Gamma irradiation effects on the activity and expression of nitric oxide synthase enzyme on human polymorphonuclear leucocytes (PMNs) in vitro

Free radicals are mediators of radiation-induced cellular damage. The aim of this study was to determine the effects of ionizing radiation on the activity and expression of inducible nitric oxide synthase enzyme (iNOS) in human polymorphonuclear leucocytes (PMNs) in vitro. Gamma irradiation that induced NO (nitrous oxide) was assessed spectrophotometrically, while iNOS mRNA was determined with RT-PCR in PMNs obtained from 10 healthy volunteers. Irradiation doses were at 0.5, 1 and 5 Gy. Results demonstrated detectable amounts of NO and ROS produced post γ-irradiation from purified PMNs, which were augmented when irradiating buffy coat leucocytes. Only buffy coat irradiated cells expressed iNOS mRNA, where there has been a dosedependent increases in the expression and activity of iNOS due to exposure to 0.5 ‐ 5 Gy. It is concluded that low levels of ionising radiation stimulate the production of NO by stimulating the activity and expression of iNOS enzyme.