Demethylation of aminopyrine

One of numerous examples of LOX-catalyzed cooxidation reactions is the oxidation and demethylation of amino derivatives of aromatic compounds. Oxidation of such compounds as 4-aminobiphenyl, a component of tobacco smoke, phenothiazine tranquillizers, and others is supposed to be the origin of their damaging effects including reproductive toxicity. Thus, LOX-catalyzed cooxidation of phenothiazine derivatives with hydrogen peroxide resulted in the formation of cation radicals [40]. Soybean LOX and human term placenta LOX catalyzed the free radical-mediated cooxidation of 4-aminobiphenyl to toxic intermediates [41]. It has been suggested that demethylation of aminopyrine by soybean LOX is mediated by the cation radicals and neutral radicals [42]. Similarly, soybean and human term placenta LOXs catalyzed N-demethylation of phenothiazines [43] and derivatives of A,A-dimethylaniline [44] and the formation of glutathione conjugate from ethacrynic acid and p-aminophenol [45,46],... 

In vitro demethylation of aminopyrine by fish liver preparations was reported by DeWaide (6). Olson et al. (32) showed the in vivo stepwise N-dealkylation of the herbicide, N3,N3-diethyl-2,4-dinitro-6-tri fluoromethyl-ra-phenylenediamine (dinitramine), by carp (Figure 1). Biotransformation products were found in... 

The structural feature of aminopyrine is similar to antipyrine except that aminopyrine has a substituent (dimethylamino group) at the C-4 position (Fig. 4). The exceptional efficacy of the aminopyrine breath test derives from the presence of multiple N-methyl groups that are readily removed by oxidative N-demethyla-tion. Hence, further oxidation of several formaldehyde molecules produced by demethylation of aminopyrine gives large volumes of labeled COj that is readily quantified. Some of the metabohtes of aminopyrine are given in Fig. 4 [30, 85, 87-90]. 

Oshino, N. and Chance, B. (1977) Properties of glutathione release observed during reduction of organic hydroperoxide, demethylation of aminopyrine and oxidation of some substances in perfused rat liver, and their implications for the physiological function of catalase. Biochem. J. 162 509-525. 

Data on the inhibition of demethylation of aminopyrine in microsomes from Phenobarbital-treated rat liver CYP by 4-X-phenoxyanilines, resulted in the delineation of QSAR 7.20. 

Results forthcoming from the literature do not always assist in building a picture of events. The observation [65] that 2- and 4-hydroxylation of biphenyl was competitively inhibited by polysorbate 80 in the hamster contrasts with the finding that in the rat, polysorbate 80 (2mM) had no effect on the linear microsomal demethylation of aminopyrine (also a Type V substrate) [66]. The question arises whether surfactants such as polysorbate 80 produce their effects by interaction as an alternative substrate or by perturbation of a membrane bound enzyme system. Commercial samples of polysorbate 80, Brij 35 and Triton X-100 all enhance the activity of a sarcosine dehydrogenase isolated from a strain of Pseudomonas, due to the presence of free oleic acid in these non-ionic surfactants. Deoxycholate and a sarcosine surfactant (N-dodecanoyl N-methyl glycine) inhibit activity [67]. Correlations between the CMC of the non-ionic surfactants and the concentrations required for enzyme activation are seen in Table 10.9. 

Principle After the test substance has been demethylated by the microsomal enzyme system of the SER (cytochrome P 450), the labelled carbon atoms are catabolized to C02. The velocity of demethylation can be measured by determining the C02 value in expired air. Catabolization of aminopyrine is enhanced with elevated activity of the cytochrome P 450 and reduced accordingly due to the loss of liver cell volume. The metabolization is independent of perfusion. Exposure to radiation is minimal. 

Table III. Apparent Michaelis—Menten Aflinity Constants of Aminopyrine N-Demethylation in Guinea Pig Microsomes under Varying Intakes of Ascorbic Acid...

Although 3-methylcholanthrene treatment stimulates the hydroxylation of 3.4-benzpyrene and zoxazolamine and the N-demethylation of 3-methyl-4-mono-methylaminoazobenzene (Table 8). it does not increase (in some cases decreases) the metabolism of ethylmorphine. hexobarbital, and aminopyrine. By contrast. 

SKF 525-A inhibits the in vitro metabolism of several barbiturates, meperidine, aminopyrine, and codeine, the formation of morphine glucuronide, and the hydrolysis of procaine and ethylglycinexylidide. However, SKF 525-A has no significant effect on the microsomal N-demethylation of monomethyl-4-aminoantipyrine, N-methylaniline or 3-methyl-4-monomethylaminoazobenzene, the O-dealkylation of phenacetin, the hydroxylation of acetanilide, or the sulphoxidation of chlorpro-mazine. 

Emetine - As an inhibitor of protein synthesis at the transcription level, emetine is also active against leukemias L-1210 and P-388, B16 melanomas, Ehrlich ascites carcinoma and Yoshida sarcoma. Pharmacologic studies showed that it effects a sympathetic blockade, antagonizes hyal-uronldase, inhibits oxydative N-demethylatlon of aminopyrine and N-ethyl-morphlne as well as the S-demethylation of 6-MP riboside in vitro. 2,143... 

Although in some animals starvation appears to have effects similar to those of protein deficiency, this is not necessarily the case. For example, in the mouse, monooxygenation is decreased but reduction of p-nitrobenzoic acid is unaffected. In male rats, hexobarbital and pentobarbital hydroxylation as well as aminopyrine A-demethylation are decreased, but aniline hydroxylation is increased. All of these activities are stimulated in the female. Water deprivation in gerbils causes an increase in P450 and a concomitant increase in hexobarbital metabolism, which is reflected in a shorter sleeping time. 

Fonne-Pfister, R., Simon, A., Salaun, J.P., and Durst, F., Xenobiotic metabolism in higher plants. Involvement of microsomal cytochrome P-450 in aminopyrine N-demethylation, Plant Sci., 55, 9-20, 1988. 

Commercial PCB Mixtures. Relatively little information is available on hepatic effects of acute-duration oral exposure to PCBs. Liver microsomal enzyme activity (aminopyrine N-demethylation and acetanilide hydroxylation) was increased in rats exposed to 0.5 mg/kg/day (lowest tested level)... 

A -demethylation (A-dealkylation) of alkylamines such as aminopyrine, A -methylbarbital, and A,A-dimethylaniline is the typical reaction catalyzed by P-450 and peroxidases [225-227]. Biomimetic oxidation of alkyl amines catalyzed by metalloporphyrins is known to yield A-dealkylated products (Scheme lOA) [228-233]. While the dealkylation reactions are the major pathway in the alkyl amine oxidation, Larsen and Jprgensen reported the oxidation of secondary amines to imines by iodosylbenzene catalyzed by Mn (TPP), Fe (TPP), and Mn (salen) (Scheme lOB) [234]. Similar A -dealkylation of A-nitrosodibenzylamine to benzaldehyde and benzyl alcohol was demonstrated by Lindsay Smith et al. as model reactions of carcinogenic A-nitrosodialkylamine metabolism by P-450 [235]. 

Fio. 7. Relationship between changes in hepatic microsomal drug metabolism (aminopyrine demethylase) and microsomal phospholipid content resulting from phenobarbital treatment Rats were injected with phenobarbital (100 mg/kg once daily) at the arrows. The left axis and the s depict demethylation FA = formaldehyde) and the right axis and O s represent phospholipids (mg/g liver). The lack of correlation between the two parameters is particularly noteworthy after discontinuation of phenobarbital. (Orrenius, Ericsson and Emster, J. Cell Biol., 28, 181, 1966.)... 

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