Relation Between Plasma Nitric Oxide Levels and Diabetic Retinopathy

Association of the endothelial nitric oxide synthase (eNOS) 4a/b polymorphism with the risk of incident diabetic retinopathy in patients with type 2 diabetes mellitus: a systematic review and updated meta-analysis

OBJECTIVE

To conduct a systematic review and updated meta-analysis on the potential association between endothelial nitric oxide synthase (eNOS) 4a/b polymorphism and the risk of developing diabetic retinopathy (DR) in patients with type 2 diabetes mellitus (T2DM) and to identify possible clinical biomarkers for early screening of DR.

MATERIALS AND METHODS

A meta-analysis based on case-control or cross-sectional studies was conducted to examine the correlation between eNOS 4a/b polymorphism and DR. Pooled odds ratio (OR) and 95% confidence interval (CI) were used to estimate the association strength.

RESULTS

We included 19 studies, covering 7838 subjects. An association was observed in Caucasians (allelic model: OR = 1.273, 95% CI: 1.006-1.610, p = .045; recessive model: OR = 0.575, 95% CI: 0.371-0.892, p = .014; dominant model: OR = 1.268, 95% CI: 1.052-1.528, p = .013; homozygote model: OR = 1.833, 95% CI: 1.176-2.856, p = .007). Moreover, population-based studies have indicated an association between eNOS 4a/b polymorphism and DR susceptibility.

CONCLUSIONS

The present study showed that intron 4a allele of eNOS 4a/b is a risk factor for DR in Caucasians with T2DM. Thus, eNOS 4a/b may be used as a biomarker for the early screening and diagnosis of DR in Caucasian T2DM patients.Key messagesEndothelial nitric oxide synthase 4a/b gene polymorphism is not associated with the risk of developing diabetic retinopathy in the overall population, Asians, or Chinese Han patients with type 2 diabetes. However, 4a is a risk factor for the development of diabetic retinopathy in Caucasians.Endothelial nitric oxide synthase 4a/b gene polymorphism is not associated with the type of diabetic retinopathy.

Retinal Physiology and Circulation: Effect of Diabetes

In this article, we present a discussion of diabetes and its complications, including the macrovascular and microvascular effects, with the latter of consequence to the retina. We will discuss the anatomy and physiology of the retina, including aspects of metabolism and mechanisms of oxygenation, with the latter accomplished via a combination of the retinal and choroidal blood circulations. Both of these vasculatures are altered in diabetes, with the retinal circulation intimately involved in the pathology of diabetic retinopathy. The later stages of diabetic retinopathy involve poorly controlled angiogenesis that is of great concern, but in our discussion, we will focus more on several alterations in the retinal circulation occurring earlier in the progression of disease, including reductions in blood flow and a possible redistribution of perfusion that may leave some areas of the retina ischemic and hypoxic. Finally, we include in this article a more recent area of investigation regarding the diabetic retinal vasculature, that is, the alterations to the endothelial surface layer that normally plays a vital role in maintaining physiological functions. © 2020 American Physiological Society. Compr Physiol 10:933-974, 2020.

Plasma angiogenesis and oxidative stress markers in patients with diabetic retinopathy

Background: Neovascularization in the retina and hyperglycaemia-induced oxidative stress are implicated in the pathogenesis of diabetic retinopathy (DR). In this study, we hypothesized that the plasma angiogenic and oxidative stress markers associated with these derangements could aid in the screening of diabetic patients who are at an increased risk of developing retinopathy.Methods: This study included normal (n = 148), type2 diabetes without retinopathy (DNR; n = 148), proliferative DR (PDR; n = 74) and non-PDR (NPDR; n = 148) subjects. Plasma concentrations of vascular endothelial growth factor-A (VEGF-A), hypoxia-inducible factor-1α (HIF-1α), matrix metalloproteinase-9 (MMP-9), pigment epithelium-derived factor (PEDF), nitric oxide (NO), soluble receptors for advanced glycation end products (sRAGE), malondialdehyde (MDA) and protein thiols were estimated.Results: A statistically significant increase was observed in the plasma concentrations of pro-angiogenic factors and markers of oxidative stress in both retinopathy groups. By contrast, the concentrations of anti-angiogenic factors and antioxidants were decreased significantly in these groups. Receiver operating characteristic analysis indicated that the plasma thresholds of HIF-1α and PEDF can be suitable markers in case of NPDR. However, in PDR, HIF-1α, NO, MMP-9 and PEDF showed high sensitivity and specificity.Conclusions: The factors associated with hypoxia, matrix degradation and angiogenic inhibition play a crucial role in predicting DR.

Activation of Retinal Angiogenesis in Hyperglycemic pdx1 -/- Zebrafish Mutants

Progression from the initial vascular response upon hyperglycemia to a proliferative stage with neovacularizations is the hallmark of proliferative diabetic retinopathy. Here, we report on the novel diabetic pdx1 ^-/- zebrafish mutant as a model for diabetic retinopathy that lacks the transcription factor pdx1 through CRISPR-Cas9-mediated gene knockout leading to disturbed pancreatic development and hyperglycemia. Larval pdx1 ^-/- mutants prominently show vasodilation of blood vessels through increased vascular thickness in the hyaloid network as direct developmental precursor of the adult retinal vasculature in zebrafish. In adult pdx1 ^-/- mutants, impaired glucose homeostasis induces increased hyperbranching and hypersprouting with new vessel formation in the retina and aggravation of the vascular alterations from the larval to the adult stage. Both vascular aspects respond to antiangiogenic and antihyperglycemic pharmacological interventions in the larval stage and are accompanied by alterations in the nitric oxide metabolism. Thus, the pdx1 ^-/- mutant represents a novel model to study mechanisms of hyperglycemia-induced retinopathy wherein extensive proangiogenic alterations in blood vessel morphology and metabolic alterations underlie the vascular phenotype.

Altered superoxide dismutase-1 activity and intercellular adhesion molecule 1 (ICAM-1) levels in patients with type 2 diabetes mellitus

Inflammation and oxidative stress are linked to type 2 diabetes mellitus (T2DM). In this work, we analyzed patients' blood markers of antioxidant capacity, oxidative stress and inflammation in individuals with T2DM, in pre-diabetes state (pre-DM) and controls without diabetes. Patients were divided into three groups, according to glycated hemoglobin A1c (HbA1c): <7%, 7-9%, and >9%. Superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities, total thiols, nitric oxide (•NO), tumor necrosis factor alpha (TNF-α) and intercellular adhesion molecule 1 (ICAM-1) levels of the individuals were measured. Plasma SOD activity was higher in T2DM subjects compared to the controls. While total thiols levels were lower in T2DM groups when compared to pre-DM, the values remained unchanged when compared to controls. ICAM-1 levels of T2DM groups were lower than in controls, while GPx activity, •NO, and TNF-α levels were similar among all groups. A positive correlation was found between SOD and HbA1c levels. Concluding, individuals with T2DM present altered SOD activity, total thiols, and ICAM-1 levels, which might contribute to further complications. There is a positive correlation between SOD activity and HbA1c levels. No apparent correlation exists between total thiols and ICAM-1 levels and with any other of the parameters evaluated in this study.

Effect of glycemic control and disease duration on cardiac autonomic function and oxidative stress in type 2 diabetes mellitus

Purpose

Cardiac autonomic neuropathy (CAN) is a commonly overlooked complication of type 2 diabetes mellitus (T2DM), with a complex pathogenesis involving hyperglycemia-induced oxidative stress which results in neuronal ischemia and cellular death. The level of hyperglycemia as well as disease duration might be significant determinants of the prognosis of T2DM, but limited studies have explored their relationship with these diabetic complications. Therefore, the purpose of this study was to examine the effect of glycemic control and disease duration on cardiac autonomic function and oxidative stress in patients with T2DM.

Methods

60 T2DM patients along with 63 healthy controls were recruited for the study. Diabetic patients were further classified based on glycemic control (HbA1c levels <8% vs. ≥8%) and disease duration (<5 vs. 5-10 vs. >10 years). All participants were assessed for cardiac autonomic function (HRR: heart rate recovery; HRV: heart rate variability), levels of antioxidant enzymes (CAT: catalase; SOD: superoxide dismutase), serum nitric oxide (NO) and other cardiometabolic risk factors (resting blood pressure, glycemic and lipid profile).

Results

T2DM patients showed a significant reduction in HRR, HRV, CAT, SOD and an increase in LFnu, LF: HF ratio and NO. These impairments were significantly greater for the group with poor glycemic control (p < 0.05). However, no difference for these parameters was observed with respect to different disease durations.

Conclusion

Cardiac autonomic regulation and endogenous antioxidant defense were compromised and levels of nitric oxide found to be raised in patients with Type 2 diabetes. These findings were more pronounced in subjects with poor glycemic control.

Nitric oxide levels in patients with diabetes mellitus: A systematic review and meta-analysis

BACKGROUND

Altered serum nitric oxide (NO) levels in patients with diabetes mellitus (DM) have been reported by different studies; however, results are still controversial. Until this date, no meta-analysis evaluated the association of NO levels with DM. Thus, this paper describes a meta-analysis conducted to evaluate if there is a relationship between NO levels and type 1 DM (T1DM) or type 2 DM (T2DM).

METHODS

A literature search was done to identify all studies that investigated NO levels between T1DM or T2DM patients (cases) and non-diabetic subjects (controls). Measurement of nitrate and nitrite (NOx - the stable NO products) were used to estimate NO concentrations because they closely reflect NO bioavailability. Weighted mean differences (WMD) of NOx levels between case and control samples were calculated for T1DM and T2DM groups.

RESULTS

Thirty studies were eligible for inclusion in the meta-analysis (8 in T1DM samples and 22 in T2DM samples). NOx levels were increased in European T1DM patients compared with controls [random effect model (REM) WMD = 8.55, 95% CI 2.88 - 14.21]. No other ethnicity was evaluated in T1DM studies. NOx levels were also increased in both European (REM WMD = 18.76, 95% CI 1.67 - 35.85) and Asian (REM WMD = 18.41, 95% CI 8.01 - 28.81) T2DM patients, but not in Latin American patients compared with controls.

CONCLUSIONS

This meta-analysis detected a significant increase in NOx levels in European T1DM patients as well as European and Asian T2DM patients. Further studies in other ethnicities are necessary to confirm these data.

Evaluation of the Serum Levels of Nitric Oxide among Diabetic Patients and its Correlation with Lipid Profile as well as Oxidative Stress in North Indian Setting

INTRODUCTION

Diabetes mellitus is a disease with a rapidly increasing prevalence, needs continue research for novel methods to both prevent and treat this disorder. Obesity and decreased physical activity are the major risk factor for the development of diabetes. Recently the emphasis is focused on oxidative stress in pathogenesis of this disease.

AIM

To assess the serum levels of Nitric Oxide (NO) among diabetic patients and its correlation with lipid profile as well as oxidative stress in north Indian setting.

MATERIALS AND METHODS

This was a cross-sectional study. Subjects suffering from type 2 diabetes for more than 1 year and age between 30 to 50 years with hyperuricaemia were included in the study. The patients were divided into three groups: Group I- Type 2 diabetics with dyslipidemia and hyperuricaemia, Group II- Type 2 diabetics with dyslipidemia and normouricaemia and Group III- Type 2 diabetics with normolipidemia and normouricaemia.

RESULTS

The nitric oxide level was significantly lower in Group I and Group II than Group III. The oxidative stress parameters had poor correlation with NO level in all the groups.

CONCLUSION

Our data suggests that there is definite role of Nitric Oxide (NO) in pathogenesis of type -2 diabetes mellitus with dyslipidemia and hyperuricaemia.

Correlation of biomarkers thiobarbituric acid reactive substance, nitric oxide and central subfield and cube average thickness in diabetic retinopathy: a cross-sectional study

BACKGROUND

To evaluate the role of thiobarbituric acid reactive substance (TBARS) and nitric oxide (NO) as biochemical biomarkers and central subfield (CST) and cube average thickness (CAT) as biomarkers for medical imaging in diabetic retinopathy.

METHODS

Forty consecutive cases of diabetic retinopathy and 20 healthy controls were included. Cases were divided into two groups: non proliferative diabetic retinopathy (n = 20) and proliferative diabetic retinopathy (n = 20) according to ETDRS classification. LogMAR visual acuity was documented. Plasma levels of TBARS, NO and glycated hemoglobin (HbA1c) were measured using standard protocol. CST and CAT were analyzed on spectral domain optical coherence tomography. Data was analyzed statistically.

RESULTS

Increased severity of diabetic retinopathy was associated with an increase in plasma levels of TBARS (F = 10.92; p < 0.001), NO (F = 21.8; p < 0.001) and HbA1c (F = 5.87; p = 0.001). Increase in CST (F = 61.51; p < 0.001) and CAT (F = 60.84; p < 0.001) was also found to be associated with increased severity of diabetic retinopathy. Pearson's correlation analysis revealed a positive correlation of TBARS with CST (r = 0.29; p = 0.038) and CAT (r = 0.31; p = 0.04). A positive correlation of NO with CST (r = 0.27; p = 0.03) and CAT (r = 0.7; p = 0.001) was also observed. On univariate analysis with logMAR visual acuity as dependent variable, a significant increase in visual acuity was observed with increase in independent variables TBARS (B = 0.22; p = 0.004), NO (B = 0.006; p < 0.001), CST (B = 0.005; p < 0.001) and CAT (B = 0.005; p < 0.001). On multivariate linear regression analysis with logMAR visual acuity as dependent variable and adjusting for other factors like duration of diabetes and HbA1c, it was observed that increase in independent variables TBARS (B = 0.07), NO (B = 0.001) and CST (B = 0.004) independently predict increase in logMAR visual acuity (p < 0.001).

CONCLUSION

Thiobarbituric acid reactive substance and nitric oxide serve as potential biochemical markers whereas central subfield and cube average thickness serve as potential biomarkers for medical imaging for severity of diabetic retinopathy. In a clinical retinal setting, CAT and CST will help in early recognition of increase in severity of diabetic retinopathy.

The effect of ubiquinone and combined antioxidant therapy on oxidative stress markers in non-proliferative diabetic retinopathy: A phase IIa, randomized, double-blind, and placebo-controlled study

Objective

To evaluate the effect of ubiquinone (Coenzyme Q10) and combined antioxidant therapy (CAT) on oxidative stress markers in non-proliferative diabetic retinopathy (NPDR) under clinical management.

Study design

In a randomized, double-blind, phase IIa, placebo-controlled, clinical trial, three study groups were formed and administered medications as follows: Group 1, Coenzyme Q10; Group 2, CAT; and Group 3, placebo.

Methods

Serum levels of the products of lipid peroxidation (LPO) and nitrites/nitrates, as markers of oxidative/nitrosative stress, were measured. As antioxidants, the total antioxidant capacity (TAC), catalase activity, and glutathione peroxidase (GPx) activity were measured.

Results

Baseline serum levels of LPO and nitrites/nitrates were significantly elevated in the three groups vs. healthy group (P < 0.0001), while final levels in the Coenzyme Q10 and CAT groups were decreased vs. normal levels (P < 0.0001). The baseline TAC was consumed in the three groups (P < 0.0001), while final results in the Coenzyme Q10 and CAT groups improved (P < 0.0001). Baseline catalase activity was increased in all groups vs. normal values (P < 0.001), while final levels in the Coenzyme Q10 (P < 0.001) and CAT groups (P < 0.0001) were decreased. GPx behaved similarly to catalase and improved in the final results (P < 0.0001).

Discussion

Adjunctive antioxidant treatment for 6 months was effective and safe for improving the oxidative stress in NPDR.

Oxidative stress-associated neuroretinal dysfunction and nitrosative stress in diabetic retinopathy

OBJECTIVE

The present study was intended to investigate whether oxidative stress is the key regulator to alter neuroretinal biochemical homeostasis and in turn aggravate the process of diabetic retinopathy by inducing nitrosative stress in the retinal neurovascular unit.

METHODS

Peripheral blood mononuclear cell reactive oxygen species level was measured by flow cytometry along with spectrophotometric detection of malondialdehyde (MDA) and glutamate from serum or plasma and a vitreous sample of study groups (i.e. subjects with proliferative diabetic retinopathy [PDR], type 2 diabetes without retinopathy [DNR] and healthy controls [HCs]). Further, nitrosative stress assessment was performed by spectrophotometric and enzyme-linked immunosorbent assay-based detection of serum and vitreous nitrite and nitrotyrosine concentrations, respectively.

RESULTS

The plasma glutamate level remains insignificant between subjects with PDR and DNR (p=0.505) or in HC (p=0.1344) individuals. However, serum MDA (p=0.0004), nitrite (p=0.0147) and nitrotyrosine (p=0.0129) were found to be strikingly higher among PDR subjects compared with the DNR group. Significantly increased levels of peripheral blood mononuclear cell reactive oxygen species (p<0.0001), vitreous glutamate (p=0.0009, p<0.0001), MDA (p=0.0058, p=0.0003), nitrite (p=0.0014, p<0.0001) and nitrotyrosine (p=0.0008, p<0.0001) were found in PDR subjects compared with DNR and HC subjects, respectively.

CONCLUSIONS

Our observation suggests that oxidative stress is associated with impairment in neuroretinal biochemical homeostasis among PDR subjects, which further augments retinal nitrosative stress and thus worsens the pathogenic process of retinopathy among PDR subjects.

Nitric oxide and oxidative stress is associated with severity of diabetic retinopathy and retinal structural alterations

BACKGROUND

The aim of the study was to determine plasma nitric oxide (NO) and lipid peroxide (LPO) levels in diabetic retinopathy and its association with severity of disease.

DESIGN

Prospective observational study.

PARTICIPANTS

A total of 60 consecutive cases and 20 healthy controls were included.

METHODS

Severity of retinopathy was graded according to early treatment diabetic retinopathy study (ETDRS) classification. Photoreceptor inner segment ellipsoid band (ISel) disruption and retinal pigment epithelium (RPE) alteration were graded using spectral domain optical coherence tomography. Data were statistically analyzed.

MAIN OUTCOME MEASURES

Plasma thiobarbituric acid reactive substances, NO assay and reduced glutathione (GSH) were measured using standard protocol.

RESULTS

Increased severity of diabetic retinopathy was significantly associated with increase in plasma levels of LPO (P < 0.05), NO (P < 0.001) and decrease in plasma levels of GSH (P < 0.0001), ISel disruption (P < 0.001) and RPE topographic alteration (P < 0.01).

CONCLUSION

Increased plasma NO levels are associated with increased severity of diabetic retinopathy. For the first time, it has been demonstrated that increased plasma LPO, NO and decreased GSH levels are associated with in vivo structural changes in inner segment ellipsoid and RPE.

Oxidants, antioxidants and mitochondrial function in non-proliferative diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a preventable cause of visual disability. The aims of the present study were to investigate levels and behavior oxidative stress markers and mitochondrial function in non-proliferative DR (NPDR) and to establish the correlation between the severity of NPDR and markers of oxidative stress and mitochondrial function.

METHODS

In a transverse analysis, type 2 diabetes mellitus (T2DM) patients with mild, moderate and severe non-proliferative DR (NPDR) were evaluated for markers of oxidative stress (i.e. products of lipid peroxidation (LPO) and nitric oxide (NO) catabolites) and antioxidant activity (i.e. total antioxidant capacity (TAC), catalase, and glutathione peroxidase (GPx) activity of erythrocytes). Mitochondrial function was also determined as the fluidity of the submitochondrial particles of platelets and the hydrolytic activity of F0 /F1 -ATPase.

RESULTS

Levels of LPO and NO were significantly increased in T2DM patients with severe NPDR (3.19 ± 0.05 μmol/mL and 45.62 ± 1.27 pmol/mL, respectively; P < 0.007 and P < 0.0001 vs levels in health volunteers, respectively), suggesting the presence of oxidative stress. TAC had significant decrease levels with minimum peak in severe retinopathy with 7.98 ± 0.48 mEq/mL (P < 0.0001). In contrast with TAC, erythrocyte catalase and GPx activity was increased in patients with severe NPDR (139.4 ± 4.4 and 117.13 ± 14.84 U/mg, respectively; P < 0.0001 vs healthy volunteers for both), suggesting an imbalance between oxidants and antioxidants. The fluidity of membrane submitochondrial particles decreased significantly in T2DM patients with mild, moderate, or severe NPDR compared with that in healthy volunteers (P < 0.0001 for all). Furthermore, there was a significant increase in the hydrolytic activity of the F0 /F1 -ATPase in T2DM patients with mild NPDR (265.07 ± 29.55 nmol/PO4 ; P < 0.0001 vs healthy volunteers), suggesting increased catabolism.

CONCLUSIONS

Patients with NPDR exhibit oxidative deregulation with decreased membrane fluidity of submitochondrial particles and increased systemic catabolism (mitochondrial dysfunction) with the potential for generalized systemic damage in T2DM.

Comparison of retinal vasodilator and constrictor responses in type 2 diabetes

PURPOSE

The retinal blood vessels provide a unique way to directly examine the human microvasculature, which is frequently damaged in individuals with diabetes. Previous studies have demonstrated that retinal flickering light-induced vasodilation and hyperoxia-induced vasoconstriction may operate by enhancing or reducing similar vasoregulatory factor(s), but a comparison between these two provocative stimuli in individuals with diabetes has not been studied. The purpose of the study was to examine the association between retinal flickering light-induced vasodilation and retinal hyperoxia-induced vasoconstriction in type 2 diabetic subjects and in healthy controls.

METHODS

Twenty men and women with type 2 diabetes and 10 men and women without diabetes between 21 and 75 years of age were recruited. Changes in retinal artery and vein diameters to flickering light and during hyperoxia (100% oxygen) stimuli were measured on the same visit using a noninvasive retinal imaging device (Dynamic Vessel Analyzer, Imedos Inc., Germany).

RESULTS

Compared with controls, diabetic subjects had impaired arterial vasodilator and vasoconstrictor responses to both flickering light and hyperoxia, respectively (both p<0.001). Merging both groups, an inverse correlation (r=-0.56; p=0.003) between the retinal artery's responses to flickering light-induced vasodilation and hyperoxia-induced vasoconstriction was demonstrated independent of glucose or insulin levels.

CONCLUSION

This suggests that both responses are attenuated to a similar degree in diabetic subjects and that the attenuation to both stimuli can be observed in retinal arteries and veins. This would suggest that similar vasoregulatory factor(s) might in part help to explain the retinal diameter responses between the two stimuli. One suggested common vasoregulator of vascular tone is nitric oxide; however, other factor(s) may be involved, which contribute to this association and require further research.

Association analysis of genetic variations of eNOS and α2β1 integrin genes with type 2 diabetic retinopathy

Background

Diabetic retinopathy (DR) is classically defined as a microvasculopathy that primarily affects the small blood vessels of the inner retina as a complication of diabetes mellitus. It has been suggested that nitric oxide (NO) and α₂β₁ integrin (a platelet receptor for collagen) play an important role in the pathogenesis of microvascular complications in DR.

Aim

The aim of this study was to investigate the association of two candidate genes involved in the regulation of retinal vasculature, endothelial nitric oxide synthase (eNOS) and α₂β₁ integrin (ITGA2) genes, with the development of DR in Egyptian patients with type 2 diabetes mellitus and to investigate whether genetic variants will affect the type of retinopathy (proliferative or nonproliferative).

Methods

In this study, 70 patients were enrolled and categorized into two groups: (1) a DR group consisting of 50 patients with DR, which was further subclassified into 25 patients with nonproliferative DR (NPDR group) and 25 patients with proliferative DR (PDR group) and (2) a diabetes without retinopathy (DWR) group, comprising 20 patients with type 2 diabetes of more than 10 years’ duration who showed no signs of DR. Associations of the genetic polymorphisms of eNOS (G894T) and ITGA2 (BgI II) were studied. Polymerase chain reaction-restriction fragment length polymorphism analysis was performed for all samples to evaluate the genotypes and correlate with the phenotype of the disease.

Results

The allele frequencies of both polymorphisms showed considerable differences between patients with and without DR. The GG genotype of G894T polymorphism of eNOS was associated with a 9.75-fold increased risk of DR (95% confidence interval 1.7–55.4) and the genotype ITGA2 BgI II (+/+) was associated with a 10.1-fold increased risk of DR (95% confidence interval 1.8–57.9), while the α₂β₁ integrin gene polymorphism of genotype distribution of both eNOS and ITGA2 polymorphisms did not differ significantly between the proliferative and nonproliferative DR groups.

Conclusion

A significant association between the G894T polymorphism of eNOS and BgI II polymorphism of ITGA2 genes and DR was observed, while there was no association between the genetic variants of those two polymorphisms and the type of retinopathy.

Nitric oxide, a janus-faced therapeutic target for diabetic microangiopathy-Friend or foe?

Accelerated atherosclerosis and microvascular complications are the leading causes of coronary heart disease, end-stage renal failure, acquired blindness and a variety of neuropathy, which could account for disabilities and high mortality rates in patients with diabetes. As the prevalence of diabetes has risen to epidemic proportions worldwide, diabetic vascular complications have now become one of the most challenging health problems. Nitric oxide (NO) is a pleiotropic molecule critical to a number of physiological and pathological processes in humans. NO not only inhibits the inflammatory-proliferative reactions in vascular wall cells, but also exerts anti-thrombogenic and endothelial cell protective properties, all of which could potentially be exploited as a therapeutic option for the treatment of vascular complications in diabetes. However, high amounts of NO produced by inducible NO synthase (iNOS) and/or peroxynitrite (ONOO(-)), a reactive intermediate of NO with superoxide anion are involved in pro-inflammatory reactions and tissue damage as well. This implies that NO is a janus-faced molecule and acts as a double-edged sword in vascular complications in diabetes. Further, NO is synthesized from l-arginine via the action of NO synthase (NOS), while NOS is blocked by endogenous l-arginine analogues such as asymmetric dimethylarginine (ADMA), a naturally occurring amino acid which is found in the plasma and various tissues. These findings suggest that amounts of NO locally produced, oxidative stress conditions and level of ADMA could determine the beneficial and detrimental effects of NO on vascular complications in diabetes. In this paper, we review the janus-faced aspects of NO in diabetic microangiopathy.

Serum nitric oxide status in patients with type 2 diabetes mellitus in Sikkim

BACKGROUND

Serum nitric oxide (NO) has emerged as a fundamental signal associated with the endothelial dysfunction in type 2 diabetes.

AIMS

To compare serum nitric oxide level among type 2 diabetic patients along with other biochemical parameters and to compare it with that of normal population in Sikkim.

SETTINGS AND DESIGN

This prospective study was carried out in the Biochemistry Department in a tertiary care teaching hospital in Sikkim on 50 type 2 diabetics compared to 100 non-diabetics.

MATERIALS AND METHODS

The un-hemolyzed blood sample was collected for estimation of biochemical parameters. Griess reaction was used for indirect assay of stable decomposition products in serum(serum nitrite and nitrate levels) as an index of NO generation. The comparison of different parameters between cases and control was done by using Student's t-test.

RESULTS

There was significant difference when age- and sex-matched cases and controls were compared in regard to waist circumference and body mass index. The values of fasting and postprandial serum glucose, and lipid profile between study group and control group differed significantly. The mean serum level of NO in the study and control group was 43.83 ± 11.3 μmoles/L and 58.85 ± 12.8 μmoles/L respectively, and this difference was statistically significant.

CONCLUSION

To sum up, serum NO was observed significantly low in diabetic participants as compared to control, along with difference in other biochemical parameters.

Effect of pan-retinal laser photocoagulation on plasma VEGF, endothelin-1 and nitric oxide in PDR

AIM

To study plasma levels of vascular endothelial growth factor (VEGF), endothelin-1(ET-1) and nitric oxide (NO) in patients with proliferative diabetic retinopathy (PDR) before and after pan-retinal photocoagulation (PRP).

METHODS

Forty patients (23 females and 17 males, mean age 48.5±12.2 years) with PDR without previous PRP therapy were studied. Blood samples were obtained before and 3 months after the last PRP session. Baseline (prelaser) plasma levels of VEGF, ET-1 and NO were compared with their levels in 30 healthy age- and sex- matched controls and also with plasma levels 3 months post-PRP.

RESULTS

Patients with PDR had significantly raised plasma VEGF (375±89ng/L), ET-1(20±5ng/L) and NO (135±53µmol/L) when compared with healthy control group (P<0.01). After PRP, there was a significant reduction in plasma VEGF (179±66ng/L), ET-1 (11±5ng/L) and NO (91±49µmol/L) levels at 3 months' follow-up but still significantly higher than healthy controls.

CONCLUSION

Patients with PDR demonstrate elevated VEGF, ET-1 and NO, which decrease after successful laser treatment.

Semicarbazide-sensitive amine oxidase activity and total nitrite and nitrate concentrations in serum: novel biochemical markers for type 2 diabetes?

The aim of this study was to evaluate the activity of semicarbazide-sensitive amine oxidase (SSAO) and the total nitrite and nitrate (NO( x )) concentrations in serum from type 2 diabetic patients and control subjects in order to evaluate if they could be used as novel diabetic markers. We studied 38 type 2 diabetic patients and 35 control subjects. Serum samples from those subjects were evaluated by radiochemical methods for SSAO activity using (14)C-benzylamine. Serum NO( x ) concentrations were obtained as an index of nitric oxide production by the Griess reaction. Serum SSAO activity was higher in type 2 diabetic patients than in control group and serum SSAO in type 2 diabetic correlated with age, serum creatinine and total cholesterol. Serum NO( x ) levels in type 2 diabetic patients were also significantly higher than those in the control group. Serum NO( x ) levels in control group correlated with serum SSAO activity. In conclusion, the increase in the SSAO activity and NO( x ) levels observed in type 2 diabetic patients could be parameters to take in account and play relevant role in diabetes development. SSAO and NO( x ) are suggested as markers for prognostic of diabetes.

Positive and negative regulation of insulin signaling by reactive oxygen and nitrogen species

Regulated production of reactive oxygen species (ROS)/reactive nitrogen species (RNS) adequately balanced by antioxidant systems is a prerequisite for the participation of these active substances in physiological processes, including insulin action. Yet, increasing evidence implicates ROS and RNS as negative regulators of insulin signaling, rendering them putative mediators in the development of insulin resistance, a common endocrine abnormality that accompanies obesity and is a risk factor of type 2 diabetes. This review deals with this dual, seemingly contradictory, function of ROS and RNS in regulating insulin action: the major processes for ROS and RNS generation and detoxification are presented, and a critical review of the evidence that they participate in the positive and negative regulation of insulin action is provided. The cellular and molecular mechanisms by which ROS and RNS are thought to participate in normal insulin action and in the induction of insulin resistance are then described. Finally, we explore the potential usefulness and the challenges in modulating the oxidant-antioxidant balance as a potentially promising, but currently disappointing, means of improving insulin action in insulin resistance-associated conditions, leading causes of human morbidity and mortality of our era.

A role for excitatory amino acids in diabetic eye disease

Diabetic retinopathy is a leading cause of vision loss. The primary clinical hallmarks are vascular changes that appear to contribute to the loss of sight. In a number of neurodegenerative disorders there is an appreciation that increased levels of excitatory amino acids are excitotoxic. The primary amino acid responsible appears to be the neurotransmitter glutamate. This review examines the nature of glutamatergic signaling at the retina and the growing evidence from clinical and animal model studies that glutamate may be playing similar excitotoxic roles at the diabetic retina.