Escherichia coli and the hemolytic-uremic syndrome

A Case Presentation of Haemolytic Uraemic Syndrome Presenting as Gastroenteritis

A 62-year-old man presented to our department with gastroenteritis. He was found to have decreased platelets and deranged renal function. A diagnosis of haemolytic uraemic syndrome was eventually made. The disease usually presents nonspecifically with gastroenteric symptoms and systemic upset at the initial stage. Without a high index of suspicion, the diagnosis can easily be missed.

Thrombotic microangiopathies: an update

Thrombotic microangiopathies (TMA) are microvascular occlusive disorders characterized by hemolytic anemia caused by fragmentation of erythrocytes and thrombocytopenia due to increased platelet aggregation and thrombus formation, eventually leading to disturbed microcirculation with reduced organ perfusion. Although several disease states may manifest as TMA, the two most relevant conditions associated with TMA are thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), characterized by prominent brain or renal lesions, respectively. However, occasionally the clinical distinction between these two conditions can be difficult. In this review, we focus on the epidemiologic and diagnostic criteria as well as on the most recent insights into the pathophysiology and treatment of these two conditions.

Advances in the pathogenesis, diagnosis and treatment of thrombotic thrombocytopenic purpura and hemolytic uremic syndrome

The thrombotic microangiopathies are microvascular occlusive disorders characterized by hemolytic anemia caused by fragmentation of erythrocytes and thrombocytopenia due to increased platelet aggregation and thrombus formation, eventually leading to disturbed microcirculation with reduced organ perfusion. Depending on whether brain or renal lesions prevail, two different entities have been described: thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS). However, not rarely the clinical distinctions between these two conditions remain questionable. Recent studies have contributed greatly to our current understanding of the molecular mechanisms leading to TTP and HUS. In this review, we briefly focus on the most important advances in the pathophysiology, diagnosis and treatment of these two thrombotic microangiopathies.

Current concepts in the diagnosis and management of thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura is a multisystem disease characterized by thrombocytopenia, hemolytic anemia, renal failure, fever, and neurologic abnormalities. Plasma exchange has revolutionized the outcome of this entity from a once fatal disease to a disease that potentially is cured or has prolonged remission. The understanding of the pathophysiology of TTP continues to evolve. Recently, investigators showed that a deficiency in a specific plasma protease responsible for cleaving vWf plays a crucial role in the familial form of TTP. This explains in part why patients usually respond to plasma exchange therapy. The identification of a mutation in a specific gene that belongs to the metalloproteinase family located at chromosome 9q34 could have important therapeutic implications. TTP can be induced by certain drugs, especially immunosuppressants, in the setting of bone marrow and solid organ transplantation. This disease also has been described in association with HIV, pregnancy, cancer, and chemotherapy. TTP remains an ideal example of how knowledge about the etiology of a disease can improve therapeutic interventions.

Two cases of non-O157:H7 Escherichia coli hemolytic uremic syndrome caused by urinary tract infection

Escherichia coli serotype O157:H7 is a leading cause of diarrhea and hemolytic uremic syndrome (HUS). Because of the limitations of current diagnostic techniques, the prevalence of non-O157:H7 Shiga toxin-producing E coli strains is not known. We describe two patients with HUS in whom no E coli O157:H7 was demonstrable in stool cultures. On culture of the urine, the first patient was found to have E coli O113:H21 strain, and the second patient had E coli O6:H1 serotype. Shiga toxin production (stx2) by the O113:H21 isolate was confirmed. The first patient required 15 days of peritoneal dialysis and subsequently recovered renal function. At last follow-up, serum creatinine was 0.9 mg/dL. The second patient had preservation of renal function throughout the acute illness with serum creatinine of 0.5 mg/dL. The clinical presentation, bacteriology, course, and outcome as well as epidemiologic implications of the increasing number of patients with E coli urinary tract infections associated with HUS are discussed. These cases illustrate the need to investigate patients with nondiarrheal HUS for infection with Shiga toxin-producing E coli of the non-O157 strain variety.

Apheresis for Renal Disease

Many primary renal diseases are associated with either antibody deposition within the glomerulus or an antibody associated autoimmunity, as may be seen with certain vasculitidies. Examples of these diseases include Goodpasture's syndrome, cryoglobulinemia, antineutrophil cytoplasmic antibody positive syndromes, and other forms of rapidly progressive glomerulonephritis. Immunoglobulins also may be nephrotoxic to the tubules such as is the case with myeloma related light chains. Given the rapid removal of immunoglobulins by therapeutic plasma exchange, this modality has been considered an appealing management option in the treatment of these renal diseases. Although not classically considered as autoimmune diseases, thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are related syndromes which often involve the kidneys. Although previously unexplained, it has been long appreciated that therapeutic plasma exchange (PE) can be a useful treatment for these microangiopathic hemolytic anemias, but the most recent insights into their pathogenesis suggest that PE may be beneficial by replacing a missing enzyme or removing pathogenic autoantibodies.

4-Aminopyrazolo[3,4-d]pyrimidine (4-APP) as a novel inhibitor of the RNA and DNA depurination induced by Shiga toxin 1

Shiga toxin 1 (Stx1) catalyses the removal of a unique and specific adenine from 28S RNA in ribosomes (RNA-N-glycosidase activity) and the release of multiple adenines from DNA (DNA glycosylase activity). Added adenine behaves as an uncompetitive inhibitor of the RNA-N-glycosidase reaction binding more tightly to the Stx1-ribosome complex than to the free enzyme. Several purine derivatives and analogues have now been assayed as inhibitors of Stx1. Most of the compounds showed only minor differences in the rank order of activity on the two enzymatic reactions catalysed by Stx1. The survey highlights the importance of the amino group in the 6-position of the pyrimidine ring of adenine. Shifting (2-aminopurine) or substituting (hypoxanthine, 6-mercapto-purine, 6-methylpurine) the group greatly decreases the inhibitory power. The presence of a second ring, besides the pyrimidine one, is strictly required. Substitution, by introducing an additional nitrogen, of the imidazole ring of adenine with triazole leads to loss of inhibitory power, while rearrangement of the nitrogen atoms of the ring from the imidazole to the pyrazole configuration greatly enhances the inhibitory power. Thus 4-aminopyrazolo[3,4-d]pyrimidine (4-APP), the isomer of adenine with the five-membered ring in the pyrazole configuration, is by far the most potent inhibitor of both enzymatic reactions catalysed by Stx1. This finding opens perspectives on therapeutic strategies to protect endothelial renal cells once endocytosis of Stx1 has occurred (haemolytic uraemic syndrome). In the RNA-N-glycosidase reaction 4-APP binds, as adenine, predominantly to the Stx1-ribosome complex (uncompetitive inhibition), while inhibition of the DNA glycosylase activity by both inhibitors is of the mixed type.

Infectious Enteritis

Initial management of acute infectious enteritis should focus on fluid and electrolyte repletion and symptomatic care. A decision to prescribe empiric antibiotic therapy should rest on clinical or epidemiologic features of the illness that suggest a treatable bacterial origin or a high-risk host. This decision should be reinforced by the detection of leukocytes or blood in the stool. If empiric therapy is indicated, a quinolone is generally the best initial choice. A stool culture yielding an enteropathogen should generally be specifically treated. A possible exception is uncomplicated Salmonella gastroenteritis in an otherwise healthy host. Nosocomial diarrhea is caused by Clostridium difficile in a minority of cases. Because diagnostic studies for this pathogen are sufficiently sensitive and specific, empiric antibiotic treatment for C. difficile is seldom indicated. Diarrhea in AIDS patients is best worked up and managed in a stepwise fashion, beginning with simple measures. Endoscopy or surgery are seldom indicated in the evaluation and management of infectious enteritis.

Therapeutic apheresis for renal disorders

Many primary renal diseases are associated with either antibody deposition within the glomerulus or an antibody associated autoimmunity, as may be seen with certain vasculitidies. Other immunoglobulins may be nephrotoxic or glomerulopathic; such may be the case with myeloma related light chains or cryoglobulins. Given the rapid removal of immunoglobulins by therapeutic plasma exchange, this modality has been considered an appealing management option in the treatment of these autoimmune related renal diseases. Although not classically considered as autoimmune diseases, thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are related syndromes which often involve the kidneys. In many cases therapeutic plasma exchange has been found to be a useful treatment modality for these microangiopathic hemolytic anemias. This paper will provide a concise review of the renal indications for therapeutic plasma exchange.

A new model of renal microvascular injury

The vascular endothelial injury with its consequent activation is actively involved in inflammation and promotion of a procoagulant state, which are likely to be of major importance in the pathogenesis of various disorders, including renal thrombotic microangiopathy. This study briefly reviews the consequences of glomerular endothelial cell injury or activation, as shown by recent experimental data.

Transition metals as protease inhibitors

An alternative approach to the development of clinically useful protease inhibitors was investigated. The approach utilized coordination chemistry of transition metal ions rather than substrate analogs to block active sites of these enzymes. In the case of serine proteases it was found that aqueous Ti(IV) is a potent inhibitor of the trypsin subclass, but not the chymotrypsin subclass. The direct binding of Ti(IV) to trypsin was made possible by the presence of a free carboxyl group at the bottom of the substrate binding pocket of the enzyme, and the five-coordinate geometry of TiO(SO4)(H2O). Although initial binding of Ti(IV) was reversible, it was followed in time by irreversible inhibition. Direct binding of octahedral or tetrahedral metal ion complexes was prevented by the inability of the enzyme active sites to promote formation of a five-coordinate transition state of the metal ion required for reaction. These studies demonstrate the ability of direct metal ion binding as a way to enhance blocking of enzyme active sites as compared with that of traditional organic inhibitors. Application of these findings was investigated by measuring the affect Ti(IV) had on growth of Escherichia coli, Salmonella typhimurium, and Pseudomonas aeruginosa. Five-coordinate titanyl sulfate completely inhibited the growth of these organisms. This suggests that five-coordinate titanyl sulfate, which is easier and less expensive to manufacture than conventional antibiotics, may be useful in controlling endemic infections of E. coli and S. typhimurium.

Seasonality and other epidemiological features of haemolytic uraemic syndrome and E. coli O157 isolates in Scotland

The main objective was to determine whether there was seasonality in presentation of haemolytic uraemic syndrome (HUS) in children and adults, and compare this with the reporting of E. coli O157. The data came from Scotland, examining admissions during 1980-95 and E. coli isolates 1984-95. Seasonality was sought by fitting a sine curve to monthly or four-weekly data throughout the year. Seasonality was present for HUS and E. coli isolates in patients under 15 years of age but not in those above that age. The highest point of the sine curve was in July/August but there was a high plateau from June to September. The timing was similar to other diarrhoeal disease. This is an epidemiological study, the purpose being to clarify the seasonal features of HUS. E. coli infection is an important food hazard and a sound knowledge of the epidemiology, could lead to optimal control. The Scottish geographic distribution is illustrated.

A new model of renal microvascular endothelial injury

Although the importance of injury with consequent activation of endothelium is well-recognized in diseases affecting the glomerular endothelial cell (GEN), research on GEN injury in vivo has been hampered by the lack of adequate animal models. Here we report the establishment and characterization of a new GEN injury model in rats. This model was induced by selective renal artery perfusion with anti-GEN IgG and resulted in the severe acute renal failure with marked platelet deposition and development of a thrombotic microangiopathy involving glomeruli. Peritubular capillary endothelial cells were also damaged that was associated with severe tubular necrosis. Although the glomerular changes were severe, half of the glomeruli recovered by day 10, while interstitial changes remained throughout our observation time course. Proliferation of GEN was observed during the recovery phase. An increased expression of endothelial nitric oxide synthase in GEN was also observed, and may be an adaptive mechanism to counteract the thrombosis and ischemia. This model should be useful to investigate the pathophysiology of renal microvascular diseases and the mechanisms of GEN injury, activation and recovery in vivo.