Hemolytic uremic syndrome

cblE-Type Homocystinuria Presenting with Features of Haemolytic-Uremic Syndrome in the Newborn Period

This study describes a cblE type of homocystinuria associated with haemolytic-uremic syndrome (HUS) features. We report on a male infant aged 43 days presenting with failure to thrive, hypotonia, pancytopaenia, HUS symptoms (microangiopathic haemolytic anaemia and thrombocytopaenia with signs of renal involvement) and fatal evolution. An underlying cobalamin disorder was diagnosed after a bone marrow examination revealed megaloblastic changes associated with hyperhomocysteinaemia. An urinary organic acid analysis revealed normal methylmalonic acid excretion. The cblE diagnosis was confirmed with a complementation analysis using skin fibroblasts and genetic studies of the MTRR gene. The patient treatment included parenteral hydroxocobalamin, carnitine, betaine and folinic acid, but there was no response. After the autopsy, the histopathological examination of the kidneys showed marked myointimal proliferation and narrowing of the vascular lumen. The central nervous system showed signs of haemorrhage that affected the putamen and the thalamus; diffuse white matter lesions with spongiosis, necrosis and severe astrogliosis were also observed. Microangiopathy was observed with an increase in vessel wall thickness, a reduction of the arterial inner diameter and capillary oedema. The signs of necrosis and haemorrhage were detected in the cerebellum, the cerebellar peduncles, the tegmentum and the bulbar olives.In conclusion, cblE should be considered when diagnosing patients presenting with HUS signs and symptoms during the newborn period. Despite early diagnosis, however, the specific treatment measures were not effective in this patient.

Shigatoxin-associated hemolytic uremic syndrome: current molecular mechanisms and future therapies

Hemolytic uremic syndrome is the leading cause of acute kidney injury in childhood. Ninety percent of cases are secondary to gastrointestinal infection with shigatoxin-producing bacteria. In this review, we discuss the molecular mechanisms of shigatoxin leading to hemolytic uremic syndrome and the emerging role of the complement system and vascular endothelial growth factor in its pathogenesis. We also review the evidence for treatment options to date, in particular antibiotics, plasma exchange, and immunoadsorption, and link this to the molecular pathology. Finally, we discuss future avenues of treatment, including shigatoxin-binding agents and complement inhibitors, such as eculizumab.

Hemolytic non-uremic syndrome

We describe three children who developed isolated but severe microangiopathic hemolytic anemia without other manifestations of hemolytic uremic syndrome (HUS) or thrombotic thrombocytopenic purpura (TTP). All three recovered without specific treatment. We propose that they represent a unique phenotype in the spectrum of TTP and HUS, which we term "hemolytic non-uremic syndrome."

A new era in the diagnosis and treatment of atypical haemolytic uraemic syndrome

The haemolytic uraemic syndrome (HUS) is characterised by haemolytic anaemia, thrombocytopenia and acute renal failure. The majority of cases are seen in childhood and are preceded by an infection with Shiga-like toxin producing Escherichia coli (STEC-HUS; so-called typical HUS). Non-STEC or atypical HUS (aHUS) is seen in 5 to 10% of all cases and occurs at all ages. These patients have a poorer outcome and prognosis than patients with STEC-HUS. New insights into the pathogenesis of aHUS were revealed by the identification of mutations in genes encoding proteins of the alternative pathway of the complement system in aHUS patients. Specific information of the causative mutation is important for individualised patient care with respect to choice and efficacy of therapy, the outcome of renal transplantation, and the selection of living donors. This new knowledge about the aetiology of the disease has stimulated the development of more specific treatment modalities. Until now, plasma therapy was used with limited success in aHUS, but recent clinical trials have demonstrated that patients with aHUS can be effectively treated with complement inhibitors, such as the monoclonal anti-C5 inhibitor eculizumab.

Thrombotic microangiopathy and associated renal disorders

Thrombotic microangiopathy (TMA) is a pathological process involving thrombocytopenia, microangiopathic haemolytic anaemia and microvascular occlusion. TMA is common to haemolytic uraemic syndrome (HUS) associated with shiga toxin or invasive pneumococcal infection, atypical HUS (aHUS), thrombotic thrombocytopenic purpura (TTP) and other disorders including malignant hypertension. HUS complicating infection with shiga toxin-producing Escherichia coli (STEC) is a significant cause of acute renal failure in children worldwide, occurring sporadically or in epidemics. Studies in aHUS have revealed genetic and acquired factors leading to dysregulation of the alternative complement pathway. TTP has been linked to reduced activity of the ADAMTS13 cleaving protease (typically with an autoantibody to ADAMTS13) with consequent disruption of von Willebrand factor multimer processing. However, the convergence of pathogenic pathways and clinical overlap create diagnostic uncertainty, especially at initial presentation. Furthermore, recent developments are challenging established management protocols. This review addresses the current understanding of molecular mechanisms underlying TMA, relating these to clinical presentation with an emphasis on renal manifestations. A diagnostic and therapeutic approach is presented, based on international guidelines, disease registries and published trials. Early treatment remains largely empirical, consisting of plasma replacement/exchange with the exception of childhood STEC-HUS or pneumococcal sepsis. Emerging therapies such as the complement C5 inhibitor eculizumab for aHUS and rituximab for TTP are discussed, as is renal transplantation for those patients who become dialysis-dependent as a result of aHUS.

Shiga toxin in enterohemorrhagic E.coli: regulation and novel anti-virulence strategies

Enterohemorrhagic Escherichia coli (EHEC) are responsible for major outbreaks of bloody diarrhea and hemolytic uremic syndrome (HUS) throughout the world. The mortality associated with EHEC infections stems from the production and release of a potent Shiga toxin (Stx) by these bacteria. Stx induces cell death in endothelial cells, primarily in the urinary tract, causing HUS. Stx was first described in Shigella dysenteriae serotype I by Kiyoshi Shiga and was discovered later in EHEC. Multiple environmental cues regulate the expression of Stx, including temperature, growth phase, antibiotics, reactive oxygen species (ROS), and quorum sensing. Currently, there is no effective treatment or prophylaxis for HUS. Because antibiotics trigger Stx production and their use to treat EHEC infections is controversial, alternative therapeutic strategies have become the focus of intense research. One such strategy explores quorum sensing inhibitors as therapeutics. These inhibitors target quorum sensing regulation of Stx expression without interfering with bacterial growth, leading to the hypothesis that these inhibitors impose less selective pressure for bacteria to develop drug resistance. In this review, we discuss factors that regulate Stx production in EHEC, as well as novel strategies to prevent and/or minimize the development of HUS in infected subjects.

Combined effect of enterocin and lipase from Enterococcus faecium NCIM5363 against food borne pathogens: mode of action studies

Food borne diseases have a major impact on public health whose epidemiology is rapidly changing. The whole cells of pathogens involved or their toxins/metabolites affect the human health apart from spoiling sensory properties of the food products finally affecting the food industry as well as consumer health. With pathogens developing mechanisms of antibiotic resistance, there has been an increased need to replace antibiotics as well as chemical additives with naturally occurring bacteriocins. Bacteriocins are known to act mainly against Gram-positive pathogens and with little or no effect towards Gram-negative enteric bacteria. In the present study, combination effect of lipase and bacteriocin produced by Enterococcus faecium NCIM5363, a highly lipolytic lactic acid bacterium against various food pathogens was assessed. The lipase in combination with enterocin exhibited a lethal effect against Gram-negative pathogens. Scanning electron microscopy studies carried out to ascertain the constitutive mode of action of lipase and enterocin revealed that the lipase degrades the cell wall of Gram-negative bacteria and creates a pore through which enterocin enters thereby resulting in cell death. The novelty of this work is the fact that this is the first report revealing the synergistic effect of lipase with enterocin against Gram-negative bacteria.

Clinical grand rounds: atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is a rare, lifethreatening, chronic, genetic disease of uncontrolled alternative pathway complement activation. The understanding of the pathophysiology and genetics of this disease has expanded over recent decades and promising new developments in the management of aHUS have emerged. Regardless of the cause of aHUS, with or without a demonstrated mutation or autoantibody, blockade of terminal complement activation through C5 is of high interest as a mechanism to ameliorate the disease. Eculizumab, an existing monoclonal antibody directed against C5 with high affinity, prevents the perpetuation of the downstream activation of the complement cascade and the damage caused by generation of the anaphylotoxin C5a and the membrane attack complex C5b-9, by blocking C5 cleavage. We report the successful use of eculizumab in a patient after kidney transplantation and discuss the disease aHUS.

The interactions of human neutrophils with shiga toxins and related plant toxins: danger or safety?

Shiga toxins and ricin are well characterized similar toxins belonging to quite different biological kingdoms. Plant and bacteria have evolved the ability to produce these powerful toxins in parallel, while humans have evolved a defense system that recognizes molecular patterns common to foreign molecules through specific receptors expressed on the surface of the main actors of innate immunity, namely monocytes and neutrophils. The interactions between these toxins and neutrophils have been widely described and have stimulated intense debate. This paper is aimed at reviewing the topic, focusing particularly on implications for the pathogenesis and diagnosis of hemolytic uremic syndrome.

Complement in glomerular disease

The role of the complement system in renal disease has long been recognized, but there have been major advances in our understanding of its role over the past decade. Complement plays a critical role not only in host's defense against infection and preventing damage to "self" tissues but also mediates tissue injury, both in the glomerulus and tubulointerstitium. Although injury may originate in the glomerulus, resulting proteinuria and complement activation within the tubular lumen may lead to tubulointerstitial damage and progressive renal disease. Recent advances in our understanding of the mechanisms by which complement mediates renal injury have led to the development of promising strategies with which complement may be targeted to prevent renal injury and its associated complications.

Common variable immunodeficiency complicated with hemolytic uremic syndrome

Common variable immunodeficiency is a primary immunodeficiency disease characterized by reduced serum immunoglobulins and heterogeneous clinical features. Recurrent pyogenic infections of upper and lower respiratory tracts are the main clinical manifestations of common variable immunodeficiency. Hemolytic uremic syndrome is a multisystemic disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, and organ ischemia due to platelet aggregation in the arterial microvasculature. This is one of the rare cases of patients diagnosed with common variable immunodeficiency, which was complicated by hemolytic uremic syndrome.

Charged and hydrophobic surfaces on the a chain of shiga-like toxin 1 recognize the C-terminal domain of ribosomal stalk proteins

Shiga-like toxins are ribosome-inactivating proteins (RIP) produced by pathogenic E. coli strains that are responsible for hemorrhagic colitis and hemolytic uremic syndrome. The catalytic A(1) chain of Shiga-like toxin 1 (SLT-1), a representative RIP, first docks onto a conserved peptide SD[D/E]DMGFGLFD located at the C-terminus of all three eukaryotic ribosomal stalk proteins and halts protein synthesis through the depurination of an adenine base in the sarcin-ricin loop of 28S rRNA. Here, we report that the A(1) chain of SLT-1 rapidly binds to and dissociates from the C-terminal peptide with a monomeric dissociation constant of 13 µM. An alanine scan performed on the conserved peptide revealed that the SLT-1 A(1) chain interacts with the anionic tripeptide DDD and the hydrophobic tetrapeptide motif FGLF within its sequence. Based on these 2 peptide motifs, SLT-1 A(1) variants were generated that displayed decreased affinities for the stalk protein C-terminus and also correlated with reduced ribosome-inactivating activities in relation to the wild-type A(1) chain. The toxin-peptide interaction and subsequent toxicity were shown to be mediated by cationic and hydrophobic docking surfaces on the SLT-1 catalytic domain. These docking surfaces are located on the opposite face of the catalytic cleft and suggest that the docking of the A(1) chain to SDDDMGFGLFD may reorient its catalytic domain to face its RNA substrate. More importantly, both the delineated A(1) chain ribosomal docking surfaces and the ribosomal peptide itself represent a target and a scaffold, respectively, for the design of generic inhibitors to block the action of RIPs.

Indicators of acute and persistent renal damage in adult thrombotic microangiopathy

Background

Thrombotic microangiopathies (TMA) in adults such as thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are life-threatening disorders if untreated. Clinical presentation is highly variable and prognostic factors for clinical course and outcome are not well established.

Methods

We performed a retrospective observational study of 62 patients with TMA, 22 males and 40 females aged 16 to 76 years, treated with plasma exchange at one center to identify clinical risk factors for the development of renal insufficiency.

Results

On admission, 39 of 62 patients (63%) had acute renal failure (ARF) with 32 patients (52%) requiring dialysis treatment. High systolic arterial pressure (SAP, p = 0.009) or mean arterial pressure (MAP, p = 0.027) on admission was associated with acute renal failure. Patients with SAP>140 mmHg on admission had a sevenfold increased risk of severe kidney disease (OR 7.464, CI 2.097–26.565). MAP>100 mmHg indicated a fourfold increased risk for acute renal failure (OR 4.261, CI 1.400–12.972). High SAP, diastolic arterial pressure (DAP), and MAP on admission were also independent risk factors for persistent renal insufficiency with the strongest correlation for high MAP. Moreover, a high C-reactive protein (CRP) level on admission correlated with renal failure in the course of the disease (p = 0.003). At discharge, renal function in 11 of 39 patients (28%) had fully recovered, 14 patients (23%) remained on dialysis, and 14 patients (23%) had non-dialysis-dependent chronic kidney disease. Seven patients (11%) died. We identified an older age as risk factor for death.

Conclusions

High blood pressure as well as high CRP serum levels on admission are associated with renal insufficiency in TMA. High blood pressure on admission is also a strong predictor of sustained renal insufficiency. Thus, adult TMA patients with high blood pressure may require special attention to prevent persistent renal failure.

Novel C3 mutation p.Lys65Gln in aHUS affects complement factor H binding

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is associated with mutations affecting complement proteins and regulators and with autoantibodies against complement factor H (CFH). Approximately half of the aHUS patients progress to end-stage renal disease. DNA analysis of the risk factor genes is important for prognosis of aHUS recurrence after renal transplantation.

METHODS

Mutational screening of C3 encoding the central complement component was performed by Sanger sequencing in 70 aHUS patients. Mutated and wild type recombinant C3b proteins were produced and their affinity to CFH was analyzed by ELISA.

RESULTS

A single novel missense change p.Lys65Gln in C3 was found in 3 aHUS patients. The alteration leads to decreased binding of C3b to CFH in vitro. All three patients acquired the illness as adults and had a first aHUS episode after renal transplantation or suffered recurrence of the disease after transplantation.

CONCLUSIONS

The novel C3 change was found in 3 aHUS patients. It results in decreased C3b binding to CFH and thus might lead to impaired C3b inactivation in vivo. The p.Lys65Gln is likely to be associated with aHUS after kidney transplantation and, therefore, might be an important prognostic factor.

Manifestation of atypical hemolytic uremic syndrome caused by novel mutations in MCP

Atypical hemolytic uremic syndrome (aHUS) is a rare disease characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. Mutations in genes encoding regulators of the alternative complement pathway (CFH, MCP, C3, CFI, CFB, THBD, and CFHR1-5) are connected with this disease. Polymorphisms (SNPs) in these genes might also influence the manifestation of aHUS. We have analyzed the genes of CFH, CFI, MCP, and C3 in a cohort of 10 unrelated Czech patients with clinically diagnosed familial aHUS. Surprisingly, 4 patients had mutations only in MCP, without mutations in any of the other genes that cause aHUS. Mutations, as yet unpublished, were widely distributed over the gene (SCR2 domain, signal peptide, and cytoplasmic region). The phenotype of the patients and their close relatives (14 individuals) was also investigated. Functional examination of MCP was also provided and proved lower expression on granulocytes in all mutations. Severity of disease varied, but onset was never earlier than 5 years of age. Penetrance of disease was 50% among carriers. We found that the severity and recurrence of the disease within families varied and might also be dependent on SNPs. Mutations in the MCP gene seems to be a common etiology of aHUS in Czech patients.

Streptococcus pneumoniae-associated hemolytic uremic syndrome in a splenectomized adult patient

A 62-year-old splenectomized woman was admitted because of upper respiratory tract symptoms, general fatigue, and purpura. Laboratory data demonstrated microangiopathic hemolytic anemia, thrombocytopenia, acute renal failure, and a positive Streptococcus pneumoniae (SP) urinary antigen test. A renal biopsy showed thrombotic microangiopathic changes. She was diagnosed with hemolytic uremic syndrome (HUS) secondary to SP infection. Methylprednisolone pulse therapy in addition to antibiotic therapy led to prompt improvement of her symptoms and laboratory abnormalities. This is the first adult case of SP-associated HUS successfully treated without hemodialysis. SP infection should be considered as a causative etiology in all splenectomized patients with HUS.

Chemokine receptor CCR1 disruption limits renal damage in a murine model of hemolytic uremic syndrome

Shiga toxin (Stx)-producing Escherichia coli is the main etiological agent that causes hemolytic uremic syndrome (HUS), a microangiopathic disease characterized by hemolytic anemia, thrombocytopenia, and acute renal failure. Although direct cytotoxic effects on endothelial cells by Stx are the primary pathogenic event, there is evidence that indicates the inflammatory response mediated by polymorphonuclear neutrophils and monocytes as the key event during HUS development. Because the chemokine receptor CCR1 participates in the pathogenesis of several renal diseases by orchestrating myeloid cell kidney infiltration, we specifically addressed the contribution of CCR1 in a murine model of HUS. We showed that Stx type 2-treated CCR1(-/-) mice have an increased survival rate associated with less functional and histological renal damage compared with control mice. Stx type 2-triggered neutrophilia and monocytosis and polymorphonuclear neutrophil and monocyte renal infiltration were significantly reduced and delayed in CCR1(-/-) mice compared with control mice. In addition, the increase of the inflammatory cytokines (tumor necrosis factor-α and IL-6) in plasma was delayed in CCR1(-/-) mice compared with control mice. These data demonstrate that CCR1 participates in cell recruitment to the kidney and amplification of the inflammatory response that contributes to HUS development. Blockade of CCR1 could be important to the design of future therapies to restrain the inflammatory response involved in the development of HUS.

Hemolytic-Uremic Syndrome in Uberlândia, MG, Brazil

Purpose. To analyze the epidemiological, clinical, and laboratory characteristics of hemolytic-uremic syndrome (HUS) in Uberlandia, MG, Brazil. Methods. A historical cohort study was performed encompassing a ten-year period from January 1994 to January 2004 in the Department of Pediatric Nephrology at a full-service hospital; demographic factors, triggering factors, time of hospitalization, supportive therapy, and disease progression were analyzed. Results. Twenty-seven children aged 5 to 99 months (median age of 14 months) were studied; 70.4% were male. Of the 27 patients, 77.8% were from urban areas and 18.5% were from rural areas. Eight of the patients (29.6%) were reported to drink raw milk, and clinical diarrhea was reported in 81.5% of cases. The most common signs and symptoms were fever and vomiting (85.1%), anuria (63.0%), seizure (33.0%), cardiac involvement (11.0%), and acute pulmonary edema (7.4%). Dialysis was performed on 20 patients (74%). The mean hospital stay was 24 days (range: 13 to 36 days). While monitoring the patients, 2 died (7.4%), 3 developed chronic kidney disease (11.0%), and 21 (77.8%) developed hypertension. Conclusion. Our results emphasize the possibility of diagnosing HUS as a cause of renal failure in childhood in both typical (postdiarrheal) and atypical forms and suggest that an investigation of the etiological agent should be made whenever possible.

Novel developments in thrombotic microangiopathies: is there a common link between hemolytic uremic syndrome and thrombotic thrombocytic purpura?

Thrombotic microangiopathies (TMA) represent a spectrum of related disorders associated with newly formed thrombi that block perfusion and thus affect the function of either renal or neurological organs and tissue. Recent years have seen a dramatic development in the field of TMA and for the two major forms hemolytic uremic syndrome (HUS) and thrombocytopenic purpura (TTP), new genetic causes and also autoimmune forms have been identified. This development indicates a similar pathophysiology and suggests that the two acute disorders are based on common principles. HUS is primarily a kidney disease and TTP also develops in the kidney and at neurological sites. In HUS thrombi formation is likely due to a deregulated complement activation and inappropriate platelet activity. In TTP thrombi formation occurs because of inappropriate processing of released multimers of von Willebrand Factor (vWF). Defining both the similarities and the unique features of each disorder will open up new ways and concepts that are relevant for diagnosis, for therapy, and for the prognostic outcome of kidney transplantations. Here we summarize the most relevant topics and timely issues that were presented and discussed at the 4th International Workshop on Thrombotic Microangiopathies held in Weimar in October 2009 (www.hus-ttp.de).

Scope and application of therapeutic apheresis: Experience from a tertiary care hospital in North India

BACKGROUND

We present here our experience with therapeutic apheresis (TA) performed for various indications, clinical response and complications in a tertiary care center over last 10 years.

STUDY DESIGN AND METHODS

Present study is a retrospective analysis of 492 TA procedures performed for 125 patients from January 2000 to December 2009. For each patient: age, gender, weight, clinical indication, pre-procedure hematological profile and ionized calcium levels were recorded. For every procedure following parameters were analyzed: type of venous access (central/peripheral), volume of blood and plasma processed, amount of anticoagulant used, procedure duration, blood flow rate, type of replacement fluid given, response to therapy and adverse reactions.

RESULTS

Of 492 TA procedures, 68.8% were performed for neurology, 20.8% hematology-oncology, 9.6% renal and 0.8% for rheumatology patients. Therapeutic plasma exchanges (n=464; 94.3%) and therapeutic cytapheresis (n=28; 6.7%) were performed in 113 and 12 patients, respectively. Majority of patients belonged to ASFA category I and II (n=124; 99.2%). The overall response rate was 84%, with encouraging response in TTP (100%), aHUS (81.8%) and in neurological disorders (88.4%). Adverse events were reported in 52.8% of patients in 14.83% of procedures.

CONCLUSION

Our results of TPE in neurological disorders and in atypical hemolytic uremic syndrome are encouraging and it is a cost effective alternative to IvIg in neurological disorders. Currently, there is a need for establishment of an Indian apheresis registry to understand the scenario of TA across the country and in the expansion of appropriate and applicable indications for TA in our setting.

Seasonal variation of HUS occurrence and VTEC infection in children with acute diarrhoea from Argentina

In order to study the seasonality of haemolytic uraemic syndrome (HUS) and verotoxigenic Escherichia coli (VTEC) infection in children, 437 patients under 6 years of age with acute diarrhoea were studied, 8% of whom progressed to HUS. VTEC was found in 10% of all of the stool samples analysed and seasonal occurrence of HUS (p < 0.01) was confirmed. VTEC infection was more prevalent in warm months, although the differences were not statistically significant. Moreover, a significant difference in the detection of O157:H7 serotype and in the vt profile between cold and warm months (autumn and winter; spring and summer, respectively) was established. The O157:H7 serotype was isolated more frequently during warm months. Moreover, a predominance of vt (2) was noted, which was partially replaced by the combination of vt (1) with vt (2) in the cold season. The results of this study indicate the seasonal variation of the disease and the presence of serotype O157:H7 and the vt types. They also reinforce the need to develop prevention programmes considering the seasonal pattern of the disease, which would generate an impact on public health. Control strategies of the pathogen in cattle in the most risky season of the year would also be of benefit.

Atypical hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is defined by the triad of mechanical hemolytic anemia, thrombocytopenia and renal impairment. Atypical HUS (aHUS) defines non Shiga-toxin-HUS and even if some authors include secondary aHUS due to Streptococcus pneumoniae or other causes, aHUS designates a primary disease due to a disorder in complement alternative pathway regulation. Atypical HUS represents 5 -10% of HUS in children, but the majority of HUS in adults. The incidence of complement-aHUS is not known precisely. However, more than 1000 aHUS patients investigated for complement abnormalities have been reported. Onset is from the neonatal period to the adult age. Most patients present with hemolytic anemia, thrombocytopenia and renal failure and 20% have extra renal manifestations. Two to 10% die and one third progress to end-stage renal failure at first episode. Half of patients have relapses. Mutations in the genes encoding complement regulatory proteins factor H, membrane cofactor protein (MCP), factor I or thrombomodulin have been demonstrated in 20-30%, 5-15%, 4-10% and 3-5% of patients respectively, and mutations in the genes of C3 convertase proteins, C3 and factor B, in 2-10% and 1-4%. In addition, 6-10% of patients have anti-factor H antibodies. Diagnosis of aHUS relies on 1) No associated disease 2) No criteria for Shigatoxin-HUS (stool culture and PCR for Shiga-toxins; serology for anti-lipopolysaccharides antibodies) 3) No criteria for thrombotic thrombocytopenic purpura (serum ADAMTS 13 activity > 10%). Investigation of the complement system is required (C3, C4, factor H and factor I plasma concentration, MCP expression on leukocytes and anti-factor H antibodies; genetic screening to identify risk factors). The disease is familial in approximately 20% of pedigrees, with an autosomal recessive or dominant mode of transmission. As penetrance of the disease is 50%, genetic counseling is difficult. Plasmatherapy has been first line treatment until presently, without unquestionable demonstration of efficiency. There is a high risk of post-transplant recurrence, except in MCP-HUS. Case reports and two phase II trials show an impressive efficacy of the complement C5 blocker eculizumab, suggesting it will be the next standard of care. Except for patients treated by intensive plasmatherapy or eculizumab, the worst prognosis is in factor H-HUS, as mortality can reach 20% and 50% of survivors do not recover renal function. Half of factor I-HUS progress to end-stage renal failure. Conversely, most patients with MCP-HUS have preserved renal function. Anti-factor H antibodies-HUS has favourable outcome if treated early.

Atypical hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is defined by the triad of mechanical hemolytic anemia, thrombocytopenia and renal impairment. Atypical HUS (aHUS) defines non Shiga-toxin-HUS and even if some authors include secondary aHUS due to Streptococcus pneumoniae or other causes, aHUS designates a primary disease due to a disorder in complement alternative pathway regulation. Atypical HUS represents 5 -10% of HUS in children, but the majority of HUS in adults. The incidence of complement-aHUS is not known precisely. However, more than 1000 aHUS patients investigated for complement abnormalities have been reported. Onset is from the neonatal period to the adult age. Most patients present with hemolytic anemia, thrombocytopenia and renal failure and 20% have extra renal manifestations. Two to 10% die and one third progress to end-stage renal failure at first episode. Half of patients have relapses. Mutations in the genes encoding complement regulatory proteins factor H, membrane cofactor protein (MCP), factor I or thrombomodulin have been demonstrated in 20-30%, 5-15%, 4-10% and 3-5% of patients respectively, and mutations in the genes of C3 convertase proteins, C3 and factor B, in 2-10% and 1-4%. In addition, 6-10% of patients have anti-factor H antibodies. Diagnosis of aHUS relies on 1) No associated disease 2) No criteria for Shigatoxin-HUS (stool culture and PCR for Shiga-toxins; serology for anti-lipopolysaccharides antibodies) 3) No criteria for thrombotic thrombocytopenic purpura (serum ADAMTS 13 activity > 10%). Investigation of the complement system is required (C3, C4, factor H and factor I plasma concentration, MCP expression on leukocytes and anti-factor H antibodies; genetic screening to identify risk factors). The disease is familial in approximately 20% of pedigrees, with an autosomal recessive or dominant mode of transmission. As penetrance of the disease is 50%, genetic counseling is difficult. Plasmatherapy has been first line treatment until presently, without unquestionable demonstration of efficiency. There is a high risk of post-transplant recurrence, except in MCP-HUS. Case reports and two phase II trials show an impressive efficacy of the complement C5 blocker eculizumab, suggesting it will be the next standard of care. Except for patients treated by intensive plasmatherapy or eculizumab, the worst prognosis is in factor H-HUS, as mortality can reach 20% and 50% of survivors do not recover renal function. Half of factor I-HUS progress to end-stage renal failure. Conversely, most patients with MCP-HUS have preserved renal function. Anti-factor H antibodies-HUS has favourable outcome if treated early.

Hemolytic uremic syndrome: new developments in pathogenesis and treatment

Hemolytic uremic syndrome is defined by the characteristic triad of microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. In children, most cases of HUS are caused by Shiga-toxin-producing bacteria, especially Escherichia coli O157:H7. Common vehicles of transmission include ground beef, unpasteurized milk, and municipal or swimming water. Shiga-toxin-associated HUS is a main cause of acute renal failure in young children. Management remains supportive as there is at present no specific therapy to ameliorate the prognosis. Immediate outcome is most often favourable but long-term renal sequelae are frequent due to nephron loss. Atypical HUS represents 5% of cases. In the past 15 years, mutations in complement regulators of the alternative pathway have been identified in almost 60% of cases, leading to excessive complement activation. The disease has a relapsing course and more than half of the patients either die or progress to end-stage renal failure. Recurrence after renal transplantation is frequent.

Clinical aspects of a nationwide epidemic of severe haemolytic uremic syndrome (HUS) in children

BACKGROUND

Report a nationwide epidemic of Shiga toxin-producing E. coli (STEC) O103:H25 causing hemolytic uremic syndrome (D+HUS) in children.

METHODS

Description of clinical presentation, complications and outcome in a nationwide outbreak.

RESULTS

Ten children (median age 4.3 years) developed HUS during the outbreak. One of these was presumed to be a part of the outbreak without microbiological proof. Eight of the patients were oligoanuric and in need of dialysis. Median need for dialysis was 15 days; one girl did not regain renal function and received a kidney transplant. Four patients had seizures and/or reduced consciousness. Cerebral oedema and herniation caused the death of a 4-year-old boy. Two patients developed necrosis of colon with perforation and one of them developed non-autoimmune diabetes.

CONCLUSION

This outbreak of STEC was characterized by a high incidence of HUS among the infected children, and many developed severe renal disease and extrarenal complications. A likely explanation is that the O103:H25 (eae and stx2-positive) strain was highly pathogen, and we suggest that this serotype should be looked for in patients with HUS caused by STEC, especially in severe forms or outbreaks.

Alternative pathway activation of complement by Shiga toxin promotes exuberant C3a formation that triggers microvascular thrombosis

Shiga toxin (Stx)-producing E.coli O157:H7 has become a global threat to public health; it is a primary cause of diarrhea-associated hemolytic uremic syndrome (HUS), a disorder of thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure with thrombi occluding renal microcirculation. In this study, we explored whether Stx triggers complement-dependent microvascular thrombosis in in vitro and in vivo experimental settings of HUS. Stx induced on human microvascular endothelial cell surface the expression of P-selectin, which bound and activated C3 via the alternative pathway, leading to thrombus formation under flow. In the search for mechanisms linking complement activation and thrombosis, we found that exuberant complement activation in response to Stx generated an increased amount of C3a that caused further endothelial P-selectin expression, thrombomodulin (TM) loss, and thrombus formation. In a murine model of HUS obtained by coinjection of Stx2 and LPS and characterized by thrombocytopenia and renal dysfunction, upregulation of glomerular endothelial P-selectin was associated with C3 and fibrin(ogen) deposits, platelet clumps, and reduced TM expression. Treatment with anti-P-selectin Ab limited glomerular C3 accumulation. Factor B-deficient mice after Stx2/LPS exhibited less thrombocytopenia and were protected against glomerular abnormalities and renal function impairment, indicating the involvement of complement activation via the alternative pathway in the glomerular thrombotic process in HUS mice. The functional role of C3a was documented by data showing that glomerular fibrin(ogen), platelet clumps, and TM loss were markedly decreased in HUS mice receiving C3aR antagonist. These results identify Stx-induced complement activation, via P-selectin, as a key mechanism of C3a-dependent microvascular thrombosis in diarrhea-associated HUS.

Clinical relevance of shiga toxin concentrations in the blood of patients with hemolytic uremic syndrome

BACKGROUND

Intestinal infections with Shiga toxin-producing Escherichia coli (STEC) in children can lead to the hemolytic uremic syndrome (HUS). Shiga toxins (Stx) released in the gut by bacteria enter the blood stream and target the kidney causing endothelial injury. Free toxins have never been detected in the blood of HUS patients, but they have been found on the surface of polymorphonuclear leukocytes (PMN).

METHODS

With respect to their clinical features, the clinical relevance of the amounts of serum Stx (cytotoxicity assay with human endothelial cells) and PMN-bound Stx (cytofluorimetric assay) in 46 patients with STEC-associated HUS was evaluated.

RESULTS

Stx-positive PMN were found in 60% of patients, whereas negligible amounts of free Stx were detected in the sera. Patients with high amounts of Stx on PMN showed preserved or slightly impaired renal function (incomplete form of HUS), whereas cases with low amounts of Stx usually presented evidence of acute renal failure.

CONCLUSIONS

These observations suggest that the extent of renal damage in children with STEC-associated HUS could depend on the concentration of Stx present on their PMN and presumably delivered by them to the kidney. As previously shown by experimental models from our laboratory, high amounts of Stx could induce a reduced release of cytokines by the renal endothelium, with a consequent lower degree of inflammation. Conversely, low toxin amounts can trigger the cytokine cascade, provoking inflammation, thereby leading to tissue damage.

Factors associated with sporadic verotoxigenic Escherichia coli infection in children with diarrhea from the Central Eastern Area of Argentina

Verotoxigenic Escherichia coli (VTEC) are one of the most important emerging foodborne pathogens and the principal cause of hemolytic uremic syndrome (HUS). This entity has been recognized worldwide as a priority issue in the field of zoonoses and public health, and Argentina is the country with the highest incidence of HUS in children less than 5 years of age.The lack of specific treatment, combined with the high morbidity rate of VTEC infection, makes prevention the main tool for reducing the incidence of HUS. The current work aimed at assessing the factors associated with sporadic VTEC infection in children with acute diarrhea from the Central Eastern area of Argentina where the incidence rate of HUS in children under 5 is the highest worldwide. A univariate analysis was performed to identify potential factors associated with VTEC infection by calculating odds ratios (OR) with 95% confidence intervals (CI). Then, a multivariate logistic regression model was performed. Interaction and association between significant factors were checked. "Recent consumption of food prepared outside home" (OR: 2.4, 95% CI 1.05-5.7) and "recent vegetables consumption" (OR=0.4; 0.2-0.8) were identified as independent factors associated with VTEC infection. We believe that the data obtained from this study further the current knowledge about the epidemiology of VTEC infection in Argentina and could be considered when planning strategies for the prevention of the disease.

Marasmius oreades agglutinin (MOA) is a chimerolectin with proteolytic activity

The Marasmius oreades mushroom lectin (MOA) is well known for its exquisite binding specificity for blood group B antigens. In addition to its N-terminal carbohydrate-binding domain, MOA possesses a C-terminal domain with unknown function, which structurally resembles hydrolytic enzymes. Here we show that MOA indeed has catalytic activity. It is a calcium-dependent cysteine protease resembling papain-like cysteine proteases, with Cys215 being the catalytic nucleophile. The possible importance of MOA's proteolytic activity for mushroom defense against pathogens is discussed.

Postoperative thrombotic thrombocytopenic purpura in an infant: case report and literature review

Thrombotic thrombocytopenic purpura is caused by an imbalance of von Willebrand factor and its cleaving protease, which leads to the formation of microthrombi in end-organs. It rarely occurs in the pediatric population. Plasma exchange can significantly reduce mortality and morbidity. We present a 14-month-old infant in whom clinical and laboratory abnormalities compatible with thrombotic thrombocytopenic purpura were noted several days after resection of a large pelvic tumor. Treatment with double volume plasma exchange on postoperative day 5 led to complete resolution of the renal failure, thrombocytopenia, anemia, and neurological manifestations. ADAMTS13 inhibitors were negative and no mutations were found in factor H, factor I, membrane cofactor protein, and thrombomodulin to account for genetic predisposition to thrombotic thrombocytopenic purpura or atypical hemolytic uremic syndrome. Postoperative anemia, thrombocytopenia, fever, and neurological deficits in children should raise the suspicion of thrombotic thrombocytopenic purpura. Early diagnosis is important because the disorder is readily and efficiently treated with plasma exchange.

Production of biologically active recombinant human factor H in Physcomitrella

The human complement regulatory serum protein factor H (FH) is a promising future biopharmaceutical. Defects in the gene encoding FH are associated with human diseases like severe kidney and retinal disorders in the form of atypical haemolytic uremic syndrome (aHUS), membranoproliferative glomerulonephritis II (MPGN II) or age-related macular degeneration (AMD). There is a current need to apply intact full-length FH for the therapy of patients with congenital or acquired defects of this protein. Application of purified or recombinant FH (rFH) to these patients is an important and promising approach for the treatment of these diseases. However, neither protein purified from plasma of healthy individuals nor recombinant protein is currently available on the market. Here, we report the first stable expression of the full-length human FH cDNA and the subsequent production of this glycoprotein in a plant system. The moss Physcomitrella patens perfectly suits the requirements for the production of complex biopharmaceuticals as this eukaryotic system not only offers an outstanding genetical accessibility, but moreover, proteins can be produced safely in scalable photobioreactors without the need for animal-derived medium compounds. Transgenic moss lines were created, which express the human FH cDNA and target the recombinant protein to the culture supernatant via a moss-derived secretion signal. Correct processing of the signal peptide and integrity of the moss-produced rFH were verified via peptide mapping by mass spectrometry. Ultimately, we show that the rFH displays complement regulatory activity comparable to FH purified from plasma.

[Atypical hemolytic-uremic syndrome related to abnormalities within the complement system]

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy (TMA) disorder characterised by the association of haemolytic anaemia, thrombocytopenia and acute renal failure. Atypical forms (non-shigatoxin related forms) may be familial or sporadic, frequently with relapses and most of them lead to end stage renal failure. During the last years, different groups have demonstrated genetic predisposition to atypical HUS (aHUS) involving five genes encoding for complement components which play a role in the activation or control of the alternative pathway: encoding factor H (CFH), accounting for 30% of aHUS; CD46 (encoding membrane cofactor protein [MCP]) accounting for approximately 10% of aHUS; CFI (encoding factor I) accounting for an estimated 5-15% of patients; C3 (encoding C3) accounting for approximately 10% of aHUS; and rarely CFB (encoding factor B). Predisposition to aHUS is inherited with incomplete penetrance. It is admitted that mutations confer a predisposition to develop aHUS rather than directly causing the disease and that a second event (genetic or environmental) is required for disease manifestation. HUS onset follows a triggering event in most cases (frequently banal seasonal infection and pregnancy). Uncontrolled C3 convertase leads to increased deposition of C3b on vascular endothelium and participates to the prothrombotic state. The phenotype of aHUS is variable ranging from mild forms, with complete recovery of renal function to severe forms with end stage renal disease within the first year after the onset. Overall, the outcome is severe with a mortality rate of 10% and with more than 60% of patients on dialysis. The most severe prognosis was in the CFH mutation group. There is a high risk of recurrence of the disease after renal transplantation in patients with mutations in CFH, CFI, CFB and C3. Plasma therapy may allow complete haematological remission but frequently with persistent renal damage. Some patients are plasma resistant and some are plasma dependent. The recent progress in the determination of the susceptibility factors for aHUS, have allowed to propose new diagnostic tests including a molecular genetic testing and may permit to consider some new specific treatments in this disease (human plasma-derived CFH or complement inhibitors).

Pandemic H1N1 influenza A infection and (atypical) HUS--more than just another trigger?

Atypical hemolytic uremic syndrome (aHUS) is caused by mutations resulting in an exceedingly active alternative complement pathway. While today more than half a dozen genes are involved in aHUS pathology, only about 50% of carriers precipitate the disease. The reason for this phenomenon remains unclear, and triggering events like intercurrent infections have been postulated. In this context, reports on the development of (a)HUS in patients concomitantly diagnosed with pandemic H1N1 influenza A (pH1N1) infection are of great interest. They establish--for the first time in the literature--the link between aHUS and pH1N1 infection. While illnesses associated with pH1N1 infections during the recent pandemics were generally mild, secondary bacterial infections (e.g. Streptococcus pneumoniae) are known in patients with influenza A infections to not only aggravate the disease course, but also serve as a possible HUS trigger. Assuming pH1N1 was the cause of HUS in the cases reported here, it remains an interesting but unanswered hypothesis whether an underlying complement defect served as a susceptibility factor, at least in a subgroup of patients. In the future, pH1N1, but also pH1N1-associated, bacterial infections will have to be considered in (a)HUS patients, and further studies will be required to examine the role of the complement system in this condition.

Shiga toxin 1 and ricin A chain bind to human polymorphonuclear leucocytes through a common receptor

The main cause of acute renal failure in children is HUS (haemolytic uraemic syndrome), a consequence of intestinal infections with Escherichia coli strains producing Stx (Shiga toxins). Stx released in the gut by the non-invasive bacteria reach the bloodstream and are targeted to cerebral and renal endothelium triggering HUS. PMN (polymorphonuclear leucocytes) seem to be involved in Stx delivery through an unidentified membrane receptor (Kd=10⁻⁸ M; 2×10⁵ binding sites) which does not allow internalization. Some experts in the field have defined the Stx-PMN interaction as non-specific and of little biological significance. In the present study, we show that the A chain of ricin, the well-known plant RIP (ribosome-inactivating protein), interacts with PMN (Kd=10⁻⁹ M; 2×10⁵ binding sites) competing for the same receptor that recognizes Stx, whereas diphtheria toxin and several agonists of TLRs (Toll-like receptors) or the mannose receptor were ineffective. No toxic effects of ricin A chain on PMN were observed, as assessed by measuring protein synthesis and the rate of spontaneous apoptosis of leucocytes. Moreover, two single-chain RIPs (gelonin and saporin S6) had the same competing effect. Thus RIPs and Stx1 share structural similarities, the same enzymatic activity and a common receptor on PMN. These observations reveal that the Stx-PMN interaction is specific, confirming that PMN recognize molecular patterns common to different foreign molecules.

Regulation of nleA in Shiga toxin-producing Escherichia coli O84:H4 strain 4795/97

Many Shiga toxin-producing Escherichia coli (STEC) strains express a type III secretion system (TTSS) encoded by the locus of enterocyte effacement (LEE). Using the TTSS, STEC is able to inject effector proteins directly into eukaryotic host cells, where they cause characteristic attaching and effacing (A/E) lesions. In addition to the LEE-encoded effectors, a number of non-LEE-encoded effectors, located on phage-associated elements, have been described. One of them, the non-LEE-encoded effector A (NleA), is widely distributed among pathogenic E. coli. In this study, we investigated the influence of environmental conditions on the expression of the phage-encoded effector nleA gene (designated nleA(4795)) present in STEC O84:H4 strain 4795/97. We demonstrated that a particular NaCl concentration and starvation stress increase the activity of the nleA(4795) promoter. Moreover, several regulators that control nleA(4795) expression were identified. The involvement of the LEE regulators Ler, GrlA, and GrlR show that nleA(4795) is integrated in the LEE regulation circuit. Furthermore, the binding of Ler to sequences upstream of nleA(4795) underlined these findings.

Genetics and complement in atypical HUS

Central to the pathogenesis of atypical hemolytic uremic syndrome (aHUS) is over-activation of the alternative pathway of complement. Following the initial discovery of mutations in the complement regulatory protein, factor H, mutations have been described in factor I, membrane cofactor protein and thrombomodulin, which also result in decreased complement regulation. Autoantibodies to factor H have also been reported to impair complement regulation in aHUS. More recently, gain of function mutations in the complement components C3 and Factor B have been seen. This review focuses on the genetic causes of aHUS, their functional consequences, and clinical effect.

Shiga toxin-associated hemolytic uremic syndrome: pathophysiology of endothelial dysfunction

Shiga toxin (Stx)-producing enterohemorrhagic Escherichia coli O157:H7 has become a global threat to public health, as a primary cause of a worldwide spread of hemorrhagic colitis complicated by diarrhea-associated hemolytic uremic syndrome (HUS), a disorder of thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure that mainly affects early childhood. Endothelial dysfunction has been recognized as the trigger event in the development of microangiopathic processes. Endothelial cells, mainly those located in the renal microvasculature, are primary targets of the toxic effects of Stx1 and 2. Stxs bound to their specific globotriaosylceramide (Gb3Cer) receptor on the cell surface trigger a cascade of signaling events, involving NF-κB activation, that induce expression of genes encoding for adhesion molecules and chemokines, and culminate in the adhesion of leukocytes to endothelial cells, thereby increasing the endothelial susceptibility to leukocyte-mediated injury. Activated endothelial cells in response to Stxs lose the normal thromboresistance phenotype and become thrombogenic, initiating microvascular thrombus formation. Evidence is emerging that complement activation in response to Stxs favors platelet thrombus formation on endothelial cells, which may play a role in amplifying the inflammation-thrombosis circuit in Stx-associated HUS.

Escherichia coli O157

Escherichia coli O157 is an uncommon but serious cause of gastroenteritis. This bacterium is noteworthy because a few, but significant, number of infected people develop the haemolytic uraemic syndrome, which is the most frequent cause of acute renal failure in children in the Americas and Europe. Many infections of E coli O157 could be prevented by the more effective application of evidence-based methods, which is especially important because once an infection has been established, no therapeutic interventions are available to lessen the risk of the development of the haemolytic uraemic syndrome. This Review takes into account the evolution and geographical distibution of E coli O157 (and its close pathogenic relatives); the many and varied routes of transmission from its major natural hosts, ruminant farm animals; and other aspects of its epidemiology, its virulence factors, the diagnosis and management of infection and their complications, the repercussions of infection including costs, and prevention.

DEAP-HUS: deficiency of CFHR plasma proteins and autoantibody-positive form of hemolytic uremic syndrome

DEAP-HUS [Deficiency of CFHR (complement factor H-related) plasma proteins and Autoantibody Positive form of Hemolytic Uremic Syndrome] represents a novel subtype of hemolytic uremic syndrome (HUS) with unique characteristics. It affects children and requires special clinical attention in terms of diagnosis and therapy. DEAP-HUS and other atypical forms of HUS share common features, such as microangiopathic hemolytic anemia, acute renal failure, and thrombocytopenia. However, DEAP-HUS has the unique combination of an acquired factor in the form of autoantibodies to the complement inhibitor Factor H and a genetic factor which, in most cases, is the chromosomal deletion of a 84-kbp fragment within human chromosome 1 that results in the absence of the CFHR1 and CFHR3 proteins in plasma. Special attention is required to diagnose and treat DEAP-HUS patients. Most patients show a favorable response to the reduction of autoantibody titers by either plasma therapy, steroid treatment, and/or immunosuppression. In addition, in those DEAP-HUS patients with end-stage renal disease, the reduction of autoantibody titers prior to transplantation is expected to prevent post-transplant disease recurrence by aiming for full complement control at the endothelial cell surface in order to minimize adverse complement and immune reactions.

Lessons from functional and structural analyses of disease-associated genetic variants in the complement alternative pathway

Complement is an essential component of innate immunity and a major trigger of inflammatory responses. A critical step in complement activation is the formation of the C3 convertase of the alternative pathway (AP), a labile bimolecular complex formed by activated fragments of the C3 and factor B components that is fundamental to provide exponential amplification of the initial complement trigger. Regulation of the AP C3 convertase is essential to maintain complement homeostasis in plasma and to protect host cells and tissues from damage by complement. During the last decade, several studies have associated genetic variations in components and regulators of the AP C3 convertase with a number of chronic inflammatory diseases and susceptibility to infection. The functional characterization of these protein variants has helped to decipher the critical pathogenic mechanisms involved in some of these complement related disorders. In addition, these functional data together with recent 3D structures of the AP C3 convertase have provided fundamental insights into the assembly, activation and regulation of the AP C3 convertase.