Comparison of Topical and Intravenous Administration of WIN 55-212-2 in Normotensive Rabbits

Δ9-Tetrahydrocannabinol Effects on Respiration and Heart Rate Across Route of Administration in Female and Male Mice

The physiological impact of cannabinoid receptor agonists is of great public health interest due to their increased use in recreational and therapeutic contexts. However, the body of literature on cannabinoid receptor agonists includes multiple confounding variables that complicate comparisons across studies, including route of administration, timeline across which phenotypes are observed, agonist dose, and sex of the study cohort. In this study, we characterized the impact of sex and route of administration on Δ9-tetrahydrocannabinol (THC)-induced changes in cardiopulmonary phenotypes in mice. Using noninvasive plethysmography and telemetry, we monitored heart rate and respiration in the same cohort of animals across aerosol, oral gavage, subcutaneous, and intraperitoneal administrations of THC (0-30 mg/kg THC for oral gavage, subcutaneous, and intraperitoneal, and 0-300 mg/ml THC for aerosol). All routes of THC administration altered respiratory minute volume and heart rate, with the direction of effects typically being consistent across dependent measures. THC primarily decreased respiration and heart rate, but females given oral gavage THC showed increased heart rate. Intraperitoneal and subcutaneous THC produced the longest-lasting effects, including THC-induced alterations in physiological parameters for up to 10 h, whereas effects of aerosolized THC were short lived. The fastest onset of effects of THC occurred for aerosolized and intraperitoneal THC. Altogether, the work herein establishes the impact of dosing route on THC-induced heart rate and respiratory alteration in male and female mice. This study highlights important differences in the timeline of cardiopulmonary response to THC following the most common preclinical routes of administration.

CB1R, CB2R and TRPV1 expression and modulation in in vivo, animal glaucoma models: A systematic review

BACKGROUND

The endocannabinoid system (ECS) is a complex biological regulatory system. Its expression and functionality have been widely investigated in ocular tissues. Recent data have reported its modulation to be valid in determining an ocular hypotensive and a neuroprotective effect in preclinical animal models of glaucoma.

AIM

This study aimed to explore the available literature on cannabinoid receptor 1 (CB₁R), cannabinoid receptor 2 (CB₂R), and transient receptor potential vanilloid 1 (TRPV1) expression in the trabecular meshwork (TM), ciliary body (CB), and retina as well as their ocular hypotensive and neuroprotective effects in preclinical, in vivo, animal glaucoma models.

MATERIALS AND METHODS

The study adhered to both PRISMA and SYRCLE guidelines. Sixty-nine full-length articles were included in the final analysis.

RESULTS

Preclinical studies indicated a widespread distribution of CB₁R, CB₂R, and TRPV1 in the TM, CB, and retina, although receptor-, age-, and species-dependent differences were observed. CB₁R and CB₂R modulation have been shown to exert ocular hypotensive effects in preclinical models via the regulation of inflow and outflow pathways. Retinal cell neuroprotection has been achieved in several experimental models, mediated by agonists and antagonists of CB₁R, CB₂R, and TRPV1.

DISCUSSION

Despite the growing body of preclinical data regarding the expression and modulation of ECS in ocular tissues, the mechanisms responsible for the hypotensive and neuroprotective efficacy exerted by this system remain largely elusive. Research on this topic is advocated to further substantiate the hypothesis that the ECS is a new potential therapeutic target in the context of glaucoma.

Synthesis and evaluation of potent and selective MGL inhibitors as a glaucoma treatment

Monoacylglycerol lipase (MGL) inhibition provides a potential treatment approach to glaucoma through the regulation of ocular 2-arachidonoylglycerol (2-AG) levels and the activation of CB1 receptors. Herein, we report the discovery of new series of carbamates as highly potent and selective MGL inhibitors. The new inhibitors showed potent nanomolar inhibitory activity against recombinant human and purified rat MGL, were selective (>1000-fold) against serine hydrolases FAAH and ABHD6 and lacked any affinity for the cannabinoid receptors CB1 and CB2. Protein-based ¹H NMR experiments indicated that inhibitor 2 rapidly formed a covalent adduct with MGL with a residence time of about 6 h. This interconversion process "intrinsic reversibility" was exploited by modifications of the ligand's size (length and bulkiness) to generate analogs with "tunable' adduct residence time (τ). Inhibitor 2 was evaluated in a normotensive murine model for assessing intraocular pressure (IOP), which could lead to glaucoma, a major cause of blindness. Inhibitor 2 was found to decrease ocular pressure by ∼4.5 mmHg in a sustained manner for at least 12 h after a single ocular application, underscoring the potential for topically-administered MGL inhibitors as a novel therapeutic target for the treatment of glaucoma.

Effect of Continuous Systemic Administration of Esmolol on Intraocular Pressure During Surgery in a Sustained Steep Trendelenburg Position

PURPOSE

To investigate the effects of continuous systemic administration of esmolol on intraocular pressure (IOP) during laparoscopic and robotic surgeries for recto-sigmoid cancer in a steep Trendelenburg position.

MATERIALS AND METHODS

A total of 50 patients undergoing laparoscopic surgery in a steep Trendelenburg position were included. Patients in the esmolol (E) group received a 0.25 mg/kg IV loading dose of esmolol before anesthesia, followed by an infusion of 15 μg/kg/min throughout the operation. Patients in the saline (S) group were infused with the same volume of normal saline. IOP and ocular perfusion pressure were measured 16 times: before anesthetic induction (T1), before administration of the study drug (T2), after administration of anesthetic induction agents (T3), after tracheal intubation (T4), 1, 3, 5, and 10 minutes after tracheal intubation (T5-T8), immediately after intraperitoneal CO2 insufflation (T9), immediately after the steep Trendelenburg position (T10), 1, 2, and 4 hours after the steep Trendelenburg position (T11-T13), just before the supine position (T14), and 10 and 30 minutes after the supine position (T15, T16).

RESULTS

The IOP increased markedly after adopting the steep Trendelenburg position, reaching 28.8±4.4 mm Hg in group S. The IOP at T13 in group S was ∼5.7 mm Hg higher than in group E. The IOP at T13 was ∼10.6 mm Hg higher than in T1 in group S, but only ∼4.4 mm Hg higher than in group E.

CONCLUSIONS

Continuous systemic administration of esmolol can alleviate the increase in IOP during a sustained steep Trendelenburg position without adverse cardiovascular effects.

The In Vivo Effects of the CB1-Positive Allosteric Modulator GAT229 on Intraocular Pressure in Ocular Normotensive and Hypertensive Mice

PURPOSE

Orthosteric cannabinoid receptor 1 (CB₁) activation leads to decreases in intraocular pressure (IOP). However, use of orthosteric CB₁ agonists chronically has several disadvantages, limiting their usefulness as clinically relevant drugs. Allosteric modulators interact with topographically distinct sites to orthosteric ligands and may be useful to circumvent some of these disadvantages. The purpose of this study was to investigate the effects of the novel CB₁-positive allosteric modulator (PAM) GAT229 on IOP.

METHODS

IOP was measured using rebound tonometry in anesthetized normotensive C57Bl/6 mice and in a genetic model of ocular hypertension [nose, eyes, ears (nee) mice] before drug administration, and at 1, 6, and 12 h thereafter.

RESULTS

In normotensive mice, topical administration of 5 μL GAT229 alone at either 0.2% or 2% did not reduce IOP. However, a subthreshold dose (0.25%) of the nonselective orthosteric CB₁ agonist WIN 55,212-2, when combined with 0.2% GAT229, significantly reduced IOP compared with vehicle at 6 and 12 h. Similarly, combination of subthreshold Δ⁹-tetrahydrocannabinol (a nonselective orthosteric CB₁ agonist; 1 mg/kg) with topical 0.2% GAT229 produced IOP lowering at 6 h. In nee mice, administration of topical 0.2% GAT229 or 10 mg/kg GAT229 alone was sufficient to lower IOP at 6 and 12 h, and 12 h, respectively.

CONCLUSIONS

The CB₁ PAM GAT229 reduces IOP in ocular hypertensive mice and enhanced CB₁-mediated IOP reduction when combined with subthreshold CB₁ orthosteric ligands in normotensive mice. Administration of CB₁ PAMs may provide a novel approach to reduce IOP with fewer of the disadvantages associated with orthosteric CB₁ activation.

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

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. The IOP was measured noninvasively using a hand-held tonometer in nonanesthetized animals. The IOP measurements were taken every 15 min for a period of 2 h after drug administration. All drugs were administered via intraperitoneal (i.p.) injections, and abn-CBD and CBG-DMH were also given topically. Both abn-CBD and CBG-DMH reduced IOP when administrated i.p. at doses of ≥2.5 mg/kg or topically at concentrations of 1%-2%. The IOP-lowering effects of abn-CBD and CBG-DMH were reduced by i.p. administration of O-1918 (2.5 mg/kg), a selective antagonist of the abn-CBD-sensitive cannabinoid-related receptor (CBx), but were unaffected by the CB(1)R antagonist, AM251 (2.5 mg/kg), or the CB(2)R antagonist, AM630 (2.5 mg/kg). In contrast, the IOP-lowering action of WIN55,212-2 was completely blocked by the CB(1)R-selective antagonist, AM251, and was unaffected by the CBx receptor antagonist, O-1918. However, similar to the nonpsychotropic cannabinoids, the ocular hypotensive actions of WIN55,212-2 were also insensitive to block by the CB(2)R antagonist, AM630. Consistent with this, the selective CB(2)R agonist, HU-308 (2 mg/kg) failed to reduce IOP in Brown Norway rats. Concurrent application of a dose of WIN55,212-2 that was subthreshold to reduce IOP (0.25 mg/kg), together with a topical dose of either abn-CBD (0.5%) or CBG-DMH (0.25%), respectively, potentiated the ocular hypotensive effect of either compound applied alone. This study demonstrates that the atypical cannabinoid, abn-CBD, and the cannabigerol analog, CBG-DMH, decrease IOP in the normotensive Brown Norway rat eye independent of CB(1)R or CB(2)R activation, via activation of CBx receptors. The enhanced decrease in IOP seen after coapplication of the CB(1)R agonist, WIN55,212-2, together with either abn-CBD or CBG-DMH, respectively, further suggests that the ocular pharmacodynamics of abn-CBD and CBG-DMH are mediated by receptor targets distinct from CB(1)R. 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.