Simultaneous immunoaffinity purification of O6-methyl, O6-ethyl-, O6-propyl- and O6-butylguanine and their analysis by gas chromatography/mass spectrometry

Quantitative analysis of biomarkers, drugs and toxins in biological samples by immunoaffinity chromatography coupled to mass spectrometry or tandem mass spectrometry: A focused review of recent applications

Immunoaffinity chromatography (IAC), mass spectrometry and especially tandem mass spectrometry (MS/MS) represent the most efficient and reliable analytical techniques for specific isolation, unequivocal identification and accurate quantification of numerous natural and synthetic substances in biological samples. This review article focuses on the combined use of these outstanding methodologies in basic and clinical research and in life sciences for the quantitative analysis of low- and high-molecular mass biomarkers, drugs and toxins in urine, plasma or serum samples, in tissue and other biologicals systems published in the last decade. The analytes discussed in some detail include the biomarkers of oxidative stress 15(S)-8-iso-prostaglandin F(2alpha) {15(S)-8-iso-PGF(2alpha)} and 3-nitrotyrosine, the major urinary metabolite of the lipid mediators cysteinyl leukotrienes, i.e., the leukotriene E(4) (LTE(4)), melatonin, and the major collagen type II neoepitope peptide in human urine.

O6-alkylguanines, dietary N-nitroso compounds, and their precursors in gastric cancer

Several N-nitroso compounds, present in foods and beverages or formed in the stomach from their precursors, act as alkylating agents. By using a highly reliable technique (high-resolution gas chromatography-mass spectrometry with negative-ion chemical ionization and selected ion recording), we measured a series of specific O6-alkylguanines in snap-frozen paired stomach tissue samples (tumor and noninvolved mucosa) obtained at surgery from 24 gastric cancer patients identified in Florence, Italy. Samples of noninvolved mucosa had higher levels of total O6-alkylguanines and more frequently detectable levels (54%) than tumor samples (29.2%). O6-propylguanine and O6-methylguanine were the single adducts most frequently detected in noninvolved mucosa and tumor tissue, respectively. Tumor samples showed higher levels of total O6-alkylguanines in female patients (p = 0.03) and among those with a diffuse histological type (p = 0.06) or seronegative for Helicobacter pylori CagA antibodies (p = 0.06). Mean dietary nitrate intake was significantly higher in patients with detectable levels of adducts in tumor samples (p = 0.03). Estimated intakes of dimethylamine and N-nitrosodimethylamine correlated with total levels of O6-alkylguanines in noninvolved gastric mucosa. These findings, although based on a small series of cases, support a role for N-nitroso compounds from dietary sources in the etiology of gastric cancer.

Affinity chromatography as a method for sample preparation in gas chromatography/mass spectrometry

Analytical chemistry aims at developing analytical methods and techniques for unequivocal identification and accurate quantitation of natural and synthetic compounds in a given matrix. Analytical methods based on the mass spectrometry (MS) technology, e.g., GC/MS and LC/MS and their variants, GC/tandem MS and LC/tandem MS, are best suited both for qualitative and quantitative analyses. GC/MS methods not only serve as reference methods, e.g., in clinical chemistry, but they are now widely and routinely used for quantitative determination of numerous analytes. However, despite inherent accuracy, analytical methods based on GC/MS commonly consist of several analytical steps, including extraction and derivatization of the analyte. In general, unequivocal identification and accurate quantification of an analyte in very low concentrations in complex matrices require further chromatographic techniques, such as high-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) for sample purification. In recent years, affinity chromatography (e.g., boronate and immunoaffinity chromatography) has been developed to a superior technique for sample preparation of numerous classes of compounds in GC/MS. In this article, the application and importance of affinity chromatography as a method for sample preparation in modern quantitative GC/MS method is described and discussed, using as examples various natural and synthetic compounds, such as arachidonic acid derivates, nitrosylated and nitrated proteins, steroids, drugs, and toxins.

Carcinogen-DNA adducts as tools in risk assessment

Genotoxic chemicals are known to react with DNA either directly or after metabolic activation to form adducts, a step thought to be relevant with respect to chemical carcinogenesis. Evaluation of cancer risk due to exposure to chemicals requires information about the internal dose which depends on individual variation in rates of metabolic activation and detoxification. The presence and the amount of specific DNA adducts provide a good indication of chemical exposure and genetic damage resulting from exposure to carcinogens and account for some of the factors affecting individual susceptibility to cancer. Analysis of DNA adducts requires that the sensitivity of the methods be sufficiently high to allow the detection of about 1 adduct/109 normal nucleotides. Most suitable methods are based on 32P-postlabelling, immunoassays or physico-chemical techniques such as HPLC coupled to synchronous fluorescence spectroscopy or gas chromatography-mass spectrometry. These methods have been used to assess human exposure to a variety of chemical carcinogens including polycyclic aromatic hydrocarbons, aromatic amines, heterocyclic aromatic amines or aflatoxins. In some instances, the use of DNA-adducts has given accurate estimates of risk.