Tissue factor is associated with the nonbacterial thrombotic endocarditis induced by a hypobaric hypoxic environment in rats

Epidemiologic and Clinical Characteristics of Marantic Endocarditis: A Systematic Review and Meta-analysis of 416 Reports

Nonbacterial thrombotic endocarditis (NBTE) is a distinctive condition marked by the presence of aseptic fibrin depositions on cardiac valves due to hypercoagulability and endocardial damage. There is a scarcity of large cohort studies clarifying factors associated with morbidity and mortality of this condition. A systematic literature review was performed utilizing the PubMed, Embase, Cochrane, and Web-of-Science databases to retrieve case reports and series documenting cases of NBTE from inception until September-2022. A descriptive analysis of basic characteristics was carried out, followed by multivariate regression analysis to identify risk factors associated with morbidity and mortality. A total of 416 case reports and series were identified, of which 450 patients were extracted. The female-to-male ratio was around 2:1 with an overall sample median age of 48 (interquartile range [IQR]:34-61). Stroke-like symptoms were the most common presentation and embolic phenomena occurred in 70% of cases, the majority of which were due to stroke. Cancer was associated with higher embolic complications (aOR:6.38, 95% CI = 3.75-10.83, p < 0.01) in comparison to other NBTE etiologies, while age, sex, and vegetation size were not (p > 0.05). All-cause in-hospital mortality was 36%, with cancer etiology being associated with higher mortality: 56% (aOR:3.64, 95% CI = 1.57-8.43, p < 0.01) in comparison to other NBTE etiologies:19%. A significant decrease in NBTE mortality was seen in recent years in comparison to admissions that occurred during the 20th century (aOR:0.07, 95% CI = 0.04-0.15, p < 0.01). While there has been an observed improvement in overall in-hospital mortality rates for patients admitted with NBTE in recent years, it is important to note that cases associated with a cancer etiology are still linked to high morbidity and mortality during hospitalization.

Diagnostic Work-Up in Patients with Nonbacterial Thrombotic Endocarditis

Nonbacterial thrombotic endocarditis (NBTE) is a form of endocarditis that occurs in patients with predisposing conditions, including malignancies, autoimmune diseases (particularly antiphospholipid antibody syndrome, which accounts for the majority of lupus-associated cases), and coagulation disturbances for which the correlation with classical determinants is unclear. The condition is commonly referred to as "marantic", "verrucous", or Libman-Sacks endocarditis, although these are not synonymous, representing clinical-pathological nuances. The clinical presentation of NBTE involves embolic events, while local valvular complications, generally regurgitation, are typically less frequent and milder compared to infective forms of endocarditis. In the past, the diagnosis of NBTE relied on post mortem examinations, while at present, the diagnosis is primarily based on echocardiography, with the priority of excluding infective endocarditis through comprehensive microbiological and serological tests. As in other forms of endocarditis, besides pathology, transesophageal echocardiography remains the diagnostic standard, while other imaging techniques hold promise as adjunctive tools for early diagnosis and differentiation from infective vegetations. These include cardiac MRI and 18FDG-PET/CT, which already represents a major diagnostic criterion of infective endocarditis in specific settings. We will herein provide a comprehensive review of the current knowledge on the clinics and therapeutics of NBTE, with a specific focus on the diagnostic tools.

Malignancy and Endocarditis: Divulging Into the Intertwined Association

Cancer is an immunosuppressive disorder with characteristic features of unchecked cell growth, invasion, and sometimes thromboembolism leading to multiple systemic sequelae, including infective endocarditis. This article has compiled some of the crucial mechanisms by which infective endocarditis occurs in cancer patients, its risk factors, and the existing treatment interventions. It has focused on the necessity of being aware that these multiple pathogeneses are involved in the development of infective endocarditis (IE) in cancer patients, which would help delineate the risk factors associated with the condition and help physicians screen better for specific red flags. Identifying these risk factors and patient-oriented therapy, targeting the necessary elements such as causative organism, patient immune status, type of cancer, choosing evidence-based treatment modalities, and to improve the outcome of the disease in an already exasperating condition called cancer.

A key role of toll-like receptor 3 in tissue factor activation through extracellular signal regulated kinase 1/2 pathway in a murine hypoxia model

Hypoxemia in the circulation can lead to venous thrombosis (VT) through tissue factor (TF) activation, but the mechanism of TF activation in hypoxia remains obscure. Ligands released from damaged tissues or cells due to hypoxia are identified by various pattern-recognition receptors (PRR), including Toll-like receptor3 (TLR3). In the present study, we investigated the mechanism of TF activation during acute hypoxia in a rat model. The expression of TLR3 and TF was analyzed by immunoblotting and RT-PCR. The TF activity was evaluated by two-stage chromogenic assay and fibrin deposition was detected by immunohistochemistry. The expression of TLR3, TF, and TF activity was increased significantly 6 h post acute hypoxia and then decreased gradually. The contribution of TLR3 in TF activation was investigated by poly I:C and TLR3 neutralizing antibody. We also found increased ERK phosphorylation both in acute hypoxia and poly I:C treatment. We further showed that the pre-treatment of TLR3 neutralizing antibody or ERK inhibitor (PD98059) 2 h prior to acute hypoxia or poly I:C treatment completely abrogated ERK phosphorylation and TF activation. The pre-treatment of TLR3 neutralizing antibody also inhibited fibrin deposition in lung vasculature. These data indicate that acute hypoxia induced TF activation is mediated through TLR3-ERK1/2 pathway.

The role of endothelial cell biology in endocarditis

The treatment of endocarditis remains a challenge for physicians, even in times of modern antibiotic treatment. Depending on its cause, endocarditis can either be of infectious or non-infectious origin. Infective endocarditis is caused by bacterial (or fungal) pathogens, and the clinical course is critically dependent on the virulence factors of the specific microorganisms involved. Therefore, the clinical type of endocarditis can be divided into an acute and more aggressive form and a subacute form (endocarditis lenta). Much of our knowledge regarding the pathogenesis of infective endocarditis is based on studies of the virulence of Staphylococcus aureus, which has become the most frequent cause of infective endocarditis nowadays. However, independently of the underlying cause of endocarditis (infectious or noninfectious), the pathogenesis involves the damage and disturbance of endothelial function and the formation of associated "vegetation". Surprisingly little is known about the specific role of the endothelium in the pathogenesis of endocarditis. This review will thus give insights into current knowledge of the pathogenesis of endocarditis with a focus on the role of the endothelium.

Non-bacterial thrombotic endocarditis

Non-bacterial thrombotic endocarditis (NBTE) is a disease characterised by the presence of vegetations on cardiac valves, which consist of fibrin and platelet aggregates and devoid of inflammation or bacteria. NBTE has increasingly been recognised as a condition associated with numerous diseases and a potentially life-threatening source of thromboembolism. NBTE is not a common entity; however it is frequently underestimated, probably due to underlying diseases (cancer, autoimmune disorders, HIV). NBTE is difficult to diagnose and relies on strong clinical suspicion. NBTE is also difficult to manage and each case should be individually managed by identifying and treating the underlying pathology. Surgical intervention is not recommended unless the patient is in acute congestive failure.

Nonbacterial Thrombotic Endocarditis in Cancer Patients: Pathogenesis, Diagnosis, and Treatment

Thrombophilia is a well-described consequence of cancer and its treatment. The pathogenesis of this phenomenon is complex and multifactorial. Nonbacterial thrombotic endocarditis (NBTE) is a serious and potentially underdiagnosed manifestation of this prothrombotic state that can cause substantial morbidity in affected patients, most notably recurrent or multiple ischemic cerebrovascular strokes. Diagnosis of NBTE requires a high degree of clinical suspicion as well as the judicious use of two-dimensional echocardiography to document the presence of valvular thrombi. In the absence of contraindications to therapy, treatment consists of systemic anticoagulation, which may ameliorate symptoms and prevent further thromboembolic episodes, as well as control of the underlying malignancy whenever possible.

ATP-sensitive potassium channels expressed by human monocytes play a role in stasis-induced thrombogenesis via tissue factor pathway

Blood stasis is one of the key risk factors in deep vein thrombosis. Localized blood oxygen and glucose depletion are main characteristics observed during stasis. However, the causal chain leading to clot formation is still obscure. According to our hypothesis, energy depletion causes opening of K(ATP) channels present on monocytes, facilitating influx of calcium and triggering tissue factor-(TF)-dependent procoagulatory activity and eventually clot formation. Using Reverse-Transcript-PCR (RT-PCR) in magnetically enriched human monocytes, mRNA transcription of the K(ATP)-channel subunits Kir6.1 and Kir6.2 could be confirmed. Membrane potential and cytosolic calcium were recorded by time-resolved flow cytometry. The specific K(ATP)-channel opener pinacidil caused a glibenclamide-sensitive hyperpolarization of monocytes and a prolongation of cytosolic calcium transients triggered by purinergic stimulation. TF-initiated whole blood clotting time (TiFaCT) was accelerated comparing 2 and 8 h of simulated in vitro blood stasis using blood of male healthy volunteers. Both with and without activation of the monocytes with 100 ng/ml LPS, the K(ATP)-channel blocker glibenclamide resulted in a significantly (p<0.001) prolonged clotting time after 8 h of stasis compared to vehicle control and LPS, respectively. In the course of stasis, flow cytometry showed an increase in monocytes expressing TF (0.1% and 1.3% after 2 and 8 h, respectively). LPS (100 ng/ml) increased the amount of TF expression significantly to 36%, whereas 30 microM glibenclamide partly reversed this increase down to 24%. Phosphatidylserine-exposure (PSE) on monocytes increased strongly during stasis by 11.2 times, a process which glibenclamide attenuated by 23%. LPS increased PSE further by 65%, which glibenclamide reduced by 50%. In conclusion, presence of integral subunits of K(ATP)-channels is demonstrated in human monocytes. These channels are able to enhance Ca(2+)-dependent intracellular signalling and can increase TF-activity and phosphatidylserine exposure thereby accelerating clot formation during stasis by monocytes.

Studies on rabbit natural and recombinant tissue factors: intracellular retention and regulation of surface expression in cultured cells

Tissue factor (TF) is the most important trigger of blood coagulation in vascular pathology. Rabbit TF, with or without (ΔC) its COOH-terminal intracellular tail, has been conjugated to green fluorescent protein (GFP) to study subcellular localization and other functions of TF. TF-GFP and TFΔC-GFP are associated with Na2CO3-resistant buoyant fractions in HEK-293 cells (lipid rafts); there is no morphological difference in the surface distribution of these or other GFP-labeled membrane proteins present in or excluded from rafts (confocal microscopy, HEK-293 cells). Endogenous TF expressed by rabbit aortic smooth muscle cells (SMCs) is also raft associated. Membranes from HEK-293 cells expressing recombinant TF-GFP or wild-type TF were equipotent to clot human plasma; however, TFΔC-GFP was ∼20-fold more active (per membrane weight). Immunoblot confirmed that the deletion mutant is more abundantly expressed, and confocal microscopy showed that it has preferential membrane localization, whereas TF-GFP is mainly intracellular (nuclear lining and multiple granules). With a similar half-life (<4 h), the two constructions differ by their intracellular retention, lower for TFΔC-GFP. In serum-starved SMCs, the expression of endogenous TF was upregulated by interleukin-1β and/or FBS treatment (immunoblot, immunofluorescence, clotting assay). However, TF secretion or surface expression was not regulated by stimuli of physiological intensity (such as stimulation of the coexpressed kinin B1receptors), although a calcium ionophore was highly active in this respect. TF is a raft-associated molecule whose surface expression (secretion) is apparently retarded or impaired by structural determinant(s) located in its COOH-terminal tail.

Changes in myosin heavy chain and its localization in rat heart in association with hypobaric hypoxia-induced pulmonary hypertension

Experimental pulmonary hypertension induced in a hypobaric hypoxic environment (HHE) is characterized by structural remodelling of the heart. In rat cardiac ventricles, pressure and volume overload are well known to be associated with changes in cardiac myosin heavy chain (MHC) isoforms. To study the effects of HHE on the MHC profile in the ventricles, 83 male Wistar rats were housed in a chamber at the equivalent of 5500 m altitude for 1-8 weeks. Pulmonary arterial pressure, right ventricular free wall (RVFW) weight, the ratio of RVFW weight over body weight (BW), the ratio of left ventricular free wall (LVFW) weight over BW, and myocyte diameter in both ventricles showed significant increases after 1 week, 2 weeks, 1 week, 6 weeks, and 4 weeks of HHE, respectively. Semi-quantitative reverse transcriptase-polymerase chain reaction revealed that beta-MHC mRNA expression was increased significantly in both ventricles at 6 and 8 weeks of HHE, whereas alpha-MHC mRNA expression was decreased significantly at 6 and 8 weeks of HHE in the right ventricle (RV) and at 6 weeks of HHE in the left ventricle (LV). The percentage of myosin containing the beta-MHC isoform was increased significantly at 4-8 weeks of HHE in RV and at 6 weeks of HHE in LV. In situ hybridization showed that the area of strong staining for beta-MHC mRNA was increased in both ventricles at 8 weeks of HHE, and showed a decrease from RVFW to cardiac septum, and from cardiac septum to LVFW. These results suggest that HHE has a significant effect on the expression of both MHC mRNA and protein in the heart, particularly in RV. These changes may reflect a role for cardiac MHC in the response to pulmonary hypertension in HHE.