Hemoglobin and DNA adducts in rats exposed to 2-nitrotoluene.

Abstract

2-Nitrotoluene (2NT) is an important commercial chemical intermediate. A recent National Toxicology Programme (NTP)-study demonstrated clear evidence of carcinogenic activity of 2NT in rats. In the present study male WELS-Fohm rats were dosed chronically with 2NT, 5 days a week for 12 weeks. Hemoglobin (Hb) adducts and hepatic DNA adducts were analyzed. After mild base treatment of Hb, 2-methylaniline (2MA) was released and quantified using gas chromatography/mass spectrometry. 2'-Deoxyguanosine (dG) and 2'-deoxyadenosine (dA) adducts of 2MA were found in hepatic DNA using electrospray-mass spectrometry (ESI-MS/MS). The dG adduct found in vivo did not co-elute with N-(2'-deoxyguanosine-8-yl)-2-methylaniline which is the expected adduct for arylamines. The dG adduct detected in the dosed rats was not present in calf thymus-DNA (ct-DNA) modified in vitro with N-acetoxy-2MA. The dA adduct detected in rats was a very minor product in ct-DNA modified in vitro. The dG and dA adducts found in the 2NT-dosed rats increased with the dose. The same increase was seen for the Hb adduct levels measured in the same animals. The increase of DNA and Hb adduct levels were supralinear. There was a very strong linear relationship between the level of dG-2MA adducts and dA-2MA adducts in hepatic DNA from rats administered 2NT over the whole dose range studied (r(2) = 0.9). A strong linear relationship also existed between the level of dG-2MA or dA-2MA adducts, in hepatic DNA, and Hb adducts, over the whole dose range (r(2) > or = 0.9). Thus, there was strong evidence to support the notion that Hb adducts were an effective surrogate marker for the hepatic DNA damage of rats chronically administered 2NT.