Association of RAGE (p.Gly82Ser) and MnSOD (p.Val16Ala) polymorphisms with diabetic retinopathy in T2DM patients from north India

Genomic profile of diabetic retinopathy in a north indian cohort

BACKGROUND

Diabetic Retinopathy (DR) is one of the major microvascular complications of diabetes. Being a complex disease, it is important to delineate the genetic and environmental factors that influence the susceptibility to DR in a population. Therefore, the present study was designed to investigate the role of genetic and lifestyle risk factors associated with DR susceptibility in a North-Indian population.

METHODS

A total of 848 subjects were enrolled, comprising of DR cases (n = 414) and healthy controls (n = 434). The Sequenom MassARRAY technology was used to perform target genome analysis of 111 SNPs across 57 candidate genes and 14 intergenic region SNPs that are involved in the metabolic pathways associated with type 2 diabetes (T2D) and DR. Allele, genotype and haplotype frequencies were determined and compared among cases and controls. Logistic regression models were used to determine genotype-phenotype and phenotype-phenotype correlations.

RESULTS

The strongest association was observed with TCF7L2 rs12255372 T allele [p < 0.0001; odds ratio (OR) = 1.81 (1.44-2.27)] and rs11196205 C allele [p < 0.0008; OR = 1.62 (1.32-1.99)]. Genotype-phenotype and phenotype-phenotype correlations were found in the present study.

CONCLUSION

Our study provides strong evidence of association between the TCF7L2 variants and DR susceptibility.

Association of candidate genes (ALR2, RAGE, and VEGF) polymorphisms with diabetic retinopathy in type 2 diabetic patients of Khyber Pakhtunkhwa, Pakistan

AIM

To evaluate the aldose reductase (ALR2, rs759853), receptor for advanced glycation end products (RAGE, rs2070600), and vascular endothelial growth factor (VEGF, rs833061) association with diabetic retinopathy in type 2 diabetic patients of Khyber Pakhtunkhwa population.

METHODS

A case-control study was conducted on a total of 550 subjects consisting of 186 with diabetic retinopathy (DR) having type 2 diabetes, 180 had type 2 diabetes (T2DM), and 184 healthy controls (HC). All the samples were subjected to DNA isolation using salting-out method followed by SNP genotyping through Tetra-ARMS PCR. Chi square and Exact Fischer tests were used for alleles and genotypes distribution. Odd ratio and confidence interval values were found out by online software Medcalc Odd ratio Calculator.

RESULTS

Multiple parameters such as random blood sugar (RBS) (p < 0.001), fasting blood sugar (FBS) (p < 0.001), HbA1c (p < 0.001), total cholesterol (p < 0.001), LDL (p < 0.001), HDL (p < 0.001), BMI (p < 0.001) and hypertension (p = 0.018) exhibited strong association with DR as compared to DM and HC. Our results displayed that the VEGF-rs833061 and RAGE- rs2070600 exhibited significant association (p < 0.05) with an increased DR risk, when compared with T2DM. In contrast, ALR2 didn't display association with DR (p > 0.05) when compared with T2DM, but showed association (p < 0.05) when compared with HC.

CONCLUSION

Statistically significant association was observed in VEGF-rs833061 and RAGE-rs2070600 with DR in type 2 diabetic patients. While, ALR2- rs759853 didn't exhibit significant association with DR. This is the first study to report the association of candidate genes (ALR2, VEGF and RAGE) with DR in type 2 diabetes of Khyber Pakhtunkhwa population. More similar research studies are recommended with larger data sets in other ethnicities both national and international.

Unconventional avenues to decelerated diabetic retinopathy

Diabetic retinopathy (DR) is an important microvascular complication of diabetes mellitus (DM), causing significant visual impairment worldwide. Current gold standards for retarding the progress of DR include blood sugar control and regular fundus screening. Despite these measures, the incidence and prevalence of DR and vision-threatening DR remain high. Given its slowly progressive course and long latent period, opportunities to contain or slow DR before it threatens vision must be explored. This narrative review assesses the recently described unconventional strategies to retard DR progression. These include gut-ocular flow, gene therapy, mitochondrial dysfunction-oxidative stress, stem cell therapeutics, neurodegeneration, anti-inflammatory treatments, lifestyle modification, and usage of phytochemicals. These therapies impact DR directly, while some of them also influence DM control. Most of these strategies are currently in the preclinical stage, and clinical evidence remains low. Nevertheless, our review suggests that these approaches have the potential for human use to prevent the progression of DR.

Genetics of Diabetic Retinopathy, a Leading Cause of Irreversible Blindness in the Industrialized World

Diabetic retinopathy (DR) is a chronic complication of diabetes and a leading cause of blindness in the industrialized world. Traditional risk factors, such as glycemic control and duration of diabetes, are unable to explain why some individuals remain protected while others progress to a more severe form of the disease. Differences are also observed in DR heritability as well as the response to anti-vascular endothelial growth factor (VEGF) treatment. This review discusses various aspects of genetics in DR to shed light on DR pathogenesis and treatment. First, we discuss the global burden of DR followed by a discussion on disease pathogenesis as well as the role genetics plays in the prevalence and progression of DR. Subsequently, we provide a review of studies related to DR’s genetic contribution, such as candidate gene studies, linkage studies, and genome-wide association studies (GWAS) as well as other clinical and meta-analysis studies that have identified putative candidate genes. With the advent of newer cutting-edge technologies, identifying the genetic components in DR has played an important role in understanding DR incidence, progression, and response to treatment, thereby developing newer therapeutic targets and therapies.

Concentration/activity of superoxide dismutase isozymes and the pro-/antioxidative status, in context of type 2 diabetes and selected single nucleotide polymorphisms (genes: INS, SOD1, SOD2, SOD3) - Preliminary findings

The alterations in concentration/activity of superoxide dismutase isozymes in the context of type 2 diabetes or obesity are well-described. Moreover, many hereditary factors, including single-nucleotide polymorphisms (SNPs) of genes for coding insulin, insulin receptors, or insulin receptor substrates (INS, INSR, IRS1, IRS2) or superoxide dismutase isozymes (SOD1, SOD2, SOD3), have been linked with the incidence of obesity and diabetes. However, the underlying changes in the plasma concentration/activity of superoxide dismutase isozymes and their potential connection with the said hereditary factors remain unexplored. Previously, we have observed that the plasma concentration/activity of superoxide dismutase isozymes differs in the context of obesity and/or rs2234694 (SOD1) and rs4880 (SOD2) and that the concentrations of SOD1, SOD2, SOD3 are correlated with each other. Intersexual variability of SOD1 concentration was detected regardless of obesity. In this study, the variability of concentration/activity of superoxide dismutase isozymes in plasma is considered in the context of type 2 diabetes and/or SNPs: rs2234694 (SOD1), rs5746105 (SOD2), rs4880 (SOD2), rs927450 (SOD2), rs8192287 (SOD3). Genotypic variability of SNP rs3842729 (INS), previously studied in the context of insulin-dependent diabetes, is investigated in terms of selected clinical parameters associated with type 2 diabetes. This study revealed higher SOD1 concentration in diabetic men compared to women, and extremely high SOD1 concentration, higher total superoxide dismutase, and copper-zinc superoxide dismutase activity, and lower superoxide dismutase and copper-zinc superoxide dismutase activity (when adjusted for the concentration of SODs) in the diabetic group regardless of sex. Multiple logistic regression, applied to explore possible links between the studied SNPs and other factors with the odds of type 2 diabetes or obesity, revealed that the genotypic variability of rs4880 (SOD2) could affect these odds, supporting the findings of several other studies.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

Association of candidate gene polymorphisms with diabetic retinopathy in Chinese patients with type 2 diabetes

AIM

To investigate the association between a set of six candidate genes and the risk of diabetic retinopathy (DR) in an urban community cohort of Chinese patients with type 2 diabetes mellitus (T2DM).

METHODS

A population-based cross-sectional study. The diabetic subjects were recruited from an urban community in Beijing and categorized into groups of proliferative diabetic retinopathy (PDR), non-proliferative diabetic retinopathy (NPDR), or diabetic without any retinopathy (DWR) based on the fundus photography and duration of diabetes. Six candidate genes, including advanced glycation end product specific receptor (AGER), aldose reductase (AKR1B1), inducible nitric oxide synthase (iNOS), pigment epithelium derived factor (PEDF), tumor necrosis factor-alpha (TNF-α), and paraoxonase 1 (PON1), were chosen based on Meta-analysis of genetic association studies for DR and biochemical pathways implicated in DR progression. The allele and genotype distribution of 21 functional single-nucleotide polymorphisms (SNPs) in those 6 candidate genes were investigated using MassARRAY genotyping system.

RESULTS

Among 1461 diabetic patients recruited from community, 569 were selected in following genotyping analysis, including 97 patients with PDR, 217 with NPDR, and 255 with DWR. For the promoter variant rs1051993 in AGER gene, the distribution of allele and genotype in PDR group differed from that in DWR group (allele: P=0.011; genotype: P=0.01). Compared with DWR, patients with PDR had lower frequencies of heterozygous genotype GT (9.8% for DWR, 1% for PDR, OR: 0.10, 95%CI: 0.01-0.72) and minor allele T (4.9% for DWR, 0.5% for PDR, OR: 0.10, 95%CI: 0.01-0.75). In multivariate model, the distribution of genotype for rs1051993 in PDR group was significantly different from that in DWR group (GT vs GG: OR: 0.07, 95%CI: 0.01-0.61, P<0.001). No association with DR was observed in other genotyped SNPs.

CONCLUSION

The data suggest a significant association of the promoter variant rs1051993 in AGER gene with PDR in Chinese cohort with T2DM.

Oxidative Stress as the Main Target in Diabetic Retinopathy Pathophysiology

Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus (DM) causing vision impairment even at young ages. There are numerous mechanisms involved in its development such as inflammation and cellular degeneration leading to endothelial and neural damage. These mechanisms are interlinked thus worsening the diabetic retinopathy outcome. In this review, we propose oxidative stress as the focus point of this complication onset.

Diabetic macular oedema: under-represented in the genetic analysis of diabetic retinopathy

Diabetic retinopathy, a complication of both type 1 and type 2 diabetes, is a complex disease and is one of the leading causes of blindness in adults worldwide. It can be divided into distinct subclasses, one of which is diabetic macular oedema. Diabetic macular oedema can occur at any time in diabetic retinopathy and is the most common cause of vision loss in patients with type 2 diabetes. The purpose of this review is to summarize the large number of genetic association studies that have been performed in cohorts of patients with type 2 diabetes and published in English-language journals up to February 2017. Many of these studies have produced positive associations with gene polymorphisms and diabetic retinopathy. However, this review highlights that within this large body of work, studies specifically addressing a genetic association with diabetic macular oedema, although present, are vastly under-represented. We also highlight that many of the studies have small patient numbers and that meta-analyses often inappropriately combine patient data sets. We conclude that there will continue to be conflicting results and no meaningful findings will be achieved if the historical approach of combining all diabetic retinopathy disease states within patient cohorts continues in future studies. This review also identifies several genes that would be interesting to analyse in large, well-defined cohorts of patients with diabetic macular oedema in future candidate gene association studies.

MnSOD Val16Ala polymorphism associated with retinopathy risk in diabetes: a PRISMA-compliant Meta-analysis of case-control studies

AIM

To investigate the association of Manganese superoxide dismutase (MnSOD) Val16Ala polymorphism with diabetic retinopathy (DR).

METHODS

PubMed, Embase, China National Knowledge Infrastructure, and Wanfang databases were searched. The pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to evaluate the strength of the association. Subgroup, sensitivity, and cumulative analyses were performed. Publication bias was also analyzed.

RESULTS

Eight studies were included in the pooled analysis. The MnSOD Val16Ala polymorphism was associated with the risk of DR under the dominant model (OR=0.66, 95%CI=0.48-0.91, P<0.0001), this result was demonstrated to be relatively stable in cumulative analysis. No significant publication bias was found. This polymorphism was also associated with the risk of DR in Caucasians under the dominant model (OR=0.64, 95%CI=0.42-0.97, P=0.04,) and in Asians under the recessive model (OR=0.31, 95%CI=0.11-0.88, P=0.03).

CONCLUSION

These findings suggest that the MnSOD Val16Ala polymorphism is a risk factor for DR, and that more attention should be paid to carriers of these susceptibility genes.

Candidate gene studies of diabetic retinopathy in human

Diabetic retinopathy (DR) is a multifactorial disease with complex pathophysiology. It is the main cause of blindness among the people in productive age. The purpose of this literature review is to highlight recent achievements in the genetics of diabetic retinopathy with particular focus on candidate gene studies. We summarized most of the available published data about candidate genes for diabetic retinopathy with the goal to identify main genetic aspects. We conclude that genetic studies reported contradictory findings and no genetic variants meet criteria of a diagnostic marker, or significantly elucidate the root of DR development. Based on these findings it is important to continue with the research in the field of DR genetics, mainly due to the fact that currently new possibilities and approaches associated with utilization of next-generation sequencing are available.

Association of genetic variants in the receptor for advanced glycation end products gene with diabetic retinopathy: A meta-analysis

BACKGROUND

Diabetic retinopathy (DR) is a major sight-threatening diabetic complication. Previous studies have examined the association of DR with multiple genetic variants in the receptor for advanced glycation end products (RAGE) gene, with inconsistent results.

OBJECTIVE

To perform a systematic literature search and conduct meta-analyses to examine the association of genetic variants in RAGE with DR.

DATA SOURCES

PubMed, Cochrane Library, Embase, Google Scholar, and HuGE.

STUDY ELIGIBILITY CRITERIA AND PARTICIPANTS

Studies were on human subjects; the studies were case-control ones and included subjects who had DR and those who did not have DR; and the studies provided genotype data for genetic variants in RAGE, separately for subjects who had and did not have DR, or provided odds ratios (ORs) and the 95% confidence intervals (CIs), or provided sufficient data for the calculation of OR and the 95% CI.

STUDY APPRAISAL AND SYNTHESIS METHODS

We used OR as a measure of association, and used random-effects model in all the meta-analyses. Between-study heterogeneity was assessed using I, and publication bias was evaluated using Egger test.

RESULTS

A total of 13 studies met the eligibility criteria and were included in our analyses. We found that Gly82Ser was significantly associated with DR (OR = 2.40, 95% CI: 1.46-3.97; P = 0.001) using a recessive model. -374T/A also showed significant association with DR under a dominant model (OR = 1.21, 95% CI: 1.03-1.43; P = 0.023). We did not find a significant association of DR with other genetic variants in RAGE.

LIMITATIONS

The number of included studies is small for some genetic variants; duration of diabetes varied across studies; most studies were conducted in Asia; and it is not clear whether the observed association can be generalized to other ethnicities; and we could not control for other potential confounding factors.

CONCLUSIONS AND IMPLICATIONS OF KEY FINDINGS

We found that Gly82Ser in RAGE showed significant association with DR. More studies with larger sample sizes that control for important risk factors, such as duration of diabetes, are needed to validate our findings.

Polymorphism 2184A/G in the AGER gene is not associated with diabetic retinopathy in Han Chinese patients with type 2 diabetes

OBJECTIVE

To assess the association between the 2184A/G polymorphism in the advanced glycosylation end product-specific receptor (AGER) gene and the susceptibility to diabetic retinopathy (DR) in Han Chinese patients with type 2 diabetes mellitus (T2DM).

METHODS

This cross-sectional genotyping study included patients with T2DM with and without DR. Genotype and allele frequencies of the 2184A/G polymorphism were detected using polymerase chain reaction-restriction fragment-length polymorphism analysis.

RESULTS

This study included 943 patients with T2DM (285 with DR [DR group] and 658 without DR [NDR group]). There were no significant differences in age, sex, body mass index, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, diastolic blood pressure, glycosylated haemoglobin, fasting blood glucose, postprandial 2-hour blood glucose, and triglycerides between the two groups. The duration of T2DM and systolic blood pressure were significantly increased in the DR group compared with the NDR group. No significant differences were found in allele (A and G) and genotype (AA, AG and GG) frequencies of the 2184A/G polymorphism between the two groups.

CONCLUSION

The 2184A/G polymorphism in the AGER gene is not associated with DR in Han Chinese patients with T2DM.

Update on genetics and diabetic retinopathy

Clinical risk factors for diabetic retinopathy (DR), such as duration of disease and degree of glucose control, do not adequately predict disease progression in individual patients, suggesting the presence of a genetic component. Multiple smaller studies have investigated genotype–phenotype correlations in genes encoding vascular endothelial growth factor, aldose reductase, the receptor for advanced glycation end products, and many others. In general, reported results have been conflicting, due to factors including small sample sizes, variations in study design, differences in clinical end points, and underlying genetic differences between study groups. At this time, there is no confirmed association with any risk allele reported. As we continue to collect data from additional studies, the role of genetics in DR may become more apparent.