Ramiprilate inhibits functional matrix metalloproteinase activity in Crohn's disease fistulas.

Increased expression of matrix metalloproteinase (MMP)-2, -3 and -9 has been demonstrated in Crohn's disease fistulas, but it is unknown whether these enzymes are biologically active and represent a therapeutic target. Therefore, we investigated the proteolytic activity of MMPs in fistula tissue and examined the effect of inhibitors, including clinically available drugs that beside their main action also suppress MMPs. Fistula specimens were obtained by surgical excision from 22 patients with Crohn's disease and from 10 patients with fistulas resulting from other causes. Colonic endoscopic biopsies from six controls were also included. Total functional MMP activity was measured by a high-pressure liquid chromatography (HPLC)-based, fluorogenic MMP-substrate cleavage assay, and the specific activity of MMP-2, -3 and -9 by the MMP Biotrak Activity Assay. The MMP inhibitors comprised ethylene-diamine-tetraacetic acid (EDTA), the synthetic broad-spectrum inhibitor, GM6001, the angiotensin-converting enzyme (ACE) inhibitor, ramiprilate, and the tetracycline, doxycycline. In Crohn's disease fistulas, about 50% of the total protease activity was attributable to MMP activity. The average total MMP activity was significantly higher (about 3.5-times) in Crohn's fistulas (471 FU/µg protein, range 49-2661) compared with non-Crohn's fistulas [134 FU/µg protein, range 0-495, (p < 0.05)] and normal colon [153 FU/µg protein, range 77-243, (p < 0.01)]. MMP-3 activity was increased in Crohn's fistulas (1.4 ng/ml, range 0-9.83) compared with non-Crohn's fistulas, [0.32 ng/ml, range 0-2.66, (p < 0.02)]. The same applied to MMP-9 activity [0.64 ng/ml, range 0-5.66 and 0.17 ng/ml, range 0-1.1, respectively (p < 0.04)]. Ramiprilate significantly decreased the average total MMP activity level by 42% and suppressed the specific MMP-3 activity by 72%, which is comparable to the effect of GM6001 (87%). Moreover, MMP-9 activity was completely blunted by ramiprilate. Doxycycline had no effect on MMP activity. Increased functional MMP activity, notably MMP-3 and -9, is present in Crohn's fistulas and may be inhibited by ramiprilate, a widely available ACE inhibitor.

Nuclear localization of TRK-A in liver cells.

The liver represents a site of expression of neurotrophins and their receptors. We have characterized the expression and intracellular localization of the nerve growth factor (NGF) receptor, Trk-A, in liver cells in vivo and in vitro. In both normal and fibrotic liver tissue, Trk-A immunostaining was present in different cell types, including parenchymal cells and cells of the inflammatory infiltrate. In hepatocytes and activated stellate cells (HSC), Trk-A showed a predominant nuclear localization, both in the presence and absence of injury. In cultured HSC, Trk-A was found to be functional, because exposure of the cells to recombinant NGF resulted in stimulation of cell migration and activation of intracellular signaling pathways, including Ras-ERK and PI3K/Akt. Remarkably, in cultured HSC, Trk-A staining was found constitutively in the nucleus. In these cells, Trk-A could be stained only by antibodies directed against the intracellular domain but not by those recognizing the extracellular portion of Trk-A suggesting that the intracellular portion of the receptor is the major determinant of nuclear Trk-A staining. In contrast to HSC, freshly isolated hepatocytes did not show any nuclear localization of the intracellular portion of Trk-A. In pheocromocytoma cells, nuclear staining for Trk-A was not present in conditions of serum deprivation, but could be induced by exposure to NGF or to a mixture of soluble mediators. We conclude that nuclear localization of the intracellular domain of Trk-A is observed constitutively in liver cells such as HSC, while in other cell types it could be induced in response to soluble factors.

Thrombopoietin stimulates migration and activates multiple signaling pathways in hepatoblastoma cells.

Thrombopoietin (TPO), a cytokine that participates in the differentiation and maturation of megakaryocytes, is produced in the liver, but only limited information is available on the biological response of liver-derived cells to TPO. In this study, we investigated whether HepG2 cells express c-Mpl, the receptor for TPO, and whether TPO elicits biological responses and intracellular signaling in this cell type. Specific transcripts for c-Mpl were detected in HepG2 cells by RT-PCR, and expression of the protein was demonstrated by Western blot analysis and immunofluorescence. Exposure of HepG2 cells to TPO was associated with a dose-dependent increase in cell migration and chemoinvasion through Matrigel-coated filters. A checkerboard analysis showed that the effects of TPO on cell migration were dependent on both chemotaxis and chemokinesis. Exposure of HepG2 cells to TPO resulted in the activation of different members of the MAPK family, including ERK and JNK, as assessed using phosphorylation-specific antibodies and immune complex kinase assays. TPO also activated phosphatidylinositol 3-kinase (PI3K) and the downstream kinase Akt in a time-dependent manner. Finally, activation of c-Mpl was associated with increased activation of nuclear factor-kappaB. With the use of specific inhibitors, tyrosine phosphorylation and activation of PI3K were found to be required for the induction of migration in response to TPO. We conclude that TPO exerts biological actions on cultured hepatoblastoma cells via activation of c-Mpl and its downstream signaling.

Thiazolidinedione treatment inhibits bile duct proliferation and fibrosis in a rat model of chronic cholestasis.

AIM: To investigate the effects of troglitazone (TGZ), an anti-diabetic drug which activates peroxisome proliferator-activated receptor-gamma (PPAR-gamma), for liver tissue repair, and the development of ductular reaction, following common bile duct ligation (BDL) in rats. METHODS: Rats were supplemented with TGZ (0.2% w/w in the pelleted food) for 1 wk before BDL or sham operation. Animals were killed at 1, 2, or 4 wk after surgery. RESULTS: The development of liver fibrosis was reduced in rats receiving TGZ, as indicated by significant decreases of procollagen type I gene expression and liver hydroxy-proline levels. Accumulation of alpha-smooth-muscle actin (SMA)-expressing cells surrounding newly formed bile ducts following BDL, as well as total hepatic levels of SMA were partially inhibited by TGZ treatment, indicating the presence of a reduced number and/or activation of hepatic stellate cells (HSC) and myofibroblasts. Development of the ductular reaction was inhibited by TGZ, as indicated by histochemical evaluation and hepatic activity of gamma-glutamyl-transferase (GGT). CONCLUSION: Treatment with thiazolidinedione reduces ductular proliferation and fibrosis in a model of chronic cholestasis, and suggests that limiting cholangiocyte proliferation may contribute to the lower development of scarring in this system.

Differential requirement of members of the MAPK family for CCL2 expression by hepatic stellate cells.

Hepatic stellate cells (HSC) coordinate the liver wound-healing response through secretion of several cytokines and chemokines, including CCL2 (formerly known as monocyte chemoattractant protein-1). In this study, we evaluated the role of different proteins of the MAPK family (ERK, p38(MAPK), and JNK) in the regulation of CCL2 expression by HSC, as an index of their proinflammatory activity. Several mediators activated all three MAPK, including TNF, IL-1, and PDGF. To assess the relative role of the different MAPKs, specific pharmacological inhibitors were used; namely, SB203580 (p38(MAPK)), SP600125 (JNK), and PD98059 (MEK/ERK). The efficacy and specificity of the different inhibitors in our cellular system were verified analyzing the enzymatic activity of the different MAPKs using in vitro kinase assays and/or testing the inhibition of phosphorylation of downstream substrates. SB203580 and SP600125 dose-dependently inhibited CCL2 secretion and gene expression induced by IL-1 or TNF. In contrast, inhibition of ERK did not affect the upregulation of CCL2 induced by the two cytokines. Finally, activin A was also found to stimulate CCL2 expression and to activate ERK, JNK, p38, and their downstream targets. Unlike in cells exposed to proinflammatory cytokines, all three MAPKs were required to induce CCL2 secretion in response to activin. We conclude that members of the MAPK family differentially regulate cytokine-induced chemokine expression in human HSC.

The chemokine CCL21 modulates lymphocyte recruitment and fibrosis in chronic hepatitis C.

BACKGROUND AND AIMS: The chemokines CCL19 and CCL21 bind CCR7, which is involved in the organization of secondary lymphoid tissue and is expressed during chronic tissue inflammation. We investigated the expression of CCL21 and CCR7 in chronic hepatitis C. The effects of CCL21 on hepatic stellate cells (HSCs) were also studied. METHODS: Expression of CCL21 was assessed by in situ hybridization and immunohistochemistry. CCR7 on T cells was analyzed by flow cytometry. Cultured human HSCs were studied in their activated phenotype. RESULTS: In patients with chronic hepatitis C, expression of CCL21 and CCR7 was up-regulated. CCL21 was detected in the portal tracts and around inflammatory lymphoid follicles, in proximity to T lymphocytes and dendritic cells, which contributed to expression of this chemokine. Expression of CCR7 was also increased in patients with primary biliary cirrhosis. Intrahepatic CD8(+) T lymphocytes isolated from patients with chronic hepatitis C had a significantly higher percentage of positivity for CCR7 than those from healthy controls, and the expression of CCR7 was associated with that of CXCR3. Cultured HSCs expressed functional CCR7, the activation of which stimulated cell migration and accelerated wound healing in an in vitro model. Exposure of HSCs to CCL21 triggered several signaling pathways, including extracellular signal-regulated kinase, Akt, and nuclear factor kappaB, resulting in induction of proinflammatory genes. CONCLUSIONS: Expression of CCL21 during chronic hepatitis C is implicated in the recruitment of T lymphocytes and the organization of inflammatory lymphoid tissue and may promote fibrogenesis in the inflamed areas via activation of CCR7 on HSCs.

Up-regulated expression of fractalkine and its receptor CX3CR1 during liver injury in humans.

BACKGROUND/AIMS: Little is known about the role of fractalkine (CX3CL1) in the liver. The aim of this study was to investigate the expression patterns of fractalkine and its receptor CX3CR1 in normal human liver and in conditions of injury. METHODS: Distribution and expression of fractalkine and its receptor were investigated using immunohistochemistry, in situ hybridization, flow cytometry and reverse transcriptase-polymerase chain reaction. In vitro experiments were conducted in HepG2 cells. RESULTS: Both fractalkine and CX3CR1 were up-regulated during chronic injury, in areas of portal and lobular inflammation. In severe acute hepatitis, fractalkine and CX3CR1 were expressed at high levels not only in areas of inflammation but also in regenerating epithelial cells within bile duct-like structures, which showed co-expression of fractalkine and cytokeratin-7 or CX3CR1. The human hepatocarcinoma cell line HepG2 expressed fractalkine at the gene and protein level, and HepG2-conditioned medium was chemotactic for cells overexpressing CX3CR1. Transcripts for CX3CR1 were detected in HepG2, and exposure of these cells to recombinant fractalkine induced cell migration. CONCLUSIONS: This study shows that the fractalkine system is up-regulated during liver damage, and suggests that fractalkine may play a role in the recruitment and adhesion of inflammatory cells and in the biology of liver epithelial cells.