IS induced aortic calcification with expression of osteoblast-specific proteins and aortic wall thickening. IS is not only a nephrotoxin but also a vascular toxin, and may contribute to the progression of aortic calcification in stage 5 CKD patients.

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.

Cardiovascular disease is a major cause of death in chronic kidney disease (CKD) 2 (1). Atherosclerosis is highly prevalent in patients with severe renal failure and advances more rapidly in individuals with renal dysfunction compared with the general population (2). Reduced kidney function is associated with the risk of cardiovascular events, even when the dysfunction is mild (3).Leukocyte-endothelial interactions play an important role in the development of atherosclerosis (4). Cell adhesion molecules belonging to the immunoglobulin superfamily, such as ICAM-1 (intercellular cell adhesion molecule-1) and VCAM-1 (vascular cell adhesion molecule-1), together with members of the selectin family, including E-selectin, are upregulated to mediate monocyte/macrophage infiltration into atherosclerotic lesions (4, 5).Indoxyl sulfate is a uremic toxin synthesized in the liver from indole, a metabolite of tryptophan produced by the intestinal flora (6). In CKD patients, the serum levels of indoxyl sulfate are increased significantly compared with those in healthy individuals (7), and a number of studies have indicated that indoxyl sulfate accelerates glomerular sclerosis, whereas its accumulation promotes renal failure (8 -10). Other studies also showed that indoxyl sulfate induces endothelial dysfunction by releasing endothelial microparticles (11) and producing reactive oxygen species (ROS) (12). However, its effect on endothelial inflammatory processes such as leukocyte recruitment to vascular endothelium has not been reported.We report for the first time that indoxyl sulfate enhances monocyte adhesion to vascular endothelium through up-regulation of E-selectin and augmentation of oxidative stress in both in vitro and in vivo models. The underlying mechanisms seem to involve activation of JNK and NF-B. Our findings reveal a previously unrecognized molecular link between uremic toxins and cardiovascular diseases. EXPERIMENTAL PROCEDURESReagents-Indoxyl sulfate, N-acetylcysteine, probenecid, RPMI 1640 medium, and Dulbecco's PBS were obtained from Sigma. The JNK phosphorylation inhibitor SP600125, the p38 MAPK phosphorylation inhibitor SB203580, the ERK1/2 inhibitor U0126, and the IB phosphorylation inhibitor BAY11-7082 were purchased from Calbiochem. Recombinant human TNF-␣ was obtained from R&D Systems (Minneapolis, MN). A monoclonal antibody against E-selectin (clone 7A9) was obtained from American Type Culture Collection (Manassas, VA) (13). Antibodies against ICAM-1, VCAM-1, the NF-B p65 subunit, and the phospho-NF-B p65 subunit and a monoclonal blocking antibody against mouse E-selectin (clone UZ4) were obtained from Santa Cruz Biotechnology, Inc. (Santa Cruz, CA). Anti-ERK, anti-phospho-ERK, anti-p38 MAPK, anti-phospho-p38 MAPK, anti-JNK, and anti-phos-* This work was supported in part by Ministry of Education, Science, and Technology Grant-in-aid for Scientific Research 10178102 and special coordination funds, a grant-in-aid from the Ministry of Culture of Japan, a grant from the Ministry of Health, Labor, and We...

Cardiovascular death commonly occurs in patients with chronic kidney disease. Indoxyl sulfate (IS), a uremic toxin, has been demonstrated in vitro as a contributory factor in cardiac fibrosis, a typical pathological finding in uremic cardiomyopathy. This study aimed to determine if cardiac fibrosis is reversible by lowering serum IS levels using an oral charcoal adsorbent, AST-120. Subtotal-nephrectomized (5/6-STNx) Sprague-Dawley rats were randomized to receive either AST-120 (AST-120, n = 13) or no treatment (vehicle, n = 17) for 12 weeks. Sham operated rats (n = 12) were used as controls. Early left ventricular (LV) diastolic dysfunction was demonstrated by an increase in peak velocity of atrial filling [A and A’ waves] and a decrease of E/A and E’/A’ ratios obtained by echocardiography. This was accompanied by a 4.5-fold increase in serum IS (p<0.001) as well as elevated tail-cuff blood pressure (p<0.001) and heart weight (p<0.001). Increased LV fibrosis (p<0.001), gene expression of pro-fibrotic (TGF-β, CTGF) and hypertrophic (ANP, β-MHC and α-skeletal muscle actin) markers, as well as TGF-β and phosphorylated NF-κB protein expression were observed in STNx + vehicle rats. Treatment with AST-120 reduced serum creatinine (by 54%, p<0.05) and urine total protein (by 27%, p<0.05) vs vehicle whilst having no effect on blood pressure (AST-120 = 227±11 vs vehicle  = 224±8 mmHg, ns) and heart weight. The increase in serum IS was prevented with AST-120 (by 100%, p<0.001) which was accompanied by reduced LV fibrosis (68%, p<0.01) and TGF-β and phosphorylated NF-κB protein expression (back to sham levels, p<0.05) despite no significant change in LV function. In conclusion, STNx resulted in increased cardiac fibrosis and circulating IS levels. Reduction of IS with AST-120 normalizes cardiac fibrosis, in a blood pressure independent manner.

Oxidative stress is suggested to play a key role in the development of cardiac hypertrophy and fibrosis in CKD. AST-120 may suppress oxidative stress and reduce cardiac damage in CKD.