5780447280

ETHYLENE GLYCOL MONOBUTYL ETHER

mary glands, and one treated mouse showed an anaplastic carcinoma of the bladder. The v-Ha-ra$ transgenic mice carrying an activated oncogene under active promotion (due to the presence of the MMTV promoter) are considered as initiated mice Le._t mice presenting a stable and heritable mutation at the Ha-ras gene. Non-genotoxic agents such as those which activate the protein kinases, or mitogenic, or methylating agents could be screened using this test (Goldsworthy et al., 1994; Vaino, 1995). The occur-rence of tumors in Ha-ras and p53 knockout transgenic mice increased as well as the latency time decreased when such animals were treated with genotoxic or non-geno-toxic agents (Breuer et al., 1991; Tennant et al., 1995). Moreover using c-Ha-ras transgenic mice, a single i.p. injection of 50 mg/kg of N-methyl-N-nitrosourea induced papillomas in the forestomach following 12 weeks at 100% incidence (łzawa et al., 1992). Using the pim 1 model, Breuer et al. (1991) showed that N-ethyl-N-nitrosourea (ENU) induced lymphomas in a dose dependent manner. With a medium dose of 60 mg/kg of ENU the incidence of lymphomas at 120 days was 90%. The pim-l transgenic mice were found approximately 25 times morę susceptible to ENU-induced lym-phomagenesis than non transgenic mice.

In our study such effects were not shown as neither the tumor occurrence nor the latency period were affected by 2-butoxyethanol treatment. Therefore it could be hy-pothesized that this Chemical does not promote initiated cells carrying the v-Ha-rar oncogene. But further studies (especially long term studies) are necessary in order to evaluate this transgenic animal model.

3.4. Hydrophobic Adducts Formation in Rats DNA

Because no differences in the methylation pattems and the formation of hydrophilic adducts were found in the DNA of 2-butoxyethanol treated and control animals, we checked further for hydrophobic adducts. Our hypothesis was that 2-butoxyethanol could be an inducer of cytochrome P₄₅₀, and could therefore lead to the formation of hydrophobic adducts as found in DNA of animals that have been treated with estro-gens. Indeed Liehr (1986) demonstrated the formation of hydrophobic DNA-adducts whose Chemical structures were not directly related to the estrogens that were injected, using the postlabelling method. Another assumption was that 2-butoxyethanol could increase the level óf the I compounds (i.e. initial compounds) present in animals after aging and/or related to the diet (Randerath, 1991). We therefore extensively screened the DNA digests after postlabelling in order to detect the formation of hydrophobic adducts in DNA from treated animals as compared to the control animals. The autora-diograms obtained after venom phosphodiesterase hydrolysis of the labelled digests are shown here (Figurę 3) sińce this improvement gave much cleanerand simpler maps than those without that treatment.

Some major adducts, which differ slightly from organ to organ, appear in both DNA from treated and control animals. These adducts were probably the so-called I-com-pounds (Randerath, 1991). No obvious differences could be seen in these DNA (Figurę 3 A,C,E,G and I for the treated animals and Figurę 3 B,D,F,H and J for the control animals). One can therefore conclude that 2-butoxyethanol did not lead to the formation of hydrophobic DNA-adducts in the treated animals.

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