Myopia-Inhibiting Concentrations of Muscarinic Receptor Antagonists Block Activation of Alpha_2A-Adrenoceptors In Vitro

Abstract

Citation: Carr BJ, Mihara K, Ramachandran R, et al. Myopia-inhibiting concentrations of muscarinic receptor antagonists block activation of alpha 2A -adrenoceptors in vitro. Invest Ophthalmol Vis Sci. 2018;59:2778-2791. https://doi.org/10.1167 PURPOSE. Myopia is a refractive disorder that degrades vision. It can be treated with atropine, a muscarinic acetylcholine receptor (mAChR) antagonist, but the mechanism is unknown. Atropine may block a-adrenoceptors at concentrations ‡0.1 mM, and another potent myopiainhibiting ligand, mamba toxin-3 (MT3), binds equally well to human mAChR M 4 and a 1A -and a 2A -adrenoceptors. We hypothesized that mAChR antagonists could inhibit myopia via a 2A -adrenoceptors, rather than mAChR M 4 . METHODS.Human mAChR M 4 (M 4 ), chicken mAChR M 4 (cM 4 ), or human a 2A -adrenergic receptor (hADRA2A) clones were cotransfected with CRE/promoter-luciferase (CRE-Luc; agonist-induced luminescence) and Renilla luciferase (RLuc; normalizing control) into human cells. Inhibition of normalized agonist-induced luminescence by antagonists (ATR: atropine; MT3; HIM: himbacine; PRZ: pirenzepine; TRP: tropicamide; OXY: oxyphenonium; QNB: 3-quinuclidinyl benzilate; DIC: dicyclomine; MEP: mepenzolate) was measured using the DualGlo Luciferase Assay System. RESULTS.Relative inhibitory potencies of mAChR antagonists at mAChR M 4 /cM 4 , from most to least potent, were QNB > OXY ‡ ATR > MEP > HIM > DIC > PRZ > TRP. MT3 was 563 less potent at cM 4 than at M 4 . Relative potencies of mAChR antagonists at hADRA2A, from most to least potent, were MT3 > HIM > ATR > OXY > PRZ > TRP > QNB > MEP; DIC did not antagonize.CONCLUSIONS. Muscarinic antagonists block hADRA2A signaling at concentrations comparable to those used to inhibit chick myopia ( ‡0.1 mM) in vivo. Relative potencies at hADRA2A, but not M 4 /cM 4 , correlate with reported abilities to inhibit chick form-deprivation myopia. mAChR antagonists might inhibit myopia via a 2 -adrenoceptors, instead of through the mAChR M 4 /cM 4 receptor subtype.

Prevention of Progression in Myopia: A Systematic Review

“…Studies in animal models reinforced the role of DA in association with light exposure, already hypothesized by Rose et al [55]. In fact, Ashby et al referred in chicks exposed to high luminance levels the failure to retard myopia development, when injected with spiperone (500 μM), a D2-dopaminergic antagonist [28]. Further studies must be performed in the future, in order to elucidate the complex relation between dopamine levels, sun light exposure and outdoor activities.…”

“…Many bio-molecular pathways have been investigated in the pathogenesis of myopia. Although the role of cholinergic, nitric oxide (NO) and, more recently, insulin pathways have been studied, the importance of dopamine (DA) remains crucial in the development of experimental myopia [27,28,29].…”

Short-Term Effect of Low-Dose Atropine and Hyperopic Defocus on Choroidal Thickness and Axial Length in Young Myopic Adults

“…The atropine eye drops used in this study were combined with benzalkonium chloride (BAK) 0.1 mg/mL, which improves penetration through the cornea [35]. Further, once inside the eye, atropine reaches the intraocular concentration of 659 nM, which is significantly higher than IC50 value for atropine (20 nM) for the human iris and ciliary muscle receptor when using carbachol as the agonist [33] and its affinity at human M4 receptor (0.125–0.25 nM) [36]. Therefore, the concentrations of atropine in the eye after a single topical application in this study are likely to be within a range capable of reaching the choroid within 60 minutes.…”

Gene expression in response to optical defocus of opposite signs reveals bidirectional mechanism of visually guided eye growth

“…Some of over 100 canonical pathways involved in the regulation of the retinal response to defocus of opposite signs are listed in the fourth column. Three pathways have been previously targeted pharmacologically for myopia control (fifth column): (1) dopamine signaling was suggested to be a target for apomorphine, reserpine, and 6-OHDA [ 52 ]; (2) nitric oxide signaling was implicated in the anti-myopic atropine effect [ 53 ]; and (3) α-adrenergic signaling was suggested to be a target of atropine, oxyphenonium, and pirenzepine [ 54 ]. BESOD, Bidirectional Emmetropization by the Sign of Optical Defocus; cAMP, cyclic adenosine monophosphate; CREB, cAMP responsive element binding protein; CNTF, ciliary neurotrophic factor; DARPP32, dopamine- and cAMP-regulated phosphoprotein 32 kDa; EIF2, eukaryotic translation initiation factor 2; eIF4, eukaryotic initiation factor 4; HIPPO, protein kinase Hippo; JAK, Janus kinase; JNK, c-Jun N-terminal kinase; mTOR, mammalian target of rapamycin; NAD, nicotinamide adenine dinucleotide; NGF, nerve growth factor; nNOS, neuronal nitric oxide synthase; PTEN, phosphatase and tensin homolog; p70S6K, ribosomal protein S6 kinase; RAN, Ras-related nuclear protein; RANK, receptor activator of nuclear factor kappa-B; SAPK, stress-activated protein kinase; Stat, signal transducer and activator of transcription protein; TNFR1, tumor necrosis factor receptor 1; Wnt, Wingless-integrated; 6-OHDA, 6-hydroxydopamine.…”