Advanced glycation end products in human diabetic lens capsules

Advanced Glycation End Products in Disease Development and Potential Interventions

Advanced glycation end products (AGEs) are a group of compounds formed through non-enzymatic reactions between reducing sugars and proteins, lipids, or nucleic acids. AGEs can be generated in the body or introduced through dietary sources and smoking. Recent clinical and animal studies have highlighted the significant role of AGEs in various health conditions. These compounds accumulate in nearly all mammalian tissues and are associated with a range of diseases, including diabetes and its complications, cardiovascular disease, and neurodegeneration. This review summarizes the major diseases linked to AGE accumulation, presenting both clinical and experimental evidence. The pathologies induced by AGEs share common mechanisms across different organs, primarily involving oxidative stress, chronic inflammation, and direct protein cross-linking. Interventions targeting AGE-related diseases focus on inhibiting AGE formation using synthetic or natural antioxidants, as well as reducing dietary AGE intake through lifestyle modifications. AGEs are recognized as significant risk factors that impact health and accelerate aging, particularly in individuals with hyperglycemia. Monitoring AGE level and implementing nutritional interventions can help maintain overall health and reduce the risk of AGE-related complications.

Emodin alleviates the damage to lens epithelial cells in diabetic cataract by repressing the p53-mediated ferroptosis pathway

BACKGROUND

Diabetic cataract (DC) is an ocular complication caused by diabetes. Currently, the main treatments for DC include pharmacological therapy and surgical intervention. The core objective of this study is to elucidate the specific mechanism of action of emodin in the treatment of DC, thereby providing potential targets for the treatment of DC.

METHODS

CCK-8 kit was used to detect the effect of emodin on the activity of lens epithelial cells (LECs). The impact of emodin on the expression of inflammatory factors and apoptosis in high glucose-induced LECs were evaluated by utilizing ELISA and flow cytometry. Then, commercial kits were performed to detect the regulatory effects of emodin on oxidative stress and ferroptosis in high glucose LECs. The potential mechanism of emodin in combating DC by inhibiting ferroptosis was analyzed by network pharmacology methods, and protein binding activity to emodin was measured by molecular docking. Besides, western blot (WB) assay was used to detect the effect of emodin on p53.

RESULTS

Firstly, the results of CCK-8 showed that emodin could effectively alleviate the decrease of LECs cell activity and Lactate dehydrogenase (LDH) release induced by high glucose. Emodin suppressed high glucose-induced apoptosis of LECs, reduced the release of inflammatory factors, and alleviated oxidative stress and ferroptosis. GO and KEGG analyses confirmed the involvement of oxidative stress (OS), inflammatory response, and ferroptosis in the process of emodin treatment for DC. Molecular docking studies showed that emodin stably bound to proteins such as TP53, TNF, IL-6, and IL-1β. Additionally, WB results indicated that emodin alleviated high glucose-induced ferroptosis by binding to p53.

CONCLUSION

Collectively, these data suggest that emodin alleviates damage to LECs by interfering with the p53-mediated ferroptosis pathway, thereby attenuating DC disease, which offered new directions for the development of new drugs.

Proximal cysteine residues in proteins promote Nε-carboxyalkylation of lysine residues by α-dicarbonyl compounds

Advanced glycation end products (AGEs) are protein modifications resulting from the chemical reaction between lysine and arginine residues in proteins, and carbonyl compounds, including glyoxal (GO) and methylglyoxal (MGO). Nε-carboxymethyllysine (CML) and Nε-carboxyethyllysine (CEL), formed by glycation from GO and MGO, are among the major AGEs in tissue proteins. Incubation with GO or MGO resulted in higher CML and CEL formation in the two cysteine residues containing αA-crystallin (αAC) than in the cysteine lacking αB-crystallin (αBC). Mass spectrometric data showed K70 and K166 to be heavily modified with CML and CEL in GO- and MGO-modified αAC. In silico analysis of the structure of αAC showed K70 and K166 to be proximal to C142. Mutation or reductive alkylation of cysteine residues in αAC significantly reduced CML and CEL formation. The addition of GSH or N-acetylcysteine enhanced CML and CEL formation in αBC. The introduction of a cysteine residue proximal to a lysine residue in αBC increased the CML and CEL accumulation. Our data showed that CML and CEL formation occurs through a hemithioacetal intermediate formed from the reaction between thiols and GO or MGO. Together, these results highlight a mechanism by which thiols influence protein AGE levels. In addition, CML and CEL are ligands for RAGE, a receptor for AGEs, which has been implicated in several aging and diabetes-associated diseases. Therefore, further understanding of the biosynthesis of CML and CEL could lead to the development of new therapies against those diseases.

Untargeted Metabolomics Reveals the Role of Lipocalin-2 in the Pathological Changes of Lens and Retina in Diabetic Mice

Purpose

To identify the role of lipocalin-2 (LCN2) in diabetic cataract (DC) and diabetic retinopathy (DR), diabetes models were established in wild-type (WT) and LCN2 gene knockout (LCN2-/-) mice by streptozotocin (STZ), this study aimed to investigate the metabolic alterations and underlying pathways in the lens and retina.

Methods

Untargeted metabolomic analysis was performed on the lenses and retinas of WT and LCN2-/- diabetic mice, and relevant pathways were predicted through bioinformatics analysis.

Results

LCN2 was notably elevated in the anterior capsules of DC and the vitreous humor of DR. Metabolic profiling of the lenses and retinas of diabetic mice indicated that the differential metabolites were mostly amino acids, fatty acids, carbohydrates, and their derivatives. In the lenses of STZ-induced WT mice, the differential abundance score (DA-score) revealed an increase in metabolites associated with the citrate (or TCA) cycle and glucagon signaling pathway, whereas a decrease was observed in metabolites related to cholesterol metabolism. After the knockout of LCN2, the DA-score indicated that the majority of metabolites involved in cholesterol metabolism, cysteine and methionine metabolism, and tryptophan metabolism were diminished. In the STZ-induced retina, there was an increase in metabolites associated with the mTOR signaling pathway, and this increase was inhibited by the knockout of LCN2.

Conclusions

Numerous metabolites exhibited substantial alterations in the lenses and retinas of diabetic mice. Untargeted metabolomics has provided insights into the function of LCN2 in DC and DR. These changes in metabolites, along with their related pathways, could be the mechanisms by which LCN2 modulated DC and DR.

Effects of Aging on Intrinsic Protein Disorder in Human Lenses and Zonules

This study aims to compare the levels of intrinsic protein disorder within the human lens and zonule proteomes and investigate the role of aging as a potential influencing factor on disorder levels. A cross-sectional proteomic analysis was employed, utilizing a dataset of 1466 proteins derived from the lens and zonule proteomes previously published by Wang et al. and De Maria et al. Bioinformatics tools, including a composition profiler and a rapid intrinsic disorder analysis online tool, were used to conduct a comparative analysis of protein disorder. Statistical tests such as ANOVA, Tukey's HSD, and chi-squared tests were applied to evaluate differences between groups. The study revealed distinct amino acid compositions for each proteome, showing a direct correlation between aging and increased protein disorder in the zonular proteomes, whereas the lens proteomes exhibited the opposite trend. Findings suggest that age-related changes in intrinsic protein disorder within the lens and zonule proteomes may be linked to structural transformations in these tissues. Understanding how protein disorder evolves with age could enhance knowledge of the molecular basis for age-related conditions such as cataracts and pseudoexfoliation, potentially leading to better therapeutic strategies.

Type 1 and type 2 diabetes predisposed to higher Nd:YAG capsulotomy rates following cataract surgery: analysis of 53,471 consecutive cases

OBJECTIVE

To assess the effect of diabetes type on Nd:YAG capsulotomy rates following cataract surgery.

DESIGN

A retrospective cohort study.

METHODS

All patients who underwent cataract extraction at the Department of Ophthalmology, Bristol Eye Hospital, Bristol, UK, between 2003 and 2017 were included. The Nd:YAG capsulotomy rate following cataract surgery was assessed and compared between nondiabetic, type 1 diabetes (T1D), and type 2 diabetes (T2D) patients. Multivariate Cox regression analysis controlling for age and sex was used to estimate hazard ratios for Nd:YAG laser capsulotomies.

RESULTS

Included were 53,471 consecutive cataract surgeries. Overall, 42,651 eyes (79.8%) were in nondiabetic patients, 823 eyes (1.5%) were in T1D patients, and 9,997 eyes (18.7%) were in T2D patients. The mean follow-up time was 6.8 ± 4.2 years. In univariate analysis, the eyes of T1D patients (p < 0.001) and T2D patients (p = 0.003) had significantly higher Nd:YAG laser capsulotomy rates than the eyes of nondiabetic patients. In Cox regression analysis adjusted for the patient's age and sex, DM1 (HR 1.692, 95%CI 1.390-2.059, P<0.001) and DM2 (HR 1.157, 95%CI 1.075-1.244, P<0.001) remained significantly predictive for higher Nd:YAG laser capsulotomy rates.

CONCLUSION

In our large cohort study, patients with T1D and T2D were predisposed to high risk for Nd:YAG capsulotomy following cataract surgery. This study may be beneficial and raise awareness regarding the assessment of posterior capsular opacification development in pseudophakic diabetic patients, particularly those with T1D. The significance of ophthalmology screening for diabetes individuals is further supported by this issue.

The Role of Immune Cells and Signaling Pathways in Diabetic Eye Disease: A Comprehensive Review

Diabetic eye disease (DED) encompasses a range of ocular complications arising from diabetes mellitus, including diabetic retinopathy, diabetic macular edema, diabetic keratopathy, diabetic cataract, and glaucoma. These conditions are leading causes of visual impairments and blindness, especially among working-age adults. Despite advancements in our understanding of DED, its underlying pathophysiological mechanisms remain incompletely understood. Chronic hyperglycemia, oxidative stress, inflammation, and neurodegeneration play central roles in the development and progression of DED, with immune-mediated processes increasingly recognized as key contributors. This review provides a comprehensive examination of the complex interactions between immune cells, inflammatory mediators, and signaling pathways implicated in the pathogenesis of DED. By delving in current research, this review aims to identify potential therapeutic targets, suggesting directions of research for future studies to address the immunopathological aspects of DED.

The Synergistic Effects of Polyol Pathway-Induced Oxidative and Osmotic Stress in the Aetiology of Diabetic Cataracts

Cataracts are the world's leading cause of blindness, and diabetes is the second leading risk factor for cataracts after old age. Despite this, no preventative treatment exists for cataracts. The altered metabolism of excess glucose during hyperglycaemia is known to be the underlying cause of diabetic cataractogenesis, resulting in localised disruptions to fibre cell morphology and cell swelling in the outer cortex of the lens. In rat models of diabetic cataracts, this damage has been shown to result from osmotic stress and oxidative stress due to the accumulation of intracellular sorbitol, the depletion of NADPH which is used to regenerate glutathione, and the generation of fructose metabolites via the polyol pathway. However, differences in lens physiology and the metabolism of glucose in the lenses of different species have prevented the translation of successful treatments in animal models into effective treatments in humans. Here, we review the stresses that arise from hyperglycaemic glucose metabolism and link these to the regionally distinct metabolic and physiological adaptations in the lens that are vulnerable to these stressors, highlighting the evidence that chronic oxidative stress together with osmotic stress underlies the aetiology of human diabetic cortical cataracts. With this information, we also highlight fundamental gaps in the knowledge that could help to inform new avenues of research if effective anti-diabetic cataract therapies are to be developed in the future.

Tissue, cellular, and molecular level determinants for eye lens stiffness and elasticity

The eye lens is a transparent, ellipsoid tissue in the anterior chamber that is required for the fine focusing of light onto the retina to transmit a clear image. The focusing function of the lens is tied to tissue transparency, refractive index, and biomechanical properties. The stiffness and elasticity or resilience of the human lens allows for shape changes during accommodation to focus light from objects near and far. It has long been hypothesized that changes in lens biomechanical properties with age lead to the loss of accommodative ability and the need for reading glasses with age. However, the cellular and molecular mechanisms that influence lens biomechanical properties and/or change with age remain unclear. Studies of lens stiffness and resilience in mouse models with genetic defects or at advanced age inform us of the cytoskeletal, structural, and morphometric parameters that are important for biomechanical stability. In this review, we will explore whether: 1) tissue level changes, including the capsule, lens volume, and nucleus volume, 2) cellular level alterations, including cell packing, suture organization, and complex membrane interdigitations, and 3) molecular scale modifications, including the F-actin and intermediate filament networks, protein modifications, lipids in the cell membrane, and hydrostatic pressure, influence overall lens biomechanical properties.

Comprehensive landscape of RNA N6-methyladenosine modification in lens epithelial cells from normal and diabetic cataract

To gain more insight into the mechanism of cataract formation from the perspective of epigenetics in the diabetic population, lens epithelium from diabetic cataract patients and health individuals were collected separately and analyzed for N6-methyladenosine (m6A)-modified RNA using methylated RNA immunoprecipitation sequencing (MeRIP-Seq). Subsequently, differential expression analysis was performed on m6A-regulated messenger RNA (mRNA), circular RNA (circRNA), and long non-coding RNA (lncRNA), followed by functional annotation using the Gene Ontology (GO) database. Furthermore, analysis of single-cell data of lens complemented the intrinsic association and cellular heterogeneity of cataract and m6A regulators. In this study, both the global expression levels and peak intensity of m6A-tagged RNAs were increased in patients with diabetic cataract. And we noted multiple core enzymes were upregulated in the diabetic cataract (DC) samples. Besides, single-cell RNA sequencing analysis of the lens revealed the heterogeneous expression of RNA m6A regulators across different cell types, and we noted that the early fiber cell cluster was also closely associated with the onset of cataract and m6A modification. The results comprehensively revealed the dynamic modification landscape of m6A on mRNA, circRNA, and lncRNA, which might provide valuable resources for future studies of the pathogenesis of DCs.

Vascular endothelial cell-derived exosomal miR-1246 facilitates posterior capsule opacification development by targeting GSK-3β in diabetes mellitus

Posterior capsule opacification (PCO) is a serious complication after cataract surgery. Diabetes could increase the occurrence of PCO, but the mechanism is still unclear. The purpose of this study is to investigate the role of small extracellular vesicles (sEVs) derived from diabetic aqueous humor in PCO process. Intraoperatively-derived aqueous humor sEVs from patients with diabetic related cataract (DRC) promoted the epithelial-mesenchymal transition (EMT) and metastasis of human lens epithelial cells (LECs). Via mouse PCO surgical model and DiI labeled fluorescence detection of sEVs, the sEVs derived from vascular endothelium were discovered directly contacting with LECs. Furthermore, we demonstrated that high-glucose-cultured human umbilical vein endothelial cells (HUVEC) -derived sEVs facilitated EMT process of HLE-B3 using co-culture model in vitro. MiRNA-seq data and GEO datasets analysis revealed that miR-1246 was essential in EMT process with diabetes. The miR-1246 was highly expressed in diabetic aqueous humor sEVs and high-glucose-treated vascular-endothelial-cell-derived sEVs. Moreover, miR-1246 promoted the metastasis and EMT process of HLE-B3 cells by directly targeting GSK-3β. Inhibiting miR-1246 could negatively regulated EMT. This finding might serve as a potential therapy for diabetic PCO.

Current Approach to the Pathogenesis of Diabetic Cataracts

Cataracts remain the first or second leading cause of blindness in all world regions. In the diabetic population, cataracts not only have a 3–5 times higher incidence than in the healthy population but also affect people at a younger age. In patients with type 1 diabetes, cataracts occur on average 20 years earlier than in the non-diabetic population. In addition, the risk of developing cataracts increases with the duration of diabetes and poor metabolic control. A better understanding of the mechanisms leading to the formation of diabetic cataracts enables more effective treatment and a holistic approach to the patient.

The lens epithelium as a major determinant in the development, maintenance, and regeneration of the crystalline lens

The crystalline lens is a transparent and refractive biconvex structure formed by lens epithelial cells (LECs) and lens fibers. Lens opacity, also known as cataracts, is the leading cause of blindness in the world. LECs are the principal cells of lens throughout human life, exhibiting different physiological properties and functions. During the embryonic stage, LECs proliferate and differentiate into lens fibers, which form the crystalline lens. Genetics and environment are vital factors that influence normal lens development. During maturation, LECs help maintain lens homeostasis through material transport, synthesis and metabolism as well as mitosis and proliferation. If disturbed, this will result in loss of lens transparency. After cataract surgery, the repair potential of LECs is activated and the structure and transparency of the regenerative tissue depends on postoperative microenvironment. This review summarizes recent research advances on the role of LECs in lens development, homeostasis, and regeneration, with a particular focus on the role of cholesterol synthesis (eg., lanosterol synthase) in lens development and homeostasis maintenance, and how the regenerative potential of LECs can be harnessed to develop surgical strategies and improve the outcomes of cataract surgery (Fig. 1). These new insights suggest that LECs are a major determinant of the physiological and pathological state of the lens. Further studies on their molecular biology will offer possibility to explore new approaches for cataract prevention and treatment.

Glucose and MMP-9 dual-responsive hydrogel with temperature sensitive self-adaptive shape and controlled drug release accelerates diabetic wound healing

Chronic diabetic wounds are an important healthcare challenge. High concentration glucose, high level of matrix metalloproteinase-9 (MMP-9), and long-term inflammation constitute the special wound environment of diabetic wounds. Tissue necrosis aggravates the formation of irregular wounds. All the above factors hinder the healing of chronic diabetic wounds. To solve these issues, a glucose and MMP-9 dual-response temperature-sensitive shape self-adaptive hydrogel (CBP/GMs@Cel&INS) was designed and constructed with polyvinyl alcohol (PVA) and chitosan grafted with phenylboric acid (CS-BA) by encapsulating insulin (INS) and gelatin microspheres containing celecoxib (GMs@Cel). Temperature-sensitive self-adaptive CBP/GMs@Cel&INS provides a new way to balance the fluid-like mobility (self-adapt to deep wounds quickly, approximately 37 °C) and solid-like elasticity (protect wounds against external forces, approximately 25 °C) of self-adaptive hydrogels, while simultaneously releasing insulin and celecoxib on-demand in the environment of high-level glucose and MMP-9. Moreover, CBP/GMs@Cel&INS exhibits remodeling and self-healing properties, enhanced adhesion strength (39.65 ± 6.58 kPa), down-regulates MMP-9, and promotes cell proliferation, migration, and glucose consumption. In diabetic full-thickness skin defect models, CBP/GMs@Cel&INS significantly alleviates inflammation and regulates the local high-level glucose and MMP-9 in the wounds, and promotes wound healing effectively through the synergistic effect of temperature-sensitive shape-adaptive character and the dual-responsive system.

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The hydrogel with temperature-sensitive adaptive shape can fill irregular wounds.

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The hydrogel on-demand releases drugs responding to diabetic wound environment.

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The hydrogel significantly accelerated diabetic wound healing.

Glycation-induced age-related illnesses, antiglycation and drug delivery strategies

OBJECTIVES

Ageing is a major cause of multiple age-related diseases. Several mechanisms have been reported to contribute to these abnormalities including glycation, oxidative stress, the polyol pathway and osmotic stress. Glycation, unlike glycosylation, is an irregular biochemical reaction to the formation of active advanced glycation end-products (AGEs), which are considered to be one of the causes of these chronic diseases. This study provides a recent and comprehensive review on the possible causes, mechanisms, types, analytical techniques, diseases and treatments of the toxic glycation end products.

KEY FINDINGS

Several mechanisms have been found to play a role in generating hyperglycaemia-induced oxidative stress including an increase in the levels of reactive oxygen species (ROS), increase in the levels of AGEs, binding of AGEs and their receptors (RAGE) and the polyol pathway and thus have been investigated as promising novel targets.

SUMMARY

This review focuses on the key mechanisms attributed to cumulative increases of glycation and pathological RAGE expression as a significant cause of multiple age-related diseases, and reporting on different aspects of antiglycation therapy as a novel approach to managing/treating age-related diseases. Additionally, historical, current and possible future antiglycation approaches will be presented focussing on novel drug delivery methods.