Insulin prevents liver damage and preserves liver function in lipopolysaccharide-induced endotoxemic rats

Background/Aims

Liver integrity and function are crucial for survival of patients suffering from trauma, operations or infections. Insulin decreased mortality and prevented the incidence of multi organ failure and infection in critically ill patients. The aim of the present study was to determine whether insulin exerts positive effects on hepatic homeostasis and function during endotoxemia.

Methods

Endotoxemic rats received either saline or insulin. Hepatic morphology and function was determined by measuring the effect of insulin on liver proteins, enzymes, hepatocyte apoptosis and proliferation including caspases-3 and -9 and Bcl-2. Intrahepatic ATP, glucose and lactate concentration were determined by bioluminescence. To determine possible molecular changes the effect of insulin on hepatic cytokine mRNA and gene profile analysis were assessed.

Results

Insulin significantly improved hepatic protein synthesis by increasing albumin and decreasing c-reactive protein, P<0.05. Insulin attenuated hepatic damage by decreasing AST and ALT, P<0.05. Improved liver morphology was due to decreased hepatocyte apoptosis along with decreased caspase-3 concentration and increased hepatocyte proliferation along with Bcl-2 concentration, P<0.05. Insulin decreased hepatic IL-1β, IL-6 and MIF mRNA and improved hepatic glucose metabolism and glycolysis, P<0.05. GeneChip analysis revealed an anti-inflammatory effect of insulin.

Conclusions

Insulin improves hepatic integrity, hepatic glucose metabolism and hepatic function by increasing cell survival and attenuating the hepatic inflammatory response in endotoxemic rats.

Introduction

Despite advances in supportive treatments sepsis and septic shock are associated with a high mortality and health care resources [1]. There are an estimated 750,000 cases per year of sepsis or septic shock in the United States and in 20–40% the cases are lethal [2]. In elderly people the incidence of sepsis or septic shock and the associated lethality rates are vastly higher than those in younger people [1], [2]. Given the increasing number of elderly the cases of sepsis will increase of about 934,000 to over one million per year in the year 2010–2020 [2]. These numbers indicate the important clinical role for a successful treatment of sepsis and septic shock, which has yet not been found.

Pathophysiologic mediators associated with hypermetabolism and catabolism are pro-and anti-inflammatory signals, proteins and cytokines [3], [4], [5], [6], [7]. The magnitude and duration of cytokine expression determines the development and incidence of tissue damage, multi organ failure (MOF) or even death [8], [9]. The liver–gut-axis was hypothesized to be of significant importance for the inflammatory reaction and hence for the incidence of MOF. The gut was called the ‘fuel’ and the liver was named the ‘engine’ for the hypermetabolic cascade [10]. The hepatic acute phase response represents a cascade of events characterized by the up-regulation of type I and type II acute phase proteins and the down-regulation of constitutive hepatic proteins that are mediated by pro-inflammatory cytokines [10]. Clinical studies have shown that a sustained or increased acute phase response maybe detrimental with the associated uncontrolled and prolonged action of acute phase proteins [10], [11], [12]. The down regulation of constitutive hepatic proteins may further augment these detrimental effects [10], [11], [12]. Another crucial factor is the integrity of the liver [13]. Sepsis causes liver damage and loss of organ integrity by increased apoptosis and necrosis with subsequently increased liver enzymes, e.g. AST and ALT [14].

Van den Berghe et al. showed that intensive insulin therapy decreased mortality in critically ill patients, including mainly patients that underwent thoracic surgery [15]. Insulin given at doses to maintain blood glucose below 110 mg/dl prevented the incidence of sepsis and multi organ failure and thus improved clinical outcome and rehabilitation [15]. The mechanisms by which insulin prevents sepsis and improves survival are not defined. Some authors have suggested that glucose control is the key mechanisms rather than insulin administration [16], [17], [18], [19], [20], [21], [22], [23]. However, there is also evidence that insulin per se exerts anti-inflammatory properties [24], [25], [26], [27], [28], [29], [30]. We have recently shown that insulin administration decreased serum pro-inflammatory mediators that was associated with decreased hepatic signal transcription factors after a severe thermal injury or during endotoxemia [29], [30], [31], [32]. As pro-inflammation encompassing cytokine expression is closely associated with cell apoptosis and damage, we hypothesized that insulin may exert a positive effect on liver structure, function and damage during endotoxemia. The aims of the study were to investigate the effect of insulin on liver integrity, function and hepatic inflammatory mediators during endotoxemia.