Mutagenic, cytotoxic, and teratogenic effects of 2‐acetylaminofluorene and reactive metabolites in vitro

Abstract

The embryotoxic, mutagenic, and cytotoxic properties of 2-acetylaminofluorene (AAF) and two of its reactive metabolites, N-acetoxy-2-acetylaminofluorene (AAAF) and 2-nitrosofluorene (NF) were assessed in vitro. A combined embryo culture/biotransformation system was used to determine the ability of these compounds to produce embryonic malformations, growth retardation, and/or embryolethality. Salmonella typhimurium auxotrophs (his-) were utilized to measure the mutagenic and cytotoxic potentials of these compounds. The parent compound, AAF, did not produce embryonic malformations or mutagenicity in the absence of an added cytochrome P-450-dependent monooxygenase system. Both metabolites produced each of the measured toxic effects without supplementation of a bioactivation system. However, the three chemicals each elicited a different spectrum of malformations. Bioactivated AAF produced neural tube abnormalities, whereas embryos treated with AAAF primarily exhibited prosencephalic malformations, and NF produced abnormalities of axial rotation or flexure. NF was approximately ten times more potent than AAAF as a direct-acting mutagen but only slightly more active in producing embryonic malformations in vitro. The results indicated that differential effects on the various measured parameters could be produced by these chemicals. The results indicated further that neither NF nor AAAF appeared to be individually responsible for the neural tube abnormalities generated by biotransformed AAF.

Maternal occupational exposure to polycyclic aromatic hydrocarbons and risk of neural tube defect‐affected pregnancies

“…These observations are generally inconclusive and as such neither support nor refute the literature. Experiments report that PAHs cause NTDs in laboratory animals (Faustman‐Watts et al,1984; Barbieri et al,1986; Stark et al,1989; Incardona et al,2004). Human populations with likely environmental exposures had elevated risk of NTDs in Canadian areas near large‐scale coke oven operations, (adjusted relative risk, 1.25; 95% CI, 1.04–1.51; Dodds and Seviour,2001) and nervous system anomalies were higher in regions in the United Kingdom exposed to total black smoke (OR, 1.10 per increase of 1000 μg/m 3 , 95% CI, 1.03–1.18; Rankin et al,2009).…”

“…Maternal exposure to PAHs has been shown in laboratory animals to cause neural tube defects (NTDs), birth defects affecting the brain and spinal cord that arise from failure of the embryonic neural tube to close in the first month of pregnancy. This effect can vary depending on the genotype of the fetus and mother, on the specific type of PAH, and on the route of exposure (Faustman‐Watts et al,1984; Barbieri et al,1986; Stark et al,1989; Incardona et al,2004). Four human studies have indicated a positive association between maternal exposure to PAHs and the risk of NTDs using residence location or biomarkers of exposure (Dodds and Seviour,2001; Rankin et al,2009; Naufal et al,2010; Ren et al,2011).…”

2‐aminofluorene bioactivation by human term placental peroxidase

“…In contrast to this, peroxidase occurs in abundant quantities in the human placentas of nonsmokers [I91 and the purified enzyme was found to avidly oxidize a wide range of model chemicals [19][20][21]. Previous mechanistic studies on teratogenicity of arylamines and related compounds have utilized the in vitro rat embryos culture assay [2][3][4][5]8] and assessed the role of microsomal cytochrome P-450 in the bioactivation by supplementing the culture media with adult rodent hepatic S9 fraction and NADPH [2-51. A possible contribution of the peroxidative pathways in the bioactivation of teratogenic arylamines was not investigated. In view of this, it was of interest to evaluate whether 2-AF can serve as a substrate for HTPP.…”

“…In vitro studies with rat embryos have shown that reactive metabolites of both acetylated and deacetylated 2-AF exhibit developmental toxicity. However, distinction exists in the type of defects produced [2][3][4][5]8]. The active metabolites of acetylated derivatives mainly produce prosencephalic hypoplasia, microcephaly, and limb bud abnormalities, while abnormalities in axial rotation (flexture) are induced by the ultimate toxicants of deacetylated compounds [2-531.…”

The potential role of redox cycling as a mechanism for chemical teratogenesis.

“…Several metabolites of 2-acetylaminofluorene (AAF) have been investigated as embryotoxins in whole embryo cultures (6,(31)(32)(33). A number of metabolites of AAF have the potential to behave as redox cyclers although this mechanism has not been seriously considered in terms of its carcinogenicity or mutagenicity.…”