Effects of the pretreatment of free radical scavengers on the expression of apoptosis after gamma-irradiation in the rat parotid gland

Kim, Hee Jin

Abstract

Apoptosis is a distinct morphological form of programmed cell death during growth, development and some diseases. Also, it is well known that the apoptosis is usually caused by carcinogens, drugs, heat and radiation in mature cells. Especially, the therapeutic radiation of the head and neck region may cause xerostomia after irradiation. Recently, there are many trial reports to explain the radiation cell death to the acute cellular changes as a programmed cell death. The author performed present study to investigate the potential role of reactive oxygen metabolites as a signal for radiation-induced apoptosis. A series of free radical scavengers, allopurinol, superoxide dismutase, dimethylthiourea were pretreated before gamma-irradiation for evaluating their ability to block apoptosis in the rat parotid gland in vivo, and the light microscopic results were evaluated and analyzed using the Tdt-mediated dUTP-biotin nick end labeling technique. The results were as follows. 1. Under the light microscope, irradiation induced apoptotic bodies in the parotid gland were revealed the intensively positive reaction on the TUNEL technique, and most apoptotic bodies were confined in the acinar system, there were rare apoptotic changes in the ductal system. 2. In all irradiated experimental groups without antioxidants pretreatment, the number of the apototic bodies was the greatest in post-irradiation 24 hour group, and then decreased as a function of time. 3. As a result on pretreatment of allopurinol that effectively inhibit xanthine oxidase before irradiation, failed to block the irradiation-induced apoptosis in the rat parotid gland. Moreover, in the postirradiation 1 day group, the apoptotic expression and destruction of the acini increased than non-irradiated experimental group. 4. As a result on pretreatment of Cu/Zn-SOD that contributes to extracellularly generated superoxides and dimethylthiourea to scavenge the hydroxyl free radicals before irradiation, two antioxidants inhibit the irradiation-induced apoptosis (P<0.001), salivary acinar structures remained intact. 5. To evaluate the synergistic effects, simultaneous pretreatments of allopurinol and Cu/Zn-SOD, Cu/Zn-SOD and DMTU were conducted. Expression of irradiation-induced apoptosis was lower than the experimental groups which not pretreated any antioxidants (P<0.001), but there was no synergism of two antioxidants. 6. Irradiation-induced apoptotic bodies crowded at the outer cortical layer including lymphatic nodules, and the aspect of apoptotic expression in the lymph node took place earlier than in the salivary acini. Taken all together, it is forecasted that the irradiation-induced apoptosis of the parotid gland is a result of primary cellular damage by oxygen or hydroxyl free radicals. Through this study, the facts that pretreatments of free radical scavengers block the irradiation-induced apoptosis were identified. But, oxygen free radicals were not produced via xanthine oxidase process, whereas, allopurinol that inhibits this reaction influenced the harmful effects on the parotid gland.