The mutagenic activity of selected compounds at the TK locus: rodent vs. human cells

LncRNA MDRL Mitigates Atherosclerosis through miR-361/SQSTM1/NLRP3 Signaling

Objective

Long non-coding RNAs (lncRNAs) play many important roles in gene regulation and disease pathogenesis. Here, we sought to determine that mitochondrial dynamic related lncRNA (MDRL) modulates NLRP3 inflammasome activation and apoptosis of vascular smooth muscle cells (VSMCs) and protects arteries against atherosclerosis.

Methods

In vivo experiments, we applied LDLR knockout (LDLR^−/−) mice fed the high-fat diet to investigate the effects of MDRL on atherosclerosis. In vitro experiments, we applied mouse aortic smooth muscle cells to determine the mechanism of MDRL in abrogating NLRP3 inflammasome and inhibiting cell apoptosis through miR-361/sequentosome 1 (SQSTM1) by TUNEL staining, quantitative RT-PCR, western blot, microribonucleoprotein immunoprecipitation, and luciferase reporter assay.

Results

Downregulated MDRL and increased NLRP3 were observed in mouse atherosclerotic plaques, accompanied with the increase of miR-361. The results showed that MDRL overexpression significantly attenuated the burden of atherosclerotic plaque and facilitated plaque stability through inhibiting NLRP3 inflammasome activation and cell apoptosis, and vice versa. Mechanically, MDRL suppressed NLRP3 inflammasome activation and VSMC apoptosis via suppressing miR-361. Furthermore, miR-361 directly bound to the 3'UTR of SQSTM1 and inhibited its translation, subsequently activating NLRP3 inflammasome. Systematic delivery of miR-361 partly counteracted the beneficial effects of MDRL overexpression on atherosclerotic development in LDLR^−/− mice.

Conclusions

In summary, MDRL alleviates NLRP3 inflammasome activation and apoptosis in VSMCs through miR-361/SQSTM1/NLRP3 pathway during atherogenesis. These data indicate that MDRL and inhibition of miR-361 represent potential therapeutic targets in atherosclerosis-related diseases.

RIFM fragrance ingredient safety assessment, 3-phenylpropyl acetate, CAS Registry Number 122-72-5

Therefore, the phenethyl formate MOE for the fertility endpoint can be calculated by dividing the phenethyl alcohol NOAEL in mg/kg/day by the total systemic exposure to phenethyl formate, 1000/0.00062 or 1612903.

Editor's Highlight: High-Throughput Functional Genomics Identifies Modulators of TCE Metabolite Genotoxicity and Candidate Susceptibility Genes

Trichloroethylene (TCE), an industrial chemical and environmental contaminant, is a human carcinogen. Reactive metabolites are implicated in renal carcinogenesis associated with TCE exposure, yet the toxicity mechanisms of these metabolites and their contribution to cancer and other adverse effects remain unclear. We employed an integrated functional genomics approach that combined functional profiling studies in yeast and avian DT40 cell models to provide new insights into the specific mechanisms contributing to toxicity associated with TCE metabolites. Genome-wide profiling studies in yeast identified the error-prone translesion synthesis (TLS) pathway as an import mechanism in response to TCE metabolites. The role of TLS DNA repair was further confirmed by functional profiling in DT40 avian cell lines, but also revealed that TLS and homologous recombination DNA repair likely play competing roles in cellular susceptibility to TCE metabolites in higher eukaryotes. These DNA repair pathways are highly conserved between yeast, DT40, and humans. We propose that in humans, mutagenic TLS is favored over homologous recombination repair in response to TCE metabolites. The results of these studies contribute to the body of evidence supporting a mutagenic mode of action for TCE-induced renal carcinogenesis mediated by reactive metabolites in humans. Our approach illustrates the potential for high-throughput in vitro functional profiling in yeast to elucidate toxicity pathways (molecular initiating events, key events) and candidate susceptibility genes for focused study.

Safety Assessment of Dichlorophene and Chlorophene1

Dichlorophene is a halogenated phenolic compound that functions as a bacteriocide and fungicide in cosmetics. Chlorophene is a halogenated phenolic compound that functions as a biocide and preservative in cosmetics. Dichlorophene was reported to be used in a total of five cosmetic formulations at concentrations of 0% to 1.0%, but Chlorophene was not reported to be used. Dichlorophene is prohibited for use in cosmetic ingredients in Japan. In Europe, the maximum authorized concentration allowed for Dichlorophene is 0.5% and for Chlorophene is 0.2%. The major impurity of Dichlorophene is the trimer 4-chloro-2,6-bis(5-chloro-2-hydroxy-benzyl)phenol. In rats, Dichlorophene sulfate, Dichlorophene monoglucuronide, and Dichlorophene diglucuronide were the major metabolites of Dichlorophene and were excreted, mainly in the urine. The glucuronic acid conjugate, the sulfate ester conjugate, and two minor metabolites of Chlorophene were the metabolites found in rat urine. Chlorophene was incompletely absorbed through the rat skin. These chemicals exhibited low toxicity in acute oral toxicity studies in several animal species. Some evidence of toxicity with both chemicals was found in short-term oral toxicity studies in mice and rats; nephropathy was the principal finding. Chronic toxicity data were not available for Dichlorophene. Rats and mice dosed with Chlorophene for 2 years had a dose-related and sex-related increase in the severity of nephropathy. In animal tests, Dichlorophene and Chlorophene were ocular irritants. No inhalation toxicity data were available for these ingredients. Dichlorophene up to 10% concentration resulted in no to minimal irritation when applied to the intact and abraded skin of rabbits. Chlorophene was severely irritating to rabbits in most dermal irritation studies. Studies on guinea pigs gave positive and negative results in sensitization tests of Dichlorophene. A dose-related contact hypersensitivity response to Chlorophene was reported in mice. No reproductive or developmental toxicity data were available for Dichlorophene, but there was some evidence of non-dose-dependent developmental toxicity with Chlorophene in rabbits. Dichlorophene was positive in the Ames mutagenicity assay, but not in mammalian or fruit fly test systems. Chlorophene was mutagenic in four in vitro mammalian test systems. Carcinogenicity studies for Dichlorophene were not found. Neoplasms were not observed in rats treated with Chlorophene for 2 years; however a significant incidence of neoplasms was observed in mice so treated. A 1-year National Toxicology Program (NTP) study concluded that Chlorophene was a cutaneous irritant and a weak skin tumor promoter but had no activity as an initiator or complete carcinogen. Dichlorophene was not a sensitizer in clinical dermal sensitization tests. Some reactions to Chlorophene occurred in some, but not all, clinical dermal sensitization tests. Positive photopatch tests to Dichlorophene were found in 13/469 patients. Although these ingredients were ocular irritants at high concentrations, the risk at concentrations which are actually used in cosmetic formulations was uncertain. Overall, the available data were insufficient to support safety of Dichlorophene or Chlorophene. Additional data needed include (1) method of manufacture and impurities data (especially the trimer in Dichlorophene); (2) photosensitization and photo-carcinogenicity data for Dichlorophene; (3) dermal reproductive and developmental toxicity data for Dichlorophene (as a function of dose); and (4) ocular irritation at concentration of use, if available.

RIFM fragrance ingredient safety assessment, benzyl butyrate, CAS Registry Number 103-37-7

The use of this material under current use conditions is supported by the existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental and reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, as well as environmental safety. Data from the suitable read across analog benzyl acetate (CAS # 140-11-4) show that this material is not genotoxic nor does it have skin sensitization potential and also provided a MOE > 100 for the repeated dose, developmental and reproductive, and local respiratory toxicity endpoints. The phototoxicity/photoallergenicity endpoint was completed based on suitable UV spectra. The environmental endpoint was completed as described in the RIFM Framework.

RIFM fragrance ingredient safety assessment, p-Isopropylbenzyl acetate, CAS Registry Number 59230-57-8

The use of this material under current use conditions is supported by the existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity, skin sensitization, as well as environmental safety. Data from the suitable read across analog, benzyl acetate (CAS # 140-11-4), show that this material is not genotoxic nor does it have skin sensitization potential. The repeated dose, developmental and reproductive, and local respiratory toxicity endpoints were completed using benzyl acetate (CAS # 140-11-4) as a suitable read across analog, which provided a MOE > 100. The phototoxicity/photoallergenicity endpoint was completed based on suitable UV spectra. The environmental endpoint was completed as described in the RIFM Framework.

RIFM fragrance ingredient safety assessment, α-Methylbenzyl acetate, CAS Registry Number 93-92-5

The use of this material under current use conditions is supported by the existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity, skin sensitization potential, as well as, environmental safety. Developmental toxicity was determined to have the most conservative systemic exposure derived NO[A]EL of 100 mg/kg/day. A gavage developmental toxicity study conducted in rats on a suitable read across analog resulted in aMOE of 3571 while considering 78.7% absorption from skin contact and 100% from inhalation. A MOE of >100 is deemed acceptable.

RIFM fragrance ingredient safety assessment, Benzyl propionate, CAS Registry Number 122-63-4

The use of this material under current use conditions is supported by the existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental toxicity, reproductive toxicity, local respiratory toxicity, phototoxicity, skin sensitization potential, as well as, environmental safety. Repeated dose toxicity was determined to have the most conservative systemic exposure derived NO[A]EL of 14.5 mg/kg/day. A dietary 2-year chronic toxicity study conducted in rats on a suitable read across analog resulted in a MOE of 1318 while considering 78.7% absorption from skin contact and 100% from inhalation. A MOE of >100 is deemed acceptable.

A toxicological and dermatological assessment of aryl alkyl alcohol simple acid ester derivatives when used as fragrance ingredients

The aryl alkyl alcohol simple acid ester derivatives (AAASAE) group of fragrance ingredients was critically evaluated for safety following a complete literature search of the pertinent data. For high end users, calculated maximum skin exposures vary widely from 0.01% to 4.17%. AAASAE exhibit a common route of primary metabolism by carboxylesterases resulting in the formation of the simple acid and an aryl alkyl alcohol. They have low acute toxicity. No significant toxicity was observed in repeat-dose toxicity tests. There was no evidence of carcinogenicity of benzyl alcohol when it was administered in the feed; gavage studies resulted in pancreatic carcinogenesis due to the corn oil vehicle. The AAASAE are not mutagenic in bacterial systems or in vitro in mammalian cells, and have little to no in vivo genotoxicity. Reproductive and developmental toxicity data show no indication of adverse effects on reproductive function and NOELs for maternal and developmental toxicity are far in excess of current exposure levels. The AAASAE are generally not irritating or sensitizing at the current levels of exposure. The Panel is of the opinion that there are no safety concerns regarding the AAASAE at the current levels of use and exposure.

The FEMA GRAS assessment of benzyl derivatives used as flavor ingredients

This publication is the eighth in a series of safety evaluations performed by the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA). In 1993, the panel initiated a comprehensive program to re-evaluate the safety of more than 1700 GRAS flavoring substances under conditions of intended use. Elements that are fundamental to the safety evaluation of flavor ingredients include exposure, structural analogy, metabolism, pharmacokinetics and toxicology. Flavor ingredients are evaluated individually and in the context of the available scientific information on the group of structurally related substances. Scientific data relevant to the safety evaluation of the use of benzyl derivatives as flavoring ingredients is evaluated. The group of benzyl derivatives was reaffirmed as GRAS (GRASr) based, in part, on their self-limiting properties as flavoring substances in food; their rapid absorption, metabolic detoxication, and excretion in humans and other animals, their low level of flavor use, the wide margins of safety between the conservative estimates of intake and the no-observed-adverse effect levels determined from subchronic and chronic studies and the lack of significant genotoxic and mutagenic potential. This evidence of safety is supported by the fact that the intake of benzyl derivatives as natural components of traditional foods is greater than their intake as intentionally added flavoring substances.

Mouse-specific carcinogens: an assessment of hazard and significance for validation of short-term carcinogenicity bioassays in transgenic mice

1. The International Conference on the Harmonisation of Technical Requirements for the Registration of Pharmaceuticals for human use (ICH) has agreed that bioassay data from only one species, the rat, supported by appropriate mutagenicity and pharmacokinetic data and also information from new (unvalidated) short term in vivo screening tests for potential carcinogenicity, could be used for the licensing of human medicines. This proposal has been supported by reviews of the utility of testing pharmaceuticals in the mouse which have concluded that the mouse bioassay contributes little to regulatory decisions. The current review was undertaken to identify 'genuine' mouse-specific carcinogens using the Gold Carcinogenicity Potency Database (CPD) for the initial identification of potential mouse-specific carcinogens from published literature. Hazard assessments were completed for these chemicals with particular attention focused on the 'genuine' mouse-specific carcinogens. The significance of such chemicals has been discussed together with consideration of on-going work on the validation of short-term carcinogenicity bioassays using transgenic mice. 2. Seventy-six potential mouse specific carcinogens were identified through the Gold Carcinogenicity Potency Database. Following more detailed consideration a total of ten chemicals were excluded from further consideration (three were multispecies carcinogens, five were considered to be non-carcinogenic in the mouse, and the data for two were uninterpretable). The review focused on the remaining 66 chemicals. There was equivocal evidence of carcinogenicity to the rat for 28 chemicals and inadequate data for a further 23 chemicals. Fifteen 'genuine' mouse-specific carcinogens were identified. These 15 chemicals comprise two genotoxic mouse-specific carcinogens (N-methylolacrylamide (924-42-5), 2,6-Dichloro-p-phenylenediamine (609-20-1); five non-genotoxic mouse-specific carcinogens 2-Aminobiphenyl.HCl (2185-92-4), Captan (133-06-2), Dieldrin (60-57-7), Diethylhexyladipate (103-23-1), and Probenicid (57-66-9); five mouse-specific carcinogens with equivocal evidence of mutagenicity were identified; (2,4-diaminophenol.2HCl (137-09-7), Dipyrone (68-89-3), Ozone (10028-15-6), Vinylidene chloride (75-35-4), and Zearalenone (17924-92-4)), and three mouse-specific carcinogens with inadequate mutagenicity data (Benzaldehyde (100-52-7), Piperonyl sulphoxide (120-62-7), Ripazepam (26308-28-1)). 3. It is suggested that the two genotoxic mouse carcinogens would have been considered as potential carcinogens in the absence of a mouse bioassay. Of the five non-genotoxic mouse-specific carcinogens; three induced tumours in mouse liver only and are considered as being of low potential hazard to human health. The remaining two chemicals would have been missed in the absence of a mouse bioassay (2-aminobiphenyl (2185-92-4) and captan (133-06-2)) and thus are good candidates for evaluation in the short term bioassays in transgenic mice currently being validated. 4. The hardest group of mouse-specific carcinogens to evaluate are those for which there is equivocal or inadequate mutagenicity data. The difficulty in evaluating these particular chemicals emphasises the need for adequate mutagenicity data in addition to adequate carcinogenicity data in order to assess potential hazards to human health. Hazard assessments and a consideration of the potential role for short-term bioassays in transgenic mice for the eight chemicals in this subgroup are presented. 5. A number of general conclusions have been derived from this review. Firstly, there are insufficient published genotoxicity data to allow a full assessment fo mutagenic potential for 57/76 of the potential mouse-specific carcinogens identified from the CPD. This is surprising given the clear value of such data in interpreting bioassay results and the much greater resources required for carcinogenicity bioassays. (ABSTRACT TRUNCATED)

The L5178Y/tk+/- mouse lymphoma specific gene and chromosomal mutation assay a phase III report of the U.S. Environmental Protection Agency Gene-Tox Program

The L5178Y/tk+/- (-)3.7.2C mouse lymphoma assay (MLA) which detects mutations affecting the heterozygous thymidine kinase (tk) locus is capable of responding to chemicals acting as clastogens as well as point mutagens. Improvements in the assay to enhance detection of this spectrum of genetic events are summarized, and criteria for evaluating the data are defined. Using these criteria, the Phase III Work Group reviewed and evaluated literature containing MLA results published from 1976 through 1993. The data base included 602 chemicals of which 343 were evaluated as positive, 44 negative, 18 equivocal, 54 apparently inappropriate for evaluation in this test system with the published protocols, and 142 that were inadequately tested, and thus a definitive call could not be made. The overall performance of the assay is summarized by chemical class, and the outcome of testing 260 chemicals in the MLA is compared with Gene-Tox and National Toxicology Program evaluations of rodent carcinogenesis bioassay results for the same chemicals. Based on the Work Group's evaluation of published MLA data for chemicals that were considered adequately tested, it is concluded that for most chemicals the L5178Y/tk+/- mouse lymphoma assay is eminently well suited for genotoxicity testing and for predicting the potential for carcinogenicity.

Long-term exposure to fluoride in drinking water and sister chromatid exchange frequency in human blood lymphocytes

The genetic toxicity of fluoride has been investigated extensively by various test systems. However, results obtained have been inconsistent. Fluoride has been reported to be non-genotoxic, genotoxic, and synergistic or antagonistic with certain mutagens. To date, there are no published human studies on the genotoxicity of fluoride. The purpose of this investigation was to determine genotoxic risks of long-term exposure to various concentrations of fluoride in drinking water in humans with normal or inadequate nutrition. Six groups of subjects with either normal or inadequate nutritional intakes were selected from areas of approximately 0.2, 1.0, or 4.8 ppm (10.5, 52.6, or 252.6 mumol/L) fluoride in water. The subjects had been continuous residents in the area for at least 35 years. Samples of drinking water, plasma, and urine were analyzed for fluoride content. Blood lymphocytes were examined to determine the frequency of sister chromatid exchange (SCE). Blood chemistry and electrolytes were also analyzed. The results showed that average daily fluoride intake as well as urine and plasma fluoride levels increased with increase in the fluoride content of the drinking water. The blood chemistry and electrolyte values were within the normal range for all populations, but several parameters were significantly different. While the numerical differences were small, the subjects with low fluoride in the water (0.11 and 0.23 ppm or 5.8 and 12.1 mumol/L) had significantly higher SCE frequencies than those with higher fluoride exposures.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanistically-based human hazard assessment of peroxisome proliferator-induced hepatocarcinogenesis

In this review we have evaluated the relationship between peroxisome proliferation and hepatocarcinogenesis. To do so, we identified all chemicals known to produce peroxisome proliferation and selected those for which there are data (on peroxisome proliferation and hepatocarcinogenesis) which meet certain criteria chosen to facilitate comparison of these phenomena. The summarised data and definition of the methodology used has been collected in appendices. These comparisons enabled us to evaluate the relationship between these phenomena using reliable data. As there is a good correlation between them, we further explored the mechanisms of action that have been proposed (direct genotoxic activity, production of hydrogen peroxide, cell proliferation and receptor activation). The relationship between these events in other species, including humans, was also reviewed and finally an overview of the assessment of human hazard is presented in section IX. Some of the first chemicals which were shown to produce peroxisome proliferation were also hepatocarcinogens whose carcinogenicity could not be readily explained by genotoxic activity. This raised the suggestion that the unusual phenomenon of peroxisome proliferation was intricately linked to the carcinogenic activity of these agents. Three questions have exercised the attention of regulatory, industrial and academic toxicology since then; are chemicals which elicit peroxisome proliferation in the liver actually a coherent class of chemical carcinogens?; does the early biological phenomenon of peroxisome proliferation have real predictive value for and mechanistic association with rodent carcinogenesis?; and what hazard/risk do these agents pose to humans that may be exposed to them? Whether peroxisome proliferators are indeed a discrete class of rodent carcinogens would appear to be the single, most important question. If so, then the assumptions and procedures relevant to human hazard and risk assessment should be applied to the class and should be essentially generic; if not, each chemical should be considered independently. Our critical analysis of the published data for over 70 agents which have been shown to possess intrinsic ability to induce peroxisome proliferation in the livers of rodents has led to the conclusion that there exists a strong correlation between peroxisome proliferation as n early effect in the liver and hepatocarcinogenicity in chronic exposure studies. An almost perfect correlation was observed between the induction of peroxisomes in the rodent liver and the eventual appearance of tumours following chronic exposure The few exceptions to this were largely explainable (section II).(ABSTRACT TRUNCATED AT 400 WORDS)

Genetic toxicity of fluoride

F- is not mutagenic in standard bacterial systems, but produces chromosome aberrations and gene mutations in cultured mammalian cells. Although there is disagreement in the literature concerning the ability of F- to induce chromosome aberrations in cultured human and rodent cells, the weight of the evidence leads to the conclusion that F- exposure results in increased chromosome aberrations in these test systems. NaF induced primarily chromatid gaps and chromatid breaks, indicating that the rodent cells are responsive in the G2 stage of the cell cycle. In contrast, studies with synchronized human cells indicated that the S phase was the most sensitive. If F- does have a cell cycle-specific effect, it could be expected that differences in the cell treatment and harvest protocols could lead to conflicting results for the induction of chromosome aberrations. Gene mutations were produced in cultured rodent and human cells in the majority of the studies. Unfortunately, a number of the in vitro and in vivo cytogenetic studies are of questionable utility because of the protocols used, the quality of the responses reported, or the interpretations of the data. The conflicting results in the in vivo cytogenetic studies are difficult to reconcile. There are reports of increased chromosome aberrations in rat bone marrow and testes, but other studies, using similar protocols and dose ranges, have reported no induced chromosome damage. Although some of the studies were performed at toxic levels of F-, other studies, including those that showed positive results, were at F- concentrations (1-5 ppm) equivalent to human exposure levels. In the majority of studies that were reported to be positive, there were high background frequencies, or the investigators reported categories of nuclear or chromosome damage that are difficult to interpret. Interestingly, many of the positive results were obtained when anaphase cells were scored, whereas similar treatment protocols in other laboratories yielded negative results when metaphase cells were the only cell type examined. It is difficult, without additional data, to determine the reasons for finding chromosome breaks in anaphase, but not metaphase, cells. Other reports have presented insufficient information to allow adequate evaluations. Therefore, at this time, the question of whether F- produces chromosome damage in vivo should be considered unresolved.

Endogenous xenobiotic enzyme levels in mammalian cells

The response of mammalian cell lines to chemicals depends, in part, on the exogenous activation system used for the induction of a biological response. This could be attributed to differences in the expression of enzymes involved in xenobiotic metabolism. We have measured the activities of benzo[a]pyrene hydroxylase, dimethylaminoazobenzene N-demethylase, catalase, superoxide dismutase, peroxidase and glutathione-S-transferase in human lymphoblast TK6, mouse lymphoma L5178Y, Chinese hamster ovary (CHO) and lung (V79) and mouse C3H10T1/2 cell lines as well as in primary hepatocytes and S9 preparations of liver from male F344 rats. Nitroreductase was also measured in some of these preparations. Human lymphoblast TK6 and mouse C3H10T1/2 cells had the capacity to metabolize dimethylaminoazobenzene and the latter cell line also metabolized benzo[a]pyrene, indicating the presence of constitutive mono-oxygenase activity. Cytochrome P450 could not be detected spectrophotometrically in the cell lines. Western blot analysis indicated that P450 from the P450IIA family is expressed in C3H10T1/2 cells. Reactivity was also observed with an antibody to P450IA2; however, the identity of this protein remains uncertain. Superoxide dismutase, catalase and peroxidase, which protect cells against oxygen radical damage, were found in all the cell lines and in rat hepatocytes and S9. The human lymphoblast TK6 cell line, however, had the least of each of these three enzymes. Glutathione-S-transferase activity was detected at varying levels in all cell types. Nitroreductase activity was high in S9 and Chinese hamster ovary cells and lower in mouse lymphoma and Chinese hamster V79 cells.