seizures, nor did it modulate the activity of Delta9THC in this model. Therefore, as far as some actions of cannabis were concerned (e.g. antispasticity), Delta9THC was the active constituent, which might be modified by the presence of other components. However, for other effects (e.g. anticonvulsant properties) Delta9THC, although active, might not be necessary for the observed effect. Above all, these results demonstrated that not all of the therapeutic actions of cannabis herb might be due to the Delta9THC content.

Antitussive effect of WIN 55212-2, a cannabinoid receptor agonist

Several lines of evidence indicate that the opioid and cannabinoid systems produce synergistic interactions. The present study examined the opioid receptors involved in the antitussive effect of WIN 55212-2 ((R)-(+)-[2,3-dihydro-5-methyl-3-[4-morpholinylmethyl]-pyrrolo-[1,2,3-de]-1,4-benzoxazin-6-yl](1-naphthyl) methanone mesylate), a high-affinity cannabinoid receptor agonist, in mice. WIN 55212-2, at doses of 0.3-3 mg/kg ip, produced a dose-dependent antitussive effect. This antitussive effect of WIN 55212-2 was antagonized by pretreatment with either methysergide (3 mg/kg ip), a 5-HT receptor antagonist, or naloxone (1 mg/kg ip), an opioid receptor antagonist. Furthermore, pretreatment with N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride (SR141716A, 3 mg/kg ip), a cannabinoid CB(1) receptor antagonist, also significantly reduced the antitussive effect of WIN 55212-2. Blockade of mu-opioid receptors by pretreatment with beta-funaltrexamine (40 mg/kg sc) significantly reduced the antitussive effect of WIN 55212-2. However, pretreatment with nor-binaltorphimine (20 mg/kg sc), a kappa-opioid receptor antagonist, did not affect the antitussive effect of WIN 55212-2. Pretreatment with naloxonazine (35 mg/kg sc), a mu(1)-opioid receptor antagonist, also did not affect the antitussive effect of WIN 55212-2. These results indicate that the antitussive effect of WIN 55212-2 is mediated by the activation of cannabinoid CB(1) receptors and mu(2) (naloxonazine-insensitive)-opioid receptors, but not mu(1) (naloxonazine-sensitive)- or kappa-opioid receptors.

The effect of cannabinoid receptor antagonism with SR141716A on antinociception induced by cocaine and the NMDA receptor antagonist, MK-801

In the rat, antinociception of supraspinal origin is observed in response to administration of cocaine or an antagonist of the NMDA receptor for glutamate. The current study was conducted to determine if endocannabinoids are involved in the antinociceptive effect of cocaine, or antagonism of NMDA receptor binding. Intraperitoneal (i.p.) administration to male rats of cocaine, or the NMDA receptor antagonist, MK-801, resulted in a significant antinociceptive response of supraspinal origin, as indicated by a significant increase in reaction time in the hot plate test of analgesia (increase in the amount of time before the animal reacted to the hot plate by licking its paws or jumping). Treatment with SR141716A, a specific antagonist of the cannabinoid (CB1) receptor, resulted in a complete reversal of cocaine-induced antinociception when administered at a dose of 5.0mg/kg. Although the 2.5 and 5.0mg/kg doses of SR141716A produced a significant reduction in the antinociceptive effect of MK-801, the effect was incomplete since the reaction time in the hot plate test remained greater than that observed in vehicle-treated controls. These findings suggest that activation of the CB1 receptor participates significantly in antinociception resulting from treatment with cocaine and with the NMDA receptor antagonist, MK-801. The partial reversal of the antinociceptive effect of MK-801 by CB1 receptor antagonism indicates other mediators of nociception, in addition to the endocannabinoids, appear to be active in the antinociceptive response to NMDA receptor antagonism.

Cardiovascular system effects of marijuana

Marijuana and delta9-tetrahydrocannabinol (THC) increase heart rate, slightly increase supine blood pressure, and on occasion produce marked orthostatic hypotension. Cardiovascular effects in animals are different, with bradycardia and hypotension the most typical response. Cardiac output increases, and peripheral vascular resistance and maximum exercise performance decrease. Tolerance to most of the initial cardiovascular effects appears rapidly. With repeated exposure, supine blood pressure decreases slightly, orthostatic hypotension disappears, blood volume increases, heart rate slows, and circulatory responses to exercise and Valsalva maneuver are diminished, consistent with centrally mediated, reduced sympathetic, and enhanced parasympathetic activity. Receptor-mediated and probably nonneuronal sites of action account for cannabinoid effects. The endocannabinoid system appears important in the modulation of many vascular functions. Marijuana's cardiovascular effects are not associated with serious health problems for most young, healthy users, although occasional myocardial infarction, stroke, and other adverse cardiovascular events are reported. Marijuana smoking by people with cardiovascular disease poses health risks because of the consequences of the resulting increased cardiac work, increased catecholamine levels, carboxyhemoglobin, and postural hypotension.