Shiga toxin induces medullary tubular injury in isolated perfused rat kidneys

RAB5A and TRAPPC6B are novel targets for Shiga toxin 2a inactivation in kidney epithelial cells

The cardinal virulence factor of human-pathogenic enterohaemorrhagic Escherichia coli (EHEC) is Shiga toxin (Stx), which causes severe extraintestinal complications including kidney failure by damaging renal endothelial cells. In EHEC pathogenesis, the disturbance of the kidney epithelium by Stx becomes increasingly recognised, but how this exactly occurs is unknown. To explore this molecularly, we investigated the Stx receptor content and transcriptomic profile of two human renal epithelial cell lines: highly Stx-sensitive ACHN cells and largely Stx-insensitive Caki-2 cells. Though both lines exhibited the Stx receptor globotriaosylceramide, RNAseq revealed strikingly different transcriptomic responses to an Stx challenge. Using RNAi to silence factors involved in ACHN cells’ Stx response, the greatest protection occurred when silencing RAB5A and TRAPPC6B, two host factors that we newly link to Stx trafficking. Silencing these factors alongside YKT6 fully prevented the cytotoxic Stx effect. Overall, our approach reveals novel subcellular targets for potential therapies against Stx-mediated kidney failure.

Effects of empagliflozin on nondiabetic salt-sensitive hypertension in uninephrectomized rats

Impaired pressure natriuresis (PN) underlies salt-sensitive hypertension, and renal inflammation and hypoxia-inducible factor-1 (HIF-1) have been implicated in the modulation of systemic hypertension. Although sodium-glucose cotransporter-2 (SGLT2) inhibitors were reported to lower blood pressure (BP) in type 2 diabetes mellitus, whether they have a role in nondiabetic hypertensive kidney diseases is unclear. The present study was undertaken to investigate whether nondiabetic salt-sensitive hypertension and accompanying renal inflammation are ameliorated by SGLT2 inhibition. Male Sprague-Dawley rats were randomly divided into three groups: sham controls (SCs), uninephrectomized controls (UCs), and empagliflozin-treated rats (ETs). All rats were fed a rodent diet with 8% NaCl throughout the study period. Empagliflozin was orally administered for 3 weeks after uninephrectomy. Systolic blood pressure was recorded weekly, and kidneys were harvested for immunoblotting, immunohistochemistry, and quantitative PCR analysis at the end of the animal experiment. Systolic BP was significantly decreased in ETs that were orally given empagliflozin for 3 weeks after uninephrectomy. Although ETs did not show any increase in weekly measured urine sodium, the right-shifted PN relationship in UCs was improved by empagliflozin treatment. The expression of HIF-1α was increased in the renal outer medulla of ETs. Consistent with this, HIF prolyl-hydroxylase-2 protein and mRNA were decreased in ETs. The abundance of CD3 and ED-1 immunostaining in UCs was reduced by empagliflozin treatment. The increased IL-1ß, gp91phox, and NOX4 mRNA levels in UCs were also reversed. Empagliflozin restored impaired PN in nondiabetic hypertensive kidney disease in association with increased renal medullary expression of HIF-1α and amelioration of renal inflammation.

Roles of Shiga Toxins in Immunopathology

Shigella species and Shiga toxin-producing Escherichia coli (STEC) are agents of bloody diarrhea that may progress to potentially lethal complications such as diarrhea-associated hemolytic uremic syndrome (D+HUS) and neurological disorders. The bacteria share the ability to produce virulence factors called Shiga toxins (Stxs). Research over the past two decades has identified Stxs as multifunctional toxins capable of inducing cell stress responses in addition to their canonical ribotoxic function inhibiting protein synthesis. Notably, Stxs are not only potent inducers of cell death, but also activate innate immune responses that may lead to inflammation, and these effects may increase the severity of organ injury in patients infected with Stx-producing bacteria. In the intestines, kidneys, and central nervous system, excessive or uncontrolled host innate and cellular immune responses triggered by Stxs may result in sensitization of cells to toxin mediated damage, leading to immunopathology and increased morbidity and mortality in animal models (including primates) and human patients. Here, we review studies describing Stx-induced innate immune responses that may be associated with tissue damage, inflammation, and complement activation. We speculate on how these processes may contribute to immunopathological responses to the toxins.

Modeling Hemolytic-Uremic Syndrome: In-Depth Characterization of Distinct Murine Models Reflecting Different Features of Human Disease

Diarrhea-positive hemolytic-uremic syndrome (HUS) is a renal disorder that results from infections with Shiga-toxin (Stx)-producing Escherichia coli. The aim of this study was to establish well-defined refined murine models of HUS that can serve as preclinical tools to elucidate molecular mechanisms of disease development. C57BL/6J mice were subjected to different doses of Stx2 purified from an E. coli O157:H7 patient isolate. Animals received 300 ng/kg Stx2 and were sacrificed on day 3 to establish an acute model with fast disease progression. Alternatively, mice received 25 ng/kg Stx2 on days 0, 3, and 6, and were sacrificed on day 7 to establish a subacute model with moderate disease progression. Indicated by a rise in hematocrit, we observed dehydration despite volume substitution in both models, which was less pronounced in mice that underwent the 7-day regime. Compared with sham-treated animals, mice subjected to Stx2 developed profound weight loss, kidney dysfunction (elevation of plasma urea, creatinine, and neutrophil gelatinase-associated lipocalin), kidney injury (tubular injury and loss of endothelial cells), thrombotic microangiopathy (arteriolar microthrombi), and hemolysis (elevation of plasma bilirubin, lactate dehydrogenase, and free hemoglobin). The degree of complement activation (C3c deposition), immune cell invasion (macrophages and T lymphocytes), apoptosis, and proliferation were significantly increased in kidneys of mice subjected to the 7-day but not in kidneys of mice subjected to the 3-day regime. However, glomerular and kidney volume remained mainly unchanged, as assessed by 3D analysis of whole mount kidneys using CD31 staining with light sheet fluorescence microscopy. Gene expression analysis of kidneys revealed a total of only 91 overlapping genes altered in both Stx2 models. In conclusion, we have developed two refined mouse models with different disease progression, both leading to hemolysis, thrombotic microangiopathy, and acute kidney dysfunction and damage as key clinical features of human HUS. While intrarenal changes (apoptosis, proliferation, complement deposition, and immune cell invasion) mainly contribute to the pathophysiology of the subacute model, prerenal pathomechanisms (hypovolemia) play a predominant role in the acute model. Both models allow the further study of the pathomechanisms of most aspects of human HUS and the testing of distinct novel treatment strategies.

Bacillus anthracis Edema Toxin Increases Fractional Free Water and Sodium Reabsorption in an Isolated Perfused Rat Kidney Model

Bacillus anthracis edema toxin (ET) consists of protective antigen (PA), necessary for host cell toxin uptake, and edema factor (EF), the toxic moiety which increases host cell cyclic AMP (cAMP). Since vasopressin stimulates renal water and sodium reabsorption via increased tubular cell cAMP levels, we hypothesized the ET would also do so. To test this hypothesis, we employed an isolated perfused rat kidney model. Kidneys were isolated and perfused with modified Krebs-Henseleit buffer. Perfusate and urine samples were obtained at baseline and every 10 min over 150 min following the addition of challenges with or without treatments to the perfusate. In kidneys perfused under constant flow or constant pressure, compared to PA challenge (n = 14 or 15 kidneys, respectively), ET (13 or 15 kidneys, respectively) progressively increased urine cAMP levels, water and sodium reabsorption, and urine osmolality and decreased urine output (P ≤ 0.04, except for sodium reabsorption under constant pressure [P = 0.17]). In ET-challenged kidneys, compared to placebo treatment, adefovir, an EF inhibitor, decreased urine cAMP levels, water and sodium reabsorption, and urine osmolality and increased urine output, while raxibacumab, a PA-directed monoclonal antibody (MAb), decreased urine cAMP levels, free water reabsorption, and urine osmolality and increased urine output (P ≤ 0.03 except for urine output with raxibacumab [P = 0.17]). Upon immunohistochemistry, aquaporin 2 was concentrated along the apical membrane of tubular cells with ET but not PA, and urine aquaporin 2 levels were higher with ET (5.52 ± 1.06 ng/ml versus 1.51 ± 0.44 ng/ml [means ± standard errors of the means {SEM}; P = 0.0001). Edema toxin has renal effects that could contribute to extravascular fluid collection characterizing anthrax infection clinically.

Role of Shiga/Vero toxins in pathogenesis

Shiga toxin (Stx) is the primary cause of severe host responses including renal and central nervous system (CNS) disease in Shiga toxin-producing E. coli (STEC) infections. The interaction of Stx with different eukaryotic cell types is described. Host responses to Stx and bacterial lipopolysaccharide (LPS) are compared as related to the features of the STEC-associated Hemolytic Uremic Syndrome (HUS). Data derived from animal models of HUS and CNS disease, in vivo, and eukaryotic cells, in vitro, are evaluated in relation to HUS disease of humans.

Shiga toxin 2 targets the murine renal collecting duct epithelium

Hemolytic-uremic syndrome (HUS) caused by Shiga toxin-producing Escherichia coli infection is a leading cause of pediatric acute renal failure. Bacterial toxins produced in the gut enter the circulation and cause a systemic toxemia and targeted cell damage. It had been previously shown that injection of Shiga toxin 2 (Stx2) and lipopolysaccharide (LPS) caused signs and symptoms of HUS in mice, but the mechanism leading to renal failure remained uncharacterized. The current study elucidated that murine cells of the glomerular filtration barrier were unresponsive to Stx2 because they lacked the receptor glycosphingolipid globotriaosylceramide (Gb(3)) in vitro and in vivo. In contrast to the analogous human cells, Stx2 did not alter inflammatory kinase activity, cytokine release, or cell viability of the murine glomerular cells. However, murine renal cortical and medullary tubular cells expressed Gb(3) and responded to Stx2 by undergoing apoptosis. Stx2-induced loss of functioning collecting ducts in vivo caused production of increased dilute urine, resulted in dehydration, and contributed to renal failure. Stx2-mediated renal dysfunction was ameliorated by administration of the nonselective caspase inhibitor Q-VD-OPH in vivo. Stx2 therefore targets the murine collecting duct, and this Stx2-induced injury can be blocked by inhibitors of apoptosis in vivo.

Shiga toxin 1 causes direct renal injury in rats

Infection with Shiga toxin (Stx)-producing Escherichia coli has been implicated to cause hemolytic uremic syndrome, which is characterized by histological abnormalities such as microvascular thrombi and tubular cell damage in the kidney. Although Stx is known to be the major virulence factor of the pathogen, it is still unclear whether Stx directly impairs renal cells in vivo to cause such histological changes and deterioration of renal function. To assess the consequence of the direct action of Stx on renal cells, left kidneys of rats were perfused with Stx1 from the renal artery through the renal vein and then revascularized. Kidneys of control animals were perfused with the vehicle alone. On day 1, apoptosis and induction of tumor necrosis factor alpha gene expression were noticed to occur in the medulla of the Stx1-perfused kidneys. On day 3, extensive tubular injuries were observed by light microscopy: aggregated platelets and monocytic infiltrates in both glomeruli and the medullary interstitium were detected by immunostaining. Tubular changes were more extensive on day 9, with areas of infarction seen in the cortex and medulla. These changes were not found to occur in the sham-operated kidneys. No obvious glomerular changes were detected by light microscopy at any time point. When nonperfused right kidneys were removed after the Stx1 perfusion of the left kidneys, the serum creatinine and blood urea nitrogen levels were increased from day 2, and acute renal failure followed on day 3. These results indicate that Stx1 caused glomerular platelet aggregation, tubular damage, and acute deterioration of renal function by acting directly on renal cells.

The role of Shiga-toxin-producing Escherichia coli in hemorrhagic colitis and hemolytic uremic syndrome

The Shiga-toxin-producing E. coli represent a major class of pathogens that have been defined over the last twenty years. They cause distinctive clinical manifestations such as afebrile bloody diarrhea with severe abdominal pain (hemorrhagic colitis) and microangiopathic hemolytic anemia with renal failure (hemolytic uremic syndrome). The most common Shiga-toxin-producing E. coli is serotype O157:H7, although at least one hundred different serotypes share the virulence traits and clinical manifestations with this organism. Understanding the pathophysicology, improving diagnostic tools, and developing a treatment strategy are important areas of ongoing investigations.

Urinary concentrating defect in rats given Shiga toxin: elevation in urinary AQP2 level associated with polyuria

Shiga toxin (Stx) plays a central role in the etiology of hemolytic uremic syndrome (HUS) associated with Stx-producing Escherichia coli infection. The deposition of Stx2 in the renal collecting duct epithelial cells of rats administered Stx2 intravenously has been demonstrated by immunohistochemistry, and these rats were shown to develop substantial morphological changes in the kidney tubules, associated with polyuria. Severe polyuria was observed as an early event with no other obvious sequelae after Stx administration, in parallel with elevated urinary level of aquaporin 2 (AQP2) water channel protein that was determined by a sandwich EIA assay. Immunoblotting revealed that Stx treatment markedly induced an elevation in urinary AQP2 level and reduction in AQP2 protein in the renal plasma membranes. Elevated urinary AQP2 level was a more sensitive marker to assess Stx-induced renal tubular damage than urinary beta2-microglobulin or N-acetyl-beta-D-glucosaminidase in rats. Stx2 caused more severe renal tubular impairment than Stx1. Change in urinary AQP2 level by Stx1 and Stx2 at non-lethal doses of 40 ng/kg and 10 ng/kg, respectively, was reversed at 7 days in association with recovery of urinary concentrating ability, suggesting that there is a causative link.

Effect of Shiga toxin and Shiga-like toxins on eukaryotic cells

Shigella dysenteriae and Shiga-toxin-producing Escherichia coli (STEC) elaborate the AB holotoxins, Shiga or Shiga-like toxins (Stx). Stx play a major role in the pathogenesis of haemorrhagic colitis and haemolytic uremic syndrome. This review provides an overview of the mechanisms of action of Stx and a model of the pathogenesis of Stx-induced disease.

Tumor necrosis factor alpha increases human cerebral endothelial cell Gb3 and sensitivity to Shiga toxin

Hemolytic uremic syndrome (HUS) is associated with intestinal infection by enterohemorrhagic Escherichia coli strains that produce Shiga toxins. Globotriaosylceramide (Gb3) is the functional receptor for Shiga toxin, and tumor necrosis factor alpha (TNF-alpha) upregulates Gb3 in both human macrovascular umbilical vein endothelial cells and human microvascular brain endothelial cells. TNF-alpha treatment enhanced Shiga toxin binding and sensitivity to toxin. This upregulation was specific for Gb3 species containing normal fatty acids (NFA). Central nervous system (CNS) pathology in HUS could involve cytokine-stimulated elevation of endothelial NFA-Gb3 levels. Differential expression of Gb3 species may be a critical determinant of Shiga toxin toxicity and of CNS involvement in HUS.

Pathogenesis, treatment, and therapeutic trials in hemolytic uremic syndrome

Diarrhea-associated hemolytic uremic syndrome is one of the most common causes of acute renal failure in childhood. Nearly all cases are the result of an antecedent infection by Shiga toxin--producing strains of Escherichia coli, especially the O157:H7 serotype. Most cases occur after ingestion of contaminated meat; however, new food sources such as leaf lettuce, alfalfa sprouts, and goat's milk have been identified, and diarrhea-associated hemolytic uremic syndrome can occur after exposure to contaminated water in recreational swimming sites. Diarrhea-associated hemolytic uremic syndrome is a systemic disease with activation of a variety of inflammatory cytokines. Kidney injury may result from direct effects of the Shiga toxin on renal tubular epithelial cells as well as endothelial cells. Early diagnosis of diarrhea-associated hemolytic uremic syndrome may be expedited by the introduction of new techniques to rapidly detect toxin and microorganism in stool samples. Optimal therapy of diarrhea-associated hemolytic uremic syndrome includes intensive management of the renal failure and serious extrarenal complications that may occur during the course of disease. The role of antibiotics in prevention and amelioration of diarrhea-associated hemolytic uremic syndrome remains controversial. Experimental therapies that are undergoing evaluation in clinical trials include SYNSORB Pk (SYNSORB Biotech, Inc., Calgary, Alberta, Canada), a drug designed to bind Shiga toxin in the lumen of gastrointestinal tract. Immunization strategies are also being developed and tested. It is hoped that with continued progress in this field the incidence of diarrhea-associated hemolytic uremic syndrome in children will be substantially reduced in the coming years.

Pathogenesis and diagnosis of Shiga toxin-producing Escherichia coli infections

Since their initial recognition 20 years ago, Shiga toxin-producing Escherichia coli (STEC) strains have emerged as an important cause of serious human gastrointestinal disease, which may result in life-threatening complications such as hemolytic-uremic syndrome. Food-borne outbreaks of STEC disease appear to be increasing and, when mass-produced and mass-distributed foods are concerned, can involve large numbers of people. Development of therapeutic and preventative strategies to combat STEC disease requires a thorough understanding of the mechanisms by which STEC organisms colonize the human intestinal tract and cause local and systemic pathological changes. While our knowledge remains incomplete, recent studies have improved our understanding of these processes, particularly the complex interaction between Shiga toxins and host cells, which is central to the pathogenesis of STEC disease. In addition, several putative accessory virulence factors have been identified and partly characterized. The capacity to limit the scale and severity of STEC disease is also dependent upon rapid and sensitive diagnostic procedures for analysis of human samples and suspect vehicles. The increased application of advanced molecular technologies in clinical laboratories has significantly improved our capacity to diagnose STEC infection early in the course of disease and to detect low levels of environmental contamination. This, in turn, has created a potential window of opportunity for future therapeutic intervention.