Plasmin-cleaved von Willebrand factor as a biomarker for microvascular thrombosis.

ABSTRACT: von Willebrand factor (VWF) is an essential contributor to microvascular thrombosis. Physiological cleavage by ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) limits its prothrombotic properties, explaining why ADAMTS13 deficiency leads to attacks of microthrombosis in patients with thrombotic thrombocytopenic purpura (TTP). We previously reported that plasminogen activation takes place during TTP attacks in these patients. Furthermore, stimulation of plasminogen activation attenuates pathogenesis in preclinical TTP models in vivo. This suggests that plasmin is an endogenous regulator of VWF thrombogenicity, in particular when ADAMTS13 falls short to prevent microvascular occlusions. VWF cleavage by plasmin is biochemically distinct from cleavage by ADAMTS13. We hypothesized that plasmin-cleaved VWF (cVWF) holds value as a biomarker of microvascular thrombosis. Here, we describe the development of a variable domain of heavy-chain-only antibody (VHH)-based bioassay that can distinguish cVWF from intact and ADAMTS13-cleaved VWF in plasma. We validate this assay by tracking cVWF release during degradation of microthombi in vitro. We demonstrate that endogenous cVWF formation takes place in patients with TTP during acute attacks of thrombotic microangiopathy but not in those in remission. Finally, we show that therapeutic plasminogen activation in a mouse model of TTP amplifies cVWF formation, which is accompanied by VWF clearance. Our combined findings indicate that cVWF is released from microthrombi in the context of microvascular occlusion.

Decreased Levels of Soluble Developmental Endothelial Locus-1 Are Associated with Thrombotic Microangiopathy in Pregnancy.

HELLP (Hemolysis, Elevated Liver enzymes and Low Platelets) syndrome is a life-threatening complication of pregnancy, which is often secondary to preeclampsia. To date, there is no biomarker in clinical use for the early stratification of women with preeclampsia who are under increased risk of HELLP syndrome. Herein, we show that the levels of circulating developmental endothelial locus-1 (DEL-1), which is an extracellular immunomodulatory protein, are decreased in patients with HELLP syndrome compared to preeclampsia. DEL-1 levels are also negatively correlated with the circulating levels of kidney injury molecule-1 (KIM-1), which is a biomarker for disorders associated with kidney damage. Receiver-operating characteristic curve analysis for DEL-1 levels and the DEL-1 to KIM-1 ratio demonstrates that these values could be used as a potential biomarker that distinguishes patients with HELLP syndrome and preeclampsia. Finally, we show that placental endothelial cells are a source for DEL-1, and that the expression of this protein in placenta from patients with HELLP syndrome is minimal. Taken together, this study shows that DEL-1 is downregulated in HELLP syndrome both in the circulation and at the affected placental tissue, suggesting a potential role for this protein as a biomarker, which must be further evaluated.

Microlyse: a thrombolytic agent that targets VWF for clearance of microvascular thrombosis.

Thrombotic microangiopathies are hallmarked by attacks of disseminated microvascular thrombosis. In thrombotic thrombocytopenic purpura (TTP), this is caused by a rise in thrombogenic ultra-large von Willebrand factor (VWF) multimers because of ADAMTS13 deficiency. We previously reported that systemic plasminogen activation is therapeutic in a TTP mouse model. In contrast to its natural activators (ie, tissue plasminogen activator and urokinase plasminogen activator [uPA]), plasminogen can directly bind to VWF. For optimal efficacy and safety, we aimed to focus and accelerate plasminogen activation at sites of microvascular occlusion. We here describe the development and characterization of Microlyse, a fusion protein consisting of a high-affinity VHH targeting the CT/CK domain of VWF and the protease domain of uPA, for localized plasminogen activation on microthrombi. Microlyse triggers targeted destruction of platelet-VWF complexes by plasmin on activated endothelial cells and in agglutination studies. At equal molar concentrations, Microlyse degrades microthrombi sevenfold more rapidly than blockade of platelet-VWF interactions with a bivalent humanized VHH (caplacizumab*). Finally, Microlyse attenuates thrombocytopenia and tissue damage (reflected by increased plasma lactate dehydrogenase activity, as well as PAI-1 and fibrinogen levels) more efficiently than caplacizumab* in an ADAMTS13-/- mouse model of TTP, without affecting hemostasis in a tail-clip bleeding model. These findings show that targeted thrombolysis of VWF by Microlyse is an effective strategy for the treatment of TTP and might hold value for other forms of VWF-driven thrombotic disease.

VEGF-VEGFR2 inhibitor-associated hyaline occlusive glomerular microangiopathy: a Japanese single-center experience.

BACKGROUND: Inhibitors of vascular endothelial growth factor (VEGF)-VEGF receptor 2 (VEGFR2) signaling, such as bevacizumab (Bmab), are used for the treatment of various advanced cancers. However, these inhibitors induce renal thrombotic microangiopathy (TMA). Recently, two European cohort studies showed a distinctive histopathological pseudothrombotic pattern different from TMA in Bmab-treated patients. METHODS: We analyzed 9 renal biopsies from proteinuric cancer patients treated with VEGF-VEGFR2 inhibitors in our Japanese cohort. Clinical and laboratory features were also assessed in these patients. RESULTS: All 9 patients had moderate to heavy proteinuria with normal or slightly elevated serum creatinine levels. On light microscopy, a patchy pattern of hemispherical/spherical lesions along glomerular capillary walls was a characteristic finding. On immunofluorescence microscopy, staining for immunoglobulins (IgM dominant) at varying intensities was observed mainly along glomerular capillary walls. Especially, hemispherical/spherical positive staining for immunoglobulins was a characteristic pattern. Immunohistochemical studies showed positive staining for immunoglobulins and negative staining for CD61-positive platelets in capillary hemispherical/spherical lesions and positive VEGF staining in podocytes. On electron microscopy, variably electron-dense material in dilated glomerular capillaries and partial effacement of podocyte foot processes were observed. After the withdrawal of VEGF-VEGFR2 inhibitors, proteinuria improved without any specific treatment in 8 patients. CONCLUSIONS: Histopathological findings in our patients treated with VEGF-VEGFR2 inhibitors were consistent with those observed in the recently described new form of Bmab-associated hyaline occlusive glomerular microangiopathy. This form should be considered in proteinuric cancer patients treated with VEGF-VEGFR2 inhibitors. Discontinuing VEGF-VEGFR2 inhibitors may lead to improvement of glomerular microangiopathy induced by these drugs.

Loss of diacylglycerol kinase ε causes thrombotic microangiopathy by impairing endothelial VEGFA signaling.

Loss of function of the lipid kinase diacylglycerol kinase ε (DGKε), encoded by the gene DGKE, causes a form of atypical hemolytic uremic syndrome that is not related to abnormalities of the alternative pathway of the complement, by mechanisms that are not understood. By generating a potentially novel endothelial specific Dgke-knockout mouse, we demonstrate that loss of Dgke in the endothelium results in impaired signaling downstream of VEGFR2 due to cellular shortage of phosphatidylinositol 4,5-biphosphate. Mechanistically, we found that, in the absence of DGKε in the endothelium, Akt fails to be activated upon VEGFR2 stimulation, resulting in defective induction of the enzyme cyclooxygenase 2 and production of prostaglandin E2 (PGE2). Treating the endothelial specific Dgke-knockout mice with a stable PGE2 analog was sufficient to reverse the clinical manifestations of thrombotic microangiopathy and proteinuria, possibly by suppressing the expression of matrix metalloproteinase 2 through PGE2-dependent upregulation of the chemokine receptor CXCR4. Our study reveals a complex array of autocrine signaling events downstream of VEGFR2 that are mediated by PGE2, that control endothelial activation and thrombogenic state, and that result in abnormalities of the glomerular filtration barrier.

Extracellular Vesicles Tune the Immune System in Renal Disease: A Focus on Systemic Lupus Erythematosus, Antiphospholipid Syndrome, Thrombotic Microangiopathy and ANCA-Vasculitis.

Extracellular vesicles (EV) are microparticles released in biological fluids by different cell types, both in physiological and pathological conditions. Owing to their ability to carry and transfer biomolecules, EV are mediators of cell-to-cell communication and are involved in the pathogenesis of several diseases. The ability of EV to modulate the immune system, the coagulation cascade, the angiogenetic process, and to drive endothelial dysfunction plays a crucial role in the pathophysiology of both autoimmune and renal diseases. Recent studies have demonstrated the involvement of EV in the control of renal homeostasis by acting as intercellular signaling molecules, mediators of inflammation and tissue regeneration. Moreover, circulating EV and urinary EV secreted by renal cells have been investigated as potential early biomarkers of renal injury. In the present review, we discuss the recent findings on the involvement of EV in autoimmunity and in renal intercellular communication. We focused on EV-mediated interaction between the immune system and the kidney in autoimmune diseases displaying common renal damage, such as antiphospholipid syndrome, systemic lupus erythematosus, thrombotic microangiopathy, and vasculitis. Although further studies are needed to extend our knowledge on EV in renal pathology, a deeper investigation of the impact of EV in kidney autoimmune diseases may also provide insight into renal biological processes. Furthermore, EV may represent promising biomarkers of renal diseases with potential future applications as diagnostic and therapeutic tools.

Complement as the enabler of carfilzomib-induced thrombotic microangiopathy.

Carfilzomib has been associated with the development of thrombotic microangiopathy (TMA) in relapsed/refractory multiple myeloma patients, a severe disease with no currently available aetiological treatment. We evaluated the potential role of terminal complement pathway in four patients with carfilzomib-induced TMA. Membrane attack complex (C5b-9) deposition on endothelial cells in culture exposed to plasma from patients during the acute phase of the disease suggests complement overactivation as a mechanism of potential endothelial damage in three out of four patients. If confirmed in larger cohorts, C5b-9 evaluation will allow early identification of patients who could benefit from complement blockade and treatment monitoring.

Reduced sensitivity of PLASMIC and French scores for the diagnosis of thrombotic thrombocytopenic purpura in older individuals.

BACKGROUND: Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disorder characterized by thrombocytopenia, microangiopathic hemolysis, and ischemic organ failure. The PLASMIC and French TTP scores can help guide clinical decisions when ADAMTS13 testing is not immediately available. Older individuals often present atypically, but the impact of age on these tools is not known. STUDY DESIGN AND METHODS: We calculated the sensitivity and specificity of the PLASMIC and French TTP scores in patients enrolled in the Johns Hopkins thrombotic microangiopathy (TMA) registry. RESULTS: Of 257 patients with TMA enrolled in the registry, we excluded patients less than 18 years of age (n = 19), with prior TMA (n = 81) or who initially presented at another hospital (n = 25). The remaining 132 patients (75 with TTP and 57 with other TMA) were analyzed. Sensitivity of a French score of 2 decreased with age and was 72.2%, 61.5%, and 46.2% for ages 18 to 39, 40 to 59, and ≥ 60 years old, respectively. A PLASMIC score ≥ 5 had higher sensitivity than the French score but this also decreased with age; sensitivity was 91.4% (95% confidence interval [CI], 76.9-98.2), 78.3% (95% CI, 56.3-92.5), and 76.9% (95% CI, 46.2-95.0) for patients 18 to 39, 40 to 59, and ≥ 60 years old, respectively. Older patients had higher platelet counts and serum creatinine than the youngest group, contributing to the loss in sensitivity. CONCLUSION: The PLASMIC and French TTP scores have reduced sensitivity at age ≥ 60 years and are less reliable in identifying TTP in older patients. A high index of suspicion and availability of rapid ADAMTS13 assays is required to correctly diagnose all patients with TTP.

Pathophysiology and Pathology of Acute Kidney Injury in Patients With COVID-19.

Acute kidney injury (AKI) is common among hospitalized patients with Coronavirus Infectious Disease 2019 (COVID-19), with the occurrence of AKI ranging from 0.5% to 80%. The variability in the occurrence of AKI has been attributed to the difference in geographic locations, race/ethnicity, and severity of illness. AKI among hospitalized patients is associated with increased length of stay and in-hospital deaths. Even patients with AKI who survive to hospital discharge are at risk of developing chronic kidney disease or end-stage kidney disease. An improved knowledge of the pathophysiology of AKI in COVID-19 is crucial to mitigate and manage AKI and to improve the survival of patients who developed AKI during COVID-19. The goal of this article is to provide our current understanding of the etiology and the pathophysiology of AKI in the setting of COVID-19.

Complement and coagulation: key triggers of COVID-19-induced multiorgan pathology.

In a stunningly short period of time, the unexpected coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has turned the unprepared world topsy-turvy. Although the rapidity with which the virus struck was indeed overwhelming, scientists throughout the world have been up to the task of deciphering the mechanisms by which SARS-CoV-2 induces the multisystem and multiorgan inflammatory responses that, collectively, contribute to the high mortality rate in affected individuals. In this issue of the JCI, Skendros and Mitsios et al. is one such team who report that the complement system plays a substantial role in creating the hyperinflammation and thrombotic microangiopathy that appear to contribute to the severity of COVID-19. In support of the hypothesis that the complement system along with neutrophils and platelets contributes to COVID-19, the authors present empirical evidence showing that treatment with the complement inhibitor compstatin Cp40 inhibited the expression of tissue factor in neutrophils. These results confirm that the complement axis plays a critical role and suggest that targeted therapy using complement inhibitors is a potential therapeutic option to treat COVID-19-induced inflammation.

Management of thrombotic microangiopathy in pregnancy and postpartum: report from an international working group.

Pregnancy and postpartum are high-risk periods for different forms of thrombotic microangiopathy (TMA). However, the management of pregnancy-associated TMA remains ill defined. This report, by an international multidisciplinary working group of obstetricians, nephrologists, hematologists, intensivists, neonatologists, and complement biologists, summarizes the current knowledge of these potentially severe disorders and proposes a practical clinical approach to diagnose and manage an episode of pregnancy-associated TMA. This approach takes into account the timing of TMA in pregnancy or postpartum, coexisting symptoms, first-line laboratory workup, and probability-based assessment of possible causes of pregnancy-associated TMA. Its aims are: to rule thrombotic thrombocytopenic purpura (TTP) in or out, with urgency, using ADAMTS13 activity testing; to consider alternative disorders with features of TMA (preeclampsia/eclampsia; hemolysis elevated liver enzymes low platelets syndrome; antiphospholipid syndrome); or, ultimately, to diagnose complement-mediated atypical hemolytic uremic syndrome (aHUS; a diagnosis of exclusion). Although they are rare, diagnosing TTP and aHUS associated with pregnancy, and postpartum, is paramount as both require urgent specific treatment.

When to consider targeted therapies in thrombotic microangiopathies in the modern era: walking the tightrope between cost, safety, and efficacy.

Thrombotic Microangiopathy (TMA) is a heterogeneous collection of syndromes that encompasses TTP, HUS, and other processes characterized by thrombocytopenia, microangiopathic hemolytic anemia, and, if untreated, organ failure and death. Novel therapies have recently been approved for the management of certain thrombotic microangiopathies, including caplacizumab for immune-mediated TTP, and eculizumab for atypical HUS. These options have complicated the standard workflow, which includes initiation of plasma exchange until ADAMTS13 testing can be resulted. Given such results may take several days, there is indecision regarding the appropriate initial management of TMA. Decisions regarding caplacizumab and eculizumab are complex, and include considerations over costs, side effects, and efficacy. In the following forum, we discuss the current data and pose possible management strategies in patients with TMA before final diagnosis can be obtained.

mTORC Pathway Activation and Effect of Sirolimus on Native Kidney Antiphospholipid Syndrome Nephropathy: A Case Report.

Despite optimal anticoagulation and blood pressure control, patients with antiphospholipid syndrome (APS) nephropathy frequently progress to kidney failure, and recurrence after transplantation is common. The mTORC (mechanistic target of rapamycin complex) pathway was recently identified as a potential intermediate and a therapeutic target in vascular lesions associated with APS nephropathy. However, these results were derived from the retrospective analysis of a small cohort of patients receiving sirolimus after kidney transplantation. Therefore, they warranted external validation and the demonstration of the potential benefit of sirolimus in native kidney APS nephropathy. We report a patient with active APS nephropathy lesions occurring on native kidneys, in which endothelial mTORC activation was substantiated at the molecular level. Treatment with sirolimus was shown on a repeat kidney biopsy to successfully inhibit the AKT/mTORC pathway and was associated with significant improvement in kidney function and lesions of vasculopathy. Drug tolerance was excellent during the entire follow-up. This case validates and extends previous observations in kidney transplant recipients and demonstrates that endothelial activation of the AKT/mTORC pathway occurs in the damaged renal vasculature of native kidneys in APS nephropathy. These findings further support the potential of precision medicine and the use of mTORC activation as a biomarker of disease activity and as therapeutic target in patients with APS nephropathy.

The alternative complement pathway activation product Ba as a marker for transplant-associated thrombotic microangiopathy.

BACKGROUND: Transplant-associated thrombotic microangiopathy (TA-TMA) occurs after hematopoietic stem cell transplantation (HSCT) and is characterized by microvascular thrombosis and end-organ injury particularly of the kidneys. TA-TMA is challenging to diagnose and treat, which can lead to long-term complications and death in patients with severe disease. Studies have shown that genetic abnormalities of the alternative complement pathway (AP) are associated with TA-TMA. We hypothesized that patients with TA-TMA may generate elevated levels of the AP activation product, Ba, compared with HSCT patients without TA-TMA. PROCEDURE: We longitudinally measured plasma levels of complement activation products C3a, Ba, and C5a in 14 HSCT patients: 7 with TA-TMA and 7 without TA-TMA. We assessed renal function by calculating estimated glomerular filtration rate (eGFR) and correlated the extent of AP activation with renal dysfunction in both patient populations. RESULTS: The median days from HSCT to study enrollment were 154 (39-237) in the TA-TMA group and 84 (39-253) in the HSCT group without TA-TMA. Median Ba levels (ng/mL) at enrollment were 1096.9 (826.5-1562.0) in the TA-TMA group and 725.7 (494.7-818.9) in the HSCT group without TA-TMA (P = 0.007). Over the study duration, Ba levels inversely correlated with eGFR. There were no differences in C3a, C5a, or sC5b9 levels between the two populations at any measured interval. CONCLUSIONS: We conclude in this preliminary study that Ba protein may serve as a marker for TA-TMA, and furthermore, that components generated in the early phase of AP activation may be involved in the pathogenesis of renal endothelial injury in TA-TMA.

Diagnostic and Risk Factors for Complement Defects in Hypertensive Emergency and Thrombotic Microangiopathy.

Hypertensive emergency can cause thrombotic microangiopathy (TMA) in the kidneys with high rates of end-stage renal disease (ESRD) and vice versa. The conundrum of hypertension as the cause of TMA or consequence of TMA on the background of defects in complement regulation remains difficult. Patients with hypertensive emergency and TMA on kidney biopsy were tested for ex vivo C5b9 formation on the endothelium and rare variants in complement genes to identify complement-mediated TMA. We identified factors associated with defects in complement regulation and poor renal outcomes. Massive ex vivo C5b9 formation was found on resting endothelial cells in 18 (69%) out of 26 cases at the presentation, including the 9 patients who carried at least one rare genetic variant. Thirteen (72%, N=18) and 3 (38%, N=8) patients with massive and normal ex vivo complement activation, respectively, progressed to ESRD (P=0.03). In contrast to BP control, inhibition of C5 activation prevented ESRD to occur in 5 (83%, N=6) patients with massive ex vivo complement activation. TMA-related graft failure occurred in 7 (47%, N=15) donor kidneys and was linked to genetic variants. The assessment of both ex vivo C5b9 formation and screening for rare variants in complement genes may categorize patients with hypertensive emergency and TMA into different groups with potential therapeutic and prognostic implications. We propose an algorithm to recognize patients at the highest risk for defects in complement regulation.

Classifications of scleroderma renal crisis and reconsideration of its pathophysiology.

Categorization of scleroderma renal crisis (SRC) as hypertensive or normotensive can potentially overlook the underlying pathophysiology that might be unique in each patient, as they often exhibit a mixture of distinct pathological characteristics of narrowly defined SRC (nd-SRC) and systemic sclerosis associated thrombocytic micro-angiopathy (SSc-TMA). In this review, we provide evidence suggesting that better categorization of patients presenting with certain clinical features of both nd-SRC and TMA will improve treatment approaches. Based on our clinical experience and literature review, distinguishing between nd-SRC and SSc-TMA is important because the association of SSc-TMA with prior steroid administration and poor prognosis was stronger than that of nd-SRC. Although the two pathological entities cannot be easily distinguished based on blood pressure, we suggest that the detailed clinical course is helpful. Typically, nd-SRC exhibits prominently elevated blood pressure and worsening of renal function initially, followed by mild thrombocytopenia. Conversely, SSc-TMA presents first with severe thrombocytopenia, followed by elevated blood pressure and renal function deterioration. The degree of involvement in each pathological condition should be considered for determination of appropriate therapeutic interventions and prognostic prediction.

Transplant-associated thrombotic microangiopathy: Diagnostic challenges and management strategies.

Transplant-associated thrombotic microangiopathy (TA-TMA) is one of the early endothelial complications post Hematopoietic Stem Cell Transplant (HSCT). Several mechanisms during HSCT can contribute to systemic capillary endothelial damage which can lead to TA-TMA among other complications as capillary leak syndrome or engraftment syndrome. Early diagnosis of TA-TMA contributes a challenge due to overlapping clinical manifestations and the absence of specific diagnostic criteria. Incidence is greatly variable between 1-76% according to risk factors of patients and the definition used to confirm the diagnosis. The mortality rates in patients who develop severe TA-TMA are in excess of 80%. Early treatment improves the outcome. This review outlines the diagnostic challenges and therapeutic options for TA-TMA.