Ability of human plasma to protect against ionising radiation is inversely correlated with age

Reactive Oxygen Species and Antioxidants in Carcinogenesis and Tumor Therapy

Strictly regulated balance between the formation and utilization of reactive oxygen species (ROS) is the basis of normal functioning of organisms. ROS play an important role in the regulation of many metabolic processes; however, excessive content of ROS leads to the development of various disorders, including oncological diseases, as a result of ROS-induced mutations in DNA. In tumors, high levels of oxygen radicals promote cell proliferation and metastasis. On the other hand, high content of ROS can trigger cell death, a phenomenon used in the antitumor therapy. Water- and lipid-soluble antioxidants, as well as antioxidant enzyme systems, can inhibit ROS generation; however, they should be used with caution. Antioxidants can suppress ROS-dependent cell proliferation and metastasis, but at the same time, they may inhibit the death of tumor cells if the antitumor therapeutic agents stimulate oxidative stress. The data on the role of antioxidants in the death of tumor cells and on the effects of antioxidants taken as dietary supplements during antitumor therapy, are contradictory. This review focuses on the mechanisms by which antioxidants can affect tumor and healthy cells.

Antioxidants in the Treatment of Cancer

Several clinical trials have produced conflicting results regarding the benefit of antioxidants in cancer therapy thus questioning the incorporation of these substances in standard treatment regimens. Vitamins E and C, selenium, carotenoids, lycopene, soy products, and green tea extract are a few substances with antioxidant properties that have been studied in detail. This article reviews the results generated over the last 20 years through in vitro and in vivo studies in various types of cancers and stages of cancer treatment. Despite the commercial popularity and the multitude of studies examining antioxidant therapy, the true role of antioxidants is yet to be determined, requiring further investigation into its propagative, causal, or protective nature.

Dietary Antioxidants and Human Cancer

Epidemiological studies show that a high intake of anti-oxidant-rich foods is inversely related to cancer risk. While animal and cell cultures confirm the anticancer effects of antioxidants, intervention trials to determine their ability to reduce cancer risk have been inconclusive, although selenium and vitamin E reduced the risk of some forms of cancer, including prostate and colon cancer, and carotenoids have been shown to help reduce breast cancer risk. Cancer treatment by radiation and anticancer drugs reduces inherent antioxidants and induces oxidative stress, which increases with disease progression. Vitamins E and C have been shown to ameliorate adverse side effects associated with free radical damage to normal cells in cancer therapy, such as mucositis and fibrosis, and to reduce the recurrence of breast cancer. While clinical studies on the effect of anti-oxidants in modulating cancer treatment are limited in number and size, experimental studies show that antioxidant vitamins and some phytochemicals selectively induce apoptosis in cancer cells but not in normal cells and prevent angiogenesis and metastatic spread, suggesting a potential role for antioxidants as adjuvants in cancer therapy.

The effects of exogenous glutathione on reduced glutathione level, glutathione peroxidase and glutathione reductase activities of rats with different ages and gender after whole-body Γ-irradiation

Age-and gender-related changes on reduced glutathione (GSH) level, glutathione peroxidase (GPx) and glutathione reductase (GR) activities in the liver of rat exposed to different dose of whole-body g-ray irradiation were determined. In addition, the effect of administration of exogenous GSH on endogenous GSH levels, GPx and GR activities was investigated. For this aim, male and female rats aged 1 and 5 moths were divided into two groups as g-ray and g-ray+GSH. Both groups were again divided into four groups as irradiated with 2, 4, 6 and 8 Gy doses. GSH level and GPx activity did not change with age while GR activity was decreased with age. Gender-dependent changes in GPx and GR activities were observed, but GSH values were not affect by sex. GSH levels, GPx and GR activities were not observed dose-associated changes of g-irradiation. GSH level and GPx activity in the 8Gy group were increased by GSH. GR activities of old male rats were found to be increased by glutathione in the 6 and 8Gy groups. These results indicate that radiation and administration of exogenous GSH affect gender-and age-dependent GSH level, GPx and GR activities in the rats.

Antioxidant protection against curative and palliative doses of ionizing irradiation in human blood decreases with aging

Reactive oxygen species (ROS) are independently recognized to play a significant role in radiation-induced damage on healthy tissue and in aging process. However, an age-related alteration of antioxidant (AO) system in radiation response in humans is poorly investigated. The aim of this paper was to evaluate the irradiation effects on the activities and expression of AO system in the blood of healthy women during aging. Blood samples were irradiated with curative and palliative doses of 2 Gy or 9 Gy γ-rays. AO capacity for detoxification of O(2)•(-) and H(2)O(2) in response to 2 Gy γ-irradiation decreases in women above 58 years, while in response to 9 Gy shows signs of weakening after 45 years of age. Due to reduction of AO capacity during aging, cytotoxic effects of curative and palliative doses of irradiation, mediated by ROS, may significantly increase in older subjects, while removal of H(2)O(2) excess could reduce them.

Influence of occupational exposure to low-dose ionizing radiation on the plasma activity of superoxide dismutase and glutathione level

Background/Aim. During exposure to low-level doses (LLD) of ionizing radiation (IR), the most of harmful effects are produced indirectly, through radiolysis of water and formation of reactive oxygen species (ROS). The antioxidant enzymes - superoxide dismutase (SOD): manganese SOD (MnSOD) and copper-zinc SOD (CuZnSOD), as well as glutathione (GSH), are the most important intracellular antioxidants in the metabolism of ROS. Overproduction of ROS challenges antioxidant enzymes. The aim of this study was to examine if previous exposure to low doses of IR induces adaptive response by means of stimulation of intracellular antioxidant defense system. Methods. We investigated a group of medical workers occupationally exposed to IR (n = 44), 29 male and 15 female. The controls (n = 33) consisted of medical workers not exposed to IR, 23 male and 10 female. The examinees from both groups worked in the same environment and matched in crucial characteristics. All measurements were performed by a calibrated thermoluminiscent dosimeter type CaF2:Mn. SOD activity and GSH content were measured spectrophotometrically in the plasma of both groups of medical workers. Half of each blood sample was irradiated by 2Gy of ? radiation, dose-rate 0.45 Gy/min, and the distance from the source of 74 cm. Results. The dosimetry results indicate that occupational doses were very low. Our results confirmed significantly higher SOD activity in the exposed vs. unexposed workers (p < 0.00006). SOD activity after irradiation of blood samples failed to show a significant difference between the exposed workers and the controls (p = 0.905), even the difference in each group before and after the irradiation was significant. In blood samples of the exposed workers expression of enzymes after the irradiation, was not as high as in the controls, or even in the case of the exposed in nuclear medicine personnel, SOD activity was decreased. There were no significant differences in the content of GSH between the groups. Conclusion. Our results pointed out that occupational exposure to low doses of IR compromised mitochondrial function. During occupational exposure, the activity of antioxidant enzymes was increased as a protection against the increased production of ROS. After high-dose irradiation dysfunction of mitochondrial system was noticed, suggesting the break-down of antioxidant defense and failure of an adaptive response. Therefore, the "chronic oxidative stress" might reduce antioxidant defense in the case of accidental exposure to high doses of IR. It could indirectly increase the incidence of some other "free radicals' diseases" in occupationally exposed personnel. .

Age-related changes in radiation-induced micronuclei among healthy adults

The aim of the present study was to establish the extent of in vitro radioresponse of lymphocytes among 62 healthy adults of both genders and to estimate the distribution of baseline micronuclei and radiosensitivity among individuals of the study population using the cytochalasin block micronucleus test. A younger study group consisted of 10 males (mean age, 22.4 years; range, 21-27) and 12 females (mean age, 24.8 years; range, 20-29), whereas an older study group consisted of 18 males (mean age, 35.1 years; range, 30-44) and 22 females (mean age, 38.5 years; range, 30-48). For evaluation of radiosensitivity blood samples were irradiated in vitro using 60Co gamma-ray source. The radiation dose employed was 2 Gy, the dose rate 0.45 Gy/min. The study revealed a significant gender effect on baseline micronuclei favoring females (Z = 3.25, P < 0.001), while yields of radiation-induced micronuclei did not differ significantly (Z = 0.56, P < 0.56) between genders. The distribution of baseline micronuclei among the individuals tested followed Poisson distribution in both study groups and in both genders, whereas the distribution of radiosensitivity among individuals of the older study group did not fulfill Poisson expectations (Kolmogorov-Smirnof test, P < 0.01). In contrast to a nonsignificant difference in radiosensitivity between males and females of the same age group (Z = 1.97, P < 0.56), a statistically significant difference in radiosensitivity between younger and older group for both genders was found (Z = 3.03, P < 0.03). Since the individuals tested were healthy, the observed variability in radiation response is considered to be an early effect of ageing.

Diminished natriuretic response to dopamine in old rats is due to an impaired D1-like receptor-signaling pathway

BACKGROUND

Dopamine (DA) causes natriuresis and diuresis, which results from activation of D1-like receptor (D1R) located on proximal tubules. Earlier, we reported that DA failed to inhibit Na,K-ATPase in proximal tubules of old Fischer 344 rats. The present study was designed to investigate the functional consequence of this phenomenon.

METHODS

Measurements of the functional (natriuretic and diuretic) response to intravenously infused DA and SKF 38393 (D1R agonist) in adult (6 month) and old (24 month) Fischer 344 rats were taken. Biochemical measurements were carried out to determine the potential defects in D1R and its signaling pathway in proximal tubules of old rats.

RESULTS

We found that intravenous infusion of DA and SKF 38393 caused natriuresis and diuresis in adult rats, but this response was blunted in old rats. In the isolated proximal tubules, DA and SKF 38393 inhibited Na,H-exchanger (NHE) in adult rats; however, this inhibition was attenuated in old rats. Radioligand binding revealed approximately 46% reduction in D1R binding sites in brush border membranes (BBMs) in old compared with adult rats. SKF 38393 stimulated [35S]GTPgammaS binding in BBM in adult rats, but not in old rats, suggesting an impaired D1R-G protein coupling. DA and SKF 38393 stimulated adenylyl cyclase (AC) activity in adult but not in the old rats. Forskolin and NaF stimulated AC activity in a comparable manner in adult and old rats, indicating no defect in AC and G proteins. DA and SKF 38393 failed to stimulate protein kinase A (PKA) activity in proximal tubules of old rats. Dibutyryl-cAMP-mediated PKA activation was also absent in old rats.

CONCLUSIONS

A decrease in D1R binding sites, a coupling defect with G proteins, and a defect in PKA activation lead to diminished DA-mediated inhibition of NHE in old rats, which may contribute to the blunted natriuretic response to DA in these animals.