Formation of bile canaliculi in long-term primary cultures of adult rat hepatocytes on permeable membrane: an ultrastructural study

Bioartificial liver systems: why, what, whither?

Acute liver disease is a life-threatening condition for which liver transplantation is the only recognized effective therapy. While etiology varies considerably, the clinical course of acute liver failure is common among the etiologies: encephalopathy progressing toward coma and multiple organ failure. Detoxification processes, such as molecular adsorbent recirculating system (MARS®) and Prometheus, have had limited success in altering blood chemistries positively in clinical evaluations, but have not been shown to be clinically effective with regard to patient survival or other clinical outcomes in any Phase III prospective, randomized trial. Bioartificial liver systems, which use liver cells (hepatocytes) to provide metabolic support as well as detoxification, have shown promising results in early clinical evaluations, but again have not demonstrated clinical significance in any Phase III prospective, randomized trial. Cell transplantation therapy has had limited success but is not practicable for wide use owing to a lack of cells (whole-organ transplantation has priority). New approaches in regenerative medicine for treatment of liver disease need to be directed toward providing a functional cell source, expandable in large quantities, for use in various applications. To this end, a novel bioreactor design is described that closely mimics the native liver cell environment and is easily scaled from microscopic (<1 ml cells) to clinical (∼600 ml cells) size, while maintaining the same local cell environment throughout the bioreactor. The bioreactor is used for study of primary liver cell isolates, liver-derived cell lines and stem/progenitor cells.

Study of potential toxic effects on rainbow trout hepatocytes of surface water treated with chlorine or alternative disinfectants

This study evaluates the effects of disinfection on the formation of toxic compounds in lake water treated with sodium hypochlorite, chlorine dioxide and peracetic acid (a disinfectant not previously used in drinking water processes). Chlorine reacts with the natural organic matter or contaminants in surface waters and produces a complex mixture of disinfection by-products (DBPs), some of which have been shown to be carcinogenic, mutagenic and/or teratogenic in animal studies. To define the potential toxicity on aquatic animals, disinfected drinking waters obtained from a pilot plant fed with water coming from Lake Trasimeno (Perugia) were collected, adsorbed by using silica C18 cartridges, and then eluted in sequence with ethylacetate, dichloromethane and methanol. The eluates were concentrated under vacuum and resuspended in dimethylsulfoxide (DMSO). Primary cultures of rainbow trout hepatocytes were exposed to three amounts of water concentrate (equivalent to 0.5, 0.25 and 0.125 l of disinfected water per ml of culture medium) for 24 h at 20 degrees C, after which their viability, glutathione content (GSH), free radical production (ROS) and cytochrome P4501A3 expression were determined. The disinfected water samples were collected during different seasons in order to evaluate a possible correlation between seasonal water variations and formation of toxic compounds. None of the water concentrates showed any cytotoxic effect or variations in GSH content, but significant increases in ROS production were detected in the autumn water concentrates from the treatments with sodium hypochlorite and chlorine dioxide. Cytochrome P4501A3 expression was not modified in the hepatocytes exposed to the water concentrates irrespective to the sampling season.

Molecular mechanism of the aryl hydrocarbon receptor activation by the fungicide iprodione in rainbow trout (Oncorhynchus mykiss) hepatocytes

The dicarboximide fungicide iprodione (Ip) causes oxidative damage as a result of the production of free oxygen radicals, and induces cytochrome P4501A3 (CYP1A3) in cultured rainbow trout hepatocytes. The aim of this study was to characterise some of the molecular mechanisms by means of which Ip activates the aryl hydrocarbon receptor (AhR) and subsequently induces the CYP1A3 gene in rainbow trout (Oncorhynchus mykiss). The study was performed using primary hepatocytes and transfected HepG2 cells with a reporter construct, in which luciferase gene expression is under the transcriptional control of a multimerised xenobiotic response elements (4XREs), or a 2.3 Kb DNA fragment (corresponding to the trout CYP1A3 gene promoter). Ip exposure increased rainbow trout hepatocyte CYP1A3 mRNA over time and increased the expression of reporter gene in HepG2, thus suggesting that Ip induces the CYP1A3 gene by activating the AhR. Genistein, a tyrosine kinase inhibitor, efficiently inhibited the Ip-mediated induction of the CYP1A3 gene as demonstrated by mRNA level decrease and the impaired activation of the luciferase reporter gene constructs. Staurosporine, an inhibitor of protein kinase C, also suppressed the induction by Ip. When the AhR antagonist alpha-naphthoflavone was added to the cultures, Ip-mediated CYP1A3 induction was suppressed. These findings are consistent with a mechanism of Ip-mediated CYP1A3 gene induction that involves the activation of the AhR complex via phosphorylation-dephosphorylation reactions.

Estrogenic activity of procymidone in rainbow trout (Oncorhynchus mykiss) hepatocytes: a possible mechanism of action

It is known that procymidone modifies sexual differentiation in vivo and in vitro, and that it induces vitellogenin (Vtg) synthesis in primary cultured rainbow trout hepatocytes. The aim of this study was to evaluate the mechanism underlying this latter in vitro estrogenic action. The cells were treated for 24 h with procymidone 150 microM (with 17beta-estradiol [E2] 20 microM as a positive control) combined with an estrogen receptor (ER) antagonist (tamoxifen 20 microM or ICI 182,780 1 microM) or, given the drug toxic action on the production of reactive oxygen species (ROS), a free radical scavenger (alpha-tocopherol 30 microM). The results from ELISA experiments provided evidence that procymidone Vtg-induction is inhibited by ER antagonists and by alpha-tocopherol suggesting that both ER and ROS are involved in this effect. The ROS detection revealed that the treatment with alpha-tocopherol and tamoxifen completely prevented ROS induction by procymidone, that was not inhibited by ICI 182,780. In exploring the mechanism mediating these events and its timing, we found that procymidone induced mitogen-activated protein kinase (MAPK) at 30 and 60 min, and that this effect was blocked by co-treatment with alpha-tocopherol. In summary, the results of the study clearly support the idea that the estrogenic activity of procymidone in primary cultured trout hepatocytes is mediated by ROS production, and that this activity is similar to that of the ligand-independent ER activation involving MAPK.

Early oxidative damage in primary cultured trout hepatocytes: a time course study

The aim of this study was to evaluate the influence of the two-step hepatocyte isolation procedure on primary cultured trout (Oncorhynchus mykiss) hepatocytes over time. We characterised the possible changes of a variety of some cellular parameters within the first 24-48 h after seeding. We followed the time dependent changes of these parameters during subsequent culture times in order to see if the cells maintained a differentiated status. Scanning electron microscopy revealed bleb formation and 20% cell damage in freshly isolated hepatocytes. During subsequent culture times the bleb dimension appear to be reduced. Heat shock proteins 70 and 50 (HSP70, HSP50) were induced by hepatocyte isolation. During the first 4 h of culture, the hepatocytes showed a variation in mitochondrial activity, an increase in free radical species (ROS), and a decrease in both glutathione (GSH) content and catalase (CAT) activity; the generation of free radicals led to an increase in the formation of 8-hydroxydeoxyguanosine (8-OHdG) in the DNA. The cells showed detectable ethoxyresorufin-O-deethylase activity after 4 h of culture, which had rapidly increased by the 24th hour. After 24 h, mitochondrial and CAT activity, free radical production, and the content of GSH and 8-OHdG returned to their original levels. P450 activity was retained for at least 48 h after seeding. Our data show that trout hepatocytes suffer significant cell injury as a result of the isolation procedure, but primary cultured cells metabolically recover from this stress after a few hours: they are capable of repairing their damaged surfaces, recovering their antioxidant defences and retaining their ability to repair DNA. Our results also confirm that trout hepatocytes in a primary culture maintain their in vivo-like metabolic activities for 3-8 days.

Estrogenic activity of procymidone in primary cultured rainbow trout hepatocytes (Oncorhynchus mykiss)

It has been shown that procymidone, a dicarboximide fungicide, alters sexual differentiation in vivo and in vitro. The aim of this study was to evaluate the estrogenic activity of this fungicide using the synthesis of vitellogenin (Vtg) in rainbow trout hepatocyte as a biological marker. The cells were treated for 24 h with procymidone 150 microM, using 17beta-estradiol 20 microM as a positive control. The doses were chosen on the basis of cell viability (Neutral Red and MTT tests) and solubility. The results show that procymidone leads to a qualitative and quantitative increase in Vtg synthesis. In Western immonoblots, the 170 and 30 kDa bands, which respectively correspond to the monomeric form of Vtg and posvitine, were brighter in cells treated with procymidone and 17beta-estradiol than those corresponding to the negative controls (cells treated for 24 h with DMSO 0.1% alone); ELISA showed that the cells treated with the fungicide and 17beta-estradiol had a 48 and 76%, respectively, higher Vtg concentration than the negative controls (P<0.01). Western blotting also revealed the induction of HSP27 (27 KDa), which further confirms the estrogenic acitivity of procymidone as it is known that the 3' region of HSP27/28 containing the gene mRNAs is induced by estrogen treatment. Procymidone increased also the production of both HSP70 protein (70 KDa) and free oxygen radicals. This last finding is in agreement with the toxic mechanism of dicarboximide fungicides. It can therefore be presumed that the estrogenic activity of procymidone in primary cultured trout hepatocytes is related to oxidative damage which, as many other studies have shown, can increase the levels of estrogens such as 17beta-estradiol, and thus increase Vtg synthesis

Response of rainbow trout (Oncorhynchus mykiss) D-11 cell line to 3-methylcholanthrene (3MC) exposure

The rainbow trout cytochrome P4501A gene subfamily consists of two members, CYP1A1 and CYP1A3, which are induced by polycyclic aromatic hydrocarbons (PAHs). In this study, we investigated the induction of cytochrome P4501A3 in the rainbow trout (Onchorhynchus mykiss) D-11 cell line after 3-methylcholanthrene (3MC) exposure by generating chimeric constructs in which a 2.3 kb fragment or portion of the 5'-flanking region of the trout cytochrome CYP1A3 gene was fused to the firefly luciferase (Luc) gene. The constructs were then transiently transfected into the trout D-11 cells and their transcriptional activity measured by luciferase assay after treatment with different 3MC concentrations. Maximal induction following exposure to 2 microM 3MC was 2.2-fold after 72 h. Deletion of the region specifying the 5' untranslated region (5'UTR) of the mRNA encoding the CYP1A3 gene increased unstimulated luciferase activity but also led to a loss of response to 3MC treatment. This finding suggests that the region specifying the 5'UTR contains a negative element that is also involved in the transcriptional response to 3MC.

Structural polarity and functional bile canaliculi in rat hepatocyte spheroids

Primary hepatocytes self-assemble into spheroids that possess tight junctions and microvilli-lined channels. We hypothesized that polarity develops gradually and that the channels structurally and functionally resemble bile canaliculi. Immunofluorescence labeling of apical and basolateral proteins demonstrated reorganization of the membrane proteins into a polarized distribution during spheroid culture. By means of fluorescent dextran diffusion and confocal microscopy, an extensive network of channels was revealed in the interior of the spheroids. These channels connected over several planes and opened to pores on the surface. To examine the content of apical proteins in the channel membranes, the bile canalicular enzyme dipeptidyl peptidase IV (DPPIV) was localized using a fluorogenic substrate, Ala-Pro-cresyl violet. The results show that DPPIV activity is heterogeneously distributed in spheroids and localized in part to channels. Bile acid excretion was then investigated to demonstrate functional polarity. A fluorescent bile acid analogue, fluorescein isothiocyanate-labeled glycocholate, was taken up into the spheroids and excreted into bile canalicular channels. Due to the structural polarity of spheroids and their ability to excrete bile into channels, they are a unique three-dimensional model of in vitro liver tissue self-assembly. (Videoanimations of some results are available at http://hugroup.cems.umn.edu/research_movies).

Effect of iprodione, a dicarboximide fungicide, on primary cultured rainbow trout (Oncorhynchus mykiss) hepatocytes

As is known from literature, iprodione, a dicarboximide fungicide, has a highly specific action, with a capacity to cause oxidative damage through production of free oxygen radicals (ROS), but it does not appear to be species selective. Since this substance is able to diffuse in water, evaluation of its capacity to induce oxidative damage in an aquatic organism such as the rainbow trout (Oncorhynchus mykiss) was considered of particular interest. A study was, therefore, undertaken to investigate the effect of iprodione on free radicals (ROS) and malondialdehyde (MDA) production, reduced glutathione (GSH) content and catalase activity (CAT), in primary cultured trout hepatocytes, following treatment with 0.2, 0.3 and 0.4 mM concentrations for a 24-h period. The iprodione 0.3 and 0.4 mM concentrations increased both ROS and MDA production and decreased GSH content and CAT activity. These results suggest that iprodione is able to produce oxidative damage in primary cultured fish hepatocytes, thus confirming that its action is specific, but not species selective. It is also well known that ROS production in fungi is due to interaction with the flavin enzyme NADPH cytochrome c reductase to the extent that the normal electron flow from NADPH to cytochrome c is blocked. In contrast, we observed that, in primary cultured trout hepatocytes, iprodione appears to have no effect on NADPH cytochrome c reductase activity. It is, therefore, possible to presume that the mechanism of oxidative damage in trout hepatocytes differs from that observed in fungi. Moreover, our experiments also demonstrate that iprodione is able to induce "in vitro" CYP1A1, leading to the conclusion that the production of ROS is due to this phenomenon.

Development and maintenance of bile canaliculi in vitro and in vivo

The apical surfaces of hepatocytes are specialized to form the boundaries of the bile canaliculi. The canaliculi function to secrete and concentrate components of the bile and to transport the bile out of the interior of the hepatic parenchymal tissue to the epithelium-lined bile ducts. Failure of the canaliculi to form and function properly can lead to biliary stasis or release of bile components into the bloodstream, both potentially life-threatening situations. Experimental analysis of canaliculus development and function has been undertaken in a number of experimental systems, ranging in complexity from intact animals to isolated hepatocyte cell cultures. These approaches each have inherent advantages and disadvantages for studying the various aspects of canaliculus development and function. This article summarizes what is known about how the functional components of the canaliculus develop and the directions that current experimental approaches are leading in analyzing this process. Studies of model epithelial systems have begun to define how interactions between components of the cytoskeleton and plasma membrane regulate the structure of polarized plasma membranes. These results are also discussed in terms of the bile canaliculus.

Morphological and biochemical characterization of primary culture of rabbit proximal kidney tubule cells grown on collagen-IV coated Millicell-CM

The aim of this study was to better characterize rabbit proximal kidney tubule cells cultured on collagen IV-coated porous inserts, as compared to the same cells seeded in standard plastic wells. Total protein contents in confluent monolayers on permeable membranes were about twofold higher than those measured in confluent cultures in plastic wells. Microscopy examinations suggested that such a difference was probably due to a higher cell density and to an impressive development of the apical brush-border membrane. Moreover, measurement of unidirectional transport of p-aminohippuric acid and tetraethylammonium bromide confirmed the high polarization level of cultures on porous inserts. Results of methyl(alpha-D-[U-14C]glyco)pyranoside uptake suggested that cell phenotype was probably influenced by culture conditions. Analysis of different markers as a function of time in culture showed decreases of alkaline phosphatase (AP), gamma-glutamyltranspeptidase (GGT), and Na(+)-K(+)-ATPase activities as well as increases in LDH, ATP, and glutathione levels, similar to those formerly reported for cells cultured in standard plastic plates. However, comparative data from 6-d-old monolayers have shown that AP, GGT, Na(+)-K(+)-ATPase, glutathione reductase (GRED), and selenium-dependent glutathione peroxidase (Se-GPX) activities were 2.8-, 2.6-, 1.6-, 1.2-, and 2.1-fold, respectively, better preserved on precoated permeable membranes. On the other hand, this paper reports for the first time in the literature that GRED and SE-GPX, two phase II detoxification enzymes, were well maintained in cultures of rabbit proximal kidney tubule cells. Our results show that culturing rabbit proximal kidney tubule cells on collagen IV-coated porous membranes was accompanied by an improvement of both morphological and biochemical properties of the cells.