Epigenetic effect of the mycotoxin fumonisin B1 on DNA methylation.

Mycotoxin fumonisin B1 (FB1) is a secondary metabolite that is produced by certain Fusarium species. Although numerous studies demonstrate toxic and carcinogenic effects of FB1, the underlying mechanisms have not been fully elucidated. In this study, we evaluated the epigenetic effects of FB1 for the first time using FLO assays, which detect epigenetic changes that affect the flocculation gene (FLO1) promoter activity in budding yeast. FLO assays showed increased reporter activities of the FLO1 promoter in the presence of 10 and 20 µM FB1. FB1 (20 µM) treatments also promoted flocculation. In subsequent in vitro methylation assays of a bacterial DNA methyltransferase (DNMT), FB1 treatments increased DNMT activities. Moreover, global DNA methylation was significantly increased in HEK293 cells treated with 100 µM FB1. Taken together, these results suggest that FB1 exposure leads to unique epigenetic alterations due to increased DNMT activities and demonstrate that FB1 may be an important risk factor for epigenetic dysfunction-associated human diseases including cancer.

Inhibitory effect of ochratoxin A on DNMT-mediated flocculation of yeast.

The mycotoxin ochratoxin A (OTA) is considered to be a human carcinogen. However, the mode of its carcinogenetic action has not been elucidated. Recently, it has become evident that epigenetic changes influence the risk of developing cancer. Since it has been revealed that the yeast flocculation displayed by the strains transformed with human DNA methyltransferases (DNMT) can be regulated by epigenetic mechanisms, we examined the effect of OTA on the transcription level of FLO1, which mediates the flocculation phenotype. OTA but not a non-carcinogenetic mycotoxin deoxynivalenol (DON) inhibited the intensity of GFP fluorescence under the transcriptional regulation of FLO1 promoter in a dose-dependent manner. At the same time, OTA had no effect on the reporter activity under the control of modified FLO1 promoter with reduced CpG motifs. In addition, it was confirmed that the flocculation and FLO1 mRNA of DNMT gene-transformed yeast (DNMT yeast) were decreased by OTA. In vitro methylation assay using a bacterial DNMT revealed an inhibitory effect of OTA on the DNMT activity, and OTA treatment reduced the frequency of abnormally shaped nuclei which were often observed in DNMT yeast. These results suggest that the carcinogenicity of OTA may involve inhibition of DNMT-mediated epigenetic regulation.

Detection of epigenetic mutagens including anthracene-derived compounds using yeast FLO1 promoter GFP reporter gene assay.

Recently, we have reported that the FLO1-mediated flocculation levels of yeast are affected by an epigenetic mutagen, alizarin. Alizarin promoted flocculation and reduced the bulk levels of histone H3 in yeast cells. Since alizarin has been known to possess carcinogenesis-promoting properties, it is important to estimate the effect of alizarin-related compounds on epigenome as measured by the flocculation of yeast. In this study, we examined the effects of two anthracene-derived compounds other than alizarin on the flocculation level of yeast. Purpurin significantly promoted the flocculation in a dose-dependent manner. While, quinizarin had a weaker promoting effect than purpurin. The strain treated with purprin showed FLO1 mRNA upregulation and reduced histone H3 expression similarly to alizarin. We also confirmed that the purprin-treated cells frequently exhibited abnormally shaped nuclei. Moreover, fluorescence intensities of green fluorescent protein (GFP) reporter under the FLO1 promoter control were dose-dependently increased by purprin and alizarin in the yeast. Taken together, these results suggest that the GFP reporter gene system utilising the FLO1 promoter is useful for the detection of epigenetic mutagens including anthracene-derived compounds.

Epigenetic mutagen as histone modulator can be detected by yeast flocculation.

We have previously reported that flocculation of a yeast co-transformed with the human DNA methyltransferase 1 (DNMT1) and DNMT3B genes was inhibited by DNMT inhibitors. It is well known that epigenetic mutagens can disturb nucleosome positioning via DNA methylation and/or histone modification. In this study we first examined the effects of trichostatin A (TSA), a histone deacetylase inhibitor, on the flocculation level of yeast. TSA dose-dependently promoted the flocculation exhibited by the yeast transformed with the DNMT genes or empty vectors. Furthermore, TSA induced the expression of the flocculin-encoding gene FLO1 The anthracene-derived alizarin, a natural madder root dye, has a potential for carcinogenesis promotion; however, the mode of action has not been elucidated. It is considered that epigenetic changes can promote cancer. Alizarin but not anthracene enhanced the flocculation level of the yeast. Similar to TSA, alizarin also upregulated FLO1 mRNA. Surprisingly, western blotting indicated that alizarin, but not anthracene, reduced the level of histone H3 in yeast, and alizarin-treated cells frequently displayed abnormally shaped nuclei. These findings suggest that alizarin uniquely influences nucleosome structure. Taken together with our previous findings, this study suggests that the DNMT gene-transformed yeast strains are a useful tool for screening various classes of epigenetic mutagens.

Human DNA methyltransferase gene-transformed yeasts display an inducible flocculation inhibited by 5-aza-2'-deoxycytidine.

Mammalian DNA methyltransferases (DNMTs) play an important role in establishing and maintaining the proper regulation of epigenetic information. However, it remains unclear whether mammalian DNMTs can be functionally expressed in yeasts, which probably lack endogenous DNMTs. We cotransformed the budding yeast Saccharomyces cerevisiae with the human DNMT1 gene, which encodes a methylation maintenance enzyme, and the DNMT3A/3B genes, which encode de novo methylation enzymes, in an expression vector also containing the GAL1 promoter, which is induced by galactose, and examined the effects of the DNMT inhibitor 5-aza-2'-deoxycytidine (5AZ) on cell growth. Transformed yeast strains grown in galactose- and glucose-containing media showed growth inhibition, and their growth rate was unaffected by 5AZ. Conversely, 5AZ, but not 2'-deoxycytidine, dose-dependently interfered with the flocculation exhibited by DNMT-gene transformants grown in glucose-containing medium. Further investigation of the properties of this flocculation indicated that it may be dependent on the expression of a Flocculin-encoding gene, FLO1. Taken together, these findings suggest that DNMT-gene transformed yeast strains functionally express these enzymes and represent a useful tool for in vivo screening for DNMT inhibitors.

Kudoa septempunctata invasion increases the permeability of human intestinal epithelial monolayer.

Kudoa septempunctata is a myxosporean parasite of Paralichthys olivaceus (olive flounder) and causes a foodborne illness that affects more than 100 cases in Japan each year. We previously reported that the consumption of raw olive flounder meat containing a high concentration of K. septempunctata spores induces transient but severe diarrhea and emesis through an unknown mechanism. Here, we demonstrate that K. septempunctata sporoplasm plays an important role in mediating the toxicity of K. septempunctata. When K. septempunctata spores were inoculated in Caco-2 human intestinal cells, K. septempunctata sporoplasms were released from spores, and they invaded the cells. Electron microscopic observations revealed that the sporoplasm invasion severely damaged the Caco-2 cells. The inoculation of K. septempunctata spores eliminated the transepithelial electrical resistance (TER) across the cell monolayer. Inhibiting the invasion of the sporoplasms prevented the observed loss in cell layer integrity, as illustrated by the rapid elimination of the TER. These results suggest that the invasion by sporoplasms severely damaged individual intestinal cells, resulting in a loss of cell monolayer integrity.

Detection of epigenetic effects of citrinin using a yeast-based bioassay.

The present study investigated the effects of citrinin (CIT) on a yeast-transformed human DNA methyltransferase (DNMT) associated with flocculation that can be inhibited by epigenetic mutagens. CIT (0.5-2 µmol/L) inhibited the flocculation levels of yeast transfected with DNMT-genes (DNMT yeast) and the reporter gene activity of FLO1, which has been associated with flocculation. In contrast, the same concentrations of CIT had little effect on reporter activity under the control of a less methylation-sensitive FLO1 promoter. It was also shown that bacterial DNMT activity could be inhibited in the presence of CIT (4 and 40 µmol/L). These results show that CIT has inhibitory activity of DNMT, suggesting that the cytotoxicity of CIT may be involved in epigenetic mutagenicity.

Functional role of DNA methylation at the FLO1 promoter in budding yeast.

We have previously reported that the transformation of the budding yeast with plasmids encoding the human DNA methyltransferases DNMT1 and DNMT3B cDNAs induces the mRNA of flocculin gene FLO1 and the flocculation phenotype. In the present study, we evaluated the effect of DNMT inhibitor in the transformed yeasts using a FLO1 promoter-based green fluorescent protein (GFP) reporter gene assay. The DNMT inhibitor, 5-aza-2΄-deoxycytidine (5AZ), decreased GFP fluorescence driven by FLO1 promoter in DNMT-genes transformed yeast (DNMT yeast). Surprisingly, the GFP activity driven by cytosine-phosphate-guanine (CpG) motif-reduced FLO1 promoter decreased both in DNMTs gene-transformed and control strains. Yeast cells transformed with expression vector encoding a maintenance enzyme DNMT1 cDNA showed a flocculation phenotype that was associated with an enhanced mRNA level of FLO1. Bisulfite sequencing revealed methylated CpG sites at the FLO1 promoter in a control strain not expressing any DNMT transgenes, and no detectable methylation at the sites was observed in cells treated with 5AZ. These results suggest that the FLO1 promoter is endogenously de novo methylated leading to the activation of FLO1 gene transcription. Furthermore, the methylation level at the FLO1 promoter is responsible for the significant differences in FLO1 promoter-driven expression of GFP in DNMT yeast.

Molecular Epidemiological Analysis of Kudoa septempunctata by Random Amplified Polymorphic DNA Analysis.

Molecular epidemiological analysis of Kudoa septempunctata isolates from 34 olive flounders associated with foodborne disease outbreaks and from 6 reference samples was performed using random amplified polymorphic DNA (RAPD) analysis. The K. septempunctata isolates analyzed in this study were divided into 8 groups. Eight isolates obtained from the large Ehime Prefecture outbreak in Japan that had occurred on October 8, 2010, were further divided into 4 groups. Eight isolates obtained from Korean samples were divided into 3 groups. These groups included isolates that had been identified from the large Ehime Prefecture outbreak. These results indicated that the Korean isolates had similar genetic backgrounds to those involved in the Ehime Prefecture outbreak. Isolates associated with outbreaks with similar dates of onset tended to be classified in the same group, suggesting that the strains involved in these incidents were genetically related. These results demonstrated that RAPD analysis is a useful molecular epidemiological analysis method for K. septempunctata.

Inactivation of Kudoa septempunctata in olive flounder meat by liquid freezing.

Kudoa septempunctata in olive flounder meat was inactivated using 3 distinct freezing methods：liquid freezing for 5 min, air blast freezing at －30℃ for 5 h, and －80℃ for 1 h. The fracture curve of olive flounder meat subjected to liquid freezing resembled that of meat stored at 4℃, indicating that the structure of olive flounder muscle was well preserved. In contrast, air blast freezing induced the disappearance of the fracture point in the fracture curve, indicating that there was deterioration in the meat quality. Liquid freezing preserved the transparency of olive flounder meat to the same degree as that of meat stored at 4°C. However, air blast freezing induced meat cloudiness. These results indicate that liquid freezing can be used for K. septempunctata inactivation without affecting the meat quality.

Structural determination of a nivalenol glucoside and development of an analytical method for the simultaneous determination of nivalenol and deoxynivalenol, and their glucosides, in wheat.

Trichothecene mycotoxins such as nivalenol and deoxynivalenol frequently contaminate foodstuffs. Recently, several trichothecene glucosides have been found in trichothecene-contaminated foods, and information about their chemistry, toxicity, and occurrence is required. In this study, a glucoside of nivalenol was isolated from nivalenol-contaminated wheat and was identified as nivalenol-3-O-ß-D-glucopyranoside. Analytical methods using a multifunctional column or an immunoaffinity column have been developed for the simultaneous determination of nivalenol, nivalenol-3-O-ß-D-glucopyranoside, deoxynivalenol, and deoxynivalenol-3-O-ß-D-glucopyranoside in wheat. The methods were validated in a single laboratory, and recovery from wheat samples spiked at four levels ranged between 86.4 and 103.5% for the immunoaffinity column cleanup. These mycotoxins in contaminated wheat samples were quantitated by the validated method. Nivalenol-3-O-ß-D-glucopyranoside was detected in the nivalenol-contaminated wheat, and the percentage of nivalenol-3-O-ß-D-glucopyranoside to nivalenol ranged from 12 to 27%. This result indicates that the analytical method developed in this study is useful for obtaining data concerning the state and level of food contamination by nivalenol, deoxynivalenol, and their glucosides.

Kudoa septempunctata was recognised by toll-like receptor 2 produced by a RAW 264 macrophage-like cell line.

Kudoa septempunctata is a myxosporean parasite that infects Paralichthys olivaceus (olive flounder). Previously, we reported that the consumption of raw P. olivaceus meat containing a high concentration of K. septempunctata spores induces transient but severe diarrhoea and emesis. In this study, we investigated the cytokine production of mouse macrophage-like RAW 264 cells stimulated with K. septempunctata. When the RAW 264 cells were incubated with the spores of K. septempunctata for 24 h, they secreted tumour necrosis factor α (TNF-α) and several chemokines, such as IP-10, MIP-1ß, and MIP-2. The secretion of TNF-α was induced in a dose-dependent manner in a bioassay using L929 cells and mouse TNF-α-specific enzyme-linked immunosorbent assay (ELISA). To identify the macrophage receptor of K. septempunctata, activation of HEK 293 cells expressing one of the Toll-like receptors (TLR) was measured using an NF-κB-dependent reporter assay. TLR2-expressing HEK 293 cells were strongly activated following stimulation with the spores. These results suggested that K. septempunctata was recognised by TLR2 on the macrophages, which were then activated and produced TNF-α.

Comparative study of deoxynivalenol, 3-acetyldeoxynivalenol, and 15-acetyldeoxynivalenol on intestinal transport and IL-8 secretion in the human cell line Caco-2.

The effects of the trichothecene mycotoxin deoxynivalenol (DON) and its acetylated derivatives, 3-acetyldeoxynivalenol (3ADON) and 15-acetyldeoxynivalenol (15ADON) on human intestinal cell Caco-2 were investigated by the studies of transepithelial transport, gene expression, and cytokine secretion. Permeability across a Caco-2 cell monolayer was evaluated by transport study. Transport rates were ranked as DON, 3ADON<15ADON in apical-basolateral direction. 15ADON showed the highest permeability, induced the highest decrease in transepithelial electrical resistance (TEER), and prompted significant Lucifer Yellow permeability. These results showed that 15ADON affect paracellular barrier function extremely. In addition, gene expressions induced by toxins were screened by DNA microarray for investigating cellular effect on Caco-2 cell. The most remarkable gene induced by DON and 15ADON was inflammatory chemokine IL-8 and thus mRNA expression and secretion of IL-8 were analyzed by PCR and ELISA. Both DON and acetylated DONs could induce mRNA expression and production of IL-8. In particular, ELISA assay showed that the ability to produce IL-8 was ranked as 3ADON

Electron microscopic study of Kudoa septempunctata infecting Paralichthys olivaceus (olive flounder).

Kudoa septempunctata is a myxosporean parasite of Paralichthys olivaceus (olive flounder) that causes more than 50 cases of foodborne illness in Japan each year. For quantitatively assessing the presence of K. septempunctata spores in the causative fish at food poisoning outbreaks, both a direct observation method using microscopy and a quantitative real-time PCR (qRT-PCR) method are officially accepted in Japan. However, lower correlations have been often noticed between the number of spores counted using the direct observation method and the DNA amount determined using the qRT-PCR method. To elucidate the cause of this discrepancy, we observed muscle tissues of infected olive flounders with K. septempunctata by transmission electron microscopy. The images demonstrated unsynchronized development of K. septempunctata spores in plasmodia found within myofibers; in other words, the plasmodium contained not only developed spores with completed shell valves but also developing spores (sporoblasts) composed of spore-forming cells without shell valves. Furthermore, the ratio between developed spores and sporoblasts varied at different parts of muscles. The direct microscopic observation method could count developed spores, whereas the qRT-PCR method could quantify the amount of not only spores but also sporoblastic cells regardless of the cellular development and differentiation. Considering that the food toxicity caused by K. septempunctata is induced by viable spores passing through the gastric environment, the direct observation method counting only developed spores is better than the qRT-PCR method for assessing the cause of foodborne illness at the outbreak as well as the risk of human illness in monitoring surveys of aquacultured or natural-water fish.

ELISA detection of Kudoa septempunctata in raw Paralichthys olivaceus (olive flounder) using a chicken anti-Kudoa antiserum.

Kudoa septempunctata is the causative agent of a foodborne disease associated with the consumption of raw Paralichthys olivaceus (olive flounder). Chickens were used to establish specific antibodies against K. septempunctata spores. A specific antiserum, CS#3, raised against sonicated spores, also recognized intact spores. The CS#3 antiserum showed high titers for sonicated and intact K. septempunctata spores and was suitable for both ELISA and immunohistochemical staining. Using homogenated raw olive flounder meat, the ELISA system detected more than 5.0×10(5) spores in 1 g of tissue, which was consistent with the number determined by microscopic examination. The preparation of rapid detection kits for K. septempunctata spores in P. olivaceus muscle tissue using immunochromatography with CS#3 antiserum should be useful for preventing the foodborne disease in the field.

Formulation of a pectin gel that efficiently traps mycotoxin deoxynivalenol and reduces its bioavailability.

We aimed to develop a new food-processing approach using pectin to reduce gastrointestinal absorption of mycotoxins. When Ca(2+) is added to low-methoxyl pectin, a gel resembling an egg box-like structure forms that is able to trap certain molecules. We examined whether or not low-methoxyl amidated pectin (LMA) and low-methoxyl non-amidated pectin (LMNA) trapped the mycotoxin deoxynivalenol (DON) after being ingested. We first determined the trapping effects of LMA and LMNA on DON in vitro under conditions similar to those in the human stomach, with results showing that LMA gel trapped DON to a greater extent than the LMNA gel. We then performed in vivo experiments and demonstrated that the LMA gel containing DON reduced DON's absorption from the gastrointestinal tract. This new food-processing technique holds great promise for reducing the bioavailability of DON in contaminated food and may be useful in mitigating the effects of other mycotoxins.

Estimated dietary exposure to mycotoxins after taking into account the cooking of staple foods in Japan.

Mycotoxins are commonly present in cereal grains and are not completely destroyed during their cooking and processing. When mycotoxins contaminate staple foods, the risk for exposure becomes serious. In East Asia, including Japan, rice is consumed as a staple food, and with the increasingly Westernized lifestyle, the consumption of wheat has increased. The mycotoxins commonly associated with rice and wheat are total aflatoxin (AFL) and ochratoxin A (OTA), respectively. This study examined the retention of AFL and OTA during the cooking of rice and pasta. AFL was retained at 83%-89% the initial level after the cooking of steamed rice. In pasta noodles, more than 60% of the OTA was retained. These results show that AFL and OTA are relatively stable during the cooking process, suggesting that a major reduction in the exposure to these mycotoxins cannot be expected to occur by cooking rice and pasta. The estimated exposure assessment at the high consumer level (95th percentile) and the mycotoxin contamination level determined by taking into account these reductions in the present study should be useful for the establishment of practical regulations for mycotoxins in staple foods.

Inter-laboratory validation and applications of quantitative real-time PCR for the detection of Kudoa septempunctata in olive flounder (Paralichthys olivaceus).

Kudoa septempunctata, a myxosporean parasite, was recently identified as the causative agent of food poisoning resulting from the consumption of raw olive flounder (Paralichthys olivaceus). A single blind inter-laboratory study, involving 5 laboratories, was conducted to validate a quantitative real-time PCR assay for the detection of the parasite. We obtained relatively constant values for log rDNA copies/g from these laboratory analyses (SD = 0.35-0.86), suggesting the validity of the real-time PCR method for the detection of K. septempunctata in P. olivaceus. Detection of K. septempunctata in muscle tissue samples collected from both sides of the fish indicated that K. septempunctata infection spreads throughout the body of P. olivaceus. K. septempunctata infection in P. olivaceus is thought to occur during the early stage of fish growth because a K. septempunctata gene was detected in 1 of 300 P. olivaceus fry tested. Feeds seem not to be sources of infection. To prevent food poisoning due to K. septempunctata, the mechanism of infection and proliferation of K. septempunctata in P. olivaceus should be elucidated, and other hosts of the parasite should be identified. The sensitive real-time PCR method described here will be a useful tool for resolving these issues.