4-Hydroxyhexenal- and 4-hydroxynonenal-modified proteins in pterygia

Oxidative stress in the eye and its role in the pathophysiology of ocular diseases

Oxidative stress occurs through an imbalance between the generation of reactive oxygen species (ROS) and the antioxidant defense mechanisms of cells. The eye is particularly exposed to oxidative stress because of its permanent exposure to light and due to several structures having high metabolic activities. The anterior part of the eye is highly exposed to ultraviolet (UV) radiation and possesses a complex antioxidant defense system to protect the retina from UV radiation. The posterior part of the eye exhibits high metabolic rates and oxygen consumption leading subsequently to a high production rate of ROS. Furthermore, inflammation, aging, genetic factors, and environmental pollution, are all elements promoting ROS generation and impairing antioxidant defense mechanisms and thereby representing risk factors leading to oxidative stress. An abnormal redox status was shown to be involved in the pathophysiology of various ocular diseases in the anterior and posterior segment of the eye. In this review, we aim to summarize the mechanisms of oxidative stress in ocular diseases to provide an updated understanding on the pathogenesis of common diseases affecting the ocular surface, the lens, the retina, and the optic nerve. Moreover, we discuss potential therapeutic approaches aimed at reducing oxidative stress in this context.

Aqueous humor and serum levels of 4-hydroxynonenal and 8-hydroxy-2'deoxyguanosine in pseudoexfoliation syndrome and glaucoma

PURPOSE

To compare the aqueous humor (AH) and serum levels of 4-hydroxynenal (4-HNE) and 8-hydroxy-2'-deoxyguanosine (8-OhdG) in patients with pseudoexfoliation syndrome (PES) and pseudoexfoliation glaucoma (PEG) with each other and with age- and sex-matched control group.

METHODS

This prospective study included 66 patients divided into three groups: PES (n = 24), PEG (n = 21), and a control group (n = 21). 4-HNE and 8-OhdG levels were analyzed using the enzyme-linked immunosorbent assay.

RESULTS

Aqueous and serum 4-HNE levels were significantly higher in the PEG (466.52 ± 62.12 pg/mL and 313.47 ± 47.41 pg/mL) and PES (290.69 ± 63.63 pg/mL and 201.53 ± 39.57 pg/mL) groups than the control group (144.02 ± 39.58 pg/mL and 99.10 ± 16.96 pg/mL; p < 0.001, for all). Both aqueous and serum levels of 4-HNE in the PEG group were significantly higher than in the PES group (p < 0.001, for both). Similar to 4-HNE, the AH 8-OhdG levels were higher in the PEG group (21.18 ± 2.23 ng/mL) compared to the PES (14.90 ± 3.37 ng/mL) and control (4.86 ± 1.94 ng/mL) groups (p < 0.001, for all). Serum 8-OhdG levels were significantly higher in the PEG and PES groups than the control (p < 0.001, for both); however, there was no significant difference between the PES and PEG groups (p = 0.097). There were strong significant correlations between the aqueous and serum levels of 4-HNE (p < 0.001, r = 0.857) and 8-OhdG (p < 0.001, r = 0.807) among all the patients.

CONCLUSIONS

Aqueous humor and serum levels of 4-HNE and 8-OhdG increased in the PES and PEG patients. These findings are potentially significant and add to the growing body of evidence concerning oxidative stress in PES and PEG.

Protective effects of Clostridium butyricum against oxidative stress induced by food processing and lipid-derived aldehydes in Caco-2 cells

The human body is almost always facing the oxidative stress caused by foodborne aldehydes such as glyoxal (GO) and methylglyoxal (MGO), 4-hydroxyhexenal (HHE), and 4-hydroxynonenal (HNE). When these aldehydes build up, they can cause a range of harm. However, a probiotic, Clostridium butyricum, can increase nuclear factor erythroid-2 related factor 2 (Nrf2) and may have the potential to relieve oxidative stress. If C. butyricum is indeed resistant to aldehydes, the advantages (accessibility, convenience, and safety) will be of great significance compared with drugs. Unfortunately, whether C. butyricum can play a role in alleviating toxic effects of foodborne aldehydes in the intestine (the first line of defense against food-derived toxin) was unclear. To investigate these, we measured the viability, ROS, autophagy, and inflammatory cytokine expression of Caco-2 which were co-cultured with C. butyricum and stimulated by the four aldehydes via Nrf2 pathway (Staphylococcus aureus and Enterococcus faecium as controls). Then, we explored the link among C. butyricum, NLRP6, and Nrf2 signaling pathways when facing the stimuli. In the present study, we demonstrated that Clostridium butyricum relieved the oxidative stress induced by the aldehydes in Caco-2. Most interestingly, we found a "complementary" relationship between NLRP6 and Nrf2 in C. butyricum treatment under aldehyde stress. Our research not only makes a contribution to the popularization of C. butyricum as a probiotic-rich food instead of medicines but also sheds new light on the application of subsequent microecological formulation of C. butyricum. KEY POINTS: • The adverse effects are caused in a dose-dependent manner by foodborne aldehydes. • Clostridium butyricum can significantly ameliorate oxidative stress. • There is a "complementary" relationship between the NLRP6 and Nrf2 signaling pathways. • Using Clostridium butyricum foods to alleviate oxidative stress shows great prospects.

Inflammation and oxidative stress induced by lipid peroxidation metabolite 4-hydroxynonenal in human corneal epithelial cells

PURPOSE

Oxidative stress is widely known to be a major contributor in the pathogenesis of dry eye disease (DED). 4-Hydroxynonenal (4-HNE), a well-known byproduct frequently measured as an indicator of oxidative stress-induced lipid peroxidation, has been shown to be elevated in both human and murine corneal DED samples. This study aims to investigate if 4-HNE is responsible for the oxidative stress in human corneal epithelial cells (HCECs) and explores the underlying mechanism by which it confers its effects.

METHODS

SV40-immortalized HCECs were cultured in minimum essential media (MEM) with 1% penicillin/streptomycin and 10% fetal bovine serum. HCECs were exposed to media with or without 4-HNE and cell culture supernatants were collected at 4 and 24 h. Cellular reactive oxygen species (ROS) measurement was performed using a 2',7'-dichlorofluorescein diacetate (DCFDA) assay kit according to the manufacturer's instructions. Protein levels of antioxidant enzymes copper/zinc superoxide dismutase 1 (SOD1) and NAD(P)H quinone dehydrogenase 1 (NQO1) were analyzed by Western blot. NF-κB activation and expression of IL-6 and IL-8 were measured using an NF-κB p65 Total SimpleStep ELISA Kit and Proteome Profiler Human Cytokine Array Kit. Cell viability was evaluated by LDH cytotoxicity assay.

RESULTS

Treatment with 4-HNE decreased cell viability of HCECs. Band intensities corresponding to levels of ROS production showed a significant increase in ROS generation after treatment with 4-HNE. 4-HNE decreased SOD1 levels and upregulated NQO1 expression in HCECs. A significant increase in activation of NF-κB and production of pro-inflammatory cytokines IL-6 and IL-8 was observed after treatment with 4-HNE. Exposure to N-acetylcysteine (NAC), an antioxidant and ROS scavenger, antagonized the oxidative effects of 4-HNE on HCECs.

CONCLUSION

4-HNE induces oxidative stress in corneal epithelial cells by increasing levels of ROS generation and modifying the expression of antioxidant enzyme levels, decreasing cell viability of HCECs in vitro. This study demonstrates a potential pathway by which 4-HNE functions to confer its detrimental effects and provides a new therapeutic target for the treatment of DED.

Does systemic inflammation play a role in patients with pterygium?

PURPOSE

To compare parameters of systemic inflammation and serum lipid levels in patients with pterygium versus healthy individuals.

METHODS

Thirty-five patients with pterygium and 30 healthy individuals were enrolled as two respective groups in a retrospective study. The participants' complete blood count (CBC) parameters and levels of serum total cholesterol, low-density lipoprotein, high-density lipoprotein (HDL), and triglycerides (TG) were obtained from digital records and compared. Their neutrophil/lymphocyte, platelet/lymphocyte, and monocyte/HDL ratios were calculated and compared as well. As secondary outcomes, longitudinal length (LL), basal length (BL), and total area (TA) of pterygium among the patients were quantitatively measured by using ImageJ software. Correlations between serum parameters and pterygium measurements were analyzed.

RESULTS

Although between-group differences in CBC parameters and the ratios were not statistically significant, HDL levels were significantly lower (p = 0.014) and TG levels significantly higher (p = 0.031) among patients with pterygium than among the controls. A positive correlation was detected between the patient's age and the pterygium's BL (p = 0.002, r = 0.516), LL (p = 0.00, r = 0.547), and TA (p = 0.00, r = 0.515). Neutrophil levels negatively correlated with LL (p = 0.025, β = - 0.308) and TA (p = 0.002, β = - 0.420).

CONCLUSION

Local instead of systemic inflammation should be considered in the management of pterygium. Besides, decreased HDL levels may indicate systemic oxidative stress in patients with the condition.

Identification and Interaction Analysis of Significant Genes and MicroRNAs in Pterygium

PURPOSE

MiRNAs have been widely analyzed in the occurrence and development of many diseases, including pterygium. This study aimed to identify the key genes and miRNAs in pterygium and to explore the underlying molecular mechanisms.

METHODS

MiRNA expression was initially extracted and pooled by published literature. Microarray data about differentially expressed genes was downloaded from Gene Expression Omnibus (GEO) database and analyzed with the R programming language. Functional and pathway enrichment analyses were performed using the database for Annotation, Visualization and Integrated Discovery (DAVID). The protein-protein interaction network was constructed with the STRING database. The associations between chemicals, differentially expressed miRNAs, and differentially expressed genes were predicted using the online resource. All the networks were constructed using Cytoscape.

RESULTS

We found that 35 miRNAs and 301 genes were significantly differentially expressed. Functional enrichment analysis showed that upregulated genes were significantly enriched in extracellular matrix (ECM) organization, while downregulated genes were mainly involved in cell death and apoptotic process. Finally, we concluded the chemical-gene affected network, miRNA-mRNA interacted networks, and significant pathway network.

CONCLUSION

We identified lists of differentially expressed miRNAs and genes and their possible interaction in pterygium. The networks indicated that ECM breakdown and EMT might be two major pathophysiological mechanisms and showed the potential significance of PI3K-Akt signalling pathway. MiR-29b-3p and collagen family (COL4A1 and COL3A1) might be new treatment target in pterygium.

Inhibitory effects of rosmarinic acid on pterygium epithelial cells through redox imbalance and induction of extrinsic and intrinsic apoptosis

Pterygium is a common tumor-like ocular disease, which may be related to exposure to chronic ultraviolet (UV) radiation. Although the standard treatment for pterygium is surgical intervention, the recurrence rate of pterygium is high when no effective inhibitory drug is used after surgery. Rosmarinic acid (RA) is a polyphenol antioxidant with many biological activities, including anti-UV and anti-tumor properties. This study aimed to examine the inhibitory effects of RA on pterygium epithelial cells (PECs). Methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay was used to examine the cell cytotoxicity of PECs after RA treatment. A fluorescent probe, DCFH-DA (2',7'-dichlorofluorescin diacetate), was stained with PECs to measure intracellular reactive oxygen species (ROS) levels. Antioxidant activity assays were used to measure the levels of superoxide dismutase (SOD) and catalase (CAT) in PECs. Western blot analysis was used to determine the protein expression of nuclear factor E2-related factor 2 (Nrf2), heme oxygenase 1 (HO-1), quinone acceptor oxidoreductase 1 (NQO1), and apoptosis-associated proteins. RA significantly reduced the cell viability of the PECs. Treatment with RA remarkably increased the Nrf2 protein expression levels in the nucleus, HO-1 and NQO1 protein expression levels, and the activities of SOD and CAT. As a result, intracellular ROS levels in PECs were decreased. Additionally, the induction of extrinsic apoptosis on PECs by RA was associated with increasing expressions levels of Fas, Fas-associated protein with death domain (FADD), tumor necrosis factor-alpha (TNF-α), and caspase 8 protein. Moreover, the induction of intrinsic apoptotic cell death in PECs was confirmed through upregulation of cytochrome c, Bax, caspase 9, and caspase 3 and downregulation of Bcl-2 and pro-caspase 3. Our study demonstrated that RA could inhibit the viability of PECs through regulation of extrinsic and intrinsic apoptosis pathways. Therefore, RA may have potential as a therapeutic medication for pterygium.

The oxidant role of 4-hydroxynonenal in corneal epithelium

4-Hydroxynonenal (4-HNE or HNE) is a main endogenous product of cellular lipid peroxidation in tissues and is reported to play pathogenic roles in eye diseases. Here we investigated the association between 4-HNE and oxidative stress in the corneal epithelium. 4-HNE suppressed the cell viability of human corneal epithelial cells (HCE) in a concentration dependent manner. 4-HNE significantly increased the level of 3-Nitrotyrosine (3-NT), a marker of oxidative stress, in HCE cells and corneal epithelium of rats by immunofluorescent staining and Western blot analysis. To its underlying mechanistic on ROS system, 4-HNE elevated the ROS generation enzyme NADPH oxidase 4 (NOX4) and induced the activation of NF-E2–related factor-2 (NRF2) and its downstream effectors: NAD(P)H dehydrogenase (quinone 1) (NQO1) and glutathione S-transferase P (GSTP). Furthermore, N-acetylcysteine (NAC), an antioxidant and ROS scavenger, antagonized the inhibitory and oxidant effects of 4-HNE on the corneal epithelial cells. In conclusion, 4-HNE plays an oxidant role in the corneal epithelium and this work provides a new strategy for the pathogenesis and treatment of corneal diseases.

Molecular Basis of Pterygium Development

Pterygium pathogenesis is mainly related to UV light exposure. However, the exact mechanisms by which it is formed have not been elucidated. Clinical advances in surgical treatment use conjunctival autografts and amniotic membranes in combination with adjuvant therapies, including mitomycin C, β-radiation, and 5-fluoroacil, to reduce recurrence. Several studies aim to unveil the molecular mechanisms underlying pterygium growth and proliferation. They demonstrate the role of different factors, such as viruses, oxidative stress, DNA methylation, apoptotic and oncogenic proteins, loss of heterozygosity, microsatellite instability, inflammatory mediators, extracellular matrix modulators, lymphangiogenesis, cell epithelial-mesenchymal transition, and alterations in cholesterol metabolism in pterygium development. Understanding the molecular basis of pterygium provides new potential therapeutic targets for its prevention and elimination. This review focuses on providing a broad overview of what is currently known regarding molecular mechanisms of pterygium pathogenesis.