Author's copy! Any use beyond the limits of copyright law without the consent of the publisher is prohibited and punishable. This applies in particular to duplications, translations, microfilming as well as storage and processing in electronic systems. Science & Research | Overview Peer-reviewed | Manuscript received: January 31, 2013 | Revision accepted: May 08, 2013 A food toxicological contemplation of mycotoxins Pablo Steinberg, Hannover Metabolism Summary In order to become toxic, aflatoxin B1 Mycotoxins are the products of the endogenous metabolism of moulds that can must be metabolically activated v infest crops and already lead to adverse health effects in mammals and humans at ( Figure 3). Aflatoxin B1 is first me- low concentrations after the consumption of contaminated feed and food, re- tabolized to the aflatoxin B1-8,9- spectively. In the following report, the main mycotoxins detected in temperate epoxide in a cytochrome P450-cat- zones, namely aflatoxins, ochratoxin A, Fusarium mycotoxins (zearalenone, tri- alyzed reaction. Thereafter, the epox- 7 chothecenes and fumonisine), ergot alkaloids, patulin and citrinin, are briefly in- ide reacts with the N -position of troduced. In this context, their underlying mechanisms of toxicity, their main toxic guanine residues of the DNA and effects in humans and animals as well as the actual burden of foods with aflato- leads to the formation of the afla- 7 xins, ochratoxin A and Fusarium mycotoxins in Germany are described. toxin B1-N -guanine adduct. This adduct is chemically unstable and Keywords: Moulds, mycotoxins, aflatoxins, ochratoxin A, Fusarium toxins can be converted to the so-called aflatoxin B1-formamidopyrimidine adduct by the opening of the imida- zole ring or can decompose by taminate food items of plant and Introduction depurination and lead to an apurinic animal origin (v Figure 1). site in DNA. Products of the endogenous metabo- lism of moulds which can be harm- In this contribution, information re- In both cases, DNA replication leads ful to humans and other living or- garding the most relevant mycotox- to gene mutations, whereby afla- ganisms, are grouped under the ge- ins from a food toxicological point of toxin B1 is a much stronger mutagen neric term „mycotoxins“. Myco- view, namely aflatoxins, ochratoxin than aflatoxin G1 and aflatoxin M1. toxins can be formed by outdoor A, Fusarium mycotoxins, ergot alka- In contrast, the aflatoxins B2, G2 und moulds (e. g. Fusarium spp.), which loids, patulin und citrinin, is sum- M2, which cannot be epoxidized, are can infest the crops already in the marized. hardly genotoxic. Aflatoxin B1 also field, as well as by indoor moulds exhibits a pronounced cytotoxicity (e. g. Aspergillus spp., Penicillium Aflatoxins which is in part due to the signifi- spp.), which can infest the harvested cant formation of covalent protein crops if they are stored inappropria- Aflatoxins are products of the en- adducts. In this case again it is the tely (i. e. too high storage humidity, dogenous metabolism of the moulds aflatoxin B1-8,9-epoxide that plays a too long intervals between the har- Aspergillus flavus, Aspergillus para- central role: It is first metabolized to vesting and the drying step or insuf- siticus and Aspergillus oryzae, which the corresponding dihydrodiol and ficient airing). Once they have been pose a great problem in tropical and then to the corresponding dialdehyde released by moulds, they may con- subtropical regions of the world. (v Figure 3). The dialdehyde in turn Consequently, aflatoxins are mainly can easily react with the ε-amino detected in imported products such groups of lysine. as nuts (pistachios, peanuts, hazel- Citation: nuts), dried fruit (figs) and spices Toxicity Steinberg P (2013) A food toxico- (pepper, paprika powder). Aflatoxin logical contemplation of myco- B1, aflatoxin B2, aflatoxin G1 and In countries, in which the contami- toxins. Ernaehrungs Umschau in- aflatoxin G2 as well as aflatoxin M1 nation of the food chain with afla- v ternational 60(9): 146–151 and aflatoxin M2 ( Figure 2), which toxins is very high, so-called aflato- This article is available online: are mainly detected in milk and milk xicoses may develop. They are cha- DOI 10.4455/eu.2013.027 products, belong to the group of the racterized by nausea, vomiting, ab- aflatoxins. dominal pain and gastrointestinal 146 Ernaehrungs Umschau international | 9/2013 bleeding, icterus, spasms, coma, Ochratoxin A O O O O pulmonary and cerebral oedema O O Ochratoxins are produced by vari- 9 R R formation as well as necroses and 8 ous Aspergillus and Penicillium fatty degeneration of the liver, kid- O O O O neys and heart. species, among others by Aspergillus H OCH3 H OCH3 ochra ceus, Aspergillus carbonarius AFB1: R = H AFB2: R = H AFM : R = OH AFM : R = OH and Penicillium verrucosum, and 1 2 Because of its extremely strong mu- O O O O tagenicity and cytotoxicity (see chemically represent amide deriva- O O tives of L-phenylalanine (v Figure R R above) aflatoxin B1 is the aflatoxin 4). with the greatest carcinogenic po- O O O OCH O OCH tential and induces liver tumours in The most frequently formed and at H 3 H 3 AFG1: R = H AFG2: R = H experimental animals. The Interna- the same time the most toxic ochra- AFGM1: R = OH AFGM2: R = OH tional Agency for Research on Can- toxin is ochratoxin A. It contami- cer (Lyon, France) which is part of nates grains and grain products, Fig. 2: Structural formulae of the most impor- the World Health Organization legumes, coffee beans, beer, wine, tant aflatoxins in food (WHO), classified aflatoxin B1 as a raisins, grape juice as well as meat AFB1/2 = aflatoxin B1/2, AFM1/2 = aflatoxin human carcinogen a decade ago [1]. products and is mainly nephrotoxic. M1/2, AFG1/2 = aflatoxin G1/2, AFGM1/2 = aflatoxin GM The chronic exposure of humans to It has been known for a long time 1/2 aflatoxin B1 also leads to the induc- that because of its structural ho- AFB -N7-G mology to the amino acid L-pheny- 1 tion of liver carcinomas. Moreover, H N - dR 2 H2N NH NH lalanine ochratoxin A is able to in- O it has been known for a number of N O O N O O O OH H2O OH O + O years that the risk to develop liver hibit competitively the phenylala- N HN H N 7 H dR dR N O O tumours increases by about a factor nine-tRNA-synthase. However, the H O O H OCH3 H O OCH above-mentioned enzyme is only 3 of 60 if humans are chronically ex- AFB 1 -FAPY DNA O O posed to aflatoxins through con- inhibited in the presence of very O O O O O 9 H H taminated food and at the same time high concentrations of ochratoxin 8 CYP O O are chronically infected with hepati- A, which in no case are achieved if H O OCH O 3 H OCH3 tis B or C viruses. It has also been humans are exposed to ochratoxin AFB1 AFB1-8,9-epoxide GSH O O A-contamined food items. Hence, H2O pointed out that a relationship be- OH O O GS H O tween the strong contamination of the inhibition of the phenylalanine- OH O O HO H H O the food chain with aflatoxins and tRNA-synthase does not explain the OCH3 O GSH adduct H O OCH the occurrence of the so-called Reye observed renal toxicity. 3 – CO2 AFB1-8,9-diol + syndrome (an acute encephalopathy HC NH3 O O O in combination with a fatty degen- Ochratoxin A induces kidney tu- (H C) O H O 2 3 O Lysin OH O O eration of the liver), most notably in mours in rats. However, the mech- H2C N H HO OCH3 O tropical countries, may exist. anism(s) that lead(s) to the forma- HO OCH3 lysine adduct Fig. 3: Metabolic activation of aflatoxin B1 to aflatoxin B1-8,9-epoxide and forma- primary production feed storage tion of covalent adducts with DNA und proteins AFB1 = aflatoxin B1; AFB1-FAPY = aflato- xin B1-formamidopyrimidine adduct; outdoor moulds indoor moulds 7 7 AFB1-N -G = aflatoxin B1-N -guanine ad- duct; CYP = cytochrome P450; dR = de- oxyribose; GSH = glutathione contamination of feed contamination of food of plant O OR1 origin O O O exposure of livestock N O H CH3 R2 OTA: R1 = H; R2 = CI contamination of food of animal OTB: R1 = H; R2 = H origin 1 2 OTC: R = C2H5; R = CI Fig. 4: Structural formulae of the most im- Fig. 1: Contamination of food items of plant and animal origin with portant ochratoxins toxins from outdoor and indoor moulds OTA/B/C = ochratoxin A/B/C Ī Ernaehrungs Umschau international | 9/2013 147 Science & Research | Overview tion of kidney tumours have been other hand, no efficient crop clean- to estrogen receptors in the uterus, controversially discussed up to the up took place in the flour mills. hypothalamus and pituitary gland. present time. Although there were Despite efforts to reduce the amount The affinity of zearalenone to the es- early indications that DNA adducts of ocharoxin A in food items, a cer- trogen receptors α and β is about one are formed in the kidneys of ochra- tain degree of contamination seems tenth to one twentieth of the affinity toxin A-treated rats, it is not clear to be unavoidable at the moment. of the endogenous estrogen 17β- whether these are oxidative DNA le- The tolerable weekly intake amounts estradiol towards the estrogen recep- sions or covalent adducts of DNA to 120 ng/kg body weight. In the tors α and β.