Emodin, an Emerging Mycotoxin, Induces Endoplasmic Reticulum Stress-Related Hepatotoxicity through IRE1α-XBP1 Axis in HepG2 Cells.

Emodin, an emerging mycotoxin, is known to be hepatotoxic, but its mechanism remains unclear. We hypothesized that emodin could induce endoplasmic reticulum (ER) stress through the inositol-requiring enzyme 1 alpha (IRE1α)-X-box-binding protein 1 (XBP1) pathway and apoptosis, which are closely correlated and contribute to hepatotoxicity. To test this hypothesis, a novel IRE1α inhibitor, STF-083010, was used. An MTT assay was used to evaluate metabolic activity, and quantitative PCR and western blotting were used to investigate the gene and protein expression of ER stress or apoptosis-related markers. Apoptosis was evaluated with flow cytometry. Results showed that emodin induced cytotoxicity in a dose-dependent manner in HepG2 cells and upregulated the expression of binding immunoglobulin protein (BiP), C/EBP homologous protein (CHOP), IRE1α, spliced XBP1, the B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax)/Bcl-2 ratio, and cleaved caspase-3. Cotreatment with emodin and STF-083010 led to the downregulation of BiP and upregulation of CHOP, the Bax/Bcl-2 ratio, and cleaved caspase-3 compared with single treatment with emodin. Furthermore, the apoptosis rate was increased in a dose-dependent manner with emodin treatment. Thus, emodin induced ER stress in HepG2 cells by activating the IRE1α-XBP1 axis and induced apoptosis, indicating that emodin can cause hepatotoxicity.

Plant-based natural flavonoids show strong inhibition of aflatoxin production and related gene expressions correlated with chemical structure.

Aflatoxins are strong carcinogenic and mutagenic fungal metabolites, and aflatoxin contamination is a critical issue in agriculture and food production. Natural flavonoids can suppress aflatoxin biosynthesis; however, the structure-activity relationship remains unclear. In the present study, a total of 36 structurally related natural flavonoids were tested against the aflatoxigenic Aspergillus flavus, both in-vitro and in-situ (on maize kernels), to investigate their structure-activity relationship and biological activity. Aflatoxin production (IC50 values: 10.85-20.09 µg/mL) and the expression of related genes (aflD, aflK, aflQ, and aflR) were found to be strongly inhibited. Structure-activity relationship studies revealed that the [-OH] or [-O-CH3] groups at position 6 of ring A and position 4' of ring B were closely associated with antifungal and antiaflatoxigenic activities. These findings provide valuable information for the development of clean and safe methods to prevent aflatoxin contamination in food.

Antifungal Activity of Essential Oil and Plant-Derived Natural Compounds against Aspergillus flavus.

Aspergillus flavus is a facultative parasite that contaminates several important food crops at both the pre- and post-harvest stages. Moreover, it is an opportunistic animal and human pathogen that causes aspergillosis diseases. A. flavus also produces the polyketide-derived carcinogenic and mutagenic secondary metabolite aflatoxin, which negatively impacts global food security and threatens human and livestock health. Recently, plant-derived natural compounds and essential oils (EOs) have shown great potential in combatting A. flavus spoilage and aflatoxin contamination. In this review, the in situ antifungal and antiaflatoxigenic properties of EOs are discussed. The mechanisms through which EOs affect A. flavus growth and aflatoxin biosynthesis are then reviewed. Indeed, several involve physical, chemical, or biochemical changes to the cell wall, cell membrane, mitochondria, and related metabolic enzymes and genes. Finally, the future perspectives towards the application of plant-derived natural compounds and EOs in food protection and novel antifungal agent development are discussed. The present review highlights the great potential of plant-derived natural compounds and EOs to protect agricultural commodities and food items from A. flavus spoilage and aflatoxin contamination, along with reducing the threat of aspergillosis diseases.

Contamination characteristics and risk assessment of aflatoxins in homemade soybean paste, a traditional fermented soybean food, in South Korea.

Soybean paste is manufactured through microbial fermentation and may become contaminated with aflatoxins. Herein, we conducted nationwide large-scale monitoring (n = 1436) over three years (2018-2020) to investigate aflatoxin levels according to geographic, demographic, manufacturing, quality factors, and risk characteristics of homemade soybean paste produced through fermentation. The mean level of total aflatoxins was 5.88 µg/kg (range, 0.01-281.92), with the most common contaminating type being the B type. Aflatoxin levels significantly differed according to the region, age of the manufacturer, type of starter used, and the amino-type nitrogen content and pH of the homemade soybean paste (p < 0.05). Aflatoxin levels was significantly higher when starters were manufactured using the traditional method (inoculation with a naturally occurring strain in the surrounding environment). The aflatoxin exposure level estimated through the average intake of homemade soybean paste in all age groups was 0.1012 ng/kg body weight/day. The risk assessment for the genotoxic and carcinogenic potential of aflatoxins using the margin of exposure approach revealed values of 3705-3954 for average intake of homemade soybean paste, indicating public health concern. These results suggest that follow-up studies and safety management strategies are needed to reduce aflatoxin levels in homemade soybean paste.

Effect of plant-based compounds on the antifungal and antiaflatoxigenic efficiency of strobilurins against Aspergillus flavus.

Aflatoxins are a group of carcinogenic and mutagenic fungal secondary metabolites that have threatened human health and global food security. Aflatoxin contamination can be controlled by applying fungicides, such as strobilurins. Although these compounds have been effective, they may be risky to the environment due to their wide usage. In this study, plant-based compounds were tested to promote the performance of strobilurins (azoxystrobin, pyraclostrobin) against aflatoxigenic Aspergillus flavus; six natural compounds, namely baicalein, nobiletin, meso-dihydroguaiaretic acid, pinoresinol, syringaresinol, and celastrol, were found to exhibit synergistic antifungal effects with strobilurins with fractional inhibitory concentration index < 0.5. Among them, baicalein showed no inhibitory effects on A. flavus when applied alone, but strongly enhanced the in vitro and in situ antifungal and antiaflatoxigenic efficacy of strobilurins and transformed them from fungistatic to fungicidal agents. Therefore, baicalein may be used as an effective natural chemosensitizing agent to improve the performance of strobilurins against A. flavus. The findings of this study provide novel insights for the development of safer and more effective strategies for the control of aflatoxin contamination.