Effects of nitric oxide donors and nitric oxide synthase substrates on ciliary muscle contracted by carbachol and endothelin for possible use in myopia prevention

Network Pharmacology, Molecular Docking, and Molecular Dynamic-Based Investigation on the Mechanism of Compound Chrysanthemum in the Treatment of Asthenopia

As a clinical empirical prescription for ophthalmology, compound chrysanthemum has been used gradually and has a good effect on eye fatigue. However, the detailed mechanisms of antiasthenopia have not been studied. In order to clarify the mechanisms of the compound chrysanthemum in the treatment of asthenopia, network pharmacology was combined with experimental study in this paper. A total of 593 genes and 39 active chemicals were identified, and both were considered to be essential to the advancement of asthenopia research. The results of the molecular docking analysis demonstrated a certain affinity between PRKACA, PRKCA, PRKCB, and their related compounds; molecular dynamic simulations assessed the stability of these receptors and ligands. The effects of compound chrysanthemum extract on ciliary muscle were studied in vitro and in vivo. By using the MTT assay, compound chrysanthemum extracts (50, 100, 200, 400, and 800 g·mL-1) showed no effect on the proliferation of rCSMCs for 24 and 48 hours. It raised nitric oxide and decreased Ca²⁺ in ciliary muscle cells isolated from the eyeballs of rats. Besides, compound chrysanthemum extract had a direct relaxing effect on the isolated gastric smooth muscle of rats by reducing the contractile tension. Furthermore, in vivo experiment results showed that, compared to the incandescent lamp-irradiated rats (model group), SD rats treated with compound chrysanthemum extracts (660 mg·kg^-1 and 1320 mg·kg^-1, orally) displayed considerably retracted pupils and increased NO content. It is also found that compound chrysanthemum extract can downregulate the mRNA expression of PKA and PKC in the calcium signaling pathway. Overall, our results suggested that compound chrysanthemum extract may lessen visual fatigue through multiple components, multiple targets, and multiple pathways.

The vital role for nitric oxide in intraocular pressure homeostasis

Catalyzed by endothelial nitric oxide (NO) synthase (eNOS) activity, NO is a gaseous signaling molecule maintaining endothelial and cardiovascular homeostasis. Principally, NO regulates the contractility of vascular smooth muscle cells and permeability of endothelial cells in response to either biochemical or biomechanical cues. In the conventional outflow pathway of the eye, the smooth muscle-like trabecular meshwork (TM) cells and Schlemm's canal (SC) endothelium control aqueous humor outflow resistance, and therefore intraocular pressure (IOP). The mechanisms by which outflow resistance is regulated are complicated, but NO appears to be a key player as enhancement or inhibition of NO signaling dramatically affects outflow function; and polymorphisms in NOS3, the gene that encodes eNOS modifies the relation between various environmental exposures and glaucoma. Based upon a comprehensive review of past foundational studies, we present a model whereby NO controls a feedback signaling loop in the conventional outflow pathway that is sensitive to changes in IOP and its oscillations. Thus, upon IOP elevation, the outflow pathway tissues distend, and the SC lumen narrows resulting in increased SC endothelial shear stress and stretch. In response, SC cells upregulate the production of NO, relaxing neighboring TM cells and increasing permeability of SC's inner wall. These IOP-dependent changes in the outflow pathway tissues reduce the resistance to aqueous humor drainage and lower IOP, which, in turn, diminishes the biomechanical signaling on SC. Similar to cardiovascular pathogenesis, dysregulation of the eNOS/NO system leads to dysfunctional outflow regulation and ocular hypertension, eventually resulting in primary open-angle glaucoma.

Therapeutic Effects of Anthocyanins for Vision and Eye Health

Anthocyanin (AC) is widely used as supplement of eye health in Europe and in East Asia. In this review, I describe AC effects to clarify the mechanism is important in order to understand the effects of AC on vision health. The bioavailability of AC is quite low but, reported as intact form and many kinds of metabolite. And AC passes through the blood-aqueous fluid barrier and blood-retinal barrier. In vitro study, AC had a relaxing effect on ciliary muscle which is important to treat both myopia and glaucoma. And AC stimulate the regeneration of rhodopsin in frog rod outer segment. Furthermore, AC could inhibit the axial length and ocular length elongation in a negative lens-induced chick myopia model. In addition, we summarized clinical studies of AC intake improved dark adaptation and transient myopic shift and the improvement on retinal blood circulation in normal tension glaucoma patients.

Aqueous Extract of Perilla frutescens var. acuta Relaxes the Ciliary Smooth Muscle by Increasing NO/cGMP Content In Vitro and In Vivo

The leaves of Perilla frutescens var. acuta (PFA) are commonly used as a traditional medicine in Korea, Japan, and China. We previously showed that PFA attenuates eye fatigue by improving visual accommodation through a clinical study. However, detailed mechanisms and chemical compounds have not been studied. In this study, we analyzed the active compounds in an aqueous extract of PFA involved in ciliary muscle relaxation in vitro and in vivo. NMR and MS analyses showed that the PFA extract contained mainly luteolin-7-O-diglucuronide and apigenin-7-O-diglucuronide. The composition after freeze-drying and spray-drying was similar. Freeze-dried PFA (50 µg/mL, 100 µg/mL, and 200 µg/mL) increased nitric oxide and cGMP levels in ciliary muscle cells isolated from the eyes of rats. [Ca²⁺]i decreased in a dose-dependent manner. Furthermore, Sprague-Dawley rats treated with freeze-dried PFA (200 mg/kg, orally) showed significantly increased cGMP levels compared with the control group and irradiated with white light. Our results suggest that PFA extract has the potential to reduce eye fatigue by relaxing ciliary muscles.

The effect of endothelin receptor antagonists in the endotoxin-induced uveitis rabbit model. Cutan Ocul Toxicol 2017;37:133-138. [PMID: 28707522 DOI: 10.1080/15569527.2017.1355317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

PURPOSE

To investigate the effect of Bosentan (non-selective endothelin receptor antagonist) and BQ123 (ET_A receptor antagonist) on intraocular inflammation in an endotoxin-induced uveitis (EIU) rabbit model.

METHODS

Uveitis was induced by intravitreal injection of lipopolysaccharide (LPS). The animals were divided into 7 groups and there were six rabbits in each group (saline, saline and ethanol, bosentan, BQ123, lipopolysaccharide (LPS), bosentan and LPS, BQ123 and LPS-injected groups). Bosentan and BQ123 were applied before LPS injection. Aqueous humour was collected at 24th hour post-injections and enucleation was performed for the evaluation of histopathological changes.

RESULTS

BQ123 decreased clinical score, cell counts and protein amount more than bosentan and it was significant for cell counts (p = 0.018). Bosentan significantly diminished inflammatory reactions more than BQ123 as shown in histopathological specimens (p = 0.002).

CONCLUSIONS

ET_A receptor blockage is effective on uveitis treatment by its protective effect on blood aqueous barrier.

Role of nitric oxide in murine conventional outflow physiology

Elevated intraocular pressure (IOP) is the main risk factor for glaucoma. Exogenous nitric oxide (NO) decreases IOP by increasing outflow facility, but whether endogenous NO production contributes to the physiological regulation of outflow facility is unclear. Outflow facility was measured by pressure-controlled perfusion in ex vivo eyes from C57BL/6 wild-type (WT) or transgenic mice expressing human endothelial NO synthase (eNOS) fused to green fluorescent protein (GFP) superimposed on the endogenously expressed murine eNOS (eNOS-GFPtg). In WT mice, exogenous NO delivered by 100 μM S-nitroso-N-acetylpenicillamine (SNAP) increased outflow facility by 62 ± 28% (SD) relative to control eyes perfused with the inactive SNAP analog N-acetyl-d-penicillamine (NAP; n = 5, P = 0.016). In contrast, in eyes from eNOS-GFPtg mice, SNAP had no effect on outflow facility relative to NAP (-9 ± 4%, P = 0.40). In WT mice, the nonselective NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME, 10 μM) decreased outflow facility by 36 ± 13% (n = 5 each, P = 0.012), but 100 μM l-NAME had no detectable effect on outflow facility (-16 ± 5%, P = 0.22). An eNOS-selective inhibitor (cavtratin, 50 μM) decreased outflow facility by 19 ± 12% in WT (P = 0.011) and 39 ± 25% in eNOS-GFPtg (P = 0.014) mice. In the conventional outflow pathway of eNOS-GFPtg mice, eNOS-GFP expression was localized to endothelial cells lining Schlemm's canal and the downstream vessels, with no apparent expression in the trabecular meshwork. These results suggest that endogenous NO production by eNOS within endothelial cells of Schlemm's canal or downstream vessels contributes to the physiological regulation of aqueous humor outflow facility in mice, representing a viable strategy to more successfully lower IOP in glaucoma.

Effect of nitric oxide compounds on monkey ciliary muscle in vitro

The effects of various nitric oxide compounds and their inhibitors on monkey ciliary muscle contraction in vitro were investigated in both the longitudinal and circular vectors. The responses to nitric oxide compounds in carbachol precontracted ciliary muscle consisted of an initial relaxation often followed by recovery to near carbachol precontracted levels while the compound was still present. Sodium nitroprusside produced the greatest relaxation responses (nearly 100% relaxation in both vectors at 10(-3) M). The highest concentrations of isosorbide dinitrate (10(-4) M) and L-arginine (10(-3) M) produced relaxation responses of approximately 50% in both vectors. 8-Bromo cyclic GMP produced the smallest relaxation responses (25-35%). Nitric oxide synthase inhibition enhanced carbachol contraction up to 20% in the longitudinal but not the circular vector. Phosphodiesterase inhibition did not further enhance the relaxation response to L-arginine. Guanylate cyclase inhibition partially attenuated the relaxation response to sodium nitroprusside. Nitric oxide generating compounds were effective in relaxing precontracted monkey ciliary muscle in vitro. Endogenous production of nitric oxide is likely involved in the regulation of the contractile response in monkey ciliary muscle. Nitric oxide generating compounds may have potential value in therapeutic areas where modulation of ciliary muscle tension is desirable.

Comparative assessment of distribution of blackcurrant anthocyanins in rabbit and rat ocular tissues

Anthocyanins (ACs) are phenolic compounds that are distributed widely in fruits and vegetables. Although consumption of these compounds has been shown to improve visual function, the distribution of ACs in ocular tissue has not been examined in detail. The aim of this study was therefore to evaluate the ocular distribution of blackcurrant anthocyanins (BCAs) in rats and rabbits after oral, intravenous (i.v.) and intraperitoneal (i.p.) administration. Identification and quantification of ACs were carried out using high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) and high-performance liquid chromatography (HPLC) with UV-visible detection, respectively. BCAs were identified in the plasma and whole eye after oral and i.p. administration in rats. No other peaks were detected in either plasma or ocular tissues after administration when the absorbance of the eluate was monitored at 520 nm. This finding indicates that intact forms of ACs were present in rats after administration of BCA. In rats given i.p. administration, the concentration of total ACs in the whole eye and some ocular tissues was higher than that measured in plasma. These results suggested that ACs detected in the ocular tissues were not due to residual blood. Following i.v. administration in rabbits, four ACs were identified in the plasma and several ocular tissues including the aqueous humor, cornea, sclera, choroid, ciliary body, iris and retina. A small amount of ACs was also detected in the vitreous and lens. In conclusion, this study demonstrated that BCAs were absorbed and distributed in ocular tissues as intact forms. Our data show clearly that intact forms of BCAs pass thorough the blood-aqueous barrier and blood-retinal barrier in both rats and rabbits.

Delphinidin-3-rutinoside relaxes the bovine ciliary smooth muscle through activation of ETB receptor and NO/cGMP pathway

Delphinidin-3-rutinoside (D3R) is the major anthocyanin component in blackcurrant (Ribes nigrum L.) fruits. We investigated the relaxation mechanism of D3R in bovine ciliary smooth muscle (CM). D3R at a concentration of 10(-5) m produced a sustained and progressive relaxation during the contraction induced by endothelin (ET)-1 in the bovine CM specimens. After the pre-treatment with D3R, the anthocyanin exerted an inhibitory effect on the ET-1-induced contraction with a concomitant increase in cyclic GMP production and decreased phosphorylation ratio of myosin light chain (RLC). The inhibitory effect of D3R was significantly attenuated in the presence of either N(G)-nitro-L-arginine (NOARG) as a nitric oxide synthase (NOS) inhibitor, carboxy-PTIO as a NO scavenger, ODQ as an inhibitor of guanylyl cyclase, or BQ788 as a selective ET(B) receptor antagonist. The atteuation with NOARG was reversed by the addition of excess L-arginine. However, iberiotoxin as a Ca2+-activated K+ channel inhibitor, propranolol as a beta-adrenoceptor antagonist, and indomethacin as a cyclooxygenase inhibitor failed to modify the inhibitory effect of D3R. Scatchard plot analysis revealed that the [125I]-ET-1 binding site constituted a single population with Kd of 54.5+/-4.6 nm and maximum binding site (B(max)) of 168.4+/-25.4 fmol/mg protein in the ciliary epithelium (CE), and Kd of 141.7+/-18.0 nm and B(max) of 357.7+/-35.8 fmol/mg protein in CM. [125I]-ET-1 binding was completely displaced by BQ788 with K(i) values of 56.7+/-10.8 pm in CE and 93.4+/-23.3 pm in CM. Meanwhile, partial displacement (approximately 40%) was observed by BQ123 as a selective ET(A) receptor antagonist in both preparations. ET(B) receptor was predominant subtype in CE and CM, whereas kinetics of the binding was different in two preparations. These results suggest that D3R possibly stimulates ET(B) receptors to produce/release NO, and results in an inhibition of myosin RLC phosphorylation and/or acceleration of dephosphorylation, thereby causing relaxation and producing an inhibitory effect on the ET-1-induced contraction in the bovine CM.

Eyeing endothelins: a cellular perspective

Endothelin is an endogenous vasoactive peptide that is considered among the most potent vasoconstrictor substances known. In addition to its vascular effects, endothelins and their receptors have been shown to be present in the eye and to have a number of ocular actions that may be important for ocular homeostasis, but, in excess can be a potential contributor to ocular neuropathy in glaucoma. The current review focuses on the cellular and molecular aspects of endothelins and its receptors in the eye with an emphasis on its relationship to ocular function and its potential role in the etiology of glaucoma pathophysiology.