QS265: Fasting Enhances Hepatic Injury from LPS: Role of TLR4

Introduction: Early enteral nutrition improves clinical outcome and reduces septic complications in critically ill trauma patients. In fact, stimulation of the gut mucosa with luminal nutrients may have beneficial effects even when given in amounts less than that required for full nutritional support. However, the protective mechanism of this effect remains to be fully elucidated. Interestingly, in fasted rats, lipopolysaccharide (LPS) initiates an inflammatory cascade that causes hepatic injury along with an upregulation of cell signaling cytokines and cyclo-oxygenase-2 (COX2). Because some of the deleterious effects of LPS are mediated by the Toll-Like Receptor 4 (TLR4) and because enteral nutrition improves outcomes in the critically ill, we hypothesized that fasting would predispose rats to LPS-induced hepatic injury via a TLR4 mediated mechanism. Methods: Rats were either fasted for 18h with free access to water or had continuous access to water and standard chow. All rats received intraperitoneal LPS (20 mg/kg) or saline, sacrificed 5h later and serum and liver harvested. Serum AST and ALT were measured as an index of liver injury. Serum cholesterol and cytokines were measured by commercially available assays. Hepatic COX2, hemeoxygenase 1 (HO1), LPS-binding protein (LBP) and TLR4 were measured by Western immunoblot. Results are mean ± SE (n=8/group; ANOVA). Results: LPS significantly increased serum AST, ALT and cytokines, and hepatic LBP, COX2, HO1 and TLR4 in all rats when compared to saline counterparts. Fasted rats given LPS had significantly higher AST, ALT, pro-inflammatory cytokines, COX2, and TLR4 when compared to fed rats receiving LPS. Fasting did not significantly affect LBP or cholesterol. In contrast to its effects on pro-inflammatory mediators, feeding did not attenuate the LPS-induced increase of anti-inflammatory cytokines or down regulate the hepatoprotective protein hemeoxygenase −1 (HO-1). Conclusions: These data suggest that the hepatoprotective effects of feeding against LPS induced hepatic injury may be secondary to a reduction in pro-inflammatory cytokines and COX2 levels while levels of anti-inflammatory cytokines and HO-1 are maintained, thus preserving inflammatory regulatory mechanisms. Moreover, these data further support the concept that enteral nutrition in critically ill patients is beneficial, and furthermore suggest that fasting may enhance the susceptibility of the liver to injury caused by septic insults via increased signaling through TLR4.