Inhibitory effects of prior low-dose X-ray irradiation on carbon tetrachloride-induced hepatopathy in acatalasemic mice

Effects of low-dose/high-dose-rate X-irradiation on oxidative stress in organs following forced swim test and its combined effects on alcohol-induced liver damage in mice

The liver's susceptibility to oxidative stress after a combination of forced swim test (FST) and low-dose-rate γ-irradiation has been observed. Therefore, this study aims to clarify the effects of low-dose (0.1 and 0.5 Gy)/high-dose-rate (1.2 Gy/min) irradiation on combined oxidative stressors-liver damage associated with FST and alcohol administration. In addition, the effects of similar irradiation on FST-induced immobility, which induces psychomotor retardation, and antioxidative effects on the brain, lungs, liver and kidneys were investigated, and the results were compared with those of a similar previous study that utilized low-dose-rate irradiation. Low-dose/high-dose-rate (especially 0.5 Gy) irradiation temporarily worsened liver antioxidant function and hepatic function with FST- and alcohol administration-related oxidative damage; however, the damages improved soon after. In addition, the increase in total glutathione content in the liver contributed to the early improvement of hepatic functions. However, pre-irradiation did not suppress immobility during the FST. The results also suggested that the effects of low-dose/high-dose-rate irradiation on the antioxidant functions of each organ after the FST were different from those of low-dose/low-dose-rate irradiation. Overall, this study provides further insights into the effects of low-dose irradiation on exposure to a combination of different oxidative stressors. It will also contribute to the elucidation of dose rate effects on oxidative stress in the low-dose irradiation range.

X-Irradiation at 0.5 Gy after the forced swim test reduces forced swimming-induced immobility in mice

The forced swim test (FST) is a screening model for antidepressant activity; it causes immobility and induces oxidative stress. We previously reported that radon inhalation has antidepressant-like effects in mice potentially through the activation of antioxidative functions upon radon inhalation. This study aimed to investigate the effect of prior and post low-dose X-irradiation (0.1, 0.5, 1.0 and 2.0 Gy) on FST-induced immobility and oxidative stress in the mouse brain, and the differences, if any, between the two. Mice received X-irradiation before or after the FST repeatedly for 5 days. In the post-FST-irradiated group, an additional FST was conducted 4 h after the last irradiation. Consequently, animals receiving prior X-irradiation (0.1 Gy) had better mobility outcomes than sham-irradiated mice; however, their levels of lipid peroxide (LPO), an oxidative stress marker, remained unchanged. However, animals that received post-FST X-irradiation (0.5 Gy) had better mobility outcomes and their LPO levels were significantly lower than those of the sham-irradiated mice. The present results indicate that 0.5 Gy X-irradiation after FST inhibits FST-induced immobility and oxidative stress in mice.

Amelioration of thioacetamide-induced hepatic encephalopathy in rats by low-dose gamma irradiation

Brain affection is a common symptom of liver insufficiency. This study aimed to evaluate the role of low-dose γ irradiation (LDR) as a potential therapeutic agent in thioacetamide (TAA)-induced hepatic encephalopathy (HE) in rats. Effects of local and whole-body irradiation (0.5 Gy) on rat brain/liver were evaluated following the induction of HE by TAA (200 mg/kg/day/for 3 successive days). Serum activities of aspartate transaminase (AST) and alanine transaminase (ALT) and ammonia level were assessed. The effect of HE on brain was evaluated through the determination of brain contents of malondialdehyde (MDA), reduced glutathione (GSH), tumor necrosis factor-alpha (TNF-α), and interleukin-1beta (IL-1β) and glutathione peroxidase (GPx) activity. Moreover, apoptotic and inflammatory changes in brain and liver tissues were assessed together with alpha-smooth muscle actin (α-SMA); fibrosis marker. Results showed correction of the biochemical parameters which was supported by the results of the immunohistochemical examinations. LDR is a promising hepato- and neurotherapy against HE.

Antioxidant and antiapoptotic effects of sea cucumber and valsartan against doxorubicin-induced cardiotoxicity in rats: The role of low dose gamma irradiation

Doxorubicin (DOX) is a highly effective antineoplastic drug; however, the clinical use of DOX is limited by its dose dependent cardiotoxicity. This study was conducted to evaluate the cardioprotective effect of sea cucumber and valsartan against DOX-induced cardiotoxicity in rats. Also, the role of exposure to low dose γ radiation (LDR) on each of them was investigated, since LDR could suppress various reactive oxygen species-related diseases. Rats received DOX (2.5mg/kg, ip) in six equal injections over a period of 2weeks, sea cucumber (14.4mg/kg, p.o) and valsartan (30mg/kg, p.o) for 8 successive weeks. Exposure to LDR (0.5Gy) was performed one day prior to DOX. Results revealed that DOX administration elevated serum levels of aspartate aminotransferase (AST), lactate dehydrogenase (LDH), creatine kinase (CK-MB) and troponin-I as well as increased cardiac lipid peroxide content and myeloperoxidase (MPO) activity. Additionally, it increased cardiac expressions of iNOS and caspase-3, accompanied by reduction in cardiac total protein and glutathione (GSH) contents. Treatment with sea cucumber or valsartan improved the cardiotoxicity of DOX. Their adjuvant therapy with LDR offers an additional benefit to the cardioprotection of the therapeutic drugs. These results confirmed by histopathological examination. In conclusion, sea cucumber and valsartan alone or combined with LDR attenuated DOX-induced cardiotoxicity via their antioxidant and anti-apoptotic activities and thus might be useful in the treatment of human patients under doxorubicin chemotherapy.

Study of antioxidative effects and anti-inflammatory effects in mice due to low-dose X-irradiation or radon inhalation

Low-dose irradiation induces various stimulating effects, especially activation of the biological defense system including antioxidative and immune functions. Oxidative stress induced by reactive oxygen species (ROS) can cause cell damage and death and can induce many types of diseases. This paper reviews new insights into inhibition of ROS-related diseases with low-dose irradiation or radon inhalation. X-irradiation (0.5 Gy) before or after carbon tetrachloride (CCl4) treatment inhibits hepatopathy in mice. X-irradiation (0.5 Gy) before ischemia-reperfusion injury or cold-induced brain injury also inhibits edema. These findings suggest that low-dose X-irradiation has antioxidative effects due to blocking the damage induced by free radicals or ROS. Moreover, radon inhalation increases superoxide dismutase activity in many organs and inhibits CCl4-induced hepatic and renal damage and streptozotocin-induced type I diabetes. These findings suggest that radon inhalation also has antioxidative effects. This antioxidative effect against CCl4-induced hepatopathy is comparable to treatment with ascorbic acid (vitamin C) at a dose of 500 mg/kg weight, or α-tocopherol (vitamin E) treatment at a dose of 300 mg/kg weight, and is due to activation of antioxidative functions. In addition, radon inhalation inhibits carrageenan-induced inflammatory paw edema, suggesting that radon inhalation has anti-inflammatory effects. Furthermore, radon inhalation inhibits formalin-induced inflammatory pain and chronic constriction injury-induced neuropathic pain, suggesting that radon inhalation relieves pain. Thus, low-dose irradiation very likely activates the defense systems in the body, and therefore, contributes to preventing or reducing ROS-related injuries, which are thought to involve peroxidation.

Prolongation of life span in the accelerated aging klotho mouse model, by low-dose-rate continuous γ irradiation

While lifespan studies provide basic information for estimating the risk of ionizing radiation, findings on the effect of low-dose/low-dose-rate irradiation on the lifespan of mammals are controversial. Here we evaluate the effect of continuous exposure to low-dose-rate γ radiation on the lifespan of mice with accelerated aging caused by mutation of the klotho gene. While control mice died within 80 days after birth, more than 10% of mice exposed continuously to 0.35 or 0.7 or mGy/h γ radiation from 40 days after birth survived for more than 80 days. Two of 50 mice survived for more than 100 days. Low-dose-rate irradiation significantly increased plasma calcium concentration in mutant mice, and concomitantly increased hepatic catalase activity. Although hepatic activity of superoxide dismutase in mutant mice decreased significantly compared to wild-type mice, continuous γ irradiation decreased the activity in mutant mice significantly. These results suggest that low-dose-rate ionizing radiation can prolong the lifespan of mice in certain settings.

Suppression of streptozotocin-induced type-1 diabetes in mice by radon inhalation

We examined the protective effect of radon inhalation on streptozotocin (STZ)-induced type-1 diabetes in mice. Mice inhaled radon at concentrations of 1000, 2500, and 5500 Bq/m3 for 24 hours before STZ administration. STZ administration induced characteristics of type-1 diabetes such as hyperglycemia and hypoinsulinemia; however, radon inhalation at doses of 1000 and 5500 Bq/m3 significantly suppressed the elevation of blood glucose in diabetic mice. Serum insulin was significantly higher in mice pre-treated with radon at a dose of 1000 Bq/m3 than in mice treated with a sham. In addition, superoxide dismutase activities and total glutathione contents were significantly higher and lipid peroxide was significantly lower in mice pre-treated with radon at doses of 1000 and 5500 Bq/m3 than in mice treated with a sham. These results were consistent with the result that radon inhalation at 1000 and 5500 Bq/m3 suppressed hyperglycemia. These findings suggested that radon inhalation suppressed STZ-induced type-1 diabetes through the enhancement of antioxidative functions in the pancreas.

Inhibitory effects of pretreatment with radon on acute alcohol-induced hepatopathy in mice

We previously reported that radon inhalation activates antioxidative functions in the liver and inhibits carbon tetrachloride-induced hepatopathy in mice. In addition, it has been reported that reactive oxygen species contribute to alcohol-induced hepatopathy. In this study, we examined the inhibitory effects of radon inhalation on acute alcohol-induced hepatopathy in mice. C57BL/6J mice were subjected to intraperitoneal injection of 50% alcohol (5 g/kg bodyweight) after inhaling approximately 4000 Bq/m³ radon for 24 h. Alcohol administration significantly increased the activities of glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT) in serum, and the levels of triglyceride and lipid peroxide in the liver, suggesting acute alcohol-induced hepatopathy. Radon inhalation activated antioxidative functions in the liver. Furthermore, pretreatment with radon inhibited the depression of hepatic functions and antioxidative functions. These findings suggested that radon inhalation activated antioxidative functions in the liver and inhibited acute alcohol-induced hepatopathy in mice.

Comparative study on the inhibitory effects of antioxidant vitamins and radon on carbon tetrachloride-induced hepatopathy

We have previously reported that radon inhalation activates anti-oxidative functions and inhibits carbon tetrachloride (CCl(4))-induced hepatopathy. It has also been reported that antioxidant vitamins can inhibit CCl(4)-induced hepatopathy. In the current study, we examined the comparative efficacy of treatment with radon, ascorbic acid and α-tocopherol on CCl(4)-induced hepatopathy. Mice were subjected to intraperitoneal injection of CCl(4) after inhaling approximately 1000 or 2000 Bq/m(3) radon for 24 h, or immediately after intraperitoneal injection of ascorbic acid (100, 300, or 500 mg/kg bodyweight) or α-tocopherol (100, 300, or 500 mg/kg bodyweight). We estimated the inhibitory effects on CCl(4)-induced hepatopathy based on hepatic function-associated parameters, oxidative damage-associated parameters and histological changes. The results revealed that the therapeutic effects of radon inhalation were almost equivalent to treatment with ascorbic acid at a dose of 500 mg/kg or α-tocopherol at a dose of 300 mg/kg. The activities of superoxide dismutase, catalase, and glutathione peroxidase in the liver were significantly higher in mice exposed to radon than in mice treated with CCl(4) alone. These findings suggest that radon inhalation has an anti-oxidative effect against CCl(4)-induced hepatopathy similar to the anti-oxidative effects of ascorbic acid or α-tocopherol due to the induction of anti-oxidative functions.

Protective effects of radon inhalation on carrageenan-induced inflammatory paw edema in mice

We assessed whether radon inhalation inhibited carrageenan-induced inflammation in mice. Carrageenan (1% v/v) was injected subcutaneously into paws of mice that had or had not inhaled approximately 2,000 Bq/m(3) of radon for 24 h. Radon inhalation significantly increased superoxide dismutase (SOD) and catalase activities and significantly decreased lipid peroxide levels in mouse paws, indicating that radon inhalation activates antioxidative functions. Carrageenan administration induced paw edema and significantly increased tumor necrosis factor-alpha (TNF-α) and nitric oxide in serum. However, radon inhalation significantly reduced carrageenan-induced paw edema. Serum TNF-α levels were lower in the radon-treated mice than in sham-treated mice. In addition, SOD and catalase activities in paws were significantly higher in the radon-treated mice than in the sham-treated mice. These findings indicated that radon inhalation had anti-inflammatory effects and inhibited carrageenan-induced inflammatory paw edema.

Inhibitory effects of prior low-dose X-irradiation on cold-induced brain injury in mouse

We examined the inhibitory effects of low-dose X-irradiation on mouse brain tissue with cold-induced injury by comparing tissue samples from three groups of mice: control, sham-irradiated cold-exposed, and X-ray-irradiated (0.5 Gy) cold-exposed mice. The water content in brain increased significantly in the sham-irradiated group following the cold-induced injury relative to the control group. However, water content in brain tissue from the X-ray-irradiated group was significantly lower than that from the sham-irradiated group. Levels of antioxidants, such as superoxide dismutase and glutathione, in brain tissue from the X-ray-irradiated group were higher than those from the sham-irradiated group. Moreover, the cold injury-induced cell death, particularly apoptosis, while low-dose irradiation inhibited cell death, especially among glial cells, but not numeral cells. These findings suggest that prior low-dose X-irradiation activated antioxidant function and inhibited cold-induced brain injury.

Activation of biodefense system by low-dose irradiation or radon inhalation and its applicable possibility for treatment of diabetes and hepatopathy

Adequate oxygen stress induced by low-dose irradiation activates biodefense system, such as induction of the synthesis of superoxide dismutase (SOD) and glutathione peroxidase. We studied the possibility for alleviation of oxidative damage, such as diabetes and nonalcoholic liver disease. Results show that low-dose γ-irradiation increases SOD activity and protects against alloxan diabetes. Prior or post-low-dose X- or γ-irradiation increases antioxidative functions in livers and inhibits ferric nitrilotriacetate and carbon tetrachloride-induced (CCl₄) hepatopathy. Moreover, radon inhalation also inhibits CCl₄-induced hepatopathy. It is highly possible that low-dose irradiation including radon inhalation activates the biodefence systems and, therefore, contributes to preventing or reducing reactive oxygen species-related diabetes and nonalcoholic liver disease, which are thought to involve peroxidation.

Suppressive effects of continuous low-dose-rate γ irradiation on diabetic nephropathy in type II diabetes mellitus model mice

It has been proposed that the development of diabetic nephropathy is caused in large part by oxidative stress. We previously showed that continuous exposure of mice to low-dose-rate γ radiation enhances antioxidant activity. Here, we studied the ameliorative effect of continuous whole-body irradiation with low-dose-rate γ rays on diabetic nephropathy. Ten-week-old female db/db mice, an experimental model for type II diabetes, were irradiated with low-dose-rate γ rays from 10 weeks of age throughout their lives. Nephropathy was studied by histological observation and biochemical analysis of serum and urine. Antioxidant activities in kidneys were determined biochemically. Continuous low-dose-rate γ radiation significantly increases life span in db/db mice. Three of 24 irradiated mice were free of glucosuria after 80 weeks of irradiation. Histological studies of kidney suggest that low-dose irradiation increases the number of normal capillaries in glomeruli. Antioxidant activities of superoxide dismutase, catalase and glutathione are significantly increased in kidneys of irradiated db/db mice. Continuous low-dose-rate γ irradiation ameliorates diabetic nephropathy and increases life span in db/db mice through the activation of renal antioxidants. These findings have noteworthy implications for radiation risk estimation of non-cancer diseases as well as for the clinical application of low-dose-rate γ radiation for diabetes treatment.

Study of the response of superoxide dismutase in mouse organs to radon using a new large-scale facility for exposing small animals to radon

We examined dose-dependent or dose rate-dependent changes of superoxide dismutase (SOD) activity using a new large-scale facility for exposing small animals to radon. Mice were exposed to radon at a concentration of 250, 500, 1000, 2000, or 4000 Bq/m(3) for 0.5, 1, 2, 4, or 8 days. When mice were exposed to radon at 2000 day•Bq/m(3), activation of SOD activities in plasma, liver, pancreas, heart, thymus, and kidney showed dose-rate effects. Our results also suggested that continuous exposure to radon increased SOD activity, but SOD activity transiently returned to normal levels at around 2 days. Moreover, we classified the organs into four groups (1. plasma, brain, lung; 2. heart, liver, pancreas, small intestine; 3. kidney, thymus; 4. stomach) based on changes in SOD activity. Thymus had the highest responsiveness and stomach had lowest. These data provide useful baseline measurements for future studies on radon effects.

Basic study on active changes in biological function of mouse liver graft in cold storage after low-dose x-irradiation

We previously reported that low-dose X-irradiation alleviates ischemia-reperfusion injury such as mouse paw edema. In this study, we examined active changes in the biological function of mouse liver grafts in cold storage after low-dose X-irradiation. Mouse livers were sham-irradiated or were irradiated with 0.25, 0.5, 1.0, or 5.0 Gy of X-ray and stored for 4, 8, 24, or 48 h in preservation or saline solution. The results show that storage for 24 h in saline solution after 0.5 Gy irradiation significantly increased the activity of superoxide dismutase (SOD) and catalase. Following storage for 4, 8, or 48 h in preservation solution, lipid peroxide levels of the 0.5 Gy irradiated group were significantly lower than those of the sham irradiated group. Following storage for 24 h in preservation solution, the activity of SOD and catalase of the 1.0 Gy irradiated group were significantly higher than those of the sham irradiated group. Hepatocytes stored in saline solution were vacuolated. However, no vacuole formation was observed in hepatocytes stored in preservation solution. These findings suggest that low-dose irradiation significantly activates antioxidative functions of liver grafts. Moreover, the dose at which enhancement of antioxidative function occurs in livers stored in preservation solution, which contains glutathione, is significantly higher than that in saline solution.

Induction of radical scavenging ability and suppression of lipid peroxidation in rat liver microsomes following whole-body, low-dose X-irradiation

PURPOSE

To investigate changes in radical scavenging ability and lipid peroxidation in liver microsomal membranes and cooperative suppression of lipid peroxidation by microsomal and cytosolic radical scavengers, 24 h after whole-body, low-dose X-irradiation of rats.

MATERIALS AND METHODS

Male Wistar rats were irradiated with 1-50 cGy of X-rays. Liver microsomal radical scavenging ability was determined using the trapping ability of 1,1-diphenyl-2-picrylhydrazyl (DPPH), a stable free radical. Microsomal alpha-tocopherol (Vit.E) content was determined using an electrochemical detector. Microsomal glutathione peroxidase (GPx) activity was determined as the consuming rate of NADPH. Microsomal lipid peroxidation was determined by the thiobarbituric acid method.

RESULTS

Low molecular weight radical scavenging ability of rat liver microsomes increased 24 h after whole-body, low-dose X-irradiation when alpha-tocopherol was included, showing a maximum level at 5-10 cGy. Microsomal GPx activity also increased 24 h after 5 cGy irradiation. The lipid peroxidation level in microsomes decreased, showing a maximal suppression at 5 cGy. High-dose irradiation-induced microsomal lipid peroxidation was strongly suppressed cooperatively by microsomal and cytosolic antioxidants induced by low-dose irradiation.

CONCLUSION

Low doses of radiation induce increases in liver microsomal antioxidants, which in turn result in enhanced suppression of microsomal lipid peroxidation cooperatively with cytosolic antioxidants induced by low-dose irradiation.

Low-dose radiation and its clinical implications: diabetes

Induction of hormesis and adaptive response by low-dose radiation (LDR) has been extensively indicated. Adaptive response induced by LDR was not only resistant to damage caused by a subsequently high-dose radiation, but also cross-resistant to other non-radiation challenges, such as chemicals. Mechanisms by which LDR induces the preventive effect on radiation- or chemical-induced tissue damage include induced or up-regulated expression of protective proteins, such as heat shock proteins and antioxidants. Since oxidative damage to tissues is a major pathogenesis of many human diseases including diabetes, this review will summarize the available data with an emphasis of the preventive effect of LDR on the development of diabetes and the therapeutic effect of LDR on diabetic cardiovascular complications. The available data indicated that pre-exposure of mice to LDR reduced the incidence of alloxan-induced diabetes, and also delayed the onset of hyperglycaemia in diabetes-prone non-obese diabetic mice. Experiments with animals indicated the effectively therapeutic effect of low-intensity or power laser (LIL or LPL) radiation on skin wound healing, which has stimulated clinical use of LIL to cure skin ulcer in diabetic patients. Mechanisms by which LDR prevents diabetes, though are unclear now, may include the induction of pancreatic antioxidants to prevent beta cell from oxidative damage and immunomodulation to preserve pancreatic function. For LIL therapeutic effect on diabetic wound healing, mechanisms may include its antioxidant action, immunomodulation, cell proliferation stimulation as well as improvement of systemic and wound-regional microcirculation. Therefore, although only a few studies indicating LDR prevention of the development of diabetes, many studies have demonstrated LDR, specifically LIL, therapeutic effectiveness of diabetic wound healing. These preliminary results are really encouraging for us to further pursue the clinical implication of LDT to diabetes-related areas.

No Different Sensitivity in Terms of Whole-Body Irradiation between Normal and Acatalasemic Mice

To elucidate the radiosensitivity of an acatalasemic mouse, we examined the time and dose-dependency in the survival rates, the lymphocytes and the intestinal epithelial cells, and the antioxidant function after 3.0 to 12.0 Gy whole body irradiation. Results showed that no significant differences between acatalasemic mice and normal mice were observed in the survival rates and the histological changes in spleens and small intestine after each irradiation. The catalase activities in livers and spleens of acatalasemic mice were significantly lower than those of normal mice and the glutathione peroxidase activity in livers of acatalasemic mice was significantly higher than that of normal mice. At 10 days after 6.0 Gy irradiation, the catalase activities in livers of acatalasemic and normal mice and that in spleens of normal mice significantly decreased compared with no-irradiation control, and there were no differences between those catalase activities. The total glutathione content in acatalasemic mice was significantly higher than that in normal mice at 10 days after 6.0 Gy irradiation. These findings suggested that the radiosensitivity of acatalasemic mice in terms of whole body irradiation doesn't significantly differ from that of normal mice, probably due to compensated sufficient contents of glutathione peroxidase and total glutathione in acatalasemic mice.

Inhibitory effects of prior low-dose x-irradiation on ischemia-reperfusion injury in mouse paw

We have reported that low-dose, unlike high-dose, irradiation enhanced antioxidation function and reduced oxidative damage. On the other hand, ischemia-reperfusion injury is induced by reactive oxygen species. In this study, we examined the inhibitory effects of prior low-dose X-irradiation on ischemia-reperfusion injury in mouse paw. BALB/c mice were irradiated by sham or 0.5 Gy of X-ray. At 4 hrs after irradiation, the left hind leg was bound 10 times with a rubber ring for 0.5, 1, or 2 hrs and the paw thickness was measured. Results show that the paw swelling thickness by ischemia for 0.5 hr was lower than that for 2 hrs. At 1 hr after reperfusion from ischemia for 1 hr, superoxide dismutase activity in serum was increased in those mice which received 0.5 Gy irradiation and in the case of the ischemia for 0.5 or 1 hr, the paw swelling thicknesses were inhibited by 0.5 Gy irradiation. In addition, interstitial edema in those mice which received 0.5 Gy irradiation was less than that in the mice which underwent by sham irradiation. These findings suggest that the ischemia-reperfusion injury is inhibited by the enhancement of antioxidation function by 0.5 Gy irradiation.

Activation of Antioxidative Enzymes Induced by Low-Dose-Rate Whole‐Body γ Irradiation: Adaptive Response in Terms of Initial DNA Damage

An adaptive response induced by long-term low-dose-rate irradiation in mice was evaluated in terms of the amount of DNA damage in the spleen analyzed by a comet assay. C57BL/ 6N female mice were irradiated with 0.5 Gy of (137)Cs gamma rays at 1.2 mGy/h; thereafter, a challenge dose (0.4, 0.8 or 1.6 Gy) at a high dose rate was given. Less DNA damage was observed in the spleen cells of preirradiated mice than in those of mice that received the challenge dose only; an adaptive response in terms of DNA damage was induced by long-term low-dose-rate irradiation in mice. The gene expression of catalase and Mn-SOD was significantly increased in the spleen after 23 days of the low-dose-rate radiation (0.5 Gy). In addition, the enzymatic activity of catalase corresponded to the gene expression level; the increase in the activity was observed at day 23 (0.5 Gy). These results suggested that an enhancement of the antioxidative capacities played an important role in the reduction of initial DNA damage by low-dose-rate radiation.

Low dose radiation induced immunomodulation: effect on macrophages and CD8+ T cells

PURPOSE

The aim of the present investigation was to study the effect of fractionated whole body low dose ionizing radiation (LDR) on the functional responses of T lymphocytes, their subpopulations and macrophages.

MATERIALS AND METHODS

C57BL/6 mice were exposed to 4 cGy from a (60)Co source, at 0.31 cGy/min, at 24 h intervals for 5 days (total dose 20 cGy). Phagocytic activity was measured by flow cytometry using Bioparticles and nitric oxide generation was estimated by spectrophotometry. Proliferation of lymphocytes in response to concanavalin A (con A) and alloantigens was measured by (3)H thymidine incorporation. Expression of cell surface markers was assessed by flow cytometric analysis of antibody labeled cells. Target cell killing by cytotoxic T cells (CTL) generated against allogenic cells was assessed by flow cytometry using PKH26 labeled target cells. Cytokines were estimated by enzyme linked immunosorbent assay.

RESULTS

Exposure to LDR enhanced nitric oxide secretion and phagocytosis. The expression of early activation antigen, CD69, was enhanced in CD8(+) T lymphocytes concomitant with enhanced proliferation in response to con A. In addition, mixed lymphocyte reaction (MLR) and CTL response were augmented and secretion of interferon gamma (IFN-gamma) was suppressed following LDR exposure.

CONCLUSIONS

LDR exposure enhanced the function of macrophages and responses of CD8(+) T cells in C57BL/6 mice.