Determination of 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP) and its metabolite 2-hydroxyamino-PhIP by liquid chromatography/electrospray ionization-ion trap mass spectrometry

Screening of non-polar heterocyclic amines in urine by microextraction in packed sorbent-fluorimetric detection and confirmation by capillary liquid chromatography

A rapid and simple procedure for the direct screening of urine samples is described. The method involves microextraction in a packed sorbent (MEPS) that is on-line coupled to a capillary liquid chromatograph with fluorimetric detection. The overall arrangement works as a screening/confirmatory system for monitoring non-polar heterocyclic aromatic amines (HAAs) in urine samples. This configuration allows the selective retention of HAAs from urine on a C(18) MEPS cartridge integrated in the needle of a micro-well plate autosampler. Retained HAAs were eluted with methanol/water (90:10, v/v) and directly injected into the fluorimetric detector. This screening method provides a yes/no binary response that may require confirmation. The samples for which the concentration of HAAs was close to or above the established threshold limit (30 ng mL(-1)) were subjected to capillary liquid chromatography (CLC) for confirmation purposes. A mobile phase of acetonitrile and triethylamine (25 mM) at pH 2.5, through a gradient of composition at a flow rate of 20 μL min(-1), resulted in good separations between the analytes in less than 11 min. This confirmation method allowed the determination of the analytes in the 10-100 ng mL(-1) range for harmane and norharmane and from 20 to 200 ng mL(-1) for 3-amino-1,4-dimethyl-5H-pyrido-[4,3-b] indole (Trp-P-1), 3-amino-1-methyl-5H-pyrido-[4,3-b] indole (Trp-P-2), 2-amino-9H-pyrido-[2,3-b] indole (AαC) and 2-amino-3-methyl-9H-pyrido-[2,3-b] indole (MeAαC), with relative standard deviation (RSD) values between 2.12% and 3.73%, and limits of detection between 1.6 and 5.6 ng mL(-1) for all the HAAs.

Contribution of mass spectrometry to the study of the Maillard reaction in food

The Maillard reaction or non-enzymatic browning corresponds to a set of reactions occurring between amines and carbonyl compounds, especially reducing sugars. The Maillard reaction is known to occur in heated, dried, or stored foods and in vivo in mammalian organisms. In food, the Maillard reaction is responsible for changes in colour, flavor, and nutritive value but also for the formation of stabilizing and mutagenic compounds. Because of the complexity of the Maillard reaction, mass spectrometry, coupled or not to separation techniques, is a key tool in this research area and we will review in this article the contribution of mass spectrometry to the understanding of this reaction. Different steps of Maillard reaction will be described and the importance and the role played by mass spectrometry will be highlighted. In addition, different approaches to investigate the Maillard reaction from the formation of Amadori products (early Maillard reaction product) to the flavor and melanoidin production will also be covered.

Human cytochrome p450 2s1: lack of activity in the metabolic activation of several cigarette smoke carcinogens and in the metabolism of nicotine

Cytochrome P450 (P450) enzymes play a critical role in the metabolic activation of a wide variety of environmental carcinogens. Recently, a novel human P450 enzyme, CYP2S1, has been identified. It is inducible by dioxin and other classical aryl hydrocarbon receptor ligands. However, little is known regarding the substrates and the functional role of CYP2S1. Since CYP2S1 is predominantly expressed in human lung and trachea, it is reasonable to speculate that CYP2S1 may play an important role in metabolizing the environmental chemicals to which human respiratory tissues are exposed. In the present study, we examined the activity of human CYP2S1 in the metabolism of nicotine and in the activation of three potent carcinogens in cigarette smoke, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), benzo[a]pyrene (BaP), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). The full-length CYP2S1 cDNA was amplified by nested polymerase chain reaction from a human lung cDNA library and was expressed in both Chinese hamster ovary (CHO) cells and Sf9 insect cells. In contrast to the positive controls, i.e., CHO cells expressing human CYP2A13 (for NNK activation) or human CYP1A1 (for BaP activation), there was no increase in NNK- or BaP-induced toxicity in the CHO cells expressing CYP2S1. The heterologously expressed CYP2S1 proteins showed no detectable activity in metabolizing nicotine and PhIP. These results clearly demonstrate that CYP2S1 does not catalyze the metabolism of nicotine and the metabolic activation of these lung carcinogens.