Assessment of DNA Binding and Oxidative DNA Damage by Acrylonitrile in Two Rat Target Tissues of Carcinogenicity: Implications for the Mechanism of Action

Abstract

Exposure to acrylonitrile induces formation of tumors at multiple sites in rats, with females being more sensitive. The present study assessed possible mechanisms of acrylonitrile tumorigenicity, covalent DNA binding, DNA breakage, and oxidative DNA damage, in two target tissues, the brain and Zymbal's glands, of sensitive female Fischer (F344) and Sprague-Dawley (SD) rats. One group received acrylonitrile in drinking water at 100 ppm for 28 days. Two other groups were administered either acrylonitrile in drinking water at 100 ppm or drinking water alone for 27 days, followed by a single oral gavage dose of 11 mg/kg bw C-acrylonitrile on day 28. A positive control group received a single dose of 5 mg/kg bw of 7-C-benzo[a]pyrene, on day 27 following the administration of drinking water for 26 days. Using liquid scintillation counting, no association of radiolabeled acrylonitrile with brain DNA was found. In accelerator mass spectrometry analysis, the association of C of acrylonitrile with DNA in brains was detected and was similar in both strains, which may reflect acrylonitrile binding to protein as well as to DNA. NucleotideP-postlabeling assay analysis of brain samples from rats of both strains yielded no evidence of acrylonitrile DNA adducts. Negative conventional comet assay results indicate the absence of direct DNA strand breaks in the brain and Zymbal's gland in both strains of rats dosed with acrylonitrile. In both rat strains, positive results in an enhanced comet assay were found only in brain samples digested with formamidopyrimidine-DNA glycosylase but not with human 8-hydroxyguanine-DNA glycosylase, indicating possible oxidative DNA damage, other than 8-oxodG formation. In conclusion, definitive evidence of DNA binding of acrylonitrile in the brain and Zymbal's gland was not obtained under the test conditions. A role for oxidative stress in tumorigenesis in the brain but not Zymbal's gland may exist.

Analysis of DNA Adducts and Mutagenic Potency and Specificity in Rats Exposed to Acrylonitrile

“…11,55 Several studies in rats given radiolabeled ACN have shown the apparent binding of radioactivity to DNA in the brain, liver, lung, stomach, and/or testicles, when determined by liquid scintillation counting 56−59 or accelerator mass spectrometry. 39 In each tissue, there was a rapid decrease in radioactivity of DNA samples collected up to 72 h after treatment, suggesting the possible formation of N7-guanine or N3-adenine adducts that are unstable and lost, largely by spontaneous depurination leaving behind apurinic sites. 60,61 DNA synthesis across an abasic site may result in mutations if there is insufficient time for closure of the site; however, abasic sites resulting from spontaneous depurination of N7-guanine adducts are efficiently repaired and do not seem to accumulate as a primary mechanism for mutagenicity and carcinogenicity of ethylene oxide or other epoxide-forming chemicals.…”

“…Findings from these experiments in rats, along with a companion report regarding parallel studies in mice, are considered in the context of an ongoing debate about the modes of action of ACN as a rodent carcinogen. 38,39 ■ MATERIALS AND METHODS H]εdCyd standards were prepared as previously described. 22,23,40 Sources for chemicals, enzymes, and reagents for DNA isolations and DNA adduct analyses were listed elsewhere.…”

Mechanisms of DNA-reactive and epigenetic chemical carcinogens: applications to carcinogenicity testing and risk assessment

“…60 Moreover, the formation of adducts in nuclear DNA by such carcinogens, which is the definitive evidence of DNA reactivity, has not been found in cells of their target tissues using sensitive techniques. 61,62 Epigenetic carcinogens must also be demonstrated to exert other primary molecular or cellular effects in their target tissues that are the basis for their carcinogenicity through actions in either of the two sequences of carcinogenesis (Fig. 1).…”

Electronic cigarette: A recent update of its toxic effects on humans

“…One research mentioned that acrylonitrile could induce lipid peroxidation and regarded it as a “potent hepatotoxic mutagen and carcinogen” (Abo‐Salem, Abd‐Ellah, & Ghonaim, ). Oxidative stress caused by acrylonitrile may contribute to formation of tumor (Williams, Kobets, Duan, & Iatropoulos, ). Besides supporting the role of oxidative stress in the progression of acrylonitrile‐induced astrocytomas, Pu, Wang, Zhou, and Klaunig () revealed that acrylonitrile could upregulate several pro‐inflammatory cytokines such as TNF‐α, IL‐1b, and Chemokine (C‐C motif) ligand 2 (Ccl2) and growth stimulatory cyclin D1 and cyclin D2.…”