Molecular analysis of sepsis-induced changes in the liver: microarray study in a porcine model of acute fecal peritonitis with fluid resuscitation

Hepatic Peroxisome Proliferator-Activated Receptor Alpha Dysfunction in Porcine Septic Shock

Despite decades of research, sepsis remains one of the most urgent unmet medical needs. Mechanistic investigations into sepsis have mainly focused on targeting inflammatory pathways; however, recent data indicate that sepsis should also be seen as a metabolic disease. Targeting metabolic dysregulations that take place in sepsis might uncover novel therapeutic opportunities. The role of peroxisome proliferator-activated receptor alpha (PPARɑ) in liver dysfunction during sepsis has recently been described, and restoring PPARɑ signaling has proven to be successful in mouse polymicrobial sepsis. To confirm that such therapy might be translated to septic patients, we analyzed metabolic perturbations in the liver of a porcine fecal peritonitis model. Resuscitation with fluids, vasopressor, antimicrobial therapy and abdominal lavage were applied to the pigs in order to mimic human clinical care. By using RNA-seq, we detected downregulated PPARɑ signaling in the livers of septic pigs and that reduced PPARɑ levels correlated well with disease severity. As PPARɑ regulates the expression of many genes involved in fatty acid oxidation, the reduced expression of these target genes, concomitant with increased free fatty acids in plasma and ectopic lipid deposition in the liver, was observed. The results obtained with pigs are in agreement with earlier observations seen in mice and support the potential of targeting defective PPARɑ signaling in clinical research.

Pathophysiology of sepsis‐induced cholestasis: A review

Sepsis is a critical condition resulting from the excessive activation of the inflammatory/immune system in response to an infection, with high mortality if treatment is not administered promptly. One of the many possible complications of sepsis is liver dysfunction with consequent cholestasis. The aim of this paper is to review the main mechanisms involved in the development of cholestasis in sepsis. Cholestasis in a septic patient must raise the suspicion that it is the consequence of the septic condition and limit the laborious attempts of finding a hepatic or biliary disease. Prompt antibiotic administration when sepsis is suspected is essential and may improve liver enzymes. Cholestasis is a syndrome with a variety of etiologies, among which sepsis is frequently overlooked, despite a number of studies and case reports in the literature demonstrating not only the association between sepsis and cholestasis but also the role of cholestasis as a prognostic factor for sepsis‐induced death.

Toll-Like Receptors -2, -3, -4 and -7 Expression Patterns in the Liver of a CLP-Induced Sepsis Mouse Model

Objective: To investigate the expression of toll-like receptors (TLRs) in the liver of septic mouse model. Materials and methods: For this study seventy-two C57BL/6J mice were utilized. Sepsis was induced by cecal ligation and puncture (CLP) in the mice of the three septic (S) groups (euthanized at 24 hours, 48 hours and 72 hours). Sham (laparotomy)- operated mice constituted the control (C) groups (euthanized at 24, 48 and 72 hours). Blood samples were drawn and liver tissues were extracted and examined histologically. The expression of TLRs 2, 3, 4 and 7 was assessed via immunohistochemistry (IHC) and qrt-PCR (quantitative- Polymerase Chain Reaction). Results: Liver function tests were elevated in all S-groups in contrast to their time-equivalent control groups (S24 versus C24, S48 versus C48 and S72 versus C72) (p < 0.05). Liver histology displayed progressive deterioration in the septic groups. IHC and qrt-PCR both showed an increased expression of all TLRs in the septic mice in comparison to their analogous control ones (p < 0.05). Analysis of livers and intestines of the septic animals proved that all TLRs were significantly expressed in higher levels in the intestinal tissues at 24h and 48h (p < 0.05) except for TLR 3 in S48 (p > 0.05); whereas at 72 hours only TLR 4 levels were significantly elevated in the intestine (p < 0.05). Conclusion: TLRs seem to be expressed in significant levels in the livers of septic rodents, indicating that they have a possible role in the pathophysiology of liver damage in septic conditions.

Differential gene expression profile of porcine livers subjected to warm ischemia alone

BACKGROUND

Livers exposed to warm ischemia (WI) are increasingly used for transplantation. The molecular mechanisms activated by WI alone (prior to procurement and transplantation) are not understood. To elucidate the pathways involved, we used microarrays to investigate the gene expression in porcine livers exposed to WI.

METHODS

Porcine livers (n = 6 group) were randomly subjected to WI periods of 15, 30 or 45 minutes. mRNA was extracted and gene expression determined by microarray analysis. Using bioinformatics software, we identified differentially expressed genes and related molecular pathways. We used the corresponding human annotation of the porcine microarray for the functional analysis.

RESULTS

Between 0 and 15 minutes of WI, 3530 genes were altered with a 2-log-fold change of <-0.58 or >+0.58 and P < .05. Between 0 and 30 minutes of WI, 4141 genes were differentially expressed; and between 0 and 45 minutes of WI, 2814 genes. At each time point, ∼50% of genes were up-regulated, whereas 50% were down-regulated. After pathway mapping, we found that the same pathways were induced for observed clustering of in the three WI periods: cell death, proliferation, inflammation, and metabolism pathways. Among the top genes that were up-regulated after 15 minutes of WI, the majority started to return to but did not reach baseline expression with increasing WI. A similar pattern was observed for the top suppressed genes.

CONCLUSIONS

WI causes rapid changes in gene expression that affect several molecular pathways. This phenomenon seems to plateau at 15 to 30 minutes of WI. These new insights in the timing and the nature of molecular pathways induced by WI alone may help to design specific interventions to alter these changes and improve the outcome of livers from cardiac death donors.

Immunohistochemical detection of interleukin-8 in inflamed porcine tissues

The objective of this study was to identify the specific localization of interleukin-8 (IL-8) in cells in situ in a variety of inflammatory processes in different tissues from pigs. Our hypothesis was that IL-8 primarily is a neutrophil related cytokine present in all extravascular neutrophils while expression also occurs in other cell types in response to an inflammatory stimulus. Using IL-8 immunohistochemistry we discovered that neutrophils were the predominant IL-8 positive cell population while epithelial cell types and endothelium of postcapillary venules could be positive when situated in close vicinity of an inflammatory lesion. Furthermore, endothelial cells of newly formed vessels in granulation tissue were positive in some specimens. Some sub-populations of inflammatory neutrophils were, however, IL-8 negative which could reflect some phase of neutrophil swarming.

Improving the function of liver grafts exposed to warm ischemia by the Leuven drug protocol: exploring the molecular basis by microarray

Livers exposed to warm ischemia (WI) before transplantation are at risk for primary nonfunction (PNF), graft dysfunction, and ischemic biliary strictures, all associated with ischemia/reperfusion injury (IRI). Our multifactorial approach, Leuven drug protocol (LDP), has been shown to reduce these effects and increase recipient survival in WI/IRI-damaged porcine liver transplantation. The aim was the identification of the molecular mechanisms responsible for the hepatoprotective effects of the LDP. Porcine livers were exposed to 45 minutes of WI, cold-stored for 4 hours, transplanted, and either modulated (LDP group; n = 3) or not modulated (control group; n = 4). In the LDP group, the donor livers were flushed with streptokinase and epoprostenol before cold perfusion; the recipients received intravenous glycine, a-1-acid-glycoprotein, FR167653 (a mitogen-activated protein kinase inhibitor), a-tocopherol, glutathione, and apotransferrin. Liver samples were taken before WI and 1 hour after reperfusion. Gene expression was determined with microarrays and molecular pathways and key regulatory genes were identified. The number of genes changed between baseline and 1 hour after reperfusion was 686 in the LDP group and 325 in the control group. The extra genes in the LDP group belonged predominantly to pathways related to cytokine activity, apoptosis, and cell proliferation. We identified 7 genes that were suppressed in the LDP group. These genes could be linked in part to the administered drugs. New potential drug targets were identified on the basis of genes induced in the control group but unaffected in the LDP group and interactions predicted by the literature. In conclusion, the LDP primarily resulted in the suppression of inflammation-regulating genes in IRI. Furthermore, the microarray technique helped us to identify additional gene targets.

Liver dysfunction and phosphatidylinositol-3-kinase signalling in early sepsis: experimental studies in rodent models of peritonitis

BACKGROUND

Hepatic dysfunction and jaundice are traditionally viewed as late features of sepsis and portend poor outcomes. We hypothesized that changes in liver function occur early in the onset of sepsis, yet pass undetected by standard laboratory tests.

METHODS AND FINDINGS

In a long-term rat model of faecal peritonitis, biotransformation and hepatobiliary transport were impaired, depending on subsequent disease severity, as early as 6 h after peritoneal contamination. Phosphatidylinositol-3-kinase (PI3K) signalling was simultaneously induced at this time point. At 15 h there was hepatocellular accumulation of bilirubin, bile acids, and xenobiotics, with disturbed bile acid conjugation and drug metabolism. Cholestasis was preceded by disruption of the bile acid and organic anion transport machinery at the canalicular pole. Inhibitors of PI3K partially prevented cytokine-induced loss of villi in cultured HepG2 cells. Notably, mice lacking the PI3Kγ gene were protected against cholestasis and impaired bile acid conjugation. This was partially confirmed by an increase in plasma bile acids (e.g., chenodeoxycholic acid [CDCA] and taurodeoxycholic acid [TDCA]) observed in 48 patients on the day severe sepsis was diagnosed; unlike bilirubin (area under the receiver-operating curve: 0.59), these bile acids predicted 28-d mortality with high sensitivity and specificity (area under the receiver-operating curve: CDCA: 0.77; TDCA: 0.72; CDCA+TDCA: 0.87).

CONCLUSIONS

Liver dysfunction is an early and commonplace event in the rat model of sepsis studied here; PI3K signalling seems to play a crucial role. All aspects of hepatic biotransformation are affected, with severity relating to subsequent prognosis. Detected changes significantly precede conventional markers and are reflected by early alterations in plasma bile acids. These observations carry important implications for the diagnosis of liver dysfunction and pharmacotherapy in the critically ill. Further clinical work is necessary to extend these concepts into clinical practice. Please see later in the article for the Editors' Summary.