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Delayed molecular responses to brain irradiation
C S Chiang1, J H Hong, A Stalder
1Department of Nuclear Science, Tsing-Hua University, Hsing-Chu, Taiwan.
Abstract:
The chance of life-threatening complications occurring late after brain irradiation limits the efficacy of this form of cancer therapy. The molecular and cellular events that trigger radiation-induced brain damage are still unknown, but since they have the potential to serve as valuable targets for therapeutic intervention they are worth delineating. In this murine study, the effect of irradiation on the expression of molecules which are known to contribute to brain damage in other model systems was examined. Expression of genes encoding cytokines (TNF-alpha/beta, IL-1 alpha/beta, IL-2, IL-3, IL-4, IL-5, IL-6 and IFN-gamma), cytokine receptors (TNF-Rp55 and p75, IL-1R- p60 and p80, IFN-gamma R, and IL-6R), the cell adhesion molecule (ICAM-1), inducible nitric oxide synthetase (iNOS), anti-chymotrypsin (EB22/5.3), and the gliotic marker (GFAP) was evaluated over a 6-month period using a sensitive RNase protection assay (RPA). We had previously demonstrated that within 24 h of brain irradiation there is an acute transitory molecular response involving TNF-alpha, IL-1, ICAM-1, EB22/5.3 and GFAP. This study shows re-elevation of TNF-alpha, EB22/5.3 and GFAP mRNA levels at 2-3 months, but only TNF-alpha mRNA was overexpressed at 6 months. These time points are when neurological abnormalities are seen after higher doses. The data suggest that TNF-alpha may be involved in late brain responses to irradiation and could contribute to clinical symptoms.
Insights
Late brain damage after cancer irradiation is a major concern. This study in mice suggests tumor necrosis factor-alpha (TNF-alpha) may play a role in these delayed neurological complications.
Area of Science:
- Neuroscience
- Oncology
- Radiology
Background:
- Late-onset complications following brain irradiation impede cancer therapy efficacy.
- The molecular mechanisms underlying radiation-induced brain damage remain largely unknown.
- Identifying these mechanisms is crucial for developing therapeutic interventions.
Purpose of the Study:
- To investigate the expression of key molecules implicated in brain damage following irradiation.
- To delineate the temporal molecular and cellular events contributing to late radiation effects in the brain.
Main Methods:
- Gene expression analysis of cytokines, cytokine receptors, cell adhesion molecules, iNOS, anti-chymotrypsin, and GFAP in a murine model.
- Utilized a sensitive RNase protection assay (RPA) over a 6-month period post-irradiation.
- Compared acute (24h) and late (2-6 months) molecular responses.
Main Results:
- Confirmed acute, transient responses of TNF-alpha, IL-1, ICAM-1, EB22/5.3, and GFAP within 24 hours.
- Observed re-elevation of TNF-alpha, EB22/5.3, and GFAP mRNA at 2-3 months.
- Found sustained overexpression of TNF-alpha mRNA at 6 months, coinciding with observed neurological abnormalities.
Conclusions:
- Data suggest a potential role for tumor necrosis factor-alpha (TNF-alpha) in the pathogenesis of late brain responses to irradiation.
- TNF-alpha may contribute to the clinical symptoms of radiation-induced brain damage.
- Further research into TNF-alpha as a therapeutic target is warranted.