Nitric Oxide (NO) Mediates the Inhibition of Form-Deprivation Myopia by Atropine in Chicks

Abstract

Myopia is the most common childhood refractive disorder. Atropine inhibits myopia progression, but its mechanism is unknown. Here, we show that myopia-prevention by atropine requires production of nitric oxide (NO). Form-deprivation myopia (FDM) was induced in week-old chicks by diffusers over the right eye (OD); the left eye (OS) remained ungoggled. On post-goggling days 1, 3, and 5, OD received intravitreally 20 µL of phosphate-buffered saline (vehicle), or vehicle plus: NO source: L-arginine (L-Arg, 60–6,000 nmol) or sodium nitroprusside (SNP, 10–1,000 nmol); atropine (240 nmol); NO inhibitors: L-NIO or L-NMMA (6 nmol); negative controls: D-Arg (10 µmol) or D-NMMA (6 nmol); or atropine plus L-NIO, L-NMMA, or D-NMMA; OS received vehicle. On day 6 post-goggling, refractive error, axial length, equatorial diameter, and wet weight were measured. Vehicle-injected goggled eyes developed significant FDM. This was inhibited by L-Arg (ED50 = 400 nmol) or SNP (ED50 = 20 nmol), but not D-Arg. Higher-dose SNP, but not L-Arg, was toxic to retina/RPE. Atropine inhibited FDM as expected; adding NOS-inhibitors (L-NIO, L-NMMA) to atropine inhibited this effect dose-dependently, but adding D-NMMA did not. Equatorial diameter, wet weight, and metrics of control eyes were not affected by any treatment. In summary, intraocular NO inhibits myopia dose-dependently and is obligatory for inhibition of myopia by atropine.

Myopia-Inhibiting Concentrations of Muscarinic Receptor Antagonists Block Activation of Alpha2A-Adrenoceptors In Vitro

“…Whether a 2 -adrenoceptor ligands can also modulate NOS (neuronal NOS, eNOS, or inducible NOS) activity or expression in retinal neurons is worth investigating further, since synthesis and release of nitric oxide are necessary for myopia inhibition by atropine, and have been associated strongly with reduction of eye growth. 57 …”

“…Currently, the site of action for atropine-mediated myopia inhibition is unknown, but best guesses identify the retina, choroid, and/ or sclera. 56 In chicks, intravitreal injection is the usual method of delivery, and concentrations of 1 to 100 mM have been used for mAChR antagonist-mediated inhibition of FDM 16,57,58 (Table 1). Unfortunately, no studies exist on the ocular distribution of atropine after intravitreal injection into chick eyes; but one study has investigated the ocular distribution, in chicks, of a single dose of intravitreally injected radioactively labeled pirenzepine.…”

The Influence of the Autonomic Nervous System on the Human Choroid

“…2002;302:397-405. Considering this evidence, muscarinic blockers could prevent myopia by stimulating the synthesis and release of nitric oxide, which in turn relaxes both vascular and nonvascular smooth muscles leading to the increase in choroidal thickness observed in this study (Chapter two, Chapter three and Chapter four). This hypothesis is in agreement with a recent study (Carr and Stell, 2016), which has shown that blockade of NO-synthesis prevented myopia inhibition by atropine.…”

“…Similarly, a recent study has demonstrated that atropine prevents myopia by inducing NO synthesis, supporting an important role of NO in this process (Carr and Stell, 2016).…”

“…Over the past five-10 years, several novel approaches to modulate NO signaling have been proposed, including increased time spent outdoors since increased light stimulates synthesis and release of NO from the retina (Hoshi et al, 2003;French et al, 2013Carr and Stell, 2016), nitric oxide-donating latanoprost (Latanoprostene bunod -LBN), which triggers the NO/cGMP signaling cascade promoting rearrangement of cytoskeletal architecture and increased cell relaxation (Cavet et al, 2014;Garcia et al, 2016), or dietary supplements (i.e. inorganic nitrate in the form of beetroot juice) that act as a substrate for NO formation (van Faassen et al, 2009;Weitzberg and Lundberg, 2013).…”