Differential response to DNA damage may explain different cancer susceptibility between small and large intestine

Area of Science:

• Gastroenterology
• Oncology
• Molecular Biology

Background:

• Large intestine (LI) cancer is a leading cause of cancer deaths, while small intestine (SI) cancer is rare.
• Oxidative DNA damage is a potential initiator of tumorigenesis.
• Differential susceptibility to cancer between SI and LI suggests distinct responses to DNA damage.

Purpose of the Study:

• To investigate if the SI is protected against cancer due to a more effective response to oxidative DNA damage compared to the LI.
• To compare the cellular and morphological responses to oxidative stress between the SI and LI.

Main Methods:

• Sixty rats were divided into three groups: dextran sodium sulfate (DSS) exposure, DSS withdrawal, and control.
• Oxidative DNA damage was quantified using 8-oxodeoxyguanosine (8-oxodG) immunohistochemistry.
• Apoptosis was assessed via TdT-mediated dUTP-biotin nick end labeling (TUNEL) assay.
• Morphological changes in crypt structure were analyzed.

Main Results:

• The SI exhibited significantly greater oxidative DNA damage (8-oxodG) than the LI.
• Apoptosis (TUNEL-positive cells) was significantly higher in the SI compared to the LI after DSS treatment.
• A positive correlation was found between DNA damage and apoptosis in the SI.
• DSS induced significant loss of crypt structure in the LI but not in the SI.

Conclusions:

• The SI demonstrates a more dynamic response to oxidative DNA damage, preserving crypt morphology and potentially offering greater cancer protection.
• The LI's response to oxidative damage leads to crypt architectural disruption, increasing susceptibility to cancer.
• Differential responses to oxidative stress may explain the observed differences in cancer incidence between the SI and LI.