Anti-Apoptotic Effect of Flavokawain A on Ochratoxin-A-Induced Endothelial Cell Injury by Attenuation of Oxidative Stress via PI3K/AKT-Mediated Nrf2 Signaling Cascade

This study investigates the endothelial protective activity of flavokawain A (FKA) against oxidative stress induced by ochratoxin A (OTA), which acts as a mycotoxin, and its primary mechanisms in in vitro models. Reactive oxygen species, in general, regulate oxidative stress that significantly contributes to the pathophysiology of endothelial dysfunctions. OTA exerts toxicity through inflammation and the accumulation of ROS. This research is aimed at exploring the defensive function of FKA against the endothelial injury triggered by OTA through the Nrf2 pathway regulated by PI3K/AKT. OTA exposure significantly increased the nuclear translocation of NFκB, whereas we found a reduction in inflammation via NFκB inhibition with FKA treatment. FKA increased the PI3K and AKT phosphorylation, which may lead to the stimulation of antioxidative and antiapoptotic signaling in HUVECs. It also upregulated the phosphorylation of Nrf2 and a concomitant expression of antioxidant genes, such as HO-1, NQO-1, and γGCLC, depending on the dose under the oxidative stress triggered by OTA. Knockdown of Nrf2 through small interfering RNA (siRNA) impedes the protective role of FKA against the endothelial toxicity induced by OTA. In addition, FKA enhanced Bcl2 activation while suppressing apoptosis marker proteins. Therefore, FKA is regarded as a potential agent against endothelial oxidative stress caused by the deterioration of the endothelium. The research findings showed that FKA plays a key role in activating the p-PI3K/p-AKT and Nrf2 signaling pathways, while suppressing caspase-dependent apoptosis.

Ochratoxin A affects oocyte maturation and subsequent embryo developmental dynamics in the juvenile sheep model

The genotoxic and nephrotoxic mycotoxin Ochratoxin A (OTA) has also been reported to have adverse effects on oocyte maturation and embryo development. Previous studies on the effects of OTA on female fertility have used micromolar concentrations, but no information is available to date on effects in a more relevant nanomolar range. This study used a juvenile sheep model to evaluate the effects of oocyte exposure to low levels of OTA on maturation, fertilization, and embryo development. Further, it was investigated whether different mechanisms of action of OTA could be responsible for varying toxic effects at different levels of exposure. Cumulus-oocyte-complexes (COCs) were exposed to 10 μmol/L-0.1 nmol/L OTA during in vitro maturation and evaluated for cumulus viability, oocyte maturation, and bioenergetic/oxidative status. COCs were subjected to in vitro fertilization, embryo culture, and embryo quality assessment via morphology, viability, bioenergetic/oxidative status, and time-lapse monitoring. At micromolar concentrations, OTA induced cytotoxic effects, by reducing cumulus expansion and oocyte maturation. OTA altered temporospatial dynamics of zygote pronuclear formation and embryo morphokinetics. Blastocysts, even morphologically normal, were found to undergo collapse events, which were probably related to boosted blastocyst mitochondrial activity. At nanomolar concentrations, OTA did not affect COC morpho-functional parameters, but impaired oocyte ability to prevent polyspermy and increased blastocyst apoptosis. In conclusion, in the female germ cell, cytotoxic nonspecific effects characterize OTA-induced toxicity at high exposure levels, whereas fine tuning-mode effects, not associated with altered cell viability and integrity, characterize OTA toxic action at low levels.

Nontoxic concentration of ochratoxin A decreases the dosage of cyclosporine A to induce chronic nephropathy model via autophagy mediated by toll-like receptor 4

Cyclosporine A (CsA) extracted from the products of fungal fermentation is used to develop a chronic nephropathy model. However, it has numerous side effects. Ochratoxin A (OTA) is a mycotoxin that induces renal injury. We developed a chronic nephropathy model to lessen the side effects of CsA by administration of nontoxic dosage of OTA, and investigated the underlying mechanism. C57BL/10 wild-type mice, toll-like receptor 4 (TLR4)-/- mice, and HK-2 cells were used in this study. The nontoxic dosage (0.25 mg/kg, qod) of OTA could significantly decrease the dosage of CsA from 30 to 20 mg/kg per day, and combination of them induced chronic nephropathy model and alleviated the side effects of onefold CsA in vivo, including cardiotoxicity, hepatotoxicity, and immunosuppression. The nontoxic concentration (0.5 μg/ml) of OTA could significantly decrease the concentration of CsA from 10 to 6 μg/ml that induced cytotoxicity, oxidative stress, and nephrotoxicity in vitro. Nontoxic concentration of OTA and low dosage of CsA activated TLR4 and autophagy. These toxic effects induced by OTA and CsA could be reversed by knockdown of TLR4 and autophagy inhibitor 3-methyladenine in vitro. Furthermore, the renal injury and autophagy induced by OTA and CsA could be attenuated in TLR4-/- mice. It suggested that a chronic nephropathy model had been successfully developed by administration of nontoxic concentration of OTA and low dosage of CsA via TLR4-mediated autophagy. The side effects of current model were significantly lesser than those of the previous model induced by onefold CsA. It provided a new tool for exploring the pathogenesis and treatment of chronic kidney disease.

Prevalence of Ochratoxin A in Poultry Feed and Meat from Jordan

BACKGROUND AND OBJECTIVE

Ochratoxin A (OTA) is a fungal metabolite produced in feed and could be transmitted to food chain through animal and considered as one of the potent carcinogenic compound. This study aimed to evaluate the levels of Ochratoxin A in both poultry feed and meat in Jordan.

MATERIALS AND METHODS

About 129 samples representing feed, corn and poultry meat were collected from different location of Jordan market and evaluated for Ochratoxin A by ELISA.

RESULTS

About 38.5% of feed sample, 50.0% of corn sample, 100.0% of feed sample found under sun light were containing an Ochratoxin A (OTA) with an average concentration of 2.90±0.26, 2.35±0.32, 10.30±0.59 μg kg-1, respectively. Also the results showed that between 66.0% (12 sample) to 100.0% (54 sample of the analyzed organs meat sample contains OTA with a concentration ranging from 1.89±0.07-7.68±0.12 μg kg-1.

CONCLUSION

The results indicated that none of the tested samples exceeded the maximum limit set by the EU limits of <50.0 ng km-1 in poultry feeds.

Modulation of Intestinal Epithelial Permeability in Differentiated Caco-2 Cells Exposed to Aflatoxin M1 and Ochratoxin A Individually or Collectively

Aflatoxin M1 (AFM1) and ochratoxin A (OTA) are mycotoxins commonly found in milk; however, their effects on intestinal epithelial cells have not been reported. In the present study, we show that AFM1 (0.12 and 12 μM) and OTA (0.2 and 20 μM) individually or collectively increased the paracellular flux of lucifer yellow and fluorescein isothiocyanate (FITC)-dextrans (4 and 40 kDa) and decreased transepithelial electrical resistance values in differentiated Caco-2 cells after 48 h of exposure, indicating increased epithelial permeability. Immunoblotting and immunofluorescent analysis revealed that AFM1, OTA, and their combination decreased the expression levels of tight junction (TJ) proteins and disrupted their structures, namely, claudin-3, claudin-4, occludin, and zonula occludens-1 (ZO-1), and p44/42 mitogen-activated protein kinase (MAPK) partially involved in the mycotoxins-induced disruption of intestinal barrier. The effects of a combination of AFM1 and OTA on intestinal barrier function were more significant (p < 0.05) than those of AFM1 and OTA alone, yielding additive or synergistic effects. The additive or synergistic effects of AFM1 and OTA on intestinal barrier function might affect human health, especially in children, and toxin risks should be considered.

The effects of heavy metal ions, phthalates and ochratoxin A on oxidation of carcinogenic aristolochic acid I causing Balkan endemic nephropathy

OBJECTIVES

Balkan endemic nephropathy (BEN) is a chronic progressive fibrosis associated with upper urothelial carcinoma (UUC). Aetiology of BEN is still not fully explained. Although carcinogenic aristolochic acid I (AAI) was proven as the major cause of BEN/UUC, this nephropathy is considered to be multifactorial. Hence, we investigated whether other factors considered as potential causes of BEN [a mycotoxin ochratoxin A (OTA), Cd, Pb, Se and As ions and organic compounds (i.e. phthalates) released from lignite deposits in BEN areas] can influence detoxication of AAI, whose concentrations are crucial for BEN development.

METHODS

Oxidation of AAI to 8-hydroxyaristolochic acid I (AAIa) in the presence of Cd, Pb, Se, As ions, dibutylphthalate (DBP), butylbenzylphthalate (BBP), bis(2-ethylhexyl)phthalate (DEHP) and OTA by rat liver microsomes was determined by HPLC.

RESULTS

Only OTA, cadmium and selenium ions, and BBP inhibited AAI oxidation by rat liver microsomes. These compounds also inhibited activities of CYP1A1 and/or CYP2C6/11 catalysing AAI demethylation in rat livers. Therefore, these CYP inhibitions can be responsible for a decrease in AAIa formation. When the combined effects of these compounds were investigated, the most efficient inhibition was caused by OTA combined with BBP and selenium ions.

CONCLUSION

The results show low effects of BBP, cadmium and selenium ions, and/or their combinations on AAI detoxication. No effects were produced by the other metal ions (Pb, As) and phthalates DBP and DEHP. This finding suggests that they do not influence AAI-mediated BEN development. In contrast, OTA might influence this process, by inhibition of AAI detoxication.

The adsorption of ochratoxin a by lactobacillus species

The objective of this study was to examine ochratoxin A (OTA) binding by three lactic acid bacteria (LAB) species: Lactobacillus plantarum, L. brevis, and L. sanfranciscensis. Experiments were conducted using MRS medium and PBS buffer contaminated with 1000 ng/mL OTA and inoculated with live or thermally inactivated bacterial biomass at a concentration of 1 or 5 mg dry weight/mL. It was found that, depending on the strain and biomass density, live bacterial cells reduced OTA content by 16.9% to 35% in MRS medium and by 14.8% to 26.4% in PBS after 24 h of contact. OTA binding was higher in the case of thermally inactivated bacterial biomass (46.2% to 59.8%). The process is very rapid: OTA was removed from PBS as early as after 30 min of contact. The binding of the toxin by cells was partially reversible under the treatment by water and 1 M HCl. The results show that OTA is adsorbed to the surface structures of the cell wall, which is promoted not only by the hydrophobic properties of the cell wall, but also by electron donor-acceptor and Lewis acid-base interactions.

Changes in biosynthesis and metabolism of glutathione upon ochratoxin A stress in Arabidopsis thaliana

Ochratoxin A (OTA) is one of the most toxic mycotoxins, which is toxic to plants and simulates oxidative stress. Glutathione is an important antioxidant in plants and is closely associated with detoxification in cells. We have previously shown that OTA exposure induces obvious expression differences in genes associated with glutathione metabolism. To characterize glutathione metabolism and understand its role in OTA phytotoxicity, we observed the accumulation of GSH in the detached leaves of Arabidopsis thaliana under OTA treatment. OTA stimulated a defense response through enhancing glutathione-S-transferase, glutathione peroxidase, glutathione reductase activities, and the transcript levels of these enzymes were increased to maintain the total glutathione content. Moreover, the level of oxidized glutathione (GSSG) was increased and the ascorbate-glutathione cycle fluctuated in response to OTA. The depletion of glutathione using buthionine sulfoximine (BSO, inhibitor of glutamate-cysteine ligase) had no profound effect on OTA toxicity, as glutathione was regenerated through the ascorbate-glutathione cycle to maintain the total glutathione content. The ROS, MDA and GSH accumulation was significantly affected in the mutant gsh1, gr1 and gpx2 after treatment with OTA, which indicated that glutathione metabolism is directly involved in the oxidative stress response of Arabidopsis thaliana subjected to OTA. In conclusion, date demonstrate that glutathione-associated metabolism is closely related with OTA stress and glutathione play a role in resistance of Arabidopsis subjected to OTA.

DNA damage and S phase arrest induced by Ochratoxin A in human embryonic kidney cells (HEK 293)

Ochratoxin A (OTA) is a ubiquitous mycotoxin with potential nephrotoxic, hepatotoxic and immunotoxic effects. The mechanisms underlying the nephrotoxicity of OTA remain obscure. To investigate DNA damage and the changes of the cell cycle distribution induced by OTA, human embryonic kidney cells (HEK 293 cells) were incubated with various concentrations of OTA for 24h in vitro. The results indicated that OTA treatment led to the production of reactive oxygen species (ROS) and to a decrease of the mitochondrial membrane potential (ΔΨm). OTA-induced DNA damage in HEK 293 cells was evidenced by DNA comet tails formation and increased expression of γ-H2AX. In addition, OTA could induce cell cycle arrest at the S phase in HEK 293 cells. The expression of key cell cycle regulatory factors that were critical to the S phase, including cyclin A2, cyclin E1, and CDK2, were further detected. The expression of cyclin A2, cyclin E1, and CDK2 were significantly decreased by OTA treatment at both the mRNA and protein levels. The apoptosis of HEK 293 cells after OTA treatment was observed using Hoechst 33342 staining. The results confirmed that OTA did induce apoptosis in HEK 293 cells. In conclusion, our results provided new insights into the molecular mechanisms by which OTA might promote nephrotoxicity.

Regulation of IL-8 promoter activity by verrucarin A in human monocytic THP-1 cells

Macrocyclic trichothecenes have been frequently detected in fungi in water-damaged buildings and exhibited higher toxicity than the well-studied trichothecenes; however, the mechanism underlying their toxicity has been poorly understood. In this study, transcriptional regulation of the cytokine interleukin (IL)-8 by a macrocyclic trichothecene, verrucarin A (VA), in human monocytic THP-1 cells is reported. Consistent with previous findings, VA was 100-fold more cytotoxic than deoxynivalenol (DON), while ochratoxin A (OA) was not cytotoxic. In cells transduced with the wild-type IL-8 promoter luciferase construct, VA induced a biphasic dose response composed of an upregulation of luciferase expression at low concentrations of 0.01-1 ng/ml and a downregulation at high levels of 10 ng/ml and higher. In contrast, DON induced a sigmoid-shaped dose response with the EC50 of 11.6 ng/ml, while OA did not markedly affect the IL-8 expression. When cells were transduced with IL-8 promoter with a mutation of transcription factor nuclear factor-κB (NF-κB)-binding site, VA (1 ng/ml), DON (1000 ng/ml), and tumor necrosis factor (TNF) α (20 ng/ml)-induced luciferase expression were impaired. In addition, the NF-κB inhibitor caffeic acid phenethyl ester inhibited VA-, DON-, and TNFα-induced luciferase expression. Mutation of the CCAAT/enhancer-binding protein (CEBP) β binding site of the IL-8 promoter affected only DON-, but not VA- and TNFα-induced luciferase expression. Taken together, these results suggested that VA activated IL-8 promoter via an NF-κB-dependent, but not CEBPβ-dependent, pathway in human monocytes.

Comparative proteomics and physiological characterization of Arabidopsis thaliana seedlings in responses to Ochratoxin A

Ochratoxin A (OTA) is a mycotoxin that is primarily produced by Aspergillus ochraceus and Penicillium verrucosum. This mycotoxin is a contaminant of food and feedstock worldwide and may induce cell death in plants. To investigate the dynamic growth process of Arabidopsis seedlings in response to OTA stress and to obtain a better understanding of the mechanism of OTA toxicity towards Arabidopsis, a comparative proteomics study using 2-DE and MALDI-TOF/TOF MS/MS was performed. Mass spectrometry analysis identified 59 and 51 differentially expressed proteins in seedlings exposed to 25 and 45 μM OTA for 7 days, respectively. OTA treatment decreased root elongation and leaf area, increased anthocyanin accumulation, damaged the photosynthetic apparatus and inhibited photosynthesis. Treatment of the seedlings with 25 μM OTA enhanced energy metabolism, whereas higher concentration of OTA (45 μM) inhibited energy metabolism in the seedlings. OTA treatment caused an increase of ROS, an enhancement of antioxidant enzyme defense responses, disturbance of redox homeostasis and activation of lipid oxidation. Glutamine and S-adenosylmethionine metabolism may also play important roles in the response to OTA. In conclusion, our study provided novel insights regarding the response of Arabidopsis to OTA at the level of the proteome. These results are expected to be highly useful for understanding the physiological responses and dissecting the OTA response pathways in higher plants.

Transcript and protein profiling analysis of OTA-induced cell death reveals the regulation of the toxicity response process in Arabidopsis thaliana

Ochratoxin A (OTA) is a toxic isocoumarin derivative produced by various species of mould which mainly grow on grain, coffee, and nuts. Recent studies have suggested that OTA induces cell death in plants. To investigate possible mechanisms of OTA phytotoxicity, both digital gene expression (DGE) transcriptomic and two-dimensional electrophoresis proteomic analyses were used, through which 3118 genes and 23 proteins were identified as being up- or down-regulated at least 2-fold in Arabidopsis leaf in response to OTA treatment. First, exposure of excised Arabidopsis thaliana leaves to OTA rapidly causes the hypersensitive reponse, significantly accelerates the increase of reactive oxygen species and malondialdehyde, and enhances antioxidant enzyme defence responses and xenobiotic detoxification. Secondly, OTA stimulation causes dynamic changes in transcription factors and activates the membrane transport system dramatically. Thirdly, a concomitant persistence of compromised photosynthesis and photorespiration is indicative of a metabolic shift from a highly active to a weak state. Finally, the data revealed that ethylene, salicylic acid, jasmonic acid, and mitogen-activated protein kinase signalling molecules mediate the process of toxicity caused by OTA. Profiling analyses on Arabidopsis in response to OTA will provide new insights into signalling transduction that modulates the OTA phytotoxicity mechanism, facilitate mapping of regulatory networks, and extend the ability to improve OTA tolerance in Arabidopsis.

Pro-inflammatory effects of ochratoxin A on nasal epithelial cells

Eosinophilic chronic rhinosinusitis (ECRS) largely consists of allergic fungal sinusitis, non-allergic fungal rhinosinusitis, aspirin-exacerbated ECRS, and superantigen-induced ECRS. The pathophysiology of ECRS is not completely understood, in particular, the role of mycotoxins remains unknown. The aim of this study was to evaluate the effects of one of the most widespread mycotoxin, ochratoxin A (OTA), on the release of pro-inflammatory cytokines such as interleukin-(IL)-6 and the CXC-chemokine IL-8 from nasal epithelial cell cultures (NEC) of subjects with and without ECRS. NEC (ECRS group: n = 16; controls: n = 7) were stimulated with OTA for 24 h. Protein concentrations of IL-6 and IL-8 levels were measured in NEC supernatants by ELISA prior and 24 h after addition of OTA. Baseline levels in the supernatants of NEC were 183.3 pg/ml for IL-6 and 384.6 pg/ml for IL-8. Stimulation with OTA induced a significant increase of IL-6 (p < 0.001) and IL-8 (p < 0.001) in both NEC of controls and ECRS, respectively. There were no significant differences between controls and ECRS. This is the first study evaluating the effects of a mycotoxin on epithelial airway cells. Our data show that the ubiquitous mycotoxin OTA has a strong pro-inflammatory effect on NEC resulting in the release of IL-6 and IL-8. Mycotoxins may promote inflammation in nasal mucosa.

Effect of ochratoxin A on broiler chicks challenged withSalmonella gallinarum

1. A study was conducted to evaluate the effects of ochratoxin A (OA) on broiler chicks challenged with Salmonella gallinarum. 2. One hundred and seventy-six 1-d-old broiler chicks were divided into two groups of 88 chicks each, with one group fed on a control mash diet and the other given a mash diet containing 2 ppm OA. On d 14, each group was further subdivided into two groups with one group infected with S. gallinarum and the other uninfected. 3. Following S. gallinarum inoculation on d 14, 4 birds from each group were killed at 1, 2, 3, 5, 7, 10, 14 and 21 d post inoculation. 4. S. gallinarum infection caused dullness, depression, weakness, increased thirst, droopy wings, ruffled feathers and greenish-yellow diarrhoea. S. gallinarum infection in the absence of OA caused 11.5% mortality which increased to 28.8% in the presence of OA. 5. Decreased body weight and reduced feed intake were observed in chicks fed on the diet containing OA. S. gallinarum infection also reduced the body weights of chicks, with the effects being more marked in chicks receiving OA. The OA diet led to increased serum levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, uric acid and creatinine, and decreased levels of total proteins, albumin, globulins, calcium and phosphorus. S. gallinarum infection did not cause significant alteration in any of the serum biochemical parameters. 6. Mortality and the severity of S. gallinarum infection in broiler chicks were increased by the presence of OA in the diet.

The influence of raw material contamination with mycotoxins on alcoholic fermentation indicators

The aim of the research was to describe the influence of selected mycotoxins on major factors (alcohol concentration, productivity, yield and energy) that are characteristic of the fermentation process of maize mashes. Indicators of the alcoholic fermentation of mashes made from raw material with low contaminations levels were compared with mashes obtained from raw material that was selectively contaminated with mycotoxins on the following concentrations: aflatoxin B(1)-11.65 ppb, B(2)-12.60 ppb, G(1)-12.34 ppb, G(2)-12.04 ppb; ochratoxin A-177.5 ppb; zearalenone-352 ppb; deoxynivalenol-2274 ppb; fumonisin B(1)-1875 ppb, B(2)-609 ppb, B(3)-195 ppb. It was found that, apart from fumonisin, all mycotoxins substantially affected the course of subsequent fermentation phases, in particular the first and the main fermentation phases. The highest drop in alcohol concentration at the main stage of the process amounted to 1% v/v and it was achieved by contamination with zearalenone. The statistically significant drop in the final fermentation yield was observed; this was caused by raw material contaminated with all studied mycotoxins, except for fumonisin. The decrease in ethanol yield in reference to the control variant ranged from 1.42 to 3.20 dm(3) of absolute alcohol out of 100 kg of starch, depending on a toxin.

Mycotoxin Ochratoxin A-induced cell death and changes in oxidative metabolism of Arabidopsis thaliana

We evaluated the phytotoxicity of mycotoxin ochratoxin A (OTA) from Aspergillus and Penicillium strains on Arabidopsis thaliana. The results demonstrate that the growth of Arabidopsis thaliana on media containing OTA was inhibited significantly. Moreover, OTA induced necrotic lesions in detached leaves, which are reminiscent of hypersensitive response lesions that are activated during plant-pathogen interactions and other abiotic stress factors. From our study, we can see that OTA exposure stimulated a biphasic oxidative burst in the leaves, resulting in the generation of hydrogen peroxide (H2O2) and superoxide anion radicals (O2(.-)) and in the concomitant down-regulation of antioxidant enzyme defense responses and up-regulation of lipid peroxidation. These results suggested that OTA damage might result from reactive oxygen species pathways. Our experiments provide a useful model plant system for research on OTA-induced plant cell death.

Acute toxicity of ochratoxin-A in marine water-reared sea bass (Dicentrarchus labrax L.)

The toxic effects of ochratoxin-A (OTA) on sea bass, Dicentrarchus labrax L., have not been previously documented. A flow-through bioassay test system was conducted in two series and a total 180 of adult marine-reared sea bass was used to estimate the acute oral 96 h median lethal concentration (LC(50)) value and behavioral changes of OTA. The data obtained were statistically evaluated using Finney's Probit Analysis Method developed by EPA. The 96 h LC(50) value for adult D. labrax was found to be 277 microg kg(-1)bwt with 95% confidence limits of 244-311 microg kg(-1)bwt. This value was calculated to be 285 microg kg(-1) bwt with Behrens-Karber's method. The two methods were relatively comparable. The acute dietary 96 h LC(50) of OTA is 9.23 mg kg(-1) diet. Additionally, the behavioral changes of sea bass were primarily observed as nervous and respiratory manifestations. We concluded that sea bass is a species highly sensitive to OTA making them a useful experimental model for aquatic mycotoxigenic problems.

Ochratoxin a lowers mRNA levels of genes encoding for key proteins of liver cell metabolism

Ochratoxin A (OTA) is a nephro- and hepatotoxic mycotoxin that frequently contaminates food and feedstuffs. Although recent studies have indicated that OTA modulates renal gene expression, little is known regarding its impact on differential gene expression in the liver. Therefore a microarray study of the HepG2 liver cell transcriptome in response to OTA exposure (0, 0.25, 2.5 micromol/l for 24 h) was performed using Affymetrix GeneChip technology. Selected microarray results were verified by real-time PCR and Western blotting as independent methods. Out of 14,500 genes present on the microarray, 13 and 250 genes were down-regulated by 0.25 and 2.5 micromol/l OTA, respectively. Reduced mRNA levels of calcineurin A beta (PPP3CB), which regulates inflammatory signalling pathways in immune cells, and of the uncoupling protein 2 (UCP2), which has been suggested to control the production of reactive oxygen species (ROS), were observed in response to 0.25 micromol/l OTA. A particularly strong down-regulation due to 2.5 micromol/l OTA was evident for the mRNA levels of insulin-like growth factor binding protein 1 (IGFBP1) and tubulin beta 1 (TUBB1) which have been demonstrated to function as a pro-survival factor in hepatocytes and as an important cytoskeletal component, respectively. In addition, many genes involved in energy and xenobiotic metabolism, including phosphoglycerate kinase 1 (PGK1), stearoyl-Coenzyme A desaturase 1 (SCD), and glutathione S-transferase omega 1 (GSTO1), were down-regulated by OTA. Furthermore, OTA significantly inhibited the capacitative calcium entry into the HepG2 cells, indicating an alteration of calcium homeostasis. Overall, OTA dose-dependently affects multiple genes encoding for key proteins of liver cell metabolism.

Ochratoxin A: The Continuing Enigma

The mycotoxin ochratoxin A (OTA) has been linked to the genesis of several disease states in both animals and humans. It has been described as nephrotoxic, carcinogenic, teratogenic, immunotoxic, and hepatotoxic in laboratory and domestic animals, as well as being thought to be the probable causal agent in the development of nephropathies (Balkan Endemic Nephropathy, BEN and Chronic Interstitial Nephropathy, CIN) and urothelial tumors in humans. As a result, several international agencies are currently attempting to define safe legal limits for OTA concentration in foodstuffs (e.g., grain, meat, wine, and coffee), in processed foods, and in animal fodder. In order to achieve this goal, an accurate risk assessment of OTA toxicity including mechanistic and epidemiological studies must be carried out. Ochratoxin has been suggested by various researchers to mediate its toxic effects via induction of apoptosis, disruption of mitochondrial respiration and/or the cytoskeleton, or, indeed, via the generation of DNA adducts. Thus, it is still unclear if the predominant mechanism is of a genotoxic or an epigenetic nature. One aspect that is clear, however, is that the toxicity of OTA is subject to and characterized by large species- and sex-specific differences, as well as an apparently strict structure-activity relationship. These considerations could be crucial in the investigation of OTA-mediated toxicity. Furthermore, the use of appropriate in vivo and in vitro model systems appears to be vital in the generation of relevant experimental data. The intention of this review is to collate and discuss the currently available data on OTA-mediated toxicity with particular focus on their relevance for the in vivo situation, and also to suggest possible future strategies for unlocking the secrets of ochratoxin A.

Tight junction proteins in keratinocytes: localization and contribution to barrier function

Recent research suggests that tight junctions (TJs) are located in the stratum granulosum, where they contribute to the barrier function of the epidermis. In this study, we investigated the formation of functional TJs in cultured normal human epidermal keratinocytes. We observed the development of permeability barrier function through the process of Ca(2+)-induced differentiation. Immunofluorescence analyses at 96 h after Ca(2+)-induced differentiation revealed concentrated portions of occludin, a TJ-specific marker, arranged as continuous lines circumscribing individual flattened suprabasal cells in areas with high concentrations of claudin-1 and -4. Transient Ca(2+) depletion reversibly disrupted the continuous network of TJ proteins and the permeability barrier. We also found that the addition of ochratoxin A weakened the permeability barrier and the expression of claudin-4. Our findings suggest that TJ proteins contribute to the permeability barrier in epidermal keratinocytes.

Carcinogen-specific gene expression profiles in short-term treated Eker and wild-type rats indicative of pathways involved in renal tumorigenesis

Eker rats heterozygous for a dominant germline mutation in the tuberous sclerosis 2 (Tsc2) tumor suppressor gene were used as a model to study renal carcinogenesis. Eker and corresponding wild-type rats were exposed to genotoxic aristolochic acid (AA) or non-genotoxic ochratoxin A (OTA) to elucidate early carcinogen-specific gene expression changes and to test whether Eker rats are more sensitive to carcinogen-induced changes in gene expression. Male Eker and wild-type rats were gavaged daily with AA (10 mg/kg body weight) or OTA (210 microg/kg body weight). After 1, 3, 7, and 14 days of exposure, renal histopathology, tubular cell proliferation, and Affymetrix gene expression profiles from renal cortex/outer medulla were analyzed. AA-treated Eker and wild-type rats were qualitatively comparable in all variables assessed, suggesting a Tsc2-independent mechanism of action. OTA treatment resulted in slightly increased cortical pathology and significantly elevated cell proliferation in both strains, although Eker rats were more sensitive. Deregulated genes involved in the phosphatidylinositol 3-kinase-AKT-Tsc2-mammalian target of rapamycin signaling, among other important genes prominent in tumorigenesis, in conjunction with the enhanced cell proliferation and presence of preneoplastic lesions suggested involvement of Tsc2 in OTA-mediated toxicity and carcinogenicity, especially as deregulation of genes involved in this pathway was more prominent in the Tsc2 mutant Eker rat.

The isolation of secondary metabolites and in vitro potent anti-cancer activity of clerodermic acid from Enicosanthum membranifolium

Four compounds were isolated from Enicosanthum membranifolium. The structures of the compounds were confirmed by spectroscopic data. Their structures were determined as N-trans-feruloyltyramine, R-(-)-mellein, clerodermic acid, and salicifoline chloride as a quaternary alkaloid compound. The structures of R-(-)-mellein and salicifoline chloride were confirmed by using X-ray diffraction. Clerodermic acid was shown to induce potent apoptosis against human leukemia HL60 cells.

The chloride dependence of the human organic anion transporter 1 (hOAT1) is blunted by mutation of a single amino acid

Organic anion transporter 1 (OAT1) is key for the secretion of organic anions in renal proximal tubules. These organic anions comprise endogenous as well as exogenous compounds including frequently used drugs of various chemical structures. The molecular basis for the polyspecificity of OAT1 is not known. Here we mutated a conserved positively charged arginine residue (Arg(466)) in the 11(th) transmembrane helix of human OAT1. The replacement by the positively charged lysine (R466K) did not impair expression of hOAT1 at the plasma membrane of Xenopus laevis oocytes but decreased the transport of p-aminohippurate (PAH) considerably. Extracellular glutarate inhibited and intracellular glutarate trans-stimulated wild type and mutated OAT1, suggesting for the mutant R466K an unimpaired interaction with dicarboxylates. However, when Arg(466) was replaced by the negatively charged aspartate (R466D), glutarate no longer interacted with the mutant. PAH uptake by wild type hOAT1 was stimulated in the presence of chloride, whereas the R466K mutant was chloride-insensitive. Likewise, the uptake of labeled glutarate or ochratoxin A was chloride-dependent in the wild type but not in R466K. Kinetic experiments revealed that chloride did not alter the apparent K(m) for PAH but influenced V(max) in wild type OAT1-expressing oocytes. In R466K mutants the apparent K(m) for PAH was similar to that of the wild type, but V(max) was not changed by chloride removal. We conclude that Arg(466) influences the binding of glutarate, but not interaction with PAH, and interacts with chloride, which is a major determinant in substrate translocation.

Lipid Peroxidation and Glutathione Levels in Porcine Kidney PK15 Cells after Individual and Combined Treatment with Fumonisin B1, Beauvericin and Ochratoxin A

Individual and combined effects of the mycotoxins fumonisin B(1), beauvericin and ochratoxin A on cell viability, lipid peroxidation (TBARS) and intracellular glutathione (GSH) were studied on porcine kidney epithelial cells (PK15). Cells were treated with 0.05, 0.5 and 5 microg/ml of each mycotoxin or the combinations of two or all three applied in equal concentrations for 24 and 48 hr. Changes in cell viability, GSH and TBARS levels showed that the cytotoxic effects of these mycotoxins were concentration- and time-dependent. After 24 hr, cell viability was significantly decreased by the exposure to 5 microg/ml of fumonisin B(1) (25%), beauvericin (30%) and ochratoxin A (35%), as compared to controls. Only ochratoxin A (5 microg/ml) increased TBARS (56%), with further significant increase (85%) after 48 hr exposure. Fumonisin B(1) and beauvericin significantly increased TBARS (57% and 80%, respectively) only when the highest dose was applied for 48 hr. After 24 hr, GSH was significantly decreased (18%) by ochratoxin A (0.05 microg/ml), whereas fumonisin B(1) and beauvericin significantly decreased GSH at the concentration of 0.5 microg/ml. Combined treatment with fumonisin B(1), beauvericin and ochratoxin A resulted mostly in additive effects especially after a 24-hr exposure, although synergistic as well as antagonistic interactions could not be excluded depending on toxin concentrations and time of exposure. This is the first report on beauvericin-induced effects on lipid peroxidation and GSH in animal cells.

Expression of COX-2 and hsp72 in peritoneal macrophages after an acute ochratoxin A treatment in mice

Ochratoxin A (OTA) is a secondary fungal metabolite produced by Aspergillus and Penicillium strains that elicits a broad spectrum of toxicological effects in animals and man. A single oral OTA administration (10 mg/kg) in mice induced after 24 h oxidative damage and polymorphonuclear leukocyte (PMN) infiltration in parenchymal organs. In fact, OTA treatment increased lipid peroxidation (via malondialdehyde formation) in kidney and liver and PMN accumulation in duodenum, as shown by myeloperoxidase activity. Following in vivo OTA treatment an increase of cyclooxygenase-2 and of heat shock protein 72 expression was evidenced in peritoneal macrophage lysates by Western blot. That OTA modulates these proteins involved in the inflammatory process indicates that the mycotoxin is able to activate immune cells. This study suggests that the oxidative stress, the neutrophil accumulation in parenchymal tissues and the modulation of inflammatory parameters in peritoneal macrophages induced by OTA are involved in its toxicity, and represent early events related to several aspects of OTA mycotoxicosis.

Immunotoxic activity of ochratoxin A

Ochratoxin A (OTA) is an immunosuppressant fungal compound, produced by toxigenic species of Aspergillus and Penicillium fungi in a wide variety of climates and geographical regions. The contamination of food by this mycotoxin takes place primarily during preharvest periods. Almost all types of food can be contaminated. In addition, its chemical stability against heat and during industrial food processing makes OTA one of the most abundant food contaminating mycotoxins. Due in part to its long serum half-life in man, almost 100% of all human blood samples from some geographic regions may be positive for OTA. The immunosuppressant activity of OTA is characterized by size reduction of vital immune organs, such as thymus, spleen, and lymph nodes, depression of antibody responses, alterations in the number and functions of immune cells, and modulation of cytokine production. The immunotoxic activity of OTA probably results from degenerative changes and cell death following necrosis and apoptosis, in combination with slow replacement of affected immune cells, due to inhibition of protein synthesis.

Ochratoxin A induces oxidative DNA damage in liver and kidney after oral dosing to rats

The nephrotoxic/carcinogenic mycotoxin ochratoxin A (OTA) occurs as a contaminant in food and feed and may be linked to human endemic Balkan nephropathy. The mechanism of OTA-derived carcinogenicity is still under debate, since reactive metabolites of OTA and DNA adducts have not been unambiguously identified. Oxidative DNA damage, however, has been observed in vitro after incubation of mammalian cells with OTA. In this study, we investigated whether OTA induces oxidative DNA damage in vivo as well. Male F344 rats were dosed with 0, 0.03, 0.1, 0.3 mg/kg bw per day OTA for 4 wk (gavage, 7 days/wk, five animals per dose group). Subsequently, oxidative DNA damage was determined in liver and kidney by the comet assay (single cell gel electrophoresis) with/without use of the repair enzyme formamido-pyrimidine-DNA-glycosylase (FPG). The administration of OTA had no effect on basic DNA damage (determined without FPG); however, OTA-mediated oxidative damage was detected with FPG treatment in kidney and liver DNA of all dose groups. Since the doses were in a range that had caused kidney tumors in a 2-year carcinogenicity study with rats, the oxidative DNA damage induced by OTA may help to explain its mechanism of carcinogenicity. For the selective induction of tumors in the kidney, increased oxidative stress in connection with severe cytotoxicity and increased cell proliferation might represent driving factors.

Transport of estrone sulfate by the novel organic anion transporter Oat6 (Slc22a20)

Recently, a novel Slc22 gene family member expressed in murine olfactory mucosa was identified and based on sequence homology proposed to be an organic anion transporter [Oat6 (Slc22a20); J. C. Monte, M. A. Nagle, S. A. Eraly, and S. K. Nigam. Biochem Biophys Res Commun 323: 429-436, 2004]. However, no functional data for Oat6 was reported. In the present study, we demonstrate that murine Oat6 mediates the inhibitable transport of estrone sulfate using both Xenopus oocyte expression assay and Chinese hamster ovary (CHO) cells stably transfected with mOat6 (CHO-mOat6). Uptake was virtually eliminated by probenecid and the anionic herbicide 2,4-dichlorophenoxyacetate. The organic anions ochratoxin A, salicylate, penicillin G, p-aminohippurate, and urate inhibited mOat6-mediated accumulation to varying degrees. Transport of estrone sulfate by mOat6 was demonstrated to be saturable, and K(m) estimates of 109.8 +/- 22.6 microM in oocytes and 44.8 +/- 7.3 microM in CHO-mOat6 cells were obtained. Inhibitory constants for 2,4-dichlorophenoxyacetate (15.7 +/- 2.0 microM), salicylate (49.0 +/- 4.4 microM), probenecid (8.3 +/- 2.5 microM), and penicillin G (1,450 +/- 480 microM) were also determined. Accumulation of estrone sulfate mediated by mOat6 was significantly trans-stimulated by glutarate, indicating that mOat6 functions as an organic anion/dicarboxylate exchanger. These data demonstrate for the first time that the novel murine gene Oat6 (Slc22a20) encodes a functional organic anion transporter and mOat6 is indeed the newest member of the OAT gene family.

Alterations induced in vitro by ochratoxin A in rat lymphoid cells

Ochratoxin A (OTA) is a nephrotoxic mycotoxin produced by species of the genus Penicillium and Aspergillus that is present in food and feed as a natural contaminant. It modifies the immune function in animals and inhibits the proliferative response of lymphocytes in vitro. The toxic effect of OTA (0.5, 2, 20 microM) in lympho-proliferative response, natural killer (NK) cell activity, cytotoxic T lymphocytes (CTL) activity and macrophages' bacteriolytic capability was studied in vitro after 1 hour of treatment. The proliferative response of lymphocytes to concanavalin A and lipopolysaccharide was not affected by OTA; the cytotoxic activity of NK cells was dose-dependent decreased; the CTL activity was significantly decreased at the lowest concentration; the bacteriolytic activity of macrophages varied only slightly. These in vitro results reproduced, at least in part, some effects detected previously in vivo. The protein synthesis inhibition and the oxidative metabolism of OTA coupled to the prostaglandin synthesis are probably implicated in NK cells' toxicity, because the effects were reverted by the addition of phenylalanine or piroxicam to the culture medium. The induction of apoptosis seems to be the principal mechanism of action in the CTL effect. The intracellular concentration of OTA after 1 hour was analysed by HPLC and was found to be proportional to the quantity of OTA added to the culture medium for the three cell types; the presence of phenylalanine and piroxicam on the culture medium did not change the intracellular OTA concentration.

The effect of ochratoxin A on the concentration of protein carbonyls in rats

The mechanism of ochratoxin A (OTA) toxicity has been found to involve the production of free radicals and consequent oxidative stress. Until now, the only studied pathway of OTA-caused oxidative damage was peroxidation of lipids. The aim of this study was to check whether OTA induced the production of protein carbonyls, markers of protein oxidation. Exposed rats (5 per group) were given daily OTA (0.5 mg kg(-1) b. w., i. p.) for 7 days, 14 days, or 21 days, and control rats solvent only (TRIS). All animals were killed 24 hours after the last treatment. The levels of OTA in plasma, kidney and liver homogenates increased gradually during the whole length of the experiment. The levels of protein carbonyls in kidney homogenates of OTA-treated rats was significantly higher after days 14 and 21 than in controls (P < 0.05). The levels of protein carbonyls in the liver was significantly higher in OTA-treated animals only after day 21 (P < 0.05). These results confirm that oxidative stress is involved in the mechanism of OTA toxicity, and that it causes the oxidation of proteins.

Unusual astrocyte reactivity caused by the food mycotoxin ochratoxin A in aggregating rat brain cell cultures

Ochratoxin A (OTA), a mycotoxin and widespread food contaminant, is known for its patent nephrotoxicity and potential neurotoxicity. Previous observations in vitro showed that in the CNS, glial cells were particularly sensitive to OTA. In the search for the molecular mechanisms underlying OTA neurotoxicity, we investigated the relationship between OTA toxicity and glial reactivity, in serum-free aggregating brain cell cultures. Using quantitative reverse transcriptase-polymerase chain reaction to analyze changes in gene expression, we found that in astrocytes, non cytotoxic concentrations of OTA down-regulated glial fibrillary acidic protein, while it up-regulated vimentin and the peroxisome proliferator-activated receptor-gamma expression. OTA also up-regulated the inducible nitric oxide synthase and the heme oxygenase-1. These OTA-induced alterations in gene expression were more pronounced in cultures at an advanced stage of maturation. The natural peroxisome proliferator-activated receptor-gamma ligand, 15-deoxy-delta(12,14) prostaglandin J2, and the cyclic AMP analog, bromo cyclic AMP, significantly attenuated the strong induction of peroxisome proliferator-activated receptor-gamma and inducible nitric oxide synthase, while they partially reversed the inhibitory effect of OTA on glial fibrillary acidic protein. The present results show that OTA affects the cytoskeletal integrity of astrocytes as well as the expression of genes pertaining to the brain inflammatory response system, and suggest that a relationship exists between the inflammatory events and the cytoskeletal changes induced by OTA. Furthermore, these results suggest that, by inducing an atypical glial reactivity, OTA may severely affect the neuroprotective capacity of glial cells.

Functional analysis of polymorphisms in the organic anion transporter, SLC22A6 (OAT1)

OBJECTIVES

The organic anion transporter, OAT1 (SLC22A6), plays a role in the renal elimination of many drugs and environmental toxins. The goal of this study was to identify and functionally characterize OAT1 variants as a first step towards understanding whether genetic variation in OAT1 may contribute to interindividual differences in renal elimination of xenobiotics.

METHODS

As part of a larger study, 276 DNA samples from an ethnically diverse population were screened and 12 coding region variants of OAT1 were identified. The non-synonymous variants were then constructed and characterized in Xenopus laevis oocytes. A small family-based clinical study was conducted to determine the renal elimination of a model OAT1 substrate, adefovir (an antiviral agent) in human subjects who possessed a non-functional variant, OAT1-R454Q.

RESULTS

Six non-synonymous variants were identified; two (OAT1-R50 H and OAT1-R293W) were present at > or = 1% in at least one ethnic population. These two variants exhibited normal uptake of p-aminohippurate, ochratoxin A and methotrexate assayed in X. laevis oocytes. One variant, OAT1-R454Q, was non-functional with respect to the above substrates. In the clinical study, there was no significant decrease in the renal secretory clearance of adefovir in family members heterozygous for OAT1-454Q in comparison to those with the reference transporter, OAT1-454R.

CONCLUSIONS

These data indicate that the coding region of OAT1 has low genetic and functional diversity and suggest that coding region variants of OAT1 may not contribute substantially to interindividual differences in renal elimination of xenobiotics.

Melatonin counteracts oxidative stress in rats fed an ochratoxin A contaminated diet

The mycotoxin ochratoxin A (OTA) is a widespread contaminant in human and animal food products. It induces a wide range of toxic effects including lipid peroxidation through the generation of free radicals. The aim of this work was to evaluate the antioxidant effects of melatonin against OTA-induced oxidative stress in liver and kidney in rats. Treated animals were fed OTA-contaminated diet (3 mg/kg) for 15 days before, during and after melatonin administration (20 mg/kg bw). The results indicate that OTA caused severe effects typical to those reported in the literature for ochratoxicosis. Melatonin alone was effective in the improving food intake, body weight gain, serum total protein, albumin, the activities of alkaline phosphatase, G-glutamyl transferase and creatinine kinase and liver and kidney glutathione peroxidase, superoxide dismutase and malondialdehyde. Rats fed OTA-contaminated diet before, during or after melatonin administration showed a significant improvement in all tested parameters toward the normal values of the controls. This improvement was most pronounced in the group pretreated with melatonin. It is concluded that melatonin exhibits a preventive effect against OTA-induced oxidative stress through its role in the scavenging of free radicals and/or the prevention of lipid peroxidation.

Ochratoxin A at nanomolar concentrations: A signal modulator in renal cells

Ochratoxin A (OTA) is a ubiquitous fungal metabolite with nephrotoxic, carcinogenic, and apoptotic potential. Toxicokinetics make the kidney the primary target organ for OTA. Due to its widespread occurrence in improperly stored foodstuff the complete and safe avoidance of OTA for humans is impossible. There are several reports showing a significant correlation between OTA exposure and certain forms of nephropathies. At nanomolar concentrations OTA leads to specific changes of function and phenotype in renal cells. The toxin interacts with certain cellular "key-molecules" (e. g., mitogen-activated protein (MAP) kinases, Ca2+), thereby disturbing cellular signalling and regulation events as well as mitochondrial function. Moreover, OTA has the ability to modulate physiological signals (e. g., angiotensin II or TNFalpha) and thereby influences cell function and cell growth and may even stable re-program the cells (e. g., altered distribution of chromosomes). This review concentrates on the effects of OTA in the nanomolar range and its interactions with cellular signalling networks in different renal cells proposing OTA to act as a signal modulator.

The Nephrotoxin Ochratoxin A Induces Key Parameters of Chronic Interstitial Nephropathy in Renal Proximal Tubular Cells

Ochratoxin A (OTA) is a nephrotoxic and cancerogenic mycotoxin. There is epidemiological evidence that OTA exposition leads to cortical interstitial nephropathies in humans. However, virtually no data are available investigating the effect of OTA on renal cortical cells with respect to induction of nephropathy. Thus, we investigated whether OTA is able to induce changes of cellular properties potentially leading to interstitial nephropathy, using proximal tubular cell lines (OK, NRK-52E). OTA decreased cell number and cell protein time and dose dependently. Accordingly we investigated the effect of 100 nM or 1000 nM OTA. The decline of cell number after OTA exposure is due to necrosis and apoptosis, as measured by LDH release or DNA ladder formation and caspase-3 activation, respectively. OTA incubation of proximal tubular cells also resulted in a loss of epithelial tightness as determined by diffusion of FITC labeled inulin. Inflammation, fibrosis and epithelial-to-mesenchymal transition are described in chronic interstitial renal disease. Therefore, we also investigated the effect of OTA on NFkappaB activity, collagen secretion and generation of alpha smooth muscle actin. OTA alone was sufficient to induce the latter parameters in proximal tubular cells. Finally, OTA is a nephrotoxcic substance and elevated activity of mitogen activated protein kinases (MAPK) is described in nephropathies. As we investigated the effect of OTA on activity of ERK, JNK and p38 by ELISA, we found that OTA activates the MAPK measured dose dependently. In summary, OTA induced phenomena typical for chronic interstitial nephropathy, like loss of cells and epithelial tightness, necrosis and apoptosis as well as markers of inflammation, fibrosis and epithelial-to-mesenchymal transition in proximal tubular cells. Thus, we could show for the first time that OTA is able to induce key parameters of nephropathy in proximal tubular cells in culture. Moreover OTA interacts with MAPK and thus may exert its specific toxic actions.

Effect of the mycotoxin, ochratoxin A, on hormone-stimulated ion transport in a cultured cell model of the renal principal cell

The mycotoxin ochratoxin A (OTA) is a common contaminant of many foodstuffs and, consequently, is present in a large proportion of tested populations of humans and commercial animals. The predominant effects of OTA are manifested in the kidney where the severity varies from salt wasting to renal carcinoma formation in a concentration-dependent fashion. The MDCK-C7 renal cell culture model responds to various hormones known to regulate electrolyte and fluid balance and was used as a model to study the chronic effects of an acute exposure to low dose OTA. The natriferic hormones aldosterone and insulin-like growth factor 1 (IGF1) both stimulate Na(+) flux in a reabsorptive direction via activation of the epithelial Na(+) channel (ENaC). In contrast, anti-diuretic hormone (ADH) stimulates three separate and temporally distinct ion transport responses, one of which is Na(+) reabsorption. Treatment of MDCK-C7 cells with OTA (100 nM) for 48 h selectively and irreversibly inhibits hormone-stimulated Na(+) reabsorption via ENaC. This effect was retained for 48 cell passages after the removal of the toxin and mimics the OTA-induced salt-wasting that has been documented in clinical studies. These studies indicate that the effect of the toxin is genomic and therefore, likely to be long lasting in exposed animals and humans.

Relative contribution of OAT and OCT transporters to organic electrolyte transport in rabbit proximal tubule

We compared the characteristics of several cloned rabbit organic electrolyte (OE) transporters expressed in cultured cells with their behavior in intact rabbit renal proximal tubules (RPT) to determine the contribution of each to basolateral uptake of the weak acid ochratoxin A (OTA) and the weak base cimetidine (CIM). The activity of organic anion transporters OAT1 and OAT3 proved to be distinguishable because OAT1 had a high affinity for PAH ( Ktof 20 μM) and did not support estrone sulfate (ES) transport, whereas OAT3 had a high affinity for ES ( Ktof 4.5 μM) and a weak interaction with PAH (IC50> 1 mM). In contrast, both transporters robustly accumulated OTA. Intact RPT also accumulated OTA, with OAT1 and OAT3 each responsible for ∼50%: ES and PAH each reduced uptake by ∼50%, and the combination of the two eliminated mediated OTA uptake. The weak base CIM was transported by OAT3 ( Ktof 80 μM) and OCT2 ( Ktof 2 μM); OCT1 had a comparatively low affinity for CIM, and CIM uptake by OAT1 was equivocal. Intact RPT accumulated CIM, with TEA and ES reducing CIM uptake by 20 and 75%, respectively, suggesting that OAT3 plays a quantitatively more significant role in CIM uptake in the early proximal tubule than OCT1/2. In single S2 segments of RPT, ES and TEA each blocked ∼50% of CIM uptake. Thus the fractional contribution of different OE transporters to renal secretion is influenced by their affinity for substrate and relative expression level in RPT.

Ochratoxin A increases permeability through tight junctions by removal of specific claudin isoforms

On interaction with the intestine, the mycotoxin ochratoxin A is know to cause rapid inflammation, diarrhea, and increased bacterial translocation. All these effects are consistent with a decrease in epithelial barrier function. However, this has not been shown directly. We determined that ochratoxin A is able to reduce the barrier properties of the model intestinal cell line Caco-2. Over 24 h, ochratoxin A reduces the transepithelial electrical resistance of Caco-2 monolayers growing on Transwell filters by ∼40%. At the same time, the permeability of the monolayer is increased with respect to 4- and 10-kDa FITC dextrans, but not to 20- or 40-kDa dextrans. Immunoblotting and immuofluorescence reveal that the decrease in barrier properties is concomitant with disappearance of claudins 3 and 4, but not claudin 1 from Caco-2 cell membranes. These results suggest that ochratoxin A is able to modulate the barrier function of Caco-2 cells by removal of specific claudin isoforms.

The effects of the Penicillium mycotoxins citrinin, cyclopiazonic acid, ochratoxin A, patulin, penicillic acid, and roquefortine C on in vitro proliferation of porcine lymphocytes

The in vitro effect of each of the Penicillium mycotoxins citrinin (CIT), cyclopiazonic acid (CPA), ochratoxin A (OTA), patulin (PAT), penicillic acid (PIA) and roquefortine C (RQC) on mitogen induced lymphocyte proliferation was determined using purified lymphocytes from 6 piglets. Dose response curves for each mycotoxin were generated and the concentrations producing 50% inhibition of cell proliferation (IC(50)) were estimated. OTA and PAT were the most potent toxins with IC(50) of 1.3 and 1.2 micromol/l, respectively (0.52 and 0.18 mg/l, respectively). Based on molar concentrations, OTA was 15, 30, 40, and 65 times more potent as an inhibitor than PIA, CIT, CPA and RQC, respectively.

Increased Renal Fibrosis and Expression of Renal Phosphatidylinositol 4-Kinase-β and Phospholipase Cγ1 Proteins in Piglets Exposed to Ochratoxin-A

Endemic nephropathy has been linked to exposure of ochratoxin-A (OA) in grains and animal products. The underlying events surrounding this form of renal injury are not well known, partly due to the lack of a suitable animal model of the disease. Therefore, in this study, a pig model of OA-induced renal injury was established and used to examine whether elements of the phosphoinositide signalling pathway are altered in this disease. Weanling piglets were fed diets containing 0, 2, and 4 ppm OA for 6 weeks. Serum creatinine and urea and renal fibrosis were monitored biweekly using serial blood samples and renal biopsies. At termination, the protein levels of renal phosphatidylinositol 4-kinase-beta (PtdIns4Kbeta) and phospholipase C(gamma1) (PLC(gamma1)) were determined using immunoblotting and scanning densitometry. Serum creatinine was elevated by 2 weeks and renal fibrosis was elevated by 4 weeks at both levels of inclusion of OA. At the end of the experimental period, kidney size and water content were elevated, as were the protein levels of renal PtdIns4Kbeta and PLC(gamma1) in OA-exposed animals. Therefore, serial biopsies can be used to track changes in renal pathology in the OA-exposed piglet. We conclude that this is a useful model for OA-induced renal injury in which the underlying molecular events associated with this form of renal injury can be studied.

Ochratoxin A affects COS cell adhesion and signaling

Ochratoxin A (OTA), a metabolite produced by strains of Aspergillus and Penicillium, has nephritogenic, carcinogenic, and teratogenic activity in animals and humans. Nanomolar concentrations of OTA promote apoptosis in a cell-type specific fashion. In this study, we have analyzed the molecular mechanism by which OTA affects COS cell adhesion and signaling resulting in an apoptotic response. OTA, at noncytotoxic doses, was able to detach collagen- and fibronectin-adherent cells from immobilized substratum. However, prior to inducing detachment of adherent cells, OTA caused apoptosis as measured by caspase-3 activation. The treatment of adherent cells by OTA caused a reduction of tyrosine phosphorylation levels of FAK and of the adapter protein paxillin. The down-regulation of FAK preceded apoptosis and cell detachment induced by OTA. The mycotoxin was also able to cause a decrease of the phosphorylation levels of the two Shc isoforms, P66 and P52, in adherent cells. Since these Shc isoforms have been implicated in the activation of protein kinase c-Src, which is required for FAK tyrosine phosphorylation, the observed dephosphorylation of FAK and of the FAK substrate paxillin by OTA could be ascribed to the early down-regulation of Shc isoforms. However, whether FAK and Shc phosphorylation contribute both to the same pathway leading to the induction of apoptosis by OTA or are involved in two parallel signaling pathways remains to be investigated.

Evaluation of spermatological parameters in ochratoxin A--challenged boars

Exposure to certain mycotoxins has been proved to contribute to fertility problems in pigs. Although ochratoxin A (OA) is one of the most common naturally occurring mycotoxins, there is little data concerning the possible effects of this toxin on sperm quality of boars. After a 4-week control period, animals were given 20 microg OA per os daily for 6 weeks, followed by a 9-week withdrawal period. Serum and seminal plasma were monitored for OA with enzyme-linked immunosorbent assay (ELISA). Spermatozoal motility was measured at 0, 24, 48, 72 and 96 h, and ejaculation volume, initial viability and progressive motility were recorded. Samples of testis and epidydimidis were evaluated histologically. Viability, initial forward motility, and motility after 24h storage were significantly reduced in the experimental group in the withdrawal period only. There were no major histological differences in number and morphology of Leydig cells and epydidimal structures between experimental and control boars. Results of the present study demonstrate that OA may affect sperm production and boar semen quality only after a lag period. Further research is required to elucidate the possibility of a direct or indirect interaction between the toxin and germ cells (spermatogonia).

Inhibition of mitochondria prevents cell death in kidney epithelial cells by intra- and extracellular acidification

BACKGROUND

Nephrotoxic substances like cisplatin or ochratoxin A (OTA) induce cell death in human proximal tubule-derived cells (IHKE cells). Mitochondria play a significant role in apoptosis and loss of their function may influence OTA- or cisplatin-induced apoptosis. Extracellular pH also plays an important role in tumor genesis. Therefore, we investigated the role of mitochondria and intra- and extracellular pH on cell death induction by cisplatin or OTA.

METHODS

IHKE cells were incubated in the presence of OTA or cisplatin, together with inhibitors of the mitochondrial metabolism, and the activity of caspase-3 was measured and DNA laddering was monitored. Adenosine triphosphate (ATP) content of the cells, lactate release into the media, and glucose consumption was determined. In addition, media and cells were acidified or alkalized artificially to investigate the effect of intra- and extracellular pH on cell death induction. Cytochrome C was immunodetected in cellular compartments.

RESULTS

Inhibition of the mitochondrial function reduced OTA- or cisplatin-induced cell death and led to considerable lactic acid production and extracellular acidification. Intra- and extracellular acidification prevented cells from cell death induced by OTA or cisplatin. No cytochrome C release from mitochondria could be detected during 24 hours of exposure to OTA or cisplatin.

CONCLUSION

We conclude that OTA- or cisplatin-induced cell death is dependent on functional and intact, ATP-producing mitochondria and that intra- and extracellular pH is crucial for induction of cell death in IHKE cells.

Depletion of intracellular Ca2+ stores sensitizes the flow-induced Ca2+ influx in rat endothelial cells

Hemodynamic shear stress elicits a rise in endothelial [Ca2+]i, which may serve as a key second messenger to regulate many flow-associated physiological and biochemical processes. In the present study, we used Mn2+ quenching of fluorescent dye Fluo3 as an assay to investigate the Ca2+ influx of rat aortic endothelial cells in response to flow. We found that the Ca2+ signaling in response to flow could be greatly influenced by the status of intracellular Ca2+ stores. Depletion of intracellular Ca2+ stores by thapsigargin (4 micromol/L) or cyclopiazonic acid (10 micromol/L) drastically sensitized the Ca2+ influx in response to flow. Ca2+-mobilizing agonist bradykinin (100 nmol/L) or ATP (100 micromol/L) had similar sensitizing effect. The effect of bradykinin or ATP was blocked by Xestospongin C and U73122, suggesting that the sensitization was related to the IP3-mediated store depletion. On the other hand, the Mn2+ quenching in response to flow was greatly reduced by ochratoxin A (100 nmol/L), an agent that could increase the filling state of intracellular Ca2+ stores. In addition, we found that depletion-sensitized Ca2+ influx in response to flow was mediated by a PKG-inhibitable cation channel and that the influx was affected by membrane potential and K+ channel activity. In conclusion, the present study argues for a critical role of intracellular Ca2+ status in determining the Ca2+ signaling in response to flow and it provides a general mechanistic explanation for the stimulatory role of blood-borne agonists on flow-induced Ca2+ influx.

Effects of ochratoxin A on micronucleus frequency in human lymphocytes

Ochratoxin A (OTA), a nephrotoxic and carcinogenic mycotoxin, was investigated to examine its potency to induce micronuclei (MN) in cultured human lymphocytes. Lymphocyte cultures were treated for the last 48 h with OTA at concentrations of 25 microM, 10 microM, 1 microM, 100 nM, 10 nM, 1 nM, and 100 microM and absolute ethanol. At the highest concentration, OTA was found to induce MN in cytokinesis-blocked lymphocytes (p < 0.05). The 25 microM OTA concentration also led to a clear decrease in the percentage of binucleated cells, probably due to cytotoxicity. OTA at the other concentrations tested did not induce MN frequency. These results indicate that a high concentration of OTA is genotoxic in cultured human lymphocytes.

[In vitro studies into the influence of ochratoxin A on the production of tumor necrosis factor alpha by the human monocytic cell line THP-1]

The influence of pure OTA and an Aspergillus-ochraceus crude toxin on the intracellular expression and the secretion of tumor necrosis factor (TNF) alpha by the monocytic cell line THP-1 was studied in vitro. After 4 hours exposure, the secretion of TNF alpha was inhibited to 50% by pure OTA in a concentration of 400 ng/ml and by crude toxin in a concentration of 100 ng/ml. The same concentrations of mycotoxins impaired the mitochondrial activity of THP-1 cells only marginally. The intracellular expression of TNF alpha was not disturbed by pure OTA in the concentrations tested, whereas crude toxin showed an inhibitory effect. The possible reasons for these findings are discussed.

Determination of the epigenetic effects of ochratoxin in a human kidney and a rat liver epithelial cell line

Epidemiological studies have implicated ochratoxin A (OTA), a fungal metabolic-contaminant of animal and human food sources, in Balkan Endemic Nephropathy and renal tumors. Many environmental toxicants operate through nongenotoxic mechanisms that epigenetically control gene expression leading to a diseased state. Gap junctional intercellular communication (GJIC) plays a central role in the epigenetic control of genes in which alteration of normal GJIC has been implicated in many human pathologies, including cancer, teratogenesis, reproductive dysfunction and peripheral neuropathies. The cell proliferative stages of human diseases, such as cancer, also involves the induction of signal transduction pathways controlling the mitogenic steps, in which the mitogen activated protein kinases (MAPK), such as extracellular receptor kinase (ERK) and p38, are central to mitogenesis. We therefore determined the effects of OTA on GJIC and MAPK in a human kidney and rat liver epithelial cell line. OTA reversibly inhibited GJIC at noncytotoxic doses in the rat liver but not the human kidney cell line. Similarly, OTA was also a strong activator of MAPK, ERK and p38, in the rat liver cells but only weakly activated ERK and had no affect on p38 in the human kidney cell line. Another hallmark of human diseases is an abnormal alteration of apoptosis, also known as programmed cell death. We used our myc-transfected cell line, which exhibits higher levels of apoptosis, to test the effects of OTA on apoptosis. OTA greatly induced apoptosis in this cell line, which is contrary to the effects of most tumor promoters. In summary, OTA exhibits tumor promoting properties in the liver, but the effects of OTA on the human kidney epithelial cells suggested a lack of tumorigenic activity assuming that these epithelial cells, like the rat liver epithelial cells, are a primary target for carcinogens. These results also indicate that the nephrotoxicity of OTA either does not involve GJIC, assuming these epithelial cells play a vital role in kidney physiology, or that a more differentiated kidney cell type is the target for OTA toxicity, of which the role of GJIC remains unknown.