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

Effects of cannabinoids on ligand-gated ion channels

Phytocannabinoids such as Δ⁹-tetrahydrocannabinol and cannabidiol, endocannabinoids such as N-arachidonoylethanolamine (anandamide) and 2-arachidonoylglycerol, and synthetic cannabinoids such as CP47,497 and JWH-018 constitute major groups of structurally diverse cannabinoids. Along with these cannabinoids, CB1 and CB2 cannabinoid receptors and enzymes involved in synthesis and degradation of endocannabinoids comprise the major components of the cannabinoid system. Although, cannabinoid receptors are known to be involved in anti-convulsant, anti-nociceptive, anti-psychotic, anti-emetic, and anti-oxidant effects of cannabinoids, in recent years, an increasing number of studies suggest that, at pharmacologically relevant concentrations, these compounds interact with several molecular targets including G-protein coupled receptors, ion channels, and enzymes in a cannabinoid-receptor independent manner. In this report, the direct actions of endo-, phyto-, and synthetic cannabinoids on the functional properties of ligand-gated ion channels and the plausible mechanisms mediating these effects were reviewed and discussed.

Possible roles of AMPK and macropinocytosis in the defense responses against Δ9-THC toxicity on HL-1 cardiomyocytes

Cannabinoids are some of the most popular recreationally used illicit drugs, and are frequently consumed along with alcoholic beverages. Although the whole body effects of cannabinoids depend largely on their effects on the central nerve system, cannabinoids could harm the heart directly, due to the presence of the endocannabinoid system including cannabinoid receptor1 and 2 (CB-R1 and CB-R2) in the heart. The aim of this study is to examine the mechanism of direct cardiotoxicity of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), the main psychoactive ingredient of cannabis. For this purpose, HL-1 murine atrial cardiac muscle cells were treated with 10 or 30 μM Δ⁹-THC, along with 100 mM ethanol to examine the possible synergistic effects of Δ⁹-THC and ethanol. Transcriptome analysis showed upregulation of the genes involved in the unfolded protein response (UPR), including Bip, CHOP, ATF4 and ATF6, in cells treated with Δ⁹-THC. Immunoblot analysis showed caspase3 activation, indicating apoptosis caused by ER stress in Δ⁹-THC-treated cells. Microscopic analysis showed that Δ⁹-THC enhances macropinocytosis, a process involved in the uptake of extracellular fluids including nutrients. Moreover Δ⁹-THC seemed to activate AMPK, a sensor of intracellular energy status and an activator of macropinocytosis. Finally, we found that compound C (AMPK inhibitor) aggravated cell death by Δ⁹-THC while AICAR (AMPK activator) ameliorated it. Collectively, these results indicate that the activation of AMPK is necessary for the survival of HL-1 cells against Δ⁹-THC toxicity. Macropinocytosis might serve as one of the survival pathways downstream of AMPK.

The Therapeutic Aspects of the Endocannabinoid System (ECS) for Cancer and their Development: From Nature to Laboratory

The endocannabinoid system (ECS) is a group of neuromodulatory lipids and their receptors, which are widely distributed in mammalian tissues. ECS regulates various cardiovascular, nervous, and immune system functions inside cells. In recent years, there has been a growing body of evidence for the use of synthetic and natural cannabinoids as potential anticancer agents. For instance, the CB1 and CB2 receptors are assumed to play an important role inside the endocannabinoid system. These receptors are abundantly expressed in the brain and fatty tissue of the human body. Despite recent developments in molecular biology, there is still a lack of knowledge about the distribution of CB1 and CB2 receptors in the human kidney and their role in kidney cancer. To address this gap, we explore and demonstrate the role of the endocannabinoid system in renal cell carcinoma (RCC). In this brief overview, we elucidate the therapeutic aspects of the endocannabinoid system for various cancers and explain how this system can be used for treating kidney cancer. Overall, this review provides new insights into cannabinoids' mechanisms of action in both in vivo and in vitro models, and focuses on recent discoveries in the field.

Differential modulation by delta9-tetrahydrocannabinol (∆9)-THC) of CD40 ligand (CD40L) expression in activated mouse splenic CD4+ T cells

The anti-inflammatory activity of cannabinoids has been widely demonstrated in experimental animal models and in humans. CD40-CD40-ligand (L) interactions are among the most crucial initiators of inflammation. This study investigated the effects of ∆(9)-THC on CD40L expression in mouse splenic T cells after activation with various stimuli. Time course studies demonstrated that peak surface expression of CD40L by CD4(+) T cells after anti-CD3/CD28 or phorbol ester plus calcium ionophore (PMA/Io) occurred 8 h post activation. Peak CD40L mRNA levels were observed at 2 h post PMA/Io treatment and at 4 h post anti-CD3/CD28 treatment. Pretreatment with ∆(9)-THC significantly impaired the upregulation of CD40L induced by anti-CD3/CD28 at both the protein and mRNA level. By contrast, ∆(9)-THC did not affect PMA/Io-induced surface CD40L expression on CD4(+) T cells. Additionally, ∆(9)-THC also attenuated anti-CD3/CD28-induced CD40L expression on CD4(+) T cells derived from CB1(-/-)/CB2(-/-) mice. We investigated whether the mechanism by which ∆(9)-THC suppressed CD40L expression involved putative cannabinoid activation of the glucocorticoid receptor (GR). Although activation of GR resulted in suppression of CD40L induction by anti-CD3/CD28, no interaction between ∆(9)-THC and GR was observed by a glucocorticoid response element (GRE) luciferase reporter assay in HEK293T cells. Collectively, these results suggest that ∆(9)-THC targets proximal T cell receptor-associated signaling in a cannabinoid receptor- and glucocorticoid receptor-independent manner. These findings identify suppression of CD40L expression as a novel part of the mechanism by which ∆(9)-THC exerts anti-inflammatory activity.

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.

Cannabinoids Delta(9)-tetrahydrocannabinol and cannabidiol differentially inhibit the lipopolysaccharide-activated NF-kappaB and interferon-beta/STAT proinflammatory pathways in BV-2 microglial cells

Cannabinoids have been shown to exert anti-inflammatory activities in various in vivo and in vitro experimental models as well as ameliorate various inflammatory degenerative diseases. However, the mechanisms of these effects are not completely understood. Using the BV-2 mouse microglial cell line and lipopolysaccharide (LPS) to induce an inflammatory response, we studied the signaling pathways engaged in the anti-inflammatory effects of cannabinoids as well as their influence on the expression of several genes known to be involved in inflammation. We found that the two major cannabinoids present in marijuana, Delta(9)-tetrahydrocannabinol (THC) and cannabidiol (CBD), decrease the production and release of proinflammatory cytokines, including interleukin-1beta, interleukin-6, and interferon (IFN)beta, from LPS-activated microglial cells. The cannabinoid anti-inflammatory action does not seem to involve the CB1 and CB2 cannabinoid receptors or the abn-CBD-sensitive receptors. In addition, we found that THC and CBD act through different, although partially overlapping, mechanisms. CBD, but not THC, reduces the activity of the NF-kappaB pathway, a primary pathway regulating the expression of proinflammatory genes. Moreover, CBD, but not THC, up-regulates the activation of the STAT3 transcription factor, an element of homeostatic mechanism(s) inducing anti-inflammatory events. Following CBD treatment, but less so with THC, we observed a decreased level of mRNA for the Socs3 gene, a main negative regulator of STATs and particularly of STAT3. However, both CBD and THC decreased the activation of the LPS-induced STAT1 transcription factor, a key player in IFNbeta-dependent proinflammatory processes. In summary, our observations show that CBD and THC vary in their effects on the anti-inflammatory pathways, including the NF-kappaB and IFNbeta-dependent pathways.

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.

Magnetically aligned bicelles to study the orientation of lipophilic ligands in membrane bilayers

Magnetically aligned bicelles were used as a model membrane to study the orientation and dynamic properties of two cannabinoids (Delta (8)-THC and Me-Delta (8)-THC) using (31)P and (2)H NMR. The uniform alignment of the bicelles allowed us to obtain well resolved deuterium spectra from a solution NMR spectrometer. The preferred orientations of Delta (8)-THC and Me-Delta (8)-THC were calculated on the basis of the measurements of individual quadrupolar splittings. Our results agree with previous experiments using multilamellar membranes as well as with molecular dynamics simulation data described here. In conjunction with our earlier report using small and fast tumbling bicelles, the present work of well aligned bicelles shows that bicelle preparations can provide either pseudoisotropic or anisotropic NMR spectra to study the conformation, orientation, and dynamic properties of ligands in membrane bilayers. Such data are of critical value for understanding the interactions of lipophilic drug molecules with membrane proteins.

The cannabinoid delta-9-tetrahydrocannabinol mediates inhibition of macrophage chemotaxis to RANTES/CCL5: linkage to the CB2 receptor

The chemotactic response of murine peritoneal macrophages to RANTES/CCL5 was inhibited significantly following pretreatment with delta-9-tetrahydrocannabinol (THC), the major psychoactive component in marijuana. Significant inhibition of this chemokine directed migratory response was obtained also when the full cannabinoid agonist CP55940 was used. The CB2 receptor-selective ligand O-2137 exerted a robust inhibition of chemotaxis while the CB1 receptor-selective ligand ACEA had a minimal effect. The THC-mediated inhibition was reversed by the CB2 receptor-specific antagonist SR144528 but not by the CB1 receptor-specific antagonist SR141716A. In addition, THC treatment had a minimal effect on the chemotactic response of peritoneal macrophages from CB2 knockout mice. Collectively, these results suggest that cannabinoids act through the CB2 receptor to transdeactivate migratory responsiveness to RANTES/CCL5. Furthermore, the results suggest that the CB2 receptor may be a constituent element of a network of G protein-coupled receptor signal transductional systems, inclusive of chemokine receptors, that act coordinately to modulate macrophage migration.

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.

Suppressive effects of cannabidiol on antigen-specific antibody production and functional activity of splenocytes in ovalbumin-sensitized BALB/c mice

Cannabidiol (CBD) and cannabis-based medicines are potential therapeutic agents. Because the immune system has been widely demonstrated to be affected by psychoactive cannabinoids, such as Delta(9)-tetrahydrocannabinol, the objective of the present studies is to investigate the immunomodulatory effect of CBD, the major non-psychoactive cannabinoid in marijuana. BALB/c mice were intraperitoneally administered with a single dose of CBD (5-20 mg/kg) prior to ovalbumin (OVA) sensitization, and the serum production of antigen-specific antibodies was measured 7 days post OVA sensitization. The serum level of OVA-specific IgM was significantly attenuated by a high dose of CBD (20 mg/kg), and OVA-specific IgG(1) and IgG(2a) by all 3 doses of CBD. Concordantly, splenocytes of mice administered with CBD (5 or 20 mg/kg) produced less IL-2, IL-4 and IFN-gamma than those of vehicle-treated controls, upon ex vivo stimulation with phorbol ester plus calcium ionophore. Likewise, T-cell mitogen (concanavalin A)-induced proliferation of splenocytes was also markedly suppressed in mice administered with CBD. Furthermore, the observed ex vivo effects of CBD on cytokine production and T-cell proliferation were confirmed in splenocytes directly exposed to CBD (1-8 microM) in vitro, indicating a direct effect by CBD. Taken together, the results demonstrated that CBD markedly suppressed antigen-specific antibody production in OVA-sensitized mice, and suggest that CBD-mediated suppression of humoral immunity could be mediated by the impaired functions of splenocytes.

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.

Receptor-independent effects of natural cannabinoids in rat peritoneal mast cells in vitro

Cannabinoids can activate CB(1) and CB(2) receptors. Since a CB(2) mRNA has been described in rat peritoneal mast cells (RPMC), we investigated a series of cannabinoids and derivatives for their capacity to stimulate RPMC. Effects of natural cannabinoids Delta(9)-tetrahydrocannabinol (Delta(9)-THC), Delta(8)-THC, endocannabinoids (anandamide, palmitoylethanolamide) and related compounds (N-decanoyl-, N-lauroyl-, N-myristoyl-, N-stearoyl- and N-oleoyl-ethanolamines; N-palmitoyl derivatives (-butylamine, -cyclohexylamine, -isopropylamine); and N-palmitoyl, O-palmitoylethanolamine), and synthetic cannabinoids including WIN 55,212-2, SR141716A and SR144528 were assessed for their capacity to induce histamine release or prime RPMC stimulated by compound 48/80. Only Delta(9)-THC and Delta(8)-THC could induce non-lytic, energy- and concentration-dependent histamine releases from RPMC (respective EC(50) values: 23.5+/-1.2; 53.4+/-20.6 microM, and maxima: 71.2+/-5.5; 55.7+/-2.7% of the total RPMC histamine content). These were not blocked by CB(1) (SR141716A) or CB(2) (SR144528) antagonists, but reduced by pertussis toxin (100 ng/ml). Endocannabinoids and analogues did neither induce histamine secretion, nor prime secretion induced by compound 48/80 (0.2 microg/ml). Delta(9)-THC and Delta(8)-THC induced in vitro histamine secretion from RPMC through CB receptor-independent interactions, partly involving G(i/o) protein activation.

Effects of cannabinoids in membrane bilayers containing cholesterol

The thermotropic and dynamic properties of the biologically active Delta(8)-tetrahydrocannabinol (Delta(8)-THC) and its inactive congener O-methyl-Delta(8)-tetrahydrocannabinol (Me-Delta(8)-THC) in DPPC/cholesterol (CHOL) bilayers have been studied using a combination of DSC and solid-state NMR spectroscopy. The obtained results showed differential effects of the two cannabinoids under study. These are summarized as follows: (a) the presence of the active compound fluidizes more significantly the DPPC/CHOL bilayers than the inactive analog as it is revealed by DSC and NMR spectroscopy results; (b) cholesterol seems to play a significant role in the way cannabinoids act in membrane bilayers; (c) the observed additional peaks in (13)C/MAS-NMR spectra which were cannabinoid specific offer an evidence of their different dynamic properties in membranes. In particular, the aromatic part of the inactive cannabinoid appears more mobile than that of the active one. This finding is in agreement with previously obtained X-ray data which locate the inactive cannabinoid in the hydrophobic core of the bilayer while the active one in the polar region; and (d) the observed downfield shift of C-1 carbon in the preparation containing the active cannabinoid is a strong evidence that Delta(8)-THC resides nearby the polar region where also cholesterol is well known to locate itself. Such downfield shift is absent when Me-Delta(8)-THC is resided in the membrane bilayer. These differential effects of the two cannabinoids propose that the phospholipid/cholesterol core of the membrane may play an important role in the mode of cannabinoid action by regulating their thermotropic and dynamic properties.

Syntheses of 1,2-di-O-palmitoyl-sn-glycero-3-phosphocholine (DPPC) and analogs with 13C- and 2H-labeled choline head groups

The syntheses of four head group labeled analogs of 1,2-di-O-palmitoyl-sn-glycero-3-phosphocholine (DPPC) (6) by a general method from 1,2-di-O-palmitoyl-sn-glycero-3-phosphatidic acid (5) have been performed. The syntheses of 1,2-di-O-palmitoyl-sn-glycero-3-phospho[alpha-13C]choline (6a) and 1,2-di-O-palmitoyl-sn-glycero-3-phospho[beta-13C]choline (6b) were performed from labeled [1-13C]glycine (1a) in 52% overall yield and from [2-13C]glycine (1b) in 56% overall yield, respectively. 1,2-Di-O-palmitoyl-sn-glycero-3-phospho[N(C2H3)3]choline (9) was prepared from 2-aminoethanol in 39% overall yield. 1,2-Di-O-palmitoyl-sn-glycero-3-phospho[alpha-C2H2]choline (12) was prepared from N,N-dimethylglycine ethyl ester in 50% overall yield.

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.

Phase behavior of mixtures of DPPC and POPG

The phase relation of dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG) has been determined by measurement of the endothermic transitions of mixtures of DPPC and POPG in 100 mM NaCl, 50 mM PIPES (pH 7.0). With the use of differential scanning calorimetry, the gel-liquid crystalline phase transitions of pure POPG and DPPC were estimated to be 274 K and 315.8 K, respectively. With mixtures, there was considerable broadening of the endotherms, but there was no evidence of immiscibility. At high and low mole fractions of DPPC, the observed transition regions are not different from that calculated assuming ideal behavior. However in the central region of the phase diagram, there were deviations from both the ideal liquidus and solidus curves. The chemical shift anisotropy of the 13C-labelled carbonyl carbon of pure DPPC was determined as a function of temperature. At 298 K, a broad peak characteristic of axially symmetric motional averaging of the shielding tensor was observed. At a temperature of 300 K, a narrow peak at 173 ppm was superimposed upon the broad peak. The magnitude of the narrow resonance increased with temperature over the range of 300 to 315 K with the spectrum obtained at the latter point almost completely devoid of any broad features. Spectra obtained with a 9:1 mole ratio of DPPC/POPG was very similar to that obtained with pure DPPC. However, with increasing amounts of POPG, both the temperature at which the narrow resonance appeared and the temperature at which only a narrow resonance was observed were reduced. Over the range of 0 to 50 mol % POPG, there was no major change in the width or shape of the spectra which contained only a broad or narrow resonance. Also for mol % of POPG of 20% and less, there was agreement between the temperature at which only the narrow component was observed and the completion of the main phase transition based on the DSC scans. However, at the two higher mol % of 33 and 50%, the temperature at which only the narrow component was observed was lower than the temperature established for the completion of the main phase transition.

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.