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Digital archive of theses discussed at the University of Pisa


Thesis etd-02272013-170208

Thesis type
Tesi di dottorato di ricerca
Thesis title
The role of N-acetylcisteine and genetic polymorphisms in XRCC1, XRCC3, GST genes in the modulation of DNA damage and tissue toxicity induced by medical ionizing radiation exposure
Academic discipline
Course of study
tutor Dott. Andreassi, Maria Grazia
  • acute skin toxicity.
  • breast cancer
  • ionizing radiation
  • N-acetilcysteine
  • radiation therapy
Graduation session start date
Ionizing procedures provide essential life-saving information, but great care must be taken regarding their possible long-term health consequences. The biological and clinical burdens of medical radiation represents a worrisome social and medical problem. DNA damage is the main initiating event by which radiation may results in cancer development. Thus considerable efforts should be made to mitigate radiation-induced cell damage. Because radiation induced cellular damage is attributed primarily to the harmful effects of free radicals, the efficacy of non-toxic radioprotectors with radical scavenging properties should be investigated in the clinical setting. These agents may inhibit or reduce free radical toxicity, thus offering protection against radiation. N-acetylcysteine (NAC) is considered a promising radio-protector for its antioxidant and anticarcinogenic properties and could be able to inhibit or reduce free radical toxicity, thus offering protection against radiation.
Moreover, recent evidences have recognized that genetic factors influence the risk of radiation-induced effects and the Seventh National Academy of Science report on Biological Effects of Ionizing Radiation (BEIR VII) included the identification of genes conferring predisposition to radiation-induced health effects as a top research need. Genetic polymorphisms in the detoxification and DNA repair genes are specifically proposed as candidates for genetic predisposition to radiation-induced biological damage. The identification and characterization of genes that enhance prediction of disease risk and improve prevention, treatment, and quality of care remain important goals in the modern imaging practice. Specifically, it is anticipated that the use of genetic markers may serve as the basis for personalized radiotherapy in which cancer management is formulated so that it optimizes the treatment plan for each patient based on their genetic background (radiogenomics).
In order to improve this knowledge, the primary aims of the project were:
- Aim 1: to evaluate the ability of NAC in conferring protection against radiation induced chromosomal DNA damage.
- Aim 2: to assess the value of functional polymorphisms of genes involved in DNA damage repair and oxidative stress response as predictive factors for the occurrence of acute skin reactions.
To reach aim 1, 65 patients undergoing invasive cardiovascular procedures received the standard hydration protocol consisting of intravenous isotonic saline for 12 h after catheterization (Group I) while 30 patients received a clinically driven double intravenous dose of NAC for 1 hour before and a standard dose for 12 hours following catheterization (Group II). Micronucleus assay (MN) was performed as biomarker of chromosomal damage and intermediate endpoint in carcinogenesis. MN frequency evaluated before, 2 and 24 hours after the radiation exposure showed a significant increase of 24.1% at 2 hours and of 21.4 % at 24 hours in the Group I (p=0.03), while the non-significant increase of MN was 13.1% at 2 hours and 8.7% at 24 hours in Group II (p=0.4). These results suggested that NAC may be an effective promising, well-tolerated antioxidant approach easily usable in the clinical practice to offer protection against DNA damage induced by ionizing radiation exposure during cardiac catheterization procedures.
To reach aim 2, skin toxicity was scored according to Radiation Therapy Oncology Group (RTOG) criteria in 59 breast cancer patients undergoing radiation therapy after conserving surgery. Single nucleotide polymorphisms (SNPs) in XRCC3 (Thr241Met), XRCC1 (Arg399Gln, and Arg194Trp) and in GSTT1 and GSTM1 were determined by PCR-RFPL analysis. According to RTOG criteria, grade 1 and 2 acute skin reactivity was observed in 24 (41%) of the 59 participants. Univariate analysis indicated that XRCC3 241Met variant (OR: 2.5 95% CI: 1.0-7.3, p=0.05) and GSTM1 null genotype (OR: 3.5 95% CI:1.2-10.4 p=0.02) as well as BMI (OR: 3.6 CI: 1.2-11, p=0.02) were associated with the risk of acute skin radiosensitivity. The logistic multivariate analysis confirmed that the two genetic variants increased the individual susceptibility to acute skin reaction. Our findings suggest that the presence of SNPs involved in DNA repair and oxidative stress may in part explain the individual response to acute skin toxicity in patients undergoing partial breast irradiation after conserving surgery. The association analysis between clinical characteristics and genotype with the acute radiation skin toxicity in breast cancer patients suggests that approaches based on (multiple) genetic markers and clinical characteristics have the potential to predict normal tissue radiosensitivity.
Although our findings are to be carefully assessed with further large, randomized studies, taken together have outmost clinical relevance since add important information to reach a personalized measure of radiation risk in order to implement tailored preventive and chemopreventive strategies.