Toxicology investigations with cell culture systems

Evaluation of nanoparticle uptake in co-culture cancer models

Co-culture models are currently bridging the gap between classical cultures and in vivo animal models. Exploring this novel approach unlocks the possibility to mimic the tumor microenvironment in vitro, through the establishment of cancer-stroma synergistic interactions. Notably, these organotypic models offer a perfect platform for the development and pre-clinical evaluation of candidate nanocarriers loaded with anti-tumoral drugs in a high throughput screening mode, with lower costs and absence of ethical issues. However, this evaluation was until now limited to co-culture systems established with precise cell ratios, not addressing the natural cell heterogeneity commonly found in different tumors. Therefore, herein the multifunctional nanocarriers efficiency was characterized in various fibroblast-MCF-7 co-culture systems containing different cell ratios, in order to unravel key design parameters that influence nanocarrier performance and the therapeutic outcome. The successful establishment of the co-culture models was confirmed by the tissue-like distribution of the different cells in culture. Nanoparticles incubation in the various co-culture systems reveals that these nanocarriers possess targeting specificity for cancer cells, indicating their suitability for being used in this illness therapy. Additionally, by using different co-culture ratios, different nanoparticle uptake profiles were obtained. These findings are of crucial importance for the future design and optimization of new drug delivery systems, since their real targeting capacity must be addressed in heterogenous cell populations, such as those found in tumors.

Choice and standardization of test protocols in cytotoxicology: A multicentre approach

A major problem that interferes with the introduction of in vitro tests for toxicological risk assessment is that of defining reliable standardized protocols. This issue was approached in the present study with an interlaboratory comparison of three cytotoxicity assays detecting chemical toxicity as impairment of cell viability in confluent cultures, reduction of colony forming ability, and inhibition of cell proliferation over 3 days of treatment. The study was performed using V79 cells, which are unable to activate indirectly-acting xenobiotics, and six chemicals with different mechanisms of action: two antioxidants (butylated hydroxyanisole and butylated hydroxytoluene), an inhibitor of protein synthesis (cycloheximide), an alkylating agent requiring metabolic activation (cyclophosphamide), an uncoupler of oxidative phosphorylation (dinitrophenol), and a genotoxic metal salt (potassium dichromate). The three tests produced the same rank of relative toxic potency for the tested chemicals, based on LC(50) values. The cell viability test appeared to be the most suited for the screening of unknown chemicals, given its simplicity and better reproducibility.

Metabolite analysis in positron emission tomography studies: examples from food sciences

Substances of various chemical structures can be labelled with appropriate positron emitting isotopes and applied as tracer compounds in PET examinations. Using dynamic data acquisition protocols, time-activity curves of radioactivity uptake in organs can be derived and the measurements of tissue tracer concentrations can be translated into quantitative values of tissue function. However, analysis of metabolites of these tracers regarding their nature and distribution in the living organism is an essential need for the quantitative analysis of PET measurements. In addition, metabolite analysis contributes to the interpretation of the images obtained as well as to the identification of pathological changes in metabolic pathways. This paper reports on representative examples of radiolabelled compounds which might be of importance in food science (e.g., amino acids, polyphenols, and model compounds for advanced glycation end products (AGEs)). Typical procedures of analysis (radio-HPLC, radio-TLC) including pre-analytical sample preparation are described. Specific challenges of the method, e.g., trace amounts of radiolabelled compounds and the influence of the often very short half-lives of positron-emitting nuclides used are highlighted. Representative results of analyses of plasma, urine, and tissue samples are presented and discussed in terms of the metabolic fate of the tracers.

Toxicology investigations with cell culture systems: 20 years after

From almost 20 years the "in vitro" model has gained a wide ground in toxicological investigation, providing advanced tools, reliable protocols, mechanistic information. These advancements have been done thanks to different approaches, addressed at improving chemical testing and validating procedures, at exploring the cellular and molecular basis of toxicity, at studying the modifications that xenobiotics undergo in the cellular environment. In this review the most advanced cellular models, the mechanisms of cell death, the techniques to monitor gene activation, following chemical exposure, is highlighted. Moreover the more recent in vitro models to approach the biotransformation issue will be presented.

Decrease in toxic potential of mixed tensides maintained below the critical micelle concentration: an in vitro study

Sodium lauryl sulphate (SLS) is an anionic tenside widely utilized in commercial topical preparations that may cause skin irritation. It has been shown that the barrier damage caused by SLS in vivo is lower when SLS is used in combination with other tensides which are able to reduce the critical micelle concentration (CMC). The aim of our study was to evaluate if the cytotoxic effect of SLS is reduced by the association with different tensides also at concentrations well below the CMC. Normal human keratinocytes from plastic surgery were grown in serum-free medium. At subconfluency, the cells were treated with SLS at a dose of 0.0025% in combination with cocamidopropyl betaine, Tween 20 and Tween 80 at the minimum toxic dose. Following tenside treatment, the culture medium was changed, and after 24 h the cells were collected for (3)H-thymidine incorporation, the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay and neutral red (NR) uptake. The cytotoxic effect on normal human keratinocytes, as evaluated by (3)H-thymidine incorporation, MTT assay and NR uptake, was significantly decreased by the combination with all the tested tensides. The correlation between cytotoxicity and physical properties was also studied by a conductimetric assay to investigate the mechanism involved in this toxicity reduction.

Effect of cyclosporin A in Lewis rats in vivo and HeLa cells in vitro

The aim of this study was to compare the effect of cyclosporin A (CsA) in inbred Lewis rats with published assessment of immunotoxicity in 'classical' outbred Wistar rats. A second purpose was to consider the contribution of a panel of in vitro assays in cell cultures when added to an immunotoxicity study in vivo. The in vivo effect of CsA was investigated in a 28-day subacute immunotoxicity study in male Lewis rats at three different concentrations: 1.25, 5 and 20 mg kg(-1). The highest dose of CsA exceeded the maximum tolerated dose. A drop in body, spleen and popliteal lymph node weight of exposed animals displayed symptoms of toxicity. At a high toxic dose, haematological changes showed a decrease in the leucocyte count and in the percentage of lymphocytes, and an increase in the percentage of polymorphonuclear leucocytes. The haematocrit was significantly dose-dependently suppressed in all rats exposed to CsA. A similar dose-dependent depression of the mean cell volume of erythrocytes was found in rats given high and middle doses of CsA. The phagocytic activity of polymorphonuclear leucocytes and monocytes also was significantly dose-dependently suppressed. No significant changes in primary antibody response to sheep erythrocytes or in vitro proliferative response of spleen lymphocytes to mitogens were found in those rats.A battery of in vitro cytotoxicity methods was selected for the evaluation of metabolic and functional activity of subcellular organelles (mitochondria, lysosomes) and for the detection of drug-induced superoxide-mediated damage in HeLa cells. This cell line was chosen because it has a lower activity of superoxide dismutase (SOD) than normal cells and is sufficiently sensitive for the detection of the induction of oxygen radicals. The in vitro results indicated a direct relationship between CsA cytotoxicity and a change in the mitochondrial enzyme activity, as well as an induction of superoxide production. The results of the study indicated that a combination of selected in vivo and in vitro methods is an inexpensive way to obtain more complex information on cell status affected by xenobiotics.

Thiram-induced cytotoxicity is accompanied by a rapid and drastic oxidation of reduced glutathione with consecutive lipid peroxidation and cell death

The toxic effect of thiram, a widely used dithiocarbamate fungicide, was investigated in cultured human skin fibroblasts. Cell survival assays demonstrated that thiram induced a dose-dependent decrease in the viable cell recovery. Thiram exposure resulted in a rapid depletion of intracellular reduced glutathione (GSH) content with a concomitant increase in oxidized glutathione (GSSG) concentration. Alteration of glutathione levels was accompanied by a dose-dependent decrease in the activity of glutathione reductase (GR), a key enzyme for the regeneration of GSH from GSSG. Thiram-exposed cells exhibited increased lipid peroxidation reflected by enhanced thiobarbituric acid reactive substances (TBARS) production, suggesting that GSH depletion and the lower GR activity gave rise to increased oxidative processes. To investigate the role of decreased GSH content in the toxicity of thiram, GSH levels were modulated prior to exposure. Pretreatment of fibroblasts with N-acetyl-L-cysteine (NAC), a GSH biosynthesis precursor, prevented both lipid peroxidation and cell death induced by thiram exposure. In contrast, thiram cytotoxicity was exacerbated by the previous depletion of cellular GSH by L-buthionine-(S,R)-sulfoximine (BSO). Taken together, these results strongly suggest that thiram induces GSH depletion, leading to oxidative stress and finally cell death.

An evaluation of thiram toxicity on cultured human skin fibroblasts

Thiram is widely used in agriculture as a fungicide and, to a lesser extent, as a vulcanizing agent in the rubber industry. In spite of the extensive use of thiram, knowledge on its toxicity and health risk remains limited, and few investigations have been performed to assess specific damage at the cellular and subcellular level. We report here the cytotoxic effects of thiram on cultured human skin fibroblasts. Our results demonstrated that thiram exposure induced a dose- and time-dependent decrease in the viable cell recovery with 100% cell death observed with a concentration of 5.0 mg/l. As judged by morphological changes and biochemical criteria, thiram-mediated cell death was not of the apoptotic but seemed to be of the necrotic type. This cell death was not associated with a modification of gene expression of different constituents of the extracellular matrix. A late increase of lactate production was evident after thiram treatment, suggesting a mitochondrial metabolic pathway dysfunction as reported by other authors using similar compounds. However, this phenomenon appeared as a secondary response to the toxic action of thiram. The cytotoxic effect of thiram is possibly due to an oxidant effect inherent to the structure of thiram and the interaction between thiram and vital cellular molecules.

The application of in vitro data in the derivation of the acceptable daily intake of food additives

The acceptable daily intake (ADI) for food additives is commonly derived from the NOAEL (no-observed-adverse-effect level) in long-term animal in vivo studies. To derive an ADI a safety or uncertainty factor (commonly 100) is applied to the NOAEL in the most sensitive test species. The 100-fold safety factor is considered to be the product of both species and inter-individual differences in toxicokinetics and toxicodynamics. Although in vitro data have previously been considered during the risk assessment of food additives, they have generally had no direct influence on the calculation of ADI values. In this review 18 food additives are evaluated for the availability of in vitro toxicity data which might be used for the derivation of a specific data-derived uncertainty factor. For the majority of the food additives reviewed, additional in vitro tests have been conducted which supplement and support the short- and long-term in vivo toxicity studies. However, it was recognized that these in vitro studies could not be used in isolation to derive an ADI; only when sufficient in vivo mechanistic data are available can such information be used in a regulatory context. Additional short-term studies are proposed for the food additives which, if conducted, would provide data that could then be used for the calculation of data-derived uncertainty factors.

In vitro testing of tensides employing monolayer cultures: a comparison with results of patch tests on human volunteers

Evaluation of the irritant potential of new products or ingredients prior to human testing is generally performed in vivo on animals. However, according to the 6th amendment and following updates of the European Community directive on cosmetic products (93/35/EEC), animal testing will be banned when suitable substitutes will be available. To know whether in vitro tests for assessment of skin irritancy provide results approaching human conditions, comparisons have to be made between data deriving from in vitro tests and skin response in humans. The aim of our study was to assess the validity of the monolayer culture system of normal human keratinocytes as a model for the evaluation of the irritant effects of detergents, by comparing in vitro cell culture data to in vivo acute skin irritancy effects of cocamidopropyl betaine (CAPB), an amphoteric compound, Tween 20 (TW20) (polysorbate 20) and Tween 80 (TW80) (polysorbate 80), representing nonionic compounds, applied to the skin of 24 healthy volunteers at a concentration similar to that employed in commercial products. As parameters for cytotoxicity, cell proliferation, cell membrane integrity and cell metabolism were assessed by cell counts, thymidine incorporation, MTT conversion, and Neutral Red uptake. In order to increase the sensitivity of the in vivo evaluation, bioengineering methods for assessment of the effects of test products on the skin were employed. Whereas all 4 in vitro methods ranked the tensides according to their toxicity in the following order: CAPB>SLS>TW20>TW80, both in vivo methods agreed in identifying SLS as the most irritating substance. Moreover, as compared with the irritation potential on human skin, all 4 in vitro tests overestimated the toxicity of CAPB. This suggests that the keratinocyte monolayer cell culture technique cannot directly replace in vivo methods, and that data obtained by this method should be interpreted cautiously.

Comparative study of the biotransformation of bepridil analogs in isolated liver cells from one rat. Relationships between structure and in vitro liver toxicity

The biotransformation of several analogs of the anti-calcium agent bepridil was studied comparatively in liver cells isolated from one rat. Three types of metabolites were identified by mass spectrometry, resulting from three phase I reactions: hydroxylation, N-debenzylation and pyrrolidine ring opening. The amount of each bepridil analog untransformed after 18 h of incubation depended on its liver toxicity rather than on its concentration in the culture medium. The proportion of phase I metabolites identified remained constant regardless of toxicity. The difference delta c (in %) between the initial concentration of the analog tested and the sum of the concentrations of untransformed material and of identified metabolites decreased with the increasing hepatocyte toxicity. The analogs tested were responsible for the liver toxicity. The presence of substituents in different positions on the N-phenyl moiety increased liver toxicity; ortho-substituted analogs were more toxic than para- or meta-substituted ones.

Fluorescence assay for the detection of adherent Candida yeasts to target cells in microtest plates

We describe an assay based on photometric analysis for the measurement of adherence of Candida species to epithelial target cells (Vero cell line). Adherent Candida cells were detected by staining the cells with the fluorescent dye Calcofluor white (CFW), which binds to chitin and glucan in the yeasts. The tests were performed on microtest plates, which were analysed automatically by fluorescence plate readers. The assay is based on the following steps: (i) coating of the microtest plates with target cells (e.g. Vero cells); (ii) infection with Candida: (iii) staining of Candida with CFW; (iv) rinsing to remove non-adherent Candida cells and unbound dye; (v) detection of adherent fluorescent Candida cells. The test was able to detect 4 x 10(4) cells ml-1. The standard deviation was +/- 8%. Day-to-day variation was +/- 10% at most. The adherence of strains of different Candida species was assayed by a standard procedure. The results confirmed the order of adherence, with C. albicans ranking first, followed by C. tropicalis, C. parapsilosis and C. glabrata.

In vitro evaluation of dental materials

Biocompatibility has been described as the ability of a material to perform with an appropriate host response in a specific application. Appropriate host response means no (or a tolerable) adverse reaction of a living system to the presence of such a material. An adverse reaction may be due to the toxicity of a dental material. Therefore toxicity may be regarded as one reason for nonbiocompatibility of a dental material. The toxicity of a dental material can be evaluated by in vitro tests, animal experiments and clinical trials. There exists a variety of different in vitro test methods. The most widely used biological systems for toxicity screening of dental materials are cell cultures. Cell cultures for toxicity screening of dental materials are valuable tools for understanding their biological behavior, if the limitations of the methods are taken into consideration, especially concerning the interpretation of the results. Further research should concentrate on better simulations of the in vivo situation in cell cultures. In this review the applications of various cell culture methods to evaluate the cytotoxicity of a wide range of dental materials, e.g. metals, alloys, polymers and cements, are described.

Different ability in PC12 clones to recover from MMC toxicity following NGF treatment

PC12 cells were cloned, and from their ability to form neurite-like processes 3 clones were selected: NGF-highly sensitive clone (HS), -moderately sensitive clone (MS), and -insensitive clone (IS). These clones were tested for the presence of specific NGF receptors by measuring the binding of 125I-labeled NGF. All 3 clones were capable of binding NGF, but the HS clone had more NGF receptors than the MS and IS clones. The effects of methyl mercuric chloride (MMC) and/or nerve growth factor (NGF) on these clones were tested. The HS clone was a little more susceptible to MMC than the MS and IS clones. When NGF was added to the culture medium in addition to MMC, cell recovery was observed. The tendency toward recovery was more prominent in the HS clone than in the IS one. Recovery in the MS clone was intermediate. These results suggest that NGF treatment can contribute to functional recovery of PC12 cloned cells from the cytotoxic effects of MMC depending on their ability to react to NGF.

Detecção da citotoxicidade de materiais biocompatíveis nas linhagens celulares MRC-5, HeLa e RC-IAL

A sensibilidade de uma linhagem celular diplóide e duas heteroplóides, para a detecção de citotoxicidade através do método de difusão em camada de ágar sobre culturas celulares, foi avaliada experimentalmente com solução de ácido ascórbico em diferentes concentrações e, na prática, frente a 562 amostras de 21 diferentes materiais industriais enviados para análise na Seção de Culturas Celulares do Instituto Adolfo Lutz. A linhagem celular heteroplóide designada RC-IAL apresentou, em relação às linhagens MRC-5 e HeLa, maior sensibilidade porque revelou a presença de efeito citotóxico nas menores concentrações utilizadas (10 e 25 ug/ml) do ácido ascórbico e apresentou maior diâmetro do halo citotóxico em 15 amostras e igual diâmetro em 16 das 43 amostras (7,6%) que resultaram positivas. Nas 43 amostras positivas, a linhagem MRC-5 não revelou citotoxicidade em 3 amostras de espuma e 1 de resina acrílica. O polivinilcloreto (PVC) e o polietileno, raramente revelaram positividade, enquanto plástico, algodão e resinas acrílicas revelaram citotoxicidade ao redor de 5%. Em vista dos resultados é discutida a proposta da utilização da linhagem RC-IAL e HeLa para a continuidade das futuras análises solicitadas ao Instituto Adolfo Lutz

Toxicity of amphotericin B emulsion to cultured canine kidney cell monolayers

The effect of amphotericin B in an emulsion formulation on the integrity of monolayers of kidney cells has been studied. Whereas a conventional solubilized amphotericin formulation (Fungizone, Squibb) caused a loss in monolayer integrity at concentrations above 1 microgram mL-1, the emulsion formulation had no measurable effect on confluence at amphotericin concentrations up to 100 micrograms mL-1. The emulsion retained a comparable antifungal activity to that of Fungizone against Saccharomyces cerevisiae in suspension culture. These results parallel the observed erythrocyte lysis data obtained previously using amphotericin B emulsions, and suggest that the emulsion formulation may have a lower toxicity and improved therapeutic potential over existing formulations.

Survey of the QSAR and in vitro approaches for developing non-animal methods to supersede the in vivo LD50 test

Quantitative structure-activity relationship (QSAR) studies and in vitro studies in which correlations with LD50 have been sought are reviewed. QSAR methods have shown some success in relating LD50 to certain physicochemical properties of the compound, particularly lipophilicity, but have been less successful in correlating LD50 with electronic properties of molecules (related to reactivity) or structural variables. It is concluded that insufficient evidence is available to determine whether QSAR methods can be of general use in predicting the acute toxicity (LD50) of chemicals, and that until further work is undertaken to develop QSARs for a much wider range of homologous series of compounds, this situation is unlikely to be resolved. New chemical descriptors that are more directly relevant to the mechanism of toxic action of the chemical should be identified. Cytotoxicity in vitro is poorly correlated with LD50, but good correlations have been obtained between toxicity in vivo and in vitro, using systems in which the toxic endpoint reflects the probable mechanism(s) of acute toxicity of the test chemical (e.g. the assessment of neurotoxins using neural cell systems). Therefore, it seems that the successful application of in vitro methods requires a better understanding of the mechanisms of acute toxicity in vivo and the development of mammalian cell culture systems that can model more closely the metabolic fate of the chemicals in vivo.

Evaluation of the Cytotoxicity of 18 Compounds in Six Rat Cell Lines

A comparison of the potential of different cell lines as a screening system for predicting general toxicity was made by measuring the cytotoxicities (CT50) of 18 compounds in six rat cell lines. The criterion for cytotoxicity was failure of the cells to attach to the substratum, which was assessed at two incubation times: 24 hours and 7 days (168 hours).

For nine of the compounds tested, an increased incubation time resulted in increased cytotoxicity; in these cases, the CT50 values at 168 hours were lower than those at 24 hours. For the majority of the compounds, the CT50 values obtained using liver, lung, intestine, kidney, heart or skin rat cell lines did not differ markedly from one line to another.

These results are discussed in terms of the similar in vitro susceptibilities of different cell types obtained from the same species.

Effect of cadmium on membrane potential in isolated rat hepatocytes

The effect of cadmium (Cd) on rat hepatocytes upon short term exposure was studied by focusing on the integrity of mitochondria and on the possible consequences of its disturbance, such as alterations in plasma membrane potential and loss of cell viability. Changes in the potential of mitochondrion and plasma membranes were monitored using [3H]triphenylmethylphosphonium (TPMP+) and [14C]SCN- probes, respectively. Isolated rat hepatocytes were exposed to increasing CdCl2 concentrations for short time periods (30-120 min). Cd measurement by atomic absorption showed that the cells efficiently accumulated Cd, as did mitochondria in situ. In CdCl2-treated cultures, it was observed that the release of TPMP+, which revealed a drop in the mitochondrial membrane potential, was time- and concentration-dependent, and that the first significant efflux was caused by a 30-min exposure to 89 microM CdCl2. No significant change in plasma membrane potential, as judged from the increase in the uptake of SCN-, was detected after 30 min, suggesting the greater precocity of the mitochondrial attack. Finally, the release of lactate dehydrogenase (LDH) occurred only after 2 h of exposure, reflecting ultimate stages of cell injury induced by Cd. These results suggest that Cd induces an alteration in mitochondrial function in hepatocytes which may lead to the loss of plasma membrane potential and cell viability. The study therefore adds further evidence of the role of mitochondria as primary targets in Cd-induced cytotoxicity.

In vitro screening for anticonvulsant-induced teratogenesis in neural primary cultures and cell lines

To establish inherent potential for the induction of neural tube defects the ability of selected anticonvulsant agents to interfere with cell division has been established in vitro using an antiproliferative assay in clonal cell lines and a cytotoxicity assay using primary cultures of cerebral cortex neurons at different stages of development. In order to evaluate the relative toxicities of these agents their in vitro effects were determined at 2-3 times the plasma therapeutic level. By these procedures valproate and the benzodiazepines, diazepam and clonazepam, exerted a potent antiproliferative action which could not be attributed to increased cytotoxicity. In contrast phenytoin was markedly cytotoxic but was without an antiproliferative action. This cytotoxicity was most pronounced during the periods of extensive fibre outgrowth. When compared to epidemiological and animal study data, agents which inhibited cell proliferation within twice therapeutic concentration were consistently associated with major neural tube malformations. However phenytoin, found to be positive in the cell cytotoxicity assay, is not associated with neural tube malformations but rather is primarily associated with mental retardation. Thus assessment of antiproliferative activity of anticonvulsant drugs may be one criterion for identification of teratogenic potential during neurulation.

The response of primary cultured adult mouse sensory neurons to ethanol, propanol, acetaldehyde and acrolein treatments

Primary cultures of adult mouse sensory neurons maintained for 8 days in vitro (8 div), in both the presence of non-neuronal cell (NNC) outgrowth and in NNC-reduced cultures, were exposed to doses of ethanol, propanol, acetaldehyde and acrolein. The effects on cell viability were monitored: LD50's of 600 microM acrolein and 100 mM propanol were obtained after 24 h exposures and after 48 h with 1 mM acetaldehyde and 500 mM ethanol. Morphological effects were evident by scanning electron microscopy with sub-acute doses for each agent, using both lower concentrations and shorter exposures. Membrane pitting of the perikaryon and a reduction in the proportion of neurons bearing neurites were common signs of toxic insult. The neurites of treated cells were thicker and more irregular than those of untreated cells; this proved a good indicator of specific neurotoxicity rather than merely a cytotoxic response. Fetal calf serum in the medium lessened the response of neurons to ethanol treatments. Comparison with other in vitro studies suggests these primary cultures are a more sensitive system than established cell lines of neuronal origin for use in neurotoxicity testing.

Toxicological Responses to Zinc, Copper and Cadmium in a Rat Intestinal Cell Line

An intestinal epithelial cell line from neonatal rat duodenum (IEC-17) was used as a model for investigating metal toxicity.

In this paper, we have further characterised toxic effects on IEC-17 cells following exposure to two physiological metals, zinc (Zn2+) and copper (Cu2+) and one non-physiological metal, cadmium (Cd2+). Time-effect experiments showed that the duration of the exposure affected the extent of cell damage only when Cu2+ and Cd2+ were used. During the first 48 hours of Zn2+ exposure, the cells were seriously affected, but subsequently were able to recover. On the other hand, a colony forming ability test and morphological observations showed a special sensitivity of this cell line to Cu2+. A possible explanation is suggested in relation to extracellular matrix formation.

Macromolecular metabolism of a differentiated rat keratinocyte culture system following exposure to sulfur mustard

A method for producing a stratified, squamous epithelium in vitro by cultivating rat keratinocytes on nylon membranes has been developed in this laboratory. This epidermal-like culture is being used to obtain a better understanding of the mechanism of skin vesication after topical exposure to the sulfur mustard bis(beta-chloroethyl) sulfide (BCES) dissolved in a selected solvent. Radiolabeled macromolecular precursors (thymidine, uridine, and leucine) have been used to study the effect of BCES on the synthesis of DNA, RNA, and protein, respectively, after topical exposure to the mustard at concentrations of 0.01-500 nmol/cm2 dissolved in 70% dimethyl sulfoxide (DMSO). From these and other studies it has been determined that exposure to even the low concentration of 0.01 nmol BCES/cm2 for 30 min results in significant inhibition of [3H]thymidine incorporation, although complete recovery occurs by 24 h. Significant inhibition of [3H]uridine and [14C]leucine incorporation is observed only after exposure to much higher concentrations of BCES (10-500 nmol/cm2). This suggests a very early lesion in macromolecular metabolism with DNA being the primary target.

Neurotoxic effects of methamphetamine assessed in three-dimensional reaggregate tissue cultures

Three-dimensional, rotation-mediated, reaggregate tissue cultures formed from dissociated fetal rostral mesencephalic tegmental (RMT) and corpus striatal (CS) or frontal cortical (FCx) cells were used to study methamphetamine neurotoxicity. Analysis of dopamine (DA), serotonin (5-HT) and gamma-aminobutyric acid (GABA) levels using HPLC techniques revealed decreases in RMT-CS and RMT-FCx reaggregate DA and 5-HT levels after treatment between 14 and 21 days in culture with methamphetamine in concentrations ranging from 10(-6)M to 10(-3)M. Dopamine cell numbers in RMT-CS and RMT-FCx reaggregates were estimated after visualization by histofluorescent techniques. Methamphetamine treatment caused decreases in DA cell numbers which paralleled the decreases in endogenous DA levels. Estimates of the accumulation of exogenous DA by RMT-CS reaggregates treated with methamphetamine showed that the amount of accumulation per cell remained fairly constant despite marked reductions in total DA cell numbers. This suggests that the reductions in endogenous DA levels following methamphetamine were secondary to loss of entire DA neurons rather than of a portion of the terminal axonal fields in the surviving neurons. Reaggregate tissue cultures are a useful tool in the study of potential neurotoxic effects of new or untested psychotherapeutic agents.

The effects of cadmium on a clonal osteogenetic cell, MC3T3-E1: inhibition of calcification and induction of metallothionein-like protein by cadmium

To clarify the effects of cadmium (Cd) on bone formation, a clonal osteogenetic cell, MC3T3-E1, was used in the present study. After 24 h of culture, Cd at 1 ppm and above decreased DNA synthesis and alkaline phosphatase activity, but Cd at 1.5 ppm caused no significant decrease in collagen content. The cells treated with Cd (0.03-1.0 ppm) for 24 h showed the dose-dependent effects on metallothionein-like protein synthesis. The marked increase of Cd content unbound to metallothionein (MT)-like protein with cadmium at 1 ppm may be responsible for the toxic effects of cadmium. After 10 days of culture, the accumulation of 45Ca to the cell layer decreased with increasing level of cadmium at 0.03 and 0.1 ppm. The cadmium-treated cell layer showed a weaker reaction to histochemical staining for mineral compared with control culture. This result suggests that Cd inhibits an initial process of calcification.

Progress and problems in evaluating and validating alternative assays in toxicology

Various techniques have been proposed and subsequently developed as potential replacements for whole-animal topical toxicology assays. Comparisons of in vitro and in vivo endpoints, the solubility of test agents, solvent effects, interactions between components of complex test samples and the standardization of data presentation are factors that influence not only individual laboratory results but interlaboratory reproducibility and the acceptance of newly developed alternative methods. Representative alternative test systems for evaluating topical toxicity are discussed. Examples of problems, data and solutions based on the authors' experience and on experience in other laboratories are reviewed. Specific problems in choosing endpoints, comparing results, recognizing responses of different types of target cell, evaluating the influences of support media in culture and interpreting published animal-based data are included.

Cadmium toxicity in kidney cells. Resistance induced by short term pretreatment in vitro and in vivo

Epithelial cells from the kidney were freshly isolated from rats pretreated by daily subcutaneous doses of CdCl2 in vivo (0.5-2 mg Cd/kg X 5). Such cells were incubated in vitro in media with different concentrations of cadmium chloride (0-200 micrograms Cd/ml). There was no inhibition of cell growth in such cells. However, in cells isolated from non-treated rats, in vitro exposure to the same concentrations of CdCl2 caused a dose dependent decrease in viability. When cells, isolated from non-treated rats were pretreated in vitro with CdCl2 (10 micrograms/ml) and subsequently exposed to cadmium chloride (0-200 micrograms/ml), a protective effect was observed, which was similar to the one observed in cells isolated from animals pretreated with CdCl2. The concentration of metallothionein in the cells treated with cadmium was increased. A lower uptake of cadmium chloride, in vitro has been observed in kidney cells pretreated in vivo or in vitro compared to nonpretreated cells. Subcellular distribution studies indicate that Cd-distribution was similar in pretreated and non-pretreated cells, but concentrations were generally lower in the pretreated cells. The decreased uptake of Cd by pretreated kidney cells is a sign of Cd-interference with cellular function. These changes are suggested as a contributing mechanism to the prevention of acute toxic effects of cadmium on the kidney.

Cytotoxic effects of wheat gliadin-derived peptides

The peptic-tryptic-cotazym (PTC) digest, obtained from bread wheat gliadin by simulating in vivo protein digestion, was more active than the PTC-digest of durum wheat gliadin in reversibly inhibiting HEp-2 cell proliferation and in increasing cellular acid phosphatase. Colony-forming ability of the cells was not affected by treatment with both bread or durum wheat gliadin peptides. The peptic-tryptic (PT) digest of bread wheat gliadin also showed agglutinating activity of HEp-2 cells.