Adenosine, adenosine receptors and glaucoma: an updated overview.

BACKGROUND: Glaucoma, a leading cause of blindness worldwide, is an optic neuropathy commonly associated with elevated intraocular pressure (IOP). The major goals of glaucoma treatments are to lower IOP and protect retinal ganglion cells. It has been revealed recently that adenosine and adenosine receptors (ARs) have important roles in IOP modulation and neuroprotection. SCOPE OF REVIEW: This article reviews recent studies on the important roles of adenosine and ARs in aqueous humor formation and outflow facility, IOP and retinal neuroprotection. MAJOR
CONCLUSIONS: Adenosine and several adenosine derivatives increase and/or decrease IOP via A2A AR. Activation of A1 AR can reduce outflow resistance and thereby lower IOP, A3 receptor antagonists prevent adenosine-induced activation of Cl(-) channels of the ciliary non-pigmented epithelial cells and thereby lower IOP. A1 and A2A agonists can reduce vascular resistance and increase retina and optic nerve head blood flow. A1 agonist and A2A antagonist can enhance the recovery of retinal function after ischemia attack. Adenosine acting at A3 receptors can attenuate the rise in calcium and retinal ganglion cells death accompanying P2X(7) receptor activation. GENERAL SIGNIFICANCE: Evidence suggested that the adenosine system is one of the potential target systems for therapeutic approaches in glaucoma.