Beta2 adrenergic receptor silencing change intraocular pressure in New Zealand rabbits.

PURPOSE/AIM: Glaucoma consists of a group of progressive optic neuropathies that are characterized by degeneration of the optic nerve and irreversible visual filed loss. Elevated intraocular pressure is the only proven treatable risk factor and commercial products used for glaucoma treatment are focused in lowering intraocular pressure. These drugs can have various undesirable side effects and this invites to look for new strategies. The purpose of this work is to study the use of a siRNA (small interfering RNA) to selectively silence beta2 adrenergic receptors and to see whether it reduces IOP (intraocular pressure). MATERIAL AND METHODS: Topical instillation of beta2 adrenergic receptors small-interfering RNA (siRNA, 25-250µg) was applied and IOP was measured with a Tonopen XL up to 9 consecutive days. The effect of such siRNA was compared to commercial compounds such as Timoftlol, Trusopt and Xalatan, and it was also analyzed if some anatomical changes occurred by microscopy. RESULTS: siRNA designed for beta2 adrenergic receptor induced a reduction of intraocular pressure (IOP) of 30±5%, compared to a control (scrambled siRNA). The results in terms of IOP decrease were similar to that found with commercial compounds but a long-lasting hypotensive action was shown by beta2 adrenergic receptor siRNA treatment as compared to commercial drugs. No apparent side effects were observed in the ocular structures. CONCLUSION: The use of siRNA against the beta2 adrenergic receptors could provide an interesting therapeutic strategy for glaucoma treatment.

Understanding the Presence and Roles of Ap4A (Diadenosine Tetraphosphate) in the Eye.

Diadenosine tetraphosphate abbreviated Ap4A is a naturally occurring dinucleotide, which is present in most of the ocular fluids. Due to its intrinsic resistance to enzyme degradation compared to mononucleotides, this molecule can exhibit profound actions on ocular tissues, including the ocular surface, ciliary body, trabecular meshwork, and probably the retina. The actions of Ap4A are mostly carried out by P2Y2 receptors, but the participation of P2X2 and P2Y6 in processes such as the regulation of intraocular pressure (IOP), together with the P2Y2, is pivotal. Beyond the physiological role, this dinucleotide can present on the ocular surface keeping a right production of tear secretion or regulating IOP. It is important to note that exogenous application of Ap4A to cells or animal models can significantly modify pathophysiological conditions and thus is an attractive therapeutic molecule. The ocular location where Ap4A actions have not been fully elucidated is in the retina. Although some analogues show interesting actions on pathological situations such as retinal detachment, little is known about the real effect of this dinucleotide, this being one of the challenges that require pursuing in the near future.

Diadenosine tetraphosphate as a potential therapeutic nucleotide to treat glaucoma.

Glaucoma is a neurodegenerative disease that produces blindness. The main factor associated with this disease is an abnormally elevated intraocular pressure (IOP). To date, some attempts have been made to demonstrate the role of nucleotides modulating IOP, but never in a model of glaucoma. The DBA/2J mouse is an animal that develops the pathology spontaneously, starting from the typical rise in IOP at 9 months of age. Using this animal model, together with a control mouse, C57BL/6J, it has been possible to monitor the elevation in IOP in the glaucomatous mice and to check the ability of the dinucleotide diadenosine tetraphosphate AKA Ap4A to reduce IOP. The topical application of Ap4A when IOP is maximal (9-12 months) reduced IOP 30.6 ± 6.6% in the DBA/2J and 17.9 ± 4.0% in the C57BL/6J mice. Concentration response curves in both animal strains produced similar pD2 values; these being 4.9 ± 0.5 and 5.1 ± 0.4 for the normotensive C57BL/6J and the glaucomatous DBA/2J respectively. Antagonist studies showed differences between the control and the glaucomatous animals. In particular, the main receptor reducing IOP in the control animal was the P2Y1 receptor and in the glaucomatous model the P2Y6, although the participation of other P2 receptors cannot be ruled out. The long-term effect of Ap4A applied three times a week for 3 months showed a clear stop in the elevation of IOP in the glaucomatous model, thus indicating the possibility of using Ap4A as an effective compound for the treatment of glaucoma.