Role of interleukin-1 and its antagonism of hepatic stellate cell proliferation and liver fibrosis in the Abcb4^(-/-) mouse model

AIM: To study the interleukin-1(IL-1) pathway as a therapeutic target for liver fibrosis in vitro and in vivo using the ATP-binding cassette transporter b4^(-/-)(Abcb4^(-/-)) mouse model.METHODS: Female and male Abcb4^(-/-) mice from 6 to 13 mo of age were analysed for the degree of cholestasis(liver serum tests), extent of liver fibrosis(hydroxyproline content and Sirius red staining) and tissue-specific activation of signalling pathways such as the IL-1 pathway [quantitative polymerase chain reaction(q PCR)]. For in vivo experiments, murine hepatic stellate cells(HSCs) were isolated via pronasecollagenase perfusion followed by density gradient centrifugation using female mice. Murine HSCs were stimulated with up to 1 ng/m L IL-1β with or without 2.5 μg/m L Anakinra, an IL-1 receptor antagonist, respectively. The proliferation of murine HSCs was assessed via the Brd U assay. The toxicity of Anakinra was evaluated via the fluorescein diacetate hydrolysis(FDH) assay. In vivo 8-wk-old Abcb4^(-/-) mice with an already fully established hepatic phenotype were treated with Anakinra(1 mg/kg body-weight daily intraperitoneally) or vehicle and liver injury and liver fibrosis were evaluated via serum tests, q PCR, hydroxyproline content and Sirius red staining. RESULTS: Liver fibrosis was less pronounced in males than in female Abcb4^(-/-) animals as defined by a lower hydroxyproline content(274 ± 64 μg/g vs 436 ± 80 μg/g liver, respectively; n = 13-15; P < 0.001; MannWhitney U-test) and lower m RNA expression of the profibrogenic tissue inhibitor of metalloproteinase-1(TIMP)(1 ± 0.41 vs 0.66 ± 0.33 fold, respectively; n = 13-15; P < 0.05; Mann-Whitney U-test). Reduced liver fibrosis was associated with significantly lower levels of F4/80 m RNA expression(1 ± 0.28 vs 0.71 ± 0.41 fold, respectively; n = 12-15; P < 0.05; Mann-Whitney U-test) and significantly lower IL-1β m RNA expression levels(1 ± 0.38 vs 0.44 ± 0.26 fold, respectively; n = 13-15; P < 0.001; Mann-Whitney U-test). No gender differences in the serum liver parameters [bilirubin; alanine aminotransferase(ALT); aspartate aminotransferase and alkaline phosphatase(AP)] were found. In vitro, the administration of IL-1β resulted in a significant increase in HSC proliferation [0.94 ± 0.72 arbitrary units(A.U.) in untreated controls, 1.12 ± 0.80 A.U. at an IL-1β concentration of 0.1 ng/m L and 1.18 ± 0.73 A.U. at an IL-1β concentration of 1 ng/m L in samples from n = 6 donor animals; P < 0.001; analyses of variance(ANOVA)]. Proliferation was reduced significantly by the addition of 2.5 μg/m L Anakinra(0.81 ± 0.60 A.U. in untreated controls, 0.92 ± 0.68 A.U. at an IL-1β concentration of 0.1 ng/m L, and 0.91 ± 0.69 A.U. at an IL-1β concentration of 1 ng/m L; in samples from n = 6 donor animals; P < 0.001; ANOVA) suggesting an anti-proliferative effect of this clinically approved IL-1 receptor antagonist. The FDH assay showed this dose to be non-toxic in HSCs. In vivo, Anakinra had no effect on the hepatic hydroxyprolinecontent, liver serum tests(ALT and AP) and profibrotic(collagen 1α1, collagen 1α2, transforming growth factor-β, and TIMP-1) and anti-fibrotic [matrix metalloproteinase 2(MMP2), MMP9 and MMP13 ] gene expression after 4 wk of treatment. Furthermore, the hepatic IL-1β and F4/80 m RNA expression levels were unaffected by Anakinra treatment.CONCLUSION: IL-1β expression is associated with the degree of liver fibrosis in Abcb4^(-/-) mice and promotes HSC proliferation. IL-1 antagonism shows antifibrotic effects in vitro but not in Abcb4^(-/-) mice.

PI 3-kinase pathway is responsible for antiapoptotic effects of atrial natriuretic peptide in rat liver transplantation

AIM:To investigate the in vivo effect of atrial natriureticpeptide(ANP)and its signaling pathway during ortho-topic rat liver transplantation.METHODS:Rats were infused with NaCl,ANP(5 μg/kg),wortmannin(WM,16 μg/kg),or a combination ofboth for 20 min.Livers were stored in UW solution(4°C)for 24 h,transplanted and reperfused.Apoptosis wasexamined by caspase-3 activity and TUNEL staining.Phosphorylation of Akt and Bad was visualized by West-ern blotting and phospho-Akt-localization by confocalmicroscopy.RESULTS:ANP-pretreatment decreased caspase-3activity and TUNEL-positive cells after cold ischemia,indicating antiapoptotic effects of ANP in vivo.The an-tiapoptotic signaling of ANP was most likely caused byphosphorylation of Akt and Bad,since pretreatment withPI 3-kinase inhibitor WM abrogated the ANP-inducedreduction of caspase-3 activity.Interestingly,analysis ofliver tissue by confocal microscopy showed translocationof phosphorylated Akt to the plasma membrane of hepa-tocytes evoked by ANP.CONCLUSION:ANP activates the PI-3-kinase pathwayin the liver in vivo leading to phosphorylation of Bad, an event triggering antiapoptotic signaling cascade inischemic liver.

Hepatocyte cytoskeleton during ischemia and reperfusion -influence of ANP-mediated p38 MAPK activation

AIM: To determine functional consequences of this activation, whereby we focused on a potential regulation of the hepatocyte cytoskeleton during ischemia and reperfusion.METHODS: For in vivo experiments, animals received ANP (5 μg/kg) intravenously. In a different experimental setting, isolated rat livers were perfused with KH-buffer ±ANP (200 nmol/L)±SB203580 (2 μmol/L). Liverswere then kept under ischemic conditions for 24 h, and either transplanted or reperfused. Actin, Hsp27, and phosphorylated Hsp27 were determined by Western blotting, p38 MAPK activity by in vitro phosphorylation assay. F-actin distribution was determined by confocal microscopy.RESULTS: We first confirmed that ANP preconditioning leads to an activation of p38 MAPK and observedalterations of the cytoskeleton in hepatocytes of ANPpreconditioned organs. ANP induced an increase of hepatic F-actin after ischemia, which could be prevented by the p38 MAPK inhibitor SB203580 but had no effect on bile flow. After ischemia untreated livers showed a translocation of Hsp27 towards the cytoskeleton and an increase in total Hsp27, whereas ANP preconditioning prohibited translocation but caused an augmentation of Hsp27 phosphorylation. This effect is also mediated via p38 MAPK, since it was abrogated by the p38 MAPK inhibitor SB203580.CONCLUSION: This study reveals that ANP-mediated p38 MAPK activation leads to changes in hepatocyte cytoskeleton involving an elevation of phosphorylated Hsp27 and thereby for the first time shows functional consequences of ANP-induced hepatic p38 MAPK activation.