Induced nitric oxide (NO) synthesis in heterologous nephrotoxic nephritis; effects of selective inhibition in neutrophil-dependent glomerulonephritis

Argininosuccinic aciduria fosters neuronal nitrosative stress reversed by Asl gene transfer

Argininosuccinate lyase (ASL) belongs to the hepatic urea cycle detoxifying ammonia, and the citrulline-nitric oxide (NO) cycle producing NO. ASL-deficient patients present argininosuccinic aciduria characterised by hyperammonaemia, multiorgan disease and neurocognitive impairment despite treatment aiming to normalise ammonaemia without considering NO imbalance. Here we show that cerebral disease in argininosuccinic aciduria involves neuronal oxidative/nitrosative stress independent of hyperammonaemia. Intravenous injection of AAV8 vector into adult or neonatal ASL-deficient mice demonstrates long-term correction of the hepatic urea cycle and the cerebral citrulline-NO cycle, respectively. Cerebral disease persists if ammonaemia only is normalised but is dramatically reduced after correction of both ammonaemia and neuronal ASL activity. This correlates with behavioural improvement and reduced cortical cell death. Thus, neuronal oxidative/nitrosative stress is a distinct pathophysiological mechanism from hyperammonaemia. Disease amelioration by simultaneous brain and liver gene transfer with one vector, to treat both metabolic pathways, provides new hope for hepatocerebral metabolic diseases.

Polymorphism of host response genes: Implications in the pathogenesis and treatment of acute renal failure

Acute inflammatory disorders are the result of an interaction between genetic and environmental factors, and are often characterized by an imbalance between pro- and anti-inflammatory host immune responses. Over the past decade, polymorphisms of host response genes have been explored as genetic risk and prognostic markers in the course and severity of acute inflammatory disorders. Increasing evidence supports an important role for inflammatory mechanisms in the pathogenesis of acute renal failure (ARF) following both ischemic and nephrotoxic injury. The use of genetic epidemiology may become a useful tool to identify patients with an altered susceptibility to developing hospital-acquired ARF, and stratify those who may benefit from preventive therapies that modulate host immune responses in a favorable way. This review summarizes the existing experimental and clinical studies supporting the role of inflammation in ARF and critically appraises studies that have examined polymorphism of immune response genes as potential determinants of susceptibility to and severity of acute inflammatory disorders. Conclusions are drawn on the application of genetic epidemiology to the field of ARF and the rationale for further research on the role of genetic markers in ARF.

Nitric oxide and glomerulonephritis

Glomerulonephritis is a common clinical condition that is caused by immune-mediated injury to the kidney and is characterized by dysfunction of the glomerular capillary filtration barrier. Nitric oxide (NO), a ubiquitous molecule with many biological functions throughout the body, has been evaluated as an inflammatory mediator in these circumstances. NO may induce glomerular injury directly or may act via stimulation of a host of other inflammatory mediators. A variety of experimental models of glomerulonephritis have been studied including those induced by infusion of antibodies to the Thy1.1 antigen or glomerular basement membrane, Heymann nephritis, and autoimmune nephritis. In virtually all of these cases there is evidence of increased NO production. Excessive production of NO by inducible nitric oxide synthase (iNOS), derived from infiltrating immune cells or resident glomerular cells, nearly always is associated with increased glomerular injury. Interventions that inhibit this enzyme result in less proteinuria and diminished glomerular damage. In contrast, NO derived from endothelial nitric oxide synthase (eNOS) may limit glomerular disease by preserving endothelial cell integrity. There are only a limited number of studies that have evaluated the impact of NO in patients with glomerulonephritis. Although the bulk of evidence supports a role of NO as a pro-inflammatory mediator in glomerulonephritis, additional work is needed to show an association between altered NO production and the severity and outcome of disease in patients with this disease. It is hoped that better understanding of the role of NO in glomerulonephritis will lead to the development of therapies to ameliorate the disease.

Normalization of nitric oxide flux improves physiological parameters of porcine kidneys maintained on pulsatile perfusion

Early endothelial damage and resultant reduction in the beneficial production of nitric oxide (NO) derived from the endothelial NO synthase (eNOS) are phenomena associated with the functional degradation of transplanted kidneys. In contrast, the inflammation characteristic of kidney preservation leads to the later, detrimental expression of the inducible NO synthase (iNOS). We reasoned that provision of low-level NO (to compensate for lack of eNOS) using the chemical NO donor S-nitrosoglutathione (GSNO), along with an iNOS inhibitor (N-omega iminoethyl-L-lysine; L-NIL), might "normalize" NO levels and therefore be beneficial in maintenance of flow. Non-heartbeating donor porcine kidneys were subjected to 30-45 min warm ischemic time and stored from 3 to 30 h, simulating the time required for national sharing. The kidneys were then machine preserved with Belzer MPS (BMP) at a set systolic pressure of 40 mmHg. Eight kidneys were perfused for 5h with BMP only (Group 1 control), 8 kidneys with BMP+GSNO only (Group 2), and 8 kidneys with BMP+GSNO+L-NIL (Group 3). Lower vascular resistance (VR) is a predictor of improved end-organ function. Both Group 2 and 3 kidneys demonstrated statistically significant reduction in VR as compared to Group 1 kidneys, with Group 3 kidneys demonstrating a greater drop in VR than Group 2. Reduced oxygen saturation suggests a higher metabolic rate. Only Group 3 had lower oxygen saturation as compared to Group 1. Increased Ca2+ concentration in the perfusate is a predictor of worse end-organ function. Group 2, but not Group 3, had a higher perfusate Ca2+ concentration than Group 1. The combination of suppression of harmful amounts of NO, while supplying a constant low-level amount of NO, may improve pulsatile kidney preservation.

Nitric oxide production in renal cells by immune complexes: Role of kinases and nuclear factor-kappaB

BACKGROUND

Interaction of deposited immune complexes (IC) with Fc receptors (FcR) on tissue cells elicits the release of inflammatory mediators leading to tissue damage. Nitric oxide (NO) radicals generated by inducible NO synthase (iNOS) are important mediators in inflammatory processes. To analyze the role of NO in IC-mediated glomerular inflammation, we studied the in vitro and in vivo expression of iNOS in renal cells [resident mesangial cells (MC), and infiltrating monocytes] induced by IC, and the possible intermediate steps between FcR occupancy and iNOS induction.

METHODS

MC and monocytes were stimulated with IgG- and IgA-containing IC, and NO production (nitrite accumulation), iNOS transcription (luciferase assay) and their expression was measured by RT-PCR and Western blot. The involvement of FcR, transcription factor nuclear factor-kappaB (NF-kappaB), and protein kinases was assessed by using Fc fragments and specific inhibitors. Immune glomerulonephritis was induced in rats, and iNOS expression and NF-kappaB activation were analyzed.

RESULTS

In MC and monocytes, IC enhanced iNOS transcription/expression and NO generation, which were attenuated by specific inhibitors of NF-kappaB. In addition, mitogen-activated protein kinase (MAPK) inhibitors decreased NO production, but did not interfere with NF-kappaB activity, suggesting that both pathways may converge downstream in the induction of iNOS. In experimental immune glomerulonephritis, increased iNOS expression correlated with proteinuria levels, and appeared colocalized with NF-kappaB in glomerular and infiltrating cells. Treatment of animals and cells with Fc fragments prevented iNOS induction and NF-kappaB activation by IC.

CONCLUSIONS

These results indicate that IC, through activation of FcR, induce iNOS expression in renal resident and recruited cells by mechanisms involving MAPK and NF-kappaB, and support the idea of the important role of local NO generation in IC-mediated glomerular injury.

Nitric oxide and glomerulonephritis

The glomerulus is a unique vascular network with the potential to express several isoforms of nitric oxide synthase (NOS). Induction of inducible NOS (iNOS) occurs as part of a rapid initial response to immune injury in glomerulonephritis (GN). Studies on rodent models suggest that this is due to activation of transcription factors by reactive oxygen species (ROS), generated in responses to Fcgamma and CR engagement. iNOS operates in a complex milieu among multiple other inflammatory mediators, changing expression of constitutive NOS (endothelial NOS, eNOS), a critical regulator of glomerular function, and auto-regulating its own expression. As yet there is no consensus as to the role of high output NO generated by iNOS in the glomerulus, although many studies have demonstrated that NO inhibition can alter the level of proteinuria and leukocyte infiltration, and other manifestations of injury such as thrombosis, proliferation, and matrix production. This article reviews the evidence accumulated from experimental studies over the past decade, and discusses how these conflicting data can be reconciled to form a working hypothesis on the role of NO in GN.

Arginase in glomerulonephritis

l-Arginine is converted to nitric oxide and citrulline by the enzyme nitric oxide synthase (NOS). Its in vivo inhibition has led to the revelation of a multitude of diverse, often conflicting functions in the inflammatory melee. l-Arginine is also converted to ornithine and urea by the enzyme arginase as a part of the hepatic urea cycle. However, a more holistic interpretation of the two pathways and the associated metabolism (summarized in Fig. 1) has led to its reassessment as a pathologically significant enzyme. This is reflected by the continued increase over the past five years of the number of publications discussing both nitric oxide and arginase. The strong association between inflammation and high arginase and NOS activity is epitomized by immune complex-induced glomerulonephritis and other glomerulonephritides. Arginase is encoded by two recently discovered genes (Arginase I and Arginase II). There is now substantial evidence for an interaction between both arginase isoforms and all three NOS isoforms in pathological situations. This review considers the relationship between Arginases I and II and the inflammation-associated isoform of NOS called NOS II. In particular, it consolidates the current understanding of arginase and associated metabolic pathways, and highlights some of the issues that are often overlooked in such studies.

Selective inhibition of inducible nitric oxide synthase enhances intraglomerular coagulation in chronic anti-Thy 1 nephritis

BACKGROUND

A particular Lewis rat substrain (LEW/Maa) develops chronic glomerulonephritis in the anti-Thy 1 model (aThy 1-GN) characterized by increased microaneurysm formation, chronic glomerular sclerosis and persistent albuminuria. This phenotype is accompanied by increased and prolonged glomerular induction of inducible nitric oxide synthase (iNOS) when compared to the LEW/Moe substrain, in which aThy 1-GN resolves quickly. We investigated the effect of selective iNOS inhibition by l-N6-(1-iminoethyl)-lysine (L-NIL) administration on aThy 1-GN in LEW/Maa rats.

METHODS

Nephritic rats were studied over a period of 7 days. L-NIL-treated animals received 20 mg/day L-NIL in the drinking water starting two days prior to disease induction. iNOS activity was determined in cultured glomeruli and in urine samples, respectively. Severity of aThy 1-GN was determined by scoring glomerular matrix expansion and microaneurysm formation, and by albuminuria measurements (ELISA). Immunohistochemical evaluation was performed including staining for macrophages (ED-1), platelets (PL-1) and fibrin deposition.

RESULTS

L-NIL treated rats (+NIL) showed a significant decrease in peak nitrate production by ex vivo cultured glomeruli, and in urinary nitrate excretion versus untreated nephritic rats (-NIL). Mean arterial pressure remained unchanged in both +NIL and -NIL rats. +NIL rats developed significantly increased albuminuria (+44%) associated with a significant increase in glomerular platelet (+45%) and fibrin deposition (+48%).

CONCLUSIONS

Selective inhibition of iNOS aggravated albuminuria in chronic aThy 1-GN in LEW/Maa rats. Induction of iNOS during the inflammatory phase of this model may be a partially protective mechanism by interfering with intraglomerular coagulation processes.

Acetaminophen inhibits iNOS gene expression in RAW 264.7 macrophages: differential regulation of NF-kappaB by acetaminophen and salicylates

Acetaminophen is a widely used analgesic and anti-inflammatory drug that is considered a good alternative to salicylates for individuals who cannot tolerate salicylates. Nitric oxide (NO) synthesized by inducible nitric oxide synthase (iNOS) has been implicated as a mediator of inflammation. Recent evidence suggests that anti-inflammatory effect of salicylates lies in the inhibition of iNOS, but nothing has been reported about the direct effect of iNOS expression by acetaminophen. The present study was designed to elucidate sequentially the action mechanisms of acetaminophen and salicylates (aspirin and sodium salicylate) on lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma)-induced iNOS expression in RAW 264.7 macrophages. Both acetaminophen and salicylates inhibited NO production and iNOS protein expression in a dose dependent manner. Acetaminophen inhibited iNOS mRNA expression, promoter activity of iNOS gene and nuclear factor-kappa B (NF-kappaB) binding activity induced by LPS plus IFN-gamma, whereas salicylates did not show any effect on them. In addition, salicylates did not affect on iNOS mRNA stability induced by LPS plus IFN-gamma. Furthermore, the inhibition of iNOS protein expression and NO production by salicylates was disappeared when salicylates were added for only 5 h to inhibit the early event of iNOS expression. Aspirin also dose dependently inhibited iNOS enzyme activity in cell-free extracts, whereas no significant differences were observed in extracts treated with sodium salicylate or acetaminophen. These findings suggest that acetaminophen may exert analgesic or anti-inflammatory effect by inhibiting iNOS expression induced by LPS plus IFN-gamma at transcriptional level by suppression of NF-kappaB binding activity, whereas salicylates exert its effect by inhibiting iNOS expression at the translational or posttranslational level.