Acetaminophen, hydrogen peroxide

Various hydroxyl and amino derivatives of aromatic compounds are oxidized by peroxidases in the presence of hydrogen peroxide, yielding neutral or cation free radicals. Thus the phenacetin metabolites p-phenetidine (4-ethoxyaniline) and acetaminophen (TV-acetyl-p-aminophenol) were oxidized by LPO or HRP into the 4-ethoxyaniline cation radical and neutral V-acetyl-4-aminophenoxyl radical, respectively [198,199]. In both cases free radicals were detected by using fast-flow ESR spectroscopy. Catechols, Dopa methyl ester (dihydrox-yphenylalanine methyl ester), and 6-hydroxy-Dopa (trihydroxyphenylalanine) were oxidized by LPO mainly to o-semiquinone free radicals [200]. Another catechol derivative adrenaline (epinephrine) was oxidized into adrenochrome in the reaction catalyzed by HRP [201], This reaction can proceed in the absence of hydrogen peroxide and accompanied by oxygen consumption. It was proposed that the oxidation of adrenaline was mediated by superoxide. HRP and LPO catalyzed the oxidation of Trolox C (an analog of a-tocopherol) into phenoxyl radical [202]. The formation of phenoxyl radicals was monitored by ESR spectroscopy, and the rate constants for the reaction of Compounds II with Trolox C were determined (Table 22.1). 

Graphite powder grade 38 (Fisher, USA) hydrogen peroxide (Merck, Germany) Nujol oil and paracetamol (acetaminophen) (Aldrich, USA). 

Soc., 1999, 121, 3435 T. Hoshi, H. Saiki, S. Kuwazawa, Y. Kobayama and A. Anzai, Polyelectrolyte multilayer film-coated electrodes for amperometric determination of hydrogen peroxide in the presence of ascorbic acid, uric acid and acetaminophen, Anal. Sci., 2000, 16, 1009 E.S. Forzani, VM. Solis and E.J. Calvo, Electrochemical behavior of polyphenol oxidase immobilized in self-assembled structures layer by layer with cationic polyallylamine, Anal. Chem., 2000, 72, 5300 Y.M. Lvov, Z. Lu, J.B. Schenkman, X. Zu and J.F. Rusling, Direct electrochemistry of myoglobin and cytochrome P450cam in alternate layer-by-layer film with DNA and other polyions, J. Am. Chem. Soc., 1998, 120, 4073. 

Peroxynitrite may be an important oxidant produced in acetaminophen-induced MPT. As discussed above, acetaminophen-induced MPT occurred with increased oxidation of the redox-sensitive dye DCFH2. This dye is readily oxidized by peroxynitrite but not by superoxide, hydrogen peroxide, or hypochlorous acid however, it may be oxidized by peroxide plus a peroxidase or a Fenton mechanism (ferrous ions plus peroxide) (Crow 1997 Myhre et al. 2003). Peroxynitrite is known to rapidly react with thiols such as N-acetylcyteine (Crow 2000), and N-acetylcysteine prevented acetaminophen-induced MPT and DCFH2 oxidation (Reid et al. 2005). The finding that nitration was predominantly in mitochondria of acetaminophen-treated mice supports the hypothesis that peroxynitrite formation occurred in that organelle (Cover et al. 2005). As pointed out above, the NOS isoform was probably not iNOS, which suggests involvement of another NOS species such as mitochondrial nitric oxide synthase (mtNOS) (Ghafourifar and Cadenas 2005). 

Figure 3 illustrates the basic set-up. Enzyme E2 is immobilized in the layer to prevent the interfering compound I from reaching the detector surface or the indicator enzyme Ei that is responsible for analyte conversion. For example, ascorbic acid and acetaminophen, which interfere with the anodic hydrogen peroxide oxidation, can be transformed into inert products by reaction with an eliminator enzyme, for example, ascorbate oxidase [18], laccase [19] or tyrosinase [20] or peroxidase [21]. 

A time course experiment of the polymer formation revealed that the polymerization of 32 occurred rapidly after the addition of hydrogen peroxide, and the product formation was almost complete within 0.5 minute from the initiation. Acetaminc hen dimer (B) and acetaminophen trim (c) were the... 

---