Propylene oxide: genotoxicity profile of a rodent nasal carcinogen

Sorption of hazardous industrial organic liquids with environmentally friendly functionalized cellulosic sorbents

The performances of five cellulosic polymers with different functional groups (cellulose, cellulose acetate, cellulose phosphate, chitosan, and chitin) as sorbents of seven frequently used hazardous polar organic liquids (acrolein, butanone peroxide, epichlorohydrin, formaldehyde, furfuryl alcohol, propylene oxide, and vinyl acetate) are investigated in this study. Amongst the cellulosic sorbents, cellulose phosphate exhibited enhanced sorption properties (as high as 3.09–7.03 g/g) against all seven polar organic liquids investigated, and chitosan and chitin also demonstrated comparable sorption efficiencies (2.28–7.72 g/g and 2.55–5.86 g/g, respectively) to those of cellulose phosphate. According to our investigation, the enhanced sorption efficiency could be achieved due to low powder density of cellulose phosphate, which is caused by the weak intramolecular interaction amongst the polymer chains. In addition, cellulose phosphate, chitosan, and chitin also showed enhanced absorbed solvent recovery percents (71.4, 60.6, and 61.1%, respectively, in average) compared with that of pristine cellulose (43.8%). With excellent sorption efficiency, enhanced solvent recovery rate, and reusability after drying, these functionalized cellulosic sorbents can be excellent candidates to replace the conventional carbon and vermiculites-based sorbents, especially for liquid polar organic spill sorption.

Association between urinary propylene oxide metabolite and the risk of dyslexia

Although it is a probable human carcinogen, propylene oxide is widely applied in industry and daily life. However, data on neurodevelopmental effects of propylene oxide exposure among children are extremely limited. We aimed to determine the urinary concentrations of propylene oxide metabolite among school-aged children and evaluate the potential association of propylene oxide exposure with risk of dyslexia. A total of 355 dyslexic children and 390 controls were recruited from three cities (Jining, Wuhan, and Hangzhou) in China, between 2017 and 2020. Urinary N-acetyl-S-(2-hydroxypropyl)-L-cysteine (i.e., 2-hydroxypropyl mercapturic acid; 2-HPMA) was measured as the biomarker of propylene oxide exposure. The detection frequency of 2-HPMA was 100%. After adjusting for potential confounders, the odds ratio (OR) for dyslexia per 2-fold increase in urinary 2-HPMA was 1.19 [95% confidence interval (95% CI): 1.01, 1.40, P = 0.042]. Compared with the lowest quartile of urinary 2-HPMA concentrations, children with the highest quartile of 2-HPMA had a 1.63-fold (95% CI: 1.03, 2.56, P = 0.036) significantly increased risk of dyslexia, with a dose-response relationship (P-trend = 0.047). This study provides epidemiological data on the potential association between propylene oxide exposure and the risk of dyslexia in children. Further studies are warranted to confirm the findings and reveal the underlying biological mechanisms.

Considerations for the Use of Mutation as a Regulatory Endpoint in Risk Assessment

Assessment of a chemical's potential to cause permanent changes in the genetic code has been a common practice in the industry and regulatory settings for decades. Furthermore, the genetic toxicity battery of tests has typically been employed during the earliest stages of the research and development programs of new product development. A positive outcome from such battery has a major impact on the chemical's utility, industrial hygiene, product stewardship practices, and product life cycle analysis, among many other decisions that need to be taken by the industry, even before the registration of a chemical is undertaken. Under the prevailing regulatory paradigm, the dichotomous (yes/no) evaluation of the chemical's genotoxic potential leads to a conservative, linear no-threshold (LNT) risk assessment, unless compelling and undeniable data to the contrary can be provided to satisfy regulators, typically in a number of different global jurisdictions. With the current advent of predictive methods, new testing paradigms, mode-of-action/adverse outcome pathways, and quantitative risk assessment approaches, various stakeholders are starting to employ these state-of-the-science methodologies to further the conversation on decision making and advance the regulatory paradigm beyond the dominant LNT status quo. This commentary describes these novel methodologies, relevant biological responses, and how these can affect internal and regulatory risk assessment approaches. Environ. Mol. Mutagen. 61:84-93, 2020. © 2019 Wiley Periodicals, Inc.

Dose and temporal evaluation of ethylene oxide-induced mutagenicity in the lungs of male big blue mice following inhalation exposure to carcinogenic concentrations

Ethylene oxide (EO) is a direct acting alkylating agent; in vitro and in vivo studies indicate that it is both a mutagen and a carcinogen. However, it remains unclear whether the mode of action (MOA) for cancer for EO is a mutagenic MOA, specifically via point mutation. To investigate the MOA for EO-induced mouse lung tumors, male Big Blue (BB) B6C3F1 mice (10/group) were exposed to EO by inhalation, 6 hr/day, 5 days/week for 4 (0, 10, 50, 100, or 200 ppm EO), 8, or 12 weeks (0, 100, or 200 ppm EO). Lung DNA samples were analyzed for cII mutant frequency (MF) at 4, 8 and 12 weeks of exposure; the mutation spectrum was analyzed for mutants from control and 200 ppm EO treatments. Although EO-induced cII MFs were 1.5- to 2.7-fold higher than the concurrent controls at 4 weeks, statistically significant increases in the cII MF were found only after 8 and 12 weeks of exposure and only at 200 ppm EO (P ≤ 0.05), which is twice the highest concentration used in the cancer bioassay. Consistent with the positive response, DNA sequencing of cII mutants showed a significant shift in the mutational spectra between control and 200 ppm EO following 8 and 12 week exposures (P ≤ 0.035), but not at 4 weeks. Thus, EO mutagenic activity in vivo was relatively weak and required higher than tumorigenic concentrations and longer than 4 weeks exposure durations. These data do not follow the classical patterns for a MOA mediated by point mutations. Environ. Mol. Mutagen. 58:122-134, 2017. © 2017 Wiley Periodicals, Inc.

Contributions of DNA repair and damage response pathways to the non-linear genotoxic responses of alkylating agents

From a risk assessment perspective, DNA-reactive agents are conventionally assumed to have genotoxic risks at all exposure levels, thus applying a linear extrapolation for low-dose responses. New approaches discussed here, including more diverse and sensitive methods for assessing DNA damage and DNA repair, strongly support the existence of measurable regions where genotoxic responses with increasing doses are insignificant relative to control. Model monofunctional alkylating agents have in vitro and in vivo datasets amenable to determination of points of departure (PoDs) for genotoxic effects. A session at the 2013 Society of Toxicology meeting provided an opportunity to survey the progress in understanding the biological basis of empirically-observed PoDs for DNA alkylating agents. Together with the literature published since, this review discusses cellular pathways activated by endogenous and exogenous alkylation DNA damage. Cells have evolved conserved processes that monitor and counteract a spontaneous steady-state level of DNA damage. The ubiquitous network of DNA repair pathways serves as the first line of defense for clearing of the DNA damage and preventing mutation. Other biological pathways discussed here that are activated by genotoxic stress include post-translational activation of cell cycle networks and transcriptional networks for apoptosis/cell death. The interactions of various DNA repair and DNA damage response pathways provide biological bases for the observed PoD behaviors seen with genotoxic compounds. Thus, after formation of DNA adducts, the activation of cellular pathways can lead to the avoidance of a mutagenic outcome. The understanding of the cellular mechanisms acting within the low-dose region will serve to better characterize risks from exposures to DNA-reactive agents at environmentally-relevant concentrations.

Formation and repair of tobacco carcinogen-derived bulky DNA adducts

DNA adducts play a central role in chemical carcinogenesis. The analysis of formation and repair of smoking-related DNA adducts remains particularly challenging as both smokers and nonsmokers exposed to smoke are repetitively under attack from complex mixtures of carcinogens such as polycyclic aromatic hydrocarbons and N-nitrosamines. The bulky DNA adducts, which usually have complex structure, are particularly important because of their biological relevance. Several known cellular DNA repair pathways have been known to operate in human cells on specific types of bulky DNA adducts, for example, nucleotide excision repair, base excision repair, and direct reversal involving O⁶-alkylguanine DNA alkyltransferase or AlkB homologs. Understanding the mechanisms of adduct formation and repair processes is critical for the assessment of cancer risk resulting from exposure to cigarette smoke, and ultimately for developing strategies of cancer prevention. This paper highlights the recent progress made in the areas concerning formation and repair of bulky DNA adducts in the context of tobacco carcinogen-associated genotoxic and carcinogenic effects.

Creating context for the use of DNA adduct data in cancer risk assessment: I. Data organization

The assessment of human cancer risk from chemical exposure requires the integration of diverse types of data. Such data involve effects at the cell and tissue levels. This report focuses on the specific utility of one type of data, namely DNA adducts. Emphasis is placed on the appreciation that such DNA adduct data cannot be used in isolation in the risk assessment process but must be used in an integrated fashion with other information. As emerging technologies provide even more sensitive quantitative measurements of DNA adducts, integration that establishes links between DNA adducts and accepted outcome measures becomes critical for risk assessment. The present report proposes an organizational approach for the assessment of DNA adduct data (e.g., type of adduct, frequency, persistence, type of repair process) in concert with other relevant data, such as dosimetry, toxicity, mutagenicity, genotoxicity, and tumor incidence, to inform characterization of the mode of action. DNA adducts are considered biomarkers of exposure, whereas gene mutations and chromosomal alterations are often biomarkers of early biological effects and also can be bioindicators of the carcinogenic process.

Toxicological considerations on the use of propylene glycol as a humectant in cigarettes

Propylene glycol (PG) is a humectant commonly used in cigarettes. Previous toxicological examinations of the effects on the addition of PG to tobacco used mixtures with several other flavoring agents. In the present work, toxicological comparisons were made of experimental cigarettes containing no added PG against otherwise similar cigarettes with three different amounts of PG added to the tobacco. The main toxicological comparison was a sub-chronic inhalation study with mainstream smoke in Sprague-Dawley rats (exposures of 150 mg/m(3) of total particulate matter, 6h exposure per day, for 90 consecutive days). The target PG concentrations in the tobacco of the four cigarette types were 0, 4, 7 and 10%. Additional studies with mainstream smoke were bacterial mutagenicity (5 Salmonella strains, both with and without metabolic activation, particulate phase only), cytotoxicity of both particulate and gas/vapor phases (using the neutral red uptake assay), and analytical chemistry (41 analytes). The graded inclusion of PG into experimental cigarettes resulted in increases in the smoke concentrations of propylene oxide, at very low concentrations. Broadly similar responses were seen across the four cigarette types, and the responses were similar to those previously described in the scientific literature. The addition of PG to experimental cigarettes reduced concentrations of some smoke components (e.g. nicotine), but had minimal effects on the biological responses. Most of the changes produced in the 90-days of exposure were resolved in a 42-day post-inhalation period.

Dose-response and operational thresholds/NOAELs for in vitro mutagenic effects from DNA-reactive mutagens, MMS and MNU

The dose-response relationships for in vitro mutagenicity induced by methylmethanesulfonate (MMS) or methylnitrosourea (MNU) in L5178Y mouse lymphoma (ML) cells were examined. DNA adducts (N7-methylguanine, N7MeG and O(6)-methylguanine, O(6)MeG) were quantified as biomarkers of exposure. Both endpoints were assessed using 5replicates/dose (4-h treatment) with MMS or MNU (0.0069-50muM), or vehicle (1% DMSO). Mutant frequency (MF) (thymidine kinase (TK) locus) was determined using the soft agar cloning methodology and a 2-day expression period; in addition, microwell and Sequester-Express-Select (SES) methods were used for MMS. Isolated DNA was acid-hydrolyzed, and adducts quantified by LC/ESI-MS/MS, using authentic and internal standards. MF dose-responses were analyzed using several statistical approaches, all of which confirmed that a threshold dose-response model provided the best fit. NOAELs for MF were 10muM MMS and 0.69muM MNU, based on ANOVA and Dunnett's test (p<0.05). N7MeG adducts were present in all cell samples, including solvent-control cells, and were increased over control levels in cells treated with >/=10muM MMS or 3.45muM MNU. O(6)MeG levels were only quantifiable at >/=10muM MNU; O(6)MeG was not quantifiable in control or MMS-treated cells at current detection limits. Thus, (1) cells treated with </=0.69muM MNU or </=10muM MMS did not demonstrate increases in TK(-) MF, but did demonstrate quantifiable levels of N7MeG adducts; and (2) the levels of N7MeG adducts did not correlate with induced MF, as MNU-treated cells had fewer N7MeG adducts but higher MF compared with MMS-treated cells, for quasi-equimolar doses. Taken together, these results demonstrate operational thresholds, defined as the highest dose for which the response is not significantly (statistically or biologically) distinguishable from the control/background values, for induction of mutations and N7MeG adducts in ML cells treated with MMS or MNU, and a lack of correlation between induced MF and levels of N7MeG adducts.

Is propylene oxide induced cell proliferation in rat nasal respiratory epithelium mediated by a severe depletion of water-soluble non-protein thiol?

Propylene oxide (PO) concentrations >or=300 ppm induced cell proliferation and tumors in rat nasal respiratory epithelium (NRE). Cell proliferation was suggested to result from depletion of glutathione (GSH) in NRE. In order to substantiate this hypothesis, cell proliferation - measured by bromodeoxyuridine incorporation into DNA of the epithelium lining middle septum, dorsal medial meatus, and medial and lateral surfaces of the nasoturbinate in transverse nasal sections taken immediately posterior to the upper incisor teeth - and water-soluble non-protein thiol (NPSH) in NRE were determined after exposing male Fischer 344 rats to 50 ppm, 100 ppm, 200 ppm, or 300 ppm PO (6 h/day, 3 days). Both parameters were also investigated after treating rats for 3 days with diethylmaleate (DEM; 2 x 250 mg/kg/day or 500 + 150 mg/kg/day) or buthionine sulfoximine (BSO; 500 mg/kg/day). Exposure to 50 ppm PO and treatment with 2 x2 50 mg/kg/day DEM resulted in NPSH levels approximating 50% and 80% of the level in untreated controls, respectively. Cell proliferation did not increase. After exposures to >or= 100 ppm PO or treatment with BSO or 500 + 150 mg/kg/day DEM, NPSH was depleted to <or=1/3 of the control level and cell proliferation increased 2.0-3.7-fold the control value. In conclusion, profound perturbation of the GSH status may represent a crucial step in PO induced rat nasal tumorigenicity.