Nuclear oxidative damage correlates with poor survival in colorectal cancer

Area of Science:

• Oncology
• Molecular Biology
• Biochemistry

Background:

• Oxidative DNA damage, specifically 8-oxo-7, 8 dihydro-2 -deoxyguanosine (8-oxo-dG) adducts, is a known pro-mutagenic lesion.
• The association between 8-oxo-dG levels and disease progression or survival in colorectal cancer (CRC) remains largely unexplored.
• Understanding the role of 8-oxo-dG in CRC pathogenesis is crucial for identifying potential biomarkers.

Purpose of the Study:

• To investigate the relationship between 8-oxo-dG levels and clinicopathological features, including disease stage and patient survival, in sporadic colorectal cancer.
• To determine the cellular localization of 8-oxo-dG within tumor tissues.

Main Methods:

• Immunohistochemistry was used to assess nuclear and cytoplasmic 8-oxo-dG levels in tumor and normal tissues from 143 CRC patients and 105 controls.
• Double immunofluorescence with manganese superoxide dismutase (MnSOD) antibodies localized cytoplasmic 8-oxo-dG to mitochondria.
• Apoptosis was evaluated using TUNEL assays.

Main Results:

• Nuclear 8-oxo-dG levels were similar in tumor and normal epithelial/stromal cells, but decreased with local spread and increased in distant disease.
• Epithelial cytoplasmic 8-oxo-dG staining was significantly higher in tumor tissue compared to normal tissue, localized to mitochondria.
• Both epithelial nuclear and stromal 8-oxo-dG staining in normal mucosa and tumor tissue correlated with patient survival, while cytoplasmic staining did not.
• Normal cells with high 8-oxo-dG levels exhibited resistance to apoptosis.

Conclusions:

• Nuclear 8-oxo-dG is a potential biomarker for colorectal cancer risk, disease progression, and survival.
• Mitochondrial localization of cytoplasmic 8-oxo-dG suggests a role in oxidative stress within CRC cells.
• Further research into 8-oxo-dG's role could lead to improved diagnostic and prognostic tools for CRC.