Aflatoxin B1 Exacerbates Genomic Instability and Apoptosis in the BTBR Autism Mouse Model via Dysregulating DNA Repair Pathway

Abstract

The pathophysiology of autism is influenced by a combination of environmental and genetic factors. Furthermore, individuals with autism appear to be at a higher risk of developing cancer. However, this is not fully understood. Aflatoxin B1 (AFB1) is a potent food pollutant carcinogen. The effects of AFB1 on genomic instability in autism have not yet been investigated. Hence, we have aimed to investigate whether repeated exposure to AFB1 causes alterations in genomic stability, a hallmark of cancer and apoptosis in the BTBR autism mouse model. The data revealed increased micronuclei generation, oxidative DNA strand breaks, and apoptosis in BTBR animals exposed to AFB1 when compared to unexposed animals. Lipid peroxidation in BTBR mice increased with a reduction in glutathione following AFB1 exposure, demonstrating an exacerbated redox imbalance. Furthermore, the expressions of some of DNA damage/repair- and apoptosis-related genes were also significantly dysregulated. Increases in the redox disturbance and dysregulation in the DNA damage/repair pathway are thus important determinants of susceptibility to AFB1-exacerbated genomic instability and apoptosis in BTBR mice. This investigation shows that AFB1-related genomic instability can accelerate the risk of cancer development. Moreover, approaches that ameliorate the redox balance and DNA damage/repair dysregulation may mitigate AFB1-caused genomic instability.

Keywords: DNA damage; DNA repair; autism; carcinogenesis; food pollutants.

Figure 1

Frequencies of micronucleated polychromatic erythrocytes (MN-PCE) in the bone marrow of mice 24 h after their last exposure to aflatoxin B1 (AFB1, 1.25 mg/kg for 28 days; mean ± SD). * p < 0.05, ** p < 0.01 vs. B6 control mice (Kruskal–Wallis test). ^b p < 0.01 vs. B6 + AFB1 (Mann–Whitney U-test).

Figure 2

Levels of DNA strand breaks (tail intensity) in the bone marrow of mice 24 h after their last exposure to aflatoxin B1 (AFB1, 1.25 mg/kg for 28 days; mean ± SD). (A) = cells incubated with buffer only, (B) = cells incubated with Fpg, and (C) = cells incubated with Endo III. * p < 0.05, ** p < 0.01 vs. B6 control mice (Kruskal–Wallis test). ^## p < 0.01 vs. B6 mice and ^b p < 0.01 vs. B6 + AFB1 (Mann–Whitney U-test).

Figure 3

A representative flow cytometry image of Annexin V-propidium iodide (PI) double-stained bone marrow cells of mice 24 h after their last exposure to aflatoxin B1 (AFB1, 1.25 mg/kg for 28 days; mean ± SD). (A) = B6 control mice, (B) = B6 mice treated with AFB1, (C) = BTBR mice, and (D) = BTBR mice treated with AFB1.

Figure 4

Relative caspase-3 activity in the bone marrow cells of mice 24 h after their last exposure to aflatoxin B1 (AFB1, 1.25 mg/kg for 28 days; mean ± SD). * p < 0.05, ** p < 0.01 vs. B6 control mice and ^b p < 0.01 vs. B6 + AFB1 (ANOVA test).

Figure 5

RT-PCR analysis of the brain tissues from mice 24 h after their last exposure to aflatoxin B1 (AFB1, 1.25 mg/kg for 28 days; mean ± SD). * p < 0.05, ** p < 0.01 vs. B6 control mice and ^a p < 0.05, ^b p < 0.01 vs. B6 + AFB1 (ANOVA test).