Search

Previous results from our laboratory showed that a methionine-rich caseinate-based (metcas) diet induces hyperhomocysteinemia in miniature pigs. In the present study, the contribution of the ileal and jejunal methionine absorption to the dietary induced hyperhomocysteinemia was evaluated by measuring the mucosal to serosal fluxes and the enterocyte incorporation in intact intestinal epithelia mounted in Ussing chambers. For 4 mo, 20 miniature pigs were daily fed control or metcas diets, and an oral combination of an angiotensin-converting enzyme inhibitor (25 mg captopril, Cp) and diuretic (12.5 mg hydrochlorothiazide, HTZ) or placebo. Ileal methionine fluxes were lower, and jejunal methionine incorporation was higher in epithelia from miniature pigs fed metcas than in that from other groups. For a given transepithelial flux of methionine, i.e., a constant amount of methionine recovered in the serosal chamber, a greater enterocyte incorporation was detected. Cp-HTZ treatment corrected the diet-induced methionine trapping in intestinal epithelia but had little effect in control animals. in separate in vitro experiments, Cp added alone significantly activated methionine fluxes in epithelia from metcas-fed miniature pigs as it did in vivo, demonstrating that Cp rather than HTZ mainly contributed to the in vivo effects of the drug combination. Our results showed that the regulation of intestinal methionine absorption compensated the diet-induced hyperhomocysteinemia and that Cp-HTZ treatment altered these adaptative changes without increasing methioninemia and homocysteinemia. INDEXING KEY WORDS: miniature pig; intestinal absorption; methionine; hyperhomocysteinemia; ACE inhibition

Background: Organophosphorus insecticides are well known to induce hepatotoxicity. One among this is chlorpyrifos (CPF), which is an insecticide inducing various toxicities including in liver. Objective: This investigation focused on CPF-induced oxidative damage in rat hepatocytes primary culture and the protective effect of Cactus cladode aqueous extract. Materials and Methods: Hepatocytes were treated with CPF (50, 75, and 150 μM) and cactus aqueous extract. On treatment for 48 h, mortality within these cells was determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide test, reactive oxygen species (ROS) levels were measured by H2DCFDA test. Furthermore, heat shock protein 70 (HSP70) and CYP1A1/2 levels were determined using western blot analysis. Annexin V and 4',6-diamidino-2-phenylindole analysis was run to determine the level of cell death and cytoprotection exerted by CPF and extracts, respectively. Results: The results showed that CPF increases the levels of H2O2 and HSP70 and induces CYP1A1/2 and mortality within these cells. In the other side of this study, the co-treatment of these cells with CPF and Cactus cladode aqueous extract showed a recovery of these parameters. It also has been found that the Cactus cladode aqueous extract has the potential to do cytoprotective effect by preventing necrosis induced by CPF. Conclusion: Taken together, these findings suggest that the toxicity exerted by CPF in hepatocytes are involved with the generation of ROS and the regulation of well-controlled programmed cell death, which could be well protected by the Cactus cladode extract pretreatment. [ABSTRACT FROM AUTHOR]

Tea is an interesting source of antioxidants capable of counteracting the oxidative stress implicated in liver diseases. We investigated the impact of antioxidant molecules provided by a mixture of teas' leaves (green, oolong, pu-erh) after different infusion durations in the prevention of oxidative stress in isolated rat hepatocytes, by comparison with pure epigallocatechin-3-gallate (EGCG), the main representative of tea catechins. Dried aqueous tea extracts (ATE) obtained after 5, 15 and 30 min infusion time were characterized for total polyphenols (gallic acid equivalent), catechins, gallic acid and caffeine (HPLC-DAD/ESI-MS) contents, and for scavenging ability against 2,2-diphenyl-1-picrylhydrazyl free radical. Hepatoprotection was evaluated through hepatocyte viability tests using tert-butyl hydroperoxide as a stress inducer, (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, neutral red uptake, real-time cellular impedance) and mitochondrial function tests. We showed that a 5-min incubation time is sufficient for an optimal bioaccessibility of tea compounds with the highest antioxidative ability, which decreases for longer durations. A 4-h pretreatment of cells with ATE significantly prevented cell death by regulating reactive oxygen species production and maintaining mitochondrial integrity. Pure EGCG, at doses similar in ATE (5–12 μM), was inefficient, suggesting a plausible synergy of several water-soluble tea compounds to explain the ATE beneficial effects. [ABSTRACT FROM AUTHOR]

Epithelial to mesenchymal transition (EMT) is an integral process in the progression of many epithelial tumors. It involves a coordinated series of events, leading to the loss of epithelial features and the acquisition of a mesenchymal phenotype, resulting in invasion and metastasis. The EMT of hepatocellular carcinoma (HCC) cells is thought to be a key event in intrahepatic dissemination and distal metastasis. In this study, we used 12-O-tet-radecanoylphorbol-13-acetate (TPA) to dissect the signaling pathways involved in the EMT of HepG2 hepatocarcinoma cells. The spectacular change in phenotype induced by TPA, leading to a pronounced spindle-shaped fibroblast-like cell morphology, required ERK1/2 activation. This ERK1/2-dependent EMT process was characterized by a loss of E-cadherin function, modification of the cytoskeleton, the acquisition of mesenchymal markers and profound changes to extracellular matrix composition and mobility. Snail was essential for E-cadherin repression, but was not sufficient for full commitment of the TPA-triggered EMT. We found that TPA triggered the formation of a complex between Snail and β-catenin that activated the Wnt pathway. This study thus provides the first evidence for the existence of a complex network governed by the ERK1/2 signaling pathway, converging on the coregulation of Snail and the Wnt/β-catenin pathway and responsible for the onset and the progression of EMT in hepatocellular carcinoma cells. [ABSTRACT FROM AUTHOR]

Bisphenol F (BPF) is present in the environment and as a contaminant of food. Humans may, therefore, be exposed to BPF, and an assessment of this risk is required. BPF has been shown to have genotoxic and endocrine-disruptor properties in a human hepatoma cell line (HepG2), which is a model system for studies of xenobiotic toxicity. In this study, we investigated the ability of HepG2 cells to biotransform BPF, because metabolism may affect the observed effects of BPF, and we compared this metabolic capacity with that of human hepatocytes. Cells were incubated for 24 hours with [3H]-BPF. The culture medium was then concentrated and its metabolites were isolated by high-performance liquid chromatography and identified by mass spectrometry. BPF was largely metabolized into the corresponding sulfate by the HepG2 cell line. BPF was metabolized into both sulfate and glucuronide by human hepatocytes, but with differences between individuals. The metabolism of BPF in both HepG2 cells and human hepatocytes suggests the existence of a detoxification pathway. Thus, these two cell models differ in metabolic capacity. It is, therefore, very important, when assessing the toxic effects of substances in vitro, to determine, in parallel, the biotransformation capacities of the model used to extrapolate in vivo. [ABSTRACT FROM AUTHOR]

Endosulfan is an organochlorine insecticide described as a potential carcinogen in humans. This insecticide was recently reported to alter the mitogen-activated protein (MAP) kinase signaling pathways and is suspected to affect cell growth and differentiation in human keratinocytes. This study was designed to assess the mitogenic, apoptogenic, and genotoxic effects of endosulfan on the HaCaT cell line. We first found that 25 µM endosulfan led to persistent extracellular signal-regulated kinase (ERK)1/2 phosphorylation with an accumulation of the phosphorylated form in the nucleus, probably caused by MAP kinase phosphatase (MKP) inhibition. As previously described under sustained ERK1/2 activation, cell growth was decreased: delayed confluency and 35% decrease of BrdU incorporation was demonstrated in endosulfan-treated keratinocytes. In addition, endosulfan has been shown to generate transient reactive oxygen species (ROS), and blocking this oxidative stress by N-acetyl cysteine (NAC) strongly prevented both persistent nuclear ERK1/2 phosphorylation and cell growth decrease. Additional experiments demonstrated that unchanged endosulfan rather than its metabolites has mutagenic effects (Ames positive without S9) and increased DNA strand breaks (Comet assay) in HaCaT cells, via a ROS-dependent mechanism. Therefore, to assess the putative pro-apoptotic response of damaged cells, caspases 3/7 activity and poly(ADP-ribose)-polymerase (PARP) cleavage were measured. The results clearly indicated that endosulfan inhibited both spontaneous and staurosporine-induced apoptosis. Taken together, these findings strongly support that endosulfan induces ROS generation leading to sustained ERK1/2 phosphorylation and decrease in cell growth. Moreover, endosulfan was found to inhibit apoptosis and this could contribute to mutant cell survival and therefore have possible carcinogenic effects. J. Cell. Physiol. 213: 177–186, 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

In vivo distribution of the neonicotinoid insecticide, imidacloprid, was followed during 72 h in six biological compartments of Apis mellifera L: head, thorax, abdomen, haemolymph, midgut and rectum. Honeybees were treated orally with 100 µg of 14C-imidacloprid per kg of bee, a dose close to the median lethal dose. Elimination half-life of total radioactivity in honeybee was 25 h. Haemolymph was the compartment with the lowest and rectum that with the highest level of total radioactivity during the whole study, with a maximum 24 h after treatment. Elimination half-life of imidacloprid in whole honeybee was 5 h. Imidacloprid was readily distributed and metabolised only by Phase I enzymes into five metabolites: 4/5-hydroxy-imidacloprid, 4,5-dihydroxy-imidacloprid, 6-chloronicotinic acid, and olefin and urea derivatives. The guanidine derivative was not detected. The urea derivative and 6-chloronicotinic acid were the main metabolites and appeared particularly in midgut and rectum. The olefin derivative and 4/5-hydroxy-imidacloprid preferentially occurred in head, thorax and abdomen, which are nicotinic acetylcholine receptor-rich tissues. Moreover, they presented a peak value around 4 h after imidacloprid ingestion. These results explain the prolongation of imidacloprid action in bees, and particularly the differences between rapid intoxication symptoms and late mortality. [ABSTRACT FROM AUTHOR]

Induction of both CYP1A1 and metallothioneins (MTs) in fish liver is increasingly being used in ecotoxicological studies. The interaction of heavy metals (Cd, Cu, Zn, Pb) with the CYP1A induction response and MT levels was studied in trout (Oncorhynchus mykiss) hepatocyte cultures. Cells were exposed to 3-methylcholanthrene (3-MC) or to increasing heavy metal concentrations or to a mixture of both (3-MC and one heavy metal). Metal cytotoxicity was assessed by the neutral red test. Ranking of toxicity was Cd(II) < Cu(II) < Zn(II) < Pb(II) (EC50: 45, 222, 873, and 945 µM, respectively). CYP1A1 expression was monitored by ethoxyresorufin-O-deethylase (EROD) activity as well as by Western and Northern blots. As expected, 3-MC induced EROD activity in a time- and dose-dependent manner (maximal induction 5 times that of the control at 0.5 µM and after a 72-h exposure period). These data were confirmed by Western blot (intense band of 55-60 KDa) and Northern blot analyses. Induction caused by 0.5 µM 3-MC was reduced to less than 50% of control by the concomitant exposure to Cd, Cu, Pb, or Zn (EC50: from 1 µM for Cd(II) to 18 µM for Pb(II)). The MTs were significantly induced in hepatocytes exposed to heavy metals for 24 h. In the presence of 3-MC (0.5 µM), MT levels were significantly lower than those found in cells treated with metals alone at 24 h only. Our results lead to the conclusion that heavy metals significantly affect CYP expression and that a CYP1A1 inducer (3-MC) can modulate the induction of MTs. These data have to be taken into consideration in biomarker monitoring. [ABSTRACT FROM AUTHOR]

The human pregnane X receptor (hPXR) is activated by a large set of endogenous and exogenous compounds and plays a critical role in the control of detoxifying enzymes and transporters regulating liver and gastrointestinal drug metabolism and clearance. hPXR is also involved in both the development of multidrug resistance and enhanced cancer cells aggressiveness. Moreover, its unintentional activation by pharmaceutical drugs can mediate drug–drug interactions and cause severe adverse events. In that context, the potential of the anticancer BRAF inhibitor dabrafenib suspected to activate hPXR and the human constitutive androstane receptor (hCAR) has not been thoroughly investigated yet. Using different reporter cellular assays, we demonstrate that dabrafenib can activate hPXR as efficiently as its reference agonist SR12813, whereas it does not activate mouse or zebrafish PXR nor hCAR. We also showed that dabrafenib binds to recombinant hPXR, induces the expression of hPXR responsive genes in colon LS174T-hPXR cancer cells and human hepatocytes and finally increases the proliferation in LS174T-hPXR cells. Our study reveals that by using a panel of different cellular techniques it is possible to improve the assessment of hPXR agonist activity for new developed drugs. [ABSTRACT FROM AUTHOR]

Abstract: Lindane, a persistent organochlorine pesticide, is recognized as a major public health concern because of its potential toxic effects on human health. Despite observations pointing to the toxicity of lindane, mechanisms underlying its deleterious effects in liver have yet to be understood. In this study, we investigated the effects of lindane on autophagic, apoptotic and necrotic cell death in primary cultured rat hepatocytes. We found that lindane deregulated the autophagic process as demonstrated by (1) the formation of enlarged acidic vesicles labeled with LC3, Rab7 and LAMP1 (specific markers of autophagic vacuole maturation), (2) the conversion of LC3-I (the cytosolic form) into LC3-II (membrane bound), (3) the deregulation of the Beclin 1 protein expression and (4) the enhanced formation of the Bcl-xL/Beclin 1 complex. Lindane induced vacuolization together with the inhibition of spontaneous and intrinsic apoptosis. This disruption of cell suicide was linked to Bcl-xL up-regulation, Bax down-expression, prevention of cytochrome c release, and inhibition of caspase-9 and -3 activities. Lindane-induced disruption of apoptosis and autophagy occurred in parallel with necrosis induction in rat hepatocytes. In consequence, we proposed that lindane toxicity in primary rat hepatocytes could be jointly attributed to the disruption of autophagic process, the inhibition of apoptotic cell death and the induction of necrosis. These events account, at least in part, for the involvement of both cytotoxic and carcinogenic signaling pathways in the action of lindane in the liver. [Copyright &y& Elsevier]

A method for the determination of chlorfenvinphos, ethion and linuron in liver samples by LC-MS/MS is described. Sample treatment was performed by using Sola™ polymeric reverse phase SPE cartridges after protein precipitation. Gradient elution using 10 mM ammonium formate in methanol (A) and 10 mM ammonium formate in water (B) was used for chromatographic separation of analytes on a Hypersil™ end-capped Gold PFP reverse phase column (100 mm × 2.1 mm, 3 μm). All analytes were quantified without interference, in positive ionization mode using multiple reaction monitoring (MRM) with chlorfenvinphos-d10 as internal standard. The whole procedure was validated according to the FDA guidelines for bioanalytical methods. The calibration curves for chlorfenvinphos, linuron and ethion compounds were linear over the concentration range of 0.005–2 μM (i.e. 0.0018–0.720 μg/mL, 0.0019–0.770 μg/mL and 0.0012–0.500 μg/mL respectively) with coefficients of determination higher than 0.998. A Lower limit of quantification of 0.005 μM was achieved for all analytes, i.e. 5.76, 6.08 and 3.84 μg/kg of liver for chlorfenvinphos, ethion and linuron respectively. Compounds extraction recovery rates ranged from 92.9 to 99.5% with a RSD of 2.3%. Intra- and inter-day accuracies were within 90.9 and 100%, and imprecision varied from 0.8 to 8.2%. Stability tests proved all analytes were stable in liver extracts during instrumental analysis (+12 °C in autosampler tray for 72 h) at the end of three successive freeze-thaw cycles and at −20 °C for up to 9 months. This accurate and robust analytical method is therefore suitable for contamination or metabolism studies. [ABSTRACT FROM AUTHOR]

General population exposure to pesticides mainly occurs via food and water consumption. However, their risk assessment for regulatory purposes does not currently consider the actual co-exposure to multiple substances. To address this concern, relevant experimental studies are needed to fill the lack of data concerning effects of mixture on human health. For the first time, the present work evaluated on human microsomes and liver cells the combined metabolic effects of, chlorfenvinphos, ethion and linuron, three pesticides usually found in vegetables of the European Union. Concentrations of these substances were measured during combined incubation experiments, thanks to a new analytical methodology previously developed. The collected data allowed for calculation and comparison of the intrinsic hepatic clearance of each pesticide from different combinations. Finally, the results showed clear inhibitory effects, depending on the association of the chemicals at stake. The major metabolic inhibitor observed was chlorfenvinphos. During co-incubation, it was able to decrease the intrinsic clearance of both linuron and ethion. These latter also showed a potential for metabolic inhibition mainly cytochrome P450-mediated in all cases. Here we demonstrated that human detoxification from a pesticide may be severely hampered in case of co-occurrence of other pesticides, as it is the case for drugs interactions, thus increasing the risk of adverse health effects. These results could contribute to improve the current challenging risk assessment of human and animal dietary to environmental chemical mixtures. [ABSTRACT FROM AUTHOR]

Oxidative stress could trigger lipid accumulation in liver and thus hepatic steatosis. Tea is able to prevent liver disorders, but a direct link between antioxidant capacities and prevention of steatosis has not been reported yet. We aimed to investigate such relationship in a rat model of high fat-high sucrose diet (HFS)-induced obesity and to explore more deeply the mechanisms in isolated hepatocytes. Wistar rats were divided into a control group (standard diet), an HFS group (high fat-sucrose diet) and an HFS+tea group (HFS diet with ad-libitum access to tea drink). Body weight, fat mass, glycemic parameters in blood, lipid and oxidative stress parameters in blood and liver were measured in each group after 14 weeks. Isolated hepatocytes were treated with the reactive oxygen species (ROS) inducer t-BHP in the presence or not of antioxidants (tempol or tea), and superoxide anion production and lipid accumulation were measured using specific fluorescent probes. We reported that the HFS diet highly increased hepatic lipids content, while tea consumption attenuated steatosis and improved the oxidative status (decrease in hepatic oxidative stress, increase in plasma total antioxidant capacity). The role of antioxidant properties of tea in such phenomenon was confirmed in primary cultured rat hepatocytes. Indeed, the increase of mitochondrial ROS production with t-BHP resulted in lipid accumulation in hepatocytes (positive linear regression), and antioxidants (tempol or tea) normalized both. We reported that the antioxidant properties of tea protect rats from an obesogenic HFS diet-induced hepatic steatosis by counteracting the ROS-dependent lipogenesis. [ABSTRACT FROM AUTHOR]