The mycotoxin patulin reacts with DNA bases with and without previous conjugation to GSH: implication for related α,β-unsaturated carbonyl compounds?

New insights into searching patulin degrading enzymes in Saccharomyces cerevisiae through proteomic and molecular docking analysis

Global warming has increased the contamination of mycotoxins. Patulin (PAT) is a harmful contaminant that poses a serious threat to food safety and human health. Saccharomyces cerevisiae biodegrades PAT by its enzymes during fermentation, which is a safe and efficient method of detoxification. However, the key degradation enzymes remain unclear. In this study, the proteomic differences of Saccharomyces cerevisiae under PAT stress were investigated. The results showed that the proteins involved in redox reactions and defense mechanisms were significantly up-regulated to resist PAT stress. Subsequently, molecular docking was used to virtual screen for degrading enzymes. Among 18 proteins, YKL069W showed the highest binding affinity to PAT and was then expressed in Escherichia coli, where the purified YKL069W completely degraded 10 μg/mL PAT at 48 h. YKL069W was demonstrated to be able to degrade PAT into E-ascladiol. Molecular dynamics simulations confirmed that YKL069W was stable in catalyzing PAT degradation with a binding free energy of - 7.5 kcal/mol. Furthermore, it was hypothesized that CYS125 and CYS101 were the key amino acid residues for degradation. This study offers new insights for the rapid screening and development of PAT degrading enzymes and provides a theoretical basis for the detoxification of mycotoxins.

Microbial detoxification of mycotoxins in food

Mycotoxins are toxic secondary metabolites produced by certain genera of fungi including but not limited to Fusarium, Aspergillus, and Penicillium. Their persistence in agricultural commodities poses a significant food safety issue owing to their carcinogenic, teratogenic, and immunosuppressive effects. Due to their inherent stability, mycotoxin levels in contaminated food often exceed the prescribed regulatory thresholds posing a risk to both humans and livestock. Although physical and chemical methods have been applied to remove mycotoxins, these approaches may reduce the nutrient quality and organoleptic properties of food. Microbial transformation of mycotoxins is a promising alternative for mycotoxin detoxification as it is more specific and environmentally friendly compared to physical/chemical methods. Here we review the biological detoxification of the major mycotoxins with a focus on microbial enzymes.

Removal of patulin by thiol-compounds: A review

Patulin (PAT) is a toxic mycotoxin usually contaminated apple juices, which leads to a serious food safety issue in the world. Thiol-compounds are a class of compounds containing the thiol (-SH) group themselves or obtained the -SH group by physical or chemical modification. They have the ability to efficiently remove patulin in apple juices with manifested negligible effects on juice quality. This review investigates the latest development in the removal of patulin using thiol-compounds, including the removal efficiencies and mechanisms of patulin, the factors influencing the removal efficiency of patulin, as well as the toxicities of thiol-compounds and safety of juices after detoxification. This review shows that thiol-compounds are promising materials for the removal or degradation of patulin in the contaminated juices.

Synthesis and biological evaluation of substituted N-(2-(1H-benzo[d]imidazol-2-yl)phenyl)cinnamides as tubulin polymerization inhibitors

A new series of N-(2-(1H-benzo[d]imidazol-2-yl)phenyl) cinnamides was prepared and evaluated for their in vitro cytotoxic activity using various cancer cell lines viz. A549 (human non-small cell lung cancer), MDA-MB-231 (human triple negative breast cancer), B16-F10 (mouse melanoma), BT-474 (human breast cancer), and 4 T1 (mouse triple negative breast cancer). In the series of tested compounds, 12h showed potent cytotoxic activity against non-small cell lung cancer cell line with IC₅₀ value of 0.29 ± 0.02 µM. The cytoxicity of most potent compound 12h was also tested on NRK-52E (normal rat kidney epithelial cell line) and showed less cytotoxicity compared to cancer cells. Tubulin polymerization assay indicated that the compound 12h was able to impede the cell division by inhibiting tubulin polymerization. Moreover, molecular docking study also suggested the binding of 12h at the colchicine-binding site of the tubulin protein. Cell cycle analysis revealed that the compound 12h arrests G2/M phase. In addition, 12h induced apoptosis in A549 cell lines was evaluated by various staining studies like acridine orange, DAPI, analysis of mitochondrial membrane potential, annexin V-FITC, and DCFDA assays.

Thiol-functionalized inactivated yeast embedded in agar aerogel for highly efficient adsorption of patulin in apple juice

The issue of patulin (PAT) contamination in apple juice has attracted widespread concern. Recently, inactivated yeast based biosorbents have shown great advantages in the removal of toxic contaminants. However, the traditional yeast adsorbents have disadvantages of a limited adsorption capacity in juice and separation difficulty. In the present work, five chemical thiol-functionalization methods were used to increase the PAT adsorption efficiency of yeast cells in apple juice. Thereinto, glutaraldehyde cross-linking increased the thiol (-SH) content of yeast cells to 1.26 mmol g^-1 and improved the PAT adsorption capacity of inactivated yeast in apple juice by 150 times. The covalent bonding of -SH and PAT played an important role in the improvement of adsorption capacity. The as-prepared thiol-modification yeast (Y-SH(Gl)) was then embedded in the agar aerogel to obtain Y-SH(Gl)@Agar free of separation. PAT adsorption of Y-SH(Gl)@Agar was consistent with the Freundlich model and the pseudo-second-order kinetic model. Moreover, Y-SH(Gl)@Agar was competent for PAT removal in apple juice and manifested negligible effects on juice quality. Cytotoxicity investigation indicated its good biocompatibility and ignorable food safety risk, thereby demonstrating that Y-SH(Gl)@Agar may be a promising adsorbent material for the control of PAT contaminant in juice.

Formation of patulin-glutathione conjugates induced by pulsed light: A tentative strategy for patulin degradation in apple juices

Patulin is a toxic mycotoxin usually associated with apple products. Due to its unhealthy effects for humans, its content is regulated by the food safety authorities. The removal or degradation of this mycotoxin in contaminated apple juices has been studied with different approaches with uneven effectiveness. However, a strategy based on the chemical reaction between patulin and glutathione (GSH), in order to generate the conjugates that are formed during cell detoxification process, is an innovative approach yet to be evaluated. In this work, the formation of patulin-GSH conjugates activated by the application of pulsed light treatments and catalyzed by Fe²⁺ ions was evaluated. The study of patulin degradation and effect of the GSH/Fe²⁺ molar ratio showed that a molar ratio of 5 allows an adequate catalytic effect of the metal ions. In addition, mono-substituted patulin-glutathione adducts were identified as the main type of generated conjugates.

Distinct Transcriptional Changes in Response to Patulin Underlie Toxin Biosorption Differences in Saccharomyces Cerevisiae

Patulin (4-hydroxy-4H-furo[3,2c]pyran-2[6H]-one) is a mycotoxin produced by a suite of fungi species. Patulin is toxic to humans and is a sporadic contaminant in products that were made from fungi-infected fruits. The baker yeast Saccharomyces cerevisiae (S. cerevisiae) has been shown to decrease patulin levels likely by converting it to the less harmful E-ascladiol, yet this capacity is dependent on the strain utilized. In this study we show that four representative strains of different S. cerevisiae lineages differ in their ability to tolerate and decrease patulin levels in solution, demonstrating that some strains are better suitable for patulin biocontrol. Indeed, we tested the biocontrol capacities of the best patulin-reducer strain (WE) in contaminated apple juice and demonstrated their potential role as an efficient natural biocontrol solution. To investigate the mechanisms behind the differences between strains, we explored transcriptomic changes of the top (WE strain) and worst (WA strain) patulin-biocontroller strains after being exposed to this toxin. Large and significant gene expression differences were found between these two strains, the majority of which represented genes associated with protein biosynthesis, cell wall composition and redox homeostasis. Interestingly, the WE isolate exhibited an overrepresentation of up-regulated genes involved in membrane components, suggesting an active role of the membrane towards patulin detoxification. In contrast, WA upregulated genes were associated with RNA metabolism and ribosome biogenesis, suggesting a patulin impact upon transcription and translation activity. These results suggest that different genotypes of S. cerevisiae encounter different stresses from patulin toxicity and that different rates of detoxification of this toxin might be related with the plasma membrane composition. Altogether, our data demonstrates the different molecular mechanisms in S. cerevisiae strains withstanding patulin exposure and opens new avenues for the selection of new patulin biocontroller strains.

A multi-endpoint approach to the combined toxic effects of patulin and ochratoxin a in human intestinal cells

Humans can be exposed to a complex and variable combination of mycotoxins. After ingestion, intestinal mucosa constitutes the first biological barrier that can be exposed to high concentrations of these toxins. The present study aimed to characterize the combined cytotoxicity, genotoxicity and impact on the gastrointestinal barrier integrity of patulin (PAT, 0.7 μM to 100 μM) and ochratoxin A (OTA, 1 μM to 200 μM) mixtures in Caco-2 cells. A dose-ratio deviation was verified for cytotoxicity, implying that OTA was mainly responsible for synergism when dominant in the mixture, while this pattern was changed to antagonism for the highest PAT concentrations. Genotoxicity (comet assay) results were compatible with an interactive DNA damaging effect at the highest PAT and OTA concentrations, not clearly mediated by the formation of oxidative DNA breaks. Regarding gastrointestinal barrier integrity, a potential synergism was attained at low levels of both mycotoxins, changing to antagonism at higher doses. The present results indicate that combined mycotoxins effects may arise at the intestinal level and should not be underestimated when evaluating their risk to human health.

Isotopic Labeling Studies Reveal the Patulin Detoxification Pathway by the Biocontrol Yeast Rhodotorula kratochvilovae LS11

Patulin (1) is a mycotoxin contaminant in fruit and vegetable products worldwide. Biocontrol agents, such as the yeast Rhodotorula kratochvilovae strain LS11, can reduce patulin (1) contamination in food. R. kratochvilovae LS11 converts patulin (1) into desoxypatulinic acid (DPA) (5), which is less cytotoxic than the mycotoxin (1) to in vitro human lymphocytes. In the present study, we report our investigations into the pathway of degradation of patulin (1) to DPA (5) by R. kratochvilovae. Isotopic labeling experiments revealed that 5 derives from patulin (1) through the hydrolysis of the γ-lactone ring and subsequent enzymatic modifications. The ability of patulin (1) and DPA (5) to cause genetic damage was also investigated by the cytokinesis-block micronucleus cytome assay on in vitro human lymphocytes. Patulin (1) was demonstrated to cause much higher chromosomal damage than DPA (5).

Patulin in Apples and Apple-Based Food Products: The Burdens and the Mitigation Strategies

Apples and apple-based products are among the most popular foods around the world for their delightful flavors and health benefits. However, the commonly found mold, Penicillium expansum invades wounded apples, causing the blue mold decay and ensuing the production of patulin, a mycotoxin that negatively affects human health. Patulin contamination in apple products has been a worldwide problem without a satisfactory solution yet. A comprehensive understanding of the factors and challenges associated with patulin accumulation in apples is essential for finding such a solution. This review will discuss the effects of the pathogenicity of Penicillium species, quality traits of apple cultivars, and environmental conditions on the severity of apple blue mold and patulin contamination. Moreover, beyond the complicated interactions of the three aforementioned factors, patulin control is also challenged by the lack of reliable detection methods in food matrices, as well as unclear degradation mechanisms and limited knowledge about the toxicities of the metabolites resulting from the degradations. As apple-based products are mainly produced with stored apples, pre- and post-harvest strategies are equally important for patulin mitigation. Before storage, disease-resistance breeding, orchard-management, and elicitor(s) application help control the patulin level by improving the storage qualities of apples and lowering fruit rot severity. From storage to processing, patulin mitigation strategies could benefit from the optimization of apple storage conditions, the elimination of rotten apples, and the safe and effective detoxification or biodegradation of patulin.

Biotoxicological Analyses of Trimeroside from Baccharis trimera Using a Battery of In Vitro Test Systems

The use in folk medicine of Baccharis trimera and recent studies on DNA damage by oxidative stress mechanisms have motivated this study. We investigated the biotoxicological effects of trimeroside from this plant. Aqueous extract from aerial parts of B. trimera was fractioned by flash chromatography for further isolation by thin-layer chromatography. The novel nor-monoterpene glycoside, trimeroside, and three flavonoids, cirsimaritin, luteolin and quercetin, were isolated. The genotoxic and mutagenic potential of trimeroside was determined by Salmonella/microsome (TA98 and TA100), comet assay, and cytokinesis-block micronucleus cytome assay (CBMN-cyt) in HepG2 cells. We also screened trimeroside into different human tumoral cell lines by sulforhodamine B (SRB) assay. Mutagenicity was detected in TA100 strain with metabolic activation. Genotoxic effects were not observed in HepG2 by comet assay. However, a decrease in the nuclear index division in the 2.0 mg·mL⁻¹ concentration and an increase of nucleoplasmic bridges in the 1.5 mg·mL⁻¹ concentration were detected by CBMN-cyt assay indicating cytotoxic and mutagenic effects. In SRB assay, trimeroside showed weak antiproliferative activity against the cell lines.

Nontarget Analysis Reveals a Bacterial Metabolite of Pyrene Implicated in the Genotoxicity of Contaminated Soil after Bioremediation

Bioremediation is an accepted technology for cleanup of soil contaminated with polycyclic aromatic hydrocarbons (PAHs), but it can increase the genotoxicity of the soil despite removal of the regulated PAHs. Although polar biotransformation products have been implicated as causative genotoxic agents, no specific product has been identified. We pursued a nontarget analytical approach combining effect-directed analysis (EDA) and metabolite profiling to compare extracts of PAH-contaminated soil from a former manufactured-gas plant site before and after treatment in a laboratory-scale aerobic bioreactor. A compound with the composition C₁₅H₈O₂ and four methylated homologues were shown to accumulate as a result of bioreactor treatment, and the C₁₅H₈O₂ compound purified from soil extracts was determined to be genotoxic. Its structure was established by nuclear magnetic resonance and mass spectroscopy as a heretofore unidentified α,β-unsaturated lactone derived from dioxygenation of pyrene at an apical ring, 2H-naphtho[2,1,8-def]chromen-2-one (NCO), which was confirmed by synthesis. The concentration of NCO in the bioreactor was 11 μg g^-1 dry soil, corresponding to 13% of the pyrene removed. It also accumulated in aerobically incubated soil from two additional PAH-contaminated sites and was formed from pyrene by two pyrene-degrading bacterial cultures known to be geographically widespread, underscoring its potential environmental significance.

The intestinal barrier as an emerging target in the toxicological assessment of mycotoxins

Mycotoxins, the secondary metabolites of fungal species, are the most frequently occurring natural food contaminants in human and animal diets. Risk assessment of mycotoxins focused as yet on their mutagenic, genotoxic and potential carcinogenic effects. Recently, there is an increasing awareness of the adverse effects of various mycotoxins on vulnerable structures in the intestines. In particular, an impairment of the barrier function of the epithelial lining cells and the sealing tight junction proteins has been noted, as this could result in an increased translocation of luminal antigens and pathogens and an excessive activation of the immune system. The current review aims to provide a summary of the available evidence regarding direct effects of various mycotoxins on the intestinal epithelial barrier. Available data, based on different cellular and animal studies, show that food-associated exposure to certain mycotoxins, especially trichothecenes and patulin, affects the intestinal barrier integrity and can result in an increased translocation of harmful stressors. It is therefore hypothesized that human exposure to certain mycotoxins, particularly deoxynivalenol, as the major trichothecene, may play an important role in etiology of various chronic intestinal inflammatory diseases, such as inflammatory bowel disease, and in the prevalence of food allergies, particularly in children.

In vitro exposure of Penicillium mycotoxins with or without a modified yeast cell wall extract (mYCW) on bovine macrophages (BoMacs)

Penicillium mycotoxins (PMs) are contaminants that are frequently found in grain or crop-based silage for animal feed. Previously, we have characterized the potential immunotoxicity of the following PMs: citrinin (CIT), ochratoxin A (OTA), patulin (PAT), mycophenolic acid (MPA), and penicillic acid (PA) by using a bovine macrophage cell line (BoMacs). In the present study, cell proliferation was used as a bioassay endpoint to evaluate the efficacy of a modified yeast cell wall extract (mYCW), for preventing PM toxicity under various in vitro conditions such as the following: pH (3, 5, 7), incubation time (1, 2, 4, 6 h), percentage of mYCW (0.05, 0.1, 0.2, 0.5, 1.0 %), and PM concentration. mYCW was most effective in preventing the toxicity of 12.88 and 25.8 μM OTA at pH 3.0 (p < 0.0001), regardless of incubation time (p < 0.0001) and the percentage of mYCW (p < 0.0001). An incubation time of 6 h (p < 0.05) or 0.5 and 1.0 % mYCW (p < 0.0001) significantly improved the efficacy of mYCW for preventing CIT toxicity. In contrast, 0.5 and 1.0 % of mYCW appeared to exacerbate the PAT toxicity (p < 0. 0001). This effect on PAT toxicity was constantly observed with higher PAT concentrations, and it reached significance at a concentration of 0.70 μM (p < 0.0001). mYCW had no effect on PA toxicity. These results suggest that mYCW may reduce OTA toxicity and, to some extent, CIT toxicity at pH 3.0. Although PAT toxicity was increased by mYCW treatment, PAT is readily degraded during heat treatment and may therefore be dealt with using other preventative measures.