Activated protein C in neuroprotection and malaria

Specific DNA aptamer-immobilized cryogel membranes as novel bioaffinity supports and their potential for the purification of activated protein C

Activated protein C (APC), a serine protease produced from zymogen protein C (PC), is the key enzyme of the protein C pathway. APC has anticoagulant, anti-inflammatory, and cytoprotective features. APC has recently been shown to significantly reduce coagulation as well as mortality in patients with severe sepsis. Herein, we aimed to develop an affinity support material that allows the purification of plasma APC for the first time. In this research, a novel APC-specific DNA aptamer-based poly(2-hydroxyethyl methacrylate-glycidyl methacrylate) (poly(HEMA-GMA/DNA-Apt)) macroporous cryogel membrane at different molar ratios was prepared using affinity binding method and their potential for purification and identification of APC was investigated. The DNA aptamer-immobilized cryogels were characterized to examine their structural and morphological properties. The effect of pH, initial concentration, temperature, ionic strength difference, and flow rate changes was examined. Selectivity studies were performed in the presence of APC and competitive proteins, and cryogel support materials were shown to have a very high affinity for APC. Adsorption capacity was found to be 89.02 mg/g. Finally, NaCl revealed efficiency for APC desorption and the reuse of cryogels was successfully tested for ten cycles.

Unraveling the Molecular Mechanisms of Activated Protein C (APC) in Mitigating Reperfusion Injury and Cardiac Ischemia: a Promising Avenue for Novel Therapeutic Interventions

Ischemic heart disease, which results from plaque formation in the coronary arteries, hinders the flow of oxygenated blood to the heart, leading to ischemia. Reperfusion injury remains a significant challenge for researchers, and the mechanisms underlying myocardial ischemia-reperfusion injury (MIRI) are not entirely understood. The review directs future research into potential targets in clinical treatment based on our present understanding of the pathophysiological mechanisms of MIRI. The study provides insights into the mechanisms underlying MIRI and offers direction for future research in this area. The use of targeted therapies may hold promise in improving cardiac function in the elderly and minimizing the adverse effects of revascularization therapies. The purpose of this review is to analyze the role of activated protein C (APC) in the pathogenesis of ischemic heart disease, heart failure, and myocardial ischemia-reperfusion injury, and discuss the potential of APC-based therapeutics.

Different PfEMP1-expressing Plasmodium falciparum variants induce divergent endothelial transcriptional responses during co-culture

The human malaria parasite Plasmodium falciparum is responsible for the majority of mortality and morbidity caused by malaria infection and differs from other human malaria species in the degree of accumulation of parasite-infected red blood cells in the microvasculature, known as cytoadherence or sequestration. In P. falciparum, cytoadherence is mediated by a protein called PfEMP1 which, due to its exposure to the host immune system, undergoes antigenic variation resulting in the expression of different PfEMP1 variants on the infected erythrocyte membrane. These PfEMP1s contain various combinations of adhesive domains, which allow for the differential engagement of a repertoire of endothelial receptors on the host microvasculature, with specific receptor usage associated with severe disease. We used a co-culture model of cytoadherence incubating human brain microvascular endothelial cells with erythrocytes infected with two parasite lines expressing different PfEMP1s that demonstrate different binding profiles to vascular endothelium. We determined the transcriptional profile of human brain microvascular endothelial cells (HBMEC) following different incubation periods with infected erythrocytes, identifying different transcriptional profiles of pathways previously found to be involved in the pathology of severe malaria, such as inflammation, apoptosis and barrier integrity, induced by the two PfEMP1 variants.

Biomarkers and the outcomes of ischemic stroke

Biomarkers are measurable substances that could be used as objective indicators for disease diagnosis, responses to treatments, and outcomes predictions. In this review, we summarized the data on a number of important biomarkers including glutamate, S100B, glial fibrillary acidic protein, receptor for advanced glycation end-products, intercellular adhesion molecule-1, von willebrand factor, matrix metalloproteinase-9, interleukin-6, tumor necrosis factor-a, activated protein C, copeptin, neuron-specific enolase, tau protein, gamma aminobutyric acid, blood glucose, endothelial progenitor cells, and circulating CD34-positive cells that could be potentially used to indicate the disease burden and/or predict clinical outcome of ischemic stroke. We examined the relationship between specific biomarkers and disease burden and outcomes and discussed the potential mechanisms underlying the relationship. The clinical significance and implications of these biomarkers were also discussed.

Natural anticoagulant discovery, the gift that keeps on giving: finding FV-Short

The complex reactions of blood coagulation are balanced by several natural anticoagulants resulting in tuned hemostasis. During several decades, the knowledge base of the natural anticoagulants has greatly increased and we have also learned about antiinflammatory and cytoprotective activities expressed by antithrombin and activated protein C (APC). Some coagulation proteins have also been found to function as anticoagulants; e.g., thrombin when bound to thrombomodulin activates protein C. Another example is factor V (FV), which in addition to being a procofactor to FVa has emerged as an anticoagulant. The discovery of APC resistance, caused by FVLeiden, as a thrombosis risk factor resulted in the identification of FV as an APC cofactor working in synergy with protein S in the regulation of FVIIIa in the Xase complex. More recently, a natural anticoagulant FV splice isoform (FV-Short) was discovered when investigating the East Texas bleeding disorder. In FV-Short, the truncated B domain exposes a high-affinity binding site for tissue factor pathway inhibitor alpha (TFPIα), and together with protein S a high-affinity trimolecular complex is generated. The FXa-inhibitory activity of TFPIα is synergistically stimulated by FV-Short and protein S. The circulating FV-Short/protein S/TFPIα complex concentration is normally low (≈0.2 nM) but provides an anticoagulant threshold. In the East Texas bleeding, the concentration of the complex, and thus the threshold, is increased 10-fold, which results in bleeding manifestations. The anticoagulant properties of FV were discovered during investigations of individual patients and follow the great tradition of bed-to-bench and bench-to-bed research in the coagulation field.

Host-directed therapies for malaria: possible applications and lessons from other indications

Host-directed therapies (HDT) are rapidly advancing as a new and clinically relevant strategy to treat infectious disease. The application of HDT can be broadly used to (i) inhibit host factors essential for pathogen development, including host protein kinases, (ii) control detrimental immune signalling, resulting from excessive release of cytokines, chemokines and extracellular vesicles and (iii) strengthen host defence mechanisms, such as tight junctions in the endothelium. For malaria and other eukaryotic parasite-causing diseases, HDTs could provide a novel avenue to combat the growing resistance seen across all antimicrobials and provide protection against the severe forms of disease through modulation of the host immune response.

An engineered activated factor V for the prevention and treatment of acute traumatic coagulopathy and bleeding in mice

^superFVa arrests severe bleeding and prevents the development of ATC after trauma.

^superFVa therapy restores functional hemostasis when initiated after onset of ATC caused by traumatic bleeding.

Acute traumatic coagulopathy (ATC) occurs in approximately 30% of patients with trauma and is associated with increased mortality. Excessive generation of activated protein C (APC) and hyperfibrinolysis are believed to be driving forces for ATC. Two mouse models were used to investigate whether an engineered activated FV variant (^superFVa) that is resistant to inactivation by APC and contains a stabilizing A2-A3 domain disulfide bond can reduce traumatic bleeding and normalize hemostasis parameters in ATC. First, ATC was induced by the combination of trauma and shock. ATC was characterized by activated partial thromboplastin time (APTT) prolongation and reductions of factor V (FV), factor VIII (FVIII), and fibrinogen but not factor II and factor X. Administration of ^superFVa normalized the APTT, returned FV and FVIII clotting activity levels to their normal range, and reduced APC and thrombin-antithrombin (TAT) levels, indicating improved hemostasis. Next, a liver laceration model was used where ATC develops as a consequence of severe bleeding. ^superFVa prophylaxis before liver laceration reduced bleeding and prevented APTT prolongation, depletion of FV and FVIII, and excessive generation of APC. Thus, prophylactic administration of ^superFVa prevented the development of ATC. ^superFVa intervention started after the development of ATC stabilized bleeding, reversed prolonged APTT, returned FV and FVIII levels to their normal range, and reduced TAT levels that were increased by ATC. In summary, ^superFVa prevented ATC and traumatic bleeding when administered prophylactically, and ^superFVa stabilized bleeding and reversed abnormal hemostasis parameters when administered while ATC was in progress. Thus, ^superFVa may be an attractive strategy to intercept ATC and mitigate traumatic bleeding.