Circulating histones as clinical biomarkers in critically ill conditions

Abstract

Extracellular histones, primarily nuclear proteins involved in chromatin organization, have emerged as key mediators in pathological processes in critically ill patients. When released into circulation due to cell death mechanisms such as NETosis, histones act as damage-associated molecular patterns (DAMPs), contributing to excessive inflammation, endothelial dysfunction, immune response dysregulation, coagulation activation, cell death, and multi-organ damage. Increasing evidence supports their role in the pathophysiology of sepsis, acute lung injury, cardiac injury, pancreatitis, and other life-threatening conditions. Given their strong association with disease severity and prognosis, circulating histones have gained attention as potential clinical biomarkers for early diagnosis, prognosis, and therapeutic monitoring in critically ill patients. This review discusses the biological roles of extracellular histones, their potential as biomarkers, different approaches to measure them, and emerging therapeutic strategies aimed at neutralizing or removing circulating histones to improve patient outcomes in severe medical conditions. Impact statement This review highlights extracellular histones as key mediators and biomarkers in sepsis, proposing their use in diagnosis, prognosis, and treatment monitoring. Integrating quantitative proteomics for the detection of circulating histones may enhance patient stratification and guide therapeutic strategies, advancing personalized medicine in critical care.

Keywords: COVID‐19; acute kidney injury; cardiac injury; critically‐ill patient; extracellular histones; lung injury; mass spectrometry; pancreatitis; renal replacement therapy; sepsis; septic shock.

Fig. 1

Mechanisms mediating the release of extracellular histones. Nuclear histones can be released from cells upon several cell death mechanisms, such as necrosis and necroptosis, apoptosis, pyroptosis, extracellular trap cell death (ETosis) of leukocytes, particularly neutrophil extracellular traps (NETosis), ferroptosis, and direct cell damage by pathogens or direct release through the formation of amphisomes. Notably, once released, histones can amplify the cytotoxic response by means of a positive feedback loop, further exacerbating tissue damage. Created in BioRender. García‐Gimenez, J. (2025) https://BioRender.com/mkat4dm

Fig. 2

The pathophysiological roles of extracellular histones in the endothelium. Extracellular histones, released during cell death, act as damage‐associated molecular patterns (DAMPs) and play a pivotal role in mediating endothelial dysfunction. These histones bind to pattern recognition receptors, such as Toll‐like receptors TLR2 and TLR4, activating downstream signaling pathways including NF‐κB. This activation promotes the transcription of pro‐inflammatory cytokines and components of the NLRP3 inflammasome. Once NLRP3 is upregulated, cellular stressors such as potassium efflux (K⁺) and increased reactive oxygen species (ROS) trigger inflammasome oligomerization. This leads to the activation of caspase‐1 and the release of mature IL‐1β and IL‐18, key mediators of hyperinflammation, and induces pyroptosis. Concurrently, extracellular histones increase membrane permeability to calcium ions (Ca²⁺), which exacerbates mitochondrial dysfunction and further amplifies ROS production. ROS contribute to the activation of the Second Mitochondria‐derived Activator of Caspases (SMAD/Diablo), promoting the intrinsic apoptotic pathway through caspase activation. Moreover, internalized histones can directly disrupt the mitochondrial membrane potential, intensifying ROS generation and reinforcing both apoptotic and pyroptotic pathways. Together, these mechanisms highlight the multifaceted cytotoxic and proinflammatory roles of extracellular histones in endothelial injury. Created in BioRender. García‐Gimenez, J. (2025) Created in BioRender. García‐Gimenez, J. (2025) https://BioRender.com/wo4c8db

Fig. 3

Integrating circulating histone measurements by MS for sepsis diagnosis, prognosis, and patient management with extracorporeal therapies. This figure presents a comprehensive approach to using quantitative mass spectrometry (MS) for personalized sepsis management. The workflow consists of two interconnected phases: (1) the patient management phase, where critically ill patients undergo blood extraction, clinical monitoring, and potential treatment with extracorporeal hemoadsorption or hemoperfusion therapies (e.g., CytoSorb®, Polymyxin B, heparin‐based membranes, and SPA‐based membranes) to remove circulating histones and other hyperinflammatory mediators; and (2) the laboratory phase, where plasma separation, processing, and LC–MS/MS analysis enable the quantification of circulating histones, providing diagnostic, prognostic, and theragnostic insights to advance personalized medicine in sepsis care. Created in BioRender. García‐Gimenez, J. (2025) https://BioRender.com/piejpbl