Elsevier

Nitric Oxide

Volume 99, 1 June 2020, Pages 17-24
Nitric Oxide

Peroxynitrite is a novel risk factor and treatment target of glaucoma

https://doi.org/10.1016/j.niox.2020.03.006Get rights and content

Highlights

  • Peroxynitrite is a novel risk factor for POAG and PACG.

  • Peroxynitrite scavenger MnTMPyP could reverse IOP in ocular hypertensive mice.

  • Peroxynitrite transduction molecule PARP1 inhibitor could reduce IOP in ocular hypertensive mice.

Abstract

To investigate the association between systemic nitrotyrosine (NT) levels and primary angle-closure glaucoma (PACG) and primary open-angle glaucoma (POAG) and the mechanism involved. A case control study was conducted in the Department of Ophthalmology & Visual Science, Eye & ENT Hospital, Fudan University from April 2017 to December 2017. A total of 400 participants were consecutively recruited into this study (100 PACG, 100 POAG and 200 controls). Multivariable logistic regression analysis was performed to identify the association between serum NT level and PACG or POAG. Clinical results were validated in cell and animal models. Among 200 glaucoma patients, 101 (50.5%) were women; the age was 57.07 ± 14.51 years. 106 (53%) control participants were women and age was 58.34 ± 14.04 years. Serum levels of NT in PACG and POAG patients are significantly higher than controls (1808.53 ± 417.76 nmol/L vs. 1270.62 ± 454.60 nmol/L, p < 0.001; 1718.63 ± 437.29 nmol/L vs. 1258.38 ± 460.72 nmol/L, p < 0.001). Further, elevated serum NT level increases the risk of developing PACG (OR = 1.003, 95% CI: 1.002 to 1.004, p < 0.001) and POAG (OR = 1.002, 95% CI: 1.002 to 1.003, p < 0.001). Consistent with the clinical data, serum and aqueous humour NT levels are significantly higher in caveolin 1 knockout (Cav1 KO) mice, an animal model of glaucoma. More importantly, peroxynitrite (PN) scavenger MnTMPyP and its transduction molecule PARP inhibitor significantly reduce intraocular pressure in Cav1 KO mice. Our data show for the first time that NT is a systemic risk factor and local treatment target of glaucoma.

Introduction

Elevated intraocular pressure (IOP) in glaucoma patients can result in progressive optic neuropathy and, if left untreated, irreversible blindness [1]. By 2040, the number of people suffering from glaucoma worldwide may increase to 111.8 million [2]. This figure is projected to 25.16 million in China By 2050 [3]. While primary open-angle glaucoma (POAG) is the more predominant form of glaucoma in Europeans and Africans, Asia accounts for about 86% of worldwide primary angle-closure glaucoma (PACG) cases, and China accounts for a vast majority (48%) of PACG in the world [2,4]. Nitric oxide (NO) is an important regulator of intraocular pressure; paradoxically, the same molecule is involved in the pathogenesis of PACG and POAG [[5], [6], [7], [8], [9], [10]]. NO can become highly damaging when it reacts with superoxide (O2) and forms much more powerful oxidant peroxynitrite (PN, ONOO).

PN is much more reactive than NO or superoxide with a half-life of 10–20 ms. No other species has a long enough half-life to travel within and between cells and having the ability to break the DNA [11]. The DNA damge in turn activates DNA nick-sensing enzyme, mostly poly (ADP-ribose) polymerase-1 (PARP-1), which triggers the cleavage of NAD+ into nicotinamide and ADP-ribose and causes depletion of NAD+ and ATP resulting in cell dysfunction, necrosis or apoptosis. The cytotoxic effects of PN centering on the participation of PARP-1 and ADP-ribose have been implicated in the pathogenesis of a variety of diseases, including circulatory shock, sepsis and inflammation, injuries of the lung and the intestine [12]. Treatment with PARP inhibitors has produced protective effects in various diseases, including cancer [13,14].

PN causes nitration of various amino acid functional groups but mostly tyrosine and forms nitrotyrosine (NT) [15]. NT level is increased in eyes [16] and lungs [17] of caveolin 1 knockout (Cav1 KO) mice, which have ocular and pulmonary hypertension. This is consistent with increased NT expression in the cells of the trabecular meshwork (TM) specimens from patients with severe POAG [18]. In the retina, glutamate induced excessive formation of PN which causes apoptosis of retinal neurons [19]. Optic nerve histology revealed NT formation in damaged optic nerve heads of patients with glaucoma [20,21]. While PACG and POAG are considered to be focal diseases, evidence has emerged systemic factors are associated with the pathogenesis of glaucoma [22,23]. Cav1 is known to interact with endothelial nitric oxide synthase (eNOS), which is an important regulator of IOP, thus affecting NO production. When eNOS binds to Cav1, its activity is inhibited. Upon stimulation, the inhibitory clamp of Cav1 is relieved and NO production occurs.

Manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride (MnTMPyP) is a metalloporphyrin that has a metal center Mn and a porphyrin ring, which serve as a PN decomposition catalyst. It is cell permeable and can attenuate the toxic effects of PN in vitro and in vivo. Treatment with MnTMPyP could reverse pulmonary hypertention in Cav1 Knockout mice [17]. Its protective effects in vivo are probably due to a combined antioxidant effect, involving superoxide dismutation and PN neutralization [24]. Based on the dual action of metalloporphyrins, the related compound MnTnBuOE-2-PyP5+has been in Phase I/II Clinical Trials on glioma patients (NCT02655601) as a radioprotector of normal brain [25].

This study aims to investigate the systemic NT level in PACG and POAG patients, and its association with the diseases. We hypothesize that systemic NT is a risk factor of POAG and PACG. Due to the short half-life and instability of PN, NT is used as a surrogate measure of PN, and the increased tyrosine nitration indicates the formation of PN.

Section snippets

Study participants and sample collection

Patients with PACG (n = 100) or POAG (n = 100) were consecutively recruited into this study between April 2017 and December 2017 from the Department of Ophthalmology & Visual Science, Eye & ENT Hospital, Fudan University. And normal controls (n = 200) were consecutively recruited from subjects who participated in yearly health screenings during the study period. PACG and POAG were diagnosed following the International Society of Geographical and Epidemiological Ophthalmology (ISGEO). The

Baseline characteristics of PACG and POAG patients

Demographic features, biochemical indices, ocular parameters of PACG, and POAG patients are shown in Table 1. For patients who had glaucoma in both eyes, ocular parameters from the right eye were used. Most of the biomedical indices, including the level of total protein, were similar between glaucoma patients and control patients. UA was slightly lower in PACG patients (p = 0.049), TG (p = 0.013) and TB (p = 0.032) was higher in POAG patients compared with controls.

Increased serum NT in PACG and POAG patients

Serum NT levels were

Main findings

We find a significantly elevated serum NT levels in PACG and POAG patients compared to control subjects. Further, high serum NT levels are significantly associated with the increased risk of PACG and POAG. All patients enrolled in our study are glaucoma patients with onset of both eyes. The statistical effect of taking ocular parameters from right eye of patients is same as from one eye of patients randomly. At the same time, the error caused by the difference between the left eye and right

Financial Support

Supported by theShanghai Clinical Medical Center of Ocular Disease (2017ZZ01020, XHS, China), State Key Program of National Natural Science Foundation of China (81430007, XHS, China), the Funds for International Cooperation of Ministry of Science and Technology (20501100001809340, XHS, China), National Natural Science Foundation China (81100662, 81371015, YL, China), BrightFocus Foundation (G2018112, YL, USA), the 211 Proect of Fudan University (EHF158351, YL, China), Young Scientists Program

Declaration of competing interest

No conflicting relationship exists for any author.

Acknowledgments

The clinical specimen and information of glaucoma patients described in this manuscript were obtained from the eye bank of Eye and ENT Hospital of Fudan University. We would like to thank all the participants and the staffs for their valuable contribution to this research.

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      It causes biological damages by oxidizing DNA and the nitration of tyrosine residues on protein (Batthyany et al., 2017; Szabo et al., 2007; Virag et al., 2003). Clinical studies from others and ourselves have shown that ONOO- is involved in the pathogenesis of POAG (Lei et al., 2020; Luthra et al., 2005; Okamoto et al., 2001; Sacca et al., 2007). In this study, our data indicated that the extended application of SNP formed ONOO-and caused nitrosative damage to the outflow tissue, which might be responsible for the IOP elevation.

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    Authorship note: YL, YTG, and MMS contributed equally to this work.

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