The role of oxidative stress in diabetic retinopathy

Effect of High-Sucrose Diet on the Occurrence and Progression of Diabetic Retinopathy and Dietary Modification Strategies

As the most serious of the many worse new pathological changes caused by diabetes, there are many risk factors for the occurrence and development of diabetic retinopathy (DR). They mainly include hyperglycemia, hypertension, hyperlipidemia and so on. Among them, hyperglycemia is the most critical cause, and plays a vital role in the pathological changes of DR. High-sucrose diets (HSDs) lead to elevated blood glucose levels in vivo, which, through oxidative stress, inflammation, the production of advanced glycation end products (AGEs) and vascular endothelial growth factor (VEGF), cause plenty of pathological damages to the retina and ultimately bring about loss of vision. The existing therapies for DR primarily target the terminal stage of the disease, when irreversible visual impairment has appeared. Therefore, early prevention is particularly critical. The early prevention of DR-related vision loss requires adjustments to dietary habits, mainly by reducing sugar intake. This article primarily discusses the risk factors, pathophysiological processes and molecular mechanisms associated with the development of DR caused by HSDs. It aims to raise awareness of the crucial role of diet in the occurrence and progression of DR, promote timely changes in dietary habits, prevent vision loss and improve the quality of life. The aim is to make people aware of the importance of diet in the occurrence and progression of DR. According to the dietary modification strategies that we give, patients can change their poor eating habits in a timely manner to avoid theoretically avoidable retinopathy and obtain an excellent prognosis.

Malondialdehyde levels in diabetic retinopathy patients: a systematic review and meta-analysis

BACKGROUND

It remains unclear whether circulating malondialdehyde (MDA) levels change in people with diabetic retinopathy (DR). This systematic review compared circulating MDA levels in diabetic people with and without DR.

METHODS

PubMed, Medline (Ovid), Embase (Ovid), and Web of Science were searched for case-control studies conducted before May 2022 in English that compared circulating MDA levels in people with and without DR. The following MeSH search terms were used: ("malondialdehyde" or "thiobarbituric acid reactive substances [TBARS]" or "lipid peroxidation" or "oxidative stress") and "diabetic retinopathy." Newcastle-Ottawa Quality Assessment Scale was used to evaluate the quality of the included studies. Random-effects pairwise meta-analysis pooled the effect size with standardized mean difference (SMD) and 95% confidence intervals (CIs).

RESULTS

This meta-analysis included 29 case-control studies with 1680 people with DR and 1799 people with diabetes but not DR. Compared to people without DR, the circulating MDA levels were higher in those with DR (SMD, 0.897; 95% CI, 0.631 to 1.162; P  < 0.001). The study did not identify credible subgroup effects or publication bias and the sensitivity analysis confirmed the robustness of the study.

CONCLUSIONS

Circulating MDA levels are higher in people with DR compared to those without. Future comparative studies that use more specific methods are required to draw firm conclusions.

REGISTRATION

PROSPERO; https://www.crd.york.ac.uk/PROSPERO/ ; No. CRD42022352640.

Three Major Causes of Metabolic Retinal Degenerations and Three Ways to Avoid Them

An imbalance of homeostasis in the retina leads to neuron loss and this eventually results in a deterioration of vision. If the stress threshold is exceeded, different protective/survival mechanisms are activated. Numerous key molecular actors contribute to prevalent metabolically induced retinal diseases-the three major challenges are age-related alterations, diabetic retinopathy and glaucoma. These diseases have complex dysregulation of glucose-, lipid-, amino acid or purine metabolism. In this review, we summarize current knowledge on possible ways of preventing or circumventing retinal degeneration by available methods. We intend to provide a unified background, common prevention and treatment rationale for these disorders and identify the mechanisms through which these actions protect the retina. We suggest a role for herbal medicines, internal neuroprotective substances and synthetic drugs targeting four processes: parainflammation and/or glial cell activation, ischemia and related reactive oxygen species and vascular endothelial growth factor accumulation, apoptosis and/or autophagy of nerve cells and an elevation of ocular perfusion pressure and/or intraocular pressure. We conclude that in order to achieve substantial preventive or therapeutic effects, at least two of the mentioned pathways should be targeted synergistically. A repositioning of some drugs is considered to use them for the cure of the other related conditions.

Micronutrients and Diabetic Retinopathy: Evidence From The National Health and Nutrition Examination Survey and a Meta-analysis

PURPOSE

To investigate the associations between circulating micronutrients (vitamins A, C, D, E, and carotenoids) and risk of diabetic retinopathy (DR).

DESIGN

Cross-sectional study and meta-analysis.

METHODS

The cross-sectional study included 517 diabetic participants aged ≥40 years in the 2005-2006 National Health and Nutrition Examination Survey. Serum vitamin D was converted to liquid chromatography-tandem mass spectrometry-equivalent results, while other micronutrients were measured using high-performance liquid chromatography. Presence of DR was determined based on non-mydriatic fundus photographs. A meta-analysis was subsequently performed, which included relevant studies published from January 01, 1990 to December 31, 2020.

RESULTS

Of the 517 included participants, DR was identified in 159 participants (25.17%). After adjusting for multiple confounders, only serum vitamin C was associated with a lower risk of DR (odds ratio [OR]: 0.60; 95% confidence interval [CI]: 0.38-0.95). A total of 35 studies were included in the subsequent meta-analysis. Comparing 1056 participants with DR to 920 controls, the pooled weighted mean difference (WMD) of vitamin C was -11.01 (95% CI: -19.35 to -2.67). Regarding vitamins D and E, the pooled WMD was -3.06 (95% CI: -5.15 to -0.96) and -3.03 (95% CI: -4.24 to -1.82), respectively. No associations were identified between DR and circulating vitamin A or carotenoids.

CONCLUSIONS

Lower levels of circulating vitamins C, D, and E were found in DR patients than those without. More high-quality studies are required to assess the real effects of micronutrients on DR.

Inflammation, oxidative stress and altered heat shock response in type 2 diabetes: the basis for new pharmacological and non-pharmacological interventions

Type 2 diabetes mellitus (DM2) is a chronic disease characterised by variable degrees of insulin resistance and impaired insulin secretion. Besides, several pieces of evidence have shown that chronic inflammation, oxidative stress, and 70 kDa heat shock proteins (HSP70) are strongly involved in DM2 and its complications, and various pharmacological and non-pharmacological treatment alternatives act in these processes/molecules to modulate them and ameliorate the disease. Besides, uncontrolled hyperglycaemia is related to several complications as diabetic retinopathy, neuropathy and hepatic, renal and cardiac complications. In this review, we address discuss the involvement of different inflammatory and pro-oxidant pathways related to DM2, and we described molecular targets modulated by therapeutics currently available to treat DM2.

Therapeutic potential of curcumin in diabetic retinopathy (Review)

Diabetic retinopathy (DR) is a type of retinal microangiopathy caused by diabetes mellitus. It has become the leading cause of blindness among working individuals worldwide. DR is becoming increasingly common among younger diabetic patients and there is a need for lifelong treatment. The pathogenic mechanisms of DR are influenced by a number of factors, such as hyperglycemia, hyperlipidemia, inflammatory response and oxidative stress, among others. Currently, the treatment methods for DR mainly include retinal photocoagulation, vitrectomy, or anti‑vascular endothelial growth factor (VEGF) therapy. However, these methods have some disadvantages and limitations. Therefore, it is a matter of great interest and urgency to discover drugs that can target the pathogenesis of DR. Since ancient times, traditional Chinese medicine practitioners have accumulated extensive experiences in the use of Chinese herbal medicine for the prevention and treatment of diseases. In the theory of traditional Chinese medicine, curcumin has the effects of promoting blood circulation and relieving pain. A number of studies have also demonstrated that curcumin has multiple biological activities, including exerting anti‑apoptotic, anti‑inflammatory, antioxidant and antitumor properties. In recent years, studies have also confirmed that curcumin can prevent a variety of diabetic complications, including diabetic nephropathy (DN). However, the preventive and curative effects of curcumin on DR and its mechanisms of action have not yet been fully elucidated. The present review aimed to explore the therapeutic potential of curcumin in diabetes mellitus and DR.

The stress response protein REDD1 as a causal factor for oxidative stress in diabetic retinopathy

Diabetic Retinopathy (DR) is a major cause of visual dysfunction, yet much remains unknown regarding the specific molecular events that contribute to diabetes-induced retinal pathophysiology. Herein, we review the impact of oxidative stress on DR, and explore evidence that supports a key role for the stress response protein regulated in development and DNA damage (REDD1) in the development of diabetes-induced oxidative stress and functional defects in vision. It is well established that REDD1 mediates the cellular response to a number of diverse stressors through repression of the central metabolic regulator known as mechanistic target of rapamycin complex 1 (mTORC1). A growing body of evidence also supports that REDD1 acts independent of mTORC1 to promote oxidative stress by both enhancing the production of reactive oxygen species and suppressing the antioxidant response. Collectively, there is strong preclinical data to support a key role for REDD1 in the development and progression of retinal complications caused by diabetes. Furthermore, early proof-of-concept clinical trials have found a degree of success in combating ischemic retinal disease through intravitreal delivery of an siRNA targeting the REDD1 mRNA. Overall, REDD1-associated signaling represents an intriguing target for novel clinical therapies that go beyond addressing the symptoms of diabetes by targeting the underlying molecular mechanisms that contribute to DR.

Anti-inflammatory Effect of Curcumin, Homotaurine, and Vitamin D3 on Human Vitreous in Patients With Diabetic Retinopathy

Purpose: To determine the levels of pro-inflammatory cytokines and soluble mediators (TNF-α, IL6, IL2, and PDGF-AB) in 28 vitreous biopsies taken from patients with proliferative diabetic retinopathy (PDR) and treated with increasing doses of curcumin (0. 5 and 1 μM), with or without homotaurine (100 μM) and vitamin D3 (50 nM). Materials and Methods: ELISA tests were performed on the supernatants from 28 vitreous biopsies that were incubated with bioactive molecules at 37°C for 20 h. The concentration of the soluble mediators was calculated from a calibration curve and expressed in pg/mL. Shapiro-Wilk test was used to verify the normality of distribution of the residuals. Continuous variables among groups were compared using the General Linear Model (GLM). Homoscedasticity was verified using Levene and Brown-Forsythe tests. Post-hoc analysis was also performed with the Tukey test. A p ≤ 0.05 was considered statistically significant. Results: The post-hoc analysis revealed statistically detectable changes in the concentrations of TNF-α, IL2, and PDGF-AB in response to the treatment with curcumin, homotaurine, and vitamin D3. Specifically, the p-values for between group comparisons are as follows: TNF-α: (untreated vs. curcumin 0.5 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.008, (curcumin 0.5 μM vs. curcumin 0.5 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.0004, (curcumin 0.5 μM vs. curcumin 1 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.02, (curcumin 1 μM vs. curcumin 0.5 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.025, and (homotaurine 100 μM + vitamin D3 50 nM vs. curcumin 0.5 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.009; IL2: (untreated vs. curcumin 0.5 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.0023, and (curcumin 0.5 μM vs. curcumin 0.5 μM+ homotaurine 100 μM + vitamin D3 50 nM) p = 0.0028; PDGF-AB: (untreated vs. curcumin 0.5 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.04, (untreated vs. curcumin 1 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.0006, (curcumin 0.5 μM vs. curcumin 1 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.006, and (homotaurine 100 μM + vitamin D3 50 nM vs. curcumin 1 μM + homotaurine 100 μM + vitamin D3 50 nM) p = 0.022. IL6 levels were not significantly affected by any treatment. Conclusions: Pro-inflammatory cytokines are associated with inflammation and angiogenesis, although there is a discrete variability in the doses of the mediators investigated among the different vitreous samples. Curcumin, homotaurine, and vitamin D3 individually have a slightly appreciable anti-inflammatory effect. However, when used in combination, these substances are able to modify the average levels of the soluble mediators of inflammation and retinal damage. Multi-target treatment may provide a therapeutic strategy for diabetic retinopathy in the future. Clinical Trial Registration : The trial was registered at clinical trials.gov as NCT04378972 on 06 May 2020 ("retrospectively registered") https://register.clinicaltrials.gov/prs/app/action/SelectProtocol?sid = S0009UI8&selectaction = Edit&uid = U0003RKC&ts = 2&cx = dstm4o.

Benefits of micronutrient supplementation for reducing the risk of wet age-related macular disease and diabetic retinopathy

Age-related macular disease and diabetic retinopathy are chronic degenerative diseases characterised by progressive visual impairment. In Europe, age-related macular disease accounts for over 15% of blindness in adults over 50 years of age, and although the burden of diabetic retinopathy in terms of vision impairment is lower, vision loss associated with diabetic retinopathy is increasing with the rising prevalence of diabetes mellitus and the ageing of the population. Late-stage age-related macular disease can be subdivided into dry (non-neovascular) or wet (neovascular or exudative) forms. The large Age-Related Eye Disease Study 2 showed that supplementation with antioxidant nutrients reduces choroids neovascularisation and reduces the risk of progression of neovascular age-related macular disease. Antioxidant micronutrient supplements have also shown promising results in preventing the pathogenesis of retinopathy in animal models of diabetes. Age-related macular disease and diabetic retinopathy are understood to share some common pathophysiological characteristics, suggesting that micronutrients have an important role in ocular health in both conditions. This article will review the current evidence for the utility of micronutrients in preventing the development and progression of neovascular age-related macular disease and diabetic retinopathy.

Taxifolin Shows Anticataractogenesis and Attenuates Diabetic Retinopathy in STZ-Diabetic Rats via Suppression of Aldose Reductase, Oxidative Stress, and MAPK Signaling Pathway

Background:

Due to the increased prevalence of diabetes-associated complications of the eye like diabetic retinopathy and cataract, the need for a novel therapeutic agent is urgent. Due to the advantages that the polyphenolic compounds enjoy in diabetes and associated complications, we postulated that Taxifolin (TXF), a poly-phenolic flavanol, could show anti-retinopathic and anti-cataract effect in diabetes-induced rats.

Methods:

TXF at a dose of 10, 25, and 50 mg/kg was given by oral route to STZ mediated diabetic rats for a time period of 10 weeks. The opacity of lens was studied after every 7 days of treatment till 10 weeks; evaluation of the severity of cataract and changes in the histology of lens as well as retina was done. Tissue homogenates of lens isolated after the end of the study were evaluated for markers of oxidative stress, levels of aldose reductase, p38MAPK, VEGF, and ERK1/2.

Results:

Outcomes suggested that TXF improved retinopathy and cataract in diabetes-induced rats. The treatment of TXF also improved the status of oxidative stress and inhibited the levels of p38MAPK, VEGF, and ERK1/2. The treatment also improved the lens opacity in diabetic rats. The results suggest that the protective effect of TXF against cataract and retinopathy may be due to the anti-oxidative potential of TXF and its inhibiting effect on VEGF, ERK1/2, p38MAPK, and aldose reductase.

Conclusion:

The study confirms that TXF is a potential candidate showing a protective effect against diabetic induced retinopathy and cataract..

Possible therapeutic effect of magnesium in ocular diseases

Magnesium (Mg2+) is one of the major elements required to maintain normal metabolism and ionic balances in ocular tissues. The physiological role of Mg2+ is mediated through maintaining the Na+-K+-ATPase on membrane, favoring energy-generating reactions, replication of DNA and protein synthesis. Despite the wide availability of this element, hypomagnesemia has been associated with many human ailments. Recent studies highlighted the association of hypomagnesemia and, thereby, supplementation of Mg2+ in the management of eye diseases. Glaucoma, senile cataract and diabetic retinopathy were associated with low level of extracellular Mg2+. The neurovascular protective effects of Mg2+ mediated through activation of endothelial nitric oxide synthase and inhibition of endothelin-1 eventually result in vasodilatation of retinal vessels. Mg2+ can maintain the lens sodium pump activity and antioxidant status and block the calcium channels and release of glutamate in nerve endings. Furthermore, it can prevent the apoptosis of retinal ganglion cells. All these effects contribute to its being a pharmacological agent against ocular diseases. However, clinical trials are scant. This article discusses the role of Mg2+ as a possible therapeutic agent in the management of glaucoma, cataract and diabetic retinopathy.

Dietary antioxidative supplements and diabetic retinopathy; a systematic review

Purpose

There is controversial data regarding the effects of dietary antioxidative supplements on diabetic retinopathy (DR). We conducted a systematic review of both observational and randomized controlled clinical trials (RCTs) to clarify whether they are effective or not.

Methods

All observational and RCTs conducted by antioxidative supplements on DR published up to 1 January 2018 in PubMed, Web of Sciences, Scopus and Cochrane Library databases were included. Exclusion criteria were animal studies, and studies conducted in Type 1 diabetes mellitus (T1DM), children or pregnant women. Main outcome measures were reporting the incidence or progression of DR in T2DM by assessment of visual fields, and measurements of oxidative and antioxidative biomarkers. The quality of reporting of included articles and risk of bias were assessed.

Results

Finally, we reached 14 observational studies and 7 RCTs that conducted on 256,259 subjects. Due to severe methodological heterogeneity, only qualitative synthesis was carried. All studies were reported a significantly lower level of antioxidants and higher level of oxidative stress biomarkers in DR compared with others. There was an inverse significant correlation between vitamin C and malondialdehyde (MDA) (r = -0.81) or DNA damage (r = -0.41). These figures were statistically significant between vitamin E and MDA (r = 0.77) or superoxide dismutase (r = 0.44). Coefficient of correlation between MDA and zinc (-0.82), coenzyme Q10 (0.56), and magnesium (-0.73) was significant. Multi-oxidants trials were shown non-significant beneficial effects on DR.

Conclusions

Although our study supports the positive effects of antioxidative supplements on DR, more high quality studies are needed to confirm.

Hyperglycemia induced early growth response-1 regulates vascular dysfunction in human retinal endothelial cells

Early growth response-1 (Egr-1) protein upregulation is reported in diabetes and vascular disorders. This study aims at deciphering its role in hyperglycemia induced changes of retinal endothelium. Human retinal endothelial cells (hRECs) were exposed to hyperglycemia (25mM) and normoglycemia (5.5mM). Gene silencing was done using siRNA against Egr-1. Transcript and protein level analysis of Egr-1 and gene targets were done using qPCR and immunoblotting respectively in hRECs, diabetic and nondiabetic human retina and immunofluorescence for localization in retinal sections. Hyperglycemia induced Egr-1 and vascular endothelial growth factor-A (VEGF-A) but not pigment epithelium derived factor (PEDF) in hRECs. Expression of Egr-1 repressor NGFI-A binding protein-2 (NAB-2) was unaltered. Egr-1 downstream gene targets, tissue factor (TF) and intercellular adhesion molecule-1 (ICAM-1) expression were increased in hRECs which was reduced by Egr-1 silencing in hyperglycemia. Diabetic retina, showed an increase in Egr-1, VEGF-A and gene target TF, ICAM-1 but not NAB-2 and PEDF similar to the changes seen in hyperglycemic hRECs. Hyperglycemic induction of Egr-1 and absence of NAB-2 repression in retinal endothelium, up-regulates downstream genes involved in pro-thrombotic and pro-inflammatory pathways linking Egr-1 in diabetes mediated vascular aberration of retina.

The unfolded protein response signaling and retinal Müller cell metabolism

The retina is one of the most energy demanding tissues in the body. Like most neurons in the central nervous system, retinal neurons consume high amounts of adenosine-5'-triphosphate (ATP) to generate visual signal and transmit the information to the brain. Disruptions in retinal metabolism can cause neuronal dysfunction and degeneration resulting in severe visual impairment and even blindness. The homeostasis of retinal metabolism is tightly controlled by multiple signaling pathways, such as the unfolded protein response (UPR), and the close interactions between retinal neurons and other retinal cell types including vascular cells and Müller glia. The UPR is a highly conserved adaptive cellular response and can be triggered by many physiological stressors and pathophysiological conditions. Activation of the UPR leads to changes in glycolytic rate, ATP production, de novo serine synthesis, and the hexosamine biosynthetic pathway, which are considered critical components of Müller glia metabolism and provide metabolic support to surrounding neurons. When these pathways are disrupted, neurodegeneration occurs rapidly. In this review, we summarize recent advance in studies of the UPR in Müller glia and highlight the potential role of the UPR in retinal degeneration through regulation of Müller glia metabolism.

The Ca2+/CaMKK2 axis mediates the telbivudine induced upregulation of creatine kinase: Implications for mechanism of antiviral nucleoside analogs' side effect

Telbivudine (LdT), a widely prescribed anti-hepatitis B virus (HBV) drug for the treatment of chronic Hepatitis B (CHB), causes adverse reactions ranging from creatine kinase (CK) elevation to myopathy. The purpose of this study was to explore the mechanism(s) of LdT induced CK elevation. The effects of LdT on mitochondrial morphology and proteins (TK2 and β-actin), oxidative stress, intracellular Ca²⁺ levels, Ca²⁺-related signaling pathway (CaMKK2/AMPK), and Ca²⁺-related biomarkers such as superoxide dismutase (SOD) and malondialdehyde (MDA) were assessed in human skeletal muscle cells (HSKMCs). The results showed that LdT induced a dose-dependent increase in CK activity in HSKMCs, without affecting mitochondrial morphology, and TK2 and β-actin protein levels, following 72 h of treatment. In addition, LdT increased Ca²⁺ production, ROS generation, MDA and lipid peroxide (LPO) levels, and activated the CaMKK2/AMPK signaling pathway. Moreover, these effects were attenuated by the BAPIA-AM (the calcium chelator). We also confirmed the presence of relevant markers (MDA, LPO, and SOD) in serum from CHB patients after LdT treatment, and found that CK was positively correlated with MDA and LPO, and negatively associated with SOD. These findings indicate that LdT induces CK elevation and oxidative stress associated with imbalance of intracellular Ca²⁺ in HSKMCs, suggesting that Ca²⁺/CaMKK2 axis imbalance may underlie human LdT-induced CK elevation. The present findings provide a solid basis for assessing the mechanism of drug-induced CK elevation, which can help develop new tools for the prevention and treatment of diseases associated with drug-induced CK elevation.

The role and therapeutic potential of melatonin in age-related ocular diseases

The eye is continuously exposed to solar UV radiation and pollutants, making it prone to oxidative attacks. In fact, oxidative damage is a major cause of age-related ocular diseases including cataract, glaucoma, age-related macular degeneration, and diabetic retinopathy. As the nature of lens cells, trabecular meshwork cells, retinal ganglion cells, retinal pigment epithelial cells, and photoreceptors is postmitotic, autophagy plays a critical role in their cellular homeostasis. In age-related ocular diseases, this process is impaired, and thus, oxidative damage becomes irreversible. Other conditions such as low-grade chronic inflammation and angiogenesis also contribute to the development of retinal diseases (glaucoma, age-related macular degeneration and diabetic retinopathy). As melatonin is known to have remarkable qualities such as antioxidant/antinitridergic, mitochondrial protector, autophagy modulator, anti-inflammatory, and anti-angiogenic, it can represent a powerful tool to counteract all these diseases. The present review analyzes the role and therapeutic potential of melatonin in age-related ocular diseases, focusing on nitro-oxidative stress, autophagy, inflammation, and angiogenesis mechanisms.

Anticataractogenesis and Antiretinopathy Effects of the Novel Protective Agent Containing the Combined Extract of Mango and Vietnamese Coriander in STZ-Diabetic Rats

The novel protectant against diabetic cataract and diabetic retinopathy is currently required due to the increased prevalence and therapeutic limitation. Based on the advantage of polyphenol on diabetic eye complications, we hypothesized that the combined extract of mango seed Vietnamese coriander (MPO), a polyphenol-rich substance, should possess anticataractogenesis and antiretinopathy in streptozotocin- (STZ-) diabetic rats. MPO at doses of 2, 10, and 50 mg/kg·BW were orally given to STZ-diabetic rats for 10 weeks. Lens opacity was evaluated every week throughout a study period whereas the evaluation of cataract severity and histological changes of both rat lens epithelium and retina together with the biochemical assays of oxidative stress status, aldose reductase, p38MAPK, ERK1/2, and VEGF were performed at the end of experiment. Our data showed that MPO improved cataract and retinopathy in STZ-diabetic rats. The improved oxidative stress status and the decreased p38MAPK, ERK1/2, and VEGF were also observed. Therefore, anticataractogenesis and antiretinopathy of MPO might occur partly via the decreased oxidative stress status and the suppression of aldose reductase, p38MAPK, ERK1/2, and VEGF. This study points out that MPO is the potential candidate protectant against diabetic cataract and diabetic retinopathy. However, the exploration for possible active ingredient (S) still requires further researches.

The Effect of Vitamin E on Oxidative Stress Indicated by Serum Malondialdehyde in Insulin-dependent Type 2 Diabetes Mellitus Patients with Retinopathy

Background:

Several studies have focused on oxidative stress on diabetes mellitus (DM). Our purpose was to investigate the impact of oxidative stress on progression of diabetic retinopathy (DR) in insulin-dependent type 2 DM patients, measuring serum malondialdehyde (MDA), as well as to examine the effect of vitamin E on DR progression in the above-mentioned patients.

Methods:

Participants in the study were 282 insulin-dependent type 2 DM patients with DR. All participants underwent a thorough ophthalmological examination, so as to grade DR, along with serum MDA measurement. All participants received 300mg vitamin E daily for 3 months and were examined again. Serum MDA pre- and post-intake of Vitamin E was the main outcome.

Results:

Serum MDA was positively associated with DR stage, while there was a statistically significant difference pre- and post-intake of vitamin E in all DR stages. In a subgroup analysis of patients with proliferative DR, there was a significant difference at baseline between patients who have received prior laser photocoagulation and the treatment naïve patients, while after intake of vitamin E, no statistically significant difference was noticed.

Conclusion:

Oxidative stress has been found to play significant role in the pathogenesis and progression of DR, while vitamin E seems to reduce MDA levels and subsequent oxidative stress, suggesting that it might have protective role in DR progression.

Mitochondrial function in Müller cells - Does it matter?

Growing evidence suggests that mitochondrial dysfunction might play a key role in the pathogenesis of age-related neurodegenerative inner retinal diseases such as diabetic retinopathy and glaucoma. Therefore, the present review provides a perspective on the impact of functional mitochondria in the most predominant glial cells of the retina, the Müller cells. Müller cells span the entire thickness of the neuroretina and are in close proximity to retinal cells including the retinal neurons that provides visual signaling to the brain. Among multiple functions, Müller cells are responsible for the removal of neurotransmitters, buffering potassium, and providing neurons with essential metabolites. Thus, Müller cells are responsible for a stable metabolic dialogue in the inner retina and their crucial role in supporting retinal neurons is indisputable. Müller cell functions require considerable energy production and previous literature has primarily emphasized glycolysis as the main energy provider. However, recent studies highlight the need of mitochondrial ATP production to upheld Müller cell functions. Therefore, the present review aims to provide an overview of the current evidence on the impact of mitochondrial functions in Müller cells.

Angiogenesis and Inflammation Crosstalk in Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most prevalent microvascular complications of diabetes and one of the most frequent causes of blindness in active age. Etiopathogenesis behind this important complication is related to several biochemical, hemodynamic and endocrine mechanisms with a preponderant initial role assumed by polyol pathways, increment of growth factors, accumulation of advanced glycation end products (AGE), activation of protein kinase C (PKC), activation of the renin-angiotensin-aldosterone system (RAAS), and leukostasis. Chronic and sustained hyperglycemia works as a trigger to the early alterations that culminate in vascular dysfunction. Hypoxia also plays an essential role in disease progression with promotion of neovascularization and vascular dystrophies with vitreous hemorrhages induction. Thus, the accumulation of fluids and protein exudates in ocular cavities leads to an opacity augmentation of the cornea that associated to neurodegeneration results in vision loss, being this a devastating characteristic of the disease final stage. During disease progression, inflammatory molecules are produced and angiogenesis occur. Furthermore, VEGF is overexpressed by the maintained hyperglycemic environment and up-regulated by tissue hypoxia. Also pro-inflammatory mediators regulated by cytokines, such as tumor necrosis factor (TNF-α) and interleukin-1 beta (IL-1β), and growth factors leads to the progression of these processes, culminating in vasopermeability (diabetes macular edema) and/or pathological angiogenesis (proliferative diabetic retinopathy). It was found a mutual contribution between inflammation and angiogenesis along the process. J. Cell. Biochem. 117: 2443-2453, 2016. © 2016 Wiley Periodicals, Inc.

Serum Oxidized LDL Levels in Type 2 Diabetic Patients with Retinopathy in Mthatha Region of the Eastern Cape Province of South Africa

Oxidized low-density lipoprotein (ox-LDL) is a powerful natural prooxidant derived from native LDL by cell-mediated oxidation. Such oxidation occurs more easily in glycated LDL as observed in diabetes mellitus. We evaluated and compared selected biomarkers of oxidative stress and total antioxidant (TAO) levels in type 2 diabetes mellitus (T2DM) patients with and without retinopathy in the Mthatha region of the Eastern Cape Province, South Africa. The participants totaled to 140 and this number comprised 98 diabetic patients on treatment, stratified by diabetes (54) and diabetes with retinopathy (44). Forty-two nondiabetic healthy controls made up the 140. Fasting plasma glucose (FPG), glycosylated hemoglobin (HbA1c), lipid profile, serum ox-LDL, thiobarbituric acid reactive substances (TBARS), and TAO levels were measured. A statistically significant increase in FPG, HbA1c, TBARS, and ox-LDL and a significant decrease in TAO levels were seen in T2DM patients with retinopathy as compared to controls. A significant negative correlation was observed between TAO and ox-LDL levels in the diabetic group. In multiple linear regression analyses, duration of diabetes, triglyceride, TAO, and LDL cholesterol were found to be significantly associated with ox-LDL. In multiple logistic regression analyses, ox-LDL [OR 1.02 (1.01–1.03), P = 0.005] was the only risk factor and was significantly associated with the presence of retinopathy.

Associations of FPG, A1C and disease duration with protein markers of oxidative damage and antioxidative defense in type 2 diabetes and diabetic retinopathy

PURPOSE

To investigate the role of protein oxidative damage and antioxidant defense in relationship to hyperglycemia measured as fasting plasma glucose (FPG), glycated hemoglobin (A1C), and duration of disease in type 2 diabetes mellitus (DM) and diabetic retinopathy (DR).

METHODS

This study recruited 23 non-diabetic subjects, 16 DM patients without any complications and 18 DR patients. The serum ischemia modified albumin (IMA) and glutathione (GSH) levels were measured. The IMA results were corrected for serum albumin. Between-group differences were studied by analysis of variance and between-variable associations were studied by Spearman's and partial correlations.

RESULTS

IMA and cIMA values were elevated, whereas GSH was decreased in both patient groups vs controls (P<0.05), and the increase in IMA formation is not related to serum albumin changes. DR patients have much severe oxidative stress (OS) status with high IMA and cIMA, and low GSH than in the DM group (P<0.05). Both FPG and A1C levels were positively associated with IMA in DM group, while in the DR group, duration of disease too had a positive association with IMA. The antioxidant GSH had negative correlations with FPG (r=-0.52, P=0.02) and IMA (r=-0.49, P=0.03) in the DR group. Partial correlation analyses predicted mutual or independent associations among parameters.

CONCLUSIONS

Severe OS in DR has been associated with increased FPG, A1C, and disease duration. Both hyperglycemia and elevated oxidative damage detected as IMA are collectively associated with depleted GSH status. Our study unravels the need for monitoring of OS in addition to standard glycemic management in DR.

Lipid peroxidation: pathophysiological and pharmacological implications in the eye

Oxygen-derived free radicals such as hydroxyl and hydroperoxyl species have been shown to oxidize phospholipids and other membrane lipid components leading to lipid peroxidation. In the eye, lipid peroxidation has been reported to play an important role in degenerative ocular diseases (age-related macular degeneration, cataract, glaucoma, diabetic retinopathy). Indeed, ocular tissues are prone to damage from reactive oxygen species due to stress from constant exposure of the eye to sunlight, atmospheric oxygen and environmental chemicals. Furthermore, free radical catalyzed peroxidation of long chain polyunsaturated acids (LCPUFAs) such as arachidonic acid and docosahexaenoic acid leads to generation of LCPUFA metabolites including isoprostanes and neuroprostanes that may further exert pharmacological/toxicological actions in ocular tissues. Evidence from literature supports the presence of endogenous defense mechanisms against reactive oxygen species in the eye, thereby presenting new avenues for the prevention and treatment of ocular degeneration. Hydrogen peroxide (H2O2) and synthetic peroxides can exert pharmacological and toxicological effects on tissues of the anterior uvea of several mammalian species. There is evidence suggesting that the retina, especially retinal ganglion cells can exhibit unique characteristics of antioxidant defense mechanisms. In the posterior segment of the eye, H2O2 and synthetic peroxides produce an inhibitory action on glutamate release (using [(3)H]-D-aspartate as a marker), in vitro and on the endogenous glutamate and glycine concentrations in vivo. In addition to peroxides, isoprostanes can elicit both excitatory and inhibitory effects on norepinephrine (NE) release from sympathetic nerves in isolated mammalian iris ciliary bodies. Whereas isoprostanes attenuate dopamine release from mammalian neural retina, in vitro, these novel arachidonic acid metabolites exhibit a biphasic regulatory effect on glutamate release from retina and can regulate amino acid neurotransmitter metabolism without inducing cell death in the retina. Furthermore, there appears to be an inhibitory role for neuroprostanes in the release of excitatory amino acid neurotransmitters in mammalian retina. The ability of peroxides and metabolites of LCPUFA to alter the integrity of neurotransmitter pools provides new potential target sites and pathways for the treatment of degenerative ocular diseases.

Association of hyperglycemia mediated increased advanced glycation and erythrocyte antioxidant enzyme activity in different stages of diabetic retinopathy

AIM

This study aimed to evaluate whether hyperglycemia mediated increased formation of advanced glycation end products (AGEs) was associated with erythrocyte antioxidant enzyme activity in subjects with different stages of diabetic retinopathy (DR).

METHODS

Serum level of AGEs was determined by enzyme linked immunosorbent assay. Erythrocyte superoxide dismutase (SOD), glutathione reductase (GR) and catalase activity were estimated by enzymatic reaction based spectrophotometric assay in patients with type 2 diabetes with proliferative diabetic retinopathy (PDR), non-proliferative diabetic retinopathy (NPDR) and no retinopathy (DNR) and also in healthy non-diabetic controls (HC).

RESULT

Erythrocyte SOD and GR activity was significantly lower among NPDR (p=0.024, 0.0017, respectively) and PDR (p=0.0003, 0.0001, respectively) subjects compared with DNR individuals. A significant inverse correlation was observed between serum AGEs and erythrocyte SOD or GR activity in DNR (p=0.0019; r=-0.3033, p=0.0021; r=-0.3015, respectively), NPDR (p=0.0001; r=-0.4602, p=0.0003; r=-0.4161, respectively), and PDR (p<0.0001; r=-0.6753, p<0.0001; r=-0.5854, respectively) individuals.

CONCLUSION

Poor glycemia may be the key factor enhancing AGE formation, which may be associated with lower erythrocyte SOD and GR activity along with increased catalase activity in DR.

Astaxanthin attenuates the apoptosis of retinal ganglion cells in db/db mice by inhibition of oxidative stress

Diabetic retinopathy is a common diabetic eye disease caused by changes in retinal ganglion cells (RGCs). It is an ocular manifestation of systemic disease, which affects up to 80% of all patients who have had diabetes for 10 years or more. The genetically diabetic db/db mouse, as a model of type-2 diabetes, shows diabetic retinopathy induced by apoptosis of RGCs. Astaxanthin is a carotenoid with powerful antioxidant properties that exists naturally in various plants, algae and seafood. Here, astaxanthin was shown to reduce the apoptosis of RGCs and improve the levels of oxidative stress markers, including superoxide anion, malondialdehyde (MDA, a marker of lipid peroxidation), 8-hydroxy-2-deoxyguanosine (8-OHdG, indicator of oxidative DNA damage) and MnSOD (manganese superoxide dismutase) activity in the retinal tissue of db/db mouse. In addition, astaxanthin attenuated hydrogen peroxide(H₂O₂)-induced apoptosis in the transformed rat retinal ganglion cell line RGC-5. Therefore, astaxanthin may be developed as an antioxidant drug to treat diabetic retinopathy.

Hesperetin rescues retinal oxidative stress, neuroinflammation and apoptosis in diabetic rats

The purpose of the study was to evaluate the effects of hesperetin (Hsp) on diabetes-induced retinal oxidative stress, neuroinflammation and apoptosis in rats. The Hsp treatment (100 mg/kg body weight) was carried for twenty four weeks in STZ-induced diabetic rats and evaluated for antioxidant (Superoxide dismutase; SOD, Catalase; CAT and glutathione; GSH) enzymes, inflammatory cytokines (TNF-α, IL-1β), caspase-3, glial fibrillary acidic protein (GFAP) and aquaporin-4(AQP4) expression. Histological changes were evaluated by light and transmission electron microscopic (LM and TEM) studies. Retinal GSH levels and anti-oxidant enzymes (SOD and CAT) activity were significantly decreased in diabetic group as compared to normal group. However, in Hsp-treated rats, retinal GSH levels were restored close to normal levels and positive modulation of anti-oxidant enzyme activity was observed. Diabetic retinae showed significantly increased expression of Pro-inflammatory cytokines (TNF-α and IL-1β) as compared to normal retinae. While Hsp-treated retinae showed significantly lower levels of cytokines as compared to diabetic retinae. Diabetic retinae showed increased caspase-3, GFAP and AQP4 expression. However, Hsp-treated retinae showed inhibitory effect on caspase-3, GFAP and AQP4 expression. LM images showed edematous Müller cell endfeet, and also degenerated photoreceptor layer; however, protective effect of Hsp was seen on Müller cell processes and photoreceptors. TEM study showed increased basement membrane (BM) thickness in diabetic retina, while relatively thin BM was recorded in Hsp-treated retina. It can be postulated that dietary flavanoids, like Hsp, can be effective for the prevention of diabetes induced neurovascular complications such as diabetic retinopathy.

Nuclear factor (erythroid-derived 2)-like 2 (NFE2L2) is a novel therapeutic target for diabetic complications

Diabetes is a leading cause of death and disability. In 2004, 3.4 million people worldwide died of symptoms relating to high blood sugar. Diabetic complications are caused by organ damage resulting from long-term exposure to high blood sugar, and include diseases such as heart failure, kidney failure, vision loss and neuropathy. The transcription factor nuclear factor (erythroid-derived 2)-like 2 (NFE2L2, also known as NRF2) is an important component of the intracellular antioxidant machinery and a target for treatment of diabetic complications. This article reviews the role of NFE2L2 in diabetic complications with a focus on diabetic nephropathy, cardiomyopathy, neuropathy and retinopathy. Activation of NFE2L2 protects against oxidative stress in vitro and in vivo, and represents an important target for prophylaxis and treatment of diabetic complications. NFE2L2 has potential clinical applications for diabetic patients in the near future.

Age related changes in lipid peroxidation and antioxidants in elderly people

Advanced age is associated with an accumulation of free radical damage, which leads to physiological and clinical modifications. Age related changes resulting from free radical reactions include increasing levels of lipid peroxides, alterations in enzyme activities and greater osmotic fragility. The present study was conducted to estimate the level of lipid peroxidation product-Malondialdehyde and antioxidants Catalase and Glutathione in elderly people. An increase in lipid peroxidation and decrease in antioxidants was observed in normal elderly people. Highly significant increase in MDA and decrease in antioxidants was observed in elderly people when complicated with diabetes and hypertension. Supplementation of antioxidants may prevent further oxidative injury in elderly people.

High concentrations of AGE-LDL and oxidized LDL in circulating immune complexes are associated with progression of retinopathy in type 1 diabetes

OBJECTIVE

To determine whether immunocomplexes (ICs) containing advanced glycation end product (AGE)-LDL (AGE-LDL) and oxidized LDL (oxLDL) contribute to the development of retinopathy over a 16-year period in subjects with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Levels of AGE-LDL and oxLDL in ICs were measured in 517 patients of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) cohort. Retinopathy was assessed by stereoscopic fundus photography. Cox proportional hazards models were used to assess the effect of AGE-LDL-ICs and oxLDL-ICs on retinopathy progression.

RESULTS

In unadjusted models, higher baseline levels of AGE-LDL-ICs and oxLDL-ICs significantly predicted progression of diabetic retinopathy outcomes. After adjustment by study-design variables (treatment group, retinopathy cohort, duration of type 1 diabetes, and baseline albumin excretion rate [AER], hemoglobin A(1c) (HbA(1c)), and Early Treatment Diabetic Retinopathy Study [ETDRS] score), one SD increase in IC levels was associated with 47% (hazard ratio [HR] 1.47 [95% CI 1.19-1.81]; AGE-LDL-IC) and 45% (1.45 [1.17-1.80]; oxLDL-IC) increased risk of developing proliferative diabetic retinopathy (PDR) and 37% (1.37 [1.12-1.66]; to both ICs) increased risk of progressing to severe nonproliferative retinopathy. Analyses were stratified by retinopathy cohort because results differed between primary and secondary cohorts. For AGE-LDL-ICs, HR for progression to PDR was 2.38 (95% CI 1.30-4.34) in the primary cohort and attenuated in the secondary cohort (1.29 [1.03-1.62]). Similar results were observed for oxLDL-ICs.

CONCLUSIONS

Increased levels of AGE-LDL and oxLDL in ICs are associated with increased risk for progression to advanced retinopathy in patients with type 1 diabetes, indicating that the antibody response to modified LDL plays a significant role in retinopathy progression.

Effects of hyperglycemia and oxidative stress on the glutamate transporters GLAST and system xc- in mouse retinal Müller glial cells

Elevated glutamate levels have been reported in humans with diabetic retinopathy. Retinal Müller glial cells regulate glutamate levels via the GLAST transporter and system x(c)(-) (cystine-glutamate exchanger). We have investigated whether transporter function and gene and/or protein expression are altered in mouse Müller cells cultured under conditions of hyperglycemia or oxidative stress (two factors implicated in diabetic retinopathy). Cells were subjected to hyperglycemic conditions (35 mM glucose) over an 8-day period or to oxidative stress conditions (induced by exposure to various concentrations of xanthine:xanthine oxidase) for 6 h. The Na(+)-dependent and -independent uptake of [(3)H] glutamate was assessed as a measure of GLAST and system x(c)(-) function, respectively. Hyperglycemia did not alter the uptake of [(3)H] glutamate by GLAST or system x(c)(-); neither gene nor protein expression decreased. Oxidative stress (70:14 or 100:20 microM xanthine:mU/ml xanthine oxidase) decreased GLAST activity by approximately 10% but increased system x(c)(-) activity by 43% and 89%, respectively. Kinetic analysis showed an oxidative-stress-induced change in V(max), but not K(m). Oxidative stress caused a 2.4-fold increase in mRNA encoding xCT, the unique component of system x(c)(-). Of the two isoforms of xCT (40 and 50 kDa), oxidative stress induced a 3.6-fold increase in the 40-kDa form localized to the plasma membrane. This is the first report of the differential expression and localization of xCT isoforms as caused by cellular stress. Increased system x(c)(-) activity in Müller cells subjected to conditions associated with diabetic retinopathy may be beneficial, as this exchanger is important for the synthesis of the antioxidant glutathione.

The effects of taurine, taurine homologs and hypotaurine on cell and membrane antioxidative system alterations caused by type 2 diabetes in rat erythrocytes

This study compared taurine, aminomethanesulfonic acid, homotaurine and hypotaurine for the ability to modify indices of oxidative stress and membrane damage associated with type 2 diabetes. In the study, male Goto-Kakizaki and Wistar-Kyoto rats were allowed free access to a high fat and normal diet, respectively, for 9 weeks. At the end of week 8, half of the animals in each group received a daily intraperitoneal dose of a sulfur compound (0.612 M/kg) for 5 days and, 24 hr after the last treatment, blood samples were withdrawn by cardiac puncture to obtain plasma and erythrocyte fractions for biochemical analyses. Relative to control values, taurine and its congeners reduced membrane damage, the formation of intracellular malondialdehyde and oxidized glutathione, and the decreases in reduced glutathione and antioxidative enzyme activities in diabetic erythrocytes. Except for a few isolated instances, all test compounds were equiprotective.

Role of NADPH oxidase and ANG II in diabetes-induced retinal leukostasis

We studied whether angiotensin II (ANG II) via superoxide may contribute to retinal leukostasis and thus to the pathogenesis of retinopathies. We studied: 1) whether intravitreal ANG II induces retinal leukostasis that is altered by antioxidants or by apocynin, a NAD(P)H oxidase inhibitor and 2) whether retinal leukostasis induced by diabetes in rats is also altered by these treatments. Rats were injected intravitreally with ANG II (20 μg in 2 μl), and divided into the following three groups: 1) untreated; 2) treated with tempol doses (∼3 mM/day) and N-acetylcysteine (NAC; ∼1 g·kg−1·day−1); and 3) treated with apocynin (∼2 mM/day), both in the drinking water. Rats with streptozotocin-induced diabetes were similarly treated. Leukostasis was evaluated 48 h after ANG II or 2 wk after diabetes induction. ANG II increased retinal leukostasis from 0.3 ± 0.5 to 3.7 ± 0.4 leukocytes/ mm2 ( P < 0.01), and these changes were markedly decreased by treatment with tempol + NAC or apocynin, and also by a blocking antibody against vascular endothelial growth factor given intravitreally ( P < 0.01). In addition, incubation of dihydroethidium-loaded retina sections with ANG II caused marked increase in superoxide formation. Compared with normal controls, retinal leukostasis in diabetic rats markedly increased from 0.2 ± 0.3 to 3.8 ± 0.1 leukocytes/mm2 ( P < 0.01). Diabetic retinal leukostasis was also decreased by treatment with tempol-NAC and normalized by apocynin. Thus increases in intravitreal ANG II can induce retinal leukostasis, which appears to be mediated via increasing superoxide generation by NAD(P)H oxidase, and by VEGF. The activity of NAD(P)H oxidase is required for leukostasis to occur in the diabetic retina.

Comparisons between the beneficial effects of different sulphonylurea treatments on ischemia-induced retinal neovascularization

The aim of this study was to assess the potential beneficial effects of gliclazide and other sulphonylureas on ischemia-induced retinal neovascularization. To produce an animal model of oxygen-induced ischemic retinopathy, 7-day-old (P7) mice were exposed to a 75% oxygen environment for 5 days. On their return to ambient air at P12, these mice were then treated with gliclazide, glibenclamide, glimepiride, or N-acetylcysteine. Gliclazide, but not glibenclamide or glimepiride, markedly suppresses retinal neovascularization. N-Acetylcysteine, however, only moderately suppresses retinal neovascularization. The number of neovascular nuclei in the retinal cross sections decreased by 29% in the gliclazide-treated mice (P<0.05 vs control). The induction of VEGF mRNA expression at P13 is significantly suppressed in the gliclazide group, relative to the control group (-44%, P<0.05). The VEGF protein expression levels at P15 were also suppressed in the gliclazide group (-43%, P<0.01). The 8-isoprostane production levels at P15 were suppressed in both the gliclazide group (-20%, P<0.05) and the N-acetylcysteine-treated group (-31%, P<0.01). Gliclazide inhibits ischemia-induced retinal neovascularization, and this is likely to be mediated in part through the downregulation of VEGF and the suppression of oxidative stress.

Bioinformatics analysis of diabetic retinopathy using functional protein sequences

Diabetic retinopathy is the leading cause of blindness among patients with diabetes mellitus. We evaluated the role of several proteins that are likely to be involved in diabetic retinopathy by employing multiple sequence alignment using ClustalW tool and constructed a phylogram tree using functional protein sequences extracted from NCBI. Phylogram was constructed using Neighbor-Joining Algorithm in bioinformatics approach. It was observed that aldose reductase and nitric oxide synthase are closely associated with diabetic retinopathy. It is likely that vascular endothelial growth factor, pro-inflammatory cytokines, advanced glycation end products, and adhesion molecules that also play a role in diabetic retinopathy may do so by modulating the activities of aldose reductase and nitric oxide synthase. These results imply that methods designed to normalize aldose reductase and nitric oxide synthase activities could be of significant benefit in the prevention and treatment of diabetic retinopathy.

The Importance of Serum Lipids in Exudative Diabetic Macular Edema in Type 2 Diabetic Patients

To evaluate the relationship between serum lipid levels and exudative diabetic maculopathy in patients with nonproliferative diabetic retinopathy, 27 patients with exudative diabetic macular edema were included in group A and 27 patients without exudative diabetic macular edema were included in group B. All 54 patients have nonproliferative diabetic retinopathy. Blood cholesterol, triglyceride, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, very low-density lipoprotein (VLDL) cholesterol, hemoglobin A1c (HbA1c), and hemoglobin levels were measured in patients in group A and group B. The mean concentration of cholesterol in group A (224.30 +/- 49.49 mg/dL), in group B (197.78 +/- 41.49 mg/dL); triglyceride in group A (199.11 +/- 90.51 mg/dL), in group B (160.78 +/- 65.30 mg/dL); HDL in group A (43.48 +/- 10.62 mmol/L), in group B (42.37 +/- 10.92 mmol/L); LDL in group A (150.59 +/- 43.96 mg/dL), in group B (124.37 +/- 40.28 mg/dL); VLDL in group A (40.52 +/- 16.54 mg/dL), in group B (37.89 +/- 23.70 mg/dL); HbA1c in group A (9.62 +/- 2.50), in group B (7.36 +/- 1.62 g/dL); and hemoglobin in group A (13.46 +/- 1.6 g/dL), in group B (13.90 +/- 1.77 g/dL). Serum cholesterol (P = 0.38), LDL (P = 0.026), and HbA1c (P = 0.000) levels were different between the two groups. Triglyceride, HDL, VLDL, and hemoglobin levels were not different between the two groups. We must consider regulation of high blood sugar and elevated total serum cholesterol or LDL levels in patients with macular edema and high hard exudates.

Comparison between erythrocyte hemoglobin and spectrin glycosylation and role of oxidative stress in type-2 diabetes mellitus

New findings on organization of blood cell cytoskeleton represent an exciting aspect of modem cell biology and hematology, which is an interesting investigation to study diabetes. The present study was undertaken in 150 subjects. Out of these, 30 subjects were controls (Group I) and 30 were type-2 diabetics without any complication (Group II), while remaining 90 subjects were type-2 diabetics with complication (Group III). We determined erythrocyte spectrin and hemoglobin glycosylation and also estimated plasma lipid peroxide, nitric oxide and erythrocyte glutathione peroxidase activity to assess the status of oxidative stress. There was a significant increase in spectrin (P<0.001) and hemoglobin (P<0.001) glycosylation in Group II and III as compared to Group I and spectrin glycosylation was nearly three times more as compared to hemoglobin, whereas plasma levels of lipid peroxide (P<0.001) as well as nitric oxide (P<0.001) were found to be significantly increased and GPx activity (P<0.001) was significantly decreased in Group II and III as compared to Group I. However, it was also observed that spectrin (P>0.05) and hemoglobin (P>0.05) glycosylation was not significantly different in Group II and III. In contrast, there was significant rise in lipid peroxide (P<0.001), nitric oxide (P<0.001) and fall in GPx activity (P<0.001) in Group III when compared to Group II. Increased erythrocyte protein glycosylation and oxidative stress is clearly evident from our study. However, to understand the exact interplay between these two mechanisms, further studies are required.

Gremlin gene expression in bovine retinal pericytes exposed to elevated glucose

AIM

To assess the influence of high extracellular glucose on the expression of the bone morphogenetic protein (BMP) antagonist, gremlin, in cultured bovine retinal pericytes (BRPC).

METHODS

BRPC were cultured under conditions of 5 mM and 30 mM d-glucose for 7 days and total RNA was isolated. Gremlin mRNA levels were correlated, by RT-PCR, with other genes implicated in the pathogenesis of diabetic retinopathy and the signalling pathways in high glucose induced gremlin expression were probed using physiological inhibitors. Gremlin expression was also examined in the retina of streptozotocin induced diabetic mice.

RESULTS

High glucose stimulated a striking increase in BRPC gremlin mRNA levels in parallel with increases in mRNA for the growth factors vascular endothelial growth factor (VEGF), transforming growth factor beta (TGFbeta), and connective tissue growth factor (CTGF) and changes in other genes including fibronectin and plasminogen activator inhibitor-1 (PAI-1). High glucose triggered gremlin expression was modulated by anti-TGFbeta antibody, by the uncoupler of oxidative phosphorylation, CCCP, and by inhibition of MAP-kinase (MAPK) activation. Striking gremlin expression was observed in the outer retina of diabetic mice and also at the level of the vascular wall.

CONCLUSIONS

Gremlin gene expression is induced in BRPC in response to elevated glucose and in the retina of the streptozotocin induced diabetic mouse. Its expression is modulated by hyperglycaemic induction of the MAPK, reactive oxygen species, and TGFbeta pathways, all of which are reported to have a role in diabetic fibrotic disease. This implicates a role for gremlin in the pathogenesis of diabetic retinopathy.

Antioxidative treatment of pregnant diabetic rats diminishes embryonic dysmorphogenesis

BACKGROUND

Diabetic pregnancy is still associated with an increased rate of congenital malformations despite extensive clinical efforts to normalize the risk for the offspring. The etiology of diabetic embryopathy is not clear; however, experimental studies have suggested a role for oxidative stress in the teratogenicity of diabetic pregnancy. The antioxidants alpha-tocopherol and ascorbate have improved fetal outcome in diabetic rodent pregnancy when supplemented in moderate to high doses. In the present work we investigated if extremely high doses of either alpha-tocopherol or ascorbate might further improve fetal outcome in offspring of diabetic rats and, in addition, if such treatment may exert any adverse effects of fetal development.

METHODS

Nondiabetic and streptozotocin diabetic female rats were fed 2, 5, 10, or 15% alpha-tocopherol or 4, 10, or 15% ascorbate in their diet.

RESULTS

Both alpha-tocopherol and ascorbate treatment improved fetal morphology in offspring of diabetic rats. There was a dose-dependent improvement for the alpha-tocopherol supplementation, in which the higher doses diminished fetal dysmorphogenesis more than the 2% diet. The ascorbate supplementation was less dose-dependent; however, the higher doses tended to improve fetal outcome more than the lower doses. No adverse effects of the antioxidants were noted in the offspring with the exception of 1 case of agnathia in a fetus of a nondiabetic rat supplemented with 15% alpha-tocopherol.

CONCLUSIONS

These results indicate that very high doses of dietary antioxidants may be needed to normalize the development of the offspring in experimental diabetic pregnancy, but that treatment with such high doses may also have adverse effects in nondiabetic pregnancy.

Effects of metabolic control and vascular complications on indices of oxidative stress in type 2 diabetic patients

The direct effect and the interaction of diabetic angiopathy and metabolic control on free radical and antioxidant activity indices was investigated in 48 patients with type 2 diabetes mellitus. Conjugated dienes (CD) and thiobarbituric acid-reacting substances (TBARS) levels were 34 and 178% of control values, respectively. An approximate two-fold decrease in plasma thiols (PSH) and erythrocyte lysate thiols (LSH) concentrations, parameters reflecting protein oxidative damage, was found. Impairment of blood antioxidant potential in diabetic patients was reflected by an 81% increase in superoxide dismutase (SOD) activity, a 30% decrease in catalase (CT), 20% decrease in glutathione peroxidase (GPx) and glutathione reductase (GR) activities as well as by lowered total antioxidant status (TAS). CD, TBARS and SOD values were positively correlated with plasma glucose concentration and glycated hemoglobin level. A negative correlation existed between levels of LSH, PSH, CT, GPx or TAS and both glucose and HbA(1c). Blood glucose control and vascular complications had strong independent effects on prooxidant-antioxidant status, apart from blood glucose and GR activity. In addition, glycemic control and diabetic vasculopathy interact in their influence on most of the free radical and antioxidant indices, except for CD, LSH levels and CT activity. Thus, we observed different mechanisms by which vascular complications and glucose control affect blood free radical indices and antioxidant status parameters in type 2 diabetic patients.

A New Parameter in the Detection of Tuberculosis Activity: Reactive Oxygen Metabolites

BACKGROUND AND OBJECTIVES

In countries with a high frequency of tuberculosis, there are problems not only with active lung tuberculosis but also with past lung tuberculosis. Cases with sequel tuberculosis very frequently present with complaints like tuberculosis, and it is very hard to determine whether it is a sequel tuberculosis complication or reactivation of tuberculosis. In this study, we measured the serum reactive oxygen metabolite (ROM) levels of patients with active pulmonary tuberculosis and healthy controls, and investigated if these metabolites can be used as a criterion for differentiation between active pulmonary tuberculosis and sequel pulmonary tuberculosis.

METHODS

40 patients with active tuberculosis, 35 patients with sequel pulmonary tuberculosis and 30 healthy control subjects with a similar age range and sex distribution were included in the study. Serum total ROM levels were detected in the patients and control group.

RESULTS

Mean serum ROM values were 994+/-236, 551+/-135 and 236+/-59 U/l among active lung tuberculosis cases, sequel lung tuberculosis cases and the healthy control group, respectively. As a result of these findings, serum ROM levels of active lung tuberculosis cases and sequel lung tuberculosis cases were significantly higher than those of the control group (both p<0.001). The serum ROM levels of active lung tuberculosis cases were also significantly higher than those of sequel lung tuberculosis cases (p<0.001).

CONCLUSIONS

In the light of our findings, it may be assumed that serum total ROM values can be used as an activity criterion in the differentiation of active lung tuberculosis and sequel lung tuberculosis.

Combined effect of probucol and insulin on cataracts of diabetic rats fed a high cholesterol diet

We investigated the effects of long-term treatment with probucol, a hypolipidemic agent with antioxidative action, insulin, or their combination on cataracts of streptozotocin-induced diabetic rats fed a high cholesterol diet. Each rat was checked for cataracts at 0, 1, 2, 4, 8, 12 and 15 weeks after streptozotocin injection. Cataracts were observed from 8 weeks in untreated hypercholesterolemic and diabetic rats and the incidence of catarats increased to 100% by 15 weeks. The incidence of cataracts in rats treated with probucol, insulin and their combination was first seen at 12, 12 and 15 weeks, respectively, and was 86%, 63% and 33%, respectively, at 15 weeks. The preventive effects of both agents alone and their combination on the cataracts were confirmed by histopathological evaluation of eyeballs. The combined treatment with both agents markedly improved hyperglycemia, hyperlipidemia and increased serum lipid peroxide levels. These results indicate that the combined treatment with probucol and insulin is useful in preventing the development and progression of diabetic cataracts.

Combined effect of vitamin E and insulin on cataracts of diabetic rats fed a high cholesterol diet

In the present study we investigated the effects of a long-term treatment with vitamin E, an antioxidant vitamin, insulin or their combination on cataracts of streptozotocin (STZ)-induced diabetic rats fed a high cholesterol diet. Each rat was checked for cataracts at 0, 1, 2, 4, 8, 12 and 15 weeks after STZ injection. Cataracts were observed from 8 weeks in the control diabetic rats and their incidence of catarats increased to 100% by 12 weeks. The incidence of cataracts in rats treated with vitamin E, insulin and their combination was first seen at 12 weeks and 56%, 20% and 10%, respectively, at 12 weeks and 78%, 50% and 20%, respectively, at 15 weeks. The preventive effects of either agent alone and their combination on the cataracts were in agreement with those obtained by histopathological evaluation of eyeballs. The combined treatment with both agents markedly improved hyperglycemia, hyperlipidemia and increased serum lipid peroxide levels. These results indicate that the combined treatment with vitamin E and insulin is useful in preventing the development and progression of diabetic cataracts.

Calcium Dobesilate in the Treatment of Diabetic Retinopathy

The incidence of diabetic retinopathy is still increasing in developed countries. Tight glycemic control and laser therapy reduce vision loss and blindness, but do not reverse existing ocular damage and only slow the progression of the disease. New pharmacologic agents that are currently under development and are specifically directed against clearly defined biochemical targets (i.e. aldose reductase inhibitors and protein kinase C-beta inhibitors) have failed to demonstrate significant efficacy in the treatment of diabetic retinopathy in clinical trials. In contrast, calcium dobesilate (2,5-dihydroxybenzenesulfonate), which was discovered more than 40 years ago and is registered for the treatment of diabetic retinopathy in more than 20 countries remains, to our knowledge, the only angioprotective agent that reduces the progression of this disease. An overall review of published studies involving calcium dobesilate (CLS 2210) depicts a rather 'non-specific' compound acting moderately, but significantly, on the various and complex disorders that contribute to diabetic retinopathy. Recent studies have shown that calcium dobesilate is a potent antioxidant, particularly against the highly damaging hydroxyl radical. In addition, it improves diabetic endothelial dysfunction, reduces apoptosis, and slows vascular cell proliferation.