Normotensive Rabbits Research Articles

Nano-structured glaucoma drainage implant safely and significantly reduces intraocular pressure in rabbits via post-operative outflow modulation

Glaucoma is a leading cause of irreversible vision loss predicted to affect more than 100 million people by 2040. Intraocular pressure (IOP) reduction prevents development of glaucoma and vision loss from glaucoma. Glaucoma surgeries reduce IOP by facilitating aqueous humor outflow through a vent fashioned from the wall of the eye (trabeculectomy) or a glaucoma drainage implant (GDI), but surgeries lose efficacy overtime, and the five-year failure rates for trabeculectomy and tube shunts are 25–45%. The majority of surgical failures occur due to fibrosis around the vent. Alternatively, surgical procedures can shunt aqueous humor too well, leading to hypotony. Electrospinning is an appealing manufacturing platform for GDIs, as it allows for incorporation of biocompatible polymers into nano- or micro-fibers that can be configured into devices of myriad combinations of dimensions and conformations. Here, small-lumen, nano-structured glaucoma shunts were manufactured with or without a degradable inner core designed to modulate aqueous humor outflow to provide immediate IOP reduction, prevent post-operative hypotony, and potentially offer significant, long-term IOP reduction. Nano-structured shunts were durable, leak-proof, and demonstrated biocompatibility and patency in rabbit eyes. Importantly, both designs prevented hypotony and significantly reduced IOP for 27 days in normotensive rabbits, demonstrating potential for clinical utility.

A Novel Non‐Prostaglandin EP2‐Receptor Agonist for Glaucoma Treatment: Omidenepag Isopropyl (DE‐117)

PurposeElevated intraocular pressure (IOP) is often associated with Primary Open‐Angle Glaucoma (POAG), an optic neuropathy that afflicts millions of people and which can cause blindness if left untreated. Omidenepag Isopropyl (OMDI; DE‐117) is a novel pro‐drug non‐prostaglandin (PG) which hydrolyzes to release its active free acid form (Omidenepag; OMD) into the aqueous humor (AQH) after topical ocular (t.o.) instillation. The purpose of the current studies was to characterize OMDI and OMD in several in vitro and in vivo model systems in order to determine its IOP‐lowering and other pharmacological properties.MethodsWell‐accepted in vitro cell‐based assays and in vivo IOP measurement techniques were utilized in the current studies.ResultsOMD was found to be a highly selective EP2 receptor (EP2R) agonist that bound to the EP2R with a high affinity (Ki = 3.6 nM) and which potently increased intracellular cAMP (EC50 = 8.3 nM). Once daily (q.d.), single t.o. dosing with OMDI (0.0001–0.01%) potently and efficaciously lowered IOP in ocular normotensive rabbits, dogs and monkeys, and also in ocular hypertensive (OHT) monkeys. Repeated t.o. dosing with OMDI in dogs did not cause tachyphylaxis of IOP reduction.Additive IOP‐lowering to OMDI was observed with Timolol, Brimonidine and Brinzolamide in rabbits and monkeys. OMDI 0.002% t.o. lowered IOP by increasing AQH efflux via trabecular meshwork (TM) and uveoscleral (UVSC) outflow pathways in OHT monkey eyes. In a phase‐3 clinical study, 0.002% OMDI (q.d.; t.o.), an optimal dose, lowered IOP by 5–7 mmHg in OHT/POAG patients (baseline IOPs of 22–34 mmHg) that was maintained over 12‐months with equivalent efficacy to Xalatan (0.005%, q.d.; t.o.). OHT/POAG patients that were low‐ or non‐responders to Xalatan (0.005%, q.d.; t.o.) exhibited significant IOP‐lowering (additional 3 mmHg) when switched to OMDI 0.002% (q.d.; t.o.). OMDI was well tolerated and produced transient conjunctival hyperemia, and mild iritis and macular edema (ME) in a few patients. However, no iris color changes, DUES, or abnormal eyelash growth were noted after 12‐month q.d. t.o. dosing with 0.002% OMDI, unlike FP‐receptor PG agonists (Bimatoprost and Latanoprost). Additive IOP‐lowering was also observed in OHT/POAG patients when OMDI (0.002%; q.d.) and Timolol (a known ocular hypotensive beta‐antagonist; 0.05%, b.i.d.) were t.o. instilled.ConclusionIn conclusion, the non‐prostaglandin organic molecule, OMD, is a highly selective and potent EP2R agonist whose isopropyl ester (OMDI) was shown to be a potent and efficacious ocular hypotensive agent in several animal species and in the OHT/POAG patient population studied. OMDI promoted AQH outflow via both the TM and UVSC pathways to lower IOP, and it achieved a comparable ocular hypotensive efficacy to Latanoprost (Xalatan 0.005% q.d.; t.o.). Additional IOP reduction was observed in Xalatan‐non/low responders when switched over to 0.002% OMDI. Additive IOP‐lowering efficacy was also observed when OMDI was t.o. dosed along with other ocular hypotensive drugs. These pharmacological and clinical efficacy features of OMDI support further development of this drug candidate for treating OHT and glaucoma.

Gelatin Nanoparticles-HPMC Hybrid System for Effective Ocular Topical Administration of Antihypertensive Agents.

The increment in ocular drug bioavailability after topical administration is one of the main challenges in pharmaceutical technology. For several years, different strategies based on nanotechnology, hydrogels or implants have been evaluated. Nowadays, the tolerance of ophthalmic preparations has become a critical issue and it is essential to the use of well tolerated excipients. In the present work, we have explored the potential of gelatin nanoparticles (GNPs) loaded with timolol maleate (TM), a beta-adrenergic blocker widely used in the clinic for glaucoma treatment and a hybrid system of TM-GNPs included in a hydroxypropyl methylcellulose (HPMC) viscous solution. The TM- loaded nanoparticles (mean particle size of 193 ± 20 nm and drug loading of 0.291 ± 0.019 mg TM/mg GNPs) were well tolerated both in vitro (human corneal cells) and in vivo. The in vivo efficacy studies performed in normotensive rabbits demonstrated that these gelatin nanoparticles were able to achieve the same hypotensive effect as a marketed formulation (0.5% TM) containing a 5-fold lower concentration of the drug. When comparing commercial and TM-GNPs formulations with the same TM dose, nanoparticles generated an increased efficacy with a significant (p < 0.05) reduction of intraocular pressure (IOP) (from 21% to 30%) and an augmentation of 1.7-fold in the area under the curve (AUC)(0–12h). On the other hand, the combination of timolol-loaded nanoparticles (TM 0.1%) and the viscous polymer HPMC 0.3%, statistically improved the IOP reduction up to 30% (4.65 mmHg) accompanied by a faster time of maximum effect (tmax = 1 h). Furthermore, the hypotensive effect was extended for four additional hours, reaching a pharmacological activity that lasted 12 h after a single instillation of this combination, and leading to an AUC(0–12h) 2.5-fold higher than the one observed for the marketed formulation. According to the data presented in this work, the use of hybrid systems that combine well tolerated gelatin nanoparticles and a viscous agent could be a promising alternative in the management of high intraocular pressure in glaucoma.

Antioxidant status in rabbit aqueous humor after instillation of ascorbyl laurate-based nanostructures.

The aim of this work was evaluate the antioxidant effect of ascorbyl laurate (ASC12) based nanostructures applied topically to the cornea of ocular normotensive and hypertensive rabbits. The ASC12 was chosen for its capacity to form liquid lyotropic crystal and keeps its free radical trapping power. The hypertension model was performed in six rabbits and was obtained by the application of intracameral injections of alpha-chymotrypsin in the right eye. A single 50 ml dose of ascorbyl laurate coagel 2% w/v (COA-ASC12) was applied topically to the cornea of six normotensive and six hypertensive rabbits. The aqueous humor samples were obtained before and after instillation of COA-ASC12 at different times (2 h and 4 h). Antioxidant capacity was determined via the reduction reaction with iron and tripyridyltriazine (FRAP) and the total proteins were measured using the Bradford reagent. The kinetic antioxidant capacity in the aqueous humor of normotensive and hypertensive rabbits showed a maxim increment at 4 h instillation. Also, the antioxidant capacity in the aqueous humor of hypertensive rabbits was ten times lower than in normotensive rabbits. This type of nanostructures has the potential to significantly improve the topical formulation for the prophylaxis and treatment of several eye diseases.

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

PurposeΔ9-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.MethodsSolid 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.ResultsA 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.ConclusionΔ9-Tetrahydrocannabinol-valine-hemisuccinate formulated in a lipid-based nanoparticulate carrier shows promise in glaucoma pharmacotherapy.Translational RelevanceGlaucoma 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.

Amphiphilic Acrylic Nanoparticles Containing the Poloxamer Star Bayfit® 10WF15 as Ophthalmic Drug Carriers.

Topical application of drops containing ocular drugs is the preferred non-invasive route to treat diseases that affect the anterior segment of the eye. However, the formulation of eye drops is a major challenge for pharmacists since the access of drugs to ocular tissues is restricted by several barriers. Acetazolamide (ACZ) is a carbonic anhydrase inhibitor used orally for the treatment of ocular hypertension in glaucoma. However, large ACZ doses are needed which results in systemic side effects. Recently, we synthesized copolymers based on 2-hydroxyethyl methacrylate (HEMA) and a functionalized three-arm poloxamer star (Bayfit-MA). The new material (HEMA/Bayfit-MA) was engineered to be transformed into nanoparticles without the use of surfactants, which represents a significant step forward in developing new ophthalmic drug delivery platforms. Acetazolamide-loaded nanocarriers (ACZ-NPs) were prepared via dialysis (224 ± 19 nm, −17.2 ± 0.4 mV). The in vitro release rate of ACZ was constant over 24 h (cumulative delivery of ACZ: 83.3 ± 8.4%). Following standard specifications, ACZ-NPs were not cytotoxic in vitro in cornea, conjunctiva, and macrophages. In normotensive rabbits, ACZ-NPs generated a significant intraocular pressure reduction compared to a conventional solution of ACZ (16.4% versus 9.6%) with the same dose of the hypotensive drug (20 µg). In comparison to previously reported studies, this formulation reduced intraocular pressure with a lower dose of ACZ. In summary, HEMA:Bayfit-MA nanoparticles may be a promising system for ocular topical treatments, showing an enhanced ocular bioavailability of ACZ after a single instillation on the ocular surface.

Osmoprotectants in Hybrid Liposome/HPMC Systems as Potential Glaucoma Treatment

The combination of acetazolamide-loaded nano-liposomes and Hydroxypropyl methylcellulose (HPMC) with similar components to the preocular tear film in an osmoprotectant media (trehalose and erythritol) is proposed as a novel strategy to increase the ocular bioavailability of poorly soluble drugs. Ophthalmic formulations based on acetazolamide-loaded liposomes, dispersed in the osmoprotectant solution (ACZ-LP) or in combination with HPMC (ACZ-LP-P) were characterized and in vivo evaluated. The pH and tonicity of both formulations resulted in physiological ranges. The inclusion of HPMC produced an increment in viscosity (from 0.9 to 4.7 mPa·s. 64.9 ± 2.6% of acetazolamide initially included in the formulation was retained in vesicles. In both formulations, a similar onset time (1 h) and effective time periods were observed (7 h) after a single instillation (25 μL) in normotensive rabbits’ eyes. The AUC0–8h of the ACZ-LP-P was 1.5-fold higher than of ACZ-LP (p < 0.001) and the maximum hypotensive effect resulted in 1.4-fold higher (p < 0.001). In addition, the formulation of ACZ in the hybrid liposome/HPMC system produced a 30.25-folds total increment in ocular bioavailability, compared with the drug solution. Excellent tolerance in rabbits’ eyes was confirmed during the study.

Renovascular Hypertension Aggravates Atherosclerosis in Cholesterol-Fed Rabbits

Background: Hypertension is a major risk factor for atherosclerotic disease. However, it is still not clear whether mechanical stress caused by hypertension directly affects the atherosclerotic development in the aorta and coronary arteries. Objectives and Methods: We generated a hypertensive (HTN) rabbit model by surgical removal of the left kidney and partial ligation of the right renal artery. After a 16-week cholesterol diet, we compared aortic and coronary atherosclerosis of HTN rabbits with those of normotensive rabbits. Results: Hypertension did not affect lipid and apolipoprotein levels in plasma but led to a 3.0-fold increase in aortic atherosclerosis and a 1.7-fold increase in coronary atherosclerosis compared with control rabbits. Enhanced atherosclerosis in HTN rabbits was caused by significant increases in macrophages and smooth muscle cells in the lesions. Furthermore, oxidized LDL contents in the lesions were significantly increased in HTN rabbits. In addition, HTN rabbits exhibited prominent hyaline arteriolosclerosis in coronary arterioles. Conclusions: These results indicate that hyper tension not only enhances atherosclerosis in large arteries including the aorta and coronary arteries but also affects hyaline arteriolosclerosis in small arteries.

Co-Delivery of Timolol and Brimonidine with a Polymer Thin-Film Intraocular Device.

We developed a polycaprolactone (PCL) co-delivery implant that achieves zero-order release of 2 ocular hypotensive agents, timolol maleate and brimonidine tartrate. We also demonstrate intraocular pressure (IOP)-lowering effects of the implant for 3 months in vivo. Two PCL thin-film compartments were attached to form a V-shaped co-delivery device using film thicknesses of ∼40 and 20 μm for timolol and brimonidine compartments, respectively. In vitro release kinetics were measured in pH- and temperature-controlled fluid chambers. Empty or drug-loaded devices were implanted intracamerally in normotensive rabbits for up to 13 weeks with weekly measurements of IOP. For ocular concentrations, rabbits were euthanized at 4, 8, or 13 weeks, aqueous fluid was collected, and ocular tissues were dissected. Drug concentrations were measured by liquid chromatography-tandem mass spectrometry. In vitro studies show zero-order release kinetics for both timolol (1.75 μg/day) and brimonidine (0.48 μg/day) for up to 60 days. In rabbit eyes, the device achieved an average aqueous fluid concentration of 98.1 ± 68.3 ng/mL for timolol and 5.5 ± 3.6 ng/mL for brimonidine. Over 13 weeks, the drug-loaded co-delivery device resulted in a statistically significant cumulative reduction in IOP compared to untreated eyes (P < 0.05) and empty-device eyes (P < 0.05). The co-delivery device demonstrated a zero-order release profile in vitro for 2 hypotensive agents over 60 days. In vivo, the device led to significant cumulative IOP reduction of 3.4 ± 1.6 mmHg over 13 weeks. Acceptable ocular tolerance was seen, and systemic drug levels were unmeasurable.

A promising drug candidate for the treatment of glaucoma based on a P2Y6-receptor agonist.

Extracellular nucleotides can regulate the production/drainage of the aqueous humor via activation of P2 receptors, thus affecting the intraocular pressure (IOP). We evaluated 5-OMe-UDP(α-B), 1A, a potent P2Y6-receptor agonist, for reducing IOP and treating glaucoma. Cell viability in the presence of 1A was measured using [3-(4, 5-dimethyl-thiazol-2-yl) 2, 5-diphenyl-tetrazolium bromide] (MTT) assay in rabbit NPE ciliary non-pigmented and corneal epithelial cells, human retinoblastoma, and liver Huh7 cells. The effect of 1A on IOP was determined in acute glaucomatous rabbit hyaluronate model and phenol-induced chronic glaucomatous rabbit model. The origin of activity of 1A was investigated by generation of a homology model of hP2Y6-R and docking studies. 1A did not exert cytotoxic effects up to 100mM vs. trusopt and timolol in MTT assay in ocular and liver cells. In normotensive rabbits, 100μM 1A vs. xalatan, trusopt, and pilocarpine reduced IOP by 45 vs. 20-30%, respectively. In the phenol animal model, 1A (100μM) showed reduction of IOP by 40 and 20%, following early and late administration, respectively. Docking results suggest that the high activity and selectivity of 1A is due to intramolecular interaction between Pα-BH3 and C5-OMe which positions 1A in a most favorable site inside the receptor. P2Y6-receptor agonist 1A effectively and safely reduces IOP in normotense, acute, and chronic glaucomatous rabbits, and hence may be suggested as a novel approach for the treatment of glaucoma.

Pharmacologic Characterization of Omidenepag Isopropyl, a Novel Selective EP2 Receptor Agonist, as an Ocular Hypotensive Agent.

The objective of this study was to investigate the pharmacologic characteristics of omidenepag isopropyl (OMDI), a compound developed as a novel intraocular pressure (IOP)-lowering agent, with better IOP control and fewer side effects than other prostanoid receptor agonists such as prostaglandin F receptor (FP) agonists. Binding activities of OMDI and its hydrolyzed form, omidenepag (OMD), to human recombinant prostanoid receptors (DP1-2, EP1-4, FP, and IP) were evaluated. Based on these binding assays, the agonistic activities of OMDI and OMD were further evaluated using cultured cells expressing selected prostanoid receptors. The pharmacokinetics of OMDI after topical administration was assessed in rabbits by measurement of the concentrations of both OMDI and OMD in aqueous humor. The ocular hypotensive effect of OMDI was evaluated in ocular normotensive rabbits, dogs, and both ocular normotensive and hypertensive monkeys. OMD was determined to be a selective EP2 receptor agonist. OMDI weakly bound to EP1; however, the agonistic activity of OMDI to this receptor was not demonstrated in the functional assay. After topical administration of OMDI, OMD was detected in aqueous humor whereas OMDI was not detectable. OMDI significantly lowered IOP in both ocular normotensive and hypertensive animals. The significant ocular hypotensive effects of OMDI were demonstrated by both single and repeated dosing, and its effective duration suggests sufficient efficacy by once-daily dosing. These studies demonstrated that OMDI is hydrolyzed in the eye to OMD, an EP2 receptor agonist, with a significant ocular hypotensive effect in both ocular normotensive and hypertensive animal models.

Long-term intraocular pressure reduction with intracameral polycaprolactone glaucoma devices that deliver a novel anti-glaucoma agent

Long-term treatment of glaucoma, a major leading cause of blindness, is challenging due to poor patient compliance. Therefore, a drug delivery device that can achieve drug release over several months can be highly beneficial for glaucoma management. Here, we evaluate the long-term pharmacokinetics and therapeutic efficacy of polycaprolactone intracameral drug delivery devices in rabbit eyes. Our study showed that a single drug delivery device loaded with a proprietary hypotensive agent, DE-117, reduced intraocular pressure in normotensive rabbits significantly for 23weeks. In addition, we demonstrated that concentration of DE-117 and its hydrolyzed active form (hDE-117) was maintained in the aqueous humor and the target tissue (iris-ciliary body) up to 24weeks. Our proof-of-concept glaucoma implant shows potential as a long-term treatment that circumvents patient compliance barriers compared to current treatment via eye drops.

Comparison of hypotensive, diuretic and renal effects between cladodes of Opuntia ficus-indica and furosemide.

To investigate the diuretic, hypotensive and renal effect of Opuntia ficus-indica in two different species in oral and intravenous administration. Diuretic activity was evaluated in rats with the plant cladode gel and aqueous extract administrated orally, and was evaluated in rabbits with plant extract administered intravenously. Single and repeated doses of cladode gel or aqueous extract of cladode were tested. Urine volume and blood and urine creatinine, sodium and potassium were measured, and creatinine clearance was calculated. The hypotensive effect of lyophilized extract of cladode was evaluated in rabbits. Two polyethylene PE50 catheters were used: one in the jugular vein for the infusion of the plant extract and the other in the carotid for the evaluation of the arterial pressure. The cladode gel or aqueous extract increased urine volume, creatinine clearance and urinary excretion of sodium and potassium without significant effect on serum creatinine or blood urea. Furosemide, gel and aqueous extract of cladode insignificantly lowered plasma potassium in rats. Intravenous administration of the lyophilized extract caused a significant decrease in mean arterial pressure in rabbits with a significant increase in urine volume and urine sodium and potassium; the effect was dose dependent. Intravenous administration of lyophilized extract did not affect plasma sodium or potassium. Gel and aqueous extract of Opuntia ficus-indica cladode have a significant diuretic effect on rats, and the lyophilized extract has a diuretic and hypotensive effect on normotensive rabbits without deterioration in renal function test. Additional studies on active ingredients are essential to pave the way for clinical studies on diuretic and hypotensive effect of the plant.

Novel agonists of melatonin receptors as promising hypotensive and neuroprotective agents for therapy of glaucoma

Melatonin is a pineal hormone that has a capacity to lower intraocular pressure; it exhibits neuroprotective and antioxidant properties that make it possible to use melatonin in the therapy of glaucoma. Analogs of melatonin having affinity to melatonin receptors are promising candidates for application as antiglaucomatous drugs. Chemical modification of the melatonin structure can in-crease efficiency, bioavailability and selectivity of these analogs. We have designed and synthe-sized a number of new 2-oxindole derivatives - ligands of melatonin MT3 subtype receptors that displayed ability to lower intraocular pressure in normotensive rabbits and high antioxidant activity against hydroxyl radical and superoxide anion-radical. The antioxidant activity of new ligands was several times higher than one of melatonin that makes them prospective therapeutic tools for the diseases that include oxidative stress. The maximal hypotensive effect of analogs was comparable to that of melatonin itself but prolonged. Combination of these properties gives an opportunity of using the presented melatonin analogs in complex therapy of glaucoma.

Long Term Glaucoma Drug Delivery Using a Topically Retained Gel/Microsphere Eye Drop

The purpose of this study was to characterize and determine the efficacy of a long-term, non-invasive gel/microsphere (GMS) eye drop for glaucoma. This novel drug delivery system is comprised of a thermoresponsive hydrogel carrier and drug-loaded polymer microspheres. In vitro release of brimonidine from the GMS drops and gel properties were quantified. A single brimonidine-loaded GMS drop was administered to 5 normotensive rabbits and intraocular pressure (IOP) was monitored for 28 days. Here we report that IOP reduction in rabbits receiving a single brimonidine GMS drop was comparable to that of rabbits receiving twice daily, standard brimonidine drops. GMS drops were retained in the inferior fornix in all animals for the length of the study. Our results suggest in vivo efficacy over 28 days from a single GMS drop and a potential decrease in systemic absorption, based on a lack of substantial IOP effects on the fellow untreated eye, compared to brimonidine twice-daily eye drops. To our knowledge, this represents the first long-term, drug-releasing depot that can be administered as a traditional eye drop.

Hemodynamic responses to magnetic stimulation of carotid sinus in normotensive rabbits.

Carotid baroreflex plays a crucial role in regulating arterial pressure. Based on this knowledge, electrical stimulation of carotid sinus was designed for treating resistant hypertension. However, the clinical implication of electrical stimulation of carotid sinus is largely restrained due to obvious invasiveness. This study aimed to evaluate the efficacy of magnetic stimulation of carotid sinus (MSCS), a noninvasive strategy, for lowering blood pressure in rabbits. MSCS with graded intensities and frequencies were systematically attempted in normotensive rabbits. Blood pressure was recorded dynamically. Sinoaortic denervation and plasma hormone level analyses were performed. When the right carotid sinus was stimulated at 1 Hz frequency, a dose-effect relationship was observed between stimulation intensity (100-250% motor threshold) and mean arterial pressure (MAP) decrement (3.6 ± 1.0 to 10.4 ± 2.3 mmHg). When stimulation intensity was fixed at 200% motor threshold, the median reduction of MAP in 1-Hz group [10.8 (8.6-14.9) mmHg] was significantly higher than that in other frequency groups (all P < 0.05). Heart rates declined transiently after the initiation of MSCS. Compared with baseline (33.9 ± 5.5 pg/ml), plasma epinephrine level increased during MSCS (88.1 ± 9.6, P = 0.002). After ipsilateral sinoaortic denervation, MAP decrement (7.0 ± 0.8 mmHg) was remarkably blunted compared with that in sham animals (13.0 ± 1.1 mmHg, P = 0.001). The current study demonstrated that MSCS treatment can lower the arterial pressure in normotensive rabbits. This preliminarily result warrants further studies to establish the efficacy of MSCS in treating refractory hypertension.

The role of hyaluronan as a drug carrier to enhance the bioavailability of extended release ophthalmic formulations. Hyaluronan-timolol ionic complexes as a model case

The aim of this work was to obtain information concerning the properties of ophthalmic formulations based on hyaluronic-drug ionic complexes, to identify the factors that determine the onset, intensity and duration of the pharmacotherapeutic effect.Dispersions of a complex of 0.5% w/v of sodium hyaluronate (HyNa) loaded with 0.5% w/v of timolol maleate (TM) were obtained and presented a counterionic condensation higher than 75%. For comparison a similar complex obtained with hyaluronic acid (HyH) was also prepared. Although the viscosity of HyNa-TM was significantly higher than that of HyH-TM, in vitro release of TM from both complexes showed a similar extended drug release profile (20–31% over 5h) controlled by diffusion and ionic exchange.Ocular pharmacokinetic study performed in normotensive rabbits showed that HyNa-TM complex exhibited attractive bioavailability properties in the aqueous humor (AUC and Cmax significantly higher and later Tmax) compared to commercial TM eye-drops. Moreover, a more prolonged period of lowered intra-ocular pressure (10h) and a more intense hypotensive activity was observed after instillation of a drop of HyNa-TM as compared to the eye-drops. Such behavior was related to the longer pre-corneal residence times (400%) observed with HyNa-TM complex. No significant changes in rabbit transcorneal permeation were detected upon complexation.These results demonstrate that the ability of HyNa to modulate TM release, together with its mucoadhesiveness related to the viscosity, affected both the pharmacokinetic and pharmacodynamic parameters. The HyNa-TM complex is a potentially useful carrier for ocular drug delivery, which could improve the TM efficacy and reduce the frequency of administration to improve patient compliance.

Co-encapsulated resveratrol and quercetin in chitosan and peg modified chitosan nanoparticles: For efficient intra ocular pressure reduction

Natural anti-oxidants resveratrol (RES) and quercetin (QUR) posses the ability to reduce intra ocular pressure efficiently. Concurrent administration of RES and QUR was able to enhance the bioavailability of RES. Present research work describes upsurge of QUR in RES loaded chitosan (CS) nanoparticles (NPs) and polyethylene glycol (PEG) modified CS NPs for improved delivery and synergic effects on reducing intra ocular pressure for the treatment of glaucoma. CS NPs and PEG modified CS NPs were prepared by ionic gelation of tripolyphosphate and CS. The synthesised NPs were spherical in shape and RES entrapment and loading efficiency in the formulation decreased with increasing PEG concentration. Particle size of the formulation increased while incorporating PEG and drugs. The crystalline nature of RES and QUR changed in the NPs and that was confirmed by XRD study. Free radical neutralising efficiency improved while incorporating QUR in the formulation. Ex-vivo corneal permeation of RES was higher from RES and QUR loaded formulation than RES alone containing NPs and free RES dispersion. RES and QUR loaded PEG modified CS NPs showed sustained and enhanced reduction of intra ocular pressure (5.5±0.5mmHg) in normotensive rabbits.

Effect of Silibinin in Lowering the Intraocular Pressure in Normotensive Rabbits: Interaction with Betaxolol

Previous reports demonstrated the effectiveness of silibinin hemisuccinate as a potential intraocular pressure-lowering agent. The exact mechanism by which silibinin exerted this effect has not yet been documented, but might suggested to interfere with aqueous humor formation. The present study was designed to evaluate the comparative efficacy of silibinin as IOP lowering agent to that of betaxolol in normotensive rabbits, and the interaction of silibinin with betaxolol as a way for investigating the possible mechanism of action of silibinin in this respect. The effects of instillation of 0.75% silibinin solution and 0.5% betaxolol eye drops in the eyes of normotensive rabbits were evaluated using indentation tonometry. The results showed that 0.75% solution of silibinin was more potent than betaxolol (0.5%) in lowering IOP in normotensive rabbits. Furthermore, the effect of pre- and post-instillation of silibinin-betaxolol combination showed a characteristic antagonistic feature. In conclusion, silibinin appears to be more potent than betaxolol in lowering IOP in normotensive rabbits; the pre- and post-instillation of silibinin provide experimental evidence for the possible antagonistic effect of betaxolol with the IOP-lowering effect of silibinin.&#x0D; Key words: silibinin, betaxolol, cAMP, PDE-inhibitors

Effect of Silibinin in Lowering the Intraocular Pressure in Normotensive Rabbits: Interaction with Pilocarpine and Cyclopentolate

Previous data indicated the effectiveness of silibinin as intraocular pressure (IOP) - lowering agent. The present study was performed to evaluate the interaction of silibinin with pilocarpine or cyclopentolate in lowering IOP in normotensive rabbits. The effects of topically instilled silibinin hemisuccinate solution (0.75%) alone or adjunctly combined with 2% pilocarpine or 1% cyclopentolate on the IOP of normotensive rabbits were evaluated using indentation tonometry. The results showed that 0.75% solution of silibinin was found more potent than pilocarpine (2% drops) in lowering IOP of normotensive rabbits, while their combination results in longer duration of action. Moreover, the elevated IOP values produced by cyclopentolate (1%drops) were decreased by silibinin, while prior instillation of cyclopentolate did not interfere with the IOP-lowering effect of silibinin. In conclusion Silibinin lowers IOP in normotensive rabbits more than pilocarpine, and their combination elongates the duration of the IOP-lowering effect. This might be due to interference with aqueous humor formation as a possible mechanism. In addition, cyclopentolate did not significantly alter the effect of silibinin on IOP.&#x0D; Key words: silibinin, IOP, pilocarpine, cyclopentolate