Combination therapy with benazepril and oral adsorbent ameliorates progressive renal fibrosis in uremic rats

BACKGROUND/AIMS: The administration of an angiotensin-converting enzyme (ACE) inhibitor or an oral adsorbent, AST-120 (Kremezin), prevents the progression of renal failure. This study was designed to determine the additional effects of AST-120 combined with an ACE inhibitor, benazepril, on the progression of renal fibrosis in uremic rats. METHODS: 5/6-nephrectomized uremic rats were divided into control uremic rats (CRF group), benazepril-treated uremic rats (CRF+B group) and uremic rats receiving benazepril and AST-120 (CRF+BK group). After 14 weeks of treatment renal function and pathological changes were investigated. RESULTS: The progression of renal dysfunction was delayed in both the CRF+B and CRF+BK groups as compared with the CRF group. In the CRF+BK group, the level of serum and urinary indoxyl sulfate and the tubular accumulation of indoxyl sulfate decreased. Both the CRF+B and CRF+BK groups showed lower glomerular sclerosis indices than the CRF group. In the CRF+BK group, but not the CRF+B group, the interstitial fibrosis area and the expression of transforming growth factor (TGF) beta1 and tissue inhibitor of metalloproteinases (TIMP) 1 were decreased as compared with the CRF group. Furthermore, the CRF+BK group showed a smaller interstitial fibrosis area and a lower renal osteopontin expression than the CRF+B group. CONCLUSION: Combination therapy of benazepril and AST-120 is more effective than benazepril alone in retarding the progression of interstitial fibrosis by reducing the expression of TGF-beta 1, TIMP-1 and osteopontin.     

An oral adsorbent, AST-120, suppresses oxidative stress in uremic rats

BACKGROUND: The production of reactive oxygen species (ROS) has been suggested to play an important role in the progression of chronic kidney disease (CKD). An oral adsorbent, AST-120, removes uremic toxins such as indoxyl sulfate (IS) and delays the progression of CKD, but the effect on ROS production is unknown. The present study aimed to determine whether AST-120 reduces oxidative stress in uremic rat kidneys using markers of ROS production such as acrolein and 8-hydroxy-2'-deoxyguanosine (8-OHdG). METHODS: Daily administration of AST-120 was started 6 weeks after 5/6 nephrectomy and continued for 18 weeks. The changes in metabolic data, serum and urine IS levels, urinary excretion of markers of oxidative stress, and renal histological findings were investigated in uremic rats with or without AST-120 treatment. RESULTS: In parallel with the increase in serum and urine IS, the serum creatinine, urinary protein and acrolein levels started to increase at 6 weeks, but urinary 8-OHdG remained unchanged and significantly increased at 18 weeks in uremic rats. AST-120 markedly and significantly attenuated increases in uremic toxins and oxidative stress levels as well as the histological changes in glomerular sclerosis, interstitial fibrosis, and the tubular staining of 8-OHdG. CONCLUSION: AST-120 suppressed the progression of CKD, at least in part, via attenuation of oxidative stress induced by uremic toxin.     

An oral sorbent reduces overload of indoxyl sulphate and gene expression of TGF-beta1 in uraemic rat kidneys.

BACKGROUND: An oral adsorbent (AST-120) delays the progression of chronic renal failure (CRF). The aims of the present study are to determine the effects of AST-120 on the localization of indoxyl sulphate in uraemic rat kidneys, and to examine whether AST-120 reduces the renal cortical gene expression of transforming growth factor (TGF)-beta1, tissue inhibitor of metalloproteinase (TIMP)-1 and pro-alpha1(I)collagen, and ameliorates glomerular and tubulointerstitial injuries in uraemic rats. METHODS: Two weeks after 5/6-nephrectomy, 10 rats were divided into pairs such that both rats in each pair exhibited almost the same levels of serum creatinine, blood urea nitrogen and creatinine clearance. One rat from each pair was assigned to a control uraemic group, the other to a uraemic group which received AST-120 everyday for 11 weeks. The localization of indoxyl sulphate was studied by immunohistochemistry using a monoclonal anti-indoxyl sulphate antibody we had developed. The renal cortical gene expression was studied by using northern blotting. RESULTS: Rats treated with AST-120 showed decreased levels of serum creatinine, blood urea nitrogen and urinary protein as well as increased levels of creatinine clearance as compared with control uraemic rats. AST-120 markedly decreased indoxyl sulphate levels in both serum and urine. Immunohistochemistry demonstrated that indoxyl sulphate was localized in the renal proximal tubular epithelial cells, especially of dilated tubules, and that AST-120 markedly reduced the tubular staining of indoxyl sulphate. AST-120 attenuated interstitial fibrosis, tubular injury as well as glomerular sclerosis, and reduced the renal gene expression of TGF-beta1, TIMP-1 and pro-alpha1(I)collagen. CONCLUSIONS: AST-120 reduces the gene expression of TGF-beta1, TIMP-1 and pro-alpha1(I)collagen in the kidneys, and delays the progression of CRF, at least in part, by alleviating the overload of indoxyl sulphate on remnant proximal tubular epithelial cells.     

Oral adsorbent AST-120 ameliorates interstitial fibrosis and transforming growth factor-beta(1) expression in spontaneously diabetic (OLETF) rats

Diabetic nephropathy is a common cause of end-stage renal disease. The administration of an oral adsorbent, AST-120, prevents the progression of chronic renal failure in uremic rats and undialyzed uremic patients. This study was designed to determine if AST-120 slows the progression of diabetic nephropathy using Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetic mellitus. At 21 weeks of age the OLETF rats were divided into 2 groups: AST-120-administered OLETF rats (n = 7), and control OLETF rats (n = 7). LETO rats, which are genetically similar to the OLETF rats but not diabetic, were also included. After the oral administration of AST-120 for 65 weeks, renal function and pathological changes were investigated in the 3 groups. The administration of AST-120 to the OLETF rats attenuated the progression of glomerular sclerosis, interstitial fibrosis, tubular injury as well as renal dysfunction, and reduced the serum and urinary levels of indoxyl sulfate. Furthermore, AST-120 administration reduced the interstitial expression of transforming growth factor (TGF)-beta(1) and tissue inhibitor of metalloproteinase (TIMP)-1, as well as interstitial infiltration of macrophages. The TGF-beta(1)-stained interstitial area showed positive correlations with the interstitial fibrosis area, the number of TIMP-1-positive cells, and the number of macrophages, and showed a negative correlation with creatinine clearance. In conclusion, AST-120 reduced the interstitial expression of TGF-beta(1) and TIMP-1, and the interstitial infiltration of macrophages, and ameliorates the progression of diabetic nephropathy in OLETF rats.     

Combination therapy with angiotensin-converting enzyme inhibitor and oral adsorbent of uremic toxins can delay the appearance of glomerular sclerosis and interstitial fibrosis in established renal failure

BACKGROUND/AIM: Angiotensin II plays a central role in the progression of chronic renal failure (CRF), and administration of angiotensin-converting enzyme inhibitor (ACEI) in rats delays the progression of CRF. However, ACEI has little effect on CRF progression in rats with established CRF. We therefore examined whether combination therapy with ACEI and oral adsorbent for uremic toxins in the gastrointestinal tract has the desired effect. METHODS: Rats subjected to subtotal nephrectomy were given enalapril at 20 mg/kg (n = 10, group E), AST-120 at 5 g (n = 10, group A), enalapril and AST-120 together at the same doses (n = 10, group EA), or no treatment (n = 10, group C) 8 weeks after the operation. The substances were administered in 100 g rat chow. All animals were pair-fed, and all were killed after 8 weeks of pair-feeding. RESULTS: Body weight did not differ between groups during the study. Blood pressure at week 8 was significantly lower in groups E and EA than in groups C and A (p < 0.05). Urinary protein excretion level and renal plasma flow rate at week 8 were significantly less in groups E and EA than in group C (p < 0.05, p < 0.01). The glomerular filtration rate at week 8 was significantly higher in group EA than in group C (p < 0.05). The glomerular sclerosis index and interstitial fibrosis area at week 8 were significantly less in group EA than in group C (p < 0.01). CONCLUSION: ACEI and AST-120 in combination can delay progression of established CRF in rats by inhibiting the appearance of glomerular sclerosis and interstitial fibrosis.     

Oral sorbent AST-120 increases renal NO synthesis in uremic rats.

OBJECTIVE: The urine level of nitric oxide (NO) metabolites, i.e., nitrates/nitrites (NOx), in chronic renal failure (CRF) is decreased because of reduced renal synthesis of NO. We determined whether the administration of an oral sorbent, AST-120, increases the urine level of NOx and the renal expression of nitric oxide synthase (NOS) isoforms in CRF rats. METHODS: Chronic renal failure rats were produced by 4/5 nephrectomy. Rats were randomized into two groups: CRF control rats, and AST-120-treated CRF rats. The AST-120 was administered to the rats at a dose of 4 g/kg with powder chow for 16 weeks, whereas powder chow alone was administered to control rats. The urine levels of NOx were measured by using a NOx colorimetric assay kit. The expression of endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS) in the kidney was determined by immunohistochemistry. Serum and urine levels of indoxyl sulfate were determined by high-performance liquid chromatography. RESULTS: Urine levels of NOx and the expression of glomerular eNOS and tubulointerstitial nNOS were significantly decreased in CRF rats compared with normal rats. The administration of AST-120 to CRF rats significantly increased urine levels of NOx and the expression of glomerular eNOS and tubulointerstitial nNOS. The administration of AST-120 to CRF rats significantly decreased urine and serum levels of indoxyl sulfate. CONCLUSIONS: The oral sorbent AST-120 increases NO synthesis in the kidneys of uremic rats by increasing the renal expression of eNOS and nNOS, through alleviation of indoxyl sulfate overload on the kidney.     

Carbonic-adsorbent AST-120 reduces overload of indoxyl sulfate and the plasma level of TGF-β1 in patients with chronic renal failure

Background We previously reported a significant increase in plasma TGF-β1 in patients with chronic renal failure (CRF). Progression of CRF may be caused by persistent renal production of TGF-β1. In CRF rat models, an oral carbonic absorbent (AST-120) reduces the expression of the TGF-β1 gene in the kidney, and delays the progression of CRF, in part by alleviating the overload of indoxyl sulfate. The aim of this study was to evaluate the effect of AST-120 on plasma levels of indoxyl sulfate and TGF-β1 in CRF patients. Methods Ten CRF patients (aged 59.3 ± 9.5 years, 5 men, serum creatinine 4.37 ± 1.72 mg/dl) were enrolled in this study. All patients maintained a regular dietary therapy and the same medication throughout the study. AST-120 was added at a dose of 6 g/day. Parameters including the slope of the reciprocal of the serum creatinine – time plot, plasma indoxyl sulfate level, and plasma and urinary levels of TGF-β1 were compared before and after the treatment with AST-120. The mean observation periods before and after the treatment were 9.7 ± 2.8 and 6.5 ± 2.9 months, respectively. Results Administration of AST-120 significantly reduced the plasma levels of indoxyl sulfate (1.42 ± 1.50 vs. 1.26 ± 1.40 mg/dl, P < 0.05) and TGF-β1 (17.9 ± 7.2 vs. 10.6 ± 4.7 ng/ml, P < 0.05) and improved the slope of the reciprocal of serum creatinine (−0.061 ± 0.041 vs. −0.032 ± 0.055 dl/mg/year, P < 0.05). Conclusions These results support the notion that indoxyl sulfate and TGF-β1 may be involved in the progression of CRF, and that the oral adsorbent AST-120 may suppress the progression, at least in part, by reducing overproduction of TGF-β1.     

Uremic toxins adsorbed by AST-120 promote tubular hypertrophy and interstitial fibrosis in nephrectomized rats

BACKGROUND: Uremic toxins have been shown to promote glomerular hypertrophy. The present study was performed to elucidate the relation between uremic toxins and tubulointerstitial changes. METHODS: Sixty male Sprague-Dawley rats underwent 2/3 nephrectomy (Nx; n = 30) and 4/5 Nx (n = 30). Experiments were initiated 2 weeks after surgery, and were performed over an 8-week period. Half of each group (Nx-A) was administered 1 g/day of an oral carbonaceous adsorbent, AST-120, with pair-feeding, and the other half (Nx-C) served as controls. All rats were sacrificed at week 8 after a clearance study. RESULTS: The shortest diameter of proximal tubules (PTD) and interstitial fibrosis area (IFA) at week 8 in 2/3 Nx-A rats was significantly decreased compared to that in 2/3 Nx-C rats (similar body weights, systolic blood pressures, glomerular filtration rates, and urinary protein excretion levels). The values of PTD and IFA, glomerular filtration rate and urinary protein excretion level at week 8 in 4/5 Nx-A rats were significantly decreased compared to those in 4/5 Nx-C rats (similar body weights and systolic blood pressures). CONCLUSION: Administration of AST-120 minimized the appearance of proximal tubular hypertrophy and interstitial fibrosis, and subsequently prevented the occurrence of proteinuria and decreased renal function. The present study indicates that uremic toxins adsorbed by AST-120 promote tubular hypertrophy and interstitial fibrosis in nephrectomized rats.     

Effects of oral adsorbent AST-120 (Kremezin) on renal function and glomerular injury in early-stage renal failure of subtotal nephrectomized rats

The aim of the present study was to determine if treatment with an oral adsorbent (AST-120, Kremezin) might decrease the urinary albumin excretion and serum indoxyl sulfate (s-IS), and prevent glomerular sclerosis in early-stage renal failure, i.e. 0.9-1.2 mg/dl of serum creatinine (s-Cr) and 60-95 mg/dl of blood urea nitrogen (BUN), in subtotal (3/4) nephrectomized rats. Levels of s-Cr and s-IS in the AST-120-treated rats were significantly lower than those in the untreated control rats. The AST-120-treated rats showed an increase of creatinine clearance. Urinary protein and indoxyl sulfate excretion in the AST-120-treated rats were also significantly lower than those in the untreated control rats. The ratio of glomerular tuft area to the area of Bowman's capsules (GT/BC) in the AST-120-treated rats was significantly lower than that in the untreated control rats. The degree of glomerular sclerosis and tubulointerstitial fibrosis in the AST-120-treated rats was significantly lower than that in the untreated control rats. Furthermore, there was a significant relationship among the degree of GT/BC, glomerular sclerosis, tubulointerstitial fibrosis and the levels of urinary protein excretion. It appears that AST-120 might decrease the accumulation of s-Cr and s-IS, and prevent glomerular sclerosis in early stage renal failure in the subtotal nephrectomized rats.     

Effect of oral adsorbent (AST-120) in the rat model of chronic renal failure induced by adriamycin]

The effect of AST-120 was examined in the rat model of CRF induced by adriamycin (ADM), which is known to induce focal glomerular sclerosis (GS). ADM (2mg/kg) was injected intravenously twice at a 3-wk interval. After 14 wks, rats were paired with control (C) and AST-120 (A) groups according to levels of BUN and proteinuria. Then, the rats were fed regular rat chow with (A, n = 10) or without (C, n = 10) AST-120. After 28 wks, there were more GS in C. Averaged sclerosis index (SI, 0-4 scale) in C was 1.97 (0.94-3.22), while 1.61 (0.60-2.97) in A. When GS was advanced in C (SI > 2.0), largely ameliorated SI was noted in A (2.61 vs. 1.97, C vs. A, p < 0.05 by paired W-test, n = 5 each). Also, in these rats, BUN, serum creatinine and Ht were all improved in A (p < 0.05). Thus, AST-120 was effective in CRF rats induced by ADM when uremia was advanced. The data also indicates that a reduction of uremic toxins could improve glomerular histology and renal function in CRF.     

Effect of oral sorbent, AST-120, on serum concentration of indoxyl sulfate in uremic rats

Indoxyl sulfate is a metabolite of tryptophan. Indole is synthesized in intestine from tryptophan by intestinal bacteria. The absorbed indole is converted to indoxyl sulfate through indoxyl in liver. Serum concentration of indoxyl sulfate is markedly increased as an inhibitor of drug-binding in uremic patients as compared with healthy subjects. Since indoxyl sulfate is bound to serum albumin, it cannot be removed efficiently by hemodialysis, and it tends to accumulate in uremic serum. To determine if oral sorbent, AST-120, could adsorb indole in intestine and then decrease serum concentration of indoxyl sulfate, it was administered to nephrectomized uremic rats. Serum concentration of indoxyl sulfate was markedly decreased in uremic rats fed with oral sorbent as compared with control uremic rats. However, serum concentrations of creatinine and urea nitrogen were not significantly decreased in the uremic rats fed with oral sorbent as compared with the control uremic rats. Serum concentration of tryptophan was not decreased but rather increased in the uremic rats fed with oral sorbent as compared with the control uremic rats. Concentration of indoxyl sulfate in bile of a uremic rat was much lower than that in the uremic serum, suggesting that the adsorption of indoxyl sulfate in intestine is not a major mechanism of decreasing the serum concentration of indoxyl sulfate. These results demonstrate that oral sorbent, AST-120, can decrease serum concentration of indoxyl sulfate in uremia due to adsorption of indole in intestine.     

Effects of oral adsorbent in the rat model of chronic renal failure.

The effects of oral adsorbent, AST-120 (Kureha Chemical Ind. Co., Tokyo), were studied in the rat model of subtotal nephrectomy. In 34 female Sprague-Dawley rats, three quarters of the renal mass were removed from the left kidney by ligation of 3 branches of the left renal artery. One week later, the right kidney was removed. Two days after right nephrectomy, control rats were fed standard rat chow ad libitum, while AST-120-treated rats were fed standard rat chow containing AST-120 ad libitum. The animals were observed for 9 weeks. Of the control rats, some became severely ill and appeared to be almost dying before 9 weeks, while paired AST-120-treated rats appeared well. Body weight was maintained better in AST-120-treated rats than in control rats. At completion of the study, levels of BUN and serum creatinine were lower and glomerular filtration rate and renal plasma flow rate were higher in AST-120-treated than in control rats (p < 0.05), although there was no statistically significant difference in proteinuria. Serum uremic peak 2a measured by high-performance liquid chromatography, which is considered to correspond to uremic toxins, was statistically lower in AST-120-treated rats (p < 0.05). Finally, a marked reduction in the degree of glomerular sclerosis was noted in AST-120-treated versus control rats (p < 0.05). The results indicate that AST-120 is effective in the treatment of chronic renal failure in terms of reducing uremic symptoms as well as preserving renal function and glomerular architecture. The data also indicate that a reduction in uremic toxins could delay the progressive damage of renal function and glomerular architecture in chronic renal failure.     

Accumulation of indoxyl sulfate in OAT1/3-positive tubular cells in kidneys of patients with chronic renal failure.

Indoxyl sulfate shows nephrotoxicity and is a stimulating factor for progression of chronic renal failure (CRF). Indoxyl sulfate is taken up by renal proximal tubular cells through organic anion transporters 1 and 3 (OAT1/3), and is accumulated in the renal proximal tubular cells of uremic rats. To determine whether indoxyl sulfate is accumulated in human OAT1/3 (hOAT1/3)-positive renal proximal tubular cells, localization of indoxyl sulfate and hOAT1/3 in the kidneys of CRF patients was determined by immunohistochemistry. Kidney samples were obtained by autopsy from 9 CRF patients (mean serum creatinine 4.7 mg/dL, ranging from 2.0 to 14.5 mg/dL) and 9 patients with non-kidney disease (mean serum creatinine 0.6 mg/dL, ranging from 0.4 to 0.9 mg/dL). Immunohistochemistry was performed using antibodies against indoxyl sulfate, hOAT1, and hOAT3. Indoxyl sulfate was localized in the hOAT1- and hOAT3-positive renal tubular cells in the kidneys of CRF patients. The indoxyl sulfate-positive area in the kidneys was markedly increased in the kidneys of CRF patients compared with patients with non-kidney disease. The indoxyl sulfate-positive area was positively correlated with serum creatinine. In conclusion, in CRF patients, indoxyl sulfate is accumulated in the tubular cells with hOAT1 and/or hOAT3 localized at the basolateral membrane. The extent of indoxyl sulfate accumulation in the kidneys is more prominent in those patients with more severe CRF.     

Uremic toxins of organic anions up-regulate PAI-1 expression by induction of NF-kappaB and free radical in proximal tubular cells

BACKGROUND: Uremic toxins have been suggested to promote progression of chronic renal failure. We have shown that organic anion transporter-mediated uptake of uremic toxins induces oxidative stress in opossum kidney renal tubular cells overexpressing the transporter. Plasminogen activator inhibitor-1 (PAI-1) and nuclear factor-kappa B (NF-kappaB) are major factors known to promote tubulointerstitial fibrosis. The present study examined the signaling pathway that is activated by uremic toxins to induce PAI-1 and activate NF-kappaB in human renal proximal tubular cells (HK-2). METHODS: Uremic toxins in the form of organic anion were examined their ability to induce oxidative stress, PAI-1 gene expression, and NF-kappaB activation in HK-2. PAI-1 expression was measured by enzyme-linked immunosorbent assay (ELISA) and the Northern blotting. Human PAI-1 promoter activity was estimated by luciferase reporter gene (NKkappaB-luc) assay. NF-kappaB activation was measured by the pNFkappaB-luc reporter gene and electrophretic gel mobility shift assay. RESULTS: Among organic anion species tested, indoxyl sulfate and indoleacetic acid induced free radical production in HK-2. A nonspecific transporter inhibitor (probenecid) suppressed the IS-stimulated radical production. Indoxyl sulfate and indoleacetic acid dose dependently increased the expressions of PAI-1 mRNA and protein in these cells. The luciferase reporter gene assay revealed that indoxyl sulfate and indoleacetic acid dose dependently activated NF-kappaB and PAI-1 promoter. Activation of NF-kappaB was also confirmed by an electrophoretic gel mobility shift assay. Both antioxidant and NF-kappaB inhibitors dose dependently inhibited the activation of PAI-1 promoter by indoxyl sulfate. CONCLUSION: Uremic toxins induce free radical production by renal tubular cells and activate NF-kappaB which, in turn, up-regulates PAI-1 expression. Thus, progression of chronic renal failure may be promoted by PAI-1 up-regulation induced by uremic toxins.     

Correction by oral adsorbent of abnormal digestive tract milieu in rats with chronic renal failure

In order to examine the mechanism by which the oral carbonaceousadsorbent, AST-120 delays the appearance of glomerular sclerosis,experiments were carried out in 120 male Sprague-Dawley ratsweighing 285–320 g. The rats were first subjected to 2/3,3/4, and 4/5 nephrectomy (n=40). The experiments were begunat 2 weeks after the surgery, and were performed over an 8-weekperiod. Half of each group (n=20) was administered 1 g/day ofliquid AST-120, and the other half received liquid vehicle solutionwith pair feeding in each group. In the 2/3 nephrectomized groupthe administration of AST-120 delayed the occurrence of glomerularhypertrophy and prevented the appearance of glomerular sclerosiswithout any significant differences in renal function, systemicblood pressure (SBP), and urinary protein excretion (U-P). Inthe 3/4 nephrectomized group the administration of AST-120 delayedthe appearance of glomerular hypertrophy and sclerosis withsignificant decreases in SBP and U-P. In the 4/5 nephrectomizedgroup the administration of AST-120 delayed the appearance ofglomerular sclerosis and prevented a decrease in renal function.It is concluded that administration of the oral adsorbent AST-120delays the occurrence of glomerular sclerosis by delaying theappearance of glomerular hypertrophy, systemic hypertension,and the increase in proteinuria. It can be therefore mentionedthat the accumulating substances in the digestive tract worsenthe abnormal milieu of chronic renal failure.     

Suppressed serum and urine levels of indoxyl sulfate by oral sorbent in experimental uremic rats.

In uremic patients, the serum concentration of indoxyl sulfate is markedly increased. To determine if oral sorbent (AST-120) suppresses the endogenous synthesis of indoxyl sulfate, it was administered to experimental uremic rats, and the serum concentration and urinary excretion of indoxyl sulfate were quantified by high-performance liquid chromatography. Oral sorbent decreased both the serum concentration and urinary excretion of indoxyl sulfate, suggesting that there was suppression of the endogenous synthesis of indoxyl sulfate by the oral sorbent. Oral sorbent did not decrease the serum concentration and urinary excretion of hippuric acid, but it did alleviate the deterioration of renal function in the experimental uremic rats.     

Inhibitory effect of oral sorbent on accumulation of albumin-bound indoxyl sulfate in serum of experimental uremic rats

Serum indoxyl sulfate, which is markedly accumulated in uremic patients, cannot be removed efficiently by hemodialysis due to its albumin binding. To determine if oral adsorbent (AST-120) can decrease its serum concentration in uremic state, oral adsorbent was administered to experimental nephrectomized uremic rats. Uremic rats fed with oral adsorbent showed a significantly lower serum concentration of indoxyl sulfate compared to control uremic rats, even when serum concentrations of urea nitrogen and creatinine were not significantly decreased in the uremic rats fed with oral adsorbent. Indoxyl sulfate was detected only at a lower concentration in bile as compared with the serum of uremic rats. These results suggest that oral adsorbent adsorbs indole, a precursor of indoxyl sulfate, in the intestine and prevents the accumulation of indoxyl sulfate in uremic rats.     

Effect of oral adsorbent AST-120 in rats with chronic renal failure--mechanism of progression of renal failure by dietary protein]

Progression of renal insufficiency was evaluated in partially nephrectomized Sprague-Dawley rats at the age of 10 weeks, fed on the low (6%), usual (20%), and high (36%) protein diet (group 6C, 20C, and 36C). Effects of oral adsorbent AST-120 on these experimental uremic models were also examined (group 6A, 20A, 36A). All the rats underwent paired feeding, and survived during the experimental period of 3 weeks. GFR (inulin clearance) and RPF (para-amino hippurate clearance), as well as Ccr was measured before the sacrifice. Initial serum creatinine and Ccr were 1.7 mg/dl and 0.27 ml/min. The rats of group 36C showed progressive elevation of serum creatinine level and decrease in Ccr. At the end of the study, GFR was significantly lower in group 36C than in group 6C and 20C (0.19, 0.68, 0.87 ml/min respectively). Significant elevation of filtration fraction in group 36C suggested that the decrease in GFR mainly resulted from low RPF. Even in group 36C, no glomerular sclerosis was histologically demonstrated in the remnant kidney, and the mean planar area of the remnant glomeruli was significantly small, which might reflect low RPF. Tubulo-interstitial changes like dilatation of the urinary space and tubular epithelial flattening were prominent in group 36C. Beneficial effect of AST-120 was obvious in high protein diet groups. GFR and RPF were rather well preserved in group 36A (0.36 and 0.78 ml/min) with normal filtration fraction. Tubulo-interstitial damage was evidently mild in group 36A. These data suggested the presence of some humoral factors, which can be adsorbed by AST-120 in gastrointestinal tract, and responsible for the deterioration of renal function and tubulo-interstitial damage induced by high protein diet in the uremic condition. Besides hyperfiltration and glomerular hypertrophy, such humoral factors as suggested in this study may contribute to the progression of chronic renal failure to some extent.     

Suppression of Klotho expression by protein-bound uremic toxins is associated with increased DNA methyltransferase expression and DNA hypermethylation

The expression of the renoprotective antiaging gene Klotho is decreased in uremia. Recent studies suggest that Klotho may be a tumor suppressor, and its expression may be repressed by DNA hypermethylation in cancer cells. Here we investigated the effects and possible mechanisms by which Klotho expression is regulated during uremia in uninephrectomized B-6 mice given the uremic toxins indoxyl sulfate or p-cresyl sulfate. Cultured human renal tubular HK2 cells treated with these toxins were used as an in vitro model. Injections of indoxyl sulfate or p-cresyl sulfate increased their serum concentrations, kidney fibrosis, CpG hypermethylation of the Klotho gene, and decreased Klotho expression in renal tubules of these mice. The expression of DNA methyltransferases 1, 3a, and 3b isoforms in HK2 cells treated with indoxyl sulfate or p-cresyl sulfate was significantly increased. Specific inhibition of DNA methyltransferase isoform 1 by 5-aza-2'-deoxycytidine caused demethylation of the Klotho gene and increased Klotho expression in vitro. Thus, inhibition of Klotho gene expression by uremic toxins correlates with gene hypermethylation, suggesting that epigenetic modification of specific genes by uremic toxins may be an important pathological mechanism of disease.