Intra-renal angiotensin II/AT1 receptor, oxidative stress, inflammation, and progressive injury in renal mass reduction

The synthetic triterpenoid RTA dh404 (CDDO-dhTFEA) restores endothelial function impaired by reduced Nrf2 activity in chronic kidney disease

Chronic kidney disease (CKD) is associated with endothelial dysfunction and accelerated cardiovascular disease, which are largely driven by systemic oxidative stress and inflammation. Oxidative stress and inflammation in CKD are associated with and, in part, due to impaired activity of the cytoprotective transcription factor Nrf2. RTA dh404 is a synthetic oleanane triterpenoid compound which potently activates Nrf2 and inhibits the pro-inflammatory transcription factor NF-κB. This study was designed to test the effects of RTA dh404 on endothelial function, inflammation, and the Nrf2-mediated antioxidative system in the aorta of rats with CKD induced by 5/6 nephrectomy. Sham-operated rats served as controls. Subgroups of CKD rats were treated orally with RTA dh404 (2 mg/kg/day) or vehicle for 12 weeks. The aortic rings from untreated CKD rats exhibited a significant reduction in the acetylcholine-induced relaxation response which was restored by RTA dh404 administration. Impaired endothelial function in the untreated CKD rats was accompanied by significant reduction of Nrf2 activity (nuclear translocation) and expression of its cytoprotective target genes, as well as accumulation of nitrotyrosine and upregulation of NAD(P)H oxidases, 12-lipoxygenase, MCP-1, and angiotensin II receptors in the aorta. These abnormalities were ameliorated by RTA dh404 administration, as demonstrated by the full or partial restoration of the expression of all the above analytes to sham control levels. Collectively, the data demonstrate that endothelial dysfunction in rats with CKD induced by 5/6 nephrectomy is associated with impaired Nrf2 activity in arterial tissue, which can be reversed with long term administration of RTA dh404.

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Endothelial dysfunction in rats with chronic kidney disease is associated with impaired aortic Nrf2 activity.

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Long-term administration of the Nrf2 activator RTA dh404 ameliorated downregulation of Nrf2 and vascular dysfunction induced by chronic kidney disease.

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Long-term administration of the Nrf2 activator RTA dh404 ameliorated chronic kidney disease-induced accumulation of nitrotyrosine and upregulation of NF-κB target genes.

Rokumi-jio-gan-containing prescriptions regulate oxidative stress through improving dyslipidemia in a subtotal nephrectomized rat model

ETHNOPHARMACOLOGICAL RELEVANCE

Rokumi-jio-gan-containing prescriptions, traditional medicine, are widely used to treat renal dysfunction in Japan.

AIM OF THE STUDY

The present study was conducted to examine whether two Rokumi-jio-gan-containing prescriptions (Hachimi-jio-gan and Bakumi-jio-gan) have an ameliorative effect on dyslipidemia in nephrectomized rats.

MATERIALS AND METHODS

Each prescription was orally administered to nephrectomized rats at 150mg/kg body weight per day for 10 weeks, and its effect was compared with vehicle-treated nephrectomized rats.

RESULTS

Rats given Hachimi-jio-gan and Bakumi-jio-gan showed an improvement of renal functional parameters such as serum urea nitrogen, creatinine, creatinine clearance, and urinary protein. The increased triglyceride, total cholesterol, non-esterified fatty acid, high-density lipoprotein cholesterol, and very low-density lipoprotein cholesterol/low-density lipoprotein cholesterol levels in serum, and triglyceride and total cholesterol contents in the kidney of nephrectomized rats were significantly decreased by Hachimi-jio-gan and Bakumi-jio-gan administration. Furthermore, Hachimi-jio-gan acts as a regulator of peroxisome proliferator-activated receptor α, sterol regulatory element binding protein (SREBP)-1, and SREBP-2. On the contrary, the increased reactive oxygen species and thiobarbituric acid-reactive substance were decreased, while superoxide dismutase and the reduced glutathione/oxidized glutathione ratio were augmented by Hachimi-jio-gan rather than Bakumi-jio-gan. The improvement of nuclear factor-kappa Bp65, cyclooxygenase-2, inducible nitric oxide synthase, NF-E2-related factor 2, and heme oxygenase-1 was marked in the group administered Bakumi-jio-gan. However, oil red O staining showed that the increased lipid deposition in the kidney of nephrectomized rats improved on Hachimi-jio-gan and Bakumi-jio-gan administration.

CONCLUSION

This study provides scientific evidence that two Rokumi-jio-gan-containing prescriptions (Hachimi-jio-gan and Bakumi-jio-gan) improve oxidative stress via dyslipidemia in the remnant kidney of nephrectomized rats.

Induction of AMPK activity corrects early pathophysiological alterations in the subtotal nephrectomy model of chronic kidney disease

The rat kidney ablation and infarction (A/I) model of subtotal or 5/6th nephrectomy is the most commonly studied model of nondiabetic chronic kidney disease (CKD). The A/I kidney at 1 wk exhibits reductions in kidney function, as determined by glomerular filtration rate, and diminished metabolic efficiency as determined by oxygen consumption per sodium transport (QO2/TNa). As renoprotective AMPK activity is affected by metabolic changes and cellular stress, we evaluated AMPK activity in this model system. We show that these early pathophysiological changes are accompanied by a paradoxical decrease in AMPK activity. Over time, these kidney parameters progressively worsen with extensive kidney structural, functional, metabolic, and fibrotic changes observed at 4 wk after A/I. We show that induction of AMPK activity with either metformin or 5-aminoimidazole-4-carboxamide ribonucleotide increases AMPK activity in this model and also corrects kidney metabolic inefficiency, improves kidney function, and ameliorates kidney fibrosis and structural alterations. We conclude that AMPK activity is reduced in the subtotal nephrectomy model of nondiabetic CKD, that altered regulation of AMPK is coincident with the progression of disease parameters, and that restoration of AMPK activity can suppress the progressive loss of function characteristic of this model. We propose that induction of AMPK activity may prove an effective therapeutic target for the treatment of nondiabetic CKD.

Exhaled breath and fecal volatile organic biomarkers of chronic kidney disease

BACKGROUND

While much is known about the effect of chronic kidney disease (CKD) on composition of body fluids little is known regarding its impact on the gases found in exhaled breath or produced by intestinal microbiome. We have recently shown significant changes in the composition of intestinal microbiome in humans and animals with CKD. This study tested the hypothesis that uremia-induced changes in cellular metabolism and intestinal microbiome may modify the volatile organic metabolites found in the exhaled breath or generated by intestinal flora.

METHODS

SD rats were randomized to CKD (5/6 nephrectomy) or control (sham operation) groups. Exhaled breath was collected by enclosing each animal in a glass chamber flushed with clean air, then sealed for 45 min and the trapped air collected. Feces were collected, dissolved in pure water, incubated at 37 degrees C in glass reactors for 24 h and the trapped air collected. Collected gases were analyzed by gas chromatography.

RESULTS

Over 50 gases were detected in the exhaled breath and 36 in cultured feces. Four gases in exhaled breath and 4 generated by cultured feces were significantly different in the two groups. The exhaled breath in CKD rats showed an early rise in isoprene and a late fall in linear aldehydes. The CKD animals' cultured feces released larger amounts of dimethyldisulfide, dimethyltrisulfide, and two thioesters.

CONCLUSIONS

CKD significantly changes the composition of exhaled breath and gaseous products of intestinal flora.

GENERAL SIGNIFICANCE

Analysis of breath and bowel gases may provide useful biomarkers for detection and progression of CKD and its complications.

Targeting the transcription factor Nrf2 to ameliorate oxidative stress and inflammation in chronic kidney disease

Oxidative stress and inflammation are mediators in the development and progression of chronic kidney disease (CKD) and its complications, and they are inseparably linked as each begets and amplifies the other. CKD-associated oxidative stress is due to increased production of reactive oxygen species (ROS) and diminished antioxidant capacity. The latter is largely caused by impaired activation of Nrf2, the transcription factor that regulates genes encoding antioxidant and detoxifying molecules. Protective effects of Nrf2 are evidenced by amelioration of oxidative stress, inflammation, and kidney disease in response to natural Nrf2 activators in animal models, while Nrf2 deletion amplifies these pathogenic pathways and leads to autoimmune nephritis. Given the role of impaired Nrf2 activity in CKD-induced oxidative stress and inflammation, interventions aimed at restoring Nrf2 may be effective in retarding CKD progression. Clinical trials of the potent Nrf2 activator bardoxolone methyl showed significant improvement in renal function in CKD patients with type 2 diabetes. However, due to unforeseen complications the BEACON trial, which was designed to investigate the effect of this drug on time to end-stage renal disease or cardiovascular death in patients with advanced CKD, was prematurely terminated. This article provides an overview of the role of impaired Nrf2 activity in the pathogenesis of CKD-associated oxidative stress and inflammation and the potential utility of targeting Nrf2 in the treatment of CKD.

Nitric oxide in afferent arterioles after uninephrectomy depends on extracellular l-arginine

Uninephrectomy (UNX) causes hyperperfusion of the contralateral remaining kidney via increased nitric oxide (NO) synthesis. Although the exact mechanism remains largely unknown, we hypothesize that this would be localized to the afferent arteriole and that it depends on cellular uptake of l-arginine. The experiments were performed in rats 2 days (early) or 6 wk (late) after UNX and compared with controls (Sham) to study acute and chronic effects on NO metabolism. Renal blood flow was increased after UNX (21 ± 2 ml·min−1·kg−1 in sham, 30 ± 3 in early, and 26 ± 1 in late, P < 0.05). NO inhibition with Nω-nitro-l-arginine methyl ester hydrochloride (l-NAME) caused a greater increase in renal vascular resistance in early UNX compared with Sham and late UNX (138 ± 24 vs. 88 ± 10, and 84 ± 7%, P < 0.01). The lower limit of autoregulation was increased both in early and late UNX compared with Sham ( P < 0.05). l-NAME did not affect the ANG II-induced contraction of isolated afferent arterioles (AA) from Sham. AA from early UNX displayed a more pronounced contraction in response to l-NAME (−57 ± 7 vs. −16 ± 7%, P < 0.05) and in the absence of l-arginine (−41 ± 4%, P < 0.05) compared with both late UNX and Sham. mRNA expression of endothelial NO synthase was reduced, whereas protein expression was unchanged. Cationic amino acid transporter-1 and -2 mRNA was increased, while protein was unaffected in isolated preglomerular resistance vessels. In conclusion, NO-dependent hyperperfusion of the remaining kidney in early UNX is associated with increased NO release from the afferent arteriole, which is highly dependent on extracellular l-arginine availability.

Role of impaired Nrf2 activation in the pathogenesis of oxidative stress and inflammation in chronic tubulo-interstitial nephropathy

BACKGROUND

Tubulo-interstitial nephropathy (TIN) is a common cause of chronic kidney disease (CKD). Consumption of an adenine-containing diet causes the accumulation of 2,8-dihydroxyadenine in the renal tubules triggering intense chronic TIN and progressive CKD in rats. CKD in this model is associated with, and largely driven by, oxidative stress and inflammation. Oxidative stress and inflammation in rats with spontaneous focal segmental glomerulosclerosis and rats with CKD induced by 5/6 nephrectomy are associated with an impaired activation of nuclear factor-erythroid-2-related factor 2 (Nrf2) which is the master regulator of genes encoding many antioxidant and detoxifying enzymes. The effect of TIN on the Nrf2 pathway and its key target genes is unknown and was investigated here.

METHODS

Sprague-Dawley rats were randomized to control and adenine-treated (rat chow-containing 0.7% adenine for 2 weeks) groups and followed up for 4 weeks.

RESULTS

The adenine-treated animals exhibited marked azotemia, impaired urinary concentrating capacity, intense tubular and glomerular damage, interstitial inflammation and fibrosis. This was associated with an increased expression of NAD(P)H oxidase, cyclooxygenase-2 and 12-lipoxygenase, and activation of NF-κB, the master regulator of pro-inflammatory cytokines and chemokines. Oxidative stress and inflammation in the kidneys of adenine-treated animals was accompanied by an impaired activation of Nrf2 and down-regulation of its target gene products including, catalase, heme oxygenase-1 and glutamate-cysteine ligase.

CONCLUSIONS

Chronic TIN is associated with impaired Nrf2 activity which contributes to the pathogenesis of oxidative stress and inflammation and amplifies their damaging effects on the kidney.

Curcumin reverses glomerular hemodynamic alterations and oxidant stress in 5/6 nephrectomized rats

The administration of curcumin before and throughout the study attenuates oxidant stress and glomerular hemodynamic alterations induced by 5/6 nephrectomy (5/6NX). The purpose of this work was to study if curcumin is able to reverse established glomerular hemodynamic alterations (e.g. hyperfiltration and glomerular hypertension) and oxidant stress in rats with 5/6NX. Curcumin (120 mg/kg) was given to rats with established renal injury (30 days after surgery) and continued for 30 days (days 31-60 of the study). All rats were studied on day 60 after surgery. Curcumin was able (a) to reverse 5/6NX-induced glomerular hypertension and hyperfiltration, (b) to induce cell proliferation and nuclear translocation of Nrf2 and (c) to reverse 5/6NX-induced oxidant stress and decrease in antioxidant enzymes. These beneficial effects of curcumin were associated with the ability of this antioxidant to reverse renal structural alterations, proteinuria, hypertension, interstitial fibrosis, fibrotic glomeruli, tubular atrophy and mesangial expansion. It has been shown for the first time that curcumin is able to reverse established oxidants stress glomerular hypertension and hyperfiltration in rats with 5/6NX. These novel findings may play a key role in the attenuation of proteinuria and progression of renal damage in rats with 5/6NX. These data suggest that curcumin may be useful to reverse established hemodynamic alterations and renal injury in patients with chronic renal failure.

Role of Oxidative Stress in the Pathogenesis of Pancreatitis: Effect of Antioxidant Therapy

Oxidative stress plays an important role in the pathogenesis of acute pancreatitis. The exact pathogenesis of pancreatitis remains unknown but several mechanisms related to oxidative and inflammatory stress are implicated. It is reasonable to surmise that antioxidants would play a protective role in ameliorating the deleterious effects of pancreatitis. We have a wealth of data from animal models that reveal a positive correlation between antioxidant drugs and improved outcomes in experimental pancreatitis. Human clinical trials with antioxidants however, have disclosed conflicting results. We review the existing pathogenesis of pancreatitis related to oxidative stress and provide of a review of current trials with antioxidant therapy.

Relationship between GFR and albuminuria in stage 1 hypertension

BACKGROUND AND OBJECTIVES

Whether glomerular hyperfiltration is implicated in the development of microalbuminuria in hypertension is not well known. This prospective study investigated the relationship between changes in GFR and microalbuminuria in hypertension.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study assessed 534 stage 1 hypertensive participants from the Hypertension and Ambulatory Recording Venetia Study (n=386 men) without microalbuminuria at baseline, who were recruited from 1990 to 1995 and followed for a median of 8.5 years. Mean age was 33.9±8.6 years and mean BP was 146.6±10.5/94.0±5.0 mmHg. Creatinine clearance and 24-hour urinary albumin were measured at study entry and end. Participants were defined as normofilterers (normo) or hyperfilterers (hyper) according to whether GFR was <150 or ≥150 ml/min per 1.73 m(2), respectively. Participants were divided into four groups based on GFR changes from baseline to follow-up end: normo→normo (n=395), normo→hyper (n=31), hyper→hyper (n=61), and hyper→normo (n=47).

RESULTS

Microalbuminuria progressively increased across the four groups and was 5.3% in normo→normo, 9.7% in normo→hyper, 16.4% in hyper→hyper, and 36.2% in hyper→normo (P<0.001). This association held true in a multivariable logistic regression in which several confounders, ambulatory BP, and other risk factors were taken into account (P<0.001). In particular, hyperfilterers whose GFR decreased to normal at study end had an adjusted odds ratio of 7.8 (95% confidence interval, 3.3-18.2) for development of microalbuminuria compared with participants with normal GFR throughout the study.

CONCLUSIONS

These data support the hypothesis for a parabolic association between GFR and urinary albumin in the early stage of hypertension.

Rokumi-jio-gan-Containing Prescriptions Attenuate Oxidative Stress, Inflammation, and Apoptosis in the Remnant Kidney

Two Rokumi-jio-gan-containing prescriptions (Hachimi-jio-gan and Bakumi-jio-gan) were selected to examine their actions in nephrectomized rats. Each prescription was given orally to rats for 10 weeks after the excision of five-sixths of their kidney volumes, and its effect was compared with non-nephrectomized and normal rats. Rats given Hachimi-jio-gan and Bakumi-jio-gan showed an improvement of renal functional parameters such as serum urea nitrogen, creatinine, creatinine clearance, and urinary protein. The nephrectomized rats exhibited the up-regulation of nicotinamide adenine dinucleotide phosphate oxidase subunits, c-Jun N-terminal kinase (JNK), phosphor-JNK, c-Jun, transforming growth factor-β₁, nuclear factor-kappa B, cyclooxygenase-2, inducible nitric oxide synthase, monocyte chemotactic protein-1, intracellular adhesion molecule-1, Bax, cytochrome c, and caspase-3, and down-regulation of NF-E2-related factor 2, heme oxygenase-1, and survivin; however, Bakumi-jio-gan administration acts as a regulator in inflammatory reactions caused by oxidative stress in renal failure. Moreover, the JNK pathway and apoptosis-related protein expressions, Bax, caspase-3, and survivin, were ameliorated to the normal levels by Hachimi-jio-gan administration. The development of renal lesions, glomerular sclerosis, tubulointerstitial damage, and arteriolar sclerotic lesions, estimated by histopathological evaluation and scoring, was strong in the groups administered Hachimi-jio-gan rather than Bakumi-jio-gan. This study suggests that Rokumi-jio-gan-containing prescriptions play a protective role in the progression of renal failure.

Curcumin alleviates oxidative stress, inflammation, and renal fibrosis in remnant kidney through the Nrf2-keap1 pathway

SCOPE

We hypothesized that curcumin, by increasing the expression of nuclear factor-erythroid-2-related factor 2 (Nrf2), could reduce oxidative stress, inflammation, and renal fibrosis in remnant kidney.

METHODS AND RESULTS

Sprague-Dawley rats were subjected to 5/6 nephrectomy and randomly assigned to untreated (Nx), curcumin-treated (75 mg/kg/day, orally), and telmisartan-treated groups (10 mg/kg/day, orally; as positive control). Sham-operated rats also served as controls. Five/sixth nephrectomy caused renal dysfunction, as evidenced by elevated proteinuria, blood urea nitrogen, and plasma creatinine, and decreased creatinine clearance that were ameliorated by curcumin or telmisartan treatment. The Nx rats demonstrated reduced Nrf2 protein expression, whereas the Kelch-like ECH-associated protein 1 was upregulated and heme oxygenase-1 level was significantly diminished. Consequently, Nx animals had significantly higher kidney malondialdehyde concentration and lower glutathione peroxidase activity, which was associated with the upregulation of nicotinamide adenine dinucleotide phosphatase oxidase subunit (p67(phox) and p22(phox) ), NF-kappaB p65, TNF-α, TGF-β1, cyclooxygenase-2, and fibronectin accumulation in remnant kidney. Interestingly, all of these changes were ameliorated by curcumin or telmisartan.

CONCLUSION

These findings demonstrate that, by modulating Nrf2-Keap1 pathway, the curcumin effectively attenuates oxidative stress, inflammation, and renal fibrosis, which suggest that curcumin hold promising potential for safe treatment of chronic kidney disease.

Vitamin E, Vitamin C, or Losartan Is Not Nephroprotectant against Cisplatin-Induced Nephrotoxicity in Presence of Estrogen in Ovariectomized Rat Model

Background. The nephroprotective effect of vitamins E and C or losartan against cisplatin (CP)- induced nephrotoxicity when they are accompanied by estrogen was investigated. Methods. The ovariectomized rats received estradiol valerate for two weeks. At the end of the first week, a single dose of CP (7 mg/kg, IP) was also administered, and they received placebo (group 1), vitamin E (group 2), vitamin C (group 3), or losartan (group 4) every day during the second week, and they were compared with another three control groups. Results. CP alone increased the serum levels of blood urea nitrogen (BUN), creatinine (Cr), and kidney tissue damage score (KTDS), significantly (P < 0.05), however at the presence of estradiol and CP, vitamin C, vitamin E, or losartan not only did not decrease these parameters, but also increased them significantly (P < 0.05). The serum level of superoxidase dismutase (SOD) was reduced by CP (P < 0.05), but it was increased when estradiol or estradiol plus vitamin C or losartan were added (P < 0.05). Conclusion. The particular pharmacological dose of estrogen used in this study abolish the nephroprotective effects vitamins C and E or losartan against CP-induced nephrotoxicity.

Factors associated with glomerular hyperfiltration in the early stage of hypertension

BACKGROUND

Glomerular hyperfiltration predicts development of nephropathy in hypertension but the factors responsible for increased glomerular filtration rate (GFR) are not well known. Aim of this study was to examine which clinical variables influence GFR in the early stage of hypertension.

METHODS

Participants were 1,106 young-to-middle-age hypertensive adults with creatinine clearance >60 ml/min/1.73 m(2). Clinic and ambulatory blood pressures (BPs) were measured and the difference between clinic and 24-h systolic BP was defined as the white-coat effect (WCE). In 606 participants, 24-h urinary epinephrine and norepinephrine were also measured. Glomerular hyperfiltration, defined as a GFR ≥150 ml/min/1.73 m(2), was present in 201 subjects.

RESULTS

Patients' mean age was 33.1 ± 8.5 years and office BP was 146 ± 10.5/94 ± 5.0 mm Hg. In multivariable linear regression, significant predictors of GFR were younger age (P < 0.0001), male gender (P < 0.0001), 24-h systolic BP (P = 0.0001), body mass (P < 0.0001), WCE (P = 0.02), log-epinephrine (P = 0.01), and coffee use (P < 0.01). In a logistic model, independent predictors of glomerular hyperfiltration were obesity (odds ratio, 95% confidence interval = 6.1, 3.8-9.8), male gender (2.9, 1.8-4.9), age <33 years (2.1, 1.5-3.1), ambulatory hypertension (2.0, 1.4-3.0), WCE >15 mm Hg (1.6, 1.1-2.3), heavy coffee use (2.0, 1.1-3.8), and epinephrine >25 mcg/24 h (1.9, 1.2-3.1).

CONCLUSIONS

The novel finding of this study is that hyper-reactivity to stress, as determined by urinary epinephrine level and WCE, and coffee use contribute to determining glomerular hyperfiltration in the early stage of hypertension. Our data may help to identify a subset of patients with glomerular hyperfiltration, who may be at increased risk of chronic kidney disease and may benefit from antihypertensive treatment.

Effects of olmesartan on arterial stiffness in rats with chronic renal failure

Background

It has been suggested that the antioxidant properties of olmesartan (OLM), an angiotensin II type 1 receptor (AT₁R) blocker, contribute to renal protection rather than blood pressure lowering effects despite the fact that causal relationships between hypertension and renal artery disease exist. This study aimed to examine the hypothesis whether the antioxidative activities of OLM were correlated to arterial stiffness, reactive oxygen species and advanced glycation end products (AGEs) formation in rats with chronic renal failure (CRF).

Methods

CRF rats were induced by 5/6 nephrectomy and randomly assigned to an OLM (10 mg/day) group or a control group. Hemodynamic states, oxidative stress, renal function and AGEs were measured after 8 weeks of OLM treatment.

Results

All the hemodynamic derangements associated with renal and cardiovascular dysfunctions were abrogated in CRF rats receiving OLM. Decreased cardiac output was normalized compared to control (p <0.05). Mean aortic pressure, total peripheral resistance and left ventricular weight/body weight ratio were reduced by 21.6% (p <0.05), 28.2% (p <0.05) and 27.2% ((p <0.05). OLM also showed beneficial effects on the oscillatory components of the ventricular after-load, including 39% reduction in aortic characteristic impedance (p < 0.05), 75.3% increase in aortic compliance (p <0.05) and 50.3% increase in wave transit time (p < 0.05). These results implied that OLM attenuated the increased systolic load of the left ventricle and prevented cardiac hypertrophy in CRF rats. Improved renal function was also reflected by increases in the clearances of BUN (28.7%) and serum creatinine (SCr, 38.8%). In addition to these functional improvements, OLM specifically reduced the levels of malondialdehyde (MDA) equivalents in aorta and serum by 14.3% and 25.1%, as well as the amount of AGEs in the aortic wall by 32% (p < 0.05) of CRF rats.

Conclusion

OLM treatment could ameliorate arterial stiffness in CRF rats with concomitant inhibition of MDA and AGEs levels through the reduction of oxidative stress in aortic wall.

Effects of the antioxidant drug tempol on renal oxygenation in mice with reduced renal mass

We tested the hypothesis that reactive oxygen species (ROS) contributed to renal hypoxia in C57BL/6 mice with &frac56; surgical reduction of renal mass (RRM). ROS can activate the mitochondrial uncoupling protein 2 (UCP-2) and increase O(2) usage. However, UCP-2 can be inactivated by glutathionylation. Mice were fed normal (NS)- or high-salt (HS) diets, and HS mice received the antioxidant drug tempol or vehicle for 3 mo. Since salt intake did not affect the tubular Na(+) transport per O(2) consumed (T(Na/)Q(O2)), further studies were confined to HS mice. RRM mice had increased excretion of 8-isoprostane F(2α) and H(2)O(2), renal expression of UCP-2 and renal O(2) extraction, and reduced T(Na/)Q(O2) (sham: 20 ± 2 vs. RRM: 10 ± 1 μmol/μmol; P < 0.05) and cortical Po(2) (sham: 43 ± 2, RRM: 29 ± 2 mmHg; P < 0.02). Tempol normalized all these parameters while further increasing compensatory renal growth and glomerular volume. RRM mice had preserved blood pressure, glomeruli, and patchy tubulointerstitial fibrosis. The patterns of protein expression in the renal cortex suggested that RRM kidneys had increased ROS from upregulated p22(phox), NOX-2, and -4 and that ROS-dependent increases in UCP-2 led to hypoxia that activated transforming growth factor-β whereas erythroid-related factor 2 (Nrf-2), glutathione peroxidase-1, and glutathione-S-transferase mu-1 were upregulated independently of ROS. We conclude that RRM activated distinct processes: a ROS-dependent activation of UCP-2 leading to inefficient renal O(2) usage and cortical hypoxia that was offset by Nrf-2-dependent glutathionylation. Thus hypoxia in RRM may be the outcome of NADPH oxidase-initiated ROS generation, leading to mitochondrial uncoupling counteracted by defense pathways coordinated by Nrf-2.

Ezetimibe alone or in combination with pitavastatin prevents kidney dysfunction in 5/6 nephrectomized rats fed high-cholesterol

We attempted to elucidate the relationship between cholesterol absorption and kidney damage by investigating the renoprotective effect of ezetimibe, a cholesterol absorption inhibitor, in 5/6 nephrectomized rats (Nx). The Nx or sham-operated rats (Sham) were fed 1% high-cholesterol diet (HC) containing ezetimibe (10 mg/[kg d]), pitavastatin (3 mg/[kg d]), or both for 8 weeks. Pathological changes, endothelial nitric oxide synthase (eNOS) messenger RNA (mRNA), and oxidative stress were assessed in the kidney. The Sham fed HC exhibited hypercholesterolemia and glomerulosclerosis with macrophage infiltration in the kidney, and ezetimibe attenuated these changes. The Nx exhibited hypercholesterolemia, increased urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), glomerulosclerosis with macrophage infiltration and interstitial fibrosis, and downregulation of eNOS mRNA. The HC increased cholesterol further and worsened the kidney damage with increased 8-OHdG. Ezetimibe attenuated the hypercholesterolemia, kidney dysfunction, and pathological changes. The beneficial effects of ezetimibe were significantly associated with reduced 8-OHdG (P < .01). Pitavastatin did not reduce cholesterol or 8-OHdG, but it did significantly suppress the kidney damage with upregulated eNOS mRNA by 2.5-fold (P < .02). The combination of ezetimibe and pitavastatin synergistically ameliorated the kidney damage. The kidney dysfunction and pathological changes were significantly associated with cholesterol, markers of cholesterol absorption (campesterol and cholestanol), and 8-OHdG (P < .001-.05). Multiple regression analysis revealed that the markers of cholesterol absorption were independently associated with the kidney damage. Ezetimibe confers renoprotective effects by inhibiting cholesterol absorption, which in turn reduces oxidative stress; and pitavastatin additively ameliorates kidney damage by increasing NO production via mechanisms independent of cholesterol reduction.

HIV gene expression deactivates redox-sensitive stress response program in mouse tubular cells both in vitro and in vivo

Human immunodeficiency virus (HIV)-1 has been reported to cause tubular cell injury both in in vivo and in vitro studies. In the present study, we evaluated the role of oxidative stress in the induction of apoptosis in HIV gene expressing mouse tubular cells in in vivo (Tg26, a transgenic mouse model of HIV-associated nephropathy) and in vitro (tubular cells were transduced with pNL4-3: ΔG/P-GFP, VSV.G psueudo typed virus) studies. Although Tg26 mice showed enhanced tubular cell reactive oxygen species (ROS) generation and apoptosis, renal tissue did not display a robust antioxidant response in the form of enhanced free radical scavenger (MnSOD/catalase) expression. Tg26 mice not only showed enhanced tubular cell expression of phospho-p66ShcA but also displayed nuclear Foxo3a translocation to the cytoplasm. These findings indicated deactivation of tubular cell Foxo3A-dependent redox-sensitive stress response program (RSSRP) in Tg26 mice. In in vitro studies, NL4-3 (pNL4-3: ΔG/P-GFP, VSV.G pseudotyped virus)-transduced mouse proximal tubular cells (NL4-3/MPTEC) displayed enhanced phosphorylation of p66ShcA. NL4-3/MPTECs also displayed greater (P < 0.01) ROS generation when compared with empty vector-transduced tubular cells; however, both diminution of p66ShcA and N-acetyl cysteine attenuated NL4-3-induced tubular cell ROS generation as well as apoptosis. In addition, both antioxidants and free radical scavengers partially inhibited HIV-induced tubular cell apoptosis. NL4-3/MPTEC displayed deactivation of RSSRP in the form of enhanced phosphorylation of Foxo3A and attenuated expression of superoxide dismutase (SOD) and catalase. Since both SOD and catalase were able to provide protection against HIV-1-induced tubular cell apoptosis, it suggests that HIV-1-induced proapoptotic effect may be a consequence of the deactivated RSSRP.

Activation of renal angiotensin type 1 receptor contributes to the pathogenesis of progressive renal injury in a rat model of chronic cardiorenal syndrome

Although chronic cardiac dysfunction is known to progressively exacerbate renal injury, a condition known as type 2 cardiorenal syndrome (CRS), the mechanism responsible is largely unknown. The present study was undertaken to clarify the mechanism of renal injury in rats with both unilateral nephrectomy (NX) and surgically induced myocardial infarction (MI), corresponding to a model of type 2 CRS. Compared with a control group, rats with both MI and NX (MI+NX) exhibited progressive proteinuria during the experimental period (34 wk after MI surgery), whereas proteinuria was not observed in rats with MI alone and was moderate in rats with NX alone. The proteinuria in rats with MI+NX was associated with renal lesions such as glomerulosclerosis and infiltration of mononuclear cells and upregulation of the renal proinflammatory and -fibrotic cytokine and angiotensin II type 1a receptor (AT1aR) genes. In contrast, plasma renin activity was lowered in rats with MI+NX. Immunohistochemistry revealed that the increased AT1R protein was present mainly in renal interstitial mononuclear cells. Olmesartan medoxomil, an AT1R blocker, markedly reduced the proteinuria and infiltration of mononuclear cells, whereas spironolactone, a mineralocorticoid receptor blocker, did not. The present findings demonstrate the pathogenetic role of renal interstitial AT1R signaling in a model of type 2 CRS, providing evidence that AT1R blockade can be a useful therapeutic option for this syndrome.

Downregulation of the renal and hepatic hydrogen sulfide (H2S)-producing enzymes and capacity in chronic kidney disease

BACKGROUND

Oxidative stress and inflammation are constant features and major mediators of progression and cardiovascular complications of chronic kidney disease (CKD). Hydrogen sulfide (H(2)S) is an endogenous signaling gas, which possesses potent anti-oxidant, anti-inflammatory, anti-hypertensive and other regulatory functions. H(2)S is produced by cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulphurtransferase (MST). Plasma H(2)S is reduced in humans with hypertension, atherosclerosis and end-stage renal disease (ESRD). Atherosclerosis, hypertension and ischemia/reperfusion-induced acute kidney injury are associated with and, in part, mediated by diminished tissue H(2)S in experimental animals. Expression of the H(2)S-producing enzymes is reduced in the circulating leukocytes of patients with ESRD. However, the effect of CKD on expression of H(2)S-producing enzymes in the diseased kidney and other tissues is unknown and was studied here.

METHODS

Subgroups of rats were subjected to 5/6 nephrectomy or sham operation and observed for 6-12 weeks. Expression of H(2)S-producing enzymes and H(2)S-producing capacity was measured in kidney, liver and brain tissues.

RESULTS

The CKD group exhibited oxidative stress and significant reduction of plasma H(2)S concentration. This was associated with marked reduction of H(2)S-producing capacity of the kidney and liver, marked downregulation of CBS, CSE and MST in the kidney and of CBS and CSE expression in the liver. However, expression of H(2)S-producing enzymes in the brain was not significantly altered in CKD rats.

CONCLUSIONS

CKD is associated with significant reduction in plasma H(2)S concentration, diminished remnant kidney and liver tissue H(2)S-producing capacity and downregulation of the H(2)S-producing enzymes. Given the potent anti-oxidant, anti-inflammatory and cytoprotective properties of H(2)S, its deficiency may contribute to progression of CKD and the associated complications.

Curcumin and enalapril ameliorate renal failure by antagonizing inflammation in 5/6 nephrectomized rats: role of phospholipase and cyclooxygenase

Previously, we showed that curcumin prevents chronic kidney disease (CKD) development in &frac56; nephrectomized (Nx) rats when given within 1 wk after Nx (Ghosh SS, Massey HD, Krieg R, Fazelbhoy ZA, Ghosh S, Sica DA, Fakhry I, Gehr TW. Am J Physiol Renal Physiol 296: F1146-F1157, 2009). To better mimic the scenario for renal disease in humans, we began curcumin and enalapril therapy when proteinuria was already established. We hypothesized that curcumin, by blocking the inflammatory mediators TNF-α and IL-1β, could also reduce cyclooxygenase (COX) and phospholipase expression in the kidney. Nx animals were divided into untreated Nx, curcumin-treated, and enalapril-treated groups. Curcumin (75 mg/kg) and enalapril (10 mg/kg) were administered for 10 wk. Renal dysfunction in the Nx group, as evidenced by elevated blood urea nitrogen, plasma creatinine, proteinuria, segmental sclerosis, and tubular dilatation, was comparably reduced by curcumin and enalapril, with only enalapril significantly lowering blood pressure. Compared with controls, Nx animals had higher plasma/kidney TNF-α and IL-1β, which were reduced by curcumin and enalapril treatment. Nx animals had significantly elevated kidney levels of cytosolic PLA(2), calcium-independent intracellular PLA(2), COX 1, and COX 2, which were comparably reduced by curcumin and enalapril. Studies in mesangial cells and macrophages were carried out to establish that the in vivo increase in PLA(2) and COX were mediated by TNF-α and IL-1β and that curcumin, by antagonizing the cytokines, could significantly reduce both PLA(2) and COX. We conclude that curcumin ameliorates CKD by blocking inflammatory signals even if it is given at a later stage of the disease.

LOX-1 and angiotensin receptors, and their interplay

The renin-angiotensin system (RAS) plays an important role in regulating blood pressure, water-salt balance and the pathogenesis of cardiovascular diseases. Angiotensin II (Ang II) is the physiologically active mediator and mediates the main pathophysiological actions in RAS. Ang II exerts the effects by activating its receptors, primarily type 1 (AT1R) and type 2 (AT2R). Most of the known pathophysiological effects of Ang II are mediated by AT1R activation. The precise physiological function of AT2R is still not clear. Generally, AT2R is considered to oppose the effects of AT1R. Lectin-like oxidized low-density lipoprotein scavenger receptor-1 (LOX-1) is one of the major receptors responsible for binding, internalizing and degrading ox-LDL. The activation of LOX-1 has been known to be related to many pathophysiological events, including endothelial dysfunction and injury, fibroblast growth, and vascular smooth muscle cell hypertrophy. Many of these alterations are present in atherosclerosis, hypertension, and myocardial ischemia and remodeling. A growing body of evidence suggests the existence of a cross-talk between LOX-1 and Ang II receptors. Their interplays are embodied in the reciprocal regulation of their expression and activity. Their interplays are involved in a series of signals. Recent studies suggests that reactive oxygen species (ROS), nitric oxide (NO), protein kinase C (PKC) and mitogen activated protein kinases (MAPKs) are important signals responsible for their cross-talk. This paper reviews these aspects of dyslipidemia and RAS activation.

Salutary effects of hemodialysis on low-density lipoprotein proinflammatory and high-density lipoprotein anti-inflammatory properties in patient with end-stage renal disease

End-stage renal disease (ESRD) causes oxidative stress, inflammation, low-density lipoprotein (LDL) oxidation, high-density lipoprotein (HDL) deficiency and accelerated atherosclerosis. Uptake of oxidized LDL by macrophages results in foam cell and plaque formation. HDL mitigates atherosclerosis via reverse cholesterol transport and inhibition of LDL oxidation. ESRD heightens LDL inflammatory activity and suppresses HDL anti-inflammatory activity. The effect of hemodialysis on the LDL and HDL inflammatory properties is unknown. By removing the potential pro-oxidant/proinflammatory uremic toxins, dialysis may attenuate LDL inflammatory and HDL anti-inflammatory properties. Conversely, exposure to dialyzer membrane and tubing and influx of impurities from dialysate can intensify LDL and HDL inflammatory activities. This study examined the effect of hemodialysis on LDL and HDL inflammatory activities. Plasma samples were obtained from 12 normal control and 26 ESRD patients before and after hemodialysis with (16 patients) or without (10 patients) heparinization. HDL and LDL were isolated and tested for monocyte chemotactic activity in cultured endothelial cells. ESRD patients had increased LDL chemotactic activity, reduced HDL anti-inflammatory activity, paraoxonase and glutathione peroxidase levels, and elevated plasma IL-6 before dialysis. Hemodialysis partially improved LDL inflammatory and HDL anti-inflammatory activities and enhanced patients' HDL ability to suppress their LDL inflammatory activity. The salutary effect on LDL inflammatory activity was significantly greater in patients dialyzed with than those without heparin. ESRD heightens LDL inflammatory and impairs HDL anti-inflammatory activities. Hemodialysis partially improves LDL and HDL inflammatory activities. The salutary effects of hemodialysis are in part mediated by heparin, which is known to possess lipolytic and antioxidant properties.

Proinflammatory role of angiotensin II in a rat nephrosis model induced by adriamycin

Introduction: Nephrotic syndrome induced by adriamycin (ADR) is an experimental model of glomerulosclerosis in humans. The AT1 receptor for angiotensin II (Ang II) is involved in the renal expression of the nuclear factor-kappa B (NF-ΚB) during this nephrosis. NF-ΚB is a transcription factor for proinflammatory effects of Ang II; however, there is no information about the role of this receptor in the renal proinflammatory events in ADR nephrosis.

Materials and methods: To determine the role of Ang II in ADR nephrosis, Sprague-Dawley rats were treated with ADR (6 mg/kg iv). One ADR group received oral losartan treatment (15 mg/kg gavage) 3 days before ADR injection and then daily for 4 weeks, and the other group water. Animals were sacrificed at week 4 and renal macrophage infiltration, ICAM-1, superoxide anion (O2-) and Ang II expressions were analysed by indirect immunofluorescence and histochemical techniques.

Results: ADR rats showed increased expression of ICAM-1, Ang II, O2- and macrophage infiltration, events that were diminished by losartan treatment. Ang II expression remained unaltered after antagonist treatment. Proteinuria was reduced after 3 weeks of treatment.

Conclusions: These data suggest that Ang II plays a role in the inflammatory events during ADR-induced nephrosis, probably mediated by AT1 receptors.

Inhibition of NF-κB-induced inflammatory responses by angiotensin II antagonists in aged rat kidney

In this study, we explored the mechanisms by which the angiotensin converting enzyme inhibitor (ACEI), enalapril, and the Ang II receptor blocker (ARB), losartan suppress oxidative stress and NF-κB activation-induced inflammatory responses in aged rat kidney. The experimentations were carried out utilizing aged (24-month-old) Brown Norway×Fischer 344 (F1) male rats which were randomized into 3 groups and administered enalapril (40 mg/kg), losartan (30 mg/kg) or placebo for 6 months (daily p.o.). The level of reactive species (RS), peroxynitrite (ONOO(-)), GSH/GSSG and lipid peroxidation were measured. The activity of the pro-inflammatory transcription factor NF-κB, and gene expression of proteins in upstream signaling cascades were measured by electro-mobility shift assay (EMSA) and Western blotting. Enalapril and losartan differentially attenuated redox imbalance and the redox-sensitive transcription factor, the NF-κB pathway. Furthermore, stimulation of the NF-κB activation pathway by phosphorylation of p65 was attenuated by both compounds. Moreover, mediation of phosphorylation of p65 by phosphorylation of IκB kinase αβ (IKKαβ) and mitogen- and stress-activated protein kinase-1 (MSK-1), were also inhibited by enalapril and losartan. Finally, both compounds also lowered expression of NF-κB-dependent inflammatory genes, such as cyclooxygenase-2 (COX-2), and inducible NO synthase (iNOS). Only losartan lowered levels of 5-lipoxygenase (5-LOX). These findings indicate that enalapril and losartan differentially suppress inflammatory responses via inhibition of oxidative stress-induced NF-κB activation in aged rat kidney.

Role of intrarenal angiotensin system activation, oxidative stress, inflammation, and impaired nuclear factor-erythroid-2-related factor 2 activity in the progression of focal glomerulosclerosis

The Imai rat is a model of spontaneous focal glomerulosclerosis, which leads to heavy proteinuria, hyperlipidemia, hypertension, and progressive renal failure. Treatment with AT1 blockers (ARBs) ameliorates proteinuria, hyperlipidemia, and nephropathy in this model. Progression of renal disease in 5/6 nephrectomized rats is associated with activation of the intrarenal angiotensin system, up-regulation of the oxidative, inflammatory, and fibrogenic pathways, and impaired activity of nuclear factor-erythroid-2-related factor 2 (Nrf2), the master regulator of genes encoding antioxidant molecules. We hypothesized that progressive nephropathy in the Imai rat is accompanied by oxidative stress, inflammation, and impaired Nrf2 activation and that amelioration of nephropathy with AT1 receptor blockade in this model may be associated with the reversal of these abnormalities. Ten-week-old Imai rats were randomized to the ARB-treated (olmesartan, 10 mg/kg/day for 24 weeks) or vehicle-treated groups. Sprague-Dawley rats served as controls. At 34 weeks of age Imai rats showed heavy proteinuria, hypoalbuminemia, hypertension, azotemia, glomerulosclerosis, tubulointerstitial inflammation, increased angiotensin II expressing cell population, up-regulations of AT1 receptor, AT2 receptor, NAD(P)H oxidase, and inflammatory mediators, activation of nuclear factor-κB and reduction of Nrf2 activity and expression of its downstream gene products in the renal cortex. ARB therapy prevented nephropathy, suppressed oxidative stress and inflammation, and restored Nrf2 activation and expression of the antioxidant enzymes. Thus progressive focal glomerulosclerosis in the Imai rats is associated with oxidative stress, inflammation, and impaired Nrf2 activation. These abnormalities are accompanied by activation of intrarenal angiotensin system and can be prevented by ARB administration.

Lipotoxicity and impaired high density lipoprotein-mediated reverse cholesterol transport in chronic kidney disease

Chronic kidney disease (CKD) is associated with a high risk of death from cardiovascular disease. Inflammation, oxidative stress, and dyslipidemia, which are common consequences of CKD, contribute to the pathogenesis of atherosclerosis and cardiovascular disease in this population. Dyslipidemia of CKD is characterized by diminished plasma high density lipoprotein (HDL) concentration, impaired HDL anti-oxidant and anti-inflammatory activities, and elevated plasma triglyceride, very low density lipoprotein (VLDL), intermediate density lipoprotein, chylomicron remnants, and oxidized lipids and lipoproteins. The constellation of inflammation, HDL deficiency, and oxidative modification of lipoproteins can cause atherosclerosis and progression of renal disease. We have recently found lipid accumulation in the remnant kidney and the wall of aorta in rats with CKD induced by 5/6 nephrectomy. This was mediated by up-regulation of scavenger receptors involved in the influx of oxidized lipids or lipoproteins, tubular reabsorption of lipid binding proteins through megalin-cubilin complexes, upregulation of fatty acid synthesis, and downregulation of fatty acid oxidation pathways. The combination of increased lipid influx, elevated production and reduced catabolism of lipids, and impaired HDL-mediated reverse cholesterol transport can promote atherosclerosis, glomerulosclerosis, and tubulointerstitial damage. Although statins can be effective in slowing CKD progression in patients with mild-to-moderate CKD, they have consistently failed to mitigate oxidative stress, inflammation, HDL deficiency, or cardiovascular mortality in the end-stage renal disease populations. Similarly, high doses of antioxidant vitamins have failed to either ameliorate oxidative stress, inflammation, or improve overall mortality in end-stage renal disease. This article is intended to provide a brief review of the effects of CKD on HDL structure and function and pathways of lipid influx, efflux, synthesis, and catabolism in the artery wall and the diseased kidney.

Prevention of angiotensin II-mediated renal oxidative stress, inflammation, and fibrosis by angiotensin-converting enzyme 2

Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase capable of metabolizing angiotensin (Ang) II into Ang 1 to 7. We hypothesized that ACE2 is a negative regulator of Ang II signaling and its adverse effects on the kidneys. Ang II infusion (1.5 mg/kg⁻¹/d⁻¹) for 4 days resulted in higher renal Ang II levels and increased nicotinamide adenine dinucleotide phosphate oxidase activity in ACE2 knockout (Ace2(-/y)) mice compared to wild-type mice. Expression of proinflammatory cytokines, interleukin-1β and chemokine (C-C motif) ligand 5, were increased in association with greater activation of extracellular-regulated kinase 1/2 and increase of protein kinase C-α levels. These changes were associated with increased expression of fibrosis-associated genes (α-smooth muscle actin, transforming growth factor-β, procollagen type Iα1) and increased protein levels of collagen I with histological evidence of increased tubulointerstitial fibrosis. Ang II-infused wild-type mice were then treated with recombinant human ACE2 (2 mg/kg⁻¹/d⁻¹, intraperitoneal). Daily treatment with recombinant human ACE2 reduced Ang II-induced pressor response and normalized renal Ang II levels and oxidative stress. These changes were associated with a suppression of Ang II-mediated activation of extracellular-regulated kinase 1/2 and protein kinase C pathway and Ang II-mediated renal fibrosis and T-lymphocyte-mediated inflammation. We conclude that loss of ACE2 enhances renal Ang II levels and Ang II-induced renal oxidative stress, resulting in greater renal injury, whereas recombinant human ACE2 prevents Ang II-induced hypertension, renal oxidative stress, and tubulointerstitial fibrosis. ACE2 is an important negative regulator of Ang II-induced renal disease and enhancing ACE2 action may have therapeutic potential for patients with kidney disease.

Connecting chronic and recurrent stress to vascular dysfunction: no relaxed role for the renin-angiotensin system

The renin-angiotensin system (RAS) is classically considered to be a protective system for volume balance and is activated during states of volume depletion. Interestingly, one of the major pathways activating the system is the sympathetic nervous system, also the primary mediator of the acute stress response. When one further examines the cells mediating the immune site of the response, which is primarily an inflammatory response leading to defense at a locally injured area, these cells all express the ANG II type 1 receptor (AGTR1). Scattered throughout the literature are reports indicating that acute and chronic stress can activate renin and increase plasma levels of components of the RAS. Moreover, there are reports describing that ANG II can modulate the distribution and function of immune cells. Since the inflammatory response is also implicated to be central in the initiation and progression of vascular damage, we propose in this review that recurrent acute stress and chronic stress can induce a state with inflammation, due to ANG II-mediated activation of inflammatory cells, specifically monocytes and lymphocytes. Such a proposal would explain a lot of the observations regarding RAS components in inflammatory cells. Despite its attractiveness, substantial research in this area would be required to substantiate this hypothesis.

Acid retention during kidney failure induces endothelin and aldosterone production which lead to progressive GFR decline, a situation ameliorated by alkali diet

Rats with 5/6 nephrectomy have metabolic acidosis with a progressive decline in the glomerular filtration rate (GFR) ameliorated by endothelin and aldosterone antagonists and by dietary alkali. Interestingly, rats with 2/3 nephrectomy have no metabolic acidosis yet have a progressive GFR decline induced by acid retention and ameliorated by dietary alkali. Because patients without metabolic acidosis but with a moderately reduced GFR have a progressive GFR decline, ameliorated by oral sodium bicarbonate, we used rats with 2/3 nephrectomy to model these patients. Kidney acid content, endothelin-1, and aldosterone (measured by microdialysis) were higher in the rats with 2/3 nephrectomy than those with a sham operation despite no differences in plasma acid-base parameters. The GFR of the former but not the latter was lower at 25 than at 1 week after nephrectomy. Endothelin and aldosterone antagonism improved the preservation of GFR; however, this remained lower at week 24 than at week 1. By contrast, the GFR at weeks 24 and 1 was not different if the rats were given dietary alkali to normalize the kidney acid content. Antagonist of endothelin and aldosterone yielded no added GFR benefit. Thus, our study shows that (1) the decline in GFR in 2/3 nephrectomy is mediated by acid retention-induced kidney endothelin and aldosterone production; (2) receptor antagonism and dietary alkali are not additive; and (3) dietary alkali better preserves GFR than both endothelin and aldosterone receptor antagonism.

Cilnidipine suppresses podocyte injury and proteinuria in metabolic syndrome rats: possible involvement of N-type calcium channel in podocyte

OBJECTIVES

Clinical studies have indicated the beneficial effect of an L/N-type calcium channel blocker (CCB), cilnidipine, on the progression of proteinuria in hypertensive patients compared with an L-type CCB, amlodipine. In the present study, we examined the effects of cilnidipine and amlodipine on the renal injury in spontaneously hypertensive rat/ND mcr-cp (SHR/ND) and their underlying mechanism.

METHODS AND RESULTS

SHR/ND were treated with vehicle (nU10), cilnidipine [33 mg/kg per day, orally (p.o.); nU11] or amlodipine (20 mg/kg per day, p.o.; nU9) for 20 weeks. SHR/ND developed proteinuria in an age-dependent manner. Cilnidipine suppressed the proteinuria greater than amlodipine did. The immunohistochemical analysis showed that N-type calcium channel and Wilm's tumor factor, a marker of podocyte, were co-expressed. SHR/ND had significantly greater desmin staining, an indicator of podocyte injury, with lower podocin and nephrin expression in the glomeruli than Wistar-Kyoto rat or SHR. Cilnidipine significantly prevented the increase in desmin staining and restored the glomerular podocin and nephrin expression compared with amlodipine. Cilnidipine also prevented the increase in renal angiotensin II content, the expression and membrane translocation of NADPH oxidase subunits and dihydroethidium staining in SHR/ND. In contrast, amlodipine failed to change these renal parameters.

CONCLUSION

These data suggest that cilnidipine suppressed the development of proteinuria greater than amlodipine possibly through inhibiting N-type calcium channel-dependent podocyte injury in SHR/ND.

Effects of a novel cystine-based glutathione precursor on oxidative stress in vascular smooth muscle cells

Chronic kidney disease (CKD) is associated with accelerated atherosclerosis and cardiovascular disease, which is largely mediated by oxidative stress. We investigated the effect of three glutathione (GSH) precursors: N-acetyl-cysteine (NAC), cystine as the physiological carrier of cysteine in GSH with added selenomethionine (F1), and NAC fortified with selenomethionine (F2) on oxidative stress induced by spermine (a uremic toxin) in cultured human aortic vascular smooth muscle cells (VSMC). VSMC were exposed to spermine (15 microM) with or without the given antioxidants (dose 50, 100, 200, and 500 microg/ml) or vehicle (control) and assessed for intracellular GSH levels, 4-hydroxy-trans-2-nonenal (4-HNE), and incorporation of 13C from glucose into alanine and protein. Spermine exposure reduced intracellular GSH levels, increased 4-HNE, and impaired glucose metabolism through reduction in pyruvate generation and/or transamination. Treatment with NAC had no effect on intracellular glutathione level. In contrast, F1 maintained intracellular GSH at control levels at all four doses. Subsequent studies performed with 200 microg/ml of F1, F2, or NAC (optimal dose) revealed normalization of 4-HNE, whereas restoration of 13C from glucose to alanine or protein to control values was only noted in the F1 group. Spermine-induced alterations in VSMC ultrastructure were prevented in approximately 90% of cells treated with F1 but only approximately 50% of cells treated with either NAC or F2. In conclusion, F1 was more effective than NAC or F2 in ameliorating spermine-induced reduction in intracellular GSH levels and cellular alterations in VSMC. The cystine-based GSH precursor (F1) is a promising antioxidant, and further studies are needed to examine the effect of this compound in preventing CKD-associated vascular disease.

Inhibition of apoptotic signalling in spermine-treated vascular smooth muscle cells by a novel glutathione precursor

CKD (chronic kidney disease) is a public health problem, mediated by haemodynamic and non-haemodynamic events including oxidative stress. We investigated the effect of two GSH (glutathione) precursors, NAC (N-acetylcysteine) and cystine as the physiological carrier of cysteine in GSH with added selenomethionine (F1) in preventing spermine (uraemic toxin)-induced apoptosis in cultured human aortic VSMC (vascular smooth muscle cells). VSMCs exposed to spermine (15 microM) with or without antioxidants (doses 50, 100, 200 and 500 microg/ml) were assessed for apoptosis, JNK (c-Jun-NH2-terminal kinase) activation and iNOS (inducible nitric oxide synthase) induction and activation of intrinsic pathway signalling. Spermine exposure resulted in activation of JNK and iNOS induction and apoptosis. NAC and F1 (dose range 50-500 microg/ml) attenuated spermine-induced acceleration of VSMC apoptosis but only F1 (at 200 and 500 microg/ml) maintained spermine-induced apoptosis at control levels. Spermine-induced JNK activation was prevented by 200 microg/ml of both NAC and F1, while iNOS induction was blocked only by F1. Notably, the adverse effects of spermine on BAX/BCL-2 ratio, cytochrome c release and caspase activation was fully attenuated by F1. In conclusion, F1 was more effective than NAC in preventing spermine-induced apoptosis and downstream changes in related signal transduction pathways in VSMCs. Further studies are needed to examine the effect of these compounds in preventing CKD-associated vascular disease.

HDL metabolism and activity in chronic kidney disease

Chronic kidney disease (CKD) is associated with development of atherosclerosis and premature death from cardiovascular disease. The predisposition of patients with CKD to atherosclerosis is driven by inflammation, oxidative stress and dyslipidemia, all of which are common features of this condition. Markers of dyslipidemia in patients with advanced CKD are impaired clearance and heightened oxidation of apolipoprotein-B-containing lipoproteins and their atherogenic remnants, and a reduction of the plasma concentration, antioxidant, and anti-inflammatory properties of high-density lipoprotein (HDL). Studies in animal models of CKD indicate that the disease promotes lipid accumulation in the artery wall and kidney, leading to atherosclerosis, glomerulosclerosis and tubulointerstitial injury. These effects seem to be mediated by an increased cellular influx of lipids, elevated cellular production and reduced cellular catabolism of fatty acids, and impaired antioxidant, anti-inflammatory and reverse lipid transport properties of HDL. Available pharmacological therapies have been largely ineffective in ameliorating oxidative stress, inflammation, HDL deficiency and/or dysfunction, and the associated atherosclerosis and cardiovascular disease in patients with end-stage renal disease. This Review aims to provide an overview of the mechanisms and consequences of CKD-induced HDL deficiency and dysfunction.

Contribution of impaired Nrf2-Keap1 pathway to oxidative stress and inflammation in chronic renal failure

Oxidative stress and inflammation are constant features and major mediators of progression of chronic kidney disease (CKD). Nuclear factor erythroid-2-related factor-2 (Nrf2) confers protection against tissue injury by orchestrating antioxidant and detoxification responses to oxidative and electrophilic stress. While sources of oxidative stress and inflammation in the remnant kidney have been extensively characterized, the effect of CKD on Nrf2 activation and expression of its downstream gene products is unknown and was investigated. Subgroups of male Sprague-Dawley rats were subjected to 5/6 nephrectomy or sham operation and observed for 6 or 12 wk. Kidneys were then harvested, and Nrf2 activity and its downstream target gene products (antioxidant and phase II enzymes) were assessed. In addition, key factors involved in promoting inflammation and oxidative stress were studied. In confirmation of earlier studies, rats with chronic renal failure exhibited increased lipid peroxidation, glutathione depletion, NF-κB activation, mononuclear cell infiltration, and upregulation of monocyte chemoattractant protein-1, NAD(P)H oxidase, cyclooxygenase-2, and 12-lipoxygenase in the remnant kidney pointing to oxidative stress and inflammation. Despite severe oxidative stress and inflammation, remnant kidney tissue Nrf2 activity (nuclear translocation) was mildly reduced at 6 wk and markedly reduced at 12 wk, whereas the Nrf2 repressor Keap1 was upregulated and the products of Nrf2 target genes [catalase, superoxide dismutase, glutathione peroxidase, heme oxygenase-1, NAD(P)H quinone oxidoreductase, and glutamate-cysteine ligase] were reduced or unchanged at 6 wk and significantly diminished at 12 wk. Thus oxidative stress and inflammation in the remnant kidney are compounded by conspicuous impairment of Nrf2 activation and consequent downregulation of the antioxidant enzymes.

High-calorie diet partially ameliorates dysregulation of intrarenal lipid metabolism in remnant kidney

Chronic renal failure (CRF) is associated with malnutrition and renal tissue accumulation of lipids, which can contribute to progression of renal disease. This study was designed to explore the effect of a high-calorie diet on pathways involved in lipid metabolism in the remnant kidney of rats with CRF. 5/6 nephrectomized rats were randomized to receive a regular diet (3.0 kcal/g) or a high-calorie diet (4.5 kcal/g) for 12 weeks. Renal lipid contents and abundance of molecules involved in cholesterol and fatty acid metabolism were studied. The CRF group consuming a regular diet exhibited growth retardation; azotemia; proteinuria; glomerulosclerosis; tubulointerstitial injury; heavy lipid accumulation in the remnant kidney; up-regulation of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), ATP-binding cassette transporter-1 (ABCA1), liver X receptor (LXR) α/β, carbohydrate-responsive element binding protein (ChREBP) and acyl-CoA carboxylase (ACC); and down-regulation of peroxisome proliferator-activated receptor-α (PPAR-α), carnitine palmitoyltransferase-1 (CPT1) and liver-type fatty acid binding protein (L-FABP). The high-calorie diet restored growth; reduced the severity of tubulointerstitial injury, proteinuria and azotemia; partially lowered renal tissue lipid contents; attenuated the up-regulation of mediators of lipid influx (LOX-1), lipid efflux (LXR-α/β and ABCA1) and fatty acid biosynthesis (ChREBP and ACC); and reversed the down-regulation of factors involved in fatty acid oxidation (PPAR-α, CPT1 and L-FABP). In conclusion, a high-calorie diet restores growth, improves renal function and structure, and lowers lipid burden in the remnant kidney. The latter is associated with and most likely due to reduction in lipid influx and enhancement of fatty acid oxidation.

Antioxidant therapy does not ameliorate oxidative stress and inflammation in patients with end-stage renal disease

Oxidative stress and inflammation are common manifestations and major mediators of cardiovascular and many other complications of end-stage renal disease (ESRD). Oxidative stress and inflammation are intimately interrelated as each can cause the other. The present study tested the hypothesis that antioxidant therapy may alleviate oxidative stress and improve inflammation in ESRD patients. We studied 37 hemodialysis patients, of whom 20 were treated daily with a combination of vitamin E, 800 lU; vitamin C, 250 mg; vitamin B6, 100 mg; vitamin B12, 250 microg; and folic acid, 10 mg; whereas 17 patients were given placebo for 8 weeks. Predialysis levels of f-2 isoprostane and protein carbonyl (markers of oxidative stress), C-reactive protein (CRP) and IL6 (markers/ mediators of inflammation) were measured prior to and at 4 and 8 weeks after the onset of therapy. Kt/V, predialysis and postdialysis blood pressure, blood hemoglobin, erythropoietin requirement, plasma ferritin and transferrin saturation, and nutritional indexes were similar among the 2 groups at baseline and remained virtually unchanged throughout the study period. Likewise, plasma f-2 isoprostane, protein carbonyl, CRP, and IL-6 levels remained unchanged and were unaffected by antioxidant administration. In conclusion, the addition of a potent antioxidant cocktail to conventional vitamin supplements had no effect on severity of ESRD-induced oxidative stress, inflammation, hypertension, anemia, or nutritional disorders in hemodialysis patients. Thus, high doses of vitamins beyond the routinely prescribed vitamin supplements do not appear to be indicated in this population.

Activation of hypoxia-inducible factor attenuates renal injury in rat remnant kidney

BACKGROUND

Chronic hypoxia in the kidney has been suggested as a final common pathway to end-stage renal disease. Hypoxia-inducible factor (HIF) is a transcription factor that regulates cellular hypoxic responses, and it is a promising target with therapeutic potential in various kidney disease models. In this study, we investigated whether HIF activation could attenuate renal injury in the rat remnant kidney model.

METHODS

Two weeks after a subtotal nephrectomy, rats received a continuous infusion of dimethyloxalylglycine (DMOG) for 4 weeks to activate HIF.

RESULTS

The DMOG infusion halted the progression of proteinuria. A histological evaluation revealed that the glomerulosclerosis and tubulointerstitial injury were significantly decreased by DMOG treatment. DMOG increased renal HIF-1alpha protein. The expression of glucose transporter-1 (GLUT-1) and prolyl hydroxylase 3 (PHD3) and the immunostaining of vascular endothelial growth factor (VEGF) were increased by DMOG. DMOG-treated rats showed less podocyte injury manifested by decreased immunostaining of desmin and the restoration of podoplanin staining. Furthermore, plasma malondialdehyde (MDA), a marker of oxidative stress, showed a tendency to decrease, and the renal expression of catalase, an antioxidant, was significantly increased by DMOG. The DMOG treatment decreased macrophage infiltration and reduced fibrosis, as manifested by decreased type IV collagen and osteopontin expression.

CONCLUSIONS

Activation of HIF by DMOG halted the progression of proteinuria and attenuated structural damage by preventing podocyte injury in the remnant kidney model. This renoprotection was accompanied by a reduction of oxidative stress, inflammation and fibrosis.

Role of postnatal dietary sodium in prenatally programmed hypertension

In this study we examined the short- and long-term impact of early life dietary sodium (Na) on prenatally programmed hypertension. Hypertension was induced in rat offspring by a maternal low protein (LP) diet. Control and LP offspring were randomized to a high (HS), standard (SS), or low (LS) Na diet after weaning. On the SS diet, the LP pups developed hypertension by 6 weeks of age. The development of hypertension was prevented by the LS diet and exacerbated by the HS diet. Kidney nitrotyrosine content, a measure of oxidative stress, was reduced by the LS diet compared with the HS diet. The modified diets had no effect on control pups. A group of animals on the SS diet was followed up to 51 weeks of age after an early life 3-week exposure to the HS or LS diet. This brief early exposure of LP animals to the LS diet prevented the later development of hypertension and ameliorated the nephrosclerosis observed after early exposure to the HS diet. The LP offspring with early exposure to LS diet had lost their salt-sensitivity when challenged with the HS diet at the age of 43-49 weeks. No effect of early life dietary Na was observed in control animals. These results show that hypertension in this model is salt sensitive and may, in part, be mediated by salt-induced renal oxidative stress and that there may exist a developmental window which allows postnatal "reprogramming" of the hypertension.

Omega-3 fatty acid supplementation attenuates oxidative stress, inflammation, and tubulointerstitial fibrosis in the remnant kidney

Significant reduction of renal mass initiates a series of hemodynamic and nonhemodynamic events which lead to proteinuria, glomerulosclerosis, tubulointerstitial injury, and end-stage renal failure. Lipid mediators derived from fatty acids participate in regulation of renal hemodynamic and nonhemodynamic processes that influence progression of renal disease. Composition of cellular fatty acids and hence related signaling responses are influenced by their dietary contents. Consumption of omega-3 fatty acids (O-3FA) has proven effective in mitigating atherosclerosis. We tested the hypothesis that O-3FA supplementation may retard progression and attenuate upregulation of pathways involved in oxidative stress, inflammation, and fibrosis in rats with renal mass reduction. Sprague-Dawley rats were subjected to 5/6 nephrectomy [chronic renal failure (CRF)] and randomly assigned to the untreated and O-3FA-treated (0.3 g.kg(-1).day(-1) by gastric gavage for 12 wk) groups. Sham-operated rats served as controls. The untreated CRF rats exhibited proteinuria, hypertension, azotemia, upregulations of renal tissue NAD(P)H oxidase, MCP-1, COX-2, PAI-1, TGF-beta, Smad2, alpha-smooth muscle actin, fibronectin, and hepatocyte growth factor, activation of ERK1/2 and NF-kappaB, downregulation of Smad7, intense mononuclear leukocyte infiltration, tubulointerstitial fibrosis, and glomerulosclerosis. O-3FA supplementation significantly lowered COX-2, NAD(P)H oxidase (NOX-4, gp91(phox), p47(phox), p22(phox)), PAI-1, TGF-beta, connective tissue growth factor, alpha-smooth muscle actin, fibronectin, Smad2, and MCP-1, raised Smad7, and attenuated ERK1/2 and NF-kappaB activation, tubulointerstitial fibrosis, and inflammation. Thus, long-term O-3FA supplementation can reduce or reverse upregulation of prooxidant, proinflammatory, and profibrotic pathways and attenuate tubulointerstitial fibrosis in the remnant kidney.

Niacin ameliorates oxidative stress, inflammation, proteinuria, and hypertension in rats with chronic renal failure

Significant reduction of renal mass causes progressive deterioration of renal function and structure which is mediated by systemic and glomerular hypertension, hyperfiltration, oxidative stress, inflammation, and dyslipidemia. Niacin is known to improve lipid metabolism and exert antioxidant/anti-inflammatory actions. Therefore, we considered that niacin supplementation may attenuate oxidative stress, inflammation, and tissue injury in the remnant kidney. To this end, 56 nephrectomized [chronic kidney disease (CKD)] rats were randomly assigned to niacin-treated (50 mg x kg(-1) x day(-1) in the drinking water for 12 wk) and untreated groups. Sham-operated rats served as controls. The untreated CKD rats exhibited azotemia, hypertension, hypertriglyceridemia, proteinuria, glomerulosclerosis, tubulointerstitial damage, upregulation of MCP-1, plasminogen activator inhibitor-1 (PAI-1), transforming growth factor (TGF)-beta, cyclooxygenase (COX)-1, COX-2, and NAD(P)H oxidase (NOX-4, gp91(phox), p47(phox) and p22(phox) subunits) and activation of NF-kappaB (IkappaB phosphorylation). Niacin administration reduced MCP-1, PAI-1, TGF-beta, p47(phox), p22(phox), COX-1, and NF-kappaB activation, ameliorated hypertension, proteinuria, glomerulosclerosis, and tubulointerstitial injury. Although niacin lowered serum creatinine and raised creatinine clearance, the differences did not reach statistical significance. Thus niacin supplementation helps to attenuate histological injury and mitigate upregulation of oxidative and inflammatory systems in the remnant kidney.

Curcumin ameliorates renal failure in 5/6 nephrectomized rats: role of inflammation

TNF-α and NF-κB play important roles in the development of inflammation in chronic renal failure (CRF). In hepatic cells, curcumin is shown to antagonize TNF-α-elicited NF-κB activation. In this study, we hypothesized that if inflammation plays a key role in renal failure then curcumin should be effective in improving CRF. The effectiveness of curcumin was compared with enalapril, a compound known to ameliorate human and experimental CRF. Investigation was conducted in Sprague-Dawley rats where CRF was induced by 5/6 nephrectomy (Nx). The Nx animals were divided into untreated (Nx), curcumin-treated (curcumin), and enalapril-treated (enalapril) groups. Sham-operated animals served as a control. Renal dysfunction in the Nx group, as evidenced by elevated blood urea nitrogen, plasma creatinine, proteinuria, segmental sclerosis, and tubular dilatation, was significantly reduced by curcumin and enalapril treatment. However, only enalapril significantly improved blood pressure. Compared with the control, the Nx animals had significantly higher plasma and kidney TNF-α, which was associated with NF-κB activation and macrophage infiltration in the kidney. These changes were effectively antagonized by curcumin and enalapril treatment. The decline in the anti-inflammatory peroxisome proliferator-activated receptor γ (PPARγ) seen in Nx animals was also counteracted by curcumin and enalapril. Studies in mesangial cells were carried out to further establish that the anti-inflammatory effect of curcumin in vivo was mediated essentially by antagonizing TNF-α. Curcumin dose dependently antagonized the TNF-α-mediated decrease in PPARγ and blocked transactivation of NF-κB and repression of PPARγ, indicating that the anti-inflamatory property of curcumin may be responsible for alleviating CRF in Nx animals.

Nephrin and endothelial injury

PURPOSE OF REVIEW

Nephrin, the main structural protein of the slit diaphragm, is expressed on the surface of glomerular podocytes and is critical in maintaining permselectivity and preventing proteinuria. This review focuses on the fate of nephrin in the context of endothelial injury and gives an update on the recent progress in understanding the pathomechanisms that lead to proteinuria.

RECENT FINDINGS

The following conditions of endothelial injury were found to induce loss of nephrin.(1) Preeclampsia, in which the associated proteinuria is induced by the soluble variant of vascular endothelial growth factor, which stimulates production of endothelin 1 (ET1) in endothelial cells. ET1 in turn triggers nephrin shedding from podocytes.(2) Hypertension, in which increased levels of angiotensin II induce podocyte apoptosis and reduce nephrin expression, leading to proteinuria in rats.(3) Diabetes and high fat diet, which lead to a significant increase in inflammatory molecules and cytokines, including MCP-1, which induces changes in podocyte cytoskeleton and nephrin loss.

SUMMARY

Recent results showed that damage to endothelial cells may alter endothelial-podocyte interaction and induces nephrin loss, a main cause of proteinuria.

Renal mass reduction results in accumulation of lipids and dysregulation of lipid regulatory proteins in the remnant kidney

A significant reduction of renal mass results in proteinuria, glomerulosclerosis, and tubulointerstitial injury, culminating in end-stage chronic renal failure (CRF). The accumulation of lipids in the kidney can cause renal disease. Uptake of oxidized lipoproteins via scavenger receptors, reabsorption of filtered protein-bound lipids via the megalin-cubilin complex, and increased glucose load per nephron can promote lipid accumulation in glomerular, tubular, and interstitial cells in CRF. Cellular lipid homeostasis is regulated by lipid influx, synthesis, catabolism, and efflux. We examined lipid-regulatory factors in the remnant kidney of rats 11 wk after nephrectomy (CRF) or sham operation. CRF resulted in azotemia, proteinuria, lipid accumulation in the kidney, upregulation of megalin, cubilin, mediators of lipid influx (scavenger receptor class A and lectin-like oxidized receptor-1), lipid efflux (liver X receptor alpha/beta and ATP-binding cassette transporter), and fatty acid biosynthesis (carbohydrate-response element binding protein, fatty acid synthase, and acetyl-CoA carboxylase). However, factors involved in cholesterol biosynthesis (sterol regulatory element binding protein, 3-hydroxy-3-methylglutaryl coenzyme A reductase, SCAP, Insig-1, and Insig-2) and fatty acid oxidation (peroxisome proliferator-activated receptor, acyl-CoA oxidase, and liver-type fatty acid binding protein) were reduced in the remnant kidney. Thus CRF results in heavy lipid accumulation in the remnant kidney, which is mediated by upregulation of pathways involved in tubular reabsorption of filtered protein-bound lipids, influx of oxidized lipoproteins and synthesis of fatty acids, and downregulation of pathways involved in fatty acid catabolism.