Comparing hemodynamics, blood gas analyses and proinflammatory cytokines in endotoxemic and severely septic rats

Abstract

Lipopolysaccharide (LPS) is often used in short-term models of inflammation. Since endotoxemia and sepsis are different entities we have recently established a short-term sepsis model in rats induced by cecal ligation and incision (CLI). This retrospective study was conducted in order to identify similarities and differences between both experimental approaches. 32 anesthetized/ventilated male rats from the following four groups were analysed (each n = 8): CTRL-group (0.9% NaCl i.v.); LPS-group (5 mg/kg i.v.); SHAM-group (laparotomy); CLI-group (1.5 cm blade incision). Mean arterial blood pressure (MAP) and blood gas parameters (arterial base excess (BE) and pH) were continuously recorded. Total observation time was 300 min. Plasma samples were obtained afterwards. LPS and CLI induced significant arterial hypotension and metabolic acidosis compared to CTRL- or SHAM-group, respectively. Yet, between the LPS- and CLI-groups, there were no differences in MAP, BE and pH. LPS significantly induced IL-1β, IL-6 and TNF-α in the plasma. In contrast, CLI showed a clear tendency towards increased IL-1β and IL-6 plasma levels and did not affect TNF-α. Our results indicate that the CLI sepsis model is suitable for short-term investigations on hemodynamic alterations and blood gas analyses during sepsis. 300 min after the proinflammatory insult, plasma concentrations of IL-1β and IL-6 in the plasma remain considerably lower after CLI compared to endotoxemia. Low TNF-α concentrations 300 min after sepsis induction could be interpreted as considerable immunosuppression during CLI sepsis.

Introduction

Despite significant progress in understanding the pathophysiology of sepsis, severe sepsis is still a major cause of death [1]. According to international consensus conferences, severe sepsis is characterized by arterial hypotension and organ dysfunction due to an infectious origin [2]. The complex situation in severe sepsis cannot be sufficiently investigated in cell culture approaches. Therefore, different animal models are essential to mirror the clinical situation [3]. For practical and ethical reasons, rodent models are widely used for immunopharmacological studies. In the past, induction of endotoxemia by intraperitoneal (i.p.) or intravenous (i.v.) injection of bacterial components (lipopolysaccharide, LPS) has been shown to be a convenient and reliable way to induce a state of (hyper-)inflammation within a very short observation time [4], [5]. However, endotoxemia and polymicrobial sepsis differ in their respective immunological alterations. Thus, results from endotoxemia trials must be interpreted with caution and are to be transferred with considerable limitations onto the complex situation during sepsis [6]. More specifically, LPS injection rapidly induces the expression of proinflammatory cytokines, which can effectively be treated with antiinflammatory drugs [7]. In contrast, clinically relevant sepsis models (i.e. cecal ligation and puncture, CLP [8]) induce systemic inflammation over a longer period of time. In addition, large trials involving antiinflammatory agents in sepsis have featured disappointing results [9], which owes tribute to the growing body of evidence that overcoming immunosuppression during sepsis is, in fact, crucial for survival [10].

Nevertheless, LPS administration remains frequently used in short-term inflammatory models for lack of short-term sepsis models. In order to fill this gap, we have recently published an acute sepsis model induced by cecal ligation and incision (CLI) [11], which has been used successfully for immunopharmacological studies [12], [13], [14]. CLI induces arterial hypotension and a state of (hyper-)inflammation within a very short observation time. In contrast to endotoxemia, CLI is induced by live bacteria and, therefore, fulfils international sepsis criteria [15].

We aimed to analyse own – to date unpublished – data from endotoxemic (LPS injection) and septic (CLI procedure) rats with respect to mortality, hemodynamics, blood gas analyses and proinflammatory cytokines in the plasma in order to identify additional differences or possible similarities between both experimental short-term approaches.