Evaluation of the mutagenicity of an N-nitroso contaminant of the sunscreen Padimate O: N-nitroso-N-methyl-p-aminobenzoic acid, 2-ethylhexyl ester (NPABAO).

The nitrosamine contaminant, N-nitroso-N-methyl-p-aminobenzoic acid, 2-ethylhexyl ester (NPABAO), of the major sunscreen ingredient Padimate O (4-N,N'-dimethylamino-benzoic acid, 2-ethylhexyl ester) was synthesized and tested for mutagenicity in the Salmonella typhimurium and mouse lymphoma L5178Y TK +/- assays. In contrast to the previously reported positive responses in S. typhimurium tester strains TA100 and TA1535 [Loeppky et al., 1991], there were no increases in the number of revertants with strains TA98, TA100, TA1535, and TA1538 in either the Salmonella plate incorporation [Ames et al., 1975] or preincubation [Yahagi et al., 1977] assays. Additional testing with Salmonella, following the modified preincubation procedure [Rogan, 1990] that gave the initial positive response, was also negative. Data from the mouse lymphoma assays were also uniformly negative. During synthesis of NPABAO, small amounts of 4-N,N'-dimethylamino-3-nitrobenzoic acid, 2-ethylhexyl ester (DMANBAO) can be formed. To determine whether the reported positive mutagenicity response of NPABAO could be the result of trace amounts of DMANBAO in the NPABAO, that compound was also synthesized and tested for mutagenicity with Salmonella. Positive responses were obtained with tester strains TA98 and TA 1538 but not with TA100 and TA1535, indicating that DMANBAO was not responsible for the increase in revertants originally reported.

Genotoxicity of multifunctional acrylates in the Salmonella/mammalian-microsome assay and mouse lymphoma TK+/-assay.

Multifunctional acrylates are being used increasingly as replacements for solvents, and occupational and general population exposure to this structural class is expanding. Four multifunctional acrylates and acrylic acid were tested for mutagenicity in the Salmonella typhimurium and mouse lymphoma L5178Y TK+/-assays. In the Salmonella assay, two of the compounds (trimethylolpropane triacrylate and trimethylolpropane trimethacrylate) showed weakly positive results with a single tester strain (TA1535) in the presence of hamster liver S9; the other three compounds were negative. All five compounds were negative in the Salmonella assay without S9 activation. In the mouse lymphoma assay, two of the compounds (acrylic acid and ethylene glycol diacrylate) were positive in both the presence and the absence of S9, one compound was positive only in the presence of S9 (ethylene glycol dimethacrylate), and one compound was positive only in the absence of S9 (trimethylolpropane triacrylate).

Mutagenicity of some alkyl nitrites used as recreational drugs.

When the AIDS epidemic was in its earliest stages, and prior to identification of HIV as the etiological factor, the use of volatile nitrites by the male homosexual community to enhance sexual activities appeared to have a significant role in this disease. Preliminary observations indicated that the portion of the male homosexual community which developed Kaposi's sarcoma were also heavy nitrite users. These nitrites had been demonstrated to be mutagenic in bacteria and thus it was postulated that they could be responsible for the appearance of the sarcoma. To evaluate further the genotoxic activity of these chemicals, six nitrites, including those most commonly used by homosexuals for sexual gratification, were selected for testing in the mouse lymphoma TK+/- and Salmonella typhimurium mutagenicity assays. One chemical, n-amyl nitrite, was negative in the mouse lymphoma assay, while the other five chemicals, n-butyl, isobutyl, iso-amyl, sec-butyl, and n-propyl nitrite, were positive. All six compounds were positive in the Salmonella assay. The mutagenic and known toxic effects of these chemicals remain a concern because a large population of teenagers and young adults continue to abuse these substances.

Genotoxicity of 6 oxime compounds in the salmonella/mammalian-microsome assay and mouse lymphoma TK +/- assay.

To aid in the selection of chemical candidates for in vivo tests, the mutagenicity of 6 oxime compounds was evaluated in the Salmonella plate incorporation assay and mouse lymphoma L5178Y TK +/- assay. All of the oximes were mutagenic in the mouse lymphoma assay in the absence of exogenous metabolic activation. Acetaldehyde oxime was also mutagenic in the presence of S9 activation. In contrast to these results, a positive response was noted only for 2-(hydroxyimino)-N-phenyl-acetamide oxime in strain TA1535 in the absence of activation in the Salmonella/microsome test.

Mutagenic activity of some coffee flavor ingredients.

The mutagenicity of 4 coffee flavor ingredients (chlorogenic acid, caffeic acid, pyrazine, and trigonelline) was evaluated in the Salmonella plate incorporation assay and mouse lymphoma L5178Y TK +/- assay. Two of the compounds, pyrazine and trigonelline, were negative in both assays. The other two compounds, caffeic acid and chlorogenic acid, were positive in the mouse lymphoma assay but negative in the Salmonella assay.

Interlaboratory evaluation of the C3H/10T1/2 cell transformation assay.

The C3H/10T1/2 transformation assay was evaluated for its responsiveness and interlaboratory reproducibility. Two laboratories participated in this study and tested a series of 46 chemicals. The majority of these chemicals were tested under code. Of the 46 chemicals tested, seven were determined to be active in both laboratories, and 14 were determined to be inactive. When the total number of chemicals is adjusted for assays considered "no test" in either one or both laboratories as well as for tests of chemicals yielding positive results in only one laboratory, reproducible responses were obtained for 21/35, or 60%, of the chemicals tested.

Mutagenic activity of 27 dyes and related chemicals in the salmonella/microsome and mouse lymphoma TK+/- assays.

A total of 27 dyes and related chemicals were tested for mutagenicity in both the Salmonella typhimurium plate-incorporation and FMN-modified assays as well as the mouse lymphoma TK+/- assay. Half of the compounds tested were monoazo dyes (14); the remainder consisted of disazo (3), aminotriphenylmethane derivatives (4), and other miscellaneous (6) color compounds. The results obtained in this study are compared with data from dyes of the same batch tested in other laboratories in the Salmonella plate-incorporation assay and in both in vitro and in vivo/in vitro UDS assays. Agreement of results from the various assays that could be compared (excluding results that were equivocal or indeterminate) ranged from 80 to 91%. Sufficient data were available to provide an overall index of in vitro activity for 15 chemicals; of these, 14 compounds could be compared to and agreed with reports of their carcinogenic potential in the literature.

Detection of mutagenic activity in the urine of rodents treated with p-rosaniline.

p-Rosaniline was fed to male and female Fischer 344 rats and B6C3F1 mice at doses of 1,000 and 2,000 ppm for male rats and 500 and 1,000 ppm for female rats and mice of both sexes. Urine was collected overnight at 1-wk intervals over a 4-wk treatment period and frozen until its use in the mutagenicity assay. The neat urine was tested in triplicate without S-9 on Salmonella tester strains TA98, TA100, TA1535, and TA1537 at 0.75, 0.5, 0.2, and 0.05 ml per plate. When sufficient urine was available, samples were tested on TA100 in the presence of S-9. Either urine samples were pretreated for 18 hr at 37 degrees C with beta-glucuronidase, or the deconjugating enzyme was added to the top agar at the time of plating in the mutagenicity assay (non-pretreatment). Direct-acting mutagenic activity was detected on TA98 in the urine from male mice, but only when using the non-pretreatment deconjugation method. No direct-acting mutagenic activity was detected in the urine of male and female rats and female mice; however, in the presence of S-9, mutagenic activity was observed in the urine of male rats and in the urine of male and female mice regardless of the deconjugation method used. The non-pretreatment method was superior for detecting direct acting mutagenic activity, and the pretreatment method was superior for detecting mutagenic activity requiring metabolic activation by S-9.

Monographs on human exposures to chemicals in the workplace.

The National Cancer Institute has contracted with Syracuse Research Corporation to produce monographs on the potential hazards of human exposure to approximately 70 chemicals used in the workplace. The monographs include detailed exposure data for specific job categories, as well as summaries of chemical and physical data, animal and human toxicological studies, short-term assays, and epidemiologic data. The information is useful for identifying suitable populations for epidemiologic research.

History, survival, and growth patterns of B6C3F1 mice and F344 rats in the National Cancer Institute Carcinogenesis Testing Program.

The history of, and rationale for, the selection of the hybrid B6C3F1 mouse (C57BL/6 female X C3h/He male) and the inbred F344 rat for National Cancer Institute (NCI) bioassays is described. Survival percentages at the end of 2-year tests and weight-gain patterns during the tests of control animals are presented to guide investigators using these same animals in similar long-term experiments. Because information on a large number of animals (9385 mice and 10,023 rats) from a number of laboratories is presented, the conclusions should serve to give general guidance to investigators holding the same animals under a diversity of husbandry conditions. The program experience has been that the B6C3F1 mouse survival at the end of a 24-month study (25.5 months of age) is 80%; the F344 survival for the same period is 75%. This contrasts with the generally held assumption that rats are longer lived than mice. For the period of time from which animal data were collected, there was a progressively slight decrease overall in survival percentage. This observation cannot be explained, and contravenes the expectation that methodological improvements in producing the animals and marked physical improvements in the testing laboratories should have resulted in improving the survival. Weight gain patterns have a distinct and somewhat similar sexual dimorphism for both rat and mouse. The males of each species grow much faster initially and then essentially level off. The female mouse grows slowly and steadily, and by 2 years of age almost equals the male; the female rat shows the same steady gain, but is much lighter than the male at 2 years of age.

Mutagenic activity of 5 thiazole compounds in the Salmonella/microsome and mouse lymphoma TK+/- assays.

To aid in the selection of chemical candidates for in vivo tests, the mutagenicity of 5 thiazole compounds was evaluated in the Salmonella plate incorporation assay and mouse lymphoma L5178Y TK+/- assay. Two of the compounds, 2-thiazolamine and 3-methyl-5-isothiazolamine, were positive in both assays; and one, thiazole, was negative. With the other 2 compounds the results were nonconcordant: 5-phenyl-2,4-thiazolediamine was negative in the Salmonella assay but positive in the mouse lymphoma assay, and C.I. Basic Red 29 was positive in the Salmonella assay while the response in the mouse lymphoma assay was considered equivocal.

Age-related neoplastic and degenerative lesions in aging male virgin and ex-breeder ACI/segHapBR rats.

A variety of neoplastic and degenerative lesions were observed in 216 aged male breeder (to 24 months of age) and virgin ACI/segHapBR rats sacrificed from 24 to 40 months of age. The most common neoplasms were pheochromocytomas, pituitary tumors, interstitial cell tumors of the testis, and tumors of the skin and subcutis. Many rats had multiple endocrine tumors. Age-related prostate hyperplasias and tumors were reported previously in these rats. Most of these tumors increased in incidence with advancing age, with few differences between virgins and ex-breeders. Testicular atrophy and tumors were more common in younger ex-breeder rats than in young virgin rats, but tumors reached a similar incidence in older virgin rats. Focal hyperplastic lesions appeared to represent the earliest stages of neoplasia in pituitary and adrenal glands, thyroid, prostate, testis, and liver. Common age-related nonneoplastic degenerative lesions were found in various tissues.

Longevity and reproductive comparisons for male ACI and Sprague-Dawley rat aging colonies.

ACI male rats had a life span approximately one-half year greater than that of Sprague-Dawley male rats. For ACI male rats, median survival was 31.5 months for virgins and 30 months for breeders; for Sprague-Dawley male rats, median survival was 24.5 months for virgins and 25 months for breeders. There was increased fertility of aged ACI males relative to Sprague-Dawley males. ACI males, approximately 2 years old, sired an average of 3.8 litters during a 6-month breeding period, while Sprague-Dawley males of similar age sired an average of 0.9 litters within an equivalent period.

Histogenesis and morphology of naturally occurring prostatic carcinoma in the ACI/segHapBR rat.

The prostates of 201 male virgin or breeder ACI (ACI/segHapBR) rats, 24 to 40 months of age were reviewed histologically, and the genesis of prostatic carcinoma was studied. At 24 months of age, 35 to 45 per cent of the rats had the earliest lesions, intraalveolar atypical hyperplasias. These lesions progressed to intraalveolar cribriform carcinomas which spread along alveoli and ducts. As the tumors enlarged, they became nodular and invaded the capsule or adjacent tissues. By 33 months, 95 to 100 per cent of the rats had intraalveolar prostatic atypical hyperplasias, and 35 to 40 per cent had invasive carcinomas. There was no difference between the incidence of these tumors in virgin or breeder rats. The ACI rat is unique model for studying the etiology and pathogenesis of naturally occurring prostatic cancer.

Homologous retinal outer segment immunization in primates. A clinical and histopathological study.

Immune intraocular inflammation was induced in primates with homologous retinal outer segments. Perivascular retinitis, uveitis, and edema of the optic nerve head were the prominent acute clinical features. Acute and chronic inflammation was seen in the central and peripheral retinal vessels and granulomatous infiltration was present in the choroid of the uvea. Selective degeneration of the outer segments of the photoreceptor cells of the retina with sparing of the inner segments and of the adjacent pigment epithelium was confirmed by light and electron microscopy. This study strongly suggests that photoreceptor outer segments are highly and specifically immunogenic. The inciting antigen has yet to be identified. Implication of rhodopsin will have to await further studies since it exists as the essential protein in the outer segment.

Total-body irradiation of canine lymphoma.

In the continuing search for models which are potentially useful for experimental therapeutics and other radiobiological studies, spontaneous lymphoma in canines has been virtually ignored. These neoplasms closely resemble their histologic counterpart in humans with respect to anatomic sites of involvement and other features. We have examined the responsiveness of canine lymphoma to total-body irradiation, and objective remissions of disease have been observed.