Elevated dimethylarginine, ATP, cytokines, metabolic remodeling involving tryptophan metabolism and potential microglial inflammation characterize primary open angle glaucoma

Abstract

Glaucoma of which primary open angle glaucoma (POAG) constitutes 75%, is the second leading cause of blindness. Elevated intra ocular pressure and Nitric oxide synthase (NOS) dysfunction are hallmarks of POAG. We analyzed clinical data, cytokine profile, ATP level, metabolomics and GEO datasets to identify features unique to POAG. N9 microglial cells are used to gain mechanistic insights. Our POAG cohort showed elevated ATP in aqueous humor and cytokines in plasma. Metabolomic analysis showed changes in 21 metabolites including Dimethylarginine (DMAG) and activation of tryptophan metabolism in POAG. Analysis of GEO data sets and previously published proteomic data sets bins genes into signaling and metabolic pathways. Pathways from reanalyzed metabolomic data from literature significantly overlapped with those from our POAG data. DMAG modulated purinergic signaling, ATP secretion and cytokine expression were inhibited by N-Ethylmaleimide, NO donors, BAPTA and purinergic receptor inhibitors. ATP induced elevated intracellular calcium level and cytokines expression were inhibited by BAPTA. Metabolomics of cell culture supernatant from ATP treated sets showed metabolic deregulation and activation of tryptophan metabolism. DMAG and ATP induced IDO1/2 and TDO2 were inhibited by N-Ethylmaleimide, sodium nitroprusside and BAPTA. Our data obtained from clinical samples and cell culture studies reveal a strong association of elevated DMAG, ATP, cytokines and activation of tryptophan metabolism with POAG. DMAG mediated ATP signaling, inflammation and metabolic remodeling in microglia might have implications in management of POAG.

Metabolomics in Primary Open Angle Glaucoma: A Systematic Review and Meta-Analysis

“…This systematic review and meta-analyses report a number of metabolites in the aqueous humor and plasma identified using comprehensive high-throughput metabolomics that is prospectively associated with human patients with POAG. Six metabolites in the aqueous humors and five from the plasma were repeatedly shown up in at least three independent studies ( Ghanem et al, 2012 ; Leruez et al, 2018 ; Buisset et al, 2019 ; Kouassi Nzoughet et al, 2019 , 2020 ; Barbosa Breda et al, 2020 ; Myer et al, 2020 ; Pulukool et al, 2021 ; Tang et al, 2021b ). Main dysregulated metabolites were summarized in Figure 5 .…”

“…For the meta-analysis, only metabolites reported in at least 3 publications were considered in the present study. Among them, six common metabolites (glutamine, creatine, glycine, lysine, alanine, and hydroxyproline) were noted in 6 studies that analyzed the aqueous humors of control and patients with POAG ( Ghanem et al, 2012 ; Buisset et al, 2019 ; Barbosa Breda et al, 2020 ; Myer et al, 2020 ; Pulukool et al, 2021 ; Tang et al, 2021b ). Since Myer et al (2020) used two methods [LC–MS/MS and nuclear magnetic resonance (NMR)] to analyze the samples and generated non-consistent outcomes, we treated the outcomes from these two methods as separate datasets.…”

Damage-Associated Molecular Patterns (DAMPs) in Retinal Disorders

“…Notably, there was a significant increase in ATP in the aqueous and vitreous humor of patients with primary open-angle glaucoma. The activation of P2X7 by ATP elevates intracellular calcium, resulting in rat RGC death [ 50 ]. In addition, significantly high levels of amyloid beta (Aβ) have been reported in the optic nerve head and aqueous humor of glaucoma patients [ 51 ].…”

Erythropoietin in Optic Neuropathies: Current Future Strategies for Optic Nerve Protection and Repair

“…However, some patients experienced continued RGCs loss despite good intraocular pressure control, suggesting the presence of other complicated mechanisms stimulating RGC death. Multifactorial mechanisms have been postulated for glaucomatous optic neuropathy, including vascular insufficiency, inflammation [66,67], excitotoxicity [68] and neurotrophic factor withdrawal [69]. Due to the complex pathogenesis of glaucoma, EPO was developed to prevent the IOP-independent RGCs loss.…”