Thrombotic thrombocytopenic purpura and the hemolytic-uremic syndrome

[Hemolytic uremic syndrome in adults]

Hemolytic uremic syndrome (HUS) is related to a renal thrombotic microangiopathy, inducing hypertension and acute renal failure (ARF). Its pathogenesis involves an activation/lesion of microvascular endothelial cells, mainly in the renal vasculature, secondary to bacterial toxins, drugs, or autoantibodies. An overactivation of the complement alternate pathway secondary to a heterozygote deficiency of regulatory proteins (factor H, factor I or MCP) or to an activating mutation of factor B or C3 can also result in HUS. Less frequently, renal microthrombi are due to an acquired or a constitutional deficiency in ADAMTS-13, the protease cleaving von Wilebrand factor. Hemolytic anemia with schistocytes, thrombocytopenia without evidence of disseminated intravascular coagulation, and renal failure are consistently found. In typical HUS, a prodromal diarrhea, with blood in the stools, is observed, related to pathogenic enterobacteria, most frequently E. Coli O157:H7. HUS may also occur in the post partum period, and is then related to a factor H or factor I deficiency. HUS may also occur after various treatments such as mitomycin C, gemcitabine, ciclosporin A, or tacrolimus, and as reported more recently bevacizumab, an anti VEGF antibody. Atypical HUS are not associated with diarrhea, may be sporadic or familial, and can be related to an overactivation of the complement alternate pathway. More recently, some of them have been related to a mutation of thrombomodulin, which also regulates the alternate pathway of complement. In adults, several HUS are encountered in the course of chronic nephropathies: nephroangiosclerosis, chronic glomerulonephritis, post irradiation nephropathy, scleroderma, disseminated lupus erythematosus, antiphospholipid syndrome. Overall the prognosis of HUS has improved, with a patient survival greater than 85% at 1 year. Chronic renal failure is observed as a sequella in 20 to 65% of the cases. Plasma infusions and plasma exchanges are effective in most of the cases to treat hemolysis and thrombocytopenia. Steroid therapy is debated, as well as immunosuppressive drugs, including rituximab, in autoimmune forms. A new monoclonal anti-C5 antibody is tested, and seems to be effective in atypical HUS with abnormal complement alternate pathway activation. If terminal renal failure occurs, renal transplantation can be performed but the risk of recurrence, which very low in post infectious forms of HUS, is about 70 to 80% in genetic forms of complement regulatory protein deficiency.

Novel ADAMTS-13 mutations in an adult with delayed onset thrombotic thrombocytopenic purpura

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is associated with congenital and acquired deficiency of ADAMTS-13, a metalloprotease that cleaves von Willebrand factor (VWF) and reduces its adhesive activity. Mutations throughout the ADAMTS13 gene have been identified in congenital TTP patients, most of whom have initial episodes during infancy or in early childhood.

PATIENTS AND METHODS

We report the case of an adult male who was diagnosed with idiopathic thrombocytopenic purpura at age 34, and with TTP 14 years later. The patient was compound heterozygous for an 18 bp in-frame deletion (C365del) in the disintegrin domain and a point mutation of R1060W in the seventh thrombospondin domain of the ADAMTS-13 gene.

CONCLUSIONS

In vitro studies found that C365del and R1060W severely impair ADAMTS-13 synthesis in transfected Hela cells, whereas the deletion mutant also failed to cleave VWF under static and flow conditions.

Fusion of HIV-1 envelope-expressing cells to human glomerular endothelial cells through an CXCR4-mediated mechanism

A central question in the pathogenesis of HIV-associated thrombotic microangiopathic (HIV-TMA) lesions is whether the HIV-1 envelope glycoprotein (HIV-1 Env) can interact directly with human glomerular endothelial cells (HGECs) through specific HIV-1 co-receptors. The goal of this study was to determine whether cultured primary HGECs express significant levels of the major HIV-1 co-receptors CD4, CXCR4, and/or CCR5 to allow fusion interactions with HIV-1. The expression of CD4, CXCR-4 and CCR-5 was assessed in cultured HGECs by reverse transcriptase-polymerase chain reaction (RT-PCR) and flow cytometry using specific antibodies. The HIV-1 Env-mediated membrane fusion of target glomerular cells was evaluated by a fluorescent dye transfer-based cell-cell fusion microscopic method. HGECs express CXCR4 mRNA and protein as determined by RT-PCR and immunostaining with phycoerythrin-conjugated anti-CXCR4 Mab 12G5. CD4 and CCR5 were not detected in HGECs, either by RT-PCR or by surface immunostaining with specific antibodies. Incubation of HGECs with cells expressing a CD4-independent envelope strain (HIV-1IIIB-8x) and the CD4-dependent envelope strain (HIV-1IIIB) resulted in transfer of fluorescent dyes of approximately 20% after 8-16 h incubation at 37 degrees C. Incubation in the presence of inhibitors (C34, which blocks six-helix bundle formation, and AMD3100, which interacts with CXCR4) reduced dye transfer by 60%-80%, confirming that the dye transfer was specific with respect to gp120-gp41-mediated fusion. Cultured primary HGECs express CXCR4 but not CD4 or CCR5. The ability of HGECs to promote fusion by a CD4-independent HIV-1 envelope glycoprotein suggests that these cells may become a potential direct target of certain HIV-1 isolates.

Foot manifestations of the thrombotic thrombocytopenic purpura hemolytic-uremic syndrome: a review and case report

The thrombotic thrombocytopenic-hemolytic uremic (TTP-HUS) syndrome is a thrombotic microangiopathy involving end-organ vascular beds. Microcirculatory thrombosis results in ischemic changes in any number of organ systems, especially the central nervous and renal systems. Musculoskeletal system involvement is less well described, but when it occurs, acral ischemia may be severe. TTP-HUS is well recognized as a complication of organ transplantation, drug therapy, in pregnancy, and as a chronic, relapsing congenital disorder. Bacterial sepsis may also result in a thrombotic microangiopathy of the central nervous and renal systems (TTP-HUS). This article presents a case report and discusses the pathogenesis and lower-extremity manifestations of TTP-HUS, and outlines management strategies.

P-selectin anchors newly released ultralarge von Willebrand factor multimers to the endothelial cell surface

von Willebrand factor (VWF) released from endothelium is ultralarge (UL) and hyperreactive. If released directly into plasma, it can spontaneously aggregate platelets, resulting in systemic thrombosis. This disastrous consequence is prevented by the ADAMTS13 (ADisintegrin and Metalloprotease with ThromboSpondin motif) cleavage of ULVWF into smaller, less active forms. We previously showed that ULVWF, on release, forms extremely long stringlike structures. ADAMTS13 cleaves these strings under flow significantly faster than it does under static conditions. As ULVWF tethering to endothelium is important for its rapid proteolysis, we investigated 2 molecules for their potential to anchor the ULVWF strings: P-selectin and integrin alpha v beta 3. We demonstrated that P-selectin anchors ULVWF to endothelium by several means. First, Chinese hamster ovary (CHO) cells expressing P-selectin specifically adhered to immobilized ULVWF and ULVWF-coated beads to immobilized P-selectin. Second, an anti-VWF antibody coimmunoprecipitates P-selectin from the histamine-activated endothelial cells. Third, P-selectin antibody or soluble P-selectin, but not a alpha v beta 3 antibody, RGDS peptide, or heparin, blocked the formation of ULVWF strings. Fourth, P-selectin expression was in clusters predominantly along the ULVWF strings. Finally, the strength of the minimal ULVWF-P-selectin bond was measured to be 7.2 pN. We, therefore, conclude that P-selectin may anchor ULVWF strings to endothelial cells and facilitate their cleavage by ADAMTS13.

Thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are distinct pathologic entities. A review of 56 autopsy cases

CONTEXT

Thrombotic thrombocytopenic purpura (TTP) and the hemolytic uremic syndrome (HUS) share many clinical features and have been difficult to separate into distinct entities. Histologic examination of organs from autopsied patients suggested that TTP and HUS have dissimilar lesions of different severity and distribution.

OBJECTIVE

To perform a retrospective observational review of autopsied patients with TTP or HUS to compare the nature and severity of the lesions found.

DESIGN

To examine the pathologic features of these conditions, we reviewed all cases among 51 350 indexed autopsies at The Johns Hopkins Hospital (Baltimore, Md) diagnosed with TTP or HUS, and included those showing multiple arteriolar thrombi or their sequela.

RESULTS

The 56 cases that met the inclusion criteria fell into 2 distinct groups, based on distribution and severity of arteriolar lesions. In 25 patients classified as having TTP, platelet-rich thrombi were present-in decreasing severity-in heart, pancreas, kidney, adrenal gland, and brain. In 31 patients with HUS, fibrin/red cell-rich thrombi were present, largely confined to the kidney and often severe, and only 6 cases showed pancreas involvement, 4 adrenal gland involvement, 2 brain involvement, and 1 heart involvement.

CONCLUSION

Despite similar clinical features and therapeutic approaches, TTP and HUS each have a characteristic constellation of histopathologic findings. This observation suggests that TTP and HUS are 2 distinct disease entities with different pathophysiologies, and that they do not represent a spectrum of the same disease process.

ADAMTS-13 rapidly cleaves newly secreted ultralarge von Willebrand factor multimers on the endothelial surface under flowing conditions

Thrombotic thrombocytopenic purpura (TTP) is a devastating thrombotic disorder caused by widespread microvascular thrombi composed of platelets and von Willebrand factor (VWF). The disorder is associated with a deficiency of the VWF-cleaving metalloprotease, ADAMTS-13, with consequent accumulation of ultralarge (UL) VWF multimers in the plasma. ULVWF multimers, unlike plasma forms of VWF, attach spontaneously to platelet GP Ibalpha, a component of the GP Ib-IX-V complex. We have found that ULVWF multimers secreted from stimulated endothelial cells (ECs) remained anchored to the endothelial surface where platelets and Chinese hamster ovary cells expressing the GP Ib-IX-V complex attached to form long beads-on-a-string structures in the presence of fluid shear stresses in both the venous (2.5 dyne/cm(2)) and arterial (20 and 50 dyne/cm(2)) ranges. Although measurement of the activity of the ADAMTS-13 VWF-cleaving metalloprotease in vitro requires prolonged incubation of the enzyme with VWF under nonphysiologic conditions, EC-derived ULVWF strings with attached platelets were cleaved within seconds to minutes in the presence of normal plasma (containing approximately 100% ADAMTS-13 activity) or in the presence of partially purified ADAMTS-13. By contrast, the strings persisted for the entire period of perfusion (10 minutes) in the presence of plasma from patients with TTP containing 0% to 10% ADAMTS-13 activity. These results suggest that cleavage of EC-derived ULVWF multimers by ADAMTS-13 is a rapid physiologic process that occurs on endothelial cell surfaces.

Thrombotic thrombocytopenic purpura: the systemic clumping "plague"

In thrombotic thrombocytopenic purpura (TTP), a multimeric form of von Willebrand factor (vWf) that is larger than ordinarily found in the plasma causes systemic platelet aggregation under the high-shear conditions of the microcirculation. A divalent cation-activated, vWf-cleaving metalloprotease that metabolizes large vWf multimers to smaller forms in normal plasma is severely reduced or absent in most patients with TTP. The vWf-cleaving metalloprotease either is not produced or is defective in children with chronic relapsing TTP. When the enzyme is provided by the infusion of normal plasma, these patients remain free of TTP symptoms for about three weeks. An IgG autoantibody to the vWf-cleaving metalloprotease is found transiently in many adult patients with acute idiopathic, recurrent, and ticlopidine/clopidogrel-associated TTP. These patients require plasma exchange, i.e., concurrent replacement of the inhibited vWf-cleaving metalloprotease by plasma infusion and plasmapheresis. The vWf-cleaving metalloprotease is present in fresh-frozen plasma, in cryoprecipitate-depleted plasma (cryosupernatant), and in plasma that has been treated with solvent and detergent. The pathophysiology of platelet aggregation in bone marrow transplantation/chemotherapy-associated thrombotic microangiopathy, and in the hemolytic-uremic syndrome, is not established. In neither condition is there a severe decrease in plasma vWf-cleaving metalloprotease activity.

Therapeutic plasma exchange in the intensive care setting

The potential to treat life-threatening conditions with therapeutic plasma exchange (TPE) is limited to a few situations. In severe pulmonary hemorrhage as a complication of several immune disorders (e.g., antiglomerular basement membrane antibody disease, Wegener's granulomatosus, lupus erythematosus), TPE should only be considered after conventional measures (mostly pulses of methylprednisolone) have been applied. Idiopathic familial and nonfamilial thrombotic thrombocytopenic purpura as well as the subset of the hemolytic uremic syndrome not associated with diarrhea are clear indications for TPE using fresh frozen plasma as replacement fluid. Patients with myasthenic crisis will also benefit from TPE and will improve within 1 day. Acute pancreatitis as a complication of the chylomicronemia syndrome has a poor prognosis and should be treated with TPE without any delay. In the case of drug overdose or intoxication, the efficiency of TPE to remove the offending drug is usually overestimated. In this situation, TPE is useful only when the plasma protein binding of the substance is high (>80%) and the volume of distribution is low (<0.2 L/kg body weight). TPE is not without risks and hazards (e.g., vascular access, bleeding, allergy), which should also be considered when discussing this extracorporeal therapy in otherwise refractory clinical conditions.