Complement dysfunction in hemolytic uremic syndrome

PURPOSE OF REVIEW: Hemolytic uremic syndrome is a rare disease of microangiopathic hemolytic anemia, low platelet count and is associated with renal impairment. The atypical form, which occurs in adult patients, is associated with defective complement control. RECENT FINDINGS: Recent data show that atypical hemolytic uremic syndrome is a genetic disease and gene mutations have been reported for factor H, membrane cofactor protein/CD46 and factor I. All corresponding gene products act in concert and control the activity of the complement convertase C3bBb. This enzyme initiates the alternative pathway as well as amplification of the complement system. Similar to genetic defects, autoantibodies which bind to factor H have been linked to the disease. Defective complement control resulting in hemolytic uremic syndrome explains the disease mechanism and allows improved diagnosis and therapy. SUMMARY: The atypical form of hemolytic uremic syndrome is associated with defective complement control and inappropriate protein function and may influence disease progression and provide new ways for treatment. Positive effects were reported upon substitution of a defective protein by plasma exchange or plasmaphoreses. The disease recurrence rate for renal transplants depends on the type of gene mutated; patients with mutations in the membrane cofactor protein gene have a better prognosis than patients with mutations in other genes.     

Platelet activation in hemolytic uremic syndrome

Platelet consumption in platelet-fibrin aggregates leading to thrombocytopenia and small vessel obstruction are major features of the hemolytic uremic syndrome (HUS). Although thrombocytopenia has been correlated to poor prognosis, the mechanisms by which thrombocytopenia develops in HUS have not been completely elucidated. However, plausible explanations have been platelet contact with thrombogenic surfaces and/or direct contact with an aggregating agent. This article summarizes several mechanisms of platelet activation, interactions with leukocytes, chemokine release, complement activation, and antimicrobial defense. Specific mechanisms are outlined by which platelets may be activated, leading to thrombocytopenia during HUS. In diarrhea-associated HUS Shiga toxin has been shown to injure the endothelium, thus exposing the subendothelium, releasing tissue factor, and rendering the vessel wall prothrombotic. Shiga toxin also binds to and activates platelets. The toxin may activate endothelial cells and platelets simultaneously. In atypical HUS the alternative complement pathway is activated because of mutations in complement regulatory proteins. Mutated factor H does not bind to endothelium and platelets efficiently, enabling complement activation on these cells. In thrombotic thrombocytopenic purpura, intravascular platelet clotting occurs due to dysfunction of the von Willebrand factor (VWF) -cleaving protease ADAMTS13. Thrombi are formed by binding of platelets to ultralarge VWF multimers.     

Coagulation changes associated with the hemolytic uremic syndrome

The hemolytic uremic syndrome (HUS) is characterized by hemolytic anemia, acute renal failure, and thrombocytopenia. The pathological correlate is thrombotic microangiopathy of glomerular capillaries and arterioles in the kidneys and almost every other organ. The presence of platelet thrombi without extensive soluble coagulation system activation is a constant feature of HUS and thrombotic thrombocytopenic purpura (TTP). Damage to the endothelial cell seems to be a central event in the pathogenesis of HUS and TTP, resulting in loss of fibrinolytic properties and subsequent thrombotic occlusion of the microvasculature. According to earlier and recent studies, a variety of hemostatic alterations have been described. Among the many findings, low platelet counts, increased von Willebrand's factor (vWF), and normal fibrinogen are almost invariably observed. The dubious long-term outcome, even of postdiarrheal HUS, which is believed to have a more favorable prognosis than HUS of other etiopathogenic origin, necessitates further investigation of the pathophysiology of thrombotic microangiopathy and meticulous reevaluation of treatment strategies aimed at interfering with the process of thrombosis early in the disease course. The intention of this article is to highlight findings possibly relevant for disease management and to give an overview of the putative pathomechanisms involved.     

非典型溶血尿毒综合征

近来研究证实非典型溶血尿毒综合征(a HUS)与多种补体成分、活化因子及调节因子基因突变密切相关,基因筛查有助于病因诊断、预测预后及肾移植结局。补体H因子相关蛋白融合基因产物是a HUS发病机制的最新研究热点,抗补体治疗能够有效控制a HUS进展、改善预后,依库珠单抗与血浆置换、免疫抑制治疗、器官移植已被纳入a HUS治疗指南。对于尚未进入终末期肾病的患者进行单独肝移植是否普遍推广有待于进一步探索。本文旨在对a HUS诊治的最新研究进展作一综述。     

Initial presentation of hemolytic uremic syndrome in a boy with systemic lupus erythematosus

Associating systemic lupus erythematosus (SLE) with an initial presentation of hemolytic uremic syndrome (HUS) is rare. We report on a 13-year-old boy admitted to our hospital with an initial complaint of bilateral knee pain and multiple petechiae on both lower extremities. Diagnosis of atypical HUS was established according to the clinical triad of HUS without a veriotoxin-producing organism in his stool and the pathological finding compatible to thrombotic microangiopathy. In addition, his symptoms fulfilled the 1982 revised criteria for the classification of SLE. After methylprednisolone and cyclophosphamide pulse therapies, his laboratory findings and general condition improved. No plasmapheresis or any plasma infusion was required.     

A case of hemolytic uremic syndrome improved with nitric oxide

Hemolytic uremic syndrome (HUS) after transplantation is difficult to treat, and there is no consensus regarding optimal mode of treatment. We attached transdermal isosorbide tape as a nitric oxide (NO) donor to patients with HUS after bone marrow transplantation (BMT). This was very effective in ameliorating the hemolysis and increasing platelet numbers. We report here the successful use of an isosorbide in a patient with HUS after transplantation. Bone Marrow Transplantation (2000) 25, 109-110.     

Quinine-induced immune thrombocytopenia associated with hemolytic uremic syndrome: a new clinical entity

Three patients are described who developed severe thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure after ingestion of quinine. In one patient, the same clinical findings recurred several months later after another exposure to quinine. Serum from one patient contained quinine-dependent IgG antibodies reactive with the platelet glycoprotein (GP) Ib/IX complex. In the second and third cases, serum contained IgG and IgM antibodies reactive with both the GP Ib/IX and IIb/IIIa complexes in the presence of quinine. Quinine appears to have induced both immune thrombocytopenia and the hemolytic uremic syndrome (HUS) in these individuals. Findings made in these cases may have implications for the pathogenesis of some forms of HUS.     

Type III hyperlipoproteinemia exaggerated by Sheehan's syndrome with advanced systemic atherosclerosis: a 28-year clinical course.

A 38-year-old Japanese woman was admitted to hospital for further examination of systemic xanthomas. She had a past history of genital bleeding during her third delivery at the age of 21 years. She was diagnosed with Sheehan's syndrome. Her serum total cholesterol and triglyceride concentrations were 500 and 898 mg/dl, respectively. She was also diagnosed as having type III hyperlipoproteinemia on the basis of the presence of a broad-beta-band on agarose gel electrophoresis and extremely high concentrations of very-low-density lipoprotein cholesterol (310 mg/dl). The diagnosis was later confirmed by her apolipoprotein E isoforms (E2/E2) and genotypes (epsilon2/epsilon2). Thyroid and corticosteroid hormone replacement therapy cured the xanthomas, but also elevated her blood pressure. The serum concentration of intermediate-density lipoprotein cholesterol was consistently high, whereas that of low-density lipoprotein cholesterol was relatively low during the follow-up. Coronary atherosclerosis had already developed by the age of 38 years, and progressed significantly over the following 28 years. Severe stenotic lesions were observed in the bilateral renal arteries and carotid arteries, and in the abdominal aorta when she was 66 years old. These findings suggest that the continuous elevation of intermediate-density lipoprotein cholesterol for a long period contributed to the development of the atherosclerotic lesions.     

New insights into postrenal transplant hemolytic uremic syndrome

After renal transplantation, hemolytic uremic syndrome (HUS) may occur either as a recurrent or de novo form. Over the past decade, much effort has been devoted to elucidating the pathogenesis of atypical HUS (aHUS). Approximately 60-70% patients with aHUS have mutations in regulatory factors of the complement system or antibodies against complement factor H. The risk of post-transplant recurrence of aHUS depends on the genetic abnormality involved, and ranges from 15% to 20% in patients with mutations in the gene that encodes membrane cofactor protein and from 50% to 100% in patients with mutations in the genes that encode circulating regulators of complement. Given the poor outcomes associated with recurrence, isolated renal transplantation had been contraindicated in patients at high risk of aHUS recurrence. However, emerging therapies, including pre-emptive plasma therapy and anti-C5 component monoclonal antibody (eculizumab) treatment have provided promising results and should further limit indications for the risky procedure of combined liver-kidney transplantation. Studies from the past 2 years have demonstrated genetic abnormalities in complement regulators in 30% of renal transplant recipients who experienced de novo HUS after renal transplantation. This finding suggests that the burden of endothelial injury in a post-transplantation setting may trigger de novo HUS in the presence of mild genetic susceptibility to HUS.     

Recurrent hemolytic uremic syndrome induced by pranoprofen]

A 25-year-old woman was admitted to our hospital because of dark red urine in 1993. A diagnosis of hemolytic uremic syndrome (HUS) because of findings of hemolytic anemia with fragmented erythrocytes, thrombocytopenia, and renal dysfunction. The patient achieved remission with steroids and diuretics. In 1998 she caught a cold and happened to take the nonsteroidal anti-inflammatory drug, pranoprofen. Six hours later, she was rehospitalized because of dark red urine. Hemolytic anemia, fragmented erythrocytes, thrombocytopenia and renal dysfunction were observed again, also. A diagnosis of HUS was made. The patient was treated with steroid pulse therapy, infusion of fresh plasma, and plasma exchange transfusion. She recovered completely. In 1993 she had taker pranoprofen just prior to her first HUS episode. This was a recurrent case of HUS induced by pranoprofen.     

Escherichia coli that cause hemolytic uremic syndrome.

Entero-hemorrhagic Escherichia coli (Shiga-like toxin or verotoxin producing E. coli) have been recognized in recent years as an important new group of enteric pathogens. They are the cause of nonspecific diarrhea and hemorrhagic colitis, and in a significant number of patients, these conditions are complicated by the development of microangiopathic hemolytic anemia. In childhood, this complication is called hemolytic uremic syndrome (HUS), and in adults, it is more typically diagnosed as thrombotic thrombocytopenic purpura (TIP). The toxin producing E. coli are the usual etiology of these syndromes when they occur in the setting of a gastrointestinal prodrome with bloody diarrhea.     

Case report: cisplatin-induced hemolytic uremic syndrome.

Two patients developed noncardiogenic pulmonary edema (NCPE), following red blood cell transfusion in a setting of acute cisplatin nephropathy. One manifested the full picture of hemolytic uremic syndrome, the other had transient features following blood transfusion. We further reviewed the clinical records on blood transfusion for all patients with cisplatin nephropathy. A third case of (NCPE) was identified in a patient with acute renal dysfunction. However, none of the 16 patients with cisplatin-induced, mild stable chronic renal impairment had pulmonary dysfunction or other laboratory evidence for microangiopathy following transfusion. Hemolytic uremic syndrome may be a rare manifestation of cisplatin toxicity. Caution is indicated in transfusing patients with acute platinum nephropathy even in the absence of overt microangiopathy. The pathogenesis of this syndrome and the cause for NCPE is unclear. The literature is reviewed and discussed.