Role of renal nitric oxide synthase in diabetic kidney disease during the chronic phase of diabetes

Nonselective and A2a-Selective Inhibition of Adenosine Receptors Modulates Renal Perfusion and Excretion Depending on the Duration of Streptozotocin-Induced Diabetes in Rats

Long-lasting hyperglycaemia may alter the role of adenosine-dependent receptors (P1R) in the control of kidney function. We investigated how P1R activity affects renal circulation and excretion in diabetic (DM) and normoglycaemic (NG) rats; the receptors' interactions with bioavailable NO and H₂O₂ were also explored. The effects of adenosine deaminase (ADA, nonselective P1R inhibitor) and P1A2a-R-selective antagonist (CSC) were examined in anaesthetised rats, both after short-lasting (2-weeks, DM-14) and established (8-weeks, DM-60) streptozotocin-induced hyperglycaemia, and in normoglycaemic age-matched animals (NG-14, NG-60, respectively). The arterial blood pressure, perfusion of the whole kidney and its regions (cortex, outer-, and inner medulla), and renal excretion were determined, along with the in situ renal tissue NO and H₂O₂ signals (selective electrodes). The ADA treatment helped to assess the P1R-dependent difference in intrarenal baseline vascular tone (vasodilation in DM and vasoconstriction in NG rats), with the difference being more pronounced between DM-60 and NG-60 animals. The CSC treatment showed that in DM-60 rats, A2aR-dependent vasodilator tone was modified differently in individual kidney zones. Renal excretion studies after the ADA and CSC treatments showed that the balance of the opposing effects of A2aRs and other P1Rs on tubular transport, seen in the initial phase, was lost in established hyperglycaemia. Regardless of the duration of the diabetes, we observed a tonic effect of A2aR activity on NO bioavailability. Dissimilarly, the involvement of P1R in tissue production of H₂O₂, observed in normoglycaemia, decreased. Our functional study provides new information on the changing interaction of adenosine in the kidney, as well as its receptors and NO and H₂O₂, in the course of streptozotocin diabetes.

The expanding roles of neuronal nitric oxide synthase (NOS1)

The nitric oxide synthases (NOS; EC 1.14.13.39) use L-arginine as a substrate to produce nitric oxide (NO) as a by-product in the tissue microenvironment. NOS1 represents the predominant NO-producing enzyme highly enriched in the brain and known to mediate multiple functions, ranging from learning and memory development to maintaining synaptic plasticity and neuronal development, Alzheimer's disease (AD), psychiatric disorders and behavioral deficits. However, accumulating evidence indicate both canonical and non-canonical roles of NOS1-derived NO in several other tissues and chronic diseases. A better understanding of NOS1-derived NO signaling, and identification and characterization of NO-metabolites in non-neuronal tissues could become useful in diagnosis and prognosis of diseases associated with NOS1 expression. Continued investigation on the roles of NOS1, therefore, will synthesize new knowledge and aid in the discovery of small molecules which could be used to titrate the activities of NOS1-derived NO signaling and NO-metabolites. Here, we address the significance of NOS1 and its byproduct NO in modifying pathophysiological events, which could be beneficial in understanding both the disease mechanisms and therapeutics.

Activation of soluble guanylyl cyclase signalling with cinaciguat improves impaired kidney function in diabetic mice

BACKGROUND AND PURPOSE

Diabetic nephropathy is the leading cause for end-stage renal disease worldwide. Until now, there is no specific therapy available. Standard treatment with inhibitors of the renin-angiotensin system just slows down progression. However, targeting the NO/sGC/cGMP pathway using sGC activators does prevent kidney damage. Thus, we investigated if the sGC activator cinaciguat was beneficial in a mouse model of diabetic nephropathy, and we analysed how mesangial cells (MCs) were affected by related conditions in cell culture.

EXPERIMENTAL APPROACH

Type 1 diabetes was induced with streptozotocin in wild-type and endothelial NOS knockout (eNOS KO) mice for 8 or 12 weeks.. Half of these mice received cinaciguat in their chow for the last 4 weeks. Kidneys from the diabetic mice were analysed with histochemical assays and by RT-PCR and western blotting. . Additionally, primary murine MCs under diabetic conditions were stimulated with 8-Br-cGMP or cinaciguat to activate the sGC/cGMP pathway.

KEY RESULTS

The diabetic eNOS KO mice developed most characteristics of diabetic nephropathy, most marked at 12 weeks. Treatment with cinaciguat markedly improved GFR, serum creatinine, mesangial expansion and kidney fibrosis in these animals. We determined expression levels of related signalling proteins. Thrombospondin 1, a key mediator in kidney diseases, was strongly up-regulated under diabetic conditions and this increase was suppressed by activation of sGC/cGMP signalling.

CONCLUSION AND IMPLICATIONS

Activation of the NO/sGC/PKG pathway with cinaciguat was beneficial in a model of diabetic nephropathy. Activators of sGC might be an appropriate therapy option in patients with Type 1 diabetes.

Nitric Oxide Gene Polymorphism is a Risk Factor for Diabetic Nephropathy and Atherosclerosis in Type 1 Diabetic Patients

AIM:

To assess the risk factor for diabetic atherosclerosis nephropathy and diabetic nephropathy in type 1 diabetic patients.

PATIENTS AND METHODS:

Thirty healthy volunteers age and sex-matched and Sixty-five type 1 diabetic patient were in rolled in the study. The mean age of patients was 17.99 ± 2.59 years, mean age of onset of diabetes was 7.00 ± 3.28 years, mean duration of diabetes was 10.91 ± 3.54 years. Glycosylated sex-matched (HbA1c) was assessed in blood samples, serum lipid profile was determined, and serum level of oxidised low-density lipoprotein (OxLDL), and nitric oxide was evaluated by enzyme-linked immunosorbent assay (ELISA) technique. Nitric oxide 894G > T genotype was analysed by (PCR-RFLP) method and confirmed by Sequencing. Assessment of the albumin / creatinine ratio was done in urine samples. Renal Doppler and Carotid intima-media thickness (cIMT) via ultrasound was also performed.

RESULTS:

OxLDL, lipid profile, albumin/creatinine ratio, cIMT and resistivity index were significantly higher in diabetic patients while nitric oxide was significantly lower. Nitric oxide genotype shows no significant difference between diabetic’s patients and controls. Diabetic patients with homozygous NO had a significantly lower serum level of Nitric oxide, a significantly higher OxLDL, albumin / creatinine ratio and lipid profile.

CONCLUSION:

diabetic patients are liable for the occurrence of early diabetic nephropathy and atherosclerosis as a result of the presence of low level of nitric oxide. Nitric oxide gene polymorphism 894G > T in diabetic patients is a risk factor for diabetic nephropathy and atherosclerosis.

Phosphodiesterase Type 5 Inhibition Reduces Albuminuria in Subjects with Overt Diabetic Nephropathy

Diabetic nephropathy (DN) is the leading cause of ESRD worldwide. Reduced bioavailability or uncoupling of nitric oxide in the kidney, leading to decreased intracellular levels of the nitric oxide pathway effector molecule cyclic guanosine monophosphate (cGMP), has been implicated in the progression of DN. Preclinical studies suggest that elevating the cGMP intracellular pool through inhibition of the cGMP-hydrolyzing enzyme phosphodiesterase type 5 (PDE5) might exert renoprotective effects in DN. To test this hypothesis, the novel, highly specific, and long-acting PDE5 inhibitor, PF-00489791, was assessed in a multinational, multicenter, randomized, double-blind, placebo-controlled, parallel group trial of subjects with type 2 diabetes mellitus and overt nephropathy receiving angiotensin converting enzyme inhibitor or angiotensin receptor blocker background therapy. In total, 256 subjects with an eGFR between 25 and 60 ml/min per 1.73 m² and macroalbuminuria defined by a urinary albumin-to-creatinine ratio >300 mg/g, were randomly assigned 3:1, respectively, to receive PF-00489791 (20 mg) or placebo orally, once daily for 12 weeks. Using the predefined primary assessment of efficacy (Bayesian analysis with informative prior), we observed a significant reduction in urinary albumin-to-creatinine ratio of 15.7% (ratio 0.843; 95% credible interval 0.73 to 0.98) in response to the 12-week treatment with PF-00489791 compared with placebo. PF-00489791 was safe and generally well tolerated in this patient population. Most common adverse events were mild in severity and included headache and upper gastrointestinal events. In conclusion, the safety and efficacy profile of PDE5 inhibitor PF-00489791 supports further investigation as a novel therapy to improve renal outcomes in DN.

Correlation of Endothelial Nitric Oxide Synthase Gene Polymorphism (GG, TT and GT Genotype) with Proteinuria and Retinopathy in Type 2 Diabetic Patients

BACKGROUND

Nephropathy is the most important leading cause of end stage renal failure in type 2 diabetic patients, so numerous studies were done to diagnose and evaluate risk factors of diabetic nephropathy (DN). Some gene polymorphisms may be associated with progression or regression of DN, so the aim of this study was to compare prevalence of eNOS gene polymorphism in diabetic patients with controls and its association with diabetic nephropathy.

MATERIALS AND METHODS

In a cross-sectional study, 94 type 2 diabetic patients and 94 normal participants were enrolled. Patients without retinopathy were excluded from this study. For all of the patients, fasting blood sugar (FBS), 2 hours post-prandial (BS), Blood Urea Nitrogen (BUN), Creatinine (Cr), 24 hours urine protein were measured in the case group. Endothelial nitric oxide synthetase gene polymorphism was evaluated in the case and control groups.

RESULTS

There was no significant difference based on age and sex between patients in case and control groups. GG genotype of eNOS was less common in the patient group compared to control group. There was no difference between prevalence of TT, GT or GG genotype based on age and sex. There was no correlation between diabetic retinopathy or proteinuria and genotypes of eNOs.

CONCLUSION

The study showed that in type 2 diabetic patients, NOS gene polymorphism was more common compared to normal population; however, there is no correlation between this gene polymorphism and proteinuria or retinopathy in these patients.

Propyl gallate plays a nephroprotective role in early stage of diabetic nephropathy associated with suppression of glomerular endothelial cell proliferation and angiogenesis

There is growing evidence suggesting that glomerular endothelial cell proliferation and angiogenesis may be responsible for the pathophysiological events in the early stage of diabetic nephropathy. This study was designed to investigate the factors related to glomerular endothelial cell proliferation and glomerular angiogenesis and assess the effect of propyl gallate on preventing these disorders in diabetic rats. We found that glomerular hypertrophy, glomerular mesangial matrix expansion, and albuminuria were significantly increased in DN rats. CD31+ endothelial cells significantly increased in glomerulus of diabetic rats. Double immunofluorescence staining showed some structurally defective vasculus tubes in glomerulus. Real-time PCR and western blot demonstrated the glomerular eNOS expression remained at the same level, while remarkable decreased NO productions and suppressed eNOS activities were observed in diabetic rats. Treatment with propyl gallate improved glomerular pathological changes, reduced endothelial cell proliferation, decreased albuminuria, and restored eNOS activity, but did not alter eNOS expression. These data suggest that endothelial cell proliferation and immature angiogenesis may be the contributors to progression of DN. Propyl gallate is a potential novel therapeutic agent on prevention of diabetic nephropathy.

Hyperfiltration and effect of nitric oxide inhibition on renal and endothelial function in humans with uncomplicated type 1 diabetes mellitus

Studies of experimental diabetes mellitus (DM) suggest that increased nitric oxide (NO) bioactivity contributes to renal hyperfiltration. However, the role of NO in mediating hyperfiltration has not been fully elucidated in humans. Our aim was to examine the effect of NO synthase inhibition on renal and peripheral vascular function in normotensive subjects with uncomplicated type 1 DM. Renal function and brachial artery flow-mediated vasodilatation (FMD) were measured before and after an intravenous infusion of the NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NMMA) in 21 healthy control and 37 type 1 DM patients. Measurements in DM participants were made under clamped euglycemic conditions. The effect of l-NMMA on circulating and urinary NO metabolites (NO(x)) and cGMP and on urinary prostanoids was also determined. Baseline characteristics were similar in the two groups. For analysis, the DM patients were divided into those with hyperfiltration (DM-H, n = 18) and normal glomerular filtration rate (GFR) levels (DM-N, n = 19). Baseline urine NO(x) and cGMP were highest in DM-H. l-NMMA led to a decline in GFR in DM-H (152 ± 16 to 140 ± 11 ml·min(-1)·1.73 m(-2)) but not DM-N or healthy control participants. The decline in effective renal plasma flow in response to l-NMMA (806 ± 112 to 539 ± 80 ml·min(-1)·1.73 m(-2)) in DM-H was also exaggerated compared with the other groups (repeated measures ANOVA, P < 0.05), along with declines in urinary NO(x) metabolites and cGMP. Baseline FMD was lowest in DM-H compared with the other groups and did not change in response to l-NMMA. l-NMMA reduced FMD and plasma markers of NO bioactivity in the healthy control and DM-N groups. In patients with uncomplicated type 1 DM, renal hyperfiltration is associated with increased NO bioactivity in the kidney and reduced NO bioactivity in the systemic circulation, suggesting a paradoxical state of high renal and low systemic vascular NO bioactivity.

Regulation of cell volume by glycosaminoglycans

Cell volume is regulated by a delicate balance between ion distribution across the plasma membrane and the osmotic properties of intra- and extracellular components. Using a fluorescent calcein indicator, we analysed the effects of glycosaminoglycans on the cell volume of hyaluronan producing fibroblasts and hyaluronan deficient HEK cells over a time period of 30 h. Exogenous glycosaminoglycans induced cell blebbing after 2 min and swelling of fibroblasts to about 110% of untreated cell volume at low concentrations which decreased at higher concentrations. HEK cells did not show cell blebbing and responded by shrinking to 65% of untreated cell volume. Heparin induced swelling of both fibroblasts and HEK cells. Hyaluronidase treatment or inhibition of hyaluronan export led to cell shrinkage indicating that the hyaluronan coat maintained fibroblasts in a swollen state. These observations were explained by the combined action of the Donnan effect and molecular crowding.

The emerging role of NO and IGF-1 in early renal hypertrophy in STZ-induced diabetic rats

BACKGROUND

Diabetic nephropathy (DN) is a major complication of diabetes mellitus, and the most common cause of end-stage renal disease. DN is characterized by early hyperfiltration and renal hypertrophy, which are associated with increased renal insulin-like growth factor-1 (IGF-1) levels. The relationship between IGF-1 and nitric oxide (NO) in DN is not established. The aim of this study was to investigate the effects of NO system modulation on the IGF-1-mediated hypertrophy and hyperfiltration during the first week after diabetes induction.

METHODS

Diabetes was induced in rats by streptozotocin (STZ) injection. Diabetic rats were treated with NO synthase inhibitor L-NG-nitroarginine methyl ester (L-NAME). Various serum IGF-binding proteins (IGFBPs) and renal IGFBP1 expression was evaluated. Urine and plasma NO(2) + NO(3) level analysis was also performed.

RESULTS

STZ induced hyperglycaemia decreased plasma insulin levels and brought about a decrease in body weight. L-NAME administration to diabetic rats significantly prevented renal hypertrophy and hyperfiltration. Serum IGFBP3, IGFBP4 and 30-kDa IGFBP fraction were all significantly reduced in diabetic rats, compared with those in non-diabetic control rats. However, the renal IGFBP1 mRNA expression in diabetic rats was significantly higher. These changes were accompanied by an increased in NO production. L-NAME administration prevented the serum IGFBP decline, without significantly affecting the renal IGFBP1 mRNA expression.

CONCLUSIONS

We have shown that increased renal IGF-1 and increased NO production during the very early stages of STZ-induced DN are associated with renal hypertrophy and hyperfiltration in diabetic rats. Modulating the IGF-1 availability to the kidney by nitric oxide synthase inhibition significantly reduced renal hypertrophy and hyperfiltration during the first week of STZ-induced diabetes mellitus.

Dysregulation of corticosterone secretion in streptozotocin-diabetic rats: modulatory role of the adrenocortical nitrergic system

An increased activity of the hypothalamo-pituitary-adrenal axis resulting in exaggerated glucocorticoid secretion has been repeatedly described in patients with diabetes mellitus and in animal models of this disease. However, it has been pointed out that experimental diabetes is accompanied by a decreased glucocorticoid response to ACTH stimulation. Because previous studies from our laboratory demonstrate the involvement of nitric oxide (NO) in the modulation of corticosterone production, present investigations were designed to evaluate 1) the impact of streptozotocin (STZ)-induced diabetes on the adrenocortical nitrergic system and 2) the role of NO in the modulation of adrenal steroidogenesis in STZ-diabetic rats. Four weeks after STZ injection, increased activity and expression levels of proteins involved in L-arginine transport and in NO synthesis were detected, and increased levels of thiobarbituric acid reactive species, carbonyl adducts, and nitrotyrosine-modified proteins were measured in the adrenocortical tissue of hyperglycemic rats. An impaired corticosterone response to ACTH was evident both in vivo and in adrenocortical cells isolated from STZ-treated animals. Inhibition of NO synthase activity resulted in higher corticosterone generation in adrenal tissue from STZ-treated rats. Moreover, a stronger inhibition of steroid output from adrenal cells by a NO donor was observed in adrenocortical Y1 cells previously subjected to high glucose (30 mM) treatment. In summary, results presented herein indicate an inhibitory effect of endogenously generated NO on steroid production, probably potentiated by hyperglycemia-induced oxidative stress, in the adrenal cortex of STZ-treated rats.

[Molecular bases of diabetic nephropathy]

The determinant of the diabetic nephropathy is hyperglycemia, but hypertension and other genetic factors are also involved. Glomerulus is the focus of the injury, where mesangial cell proliferation and extracellular matrix occur because of the increase of the intra- and extracellular glucose concentration and overexpression of GLUT1. Sequentially, there are increases in the flow by the poliol pathway, oxidative stress, increased intracellular production of advanced glycation end products (AGEs), activation of the PKC pathway, increase of the activity of the hexosamine pathway, and activation of TGF-beta1. High glucose concentrations also increase angiotensin II (AII) levels. Therefore, glucose and AII exert similar effects in inducing extracellular matrix formation in the mesangial cells, using similar transductional signal, which increases TGF-beta1 levels. In this review we focus in the effect of glucose and AII in the mesangial cells in causing the events related to the genesis of diabetic nephropathy. The alterations in the signal pathways discussed in this review give support to the observational studies and clinical assays, where metabolic and antihypertensive controls obtained with angiotensin-converting inhibitors have shown important and additive effect in the prevention of the beginning and progression of diabetic nephropathy. New therapeutic strategies directed to the described intracellular events may give future additional benefits.

Experimental models for nephropathy

Nephropathy is a leading cause of morbidity and mortality and its prevalence is continuously increasing in industrialised nations. Nephropathy is characterised to varying degrees by nodular glomerulosclerosis, glomerular basement membrane thickness and mesangial expansion, leading to a decline in glomerular filtration rate, persistent elevated albuminuria, elevated arterial blood pressure and fluid retention. Hyperglycaemia, hyperlipidaemia and hypertension are considered to be the major risk factors implicated in the progression of nephropathy.Various signalling systems, such as vasoconstrictor peptides, inflammatory mediators, growth factors and adhesion molecules, are involved in the pathogenesis of nephropathy.At present, no promising therapy is available to treat patients with nephropathy due to lack of understanding of signalling culprits involved in the pathogenesis of nephropathy. Animal models are being developed to better understand the disease pathogenesis and develop drugs for nephropathy. In the present review, we have discussed various animal models for nephropathy, which may open vistas for developing new drugs to treat nephropathy.

Succinate receptor GPR91 provides a direct link between high glucose levels and renin release in murine and rabbit kidney

Diabetes mellitus is the most common and rapidly growing cause of end-stage renal disease in developed countries. A classic hallmark of early diabetes mellitus includes activation of the renin-angiotensin system (RAS), which may lead to hypertension and renal tissue injury, but the mechanism of RAS activation is elusive. Here we identified a paracrine signaling pathway in the kidney in which high levels of glucose directly triggered the release of the prohypertensive hormone renin. The signaling cascade involved the local accumulation of succinate and activation of the kidney-specific G protein-coupled metabolic receptor, GPR91, in the glomerular endothelium as observed in rat, mouse, and rabbit kidney sections. Elements of signal transduction included endothelial Ca2+, the production of NO and prostaglandin (PGE2), and their paracrine actions on adjacent renin-producing cells. This GPR91 signaling cascade may serve to modulate kidney function and help remove metabolic waste products through renal hyperfiltration, and it could also link metabolic diseases, such as diabetes, or metabolic syndrome with RAS overactivation, systemic hypertension, and organ injury.

Dynamic myogenic autoregulation in the rat kidney: a whole-organ model

A transient 1D mathematical model of whole-organ renal autoregulation in the rat is presented, examining the myogenic response on multiple levels of the renal vasculature. Morphological data derived from micro-CT imaging were employed to divide the vasculature via a Strahler ordering scheme. A previously published model of the myogenic response based on wall tension is expanded and adapted to fit the response of each level, corresponding to a distally dominant resistance distribution with the highest contributions localized to the afferent arterioles and interlobular arteries. The mathematical model was further developed to include the effects of in vivo viscosity variation and flow-induced dilation via endothelial nitric oxide production. Computer simulations of the autoregulatory response to pressure perturbations were examined and compared with experimental data. The model supports the hypothesis that change in circumferential wall tension is the catalyst for the myogenic response. The model provides a basis for examining the steady state and transient characteristics of the whole-organ renal myogenic response in the rat, as well as the modulatory influences of metabolic and hemodynamic factors.