**3.1 Mechanisms of toxicity**

The majority of aflatoxins' toxicological implications and mechanisms remain unknown. An extensive study of the causes of aflatoxins' toxicity was done to provide

#### **Figure 1.**

*Aflatoxins have a metabolic route that involves protein binding (toxicity) or DNA reactions (cancers). Hydroxylated metabolites, such as aflatoxin M1, GSH, glutathione, and the epoxide, are some of the hazardous secondary products of this system.*

*Aflatoxins: Toxicity, Occurrences and Chronic Exposure DOI: http://dx.doi.org/10.5772/intechopen.105723*

#### **Figure 2.**

*Main aflatoxin B1 toxicity mechanisms are mediated by oxidative stress and AFB1-exo-8,9 epoxide. NB: ROS also affects proteins, RNA molecules, and immunity as does AFBO. Abbreviations: AFBO: Aflatoxin B1-exo-8,9-epoxide; NA: Nucleic acids; ROS: Reactive oxygen species; LPO: Lipid peroxidation; ODD: Oxidative DNA damage; Acr: Acrolein; Cro: Crotonaldehyde; Acet: Acetaldehyde; HNE: 4-Hydroxy-2-Nonenal; uFA: Unsaturated fatty acids; IL1β: Interleukin 1β, IL6: Interleukin 6; TNFα: Tumor necrotizing factor α; P-dG: Cyclic Propano-Deoxyguanosine; Igs: Immunoglobulins [3].*

a scientific foundation for the development of preventive and control strategies. Authorities in charge of food safety might use a deep grasp of the subject as a scientific tool to attain regulatory objectives. The majority of study on AFB1 has focused on its mutagenesis capabilities, which have been related to the AFB1-exo-8,9 epoxide since its discovery as an intermediate metabolite (AFBO) [3]. AFBO mixes with biological macromolecules as nucleic acids, proteins, and phospholipids to affect genetic, metabolic, signaling, and cell structure [33]. However, new evidence is developing that AFB1 causing oxidative stress (OS) has an equal or higher influence on cell function and integrity [34]. **Figure 2** summarizes the AFB1 toxicity pathways that operate on genomic DNA, other functional macromolecules, and immunocompetent cells to generate genotoxicity, immunotoxicity, and acute intoxication.

#### **3.2 Aflatoxins lead to other chronic infections**

Chronic ailments result from a lifetime of low-dose aflatoxins exposure, the most prevalent and deadly of which is cancer. While aflatoxins have long been linked to primary liver malignancies including HCC and bile duct hyperplasia, they have also been linked to cancers of the kidney, pancreas, bladder, bone, and viscera [3]. Again, aflatoxins have been linked to lung and skin malignancies in workers who breathe them or come into close contact with them. Immunosuppression, teratogenicity, mutagenicity, cytotoxicity, and estrogenic effects are induced in mammals due to long-term exposure to aflatoxins. Aflatoxins have also been thought to contribute

to childhood diseases such as kwashiorkor and growth failure by interfering with micronutrient absorption, protein synthesis, and metabolic enzyme performance [3].

#### **3.3 Acute toxicity**

Although the cause of acute aflatoxicosis is unknown, when aflatoxins interrelate with large biological molecules such as proteins, phospholipids, and nucleic acids, they form various adducts that interfere with the physiological and structural functions of these biological molecules. Aflatoxin-protein adducts have been related to acute intoxication because they inhibit protein synthesis, particularly enzymes implicated in essential functions such as metabolic pathways, protein synthesis, DNA replication and repair, and immunological response. There is a growing body of evidence that cell, mitochondrial, and endoplasmic reticulum membrane disruption is due to aflatoxin-phospholipid adducts and ROS-induced LPO [33]. As reported by a scientific study on AFB1's acute toxicity in chicken birds, aflatoxin–dihydrodiol (AF– dhd) is the main metabolite responsible for acute aflatoxicosis since it is the important metabolite that leads to the formation of aflatoxin–albumin adducts [35]. AFB2a has shown a covalent association with cellular proteins and phospholipids, resulting in the linkage of long-chain fatty acids and protein adducts, which may lead to acute aflatoxicosis [33]. Long-term exposure to low levels of aflatoxins, on the other hand, can cause symptoms similar to acute aflatoxicosis; however, as previously mentioned, these symptoms can be mitigated by the removal of harmful substances by phase II enzymes and cellular absorption of free radicals, as well as DNA repair to prevent mutations. Alternatively, these effects may build over time with repeated low-dose exposure, eventually leading to liver cancer as a common side effect [3]. When the dose is excessively high, a rapid rise in a short time might cause acute aflatoxicosis. Excessive amounts of aflatoxins can overwhelm the cell's detoxification capacity, driving the toxins' metabolism toward the production of toxic metabolites, resulting in severe DNA damage, cell growth disruption, asexual cloning by the DNA, metabolic disorders, cytotoxicity, and tissue necrosis, eventually leading to organ failure in a short time. This is especially important because the harmful effects of aflatoxin accumulate over time (Colakoglu and Donmez, 2012), which could lead to more devastating situations than cancers that have been more established.

#### **3.4 Cancers caused by prolonged aflatoxin exposure**

Aflatoxin has been speculated to cause liver cancer in humans, but it can also cause lung cancer in people who work with infected crops. Mutations in the tumorsuppressing gene P53, as well as the activation of dominant oncogenes, induce hepatomas [37]. The cancer risk from aflatoxin exposure has been well documented and is based on a lifetime dose [38]. The International Cancer Research Institute has categorized aflatoxin as a Class 1 carcinogen, resulting in its regulation to very low levels in traded commodities (20 ppb in grains and 0.5 ppb in milk in the United States; 4 ppb in foods in several European nations) [37]. Hepatitis B and C virus (HBV/HCV) outbreaks, on the other hand, affect roughly 20% of the population in several poor countries, appearing to have a good synergy with these biological agents for liver cancer. Aflatoxin is 30 times more potent in people with hepatitis B surface antigen than in people without the virus, and when HBV infection and aflatoxin exposure are coupled, the relative risk of cancer in HBV patients climbs from 5 to 60 [18]. In some areas where aflatoxin contamination and HBV coexist, hepatomas are the

most common malignancy (64 percent of malignancies; 25) and may be the primary cause of mortality.

Aflatoxin B1 is expected to cause between 25,200 and 155,000 cases of liver cancer per year, with 40% of cases occurring in Sub-Saharan Africa, where aflatoxininduced liver cancer accounts for one-third of all liver cancer occurrences [39]. Aflatoxin B1 is expected to cause between 25,200 and 155,000 cases of liver cancer per year, with 40% of cases occurring in Sub-Saharan Africa, where aflatoxin-induced liver cancer accounts for one-third of all liver cancer occurrences [40].

## **3.5 Teratogenicity**

Aflatoxin exposure in pregnant women or birds can affect unfertilized eggs or embryos in utero, resulting in a variety of poor health effects and abnormal gestation/incubation outcomes [41]. Aflatoxin or its metabolites are transmitted to the infant during pregnancy and processed using the same mechanisms as adults [42]. In pregnant women, it has been demonstrated by scientific kinds of literature that, aflatoxins can be transferred from mothers to offspring through blood circulations. In fetal cord blood and maternal blood samples, aflatoxin metabolites, aflatoxin-DNA, and aflatoxin–albumin adducts, as well as biomarkers derived from them, were found [42]. As a result, fetal growth restriction, fetal loss, or premature birth may occur in significantly exposed mothers' pregnancies. An adverse association between birth weight and the levels of suitable biomarkers in the cord blood has been extensively documented in people and animals when growth restriction is present [43]. However, little research has shown excess aflatoxin accumulations by pregnant women to stillbirth, and research on the link between excess aflatoxin consumption by pregnant women and premature birth and fetal loss is confusing or contradictory [44]. Furthermore, an enriched aflatoxin diet harms pregnant women's state of complete physical, mental and social well-being and exposes their fetuses to congenital defects as a result of indirect impacts. Increased systemic inflammation, for example, is caused by overexpression of maternal pro-inflammatory cytokines and/or downregulation of anti-inflammatory cytokines, which affects and causes placental insufficiency, resulting in poor fetal growth, miscarriage, stillbirth, or premature birth [41]. Anemia and high aflatoxin intake were found to be linked in a cross-sectional study of Ghanaian women, as evaluated by the AFB-albumin adduct in the mothers' serum [45]. However, there is no evidence of a relationship between aflatoxins exposure and inflammation-induced anemia in pregnant women [3].

#### **3.6 Genotoxicity caused by oxidative stress**

Although the creation of aflatoxin-N7-gua DNA adducts has been attributed to the majority of aflatoxins' mutagenicity, it is becoming clear that oxidative stress (OS) created by AFB1 metabolism is also a role [46]. The OS can cause oxidative DNA damage (ODD) either directly on DNA or indirectly through membrane phospholipid lipid peroxidation by-products (LPO). OS is caused by the release of large amounts of reactive oxygen species (ROS) from the breakdown of AFB1 by CYP450 enzymes in the liver, which can damage DNA's nitrogen bases and deoxyribose moieties, resulting in in in over 100 distinct DNA adducts [3]. The most well-known and examined of these adducts is 7,8-dihydro-8-oxo-20-deoxyguanosine (8-hydroxydeoxyguanosine, 8-oxo-dG, 8-OH-dG), which is commonly employed as a biomarker for oxidative DNA damage [3]. Intraperitoneal injection of AFB1 into rats elevated 8-oxo-dG

levels in the liver in a dose- and time-dependent manner, which was avoided by pretreatment of animals with the antioxidants selenium and deferoxamine, establishing the relationship between the adduct and Aflatoxin-induced oxidative stress [3]. latest scientific work found no notable increase in seven ROS-modified bases in the liver tissues of rats treated with 7.5 mg/kg AFB1, including 8-oxo-dG, when compared to control rats (untreated); however, levels of 8,50 -cyclo-20 -deoxyadenosine, another DNA adduct from the oxidative attack of the adenine base, increased significantly [47]. By organisms, organs, tissue, sub-cellular component, and cell cycle, the quantity of oxidative DNA damage, the kind of adduct produced, and the effectiveness and speed of DNA repair have all been found to differ [3]. AFG1 increased the expression of tumor necrosis factor (TNF)- and CYP2A13 in mouse alveolar type II (AT-II) cells of lung tissues, as well as in vitro in human AT-II-like cells (A549), which mediate inflammation by increasing the number of -H2AX- and 8-OHdG-positive cells in inflamed tissues, according to a recent scientific study [48]. The inflammatory response generated by TNF increases the expression of CYP2A13, which keeps AFG1 active and causes ODD, as seen by increased expression of the DNA damage marker -H2AX. GT transversion mutations are caused by 8-oxo-dG lesions, which are similar to AFBO-derived DNA adducts but do not pick out the p53 gene and necessitate the use of additional processes and DNA polymerases [35].
