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Albert Geerts

Publications and source records attributed to Albert Geerts.

18 recordsLinked to original sources
PubMed2006

Trichostatin a enhances gap junctional intercellular communication in primary cultures of adult rat hepatocytes.

The effects of histone deacetylase inhibitor Trichostatin A (TSA) on connexin (Cx) expression and gap junctional intercellular communication (GJIC) were investigated in primary cultures of adult rat hepatocytes. GJIC was monitored by using the scrape-loading/dye transfer method. Immunoblotting and immunocytochemistry were used to investigate Cx protein levels and localization. Cx gene expression was studied by means of quantitative reverse transcriptase-polymerase chain reaction. TSA increased Cx32 protein levels and affected negatively the Cx26 protein levels. The latter was preferentially located in the cytosol of cultured cells. TSA also promoted the appearance of Cx43 in the nuclear compartment of primary cultured hepatocytes. Overall, this resulted in enhanced GJIC activity. It is important to note that the time of onset of TSA treatment was crucial for the extent of its outcome and that the effects of TSA on Cx protein levels occurred independently of transcriptional changes. TSA differentially affects Cx proteins in primary rat hepatocyte cultures, suggesting distinct regulation and/or distinct roles of the different Cx species in the control of hepatic homeostasis. TSA enhances GJIC between primary cultured rat hepatocytes, an interesting finding supporting its use to further optimize liver-based in vitro models for pharmacotoxicological purposes.

Acetylation↗
PubMed2005

Somatostatin at nanomolar concentration reduces collagen I and III synthesis by, but not proliferation of activated rat hepatic stellate cells.

Previous studies have shown antifibrotic effects of somatostatin. Since hepatic stellate cells (HSC) express somatostatin receptors and play a key role in hepatic fibrogenesis, we investigated the in vitro antifibrotic effect of somatostatin on rat HSC. At day 12 after isolation, cells were exposed to different concentrations of somatostatin (10(-6)-10(-9) mol l(-1)). mRNA expression of collagen types I and III, and of smooth muscle alpha-actin (alpha-SMA) was analysed by Northern blotting. At 10(-9) mol l(-1), somatostatin significantly reduced mRNA expression of collagen I (72.3 +/- 10.7%; 95% confidence interval (95% CI): 45.5-99.0), collagen III (79.0 +/- 4.5%; 95% CI: 67.6-90.4) and alpha-SMA (65.7 +/- 5.9%; 95% CI: 51.1-80.2), as compared to control normalized at 100%. These results were confirmed by quantitative RT-PCR. Cycloheximide experiments indicated that somatostatin has no direct transcriptional effect.Using immunoprecipitation, we demonstrated that somatostatin also decreased de novo synthesis of collagen I (73 +/-10%; 95% CI: 48-98%), collagen III (65 +/- 13%; 95% CI: 33-97%) and alpha-SMA (47 +/- 9%; 95% CI: 25-69%). Remarkably, at higher concentrations, somatostatin did not suppress collagen mRNA expression nor de novo protein synthesis. We ascribe this observation to desensitization of the cells for somatostatin. Cell proliferation, as measured by 5-bromo-2'-deoxyuridine labelling, was not altered by somatostatin. No significant effect on the intermediate and actin cytoskeleton were detected by immunohistochemistry and Western blotting. Our findings imply that in vivo antifibrotic effects of somatostatin could result partially from a direct action of somatostatin on HSC, but other, in vivo effects are probably also involved.

Actins↗
PubMed2004

Neural connections between the hypothalamus and the liver.

After receiving information from afferent nerves, the hypothalamus sends signals to peripheral organs, including the liver, to keep homeostasis. There are two ways for the hypothalamus to signal to the peripheral organs: by stimulating the autonomic nerves and by releasing hormones from the pituitary gland. In order to reveal the involvement of the autonomic nervous system in liver function, we focus in this study on autonomic nerves and neuroendocrine connections between the hypothalamus and the liver. The hypothalamus consists of three major areas: lateral, medial, and periventricular. Each area has some nuclei. There are two important nuclei and one area in the hypothalamus that send out the neural autonomic information to the peripheral organs: the ventromedial hypothalamic nucleus (VMH) in the medial area, the lateral hypothalamic area (LHA), and the periventricular hypothalamic nucleus (PVN) in the periventricular area. VMH sends sympathetic signals to the liver via the celiac ganglia, the LHA sends parasympathetic signals to the liver via the vagal nerve, and the PVN integrates information from other areas of the hypothalamus and sends both autonomic signals to the liver. As for the afferent nerves, there are two pathways: a vagal afferent and a dorsal afferent nerve pathway. Vagal afferent nerves are thought to play a role as sensors in the peripheral organs and to send signals to the brain, including the hypothalamus, via nodosa ganglia of the vagal nerve. On the other hand, dorsal afferent nerves are primary sensory nerves that send signals to the brain via lower thoracic dorsal root ganglia. In the liver, many nerves contain classical neurotransmitters (noradrenaline and acetylcholine) and neuropeptides (substance P, calcitonin gene-related peptide, neuropeptide Y, vasoactive intestinal polypeptide, somatostatin, glucagon, glucagon-like peptide, neurotensin, serotonin, and galanin). Their distribution in the liver is species-dependent. Some of these nerves are thought to be involved in the regulation of hepatic function as well as of hemodynamics. In addition to direct neural connections, the hypothalamus can affect metabolic functions by neuroendocrine connections: the hypothalamus-pancreas axis, the hypothalamus-adrenal axis, and the hypothalamus-pituitary axis. In the hypothalamus-pancreas axis, autonomic nerves release glucagon and insulin, which directly enter the liver and affect liver metabolism. In the hypothalamus-adrenal axis, autonomic nerves release catecholamines such as adrenaline and noradrenaline from the adrenal medulla, which also affects liver metabolism. In the hypothalamus-pituitary axis, release of glucocorticoids and thyroid hormones is stimulated by pituitary hormones. Both groups of hormones modulate hepatic metabolism. Taken together, the hypothalamus controls liver functions by neural and neuroendocrine connections.

Adrenal Glands↗
PubMed2004

Differential modulation of rat hepatic stellate phenotype by natural and synthetic retinoids.

Activation of hepatic stellate cells (HSC) is a central event in the pathogenesis of liver fibrosis during chronic liver injury. We examined the expression of retinoic acid (RAR) and retinoid X receptors (RXR) during HSC activation and evaluated the influence of natural and synthetic retinoic acids (RA) on the phenotype of culture-activated HSC. The expression of the major RAR/RXR subtypes and isoforms was analyzed by Northern hybridization. Presence of functional receptor proteins was established by gel shift analysis. Retinoic acids, RAR, and RXR selective agonists and an RAR antagonist were used to evaluate the effects of retinoid signalling on matrix synthesis by Northern blotting and immunoprecipitation, and on cell proliferation by BrdU incorporation. The 9-cisRA and synthetic RXR agonists reduced HSC proliferation and synthesis of collagen I and fibronectin. All-trans RA and RAR agonists both reduced the synthesis of collagen I, collagen III, and fibronectin, but showed a different effect on cell proliferation. Synthetic RAR agonists did not affect HSC proliferation, indicating that ATRA inhibits cell growth independent of its interaction with RARs. In contrast, RAR specific antagonists enhance HSC proliferation and demonstrate that RARs control proliferation in a negative way. In conclusion, natural RAs and synthetic RAR or RXR specific ligands exert differential effects on activated HSC. Our observations may explain prior divergent results obtained following retinoid administration to cultured stellate cells or to animals subjected to fibrogenic stimuli.

Alitretinoin↗
PubMed2003

The preferential homing of a platelet derived growth factor receptor-recognizing macromolecule to fibroblast-like cells in fibrotic tissue.

Platelet derived growth factor (PDGF) is a key factor in the induction and progression of fibrotic diseases with the activated fibroblast as its target cell. Drug targeting to the PDGF-receptor is explored as a new approach to treat this disease. Therefore, we constructed a macromolecule with affinity for the PDGF-beta receptor by modification of albumin with a small peptide that recognises this PDGF-beta receptor. The binding of the peptide-modified albumin (pPB-HSA) to the PDGF-beta receptor was confirmed in competition studies with PDGF-BB using NIH/3T3-fibroblasts and activated hepatic stellate cells. Furthermore, pPB-HSA was able to reduce PDGF-BB-induced fibroblast proliferation in vitro, and proved to be devoid of proliferation-inducing activity itself. We assessed the distribution of pPB-HSA in vivo in two models of fibrosis and related the distribution of pPB-HSA to PDGF-beta receptor density. In rats with liver fibrosis (bile duct ligation model), pPB-HSA quickly accumulated in the liver in contrast to unmodified HSA (P<0.001). The major part of pPB-HSA in the fibrotic liver was localized in hepatic stellate cells. In rats with renal fibrosis (anti-Thy1.1 model), pPB-HSA also homed to the cells that expressed the PDGF-beta receptor, i.e. the mesangial cells in the glomeruli of the kidney. These results indicate that pPB-HSA may be applied as a macromolecular drug-carrier that accumulates specifically in cells expressing the PDGF-beta receptor, thus allowing a selective delivery of anti-fibrotic agents to these cells.

3T3 Cells↗
PubMed2003

Effect of HMG-CoA reductase inhibitors on proliferation and protein synthesis by rat hepatic stellate cells.

BACKGROUND/AIMS: 3-Hydroxy-3-methylglutaryl coenzyme A reductase inhibitors called statins, have besides their cholesterol-lowering function, therapeutic value in conditions such as neo-angiogenesis and atherosclerosis. We investigated the effect of two statins on the proliferation rate and protein steady state levels of hepatic stellate cells (HSC). METHODS: Cellular DNA synthesis under the influence of statins and/or platelet derived growth factor (PDGF) and mevalonate was evaluated by measuring BrdU incorporation. Synthesis of collagens type I, III, IV and fibronectin was quantified by ELISA. Additionally, we examined the influence of simvastatin on isoprenylation of Ras and RhoA proteins. RESULTS: Lovastatin and simvastatin induced a dose-dependent inhibition of the proliferation rate of HSC. Subsequent addition of PDGF and/or mevalonate, after long-term exposure of simvastatin to HSC, did not reverse simvastatins' antiproliferative effect. Lovastatin and simvastatin reduced the protein steady state level of collagens type I (-40%), III (-45%) and IV (-27%). Membrane bound Ras steady state levels decreased under the influence of simvastatin. Membrane bound RhoA remained unaltered, whereas, cytosolic RhoA protein level was strongly reduced. CONCLUSIONS: Our data showed that lovastatin and simvastatin inhibited HSC proliferation and collagen steady state levels by mechanisms independent of their lipid reducing activities.

Animals↗
PubMed2003

Trichostatin A induces differential cell cycle arrests but does not induce apoptosis in primary cultures of mitogen-stimulated rat hepatocytes.

BACKGROUND/AIMS: The effects of Trichostatin A (TSA), a drug candidate for cancer therapy, on proliferation and survival of primary hepatocytes, the major site of xenobiotic biotransformation and primary target of drug-induced toxicity, were investigated. METHODS: DNA replication was measured using [methyl-3H]-thymidine incorporation. Cell cycle markers were analyzed by Western and Northern blottings. Necrosis and apoptosis were monitored by LDH release, caspase-3-activation, respectively. RESULTS: We identified two distinct cell cycle arrests, prior DNA replication, in two experimental conditions. First, perfusion of the liver in presence of TSA, prevented c-jun and cyclin D1 induction, characteristic for G1 entry and progression through late G1, respectively. Secondly, TSA treatment of isolated hepatocytes, located in early G1, led to an early S-phase arrest evidenced by the absence of the S/G2/M marker, CDK1. TSA upregulated the expression of the anti-apoptotic protein Bcl(xL) and did not increase caspase-3-activity and LDH release. CONCLUSIONS: TSA inhibits hepatocyte proliferation at different steps of the cell cycle. Our data suggest that this inhibition may involve downregulation of distinct subsets of genes. TSA does not induce apoptosis in primary hepatocytes, in contrast to what has been observed in hepatoma cells. This finding supports its use in the treatment of proliferative disorders.

Animals↗
PubMed2003

Peroxisome proliferator-activated receptor-beta signaling contributes to enhanced proliferation of hepatic stellate cells.

BACKGROUND & AIMS: The peroxisome proliferator-activated nuclear receptors (PPAR-alpha, PPAR-beta, and PPAR-gamma), which modulate the expression of genes involved in energy homeostasis, cell cycle, and immune function, may play a role in hepatic stellate cell activation. Previous studies focused on the decreased expression of PPAR-gamma in hepatic stellate cell activation but did not investigate the expression and role of the PPAR-alpha and -beta isotypes. The aim of this study was to evaluate the expression of the different PPARs during hepatic stellate cell activation in vitro and in situ and to analyze possible factors that might contribute to their expression. In a second part of the study, the effect of a PPAR-beta agonist on acute liver injury was evaluated. METHODS: The effects of PPAR isotype-specific ligands on hepatic stellate cell transition were evaluated by bromodeoxyuridine incorporation, gel shifts, immunoprecipitation, and use of antisense PPAR-beta RNA-expressing adenoviruses. Tumor necrosis factor alpha-induced PPAR-beta phosphorylation and expression was evaluated by metabolic labeling and by using specific P38 inhibitors. RESULTS: Hepatic stellate cells constitutively express high levels of PPAR-beta, which become further induced during culture activation and in vivo fibrogenesis. No significant expression of PPAR-alpha or -gamma was found. Stimulation of the P38 mitogen-activated protein kinase pathway modulated the expression of PPAR-beta. Transcriptional activation of PPAR-beta by L165041 enhanced hepatic stellate cell proliferation. Treatment of rats with a single bolus of CCl(4) in combination with L165041 further enhanced the expression of fibrotic markers. CONCLUSIONS: PPAR-beta is an important signal-transducing factor contributing to hepatic stellate cell proliferation during acute and chronic liver inflammation.

Acute Disease↗
PubMed2003

Antifibrogenic effects of canrenone, an antialdosteronic drug, on human hepatic stellate cells.

BACKGROUND & AIMS: Several lines of evidence indicate that aldosterone antagonists may exert direct antifibrogenic effects. The aim of this study was to evaluate the possible direct antifibrogenic effects of canrenone, the active metabolite of spironolactone, in activated human hepatic stellate cells. METHODS: The effects of canrenone were assessed on platelet-derived growth factor-induced mitogenic and chemotactic effects and the increased de novo synthesis of different extracellular matrix components induced by transforming growth factor-beta1. RESULTS: Canrenone dose-dependently reduced platelet-derived growth factor-induced cell proliferation and motility. This effect was not associated with either changes in the phosphorylation of platelet-derived growth factor receptor and phospholipase C gamma or in the activation of the Ras/extracellular signal-regulated kinase pathway, whereas it was accompanied by a dose-dependent inhibition of platelet-derived growth factor-induced phosphatidylinositol 3-kinase activity. In addition, canrenone inhibited the activity of the Na(+)/H(+) exchanger 1 induced by platelet-derived growth factor. The effect of canrenone on Na(+)/H(+) exchanger 1 activity was reproduced by phosphatidylinositol 3-kinase inhibitors, thus supporting an inhibitory action of canrenone on phosphatidylinositol 3-kinase activity. To further address this possibility, the action of canrenone was compared with that of 2 established Na(+)/H(+) exchanger 1 inhibitors: ethylisopropylamiloride and cariporide. Whereas ethylisopropylamiloride was able to inhibit platelet-derived growth factor-induced phosphatidylinositol 3-kinase activity, cariporide was without any effect. Both compounds reproduced the effects of canrenone on platelet-derived growth factor-induced mitogenesis and chemotaxis. Finally, canrenone was able to reduce transforming growth factor-beta1-induced de novo synthesis of procollagen type I/IV and fibronectin and thrombin-induced hepatic stellate cell contraction. CONCLUSIONS: These results indicate that canrenone may be active as an antifibrogenic drug.

Aldosterone↗
PubMed2002

Trichostatin A, a histone deacetylase inhibitor, suppresses collagen synthesis and prevents TGF-beta(1)-induced fibrogenesis in skin fibroblasts.

Excessive production of collagens by alpha-smooth muscle actin (alpha-SMA)-positive myofibroblasts leads to fibrotic skin diseases, such as hypertrophic scarring. This process is characterized by an imbalance between extracellular matrix (ECM) synthesis and degradation, while transforming growth factor beta (TGF-beta(1)), known to be a key mediator of fibrogenesis, is up-regulated. In this study we have investigated the possible antifibrogenic effect of Trichostatin A (TSA), a histone deacetylase inhibitor, on rat skin fibroblasts in culture. mRNA steady-state levels and de novo protein synthesis of procollagen types I and III and alpha-SMA were inhibited when skin fibroblasts were treated with 100 nM TSA with or without TGF-beta(1). While the transcription rate of the procollagen alpha1(I) gene was increased following TSA or TGF-beta(1) treatment, TSA abrogated the stimulatory effect of TGF-beta(1) on procollagen alpha1(I) transcription when both compounds were added simultaneously. The reduction of procollagen alpha1(I) and alpha1(III) mRNA steady-state levels by TSA did not require de novo protein synthesis, while the effect of TSA on alpha-SMA mRNA steady-state levels was cycloheximide-sensitive. Interestingly, TSA affected TGF-beta(1) and its downstream mediators, i.e., the Smad family proteins. TSA strongly induced in a biphasic way the expression of 5'TG3' interacting factor (TGIF), a known endogenous corepressor molecule of the TGF-beta(1) signaling pathway. Addition of exogenous TGF-beta(1) did not interfere with the effect of TSA on the TGIF mRNA level. Our study shows that inhibition of histone deacetylases by TSA reduces expression of fibrosis-related genes in skin fibroblasts and this coincides by alterations in the TGF-beta(1) signaling pathway.

Animals↗
PubMed2002

The histone-deacetylase inhibitor Trichostatin A blocks proliferation and triggers apoptotic programs in hepatoma cells.

BACKGROUND/AIMS: Effective treatment for hepatocellular carcinoma is urgently needed. The histone-deacetylase inhibitor Trichostatin A (TSA) was shown to induce apoptosis in non-hepatic cells at submicromolar concentrations. However, the effect of TSA on hepatoma cells is unknown. METHODS: The hepatoma cells HepG2, MH1C1, Hepa1-6 and Hep1B as well as human fibroblasts (control cells) were exposed to TSA (10(-6) to 10(-9)M). Cell proliferation was assessed by measuring DNA-synthesis and cell numbers. Apoptosis was quantified by flow cytometry and by the TdT-mediated dUTP nick-end labeling method. Expression patterns of cell cycle- and/or apoptosis-associated p27, p21(cip/waf), bax, bcl-2, cyclin A and (pro)-caspase 3 were studied using quantitative Western blotting. Activation of caspase 3 was analyzed via a colorimetric assay. RESULTS: 10(-6)M TSA inhibited DNA-synthesis by 46% (HepG2) to 64% (MH1C1) after 24h, inducing a G(2)/M-phase arrest and apoptosis. TSA increased activation of caspase 3 and expression of cyclin A, p2l(cip/waf), bax and (pro)-caspase 3, while bcl-2 was downregulated. Human fibroblasts remained unaffected. CONCLUSIONS: TSA inhibits hepatoma cell growth in vitro, which are otherwise particularly resistant to chemotherapy. Its anti-proliferative activity is paralleled by a comparable rate of apoptosis. TSA may be a promising agent for treatment of hepatocellular carcinoma in vivo.

Apoptosis↗
PubMed2002

Actin filament formation, reorganization and migration are impaired in hepatic stellate cells under influence of trichostatin A, a histone deacetylase inhibitor.

BACKGROUND/AIMS: Previously, trichostatin A (TSA), a histone deacetylase inhibitor, has been shown to exhibit strong antifibrotic characteristics in hepatic stellate cells (HSC), which are known to play a central role in chronic liver diseases. TSA retained a more quiescent phenotype in spite of culture conditions that favor transdifferentiation into activated HSC. METHODS: To identify TSA-sensitive genes, differential mRNA display, Northern and Western blot analysis were used and genes were functionally validated by using contraction and motility assays. RESULTS: TSA prevented new actin filament formation by down-regulation of two nucleating proteins, actin related protein 2 (Arp2) and Arp3, and by up-regulation of adducin like protein 70 (ADDL70) and gelsolin, two capping proteins. RhoA, a key mediator in the development of the actin cytoskeleton, decreased following TSA exposure. Expression of proteins of Class III intermediate filaments was affected by TSA. Furthermore, F-actin and G-actin were expressed heterogeneously under influence of TSA. Functionally, TSA treatment abrogated migration of quiescent HSC, while migration was reduced in transitional HSC. The endothelin-1-induced contractility properties of HSC was not affected by TSA. CONCLUSIONS: These data indicate that TSA affects the development of the actin cytoskeleton in quiescent HSC and thereby abrogates the process of HSC transdifferentiation.

Actin Cytoskeleton↗
PubMed2002

Insulin-like growth factor (IGF)-I binding to a cell membrane associated IGF binding protein-3 acid-labile subunit complex in human anterior pituitary gland.

The binding characteristics of [(125) I]insulin-like growth factor (IGF)-I were studied in human brain and pituitary gland. Competition binding studies with DES(1-3)IGF-I and R(3) -IGF-I, which display high affinity for the IGF-I receptor and low affinity for IGF binding proteins (IGFBPs), were performed to distinguish [(125) I]IGF-I binding to IGF-I receptors and IGFBPs. Specific [(125) I]IGF-I binding in brain regions and the posterior pituitary was completely displaced by DES(1-3)IGF-I and R(3) -IGF-I, indicating binding to IGF-I receptors. In contrast, [(125) I]IGF-I binding in the anterior pituitary was not displaced by DES(1-3)IGF-I and R(3) -IGF-I, suggesting binding to an IGF-binding site that is different from the IGF-I receptor. Binding affinity of IGF-I to this site was about 10-fold lower than for the IGF-I receptor. Using western immunoblotting we were also unable to detect IGF-I receptors in human anterior pituitary. Instead, western immunoblotting and immunoprecipitation experiments showed a 150-kDa IGFBP-3-acid labile subunit (ALS) complex in the anterior pituitary and not in the posterior pituitary and other brain regions. RT-PCR experiments showed the expression of ALS mRNA in human anterior pituitary indicating that the anterior pituitary synthesizes ALS. In the brain regions and posterior pituitary, IGFBP-3 was easily washed away during pre-incubation procedures as used in the [(125) I]IGF-I binding experiments. In contrast, the IGFBP-3 complex in the anterior pituitary could not be removed by these washing procedures. Our results indicate that the human anterior pituitary contains a not previously described tightly cell membrane-bound 150-kDa IGFBP-3-ALS complex that is absent in brain and posterior pituitary.

Aged↗
PubMed2002

Endogenous interleukin-10 modulates fibrosis and regeneration in experimental chronic pancreatitis.

Interleukin (IL)-10, a potent anti-inflammatory cytokine, limits the severity of acute pancreatitis and downregulates transforming growth factor (TGF)-beta release by inflammatory cells on stimulation. Proinflammatory mediators, reactive oxygen species, and TGF-beta can activate pancreatic stellate cells and their synthesis of collagen I and III. This study evaluates the role of endogenous IL-10 in the modulation of the regeneration phase following acute pancreatitis and in the development of pancreatic fibrosis. IL-10 knockout (KO) mice and their C57BL/6 controls were submitted to repeated courses (3/wk, during 6 wk, followed by 1 wk of recovery) of cerulein-induced acute pancreatitis. TGF-beta(1) release was measured on plasma, and its pancreatic expression was assessed by quantitative RT-PCR and immunohistochemistry. Intrapancreatic IL-10 gene expression was assessed by semiquantitative RT-PCR, and intrapancreatic collagen content was assessed by picrosirius staining. Activated stellate cells were detected by immunohistochemistry. S phase intrapancreatic cells were marked using tritiated thymidine labeling. After repeated acute pancreatitis, IL-10 KO mice had more severe histological lesions and fibrosis (intrapancreatic collagen content) than controls. TGF-beta(1) plasma levels, intrapancreatic transcription, and expression by ductal and interstitial cells, as well as the number of activated stellate cells, were significantly higher. IL-10 KO mice disclosed significantly fewer acinar cells in S phase, whereas the opposite was observed for pseudotubular cells. Endogenous IL-10 controls the regeneration phase and limits the severity of fibrosis and glandular atrophy induced by repeated episodes of acute pancreatitis in mice.

Acute Disease↗