Ochratoxin A upregulates biomarkers associated with hypoxia and transformation in human kidney cells

HIF-1α is a "brake" in JNK-mediated activation of amyloid protein precursor and hyperphosphorylation of tau induced by T-2 toxin in BV2 cells

Mycotoxins have been shown to activate multiple mechanisms that may potentially lead to the progression of Alzheimer's disease (AD). Overexpression/aberrant cleavage of amyloid precursor protein (APP) and hyperphosphorylation of tau (P-tau) is hallmark pathologies of AD. Recent advances suggest that the neurotoxic effects of mycotoxins involve c-Jun N-terminal kinase (JNK) and hypoxia-inducible factor-1α (HIF-1α) signaling, which are closely linked to the pathogenesis of AD. Due to the high toxicity and broad contamination of T-2 toxin, we assessed how T-2 toxin exposure alters APP and P-tau formation in BV2 cells and determined the underlying roles of HIF-1α and JNK signaling. The findings revealed that T-2 toxin stimulated the expression of HIF-1α and hypoxic stress factors in addition to increasing the expression of APP and P-tau. Additionally, HIF-1α acted as a "brake" on the induction of APP and P-tau expression by negatively regulating these proteins. Notably, T-2 toxin activated JNK signaling, which broke this "brake" to promote the formation of APP and P-tau. Furthermore, the cytoskeleton was an essential target for T-2 toxin to exert cytotoxicity, and JNK/HIF-1α participated in this damage. Collectively, when the T-2 toxin induces the production of APP and P-tau, JNK might interfere with HIF-1α's protective function. This study will provide clues for further research on the neurotoxicity of mycotoxins.

Ochratoxin A Induces Renal Cell Ferroptosis by Disrupting Iron Homeostasis and Increasing ROS

Mycotoxin ochratoxin A (OTA) is a critical food safety concern due to its nephron-toxic effects and is detected in a wide range of food and feedstuffs. OTA nephrotoxicity is related to oxidative stress and damage. However, the mediator(s) of the excessive oxidative stress is unclear. The current study used human kidney cell lines to investigate whether and how intracellular iron contributed to OTA-induced ROS accumulation and how OTA-induced iron-dependent ferroptotic cell death. Our results showed that OTA treatment affected the cell viability and induced the typical characteristics of cell ferroptosis. Furthermore, gene and protein expression results indicated that OTA disrupted iron homeostasis by upregulating the expression levels of iron importer TFR1 and FTH, while downregulating the expression level of iron exporter FPN and dramatically increasing its negative regulator Hepcidin. The changes were consistent with the induction of intracellular iron accumulation and elevated levels of oxidative stress and lipid peroxidation. Additionally, co-treatment with OTA and an iron chelator significantly improved cell viability, reduced cellular total iron and ROS, and reversed OTA-induced changes in iron metabolism gene expression levels. Interestingly, the addition of a ROS scavenger also reversed cell death and changes in mRNA and protein expression levels of iron metabolism genes but to a lesser degree than that of the iron-chelating agent. Our results revealed that OTA induced ferroptosis in renal cells by disrupting iron homeostasis and increasing ROS.

Resveratrol attenuates high glucose-induced inflammation and improves glucose metabolism in HepG2 cells

Diabetes mellitus (DM) is characterized by impaired glucose and insulin metabolism, resulting in chronic hyperglycemia. Hyperglycemia-induced inflammation is linked to the onset and progression of diabetes. Resveratrol (RES), a polyphenol phytoalexin, is studied in diabetes therapeutics research. This study evaluates the effect of RES on inflammation and glucose metabolism in HepG2 cells exposed to high glucose. Inflammation and glucose metabolism-related genes were investigated using qPCR. Further, inflammatory genes were analyzed by applying ELISA and Bioplex assays. High glucose significantly increases IKK-α, IKB-α, and NF-kB expression compared to controls. Increased NF-kB expression was followed by increased expression of pro-inflammatory cytokines, such as TNF-α, IL-6, IL-β, and COX2. RES treatment significantly reduced the expression of NF-kB, IKK-α, and IKB-α, as well as pro-inflammatory cytokines. High glucose levels reduced the expression of TGFβ1, while treatment with RES increased the expression of TGFβ1. As glucose levels increased, PEPCK expression was reduced, and GCK expression was increased in HepG2 cells treated with RES. Further, HepG2 cells cultured with high glucose showed significant increases in KLF7 and HIF1A but decreased SIRT1. Moreover, RES significantly increased SIRT1 expression and reduced KLF7 and HIF1A expression levels. Our results indicated that RES could attenuate high glucose-induced inflammation and enhance glucose metabolism in HepG2 cells.

Neurodegenerative Proteinopathies Induced by Environmental Pollutants: Heat Shock Proteins and Proteasome as Promising Therapeutic Tools

Environmental pollutants' (EPs) amount and diversity have increased in recent years due to anthropogenic activity. Several neurodegenerative diseases (NDs) are theorized to be related to EPs, as their incidence has increased in a similar way to human EPs exposure and they reproduce the main ND hallmarks. EPs induce several neurotoxic effects, including accumulation and gradual deposition of misfolded toxic proteins, producing neuronal malfunction and cell death. Cells possess different mechanisms to eliminate these toxic proteins, including heat shock proteins (HSPs) and the proteasome system. The accumulation and deleterious effects of toxic proteins are induced through HSPs and disruption of proteasome proteins' homeostatic function by exposure to EPs. A therapeutic approach has been proposed to reduce accumulation of toxic proteins through treatment with recombinant HSPs/proteasome or the use of compounds that increase their expression or activity. Our aim is to review the current literature on NDs related to EP exposure and their relationship with the disruption of the proteasome system and HSPs, as well as to discuss the toxic effects of dysfunction of HSPs and proteasome and the contradictory effects described in the literature. Lastly, we cover the therapeutic use of developed drugs and recombinant proteasome/HSPs to eliminate toxic proteins and prevent/treat EP-induced neurodegeneration.

Deoxynivalenol: Emerging Toxic Mechanisms and Control Strategies, Current and Future Perspectives

Deoxynivalenol (DON) is the most frequently present mycotoxin contaminant in food and feed, causing a variety of toxic effects in humans and animals. Currently, a series of mechanisms involved in DON toxicity have been identified. In addition to the activation of oxidative stress and the MAPK signaling pathway, DON can activate hypoxia-inducible factor-1α, which further regulates reactive oxygen species production and cancer cell apoptosis. Noncoding RNA and signaling pathways including Wnt/β-catenin, FOXO, and TLR4/NF-κB also participate in DON toxicity. The intestinal microbiota and the brain-gut axis play a crucial role in DON-induced growth inhibition. In view of the synergistic toxic effect of DON and other mycotoxins, strategies to detect DON and control it biologically and the development of enzymes for the biodegradation of various mycotoxins and their introduction in the market are the current and future research hotspots.

Mycotoxins Have a Potential of Inducing Cell Senescence: A New Understanding of Mycotoxin Immunotoxicity

Mycotoxins result in immune dysfunction and cause immune diseases in animals and humans. However, the mechanisms of immunotoxicity involved in mycotoxins have not been fully explored, and emerging evidence suggests that these toxins may promote their immunotoxicity via cellular senescence. Mycotoxins induce cell senescence after DNA damage, and activate signaling via the NF-κB and JNK pathways to promote the secretion of senescence-associated secretory phenotype (SASP) cytokines including IL-6, IL-8, and TNF-α. DNA damage can also over-activate or cleave poly (ADP-ribose) polymerase-1 (PARP-1), increase the expression of cell cycle inhibitory proteins p21, and p53, and induce cell cycle arrest and then senescence. These senescent cells further down-regulate proliferation-related genes and overexpress inflammatory factors resulting in chronic inflammation and eventual immune exhaustion. Here we review the underlying mechanisms by which mycotoxins trigger cell senescence and the potential roles of SASP and PARP in these pathways. This work will help to further understand the mechanisms of immunotoxicity involved in mycotoxins.

Mycotoxins and cellular senescence: the impact of oxidative stress, hypoxia, and immunosuppression

Mycotoxins induce oxidative stress, hypoxia, and cause immunosuppressive effects. Moreover, emerging evidence show that mycotoxins have a potential of inducing cellular senescence, which are involved in their immunomodulatory effects. Mycotoxins upregulate the expression of senescence markers γ-H2AX, senescence-associated β-galactosidase, p53, p16, and senescence-associated secretory phenotype (SASP) inflammatory factors. Moreover, mycotoxins cause senescence-associated cell cycle arrest by diminishing cyclin D₁ and Cdk4 pathways, as well as increasing the expression of p53, p21, and CDK6. Mycotoxins may induce cellular senescence by activating reactive oxygen species (ROS)-induced oxidative stress. In addition, hypoxia acts as a double-edged sword on cell senescence; it could both act as the stress-induced senescence and also hinder the onset of cellular senescence. The SASP inflammatory factors have the ability to induce an immunosuppressive environment, while mycotoxins directly cause immunosuppression. Therefore, there is a potential relationship between mycotoxins and cellular senescence that synergistically cause immunosuppression. However, most of the current studies have involved the effect of mycotoxins on cell cycle arrest, but only limited in-depth research has been carried out to link the occurrence of this condition (cell cycle arrest) with cellular senescence.

Hypoxia and Cellular Senescence, Emerging Toxic Mechanisms of Mycotoxins and Toxins: A New Understanding of the Negative Immune Regulations

Mycotoxin contamination is an important issue that has plagued the world [...]

HIF-1α inhibits T-2 toxin-mediated "immune evasion" process by negatively regulating PD-1/PD-L1

Trichothecene mycotoxins have a strong immunosuppressive effect, which may even escape host immune surveillance and damage the immune repair to show an "immune evasion" effect. Increasing lines of evidence have shown that hypoxia and hypoxia-inducible factors (HIFs) are key mediators of trichothecenes, and these toxins appear to be closely related to the "immune evasion" mechanisms. Therefore, we used RAW264.7 cell model to explore the association of T-2 toxins with "immune evasion" process and hypoxia, as well as their cross-linking effects induced by T-2 toxin. Our results showed that HIF-1α is an important toxicity target of T-2 toxin, which could induce intracellular hypoxia. T-2 toxin induced an "immune evasion" process by activating the PD-1/PD-L1 signaling pathway. Interestingly, when HIF-1α activation was blocked, the "immune evasion" process regulated by PD-1/PD-L1 signaling was activated, resulting in the cells damage, suggesting that hypoxia induced by T-2 toxin plays a protective role for RAW264.7 cell damage. Thus, our work shows that HIF-1α inhibits T-2 toxin-mediated "immune evasion" process by negatively regulating PD-1/PD-L1signaling. This study contributes to a better understanding of the immunotoxicity mechanism of trichothecenes.

A review of toxigenic fungi and mycotoxins in feeds and food commodities in West Africa

Fungal contamination is a threat to food safety in West Africa with implications for food and feed due to their climate, which is characterised by high temperatures and high relative humidity, which are environmental favourable for fast fungal growth and mycotoxin production. This report gives perspective on studies on toxigenic fungi (Aspergillus, Fusarium and Penicillium) and their toxins, mainly aflatoxins, fumonisins and ochratoxins commonly found in some West African countries, including Benin, Burkina Faso, Gambia, Ghana, Ivory Coast, Mali, Nigeria, Senegal, Sierra Leone, and Togo. Only four of these countries have mycotoxins regulations in place for feeds and food products (Ghana, Ivory Coast, Nigeria, and Senegal). Food commodities that are widely consumed and were thoroughly investigated in this region include cereals, peanuts, cassava chips (flakes), cassava flour, chilies, peanuts, locust beans, melon, and yam products. In conclusion, authorities and scientists needed to consider research and approaches to monitor mycotoxins in foods and feeds produced and consumed in West Africa.

Ochratoxin A-Induced Nephrotoxicity: Up-to-Date Evidence

Ochratoxin A (OTA) is a mycotoxin widely found in various foods and feeds that have a deleterious effect on humans and animals. It has been shown that OTA causes multiorgan toxicity, and the kidney is the main target of OTA among them. This present article aims to review recent and latest intracellular molecular interactions and signaling pathways of OTA-induced nephrotoxicity. Pyroptosis, lipotoxicity, organic anionic membrane transporter, autophagy, the ubiquitin-proteasome system, and histone acetyltransferase have been involved in the renal toxicity caused by OTA. Meanwhile, the literature reviewed the alternative or method against OTA toxicity by reducing ROS production, oxidative stress, activating the Nrf2 pathway, through using nanoparticles, a natural flavonoid, and metal supplement. The present review discloses the molecular mechanism of OTA-induced nephrotoxicity, providing opinions and strategies against OTA toxicity.

Hypothesis: Long non-coding RNA is a potential target of mycotoxins

The molecular target of mycotoxins is not fully understood. Extensive data derived from cell and animal experimental studies demonstrate that long non-coding RNAs (lncRNAs) play crucial roles in mycotoxin-induced toxicities. Mycotoxins stimulate the upregulation/downregulation of lncRNA expression, which further promote apoptosis, is related to the mTOR/FoxO signaling pathway, and contributes to tumor cell growth, death, and liver and chondrocyte damage. Moreover, lncRNA can establish interactions with NF-κB and cause immune evasion. These preliminary data suggest that lncRNAs are involved in potential upstream regulatory events and further regulate downstream apoptosis, oxidative stress, and anti-apoptotic events that affect cell death and survival. Therefore, we hypothesize that lncRNAs are potential targets of mycotoxins. Investigation of the expression of the potential target lncRNAs by mycotoxin-mediated stimulation, and exploration of the upstream and downstream relationship between lncRNA and the key proteins involved in mycotoxin toxicity, should be performed. This Hypothesis provides clues for further understanding of the molecular mechanisms of mycotoxins.

Hypoxia, oxidative stress, and immune evasion: a trinity of the trichothecenes T-2 toxin and deoxynivalenol (DON)

T-2 toxin and deoxynivalenol (DON) are type A and B trichothecenes, respectively. They widely occur as pollutants in food and crops and cause a series of toxicities, including immunotoxicity, hepatotoxicity, and neurotoxicity. Oxidative stress is the primary mechanistic basis of these toxic effects. Increasing amounts of evidence have shown that mitochondria are significant targets of apoptosis caused by T-2 toxin- and DON-induced oxidative stress via regulation of Bax/B-cell lymphoma-2 and caspase-3/caspase-9 signaling. DNA methylation and autophagy are involved in oxidative stress related to apoptosis, and hypoxia and immune evasion are related to oxidative stress in this context. Hypoxia induces oxidative stress by stimulating mitochondrial reactive oxygen species production and regulates the expression of cytokines, such as interleukin-1β and tumor necrosis factor-α. Programmed cell death-ligand 1 is upregulated by these cytokines and by hypoxia-inducible factor-1, which allows it to bind to programmed cell death-1 to enable escape of immune cell surveillance and achievement of immune evasion. This review concentrates on novel findings regarding the oxidative stress mechanisms of the trichothecenes T-2 toxin and DON. Importantly, we discuss the new evidence regarding the connection of hypoxia and immune evasion with oxidative stress in this context. Finally, the trinity of hypoxia, oxidative stress and immune evasion is highlighted. This work will be conducive to an improved understanding of the oxidative stress caused by trichothecene mycotoxins.

Toxicological and physiological effects of successive exposure to ochratoxin A at food regulatory limits

Ochratoxin A (OTA), a potent mycotoxin, is a common contaminant of agro-products, which seriously threatens food safety. The OTA regulatory limits vary from different countries/regions. However, little is known about the toxicological effects of successive exposure to regulatory levels of OTA. In this study, feedstuffs contaminated with 0.5-20 μg kg^-1 OTA were evaluated in Sprague-Dawley (SD) rats. During the study, poisoning-associated behaviors, and significant differences of body weight and food intake, were not observed between OTA-treated rats and control group. However, the renal function indexes of blood urea nitrogen (BUN) and creatinine (CR) increased, and architecture destruction of glomeruli and tubuli was observed from the OTA-treated groups. The apoptosis study indicated that at a concentration of 20 μg kg^-1, OTA modulated apoptosis in renal tissues via the Bcl-2/Bax pathway. The results of this study suggest that exposure to low doses of OTA successively at levels lower than the regulatory limits of certain countries could induce nephrotoxicity, and modulate apoptosis. Therefore, agencies pertaining to food safety should establish strict OTA regulatory limits for food and feedstuff.

Transcriptome Analysis Reveals the AhR, Smad2/3, and HIF-1α Pathways as the Mechanism of Ochratoxin A Toxicity in Kidney Cells

Ochratoxin A (OTA) is a mycotoxin occurring in foods consumed by humans. Recently, there has been growing global concern regarding OTA toxicity. The main target organ of OTA is the kidney, but the mechanism underlying renal toxicity is not well known. In this study, human-derived proximal tubular epithelial cells, HK-2 cells, were used for RNA-sequencing (RNA-seq) and transcriptome analysis. In total, 3193 differentially expressed genes were identified upon treatment with 200 nM OTA in HK-2 cells; of these, 2224 were upregulated and 969 were downregulated. Transcriptome analysis revealed that OTA significantly affects hypoxia, epithelial-mesenchymal transition (EMT), apoptosis, and xenobiotic metabolism pathways in kidney cells. Quantitative real-time PCR analysis showed gene expression patterns similar to RNA-seq analysis. Expression of EMT markers (E-cadherin and fibronectin), apoptosis markers (caspase-3 and Bax), and kidney injury molecule-1 (KIM-1) was suppressed by inhibiting AhR expression using siRNA, and the related transcription factors, Smad2/3, and HIF-1α were downregulated. Smad2/3 suppression with siRNA could inhibit fibronetcin, caspase-3, Bax, and KIM-1 expression. Fibronetcin, caspase-3, Bax, and KIM-1 expression could be increased with HIF-1α suppression with siRNA. Taken together, these findings suggest that OTA-mediated kidney toxicity via the AhR-Smad2/3-HIF-1α signaling pathways leads to induction of EMT, apoptosis, and kidney injury.

Mycotoxins: Biotransformation and Bioavailability Assessment Using Caco-2 Cell Monolayer

The determination of mycotoxins content in food is not sufficient for the prediction of their potential in vivo cytotoxicity because it does not reflect their bioavailability and mutual interactions within complex matrices, which may significantly alter the toxic effects. Moreover, many mycotoxins undergo biotransformation and metabolization during the intestinal absorption process. Biotransformation is predominantly the conversion of mycotoxins meditated by cytochrome P450 and other enzymes. This should transform the toxins to nontoxic metabolites but it may possibly result in unexpectedly high toxicity. Therefore, the verification of biotransformation and bioavailability provides valuable information to correctly interpret occurrence data and biomonitoring results. Among all of the methods available, the in vitro models using monolayer formed by epithelial cells from the human colon (Caco-2 cell) have been extensively used for evaluating the permeability, bioavailability, intestinal transport, and metabolism of toxic and biologically active compounds. Here, the strengths and limitations of both in vivo and in vitro techniques used to determine bioavailability are reviewed, along with current detailed data about biotransformation of mycotoxins. Furthermore, the molecular mechanism of mycotoxin effects is also discussed regarding the disorder of intestinal barrier integrity induced by mycotoxins.

The neurotoxicity of trichothecenes T-2 toxin and deoxynivalenol (DON): Current status and future perspectives

During the last decade, the neurotoxicity of the trichothecenes T-2 toxin and deoxynivalenol (DON) has been a major concern, and many important findings have been reported on this topic. Through a summary of relevant research reports in recent years, we discuss the potential neurotoxic mechanisms of T-2 toxin and DON. In neuronal cells, T-2 toxin induces mitochondrial dysfunction and oxidative stress through a series of signalling pathways, including Nrf2/HO-1 and p53. This toxin crosses the blood-brain barrier (BBB) by altering permeability and induces oxidative stress responses, including ROS generation, lipid peroxidation, and protein carbonyl formation. Cellular metabolites (for example, HT-2 toxin) further promote neurotoxic effects. The type B trichothecene DON induces neuronal cell apoptosis via the MAPK and mitochondrial apoptosis pathways. This molecule induces inflammation of the central nervous system, increasing the expression of proinflammatory molecules. DON directly affects brain neurons and glial cells after passing through the BBB and affects the vitality and function of astrocytes and microglia. Exposure to trichothecenes alters brain dopamine levels, decreases ganglion area, and further induces brain damage. In this review, we mainly discuss the neurotoxicity of T-2 toxin and DON. However, our main goal was to reveal the potential mechanism(s) and offer new topics, including the potential of hypoxia-inducible factors, immune evasion, and exosomes, for future research in this context. This review should help elucidate the neurotoxic mechanism of trichothecenes and provides some potential inspiration for the follow-up study of neurotoxicity of mycotoxins.

Protective Effect of Astaxanthin on Ochratoxin A-Induced Kidney Injury to Mice by Regulating Oxidative Stress-Related NRF2/KEAP1 Pathway

The present study aimed to investigate the effects of astaxanthin (ASX) on ochratoxin A (OTA)-induced renal oxidative stress and its mechanism of action. Serum kidney markers, histomorphology, ultrastructural observation, and oxidative stress indicators were assessed. Meanwhile, quantitative real-time reverse transcription PCR and western blotting detection of NRF2 (encoding nuclear factor, erythroid 2 like) and members of the NRF2/KEAP1 signaling pathway (KEAP1 (encoding Kelch-like ECH-associated protein), NQO1 (encoding NAD(P)H quinone dehydrogenase), HO-1 (encoding heme oxygenase 1), γ-GCS (gamma-glutamylcysteine synthetase), and GSH-Px (glutathione peroxidase 1)) were performed. Compared with the control group, the OTA-treated group showed significantly increased levels of serum UA (uric acid) and BUN (blood urea nitrogen), tubular epithelial cells were swollen and degenerated, and the levels of antioxidant enzymes decreased significantly, and the expression of NRF2 (cytoplasm), NQO1, HO-1, γ-GCS, and GSH-Px decreased significantly. More importantly, after ASX pretreatment, compared with the OTA group, serum markers were decreased, epithelial cells appeared normal; the expression of antioxidant enzymes increased significantly, NQO1, HO-1, γ-GCS and GSH-Px levels increased significantly, and ASX promoted the transfer of NRF2 from the cytoplasm to the nucleus. These results highlight the protective ability of ASX in renal injury caused by OTA exposure, and provide theoretical support for ASX’s role in other mycotoxin-induced damage.