Cytotoxicity of aflatoxin B1 and its chemically synthesised epoxide derivative on the A549 human epithelioid lung cell line

Aflatoxin B1: metabolism, toxicology, and its involvement in oxidative stress and cancer development

Aflatoxins are a class of carcinogenic mycotoxins produced by Aspergillus fungi, which are widely distributed in nature. Aflatoxin B1 (AFB1) is the most toxic of these compounds and its metabolites have a variety of biological activities, including acute toxicity, teratogenicity, mutagenicity and carcinogenicity, which has been well-characterized to lead to the development of hepatocellular carcinoma (HCC) in humans and animals. This review focuses on the metabolism of AFB1, including epoxidation and DNA adduction, as it concerns the initiation of cancer and the underlying mechanisms. In addition to DNA adduction, inflammation and oxidative stress caused by AFB1 can also participate in the occurrence of cancer. Therefore, the main carcinogenic mechanism of AFB1 related ROS is summarized. This review also describes recent reports of AFB1 exposures in occupational settings. It is hoped that people will pay more attention to occupational health, in order to reduce the incidence of cancer caused by occupational exposure.

Human multi-organ chip co-culture of bronchial lung culture and liver spheroids for substance exposure studies

Extrapolation of cell culture-based test results to in vivo effects is limited, as cell cultures fail to emulate organ complexity and multi-tissue crosstalk. Biology-inspired microphysiological systems provide preclinical insights into absorption, distribution, metabolism, excretion, and toxicity of substances in vitro by using human three-dimensional organotypic cultures. We co-cultured a human lung equivalent from the commercially available bronchial MucilAir culture and human liver spheroids from HepaRG cells to assess the potential toxicity of inhaled substances under conditions that permit organ crosstalk. We designed a new HUMIMIC Chip with optimized medium supply and oxygenation of the organ cultures and cultivated them on-chip for 14 days in separate culture compartments of a closed circulatory perfusion system, demonstrating the viability and homeostasis of the tissue cultures. A single-dose treatment of the hepatotoxic and carcinogenic aflatoxin B₁ impaired functionality in bronchial MucilAir tissues in monoculture but showed a protective effect when the tissues were co-cultured with liver spheroids, indicating that crosstalk can be achieved in this new human lung–liver co-culture. The setup described here may be used to determine the effects of exposure to inhaled substances on a systemic level.

Aflatoxin production and in vitro toxicity of Aspergilli section Flavi isolated from air samples collected from different environments

Aspergilli section Flavi, originally isolated from air samples collected from inhabited apartments (AP), unoccupied basements (BS), and processing facilities of a grain mill (GM), were analyzed for their potential to produce aflatoxin B₁ (AFB₁) on solid media. The isolates were further characterized with regard to their cytotoxic, genotoxic, and pro-inflammatory properties in vitro. Aspergilli were identified based on partial calmodulin (CaM) gene sequencing; the producing capacities of isolates were analyzed by HPLC/FLD and confirmed by genes in biosynthesis (aflR, norA, omtA). In the grain mill, the Aspergilli section Flavi (up to 1.3 × 10⁶ cfu/m³) dominated by AFB₁-producing Aspergillus flavus (71%, 4.5-5254 ng/ml) which showed a serious health risk for workers. Living environments were not relevant sources of exposure. After 24 h, AFB₁ (1-100 μmol/l) reduced cell viability (MTT test) in both A549 cells and THP-1 macrophage-like cells without reaching IC₅₀. In A549 cells, the extract of the AFB₁-producing A. flavus significantly decreased cell viability but not below 50%. THP-1 macrophage-like cells were more sensitive to both extracts, but IC₅₀ was obtained only for the AFB₁-producing strain (0.37 mg/ml; AFB₁ 2.78 μmol/l). AFB₁ (1 and 10 μmol/l) induced significant DNA damage (tail intensity, alkaline comet assay) in A549 cells in contrast to Aspergilli extracts. AFB₁ elevated IL-6 and IL-8, while Aspergilli extracts increased IL-1β, TNF-α, and IL-17 release in THP-1 macrophages (ELISA). Chronic exposure to AFB₁ and/or other metabolites in airborne A. flavus from occupational environments may stimulate epithelial damage of airways accompanied by lowered macrophage viability.

A lung/liver-on-a-chip platform for acute and chronic toxicity studies

The merging of three-dimensional in vitro models with multi-organ-on-a-chip (MOC) technology has taken in vitro assessment of chemicals to an unprecedented level. By connecting multiple organotypic models, MOC allows for the crosstalk between different organs to be studied to evaluate a compound's safety and efficacy better than with single cultures. The technology could also improve the toxicological assessment of aerosols that have been implicated in the development of chronic obstructive pulmonary disease, asthma, or lung cancer. Here we report the development of a lung/liver-on-a-chip, connecting in a single circuit, normal human bronchial epithelial (NHBE) cells cultured at the air-liquid interface (ALI), and HepaRG™ liver spheroids. Maintenance of the individual tissues in the chip increased NHBE ALI tissue transepithelial electrical resistance and decreased HepaRG™ spheroid adenosine triphosphate content as well as cytochrome P450 (CYP) 1A1/1B1 inducibility. CYP inducibility was partly restored when HepaRG™ spheroids were cocultured with NHBE ALI tissues. Both tissues remained viable and functional for 28 days when cocultured in the chip. The capacity of the HepaRG™ spheroids to metabolize compounds present in the medium and to modulate their toxicity was proven using aflatoxin B1 (AFB1). AFB1 toxicity in NHBE ALI tissues decreased when HepaRG™ spheroids were present in the same chip circuit, proving that the HepaRG™-mediated detoxification is protecting/decreasing from AFB1-mediated cytotoxicity. The lung/liver-on-a-chip platform presented here offers new opportunities to study the toxicity of inhaled aerosols or to demonstrate the safety and efficacy of new drug candidates targeting the human lung.

Aspergillus spp. prevalence in different Portuguese occupational environments: What is the real scenario in high load settings?

The genus Aspergillus is one of the most prevalent regarding fungi in several highly contaminated occupational environments. The goal of the current study was to assess the prevalence of Aspergillus spp. in different settings, focusing on those where a higher load of fungal contamination is expected according to the European Agency for Safety and Health at Work. A specific protocol to ensure a more accurate assessment of the exposure to Aspergillus spp. is proposed aimed at allowing a detailed risk characterization and management. Two wastewater treatment plants, one wastewater elevation plant, four waste treatment plants, three cork industries, five slaughter houses, four feed industries, one poultry pavilion, and two swineries, all located in the outskirts of Lisbon, were assessed. In total, 125 air samples and 125 surface samples were collected and analysed by culture-based methods. Real-time polymerase chain reaction was performed to detect fungal presence in 100 samples, targeting the Aspergillus sections Circumdati, Flavi, and Fumigati. The highest prevalence of Aspergillus spp. was found in wastewater treatment plants (69.3%; 31.1%), waste treatment plants (34.8%; 73.6%), and poultry feed industry (6.3%; 26.1%), in air and surfaces, respectively. Aspergillus spp. was also prevalent in cork industry (0.9%; 23.4%), slaughter houses (1.6%; 17.7%), and swineries (7.4%; 9.5%), in air and surfaces, respectively. The Aspergillus sections more prevalent in the air and surfaces of all the assessed settings were the Nigri section (47.46%; 44.71%, respectively), followed by Fumigati (22.28%; 27.97%, respectively) and Flavi (10.78%; 11.45%, respectively) sections. Aspergillus section Fumigati was successfully amplified by qPCR in 18 sampling sites where the presence of this fungal species had not been identified by conventional methods. It should be highlighted that the occupational exposure burden is due not only to the Aspergillus load, but also to the toxigenic potential of this genus. Based on our results, a protocol relied in the application of conventional and molecular methods in parallel is herein suggested aimed at allowing a better risk characterization and management.

Filamentous Fungi and Mycotoxins in Cheese: A Review

Important fungi growing on cheese include Penicillium, Aspergillus, Cladosporium, Geotrichum, Mucor, and Trichoderma. For some cheeses, such as Camembert, Roquefort, molds are intentionally added. However, some contaminating or technological fungal species have the potential to produce undesirable metabolites such as mycotoxins. The most hazardous mycotoxins found in cheese, ochratoxin A and aflatoxin M1, are produced by unwanted fungal species either via direct cheese contamination or indirect milk contamination (animal feed contamination), respectively. To date, no human food poisoning cases have been associated with contaminated cheese consumption. However, although some studies state that cheese is an unfavorable matrix for mycotoxin production; these metabolites are actually detected in cheeses at various concentrations. In this context, questions can be raised concerning mycotoxin production in cheese, the biotic and abiotic factors influencing their production, mycotoxin relative toxicity as well as the methods used for detection and quantification. This review emphasizes future challenges that need to be addressed by the scientific community, fungal culture manufacturers, and artisanal and industrial cheese producers.

Cytotoxicity and genotoxicity of versicolorins and 5-methoxysterigmatocystin in A549 cells

Aspergillus versicolor and A. flavus are primary colonizers in damp dwellings, and they produce sterigmatocystin (ST) and aflatoxin B1 (AFB(1)), respectively. These hepatotoxic and carcinogenic mycotoxins and their precursors and derivates possess a furofuran ring, which has proven responsible for their toxicity. The aim of this study was to investigate the cytotoxicity and genotoxicity of versicolorin A (VER A) and versicolorin B (VER B), as the furofuran precursors of aflatoxins and ST, and of 5-methoxysterigmatocystin (5-MET-ST), a methoxy derivative of ST, in human adenocarcinoma lung cells A549. The IC(50) values of the tested compounds were obtained by the cell proliferation MTT test as follows: 109 ± 3.5 μM (VER A), 172 ± 4 μM (VER B) and 181 ± 2.6 μM (5-MET-ST). The comet assay and micronucleus test were used to assess their genotoxic potential after 24 h of treatment with concentrations corresponding to ½ and ¼ IC(50) in comparison with AFB(1) and ST, applied in concentrations corresponding to ½ IC(50), as previously determined in A549 cells. DNA damage parameters assessed by the comet assay were tail length, tail intensity and tail moment, while the level of DNA damage in the micronucleus test was evaluated by the number of formed micronuclei (MN), nuclear buds (NB) and nucleoplasmic bridges (NPB) in 1,000 binucleated cells. Considering the three comet parameters, all applied toxins exerted significant DNA damage compared to the control, while ST and VER B produced the highest DNA damage. All toxins provoked a statistically significant increase in MN, and a slightly decreased formation of NB and NPB. AFB(1), ST and 20 μM VER A showed a statistically significant increase in all three micronucleus parameters compared to the control, and the highest increase in the number of MN occurred in cells treated with 50 μM VER A. The differences between results obtained by the micronucleus test and comet assay could be explained by the fact that the micronucleus detects irreversible DNA damage, which is usually correlated with the previously determined cytotoxic potential of the AFB(1) precursors.

The individual and combined effects of deoxynivalenol and aflatoxin B₁on primary hepatocytes of Cyprinus carpio

Aflatoxin B₁ (AFB₁) and deoxynivalenol (DON) are important food-borne mycotoxins that have been implicated in animal and human health. In this study, individual and combinative effects of AFB₁ and DON were tested in primary hepatocytes of Cyprinus carpio. The results indicated that the combinative effects of AFB₁ and DON (0.01 μg/mL AFB₁ and 0.25 μg/mL DON; 0.02 μg/mL AFB₁ and 0.25 μg/mL DON; 0.02 μg/mL AFB₁ and 0.5 μg/mL DON) were higher than that of individual mycotoxin (P < 0.05). The activity of AST, ALT and LDH in cell supernatant was higher than that of control group (P < 0.05) when the mycotoxins were exposed to primary hepatocytes for 4 h. The decreased cell number was observed in tested group by inverted light microscopy. The mitochondrial swelling, endoplasmic reticulum dilation and a lot of lipid droplets were observed in primary hepatocytes by transmission electron microscope. Therefore, this combination was classified as an additive response of the two mycotoxins.

Effect of competition on the production and activity of secondary metabolites in Aspergillus species

Secondary metabolites are of intense interest to humans due to their pharmaceutical and/or toxic properties. Also, these metabolites are clinically relevant because of their importance in fungal pathogenesis. Aspergillus species secrete secondary metabolites when grown individually and in the presence of other fungal species. However, it is not known whether secreted secondary metabolites provide a competitive advantage over other fungal species, or whether competition has any effect on the production of those metabolites. Here, we have performed co-cultivation competition assays among different species of Aspergillus to determine relative species fitness in culture, and to analyze the presence of possible antifungal activity of secondary metabolites in extracts. The results show that, for the most part, at 30 degrees C only one species is able to survive direct competition with a second species. In contrast, survival of both competitors was often observed at 37 degrees C. Consistent with these observations, antifungal activity of extracts from cultures grown at 30 degrees C was greater than that of extract from cultures at 37 degrees C. Interestingly, culture extracts from all species studied had some degree of antifungal activity, but in general, the extracts had greater antifungal activity when species were grown in the presence of a competitor. Using gas chromatography it was determined that the composition of extracts changed due to competition and a shift in temperature. These findings indicate that co-cultivation could be a very promising method for inducing and characterizing novel antifungal compounds produced by species of Aspergillus.

Aspergillus mycotoxins and their effect on the host

Aspergillus fumigatus is known to produce various immunosuppressive mycotoxins including gliotoxin. However, none of these mycotoxins has been confirmed as being directly related to the pathogenesis of aspergilli. Recent studies have made substantial progress in the determination of mycotoxins as virulence factors. Gliotoxin was found to be produced much faster than previously believed under certain culture conditions, such as at 37 degrees C and under high oxygen content, which is close to the environment in the host. Gliotoxin was also found to be detectable in the sera of aspergillosis mice and of aspergillosis patients. Based on these findings, it is becoming evident that gliotoxin is produced in the infected organs of patients of aspergillosis at a significant level. In addition to these known mycotoxins, A. fumigatus produces many mycotoxins apparently different from known toxins. From the aspect of gene analysis, the deletion of laeA was found to block the expression of metabolic gene clusters such as sterigmatocystin, and the gene is also expected to be related to the production of gliotoxin. The significance of mycotoxins as virulence factors will hopefully be clarified in the near future.

Metabolism and bioactivation of toxicants in the lung. The in vitro cellular approach

Lung is a target organ for the toxicity of inhalated compounds. The respiratory tract is frequently exposed to elevated concentrations of these compounds and become the primary target site for toxicity. Occupational, accidental or prolonged exposure to a great variety of chemicals may result in acute or delayed injury to cells of the respiratory tract. Nevertheless, lung has a significant capability of biotransforming such compounds with the aim of reducing its potential toxicity. In some instances, the biotransformation of a given compound can result in the generation of more reactive, and frequently more toxic, metabolites. Indeed, lung tissue is known to activate pro-carcinogens (i.e. polycyclic aromatic hydrocarbons or N-nitrosamines) into more reactive intermediates that easily form DNA adducts. Lungs express several enzymes involved in the metabolising of xenobiotics. Among them, cytochrome P450 enzymes are major players in the oxidative metabolism as well metabolic bioactivation of many organic toxicants, including pro-carcinogens. Xenobiotic-metabolising P450 enzymes are expressed in bronchial and bronchiolar epithelium, Clara cells, type II pneumocytes, and alveolar macrophages Individual CYP isoforms have different patterns of localisation within pulmonary tissue. With the aid of sensitive techniques (i.e. reverse transcriptase-polymerase chain reaction, RT-PCR) it has become possible to detect CYP1A1, CYP1B1, CYP2A6, CYP2B6, CYP2E1 and CYP3A5 mRNAs in lung cells. Less conclusive results have been obtained concerning CYP2Cs, CYP2D6 and CYP3A4. CYP3A5 protein appears to be widely present in all lung samples and is localised in the ciliated and mucous cells of the bronchial wall, bronchial glands, bronchiolar ciliated epithelium and in type I and type II alveolar epithelium. Lung cells also express Phase II enzymes such as epoxide hydrolase, UGT1A (glucuronyl transferase) and GST-P1 (glutathione S-transferase), which largely act as detoxifying enzymes. A key question concerning organ-specific chemical toxicity is whether the actual target has the capacity to activate (or efficiently inactivate) chemicals. Results of several studies indicate that the different xenobiotic-metabolising CYPs, present in the human lung and lung-derived cell lines, likely contribute to in situ activation of pulmonary toxins, among them, pro-carcinogens. Some CYPs, in particular CYP1A, are polymorphic and inducible. Interindividual differences in the expression of these CYPs may explain the different risk of developing lung toxicity (possibly cancer), by agents that require metabolic activation. Few cell lines, principally A549, have been used with variable success as an experimental model for investigating the mechanisms of toxicity. Although RT-PCR analysis has evidenced the presence of the major human pulmonary CYP mRNAs, the measurable P450 specific activities are, however, far below those present in human lungs. Detection of the toxicity elicited by reactive metabolites requires the use of metabolically competent cells; consequently, better performing cells are needed to ensure realistic in vitro prediction of toxicity. Genetic manipulation of lung-derived cells allowing them to re-express key biotransformation enzymes appear to be a promising strategy to improve their functionality and metabolic performance.

Susceptibility and biomarker knowledge for improvement of environmental health

At the international level, environmental health problems are usually most serious in countries that have the least resources to deal with the problems. Therefore, international efforts have been initiated to achieve equitable environmental health globally. One approach is to conduct international collaborative studies. This approach has been successful in the building of scientific infrastructure in these countries so that they can address their own environmental health concerns and to sustain the environmental health programs. Using liver and oral cancers as models for discussion, examples of success in the identification of etiology and the mechanisms for the diseases are provided. For example, biomarkers are used to provide early warning signals for the disease. In addition, the application of the collected information for developing disease prevention and intervention programs is presented. Expertise in genetic susceptibility is used to provide a more precise understanding of the cancer process. With the precise knowledge, the information can potentially be used to screen for high-risk individuals and to develop "designer" intervention procedures against specific biochemical defects. Success in disease prevention is dependent upon multidisciplinary collaborations at the local and international levels.