Toxicity of the mycotoxin citrinin and its metabolite dihydrocitrinone and of mixtures of citrinin and ochratoxin A in vitro

Metabolism-dependent cytotoxicity of citrinin and ochratoxin A alone and in combination as assessed adopting integrated discrete multiple organ co-culture (IdMOC)

Citrinin (CTN) and ochratoxin A (OTA) can be present as co-contaminants in cereals, foods and feed commodities, and can affect human health. Metabolism-dependent toxicity of these two mycotoxins, separately as well as in combination, is not yet understood. To fill this gap we adopted integrated discrete multiple organ co-culture (IdMOC) technique, which obviates animal experiments from the perspectives of species difference as well as animal welfare concerns. IdMOC facilitates co-culture of a metabolically competent cell (HepG2) and a metabolically incompetent cell (3T3) that are physically separated but provides for extracellular product(s) from one cell to interact with the other. After ascertaining that HepG2 is metabolically competent and 3T3 is not, adopting luciferin-IPA metabolism assay, CTN and OTA were tested separately and in combination in the co-culture set-up, when both proved to be metabolism-dependent cytotoxic agents. Hepatocytes metabolize CTN into a diffusible product that is cytotoxic to 3T3 cells but the cytotoxicity of OTA appears to be limited to the hepatocytes, i.e., local acting. As a combination at a concentration of 20% of IC₅₀ of each, CTN forms a reactive metabolite that diffuses out of HepG2 to cause cytotoxicity to 3T3 cells synergistically with OTA parent molecule. The CYP isoenzymes involved in the metabolism OTA and CTN were identified adopting in silico methods which indicated that OTA and CTN can bind CYP proteins at specific sites.

PRESENCE OF CITRININ IN GRAINS AND ITS POSSIBLE HEALTH EFFECTS

Background:

Citrinin is a mycotoxin produced by several species of the genera Aspergillus, Penicillium and Monascus and it occurs mainly in stored grain. Citrinin is generally formed after harvest and occurs mainly in stored grains, it also occurs in other plant products. Often, the co-occurrence with other mycotoxins is observed, especially ochratoxin A, which is usually associated with endemic nephropathy. At the European Union level, systematic monitoring of Citrinin in grains began with the aim of determining its highest permissible amount in food. Thus, far the systematic monitoring of the above mentioned mycotoxin in Croatia is yet to begin.

Materials and Methods:

The main goal of this study was to determine the presence of Citrinin in grains sampled in the area of Međimurje, Osijek-Baranja, Vukovar-Srijem and Brod-Posavina County. For the purpose of identification and quantification of citrinin, high performance liquid chromatograph (HPLC) with fluorescence was used (Calibration curve k > 0.999; Intra assay CV = 2.1%; Inter assay CV = 4.3%; LOQ < 1 μg/kg).

Results:

From the area of Međimurje County, 10 samples of corn and 10 samples of wheat were analyzed. None of the samples contained Citrinin (<1 μg/kg). From the area of Osijek-Baranja and Vukovar-Srijem County, 15 samples from each County were analyzed. The mean value for the samples of Osijek-Baranja County was 19.63 μg/kg (median=15.8 μg/kg), while for Vukovar-Srijem County the mean value of citrinin was 14,6 μg/kg (median=1.23 μg/kg). From 5 analyzed samples from Brod-Posavina County, one of the samples contained citrinin in the amount of 23.8 μg/kg, while the registered amounts in the other samples were <1 μg/kg.

Conclusion:

The results show that grains from several Counties contain certain amounts of Citrinin possibly indicating a significant intake of citrinin in humans. It must be stated that grains and grain-based products are the basis of everyday diet of all age groups, especially small children, where higher intake of citrinin can occur. Consequently, we emphasize the need for systematic analysis of larger amount of samples, from both large grains and small grains, especially in the area of Brod-Posavina County, in order to obtain more realistic notion of citrinin contamination of grains and to asses the health risk in humans.

Challenges in risk assessment of multiple mycotoxins in food

Most fungi are able to produce several mycotoxins simultaneously and, consequently, to contaminate a wide variety of foodstuffs. Therefore, the risk of human co-exposure to multiple mycotoxins is real, raising a growing concern about their potential impact on human health. Besides, government and industry regulations are usually based on individual toxicities, and do not take into account the complex dynamics associated with interactions between co-occurring groups of mycotoxins. The present work assembles, for the first time, the challenges posed by the likelihood of human co-exposure to these toxins and the possibility of interactive effects occurring after absorption, towards knowledge generation to support a more accurate human risk assessment. Regarding hazard assessment, a physiologically-based framework is proposed in order to infer the health effects from exposure to multiple mycotoxins in food, including knowledge on the bioaccessibility, toxicokinetics and toxicodynamics of single and combined toxins. The prioritisation of the most relevant mixtures to be tested under experimental conditions that attempt to mimic human exposure and the use of adequate mathematical approaches to evaluate interactions, particularly concerning the combined genotoxicity, were identified as the main challenges for hazard assessment. Regarding exposure assessment, the need of harmonised food consumption data, availability of multianalyte methods for mycotoxin quantification, management of left-censored data, use of probabilistic models and multibiomarker approaches are highlighted, in order to develop a more precise and realistic exposure assessment. To conclude, further studies on hazard and exposure assessment of multiple mycotoxins, using harmonised methodologies, are crucial towards an improvement of data quality and a more reliable and robust risk characterisation, which is central for risk management and, consequently, to prevent mycotoxins-associated adverse effects. A deep understanding of the nature of interactions between multiple mycotoxins will contribute to draw real conclusions on the health impact of human exposure to mycotoxin mixtures.

Different Toxicity Mechanisms for Citrinin and Ochratoxin A Revealed by Transcriptomic Analysis in Yeast

Citrinin (CIT) and ochratoxin A (OTA) are important mycotoxins, which frequently co-contaminate foodstuff. In order to assess the toxicologic threat posed by the two mycotoxins separately or in combination, their biological effects were studied here using genomic transcription profiling and specific live cell gene expression reporters in yeast cells. Both CIT and OTA cause highly transient transcriptional activation of different stress genes, which is greatly enhanced by the disruption of the multidrug exporter Pdr5. Therefore, we performed genome-wide transcription profiling experiments with the pdr5 mutant in response to acute CIT, OTA, or combined CIT/OTA exposure. We found that CIT and OTA activate divergent and largely nonoverlapping gene sets in yeast. CIT mainly caused the rapid induction of antioxidant and drug extrusion-related gene functions, while OTA mainly deregulated developmental genes related with yeast sporulation and sexual reproduction, having only a minor effect on the antioxidant response. The simultaneous exposure to CIT and OTA gave rise to a genomic response, which combined the specific features of the separated mycotoxin treatments. The application of stress-specific mutants and reporter gene fusions further confirmed that both mycotoxins have divergent biological effects in cells. Our results indicate that CIT exposure causes a strong oxidative stress, which triggers a massive transcriptional antioxidant and drug extrusion response, while OTA mainly deregulates developmental genes and only marginally induces the antioxidant defense.

Evaluation of renal in vitro models used in ochratoxin research

Ochratoxin A (OTA) induces renal carcinomas in rodents with a specific localisation in the S3 segment of proximal tubules and distinct early severe tissue alterations, which have been observed also in other species. Pronounced species- and sex-specific differences in toxicity occur and similar effects cannot be excluded in humans, however precise mechanism(s) remain elusive until today. In such cases, the use of in vitro models for mechanistic investigations can be very useful; in particular if a non-genotoxic mechanism of cancer formation is assumed which include cytotoxic effects. However, potential genotoxic mechanisms can also be investigated in vitro. A crucial issue of in vitro research is the choice of the appropriate cell model. Apparently, the cellular target of OTA is the renal proximal tubular cell; therefore cells from this tissue area are the most reasonable model. Furthermore, cells from affected species should be used and can be compared to cells of human origin. Another important parameter is whether to use primary cultures or to choose a cell line from the huge variety of cell lines available. In any case, important characteristics and quality controls need to be verified beforehand. Therefore, this review discusses the renal in vitro models that have been used for the investigation of renal ochratoxin toxicity. In particular, we discuss the choice of the models and the essential parameters making them suitable models for ochratoxin research together with exemplary results from this research. Furthermore, new promising models such as hTERT-immortalised cells and 3D-cultures are briefly discussed.

A quantitative UHPLC-MS/MS method for citrinin and ochratoxin A detection in food, feed and red yeast rice food supplements

Mycotoxins may cause deleterious effects (among others nephrogenic, hepatogenic, carcinogenic, teratogenic, neurogenic) in animals and humans, therefore they have been intensely studied and monitored over the years. For citrinin (CIT), a nephrotoxic mycotoxin, however, this has not yet been the case. According to the latest European Food Safety Authority report, a correct risk assessment of CIT was not possible due to the lack of occurrence data. Besides, traces of CIT or its metabolite, dehydrocitrinone are widely (in up to 90% of samples) present in human urine according to recent Belgian and German scientific reports, which might imply chronic exposure. Only recently, a European maximum limit has been set for CIT in cholesterol reducing food supplements including red yeast fermented rice (RYR). During production of RYR through fungal (among others Monascus purpureus) fermentation of rice other components, like CIT, as well as nephrotoxic ochratoxin A (OTA) may form. Consequently, the present work attempted develop to a robust and routinely applicable ultra-high performance liquid chromatographytandem mass spectrometry (UHPLC-MS/MS) method for the analysis of CIT and OTA in food, feed and in RYR food supplements. The method was successfully validated based on EU/657/2002 and EU/519/2014 in RYR food supplements and wheat flour, achieving respective limits of quantification (LOQ) for CIT of 0.4 μg/kg and 0.1 μg/kg and for OTA of 15 μg/kg and 0.4 μg/kg. The average between-day recoveries varied from 72 to 110% with relative standard deviations ≤16%. Single-day validation in rice, curry and apple matrices showed LOQs ranging from 0.3-1.0 μg/kg. Next, the occurrence of CIT/OTA was surveyed in 138 RYR, food and feed samples, proving the potential of this method for future data acquisition within a risk assessment framework specifically for CIT, while also gaining information about the (co-)occurrence of OTA in edible matrices.

Natural Co-Occurrence of Mycotoxins in Foods and Feeds and Their in vitro Combined Toxicological Effects

Some foods and feeds are often contaminated by numerous mycotoxins, but most studies have focused on the occurrence and toxicology of a single mycotoxin. Regulations throughout the world do not consider the combined effects of mycotoxins. However, several surveys have reported the natural co-occurrence of mycotoxins from all over the world. Most of the published data has concerned the major mycotoxins aflatoxins (AFs), ochratoxin A (OTA), zearalenone (ZEA), fumonisins (FUM) and trichothecenes (TCTs), especially deoxynivalenol (DON). Concerning cereals and derived cereal product samples, among the 127 mycotoxin combinations described in the literature, AFs+FUM, DON+ZEA, AFs+OTA, and FUM+ZEA are the most observed. However, only a few studies specified the number of co-occurring mycotoxins with the percentage of the co-contaminated samples, as well as the main combinations found. Studies of mycotoxin combination toxicity showed antagonist, additive or synergic effects depending on the tested species, cell model or mixture, and were not necessarily time- or dose-dependent. This review summarizes the findings on mycotoxins and their co-occurrence in various foods and feeds from all over the world as well as in vitro experimental data on their combined toxicity.

Mycotoxins: cytotoxicity and biotransformation in animal cells

Mycotoxins are secondary metabolites produced by many microfungi. Hitherto, over 300 mycotoxins with diverse structures have been identified. They contaminate most cereals and feedstuffs, which threaten human and animal health by exerting acute, sub-acute and chronic toxicological effects, with some considered as carcinogens. Many mycotoxins at low concentrations are able to induce the expression of cytochrome P450 and other enzymes implicated in the biotransformation and metabolization of mycotoxins in vivo and in vitro. Mycotoxins and their metabolites elicit different cellular disorders and adverse effects such as oxidative stress, inhibition of translation, DNA damage and apoptosis in host cells, thus causing various kinds of cytotoxicities. In this review, we summarize the biotransformation of mycotoxins in animal cells by CYP450 isoforms and other enzymes, their altered expression under mycotoxin exposure, and recent progress in mycotoxin cytotoxicity in different cell lines. Furthermore, we try to generalize the molecular mechanisms of mycotoxin effects in human and animal cells.

Biomonitoring of Mycotoxins in Urine: Pilot Study in Mill Workers

Contamination of grains with mycotoxins results in a dietary background exposure of the general population. In occupational settings such as during processing of raw materials as in milling, an additional mycotoxin exposure by inhalation is possible. Biomonitoring is an integrative approach to assess human exposure from various sources and by all routes. To investigate possible workplace exposure to mycotoxins, a pilot study was conducted that compared levels of urinary biomarkers in mill workers to those in a control group with dietary mycotoxin intake alone. Workers (n = 17) from three grain mills in North Rhine Westphalia, Germany, provided spot urines during shift; volunteers (n = 13, IfADo staff) with matched age structure served as control group. The mycotoxins selected for biomarker analysis were citrinin (CIT) deoxynivalenol (DON), ochratoxin A (OTA), and zearalenone (ZEN). Immunoaffinity columns (CIT, DON, ZEN) or liquid-liquid extraction (OTA) was employed for urine sample cleanup prior to targeted analysis by liquid chromatography with tandem mass spectrometry (LC-MS/MS) or by high-performance liquid chromatography (HPLC). In addition, mycotoxin metabolites that may be formed in the organism were analyzed, including deepoxy-deoxynivalenol (DOM-1), ochratoxin alpha (OTα), dihydrocitrinone (DH-CIT), and α- and β-zearalenol (α- and β-ZEL), as well as phase II metabolites that were hydrolyzed with β-glucuronidase/arylsulfatase prior to sample cleanup. All analyte concentrations were adjusted for creatinine (crea) content in the spot urine samples. Citrinin, DON, OTA, and ZEN were detected in nearly all urine samples from mill workers and controls. Interestingly, DH-CIT was found at higher mean levels than the parent compound (~0.14 and 0.045 µg/g crea, respectively), suggesting an effective metabolism of CIT in humans. Other metabolites DOM-1, OTα, and α- and β-ZEL were detected less frequently in urine. Deoxynivalenol was detected at the highest concentrations (mean ~6 µg/g crea), followed by OTA (mean ~0.08 µg/g crea); ZEN (mean ~0.03 µg/g crea) and its metabolites appeared in urine at lower levels. Mycotoxin biomarker levels in urine from mill workers and controls were not significantly different. From these results it is concluded that biomarker levels measured in urine samples from the two cohorts reflect mainly dietary mycotoxin exposure. An additional occupational (inhalational) exposure of mill workers, if any, is apparently low at the investigated workplaces.

Urinary biomarkers of ochratoxin A and citrinin exposure in two Bangladeshi cohorts: follow-up study on regional and seasonal influences

Biomonitoring studies can provide valuable insights into human mycotoxin exposure, especially when food contaminant data are scarce or unavailable as in Bangladesh. First biomonitoring data in Bangladeshi adults indicated exposure to the nephrotoxic mycotoxins ochratoxin A (OTA) and citrinin (CIT). This led us to conduct a follow-up study with analysis of urinary biomarkers for both CIT and OTA to investigate regional and seasonal influences on mycotoxin exposure in two Bangladeshi cohorts. In total, 164 urines were collected (n = 69 in summer, n = 95 in winter) from residents of a rural and an urban area, among which there were 62 participants enrolled in both sampling periods. Most urines had detectable biomarker levels (OTA, CIT and its metabolite dihydrocitrinone, HO-CIT), with more or less pronounced differences with regard to season and region. In both cohorts, OTA was found at a mean level of 0.06 ± 0.10 ng/mL urine (range 0.01-0.55 ng/mL) in summer and a mean of 0.19 ± 0.38 ng/mL (range 0.01-1.75 ng/mL) in winter season. A season difference was significant in the rural cohort, but not in the urban cohort, and slightly higher mean OTA levels in the rural compared to the urban cohort were only observed in winter urines. CIT biomarkers showed more pronounced variations, with a CIT mean of 0.10 ± 0.17 ng/mL (range 0.02-1.22 ng/mL) and HO-CIT mean of 0.42 ± 0.98 ng/mL (range 0.02-5.39 ng/mL) in summer, and CIT mean of 0.59 ± 0.98 ng/mL (range 0.05-5.03 ng/mL) and HO-CIT mean of 3.18 ± 8.49 ng/mL (range 0.02-46.44 ng/mL) in winter urines of both cohorts. In both seasons, total CIT biomarker concentrations were significantly higher in the rural cohort than in the urban cohort. A provisional daily intake for CIT was calculated and exceeded a preliminary value set by EFSA (0.2 µg/kg/d) in 10 and 24 % of participants in summer and winter, respectively. No significant correlations were found between urinary biomarker levels and intake of certain types of food, except for a positive trend for higher rice consumption. Our results in the Bangladeshi population indicate frequent co-exposure to nephrotoxic mycotoxin food contaminants that vary by season and region.

Interaction of Citrinin with Human Serum Albumin

Citrinin (CIT) is a mycotoxin produced by several Aspergillus, Penicillium, and Monascus species. CIT occurs worldwide in different foods and drinks and causes health problems for humans and animals. Human serum albumin (HSA) is the most abundant plasma protein in human circulation. Albumin forms stable complexes with many drugs and xenobiotics; therefore, HSA commonly plays important role in the pharmacokinetics or toxicokinetics of numerous compounds. However, the interaction of CIT with HSA is poorly characterized yet. In this study, the complex formation of CIT with HSA was investigated using fluorescence spectroscopy and ultrafiltration techniques. For the deeper understanding of the interaction, thermodynamic, and molecular modeling studies were performed as well. Our results suggest that CIT forms stable complex with HSA (logK ~ 5.3) and its primary binding site is located in subdomain IIA (Sudlow’s Site I). In vitro cell experiments also recommend that CIT-HSA interaction may have biological relevance. Finally, the complex formations of CIT with bovine, porcine, and rat serum albumin were investigated, in order to test the potential species differences of CIT-albumin interactions.

Comparative Ochratoxin Toxicity: A Review of the Available Data

Ochratoxins are a group of mycotoxins produced by a variety of moulds. Ochratoxin A (OTA), the most prominent member of this toxin family, was first described by van der Merwe et al. in Nature in 1965. Dietary exposure to OTA represents a serious health issue and has been associated with several human and animal diseases including poultry ochratoxicosis, porcine nephropathy, human endemic nephropathies and urinary tract tumours in humans. More than 30 years ago, OTA was shown to be carcinogenic in rodents and since then extensive research has been performed in order to investigate its mode of action, however, this is still under debate. OTA is regarded as the most toxic family member, however, other ochratoxins or their metabolites and, in particular, ochratoxin mixtures or combinations with other mycotoxins may represent serious threats to human and animal health. This review summarises and evaluates current knowledge about the differential and comparative toxicity of the ochratoxin group.

Hepatotoxic effect of ochratoxin A and citrinin, alone and in combination, and protective effect of vitamin E: In vitro study in HepG2 cell

Ochratoxin A (OTA) and citrinin (CTN) are the most commonly co-occurring mycotoxins in a wide variety of food and feed commodities. The major target organ of these toxins is kidney but liver could also be a target organ. The combined toxicity of these two toxins in kidney cells has been studied but not in liver cell. In this study HepG2 cells were exposed to OTA and CTN, alone and in combination, with a view to compare the molecular and cellular mechanisms underlying OTA, CTN and OTA + CTN hepatotoxicity. OTA and CTN alone as well as in combination affected the viability of HepG2 cells in a dose-dependent manner. OTA + CTN, at a dose of 20% of IC50 of each, produced effect almost similar to that produced by either of the toxins at its IC50 concentration, indicating that the two toxins in combination act synergistically. The cytotoxicity of OTA + CTN on hepatocytes is mediated by increased level of intracellular ROS followed/accompanied by DNA strand breaks and mitochondria-mediated intrinsic apoptosis. Co-treatment of vitamin E (Vit E) with OTA, CTN and OTA + CTN reduced the levels of ROS and the cytotoxicity. But the genotoxic effect of OTA and OTA + CTN was not completely alleviated by Vit E treatment whereas the DNA damage as caused by CTN when treated alone was obviated, indicating that OTA induces DNA damage directly whereas CTN induces ROS-mediated DNA damage and OTA + CTN combination induces DNA damage not exclusively relying on but influenced by ROS generation. Taken together, these findings indicate that OTA and CTN in combination affect hepatocytes at very low concentrations and, thereby, pose a potential threat to public and animal health.

First results on citrinin biomarkers in urines from rural and urban cohorts in Bangladesh

Citrinin (CIT) is a mycotoxin contaminant in food commodities and can co-occur with ochratoxin A (OTA), another nephrotoxic contaminant in food and feed. Presence of OTA in maize from Bangladesh has been reported, but no data exist on CIT occurrence in food or feed in Bangladesh. Since biomonitoring provides the best approach to assess human exposure to contaminants from various sources and by all routes, a validated method for biomarker analysis has been used to investigate the presence of CIT and its metabolite dihydrocitrinone (HO-CIT) in urines from two Bangladeshi cohorts: Both analytes were determined in urine samples collected from inhabitants of a rural (n=32) and an urban (n=37) area in the Rajshahi district of Bangladesh. After cleanup by immunoaffinity columns, extracts were analyzed by LC-MS/MS; the limits of detection for CIT and HO-CIT in urine were 0.02 and 0.05 ng/mL, respectively. CIT and HO-CIT were detectable in 94 and 71% of all urine samples. Urinary biomarker levels did not show significant correlations with age, gender, and body mass index of the donors. However, excretion of CIT together with its metabolite HO-CIT was significantly higher (p<0.01) in the rural cohort (mean 1.1±1.9 ng/mL) than in the urban cohort (mean 0.14±0.14 ng/mL). This clearly indicates differences in mycotoxin exposure. As food habits differ between rural and urban people and also their main areas of occupation, further research is needed with regard to the major contributors of CIT exposure in the two cohorts. In conclusion, this first biomarker analysis indicates widespread and variable exposure to CIT in Bangladeshi adults.

Analysis of Statistical Methods Currently used in Toxicology Journals

Statistical methods are frequently used in toxicology, yet it is not clear whether the methods employed by the studies are used consistently and conducted based on sound statistical grounds. The purpose of this paper is to describe statistical methods used in top toxicology journals. More specifically, we sampled 30 papers published in 2014 from Toxicology and Applied Pharmacology, Archives of Toxicology, and Toxicological Science and described methodologies used to provide descriptive and inferential statistics. One hundred thirteen endpoints were observed in those 30 papers, and most studies had sample size less than 10, with the median and the mode being 6 and 3 & 6, respectively. Mean (105/113, 93%) was dominantly used to measure central tendency, and standard error of the mean (64/113, 57%) and standard deviation (39/113, 34%) were used to measure dispersion, while few studies provide justifications regarding why the methods being selected. Inferential statistics were frequently conducted (93/113, 82%), with one-way ANOVA being most popular (52/93, 56%), yet few studies conducted either normality or equal variance test. These results suggest that more consistent and appropriate use of statistical method is necessary which may enhance the role of toxicology in public health.

Occurrence of the mycotoxin citrinin and its metabolite dihydrocitrinone in urines of German adults

As data on food contamination with the mycotoxin citrinin (CIT) are scarce, a recently developed method for biomarker analysis (Blaszkewicz et al. in Arch Toxicol 87:1087-1094, 2013) was applied to investigate CIT exposure of German adults. CIT and its human metabolite dihydrocitrinone (HO-CIT) were determined in urine samples from a group of 50 healthy adults (n = 27 females and n = 23 males). After cleanup by immunoaffinity (CitriTest®) columns, extracts were analyzed by LC-MS/MS. The mycotoxin and its major metabolite HO-CIT were detected in 82 and 84 % of all urine samples, at concentrations ranging from 0.02 (limit of detection, LOD) to 0.08 ng/mL for CIT, and 0.05 (LOD) to 0.51 ng/mL for HO-CIT. Median urine analyte levels in the cohort were 0.03 (CIT) and 0.06 ng/mL (OH-CIT) or adjusted to creatinine 20.2 ng/g crea (CIT) and 60.9 ng/g crea (HO-CIT), respectively. Except for higher urinary CIT levels in males, differences between subgroups were not significant. This first biomarker analysis indicates widespread and variable exposure to CIT in German adults, and conversion of ingested mycotoxin to its less toxic metabolite HO-CIT, which may serve as biomarker of exposure in addition to the parent compound.

Toxicity mechanisms of the food contaminant citrinin: application of a quantitative yeast model

Mycotoxins are important food contaminants and a serious threat for human nutrition. However, in many cases the mechanisms of toxicity for this diverse group of metabolites are poorly understood. Here we apply live cell gene expression reporters in yeast as a quantitative model to unravel the cellular defense mechanisms in response to the mycotoxin citrinin. We find that citrinin triggers a fast and dose dependent activation of stress responsive promoters such as GRE2 or SOD2. More specifically, oxidative stress responsive pathways via the transcription factors Yap1 and Skn7 are critically implied in the response to citrinin. Additionally, genes in various multidrug resistance transport systems are functionally involved in the resistance to citrinin. Our study identifies the antioxidant defense as a major physiological response in the case of citrinin. In general, our results show that the use of live cell gene expression reporters in yeast are a powerful tool to identify toxicity targets and detoxification mechanisms of a broad range of food contaminants relevant for human nutrition.