OC 78.5 - Systemic snakebite envenoming causes histone-induced thrombocytopaenia

Wednesday, June 28, 2023

11:15 – 11:30 ET

Room: 515

Session Available As: On-Demand

Presenting Author(s)

Jeremy J. Schofield, BMBS

PhD Student
University of Liverpool
Liverpool, England, United Kingdom

Co-Author(s)

SA

Simon T. Abrams

Associate reader
University of Liverpool
Liverpool, England, United Kingdom
YA

Yasir Alhamdi

Research Fellow
University of Liverpool
Liverpool, England, United Kingdom
SA

Stuart Ainsworth

UKRI Future Leader Fellow
Liverpool School of Tropical Medicine
Liverpool, England, United Kingdom
CE

Chloe Evans

Research Assistant
Liverpool School of Tropical Medicine
Liverpool, England, United Kingdom
LA

Laura-Oana Albulescu

Post-Doctoral Research Associate
Liverpool School of Tropical Medicine
Liverpool, England, United Kingdom
SM

Stefanie Menzies

Senior Research Associate
Liverpool School of Tropical Medicine
Liverpool, England, United Kingdom
BE

Becky Edge

Research Assistant
Liverpool School of Tropical Medicine
Liverpool, England, United Kingdom
RH

Robert Harrison

Professor
Liverpool School of Tropical Medicine
Liverpool, England, United Kingdom
JY

Jun X. Yong

Clinical research fellow
University of Liverpool
Liverpool, England, United Kingdom
GW

Guozheng Wang

Professor
University of Liverpool
Liverpool, England, United Kingdom
NC

Nicholas Casewell

Professsor
Liverpool School of Tropical Medicine
Liverpool, England, United Kingdom
CT

Cheng-Hock Toh

Professor
University of Liverpool
Liverpool, England, United Kingdom

Background: There are 1.8 million snakebite envenomings each year, causing 138,000 deaths and 400,000-500,000 cases of long-term morbidity. WHO classifies snakebites as a priority neglected tropical disease with urgent need for new therapies.

Snake envenoming can induce haemotoxicity, neurotoxicity, or cytotoxicity. Thrombocytopaenia is a pathological feature but its cause is unclear.

Aims: This study aimed to determine whether (1) cytotoxic histones are released into circulation following cell death in systemic envenoming and (2) thrombocytopaenia is caused by venoms or cytotoxic histones.

Methods: Four venoms from three cobra species (genus Naja) were used. Mice were injected intravenously with either N. nigricollis (east and west African forms), N. pallida (cytotoxic) or N. haje (neurotoxic) venoms, with and without anti-histone antibody (ahscFv). Circulating histones and platelet counts were quantified. Washed human platelets were incubated in vitro (20mins) with either venom (25μg/ml) or histones (0-100μg/ml). Platelet activation was monitored by flow cytometry (anti-CD62P antibody).

Results: Systemic envenoming with cytotoxic venoms resulted in significant elevations of circulating histones within 90mins (N. nigricollis; 74.6±10.0μg/ml and 88.0±25.5μg/ml, N. pallida; 129.0±25.0μg/ml), which was not observed with neurotoxic envenoming (N. haje; 0.0±0.2μg/ml). Thrombocytopaenia was associated with elevated circulating histones following cytotoxic venoms, and platelet counts remained normal post neurotoxic envenoming. Thrombocytopaenia associated with cytotoxic envenoming was abrogated with anti-histone antibody infusion. Incubating pathological levels of either cytotoxic (N. nigricollis; 7.8±4.6% and 9.6±3.4%, N. pallida 7.5±4.2%) or neurotoxic (N. haje; 8.5±2.5%) venoms with washed platelets did not affect platelet activation compared to untreated platelets (UT; 5.0±0.5%). Pathological levels of extracellular histones (25μg/ml; 37.4±12.0%, 50μg/ml; 50.2±3.0%, 100μg/ml; 77.2±11.6%) directly caused significant platelet activation.

Conclusion(s): These results suggest that envenoming-associated thrombocytopaenia is caused by circulating histones and not by the venoms directly. This provides a potential therapeutic target, additional to anti-venom strategies in reducing haemostatic abnormalities and improving outcomes.

Learning Objectives:

Outline why research is important in the neglected tropical disease of snakebite envenoming
Analyse the role of extracellular histones in snakebite envenoming associated thrombocytopaenia
Predict how anti-histone therapy may provide therapeutic benefit in snakebite envenoming