Dinucleoside polyphosphates in the eye: from physiology to therapeutics.

Diadenosine polyphosphates are a family of dinucleotides with emerging biochemical, physiological, pharmacological and therapeutic properties in the eye and other tissues. These compounds are formed by two adenosine moieties linked by their ribose 5'-ends to a variable number of phosphates. Diadenosine polyphosphates are present as active components of ocular secretions such as tears and aqueous humour and they can activate P2 purinergic receptors present on the ocular surface, anterior segment and retina. Both metabotropic and ionotropic actions mediated by P2Y and P2X receptors, respectively are responsible for the control of processes such as induction of tear secretion, lysozyme production or acceleration of corneal wound healing. Inside the eye the dinucleotide Ap(4)A can reduce intraocular pressure by acting on P2Y(1) receptors present in trabecular meshwork cells and on P2X(2) receptors present on the cholinergic terminals located in the ciliary muscle. In the retina, derivatives of diadenosine polyphosphates can improve the re-absorption of fluids in retinal detachment. Altogether, diadenosine polyphosphates are not only dinucleotides with roles in the physiology of the eye but it is also possible that their properties may serve to help in the treatment of some ocular pathologies.