Dermal carcinogenicity study by mouse-skin painting with 2,4-toluendediamine alone or in representative hair dye formulations

Dermal exposure to toluene diisocyanate and respiratory cancer risk

Human exposure to toluene diisocyanate (TDI) occurs mainly through inhalation of vapors in occupational settings where TDI is produced or used, but dermal exposure to TDI is also possible during some operations. Because of a recent epidemiology study reporting a possible association with lung cancer risk in workers with potential dermal exposure to TDI, we evaluated the evidence from epidemiological, toxicological, and toxicokinetic studies to assess whether it is likely that dermal exposure to TDI can cause human respiratory cancers. We found that the reported associations with respiratory cancers in the epidemiology studies do not support TDI as a causal factor, as there are other explanations that are more likely than causation, such as confounding by smoking and low socioeconomic status. Experimental animal and genotoxicity studies indicate that the carcinogenic potential of TDI depends on its conversion to toluene diamine (TDA), and there is no evidence of systemic availability of TDA after dermal or inhalation exposure to TDI. Also, systemic uptake of TDI is very low after dermal exposure, and any absorbed TDI is more likely to react with biomolecules on or below the skin surface than to form TDA. Even if some TDA formation occurred after dermal exposure to TDI, TDA does not induce respiratory tract tumors in experimental animals after either dermal or oral exposure. We conclude that the available evidence indicates that dermal TDI exposure does not cause respiratory cancers in humans.

6 Final Report on the Safety Assessment of p-Phenylenediamine

p-Phenylenediamine is a cosmetic hair dye intermediate used in permanent hair coloring products at concentrations of up to 5 percent (diluted 1:1 with an oxidizing agent prior to application). The extensive animal toxicity test data on p-Phenylenediamine and permanent cosmetic hair dyes containing this compound show that the degree of toxicity varies with concentration, test system and animal species. Animal data support a conclusion that this compound is neither a teratogen nor a carcinogen. Epidemiological data also support that hair dyes containing this ingredient are not carcinogenic. p-Phenylenediamine is a sensitizer and some persons may be sensitized under intended conditions of use.

For those persons not sensitized, it is concluded that p-Phenylenediamine is safe as a hair dye ingredient at the current concentrations of use.

Final Report on the Safety Assessment of Toluene-2,5-Diamine, Toluene-2,5-Diamine Sulfate, and Toluene-3,4-Diamine

The diaminotoluenes 2,5-TD, 2,5-TDS, and 3,4-TD are used as colorants in permanent hair dyes and tints. 2,5-TD is used at concentrations up to 1 % and 2,5-TDS is used up to 5%. The major routes of excretion after cutaneous absorption by rats were through the urine and feces. The oral LD50 of 2,5-TDS in rats was 98 mg/kg. There was no evidence of percutaneous toxicity to rabbits when 6% 2,5-TDS was applied to intact or abraded skin. In a two-year study, no toxicity was reported in rats receiving biweekly cutaneous applications of formulations containing 3% or 4% 2,5-TD. Mice were also unaffected by 3% 2,5-TDS in an 18-month study, or by 3% 2,5-TD in a two-year study. Rabbits had a slight dermal irritation response after exposure to 2.5% 2,5-TDS, but no irritation occurred in guinea pigs after exposure to 10% solutions of 2,5-TDS or 3,4-TD. 2,5-TD (2.5%) caused mild, transitory conjunctival inflammation in rabbits. The results of sensitization tests of 2,5-TD, 2,5-TDS, and 3,4-TD indicated that each of these diaminotoluenes were sensitizers to laboratory animals and humans. 2,5-TDS was toxic to pregnant rats and their embryos at oral doses of 80 mg/kg/day. Doses between 10 and 50 mg/kg/day did not cause congenital or maternal abnormalities. o-Toluenediamine, a mixture of 2,3-TD and 3,4-TD (40:60), was not teratogenic when administered orally to rats or rabbits. Cutaneous exposure to hair dye formulations containing 3% 2,5-TDS caused a statistically significant increase in fetal skeletal anomalies in rats. Rats treated with 6% 2,5-TDS did not have this adverse response. In a two-generation reproduction study, mice receiving dermal applications of hair-dye formulations containing either 3% or 6% 2,5-TDS had no signs of pharmacotoxicity, teratogenicity, or reproductive abnormalities. The results cited from various mutagenicity assays of 2,5-TD, 2,5-TDS, and 3,4-TD varied in accordance with the assay system and protocols used. 2,5-TD and 2,5-TDS were noncarci-nogenic to rats and mice in both oral and dermal exposure studies. On the basis of the animal and clinical data presented in this report, and the required labeling, it is concluded that Toluene-2,5-Diamine Sulfate and Toluene-3,4-Diamine are safe as cosmetic ingredients in the present practices of use.

5: Final Report on the Safety Assessment of 2-Methylresorcinol and Resorcinol

2-Methylresorcinol and Resorcinol are most frequently used in cosmetic hair dye formulations at concentrations between 1 and 5%. The results of cutaneous and oral feeding studies have indicated that both 2-Methylresorcinol and resorcinol are readily absorbed by rodents and are rapidly eliminated. Acute oral toxicity studies indicate that 2-Methylresorcinol is moderately toxic and Resorcinol is slightly to moderately toxic. Subchronic feeding and dermal studies of bothingredients produced no significant effects. A chronic dermal study was uneventful. Significant skin effects were observed in mice, but not in rabbits, following dermal application of Resorcinol at 5%. A 10% Resorcinol solution was not irritating to guinea pigs. A 2.5% 2-Methylresorcinol solution was classified as a primary irritant in rabbits, but 10% 2-Methylresorcinol was not irritating to guinea pigs. 2-Methylresorcinol was not an ocular irritant at 2.5%, but irritation was produced at 5% concentration in unwashed rabbit eyes. Neither 2-Methylresorcinol at 5% nor Resorcinol at 3% produced sensitization in guinea pigs. 2-Methylresorcinol was not photoallergenic to guinea pigs but was a sensitizer at 10%. Resorcinol was not photoallergenic to guinea pigs but was a sensitizer at 10%. Resorcinol and 2-Methylresorcinol were nonmutagenic in microbial and tissue culture assays for mutagenicity. Topically applied hair dyes containing 2-Methylresorcinol and Resorcinol were negative for carcinogenicity. Resorcinol showed no cocarcinogenic potential when tested on mice and rats. 2-Methylresorcinol at 3% concentration produced no evidence of irritation or sensitization in human subjects. Resorcinol was a mild skin irritant and rare sensitizer in clinical testing, but not when tested on nonclinical groups. On the basis of the available animal and clinical data, it is concluded that 2-Methylresorcinol and Resorcinol are safe as cosmeticingredients in the present practices of use and concentrations.

Mouse Skin Bioassay for Chemical Carcinogens

The mouse skin initiation/promotion bioassay is one of the proposed bioassays of the Carcinogenesis Testing Matrix for tier II (Bull and Pereira, 1980). A review of the literature indicated that 544 chemicals and substances have been examined by application to mouse skin for carcinogenic activity. Poly-cyclic aromatic hydrocarbons, direct acting alkylating agents, and environmental samples of complex mixtures and subtractions of them that include condensates of automobile exhaust and cigarette smoke have been demonstrated to be carcinogenic by the mouse skin bioassay. Chemical classes of carcinogens that have not been demonstrated to contain initiation and carcinogens in mouse skin include azoxy, diazo, halogenated methanes, hydrazine, inorganics, steroids, and sulfonates. The mouse skin assay can be modified so mat the test substance is administered systemically i.e., oral and intraperitoneal and the promoter applied topically. This modification has the potential of increasing the number of chemical classes detected in the mouse skin initiation/promotion bioassay.

Risk evaluation of occupational exposure to methylene dianiline and toluene diamine in polyurethane foam

Methylene diphenylisocyanate (MDI) and toluene diisocyanate (TDI) are widely used in industry to produce polyurethane foam products. Small amounts of methylenedianiline (MDA) and toluene diamine (TDA) are released during MDI and TDI polymerization and may be present in newly finished polyurethane foam parts. MDA and TDA concentrations in foam decline exponentially within several hours of demolding. MDA and the 2,4-isomer of TDA are known animal carcinogens and, in addition, have significant non-carcinogenic health effects. Our goal was to determine whether worker exposure to MDA or TDA in freshly produced polyurethane foams was associated with unacceptable health risks. Sampling and analysis of the fresh foam indicated that MDA and TDA concentrations varied considerably among products, but concentrations in all materials evaluated declined rapidly over time. We found that, under a worst-case exposure scenario, cancer risks from TDA exposure were approximately 5-10 6, whereas cancer risks from MDA exposure resulted in a tumorigenic margin of exposure (MOE) of 85 000. Non-cancer chronic hazard indices were well below 1.0. Therefore, the potential cancer and non-cancer health risks from MDA or TDA exposure to newly manufactured foam parts appear to fall well within acceptable health risk criteria.

Final Amended Report of the Safety Assessment of Toluene-2,5-Diamine, Toluene-2,5-Diamine Sulfate, and Toluene-3,4-Diamine as Used in Cosmetics

Toluene-2,5-diamine, toluene-2,5-diamine sulfate, and toluene-3,4-diamine are diaminotoluenes used as colorants in permanent hair dyes and tints. Toluene-2,5-diamine is used in 79 products at concentrations up to 3%; toluene-2,5-diamine sulfate is used in 168 products at concentrations up to 4%. Toluene-3,4-diamine does not appear to be in current use. Previously, the Cosmetic Ingredient Review Expert Panel determined that all 3 ingredients were safe for use as hair dyes. New data suggest that differences in toxicity, especially with respect to carcinogenicity, may exist as a function of placement of amine groups around the benzene ring. The Expert Panel concluded that toluene-2,5-diamine and toluene-2,5-diamine sulfate and are safe as hair dye ingredients in the present practices of use and concentrations but that there are insufficient data supporting the safety of toluene-3,4-diamine.

The debate on carcinogenicity of permanent hair dyes: new insights

Oxidative (permanent) hair dyes contain one or several "primary intermediates" (e.g., p-phenylenediamines, p-aminophenols) and "couplers" (e.g., m-aminophenols, m-hydroxyphenols). In the presence of peroxide, the primary intermediate(s) and the coupler(s) undergo a chemical reaction to form colored oligomers. In the 1970s a number of aromatic amines used in oxidative hair dyes were identified as mutagenic and/or carcinogenic in rodents after lifetime oral administration. In response, regulatory action was taken, and some hair dye ingredients were banned in the European Union. Although recent results suggest that the main "primary intermediate" of oxidative hair dyes, p-phenylenediamine, has a weak genotoxic potential in vitro, it was not mutagenic in a mixture with nonmutagenic couplers, if tested under conditions comparable to those of practical use. Under conditions of use of permanent hair dyes, between 0.1 and 0.5% of the applied p-phenylenediamine may be absorbed through the skin. Acetylation in the skin is a key metabolic step for the primary intermediates p-phenylenediamine and p-aminophenol. Because of the involvement of aromatic amines, the discussion on the carcinogenicity of hair dyes in humans has been focused on urothelial cancer. Numerous epidemiological studies have investigated the risk of bladder cancer associated with the profession as a hairdresser, as well as the risk to consumers of hair dyes. Although some earlier studies suggested an overrepresentation of bladder cancer in male hairdressers, the majority of modern studies do not show an increase in relevant bladder cancer risk for professional or personal use of oxidative hair dyes. Today, there seems to be no relevant bladder cancer risk from the use of oxidative hair dyes. Such a conclusion can be derived from new toxicokinetic and metabolism investigations and is in general accordance with current epidemiological data. Human urothelial cancers, chemically induced by aromatic amines, have typical latency times often longer than 20 years. Since earlier exposures could have an impact decades later, the possibility of bladder cancer in hairdressers having intensively worked with permanent hair dyes during earlier decades (prior to the 1980s) should be taken into account.

Toxicity and human health risk of hair dyes

Hair dyes and their ingredients have moderate to low acute toxicity. Human poisoning accidents are rare and have only been reported following oral ingestion. Contact sensitisation to hair dyes has been a safety issue, mainly as a consequence of unprotected professional exposure. Although the use of hair dyes has dramatically increased in industrialised countries during the last decades, the prevalence of sensitisation to hair dyes in the general and professional populations has stabilised or declined. In vitro genotoxicity tests on hair dye ingredients frequently had positive results, although their correlation with in vivo carcinogenicity for the chemical class of oxidative hair dye ingredients (aromatic amines) is uncertain. Positive in vivo genotoxicity results on hair dyes are rare. Studies in man found no evidence of genotoxic effects of hair dyes or their ingredients. On the basis of mechanistic studies, some in vivo positive hair dye ingredients (p-aminophenol, Lawsone) have been shown to pose no or negligible risk to human health. Although a recent case-control epidemiology study suggested an association of hair dye use and bladder cancer, a number of other studies, including prospective investigations on large populations, found no or negative correlations for bladder or other cancers. Although in vivo topical carcinogenicity studies on hair dye ingredients or commercial formulations yielded no evidence for systemic toxicity or carcinogenicity, oral carcinogenicity studies on hair dye ingredients at oral doses up to the maximum tolerated dose (MTD) suggested that some ingredients are carcinogenic in rodents. Human systemic exposure to various (14)C-labelled oxidative hair dyes under conditions of use was below 1.0% of the amount applied. Conservative risk assessments suggested no or negligible cancer risk, including for ingredients that were found to be positive in oral carcinogenicity studies. The results of reproductive toxicity studies and epidemiological investigations suggested that hair dyes and their ingredients pose no risk of adverse reproductive effects. In conclusion, the weight of evidence suggests that consumer or professional exposure to hair dyes poses no carcinogenic or other human health risks.

Toxicology review and risk assessment of resorcinol: thyroid effects

Resorcinol administered at high doses to rodents can disrupt thyroid hormone synthesis and can produce goitrogenic effects. These effects were not seen in a 2-year bioassay at doses of up to 520 mg/kg/day. There are species-specific differences in synthesis, binding, and transport of thyroid hormone that complicate interpretation of goitrogenesis in rodents. Clinical case reports from patients undergoing resorcinol therapy for dermatological indications reveal thyroid side effects when copious amounts of resorcinol-containing ointments are applied to integrity-compromised skin for months to years. Effect levels were greater than 34 mg/kg/day. Occupational epidemiology studies provide no evidence that exposure to resorcinol at levels greater than found in the general environment causes thyroid dysfunction. Studies investigating the relationship between endemic goiter and exposure to "phenolics," including resorcinol, in drinking water do not fulfill accepted scientific criteria for establishing resorcinol as a cause of thyroid disease. Those reports neither quantify exposure levels nor demonstrate dose-response relationships or rule out confounding by the multiple other chemicals present in water supplies, by bacterial contamination of water, or by nutritional factors. A risk assessment comparing potential worst-case exposures to resorcinol through its use in dermatological preparations supports the conclusion that under real-world conditions, human exposures to resorcinol are not expected to cause adverse effects on thyroid function.

High-performance liquid chromatographic separation and tandem mass spectrometric identification of breakdown products associated with the biological hydrolysis of a biomedical polyurethane

As part of ongoing investigations into the biological degradation of biomaterials, methods have been developed to isolate and chemically analyze polymer biodegradation products. The use of these methods can provide information on the biodegradation product profiles and yield concentration levels for the isolated products. The latter information is required to assess the toxicological nature of biomaterials and their related degradation products. In this study a model biomedical polyurethane was synthesized with toluene diisocyanate, polyester diol and ethylene diamine, and then incubated at 37 degrees C in a biological solution containing enzyme. The biodegradation products were isolated from the in vitro system and prepared for HPLC analysis, by using a combination of ultrafiltration, freeze drying and liquid-solid extraction. The ultrafiltration and the liquid-solid extraction effectively removed protein contamination. The separation of more than 20 degradation products, with gradient HPLC, was optimized using a photodiode array detector. The separated degradation products were identified using a tandem mass spectrometer. The model polyurethane was labeled with 14C in different segments, in order to assist in confirming the efficiency of the sample preparation and isolation methods. A detection limit of 2 ng was found. No toluene diamine - a suspected human carcinogen associated with some medical implants - could be found in the test samples. This represents a significant finding since the amount of this injected sample actually contained a total of 28 microg of degradation products isolated from the incubation medium.

Breast implants and cancer

BACKGROUND

Although silicone breast implants have been linked to various short-term complications, less is known about their long-range effects. Most attention has focused on connective tissue disorders, but the range of immunologic disturbances observed in women with implants suggests that consideration also be given to other chronic diseases, including cancer. The greatest attention has focused on breast cancer, given clinical reports suggesting an association and observations that mammographic visualization is deterred by implants. Findings from epidemiologic studies, however, actually suggest that breast cancer risk might be reduced among women with implants, although the biologic mechanism remains undefined. In addition, most studies do not suggest that women with breast implants have more advanced breast cancer at diagnosis or a worse prognosis than those without implants. The majority of studies have focused on women who received implants for cosmetic reasons, with little previous investigation of women who received implants for breast reconstruction following cancer surgery. In terms of other cancers, animal as well as clinical data suggest potential risks of sarcomas and hematologic cancers, including multiple myeloma. The risk of these cancers has not yet been adequately addressed by epidemiologic studies, although several ongoing studies should provide insights. It will be important for studies to consider effects of other lifestyle factors as well as to analyze relationships according to duration of implantation, a demonstrated determinant of implant deterioration. In addition, consideration should be given to type of implant, including implants with polyurethane foam covers, which can leak toluene diamine, a demonstrated carcinogen in animals.

Biodegradation of a poly(ester)urea-urethane by cholesterol esterase: isolation and identification of principal biodegradation products

Synthesized poly(ester)urea-urethanes with 14C-labeled toluene diisocyanate or 14C-labeled chain extender ethylene diamine were incubated with cholesterol esterase in a phosphate buffer solution at 37 degrees C. A number of biodegradation products, generated at the level of 2.8 micrograms/cm2 of polymer surface area, were isolated from this simulated physiologic system. Individual products were obtained by separation with reversed-phase high-performance liquid chromatography. The two different radiolabels were used to assist in the identification of degradation products from hard- and soft-segment domains. Approximately 20 degradation products were isolated; however, toluene diamine (TDA) was not detected from the chromatographic separation. Two principal products were identified by tandem mass spectrometry. Both products are TDA derivatives (secondary aromatic diamine) substituted with end units of the polyester segment at N and N' positions of TDA. The absence of free TDA suggests that there could be a stabilization of urethane and urea linkages within the toluene diisocyanate (TDI) segments of the polyurethanes. For TDI-synthesized polymers, this finding raises awareness to the potential biological importance of degradation products other than TDA, particularly to their interaction with surrounding cells.

Non-carcinogenicity of 2,2'--(4-aminophenyl)imino-bisethanol sulfate in a long-term feeding study in Fischer 344 rats

2,2'-[(4-aminophenyl)imino]bisethanol sulfate (4APE) was administered at dietary levels of 0 (control), 300, 1000 and 3000 ppm to groups of 50 male and 50 female Fischer 344/DuCrj rats for 104 wk. As slight body weight retardation was observed in the male 3000 ppm group in the preliminary 13-wk feeding study, this dose was selected for the highest exposure level. Mean body weights of both sexes in the 3000 ppm group were lower than those of the controls from wk 2 to termination. However, there were no treatment-related clinical signs or adverse effects on survival rate, food consumption or haematology data. Very slight but statistically significant increases in relative thyroid weights were found in males of the 3000 ppm group, but there was no significant treatment-related increase in the incidence of any non-neoplastic or neoplastic lesions. Thus, under the experimental conditions used, 4APE was not carcinogenic in Fischer 344 rats of either sex.

Epidemiologic follow-up studies of breast augmentation patients

Although hundreds of thousands of women in this country have had augmentation mammaplasty, little is known about long-term effects. Clinical studies have documented a decreased ability to detect breast lesions in women with implants, leading to concerns regarding breast cancer risk. There is also anecdotal evidence that implants might have effects on a variety of immune conditions. More recently, concern over carcinogenic effects has heightened given findings that the polyurethane foam, used in a minority of implants to envelope silicone gel, contains chemicals linked to cancer in laboratory animals. Only a few epidemiologic studies on long-term effects have been published, and all have had methodologic limitations, including the possibility of inappropriate comparison rates, limited and/or incomplete follow-up, absence of information on patients characteristics, and lack of specific information on types of implanted material. Several case-control and cohort studies are currently underway which are attempting to overcome methodologic limitations of previous studies. Past descriptive and analytic studies are reviewed. In addition, ongoing follow-up efforts are discussed, with attention given to the methodologic adjuncts necessary for allowing valid assessments of long-term disease effects.

An epidemiologic case-control study of breast cancer and exposure to hair dyes

An epidemiologic case-control study of 1617 patients with a primary breast cancer and 1617 control subjects was conducted to test the hypothesis that use of hair dyes is related to breast cancer. No overall association was observed between breast cancer risk and "ever use" of hair dyes (odds ratio, 1.04; 95% confidence interval, 0.90 to 1.21), age when hair dye use started and age when it stopped, duration of hair dye use (years), types of hair dyes used, and estimated lifetime number of individual applications. The current data set also failed to show an increased risk for breast cancer in women who had been diagnosed with benign breast disease and were exposed to hair dyes.

Breast augmentation: a risk factor for breast cancer?

BACKGROUND

A relation between breast augmentation and the subsequent risk of breast cancer has been postulated. Since an estimated 2 million women in the United States alone have received breast implants, even a small increase in the risk of breast cancer could have considerable public health consequences.

METHODS

We performed a population-based nonconcurrent cohort-linkage study. All women in Alberta, Canada, who underwent cosmetic breast augmentation from 1973 through 1986 were included in the implant cohort (n = 11,676). This cohort was compared with the cohort of all women in Alberta in whom a first primary breast cancer was diagnosed (n = 13,557). The expected number of breast-cancer cases in the implant cohort was estimated by applying age-specific and calendar year--specific incidence rates of breast cancer (obtained from the Alberta Cancer Registry) to the implant cohort. Standardized incidence ratios were calculated by dividing the observed by the expected number of breast-cancer cases in the implant cohort.

RESULTS

Forty-one patients with implants were subsequently found to have breast cancer. The expected number was 86.2. The standardized incidence ratio was thus 47.6 percent, significantly lower than expected (P less than 0.01). The average length of follow-up in the implant cohort was 10.2 years, and the average length of time from breast augmentation to the diagnosis of breast cancer was 7.5 years.

CONCLUSIONS

Women who undergo breast augmentation with silicone implants have a lower risk of breast cancer than the general population. This finding suggests that these women are drawn from a population already at low risk and that the implants do not substantially increase the risk.

Carcinogenicity and toxicity study of m-phenylenediamine administered in the drinking-water to (C57BL/6 x C3H/He)F1 mice

m-Phenylenediamine (m-PDA, CAS: 108-45-2), a component of hair-dye formulations, was administered in the drinking-water to groups of female and male (C57BL/6 x C3H/He)F1 (B6C3F1) mice at concentrations of 0.02 or 0.04% for 78 wk. All the surviving mice were killed after a further 5-7 wk on untreated drinking-water, 83-85 wk after the start of treatment. Survival of the treated mice was similar to that of the corresponding controls. Body weights were significantly lower in high-dose females and males and somewhat lower in low-dose females than in the controls. The incidences of hepatocellular tumours were low to moderate in all male groups and in the control females, but the treated groups had significantly lower incidences than the controls. A few tumours of the lungs, haematopoietic organs and other organs and tissues were observed in all female and male groups. However, there were no statistically significant increases in the incidences of tumours in these organs and tissues in m-PDA-treated mice of either sex. Under the conditions of this study m-PDA showed no carcinogenic potential in either female or male B6C3F1 mice when administered in drinking-water. No non-neoplastic changes attributable to the compound were found in the treated mice, except for the deposition of brown pigment in follicular epithelial cells of the thyroid gland and in macrophages in some organs and tissues, and pigment impregnation of the bronchioli.

Locus specificity of mutagenicity of 2,4-diaminotoluene in both L5178Y mouse lymphoma and AT3-2 Chinese hamster ovary cells

2,4-Diaminotoluene, a hepatocarcinogenic aromatic amine, was tested for mutagenic potential at both the autosomal tk locus and the sex-linked hgprt locus of both L5178Y 3.7.2C mouse lymphoma cells and Chinese hamster ovary (CHO) AT3-2 cells. This compound was mutagenic in both cell types at the tk locus but not at the hgprt locus. Mutagenic activity was observed in L5178Y cells only in the absence of exogenous metabolic activation, but was observed in CHO-AT3-2 cells both with and without activation.

In vitro cell transformation screening of 4 toluene diamine isomers

2,4-, 2,5-, 2,6- and 3,4-Toluene diamine (TDA) were tested for their ability to enhance the transformation of primary hamster embryo cells (HEC) by Simian adenovirus 7 (SA7) when administered either prior to or after virus inoculation and for their ability to transform secondary HEC. 2,4-TDA was inactive when given prior to SA7, but active if given after. 2,5-TDA was active in both protocols. 2,6-TDA was marginally active if administered before virus and was the most active of the isomers when administered after virus. 3,4-TDA was the most active compound when added prior to SA7, and was also active when given after virus. All the isomers were capable of producing good dose--responses and absolute increases in the number of virus-transformed foci per dish in one or both of the experimental regimens. Each isomer chemically transformed secondary HEC but good dose--responses were rare, and none of the chemicals were active in more than 50% of the 5 or 6 separate tests performed on each.

Mutagenicity and irreversible binding of the hepatocarcinogen, 2,4-diaminotoluene

Mutagenicity of 2,4-diaminotoluene (DAT) in the Salmonella mutagenicity assay was increased with liver fractions from phenobarbital (PB) or beta-naphthoflavone (BNF) treated rats. Substitutions of the hydrogens in the methyl group of 2,4-DAT with deuterium resulted in a decrease in mutagenicity. Incubation of rat liver microsomes with tritiated 2,4-DAT in the presence of NADPH led to the formation of irreversibly bound products to microsomal protein. The rates of binding were not increased using microsomes from PB or BNF-treated rats and was not altered by deuterium substitution in the methyl group. Addition of superoxide dismutase, glutathione (GSH) or rat liver supernatant reduced 2,4-DAT irreversible binding, whereas 2,4-DAT mutagenicity was unaffected by superoxide dismutase addition. Injection of tritiated 2,4-DAT 100 mg/kg to rats lead to its irreversible binding to liver protein and ribosomal RNA and to kidney protein in vivo, again protein binding was not increased after prior treatment with PB or BNF. No irreversible interaction of tritiated 2,4-DAT with DNA either in vitro or in vivo could be demonstrated.

The effect of 2,4-diaminotoluene and isomers of dinitrotoluene on unscheduled DNA synthesis in primary rat hepatocytes

The important industrial chemicals 2,4-dinitrotoluene (DNT) and 2,4-diaminotoluene (DAT) are hepatocarcinogens in rats. Technical grade DNT contains approximately 76% 2,4-DNT, 19% 2,6-DNT, and lesser amounts of the other isomers. The ability of 2,4-DAT, technical grade 2,4-DNT, and the purified isomers 2,3-DNT, 2,4-DNT, 2,5-DNT, 2,6-DNT, 3,4-DNT and 3,5-DNT to damage the DNA of primary rat hepatocytes was examined. Male Fischer-344 rats were perfused in situ, single cell suspensions were obtained after liver dissociation, and cultures of these cells were treated in the presence of 3H-thymidine. Autoradiography was employed to visualize label incorporation following repair of DNA. At the nontoxic (as judged by cell morphology) doses of 1 x 10(-4) M and below, only 2,4-DAT induced a significant response (ie an average greater than 5 grains net/nucleus). The activity seen with 2,4-DAT suggests that damage to the DNA of the hepatocytes may play a role in its carcinogenic activity and is consistent with the proposal that the induction of DNA repair in primary hepatocytes is of value in predicting the activity of aromatic amino compounds. However, the carcinogenic activity of the dinitrotoluenes was not reflected as DNA repair in the isolated hepatocyte, indicating that additional factors involving the whole animal also play a role in the mechanism of action of DNT.

Effects of repeated applications of two semi-permanent hair dyes to the skin of A and DBAf mice

Two proprietary semi-permanent hair dyes were tested for carcinogenicity in A and DBAf mice by repeated topical applications in aqueous acetone. Mice of both strains developed lymphoid tumours but experimental differences were marked only in DBAf mice. A number of tumours of the ovary and uterus, and some skin papillomas near the penis, occured in dye-treated but not in control DBAf mice. As many hair-dye constituents are known mutagens, adequate carcinogenicity testing of these substances, and epidemiological study of exposed human populations, are needed for evaluating possible health hazard from hair dyeing.

Mutagenicity of hair dye components relative to the carcinogen benzidine in Drosophila melanogaster

A comparative assay was undertaken in Drosophila melanogaster for the assessment of the mutagenic efficiency of the hair dye components m-toluene-diamine (m-TD) and 4-nitro-o-phenylenediamine (4-NOPD) relative to the aromatic amine human carcinogen benzidine (Bzd). The compounds were injected at equimolar dose ranges (5-20 mM) around the testes of adult males and their mutagenicities were measured separately on the various stages of spermatogenesis. Genetic activity was simultaneously assayed with respect to the overall induction of the X-chromosome recessives (lethals and visibles) relative to the specific effects on rDNA (expressed as bobbed mutations). All compounds exerted decisive mutagenicity both on the X-chromosome and the RNA genes, although their activities on the different genic sites varied between compounds and as a function of cell stage, but not in response to changes in dose, within the investigated molarity range. The mutagenicities and selectivities of the test compounds for rDNA gradually decreased in the order Bzd greater than m-TD greater than 4-NOPD, which correlated with the evidence-so far-about their carcinogenicities.

Correlation of bacterial mutagenicity and hamster cell transformation with tumorigenicity induced by 2,4-toluenediamine

In the presence of rat liver microsome enzymes, 2,4-toluenediamine (TDA) was mutagenic for several tester strains of Salmonella typhimurium. TDA induced morphological transformation in an in vitro carcinogenesis system using secondary culture target cells prepared from cryopreserved primary Syrian hamster embryo cells. These results now correlate bacterial mutagenicity and in vitro morphological transformation with the reported tumorigenicity of this compound.

Short term screening tests for carcinogens

There are now short term tests with a high predictive value for mammalian carcinogens. Many of them are based on the ability to detect damage to DNA in bacteria or mammalian cells after metabolic activation by microsomal enzymes. Their introduction will enable provisional safety assessments to be made for the many thousands of industrial and environmental chemicals for which long-term animal testing cannot at present be considered.