Exposure to ionizing radiation (IR) is associated with increased DNA damage and leads to stress response and inflammation, even carcinogenesis and cell death. IR produces free radicals and other reactive substance and induces reactive oxygen species (ROS) which is main mechanism involved in DNA damage. ROS interacts with critical macromolecules such as DNA and oxidizes DNA [12]. There is a cross talk between ROS mediated inflammation and DNA damage. IR modulates several signaling pathways resulting in transcription factor activation. In response to DNA damage, IR activates inflammatory process through expression of proinflammatory cytokines such as interleukin-1 and 6 (IL-1 and IL-6) and mediators of cytokines such as nuclear factor-kappa B and tumor necrosis factor-alpha (TNF-α) [34]. Theses cytokines has an anti-apoptotic effect and promotes cell proliferation [56]. Several studies demonstrated that antioxidants scavenged free radicals in the irradiated cells and resulted in decreased inflammation process [789].

Mefenamic acid (MEF) is a non-steroidal anti-inflammatory drug (NSAID) relieving dental and menstrual pains. It is typically prescribed for oral administration. MEF provided significant protection against the elevation of lipid peroxidation, protein oxidation, levels of TNF-α and IL-1β and finally decreased inflammation in the brain of rat [1011]. In vitro , MEF could also reduce ROS production, lipid peroxidation, and protein oxidation [1213]. IR induced genotoxicity is wellknown to increase the risk of developing malignancy and to be linked to IR induced inflammatory processes suggesting that an anti-inflammatory drug may protect IR induced DNA damages. The effect of anti-inflammatory MEF has not been clearly revealed yet on irradiated normal human cells. Thus we investigated the IR induced genotoxicity on human normal lymphocytes priming with or without MEF.

A typical binucleated lymphocyte with micronucleus is shown in Fig. 1. The mean frequency of micronuclei in irradiated three volunteers was 9.23 ± 0.63, while that in non-irradiated control samples was 0.63 ± 0.21. It showed a statistically significant (p < 0.001) increase (14-fold rise) in the frequency of micronuclei in irradiated samples at dose of 1.5 Gy (Table 1). In irradiated samples with MEF, the frequency of micronuclei at the concentrations of 5, 10, 50, or 100 µM were 9.10 ± 0.71, 7.80 ± 0.40, 6.10 ± 0.62, and 5.73 ± 0.51, respectively (Fig. 2 and Table 1). The data demonstrate that irradiated samples with MEF at concentrations of 10, 50, and 100 µM exhibited a significant decrease in the frequency of micronuclei as compared to irradiated samples without MEF. Total micronuclei frequencies were reduced by 1.4%, 15%, 34%, and 38% in irradiated samples with MEF at concentrations of 5, 10, 50, or 100 µM, respectively, compared to irradiated samples without MEF (Table 1). Among irradiated samples with MEF, a statistically significant difference in micronuclei was observed between doses 10 and 50 µM of MEF. It is interesting, the frequency of micronuclei in non-irradiated sample with MEF at concentration of 10 and 100 µM was significantly lower than control group (p < 0.05).

In this study, we showed priming of human lymphocytes with MEF markedly reduced genotoxicity induced by IR. The frequency of micronuclei was reduced with pretreatment of MEF. MEF is widely used as an anti-inflammatory drug for relieving of pain and inflammation [15]. MEF belongs to NSAID, and the mechanism of action is partially attributed to capability of inhibiting the cyclooxygenase-2 (COX-2) enzyme, an essential component of the inflammatory process [1617]. MEF has an inhibitory effect on the proliferation of cancer cells such as liver and colon cancer cells. Different mechanisms are proposed for anti-cancer effect of MEF to be caspase-3 pathway and inhibiting of the synthesis of hyaluronic acid and cyclooxygenase [18192021]. COX-2 is frequently over expressed in various cancer tissues, thus inhibition of COX-2 by NSAID is suggested as a strategy for cancer treatment and prevention [2021222324]. While inflammatory environment is linked to DNA damage and death in normal cells, proinflammatory cytokines are involved in cancer cell growth [2526]. Inflammatory cytokines secreted by tumor activate the necessary pathways to facilitate cancer cells proliferation [27], It is recommended that blockade of inflammation process by NSAIDs inhibit cancer progression. In the normal cells, exposure to IR initiates secretion of inflammatory cytokines, which is involved in DNA damage [2829]. Mukherjee et al. [30] showed that NSAIDs could reduce radiation-induced chromosomal instability in vivo. In this study we showed that MEF mitigated IR induced DNA damage in human lymphocytes. It is well documented that free radicals and inflammation are main triggers for IRinduced DNA damage. Normal cell is going to dysfunction in inflammatory process. It is cleared that anti-inflammatory effect of MEF by inhibiting of COX-2 and decreasing secretion of cytokines is main proposed mechanisms for radioprotective effect of MEF. Whereas MEF has anti-cancer effect, it likely protects, in vitro , normal cell against IR induced DNA damage. This result provides a new indication of MEF for protection of normal cells during radiation therapy in treatment of cancer patients. Future studies are needed to find the exact mechanism such as detailed pathways for the radioprotective effect of MEF.