The relation between fibrinogen level, neutrophil activity and nucleosomes in the onset of disseminated intravascular coagulation in the critically ill

Prostate Tissue-Induced Platelet Activation and Platelet-Neutrophil Aggregation Following Transurethral Resection of the Prostate Surgery: An In Vitro Study

Background: This study aimed to investigate the effects of prostate tissue on platelet activation markers, primarily assessed through P-selectin expression, and to assess the formation of platelet-leukocyte aggregations in response to prostate tissue exposure. Furthermore, we compared platelet activation induced by prostate tissue homogenates with that induced by thrombin stimulation. These processes may play a role in the development of disseminated intravascular coagulation (DIC) following transurethral resection of the prostate (TURP). Methods: We collected prostate tissue samples from 12 patients undergoing TURP. The samples were homogenized and used to stimulate platelet-rich plasma in vitro. Flow cytometry was used to measure platelet P-selectin expression and platelet-leukocyte aggregation. Additionally, four experimental groups were established: (A) saline control, (B) thrombin stimulation, (C) phosphate-buffered saline (PBS) control, and (D) prostate tissue homogenate. Data were analyzed to assess the impact of prostate tissue and thrombin on platelet activation and platelet-leukocyte interactions. Results: Prostate tissue homogenates significantly increased platelet P-selectin expression and platelet-neutrophil aggregation compared with the control groups (p < 0.05). Overall, platelet-leukocyte aggregation was not significantly different between the thrombin and prostate tissue groups. However, prostate tissue exposure did not significantly affect platelet-monocyte and platelet-lymphocyte aggregations. Conclusions: Prostate tissue exposure during TURP induces platelet activation, particularly platelet P-selectin expression and platelet-neutrophil aggregation, suggesting a potential mechanism for DIC development. These findings highlight the importance of monitoring platelet activity in patients undergoing TURP and indicate that interventions targeting platelet P-selectin expression and platelet-neutrophil interactions may help mitigate DIC risk.

Fibrinogen binding to histones in circulation protects against adverse cellular and clinical outcomes

BACKGROUND

Circulating histones are released by extensive tissue injury or cell death and play important pathogenic roles in critical illnesses. Their interaction with circulating plasma components and the potential roles in the clinical setting are not fully understood.

OBJECTIVES

We aimed to characterize the interaction of histones with fibrinogen and explore its roles in vitro, in vivo, and in patient samples.

METHODS

Histone-fibrinogen binding was assessed by electrophoresis and enzyme-linked immunosorbent assay-based affinity assay. Functional significance was explored using washed platelets and endothelial cells in vitro and histone-infusion mouse models in vivo. To determine clinical translatability, a retrospective single-center cohort study was conducted on patients requiring intensive care admission (n = 199) and validated in a cohort of hospitalized patients with COVID-19 (n = 69).

RESULTS

Fibrinogen binds histones through its D-domain with high affinity (calf thymus histones, KD = 18.0 ± 5.6 nM; histone 3, KD = 2.7 ± 0.8 nM; and histone 4, KD = 2.0 ± 0.7 nM) and significantly reduces histone-induced endothelial damage and platelet aggregation in vitro and in vivo in a histone-infusion mouse model. Physiologic concentrations of fibrinogen can neutralize low levels of circulating histones and increase the cytotoxicity threshold of histones to 50 μg/mL. In a cohort of patients requiring intensive care, a histone:fibrinogen ratio of ≥6 on admission was associated with moderate-severe thrombocytopenia and independently predicted mortality. This finding was validated in a cohort of hospitalized patients with COVID-19.

CONCLUSION

Fibrinogen buffers the cytotoxic properties of circulating histones. Detection and monitoring of circulating histones and histone:fibrinogen ratios will help identify critically ill patients at highest risk of adverse outcomes who might benefit from antihistone therapy.

Cell-free histones and the cell-based model of coagulation

The cell-based model of coagulation remains the basis of our current understanding of clinical hemostasis and thrombosis. Its advancement on the coagulation cascade model has enabled new prohemostatic and anticoagulant treatments to be developed. In the past decade, there has been increasing evidence of the procoagulant properties of extracellular, cell-free histones (CFHs). Although high levels of circulating CFHs released following extensive cell death in acute critical illnesses, such as sepsis and trauma, have been associated with adverse coagulation outcomes, including disseminated intravascular coagulation, new information has also emerged on how its local effects contribute to physiological clot formation. CFHs initiate coagulation by tissue factor exposure, either by destruction of the endovascular barrier or induction of endoluminal tissue factor expression on endothelia and monocytes. CFHs can also bind prothrombin directly, generating thrombin via the alternative prothrombinase pathway. In amplifying and augmenting the procoagulant signal, CFHs activate and aggregate platelets, increase procoagulant material bioavailability through platelet degranulation and Weibel-Palade body exocytosis, activate intrinsic coagulation via platelet polyphosphate release, and induce phosphatidylserine exposure. CFHs also inhibit protein C activation and downregulate thrombomodulin expression to reduce anti-inflammatory and anticoagulant effects. In consolidating clot formation, CFHs augment the fibrin polymer to confer fibrinolytic resistance and integrate neutrophil extracellular traps into the clot structure. Such new information holds the promise of new therapeutic developments, including improved targeting of immunothrombotic pathologies in acute critical illnesses.