Inflammatory Response to Intravenously Administered Lipopolysaccharide (LPS) in the Bone Marrow of Healthy Volunteers As a Model for Early Phase Drug Development

Introduction

Inflammatory responses in the peripheral and central hematological compartments are important for identification of new biomarkers and drug targets in early phase drug development. There is an increasing interest to investigate the modulation of the inflammatory response upon experimental drug exposure using cellular and molecular analyses, specifically in the central compartment. The lipopolysaccharide (LPS) challenge model allows to study TLR4-mediated local and systemic inflammation and therefore the effects of anti-inflammatory compounds. In addition, there is an interest in the effects of TLR4 agonists on early immune cell populations. The aim of the current study is to investigate the effects of intravenous (i.v.) LPS on the peripheral blood and central bone marrow compartment and to perform a proof-of-methodology study for bone marrow analysis in early phase drug research in healthy volunteers.

Methods

This was an open-label study in 13 healthy young male subjects, aged 18 - 35 years (inclusive). The study was conducted at the Centre for Human Drug Research, Leiden, The Netherlands. The study protocol was approved by the Medical Ethics Committee. All subjects provided written informed consent prior to any study activity. Subjects were divided into control group (n=3), 1 ng/kg i.v. LPS group (n=5) and 2 ng/kg i.v. LPS group (n=5). Blood and bone marrow samples were collected at baseline and at 4h post-dose timepoints. Primary objective was to evaluate the safety and tolerability of bone marrow sampling in healthy volunteers, by continuous safety monitoring, visual analogue scale (VAS) for pain and subject experience questionnaires. To investigate the pharmacodynamic (PD) effects of i.v. LPS challenge on the bone marrow and whole-blood immune compartments, flow cytometry, cytokine analysis and RNA sequencing was performed.

Results

All 13 subjects completed the study. Adverse events were mild and reversible, and included puncture site pain related to bone marrow puncture, and flu-like symptoms related to LPS administration. Twelve subjects (92%) indicated they would undergo the procedure again in the future. There was an observable difference in VAS pain score between the baseline bone marrow puncture and LPS treatment groups, but no difference between 1 ng/kg and 2 ng/kg groups. Phenotypic changes of inflammatory signatures in peripheral blood and bone marrow cell populations upon LPS administration were detected by multi-parameter flow cytometry. An LPS-induced inflammatory cytokine profile was present. RNA sequencing revealed differential gene expression in inflammatory gene signatures between peripheral blood mononuclear cells and bone marrow cells.

Conclusion

We demonstrated that bone marrow analysis is feasible and well-tolerable in early phase studies with healthy volunteers and can be used to assess inflammatory responses in the central hematological compartment upon systemic LPS challenge. Access to bone marrow can provide important novel insights into drug effects on the hematopoiesis and differentiation of immune cells and provides added value to early drug development.