Thrombotic microangiopathy, hemolytic uremic syndrome, and thrombotic thrombocytopenic purpura

Acute Progression of Adult-Onset Atypical Hemolytic-Uremic Syndrome due to CFH Mutation: A Case Report

Atypical hemolytic-uremic syndrome (aHUS), unlike typical HUS, is not due to bacteria but rather to an idiopathic or genetic cause that promotes dysregulation of the alternative complement pathway. It leads to hemolytic anemia, thrombocytopenia, and renal impairment. Although aHUS secondary to a genetic mutation is relatively rare, when occurring due to a mutation in Factor H (CFH), it usually presents with younger onset and has a more severe course, which in the majority ends with end-stage renal failure. Paradoxically to most available data, our case features acute aHUS due to a CFH mutation with late onset (38-year-old) and rapid progression to end-stage renal disease. Due to current data indicating a high risk of graft failure in such patients, the diagnosis of aHUS secondary to a genetic cause has disqualified our patient from a living (family) donor renal transplantation and left her with no other option but to begin permanent renal replacement therapy.

Catastrophic antiphospholipid antibody syndrome in a child with thrombotic microangiopathy

Thrombotic microangiopathic hemolytic anemia (TMHA) is not uncommon in clinical nephrology practice while antiphospholipid syndrome (APS) is uncommon. Although less than 1% of patients with APS develop catastrophic APS (CAPS), its potential lethal outcome because of thrombosis in multiple organs and subsequent multiorgan failure emphasizes its importance in nephrology practice. Here is a case of catastrophic APS in a 7-year-old girl, who presented to us with TMHA associated with antiphospholipid antibodies and subsequently died because of CAPS.

Cardiovascular disease after Escherichia coli O157:H7 gastroenteritis

BACKGROUND

Escherichia coli O157:H7 is one cause of acute bacterial gastroenteritis, which can be devastating in outbreak situations. We studied the risk of cardiovascular disease following such an outbreak in Walkerton, Ontario, in May 2000.

METHODS

In this community-based cohort study, we linked data from the Walkerton Health Study (2002-2008) to Ontario's large healthcare databases. We included 4 groups of adults: 3 groups of Walkerton participants (153 with severe gastroenteritis, 414 with mild gastroenteritis, 331 with no gastroenteritis) and a group of 11 263 residents from the surrounding communities that were unaffected by the outbreak. The primary outcome was a composite of death or first major cardiovascular event (admission to hospital for acute myocardial infarction, stroke or congestive heart failure, or evidence of associated procedures). The secondary outcome was first major cardiovascular event censored for death. Adults were followed for an average of 7.4 years.

RESULTS

During the study period, 1174 adults (9.7%) died or experienced a major cardiovascular event. Compared with residents of the surrounding communities, the risk of death or cardiovascular event was not elevated among Walkerton participants with severe or mild gastroenteritis (hazard ratio [HR] for severe gastroenteritis 0.74, 95% confidence interval [CI] 0.38-1.43, mild gastroenteritis HR 0.64, 95% CI 0.42-0.98). Compared with Walkerton participants who had no gastroenteritis, risk of death or cardiovascular event was not elevated among participants with severe or mild gastroenteritis.

INTERPRETATION

There was no increase in the risk of cardiovascular disease in the decade following acute infection during a major E. coli O157:H7 outbreak.

Endothelial cells and thrombotic microangiopathy

Thrombotic microangiopathy represents the clinical picture of thrombocytopenia and hemolytic anemia in the setting of small blood vessel thrombosis, accompanied by varying degrees of organ dysfunction. Well known to both nephrologists and hematologists alike, among the most common and best-studied thrombotic microangiopathy are hemolytic-uremic syndrome and thrombotic thrombocytopenic purpura. Despite sharing a strong clinical and historical relationship, these disorders represent distinct clinical and pathophysiological entities. This article reviews recent progress into the pathogenesis of thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome, focusing on events taking place at the endothelial surface.

Renal and neurological involvement in typical Shiga toxin-associated HUS

Shiga toxin-producing Escherichia coli-associated haemolytic uraemic syndrome (STEC-HUS) is one of the most important causes of acute kidney injury in patients of all ages, especially in children. It can occur sporadically or in outbreaks. STEC-HUS is a systemic illness caused by toxin-mediated injury to the vascular endothelium and a generalized inflammatory response. The kidney and the brain are the two primary target organs. Nearly 40% of patients with STEC-HUS require at least temporary renal replacement therapy and up to 20% will have permanent residual kidney dysfunction. Neurological injury can be sudden and severe and is the most frequent cause of acute mortality in patients with STEC-HUS. Over the past 30 years, a wide range of inflammatory mediators have been linked to the pathogenesis of STEC-HUS and associated renal and neurological complications. Recently, evidence has accumulated that abnormal activation of the alternative pathway of complement occurs in patients with STEC-HUS. In the large outbreak of STEC-HUS caused by E. coli O104:H4 that occurred in Germany in May 2011, a large number of patients received eculizumab, a monoclonal antibody directed against C5, in an open-label manner. We describe the experience with eculizumab under these emergent circumstances at one large centre.

STEC-HUS, atypical HUS and TTP are all diseases of complement activation

Haemolytic uraemic syndrome (HUS) and thrombotic thrombocytopaenic purpura (TTP) are diseases characterized by microvascular thrombosis, with consequent thrombocytopaenia, haemolytic anaemia and dysfunction of affected organs. Advances in our understanding of the molecular pathology led to the recognition of three different diseases: typical HUS caused by Shiga toxin-producing Escherichia coli (STEC-HUS); atypical HUS (aHUS), associated with genetic or acquired disorders of regulatory components of the complement system; and TTP that results from a deficiency of ADAMTS13, a plasma metalloprotease that cleaves von Willebrand factor. In this Review, we discuss data indicating that complement hyperactivation is a common pathogenetic effector that leads to endothelial damage and microvascular thrombosis in all three diseases. In STEC-HUS, the toxin triggers endothelial complement deposition through the upregulation of P-selectin and possibly interferes with the activity of complement regulatory molecules. In aHUS, mutations in the genes coding for complement components predispose to hyperactivation of the alternative pathway of complement. In TTP, severe ADAMTS13 deficiency leads to generation of massive platelet thrombi, which might contribute to complement activation. More importantly, evidence is emerging that pharmacological targeting of complement with the anti-C5 monoclonal antibody eculizumab can effectively treat not only aHUS for which it is indicated, but also STEC-HUS and TTP in some circumstances.

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.

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.

Shiga toxin 1 induces on lipopolysaccharide-treated astrocytes the release of tumor necrosis factor-alpha that alter brain-like endothelium integrity

The hemolytic uremic syndrome (HUS) is characterized by hemolytic anemia, thrombocytopenia and renal dysfunction. The typical form of HUS is generally associated with infections by Gram-negative Shiga toxin (Stx)-producing Escherichia coli (STEC). Endothelial dysfunction induced by Stx is central, but bacterial lipopolysaccharide (LPS) and neutrophils (PMN) contribute to the pathophysiology. Although renal failure is characteristic of this syndrome, neurological complications occur in severe cases and is usually associated with death. Impaired blood-brain barrier (BBB) is associated with damage to cerebral endothelial cells (ECs) that comprise the BBB. Astrocytes (ASTs) are inflammatory cells in the brain and determine the BBB function. ASTs are in close proximity to ECs, hence the study of the effects of Stx1 and LPS on ASTs, and the influence of their response on ECs is essential. We have previously demonstrated that Stx1 and LPS induced activation of rat ASTs and the release of inflammatory factors such as TNF-α, nitric oxide and chemokines. Here, we demonstrate that rat ASTs-derived factors alter permeability of ECs with brain properties (HUVECd); suggesting that functional properties of BBB could also be affected. Additionally, these factors activate HUVECd and render them into a proagregant state promoting PMN and platelets adhesion. Moreover, these effects were dependent on ASTs secreted-TNF-α. Stx1 and LPS-induced ASTs response could influence brain ECs integrity and BBB function once Stx and factors associated to the STEC infection reach the brain parenchyma and therefore contribute to the development of the neuropathology observed in HUS.

Hemolytic-uremic syndrome (HUS) is generally caused by Shiga toxin (Stx)-producing Escherichia coli but bacterial lipopolysaccharide (LPS) and neutrophils (PMN) contribute to the pathophysiology. Acute renal failure is the main feature of HUS, but in severe cases, patients develop neurological complications, which are usually associated with death. Although the mechanisms of neurological damage remain uncertain, alterations/injury of brain endothelial cells (ECs) which constitute the blood-brain barrier (BBB) is clear. Astrocytes (ASTs) are inflammatory cells enclosing ECs and are responsible of the normal function of the barrier. We have recently demonstrated that Stx1, one of the most common types of Stx, induce an inflammatory response in LPS-treated ASTs. We then study the effects of factors released by ASTs in response to LPS and/or Stx1 on brain-like ECs. We demonstrate that Stx1 induces in LPS-treated ASTs the release of factors that alter brain properties in ECs, including the permeability; turning them more susceptible to Stx1 toxic effects. Furthermore, they activate ECs, neutrophils (PMN) and platelets and render ECs into a proagregant state promoting PMN and platelet adhesion. Our results suggest that ASTs could influence brain ECs integrity and BBB function once Stx in combination with bacterial factors reach the brain parenchyma.

Thrombotic microangiopathy: a role for magnesium?

Despite advances in more recent years, the pathophysiology and especially treatment modalities of thrombotic microangiopathy (TMA) largely remain enigmatic. Disruption of endothelial homeostasis plays an essential role in TMA. Considering the proven causal association between magnesium and both endothelial function and platelet aggregability, we speculate that a magnesium deficit could influence the course of TMA and the related haemolytic uraemic syndrome and thrombotic thrombocytopenic purpura. A predisposition towards TMA is seen in many conditions with both extracellular and intracellular magnesium deficiency. We propose a rationale for magnesium supplementation in TMA, in analogy with its evidence-based therapeutic application in pre-eclampsia and suggest, based on theoretical grounds, that it might attenuate the development of TMA, minimise its severity and prevent its recurrence. This is based on several lines of evidence from both in vitro and in vivo data showing dose-dependent effects of magnesium supplementation on nitric oxide production, platelet aggregability and inflammation. Our hypothesis, which is further amenable to assessment in animal models before therapeutic applications in humans are implemented, could be explored both in vitro and in vivo to decipher the potential role of magnesium deficit in TMA and of the effects of its supplementation.

Atypical hemolytic uremic syndrome in children: complement mutations and clinical characteristics

BACKGROUND

Mutations in complement factor H (CFH), factor I (CFI), factor B (CFB), thrombomodulin (THBD), C3 and membrane cofactor protein (MCP), and autoantibodies against factor H (αFH) with or without a homozygous deletion in CFH-related protein 1 and 3 (∆CFHR1/3) predispose development of atypical hemolytic uremic syndrome (aHUS).

METHODS

Different mutations in genes encoding complement proteins in 45 pediatric aHUS patients were retrospectively linked with clinical features, treatment, and outcome.

RESULTS

In 47% of the study participants, potentially pathogenic genetic anomalies were found (5xCFH, 4xMCP, and 4xC3, 3xCFI, 2xCFB, 6xαFH, of which five had ∆CFHR1/3); four patients carried combined genetic defects or a mutation, together with αFH. In the majority (87%), disease onset was preceeded by a triggering event; in 25% of cases diarrhea was the presenting symptom. More than 50% had normal serum C3 levels at presentation. Relapses were seen in half of the patients, and there was renal graft failure in all except one case following transplant.

CONCLUSIONS

Performing adequate DNA analysis is essential for treatment and positive outcome in children with aHUS. The impact of intensive initial therapy and renal replacement therapy, as well as the high risk of recurrence of aHUS in renal transplant, warrants further understanding of the pathogenesis, which will lead to better treatment options.

Idiopathic combined, autoantibody-mediated ADAMTS-13/factor H deficiency in thrombotic thrombocytopenic purpura-hemolytic uremic syndrome in a 17-year-old woman: a case report

Introduction

Thrombotic thrombocytopenic purpura-hemolytic uremic syndrome is a life-threatening condition with various etiopathogeneses. Without therapy approximately 90% of all patients die from the disease.

Case presentation

We report the case of a 17-year-old Caucasian woman with widespread hematomas and headache. Due to hemolytic anemia, thrombocytopenia, and schistocytosis, thrombotic thrombocytopenic purpura-hemolytic uremic syndrome was suspected and plasma exchange therapy was initiated immediately. Since her thrombocyte level did not increase during the first week of therapy, plasma treatment had to be intensified to a twice-daily schedule. Further diagnostics showed markedly reduced activities of both ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 - also known as von Willebrand factor-cleaving protease) and factor H. Test results for antibodies against both proteins were positive. While plasma exchange therapy was continued, rituximab was given once weekly for four consecutive weeks. After the last dose, thrombocytes and activities of ADAMTS-13 and factor H increased into the normal range. Our patient improved and was discharged from the hospital.

Conclusions

Since no clinical symptoms/laboratory findings indicated a malignant or specific autoimmune-mediated disorder, the diagnosis made was thrombotic thrombocytopenic purpura-hemolytic uremic syndrome due to idiopathic combined, autoantibody-mediated ADAMTS-13/factor H deficiency.

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.

Management of an acute outbreak of diarrhoea-associated haemolytic uraemic syndrome with early plasma exchange in adults from southern Denmark: an observational study

BACKGROUND

Diarrhoea-associated haemolytic uraemic syndrome in adults is a life-threatening, but rare multisystem disorder that is characterised by acute haemolytic anaemia, thrombocytopenia, and renal insufficiency. We aimed to assess the success of management of this disorder with plasma exchange therapy.

METHODS

Patients diagnosed with diarrhoea-associated haemolytic uraemic syndrome in southern Denmark were treated with daily plasma exchange by centrifugation and substitution with fresh frozen plasma. Stool culture and serological testing was done to identify the cause of disease, and the success of management with plasma exchange therapy was assessed from change in platelet count, glomerular filtration rate, and lactate dehydrogenase.

FINDINGS

During May 25-28, 2011, five patients with a median age of 62 years (range 44-70) presented with diarrhoea-associated haemolytic uraemic syndrome, which was caused by an unusual Shiga-toxin-producing Escherichia coli serotype O104:H4. Strains of E coli showed a high resistance to third-generation cephalosporins because the strains had extended-spectrum β lactamases. After plasma exchange, median platelet count and glomerular filtration rate increased, median lactate dehydrogenase concentration decreased, and neurological status improved. The time interval from onset of bloody diarrhoea to start of plasma exchange had an inverse correlation with reduction of lactate dehydrogenase concentrations by plasma exchange (p=0.02). All patients were discharged with normal neurological status at 7 days (range 5-8) after starting plasma exchange.

INTERPRETATION

Early plasma exchange might ameliorate the course of diarrhoea-associated haemolytic uraemic syndrome in adults. However, this finding should be verified in randomised controlled trials

FUNDING

None.

Is complement a culprit in infection-induced forms of haemolytic uraemic syndrome?

Haemolytic uraemic syndrome (HUS) accounts for the most common cause of childhood acute renal failure. Characterized by the classical triad of a microangiopathic haemolytic anaemia, thrombocytopaenia and acute renal failure, HUS occurs as a result of Shiga-toxin producing microbes in 90% of cases. The remaining 10% of cases represent a heterogeneous subgroup in which inherited and acquired forms of complement dysregulation have been described in up to 60%. Emerging evidence suggests that microbes associated with HUS exhibit interaction with the complement system. With the advent of improved genetic diagnosis, it is likely that certain cases of infection-induced HUS may be attributed to underlying defects in complement components. This review summarises the interplay between complement and infection in the pathogenesis of HUS.

Transplant-associated thrombotic microangiopathy in pediatric patients treated with sirolimus and tacrolimus

BACKGROUND

Transplant-associated thrombotic microangiopathy (TMA) syndromes are reported to occur with increased frequency in transplant patients treated with siroliumus combined with a calcineurin inhibitor. We performed a retrospective study of all pediatric transplant patients at City of Hope who were administered combined tacrolimus/sirolimus (TAC/SIR) to determine the occurrence of TMA.

PROCEDURE

This analysis includes 41 consecutive patients between the ages of 2 and 20 (median age 9.1) who received an allogeneic hematopoietic stem cell transplant from any source and also received TAC/SIR for prevention or treatment of GVHD. Of those 41 patients, 20 received TAC/SIR as GVHD prohpylaxis and were designated the preventative group (PG), while 21 received TAC/SIR as treatment for GVHD and were designated the therapy group (TG). TMA occurrence in both groups was documented from day -1 of transplant to day 60 for the PG, and until 30 days after last dose for the TG. TMA was defined according to 2005 consensus criteria.

RESULTS

Five of twenty patients in the PG, and five of twenty one in the TG, experienced TMA, with an overall rate of 23.8% for the population. All ten patients with TMA showed elevated levels of TAC, SIR or both and nine of ten suffered from organ injury due to regimen-related toxicity or GVHD.

CONCLUSION

Physicians should exercise caution in the use of TAC/SIR in pediatric patients due to a high rate of TMA. It is not recommended for heavily pre-treated patients and peak levels of TAC/SIR must be very carefully controlled.

Advances in our understanding of the pathogenesis of glomerular thrombotic microangiopathy

Glomerular thrombotic microangiopathy is a hallmark feature of haemolytic uraemic syndrome, the leading cause of acute renal failure in childhood. This paper is a review of the different mechanistic pathways that lead to this histological picture in the kidney. It will focus on atypical HUS and complement dysregulation, but will also highlight some other recent advances in our understanding of this condition, including the potential role of the molecule vascular endothelial growth factor-A (VEGF-A).

Targeting von Willebrand factor and platelet glycoprotein Ib receptor

Atherothrombotic events, such as acute coronary syndrome or stroke, are the result of platelet activation. Von Willebrand factor (vWF), a multimeric glycoprotein, plays a key role in aggregation of platelets, especially under high-shear conditions. Acting as bridging element or ligand between damaged endothelial sites and the glycoprotein Ib (GPIb) receptor on platelets, vWF is responsible for platelet adhesion and aggregation. This vWF activation and further platelet aggregation mainly occurs under high shear stress present in small arterioles or during deficiency of the vWF-cleaving protease ADAMTS13. There are several substances targeting vWF itself or its binding receptor GPIb on platelets. Two antibodies are directed against vWF: AJW200, an IgG4 humanized monoclonal antibody, and 82D6A3, a monoclonal antibody of the collagen-binding A-3 domain of vWF. ALX-0081 and ALX-0681 are bivalent humanized nanobodies targeting the GPIb binding site of vWF. Aptamers are oligonucleotides with drug-like properties that share some of the attributes of monoclonal antibodies. ARC1779 is a second-generation, nuclease-resistant aptamer, binding to the activated vWF A1 domain and ARC15105 is a chemically advanced follower with an assumed higher affinity to vWF. Antibodies targeting GPIbα are h6B4-Fab, a murine monoclonal antibody; GPG-290, a recombinant, chimeric protein containing the amino-terminal 290 amino acids of GPIbα linked to human IgG1 Fc; and the monoclonal antibody SZ2. There are a number of promising preclinical results and development of some agents (AJW 200, ARC1779 and ALX-0081) has already reached Phase II trials.

Combination of everolimus with calcineurin inhibitor medication resulted in post-transplant haemolytic uraemic syndrome in lung transplant recipients--a case series

BACKGROUND

Post-transplant haemolytic uraemic syndrome (HUS) is a rare but serious disease with a high mortality rate, when left untreated. Immunosuppressive drugs like calcineurin inhibitors as well as mammalian target of rapamycin inhibitors have been reported as causative agents for post-transplant HUS.

METHODS

A retrospective observational study was performed in lung transplant recipients, who took part in an interventional study, in two centres. Haemoglobin, platelets, creatinine and lactate dehydrogenase levels were monitored during routine follow-up and patients with deteriorating kidney function were screened for post-transplant HUS. All cases of post-transplant HUS were identified by clinical and laboratory findings. Outcome was recorded until 6 months after diagnosis.

RESULTS

A total of 2188 visits in 512 lung transplant recipients (outpatients) were analysed. Out of those, 126 patients took part in an interventional study. In this study, 67 were switched to everolimus in combination with calcineurin inhibitors 4 weeks after transplantation, 59 patients remained on standard immunosuppression (calcineurin inhibitors, mycophenolate mofetil and prednisolone). Five cases of post-transplant HUS were identified in the everolimus group. None of the patients had evidence of gastrointestinal infection or preexisting renal disease. Post-transplant HUS was treated with therapeutic plasma exchange and methylprednisolone pulse therapy. Everolimus was discontinued in all five patients. This treatment regimen led to normalization of haemoglobin, platelets and improved renal function. Two patients developed end-stage renal failure and were maintained on haemodialysis. One patient died due to multiorgan failure. Improvement of renal function was seen in two patients. No further cases were recorded in patients without everolimus during the study period.

CONCLUSIONS

Our data should raise the awareness of post-transplant HUS in lung transplant recipients. Post-transplant HUS is a rare disease, but it is a serious cause of acute renal failure in lung transplant recipients treated with a combination of everolimus and calcineurin inhibitors.

Suspicious neuroimaging pattern of thrombotic microangiopathy

The TMAs are a group of microvascular occlusive disorders characterized by thrombocytopenia and intravascular hemolysis. Literature review reveals a spectrum of neuroimaging findings, including a single case report of multifocal hemorrhagic infarctions. We present a series of 12 patients with TMA demonstrating a similar pattern of multifocal cortical and subcortical hemorrhagic infarctions.

Thrombotic microangiopathy associated with tuberculous infection

A 32-year-old man was diagnosed as having thrombotic microangiopathy (TMA) and treated by plasma exchange (PE). During the course of admission, he was also newly diagnosed with pulmonary tuberculosis, tuberculous peritonitis and pleuritis, which was thought to be the cause of the TMA. There are only a few previous reports on TMA associated with tuberculous infection. Although its pathogenetic mechanism is not well understood, it would be valuable to recognize that this worldwide infectious disease could cause TMA.

Thrombotic microangiopathy presenting with a considerable accumulation of ascites: a case report

A 46-year-old man presented with fever, thrombocytopenia, and a considerable accumulation of ascites. Although prednisolone and intravenous cyclophosphamide pulse (IVCY) were effective, he experienced recurrence. Renal insufficiency and hemolytic anemia developed subsequently. Schistocytes, negative Coombs' test, and elevated lactate dehydrogenase levels indicated thrombotic microangiopathy (TMA). He recovered well after receiving plasma infusion, IVCY, and prednisolone. Renal biopsy revealed subendothelial widening, thereby confirming TMA. This is a very rare case of TMA that presented with a considerable volume of ascites.

The development of atypical hemolytic uremic syndrome depends on complement C5

Gene variants in the alternative pathway of the complement system strongly associate with atypical hemolytic uremic syndrome (aHUS), presumably by predisposing to increased complement activation within the kidney. Complement factor H (CFH) is the major regulator of complement activation through the alternative pathway. Factor H-deficient mice transgenically expressing a mutant CFH protein (Cfh(-/-).FHΔ16-20) that functionally mimics the CFH mutations reported in aHUS patients spontaneously develop thrombotic microangiopathy. To investigate the role of complement C5 activation in this aHUS model, we generated C5-deficient Cfh(-/-).FHΔ16-20 mice. Both C5-sufficient and C5-deficient Cfh(-/-).FHΔ16-20 mice had abnormal C3 deposition within the kidney, but spontaneous aHUS did not develop in any of the C5-deficient mice. Furthermore, although Cfh(-/-).FHΔ16-20 animals demonstrated marked hypersensitivity to experimentally triggered renal injury, animals with concomitant C5 deficiency did not. These data demonstrate a critical role for C5 activation in both spontaneous aHUS and experimentally triggered renal injury in animals with defective complement factor H function. This study provides a rationale to investigate therapeutic inhibition of C5 in human aHUS.

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.

Guidelines on the use of therapeutic apheresis in clinical practice--evidence-based approach from the Apheresis Applications Committee of the American Society for Apheresis

The American Society for Apheresis (ASFA) Apheresis Applications Committee is charged with a review and categorization of indications for therapeutic apheresis. Beginning with the 2007 ASFA Special Issue (fourth edition), the subcommittee has incorporated systematic review and evidence-based approach in the grading and categorization of indications. This Fifth ASFA Special Issue has further improved the process of using evidence-based medicine in the recommendations by refining the category definitions and by adding a grade of recommendation based on widely accepted GRADE system. The concept of a fact sheet was introduced in the Fourth edition and is only slightly modified in this current edition. The fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis. The article consists of 59 fact sheets devoted to each disease entity currently categorized by the ASFA as category I through III. Category IV indications are also listed.

Relative role of genetic complement abnormalities in sporadic and familial aHUS and their impact on clinical phenotype

BACKGROUND AND OBJECTIVES

Hemolytic uremic syndrome (HUS) is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. Most childhood cases are caused by Shiga toxin-producing bacteria. The other form, atypical HUS (aHUS), accounts for 10% of cases and has a poor prognosis. Genetic complement abnormalities have been found in aHUS.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

We screened 273 consecutive patients with aHUS for complement abnormalities and studied their role in predicting clinical phenotype and response to treatment. We compared mutation frequencies and localization and clinical outcome in familial (82) and sporadic (191) cases.

RESULTS

In >70% of sporadic and familial cases, gene mutations, disease-associated factor H (CFH) polymorphisms, or anti-CFH autoantibodies were found. Either mutations or CFH polymorphisms were also found in the majority of patients with secondary aHUS, suggesting a genetic predisposition. Familial cases showed a higher prevalence of mutations in SCR20 of CFH and more severe disease than sporadic cases. Patients with CFH or THBD (thrombomodulin) mutations had the earliest onset and highest mortality. Membrane-cofactor protein (MCP) mutations were associated with the best prognosis. Plasma therapy induced remission in 55 to 80% of episodes in patients with CFH, C3, or THBD mutations or autoantibodies, whereas patients with CFI (factor I) mutations were poor responders. aHUS recurred frequently after kidney transplantation except for patients with MCP mutations.

CONCLUSIONS

Results underline the need of genetic screening for all susceptibility factors as part of clinical management of aHUS and for identification of patients who could safely benefit from kidney transplant.

Thrombotic microangiopathy: new insights

PURPOSE OF REVIEW

In the following study new aspects and insights into the epidemiology, pathogenesis and typical morphology of kidney involvement in thrombotic microangiopathy (TMA) are discussed. TMA comprises a spectrum of microvascular thrombosis syndromes associated with multiple pathogenetic factors, that is, typical and atypical haemolytic uraemic syndrome (HUS), thrombotic thrombocytopenic purpura (TTP), malignant hypertension, drugs or systemic autoimmune diseases or antibody-mediated rejection.

RECENT FINDINGS

The present article will put particular emphasis on new pathophysiological insights into the development of TMA in the various settings. In addition, new options in the therapeutic management of TMA in atypical HUS are discussed. The pathogenesis of TMA in atypical HUS primarily involves hereditary or acquired deficiencies and disturbances of the complement system. Eculizumab is a promising new therapeutic option that has been discovered recently.

SUMMARY

In HUS/TTP the kidney shows characteristic vascular changes due to endothelial damage, that is, TMA, which should be clinically and morphologically differentiated from other diseases. Recent genetic and molecular studies have shed more light on the pathogenesis of TMA in atypical HUS, that is, disturbances of various aspects of the complement system, and in TTP, that is, von Willebrand factor regulation by ADAMTS13, which are also helpful in the differential diagnosis.

Non-O157 Shiga toxin-producing Escherichia coli in foods

Non-O157 Shiga toxin-producing Escherichia coli (STEC) strains have been linked to outbreaks and sporadic cases of illness worldwide. Illnesses linked to STEC serotypes other than O157:H7 appear to be on the rise in the United States and worldwide, indicating that some of these organisms may be emerging pathogens. As more laboratories are testing for these organisms in clinical samples, more cases are uncovered. Some cases of non-O157 STEC illness appear to be as severe as cases associated with O157, although in general cases attributed to non-O157 are less severe. There is much variation in virulence potential within STEC serotypes, and many may not be pathogenic. Of more than 400 serotypes isolated, fewer than 10 serotypes cause the majority of STEC-related human illnesses. Various virulence factors are involved in non-O157 STEC pathogenicity; the combined presence of both eae and stx genes has been associated with enhanced virulence. A scientific definition of a pathogenic STEC has not yet been accepted. Several laboratories have attempted to develop detection and identification methods, and although substantial progress has been made, a practical method of STEC detection has yet to be validated. Worldwide, foods associated with non-O157 STEC illness include sausage, ice cream, milk, and lettuce, among others. Results from several studies suggest that control measures for O157 may be effective for non-O157 STEC. More research is needed to uncover unique characteristics and resistances of non-O157 STEC strains if they exist. The public health significance of non-O157 STEC and the implications for industry practices and regulatory actions are discussed.

The complement inhibitors Crry and factor H are critical for preventing autologous complement activation on renal tubular epithelial cells

Congenital and acquired deficiencies of complement regulatory proteins are associated with pathologic complement activation in several renal diseases. To elucidate the mechanisms by which renal tubular epithelial cells (TECs) control the complement system, we examined the expression of complement regulatory proteins by the cells. We found that Crry is the only membrane-bound complement regulator expressed by murine TECs, and its expression is concentrated on the basolateral surface. Consistent with the polarized localization of Crry, less complement activation was observed when the basolateral surface of TECs was exposed to serum than when the apical surface was exposed. Furthermore, greater complement activation occurred when the basolateral surface of TECs from Crry(-/-)fB(-/-) mice was exposed to normal serum compared with TECs from wild-type mice. Complement activation on the apical and basolateral surfaces was also greater when factor H, an alternative pathway regulatory protein found in serum, was blocked from interacting with the cells. Finally, we injected Crry(-/-)fB(-/-) and Crry(+/+)fB(-/-) mice with purified factor B (an essential protein of the alternative pathway). Spontaneous complement activation was seen on the tubules of Crry(-/-)fB(-/-) mice after injection with factor B, and the mice developed acute tubular injury. These studies indicate that factor H and Crry regulate complement activation on the basolateral surface of TECs and that factor H regulates complement activation on the apical surface. However, congenital deficiency of Crry or reduced expression of the protein on the basolateral surface of injured cells permits spontaneous complement activation and tubular injury.

Atypical hemolytic uremic syndrome and mutation analysis of factor H gene in two Tunisian families

We carried out a protein and genetic investigation of the factor H gene mutations within two families presenting with a diagnostic suspicion of atypical hemolytic uremic syndrome (aHUS). The results within the patients of the first family revealed a factor H-deficiency. Direct sequencing allowed the detection of a 4-nucleotide deletion in the factor H gene. This deletion was found as the homozygote form in the proband and as the heterozygote form in the parents. Protein and functional analyses of the complement system were normal in all members of the second family. However, the molecular investigation for the father showed the presence of an amino acid substitution in the FH gene. Unfortunately, his two affected children died without being investigated for mutations. The functional consequences of these abnormal proteins are still to be demonstrated.

C3b and factor H: key components of the complement system

In all three complement pathways, the central molecule is C3, which, upon activation cleavage, forms the major opsonin C3b - the key component of complement. C3b is also essential for propagation of the complement cascade to the stage of the lytic terminal complement complexes. In order to prevent damage to self cells and tissues and restrict overconsumption of the complement components, C3b molecules need to be controlled by factor H. Defect in C3 functions leads to compromised microbial defence and increased susceptibility to certain autoimmune diseases. Deficiency of factor H, or a functional defect in its N terminus, often leads to membranoproliferative glomerulonephritis and complement depletion, owing to continuous overconsumption of C3. Defect in the factor H C terminus leads to a dramatically increased risk of atypical hemolytic uremic syndrome. In addition, recently, a polymorphism in the middle part of factor H (Y402H) has been shown to be the major risk factor for the most common cause of blindness in the industrialized world: age-related macular degeneration. In future, analysis of patient samples for defects in these key complement components may prove useful in diagnosis of these diseases and new therapeutic targets will certainly be the aim for use in the recently recognized factor H-related diseases.

Both domain 19 and domain 20 of factor H are involved in binding to complement C3b and C3d

Factor H (FH) regulates the alternative pathway of complement in plasma and mediates discrimination of cellular surfaces to alternative pathway activators and non-activators. The carboxyl-terminal domains 19 and 20 of FH are essential in target discrimination and are known to contain binding sites for the C3d part of C3b, heparin, and endothelial cells. Mutations in FH19-20 are frequently found in patients with atypical haemolytic uremic syndrome (aHUS). Most aHUS-associated and some other mutations have been shown to lead to impaired binding to C3d and C3b by the recombinant FH19-20 fragment. Most of these mutated residues, such as R1203, are located close to each other in domain 20 but some, such as Q1139, are located in domain 19. We generated mutant proteins Q1139A and R1203A of FH19-20 and showed that their binding to C3d and C3b was clearly impaired. To show that the effects on C3d/C3b binding are due to direct interactions rather than structural changes, we solved the X-ray crystal structures of the R1203A and Q1139A mutant proteins at 1.65 and 2.0A, respectively. Neither of the mutations caused any overall structural changes in FH19-20. It is thus evident that Q1139 in domain 19 and R1203 in domain 20 are directly involved in binding to the C3d part of C3b and therefore both the domains are involved in the interaction with C3d and C3b. This explains why several aHUS-associated FH mutations are found within domain 19 in addition to domain 20.

Endothelial von Willebrand factor release due to eNOS deficiency predisposes to thrombotic microangiopathy in mouse aging kidney

Endothelial dysfunction is critical in the decline of renal function with. By using endothelial nitric oxide synthase knockout (eNOSKO) mice, we tested the hypothesis that a lack of endothelial nitric oxide synthase accelerates renal injury in the aging kidney. In contrast to control mice and young eNOSKO mice, aging eNOSKO mice showed greater renal injury and in particular developed a thrombotic microangiopathy, with mesangiolysis, endothelial swelling, endothelial cell loss, double-contour appearance of glomerular basement membrane (GBM), and thrombus formation. Thrombi, which were composed of fibrin, platelets, and von Willebrand factor (vWF), were identified predominantly in glomerular capillaries and rarely in arterioles, but not in larger vessels. In the tubulointerstitium, tubular degeneration and macrophage infiltration were also prominent in aging eNOSKO mice. Intraluminal vWF deposition was accompanied with thrombus formation, whereas mesangial deposition of vWF was associated with mesangial matrix expansion. Furthermore, the mesangial vWF deposition was detectable in young eNOSKO mice in which severe glomerular injury had not yet developed. Finally, a higher level of serum P-selectin in eNOSKO mice was consistent with the vWF behavior and suggested exocytosis of the Weibel-Palade body by the endothelium. In conclusion, a lack of endothelial nitric oxide synthase resulted in the development of glomerular thrombotic microangiopathy. A lack of nitric oxide likely contributed to the release of vWF, leading to thrombus formation in this model.

Etanercept-refractory adult-onset Still's disease with thrombotic thrombocytopenic purpura successfully treated with tocilizumab

We report the case of a 69-year-old Japanese woman who presented with thrombotic thrombocytopenic purpura (TTP) which had manifested soon after the onset of adult-onset Still's disease (AOSD). Her disease was multi-drug resistant. She had undergone treatment with high-dose glucocorticoids, two courses of steroid pulse therapy, and cyclosporine A. The patient initially had a favorable response to the administration of etanercept (an anti-tumor necrosis factor agent) and glucocorticoids. However, her disease became refractory to etanercept after 6 months. Therefore, we administered tocilizumab (a humanized monoclonal anti-IL-6 receptor antibody) which dramatically improved the patient's refractory AOSD with TTP. This is the first report of an effective treatment for AOSD with TTP using the biological agents. Our report strongly suggests that biological agents, especially a humanized monoclonal anti-IL-6 receptor antibody, may be a new option for a safe and effective treatment of multi-drug-resistant AOSD and TTP associated with AOSD.

Pathogenesis of Escherichia coli O157:H7 strain 86-24 following oral infection of BALB/c mice with an intact commensal flora

Escherichia coli O157:H7 is a food-borne pathogen that can cause hemorrhagic colitis and, occasionally, hemolytic uremic syndrome, a sequela of infection that can result in renal failure and death. Here we sought to model the pathogenesis of orally-administered E. coli O157:H7 in BALB/c mice with an intact intestinal flora. First, we defined the optimal dose that permitted sustained fecal shedding of E. coli O157:H7 over 7 days ( approximately 10(9) colony forming units). Next, we monitored the load of E. coli O157:H7 in intestinal sections over time and observed that the cecum was consistently the tissue with the highest E. coli O157:H7 recovery. We then followed the expression of two key E. coli O157:H7 virulence factors, the adhesin intimin and Shiga toxin type 2, and detected both proteins early in infection when bacterial burdens were highest. Additionally, we noted that during infection, animals lost weight and approximately 30% died. Moribund animals also exhibited elevated levels of blood urea nitrogen, and, on necropsy, showed evidence of renal tubular damage. We conclude that conventional mice inoculated orally with high doses of E. coli O157:H7 can be used to model both intestinal colonization and subsequent development of certain extraintestinal manifestations of E. coli O157:H7 disease.

Clinical practice. Today's understanding of the haemolytic uraemic syndrome

The haemolytic uraemic syndrome (HUS) includes the triad of haemolytic anaemia, thrombocytopenia, and acute renal failure. The classical form [D(+) HUS] is caused by infectious agents, and it is a common cause of acute renal failure in children. The enterohaemorrhagic Escherichia coli-producing Shiga toxin (Stx) is the most common infectious agent causing HUS. Other infectious agents are Shigella and Streptococcus pneumoniae. Infections by S. pneumoniae can be particularly severe and has a higher acute mortality and a higher long-term morbidity compared to HUS by Stx. Atypical HUS [D(-)Stx(-)HUS] are often used by paediatricians to indicate a presentation of HUS without preceding diarrhoea. Almost all patients with D(-)Stx(-)HUS have a defect in the alternative pathway, for example, mutations in the genes for complement factor H, factor I, and membrane co-factor protein. Mutations in the factor H gene are described more often. The majority of children with D(+) HUS develop some degree of renal insufficiency, and approximately two thirds of children with HUS will require dialysis therapy, while about one third will have milder renal involvement without the need for dialysis therapy. General management of acute renal failure includes appropriate fluid and electrolyte management, antihypertensive therapy, and the initiation of renal replacement therapy when appropriate. Specific management issues in HUS include management of the haematological complications of HUS, monitoring for extra-renal involvement, avoiding antidiarrhoeal drugs, and possibly avoiding of antibiotic therapy. In addition to the obligatory supportive treatment and tight control of hypertension, there is anecdotal evidence that plasma therapy may induce remission and, in some cases, maintain it. Fresh frozen plasma contains factor H at physiological concentrations. A new therapy for D(-)Stx(-)HUS is a humanised monoclonal antibody (Eculizumab) that blocks complement activity by cleavage of the complement protein C5. It prevents the generation of the inflammatory peptide C5a and the cytotoxic membrane-attack complex C5b-9. We have first positive results, but it is still not approved for HUS.

An unusual cause of acute renal failure in sickle cell disease

A young female with sickle cell disease was treated for biopsy-proven IgA nephropathy. Serum creatinine levels resolved to normal range, but a year later, she presented with oedema, hypertension and acute renal failure. A repeat renal biopsy showed acute-on-chronic thrombotic microangiopathy (TMA). We suggest that circulating microparticles could be a pathophysiological link between sickle cell disease and the development of renal TMA. This case emphasizes the importance of a further biopsy for acutely declining renal function, even when a definite diagnosis has been made from a previous biopsy.

Mac-1 (CD11b/CD18) links inflammation and thrombosis after glomerular injury

BACKGROUND

Inflammation and thrombosis coexist in several disorders. Although it is recognized that leukocytes may induce a procoagulant state at sites of inflammation, the critical molecular determinants of this process remain largely unknown.

METHODS AND RESULTS

To examine mechanisms of inflammation-induced thrombosis, we developed a murine model of thrombotic glomerulonephritis (TGN), a known cause of acute renal failure in patients. This model, induced by lipopolysaccharide and antibody to the glomerular basement membrane, led to rapid glomerular neutrophil recruitment, thrombotic glomerular lesions with endothelial cell injury, and renal dysfunction. In mice immunodepleted of neutrophils or lacking the leukocyte-specific integrin Mac-1, neutrophil recruitment, endothelial injury, glomerular thrombosis, and acute renal failure were markedly attenuated despite the robust generation of renal cytokines. Neutrophil elastase is a likely effector of Mac-1 because its activity was reduced in Mac-1-deficient mice and the phenotype in mice deficient in Mac-1 or neutrophil elastase was similar. Platelets accumulated in glomerular capillaries within 4 hours of TGN before evidence of thrombosis. Platelet immunodepletion before TGN markedly exacerbated hematuria (hemorrhage), inflammation, and injury, whereas thrombocytopenic Mac-1-deficient mice remained resistant to disease, indicating that initial glomerular platelet deposition protects the vessel wall from neutrophil-mediated sequelae. The subsequent thrombosis relied on the interaction of Mac-1 on recruited neutrophils with glycoprotein Ibalpha on platelets as antibody-mediated disruption of this interaction attenuated TGN without affecting renal neutrophil accumulation.

CONCLUSIONS

These observations establish Mac-1 on neutrophils as a critical molecular link between inflammation and thrombosis and suggest it as an attractive target for antithrombotic therapy.