©2001 CRC Press LLC chapter ten Mycotoxins and other toxins from unicellular organisms Anything green, that grew out of the mould, Was a wonderful drug to our fathers of old. — Anonymous Introduction Mycotoxins are a group of chemically diverse and complex substances present in a wide variety of filamentous fungi (molds). They are secondary metabolites of fungal metabolism of uncertain function. Some may have a survival advantage by virtue of their toxicity to competing organisms in the microenvironment. The biological function of others is unclear, but many have significant biological activity and several are toxic to mammals. They therefore have significant public health and economic implications. It is estimated that 25% of the world's annual food crops are contaminated by mycotoxins. Some mycotoxins are of interest to pharmacologists and toxicologists because they have served as research tools to study cell function and to identify various types of neurotransmitters and blocking agents. Poisonous mushrooms are solid (not filamentous), spore-forming fungi that also con- stitute a health hazard and which have historic, pharmacological signifi- cance, but they are considered separately in Chapter 11. Some human health problems due to mycotoxins Reports of toxicity from molds are as old as recorded history. Ergotism The oldest recorded source of fungus poisoning is ergotism. Ergot is the common name for the fungus Claviceps purpurpea that affects cereal grains, especially rye, and that produces a number of very potent pharmacologically ©2001 CRC Press LLC active agents that cause toxic reactions when people eat bread made from contaminated flour. Periodic epidemics of ergotism have occurred through- out history, and in medieval times these were often attributed to supernatural causes. The earliest reference to ergot seems to have been on an Assyrian tablet circa 6000 B.C. which refers to “a noxious pustule in the ear of grain.” The Parsees, an ancient religious community in India, referred in their writ- ings to noxious grasses that caused women to abort and to die shortly thereafter. The ancient Greeks escaped the scourge of ergotism because they never developed a taste for rye bread, which they referred to by a phrase that translates roughly as “that filthy Macedonian muck.” Because rye bread did not reach Europe until after the decline of the Roman Empire, few if any references to ergotism exist in Roman writings. There was an early association of ergot with St. Anthony of Egypt, who lived sometime between 250 and 350 A.D. St. Anthony is considered to be the founder of Christian monastic life and spent long sojourns in the desert, experiencing visions and hallucinations. These frequently involved attacks by Satan in various guises (wild beasts, soldiers, and women) that either physically attacked him or tempted him. Contemporary witnesses claimed that he behaved like an individual being physically abused. Because the signs and symptoms of ergot poisoning resembled his attacks, sufferers in the Middle Ages attached religious significance to them and they came to be known as “St. Anthony's Fire” (or sometimes “Holy Fire”). In 1100, the Monastery of the Hospitillers of St. Anthony was established at La Motte in France. It became the site of pilgrimages by those afflicted with this malady. The signs and symptoms included intense burning pain in the extremities followed by a blackened, necrotic appearance; hence the association with fire. Epidemics of madness in the Middle Ages may also have been the result of ergotism. Ergot was employed as an abortifacient long before it was known to be the cause of St. Anthony's Fire, and this use continued well into the nine- teenth century when it was finally abandoned because of its highly toxic nature. One of the components of ergot is still employed to stop postpartum hemorrhage because it constricts blood vessels and contracts the uterus. To summarize, the symptoms of ergotism include drowsiness, nausea, vomit- ing, muscle twitch, staggering, gangrene, hallucinations, and abortion. Ergot contains a veritable potpourri of pharmacological agents that were charac- terized by Sir Henry Dale in the early 1900s and contributed to the devel- opment of many new drugs. The active components of ergot, the ergot alkaloids, are all derivatives of lysergic acid. They bear some molecular resemblance to adrenaline (epi- nephrine), dopamine, and serotonin — all central neurotransmitters. Meth- ysergide is the precursor of LSD. Two derivatives still have medicinal appli- cation. Ergometrine (ergonovine) is the one used to control postpartum bleeding. Ergotamine is a powerful vasoconstrictor responsible for the gan- grene of ergotism. In very small doses it can be used to treat migrane. ©2001 CRC Press LLC Ergotism also affects farm livestock, causing similar signs and, in addition, loss of milk production in cattle and necrotic combs, feet, and beaks in poultry. Aleukia Aleukia (literally “absence of white cells”) occurs when millet and other grains that have become moldy are consumed. The toxin is a tricothecene from species of Fusarium and it damages bone marrow. Because of severe food shortages in Russia during World War II, the eating of moldy grain resulted in several epidemics of aleukia, including a very large one in 1944. The mortality rate of those with marrow damage was 60%. Other symptoms included hemorrhages in the skin and mucous membranes. The condition is also referred to as alimentary toxic aleukia. Aflatoxins Aflatoxins are a family of heterocyclic, oxygen-containing compounds secreted by the molds Aspergillus flavus and A. parasiticus . These molds grow abundantly on many kinds of plants in very hot conditions. Peanuts are especially prone to infection. Taste is not affected and the toxins are heat stable. Aflatoxin B 1 (AFB 1 ) is the most frequently encountered member of the group and it is a potent carcinogen in experimental animals (rodents, birds, and fish). Rats fed a diet containing 15 ppb AFB 1 develop hepatitis, which is often followed by cancer of the liver. Epidemiological studies of populations in Uganda, Kenya, and Thailand have shown a close correlation between the incidence of liver cancer and the consumption of food contain- ing aflatoxins. It is estimated that the risk factor for liver cancer is increased 10 times by AFB 1 . Infectious hepatitis also increases the risk by a factor of 10. If present together, the risk is increased 100-fold. Other aflatoxins include B 2 , G 1 , and G 2 . Lactating cattle excrete hydroxylated metabolites M 1 and M 2 in milk. These have lower toxicity than the parent compounds but are of concern because of the large amount of milk consumed by infants and young children. Thus, this natural carcinogen, at least as potent as TCDD in animal studies, is strongly implicated as a cause of human cancer, unlike the latter synthetic agent, that has received much more media coverage. Experiments employing human liver microsomal preparations indicate that cytochrome P450 (Cyp) 3A4 is largely responsible for the formation from AFB 1 of the 8,9- endo -epoxide, a genotoxic metabolite. Cyp 1A2 also forms this epoxide but is much less active. It forms other, nongenotoxic metabolites and thus may play a role in detoxification. An inhibitor of Cyp 1A2, alpha-naphthofla- vone, increased the formation of the 8,9-epoxide. The exo -epoxide of AFB 1 (i.e., preformed before ingestion) is detoxified by conjugation with glu- tathione. Experimental evidence suggests that species differences in toxicity are due to differences in the rate and extent of conjugation with glutathione. ©2001 CRC Press LLC Whereas rat liver cytosol conjugated endo-epoxide, mouse liver cytosol con- jugated the exo -epoxide almost exclusively and both were much more active than the cytosol of human liver cells. The mucus cells of the intestine also make the 8,9-epoxide, but because they are sloughed frequently, this does not constitute a risk factor for cancer. Other aflatoxins found together are B 2 , G 1 , and G 2 . Acute toxicity also can occur in humans. In 1974, an outbreak in India resulted in about 100 deaths, and in Kenya 12 died in an outbreak in the early 1980s. The aflatoxin story began in 1960 with a serious and mysterious outbreak of a disease in turkeys in Great Britain. Turkey poults developed loss of appetite, feeble fluttering, lethargy, and frequently died within a few days. Necropsies revealed hemorrhage and necrosis of the liver and kidney. The disease was dubbed “X” disease. Outbreaks also occurred in ducklings in Europe, the United Kingdom, and Africa. The common denominator was groundnut (peanut) meal used as feed and subsequently shown to be con- taminated with A. flavus . Livestock (mammals) may also be affected. Death has occurred in humans consuming an estimated 6 mg/day of aflatoxin B 1 . In North America, there is concern about the long-term effects of con- suming low levels of aflatoxins and monitoring systems are in place. Fortu- nately, the mold is not adapted to the colder northern climate so that Cana- dian-grown peanuts are free of the toxins. The majority of peanuts and peanut butter are still imported from subtropical climes, however. Peanuts are not the only source of these toxins. Because of drought conditions in the United States in the summer of 1988, up to 30% of the corn crop may have been contaminated. The Quaker Oats Co. was turning away almost one truckload in five at its Cedar Rapids (Iowa) plant in the fall of 1988. The company tests six samples from each truck. Inspections of the 340,000 tons of corn crossing the Canada–U.S. border annually were stepped up in 1988–1989 by Agriculture Canada. The general structure of aflatoxins is shown in Figure 37. Fumonisins Produced by Fusarium monilforme and F. proliferatum , these mycotoxins are ubiquitous in many parts of the world, including South Africa where they were first identified and many states bordering the Great Lakes. All of the fumonisins (FB 1 , FB 2 , FB 3 ) are potentially carcinogenic. Many experts feel that it will become the most significant mycotoxin for human health. FB 1 has been shown to be carcinogenic for animals (a promoter and initiator of liver cancer in rats), and there is a high degree of correlation between the incidence of esophageal cancer in humans and the presence of FB 1 in corn in specific areas of South Africa. The fungus infects corn, millet, sorghum, and rice around the world. Fumonisins are toxic for many species of animals, espe- cially horses, and outbreaks have caused numerous deaths in horses and ©2001 CRC Press LLC swine in Texas, Iowa, and Arizona. Severely infected corncobs may contain up to 900 mg/kg. Symptomatology in various species is as folllows: • Swine : vomiting, convulsions, sudden death, abortion, pulmonary edema (porcine pulmonary edema syndrome). Symptoms may occur at levels above 20 to 50 mg/kg of FB 1 . • Poultry : ataxia, paralysis, sudden death, stunted growth. Toxicosis occurs at levels of contamination of 10 to 25 mg/kg of FB 1 . • Cattle : poor weight gain, liver damage. • Horses : equine leukoencephalomalacia (ELEM), brain degenera- tion with focal necrosis, blindness, wild behavior, liver damage, staggering, ataxia. Symptoms may occur at levels of 10 mg FB 1 /kg over 40 days. FB 1 , FB 2 , and hydrolyzed FB 1 have been shown to be specific inhibitors of de novo sphingolipid synthesis and sphingolipid turnover. FB 1 has been shown to inhibit sphingosine (sphinganine) N-acetyltransferase, leading to the accumulation of sphyngoid bases. This has been shown to stimulate DNA synthesis, and it is hypothesized that this interference with normal cell function could account for the toxicity of fumonisins. The fumonisins are themselves analogs of sphingosine, with structural similarities to the phorbol esters, which are known carcinogens (see Chapter 11). The general structure of fumonisins is shown in Figure 37. Figure 37 Chemical structures of aflatoxins and fumonisins. O O O O AFB 1 R1 R3 R2R1 CH3 NH2 CH3CH3 OH AFB 1 8,9-Epoxide O CH 3O O O O O O O CH 3O Fumonisin B1: R1 = 0-PTCA*, R2 = R3 = OH Fumonisin B 2: R1 = 0-PTCA, R2 = H, R3 = OH *PTCA = Propanetricarboxylic acid ©2001 CRC Press LLC Other mycotoxic hazards to human health Several mycotoxins may be potential health hazards by virtue of direct toxic effects or because of carcinogenic or teratogenic properties, although it must be emphasized that hard evidence linking these to human health problems is scanty. Ochratoxin A is formed by Aspergillus and Penicillium species. It has been shown to be embryotoxic and teratogenic in several laboratory species of mammals (pig, dog, mouse, rat) and birds and is therefore viewed as a potential human teratogen. Acute effects in animals (including swine and poultry) include renal and hepatic destruction. Both humoral and cel- lular immune systems are adversely affected. Contamination of bread and cereals has been documented in parts of central Europe (Yugoslavia, Bul- garia, Poland, and Germany) and levels have been detected in human milk, urine, blood, and kidneys. Patulin is potentially a carcinogenic toxin produced by several species of fungi, including some Penicillium spp. It is a highly potent inhibitor of RNA polymerase, having a strong affinity for sulfhydryl groups. It therefore inhibits many enzymes. Teratogenicity has not been demonstrated in mam- mals but embryolethality occurs at higher doses (2 mg/kg i.p.). A common source of patulin is Penicillium expansum , a common spoilage microorganism in apples. Apple juice can sometimes contain significant amounts of patulin. Acute toxicity in rodents is manifested primarily as gastrointestinal symp- toms, including hemorrhage. Carcinogenicity studies in rats were negative, but clastogenic activity has been shown in some systems. T-2 toxin is produced by various Fusaria and is both potent and common. It inhibits protein and DNA synthesis and is therefore potentially teratogenic and carcinogenic. Acute effects include loss of appetite and vomiting. Fungi tend to produce mixtures of toxins so that exposure to a single agent is unlikely to occur. There is some experimental evidence that ochra- toxin A potentiates the teratogenic effects of T-2. It must be emphasized that any mycotoxin that has been shown to be toxic in several mammalian species (including various farm livestock) must be regarded as potentially toxic for humans. Economic impact of mycotoxins In addition to their direct effects on human health, mycotoxins have a tre- mendous impact on agriculture. Through spoilage, field crops are rendered useless for animal or human consumption (the loss of 20% of the corn crop noted above is one example). Poor weight gain and outright illness occur in livestock that consume contaminated feeds. Losses are difficult to estimate but they undoubtedly run to many millions and possibly billions of dollars in North America. The presence of trace quantities in meat, dairy products, and eggs constitutes a further, if largely unconfirmed, health hazard to people. In the Great Lakes basin, various species of Fusarium are the most ©2001 CRC Press LLC common offenders, especially in eastern Canada. They may produce a host of toxins with potent pharmacological actions. Fusarium life cycle Fusarium graminearum is the fungus responsible for maize ear rot in corn and head blight in wheat. Its life cycle is typical of all Fusaria . Spores survive in crop debris from the previous season (stubble, stalks and seeds) to re-infect the next year's crop. Intensive farming practices that involve planting suscep- tible species in the same fields year after year thus favor the spread of infec- tion. Birds such as starlings and red-winged blackbirds, which puncture the corn kernels to eat the milk, may also spread spores. Insects such as the picnic or corn-sap beetle seek out damaged kernels and also may spread spores. Certain weather conditions favor the spread of infection. Fungus growth is favored by warmth (15 to 35°C) and by surface wetness for more than 48 hr. After the infection is established, weather is not critical to the produc- tion of the toxin. Mold growth will continue throughout the season, and even afterward if not properly dried or if storage conditions are poor (too damp, too warm, poor air circulation). Mold growth can even occur during feed preparation and in poorly cleaned feed troughs. Late harvest may allow the growth of another fungus, F. sporotrichiodes , which produces the toxins T-2, HT-2, and diacetoxyscirpenol. Contaminated grains thus will contain complex mixtures of toxins and metabolites. The following is a list of the other important ones and their effects. Trichothecenes Zearalonone This estrogen-like toxin causes (in swine) swollen, red vulva, vaginal and rectal prolapse, vulval enlargement in piglets, and fertility problems. Devel- opmental defects and lethality have been shown in some laboratory species. Vomitoxin (deoxynivalenol or DON) This trichothecene causes decreased feed intake and reduced weight gain in pigs at about 2 mg/kg of feed, vomiting, and refusal of feed at very high concentrations (>20 mg/kg feed). DON will be used as a “prototype” mycotoxin to illustrate agricultural problems associated with these agents (see below). Species differences in DON toxicokinetics Swine appear to be much more sensitive to the anorexic and weight loss effects of DON than ruminants (cattle, sheep) or poultry, which are very ©2001 CRC Press LLC tolerant. In one study, laying hens actually preferred a diet containing 5 ppm DON in preference to clean feed. These differences are due, in part, to differences in absorption and, in part, to differences in biotransformation and elimination. Studies with radiolabeled DON indicated that sheep absorbed 9% or less of an orally administered dose, in turkeys 20% or less was absorbed, whereas pigs absorbed up to 85% of a single oral dose. Intravenous administration of radiolabeled DON in sheep revealed an initial distribution phase (t 1/2 = 18 min) followed by an elimination phase (t 1/2 = 66 min). A glucuronide conjugate was formed and comprised 15 to 20% of plasma levels. In turkeys there was an extremely rapid distribution phase (t 1/2 = 3.6 min), a rapid elimination phase (t 1/2 = 46 min), and the formation of a conjugate (probably glucuronide) comprising up to 10% of the total dose. Again, swine showed a much different picture. There was a very rapid distribution phase (t 1/2 = 5.8 min), a secondary slower distribution phase (t 1/2 = 96.7 min), and a very prolonged terminal elimination phase (up to 510 min). There was no evidence of significant biotransformation in swine. Thus, it took 7 to 10 times longer for swine to clear the toxin than for the other two species. Toxicity is a function of many factors: the concentration of toxin reaching the target organ (which in turn is affected by the rate of absorption at the portal of entry), the extent of distribution to non-target sites (i.e., where no toxic effects occur), the rate and extent of biotransformation to nontoxic metabolites (or to toxic ones as the case may be), and the rate of elimination in urine and feces. The effect of species differences in some of these factors was introduced in Chapter 2. Volume of distribution (Vd) and clearance data provide some information regarding the fate of the absorbed toxin. The apparent Vd is a mathematical calculation of the volume of diluent required to dilute an administered dose of a substance (usually intravenously) to the observed concentration. Vd = M/C where M = mass (amount of substance) and C = concentration of substance. Calculations of Vd for DON yielded values of 0.167 L/kg for sheep vs. 1.3 L/kg for swine, suggesting that in the former DON was confined mainly to the extracellular fluid, whereas in the latter it was taken up by tissues. Initial systemic clearances were not all that different, being 1.37 mL/min/kg for sheep and 1.81 mL/min/kg for swine. An interpretation of this data suggests that DON is initially rapidly distributed to tissues and then slowly released back into the plasma, yielding the slow, terminal elimination phase. Turkeys also had a very large Vd (2.33 L/kg), but they also had an extremely rapid clearance (35.0 mL/min/kg), indicating that DON was rapidly distributed to tissue compartments but not held there. Thus, the extreme sensitivity of swine to DON is the result of: • High oral bioavailability • Wide distribution to tissues • Slow elimination from the body • Minimal detoxification through biotransformation ©2001 CRC Press LLC Other trichothecenes T-2 and HT-2 toxins and diacetoxyscirpenol are more toxic than DON and cause reduced feed intake, vomiting, irritation of the skin and gastrointesti- nal tract, neurotoxicity, teratogenicity, impaired immune function, and hem- orrhage. Adverse effects seen in farm animals are generally caused by mix- tures of these toxins rather than by a single toxin. Blending of several grains in the preparation of feed may further contribute to the toxic diversity of the mixture. Potentiation of effects may occur. Thus, DON at the subthresh- old level of 1 mg/kg plus low (ppb) concentrations of T-2 and other uniden- tified toxins may cause severe toxic manifestations in a sensitive species such as swine. The chemical structures of some of these toxins are shown in Figure 38. Figure 38 Chemical structures of several mycotoxins. HO OH OH OH CH 3 CH 3 CH 3 R 3 R 2 HH OH CH 2 R 1 CH 3 CH 3 CH 2 OH O O O O O O H HH Zearalenone O O Deoxynivalenol ( DON, vomitoxin ) T - 2 : CH 3 COO at R 1 and R 2 , ( CH 3 ) 2 CHCH 2 COO at R 3 HT - 2 : OH at R 1 , CH 3 COO at R 2 , (CH 3 ) 2 CHCH 2 COO at R 3 Diacetoxyscirpenol ( DAS ) : CH 3 COO at R 1 and R 2 , H at R 3 ©2001 CRC Press LLC Detoxification of grains Because of the diverse chemical properties of the mycotoxins, physical and chemical procedures that are effective against one toxin may have little or no influence on the toxicity of others. Thus, there is no single process that can be used. The most important control factor must be the avoidance of conditions favoring fungal growth at all stages of food production. Harvesting and milling Infected kernels may represent less than 5% of all the grain. They may be broken or shriveled and in wheat may take on a “tombstone” appearance. In corn, the tips of cobs may have shriveled, highly infected kernels con- taining up to 3000 mg/kg of DON. Grain dust may be very contaminated. Screening and blowing will remove much of the dust, particles, and with- ered kernels. Wet milling of corn has been shown to remove about two thirds of the T-2 toxin, but milling had little effect on the DON content of flour from hard wheat, nor did baking the flour into bread. Some milling procedures may actually increase the DON content of the finished product. In mild infections, washing and roasting may significantly reduce toxin levels. Chemical treatments Laboratory tests have shown that moist ozone, ammonia, microwaving, and convection heating reduce DON concentrations in moldy grain. Aqueous sodium bisulfite plus heat effected a complete detoxification. Studies have shown that this technique resulted in normal feed intake and weight gains when contaminated corn was treated and fed to swine. Binding agents The addition of binding agents, such as bentonite, anionic and cationic resins, and vermiculite-hydrobiotite were tested on the toxicity of T-2 in rats. Ben- tonite prevented T-2 toxicosis by blocking intestinal absorption. Polyvi- nylpyrrolidone or ammonium carbonate had no effect on DON toxicity in swine. Alfalfa fiber has been shown to partially overcome the growth- depressing effect of zearalenone in rats but not the estrogenic effects in swine. Other techniques Dilution of contaminated feed with clean feed will improve palatability and feed consumption. More concentrated diets with respect to calories, protein, etc. may overcome the effects of a moderate reduction in feed intake. Exper- imentally, antibodies against zearalenone have been raised in swine and shown promise in protecting against its toxic effects. [...]... conjugation of aflatoxin B1 exo- and endo-epoxides by rat and human glutathione-S-transferases, Chem Res Toxicol., 5, 470–478, 1992 Raney, K.D., Shimada, T et al., Oxidation of aflatoxins and sterigmatocystin by human liver microsomes: significance of aflatoxin Q1 as a detoxication product of aflatoxin B1, Chem Res Toxicol., 5, 202– 210, 1992 Schroeder, J.J., Crane, H.M., Xia, J., Liotta, D.C., and Merrill, A.M., Disruption... closeness to us on the phylogenetic tree, fruit- and plant-eating primates are generally more efficient metabolizers of xenobiotics than humans In further support of this theory, it can be pointed out that the t 1/2 for amphetamine is about 86 min in both the rabbit and the horse, but is 390 min for the cat and 300 min for humans The question of mycotoxin residues in human food sources remains largely unanswered,... 1995 Nair, M.G., Fumonisins and human health, Ann Trop Paediatr., 18 (Suppl.), S47–S52, 1998 Pitt, J.I., Toxigenic fungi and mycotoxins, Br Med Bull., 56, 184–192, 2000 Rheeder, J.P., Marasas, W.F.O et al., Fusarium moniliforme and fumonisins in corn in relation to human cancer in Transkei, Phytopathology, 82, 352–357, 1992 Raney, K.D., Meyer, D.J., Ketterer, B., Harris, T.M., and Guengerich, F.P., Glutathione... of which can be fatal to a human Lab animals may show ©2001 CRC Press LLC symptoms at 10 6 µg/kg Botulinum toxin blocks the release of acetylcholine from peripheral nerve endings Further reading Eaton, L and Gallagher, E.P., Mechanisms of aflatoxin carcinogenesis, Annu Rev Pharmacol Toxicol., 34, 135–172, 1994 Marasas, W.F., Fumonisins: their implications for human and animal health, Nat Toxins, 3, 193–198,... practical way of detoxifying corn and wheat contaminated with mycotoxins 3 Which of the following statements is/are true? a There is no evidence that fumonisins are carcinogenic for humans b Zearalenone has estrogen-like activity c Aflatoxins are not toxic for poultry d Ochratoxin causes renal damage in swine and poultry 4 The symptoms of ergot poisoning: a Are similar for humans and animals b Include nausea,... or False a Aflatoxin B1 8,9-epoxide is genotoxic b Aflatoxin B1 epoxides are formed exclusively after ingestion of AFB1 c Conjugation with glutathione is an important means of detoxifying AFB1 epoxide d The 8,9-epoxide is formed exclusively by Cyp 1A2 e Cyp 3A4 is the main source of 8,9-endo-epoxide f Species differences in the rate and extent of glutathione congugation of 8,9-epoxide may account for... and Merrill, A.M., Disruption of sphingolipid metabolism and stimulation of DNA synthesis by fumonisin B1 A molecular mechanism for carcinogenesis associated with Fusarium moniliforme, J Biol Chem., 269, 3475–3481, 1994 Shepphard, G.S., Theil, P.G., Stockenstrom, S., and Sydenham, E.W., World-wide survey of fumonisin contamination of corn and corn-based products, J AOAC Int., 79, 671–687, 1996 Shier,... pentapeptides that are hepatotoxic and have caused numerous deaths when they contaminate drinking water Some strains of that ubiquitous organism Staphylococcus aureus are capable of producing a protein enterotoxin, 1 µg of which can induce vomiting, severe colic, and profuse diarrhea The bacteria are usually introduced to foods from infected handlers, and they proliferate in warmth and especially in creamy foods... antibacterial and antifungal antibiotics, many of which have significant mammalian toxicity Many others were tested and discarded because of their high toxicity Some antibiotics are teratogenic and are used in the treatment of cancer because of their effects on cell reproduction (e.g., actinomycin D, doxorubicin, adriamycin) Some organisms may be directly responsible for poisonings in humans The blue-green... 35th Report of the Joint FAO/WHO Expert Committee on Food Additives WHO, Geneva, 1990, 29–30 Review questions For Questions 1 to 10, use the following code: Answer A if statements a, b, and c are correct Answer B if statements a and c are correct Answer C if statements b and d are correct Answer D if statement d only is correct Answer E if all statements (a, b, c, d) are correct ©2001 CRC Press LLC . exo - and endo -epoxides by rat and human glu- tathione-S-transferases, Chem. Res. Toxicol ., 5, 470–478, 1992. Raney, K.D., Shimada, T. et al., Oxidation of aflatoxins and sterigmatocystin. filamentous), spore-forming fungi that also con- stitute a health hazard and which have historic, pharmacological signi - cance, but they are considered separately in Chapter 11. Some human health problems. Other trichothecenes T-2 and HT-2 toxins and diacetoxyscirpenol are more toxic than DON and cause reduced feed intake, vomiting, irritation of the skin and gastrointesti- nal tract, neurotoxicity,