Aflatoxins types

Assessment of whether a chemical has the potential to cause adverse effects in humans arises usually from direct observation of an effect in animals or humans, such as the acute poisoning episodes that have occurred when potatoes contain high levels of glycoalkaloids. Epidemiological studies have also been used to infer a possible relationship between intake of a particular type of food, or constituent of that food, and the potential to cause an adverse effect. Such observations led to the characterisation of the aflatoxins as human carcinogens. However, natural toxic substances that occur in plant foods have often been identified through observations in animals, particularly farm animals. It was observations of adverse effects in farm animals that led to the further characterisation of the phytoestrogens and the mycotoxins. In other instances, the concern arises from the chemical similarity to other known toxins. 

Affinity driven molecular transfer (ADMT) system, 78 264-265 Affinity ligands, 6 390 types of, 6 393-394, 396t Affinity method, 10 339 Affinity resins, 20 197 Affinity-selected libraries, 72 515-517 Affymatrix GeneChip HFV PRT, 76 390 Aflatoxins, 72 84... 

Figure 9.1 Different types of aflatoxins (a) aflatoxin Bi, (b) aflatoxin B2, (c) aflatoxin Gi, (d) aflatoxin G2, (e) aflatoxin Mi.

Risk is the probability that some harmful event will occur. What is the probability that certain types of cancer will develop in populations exposed to aflatoxin in peanut products or benzene from gasoline What is the likelihood that workers exposed to lead will develop nervous system disorders ... 

Before embarking on what is perhaps an overly systematic approach to our subject, we should attempt to develop a bird s-eye view of the entire landscape. We shall use a specific example - the case of a group of chemicals called aflatoxins - to illustrate the type of problem this book is designed to explore. 

Because 1,4-dichlorobenzene is a liver toxin, it probably can interact with other chemicals that are liver toxicants. These toxicants are many, and include ethanol, halogenated hydrocarbons (chloroform, carbon tetrachloride, etc ), benzene, and other haloalkanes and haloalkenes. In addition, 1,4-dichlorobenzene toxicity may also be exacerbated by concurrent exposure with acetaminophen, heavy metals (copper, iron, arsenic), aflatoxins, pyrrolizidine alkaloids (from some types of plants), high levels of vitamin A, and hepatitis viruses. Such interactions could either be additive or S5mergistic effects. 

DETAILS - Aflatoxins are the poisonous product of a group of polynuclear molds that grow on peanuts, com and in cottonseed meal. They are responsible for the Turkey X" disease which occasionally devastates the poultry industry. The presence of the mold doesn t always indicate presence of the toxin. Toxin production is dependent on various factors such as moisture and temperature. There are two basic types of aflatoxins, both of which are fluorescent under UV (black) light. Once the mold has been identified, the UVI ight is an excellent way to check for toxin production. Aflatoxin B glows blue, while Aflatoxm G glows... 

Both benign and malignant liver tumors may arise from exposure to hepatotoxins and can be derived from various cell types. Thus, adenomas have been associated with the use of contraceptive steroids and exposure to aflatoxin Bi, and dimethylnitrosamine can produce hepatocellular carcinomas, whereas vinyl chloride causes hemangiosarcomas derived from the vasculature (see chap. 7). 

Recently, in many demanding sample preparation situations, more selective sorbents have been used. Affinity type sorbents, particularly immunosorbents, have gained popularity in trace analysis, not only for biological macromolecules but also for small molecules, like aflatoxins. MIPs have properties resembling those of affinity phases and therefore they may find unique applications where other sample pretreatment methods are tedious. This relates both to the separation of a single analyte and to the separation of a group of related analytes from the sample matrix. 

Adducts to hemoglobin are perhaps the most useful means of biological monitoring by adduct formation. Hemoglobin is, of course, present in blood, which is the most accurate type of sample for biological monitoring. Adducts to blood plasma albumin are also useful monitors and have been applied to the determination of exposure to toluene diisocyanate, benzo(a)pyrene, styrene, styrene oxide, and aflatoxin Bj. The DNA adduct of styrene oxide has been measured to indicate exposure to carcinogenic styrene oxide.12... 

There is little in the literature relative to vitamin A and colon cancer in human populations. Experimental animal studies, however, strongly suggest that vitamin A deficiency may have a role in this type of cancer. We have shown that a deficiency of vitamin A increased DMH-induced tumors and shortened the lag time for induction, compared to normally supplemented controls (72). More recently (73) we have confirmed a protective role for vitamin A in colon carcinogenesis (Table XVII). Furthermore, we have shown (74) that vitamin A deficiency can result in colon tumors in rats given aflatoxin (AFB ) which is normally a liver carcinogen (Table XVIII). The colon tumors associated with the hepatocarcinogen AFB.. appear to be a result of differences in metabolism and binding of AFB or its metabolite ) to colon DNA under conditions of vitamin A deficiency (75). 

Many natural compounds, such as dihydroclerodin [ 17] or aflatoxin B2 [ 18,19] contain bicyclic acetal units of type furo[2,3b]furan. The synthesis of perhydrofuro[2,3fo]furans and perhydrofuro[2,3fo]pyrans was achieved by... 

Fig. 1. Chemical structure of aflatoxins. (a) The B-type aflatoxins are characterized hy a cyclopeutane E-ring. These compoimds have a hlue fluorescence under long-wavelength ultraviolet hght (h) The G-type aflatoxins have a xanthone ring in place of the cyclopentane, (c) Aflatoxins of the B2 and G2 type have a saturated bis-furanyl ring. Only the bis-firran is shown, (d) Aflatoxins of the Bi and Gi type have a hydrated his-furanyl structure.

Watanabe CMH, Townsend CA. Initial characterisation of a type 1 fatty acid synthase and polyketide synthase multienzyme complex NorS in the biosynthesis of aflatoxin Bi. Chem. Biol. 2002 9 981-988. 

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