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

Molecular mechanisms and therapeutic strategies of chronic renal injury: the role of nuclear factor kappaB activation in the development of renal fibrosis

Tubulointerstitial fibrosis is a common feature of many progressive renal diseases and is a main determinant that leads to an irreversible loss of renal function. In chronic cyclosporin A nephrotoxicity, we previously reported that inflammatory responses such as macrophage infiltration preceded interstitial fibrosis. This inflammation was accompanied by an elevation in renal nuclear factor kappaB (NF-kappaB) activity. Similar findings were obtained in chronic tacrolimus nephrotoxicity and obstructive nephropathy. Inhibition of NF-kappaB markedly attenuated renal inflammation and interstitial fibrosis in these models. Furthermore, administration of oral adsorbent (Kremezin) significantly attenuated the increase in renal NF-kappaB activity and concomitantly reduced interstitial inflammation and renal fibrosis in chronic renal failure rats. Elimination of indoxyl sulfate by this adsorbent is likely involved in this mechanism since it is known that indoxyl sulfate activates NF-kappaB in renal tubular cells. It is suggested that strategy aiming at NF-kappaB inhibition is important to prevent the progression of renal fibrosis.

Uremic toxin and bone metabolism

Patients with end-stage renal disease (ESRD) develop various kinds of abnormalities in bone and mineral metabolism, widely known as renal osteodystrophy (ROD). Although the pathogenesis of ESRD may be similar in many patients, the response of the bone varies widely, ranging from high to low turnover. ROD is classified into several types, depending on the status of bone turnover, by histomorphometric analysis using bone biopsy samples [1,2]. In the mild type, bone metabolism is closest to that of persons with normal renal function. In osteitis fibrosa, bone turnover is abnormally activated. This is a condition of high-turnover bone. A portion of the calcified bone loses its lamellar structure and appears as woven bone. In the cortical bone also, bone resorption by osteoclasts is active, and a general picture of bone marrow tissue infiltration and the formation of cancellous bone can be observed. In osteomalacia, the bone surface is covered with uncalcified osteoid. This condition is induced by aluminum accumulation or vitamin D deficiency. The mixed type possesses characteristics of both osteitis fibrosa and osteomalacia. The bone turnover is so markedly accelerated that calcification of the osteoid cannot keep pace. In the adynamic bone type, bone resorption and bone formation are both lowered. While bone turnover is decreased, there is little osteoid. The existence of these various types probably accounts for the diversity in degree of renal impairment, serum parathyroid hormone (PTH) level, and serum vitamin D level in patients with ROD. However, all patients share a common factor, i.e., the presence of a uremic condition.

Induction of PAI-1 expression by tumor necrosis factor alpha in endothelial cells is mediated by its responsive element located in the 4G/5G site

Plasminogen activator inhibitor type 1 (PAI-1) is induced by many proinflammatory and pro-oxidant factors. Among them, tumor necrosis factor alpha (TNFalpha), a pivotal early mediator that regulates and amplifies the development of inflammation, is one of the strongest PAI-1 synthesis activators. Location of the TNFalpha response element in the PAI-1 promoter is still ambiguous. In this study, we attempted to evaluate the significance of the element located in the 4G/5G site of the PAI-1 promoter in the TNFalpha stimulation of PAI-1 expression in endothelial cells. PAI-1 expression was monitored at: (a) the level of mRNA using real-time PCR, (b) PAI-1 gene transcription by transfection reporter assays, and (c) protein synthesis using the enzyme immunoassay. NF-kappaB activity was monitored using the electrophoretic mobility shift assay. Its activity was modified by either antisense oligonucleotides or transfection of endothelial cells with the wild-type or mutated IkappaBalpha. We have shown that TNFalpha-induced expression and gene transcription of PAI-1 involves a regulatory region present in segment -664/-680 of the PAI-1 promoter. This reaction involves the TNFalpha-induced generation of superoxide leading to activation of NF-kappaB, and can be abolished by antioxidants and by overexpression of a super-suppressor phosphorylation-resistant IkappaBalpha. Stimulation of PAI-1 under these conditions involves the motif of the PAI-1 promoter adjacent to the 4G/5G site, which can directly interact with NF-kappaB. We show that activation of PAI-1 gene by TNFalpha and reactive oxygen species is mediated by interaction of NF-kappaB with the cis-acting element located in the -675 4G/5G insertion/deletion in the PAI-1 promoter.

Aminoethyl-substituted indole-3-acetic acids for the preparation of tagged and carrier-linked auxin

Indole-3-acetic acid is an indispensable hormone (auxin) in plants and an important metabolite in humans, animals, and microorganisms. Here we introduce its 5- and 6-(2-aminoethyl)-derivatives for use in the design of novel research tools, such as immobilized and carrier-linked forms of indole-3-acetic acid and its conjugates with biochemical tags or biocompatible molecular probes. The aliphatic nitrogens of 5- and 6-(2-aminoethyl)indole were acetylated and the products were converted to the corresponding 3-(N,N-dimethylamino)methyl derivatives (gramines). These were reacted with cyanide. Saponification of the resulting acetonitriles was accompanied by N-deprotection to yield 5- and 6-(2-aminoethyl)indole-3-acetic acids. The latter were chemically stable and could be linked, via their amino groups, and without prior protection of their carboxyl moieties, to bovine serum albumin and to biotin, including appropriate spacer modules. One of the protein conjugates was used to elicit the formation of monoclonal antibodies, which were evaluated using the biotin conjugates in an enzyme-linked immunosorbent assay employing streptavidin-coupled alkaline phosphatase, and thus shown to recognize predominantly the indole-3-acetic acid moiety.

Kidney in early atherosclerosis

Atherosclerosis represents one of the major causes of premature death in the United States today, and it is frequently associated with, exacerbates, and is aggravated by chronic kidney disease (CKD). Atherosclerosis integrates the response to a number of insults, and consequently, the accelerated atherosclerosis found in CKD patients is associated with activation of a variety of humoral and tissue mechanisms. Hypertension, diabetes, dyslipidemia, obesity, metabolic syndrome, and additional nontraditional risk factors can damage the kidney directly and by promoting intrarenal atherogenesis, even in the absence of obstructive lesions in the renal artery. Evidence indicates that increased oxidative stress and inflammation may mediate a large part of the effects of risk factors on the kidney. In turn, progressive deterioration of renal function in CKD may lead to dyslipidemia or accumulation of uremic toxins, which can induce production of free radicals and activate proinflammatory and fibrogenic factors, leading to vascular endothelial cell dysfunction and injury, and favoring development of atherosclerosis. Therefore, the kidney can be a villain or a victim during atherogenesis. The purpose of this review is to provide new insights into the mechanisms by which atherogenic factors may instigate early renal injury.

Differential contributions of rOat1 (Slc22a6) and rOat3 (Slc22a8) to the in vivo renal uptake of uremic toxins in rats

PURPOSE

Evidence suggests that uremic toxins such as hippurate (HA), indoleacetate (IA), indoxyl sulfate (IS), and 3-carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF) promote the progression of renal failure by damaging tubular cells via rat organic anion transporter 1 (rOat1) and rOat3 on the basolateral membrane of the proximal tubules. The purpose of the current study is to evaluate the in vivo transport mechanism responsible for their renal uptake.

METHODS

We investigated the uremic toxins transport mechanism using the abdominal aorta injection technique [i.e., kidney uptake index (KUI) method], assuming minimal mixing of the bolus with serum protein from circulating serum.

RESULTS

Maximum mixing was estimated to be 5.8% of rat serum by measuring estrone sulfate extraction after addition of 0-90% rat serum to the arterial injection solution. Saturable renal uptake of p-aminohippurate (PAH, K(m) = 408 microM) and benzylpenicillin (PCG, K(m) = 346 microM) was observed, respectively. The uptake of PAH and PCG was inhibited in a dose-dependent manner by unlabeled PCG (IC(50) = 47.3 mM) and PAH (IC(50) = 512 microM), respectively, suggesting that different transporters are responsible for their uptake. A number of uremic toxins inhibited the renal uptake of PAH and PCG. Excess PAH, which could inhibit rOat1 and rOat3, completely inhibited the saturable uptake of IA, IS, and CMPF by the kidney, and by 85% for HA uptake. PCG inhibited the total saturable uptake of HA, IA, IS, and CMPF by 10%, 10%, 45%, and 65%, respectively, at the concentration selective for rOat3.

CONCLUSIONS

rOat1 could be the primary mediator of the renal uptake of HA and IA, accounting for approximately 75% and 90% of their transport, respectively. rOat1 and rOat3 contributed equally to the renal uptake of IS. rOat3 could account for about 65% of the uptake of CMPF under in vivo physiologic conditions. These results suggest that rOat1 and rOat3 play an important role in the renal uptake of uremic toxins and the induction of their nephrotoxicity.

Oxidative stress and hypoxia: implications for plasminogen activator inhibitor-1 expression

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of urokinase-type and tissue-type plasminogen activators. It has gained special interest among clinicians because a number of pathological conditions, such as myocardial infarction, atherosclerosis, thrombosis, several types of cancer, and the metabolic syndrome, as well as type 2 diabetes mellitus, are associated with increased PAI-1 levels. Interestingly, a number of these diseases are also accompanied by oxidative stress and the enhanced production of reactive oxygen species or tissue hypoxia. This article tries to summarize some aspects leading to enhanced PAI-1 production under oxidative stress or hypoxia.

Enhanced plasminogen activator inhibitor-1 expression in transgenic mice with hepatocyte-specific overexpression of superoxide dismutase or glutathione peroxidase

In this study, we developed a double-transgenic mouse model allowing hepatocyte-specific and regulated expression of the redox-modifying enzymes copper/zinc superoxide dismutase (SOD) and glutathione peroxidase (GPX) by using a tetracycline-regulatable gene expression system. Within this system, the SOD and GPX level can be regulated deliberately by addition or removal of doxycycline hydrochloride to the drinking water. As reactive oxygen species (ROS) have been implicated in a number of pathological conditions, such as atherosclerosis, thrombosis, or liver fibrosis, processes that are also frequently associated with enhanced levels of plasminogen activator inhibitor-1 (PAI-1), it was the aim of the present study to investigate the influence of SOD and GPX overexpression on the regulation of PAI-1. PAI-1 mRNA and protein levels in tetracycline transactivator-dependent SOD-overexpressing double-transgenic mice reached values 2.5- to threefold above the normal mRNA level. By applying doxycycline, a deinduction of the PAI-1 levels was observed. By using the same protocol, PAI-1 mRNA and protein levels were enhanced in GPX double-transgenic mice, and again this response was blunted by the addition of doxycycline. These studies provide some new information regarding the role of ROS within the proteolytic processes in hepatocytes that require PAI-1.

Counter-regulatory effects of procalcitonin and indoxyl sulphate on net albumin secretion by cultured rat hepatocytes

BACKGROUND

Although hypoalbuminaemia is a significant predictor of mortality in haemodialysis (HD) patients, the pathophysiological mechanisms involved remain to be determined. Albumin is a negative acute-phase reactant and many proinflammatory substances are elevated in HD patients. We investigated factors that may affect liver albumin synthesis.

METHODS

Hepatocytes were isolated from rat livers and were cultured with interleukin (IL)-4, IL-6, IL-12, tumor necrosis factor (TNF)-alpha, procalcitonin (PCT), a sensitive marker of infection, and indoxyl sulphate (IS), a uraemic toxin. Albumin levels in the supernatant were measured by enzyme-linked immunosorbent assay. Albumin mRNA expression was determined by reverse transcriptase polymerase chain reaction.

RESULTS

IL-6 and TNF-alpha significantly decreased albumin levels in a dose-dependent manner (P<0.01 and P<0.05, respectively). In contrast, IL-4 and IL-12 did not modulate albumin production. PCT and IS significantly and dose-dependently increased albumin levels (both P<0.01). PCT increased albumin mRNA expression in the hepatocytes (P = 0.05) and dose-dependently abrogated IL-6-induced suppression of albumin synthesis (P<0.01). IS also blocked the IL-6-induced decrease in net albumin secretion (P<0.01).

CONCLUSION

Our findings indicate that PCT and IS protect against suppression of hepatic albumin synthesis caused by proinflammatory cytokines, suggesting their potential role in preventing hypoalbuminaemia in HD patients.

Expression of type-1 plasminogen activator inhibitor in the kidney of diabetic rat models

INTRODUCTION

Intrarenal coagulation and fibrinolysis are thought to be involved in the pathogenesis of diabetic nephropathy. However, gene expression of fibrinolytic factors in diabetic nephropathy has not been clearly defined. Therefore we determined the gene expression of fibrinolytic factors in the kidneys of diabetic rats.

MATERIALS AND METHODS

As a model of type1 diabetes male Sprague-Dawley rats were used. They were divided into three groups: control, streptozotocin (STZ)-induced diabetic, and insulin-treated diabetic. Otsuka Long-Evans Tokushima Fatty (OLETF) rats were used as a model of type 2 diabetes; and Long-Evans Tokushima Otsuka (LETO) rats, as the control. Renal gene expressions of type-1 plasminogen activator inhibitor (PAI-1), tissue-type PA (tPA), and urokinase-type PA (uPA) were examined by real-time PCR. Localization of PAI-1 mRNA was investigated by in situ hybridization.

RESULTS

Renal PAI-1 mRNA levels (versus control) were increased by 60-80% in STZ-induced diabetic rats (10 days or 3 weeks post STZ injection); and insulin treatment reduced this increased expression to the control level. In OLETF rats (38 weeks old), the renal PAI-1 mRNA level was 2.5-fold higher than that in age-matched LETO rats. Both tPA and uPA mRNA levels were significantly lower than those in LETO rats. PAI-1 mRNA was observed in intraglomerular cells and tubular epithelial cells of both models.

CONCLUSIONS

Renal PAI-1 gene expression is up-regulated in both type 1 and type 2 diabetic rats, and changes in gene expressions of fibrinolytic factors may play important roles in the development and pathogenesis of diabetic nephropathy.