1. Introduction
Sepsis and systemic inflammatory response syndrome (SIRS) are systemic reactions to different inflammatory stimuli such as infection, burns, and trauma [1]. A strict regulation of the inflammatory process is necessary in order to mantain a correct balance between protective or tissue-damaging inflammatory response. If the inflammatory reaction becomes unregulated, systemic and excessive activation of innate immunity results in SIRS or sepsis.
The incidence of sepsis in North America is of 3 cases per 1000 persons, with an estimated increase rate of 1.5% per year. The mortality rate associated with sepsis (40–60%) is so high as to make sepsis the leading cause of death in noncoronary intensive units and one of the major burdens for the healthcare systems throughout the world [2].
Although it has been proposed more than 30 years ago, as experimental model for sepsis induction [3], the CLP model has been considered to be the gold-standard model of sepsis [4]. Sepsis, together with hypotension, acute respiratory distress syndrome (ARDS), hepatic failure, disseminated intravascular coagulation, and organ dysfunction, is associated with a poor prognosis. These alterations occur first in the lung and then in the liver [5].
Bacterial proliferation, endotoxin production, and exotoxin are able to induce an overexpression of pro-inflammatory madiators by macrophages, monocytes, endothelial cells, and neutrophils, thus leading to tissue injuries and organs failure [5, 6][5][6].
The NF-κB transcription factor system is known to control the expression of a number of genes involved in the innate immune response of the body against infection and inflammation. Genes responsible for immunoreceptors, cytokines, chemokines, and apoptosis are all modulated by this important family of transcription factors [7]. NF-κB activity is reported to be impaired in chronic inflammation [8]. Recently, we showed that inhibition of NF-κB succeeded in maintaining the balance between pro- and anti-inflammatory cytokines in vivo in a model of polymicrobial sepsis [6]. Phosphorylation of NF-κB and thus transcription of proinflammatory mediators are promoted by the activation of various mitogen-activated protein kinases (MAPKs). MAPKs, such as ERK1/2 and JNK, in turn are activated by bacterial products, cytokines, and chemokines [6–9][6][7][8][9]. Indeed, JNK is a crucial mediator involved in the activation of proinflammatory cytokines and apoptosis in different cells [9–11][9][10][11]. During septic shock, proinflammatory cytokines such as TNF-α, IL-1β, and IL-6 are dramatically increased to block the infection and tissue damage [6, 12–15][6][12][13][14][15]. Other late mediators of inflammation such as HMGB-1 have been involved in septic shock. In fact, it has been showed that suppressing the HMGB-1 activity exert positive effects in experimental sepsis [16].
Previous in vitro experiments demonstrated that SP600125 acts as MAPKs inhibitor, exhibiting a greater selectivity for all the 3 isoforms of JNK (JNK-1, JNK-2, and JNK-3) rather than for the other kinases; indeed, SP600125 inhibit JNK at a lower concentration then those required to inhibit ERK and p38 (IC50 0.04 μM vs > 10 μM), as previously reported [16]. Furthermore, the dose of 15 mg/kg was described as being able to block the expression of TNF-α in a murine model of endotoxin-induced inflammation [16]. Moreover, Bennett et al. showed that the JNK inhibitor significantly reduces the inflammatory response in a model of peritonitis induced lung damage [16, 17][16][17]. In light of these considerations, we hypothesized that inhibition of JNK signalling might improve systemic sepsis.
Therefore, aim of our study was to investigate the efficacy and the molecular mechanism of SP600125 in this murine model of polymicrobial sepsis.