Myelin basic protein is an endogenous inhibitor of the high-affinity cannabinoid binding site in brain

Adhesive properties and inflammatory potential of citrullinated myelin basic protein peptide 45-89

Deimination of arginyl residue of myelin basic protein (MBP) reduces cationicity of MBP and impedes the normal myelin membrane assembly. Less ordered structure of MBP is more susceptible to proteolytic attack that may lead to the release of highly immunogenic deiminated peptides into extracellular milieu. We have studied the association of peptides 45-89 derived from citrullinated MBP (C8 isomer) and phosphorylated MBP (C3 isomer) with the myelin lipids in a model membrane system using optical waveguide lightmode spectrometry. The analysis of association/dissociation kinetics to planar lipids under controlled hydrodynamic conditions has shown that MBP 45-89 peptide from citrullinated C8 isomer is less effectively adsorbed on the lipid membrane, than peptide from phosphorylated C3 isomer and packing densities for phosphorylated 45-89 MBP peptide is higher than for citrullinated forms. On the other hand, our results shown that continuous (24 h) exposure of mixed oligodendrocyte/microglial cells to peptides 45-89 from MBP-C8 induces apoptosis via mitochondrial pathway. In addition, peptides 45-89 stimulated the secretion of nitric oxide from microglial cells via induction of iNOS and decreased the level of the inhibitory protein IkB, indicating involvement of the transcription factor NF-kB in these processes. Our results suggest that some citrullinated peptides, initially released from oligodendrocytes, might activate microglia, which produces reactive nitrogen species and generates in turn fatal feedbacks that kill oligodendrocytes.

Why so impulsive? White matter alterations are associated with impulsivity in chronic marijuana smokers

Difficulty monitoring and inhibiting impulsive behaviors has been reported in marijuana (MJ) smokers; neuroimaging studies, which examined frontal systems in chronic MJ smokers, have reported alterations during inhibitory tasks. Diffusion tensor imaging (DTI) provides a quantitative estimate of white matter integrity at the microstructural level. We applied DTI, clinical ratings, and impulsivity measures to explore the hypotheses that chronic, heavy MJ smokers would demonstrate alterations in white matter microstructure and a different association between white matter measures and impulsivity relative to nonsmoking control subjects (NS). Fractional anisotropy (FA), a measure of directional coherence, and trace, a measure of overall diffusivity, were calculated for 6 locations including bilateral frontal regions in 15 chronic MJ smokers and 15 NS. Subjects completed clinical rating scales, including the Barratt Impulsivity Scale (BIS). Analyses revealed significant reductions in left frontal FA in MJ smokers relative to NS and significantly higher levels of trace in the right genu. MJ smokers also had significantly higher BIS total and motor subscale scores relative to NS, which were positively correlated with left frontal FA values. Finally, age of onset of MJ use was positively correlated with frontal FA values and inversely related to trace. These data represent the first report of significant alterations in frontal white matter tracts associated with measures of impulsivity in chronic MJ smokers. Early MJ use may result in reduced FA and increased diffusivity, which may be associated with increased impulsivity, and ultimately contribute to the initiation of MJ use or the inability to discontinue use.

Pharmacological characterization of novel water-soluble cannabinoids

Presently, there are numerous structural classes of cannabinoid receptor agonists, all of which require solubilization for experimental purposes. One strategy for solubilizing water-insoluble tetrahydrocannabinols is conversion of the phenolic hydroxyl to a morpholinobutyryloxy substituent. The hydrochloride salts of these analogs are water-soluble and active in vivo when administered in saline. The present investigation demonstrated that hydrochloride salts of numerous substituted butyryloxy esters are water-soluble and highly potent. The substitutions include piperidine, piperazine, and alkyl-substituted amino moieties. It was also discovered that incorporation of a nitrogenous moiety in the alkyl side chain increased the pharmacological potency of tetrahydrocannabinol. For example, an analog containing a pyrazole in the side chain (O-2545) was found to have high affinity and efficacy at cannabinoid 1 (CB(1)) and CB(2) receptors, and when dissolved in saline, it was highly efficacious when administered either intravenously or intracerebroventricularly to mice. A series of carboxamido and carboxylic acid amide analogs exhibited high pharmacological potency, but their hydrochloride salts were not water-soluble. On the other hand, incorporation of imidazoles into the terminus of the side chain led to water-soluble hydrochloride salts that were highly potent when administered in saline to laboratory animals. It is now possible to conduct cannabinoid research with agonists that are water-soluble and thus obviating the need of solubilizing agents.

Current evidence supporting a role of cannabinoid CB1 receptor (CB1R) antagonists as potential pharmacotherapies for drug abuse disorders

Since the discovery of the cannabinoid CB1 receptor (CB1R) in 1988, and subsequently of the CB2 receptor (CB2R) in 1993, there has been an exponential growth of research investigating the functions of the endocannabinoid system. The roles of CB1Rs have been of particular interest to behavioral pharmacologists because of their selective presence within the central nervous system (CNS) and because of their association with brain-reward circuits involving mesocorticolimbic dopamine systems. One potential role that has become of considerable recent focus is the ability of CB1Rs to modulate the effects of drugs of abuse. Many drugs of abuse elevate dopamine levels, and the ability of CB1R antagonists or inverse agonists to attenuate these elevations has suggested their potential application as pharmacotherapies for treating drug abuse disorders. With the identification of the selective CB1R antagonist, SR141716, in 1994, and its subsequent widespread availability, there has been a rapid expansion of research investigating its ability to modulate the effects of drugs of abuse. The preliminary clinical reports of its success in retarding relapse in tobacco users have accelerated this expansion. This report critically reviews preclinical and clinical studies involving the ability of CB1R antagonists to attenuate the effects of drugs of abuse, while providing an overview of the neuroanatomical and neurochemical points of contact between the endocannabinoid system and systems mediating abuse-related effects.

Assessment of cannabinoid induced gene changes: tolerance and neuroprotection

The analysis of gene changes associated with exposure to cannabinoids is critical due to the multiple possible signaling pathways potentially affected by cannabinoid receptor activation. A comparison of altered gene profiles under two different conditions, one in vivo (chronic exposure to delta-9-THC) and the other in vitro (neuroprotection mediated by WIN55212-2), was made to determine whether it was possible to identify common genes that were affected. Up and down-regulated sets of genes are described. Genes affected in one or the other circumstance include alterations in a 14-3-3 regulator protein of PKC, CREB, BDNF and GABA receptor subunit proteins, as well as several genes associated with known cannabinoid receptor-coupled signaling pathways. Unexpectedly, several genes that were altered in both circumstances were associated with synaptic and membrane structure, motility and neuron growth. These included, neuronal cell adhesion molecule (NCAM), hyloronidan motility receptor, and myelin proteolipid protein. While the basis for involvement of these particular genes in cannabinoid receptor activated functional processes within the cell is still not well understood, awareness that significant numbers of genes and presumably proteins are changed following either acute or long-term exposure may provide new insight into their effects.

From cannabis to cannabinergics: new therapeutic opportunities

The molecular basis of cannabinoid activity is better understood since the discovery of the CB(1) receptor in the mammalian brain and the CB(2) receptor in peripheral tissues. Subsequently, an endogenous CB(1) receptor ligand, arachidonylethanolamide (anandamide), was isolated from porcine brain and shown to be metabolized by the enzyme arachidonylethanolamide amidohydrolase or fatty acid amide hydrolase. Recently, we have characterized a reuptake system for the transport of anandamide across the cell membrane, and have shown that selective inhibition of this transporter is associated with analgesia and peripheral vasodilation. The four cannabinoid system proteins, including the CB(1) and CB(2) receptors, fatty acid amide hydrolase, and the anandamide transporter, are excellent targets for the development of novel medications for various conditions, including pain, immunosuppression, peripheral vascular disease, appetite enhancement or suppression, and motor disorders. During the last decade, numerous selective ligands for each of these proteins were designed and synthesized. Many of these agents serve as important molecular probes, providing structural information about their binding sites, as well as pharmacological tools imparting information about the roles of their targets in physiological and disease states. All of the above compounds that modulate the functions of the endocannabinoid system can be collectively described under the term cannabinergics, regardless of chemical classification or type of resultant pharmacological action.

Large-scale analysis of gene expression changes during acute and chronic exposure to [Delta]9-THC in rats

Large-scale cDNA microarrays were employed to assess transient changes in gene expression levels following acute and chronic exposure to cannabinoids in rats. A total of 24,456 cDNA clones were randomly selected from a rat brain cDNA library, amplified by PCR, and arrayed at high density to investigate differential gene expression profiles following acute (24 h), intermediate (7 days), and chronic (21 days) exposure to Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the psychoactive ingredient of marijuana. Hippocampal mRNA probes labeled with (33)P obtained from both vehicle and Delta(9)-THC-treated animals were hybridized with identical cDNA microarrays. Results revealed a total of 49 different genes altered by Delta(9)-THC exposure; of these, 28 were identified, 10 had homologies to expressed sequence tags (ESTs), and 11 had no homology to known sequences in the GenBank database. Chronic or acute cannabinoid receptor activation altered expression of several genes (i.e., prostaglandin D synthase, calmodulin) involved in biochemical cascades of cannabinoid synthesis or cannabinoid effector systems. Other genes [i.e., neural cell adhesion molecule (NCAM), myelin basic protein], whose relation to cannabinoid system function was not immediately obvious, were also significantly altered. Verification of the changes obtained with the large-scale screen was determined by RNA dot blots in different groups of animals treated the same as those in the large-scale screen. Results are discussed in terms of the different types of genes affected at different times during chronic Delta(9)-THC exposure.

Biochemistry of the endogenous ligands of cannabinoid receptors

In 1992 the discovery of the first endogenous ligand of cannabinoid receptors, anandamide, provided conclusive support to the hypothesis that an "endogenous cannabinoid regulatory system" exists in mammalian nervous tissue. Anandamide (N-arachidonoyl-ethanolamine) was the first of a series of long-chain fatty acid derivatives, including two other polyunsaturated N-acylethanolamines and 2-arachidonoyl-glycerol, found to exert cannabimimetic properties in either central or peripheral tissues. Here we review the current knowledge on the biochemical bases of the formation and inactivation of endogenous cannabinoid ligands as well as of their interaction with cannabinoid receptor subtypes.

Cannabinoid receptor CB1 mRNA is highly expressed in the rat ciliary body: implications for the antiglaucoma properties of marihuana

We used RT-PCR to measure relative differences in cannabinoid receptor (CB) mRNAs in the rat eye, comparing CB1 or CB2 transcripts to that of the normalizing reference gene beta2 microglobulin (beta2m). Significantly higher levels of CB1 mRNA levels were found in the ciliary body (0.84+/-0.05% of beta2m) than in the iris, (0.34+/-0.04% of beta2m), retina (0.07+/-0.005% of beta2m) and choroid (0.06+/-0.005% of beta2m). CB2 mRNA was undetectable. This expression pattern supports a specific role for the CB1 receptor in controlling intraocular pressure, helping to explain the antiglaucoma property of cannabinoids.

Atypical location of cannabinoid receptors in white matter areas during rat brain development

Previous evidence suggests that the endogenous cannabinoid system could emerge and be operative early during brain development. In the present study, we have explored the distribution of specific binding for cannabinoid receptors in rat brain at gestational day 21 (GD21), postnatal days 5 (PND5) and 30 (PND30), and at adult age (> 70 days after birth) by using autoradiography with [3H]CP-55,940. Our results indicated that specific binding for cannabinoid receptors can be detected in the brain of rat fetuses at GD21 in the classic areas that contain these receptors in adulthood-in particular, in the cerebellum and the hippocampus and, to a lesser extent, in the basal ganglia, several limbic structures, and cerebral cortex. The density of cannabinoid receptors in all these structures increased progressively at all postnatal ages studied until reaching the classical adult values in 70-day-old animals. Interestingly, cannabinoid receptor binding can also be detected at GD21 in regions, in which they are scarcely distributed or not located in the adult brain and that have the particularity of all being enriched in neuronal fibers. Among these were the corpus callosum, anterior commissure, stria terminalis, fornix, white matter areas of brainstem, and others. This atypical location was quantitatively high at GD21, tended to wane at PND5, and practically disappeared at PND30 and in adulthood, with the only exception being the anterior commissure, which exhibited a moderate density for cannabinoid receptors. Moreover, the binding of [3H]CP-55,940 to cannabinoid receptors in the white matter regions at GD21 seems to be functional and involves a GTP-binding protein-mediated mechanism. Thus, the activation of these receptors with an agonist such as WIN-55,212-2 increased the binding of [35S]-guanylyl-5'-O-(gamma-thio)-triphosphate, measured by autoradiography, in the corpus callosum and white matter areas of brainstem of fetuses at GD21. This increase was reversed by coincubation of WIN-55,212-2 with SR141716, a cannabinoid receptor antagonist. As this antagonist is specific for the cerebral cannabinoid receptor subtype, called CB1, we can assert that the signal found for cannabinoid receptor binding in the fetal and early postnatal brain likely corresponds to this receptor subtype. Collectively, all these data suggest the existence of a transient period of the brain development in the rat, around the last days of the fetal period and the first days of postnatal life, in which CB1 receptors appear located in neuronal fiber-enriched areas. During this period, CB1 receptors would be already functional acting through a GTP-binding protein-mediated mechanism. After this transient period, they progressively acquire the pattern of adult distribution. All this accounts for a specific role of the endogenous cannabinoid system in brain development.

Pharmacological evaluation of water soluble cannabinoids and related analogs

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

High-affinity cannabinoid binding site: regulation by ions, ascorbic acid, and nucleotides

The high-affinity cannabinoid site in rat brain is an integral component of brain membranes that recognizes cannabinoids with inhibitory constants (Ki) in the nanomolar range. To clarify its physiological role, we studied the regulation of [3H]5'-trimethylammonium delta 8-tetrahydrocannabinol ([3H]TMA) binding. The site is inhibited by heavy metal ions, such as La3+, at low micromolar concentrations; divalent cations, such as Ca2+ and Mg2+, inhibit [3H]TMA binding, though at somewhat higher concentrations. In contrast, [3H]TMA binding is stimulated by Fe2+, Cu2+, and Hg2+ ions. Ascorbic acid and its analogs are also stimulators of cannabinoid binding at low micromolar concentrations. Stimulation of [3H]TMA binding by ascorbate or ions is dependent upon molecular oxygen, but is not inhibited by metabolic poisons. Metabolically stable nucleoside triphosphate analogs enhance [3H]TMA binding by different mechanisms, with hydrolysis of a high-energy phosphate bond apparently requisite for these influences. These results suggest that the cannabinoid binding site is associated with a nucleotide-utilizing protein possessing multiple regulatory subsites.