Profiles of Coagulation and Fibrinolysis Activation-Associated Molecular Markers of Atypical Hemolytic Uremic Syndrome in the Acute Phase

Complement and coagulation crosstalk - Factor H in the spotlight

The immune complement and the coagulation systems are blood-based proteolytic cascades that are activated by pathway-specific triggers, based on protein-protein interactions and enzymatic cleavage reactions. Activation of these systems is finely balanced and controlled through specific regulatory mechanisms. The complement and coagulation systems are generally viewed as distinct, but have common evolutionary origins, and several interactions between these homologous systems have been reported. This complement and coagulation crosstalk can affect activation, amplification and regulatory functions in both systems. In this review, we summarize the literature on coagulation factors contributing to complement alternative pathway activation and regulation and highlight molecular interactions of the complement alternative pathway regulator factor H with several coagulation factors. We propose a mechanism where factor H interactions with coagulation factors may contribute to both complement and coagulation activation and regulation within the haemostatic system and fibrin clot microenvironment and introduce the emerging role of factor H as a modulator of coagulation. Finally, we discuss the potential impact of these protein interactions in diseases associated with factor H dysregulation or deficiency as well as evidence of coagulation dysfunction.

The pathophysiology, diagnosis, and management of sepsis-associated disseminated intravascular coagulation

BACKGROUND

The International Society on Thrombosis and Haemostasis (ISTH) released overt disseminated intravascular coagulation (DIC) diagnostic criteria in 2001. Since then, DIC has been understood as the end-stage consumptive coagulopathy and not the therapeutic target. However, DIC is not merely a decompensated coagulation disorder, but also includes early stages with systemic activation in coagulation. Thus, the ISTH has recently released sepsis-induced coagulopathy (SIC) criteria that can diagnose compensated-phase of coagulopathy with readily available biomarkers.

MAIN BODY

DIC is a laboratory-based diagnosis due to various critical conditions, although sepsis is the most common underlying disease. The pathophysiology of sepsis-associated DIC is multifactorial, and in addition to coagulation activation with suppressed fibrinolysis, multiple inflammatory responses are initiated by activated leukocytes, platelets, and vascular endothelial cells as part of thromboinflammation. Although overt DIC diagnostic criteria were established by ISTH to diagnose the advanced stage of DIC, additional criteria that can detect an earlier stage of DIC were needed for potential therapeutic considerations. Accordingly, the ISTH introduced SIC criteria in 2019 that are easy to use and require only platelet count, prothrombin time-international normalized ratio, and Sequential Organ Failure Assessment Score. SIC score can be used to evaluate disease severity and determine the timing of potential therapeutic interventions. One of the major disadvantages in treating sepsis-associated DIC is the lack of availability of specific therapeutic approaches beyond treating the underlying infection. Clinical trials to date have failed because included patients who were not coagulopathic. Nevertheless, in addition to infection control, anticoagulant therapy will be the choice for sepsis-associated DIC. Therefore, the efficacy of heparin, antithrombin, and recombinant thrombomodulin has to be proven in future clinical studies.

CONCLUSION

It is necessary to develop a novel therapeutic strategy against sepsis-associated DIC and improve the outcomes. Consequently, we recommend screening and monitoring DIC using SIC scoring system.

The role of the complement system in kidney glomerular capillary thrombosis

The complement system is part of the innate immune system. The crucial step in activating the complement system is the generation and regulation of C3 convertase complexes, which are needed to generate opsonins that promote phagocytosis, to generate C3a that regulates inflammation, and to initiate the lytic terminal pathway through the generation and activity of C5 convertases. A growing body of evidence has highlighted the interplay between the complement system, coagulation system, platelets, neutrophils, and endothelial cells. The kidneys are highly susceptible to complement-mediated injury in several genetic, infectious, and autoimmune diseases. Atypical hemolytic uremic syndrome (aHUS) and lupus nephritis (LN) are both characterized by thrombosis in the glomerular capillaries of the kidneys. In aHUS, congenital or acquired defects in complement regulators may trigger platelet aggregation and activation, resulting in the formation of platelet-rich thrombi in the kidneys. Because glomerular vasculopathy is usually noted with immunoglobulin and complement accumulation in LN, complement-mediated activation of tissue factors could partly explain the autoimmune mechanism of thrombosis. Thus, kidney glomerular capillary thrombosis is mediated by complement dysregulation and may also be associated with complement overactivation. Further investigation is required to clarify the interaction between these vascular components and develop specific therapeutic approaches.

A Limited Course of Eculizumab in a Child with the Atypical Hemolytic Uremic Syndrome and Pre-B Acute Lymphoblastic Leukemia on Maintenance Therapy: Case Report and Literature Review

Acute lymphoblastic leukemia (ALL) is considered a possible risk for the occurrence of thrombotic microangiopathies. We present a girl with pre-B ALL successfully treated according to the BFM ALL IC-2009 protocol on maintenance therapy followed by aHUS occurrence. This is the seventh case of HUS/aHUS on ALL maintenance therapy and the first with clearly documented eculizumab use in the early stage of aHUS/secondary TMA. Standard and additional parameters were used in aHUS monitoring alongside the reticulocyte production index adjusted for age (RPI/A) and the aspartate aminotransferase-to-platelet ratio index (APRI) as markers of hemolysis and rapid response following treatment. RPI/A and APRI are markers of bone marrow response to anemia serving as red blood cell vs. platelet recovery markers. Together they mark the exact recovery point of thrombotic microangiopathy and serve as a prognostic marker of eculizumab treatment success. During the 8-month treatment and 6-month follow-up, no recurrence of hemolysis, ALL relapse, or renal damage were observed. A systematic review of the literature revealed 14/312 articles; five children had aHUS before the onset of ALL, and two children had both diseases concurrently. At least 3/7 patients are attributed to aHUS, of whom 2/7 have renal damage. Potential undiagnosed/unpublished cases may be assumed.

The utility of platelet activation biomarkers in thrombotic microangiopathies

Primary thrombotic microangiopathies (TMAs) are observed in thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), while secondary TMAs have a wide range of etiologies. Early diagnosis and treatment of TMA are critical for patient well-being; however, distinguishing TTP from HUS on presentation is particularly challenging. Thrombocytopenia and platelet activation are central to different types of TMAs, thus limiting the utility of standard diagnostic approaches to evaluate the platelet function and hemostatic capacity. Alternative means of quantifying and monitoring changes to platelet activation and function are urgently needed. Activated platelets have been shown to interact with proteins of the complement and coagulation cascades and form part of inflammation processes engaged in TMA. Increased levels of platelet surface receptors as well as increased plasma levels of platelet-derived soluble proteins have been reported in TMAs. Elevated levels of platelet-leukocyte aggregates and platelet microparticles are also reported in different types of TMAs. Larger prospective evaluations of platelet activation markers in TMA using standardized assays, with comparison to cohorts of patients with thrombosis, coagulopathy, and thrombocytopenia, to evaluate the clinical usefulness of platelet markers in TMA are now needed. This review will summarize the current knowledge around platelet activation markers and critically evaluate their utility in diagnosis and prognosis of TMA patients.

Association between plasma complement factor H concentration and clinical outcomes in patients with sepsis

Aim

The complement system is important for defending against pathogens, however, excessive complement activation is associated with a poor prognosis and organ dysfunction in sepsis. Complement factor H (CFH) acts to prevent excessive complement activation and damage to the self through the regulation of the complement alternative pathway. We investigated the association between plasma CFH levels on admission to the intensive care unit (ICU) and 90‐day mortality, severity scores, and organ dysfunction in patients with sepsis.

Methods

We assessed the relationship between the plasma CFH on admission to the ICU and 90‐day mortality, severity scores such as the Acute Physiology and Chronic Health Evaluation II score, Sequential Organ Failure Assessment score, and Simplified Acute Physiology Score 2, and organ dysfunction.

Results

This analysis included 62 patients. The plasma CFH levels were significantly lower in 90‐day non‐survivors than in survivors (70.0 μg/mL [interquartile range, 51.2–97.6] versus 104.8 μg/mL [interquartile range, 66.8–124.2]; P = 0.006) . The plasma CFH levels were associated with 90‐day mortality (odds ratio 0.977; 95% confidence interval, 0.957–0.994; P = 0.01). The plasma CFH levels were negatively correlated with severity scores. The Sequential Organ Failure Assessment scores for the coagulation and neurological components were negatively correlated with the CFH concentration.

Conclusion

Lower plasma levels of CFH were associated with increased severity and mortality in patients with sepsis on admission to the ICU and were correlated with central nervous system dysfunction and coagulopathy.

Microvascular thrombosis: experimental and clinical implications

A significant amount of clinical and research interest in thrombosis is focused on large vessels (eg, stroke, myocardial infarction, deep venous thrombosis, etc.); however, thrombosis is often present in the microcirculation in a variety of significant human diseases, such as disseminated intravascular coagulation, thrombotic microangiopathy, sickle cell disease, and others. Further, microvascular thrombosis has recently been demonstrated in patients with COVID-19, and has been proposed to mediate the pathogenesis of organ injury in this disease. In many of these conditions, microvascular thrombosis is accompanied by inflammation, an association referred to as thromboinflammation. In this review, we discuss endogenous regulatory mechanisms that prevent thrombosis in the microcirculation, experimental approaches to induce microvascular thrombi, and clinical conditions associated with microvascular thrombosis. A greater understanding of the links between inflammation and thrombosis in the microcirculation is anticipated to provide optimal therapeutic targets for patients with diseases accompanied by microvascular thrombosis.

Quetiapine-induced thrombotic microangiopathy in a patient on maintenance dialysis

Quetiapine has been reported to cause immune-mediated thrombotic microangiopathy (TMA), although few cases have been reported thus far. A 71-year-old man with autosomal dominant polycystic kidney disease on maintenance dialysis was hospitalized with a hemorrhagic basal ganglia stroke, and was treated with 25 mg quetiapine for delirium from day 4 of admission. There was no worsening of consciousness, fever, diarrhea, or elevated blood pressure during the hospitalization. Gingival bleeding appeared on day 35, and the platelet count on day 38 was 0.5 × 10⁴/μL (13.2 × 10⁴/μL on day 16). The presence of 1% schistocytes, high LDH level, inability to measure haptoglobin, negative direct Coombs test, and normal prothrombin time and activated partial thromboplastin time indicated TMA. We considered an exclusionary diagnosis of drug-induced TMA, because of normal ADAMTS13 activity, no evidence of complement activation and the absence of Shiga toxin or symptoms of collagen disease or cancer. Quetiapine was the most likely causative factor; however, all drugs, including heparin, were discontinued or changed. Due to persistent microbleeding, platelet transfusions were performed several times. After only quetiapine was discontinued, the platelet count recovered smoothly to 3.1 and 7.2 × 10⁴/μL on days 45 and 72, respectively; LDH and fibrinogen levels normalized on day 47. All medications, except quetiapine, were restarted sequentially after day 47, without subsequent thrombocytopenia. Platelet activation predominantly by a drug-dependent antibody might be the etiology of quetiapine-induced TMA. Plasmapheresis may not be necessary for quetiapine, because of its unproven efficacy in drug-induced TMA.