Development Of Thrombotic Microangiopathy Research Articles

Chronic Thrombotic Microangiopathy Secondary to Chemotherapy for Urothelial Carcinoma in a Patient With a History of Wegener Granulomatosis

We present the case of a 62-year-old man with a history of Wegener granulomatosis who developed chronic thrombotic microangiopathy attributed to gemcitabine chemotherapy. Wegener granulomatosis had been diagnosed 15 years earlier, and the patient was treated using cyclophosphamide and prednisone, then maintained on mycophenolate mofetil and prednisone. Four years previously, he had been treated with mitomycin C for urothelial carcinoma and at the time of presentation had developed significant anemia and thrombocytopenia after a course of gemcitabine and carboplatin due to metastasis of the carcinoma. He was managed using red blood cell and platelet transfusions but then developed acute kidney injury, along with progressive dyspnea and pulmonary infiltrates. Imaging studies showed bilateral ureteral obstruction requiring placement of nephrostomy tubes. Because of concern about a flare of Wegener granulomatosis after withdrawing maintenance immunosuppression in the context of the malignancy, a kidney biopsy was performed that showed chronic thrombotic microangiopathy, likely secondary to gemcitabine chemotherapy. Clinical, laboratory, and pathologic findings of this case are discussed to illustrate the natural history of thrombotic microangiopathy associated with gemcitabine chemotherapy.

Thrombotic microangiopathy in adult-onset Still's disease: case report and review of the literature

Coexistence of thrombotic microangiopathy and adult-onset Still's disease is extremely rare. There is increasing evidence that this association could be more than just coincidental. We report on the case of a 34-year-old male diagnosed with adult-onset Still's disease and successfully treated with intravenous glucocorticoids. Nine months after onset the patient exhibited the presence of asymptomatic thrombocytopenia during treatment with chloroquine. The physical status was unremarkable except for pallor of the skin and mucosa. Laboratory evaluation revealed profound thrombocytopenia and hemolytic anemia. Coombs' tests were negative; renal function tests were all normal. The peripheral blood smear showed frequent schistocytes. Based on the presence of thrombocytopenia and microangiopathic hemolytic anemia, and with the exclusion of other known causes, the patient was diagnosed with thrombotic microangiopathy and successfully treated with plasma exchange and intravenous glucocorticoids. We also review the literature on the association between adult-onset Still's disease and thrombotic microangiopathy; our case is the 15(th) report on such an association. The mean age at onset of adult Still's disease in these cases was 31.60 years and the interval between the diagnosis of Still's disease and the onset of thrombotic microangiopathy ranged from 3 days to 17 years, with a female/male ratio of 2 : 1. In more than half the patients thrombotic microangiopathy occurred within the first 6 months after the diagnosis of the Still's disease. Eleven of the 15 (73%) patients were treated with plasmapheresis in addition to glucocorticoid therapy: eight of 11 (73%) had complete remission, the other three had permanent visual impairment and/or digital ischemia. Of the four patients who were not treated with plasmapheresis, two died, one developed end-stage renal disease and one had complete remission. Awareness of the possible development of thrombotic microangiopathy in patients with adult-onset Still's disease is critical, so that treatment can be initiated early and the complications and recurrence of thrombotic microangiopathy prevented. Patients with adult-onset Still's disease should be closely monitored for signs and symptoms of thrombotic microangiopathy during the first six months after diagnosis of the Still's disease.

Renal and Cardiac Endothelial Heterogeneity Impact Acute Vascular Rejection in Pig-to-Baboon Xenotransplantation

Xenograft outcomes are dictated by xenoantigen expression, for example, Gal alpha1, 3Gal (Gal), but might also depend on differing vascular responses. We investigated whether differential vascular gene expression in kidney and cardiac xenografts correlate with development of thrombotic microangiopathy (TM) and consumptive coagulation (CC). Immunosuppressed baboons underwent miniswine or hDAF pig kidney (n = 6) or heart (n = 7), or Gal-transferase gene-knockout (GalT-KO) (thymo)kidney transplantation (n = 14). Porcine cDNA miniarrays determined donor proinflammatory, apoptosis-related and vascular coagulant/fibrinolytic gene expression at defined time points; validated by mRNA, protein levels and immunopathology. hDAF-transgenic and GalT-KO xenografts, (particularly thymokidneys) exhibited prolonged survival. CC was seen with Gal-expressing porcine kidneys (3 of 6), only 1 of 7 baboons postcardiac xenotransplantation and was infrequent following GalT-KO grafts (1 of 14). Protective-type genes (heme oxygenase-I, superoxide dismutases and CD39) together with von Willebrand factor and P-selectin were upregulated in all renal grafts. Transcriptional responses in Gal-expressing xenografts were comparable to those seen in the infrequent GalT-KO rejection. In cardiac xenografts, fibrin deposition was associated with increased plasminogen activator inhibitor-1 expression establishing that gene expression profiles in renal and cardiac xenografts differ in a quantitative manner. These findings suggest that therapeutic targets may differ for renal and cardiac xenotransplants.

The vascular and coagulation issues in xenotransplantation

Vascular injury is a complex process that is central to the rejection of solid-organ xenografts in the preclinical pig-to-primate model of xenotransplantation. This review summarizes recent work that provides insights into the mechanisms of vascular injury in GalT KO pig xenografts. Several groups have reported further evidence for the importance of preexisting and elicited non-GalT antibodies, which are capable of fixing complement and activating graft endothelial cells. One important study showed that without complete suppression of these antibodies, there is a progressive activation and injury of xenograft endothelium, resulting in the development of thrombotic microangiopathy and graft loss. The mechanism of molecular incompatibilities affecting the control of coagulation across the species barrier has been examined in finer detail. The failure of pig thrombomodulin to promote activation of human protein C was found to be due to a deficiency in cofactor activity rather than to its capacity to bind human thrombin. On a positive note, pig tissue factor pathway inhibitor appears to be capable of efficiently regulating the human tissue factor pathway, contrary to earlier reports. We and others remain optimistic that overexpressing complement regulators anticoagulant proteins or both on the GalT knockout background will provide a significant protective effect, but definitive testing of this approach in the preclinical model is still forthcoming. Preventing the activation of xenograft endothelium and consequent intravascular coagulation is critical to the future success of solid-organ xenotransplantation.

Protein Phosphatase 2B Inhibition Promotes the Secretion of Von Willebrand Factor from Endothelial Cells

Ultra-large von Willebrand factor (ULVWF) multimers secreted from the Weibel-Palade bodies (WPBs) of endothelial cells plays a crucial role in the development of thrombotic microangiopathies. Secretion of WPB contents is regulated, in part, by the phosphorylation of vesicle trafficking proteins that constitutes the endothelial exocytotic machinery. In comparison to agonist-induced, protein kinase-dependent signaling pathways that regulate the exocytosis of WPB contents, a role for protein phosphatases in regulating endothelial exocytosis is currently undefined. In this study, we show that inhibition of serine/threonine protein phosphatase 2B (PP2B) activity by cyclosporine A (CsA), tacrolimus (FK506) or a cell-permeable PP2B autoinhibitory (AI) peptide promotes the secretion of hyper-adhesive ULVWF from human umbilical vein endothelial cells (HUVECs) in the absence of any other endothelial cell-stimulating agent. PP2B inhibitor-induced secretion and anchorage of ULVWF strings from HUVECs induce the tethering of adhesive platelets. In support of a role for PP2B in VWF secretion, we demonstrated that the catalytic subunit of PP2B expressed as a GST fusion protein interacts with the vesicle trafficking protein, Munc18c. Serine phosphorylation of Munc18c, which promotes granule exocytosis in other secretory cells, was significantly increased in CsA-treated HUVECs, suggesting that this process may be involved in CsA-mediated WPB exocytosis and secretion of VWF. Furthermore, plasma VWF antigen levels were also enhanced in CsA-treated mice, and siRNA-mediated knockdown of PP2Bb in HUVECs significantly enhanced VWF secretion. These observations suggest that CsA promotes VWF release, at least in part by inhibition of PP2B activity. These observations are compatible with the clinically observed association of CsA treatment and increased plasma VWF levels in humans, as well as the association between prolonged exposure to CsA and thrombotic microangiopathy in a subset of exposed patients.

Alterations of ADAMTS-13 Activity as a Common Indicator of the Endothelial Dysfunction Developing in Different Thrombotic Microangiopathies.

Injury to the endothelial cell is a key factor for the initiation and development of thrombotic microangiopathies (TMA). Endothelial dysfunction implies alterations of the von Willebrand factor (vWF) pathway. Severe deficiency of the vWF-cleaving protease activity has been traditionally associated with thrombotic thrombocytopenic purpura (TTP). However, there is ongoing evidence indicating that ADAMTS-13 may be a causal factor in the pathogenesis of other TMA.We evaluated whether ADAMTS-13 deficiency and autoantibodies inactivating the protease were prevalent in TMA with different physiopathological origin. Patients included in the study presented TMA associated with: TTP (n=13), hemolytic uremic syndrome (HUS) (n=4), gastrointestinal angiodysplasia (GA) (n=11), or stem cell transplantation (SCT) (n=3). We measured ADAMTS-13 activity and antigen (ADAMTS-13:Ag), the presence and inhibitory activity of autoantibodies to the protease, vWF:Ag, and vWF:multimeric pattern. ADAMTS-13 activity and inhibitory activity of autoantibodies were analyzed using a modification of the immunoblotting assay described by Furlan et al (1996). ADAMTS-13:Ag and the presence of IgG were measured by ELISA kits.The vWF:multimeric pattern was resolved by electrophoresis in agarose gels.In patients with TTP, undetectable ADAMTS-13 activity was found in 10 out of 13 patients, 9 of which had IgG against the metalloprotease and reduced ADAMTS-13:Ag levels. Plasma exchange normalized the ADAMTS-13:Ag levels and decreased IgG title. Interestingly, one case of TTP with autoantibodies was associated with clopidogrel treatment. Levels of vWF:Ag in these patients varied from 50 to 180%.As for patients with HUS, in 2 out of 4 ADAMTS-13 activity was absent and ADAMTS-13:Ag was reduced, but no IgG to the metalloprotease was detected. It should be pointed out that one of the cases of HUS was subsequent to cocaine abuse. In TMA associated with SCT and GA, ADAMTS-13 activity was around 20% in all the patients studied, although levels of the metalloprotease were within the control range (700–1400ng/ml). vWF:Ag levels were found to be significantly increased (to around 200%) in the former group of patients.In summary, presence of autoantibodies to ADAMTS-13 concurred with decreased antigen levels, reinforcing the hypothesis of an accelerated clearance of the metalloprotease in vivo. Among the patients studied, we found a clopidogrel associated TTP and a cocaine caused HUS. Presence of antibodies to ADAMTS-13 associated with clopidogrel treatment would suggest an immunological mechanism, which cannot be ruled out in the case of cocaine associated HUS. Overall, our results indicate that the absence of ADAMTS-13 activity is not specific for TTP. A reduced activity of the metalloprotease may be an indicator of endothelial dysfuntion as a common feature in different TMA.

Sodium transport antagonism reduces thrombotic microangiopathy in stroke-prone spontaneously hypertensive rats.

We examined whether amiloride, an agent that possesses epithelial sodium channel (ENaC)- and sodium/hydrogen exchange (NHE)-inhibitory activities, would exhibit renal vascular protection in saline-drinking, stroke-prone spontaneously hypertensive rats (SHRSP). SHRSP received amiloride (1.0 mg.kg(-1).day(-1), n = 6) or deionized water (3 mg.kg(-1).day(-1), n = 6) for 5 wk starting at 61 days of age. Systolic blood pressure (SBP) did not differ among the groups, and there was no difference in the average daily urine output, sodium excretion, or potassium excretion. Terminal urinary protein excretion, blood urea nitrogen, and renal thrombotic microangiopathic lesions were markedly reduced in the amiloride group with no difference in plasma renin activity (PRA). In a survival protocol, SHRSP infused subcutaneously with benzamil (0.7 mg.kg(-1).day(-1), n = 8), a selective ENaC inhibitor, dimethylamiloride (0.7 mg.kg(-1).day(-1), n = 8), a selective NHE inhibitor, or vehicle (n = 7) had comparable SBP. Dimethylamiloride nonetheless prolonged survival of SHRSP (P < 0.005 vs. vehicle), and benzamil-treated SHRSP lived even longer (P < 0.0001 vs. vehicle; P < 0.05 vs. dimethylamiloride). In a separate series, plasma potassium concentration was elevated by dimethylamiloride (3.4 +/- 0.1 meq/l, n = 8) and benzamil (3.3 +/- 0.1 meq/l, n = 8) relative to vehicle (3.0 +/- 0.1 meq/l, n = 8) at 4 but not at 24 h after dosing. These findings suggest the involvement of a sodium transport mechanism in the development of thrombotic microangiopathy in SHRSP, unrelated to marked changes in arterial pressure, PRA, plasma potassium, or urinary water and electrolyte excretion.

Relative effects of GAL+ and GALlow/- porcine hematopoietic cells on primate platelet aggregation and endothelial cell activation: implications for the induction of mixed hematopoietic chimerism in the pig-to-primate model.

The induction of porcine hematopoietic cell chimerism in preconditioned baboons has been hampered by the development of thrombotic microangiopathy. As pigs that lack expression of Gal alpha 1,3 Gal (Gal) may become available in the near future, we have explored the effects of porcine hematopoietic cells that express low or no Gal (Gal(low/-)) on baboon platelet aggregation and on human umbilical vein endothelial cell (HUVEC) activation. Porcine mobilized peripheral blood progenitor cells (PBPC; Gal(+)) and bone marrow mononuclear cells (BM; Gal(+) or Gal(low/-)) were investigated for their potential to (i) induce aggregation of baboon platelets, and (ii) to activate endothelial cells as measured by increased expression of vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and E-selectin on HUVEC. alpha-Galactosidase-treated PBPC were also investigated for their effect on platelet aggregation. Gal(+) PBPC and Gal(+) BM cells (10(7)) induced aggregation of baboon platelets by 42 and 31%, respectively, whereas Gal(low/-) BM cells did not induce any platelet aggregation. alpha-Galactosidase-treated PBPC induced less platelet aggregation than untreated PBPC. Gal(+) PBPC and Gal(+) BM cells (10(7)) increased expression of VCAM-1, ICAM-1 and E-selectin on HUVEC, whereas Gal(low/-) BM cells did not. In contrast to Gal(+) PBPC or BM, Gal(low/-) BM cells do not induce aggregation of baboon platelets or activate HUVEC. The induction of tolerance through mixed hematopoietic cell chimerism may be facilitated when alpha-galactosyltransferase-knockout pigs become available.

Aldosterone plays a pivotal role in the pathogenesis of thrombotic microangiopathy in SHRSP.

Angiotensin-converting enzyme inhibitors and aldosterone receptor antagonists ameliorate malignant nephrosclerotic lesions of thrombotic microangiopathy in salt-loaded, stroke-prone, spontaneously hypertensive rats (SHRSP) without controlling hypertension. This suggests that angiotensin II (Ang II) and/or aldosterone (ALDO) plays a critical role in renal injury in this model. For evaluating their relative roles in the pathogenesis of thrombotic microangiopathy, SHRSP were adrenalectomized and infused with vehicle, Ang II, or ALDO or were sham-operated for adrenalectomy (SHAM). Saline-drinking rats were assigned to one of four groups: SHAM, adrenalectomy, adrenalectomy + Ang II (25 ng/min, subcutaneously), or adrenalectomy + ALDO (40 micro g/kg per d, subcutaneously). All SHRSP received dexamethasone (12 micro g/kg per d, subcutaneously). Adrenalectomy did not show changes in body weight, plasma creatinine, sodium and potassium, and daily urinary sodium and potassium excretion; did not prevent hypertension but prevented proteinuria (12 +/- 1 versus 49 +/- 3 mg/d; P < 0.01); and abrogated thrombotic microangiopathy and decreased plasma aldosterone (<16 versus 710 +/- 91 pg/ml; P < 0.001) compared with SHAM. Systolic BP in adrenalectomy + Ang II and adrenalectomy + ALDO (238 +/- 8 and 241 +/- 9 mmHg, respectively) was similar to SHAM. Despite Ang II infusion, proteinuria (17 +/- 9 mg/d) and thrombotic microangiopathy and plasma aldosterone (18 +/- 18 pg/ml) remained low but daily urinary excretion of sodium and potassium were not different from adrenalectomy + ALDO. Adrenalectomy + ALDO showed plasma aldosterone levels of 735 +/- 147 pg/ml; plasma potassium was lower; plasma creatinine and proteinuria (78 +/- 7 mg/d) were greater and thrombotic microangiopathy lesions were comparable to SHAM. These results demonstrate a pivotal role for aldosterone in the development of thrombotic microangiopathy, independent of hypertension.

Antiphospholipid antibody syndrome and renal disease.

The antiphospholipid syndrome is a disorder of hypercoagulability in association with circulating antiphospholipid antibodies directed against epitopes on oxidized phospholipids complexed with a glycoprotein, beta 2-glycoprotein I, or against the glycoprotein itself. Disorders associated with antiphospholipid antibodies but not the antiphospholipid syndrome, such as HIV and hepatitis C infection, appear to lack antibodies to beta 2-glycoprotein I. Patients with systemic lupus erythematosus have a high incidence of antiphospholipid antibodies with a high risk of thrombosis, often associated with anticardiolipin antibodies, beta 2-glyocoprotein I antibodies, and the presence of the lupus anticoagulant. Antiphospholipid antibodies are a significant cause of morbidity and mortality in renal patients with and without systemic lupus erythematosus. Renal manifestations include thrombotic microangiopathy and large vessel thrombosis. In patients with end-stage renal disease, antiphospholipid antibodies are prevalent and may increase in frequency with time on dialysis, possibly as a result of oxidative stress incurred during dialysis. The presence of anticardiolipin antibodies have been associated with a high incidence of hemodialysis access clotting. In renal transplant recipients, the incidence of antiphospholipid antibodies is also elevated and may be associated with a higher incidence of primary graft non-function. Although patients with systemic lupus erythematosus have similar renal allograft survival rates to the general population, survival is worse for those patients who are also antiphospholipid antibody positive. Additionally, in hepatitis C positive renal transplant recipients, the presence of anticardiolipin antibodies confers an increased risk of thrombotic complications and the development of thrombotic microangiopathy. Treatment of antiphospholipid antibody syndrome remains centered around anticoagulation with warfarin. The use of immunosuppressive agents has had no dramatic effect on antiphospholipid antibody titers and little clinical effect on thrombotic events.

Cyclosporine and tacrolimus–associated thrombotic microangiopathy

The development of thrombotic microangiopathy (TMA) associated with the use of cyclosporine has been well documented. Treatments have included discontinuation or reduction of cyclosporine dose with or without concurrent plasma exchange, plasma infusion, anticoagulation, and intravenous immunoglobulin G infusion. However, for recipients of organ transplantation, removing the inciting agent is not without the attendant risk of precipitating acute rejection and graft loss. The last decade has seen the emergence of tacrolimus as a potent immunosuppressive agent with mechanisms of action virtually identical to those of cyclosporine. As a result, switching to tacrolimus has been reported to be a viable therapeutic option in the setting of cyclosporine-induced TMA. With the more widespread application of tacrolimus in organ transplantation, tacrolimus-associated TMA has also been recognized. However, literature regarding the incidence of the recurrence of TMA in patients exposed sequentially to cyclosporine and tacrolimus is limited. We report a case of a living donor renal transplant recipient who developed cyclosporine-induced TMA that responded to the withdrawal of cyclosporine in conjunction with plasmapheresis and fresh frozen plasma replacement therapy. Introduction of tacrolimus as an alternative immunosuppressive agent resulted in the recurrence of TMA and the subsequent loss of the renal allograft. Patients who are switched from cyclosporine to tacrolimus or vice versa should be closely monitored for the signs and symptoms of recurrent TMA.