The maillard reaction in eye diseases

Glipizide inhibits the glycation of alpha-crystallin: A combined in vitro and in silico approach in retinopathy management

In human eye, structural proteins, known as crystallins, play a crucial role in maintaining the eye's refractive index. These crystallins constitute majority of the total soluble proteins found in the eye lens. Among them, α-crystallins (α-CR) is one of the major components. Under hyperglycaemic conditions, crystallins become susceptible to glycation that ultimately leads to advanced glycation endproducts (AGEs) formation. Glipizide is a well-known oral medication used in controlling levels of blood sugar, this drug stimulates the insulin release from pancreas. However, this drug has not been thoroughly investigated for its impact on α-CR glycation. In this study, we explored glipizide's protective role against glucose-induced α-CR glycation. Remarkably, glipizide effectively inhibited the formation of early glycation products, ultimately reducing AGEs formation. Additionally, glipizide provides protection against modifications of free lysine residues and lowered the carbonyl content. To gain deeper insights into mechanism of inhibition, we turn to binding studies and bioinformatics. Glipizide formed stable complex with α-CR with values of Gibbs energy ranging from -5.848 to -6.695 kcal/mol. Molecular docking revealed the binding energy as -6.5 kcal/mol and lysine residues emerged as a prominent among the key interacting residues. Notably, glipizide appears to mask lysine residues, thereby contributing to the inhibition of α-CR glycation. Furthermore, analysis of molecular simulation data reinforces the stability of this complex. Consequently, the stable α-CR-glipizide complex may prevent glucose from binding to α-CR. Overall, glipizide holds promise as a preventive measure against glycation of eye lens proteins, potentially benefiting in diabetic retinopathy.

Pharmacological treatments for the correction of presbyopia

Presbyopia affects between 1.7 and 2 billion people worldwide. Presbyopia significantly impacts productivity and quality of life in both developed and developing countries. During accommodation, the human eye changes its dioptric power by altering the shape of the lens, but the exact nature of this change has not been fully explained. Recently, topical treatments have been marketed for the treatment of presbyopia and others are under investigation. In order to prepare a review of these novel therapies, we searched the major biomedical search engines. We found 15 randomized clinical trials and 12 reviews that met our review criteria. There are two different strategies for this purpose, the pinhole effect that increases depth of focus and "crystalline lens relaxation" for which parasympathetic mimetics and lens oxidation intermediates have been used. The results are generally favorable in terms of improvement of near visual acuity, although the follow-up period of the studies is short. These are novel strategies in the early stages of research that could be useful in the treatment of presbyopia.

Fructosyl Amino Oxidase as a Therapeutic Enzyme in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is an age-related disorder that is a global public health problem. The non-enzymatic Maillard reaction results in the formation of advanced glycation end products (AGEs). Accumulation of AGEs in drusen plays a key role in AMD. AGE-reducing drugs may contribute to the prevention and treatment of AGE-related disease. Fructosamine oxidase (FAOD) acts on fructosyl lysine and fructosyl valine. Based upon the published results of fructosamine 3-kinase (FN3K) and FAOD obtained in cataract and presbyopia, we studied ex vivo FAOD treatment as a non-invasive AMD therapy. On glycolaldehyde-treated porcine retinas, FAOD significantly reduced AGE autofluorescence (p = 0.001). FAOD treatment results in a breakdown of AGEs, as evidenced using UV fluorescence, near-infrared microspectroscopy on stained tissue sections of human retina, and gel permeation chromatography. Drusen are accumulations of AGEs that build up between Bruch's membrane and the retinal pigment epithelium. On microscopy slides of human retina affected by AMD, a significant reduction in drusen surface to 45 ± 21% was observed following FAOD treatment. Enzymatic digestion followed by mass spectrometry of fructose- and glucose-based AGEs (produced in vitro) revealed a broader spectrum of substrates for FAOD, as compared to FN3K, including the following: fructosyllysine, carboxymethyllysine, carboxyethyllysine, and imidazolone. In contrast to FN3K digestion, agmatine (4-aminobutyl-guanidine) was formed following FAOD treatment in vitro. The present study highlights the therapeutic potential of FAOD in AMD by repairing glycation-induced damage.

A narrative review on dietary components and patterns and age-related macular degeneration

Age-related macular degeneration (AMD) is one of the most prevalent eye diseases among the ageing population worldwide. It is a leading cause of blindness in individuals over 55, particularly in industrialised Western countries. The prevalence of AMD increases with age, and genetic factors and environmental influences are believed to contribute to its development. Among the environmental factors, diet plays a significant role in AMD. This review explores the association between dietary components, dietary patterns and AMD. Various nutrients, non-nutrient substances and dietary models that have the potential to counteract oxidative stress and inflammation, which are underlying mechanisms of AMD, are discussed. Consuming fruits, vegetables, fish and seafood, whole grains, olive oil, nuts and low-glycaemic-index foods has been highlighted as beneficial for reducing the risk of AMD. Adhering to the Mediterranean diet, which encompasses these elements, can be recommended as a dietary pattern for AMD. Furthermore, the modulation of the gut microbiota through dietary interventions and probiotics has shown promise in managing AMD.

Oxidative stress, epigenetic regulation and pathological processes of lens epithelial cells underlying diabetic cataract

Background

Cataract is a blinding disease worldwide. It is an age-related disease that mainly occurs in people over 65 years old. Cataract is also prevalent in patients with diabetes mellites (DM). The pathological mechanisms underlying diabetic cataract (DC) are more complex than that of age-related cataract. Studies have identified that polyol pathway, advanced glycation end products (AGEs) and oxidative stress are the primary pathogenesis of DC. In recent years, molecular-level regulations and pathological processes of lens epithelial cells (LECs) have been confirmed to play roles in the initiation and progression of DC. A comprehensive understanding and elucidation of how chronic hyperglycemia drives molecular-level regulations and cytopathological processes in the lens will shed lights on the prevention, delay and treatment of DC.

Main text

Excessive glucose in the lens enhances polyol pathway and AGEs formation. Polyol pathway causes imbalance in the ratio of NADPH/NADP+ and NADH/NAD+. Decrease in NADPH/NADP+ ratio compromises antioxidant enzymes, while increase in NADH/NAD+ ratio promotes reactive oxygen species (ROS) overproduction in mitochondria, resulting in oxidative stress. Oxidative stress in the lens causes oxidation of DNA, proteins and lipids, leading to abnormalities in their structure and functions. Glycation of proteins by AGEs decreases solubility of proteins. High glucose triggered epigenetic regulations directly or indirectly affect expressions of genes and proteins in LECs. Changes in autophagic activity, increases in fibrosis and apoptosis of LECs destroy the morphological structure and physiological functions of the lens epithelium, disrupting lens homeostasis.

Conclusions

In both diabetic animal models and diabetics, oxidative stress plays crucial roles in the formation of cataract. Epigenetic regulations, include lncRNA, circRNA, microRNA, methylation of RNA and DNA, histone acetylation and pathological processes, include autophagy, fibrosis and apoptosis of LECs also involved in DC.

Topical Application of Deglycating Enzymes as an Alternative Non-Invasive Treatment for Presbyopia

Presbyopia is an age-related vision disorder that is a global public health problem. Up to 85% of people aged ≥40 years develop presbyopia. In 2015, 1.8 billion people globally had presbyopia. Of those with significant near vision disabilities due to uncorrected presbyopia, 94% live in developing countries. Presbyopia is undercorrected in many countries, with reading glasses available for only 6-45% of patients living in developing countries. The high prevalence of uncorrected presbyopia in these parts of the world is due to the lack of adequate diagnosis and affordable treatment. The formation of advanced glycation end products (AGEs) is a non-enzymatic process known as the Maillard reaction. The accumulation of AGEs in the lens contributes to lens aging (leading to presbyopia and cataract formation). Non-enzymatic lens protein glycation induces the gradual accumulation of AGEs in aging lenses. AGE-reducing compounds may be effective at preventing and treating AGE-related processes. Fructosyl-amino acid oxidase (FAOD) is active on both fructosyl lysine and fructosyl valine. As the crosslinks encountered in presbyopia are mainly non-disulfide bridges, and based on the positive results of deglycating enzymes in cataracts (another disease caused by glycation of lens proteins), we studied the ex vivo effects of topical FAOD treatment on the power of human lenses as a new potential non-invasive treatment for presbyopia. This study demonstrated that topical FAOD treatment resulted in an increase in lens power, which is approximately equivalent to the correction obtained by most reading glasses. The best results were obtained for the newer lenses. Simultaneously, a decrease in lens opacity was observed, which improved lens quality. We also demonstrated that topical FAOD treatment results in a breakdown of AGEs, as evidenced by gel permeation chromatography and a marked reduction in autofluorescence. This study demonstrated the therapeutic potential of topical FAOD treatment in presbyopia.

Butein Inhibits the Glycation of α-Crystallin: An Approach in Prevention of Retinopathy

The aggregation of lens proteins induced by glycation is one of the key drivers of diabetic retinopathy and development of diabetic cataracts. Moreover, glycation also causes numerous alterations not only to the tertiary structure of lens proteins but also to serum proteins. There are also evidences of covalent crosslinking among lens crystallins resulting in development of cataract. In this article, the inhibitory potential of butein was tested against the glucose induced glycation and the aggregation α-crystallin (α-cry). The results showed that there was inhibition of advanced glycation products (78.28%) and early glycation products (86.30%) following the treatment of butein. Additionally, the presence of butein caused a significant improvement in the tested biochemical markers of glycation. The treatment with butein reduced the free lysine modification to 23.67%. The secondary and tertiary structural distortions of α-cry were also protected. The mechanism of inhibition further investigated at the molecular level using biophysical and computational techniques. The interaction data showed the butein exhibited strong affinity towards the α-cry. The binding event was entropically driven and energetically favourable. The Gibb's free energy of the interaction was found to be -5.99 to -7.17 kcal mol^-1. The binding site of butein in α-cry was deciphered by molecular docking and the dynamics was studied using molecular dynamics (MD) simulations. The simulation data showed that butein formed stable complex with α-cry under physiological conditions. Most of the tested parameters from molecular simulations, such as secondary structure, was found to be stable. The data clearly show the potential of butein in inhibiting the glycation induced aggregation of α-cry and hence can be developed as useful inhibitor in the management of diabetic cataract and retinopathy.

Noncoding RNAs in cataract formation: star molecules emerge in an endless stream

For decades, research on the pathological mechanism of cataracts has usually focused on the abnormal protein changes caused by a series of risk factors. However, an entire class of molecules, termed non-coding RNA (ncRNA), was discovered in recent years and proven to be heavily involved in cataract formation. Recent studies have recognized the key regulatory roles of ncRNAs in cataracts by shaping cellular activities such as proliferation, apoptosis, migration and epithelial-mesenchymal transition (EMT). This review summarizes our current insight into the biogenesis, properties and functions of ncRNAs and then discusses the development of research on ncRNAs in cataracts. Considering the significant role of ncRNA in cataract formation, research on novel associated regulatory mechanisms is urgently needed, and the development of therapeutic alternatives for the treatment of cataracts seems promising.

Revisiting Methodologies for In Vitro Preparations of Advanced Glycation End Products

Chronic elevation of sugar and oxidative stress generally results in development of advanced glycation end products (AGEs) in diabetic individuals. Accumulation of AGEs in an individual can give rise to the activation of several pathways that will ultimately lead to various complications. Such AGEs can also be prepared in an in vitro environment. For an in vitro preparation of advanced glycation end products (AGEs), proteins, lipids, or nucleic acids are generally required to be incubated with reducing sugars at a physiological temperature or higher depending upon the protocol optimized for its preparation. Certain other factors are also optimized and added to the buffer to hasten its preparation or alter the properties of prepared AGEs. Through this review, we intend to highlight the various studies related to the experimental procedures for the preparation of different types of AGEs. In addition, we present the comparative study of methodologies optimized for the preparation of AGEs.

Crystallins as Important Pathogenic Targets for Accumulation of Structural Damages Resulting in Protein Aggregation and Cataract Development: Introduction to This Special Issue of Biochemistry (Moscow)

This issue of Biochemistry (Moscow) is dedicated to the role of protein misfolding and aggregation in cataract development. In fact, many genetic mutations or chemical and physical deleterious factors can initiate alterations in the macrostructural order and proper folding of eye lens proteins, which in some cases result in the formation of large light-scattering aggregates, affecting the quality of vision and making lens more prone to cataract development. Diabetes mellitus, which is associated with oxidative stress and mass production of highly reactive compounds, can accelerate unfolding and aggregation of eye lens proteins. This journal issue contains reviews and research articles that describe the destructive effects of mutations and highly reactive metabolites on the structure and function of lens crystallin proteins, as well important molecules in the lens's natural defense system involved in protection against deleterious effects of the physical and chemical factors.

Protein posttranslational modification (PTM) by glycation: Role in lens aging and age-related cataractogenesis

Crystallins, the most prevalent lens proteins, have no turnover throughout the entire human lifespan. These long-lived proteins are susceptible to post-synthetic modifications, including oxidation and glycation, which are believed to be some of the primary mechanisms for age-related cataractogenesis. Thanks to high glutathione (GSH) and ascorbic acid (ASA) levels as well as low oxygen content, the human lens is able to maintain its transparency for several decades. Aging accumulates substantial changes in the human lens, including a decreased glutathione concentration, increased reactive oxygen species (ROS) formation, impaired antioxidative defense capacity, and increased redox-active metal ions, which induce glucose and ascorbic acid degradation and protein glycation. The glycated lens crystallins are either prone to UVA mediated free radical production or they attract metal ion binding, which can trigger additional protein oxidation and modification. This vicious cycle is expected to be exacerbated with older age or diabetic conditions. ASA serves as an antioxidant in the human lens under reducing conditions to protect the human lens from damage, but ASA converts to the pro-oxidative role and causes lens protein damage by ascorbylation in high oxidation or enriched redox-active metal ion conditions. This review is dedicated in honor of Dr. Frank Giblin, a great friend and superb scientist, whose pioneering and relentless work over the past 45 years has provided critical insight into lens redox regulation and glutathione homeostasis during aging and cataractogenesis.

A Potential Role for Fructosamine-3-Kinase in Cataract Treatment

Cataracts are the major cause of blindness worldwide, largely resulting from aging and diabetes mellitus. Advanced glycation end products (AGEs) have been identified as major contributors in cataract formation because they alter lens protein structure and stability and induce covalent cross-linking, aggregation, and insolubilization of lens crystallins. We investigated the potential of the deglycating enzyme fructosamine-3-kinase (FN3K) in the disruption of AGEs in cataractous lenses. Macroscopic changes of equine lenses were evaluated after ex vivo intravitreal FN3K injection. The mechanical properties of an equine lens pair were evaluated after treatment with saline and FN3K. AGE-type autofluorescence (AF) was measured to assess the time-dependent effects of FN3K on glycolaldehyde-induced AGE-modified porcine lens fragments and to evaluate its actions on intact lenses after in vivo intravitreal FN3K injection of murine eyes. A potential immune response after injection was evaluated by analysis of IL-2, TNFα, and IFNγ using an ELISA kit. Dose- and time-dependent AF kinetics were analyzed on pooled human lens fragments. Furthermore, AF measurements and a time-lapse of macroscopic changes were performed on intact cataractous human eye lenses after incubation with an FN3K solution. At last, AF measurements were performed on cataractous human eyes after crossover topical treatment with either saline- or FN3K-containing drops. While the lenses of the equine FN3K-treated eyes appeared to be clear, the saline-treated lenses had a yellowish-brown color. Following FN3K treatment, color restoration could be observed within 30 min. The extension rate of the equine FN3K-treated lens was more than twice the extension rate of the saline-treated lens. FN3K treatment induced significant time-dependent decreases in AGE-related AF values in the AGE-modified porcine lens fragments. Furthermore, in vivo intravitreal FN3K injection of murine eyes significantly reduced AF values of the lenses. Treatment did not provoke a systemic immune response in mice. AF kinetics of FN3K-treated cataractous human lens suspensions revealed dose- and time-dependent decreases. Incubation of cataractous human eye lenses with FN3K resulted in a macroscopic lighter color of the cortex and a decrease in AF values. At last, crossover topical treatment of intact human eyes revealed a decrease in AF values during FN3K treatment, while showing no notable changes with saline. Our study suggests, for the first time, a potential additional role of FN3K as an alternative treatment for AGE-related cataracts.

Pseudoexfoliation syndrome in diabetic patients: transmission electron microscopy study of anterior lens epithelial cells

Purpose: to examine the lens epithelial cells in diabetic patients with pseudoexfoliation to ultramicroscope and to compare the findings with those of patients without diabetes mellitus (DM) and/or without pseudoexfoliation (PEX).

Materials and Methods: Forty patients aged 65-86 years were enrolled in the study. All patients had senile cataract and were divided into four groups of ten patients in each group. Group I: patients without pseudoexfoliation, without DM, Group II: without pseudoexfoliation, with DM, Group III: with pseudoexfoliation, without DM, Group IV (Pseudoexfoliation-Diabetic Group): with pseudoexfoliation, with DM. In all cases, part of the central portion of anterior lens capsule was removed during routine cataract surgery, and was properly prepared in order to be examined under a transmission electron microscope.

Results: In the control group, mainly degenerative alterations to varying extents were observed. In all groups, intracellular and extracellular oedema, multilayering, apoptosis, completely destroyed cells adjacent to normal cellswere described. In the diabetic group, alterations were more severe with respect to group I. In PEX cases, the additionalirregularity of the epithelium surface, loose intercellular connection, as well as the loose connection between cells and basement membrane were described with the presence of PEX material free and within the basement membrane. In cases with PEX and DM, degenerative alterations and PEX material were observed as well, but the epithelium was better conserved compared to the PEX group.

Conclusion: the observed lesions were more extended and more frequent in the pseudoexfoliation group, followed by the diabetic group. The pseudoexfoliation-diabetic group presented less intense modifications raising questions about the interaction of these different diseases.

Abbreviations: DM = Diabetes Mellitus, PEX = Pseudoexfoliation, PXM = Pseudoexfoliative Material, AD = Alzheimer disease, TGF-β1 = Transforming Growth Factor beta 1, WHO = World Health Organization, LEC = Lens Epithelium Cells, BM = Basement Membrane, CM = Cytoplasmic Membrane

Complexes of Copper and Iron with Pyridoxamine, Ascorbic Acid, and a Model Amadori Compound: Exploring Pyridoxamine's Secondary Antioxidant Activity

The thermodynamic stability of 11 complexes of Cu(II) and 26 complexes of Fe(III) is studied, comprising the ligands pyridoxamine (PM), ascorbic acid (ASC), and a model Amadori compound (AMD). In addition, the secondary antioxidant activity of PM is analyzed when chelating both Cu(II) and Fe(III), relative to the rate constant of the first step of the Haber-Weiss cycle, in the presence of the superoxide radical anion (O2•-) or ascorbate (ASC^-). Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. The aqueous environment is modeled by making use of the SMD solvation method in all calculations. This level of theory accurately reproduces the experimental data available. When put in perspective with the stability of various complexes of aminoguanidine (AG) (which we have previously studied), the following stability trends can be found for the Cu(II) and Fe(III) complexes, respectively: ASC < AG < AMD < PM and AG < ASC < AMD < PM. The most stable complex of Cu(II) with PM (with two bidentate ligands) presents a ΔGf0 value of -35.8 kcal/mol, whereas the Fe(III) complex with the highest stability (with three bidentate ligands) possesses a ΔGf0 of -58.9 kcal/mol. These complexes can significantly reduce the rate constant of the first step of the Haber-Weiss cycle with both O2•- and ASC^-. In the case of the copper-containing reaction, the rates are reduced up to 9.70 × 10³ and 4.09 × 10¹³ times, respectively. With iron, the rates become 1.78 × 10³ and 4.45 × 10¹⁵ times smaller, respectively. Thus, PM presents significant secondary antioxidant activity since it is able to inhibit the production of ·OH radicals. This work concludes a series of studies on secondary antioxidant activity and allows potentially new glycation inhibitors to be investigated and compared relative to both PM and AG.

Antiglycation Activity of Triazole Schiff's Bases Against Fructosemediated Glycation: In Vitro and In Silico Study

BACKGROUND

Advanced glycation end products (AGEs) are known to be involved in the pathophysiology of diabetic complications, neurodegenerative diseases, and aging. Preventing the formation of AGEs can be helpful in the management of these diseases.

OBJECTIVES

Two classes of previously synthesized traizole Schiff's bases (4H-1,2,4-triazole-4- Schiff's bases 1-14, and 4H-1,2,4-triazole-3-Schiff's bases 15-23) were evaluated for their in vitro antiglycation activity.

METHODS

In vitro fructose-mediated human serum albumin (HSA) glycation assay was employed to assess the antiglycation activity of triazole Schiff's bases. The active compounds were subjected to cytotoxicity analysis by MTT assay on mouse fibroblast (3T3) cell line. Molecular docking and simulation studies were carried out to evaluate the interactions and stability of compounds with HSA. Anti-hyperglycemic and antioxidant activities of selected non-cytotoxic compounds were evaluated by in vitro α-glucosidase inhibition, and DPPH free radical scavenging assays, respectively.

RESULTS

Compound 1 (IC50=47.30±0.38 µM) from 4H-1,2,4-triazole-4-Schiff's bases has exhibited antiglycation activity comparable to standard rutin (IC50=54.5±0.05 µM) along with a stable RMSD profile in MD simulation studies. Compound 1 also exhibited a potent α-glucosidase inhibitory activity, and moderate antioxidant property. Other derivatives showed a weak antiglycation activity with IC50 values between 248.1-637.7 µM. Compounds with potential antiglycation profile were found to be non-cytotoxic in a cellular assay.

CONCLUSION

The study identifies triazole Schiff's bases active against fructose-mediated glycation of HSA, thus indicates their potential against late diabetic complications due to production of advancedend products (AGEs).

Prevention of Diabetic Complications by Walnut Leaf Extract via Changing Aldose Reductase Activity: An Experiment in Diabetic Rat Tissue

BACKGROUND

Increased activity of aldose reductase (AR) is one of the mechanisms involved in the development of diabetic complications. Inhibiting AR can be a target to prevent diabetes complications. This study is aimed at evaluating the effect of cyclohexane (CH) and ethanol extracts (ET) of walnut leaves on AR activity in the lens and testis of diabetic rats.

METHODS

Fifty-six male rats classified into seven groups as control and treatment groups and treated for 30 days. The treatment groups were treated with different concentrations of ET and CH. The diabetic control (DC) group was exposed to streptozotocin. AR activity was measured in the lens and testis. The expression of AR in the testis was evaluated by the immunohistochemistry method.

RESULTS

Both extracts significantly reduced the AR activity (ng/mg of tissue protein) in the testis (0.034 ± 0.004, 0.038 ± 0.010, and 0.040 ± 0.007 in the treatment groups vs. 0.075 ± 0.007 in the DC group) and lens (1.66 ± 0.09, 2.70 ± 0.47, and 1.77 ± 0.20 in the treatment groups vs. 6.29 ± 0.48 in the DC group) of the treatment group compared to those of the DC group (P < 0.05). AR expression in the testes of the treatment groups was decreased compared with that of the DC group (P < 0.0001).

CONCLUSION

Walnut leaf extracts can reduce the activity and localization of AR in the testes and its activity in the lens of diabetic rats.

Theoretical Study of the Iron Complexes with Aminoguanidine: Investigating Secondary Antioxidant Activity

A thorough analysis of the thermodynamic stability of various complexes of aminoguanidine (AG) with Fe(III) at a physiological pH is presented. Moreover, the secondary antioxidant activity of AG is studied with respect to its kinetic role in the Fe(III) reduction to Fe(II) when reacting with the superoxide radical anion or ascorbate. Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. Solvent effects (water) are taken into account in both geometry optimizations and frequency calculations employing the SMD solvation method. Even though the results of this study show that AG can form an extensive number of stable complexes with Fe(III), none of these can reduce the rate constant of the initial step of the Haber-Weiss cycle when the reducing agent is O2•-. However, when the reductant is the ascorbate anion, AG is capable of reducing the rate constant of this reaction significantly, to the point of inhibiting the production of •OH radicals. In fact, the most stable complex of Fe(III) with AG, having a ∆Gf° of -37.9 kcal/mol, can reduce the rate constant of this reaction by 7.9 × 105 times. Thus, AG possesses secondary antioxidant activity relative to the Fe(III)/Fe(II) reduction with ascorbate, but not with O2•-. Similar results have also been found for AG relative to the Cu(II)/Cu(I) reduction, in agreement with experimental results.

Theoretical Study of the Iron Complexes with Lipoic and Dihydrolipoic Acids: Exploring Secondary Antioxidant Activity

The thermodynamic stability of twenty-nine Fe(III) complexes with various deprotonated forms of lipoic (LA) and dihydrolipoic (DHLA) acids, with coordination numbers 4, 5 and 6, is studied at the M06(SMD)/6-31++G(d,p) level of theory in water under physiological pH conditions at 298.15 K. Even though the complexes with LA- are more stable than those with DHLA-, the most thermodynamically stable Fe(III) complexes involve DHLA2-. The twenty-four exergonic complexes are used to evaluate the secondary antioxidant activity of DHLA and LA relative to the Fe(III)/Fe(II) reduction by O2•- and ascorbate. Rate constants for the single-electron transfer (SET) reactions are calculated. The thermodynamic stability of the Fe(III) complexes does not fully correlate with the rate constant of their SET reactions, but more exergonic complexes usually exhibit smaller SET rate constants. Some Cu(II) complexes and their reduction to Cu(I) are also studied at the same level of theory for comparison. The Fe(III) complexes appear to be more stable than their Cu(II) counterparts. Relative to the Fe(III)/Fe(II) reduction with ascorbate, DHLA can fully inhibit the formation of •OH radicals, but not by reaction with O2•-. Relative to the Cu(II)/Cu(I) reduction with ascorbate, the effects of DHLA are moderate/high, and with O2•- they are minor. LA has minor to negligible inhibition effects in all the cases considered.

Theoretical Study of the Copper Complexes with Aminoguanidine: Investigating Secondary Antioxidant Activity

A systematic study of the thermodynamic stability of various Cu(II) complexes with aminoguanidine (AG) is performed, together with the study of its secondary antioxidant activity. Calculations have been carried out at the M05(SMD)/6-311+G(d,p) level of theory using water as the solvent. The results obtained indicate that AG is capable of forming a wide array of stable coordination compounds with Cu(II) under physiological pH conditions, and it possesses some degree of secondary antioxidant activity when coordinating to copper. The most thermodynamically stable complex can slow down 2.8 times the first step of the Haber-Weiss cycle (from 7.71 × 109 to 2.80 × 109 M-1 s-1) and slightly reduce the potential damage that the formation of •OH radicals can cause. The results of this research add to previous knowledge on this molecule, which could be used as a potential glycation inhibitor.

How Does Pyridoxamine Inhibit the Formation of Advanced Glycation End Products? The Role of Its Primary Antioxidant Activity

Pyridoxamine, one of the natural forms of vitamin B6, is known to be an effective inhibitor of the formation of advanced glycation end products (AGEs), which are closely related to various human diseases. Pyridoxamine forms stable complexes with metal ions that catalyze the oxidative reactions taking place in the advanced stages of the protein glycation cascade. It also reacts with reactive carbonyl compounds generated as byproducts of protein glycation, thereby preventing further protein damage. We applied Density Functional Theory to study the primary antioxidant activity of pyridoxamine towards three oxygen-centered radicals (•OOH, •OOCH3 and •OCH3) to find out whether this activity may also play a crucial role in the context of protein glycation inhibition. Our results show that, at physiological pH, pyridoxamine can trap the •OCH3 radical, in both aqueous and lipidic media, with rate constants in the diffusion limit (>1.0 × 108 M - 1 s - 1 ). The quickest pathways involve the transfer of the hydrogen atoms from the protonated pyridine nitrogen, the protonated amino group or the phenolic group. Its reactivity towards •OOH and •OOCH3 is smaller, but pyridoxamine can still scavenge them with moderate rate constants in aqueous media. Since reactive oxygen species are also involved in the formation of AGEs, these results highlight that the antioxidant capacity of pyridoxamine is also relevant to explain its inhibitory role on the glycation process.

Biocatalytic Reversal of Advanced Glycation End Product Modification

Advanced glycation end products (AGEs) are a heterogeneous group of molecules that emerge from the condensation of sugars and proteins through the Maillard reaction. Despite a significant number of studies showing strong associations between AGEs and the pathologies of aging-related illnesses, it has been a challenge to establish AGEs as causal agents primarily due to the lack of tools in reversing AGE modifications at the molecular level. Herein, we show that MnmC, an enzyme involved in a bacterial tRNA-modification pathway, is capable of reversing the AGEs carboxyethyl-lysine (CEL) and carboxymethyl-lysine (CML) back to their native lysine structure. Combining structural homology analysis, site-directed mutagenesis, and protein domain dissection studies, we generated a variant of MnmC with improved catalytic properties against CEL in its free amino acid form. We show that this enzyme variant is also active on a CEL-modified peptidomimetic and an AGE-containing peptide that has been established as an authentic ligand of the receptor for AGEs (RAGE). Our data demonstrate that MnmC variants are promising lead catalysts toward the development of AGE-reversal tools and a better understanding of AGE biology.

Cataract in diabetes mellitus

Diabetes mellitus (DM) is a chronic systemic disease that has increases in prevalence over time. DM can affect all ocular structures, with cataract being the most common ocular complication. Cataract is the leading cause of blindness worldwide. Due to several mechanisms, there is an increased incidence of cataract formation in the diabetic population. Advancements in technology have now made cataract surgery a common and safe procedure. However, the diabetic population is still at risk of vision-threatening complications, such as diabetic macular edema (ME), postoperative ME, diabetic retinopathy progression, and posterior capsular opacification.

Chronic hyperglycemia mediated physiological alteration and metabolic distortion leads to organ dysfunction, infection, cancer progression and other pathophysiological consequences: An update on glucose toxicity

Chronic exposure of glucose rich environment creates several physiological and pathophysiological changes. There are several pathways by which hyperglycemia exacerbate its toxic effect on cells, tissues and organ systems. Hyperglycemia can induce oxidative stress, upsurge polyol pathway, activate protein kinase C (PKC), enhance hexosamine biosynthetic pathway (HBP), promote the formation of advanced glycation end-products (AGEs) and finally alters gene expressions. Prolonged hyperglycemic condition leads to severe diabetic condition by damaging the pancreatic β-cell and inducing insulin resistance. Numerous complications have been associated with diabetes, thus it has become a major health issue in the 21st century and has received serious attention. Dysregulation in the cardiovascular and reproductive systems along with nephropathy, retinopathy, neuropathy, diabetic foot ulcer may arise in the advanced stages of diabetes. High glucose level also encourages proliferation of cancer cells, development of osteoarthritis and potentiates a suitable environment for infections. This review culminates how elevated glucose level carries out its toxicity in cells, metabolic distortion along with organ dysfunction and elucidates the complications associated with chronic hyperglycemia.

Glycation induced conformational transitions in cystatin proceed to form biotoxic aggregates: A multidimensional analysis

Hyperglycaemic conditions facilitate the glycation of serum proteins which may have predisposition to aggregation and thus lead to complications. The current study investigates the glycation induced structural and functional modifications of chickpea cystatin (CPC) as well as biological toxicity of the modified protein forms, using CPC-glucose as a model system. Several structural intermediates were formed during the incubation of CPC with glucose (day 4, 8, 12, & 16) as revealed by circular dichroism (CD), altered intrinsic fluorescence, and high ANS binding. Further incubation of CPC with glucose (day 21) formed abundant β structures as revealed by Fourier transform infrared spectroscopy and CD analysis which may be due to the aggregation of protein. High thioflavin T fluorescence intensity and increased Congo red absorbance together with enhanced turbidity and Rayleigh scattering by this modified form confirmed the aggregation. Electron microscopy finally provided the valid physical authentication about the presence of aggregate structures. Functional inactivation of glucose incubated CPC was also observed with time. Single cell electrophoresis of lymphocytes and plasmid nicking assays in the presence of modified CPC showed the DNA damage which confirmed its biological toxicity. Hence, our study suggests that glycation of CPC not only leads to structural and functional alterations in proteins but also to biotoxic AGEs and aggregates.

Biomechanics and structure of the cornea: implications and association with corneal disorders

Recent studies have shown that alterations in corneal biomechanical properties are associated with corneal pathologies, particularly corneal ectasia. Moreover, these alterations may have implications with regard to the outcomes of therapeutic modalities and corneal refractive surgeries. We address corneal anatomy and its relevance to corneal biomechanical characteristics, as well as ocular and systemic conditions associated with changes in corneal biomechanics.

Proteomic profile of the lens in a streptozotocin-induced diabetic rat model using shotgun proteomics

Streptozotocin (STZ)-induced diabetic rats (STZ rats) were used to investigate diabetic cataracts. In the current study, a shotgun liquid chromatography (LC)/mass spectrometry (MS)-based global proteomic analysis method was used to examine the mechanism of lens opacification as a result of hyperglycemia in STZ rats. The 6-week old Wistar rats were injected with STZ for 2 days (100 mg/kg/day, i.p.) and housed for 3 weeks. The plasma glucose levels were identified to be significantly higher when compared with the normal rats and insulin was not detected in the STZ rats. Furthermore, opacification of the cortical epithelium was observed in the lenses of STZ rats. A total of 235 proteins were identified in the lenses of the STZ rats and 229 in the lenses of the normal rats. A label-free semi-quantitative method, based on spectral counting, identified 52 proteins that were differentially expressed in the lenses of STZ rats compared with normal rats. In particular, superoxide dismutase, which is a critical antioxidant enzyme that detoxifies superoxide through redox cycling, was downregulated when analyzed by the semi-quantitative method. In addition, phosphorylated-p38, which is important in the signaling pathway involved in the oxidative stress response, was significantly increased in the lenses of STZ rats when compared with normal rats (P<0.05). Thus, the changes in protein expression were evaluated in the lenses of STZ rats using a shotgun LC/MS-based global proteomic analysis approach, and a decrease in antioxidant enzymes and an increase in oxidative stress were identified in the lenses of STZ rats. Further studies are required to examine the role of these proteins in the onset or progression of diabetic cataracts.

Potential of CeCl3@mSiO2 nanoparticles in alleviating diabetic cataract development and progression

Cataract is a major cause of visual impairment for diabetic patients. It is imperative to develop efficient therapeutic agents against diabetic cataract (DC) because diabetes confers higher risk for complications after cataract surgery. We have previously reported the role of CeCl₃ loaded mesoporous silica (CeCl₃@mSiO₂) nanoparticles in reducing the oxidative stress of lens epithelial cells. However, the potential of CeCl₃@mSiO₂ in preventing diabetic cataract development remains unclear. In this study, we applied CeCl₃@mSiO₂ nanoparticles with a size of 87.6±8.9nm to streptozotocin-induced diabetic cataract rat model by intraperitoneal injection. Our results showed that CeCl₃@mSiO₂ efficiently ameliorated the progression of DC. Consistent with antioxidant effect of CeCl₃@mSiO₂in vitro, administration of CeCl₃@mSiO₂ significantly abrogated hyperglycemia-mediated upregulation of advanced glycation end products, lipid peroxidation and protein carbonylation in animal lens. Taken together, our study provides a potential nanodrug to manage the development of DC.

Nutraceuticals in prevention of cataract - An evidence based approach

Cataract is a principal cause of blindness in the world and is characterized by clouding of eye's natural lens. Surgery is the major therapeutic step taken to cure cataract; however, it is having its own limitations and complications such as iris prolapse, raised IOP, infection, cystoid macular edema and posterior capsular opacification (PCO). So world is looking toward more robust and natural ways to prevent cataract. One of the important factors that can play a role in prevention of any and many diseases is diet of the people. The inclusion of certain naturally occurring food and nutraceuticals is coming up as a best alternative for curing cataract because of their presumed safety, potential nutritional and therapeutic effects. Some nutraceuticals can act as an anticataract agent through some or the other molecular mechanism if consumed by normal population deliberately or inadvertently.

Protective effect of Tephrosia purpurea in diabetic cataract through aldose reductase inhibitory activity

PURPOSE

Tephrosia purpurea (T. purpurea) has been reported to prevent cataract formation in senile cataract model as well as proven effective in STZ induced type 1 diabetes. Aldose reductase (AR) is a key enzyme in the intracellular polyol pathway responsible for the development of diabetic cataract.

OBJECTIVE

To investigate the effects of T. purpurea in the light of inhibition of aldose reductase enzyme in polyol pathway.

METHODS

We studied the effects of alcoholic extract and flavonoid fraction of T. purpurea in streptozotocin (STZ, 45mg/kg, i.v.)-induced type I diabetic cataract in rats. The animals were divided into five groups as control, control treated with alcoholic and flavonoid fraction, diabetic control and diabetic treated with alcoholic and flavonoid fraction. In-vitro aldose reductase inhibitory activity was also evaluated. Further, molecular docking study was performed with crystal structure of aldose reductase and its known chemical constituents of the plant.

RESULTS

The IC₅₀ value of alcoholic extract for aldose reductase inhibition was found to be 209.13μg/ml, and that of flavonoid fraction was found to be 46.73μg/ml. Administration of STZ produced significantly abnormal levels of serum glucose, serum insulin, soluble protein and antioxidants in the lens homogenate. Treatment with alcoholic extract and flavonoid fraction of T. purpurea were able to normalize these levels. Some of the active constituents of T. purpurea showed significant interactions with aldose reductase enzyme in molecular docking studies.

CONCLUSIONS

Our data suggested that both the extracts might be helpful in delaying the development of diabetic cataract due to the presence of rutin and quercetin. This beneficial effect may be due to its significant inhibition of aldose reductase enzyme and anti-oxidant activity.

Corneal Biomechanical Properties in Aspirin Users

<b><i>Purpose:</i></b> To analyze corneal biomechanical properties in aspirin users using an ocular response analyzer. <b><i>Methods:</i></b> This study included 80 eyes of 40 aspirin users and 80 eyes of 40 individuals who did not use aspirin. Corneal hysteresis (CH), the corneal resistance factor (CRF), Goldman-correlated intraocular pressure (IOPg), and corneal compensated intraocular pressure (IOPcc) were measured in all participants. The independent samples t test was used to compare measurements in the aspirin users and nonusers in the total study population, and in the diabetic patient subgroup. Pearson's correlation analysis was used to examine the relationship between the measured variables in the aspirin users and nonusers. <b><i>Results:</i></b> Aspirin users (59.08 ± 11.83 years) were older than nonusers (39.82 ± 12.97 years; p < 0.001). The mean CH was significantly lower in the aspirin user group than in the nonuser group (p = 0.013). Mean IOPg and mean IOPcc were also significantly higher in the aspirin user group (p = 0.027 and p = 0.002, respectively). The mean CRF was lower in the aspirin user group, but not significantly (p = 0.70). There was a positive correlation between CH and CRF (r = 0.767, p < 0.001), and between CRF and IOPg (r = 0.680, p < 0.001), and a negative correlation between CH and IOPcc (r = -0.415, p < 0.001). <b><i>Conclusions:</i></b> Aspirin should be taken into account when interpreting the results of corneal biomechanical measurements.

Ocular complications of diabetes mellitus

Diabetes mellitus (DM) is a important health problem that induces ernestful complications and it causes significant morbidity owing to specific microvascular complications such as, retinopathy, nephropathy and neuropathy, and macrovascular complications such as, ischaemic heart disease, and peripheral vasculopathy. It can affect children, young people and adults and is becoming more common. Ocular complications associated with DM are progressive and rapidly becoming the world's most significant cause of morbidity and are preventable with early detection and timely treatment. This review provides an overview of five main ocular complications associated with DM, diabetic retinopathy and papillopathy, cataract, glaucoma, and ocular surface diseases.

Aldose reductase expression as a risk factor for cataract

Aldose reductase (AR) is thought to play a role in the pathogenesis of diabetic eye diseases, including cataract and retinopathy. However, not all diabetics develop ocular complications. Paradoxically, some diabetics with poor metabolic control appear to be protected against retinopathy, while others with a history of excellent metabolic control develop severe complications. These observations indicate that one or more risk factors may influence the likelihood that an individual with diabetes will develop cataracts and/or retinopathy. We hypothesize that an elevated level of AR gene expression could confer higher risk for development of diabetic eye disease. To investigate this hypothesis, we examined the onset and severity of diabetes-induced cataract in transgenic mice, designated AR-TG, that were either heterozygous or homozygous for the human AR (AKR1B1) transgene construct. AR-TG mice homozygous for the transgene demonstrated a conditional cataract phenotype, whereby they developed lens vacuoles and cataract-associated structural changes only after induction of experimental diabetes; no such changes were observed in AR-TG heterozygotes or nontransgenic mice with or without experimental diabetes induction. We observed that nondiabetic AR-TG mice did not show lens structural changes even though they had lenticular sorbitol levels almost as high as the diabetic AR-TG lenses that showed early signs of cataract. Over-expression of AR led to increases in the ratio of activated to total levels of extracellular signal-regulated kinase (ERK1/2) and c-Jun N-terminal (JNK1/2), which are known to be involved in cell growth and apoptosis, respectively. After diabetes induction, AR-TG but not WT controls had decreased levels of phosphorylated as well as total ERK1/2 and JNK1/2 compared to their nondiabetic counterparts. These results indicate that high AR expression in the context of hyperglycemia and insulin deficiency may constitute a risk factor that could predispose the lens to disturbances in signaling through the ERK and JNK pathways and thereby alter the balance of cell growth and apoptosis that is critical to lens transparency and homeostasis.

Emerging role of advanced glycation-end products (AGEs) in the pathobiology of eye diseases

Advanced glycation end products (AGEs) have been implicated in vision loss associated with macula degeneration, cataract formation, diabetic retinopathy and glaucoma. This pathogenic potential is mainly attributed to their accumulation in ocular tissues where they mediate aberrant crosslinking of extracellular matrix proteins and disruption of endothelial junctional complexes that affects cell permeability, mediates angiogenesis and breakdown of the inner blood-retinal barrier. Furthermore, AGEs severely affect cellular metabolism by disrupting ATP production, enhancing oxidative stress and modulating gene expression of anti-angiogenic and anti-inflammatory genes. Elucidation of AGE-induced mechanisms of action in different eye compartments will help in the understanding of the complex cellular and molecular processes associated with eye diseases. Several pharmaceutical agents with anti-glycating and anti-oxidant properties as well as AGE crosslink 'breakers' have been currently applied to eye diseases. The role of diet and the beneficial effects of certain nutriceuticals provide an alternative way to manage chronic visual disorders that affect the quality of life of millions of people.

Accelerated bilateral cataract formation as a first manifestation of diabetes mellitus

There is a proved relationship between diabetes mellitus and the cataract formation. The incidence of this is usually related to the duration of diabetes. In this manuscript we report a 15 years old female presented to the emergency room with a 4 hour history of rapid bilateral diminished vision, initially diagnosed with idiopathic cataracts, but after more laboratory evaluations revealed new-onset type 1 diabetes mellitus without ketosis.

Advanced glycation end products and diabetic complications

During long standing hyperglycaemic state in diabetes mellitus, glucose forms covalent adducts with the plasma proteins through a non-enzymatic process known as glycation. Protein glycation and formation of advanced glycation end products (AGEs) play an important role in the pathogenesis of diabetic complications like retinopathy, nephropathy, neuropathy, cardiomyopathy along with some other diseases such as rheumatoid arthritis, osteoporosis and aging. Glycation of proteins interferes with their normal functions by disrupting molecular conformation, altering enzymatic activity, and interfering with receptor functioning. AGEs form intra- and extracellular cross linking not only with proteins, but with some other endogenous key molecules including lipids and nucleic acids to contribute in the development of diabetic complications. Recent studies suggest that AGEs interact with plasma membrane localized receptors for AGEs (RAGE) to alter intracellular signaling, gene expression, release of pro-inflammatory molecules and free radicals. The present review discusses the glycation of plasma proteins such as albumin, fibrinogen, globulins and collagen to form different types of AGEs. Furthermore, the role of AGEs in the pathogenesis of diabetic complications including retinopathy, cataract, neuropathy, nephropathy and cardiomyopathy is also discussed.

Advanced glycation end products and diabetic complications

During long standing hyperglycaemic state in diabetes mellitus, glucose forms covalent adducts with the plasma proteins through a non-enzymatic process known as glycation. Protein glycation and formation of advanced glycation end products (AGEs) play an important role in the pathogenesis of diabetic complications like retinopathy, nephropathy, neuropathy, cardiomyopathy along with some other diseases such as rheumatoid arthritis, osteoporosis and aging. Glycation of proteins interferes with their normal functions by disrupting molecular conformation, altering enzymatic activity, and interfering with receptor functioning. AGEs form intra- and extracellular cross linking not only with proteins, but with some other endogenous key molecules including lipids and nucleic acids to contribute in the development of diabetic complications. Recent studies suggest that AGEs interact with plasma membrane localized receptors for AGEs (RAGE) to alter intracellular signaling, gene expression, release of pro-inflammatory molecules and free radicals. The present review discusses the glycation of plasma proteins such as albumin, fibrinogen, globulins and collagen to form different types of AGEs. Furthermore, the role of AGEs in the pathogenesis of diabetic complications including retinopathy, cataract, neuropathy, nephropathy and cardiomyopathy is also discussed.

Tuning a 96-well microtiter plate fluorescence-based assay to identify AGE inhibitors in crude plant extracts

Advanced glycation end-products (AGEs) are involved in the pathogenesis of numerous diseases. Among them, cellular accumulation of AGEs contributes to vascular complications in diabetes. Besides using drugs to lower blood sugar, a balanced diet and the intake of herbal products potentially limiting AGE formation could be considered beneficial for patients’ health. The current paper presents a simple and cheap high-throughput screening (HTS) assay based on AGE fluorescence and suitable for plant extract screening. We have already implemented an HTS assay based on vesperlysines-like fluorescing AGEs quickly (24 h) formed from BSA and ribose under physiological conditions. However, interference was noted when fluorescent compounds and/or complex mixtures were tested. To overcome these problems and apply this HTS assay to plant extracts, we developed a technique for systematic quantification of both vesperlysines (λ_exc 370 nm; λ_em 440 nm) and pentosidine-like (λ_exc 335 nm; λ_em 385 nm) AGEs. In a batch of medicinal and food plant extracts, hits were selected as soon as fluorescence decreased under a fixed threshold for at least one wavelength. Hits revealed during this study appeared to contain well-known and powerful anti-AGE substances, thus demonstrating the suitability of this assay for screening crude extracts (0.1 mg/mL). Finally, quercetin was found to be a more powerful reference compound than aminoguanidine in such assay.

Silica-based cerium (III) chloride nanoparticles prevent the fructose-induced glycation of α-crystallin and H₂O₂-induced oxidative stress in human lens epithelial cells

This study aimed to investigate whether silica-cerium (III) chloride (CeCl3) nanoparticles could inhibit the formation of advanced glycation end-products (AGEs) and reduce oxidative stress. Silica-CeCl3 nanoparticles were synthesised by adsorption and embedment with micro-silica materials, forming uniform nanoparticles with a diameter of approximately 130 nm. Chaperone activity assays and AGEs formation assays, and intracellular reactive assays were adopted in this study to evaluate CeCl3 nanoparticles effect. UV-visible spectrometry showed that silica-CeCl3 nanoparticles at low concentrations rapidly formed tentatively stable conjugations with α-crystallin, greatly enhancing the chaperone activity of α-crystallin. Moreover, silica-CeCl3 nanoparticles markedly inhibited the fructose-induced glycation of α-crystallin, showing an advantage over the control drugs aminoguanidine and carnosine. Silica-CeCl3 nanoparticles also reduced intracellular reactive oxygen species production and restored glutathione levels in H2O2-treated human lens epithelial cells. These findings suggest that silica-CeCl3 may be used as a novel agent for the prevention of cataractogenesis.

Controlling the mechanical properties of three-dimensional matrices via non-enzymatic collagen glycation

The mechanical properties of the extracellular matrix play an important role in maintaining cellular function and overall tissue homeostasis. Recently, a number of hydrogel systems have been developed to investigate the role of matrix mechanics in mediating cell behavior within three-dimensional environments. However, many of the techniques used to modify the stiffness of the matrix also alter properties that are important to cellular function including matrix density, porosity and binding site frequency, or rely on amorphous synthetic materials. In a recent publication, we described the fabrication, characterization and utilization of collagen gels that have been non-enzymatically glycated in their unpolymerized form to produce matrices of varying stiffness. Using these scaffolds, we showed that the mechanical properties of the resulting collagen gels could be increased 3-fold without significantly altering the collagen fiber architecture. Using these matrices, we found that endothelial cell spreading and outgrowth from multi-cellular spheroids changes as a function of the stiffness of the matrix. Our results demonstrate that non-enzymatic collagen glycation is a tractable technique that can be used to study the role of 3D stiffness in mediating cellular function. This commentary will review some of the current methods that are being used to modulate matrix mechanics and discuss how our recent work using non-enzymatic collagen glycation can contribute to this field.

Multimodal Highlighting of Structural Abnormalities in Diabetic Rat and Human Corneas

PURPOSE

This study aimed to highlight structural corneal changes in a model of type 2 diabetes, using in vivo corneal confocal microscopy (CCM). The abnormalities were also characterized by transmission electron microscopy (TEM) and second harmonic generation (SHG) microscopy in rat and human corneas.

METHODS

Goto-Kakizaki (GK) rats were observed at age 12 weeks (n = 3) and 1 year (n = 6), and compared to age-matched controls. After in vivo CCM examination, TEM and SHG microscopy were used to characterize the ultrastructure and the three-dimensional organization of the abnormalities. Human corneas from diabetic (n = 3) and nondiabetic (n = 3) patients were also included in the study.

RESULTS

In the basal epithelium of GK rats, CCM revealed focal hyper-reflective areas, and histology showed proliferative cells with irregular basement membrane. In the anterior stroma, extracellular matrix modifications were detected by CCM and confirmed in histology. In the Descemet's membrane periphery of all the diabetic corneas, hyper-reflective deposits were highlighted using CCM and characterized as long-spacing collagen fibrils by TEM. SHG microscopy revealed these deposits with high contrast, allowing specific detection in diabetic human and rat corneas without preparation and characterization of their three-dimensional organization.

CONCLUSION

Pathologic findings were observed early in the development of diabetes in GK rats. Similar abnormalities have been found in corneas from diabetic patients.

TRANSLATIONAL RELEVANCE

This multidisciplinary study highlights diabetes-induced corneal abnormalities in an animal model, but also in diabetic donors. This could constitute a potential early marker for diagnosis of hyperglycemia-induced tissue changes.

Tuning three-dimensional collagen matrix stiffness independently of collagen concentration modulates endothelial cell behavior

Numerous studies have described the effects of matrix stiffening on cell behavior using two-dimensional synthetic surfaces; however, less is known about the effects of matrix stiffening on cells embedded in three-dimensional in vivo-like matrices. A primary limitation in investigating the effects of matrix stiffness in three dimensions is the lack of materials that can be tuned to control stiffness independently of matrix density. Here, we use collagen-based scaffolds where the mechanical properties are tuned using non-enzymatic glycation of the collagen in solution, prior to polymerization. Collagen solutions glycated prior to polymerization result in collagen gels with a threefold increase in compressive modulus without significant changes to the collagen architecture. Using these scaffolds, we show that endothelial cell spreading increases with matrix stiffness, as does the number and length of angiogenic sprouts and the overall spheroid outgrowth. Differences in sprout length are maintained even when the receptor for advanced glycation end products is inhibited. Our results demonstrate the ability to de-couple matrix stiffness from matrix density and structure in collagen gels, and that increased matrix stiffness results in increased sprouting and outgrowth.

Photooxidation of glycated and non-glycated phosphatidylethanolamines monitored by mass spectrometry

Phosphatidylethanolamines (PE) are one of the major components of cells membranes, namely in skin and in retina, that are continuously exposed to solar UV radiation being major targets of photooxidation damage. In addition, due to the presence of the free amine group, PE can also undergo glycation, in hyperglycemic conditions which may increase the susceptibility to oxidation. The aim of this study is to develop a model, based on mass spectrometry (MS) analysis, to identify photooxidative degradation of selected PE (POPE: PE 16:0/18:1, PLPE: PE 16:0/18:2, PAPE: PE 16:0/20:4) and glycated PEs due to UV irradiation. Photooxidation products were analysed by electrospray ionization MS (ESI-MS) and tandem MS (ESI-MS/MS) in positive and negative mode. Emphasis is placed in the influence of glycation in the generation of distinct photooxidation products. ESI-MS spectra of PE after UV photo-irradiation showed mainly hydroperoxy derivatives, due to oxidation of unsaturated fatty acyl chains. Glycated PE gave rise to several new photooxidation products formed due to oxidative cleavages of the glucose moiety, namely between C1 and C2, C2 and C3, and C5 and C6 of this sugar unit. These new products were identified by ESI-MS/MS in positive mode showing distinct neutral loss depending on the different structure of the polar head group. These new identified advanced glycated photooxidation products may have a deleterious role in the etiology of diabetic retinopathy and in diabetic retinal microvascular complications.

Risk factors for incident cortical, nuclear, posterior subcapsular, and mixed lens opacities: the Los Angeles Latino eye study

PURPOSE

To identify sociodemographic and biological risk factors associated with the 4-year incidence of nuclear, cortical, posterior subcapsular (PSC), and mixed lens opacities.

DESIGN

Population-based, longitudinal study.

PARTICIPANTS

We included 4658 Latinos ≥40 years from 6 census tracts in Los Angeles, California.

METHODS

Participants underwent an interview and detailed eye examination, including best-corrected visual acuity and slit-lamp assessment of lens opacities using the Lens Opacities Classification System II (LOCS II) at baseline and again 4 years later. Each opacity type was defined in persons with a LOCS II score of ≥2. Univariate and forward stepwise logistic regression analyses were used to identify independent baseline risk factors associated with 4-year incidence of nuclear only, cortical only, PSC only, and mixed (when >1 opacity type developed in a person) lens opacities. These comprised 4 mutually exclusive groups, and were based on person rather than eye.

MAIN OUTCOME MEASURES

Odds ratios for independent risk factors associated with 4-year incidence of nuclear-only, cortical-only, PSC-only, and mixed lens opacities.

RESULTS

Of the 3471 participants with gradable lenses in the same eye at baseline and 4-year follow-up, 200 (5.8%) had incident nuclear-only opacities, 151 (4.1%) had incident cortical-only opacities, 16 (0.5%) had incident PSC-only lens opacities, and 88 (2.5%) had mixed lens opacities. Independent baseline risk factors for incident nuclear-only lens opacities included older age, current smoking, and presence of diabetes. Independent risk factors for incident cortical-only lens opacities included older age and having diabetes at baseline. Female gender was an independent risk factor for incident PSC-only lens opacities. Older age and presence of diabetes at baseline examination were independent risk factors for incident mixed lens opacities. Specifically, in diabetics, higher levels of hemoglobin A1c was associated with greater risk for 4-year incident nuclear-only, cortical-only and mixed lens opacities.

CONCLUSIONS

Improved diabetic control and smoking prevention may reduce the risk of developing lens opacities. Understanding both modifiable and nonmodifiable risk factors provides insight into the development of lens opacification.

Osmotic stress induced oxidative damage: possible mechanism of cataract formation in diabetes

Chronic hyperglycemia causes increased level of reactive oxygen species which is thought to be involved in the pathogenesis of diabetes associated complications including cataract. In diabetic cataractous lens, over production of free radicals and decreased capacity of antioxidant defense system are the major contributors to oxidative damage by polyol pathway and advanced glycation end products. The current study focused on analysis of factors associated with osmotic imbalance and oxidative stress in aging and diabetic human cataractous lenses. We examined activities of polyol pathway enzymes, G6PD and glutathione system in lenses from subjects suffering from cataract due to aging and diabetes. We observed elevated activities of aldose reductase and sorbitol dehydrogenase while G6PD and glutathione system enzyme activities were found to be lower in cataractous subjects suffering from diabetes. The findings from the current study support the premise that osmotic imbalance, AGEs formation and oxidative stress contribute synergistically to the development of lens opacity in hyperglycemia.

Co-localisation of advanced glycation end products and D-β-aspartic acid-containing proteins in gelatinous drop-like corneal dystrophy

PURPOSE

Gelatinous drop-like corneal dystrophy (GDLD), also known as familial subepithelial corneal amyloidosis, is an autosomal recessive disorder that causes progressive corneal opacity due to accumulation of amyloid fibrils in the corneal stroma. Genetic analyses have revealed that a mutation in membrane component chromosome 1 surface marker 1 gene is responsible for GDLD. However, the mechanism of amyloid formation in the corneal stroma remains unclear. The present study attempted to reveal the role of advanced glycation end products (AGE) and d-amino acids in amyloid formation in GDLD.

METHODS

Informed consent was obtained from five patients with GDLD, three patients with bullous keratopathy and three patients with interstitial keratitis and all the specimens were analysed. Localisation of amyloid fibrils was analysed using Congo-red and thioflavin T staining. In addition, the localisation of AGE (N(ε)-carboxy(methyl)-L-lysine, pyrraline and pentosidine) and D-β-aspartic acid-containing proteins, a major form of d-amino acid-containing proteins, was analysed immunohistochemically.

RESULTS

In all GDLD specimens, strong immunoreactivity to AGE and D-β-aspartic acid-containing proteins was detected in the subepithelial amyloid-rich region. In contrast, amyloid fibrils, AGE, or D-amino acid-containing proteins were slightly detected in the corneal stroma of patients with bullous keratopathy and interstitial keratitis.

CONCLUSIONS

Abnormally accumulated proteins rich in AGE and D-β-aspartic acid co-localise in the amyloid lesions in GDLD. These results indicate that non-enzymatic post-translational modifications of proteins, including AGE formation and isomerisation of aspartyl residues, will be the cause as well as the result of amyloid fibril formations in GDLD.

Beneficial influence of fungal metabolite nigerloxin on eye lens abnormalities in experimental diabetes

Osmotic and oxidative stress have been implicated in the pathogenesis of diabetic cataract. Nigerloxin, a fungal metabolite, has been shown to possess aldose reductase inhibitory and free radical scavenging potential, in vitro. In the present study, the beneficial influence of nigerloxin was investigated on diabetes-induced alteration in the eye lens of rats treated with streptozotocin. Groups of diabetic rats were administered nigerloxin orally (100 mg·(kg body mass)–1·day–1) for 30 days. The activity of lens polyol pathway enzymes (aldose reductase and sorbitol dehydrogenase), lipid peroxides, and advanced glycation end products (AGEs) were increased in the diabetic animals. Levels of glutathione as well as the activity of antioxidant enzymes (superoxide dismutase, glutathione-S-transferase, and glutathione peroxidase) were decreased in the eye lens of the diabetic animals. The administration of nigerloxin significantly decreased levels of lipid peroxides and AGEs in the lens of the diabetic rats. Increase in the activity of aldose reductase and sorbitol dehydrogenase in the lens was countered by nigerloxin treatment. The activity of glutathione and antioxidant enzyme in the lens was significantly elevated in nigerloxin-treated diabetic rats. Examination of the treated rats’ eyes indicated that nigerloxin delayed cataractogenesis in the diabetic rats. The results suggest the beneficial countering of polyol pathway enzymes and potentiation of the antioxidant defense system by nigerloxin in diabetic animals, implicating its potential in ameliorating cataracts in diabetics.