Species- and sex-specific renal cytotoxicity of ochratoxin A and B in vitro

Effects of acute insecticide exposure on neuronal activity in vitro in rat cortical cultures

Exposure to pesticides, such as carbamates, organophosphates, organochlorines and pyrethroids, has been linked to various health problems, including neurotoxicity. Although most in vivo studies use only male rodents, some studies have shown in vivo sex-specific effects after acute exposure. Since in vivo studies are costly and require a large number of animals, in vitro assays that take sex-specific effects into account are urgently needed. We therefore assessed the acute effects of exposure to different carbamates (methomyl, aldicarb and carbaryl), organophosphates (chlorpyrifos (CPF), chlorpyrifos-oxon (CPO) and 3,5,6-trichloropyridinol), organochlorines (endosulfan, dieldrin and lindane) and pyrethroids (permethrin, alpha-cypermethrin and 3-phenoxy-benzoic acid (3-PBA)) on neuronal network function in sex-separated rat primary cortical cultures using micro-electrode array (MEA) recordings. Our results indicate that exposure to the carbamate carbaryl and the organophosphates CPF and CPO decreased neuronal activity, with CPO being the most potent. Notably, (network) burst patterns differed between CPF and CPO, with CPO inducing fewer, but more intense (network) bursts. Exposure to low micromolar levels of endosulfan induced a hyperexcitation, most likely due to the antagonistic effects on GABA receptors. Interestingly, females were more sensitive to endosulfan than males. Exposure to dieldrin and lindane also increased neuronal activity, albeit less than endosulfan and without sex-specific effects. Exposure to type I pyrethroid permethrin increased neuronal activity, while exposure to type II pyrethroid alpha-cypermethrin strongly decreased neuronal activity. The increase seen after permethrin exposure was more pronounced in males than in females. Together, these results show that acute exposure to different classes of pesticides exerts differential effects on neuronal activity. Moreover, it shows that MEA recordings are suited to detect sex-specific neurotoxic effects in vitro.

Protective Effect of alpha-Tocopherol against Ochratoxin A in Kidney Cell Line HK-2

Food safety is a top priority for the protection of infants and young children. Ochratoxin A (OTA) is an emerging concern due to its high toxicity and occurrence in a wide range of agricultural crops and their derived food products including those foods and snacks destined for infants and young children. OTA is considered as a possible human carcinogen and its main target organ is the kidney. The objective of this study was to investigate the protective effect of α-tocopherol against oxidative stress induced by OTA using human proximal tubule epithelial cells (HK-2). OTA showed dose-dependent increase in cytotoxicity (IC₅₀ = 161 nM, p<0.05) at 48 h, while treatment up to 2 mM α-tocopherol did not change cell viability. Levels of the reduced form of glutathione (GSH) were decreased with α-tocopherol treatment, although the ratio of the oxidative form (GSSG) to GSH remained the same. Among several genes associated with oxidative stress, expression of superoxide dismutase 1 (SOD1), catalase (CAT), glutathione reductase (GSR), and kidney injury molecule-1 (KIM-1) were significantly up-regulated by OTA treatment. CAT and GSR showed decreased expression at 0.5 - 2 mM α-tocopherol and OTA at IC₅₀ value, KIM-1 was decreased at 0.5 mM α-tocopherol and OTA at IC₅₀ value, and nuclear factor erythroid 2-related factor 2 (Nrf2) was decreased at 0.5 - 1 mM α-tocopherol and OTA at IC₅₀ value. In addition, the levels of malondialdehyde (MDA) were increased significantly by OTA while significantly decreased by α-tocopherol. The results show that α-tocopherol may alleviate potential OTA-induced renal damage and oxidative stress through reducing cytotoxicity and enhancing the antioxidant defense systems.

Cytotoxicity of Mycotoxins and Their Combinations on Different Cell Lines: A Review

Mycotoxins are secondary metabolites of molds and mainly produced by species of the genera Aspergillus, Penicillium and Fusarium. They can be synthesized on the field, during harvest as well as during storage. They are fairly stable compounds and difficult to remove. Among several hundreds of mycotoxins, according to the WHO, ochratoxin A, aflatoxins, zearalenone, deoxynivalenol, patulin, fumonisins as well as T-2 and HT-2 toxins deserve special attention. Cytotoxicity is one of the most important adverse properties of mycotoxins and is generally assessed via the MTT assay, the neutral red assay, the LDH assay, the CCK-8 assay and the ATP test in different cell lines. The apoptotic cell ratio is mainly assessed via flow cytometry. Aside from the assessment of the toxicity of individual mycotoxins, it is important to determine the cytotoxicity of mycotoxin combinations. Such combinations often exhibit stronger cytotoxicity than individual mycotoxins. The cytotoxicity of different mycotoxins often depends on the cell line used in the experiment and is frequently time- and dose-dependent. A major drawback of assessing mycotoxin cytotoxicity in cell lines is the lack of interaction typical for complex organisms (for example, immune responses).

The individual and combined effects of ochratoxin A with citrinin and their metabolites (ochratoxin B, ochratoxin C, and dihydrocitrinone) on 2D/3D cell cultures, and zebrafish embryo models

Ochratoxin A and citrinin are nephrotoxic mycotoxins produced by Aspergillus, Penicillium, and/or Monascus species. The combined effects of ochratoxin A and citrinin have been examined in more studies; however, only limited data are available regarding the co-exposure to their metabolites. In this investigation, the individual toxic effects of ochratoxin A, ochratoxin B, ochratoxin C, citrinin, and dihydrocitrinone were tested as well as the combinations of ochratoxin A with the latter mycotoxins were examined on 2D and 3D cell cultures, and on zebrafish embryos. Our results demonstrate that even subtoxic concentrations of certain mycotoxins can increase the toxic impact of ochratoxin A. In addition, typically additive effects or synergism were observed as the combined effects of mycotoxins tested. These observations highlight that different cell lines (e.g. MDBK vs. MDCK), cell cultures (e.g. 2D vs. 3D), and models (e.g. in vitro vs. in vivo) can show different (sometimes opposite) impacts. Mycotoxin combinations considerably increased miR-731 levels in zebrafish embryos, which is an early marker of the toxicity on kidney development. These results underline that the co-exposure to mycotoxins (and/or mycotoxin metabolites) should be seriously considered, since even the barely toxic mycotoxins (or metabolites) in combinations can cause significant toxicity.

Human Proximal Tubule Epithelial Cells (HK-2) as a Sensitive In Vitro System for Ochratoxin A Induced Oxidative Stress

Ochratoxin A (OTA) is a mycotoxin that is potentially carcinogenic to humans. Although its mechanism remains unclear, oxidative stress has been recognized as a plausible cause for the potent renal carcinogenicity observed in experimental animals. The effect of OTA on oxidative stress parameters in two cell lines of LLC-PK1 and HK-2 derived from the kidneys of pig and human, respectively, were investigated and compared. We found that the cytotoxicity of OTA on LLC-PK1 and HK-2 cells was dose- and time-dependent in both cell lines. Furthermore, increased intracellular reactive oxygen species (ROS) induced by OTA in both cell lines were observed in a time-dependent manner. Glutathione (GSH) was depleted by OTA at >48 h in HK-2 but not in LLC-PK1 cells. While the mRNA levels of glucose-6-phosphate dehydrogenase (G6PD) and glutathione peroxidase 1 (GPX1) in LLC-PK1 were down-regulated by 0.67- and 0.66-fold, respectively, those of catalase (CAT), glutathione reductase (GSR), and superoxide dismutase 1 (SOD) in HK-2 were up-regulated by 2.20-, 2.24-, and 2.75-fold, respectively, after 72 h exposure to OTA. Based on these results, we conclude that HK-2 cells are more sensitive to OTA-mediated toxicity than LLC-PK1, and OTA can cause a significant oxidative stress in HK-2 as indicated by changes in the parameter evaluated.

Cytotoxicity of Mycotoxins Frequently Present in Aquafeeds to the Fish Cell Line RTGill-W1

In the last decades, the aquaculture industry has introduced plant-based ingredients as a source of protein in aquafeeds. This has led to mycotoxin contaminations, representing an ecological, health and economic problem. The aim of this study was to determine in the RTgill-W1 fish cell line the toxicity of fifteen mycotoxins of common occurrence in aquafeeds. To identify the most sensitive endpoint of toxicity, the triple assay was used. It consisted of three assays: alamarBlue, Neutral Red Uptake and CFDA-AM, which revealed the mitochondrial activity, the lysosomal integrity and the plasma membrane integrity, respectively. Most of the assayed mycotoxins were toxic predominantly at lysosomal level (enniatins, beauvericin, zearalenone, ochratoxin A, deoxynivalenol (DON) and its acetylated metabolites 15-O-acetyl-DON and 3-acetyl-DON). Aflatoxins B1 and B2 exerted the greatest effects at mitochondrial level, while fumonisins B1 and B2 and nivalenol were not toxic up to 100 µg/mL. In general, low toxicity was observed at plasma membrane level. The vast majority of the mycotoxins assayed exerted a pronounced acute effect in the fish RTgill-W1 cell line, emphasizing the need for further studies to ascertain the impact of mycotoxin contamination of fish feeds in the aquaculture industry and to establish safe limits in aquafeeds.

Evaluation of renal in vitro models used in ochratoxin research

Ochratoxin A (OTA) induces renal carcinomas in rodents with a specific localisation in the S3 segment of proximal tubules and distinct early severe tissue alterations, which have been observed also in other species. Pronounced species- and sex-specific differences in toxicity occur and similar effects cannot be excluded in humans, however precise mechanism(s) remain elusive until today. In such cases, the use of in vitro models for mechanistic investigations can be very useful; in particular if a non-genotoxic mechanism of cancer formation is assumed which include cytotoxic effects. However, potential genotoxic mechanisms can also be investigated in vitro. A crucial issue of in vitro research is the choice of the appropriate cell model. Apparently, the cellular target of OTA is the renal proximal tubular cell; therefore cells from this tissue area are the most reasonable model. Furthermore, cells from affected species should be used and can be compared to cells of human origin. Another important parameter is whether to use primary cultures or to choose a cell line from the huge variety of cell lines available. In any case, important characteristics and quality controls need to be verified beforehand. Therefore, this review discusses the renal in vitro models that have been used for the investigation of renal ochratoxin toxicity. In particular, we discuss the choice of the models and the essential parameters making them suitable models for ochratoxin research together with exemplary results from this research. Furthermore, new promising models such as hTERT-immortalised cells and 3D-cultures are briefly discussed.

Comparative Ochratoxin Toxicity: A Review of the Available Data

Ochratoxins are a group of mycotoxins produced by a variety of moulds. Ochratoxin A (OTA), the most prominent member of this toxin family, was first described by van der Merwe et al. in Nature in 1965. Dietary exposure to OTA represents a serious health issue and has been associated with several human and animal diseases including poultry ochratoxicosis, porcine nephropathy, human endemic nephropathies and urinary tract tumours in humans. More than 30 years ago, OTA was shown to be carcinogenic in rodents and since then extensive research has been performed in order to investigate its mode of action, however, this is still under debate. OTA is regarded as the most toxic family member, however, other ochratoxins or their metabolites and, in particular, ochratoxin mixtures or combinations with other mycotoxins may represent serious threats to human and animal health. This review summarises and evaluates current knowledge about the differential and comparative toxicity of the ochratoxin group.

Primary porcine proximal tubular cells as an alternative to human primary renal cells in vitro: an initial characterization

Background

A good in vitro model should approximate an in vivo-like behavior as closely as possible in order to reflect most likely the in vivo situation. Regarding renal physiology of different species, humans are more closely related to pigs than to rodents, therefore primary porcine kidney cells (PKC) and their subsequent cell strain could be a valid alternative to primary human cells for renal in vitro toxicology. For this PKC must display inherent characteristics (e.g. structural organization) and functions (e.g. transepithelial transport) as observed under in vivo conditions within the respective part of the kidney.

Results

We carried out a comprehensive characterization of PKC and their subsequent cell strain, including morphology and growth as well as transporter expression and functionality. The data presented here demonstrate that PKC express various transporters including pMrp1 (abcc1), pMrp2 (abcc2), pOat1 (slc22a6) and pOat3 (slc22a8), whereas pMdr1 (abcb1) and pOatp1a2 (slco1a2) mRNA could not be detected in either the PKCs or in the porcine cortical tissue. Functionality of the transporters was demonstrated by determining the specific PAH transport kinetics.

Conclusions

On the basis of the presented results it can be concluded that PKC and to some extent their subsequent cell strain represent a valuable model for in vitro toxicology, which might be used as an alternative to human primary cells.

A review on ochratoxin A transcriptomic studies

The mycotoxin Ochratoxin A (OTA) is a potent renal carcinogen in male rats. Transcriptomic studies on OTA (4 in vitro, 6 in vivo, 2 in vitro/in vivo) have been reviewed. The aim of 6 of them was mainly mechanistic whereas the rest had mostly predictive (1) or evaluation (5) purposes. An overall tendency towards gene expression downregulation was observed, probably as a result of protein synthesis inhibition. DNA damage response genes were not deregulated in most of the studies. Genes involved in acute renal injury, cell survival and cell proliferation were upregulated in several in vivo studies. Apoptosis genes were deregulated in vitro but less affected in vivo; activation of several MAPKs has been observed. Many genes related to oxidative stress or involved in cell-to-cell interaction pathways (Wnt) or cytoskeleton structure appeared to be deregulated either in vitro or in vivo. Regucalcin was highly downregulated in vivo and other calcium homeostasis genes were significantly deregulated in vitro. Genes related to OTA transport (OATs) and metabolism (CYPs) appeared downregulated in vivo. Overall, the mechanism of action of OTA remains unclear, however transcriptomic data have contributed to new mechanistic hypothesis generation and to in vitro-in vivo comparison.

Cross-talk between microRNAs, nuclear factor E2-related factor 2, and heme oxygenase-1 in ochratoxin A-induced toxic effects in renal proximal tubular epithelial cells

SCOPE

Ochratoxin A (OTA) is a mycotoxin exhibiting nephrotoxic and potential carcinogenic activity. We investigated the cross-talk between microRNAs, nuclear factor E2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) in ochratoxin A-mediated effects.

METHODS AND RESULTS

In porcine renal proximal tubular cells, OTA increased expression of profibrotic transforming growth factors β (TGFβ) while concomitantly decreasing expression of Nrf2, HO-1, and erythropoietin. Adenoviral overexpression of Nrf2 counteracted OTA-mediated reduction in HO-1 and erythropoietin expression and cell proliferation as well as increase in reactive oxygen species (ROS) generation and TGFβ expression. Additionally, inhibition of HO activity enhanced whereas adenoviral overexpression of HO-1 reduced expression of TGFβ. Moreover, antioxidants, N-acetyl-cysteine and desferioxamine, prevented OTA-mediated enhancement of ROS generation, and TGFβ expression. Finally, OTA modulated microRNA processing by upregulating LINeage protein 28 and DiGeorge syndrome critical region-8, increasing the total pool of cellular microRNAs and elevating the expression of miR-132 and miR-200c. Inhibition of miR-132 by specific antagomir restored the OTA-driven reduction in Nrf2 expression. Moreover, anti-miR-132 and anti-miR-200c counteracted OTA-mediated decrease in HO-1 levels as well as increase in ROS production and TGFβ expression.

CONCLUSION

We showed that attenuation of Nrf2 and HO-1 expression through induction of miR-132 and miR-200c by OTA elevates ROS levels and profibrotic TGFβ expression.

Toxin content and cytotoxicity of algal dietary supplements

Blue-green algae (Spirulina sp., Aphanizomenon flos-aquae) and Chlorella sp. are commercially distributed as organic algae dietary supplements. Cyanobacterial dietary products in particular have raised serious concerns, as they appeared to be contaminated with toxins e.g. microcystins (MCs) and consumers repeatedly reported adverse health effects following consumption of these products. The aim of this study was to determine the toxin contamination and the in vitro cytotoxicity of algae dietary supplement products marketed in Germany. In thirteen products consisting of Aph. flos-aquae, Spirulina and Chlorella or mixtures thereof, MCs, nodularins, saxitoxins, anatoxin-a and cylindrospermopsin were analyzed. Five products tested in an earlier market study were re-analyzed for comparison. Product samples were extracted and analyzed for cytotoxicity in A549 cells as well as for toxin levels by (1) phosphatase inhibition assay (PPIA), (2) Adda-ELISA and (3) LC-MS/MS. In addition, all samples were analyzed by PCR for the presence of the mcyE gene, a part of the microcystin and nodularin synthetase gene cluster. Only Aph. flos-aquae products were tested positive for MCs as well as the presence of mcyE. The contamination levels of the MC-positive samples were ≤ 1 μg MC-LR equivalents g(-1) dw. None of the other toxins were found in any of the products. However, extracts from all products were cytotoxic. In light of the findings, the distribution and commercial sale of Aph. flos-aquae products, whether pure or mixed formulations, for human consumption appear highly questionable.

Displacement immunoassay for the detection of ochratoxin A using ochratoxin B modified glass beads

We report here the development of a new assay for the detection of ochratoxin A (OTA) based on the use of its dechlorinated analogue, ochratoxin B (OTB), in a displacement immunoassay. OTB was immobilised on controlled-pore glass beads followed by the binding of anti-OTA antibody, with anti-IgG antibody peroxidase conjugate used as a label. In this manner, an original bio-sensing material was obtained. Upon incubation of this material with OTA, the toxin competes with OTB for the binding sites of the anti-OTA antibodies and releases the antibody-tagged peroxidase complex into the solution. Compared to classic competitive immunoassays, this newly developed displacement immunoassay presents a similar detection limit and assay time. Moreover, the detection, based on the activity of the horseradish peroxidase, is performed for the first time in situ using wine samples.

Aristolochic acid I and ochratoxin A differentially regulate VEGF expression in porcine kidney epithelial cells--the involvement of SP-1 and HIFs transcription factors

Aristolochic acid I (AAI) and ochratoxin A (OTA) cause chronic kidney diseases. Recently, the contribution of hypoxic injuries and angiogenic disturbances to nephropathies has been suggested, but underlying mechanisms have not been fully clarified yet.

In porcine kidney epithelial cell line, LLC-PK1 cells, treatment with non-toxic doses of AAI increased whereas with OTA decreased production of vascular endothelial growth factor (VEGF), the angiogenic factor with well-defined functions in kidney. Moreover, the activity of transcription factors regulating VEGF expression was differentially affected by examined compounds. Activity of hypoxia inducible factors (HIFs) and SP-1 was increased by AAI but diminished by OTA. Interestingly, AP-1 activity was inhibited while NFκB was not influenced by both toxins. Mithramycin A, a SP-1 inhibitor, as well as chetomin, an inhibitor of HIFs, reversed AAI-induced up-regulation of VEGF synthesis, indicating the importance of SP-1 and HIFs in this effect. Additionally, adenoviral overexpression of HIF-2α but not HIF-1α prevented OTA-diminished VEGF production suggesting the protective effect of this isoform towards the consequences exerted by OTA.

These observations provide new insight into complex impact of AAI and OTA on angiogenic gene regulation. Additionally, it adds to our understanding of hypoxia influence on nephropathies pathology.

Development and characterization of a monoclonal antibody against Ochratoxin B and its application in ELISA

A monoclonal antibody specific to ochratoxin B (OTB) was employed for the development of an indirect competitive OTB-ELISA. The optimized OTB-ELISA resulted in a limit of detection (LOD) for OTB of 3 µg/L (8 nM), a limit of quantification (LOQ) of 3.7 µg/L (10 nM), and a 50% inhibitory concentration (IC(50)) of 150 nM. Due to very low cross-reactivity to OTA (2.7%) and structurally related molecules (0%), this OTB-ELISA was found to be suitable to detect OTB with excellent precision in different matrices, i.e., beer, coffee and wine. Therefore, this OTB-ELISA will allow screening of OTB in food and feed products.

The use of the Integrated Discrete Multiple Organ Co-culture (IdMOC) system for the evaluation of multiple organ toxicity

The application of the Integrated Discrete Multiple Organ Co-culture (IdMOC) system in the evaluation of organ-specific toxicity is reviewed. In vitro approaches to predict in vivo toxicity have met with limited success, mainly because of the complexity of in vivo toxic responses. In vivo properties that are not well-represented in vitro include organ-specific responses, multiple organ metabolism, and multiple organ interactions. The IdMOC system has been developed to address these deficiencies. The system uses a 'wells-within-a-well' concept for the co-culturing of cells or tissue slices from different organs as physically separated (discrete) entities in the small inner wells. These inner wells are nevertheless interconnected (integrated) by overlying culture medium in the large outer containing well. The IdMOC system thereby models the in vivo situation, in which multiple organs are physically separated but interconnected by the systemic circulation, permitting multiple organ interactions. The IdMOC system, with either cells or tissue slices from multiple organs, can be used to evaluate cell type-specific or organ-specific toxicity.

Oxidative stress induced by ochratoxin A in LLC-PK1 cell line and the chemoprotective effects of carnosic acid

Mycotoxins are secondary metabolites of various moulds that contaminate several alimentary substrates. One of the most dangerous of these is ochratoxin A (OTA). Reactive oxygen species (ROS) play an important role in the toxicity mechanism of OTA, so the use of natural or synthetic free radical scavengers could be a potential chemopreventive strategy. Carnosic acid (CA) is the major polyphenolic compound present in rosemary plants. This work aimed to determine whether CA could counteract OTA-induced cell damage. Free radical scavenging properties of CA were chemically determined at pH 7.4. Cytotoxicity of CA and OTA on LLC-PK1 cells, and the protective effects of CA, were assessed using the Alamar Blue test. The effects in vitro of CA pre-treatment on the production of ROS, the DNA oxidation and the induction of apoptosis induced by OTA were studied. It was found that CA has free radical scavenging properties at both the considered pH values. Moreover, a pre-treatment of 24 h with 10, 20 and 30 µM CA is able to reduce OTA-induced cytotoxicity; a pre-treatment of 24 h with 20 and 30 µM CA achieved ROS reduction and with 30 µM CA decreased the OTA-induced increase of 8-OH-2'-deoxyguanosine and of DNA fragmentation in LLC-PK1. These findings suggest a starting point to develop alimentary strategies against OTAinduced cell damage. Moreover, our results provide further evidence that oxidative stress plays an important role in the OTA cytotoxicity mechanism.

Catechins: natural free-radical scavengers against ochratoxin A-induced cell damage in a pig kidney cell line (LLC-PK1)

Besides aflatoxin B1, recent findings suggested that oxidative stress plays an important role in the toxicity of an other mycotoxin: ochratoxin A (OTA). The protective effect of two catechins (epigallocatechin gallate, EGCG, and epicatechin gallate, ECG) against OTA-induced cytotoxicity was investigated in a pig kidney cell line (LLC-PK1). The ability of the catechins to reduce ROS production and DNA fragmentation induced by OTA was also investigated. Our experiments proved the significant cytoprotective effects of the molecules in vitro from OTA-induced cell damage. In particular a 24h pre-treatment with EGCG or ECG restored cell viability with respect to OTA alone. Pre-treatment with EGCG at low concentration for 8 days protected cells from OTA-induced cell death. Moreover both catechins reduced OTA-induced ROS production. A reduction of OTA-induced DNA fragmentation was found for LLC-PK1 cells pre-treated with EGCG and ECG. The free-radical scavenging capacity of both catechins was tested with the Briggs-Rauscher oscillating method (pH approximately 2) and the TEAC assay (pH 7.4). The results show a good scavenging power according with inhibition of ROS production. Catechins could be useful to develop alimentary strategies for both humans and animals to prevent OTA-induced cytotoxicity.

Production and characterization of monoclonal antibodies against ochratoxin B

Monoclonal antibodies against ochratoxin B (OTB) were generated by immunizing Balb/c mice with OTB conjugated to keyhole limpet hemocyanin (KLH) via carbodiimide reactions with CHMC and EDAC. A stable hybridoma cell line 2F1.E10 was produced by fusion of murine splenocytes and myeloma cells. The obtained antibodies were characterized using an indirect competitive ELISA. The detection limit was calculated (27+/-2 nM OTB) and 50% binding inhibition was reached at 500 nM free OTB. A low cross-reactivity to ochratoxin A (OTA) of 3.3% and no cross-reactivities to either coumarin or DL-phenylalanine were observed, suggesting a highly specific OTB antibody. The antibody type was identified as IgG class 1 with the light chain being of the kappa configuration. These antibodies can be used in an indirect competitive ELISA to detect OTB in the nanomolar to micromolar concentration range and may be useful for the analysis of contaminated food items.

Effects of repeated ochratoxin exposure on renal cells in vitro

In the present study an in vitro model of subchronic repeated exposure to OTA and OTB was employed to generate ochratoxin-derived subpopulations of human and porcine proximal tubular cells (HKC, IHKE, PKC, LLC-PK1). These cell subpopulations were subsequently used to investigate effects on cell proliferation rates, expression of marker proteins (cytokeratins, vimentin) and the acute cytotoxicity of OTA and OTB (MTT reduction, neutral red uptake, cell number). The hypothesis was tested whether repeated exposure at moderate concentrations of these toxins could provide for a reduced sensitivity of selected cell subpopulations to subsequent toxin exposure. Despite the observed increased cell population doubling times and the reduced sensitivity toward OTA and OTB exposure of some cell types, with the exception of the primary human epithelial cells, no overt changes in the expression of cytokeratin and vimentin could be determined. The presented data, however suggest that repeated exposure of renal epithelial cells to ochratoxins A or B will provide for a subpopulation of cells with reduced ochratoxin-sensitivity and alterations in growth characteristics.

Human primary renal cells as a model for toxicity assessment of chemo-therapeutic drugs

Chemo-therapeutic drugs act on cancerous and normal cells non-selectively and often cause organ impairments during treatment. Improving safety or reducing toxicity becomes an important challenge for developing better anticancer drugs. In the present study, effects of selected anticancer drugs (camptothecin, doxorubicin, colchicine, paclitaxel, cisplatin, and carboplatin) on cell viability and proliferation was investigated. The anti-proliferative activity of each drug on cancer cells (human hepatoma HepG2) and human primary renal proximal tubule cells (hRPTECs and LLC-PK1) was determined with the [(3)H]thymidine incorporation assay. Results indicated all six drugs blocked cell proliferation in cancer and normal cells. When the anti-proliferation potency was ranked in hRPTECs based on EC50 values, camptothecin is the most potent, followed by doxorubicin, paclitaxel, colchicine, cisplatin and carboplatin. Cytotoxicity of drugs to hRPTECs was assessed with the ATP bioluminescence assay. Doxorubicin and cisplatin were known to induce nephrotoxicity in vivo and they were indeed cytotoxic to hRPTECs in our study with EC50 values at 11.2 and 39.6 microM. All other drugs are not cytotoxic in the concentrations tested. These drugs typically displayed separation of EC50s between potency (anti-proliferation) and cytotoxicity. The dose separation provides a concentration range for each drug to act on cell proliferation without induction of significant cytotoxicity. Our results suggest that hRPTEC system can serve as an in vitro model for assessing potential nephrotoxicity of chemo-therapeutic drugs.

In vitro investigation of individual and combined cytotoxic effects of ochratoxin A and other selected mycotoxins on renal cells

Hundreds of mycotoxins are known to date and many of them are of great interest with regard to human and animal health since they are detected frequently in plant-derived products. Various mycotoxins may occur simultaneously, depending on the environmental and substrate conditions. Considering this coincident production, it is very likely, that humans and animals are always exposed to mixtures rather than to individual compounds. Therefore, future risk assessments should consider mixture toxicity data. This is particularly true for ochratoxin A (OTA), ochratoxin B (OTB), citrinin (CIT) and occasionally for patulin (PAT) as they are all produced by a number of Penicillium and Aspergillus species. Therefore, these four toxins were chosen to study the interactive effects in vitro, using the well-established porcine renal cell line LLC-PK1 and the MTT reduction test as a cytotoxicity endpoint. By application of a step-wise approach to test combination toxicity, using various full factorial as well as a central composite experimental designs, the interactive (synergistic) cytotoxic effects of the these four toxins were assessed. The results obtained in this study confirm a potential for interactive (synergistic) effects of CIT and OTA and possibly other mycotoxins in cells of renal origin.

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.

Biotransformation and nephrotoxicity of ochratoxin B in rats

Ochratoxin B (OTB), a secondary metabolite of Aspergillus ochraceus, is the nonchlorinated analogue of the mycotoxin ochratoxin A (OTA), which is one of the most potent renal carcinogens in rodents. Despite the closely related structure, OTB is considered to be of much lower toxicity. OTA is poorly metabolized and slowly eliminated, and this may play an important role in OTA toxicity, carcinogenicity, and organ specificity. Since little is known regarding biotransformation and renal toxicity of OTB, the aim of this study was to investigate biotransformation of OTB in rats and to characterize the nephrotoxicity and cytotoxicity of OTB. Male F344 rats were administered either a single dose of OTB (10 mg/kg bw) or repeated doses (2 mg/kg bw, 5 days/week for 2 weeks) and euthanized 72 h after the last dosing. In proximal tubule cells of animals treated with a single high dose of OTB, a slight increase in mitotic figures was observed, but no treatment-related changes were evident in clinical chemistry, in renal function, and histopathology after repeated administration. Excretion of OTB and metabolites in urine and feces was analyzed using both HPLC with fluorescence detection and LC-MS/MS. Ochratoxin beta, which results from cleavage of the peptide bond, was the major metabolite excreted in urine in addition to small amounts of 4-hydroxy-OTB. In total, 19% of the administered dose was recovered as OTB and ochratoxin beta in urine and feces within 72 h after a single dose. In contrast to OTA, no tissue-specific retention of OTB was evident after single and repeated administration. In LLC-PK1 cells, a renal cell culture system that retains much of the specific features of the proximal tubule, only minor differences in the extent of cytotoxicity of OTA and OTB were observed. At low concentrations (< 25 microM), treatment with OTA was slightly more toxic, whereas reduction in cell viability was similar at concentrations up to 100 microM. In summary, these data suggest that OTA and OTB have a similar potential to induce cytotoxicity in vitro, but large differences in their potential to induce nephrotoxicity in rodents. OTB is more extensively metabolized and more rapidly eliminated than OTA. The lack of specific retention of OTB in the kidneys and the differences in toxicokinetics may therefore provide an explanation for the lower toxicity of OTB.

Metabolism-mediated cytotoxicity of ochratoxin A

Ochratoxin A (OTA) is produced by various strains of Aspergillus and Penicillium and is a common contaminant of food commodities. OTA is metabolised by cytochrome P450 (CYP450) enzymes resulting in hydroxylated metabolites, 4R-OH-OTA and 4S-OH-OTA, and possibly in other minor metabolites including OTA-quinones. However, until now conflicting data have been presented regarding the role of biotransformation products in the adverse effects of OTA. Hence, the aim of this study was to further assess the metabolism-mediated cytotoxicity of OTA in an in vitro model encompassing NIH/3T3 cells, stably expressing the human CYP450 enzymes CYP2C9 and CYP3A4, respectively. In addition, modulation of the cellular glutathione (GSH) content was used to identify a role of GSH in OTA-induced cytotoxicity. Following exposure to OTA, cells expressing CYP2C9 showed a significant reduction in neutral red (NR) uptake but not in Alamar blue (AB) reduction, as compared to the control LNCX cells which do not express CYP450 enzymes. CYP3A4-expressing cells showed no difference in viability from control LNCX cells. When pre-treated with l-buthionine S,R-sulphoximine (BSO) to deplete GSH, CYP2C9-expressing cells showed also a loss of cell viability as compared to LNCX cells, although to a lesser extent as compared to non-depleted CYP2C9-expressing cells. Data presented in this study support previous findings, indicating that different biotransformation pathways contribute to the cytotoxicity induced by OTA.

Species- and sex-specific variations in binding of ochratoxin A by renal proteins in vitro

The mycotoxin ochratoxin A (OTA) is a potent renal carcinogen in rodents and induces renal fibrosis in pigs. Furthermore, OTA has been associated with the development of renal tumors and nephropathies in humans. Large species- and sex-differences are observed in sensitivity toward OTA-mediated toxicity and carcinogenicity, yet neither the mechanism(s) resulting in OTA toxicity nor the reasons for the observed species- and sex-specificities are known. This paper investigated variations in OTA handling viz binding to renal proteins which could possibly explain the observed differences in OTA susceptibility in vivo and in vitro. The results obtained via a modification of a standard receptor-binding assay demonstrated the presence of at least one homogeneous binding component in renal cortical homogenates from pig, mouse, rat and humans. This component was shown to bind OTA in a specific and saturable manner. A range of compounds selected for their affinity for steroid receptors and/or for various known organic anion transporters were employed in a competition assay to answer the question whether this homogenous OTA binding component represents a steroid-like receptor component or one of the known organic anion transporters of the kidney. Although many of the compounds were able to compete with OTA for protein-binding, the competition patterns displayed a distinct species specificity and did not correspond to the competition patterns associated with presently known organic anion transporters of the kidney in the mouse, rat or human. The data thus suggests the presence of a new organic anion transporter or more likely, a cytosolic binding component of unknown function with high affinity and capacity for OTA binding in humans, rats, mice and possibly pigs.