Risk of advanced diabetic nephropathy in type 1 diabetes is associated with endothelial nitric oxide synthase gene polymorphism

Evaluation of Sechium edule fruit attenuation impact on the cardiomyopathy of the STZ-induced diabetic rats

Sechium edule, commonly known as chayote is known for its low glycemic index, high fiber content, and rich nutritional profile, which suggests it may be beneficial for individuals with diabetes. While research specifically examining the impact of chayote on diabetes is limited, this study screened its biological impacts by using different biomarkers on streptozotocin-induced diabetic (STZ-ID) rats. The ethanolic extract of the Sechium edule fruits was assessed for different phytochemical, biochemical, and anti-diabetic properties. In the results, chayote extract had high phenolic and flavonoid contents respectively (39.25 ± 0.65 mg/mL and 12.16 ± 0.50 mg/mL). These high phenolic and flavonoid contents showed high implications on STZ-ID rats. Altogether 200 and 400 mg/kg of the extract considerably reduced the blood sugar level and enhanced the lipid profile of the STZ-ID rats. Additionally, they have decreased blood urea and serum creatinine levels. Besides, the levels of SGOT, SGPT, LDH, sodium, and potassium ions were significantly lowered after the administration period. More importantly, the electrocardiogram (ECG) parameters such as QT, RR, and QTc which were prolonged in the diabetic rats were downregulated after 35 days of administration of S. edule extract (400 mg/kg). And, the histological examination of the pancreas and kidney showed marked improvement in structural features of 200 and 400 mg/kg groups when compared to the diabetic control group. Where the increase in the glucose levels was positively correlated with QT, RR, and QTc (r2 = 0.76, r2 = 0.76, and r2 = 0.43) which means that ECG could significantly reflect the diabetes glucose levels. In conclusion, our findings showed that the fruit extract exerts a high potential to reduce artifacts secondary to diabetes which can be strongly suggested for diabetic candidates. However, there is a need to study the molecular mechanisms of the extract in combating artifacts secondary to diabetes in experimental animals.

Associations between the polymorphisms of main components in PI3K/Akt pathway and risk of diabetic kidney disease: A meta-analysis

AIMS

Diabetic kidney disease (DKD) is a severe microvascular complication frequently associated with type 1 and type 2 diabetes mellitus. The objective of this work was to evaluate the relevance of PI3K/Akt pathway polymorphisms and DKD susceptibility by a meta-analysis.

METHODS

Case-control studies related to the relationship between PI3K/Akt pathway polymorphisms and DKD risk were searched from Pubmed, Embase, Cochrane Library, SINOMED, CNKI, and Wanfang databases. Statistical analysis and heterogeneity test were conducted by Review Manager 5.4.

RESULTS

Totally, 52 eligible studies were enrolled, including seven single nucleotide polymorphisms (SNPs) for four genes in the PI3K/AKT pathway (GNB3: rs5443; eNOS: rs1799983, rs869109213, rs2070744; IL-6: rs1800795, rs1800796; TNFα: rs1800629). The "M" allele of eNOS rs1799983 was related to the increased risk of DKD under random effects model, especially in Asian population (Overall:M vs. W: I2  = 75%, OR = 1.29, 95%CI 1.07-1.56; MM + WM vs. WW: I2  = 75%, OR = 1.50, 95%CI 1.21-1.86). The "M" allele of eNOS rs869109213 was implicated with higher prevalence of DKD under random effects model, especially in Asian population (Overall:M vs. W: I2  = 63%, OR = 1.43, 95%CI 1.22-1.68; MM + WM vs. WW: I2  = 50%, OR = 1.36, 95%CI 1.16-1.58; MM vs. WM + WW: I2  = 59%, OR = 2.20, 95%CI 1.41-3.43). The "M" allele of eNOS rs2070744 was implicated with higher prevalence of DKD under random effects model, especially in Indian population (Overall: M vs. W: I2  = 47%, OR = 1.35, 95%CI 1.15-1.59; MM + WM vs. WW: I2  = 45%, OR = 1.32, 95%CI 1.07-1.62; MM vs. WM + WW: I2  = 65%, OR = 2.29, 95%CI 1.39-3.77). The "M" allele of IL-6 rs1800796 was predominately associated with higher DKD risks under random effects model, especially in Asian population (Overall: M versus W: I2  = 23%, OR = 1.49, 95%CI 1.21-1.84; MM + WM vs. WW: I2  = 1%, OR = 1.43, 95%CI 1.15-1.77; MM + WM vs. WW: I2  = 71%, OR = 2.77, 95%CI 1.09-7.06).

CONCLUSIONS

This meta-analysis indicated that polymorphisms in the PI3K/Akt pathway in eNOS rs1799983, rs869109213, rs2070744, and IL-6 rs1800796 were related to the increased risk of DKD.

Diabetic Nephropathy and Gaseous Modulators

Diabetic nephropathy (DN) remains the leading cause of vascular morbidity and mortality in diabetes patients. Despite the progress in understanding the diabetic disease process and advanced management of nephropathy, a number of patients still progress to end-stage renal disease (ESRD). The underlying mechanism still needs to be clarified. Gaseous signaling molecules, so-called gasotransmitters, such as nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), have been shown to play an essential role in the development, progression, and ramification of DN depending on their availability and physiological actions. Although the studies on gasotransmitter regulations of DN are still emerging, the evidence revealed an aberrant level of gasotransmitters in patients with diabetes. In studies, different gasotransmitter donors have been implicated in ameliorating diabetic renal dysfunction. In this perspective, we summarized an overview of the recent advances in the physiological relevance of the gaseous molecules and their multifaceted interaction with other potential factors, such as extracellular matrix (ECM), in the severity modulation of DN. Moreover, the perspective of the present review highlights the possible therapeutic interventions of gasotransmitters in ameliorating this dreaded disease.

Association between the Polymorphisms rs2070744, 4b/a and rs1799983 of the NOS3 Gene with Chronic Kidney Disease of Uncertain or Non-Traditional Etiology in Mexican Patients

Background and Objectives: Chronic Kidney Disease of uncertain or non-traditional etiology (CKDnT) is a form of chronic kidney disease of undetermined etiology (CKDu) and is not associated with traditional risk factors. The aim of this study was to investigate the association of polymorphisms rs2070744, 4b/a and rs1799983 of the NOS3 gene with CKDnT in Mexican patients. Materials and Methods: We included 105 patients with CKDnT and 90 controls. Genotyping was performed by PCR-RFLP's, genotypic and allelic frequencies were determined and compared between the two groups using χ2 analysis, and differences were expressed as odd ratios with 95% confidence intervals (CI). Values of p < 0.05 were considered statistically significant. Results: Overall, 80% of patients were male. The rs1799983 polymorphism in NOS3 was found to be associated with CKDnT in the Mexican population (p = 0.006) (OR = 0.397; 95% CI, 0.192-0.817) under a dominant model. The genotype frequency was significantly different between the CKDnT and control groups (χ2 = 8.298, p = 0.016). Conclusions: The results of this study indicate that there is an association between the rs2070744 polymorphism and CKDnT in the Mexican population. This polymorphism can play an important role in the pathophysiology of CKDnT whenever there is previous endothelial dysfunction.

Metformin Is Associated with the Inhibition of Renal Artery AT1R/ET-1/iNOS Axis in a Rat Model of Diabetic Nephropathy with Suppression of Inflammation and Oxidative Stress and Kidney Injury

Diabetes is the most common cause of end-stage renal disease, also called kidney failure. The link between the renal artery receptor angiotensin II type I (AT1R) and endothelin-1 (ET-1), involved in vasoconstriction, oxidative stress, inflammation and kidney fibrosis (collagen) in diabetes-induced nephropathy with and without metformin incorporation has not been previously studied. Diabetes (type 2) was induced in rats and another group started metformin (200 mg/kg) treatment 2 weeks prior to the induction of diabetes and continued on metformin until being culled at week 12. Diabetes significantly (p < 0.0001) modulated renal artery tissue levels of AT1R, ET-1, inducible nitric oxide synthase (iNOS), endothelial NOS (eNOS), and the advanced glycation end products that were protected by metformin. In addition, diabetes-induced inflammation, oxidative stress, hypertension, ketonuria, mesangial matrix expansion, and kidney collagen were significantly reduced by metformin. A significant correlation between the AT1R/ET-1/iNOS axis, inflammation, fibrosis and glycemia was observed. Thus, diabetes is associated with the augmentation of the renal artery AT1R/ET-1/iNOS axis as well as renal injury and hypertension while being protected by metformin.

Therapeutic potential of pro-resolving mediators in diabetic kidney disease

Renal microvascular disease associated with diabetes [Diabetic kidney disease - DKD] is the leading cause of chronic kidney disease. In DKD, glomerular basement membrane thickening, mesangial expansion, endothelial dysfunction, podocyte cell loss and renal tubule injury contribute to progressive glomerulosclerosis and tubulointerstitial fibrosis. Chronic inflammation is recognized as a major pathogenic mechanism for DKD, with resident and circulating immune cells interacting with local kidney cell populations to provoke an inflammatory response. The onset of inflammation is driven by the release of well described proinflammatory mediators, and this is typically followed by a resolution phase. Inflammation resolution is achieved through the bioactions of endogenous specialized pro-resolving lipid mediators (SPMs). As our understanding of SPMs advances 'resolution pharmacology' based approaches using these molecules are being explored in DKD.

Association of eNOS and MCP-1 Genetic Variants with Type 2 Diabetes and Diabetic Nephropathy Susceptibility: A Case-Control and Meta-Analysis Study

Type 2 diabetes (T2D) and its secondary complications result from the complex interplay of genetic and environmental factors. To understand the role of these factors on disease susceptibility, the present study was conducted to assess the association of eNOS and MCP-1 variants with T2D and diabetic nephropathy (DN) in two ethnically and geographically different cohorts from North India. A total of 1313 subjects from two cohorts were genotyped for eNOS (rs2070744, rs869109213 and rs1799983) and MCP-1 (rs1024611 and rs3917887) variants. Cohort-I (Punjab) comprised 461 T2D cases (204 T2D with DN and 257 T2D without DN) and 315 healthy controls. Cohort-II (Jammu and Kashmir) included 337 T2D (150 T2D with DN and 187 T2D without DN) and 200 controls. Allele, genotype and haplotype frequencies were compared among the studied participants, and phenotype-genotype interactions were determined. Meta-analysis was performed to investigate the association between the selected variants and disease susceptibility. All three eNOS variants were associated with 1.5-4.0-fold risk of DN in both cohorts. MCP-1 rs1024611 conferred twofold risk towards DN progression in cohort-II, while rs3917887 provided twofold risk for both T2D and DN in both cohorts. eNOS and MCP-1 haplotypes conferred risk for T2D and DN susceptibility. Phenotype-genotype interactions showed significant associations between the studied variants and anthropometric and biochemical parameters. In meta-analysis, all eNOS variants conferred risk towards DN progression, whereas no significant association was observed for MCP-1 rs1024611. We show evidences for an association of eNOS and MCP-1 variants with T2D and DN susceptibility.

The glomerular filtration barrier: a structural target for novel kidney therapies

Loss of normal kidney function affects more than 10% of the population and contributes to morbidity and mortality. Kidney diseases are currently treated with immunosuppressive agents, antihypertensives and diuretics with partial but limited success. Most kidney disease is characterized by breakdown of the glomerular filtration barrier (GFB). Specialized podocyte cells maintain the GFB, and structure-function experiments and studies of intercellular communication between the podocytes and other GFB cells, combined with advances from genetics and genomics, have laid the groundwork for a new generation of therapies that directly intervene at the GFB. These include inhibitors of apolipoprotein L1 (APOL1), short transient receptor potential channels (TRPCs), soluble fms-like tyrosine kinase 1 (sFLT1; also known as soluble vascular endothelial growth factor receptor 1), roundabout homologue 2 (ROBO2), endothelin receptor A, soluble urokinase plasminogen activator surface receptor (suPAR) and substrate intermediates for coenzyme Q10 (CoQ₁₀). These molecular targets converge on two key components of GFB biology: mitochondrial function and the actin-myosin contractile machinery. This Review discusses therapies and developments focused on maintaining GFB integrity, and the emerging questions in this evolving field.

Association Between Endothelial Nitric Oxide Synthase (eNOS) -786 T/C and 27-bp VNTR 4b/a Polymorphisms and Preeclampsia Development

The aim of the present study was to analyze the distribution of genotypes and haplotypes of functional eNOS gene polymorphisms in the promoter (-786 T/C), intron 4 (VNTR4b/a) and exon 7 (894 G/T), in Serbian population of pregnant women, and establish a possible association between these polymorphisms and preeclampsia development. DNA was isolated from venous blood samples of 50 heathy pregnant women and 50 preeclampsia patients. Polymerase Chain Reaction/Restriction Fragment Length Polymorphism (PCR/RFLP) technique, with appropriate sets of primers and specific restriction enzymes, was used to determine polymorphisms in eNOS gene. Statistical analysis was done using the SPSS and HAPLOVIEW software packages. eNOS -786 T/C polymorphism was significantly associated with preeclampsia (P = 0.006). Homozygotes for the VNTR polymorphism had also an elevated risk of developing preeclampsia (OR=7.68, 95%CI (0.89-65.98)), especially the mild (OR=9.33, 95%CI (0.98-88.57)) and late form (OR=8.52, 95%CI (0.90-80.58)). The 894 G/T polymorphism was not associated with preeclampsia. "G-C-b" and "T-4a-T" haplotypes were more frequent in preeclampsia, though without reaching statistical significance. -786 T/C and VNTR 4b/a eNOS gene polymorphisms were associated with preeclampsia risk in Serbian patients.

Homoarginine ameliorates diabetic nephropathy independent of nitric oxide synthase-3

Recently we showed that homoarginine supplementation confers kidney protection in diabetic mouse models. In this study we tested whether the protective effect of homoarginine is nitric oxide synthase-3 (NOS3)-independent in diabetic nephropathy (DN). Experiments were conducted in NOS3 deficient (NOS3-/- ) mice and their wild type littermate using multiple low doses of vehicle or streptozotocin and treated with homoarginine via drinking water for 24 weeks. Homoarginine supplementation for 24 weeks in diabetic NOS3-/- mice significantly attenuated albuminuria, increased blood urea nitrogen, histopathological changes and kidney fibrosis, kidney fibrotic markers, and kidney macrophage recruitment compared with vehicle-treated diabetic NOS3-/- mice. Furthermore, homoarginine supplementation restored kidney mitochondrial function following diabetes. Importantly, there were no significant changes in kidney NOS1 or NOS2 mRNA expression between all groups. In addition, homoarginine supplementation improved cardiac function and reduced cardiac fibrosis following diabetes. These data demonstrate that the protective effect of homoarginine is independent of NOS3, which will ultimately change our understanding of the mechanism(s) by which homoarginine induce renal and cardiac protection in DN. Homoarginine protective effect in DN could be mediated via improving mitochondrial function.

Glomerular endothelial cells versus podocytes as the cellular target in diabetic nephropathy

It usually takes several years (in some cases, decades) for predisposed individuals to move from the onset of type 1 or type 2 diabetes to the development of microalbuminuria, the first sign of diabetic nephropathy. This long, complication-free, period represents the best possible moment to start a successful preventive strategy (primary prevention) aimed to avoid or at least to postpone the increase of albumin excretion rate. Prevention is based on understanding and counteracting the initial mechanisms leading to the development of the disease and unfortunately, in case of diabetic nephropathy, most of them remain unclear. Little is also known about which, among endothelial cells and podocytes, represent the first glomerular target of the complication. Selective damage of the endothelium or of the podocyte results, as a common consequence, in an increase of albumin excretion rate. Albuminuria by itself cannot therefore be of help to solve the case. Endothelium and podocytes are involved in a continuous cross-talk and by studying the impact of diabetes on this "communication" process it should be possible to obtain some information regarding the weak component of the glomerular filter. Finally, the careful investigation of the mechanisms leading to the development podocyturia, a recently identified glomerular dysfunction associated to the pathogenesis of diabetic nephropathy, could contribute to shed some more light on the very early stages of this complication.

Cellular and molecular mechanisms of kidney fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. It is considered as the underlying pathological process of chronic kidney disease (CKD), which affects more than 10% of world population and for which treatment options are limited. Renal fibrosis is defined by excessive deposition of extracellular matrix, which disrupts and replaces the functional parenchyma that leads to organ failure. Kidney's histological structure can be divided into three main compartments, all of which can be affected by fibrosis, specifically termed glomerulosclerosis in glomeruli, interstitial fibrosis in tubulointerstitium and arteriosclerosis and perivascular fibrosis in vasculature. In this review, we summarized the different appearance, cellular origin and major emerging processes and mediators of fibrosis in each compartment. We also depicted and discussed the challenges in translation of anti-fibrotic treatment to clinical practice and discuss possible solutions and future directions.

The kallikrein-kinin system in diabetic kidney disease

PURPOSE OF REVIEW

Diabetic kidney disease (DKD) is one of the most common complications in diabetes mellitus and accounts for a large proportion of clinical nephrology practice. Studies have shown that the kallikrein-kinin system (KKS) may be involved in several pathogenic mechanisms that contribute to DKD, including oxidative stress, inflammatory cytokines, and profibrotic autacoids. This review focuses on recent research advance on the potential role of the KKS in the development of DKD and its clinical relevance.

RECENT FINDINGS

A number of recent studies support the idea that there is a protective role of the KKS in diabetes. For example, agents that activate the KKS have shown strong renal protective effects that might highlight its potential to change the clinical practice. In addition, diabetic mice lacking both bradykinin B2 and B1 receptors have worse kidney lesions as compared with wild-type diabetic mice.

SUMMARY

Current basic research has demonstrated that pharmacological activation of the KKS improves renal outcomes in diabetes. These findings suggest that this system may be a therapeutic target in preventing and treating DKD.

Translational science in albuminuria: a new view of de novo albuminuria under chronic RAS suppression

The development of de novo albuminuria during chronic renin–angiotensin system (RAS) suppression is a clinical entity that remains poorly recognized in the biomedical literature. It represents a clear increment in global cardiovascular (CV) and renal risk that cannot be counteracted by RAS suppression. Although not specifically considered, it is clear that this entity is present in most published and ongoing trials dealing with the different forms of CV and renal disease. In this review, we focus on the mechanisms promoting albuminuria, and the predictors and new markers of de novo albuminuria, as well as the potential treatment options to counteract the excretion of albumin. The increase in risk that accompanies de novo albuminuria supports the search for early markers and predictors that will allow practising physicians to assess and prevent the development of de novo albuminuria in their patients.

Comparison of Saliva Nitric Oxide between Chronic Kidney Disease Before and After Dialysis and with Control Group

Introduction:

Chronic Kidney Disease (CKD) is a chronic progressive disorder and a major cause of death and disability in all countries. In the kidneys, Nitric Oxide (NO) has involved in several important cellular processes including glomerular and modular hemodynamics set-out, tubular - glomerular feedback reaction, renin releasing and extracellular fluid volume but NO can act as an inflammatory mediator and oxidative stress factor in high levels.

Aim:

The aim of this study was to evaluate salivary levels of NO in patients with chronic kidney disease on dialysis compared to the healthy subjects and evaluate the effect of dialysis on the level of NO in saliva.

Materials & Methods:

In this case-control study, 30 hemodialysis patients and 30 healthy controls that were matched for age and sex were selected. Unstimulated saliva samples were collected from all subjects. In the patient’s group, half an hour before starting dialysis first sampling and two hours after the completion of dialysis second sampling were collected. NO concentration in the samples was measured by using the Griess method. For data analysis, SPSS software version 16, Mann Whitney-U and Wilcoxon test were used. The level of significance was considered 0.05.

Results:

Mann-Whitney U test showed that the average concentration of salivary NO in patients with CKD (pre-dialysis and after dialysis) was higher than in the control group. The average concentration of salivary NO in patients with CKD was reduced after hemodialysis.

Conclusion:

Hemodialysis reduces salivary NO levels in CKD patients. It seems that hemodialysis has a role in decreasing the concentration of this inflammatory mediator and oxidative stress.

Glomerular Endothelial Cell Stress and Cross-Talk With Podocytes in Early [corrected] Diabetic Kidney Disease

Diabetic kidney disease (DKD) is one of the major causes of morbidity and mortality in diabetic patients and also the leading single cause of end-stage renal disease in the United States. A large proportion of diabetic patients develop DKD and others don't, even with comparable blood glucose levels, indicating a significant genetic component of disease susceptibility. The glomerulus is the primary site of diabetic injury in the kidney, glomerular hypertrophy and podocyte depletion are glomerular hallmarks of progressive DKD, and the degree of podocyte loss correlates with severity of the disease. We know that chronic hyperglycemia contributes to both microvascular and macrovascular complications, as well as podocyte injury. We are beginning to understand the role of glomerular endothelial injury, as well as the involvement of reactive oxygen species and mitochondrial stress, which play a direct role in DKD and in other diabetic complications. There is, however, a gap in our knowledge that links genetic susceptibility to early molecular mechanisms and proteinuria in DKD. Emerging research that explores glomerular cell's specific responses to diabetes and cell cross-talk will provide mechanistic clues that underlie DKD and provide novel avenues for therapeutic intervention.

Acute Kidney Injury and Progression of Diabetic Kidney Disease

Diabetic kidney disease, commonly termed diabetic nephropathy (DN), is the most common cause of end-stage kidney disease (ESKD) worldwide. The characteristic histopathology of DN includes glomerular basement membrane thickening, mesangial expansion, nodular glomerular sclerosis, and tubulointerstitial fibrosis. Diabetes is associated with a number of metabolic derangements, such as reactive oxygen species overproduction, hypoxic state, mitochondrial dysfunction, and inflammation. In the past few decades, our knowledge of DN has advanced considerably although much needs to be learned. The traditional paradigm of glomerulus-centered pathophysiology has expanded to the tubule-interstitium, the immune response and inflammation. Biomarkers of proximal tubule injury have been shown to correlate with DN progression, independent of traditional glomerular injury biomarkers such as albuminuria. In this review, we summarize mechanisms of increased susceptibility to acute kidney injury in diabetes mellitus and the roles played by many kidney cell types to facilitate maladaptive responses leading to chronic and end-stage kidney disease.

The profile of selected single nucleotide polymorphisms in patients with hypertension and heart failure with preserved and mid-range ejection fraction

The study aimed to assess the clinical significance of selected single nucleotide polymorphisms (SNPs) in patients with diastolic heart failure (HF): inflammation [-174 G/C Interleukin -6 (IL-6) rs1800795, tumor necrosis factor (TNF)-608 G/A rs1800629], fibrosis [Arg25Pro transforming growth factor β (TGF β) rs1800471], endothelial function [-786 T/C nitric oxide synthase (NOS) rs2070744], glucose and lipid metabolism [Pro12Ala peroxisome proliferator activated receptor (PPAR)γ rs1801282], and vitamin D metabolism [cytochrome P450 27B1 (CYP27B1) C-1260A].110 patients with HF with preserved and mid-range ejection fraction (HFpEF and HFmrEF) were recruited. GG homozygotes in 174 G/C of IL6 polymorphism are characterized by higher values of estimated glomerular filtration rate based on the study Modification of Diet in Renal Disease (eGFR MDRD) and C allele in the NOS polymorphism and AA profile in C-1260A of CYP27B1 polymorphism correlated with a lower eGFR (MDRD). In multivariate analysis the CG genotype for 174 G/C of IL-6 and allele A in C-1260A of CYP27B1 are the only SNPs independently associated with worse course of HFpEF and HFmrEF. These data confirm the importance of the selected SNPs in aggravation and complications of hypertension.

Association of the nitric oxide synthase (eNOS) gene polymorphism with increased risk for both lupus glomerulonephritis and rheumatoid arthritis in a single genetically homogeneous population

Nitric oxide (NO), a short-lived gaseous free radical, synthesized from L-arginine by NO synthases (NOS), is a potent mediator of biologic responses involved in the pathogenesis of autoimmune rheumatic diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Most biological necessary NO is produced by the family of three NOS. To date, several functionally relevant genetic polymorphisms in the eNOS gene have been associated with various vascular, infectious and autoimmune diseases. To our knowledge, no study has explored these polymorphisms for both SLE and RA in the same population. The objective of this study was to investigate the influence of the eNOS gene intron 4 a/b VNTR polymorphism (a 27-base-pair tandem repeat-based polymorphism) on susceptibility to SLE and RA in patients living in the island of Crete, a genetically homogeneous population. A group of 145 healthy subjects and 190 SLE patients were included in this study. Similarly, a second group of 235 healthy controls and 202 RA patients were analysed. In both cases, patients and controls were sex- and age-matched. Herein we report that the presence of a/b genotype of the eNOS gene may act as a risk factor not for the presence of SLE but for the development of glomerulonephritis (OR 2.71, 95% CI: 1.4—5.2), while it may be a susceptibility gene for RA (OR: 2.005, 95% CI: 1.31—3.07). Thus, in our population, the a/b genotype of the eNOS gene represents a severity rather than a susceptibility genotype for SLE. Lupus (2007) 16, 867—874.

Endothelial Dysfunction in Type 2 Diabetes Mellitus

Endothelial dysfunction is an imbalance in the production of vasodilator factors and when this balance is disrupted, it predisposes the vasculature towards pro-thrombotic and pro-atherogenic effects. This results in vasoconstriction, leukocyte adherence, platelet activation, mitogenesis, pro-oxidation, impaired coagulation and nitric oxide production, vascular inflammation, atherosclerosis and thrombosis. Endothelial dysfunction is focussed as it is a potential contributor to the pathogenesis of vascular disease in diabetes mellitus. Under physiological conditions, there is a balanced release of endothelial-derived relaxing and contracting factors, but this delicate balance is altered in diabetes mellitus and atherosclerosis, thereby contributing to further progression of vascular and end-organ damage. This review focuses on endothelial dysfunction in atherosclerosis, insulin resistance, metabolic syndrome, oxidative stress associated with diabetes mellitus, markers and genetics that are implicated in endothelial dysfunction.

Renal endothelial dysfunction in diabetic nephropathy

Endothelial dysfunction has been posited to play an important role in the pathogenesis of diabetic nephropathy (DN). Due to the heterogeneity of endothelial cells (ECs), it is difficult to generalize about endothelial responses to diabetic stimuli. At present, there are limited techniques fordirectly measuring EC function in vivo, so diagnosis of endothelial disorders still largely depends on indirect assessment of mediators arising from EC injury. In the kidney microcirculation, both afferent and efferent arteries, arterioles and glomerular endothelial cells (GEnC) have all been implicated as targets of diabetic injury. Both hyperglycemia per se, as well as the metabolic consequences of glucose dysregulation, are thought to lead to endothelial cell dysfunction. In this regard, endothelial nitric oxide synthase (eNOS) plays a central role in EC dysfunction. Impaired eNOS activity can occur at numerous levels, including enzyme uncoupling, post-translational modifications, internalization and decreased expression. Reduced nitric oxide (NO) bioavailability exacerbates oxidative stress, further promoting endothelial dysfunction and injury. The injured ECs may then function as active signal transducers of metabolic, hemodynamic and inflammatory factors that modify the function and morphology of the vessel wall and interact with adjacent cells, which may activate a cascade of inflammatory and proliferative and profibrotic responses in progressive DN. Both pharmacological approaches and potential regenerative therapies hold promise for restoration of impaired endothelial cells in diabetic nephropathy.

Research progress in signalling pathway in diabetic nephropathy

Diabetic nephropathy, a lethal diabetic complication, is a leading cause of end-stage renal disease, which is pathologically characterized by thickened tubular basal and glomerular membranes, accumulated extracellular matrix, and progressive mesangial hypertrophy. Growing evidence indicates that diabetic nephropathy is induced by multiple conditions, such as glucose metabolism disorder, oxidative stress, numerous inflammatory factors and cytokines, and haemodynamic changes that lead to the occurrence and development of diabetic nephropathy based on genetic susceptibility. A variety of abnormalities in the signalling pathway may interact to produce these pathologic processes. Research has aimed to highlight the signalling pathway mechanisms that lead to diabetic nephropathy so that preventative strategies and effective therapies might be developed. In this review, important pathways that appear to be involved in driving these processes are discussed.

Activation of nuclear factor erythroid 2-related factor 2 coordinates dimethylarginine dimethylaminohydrolase/PPAR-γ/endothelial nitric oxide synthase pathways that enhance nitric oxide generation in human glomerular endothelial cells

Dimethylarginine dimethylaminohydrolase (DDAH) degrades asymmetric dimethylarginine, which inhibits nitric oxide (NO) synthase (NOS). Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcriptional factor that binds to antioxidant response elements and transcribes many antioxidant genes. Because the promoters of the human DDAH-1 and DDAH-2, endothelial NOS (eNOS) and PPAR-γ genes contain 2 to 3 putative antioxidant response elements, we hypothesized that they were regulated by Nrf2/antioxidant response element. Incubation of human renal glomerular endothelial cells with the Nrf2 activator tert-butylhydroquinone (20 μmol·L(-1)) significantly (P<0.05) increased NO and activities of NOS and DDAH and decreased asymmetric dimethylarginine. It upregulated genes for hemoxygenase-1, eNOS, DDAH-1, DDAH-2, and PPAR-γ and partitioned Nrf2 into the nucleus. Knockdown of Nrf2 abolished these effects. Nrf2 bound to one antioxidant response element on DDAH-1 and DDAH-2 and PPAR-γ promoters but not to the eNOS promoter. An increased eNOS and phosphorylated eNOS (P-eNOSser-1177) expression with tert-butylhydroquinone was prevented by knockdown of PPAR-γ. Expression of Nrf2 was reduced by knockdown of PPAR-γ, whereas PPAR-γ was reduced by knockdown of Nrf2, thereby demonstrating 2-way positive interactions. Thus, Nrf2 transcribes HO-1 and other genes to reduce reactive oxygen species, and DDAH-1 and DDAH-2 to reduce asymmetric dimethylarginine and PPAR-γ to increase eNOS and its phosphorylation and activity thereby coordinating 3 pathways that enhance endothelial NO generation.

Association of the endothelial nitric oxide synthase gene G894T polymorphism with the risk of diabetic nephropathy in Qassim region, Saudi Arabia-A pilot study

BACKGROUND

Diabetic nephropathy (DN) is a chronic microangiopathic complication of type 2 diabetes mellitus (DM).Vascular endothelial dysfunction resulting from impaired nitric oxide synthase (NOS) activity in the vascular endothelial cells has been suggested as playing an important role in the pathogenesis of diabetic nephropathy (DN). Endothelial nitric oxide synthase (E-NOS) gene G894T polymorphism has been reported to be associated with endothelial dysfunction leading to DN. Our objective was to evaluate the association of G894T polymorphism of eNOS gene with the risk of DN among type 2 diabetic Saudi patients.

METHODS

One hundred and twenty subjects were included in this study. They were divided into three groups. Group I, 40 controls. Group II, 40 type 2 diabetic patients without nephropathy. Group III, 40 type2 diabetic patients with nephropathy. Endothelial nitric oxide synthase (eNOS) G894Tpolymorphism was detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Plasma nitric oxide (NO) levels were estimated.

RESULTS

E-NOS genotype frequency showed non-significant differences among the all studied groups (p > 0.05). Both diabetic groups had significantly higher plasma nitrate levels than in controls with a significant increase in group III than in group II patients (all p < 0.0001). E NOS 894TT genotype was associated with higher plasma nitrate levels in all groups.

CONCLUSION

E-NOS gene SNP is not considered as genetic risk factor for DN among type 2 diabetic Saudi patients. The higher plasma levels of nitrates as a marker of oxidative stress in diabetic patients with nephropathy suggest the possible role of oxidative stress but not e-NOS gene SNP in pathogenesis of the DN.

Glomerular endothelial cell injury and cross talk in diabetic kidney disease

Diabetic kidney disease (DKD) remains a leading cause of new-onset end-stage renal disease (ESRD), and yet, at present, the treatment is still very limited. A better understanding of the pathogenesis of DKD is therefore necessary to develop more effective therapies. Increasing evidence suggests that glomerular endothelial cell (GEC) injury plays a major role in the development and progression of DKD. Alteration of the glomerular endothelial cell surface layer, including its major component, glycocalyx, is a leading cause of microalbuminuria observed in early DKD. Many studies suggest a presence of cross talk between glomerular cells, such as between GEC and mesangial cells or GEC and podocytes. PDGFB/PDGFRβ is a major mediator for GEC and mesangial cell cross talk, while vascular endothelial growth factor (VEGF), angiopoietins, and endothelin-1 are the major mediators for GEC and podocyte communication. In DKD, GEC injury may lead to podocyte damage, while podocyte loss further exacerbates GEC injury, forming a vicious cycle. Therefore, GEC injury may predispose to albuminuria in diabetes either directly or indirectly by communication with neighboring podocytes and mesangial cells via secreted mediators. Identification of novel mediators of glomerular cell cross talk, such as microRNAs, will lead to a better understanding of the pathogenesis of DKD. Targeting these mediators may be a novel approach to develop more effective therapy for DKD.

Association between genetic polymorphisms of ACE & eNOS and diabetic nephropathy

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease, with multiple genetic and environmental factors involving in its etiology. ACE and eNOS gene were considered to have important roles in the development and progression of DN. In this study, a case-control study was carried out to investigate the effects of 7 SNPs in ACE gene and 2 SNPs in eNOS gene in the development of DN in Northern China.7 SNPs including A240T, A2350G, A5466C, A2215G, T3892C, C1237T and C3409T of ACE gene and 2 SNPs (G894T and T786C) of eNOS gene were genotyped by polymerase chain reaction restriction fragment length polymorphism method. 431 type 2 diabetic patients with nephropathy (cases) were compared to 420 type 2 diabetic patients without nephropathy (controls) in the study. Data were analyzed by SPSS 17.0 and HaploView software. The frequency distribution of A2350G, 4 haplotyps in ACE gene and G894T in eNOS gene were demonstrated to be different between case and control groups significantly. Whereas other SNPs and haplotypes had no differences in two cohorts. The results revealed that variations of ACE and eNOS gene had association with DN, which indicated ACE and eNOS gene may play an important role in pathogenesis of DN in Northern Chinese Han population.

Nitric oxide system and diabetic nephropathy

About 30% of patients with type 2 diabetes mellitus develop clinically overt nephropathy. Hyperglycemia is necessary, but not sufficient, to cause the renal damage that leads to kidney failure. Diabetic nephropathy (DN) is a multifactorial disorder that results from interaction between environmental and genetic factors. In the present article we will review the role of the nitric oxide synthase (NOS) in the pathogenesis of DN.Nitric oxide (NO) is a short-lived gaseous lipophilic molecule produced in almost all tissues, and it has three distinct genes that encode three NOS isoforms: neuronal (nNOS), inducible (iNOS) and endothelial (eNOS).The correct function of the endothelium depends on NO, participating in hemostasis control, vascular tone regulation, proliferation of vascular smooth muscle cells and blood pressure homeostasis, among other features. In the kidney, NO plays many different roles, including control of renal and glomerular hemodynamics. The net effect of NO in the kidney is to promote natriuresis and diuresis, along with renal adaptation to dietary salt intake.The eNOS gene has been considered a potential candidate gene for DN susceptibility. Three polymorphisms have been extensively researched: G894T missense mutation (rs1799983), a 27-bp repeat in intron 4, and the T786C single nucleotide polymorphism (SNP) in the promoter (rs2070744). However, the potential link between eNOS gene variants and the induction and progression of DN yielded contradictory results in the literature.In conclusion, NOS seems to be involve in the development and progression of DN. Despite the discrepant results of many studies, the eNOS gene is also a good candidate gene for DN.

Endothelial nitric oxide synthase gene polymorphisms and risk of diabetic nephropathy: a systematic review and meta-analysis

Background

Nitric oxide (NO) has numerous functions in the kidney, including control of renal and glomerular hemodynamics, by interfering at multiple pathological and physiologically critical steps of nephron function. Endothelial NOS (eNOS) gene has been considered a potential candidate gene to diabetic nephropathy (DN) susceptibility. Endothelial nitric oxide synthase gene (eNOS-3) polymorphisms have been associated with DN, however some studies do not confirm this association. The analyzed polymorphisms were 4b/4a, T-786C, and G986T.

Methods

The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement was used in this report. Case–control studies that had diabetic patients with DN as cases and diabetic patients without nephropathy as controls, as well as that evaluated at least one of the three polymorphisms of interest were considered eligible. All studies published up until December 31^st, 2012 were identified by searching electronic databases. Hardy-Weinberg equilibrium assessment was performed. Gene-disease association was measured using odds ratio estimation based on the following genetic contrast/models: (1) allele contrast; (2) additive model; (3) recessive model; (4) dominant model and (4) co-dominant model.

Results

Twenty-two studies were eligible for meta-analysis (4b/a: 15 studies, T-786C: 5 studies, and G984T: 12 studies). Considering 4b/a polymorphism, an association with DN was observed for all genetic models: allele contrast (OR = 1.14, CI: 1.04-1.25); additive (OR = 1.77, CI: 1.37-2.28); recessive (OR = 1.77, CI: 1.38-2,27); dominant (OR = 1.12, CI: 1.01-1.24), with the exception for co-dominance model. As well, T-786C polymorphism showed association with all models, with exception for co-dominance model: allele contrast (OR = 1.22, CI: 1.07-1.39), additive (OR = 1.52, CI: 1.18-1.97), recessive (OR = 1.50, CI: 1.16-1.93), and dominant (OR = 1.11, CI: 1.01-1.23). For the G894T polymorphism, an association with DN was observed in allelic contrast (OR = 1.12, CI: 1.03-1.25) and co-dominance models (OR = 1.13, CI: 1.04-1.37).

Conclusions

In the present study, there was association of DN with eNOS 4b/a and T-786C polymorphism, which held in all genetic models tested, except for co-dominance model. G894T polymorphism was associated with DN only in allele contrast and in co-dominance model. This data suggested that the eNOS gene could play a role in the development of DN.

Role of endothelial nitric oxide synthase in diabetic nephropathy: lessons from diabetic eNOS knockout mice

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease in many countries. The animal models that recapitulate human DN undoubtedly facilitate our understanding of this disease and promote the development of new diagnostic markers and therapeutic interventions. Based on the clinical evidence showing the association of eNOS dysfunction with advanced DN, we and others have created diabetic mice that lack eNOS expression and shown that eNOS-deficient diabetic mice exhibit advanced nephropathic changes with distinct features of progressive DN, including pronounced albuminuria, nodular glomerulosclerosis, mesangiolysis, and arteriolar hyalinosis. These studies clearly defined a critical role of eNOS in DN and developed a robust animal model of this disease, which enables us to study the pathogenic mechanisms of progressive DN. Further, recent studies with this animal model have explored the novel mechanisms by which eNOS deficiency causes advanced DN and provided many new insights into the pathogenesis of DN. Therefore, here we summarize the findings obtained with this animal model and discuss the roles of eNOS in DN, unresolved issues, and future investigations of this animal model study.

Genetic variance in nitric oxide synthase and endothelin genes among children with and without endothelial dysfunction

Background

The presence of endothelial dysfunction (ED) constitutes an early risk factor for cardiovascular disease (CVD) in children. Nitric oxide (NO) and endothelin (EDN) are generated in endothelial cells and are critical regulators of vascular function, with ED resulting from an imbalance between these two molecules. We hypothesized that genetic variants in NO synthase and EDN isoforms and its receptors (EDNRA and EDNRB) may account for a proportion of the risk for ED in developing children.

Methods

Consecutive children (ages 5–10 years) were prospectively recruited from the community. Time to peak post-occlusive reperfusion (Tmax) was considered as the indicator of either normal endothelial function (NEF; Tmax < 45 sec) or ED (Tmax ≥ 45 sec). Lipid profiles, high sensitivity C-reactive protein (hsCRP), fasting glucose and insulin were assayed using ELISA. Genomic DNA from peripheral blood was extracted and genotyped for NOS1 (209 SNPs), NOS2 (122 SNPs), NOS3 (50 SNPs), EDN1 (43 SNPs), EDN2 (48 SNPs), EDN3 (14 SNPs), EDNRA (27 SNPs), and EDNRB (23 SNPs) using a custom SNPs array. Linkage disequilibrium was analyzed using Haploview version 4.2 software.

Results

The relative frequencies of SNPs were evaluated in 122 children, 84 with NEF and 38 with ED. The frequencies of NOS1 (11 SNPs), and EDN1 (2 SNPs) were differentially distributed between NEF vs. ED, and no significant differences emerged for all other genes. Significant SNPs for NOS1 and EDN1 SNPs were further validated with RT-PCR.

Conclusions

Genetic variants in the NOS1 and EDN1 genes appear to account for important components of the variance in endothelial function, particularly when concurrent risk factors such as obesity exist. Thus, analysis of genotype-phenotype interactions in children at risk for ED will be critical for more accurate formulation of categorical CVD risk estimates.

Polymorphisms in nitric oxide synthase and endothelin genes among children with obstructive sleep apnea

Background

Obstructive sleep apnea (OSA) is associated with adverse and interdependent cognitive and cardiovascular consequences. Increasing evidence suggests that nitric oxide synthase (NOS) and endothelin family (EDN) genes underlie mechanistic aspects of OSA-associated morbidities. We aimed to identify single nucleotide polymorphisms (SNPs) in the NOS family (3 isoforms), and EDN family (3 isoforms) to identify potential associations of these SNPs in children with OSA.

Methods

A pediatric community cohort (ages 5–10 years) enriched for snoring underwent overnight polysomnographic (NPSG) and a fasting morning blood draw. The diagnostic criteria for OSA were an obstructive apnea-hypopnea Index (AHI) >2/h total sleep time (TST), snoring during the night, and a nadir oxyhemoglobin saturation <92%. Control children were defined as non-snoring children with AHI <2/h TST (NOSA). Endothelial function was assessed using a modified post-occlusive hyperemic test. The time to peak reperfusion (Tmax) was considered as the indicator for normal endothelial function (NEF; Tmax<45 sec), or ED (Tmax≥45 sec). Genomic DNA from peripheral blood was extracted and allelic frequencies were assessed for, NOS1 (209 SNPs), NOS2 (122 SNPs), NOS3 (50 SNPs), EDN1 (43 SNPs), EDN2 (48 SNPs), EDN3 (14 SNPs), endothelin receptor A, EDNRA, (27 SNPs), and endothelin receptor B, EDNRB (23 SNPs) using a custom SNPs array. The relative frequencies of NOS-1,-2, and −3, and EDN-1,-2,-3,-EDNRA, and-EDNRB genotypes were evaluated in 608 subjects [128 with OSA, and 480 without OSA (NOSA)]. Furthermore, subjects with OSA were divided into 2 subgroups: OSA with normal endothelial function (OSA-NEF), and OSA with endothelial dysfunction (OSA-ED). Linkage disequilibrium was analyzed using Haploview version 4.2 software.

Results

For NOSA vs. OSA groups, 15 differentially distributed SNPs for NOS1 gene, and 1 SNP for NOS3 emerged, while 4 SNPs for EDN1 and 1 SNP for both EDN2 and EDN3 were identified. However, in the smaller sub-group for whom endothelial function was available, none of the significant SNPs was retained due to lack of statistical power.

Conclusions

Differences in the distribution of polymorphisms among NOS and EDN gene families suggest that these SNPs could play a contributory role in the pathophysiology and risk of OSA-induced cardiovascular morbidity. Thus, analysis of genotype-phenotype interactions in children with OSA may assist in the formulation of categorical risk estimates.

The renal endothelium in diabetic nephropathy

Diabetic nephropathy is the leading cause of end-stage renal disease. Diabetes mellitus is characterized by generalized endothelial dysfunction. However, recent data also emphasizes the role of local renal endothelium dysfunction in the pathogenesis of diabetic nephropathy. Hyperglycemia triggers a complex network of signal-transduction molecules, transcription factors, and mediators that culminate in endothelial dysfunction. In the glomerulus, vascular endothelial growth factor-A (VEGF)-induced neoangiogenesis may contribute to the initial hyperfiltration and microalbuminuria due to increased filtration area and immaturity of the neovessels, respectively. However, subsequent decrease in podocytes number decreases VEGF production resulting in capillary rarefaction and decreased glomerular filtration rate (GFR). Decreased nitric oxide availability also plays a significant role in the development of advanced lesions of diabetic nephropathy through disruption of glomerular autoregulation, uncontrolled VEGF action, release of prothrombotic substances by endothelial cells and angiotensin-II-independent aldosterone production. In addition, disturbances in endothelial glycocalyx contribute to decreased permselectivity and microalbuminuria; whereas there are recent evidences that reduced glomerular fenestral endothelium leads to decreased GFR levels. Endothelial repair mechanisms are also impaired in diabetes, since circulating endothelial progenitor cells number is decreased in diabetic patients with microalbuminuria. Finally, in the context of elevated profibrotic cytokine transforming growth factor-β levels, endothelial cells also confer to the deteriorating process of fibrosis in advanced diabetic nephropathy through endothelial to mesenchymal transition.

Endothelial nitric oxide synthase gene polymorphisms and renal responsiveness to RAS inhibition therapy in type 2 diabetic Asian Indians

AIM

To investigate the association of functional single nucleotide polymorphisms (SNPs) of the endothelial nitric oxide synthase gene (eNOS) gene (T-786C, G894T) and one variable number tandem repeat polymorphism (aa 27VNTR bb) with reno-protective response to angiotensin converting enzyme inhibitors (ACEI) and angiotensin receptor blockers (ARB) therapy in North Indian type 2 diabetic mellitus (T2DM) subjects with cases having diabetic nephropathy (DN) and controls without DN.

METHOD

We genotyped three polymorphisms of eNOS (two SNPs: T-786C, G894T and one 27 VNTR) in T2DM patients with overt nephropathy (cases: n=320) and T2DM patients without overt nephropathy (controls: n=490), using validated PCR-RFLP assays. These 810 North Indian T2DM patients treated with ACEI or ARB after diagnosis were followed up for 3 years. Percent changes in eGFR, urinary albumin excretion (UAE), serum creatinine at the end of 3 years of treatment were taken as end points of renoprotective response.

RESULT

We observed that in normoalbuminuric patients, eNOS -786 CC genotype and haplotypes C-b-G and C-b-T were associated with lesser renoprotective response to ACEI. While, in macroalbuminurics, eNOS -786 CC genotype, haplotypes C-b-G and C-b-T and 27VNTR aa were associated with better renoprotective response to ACEI/ARB.

CONCLUSION

Our results showed that eNOS T-786C CC genotype and 27VNTR individually and in interaction with other eNOS SNPs modulate renoprotective efficacy of ACEI and ARB in T2DM patients, depending on the status of proteinuria.

Glomerular endothelial cell injury and damage precedes that of podocytes in adriamycin-induced nephropathy

The role of podocytes in the development and progression of glomerular disease has been extensively investigated in the past decade. However, the importance of glomerular endothelial cells in the pathogenesis of proteinuria and glomerulosclerosis has been largely ignored. Recent studies have demonstrated that endothelial nitric oxide synthatase (eNOS) deficiency exacerbates renal injury in anti-GBM and remnant kidney models and accelerates diabetic kidney damage. Increasing evidence also demonstrates the importance of the glomerular endothelium in preventing proteinuria. We hypothesize that endothelial dysfunction can initiate and promote the development and progression of glomerulopathy. Administration of adriamycin (ADR) to C57BL/6 mice, normally an ADR resistant strain, with an eNOS deficiency induced overt proteinuria, severe glomerulosclerosis, interstitial fibrosis and inflammation. We also examined glomerular endothelial cell and podocyte injury in ADR-induced nephropathy in Balb/c mice, an ADR susceptible strain, by immunostaining, TUNEL and Western blotting. Interestingly, down-regulation of eNOS and the appearance of apoptotic glomerular endothelial cells occurred as early as 24 hours after ADR injection, whilst synaptopodin, a functional podocyte marker, was reduced 7 days after ADR injection and coincided with a significant increase in the number of apoptotic podocytes. Furthermore, conditioned media from mouse microvascular endothelial cells over-expressing GFP-eNOS protected podocytes from TNF-α-induced loss of synaptopodin. In conclusion, our study demonstrated that endothelial dysfunction and damage precedes podocyte injury in ADR-induced nephropathy. Glomerular endothelial cells may protect podocytes from inflammatory insult. Understanding the role of glomerular endothelial dysfunction in the development of kidney disease will facilitate in the design of novel strategies to treat kidney disease.

Uncoupling of VEGF with endothelial NO as a potential mechanism for abnormal angiogenesis in the diabetic nephropathy

Abnormal angiogenesis is a well characterized complication in diabetic retinopathy and is now recognized as a feature of diabetic nephropathy. The primary growth factor driving the increased angiogenesis in diabetic retinopathy and nephropathy is vascular endothelial growth factor (VEGF). While VEGF is considered an important growth factor for maintaining glomerular capillary integrity and function, increased action of VEGF in diabetic renal disease may carry adverse consequences. Studies by our group suggest that the effects of VEGF are amplified in the setting of endothelial dysfunction and low nitric oxide (NO) levels, which are a common feature in the diabetic state. The lack of NO may amplify the effects of VEGF to induce inflammation (via effects on the macrophage) and may lead to dysregulation of the vasculature, exacerbating features of diabetic renal disease. In this review, we summarize how an "uncoupling" of the VEGF-NO axis may contribute to the pathology of the diabetic kidney.

Endothelial nitric oxide synthase gene polymorphism and type 2 diabetic retinopathy among Asian Indians

Endothelial nitric oxide synthase (eNOS) has been shown to play an essential role in retinal vascular function, and disequilibrium in its production can lead to diabetic retinopathy (DR). Genetic polymorphisms of eNOS gene have been suggested to play a role in nitric oxide (NO) abnormalities which may contribute to the development and progression of DR. In view of the variable results that have been reported for the association between eNOS gene polymorphisms and DR, the present study was designed to study the association and interaction between eNOS gene polymorphisms and the development and progression of DR in Asian Indian type 2 diabetes mellitus patients (T2DM). We screened 1,720 T2DM patients, belonging to two independently ascertained cohorts out of which 1,446 were genotyped for three polymorphisms of eNOS (two SNPs: T-786C, G894T and one 27-bp repeat polymorphism in intron 4 (27VNTR)) using validated PCR-RFLP assays. In both the cohorts, consistently lower prevalence and decreased risk of DR was observed in patients with ba, aa and ba + aa genotype of 27VNTR (a/b), C-a-G and C-a-T haplotype (allele of T-786C, 27VNTR a/b and G894T) carrying "C" allele of T-786C and "a" allele of 27VNTR (a/b). Also, mean NO levels in T2DM subjects carrying ba + aa genotype were higher as compared to bb genotype. Our results suggest that eNOS genotypes 27VNTR carrying "aa" genotype is an independent protective factor for DR and is associated with low risk of DR.

The endothelium in diabetic nephropathy

The long-term complications of diabetes are characterized by pathologic changes in both the microvasculature and conduit vessels. Although the fenestrated glomerular endothelium classically has been viewed as providing little in the way of an impediment to macromolecular flow, increasing evidence illustrates that this is not the case. Rather, hyperglycemia-mediated endothelial injury may predispose to albuminuria in diabetes both through direct effects and through bidirectional communication with neighboring podocytes. Although neo-angiogenesis of the glomerular capillaries may be a feature of early diabetes, particularly in the experimental setting, loss of capillaries in the glomerulus and in the interstitium are key events that each correlate closely with declining glomerular filtration rate in patients with diabetic nephropathy. The hypoxic milieu that follows the microvascular rarefaction provides a potent stimulus for fibrogenesis, leading to the glomerulosclerosis and tubulointerstitial fibrosis that characterize advanced diabetic kidney disease. Given the pivotal role the endothelium plays in both the development and the progression of diabetic nephropathy we need effective strategies that prevent its loss or accelerate its regeneration. Such advances likely will lead not only to improved tissue oxygenation and reduced fibrosis, but also to improved long-term renal function.

Effects of stimulation of soluble guanylate cyclase on diabetic nephropathy in diabetic eNOS knockout mice on top of angiotensin II receptor blockade

The prevalence of diabetes mellitus and its complications, such as diabetic nephropathy (DN), is rising worldwide and prevention and treatment are therefore becoming increasingly important. Therapy of DN is particularly important for patients who do not adequately respond to angiotensin receptor blocker (ARB) treatment. Novel approaches include the stimulation of soluble guanylate cyclase (sGC) as it is reported to have beneficial effects on cardiac and renal damage. We aimed to investigate the effects of the sGC stimulator riociguat and ARB telmisartan on kidney function and structure in a hypertensive model of diabetic nephropathy. Seventy-six diabetic male eNOS knockout C57BL/6J mice were randomly divided after having received streptozotocin: telmisartan (1 mg/kg/d), riociguat (3 mg/kg/d), riociguat+telmisartan (3+1 mg/kg/d), and vehicle. Fourteen mice were used as non-diabetic controls. Treatment duration was 11 weeks. Glucose concentrations were increased and similar in all diabetic groups. Telmisartan insignificantly reduced blood pressure by 5.9 mmHg compared with diabetic controls (111.2±2.3 mmHg vs. 117.1±2.2 mmHg; p = 0.071). Treatment with riociguat both alone and in combination with telmisartan led to a significant reduction of blood pressure towards diabetic vehicle (105.2±2.5 mmHg and 105.0±3.2 mmHg, respectively, vs. 117.1±2.2 mmHg). Combined treatment also significantly decreased albuminuria compared with diabetic controls (47.3±9.6 µg/24 h vs. 170.8±34.2 µg/24 h; p = 0.002) reaching levels similar to those of non-diabetic controls (34.4±10.6 µg/24 h), whereas the reduction by single treatment with either telmisartan (97.8±26.4 µg/24 h) or riociguat (97.1±15.7 µg/24 h) was not statistically significant. The combination treatment led to a significant (p<0.01) decrease of tissue immunoreactivity of malondialdehyde, as consequence of reduced oxidative stress. In conclusion, stimulation of sGC significantly reduced urinary albumin excretion in diabetic eNOS knockout mice treated already with ARB. Thus, this new drug class on top of standard ARBs administration may offer a new therapeutic approach for patients resistant to ARB treatment.

Concomitant presence of endothelial nitric oxide 894T and angiotensin II-converting enzyme D alleles are associated with diabetic nephropathy in a Kurdish population from Western Iran

AIM

The present study investigated the influence of insertion (I)/deletion (D) polymorphism of the angiotensin II-converting enzyme (ACE) gene in combination with endothelial nitric oxide (eNOS) G894T polymorphism on the predisposition to diabetic nephropathy (DN).

METHODS

Using polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (PCR-RFLP) method, the ACE and eNOS polymorphisms were genotyped in 72 microalbuminuric, 68 macroalbuminuric and 72 normoalbuinuric type 2 diabetes mellitus (T2DM) patients from Western Iran.

RESULTS

The presence of eNOS T or ACE D allele was not associated with increased risk of macroalbuminuria (odds ratio (OR) = 1.36, P = 0.27 and OR = 1.6, P = 0.062, respectively). However, in the presence of both alleles there was a trend towards increased risk of macroalbuminuria (fivefold, P = 0.05).

CONCLUSION

Our study indicates that the concomitant presence of both ACE D and eNOS T alleles tends to be associated with an elevation risk of macroalbuminuria compared with the presence of each polymorphism alone. This risk could be attributed to the increasing activity of ACE and angiotensin II level in the presence of D allele and decreasing NO production in the presence of T allele accelerating diabetic nephropathy.

The kallikrein-kinin system in diabetic nephropathy

Diabetic nephropathy is the major cause of end-stage renal disease worldwide. Although the renin-angiotensin system has been implicated in the pathogenesis of diabetic nephropathy, angiotensin I-converting enzyme inhibitors have a beneficial effect on diabetic nephropathy independently of their effects on blood pressure and plasma angiotensin II levels. This suggests that the kallikrein-kinin system (KKS) is also involved in the disease. To study the role of the KKS in diabetic nephropathy, mice lacking either the bradykinin B1 receptor (B1R) or the bradykinin B2 receptor (B2R) have been commonly used. However, because absence of either receptor causes enhanced expression of the other, it is difficult to determine the precise functions of each receptor. This difficulty has recently been overcome by comparing mice lacking both receptors with mice lacking each receptor. Deletion of both B1R and B2R reduces nitric oxide (NO) production and aggravates renal diabetic phenotypes, relevant to either lack of B1R or B2R, demonstrating that both B1R and B2R exert protective effects on diabetic nephropathy presumably via NO. Here, we review previous epidemiological and experimental studies, and discuss novel insights regarding the therapeutic implications of the importance of the KKS in averting diabetic nephropathy.

Endothelial nitric oxide synthase gene polymorphisms and the risk of diabetic nephropathy in type 2 diabetes mellitus

Endothelial dysfunction plays an important role in the pathogenesis of diabetic vascular disease, including diabetic nephropathy (DN). Endothelial nitric oxide synthase (eNOS) gene polymorphisms that affect eNOS activity are associated with endothelial dysfunction. The aim of this study was to evaluate the association of three polymorphisms of the eNOS gene (894G>T, -786T>C, and 27-bp-VNTR) with the risk of DN among type 2 diabetic patients. A total of 400 type 2 diabetic patients were enrolled in this study. The DN group comprised 200 patients; the group of diabetics without nephropathy comprised another 200 patients. Genetic analysis for eNOS gene polymorphisms was done in all subjects. Measurement of nitric oxide levels was estimated. The C allele for -786T>C and the T allele for 894G>T were significantly more frequent in diabetics with nephropathy than in diabetics without nephropathy (p<0.001; odds ratio [OR] and 95% confidence interval [CI] for the C allele=1.64 [1.24-2.17] and p<0.001; OR and 95% CI=1.7 [1.27-2.26] for the T allele). The haplotypes CTa (with all the mutant alleles) and CTb were significantly more common in patients with DN (p=0.01 and 0.003, respectively). These results suggested that the eNOS polymorphisms might represent genetic determinants for developing DN in type 2 diabetic Egyptians.

The 4a/4a genotype of the VNTR polymorphism for endothelial nitric oxide synthase (eNOS) gene predicts risk for proliferative diabetic retinopathy in Slovenian patients (Caucasians) with type 2 diabetes mellitus

Thus far only a limited number of studies examined the association between endothelial nitric oxide synthase (eNOS) polymorphisms and proliferative diabetic retinopathy (PDR). In this report, two polymorphisms in the eNOS gene have been investigated, namely the 894G>T (Glu298Asp) and a 27 bp VNTR (4b/4a), to assess their possible relationships to PDR among Slovenian (Caucasians) type 2 diabetic patients. This cross-sectional case-control study enrolled 577 unrelated Slovenian subjects (Caucasians) with type 2 diabetes mellitus. The case group consisted of 172 patients with PDR and the control group had 405 patients who had no clinical signs of diabetic retinopathy (DR) but did have type 2 diabetes for more than 10 years' duration. Genotyping of eNOS polymorphisms was carried out with conventional and real-time PCR assays. A significantly higher frequency of the eNOS minor "4a" allele was found in patients with PDR than in controls (23.6 versus 17.7%, p = 0.01). Moreover, the univariate analysis showed a significant association of the 27 bp VNTR 4a/4a genotype and PDR in the recessive model. The odds ratio (OR) of PDR for the 4a/4a genotype to 4b/4a plus 4b/4b was 2.9 (95% CI 1.3-6.2, p = 0.005). Further, the presence of 4a/a genotype was associated with a 3.4-fold (95% CI 1.4-8.6, p = 0.009) increased risk for PDR while adjusted for other risk factors. This is the first study to implicate eNOS 4a/4a homozygous deletion, and hence the "4a" allele, as the genetic risk factors for PDR in Caucasians.

Assessment of diabetic nephropathy in the Akita mouse

Akita mice have type 1 diabetes mellitus caused by a spontaneous point mutation in the Ins2 gene which leads to misfolding of insulin, resulting in pancreatic β-cell failure. Akita mice develop pronounced and sustained hyperglycemia, high levels of albuminuria, and consistent histopathological changes, suggesting that these mice may be suitable as an experimental platform for modeling diabetic nephropathy. One key feature of diabetic kidney disease in Akita mice is that the severity of renal injury is significantly influenced by genetic background. In this chapter, we describe the Akita model and present some of the experimental studies utilizing Akita mice as a model of type 1 diabetes. For example, deficiency in bradykinin receptors, endothelial nitric oxide synthase, or angiotensin-converting enzyme 2 leads to development of functionally and structurally more advanced diabetic nephropathy in these mice, while ketogenic diet has been shown to reverse kidney injury associated with diabetes. This chapter also describes the application of 24-h urine collections from mice for careful measurement of urinary albumin excretion.

Role of blood pressure and the renin-angiotensin system in development of diabetic nephropathy (DN) in eNOS-/- db/db mice

Randomized clinical trials have clearly shown that inhibition of the renin-angiotensin system (RAS) will slow the rate of progression of diabetic nephropathy, but controversy remains about whether the observed beneficial effects result from more than control of blood pressure. Deletion of eNOS in a model of type II diabetes, db/db mice (eNOS(-/-) db/db), induces an accelerated nephropathy and provides an excellent model of human diabetic nephropathy. As is frequently seen in type II diabetes, blood pressure is moderately elevated in eNOS(-/-) db/db mice. To determine the role of elevated blood pressure per se vs. additional deleterious effects of the RAS in mediation of disease progression, 8-wk-old eNOS(-/-) db/db mice were randomly divided into three groups: vehicle, treatment with the angiotensin-converting enzyme inhibitor (ACEI) captopril, or treatment with "triple therapy" (hydralazine, resperine, hydrocholorothiazide), and the animals were euthanized after treatment for 12 wk. Blood pressure was reduced to comparable levels with ACE inhibition or triple therapy. Although both treatment regimens decreased development of diabetic nephropathy, ACE inhibition led to more profound reductions in albuminuria, glomerulosclerosis, markers of tubulointerstitial injury, macrophage infiltration, and markers of inflammation. Therefore, this animal model suggests that while there is an important role for blood pressure control, RAS blockade provides additional benefits in slowing the progression of diabetic nephropathy.