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A toxicogenomic approach for the risk assessment of the food contaminant acetamide.

ABSTRACT: Acetamide (CAS 60-35-5) is detected in common foods. Chronic rodent bioassays led to its classification as a group 2B possible human carcinogen due to the induction of liver tumors in rats. We used a toxicogenomics approach in Wistar rats gavaged daily for 7 or 28 days at doses of 300 to 1500 mg/kg/day (mkd) to determine a point of departure (POD) and investigate its mode of action (MoA). Ki67 labeling was increased at doses ?750 mkd up to 3.3-fold representing the most sensitive apical endpoint. Differential gene expression analysis by RNA-Seq identified 1110 and 1814 differentially expressed genes in male and female rats, respectively, following 28 days of treatment. Down-regulated genes were associated with lipid metabolism while up-regulated genes included cell signaling, immune response, and cell cycle functions. Benchmark dose (BMD) modeling of the Ki67 labeling index determined the BMD10 lower confidence limit (BMDL10) as 190 mkd. Transcriptional BMD modeling revealed excellent concordance between transcriptional POD and apical endpoints. Collectively, these results indicate that acetamide is most likely acting through a mitogenic MoA, though specific key initiating molecular events could not be elucidated. A POD value of 190 mkd determined for cell proliferation is suggested for risk assessment purposes.

SUBMITTER: Nault R

PROVIDER: S-EPMC7014822 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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A toxicogenomic approach for the risk assessment of the food contaminant acetamide.

Nault Rance R Bals Bryan B Teymouri Farzaneh F Black Michael B MB Andersen Melvin E ME McMullen Patrick D PD Krishnan Seetha S Kuravadi Nagesh N Paul Neetha N Kumar Santhosh S Kannan Kamala K Jayachandra K C KC Alagappan Lakshmanan L Patel Bhavesh Dhirajlal BD Bogen Kenneth T KT Gollapudi Bhaskar B BB Klaunig James E JE Zacharewski Tim R TR Bringi Venkataraman V

Toxicology and applied pharmacology 20191224

Acetamide (CAS 60-35-5) is detected in common foods. Chronic rodent bioassays led to its classification as a group 2B possible human carcinogen due to the induction of liver tumors in rats. We used a toxicogenomics approach in Wistar rats gavaged daily for 7 or 28 days at doses of 300 to 1500 mg/kg/day (mkd) to determine a point of departure (POD) and investigate its mode of action (MoA). Ki67 labeling was increased at doses ≥750 mkd up to 3.3-fold representing the most sensitive apical endpoint ...[more]

PMID: 31881176

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Project description:Acetamide (CAS 60-35-5) is detected in common foods including milk, eggs, beef, and roasted coffee beans. Chronic rodent bioassays using high doses (≥1000 mg/kg/day) suggest acetamide is a group 2B possible human carcinogen due to the induction of liver tumors. Weight-of-evidence indicates acetamide is not genotoxic, and therefore a threshold response is expected. We used a toxicogenomics approach in Wistar rats gavaged daily for 7 and 28 days to determine the benchmark dose (BMD), and investigate its mode of action from differential gene expression. Two exposure experiements were carried out in succsession. An initial dose range finding experiment used male Wistar rats gavaged daily for 7 days at 0, 30, 100, 300 and 1000 mg/kd/day. A second experiment used both male and female Wistar rats exposed for 7 and 28 days to 0, 300,500,750,1000 and 1500 mg/kg/day. No treatment related changes in terminal body weight, clinical chemistry, or histopathology were observed at doses of 30, 100, or 300 mkd. At 1000 mkd, the dose reported to elicit carcinogenesis, liver weights decreased 1.3-fold with the presence of single cell necrosis, hepatocyte vacuolization, and increased mitotic activity consistent with a 4.2 fold increase in the cell proliferation index. Accordingly, plasma ALT and AST were increased 2.0- and 2.2-fold, respectively. RNA-Seq analysis identified 1 differentially expressed gene at 300 mkd, and 2,685 at 1000 mkd (|fold-change| ≥ 1.5 and FDR ≤ 0.05). Down-regulated genes were associated with lipid metabolism while up-regulated genes included cell signaling, immune response, and cell cycle functions. Collectively, these results revealed a no-observable adverse effect level (NOAEL) and no-observed-transcriptional effect level (NOTEL) at 300 mkd, warranting further investigation at doses between 300 and 1000 mkd to identify the benchmark dose (BMD). Functional enrichment indicates perturbation of cell cycle and lipid metabolism, though a more refined dose-response evaluation will be needed to demonstrate dose-dependent effects related to the MOA of acetamide. Funding by the Bill and Melinda Gates Foundation (OPP1142801).

Project description:BackgroundIn the absence of current cumulative dietary exposure assessments, this analysis was conducted to estimate exposure to multiple dietary contaminants for children, who are more vulnerable to toxic exposure than adults.MethodsWe estimated exposure to multiple food contaminants based on dietary data from preschool-age children (2-4 years, n=207), school-age children (5-7 years, n=157), parents of young children (n=446), and older adults (n=149). We compared exposure estimates for eleven toxic compounds (acrylamide, arsenic, lead, mercury, chlorpyrifos, permethrin, endosulfan, dieldrin, chlordane, DDE, and dioxin) based on self-reported food frequency data by age group. To determine if cancer and non-cancer benchmark levels were exceeded, chemical levels in food were derived from publicly available databases including the Total Diet Study.ResultsCancer benchmark levels were exceeded by all children (100%) for arsenic, dieldrin, DDE, and dioxins. Non-cancer benchmarks were exceeded by >95% of preschool-age children for acrylamide and by 10% of preschool-age children for mercury. Preschool-age children had significantly higher estimated intakes of 6 of 11 compounds compared to school-age children (p<0.0001 to p=0.02). Based on self-reported dietary data, the greatest exposure to pesticides from foods included in this analysis were tomatoes, peaches, apples, peppers, grapes, lettuce, broccoli, strawberries, spinach, dairy, pears, green beans, and celery.ConclusionsDietary strategies to reduce exposure to toxic compounds for which cancer and non-cancer benchmarks are exceeded by children vary by compound. These strategies include consuming organically produced dairy and selected fruits and vegetables to reduce pesticide intake, consuming less animal foods (meat, dairy, and fish) to reduce intake of persistent organic pollutants and metals, and consuming lower quantities of chips, cereal, crackers, and other processed carbohydrate foods to reduce acrylamide intake.

Dataset Information

A toxicogenomic approach for the risk assessment of the food contaminant acetamide.

Publications

A toxicogenomic approach for the risk assessment of the food contaminant acetamide.

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