Effects of occupational exposure to radioactive beams on oxidative DNA damage in Radiography staff in Isfahan's public hospitals

Abstract

Background: Although ionizing radiation is very effective in medical science to diagnose and treat diseases, it can also be the cause of cancer. Ionizing radiation produces free radicals which lead to oxidative DNA damage. 8-Hydroxy-2'-deoxyguanosine level (8-OHdG), oxidative modification of Guanine excreted in the urine, is one of the most sensitive biomarkers of oxidative DNA cell damage. Formation of 8-OHdG in serum, leukocytes, and urine is often measured to investigate the level of oxidative stress in humans. This compound is a known carcinogenic substance that is conjugated to thymidine, and G: C → T: A conversion occurs. Increasing the base level of DNA oxidation is accompanied by various diseases including diabetes mellitus, cancer, degenerative diseases of the nervous system, and the renal terminal diseases. The level of oxidative DNA lesions depends on several factors, including environmental risks and genotoxic factors, smoking, alcohol consumption, intracellular and extracellular metabolism, and exposure to the ionizing radiation. Oxidative stress is thought to be associated with the tumor formation. Therefore, determining the level of 8-OHdG can determine the individual's susceptibility to develop a tumor and the resulting in emergence of cancer. Various methods have been developed for quantitative measurement of 8-OHdG in human DNA specimens, which include HPLC, GC/MS, the chemistry of immunity texture, and the ELISA test. The most sensitive method is to measure the FPG (the enzyme formamidopyrimidine glycolase DNA) and CG/MS. For some difficulties for determination of 8-hydroxy2-deoxyguanosine by chromatographic methods (such as expensive required instruments and difficult derivatization procedure), most researchers tend to determine 8-hydroxy2-deoxyguanosine with the available commercial ELISA kits. However, it is notable that rate of detection of GC/MS method for determination of 8-hydroxy2-deoxyguanosine is at least 10 times better than ELISA method and there is no possibility for false positive or negative results in GC/MS determination. One of the environmental factors that affect human physiology and DNA oxidative damage is ionizing radiation, which has been investigated and documented sufficiently during the past century and after nuclear incidents and inhalation of or exposure to ionizing radiation. Regardless of environmental exposure, artificial resources of ionizing radiation are used increasingly. Several studies have reported that the concentration of 8-OHdG increases with exposure to low-dose ionizing radiation. The findings of a study showed that levels of 8-OHdG in urine of individuals exposed to ionizing radiation were significantly higher than those who did not have exposure. The increasing use of radiological equipment, the development of radiological treatment strategies, and the increasing availability of ionizing radiation for therapeutic purposes have increased concerns over the dose of radiation received by personnel. Despite the unique benefits of ionizing radiation, radiation protection is a potential source of potential risks such as cancer and genetic abnormalities. The risk of cancer caused by diagnostic radiology is estimated to be about 0.6 to 6. It is estimated that the dose resulting from the annual diagnostic radiology tests is responsible for 1 and 4 cases of cancer in the population of Japan and the United States, respectively. Although the dose of most diagnostic radiological tests is very low, the rapid increase in the use of radiographic tests in the last two decades has caused a wave of concern about the carcinogenic effects of ionizing radiation. There are more than 3 million radiographic tests and more than 100,000 nuclear medicine tests in the world every day. Staff in the radiology and radiotherapy departments are exposed to the cumulative effects of ionizing radiation. The limit dose varies for radiology staff and the general public. In radiology staff, the effective annual dose is 20 millisieverts. Therefore, it is necessary to study the degree of can er susceptibility through biological monitoring in radiologists. The purpose of this study was to measure the concentration of 8-Hydroxy-2'-deoxyguanosine (8-OHdG) in the urine of Radiography staff as a biomarker of oxidative damage and to compare it with the non-radiation workers group. Methods: In this case-control study, 70 samples were selected in two groups. 35 staffs were various radiologists’ groups working in Isfahan's public hospitals (including nuclear medicine, radiology, radiotherapy and CT scans) and 35 employees who had no exposure to radiation. Due to the limited number of radiography staff in the state hospitals of Isfahan, especially the radiotherapy and nuclear medicine groups, and the lack of cooperation between hospitals and private centers, the minimum considered number was 35 radiographers and 35 non-radiation workers. After coordinating with the management of the hospitals, informed consent was obtained from each of the participants. Initially, a checklist of participants' demographic information (gender, age, work experience, and type of occupational group) was prepared. The inclusion criteria to the study were investigated via a checklist for the radiographers and the non-radiation workers.When refusing urine, smoking, drinking tea and coffee during work shifts, drinking alcohol, take medication even a few days before sampling, suffer from acute and chronic diseases (such as cancer, diabetes, renal terminal diseases, degenerative diseases of the nervous system, hypertension, or any other known disease), as well as in the radiologist’s group, if employed in a second job facing ionizing radiation, samples were removed from the study and selected personnel at the end of the shift, an urine sample was taken to determine the 8-OHdG concentration. The samples were extracted by SPE (solid-phase extraction) method and then the concentration of the substance was read by GC/MS device. The concentration of creatinine in the urine was measured in an approved medical laboratory using its commercial kit purchased from Sigma Diagnostics. Preparation and clean-up of urine samples were performed according to a previously described method with some modifications. Waters Oasis® HLB Vac cartridges (60 mg of packing material) were used for cleaning-up of urine samples. After each step of the clean-up process, the cartridges were entirely dried under vacuum to avoid cross-contamination and to maximize the required recovery. Each cartridge was only used to clean-up one urine sample. The analysis was performed on a quadruple Agilent GC-MS D: model 7890A (Agilent Technologies, Palo Alto, CA, USA) coupled to a mass selective detector model 5975C inert, equipped with a split/splitless injector. Quantification was performed at the selected ion monitoring (SIM) mode based on the selection of mass peaks with the highest intensity for 8OHdG to gain the highest possible sensitivity, (m/z 207). Finally, the data from the determination of 8-OHdG concentration were analyzed through SPss software version 26. For this purpose, chi-square test was used to compare the qualitative data, and the independent t-test was used to determine the concentration of 8-OHdG in the two groups. Then one-way Anova and tukey post hoc tests were applied to compare the concentration of 8-OHdG in different groups of radiographers. Results: The results showed that the average concentration of 8-OHdG in radiologists’ urine (259/4±31.07 ng/mg creatinine) has a significant difference with the average concentrations of this material in non-radilogists’ urine (141/1±21/8 ng/mg creatinine) (P=0.003). Further analysis of the data showed that the mean concentration of 8- hydroxy-2-deoxy-guanosine in urine was also found in different groups of radiographers, as follows: One-way ANOVA showed that there was a significant difference in the mean concentration of 8-hydroxy-2-deoxy-guanosine in urine between different occupations (P = 0.013). The tukey post hoc test showed that the mean concentration of urine in people with nuclear medicine occupation was sig ificantly higher than the ones with occupations such as radiotherapy (P = 0.02), radiology (P =0.014). However, there were no significant differences between the nuclear medicine and CT scan(P =0.09). Conclusion: Several studies have reported that the concentration of 8-OHdG increases with exposure to low-dose ionizing radiation. The findings of a study showed that levels of 8-OHdG in urine of individuals exposed to ionizing radiation were significantly higher than those who did not have exposure. The results of this study, which was done for the first time in the country by using solid-phase extraction method for data extraction and then analyzing by GC/ MS to determining 8-OHdG level in urine, indicated that Ionizing radiation has been affected in the increase of 8-OHdG level as a potential biomarker of oxidative DNA damage. Increasing the concentration of 8-hydroxy2-deoxyguanosine in the urine of the nuclear medicine group indicates that with the higher the amount of radiation, the oxidative damage will be more. The dose received by staff working in the nuclear medicine group is higher than other workers due to work in the banned area (little distance of the technician from the source of radiation) than the rest of the staff. The higher the distance with the source, the lower the exposure. Any object between the technician and the source of radiation will reduce the amount of exposure, and as a general rule, if the object or matter between the technician and the source of the beam is denser, the better protection will be provide. Inevitably, compliance with the radiation safety principles by radiologists will reduce their radiation, which includes: reducing the exposure time to radiation, increasing the distance from the source, placing a protective shield between the person and the radiation source and protecting itself against radioactive contamination using appropriate clothing. Given the relation between oxidative stress and cancer, it seems that the consumption of antioxidants, such as vitamin E and C, and Beta-carotene is beneficial in preventing cancer. Also, the effect of exercise on oxidative stress has been investigated in some studies. Oxidative DNA damage in athletes is less than that of non-athletes. This may be due to the history of regular resistance exercises in bodybuilding athletes, and it is possible that antioxidant capacity in athletes may be developed due to regular exercises. © 2020 Iran University of Medical Sciences. All rights reserved.