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.

Analysis of Chlorination, Nitration, and Nitrosylation of Tyrosine and Oxidation of Methionine and Cysteine in Hemoglobin from Type 2 Diabetes Mellitus Patients by Nanoflow Liquid Chromatography Tandem Mass Spectrometry

“…Hemoglobin adducts of 2-nitrotoluene were reported to be an effective surrogate biomarker for the hepatic DNA damage of rats chronically administered 2-nitrotoluene because the dose-dependent increase of hemoglobin adduct and that of DNA adduct are highly correlated. 69 Therefore, protein adducts have been used as biomarkers for exposure to carcinogens because they are present in higher amounts than DNA adducts and proteins are relatively more accessible than DNA. 70 Analysis of protein adducts were performed by immunoassay or by analysis of Edman degradation products using gas chromatography or liquid chromatography coupled with mass spectrometry.…”

Hemoglobin Adducts and Urinary Metabolites of Arylamines and Nitroarenes

“…The N -hydroxyarylamines and the N -glucuronide are transported through the blood in the bladder. The acidic pH of the urine catalyzes the formation of the nitrenium ion (= very short-lived intermediate) , that gives rise to DNA adducts. , In animal experiments, DNA adducts of arylamines and nitroarenes have been found also in other organs. ,, In blood, N -hydroxyarylamines are taken up in the erythrocytes and oxidized to the nitrosoarenes with the formation of metHb. This process is known as the Kiese Redox-cycle .…”

Biomarkers of Exposure, Effect, and Susceptibility in Workers Exposed to Nitrotoluenes

“…2NT, 24DNT, and 26DNT form Hb-and DNA-adducts in rats (13)(14)(15)(16). Detoxification products are formed after N-acetylation catalyzed by N-acetyltransferase 2 (NAT2), N-sulfo-conjugation (catalyzed by SULT), and by reaction with glutathione [with and without glutathione S-transferase (GST) catalysis].…”