Short term cultures for drug assays: general considerations

Cell Culture in the Biological Evaluation of Dental Materials: A Review

Systematic research on dental materials began after World War I. For a long time the research was focused on the physical properties of the materials, and papers dealing with biological aspects were scarce. By the late 1950s a growing interest in biological responses to dental materials developed, and from the 1970s biological and physical evaluations were deemed equally important (1).

Mammalian cells have been maintained in vitro since the early years of this century, but the use of cultured cells to evaluate the effects of chemicals and drugs is a more recent occurrence. The first practical application of this technique was in pharmacological investigations (2), but applications in other fields soon followed, and in 1955 the first studies were reported where a cell culture technique had been applied to the biological evaluation of dental materials (3,4). Since then the use of cell culture systems in dental materials research has grown rapidly. The main application has been for the assessment of cytotoxic effects, and the purpose of this paper is to review different test methods and discuss some facets of the problems posed by the cytotoxicity testing of dental materials.

3 Final Report on the Safety Assessment of Methylparaben, Ethylparaben, Propylparaben, and Butylparaben

The Parabens are esters of p-hydroxybenzoic acid (PHBA) and are the most commonly used as preservatives in cosmetic formulations. Data obtained from chronic administration studies indicate that Parabens are rapidly absorbed, metabolized, and excreted.

Acute chronic and subchronic toxicity studies in animals indicate that Parabens are practically nontoxic by various routes of administration. Methylparaben and Ethylparaben at 100 percent concentration were slightly irritating when instilled into the eyes of rabbits.

Numerous in vitro mutagenicity studies indicate that the Parabens are non-mutagenic. Methylparaben was noncarcinogenic when injected in rodents or when administered intravaginally in rats. Cocarcinogenesis studies on Propyl- and Methylparaben were negative. Teratogenic studies on Methyl- and Ethylparaben were also negative.

Parabens are practically nonirritating and nonsensitizing in the human population with normal skin. Paraben sensitization has been reported when Paraben-containing medicaments have been applied to damaged or broken skin. Photo-contact sensitization and phototoxicity tests on product formations of Methyl-, Propyl-, and/or Butylparaben gave no evidence of significant photoreactivity.

It is concluded that Methylparaben, Ethylparaben, Propylparaben, and Butylparaben are safe as cosmetic ingredients in the present practices of use.

Creeping, drinking, dying: the cinematic portal and the microscopic world of the twentieth-century cell

Film scholars have long posed the question of the specificity of the film medium and the apparatus of cinema, asking what is unique to cinema, how it constrains and enables filmmakers and audiences in particular ways that other media do not. This question has rarely been considered in relation to scientific film, and here it is posed within the specific context of cell biology: What does the use oftime-based media such as film coupled with the microscope allow scientists to experience that other visualization practices do not? Examining three episodes in the twentieth-century study of the cell, this article argues that the apparatus ofmicrocinematography constitutes what might be thought of as a technical portal to another world, a door that determines the experience of the world that lies on the other side of it. In this case, the design of apparatuses to capture time-lapsed images enabled the acceleration of cellular time, bringing it into the realm of human perception and experience. Further, the experience of the cellular temporal world was part of a distinct kind of cell biology, one that was focused on behavior rather than structure, focused on the relation between cells, and between the cell and its milieu rather than on cell-intrinsic features such as chromosomes or organelles. As such, the instruments and technical design of the microcinematographic apparatus may be understood as a kind of materialized epistemology, the history of which can elucidate how cinema was and is used to produce scientific knowledge.

Final Amended Report on the Safety Assessment of Methylparaben, Ethylparaben, Propylparaben, Isopropylparaben, Butylparaben, Isobutylparaben, and Benzylparaben as used in Cosmetic Products

Parabens is the name given to a group of p-hydroxybenzoic acid (PHBA) esters used in over 22,000 cosmetics as preservatives at concentrations up to 0.8% (mixtures of parabens) or up to 0.4% (single paraben). The group includes Methylparaben, Ethylparaben, Propylparaben, Isopropylparaben, Butylparaben, Isobutylparaben, and Benzylparaben. Industry estimates of the daily use of cosmetic products that may contain parabens were 17.76 g for adults and 378 mg for infants. Parabens in cosmetic formulations applied to skin penetrate the stratum corneum in inverse relation to the ester chain length. Carboxylesterases hydrolyze parabens in the skin. Parabens do not accumulate in the body. Serum concentrations of parabens, even after intravenous administration, quickly decline and remain low. Acute toxicity studies in animals indicate that parabens are not significantly toxic by various routes of administration. Subchronic and chronic oral studies indicate that parabens are practically nontoxic. Numerous genotoxicity studies, including Ames testing, dominant lethal assay, hostmediated assay, and cytogenic assays, indicate that the Parabens are generally nonmutagenic, although Ethylparaben and Methylparaben did increase chromosomal aberrations in a Chinese Hamster ovary cell assay. Ethylparaben, Propylparaben, and Butylparaben in the diet produced cell proliferation in the forestomach of rats, with the activity directly related to chain length of the alkyl chain, but Isobutylparaben and Butylparaben were noncarcinogenic in a mouse chronic feeding study. Methylparaben was noncarcinogenic when injected subcutaneously in mice or rats, or when administered intravaginally in rats, and was not cocarcinogenic when injected subcutaneously in mice. Propylparaben was noncarcinogenic in a study of transplacental carcinogenesis. Methylparaben was nonteratogenic in rabbits, rats, mice, and hamsters, and Ethylparaben was nonteratogenic in rats. Parabens, even at levels that produce maternal toxicity, do not produce fetal anomalies in animal studies. Parabens have been extensively studied to evaluate male reproductive toxicity. In one in vitro study, sperm were not viabile at concentrations as low as 6 mg/ml Methylparaben, 8 mg/ml Ethylparaben, 3 mg/ml Propylparaben, or 1 mg/ml Butylparaben, but an in vivo study of 0.1% or 1.0% Methylparaben or Ethylparaben in the diet of mice reported no spermatotoxic effects. Propylparaben did affect sperm counts at all levels from 0.01% to 1.0%. Epididymis and seminal vesicle weight decreases were reported in rats given a 1% oral Butylparaben dose; and decreased sperm number and motile activity in F1 offspring of rats maternally exposed to 100 mg/kg day–1 were reported. Decreased sperm numbers and activity were reported in F1 offspring of female rats given Butylparaben (in DMSO) by subcutaneous injection at 100 or 200 mg/kg day–1, but there were no abnormalities in the reproductive organs. Methylparaben was studied using rats at levels in the diet up to an estimated mean dose of 1141.1 mg/kg day–1 with no adverse testicular effects. Butylparaben was studied using rats at levels in the diet up to an estimated mean dose of 1087.6 mg/kg day–1 in a repeat of the study noted above, but using a larger number of animals and a staging analysis of testicular effects—no adverse reproductive effects were found. Butylparaben does bind to estrogen receptors in isolated rat uteri, but with an affinity orders of magnitude less than natural estradiol. Relative binding (diethylstilbesterol binding affinity set at 100) to the human estrogen receptors α and β increases as a function of chain length from not detectable for Methylparaben to 0.267 ± 0.027 for human estrogen receptor α and 0.340 ± 0.031 for human estrogen receptor β for Isobutylparaben. In a study of androgen receptor binding, Propylparaben exhibited weak competitive binding, but Methylparaben had no binding effect at all. PHBA at 5 mg/kg day–1 subcutaneously (s.c.) was reported to produce an estrogenic response in one uterotrophic assay using mice, but there was no response in another study using rats (s.c. up to 5 mg/kg day–1) and mice (s.c. up to 100 mg/kg day–1) and in a study using rats (s.c. up to 100 mg/kg day–1). Methylparaben failed to produce any effect in uterotrophic assays in two laboratories, but did produce an effect in other studies from another laboratory. The potency of Methylparaben was at least 1000 × less when compared to natural estradiol. The same pattern was reported for Ethylparaben, Propylparaben, and Butylparaben when potency was compared to natural estradiol. In two studies, Isobutylparaben did produce an estrogenic response in the uterotrophic assay, but the potency was at least 240,000 × less than estradiol. In one study, Benzylparaben produced an estrogenic response in the uterotrophic assay, but the potency was at least 330,000 × less than estradiol. Estrogenic activity of parabens and PHBA was increased in human breast cancer cells in vitro, but the increases were around 4 orders of magnitude less than that produced by estradiol. Parabens are practically nonirritating and nonsensitizing in the population with normal skin. Paraben sensitization has occurred and continues to be reported in the case literature, but principally when exposure involves damaged or broken skin. Even when patients with chronic dermatitis are patch-tested to a parabens mix, parabens generally induce sensitization in less than 4% of such individuals. Many patients sensitized to paraben-containing medications can wear cosmetics containing these ingredients with no adverse effects. Clinical patch testing data available over the past 20 years demonstrate no significant change in the overall portion of dermatitis patients that test positive for parabens. As reviewed by the Cosmetic Ingredient Review (CIR) Expert Panel, the available acute, subchronic, and chronic toxicity tests, using a range of exposure routes, demonstrate a low order of parabens' toxicity at concentrations that would be used in cosmetics. Parabens are rarely irritating or sensitizing to normal human skin at concentrations used in cosmetics. Although parabens do penetrate the stratum corneum, metabolism of parabens takes place within viable skin, which is likely to result in only 1% unmetabolized parabens available for absorption into the body. The Expert Panel did consider data in the category of endocrine disruption, including male reproductive toxicity and various estrogenic activity studies. The CIR Expert Panel compared exposures to parabens resulting from use of cosmetic products to a no observed adverse effect level (NOAEL) of 1000 mg/kg day–1 based on the most statistically powerful and well-conducted study of the effects of Butylparabens on the male reproductive system. The CIR Expert Panel considered exposures to cosmetic products containing a single parabens preservative (use level of 0.4%) separately from products containing multiple parabens (use level of 0.8%) and infant exposures separately from adult exposures in determining margins of safety (MOS). The MOS for infants ranged from ~6000 for single paraben products to ~3000 for multiple paraben products. The MOS for adults ranged from 1690 for single paraben products to 840 for multiple paraben products. The Expert Panel considers that these MOS determinations are conservative and likely represent an overestimate of the possibility of an adverse effect (e.g., use concentrations may be lower, penetration may be less) and support the safety of cosmetic products in which parabens preservatives are used.

Methylparaben potentiates UV-induced damage of skin keratinocytes

For many years, methylparaben (MP) has been used as a preservative in cosmetics. In this study, we investigated the effects of ultraviolet-B (UVB) exposure on MP-treated human skin keratinocytes. HaCaT keratinocyte was cultured in MP-containing medium for 24h, exposed to UVB (15 or 30 mJ/cm(2)) and further cultured for another 24h. Subsequent cellular viability was quantified by MTT-based assay and cell death was qualified by fluorescent microscopy and flow cytometry. Oxidative stress, nitric oxide (NO) production and cellular lipid peroxidation were measured using fluorescent probes. In addition, activation of nuclear factor kappa B and activator protein-1 was assessed by electro-mobility gel-shift assay. Practical concentrations of MP (0.003%) had a little or no effect on cellular viability, oxidative stress, NO production, lipid peroxidation and activation of nuclear transcription factors in HaCaT keratinocytes. Low-dose UVB also had little or no effect on these parameters in HaCaT keratinocytes. However, UVB exposure significantly increased cell death, oxidative stress, NO production, lipid peroxidation and activation of transcription factors in MP-treated HaCaT keratinocytes. These results indicate that MP, which has been considered a safe preservative in cosmetics, may have harmful effects on human skin when exposed to sunlight.

An evaluation of the in vitro cytotoxicities of 50 chemicals by using an electrical current exclusion method versus the neutral red uptake and MTT assays

According to the 2001 National Institutes of Health guidance document on using in vitro data to estimate in vivo starting doses for acute toxicity, the performance of the electrical current exclusion method (ECE) was studied for its suitability as an in vitro cytotoxicity test. In a comparative study, two established in vitro assays based on the quantification of metabolic processes necessary for cell proliferation or organelle integrity (the MTT/WST-8 [WST-8] assay and the neutral red uptake [NRU] assay), and two cytoplasm membrane integrity assays (the trypan blue exclusion [TB] and ECE methods), were performed. IC50 values were evaluated for 50 chemicals ranging from low to high toxicity, 46 of which are listed in Halles Registry of Cytotoxicity (RC). A high correlation was found between the IC50 values obtained in this study and the IC50 data published in the RC. The assay sensitivity was highest for the ECE method, and decreased from the WST-8 assay to the NRU assay to the TB assay. The consistent results of the ECE method are based on technical standardisation, high counting rate, and the ability to combine cell viability and cell volume analysis for detection of the first signs of cell necrosis and damage of the cytoplasmic membrane caused by cytotoxic agents.

Evaluation of the health aspects of methyl paraben: a review of the published literature

Methyl paraben (CAS No. 99-76-3) is a methyl ester of p-hydroxybenzoic acid. It is a stable, non-volatile compound used as an antimicrobial preservative in foods, drugs and cosmetics for over 50 years. Methyl paraben is readily and completely absorbed through the skin and from the gastrointestinal tract. It is hydrolyzed to p-hydroxybenzoic acid, conjugated, and the conjugates are rapidly excreted in the urine. There is no evidence of accumulation. Acute toxicity studies in animals indicate that methyl paraben is practically non-toxic by both oral and parenteral routes. In a population with normal skin, methyl paraben is practically non-irritating and non-sensitizing. In chronic administration studies, no-observed-effect levels (NOEL) as high as 1050 mg/kg have been reported and a no-observed-adverse-effect level (NOAEL) in the rat of 5700 mg/kg is posited. Methyl paraben is not carcinogenic or mutagenic. It is not teratogenic or embryotoxic and is negative in the uterotrophic assay. The mechanism of cytotoxic action of parabens may be linked to mitochondrial failure dependent on induction of membrane permeability transition accompanied by the mitochondrial depolarization and depletion of cellular ATP through uncoupling of oxidative phosphorylation. Parabens are reported to cause contact dermatitis reactions in some individuals on cutaneous exposure. Parabens have been implicated in numerous cases of contact sensitivity associated with cutaneous exposure; however, the mechanism of this sensitivity is unknown. Sensitization has occurred when medications containing parabens have been applied to damaged or broken skin. Allergic reactions to ingested parabens have been reported, although rigorous evidence of the allergenicity of ingested paraben is lacking.

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.

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.

Comparative studies on in vitro human tumor clonogenic assay (HTCA) and in vivo nude mouse-isotope assay (NM-IA)

Comparative studies between the in vitro human tumor clonogenic assay (HTCA) and nude mouse-isotope assay (NM-IA), in which the final evaluation was made with 3H-thymidine incorporations of tumor cells transplanted into nude mice, were performed simultaneously on 60 fresh human tumors. Tissues used included 27 gastric cancers, 10 breast cancers, 7 colorectal cancers, 4 gallbladder cancers, 4 sarcomas, 3 lymphomas, and 5 other tumors. Mitomycin C (MMC), 5-fluorouracil (5-FU), cyclophosphamide (CPM) and adriamycin (ADM) were tested. The overall evaluable rate was 66.7 per cent in HTCA and 83.3 per cent in NM-IA, respectively. When the per cent survival in HTCA and the per cent inhibition in NM-IA less than 50 per cent was defined as drug sensitive, the drug sensitive rates of MMC, 5-FU, CPM, and ADM were 23.1, 16.7, 11.8, and 27.8 per cent in HTCA and 17.6, 18.4, 22.4, and 25.5 per cent in NM-IA, respectively. Although statistically significant correlations between the results of HTCA and those of NM-IA were obtained for MMC and ADM, no correlation was observed for 5-FU and CPM. The overall predictive accuracy rate of clinical response was 83.3 per cent (true positive rate 50 per cent and true negative rate 92.9 per cent) in HTCA and 76.0 per cent (true positive rate 37.5 per cent and true negative rate 93.8 per cent) in NM-IA, respectively.

Screening of toxic compounds in mammalian cell cultures

The cytotoxic concentrations of about 100 randomly selected drugs and chemicals, tested on HeLa cells in the MIT-24 system and/or in primary cultures of fetal chicken cells, were compared with the lethal doses and/or concentrations of the agents in the mouse and in man. Most agents (80%) had a similar toxicity in vitro and in vivo, suggesting a lethal interference in man with basal functions common to all specialized human tissues as well as cultured cells, i.e., basal cytotoxicity. This high frequency of basally cytotoxic agents opens possibilities for screening chemicals for toxicity and for studying cytotoxic mechanisms with a standard battery of a few appropriate cell tests. This battery may be used in three ways: (1) to study cytotoxic mechanisms of all chemicals, and apply the resulting knowledge to understanding toxicity in man of basally cytotoxic agents; (2) to supplement conventional animal tests in acute toxicity test programs; (3) to screen chemicals and extracts for their potential basal cytotoxicity. To validate these ideas and to select suitable tests for the battery, results from cytotoxicity tests on a wide variety of chemicals in several in vitro systems must be compared with one another and with the toxicity of the agents in animals and man.

Toxicology investigations with cell culture systems

This review concerns some of the cell culture systems that are most frequently used in toxicology investigations. In particular, it sets out to evaluate the effectiveness of these cell culture systems in assessing the toxic potential of chemicals. Metabolic studies and general and specific toxicology investigations are highlighted. Specific toxicology investigations relate to the effects of the tests substances on the highly specialized functions typical of the cell systems chosen. The general toxicology investigations include most of the other studies where differentiated or undifferentiated cells have been used to evaluate the effects of the tested substances on common basic biochemical processes essential for life. Lastly, we have attempted to focus attention on the most promising applications of cell cultures in toxicology studies for the near future and to identify those areas where further research is needed. Because of the several excellent reviews that already exist, we have decided not to consider cell cultures utilized in screening potential mutagens and carcinogens. We have also excluded investigations of drug therapeutic effects and action mechanisms of drugs.

Preliminary studies on the validity of in vitro measurement of drug toxicity using HeLa cells. I. Comparative in vitro cytotoxicity of 27 drugs

Combined drug toxicity to HeLa cells was studied in vitro with use of the microtitre MIT-24 test system. Whether drug toxicity to HeLa cells is representative of drug toxicity to other cultivated cells was investigated by a comparison of the MIT-24 toxicity of 27 drugs to HeLa cells with their toxicity to various permanent cell lines and more differentiated primary cell cultures as reported in the literature, together with original recordings of the MIT-24 toxicity of 9 of the drugs to human fetal kidney cells. A similarity of drug toxicity to all cell types was found. Thus the MIT-24 recordings may be representative of a basal drug cytotoxicity, probably corresponding to local drug irritation and to causal systemic drug toxicity.

Toxicity to HeLa cell of 205 drugs as determined by the metabolic inhibition test supplemented by microscopy

The toxicity of 205 drugs to HeLa cells was evaluated by the Metabolic Inhibition Test supplemented by microscopy. Two end points of cyto-inhibition were estimated; total and partial inhibition after 24 h, based on absence or scarcity of spindle-shaped cells, respectively, and total and partial inhibition after 7 days, based on different degrees of basic pH change of the phenol red included in the cell medium. Direct drug-induced pH changes and precipitates in the cultures were also recorded. Many drugs were found to induce a culture zone with a particularly low pH after 7 days of incubation, at concentrations below the cyto-inhibitory concentration. Forty-three drugs regularly caused this hyperacid reaction, while 44 drugs caused the reaction irregularly. Since the reaction was always continuous with the cyto-inhibitory zone, it was provisionally judged to represent excitatory cell injury. Since many of the drugs which regularly induced the reaction are also known to induce proliferation of the endoplasmic reticulum in various cells, the reaction may be related to this and allied effects. Many drugs that are known to accumulate in cells displayed a high inhibitory toxicity, which might have been due to the paucity of cells in the test system. However, the high 7-day inhibitory toxicity shown by antineoplastic and some anti-inflammatory drugs, including triamterene and disulfiram, may constitute a genuine antimetabolic drug action. Seven grand mal antiepileptics were only very slightly toxic as compared with their precipitating tendency, which may be of significance in their therapeutic action.

The interface of toxicology and tissue culture and reflections on the carnation test

The convergence of an imperative for expanded testing of chemicals before they are released into the environment and the maturation of tissue culture as an important tool for biomedical research, has led to the development of in vitro methods for toxicological evaluation. Of the several facets of the interface -- screening, mechanisms, personnel monitoring, and risk assessment -- screening has the broadest interface. The success which has been achieved to date stems from a recognition of the limitations as well as the attributes of in vitro research, extensive validation of specific tests (especially for mutagenesis and carcinogenesis), and the use of test batteries rather than single tests.

Screening of toxic compounds in tissue culture

To screen toxicity of chemicals most often easily manageable cultures of less differentiated cells have been used. This work includes 3 fields: (i) Screening of chemicals and fermentation broths for their cytoinhibitory effect, to predict antineoplastic activity. A related practical approach is to achieve optimal antitumour drug therapy by testing drugs on cultures of tumour cells from the patient. (ii) Screening of metal and plastic materials used in medicine, surgery and dentistry for their cytoinhibitory effect to predict local irritation. (iii) Screening of the mutagenicity or transformation capacity of chemicals in tissue culture, to predict their carcinogenicity. In addition, organ-specific cultures of most specialized cells (hepatocytes, ova, nerve cells, heart cells, skin cells, respiratory mucosa, and macrophages) have also been used to predict drug action on corresponding targets in the body. The author's group has focused on 2 new uses of standard cells for screening chemical toxicity: (i) Comparisons of in vitro cytotoxicity with in vivo toxicity of 85 randomly selected drugs indicated that for most drugs a systemic lethal action was brought about by cytotoxicity. A screening model is advocated by which results of cytotoxicity tests are compared with systemic toxicity in vivo to evaluate the systemic cytotoxicity of chemicals. (ii) Combinations of compounds with a cytotoxic lethal action in man indicated by the previous method have been screened in vitro for their combined systemic toxicity. By systematic comparison of results from standardized in vitro tests with in vivo toxicity, steps have been taken to resolve the question of the relevance of screening in tissue culture and to contribute to the development of an emerging subdiscipline to toxicology -- in vitro cytotoxicology.

Cell models in the study of mechanisms of toxicity

Cell models, particularly in vitro systems, allow studies of toxicological mechanisms to be made under controlled conditions. One way that such mechanisms can be studied is by determining the reproducible changes that toxins induce, at the electron microscopic level, in the structure of cultured cells. A detailed description of such a study is given and includes preparation of the cell model, treatment of the cells, assessment of toxin-induced changes, and some general conclusions derived from experiments with this cell model. Other models which have been used for toxicological studies are also discussed with reference to advantages, limitations and potential applications.