Effect of biological toxins on gap-junctional intercellular communication in Chinese hamster V79 cells

An update on T2-toxins: metabolism, immunotoxicity mechanism and human assessment exposure of intestinal microbiota

Mycotoxins are naturally produced secondary metabolites or low molecular organic compounds produced by fungus with high diversification, which cause mycotoxicosis (food contamination) in humans and animals. T-2 toxin is simply one of the metabolites belonging to fungi trichothecene mycotoxin. Specifically, Trichothecenes-2 (T-2) mycotoxin of genus fusarium is considered one of the most hotspot agricultural commodities and carcinogenic compounds worldwide. There are well-known examples of salmonellosis in mice and pigs, necrotic enteritis in chickens, catfish enteric septicemia and colibacillosis in pigs as T-2 toxic agent. On the other hand, it has shown a significant reduction in the Salmonella population's aptitude in the pig intestinal tract. Although the impact of the excess Fusarium contaminants on humans in creating infectious illness is less well-known, some toxins are harmful; for example, salmonellosis and colibacillosis have been frequently observed in humans. More than 20 different metabolites are synthesized and excreted after ingestion, but the T-2 toxin is one of the most protuberant metabolites. Less absorption of mycotoxins in intestinal tract results in biotransformation of toxic metabolites into less toxic variants. In addition to these, effects of microbiota on harmful mycotoxins are not limited to intestinal tract, it may harm the other human vital organs. However, detoxification of microbiota is considered as an alternative way to decontaminate the feed for both animals and humans. These transformations of toxic metabolites depend upon the formation of metabolites. This study is complete in all perspectives regarding interactions between microbiota and mycotoxins, their mechanism and practical applications based on experimental studies.

Deoxynivalenol induced mouse skin tumor initiation: Elucidation of molecular mechanisms in human HaCaT keratinocytes

Among food contaminants, mycotoxins are toxic to both human and animal health. Our prior studies suggest that Deoxynivalenol (DON), a mycotoxin, behaves as a tumor promoter by inducing edema, hyperplasia, ODC activity and activation of MAPK's in mouse skin. In this study, topical application of DON, 336 and 672 nmol significantly enhanced ROS levels, DNA damage and apoptosis with concomitant downregulation of Ki-67, cyclin D, cyclin E, cyclin A and cyclin-dependent kinases (CDK4 and CDK2) thereby resulting in tumor initiation in mouse skin. Further, the elucidation of molecular mechanisms of tumor initiation by DON (0.42-3.37 nmol/ml) in HaCaT keratinocytes, revealed (i) enhanced ROS generation with cell cycle phase arrest in G0/G1 phase, (ii) increase in levels of 8-OxoG (6-24 hr) and γH2AX protein, (iii) significant enhancement in oxidative stress marker enzymes LPO, GSH, GR with concomitant decrease in antioxidant enzymes catalase, GPx, GST, SOD and mitochondrial membrane potential after DON (1.68 nmol) treatment, (iv) suppression of Nrf2 translocation to nucleus, enhanced phosphorylation with subsequent activation ERK1/2, p38 and JNK MAPK's following DON (1.68 nmol) treatment, (v) overexpression of c-jun, c-fos proteins, upregulation of Bax along with downregulation of Bcl-2 proteins, (vi) increase in cytochrome-c, caspase-9, caspase-3 and poly ADP ribose polymerase levels leads to apoptosis. Pretreatment of superoxide dismutase, mannitol and ethanol to HaCaT cells resulted in significant reduction in ROS levels and apoptosis indicating the role of superoxide and hydroxyl radicals in DON induced apoptosis as an early event and skin tumor initiation as a late event.

Ochratoxin A and T-2 Toxin Induce Clonogenicity and Cell Migration in Human Colon Carcinoma and Fetal Lung Fibroblast Cell Lines

T-2 toxin and Ochratoxin A (OTA) are toxic secondary metabolites produced by various fungi, and together they contaminate feedstuffs worldwide. T-2 toxin and OTA may exert carcinogenic action in rodent. Despite the various in vivo experiments, carcinogenicity of these two mycotoxins has not yet been proven for human. In this current study, we proposed to investigate, in Human colon carcinoma cells and fetal lung fibroblast-like cells transfected with MYC, the effect of T-2 toxin and OTA on cell clonogenicity and cell migration. Results of the present investigation showed that T2-toxin as well as OTA has an important clonogenic effect in all cell lines, suggesting that these mycotoxins could promote the transcription of c-myc gene. Furthermore, T-2 toxin and OTA enhanced the migration effect of HCT116 cells at very low concentrations, proposing that these mycotoxins may exhibit carcinogenesis-like properties in the studied cells.

Palytoxin causes nonoxidative necrotic damage to PC12 cells in culture

Palytoxin (PTX) is a potent marine toxin that causies serious damage to various tissues and organs. It has been reported to affect the transport of cations across the plasma membranes, which is commonly recognized as being the principal mechanism of its highly toxic action on mammals, including humans. However, although some marine toxins have been shown to cause toxic effects on the nervous system by interfering with the transmission of nerve impulses, the effect of PTX on neuronal cells has not yet been fully elucidated. Therefore, the toxic action of PTX on PC12 cells was examined as an in vitro model experiment to elucidate the neurotoxic properties of this toxin, and PTX was shown to reduce the viability of PC12 cells in a concentration-dependent manner. The cytotoxic action of PTX was not significantly altered by the presence of the antioxidant N-acetylcysteine and reduced-form glutathione in the cultures. Fluorescence staining of the cells and the electrophoretic analysis of genomic DNA showed that PTX failed to cause chromatin condensation and DNA fragmentation within the cells. On the other hand, the exposure to PTX caused positive staining of the cytoplasmic space of the cells with propidium iodide and the release of lactate dehydrogenase into the culture medium. Based on these observations, PTX is considered to cause cell death as a consequence of disrupting the plasma membranes, thus causing nonoxidative necrotic damage to PC12 cells.

T-2 Toxin: Incidence and Toxicity in Poultry

T-2 toxin is the most toxic type A trichothecene mycotoxin. It is the secondary metabolite of the Fusarium fungi, and is common in grain and animal feed. Toxic effects have been shown both in experimental animals and in livestock. It has been implicated in several outbreaks of human mycotoxicoses. Toxic effects in poultry include inhibition of protein, DNA, and RNA synthesis, cytotoxicity, immunomodulation, cell lesions in the digestive tract, organs and skin, neural disturbances and low performance in poultry production (decreased weight gain, egg production, and hatchability). Concentrations of T-2 toxin in feed are usually low, and its immunosuppressive effects and secondary infections often make diagnosis difficult. If at the onset of the disease, a change in diet leads to health and performance improvements in animals, this may point to mycotoxin poisoning. Regular control of grain and feed samples is a valuable preventive measure, and it is accurate only if representative samples are tested. This article reviews the incidence and toxic effects of T-2 toxin in poultry.

Mini-review of studies on the carcinogenicity of deoxynivalenol

The purpose of this article is to make a summary of the information regarding the researches on the carcinogenicity of DON and to discuss implications on future researches. Publications of experiments were collected through databases, experts, previous reviews, citation tracking. To guarantee the quality of the studies included in this review, we set up different criteria for different kinds of studies. As a result, all three gene mutation assays had negative results; all four chromosome aberration tests had positive results, even one of which had a dose-response effect; six from ten DNA damage/repair tests had positive results and tow of those six ones had dose-response effects; one mammalian cell malignant transformation assay showed positive result; two from three medium-term and long-term carcinogenicity studies had negative results; all six epidemiologic studies had positive results. In conclusion, DON cannot be classified as carcinogen according to these tests and studies because the results from the short-term in vitro studies were quite contradictory, and the results from the medium-term and long-term in vivo studies and from the epidemiological studies in humane beings were invalid due to their poor methodology quality. It is necessary to make more and better researches on the carcinogenicity of DON considering its chronic and low level of exposure to the human beings.

In vivoandin vitroeffects of the mycotoxins zearalenone and deoxynivalenol on different non-reproductive and reproductive organs in female pigs: A review

This review summarizes the toxicological data on the effects of the mycotoxins zearalenone (ZON), its metabolites, and deoxynivalenol (DON) on different parameters relating to reproductive and non-reproductive organs in female pigs. In vivo, 22 mg ZON kg(-1) in the diet cause alterations in the reproductive tract of swine such as in the uterus, and affects follicular and embryo development. ZON and its metabolites have been shown to bind competitively to oestrogen receptors in an in vitro system. The feeding of pigs with a 9 mg DON kg(-1)-contaminated diet can act on protein synthesis, humoral and cellular immune response depending on dose, exposure and timing of functional immune assay, and affect liver and spleen cell structures. Beside these effects, reproductive alterations were observed in pigs, too. Both in vivo and in vitro exposure to DON decreased oocyte and embryo development. In vitro application of DON to uterine cells inhibits their proliferation rate and modulates the process of translation at a different molecular level when compared with the in vivo application. The histopathological results provide evidence of spleen and liver dysfunction in the absence of clinical signs, especially in pigs fed higher concentrations of Fusarium toxin-contaminated wheat. Prepuberal gilts react more sensitively to DON > ZON feeding compared with pregnant sows. In the liver, histopathological changes such as glycogen decrease and interlobular collagen uptake were only observed in prepuberal gilts, whereas enhancement of haemosiderin was found in both perpuberal gilts and pregnant sows. This review presents some of the current knowledge on the biological activities of ZON and DON in pig. Altogether, ZON affects reproduction of pigs most seriously because it possesses oestrogenic activity. However, DON affects reproduction in pigs via indirect effects such as reduced feed intake, resulting in reduced growth or impairment of function in vital organs such as liver and spleen.

Comparison of extraction and clean-up procedures for analysis of zearalenone in corn, rice and wheat grains by high-performance liquid chromatography with photodiode array and fluorescence detection

The aim of this work was the optimization of some procedures usually used in the analysis of zearalenone (ZEA) in corn and other cereals by high-performance liquid chromatography (HPLC) with photodiode array and/or fluorescence detection. The comparison of five extraction solvents is presented. Three solid-phase extraction cartridges (C-18, silica, Florisil) and immuno-affinity columns were also compared to obtain the best recovery of the mycotoxin with the minimal presence of co-extractives in the chromatograms. Mixtures of methanol-1% aqueous NaCl (80.20 or 60:40 v/v) were the best extraction solvents. Florisil provided higher recovery of ZEA than C-18, and silica proved unsuitable. The immuno-affinity column was very efficient in cleaning the extracts, but its sample capacity was lower than that of SPE columns due to saturation. The mobile phase (methanol-water 80:20 v/v) gave a low retention time for ZEA (approximately 5 min), high sensitivity and acceptable separation between this mycotoxin and alpha-zearalenol. The optimized protocol is straightforward, provides high ZEA recoveries in spiked corn (mean 102.4%), has an acceptable sensitivity and has a lack of interference with fluorescence detection (detection limit 4 ng ZEA g(-1) corn). The photodiode array detector was useful, except at very low ZEA levels, to confirm the identity of the mycotoxin. The method was applied to search for ZEA accumulation in corn, wheat and rice grains inoculated with selected strains of Fusarium graminearum, F. oxysporum and method was applied to search for ZEA accumulation in corn, wheat and rice grains inoculated with selected strains of Fusarium graminearum, F. oxysporum and F. culmorum.

Use of a cell transformation assay with established cell lines, and a metabolic cooperation assay with V79 cells for the detection of tumour promoters: a review

Extensive studies on the safety evaluation of chemicals have indicated that a considerable number of non-genotoxic chemicals are carcinogenic. Tumour promoters are likely to be among these non-genotoxic carcinogens, and their detection is considered to be an important approach to the prevention of cancer. In this review, the results are summarised for in vitro transformation assays involving established cell lines, and for an assay for inhibition of gap junctional intercellular communication for the detection of tumour promoters, which involves V79 cells. Although the number of chemicals examined is still too small to permit a full evaluation of the correlation between in vitro cell transformation and in vivo carcinogenicity, it is clear that the sensitivity of the focus formation assay is very high. In the case of the metabolic cooperation assay, the sensitivity appears to be rather poor, but the assay can be considered to be useful because of its simple procedure and its considerable database. These in vitro assays for tumour promoters are recommended as useful tools for the detection of non-genotoxic carcinogens.

Differential upregulation of TNF-alpha, IL-6, and IL-8 production by deoxynivalenol (vomitoxin) and other 8-ketotrichothecenes in a human macrophage model

The effects of deoxynivalenol (DON or vomitoxin) and four closely related 8-ketotrichothecenes on proinflammatory cytokine and chemokine production were evaluated in a clonal human macrophage model. U-937 cells, which represent a human monocytelike histocytic lymphoma, were differentiated into macrophages by preincubation with phorbol 12-myristate 13-acetate (PMA). Differentiated macrophages were incubated with DON in the absence or presence of lipopolysaccharide (LPS), and supernatant was analyzed by enzyme-linked immunosorbent assay (ELISA) for the proinflammatory cytokines interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha), and for the chemokine interleukin-8 (IL-8). In the absence of LPS, DON at 500 or 1,000 ng/ml upregulated TNF-alpha production as early as 3 h and up to 6 h, whereas 100 to 1,000 ng/ml of DON significantly increased production of IL-6 from 3 to 24 h and IL-8 from 6 to 48 h. In cells costimulated with 0.2 microg/ml LPS, DON at 500 or 1000 ng/ml markedly superinduced TNF-alpha and IL-8 production. Although 100 ng/ml of DON also potentiated LPS-induced IL-6 production, 500 or 1,000 ng/ ml of the toxin suppressed the LPS-induced IL-6 response. Four other 8-ketotrichothecenes, fusarenon X, nivalenol, 3-acetyl DON, and 15-acetyl DON, were also capable of upregulating or suppressing TNF-alpha, IL-6, and IL-8 production at concentrations similar to that of DON. In total, the results suggest that DON and other 8-ketotrichothecenes have the potential to both directly induce and superinduce proinflammatory cytokine and chemokine expression in human macrophages, even at toxin concentrations that are cytotoxic.

Genotoxic effects of three Fusarium mycotoxins, fumonisin B1, moniliformin and vomitoxin in bacteria and in primary cultures of rat hepatocytes

The genotoxic effects of three widespread Fusarium toxins, vomitoxin (VOM), moniliformin (MON) and fumonisin B1 (FB1) were investigated in bacterial tests and in micronucleus (MN) and chromosomal aberration (CA) assays with primary rat hepatocytes. All three toxins were devoid of activity in gene mutation assays with Salmonella typhimurium strains TA98 and TA100 and in SOS chromotests with E. coli strain PQ37 in the presence and absence of metabolic activation. FB1 and VOM gave negative results in differential DNA repair assays with E. coli K-12 strains (343/753, uvrB/recA and 343/765, uvr+/rec+); with MON, a marginal effect was seen in the absence of metabolic activation mix at relatively high concentrations (> or = 55 micrograms/ml). In metabolically competent rat hepatocytes stimulated to proliferate with EGF and subphysiological Ca2+ concentrations, a decrease of cell division was observed with all three toxins at concentrations > or = 10 micrograms/ml, VOM was strongly cytotoxic at 100 micrograms/ml. All three mycotoxins caused moderate increases of the MN frequencies at low concentrations (< or = 1 microgram/ml), but no clear dose-response effects were seen and at higher exposure levels the MN frequencies declined. In the CA experiments with hepatocytes, pronounced dose-dependent effects were observed with all three toxins. MON caused a 9-fold increase over the spontaneous background level after exposure of the cells to 1 microgram/ml for 3 h, with FB1 and VOM, the increases were 6- to 7-fold under identical experimental conditions. This is the first report on clastogenic effects of VOM and FB1 in mammalian cells, with MON induction of CAs in V-79 cells has been described earlier. Since all three mycotoxins caused CAs at very low concentration levels in liver cells in vitro, it is possible that such effects may also occur in humans and mammals upon consumption of Fusarium-infected cereals.

Lack of initiation and promotion potential of deoxynivalenol for skin tumorigenesis in Sencar mice

The mycotoxin deoxynivalenol (DON; vomitoxin) was tested for its potential to initiate or promote skin tumours through a two-stage treatment regimen in female Sencar mice. DON's capability for initiation was tested by applying a single topical dose (200 micrograms) followed by multiple treatments of the promoter phorbol 12-myristate 13-acetate (PMA). The test for promotion involved initiation with the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) followed by multiple DON treatments (50 micrograms). Appropriate control groups were included in the study design. Mice were observed for 26 wk and skin tumours were counted. Results of the study showed that DON was not an initiator or a promoter. When DON was tested as an initiator, there were no statistically significant differences in the number of cumulative tumours or the number of tumour-bearing mice between the DON-initiated/PMA-promoted group and its control, the vehicle-initiated/PMA-promoted group. When DON was administered as a promoter, no tumours were observed. Histopathology of the skin revealed that DON induced a mild diffuse squamous hyperplasia, but there was no progression of the lesion to neoplasia.

Cell culture assays for chemicals with tumor-promoting or tumor-inhibiting activity based on the modulation of intercellular communication

The ability of chemicals with tumor-promoting or tumor-inhibiting activity to modulate gap junctional intercellular communication is reviewed. The two most extensively used types of assays for screening tests are (1) metabolic cooperation assays involving exchange between cells of precursors of nucleic acid synthesis and (2) dye-transfer assays that measure exchange of fluorescent dye from loaded cells to adjacent cells. About 300 substances of different biological activities have been studied using various assays. For tumor promoters/epigenetic carcinogens, metabolic cooperation assays have a sensitivity of 62% and dye-transfer assays 60%. Thirty percent of DNA-reactive carcinogens also possess the ability to uncouple cells. The complete estimation of the predictive power of these assays could not be made because the majority of the substances studied for intercellular communication effects in vitro have not yet been studied for promoting activity in vivo. Both metabolic cooperation assays and dye transfer assays respond well to the following classes of substances: phorbol esters, organochlorine pesticides, polybrominated biphenyls, promoters for urinary bladder, some biological toxins, peroxisome proliferators, and some complex mixtures. Results of in vitro assays for such tumor promoters/nongenotoxic carcinogens, such as some bile acids, some peroxides, alkanes, some hormones, mineral dusts, ascorbic acid, okadaic acid, and benz(e)pyrene, do not correlate with the data of in vivo two-stage or complete carcinogenesis. Enhancement of intercellular communication was found for 18 chemicals. Among these, cAMP, retinoids, and carotenoids have demonstrated inhibition of carcinogenesis. We examine a number of factors that are important for routine screening, including the requirement for biotransformation for some agents to exert effects on gap junctions. We also discuss the mechanisms of tumor promoter and tumor inhibitor effects on gap junctional permeability, including influences of protein kinase activation, changes in proton and Ca2+ intracellular concentrations, and effects of oxy radical production.

Inhibition of intercellular communication in Chinese hamster V79 cells by fractionated asphalt fume condensates

Asphalt fume condensate is a skin carcinogen in mice, yet this complex mixture contains relatively low levels of known carcinogenic initiators. Consequently, its biological activity has been attributed to the presence of cocarcinogenic or tumor-promoting agents. One of several proposed mechanisms of tumor promotion is inhibition of intercellular communication. In an attempt to determine if asphalt fume has tumor-promoting potential inhibition of intercellular communication was measured in V79 cells exposed to fractionated asphalt fume condensate. Fume from air-blown Arabian crude asphalt was trapped and separated into five fractions by preparative-scale high-pressure liquid chromatography. The parent fume condensate and the five fractions inhibited intercellular communication in a concentration-dependent fashion, with a minimum effective concentration of 2.5 microgram/ml for the most potent fraction. Cytotoxicity assays were performed at the same time and concentrations as the metabolic cooperation assays. Cytotoxic responses paralleled the inhibition of intercellular communication.

Comparative study on the natural occurrence of Fusarium mycotoxins (trichothecenes and zearalenone) in corn and wheat from high- and low-risk areas for human esophageal cancer in China

A comparative study on the natural occurrence of Fusarium toxins was done with 47 corn and 30 wheat samples collected in 1989 from Linxian and Shangqiu Counties in Henan Province, People's Republic of China, high- and low-risk areas, respectively, for esophageal cancer. Three trichothecenes (deoxynivalenol [DON], 15-acetyldeoxynivalenol [15-ADON], and nivalenol [NIV]) and zearalenone (ZEA) were detected in corn samples, and DON, NIV, and ZEA were found in wheat samples. Compared with Shangqiu corn, the incidence and mean level of DON in Linxian were 2.4 and 5.8 times higher, respectively, and those of 15-ADON were 16.3 and 2.6 times higher, respectively. The incidence and level of trichothecenes in wheat samples were significantly lower than those in corn. However, the level of DON in Linxian wheat was 3.3 times higher than in Shangqiu wheat. This is the first report indicating a significant difference in the natural occurrence of Fusarium toxins in main staple foods between high- and low-risk areas for esophageal cancer in the People's Republic of China.

The effect of complete carcinogens on intercellular transfer of lucifer yellow in fibroblast culture

The effect on permeability of gap junctions of complete powerful carcinogens, 3-methylcholanthrene (MC), 7,12-dimethylbenz(a)anthracene (DMBA), ethyl methanesulfonate (EMS), and weak carcinogens, benz(a)anthracene (BA), benzo(e)pyrene (B(e)P) as well as the aryl-hydroxylase inhibitor 7,8-benzoflavone (7,8-BF) has been studied with the use of a dye-coupling technique and transformed Djungarian hamster DM15 fibroblasts. MC, EMS and 7,8-BF were found to exert a strong inhibitory effect on cell-to-cell dye transfer. BA and DMBA had the uncoupling activity only in 2 out of 4 experiments. B(e)P was not shown to affect LY transfer between DM15 cells. The uncoupling effect of MC, 7,8-BF and EMS (only when EMS used at the concentration of 600 micrograms/ml but not 1000 micrograms/ml) appeared reversible. The causes of failure to detect DMBA and B(e)P effects on gap junctions are discussed.