Cellular and molecular mechanisms of aflatoxin B1-mediated neurotoxicity: The therapeutic role of natural bioactive compounds

Aflatoxin B1 Instigated Redox Imbalance is Accompanied by Amplified Indoleamine 2,3-Dioxygenase/tryptophan Catabolism in the Spleen and Erythrocyte of Male Wistar Rats: Protective Influence of Dietary Rutin

INTRODUCTION

Rutin, a dietary flavonoid, exhibits anti-inflammatory, antioxidant, and immunomodulatory properties. The underlying mechanism of protection of rutin against Aflatoxin B1 (AFB1)-induced immunotoxicity is not completely elucidated. This study investigated the protective effect of rutin against Aflatoxin B1 (AFB1)-induced immunotoxicity in male Wistar rats, supported by molecular docking and dynamics simulations.

METHODS

Forty male Wistar rats were grouped into five: control (corn oil), AFB1 (0.75 mg/kg bwt), AFB1 (1.5 mg/kg bwt), rutin (50 mg/kg bwt), and AFB1 (1.5 mg/kg bwt) + Rutin (50 mg/kg bwt) orally for 30 days.

RESULTS

AFB1 exposure increased (p < 0.05) oxidative and inflammatory markers, altered hematological indices, and caused histological damage in the spleen and bone marrow. Elevated indoleamine 2,3-dioxygenase (IDO) activity, reduced CD4+ T cells, and unchanged tryptophan 2,3-dioxygenase (TDO) activity were also observed. Docking revealed strong binding affinities for AFB1 (-9.5 kcal/mol), rutin (-9.7 kcal/mol), and AFB1-rutin (-10.4 kcal/mol) with IDO. Rutin co-treatment restored oxidative, inflammatory, and hematological indices, mitigated histological damage, and normalized CD4+ T cells and IDO activity, as supported by computational studies.

DISCUSSION

The activities/expression of immunosuppressive indoleamine 2, 3-dioxygenase is mostly regulated by inflammation and oxidative stress. This study provides new insights into the mechanisms underlying the modulation of immunotoxicity of AFB1 by dietary rutin.

Protective Effects of Propolis Supplementation on Aflatoxin B1-Induced Oxidative Stress, Antioxidant Status, Intestinal Barrier Damage, and Gut Microbiota in Rats

Aflatoxin B1 (AFB1) is common in the diets of humans and animals and often leads to adverse health effects. Propolis, with its strong antioxidant activity, can reduce oxidative stress and modulate gut microbiota composition. However, the underlying mechanism by which propolis alleviates AFB1-induced intestinal barrier damage remains unclear. This study was designed to investigate the protective effects of oral propolis supplementation in AFB1-exposed rats. Thirty-two male Sprague-Dawley rats were divided into four groups: control, AFB1, propolis, and AFB1+propolis. After 4 weeks, serum oxidative stress markers were examined, and gut microbiota was analyzed by 16S rRNA sequencing. Intestinal sections were processed by Hematoxylin & Eosin staining, and the expression level of tight junction proteins was assessed by immunostaining. Propolis supplementation in AFB1-exposed rats tended to decrease oxidative stress, and it also restructured the gut microbiota by preventing a decrease in the relative abundances of Lactobacillus, Roseburia, and Phascolarctobacterium. Propolis restored intestinal permeability impaired by AFB1 by ameliorating intestinal morphological damage and increasing the expression levels of tight junction proteins. Propolis supplementation may contribute to the modulation of gut microbiota by alleviating oxidative stress and improving intestinal barrier damage in AFB1-exposed rats.

Nanopore single-molecule investigation of aflatoxin B1-aptamer interactions for evolving the aptamer

By utilizing characteristic blocking signatures, the interactions between aflatoxin B1 (AFB1) and its aptamer were investigated. Furthermore, its aptamer sequence was evolved to have a higher affinity (Kd) calculated to be 18.74 nM for AFB1 than previous reports. This evolved aptamer-based nanopore strategy enabled the sensitive detection of trace AFB1 with a linear range from 0.5 to 100 nM.

Signal-enhanced electrochemical sensor employing MWCNTs/CMK-3/AuNPs and Au@Pd core-shell structure for sensitive determination of AFB1 in complex matrix

A sandwich electrochemical sensor was fabricated based on multi-walled carbon nanotubes/ordered mesoporous carbon/AuNP (MWCNTs/CMK-3/AuNP) nanocomposites and porous core-shell nanoparticles Au@PdNPs to achieve rapid and sensitive detection of AFB1 in complex matrices. MWCNTs/CMK-3/AuNP nanocomposite, which was prepared by self-assembly method, served as a substrate material to increase the aptamer loading and improve the conductivity and electrocatalytic activity of the electrode for the first signal amplification. Then, Au@PdNPs, which were synthesized by one-pot aqueous phase method, were applied as nanocarriers loaded with plenty of capture probe antibody (Ab) and signal molecule toluidine blue (Tb) to form the Au@PdNPs-Ab-Tb bioconjugates for secondary signal amplification. The sensing system could still significantly improve the signal output intensity even in the presence of ultra-low concentration target compound due to the dual signal amplification of MWCNTs/CMK-3/AuNP nanocomposites and Au@PdNPs-Ab-Tb. The method exhibited high selectivity, low detection limit (9.13 fg/mL), and strong stability to differentiate AFB1 from other mycotoxins. Furthermore, the sensor has been successfully applied to the quantitative determination of AFB1 in corn, malt, and six herbs, which has potential applications in food safety, quality control, and environmental monitoring.

Effect of Lactiplantibacillus plantarum on the growth, hemato-biochemical, inflammation, apoptosis, oxidative stress markers, involved gens and histopathological alterations in growing rabbits challenged with aflatoxin B1

Aflatoxin B1 (AFB1) is a significant pollutant found in food and feed, posing a threat to public health. The objective of this study was to assess the effect of Lactiplantibacillus plantarum (LACP) against AFB1 in growing rabbits by investigating growth, serum metabolites, immunity, antioxidant capacity, and inflammatory response. A total of 60 growing male rabbits (721.5 ± 2.68g) were allocated to 4 experimental groups. The control group receiving only a basal diet, the AFB1 group (0.3 mg AFB1/kg diet), the LACP group (1 × 109 cfu/g /kg diet), and the combination group (1 × 109 cfu/g + 0.3 mg AFB1/kg diet; AFB1+ LACP) for 8 wk. The administration of AFB1 alone significantly decreased the final body weight, body gain, and feed intake, while significantly increasing the feed conversion ratio (P < 0.05). A significant decline in total proteins and globulins, along with elevated levels of hepatic enzymes (AST, ALP, ALT, and GGT) and renal function markers (creatinine and uric acid), were observed in the AFB1-contaminated group (P < 0.05). Immunoglobulins (IgG and IgM) were significantly decreased, alongside a significant elevation of triglycerides, direct bilirubin, and indirect bilirubin in growing rabbits fed diets with AFB1 (P < 0.05). Supplementing the AFB1 diet with LACP restored the growth reduction, improved liver (AST, ALP, ALT, and GGT) and kidney (creatinine and uric acid) functions, and enhanced immune markers in rabbit serum (P < 0.05). Antioxidant indices (SOD, GSH, and CAT) were significantly decreased in the AFB1 group (P < 0.05). However, the addition of LACP to the AFB1-contaminated diets improved antioxidant capacity and malondialdehyde (MDA) and protein carbonylation (PC) in hepatic tissues of rabbits (P < 0.05). Serum interlukin-4 (IL-4) and interferon gamma (IFN-γ) levels were significantly increased in the AFB1 group (P < 0.05), but the addition of LACP significantly reversed this elevation. AFB1 downregulated the expression of immune-inflammatory genes such Nrf2, IL-10, and BCL-2 genes, while up-regulating the caspase-3 (CASP3) gene (P < 0.05). Supplementing AFB1 diet with LACP significantly decreased the expression of immune-inflammatory genes (Nrf2, IL-10, and BCL-2) and reduced the expression of the apoptotic-related gene CASP3. This study highlights the potential of L. plantarum (1 × 109 cfu/g /kg diet) as a protective agent against AFB1 in growing rabbits by enhancing antioxidant and immune function and reducing apoptosis and inflammation pathways.

Detoxification of Aflatoxin B1 by Phytochemicals in Agriculture and Food Science

Aflatoxin B1 (AFB1), the most toxic and harmful mycotoxin, has a high likelihood of occurring in animal feed and human food, which seriously affects agriculture and food safety and endangers animal and human health. Recently, natural plant products have attracted widespread attention due to their low toxicity, high biocompatibility, and simple composition, indicating significant potential for resisting AFB1. The mechanisms by which these phytochemicals resist toxins mainly involve antioxidative, anti-inflammatory, and antiapoptotic pathways. Moreover, these substances also inhibit the genotoxicity of AFB1 by directly influencing its metabolism in vivo, which contributes to its elimination. Here, we review various phytochemicals that resist AFB1 and their anti-AFB1 mechanisms in different animals, as well as the common characteristics of phytochemicals with anti-AFB1 function. Additionally, the shortcomings of current research and future research directions will be discussed. Overall, this comprehensive summary contributes to the better application of phytochemicals in agriculture and food safety.

Combined Strategies for Improving Aflatoxin B1 Degradation Ability and Yield of a Bacillus licheniformis CotA-Laccase

Aflatoxin B1 (AFB1) contamination is a serious threat to nutritional safety and public health. The CotA-laccase from Bacillus licheniformis ANSB821 previously reported by our laboratory showed great potential to degrade AFB1 without redox mediators. However, the use of this CotA-laccase to remove AFB1 in animal feed is limited because of its low catalytic efficiency and low expression level. In order to make better use of this excellent enzyme to effectively degrade AFB1, twelve mutants of CotA-laccase were constructed by site-directed mutagenesis. Among these mutants, E186A and E186R showed the best degradation ability of AFB1, with degradation ratios of 82.2% and 91.8% within 12 h, which were 1.6- and 1.8-times higher than those of the wild-type CotA-laccase, respectively. The catalytic efficiencies (kcat/Km) of E186A and E186R were found to be 1.8- and 3.2-times higher, respectively, than those of the wild-type CotA-laccase. Then the expression vectors pPICZαA-N-E186A and pPICZαA-N-E186R with an optimized signal peptide were constructed and transformed into Pichia pastoris GS115. The optimized signal peptide improved the secretory expressions of E186A and E186R in P. pastoris GS115. Collectively, the current study provided ideal candidate CotA-laccase mutants for AFB1 detoxification in food and animal feed and a feasible protocol, which was desperately needed for the industrial production of CotA-laccases.

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.

Food-Grade Expression of Two Laccases in Pichia pastoris and Study on Their Enzymatic Degradation Characteristics for Mycotoxins

Mycotoxin contamination poses substantial health risks to humans and animals. In this study, the two laccases PpLac1 and AoLac2 from Pleurotus pulmonarius and Aspergillus oryzae were selected and heterologously expressed in Pichia pastoris in a food-grade manner to detoxify aflatoxin B1 (AFB1), zearalenone (ZEN), and deoxynivalenol (DON). Both laccases exhibited degradation activity toward these three mycotoxins, while the efficiency of these for DON was relatively low. Therefore, molecular docking between these laccases and DON was conducted to analyze their potential interaction mechanisms. Furthermore, the degradation conditions of AFB1 and ZEN by the two laccases were optimized, and the optimal degradation rates for AFB1 and ZEN by PpLac1 reached 78.51 and 78.90%, while those for AFB1 and ZEN by AoLac2 reached 72.27 and 80.60%, respectively. The laccases PpLac1 and AoLac2 successfully transformed AFB1 and ZEN into the compounds AFQ1 and 15-OH-ZEN, which were 90 and 98% less toxic than the original compounds, respectively. Moreover, the culture supernatants demonstrated effective mycotoxin degradation results for AFB1 and ZEN in contaminated feed samples. The residual levels of AFB1 and ZEN in all samples ranged from 6.61 to 8.72 μg/kg and 3.44 to 98.15 μg/kg, respectively, and these levels were below the limit set by the European Union standards. All of the results in this study indicated that the two laccases have excellent application potential in the feed industry.

Improvement of aflatoxin B1 degradation ability by Bacillus licheniformis CotA-laccase Q441A mutant

Aflatoxin B1 (AFB1) contamination seriously threatens nutritional safety and common health. Bacterial CotA-laccases have great potential to degrade AFB1 without redox mediators. However, CotA-laccases are limited because of the low catalytic activity as the spore-bound nature. The AFB1 degradation ability of CotA-laccase from Bacillus licheniformis ANSB821 has been reported by a previous study in our laboratory. In this study, a Q441A mutant was constructed to enhance the activity of CotA-laccase to degrade AFB1. After the site-directed mutation, the mutant Q441A showed a 1.73-fold higher catalytic efficiency (kcat/Km) towards AFB1 than the wild-type CotA-laccase did. The degradation rate of AFB1 by Q441A mutant was higher than that by wild-type CotA-laccase in the pH range from 5.0 to 9.0. In addition, the thermostability was improved after mutation. Based on the structure analysis of CotA-laccase, the higher catalytic efficiency of Q441A for AFB1 may be due to the smaller steric hindrance of Ala441 than Gln441. This is the first research to enhance the degradation efficiency of AFB1 by CotA-laccase with site-directed mutagenesis. In summary, the mutant Q441A will be a suitable candidate for highly effective detoxification of AFB1 in the future.