Ocular disposition of the hemiglutarate ester prodrug of ∆⁹-Tetrahydrocannabinol from various ophthalmic formulations

Formulation and In Vitro-Ex vivo Evaluation of Cannabidiol and Cannabidiol-Valine-Hemisuccinate Loaded Lipid-Based Nanoformulations for Ocular Applications

The goal of this investigation is to develop stable ophthalmic nanoformulations containing cannabidiol (CBD) and its analog cannabidiol-valine-hemisuccinate (CBD-VHS) for improved ocular delivery. Two nanoformulations, nanoemulsion (NE) and nanomicelles (NMC), were developed and evaluated for physicochemical characteristics, drug-excipient compatibility, sterilization, thermal analysis, surface morphology, ex-vivo transcorneal permeation, corneal deposition, and stability. The saturation solubility studies revealed that among the surfactants tested, Cremophor EL had the highest solubilizing capacity for CBD (23.3 ± 0.1 mg/mL) and CBD-VHS (11.2 ± 0.2 mg/mL). The globule size for the lead CBD formulations (NE and NMC) ranged between 205 and 270 nm while CBD-VHS-NMC formulation had a particle size of about 78 nm. The sterilized formulations, except for CBD-VHS-NMC at 40 °C, were stable for three months of storage (last time point tested). Release, in terms of CBD, in the in-vitro release/diffusion studies over 18 h, were faster from the CBD-VHS nanomicelles (38 %) compared to that from the CBD nanoemulsion (16 %) and nanomicelles (33 %). Transcorneal permeation studies revealed improvement in CBD permeability and flux with both formulations; however, a greater improvement was observed with the NMC formulation compared to the NE formulation. In conclusion, the nanoformulations prepared could serve as efficient topical ocular drug delivery platforms for CBD and its analog.

LC-MS/MS quantitation of non-psychotropic cannabinoid cannabidiol in aqueous humor

Cannabidiol (CBD) is the most abundant non-psychotropic phytocannabinoid isolated from Cannabis sativa. To support preclinical studies of ocular pharmacology of CBD, a bioanalytical method was developed and validated for quantification of CBD in aqueous humor using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Aqueous humor samples were subjected to protein precipitation by acetonitrile, followed by chromatographic separation using reversed phase LC on a Raptor ARC-18 column with mobile phase A: 0.1 % (v/v) formic acid in water (B) 0.1 % formic acid in acetonitrile (B) as eluents. Detection was carried out with a triple quadrupole mass spectrometer with electrospray ionization operated in positive ion mode. Stable-isotope labeled CBD (CBD-d3) was used as internal standard. The total run time was 8 min. Quantification was accomplished within the validated concentration range of 0.5-500 ng/mL for CBD using a 5 µL sample. The lower limit of quantitation was 0.5 ng/mL. Inter- and intra-day precision is 4.737-7.620 % and 3.426-5.830 %, respectively. Inter- and intra-day accuracy ranged between 99.01 % and 100.2 % and 99.85-101.4 % respectively. The extraction recoveries were found to be 66.06 ± 5.146 %. The established method was successfully applied to investigate ocular pharmacokinetics of CBD in mice. Following intraperitoneal (i.p.) administration of 50 mg/kg CBD, its concentration reaches a Cmax of 71.55 ± 36.64 ng/mL in aqueous humor, with a Tmax of 2 h and a half-life of 1.046 h. The AUC was 183.4 ± 49.17 ng * h/mL. The development and validation of this LC-MS/MS method is an important step toward the goal of assessing the aqueous humor concentrations of CBD and correlating the concentrations of this phytocannabinoid with its ocular pharmacologic effects.

Cannabidiol Loaded Topical Ophthalmic Nanoemulsion Lowers Intraocular Pressure in Normotensive Dutch-Belted Rabbits

Cannabidiol (CBD) is the major non-psychoactive and most widely studied of the cannabinoid constituents and has great therapeutic potential in a variety of diseases. However, contradictory reports in the literature with respect to CBD's effect on intraocular pressure (IOP) have raised concerns and halted research exploring its use in ocular therapeutics. Therefore, the current investigation aimed to further evaluate CBD's impact on the IOP in the rabbit model. CBD nanoemulsions, containing Carbopol® 940 NF as a mucoadhesive agent (CBD-NEC), were prepared using hot-homogenization followed by probe sonication. The stability of the formulations post-moist-heat sterilization, in terms of physical and chemical characteristics, was studied for three different storage conditions. The effect of the formulation on the intraocular pressure (IOP) profile in normotensive Dutch Belted male rabbits was then examined. The lead CBD-NEC formulation (1% w/v CBD) exhibited a globule size of 259 ± 2.0 nm, 0.27 ± 0.01 PDI, and 23.2 ± 0.4 cP viscosity, and was physically and chemically stable for one month (last time point tested) at 4 °C, 25 °C, and 40 °C. CBD-NEC significantly lowered the IOP in the treated eyes for up to 360 min, with a peak drop in IOP of 4.5 mmHg observed at the 150 min time point, post-topical application. The IOP of the contralateral eye (untreated) was also observed to be lowered significantly, but the effect lasted up to the 180 min time point only. Overall, topically administered CBD, formulated in a mucoadhesive nanoemulsion formulation, reduced the IOP in the animal model studied. The results support further exploration of CBD as a therapeutic option for various inflammation-based ocular diseases.

The Relationship Between Plasma Tetrahydrocannabinol Levels and Intraocular Pressure in Healthy Adult Subjects

Background

Δ9-tetrahydrocannabinol (THC) has been shown to decreased intraocular pressure (IOP). This project aims to define the relationship between plasma THC levels and IOP in healthy adult subjects.

Methods

Eleven healthy subjects received a single dose of inhaled cannabis that was self-administered in negative pressure rooms. Measurements of IOP and plasma THC levels were taken at baseline and every 30 min for 1 h and afterwards every hour for 4 h. IOP reduction and percent change in IOP over time were calculated. Linear regression models were used to measure the relationship between IOP and plasma THC levels. Two line linear regression models with F-tests were used to detect change points in the regression. Then, Pearson correlations were computed based on the change point.

Results

Twenty-two eyes met inclusion criteria. The average peak percentage decrease in IOP was 16% at 60 min. Percent IOP reduction as well as total IOP reduction demonstrated a negative correlation with THC plasma levels showing r-values of −0.81 and −0.70, respectively. F-tests revealed a change point in the regression for plasma levels >20 ng/ml. For levels >20 ng/ml, the correlation coefficients changed significantly with r-values of 0.21 and 0.29 (p < 0.01).

Conclusion

Plasma THC levels are significantly correlated with IOP reduction up to plasma levels of 20 ng/ml. Plasma levels >20 ng/ml were not correlated with further decrease in IOP. More research is needed to determine the efficacy of THC in reducing IOP for eyes with ocular hypertension and glaucoma.

Advances in medical therapy for glaucoma

PURPOSE OF REVIEW

To discuss a new class of medication that has recently become available for the treatment of glaucoma; as well as share insights into developments in glaucoma medicine administration which has the potential to revolutionize medical therapy for glaucoma.

RECENT FINDINGS

Newly available eye drops, netarsudil 0.02% and latanoprostene bunod 0.024%, are improving aqueous outflow through the conventional outflow tract. Other new developments in medical glaucoma are focused on alternative methods for sustained glaucoma medication delivery.

SUMMARY

Newer medications may be able to extend the duration of medically controlled glaucoma, delaying or possibly eliminating the need of glaucoma surgery for some patients. Alternative methods of delivery for glaucoma medications may be a key factor in improving outcomes with currently available medications.

Cannabinoids and the eye

Cannabis ranks among the most commonly used psychotropic drugs worldwide. In the context of the global movement toward more widespread legalisation, there is a growing need toward developing a better understanding of the physiological and pathological effects. We provide an overview of the current evidence on the effects of cannabinoids on the eye. Of the identified cannabinoids, Δ⁹-tetrahydrocannabinol is recognized to be the primary psychotropic compound, and cannabidiol is the predominant nonpsychoactive ingredient. Despite demonstrating ocular hypotensive and neuroprotective activity, the use of cannabinoids as a treatment for glaucoma is limited by a large number of potential systemic and ophthalmic side effects. Anterior segment effects of cannabinoids are complex, with preliminary evidence showing decreased corneal endothelial density in chronic cannabinoid users. Experiments in rodents, however, have shown potential promise for the treatment of ocular surface injury via antinociceptive and antiinflammatory effects. Electroretinography studies demonstrating adverse effects on photoreceptor, bipolar, and ganglion cell function suggest links between cannabis and neuroretinal dysfunction. Neuro-ophthalmic associations include ocular motility deficits and decrements in smooth pursuit and saccadic eye movements, although potential therapeutic effects for congenital and acquired nystagmus have been observed.

Δ9-Tetrahydrocannabinol Derivative-Loaded Nanoformulation Lowers Intraocular Pressure in Normotensive Rabbits

PURPOSE

Δ9-Tetrahydrocannabinol-valine-hemisuccinate, a hydrophilic prodrug of Δ9-tetrahydrocannabinol, synthesized with the aim of improving the ocular bioavailability of the parent molecule, was investigated in a lipid-based nanoparticle dosage form for ocular delivery.

METHODS

Solid lipid nanoparticles (SLNs) of Δ9-tetrahydrocannabinol-valine-hemisuccinate and Δ9-tetrahydrocannabinol, along with a nanoemulsion of Δ9-tetrahydrocannabinol-valine-hemisuccinate, were tested for glaucoma management in a normotensive rabbit model by using a multiple-dosing protocol. Marketed formulations of timolol maleate and pilocarpine HCl were also tested for their pharmacodynamic profile, post-single dose administration.

RESULTS

A peak intraocular pressure (IOP) drop of 30% from baseline was observed in rabbits treated with SLNs loaded with Δ9-tetrahydrocannabinol-valine-hemisuccinate at 90 minutes. Treated eyes of rabbits receiving Δ9-tetrahydrocannabinol-valine-hemisuccinate SLNs had significantly lower IOP than untreated eyes until 360 minutes, whereas the group receiving the emulsion formulation showed a drop in IOP until 90 minutes only. In comparison to marketed pilocarpine and timolol maleate ophthalmic solutions, Δ9-tetrahydrocannabinol-valine-hemisuccinate SLNs produced a greater effect on IOP in terms of both intensity and duration. In terms of tissue concentrations, significantly higher concentrations of Δ9-tetrahydrocannabinol-valine-hemisuccinate were observed in iris-ciliary bodies and retina-choroid with SLNs.

CONCLUSION

Δ9-Tetrahydrocannabinol-valine-hemisuccinate formulated in a lipid-based nanoparticulate carrier shows promise in glaucoma pharmacotherapy.

TRANSLATIONAL RELEVANCE

Glaucoma therapies usually focus on decreased aqueous humor production and increased outflow. However, such therapy is not curative, and there lies a need in preclinical research to focus efforts on agents that not only affect the aqueous humor dynamics but also provide neuroprotection. Historically, there have been bench-scale studies looking at retinal ganglion cell death post-axonal injury. However, for a smooth translation of this in vitro activity to the clinic, animal models examining IOP reduction, i.e., connecting the neuroprotective activity to a measurable outcome in glaucoma management (IOP), need to be investigated. This study investigated the IOP reduction efficacy of cannabinoids for glaucoma pharmacotherapy in a normotensive rabbit model, bringing forth a new class of agents with the potential of IOP reduction and improved permeation to the back of the eye, possibly providing neuroprotective benefits in glaucoma management.

Neuroprotection by (endo)Cannabinoids in Glaucoma and Retinal Neurodegenerative Diseases

BACKGROUND

Emerging neuroprotective strategies are being explored to preserve the retina from degeneration, that occurs in eye pathologies like glaucoma, diabetic retinopathy, age-related macular degeneration, and retinitis pigmentosa. Incidentally, neuroprotection of retina is a defending mechanism designed to prevent or delay neuronal cell death, and to maintain neural function following an initial insult, thus avoiding loss of vision.

METHODS

Numerous studies have investigated potential neuroprotective properties of plant-derived phytocannabinoids, as well as of their endogenous counterparts collectively termed endocannabinoids (eCBs), in several degenerative diseases of the retina. eCBs are a group of neuromodulators that, mainly by activating G protein-coupled type-1 and type-2 cannabinoid (CB1 and CB2) receptors, trigger multiple signal transduction cascades that modulate central and peripheral cell functions. A fine balance between biosynthetic and degrading enzymes that control the right concentration of eCBs has been shown to provide neuroprotection in traumatic, ischemic, inflammatory and neurotoxic damage of the brain.

RESULTS

Since the existence of eCBs and their binding receptors was documented in the retina of numerous species (from fishes to primates), their involvement in the visual processing has been demonstrated, more recently with a focus on retinal neurodegeneration and neuroprotection.

CONCLUSION

The aim of this review is to present a modern view of the endocannabinoid system, in order to discuss in a better perspective available data from preclinical studies on the use of eCBs as new neuroprotective agents, potentially useful to prevent glaucoma and retinal neurodegenerative diseases.

Ocular Disposition of ∆8-Tetrahydrocannabinol from Various Topical Ophthalmic Formulations

The purposes of this project are to enhance the trans-membrane penetration of Δ⁸-Tetrahydrocannabinol (Δ⁸-THC) and to study the effect of various lipid based systems in delivering the compound, non-invasively, to anterior and posterior ocular chambers. Solid lipid nanoparticles (SLNs), fast gelling films were manufactured using high pressure homogenization and melt cast techniques, respectively. The formulations were characterized for drug content, entrapment efficiency, particle size and subsequently evaluated in vitro for trans-corneal permeation. In vivo, the drug disposition was tested via topical administration in albino rabbits. The eye globes were enucleated at the end of experiment and tissues were analyzed for drug content. All formulations showed favorable physicochemical characteristics in terms of particle size, entrapment efficiency, and drug content. In vitro, the formulations exhibited a transcorneal flux that depended on the formulation's drug load. An increase in drug load from 0.1 to 0.75% resulted in 12- to16-folds increase in permeation. In vivo, the film was able to deliver THC to all the tissues with high accumulations in cornea and sclera. The SLNs showed a greater ability in delivering THC to all the tissues, at a significantly lower drug load, due to their colloidal size range, which in turn enhanced corneal epithelial membrane penetration. The topical formulations evaluated in the present study were able to successfully deliver Δ⁸-THC in therapeutically meaningful concentrations (EC₅₀ values for CB₁: 6 nM and CB₂: 0.4 nM) to all ocular tissues except the vitreous humor, with pronounced tissue penetration achieved using SLNs as a Δ⁸-THC delivery vehicle.

Development of a Δ9-Tetrahydrocannabinol Amino Acid-Dicarboxylate Prodrug With Improved Ocular Bioavailability

Purpose

The aim of the present study was to evaluate the utility of the relatively hydrophilic Δ⁹-tetrahydrocannabinol (THC) prodrugs, mono and di-valine esters (THC-Val and THC-Val-Val) and the amino acid (valine)-dicarboxylic acid (hemisuccinate) ester (THC-Val-HS), with respect to ocular penetration and intraocular pressure (IOP) lowering activity. THC, timolol, and pilocarpine eye drops were used as controls.

Methods

THC-Val, THC-Val-Val, and THC-Val-HS were synthesized and chemically characterized. Aqueous solubility and in vitro transcorneal permeability of THC and the prodrugs, in the presence of various surfactants and cyclodextrins, were determined. Two formulations were evaluated for therapeutic activity in the α-chymotrypsin induced rabbit glaucoma model, and the results were compared against controls comprising of THC emulsion and marketed timolol maleate and pilocarpine eye drops.

Results

THC-Val-HS demonstrated markedly improved solubility (96-fold) and in vitro permeability compared to THC. Selected formulations containing THC-Val-HS effectively delivered THC to the anterior segment ocular tissues in the anesthetized rabbits: 62.1 ng/100 μL of aqueous humor (AH) and 51.4 ng/50 mg of iris ciliary bodies (IC) (total THC). The duration and extent of IOP lowering induced by THC-Val-HS was 1 hour longer and 10% greater, respectively, than that obtained with THC and was comparable with the pilocarpine eye drops. Timolol ophthalmic drops, however, exhibited a longer duration of activity. Both THC and THC-Val-HS were detected in the ocular tissues following multiple dosing of THC-Val-HS in conscious animals. The concentration of THC in the iris-ciliary bodies at the 60- and 120-minute time points (53 and 57.4 ng/50 mg) were significantly greater than that of THC-Val-HS (24.2 and 11.3 ng/50 mg). Moreover, at the two time points studied, the concentration of THC was observed to increase or stay relatively constant, whereas THC-Val-HS concentration decreased by at least 50%. A similar trend was observed in the retina-choroid tissues.

Conclusions

A combination of prodrug derivatization and formulation development approaches significantly improved the penetration of THC into the anterior segment of the eye following topical application. Enhanced ocular penetration resulted in significantly improved IOP-lowering activity.

Advances in the use of prodrugs for drug delivery to the eye

INTRODUCTION

Ocular drug delivery is presented with many challenges, taking into account the distinctive structure of the eye. The prodrug approach has been, and is being, employed to overcome such barriers for some drug molecules, utilizing a chemical modification approach rather than a formulation-based approach. A prodrug strategy involves modification of the active moiety into various derivatives in a fashion that imparts some advantage, such as membrane permeability, site specificity, transporter targeting and improved aqueous solubility, over the parent compound. Areas covered: The following review is a comprehensive summary of various novel methodologies and strategies reported over the past few years in the area of ocular drug delivery. Some of the strategies discussed involve polymer and lipid conjugation with the drug moiety to impart hydrophilicity or lipophilicity, or to target nutrient transporters by conjugation with transporter-specific moieties and retrometabolic drug design. Expert opinion: The application of prodrug strategies provides an option for enhancing drug penetration into the ocular tissues, and overall ocular bioavailability, with minimum disruption of the ocular diffusion barriers. Although success of the prodrug strategy is contingent on various factors, such as the chemical structure of the parent molecule, aqueous solubility and solution stability, capacity of targeted transporters and bioreversion characteristics, this approach has been successfully utilized, commercially and therapeutically, in several cases.