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

Ascorbic acid export from human donor lenses: Is the lens a source of ascorbic acid in the ocular humors?

In previous work, we have shown that the lens acts a reservoir of the antioxidant glutathione (GSH), capable of exporting this antioxidant into the ocular humors and potentially protecting the tissues of the eye that interface with these humors from oxidative stress. In this study, we have extended this work by examining whether the lens acts as a source of ascorbic acid (AsA) to maintain the high levels of AsA known to be present in the ocular humors either by the direct export of AsA into the humors and/or by functioning as a recycling site for AsA, via the direct uptake of oxidised ascorbate (DHA) from the humors, its regeneration to AsA in the lens and then its subsequent export back into the humors. To test this, human lenses of varying ages were cultured for 1 h under hypoxic conditions and AsA/DHA levels measured in the media and in the lens. Human lenses were also cultured in compartmentalised chambers to determine whether efflux of AsA/DHA occurs at the anterior or posterior surface. Immunohistochemistry was performed on human donor lenses and sections labelled with antibodies against GLUT1, a putative DHA uptake transporter. Vitreous humor was collected from patients undergoing vitrectomy who either had a natural clear lens, an artificial intraocular implant (IOL) or a cataractous lens, and AsA/DHA and GSH and oxidised GSH (GSSG) measured. We found that cultured human donor lenses released both AsA and DHA into the media. Culturing of lenses in a compartmentalised chamber revealed that AsA and DHA efflux occurs at both surfaces, with relatively equal amounts of AsA and DHA released from each surface. The posterior surface of the lens was shown to express the GLUT1 transporter. Analysis of vitreous samples from patients undergoing vitrectomy revealed that vitreous GSH and AsA levels were similar between the natural lens group, IOL and cataractous lens group. Taken together, while human donor lenses were shown to export AsA and DHA into the surrounding media, the amount of AsA and DHA released from donor lenses was low and not sufficient to sustain the high levels of total AsA normally present in the humors. This suggests that although the lens is not the main source for maintaining high levels of AsA in the ocular humors, the lens may help to support local AsA levels close to the lens.

Oxidative stress and antioxidants in cataract development

PURPOSE OF REVIEW

Oxidative stress plays a central role in cataract pathogenesis, a leading cause of global blindness. This review delves into the role of oxidative stress in cataract development and key biomarkers - glutathione (GSH), superoxide dismutase (SOD), malondialdehyde (MDA), and 4-hydroxynonenal (4-HNE) - to clarify their functions and potential applications in predictive diagnostics and therapies.

RECENT FINDINGS

Antioxidants serve as pivotal markers in cataract pathogenesis. GSH affects the central lens due to factors such as enzyme depletion and altered connexin expression, impairing GSH diffusion. Age-related oxidative stress may hinder GSH transport via connexin channels or an internal microcirculation system. N-acetylcysteine, a GSH precursor, shows promise in mitigating lens opacity when applied topically. Additionally, SOD, particularly SOD1, correlates with increased cataract development and gel formulations have exhibited protective effects against posterior subscapular cataracts. Lastly, markers of lipid peroxidation, MDA and 4-HNE, have been shown to reflect disease severity. Studies suggest a potential link between 4-HNE and connexin channel modification, possibly contributing to reduced GSH levels.

SUMMARY

Oxidative stress is a significant contributor to cataract development, underscoring the importance of antioxidants in diagnosis and treatment. Notably, GSH depletion, SOD decline, and lipid peroxidation markers are pivotal factors in cataract pathogenesis, offering promising avenues for both diagnosis and therapeutic intervention.

Current Approach to the Pathogenesis of Diabetic Cataracts

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

Selenium intake help prevent age-related cataract formation: Evidence from NHANES 2001-2008

Introduction

Cataract is one of the leading causes of blindness and visual impairment, about 16 million people around the world. Trace elements play an important role in a variety of the processes in human body. This study aimed to investigate the association between daily dietary intake of trace elements and age-related cataract incidence based on data from the National Health and Nutrition Examination Survey (NHANES) 2001-2008.

Methods

Iron, zinc, copper, and selenium were conducted in this study among subjects aged 50 years and older for African Americans and 55 and older in US adults. Multivariate logistic regression analysis was used in different models to investigate the association of trace elements intake and cataract.

Results

After screening, 7,525 subjects were ultimately included in this study. A significant negative association was found between selenium intake and cataract incidence in adjusted models using multivariate logistic regression analysis (model 1: OR = 0.998, 95% CI = 0.997-1.000; model 2: OR = 0.997, 95% CI = 0.995-1.000; and model 3: OR = 0.998, 95% CI = 0.995-1.000). After dividing selenium intake into quintiles, significant negative associations between selenium intake and cataract were observed in the first quintile of model 3, the fourth and fifth quintiles of all models. In subgroup analyses adjusted for age and sex, a significant negative association was observed only in women aged 65-74 years.

Discussion

Our study points out that maintaining daily dietary selenium intake at higher levels is helpful for cataract prevention, and that increasing daily dietary selenium intake in American women aged 65-74 years may contribute to the prevention of age-related cataract. The intakes of iron, zinc, copper may not be associated with age-related cataract.

Review of glucose oxidase as a feed additive: production, engineering, applications, growth-promoting mechanisms, and outlook

The regulation and prohibition of antibiotics used as growth promoters (AGP) in the feed field are increasing because they cause antimicrobial resistance and drug residue issues and threaten community health. Recently, glucose oxidase (GOx) has attracted increasing interest in the feed industry as an alternative to antibiotics. GOx specifically catalyzes the production of gluconic acid (GA) and hydrogen peroxide (H₂O₂) by consuming molecular oxygen, and plays an important role in relieving oxidative stress, preserving health, and promoting animal growth. To expand the application of GOx in the feed field, considerable efforts have been made to mine new genetic resources. Efforts have also been made to heterologously overexpress relevant genes to reduce production costs and to engineer proteins by modifying enzyme properties, both of which are bottleneck problems that limit industrial feed applications. Herein, the: different sources, diverse biochemical properties, distinct structural features, and various strategies of GOx engineering and heterologous overexpression are summarized. The mechanism through which GOx promotes growth in animal production, including the improvement of antioxidant capacity, maintenance of intestinal microbiota homeostasis, and enhancement of gut function, are also systematically addressed. Finally, a new perspective is provided for the future development of GOx applications in the feed field.

Dietary inclusion of glucose oxidase supplementation to corn-wheat-based diet enhance growth performance, nutrient digestibility, blood profile of lactating sows

The objective of this study is to investigate the effect of dietary glucose oxidase (GOx) supplementation on the reproductive performance, litter performance, total tract digestibility, and blood profile of lactating sows fed corn-wheat-based diet. A total of twenty multiparous sows (Landrace × Yorkshire) were allocated into one of four treatments with five replicates per treatment. The dietary treatments were as follows: CON (Basal diet), GO1 (basal diet + 200 U GOx/kg), GO2 (basal diet + 300 U GOx/kg), GO3 (basal diet + 400 U Gox/kg). Dietary GOx supplementation did not affect lactating sow’s reproduction performance as well as body weight, backfat thickness, and body condition score during pre and post farrowing, and at weaning (p > 0.05). However, after farrowing to weaning period lactating sow’s fed GOx supplement has linearly (p = 0.0196) decreased the bodyweight loss. While, there were no effects (p > 0.05) observed on sows backfat thickness loss, average daily feed intake, and estrus interval among treatment groups. Dietary supplementation of GOx has linearly improved the body weight gain (p = 0.049) and average daily gain (p = 0.040) of suckling piglets. The total tract digestibility of dry matter and nitrogen was linearly increased with the graded level of GOx supplement. Also, a linear effect was observed on the glucose and superoxide dismutase of blood profile with the dietary inclusion of GOx. In summary, our finding indicates that the dietary inclusion of GOx supplement with corn-wheat-based diet had a beneficial effect on the nutrient digestibility and blood profile of lactating sows and improved the growth performance of suckling piglets.

Effect of thioltransferase on oxidative stress induced by high glucose and advanced glycation end products in human lens epithelial cells

AIM

To study the effect of thioltransferase (TTase) on oxidative stress in human lens epithelial cells (HLECs) induced by high glucose and advanced glycation end products (AGEs).

METHODS

HLECs were treated with 35.5 mmol/L glucose or 1.5 mg/mL AGEs modified bovine serum albumin (AGEs-BSA) as the experimental groups, respectively. Cells were collected at the time point of 1, 2, 3, and 4d. The TTase activity were measured accordingly. TTase mRNA levels were detected by quantitative reverse transcription polymerase chain response (qRT-RCR) and its protein level was detected by Western blot. The siRNA was used to knock down the expression of TTase. The activity of catalase (CAT) and superoxide dismutase (SOD), the content of reactive oxygen species (ROS) and the ratio of oxidized glutathione/total glutathione (GSSG/T-GSH) were assessed in different groups, respectively.

RESULTS

The level of TTase mRNA gradually increased and reached the top at 2d, then it decreased to the normal level at 4d, and the TTase activity increased from 2 to 3d in both high glucose and AGEs-BSA groups. The TTase expression elevated from 2d in high glucose group, and it began to rise from 3d in AGEs-BSA group. The activity of CAT and SOD showed a decrease and the content of ROS and the ratio of GSSG/T-GSH showed an increase in high glucose and AGEs-BSA group. These biochemical alterations were more prominent in the groups with TTase siRNA.

CONCLUSION

High glucose and AGEs can increase ROS content in HLECs; therefore, it induces oxidative stress. This may result in the decreased GSH and increased GSSG content, impaired activity of SOD and CAT. The up-regulated TTase likely provides oxidation damage repair induced by high glucose and AGEs in the early stage.

Dietary supplementation of Aspergillus niger-expressed glucose oxidase ameliorates weaning stress and improves growth performance in weaning pigs

Weaning is one of the most stressful events in the pig's life, which disrupts physiological balance and leads to oxidative stress. It is reported that glucose oxidase supplementation could alleviate oxidative stress in animals by increasing the concentration of antioxidant enzymes in vivo. The purpose of this study was to evaluate the effects of dietary supplementation of Aspergillus niger-expressed glucose oxidase (AN-GOX) on growth performance, nutrient digestibility, faecal microbiota, faecal gas emission and serum antioxidant enzyme parameters in weaning pigs. A total of 120 21-day-old weaning pigs [(Yorkshire ×Landrace) × Duroc] with an initial body weight of 6.54 ± 0.55 kg were used in a 21-day experiment (phase 1, days 1-7; phase 2, days 8-21) with a completely randomized block design. Pigs were randomly divided into 4 treatment groups with 6 replicate pens per treatment and 5 pigs per pen (2 barrows and 3 gilts). Dietary treatments were corn-soybean meal-based basal diet supplemented with 0, 0.01, 0.03 or 0.05% AN-GOX (1000 unit/g). The results of this study showed that average daily gain during days 1-7 and 1-21 and the concentrations of serum glutathione peroxidase and glutathione increased linearly at graduated doses of AN-GOX increased in the diet. However, dietary supplementation of AN-GOX had no effects on the apparent nutrient digestibility, faecal microbiota and faecal gas emission. In conclusion, supplementing AN-GOX to the diet of weaning pigs ameliorated weaning stress, which manifested as the increase in serum antioxidant enzyme levels, thus improving growth performance. The suitable dosage of AN-GOX used in the diet of weaning pigs was 0.05%.

Assessment of cataract forming effect of diabetes in young adults by lens densitometer

PURPOSE

To investigate the effect of the diabetes on cataract formation by Pentacam Scheimpflug topography system.

MATERIALS AND METHODS

Thirty diabetic patients and thirty-five healthy control subjects were included in the study. Exclusion criteria were smoking, high refractive error, any systemic disease or drug usage associated with cataract formation and to have diabetic retinopathy. The duration of diabetes and HbA1c level were recorded. A comprehensive ophthalmologic examination was performed in all cases. Pentacam (Oculus, Wetzlar, Germany) three-dimensional lens densitometer module was used to measure density of anterior, nuclear and posterior lens regions.

RESULTS

Mean age of group 1 and group 2 was 37.80 ± 5.51 years and 36.51 ± 3.77 years, respectively. There were not any difference between groups in the means of age and sex (P = .271; P = .700). The mean duration of diabetes in group 1 was 4.23 ± 3.71 years (6 months-10 year). The mean HbA1c level was 8.12 ± 2.07% (5.4-12.7%). Anterior, nuclear and posterior mean lens densitometry measurements were significantly higher in group 1 (diabetic group) than group 2 (control group) [(8.90 ± 0.59%; 8.05 ± 0.72% P =  < .001), (7.52 ± 0.31%; 7.00 ± 0.59% P =  < .001), (7.25 ± 0.31%; 6.90 ± 0.73% P = .006), respectively].

CONCLUSION

Diabetes may have cataractous effect in anterior, nuclear and posterior regions of the lens.

Illicium verum extracts and probiotics with added glucose oxidase promote antioxidant capacity through upregulating hepatic and jejunal Nrf2/Keap1 of weaned piglets

Accumulating evidences indicate that plant extracts and probiotics are effective antioxidant substitutes which play important roles in animal production. However, the comparative study of the mechanism underlying the antioxidant property of Illicium verum extracts (IVE) and probiotics with added glucose oxidase (PGO) on piglets remains to be explored. This study evaluated the difference and the interaction effect of IVE and PGO on serum, liver, and jejunum antioxidant capacity of weaned piglets. A total of 32 weaned piglets (Duroc × Landrace × Yorkshire) at the age of 28 d with an average body weight of 14.96 ± 0.32 kg were randomly divided into four treatments with eight replicates per treatment in a 2 × 2 factorial arrangement. Treatments included basal diet (IVE-PGO-), basal diet + 1,000 mg/kg PGO (IVE-PGO+), basal diet + 500 mg/kg IVE (IVE+PGO-), and basal diet + 500 mg/kg IVE + 1,000 mg/kg PGO (IVE+PGO+). All the piglets were housed individually for the 42-d trial period after 7-d adaptation. The piglets were euthanized at the end of the experiment and the liver and jejunum samples were taken and subjected to immunohistochemistry, Western blotting, as well as antioxidant and qRT-PCR analysis. Significant interactions were observed between IVE and PGO for total superoxide dismutase (T-SOD) and glutathione peroxidase (GSH-Px) in serum (42 d), liver, and jejunum; malondialdehyde (MDA) in serum (21 d); and mRNA and protein expression of kelch sample related protein-1 (Keap1) and nuclear factor erythroid-2 related factor (Nrf2)/Keap1 in the liver and jejunum (P < 0.05). Both IVE and PGO improved (P < 0.05) T-SOD and GSH-Px in the serum (42 d), liver, and jejunum, and the mRNA and protein expression of Nrf2 and Nrf2/Keap1 in the liver and jejunum, but decreased (P < 0.05) MDA in the serum (21 d) and the mRNA and protein expression of Keap1 in the liver and jejunum. Immunohistochemical results confirmed that IVE and PGO enhanced the positive reactions of Nrf2 but weakened Keap1 in both the liver and jejunum. In conclusion, the results confirmed that IVE (500 mg/kg) and PGO (1,000 mg/kg) can improve the antioxidant capacity of weaned piglets and that the interaction effect between IVE and PGO is significant. At the same time, the fact that IVE and PGO activate the Nrf2/Keap1 in the liver and jejunum signaling pathway suggests that they play an important role in the ameliorative antioxidant capacity of weaned piglets. Therefore, the combination of IVE and PGO could be recommended as a new potential alternative to antibiotics in piglets' diets.

Characterisation of Glutathione Export from Human Donor Lenses

Purpose

To investigate whether human donor lenses are capable of exporting reduced glutathione.

Methods

Human lenses of varying ages were cultured in artificial aqueous humor for 1 hour under hypoxic conditions to mimic the physiologic environment and reduced glutathione (GSH) and oxidized glutathione (GSSG) levels measured in the media and in the lens.

Results

Human donor lenses released both GSH and GSSG into the media. Donor lenses cultured in the presence of acivicin, a γ-glutamyltranspeptidase inhibitor, exhibited a significant increase in GSSG levels (P < 0.05), indicating that GSSG undergoes degradation into its constituent amino acids. Screening of GSH/GSSG efflux transporters revealed Mrp1, Mrp4, and Mrp5 to be present at the transcript level, but only Mrp5 was expressed at the protein level. Blocking Mrp5 function with the Mrp inhibitor MK571 led to a significant decrease in GSSG efflux (P < 0.05), indicating that Mrp5 is likely to be involved in mediating GSSG efflux. Measurements of efflux from the anterior and posterior surface of the lens revealed that GSH and GSSG efflux occurs at both surfaces but predominantly at the anterior surface.

Conclusions

Human lenses export GSH and GSSG into the surrounding ocular humors, which can be recycled by the lens to maintain intracellular GSH homeostasis or used by neighboring tissues to maintain GSH levels.

Translational Relevance

Early removal of a clear lens, as occurs to treat myopia and presbyopia, would eliminate this GSH reservoir and reduce the supply of GSH to other tissues, which, over time, may have clinical implications for the progression of other ocular diseases associated with oxidative stress.

A novel compound AB38b attenuates oxidative stress and ECM protein accumulation in kidneys of diabetic mice through modulation of Keap1/Nrf2 signaling

Extracellular matrix (ECM) deposition following reactive oxygen species (ROS) overproduction has a key role in diabetic nephropathy (DN), thus, antioxidant therapy is considered as a promising strategy for treating DN. Here, we investigated the therapeutic effects of AB38b, a novel synthetic α, β-unsaturated ketone compound, on the oxidative stress (OS) and ECM accumulation in type 2 diabetes mice, and tried to clarify the mechanisms underlying the effects in high glucose (HG, 30 mM)-treated mouse glomerular mesangial cells (GMCs). Type 2 diabetes model was established in mice with high-fat diet feeding combined with streptozocin intraperitoneal administration. The diabetic mice were then treated with AB38b (10, 20, 40 mg· kg^-1· d^-1, ig) or a positive control drug resveratrol (40 mg· kg^-1· d^-1, ig) for 8 weeks. We showed that administration of AB38b or resveratrol prevented the increases in malondialdehyde level, lactate dehydrogenase release, and laminin and type IV collagen deposition in the diabetic kidney. Simultaneously, AB38b or resveratrol markedly lowered the level of Keap1, accompanied by evident activation of Nrf2 signaling in the diabetic kidney. The underlying mechanisms of antioxidant effect of AB38b were explored in HG-treated mouse GMCs. AB38b (2.5-10 μM) or resveratrol (10 μM) significantly alleviated OS and ECM accumulation in HG-treated GMCs. Furthermore, AB38b or resveratrol treatment effectively activated Nrf2 signaling by inhibiting Keap1 expression without affecting the interaction between Keap1 and Nrf2. Besides, AB38b treatment effectively suppressed the ubiquitination of Nrf2. Taken together, this study demonstrates that AB38b ameliorates experimental DN through antioxidation and modulation of Keap1/Nrf2 signaling pathway.

Novel biphenyl diester derivative AB-38b inhibits NLRP3 inflammasome through Nrf2 activation in diabetic nephropathy

Inflammation reaction mediated by NLRP3 inflammasome and Nrf2-related oxidative stress are vital participants in the development of diabetic nephropathy (DN) and closely associated to kidney fibrosis. Nrf2, a known antioxidative transcription factor, has been reported to activate NLRP3 inflammasome through its downstream factors (HO-1, NQO1, etc.) recently. AB38b is a newly synthesized biphenyl diester derivative with a Nrf2 activation property. This research aims to evaluate the renal protective effects of AB-38b and to elucidate the anti-inflammation mechanisms involved. Type 2 diabetic mice induced by high fat diet with streptozocin (STZ) and high glucose-cultured mouse glomerular mesangial cells (GMCs) were used in current study. Results showed that administration of AB-38b improved the kidney function while attenuated renal fibrosis progression in diabetic mice together with reducing the extracellular matrix (ECM) accumulation of GMCs cultured in high glucose. Mechanistically, treatment with AB-38b significantly decreased the high level of NLRP3 inflammasome in diabetic condition by inhibiting the ROS/TXNIP/NLRP3 signaling pathway. And meanwhile, AB-38b treatment effectively improved Nrf2 signaling during diabetic condition. Furthermore, knocking down the gene expression of Nrf2 by siRNA in GMCs abolished the inhibition effect of AB-38b on NLRP3 inflammasome activation and ECM accumulation. Taken together, our data suggest that AB-38b was able to improve the renal function of diabetic mice, and the NLRP3 inflammasome inhibition effect of AB-38b was responsible for the renal protective effect. Further exploration indicate that Nrf2 plays pivotal role in AB-38b's attenuation of DN progression through inhibiting NLRP3 inflammasome activation.

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.

Cataract surgery in diabetes mellitus: A systematic review

India is considered the diabetes capital of the world, and a significant proportion of patients undergoing cataract surgery are diabetic. Considering this, we reviewed the principles and guidelines of managing cataract in patients with diabetes. The preoperative, intraoperative, and postoperative factors are of paramount importance in the management of diabetic cataract patients. Particularly, the early recognition and treatment of diabetic retinopathy or maculopathy before cataract surgery influence the final visual outcome and play a major role in perioperative decision-making. Better understanding of various factors responsible for favorable outcome of cataract surgery in diabetic patients may guide us in better overalll management of these patients and optimizing the results.

Quercetin inhibited epithelial mesenchymal transition in diabetic rats, high-glucose-cultured lens, and SRA01/04 cells through transforming growth factor-β2/phosphoinositide 3-kinase/Akt pathway

Diabetic cataract (DC), an identified life-threatening secondary complication of diabetes mellitus, has proven to be a dilemma because of its multifactorial caused and progression. An increasing number of studies have shown that in addition to the maillard reaction, enhanced polyol pathway, and oxidative insults, epithelial mesenchymal transition (EMT) is related to the prevalence of DC. Quercetin, a classic flavonoid with multiple pharmacological effects has been reported to possess therapeutic efficacy in the management and treatment of this disease. However, the mechanism underlying its therapeutic efficacy in EMT of lens epithelial cells (SRA01/04) and contribution to resolving DC remains a mystery. Therefore, in this study, we investigated the effects of quercetin on EMT of SRA01/04 and high-glucose (HG)-induced lens opacity accompanied by lens fibrosis induced by type-1 diabetes. Furthermore, we sought to clarify the specific mechanisms underlying these effects. At week 14 after streptozotocin (STZ) intraperitoneal administration, diabetic rats showed lens opacity accompanied with diminished antioxidant function, enhanced polyol pathway activity, and non-enzymatic glycation. Western blotting confirmed EMT in rat SRA01/04 cells with significantly increased α-smooth muscle actin (α-SMA) and decreased E-cadherin expressions. Treatment of the lens with quercetin ameliorated the oxidative stress, inhibited aldose reductase (AR) activation, reduced advanced glycation end product (AGE) production, and finally suppressed EMT in the early stages. Our in vitro results showed that high-glucose activated the transforming growth factor-β2/phosphoinositide 3-kinase/protein kinase B (TGF-β2/PI3K/Akt) signalling and EMT in SRA01/04 cells. Further, induced oxidative stress, activation of aldose reductase, and accumulation of advanced glycation end products were also involved in this process. Quercetin was potent enough to effectively ameliorate the high glucose (HG)-induced EMT of SRA01/04 cells by inhibiting the activation of TGF-β2/PI3K/Akt, enhancing the antioxidant capacity, inhibiting AR activity, and reducing AGE production. From the whole animal to tissues, and finally the cellular level, our results provide considerable evidence of the therapeutic potential of quercetin for DC. This might be due to its inhibition of EMT mediated through inhibition of the TGF-β/PI3K/Akt pathway.

MiR-30a inhibits BECN1-mediated autophagy in diabetic cataract

Purpose

To investigate the role of microRNAs in the regulation of autophagy and apoptosis in lens epithelial cells (LECs) during diabetic cataract formation.

Methods

A miRNA microarray study and quantitative real-time PCR were performed to identify the expression of miRNAs in LECs of diabetic cataract. Human LECs were cultured in high glucose conditions as a diabetic cataract model. BECN1 and LC3B were detected by Western blotting and quantitative real-time PCR. The extent of apoptosis was measured using FACSCalibur flow cytometry.

Results

Downregulation of miR-30a was identified in LECs attached to diabetic cataract tissues. By the bioinformatic assay and the luciferase activity assay, BECN1 was found to be a direct target of miR-30a. MiR-30a reduced the BECN1-mediated autophagy activity induced by high glucose in LECs in vitro. The ratio of LECs apoptosis was also decreased.

Conclusion

MiR-30a was involved in the inhibition of autophagy by targeting BECN1 in LECs in human diabetic cataract.

Does oxidative stress play any role in diabetic cataract formation? ----Re-evaluation using a thioltransferase gene knockout mouse model

Oxidative stress is a known risk factor in senile cataract formation. In recent years, it has been suggested that oxidation may also be associated with cataract induced by hyperglycemia, but this concept has not been well examined or validated. Since thioltransferase (TTase) is one of the key enzymes that regulates redox homeostasis and protects against oxidative stress in the lens, we have used TTase gene knockout (KO) mice as a model to examine this new concept. Lenses from 4 months old TTase KO and wild-type (WT) mice were incubated in TC199 culture medium containing 30 mM glucose for 48 h. Each lens was assessed for opacity, graded by LOCSII system, and the wet weight was recorded after which it was homogenized in lysis buffer and analyzed for water-soluble protein and free glutathione (GSH). In vivo studies were carried out using 4 months old TTase KO and WT mouse groups. Each mouse received two consecutive days of intraperitoneal streptozotozin (STZ) injections to induce diabetes. The lenses were examined weekly for 4 weeks using a slit-lamp biomicroscope, and then extracted and analyzed for levels of GSH, water-soluble protein, ATP and protein-GSH mixed disulfide (PSSG). TTase KO lenses cultured in high glucose developed a mild cortical opacity but slightly more than that of the WT lenses. Both groups had similar contents of soluble proteins and GSH. Exposure to high glucose did not change the soluble protein level but did suppress GSH by 20% in lenses with or without TTase. STZ-induced diabetic KO mice also developed a higher degree of mild cortical lens opacity compared to that of the diabetic WT controls. Similar 15-20% losses in lens GSH and ATP were found after one-month induced diabetes in WT and KO mice. There was a 20% greater amount of PSSG in the lenses of TTase KO than the WT control. Under diabetic condition, both groups displayed more glutathionylated proteins in the beta-actin (42 kDa) and lens crystallin proteins (18-22 kDa) regions, and some additional modified proteins at 15-17 kDa and 60-70 kDa, with a total 20-30% PSSG increment in both groups. In conclusion, we have found that hyperglycemia induced some oxidative stress-associated biochemical changes with mild lens opacity in both WT and KO mice. However, these changes were only marginally higher in the TTase KO mouse than that of the WT control, suggesting that TTase deletion may only play a minor role in the early stage of hyperglycemia-induced cataract formation in the mice.

Effects of histone acetylation on superoxide dismutase 1 gene expression in the pathogenesis of senile cataract

Histone acetylation plays key roles in gene expression, but its effects on superoxide dismutase 1 (SOD1) expression in senile cataract remains unknown. To address this problem, the study was to investigate the influence of histone acetylation on SOD1 expression and its effects in the pathogenesis of senile cataract. Senile cataract was classified into three types—nuclear cataract (NC), cortical cataract (CC), and posterior subcapsular cataract (SC)—using the Lens Opacities Classification System III. In senile cataracts, SOD1 expression decreased significantly. Both H3 and H4 were deacetylated at −600 bp of the SOD1 promoter of cataract lenses, and hypoacetylated at −1500, −1200, and −900 bp. In hypoacetylated histones, the hypoacetylation pattern differed among the cataracts. In vitro, anacardic acid (AA) significantly reduced H3 and H4 acetylation at the SOD1 promoter, decreased protein expression, and induced cataract formation in rabbits. AA also inhibited HLEC viability and increased cell apoptosis. In contrast, trichostatin A (TSA) was able to efficaciously stop AA’s effects on both rabbit lenses and HLECs. Decreased histone acetylation at the SOD1 promoter is associated with declined SOD1 expression in senile cataracts. Histone acetylation plays an essential role in the regulation of SOD1 expression and in the pathogenesis of senile cataracts.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

Liver specific expression of Cu/ZnSOD extends the lifespan of Sod1 null mice

Genetic ablation of CuZn-superoxide dismutase (Sod1) in mice (Sod1(-/-) mice) leads to shortened lifespan with a dramatic increase in hepatocellular carcinoma and accelerated aging phenotypes, including early onset sarcopenia. To study the tissue specific effects of oxidative stress in the Sod1(-/-) mice, we generated mice that only express the human SOD1 gene specifically in the liver of Sod1(-/-) mice (Sod1(-/-)/hSOD1(alb) mice). Expression of hSOD1 in the liver of Sod1(-/-) mice improved liver function, reduced oxidative damage in liver, and partially restored the expression of several genes involved in tumorigenesis, which are abnormally expressed in the livers of the Sod1(-/-) mice. However, liver specific expression of hSOD1 did not prevent the loss of body weight and muscle mass and alterations in the structure of neuromuscular junctions. The expression of hSOD1 in the liver of Sod1(-/-) mice significantly improved the lifespan of Sod1(-/-) mice; however, the lifespan of the Sod1(-/-)/hSOD1(alb) mice was still significantly shorter than wild type mice.

Diabetic cataract-pathogenesis, epidemiology and treatment

Cataract in diabetic patients is a major cause of blindness in developed and developing countries. The pathogenesis of diabetic cataract development is still not fully understood. Recent basic research studies have emphasized the role of the polyol pathway in the initiation of the disease process. Population-based studies have greatly increased our knowledge concerning the association between diabetes and cataract formation and have defined risk factors for the development of cataract. Diabetic patients also have a higher risk of complications after phacoemulsification cataract surgery compared to nondiabetics. Aldose-reductase inhibitors and antioxidants have been proven beneficial in the prevention or treatment of this sightthreatening condition in in vitro and in vivo experimental studies. This paper provides an overview of the pathogenesis of diabetic cataract, clinical studies investigating the association between diabetes and cataract development, and current treatment of cataract in diabetics.

Age-dependent increases in interstitial collagenase and MAP Kinase levels are exacerbated by superoxide dismutase deficiencies

Many age-associated degenerative diseases commonly involve degradation of the extracellular matrix and aberrant matrix metalloproteinase-1 (MMP-1) expression. In diverse cell lines MMP-1 or interstitial collagenase (CL) expression is tightly regulated through a network of signals involving reactive oxygen species (ROS). However, whether the in vivo age-associated increase in CL expression is also sensitive to ROS-mediated signaling has not been established. To evaluate the contribution of ROS to the age-dependent increase in CL we monitored the levels of murine CL in two well-established models of oxidant stress. Analysis of murine CL levels in mice deficient in either of the intracellular superoxide dismutases (Sod2(+/-) or Sod1(-/-)) revealed its age- and redox-dependent expression relative to WT controls. Both age- and redox-dependent increases in murine CL expression were associated with elevations in phosphorylation of the MAP Kinases, Erk, JNK and p38. CL expression was highest in renal and skeletal muscle tissue from the aged Sod1(-/-) mice and was associated with a decrease in collagen staining. These findings suggest that MAPK signaling and CL production are both age- and redox-responsive. The redox sensitivity of age-associated CL expression suggests that degenerative disease associated with aberrant matrix remodeling and oxidant stress may be amenable to antioxidant-based therapies.

Liquid-chromatographic and mass-spectrometric identification of lens proteins using microwave-assisted digestion with trypsin-immobilized magnetic nanoparticles

We used a newly developed method combining trypsin-immobilized magnetic nanoparticles (TIMNs) and microwave-assisted protein digestion to study the proteins of human lens tissue. The digested proteins were identified by liquid chromatography and mass spectrometry. The lens proteins were digested under optimized conditions (digestion time 1 min, microwave power 400 W, trypsin-to-protein ratio 1:5) determined using bovine serum albumin as the standard protein, before liquid-chromatographic and mass-spectrometric analysis. Twenty-six proteins were identified with the new digestion method compared with 11 proteins identified with traditional in-solution digestion (12h). gamma-Crystallin, beta-crystallin, and superoxide dismutase 1 proteins, identified with the microwave-assisted method but not the traditional method, are related to cataract development according to some studies. The TIMNs were easily separated from the digestion products. This new digestion method could prove extremely useful for large-scale proteomic analyses.