Adaptive Response Induced By Low Dose Microwave On Bleomycin-caused DNA Damages In Mice

Objective：To explore the adaptive response induced by low dose radio-frequency (RF)radiation on bleomycin-caused DNA damages in mice.Methods:1. To determin the primary DNA damage in the form of alkali labile base damageand single strand breaks in the DNA of peripheral blood leukocytes, a total of48adultmale ICR mice were used. After7days quarantine period, a randomized block designwas used to divide the mice into the following6group: Control group, Sham exposuregroup, BLM group, RF group, RF+BLM group, Sham+BLM group,8animals in eachgroup. Control group: un-exposed controls; BLM group: BLM, intra-peritonealinjection,37.5mg/kg body weight alone; RF group and RF+BLM group:900MHzradiofrequency fields (RF) exposure at120μW/cm2power density for4h/day for7days; Sham group and Sham exposure+BLM group: sham exposure for4h/day for7days. On day7, at4hours after the last RF/sham exposure, animals in groups BLM,RF+BLM and Sham+BLM were suffered with37.5mg/kg body weight BLMintra-peritoneal injection. Twenty minutes later, all mice were sacrificed. The primaryDNA damage in the form of alkali labile base damage and single strand breaks in theDNA of peripheral blood leukocytes was determined using the alkaline comet assay.To detect8-OHdG levels in plasma, liver and lung tissues, a total of48adult maleICR mice were used. The experimental protocol was the same as described above. After7days quarantine period, a randomized block design was used to divide the mice into6groups,8animals in each group (controls, RF/sham+/-BLM). Seventy-two hours later, all mice were sacrificed. Plasma, liver and lung tissues were collected immediately aftermice sacrifice. Levels of8-OHdG in plasma, liver and lung tissues were determinedwith commercial ELISA kit.2. To study the kinetics of DNA repair in peripheral blood leukocytes, a total of48adult male ICR mice were used. After7days quarantine period, a randomized blockdesign was used to divide the mice into the following6group: Control group, Shamexposure group, BLM group, RF group, RF+BLM group, Sham+BLM group,8animalsin each group. Control group: un-exposed controls; BLM group: BLM, intra-peritonealinjection,37.5mg/kg body weight alone; RF group and RF+BLM group:900MHzradiofrequency fields (RF) exposure at120μW/cm2power density for4h/day for7days; Sham group and Sham exposure+BLM group: sham exposure for4h/day for7days. On day7, at4hours after the last RF/sham exposure, animals in groups BLM,RF+BLM and Sham+BLM were suffered with37.5mg/kg body weight BLMintra-peritoneal injection. Twenty minutes later, all mice were sacrificed. From eachanimal, a small aliquot of blood was used immediately to determine the BLM-inducedprimary DNA damage while similar aliquots were used at30minute intervals todetermine the damage repair kinetics.3. To detect Nitric oxide (NO), superoxide dismutase (SOD) and malondialdehyde(MDA) levels in plama, a total of48adult male ICR mice were used. After7daysquarantine period, a randomized block design was used to divide the mice into thefollowing6group: Control group, Sham exposure group, BLM group, RF group,RF+BLM group, Sham+BLM group,8animals in each group. Control group:un-exposed controls; BLM group: BLM, intra-peritoneal injection,37.5mg/kg bodyweight alone; RF group and RF+BLM group:900MHz radiofrequency fields (RF)exposure at120μW/cm2power density for4h/day for7days; Sham group and Shamexposure+BLM group: sham exposure for4h/day for7days. On day7, at4hours afterthe last RF/sham exposure, animals in groups BLM, RF+BLM and Sham+BLM weresuffered with37.5mg/kg body weight BLM intra-peritoneal injection. Two hours later,all mice were sacrificed and plasma was collected. Levels of NO, MDA and SOD in plasma were determined with commercial ELISA kit.To investigate the oxidative damage in liver and lung tissues, another48adult maleICR mice were used with the same treatment procedure described above. Mice weresacrificed and liver and lung tissues were collected30minutes after treatment. Levels ofNO, MDA and SOD in liver and lung tissues were determined with commercial ELISA kit.Result:1. The results of alkaline comet assay and the concentration of8-OHdG in livertissues indicated that the extent of DNA damage were similar in control animals andthose exposed to radiofrequency fields alone. Mice which were pre-exposed toradiofrequency radiation for7day,4h/d, and then subjected to BLM showedprogressively decreased damage and were significantly different from those exposed toBLM alone. Exposure of mice to BLM resulted in a significant increase in DNAdamage compared to those control animals.2. The results of alkaline comet assay showed that there was no significantincrease in DNA damages induced by RF exposure per se. Compared with the animalsinjected with BLM alone, mice exposed to RF+BLM showed accelerated repair ofBLM-induced DNA damage which was returned to control levels in150minutes.3. Compared with control group, levels of NO in liver and lung tissuessignificantly increased in mice exposed to BLM alone, while levels of SOD in plasma,liver and lung tissues significantly decreased. There was a significant increase of MDAlevel in plasma, liver and lung tissues of BLM injected animals compared to controlanimals. Compared with the animals injected with BLM alone, mice exposed toRF+BLM showed significant decrease of NO level in liver and lung tissues, significantincrease of SOD level in lung tissues and significant decreased MDA level in plasmaand liver tissues. The levels of NO, SOD and MDA was similar in control animals andthose exposed to radiofrequency fields alone. There were no significant differences inany of these indices between mice injected with BLM and exposed to sham+BLM. Conclusions：1. Pre-exposure with120μW/cm2low dose RF could induce adaptive response onDNA damage caused by BLM in mice.2. Low dose RF induced adaptive response may be due to efficient and fasterkinetics of DNA repair.3. Oxidative stress may be involved in the underlying mechanism of adaptiveresponse induced by low dose RF radiation.