Who didn't want x-ray vision as a kid? Nowadays, we know more about its dark side; for example, ionizing radiation can induce DNA double-strand breaks (DSBs), which can jump start carcinogenesis. While it has been suggested that antioxidant pre-treatment with vitamin C or n-acetylcysteine (NAC) may reduce DSB induction, clinical data in humans are lacking. In a research correspondence letter in JACC, Julia Stehli, MD, and colleagues report results from their single-center study that tested whether these antioxidants could protect against radiation-induced DNA damage.

In this double-blind, placebo-controlled study, participants were assigned to one of three groups:

• Group A: 29 controls who did not undergo x-ray–based examinations
• Group B: 30 patients exposed to low-dose (<3 mSv) coronary computed tomography angiography (CCTA)
• Group C: 29 patients exposed to higher radiation dose (>9 mSv) through complex catheter-based cardiac intervention

To measure the impact of x-ray exposure on patients' DNA, peripheral blood lymphocytes were measured before the randomized intravenous infusion (saline or 1.2 g NAC or 3 g vitamin C) and repeated within minutes after the end of the cardiac examination.

The median effective radiation dose differed among all groups: A (0; interquartile range [IQR] 0-0); B (2.0; IQR 1.4-2.4); and C (29.0; IQR 15.5-52.6). The researchers also noted a substantially higher DSB induction after high-dose radiation exposure (expressed as excess foci), compared with low-dose exposure by CCTA.

Although antioxidant pre-treatment produced no impact on DSBs in Group A and Group B, it yielded a significant reduction in excess foci (–66%) compared to placebo (0.1 vs. 0.3; p < 0.05) in Group C participants. The excess foci effect of vitamin C in this group was also more pronounced than the effect of NAC: –87% vs. –43% (p = 0.005).

Because they can trigger DNA instability and exert tumorigenic effects, most consider DSBs the most important genetic lesions. Therefore, "it seems reasonable to deduce that the observed substantial reduction of DSBs in lymphocytes by about two-thirds may translate into a reduction of carcinogenic risk," Dr. Stehli and colleagues concluded. They cautioned that these observations stem only from an acute effect study with one cell type, and do not offer a firm conclusion on antioxidants and radiation.

Stehli J, Fuchs TA, Ghadri JR, et al. J Am Coll Cardiol. 2014;64:117-8.