Long term cell culture of rat liver epithelial cells retaining some hepatic functions

Determination of queuosine derivatives by reverse-phase liquid chromatography for the hypomodification study of Q-bearing tRNAs from various mammal liver cells

Three queuosine derivatives (Q-derivatives) have been found at position 34 of four mammalian so-called Q-tRNAs: queuosine (Q) in tRNA(Asn) and tRNA(His), mannosyl-queuosine (manQ) in tRNA(Asp), and galactosyl-queuosine (galQ) in tRNA(Tyr). An analytical procedure based on the combined means of purified tRNA isolation from liver cells and ribonucleoside analysis by reverse-phase high performance liquid chromatography coupled with real-time UV-spectrometry (RPLC-UV) was developed for the quantitative analysis of the three Q-derivatives present in total tRNA from liver tissues and liver cell cultures. Using this analytical procedure, the rates of Q-tRNA modification were studied in total tRNAs from various mammalian hepatic cells. Our results show that the four Q-tRNAs are fully modified in liver tissues from adult mammals, regardless of the mammal species. However, a lack in the Q-modification level was observed in Q-tRNAs from newborn rat liver, as well in Q-tRNAs from normal rat liver cell cultures growing in a low queuine content medium, and from a rat hepatoma cell line. It is noteworthy that in all cases of Q-tRNA hypomodification, our analytical procedure showed that tRNA(Asp) is always the least affected by the hypomodification. The biological significance of this phenomenon is discussed.

Liver stem cells: a potential source of hepatocytes for the treatment of human liver disease

Severe liver injury often leads to the proliferation of oval cells, which differentiate along hepatocytic and biliary lineages. Because oval cells proliferate only when hepatocyte replication is impaired, they are considered to be the progeny of facultative liver stem cells (FLSCs). Identification and isolation of FLSCs has been hampered by the lack of markers that delineate these bipotential progenitors. We hypothesized that transition ductal cells are FLSCs because they are located in a unique anatomical niche sharing tight junctions with a neighboring hepatocyte and another terminal ductular cell. Alternatively, it has been proposed recently that bone marrow-derived stem cells are FLSCs since these cells differentiate along the hepatic lineage following colonization of the liver. The intent of this review is to provide insight into the nature and origin of liver stem cells and to explore the possibility that stem cell technology may lead to the development of clinical modalities for the treatment of human liver disease.

Altered response to growth factors in rat epithelial liver cells overexpressing human c-Fos protein

Human c-fos cDNA was transfected into normal rat liver epithelial (REL) cells to identify cellular modifications associated with high expression of c-Fos protein. Responses to EGF and TGF beta were examined in the different cell lines, under anchorage-dependent and -independent conditions. Sensitivity to both factors was modified in transfected cells. While parental cells in monolayer did not respond to EGF, c-fos containing cells growth was stimulated by this factor. Overexpression of c-Fos protein led to an enhanced TGF beta-induced growth inhibition under anchorage dependent conditions, and TGF beta abolished spontaneous growth in soft agar of the cell lines containing c-fos oncogene. The mechanisms underlying the increased sensitivity to TGF beta in c-fos transfected cells are still to be determined.

Cytokeratin 14 expression in rat liver cells in culture and localization in vivo

Rat liver epithelial cells (LECs) are non-parenchymal proliferating cells that readily emerge in primary culture and can be established as cell lines, but their in vivo cell(s) of origin is unclear. We reported recently some evidence indicating that the LEC line, T51B, contains two cytokeratins (CKs) equivalent to human CK8 and CK14 respectively. T51B cells also contain vimentin assembled as a network of intermediate filaments distinct from that of the CKs. In the present study, we examined the expression of CK14 gene in various LEC preparations and a Triton-resistant rat skin cytoskeletal fraction, and then assessed its usefulness as an LEC specific marker in the liver. Northern and Western blot analyses with cDNAs and antibodies for CK8, CK14, CK18 and vimentin confirmed that rat hepatocytes express CK8 and CK18 genes only, whereas T51B cells express CK8, CK14 and vimentin genes in the absence of CK18. CK14 was also present in LECs derived as primary from embryonic-day 12 rat liver and secondary cultures from 4-day-old rat liver. Primary cultures of oval cells isolated from 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) treated rat liver (an enriched source of biliary epithelial cells) contained CK14 mRNAs which were slightly shorter than those in LECs. The analyses of CK5 (the usual partner of CK14) gene expression using specific cDNA and antibody clearly demonstrated its absence in LECs. In situ double immunolocalization analyses by laser scanning confocal microscopy showed that CK14 was not present in hepatocytes (HES6+ cells) and was expressed in some biliary epithelial (BDS7+ cells). CK14-positive cells were also found in the Glisson's capsule. However, CK14-positive cells of the portal region were vimentin negative, whereas those of the Glisson's capsule were vimentin positive. Our results suggest that CK14 gene expression is part of the differentiation program of two types of LECs and that this differential CK14 gene expression can be used as a new means to type LECs in culture and in vivo.

Characterization of trans-immortalized hepatic cell lines established from transgenic mice

Hepato-specific regulatory (promoter/enhancer) DNA sequences were used for targeting the expression of onc genes, such as murine c-myc and Simian Virus 40 T Antigen, to hepatocytes of transgenic mice which subsequently developed hepatocellular carcinomas after a variable period of time (depending on the type of onc gene employed). Several trans-immortalized cell lines were established and compared with respect to the expression of adult hepatic markers and response to growth factors. Despite the morphological differences observed between trans-hepatomas, owing to the expression of the two different onc genes, all tumor-derived cell lines behaved in a comparable fashion during long-term culture displaying an adult hepatic phenotype for at least 40 passages. They differed, however, in response to epidermal growth factor. When the gene coding for human alpha 1-antitrypsin was placed under the control of the same hepato-specific promoter/enhancer, high levels of the human recombinant protein could be harvested from the supernatants of trans-hepatoma-derived cell lines.

Alternate hydroxylating activities in newborn rat adrenal cells in primary culture

During the course of a study to produce reference compounds, the metabolism of tetrahydrogenated derivatives (ring A reduced) of progesterone, 6 alpha-hydroxyprogesterone, 11-deoxycorticosterone and corticosterone in newborn rat adrenal cells in primary culture was studied. Analysis of the metabolites was made by gas chromatography-mass spectrometry. Most products resulted from the enzymatic reactions of 11 beta-, 18- and 21-hydroxylation, reduction of the 20-oxo group and oxidoreduction of the 3-hydroxyl group. However, unexpected metabolites were produced from the incubation of 3 beta, 5 alpha-tetrahydroprogesterone and 6 alpha-hydroxy-3 alpha, 5 beta-tetrahydroprogesterone. They resulted from the 16 alpha-hydroxylation of the precursors and probably from the 15 alpha-, 16 beta- and 17 alpha-hydroxylation of 6 alpha-hydroxy-3 alpha, 5 beta-tetrahydroprogesterone. These hydroxylating activities are weak and were not detected from the endogenous steroidogenesis. They were not detected either from the incubation of exogenous steroids with a 3-oxo-4-ene structure or from steroids with a 21-hydroxyl substituent. They result only from substrates showing diminished or no affinity towards the 11 beta/18- and 21-steroid hydroxylase systems. These unusual hydroxylations could be catalyzed by monooxygenase systems in the endoplasmic reticulum similar to those present in the liver or by the monooxygenase systems specific to steroidogenesis. In particular, the reaction specificity of cytochrome P-450(11) beta could be altered by the presence of a 6 alpha-hydroxyl group in a tetrahydrogenated steroid.

Gas chromatographic-mass spectrometric study of deacetylation and oxidation of 2-acetylaminofluorene by rat liver epithelial cell lines upon cocarcinogen induction

Cell line cultures from postnatal and adult rats were incubated with 5-100 mumol/l [9-14C]-2-acetylaminofluorene. On incubation of 10 mumol/l, ring-hydroxylated metabolites, expressed as nmol hydroxy-2-acetylaminofluorene (OH-2-AAF)/mg cell protein/24 h, were 9-OH- 1.28 +/- 0.37, 7-OH- 1.08 +/- 0.28 and 5-OH- 0.30 +/- 0.08, and deacetylated 2-AAF (2-AF) 1.20 +/- 0.18. For 5, 10, 50 and 100 mumol/l 2-AAF, the total production of OH-2-AAF (same units) and 2-AF (%) were, respectively, 0.86 (0%), 3.86 (35%), 17.8 (60%) and 35.03 (89%). On preincubation with phenobarbital (BP) or 3-methylcholanthrene (3-MC) and then incubation of 10 mumol/l 2-AAF, the total synthesis of OH-2-AAF increased 1.9-fold (PB) and 2.5-fold (3-MC). In addition, four other OH-2-AAF (1-OH-, 3-OH- and two unknown OH-2-AAF) were produced and glucuronidation of all metabolites was induced and amounted to 57% of the total after PB and 75% after 3-MC preincubation. Metyrapone or alpha-naphthoflavone inhibition of BP or 3-MC, respectively, markedly affected the production of free and conjugated metabolites and, almost completely, the deacetylation of 2-AAF.

Use of aggregating cell cultures for toxicological studies

Relatively simple techniques are now available which allow the preparation of large quantities of highly reproducible aggregate cultures from fetal rat brain or liver cells, and to grow them in a chemically defined medium. Since these cultures exhibit extensive histotypic cellular reorganization and maturation, they offer unique possibilities for developmental studies. Therefore, the purpose of the present study was to investigate the usefulness of these cultures in developmental toxicology. Aggregating brain cell cultures were exposed at different developmental stages to model drugs (i.e., antimitotic, neurotoxic, and teratogenic agents) and assayed for their responsiveness by measuring a set of biochemical parameters (i.e., total protein and DNA content, cell type-specific enzyme activities) which permit a monitoring of cellular growth and maturation. It was found that each test compound elicited a distinct, dose-dependent response pattern, which may ultimately serve to screen and classify toxic drugs by using mechanistic criteria. In addition, it could be shown that aggregating liver cell cultures are capable of toxic drug activation, and that they can be used in co-culture with brain cell aggregates, providing a potential model for complementary toxicological and metabolic studies.

Biosynthesis of the third component of complement in rat liver epithelial cell lines and its stimulation by effector molecules from cultured human mononuclear cells

Rat liver epithelial cell lines, growing in a serum-supplemented medium, synthesize and secrete into the culture medium the third component of complement (C3). We studied the regulation of C3 production in this system. We found that human peripheral blood mononuclear leukocytes in culture released one or more soluble factors which stimulated rat liver epithelial cells to produce increased quantities of C3. This stimulating effect was strongly enhanced when the mononuclear cell cultures were treated with phytohemagglutinin, a T-lymphocyte mitogen. The factor(s) failed to enhance C3 biosynthesis by rat dermal fibroblasts, which are known to produce this protein. This reveals a tissue-specific differential response between the fibroblasts and the liver epithelial cells. The physical and chemical characteristics, such as heat sensitivity, 2.8 M ammonium sulphate precipitation, and lower activity after digestion by proteases unambiguously indicate that the effector molecules are proteins. When the crude supernatant of mononuclear leukocytes was fractionated by gel filtration, the stimulating factor(s) eluted as two peaks with apparent molecular weight of 25 to 60 and 15 to 20 kdalton, respectively. As to the cellular origin of the C3-stimulating factor(s), several observations were made: (a) in separate cultures containing either T-cells or monocyte-enriched populations from the same sample of blood mononuclear cells, no activity was detected in the presence or absence of phytohemagglutinin, (b) conditioned media from each of these cultures could not substitute for the corresponding intact cell populations, and (c) the addition of purified T-cells to the monocyte-enriched population in the presence of phytohemagglutinin restored the production of the stimulating activity by the mixed culture. Finally, experiments were carried out to verify whether monokine interleukin 1 affects the hepatic C3 biosynthesis. It was demonstrated that interleukin 1 enhanced this biosynthesis, but could not completely substitute for conditioned medium from stimulated mononuclear cells.

Biosynthesis of sterols and bile acids in rat liver epithelial cell lines

A rat liver epithelial cell line growing in a serum-supplemented medium expressed biosynthetic pathways of bile sterols and of free and conjugated chenodeoxycholic and cholic acids, the main primary bile acids of the liver. They were identified and measured by gas chromatography-mass spectrometry. The bile steroid secretion in the serum-supplemented cell line was established upon incubation in a serum-free medium which was demonstrated to sustain cell growth, allowing elimination of the interference of exogenous bile steroids and effectors. The free bile acid secretion was also expressed in a subline adapted to proliferate in this serum-free medium, i.e., a basal medium supplemented with 4 g/l albumin carrying 7.6 muequiv./l of a mixture of six long-chain free fatty acids but without any addition of hormones and growth factors. In addition, the rat liver epithelial cell line growing in the serum-supplemented medium maintained, with time, a steady-state of bile acid secretion over a lifespan of 500 days. In the two types of liver epithelial cell lines, dexamethasone and chenodeoxycholic acid supplementation exerted, individually, either a stimulating or an inhibiting effect on the bile acid secretion concurrently with the hydroxylation of chenodeoxycholic acid into alpha-muricholic acid.

Progression of spontaneous malignant transformation of epithelial rat liver cell lines

Cultured epithelial cell lines from normal rat livers were shown to undergo gradual transformation and malignancy which increased with time. Morphological changes appeared both before and after cells had attained a malignant state, as detected by agar tests. The progression of the degree of malignancy was determined by the morphological appearance of the cells, the increase in the number and size of cell colonies in soft agar, the expression of gamma glutamyl transferase (gamma GT) and the shortening of the latency period necessary for tumor formation after transplantation to syngeneic rats of cells from sequential passages.

Oxidoreductive and hydroxylating metabolism of progesterone in rat liver epithelial cell lines

Mechanisms and sequences of reduction and hydroxylation of progesterone into 6-hydroxypregnanolones were studied in proliferating rat liver epithelial cell cultures. These cell lines had an intense metabolic activity and all the metabolites were unconjugated. The formation of 3 alpha,6 alpha- and 3 beta,6 alpha-dihydroxy-5 alpha-pregnan-20-one was observed when the cells were incubated with progesterone, 5 alpha-pregnane-3,20-dione, 3 alpha- or 3 beta-hydroxy-5 alpha-pregnan-20-one and 6 alpha-hydroxy-5 alpha-pregnane-3,20-dione but not with 6 alpha- or 6 beta-hydroxyprogesterone, 5 beta-pregnane-3,20-dione, 3 alpha- or 3 beta-hydroxy-5 beta-pregnan-20-one. These findings indicate that the potential precursors of the 6 alpha-hydroxypregnanolones have a 5 alpha-configuration. The reduction of 5 alpha-pregnane-3,20-dione at C-3 followed by a 6 alpha-hydroxylation can be postulated as the major, if not the only, metabolic pathway. However, the possibility that 6 alpha-hydroxylation may occur prior to reduction of the C-3 oxo group cannot be entirely ruled out. The stereospecificity of reduction at C-5 and hydroxylation at C-6 are discussed and compared with 6-hydroxylated progesterone metabolites found in man and some other mammals during pregnancy and the neonatal period.

Rat liver epithelial cell cultures in a serum-free medium: primary cultures and derived cell lines expressing differentiated functions

Rat liver epithelial cells explanted in a serum-free medium (SFM) composed of Ham's F10 basal medium plus free fatty acids adsorbed on bovine albumin gave successful rise to primary cultures and then to long-term cell lines that expressed liver functions; induction of L-tyrosine aminotransferase by glucocorticoids, hepatic pattern of progesterone metabolism, and biosynthesis of murine primary bile acids; chenodeoxycholic and cholic acid common to higher vertebrates and alpha-muricholic acid specific of the rat bile.

Time course study of L-tyrosine aminotransferase induction in rat liver cell lines

The enhancement of L-tyrosine aminotransferase activity by dexamethasone, an exclusive function of the liver, was serially measured at different passages of eight rat liver epithelial cell lines initiated and continuously grown in either a serum-supplemented medium or a serum-free medium. The enzyme basal activity was found to be 5.4 +/- 1.8 mU for cell lines in serum and 6.8 +/- 3.4 mU for cell lines without serum. Under the influence of dexamethasone (10(-6) mol/l for 5 hours) this basal level could be increased up to 2.9 fold in the presence of serum and 2.5 fold in its absence when investigations were carried out at early passages. During the following subcultures the induction ratio gradually declined and scarcely any induction could be detected after the 15th passage for cells grown in serum and after the 25th passage for cell lines grown without serum.

Repeated establishment of diploid epithelial cell cultures from normal and partially hepatectomized rats

A number of liver epithelial cell cultures were established from 10 to 12-d-old sucklings, 6 to 8-wk-old young adults, or from 2 to 18-month-old partially hepatectomized rats. Improvements in the methods for cell isolation and culture yielded replicating cells from every experiment and they were maintained for different periods with regular passages. The proliferative potential in vitro of adult rat liver cells could be increased if the rats were subjected to partial hepatectomy before cell isolation. In the early passages, the majority of the cells were found to have a true diploid karyotype as studied by the Giemsa-banding technique. Under the culture conditions described, a very high percentage of cells remained in the diploid range for, in most cases, at least 4 months and in some cases for up to 6 months. Afterward, the karyotype was unstable, but no "crisis" period was seen before the cells became aneuploid. Until this time, the growth characteristics of the cells also followed a normal pattern showing density dependent inhibition of division and a lack of markers associated with malignancy. The cultured liver cells exhibited a number of liver specific properties when they were maintained as a confluent monolayer. The early passages of diploid epithelial cell cultures derived from normal and regenerating rat liver are good models for studies of the regulation of cell division and the changes that are related to carcinogenesis.

Biotransformation of allylbenzene analogues in vivo and in vitro through the epoxide-diol pathway

1. The epoxidation of allylbenzene, safrole, estragole, eugenol and eugenol methyl ether was investigated in rats pretreated with these compounds and also in vitro using hepatic microsomal preparations and adult rat liver cell cultures. 2. Dihydrodiols were detected in the urine and liver of rats pretreated with allylbenzene compounds. Similarly, incubation of allylbenzene epoxides with hepatic microsomal preparations and adult rat liver cell cultures gave rise to the formation of dihydrodiols.

Synthesis and degradation of xanthine dehydrogenase in chick liver. In vivo and in vitro studies

The present study describes the (xanthine:NAD+ oxidoreductase, EC 1.2.1.37) synthesis and degradation of chick liver xanthine dehydrogenase in vivo and in organ cultures. The results indicate that control of xanthine dehydrogenase activity is mediated by changes in the rate of enzyme synthesis, but that degradation rates are unaffected. The results also suggest that xanthine dehydrogenase synthesis occurs through a previously unreported intermediate. Detected in cultures of liver tissue, this intermediate apparently is not converted into an active enzyme. A model of synthesis and degradation for xanthine dehydrogenase proposes that the synthesis of the enzyme is proportional to messenger RNA and includes an inactive enzyme precursor and a second inactive intermediate prior to degradation. Integrated mathematical solutions describing the concentration of intermediates as a function of time can be found explicitly for simple models. The appendix to this paper extrapolates solutions for one-, two- and three-step models to generate a mathematical solution for an 'n'-step model containing 'n' intermediates. The rate constants in the solutions can be found experimentally.

Primary monolayer cultures of postnatal rat liver cells with extended differentiated functions

Monolayers of liver cells cultured from postnatal rats were grown in two types of media. One set of cultures was grown in selective medium which contained ornithine but was deficient in arginine; the other set was grown in nonselective medium which contained arginine but no ornithine. The cultures that were grown in the nonselective medium contained primarily a mixture of two cell types found in the liver: parenchymal hepatocytes and fibroblast-like cells. The fibroblast cells tended to overgrow the hepatocytes after several days in culture. In contrast, fibroblast overgrowth was inhibited in cultures grown in the selective, arginine-deficient medium, thereby resulting in relatively pure cultures of functional parenchymal hepatocytes. Comparative studies of sulfobromophthalein (BSP) uptake showed that the cultures grown in selective medium continued to be active much longer than the cultures grown in the nonselective medium. Pyruvate kinase assays revealed that the cultures grown in selective medium contained primarily the L-isoenzyme type which is characteristic of parenchymal hepatocytes. Cultures grown in nonselective medium contained a mixture of L- and M-isoenzymes which is indicative of nonparenchymal liver cells. The reported results indicate that selective, arginine-deficient medium permits primarily the growth of parenchymal hepatocytes found in neonatal rat liver.

Genetic and hormonal regulation of steroid hydroxylases and drug metabolizing enzymes in rat liver

Two microsomal steroid hydroxylase activities (cholesterol-7alpha-hydroxylase and progesterone-16alpha-hydroxylase) were measured in the livers of Sprague-Dawley and Wistar rats and compared to three other monooxygenase activities (aryl hydrocarbon hydroxylase, p-nitro-anisole-O-demethylase and aminopyrine-N-demethylase). Cholesterol-7alpha-hydroxylase behaves in a very unique manner. It is the only one of the studied enzymes to be more active in the female than in the male, it is very poorly induced by phenobarbital and methylcholanthrene, but responds quickly to the administration of glucocorticoids. In fact, the cholesterol-7alpha-hydroxylase activity presents a very pronounced circadian rhythm which is under the control of the hypothalamo-adrenal axis. Marked differences are also found in the response of the various enzymatic activities to the administration of inducers as well as in their relative activities in untreated male and female animals.

Conditions affecting primary cell cultures of functional adult rat hepatocytes. II. Dexamethasone enhanced longevity and maintenance of morphology

Primary monolayer cell cultures of adult rat hepatocytes underwent change in morphology and substantial cell loss between 1 and 3 days postinoculation. Dexamethasone-supplementation (1 micronM) of the culture medium maintained the polygonal epithelial morphology of the hepatocytes and increased longevity such that over 80% of the cells survived for 3 days and at least 30% for 8 or 9 days. This enhancement of survival was obtained up to 48 hr postinoculation, but the earlier the time of dexamethason supplementation the greater the effect. Removal of dexamethasone resulted in a decrease in longevity. The positive effect of dexamethasone on longevity was observed following dexamethasone replacement of insulin in supplemented cultures, but the combination of insulin and dexamethasone resulted in poorer survival than with dexamethasone alone. The results are interpreted to indicate that dexamethasone provided a requirement of the in vitro environment for survival and suggest that elaboration of a complex medium is required to maintain hepatocytes in culture.

Conditions affecting primary cell cultures of functional adult rat hepatocytes. 1. The effect of insulin

The conditions for obtaining representative, primary adult rat hepatocyte cultures were explored. The methods applied included enzymatic liver perfusion which was nondestructive to hepatocytes, the prevention of aggregation of dissociated cells and the selective attachment of viable cells. These procedures yielded a recovery of 50% of the liver cells which gave rise to cultures representing 14% of the total liver cells. The cultures were composed of homogeneous epithelial-like cells cytologically similar to hepatocytes and possessed a number of liver-specific enzymes. There was virtually no cell division initially and most cells died between 24 and 48 hr. Insulin enhanced the attachment of the liver cells, altered their morphology, but did not prolong cell survival.

Separation and characterization of the reduced metabolites of the 18-hydroxydeoxycorticosterone hormone by gas-liquid chromatography-mass spectrometry. Occurrence of stereoisomeric forms in rat adrenals and liver

In order to study the metabolism of 18-OH-11-deoxycorticosterone, the mineralocorticoid hormone responsible for hypertension in rats and humans, we have synthesized the following dihydrogenated and tetrahydrogenated reference derivatives: 18,21-dihydroxy-5alpha-pregnane-3,20-dione, 18,21-dihydroxy-5beta-pregnane-3,20-dione, 3alpha,18,21-trihydroxy-5alpha-pregnan-20-one (I), 3beta,18,21-trihydroxy-5alpha-pregnan-20-one (II), 3alpha,18,21-trihydroxy-5beta-pregnan-20-one (III) and 3beta,18,21-trihydroxy-5beta-pregnan-20-one (IV). A complete separation of these compounds from each other and from tetrahydrocorticosterone isomers has been realized only by the association of thin-layer chromatography and gas-liquid chromatography on high-efficiency glass capillary columns. Characterization by gas-liquid chromatography-mas spectrometry is described. The stereoisomer distribution in rats is: adrenals of adult males and females (compounds I and II in the ratio 4:1); adrenals of 23-day-old males and females (compounds I, II and III, 11:11:3); liver of females (compound I and traces of III); and the liver of adult male (compounds II, III and IV, 4.5:4.5:1).