Marijuana in the new millennium: perspectives for cannabinoid research

NMR structural comparison of the cytoplasmic juxtamembrane domains of G-protein-coupled CB1 and CB2 receptors in membrane mimetic dodecylphosphocholine micelles

The fourth cytoplasmic domain, the so-called C-terminal juxtamembrane segment or helix VIII, has been identified in numerous G-protein-coupled receptors and exhibits unique functional characteristics. Efforts have been devoted to studying the juxtamembrane segment in order to understand the biological importance of the segment in G-protein activation of the cannabinoid CB1 and CB2 receptors. Recent biochemical data revealed that the CB1 C-terminal juxtamembrane peptide fragment CB1-(401-417) can directly activate the G-protein and also showed that the specificity of the signal transduction activation by the C-terminal juxtamembrane region is unique to the CB1 receptor but not to the CB2 receptor (Mukhopadhyay, S., and Howlett, A. C. (2001) Eur. J. Biochem. 268, 499-505). However, there is experimental work, not yet reported, on the conformational analyses and structural comparison between the respective helix VIII segments of the two receptors. In the present study, we have examined the conformational specificities of the cytoplasmic helical domains for both cannabinoid receptors. Three-dimensional structural features of two synthetic CB1 and CB2 peptides, CB1I397-G418 and CB2I298-K319, respectively, in membrane mimetic DPC micelles were studied using a combined high resolution NMR and computer modeling approach. Comparisons of the NMR-determined structures of the two peptides as well as their correspondent mutant peptides revealed their conformational properties and salt bridge dissimilarity, which might help us to understand the different structural roles of the fourth cytoplasmic helices in the function and regulation of CB1 and CB2 receptors.

Lack of cross-tolerance to the antinociceptive effects of systemic and topical cannabinoids in morphine-tolerant mice

Opioids and cannabinoids produce antinociception through activity at spinal, supraspinal and peripheral sites. Tolerance to the antinociceptive effects of both the opioids and the cannabinoids develop when these agents are administered chronically. Although mutual potentiation of antinociceptive effects have been reported between opioids and cannabinoids, the development of antinociceptive cross-tolerance between these systems has not been demonstrated consistently. In the present investigation, we explored the possibility of antinociceptive cross-tolerance between systemic or topical morphine and systemic or topical cannabinoids in mice. Mice were made tolerant to morphine either by the subcutaneous (s.c.) implantation of a morphine pellet or repeated topical administration and then challenged with the mixed CB(1) and CB(2) receptor agonist WIN 55, 212-2 given s.c. or topically. Antinociception was indicated by increased tail-flick latencies to noxious radiant heat. Implantation with morphine pellets did not attenuate the antinociceptive potency of systemic or topical WIN 55,212-2. Moreover, twice-daily topical administration of morphine did not attenuate the antinociceptive potency of WIN 55,212-2 applied topically. These observations suggest that opioids and cannabinoids produce antinociception through mechanisms that are independent of each other at either the systemic or peripheral levels.

Differential distribution of functional cannabinoid CB1 receptors in the mouse gastroenteric tract

Recently, the gastrointestinal pharmacology of cannabinoid CB(1) receptors has been extensively explored. We employed western blotting and immunohistochemistry techniques to study the distribution of the cannabinoid CB(1) receptor protein in the mouse gastroenteric tract. The cannabinoid CB(1) receptor peptide was detected by western blotting only in its glycosylated form (63 kDa) with a significant differential distribution. The highest levels of expression were detected in the stomach and in the colon, while the pyloric valve was devoid of any cannabinoid CB(1) receptor protein. The immunohistochemical study showed intense cannabinoid CB(1) receptor immunoreactivity in ganglia subadjacent to the gastric epithelium and in the smooth muscle layers of both the small and large intestine. Only the small intestine showed (-)-3-[2-hydroxyl-4-(1,1-dimethylheptyl)-phenyl]-4-(3-hydroxylpropyl) cyclohexan-1-ol) ([3H]CP 55,940) specific binding (27%). These receptors mediated pharmacologically significant effects since the cannabinoid CB(1) receptor agonist R(-)-7-hydroxy-delta-6-tetra-hydrocannabinol-dimethylheptyl (HU 210) dose dependently inhibited gastrointestinal transit up to 70%, while the cannabinoid CB(1) receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide (SR 141716A) increased gastrointestinal transit. Moreover, the dose of 0.3 microg/kg of HU 210, devoid per se of any activity on mouse intestinal propulsion, blocked the increased gastroenteric transit induced by the cannabinoid CB(1) antagonist SR 141716A.

The effects of cannabinoids on the pharmacokinetics of indinavir and nelfinavir

BACKGROUND AND OBJECTIVES

The use of cannabinoids for appetite stimulation and the management of wasting and antiretroviral side-effects has become a common practice in the care of HIV-infected individuals. We present pharmacokinetic data from a randomized placebo-controlled study designed to evaluate the metabolic effects of smoked marijuana and dronabinol in HIV-infected patients receiving indinavir (IDV) or nelfinavir (NFV).

METHODS

Subjects on stable regimens containing IDV 800 mg every 8 h (n = 28) or NFV 750 mg three time a day (n = 34) were randomized to one of three treatment arms: 3.95% THC marijuana cigarettes, dronabinol 2.5 mg capsules or placebo capsules administered three times daily. Serial blood sampling was performed at baseline and on day 14 of treatment. The changes in NFV and IDV pharmacokinetics were measured as the median percentage change from baseline.

RESULTS

At day 14, the 8-h area under the curve (AUC(8)) changed by -10.2% (P = 0.15), maximum concentration (C(max)) by -17.4% (P = 0.46), and minimum concentration (C(min)) by -12.2% (P = 0.28) for patients in the NFV marijuana arm (n = 11). Similar decreases had occurred by day 14 among patients in the IDV marijuana arm (n = 9): AUC8 had changed by -14.5% (P = 0.074), C(max) by -14.1% (P = 0.039), and C(min) by -33.7% (P = 0.65).

CONCLUSION

Despite a statistically significant decrease in C(max) of IDV in the marijuana arm, the magnitude of changes in IDV and NFV pharmacokinetic parameters in the marijuana arm are likely to have no short-term clinical consequence. The use of marijuana or dronabinol is unlikely to impact antiretroviral efficacy.

Inhibitory effect of palmitoylethanolamide on gastrointestinal motility in mice

1. We have studied the effect of palmitoylethanolamide (PEA, 2.5 - 30 mg kg(-1), i.p.) on upper gastrointestinal transit in control mice and in mice with chronic intestinal inflammation induced by croton oil. 2. PEA significantly and dose-dependently decreased intestinal transit. The inhibitory effect of PEA (10 mg kg(-1)) was not modified by the cannabinoid CB(1) receptor antagonist SR141716A (0.3 mg kg(-1), i.p.), the cannabinoid CB(2) receptor antagonist SR144528 (1 mg kg(-1), i.p.), N(G)-nitro-L-arginine methyl ester (L-NAME, 25 mg kg(-1), i.p.), yohimbine (1 mg kg(-1), i.p.), naloxone (2 mg kg(-1), i.p.) or hexamethonium (1 mg kg(-1), i.p.). 3. PEA levels were significantly decreased in the small intestine of croton oil-treated mice. In these animals, PEA also inhibited motility and this effect was not counteracted by SR141716A (0.3 mg kg(-1)), or SR144528 (1 mg kg(-1)). 4. Pre-treatment of mice with the amidase inhibitor phenylmethyl sulphonil fluoride (PMSF, 30 mg kg(-1), i.p.) did not modify the inhibitory effect of PEA, either in control or in mice with inflammation. 5. It is concluded that PEA inhibits intestinal motility with a peripheral mechanism independent from cannabinoid receptor activation. The decreased levels of PEA in croton oil-treated might contribute, at least in part, to the exaggerated transit observed during chronic intestinal inflammation.

Cannabinoid CB1-receptor mediated regulation of gastrointestinal motility in mice in a model of intestinal inflammation

1. We have studied the effect of cannabinoid agonists (CP 55,940 and cannabinol) on intestinal motility in a model of intestinal inflammation (induced by oral croton oil in mice) and measured cannabinoid receptor expression, endocannabinoids (anandamide and 2-arachidonylglycerol) and anandamide amidohydrolase activity both in physiological and pathophysiological states. 2. CP 55,940 (0.03 - 10 nmol mouse(-1)) and cannabinol (10 - 3000 nmol mouse(-1)) were more active in delaying intestinal motility in croton oil-treated mice than in control mice. These inhibitory effects were counteracted by the selective cannabinoid CB(1) receptor antagonist SR141716A (16 nmol mouse(-1)). SR141716A (1 - 300 nmol mouse(-1)), administered alone, increased intestinal motility to the same extent in both control and croton oil-treated mice. 3. Croton oil-induced intestinal inflammation was associated with an increased expression of CB(1) receptor, an unprecedented example of up-regulation of cannabinoid receptors during inflammation. 4. High levels of anandamide and 2-arachidonylglycerol were detected in the small intestine, although no differences were observed between control and croton oil-treated mice; by contrast anandamide amidohydrolase activity increased 2 fold in the inflamed small intestine. 5. It is concluded that inflammation of the gut increases the potency of cannabinoid agonists possibly by 'up-regulating' CB(1) receptor expression; in addition, endocannabinoids, whose turnover is increased in inflamed gut, might tonically inhibit intestinal motility.