Investigation of rifampicin-induced hepatotoxicity in rat hepatocytes maintained in gel entrapment culture

Rifampicin-induced hepatotoxicity has been well recognized in animals and patients. However, it is undetectable in cultured hepatocyte monolayers in vitro at the equivalent toxic concentration in vivo. This study investigated the rifampicin-induced toxicity on rat hepatocytes in gel entrapment vs. in monolayer culture. Thiazolyl tetrazolium reduction and albumin secretion were routinely detected to identify the toxic responses of rat hepatocytes to rifampicin, while reactive oxygen species (ROS) accumulation and intracellular glutathione (GSH) content were assayed as biomarkers of oxidative stress. In addition, Nile red staining and malondialdehyde (MDA) generation were, respectively, used as endpoints for lipid accumulation and peroxidation. After treatment of hepatocytes for 96 h at a serum rifampicin concentration (12 μM), gel-entrapped rat hepatocytes showed significant cellular damage indicated by alternations of all parameters indicated above, while hepatocyte monolayers did not show severe responses. In contrast to a lack of protections by cytochrome P 450 inhibitors, the ROS scavenger (glycyrrhizic acid) and thiol compounds (N-acetylcysteine and GSH) significantly reduced rifampicin toxicity in gel-entrapped hepatocytes. It appears that gel-entrapped rat hepatocytes reflected significant hepatotoxicity of rifampicin in vivo, and this toxicity was most possibly associated with oxidative stress and lipid accumulation.     

Tanshinone I increases CYP1A2 protein expression and enzyme activity in primary rat hepatocytes

This study investigated the effects of Danshen and its active ingredients on the protein expression and enzymatic activity of CYP1A2 in primary rat hepatocytes. The ethanolic extract of Danshen roots (containing mainly tanshinones) inhibited CYP1A2-catalyzed phenacetin O-deethylation (IC₅₀ = 24.6 μg/ml) in primary rat hepatocytes while the water extract containing mainly salvianolic acid B and danshenshu had no effect. Individual tanshinones such as cryptotanshinone, dihydrotanshinone, tanshinone IIA inhibited the CYP1A2-mediated metabolism with IC₅₀ values at 12.9, 17.4 and 31.9 μM, respectively. After 4-day treatment of the rat hepatocytes, the ethanolic extract of Danshen and tanshinone I increased rat CYP1A2 activity by 6.8- and 5.2-fold, respectively, with a concomitant up-regulation of CYP1A2 protein level by 13.5- and 6.5-fold, respectively. CYP1A2 induction correlated with the up-regulation of mRNA level of aryl hydrocarbon receptor (AhR), which suggested a positive feedback mechanism of tanshinone I-mediated CYP1A2 induction. A formulated Danshen pill (containing mainly danshensu and salvianolic acid B and the tanshinones) up-regulated CYP1A2 protein expression and enzyme activity, but danshensu and salvianolic acid B, when used individually, did not affect CYP1A2 activity. This study was the first report on the Janus action of the tanshinones on rat CYP1A2 activity.     

Regulation of phenobarbital-induction of CYP2B and CYP3A genes in rat cultured hepatocytes: involvement of several serine/threonine protein kinases and phosphatases

We investigated the involvement of diverse protein kinases and phosphatases in the transduction pathways elicited by phenobarbital (PB), a well-known inducer of some hepatic cytochromes P450 (CYP). Different inhibitors or activators of protein kinases or phosphatases were assessed for their ability to modulate PB-induction of CYP2B and CYP3A mRNA expression. Rat hepatocytes in primary culture were treated with the test compounds one hour prior to, and then continuously, in the absence or presence of 1 mmol/L PB for 24 h. By northern blot analysis of CYP2B1/2 and 3A1/2 gene expression, we first confirmed the negative role of the adenosine 3′:5′ cyclic monophosphate (cAMP)/protein kinase A pathway and the positive role of some serine/threonine protein phosphatases in the mechanism of PB-induction. The present data further suggested that Ca²⁺/calmodulin-dependent protein kinases II (independently of Ca²⁺) and extracellular signal-regulated kinases 1/2 (ERK1/2) might function respectively as positive and negative regulator in the PB-induction of CYP2B and CYP3A. In contrast, protein kinases C and phosphatidylinositol-3-kinase did not appear to be involved, while the role of tyrosine kinases remained unclear. We conclude that a complex network of phosphorylation/dephosphorylation events might be crucial for PB-induction of rat CYP2B and CYP3A. This revised version was published online in July 2006 with corrections to the Cover Date.     

In vitro 3-D culture demonstrates incompetence in improving maintenance ability of primary hepatocytes

Primary hepatocytes (PHs) are considered the ‘gold standard’ in drug screening owing to their ability to express many drug-metabolizing enzymes and transporters. Culturing hepatocytes and maintaining their fate in vitro is a major issue since last decade. The main problem with in vitro hepatocytes culture is that they rapidly lose their hepatic morphology and liver-specific functions in culture. Herein, we isolated rat PHs, and cultured them in monolayers (2-D) and spheroids (3-D). The 2-D-cultured PHs exhibited elongated morphology, whereas the 3-D-cultured PHs exhibited spheroid morphology with gradual diameter decrease until 7 days. After 7 days of in vitro culture, PHs were analyzed for the expression of hepatic (Alb, Tf, and Afp) and apoptotic markers (Bax and Bcl2), and co-expression of CYP3A1 and Abumin after 2 and 7 days. Furthermore, in both cultures, PHs were induced with 3-methylcholanthrene (3-MC, Cyp1a-specific inducer) and dexamethasone (Cyp3a-specific inducer) for 48 and 72?h, respectively. The mRNA levels of Cyp1a and Cyp3a were analyzed in induced (3-MC, dexamethasone) and non-induced PHs. After 7 days of in vitro culture, PHs exhibited dramatic downregulation of hepatic marker expression in both cultures. Furthermore, apoptotic marker expression was higher in the 2-D-cultured PHs than 3-D-cultured PHs. The mRNA levels of Cyp1a and Cyp3a indicated higher RNA content in the 2-D-cultured PHs after 48?h of induction. Therefore, we concluded that there was no significant difference between the culture systems, and further studies are required to identify the essential components for in vitro PH culture rather than culture systems.     

Influence of medium composition and culture conditions on glutathione S-transferase activity in adult rat hepatocytes during culture

Summary Glutathione S-transferase (GST) activity was measured in adult rat hepatocytes during either pure culture or coculture with another rat liver cell type in various media. Addition of nicotinamide, selenium, or dimethylsulfoxide, deprivation of cyst(e)ie and the use of two complex media were tested. Whatever the conditions used, after a constant decrease during the first 24 h, GST remained active over the whole culture period (1–2 wk). However, various patterns were observed: GST activity either remained relatively stable to approximately 50% of the initial value or showed a moderate or strong increase. The highest values were found in pure hepatocyte cultures maintained in the presence of nicotinamide or dimethylsulfoxide. Similar changes were observed using 1-chloro-2,4-dinitrobenzene or 1,2-dichloro-4-nitrobenzene as substrates for GST. Addition of 10⁻⁴ M indomethacin resulted in 37 to 60% inhibition of enzyme activity. Thus, these results demonstrate that GST remained expressed during culture but its levels markedly varied depending on the medium composition and type and age of culture. Y. V. was supported by Instituut voor Wetenschappel?k Onderzoek in Landbouw en Nijverheid. This work was supported by INSERM.     

Reduced and oxidized glutathione contents in adult rat hepatocytes under various culture conditions

Reduced and oxidized glutathione contents of adult rat hepatocytes in pure culture and in co-culture with rat epithelial cells were measured under various medium conditions. To the standard medium fetal calf serum, nicotinamide, H₂SeO₃, dimethylsulphoxide or no supplements were added. For freshly isolated hepatocytes, intracellular contents of 24 ± 7 nmol reduced and 0.7 ± 0.2 nmol oxidized glutathione/mg cellular protein were obtained, respectively. In pure culture as well as in co-culture and regardless of th medium conditions involved, the protein content stays constant during the culture time with the exception of a decrease in protein content after 6 days of pure culture, caused by deterioration and loss of the hepatocytes. In both culture systems, an initial increase in intracellular reduced glutathione levels was observed, followed by a decrease and a quick normalisation in co-culture. On the contrary, in pure culture, the decrease was slower, but not transient and a stabilized situation was never reached. The various supplementations of the culture media had no significant effect on the intracellular reduced glutathione contents of both culture systems. As far as the intra- and the extracellular oxidized glutathione contents and the extracellular reduced form are concerned, these were only present in small amounts.Abbreviations BSA bovine serum albumin - DMSO medium supplemented with 2% dimethylsulphoxide - FCS- medium without fetal calf serum - FCS+ medium supplemented with 10% fetal calf serum - GSH reduced glutathione - GSSG oxidized glutathione - HPLC high performance liquid chromatography - MEM minimal essential medium - Nic medium supplemented with 25 mM nicotinamide - PBS phosphate buffered saline - Se medium supplemented with 0.1 µM selenium - st standard medium     

DNA damage and cell death induced by 1,2-dibromo-3-chloropropane (DBCP) and structural analogs in monolayer culture of rat hepatocytes: 3-aminobenzamide inhibits the toxicity of DBCP

1,2-Dibromo-3-chloropropane (DBCP) and a number of halogenated propane analogs induced DNA damage in rat hepatocytes in vitro measured by an automated alkaline elution method. Short-term (2 hrs) cytotoxic effects of DBCP were not observed until the DBCP concentration exceeded 1 mM. The short-term cytotoxicity of all the DBCP analogs occurred in the same concentration range. Significant membrane damage, measured as cell detachment, was observed after extended exposure to lower concentrations of DBCP (100 M) for 20 hrs. The relative, delayed cytotoxic effect of DBCP and analogs correlated with their ability to cause DNA damage. In general, the halogenated propanes with more bromines relative to chlorines were the more potent compounds. Propane analogs lacking the third halogen had little cytotoxic activity. The addition of the proposed specific poly(ADP-ribosyl)transferase inhibitor 3-aminobenzamide (3-ABA) protected against DBCP-induced cytotoxic effects and NAD⁺ depletion. However, 3-ABA also reduced DBCP-induced DNA damage, DBCP metabolic loss, and the formation of water soluble and covalently bound DBCP metabolites. Thus, 3-ABA may block DBCP-induced cell death by decreasing the formation of reactive DBCP-metabolites.Abbreviations 3-ABA 3-aminobenzamide - 3-AB acid 3-aminobenzoic acid - Asc ascorbate - BSA bovine serum albumin - DBCP, 1,2-diB-3-CP 1,2-dibromo-3-chloropropane - DMSO dimethylsulfoxide - DPPD N,N-diphenyl-p-phenylenediamine - GSH glutathione - Hoechst 33258 [2(2-(4-hydroxy-phenyl)-6-benzimidazole-6-(1-methyl-4-piperazyl)-benzimidazole trihydrochloride)] - 1,2,3-triBP 1,2,3-tribromopropane - 1,3-diB-2-CP 1,3-dibromo-2-chloropropane - 1,3-diC-2-BP 1,3-dichloro-2-bromopropane - 1,2,3-triCP 1,2,3-trichloropropane - 1,2-diBP 1,2-dibromopropane     

Changes in some chromatin and cytoplasmic enzymes of perinatal rat hepatocytes during culture

Summary Hepatocytes prepared from rats at various perinatal stages were cultured in selective medium that does not allow fibroblastic cell growth. Cell population remained homogeneous during the culture. Hepatocytes undergo divisions for a period, which varies according to the stage of development of the rat. Light and electron microscope observations showed the presence of numerous cytoplasmic organelles; moreover, hydrocortisone-induced structures similar to bile canaliculi. Chromatin protein kinase decreased rapidly during culture except in samples prepared from 17-day fetuses in which it remained unchanged for 2 days and decreased to a lesser extent afterwards. Chromatin nonhistone proteins were incubated with (γ-³²P) ATP and the phosphorylation pattern analyzed on polyacrylamide gels. Many radioactive peaks were observed in chromatin proteins from 17-day fetuses; they were much lower in proteins from 19-day fetuses. The phosphorylation pattern was analyzed in hepatocytes after 2 days of culture. Many radioactive peaks were observed with proteins from heapatocytes taken from 17-day fetuses; no radioactivity was observed in proteins from 19-day fetuses. This is in contrast with the absence of radioactive peaks in chromatin proteins from adult rat hepatocytes. In cytoplasm, aldolase and pyruvate kinase specific activities varied according to the age of the rat. They strongly decreased during culture except in hepatocytes from 15-and 17-day fetuses, in which they remained stable for at least 5 days. The stability of chromatin and cytoplasmic enzymes in hepatocytes from 17-day fetuses could result from their ability to be regulated by hormones that are secreted at this stage of development.     

Influence of collagen gel substrata on certain biochemical activities of hepatocytes in primary culture

In order to study the influence of cell shape as modulated by the extracellular matrix on the cellular activity, hepatocytes isolated from liver were maintained on collagen I coated plastic substrata and collage I gel substrata and certain hepatocyte specific functions were investigated. The incorporation of³[H]-leucine into total proteins and albumin secreted by cells maintained on collagen gel was found to be significantly higher compared to those maintained on a collagen coated plastic substrata, indicating that hepatocytes on collagen gel have an enhanced albumin synthesizing capacity. Increased incorporation of³⁵[S]-sulphate into total proteoglycans (PG) and a relatively higher fraction of the³⁵[S]-PG in the extracellular space showed an increased rate of synthesis and secretion of sulphated PGs by cells maintained on collagen gels. But in contrast to the above results, the incorporation of³[H]-leucine into cytokeratins C₈, C₁₈ and actin were significantly low in cells maintained on collagen gel. The tyrosine amino transferase activity exhibited by hepatocytes preincubated with dexamethasone on collagen gel was also significantly low. The different forms of collagen substrata appeared to have no effect on the amino acid transport by hepatocytes, further suggesting that the various hepatocyte specific functions are not uniformly altered when hepatocytes are maintained on three-dimensional collagen gel substrata. These results indicate that the shape of the cell as determined by the nature of the matrix substratum influences the synthetic activity of secretory proteins and those remaining intracellularly, differently.     

Effects of vanadate on 6-phosphofructo 2-kinase activity and fructose 2,6-bisphosphate levels in cultured rat hepatocytes

The presence of vanadate in primary cultures of rat hepatocytes produced a significant increase in the concentration of fructose 2,6-bisphosphate and in the activity of 6-phosphofructo 2-kinase. Compared with insulin, vanadate had a more potent action on the metabolite increase, but a similar effect on the 6-phosphofructo 2-kinase activity. Both the insulin- and the vanadate-dependent enhancements of 6-phosphofructo 2-kinase were inhibited by cycloheximide which specifically blocks protein synthesis on the translational level, suggesting that the increase of the enzyme activity was due to induction rather than to a change in the catalytic activity.     

Amino acid and energy requirements for rat hepatocytes in primary culture

Summary The amino acid and energy requirements of rat hepatocytes in suspension and early culture were investigated. Among a number of potential energy substrates tested, pyruvate (20 mM) was found to be most effective in stimulating hepatocytic protein synthesis. Amino acids stimulated protein synthesis both as energy substrates and as protein precursors. An amino acid mixture was designed to provide maximal inhibition of protein degradation as well as maximal stimulation of protein synthesis. In a defined medium containing amino acids at these concentrations, and supplemented with glucocorticoid hormone and insulin, hepatocytes could be maintained—on a collagen substratum—for at least a week without any significant net loss of cells or cellular protein. The work was supported by grants from The Norwegian Cancer Society and from The Norwegian Council for Science and the Humanities. An erratum to this article is available at .     

Analysis of cell viability and differential activity of mouse hepatocytes under 3D and 2D culture in agarose gel

Three-dimensional (3D) and two-dimensional (2D) cultures of hepatocytes in various concentrations (0.3–0.7%) of agarose gel revealed that the hepatocytes under 3D cultures in 0.3% agarose gel possess long-term (>3 weeks) viability, significant self-assembly to form tissue like aggregates, low lactate dehydrogenase release and high albumin synthesis. These were in contrast to 2D culture of hepatocytes. Our results suggest that the 3D culture of hepatocytes in agarose gel favors aggregate formation of functionally active cells and would be useful for liver transplantation as well as to analyze hepatocytes biology.     

The effects of cell density, attachment substratum and dexamethasone on spontaneous apoptosis of rat hepatocytes in primary culture

Summary The rates of spontaneous cell detachment, cell viability, and apoptosis in primary cultures of rat hepatocytes plated at high and low density were compared. Apoptosis was frequent in detached cells, and the rates of cell detachment and apoptosis were greater in high-density than in low-density cultures. Among attached cells, more cells had condensed or fragmented nuclei in high-density than in low-density cultures. Further, ladder-like DNA fragmentation was not seen in low-cell-density cultures but was clearly evident in high-density cultures. Bax was more highly expressed in cells cultured at high density, and on collagen vs. matrigel, whereas changes of Bcl-2 and Fas expression observed in culture appeared unrelated to the rate of apoptosis. The rate of hepatocyte apoptosis appeared to be identical in low-density cultures on collagen 1 and matrigel, but when cells were cultured at high density, matrigel suppressed apoptosis by more than 50% at 36 h. In hepatocytes cultured on collagen 1, dexamethasone (0.1 μM) suppressed apoptosis in both low- and high-density cultures; higher doses had no further effects. In high density cultures, aurintricarboxylic acid (10 μM) suppressed apoptosis and this improved cell attachment at 48 h. It is concluded that cell viability in primary cultures of rat hepatocytes grown on collagen I is dependent on optimal culture density and that the cell population is regulated, at least in part, by apoptosis. Corticosteroids suppress spontaneous apoptosis of cultured hepatocytes in a non-dose-dependent manner, whereas matrigel abolishes apoptosis induced by increasing cell density. Bax may be an important protein in the cell density and cell matrix-dependent regulation of apoptosis in cultured hepatocytes.     

Isozyme differentiation of aldolase and pyruvate kinase in fetal,regenerating, preneoplastic,and malignant rat hepatocytes during culture

Summary Aldolase and pyruvate kinase isozymes were investigated in cultured hepatocytes from fetal, regenerating, and 2-acetyl-aminofluorene-fed rat liver as well as in some epithelial liver cell lines. Our results show that: (a) cell proliferation and prolonged expression of specific isozymes were found only in cultured hepatocytes from 17-day old fetuses; (b) the fetal type of pyruvate kinase expressed in regenerating and carcinogen-treated liver was temporarily lost only in cultured hepatocytes from regenerating liver; (c) the adult type of aldolase and pyruvate kinase was absent in one epithelial cell line derived from a carcinogen-treated liver and in the hepatoma tissue cell (HTC) line but was found in the Faza clone of the Reuber H₃₅ cell line during the 50 first passages in vitro; and (d) the isozyme pattern of pyruvate kinase was always more strongly shifted than that of aldolase. The observations suggest that: (a) hepatocytes from carcinogen-treated liver exhibit the same lack of ability to proliferate in primary culture as normal adult hepatocytes; (b) adult hepatocytes can produce fetal isozymes without prior cell division; (c) pyruvate kinase is a stronger marker of dedifferentiation (retrodifferentiation) than aldolase; and (d) regulatory processes of isozyme expression are different during ontogenesis, regeneration, and hepatocarcinogenesis. This work was supported by the “Institut National de la Santé et de la Recherche Médicale” and the “Fondation pour la Recherche Medicale Fran?aise”     

Effects of antibiotics on protein synthesis and degradation in primary cultures of rat hepatocytes

Summary In primary hepatocyte cultures, maintained in a protein-free medium, streptomycin, penicillin, and Garamycin (gentamicin) all inhibited protein synthesis at concentrations above 0.1 mM. Some inhibition was also observed with the fungicide Mycostatin at 100 U/ml. Hepatocytic protein degradation was markedly inhibited by penicillin at concentrations above 0.1 mM, whereas streptomycin and Garamycin only showed slight inhibition at concentrations in excess of 1 mM. None of the antibiotics had any detectable effect on the structural integrity (viability) of the cells. The work was supported by grants from The Norwegian Cancer Society and The Norwegian Council for Science and the Humanities     

Differential effects of chloroquine on cardiolipin biosynthesis in hepatocytes and H9c2 cardiac cells

Chloroquine is a potent lysomotropic therapeutic agent used in the treatment of malaria. The mechanism of the chloroquine-mediated modulation of new cardiolipin biosynthesis in isolated rat liver hepatocytes and H9c2 cardiac myoblast cells was addressed in this study. Hepatocytes or H9c2 cells were incubated with [1,3-³H]glycerol in the absence or presence of chloroquine and cardiolipin biosynthesis was examined. The presence of chloroquine in the incubation medium of hepatocytes resulted in a rapid accumulation of radioactivity in cardiolipin indicating an elevated de novo biosynthesis. In contrast, chloroquine caused a reduction in radioactivity incorporated into cardiolipin in H9c2 cells. The presence of brefeldin A, colchicine or 3-methyladenine did not effect radioactivity incorporated into cardiolipin nor the chloroquine-mediated stimulation of cardiolipin biosynthesis in hepatocytes indicating that vesicular transport, cytoskeletal elements or increased autophagy were not involved in de novo cardiolipin biosynthesis induced by chloroquine. The addition of chloroquine to isolated rat liver membrane fractions did not affect the activity of the enzymes of de novo cardiolipin biosynthesis but resulted in an inhibition of mitochondrial cytidine-5-diphosphate-1,2-diacyl-sn-glycerol hydrolase activity. The mechanism for the reduction in cardiolipin biosynthesis in H9c2 cells was a chloroquine-mediated inhibition of glycerol uptake and this did not involve impairment of lysosomal function. The kinetics of the chloroquine-mediated inhibition of glycerol uptake indicated the presence of a glycerol transporter in H9c2 cells. The results of this study clearly indicate that chloroquine has markedly different effects on glycerol uptake and cardiolipin biosynthesis in hepatocytes and H9c2 cardiac cells     

Purification and the immunological characterization of rat protein phosphatase 2A: enzyme levels in diabetic liver and heart

Summary Protein phosphatase 2A₁ was purified from rat skeletal muscle and used to produce antisera to the three subunits of the holoenzyme. Affinity purified antibodies specific for the subunits of the phosphatase enzyme were found to recognize the type 2A₁ and 2A₂ phosphatase from rat skeletal muscle, heart, liver, brain and erythrocytes and were used to investigate the effects of diabetes on the levels of this enzyme in liver and heart. Phosphorylase phosphatase assays coupled with immunoblot analysis of fractionated rat liver and heart cytosol from normal and diabetic animals show no apparent differences in the quantity or activity of these enzymes following the induction of alloxan diabetes. When considering these results and the normal physiological concentrations of known effectors of these enzymes, it is likely that protein phosphatase 2A₁ and 2A₂ are not responsible for the dephosphorylation of phosphorylase a under physiological conditions.     

Thapsigargin,a selective inhibitor of sarco-endoplasmic reticulum Ca<Superscript>2+</Superscript>-ATPases,modulates nitric oxide production and cell death of primary rat hepatocytes in culture

Increased cytosolic calcium ([Ca²⁺] _i ) and nitric oxide (NO) are suggested to be associated with apoptosis that is a main feature of many liver diseases and is characterized by biochemical and morphological features. We sought to investigate the events of increase in [Ca²⁺] _i and endoplasmic reticulum (ER) calcium depletion by thapsigargin (TG), a selective inhibitor of sarco-ER-Ca²⁺-ATPases, in relation to NO production and apoptotic and necrotic markers of cell death in primary rat hepatocyte culture. Cultured hepatocytes were treated with TG (1 and 5 μmol/L) for 0–24 or 24–48 h. NO production and inducible NO synthase (iNOS) expression were determined as nitrite levels and by iNOS-specific antibody, respectively. Hepatocyte apoptosis was estimated by caspase-3 activity, cytosolic cytochrome c content and DNA fragmentation, and morphologically using Annexin-V/propidium iodide staining. Hepatocyte viability and mitochondrial activity were evaluated by ALT leakage and MTT test. Increasing basal [Ca²⁺] _i by TG, NO production and apoptotic/necrotic parameters were altered in different ways, depending on TG concentration and incubation time. During 0–24 h, TG dose-dependently decreased iNOS-mediated spontaneous NO production and simultaneously enhanced hepatocyte apoptosis. In addition, TG 5 μmol/L produced secondary necrosis. During 24–48 h, TG dose-dependently enhanced basal NO production and rate of necrosis. TG 5 μmol/L further promoted mitochondrial damage as demonstrated by cytochrome c release. A selective iNOS inhibitor, aminoguanidine, suppressed TG-stimulated NO production and ALT leakage from hepatocytes after 24–48 h. Our data suggest that the extent of the [Ca²⁺] _i increase and the modulation of NO production due to TG treatment contribute to hepatocyte apoptotic and/or necrotic events.