The neglected foodborne mycotoxin Fusaric acid induces bioenergetic adaptations by switching energy metabolism from mitochondrial processes to glycolysis in a human liver (HepG2) cell line

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-enhanced glycolysis induces inflammatory responses in human gastric epithelium cells through mTOR/HIF-1α signaling pathway

Ochratoxin A (OTA) is a mycotoxin commonly found in several food commodities worldwide with potential nephrotoxic, hepatotoxic and carcinogenic effects. We previously showed for the first time that OTA treatment enhanced glycolysis in human gastric epithelium (GES-1) cells in vitro. Here, we found that OTA exposure activated inflammatory responses, evidenced by increasing of NF-κB signaling pathway-related protein (p-p65 and p-IκBα) expressions and elevating of inflammatory cytokine (IL-1β and IL-6) mRNA expressions in GES-1 cells. To elucidate the role of glycolysis in inflammatory effects triggered by OTA, we pretreated GES-1 cells with glycolysis inhibitor (2-deoxy-D-glucose, 2-DG) before OTA exposure. The result showed that 2-DG reduced the protein expressions of p-p65 and p-IκBα and alleviated the mRNA expressions of inflammatory cytokines in OTA-treated GES-1 cells. Furthermore, OTA activated the mTOR/HIF-1α pathway by increasing the protein expressions of p-mTOR, p-eIF4E and HIF-1α, and inhibition of mTOR with rapamycin or silencing HIF-1α with siRNA significantly attenuated OTA-enhanced glycolysis by reducing glycolysis related genes and thereby decreasing inflammatory effects of GES-1 cells. These results demonstrate that OTA activates inflammatory responses in GES-1 cells and this is controlled by mTOR/HIF-1α pathway-mediated glycolysis enhancement. Our findings provide a novel mechanistic view into OTA-induced gastric cytotoxicity.

HIF-1α Mediates Arsenic-Induced Metabolic Reprogramming in Lung Bronchial Epithelial Cells

Arsenic is a common environmental pollutant that can cause damage to multiple systems and organs in the body. The lungs are particularly sensitive to arsenic exposure, and respiratory disease is thought to be the leading cause of death from arsenic poisoning. Our previous study found that human bronchial epithelial (HBE) cells treated with NaAsO₂ exhibited mitochondrial dysfunction accompanied by elevated HIF-1α; however, the molecular mechanism was unclear. The aim of the current study was to confirm the role of HIF-1α in arsenic-induced mitochondrial damage. The results of this study indicated that NaAsO₂ treatment induced mitochondrial ultrastructure impairment and depolarization of the mitochondrial membrane potential. Furthermore, NaAsO₂ induced a significant decrease in basal respiration, maximal respiration, spare respiratory capacity, ATP (adenosine-triphosphate)-associated mitochondrial respiration and proton leakage in HBE cells (P < 0.05), while promoting an increase in ECAR (extracellular acidification rate) values. To clarify the role of HIF-1α, the effect of HIF-1α siRNA on NaAsO₂-induced glycolysis in HBE cells was examined, and the results showed that HIF-1α siRNA reversed the NaAsO₂-induced elevation in PKM2 (Tyr105), HIF-1α, GLUT1 and HK2 protein expression and decreased the NaAsO₂-mediated glycolysis level, glycolytic capacity and glycolytic reserve. These findings suggest that targeting metabolic dysregulation has significant implications for targeting arsenic-induced lung injury and that HIF-1α is an exciting new therapeutic target for the treatment of arsenic-induced lung injury.

Fumonisin B1 disrupts mitochondrial function in oxidatively poised HepG2 liver cells by disrupting oxidative phosphorylation complexes and potential participation of lincRNA-p21

Fumonisin B₁ (FB₁) is etiologically linked to cancer, yet the underlying mechanisms remain largely unclear. It is also not known if mitochondrial dysfunction is involved as a contributor to FB₁-induced metabolic toxicity. This study investigated the effects of FB₁ on mitochondrial toxicity and its implications in cultured human liver (HepG2) cells. HepG2 cells poised to undergo oxidative and glycolytic metabolism were exposed to FB₁ for 6 h. We determined mitochondrial toxicity, reducing equivalent levels and mitochondrial sirtuin activity using luminometric, fluorometric and spectrophotometric methods. Molecular pathways involved were determined using western blots and PCR. Our data confirm that FB₁ is a mitochondrial toxin capable of disrupting the stability of complexes I and V of the mitochondrial electron transport and decreasing the NAD:NADH ratio in galactose supplemented HepG2 cells. We further showed that in cells treated with FB₁, p53 acts as a metabolic stress-responsive transcription factor that induces the expression of lincRNA-p21, which plays a crucial role in stabilising HIF-1α. The findings provide novel insights into the impact of this mycotoxin in the dysregulation of energy metabolism and may contribute to the growing body of evidence of its tumor promoting effects.

AFB1 and OTA Promote Immune Toxicity in Human LymphoBlastic T Cells at Transcriptomic Level

Aflatoxin B1 (AFB1) and ochratoxin A (OTA) are typical contaminants of food and feed, which have serious implications for human and animal health, even at low concentrations. Therefore, a transcriptomic study was carried out to analyze gene expression changes triggered by low doses of AFB1 and OTA (100 nM; 7 days), individually and combined, in human lymphoblastic T cells. RNA-sequencing analysis showed that AFB1-exposure resulted in 99 differential gene expressions (DEGs), while 77 DEGs were obtained in OTA-exposure and 3236 DEGs in the combined one. Overall, 16% of human genome expression was altered. Gene ontology analysis revealed, for all studied conditions, biological processes and molecular functions typically associated with the immune system. PathVisio analysis pointed to ataxia telangiectasia mutated signaling as the most significantly altered pathway in AFB1-exposure, glycolysis in OTA-exposure, and ferroptosis in the mixed condition (Z-score > 1.96; adjusted p-value ≤ 0.05). Thus, the results demonstrated the potential DNA damage caused by AFB1, the possible metabolic reprogramming promoted by OTA, and the plausible cell death with oxidative stress prompted by the mixed exposure. They may be considered viable mechanisms of action to promote immune toxicity in vitro.

A target fishing study to spot possible biological targets of fusaric acid: Inhibition of protein kinase-A and insights on the underpinning mechanisms

Fusaric acid is a secondary metabolite produced by various Fusarium fungi, present with relatively high incidence in Fusarium-contaminated foods. It was already described as phytotoxic and cytotoxic. However, the understanding of its molecular mechanisms is still fragmentary and further data are needed to ensure an informed assessment of the risk related to its presence in food. This work applied an integrated in silico/in vitro approach to reveal novel potential biological activities of fusaric acid and to investigate the underpinning mechanisms. An in silico reverse screening was used to identify novel biological targets for fusaric acid. Computational results indicated as target protein kinase-A, which was confirmed with biochemical cell-free assays providing evidence of its actual inhibitory potential. Cell-based experiments on intestinal cells (HCEC-1CT cells) identified the mitochondrial network and cell membranes as potentially affected organelles, possibly resulting from PKA inhibition. The integration of 3D molecular modeling supported the plausibility of fusaric acid-dependent inhibition. From the hazard identification perspective, considering the Low Observed Adverse Effect Level described here (0.1 mM) and the possible level of contamination in food, fusaric acid might raise concern from a food safety standpoint and the gastrointestinal tract was described as a meaningful system to investigate with priority.

Changes in energy metabolism and macrophage polarization: Potential mechanisms of arsenic-induced lung injury

Exposure to arsenic is epidemiologically associated with increased lung disease. In detailing the mechanism by which arsenic exposure leads to disease, studies have emphasized that metabolic reprogramming and immune dysfunction are related to arsenic-induced lung injury. However, the association between the mechanisms listed above is not well understood. Thus, the current study aimed to investigate the interaction of energy metabolism and macrophage polarization, by which arsenic exposure adversely induced lung injury in both in vitro and human studies. First, we confirmed a shift to glycolytic metabolism resulting from mitochondrial dysfunction. This shift was accompanied by an increase in the levels of phosphorylated PDHE1α (S293) and PDK1 and a concomitant marked increase in several key markers of the HIF-1α signaling pathway (HIF-1α, p-PKM2, GLUT1 and HK-2). In addition, utilizing an in vitro model in which lung epithelial cells are cultured with macrophages, we determined that arsenic treatment polarizes macrophages towards the M2 phenotype through lactate. In the human study, the serum lactate and TGF-β levels were higher in arsenic-exposed subjects than that in reference subjects (t= 4.50, 6.24, both p < 0.05), while FVC and FEV1 were both lower (t= 5.47, 7.59, both p < 0.05). Pearson correlation analyses showed a significant negative correlation between the serum TGF-β and lactate levels and the lung function parameters (p_correlation<0.05). In mediation analyses, lactate and TGF-β significantly mediated 24.3% and 9.0%, respectively, of the association between arsenic and FVC (p_mediation<0.05), while lactate and TGF-β significantly mediated 22.2% and 12.5%, respectively, of the association between arsenic and FEV1 (p_mediation<0.05). Together, the results of the in vitro and human studies indicated that there is complex communication between metabolic reprogramming and immune dysfunction, resulting in exacerbated effects in a feedback loop with increased arsenic-induced lung damage.

Ochratoxin A induces reprogramming of glucose metabolism by switching energy metabolism from oxidative phosphorylation to glycolysis in human gastric epithelium GES-1 cells in vitro

Ochratoxin A (OTA) is a ubiquitous mycotoxin with potential nephrotoxic, hepatotoxic and immunotoxic effects. We previously demonstrated that OTA could cause mitochondrial function disturbance in GES-1 cells in vitro, which lead to the presumption that the glucose metabolism of GES-1 cells will be altered by OTA. Therefore in the present study, we explored the toxicity of OTA on glucose metabolism of GES-1 cells and the molecular mechanism. We found that OTA could induce aerobic glycolysis, evidenced shown by increase of glucose consumption, lactate production and cellular ATP concentration. We further detected expressions of GLUT1 and glycolytic enzymes including HK2, PFK1, PKM2 and LDHA as well as tricarboxylic acid (TCA) cycle-associated enzymes including IDH1, OGDH and CS. The results showed that expression of GLUT1 as well as the activities and expressions of HK2, PFK1 and LDHA were significantly increased while IDH1 and OGDH were reduced by OTA. As to PKM2, western blot showed that OTA could elevated the phospho-PKM2 Ser37 protein level and induce the nuclear accumulation of PKM2, which was further supported by immunofluorescence analyses, in addition, pyruvate kinase activity was reduced by OTA. In conclusion, these findings suggest that OTA exposure induces the metabolic shift from oxidative phosphorylation to aerobic glycolysis via regulating the activities and expressions of glycolysis and TCA-cycle associated molecules in GES-1 cells.

Molecular docking and mechanisms of fusaric acid induced mitochondrial sirtuin aberrations in glycolytically and oxidatively poised human hepatocellular carcinoma (HepG2) cells

Fusaric acid (FA) is a ubiquitous yet neglected mycotoxin. The toxicity of FA is associated with mitochondrial dysfunction and oxidative stress. Sirtuins (SIRTs) are key mediators of cell stress responses through deacetylation of antioxidant, mitochondrial maintenance and energy metabolism proteins. Dietary bioactive compounds have profound effects on SIRT activity, however little is known regarding common foodborne toxins and SIRTs. In this study the interaction of FA with mitochondrial SIRTs - SIRT3 and SIRT5, were firstly studied by molecular docking. Thereafter we substantiated the in silico findings by investigating the effect of FA on expression profiles of SIRT3 and SIRT5, and transcriptional and post-transcriptional regulators, PGC-1α and miRNA-30c using western blots and qPCR in vitro. FA was predicted to bind to the active site of SIRT3 and SIRT5 having implications for biological activity. Furthermore, protein expression of SIRT3 and SIRT5 was down-regulated despite elevated mRNA levels. Further experimentation revealed post-transcriptional regulation of both SIRTs as evidenced by elevated miRNA-30c despite induction of PGC-1α. This study highlights the potential of a diet contaminated with FA to dysregulate mitochondrial specific proteins that can lead to initiation and progression of sirtuin related diseases including cancer and insulin resistance.