Nitric oxide and kidney oxygenation

The Effects of Baicalin on Myoglobinuric Acute Renal Failure in Rats

Background:

Myoglobinuric acute kidney injury is a uremic syndrome that develops due to damage of skeletal muscle. Free radicals and nitric oxide play an important role in the pathogenesis of myoglobinuric acute kidney injury. Baicalin has multiple bioactivities, including antimicrobial, anti-inflammatory and antioxidant properties and is a potent free radical scavenger.

Aims:

To investigate the nephroprotective mechanism of baicalin on myoglobinuric acute kidney injury.

Study Design:

Animal experimentation.

Methods:

In our study, male Sprague Dawley rats were divided into 4 groups. Control (n=8), Baicalin (n=8), myoglobinuric acute kidney injury (n=10) and myoglobinuric acute kidney injury + baicalin (n=10). The rats were deprived of water for 24 hours before receiving intramuscular injection. The control and baicalin groups were injected intramuscularly with saline (8 ml/kg), and the myoglobinuric acute kidney injury and myoglobinuric acute kidney injury + baicalin groups were given 50% glycerol 8 ml/kg. One hour later, the control and myoglobinuric acute kidney injury groups received saline intraperitoneally, and the baicalin and myoglobinuric acute kidney injury + baicalin groups were given 200 mg/kg baicalin. Twenty-four hours after the glycerol injection, urine and blood samples were taken, and the kidneys of the rats were harvested under intraperitoneally injections of anaesthesia.

Results:

We found that the levels of creatinine, urea, nitric oxide, alanine transaminase, aspartate aminotransferase, creatine kinase in serum samples, malondialdehyde, nitric oxide, inducible nitric oxide synthase, and endothelial nitric oxide synthase concentrations in renal tissue were increased in the myoglobinuric acute kidney injury group compared with the control group (p<0.05). The nitric oxide and glutathione levels in the kidney were significantly decreased in the myoglobinuric acute kidney injury + baicalin group compared with the myoglobinuric acute kidney injury group (p<0.05). There were no significant differences between any other parameters.

Conclusion:

Our results did not show any protective effect of baicalin on myoglobinuric acute kidney injury, possibly because the different effective factors in the pathogenesis of experimental myoglobinuric acute kidney injury used in this experiment deviate from other experimental models. Moreover, detailed studies are needed to clarify the effects of baicalin in different doses and treatment durations in glycerol-induced acute kidney injury model.

A mechanistic link between renal ischemia and fibrosis

Renal fibrosis is characterized by tubular cell atrophy and accumulation of extracellular matrix. Fibroblast activation becomes evident in areas surrounding atrophic tubules, with rarefaction of peritubular capillaries. Tubulointerstitial hypoxia is the final common pathway in progressive kidney disease. Hypoxia suppresses tubular epithelial growth and leads to failure of remodeling by facilitating dedifferentiation and apoptosis. Profibrotic factors such as transforming growth factor-β (TGF-β) mediate fibroblast activation, and recruited leukocytes, which appear in hypoxic areas, contribute to fibrosis. While resident renal cells adapt to the hypoxic environment via upregulation of relevant genes by hypoxia-inducible factor (HIF) family members, hypoxic adaptation via HIF may not be sufficient in chronic kidney disease (CKD) due to multiple factors. Thus, restoration of HIF-mediated responses may contribute to amelioration of CKD pathology. Studies to date have reported that HIF activation reduces inflammation and oxidative stress and ameliorates injury by decreasing tubular cell apoptosis and restoring peritubular capillary network. Prolyl hydroxylase domain (PHD) inhibitors that specifically activate HIF are currently evaluated for the treatment of renal anemia and may be effective for the treatment of CKD.

Endothelial nitric oxide synthase (eNOS) 4b/a polymorphism and the risk of diabetic nephropathy in type 2 diabetes mellitus: A meta-analysis

Many studies have accessed the association between eNOS-4b/a polymorphism and the risk of diabetic nephropathy (DN) among type 2 diabetic subjects. However, the results are conflicting and inconclusive. The aim of current meta-analysis was to more precisely estimate the relationship. Pubmed, Embase, the China National Knowledge Infrastructure and the Wanfang Database were searched for articles published up to May 26th, 2013 that addressed eNOS-4b/a polymorphism and the risk of DN among type 2 diabetic subjects. 18 studies were included in this meta-analysis. eNOS-4b/a polymorphisms were associated with an overall significantly increased risk of DN (allele model: OR = 1.44, 95% CI = 1.14-1.82; additive model: OR = 2.03, 95% CI = 1.14-3.62; dominant model: OR = 1.34, 95% CI = 1.07-1.68; recessive model: OR = 2.01, 95% CI = 1.12-3.61). Subgroup analysis revealed a significant association between the eNOS-4b/a polymorphism and DN in Asian population, especially in Chinese population, but not in non Asian populations. Our meta-analysis supported an association between the 4b/a polymorphism of eNOS gene and increased risk of DN in type 2 diabetes among Asians, especially in Chinese population.

Pathophysiology of the diabetic kidney

Diabetes mellitus contributes greatly to morbidity, mortality, and overall health care costs. In major part, these outcomes derive from the high incidence of progressive kidney dysfunction in patients with diabetes making diabetic nephropathy a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved and of the early dysfunctions observed in the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. Here we review the pathophysiological changes that occur in the kidney in response to hyperglycemia, including the cellular responses to high glucose and the responses in vascular, glomerular, podocyte, and tubular function. The molecular basis, characteristics, and consequences of the unique growth phenotypes observed in the diabetic kidney, including glomerular structures and tubular segments, are outlined. We delineate mechanisms of early diabetic glomerular hyperfiltration including primary vascular events as well as the primary role of tubular growth, hyperreabsorption, and tubuloglomerular communication as part of a "tubulocentric" concept of early diabetic kidney function. The latter also explains the "salt paradox" of the early diabetic kidney, that is, a unique and inverse relationship between glomerular filtration rate and dietary salt intake. The mechanisms and consequences of the intrarenal activation of the renin-angiotensin system and of diabetes-induced tubular glycogen accumulation are discussed. Moreover, we aim to link the changes that occur early in the diabetic kidney including the growth phenotype, oxidative stress, hypoxia, and formation of advanced glycation end products to mechanisms involved in progressive kidney disease.

Metabolic control of renin secretion

One emerging topic in renin-angiotensin system (RAS) research is the direct local control of renin synthesis and release by endogenous metabolic intermediates. During the past few years, our laboratory has characterized the localization and signaling of the novel metabolic receptor GPR91 in the normal and diabetic kidney and established GPR91 as a new, direct link between high glucose and RAS activation in diabetes. GPR91 (also called SUCNR1) binds tricarboxylic acid (TCA) cycle intermediate succinate which can rapidly accumulate in the local tissue environment when energy supply and demand are out of balance. In a variety of physiological and pathological conditions associated with metabolic stress, succinate signaling via GPR91 appears to be an important mediator or modulator of renin secretion. This review summarizes our current knowledge on the control of renin release by molecules of endogenous metabolic pathways with the main focus on succinate/GPR91.

New approach to beta cell function screening by nitric oxide assessment of obese individuals at the population level

Background

Approximately 27% of Americans today are obese, and this condition increases the prevalence of metabolic syndrome and diabetes. The UK Prospective Diabetes Study suggests that loss of beta cell function can begin at least 10 years before diagnosis, and mean beta cell function is already less than 50% at diagnosis. The aim of this research was to assess the possibility of detecting loss of beta cell function in obese patients by a novel approach involving nitric oxide assessment using a combination of technologies.

Materials and methods

One hundred and fifteen obese patients (93 women, 22 men) of mean age 39 (range 17–62) years, who were candidates for bariatric surgery were included in the study, and underwent laboratory tests, including fasting blood glucose, fasting insulin plasma, and examination with the Electro Sensor complex. The Electro Sensor complex offers a new way to assess nitric oxide production using five technologies managed by software, ie, the galvanic skin response, photoelectrical plethysmography, heart rate variability analysis, bioimpedance analysis, and blood pressure oscillometric measurements. The homeostasis model assessment 2% beta cell function (HOMA2% β) algorithm was calculated from fasting blood glucose and fasting insulin plasma using free software provided by The University of Oxford Diabetes Trial Unit. The Electro Sensor complex percent beta (ESC% β) algorithm was calculated from the Electro Sensor complex data and statistical neural network. Statistical analysis was performed to correlate ESC% β and HOMA2% β using the coefficient of correlation and Spearman’s coefficient of rank correlation. Receiver-operating characteristic curves were also constructed to determine the specificity and sensitivity of ESC% β in detecting a HOMA2% β value < 100.

Results

The coefficient of correlation between ESC% β and HOMA2% β was 0.72 (using log values) and the Spearman’s coefficient of rank correlation (rho) was 0.799 (P < 0.0001). ESC% β had a sensitivity of 77.14% and specificity of 78.21% (cutoff ≤ 157, corresponding to 40% after conversion into a 0%–100% scale) to detect a HOMA2% β value < 100 (P < 0.0001).

Conclusion

The ESC% β algorithm has a high predictive correlation with HOMA2% β, and good specificity and sensitivity to detect a HOMA2% β value < 100. Therefore, the Electro Sensor complex enabling nitric oxide assessment represents a novel method of screening for beta cell function in the obese population on a large scale. Such a tool, which is easy to administer, noninvasive, and cost-effective, would be of great benefit for widespread screening of beta cell function in obese patients.

Idiopathic Recurrent Calcium Urolithiasis (IRCU): pathophysiology evaluated in light of oxidative metabolism, without and with variation of several biomarkers in fasting urine and plasma--a comparison of stone-free and -bearing male patients, emphasizing mineral, acid-base, blood pressure and protein status

BACKGROUND

IRCU is traditionally considered as life?style disease (associations with, among others, overweight, obesity, hypertension, type-2 diabetes), arising from excess, in 24 h urine, of calcium (Ca) salts (calcium oxalate (CaOx), calcium phosphate (CaPi)), supersaturation of, and crystallization in, tubular fluid and urine, causing crystal-induced epithelial cell damage, proteinuria, crystal aggregation and uroliths.

METHODS

Another picture emerges from the present uncontrolled study of 154 male adult IRCU patients (75 stone-bearing (SB) and 79 age-matched stone-free (SF)), in whom stone-forming and other parameters in fasting urine and plasma were contrasted with five biomarkers (see footnote) of oxidative metabolism (OM), without and with variation of markers.

RESULTS

1) In SB vs. SF unstratified OM biomarkers were statistically unchanged, but the majority of patients was overweight; despite, in SB vs. SF urine pH, total and non-albumin protein concentration were elevated, fractional urinary uric acid excretion and blood bicarbonate decreased, whereas urine volume, sodium, supersaturation with CaOx and CaPi (as hydroxyapatite) were unchanged; 2) upon variation of OM markers (strata below and above median) numerous stone parameters differed significantly, among others urine volume, total protein, Ca/Pi ratio, pH, sodium, potassium, plasma Ca/Pi ratio and parathyroid hormone, blood pressure, renal excretion of non-albumin protein and other substances; 3) a significant shift from SF to SB patients occurred with increase of urine pH, decrease of blood bicarbonate, and increase of diastolic blood pressure, whereas increase of plasma uric acid impacted only marginally; 4) in both SF and SB patients a strong curvilinear relationship links a rise of urine Ca/Pi to urine Ca/Pi divided by plasma Ca/Pi, but in SB urine Ca/Pi failed to correlate significantly with urine hydroxyapatite supersaturation; 5) also in SB, plasma Ca/Pi and urinary nitrate were negatively correlated, whereas in SF plasma Ca/Pi ratio, PTH and body mass index correlated positively; 6) multivariate regression analysis revealed that PTH, body mass index and nitrate together could explain 22 (p = 0.002) and only 7 (p = 0.06) per cent of variation of plasma Ca/Pi in SF and SB, respectively.

CONCLUSIONS

In IRCU a) numerous constituents of fasting urine, plasma, blood and blood pressure change in response to variation of OM biomarkers, suggesting involvement of OM imbalance as factor in functional deterioration of tissue; b) in the majority of patients a positive exponential relationship links urine Ca/Pi to urine Ca/Pi divided by plasma Ca/Pi, presumably to accumulate Ca outside tubular lumen, thereby minimizing intratubular and urinary Ca salt crystallization; c) alteration of interactions of low urine nitrate, PTH and Ca/Pi in plasma may be of importance in formation of new Ca stone and co-regulation of dynamics of blood vasculature; d) overweight, combined with OM-modified renal interstitial environment appears to facilitate these processes, carrying the risk that CaPi mineral develops within or/and close to blood vessel tissue, and spreads towards urothelium. - For future research focussing on IRCU pathogenesis studies are recommended on the role of affluent lifestyle mediated renal ischemia, mild hypertensive nephropathy, rise of uric acid precursor oxypurines and uricemia, clarifying also why loss of significance of interrelationships of OM biomarkers with traditional Ca stone risk factors is characteristic for SB patients.

Noninvasive evaluation of kidney hypoxia and fibrosis using magnetic resonance imaging

Interstitial fibrosis and hypoxia accelerate the progression of CKD, but clinical tools to quantitate these factors in patients are lacking. Here, we evaluated the use of two magnetic resonance imaging (MRI) techniques, diffusion-weighted (DW)-MRI and blood oxygen level-dependent (BOLD)-MRI, to assess kidney fibrosis and hypoxia of the cortex in 142 patients with either diabetic nephropathy (n = 43), CKD without diabetes (n = 76), or acute kidney injury (AKI) (n = 23). Apparent diffusion coefficient (ADC) values of DW-MRI correlated with estimated glomerular filtration rates (eGFR) in the diabetic nephropathy and CKD groups (r(2) = 0.56 and r(2) = 0.46, respectively). Although the T2* values of BOLD-MRI and eGFR displayed good correlation in the CKD group (r(2) = 0.38), we did not observe a significant correlation between these values in the diabetic nephropathy group, suggesting that factors other than tubulointerstitial alteration determine the degree of hypoxia in the renal cortex. In the AKI group, neither the T2* nor ADC values correlated with eGFR. Renal biopsies from patients with CKD demonstrated that the T2* and ADC MRI values correlated with renal pathology. Taken together, ADC and T2* values appear to serve as accurate indices for evaluating renal tubulointerstitial alterations and parenchymal hypoxia, respectively, in the cortex. Functional MRI can thus contribute to multilateral, noninvasive, in vivo assessment of kidney function.

The proximal tubule in the pathophysiology of the diabetic kidney

Diabetic nephropathy is a leading cause of end-stage renal disease. A better understanding of the molecular mechanism involved in the early changes of the diabetic kidney may permit the development of new strategies to prevent diabetic nephropathy. This review focuses on the proximal tubule in the early diabetic kidney, particularly on its exposure and response to high glucose levels, albuminuria, and other factors in the diabetic glomerular filtrate, the hyperreabsorption of glucose, the unique molecular signature of the tubular growth phenotype, including aspects of senescence, and the resulting cellular and functional consequences. The latter includes the local release of proinflammatory chemokines and changes in proximal tubular salt and fluid reabsorption, which form the basis for the strong tubular control of glomerular filtration in the early diabetic kidney, including glomerular hyperfiltration and odd responses like the salt paradox. Importantly, these early proximal tubular changes can set the stage for oxidative stress, inflammation, hypoxia, and tubulointerstitial fibrosis, and thereby for the progression of diabetic renal disease.

High glucose and renin release: the role of succinate and GPR91

Diabetes mellitus is the most common and rapidly growing cause of end-stage renal disease. A classic hallmark of diabetes pathology is the activation of the intrarenal renin-angiotensin system (RAS), which may lead to hypertension and renal tissue injury, but the mechanism of RAS activation has been elusive. Recently, we described the intrarenal localization of the novel metabolic receptor GPR91 and established some of its functions in diabetes. These include the triggering of renin release in early diabetes via both vascular (endothelial) and tubular (macula densa) sites in the juxtaglomerular apparatus as well as the activation of MAP kinases in the distal nephron-collecting duct, which are important signaling mechanisms in diabetic nephropathy (DN) and renal fibrosis. GPR91 is a cell surface receptor for succinate and during the past few years it has provided a new paradigm for the mechanism of cell stress response in many organs. Beyond its traditional role in the tricarboxylic acid cycle, succinate now has an unexpected hormone-like signaling function, which may provide a feedback between local tissue metabolism, mitochondrial stress, and organ functions. Succinate accumulation in the local tissue environment and GPR91 signaling appear to be important early mechanisms by which cells detect and respond to hyperglycemia and trigger tissue injury in DN. Also, the distal nephron-collecting duct system, which is the major source of (pro)renin in diabetes and has the highest level of GPR91 expression in the kidney, may have an important, active, and early role in the pathogenesis of DN in contrast to the existing glomerulus-centric paradigm.

Dietary protein and blood pressure: a systematic review

BACKGROUND

Elevated blood pressure (BP), which is a major risk factor for cardiovascular disease, is highly prevalent worldwide. Recently, interest has grown in the role of dietary protein in human BP. We performed a systematic review of all published scientific literature on dietary protein, including protein from various sources, in relation to human BP.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a MEDLINE search and a manual search to identify English language studies on the association between protein and blood pressure, published before June 2010. A total of 46 papers met the inclusion criteria. Most observational studies showed no association or an inverse association between total dietary protein and BP or incident hypertension. Results of biomarker studies and randomized controlled trials indicated a beneficial effect of protein on BP. This beneficial effect may be mainly driven by plant protein, according to results in observational studies. Data on protein from specific sources (e.g. from fish, dairy, grain, soy, and nut) were scarce. There was some evidence that BP in people with elevated BP and/or older age could be more sensitive to dietary protein.

CONCLUSIONS/SIGNIFICANCE

In conclusion, evidence suggests a small beneficial effect of protein on BP, especially for plant protein. A blood pressure lowering effect of protein may have important public health implications. However, this warrants further investigation in randomized controlled trials. Furthermore, more data are needed on protein from specific sources in relation to BP, and on the protein-BP relation in population subgroups.

The roles of NADPH-oxidase and nNOS for the increased oxidative stress and the oxygen consumption in the diabetic kidney

BACKGROUND

Sustained hyperglycaemia induces increased renal oxygen consumption resulting in reduced oxygen availability in the diabetic kidney. We investigated the roles of the nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase and the neuronal nitric oxide synthase (nNOS) for the increased oxygen consumption in streptozotocin-diabetic rats.

METHODS

Oxygen consumption was measured in isolated proximal tubular cells (PTC) from streptozotocin-induced diabetic rats (n = 7-9 per group) with and without chronic treatment with apocynin, a NADPH-oxidase inhibitor, or S-methyl-L-thiocitrulline (SMTC), a selective nNOS inhibitor, or a combination of the two and the results were compared to normoglycaemic controls (n = 10). Oxidative stress was estimated from thiobarbituric acid reactive substances and protein expression measured by Western blot.

RESULTS

Proximal tubular cells from untreated diabetic rats had increased oxygen consumption compared to controls (40.6 +/- 7.9 versus 10.9 +/- 2.0 nmol/mg protein/min). All treatments reduced the diabetes-induced increase in oxygen consumption (apocynin 10.5 +/- 1.7, SMTC 19.7 +/- 3.0 and apocynin + SMTC 21.6 +/- 3.6 nmol/mg protein/min). Neither apocynin nor SMTC had any effect on the oxygen consumption in cells pre-incubated with ouabain, an inhibitor of active electrolyte transport. Oxidative stress was elevated in the diabetic kidney and inhibited by all treatments. The increased oxygen consumption by diabetic proximal tubular cells correlated with increased protein expressions of p47(phox) and nNOS and the treatments prevented these increases.

CONCLUSIONS

Diabetes induces oxidative stress, which increases oxygen consumption in proximal tubular cells. Inhibition of either NADPH-oxidase or nNOS prevented the increased oxygen consumption. The effect of blocking both these enzymes was less than additive suggesting overlapping pathways which warrant further studies.

Amino acid and protein metabolism in the human kidney and in patients with chronic kidney disease

The progressive loss of kidney function in patients with chronic kidney disease (CKD) is associated with a number of complications, including cardiovascular diseases, anemia, hyperparathyroidism, inflammation, metabolic acidosis, malnutrition and protein-energy wasting. The excess cardiovascular risk related to CKD is due in part to a higher prevalence of traditional atherosclerotic risk factors, in part to non-traditional, emerging risk factors peculiar to CKD. While even minor renal dysfunction is an independent predictor of adverse cardiovascular prognosis, nutritional changes are more often observed in an advanced setting. In addition, factors related to renal-replacement treatment may be implicated in the pathogenesis of heart disease and protein-energy wasting in dialysis-treated patients. Progressive alterations in kidney metabolism may cause progressive effects on cardiovascular status and nutrition. Altered kidney amino acid/protein metabolism and or excretion may be a key factor in the homeostasis of several vasoactive compounds and hormones in patients with more advanced disease. In this discussion recent research regarding the kidney handling of amino acids and protein turnover and their potential link with cardiovascular disease, progressive kidney dysfunction and nutritional status are reviewed.

The role of hypoxia, increased oxygen consumption, and hypoxia-inducible factor-1 alpha in progression of chronic kidney disease

PURPOSE OF REVIEW

Tubulointerstitial hypoxia in the kidney has been considered a hallmark of injury and mediator of disease progression. This review focuses on hypoxia-inducible factor (HIF)-1, a master transcription factor in cellular adaptation to hypoxia.

RECENT FINDINGS

HIF-1alpha is expressed in the hypoxic tubular epithelium as well in as the papillary interstitium and glomerular epithelial cells. Although HIF-1 plays a protective role in a number of acute kidney injury models when overexpressed, its activation in chronic kidney disease results in multiple phenotypic changes, depending on the pathological context.

SUMMARY

Hypoxia, especially HIF-1, is a critical mediator in the pathogenesis of chronic kidney disease. Underlying molecular mechanisms, together with responsible HIF target genes, are currently under investigation.

Systemic nitric oxide clamping in normal humans guided by total peripheral resistance

AIM

We wanted to stabilize the availability of nitric oxide (NO) at levels compatible with normal systemic haemodynamics to provide a model for studies of complex regulations in the absence of changes in NO levels.

METHODS

Normal volunteers (23-28 years) were infused i.v. with the nitric oxide synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) at 0.5 mg kg(-1) h(-1). One hour later, the NO donor sodium nitroprusside (SNP) was co-infused in doses eliminating the haemodynamic effects of l-NAME. Haemodynamic measurements included blood pressure (MABP) and cardiac output (CO) by impedance cardiography.

RESULTS

l-NAME increased MABP and total peripheral resistance (TPR, 1.02 + or - 0.05 to 1.36 + or - 0.07 mmHg s mL(-1), mean + or - SEM, P < 0.001). With SNP, TPR fell to a stable value slightly below control (0.92 + or - 0.05 mmHg s mL(-1), P < 0.05). CO decreased with l-NAME (5.8 + or - 0.3 to 4.7 + or - 0.3 L min(-1), P < 0.01) and returned to control when SNP was added (6.0 + or - 0.3 L min(-1)). A decrease in plasma noradrenaline (42%, P < 0.01) during l-NAME administration was completely reversed by SNP. Plasma renin activity decreased during l-NAME administration and returned towards normal after addition of SNP. In contrast, plasma aldosterone was increased by l-NAME and remained elevated.

CONCLUSIONS

Concomitant NOS inhibition and NO donor administration can be adjusted to maintain TPR at control level for hours. This approach may be useful in protocols in which stabilization of the peripheral supply of NO is required. However, the dissociation between renin and aldosterone secretion needs further investigation.

A meta-analysis of three polymorphisms in the endothelial nitric oxide synthase gene (NOS3) and their effect on the risk of diabetic nephropathy

A number of association studies have investigated the role of the nitric oxide synthase 3 (NOS3) gene in the development of diabetic nephropathy (DN). However, results have been inconclusive, largely because the studies have focused on a variety of different polymorphisms and generate inconsistent results. We performed a meta-analysis of 28 association studies focusing on three polymorphisms in the NOS3 gene (G894T (Glu289Asp), 4b/a, and T-786C) and the risk of DN published before July 2009, covering a total of 10,364 subjects. Although significant heterogeneity was initially found in the analysis of G894T, it did not remain when analysis was done by ethnic subgroups. 894T was negatively associated with DN in Caucasian populations of European origin (OR = 0.896, 0.817-0.983, 95% CI), but was positively associated with DN in East Asian (OR = 2.02, 1.20-3.42, 95% CI) and other populations. Association of the 4b/a variant was observed when studies involving microalbuminuria were excluded (OR = 1.19, 1.02-1.39, 95% CI). The T-786C variant showed an overall weak association (OR = 1.16, 1.01-1.34, 95% CI) with little heterogeneity. In summary, our meta-analysis of the effect of NOS3 gene polymorphisms on the risk of DN supports the involvement of the NOS3 gene in the pathogenesis of DN.

Diabetic nephropathy: a disorder of oxygen metabolism?

Chronic hypoxia induces sequential abnormalities in oxygen metabolism (for example, oxidative stress, nitrosative stress, advanced glycation, carbonyl stress, endoplasmic reticulum stress) in the kidneys of individuals with diabetes. Identification of these abnormalities improves our understanding of therapeutic benefits that can be achieved with antihypertensive agents, the control of hyperglycemia and/or hyperinsulinemia and the dietary correction of obesity. Key to the body's defense against hypoxia is hypoxia-inducible factor, the activity of which is modulated by prolyl hydroxylases (PHDs)-oxygen sensors whose inhibition may prove therapeutic. Renal benefits of small-molecule PHD inhibitors have been documented in several animal models, including those of diabetic nephropathy. Three different PHD isoforms have been identified (PHD1, PHD2 and PHD3) and their respective roles have been delineated in knockout mouse studies. Unfortunately, none of the current inhibitors is specific for a distinct PHD isoform. Nonspecific inhibition of PHDs might induce adverse effects, such as those associated with PHD2 inhibition. Specific disruption of PHD1 induces hypoxic tolerance, without angiogenesis and erythrocytosis, through the reprogramming of basal oxygen metabolism and decreased generation of oxidative stress in hypoxic mitochondria. A specific PHD1 inhibitor might, therefore, offer a novel therapy for abnormal oxygen metabolism not only in the diabetic kidney, but also in other diseases for which hypoxia is a final, common pathway.

Nitric oxide originating from NOS1 controls oxygen utilization and electrolyte transport efficiency in the diabetic kidney

Nitric oxide (NO) is a potent regulator of both vascular tone and cellular oxygen consumption (Q(O(2)). Diabetic kidneys have reduced NO availability and increased Q(O(2)). However, the exact nitric oxide synthase (NOS) isoform regulating Q(O(2)), hemodynamics, and excretory function in the diabetic kidney remains unclear. We therefore investigated the effects of both selective neuronal NOS (NOS1) inhibition and nonselective NOS inhibition. Oxygen utilization, electrolyte transport efficiency [tubular Na(+) transport (T(Na))/Q(O(2))], renal blood flow (RBF), glomerular filtration rate (GFR), and mean arterial pressure (MAP) were measured in vivo in control and streptozotocin-diabetic rats before and after administration of the selective NOS1 inhibitor S-methyl-L-thiocitrulline (SMTC) or the nonselective NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). Diabetic rats had higher baseline Q(O(2)) and GFR than control rats, although RBF was similar in the groups. SMTC and L-NAME increased Q(O(2)) and reduced T(Na)/Q(O(2)) only in the diabetic animals, whereas both inhibitors increased MAP and reduced RBF in both groups. GFR was reduced by L-NAME, but SMTC had no effect in either group. Carbachol increased RBF and decreased MAP in SMTC-treated rats, whereas it had no effect in L-NAME-treated rats, indicating that SMTC selectively inhibited NOS1. In conclusion, NO regulates RBF and GFR similarly in both control and diabetic rats. However, selective NOS1 inhibition increased Qo(2) and reduced T(Na)/Q(O(2)) in the diabetic rat kidney, indicating a pivotal role of NO produced by NOS1 in maintaining control of Q(O(2)) and tissue oxygenation in these kidneys.