Cannabinoids in the treatment of glaucoma

Cyclooxygenase-2 and tissue inhibitor of matrix metalloproteinases-1 confer the antimigratory effect of cannabinoids on human trabecular meshwork cells

Cannabinoids have received considerable attention as potential antiglaucomatous drugs. Recently, prostaglandins (PG) have been suggested to contribute to this effect. Within the factors conferring the development of glaucoma, depletion of the aqueous humor outflow-regulating trabecular meshwork (TM) cells elicited by migration from the outflow system is considered to play a pivotal role. This study therefore investigates the impact of two cannabinoids, Delta(9)-tetrahydrocannabinol (THC) and R(+)-methanandamide (MA), on the migration of human TM cells and the involvement of the PG-synthesizing enzyme cyclooxygenase-2 (COX-2) and one of its potential downstream targets, the tissue inhibitor of matrix metalloproteinases-1 (TIMP-1), to this response. Using Boyden chamber assays cannabinoids were shown to elicit an antimigratory effect that was reversed by antagonists for CB(1) as well as CB(2) receptors and accompanied by upregulation of COX-2 and TIMP-1 expression and PGE(2) synthesis. Knockdown of cannabinoid-induced COX-2 or TIMP-1 expression by siRNA or inhibition of COX-2 activity by NS-398 led to a significant suppression of this antimigratory action. Migration was also diminished by the major COX-2 product PGE(2) and by recombinant TIMP-1. Experiments using selective E prostanoid (EP) receptor agonists and antagonists revealed that decreased migration by PGE(2), THC and MA was mediated via EP(2) and EP(4) receptors. Finally, the cannabinoid-mediated increases of TIMP-1 levels were abolished by NS-398, and PGE(2) was shown to elicit a concentration-dependent increase of TIMP-1. Collectively, this data demonstrate a COX-2-dependent upregulation of TIMP-1 conferring the antimigratory action of cannabinoids. A decreased migration reducing TM cell loss in glaucoma might be involved in the antiglaucomatous action of cannabinoids.

3-Heterocycle-phenyl N-alkylcarbamates as FAAH inhibitors: design, synthesis and 3D-QSAR studies

Carbamates are a well-established class of fatty acid amide hydrolase (FAAH) inhibitors. Here we describe the synthesis of meta-substituted phenolic N-alkyl/aryl carbamates and their in vitro FAAH inhibitory activities. The most potent compound, 3-(oxazol-2yl)phenyl cyclohexylcarbamate (2 a), inhibited FAAH with a sub-nanomolar IC(50) value (IC(50)=0.74 nM). Additionally, we developed and validated three-dimensional quantitative structure-activity relationships (QSAR) models of FAAH inhibition combining the newly disclosed carbamates with our previously published inhibitors to give a total set of 99 compounds. Prior to 3D-QSAR modeling, the degree of correlation between FAAH inhibition and in silico reactivity was also established. Both 3D-QSAR methods used, CoMSIA and GRID/GOLPE, produced statistically significant models with coefficient of correlation for external prediction (R(2) (PRED)) values of 0.732 and 0.760, respectively. These models could be of high value in further FAAH inhibitor design.

Endocannabinoids in the retina: from marijuana to neuroprotection

The active component of the marijuana plant Cannabis sativa, Delta9-tetrahydrocannabinol (THC), produces numerous beneficial effects, including analgesia, appetite stimulation and nausea reduction, in addition to its psychotropic effects. THC mimics the action of endogenous fatty acid derivatives, referred to as endocannabinoids. The effects of THC and the endocannabinoids are mediated largely by metabotropic receptors that are distributed throughout the nervous and peripheral organ systems. There is great interest in endocannabinoids for their role in neuroplasticity as well as for therapeutic use in numerous conditions, including pain, stroke, cancer, obesity, osteoporosis, fertility, neurodegenerative diseases, multiple sclerosis, glaucoma and inflammatory diseases, among others. However, there has been relatively far less research on this topic in the eye and retina compared with the brain and other organ systems. The purpose of this review is to introduce the "cannabinergic" field to the retinal community. All of the fundamental works on cannabinoids have been performed in non-retinal preparations, necessitating extensive dependence on this literature for background. Happily, the retinal cannabinoid system has much in common with other regions of the central nervous system. For example, there is general agreement that cannabinoids suppress dopamine release and presynaptically reduce transmitter release from cones and bipolar cells. How these effects relate to light and dark adaptations, receptive field formation, temporal properties of ganglion cells or visual perception are unknown. The presence of multiple endocannabinoids, degradative enzymes with their bioactive metabolites, and receptors provides a broad spectrum of opportunities for basic research and to identify targets for therapeutic application to retinal diseases.

Aqueous humor outflow effects of 2-arachidonylglycerol

This study was conducted to test the effects of 2-arachidonylglycerol (2-AG), an endocannabinoid, on aqueous humor outflow facility, to study the cellular mechanisms of 2-AG, and to investigate the possible existence and activity of monoacylgylcerol lipase (MGL), a 2-AG metabolic enzyme, in the trabecular meshwork (TM). The effects of 2-AG on aqueous humor outflow facility were measured using an anterior segment perfused organ culture model. The expression and activity of MGL in TM tissues were assessed using Western blot analysis and an enzyme activity assay respectively. 2-AG induced activation of p42/44 mitogen-activated protein (MAP) kinase was determined by Western blot analysis using an anti-phospho p42/44 MAP kinase antibody. AlexaFluor 488-labeled phalloidin staining was used to examine actin filament in cultured TM cells. Administration of 10nM of 2-AG caused a transient enhancement of aqueous humor outflow. In the presence of 100nM of LY2183240, an inhibitor of MGL, the effect of 10nM of 2-AG on outflow was prolonged by at least 4h. The 2-AG-induced enhancement of outflow was blocked by SR141716A, a CB1 antagonist, and SR144528, a CB2 antagonist. In Western blot studies, a 35kDa band representing MGL was detected on TM tissues with an anti-MGL antibody. The 2-AG enzymatic hydrolysis activity was detected in TM tissues and this activity was reduced by 70.1+/-5.3% with the addition of 100 nM of LY2183240. Treatment of trabecular meshwork cells with 10nM of 2-AG plus 100 nM LY2183240 for 5h evoked phosphorylation of p42/44 MAP kinase. The 2-AG-induced enhancement of p42/44 MAP kinase phosphorylation was blocked by pretreatment with SR141716A, SR144528, as well as PD98059, an inhibitor of the p42/44 MAP kinase pathway. In addition, the outflow-enhancing effect of 2-AG was blocked by pretreatment with PD98059. Furthermore, treatment with 2-AG plus LY2183240 caused rounding of TM cells and a reduction of actin stress fibers in TM cells. Pretreatment with SR141716A, SR144528, and PD98059 blocked these 2-AG-induced morphology and cytoskeleton changes in TM cells. In conclusion, the results from this study demonstrate that administration of 2-AG increases aqueous humor outflow facility and this effect of 2-AG is mediated through both the CB1 and CB2 cannabinoid receptors. In addition, this study reveals the existence and the activity of MGL, a 2-AG metabolizing enzyme, in the TM tissues. Furthermore, this study suggests that 2-AG-induced enhancement of outflow facility involves the p42/44 MAP kinase signaling pathway and changes in actin cytoskeletons in TM cells.

Topical WIN55212-2 alleviates intraocular hypertension in rats through a CB1 receptor mediated mechanism of action

INTRODUCTION

Systemically administered cannabinoids can reduce intraocular pressure (IOP), but produce undesirable cardiovascular and central nervous system effects. In a chronic model of ocular hypertension, we examined the efficacy of acute topical administration of WIN55212-2 (WIN) in a novel commercially available vehicle and in combination with timolol.

METHODS

IOP was chronically elevated by the surgical ligature of vortex veins in Sprague Dawley rats. IOP was measured by using Goldmann applanation tonometry. IOP, blood pressure (BP), and heart rate (HR) were measured at baseline and 30, 60, 90, and 120 min after the topical administration of WIN 1.0%, 0.25%, 0.06%, or 0.015%, the commercially available vehicle, timolol 0.5%, or a combination of WIN and timolol. SR141716 (CB1 antagonist) or SR144528 (CB2 antagonist) was administered topically 30 min before WIN to determine receptor specificity. To determine ocular and systemic penetration, 3H WIN 55212-2 was administered topically and tissues were collected at 60 and 120 min. Ocular irritation was evaluated by slit-lamp examination (SLE) at baseline and 120 min.

RESULTS

WIN significantly decreased IOP in the hypertensive eye, with no BP or HR effects. SR141716 pretreatment significantly inhibited the IOP effects of WIN 1.0% in a dose-dependent manner, while SR 144528 was not as effective. No significant additive effects were observed by combining WIN (0.5% or 1.0%) with timolol 0.5%. WIN was retained in ocular tissue with a t1/2 of 80-100 min. SLE at 120 min revealed no solvent or drug-related toxic effects.

CONCLUSIONS

In a chronic ocular hypertensive rat model, topically applied WIN is an effective, nontoxic ocular hypotensive agent with no hemodynamic side-effects. This effect was predominantly CB1 receptor mediated, but some CB2 contribution could not be ruled out.

History of cannabis and its preparations in saga, science, and sobriquet

Cannabis sativa L. is possibly one of the oldest plants cultivated by man, but has remained a source of controversy throughout its history. Whether pariah or panacea, this most versatile botanical has provided a mirror to medicine and has pointed the way in the last two decades toward a host of medical challenges from analgesia to weight loss through the discovery of its myriad biochemical attributes and the endocannabinoid system wherein many of its components operate. This study surveys the history of cannabis, its genetics and preparations. A review of cannabis usage in Ancient Egypt will serve as an archetype, while examining first mentions from various Old World cultures and their pertinence for contemporary scientific investigation. Cannabis historians of the past have provided promising clues to potential treatments for a wide array of currently puzzling medical syndromes including chronic pain, spasticity, cancer, seizure disorders, nausea, anorexia, and infectious disease that remain challenges for 21st century medicine. Information gleaned from the history of cannabis administration in its various forms may provide useful points of departure for research into novel delivery techniques and standardization of cannabis-based medicines that will allow their prescription for treatment of these intractable medical conditions.

Short- and long-term plasticity of the endocannabinoid system in neuropsychiatric and neurological disorders

The activity of the endocannabinoid system, in terms of the levels of the endocannabinoids and of cannabinoid receptors, or of the functional coupling of the latter to a biological response, undergoes to remodelling during pathological conditions. In the CNS, these changes, depending also on the nature of the disorder, can be transient or long-lasting, occur only in those tissues involved in the pathological condition and usually aim at restoring the physiological homeostasis by reducing excitotoxicity, inflammation and neuronal death. However, during chronic disorders, prolonged activation of the endocannabinoid system might also contribute to the symptoms of the pathology. Whilst acute changes of the tissue levels of the endocannabinoids reflect the "on demand" nature of their biosynthesis and release, and hence are effected mostly through regulation of the biosynthetic enzymes, chronic changes seem to be mostly due to longer-lasting alterations in the expression of anabolic and catabolic enzymes. The possibility of obtaining therapeutic advantage from endocannabinoid plasticity in neuropsychiatric and neurological disorders is discussed in this review article.

Metabolically labile cannabinoid esters: A ‘soft drug’ approach for the development of cannabinoid-based therapeutic drugs

Biphenylic ester derivatives, designed by using a 'soft-drug' approach, proved to possess good binding properties toward cannabinoid CB(1) and CB(2) receptors and, at the same time, their metabolically labile ester portion would promote a rapid systemic inactivation. This may constitute a possible solution to the psychotropic side effects encountered when cannabinoids are therapeutically employed as local analgesic or antiglaucoma agents.

Design, synthesis, and in vitro evaluation of carbamate derivatives of 2-benzoxazolyl- and 2-benzothiazolyl-(3-hydroxyphenyl)-methanones as novel fatty acid amide hydrolase inhibitors

Fatty acid amide hydrolase (FAAH) is an intracellular serine hydrolase, which catalyzes the hydrolysis of the endocannabinoid N-arachidonoylethanolamide to arachidonic acid and ethanolamine. FAAH also hydrolyzes another endocannabinoid, 2-arachidonoylglycerol (2-AG). However, 2-AG has been assumed to be hydrolyzed mainly by monoacylglycerol lipase (MAGL) or a MAGL-like enzyme. Inhibition of FAAH or MAGL activity might lead to beneficial effects in many physiological disorders such as pain, inflammation, and anxiety due to increased endocannabinoid-induced activation of cannabinoid receptors CB1 and CB2. In the present study, a total of 34 novel compounds were designed, synthesized, characterized, and tested against FAAH and MAGL-like enzyme activity. Altogether, 16 compounds were found to inhibit FAAH with half-maximal inhibition concentrations (IC50) between 28 and 380 nM. All the active compounds belong to the structural family of carbamates. Compounds 14 and 18 were found to be the most potent FAAH inhibitors, which may serve as lead structures for novel FAAH inhibitors.

Oxaza adamantyl cannabinoids. A new class of cannabinoid receptor probes

The preparation of C3 oxaza adamantyl cannabinoids has been described starting from phloroglucinol. Straightforward manipulations of the aromatic ring lead to a bromononaflate that is a benzyne precursor and that serves as a common intermediate for the synthesis of diverse C3-substituted tricyclic cannabinoids. Generation of the benzyne in the presence of an oxaza adamantyl amide anion results in efficient and regiospecific addition to C3 of the aromatic ring. This represents an attractive strategy for the synthesis of classical tricyclic cannabinoids that bear a modified aromatic appendage. The oxaza adamantyl cannabinoids that have been prepared represent a new class of ligands for the CB1 and CB2 receptors.

Fixed-combination and emerging glaucoma therapies

Ocular hypotensive agents are the only approved pharmacotherapy for glaucoma. Despite significant advances during the past two decades, a large proportion of glaucoma patients require more than one drug. The most recent additions to the armamentarium of antiglaucoma drugs are fixed-combination products for the glaucoma patient who is insufficiently responsive to monotherapy. Fixed-combination products have the combined efficacy of two ocular hypotensive drugs, and the convenience of a two-drug treatment regimen in a single container, which may aid patient adherence to treatment. Available fixed-combination products consist of timolol 0.5% as an invariant with brimonidine 0.2%, dorzolamide 2%, travoprost 0.004%, latanoprost 0.005% or bimatoprost 0.03%. Research on more advanced antiglaucoma medications continues. Promising new directions appear to be the Rho-kinase inhibitors, microtubule-disrupting agents, serotonergics and cannabimimetics. Efforts continue to improve existing antiglaucoma drugs in an attempt to design second-generation cholinomimetics, adrenergics, prostaglandins and prostamides.

Anti-inflammatory property of the cannabinoid receptor-2-selective agonist JWH-133 in a rodent model of autoimmune uveoretinitis

Previous studies have shown that cannabinoids have anti-inflammatory and immune-modulating effects, but the precise mechanisms of action remain to be elucidated. In this study, we investigated the effect of JWH 133, a selective agonist for cannabinoid receptor 2, the main receptor expressed on immune cells, in a model of autoimmune disease, experimental autoimmune uveoretinitis (EAU). JWH 133 suppressed EAU in a dose-dependent manner (0.015-15 mg/kg), and the suppressive effect could be achieved in the disease-induction stage and the effector stage. Leukocytes from mice, which had been treated with JWH 133, had diminished responses to retinal peptide and mitogen Con A stimulation in vitro. In vivo JWH 133 treatment also abrogated leukocyte cytokine/chemokine production. Further in vitro studies indicated that JWH 133 down-regulated the TLR4 via Myd88 signal transduction, which may be responsible for its moderate, suppressive effect on antigen presentation. In vivo JWH 133 treatment (1 mg/kg) also suppressed leukocyte trafficking (rolling and infiltration) in inflamed retina as a result of an effect on reducing adhesion molecules CD162 (P-selectin glycoprotein ligand 1) and CD11a (LFA-1) expression on T cells. In conclusion, the cannabinoid agonist JWH 133 has a high in vivo, anti-inflammatory property and may exert its effect via inhibiting the activation and function of autoreactive T cells and preventing leukocyte trafficking into the inflamed tissue.

The cannabinoid system and its pharmacological manipulation--a review, with emphasis upon the uptake and hydrolysis of anandamide

Although cannabis has been used both recreationally and for medicinal purposes since ancient times, it was not until the 1990s that the receptors responsible for many of the actions of Delta(9)-tetrahydrocannabinol, the main psychoactive ingredient of cannabis, were cloned. Since then, our knowledge of the endogenous cannabinoid system, its physiology, pharmacology and therapeutic potential have expanded enormously. In the present review, the cannabinoid system is described, with particular emphasis on the mechanisms of removal and metabolism of the endocannabinoid signalling molecule anandamide. The current literature shows that cells can accumulate anandamide, and that this process can be disrupted pharmacologically, but that the nature of the mechanism(s) involved remains a matter of some debate. The main enzyme for the hydrolysis of anandamide, fatty acid amide hydrolase, is well characterized, and molecules selectively inhibiting this enzyme have potential therapeutic utility in a number of areas, in particular for the treatment of pain conditions.

Changes in endocannabinoid and palmitoylethanolamide levels in eye tissues of patients with diabetic retinopathy and age-related macular degeneration

Cannabinoid receptors and the endocannabinoids (anandamide (N-arachidonoylethanolamine--AEA) and 2-arachidonoylglycerol (2-AG)), as well as the AEA congener, palmitoylethanolamide (PEA), are involved in ocular physiology. We measured endocannabinoid and PEA levels by isotope-dilution liquid chromatography-mass spectrometric analysis in post-mortem eye tissues of patients with diabetic retinopathy (DR) or age-related macular degeneration (AMD). In eyes with DR, significantly enhanced levels of AEA were found in the retina ( approximately 1.8-fold), ciliary body ( approximately 1.5-fold) and, to a lesser extent, cornea ( approximately 1.3-fold). Surprisingly, 2-AG levels were significantly higher ( approximately 3-fold) only in the iris, whereas PEA levels only slightly increased ( approximately 1.3-fold) in the ciliary body. In eyes with AMD, significantly enhanced levels of AEA were found in the choroid ( approximately 1.3-fold), ciliary body ( approximately 1.4-fold) and cornea ( approximately 1.4-fold), whereas in the retina only a trend towards an increase ( approximately 1.5-fold) was observed. The tissue- and disease-selective nature of the changes observed suggests that the compounds analyzed here may play different roles in the control of eye function under different pathological conditions.

Effect of sublingual application of cannabinoids on intraocular pressure: a pilot study

PURPOSE

The purpose of this study was to assess the effect on intraocular pressure (IOP) and the safety and tolerability of oromucosal administration of a low dose of delta-9-tetrahydrocannabinol (Delta-9-THC) and cannabidiol (CBD).

PATIENTS AND METHODS

A randomized, double-masked, placebo-controlled, 4 way crossover study was conducted at a single center, using cannabis-based medicinal extract of Delta-9-THC and CBD. Six patients with ocular hypertension or early primary open angle glaucoma received a single sublingual dose at 8 AM of 5 mg Delta-9-THC, 20 mg CBD, 40 mg CBD, or placebo. Main outcome measure was IOP. Secondary outcomes included visual acuity, vital signs, and psychotropic effects.

RESULTS

Two hours after sublingual administration of 5 mg Delta-9-THC, the IOP was significantly lower than after placebo (23.5 mm Hg vs. 27.3 mm Hg, P=0.026). The IOP returned to baseline level after the 4-hour IOP measurement. CBD administration did not reduce the IOP at any time. However, the higher dose of CBD (40 mg) produced a transient elevation of IOP at 4 hours after administration, from 23.2 to 25.9 mm Hg (P=0.028). Vital signs and visual acuity were not significantly changed. One patient experienced a transient and mild paniclike reaction after Delta-9-THC administration.

CONCLUSIONS

A single 5 mg sublingual dose of Delta-9-THC reduced the IOP temporarily and was well tolerated by most patients. Sublingual administration of 20 mg CBD did not reduce IOP, whereas 40 mg CBD produced a transient increase IOP rise.

Ocular hypotensive effects of an intratracheally delivered liposomal delta9-tetrahydrocannabinol preparation in rats

This study investigated the effect of an intratracheal (i.t.) administration of a liposome-entrapped Delta9-tetrahydrocannabinol (LTHC) preparation on intraocular pressure (IOP) in nonanaesthetized Brown Norway rats. The ocular hypotensive effects of i.t. LTHC were compared to that of intraperitoneal (i.p.) LTHC administration. All i.t. LTHC doses >0.05 mg/kg significantly decreased IOP (P < 0.05) within 30 min of administration, and doses of i.t. LTHC >0.1 mg/kg decreased IOP within 15 min of administration. A maximal reduction in IOP of 2.32 +/- 0.27 mmHg (n = 4) was seen with 1.0 mg/kg of i.t. LTHC. In comparison, no significant IOP drop was apparent prior to 30 min with all doses (0.01-1.0 mg/kg) of i.p. LTHC tested, although a similar maximum drop in IOP (2.15 +/- 0.12 mmHg; n = 8) was obtained with 1.0 mg/kg of LTHC. The ED(50) for i.t. and i.p. LTHC was 0.08 mg/kg and 0.12 mg/kg, respectively. The IOP-lowering effects of i.p. LTHC (0.2 mg/kg) were reduced by 14% and 80% by 0.25 mg/kg (n = 6) and 2.5 mg/kg (n = 6), respectively, of the CB1R antagonist, SR141716A. In conclusion, i.t. LTHC was superior to i.p. LTHC in producing a more rapid and potent decrease in IOP. The IOP-lowering effect of LTHC was blocked by the CB1R-selective antagonist, SR141716A, suggesting that CB1Rs contribute to the ocular hypotensive effect of Delta9-tetrahydrocannabinol.

Inhibition of potassium- and ischemia-evoked [3H] D-aspartate release from isolated bovine retina by cannabinoids

We investigated the effect of cannabinoids on potassium chloride (K+)- and ischemia-induced [3H]D-aspartate release from isolated bovine retinae. The superfusion method was employed for studies of [3H]-neurotransmitter release. Cannabinoid receptor CB1 agonists, but not the CB2 agonist JWH 015, inhibited K+ -induced [3H]D-aspartate release from bovine retinae with the following rank order of activity: anandamide > ACEA > methanandamide > WIN 55,212-2. In the ischemic model, the rank order of activity was as follows: methanandamide > ACEA > WIN 55,212-2. The CB1 receptor antagonist AM 251 blocked inhibitory responses produced by cannabinoids in both experimental conditions. In conclusion, cannabinoids inhibit evoked [3H]D-aspartate release from isolated bovine retinae via an effect on CB1 receptors.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.

Synthesis, cannabinoid receptor activity, and enzymatic stability of reversed amide derivatives of arachidonoyl ethanolamide

Retroanandamide (2f) and its 10 analogues (1a-e, 2a-e) were synthesized and evaluated for the cannabinoid receptor activation by a [35S]GTPgammaS binding assay using rat cerebellar membranes, and Chinese hamster ovary cell membranes expressing human CB2 receptors. The primary goal of the study was to develop cannabinoid receptor agonists having improved enzymatic stability compared to endogenous N-arachidonoyl ethanolamide (AEA). Furthermore, by reversing the amide bond of AEA, the formation of arachidonic acid would be prevented. Finally, an effect of the carbonyl carbon position on the cannabinoid receptor activity was explored by synthesizing retroanandamide analogues having different chain lengths (1a-e, C19; 2a-f, C20). All the synthesized compounds, except 2c, behaved as partial agonists for the both cannabinoid receptors. In rat brain homogenate, the reversed amides possessed significantly higher stability against FAAH induced degradation than AEA. Therefore, the reversed amide analogues of AEA may serve as enzymatically stable structural basis for the drug design based on the endogenous cannabinoids.

Cannabinoids in medicine: A review of their therapeutic potential

In order to assess the current knowledge on the therapeutic potential of cannabinoids, a meta-analysis was performed through Medline and PubMed up to July 1, 2005. The key words used were cannabis, marijuana, marihuana, hashish, hashich, haschich, cannabinoids, tetrahydrocannabinol, THC, dronabinol, nabilone, levonantradol, randomised, randomized, double-blind, simple blind, placebo-controlled, and human. The research also included the reports and reviews published in English, French and Spanish. For the final selection, only properly controlled clinical trials were retained, thus open-label studies were excluded. Seventy-two controlled studies evaluating the therapeutic effects of cannabinoids were identified. For each clinical trial, the country where the project was held, the number of patients assessed, the type of study and comparisons done, the products and the dosages used, their efficacy and their adverse effects are described. Cannabinoids present an interesting therapeutic potential as antiemetics, appetite stimulants in debilitating diseases (cancer and AIDS), analgesics, and in the treatment of multiple sclerosis, spinal cord injuries, Tourette's syndrome, epilepsy and glaucoma.

CANNABINOID RECEPTORS AS THERAPEUTIC TARGETS

CB1 and CB2 cannabinoid receptors are the primary targets of endogenous cannabinoids (endocannabinoids). These G protein-coupled receptors play an important role in many processes, including metabolic regulation, craving, pain, anxiety, bone growth, and immune function. Cannabinoid receptors can be engaged directly by agonists or antagonists, or indirectly by manipulating endocannabinoid metabolism. In the past several years, it has become apparent from preclinical studies that therapies either directly or indirectly influencing cannabinoid receptors might be clinically useful. This review considers the components of the endocannabinoid system and discusses some of the most promising endocannabinoid-based therapies.

In-vitro corneal permeation of cannabinoids and their water-soluble phosphate ester prodrugs

Topically administered cannabinoids have been shown to reduce intraocular pressure by interacting with the ocular cannabinoid receptor. Most cannabinoids have very poor aqueous solubility, which limits their pharmaceutical development and usefulness. In this study, permeation of three cannabinoids (arachidonylethanolamide, R-methanandamide and noladin ether) and their water-soluble phosphate ester prodrugs across isolated rabbit cornea was investigated in vitro. Hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was used to solubilize the parent cannabinoids in permeation studies to achieve the required concentration in donor and receiving cells. Highest fluxes were obtained with lipophilic parent compounds administered with HP-beta-CD, and the fluxes of phosphate esters were 45-70% that of their corresponding parent compounds. Phosphate esters hydrolysed on the surface of the cornea or during the permeation to release the lipophilic parent compound, which further permeated the cornea. No phosphate esters were detected on the endothelial side of the cornea. Although the phosphate esters had lower fluxes than their corresponding parent compounds in these HP-beta-CD formulations, the results are promising and the fluxes of phosphate esters are significantly higher than the fluxes of parent compounds administered as a suspension (due to their low aqueous solubility) without HP-beta-CD.

Evidence for the use of nutritional supplements and herbal medicines in common eye diseases

PURPOSE

To provide a perspective by reviewing the evidence for the role of nutritional supplements and herbal medicines in the common causes of visual impairment.

DESIGN

Retrospective literature review.

METHODS

Published studies and information found in PubMed, International Bibliographic Information of Dietary Supplements, and selected websites were reviewed for the role of nutritional and herbal medicines in the treatment of age-related macular degeneration, cataract, diabetic retinopathy, and glaucoma. The studies were evaluated systematically for their study design, study population, benefits, risks, biases, and criteria for the categorization of the level of evidence.

RESULTS

The available evidence does support the use of certain vitamins and minerals in patients with certain forms of age-related macular degeneration. For cataracts, the available evidence does not support these supplements to prevent or treat cataracts in healthy individuals. For diabetic retinopathy and glaucoma, the available evidence does not support the use of these supplements. In the category of herbal medicines, the available evidence does not support the use of herbal medicines for any of these ocular diseases.

CONCLUSION

Because of the widespread use of nutritional supplements and herbal medicines, ophthalmologists should be aware of their use so that they can inform patients properly when the supplements and herbal medicine are being used for eye disease.

R(+)-Methanandamide and Other Cannabinoids Induce the Expression of Cyclooxygenase-2 and Matrix Metalloproteinases in Human Nonpigmented Ciliary Epithelial Cells

Prostaglandins (PGs) and matrix metalloproteinases (MMP) have been implicated in lowering intraocular pressure (IOP) by facilitating aqueous humor outflow. A possible role of cyclooxygenase-2 (COX-2) in this process was emphasized by findings showing an impaired COX-2 expression in the nonpigmented ciliary epithelium (NPE) of patients with primary open-angle glaucoma. Using human NPE cells, the present study therefore investigated the effect of the IOP-lowering cannabinoid R(+)-methanandamide [R(+)-MA] on the expression of COX-2 and different MMPs and tissue inhibitors of MMPs (TIMPs). R(+)-MA led to a concentration- and time-dependent increase of COX-2 mRNA expression. R(+)-MA-induced COX-2 expression was accompanied by time-dependent phosphorylations of p38 mitogen-activated protein kinase (MAPK) and p42/44 MAPK and was abrogated by inhibitors of both pathways. Moreover, R(+)-MA increased the mRNA and protein expression of MMP-1, MMP-3, MMP-9, and TIMP-1 but not that of MMP-2 and TIMP-2. Inhibition of COX-2 activity with NS-398 [N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulfonamide] was associated with a virtually complete suppression of R(+)-MA-induced MMP-9 and TIMP-1 expression. Consistent with these data, MMP-9 and TIMP-1 expression was also induced by PGE2, a major COX-2 product. Two other COX-2-inducing cannabinoids, anandamide and Delta9-tetrahydrocannabinol, caused the same pattern of MMP and TIMP expression as R(+)-MA both in the absence and presence of NS-398. Altogether, cannabinoids induce the production of several outflow-facilitating mediators in the human NPE. Our results further imply an involvement of COX-2-dependent PGs in MMP-9 and TIMP-1 expression. In conclusion, stimulation of intraocular COX-2 and MMP expression may represent a potential mechanism contributing to the IOP-lowering action of different cannabinoids.

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

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

Cannabis and endocannabinoid modulators: Therapeutic promises and challenges

The discovery that botanical cannabinoids such as delta-9 tetrahydrocannabinol exert some of their effect through binding specific cannabinoid receptor sites has led to the discovery of an endocannabinoid signaling system, which in turn has spurred research into the mechanisms of action and addiction potential of cannabis on the one hand, while opening the possibility of developing novel therapeutic agents on the other. This paper reviews current understanding of CB1, CB2, and other possible cannabinoid receptors, their arachidonic acid derived ligands (e.g. anandamide; 2 arachidonoyl glycerol), and their possible physiological roles. CB1 is heavily represented in the central nervous system, but is found in other tissues as well; CB2 tends to be localized to immune cells. Activation of the endocannabinoid system can result in enhanced or dampened activity in various neural circuits depending on their own state of activation. This suggests that one function of the endocannabinoid system may be to maintain steady state. The therapeutic action of botanical cannabis or of synthetic molecules that are agonists, antagonists, or which may otherwise modify endocannabinoid metabolism and activity indicates they may have promise as neuroprotectants, and may be of value in the treatment of certain types of pain, epilepsy, spasticity, eating disorders, inflammation, and possibly blood pressure control.

A tale of two cannabinoids: the therapeutic rationale for combining tetrahydrocannabinol and cannabidiol

This study examines the current knowledge of physiological and clinical effects of tetrahydrocannabinol (THC) and cannabidiol (CBD) and presents a rationale for their combination in pharmaceutical preparations. Cannabinoid and vanilloid receptor effects as well as non-receptor mechanisms are explored, such as the capability of THC and CBD to act as anti-inflammatory substances independent of cyclo-oxygenase (COX) inhibition. CBD is demonstrated to antagonise some undesirable effects of THC including intoxication, sedation and tachycardia, while contributing analgesic, anti-emetic, and anti-carcinogenic properties in its own right. In modern clinical trials, this has permitted the administration of higher doses of THC, providing evidence for clinical efficacy and safety for cannabis based extracts in treatment of spasticity, central pain and lower urinary tract symptoms in multiple sclerosis, as well as sleep disturbances, peripheral neuropathic pain, brachial plexus avulsion symptoms, rheumatoid arthritis and intractable cancer pain. Prospects for future application of whole cannabis extracts in neuroprotection, drug dependency, and neoplastic disorders are further examined. The hypothesis that the combination of THC and CBD increases clinical efficacy while reducing adverse events is supported.

Effects of RM-β-CD on sublingual bioavailability of Δ9-tetrahydrocannabinol in rabbits

The purpose of the present study was to develop novel cyclodextrin-containing sublingual formulations of cannabinoids. Complexation of model cannabinoids, Delta(9)-tetrahydrocannabinol (THC) and cannabidiol (CBD), with randomly methylated beta-cyclodextrin (RM-beta-CD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD), were studied by the phase-solubility method. Due to better complexation efficiency, RM-beta-CD was selected for further studies. Solid THC/RM-beta-CD and CBD/RM-beta-CD complexes were prepared by freeze-drying. The dissolutions of both THC and CBD in the presence and absence of RM-beta-CD were determined. THC was selected for in vivo studies: the pharmacokinetics of THC after both sublingual and oral administrations of ethanolic THC and THC/RM-beta-CD complex solutions were studied in rabbits. The aqueous solubility of CBD and THC increased as a function of CD concentration, showing A(L)- and A(P)-type diagrams for HP-beta-CD and RM-beta-CD, respectively. Dissolution rates of THC/RM-beta-CD and CBD/RM-beta-CD complexes were significantly (p < 0.05) higher than those of plain THC and plain CBD, respectively. The absolute bioavailability (F) of THC decreased in the following order: sublingual THC/RM-beta-CD solution (F = 12.1+/-1.4%; mean+/-S.D.; n = 4) > oral THC/RM-beta-CD solution (F = 4.0+/-6.0%) > or = sublingual ethanolic THC solution (F = 3.8+/-2.8%) > oral ethanolic THC solution (F = 1.3+/-1.4%). These results demonstrate that RM-beta-CD increases both the aqueous solubility and dissolution rate of these cannabinoids, making the development of novel sublingual formulation possible. These results also suggest that the sublingual administration of a THC/RM-beta-CD complex substantially increases the bioavailability of THC in rabbits.

Finding of endocannabinoids in human eye tissues: Implications for glaucoma

Cannabinoid CB(1) receptors are involved in ocular physiology and may regulate intraocular pressure (IOP). However, endocannabinoid levels in human ocular tissues of cornea, iris, ciliary body, retina, and choroid from normal and glaucomatous donors have not been investigated. Anandamide (N-arachidonoylethanolamine; AEA), 2-arachidonoylglycerol (2-AG), and the anandamide congener, palmitoylethanolamide (PEA), were detected in all the human tissues examined. In eyes from patients with glaucoma, significantly decreased 2-AG and PEA levels were detected in the ciliary body, an important tissue in the regulation of IOP. The findings suggest that these endogenous compounds may have a role in this disease, particularly with respect to regulation of IOP.

Human studies of cannabinoids and medicinal cannabis

Cannabis has been known as a medicine for several thousand years across many cultures. It reached a position of prominence within Western medicine in the nineteenth century but became mired in disrepute and legal controls early in the twentieth century. Despite unremitting world-wide suppression, recreational cannabis exploded into popular culture in the 1960s and has remained easily obtainable on the black market in most countries ever since. This ready availability has allowed many thousands of patients to rediscover the apparent power of the drug to alleviate symptoms of some of the most cruel and refractory diseases known to humankind. Pioneering clinical research in the last quarter of the twentieth century has given some support to these anecdotal reports, but the methodological challenges to human research involving a pariah drug are formidable. Studies have tended to be small, imperfectly controlled, and have often incorporated unsatisfactory synthetic cannabinoid analogues or smoked herbal material of uncertain composition and irregular bioavailability. As a result, the scientific evaluation of medicinal cannabis in humans is still in its infancy. New possibilities in human research have been opened up by the discovery of the endocannabinoid system, a rapidly expanding knowledge of cannabinoid pharmacology, and a more sympathetic political environment in several countries. More and more scientists and clinicians are becoming interested in exploring the potential of cannabis-based medicines. Future targets will extend beyond symptom relief into disease modification, and already cannabinoids seem to offer particular promise in the treatment of certain inflammatory and neurodegenerative conditions. This chapter will begin with an outline of the development and current status of legal controls pertaining to cannabis, following which the existing human research will be reviewed. Some key safety issues will then be considered, and the chapter will conclude with some suggestions as to future directions for human research.

[Endocannabinoids in the central nervous system]

The major psychoactive component of cannabis derivatives, delta9-THC, activates two G-protein coupled receptors: CB1 and CB2. Soon after the discovery of these receptors, their endogenous ligands were identified: lipid metabolites of arachidonic acid, named endocannabinoids. The two major main and most studied endocannabinoids are anandamide and 2-arachidonyl-glycerol. The CB1 receptor is massively expressed through-out the central nervous system whereas CB2 expression seems restricted to immune cells. Following endocannabinoid binding, CB1 receptors modulate second messenger cascades (inhibition of adenylate cyclase, activation of mitogen-activated protein kinases and of focal-adhesion kinases) as well as ionic conductances (inhibition of voltage-dependent calcium channels, activation of several potassium channels). Endocannabinoids transiently silence synapses by decreasing neurotransmitter release, play major parts in various forms of synaptic plasticity because of their ability to behave as retrograde messengers and activate non-cannabinoid receptors (such as vanilloid receptor type-1), illustrating the complexity of the endocannabinoid system. The diverse cellular targets of endocannabinoids are at the origin of the promising therapeutic potentials of the endocannabinoid system.

Cannabis improves night vision: a case study of dark adaptometry and scotopic sensitivity in kif smokers of the Rif mountains of northern Morocco

Previous reports have documented an improvement in night vision among Jamaican fishermen after ingestion of a crude tincture of herbal cannabis, while two members of this group noted that Moroccan fishermen and mountain dwellers observe an analogous improvement after smoking kif, sifted Cannabis sativa mixed with tobacco (Nicotiana rustica). Field-testing of night vision has become possible with a portable device, the LKC Technologies Scotopic Sensitivity Tester-1 (SST-1). This study examines the results of double-blinded graduated THC administration 0-20 mg (as Marinol) versus placebo in one subject on measures of dark adaptometry and scotopic sensitivity. Analogous field studies were performed in Morocco with the SST-1 in three subjects before and after smoking kif. In both test situations, improvements in night vision measures were noted after THC or cannabis. It is believed that this effect is dose-dependent and cannabinoid-mediated at the retinal level. Further testing may assess possible clinical application of these results in retinitis pigmentosa or other conditions.

Cannabinoid agonists induce contractile responses through Gi/o-dependent activation of phospholipase C in the bovine ciliary muscle

This study was undertaken to investigate the effect of some cannabinoid agonists on the bovine ciliary muscle. Both anandamide and CP 55,940 (cis-3-(2-hydroxy-4-(1,1-dimethyl heptyl) phenyl)-trans-4-(3-hydroxypropyl) cyclohexanol) produced a concentration-dependent contractile response in ciliary muscle. These responses were inhibited by SR 141716A (N-[piperidin-1-yl]-5-(4-cholophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide) (0.1 and 1 microM) but not by SR 144528 (N-[1S)-endo-1,3,3-trimethyl bicyclo[2.2.1] heptan-2-yl] 5-(4-chloro-3-methylphenyl)-1-(4 methoxy benzyl)-pyrazole-3-carboxamide) (1 and 10 microM). A preincubation with G(i/o) protein inhibitor pertussis toxin (500 ng/ml) for 20 min inhibited the contractile action of anandamide and CP 55,940. In addition, the phospholipase C inhibitor U73122 (1[6-[[(17 beta)-3-methoxyestra-1,3,5(10)-trien-17-yl] amino] hexyl]-1H-pyrrole-2,5-dione) blocked the anandamide- and CP 55,940-induced contractions, whereas the protein kinase C activator, phorbol 12,13 dibutyrate (PDBu) significantly potentiated the contractions evoked by cannabinoid receptor agonists. We evaluated the binding of [(3)H]CP 55,940, which specifically labelled a single class of cannabinoid sites with affinity in low subnanomolar range (K(d)=0.6 nM) and the maximal number of binding sites of 1243 fmol/mg protein. Binding of [(3)H]CP 55,940 was inhibited by ligands having a major selectivity for cannabinoid (CB(1)) receptors. These findings provide strong evidence of the involvement of cannabinoid CB(1) receptors promoting contraction in the bovine ciliary muscle. Furthermore, the action of cannabinoid receptor agonists appears to be mediated via phospholipase C. These data also contribute to elucidate the cannabinoid CB(1) receptor pivotal role in the modulation of intraocular pressure and to show that cannabinoid receptor agonists may be regarded as potential antiglaucoma agents.

Cannabinoids and glaucoma

Glaucoma is one of the leading causes of blindness in the world. In spite of the diverse therapeutic possibilities, new and better treatments for glaucoma are highly desirable. Cannabinoids effectively lower the intraocular pressure (IOP) and have neuroprotective actions. Thus, they could potentially be useful in the treatment of glaucoma. The purpose of this article is to provide the reader with an overview of the latest achievements in research into the potential use of cannabinoids for glaucoma.

Medical marijuana initiatives : are they justified? How successful are they likely to be?

The principal constituent of cannabis, Delta(9)-tetrahydrocannabinol (THC), is moderately effective in treating nausea and vomiting, appetite loss, and acute and chronic pain. Oral THC (dronabinol) and the synthetic cannabinoid, nabilone, have been registered for medical use in the US and UK, but they have not been widely used because patients find it difficult to titrate doses of these drugs. Advocates for the medical use of cannabis argue that patients should be allowed to smoke cannabis to relieve these above-mentioned symptoms. Some US state governments have legislated to allow the medical prescription of cannabis, but the US federal government has tried to prevent patients from obtaining cannabis and threatened physicians who prescribe it with criminal prosecution or loss of their licence to practise. In the UK and Australia, committees of inquiry have recommended medical prescription (UK) and exemption from criminal prosecution (New South Wales, Australia), but governments have not accepted these recommendations. The Canadian government allows an exemption from criminal prosecution to patients with specified medical conditions. It has recently legislated to provide cannabis on medical prescription to registered patients, but this scheme so far has not been implemented. Some advocates argue that legalising cannabis is the only way to ensure that patients can use it for medical purposes. However, this would be contrary to international drug control treaties and is electorally unpopular. The best prospects for the medical use of cannabinoids lie in finding ways to deliver THC that do not involve smoking and in developing synthetic cannabinoids that produce therapeutic effects with a minimum of psychoactive effects. While awaiting these developments, patients with specified medical conditions could be given exemptions from criminal prosecution to grow cannabis for their own use, at their own risk.

The therapeutic potential of cannabis

Research of the cannabinoid system has many similarities with that of the opioid system. In both instances, studies into drug-producing plants led to the discovery of an endogenous control system with a central role in neurobiology. Few compounds have had as much positive press from patients as those of the cannabinoid system. While these claims are investigated in disorders such as multiple sclerosis spasticity and pain, basic research is discovering interesting members of this family of compounds that have previously unknown qualities, the most notable of which is the capacity for neuroprotection. Large randomised clinical trials of the better known compounds are in progress. Even if the results of these studies are not as positive as many expect them to be, that we are only just beginning to appreciate the huge therapeutic potential of this family of compounds is clear.