[Radioprotection of human endothelial cells by sodium selenite]

Selenium does not affect radiosensitivity of breast cancer cell lines

Supplementation with the antioxidant selenium is frequently performed in breast cancer patients to protect the normal tissue from radiation-induced side effects. However, concerns exist whether selenium also protects tumor cells from radiation-induced cell kill and thereby reduces the efficacy of radiotherapy. In this work, the effect of selenium administration on the radiosensitivity of breast cancer cells was evaluated in vitro. Physiological relevant selenium concentrations (70 and 140 µg/l) did not affect DNA double-strand breaks (γH2AX foci) after 4-Gy X-ray irradiation. Also apoptosis (caspase 3/7) after irradiation with 10 Gy was not influenced by selenium treatment in MDA-MB-231 and MCF7 cells. Most importantly, selenium supplementation did not impair the clonogenic survival of the breast cancer cell lines after irradiation (0, 2, 4, 6, 8 Gy). The data suggest that physiological relevant selenium concentrations administered in combination with radiation therapy do not deteriorate the efficacy of radiotherapy in breast cancer patients. However, randomized clinical trials comparing the effectiveness of radiotherapy and the associated side effects in patients with and without selenium supplementation are recommended.

Selenium in Radiation Oncology-15 Years of Experiences in Germany

Introduction: Se measurement and supplementation in radiation oncology is a controversial issue. The German Working Group Trace Elements and Electrolytes in Oncology (AKTE) has conducted a number of studies on this issue, which are summarized in this review. Strategies have been tested and developed, aiming to stratify the patients with a potential need for supplemental Se and how best to monitor Se supplementation with respect to health effects and risks. Methods: We analyzed blood and tissue Se-levels of different tumor patients (n = 512). Two randomized phase III clinical studies were conducted for testing a potential radioprotective effect of supplemental Se during radiation therapy in patients with uterine cancer (n = 81) and head and neck tumor patients (n = 39). Results: A relative Se deficit in whole blood or serum was detected in the majority of tumor patients (carcinomas of the uterus, head and neck, lung, rectal or prostate cancer). In prostate cancer, tissue Se concentrations were relatively elevated in the carcinoma centre as compared to the surrounding compartment or as compared to tumor samples from patients with benign prostatic hyperplasia. Adjuvant Se supplementation successfully corrected Se-deficiency in the patients analyzed and decreased radiotherapy-induced diarrhea in a randomized study of radiotherapy patients with carcinomas of the uterus. Survival data imply that Se supplementation did not interfere with radiation success. Some positive effects of supplemental Se in the prevention of ageusia (loss of taste) and dysphagia due to radiotherapy were noted in a second randomized trial in patients with head and neck cancer. We have not observed any adverse effects of supplemental Se in our studies. Conclusions: Se supplementation yielded promising results concerning radioprotection in tumor patients and should be considered as a promising adjuvant treatment option in subjects with a relative Se deficit.

Protective effects of sodium selenite supplementation against irradiation-induced damage in non-cancerous human esophageal cells

The administration of radioprotective compounds is one approach to preventing radiation damage in non-cancerous tissues. Therefore, radioprotective compounds are crucial in clinical radiotherapy. Selenium is a radioprotective compound that has been used in previous clinical studies of radiotherapy. However, evidence regarding the effectiveness of selenium in radiotherapy and the mechanisms underlying the selenium-induced reduction of the side effects of radiotherapy remains insufficient. To further investigate the effectiveness of selenium in radiotherapy, the present study examined the protective effects of sodium selenite supplementation administered prior to X-ray radiation treatment in CHEK-1 non-cancerous human esophageal cells. Sodium selenite supplementation increased glutathione peroxidase 1 (GPx-1) activity in a dose- and time-dependent manner. The sodium selenite dose that induced the highest GPx-1 activity was determined to be 50 nM for 72 h prior to radiotherapy. The half-maximal inhibitory concentration of sodium selenite in CHEK-1 cells was 3.6 µM. Sodium selenite supplementation increased the survival rate of the cells in a dose-dependent manner and enhanced the degree of cell viability at 72 h post-irradiation (P<0.05). Combined treatment with 50 nM sodium selenite and 2 gray (Gy) X-ray irradiation decreased the number of sub-G₁ cells from 5.9 to 4.2% (P<0.05) and increased the proportion of G₁ cells from 58.8 to 62.1%, compared with 2 Gy X-ray irradiation alone; however, this difference was not statistically significant (P=1.00). Western blot analysis revealed that treatment with 2 Gy X-ray irradiation significantly increased the expression levels of cleaved poly (ADP-ribose) polymerase (PARP; P<0.05). In addition, combined treatment with 50 nM sodium selenite and 2 Gy X-ray irradiation reduced the expression levels of cleaved PARP protein, compared with 2 Gy X-ray irradiation alone; however, this reduction was not statistically significant (P=0.423). These results suggest that 50 nM sodium selenite supplementation administered for 72 h prior to irradiation may protect CHEK-1 cells from irradiation-induced damage by inhibiting irradiation-induced apoptosis. Therefore, sodium selenite is a potential radioprotective compound for non-cancerous cells in clinical radiotherapy.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Selenium in oncology: from chemistry to clinics

The essential trace element selenium, which is a crucial cofactor in the most important endogenous antioxidative systems of the human body, is attracting more and more the attention of both laypersons and expert groups. The interest of oncologists mainly focuses in the following clinical aspects: radioprotection of normal tissues, radiosensitizing in malignant tumors, antiedematous effect, prognostic impact of selenium, and effects in primary and secondary cancer prevention. Selenium is a constituent of the small group of selenocysteine-containing selenoproteins and elicits important structural and enzymatic functions. Selenium deficiency has been linked to increased infection risk and adverse mood states. It has been shown to possess cancer-preventive and cytoprotective activities in both animal models and humans. It is well established that Se has a key role in redox regulation and antioxidant function, and hence in membrane integrity, energy metabolism and protection against DNA damage. Recent clinical trials have shown the importance of selenium in clinical oncology. Our own clinical study involving 48 patients suggest that selenium has a positive effect on radiation-associated secondary lymphedema in patients with limb edemas, as well as in the head and neck region, including endolaryngeal edema. Another randomized phase III study of our group was performed to examine the cytoprotective properties of selenium in radiation oncology. The aim was to evaluate whether sodium selenite is able to compensate a preexisting selenium deficiency and to prevent radiation induced diarrhea in adjuvant radiotherapy for pelvic gynecologic malignancies. Through this study, the significant benefits of sodium selenite supplementation with regards to selenium deficiency and radiotherapy induced diarrhea in patients with cervical and uterine cancer has been shown for the first time in a prospective randomized trial. Survival data imply that supplementation with selenium does not interfere with the positive biological effects of radiation treatment and might constitute a valuable adjuvant therapy option especially in marginally supplied individuals. More recently there were emerging concerns coming up from two large clinical prevention trials (NPC, SELECT), that selenium increases the possible risk of developing diabetes type II. Despite obvious flaws of both studies and good counterarguments, a controversial debate remains on the possible advantage and risks of selenium in cancer prevention. However, in the light of the recent clinical trials the potential benefits of selenium supplementation in tumor patients are undeniable, even if further research is needed.

Selenium for alleviating the side effects of chemotherapy, radiotherapy and surgery in cancer patients

BACKGROUND

Selenium supplements are frequently used by cancer patients. Selenium is an essential trace element and is involved in antioxidant protection and redox-regulation in humans. Several adverse effects of radiotherapy and chemotherapy in cancer patients as well as cellular processes that maintain chronic lymphoedema have been linked to oxidative cell damage in the human body. Selenium has recently been investigated as a remedy against chemotherapy and radiotherapy-associated side effects as well as its effects on lymphoedema.

OBJECTIVES

This review assessed the effects of supplementary selenium on adverse effects of conventional radiotherapy, chemotherapy, or surgery, in oncologic patients and on quality of life or performance status during and after oncologic treatment.

SEARCH STRATEGY

We searched the Cochrane Pain, Palliative & Supportive Care Trials Register, the Cochrane Database of Systematic Reviews (The Cochrane Library , Issue 2, 2004), Medline (1966 - Sep 2004), Embase (1980 - 2004 week 12), SIGLE (October 2004), Cancerlit (October 2004), Clinical Contents in Medicine CCMed (October 2004), the German Register of Cancer Studies (October 2004), the NCI Clinical Trials Register (October 2004), the International Standard Randomised Controlled Trial Number Register ISRCTN (October 2004) and the Meta-Register of Controlled Trials mRCT (October 2004), reference lists and the archive of our working group. We contacted manufacturers of selenium supplements and investigators.

SELECTION CRITERIA

Randomised-controlled trials of selenium mono-supplements in cancer patients undergoing tumour specific therapy such as chemotherapy, radiotherapy or surgery.

DATA COLLECTION AND ANALYSIS

Two review authors independently checked trials for eligibility, extracted data and assessed trial quality. We sought additional information from investigators when required.

MAIN RESULTS

Two trials have been included, a randomised controlled trial with 60 participants at the beginning of the study investigating secondary lymphoedema and an ongoing trial with preliminary results of 63 participants investigating radiotherapy induced diarrhoea as a secondary outcome. Both trials had drawbacks with regard to study quality and reporting. The trial on secondary lymphoedema reported a decreased number of recurrent erysipela infections in the selenium supplementation group compared to placebo. However, results must be interpreted with caution and cannot be generalised to other populations. The ongoing trial on radiotherapy associated diarrhoea preliminarily reported a lower incidence of diarrhoea in patients receiving selenium supplementation concomitant to pelvic radiation, however, no data were presented. Publication of final results must be awaited to discuss these findings in detail. No randomised controlled trials were found studying the effect of selenium supplementation on other therapy-associated toxicities or quality of life or performance status in cancer patients.

AUTHORS' CONCLUSIONS

There is insufficient evidence at present that selenium supplementation alleviates the side effects of tumour specific chemotherapy or radiotherapy treatments. Or, that it improves the after effects of surgery, or improves quality of life in cancer patients or reduces secondary lymphoedema. To date research findings do not provide a basis for any recommendation in favour or against selenium supplementation in cancer patients. Potential hazards of supplementing a trace mineral should be kept in mind.