Effect of high-glucose levels on protein oxidation in cultured lens cells, and in crystalline and albumin solution and its inhibition by vitamin B6 and N-acetylcysteine: its possible relevance to cataract formation in diabetes

Research progress on antioxidants and protein aggregation inhibitors in cataract prevention and therapy (Review)

Cataracts are primarily caused by aging or gene mutations and are the leading cause of blindness globally. As the older population increases, the number of patients with a cataract is expected to grow rapidly. At present, cataract surgery to replace the lens with an artificial intraocular lens is the principal treatment method. However, surgery has several drawbacks, including economic burdens and complications such as inflammation, xerophthalmia, macular edema and posterior capsular opacification. Thus, developing an effective non‑surgical treatment strategy is beneficial to both patients and public health. Mechanistically, cataract formation may be due to various reasons but is primarily initiated and promoted by oxidative stress and is closely associated with crystallin aggregation. In the present review, the current research progress on anti‑cataract drugs, including antioxidants and protein aggregation inhibitors is examined. It summarizes strategies for preventing and treating cataract through cell apoptosis and protein aggregation inhibition while discussing their limitations and further prospects.

Oxidative Stress in Cataract Formation: Is There a Treatment Approach on the Horizon?

Cataracts, a leading cause of blindness worldwide, are closely linked to oxidative stress-induced damage to lens epithelial cells (LECs). Key factors contributing to cataract formation include aging, arterial hypertension, and diabetes mellitus. Given the high global prevalence of cataracts, the burden of cataract-related visual impairment is substantial, highlighting the need for pharmacological strategies to supplement surgical interventions. Understanding the molecular pathways involved in oxidative stress during cataract development may offer valuable insights for designing novel therapeutic approaches. This review explores the role of oxidative stress in cataract formation, focusing on critical mechanisms, such as mitochondrial dysfunction, endoplasmic reticulum stress, loss of gap junctions, and various cell death pathways in LECs. Additionally, we discuss emerging therapeutic strategies and potential targeting options, including antioxidant-based treatments.

N-acetylcysteine Clinical Applications

This study aims to evaluate the therapeutic application of N-acetylcysteine (NAC) as a treatment or adjunct therapy for various medical conditions. While its efficacy in treating acetaminophen overdose, cystic fibrosis, and chronic obstructive pulmonary disease is well-established, emerging evidence suggests that NAC may also benefit a broader spectrum of illnesses due to its safety, simplicity, and affordability. A comprehensive review was conducted by searching PubMed, relevant books, and conference proceedings for publications discussing NAC about the specified health conditions. The clinically relevant data were analysed using the American Family Physician Evidence-Based Medicine Toolkit, following a standard integrated review methodology. NAC shows potential as an adjunctive treatment for a wide range of medical conditions, particularly chronic diseases. It may be beneficial for polycystic ovary syndrome, endometriosis, male infertility, cataracts, glaucoma, dry eye syndrome, parkinsonism, multiple sclerosis, Alzheimer's disease, stroke outcomes, non-acetaminophen-induced acute liver failure, Crohn's disease, ulcerative colitis, schizophrenia, bipolar disorder, and obsessive-compulsive disorder. Although evidence for some conditions is less robust, NAC's therapeutic potential warrants further investigation. Given the aging population and the decline in glutathione levels, the use of NAC should be considered across a variety of medical conditions. This paper suggests that NAC supplementation could play a significant role in reducing morbidity and mortality associated with numerous chronic diseases.

The impact of vitamin E, vitamin B6, and niacin intake on cataract incidence based on NHANES 2005-2008 data

Objective

This investigation aims to elucidate the correlations between dietary intakes of vitamin E, B6, and niacin and the incidence of cataracts, utilizing the comprehensive NHANES 2005-2008 dataset to affirm the prophylactic roles of these nutrients against cataract formation.

Methods

Using data from the NHANES 2005-2008 cycles, this analysis concentrated on 7,247 subjects after exclusion based on incomplete dietary or cataract data. The identification of cataracts was determined through participants' self-reported ophthalmic surgical history. Nutritional intake was gauged using the automated multiple pass method, and the data were analyzed using logistic and quantile regression analyses to investigate the relationship between vitamin consumption and cataract prevalence.

Results

Our analysis identified significant inverse associations between the intake of vitamins E, B6, and niacin and the risk of cataract development. Specifically, higher intakes of vitamin B6 (OR = 0.85, 95% CI = 0.76-0.96, p = 0.0073) and niacin (OR = 0.98, 95% CI = 0.97-1.00, p = 0.0067) in the top quartile were significantly associated with a reduced likelihood of cataract occurrence. Vitamin E intake showed a consistent reduction in cataract risk across different intake levels (OR = 0.96, 95% CI = 0.94-0.99, p = 0.0087), demonstrating a nonlinear inverse correlation.

Conclusion

The outcomes indicate that elevated consumption of vitamin B6 and niacin, in conjunction with regular vitamin E intake, may have the potential to delay or prevent cataract genesis. These results suggest a novel nutritional strategy for cataract prevention and management, advocating that focused nutrient supplementation could be instrumental in preserving eye health and reducing the risk of cataracts. Further research is recommended to validate these findings and establish optimal dosages for maximum benefit.

PET imaging for the early evaluation of ocular inflammation in diabetic rats by using [18F]-DPA-714

Ocular complications of diabetes mellitus (DM) are the leading cause of vision loss. Ocular inflammation often occurs in the early stage of DM; however, there are no proven quantitative methods to evaluate the inflammatory status of eyes in DM. The 18 kDa translocator protein (TSPO) is an evolutionarily conserved cholesterol binding protein localized in the outer mitochondrial membrane. It is a biomarker of activated microglia/macrophages; however, its role in ocular inflammation is unclear. In this study, fluorine-18-DPA-714 ([18F]-DPA-714) was evaluated as a specific TSPO probe by cell uptake, cell binding assays and micro positron emission tomography (microPET) imaging in both in vitro and in vivo models. Primary microglia/macrophages (PMs) extracted from the cornea, retina, choroid or sclera of neonatal rats with or without high glucose (50 mM) treatment were used as the in vitro model. Sprague-Dawley (SD) rats that received an intraperitoneal administration of streptozotocin (STZ, 60 mg/kg once) were used as the in vivo model. Increased cell uptake and high binding affinity of [18F]-DPA-714 were observed in primary PMs under hyperglycemic stress. These findings were consistent with cellular morphological changes, cell activation, and TSPO up-regulation. [18F]-DPA-714 PET imaging and biodistribution in the eyes of DM rats revealed that inflammation initiates in microglia/macrophages in the early stages (3 weeks and 6 weeks), corresponding with up-regulated TSPO levels. Thus, [18F]-DPA-714 microPET imaging may be an effective approach for the early evaluation of ocular inflammation in DM.

RENAL PROTECTIVE EFFECT AND CLINICAL ANALYSIS OF VITAMIN B 6 IN PATIENTS WITH SEPSIS

ABSTRACT

Objective: To investigate the protective effect and possible mechanisms of vitamin B 6 against renal injury in patients with sepsis. Methods: A total of 128 patients with sepsis who met the entry criteria in multiple centers were randomly divided into experimental (intravenous vitamin B 6 therapy) and control (intravenous 0.9% sodium chloride therapy) groups based on usual care. Clinical data, the inflammatory response indicators interleukin 6 (IL-6), interleukin 8 (IL-8), tumor necrosis factor (TNF-α), and endothelin-1 (ET-1), the oxidative stress response indicators superoxide dismutase, glutathione and malondialdehyde, and renal function (assessed by blood urea nitrogen, serum creatinine, and renal resistance index monitored by ultrasound) were compared between the two groups. Results: After 7 d of treatment, the IL-6, IL-8, TNF-α, and ET-1 levels in the experimental group were significantly lower than those in the control group, the oxidative stress response indicators were significantly improved in the experimental group and the blood urea nitrogen, serum creatinine, and renal resistance index values in the experimental group were significantly lower than those in the control group ( P < 0.05). There was no statistical difference between the two groups in the rate of renal replacement therapy and 28 d mortality ( P > 0.05). However, the intensive care unit length of stay and the total hospitalization expenses in the experimental group were significantly lower than those in the control group ( P < 0.05). Conclusion: The administration of vitamin B 6 in the treatment of patients with sepsis attenuates renal injury, and the mechanism may be related to pyridoxine decreasing the levels of inflammatory mediators and their regulation by redox stress.

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.

Analysis of N6-methyladenosine-modified mRNAs in diabetic cataract

BACKGROUND

Cataracts remain a prime reason for visual disturbance and blindness all over the world, despite the capacity for successful surgical replacement with artificial lenses. Diabetic cataract (DC), a metabolic complication, usually occurs at an earlier age and progresses faster than age-related cataracts. Evidence has linked N6-methyladenosine (m6A) to DC progression. However, there exists a lack of understanding regarding RNA m6A modifications and the role of m6A in DC pathogenesis.

AIM

To elucidate the role played by altered m6A and differentially expressed mRNAs (DEmRNAs) in DC.

METHODS

Anterior lens capsules were collected from the control subjects and patients with DC. M6A epitranscriptomic microarray was performed to investigate the altered m6A modifications and determine the DEmRNAs. Through Gene Ontology and pathway enrichment (Kyoto Encyclopedia of Genes and Genomes) analyses, the potential role played by dysregulated m6A modification was predicted. Real-time polymerase chain reaction was further carried out to identify the dysregulated expression of RNA methyltransferases, demethylases, and readers.

RESULTS

Increased m6A abundance levels were found in the total mRNA of DC samples. Bioinformatics analysis predicted that ferroptosis pathways could be associated with m6A-modified mRNAs. The levels of five methylation-related genes-RBM15, WTAP, ALKBH5, FTO, and YTHDF1-were upregulated in DC samples. Upregulation of RBM15 expression was verified in SRA01/04 cells with high-glucose medium and in samples from DC patients.

CONCLUSION

M6a mRNA modifications may be involved in DC progression via the ferroptosis pathway, rendering novel insights into therapeutic strategies for DC.

Serum glycoprotein non-metastatic melanoma protein B (GPNMB) level as a potential biomarker for diabetes mellitus-related cataract: A cross-sectional study

BACKGROUND

Diabetes mellitus (DM), a metabolic disease that has attracted significant research and clinical attention over the years, can affect the eye structure and induce cataract in patients diagnosed with DM. Recent studies have indicated the relationship between glycoprotein non-metastatic melanoma protein B (GPNMB) and DM and DM-related renal dysfunction. However, the role of circulating GPNMB in DM-associated cataract is still unknown. In this study, we explored the potential of serum GPNMB as a biomarker for DM and DM-associated cataract.

METHODS

A total of 406 subjects were enrolled, including 60 and 346 subjects with and without DM, respectively. The presence of cataract was evaluated and serum GPNMB levels were measured using a commercial enzyme-linked immunosorbent assay kit.

RESULTS

Serum GPNMB levels were higher in diabetic individuals and subjects with cataract than in those without DM or cataract. Subjects in the highest GPNMB tertile group were more likely to have metabolic disorder, cataract, and DM. Analysis performed in subjects with DM elucidated the correlation between serum GPNMB levels and cataract. Receiver operating characteristic (ROC) curve analysis also indicated that GPNMB could be used to diagnose DM and cataract. Multivariable logistic regression analysis illustrated that GPNMB levels were independently associated with DM and cataract. DM was also found to be an independent risk factor for cataract. Further surveys revealed the combination of serum GPNMB levels and presence of DM was associated with a more precise identification of cataract than either factor alone.

CONCLUSIONS

Increased circulating GPNMB levels are associated with DM and cataract and can be used as a biomarker of DM-associated cataract.

Nitro Dihydrocapsaicin, a Non-Pungent Capsaicin Analogue, Inhibits Cellular Senescence of Lens Epithelial Cells via Upregulation of SIRT1

Diabetic cataracts are a common complication that can cause blindness among patients with diabetes mellitus. A novel nitro dihydrocapsaicin (NDHC), a capsaicin analog, was constructed to have a non-pungency effect. The objective of this research was to study the effect of NDHC on human lens epithelial (HLE) cells that lost function from hyperglycemia. HLE cells were pretreated with NDHC before an exposure to high glucose (HG) conditions. The results show that NDHC promoted a deacceleration of cellular senescence in HLE cells. This inhibition of cellular senescence was characterized by a delayed cell growth and lower production of reactive oxygen species (ROS) as well as decreased SA-β-galactosidase activity. Additionally, the expression of Sirt1 protein sharply increased, while the expression of p21 and phospho-p38 proteins decreased. These findings provide evidence that NDHC could exert a pharmacologically protective effect by inhibiting the senescence program of lens cells during diabetic cataracts.

MiR-29a Alleviates High Glucose-induced Inflammation and Mitochondrial Dysfunction via Modulation of IL-6/STAT3 in Diabetic Cataracts

Background: This in vitro study was designed to reveal the role of miR-29a in high glucose-induced cellular injury through the modulation of IL-6/STAT3 in diabetic cataracts.Methods: The expression of miR-29a and STAT3 in the lens capsules of patients with or without diabetes was determined by RT-PCR. The levels of the IL-6 proinflammatory cytokine in the aqueous humor were detected by ELISA. HLE B-3 cells were cultured in normal glucose (NG; 5 mM) or high glucose (HG; 40 mM). After transfection with miR-29a, si-STAT3, or a negative control vector, the levels of IL-6 and STAT3 were detected. A CCK-8 assay was used to determine cell viability. We used flow cytometry to assess changes in reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP), and apoptosis induced by oxidative stress. Western blotting was used to determine the expression of the oxidative injury markers superoxide dismutase (SOD) and malondialdehyde (MDA) and the apoptosis markers Bcl-2 and Bax.Results: Reduced miR-29a, increased STAT3 expression, and IL-6 release were demonstrated in the lens capsules and aqueous humor of patients with diabetes. The stimulation of apoptosis and the loss of MMP induced by HG were attenuated by transfection with a miR-29a mimic and si-STAT3. ROS production, increased MDA content, decreased SOD activity, and upregulation of the apoptotic proteins Bcl-2/Bax were also partially alleviated by miR-29a overexpression, which shows their roles in oxidative injury. Furthermore, transfection with a STAT3 overexpression vector reversed the effects of miR-29a.Conclusions: In conclusion, miR-29a mitigated HG-induced oxidative injury and exerted protective effects via IL-6/STAT3 signaling. Thus, miR-29a may be a potential therapeutic agent for diabetic cataracts.

Pyridoxine (VB6 ) restores the down-regulation of serine palmitoyltransferase mRNA expression in keratinocytes cultured in highly oxidative conditions through enhancement of the intracellular antioxidant system

BACKGROUND

Pyridoxine (VB₆ ), which acts as a coenzyme in the biosynthesis of niacin, is formulated in pharmaceuticals to treat skin roughness. However, the mechanism of action of VB₆ is not known precisely.

OBJECTIVE

This study was conducted to clarify the influence of highly oxidative conditions on the expression of skin moisture-related mRNAs and to evaluate the preventive effects of VB₆ focusing on antioxidant behaviour.

METHODS

Intracellular levels of reactive oxygen species (ROS) in normal human epidermal keratinocytes (NHEKs) were determined using the 2',7'-dichlorofluorescein diacetate assay. Real-time PCR was employed to investigate the influence of higher oxidative conditions on the expression of mRNAs encoding serine palmitoyl transferase (SPT) and filaggrin, and to characterize the mechanism of the antioxidant effect of VB₆ . Intracellular glutathione was quantified using an assay based on the glutathione recycling system with 5,5'-dithiobis (2-nitrobenzoic acid) reagent and glutathione reductase. Carbonylated proteins (CPs) were semi-quantified by detecting aldehyde residues.

RESULTS

Treatment of NHEKs with BSO increased the level of intracellular CPs by interfering with intracellular glutathione synthesis. Further, treatment with BSO down-regulated the expression level of SPT mRNA, but VB₆ restored SPT mRNA expression in BSO-treated NHEKs. VB₆ decreased the level of intracellular CPs with or without BSO treatment in a dose-dependent manner. In addition, VB₆ increased levels of intracellular NADH/NADPH and glutathione through the activation of nuclear factor E2-related factor 2 (Nrf2) signalling.

CONCLUSION

These results suggest that highly oxidative conditions cause an impaired skin barrier function due to the down-regulation of SPT that results in skin roughness. VB₆ improved the down-regulation of SPT mRNA expression initiated by highly oxidative conditions by enhancing the intracellular antioxidant system.

Polyamine Oxidase Is Involved in Spermidine Reduction of Transglutaminase Type 2-Catalyzed βH-Crystallins Polymerization in Calcium-Induced Experimental Cataract

In an in vitro Ca2+-induced cataract model, the progression of opacification is paralleled by a rapid decrease of the endogenous levels of spermidine (SPD) and an increase of transglutaminase type 2 (TG2, EC 2.3.2.13)-catalyzed lens crystallins cross-linking by protein-bound N1-N8-bis(γ-glutamyl) SPD. This pattern was reversed adding exogenous SPD to the incubation resulting in a delayed loss of transparency of the rabbit lens. The present report shows evidence on the main incorporation of SPD by the catalytic activity of TG2, toward βH-crystallins and in particular to the βB2- and mostly in βB3-crystallins. The increase of endogenous SPD in the cultured rabbit lens showed the activation of a flavin adenine dinucleotide (FAD)-dependent polyamine oxidases (PAO EC 1.5.3.11). As it is known that FAD-PAO degrades the N8-terminal reactive portion of N1-mono(γ-glutamyl) SPD, the protein-bound N8-mono(γ-glutamyl) SPD was found the mainly available derivative for the potential formation of βB3-crystallins cross-links by protein-bound N1-N8-bis(γ-glutamyl)SPD. In conclusion, FAD-PAO degradation of the N8-terminal reactive residue of the crystallins bound N1-mono(γ-glutamyl)SPD together with the increased concentration of exogenous SPD, leading to saturation of glutamine residues on the substrate proteins, drastically reduces N1-N8-bis(γ-glutamyl)SPD crosslinks formation, preventing crystallins polymerization and avoiding rabbit lens opacification. The ability of SPD and MDL 72527 to modulate the activities of TG2 and FAD-PAO involved in the mechanism of lens opacification suggests a potential strategy for the prevention of senile cataract.

Decorin inhibits glucose-induced lens epithelial cell apoptosis via suppressing p22phox-p38 MAPK signaling pathway

PURPOSE

To determine the effect of decorin on oxidative stress and apoptosis of human lens epithelial (HLE) cells under high glucose condition.

METHODS

HLE cell line (HLEB3) was incubated in normal glucose (5.5 mM) or high glucose (60 mM) medium. Decorin (50 nM) was applied 2 hours before high glucose medium was added. Apoptosis detection was executed by flow cytometry and western blotting (analysis of bcl-2 and bax). Oxidative stress level was measured by the generation of reactive oxygen species (ROS), glutathione peroxidase (GSH) and superoxide dismutase (SOD). P38 mitogen-activated protein kinase (MAPK) phosphorylation, the expression of p22phox of HLE cells and human lens anterior capsules were detected by western blotting. Small interfering RNA transfection to p22phox and p38 MAPK was also carried out on HLEB3.

RESULTS

High glucose caused HLE cells oxidative stress and apoptosis exhibiting the increase of apoptotic cells and ROS production and decrease of bcl-2/bax ratio, GSH/GSSG ration and SOD activity. P22phox and phospho-p38 MAPK were upregulated in high glucose treated HLEB3 cells. Knocking down p22phox or p38 by siRNAs can reduce high glucose induced cell apoptosis and oxidative stress level. Silencing p22phox by siRNA can downregulate the phosphorylation of p38 MAPK. Decorin can inhibit the apoptosis, oxidative stress level and the induction of p22phox and phospho-p38 of HLEB3 induced by high glucose. Furthermore, the expression of p22phox and p38 were found significantly increased in lens anterior capsules of diabetic cataract patients compared to that of normal age-related cataract patients.

CONCLUSIONS

Results showed that p22phox-p38 pathway may be participated in high glucose induced lens epithelial cell injury, decorin may inhibit the high glucose induced apoptosis and oxidative stress injury by suppressing this pathway in part.

Current Trends in the Pharmacotherapy of Cataracts

Cataracts, one of the leading causes of preventable blindness worldwide, refers to lens degradation that is characterized by clouding, with consequent blurry vision. As life expectancies improve, the number of people affected with cataracts is predicted to increase worldwide, especially in low-income nations with limited access to surgery. Although cataract surgery is considered safe, it is associated with some complications such as retinal detachment, warranting a search for cheap, pharmacological alternatives to the management of this ocular disease. The lens is richly endowed with a complex system of non-enzymatic and enzymatic antioxidants which scavenge reactive oxygen species to preserve lens proteins. Depletion and/or failure in this primary antioxidant defense system contributes to the damage observed in lenticular molecules and their repair mechanisms, ultimately causing cataracts. Several attempts have been made to counteract experimentally induced cataract using in vitro, ex vivo, and in vivo techniques. The majority of the anti-cataract compounds tested, including plant extracts and naturally-occurring compounds, lies in their antioxidant and/or free radical scavenging and/or anti-inflammatory propensity. In addition to providing an overview of the pathophysiology of cataracts, this review focuses on the role of various categories of natural and synthetic compounds on experimentally-induced cataracts.

Pyridoxine Decreases Oxidative Stress on Human Erythrocyte Membrane Protein in vitro

Background:

Pyridoxine has reduction and prevention against the levels of reactive oxygen species in in vitro studies. However, the biochemical mechanism that explains this behavior has not yet been fully clarified.

Objective:

To evaluate the effect of pyridoxine against oxidative damage on the membrane of human erythrocytes.

Methods:

Cumene hydroperoxide was used to induce oxidative stress in protein and lipid. Human erythrocytes were incubated with pyridoxine and cumene hydroperoxide, either alone or together for 8 h. Oxidative damage was determined by measuring lipid peroxidation and membrane protein carbonylation.

Results:

The results indicate that the malondialdehyde concentration decreased with increasing concentration of pyridoxine. The membrane protein content also decreased with increasing concentration of vitamin B6, which was confirmed by the decreased signal intensity in the western blot when compared to control without pyridoxine. Results demonstrate that pyridoxine can significantly decrease lipid peroxidation and protein carbonylation in red cell membrane exposed to high concentrations of oxidant agent.

Conclusion:

Pyridoxine showed a protective effect against the oxidative stress in human erythrocytes in vitro, inhibiting the carbonylation and the oxidative damage of erythrocyte membrane proteins. To date, such an effect has not yet been reported in terms of protein oxidation.

Protective effect of selenium supplementation following oxidative stress mediated by glucose on retinal pigment epithelium

There are many conditions that affect the retina. However, diabetic retinopathy (RD) as a complication of Diabetes Mellitus continues to be the leading cause of blindness in working people globally. Diabetic retinopathy is an ocular complication of diabetes that is caused by the deterioration of the blood vessels that supply the retina, which has the consequence that the vision deteriorates irreversibly. The retina, and specifically the retinal pigment epithelium (RPE) is the only neural tissue that is exposed directly and frequently to light, which favors the oxidation of lipids that become extremely toxic to the cells of the retina. The RPE is a natural barrier playing an important role in the absorption of light and reduction of light scatter within the eye. In addition, the retina is the tissue that proportionally consumes more oxygen, which generates a high production of reactive oxygen species (ROS). The retina is particularly sensitive to hyperglycemia and oxidative stress. The eye tissues are enriched in certain antioxidants in the form of metabolic enzymes or small molecules. Since selenium is essential for regulating the activity of the enzymes involved in protection against oxidative stress, providing selenium to the ocular tissues could be useful for the treatment of different ocular pathologies. Thus, the aim of this study is to investigate the potential efficacy of selenium in human RPE against glucose-induced oxidative stress and its implications for GPx activity. Chromatographic techniques based on HPLC-ICP-MS will be applied in combination with isotope pattern deconvolution (IPD) to study the effects of selenium supplementation and hyperglycemia in an in vitro model of RPE cells.

LncRNA MALAT1 promotes the apoptosis and oxidative stress of human lens epithelial cells via p38MAPK pathway in diabetic cataract

BACKGROUND

LncRNAs are involved in various biological processes and disorders. We aimed to investigate the role of lncRNA MALAT1 deregulation in the pathogenic mechanism of diabetic cataract (DC).

METHODS

The expression of MALAT1 in the tissues and cells was detected by qRT-PCR. The levels of SP1, p38 and apoptosis-related protein were assessed by Western blot assay. Chromatin immunoprecipitation assay and Dual luciferase assay were performed to evaluate the relationship between SP1 and MALAT1. The viability and apoptosis of human lens epithelial cells (HLECs) were analyzed by MTT assay and flow cytometry. The levels of malonyldialdehyde (MDA), superoxide dismutase (SOD) and phospholipid hydroperoxide glutathione peroxidase (GSH-Px) were used to examine the level of oxidative stress.

RESULTS

MALAT1 not only was aberrantly expressed in DC anterior lens capsule tissues and high glucose (HG)-treated HLECs, but also were up-regulated by HG to promote the apoptosis and oxidative stress of HLECs. HG induced the up-regulation of MALAT1 via SP1 binding MALAT1 promoter regions in HLECs. Moreover, p38 was up-regulated in HG-treated HLECs, and knockdown of p38 reversed the effect of MALAT1 over-expression on HLECs.

CONCLUSION

HG induced the up-regulation of MALAT1 in HLECs via SP1 binding SP1 binding MALAT1, which promoted the apoptosis and oxidative stress of HLECs through the activation of p38MAPK signaling pathway.

The Emerging Role of Vitamin B6 in Inflammation and Carcinogenesis

Vitamin B6 serves as a coenzyme catalyzing more than 150 enzymes regulating metabolism and synthesis of proteins, carbohydrates, lipids, heme, and important bioactive metabolites. For several years vitamin B6 and its vitamers (B6) were recognized as antioxidant and antiinflammatory and in modulating immunity and gene expression. During the last 10 years, there were growing reports implicating B6 in inflammation and inflammation-related chronic illnesses including cancer. It is unclear if the deficiency of B6 or additional intake of B6, above the current requirement, should be the focus. Whether the current recommended daily intake for B6 is adequate should be revisited, since B6 is important to human health beyond its role as a coenzyme and its status is affected by many factors including but not limited to age, obesity, and inflammation associated with chronic illnesses. A link between inflammation B6 status and carcinogenesis is not yet completely understood. B6-mediated synthesis of H₂S, a gasotransmitter, and taurine in health and disease, especially in maintaining mitochondrial integrity and biogenesis and inflammation, remains an important area to be explored. Recent developments in the molecular role of B6 and its direct interaction with inflammasomes, and nuclear receptor corepressor and coactivator, receptor-interacting protein 140, provide a strong impetus to further explore the multifaceted role of B6 in carcinogenesis and human health.

High-dose B-vitamin supplements and risk for age-related cataract: a population-based prospective study of men and women

Previous studies that have investigated the association between B-vitamin supplement use and risk for cataract yield conflicting results. The aim of this study was to examine the association between use of high-dose B-vitamin supplements (approximately 10 times recommended daily intake) and risk for age-related cataract in a population-based prospective study of 13 757 women from the Swedish Mammography Cohort and 22 823 men from the Cohort of Swedish Men. Dietary supplement use and potential confounders were assessed using a questionnaire at baseline. Information on cataract diagnosis and extraction was obtained through linkage to registers. During the follow-up period between January 1998 and December 2011, we identified 8395 cataract cases (3851 for women and 4544 for men). The use of B vitamins plus other supplements and B vitamins only was associated with 9 % (95 % CI 2, 17) and 27 % (95 % CI 12, 43) increased risk for cataract, respectively. The hazard ratios for use of B vitamins only and risk for cataract stratified by different age groups were as follows: <60 years: 1·88 (95 % CI 1·47, 2·39); 60–69 years: 1·21 (95 % CI 0·96, 1·53); and ≥70 years: 1·09 (95 % CI 0·91, 1·31) (Pinteraction=0·002). Our results suggest that the use of high-dose B-vitamin supplements was associated with an increased risk for cataract. This association might be confined to younger participants.

Review: Targeting therapeutics against glutathione depletion in diabetes and its complications

Glutathione (GSH) is the most abundant intracellular antioxidant, the dysregulation of which is widely implicated in disease states. There is in vitro and clinical evidence that abnormal glutathione status is involved in β-cell dysfunction and in the pathogenesis of long-term complications of diabetes. Interest has developed in the potential for therapeutic modification of glutathione status in the treatment of diabetes. There is evidence which supports the use of glutathione pro-drugs, lipoic acid and vitamin supplementation but further studies are required before these enter widespread use. Studies into the role of oxidative stress in diabetes rely heavily on the ability to measure glutathione, which has been a problematic analyte to measure in the laboratory. New electrochemical methods being developed should speed up the rate at which data can be accumulated and will help define clinical utility for its measurement.

EAAT and Xc⁻ Exchanger Inhibition Depletes Glutathione in the Transformed Human Lens Epithelial Cell Line SRA 01/04

PURPOSE

Maintaining the high glutathione (GSH; tripeptide of glutamate, cysteine and glycine) levels in the lens cortex promotes lens health. The role of glutamate/aspartate (Glu/Asp) transporters and the cystine (Cys)/Glu exchanger (Xc(-) exchanger) in maintaining GSH in transformed human lens epithelial cells (SRA 01/04) was investigated.

METHODS

Detection and differentiation of excitatory amino acid transporters (EAAT1-5) and the Xc(-) exchanger was performed by the uptake of radiolabeled l-Glu, d-Asp and l-Cys in the presence and absence of Na(+), substrate-specific inhibition studies and Western-blot analysis. Reductions in GSH levels post-inhibition of Xc(-) exchanger and EAAT activities by substrate inhibitors demonstrated the roles of EAAT and Xc(-) exchanger in maintaining GSH.

RESULTS

Glu and d-Asp uptake in HLEC was Na(+)-dependent. Strong inhibition by substrate-specific Glu/Asp uptake inhibitors and weak inhibition by kainic acid (KA) was consistent with Na(+)-dependent EAAT1/3/4/5 activity and weak EAAT2 activity, respectively. Na(+)-independency and Glu inhibition of Cys uptake were consistent with Xc(-) exchanger activity, but inhibition of Na(+)-dependent Cys uptake by N-acetylcysteine suggests Cys uptake by EAAT3. EAAT1-5 and xCT (Xc(-) exchanger light chain) immunoreactive peptides were detected by Western-blot analysis of HLEC lysates. EAAT and Xc(-) exchanger inhibition by substrate antagonists depleted GSH concentrations by 15-28% (p's ≤ 0.02), while GSH synthesis inhibition by buthionine sulfoximine depleted GSH by 33% (p = 0.008).

CONCLUSION

Inhibition of Glu and Cys uptake by EAAT and Xc(-) exchanger antagonists depletes GSH in human lens epithelial cells. These in vitro results support pivotal roles for EAAT and Xc(-) exchanger activities in maintaining GSH and protection against oxidative stress in cortical lens epithelium.

Effect of methionine sulfoxide reductase B1 silencing on high-glucose-induced apoptosis of human lens epithelial cells

AIMS

To determine roles of methionine sulfoxide reductase B1 (MsrB1) in protecting lens mitochondria against oxidative damage, the influences of MsrB1 gene silencing on high-glucose-induced apoptosis in human lens epithelial (HLE) cells were studied.

MAIN METHODS

Our study used four groups of cells: normal control, MsrB1 gene silenced, high glucose (30mM) exposed and MsrB1 gene silenced cells followed with high glucose exposure. In all cases we detected cell viability, cell apoptosis rate, intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) levels, alteration of mitochondrial membrane potential, release of mitochondrial cytochrome c as well as an increase in activity of caspase-3.

KEY FINDINGS

The results showed that MsrB1 gene silencing by short interfering RNA (siRNA) in HLE cells clearly resulted in oxidative stress, decrease in mitochondrial membrane potential and release of mitochondrial cytochrome c as well as an increase in activity of caspase-3 and the percentage of apoptotic cells. When MsrB1-silenced HLE cells were exposed to high glucose, characteristic of high-glucose-induced mitochondrial dysfunctions were further exacerbated.

SIGNIFICANCE

MsrB1 plays important roles in protecting HLE cell mitochondria against oxidative damage and inhibits oxidative stress-induced apoptosis in diabetic cataracts by scavenging ROS.

Cellular dysfunction in diabetes as maladaptive response to mitochondrial oxidative stress

Oxidative stress has been implicated in diabetes long-term complications. In this paper, we summarize the growing evidence suggesting that hyperglycemia-induced overproduction of superoxide by mitochondrial electron transport chain triggers a maladaptive response by affecting several metabolic and signaling pathways involved in the pathophysiology of cellular dysfunction and diabetic complications. In particular, it is our goal to describe physiological mechanisms underlying the mitochondrial free radical production and regulation to explain the oxidative stress derived from a high intracellular glucose concentration and the resulting maladaptive response that leads to a cellular dysfunction and pathological state. Finally, we outline potential therapies for diabetes focused to the prevention of mitochondrial oxidative damage.

Vitamin B6: beyond coenzyme functions

Endogenous reactive intermediates such as photoexcited states of tissue chromophores, reactive oxygen species (ROS), reactive carbonyl species (RCS), and transition metal ions are mediators of tissue damage involved in initiation and progression of human pathologies including tumorigenesis, atherosclerosis, diabetes, and neurodegenerative disease. A large body of evidence now suggests that B6 vitamers antagonize the harmful activity of endogenous reactive intermediates fulfilling a very different role than that established as a cofactor for numerous enzymes. In this chapter, the structural basis of vitamin B6 activity as a potent antioxidant, metal chelator, carbonyl scavenger, and photosensitizer is presented and the physiological relevance is discussed.

Spermidine delays eye lens opacification in vitro by suppressing transglutaminase-catalyzed crystallin cross-linking

A Ca(2+)-dependent TG activity, identified in the eye lens of several mammalian species, has long been implicated in cataract formation. The precise mechanism of the involvement of this enzyme in this process remains unclear. The purpose of this work was to investigate the modulatory effect of polyamines on TG activity during rabbit eye lens in vitro opacification. We observed, in an in vitro Ca(2+)-induced cataract model, a rapid decrease of the endogenous levels of SPD with the progression of opacification, paralleled by an increase of crystallin cross-linking by bis(γ-glutamyl)SPD. This pattern was reversed adding exogenous SPD to the incubation medium. Indeed, endogenous SPD levels were restored and cross-linking by bis(γ-glutamyl)SPD were drastically reduced. Surprisingly, under this experimental condition, the loss of transparency of lens was delayed. We found that exogenous SPD incubation led to a remarkable increase of mono(γ-glutamyl)SPD, likely responsible of the inhibition of cross-linking of lens crystallins and of the transparency persistence.

Association between folate status, diabetes, antihypertensive medication and age-related cataracts in elderly Taiwanese

OBJECTIVE

To evaluate possible risk factors for cataract in elderly Taiwanese, and to investigate whether the relationship between age and cataract in older persons is modified by other cataract-associated risk factors.

PARTICIPANTS

A cross-sectional study of 661 males and 645 females aged ≥ 65 yrs was conducted as part of the Elderly Nutrition and Health Survey in Taiwan (1999-2000) (Elderly NAHSIT).

METHODS

Self-reported cataracts were defined as any incidence of cataract that was diagnosed by a physician and treated by anticataractic drugs based on the medical history section of the Elderly NAHSIT. Potential risk factors for cataract were determined by multiple logistic regression analysis of data obtained from the health examination, blood biochemistry and interviewer-administered questionnaires.

RESULTS

Results showed that the prevalence of self-reported cataract increased with age and was significantly higher in older women than in older men. Cataracts were associated with age, diabetes, antihypertensive medication and folate insufficiency in older men, and with age and antihypertensive medication in older women. Folate insufficiency remained associated with cataract in older men who had adequate vitamin B2, B6 and B12 status. Folate insufficiency was associated with cataract after adjustment for other risk factors in older men aged ≥ 75 yrs, while in older men aged 65-74 yrs, only diabetes and antihypertensive medication remained associated with cataract. In addition, age ≥ 75 yrs remained a risk factor for cataract in those without diabetes, not taking hypertensive medication and with normal folate status. Further analysis showed that the strength of the association between age ≥ 75 yrs in older men and cataracts was increased about 1.5-fold when combined with folate insufficiency (interaction p= 0.0198), and increased about 1.8-fold when combined with use of antihypertensive medication (interaction p = 0.0214).

CONCLUSION

Our results suggest that the combination of age ≥ 75 yrs in older men with either folate insufficiency or use of antihypertensive medication had an additive effect on the risk of cataract. Maintenance of good folate status should be emphasized to reduce the risk of cataract in the Taiwanese elderly, especially men.

Hyperglycemia-induced alterations in synaptosomal membrane fluidity and activity of membrane bound enzymes: beneficial effect of N-acetylcysteine supplementation

Diabetic encephalopathy is characterized by impaired cognitive functions that appear to underlie neuronal damage triggered by glucose driven oxidative stress. Hyperglycemia-induced oxidative stress in diabetic brain may initiate structural and functional changes in synaptosomal membranes. The objective of the present study was to examine the neuroprotective role of N-acetylcysteine (NAC) in hyperglycemia-induced alterations in lipid composition and activity of membrane bound enzymes (Na(+),K(+)-ATPase and Ca(2+)-ATPase) in the rodent model of type 1 diabetes. Male Wistar rats weighing between 180 and 200 g were rendered diabetic by a single injection of streptozotocin (50 mg/kg body weight, i.p.). The diabetic animals were administered NAC (1.4-1.5 g/kg body weight) for eight weeks and lipid composition along with membrane fluidity were determined. A significant increase in lipid peroxidation was observed in cerebral cortex of diabetic rats. NAC administration on the other hand lowered the hyperglycemia-induced lipid peroxidation to near control levels. The increased lipid peroxidation following chronic hyperglycemia was accompanied by a significant increase in the total lipids which can be attributed to increase in the levels of cholesterol, triglycerides and glycolipids. On the contrary phospholipid and ganglioside levels were decreased. Hyperglycemia-induced increase in cholesterol to phospholipid ratio reflected decrease in membrane fluidity. Fluorescence polarization (p) with DPH also confirmed decrease in synaptosomal membrane fluidity that influenced the activity of membrane bound enzymes. An inverse correlation was found between fluorescence polarization with the activities of Na(+),K(+)-ATPase (r(2)=0.416, P<0.05) and Ca(2+) ATPase (r(2)=0.604, P<0.05). NAC was found to significantly improve lipid composition, restore membrane fluidity and activity of membrane bound enzymes. Our results clearly suggest perturbations in lipid composition and membrane fluidity as a major factor in the development of diabetic encephalopathy. Furthermore, NAC administration ameliorated the effect of hyperglycemia on oxidative stress and alterations in lipid composition thereby restoring membrane fluidity and activity of membrane bound enzymes.

Plasma Homocysteine, Folate and Vitamin B(12) levels in senile cataract

Elevated plasma Homocysteine level is an independent risk factor for age related (senile) cataract. Certain nutritional deficiencies, in particular Folate, Vitamin B(12), Vitamin B(6) relate inversely with Homocysteine level. This study was undertaken to evaluate the plasma level of Vitamin B(12), Folate, and Homocysteine of cataract patients and to study the interplay between them. Serum Homocysteine level is significantly increased in cataract patients when compared with control (p< 0.001). There was a significant decrease in the level of Folate as compared with control (p<0.001). There was a negative correlation between Homocysteine vs. Vitamin B(12) (p<0.01) and Folate (p<0.01) in the Cataract patients. Our findings suggest that increased plasma Homocysteine level is associated with decreased plasma levels of Folate and VitaminB(12) in Cataract patients, which might have a possible role in the root cause of cataract pathogenesis.

Propagation of protein glycation damage involves modification of tryptophan residues via reactive oxygen species: inhibition by pyridoxamine

Nonenzymatic modification of proteins is one of the key pathogenic factors in diabetic complications. Uncovering the mechanisms of protein damage caused by glucose is fundamental to understanding this pathogenesis and in the development of new therapies. We investigated whether the mechanism involving reactive oxygen species can propagate protein damage in glycation reactions beyond the classical modifications of lysine and arginine residues. We have demonstrated that glucose can cause specific oxidative modification of tryptophan residues in lysozyme and inhibit lysozyme activity. Furthermore, modification of tryptophan residues was also induced by purified albumin-Amadori, a ribose-derived model glycation intermediate. The AGE inhibitor pyridoxamine (PM) prevented the tryptophan modification, whereas another AGE inhibitor and strong carbonyl scavenger, aminoguanidine, was ineffective. PM specifically inhibited generation of hydroxyl radical from albumin-Amadori and protected tryptophan from oxidation by hydroxyl radical species. We conclude that oxidative degradation of either glucose or the protein-Amadori intermediate causes oxidative modification of protein tryptophan residues via hydroxyl radical and can affect protein function under physiologically relevant conditions. This oxidative stress-induced structural and functional protein damage can be ameliorated by PM via sequestration of catalytic metal ions and scavenging of hydroxyl radical, a mechanism that may contribute to the reported therapeutic effects of PM in the complications of diabetes.

Effects of oxidative modifications induced by the glycation of bovine serum albumin on its structure and on cultured adipose cells

Non-enzymatic glycosylation (glycation) and oxidative damages represent major research areas insofar as such modifications of proteins are frequently observed in numerous states of disease. Albumin undergoes structural and functional alterations, caused by increased glycosylation during non insulin-dependent diabetes mellitus, which is closely linked with the early occurrence of vascular complications. In this work, we first characterized structural modifications induced by the glycation of bovine serum albumin (BSA). A pathophysiological effect of glycated BSA was identified in primary cultures of human adipocytes as it induces an accumulation of oxidatively modified proteins in these cells. BSA was incubated in the presence or absence of physiological, pathological or supra-physiological concentrations of glucose at 37 degrees C for 7 weeks. Enhanced BSA glycation percentages were determined using boronate affinity columns. The occurrence of oxidative modifications was found to be enhanced in glycated BSA, after determination of the free thiol groups content, electrophoretic migration and infrared spectrometry spectra. An accumulation of carbonyl-modified proteins and an increased release of isoprostane were observed in cell media following the exposure of adipocytes to glycated albumin. These results provide a new possible mechanism for enhanced oxidative damages in diabetes.

Glycolaldehyde induces growth inhibition and oxidative stress in human breast cancer cells

Glycolaldehyde (GA) is formed by oxidative degradation of glucose, from glycated proteins, lipid peroxidation, and oxidation of amino acids, and by human neutrophils during phagocytosis. The exact purpose of GA production by phagocytes is unclear, but it is tempting to speculate that it is part of the defense against invading bacteria and tumor cells. We have already reported that GA induces apoptosis in breast cancer cells. Because the GA carbonyl group cannot be blocked by cyclization, it is prone to enolization followed by air oxidation with concomitant production of glyoxal and superoxide. Since both these products can induce oxidative stress, in this work we focused on the ability of GA to cause oxidative cell damage. MCF7 human breast cancer cells were incubated with different GA concentrations and O2*- production, lipid peroxidation, and carbonylated protein were assessed. GA was cytotoxic at 20 microM, inhibiting cell proliferation, and at 100 microM, induced p53 expression and caused apoptosis. These events were accompanied by increases of O2*- production, lipid peroxidation, and accumulation of protein carbonyl. It thus appears that alpha-hydroxy aldehydes can induce oxidative stress. Prevention of oxidative stress, however, did not abolish the effects of GA on cell growth and viability, which appeared to be a direct consequence of glyoxal toxicity.

In vitro glucose-induced cataract in copper-zinc superoxide dismutase null mice

The purpose of this study was to evaluate the involvement of the superoxide radical in glucose-induced cataract using lenses from mice lacking the cytosolic copper-zinc superoxide dismutase (SOD1). Lenses from wild-type mice and SOD1 null mice were kept in organ culture with either 5.6 or 55.6 mM glucose for 6 days. The cataract formation was followed with digital image analysis and ocular staging. The lens damage was further quantified by analysis of the leakage of lactate dehydrogenase into the medium by the uptake of 86Rb and by determining the water content of the lenses. The formation of superoxide radicals in the lenses was assessed with lucigenin-derived chemiluminescence. Immunohistochemical staining for SOD1 was also performed on murine lenses. The SOD1 null lenses exposed to high glucose developed more cataract showed an increased leakage of lactate dehydrogenase and developed more oedema compared to the control lenses. At 5.6 mM glucose there was no difference between the SOD1 null and wild-type lenses. Staining for SOD1 was seen primarily in the cortex of the wild-type lens. This in vitro model suggests an involvement of the superoxide radical and a protective effect of SOD1 in glucose-induced cataract formation.

Role of protein kinase C and oxidative stress in interleukin-1beta-induced human proximal tubule cell injury and fibrogenesis

BACKGROUND

Interleukin (IL)-1beta, a pro-inflammatory macrophage-derived cytokine, is implicated as a key mediator of interstitial fibrosis and tubular loss or injury in progressive renal insufficiency. This study investigates some of the mechanisms of action of IL-1beta on the proximal tubule.

METHODS

Confluent cultures of primary human proximal tubule cells (PTC) were incubated in serum-free media supplemented with either IL-1beta (0-4 ng/mL), phorbol-12-myristate 13-acetate (PMA, protein kinase C activator) (6.25-100 nmol/L), or vehicle (control), together with a non-specific protein kinase C inhibitor (H7), a specific protein kinase C inhibitor (BIM-1), an anti-oxidant (NAC) or a NADPH oxidase inhibitor (AEBSF).

RESULTS

Interleukin-1beta-treated PTC exhibited time-dependent increases in fibronectin secretion (ELISA), cell injury (LDH release) and reactive nitrogen species (RNS) release (Griess assay). Proximal tubule cell DNA synthesis (thymidine incorporation) was also significantly suppressed. The effects of IL-1beta, which were reproduced by incubation of PTC with PMA (6.25-100 nmol/L), were blocked by H7 but not by BIM-1. The anti-oxidant (4 mmol/L) partially blocked IL-1beta-induced fibronectin secretion by PTC, but did not affect IL-1beta-induced LDH release, RNS release or growth inhibition. The NADPH oxidase inhibitor (AEBSF) significantly attenuated all observed deleterious effects of IL-1beta on PTC.

CONCLUSION

Interleukin-1beta directly induces proximal tubule injury, extracellular matrix production and impaired growth. The anti-oxidant, NAC, appears to ameliorate part of the fibrogenic effect of IL-1beta on PTC through mechanisms that do not significantly involve protein kinase C activation or nitric oxide release.

Advanced glycation end products and oxidative stress are increased in chronic allograft nephropathy

BACKGROUND

The histologic picture of chronic allograft nephropathy (CAN) resembles early arteriosclerotic lesion. Oxidative stress and advanced glycation end products (AGES) have been implicated in the pathogenesis of atherosclerosis and progression of renal disease.

METHODS

The authors serially measured the plasma malonyldialdehyde (MDA), carbonyl protein (CP), pentosidine, and argpyramidine levels in 11 postrenal transplant patients with normal renal function (KPT) and 10 patients with biopsy proven CAN at 1, 3, 6, 9 through 12, and 18 through 24 months posttransplant. Data were also obtained in 16 controls and 13 patients with chronic renal failure (CRF).

RESULTS

Although serum creatinine, MDA, CP, pentosidine, and argpyrimidine levels decreased during follow-up in KPT, it progressively increased in patients with CAN. The mean serum creatinine level was higher in patients with CRF (3.3 +/- 0.8 mg/dL [291.7 +/- 70.7 micromol/L]) and CAN (2.4 +/- 1.1 mg/dL [212.1 +/- 96.6 micromol/L]) than in controls (1.2 +/- 0.3 mg/dL [105.8 +/- 26.7 micromol/L]) and KPT patients (1.2 +/- 0.2 mg/dL [109.7 +/- 17.7 micromol/L]; P < 0.001). Markers of oxidative stress and AGEs measured at 18 to 24 months posttransplant in patients with CAN were higher than in KPT, controls, and CRF patients. MDA (nmol/mL) was significantly higher in patients with CAN (1.30 +/- 0.30) compared with controls (0.53 +/- 0.12), KPT (0.52 +/- 0.15), and CRF (0.74 +/- 0.27) groups (P < 0.001). Plasma CP (nmol/mg protein) in patients with CAN (4.3 +/- 1.00) was higher than in controls (1.90 +/- 0.69) and KPT (2.62 +/- 1.00) groups at the same time-point (P < 0.001), but comparable with CRF (2.69 +/- 1.20). Plasma pentosidine (pmol/micromol protein) level in patients with CAN (19.69 +/- 5.05) was higher compared with controls (2.49 +/- 0.86), CRF (13.10 +/- 3.68), and KPT (14.32 +/- 6.28) groups (P < 0.001). Plasma argpyrimidine (pmol/10 micromol protein) was higher in patients with CAN (123.8 +/- 17.9) compared with controls (4.81 +/- 1.91), CRF (56.92 +/- 29.67), and KPT (31.1 +/- 11.1; P < 0.001) groups.

CONCLUSION

Oxidative stress and AGEs are increased in patients with CAN, which cannot be explained by the decline in renal function alone. Oxidative stress and AGEs may be one among the nonimmune mediators of CAN.

Antioxidant activity of a Schiff base of pyridoxal and aminoguanidine

We recently reported that PL-AG, a Schiff base of pyridoxal and aminoguanidine, was more effective than aminoguanidine (AG), a well-known anti-diabetic-complication compound, in preventing nephropathy in diabetic mice and presented brief data indicating the antioxidant activity of the adduct. In the present study, we additionally investigated the inhibitory activity of PL-AG in comparison with that of AG against in vitro and in vivo oxidation. PL-AG was more potent than AG and reference compounds such as pyridoxal and pyridoxamine in any of the five antioxidant activities examined in vitro, i.e., hydrogen peroxide-scavenging, hydroxyl radical-scavenging, superoxide radical-scavenging, ascorbic acid-autoxidation inhibitory, and low-density lipoprotein (LDL)-oxidation inhibitory activities, the last two of which were assessed in the presence of Cu(2+). Unlike AG, PL-AG did not show the pro-oxidant activity. The inhibitory activity of PL-AG against lipid peroxidation in diabetic rats was higher than that of AG, for example, the amounts of malondialdehyde in erythrocytes (nmol/g hemoglobin; mean +/- SD) in normal, untreated diabetic, AG-treated diabetic, and PL-AG-treated diabetic rats were 3.53 +/- 0.35, 4.99 +/- 0.23, 4.65 +/- 0.45, and 4.06 +/- 0.35, respectively. A fluorescent substance different from PL-AG was found in the plasma and urine of rats treated with PL-AG. The chemical structure of this substance, i.e., oxidized PL-AG, was determined by a combination of nuclear magnetic resonance, mass, and infrared spectrometry. AG dramatically decreased the pyridoxal phosphate level in the diabetic rat liver, whereas PL-AG only moderately affected it. Our results indicate that the antioxidant activity of PL-AG is due to its chelation with transition metal ions and to scavenging of reactive oxygen species. They also suggest that PL-AG is more promising for the treatment of diabetic complications than AG.

Glucose-induced changes in the phenotype of human peritoneal mesothelial cells: effect of L-2-oxothiazolidine carboxylic acid

BACKGROUND

During peritoneal dialysis, mesothelial cells are chronically exposed to high concentrations of glucose. Therefore, the cytotoxic effect of glucose may alter the function and reactivity of these cells.

METHODS

For 4 weeks, human peritoneal mesothelial cells were cultured in vitroin medium supplemented with 45 mM glucose or 45 mM mannitol or with 45 mM glucose and 1 mM L-2-oxothiazolidine-4-carboxylic acid (OTZ), the latter being a precursor for glutathione synthesis. Peroxidation of the mesothelial cell lipids, synthetic activity and reaction of these cells to peritoneal dialysis fluids were studied.

RESULTS

In contrast to mannitol, glucose enhanced the peroxidation of the cellular lipids (+65%, p < 0.01) an effect that was prevented by OTZ. Synthesis of hyaluronan and vascular endothelial growth factor was reduced in mesothelial cells treated with glucose by 36% (p < 0.01) and 44% (p < 0.05), respectively; both glucose effects were reversed when cells were incubated with glucose plus OTZ. Monocyte chemoattractant protein-1 synthesis by cells exposed to glucose was increased by 31% (p < 001), and again that effect was prevented by OTZ. Glucose and mannitol stimulated synthesis of fibronectin (+32%, p < 0.05). Mesothelial cells chronically exposed to glucose became activated after subsequent exposure to the dialysis fluid, as reflected by the increased release of interleukin (IL)-6, in contrast to control mesothelial cells, in which IL-6 synthesis was suppressed.

CONCLUSIONS

Chronic exposure of mesothelial cells to glucose changes their synthetic activity and their reaction after exposure to dialysis fluids. Some of these effects are prevented by OTZ, which suggests that glucose-induced free radicals are responsible for a change in mesothelial cell phenotype under the conditions of peritoneal dialysis.