ROS and PDFG-β receptors are critically involved in indoxyl sulfate actions that promote vascular smooth muscle cell proliferation and migration

Oxidized high-density lipoprotein induces the proliferation and migration of vascular smooth muscle cells by promoting the production of ROS

AIM

As the major atheroprotective particle in plasma, high-density lipoprotein(HDL) is oxidized during atherosclerotic processes. Oxidized HDL(ox-HDL) may lose its cardioprotective properties and develop a proinflammatory and proatherogenic phenotype. The proliferation and migration of vascular smooth muscle cells(VSMCs) play a crucial role in atherogenesis. However, the influence of ox-HDL on VSMC proliferation and migration remains poorly understood.

METHODS

VSMCs were treated with native HDL(N-HDL) or ox-HDL at varying concentrations for different time intervals and used in several analyses. The degree of cell proliferation was assayed using CCK-8 kits. The level of cell migration was determined using a Transwell chamber and scratch-wound assay. The presence of intracellular reactive oxygen species(ROS) was detected based on ROS-mediated 2',7'-dichlorofluorescein fluorescence. The activation of NADPH oxidase was measured in terms of the Rac1 activity and NADP(＋)/NADPH ratio.

RESULTS

Compared to N-HDL, ox-HDL significantly promoted VSMC proliferation and migration in a dose-dependent manner. In addition, ox-HDL remarkably activated NADPH oxidase and enhanced ROS generation in the VSMCs. Diphenyleneiodonium chloride, an inhibitor of NADPH oxidase, and N-acetylcysteine, a ROS scavenger, efficiently inhibited the ROS production triggered by ox-HDL and subsequently blocked the proliferating and migrating effects of ox-HDL in the VSMCs.

CONCLUSIONS

Ox-HDL significantly induces VSMC proliferation and migration by promoting NADPH oxidase activation and ROS production. Furthermore, the inhibition of NADPH oxidase and ROS generation blocks the proliferation and migration of VSMCs induced by ox-HDL. These proliferating and migrating effects of ox-HDL are closely related to its proinflammatory and proatherogenic roles.

Proteomic analysis identifies an NADPH oxidase 1 (Nox1)-mediated role for actin-related protein 2/3 complex subunit 2 (ARPC2) in promoting smooth muscle cell migration

A variety of vascular pathologies, including hypertension, restenosis and atherosclerosis, are characterized by vascular smooth muscle cell (VSMC) hypertrophy and migration. NADPH oxidase 1 (Nox1) plays a pivotal role in these phenotypes via distinct downstream signaling. However, the mediators differentiating these distinct phenotypes and their precise role in vascular disease are still not clear. The present study was designed to identify novel targets of VSMC Nox1 signaling using 2D Differential In-Gel Electrophoresis and Mass Spectrometry (2D-DIGE/MS). VSMC treatment with scrambled (Scrmb) or Nox1 siRNA and incubation with the oxidant hydrogen peroxide (H₂O₂; 50 μM, 3 h) followed by 2D-DIGE/MS on cell lysates identified 10 target proteins. Among these proteins, actin-related protein 2/3 complex subunit 2 (ARPC2) with no previous link to Nox isozymes, H₂O₂, or other reactive oxygen species (ROS), was identified and postulated to play an intermediary role in VSMC migration. Western blot confirmed that Nox1 mediates H₂O₂-induced ARPC2 expression in VSMC. Treatment with a p38 MAPK inhibitor (SB203580) resulted in reduced ARPC2 expression in H₂O₂-treated VSMC. Additionally, wound-healing “scratch” assay confirmed that H₂O₂ stimulates VSMC migration via Nox1. Importantly, gene silencing of ARPC2 suppressed H₂O₂-stimulated VSMC migration. These results demonstrate for the first time that Nox1-mediated VSMC migration involves ARPC2 as a downstream signaling target.

p-Cresyl sulfate induces osteoblast dysfunction through activating JNK and p38 MAPK pathways

Recent data suggest that several uremic toxins may contribute to the development of bone abnormalities in chronic kidney disease. p-Cresyl sulfate (PCS), the sulfate conjugate of p-cresol, is a protein-bound uremic toxin associated with the progression of chronic kidney disease, cardiovascular risk, and mortality. However, the effects of PCS on bone metabolism remain unclear. In the present study, we evaluated the toxic effects of PCS on primary mouse osteoblasts, compared with an extensively studied uremic toxin indoxyl sulfate (IS). Pre-treatment of osteoblasts with PCS at 0.125 mM and above significantly decreased parathyroid hormone (PTH)-induced cAMP production in a dose-dependent manner. PCS also induced a significant increase in intracellular production of reactive oxygen species (ROS) at 0.25 mM and above, but not at lower concentrations. PCS at 0.125 mM (a concentration that did not induce significant ROS increase) decreased cell viability by augmenting DNA fragmentation and reducing cell proliferation. Inhibition of JNK and p38 mitogen-activated protein kinase (MAPK) abolished the PCS-induced increase in DNA fragmentation and decrease in cAMP production in osteoblastic cells. Compared with PCS, IS induced ROS production at 0.05 mM but did not reduce cAMP production from 0.05 to 0.5 mM. IS induced decrease in cell viability and increase in DNA fragmentation at 0.5mM only. These results suggest that PCS damages osteoblastic cells through not only increasing ROS production but also activating JNK/p38 MAPKs, which is different from the mechanism of injury by IS. These damages of osteoblasts induced by PCS may play a critical role in impairing bone metabolism in patients with chronic kidney disease in whom PCS accumulates.

Feruloyl-L-arabinose attenuates migration, invasion and production of reactive oxygen species in H1299 lung cancer cells

Ferulic acid (FA), a phenolic compound, is an abundant dietary antioxidant and exerts the mitogenic effect on cells. Recently, we isolated an active FA derivative, namely feruloyl-L-arabinose (FAA), from coba husk. The aim of this study was to investigate the effects of FAA on the proliferation, migration and invasion of H1299 human lung cancer cells. Our results showed a strong antioxidant potential of FAA. Additionally, FAA inhibited the migration and invasion ability, while causing a significant accumulation of G2/M-population, of H1299 tumor cells in a dose-dependent manner, whereas no significant change on cell proliferation was observed. Results from the wound healing assay revealed that cell migration ability was markedly inhibited by FAA treatments. Similarly, results of gelatin zymography study showed that FAA treatments significantly decreased the activities of matrix metalloproteinase (MMP)-2 and MMP-9, suggesting that FAA-mediated inhibition on migration and invasion of lung cancer cells may be achieved by the down-regulation of the MMPs activities. Taken together, our present work provides a new insight into the novel inhibitory function of FAA on cell migration in H1299 cells, suggesting its promising role in the chemoprevention of lung cancer.

Indoxyl sulfate, a uremic toxin, downregulates renal expression of Nrf2 through activation of NF-κB

Background

Indoxyl sulfate, a uremic toxin, is accumulated in the serum of chronic kidney disease (CKD) patients, accelerating the progression of CKD. In CKD rat kidney, the expressions of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and its related genes are downregulated. AST-120, an oral sorbent, reduces serum indoxyl sulfate and slows the progression of CKD. The present study aimed to determine whether indoxyl sulfate downregulates Nrf2 expression in human proximal tubular cells and rat kidneys and whether AST-120 upregulates Nrf2 expression in CKD rat kidneys.

Methods

Effects of indoxyl sulfate on expression of Nrf2 were determined using HK-2 cells as human proximal tubular cells and the following animals: (1) Dahl salt-resistant normotensive rats (DN), (2) Dahl salt-resistant normotensive indoxyl sulfate-administered rats (DN+IS), (3) Dahl salt-sensitive hypertensive rats (DH), and (4) Dahl salt-sensitive hypertensive indoxyl sulfate-administered rats (DH+IS). Further, AST-120 was administered to subtotally nephrectomized CKD rats to determine its effect on the expression of Nrf2.

Results

Indoxyl sulfate downregulated Nrf2 expression in HK-2 cells. The indoxyl sulfate-induced downregulation of Nrf2 expression was alleviated by an inhibitor of nuclear factor-κB (NF-κB) (pyrrolidine dithiocarbamate) and small interfering RNA specific to NF-κB p65. DN+IS, DH, and DH+IS rats showed decreased renal expression of Nrf2 and its downstream target genes, heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1), and increased renal expression of 8-hydroxydeoxyguanosine (8-OHdG), a marker of reactive oxygen species (ROS), compared with DN. Thus, indoxyl sulfate, as well as hypertension, downregulated renal expression of Nrf2 in rats. AST-120 upregulated renal expression of Nrf2, HO-1 and NQO1 and suppressed renal expression of 8-OHdG compared with control CKD rats.

Conclusions

Indoxyl sulfate downregulates renal expression of Nrf2 through activation of NF-κB, followed by downregulation of HO-1 and NQO1 and increased production of ROS. Further, AST-120 upregulates renal expression of Nrf2 in CKD rats by removing serum indoxyl sulfate, followed by upregulation of HO-1 and NQO1 and decreased production of ROS.

Association between uremic toxins and depression in patients with chronic kidney disease undergoing maintenance hemodialysis

OBJECTIVE

Patients with chronic kidney disease (CKD) who are undergoing maintenance hemodialysis have a higher prevalence of depression than the general population. The underlying cause of this association is unknown, but may be related to accumulation of uremic toxins. Little is known about the association of accumulation of uremic toxins and depression in hemodialysis patients.

METHOD

We conducted a cross-sectional study of 209 CKD patients from a single institution to evaluate the associations of a soluble small uremic toxin (urea), a soluble large uremic toxin (β2 microglobulin) and two protein-bound uremic toxins [total p-cresol sulfate (PCS) and indoxyl sulfate (IS)] with the presence of depression.

RESULTS

A total of 47 patients (22.4%) had depression. Depressive patients had lower body mass index, lower serum creatinine, lower serum albumin and lower total IS. Univariate and multivariate logistic regression analyses that adjusted for age, gender and other statistically significant variables indicated that depression was significantly and independently associated with lower serum albumin and lower total IS. The levels of urea, β2 microglobulin and PCS were not significantly associated with depression.

CONCLUSION

Our results indicate that depression in patients with CKD was significantly and independently associated with lower serum albumin and lower total IS. However, the pathological mechanisms underlying these associations are unknown.

Free p-cresol sulfate is associated with survival and function of vascular access in chronic hemodialysis patients

BACKGROUND

Protein-bound uremic toxins indoxyl sulfate (IS) and p-cresol sulfate (p-CS) have been implicated as an important factor in uremic syndrome. Recent evidence indicates that both IS and p-CS are predictors of cardiovascular as well as all-cause mortality among chronic dialysis patients. We conducted a study to analyze the relationship between IS and p-CS and vascular access (VA) outcome in chronic hemodialysis (HD) patients.

METHODS

A total of 91 chronic stable HD patients were divided into groups according to survival of VA and frequency of VA dysfunction. Demographic and biochemical data were reviewed and recorded. Serum levels of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1, and the total and free forms of IS and p-CS were determined.

RESULTS

Patients with a history of frequent VA failure and dysfunction had lower albumin and higher levels of ICAM-1, free IS, free and total p-CS. Diabetes was associated with higher IS and p-CS. Logistic regression revealed that diabetes and free p-CS were independent factors associated with poor outcome of VA.

CONCLUSION

Endothelial dysfunction and uremic toxins were associated with survival and function of VA. Diabetes and free p-CS were significantly related to the outcome of VA among chronic HD patients.

Nrf2-keap1 system versus NF-κB: the good and the evil in chronic kidney disease?

Inflammation and oxidative stress are two major components involved in the atherogenic process generated by the innate immune response to lipoprotein peroxidation, which is accelerated in patients with chronic kidney disease (CKD). Whereas the redox-sensitive transcription factor nuclear factor-κB (NF-κB) plays an important role in the coordinated expression of inflammatory genes, the nuclear factor E2-related factor 2 (Nrf2) is the transcription factor that is responsible for both constitutive and inducible expression of antioxidant response element (ARE)-regulated genes. Thus, Nrf2 can regulate antioxidant and anti-inflammatory cellular responses of this system, playing an important protective role on the development of the uremic phenotype. This review describes the Nrf2 system and its possible role in CKD patients.

Indoxyl sulfate induces nephrovascular senescence

Indoxyl sulfate is markedly accumulated in the serum of chronic kidney disease (CKD) patients. The oral sorbent AST-120 reduces serum levels of indoxyl sulfate in CKD patients by adsorbing indole, a precursor of indoxyl sulfate, in the intestine. Indoxyl sulfate is taken up by proximal tubular cells through organic anion transporters (OAT1, OAT3), and it induces reactive oxygen species (ROS) with impairment of cellular antioxidative system. Indoxyl sulfate stimulates progression of CKD by increasing renal expression of profibrotic cytokines such as transforming growth factor beta 1. Further, it promotes the expression of p53 by ROS-induced activation of nuclear factor kappa B, thereby accelerating senescence of proximal tubular cells with progression of CKD. Administration of indoxyl sulfate to hypertensive rats reduces renal expression of Klotho and promotes cell senescence, with expression of senescence-associated beta-galactosidase, p53, p21, p16, and retinoblastoma protein, accompanied by kidney fibrosis. Indoxyl sulfate downregulates Klotho expression in the kidneys through production of ROS and activation of nuclear factor kappa B in proximal tubular cells. It promotes cell senescence, with expression of senescence-associated beta-galactosidase, p53, p21, p16, and retinoblastoma protein, in the aorta of hypertensive rats. It also promotes aortic calcification and aortic wall thickening in hypertensive rats with expression of osteoblast-specific proteins, induces ROS in vascular smooth muscle cells and vascular endothelial cells, stimulates proliferation and osteoblastic transdifferentiation of vascular smooth muscle cells, and inhibits viability and nitric oxide production of vascular endothelial cells. Thus, indoxyl sulfate accelerates the progression of not only CKD but also of cardiovascular disease by inducing nephrovascular cell senescence.

NF-κB plays an important role in indoxyl sulfate-induced cellular senescence, fibrotic gene expression, and inhibition of proliferation in proximal tubular cells

We previously demonstrated that indoxyl sulfate induces senescence and dysfunction of proximal tubular cells by activating p53 expression. However, little is known about the role of nuclear factor (NF)-κB in these processes. The present study examines whether activation (phosphorylation) of NF-κB by indoxyl sulfate promotes senescence and dysfunction in human proximal tubular cells (HK-2 cells). Indoxyl sulfate induced phosphorylation of NF-κB p65 on Ser-276, which was suppressed by N-acetylcysteine, an antioxidant. Furthermore, indoxyl sulfate induced NF-κB p65 expression. Inhibitors of NF-κB (pyrrolidine dithiocarbamate and isohelenin) and NF-κB p65 small interfering RNA (siRNA) suppressed indoxyl sulfate-induced senescence-associated β-galactosidase activity and expression of p53, transforming growth factor (TGF)-β1, and α-smoothe muscle actin (SMA). The induction of p53 expression and p53 promoter activity by indoxyl sulfate were inhibited by pifithrin-α, p-nitro, an inhibitor of p53, whereas p53-transfected cells showed enhanced p53 promoter activity. NF-κB inhibitors suppressed indoxyl sulfate-induced p21 expression, whereas NF-κB p65 siRNA enhanced its expression. NF-κB inhibitors partially alleviated indoxyl sulfate-induced inhibition of cellular proliferation. NF-κB p65 siRNA-transfected cells showed less proliferation in the presence of indoxyl sulfate than control cells. Phosphorylated NF-κB p65 was expressed and colocalized with p53, p21, β-galactosidase, TGF-β1, and α-SMA in the kidneys of chronic renal failure (CRF) rats. AST-120, which reduces serum indoxyl sulfate level, suppressed their expression in the CRF rat kidneys. Taken together, NF-κB plays an important role in indoxyl sulfate-induced cellular senescence, fibrotic gene expression, and inhibition of proliferation in proximal tubular cells. More notably, indoxyl sulfate accelerates proximal tubular cell senescence with progression of CRF through reactive oxygen species-NF-κB-p53 pathway.

Alleviation of cisplatin-induced acute kidney injury using phytochemical polyphenols is accompanied by reduced accumulation of indoxyl sulfate in rats

BACKGROUND

Polyphenols such as quercetin have been reported to prevent cisplatin-induced acute kidney injury (AKI). Indoxyl sulfate (IS), a uremic toxin generated in the liver, is increased in cisplatin AKI. The present study examined the effect of phytochemical polyphenols on serum and renal accumulations of IS in association with cisplatin AKI.

METHODS

Sprague-Dawley rats were treated with cisplatin (10 mg/kg body weight) by intraperitoneal injection. Polyphenols were orally administered at -24, -1, 24 and 48 h before or after cisplatin injection. Serum levels of IS, cisplatin, serum creatinine (SCr), blood urea nitrogen (BUN) and electrolytes were measured. By using an in vitro assay system with rat liver S9 fraction, the inhibitory potencies of several compounds on IS production were determined.

RESULTS

Injection of cisplatin in rats markedly elevated the SCr and BUN levels, which were accompanied by tubular injuries and the expression of kidney injury molecule-1 (Kim-1). By contrast, quercetin significantly suppressed the SCr and BUN levels in the cisplatin-treated rats and protected them against renal injury with the decreased expression of Kim-1. Quercetin had no effect on serum and renal levels of cisplatin. In addition, quercetin had no effect on cisplatin-induced renal accumulation of malondialdehyde. IS concentrations in serum, kidney, liver, intestine and lung were markedly elevated by cisplatin treatment, whereas quercetin suppressed the serum and tissue IS levels. An in vitro kinetic assay revealed that quercetin displayed a potent inhibitory effect on hepatic production of IS.

CONCLUSION

Inhibition of IS accumulation by oral administration of quercetin alleviates cisplatin-induced AKI.

Indoxyl sulfate induces epithelial-to-mesenchymal transition in rat kidneys and human proximal tubular cells

BACKGROUND/AIMS

Indoxyl sulfate (IS) is a uremic toxin that accelerates the progression of chronic kidney disease (CKD). This study aimed to determine if IS induces epithelial-to-mesenchymal transition (EMT) in the kidneys of hypertensive rats and human proximal tubular cells (HK-2).

METHODS

EMT was evaluated by immunohistochemistry, reverse transcription-polymerase chain reaction and immunoblotting of the epithelial markers E-cadherin and zonula occludens-1 (ZO-1), and the mesenchymal marker α-smooth muscle actin (α-SMA). Rat groups consisted of (1) Dahl salt-resistant normotensive rats (DN), (2) Dahl salt-resistant normotensive IS-administered rats (DN+IS), (3) Dahl salt-sensitive hypertensive rats (DH), and (4) Dahl salt-sensitive hypertensive IS-administered rats (DH+IS). HK-2 cells were incubated with or without IS.

RESULTS

In kidneys, DH rats showed reduced expression of E-cadherin and ZO-1, and enhanced expression of α-SMA compared with DN rats. DN+IS and DH+IS rats showed reduced expression of E-cadherin and ZO-1, and enhanced expression of α-SMA compared with DN and DH rats, respectively. DH+IS and DH rats showed increased Masson's trichrome-positive fibrosis areas compared with DH and DN, respectively. IS-treated HK-2 cells showed reduced expression of E-cadherin and ZO-1, and enhanced expression of α-SMA.

CONCLUSION

IS induces EMT in the kidneys of hypertensive rats and in human proximal tubular cells.

Reduction of reactive oxygen species prevents hypoxia-induced CREB depletion in pulmonary artery smooth muscle cells

Hypoxia-induced pulmonary arterial hypertension (PAH) is a deadly disease characterized by progressive remodeling and persistent vasoconstriction of the pulmonary arterial system. Remodeling of the pulmonary artery (PA) involves smooth muscle cell (SMC) proliferation, hypertrophy, migration, and elevated extracellular matrix (ECM) production elicited by mitogens and oxidants produced in response to hypoxic insult. We previously reported that the transcription factor cAMP response element binding protein (CREB) is depleted in medial PA SMCs in remodeled, hypertensive vessels in rats or calves exposed to chronic hypoxia. In culture, CREB loss can be induced in PA SMCs by exogenous oxidants or platelet-derived growth factor. Forced depletion of CREB with small interfering RNA (siRNA) in PA SMCs is sufficient to induce their proliferation, hypertrophy, migration, dedifferentiation, and ECM production. This suggests that oxidant and/or mitogen-induced loss of CREB in medial SMCs is, in part, responsible for PA thickening. Here, we tested whether oxidant scavengers could prevent the loss of CREB in PA SMCs and inhibit SMC proliferation, migration, and ECM production using in vitro and in vivo models. Exposure of PA SMCs to hypoxia induced hydrogen peroxide (H2O2) production and loss of CREB. Treatment of SMCs with exogenous H2O2 or a second oxidant, Sin-1, elicited CREB depletion under normoxic conditions. Exogenous H2O2 also induced SMC proliferation, migration, and increased elastin levels as did forced depletion of CREB. In vivo, hypoxia-induced thickening of the PA wall was suppressed by the superoxide dismutase mimetic, Tempol, which also prevented the loss of CREB in medial SMCs. Tempol also reduced hypoxia-induced SMC proliferation and elastin deposition in the PA. The data indicate that CREB levels in the arterial wall are regulated in part by oxidants produced in response to hypoxia and that CREB plays a crucial role in regulating SMC phenotype and PA remodeling.

Clopidogrel effectively suppresses endothelial microparticle generation induced by indoxyl sulfate via inhibition of the p38 mitogen-activated protein kinase pathway

BACKGROUND/AIMS

Endothelial microparticles (EMPs) are closely associated with vascular dysfunction. We investigated the effects of several drugs on EMP generation in human umbilical vein endothelial cells (HUVECs), and the involvement of the mitogen-activated protein kinase (MAPK) in EMP generation.

METHODS

CD31+CD42-EMP counts were measured by flow cytometry in supernatants of HUVECs incubated with indoxyl sulfate. The EMP responses to losartan, lovastatin, clopidogrel, and mesoglycan were examined. We then measured the effects of MAPK inhibitors on EMPs.

RESULTS

(1) Indoxyl sulfate induced EMP release in HUVECs in a dose-dependent fashion; (2) all drugs (10-50 μM) inhibited EMP generation induced by indoxyl sulfate, with clopidogrel being the most effective; (3) the p38 MAPK inhibitor suppressed EMP generation induced by indoxyl sulfate, and (4) clopidogrel significantly suppressed MAPK signaling activated by indoxyl sulfate, with the most potency on p38.

CONCLUSION

The p38 signaling involves EMP generation induced by indoxyl sulfate and is effectively suppressed by clopidogrel.

Exposure to uremic serum induces a procalcific phenotype in human mesenchymal stem cells

OBJECTIVE

Medial artery calcification in patients with chronic kidney disease proceeds through intramembranous ossification resulting from osteoblast-induced calcification of the collagen extracellular matrix. The current study is based on the hypothesis that mesenchymal stem cells (MSC) constitute critical cells for procalcific extracellular matrix remodeling in patients with chronic kidney disease.

METHODS AND RESULTS

Human MSC were cultured in media supplemented with pooled sera from either healthy or uremic patients (20%). Exposure to uremic serum enhanced the proliferation of MSC (cell counting, BrdU incorporation) whereas apoptosis and necrosis were not affected (annexin V and 7-amino-actinomycin staining). Uremic serum-exposed MSC recapitulated osteogenesis by matrix calcification and expression of bone-related genes (bone morphogenetic protein [BMP]-2 receptor, alkaline phosphatase, osteopontin, and Runx2) in 35 days. The uremic serum-induced osteogenesis was completely blocked by a BMP-2/4 neutralizing antibody or the natural antagonist NOGGIN. Calcification and matrix remodeling were further analyzed in a collagen-embedded osteogenesis model recapitulating the vascular collagen I/III environment. The uremic serum-induced calcification was shown to occur along collagen fibers as shown by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and von Kossa staining and was accompanied by extensive matrix remodeling.

CONCLUSIONS

Uremic serum induced in a BMP-2/4-dependent manner an osteoblast-like phenotype in MSC accompanied by matrix remodeling and calcification.

Hydroxytyrosol induces proliferation and cytoprotection against oxidative injury in vascular endothelial cells: role of Nrf2 activation and HO-1 induction

Hydroxytyrosol (HT), a phenolic compound in olive oil and leaves, has been reported to prevent various human pathologies including cardiovascular diseases. This study investigated the effects of HT on proliferation and protection against oxidative stress-induced damage in vascular endothelial cells (VECs) and the molecular mechanism(s) involved. Treatment of VECs with HT increased cell proliferation, promoted wound repair, and protected cells against H(2)O(2) cytotoxicity through the activation of Akt and ERK1/2, but not p38 MAPK. HT increased the expression and nuclear translocation of nuclear factor-E2-related factor-2 (Nrf2). Nrf2 expression was attenuated by LY294002 and U0126, inhibitors of phosphatidylinositol-3-kinase and MEK1/2, respectively. Nrf2 siRNA decreased both proliferative and cytoprotective effects of HT and abrogated HO-1 induction. Moreover, HO-1 inhibition with HO-1 siRNA or zinc protoporphyrin IX significantly prevented HT-induced cell proliferation, cytoprotection, and reduction in intracellular reactive oxygen species (ROS), suggesting that HO-1 is involved in these HT functions. The findings demonstrate that HT positively regulates the antioxidant defense system in VECs through the activation of Nrf2 followed by cell proliferation and resistance to vascular injury. The present study provides a molecular basis for the contribution of HT in the Mediterranean diet to the prevention of cardiovascular diseases.

Indoxyl sulfate downregulates renal expression of Klotho through production of ROS and activation of nuclear factor-ĸB

BACKGROUND/AIM

Klotho, an anti-aging gene, is expressed in the kidneys, and its renal expression is decreased in chronic kidney disease (CKD). The present study aimed to examine whether renal expression of Klotho is regulated by indoxyl sulfate, a uremic toxin, using rat kidneys and human proximal tubular cells (HK-2).

METHODS

The effect of indoxyl sulfate on renal expression of Klotho was examined using (1) Dahl salt-resistant normotensive rats (DN), (2) Dahl salt-resistant normotensive indoxyl sulfate-administered rats (DN+IS), (3) Dahl salt-sensitive hypertensive rats (DH), and (4) Dahl salt-sensitive hypertensive indoxyl sulfate-administered rats (DH+IS). The effects of indoxyl sulfate, inhibitors of nuclear factor-κB (NF-κB) and an antioxidant on the expression of Klotho in HK-2 cells were examined.

RESULTS

DH+IS and DN+IS rats showed decreased expression of Klotho mRNA in the kidneys as compared with DH and DN rats, respectively. Indoxyl sulfate suppressed the expression of Klotho mRNA and protein in HK-2 cells, whereas an antioxidant, N-acetylcysteine, and NF-κB inhibitors, pyrrolidine dithiocarbamate and isohelenin, alleviated these effects.

CONCLUSIONS

Indoxyl sulfate downregulates Klotho expression in kidneys through production of reactive oxygen species and activation of NF-κB in proximal tubular cells. Indoxyl sulfate may be involved in reduced renal expression of Klotho in CKD.

Increased levels of total P-Cresylsulphate and indoxyl sulphate are associated with coronary artery disease in patients with diabetic nephropathy

BACKGROUND

Indoxyl sulphate (IS) and p-cresylsulphate (PCS) are uremic toxins with similar protein-binding, dialytic clearance, and proinflammatory features. Few studies have evaluated the possible associations between these solutes and coronary artery disease (CAD) in type 2 diabetes (T2D) patients.

METHODS

A hospital-based case control study was performed. A total of 209 T2D patients were divided into two groups based on the presence/absence of significant CAD (≥50% luminal reduction). Serum total PCS and IS levels were measured using the Ultra Performance LC System. The relationship between total PCS and IS levels were investigated. Coronary calcium scores and the modified Gensini score were analyzed.

RESULTS

Serum total PCS and IS levels were significantly higher in patients with both T2D and significant CAD, than in non-diabetic control subjects and T2D patients without CAD (all p < 0.05). Logistic regression analysis revealed independent and significant associations between the two solutes and CAD status. Serum total PCS, IS, and numbers of diseased vessels were elevated in groups with estimated glomerular filtration rate (eGFR) of 60-89 ml/min/1.73 m2 and below. Also, serum total PCS and IS levels were significantly associated with eGFR, coronary calcium scores, Gensini score, adipocytokines (adiponectin, visfatin, and leptin), and total white blood cell count.

CONCLUSIONS

Serum total PCS and IS levels were elevated in patients with T2D and CAD. These increases were associated with renal function deterioration, inflammation, and coronary atherosclerosis.

Long-term clinical outcomes following drug-eluting or bare-metal stent placement in patients with severely reduced GFR: Results of the Massachusetts Data Analysis Center (Mass-DAC) State Registry

BACKGROUND

Patients with chronic kidney disease have been under-represented in randomized trials of drug-eluting stents relative to bare-metal stents and are at high risk of mortality.

STUDY DESIGN

Cohort study with propensity score matching.

SETTINGS & PARTICIPANTS

All adults with chronic kidney disease and severely decreased glomerular filtration rate (GFR; serum creatinine >2.0 mg/dL or dialysis dependence) undergoing percutaneous coronary intervention with stent placement between April 1, 2003, and September 30, 2005, at all acute-care nonfederal hospitals in Massachusetts.

PREDICTOR

Patients were classified as drug-eluting stent-treated if all stents were drug eluting and bare-metal stent-treated if all stents were bare metal. Patients treated with both types of stents were excluded from the primary analysis.

OUTCOMES & MEASUREMENTS

2-year crude mortality risk differences (drug-eluting - bare-metal stents) were determined from vital statistics records, and risk-adjusted mortality, myocardial infraction (MI), and revascularization differences were estimated using propensity score matching of patients with severely reduced GFR based on clinical and procedural information collected at the index admission.

RESULTS

1,749 patients with severely reduced GFR (24% dialysis dependent) were treated with drug-eluting (n = 1,256) or bare-metal stents (n = 493) during the study. Overall 2-year mortality was 32.8% (unadjusted drug-eluting stent vs bare-metal stent; 30.1% vs 39.8%; P < 0.001). After propensity score matching 431 patients with a drug-eluting stent to 431 patients with a bare-metal stent, 2-year risk-adjusted mortality, MI, and target-vessel revascularization rates were 39.4% versus 37.4% (risk difference, 2.1%; 95% CI, -4.3 to 8.5; P = 0.5), 16.0% versus 19.0% (risk difference, -3.0%; 95% CI, -8.2 to 2.1; P = 0.3), and 13.0% versus 17.6% (risk difference, -4.6%; 95% CI, -9.5 to 0.3; P = 0.06).

LIMITATIONS

Observational design, ascertainment of serum creatinine level >2.0 mg/dL and dialysis dependence from case report forms.

CONCLUSIONS

In patients with severely decreased GFR, treatment with drug-eluting stents was associated with a modest decrease in target-vessel revascularization not reaching statistical significance and was not associated with a difference in risk-adjusted rates of mortality or MI at 2 years compared with bare-metal stents.

Senescence and dysfunction of proximal tubular cells are associated with activated p53 expression by indoxyl sulfate

Various uremic toxins accumulate in patients with chronic renal failure (CRF) and one of them is indoxyl sulfate, which accelerates the progression of CRF through unknown mechanisms. The present study investigates how indoxyl sulfate promotes CRF using the proximal tubular cell line HK-2 and CRF rats. Indoxyl sulfate inhibited serum-induced cell proliferation and promoted the activation of senescence-associated β-galactosidase, a marker of cellular senescence, and the expression of α-smooth muscle actin (α-SMA), a marker of fibrosis, through inducing p53 expression and phosphorylation. Pifithrin-α, p-nitro, a p53 inhibitor, blocked these effects. Indoxyl sulfate evoked reactive oxygen species (ROS), and the antioxidant N-acetylcysteine inhibited indoxyl sulfate-induced p53 expression and phosphorylation, as well as indoxyl sulfate-induced α-SMA expression. We previously demonstrated that although cellular senescence and fibrosis are detectable in the kidneys of CRF rats, the oral adsorbent AST-120 repressed these effects. Here, we found that β-galactosidase, p53 and α-SMA were expressed and colocalized in the renal tubules of CRF rats, whereas AST-120 decreased the expression of these genes. Taken together, these findings indicate that indoxyl sulfate induces the expression and phosphorylation of p53 though ROS production, thus inhibiting cell proliferation and promoting cellular senescence and renal fibrosis.

p-Cresyl sulphate and indoxyl sulphate predict progression of chronic kidney disease

Background. Indoxyl sulphate (IS) and p-cresyl sulphate (PCS) are uraemic toxins that have similar protein binding, dialytic clearance and proinflammatory features. However, only a few prospective studies have evaluated possible associations between these two retained solutes and renal disease progression in chronic kidney disease (CKD) patients.

Methods. This prospective observational study evaluated independent associations between serum total IS and PCS with renal progression in a selected cohort of patients having different stages of CKD. Baseline PCS and IS were correlated with renal progression [defined as decrements in estimated glomerular filtration rate (eGFR) > 50% from baseline or progression to end-stage renal disease (ESRD)] and death during a follow-up period of 24 months.

Results. Of 268 patients, 35 (13.1%) had renal progression and 14 (5.2%) died after a mean follow-up of 21 ± 3 months. Univariate Cox regression analysis followed by multivariate analysis showed that high-serum PCS levels were associated with renal progression and all-cause mortality independent of age, gender, diabetes status, albumin levels, serum IS, serum creatinine, Ca × P product, intact parathyroid hormone, haemoglobin or high-sensitivity C-reactive protein level. Serum IS was only associated with renal progression; however, the predictive power of serum IS was weakened when serum PCS was also present in the analytical model.

Conclusions. In addition to traditional and uraemia-related risk factors such as renal function, serum IS and PCS levels may help in predicting the risk of renal progression in patients having different stages of CKD.

Emerging roles of PDGF-D signaling pathway in tumor development and progression

Platelet-derived growth factor-D (PDGF-D) can regulate many cellular processes, including cell proliferation, apoptosis, transformation, migration, invasion, angiogenesis and metastasis. Therefore PDGF-D signaling has been considered to be important in human malignancies, and thus PDGF-D signaling may represent a novel therapeutic target, and as such suggests that the development of agents that will target PDGF-D signaling is likely to have a significant therapeutic impact on human cancers. This mini-review describes the mechanisms of signal transduction associated with PDGF-D signaling to support the role of PDGF-D in the carcinogenesis. Moreover, we summarize data on several PDGF-D inhibitors especially naturally occurring "chemopreventive agent" such an indole compound, which we believe could serve as a novel agent for the prevention of tumor progression and/or treatment of human malignancies by targeted inactivation of PDGF-D signaling.