Carcinogenic secondary metabolites

Neither the mechanism by which benzene damages bone marrow nor its role in the leukemia process are well understood. It is generally beheved that the toxic factor(s) is a metaboHte of benzene (107). Benzene is oxidized in the fiver to phenol [108-95-2] as the primary metabolite with hydroquinone [123-31-9] catechol [120-80-9] muconic acid [505-70-4] and 1,2,4-trihydroxybenzene [533-73-3] as significant secondary metabolites (108). Although the identity of the actual toxic metabolite or combination of metabolites responsible for the hematological abnormalities is not known, evidence suggests that benzene oxide, hydroquinone, benzoquinone, or muconic acid derivatives are possibly the ultimate carcinogenic species (96,103,107—112). 

Many mycotoxin diseases are associated with various species of fungal genera and their secondary metabolites.The adverse effect of fungal products have caused mass poisoning in both man and farm animals as shown in Table 1. As far as public health problems are concerned, Aflatoxin is well known as one of the most important environmental toxicants, since its potent hepato-carcinogenicity has been demonstrated in various experimental animals and its natural production in cereal and grains has been shown by chemical analysis. 

Mycotoxins are defined as mould derived secondary metabolites, Ochratoxin A and aflatoxin B being the most widely studied. Ochratoxin A (OTA), produced by Aspergillus ochraeus and Penicillium verrucosum, can be found as a contaminant in grain, beer, coffee and meat. OTA is nephrotoxic, carcinogenic and genotoxic [235]. 

Aflatoxins are highly toxic and carcinogenic coumarin derivatives of a complex structure, e.g. aflatoxin 17. It is formed as a secondary metabolite by Aspergillus flavus which occurs in mouldy food. 

Mycotoxins are secondary metabolites of fungi which can cause acute toxic, mutagenic, teratogenic, and carcinogenic effects in animals. The fact that mycotoxins, such as aflatoxin, are among the most potent animal toxins and carcinogens known, warrants concern about the contamination of the human food supply, including dairy products, with mycotoxins. 

The acetylenes and linear furanocoumarins (psoralens) are examples of bioactive secondary metabolites that have been considered undesirable in plant foods due to their toxic effects. Some acetylenes are known to be potent skin sensitizers and irritants, and neurotoxic in high concentrations, but have also been shown to have a pronounced selective cytotoxic activity against various cancer cells. Due to their role in plant defence many acetylenes and psoralens are considered natural pesticides or in some cases phytoalexins since their formation is often induced in plants as a response to external stimuh. Psoralens are photoactivated secondary metabolites that have been used since ancient times to treat human skin disorders. However, the use of these furanocoumarins in medicine has been associated with increased incidence of skin cancer, and a number of studies have also demonstrated that the furanocoumarins can be carcinogenic, mutagenic, photodermatitic and to have reproductive toxicity. 

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