Carcinogen procarcinogen

Assay system Noncarcinogen Ultimate carcinogen Procarcinogen Ultimate + procarcinogens (combined) ... 

All carcinogens Ultimate carcinogens Procarcinogens Noncarcinogens Unknown carcinogenicity... 

Nitrogen species, such as nitrate and nitrite, are known to be confirmed procarcinogens. The excessive input of these nitrogen compounds with food and drinking water in the presence of tertiary amines, for instance, from medicines, can lead to the formation of carcinogenic N-nitrosoamines. 

Formation of a dihydrodiol by hydration of epoxide groups can be an important detoxication process in that the product is often much less reactive to potential receptors than is the epoxide. However, this is not invariably the case because some dihydrodiols may undergo further epoxidation to form even more reactive metabolites. As shown in Figure 7.3, this can happen with benzo(a)pyrene 7,8-epoxide, which becomes oxidized to carcinogenic benzo(a)pyrene 7,8-diol-9,10-epoxide. The parent polycyclic aromatic hydrocarbon benzo(a)pyrene is classified as a procarcinogen, or precarcinogen, in that metabolic action is required to convert it to a species, in this case benzo(a)pyrene 7,8-diol-9,10-epoxide, which is carcinogenic as such. 

These short-lived species, in turn, promote the propagation of chain peroxidation of membrane lipids, thus disrupting the cellular integrity, or they may oxidize also various xenobiotics that are in the vicinity. Indeed, the hydroperoxide dependent oxidation process has been implicated as one of the mechanisms of conversion of procarcinogens to carcinogens (6,9) ... 

Aryl hydrocarbon hydroxylase (AHH) is a complex mixed function oxidase enzyme which converts polycyclic aromatic hydrocarbons such as DMBA to more hydrophilic and readily excretable products. During this process metabolites that are more carcinogenic than the parent compound can be produced. The distribution of MFO enzymes, their activity, and the balance between conversion of procarcinogens to active carcinogens and their detoxification is probably a... 

Over 700 chemical and physical agents have been tested with strains of cerevisiae, . porobe, N. crassa, or A. nidulans. The results are being tabulated and related to chemical structure, physical state, carcinogenicity, and procarcinogenicity by the GENE-TOX Program.112 199 258 398 520... 

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