Hepatic gene expression during endotoxemia

Targeting STAT3: A crucial modulator of sepsis

Signal transducer and activator of transcription 3 (STAT3) is a cellular signal transcription factor that has recently attracted a great deal of attention. It can trigger a variety of genes transcription in response to cytokines and growth factors stimulation, which plays an important role in many cellular biological processes involved in anti/proinflammatory responses. Sepsis is a life-threatening organ dysfunction resulting from dysregulated host responses to infection. As a converging point of multiple inflammatory responses pathways, accumulating studies have presented the elaborate network of STAT3 in sepsis pathophysiology; these results generally indicate a promising therapeutic application for targeting STAT3 in the treatment of sepsis. In the present review, we evaluated the published literature describing the use of STAT3 in the treatment of experimental and clinical sepsis. The information presented here may be useful for the design of future studies and may highlight the potential of STAT3 as a future biomarker and therapeutic target for sepsis.

Hepatic-Specific Decrease in the Expression of Selenoenzymes and Factors Essential for Selenium Processing After Endotoxemia

Background

Selenium (Se) levels decrease in the circulation during acute inflammatory states and sepsis, and are inversely associated with morbidity and mortality. A more specific understanding of where selenoproteins and Se processing are compromised during insult is needed. We investigated the acute signaling response in selenoenzymes and Se processing machinery in multiple organs after innate immune activation in response to systemic lipopolysaccharide (LPS).

Methods

Wild type (WT) adult male C57/B6 mice were exposed to LPS (5 mg/kg, intraperitoneal). Blood, liver, lung, kidney and spleen were collected from control mice as well as 2, 4, 8, and 24 h after LPS. Plasma Se concentration was determined by ICP-MS. Liver, lung, kidney and spleen were evaluated for mRNA and protein content of selenoenzymes and proteins required to process Se.

Results

After 8 h of endotoxemia, plasma levels of Se and the Se transporter protein, SELENOP were significantly decreased. Consistent with this timing, the transcription and protein content of several hepatic selenoenzymes, including SELENOP, glutathione peroxidase 1 and 4 were significantly decreased. Furthermore, hepatic transcription and protein content of factors required for the Se processing, including selenophosphate synthetase 2 (Sps2), phosphoseryl tRNA kinase (Pstk), selenocysteine synthase (SepsecS), and selenocysteine lyase (Scly) were significantly decreased. Significant LPS-induced downregulation of these key selenium processing enzymes was observed in isolated hepatocytes. In contrast to the acute and dynamic changes observed in the liver, selenoenzymes did not decrease in the lung, kidney or spleen.

Conclusion

Hepatic selenoenzyme production and Se processing factors decreased after endotoxemia. This was temporally associated with decreased circulating Se. In contrast to these active changes in the regulation of Se processing in the liver, selenoenzymes did not decrease in the lung, kidney or spleen. These findings highlight the need to further study the impact of innate immune challenges on Se processing in the liver and the impact of targeted therapeutic Se replacement strategies during innate immune challenge.

Inactivation of Sirt1 in mouse livers protects against endotoxemic liver injury by acetylating and activating NF-κB

Sirtuin 1 (Sirt1) is a deacetylase that regulates many cellular processes in the liver, and so far its role in endotoxemic liver injury is elusive. So we conditionally inactivate Sirt1 in murine hepatocytes to determine its role in d-galactosamine (GalN)/lipopolysaccharide (LPS)-induced liver damage, which is a well-established experimental model mimicking septic liver injury and fulminant hepatitis. Ablation of Sirt1 shows remarkable protection against GalN/LPS-induced liver injury, which is a result of enhanced NF-κB response because knockdown of RelA/p65 negates the protective effect of Sirt1 knockout. Mechanistically, NF-κB p65 is maintained in a hyperacetylated, DNA-binding competent state in tumor necrosis factor-α (TNF-α)-challenged albumin-Cre⁺ (AlbCre⁺) hepatocytes. Transfection of hepatocytes with a recombinant acetylated p65 expression construct replicates the protection afforded by Sirt1 knockout. Transfection of AlbCre⁺ hepatocytes with a recombinant wild-type Sirt1 construct, rather than a deacetylase-defective one, compromises NF-κB activation and resensitizes hepatocytes to TNF-α-induced apoptosis. Taken together, our results demonstrate that Sirt1 deacetylates p65 and compromises NF-κB activity in hepatocytes when confronted with LPS/TNF-α stimulation, leading to increased susceptibility to endotoxemic injury. These findings identify a possible protein effector to maneuver the hepatic NF-κB signaling pathway under inflammatory circumstances and a feasible way to increase hepatocellular resistance to endotoxin/TNF-α toxicity.

Deferoxamine but not dexrazoxane alleviates liver injury induced by endotoxemia in rats

The purpose of the present study was to compare the activity of two different clinically available iron chelators on the development of acute liver injury after administration of the bacterial endotoxin (lipopolysaccharide [LPS]) in rats. Lipopolysaccharide was administered either alone or after pretreatment with dexrazoxane (DEX) or deferoxamine (DFO). Control groups received only saline or its combination with either chelator. After 8 h, untreated LPS rats developed liver injury, with signs of inflammation and oxidative stress. Lipopolysaccharide reduced plasma iron concentrations in association with increased production of hepcidin and the reduced liver expression of ferroportin. Administration of chelating agents to LPS animals showed distinct effects. Although both drugs were able to reduce liver iron content, together with corresponding changes in hepcidin and ferroportin expressions, only DFO showed a protective effect against liver injury despite relatively small liver concentrations. In sharp contrast, DEX failed to improve any hallmark of liver injury and even worsened the GSH/GSSG ratio, the indicator of oxidative stress in the tissue. High-performance liquid chromatography-mass spectrometry analysis showed marked liver accumulation of iron-chelating metabolite of DEX (ADR-925), whereas the parent compound was undetectable. Further downregulation of transporters involved in bile formation was observed after DFO in the LPS group as well as in healthy animals. Neither chelator imposed significant liver injury in healthy animals. In conclusion, we demonstrated marked differences in the modulation of endotoxemic liver impairment between two iron chelators, implicating that particular qualities of chelating agents may be of crucial importance.

Burn plus lipopolysaccharide augments endoplasmic reticulum stress and NLRP3 inflammasome activation and reduces PGC-1α in liver

Extensively burned patients often suffer from sepsis (especially caused by Pseudomonas aeruginosa), which may prolong metabolic derangement, contribute to multiple organ failure, and increase mortality. The molecular and cellular mechanisms of such infection-related metabolic derangement and organ dysfunction are unclear. We have previously shown that severely burned patients have significant and persisting hepatic endoplasmic reticulum (ER) stress. We hypothesized that ER stress and the unfolded protein response correlate with NOD-like receptor, pyrin domain containing 3 (NLRP3) inflammasome activation in burn. These may trigger profound metabolic changes in the liver, which form the pathological basis of liver damage and liver dysfunction after burn injury. A two-hit rat model was established by a 60% total body surface area scald burn and intraperitoneal injection of P. aeruginosa-derived lipopolysaccharide (LPS) 3 days after burn. One day later, animals were killed, and liver tissue samples were collected for gene expression and protein analysis of NLRP3 inflammasome activation, ER stress, and glucose and lipid metabolism. Liver damage was assessed by plasma markers (alanine aminotransferase and aspartate aminotransferase) and liver immunohistochemical analysis. Our results showed that burn injury and LPS injection induced inflammasome activation in liver and augmented hepatic ER stress and liver damage. Although there was an increased metabolic demand after burn, hepatic NLRP3 inflammasome activation corresponded to inhibition of PGC-1α (peroxisome proliferator-activated receptor γ-coactivator 1α) and its upstream regulators protein kinase A catalyst unit, AMP-activated protein kinase α, and sirtuin-1 may provide a mechanism for the enhanced metabolic derangement after major burn injury plus sepsis. In conclusion, burn + LPS augments inflammasome activation and ER stress in liver, which in turn contribute to postburn metabolic derangement.

Inhibitor of nuclear factor-κB, SN50, attenuates lipopolysaccharide-induced lung injury in an isolated and perfused rat lung model

NF-κB cell permeable inhibitory peptide (SN50) inhibits translocation of nuclear factor-κB (NF-κB) and production of inflammatory cytokines that are implicated in lipopolysaccharide (LPS)-induced lung injury (LPSLI). However, the protective effect of SN50 in LPSLI is unclear. We explored the cellular and molecular mechanisms of SN50 treatment in LPSLI. LPSLI was induced by intratracheal instillation of 10 mg/kg LPS using an isolated and perfused rat lung model. SN50 was administered in the perfusate 15 minutes before LPS was administered. Hemodynamics, lung histologic change, inflammatory responses, and activation of apoptotic pathways were evaluated. After LPSLI, increased pulmonary vascular permeability and lung weight gain was observed. The levels of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, myeloperoxidase, and macrophage inflammatory protein-2 increased in bronchoalveolar lavage fluids. Lung-tissue expression of TNF-α, IL-1β, mitogen-activated protein kinases (MAPKs), caspase-3, p-AKT (serine-threonine kinase, also known as protein kinase B), and plasminogen activator inhibitor-1 (PAI-1) was greater in the LPS group compared with controls. Upregulation and activation of NF-κB was associated with increased lung injury in LPSLI. SN50 attenuated the inflammatory responses, including expression of IL-1β, TNF-α, myeloperoxidase, MAPKs, PAI-1, and NF-κB; downregulation of apoptosis indicated by caspase-3 and p-AKT expression was also observed. In addition, SN50 mitigated the increase in the lung weight, pulmonary vascular permeability, and lung injury. In conclusion, LPSLI is associated with inflammatory responses, apoptosis, and coagulation. NF-κB is an important therapeutic target in the treatment of LPSLI. SN50 inhibits translocation of NF-κB and attenuates LPSLI.

Insulin hypersensitivity induced by hepatic PTEN gene ablation protects from murine endotoxemia

Sepsis still remains a major cause for morbidity and mortality in patients. The molecular mechanisms underlying the disease are still enigmatic. A great number of therapeutic approaches have failed and treatment strategies are limited to date. Among those few admitted for clinical intervention, intensive insulin treatment has proven to be effective in the reduction of disease related complications in critically ill patients. Insulin effectively reduces glucose levels and thereby contributes to protection. On the other hand insulin is a potent signaling pathway activator. One of those is the PI3K signaling axis. Activation of PI3K is known to limit pro-inflammatory gene expression. Here we can show that in a mouse model of insulin hypersensitivity induced by the deletion of the PI3K antagonist PTEN, specifically in hepatic tissue, significant protection is conferred in murine models of lethal endotoxemia and sepsis. Acute inflammatory responses are diminished, glucose metabolism normalized and vascular activation is reduced. Furthermore we investigated the hepatic gene expression profile of relevant anti-inflammatory genes in PTEN deficient mice and found marked upregulation of PPARγ and HO-1. We conclude from our data that insulin hypersensitivity via sustained activation of the PI3K signaling pathway exerts protective effects in acute inflammatory processes.

Efficacy of specific IgY for treatment of lipopolysaccharide-induced endotoxemia using a mouse model

AIMS

To estimate the efficacy of specific egg yolk immunoglobulin (IgY) for the treatment of lipopolysaccharide (LPS)-induced endotoxemia using a mouse model.

METHODS AND RESULTS

Specific IgY was obtained from the yolk of hens immunized with formaldehyde-killed Escherichia coli O111 and showed a high binding activity to LPS when subjected to an ELISA. Endotoxemia was induced in mice by intraperitoneal injection of LPS at a dose of 20 mg kg(-1) for measuring survival rate and 10 mg kg(-1) for cytokine measurement. The survival rate of mice treated with 200 mg kg(-1) specific IgY or 5 mg kg(-1) dexamethasone was 70% while none of the mice in the normal saline-treated group survived more than 7 days. Specific IgY significantly (P < 0.05) decreased tumour necrosis factor-α (TNF-α) level and increased interleukin-10 (IL-10) level in the serum of endotoxemia mice. Specific IgY had less of an effect on TNF-α than dexamethasone, while its effect on increasing IL-10 was stronger than dexamethasone. Haematoxylin and eosin-stained sections indicated that IgY attenuated the damage to the lung and liver observed in mice with endotoxemia.

CONCLUSIONS

The specific IgY increased the survival rate of mice with endotoxemia induced by LPS, down-regulated TNF-α and up-regulated IL-10 in serum and attenuated the extent of damage to the lung and liver.

SIGNIFICANCE AND IMPACT OF THE STUDY

The specific IgY has potential for the treatment of LPS-induced endotoxemia.

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

Sepsis and septic shock are frequently encountered in the intensive care unit. Despite the evolution of intensive care medicine during the last decades, septic shock is still associated with high mortality and complications of sepsis such as cholestasis, liver dysfunction, and massive intravascular volume deficit. Little is known about the whole pattern of changes at the transcriptional level during the development of acute sepsis. Here we present a detailed molecular biological analysis of the events in the liver during the first day of acute bacterial infection in a clinically relevant model of porcine peritoneal sepsis. Before and 21 h after induction of sepsis by autologous fecal inoculum, liver samples were taken for microarray analysis. There were two groups of animals (7 control and 8 sepsis), two of each group where used in microarray, the remaining were used for confirmation of selected genes by real-time polymerase chain reaction. Pathway analysis revealed that in acute sepsis, gene expression was significantly changed in processes related to apoptosis, inflammation, and oxidant/redox balance. Although after 21 h these animals are expected to die within the next 3 to 4 h from massive complications, functional induction of apoptosis could not be confirmed. Computer analysis identified three key regulator genes (IL8, CCL2, and CXCL2) among the first genes to be upregulated specifically in the sepsis group, and these can directly or indirectly control the bulk of the sepsis response. Induction of inflammatory mediators by sepsis was supported by the detection of corresponding cytokines (interleukin 6 and interleukin 8) in the blood.