Rat hepatocyte primary cell cultures. III. Improved dissociation and attachment techniques and the enhancement of survival by culture medium

Challenges and Opportunities in the Design of Liver-on-Chip Microdevices

The liver is the central hub of xenobiotic metabolism and consequently the organ most prone to cosmetic- and drug-induced toxicity. Failure to detect liver toxicity or to assess compound clearance during product development is a major cause of postmarketing product withdrawal, with disastrous clinical and financial consequences. While small animals are still the preferred model in drug development, the recent ban on animal use in the European Union created a pressing need to develop precise and efficient tools to detect human liver toxicity during cosmetic development. This article includes a brief review of liver development, organization, and function and focuses on the state of the art of long-term cell culture, including hepatocyte cell sources, heterotypic cell-cell interactions, oxygen demands, and culture medium formulation. Finally, the article reviews emerging liver-on-chip devices and discusses the advantages and pitfalls of individual designs. The goal of this review is to provide a framework to design liver-on-chip devices and criteria with which to evaluate this emerging technology.

Serum-free culture of primary human hepatocytes in a miniaturized hollow-fibre membrane bioreactor for pharmacological in vitro studies

Primary human hepatocytes represent an important cell source for in vitro investigation of hepatic drug metabolism and disposition. In this study, a multi-compartment capillary membrane-based bioreactor technology for three-dimensional (3D) perfusion culture was further developed and miniaturized to a volume of less than 0.5 ml to reduce demand for cells. The miniaturized bioreactor was composed of two capillary layers, each made of alternately arranged oxygen and medium capillaries serving as a 3D culture for the cells. Metabolic activity and stability of primary human hepatocytes was studied in this bioreactor in the presence of 2.5% fetal calf serum (FCS) under serum-free conditions over a culture period of 10 days. The miniaturized bioreactor showed functions comparable to previously reported data for larger variants. Glucose and lactate metabolism, urea production, albumin synthesis and release of intracellular enzymes (AST, ALT, GLDH) showed no significant differences between serum-free and serum-supplemented bioreactors. Activities of human-relevant cytochrome P450 (CYP) isoenzymes (CYP1A2, CYP3A4/5, CYP2C9, CYP2D6, CYP2B6) analyzed by determination of product formation rates from selective probe substrates were also comparable in both groups. Gene expression analysis showed moderately higher expression in the majority of CYP enzymes, transport proteins and enzymes of Phase II metabolism in the serum-free bioreactors compared to those maintained with FCS. In conclusion, the miniaturized bioreactor maintained stable function over the investigated period and thus provides a suitable system for pharmacological studies on primary human hepatocytes under defined serum-free conditions.

The immortalisation of rat hepatocytes by transfection with SV40 sequences

Abbreviations EGTA - ethylene bis(oxyethylenenitrilo)-tetraacetic acid; F12 - Ham's F12; FBS - foetal bovine serum; HBSS - Hank's balanced salt solution; HDM - hormonally defined medium; HEPES - 4-(2-hydroxyethyl)-1-piperazine ethanesulphonic acid; NBS - new born calf serum; WME - Williams' medium E.

Safety evaluation of Evesse EPC, an apple polyphenol extract rich in flavan-3-ols

The safety of the apple polyphenol extract EvesseEPC, which is rich in flavan-3-ols, particularly epicatechin, was evaluated. Both in a bacterial reverse mutation test and a mouse lymphoma assay, EvesseEPC showed a positive response in vitro. In vivo studies (UDS test in hepatocytes, bone marrow micronucleus test and comet assay in intestinal cells) were all negative and hence Evesse EPC is considered not to have genotoxic properties in vivo. In a 90-day study in rats, EvesseEPC was administered at dietary levels of 0%, 1.25%, 2% and 3.25%. Body weights were decreased in the high-dose group in both sexes without effects on feed or water intake. In the high-dose group, thrombocytes (males) and creatinine (both sexes) were decreased, prothrombin time (males) was increased, and liver, kidneys and spleen weights were increased (males), without histological correlates. Diffuse acinar cell hypertrophy, observed in the parotid salivary glands in all treatment groups, was not considered as adverse and presumably reflected a local, reversible and adaptive response to direct contact with EvesseEPC. The NOAEL for EvesseEPC in rats was 2% in the diet, equivalent to an overall average intake of 1.3 and 1.5 g/kg body weight/day for males and females, respectively.

Effects of Tinospora cordifolia (Menispermaceae) on the proliferation, osteogenic differentiation and mineralization of osteoblast model systems in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Ancient Indian ayurvedic literature prescribes Tinospora cordifolia as a remedy to rheumatoid arthritis, inflammatory and allied diseases of musculo skeletal system.

AIM

To investigate the effects of the alcoholic extract of Tinospora cordifolia (TC) on the proliferation, differentiation and mineralization of bone like matrix on osteoblast model systems in vitro and hence its possible use as a potential anti-osteoporotic agent.

MATERIALS AND METHODS

Two in vitro osteoblast model systems were used in the study viz., human osteoblast-like cells MG-63 and primary osteoblast cells isolated from femur of rats. Cell growth and viability was assessed by standard colorimetric assays like MTT assay. The cell differentiation into osteoblastic lineage was evaluated by the activities of bone marker alkaline phosphatase. The effect of the extract on matrix mineralization was assessed by alizarin red-s staining and Von kossa staining. Cell morphology was studied by phase contrast microscopy and light microscopy (Giemsa/crystal violet staining).

RESULTS

Results indicate that the alcoholic extract of TC at a dosage of 25μg/ml stimulated the growth of osteoblasts, increased the differentiation of cells into osteoblastic lineage and increased the mineralization of bone like matrix on both the osteoblast model systems used in the study. Cell morphology studies clearly indicated the increase in cell numbers and absence of adverse change in the cell morphology on treatment with the extract.

CONCLUSION

TC extract has a potential influence on osteogenesis and hence its use could be explored as a potential anti-osteoporotic agent.

The acute, genetic, developmental and inhalation toxicology of trans-1,3,3,3-tetrafluoropropene (HFO-1234ze)

HFO-1234ze is being developed as a refrigerant, propellant, and foam-blowing agent because it has a very low global warming potential (less than 10), as contrasted to the hydrofluorocarbons with values of over 500. Several toxicology studies were conducted to develop a toxicology profile for this material. There was no lethality in mice and rats receiving single 4-hour exposures up to 103,300 or 207,000 ppm, respectively. Exposures up to 120,000 ppm did not induce cardiac sensitization to adrenalin. Rats were exposed to HFO-1234ze at levels of 5,000, 20,000, and 50,000 ppm 6 hours/day 5 days/week for 2 weeks. Predominate findings of increased liver and kidney weights and histopathological changes in the liver and heart suggested that these organs were the targets for HFO-1234ze toxicity. In a 4-week study at 1000, 5000, 10,000, and 15,000 ppm, the only organ showing treatment-related effects was the heart. In a 90-day study with exposures of 1500, 5000, and 15,000 ppm 6 hours/day 5 days/week, again, the heart was the only target organ. The findings consisted of focal and multifocal mononuclear cell infiltrates in the heart. There was no evidence of fibrosis, and, when compared to the 2- and 4-week studies, there did not appear to be an increase in severity with length of exposure. HFO-1234ze was inactive in a mouse and rat micronucleus assay, an Ames assay, and an unscheduled DNA synthesis assay and was not clastogenic in human lymphocytes. It was also not a developmental toxin in either the rat or rabbit, even at exposure levels up to15,000 ppm.

Modulating effect of Leptadenia reticulata (Retz) Wight & arn against chromate (VI)-induced immunosuppression and oxidative stress on mouse splenic lymphocytes and bone marrow derived macrophages

ETHNOPHARMACOLOGICAL RELEVANCE

Leptadenia reticulata (Retz) Wight & arn is mentioned in the ancient ayurvedic literature as an immune booster and rejuvenator.

AIMS OF THE STUDY

To investigate, the effects of different forms of the extract of Leptadenia reticulata [Aqueous extract (JAE), Padavashesha kashaya (JPK) and Tarpana kashaya (JTK)] to alleviate the experimental immunosuppression induced by the immunotoxicant chromate (VI) in vitro.

MATERIALS AND METHODS

Standard cell proliferation and cytotoxicity assays like MTT assay, trypan blue dye exclusion test, neutral red dye uptake test, NBT reduction test, determination of percentage cell survival and estimation of markers of oxidative stress were performed in the study. The study was conducted on primary cultures of mouse splenic lymphocytes and bone marrow derived macrophages.

RESULTS AND CONCLUSIONS

Treatment with all the three forms of the extract used in the study offered protection against chromate (VI)-induced immunosuppression and the overall protective effect was found to be superior in the case of the aqueous extract of Leptadenia reticulata (JAE). These results confirm that Leptadenia reticulata acts as a modulator and alleviates the immunosuppressive conditions induced by chromate (VI).

Sandwich-cultured hepatocytes: an in vitro model to evaluate hepatobiliary transporter-based drug interactions and hepatotoxicity

Sandwich-cultured hepatocytes (SCH) are a powerful in vitro tool that can be utilized to study hepatobiliary drug transport, species differences in drug transport, transport protein regulation, drug-drug interactions, and hepatotoxicity. This review provides an up-to-date summary of the SCH model, including a brief history of, and introduction to, the use of SCH, as well as methodology to evaluate hepatobiliary drug disposition. A summary of the literature that has utilized this model to examine the interplay between drug-metabolizing enzymes and transport proteins, drug-drug interactions at the transport level, and hepatotoxicity as a result of altered hepatic transport also is provided.

Morphological and functional studies of rat hepatocytes on a hydrophobic or hydrophilic polydimethylsiloxane surface

This study describes the morphological and functional behavior of rat hepatocytes on a polydimethylsiloxane (PDMS)-coated surface. Hepatocytes were cultured on hydrophobic or hydrophilic PDMS-coated surfaces in serum-free and serum-containing media. In the serum-free medium, almost all hepatocytes adhered onto the surface irrespective of the wettability, with a cell adhesion ratio of >90% at 24h. In the serum-containing medium, although they strongly adhered onto the hydrophilic surface (cell adhesion ratio >85%), the ratio on the hydrophobic surface was <15%. Furthermore, hepatocytes in the serum-free medium gradually formed spheroids irrespective of the surface characteristics; however, on the hydrophilic surface in the serum-containing medium, they maintained a monolayer configuration for up to 10 days, and their numbers gradually decreased over time. Expression levels of the functional activities (albumin secretion and ammonia removal) and the cell-cell adhesion molecules (cadherin and connexin-32) were higher in the hepatocytes that formed spheroids compared to those which assumed a monolayer configuration, and these levels were maintained for at least 10 days. These results suggest that the wettability of PDMS and the composition of the culture medium together control the cell adhesion, morphology and expression of functional genes in hepatocytes.

Primary hepatocytes: current understanding of the regulation of metabolic enzymes and transporter proteins, and pharmaceutical practice for the use of hepatocytes in metabolism, enzyme induction, transporter, clearance, and hepatotoxicity studies

This review brings you up-to-date with the hepatocyte research on: 1) in vitro-in vivo correlations of metabolism and clearance; 2) CYP enzyme induction, regulation, and cross-talk using human hepatocytes and hepatocyte-like cell lines; 3) the function and regulation of hepatic transporters and models used to elucidate their role in drug clearance; 4) mechanisms and examples of idiosyncratic and intrinsic hepatotoxicity; and 5) alternative cell systems to primary human hepatocytes. We also report pharmaceutical perspectives of these topics and compare methods and interpretations for the drug development process.

Integration of technologies for hepatic tissue engineering

The liver is the largest internal organ in the body, responsible for over 500 metabolic, regulatory, and immune functions. Loss of liver function leads to liver failure which causes over 25,000 deaths/year in the United States. Efforts in the field of hepatic tissue engineering include the design of bioartificial liver systems to prolong patient's lives during liver failure, for drug toxicity screening and for the study of liver regeneration, ischemia/reperfusion injury, fibrosis, viral infection, and inflammation. This chapter will overview the current state-of-the-art in hepatology including isolated perfused liver, culture of liver slices and tissue explants, hepatocyte culture on collagen "sandwich" and spheroids, coculture of hepatocytes with non-parenchymal cells, and the integration of these culture techniques with microfluidics and reactor design. This work will discuss the role of oxygen and medium composition in hepatocyte culture and present promising new technologies for hepatocyte proliferation and function. We will also discuss liver development, architecture, and function as they relate to these culture techniques. Finally, we will review current opportunities and major challenges in integrating cell culture, bioreactor design, and microtechnology to develop new systems for novel applications.

Effect of culture conditions on the expression and function of Bsep, Mrp2, and Mdr1a/b in sandwich-cultured rat hepatocytes

Rat hepatocytes cultured in a sandwich configuration form functional canalicular networks. The influence of extracellular matrix configuration, medium composition, and confluency on the expression and function of Bsep, Mrp2, and Mdr1a/b in sandwich-cultured (SC) rat hepatocytes was examined. Primary rat hepatocytes were: (1) maintained in various extracellular matrix sandwich configurations, (2) cultured in Dulbecco's modified Eagle's medium (DMEM), Modified Chee's medium (MCM) or Williams' E medium (WME), and/or (3) plated at decreasing cell density. Bsep, Mrp2, and Mrdr1a/b expression in day 4 SC rat hepatocytes was assessed by Western blot; function was measured by accumulation of taurocholate, 5(and 6)-carboxy-2',7'-dichlorofluorescein, and rhodamine 123, respectively, in canalicular networks. In general, the extracellular matrix conditions examined resulted in similar protein expression and function. Function of Bsep, Mrp2, and Mdr1a/b was higher in SC rat hepatocytes maintained in DMEM or WME. Mrp2 and Mdr1a/b expression, representative of total cellular content, did not always correlate directly with function, which should be reflective of canalicular membrane expression. Mrp2 expression decreased significantly as cell density decreased in SC hepatocytes. Low plating density in Biocoat plates resulted in poor canalicular network formation and reduced function of Mrp2 and Mdr1a/b. Expression and/or function of Mrp2 and Mdr1a/b in rat hepatocytes cultured in a sandwich configuration may be influenced by plating density and media type.

Hepatoprotective and antioxidant effects ofAlnus japonica extracts on acetaminophen-induced hepatotoxicity in rats

The stem bark of the Betulaceae plant Alnus japonica, which is indigenous to Korea, has been used as a popular folk medicine for hepatitis and cancer. In this study, the antioxidant activity of the crude extract and the hepatoprotective activities on acetaminophen (AAP)-induced toxicity in the rat liver were evaluated. We investigated the effect of the methanol (AJM) and solvent fracton of the stem bark of Alnus japonica (AJ) on AAP-induced hepatotoxicity in rats. In rat hepatocyte culture, pretreatment with AJM (50, 100, 150 and 200 microg/ml) significantly decreased the cytotoxicity of AAP in a dose-dependent manner. The pretreated with EtOAc and BuOH fraction led to an increase in free radical scavenging activity and a decrease in inhibition of lipid peroxidation, both superoxide dismutase and catalase prevent the hepatotoxicity by AAP in the treatment of A. japonica fraction. We conclude that AJ is an important antioxidant in AAP-induced live hepatotoxicity and that extract of AJM plays a hepatoprotective effects in the against AAP-induced cytotoxicity in cultured rat hepatocytes in vitro. Pending more evaluation for safety and efficacy, AJ can potentially be used in mitigating AAP-induced hepatotoxicity.

Analysis of in vivo and in vitro DNA strand breaks from trihalomethane exposure

BACKGROUND: Epidemiological studies have linked the consumption of chlorinated surface waters to an increased risk of two major causes of human mortality, colorectal and bladder cancer. Trihalomethanes (THMs) are by-products formed when chlorine is used to disinfect drinking water. The purpose of this study was to examine the ability of the THMs, trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and tribromomethane (TBM), to induce DNA strand breaks (SB) in (1) CCRF-CEM human lymphoblastic leukemia cells, (2) primary rat hepatocytes (PRH) exposed in vitro, and (3) rats exposed by gavage or drinking water. METHODS: DNA SB were measured by the DNA alkaline unwinding assay (DAUA). CCRF-CEM cells were exposed to individual THMs for 2 hr. Half of the cells were immediately analyzed for DNA SB and half were transferred into fresh culture medium and incubated for an additional 22 hr before testing for DNA SB. PRH were exposed to individual THMs for 4 hr then assayed for DNA SB. F344/N rats were exposed to individual THMs for 4 hr, 2 weeks, and to BDCM for 5 wk then tested for DNA SB. RESULTS: CCRF-CEM cells exposed to 5- or 10-mM brominated THMs for 2 hr produced DNA SB. The order of activity was TBM>DBCM>BDCM; TCM was inactive. Following a 22-hr recovery period, all groups had fewer SB except 10-mM DBCM and 1-mM TBM. CCRF-CEM cells were found to be positive for the GSTT1-1 gene, however no activity was detected. No DNA SB, unassociated with cytotoxicity, were observed in PRH or F344/N rats exposed to individual THMs. CONCLUSION: CCRF-CEM cells exposed to the brominated THMs at 5 or 10 mM for 2 hr showed a significant increase in DNA SB when compared to control cells. Additionally, CCRF-CEM cells exposed to DBCM and TBM appeared to have compromised DNA repair capacity as demonstrated by an increased amount of DNA SB at 22 hr following exposure. CCRF-CEM cells were found to be positive for the GSTT1-1 gene, however no activity was detected. No DNA SB were observed in PRH or F344/N rats exposed to individual THMs.

Final report on the safety assessment of Acrylates Copolymer and 33 related cosmetic ingredients

Ingredients in the Acrylates Copolymer group all contain the monomers acrylic acid or methacrylic acid or one of their salts or esters. These ingredients are considered similar in that they are uniformly produced in chemical reactions that leave very little residual monomer. Although residual acrylic acid may be as high as 1500 ppm, typical levels are 10 to 1000 ppm. There is sufficient odor if residual monomers are present to cause producers to keep levels as low as possible. These ingredients function in cosmetics as binders, film formers, hair fixatives, suspending agents, viscosity-increasing agents, and emulsion stabilizers. Concentrations may be as high as 25% if used as a binder, film former, or fixative; or as low as 0.5% if used as a viscosity-increasing agent, suspending agent, or emulsion stabilizer. These very large polymers exhibit little toxicity. In rabbits and guinea pigs, Acrylates Copolymer did produce irritation, but no evidence of sensitization was found. The principle concern regarding the use of these polymer ingredients is the presence of toxic residual monomers. In particular, although 2-ethylhexyl acrylate was not genotoxic, it was carcinogenic when applied at a concentration of 21% to the skin of C3H mice. Lower concentrations (2.5%) and stop-dose studies at high concentrations (43%) were not carcinogenic. 2-Ethylhexyl acrylate was not carcinogenic in studies using NMRI mice. Whether an increase in carcinogenesis was seen or not, there was evidence of severe dermal irritation in these 2-ethylhexyl acrylate studies. Another concern regarding residual monomers was inhalation toxicity. Although the acrylic acid monomer is a nasal irritant, exposure to the monomer from use of these polymers in cosmetic formulations would always be less than the established occupational exposure limits for nasal irritation. Although there appears to be a huge variation in the mix of monomers used in the synthesis of these polymers, they are similar in that the polymers, except for dermal irritation, are not significantly toxic, and residual monomer levels are kept as low as possible. Although the monomers may be toxic, the levels that would be found in cosmetic formulations are not considered to present a safety risk. Accordingly, these Acrylate Copolymers are considered safe for use in cosmetic formulations when formulated to avoid irritation.

The protective effects of Propolis on hepatic injury and its mechanism

AbstractPropolis (PP) is a sticky substance that is collected from plants by honeybees. The purpose of this study was to investigate the protective effects of PP on hepatotoxicity induced by acetaminophen (AA, paracetamol) and the mechanism of its hepatoprotective effect. In rat hepatocyte culture, pretreatment with PP (1, 10, 100, 200 and 400 microg/mL, 24 h) significantly decreased the cytotoxicity of AA (0.5 mm) in a dose-dependent manner. In mice, pretreatment with PP (10 and 25 mg/kg, p.o., 7 days) also decreased the mortality and the incidence and severity of hepatic necrosis induced by AA (400 mg/kg, i.p.). After treatment with PP for 7 days, the hepatic enzyme activities of cytochrome P450 monooxygenases (P450s), UDP-glucuronyltransferase, phenolsulphotransferase (PST), glutathione S-transferase (GST) were measured in both rats and mice. In rats, PP (50 and 100 mg/kg, p.o.) decreased the activity of P4502E1, but significantly increased the activities of GST and PST. On the other hand, in mice treated with PP (10 and 25 mg/kg, p.o.), the activities of P4501A2, 2B1, 3A4 and 2E1 were dramatically inhibited, and the activity of PST was significantly enhanced. These results suggest that PP has a protective effect on hepatic injury, and that its effect may be explained by inhibition of phase I enzymes and induction of phase II enzymes.

Ciprofloxacin: in vivo genotoxicity studies

The fluoroquinolone ciprofloxacin is widely used in antimicrobial therapy. It inhibits the bacterial gyrase and in high concentrations in vitro also the functionally related eukaryotic topoisomerase-II, which resulted in genotoxic effects in several in vitro tests. In order to evaluate the relevance of these findings, ciprofloxacin was tested in vivo for genotoxic activity using the following test systems: micronucleus test in bone marrow of mice, cytogenetic chromosome analysis in Chinese hamster, dominant lethal assay in male mice and UDS tests in primary rat and mouse hepatocytes in vivo. These results are compared with already published in vitro and in vivo studies with ciprofloxacin. All in vivo genotoxicity revealed no genotoxic effect for ciprofloxacin. In addition, ciprofloxacin was found to be non-carcinogenic in two rodent long-term bioassays. Therefore, ciprofloxacin is considered to be safe for therapeutic use.

Bioactivation and toxicity in vitro of HCFC-123 and HCFC-141b: role of cytochrome P450

The bioactivation and cytotoxicity in vitro of 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1,1-dichloro-1-fluoroethane (HCFC-141b), two replacements for some ozone-depleting chlorofluorocarbons (CFC), were investigated in rat liver microsomes and isolated rat hepatocytes. Both compounds were activated by cytochrome P450 to reactive metabolites, as indicated by: (i) the depletion of exogenous and cellular glutathione, (ii) the increased LDH release from hepatocytes, (iii) the loss of microsomal P450 content and activities, and (iv) the formation of free radical species observed in the presence of the two compounds. Moreover, the formation of two stable metabolites and an increased production of conjugated dienes, a marker of lipid peroxidation, were observed for both HCFC-123 and HCFC-141b. The biotransformation of both compounds by pyridine- and phenobarbital-induced rat liver microsomes and the inhibition of LDH release by 4-methylpyrazole and troleandomycin indicate that P450 2E1, 2B and, possibly, also 3A are the isoforms involved in the bioactivation and toxicity of HCFC-123 and HCFC-141b in the rat.

Carcinogen induced unscheduled DNA synthesis in mouse hepatocytes

Mouse primary liver cell cultures were examined for evidence of unscheduled DNA synthesis (UDS) following treatment with the carcinogens; dimethylnitrosamine (DMNA), diethylnitrosamine (DENA), 2-acetylaminofluorene (2-AAF), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), benzo(a)pyrene (BP), dimethylbenzanthracene (DMBA), 1,1,-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), safrole, diethylstilbestrol (DES), aflatoxin B1 (AFB1), and dieldrin and the noncarcinogens; dimethylformamide (DMF), fluorene, and pyrene. Mouse hepatocyte cultures were simultaneously treated with three concentrations of each compound and 3H-thymidine. After 24 hrs, cells were fixed and processed for autoradiography. 3H-thymidine incorporation in both experimental and control cell nuclei, as evidenced by autoradiographic grains, was quantitated microscopically. DMNA, DENA, 2-AAF, MNNG, BP, AFB1 and DMBA significantly increased UDS over untreated cells at all concentrations studied. DDT, DMF, fluorene, pyrene, safrole, DES, and dieldrin were negative for UDS in all concentrations examined. DMNA, 2-AAF and MNNG were also studied for UDS induction in 2 hr old, 1 day old and 4 day old cultures. A progressive decrease in UDS with increased time after plating was found in DMNA and 2-AAF treated cultures. After 4 days DMNA and 2-AAF induced UDS only at the highest concentrations examined (10(-3) M and 10(-4) M respectively). MNNG induced UDS at all time periods and concentrations sampled. An attempt to enhance the sensitivity of the UDS assay by inducing the mixed function oxidative enzyme activity in the hepatocytes with phenobarbital administered in vivo resulted in no statistically significant increase in UDS with DMNA, 2-AAF, MNNG, DDT, and dieldrin when compared with cells from non-induced animals.

Optimization of culture conditions for determining hepatobiliary disposition of taurocholate in sandwich-cultured rat hepatocytes

This study was undertaken to examine the influence of time and volume of collagen overlay, type of media, and media additives on taurocholate (TC) accumulation and biliary excretion in hepatocytes cultured in a collagen-sandwich configuration. Hepatocytes were isolated from male Wistar rats by in situ perfusion with collagenase, seeded onto collagen-coated 60-mm dishes, overlaid with gelled collagen, and cultured for 4 d. Experiments to examine the influence of time and volume of collagen overlay were conducted in Dulbecco's modified Eagle's medium (DMEM) + 1.0 microM dexamethasone (DEX) + 5% fetal bovine serum (FBS). Hepatocytes were overlaid at 0 h with 0.1 or 0.2 ml collagen, or at 24 h with 0.1 or 0.2 ml collagen. The influence of media type and additives was examined in hepatocytes overlaid at 0 h with 0.2 ml collagen and incubated in DMEM + 0.1 microM DEX, DMEM +/- 0.1 microM DEX + 5% FBS, Williams' medium E + 0.1 microM DEX + 1% ITS+, DMEM + 1.0 microM DEX, DMEM + 1.0 microM DEX + 5% FBS, or modified Chee's medium (MCM) + 0.1 microM DEX + 1% ITS+. [3H] TC accumulation by hepatocytes in Hank's balanced salt solution (HBSS) and Ca2+-free HBSS was measured, and the biliary-exeretion index (BEI: percentage of accumulated TC localized in the canalicular compartment) was calculated. Light microscopy and carboxydichlorofluorescein fluorescence were employed to examine the cellular and canalicular morphologies. The volume of collagen used for both the substratum and the overlay did not affect TC accumulation or biliary excretion. The BEI tended to be higher in cells overlaid at 24 h (BEI = 0.649 [0.1 ml collagen]; BEI = 0.659 [0.2 ml collagen]) compared with those overlaid at 0 h after seeding (BEI = 0.538 [0.1 ml collagen]; BEI = 0.517 [0.2 ml collagen]), although the differences were not statistically significant. Hepatocytes cultured in MCM produced consistently the lowest BEI of TC (BEI = 0.396). Differing DEX concentrations (0.1 microM versus 1.0 microM) with or without 5% FBS did not appear to have a significant effect on the BEI of TC.

Ames assays and unscheduled DNA synthesis assays on 2, 4-dichlorophenoxyacetic acid and its derivatives

2,4-dichlorophenoxyacetic acid and several of its derivatives (collectively known as 2,4-D) are herbicides used to control a wide variety of broadleaf and woody plants. The genetic toxicity in vitro of 2,4-D and seven of its salts and esters were examined by employing gene mutation in bacteria (Ames test) and induction of DNA damage and repair in rat hepatocytes. In addition, an in vivo unscheduled DNA synthesis (UDS) assay was performed on 2,4-D. There were no indications of genotoxic potential for 2,4-D acid, or any of its derivatives, in these assays. These results are consistent with the reported lack of carcinogenic potential for 2,4-D in both mice and rats.

The current status of primary hepatocyte culture

Recently, there have been significant advances toward the development of culture conditions that promote proliferation of primary rodent hepatocytes. There are two major methods for the multiplication of hepatocytes in vitro: one is the use of nicotinamide, the other is the use of a nutrient-rich medium. In the medium containing a high concentration of nicotinamide and a growth factor, primary hepatocytes can proliferate well. In this culture condition small mononucleate cells, which are named small hepatocytes, appear and form colonies. Small hepatocytes have a high potential to proliferate while maintaining hepatic characteristics, and can differentiate into mature ones. On the other hand, combining the nutrient-rich medium with 2% DMSO, the proliferated hepatocytes can recover the hepatic differentiated functions and maintain them for a long time. In this review I describe the culture conditions for the proliferation and differentiation of primary hepatocytes and discuss the small hepatocytes, especially their roles in liver growth.

Indirect dexamethasone down-regulation of the liver fatty acid-binding protein expression in rat liver

The effects of glucocorticoids on the regulation of the liver fatty acid-binding protein (L-FABP) were studied in vivo and in primary culture of hepatocytes in rats. No change in L-FABP cytosolic content and mRNA levels occurred after adrenalectomy. By contrast, a twofold decrease in L-FABP expression was found in dexamethasone (Dex) treated rats. In primary culture of rat hepatocytes, insulin did not modify the L-FABP mRNA levels, whereas Dex produced a significant decrease. This down-regulation was independent of specific glucocorticoid receptors, of alteration in the turnover of L-FABP mRNA and did not require a de novo protein synthesis. However, it was totally prevented when 320 microM oleic acid was added in the culture medium. These findings show that the dex-mediated down-regulation of the L-FABP expression found in vivo is not due to a direct endocrine effect, but is likely secondary to changes in cellular lipid metabolism.

Effects of phenobarbital and 3-methylcholanthrene induction on the formation of three glucuronide metabolites of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, NNK

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a tobacco specific carcinogen believed to be a causative agent for human lung cancer. To exert its carcinogenic potential, NNK must be metabolically activated, by alpha-hydroxylation, at either the methyl or methylene carbons adjacent to the N-nitroso group. We recently reported the presence of a glucuronide conjugate of 4-(hydroxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (alpha-hydroxymethylNNK-Gluc) in the urine of Phenobarbital (PB) treated rats, and in the media of PB induced hepatocytes incubated with NNK. PB induces the alpha-hydroxylation of NNK, which generates the aglycon, as well as several UDP-glucuronosyl transferases. In the study presented here, we compared the metabolism of NNK to alpha-hydroxymethylNNK-Gluc by PB induced, 3-methylcholanthrene (3-MC) induced and control rat hepatocytes. Media was analyzed for the products of alpha-hydroxylation, N-oxidation and glucuronidation by radioflow HPLC. PB induced both N-oxidation and alpha-hydroxylation of NNK. 3-MC did not induce N-oxidation but induced alpha-hydroxylation more than 10-fold. alpha-HydroxymethylNNK-Gluc was not detected (< 0.05% total metabolites) when control hepatocytes were incubated with 1 to 100 microM NNK. When 3-MC and PB induced hepatocytes were incubated with 1-100 microM NNK alpha-hydroxymethylNNK-Gluc, expressed as the average percent of metabolites, accounted for 0.725 +/- 0.27 and 1.35 +/- 0.24% (+/-S.D.) of the NNK metabolites, respectively. The percent of NNK metabolized to alpha-hydroxymethylNNK-Gluc is small. But this glucuronide is potentially important in NNK carcinogenesis, since its formation results in the direct conjugation of an active metabolite responsible for DNA adduct formation. When PB induced rats were injected with NNK the level of NNK hemoglobin adducts, which can serve as surrogates for DNA adducts, decreased 50% compared to control rats administered NNK. Hepatic microsomal metabolism increased 2-fold and urinary alpha-hydroxymethylNNK-Gluc increased more than 10-fold in PB treated rats. One explanation for the decrease in NNK hemoglobin adducts may be a PB induced increase in the glucuronidation of alpha-hydroxymethylNNK, the metabolite responsible for adduct formation.

Up-regulation of the expression of the gene for liver fatty acid-binding protein by long-chain fatty acids

The role of fatty acids in the expression of the gene for liver fatty acid-binding protein (L-FABP) was investigated in the well-differentiated FAO rat hepatoma cell line. Cells were maintained in serum-free medium containing 40 microM BSA/320 microM oleate. Western blot analysis showed that oleate triggered an approx. 4-fold increase in the cytosolic L-FABP level in 16 h. Oleate specifically stimulated L-FABP mRNA in time-dependent and dose-dependent manners with a maximum 7-fold increase at 16 h in FAO cells. Preincubation of FAO cells with cycloheximide prevented the oleate-mediated induction of L-FABP mRNA, showing that protein synthesis was required for the action of fatty acids. Run-on transcription assays demonstrated that the control of L-FABP gene expression by oleate was, at least in part, transcriptional. Palmitic acid, oleic acid, linoleic acid, linolenic acid and arachidonic acid were similarly potent whereas octanoic acid was inefficient. This regulation was also found in normal hepatocytes. Therefore long-chain fatty acids are strong inducers of L-FABP gene expression. FAO cells constitute a useful tool for studying the underlying mechanism of fatty acid action.

Metformin induces an agonist-specific increase in albumin production by primary cultured rat hepatocytes

Metformin (MET) is known to increase several biological effects of insulin (INS), but there is no information concerning its direct effects on protein synthesis. We studied the action of MET on albumin production by primary cultures of freshly isolated rat hepatocytes, alone or in combination with various agonists: INS, IGF-1, EGF, thyroxin, and dexamethasone. While having no effect alone, MET in vitro potentiates the effects of INS, IGF-1, and EGF. When this increasing effect toward INS was studied over a broad concentration range, MET appeared to improve low-acting INS levels and to intensify the maximal INS effects. In contrast, MET did not change the production of albumin stimulated by thyroxin or dexamethasone. Animals chronically pretreated with MET in vivo showed a higher yield of isolated hepatocytes, better attachment, and especially higher viability after liver perfusion and during cell culture. This may largely explain why basal albumin rates were higher than in in vitro-treated cells. The effect of MET in the presence of the agonists exhibited the same agonist-specificity as in vitro. Our data provide new insights into the pharmacology of MET by showing that hepatic protein synthesis is increased by MET and INS. From the specificity of action of MET towards INS, IGF-1, and EGF (but not thyroxin or dexamethasone), we hypothesize that this biguanide may act on intracellular pathways located between membrane receptors and sites of branching in the signaling cascades shared by these agonists.

Evaluation of the genetic toxicity of the organophosphate insecticide chlorpyrifos

The genetic toxicity of chlorpyrifos [O,O,-diethyl-O-(3,5,6-trichloro-2- pyridinyl)phosphorothioate, C.A.S. Number: 2921-88-2)], an organophosphate insecticide, was examined by employing several end points such as gene mutations in bacteria (Ames test) and mammalian cell cultures (CHO/HGPRT assay), cytogenetic abnormalities in mammalian cells both in vitro (rat lymphocyte chromosomal aberration test, RLCAT) and in vivo (mouse bone marrow micronucleus test) and induction of DNA damage and repair in rat hepatocytes in vitro. There was no indication of genotoxic activity for chlorpyrifos in any of these assays. These results are consistent with the reported lack of carcinogenic potential for chlorpyrifos in both mice and rats.

Improved sensitivity of the unscheduled DNA synthesis assay in primary rat hepatocytes following culture in serum-free defined media

The unscheduled DNA synthesis (UDS) assay has been used extensively for the in vitro detection of DNA damage caused by compound exposure. However, the in vitro UDS assay has been insensitive for the detection of certain chemicals, particularly nitroaromatic compounds, that are positive in bacterial mutation assays. Recently, studies have been reported which describe alterations in the hepatocyte membrane following collagenase perfusion. Independently, a method for serum-free tissue culture has been developed which results in the up-regulation of cell surface receptors and which may restore membrane functions. Fourteen compounds, including seven nitroaromatics, were evaluated in the in vitro UDS assay employing a serum-free procedure. Five compounds that were previously reported positive in the standard in vitro UDS assay were also found positive using the serum-free method. In addition, five of the nitroaromatic compounds produced positive results with the serum-free method. 1-Methyl-3-nitro-1-nitrosoguanidine and 2-acetylaminofluorene, routinely used as positive controls in the UDS assay, showed greater activity in the serum-free assay. These results suggest that the use of serum-free media improves the sensitivity of the in vitro UDS assay and that the serum-free procedure potentially offers an effective alternative to the more labor intensive and more costly in vivo UDS assay.

A continuous culture of pluripotent fetal hepatocytes derived from the 8-day epiblast of the pig

Continuous cultures of pluripotent parenchymal hepatocytes were derived from the epiblasts of 8-day-old pig blastocysts. The cells were polygonal and had phase-contrast dark, granular cytoplasm with prominent nuclei and nucleoli. These feeder-dependent cell cultures differentiated into large, multicellular, secretory, duct-like structures or formed small canaliculi between individual cells. Alternatively, the cells accumulated droplets that stained intensely with Oil Red O, a lipid-specific stain. Alpha-fetoprotein (AFP), albumin, and beta-fibrinogen mRNAs were expressed as the cells differentiated in culture. Serum-free medium that was conditioned by the cells contained transferrin, AFP, and albumin. The growth and viability of the cells were inhibited by transforming growth factor beta 1 (TGF beta 1) at concentrations > or = 1 ng/ml. The cell cultures grew slowly with doubling times of 2 to 3 d. One of the cultures, pig inner cell mass-19 (PICM-19), was passaged continuously for over 2 yr [> 100 population doublings (PD)] and appears to be an infinitely self-renewing cell population. The stem cell characteristics of the epiblast-derived fetal hepatocytes indicate that the cells may be unique for investigations of liver differentiation and organogenesis.

Colony isolation and secondary culture of fetal porcine hepatocytes on STO feeder cells

The secondary culture of non-transformed parenchymal hepatocytes has not been possible. STO feeder cell-dependent secondary cultures of fetal pig hepatocytes were established by colony isolation from primary cultures of 26-d fetal livers. The liver cells had the typical polygonal morphology of parenchymal hepatocytes. They also spontaneously differentiated to form small biliary canaliculi between individual cells or progressed further to large multicellular duct-like structures or cells undergoing gross lipid accumulation and secretion. The secondary hepatocyte cultures expressed alpha-fetoprotein (AFP), albumin, and beta-fibrinogen mRNA, and conditioned medium from the cells contained elevated levels of transferrin and albumin. STO feeder cell co-culture may be useful for the sustainable culture of hepatocytes from other species.

Synthesis of neoglycopeptides and analyses of their biodistribution in vivo to identify tissue specific uptake and novel putative membrane lectins

Complex type N-linked oligosaccharides derived from fetuin, fibrinogen and thyroglobulin were coupled to acetyltyrosine affording a series of neoglycopeptides with retention of terminal structures and the beta-anomeric configuration of their reducing end N-acetylglycosamine residue. The neoglycopeptides thus synthesized could be labelled to high specific activities with 125I in the aromatic side chain of tyrosine. Analysis of the fate of these neoglycopeptides in conjunction with inhibition with asialofetuin and oligosaccharides of defined structure in mice in vivo revealed the uptake of galactosylated biantennary compound by kidneys, in addition to the known itinerary of triantennary galactosylated complex oligosaccharide from fetuin to liver and the galactosylated biantennary chain with fucosylation in the core to bone marrows. On the other hand, the agalacto, aglucosamino biantennary chains with and without fucosylation in the core region are taken up by submaxillary glands while the conserved trimannosyl core with fucose is primarily concentrated in stomach tissue. These studies thus define new routes for the uptake of complex N-linked glycans and also subserve to identify lectins presumably involved in their recognition.

Glutathione S-transferases and P-glycoprotein in normal rat hepatocytes and hepatoma cells: analysis using flow cytometry

Using indirect immunofluorescence with fluorescein isothiocyanate-conjugated antibodies, in combination with flow cytometry (FCM), we have developed a technique to detect the alpha, mu and pi isozymes of GST in cell suspensions from normal rat liver, and in H4IIE cells, a rat hepatoma cell line. Cell suspensions fixed in 1% paraformaldehyde were observed to require cell membrane permeation with lysolecithin to allow access and binding of antibodies to immunoreactive proteins within the cytoplasm. FCM analysis indicated normal rat hepatocytes to be positive for GST alpha and mu, but not GST pi, and the H4IIE cells to be positive for all three GST isozymes. Further analysis by FCM for the expression of P-glycoprotein (mdr), a membrane-associated protein product of the multidrug resistance gene, showed an association between the presence of GST pi and mdr in the two cell types. Thus, mdr was detected in significant amounts in H4IIE cells, but not in rat hepatocytes. The method described here has potential applications in screening, sorting and further characterisation for GST pi-positive hepatocytes for mechanistic studies during sequential rat liver carcinogenesis, as well as for characterisation of human tumors for the expression of different GST isozymes and P-glycoprotein during therapeutic management.

Analysis of the adenylate cyclase signalling system, and alterations induced by culture with insulin, in a novel SV40-DNA-immortalized hepatocyte cell line (P9 cells)

An immortalized cell line, called P9, was derived from hepatocytes by transfection with SV40 DNA. These cells expressed enzyme activities characteristic of hepatocytes, namely glucose-6-phosphatase, glycogen phosphorylase, bilirubin glucuronyltransferase and both glucagon- and prostaglandin E1 (PGE1)-stimulated adenylate cyclase activities, albeit at decreased levels compared with native hepatocytes. Levels of the G-protein subunits alpha-Gi-2, alpha-Gi-3, G beta and the 'long' form of alpha-G2 (45 kDa) were approximately 4-fold higher relative to native hepatocytes, whereas those of the 'short' form of alpha-G2 (42 kDa) were lower by approximately 40%. Associated with this were marked alterations in the guanine nucleotide regulation of adenylate cyclase. Receptor-mediated stimulation, achieved by either PGE1 or glucagon, was apparent in P9 cells, although the latter was only evident upon amplification with forskolin. Glucagon-stimulated cyclic AMP accumulation in P9 cells did not exhibit desensitization, as in hepatocytes, nor was the phosphorylation of alpha-Gi-2 evident. Culture of P9 cells with insulin led to a dose-dependent decrease (EC50 0.2 +/- 0.1 nM) in the ability of PGE1 to stimulate adenylate cyclase activity, with the maximum effect attained after approximately 6 h. A comparable attenuation of stimulation was seen for glucagon- and guanine-nucleotide-stimulated adenylate cyclase activities. In cells cultured with insulin, lower levels of GTP were required to stimulate adenylate cyclase, ADP-ribosylation of the 45 kDa form of alpha-Gs with cholera toxin was attenuated, and the expression of both alpha Gi-2 and alpha-Gi-3 was increased. It is suggested that the expression of alpha-Gi-2 and alpha-Gi-3 may be directly regulated by the action of insulin in hepatocytes and P9 cells.

Comparative metabolism of bis(2-methoxyethyl)ether in isolated rat hepatocytes and in the intact rat: effects of ethanol on in vitro metabolism

The metabolism of the reproductive and developmental toxicant bis(2-methoxyethyl)ether (diglyme) was studied in isolated rat hepatocytes and in the intact rat. Male Sprague-Dawley rats (190-220 g) were used in both studies. Hepatocytes, isolated by a two-step in situ collagenase perfusion of the liver, were cultured as monolayers and incubated with [14C]diglyme at 1, 10, 30, and 50 microM for up to 48 h. For the in vivo study, rats were given single oral doses of [14C]diglyme at 5.1 mmol/kg body wt, and urine was collected for up to 96 h. Radioactive compounds in the culture medium or in the urine were separated by high performance liquid chromatography and quantified with an in-line radioactivity monitor. Metabolites were identified by comparison of their chromatographic retention times and their mass spectra with those of authentic compounds. The principal metabolite from hepatocytes and in the urine was (2-methoxyethoxy)acetic acid (MEAA). This metabolite accounted for approximately 36% of the radioactivity in the 48-h culture medium and about 67% of the administered dose in the 48-h urine. Other prominent metabolites common to both systems included 2-(2-methoxyethoxy)ethanol, methoxyacetic acid (MAA), 2-methoxyethanol, and diglycolic acid. The diglyme metabolite profiles from urine and from hepatocytes were qualitatively similar, demonstrating that, in the rat, hepatocytes serve as a good model system for predicting the urinary metabolites of diglyme. Moreover, MEAA was shown to be the metabolite best suited for use as a short-term biological marker of exposure to diglyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparisons of protein changes in human and rodent hepatocytes induced by the rat-specific carcinogen, methapyrilene

There is a growing concern that the rodent bioassay may not always serve as an appropriate model to assess the carcinogenic risk for humans exposed to certain compounds. Mechanistic research that examines the effects of a compound in rodent and man could help in the interpretation of bioassay results. This paper reports a novel use of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) technology to assess similarities and differences in the response of rodents and humans to the rat-specific hepatocarcinogen, methapyrilene (MP). A sequential examination of rodent and human hepatic proteins was conducted following in vivo exposure of rats and mice and in vitro exposure of rat, mouse, and human hepatocytes to MP. Results showed that covalent modifications observed in rats and mice in vivo were duplicated both qualitatively and quantitatively in the corresponding in vitro systems and that these modifications correlated with carcinogenic susceptibility. Covalent modifications in human hepatocytes were minimal despite exposure to concentrations of MP that were 6-fold higher than those used in rodent hepatocytes. These studies suggest that in the case of MP the rat is not the most appropriate model for assessing the human situation. Furthermore, these data show that in vitro-in vivo comparisons based on 2-D PAGE may provide adjunctive information for extrapolating rodent toxicity/bioassay results to human risk assessment.

Crude liver membrane fractions as substrate preserve liver-specific functions in long-term, serum-free rat hepatocyte cultures

Over time, rat hepatocytes cultured on collagen lose the capacity to express liver-specific functions. The influence on this degradation process of an alternative substratum--crude membrane fractions prepared from the liver of the same rat strain--was investigated. Freshly isolated rat hepatocytes were cultured in serum-free Williams E medium supplemented with aprotinin, selenium, dexamethasone, and insulin in flasks coated with a mixture of rat liver crude membrane fractions:collagen type I (100:1). The cells adhered firmly, exhibiting minimal spreading and remaining grouped in columns or in cell islands, and retained their liver-specific functions for more than 1 wk. Hepatocytes secreted substantially higher amounts of albumin than cells cultured on collagen-coated dishes, and on Days 1 and 9 in culture the total P-450 content was 72 and 40%, respectively, of that of freshly isolated cells. On Day 6, the 7-ethoxyresorufin-O-deethylase and the aldrin epoxidase activities were still more than 50% that of freshly isolated hepatocytes. Exposure to phenobarbital on Days 3 to 6 increased the total cytochrome P-450 content twofold; exposure to 3-methylcholanthrene increased the activity of the corresponding cytochrome P-450 isoforms to 20 times that observed in untreated cultures and 6 times that observed in freshly isolated cells. Thus, given the ease with which they are prepared, the use of crude membrane fractions combined with culture medium supplemented with aprotinin and selenium can facilitate the preparation of reproducible cultures suitable for long-term in vitro pharmacotoxicologic studies using rat hepatocytes.

DNA alkylation and mutagenicity of related hydroxypropylating and methylating agents in V79 cells

N-Nitrosobis (2-hydroxypropyl) amine (BHP) and N-nitrosobis (2-oxopropyl) amine (BOP) require metabolism to be carcinogenic and mutagenic. This metabolism produces hydroxypropylating and methylating alkylating species. To measure the effects of these species, we compared the action of direct-acting model compounds that are hydroxypropylating or methylating agents with those of BHP and BOP. Mutagenicity in V79 cells and the alkylation of V79 cell DNA were measured. The model compounds were ethyl-N-nitroso (2-oxopropyl) carbamate (NOPC), a methylating agent, and its 2-hydroxypropyl congener (NHPC), a hydroxypropylating agent. BHP and BOP were metabolized by hepatocytes from male Syrian hamsters. At the highest dose (2 mM) BOP produced 12 times more mutants than BHP but only 2.5 times more O6 methylguanine (O6MeG) than BHP. When a pancreas duct homogenate was used, 87 (BOP) and six (BHP) mutants/10(6) survivors were measured. When hepatocytes (not a homogenate) were used to metabolize BOP, 351 mumol O6MeG/mol guanine (G) and 39 mumol O6 (2-hydroxypropyl) G (O6HpG)/mole G were found in V79 DNA. When a pancreas duct homogenate was used BHP produced O6HpG (65 mumol/mol G) and BOP O6MeG (20 mumol/mol G). NOPC produced five times more mutants than NHPC, over the range of doses. At the highest dose (10 microM) it produced less (70%) O6alkylG than NHPC. These data show that methylation was a more mutagenic lesion than hydroxypropylation. There was no evidence of a correlation between mutagenicity and the formation of O6alkylG.

Cytotoxicity of tacrine and velnacrine metabolites in cultured rat, dog and human hepatocytes

Clinical trials with tacrine (THA) and its principal (1-OH) metabolite (velnacrine) for the treatment of Alzheimer's disease have been hampered by adverse hepatic events that were undetected in preclinical studies. As part of integrated in vivo/in vitro efforts to characterize the role of metabolites in these events, cultured cells were evaluated for their suitability for further mechanistic studies. The relative cytotoxic potentials of THA, three monohydroxy metabolites of THA (including velnacrine, a racemate), the two velnacrine enantiomers, and several known and suspected dihydroxy velnacrine metabolites were determined. Cytotoxicity was evaluated in 24-hour cultures by morphology and by the Neutral Red Uptake Assay. All test articles were evaluated in primary rat hepatocytes and in a human hepatoma cell line (HepG2). THA and velnacrine were also tested in a rat hepatoma cell line (H4) and in primary dog hepatocytes. The metabolic competency of each cell type was determined. Sensitivity to THA and velnacrine was greatest in H4 cells, followed by primary rat and HepG2 cells; dog cells were least sensitive. In HepG2 cells, THA was clearly more cytotoxic (LC50:54 micrograms/ml) than its monohydroxy metabolites (LC50 values: 84 to 190 micrograms/ml); dihydroxy velnacrine metabolites were the least cytotoxic (LC50 values:251 to 434 micrograms/ml); the relative order was comparable in primary rat hepatocytes. Roles for reactive metabolites and/or altered metabolic capabilities of Alzheimer's patients are suggested.

Mutation of V79 cells by N-dialkylnitrosamines after activation by hamster pancreas duct cells

Pancreas duct epithelial cells (DEC), isolated from hamsters and cultured for up to 25 days, were able to metabolize N-nitrosobis(2-oxopropyl)amine (BOP) to species that were mutagenic in V79 cells. There was no decline in the nitrosamine-activating ability of DEC over the period of observation (25 d). DEC activated N-nitrosobis(2-hydroxypropyl)amine (BHP), N-nitrosodiethylamine (DEN), N-nitrosodimethylamine (DMN) and N-nitrosomethyl(2-oxopropyl)amine (MOP) and BOP in the same assay, although the mutation frequencies for BHP, DEN and DMN were barely different from that for the controls (4 +/- 1 mutants/10(6) cells). The mutation frequencies for a dose of 0.1 mM were BHP, 2 +/- 1; BOP, 113 +/- 7; DEN, 8 +/- 1; DMN, 5 +/- 2; and MOP, 18 +/- 3 (mutants/10(6) cells; means +/- SE). When hepatocytes were used the mutation frequencies were BHP, 3 +/- 1; BOP, 60 +/- 3; DEN, 8 +/- 2; DMN, 8 +/- 2; and MOP, 121 +/- 10. BOP was toxic to the DEC at doses above 0.1 mM. Experiments in which co-factors were omitted from the medium suggested that an isoform(s) of the cytochrome P-450 IIIA family was involved, directly or indirectly, in BOP activation.

Evaluation of genotoxicity of tert.-butylhydroquinone in an hepatocyte-mediated assay with V79 Chinese hamster lung cells and in strain D7 of Saccharomyces cerevisiae

tert.-Butylhydroquinone (TBHQ) has been reported to be genotoxic in some short-term assays but non-genotoxic in others. We have examined cytotoxicity and genotoxicity of TBHQ, a principal metabolite of the phenolic antioxidant 2(3)-tert.-butyl-4-hydroxyanisole (BHA), in an hepatocyte-mediated assay with V79 Chinese hamster lung cells including both sister-chromatid exchange (SCE) and thioguanine-resistance (TGR) endpoints. The ability of BHA and of TBHQ to elicit a genotoxic response in Saccharomyces cerevisiae strain D7 was also investigated. In V79 cytotoxicity tests, TBHQ without hepatocytes produced a 50% reduction in colony formation at 4.2 micrograms/ml and was lethal to 100% of the cells at concentrations above 5 micrograms/ml. At partially cytotoxic dose levels, (0.17-3.4 micrograms/ml of medium), TBHQ sometimes increased significantly the frequency of SCE. TBHQ also produced sporadic statistically significant increases in the mutation frequency at the HGPRTase (TGR) gene locus when tested alone or with activation by rat or hamster hepatocytes. Mitotic gene conversion and reverse mutation were not induced in strain D7 of Saccharomyces cerevisiae by exposure to BHA or to TBHQ for 4 h at concentrations as high as 200 micrograms/ml for BHA or 500 micrograms/ml for TBHQ, either alone or with activation by rat-liver S9. Incubation of the yeast cells with BHA or TBHQ for 24 h in growth medium without activation also did not induce genotoxic activity. The slight and sporadic response to TBHQ in the V79 test system may indicate weak genotoxicity which is sensitive to slight differences in test conditions. The classification and test strategies adopted for compounds such as TBHQ could have important implications for regulatory decisions and for the validation of short-term tests.

Effects of selected secondary metabolites of Fusarium moniliforme on unscheduled synthesis of DNA by rat primary hepatocytes

The Fusarium moniliforme mycotoxins--fusarin C, fumonisin B1, moniliformin and bikaverin--were evaluated for genotoxicity by their ability to induce unscheduled DNA synthesis (UDS) in primary rat hepatocytes. Isolated hepatocytes were exposed to several concentrations of moniliformin (5.0-500 microM), bikaverin (1.0-500 microM), fumonisin B1 (0.5-250 microM), or fusarin C (1.0-100 microM). Aflatoxin B1, a known inducer of UDS, was included as a positive control. UDS was determined by autoradiography of cells after their exposure to [3H]thymidine. The highest doses of fusarin C and bikaverin caused cell death, but no cytotoxicity was observed in cells exposed to moniliformin or fumonisin B1. Fumonisin B1, moniliformin and bikaverin were not genotoxic in the UDS assay. The results of the UDS assay with fusarin C were inconclusive since a marginal effect on UDS was obtained.