Khan Mohammed A, Van Dyk Jake, Yeung Ivan W T, Hill Richard P
Research Division, Ontario Cancer Institute/Princess Margaret Hospital, Princess Margaret Hospital, University Health Network, 610 University Avenue, Toronto, Ontario, Canada M5G 2M9.
Radiother Oncol. 2003 Jan;66(1):95-102. doi: 10.1016/s0167-8140(02)00325-0.
These studies were designed to examine radiation-induced in-field and out-of-field DNA damage in rat lung as a function of dose and various volumes of irradiation. They also determined whether superoxide dismutase (SOD) and nitro-L-arginine methyl ester (L-NAME) protected against this damage.
The whole lung, or various volumes of the lower or upper lungs of Sprague-Dawley rats were exposed to doses up to 20 Gy of 60Co gamma rays. Radiation-induced DNA damage was quantified in fibroblasts obtained at 18 h after irradiation from both irradiated and shielded lung regions using a micronucleus assay. The radioprotective role of SOD (CuZnSOD: 10 mg/kg body weight; MnSOD: 50-100mg/kg body weight) and L-NAME (0.2 mg/kg body weight.) in vivo was determined by injecting them into rats 30 min before or immediately after a dose of 10 Gy.
Micronucleus formation was approximately linear with dose up to 15 Gy. When 70% of the lung volume was irradiated with 10 Gy, irradiated lower lung gave similar numbers of micronuclei (MN)/binucleate cell (BN) to that observed following whole lung irradiation (0.91 MN/BN), whereas the irradiated upper lung gave only 0.66 MN/BN. Following lower lung irradiation, the shielded upper lung (30% of lung volume) showed substantial (out-of-field) damage (0.43 MN/BN). When 30% of the lung was given 10 Gy, irradiated upper or lower lung showed similar amounts of in-field damage (0.43 MN/BN) but this was smaller than that seen following irradiation of 70% of the lung volume. For 30% lower lung irradiation, the shielded upper lung showed only a small out-of-field effect (0.1 MN/BN). For both volumes of irradiation there was a similar or smaller effect in the shielded lower lung after upper lung irradiation. Injection of SOD before or L-NAME after 10 Gy to the lower 70% lung volume resulted in a reduction in DNA damage both in-field and out-of-field but the percentage was much greater for out-of-field damage (50-60%) than for in-field damage (10-30%). Following whole lung irradiation (10 Gy) significantly greater DNA damage was observed in fibroblasts from the left lung than from the right lung (0.93 MN/BN vs. 0.82 MN/BN). Following whole lung irradiation there was no significant difference in DNA damage observed in fibroblasts from the lower lung and the upper lung.
With partial lung irradiation the lower lung sustains more in-field DNA damage following irradiation than the upper lung, whereas out-of-field effects are observed primarily in the upper lung (i.e. following lower lung irradiation). Following whole lung irradiation the left lung sustains more damage than the right lung but there is no difference between the upper and lower lung. The protective effects of SOD and L-NAME suggest that inflammatory cytokines induced by the irradiation may be involved in the initiation of a reaction resulting in the production of reactive oxyradicals and nitric oxide that cause indirect DNA damage both in and out of the radiation field.
这些研究旨在研究大鼠肺部辐射诱导的野内和野外DNA损伤与剂量及不同照射体积的关系。同时还确定超氧化物歧化酶（SOD）和硝基-L-精氨酸甲酯（L-NAME）是否能预防这种损伤。
将Sprague-Dawley大鼠的全肺或下肺或上肺的不同体积暴露于高达20 Gy的60Coγ射线剂量下。使用微核试验对照射后18小时从照射和屏蔽肺区域获得的成纤维细胞中的辐射诱导DNA损伤进行定量。通过在10 Gy剂量前30分钟或后立即将SOD（铜锌超氧化物歧化酶：10 mg/kg体重；锰超氧化物歧化酶：50 - 100 mg/kg体重）和L-NAME（0.2 mg/kg体重）注射到大鼠体内，来确定它们在体内的辐射防护作用。
在高达15 Gy的剂量下，微核形成与剂量大致呈线性关系。当70%的肺体积接受10 Gy照射时，照射的下肺产生的微核数（MN）/双核细胞（BN）与全肺照射后观察到的相似（0.91 MN/BN），而照射的上肺仅产生0.66 MN/BN。下肺照射后，屏蔽的上肺（肺体积的30%）显示出明显的（野外）损伤（0.43 MN/BN）。当30%的肺接受10 Gy照射时，照射的上肺或下肺显示出相似程度的野内损伤（0.43 MN/BN），但小于70%肺体积照射后的损伤。对于30%下肺照射，屏蔽的上肺仅显示出较小的野外效应（0.1 MN/BN）。对于两种照射体积，上肺照射后屏蔽的下肺效应相似或较小。在70%下肺体积接受10 Gy照射前注射SOD或照射后注射L-NAME，可导致野内和野外DNA损伤均减少，但野外损伤减少的百分比（约50 - 60%）远高于野内损伤（10 - 30%）。全肺照射（10 Gy）后，观察到左肺成纤维细胞中的DNA损伤明显大于右肺（0.93 MN/BN对0.82 MN/BN）。全肺照射后，下肺和成纤维细胞中的DNA损伤与上肺相比没有显著差异。
部分肺照射时，下肺照射后野内DNA损伤比上肺更严重，而野外效应主要在上肺观察到（如下肺照射后）。全肺照射后，左肺比右肺损伤更严重，但上肺和下肺之间没有差异。SOD和L-NAME的保护作用表明，照射诱导的炎性细胞因子可能参与引发导致活性氧自由基和一氧化氮产生的反应，从而在辐射场内和场外造成间接DNA损伤。
