Molecular mechanisms of diabetic retinopathy, general preventive strategies, and novel therapeutic targets

The growing number of people with diabetes worldwide suggests that diabetic retinopathy (DR) and diabetic macular edema (DME) will continue to be sight threatening factors. The pathogenesis of diabetic retinopathy is a widespread cause of visual impairment in the world and a range of hyperglycemia-linked pathways have been implicated in the initiation and progression of this condition. Despite understanding the polyol pathway flux, activation of protein kinase C (KPC) isoforms, increased hexosamine pathway flux, and increased advanced glycation end-product (AGE) formation, pathogenic mechanisms underlying diabetes induced vision loss are not fully understood. The purpose of this paper is to review molecular mechanisms that regulate cell survival and apoptosis of retinal cells and discuss new and exciting therapeutic targets with comparison to the old and inefficient preventive strategies. This review highlights the recent advancements in understanding hyperglycemia-induced biochemical and molecular alterations, systemic metabolic factors, and aberrant activation of signaling cascades that ultimately lead to activation of a number of transcription factors causing functional and structural damage to retinal cells. It also reviews the established interventions and emerging molecular targets to avert diabetic retinopathy and its associated risk factors.

Differential expression and role of hyperglycemia induced oxidative stress in epigenetic regulation of β1, β2 and β3-adrenergic receptors in retinal endothelial cells

BACKGROUND

Aberrant epigenetic profiles are concomitant with a spectrum of developmental defects and diseases. Role of methylation is an increasingly accepted factor in the pathophysiology of diabetes and its associated complications. This study aims to examine the correlation between oxidative stress and methylation of β1, β2 and β3-adrenergic receptors and to analyze the differential variability in the expression of these genes under hyperglycemic conditions.

METHODS

Human retinal endothelial cells were cultured in CSC complete medium in normal (5 mM) or high (25 mM) glucose to mimic a diabetic condition. Reverse transcription PCR and Western Blotting were performed to examine the expression of β1, β2 and β3-adrenergic receptors. For detections, immunocytochemistry was used. Bisulfite sequencing method was used for promoter methylation analysis. Apoptosis was determined by the terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. Dichlorodihydrofluorescein diacetate (DCFH-DA) assay was used to measure reactive oxygen species (ROS) production in the cells.

RESULTS

β1 and β3-adrenergic receptors were expressed in retinal endothelial cells while β2-adrenergic receptor was not detectable both at protein and mRNA levels. Hyperglycemia had no significant effect on β1 and β2-adrenergic receptors methylation and expression however β3-adrenergic receptors showed a significantly higher expression (p < 0.05) and methylation (p < 0.01) in high and low glucose concentration respectively. Apoptosis and oxidative stress were inversely correlated with β3-adrenergic receptors methylation with no significant effect on β1 and β2-adrenergic receptors. β2-adrenergic receptor was hypermethylated with halted expression.

CONCLUSION

Our study demonstrates that β1 and β3-adrenergic receptors expressed in human retinal endothelial cells. Oxidative stress and apoptosis are inversely proportional to the extent of promoter methylation, suggesting that methylation loss might be due to oxidative stress-induced DNA damage.

Glutamine treatment attenuates hyperglycemia-induced mitochondrial stress and apoptosis in umbilical vein endothelial cells

OBJECTIVE

The aim of this study was to determine the in vitro effect of glutamine and insulin on apoptosis, mitochondrial membrane potential, cell permeability, and inflammatory cytokines in hyperglycemic umbilical vein endothelial cells.

MATERIALS AND METHODS

Human umbilical vein endothelial cells were grown and subjected to glutamine and insulin to examine the effects of these agents on the hyperglycemic state. Mitochondrial function and the production of inflammatory cytokines were assessed using fluorescence analysis and multiple cytotoxicity assays. Apoptosis was analyzed by the terminal deoxynucleotidyl transferase dUTP nick end-labeling assay.

RESULTS

Glutamine maintains the integrity of the mitochondria by reducing the cell permeability and cytochrome c levels and increasing the mitochondrial membrane potential. The cytochrome c level was significantly (p<0.005) reduced when the cells were treated with glutamine. An apoptosis assay revealed significantly reduced apoptosis (p<0.005) in the glutamine-treated cells. Moreover, glutamine alone or in combination with insulin modulated inflammatory cytokine levels. Interleukin-10, interleukin-6, and vascular endothelial growth factor were up-regulated while tumor necrosis factor-α was down-regulated after treatment with glutamine.

CONCLUSION

Glutamine, either alone or in combination with insulin, can positively modulate the mitochondrial stress and cell permeability in umbilical vein endothelial cells. Glutamine regulates the expression of inflammatory cytokines and maintains the balance of the mitochondria in a cytoprotective manner.

Molecular study of HCV detection, genotypes and their routes of transmission in North West Frontier Province, Pakistan

OBJECTIVE

To determine hepatitis C virus (HCV) genotypes and explore the associated risk factors in chronic HCV patients.

METHODS

A total of 116 patients with chronic hepatitis C were subjected to polymerase chain reaction (PCR) based detection out of which 112 chronic HCV patients [53 male (47.32%), 59 female (52.68%); mean age (43.76±16.40) years; mean BMI (23.8±3.9) kg] were enrolled in this study. The frequency of 6 HCV genotypes and associated risk factors were evaluated from five districts of North West Frontier Province (NWFP).

RESULTS

Genotype 3 was the most prevalent in 73 samples (65.17%) followed by genotype 1 in 24 (21.42%) and genotype 2 in 13 (11.60%) samples. Genotype 3 had significantly high prevalence (P=0.000 2). The results showed that 48 (42.85%) samples were infected with HCV 3a; 25 (22.32%) with 3b; 14 (12.50%) with 1a; 10 (8.92%) with 1b; 11 (9.82%) with 2a; 2 (1.78%) with 2b; and 2 were untypable. The distribution of HCV genotypes in Mardan, Charsadda, Peshawar, Sawabi and Nowshehra districts was different. Use of unsterile equipment for medication, barbers and previous history of hospitalization were the main risk factors for HCV transmission.

CONCLUSIONS

Genotype 3a and 3b, 1a, 1b and 2a are the common genotypes in NWFP. Genotype 4, 5, and 6 can not be found in a single sample. The level of awareness about various modes of transmission of HCV among the population is found to be very low.

Gelam Honey Attenuates the Oxidative Stress-Induced Inflammatory Pathways in Pancreatic Hamster Cells

Purpose. Type 2 diabetes consists of progressive hyperglycemia and insulin resistance, which could result from glucose toxicity, inflammatory cytokines, and oxidative stress. In the present study we investigated the effect of Gelam honey and quercetin on the oxidative stress-induced inflammatory pathways and the proinflammatory cytokines. Methods. HIT-T15 cells were cultured and preincubated with the extract of Gelam honey (20, 40, 60, and 80 μg/mL), as well as quercetin (20, 40, 60, and 80 μM), prior to stimulation by 20 and 50 mM glucose. Results. HIT-T15 cells cultured under hyperglycemic condition showed a significant increase in the inflammatory pathways by phosphorylating JNK, IKK-β, and IRS-1 at Ser307 (p < 0.05). There was a significant decrease in the phosphorylation of Akt at Ser473 (p < 0.05). Pretreatment with Gelam honey and quercetin reduced the expression of phosphorylated JNK, IKK-β, and IRS-1, thereby significantly reducing the expression of proinflammatory cytokines like TNF-α, IL-6, and IL-1β (p < 0.05). At the same time there was a significant increase in the phosphorylated Akt showing the protective effects against inflammation and insulin resistance (p < 0.05). In conclusion, our data suggest the potential use of the extract from Gelam honey and quercetin in modulating the inflammation induced insulin signaling pathways.

Hyperglycemia-induced oxidative stress and epigenetic regulation of ET-1 gene in endothelial cells

Introduction: Hyperglycemia-induced endothelial dysfunction and the subsequent increase of oxidative stress could lead to aberrant regulation of various genes which are responsible for a range of functions. This study aims to find out how hyperglycemia affect oxidative stress and then the expression and methylation of endothelin 1 (ET-1) gene in in human umbilical vein endothelial cells (HUVEC). Methods: Cells were cultured in growth medium and exposed to low and high glucose concentrations to mimic normal and diabetic condition respectively. Computational analysis were performed using UCSC genome browser and eukaryotic promoter database (EPD). The expression of ET-1 gene was investigated by real time PCR. Cytotoxicity and oxidative stress were determined by MTT and DCFH-DA assays respectively. Promoter methylation was assessed by the bisulfite sequencing method. Results: DCFH-DA assay showed that hyperglycemia can significantly increase the regulation of reactive oxygen species synthesis. The relative expression of ET-1 gene was increased due to exposure to high glucose concentration. MTT assay revealed reduced viability of cells due to the glucose induced damage. Methylation analysis revealed hypomethylation of the promoter of ET-1 however the difference was not significant. Out of 175 CpGs at 25 CpG sites, only 36 CpGs were methylated (20.5% methylation) in cell treated with normal glucose. Upon exposure to high glucose only 30 CpGs were methylated in 175 CpGs at 25 CpG sites (17.1% methylation). Discussion: Our study concludes a significantly high expression of ET-1 gene in response to high glucose exposure in HUVECs. It also reports that hyperglycemic condition leads to elevated oxidative stress. No significant change was found in methylation when cells were treated with high and low glucose concentrations.

Heparin-Loaded Alginate Hydrogels: Characterization and Molecular Mechanisms of Their Angiogenic and Anti-Microbial Potential

Background: Chronic wounds continue to be a global concern that demands substantial resources from the healthcare system. The process of cutaneous wound healing is complex, involving inflammation, blood clotting, angiogenesis, migration and remodeling. In the present study, commercially available alginate wound dressings were loaded with heparin. The purpose of the study was to enhance the angiogenic potential of alginate wound dressings and analyze the antibacterial activity, biocompatibility and other relevant properties. We also aimed to conduct some molecular and gene expression studies to elaborate on the mechanisms through which heparin induces angiogenesis. Methods: The physical properties of the hydrogels were evaluated by Fourier transform infrared spectroscopy (FTIR). Swelling ability was measured by soaking hydrogels in the Phosphate buffer at 37 °C, and cell studies were conducted to evaluate the cytotoxicity and biocompatibility of hydrogels in NIH3T3 (fibroblasts). Real-time PCR was conducted to check the molecular mechanisms of heparin/alginate-induced angiogenesis. The physical properties of the hydrogels were evaluated by Fourier transform infrared spectroscopy (FTIR). Results: FTIR confirmed the formation of heparin-loaded alginate wound dressing and the compatibility of both heparin and alginate. Among all, 10 µg/mL concentration of heparin showed the best antibacterial activity against E. coli. The swelling was considerably increased up to 1500% within 1 h. Alamar Blue assay revealed no cytotoxic effect on NIH3T3. Heparin showed good anti-microbial properties and inhibited the growth of E. coli in zones with a diameter of 18 mm. The expression analysis suggested that heparin probably exerts its pro-angiogenetic effect through VEGF and cPGE. Conclusions: We report that heparin-loaded alginate dressings are not cytotoxic and offer increased angiogenic and anti-bacterial potential. The angiogenesis is apparently taken through the VEGF pathway.

Stimulation of β-adrenergic receptors plays a protective role via increased expression of RAF-1 and PDX-1 in hyperglycemic rat pancreatic islet (RIN-m5F) cells

INTRODUCTION

It is a widely held view that a progressive reduction of beta-cell mass occurs in the progression of diabetes. RAF-1 kinase and pancreas duodenal homeobox 1 (PDX-1) are major factors that promote survival of cells and maintain normal insulin functions. In this study we investigated the effect of a β-adrenergic receptor agonist and antagonist on RAF-1 and PDX-1, and their respective effects on apoptosis and insulin release in RIN-m5F cells.

MATERIAL AND METHODS

RIN-m5F cells were cultured in normal (5 mM) and high (25 mM) glucose to mimic diabetic conditions, followed by treatment with 5 µM, 10 µM and 20 µM of isoproterenol and isoproterenol + propranolol for 6, 12 and 24 h. Western blotting and reverse transcription analysis were performed to examine the expression of RAF-1 and PDX-1. Annexin-V-FITC and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assays were used to investigate apoptosis. ELISA was used to measure insulin levels. Reverse transcription polymerase chain reaction was conducted to investigate the expression of genes.

RESULTS

Stimulation of β-adrenergic receptors with isoproterenol significantly induced RAF-1 and PDX-1 genes in a concentration-dependent and time-independent manner. Changes were significant both at protein and mRNA levels. Up-regulation of RAF-1 and PDX-1 was accompanied by improved insulin levels and reduced apoptosis. Concentrations of 10 µM and 20 µM for 12 and 24 h were more effective in achieving significant differences in the experimental and control groups. Propranolol reversed the effect of isoproterenol mostly at maximum concentrations and time periods.

CONCLUSIONS

A positive effect of a β-adrenergic agonist on RAF-1 and PDX-1, reduction in β-cell apoptosis and improved insulin contents can help to understand the pathogenesis of diabetes and to develop novel approaches for the β-cell dysfunction in diabetes.

Long-Term Impact of Multiple Micronutrient Supplementation on Micronutrient Status, Hemoglobin Level, and Growth in Children 24 to 59 Months of Age: A Non-Randomized Community-Based Trial from Pakistan

Cost-effective interventions are needed to address undernutrition, particularly micronutrient deficiencies, which are common in children under the age of five in low- and middle-income countries. A community-based, non-randomized clinical trial was undertaken in the Kurram district of Khyber Pakhtunkhwa from January 2018 to June 2019, to evaluate the effect of locally produced micronutrient powder (local name: Vita-Mixe) on plasma micronutrient status, hemoglobin level, and anthropometric outcomes. Children aged 24-48 months old were recruited and allocated to the intervention and control arm of the study. The enrolled children in the intervention arm received one micronutrient powder (MNP) sachet for consumption on alternate days for 12 months. To assess the impact of the intervention on plasma levels of zinc, vitamin D, vitamin A, and hemoglobin level, blood samples were taken at baseline and after one year following the intervention. The analysis was conducted using Enzyme-Linked Immunosorbent Assay (ELISA), atomic absorption spectrometry, and an automated hematology analyzer. For the impact on growth parameters, the anthropometric assessment was performed using WHO standard guidelines. A 24 h dietary recall interview was used to assess the nutrient intake adequacy. Results showed that in the intervention arm, children had on average a 7.52 ng/mL (95% CI 5.11-9.92, p-value < 0.001) increase in the plasma level of vitamin A, 4.80 ng/mL (95% CI 1.63-7.95, p-value < 0.002) increase in vitamin D levels and 33.85 µg/dL (95% CI 24.40-43.30, p-value < 0.001) increase in the plasma zinc level, as well as a 2.0g/dL (95% CI 1.64-2.40, p-value < 0.001) increase in hemoglobin level. Statistically significant improvement was observed in the weight-for-height z-score (WHZ) (from -1.0 ± 0.88 to -0.40 ± 1.01, p < 0.001) and weight-for-age z-score (WAZ) (from -1.40 ± 0.50 to -1.05 ± 0.49, p < 0.001) in the intervention group compared to the control group. No statistically significant change was observed in the height-for-age z-score (HAZ) in the intervention group (p = 0.93). In conclusion, micronutrient powder supplementation is a cost-effective intervention to improve the micronutrient status, hemoglobin level, and growth parameters in under-five children, which can be scaled up in the existing health system to address the alarming rates of undernutrition in Pakistan and other developing countries.