Transitory models of experimentally induced intraocular pressure changes in the rabbit. A reappraisal

In vitro and in vivo efficacy of SYL040012, a novel siRNA compound for treatment of glaucoma

Glaucoma is a progressive ocular syndrome characterized by degeneration of the optic nerve and irreversible visual field loss. Elevated intraocular pressure (IOP) is the main risk factor for glaucoma. Increased IOP is the result of an imbalance between synthesis and outflow of aqueous humor (AH). Blocking β2 adrenergic receptor (ADRB2) has shown to reduce IOP by decreasing production of AH at the ciliary body (CB). SYL040012 is a siRNA designed to specifically silence ADRB2 currently under development for glaucoma treatment. Here, we show that SYL040012 specifically reduces ADRB2 expression in cell cultures and eye tissues. The compound enters the eye shortly after administration in eye drops and is rapidly distributed among structures of the anterior segment of the eye. In addition, SYL040012 is actively taken up by cells of the CB but not by cells of systemic organs such as the lungs, where inhibition of ADRB2 could cause undesirable side effects. Moreover, SYL040012 reduces IOP in normotensive and hypertensive animal models and the effect appears to be long lasting and extremely well tolerated both locally and systemically.

Current status of prostaglandin therapy: latanoprost and unoprostone

Latanoprost, a prostaglandin F(2alpha) analog prodrug, and unoprostone, an analog of a prostaglandin metabolite, have been shown to be effective in decreasing intraocular pressure when used alone or in combination with other ocular hypotensive agents. The increase in the uveoscleral outflow and some of the side effects are probably FP-receptor mediated, which may account for some differences between the cited drugs. This article reviews the recent literature available on the clinical efficacy of these prostanoids, as well as the studies directly comparing these drugs.

Ocular hypotension induced by topical dopaminergic drugs and phosphodiesterase inhibitors

The aim of this work was to investigate the ocular hypotensive activity of some topically administered cAMP-phosphodiesterase inhibitors alone and in combination with dopaminergic compounds. Experiments were performed with ocular normotensive rabbits and during transitory induced ocular hyper- or hypotension. An ocular hypotensive effect was observed after instillation of aminophylline, dyphylline, pentoxifylline, caffeine, and iso-caffeine, but not following topical hydroxypropyl-1,3-dimethylxanthine. Dopaminergic compounds were also studied in order to be combined with phosphodiesterase inhibitors as ocular anti-hypertensive treatment. Significant ocular hypotensive activity was observed after topical application of trifluperidol, fluphenazine, thiothixene, and the S(-) enantiomer of 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP). Of the cAMP-phosphodiesterase inhibitors that were tested, pentoxifylline was the most interesting compound, with good ocular tolerance, significant reduction in intra-ocular pressure, and potential retinal microvascular benefits. After allowing adequate time for pentoxifylline to reach its maximal activity, trifluperidol or S(-)-3-PPP was also instilled. A more pronounced ocular hypotensive effect was then observed. The findings of this study may suggest that administration of eye-drops combining drugs acting by separate ways on second messengers involved in the regulation of intra-ocular pressure (e.g. cyclic AMP) could be used to reduce intra-ocular pressure during glaucoma.

Ocular actions of an octahydrobenzo[f]quinoline: Ha117

An octahydrobenzo[f]quinoline compound, Ha117, was examined for activity on: (1) intraocular pressure and in normal, sympathectomized and water loaded rabbits and aqueous flow rate in normal and sympathectomized rabbits, respectively; (2) contractions of the cat nictitating membrane elicited by electrical stimulation of cervical sympathetic nerves; (3) cAMP accumulation in the isolated rabbit iris root-ciliary body preparation. Ha117 lowered intraocular pressure and aqueous flow rate in normal but not in sympathectomized rabbits. Elevated intraocular pressure produced by water loading was suppressed by Ha117 and pretreatment with metoclopramide antagonized the inhibitory effect of Ha117. Neuronally mediated contractions of the nictitating membrane were inhibited in a dose-related fashion by Ha117, and inhibitory effects were antagonized by domperidone. Ha117 and an analog, Ha118, did not suppress isoproterenol- and vasoactive intestinal peptide-induced accumulation of cAMP in the rabbit iris root/ciliary body. In vivo results in rabbit and cat models suggest that the ocular hypotensive effect of Ha117 is mediated by an action on prejunctional dopamine (DA2) receptors. In vitro data in the rabbit iris root/ciliary body suggest that Ha117 and Ha118-induced lowering of intraocular pressure does not involve postjunctional suppression of cAMP accumulation.