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PXR activators are used to treat pruritus in chronic inflammatory liver diseases such as primary biliary cirrhosis (PBC). The aims of this study were to determine whether PXR activators could have an additional benefit of inhibiting inflammation in the liver, and determine whether cyclosporin A – which more effectively prevents PBC recurrence in transplanted patients than FK506 – is a PXR activator. In SJL/J mice (which have constitutively high levels of hepatic portal tract inflammatory cell recruitment), feeding a PXR activator inhibited inflammation, TNFα and Il-1α mRNA expression in SJL/J-PXR +/+, but not SJL/J-PXR −/−. Monocytic cells – a major source of inflammatory mediators such as TNFα – expressed the PXR and PXR activators inhibited endotoxin-induced NF-κB activation and TNFα expression. PXR activation also inhibited endotoxin-stimulated TNFα secretion from liver monocytes/macrophages isolated from PXR +/+ mice, but not from cells isolated from PXR −/− mice. To confirm that PXR activation inhibits NF-κB in vivo, 3x-κB-luc fibrotic mice (which express a luciferase gene regulated by NF-κB) were imaged after treatment with the hepatotoxin CCl 4.

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PXR activator inhibited the induction of hepatic NF-κB activity without affecting CCl 4 toxicity/hepatic damage. Using a PXR reporter gene assay, cyclosporin A – but not FK506 – was shown to be a direct PXR activator, and also to induce expression of the classic PXR-regulated CYP3A4 gene in human hepatocytes and in a cell line null for the FXR, a nuclear receptor with similar properties to the PXR.

Devid siberi iskusstvo egoizma chitatj. Conclusion: PXR activation is anti-inflammatory in the liver and the effects of cyclosporin A in PBC disease recurrence may be mediated in part via the PXR. Since PXR activation promotes hepatocyte growth and is also anti-fibrogenic, the PXR may be an excellent drug target for the treatment of chronic inflammatory liver disease. Abbreviations: ALT, alanine aminotransferase; CsA, cyclosporin A; GT, gliotoxin; GAPDH, glyceradehyde 3 phosphate dehydrogenase; HYP, hyperforin; IKK2-In, IκB kinase 2 inhibitor; LPS, lipopolysaccharide; METYR, metyrapone; MTS, ([3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium salt; PBC, primary biliary cirrhosis; PCN, pregnenolone 16α carbonitrile; PTI, portal tract inflammation; PPARγ, peroxiome proliferator activated receptor γ; PXR, pregnane X receptor; RIF, rifampicin; SULF, sulfasalazine; TLR4, toll-like receptor 4; TNFα, tumour necrosis factor-α. 1. Introduction The pregnane X receptor (PXR) is a member of the nuclear receptor gene superfamily of ligand-activated transcription factors expressed most prominently in hepatocytes and gut epithelium.

The ligand binding site of the PXR is activated by a range of structurally diverse xenobiotics such as the antibiotic rifampicin (RIF) and endobiotics (e.g. On activation, the PXR regulates the expression of a sub-set of genes encoding drug metabolising (e.g. CYP3A) and drug transporter proteins (e.g. MRP2), that contain response elements within their promoters. The canonical function of the PXR is therefore to sense elevations in xenobiotics and endobiotics and to orchestrate a response that promotes xenobiotic/endobiotic metabolism and excretion. Recent work in this laboratory has revealed that the PXR has a non-canonical function that results in an inhibition in the progression of liver fibrosis. Human fibrogenic myofibroblasts express significant levels of PXR mRNA and protein and treatment with PXR activators inhibits their trans-differentiation from hepatic stellate cells to fibrogenic myofibroblasts; inhibits myofibroblast expression of the major pro-fibrogenic cytokine TGFβ and markedly slows myofibroblast proliferation in vitro.