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

Oxidative stress and inflammation: Implications in uremia and hemodialysis

Oxidative response and inflammation constitute a major defense against infections, but if not properly regulated they could also lead to a number of deleterious effects. Patients affected by different stages of acute and chronic kidney disease, particularly patients on hemodialysis, present a marked activation of oxidative and inflammatory processes. This condition exposes these patients to an elevated risk of morbidity and mortality. This Review is up to date and it analyses the newest notions about pathophysiological mechanisms of oxidative stress and inflammation in patients with renal diseases, also considering the different strategies studied to counterbalance this high risk state.

Antioxidant supplementation reduces skeletal muscle mitochondrial biogenesis

PURPOSE

Exercise increases the production of reactive oxygen species (ROS) in skeletal muscle, and athletes often consume antioxidant supplements in the belief they will attenuate ROS-related muscle damage and fatigue during exercise. However, exercise-induced ROS may regulate beneficial skeletal muscle adaptations, such as increased mitochondrial biogenesis. We therefore investigated the effects of long-term antioxidant supplementation with vitamin E and α-lipoic acid on changes in markers of mitochondrial biogenesis in the skeletal muscle of exercise-trained and sedentary rats.

METHODS

Male Wistar rats were divided into four groups: 1) sedentary control diet, 2) sedentary antioxidant diet, 3) exercise control diet, and 4) exercise antioxidant diet. Animals ran on a treadmill 4 d · wk at ∼ 70%VO2max for up to 90 min · d for 14 wk.

RESULTS

Consistent with the augmentation of skeletal muscle mitochondrial biogenesis and antioxidant defenses, after training there were significant increases in peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) messenger RNA (mRNA) and protein, cytochrome C oxidase subunit IV (COX IV) and cytochrome C protein abundance, citrate synthase activity, Nfe2l2, and SOD2 protein (P < 0.05). Antioxidant supplementation reduced PGC-1α mRNA, PGC-1α and COX IV protein, and citrate synthase enzyme activity (P < 0.05) in both sedentary and exercise-trained rats.

CONCLUSIONS

Vitamin E and α-lipoic acid supplementation suppresses skeletal muscle mitochondrial biogenesis, regardless of training status.

Epigallocatechin-3-gallate prevents lupus nephritis development in mice via enhancing the Nrf2 antioxidant pathway and inhibiting NLRP3 inflammasome activation

Patients with lupus nephritis show an impaired oxidative status and increased levels of interleukin (IL)-1β and IL-18, which are closely linked to inflammation and correlated with disease activity. Although epigallocatechin-3-gallate (EGCG), the major bioactive polyphenol present in green tea with antioxidant and free radical scavenging activities, has been reported to have anti-inflammatory effects by inhibiting nuclear factor-kappa B (NF-κB)-mediated inflammatory responses in vivo, its effectiveness for the treatment of lupus nephritis is still unknown. In the present study, 12-week-old New Zealand black/white (NZB/W) F1 lupus-prone mice were treated daily with EGCG by gavage until sacrificed at 34 weeks old for clinical, pathological, and mechanistic evaluation. We found that the administration (1) prevented proteinuria, renal function impairment, and severe renal lesions; (2) increased renal nuclear factor E2-related factor 2 (Nrf2) and glutathione peroxidase activity; (3) reduced renal oxidative stress, NF-κB activation, and NLRP3 mRNA/protein expression and protein levels of mature caspase-1, IL-1β, and IL-18; and (4) enhanced splenic regulatory T (Treg) cell activity. Our data clearly demonstrate that EGCG has prophylactic effects on lupus nephritis in these mice that are highly associated with its effects of enhancing the Nrf2 antioxidant signaling pathway, decreasing renal NLRP3 inflammasome activation, and increasing systemic Treg cell activity.

Activated microglia decrease histone acetylation and Nrf2-inducible anti-oxidant defence in astrocytes: restoring effects of inhibitors of HDACs, p38 MAPK and GSK3β

Histone deacetylase (HDAC) inhibitors have promising neuroprotective and anti-inflammatory properties although the exact mechanisms are unclear. We have earlier showed that factors from lipopolysaccharide (LPS)-activated microglia can down-regulate the astroglial nuclear factor-erythroid 2-related factor 2 (Nrf2)-inducible anti-oxidant defence. Here we have evaluated whether histone modification and activation of GSK3β are involved in these negative effects of microglia. Microglia were cultured for 24 h in serum-free culture medium to achieve microglia-conditioned medium from non-activated cells (MCM(0)) or activated with 10 ng/mL of LPS to produce MCM(10). Astrocyte-rich cultures treated with MCM(10) showed a time-dependent (0-72 h) increase in astroglial HDAC activity that correlated with lower levels of acetylation of histones H3 and H4 and decreased levels of the transcription factor Nrf2 and γ-glutamyl cysteine ligase modulatory subunit (γGCL-M) protein levels. The HDAC inhibitors valproic acid (VPA) and trichostatin-A (TSA) elevated the histone acetylation levels, restored the Nrf2-inducible anti-oxidant defence and conferred protection from oxidative stress-induced (H(2)O(2)) death in astrocyte-rich cultures exposed to MCM(10). Inhibitors of GSK3β (lithium) and p38 MAPK (SB203580) signaling pathways restored the depressed histone acetylation and Nrf2-related transcription whereas an inhibitor of Akt (Ly294002) caused a further decrease in Nrf2-related transcription. In conclusion, the study shows that well tolerated drugs such as VPA and lithium can restore an inflammatory induced depression in the Nrf2-inducible antioxidant defence, possibly via normalised histone acetylation levels.

Effect of bardoxolone methyl on kidney function in patients with T2D and Stage 3b-4 CKD

BACKGROUND/AIMS

Bardoxolone methyl, a novel synthetic triterpenoid, induces Nrf2, a transcription factor known to play a key role in decreasing oxidative stress and the production of pro-inflammatory molecules.

METHODS

This exploratory multi-center, open-label study assessed the clinical activity and safety of bardoxolone methyl in 20 patients with moderate to severe chronic kidney disease and type 2 diabetes. Patients received 25 mg of bardoxolone methyl daily for 28 days, followed by 75 mg daily for another 28 days.

RESULTS

The study achieved its primary efficacy endpoint, as demonstrated by a significant increase from baseline in estimated glomerular filtration rate (eGFR) of 7.2 ml/min/1.73 m2 (p < 0.001). Improvements were seen in approximately 90% of patients and showed a dose- and time-dependent increase in eGFR. The eGFR change paralleled a significant reduction in serum creatinine (-0.3 mg/dl) and blood urea nitrogen (-4.9 mg/dl), along with an increase in creatinine clearance (+14.6 ml/min/1.73 m2), without a change in the 24-hour creatinine excretion rate. Markers of vascular injury and inflammation were improved by treatment with bardoxolone. No life-threatening adverse events or drug-related serious adverse events were reported.

CONCLUSIONS

The results describe an apparent increase in kidney function following relatively short-term treatment with bardoxolone methyl, a promising new agent that warrants placebo-controlled studies to define its long-term effects on renal function.

Antroquinonol reduces oxidative stress by enhancing the Nrf2 signaling pathway and inhibits inflammation and sclerosis in focal segmental glomerulosclerosis mice

Oxidative stress, inflammation, and fibrosis are involved in the development and progression of focal segmental glomerulosclerosis (FSGS), a common form of idiopathic nephrotic syndrome that represents a therapeutic challenge because it has a poor response to steroids. Antroquinonol (Antroq), a purified compound, is a major active component of a mushroom, namely Antrodia camphorata, that grows in the camphor tree in Taiwan, and it has inhibitory effects on nitric oxide production and inflammatory reactions. We hypothesized that Antroq might ameliorate FSGS renal lesions by modulating the pathogenic pathways of oxidative stress, inflammation, and glomerular sclerosis in the kidney. We demonstrate that Antroq significantly (1) attenuates proteinuria, renal dysfunction, and glomerulopathy, including epithelial hyperplasia lesions and podocyte injury; (2) reduces oxidative stress, leukocyte infiltration, and expression of fibrosis-related proteins in the kidney; (3) increases renal nuclear factor E2-related factor 2 (Nrf2) and glutathione peroxidase activity; and (4) inhibits renal nuclear factor-κB (NF-κB) activation and decreases levels of transforming growth factor (TGF)-β1 in serum and kidney tissue in a mouse FSGS model. Our data suggest that Antroq might be a potential therapeutic agent for FSGS, acting by boosting Nrf2 activation and suppressing NF-κB-dependent inflammatory and TGF-β1-mediated fibrosis pathways in the 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.

The Nrf2-inducible antioxidant defense in astrocytes can be both up- and down-regulated by activated microglia:Involvement of p38 MAPK

The effects of microglia-conditioned medium (MCM) on the inducible Nrf2 system in astrocyte-rich cultures were investigated by determination of glutathione (GSH) levels, γglutamylcysteine ligase (γGCL) activity, the protein levels of Nrf2, Keap1, the modulatory subunit of γGCL (γGCL-M) and activated MAP kinases (ERK1/2, JNK and p38). Microglia were either cultured for 24 h in serum-free culture medium to achieve microglia-conditioned medium from non-activated cells (MCM(0) ), used as control condition, or activated with different concentrations (0.1-1,000 ng mL(-1) ) of lipopolysaccharide (LPS) to produce MCM(0.1-1,000) . Acute exposure (24 h) to MCM(100) increased GSH, γGCL activity, the protein levels of γGCL-M, Nrf2, and activated JNK and ERK1/2 in astrocyte-rich cultures. In contrast, treatment with MCM(10) for 24 h decreased components of the Nrf2 system in parallel with activation of p38 MAPK. Stimulation of the Nrf2 system by tBHQ was partly intact after 24 h but blocked after 72 h treatment with MCM(10) and MCM(100) . This down-regulation after 72 h correlated with activation of p38 MAPK and lack of ERK1/2 and JNK activation. The negative effects were partly reversed by an inhibitor of p38 which restored tBHQ mediated protection against oxidative stress. In conclusion, the study showed a negative effect of MCM(10) on the inducible anti-oxidant defense in astrocyte-rich cultures at both 24 and 72 h that correlated with activation of p38 and was partly reversed by a p38 inhibitor. A transient protective effect of MCM(100) on astrocyte-rich cultures against H(2)O(2) toxicity was observed at 24 h which coincided with activation of JNK and ERK1/2.

The Nrf2-Keap1 cellular defense pathway and heat shock protein 70 (Hsp70) response. Role in protection against oxidative stress in early neonatal unilateral ureteral obstruction (UUO)

Perturbation of renal tubular antioxidants and overproduction of reactive oxygen species may amplify the proinflammatory state of renal obstruction, culminating in oxidative stress and tubular loss. Here, we analyzed the heat shock protein 70 (Hsp70) response and the function and signal transduction of NF-E2-related protein 2 (Nrf2) transcription factor on oxidative stress modulation in obstruction. Rats were subjected to unilateral ureteral obstruction or sham operation and kidneys harvested at 5, 7, 10, and 14 days after obstruction. Hsp70 expression and Nrf2 activity and its downstream target gene products were assessed. After 10 and 14 days of obstruction, enhanced lipid peroxidation through higher thiobarbituric acid reactive substances levels and increased oxidative stress resulted in reduced total antioxidant activity and enhanced nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase activity were demonstrated. This was accompanied by decreased inducible Hsp70 expression and a progressive reduction of nuclear Nrf2 and its target gene products glutathione S-transferase A2 (GSTA2) and NADPH/quinone oxidoreductase 1 (NQO1), whereas the Nrf2 repressor Kelch-like ECH-associated protein-1 (Keap1) was upregulated. By contrast, on early obstruction for 7 days, lack of increased oxidative markers associated with higher inducible Hsp70 protein levels and a rapid nuclear accumulation of Nrf2, Keap1 downregulation, and mRNA induction of the identified Nrf2-dependent genes, NQO1 and GSTA2, were shown. For these results, we suggest that the magnitude of cytoprotection in early obstruction depends on the combined contribution of induced activation of Nrf2 upregulating its downstream gene products and Hsp70 response. Impaired ability to mount the biological response to the prevailing oxidative stress leading to renal injury was shown in prolonged obstruction.

Exacerbation of diabetes-induced testicular apoptosis by zinc deficiency is most likely associated with oxidative stress, p38 MAPK activation, and p53 activation in mice

Since diabetes induces testicular oxidative damage and cell death, and zinc (Zn) plays an important role in the spermatogenesis, the objective of the present study was to define the effects of Zn deficiency on diabetes-induced testicular apoptosis and associated mechanisms. Zn deficiency was induced by chronic treatment of normal and diabetic mice with N,N,N',N'-tetrakis (2-pyridylemethyl) ethylenediamine (TPEN) chelation. After diabetes onset, mice were given intraperitoneally TPEN at 5mg/kg daily for four months, which, like diabetes, induced a significant decrease in testicular Zn level. TUNEL staining revealed that testicular apoptosis was significantly increased along with an increased Bax/Bcl-2 ratio, in diabetic mice and TPEN-treated normal mice. Zn deficiency significantly exacerbated diabetes-induced testicular apoptosis, along with significantly increased oxidative and nitrosative damage and down-regulation of antioxidant Nrf2 expression. Increased oxidative stress was associated with an increase in activation of p38 MAPK and p53 protein in diabetic testis, which was worsened in the testes of diabetic mice with Zn deficiency. Diabetes also induced a significant increase in endoplasmic reticulum stress and associated cell death, which was not affected by Zn deficiency. These results suggest that like diabetes, chronic depletion of Zn with TPEN induces testicular oxidative stress and damage, along with the activation of p38 MAPK and p53 signaling and mitochondria-related apoptotic cell death. Therefore, prevention of Zn deficiency for diabetic patients is important in order to avoid the exacerbation of diabetic effects on testicular cells death.

Superoxide anion and hydrogen peroxide-induced signaling and damage in angiotensin II and aldosterone action

The formation of reactive oxygen species (ROS) can be induced by xenobiotic substances, such as redox cycling molecules, but also by endogenous substances such as hormones and cytokines. Recent research shows the importance of ROS in cellular signaling. Here, the signaling pathways of the two blood pressure-regulating hormones angiotensin II and aldosterone are presented, focusing on both their physiological effects and the change of signaling owing to the action of increased concentrations or prolonged exposure. When present in high concentrations, both angiotensin II and aldosterone, as various other endogenous substances, activate NADPH oxidase, which produces superoxide. In this review the generation of superoxide anions and hydrogen peroxide in cells stimulated with angiotensin II or aldosterone, as well as the subsequently induced signaling processes and DNA damage is discussed.

High-calorie diet with moderate protein restriction prevents cachexia and ameliorates oxidative stress, inflammation and proteinuria in experimental chronic kidney disease

BACKGROUND

In earlier studies we found that a high-fat, high-energy diet (HFED) attenuates proteinuria, azotemia and lipid accumulation in the remnant kidney of rats subjected to 5/6 nephrectomy. This study was conducted to explore the mechanism of the salutary effect of HFED in association with moderate protein restriction in this model.

METHODS

The 5/6 nephrectomized male rats were randomized to receive regular rat chow (CRF group, n = 6) or HFED diet (CRF + HFED, n = 7) for 12 weeks. Sham-operated rats served as controls (n = 6).

RESULTS

The CRF group exhibited azotemia, hypertension, proteinuria, diminished body weight, oxidative stress, glomerulosclerosis, tubulo-interstitial inflammation and upregulation of pro-oxidant [NAD(P)H oxidase], pro-inflammatory (NF-κB activation, increased MCP-1, lipoxygenase, ICAM-1, VCAM-1), pro-fibrotic (TGF-β, CTGF) and pro-apoptotic pathways (Bax, caspase-3) in the remnant kidney. Consumption of the HFED resulted in a 66% increment in lipid intake, 8% increment in carbohydrate intake and a 24% reduction in protein intake. The CRF + HFED group gained weight normally, had increments in leptin and adiponectin levels, and despite increments in plasma cholesterol and fatty acids, showed significant attenuation of oxidative stress, proteinuria and inflammation, and partial reversal of the remnant kidney upregulation of pro-oxidant, pro-inflammatory, pro-fibrotic and pro-apoptotic pathways.

CONCLUSION

Consumption of high-energy diet in association with mild protein restriction results in suppression of upregulated pathways that drive progression of renal injury in the remnant kidney model. These findings may have relevance in the management of chronic kidney disease in humans.

MRI correlates of protein deposition and disease severity in postmortem frontotemporal lobar degeneration

BACKGROUND

Frontotemporal lobar degeneration (FTLD) can be classified based on the presence of the microtubule-associated protein tau and the TAR DNA binding protein-43 (TDP-43). Future treatments will likely target these proteins, therefore it is important to identify biomarkers to help predict protein biochemistry.

OBJECTIVE

To determine whether there is an MRI signature pattern of tau or TDP-43 using a large cohort of FTLD subjects and to investigate how patterns of atrophy change according to disease severity using a large autopsy-confirmed cohort of FTLD subjects.

METHODS

Patterns of gray matter loss were assessed using voxel-based morphometry in 37 tau-positive and 44 TDP-43-positive subjects compared to 35 age and gender-matched controls, and compared to each other. Comparisons were also repeated in behavioral variant frontotemporal dementia (bvFTD) subjects (n = 15 tau-positive and n = 30 TDP-43-positive). Patterns of atrophy were also assessed according to performance on the Clinical Dementia Rating (CDR) scale and Mini-Mental State Examination (MMSE).

RESULTS

The tau-positive and TDP-43-positive groups showed patterns of frontotemporal gray matter loss compared to controls with no differences observed between the groups, for all subjects and for bvFTD subjects. Patterns of gray matter loss increased in a graded manner by CDR and MMSE with loss in the frontal lobes, insula and hippocampus in mild subjects, spreading to the temporal and parietal cortices and striatum in more advanced disease.

CONCLUSION

There is no signature pattern of atrophy for tau or TDP-43; however, patterns of atrophy in FTLD progress with measures of clinical disease severity.