In vitro combinatory effects of the Alternaria mycotoxins alternariol and altertoxin II and potentially involved miRNAs

The characteristics, occurrence, and toxicological effects of alternariol: a mycotoxin

Alternaria species are mycotoxin-producing fungi known to infect fresh produce and to cause their spoilage. Humans get exposed to fungal secondary metabolites known as mycotoxin via the ingestion of contaminated food. Alternariol (AOH) (C14H10O5) is an isocoumarins produced by different species of Alternaria including Alternaria alternata. AOH is often found in grain, fruits and fruits-based food products with high levels in legumes, nuts, and tomatoes. AOH was first discovered in 1953, and it is nowadays linked to esophagus cancer and endocrine disruption due to its similarity to estrogen. Although considered as an emerging mycotoxin with no regulated levels in food, AOH occurs in highly consumed dietary products and has been detected in various masked forms, which adds to its occurrence. Therefore, this comprehensive review was developed to give an overview on recent literature in the field of AOH. The current study summarizes published data on occurrence levels of AOH in different food products in the last ten years and evaluates those levels in comparison to recommended levels by the regulating entities. Such surveillance facilitates the work of health risk assessors and highlights commodities that are most in need of AOH levels regulation. In addition, the effects of AOH on cells and animal models were summarized in two tables; data include the last two-year literature studies. The review addresses also the main characteristics of AOH and the possible human exposure routes, the populations at risk, and the effect of anthropogenic activities on the widespread of the mycotoxin. The commonly used detection and control methods described in the latest literature are also discussed to guide future researchers to focus on mitigating mycotoxins contamination in the food industry. This review aims mainly to serve as a guideline on AOH for mycotoxin regulation developers and health risk assessors.

Toxicodynamic of combined mycotoxins: MicroRNAs and acute-phase proteins as diagnostic biomarkers

Mycotoxins, ubiquitous contaminants in food, present a global threat to human health and well-being. Mitigation efforts, such as the implementation of sound agricultural practices, thorough food processing, and the advancement of mycotoxin control technologies, have been instrumental in reducing mycotoxin exposure and associated toxicity. To comprehensively assess mycotoxins and their toxicodynamic implications, the deployment of effective and predictive strategies is imperative. Understanding the manner of action, transformation, and cumulative toxic effects of mycotoxins, moreover, their interactions with food matrices can be gleaned through gene expression and transcriptome analyses at cellular and molecular levels. MicroRNAs (miRNAs) govern the expression of target genes and enzymes that play pivotal roles in physiological, pathological, and toxicological responses, whereas acute phase proteins (APPs) exert regulatory control over the metabolism of therapeutic agents, both endogenously and posttranscriptionally. Consequently, this review aims to consolidate current knowledge concerning the regulatory role of miRNAs in the initiation of toxicological pathways by mycotoxins and explores the potential of APPs as biomarkers following mycotoxin exposure. The findings of this research highlight the potential utility of miRNAs and APPs as indicators for the detection and management of mycotoxins in food through biological processes. These markers offer promising avenues for enhancing the safety and quality of food products.

Hazard characterization of Alternaria toxins to identify data gaps and improve risk assessment for human health

Fungi of the genus Alternaria are ubiquitous plant pathogens and saprophytes which are able to grow under varying temperature and moisture conditions as well as on a large range of substrates. A spectrum of structurally diverse secondary metabolites with toxic potential has been identified, but occurrence and relative proportion of the different metabolites in complex mixtures depend on strain, substrate, and growth conditions. This review compiles the available knowledge on hazard identification and characterization of Alternaria toxins. Alternariol (AOH), its monomethylether AME and the perylene quinones altertoxin I (ATX-I), ATX-II, ATX-III, alterperylenol (ALP), and stemphyltoxin III (STTX-III) showed in vitro genotoxic and mutagenic properties. Of all identified Alternaria toxins, the epoxide-bearing analogs ATX-II, ATX-III, and STTX-III show the highest cytotoxic, genotoxic, and mutagenic potential in vitro. Under hormone-sensitive conditions, AOH and AME act as moderate xenoestrogens, but in silico modeling predicts further Alternaria toxins as potential estrogenic factors. Recent studies indicate also an immunosuppressive role of AOH and ATX-II; however, no data are available for the majority of Alternaria toxins. Overall, hazard characterization of Alternaria toxins focused, so far, primarily on the commercially available dibenzo-α-pyrones AOH and AME and tenuazonic acid (TeA). Limited data sets are available for altersetin (ALS), altenuene (ALT), and tentoxin (TEN). The occurrence and toxicological relevance of perylene quinone-based Alternaria toxins still remain to be fully elucidated. We identified data gaps on hazard identification and characterization crucial to improve risk assessment of Alternaria mycotoxins for consumers and occupationally exposed workers.

Genotoxic and Mutagenic Effects of the Alternaria Mycotoxin Alternariol in Combination with the Process Contaminant Acrylamide

Humans are constantly exposed to mixtures of different xenobiotics through their diet. One emerging concern is the Alternaria mycotoxin alternariol (AOH), which can occur in foods typically contaminated by the process contaminant acrylamide (AA). AA is a byproduct of the Maillard reaction produced in carbohydrate-rich foods during thermal processing. Given the genotoxic properties of AOH and AA as single compounds, as well as their potential co-occurrence in food, this study aimed to assess the cytotoxic, genotoxic, and mutagenic effects of these compounds in combination. Genotoxicity was assessed in HepG2 cells by quantifying the phosphorylation of the histone γ-H2AX, induced as a response to DNA double-strand breaks (DSBs). Mutagenicity was tested in Salmonella typhimurium strains TA98 and TA100 by applying the Ames microplate format test. Our results showed the ability of AOH and AA to induce DSBs and increase revertant numbers in S. typhimurium TA100, with AOH being more potent than AA. However, no synergistic effects were observed during the combined treatments. Notably, the results of the study suggest that the compounds exert mutagenic effects primarily through base pair substitutions. In summary, the data indicate no immediate cause for concern regarding synergistic health risks associated with the consumption of foods co-contaminated with AOH and AA.

Estrogen receptor α mediates alternariol-induced apoptosis and modulation of the invasiveness of ovarian cancer cells

Mycotoxins are secondary metabolites of fungi that may affect both human and animal health. Some of them possess estrogenic activity, due to direct binding to estrogen receptors (ERs) and hence disturb the hormonal balance of the organism. Alternariol (AOH) was previously reported as genotoxic, estrogenic and immunomodulatory agent. However, detailed mechanism of its action has not been fully elucidated. Estrogen receptor α (ERα) was previously reported to modulate the proliferation and invasiveness of ovarian cancer cells. Thus, we decided to verify whether estrogenic-like mycotoxin may affect ovarian cancer cells via ERα. The results showed that AOH induces apoptosis and oxidative stress and that these effects are partially modulated by ERα. Moreover, AOH decreases the invasion and migration of ovarian cancer cells and promotes changes in the expression of genes and proteins that are associated with the invasiveness of cancer i.e. MMP9, SNAIL1/2, ZEB1/2, VIM, CDH1 and CDH2. In conclusion, we postulate that AOH might significantly affect the viability and invasiveness of ovarian cancer cells via modulation of ERα and therefore possibly act as an endocrine disruptive agent in ovarian cancer cells.

Cytotoxicities of Co-occurring alternariol, alternariol monomethyl ether and tenuazonic acid on human gastric epithelial cells

Alternariol (AOH), alternariol monomethyl ether (AME) and tenuazonic acid (TeA) are the three major Alternaria toxin contaminants in food. In the present study, we conducted their single and combined toxicity analyses using human gastric epithelial cell line (GES-1) that was first exposed to the toxins when they entered the human body. By comparing the cytotoxicity IC50, we found that compared to several other mycotoxins with limit standards there was cytotoxicity DON > OTA > AME > AOH > ZEN > TeA. Further, we obtained combination index (CI)-isobologram equation by the Chou-Talalay method according to a toxin ratio of 1:1:2 and carried out the combined toxicity analysis of the three binary and ternary compounds, and the results showed that AOH + AME + TeA showed synergistic toxic effects. Based on the co-occurring status, we also carried out the combined toxicity analysis of AME and AOH at different ratios and found antagonistic effects at low cytotoxic concentrations as well as synergistic and additive effects at high concentrations. Also, we found that all three and their combinations caused apoptosis, activation of caspase-3 cleavage, activation of DNA damage pathways ATR-Chk1-P53 and ATM-Chk2-P53. In conclusion, we used GES-1 cells to inform the risk of coaction of AOH, AME, and TeA in dietary exposure.

Next-generation biomonitoring of the early-life chemical exposome in neonatal and infant development

Exposure to synthetic and natural chemicals is a major environmental risk factor in the etiology of many chronic diseases. Investigating complex co-exposures is necessary for a holistic assessment in exposome-wide association studies. In this work, a sensitive liquid chromatography-tandem mass spectrometry approach was developed and validated. The assay enables the analysis of more than 80 highly-diverse xenobiotics in urine, serum/plasma, and breast milk; with detection limits generally in the pg-ng mL-1 range. In plasma of extremely-premature infants, 27 xenobiotics are identified; including contamination with plasticizers, perfluorinated alkylated substances and parabens. In breast milk samples collected longitudinally over the first 211 days post-partum, 29 analytes are detected, including pyrrolizidine- and tropane alkaloids which have not been identified in this matrix before. A preliminary estimation of daily toxicant intake via breast milk is conducted. In conclusion, we observe significant early-life co-exposure to multiple toxicants, and demonstrate the method's applicability for large-scale exposomics-type cohort studies.

Fungal Melanin Biosynthesis Pathway as Source for Fungal Toxins

Contamination of food and feed with toxin-producing fungi is a major threat in agriculture and for human health. The filamentous fungus Alternaria alternata is one of the most widespread postharvest contaminants and a weak plant pathogen. It produces a large variety of secondary metabolites with alternariol and its derivatives as characteristic mycotoxin. Other important phyto- and mycotoxins are perylene quinones (PQs), some of which have anticancer properties. Here, we discovered that the PQ altertoxin (ATX) biosynthesis shares most enzymes with the 1,8-dihydroxynaphthalene (1,8-DHN) melanin pathway. However, melanin was formed in aerial hyphae and spores, and ATXs were synthesized in substrate hyphae. This spatial separation is achieved through the promiscuity of a polyketide synthase, presumably producing a pentaketide (T4HN), a hexaketide (AT4HN), and a heptaketide (YWA1) as products. T4HN directly enters the altertoxin and DHN melanin pathway, whereas AT4HN and YWA1 can be converted only in aerial hyphae, which probably leads to a higher T4HN concentration, favoring 1,8-DHN melanin formation. Whereas the production of ATXs was strictly dependent on the CmrA transcription factor, melanin could still be produced in the absence of CmrA to some extent. This suggests that different cues regulate melanin and toxin formation. Since DHN melanin is produced by many fungi, PQs or related compounds may be produced in many more fungi than so far assumed.

Alternaria alternata Mycotoxins Activate the Aryl Hydrocarbon Receptor and Nrf2-ARE Pathway to Alter the Structure and Immune Response of Colon Epithelial Cells

After ingestion of food commodities, the gastrointestinal tract (GIT) poses the first barrier against xenobiotics and pathogens. Therefore, it is regularly confronted with external stressors potentially affecting the inflammatory response and the epithelial barrier. Alternaria mycotoxins such as alternariol (AOH) and altertoxin II (ATX-II) are frequently occurring food and feed contaminants that are described for their immunomodulatory capacities. Hence, this study aimed at exploring the effect of AOH and ATX-II as single compounds or binary mixtures on the immune response and epithelial homeostasis in noncancerous colon epithelial cells HCEC-1CT. Both toxins suppressed mRNA levels of proinflammatory mediators interleukin-8 (IL-8), tumor necrosis factor α (TNF-α), and secretion of IL-8, as well as mRNA levels of the matrix metallopeptidase 2 (MMP-2). Binary combinations of AOH and ATX-II reduced the response of the single toxins. Additionally, AOH and ATX-II modified immunolocalization of transmembrane proteins such as integrin β1, zona occludens 1 (ZO-1), claudin 4 (Cldn 4), and occludin (Ocln), which support colonic tissue homeostasis and intestinal barrier function. Moreover, the cellular distribution of ZO-1 was affected by ATX-II. Mechanistically, these effects could be traced back to the involvement of several transcription factors. AOH activated the nuclear translocation of the aryl hydrocarbon receptor (AhR) and the nuclear factor erythroid 2-related factor 2 (Nrf2), governing cell metabolic competence and structural integrity. This was accompanied by altered distribution of the NF-κB p65 protein, an important regulator of inflammatory response. ATX-II also induced AhR and Nrf2 translocation, albeit failing to substantiate the effect of AOH on the colonic epithelium. Hence, both toxins coherently repress the intestinal immune response on the cytokine transcriptional and protein levels. Furthermore, both mycotoxins affected the colonic epithelial integrity by altering the cell architecture.

Identification of potential pathways and microRNA-mRNA networks associated with benzene metabolite hydroquinone-induced hematotoxicity in human leukemia K562 cells

Background

Hydroquinone (HQ) is a phenolic metabolite of benzene with a potential risk for hematological disorders and hematotoxicity in humans. In the present study, an integrative analysis of microRNA (miRNA) and mRNA expressions was performed to identify potential pathways and miRNA-mRNA network associated with benzene metabolite hydroquinone-induced hematotoxicity.

Methods

K562 cells were treated with 40 μM HQ for 72 h, mRNA and miRNA expression changes were examined using transcriptomic profiles and miRNA microarray, and then bioinformatics analysis was performed.

Results

Out of all the differentially expressed genes (DEGs) and differentially expressed miRNAs (DEMs) induced by HQ, 1482 DEGs and 10 DEMs were up-regulated, and 1594 DEGs and 42 DEMs were down-regulated. HQ-induced DEGs were involved in oxidative stress, apoptosis, DNA methylation, histone acetylation and cellular response to leukemia inhibitory factor GO terms, as well as metabolic, Wnt/β-catenin, NF-κB, and leukemia-related pathways. The regulatory network of mRNAs and miRNAs includes 23 miRNAs, 1108 target genes, and 2304 potential miRNAs-mRNAs pairs. MiR-1246 and miR-224 had the potential to be major regulators in HQ-exposed K562 cells based on the miRNAs-mRNAs network.

Conclusions

This study reinforces the use of in vitro model of HQ exposure and bioinformatic approaches to advance our knowledge on molecular mechanisms of benzene hematotoxicity at the RNA level.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-022-00556-8.

Cereulide and Deoxynivalenol Increase LC3 Protein Levels in HepG2 Liver Cells

Food contaminants of bacterial or fungal origin frequently contaminate staple foods to various extents. Among others, the bacterial toxin cereulide (CER) and the mycotoxin deoxynivalenol (DON) co-occur in a mixed diet and are absorbed by the human body. Both toxins exert dis-tinctive mitotoxic potential. As damaged mitochondria are removed via autophagy, mitochondrial and lysosomal toxicity were assessed by applying low doses of single and combined toxins (CER 0.1-50 ng/mL; DON 0.01-5 µg/mL) to HepG2 liver cells. In addition to cytotoxicity assays, RT-qPCR was performed to investigate genes involved in lysosomal biogenesis and autophagy. CER and DON caused significant cytotoxicity on HepG2 cells after 5 and 24 h over a broad concentration range. CER, alone and in combination with DON, increased the transcription of the autophagy related genes coding for the microtubule associated protein 1A/1B light chain 3 (LC3) and sequestome 1 (SQSTM1) as well as LC3 protein expression which was determined using immunocytochemistry. DON increased LC3 protein expression without induction of gene transcription, hence it seems plausible that CER and DON act on different pathways. The results support the hypothesis that CER induces autophagy via the LC3 pathway and damaged mitochondria are therefore eliminated.

Alternaria toxins-Still emerging?

Alternaria molds are known to cause the contamination of food with their secondary metabolites, a chemically very heterogeneous group of compounds. Yet, after decades of research on the occurrence and the toxicity of Alternaria toxins in academia, no regulation has been implemented yet, thus leaving these potential food contaminants in the status of so-called "emerging mycotoxins". However, research on this topic has been far from static, leading to the European Food Safety Authority repeatedly calling for more data on the occurrence and toxicity of genotoxic metabolites such as alternariol (AOH) and its monomethyl ether (AME). To give an overview on recent developments in the field, this comprehensive review summarizes published data and addresses current challenges arising from the chemical complexity of Alternaria's metabolome, mixture effects and the emergence of novel biological targets like cell membranes or the interaction with different receptors. Besides toxicodynamics, we review recent research on toxicokinetics, including the first in vivo studies which incorporated the rarely investigated-but highly genotoxic-perylene quinones. Furthermore, a particular focus lies on the advances of liquid chromatography/tandem mass spectrometry (LC-MS/MS)-based analytical tools for determining a broader spectrum of Alternaria toxins including modified/masked forms and assessing exposure via human biomonitoring (HBM).

An 8 miRNA-Based Risk Score System for Predicting the Prognosis of Patients With Papillary Thyroid Cancer

Background:

Dysregulation of microRNAs (miRNAs) in papillary thyroid cancer (PTC) might influence prognosis of PTC. This study is aimed to develop a risk score system for predicting prognosis of PTC.

Methods:

The miRNA and gene expression profiles of PTC were obtained from The Cancer Genome Atlas database. PTC samples were randomly separated into training set (n = 248) and validation set (n = 248). The differentially expressed miRNAs (DE-miRNAs) in the training set were screened using limma package. The independent prognosis-associated DE-miRNAs were identified for building a risk score system. Risk score of PTC samples in the training set was calculated and samples were divided into high risk group and low risk group. Kaplan-Meier curves and receiver operating characteristic (ROC) curve were used to assess the accuracy of the risk score system in the training set, validation set and entire set. Finally, a miRNA-gene regulatory network was visualized by Cytoscape software, followed by enrichment analysis.

Results:

Totally, 162 DE-miRNAs between tumor and control groups in the training set were identified. An 8 independent prognosis-associated DE-miRNAs, (including miR-1179, miR-133b, miR-3194, miR-3912, miR-548j, miR-6720, miR-6734, and miR-6843) based risk score system was developed. The area under ROC curve in the training set, validation set and entire set was all above 0.93. A miRNA-gene regulatory network involving the 8 DE-miRNAs were built and functional enrichment analysis suggested the genes in the network were significantly enriched into 13 pathways, including calcium signaling pathway and hedgehog signaling pathway.

Conclusion:

The risk score system developed this study might be used for predicting the prognosis of PTC. Besides, the 8 miRNAs might affect the prognosis of PTC via hedgehog signaling pathway and calcium signaling pathway.

Gut microbiota and undigested food constituents modify toxin composition and suppress the genotoxicity of a naturally occurring mixture of Alternaria toxins in vitro

Molds of the genus Alternaria produce several mycotoxins, some of which may pose a threat for health due to their genotoxicity. Due to the lack of adequate toxicological and occurrence data, they are currently not regulated. Interactions between mycotoxins, gut microbiota and food constituents might occur after food ingestion, modifying the bioavailability and, therefore, overall toxicity of mycotoxins. The present work aimed to investigate the impact of in vitro short-term fecal incubation on the in vitro DNA-damaging effects exerted by 5 µg/mL of an Alternaria alternata extract, containing, among others, 15 nM alternariol, 12 nM alternariol monomethyl ether, 241 nM altertoxin II and 301 nM stemphyltoxin III, all of which are known as genotoxic. The involvement of microorganisms, undigested food constituents and soluble substances of human fecal samples in modifying the composition and the genotoxicity of the extract was investigated through the application of LC-MS/MS analysis and comet assays in HT-29 cells. Results showed that the potential of the mycotoxins to induce DNA strand breaks was almost completely quenched, even before anaerobic incubation, by contact with the different fractions of the fecal samples, while the potency to induce formamidopyrimidine DNA glycosylase (FPG)-sensitive sites was only slightly reduced. These effects were in line with a reduction of mycotoxin concentrations found in samples analyzed by LC-MS/MS. Although a direct correlation between the metabolic activity of the gut microbiota and modifications in mycotoxin contents was not clearly observed, adsorptive phenomena to bacterial cells and to undigested food constituents might explain the observed modifications.

Alternaria alternata Toxins Synergistically Activate the Aryl Hydrocarbon Receptor Pathway In Vitro

Alternaria molds simultaneously produce a large variety of mycotoxins, of which several were previously reported to induce enzymes of phase I metabolism through aryl hydrocarbon receptor activation. Thus, we investigated the potential of naturally occurring Alternaria toxin mixtures to induce Cytochrome P450 (CYP) 1A1/1A2/1B1 activity. Two variants of an extract from cultured Alternaria alternata, as well as the toxins alternariol (AOH), alternariol monomethyl ether (AME), altertoxin I (ATX-I), and altertoxin II (ATX-II), were tested singularly and in binary mixtures applying the 7-ethoxy-resorufin-O-deethylase (EROD) assay in MCF-7 breast cancer cells. Sub-cytotoxic concentrations of the two toxin mixtures, as well as ATX-I, ATX-II and AOH, exhibited dose-dependent enhancements of CYP 1 activity. ATX-I and ATX-II interacted synergistically in this respect, demonstrating the two perylene quinones as major contributors to the extract’s potential. Binary mixtures between AOH and the two altertoxins respectively exhibited concentration-dependent antagonistic as well as synergistic combinatory effects. Notably, AME showed no efficacy towards EROD enzyme activity or impact on other toxins’ efficacy. Hence, this study provides insights into synergistic and other combinatory effects of Alternaria toxins in natural co-occurrence scenarios in the context of AhR signalling pathway activation in breast cancer cells.

Fungal Diversity and Mycotoxins in Low Moisture Content Ready-To-Eat Foods in Nigeria

Low moisture content ready-to-eat foods vended in Nigerian markets could be pre-packaged or packaged at point of sale. These foods are widely and frequently consumed across Nigeria as quick foods. Despite their importance in the daily diets of Nigerians, a comprehensive study on the diversity of fungi, fungal metabolite production potential, and mycotoxin contamination in the foods has not yet been reported. Therefore, this study assessed the diversity of fungi in 70 samples of low moisture content ready-to-eat foods [cheese balls, garri (cassava-based), granola (a mix of cereals and nuts) and popcorn] in Nigeria by applying a polyphasic approach including morphological examination, genera/species-specific gene marker sequencing and secondary metabolite profiling of fungal cultures. Additionally, mycotoxin levels in the foods were determined by LC-MS/MS. Fungal strains (n = 148) were recovered only from garri. Molecular analysis of 107 representative isolates revealed 27 species belonging to 12 genera: Acremonium, Allophoma, Aspergillus, Cladosporium, Fusarium, Microdochium, Penicillium, Sarocladium, Talaromyces, and Tolypocladium in the Ascomycota, and Fomitopsis and Trametes in the Basidiomycota. To the best of our knowledge Allophoma, Fomitopsis, Microdochium, Tolypocladium, and Trametes are reported in African food for the first time. A total of 21 uncommon metabolites were found in cultures of the following species: andrastin A and sporogen AO1 in Aspergillus flavus; paspalin in A. brunneoviolaceus; lecanoic acid and rugulusovin in A. sydowii; sclerotin A in P. citrinum and Talaromyces siamensis; barceloneic acid, festuclavine, fumigaclavine, isochromophilons (IV, VI, and IX), ochrephilone, sclerotioramin, and sclerotiorin in P. sclerotium; epoxyagroclavine, infectopyron, methylorsellinic acid and trichodermamide C in P. steckii; moniliformin and sporogen AO1 in P. copticola; and aminodimethyloctadecanol in Tolypocladium. Twenty-four mycotoxins in addition to other 73 fungal and plant toxins were quantified in the foods. In garri, cheeseballs, popcorn and granola were 1, 6, 12, and 23 mycotoxins detected, respectively. Deoxynivalenol, fumonisins, moniliformin, aflatoxins and citrinin contaminated 37, 31, 31, 20, and 14% of all food samples, respectively. Overall, citrinin had the highest mean concentration of 1481 μg/kg in the foods, suggesting high citrinin exposures in the Nigerian populace. Fungal and mycotoxin contamination of the foods depend on pre-food and post-food processing practices.

Assessing the Effect of Mycotoxin Combinations: Which Mathematical Model Is (the Most) Appropriate?

In the past decades, many studies have examined the nature of the interaction between mycotoxins in biological models classifying interaction effects as antagonisms, additive effects, or synergisms based on a comparison of the observed effect with the expected effect of combination. Among several described mathematical models, the arithmetic definition of additivity and factorial analysis of variance were the most commonly used in mycotoxicology. These models are incorrectly based on the assumption that mycotoxin dose-effect curves are linear. More appropriate mathematical models for assessing mycotoxin interactions include Bliss independence, Loewe’s additivity law, combination index, and isobologram analysis, Chou-Talalays median-effect approach, response surface, code for the identification of synergism numerically efficient (CISNE) and MixLow method. However, it seems that neither model is ideal. This review discusses the advantages and disadvantages of these mathematical models.

Combinatory estrogenic effects of bisphenol A in mixtures with alternariol and zearalenone in human endometrial cells

Humans are typically exposed to mixtures of substances, whereby their bioactivity can be significantly altered by co-occurring compounds. Thus, over the last years, research on combinatory effects has gained increasing attention. In particular, several xenoestrogens have been recently reported to interact synergistically, among them alternariol (AOH) and zearalenone (ZEN), two toxins produced by molds which contaminate crops or food commodities. Bisphenol A (BPA) is a potential food contaminant arising from its use in plastics and represents a well-known xenoestrogen, acting as an endocrine disruptor. However, little research was yet conducted on its impact on the bioactivity of other xenoestrogens, and vice versa. Thus, in this study, we focused on combinatory estrogenic effects of BPA with AOH and ZEN in Ishikawa cells, which represent a well-established, estrogen-sensitive human cell model. Estrogenic stimuli of the single compounds and binary combinations in constant concentration ratios were measured by assessing the activity of alkaline phosphatase, a natural reporter gene for estrogen receptor activation. In parallel, cytotoxicity was monitored by neutral red assay. For statistical analysis of combinatory effects the "combination index" model was applied. In combination with ZEN, BPA was found to cause additive estrogenic effects. Mixtures of BPA with AOH expressed moderately antagonistic to nearly additive combinatory effects, depending on the concentration ratio. Although no synergistic effects were measured in the applied chemical mixtures, additive estrogenic stimuli were observed, underlining the importance to consider the cumulative impact of endocrine active factors out of different sources and structural classes.

Co-Occurrence and Combinatory Effects of Alternaria Mycotoxins and other Xenobiotics of Food Origin: Current Scenario and Future Perspectives

Mycotoxins are low-molecular weight compounds produced by diverse genera of molds that may contaminate food and feed threatening the health of humans and animals. Recent findings underline the importance of studying the combined occurrence of multiple mycotoxins and the relevance of assessing the toxicity their simultaneous exposure may cause in living organisms. In this context, for the first time, this work has critically reviewed the most relevant data concerning the occurrence and toxicity of mycotoxins produced by Alternaria spp., which are among the most important emerging risks to be assessed in food safety, alone or in combination with other mycotoxins and bioactive food constituents. According to the literature covered, multiple Alternaria mycotoxins may often occur simultaneously in contaminated food, along with several other mycotoxins and food bioactives inherently present in the studied matrices. Although the toxicity of combinations naturally found in food has been rarely assessed experimentally, the data collected so far, clearly point out that chemical mixtures may differ in their toxicity compared to the effect of toxins tested individually. The data presented here may provide a solid foothold to better support the risk assessment of Alternaria mycotoxins highlighting the actual role of chemical mixtures on influencing their toxicity.

Red- and Blue-Light Sensing in the Plant Pathogen Alternaria alternata Depends on Phytochrome and the White-Collar Protein LreA

Light controls many processes in filamentous fungi. The study of light regulation in a number of model organisms revealed an unexpected complexity. Although the molecular components for light sensing appear to be widely conserved in fungal genomes, the regulatory circuits and the sensitivity of certain species toward specific wavelengths seem different. In N. crassa, most light responses are triggered by blue light, whereas in A. nidulans, red light plays a dominant role. In Alternaria alternata, both blue and red light appear to be important. In A. alternata, photoreceptors control morphogenetic pathways, the homeostasis of reactive oxygen species, and the production of secondary metabolites. On the other hand, high-osmolarity sensing required FphA and LreA, indicating a sophisticated cross talk between light and stress signaling.

The filamentous fungus Alternaria alternata is a common postharvest contaminant of food and feed, and some strains are plant pathogens. Many processes in A. alternata are triggered by light. Interestingly, blue light inhibits sporulation, and red light reverses the effect, suggesting interactions between light-sensing systems. The genome encodes a phytochrome (FphA), a white collar 1 (WC-1) orthologue (LreA), an opsin (NopA), and a cryptochrome (CryA) as putative photoreceptors. Here, we investigated the role of FphA and LreA and the interplay with the high-osmolarity glycerol (HOG) mitogen-activated protein (MAP) kinase pathway. We created loss-of function mutations for fphA, lreA, and hogA using CRISPR-Cas9 technology. Sporulation was reduced in all three mutant strains already in the dark, suggesting functions of the photoreceptors FphA and LreA independent of light perception. Germination of conidia was delayed in red, blue, green, and far-red light. We found that light induction of ccgA (clock-controlled gene in Neurospora crassa and light-induced gene in Aspergillus nidulans) and the catalase gene catA depended on FphA, LreA, and HogA. Light induction of ferA (a putative ferrochelatase gene) and bliC (bli-3, light regulated, unknown function) required LreA and HogA but not FphA. Blue- and green-light stimulation of alternariol formation depended on LreA. A lack of FphA or LreA led to enhanced resistance toward oxidative stress due to the upregulation of catalases and superoxide dismutases. Light activation of FphA resulted in increased phosphorylation and nuclear accumulation of HogA. Our results show that germination, sporulation, and secondary metabolism are light regulated in A. alternata with distinct and overlapping roles of blue- and red-light photosensors.

Functional impairment triggered by altertoxin II (ATXII) in intestinal cells in vitro: cross-talk between cytotoxicity and mechanotransduction

Intestinal cells are able to continuously integrate response to multiple stimuli/stressors; these include the concomitant activation of “chemically driven” pathways, of paramount importance in the response to toxicants, as well as physical stimulation derived from motility. Altertoxin II (ATXII, 0.1, 1 and 10 µM), a mycotoxin produced by the food contaminant fungus Alternaria alternata was studied in HT-29 intestinal adenocarcinoma cells and in non-transformed intestinal epithelial cells, HCEC. One-hour incubation with ATXII was sufficient to trigger irreversible cytotoxicity in both cell types, as well as to modify cellular responses to concomitant pro-oxidant challenge (H₂O₂, 100–500 µM, DCF-DA assay) suggesting that even relatively short-time exposure of the intestinal cells could be sufficient to alter their functionality. Combination of ATXII (1 µM) with physical stimulation typical of the intestinal compartment (shear stress) revealed differential response of tumor-derived epithelial cells HT-29 in comparison to HCEC, in particular in the localization of the transcription factor Nrf2 (NF-E2-related factor 2). Moreover, ATXII reduced the migratory potential of HCEC as well as their membrane fluidity, but had no respective impact on HT-29 cells. Taken together, ATXII appeared to alter predominantly membrane functionality in HCEC thus hampering crucial functions for cellular motility/turnover, as well as barrier function of healthy intestinal cells and had very limited activity on the tumor counterparts.

The mycotoxin alternariol suppresses lipopolysaccharide-induced inflammation in THP-1 derived macrophages targeting the NF-κB signalling pathway

Alternariol (AOH) is a secondary metabolite formed by black mold of the genus Alternaria alternata. Due to limited hazard and occurrence data, AOH is still considered as an “emerging mycotoxin” and, as such, not monitored and regulated yet. Recent studies indicate immunosuppressive effects in vitro by altering the expression of CD molecules and proinflammatory cytokines, which are indispensable in mounting an innate immune response. However, the mode of action by which AOH exerts its immunosuppressive effects has not been unraveled yet. The present study aimed to characterise the impact of AOH on the nuclear factor kappa B (NF-κB) pathway, the expression of NF-κB target cytokines and involved regulatory microRNAs (miRNAs). In THP-1 derived macrophages, AOH (1–20 µM) was found to suppress lipopolysaccharide (LPS)-induced NF-κB pathway activation, decrease secretion of the proinflammatory cytokines IL-8, IL-6, TNF-α and to induce secretion of the anti-inflammatory IL-10. Thereby, a distinct pattern of cytokine mRNA levels was monitored, varying between short- and long-term exposure. Concomitantly, AOH (2–20 µM) affected the transcription levels of miR-146a and miR-155 in LPS-stimulated THP-1 derived macrophages dose-dependently by down- and upregulation, respectively. In contrast, transcription of miR-16 and miR-125b, two other immune-related miRNAs, was not modulated. In the absence of a LPS stimulus, AOH (20 µM) did not affect basal NF-κB activity, but increased IL-10 transcription. Collectively, our results indicate, that AOH itself does not induce a proinflammatory immune response in human macrophages; however, in an inflamed environment it possesses the ability to repress inflammation by targeting the NF-κB signalling pathway and regulatory miRNAs.

Chemotaxonomy of Mycotoxigenic Small-Spored Alternaria Fungi - Do Multitoxin Mixtures Act as an Indicator for Species Differentiation?

Necrotrophic as well as saprophytic small-spored Alternaria (A.) species are annually responsible for major losses of agricultural products, such as cereal crops, associated with the contamination of food and feedstuff with potential health-endangering Alternaria toxins. Knowledge of the metabolic capabilities of different species-groups to form mycotoxins is of importance for a reliable risk assessment. 93 Alternaria strains belonging to the four species groups Alternaria tenuissima, A. arborescens, A. alternata, and A. infectoria were isolated from winter wheat kernels harvested from fields in Germany and Russia and incubated under equal conditions. Chemical analysis by means of an HPLC-MS/MS multi-Alternaria-toxin-method showed that 95% of all strains were able to form at least one of the targeted 17 non-host specific Alternaria toxins. Simultaneous production of up to 15 (modified) Alternaria toxins by members of the A. tenuissima, A. arborescens, A. alternata species-groups and up to seven toxins by A. infectoria strains was demonstrated. Overall tenuazonic acid was the most extensively formed mycotoxin followed by alternariol and alternariol mono methylether, whereas altertoxin I was the most frequently detected toxin. Sulfoconjugated modifications of alternariol, alternariol mono methylether, altenuisol and altenuene were frequently determined. Unknown perylene quinone derivatives were additionally detected. Strains of the species-group A. infectoria could be segregated from strains of the other three species-groups due to significantly lower toxin levels and the specific production of infectopyrone. Apart from infectopyrone, alterperylenol was also frequently produced by 95% of the A. infectoria strains. Neither by the concentration nor by the composition of the targeted Alternaria toxins a differentiation between the species-groups A. alternata, A. tenuissima and A. arborescens was possible.

Tracking emerging mycotoxins in food: development of an LC-MS/MS method for free and modified Alternaria toxins

Mycotoxins produced by Alternaria fungi are ubiquitous food contaminants, but analytical methods for generating comprehensive exposure data are rare. We describe the development of an LC-MS/MS method covering 17 toxins for investigating the natural occurrence of free and modified Alternaria toxins in tomato sauce, sunflower seed oil, and wheat flour. Target analytes included alternariol (AOH), AOH-3-glucoside, AOH-9-glucoside, AOH-3-sulfate, alternariol monomethyl ether (AME), AME-3-glucoside, AME-3-sulfate, altenuene, isoaltenuene, tenuazonic acid (TeA), tentoxin (TEN), altertoxin I and II, alterperylenol, stemphyltoxin III, altenusin, and altenuic acid III. Extensive optimization resulted in a time- and cost-effective sample preparation protocol and a chromatographic baseline separation of included isomers. Overall, adequate limits of detection (0.03–9 ng/g) and quantitation (0.6–18 ng/g), intermediate precision (9–44%), and relative recovery values (75–100%) were achieved. However, stemphyltoxin III, AOH-3-sulfate, AME-3-sulfate, altenusin, and altenuic acid III showed recoveries in wheat flour below 70%, while their performance was stable and reproducible. Our pilot study with samples from the Austrian retail market demonstrated that tomato sauces (n = 12) contained AOH, AME, TeA, and TEN in concentrations up to 20, 4, 322, and 0.6 ng/g, while sunflower seed oil (n = 7) and wheat flour samples (n = 9) were contaminated at comparatively lower levels. Interestingly and of relevance for risk assessment, AOH-9-glucoside, discovered for the first time in naturally contaminated food items, and AME-3-sulfate were found in concentrations similar to their parent toxins. In conclusion, the established multi-analyte method proved to be fit for purpose for generating comprehensive Alternaria toxin occurrence data in different food matrices.

Graphical abstract

microRNA expression profiles of scar and normal tissue from patients with posterior urethral stricture caused by pelvic fracture urethral distraction defects

Pelvic fracture urethral distraction defect (PFUDD) seriously affects the quality of life of patients. At present, there are few effective drug treatments available for PFUDD-induced urethral stricture, which is associated with fibrosis and scar formation in urethra lumen. Emerging evidence suggests that microRNAs (miRNAs/miRs) may be involved in the regulation of fibrosis, and analysis of miRNA expression profiles in urethral scar and normal urethra tissues may therefore benefit the discovery of novel treatments for urethral stricture with micro invasive procedures. In the present study, miRNA sequencing and quantitative polymerase chain reaction (qPCR) validation using paired scar and normal tissues from patients with PFUDD, and functional analysis of the miRNAs involved in the fibrosis associated signaling pathway was performed. A total of 94 differentially expressed miRNAs were identified in the scar tissue of patients with PFUDD. Among them, 26 miRNAs had significantly altered expression in the scar tissue compared with the normal tissue from the same patient. qPCR validation confirmed that miR-129-5p was overexpressed in scar tissue. The TGF-β pathway-associated functions of a total of 5 miRNAs (hsa-miR-129-5p, hsa-miR-135a-5p, hsa-miR-363-3p, hsa-miR-6720-3p and hsa-miR-9-5p) were further analyzed, as well as their key molecular targets and functional mechanisms in signaling regulation. To conclude the miRNA sequencing indicated a significantly altered expression of hsa-miR-129-5p, hsa-miR-135a-5p, hsa-miR-363-3p, hsa-miR-6720-3p and hsa-miR-9-5p in patients with PFUDD. These miRNAs and their potential target genes were associated with fibrosis in several diseases, and the data from the present study may help explore potential miRNA targets for future precision treatments for urethral stricture.

Genome-wide miRNA response to anacardic acid in breast cancer cells

MicroRNAs are biomarkers and potential therapeutic targets for breast cancer. Anacardic acid (AnAc) is a dietary phenolic lipid that inhibits both MCF-7 estrogen receptor α (ERα) positive and MDA-MB-231 triple negative breast cancer (TNBC) cell proliferation with IC50s of 13.5 and 35 μM, respectively. To identify potential mediators of AnAc action in breast cancer, we profiled the genome-wide microRNA transcriptome (microRNAome) in these two cell lines altered by the AnAc 24:1n5 congener. Whole genome expression profiling (RNA-seq) and subsequent network analysis in MetaCore Gene Ontology (GO) algorithm was used to characterize the biological pathways altered by AnAc. In MCF-7 cells, 69 AnAc-responsive miRNAs were identified, e.g., increased let-7a and reduced miR-584. Fewer, i.e., 37 AnAc-responsive miRNAs were identified in MDA-MB-231 cells, e.g., decreased miR-23b and increased miR-1257. Only two miRNAs were increased by AnAc in both cell lines: miR-612 and miR-20b; however, opposite miRNA arm preference was noted: miR-20b-3p and miR-20b-5p were upregulated in MCF-7 and MDA-MB-231, respectively. miR-20b-5p target EFNB2 transcript levels were reduced by AnAc in MDA-MB-231 cells. AnAc reduced miR-378g that targets VIM (vimentin) and VIM mRNA transcript expression was increased in AnAc-treated MCF-7 cells, suggesting a reciprocal relationship. The top three enriched GO terms for AnAc-treated MCF-7 cells were B cell receptor signaling pathway and ribosomal large subunit biogenesis and S-adenosylmethionine metabolic process for AnAc-treated MDA-MB-231 cells. The pathways modulated by these AnAc-regulated miRNAs suggest that key nodal molecules, e.g., Cyclin D1, MYC, c-FOS, PPARγ, and SIN3, are targets of AnAc activity.

Establishment of CRISPR/Cas9 in Alternaria alternata

The filamentous fungus Alternaria alternata is a potent producer of many secondary metabolites, some of which like alternariol or alternariol-methyl ether are toxic and/or cancerogenic. Many Alternaria species do not only cause post-harvest losses of food and feed, but are aggressive plant pathogens. Despite the great economic importance and the large number of research groups working with the fungus, the molecular toolbox is rather underdeveloped. Gene deletions often result in heterokaryotic strains and therefore, gene-function analyses are rather tedious. In addition, A. alternata lacks a sexual cycle and classical genetic approaches cannot be combined with molecular biological methods. Here, we show that CRISPR/Cas9 can be efficiently used for gene inactivation. Two genes of the melanin biosynthesis pathway, pksA and brm2, were chosen as targets. Several white mutants were obtained after several rounds of strain purification through protoplast regeneration or spore inoculation. Mutation of the genes was due to deletions from 1bp to 1.5kbp. The CRISPR/Cas9 system was also used to inactivate the orotidine-5-phosphate decarboxylase gene pyrG to create a uracil-auxotrophic strain. The strain was counter-selected with fluor-orotic acid and could be re-transformed with pyrG from Aspergillus fumigatus and pyr-4 from Neurospora crassa. In order to test the functioning of GFP, the fluorescent protein was fused to a nuclear localization signal derived from the StuA transcription factor of Aspergillus nidulans. After transformation bright nuclei were visible.