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Toxicokinetics and toxicodynamics of ochratoxin A, an update

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Abstract

Ochratoxin A (OTA) is a mycotoxin produced by fungi of two genera: Penicillium and Aspergillus. OTA has been shown to be nephrotoxic, hepatotoxic, teratogenic and immunotoxic to several species of animals and to cause kidney and liver tumours in mice and rats. Because of differences in the physiology of animal species, wide variations are seen in the toxicokinetic patterns of absorption, distribution and elimination of the toxin. Biotransformation of OTA has not been entirely elucidated. At present, data regarding OTA metabolism are controversial. Several metabolites have been characterized in vitro and/or in vivo, whereas other metabolites remain to be characterized. Several major mechanisms have been shown as involved in the toxicity of OTA: inhibition of protein synthesis, promotion of membrane peroxidation, disruption of calcium homeostasis, inhibition of mitochondrial respiration and DNA damage. The contribution of metabolites in OTA genotoxicity and carcinogenicity is still unclear. The genotoxic status of OTA is still controversial because contradictory results were obtained in various microbial and mammalian tests, notably regarding the formation of DNA adducts. More recent studies are focused on the OTA ability to disturb cellular signalling and regulation, to modulate physiological signals and thereby to influence cells viability and proliferation. The present paper offers an update on these different issues. In addition since humans and animals are likely to be simultaneously exposed to several mycotoxins, especially through their diet, the little information available on the combined effects of OTA and other mycotoxins has also been reviewed.

Introduction

Ochratoxins are a group of secondary metabolites produced by fungi of two genera: Penicillium and Aspergillus. Except ochratoxin α (OTα), the ochratoxins comprise a polyketide-derived dihydroisocoumarin moiety linked via the 7-carboxy group to l-β-phenylalanine by an amide bond. Ochratoxins consist of ochratoxin A (OTA), its methyl ester, its ethyl ester also known as ochratoxin C (OTC), 4-hydroxyochratoxin A (4-OH OTA), ochratoxin B (OTB) and its methyl and ethyl esters and ochratoxin α (OTα), where the phenylalanine moiety is missing (Fig. 1).

OTA is the most toxic member in the group. It was first isolated from Aspergillus ochraceus Wilh. in a laboratory screening for toxigenic fungi [1]. Its configuration was determined using optical rotatory dispersion spectroscopy [2], [3]. The empirical formula is C20H18O6NCl and the molecular weight is 403.82. The IUPAC developed formula of OTA is l-phenylalanine-N-[(5-chloro-3,4-dihydro-8-hydroxy-3-methyl-1-oxo-1H-2-benzopyran-7-yl)carbonyl]-(R)-isocoumarin (Fig. 2).

The chemical abstract specification (CAS) of OTA is 303-47-9. It is a white, crystalline compound, highly soluble in polar organic solvents, slightly soluble in water and soluble in aqueous sodium hydrogen carbonate. The melting points are 90 and 171 °C, when recrystallized from benzene (containing 1 mol benzene/mol) or xylene, respectively [4]. OTA exhibits UV adsorption: λmaxMeOH(nm;ε)=333(6400)[5]. The fluorescence emission maximum is at 467 nm in 96% ethanol and 428 nm in absolute ethanol. The infrared spectrum in chloroform includes peaks at 3380, 1723, 1678 and 1655 cm−1[6]. OTA has weak acidic properties. The pKa values are in the ranges 4.2–4.4 and 7.0–7.3, respectively, for the carboxyl group of the phenylalanine moiety and the phenolic hydroxyl group of the isocoumarin part [7], [8], [9].

OTA production is dependent on different factors such as temperature, water activity (aw) and medium composition, which affect the physiology of fungal producers.

In cool and temperate regions, OTA is mainly produced by Penicillium verrucosum[10], [11], [12], [13] or P. nordicum[12], [13]. P. verrucosum mainly contaminates plants such as cereal crops, whereas P. nordicum has been mainly detected in meat products and cheese [12]. In tropical and semitropical regions, OTA is mainly produced by Aspergillus ochraceus[14], [15], [16]. A. ochraceus is also referred to as A. allutaceus var allutaceus Berkely and Curtis [14]. A. ochraceus have been reported in a large variety of matters like nuts, dried peanuts, beans, spices, green coffee beans and dried fruits, but also in processed meat and smoked and salted fish [16]. Two other species of Aspergillus section Nigri, respectively, A. niger var niger[17], [18] and A. carbonarius[19], [20] have been reported as OTA producers. The OTA contamination of substrata such as cereals, oilseeds and mixed feeds in warm zones is thought to be due to A. niger var niger in addition to A. ochraceus species [21], whereas A. carbonarius seems to be more common on grapes, raisins and coffee [22], [23]. Recently, Samson et al. [24] isolated two new OTA producing Aspergillus species from coffee beans. These species, A. lacticoffeatus and A. sclerotioniger, need further investigations and are provisionally accepted in section Nigri. In addition, another Aspergillus species, A. alliaceus also named Petromyces alliaceus and isolated from onions [25], has been previously reported as OTA producer under laboratory conditions [26]. This species has been suspected to be responsible for the occasional OTA contamination in Californian figs [27], [28] and Argentinean medicinal herbs [29].

The biosynthetic pathway for OTA has not yet been completely established. However, labelling experiments using both 14C- and 13C-labelled precursors showed that the phenylalanine moiety originates from the shikimate pathway and the dihydroisocoumarin moiety from the pentaketide pathway (Fig. 3). The first step in the synthesis of the isocoumarin polyketide consists in the condensation of one acetate unit (acetyl-CoA) to four malonate units. Recent data showed that this step requires the activity of a polyketide synthase [30]. Moreover, the gene encoding polyketide synthase appears to be very different between Penicillium and Aspergillus species [30], [31]. In A. ochraceus, the gene of polyketide synthase is expressed only under OTA permissive conditions and only during the early stages of the mycotoxin synthesis [30]. No such data are presently available on Penicillium. In Penicillium species, Geisen et al. [31] observed that P. nordicum and P. verrucosum use two different polyketide synthases for OTA synthesis. This difference is probably related to the P. verrucosum ability to produce CIT, also a polyketide-based mycotoxin, in addition to OTA. Once formed, the polyketide chain is modified through the formation of a lactone ring (synthesis of mellein) and the addition of a carboxyl group derived from the C1 pool such as S-methylmethionine and sodium formate (synthesis of ochratoxin β) [32]. Subsequently, the chlorine atom is incorporated through the action of chloroperoxidase (synthesis of Ochratoxin α, OTα). Ultimately, ochratoxin A synthetase catalyzes the linking of OTα to phenylalanine (synthesis of OTA) [33], [34].

Section snippets

Toxicokinetics

Both toxicokinetic (the changes of concentrations of a compound in the organism over time) and toxicodynamic (the dynamic interactions of a compound with biological targets and their downstream biological effects) factors determine the toxicity of OTA.

Upon absorption from the gastrointestinal tract, OTA binds to serum proteins. Considerable variations in serum half-lives across species are known to be dependent on the affinity and degree of protein binding. Reabsorption of OTA from the

Toxicodynamics

Several hypotheses on the mechanism of interaction of OTA and its metabolites with endogenous molecules have been put forward to explain its toxicity. They are related to specific interactions, based on highly specific binding onto specific sites of a target molecule and, non-specific interactions, based on the chemical reactivity of OTA and its metabolites and their vicinity to the target molecule.

Conclusions and future perspectives

OTA has been classified as a nephrotoxic, hepatotoxic, immunotoxic and teratogenic compound. As a natural poison contaminating a large variety of plant products and leading to the presence of residues in the products of animal origin, OTA contributes to the contamination of humans. At common concentrations in food, OTA may also be regarded as a modulator of cellular signalling and not as a classical toxin. In addition, OTA is reasonably anticipated to be a possible human carcinogen based on

References (237)

  • J.P. Harris et al.

    Biosynthesis of ochratoxins by Aspergillus ochraceus

    Phytochemistry

    (2001)
  • S. Kumagai et al.

    Intestinal absorption and secretion of ochratoxin A in the rat

    Toxicol. Appl. Pharmacol.

    (1982)
  • A. Roth et al.

    Evidence of an enterohepatic circulation of ochratoxin A in mice

    Toxicology

    (1988)
  • V. Berger et al.

    Interaction of ochratoxin A with human intestinal CaCo-2 cells: possible implication of a multidrug resistance-associated proteins (MRP2)

    Toxicol. Lett.

    (2003)
  • P. Galtier et al.

    The pharmacokinetic profiles of ochratoxin A in pigs, rabbit and chicken

    Food Cosmet. Toxicol.

    (1981)
  • F.S. Chu

    Interaction of ochratoxin A with bovine serum albumine

    Arch. Biochem. Biophys.

    (1971)
  • S. Kumagai

    Ochratoxin A: plasma concentration and excretion into bile and urine in albumin-deficient rats

    Food Chem. Toxicol.

    (1985)
  • G. Schwerdt et al.

    Ochratoxin A-binding proteins in rat organs and plasma and different cell lines of the kidney

    Toxicology

    (1999)
  • S. Li et al.

    Pharmacokinetics of ochratoxin A and its metabolites in rats

    Toxicol. Appl. Pharmacol.

    (1997)
  • L.E. Appelgren et al.

    Distribution of 14C-labelled ochratoxin A in pregnant mice

    Food. Chem. Toxicol.

    (1983)
  • B. Zimmerli et al.

    Determination of ochratoxin A at ppt level in human blood, serum, milk and some foodstuffs by high performance liquid chromatography with enhanced fluorescence detection and immunoaffinity column clean-up; methodology and Swiss data

    J. Chromatogr. B

    (1995)
  • S.H. Cha et al.

    Molecular cloning and characterization of multispecific organic anion transporter 4 expressed in the placenta

    J. Biol. Chem.

    (2000)
  • R. Fuchs et al.

    Carbon-14-ochratoxin A distribution in the Japanese quail (Coturnix coturnix japonica) monitored by whole-body autography

    Poult. Sci.

    (1988)
  • K.Y. Jung et al.

    Characterization of ochratoxin A transport by human organic anion transporters

    Life Sci.

    (2001)
  • E. Bahnemann et al.

    Renal transepithelial secretion of ochratoxin A in the non-filtering toad kidney

    Toxicology

    (1997)
  • I. Leier et al.

    ATP-dependent para-aminohippurate transport by apical multidrug resistance protein MRP2

    Kidney Int.

    (2000)
  • E. Babu et al.

    Role of human anion transporter 4 in the transport of ochratoxin A

    Biochem. Biophys. Acta

    (2002)
  • G. Schwerdt et al.

    Apical-to-basolateral transepithelial transport of ochratoxin A by two subtypes of Madin–Darby canine kidney cells

    Biochem. Biophys. Acta

    (1997)
  • S. Suzuki et al.

    The pharmacokinetics of ochratoxin A in rats

    Japan J. Pharmacol.

    (1977)
  • K.J. van der Merwe et al.

    Ochratoxin A, a toxic metabolite produced by Aspergillus ochraceus Wilh.

    Nature

    (1965)
  • P.S. Steyn

    Ochratoxin and other dihydroisocoumarins

  • V. Betina

    Mycotoxins, Chemical, Biological and Environmental Aspects

    (1989)
  • A.E. Pohland et al.

    Physicochemical data for some selected mycotoxins

    Pure Appl. Chem.

    (1982)
  • T. Kuipper-Goodman et al.

    Risk assessment of the mycotoxin ochratoxin A

    Biomed. Environ. Sci.

    (1989)
  • F.S. Chu

    Studies on ochratoxins

    CRC Crit. Rev. Toxicol.

    (1974)
  • P. Galtier

    Pharmacokinetics of ochratoxin A in Animals

    IARC Sci. Publ.

    (1991)
  • J.I. Pitt et al.

    Fungi and Food Spoilage

    (1997)
  • J.P. Pitt

    Penicillium viridicatum, Penicillium verrucosum and the production of ochratoxin A

    Appl. Environ. Microbiol.

    (1987)
  • T.O. Larsen et al.

    Biochemical characterization of ochratoxin A-producing strains of the genus Penicillium

    Appl. Environ. Microbiol.

    (2001)
  • Z. Kozakiewicz, Aspergillus species on stored products, Mycological paper no. 161, CAB International Mycological...
  • WHO/FAO, Ochratoxin A, in: Safety Evaluation of Certain Mycotoxins in Food, vol. 47, WHO Food Additives Series, 2001,...
  • M.L. Abarca et al.

    Ochratoxin A production by strains of Aspergillus niger var niger

    Appl. Environ. Microbiol.

    (1994)
  • J. Teren et al.

    Immunochemical detection of ochratoxin A in black Aspergillus strain

    Mycopathologia

    (1996)
  • D. Mitchell et al.

    Water and temperature relations of growth and ochratoxin A production by Aspergillus carbonarius strains from grapes in Europe and Israel

    J. Appl. Microbiol.

    (2004)
  • L. Sage et al.

    Fungal flora and ochratoxin A production in grapes and musts from France

    J. Agric. Food Chem.

    (2002)
  • R.A. Samson et al.

    New ochratoxin A or sclerotium producing species in Aspergillus section Nigri

    Stud. Mycol.

    (2004)
  • E.B. Lillehoj et al.

    Bioproduction of 14C Ochratoxin A in submerged culture

    Appl. Environ. Microbiol.

    (1978)
  • M.O. Moss

    Mode of formation of ochratoxin A

    Food Addit. Contam.

    (1996)
  • P. Bayman et al.

    Ochratoxin production by the Aspergillus ochraceus group and Aspergillus alliaceus

    Appl. Environ. Microbiol.

    (2002)
  • J. Varga et al.

    Evolutionary relationships among Aspergillus species producing economically important mycotoxins

    Food Technol. Biotechnol.

    (2003)
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