Background
Alternaria is an important type of fungus among the Deuteromycetes. It is plant pathogenic and can cause a variety of economic plant diseases, such as Japanese pear black spot, tobacco brown spot, tomato early blight, potato early blight and citrus seedling chlorosis. It mainly contaminates grains and feeds through field infection and storage contact, causing field and post-harvest crop losses. Alternaria can grow and reproduce in low temperature environments and is the main microorganism that causes spoilage of fruits, vegetables and refrigerated foods. Alternaria can produce more than 70 kinds of mycotoxins and phytotoxins, called Alternaria toxins, but only a part of Alternaria toxins occurs in grains and has obvious toxicological significance. Studies have shown that ingestion of grains and feeds contaminated with Alternaria toxins by humans and animals can lead to acute or chronic poisoning, and some Alternaria toxins also have teratogenic, carcinogenic and mutagenic effects.
Figure 1. Morphological characteristics, growth pattern, colony morphology and microscopic examination of Alternaria species. (Source: Meena M, et al. 2017)
The toxins produced by Alternaria alternata with obvious toxicological significance mainly include alternariol (AOH), alternariol monomethyl ether (AME), altenuene (ALT), tenuazonic acid (TeA), alternaria alternata toxin (AAL), altertoxin (ATXs) and tentoxin (TEN). According to the different chemical structures of toxins, they can be divided into 5 categories: AOH, AME and ALT belong to diphenyl-α-pyrone; TeA belongs to tetramic acid derivatives; ATXs belongs to dinaphthoquinone (pentaquinone); AAL belongs to tricarboxylic acid ester compounds; other structures including TEN. Alternaria alternata is the main fungus that contaminates grains, and the detection rate is extremely high. Compared with fruits and vegetables, there are few strains of Alternaria parasitic on grains. The main toxin-producing Alternaria fungi include A. alternata (Fr.) Keissler, A. tenuissima (Kunze) Wiltshire, and A. triticina Prasadaet Prabhu, which are commonly found in wheat, barley, and oats. Among them, A. alternata is the main fungal strain in Argentine durum wheat. Among American wheat contaminated by Alternaria, A. alternata accounts for 74.6% and A. tenuissima accounts for 4.5%; among the strains that can produce one or more Alternaria toxins, A. alternata accounts for 77.9% and A. tenuissima accounts for 77.8%.
AOH is genotoxic and mutagenic, and can cause cell cycle arrest and apoptosis. Its biological activities and functions include inhibiting cell proliferation, inhibiting the activity of topoisomerase I and II, and destroying the DNA integrity of Chinese hamster fibroblasts (V79), human liver cancer cells (HepG2), human colon cancer cells (HT29), and human lung cancer cells (A431). AOH hydroxylation can lead to the production of reactive oxygen species. Excessive reactive oxygen species can cause oxidative stress. Reactive oxygen species induce unsaturated fatty acids. Molecular oxygen and free radicals oxidize unsaturated fatty acids through non-enzymatic reactions, leading to a chain reaction of free radical-induced lipid peroxidation. Studies have shown that AOH can cause oxidative stress in human colon cancer cells (caco-2), but it only exhibits cytotoxicity at high concentrations. Some researchers have also studied the effects of AOH on the human adrenal sebaceous lipoma cell line H295R and found that AOH affects endocrine activity by interfering with the production pathway of sterols and has weak estrogen toxicity. Current research is mostly focused on a single Alternaria toxin, but Alternaria toxins in nature often occur simultaneously and act synergistically on humans and animals. Therefore, a method for simultaneously detecting multiple Alternaria toxins in different food matrices should be established to optimize the toxin extraction and purification steps. Since immunological detection methods are simple to operate, rapid and accurate, low in cost, and have a large detection capacity, they can be used as one of the rapid detection methods for Alternaria toxins and have potential application value.
Alternative Names
AOH
3,7,9-Trihydroxy-1-methyl-6H-dibenzo[b,d]pyran-6-one
References
- 1. Meena M, et al. Isolation, characterization and toxicological potential of Alternaria-mycotoxins (TeA, AOH and AME) in different Alternaria species from various regions of India. Sci Rep. 2017, 7(1):8777.
References
An updated overview of anticancer effects of alternariol and its derivatives: underlying molecular mechanisms
Front Pharmacol
Authors: Islam MT, Martorell M, González-Contreras C, Villagran M, Mardones L, Tynybekov B, Docea AO, Abdull Razis AF, Modu B, Calina D, Sharifi-Rad J
Abstract
Alternariol is a toxic metabolite of Alternaria fungi and studies have shown multiple potential pharmacological effects. To outline the anticancer effects and mechanisms of alternariol and its derivatives based on database reports, an updated search of PubMed/MedLine, ScienceDirect, Web of Science, and Scopus databases was performed with relevant keywords for published articles. The studies found to suggest that this mycotoxin and/or its derivatives have potential anticancer effects in many pharmacological preclinical test systems. Scientific reports indicate that alternariol and/or its derivatives exhibit anticancer through several pathways, including cytotoxic, reactive oxygen species leading to oxidative stress and mitochondrial dysfunction-linked cytotoxic effect, anti-inflammatory, cell cycle arrest, apoptotic cell death, genotoxic and mutagenic, anti-proliferative, autophagy, and estrogenic and clastogenic mechanisms. In light of these results, alternariol may be one of the hopeful chemotherapeutic agents.
The characteristics, occurrence, and toxicological effects of alternariol: a mycotoxin
Arch Toxicol
Authors: Saleh I, Zeidan R, Abu-Dieyeh M
Abstract
Alternaria species are mycotoxin-producing fungi known to infect fresh produce and to cause their spoilage. Humans get exposed to fungal secondary metabolites known as mycotoxin via the ingestion of contaminated food. Alternariol (AOH) (C14H10O5) is an isocoumarins produced by different species of Alternaria including Alternaria alternata. AOH is often found in grain, fruits and fruits-based food products with high levels in legumes, nuts, and tomatoes. AOH was first discovered in 1953, and it is nowadays linked to esophagus cancer and endocrine disruption due to its similarity to estrogen. Although considered as an emerging mycotoxin with no regulated levels in food, AOH occurs in highly consumed dietary products and has been detected in various masked forms, which adds to its occurrence. Therefore, this comprehensive review was developed to give an overview on recent literature in the field of AOH. The current study summarizes published data on occurrence levels of AOH in different food products in the last ten years and evaluates those levels in comparison to recommended levels by the regulating entities. Such surveillance facilitates the work of health risk assessors and highlights commodities that are most in need of AOH levels regulation. In addition, the effects of AOH on cells and animal models were summarized in two tables; data include the last two-year literature studies. The review addresses also the main characteristics of AOH and the possible human exposure routes, the populations at risk, and the effect of anthropogenic activities on the widespread of the mycotoxin. The commonly used detection and control methods described in the latest literature are also discussed to guide future researchers to focus on mitigating mycotoxins contamination in the food industry. This review aims mainly to serve as a guideline on AOH for mycotoxin regulation developers and health risk assessors.
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