The orientation of (-)-delta 9-tetrahydrocannabinol in DPPC bilayers as determined from solid-state 2H-NMR

One for the Price of Two…Are Bivalent Ligands Targeting Cannabinoid Receptor Dimers Capable of Simultaneously Binding to both Receptors?

Bivalent ligands bridging two G-protein-coupled receptors (GPCRs) provide valuable pharmacological tools to target oligomers. The success of therapeutically targeting the cannabinoid CB1 receptor has been limited, in part due to its widespread neuronal distribution. Therefore, CB1 ligands targeting oligomers that exhibit restricted distribution or altered pharmacology are highly desirable, and several bivalent ligands containing a CB1 pharmacophore have been reported. Bivalent ligand action presumes that the ligand simultaneously binds to both receptors within the dimeric complex. However, based on the current understanding of CB1 ligand binding, existing bivalent ligands are too short to bind both receptors simultaneously. However, ligands with longer linkers may not be the solution, because evidence suggests that ligands enter CB1 through the lipid bilayer and, thus, linkers are unlikely to exit the receptor through its external face. Thus, the entire premise of designing bivalent ligands targeting CB1 must be revisited.

17β-estradiol (E2) in membranes: Orientation and dynamic properties

Non-genomic membrane effects of estrogens are of great interest because of the diverse biological activities they may elicit. To further our understanding of the molecular features of the interaction between estrogenic hormones and membrane bilayers, we have determined the preferred orientation, location, and dynamic properties of 17β-estradiol (E2) in two different phospholipid membrane environments using (2)H-NMR and 2D (1)H-(13)C HSQC in conjunction with molecular dynamics simulations. Unequivocal spectral assignments to specific (2)H labels were made possible by synthesizing six selectively deuterated E2 molecules. The data allow us to conclude that the E2 molecule adopts a nearly "horizontal" orientation in the membrane bilayer with its long axis essentially perpendicular to the lipid acyl-chains. All four rings of the E2 molecule are located near the membrane interface, allowing both the E2 3-OH and the 17β-OH groups to engage in hydrogen bonding and electrostatic interactions with polar phospholipid groups. The findings augment our knowledge of the molecular interactions between E2 and membrane bilayer and highlight the asymmetric nature of the dynamic motions of the rigid E2 molecule in a membrane environment.

2012 Division of medicinal chemistry award address. Trekking the cannabinoid road: a personal perspective

My involvement with the field of cannabinoids spans close to 3 decades and covers a major part of my scientific career. It also reflects the robust progress in this initially largely unexplored area of biology. During this period of time, I have witnessed the growth of modern cannabinoid biology, starting from the discovery of its two receptors and followed by the characterization of its endogenous ligands and the identification of the enzyme systems involved in their biosynthesis and biotransformation. I was fortunate enough to start at the beginning of this new era and participate in a number of the new discoveries. It has been a very exciting journey. With coverage of some key aspects of my work during this period of "modern cannabinoid research," this Award Address, in part historical, intends to give an account of how the field grew, the key discoveries, and the most promising directions for the future.

The interaction of cannabinoid receptor agonists, CP55940 and WIN55212-2 with membranes using solid state 2H NMR

Two key commonly used cannabinergic agonists, CP55940 and WIN55212-2, are investigated for their effects on the lipid membrane bilayer using (2)H solid state NMR, and the results are compared with our earlier work with delta-9-tetrahydrocannabinol (Δ(9)-THC). To study the effects of these ligands we used hydrated bilayers of dipalmitoylphosphatidylcholine (DPPC) deuterated at the 2' and 16' positions of both acyl chains with deuterium atoms serving as probes for the dynamic and phase changes at the membrane interface and at the bilayer center respectively. All three cannabinergic ligands lower the phospholipid membrane phase transition temperature, increase the lipid sn-2 chain order parameter at the membrane interface and decrease the order at the center of the bilayer. Our studies show that the cannabinoid ligands induce lateral phase separation in the lipid membrane at physiological temperatures. During the lipid membrane phase transition, the cooperative dynamic process whereby the C-(2)H segments at the interface and center of the bilayer spontaneously reach the fast exchange regime ((2)H NMR timescale) is distinctively modulated by the two cannabinoids. Specifically, CP55940 is slightly more efficient at inducing liquid crystalline-type (2)H NMR spectral features at the membrane interface compared to WIN55212-2. In contrast, WIN55212-2 has a far superior ability to induce liquid crystalline-type spectral features at the center of the bilayer, and it increases the order parameter of the sn-1 chain in addition to the sn-2 chain of the lipids. These observations suggest the cannabinoid ligands may influence lipid membrane domain formations and there may be contributions to their cannabinergic activities through lipid membrane microdomain related mechanisms. Our work demonstrates that experimental design strategies utilizing specifically deuterium labeled lipids yield more detailed insights concerning the properties of lipid bilayers.

Location, structure, and dynamics of the synthetic cannabinoid ligand CP-55,940 in lipid bilayers

The widely used hydrophobic cannabinoid ligand CP-55,940 partitions with high efficiency into biomembranes. We studied the location, orientation, and dynamics of CP-55,940 in POPC bilayers by solid-state NMR. Chemical-shift perturbation of POPC protons from the aromatic ring-current effect, as well as 1H NMR cross-relaxation rates, locate the hydroxyphenyl ring of the ligand near the lipid glycerol, carbonyls, and upper acyl-chain methylenes. Order parameters of the hydroxyphenyl ring determined by the 1H-13C DIPSHIFT experiment indicate that the bond between the hydroxyphenyl and hydroxycyclohexyl rings is oriented perpendicular to the bilayer normal. 2H NMR order parameters of the nonyl tail are very low, indicating that the hydrophobic chain maintains a high level of conformational flexibility in the membrane. Lateral diffusion rates of CP-55,940 and POPC were measured by 1H magic-angle spinning NMR with pulsed magnetic field gradients. The rate of CP-55,940 diffusion is comparable to the rate of lipid diffusion. The magnitude of cross-relaxation and diffusion rates suggests that associations between CP-55,940 and lipids are with lifetimes of a fraction of a microsecond. With its flexible hydrophobic tail, CP-55,940 may efficiently approach the binding site of the cannabinoid receptor from the lipid-water interface by lateral diffusion.

The total synthesis of 2-O-arachidonoyl-1-O-stearoyl-sn-glycero-3-phosphocholine-1,3,1'-(13)C3 and -2,1'-(13)C2 by a novel chemoenzymatic method

2-O-Arachidonoyl-1-O-stearoyl-sn-glycero-3-phosphocholine was synthesized with carbon-13 enrichment of the three glycerol carbons and the carbonyl of the stearoyl group. Phospholipase A(2) was utilized to give optically pure lyso-PC, and only 3% acyl migration occurred during reacylation with arachidonic acid anhydride. This phospholipid is an important biosynthetic precursor of arachidonic acid metabolites as well as the endocannabinoid 2-arachidonoylglycerol (2-AG), and is now available for NMR studies.

Cannabinoid receptors in brain: pharmacogenetics, neuropharmacology, neurotoxicology, and potential therapeutic applications

Much progress has been achieved in cannabinoid research. A major breakthrough in marijuana-cannabinoid research has been the discovery of a previously unknown but elaborate endogenous endocannabinoid system (ECS), complete with endocannabinoids and enzymes for their biosynthesis and degradation with genes encoding two distinct cannabinoid (CB1 and CB2) receptors (CBRs) that are activated by endocannabinoids, cannabinoids, and marijuana use. Physical and genetic localization of the CBR genes CNR1 and CNR2 have been mapped to chromosome 6 and 1, respectively. A number of variations in CBR genes have been associated with human disorders including osteoporosis, attention deficit hyperactivity disorder (ADHD), posttraumatic stress disorder (PTSD), drug dependency, obesity, and depression. Other family of lipid receptors including vanilloid (VR1) and lysophosphatidic acid (LPA) receptors appear to be related to the CBRs at the phylogenetic level. The ubiquitous abundance and differential distribution of the ECS in the human body and brain along with the coupling to many signal transduction pathways may explain the effects in most biological system and the myriad behavioral effects associated with smoking marijuana. The neuropharmacological and neuroprotective features of phytocannabinoids and endocannabinoid associated neurogenesis have revealed roles for the use of cannabinoids in neurodegenerative pathologies with less neurotoxicity. The remarkable progress in understanding the biological actions of marijuana and cannabinoids have provided much richer results than previously appreciated cannabinoid genomics and raised a number of critical issues on the molecular mechanisms of cannabinoid induced behavioral and biochemical alterations. These advances will allow specific therapeutic targeting of the different components of the ECS in health and disease. This review focuses on these recent advances in cannabinoid genomics and the surprising new fundamental roles that the ECS plays in the retrograde signaling associated with cannabinoid inhibition of neurotransmitter release to the genetic basis of the effects of marijuana use and pharmacotherpeutic applications and limitations. Much evidence is provided for the complex CNR1 and CNR2 gene structures and their associated regulatory elements. Thus, understanding the ECS in the human body and brain will contribute to elucidating this natural regulatory mechanism in health and disease.

The molecular features of membrane perturbation by anaesthetic steroids: a study using differential scanning calorimetry, small angle X-ray diffraction and solid state 2H NMR

We have studied the interactions of the anaesthetic steroid alphaxalone and its inactive isomer delta 16-alphaxalone with model membrane bilayers using differential scanning calorimetry, small angle X-ray diffraction and solid state NMR. Our data show that the anaesthetic steroid broadens the membrane phase transition and increases the ratio of gauche to trans conformers in the membrane. Delta 16-Alphaxalone has only small effects on membrane and incorporates to a limited degree in the bilayer. The amphipathic anaesthetic steroid alphaxalone is located near the membrane interface (the junction of the polar and hydrophobic regions of the phospholipids forming the bilayer). It orients with its long axis parallel to the chains of the lipid membranes and its 3 alpha-hydroxyl group near the sn-2 carbonyl. Anchoring of the steroid at the membrane interface and imperfect packing with the bilayer chains may be involved in membrane perturbation and eventually lead to anaesthesia.

Structural divergence among cannabinoids influences membrane dynamics: A 2H Solid-State NMR analysis

Cannabinoids are compounds that can modulate neuronal functions and immune responses via their activity at the CB(1) receptor. We used (2)H NMR order parameters and relaxation rate determination to delineate the behavior of magnetically aligned phospholipid bilayers in the presence of several structurally distinct cannabinoid ligands. THC (Delta(9)-Tetrahydrocannabinol) and WIN-55,212-2 were found to lower the phase transition temperature of the DMPC and to destabilize their acyl chains leading to a lower average S(CD) ( approximately 0.13), while methanandamide and CP-55,940 exhibited unusual properties within the lipid bilayer resulting in a greater average S(CD) ( approximately 0.14) at the top of the phospholipid upper chain. The CB(1) antagonist AM281 had average S(CD) values that were higher than the pure DMPC lipids, indicating a stabilization of the lipid bilayer. R(1Z) versus |S(CD)|(2) plots indicated that the membrane fluidity is increased in the presence of THC and WIN-55,212-2. The interaction of CP-55,940 with a variety of zwitterionic and charged membranes was also assessed. The unusual effect of CP-55,940 was present only in bicelles composed of DMPC. These studies strongly suggest that cannabinoid action on the membrane depends upon membrane composition as well as the structure of the cannabinoid ligands.

How lipophilic cannabinergic ligands reach their receptor sites

It is postulated that lipophilic ligands reach their sites of action on membrane-bound functional proteins through fast lateral diffusion across the membrane bilayer. We have shown using NMR experiments that such ligands when incorporated in a membrane system assume a preferred orientation and conformation. While occupying a specific location within the bilayer, these molecules undergo fast lateral diffusion which allows them to engage in productive interactions with their respective protein sites of action. The proposed model is discussed using a group of classical and non-classical cannabinoids as well as the endogenous cannabinoid ligand anandamide.

Lipids, lipid rafts and caveolae: Their importance for GPCR signaling and their centrality to the endocannabinoid system

Scientific views of cell membrane organization are presently changing. Rather than serving only as the medium through which membrane proteins diffuse, lipid bilayers have now been shown to form compartmentalized domains with different biophysical properties (rafts/caveolae). For membrane proteins such as the G protein coupled receptors (GPCRs), a raft domain provides a platform for the assembly of signaling complexes and prevents cross-talk between pathways. Lipid composition also has a strong influence on the conformational activity of GPCRs. For certain GPCRs, such as the cannabinoid receptors, the lipid bilayer has additional significance. Endocannabinoids such as anandamide (AEA) are created in a lipid bilayer from lipid and act at the membrane embedded CB1 receptor. Endocannabinoids exiting the CB1 receptor are transported either by a carrier-mediated or a simple diffusion process to the membrane of the postsynaptic cell. Following cellular uptake, perhaps via caveolae/lipid raft-related endocytosis, AEA is rapidly metabolized by a membrane-associated enzyme, fatty acid amide hydrolase (FAAH) located in the endoplasmic reticulum. The entry point for AEA into FAAH appears to be from the lipid bilayer. This review explores the importance of lipid composition and lipid rafts to GPCR signaling and then focuses on the intimate relationship that exists between the lipid environment and the endocannabinoid system.

The Conformation, Location, and Dynamic Properties of the Endocannabinoid Ligand Anandamide in a Membrane Bilayer

The endogenous cannabinoid ligand anandamide is biosynthesized from membrane phospholipid precursors and is believed to reach its sites of action on the CB1 and CB2 receptors through fast lateral diffusion within the cell membrane. To gain a better insight on the stereochemical features of its association with the cell membrane and its interaction with the cannabinoid receptors, we have studied its conformation, location, and dynamic properties in a dipalmitoylphosphatidylcholine multilamellar model membrane bilayer system. By exploiting the bilayer lattice as an internal three-dimensional reference grid, the conformation and location of anandamide were determined by measuring selected inter- and intramolecular distances between strategically introduced isotopic labels using the rotational echo double resonance (REDOR) NMR method. A molecular model was proposed to represent the structural features of our anandamide/lipid system and was subsequently used in calculating the multispin dephasing curves. Our results demonstrate that anandamide adopts an extended conformation within the membrane with its headgroup at the level of the phospholipid polar group and its terminal methyl group near the bilayer center. Parallel static (2)H NMR experiments further confirmed these findings and provided evidence that anandamide experiences dynamic properties similar to those of the membrane phospholipids and produces no perturbation to the bilayer. Our results are congruent with a hypothesis that anandamide approaches its binding site by laterally diffusing within one membrane leaflet in an extended conformation and interacts with a hydrophobic groove formed by helices 3 and 6 of CB1, where its terminal carbon is positioned close to a key cysteine residue in helix 6 leading to receptor activation.

Tetrahydrocannabinol (THC) alters synthesis and release of surfactant-related material in isolated fetal rabbit type II cells

Over the years, there has been a great deal of interest in the biological consequences of marijuana use. While evidence indicates that cannabinoids may have therapeutic uses in alleviating certain disease discomfort, there is little recent information on potential health risks, particularly related to the developing fetus. The present study was undertaken to determine the effects of delta 9-tetrahydrocannabinol (THC), the major psychoactive component in marijuana on fetal lung development specifically related to surfactant production. The rationale for the choice of this model lies in the importance of adequate lung development and surfactant production for the successful transition of the fetus to an air-breathing environment. Lung type II cells, the source of pulmonary surfactant, were isolated from fetal rabbit lungs on the 24th gestational day and incubated concurrently with various concentrations of THC and [3H]choline to label disaturated phosphatidylcholine (DSPC) the major surface-active phospholipid of surfactant. Under these conditions THC significantly reduced radiolabelling of DSPC and at the highest concentration (10(-4) M) induced release of DSPC. Pulse-chase studies were also conducted. Cells were prelabelled with [3H]choline, removed to fresh medium with THC (10(-4) M) and incubated for various time periods. Aqueous- and organic-soluble intermediates of DSPC formation were isolated. THC induced a significant increase in radiolabelling of CDPcholine, the rate-limiting conversion in DSPC synthesis. Radiolabelling of total phosphatidylcholine and DSPC was also significantly increased. Assay of CTP: cholinephosphate cytidylyltransferase which enzymatically converts cholinephosphate to CDPcholine showed that THC and phosphatidylglycerol (PG) both induced activation of the enzyme in fetal lung cytosol but not in the membranes. This effect of THC and PG was not additive. THC activated the enzyme only in fetal and not adult rabbit lung. The ability of THC to induce release of surfactant related material was also examined. In cells prelabelled with [3H]choline, THC induced release of [3H]DSPC in both cultured and freshly isolated fetal type II cells. These results suggest THC reduces formation of surfactant DSPC, probably through alterations in membrane dynamics. However, intracellular THC may actually increase formation of DSPC through an effect on the rate-limiting enzyme. THC also increases release of previously formed surfactant-related material.

Endocannabinoids and cannabinoid receptor genetics

This review presents the remarkable advances that have been achieved in marijuana (cannabinoid) research, with the discovery of specific receptors and the existence of naturally occurring cannabis-like substances in the human body and brain. The last decade has seen more rapid progress in marijuana research than any time in the thousands of years that marijuana has been used by humans, particularly in cannabinoid genomics. The cDNA and genomic sequences encoding G protein-coupled cannabinoid receptors (Cnrs) from several species have now been cloned. Endogenous cannabinoids (endocannabinoids), synthetic and hydrolyzing enzymes and transporters that define neurochemically-specific cannabinoid brain pathways have been identified. Endocannabinoid lipid signaling molecules alter activity at G protein-coupled receptors (GPCR) and possibly at anandamide-gated ion channels, such as vanilloid receptors. Availability of increasingly-specific CB1 and CB2 Cnr antagonists and of CB1 and CB2 Cnr knockout mice have increased our understanding of these cannabinoid systems and provides tantalizing evidence for even more G protein-coupled Cnrs. Initial studies of the Cnr gene structure, regulation and polymorphisms whet our appetite for more information about these interesting genes, their variants and roles in vulnerabilities to addictions and other neuropsychiatric disorders. Behavioral studies of cannabinoids document the complex interactions between rewarding and aversive effects of these drugs. Pursuing cannabinoid-related molecular, pharmacological and behavioral leads will add greatly to our understanding of endogenous brain neuromodulator systems, abused substances and potential therapeutics. This review of CB1 and CB2 Cnr genes in human and animal brain and their neurobiological effects provide a basis for many of these studies. Therefore, understanding the physiological cannabinoid control system in the human body and brain will contribute to elucidating this natural regulatory mechanism in health and disease.

Differential membrane fluidization by active and inactive cannabinoid analogues

The effects of the two cannabinomimetic drugs (-)-2-(6a,7,10,10a-tetrahydro-6,6,9-trimethyl-1-hydroxy-6H-dibenzo[b,d]pyranyl-2-(hexyl)-1,3-dithiolane (AMG-3) and its pharmacologically less active 1-methoxy analogue (AMG-18) on the thermotropic and structural properties of dipalmitoyl-sn-glycero-3-phosphorylcholine (DPPC) liposomes have been studied by X-ray diffraction and differential scanning calorimetry (DSC). DSC data revealed that the incorporation of the drugs affect differently the thermotropic properties of DPPC. The presence of the more active drug distinctly broadened and attenuated both the pretransition and main phase transition of DPPC bilayers, while the inactive analogue had only minor effects. Small and wide angle X-ray diffraction data showed that the two cannabinoids have different effects on the lipid phase structures and on the hydrocarbon chain packing. The pharmacologically active analogue, AMG-3, was found to efficiently fluidize domains of the lipids in the L(beta)' gel phase, and to perturb the regular multibilayer lattice. In the liquid crystalline L(alpha) phase, AMG-3 was also found to cause irregularities in packing, suggesting that the drug induces local curvature. At the same concentration, the inactive AMG-18 had only minor structural effects on the lipids. At about 10-fold or higher concentrations, AMG-18 was found to produce similar but still less pronounced effects in comparison to those observed by AMG-3. The dose-dependent, different thermotropic and structural effects by the two cannabinoid analogues suggest that these may be related to their biological activity.

Topography and thermotropic properties of cannabinoids in brain sphingomyelin bilayers

In our previous publications we compared the locations of the biologically active (-)-delta 8-tetrahydrocannabinol (delta 8-THC) with that of its inactive analog O-methyl-(-)-delta 8-tetrahydrocannabinol (Me-delta 8-THC) in the liquid crystalline phase of partially hydrated dimyristoylphosphatidylcholine (DMPC) bilayers (Mavromoustakos et al. (1990) Biophys. Acta 1024, 336-344; Yang et al. (1993) Life Sci. 53, 117-122). delta 8-THC was shown to localize itself preferentially in the vicinity of the membrane interface with its phenolic hydroxyl group anchored near the carbonyl groups of DMPC while the more lipophilic Me-delta 8-THC is located deeper towards the center of the bilayer. In the present publication we studied and compared the topography of the two analogs in the gel phase of brain sphingomyelin bilayers. Again we found that delta 8-THC is located near the membrane interface approximately 15 A from the center of the bilayer while its inactive analog localizes deeper in the bilayer at an average site only 8 A from the center of the membrane bilayer. It thus, appears that both analogs preferentially localize in distinct sites within the membrane bilayer which are independent of the mesomorphic state and the nature of the phospholipid. Our results suggest that in the more complex environment of biological membrane which is composed of different phospholipids and proteins the two analogs are expected to prefer different average locations within the bilayer, a property which may in part explain the observed differences in their biological activities.

Studies on the thermotropic effects of cannabinoids on phosphatidylcholine bilayers using differential scanning calorimetry and small angle X-ray diffraction

We have studied the thermotropic properties of a wide variety of cannabinoids in DPPC bilayers. The molecules under study were divided into four classes: (a) classical cannabinoids possessing a phenolic hydroxyl group; (b) delta9-THC metabolites with an additional hydroxyl group on the C ring; (c) non-classical cannabinoids, and (d) cannabinoids with a protected phenolic hydroxyl group. The results showed that the first three groups have similar effects on the thermotropic properties of DPPC bilayers up to x = 0.05 (molar ratio) and that these effects do not parallel their biological activity. For concentrations less than x = 0.01, cannabinoids affect mainly the pretransition temperature in a progressive manner until its final abolishment. At x = 0.05, they further affect the main phase transition by lowering its phase transition temperature and broadening its half width. At high concentrations the thermograms have multiple components, indicating that membranes are no longer homogeneous but rather consist of different domains. At these concentrations cannabinoids with more hydroxyl groups give simpler thermograms. Low concentrations of cannabinoids in group d affect significantly the pretransition temperature, while high concentrations affect only marginally the main phase transition by slightly lowering its temperature and broadening its half width. These results point out the importance of the phenolic hydroxyl group in inducing membrane perturbations. The d-spacing data from our small angle X-ray diffraction experiments show that delta8-THC produces significant structural changes in the lipid bilayer, including the gel-phase tilting angle, the intermolecular cooperativity and the gauche:trans conformer ratio. Conversely, the inactive analog Me-delta8-THC does not cause drastic changes to the bilayer structure.

Delta-9-tetrahydrocannabinol treatment results in a suppression of interleukin-2-induced cellular activities in human and murine lymphocytes

Delta-9-tetrahydrocannabinol (THC), the major psychoactive component in marijuana, has been shown to suppress a variety of interleukin-2-(IL-2)-dependent cellular functions in both murine and human lymphocytes. These effects were examined in both human peripheral blood lymphocytes (hPBL) and the IL-2-dependent murine cytotoxic T-cell line CTLL-2. Interleukin-2-induced thymidine uptake and uridine uptake were suppressed in a dose related manner when cells were co-incubated for 48 h with 100 U rhIL-2/ml and 1-10 micrograms THC/ml. Interleukin-2-induced protein synthesis was also suppressed in a dose related manner over this THC concentration range, with the hPBL being more susceptible to the suppressive effect of THC than the CTLL-2 cells. Autoradiographic analysis of the synthesized proteins from hPBL cell lysates reveals a generalized suppression of all nascent proteins in THC-treated cultures. Human natural killer cell activity is only affected at the highest concentration tested (10 micrograms THC/ml) while lymphokine-(IL-2)-activated natural killer cell activity is affected throughout the range of 1-10 micrograms THC/ml. Together these results suggest that THC interferes with the IL-2:IL-2 receptor signaling cascade at one or possibly many points causing a decrease in IL-2-induced metabolic activity and cytolytic function.

In vitro activation of brain protein kinase C by the cannabinoids

The cannabinoids have been shown to affect both membrane lipid ordering and the activities of several membrane-associated proteins. We have investigated the effects of the cannabinoids on protein kinase C, a lipid-dependent enzyme that functions as an important regulator of signal-transduction processes in the brain. The naturally occurring cannabinoid delta 9-tetrahydrocannabinol (delta 9-THC) increased the activity of protein kinase C isolated from rat forebrain at concentrations of 10 microM and above. 11-OH-delta 9-THC, cannabinol and cannabidiol also increased protein kinase C activity in the same concentration range. delta 9-THC (10 microM) decreased the Kact of protein kinase C for calcium from 28 microM to 18 microM and had no effect on the phosphatidylserine concentration-stimulation relationship. At a concentration of 30 microM, delta 9-THC increased the binding of [3H]phorbol-12,13-dibutyrate ([3H]PDBu) to protein kinase C and decreased the Kd for [3H]PDBu from 8.2 nM to 5.4 nM. delta 9-THC also had effects on lipid ordering of PS micelles, producing a significant increase in the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene at a concentration of 10 microM. These data suggest that delta 9-THC activates protein kinase C via a novel mechanism, possibly as a result of effects on vesicle lipid physical characteristics.

Topography of tetrahydrocannabinol in model membranes using neutron diffraction

Small-angle neutron scattering was used to determine the intralamellar location of (-)-delta 8-tetrahydrocannabinol (delta 8-THC) in hydrated dipalmitoylphosphatidylcholine (DPPC) bilayers. Nuclear scattering density profiles were calculated from measurements on deuterium and non-deuterium-labelled inclusions (8.3% (w/w)) of delta 8-THC in DPPC multilayer samples. By comparing pairs of such nuclear density profiles, the locations of the deuterium labels were determined. Present results on the topography of delta 8-THC in membranes are compared with earlier X-ray measurements using iodine labelling. Whereas the position of the phenolic hydroxy group is similar in both types of measurement, a difference is found in the conformation of the terminal methyl groups of the cannabinoid side-chains. The X-ray measurements on dimyristoylphosphatidylcholine (DMPC) indicated that the iodine-labelled cannabinoid side-chains assume an all-trans orientation with the terminal iodine atom pointing inward into the membrane away from the tricyclic region while the neutron measurements indicate that the terminal CH3 group of delta 8-THC aligns itself at the level of the tricyclic ring system implying that the side chain exists in a more compact conformation perpendicular to the DPPC hydrocarbons. A Gaussian function analysis of the data indicates that the delta 8-THC molecule is significantly delocalized in the DPPC membrane in the liquid crystal phase. The mean location of delta 8-THC suggests that the active site on a membrane-embedded receptor protein will lie near the polar interface at the base of the phospholipid headgroups.

Amphipathic interactions of cannabinoids with membranes. A comparison between delta 8-THC and its O-methyl analog using differential scanning calorimetry, X-ray diffraction and solid state 2H-NMR

The effects of (-)-delta 8-tetrahydrocannabinol (delta 8-THC) and its biologically inactive O-methyl ether analog on model phospholipid membranes were studied using a combination of differential scanning calorimetry (DSC), small angle X-ray diffraction and solid state 2H-NMR. The focus of this work is on the amphipathic interactions of cannabinoids with membranes and the role of the free phenolic hydroxyl group which is the only structural difference between these two cannabinoids. Identically prepared aqueous multilamellar dispersions of phosphatidylcholines in the absence and presence of cannabinoids were used. The DSC thermograms and X-ray diffraction patterns of these preparations allowed us to detect the strikingly different manners in which these two cannabinoids affect the thermotropic properties and the thickness of the bilayer. In order study the effects of the cannabinoids on different regions of the bilayer, we used solid state 2H-NMR with four sets of model membranes from dipalmitoylphosphatidylcholine deuterated in different sites, viz., the choline trimethylammonium head group, or one of the following three groups in the acyl chains; the 2'-methylene, 7'-methylene, 16'-methyl groups. Analysis of quadrupolar splittings indicated that delta 8-THC resides near the bilayer interface and the inactive analog sinks deeper towards the hydrophobic region. The temperature dependence of the solid state 2H-NMR spectra showed that, during the bilayer phase transition, the disordering of the choline head groups is a separate event from the melting of the acyl chains, and that amphipathic interactions between delta 8-THC and the membrane separate these two events further apart in temperature. The inactive analog lacks the ability to induce such a perturbation.

Influence of marihuana on cellular structures and biochemical activities

Cannabinoids are known to affect a number of cellular systems and functions, but the basis for their action is unclear. In this paper we review the current evidence describing cannabinoid effects on various levels of cellular structure and activity and we present our current studies on the influence of delta-9-tetrahydrocannabinol, cannabidiol and cannabinol on one cellular system, the cytoskeleton. The organization of two cytoskeletal structures, microtubules and microfilaments, were examined and the mRNA levels of tubulin and actin, the major protein components of microtubules and microfilaments, respectively, were analysed.

Solid state 2H-NMR as a method for determining the orientation of cannabinoid analogs in membranes

In order to investigate the correlation between the pharmacological activities of cannabinoids and the geometric features of their interactions with membranes, we have calculated the molecular orientations of five analogs in model membrane bilayers. The studies involved the stereospecific 2H-labeling of each analog in different positions and the use of solid state 2H-NMR. The cannabinoids included in our study are (-)-delta 9-tetrahydrocannabinol (THC), (-)-delta 8-THC and its methylated ether analog (-)-O-methyl-delta 8-THC, as well as two hexahydrocannabinols (HHC) having an additional hydroxyl in the 11-position, (-)-11-OH-9 alpha-HHC and (-)-11-OH-9 beta-HHC. A new algorithm is used to circumvent the problem of deuterium quadrupolar splitting signs. The method has general applicability for calculating the orientation of a molecule in a anisotropic environment. Our calculations show that the biological inactive O-methyl-delta 8-THC orients with its long axis parallel to the lipid acyl chains, whereas the psychoactive cannabinoids assume "awkward" orientations in which the hydroxyl groups are pointing towards the bilayer interface, presumably to maximize the amphipathic interaction with the membrane. To produce their biological effects, cannabinoids may need to acquire an appropriate location and orientation in the membrane bilayer so that, through lateral diffusion, they can reach their sites of action and interact productively with these sites.

Pharmacological evaluation of halogenated delta 8-THC analogs

-(-)-5'-Bromo-delta 8-THC, (-)-5'-trifluoromethyl-delta 8-THC, (-)-5'-iodo-delta 8-THC, (-)-5'-fluoro-delta 8-THC, (-)-11-fluoro-delta 8-THC and (-)-2-iodo-delta 8-THC were synthesized and evaluated in male ICR mice for their effects on sedation, temperature, catalepsy and antinociception following intravenous injection. The analogs were also tested for relative affinities for cannabinoid binding sites derived from rat cortex membranes, using [3H] CP-55,940 as the tritiated ligand. The results showed that the 5'-bromo, 5'-iodo and 5'-trifluoromethyl analogs were 2-40 times more potent than (-)-delta 8-THC in all biological tests, while the 5'-fluoro and 11-fluoro derivatives were less active. With the 2-iodo analog, a 12-fold separation was observed between antinociception and sedation, pointing to the importance of the side chain orientation in determining cannabinoid activity and to the possible involvement of more than one cannabinoid receptor site. The pharmacological data closely paralleled the data obtained from the binding assay.

PET studies in the primate brain and biodistribution in mice using (-)-5'-18F-delta 8-THC

Cannabinoids, the active constituents of marijuana, are known to have many therapeutic properties; however, their exact mechanism of action is not well understood. In an effort to obtain more information concerning the pharmacokinetics and biodistribution of psychoactive THC analogs we synthesized (-)-18F-delta 8-THC and studied its biodistribution in mice and baboon brains. The analog was obtained by nucleophilic fluorination of the ditriflate ester of (-)-5'-OH-delta 8-THC with K18F/Kryptofix followed by deprotection with LiAIH4 and purification with HPLC in 8% yield in a 90-min synthesis from EOB. The uptake of (-)-5'-18F-delta 8-THC in mouse tissue was high at 5 min, but radioactivity declined rapidly in almost all the tissues studied. Following IV administration, (-)-5'-18F-delta 8-THC uptake in baboon brain was similar in the basal ganglia, thalamus and cerebellum, and the clearance from these regions was relatively rapid. Also, a study from baboon plasma clearance of (-)-5'-18F-delta 8-THC showed rapid metabolism of the analog.

The perturbation of model membranes by (-)-delta 9-tetrahydrocannabinol. Studies using solid-state 2H- and 13C-NMR

The effects of (-)-delta 9-tetrahydrocannabinol (delta 9-THC) on model phospholipid membranes were studied using solid-state 2H and 13C nuclear magnetic resonance spectroscopy. Aqueous multilamellar dispersions of dipalmitoylphosphatidylcholine with specific 2H- and 13C-labels as endogenous probes at the C7, methylene and the carbonyl groups, respectively, of the sn-2 chain were used to study the conformational and dynamic properties of the bilayer as a function of temperature and drug concentration. The drug molecule decreases the phase transition temperature of the bilayer in a concentration dependent manner up to 20 molar percent when full saturation has occurred. The 2H spectra show that delta 9-THC broadens the phase transition during which the spectra acquire a characteristic shape of a two-component system exchanging at an intermediate rate (approximately 10(6) s-1) with some liquid crystalline features. Such spectra provide information related to the melting of the phospholipid chains. At intermediate temperatures, the 13C spectra show a gel-like and a liquid-crystalline-like exchanging components and provide information about a conformational change at the phospholipid glycerol backbone occurring at or near the pretransition. The spectral composition and rate of exchange are both dependent on drug concentration. We have carried out computer simulations of the 13C spectra and obtained conformational information related to the phase transition process in the bilayer from gel to liquid crystal. Our studies show that delta 9-THC has a stronger effect on the sn-2 carbonyl near the bilayer interface than on the lipid chains and serve to describe the membrane perturbing effects of cannabinoids in molecular terms.

Study of the topography of cannabinoids in model membranes using X-ray diffraction

Small-angle X-ray diffraction was used to determine the topography of (-)-delta 8-tetrahydrocannabinol in partially hydrated dimyristoylphosphatidylcholine bilayers. Electron density profiles of lipid bilayers in the presence and absence of the cannabinoid were calculated using Fourier transform. Step-function equivalent profiles were then constructed to obtain the absolute electron density scale. We have compared the electron density profiles of the above preparations to determine the location of the drug molecule in the bilayer. By using (-)-5'-iodo-delta 8-tetrahydrocannabinol in parallel experiments, we were also able to locate the iodine atom in the bilayer and deduce the conformation of the cannabinoid side alkyl chain. All comparisons were made between different preparations having the same mesomorphic form and total period repeat distance. To achieve this, we have carried out X-ray diffraction experiments at various temperatures to cover the different mesomorphic phases and combined our data with the corresponding results from differential scanning calorimetry. Based on the results of this work and previous data on the orientation of the cannabinoid in model membranes, we concluded that the phenolic hydroxy group of the drug molecule exists near the carbonyl groups of DMPC and that the average position of the iodine atom is approx. 5.5 A from the center (terminal methyl region) of the DMPC bilayer. This requires the cannabinoid side-chain to assume an orientation parallel to the bilayer chains.

The molecular basis of cannabinoid activity

Cannabinoids have been known to exhibit a wide variety of biological effects. Over the past fifty years numerous analogs were synthesized in an attempt to understand the structural requirements for each cannabinoid activity. Only recently, however, some important findings have focused new attention on this field of research. These findings include: (a) The development of novel "non-classical" potent cannabinoid analogs which exhibit similar pharmacological profiles with their "classical" counterparts; (b) The demonstration that there are specific cannabinoid binding sites in cell cultures as well as in mammalian brains; (c) Biophysical studies related to the interactions of cannabinoids with membranes which lead to a better understanding of those molecular properties which are required for cannabinoid activity; (d) Detailed and uniform pharmacological testing on a sizeable number of analogs allowing for a more detailed dissection of the cannabinoid effects and respective "structure activity relationships." The newly increased interest in cannabinoid research opens the door for a better understanding and potential treatment in cases of abuse as well as novel therapeutic opportunities through the design and synthesis of pharmacologically more selective analogs.