ENDOTOXIN INCREASES PLASMA SOLUBLE TUMOR NECROSIS FACTOR-RELATED APOPTOSIS-INDUCING LIGAND LEVEL MEDIATED BY THE p38 MITOGEN-ACTIVATED PROTEIN KINASE SIGNALING PATHWAY Marjolin N. Lub-de Hooge,* Steven de Jong, † Claudine Vermot-Desroches, § Jaap E. Tulleken, ‡ Elisabeth G. E. de Vries, † and Jan G. Zijlstra ‡ Departments of *Hospital Pharmacy, † Medical Oncology, and ‡ Intensive and Respiratory Care, Groningen University Hospital, The Netherlands; and § Diaclone, Besançon, France Received 3 Dec 2003; first review competed 15 Dec 2003; accepted in final form 4 May 2004 ABSTRACT—Despite extensive knowledge about the mechanisms behind sepsis, this syndrome still caries a large morbidity and mortality rate. Dysregulated immune and coagulation systems are held responsible. However, additional pathophysiological mechanisms such as uncontrolled apoptosis induced by death receptor ligands might well play a role. P38 mitogen-activated protein (MAP) kinase inhibitors are considered as potential drugs in inflammatory diseases. Therefore, the effect of endotoxin administration on the response of soluble(s) tumor necrosis factor-related apoptosis- inducing ligand (sTRAIL), a death receptor ligand, and the role of p38 MAP kinase inhibition was studied in 21 human volunteers. The volunteers received 30 min before the endotoxin infusion a single oral dose of placebo or the selective p38 MAP kinase inhibitor drug, RWJ-67657. Plasma sTRAIL increased 10-fold to 6564 ± 511 pg/mL after 2.5 h. This increase was blocked completely by the highest dose of RW-J6765.This is the first report showing that endotoxin increases sTRAIL where the p38 MAP kinase signaling pathway is involved. KEYWORDS—Endotoxemia, sepsis, TRAIL, apoptosis, p38 MAPK INTRODUCTION Intensive research has brought us an enormous body of knowledge about sepsis and the mechanisms behind it (1, 2). The involvement of the immune and the coagulation system has received much attention. Currently, dysregulation of the immune system is considered to be the most important factor that determines outcome. Overreaction and immunoparalysis have been suggested to be possible mechanisms (2–4). This resulted in the first treatment mode, namely infusion of recom- binant human activated protein C, that interfered with both mechanisms. The compound was safe and well tolerated and demonstrated a dose-dependent reduction in D-dimer and inter- leukin 6 levels relative to placebo, and a significant effect on mortality (5). Despite this new treatment option, sepsis is still a syndrome with a high mortality rate (6). There seem to be additional factors playing a role in the outcome of sepsis (1, 4). One of these factors might be the occurrence of apoptosis, or programmed cell death (7). Although the role of apoptosis in the regulation of the immune response is well recognized, its role in the dysfunction of other organs and in the mortality due to sepsis is less clear (2, 8–11). Apoptosis plays a physiological role in the immune regulation. Humoral factors, cytokines, and chemokines determine the activity and the longevity of the cellular components of the immune system. Tumor necrosis factor (TNF), the first and best-known member of the TNF superfamily, is one of the key players in the sepsis orchestra. In addition its role in augmentation of the immune response in early sepsis, TNF is also involved in apoptosis of superfluous cells during the later phases of sepsis (12). TNF is one of the bridges between the inflammatory reaction and apoptosis. The role of the other members of the TNF superfamily, FAS-ligand (FasL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), also known as death ligands, is far less known and therefore certainly deserves to be studied. There are indi- cations found for pathways other than TNF in sepsis-related apoptosis in studies with endotoxin challenge in mice (13). In organs, extensive apoptosis was observed, and the data suggested the existence not only of an endotoxin-driven acti- vation for thymic apoptosis, but also of an endotoxin- independent, TNF-independent pathway activating widespread apoptosis in this murine sepsis model. TRAIL, a transmembrane (type II) glycoprotein, is poten- tially involved in these pathways. The extracellular domain is homologous to the TNF family members TNF and FasL. TNF, FasL, and TRAIL exist physiologically in a biologically active soluble homotrimeric form. Ligand binding to the receptors leads to the induction of diverse physiologic responses, includ- ing inflammation and apoptosis. TRAIL triggers apoptosis through interaction with the cell membrane death receptors DR4 (TRAIL-R1) and DR5 (TRAIL-R2) (14). In contrast to other members of the TNF family, mRNA for TRAIL is detected in a wide range of tissues, including peripheral blood lymphocytes, spleen, small intestine, colon, and placenta, but not in brain, liver, or testis. Interestingly, TRAIL is considered not to induce apoptosis in normal cells, whereas it is believed to play an important role in tumor control (15). However, there are increasing indications that TRAIL is also involved in inflammatory processes. In vitro lipopolysaccharide (LPS) stimulates the release of soluble (s) TRAIL from monocytes Address reprint requests to Dr. J. G. Zijlstra, Intensive Care Unit, Department of Internal Medicine, University Hospital Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands. E-mail: j.g.zijlstra@int.azg.nl. The costs of the study were reimbursed by the Robert Wood Johnson foundation. None of the authors has personal financial interest. DOI: 10.1097/01.shk.0000132486.82177.ec SHOCK, Vol. 22, No. 2, pp. 186–188, 2004 186