J Korean Med Sci.  2022 Aug;37(30):e235. 10.3346/jkms.2022.37.e235.

The Risk of Gastrointestinal Cancer on Daily Intake of Low-Dose BaP in C57BL/6 for 60 Days

• Zheng Z
• Park JK
• Kwon OW
• Ahn SH
• Kwon YJ
• Jiang L
• Zhu S
• Park BH

• KMID: 2532229
• DOI: http://doi.org/10.3346/jkms.2022.37.e235

Abstract

Background
Benzo(a)pyrene (BaP) is a carcinogenic compound in contaminated foodstuffs. The effect of oral intake of the environmental carcinogen BaP under low doses and frequent exposure on a digestive system has not been thoroughly verified.
Methods
In this regard, this study was conducted to prove the toxicity effects of BaP on the stomach and colon tissue after exposure to C57BL/6 mouse (3 and 6 µg/kg) following daily oral administration for 60 days. This study investigated acute gastric mucosal injury, severe gastric edema, cell infiltration, and mononuclear cells, multifocal cells, and tumoral inflammatory cells.
Results
The results of ELISA showed that the expression of serum interleukin (IL)-6 and tumor necrosis factor-α in the BaP exposure group were significantly increased, and a high level of DNA adduct distribution in their stomach and colon. Moreover, this study has confirmed the expression of early carcinogenesis markers: nuclear factor (NF)-κB, p53, IL-6, superoxide dismutase 1 (SOD1), mucin (MUC1 and MUC2), and β-catenin in the stomach and colon, and showed that there was a significant increase in IL-6, NF-κB, SOD1, β-catenin, and MUC1 (P< 0.05). At the same time, there was a significant decrease in MUC2 and p53 (P < 0.05). Thus, even in low doses, oral intake of BaP can induce DNA damage, increasing the potential risk of gastrointestinal cancer.
Conclusion
This study will provide a scientific basis for researching environmental contaminated food and intestinal health following daily oral administration of BaP.

Keyword

Benzo(a)pyrene; Gastrointestinal Cancer; Oral Intake; Low-Dose; p53; MUC

Figure

• 

  Fig. 1 Histopathological changes in the stomach and colon of mice after daily oral intake of 3 or 6 µg/kg BaP for 60 days, respectively. No histologic damage in the stomach and colon is observed in mice with vehicle controls. A large number of cell infiltration and inflammatory cells of the stomach, parts of the crypts cells destroyed, and the surface epithelium damaged in the colon are observed following oral intake of 3 µg/kg BaP, respectively. The inflammatory cells are induced by oral intake of 6 µg/kg BaP. The mononuclear cells, and multifocal cells in the stomach and the colon are induced following oral intake of 6 µg/kg BaP, in which the crypts cells destroyed in the colon are observed.BaP = benzo(a)pyrene.

• 

  Fig. 2 Histologic expression of the antioxidant enzyme, the pro-inflammatory oncogenic cytokine, the tumor transcription factor, and the Wnt signaling cascade regulator of stomach and colon tissues are detected using immunohistochemical stains after daily oral intake of BaP for 60 days. SOD, IL-6, NF-κB, and β-catenin are expressed (yellowish-brown color) in the stomach and colon of mice, respectively.BaP = benzo(a)pyrene, SOD = superoxide dismutase, IL = interleukin, NF = nuclear factor.

• 

  Fig. 3 Histologic expression of the indicator cancer markers: MUC2, p53, and MUC1 in stomach and colon tissues, are detected by using immunohistochemical stains after daily oral intake of BaP for 60 days. MUC2, p53, and MUC1 in the stomach and colon of mice, respectively.MUC = mucin glycoprotein, BaP = benzo(a)pyrene.

• 

  Fig. 4 Expression levels of the antioxidant enzyme, the pro-inflammatory oncogenic cytokine, the tumor transcription factor, and the Wnt signaling cascade regulator in the stomach and the colon tissue of mice are induced (n = 8). The stomach and the colon tissue were collected from mice after daily oral intake of BaP for 60 days. (A) Performing western blot analysis of IL-6, NF-κB, SOD1, β-catenin using antibodies and this graph illustrating the changes in the levels of IL-6, NF-κB, SOD1, β-catenin in the stomach were evaluated and compared to oral intake of controls vehicle (Con) and 3 µg/kg BaP (1) or 6 µg/kg BaP (2). (B) Performing western blot analysis of IL-6, NF-κB, SOD1, β-catenin in the colon tissues, and these graphs illustrating the changes in the levels of those were evaluated and compared. The densitometric values were normalized to levels of GAPDH expressed in each group. All data expressed the mean ± standard deviation of eight mice in each group.aCompared to the control mice, the difference was statistically significant (P < 0.05); bCompared to mice between oral intake of 3 µg/kg BaP and 6 µg/kg BaP, the difference was statistically significant (P <0.05).BaP = benzo(a)pyrene, IL = interleukin, NF = nuclear factor, SOD = superoxide dismutase, GAPDH = glyceraldehyde 3-phosphate dehydrogenase.

• 

  Fig. 5 Expression levels of the indicator cancer markers: MUC1, p53, and MUC2 in the stomach and the colon tissue of mice are induced (n = 8). The stomach and the colon tissue were collected from mice after daily oral intake of BaP for 60 days. (A) Performing western blot analysis of MUC1 using antibodies. (B) These graphs illustrate the changes in the levels of MUC1 in the stomach of each group; (C) Performing western blot analysis of p53 using antibodies, and (D) these graphs illustrate the changes in the levels of p53 in the stomach were evaluated and compared to oral intake of controls vehicle (Con) and 3 µg/kg BaP (1) or 6 µg/kg BaP (2). (E) Performing western blot analysis of MUC1, MUC2, and p53 in the colon tissues. (F, G, H) The graphs illustrating the changes in MUC1, MUC2, and p53 levels were evaluated and compared. The densitometric values were normalized to levels of GAPDH expressed in each group. All data expressed the mean ± standard deviation of eight mice in each group.MUC = mucin glycoprotein, BaP = benzo(a)pyrene, GAPDH = glyceraldehyde 3-phosphate dehydrogenase.aThe difference was statistically significant (P < 0.05).

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