Looking into aqueous humor through metabolomics spectacles − exploring its metabolic characteristics in relation to myopia

Abstract

Aqueous humor is the transparent fluid found in the anterior chamber of the eye that provides the metabolic requirements to the avascular tissues surrounding it. Despite the fact that metabolomics could be a powerful tool in the characterization of this biofluid and in revealing metabolic signatures of common ocular diseases such as myopia, it has never to our knowledge previously been applied in humans. In this research a novel method for the analysis of aqueous humor is presented to show its application in the characterization of this biofluid using CE-MS. The method was extended to a dual platform method (CE-MS and LC-MS) in order to compare samples from patients with different severities of myopia in order to explore the disease from the metabolic phenotype point of view. With this method, a profound knowledge of the metabolites present in human aqueous humor has been obtained: over 40 metabolites were reproducibly and simultaneously identified from a low volume of sample by CE-MS, including among others, a vast number of amino acids and derivatives. When this method was extended to study groups of patients with high or low myopia in both CE-MS and LC-MS, it has been possible to identify over 20 significantly different metabolite and lipid signatures that distinguish patients based on the severity of myopia. Among these, the most notable higher abundant metabolites in high myopia were aminooctanoic acid, arginine, citrulline and sphinganine while features of low myopia were aminoundecanoic acid, dihydro-retinoic acid and cysteinylglycine disulfide. This dual platform approach offered complementarity such that different metabolites were detected in each technique. Together the experiments presented provide a whelm of valuable information about human aqueous humor and myopia, proving the utility of non-targeted metabolomics for the first time in analyzing this type of sample and the metabolic phenotype of this disease.

Clinical Metabolomics and Glaucoma

“…In ophthalmology, metabolomics has been used to study various eye diseases including glaucoma [10][11][12][13][14][15][16] , age-related macular degeneration [17][18][19] , diabetic retinopathy [20][21][22] , keratoconus [23] , refractive error [24,25] , retinal detachment [26] , uveitis [27,28] , dry eye [29,30] , and other ocular surface diseases [31] . Analyses have been performed on tear fluid [23,[29][30][31][32] , aqueous humor [24,25,33,34] , vitreous humor [20,26,27,35,36] , cornea [37][38][39] , conjunctiva [40] , and lens [41,42] samples.…”

“…Analyses have been performed on tear fluid [23,[29][30][31][32] , aqueous humor [24,25,33,34] , vitreous humor [20,26,27,35,36] , cornea [37][38][39] , conjunctiva [40] , and lens [41,42] samples.…”

LC-MS-Based Metabolic Fingerprinting of Aqueous Humor

“…AH is a transparent fluid produced by the ciliary body that passes from the posterior chamber through the pupil into the anterior chamber, where it drains out of the eye [12]. It supplies nutrients and removes metabolic waste from avascular tissues in the eye [13].…”

“…Homeostasis of AH is required to maintain adequate intraocular pressure as well as optical and refractive properties of the eye [14]. AH is a complex mixture known to contain electrolytes, glucose, urea, antioxidants (e.g., glutathione and ascorbic acid), organic solutes, several proteins (e.g., growth factors and cytokines), and oxygen and carbon dioxide [12, 14]. Until now, only a few articles in which metabolomics has been applied to analyze AH have been published [12, 15–18].…”

Capillary electrophoresis mass spectrometry based metabolomics

“…While Fuji [138] used the uniqueness of CE-MS to identify metabolites in brain tissue specific to Schizophrenia. The remainder of Table 3 lists publications related to lifestyle; alcohol intake [125], physical activity [150]], microbiome [142,145,147] and to various diseases; eye disease [140,141], inborn errors of metabolism [143], kidney disease [144], diabetes [139], metabolic syndrome [149], osteoporosis [129] and encephalopathy [148]. These publications represent a variety of subjects and sample types [serum plasma, cultured cells, PBMCs, tissue] that are amendable to CE-MS metabolomics profiling, specifically, polar hydrophilic metabolites found in critical pathways such as amino acid metabolism, central energy metabolism, inflammation, stress oxidative pathways, glycolysis, cancer metabolism, and lipid transportation.…”