Adsorption, simple binding and complex binding of rat hepatocytes to various in vitro substrata

Activation of cAMP (EPAC2) signaling pathway promotes hepatocyte attachment

Primary Human Hepatocyte (PHH) remains undefeated as the gold standard in hepatic studies. Despite its valuable properties, partial attachment loss due to the extraction process and cryopreservation remained the main hurdle in its application. We hypothesized that we could overcome the loss of PHH cell attachment through thawing protocol adjustment and medium composition. We reported a novel use of a medium designed for iPSC-derived hepatocytes, increasing PHH attachment on the collagen matrix. Delving further into the medium composition, we discovered that removing BSA and exposure to cAMP activators such as IBMX and Forskolin benefit PHH attachment. We found that activating EPAC2, the cAMP downstream effector, by S-220 significantly increased PHH attachment. We also found that EPAC2 activation induced bile canaliculi formation in iPS-derived hepatocytes. Combining these factors in studies involving PHH or iPS-hepatocyte culture provides promising means to improve cell attachment and maintenance of hepatic function.

STAT3 is required for IL-6-gp130-dependent activation of hepcidin in vivo

BACKGROUND & AIMS

Hepcidin is a peptide hormone that is central to the regulation of iron homeostasis. In response to interleukin 6 (IL-6), hepatocytes produce hepcidin that decreases iron release/transfer from enterocytes and macrophages and causes hypoferremia. To clarify the molecular pathways involved in hepcidin activation by IL-6, we used different mice strains in which the main IL-6/gp130 signaling pathways have been genetically disrupted.

METHODS

We generated mice with hepatocyte-specific deletion of the IL-6 signal-transducing gp130 receptor (alfpgp130 (LoxP/LoxP)), with a gp130 receptor lacking the essential region for STAT1 and -3 activation (alfpCre gp130(DeltaSTAT/LoxP)) or mice expressing a gp130 allele lacking the essential tyrosine for RAS-MAPK activation (alfpCregp130(Y757F/LoxP)). We studied gp130-dependent pathways and hepcidin mRNA expression by Western blot, reverse-transcription polymerase chain reaction, and Northern blot in vivo and ex vivo.

RESULTS

IL-6 stimulated phospho STAT3, serum amyloid A (SAA), and suppressor of cytokine signaling 3 (SOCS3) expression in livers of wild-type and alfpCregp130(Y757F/LoxP) mice, whereas this response was blocked in alfpCre gp130(LoxP/LoxP) and alfpCre gp130(DeltaSTAT/LoxP) mice. In wild-type and alfpCregp130(Y757F/LoxP) animals, significantly higher hepcidin mRNA expression was found 3 to 6 hours after IL-6 stimulation. In contrast, no IL-6-dependent regulation of hepcidin mRNA expression was found in alfpgp130 (DeltaSTAT/LoxP) and AlfpCre gp130 (LoxP/LoxP) animals. In primary hepatocytes, higher hepcidin mRNA expression after IL-6 stimulation was only observed when gp130-STAT3-dependent signaling was intact.

CONCLUSIONS

We have demonstrated that both in vivo and in vitro STAT3 is the key transcription factor responsible for IL-6 activation of hepcidin gene expression in the liver.

Retention of structural and functional polarity in cultured skate hepatocytes undergoing in vitro morphogenesis

The present study characterized a primary culture model of hepatocytes isolated from the little skate, Leucoraja erinacea, that maintain remarkable structural and functional polarity over 7 days in culture. Skate hepatocytes were isolated as clusters of 3-20 hepatocytes surrounding a bile canaliculus, rather than as single cells. Trypan blue and propidium iodide exclusion was found to be >98%, and the cells maintained high intracellular concentrations of K+, ATP, and reduced glutathione (GSH), and high ratios of ATP/ADP and GSH/GSSG. Glutathione S-transferase activity remained constant, whereas cytochrome P450 activity declined to 16% of initial levels after 7 days. Quantitative RT-PCR analysis revealed that the mRNA levels of several genes remained constant over the 7-day period, whereas Bsep, the canalicular bile salt export pump, levels declined slowly to 30% of initial values. In the presence of dexamethasone, the cells underwent a morphogenesis in which the clusters reannealed into a three-dimensional network of chords. During this morphogenesis, skate hepatocytes clusters maintained a polarized distribution of actin filaments and microtubules, as well as apical and basolateral membrane domains. Polarity of membrane transport systems was confirmed both morphologically, using antibodies raised against Bsep and Mrp2, the canalicular multispecific organic anion transporter, and functionally, by monitoring secretion of the fluorescent organic anions NBD-taurocholate, a Bsep substrate, and fluorescein-methotrexate, an Mrp2 substrate, into the bile canalicular spaces. Overall, the results indicate that in contrast with mammalian hepatocytes, isolated skate hepatocyte clusters retain polarity in culture, and provide an excellent system for investigating long-term effects of drugs and xenobiotics on hepatobiliary functions, and for studying in vitro morphogenesis.

Stimulation of hepatocytic AMP-activated protein kinase by okadaic acid and other autophagy-suppressive toxins

Autophagic activity in isolated rat hepatocytes is strongly suppressed by OA (okadaic acid) and other PP (protein phosphatase)-inhibitory toxins as well as by AICAR (5-aminoimidazole-4-carboxamide riboside), a direct activator of AMPK (AMP-activated protein kinase). To investigate whether AMPK is a mediator of the effects of the toxin, a phosphospecific antibody directed against the activation of phosphorylation of the AMPK alpha (catalytic)-subunit at Thr172 was used to assess the activation status of this enzyme. AICAR as well as all the toxins tested (OA, microcystin-LR, calyculin A, cantharidin and tautomycin) induced strong, dose-dependent AMPKalpha phosphorylation, correlating with AMPK activity in situ (in intact hepatocytes) as measured by the AMPK-dependent phosphorylation of acetyl-CoA carboxylase at Ser79. All treatments induced the appearance of multiple, phosphatase-sensitive, low-mobility forms of the AMPK alpha-subunit, consistent with phosphorylation at several sites other than Thr172. The flavonoid naringin, an effective antagonist of OA-induced autophagy suppression, inhibited the AMPK phosphorylation and mobility shifting induced by AICAR, OA or microcystin, but not the changes induced by calyculin A or cantharidin. AMPK may thus be activated both by a naringin-sensitive and a naringin-resistant mechanism, probably involving the PPs PP2A and PP1 respectively. Neither the Thr172-phosphorylating protein kinase LKB1 nor the Thr172-dephosphorylating PP, PP2C, were mobility-shifted after treatment with toxins or AICAR, whereas a slight mobility shifting of the regulatory AMPK beta-subunit was indicated. Immunoblotting with a phosphospecific antibody against pSer108 at the beta-subunit revealed a naringin-sensitive phosphorylation induced by OA, microcystin and AICAR and a naringin-resistant phosphorylation induced by calyculin A and cantharidin, suggesting that beta-subunit phosphorylation could play a role in AMPK activation. Naringin antagonized the autophagy-suppressive effects of AICAR and OA, but not the autophagy suppression caused by cantharidin, consistent with AMPK-mediated inhibition of autophagy by toxins as well as by AICAR.

The IL-6–gp130–STAT3 pathway in hepatocytes triggers liver protection in T cell–mediated liver injury

Increasing evidence demonstrates that IL-6 has a protective role during liver injury. IL-6 activates intracellular pathways via the gp130 receptor. In order to identify IL-6-gp130 pathways involved in mediating liver protection, we analyzed hepatocyte-specific gp130 knockout mice in a concanavalin A-induced (Con A-induced) model of immune-mediated hepatitis. We demonstrated that IL-6-gp130-dependent pathways in hepatocytes alone are sufficient for triggering protection in Con A-induced hepatitis. gp130-STAT3 signaling in hepatocytes mediates the IL-6-triggered protective effect. This was demonstrated by analysis of IL-6-induced protection in mice selectively deficient for gp130-dependent STAT1/3 or gp130-SHP2-RAS signaling in hepatocytes. To identify IL-6-gp130-STAT1/3 dependently expressed liver-protective factors, we performed gene array analysis of hepatic gene expression in hepatocyte-specific gp130(-/-) mice as well as in gp130-STAT1/3- and gp130-SHP2-RAS-MAPK-deficient mice. The mouse IL-8 ortholog KC (also known as Gro-alpha) and serum amyloid A2 (SAA2) was identified as differentially IL-6-gp130-STAT3-regulated genes. Hepatic expression of KC and SAA2 mediate the liver-protective potential of IL-6, since treatment with recombinant KC or serum SAA2 effectively reduced liver injury during Con A-induced hepatitis. In summary, this study defines IL-6-gp130-STAT3-dependent gene expression in hepatocytes that mediates IL-6-triggered protection in immune-mediated Con A-induced hepatitis. Additionally, we identified the IL-6-gp130-STAT3-dependent proteins KC and SAA2 as new candidates for therapeutic targets in liver diseases.

The IL-6-gp130-STAT3 pathway in hepatocytes triggers liver protection in T cell-mediated liver injury

Increasing evidence demonstrates that IL-6 has a protective role during liver injury. IL-6 activates intracellular pathways via the gp130 receptor. In order to identify IL-6-gp130 pathways involved in mediating liver protection, we analyzed hepatocyte-specific gp130 knockout mice in a concanavalin A-induced (Con A-induced) model of immune-mediated hepatitis. We demonstrated that IL-6-gp130-dependent pathways in hepatocytes alone are sufficient for triggering protection in Con A-induced hepatitis. gp130-STAT3 signaling in hepatocytes mediates the IL-6-triggered protective effect. This was demonstrated by analysis of IL-6-induced protection in mice selectively deficient for gp130-dependent STAT1/3 or gp130-SHP2-RAS signaling in hepatocytes. To identify IL-6-gp130-STAT1/3 dependently expressed liver-protective factors, we performed gene array analysis of hepatic gene expression in hepatocyte-specific gp130(-/-) mice as well as in gp130-STAT1/3- and gp130-SHP2-RAS-MAPK-deficient mice. The mouse IL-8 ortholog KC (also known as Gro-alpha) and serum amyloid A2 (SAA2) was identified as differentially IL-6-gp130-STAT3-regulated genes. Hepatic expression of KC and SAA2 mediate the liver-protective potential of IL-6, since treatment with recombinant KC or serum SAA2 effectively reduced liver injury during Con A-induced hepatitis. In summary, this study defines IL-6-gp130-STAT3-dependent gene expression in hepatocytes that mediates IL-6-triggered protection in immune-mediated Con A-induced hepatitis. Additionally, we identified the IL-6-gp130-STAT3-dependent proteins KC and SAA2 as new candidates for therapeutic targets in liver diseases.

Adhesion Behavior of Peritoneal Cells on the Surface of Self-Assembled Triblock Copolymer Hydrogels

Adhesion behavior of cells to the surface of physical hydrogel membranes prepared by water-induced self-organization of precisely synthesized ABA-triblock copolymers comprised of poly(beta-benzyl L-aspartate) (PBLA) as A segment and poly(ethylene oxide) (PEO, molecular weight = 20 000) as the B segment were investigated. The cast film from the methylenechloride solution of these copolymers swelled in water very rapidly forming hydrogels (100-400% water content of total weight). The content of PBLA affected the strength, the hydrophobicity, and the amount of water involved in the hydrogel surface. During the early stage of cultivation with murine peritoneal cells, cell adhesion on the hydrogels of PEO and PBLA with 18 (20K18) and 25 (20K25) monomeric units was not observed, while adhesion on the hydrogels of PEO and PBLA with 32 (20K32) and 55 (20K55) monomeric units was successful, suggesting more than 12 mol % in PBLA content is necessary for adhesion of these cells. Although cell spreading on the hydrogels of 20K18, 20K25, and 20K32 was not sufficient, the hydrogel of 20K55 allowed cell adhesion and spreading to be bipolar with leading edge whose raffling is active with pseudopodium and lamellipodium as well as PBLA homopolymer, suggesting active motility of these cells. Remarkably, prolonged incubation restored adhesiveness onto the films at 20K18 in contrast to adhesion with 20K25 despite low hydrophobicity. It is conceivable that adaptation of proteins and chemical changes to the surface during the culture period may participate in these phenomena. Mechanical properties and interaction between cell and these copolymer hydrogels could be controlled by composition of block segments, and optimization for implants could also be attainable.

Naringin-sensitive phosphorylation of plectin, a cytoskeletal cross-linking protein, in isolated rat hepatocytes

To identify phosphoproteins that might play a role in naringin-sensitive hepatocellular cytoskeletal disruption and apoptosis induced by algal toxins, hepatocyte extracts were separated by gel electrophoresis and immunostained with a phosphothreonine-directed antibody. Use of dilute (5%) polyacrylamide gels containing 6 m urea allowed the resolution of one very large (approximately 500-kDa) okadaic acid- and naringin-sensitive phosphoprotein, identified by tryptic fingerprinting, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and immunostaining as the cytolinker protein, plectin. The naringin-sensitive phosphorylation induced by okadaic acid and microcystin-LR probably reflected inhibition of a type 2A protein phosphatase, whereas the naringin-resistant phosphorylation induced by calyculin A, tautomycin, and cantharidin probably involved a type 1 phosphatase. Okadaic acid caused a collapse of the plectin-immunostaining bile canalicular sheaths and the general cytoskeletal plectin network into numerous medium-sized plectin aggregates. Inhibitors of protein kinase C, cAMP-dependent protein kinase, or Ca(2+)/calmodulin-dependent kinase II had moderate or no protective effects on plectin network disruption, whereas naringin offered 86% protection. Okadaic acid induced a naringin-sensitive phosphorylation of AMP-activated protein kinase (AMPK), the stress-activated protein kinases SEK1 and JNK, and S6 kinase. The AMPK-activating kinase (AMPKK) is likely to be the target of inhibition by naringin, the other kinases serving as downstream components of an AMPKK-initiated signaling pathway.

Behavior of a cell line derived from normal human hepatocytes on non-physiological and physiological-type substrates: evidence for enhancement of secretion of liver-specific proteins by a three-dimensional growth pattern

The behavior of a recently described cell line, HH25, derived from normal human hepatocytes, has been investigated on several different substrates--tissue-culture plastic, glass, a thin layer of rat-tail collagen I, and thin layers or thick gels of extracellular matrix derived from the Engelbreth-Holm-Swarm murine sarcoma (EHS matrix). Cellular morphology, proliferation, and secretion of three hepatocyte-specific proteins (albumin, alpha1 acid glycoprotein, and alpha1 antitrypsin) have been examined. There were no differences in morphology, proliferation, or differentiated function in the cells on either plastic, glass, collagen, I, or a thin layer of EHS matrix, but on a thick EHS matrix gel the cells altered their morphology (forming three-dimensional colonies with canalicular-like structures) and their production of albumin and alpha1 acid glycoprotein was enhanced. This suggests that the enhanced differentiated function is associated with the morphological change (occurring only on the thick EHS gel) rather than with receptor-mediated cell-matrix interactions (which can also occur on the thin layer of EHS matrix). This cell line is therefore a good in vitro cellular model for the investigation of the roles of morphological changes and of cell-cell and cell-matrix interactions in the control of human hepatocyte behavior without the need for an extensive source of primary tissue.

Influence of nidogen complexed or not with laminin on attachment, spreading, and albumin and laminin B2 mRNA levels of rat hepatocytes

Nidogen/entactin is a Mr = 150,000 glycoprotein which is present within basement membranes in a noncovalent stable complex with laminin. We have studied the effects of nidogen/entactin complexed or not with laminin on attachment, spreading, and functions of adult rat hepatocytes in primary culture. Freshly isolated hepatocytes attached on either recombinant or EHS-derived nidogen, although to a lesser extent than on laminin/nidogen complex, laminin, and E8 and P1 fragments of laminin. Hepatocytes bound on a nidogen fragment bearing the N-terminal and rod-like domains but not on either the N-terminal globules or the rod-like domain which contains a RGD sequence. Attachment of hepatocytes on nidogen and laminin/nidogen complex was inhibited by anti-beta 1 integrin antibodies. Hepatocytes remained rounded on nidogen and laminin, whereas they rapidly spread on laminin/nidogen complex and collagen IV. Nidogen, laminin, and laminin/nidogen complex transiently maintained high steady-state albumin mRNA levels in cultured hepatocytes, but a decrease in albumin mRNA content was observed after 24 h, independently of the substrates. Actinomycin D and cycloheximide treatment indicated that the transient effect of these substrates on albumin expression was related to post-transcriptional mechanisms. Laminin B2 mRNAs were not detectable in freshly isolated hepatocytes but were expressed in 4 h hepatocyte cultures. After 24 h, a dramatic increase in the steady-state level of laminin B2 mRNA was found in hepatocytes cultured on nidogen and laminin/nidogen complex. This effect was slightly prevented in hepatocytes plated on laminin. These results show that interactions of hepatocytes with nidogen/entactin in vitro result only in a transient modulation of hepatocyte functions.

Use of hepatocyte cultures for liver support bioreactors

Hybrid artificial liver systems are being developed as extracorporeal temporary liver support therapy. Here, an overview is given with emphasis on hepatocyte culture models for bioreactors, in vitro studies, animal studies and the clinical application of hybrid liver support systems. In vitro studies show long term external metabolic functions of primary isolated hepatocytes in bioreactors. These systems are capable of supporting essential liver functions. Animal experiments show the possibility of upscaling the bioreactors for clinical treatment. Since there is no reliable animal model for investigations on the treatment of acute liver failure, the promising results of these studies have limited relevance. The small number of clinical studies are not sufficient to give statements about a clinical improvement of therapy of acute liver failure. Although important progress has been made in the development of the systems, multiple different hepatocyte culture models and bioreactor constructions are discussed in the literature, indicating competition in this field of medical research.

Effects of various medium formulations and attachment substrata on the performance of cultured ruminant hepatocytes in biotransformation studies

1. A procedure for the isolation and primary culture of hepatocytes from goat and cattle is described. Hepatocyte culture performance was monitored for 51 h by measuring viability, cytochrome P-450 maintenance, dealkylation of scoparone and ethylmorphine, and glucuronidation of phenol red. 2. Culture medium composition is discussed in relation to differences between splanchnic blood composition of ruminant and monogastric animal species. Main differences are in glucose and volatile fatty acid concentrations. Modified Williams' E culture medium did not yield higher culture performance than non-modified Williams' E. 3. Coating of culture dishes with either collagen or fibronectin did not improve culture performance. 4. Williams' E, although developed for rodent cells, proves to be a suitable basal medium for ruminant hepatocytes. In this medium, culture quality is high for at least several days. 5. In cultured goat hepatocytes, biotransformation rate for scoparone amounted to 20 nmol/mg protein per h, for ethylmorphine 96 nmol/mg protein per h and for phenol red 2 nmol/mg protein per h. Biotransformation activity in cow hepatocytes is approximately half that in goat hepatocytes.

Characterization and induction of xenobiotic metabolizing enzyme activities in a primary culture of rainbow trout hepatocytes

1. A primary cell culture from rainbow trout (Oncorhynchus mykiss) liver was prepared and evaluated for biotransformation of xenobiotics. 2. The hepatocytes maintained cytochrome P-450 content, as well as their cytochrome P-450-dependent activities, stable for 5-6 days in serum-free medium. Protein and glutathione levels, as well as other enzyme activities important for biotransformation, were close to their fresh cell levels throughout the culture period. 3. The cells were also responsive to cytochrome P-450 inducers. Both beta-naphthoflavone (BNF) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) caused an increase in ethoxyresorufin O-deethylase (EROD) activity, which was dose-dependent over the concentration ranges of 3.6-360 nM and 2.5-100 pM, respectively. The induced activities in BNF exposed cells returned to basal levels within 48 h after replacing the medium with a BNF-free medium. Exposure of cells to TCDD (100 pM) for 48 h induced EROD activity which, in contrast to response of BNF-exposed cells, continued to increase after the medium had been replaced with TCDD-free medium. 4. The results show that trout hepatocytes in primary culture afford a reliable in vitro method for studying the regulation and functions of xenobiotic biotransformation enzymes, and for defining toxic effects of aquatic pollutants in cells.

Three-dimensional studies of the cytoskeleton of cultured hepatocytes: a quick-freezing and deep-etching study

The ultrastructure of the cytoskeleton of cultured mouse hepatocytes was studied by a quick-freezing and deep-etching method. Isolated mouse hepatocytes were cultured on collagen gels for 48 h, fixed in paraformaldehyde and centrifuged to prepare cell pellets. The hepatocytes were split open to remove cytoplasmic soluble proteins for replica preparations. Some specimens were decorated with anti-actin antibody or S1 myosin fragments to identify actin filaments. They were quickly frozen in isopentane-propane mixture, fractured in liquid nitrogen, deeply etched in a freeze-fracture machine and rotary shadowed by platinum and carbon. The basal cell membranes of hepatocytes were in contact with the collagen gels and the apical surface faced the culture medium. Networks of actin filaments were attached to the apical cell membranes, but intermediate filaments were localized along the basal layer. Some intermediate filaments were associated with cell organelles, such as the endoplasmic reticulum. The Golgi apparatus was less associated with the cytoskeleton and showed synthesized materials in the cisternae. Cytoskeletal organization in cultured hepatocytes was revealed three-dimensionally, indicating that the interaction of cell membranes with collagen gels is important for the organization of the cytoskeleton.

Peroxisomal fatty acyl-CoA oxidase is not regulated by triiodothyronine

In studies using primary cultures of adult rat hepatocytes in serum-free medium, peroxisomal fatty acyl-CoA oxidase activity was not altered by the presence of 3,5,3'-triiodothyronine, whereas time- and dose-dependent increases in the thyroid hormone-responsive enzyme mitochondrial glycero-3-phosphate dehydrogenase were seen. Activity of peroxisomal oxidase was stimulated with clofibric acid in the absence of 3,5,3'-triiodothyronine. The results demonstrate that hepatic peroxisomal fatty acyl-CoA oxidase activity is not directly regulated by 3,5,3'-triiodothyronine and that stimulation of peroxisomal fatty acyl-CoA oxidase activity by clofibric acid does not require thyroid hormone.

A Mr 80K hepatocyte surface protein(s) interacts with basement membrane components

We have identified a Mr 80K cell surface protein(s) from adult rat hepatocytes that binds basement membrane components, including collagen IV, heparan sulfate proteoglycan, and laminin. Freshly isolated hepatocytes were cell surface-labeled with 125I using the lactoperoxidase-catalyzed method, and detergent-solubilized membrane proteins were chromatographed on affinity columns prepared with purified basement membrane components. A Mr 80K protein was eluted with 0.15-1 M NaCl from a collagen IV column. Two proteins (Mr 80K and 38K) were eluted from a heparan sulfate proteoglycan column. The larger protein was also eluted from a column made with heparan sulfate side chains. Several proteins (Mr 80K, 67K, 45K, and 32K) bound to an affinity chromatography column made with the laminin A chain-derived synthetic peptide PA22-2, which is active for promoting cell attachment. When fractions eluted from these columns were analyzed by two-dimensional gel electrophoresis, the Mr 80K proteins showed similar patterns with a pI ranging from 8 to 9. The Mr 80K protein(s) may have an important role in the interaction of hepatocytes with basement membrane.

Selective oxidation of mitochondrial glutathione in cultured rat adrenal cells and its relation to polycyclic aromatic hydrocarbon-induced cytotoxicity

Primary cultures of rat adrenal cells, as well as rat adrenals in vivo, are sensitive to the potent carcinogen 7,12-dimethylbenz[a]anthracene and its liver metabolite 7-hydroxymethyl-12-methylbenz[a]anthracene, whereas unmethylated polycyclic aromatic hydrocarbons like benzo[a]pyrene or benzo[a]anthracene are ineffective. The adrenocorticolytic potencies of the hydrocarbons are affected by adrenocorticotrophic hormone and various steroids, cytochrome P450 inhibitors, and antioxidants. In the present investigation digitonin was used to fractionate cultured rat adrenal cells. It was found that the mitochondria and cytosol of the cells contained 3-5 nmol/10(6) cells (approximately 15%) and 20-30 nmol/10(6) cells (approximately 85%) of the total soluble cellular glutathione equivalents, respectively. After exposing the cells to 7-hydroxymethyl-12-methylbenz[a]anthracene in the culture medium, a time- and concentration-dependent selective oxidation of mitochondrial glutathione was observed, whereas the effect on the cytosolic glutathione was negligible. Under the same conditions, 7,12-dimethylbenz[a]anthracene and benzo[a]pyrene were unable to alter the redox levels of the subcellular pools of glutathione. Omission of adrenocorticotrophic hormone lowered the oxidation of mitochondrial glutathione induced by 7-hydroxymethyl-12-methylbenz[a]anthracene about twofold. The results suggest that rat adrenal cells contain two separate pools of glutathione, one cytosolic and one mitochondrial, of which the latter is selectively influenced by 7-hydroxymethyl-12-methylbenz[a]anthracene. Moreover, it is concluded that rat adrenal cells offer a unique model system for general studies of the effects of a selective oxidation of mitochondrial glutathione on various cell functions. These effects may constitute early changes in cytotoxicity, preceding, e.g., membrane damage and loss of cytosolic components.

The in vitro unscheduled DNA synthesis (UDS) assay in rat primary hepatocytes. Validation of improved methods for primary culture including data on the lack of effect of ionizing radiation

The in vitro unscheduled DNA synthesis (UDS) assay was evaluated for inclusion in a battery of assays used at The Upjohn Company for evaluation of lead compounds in the development of new and existing drug entities. This evaluation process encompassed aspects of the isolation of hepatocytes and tests of reference mutagens and genotoxins. The flow rate of perfusion solutions and their temperatures were critical in the isolation of high viability hepatocytes in good yield. The attachment of freshly isolated hepatocytes to coverslips was greatly enhanced by coating the coverslips with type III collagen. Results of testing 12 known genotoxic agents (UV light, cyclophosphamide, 7,12-dimethylbenzanthracene, dimethylnitrosamine, diethylnitrosamine, 2-acetylaminofluorene, benzo[a]pyrene, methyl methanesulfonate, ethyl methanesulfonate, N-propyl-N'-nitro-N-nitrosoguanidine, benzidine and 4-aminobiphenyl) were in agreement with the literature. The use of X-ray did not induce unscheduled DNA synthesis in hepatocytes. This latter finding draws attention to the inability of this assay to detect agents which result in 'short-patch' repair of damage.

Primary cultures of hepatocytes in serum and hormone-free medium: identification of conditions which stimulate an in vivo-like induction of G6PD

Recent results from several laboratories suggest that complex interactions between hormones and dietary carbohydrate may be responsible for regulating the induction of several hepatic lipogenic enzymes. Elucidation of these interactions requires the ability to culture hepatocytes for several days in serum-free medium where the hormones or carbohydrate or both present is strictly controlled. The functional response of primary adult rat hepatocytes was examined in a medium without exposure to serum, hormones, or carbohydrates and on three substrata commonly used to culture cells in a defined medium. Hepatocytes cultured on a floating collagen gel in which is embedded a nylon mesh possess cell attachment and morphologic characteristics superior to either cells cultured on a collagen-coated or fibronectin(Fn)-coated substratum. Cells cultured on the gel-mesh system retain insulin responsivity, as measured by protein synthesis rates and glucose-6-phosphate dehydrogenase (G6PD) induction, for at least 6 d in culture. Under these conditions, insulin, dexamethasone, and fructose increase G6PD specific activity to levels comparable to that seen in an induced animal. Hepatocytes cultured on the gel-mesh system tolerate restricted medium conditions better than cells cultured on collagen or Fn-coated substratum, and remain viable for sufficient times to allow, for the first time, full expression and maximal induction (i.e. like in vivo) of G6PD in cultured cells. This system represents a satisfactory model for in vivo liver metabolism and a superior system for studying the effects of hormones and metabolites on G6PD levels, as well as other nutritional-hormonally regulated enzymes.

Specificity and valency of concanavalin A in neuron-substratum adhesion and redistribution of cell surface receptors

Neurons seeded in culture as spherical cells flatten partially to form lamellipodia by which they adhere to the substratum. Lamellipodium formation is stimulated specifically by concanavalin A (Con A) and other mannose-binding lectins in several types of neuronal cells, but not in similarly treated fibroblasts. Conditions that block much of the adsorption of Con A to the substratum have no effect on stimulation of lamellipodium formation by Con A. This suggests that Con A acts in solution on neurons and does not directly bind them to their substrata. Succinylated-Con A (bivalent) binds to the same receptors as native Con A (tetravalent) but does not elicit lamellipodium extension unless crosslinked with anti-Con A IgG. Treatment of neurons with Con A produces local changes in the composition of the cell surface resulting from redistribution of lectin receptor complexes. This redistribution is not as great with SCon A and, like lamellipodium formation, is sensitive to the valency of Con A. A variety of treatments (4 degrees C, trifluoperazine, nordihydroguaiaretic acid, 4-bromphenacyl bromide, and cytochalasin D), inhibit both Con A-receptor redistribution and lamellipodium extension by neurons. Other treatments (colchicine and cycloheximide) prevented neither lamellipodium formation nor redistribution.

Endocytosis of asialo-glycoproteins and attachment to asialo-glycoproteins of hepatocytes from carcinogen-treated rats

Endocytosis and degradation of asialo-glycoprotein were investigated in hepatocytes from carcinogen-treated rats. The cells were isolated at an early stage of carcinogenesis after a sequential treatment with diethylnitrosamine and 2-acetylaminofluorene. Hepatocytes at this pre-nodular stage take up asialo-orosomucoid at a lower rate than hepatocytes from normal rats, whereas degradation of the protein occurs at a similar rate in the two populations. The lower rate of uptake appears to result from a decreased binding capacity in treated hepatocytes. The reduced binding capacity leads to slower kinetics of cell attachment to a substratum of asialo-glycoprotein. The lower number of receptors did not seem to be confined to a particular subpopulation of hepatocytes. Diploid and tetraploid hepatocytes, isolated by centrifugal elutriation, displayed the same reduction in binding capacity.

Modulation of protein synthesis and secretion by substratum in primary cultures of rat hepatocytes

Hepatocytes isolated by perfusion of adult rat liver and cultured on substrata consisting of one or more of the major components of the liver biomatrix (fibronectin, laminin, type IV collagen) have been examined for the synthesis of defined proteins. Under these conditions, tyrosine amino transferase, a marker of hepatocyte function, is maintained at similar levels in response to dexamethasone over 5 days in culture on each substratum, and total cellular protein synthesis remains constant. By contrast, there is a rapid decrease in synthesis and secretion of albumin and a 3-7-fold increase in synthesis and secretion of alpha-fetoprotein which are most marked on a laminin substratum, but least evident on type IV collagen, and an increased synthesis of fibronectin and type IV collagen. The newly synthesized matrix proteins are present in the cell layer as well as in cell secretions. The enhanced synthesis of fibronectin is less in cells seeded onto a fibronectin substratum than on laminin or type IV collagen substrata, and its synthesis by hepatocytes seeded onto a mixed substratum of laminin and fibronectin is down-regulated by fibronectin in a dose-related manner. Similarly, type IV collagen synthesis is less when the cells are seeded on the homologous matrix protein substratum than on heterologous substrata. These results indicate that hepatocytes cultured in serum-free medium on substrata composed of components of the liver biomatrix maintain certain functions of the differentiated state (tyrosine amino transferase), lose others (albumin secretion) and switch to increased synthesis of matrix components as well as fetal markers such as alpha-fetoprotein. The magnitude of these effects depends on the substratum on which the hepatocytes are cultured.

New method of hepatocyte transplantation and extracorporeal liver support

A technique has been developed by the authors that allows hepatocyte attachment on collagen-coated microcarriers resulting in prolonged hepatocyte viability and function both in vivo and in vitro. Rat hepatocytes were obtained by portal vein collagenase perfusion. Intraperitoneally transplanted microcarrier-attached normal hepatocytes into congeneic Gunn rats were functioning 3-4 weeks later, as shown by the presence and persistence of conjugated bilirubin in recipient bile, sustained decrease in serum bilirubin, uptake of Tc99m-DESIDA, and morphologic criteria. Intraperitoneal transplantation of normal microcarrier-attached hepatocytes into genetically albumin deficient rats (NAR) resulted in marked increase in plasma albumin levels (6 days without and 21 days with Cyclosporin A immunosuppression). Microcarrier-attached hepatocytes transplanted after 2 weeks of storage at -80 C into congeneic Gunn rats were viable and functional as assessed by criteria outlined above. An extracorporeal liver perfusion system was developed using the microcarrier-attached hepatocytes that was capable of synthesizing and conjugating bilirubin and synthesizing liver-specific proteins.

Attachment and long term survival of adult rat hepatocytes in primary monolayer cultures: comparison of different substrata and tissue culture media formulations

Long-term monolayer cultures of adult rat hepatocytes were tested for their ability to glucuronize phenol red and to maintain initial levels of cell proteins, glucose consumption, and lactic acid production. Lactate dehydrogenase leakage served as an index of culture status because a high value indicates cell death. Three tissue culture (TC) media formulations were the main variables introduced to determine ideal conditions for cell survival in vitro. Investigations of long-term cultures were preceded by studies of hepatocyte attachment to polystyrene surfaces. This attachment was influenced by the amount of substrate deposited and the number of cells seeded, but not by the uniformity of the substrate coating. A statistical analysis of our data revealed that in the absence of fetal bovine serum (FBS), air dried collagen (ADC) and Biomatrix (BMX) were superior to saline precipitated collagen and fibronectin as attachment substrates. In the presence of 10% FBS, all of the substrates performed equally. Chee's Medium (CEM) proved to be the best for preserving cell proteins over a time course of 28 d and Williams' E medium also performed adequately up to 14 d. The glucuronization of phenol red was at 50% of initial values at Day 7 in CEM-ADC hepatocytes in contrast to 30% for cells in Williams' E medium and 5% for cells grown in Waymouth's. At 14 d glucuronization was still present at 40% of original values in CEM-ADC cells but had ceased in the other two media. When BMX was used, none of the TC media supported glucuronization levels comparable to ADC cells.

Characteristics of a BHK cell variant defective in the cell-substratum contact process

In this paper we document the phenotypic characteristics of a novel BHK cell adhesion variant designated FN-2. Unlike parental cells, FN-2 cells did not attach to fibronectin (pFN)-coated dishes, even after 4-hr incubations on dishes treated with 100 micrograms/ml of pFN. Mixing experiments with the variant and parental cells revealed that the parental cells attached normally in the presence of a ninefold excess of variant cells and the variant cells failed to attach in the presence of a ninefold excess of parental cells. Therefore, the defect in FN-2 cells could not be explained by secretion of a factor inhibiting attachment or lack of secretion of a factor required for attachment. Also, the inability of FN-2 cells to attach to pFN-coated dishes could not be explained by an absence of cell pFN receptors since the variant cells bound normal numbers of small (ca. 0.8 micron) pFN-coated latex beads, although they phagocytosed the beads poorly compared to parental cells. Also, the variant cells were not able to bind large (5.7 or 16.8 microns) pFN-coated beads. When tested on dishes coated with ligands that, unlike fibronectin, have a high affinity for cell surface receptors, e.g., lectins and anti-BHK antibodies, FN-2 cells were observed to attach at a rate similar to that of parental cells but spread much more slowly. The phenotypic characteristics of FN-2 cells suggest that they are deficient in what previously has been called the "cell contact" process in cell adhesion. It is proposed that the cell contact process is the initial formation by an individual cell of a sufficient number of cell-substratum bonds to resist the shear forces operationally used to define "attachment," and that more cell-substratum bonds are necessary for cell attachment to large substrata (dishes or large beads) than for attachment to small substrata (small beads). The molecular defect in FN-2 cells was studied by electroblotting analysis. A high molecular weight (ca. 370 kd) glycoprotein detected by blotting with anti-BHK antibodies and ConA that was present in parental cell membranes was reduced or absent in the variant cells.

Influence of hormones and growth factors on viability, DNA, and protein content of adult hepatocytes in primary culture

The survival of adult rat hepatocytes in monolayer culture was studied in the presence of different hormones (neurotensin, oxytocin, thyrotropin releasing hormone, luteinizing hormone releasing hormone, cholecalciferol, bradykinin, substance P, aldosterone, melanocyte stimulating hormone, 3,3',5-triiodo-1-thyronine, corticosterone, human growth hormone, glucagon, insulin, progesterone, testosterone, estradiol, and dexamethasone phosphate) or growth factors (fetal bovine serum). For this purpose trypan blue exclusion, lactate dehydrogenase, and DNA and protein content were measured at 24 and 72 h of culture. 10(-7) M Dexamethasone, a mixture of eight hormones, 10% fetal bovine serum, and a combination of the latter two supplements caused a more than 64% higher DNA content at 72 h when compared to control cultures. A striking agreement of these results with changes of lactate dehydrogenase leakage was observed, whereas trypan blue exclusion gave erratic results. Considerable changes of cell arrangement apparently specific for each supplement were observed by low magnification microscopy. It is concluded that glucocorticoids and fetal bovine serum have an outstanding effect on cell viability and that DNA or protein content or both are reliable indicators of cell viability in amitotic cultures.

Amphiphilic cationic peptides mediate cell adhesion to plastic surfaces

Four amphiphilic peptides, each with net charges of +2 or more at neutrality and molecular weights under 4 kilodaltons, were found to mediate the adhesion of normal rat kidney fibroblasts to polystyrene surfaces. Two of these peptides, a model for calcitonin (peptide 1, MCT) and melittin (peptide 2, MEL), form amphiphilic alpha-helical structures at aqueous/nonpolar interfaces. The other two, a luteinizing hormone-releasing hormone model (peptide 3, LHM) and a platelet factor model (peptide 4, MPF) form beta-strand structures in amphiphilic environments. Although it contains only 10 residues, LHM mediated adhesion to surfaces coated with solutions containing as little as 10 pmoles/ml of peptide. All four of these peptides were capable of forming monolayers at air-buffer interfaces with collapse pressures greater than 20 dynes/cm. None of these four peptides contains the tetrapeptide sequence Arg-Gly-Asp-Ser, which has been associated with fibronectin-mediated cell adhesion. Ten polypeptides that also lacked the sequence Arg-Gly-Asp-Ser but were nonamphiphilic and/or had net charges less than +2 at neutrality were all incapable of mediating cell adhesion (Pierschbacher and Ruoslahti, 1984). The morphologies of NRK cells spread on polystyrene coated with peptide LHM resemble the morphologies on fibronectin-coated surfaces, whereas cells spread on surfaces coated with MCT or MEL exhibit strikingly different morphologies. The adhesiveness of MCT, MEL, LHM, and MPF implies that many amphiphilic cationic peptides could prove useful as well defined adhesive substrata for cell culture and for studies of the mechanism of cell adhesion.

Monolayer culture of parenchymal rat hepatocytes on collagen-coated microcarriers. A hepatocyte system for short- and long-term metabolic studies

A method is described for the attachment to and monolayer culture of adult rat hepatocytes on collagen-coated or fibronectin-coated microbeads or both in a chemically defined serum-free medium. Protein synthesis measured by the incorporation of [3H]leucine into protein was four-fold higher in the hepatocyte microcarrier cultures than in isolated hepatocyte suspensions. The hepatocyte microcarrier cultures showed acute responsiveness to insulin of fatty acid synthesis, glucose incorporation into glycogen, and decarboxylation of [1-14 C]pyruvate. Microcarrier-cultured hepatocytes have the combined advantages of monolayer culture and suspension systems. They are a potential tool for the study of long-term as well as acute effects of hormones.

Reduced autophagic activity, improved protein balance and enhanced in vitro survival of hepatocytes isolated from carcinogen-treated rats

Sequential carcinogen treatment (diethylnitrosamine/partial hepatectomy followed by 2-acetylaminofluorene (2-AAF] induced multiple hepatocarcinomas in rats with 100% certainty within a year. Enzyme-altered lesions, i.e. gamma-glutamyltranspeptidase (GGT)-positive and/or ATPase-negative cell foci, were numerous already at 8 weeks, and suspensions of purified hepatocytes isolated (by collagenase perfusion) at this time contained 30-40% GGT-positive cells. These hepatocyte suspensions were markedly deficient with respect to autophagic protein degradation (in comparison with cell suspensions from normal rats), and the cells lost less protein and survived much better than normal hepatocytes in culture under conditions of amino acid deprivation (which activates the autophagic mechanism). The anabolic advantage of reduced autophagy may possibly contribute to the selective outgrowth of preneoplastic cells during the earliest stage of liver carcinogenesis. Inclusion of the autophagy inhibitor 3-methyladenine in the culture medium elevated the survival of normal hepatocytes up to the level seen with hepatocytes from carcinogen-treated animals, suggesting that protection of normal cells by autophagy suppression may be a potentially interesting therapeutic principle.

Glutathione status in primary cultures of rat hepatocytes and its role in cell attachment to collagen

In primary cultures of rat hepatocytes the intracellular level of reduced glutathione (GSH) declines to approx. 50% of that observed in freshly isolated cells within 1 h of culture. Pretreatment of freshly isolated hepatocytes with diethylmaleate (DEM) to deplete GSH and inhibition of glutathione synthesis by buthionine sulfoximine (BSO) markedly decrease the proportion of cells attaching to the collagen coated culture dishes. A positive correlation between the intracellular content of GSH and the ability of hepatocytes to attach to collagen is observed. Presence of dithiothreitol (DTT) in the culture medium efficiently prevents hepatocyte attachment. A net increase in hepatocyte disulfides is also observed after the first hours of culture. The formation of disulfides seems to be essential for the attachment of hepatocytes to collagen. The depletion of GSH in the early period of culture is probably due to its regulatory function of thiol/disulfide groups in proteins and/or its involvement in the synthesis of essential cytoskeletal proteins.

Hamster hepatocytes in culture as a model for acetaminophen toxicity studies with inhibitors of drug metabolism

A hamster hepatocyte system was developed for use in studying the toxicity of acetaminophen (APAP). The cells were isolated and placed in culture conditions in petri dishes containing a film of collagen. Hepatocytes, after attachment to collagen, were exposed for various periods of time to different concentrations of APAP. Hepatocytes exposed to APAP exhibited concentration- and time-dependent GSH depletion followed by cytoplasmic enzyme leakage and an increase in malondialdehyde content (TBA-reactive material). These effects were reduced by the drug metabolism inhibitors metyrapone, piperonyl butoxide, and dithiocarb. Removal of APAP and its unbound metabolites from cells prior to 1.5 hr followed by culture in drug-free medium resulted in no observable damage to the cells over a 24-hr period. Removal of drug after longer exposure times followed by culture in fresh medium resulted in eventual cell damage. This finding showed that deleterious changes caused by APAP occurred over a 1.5-hr period after which eventual hepatocyte damage could not be reversed by removal of the drug. Further experiments showed that metyrapone and dithiocarb had some protective effect when added after APAP had been completely removed from damaged cells. This result indicates that these agents have a protective action separate from, and in addition to, their ability to inhibit APAP oxidation via cytochromes P-450.

Degradation of transplanted mitochondrial proteins by hepatocyte monolayers

Reductively [3H]methylated rat mitochondria and mitochondrial-outer-membrane vesicles and mitochondrial-outer-membrane vesicles where monoamine oxidase is irreversibly labelled by [3H]pargyline have been transplanted into hepatocytes by poly(ethylene glycol)-mediated organelle or organelle-vesicle cell fusion. During subsequent culture of hepatocyte monolayers for 4-5 days, under conditions which mimic endogenous catabolic rates in vivo the transplanted organelle proteins retain their degradation characteristics observed in vivo (e.g. mitochondria: average t 1/2 72.5 h; monoamine oxidase: t1/2 55 h). In all cases protein degradation with first-order kinetics is only observed after an initial lag period (i.e. 24-30 h after fusion). Transplantation of fluorescein-conjugated organelles showed that the fluorescent material is rapidly internalized (average t1/2 1-6 h) and uniformly distributed in the cytoplasm. During a subsequent 18-24 h period (which corresponds to the lag period for intracellular destruction of transplanted mitochondrial material) the transplanted material is translocated to assume a perinuclear distribution. The destruction of transplanted mitochondrial proteins is compared with endogenous mitoribosomally synthesized proteins (average t1/2 52.5 h). Percoll fractionation of cell homogenates containing transplanted mitochondrial outer membranes where the enzyme monoamine oxidase is irreversibly labelled with [3H]pargyline shows a distribution of enzyme similar to lysosomal acid phosphatase. After transplantation of reductively methylated 3H-labelled mitochondrial-outer-membrane vesicles the cells were treated with leupeptin to alter lysosomal density. This treatment leads to the predominant association of acid phosphatase with dense structures, whereas the 3H-labelled transplanted material predominantly does not change density. Therefore transplanted mitochondrial-outer-membrane proteins are found in intracellular vesicular structures from which the proteins are donated for destruction, at least in part, by a lysosomal mechanism.

RNA synthesis in primary cultures of adult rat hepatocytes

The ability of hepatocyte monolayers to synthesize RNA was investigated by measuring [3H]orotic acid incorporation into RNA and the total nuclear RNA polymerase activity as a function of the time in culture. The results demonstrate that primary cultures of hepatocytes maintained in a chemically defined serum- and hormone-free medium are able to synthesize RNA actively. This ability increases within the first 2 d of culture, despite the concomitant decrease in [3H]orotic acid uptake, and decreases only after 3 d. Factors such as serum, insulin, and dexamethasone, known to improve maintenance of functional hepatocytes, markedly stimulate the uptake of labeled precursor without apparently affecting the rate of RNA synthesis by cultured cells. It is suggested that the culture of adult rat hepatocytes provides a useful experimental model for the studies of hormonal regulation of transcription in liver.

Influence of cell shape and surface charge on attachment of Mycoplasma pneumoniae to glass surfaces

Attachment of Mycoplasma pneumoniae to glass is reduced in the presence of protein, and fatty acid-free bovine serum albumin is more effective than Cohn fraction V. Cultures in the early log phase (pH 7.45 to 7.25) and cultures in the stationary or decline phase (pH 6.9 to 6.4) were more sensitive to this inhibiting effect of protein-containing buffer. Treatment of the glass surface with bovine serum albumin, concanavalin A, or polylysine reduced attachment of the mycoplasma cells. The inhibiting effects of both proteins in buffer or on the glass surface could be overcome by the addition of glucose. Modification of the mycoplasma surface charge by blocking of carboxyl groups or neutralization of ionic lipids by tetracaine altered the attachment level, whereas fibronectin and its corresponding antiserum were without effect. The results suggest that the mycoplasma interaction with glass is a complex multifactorial process. In protein-free buffer both hydrophobic and electrostatic forces are involved; in protein-containing fluid, other factors seem to be involved. The energy required for this type of attachment could be necessary for maintenance of cell shape or synthesis of polypeptides.

Primary cultures and the levels of cytochrome P450 in hepatocytes from mouse, rat, hamster, and rabbit liver

Hepatocyte primary cultures (HPC) derived from rat, mouse, hamster, and rabbit liver were characterized for a variety of parameters. The conditions that maximized recovery, attachment, and survival varied between species. Hepatocytes from all four species were capable of attaching in serum-free Williams' medium E (WME), but optimal attachment as monolayer cultures was achieved for mouse and hamster HPC in medium receiving 1% calf serum supplementation. Hamster hepatocytes required additional cations, whereas rabbit and rat hepatocytes displayed maximal attachment in medium supplemented with 10% calf serum. Survival of mouse and rabbit hepatocytes after 24 h in serum supplemented media was in the order of 90%. Rat and hamster hepatocyte 24 h survival was approximately 70 and 60%, respectively, and was not significantly affected by serum supplementation. Hepatocytes from each species varied in their content of cytochrome P450 at the time of isolation and in the rate of reduction during culture. Mouse and rat hepatocytes demonstrated the most rapid decline in content during the initial 24 h in culture, whereas concentrations in rabbit hepatocytes were virtually unchanged. The rate of decline in P450 concentrations in hamster hepatocytes was intermediate between those displayed by rat and rabbit hepatocytes. These studies have delineated conditions useful for the culture of hepatocytes from four species and have documented the status of an important parameter of their functional capability.

Amino acid and energy requirements for rat hepatocytes in primary culture

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.