Aflatoxin G₁ induced TNF‐α‐dependent lung inflammation to enhance DNA damage in alveolar epithelial cells

Abstract

Aflatoxin G1 (AFG1), a member of the AF family with cytotoxic and carcinogenic properties, could cause DNA damage in alveolar type II (AT‐II) cells and induce lung adenocarcinoma. Recently, we found AFG1 could induce chronic lung inflammation associated with oxidative stress in the protumor stage. Chronic inflammation plays a critical role in cigarette smoke or benzo[a]pyrene‐induced lung tissues damage. However, it is unclear whether and how AFG1‐induced lung inflammation affects DNA damage in AT‐II cells. In this study, we found increased DNA damage and cytochrome P450 (CYP2A13) expression in AFG1‐induced inflamed lung tissues. Furthermore, we treated the mice with a soluble tumor necrosis factor (TNF)‐α receptor and AFG1 and found that TNF‐α neutralization inhibited the AFG1‐induced chronic lung inflammation in vivo, and then reversed the CYP2A13 expression and DNA damage in AT‐II cells. The results suggest that AFG1 induces TNF‐α‐dependent lung inflammation to regulate 2A13 expression and enhance DNA damage in AT‐II cells. Then, we treated the primary mice AT‐II cells and human AT‐II like cells (A549) with AFG1 and TNF‐α and found that TNF‐α enhanced the AFG1‐induced DNA damage in mice AT‐II cells as well as A549 cells in vitro. In AFG1‐exposed A549 cells, TNF‐α‐enhanced DNA damage and apoptosis were reversed by CYP2A13 small interfering RNA. Blocking NF‐κB pathway inhibited the TNF‐α‐enhanced CYP2A13 upregulation and DNA damage confirming that the CYP2A13 upregulation by TNF‐α plays an essential role in the activation of AFG1 under inflammatory conditions. Taken together, our findings suggest that AFG1 induces TNF‐α‐dependent lung inflammation, which upregulates CYP2A13 to promote the metabolic activation of AFG1 and enhance oxidative DNA damage in AT‐II cells.

Fucoidan Ameliorates Oxidative Stress, Inflammation, DNA Damage, and Hepatorenal Injuries in Diabetic Rats Intoxicated with Aflatoxin B1

“…Further, these radicals attack the cellular DNA, as evidenced by the increased levels of serum 8-OHDG (Figure 1). In addition, AFB 1 metabolites form AFB 1 -DNA adducts that induce DNA and cell damages and inhibit enzyme and protein synthesis through binding to nucleoproteins and nucleic acids [49]. Diabetes mellitus and AFB 1 intoxication-induced oxidative stress in this study were associated with increased production of proinflammatory cytokines, IL-1β, IL-6, and TNF-α ( Figure 1) leading to hepatorenal injuries and the elevation of activities and levels of their function biomarkers.…”

Chronic and Acute Toxicities of Aflatoxins: Mechanisms of Action

“…The lung appears to be the most common target for DNA damage with 8-oxo-dG accumulating mainly in mitochondria and the nucleus [74,77,78]. A recent study demonstrated that AFG1 upregulated the expression of tumor necrosis factor (TNF)-α and CYP2A13 in mice alveolar type II (AT-II) cells of lung tissues, and in vitro in human AT-II-like cells (A549), which mediate an inflammation with increased numbers of γ-H2AXand 8-OHdG-positive cells in the inflamed tissues [79]. According to the authors, the inflammatory reaction induced by TNF-α upregulates the expression of CYP2A13, which in turn sustains active metabolism of AFG1 leading to ODD, as evidenced by the increased expression of the DNA damage marker γ-H2AX.…”

“…Intermittent intake of AFB1 simulating the actual situation was also reported to result in an alternation of suppressive and stimulatory/compensatory effects upon exposure and resting (aflatoxin-free diet) periods, respectively [119]. Despite the conflicting data and lack of consensus regarding the cytokine types induced in response to aflatoxin exposure, the unnecessary upregulation of the immune response stimulates the production of tissue-damaging inflammatory molecules and free radicals leading to chronic inflammation, cancer, and nervous system degenerative diseases [21,79]. Moreover, low levels of a mixture of aflatoxins (AFB1, AFB2, AFG1, and AFG2) increased the antigen-presenting capacity of dendritic cells that stimulate T-cell proliferation, which has been suggested to breakdown the immunological tolerance and increase host susceptibility [134].…”

Lung adenocarcinoma‐related TNF‐α‐dependent inflammation upregulates MHC‐II on alveolar type II cells through CXCR‐2 to contribute to Treg expansion

“…The mice were euthanized and lung tissue was collected, after which total lung mononuclear cells were isolated using a previously described technique. 29,31 Fc receptors were blocked with anti-CD16/32 antibodies for 10 minutes, and the cells were then stained with antibodies against CD4 and CD25 for 30 minutes. The cells were analyzed using a flow cytometer (BD, FACS Calibur).…”