Amination of Tyrosine in Liver Cytosol Protein of Male F344 Rats Treated with 2-Nitropropane, 2-Nitrobutane, 3-Nitropentane, or Acetoxime

Abstract

Previously, the secondary nitroalkane 2-nitropropane, a strong hepatocarcinogen in rats, had been shown to induce the formation of 8-aminoguanine in both DNA and RNA of rat liver through a sulfotransferase-mediated pathway. This pathway was postulated to convert the carcinogen into an aminating species [Sodum, R. S., et al. (1994) Chem. Res. Toxicol. 7, 344-351]. To submit this postulate to further test, we examined liver proteins of rats treated with 2-nitropropane, other carcinogenic secondary nitroalkanes, or the related rat liver tumorigen acetoxime for the presence of 3-aminotyrosine, the expected product of tyrosine amination. Using ion-pair and/or cation-exchange high-performance liquid chromatography with electrochemical detection, we found that the liver cytosolic proteins of these animals contained 0.1-1.5 mol of 3-aminotyrosine/10(3) mol of tyrosine. Treatment with the noncarcinogenic primary nitroalkane 1-nitropropane or with other primary nitroalkanes did not produce an analogous increase in the aminated amino acid (level of detection estimated at approximately 0.01 mol/10(3) mol of tyrosine). To our knowledge, this is the first report of the modification of protein tyrosine in vivo by a carcinogen. In vitro studies with acetoxime-O-sulfonate and hydroxylamine-O-sulfonate showed that these proposed intermediates in the activation pathway of 2-nitropropane react with guanosine to give 8-aminoguanosine, N1-aminoguanosine, and 8-oxoguanosine and also react with tyrosine to give 3-aminotyrosine and 3-hydroxytyrosine. The in vitro amination and oxidation of guanosine at C8 were also produced by acetophenoxime-O-sulfonate and 2-heptanoxime-O-sulfonate. These results provide additional evidence for the production of a reactive species capable of aminating nucleic acids and proteins from 2-nitropropane and other carcinogenic secondary nitroalkanes by a pathway involving oxime- and hydroxylamine-O-sulfonates as intermediates.

N2-Amination of Guanine to 2-Hydrazinohypoxanthine, a Novel in Vivo Nucleic Acid Modification Produced by the Hepatocarcinogen 2-Nitropropane

“…We have previously demonstrated by in vivo and in vitro studies that aryl sulfotransferase is essential for the formation of all three RNA and DNA nucleoside modifications, a finding recently corroborated by others (7,8). We have also proposed the formation of an unsubstituted nitrenium ion, NH 2 + (7), as an ultimate reactive species in the activation pathway of 2-nitropropane (Scheme 1) capable of aminating proteins and nucleic acids (6,7,9). The observed reactions of hydroxylamine-O-sulfonic acid, a proposed metabolic intermediate (6) in Scheme 1, with guanosine to generate both 8-amino-and 8-oxoguanines (Scheme 2), and tyrosine to give 3-aminotyrosine, support the proposed pathway (6,9).…”

Determination of 3-Nitrotyrosine by High-Pressure Liquid Chromatography with a Dual-Mode Electrochemical Detector

“…The stepwise nature of the hydrodynamic voltammetry curve of the reduced species in Fig. 1B which is markedly different from that shown by 3-aminotyrosine (34), suggests that the reduction of 3-nitrotyrosine may proceed through several intermediates, probably including the nitroso and the hydroxylamine forms. Voltages higher than ϩ0.6 V were not used at the downstream electrode to minimize the background current.…”

Analysis of free and protein-bound nitrotyrosine in human plasma by a gas chromatography/mass spectrometry method that avoids nitration artifacts

“…HPLC coupled with electrochemical detection is reported to be the most sensitive method [21] but has the disadvantage that nitrotyrosine is reduced to 3-aminotyrosine to ensure satisfactory sensitivity [22]. Moreover, 3-aminotyrosine is reported to be produced in i o (0.1-1.5 mol of 3-aminotyrosine\10 kmol of tyrosine) [23] via tyrosine amination, so endogenous 3-aminotyrosine might cause interference with the sample of interest. HPLC with electrochemical detection has been used to measure 3-nitrotyrosine in a range of disease states [17][18][19][20][21][22][23][24].…”

“…Moreover, 3-aminotyrosine is reported to be produced in i o (0.1-1.5 mol of 3-aminotyrosine\10 kmol of tyrosine) [23] via tyrosine amination, so endogenous 3-aminotyrosine might cause interference with the sample of interest. HPLC with electrochemical detection has been used to measure 3-nitrotyrosine in a range of disease states [17][18][19][20][21][22][23][24]. In one study the concentration of nitrotyrosine in human plasma proteins was reported as 2.3 µmol\mol of tyrosine [18] (0.2 ng\mg) and in another as being below the limit of detection to 4.2 ng\mg [2].…”