INDIVIDUAL AND COMBINED CYTOTOXIC EFFECTS OF THE MAJOR FOUR AFLATOXINS IN DIFFERENT IN VITRO STABILIZED SYSTEMS

Co-occurrence of mycotoxins: A review on bioanalytical methods for simultaneous analysis in human biological samples, mixture toxicity and risk assessment strategies

Mycotoxins are the toxic chemical substances that are produced by various fungal species and some of these are harmful to humans. Mycotoxins are ubiquitous in nature and humans could be exposed to multiple mycotoxins simultaneously. Unfortunately, exposure to mixed mycotoxins is not very well studied. Various studies have demonstrated the capacity of mycotoxins to show synergistic effect in the presence of other mycotoxins, thus, increasing the risk of toxicity. Hence, it is important to monitor mixed mycotoxins in human biological samples which would serve as a crucial information for risk assessment. Through this review paper, we aim to summarize the mixture toxicity of mycotoxins and the various bio-analytical techniques that are being used for the simultaneous analysis of mixed mycotoxins in human biological samples. Different sample preparation and clean-up techniques employed till date for eliminating the interferences from human biological samples without affecting the analyses of the mycotoxins are also discussed. Further, a brief introduction of risk assessment strategies that have been or could be adopted for multiple mycotoxin risk assessments is also mentioned. To the best of our knowledge, this is the first review that focuses solely on the occurrence of multiple mycotoxins in human biological samples as well as their risk assessment strategies.

Human biomonitoring of multiple mycotoxins in hair: first large-scale pilot study

Human biomonitoring (HBM) represents the most accurate approach for assessing the exposure to mycotoxins, but traditional matrices fail to provide information about long-term exposure due to the rapid excretion rates and short half-lives of mycotoxins. Hair emerges as a promising matrix considering that contaminants can form stable links with hair components, such as keratins and melanin. Hence, the aim of the present study was to monitor the presence of up to ten mycotoxins (aflatoxins and Fusarium mycotoxins) in human hair samples (n=100) through a high-performance liquid chromatography coupled to Q-TOF high resolution mass spectrometry. A prevalence of 43% at concentrations ranging from 2.7 to 106.1 ng/g was observed, being enniatins and aflatoxin B1 the most prevalent compounds. Co-occurrence of up to three mycotoxins was observed in 42% of the positive samples. Retrospective untargeted analysis of hair samples tentatively identified up to 128 mycotoxins and related metabolites. These results confirm the accumulation of toxicologically relevant mycotoxins in hair matrix, thus standing as a suitable matrix for assessing long-term exposure.

Mycotoxins co-contamination: Methodological aspects and biological relevance of combined toxicity studies

Mycotoxins are secondary fungal metabolites produced mainly by Aspergillus, Penicillium, and Fusarium. As evidenced by large-scale surveys, humans and animals are simultaneously exposed to several mycotoxins. Simultaneous exposure could result in synergistic, additive or antagonistic effects. However, most toxicity studies addressed the effects of mycotoxins separately. We present the experimental designs and we discuss the conclusions drawn from in vitro experiments exploring toxicological interactions of mycotoxins. We report more than 80 publications related to mycotoxin interactions. The studies explored combinations involving the regulated groups of mycotoxins, especially aflatoxins, ochratoxins, fumonisins, zearalenone and trichothecenes, but also the "emerging" mycotoxins beauvericin and enniatins. Over 50 publications are based on the arithmetic model of additivity. Few studies used the factorial designs or the theoretical biology-based models of additivity. The latter approaches are gaining increased attention. These analyses allow determination of the type of interaction and, optionally, its magnitude. The type of interaction reported for mycotoxin combinations depended on several factors, in particular cell models and the tested dose ranges. However, synergy among Fusarium toxins was highlighted in several studies. This review indicates that well-addressed in vitro studies remain valuable tools for the screening of interactive potential in mycotoxin mixtures.

Cytoprotective effect of palm kernel cake phenolics against aflatoxin B1-induced cell damage and its underlying mechanism of action

Background

Palm kernel cake (PKC), a by-product of the palm oil industry is abundantly available in many tropical and subtropical countries. The product is known to contain high levels of phenolic compounds that may impede the deleterious effects of fungal mycotoxins. This study focused on the evaluation of PKC phenolics as a potential cytoprotective agent towards aflatoxin B1 (AFB1)-induced cell damage.

Methods

The phenolic compounds of PKC were obtained by solvent extraction and the product rich in phenolic compounds was labeled as phenolic-enriched fraction (PEF). This fraction was evaluated for its phenolic compounds composition. The antioxidant activity of PEF was determined by using 1,1-diphenyl-2-picryl-hydrazil scavenging activity, ferric reducing antioxidant power, inhibition of ß-carotene bleaching, and thiobarbituric acid reactive substances assays. The cytotoxicity assay and molecular biomarkers analyses were performed to evaluate the cytoprotective effects of PEF towards aflatoxin B1 (AFB1)-induced cell damage.

Results

The results showed that PEF contained gallic acid, pyrogallol, vanillic acid, caffeic acid, syringic acid, epicatechin, catechin and ferulic acid. The PEF exhibited free radical scavenging activity, ferric reducing antioxidant power, ß-carotene bleaching inhibition and thiobarbituric acid reactive substances inhibition. The PEF demonstrated cytoprotective effects in AFB1-treated chicken hepatocytes by reducing the cellular lipid peroxidation and enhancing antioxidant enzymes production. The viability of AFB1-treated hepatocytes was improved by PEF through up-regulation of oxidative stress tolerance genes and down-regulation of pro-inflammatory and apoptosis associated genes.

Conclusions

The present findings supported the proposition that the phenolic compounds present in PKC could be a potential cytoprotective agent towards AFB1 cytotoxicity.

Mycotoxin mechanisms of action and health impact: ‘in vitro’ or ‘in vivo’ tests, that is the question

The aim of this paper is to present examples of in vitro and in vivo tests for mycotoxin mechanisms of action and evaluation of health effects, with a focus on the gut environment and toxicity testing. In vivo investigations may provide information on the net effects of mycotoxins in whole animals, whereas in vitro models represent effective tools to perform simplified experiments under uniform and well-controlled conditions and a suitable alternative to in vivo animal testing providing insights not achievable with animal studies. The main limits of in vitro models are the lack of interactions with other cells and extracellular factors, lack of hormonal or immunological influences, and lack or different levels of in vitro expression of genes involved in the overall response to mycotoxins. The translation of in vitro data into meaningful in vivo effects remains an unsolved problem. The main issues to be considered are the mycotoxin concentration range in accordance with levels encountered in realistic situations, the identification of reliable biomarkers of mycotoxin toxicity, the measurement of the chronic toxicity, the evaluation of single- or multi-toxin challenge. The gastrointestinal wall is the first barrier preventing the entry of undesirable substances. The intestinal epithelium can be exposed to high concentrations of mycotoxins upon ingestion of contaminated food and the amount of mycotoxin consumed via food does not always reflect the amount available to exert toxic actions in a target organ. In vitro digestion models in combination with intestinal epithelial cells are powerful tools to screen and predict the in vivo bioavailability and digestibility of mycotoxins in contaminated food and correctly estimate health effects. In conclusion, in vitro and in vivo tests are complementary approaches for providing a more accurate picture of the health impact of mycotoxins and improved understanding and evaluation of relevant dietary exposure and risk scenarios.

Cell-based models for mycotoxin screening and toxicity evaluation: an update

This review presents the applications of cell-based models in mycotoxin research, with a focus on models for mycotoxin screening and cytotoxicity evaluation. Various cell-based models, cell and cell culture condition related factors, toxicity endpoints and culture systems as well as predictive value of cell-based bioassays are reviewed. Advantages, drawbacks and technical problems regarding set up and validation of consistent, robust, reproducible and high-throughput cell-based models are discussed. Various cell-based models have been developed and used as screening tests for mycotoxins but the data obtained are difficult to compare. However, the results highlight the potential of cell-based models as promising in vitro platforms for the initial screening and cytotoxicity evaluation of mycotoxins and as a significant analytical approach in mycotoxin research before any animal or human clinical studies. To develop cell-based models as powerful high-throughput laboratory platforms for the analysis of large numbers of samples, there are mainly two fundamental requirements that should be met, i.e. the availability of easy-to-use and, if possible, automated cell platforms and the possibility to obtain reproducible results that are comparable between laboratories. The transition from a research model to a test model still needs optimisation, standardisation, and validation of analytical protocols. The validation of a cell-based bioassay is a complex process, as several critical points, such as the choice of the cellular model, the assay procedures, and the appropriate use and interpretation of the results, must be strictly defined to ensure more consistency in the results. The development of cell-based models exploring the third dimension together with automation and miniaturisation will bring cellular platforms to a level appropriate for cost-effective and large-scale analysis in the field of mycotoxin research.