Recent reports have demonstrated that liver X receptors (LXRs) of the nuclear receptor family have anti-inflammatory effects on macrophages. Here we examine whether activation of LXR by the synthetic agonist GW3965 can ameliorate the liver injury/dysfunction caused by endotoxins in the rat. Male Wistar rats received GW3965 (0.3 mg/kg) or vehicle (50% dimethyl sulfoxide) 30 min before coadministration of lipopolysaccharide (LPS, 5 mg/kg i.v.) and peptidoglycan (1 mg/kg i.v.). Treatment with GW3965 attenuated the increase in the plasma levels of alanine aminotransferase and bilirubin (markers of liver injury/dysfunction) as well as the focal hepatocyte necrosis (histology) caused by coadministration of LPS and peptidoglycan. This protective effect of GW3965 treatment was associated with reduced infiltration of mast cells in the liver (histopathology) and reduced gene expression of the chemokines eotaxins 1 and 2, whereas MIP-2 mRNA levels were not affected. Plasma levels of tumor necrosis factor alpha and prostaglandin E2 were significantly attenuated by GW3965, whereas plasma interleukins 6 and 10 were not altered. High expression of LXRalpha mRNA was observed in Kupffer cell cultures, suggesting that Kupffer cells are targets of GW3965. Subsequent in vitro studies in Kupffer cells demonstrated that exposure to GW3965 attenuated the LPS-induced release of tumor necrosis factor alpha and prostaglandin E2 in a dose-dependent manner. In conclusion, this study demonstrates that activation of LXR by GW3965 protects against liver injury and dysfunction in a rat model of endotoxemia, in part by exerting an anti-inflammatory effect on Kupffer cells.

Aberrant regulation of innate immune responses and uncontrolled cytokine bursts are hallmarks of sepsis and endotoxemia. Activation of the nuclear liver X receptor (LXR) was recently demonstrated to suppress inflammatory genes. Our aim was to investigate the expression of LXR in human monocytes under normal and endotoxemic conditions and to study the influence of LXR activation on endotoxin-induced cytokine synthesis and release. Adherent human monocytes or whole blood were pretreated with a synthetic LXR agonist (3-{3-[(2-chloro-3-trifluoromethyl-benzyl)-(2,2-diphenyl-ethyl)-amino]-propoxy}-phenyl)-acetic acid) and subsequently challenged with LPS (from Escherichia coli) or peptidoglycan (from Staphylococcus aureus). Cytokine release was assessed by a Multiplex antibody bead kit, and cytokine mRNA levels were measured by real-time reverse-transcriptase-polymerase chain reaction. We found that LXRalpha mRNA was up-regulated in CD14+ monocytes in LPS-challenged blood, whereas LXRbeta mRNA was not altered. Addition of 3-{3-[(2-chloro-3-trifluoromethyl-benzyl)-(2,2-diphenyl-ethyl)-amino]-propoxy}-phenyl)-acetic acid to monocytes suppressed the LPS-induced release of IL-1beta, IL-6, IL-8, IL-10, IL-12p40, TMF-alpha, macrophage inflammatory protein 1alpha, macrophage inflammatory protein 1beta, and monocyte chemoattractant protein 1 in a concentration-dependent manner. Surprisingly, an accompanying decrease in cytokine mRNA accumulation was not observed. The suppressed cytokine release could not be explained by a diminished transport of mRNA out of the nucleus or a decreased secretion of cytokines. We propose that LXR is a key regulator of cytokine release in LPS-challenged human monocytes, possibly by interfering with translational events.

Patients with vitamin A/retinol deficiency are shown to be prone to infections and to suffer from increased inflammation, effects which can be remedied by vitamin A supplements. We aimed to study how human monocytes from the peripheral venous blood of healthy donors acted within the initial hours after adherence and exposure to bacterial endotoxin in the presence or absence of the 9-cis-isomer of retinoic acid (9cisRA). We found that adherent human monocytes were dominated by the CD14dimCD16+ subtype. Pretreatment with 9cisRA for 1 h significantly decreased lipopolysaccharide (LPS)-induced mRNA expression and protein release of tumor necrosis factor (TNF)α, interleukin (IL)-6 and chemokine ligands (CCL)3 and CCL4. In contrast, treatment with 9cisRA rapidly enhanced the production of monocyte chemoattractive protein/CCL2. 9cisRA treatment also led to enhanced migration of classical CD14high monocytes in a transwell in vitro system. We conclude that 9cisRA treatment of human adherent monocytes attenuates the inflammatory responses to LPS and induces the attraction of classical monocytes, a feature which may help explain why supplements administered to vitamin A-deficient patients counteract inflammation and increases the ability to fight infections.

Previous studies have implicated a role of bacterial DNA, containing unmethylated cytosine‐phosphate‐guanosine (CpG) motifs, in the initiation of systemic inflammation. This is based on the ability of CpG‐DNA to act in synergy with lipopolysaccharide (LPS) to trigger tumor necrosis factor alpha (TNFα) production in murine monocytes and to enhance LPS toxicity in rodents. In this study we investigated the capacity of CpG‐DNA to trigger and modulate cytokine responses in human leukocytes. A human blood assay, as well as isolated cultures of monocytes and neutrophils, was exposed to the synthetic oligodeoxynucleotides (ODNs) CpG ODN (2006) and GpC ODN (2006‐GC), alone or in combination with peptidoglycan or LPS. Plasma or supernatants were isolated and analyzed for TNFα, interleukin‐1 beta (IL‐1β), IL‐6 and IL‐8 by ELISA. In the blood, 2006 (but not 2006‐GC) induced the release of TNFα (P < 0.05) and possibly IL‐1β and IL‐6. IL‐8 was induced in a CpG‐independent manner. When co‐administered with peptidoglycan, both ODNs enhanced the release of cytokines, but not consistently CpG dependent. When co‐administered with LPS, only IL‐8 values were enhanced, whereas IL‐6 was suppressed at early time points. In monocyte and neutrophil cultures, CpG dependent induction of cytokine release was not observed. However, both ODNs inhibited LPS‐induced IL‐6. In conclusion, the capacity of CpG DNA to trigger the release of TNFα and to enhance LPS‐induced release of this cytokine is confirmed in human whole blood, but not in adherent human monocytes. Most effects of the ODNs on cytokine release in human leukocytes were CpG independent.