Category Archives: Glaucoma

Turning Down the Thermostat: Modulating the Endocannabinoid System in Ocular Inflammation and Pain.

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“The endocannabinoid system (ECS) has emerged as an important regulator of both physiological and pathological processes. Notably, this endogenous system plays a key role in the modulation of pain and inflammation in a number of tissues.

The components of the ECS, including endocannabinoids, their cognate enzymes and cannabinoid receptors, are localized in the eye, and evidence indicates that ECS modulation plays a role in ocular disease states.

Of these diseases, ocular inflammation presents a significant medical problem, given that current clinical treatments can be ineffective or are associated with intolerable side-effects. Furthermore, a prominent comorbidity of ocular inflammation is pain, including neuropathic pain, for which therapeutic options remain limited.

Recent evidence supports the use of drugs targeting the ECS for the treatment of ocular inflammation and pain in animal models; however, the potential for therapeutic use of cannabinoid drugs in the eye has not been thoroughly investigated at this time.

This review will highlight evidence from experimental studies identifying components of the ocular ECS and discuss the functional role of the ECS during different ocular inflammatory disease states, including uveitis and corneal keratitis.

Candidate ECS targeted therapies will be discussed, drawing on experimental results obtained from both ocular and non-ocular tissue(s), together with their potential application for the treatment of ocular inflammation and pain.”

https://www.ncbi.nlm.nih.gov/pubmed/27695415

Important role of endocannabinoid signaling in the development of functional vision and locomotion in zebrafish.

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“The developmental role of the endocannabinoid system still remains to be fully understood.

Here, we report the presence of a complete endocannabinoid system during zebrafish development and show that the genes that code for enzymes that catalyze the anabolism and catabolism (mgll and dagla) of the endocannabinoid, 2-AG (2-arachidonoylglycerol), as well as 2-AG main receptor in the brain, cannabinoid receptor type 1, are coexpressed in defined regions of axonal growth.

By using morpholino-induced transient knockdown of the zebrafish Daglα homolog and its pharmacologic rescue, we suggest that synthesis of 2-AG is implicated in the control of axon formation in the midbrain-hindbrain region and that animals that lack Daglα display abnormal physiological behaviors in tests that measure stereotyped movement and motion perception.

Our results suggest that the well-established role for 2-AG in axonal outgrowth has implications for the control of vision and movement in zebrafish and, thus, is likely common to all vertebrates.”

http://www.ncbi.nlm.nih.gov/pubmed/27623930

Cannabinoid 2 receptor is a novel anti-inflammatory target in experimental proliferative vitreoretinopathy.

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“Proliferative vitreoretinopathy (PVR) can develop after ocular trauma or inflammation and is a common complication of surgery to correct retinal detachment.

Currently, there are no pharmacological treatments for PVR.

Cannabinoids acting at cannabinoid 2 receptor (CB2R) can decrease inflammation and fibrosis.

The objective of this study was to examine the anti-inflammatory actions of CB2R as a candidate novel therapeutic target in experimental PVR.

In conclusion, our results indicate that intervention at early stage PVR with CB2R agonists reduces ocular inflammation and disease severity.

CB2R may represent a therapeutic target to prevent PVR progression and vision loss.”

http://www.ncbi.nlm.nih.gov/pubmed/27569993

Endocannabinoid signaling enhances visual responses through modulation of intracellular chloride levels in retinal ganglion cells.

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“Type 1 cannabinoid receptors (CB1Rs) are widely expressed in the vertebrate retina but the role of endocannabinoids in vision is not fully understood. Here we identified a novel mechanism underlying a CB1R-mediated increase in retinal ganglion cell (RGC) intrinsic excitability acting through AMPK-dependent inhibition of NKCC1 activity.

Clomeleon imaging and patch clamp recordings revealed that inhibition of NKCC1 downstream of CB1R activation reduces intracellular Cl– levels in RGCs, hyperpolarizing the resting membrane potential. We confirmed that such hyperpolarization enhances RGC action potential firing in response to subsequent depolarization, consistent with the increased intrinsic excitability of RGCs observed with CB1R activation.

Using a dot avoidance assay in freely swimming Xenopus tadpoles we demonstrate that CB1R activation markedly improves visual contrast sensitivity under low light conditions.

These results highlight a role for endocannabinoids in vision, and present a novel mechanism for cannabinoid modulation of neuronal activity through Cl– regulation.”

http://www.ncbi.nlm.nih.gov/pubmed/27501334

Scotopic vision in the monkey is modulated by the G protein-coupled receptor 55.

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“The endogenous cannabinoid system plays important roles in the retina of mice and monkeys via their classic CB1 and CB2 receptors.

We have previously reported that the G protein-coupled receptor 55 (GPR55), a putative cannabinoid receptor, is exclusively expressed in rod photoreceptors in the monkey retina, suggesting its possible role in scotopic vision.

These results support the hypothesis that GPR55 plays an instrumental role in mediating scotopic vision.”

http://www.ncbi.nlm.nih.gov/pubmed/27485069

Nonpsychotropic cannabinoids, abnormal cannabidiol and canabigerol-dimethyl heptyl, act at novel cannabinoid receptors to reduce intraocular pressure.

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“The objective of our study was to examine the pharmacology of the intraocular pressure (IOP)-lowering actions of the behaviorally inactive cannabinoids, abnormal cannabidiol (abn-CBD), and a cannabigerol analog, cannabigerol-dimethyl heptyl (CBG-DMH), in comparison to that of the nonselective cannabinoid 1 receptor (CB(1)R) and CB(2)R agonist, WIN55,212-2, in Brown Norway rats.

These results indicate that both CBG-DMH and abn-CBD have the potential for further investigation as novel ocular hypotensive cannabinoids devoid of CB(1)R-mediated side-effects.”

http://www.ncbi.nlm.nih.gov/pubmed/21770780

Harnessing the Endocannabinoid 2-Arachidonoylglycerol to Lower Intraocular Pressure in a Murine Model.

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“Cannabinoids, such as Δ9-THC, act through an endogenous signaling system in the vertebrate eye that reduces IOP via CB1 receptors.

Endogenous cannabinoid (eCB) ligand, 2-arachidonoyl glycerol (2-AG), likewise activates CB1 and is metabolized by monoacylglycerol lipase (MAGL). We investigated ocular 2-AG and its regulation by MAGL and the therapeutic potential of harnessing eCBs to lower IOP.

Our data confirm a central role for MAGL in metabolism of ocular 2-AG and related lipid species, and that endogenous 2-AG can be harnessed to reduce IOP. The MAGL blocker KML29 has promise as a therapeutic agent, while JZL184 may have difficulty crossing the cornea.

These data, combined with the relative specificity of MAGL for ocular monoacylglycerols and the lack of desensitization in MAGL-/- mice, suggest that the development of an optimized MAGL blocker offers therapeutic potential for treatment of elevated IOP.”

http://www.ncbi.nlm.nih.gov/pubmed/27333182

Cannabinoids in the Brain: New Vistas on an Old Dilemma

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“The use of cannabis as a therapeutic and recreational substance goes back to thousands of years throughout Asia, Middle East, Southern Africa, and South America.

The discovery of Δ-9-tetrahydrocannabinol (Δ9-THC) by Mechoulam and Gaoni in the midsixties as the major psychoactive constituent of cannabis sativa led to another important discovery, namely, its specific binding site that was isolated and cloned in 1990. This first cannabinoid receptor was coined CB1R and triggered a number of investigations on its expression, localization, and function within the body tissue including the brain, in various species. This was followed by the discovery in 1992 of the first endocannabinoid (eCB), anandamide, followed by another cannabinoid receptor CB2R and a second endocannabinoid called 2-arachidonoylglycerol (2-AG). Later on, some of the enzymes responsible for their synthesis (N-acyl phosphatidylethanolamine phospholipase D (NAPE-PLD); diacylglycerol lipase (DAGL)) and degradation (fatty acid amide hydrolase (FAAH); monoacylglycerol lipase (MAGL)) were identified.

Studies on the expression and localization of the cannabinoid receptors in the brain have burgeoned in the last decade and have furnished valuable data on their putative involvement in various sensory-motor and cognitive functions in diverse animal species, including Man. These studies have recently received substantial attention from pharmaceutical companies as a potential source for novel treatments. Additionally, the dilemma of legalizing the use of cannabis in some countries makes the investigation on cannabinoid systems more momentous. This special issue is therefore timely and brings historical and groundbreaking novel research on the role of these cannabinoid receptors in the mammalian central nervous system (CNS).

We hope that the collected papers in this special issue will contribute to the understanding of the various mechanisms involved in the functions of the endocannabinoid system and the development of new pharmaceutical tools to treat visual disorders.”

http://www.hindawi.com/journals/np/2016/9146713/

ENDOCANNABINOID SYSTEM: A multi-facet therapeutic target.

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“Cannabis sativa is also popularly known as marijuana. It is being cultivated and used by man for recreational and medicinal purposes from many centuries.

Study of cannabinoids was at bay for very long time and its therapeutic value could not be adequately harnessed due to its legal status as proscribed drug in most of the countries.

The research of drugs acting on endocannabinoid system has seen many ups and down in recent past. Presently, it is known that endocannabinoids has role in pathology of many disorders and they also serve “protective role” in many medical conditions.

Several diseases like emesis, pain, inflammation, multiple sclerosis, anorexia, epilepsy, glaucoma, schizophrenia, cardiovascular disorders, cancer, obesity, metabolic syndrome related diseases, Parkinson’s disease, Huntington’s disease, Alzheimer’s disease and Tourette’s syndrome could possibly be treated by drugs modulating endocannabinoid system.

Presently, cannabinoid receptor agonists like nabilone and dronabinol are used for reducing the chemotherapy induced vomiting. Sativex (cannabidiol and THC combination) is approved in the UK, Spain and New Zealand to treat spasticity due to multiple sclerosis. In US it is under investigation for cancer pain, another drug Epidiolex (cannabidiol) is also under investigation in US for childhood seizures. Rimonabant, CB1 receptor antagonist appeared as a promising anti-obesity drug during clinical trials but it also exhibited remarkable psychiatric side effect profile. Due to which the US Food and Drug Administration did not approve Rimonabant in US. It sale was also suspended across the EU in 2008.

Recent discontinuation of clinical trial related to FAAH inhibitor due to occurrence of serious adverse events in the participating subjects could be discouraging for the research fraternity. Despite of some mishaps in clinical trials related to drugs acting on endocannabinoid system, still lot of research is being carried out to explore and establish the therapeutic targets for both cannabinoid receptor agonists and antagonists.

One challenge is to develop drugs that target only cannabinoid receptors in a particular tissue and another is to invent drugs that acts selectively on cannabinoid receptors located outside the blood brain barrier. Besides this, development of the suitable dosage forms with maximum efficacy and minimum adverse effects is also warranted.

Another angle to be introspected for therapeutic abilities of this group of drugs is non-CB1 and non-CB2 receptor targets for cannabinoids.

In order to successfully exploit the therapeutic potential of endocannabinoid system, it is imperative to further characterize the endocannabinoid system in terms of identification of the exact cellular location of cannabinoid receptors and their role as “protective” and “disease inducing substance”, time-dependent changes in the expression of cannabinoid receptors.”

http://www.ncbi.nlm.nih.gov/pubmed/27086601

Cannabinoid Receptors CB1 and CB2 Modulate the Electroretinographic Waves in Vervet Monkeys.

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“The expression patterns of the cannabinoid receptor type 1 (CB1R) and the cannabinoid receptor type 2 (CB2R) are well documented in rodents and primates.

In vervet monkeys, CB1R is present in the retinal neurons (photoreceptors, horizontal cells, bipolar cells, amacrine cells, and ganglion cells) and CB2R is exclusively found in the retinal glia (Müller cells). However, the role of these cannabinoid receptors in normal primate retinal function remains elusive.

Using full-field electroretinography in adult vervet monkeys, we recorded changes in neural activity following the blockade of CB1R and CB2R by the intravitreal administration of their antagonists (AM251 and AM630, resp.) in photopic and scotopic conditions.

Our results show that AM251 increases the photopic a-wave amplitude at high flash intensities, whereas AM630 increases the amplitude of both the photopic a- and b-waves.In scotopic conditions, both blockers increased the b-wave amplitude but did not change the a-wave amplitude.

These findings suggest an important role of CB1R and CB2R in primate retinal function.”

http://www.ncbi.nlm.nih.gov/pubmed/27069692