Metabolomics Reveals Differences in Aqueous Humor Composition in Patients With and Without Pseudoexfoliation Syndrome

Comparative study of the ciliary body and iris morphology in the anterior eye chamber of five different vertebrate classes

One crucial component of the optical system is the ciliary body (CB). This body secretes the aqueous humour, which is essential to maintain the internal eye pressure as well as the clearness of the lens and cornea. The histological study was designed to provide the morphological differences of CB and iris in the anterior eye chambers of the following vertebrate classes: fish (grass carp), amphibians (Arabian toad), reptiles (semiaquatic turtle, fan-footed gecko, ocellated skink, Egyptian spiny-tailed lizard, Arabian horned viper), birds (common pigeon, common quail, common kestrel), and mammals (BALB/c mouse, rabbit, golden hamster, desert hedgehog, lesser Egyptian jerboa, Egyptian fruit bat). The results showed distinct morphological appearances of the CB and iris in each species, ranging from fish to mammals. The present comparative study concluded that the morphological structure of the CB and iris is the adaptation of species to either their lifestyle or survival in specific habitats.

Critical Factors in Sample Collection and Preparation for Clinical Metabolomics of Underexplored Biological Specimens

This review article compiles critical pre-analytical factors for sample collection and extraction of eight uncommon or underexplored biological specimens (human breast milk, ocular fluids, sebum, seminal plasma, sweat, hair, saliva, and cerebrospinal fluid) under the perspective of clinical metabolomics. These samples are interesting for metabolomics studies as they reflect the status of living organisms and can be applied for diagnostic purposes and biomarker discovery. Pre-collection and collection procedures are critical, requiring protocols to be standardized to avoid contamination and bias. Such procedures must consider cleaning the collection area, sample stimulation, diet, and food and drug intake, among other factors that impact the lack of homogeneity of the sample group. Precipitation of proteins and removal of salts and cell debris are the most used sample preparation procedures. This review intends to provide a global view of the practical aspects that most impact results, serving as a starting point for the designing of metabolomic experiments.

Adaptation of the AbsoluteIDQ p180 kit to the analysis of metabolites in the human aqueous humor

The aim of this study was to use the commercial kit AbsoluteIDQ p180 (Biocrates) for the quantification of metabolites in aqueous humor (AH), as well as to determine the optimal volume of AH that is necessary to obtain reliable and reproducible results. Different volumes of AH (10 µl, 20 µl, and 30 µl) were tested. Of the 188 metabolites measurable with the Biocrates kit, 69 were detected in AH. Depending on the volume used, 41, 51, and 63 metabolites were measured using 10 µl, 20 µl, and 30 µl of AH, respectively. The repeatability of the measurements improved with increasing AH volume. Considering only those metabolites that were obtained with a CV < 15%, 34 metabolites at 10 µl, 41 at 20 µl, and 44 at 30 µl AH were received. On this basis, it can be concluded that the tested method can be successfully applied to analyze metabolites in the human AH. To achieve the most comprehensive detection range and highest repeatability of measurements, it is recommended to use 30 µl AH.

Correlation analysis of aqueous humor metabolomics with myopic axial length and choroidal parameters

BACKGROUND

To explore differential metabolites in the aqueous humor of patients with different axial lengths and their correlations with axial length and choroidal parameters.

METHODS

In this study, we included 12 patients with axial lengths less than 24 mm, 11 patients with axial lengths between 24 and 26 mm, and 11 patients with axial lengths greater than 26 mm. We collected their aqueous humor samples during cataract surgery for liquid chromatography-mass spectrometry metabolomic analysis. Simultaneously, we collected relevant clinical parameters such as axial length, subfoveal choroidal thickness, and choroidal vascular index. Correlations between clinical data, differential metabolites, and clinical indicators were analyzed. In addition, we plotted receiver operating characteristic curves.

RESULTS

The results showed that axial length was significantly negatively correlated with choroidal thickness (r=-0.7446, P < 0.0001), and that several differential metabolites were significantly correlated with certain clinical parameters. After analyzing receiver operating characteristic curves, 5-methoxytryptophol and cerulenin were found to have excellent discriminative power, demonstrating their potential as biomarkers. In the enrichment analysis, we found that the differential metabolites among each group were involved in several special pathways (Taurine and Hypotaurine Metabolism, Vitamin B6 Metabolism, Pantothenate, and coenzyme A Biosynthesis), suggesting that abnormalities in these metabolic pathways may play a role in the process of axial myopia.

CONCLUSIONS

Our study identified alterations in certain metabolic pathways in different axial lengths. At the same time, we found several metabolites with significant correlation with clinical indicators, among which 5-methoxytryptophol and cerulenin were associated with axial myopia.

CLINICAL TRIAL REGISTRATION

Registration date:11/04/2022.

TRIAL REGISTRATION NUMBER

ChiCTR2200058575.

TRIAL REGISTRY

The First Affiliated Hospital of the Zhejiang University School of Medicine.

Extent of interocular (a)symmetry based on the metabolomic profile of human aqueous humor

Aims: Interocular comparison of the metabolomic signature of aqueous humor (AH) was performed. The aim of the study was to quantitatively evaluate the symmetry in concentrations of various metabolites belonging to different categories.

Methods: The study included AH samples from 23 patients, 74.17 ± 11.52 years old, undergoing simultaneous bilateral cataract surgery at the Ophthalmology Department of the Medical University of Bialystok, Poland. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS)-based targeted metabolomics and lipidomics analyses of AH samples were performed using the AbsoluteIDQ® p180 kit. Out of 188 metabolites available in the kit, 67 were measured in the majority (&gt;70%) of the samples: 21/21 amino acids, 10/22 biogenic amines, 9/40 acylcarnitines, 0/14 lysophosphatidylcholines, 21/76 phosphatidylcholines, 5/15 sphingolipids, and 1/1sum of hexoses.

Results: The comparison of both eyes revealed that the concentrations of metabolites did not differ significantly (p &lt; 0.05) except for taurine (p = 0.037). There was moderate-to-strong positive interocular correlation (r &gt; 0.5) between most metabolites regarding concentration. This was confirmed by the high intraclass correlation coefficient (ICC) values of different levels, which varied for the different metabolites. However, there were exceptions. Correlations were not significant for 2 acylcarnitines (tiglylcarnitine and decadienylcarnitine) and 3 glycerophospholipids (PC aa C32:3, PC aa C40:2, and PC aa C40:5).

Conclusion: With a few exceptions, a single eye was found to be representative of the fellow eye in terms of the concentration of most of the analyzed metabolites. The degree of intraindividual variability in the AH of fellow eyes differs for particular metabolites/metabolite categories.

Relationship between plasma amino acid and carnitine levels and primary angle-closure glaucoma based on mass spectrometry metabolomics

World blindness is primarily caused by glaucoma. It has been predicted that by 2040, 118 million individuals will have glaucoma. Among Asians and Africans, primary angle-closure glaucoma (PACG) is the most prevalent type of glaucoma, for which treatment options are currently very limited. At present, lowering intraocular pressure (IOP) is the primary approach for PACG treatment. However, some PACG patients with decreased IOP measurements still advance. Additionally, because of the complicated pathophysiology, there are no biomarkers for diagnosis. Metabolomics is the study of the metabolites produced by all cellular processes in a biological sample, providing a method for identifying biomarkers and early diagnosis. Nevertheless, metabolomics has infrequently been applied to PACG. Previous research conducted by our lab on plasma metabolite fatty acids in PACG patients revealed reduced free fatty acid (FFA) levels, which may be connected to lipid peroxidation. To ascertain the relationship between other metabolites and PACG. We compared levels of amino acids and carnitine in patients with PACG (n = 147) and non-glaucoma (n = 340). Using metabolomics analysis, twenty-one amino acids and twenty-six carnitines (a total of ninety-six indicators) were examined. Odds ratios (OR) and 95% confidence intervals (CI) for these metabolites in relation to PACG were calculated. The relationship between ocular measures and metabolites was assessed by Spearman's rank correlation. Predictive performance was evaluated using the receiver operating characteristic (ROC). The C8/C2 level was comparable across patients with PACG and individuals without glaucoma based on the Wilcoxon rank-sum test. The PACG group had lower levels of Arginine (Arg), Ornithine (Orn), Arg/Orn, Orn/Cit, and C26/C20 than the nonglaucoma group, whereas Cit/Arg and C4/C2 ratios were greater. Both univariate and multivariate models showed a negative correlation between Orn and Orn/Cit and PACG. In the univariate model, palmitoylcarnitine (C16) had a negative correlation with PACG. According to our findings, metabolic profiles of plasma amino acids and carnitine between PACG patients and controls are different. The combination of amino acids and carnitine increased the predictive value of PACG. The Orn and Arg were negatively correlated with the local ocular neurodegenerative pathology. We speculate lipid peroxidation may explain the reduction in C16, and the decrease in Orn may be associated with hyperammonia neurotoxicity.

Antioxidant Defense and Pseudoexfoliation Syndrome: An Updated Review

Oxidative stress (OS) affects the anterior ocular tissues, rendering them susceptible to several eye diseases. On the other hand, protection of the eye from harmful factors is achieved by unique defense mechanisms, including enzymatic and non-enzymatic antioxidants. The imbalance between oxidants and antioxidants could be the cause of pseudoexfoliation syndrome (PEXS), a condition of defective extracellular matrix (ECM) remodeling. A systematic English-language literature review was conducted from May 2022 to June 2022. The main antioxidant enzymes protecting the eye from reactive oxygen species (ROS) are superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), which catalyze the reduction of specific types of ROS. Similarly, non-enzymatic antioxidants such as vitamins A, E and C, carotenoids and glutathione (GSH) are involved in removing ROS from the cells. PEXS is a genetic disease, however, environmental and dietary factors also influence its development. Additionally, many OS products disrupting the ECM remodeling process and modifying the antioxidative defense status could lead to PEXS. This review discusses the antioxidative defense of the eye in association with PEXS, and the intricate link between OS and PEXS. Understanding the pathways of PEXS evolution, and developing new methods to reduce OS, are crucial to control and treat this disease. However, further studies are required to elucidate the molecular pathogenesis of PEXS.

Emerging roles of oxidative stress in the pathogenesis of pseudoexfoliation syndrome (Review)

Pseudoexfoliation syndrome (PEXS) is a systemic disease caused by defects in the extracellular matrix (ECM) remodelling process leading to the chronic deposition of extracellular, fibrillary, white flaky pseudoexfoliation material (PEXM) throughout the body. Specifically, PEXM deposits on the lens capsule cause open-angle glaucoma, cataracts and blindness in patients with PEXS. Several gene single nucleotide polymorphisms are linked to the development of PEXS in humans, including lysyl oxidase-like 1 gene, clusterin and fibulin-5. The exact reason for the PEXM generation and its resulting pathogenesis is not well understood. However, defective ECM remodelling and oxidative stress (OS) have been hypothesized as significant events leading to the PEXM. Specifically, the link between OS and PEXS has been well studied, although the investigation is still ongoing. The present review explored recent advances in various aspects of PEXS and the involvement of OS in the eye for PEXS development.