Effects of Dinucleoside Polyphosphates on Trabecular Meshwork Cells and Aqueous Humor Outflow Facility

Abstract

The most important risk factor for the development of glaucoma is elevated intraocular pressure (IOP). Hypotensive drugs decrease IOP, preventing optic nerve damage and further vision loss. The balance between aqueous humor (AH) production and drainage determines IOP, and problems in AH outflow pathways are associated with open-angle glaucoma development. Previous studies have shown the presence of diadenosine tetraphosphate (Ap 4 A) and pentaphosphate (Ap 5 A) in the AH. Topic application of Ap 4 A to the cornea decreased IOP, whereas Ap 5 A increased it. Because dinucleoside polyphosphates stimulate P2Y purinergic receptors, we studied their presence in trabecular meshwork (TM) cells. Additionally, the effects of diadenosine polyphosphates (Ap n As; n ϭ 3-5) and Up 4 U (P 1 ,P 4 -(diuridine 5Ј)-tetraphosphate; INS365) in outflow facility were tested. P2Y 1 , P2Y 2 , and P2Y 4 receptors were detected in TM cells by Western blot and immunocytochemistry. In TM cells, Ap 3 A, Ap 4 A, and Ap 5 A induced discrete intracellular calcium concentration ([Ca 2ϩ ] i ) mobilizations compared with higher and more sustained [Ca 2ϩ ] i mobilizations after Up 4 U application. In bovine ocular anterior segments perfused at constant pressure, 1 M Ap 3 A or Ap 4 A increased outflow facility, whereas Up 4 U or Ap 5 A did not modify it. 2-MeSADP, a selective P2Y 1 agonist, induced outflow facility increases similar to those obtained after Ap 3 A and Ap 4 A, and these were prevented by addition of the selective P2Y 1 receptor antagonist MRS-2179 (2Ј-deoxy-N 6 -methyladenosine-3Ј,5Ј-diphosphate). Our results demonstrate that the hypotensive effect of Ap 4 A and other dinucleotides is mediated, at least in part, by increasing trabecular outflow facility through activation of P2Y 1 receptors. The latter would seem to be an interesting target in the development of antiglaucomatous drugs to selectively increase AH outflow.In the eye, elevated intraocular pressure (IOP) due to impaired aqueous humor (AH) drainage is a major risk factor in the development of glaucoma. Glaucoma is the most important cause of irreversible nontraumatic blindness in the world and affects more than 66 million people. The main determinant of IOP is the volume of AH contained in the anterior and posterior chambers. AH is produced in the ciliary epithelium and eliminated through the outflow pathways in the anterior chamber angle. In several species, but especially in the primate eye, most AH flows through the trabecular meshwork (TM), a sponge-like filtering tissue, where it reaches Schlemm's canal and the collector channels before finally entering the venous system. The structure of the TM and its ability to modify its resistance to AH outflow play a key role in maintaining the IOP in the anterior chamber within its physiological range. TM cells express several receptors to substances released either in the AH from different ocular tissues (Mitchell et al., 1998;Coca-Prados et al., 1999) or from ocular innervation (Selbach et al., 2000) in physiologic...

Diadenosine tetraphosphate as a potential therapeutic nucleotide to treat glaucoma

“…The effect reducing IOP through P2Y 1 receptors triggered by Ap 4 A has been quoted previously [13]. Moreover, this effect has been linked to the presence of P2Y 1 receptors in the place when the aqueous humour is drained, the trabecular meshwork [33].…”

“…The reasons for such differences are the targets of Ap 4 A and dorzolamide. While Ap 4 A can act on different purinergic receptors, some producing ocular hypertension (P2Y 2 [14]) and other hypotension (P2Y 1 [13] and P2Y 6 [29]), dorzolamide acts straight on carbonic anhydrases, reducing aqueous humour production [30]. So, it is clear that the dinucleotide final effect on IOP is the consequence of acting on several receptors (some reducing, some increasing IOP) while dorzolamide acts only on carbonic anhydrases.…”

“…Ap 4 A has been described as P2Y 1 , P2Y 2 and P2Y 6 selective agonist and P2Y 13 selective antagonist [19][20][21][22]. *** *** Fig.…”

“…Nevertheless, when the actions of this dinucleotide are studied individually, either in the trabecular meshwork or in the ciliary body, the results seem to be contradictory [13,14]. To complicate the complexity of dinucleotides in the regulation of aqueous humour dynamics even more, studies have shown that glaucomatous patients present increased levels of Ap 4 A in their aqueous humour [7], which were almost 15 times higher in glaucoma patients than in healthy individuals.…”

The role of dinucleoside polyphosphates on the ocular surface and other eye structures

“…Effect on the trabecular meshwork. Trabecular meshwork presents many P2Y receptors, mainly P2Y 1 , P2Y 2 , and P2Y 4 in bovine TM cells (Soto et al, 2005) and P2Y 11 in a cellular line of human trabecular meshwork (Crosson et al, 2004). Diadenosine polyphosphates do not activate all these receptors in the same way.…”