Plasma selenium levels in patients with advanced upper gastrointestinal cancer

Recent advances in clinical studies of selenium supplementation in radiotherapy

BACKGROUND

Radiotherapy is one of the most important and common therapies for cancer patients. Selenium has been shown to be capable of reducing the side effects of radiotherapy because selenoproteins have anti-oxidative functions against reactive oxygen species that are induced by the radiation. They also function in DNA-repair and cytokine control.

PURPOSE

We explored the benefits and risks of selenium supplementation in radiotherapy in our previous review to establish guidelines. In the current study, we expanded the search to cover recent advances in clinical studies of selenium supplementation in radiotherapy.

METHODS

We conducted an initial screening in the PubMed using the MeSH terms and keywords "selenium", "radiation", "therapy", and "radiotherapy" using the same methodology applied in our previous review. We identified 121 articles published between January 2013 and December 2019. We then identified eight articles (six studies) on selenium and radiotherapy by excluding 113 articles.

RESULTS

In selenium supplementation studies, selenium doses of 300-500 μg/day with duration of 10 days to 6 months were used. Selenium supplementation improved the selenium nutritional conditions of the patients and reduced the side effects of radiotherapy. Selenium supplementation did not reduce the effectiveness of radiotherapy, and no toxicities were reported.

CONCLUSION

The results of our previous and current reviews showed that selenium supplementation offers specific benefits for several cancer types treated with radiotherapy. Here, we suggest a new guideline for selenium supplementation in radiotherapy. We recommend determining the selenium status of the patients before radiotherapy, and in cases of deficiency (<100 μg/L serum selenium level), selenium supplement can be beneficial.

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.

Updates on clinical studies of selenium supplementation in radiotherapy

To establish guidelines for the selenium supplementation in radiotherapy we assessed the benefits and risks of selenium supplementation in radiotherapy. Clinical studies on the use of selenium in radiotherapy were searched in the PubMed electronic database in January 2013. Sixteen clinical studies were identified among the 167 articles selected in the initial search. Ten articles were observational studies, and the other 6 articles reported studies on the effects of selenium supplementation in patients with cancer who underwent radiotherapy. The studies were conducted worldwide including European, American and Asian countries between 1987 and 2012. Plasma, serum or whole blood selenium levels were common parameters used to assess the effects of radiotherapy and the selenium supplementation status. Selenium supplementation improved the general conditions of the patients, improved their quality of life and reduced the side effects of radiotherapy. At the dose of selenium used in these studies (200–500 μg/day), selenium supplementation did not reduce the effectiveness of radiotherapy, and no toxicities were reported. Selenium supplementation may offer specific benefits for several types of cancer patients who undergo radiotherapy. Because high-dose selenium and long-term supplementation may be unsafe due to selenium toxicity, more evidence-based information and additional research are needed to ensure the therapeutic benefits of selenium supplementation.

Selenium and preeclampsia: A global perspective

Preeclampsia is a complex multisystem disorder of pregnancy where oxidative stress plays an important aetiological role. The role of selenium in the synthesis of endogenous antioxidants is well documented, and a significant reduction in selenium has been reported in preeclamptic women. The objective of this study was to map global selenium status and preeclampsia incidence. This study identified peer reviewed journal articles reporting national preeclampsia incidence (%) and matched these with reported values of selenium intake and plasma/serum selenium concentrations (μg/L). Matched data were obtained for 45 regions, reporting 6456,570 births, spanning Europe, Asia, Australasia, Africa, North and South America. Increasing plasma selenium concentration was found to be correlated with a reduction in preeclampsia incidence (Pearson's r=-0.604, P<0.0001). Countries with a reported serum/plasma selenium level of ⩾95μg/L were considered selenium sufficient and a significant reduction in preeclampsia incidence for countries above this value (P=0.0007) was noted. Significant reductions in preeclampsia incidence were found to coincide with increases in plasma/serum selenium concentration in the New Zealand (P=0.0003) and Finland (0.0028) populations following Government intervention. This study supports the hypothesis that selenium supplementation may be beneficial in reducing oxidative stress in women at risk of preeclampsia.

Selenium and cancer: some nutritional aspects

The level of selenium in cancer patients is lower than that in control subjects. However, low selenium levels in body fluids can be due to the malnutrition observed in these patients. There is evidence from epidemiologic studies that high dietary selenium intakes and high selenium status in people are associated with lower cancer mortality. However, contradictory information has been found in some prospective studies. The presence of other nutrients in selenium-rich foods can influence the role of the selenium in cancer etiology. Therefore, there are selenium antagonistic elements that inhibit the anticarcinogenic effects of selenium and other antioxidant micronutrients such as ascorbic acid, retinol, beta-carotene, alpha-tocopherol, and some other elements have a synergistic effect on the prevention of cancer.

[Effect of selenium on the side effect profile of adjuvant chemotherapy/radiotherapy in patients with breast carcinoma. Design for a clinical study]

Selenium is a very important component of the antioxidative protective mechanism which belong to every cell. By chemotherapy and radiotherapy a strong increase of free oxygen radicals is induced leading to a damage also of normal tissue. This phenomenon is registered as adverse drug reactions. Since, in addition, tumor patients frequently have low selenium blood levels the application of higher doses of selenium in connection with chemo- and radiotherapy will induce the toxicity of the treatment without lowering the efficiency. Within the presented prospective randomized placebo-controlled double-blind phase-III study we intend to answer the question whether the application of higher doses of sodium selenite will reduce the toxicity of chemotherapy and radiotherapy. Primary targets of the study are therefore the evaluation of toxicity according to CTC-criteria and of life quality.

Blood selenium and glutathione peroxidase status in patients with colorectal cancer

PURPOSE

It is still controversial whether a low selenium level and a reduced activity of the selenium-dependent enzyme, glutathione peroxidase, in blood are associated with an increased risk and poor prognosis of cancer in humans. This study evaluates whether colorectal cancer patients have lower serum selenium and glutathione peroxidase levels than a gender-matched and age-matched control group and whether there is a correlation to clinical data and prognosis.

METHODS

In a retrospective study, serum selenium and glutathione peroxidase activity of 106 patients with colorectal cancer were determined. Clinical data were provided by our long-term follow-up program for colorectal cancer patients.

RESULTS

Patients with a selenium level <70 microg/l had a significantly lower mean survival time and a lower cumulative cancer-related survival rate than patients with a selenium level >70 microg/l (P = 0.0009). When considering the different tumor stages, a decline of the mean selenium level in the T4 carcinoma group was found in the analysis of variance (P < 0.05). The lowest selenium level was found for patients with advanced tumor disease and in a preoperative situation, ie., high tumor burden. In comparison with the control group, the cancer group showed a significant reduction of serum glutathione peroxidase activity (P < 0.01) but no significant difference in selenium level.

CONCLUSIONS

These results support the hypothesis of an association between low selenium level and advanced tumor disease. From our data, it cannot be decided whether this phenomenon is more likely to be a consequence or a causative factor for development and course of the disease.

Gastric tissue selenium levels in healthy persons, cancer and non-cancer patients with different kinds of mucosal damage

The gastric tissue levels of selenium (Se) were examined in 15 healthy subjects aged 18-43 (mean 36 +/- 12) years, 17 patients with stomach cancer aged 23-79 (mean 60 +/- 17) years, 20 patients with mild gastritis aged 18-65 (mean 35 +/- 12) years, 13 patients with chronic gastritis aged 28-69 (mean 47 +/- 15) years, 33 patients with erosive gastritis aged 16-70 (mean 49 +/- 17) years and 23 patients with ulcers aged 22-76 (mean 49 +/- 17) years. The Se concentration was determined by electrothermal atomic absorption spectrometry (ETAAS) with palladium as a matrix modifier. The mean +/- the standard deviation (SD) of the gastric tissue Se levels were 473 +/- 80, 36 +/- 9.0, 355 +/- 243, 567 +/- 246, 571 +/- 241 and 813 +/- 427 micrograms/Kg in healthy subjects and in patients with cancer, ulcers, mild gastritis, chronic gastritis and erosive gastritis, respectively. The Se concentration in the biopsies of patients with gastric ulceration and cancer were significantly lower than that in patients with gastritis (p < 0.05) and the other conditions (p < 0.0001).

Inhibitory effect of selenium on hamster pancreatic cancer induction by N'-nitrosobis(2-oxopropyl)amine

The effect of selenium intake on the development of pancreatic cancer was investigated in female Syrian golden hamsters. Four-week-old hamsters were divided into 2 groups according to the selenium level in their drinking water and were fed a purified diet containing less than 0.05 ppm selenium. Starting 4 weeks later, groups received 10 s.c. injections at weekly intervals of N'-nitrosobis(2-oxopropyl)amine (BOP) dissolved in saline, while controls received saline alone. When the animals were killed 18 weeks after the last injection, palpable tumors were less frequent in the high-selenium group than in animals receiving low-selenium supplement, the numbers of histologically diagnosed cancerous lesions also being significantly reduced by high selenium intake. The selenium level and glutathione peroxidase activity in serum and pancreas were significantly greater in the high-selenium group. Moreover, selenium levels and glutathione peroxidase activity were both significantly higher in tumor-bearing tissue. The results suggest that glutathione peroxidase is involved as an intermediate factor in prevention of carcinogenesis by selenium.

Determination of selenium in blood components by X-ray emission spectrometry. Procedures, concentration levels, and health implications

Sampling, storing, sample pretreatment, and experimental conditions for selenium (Se) determination in human serum, plasma, and whole blood by X-ray emission spectrometric (XRS) methods are described. Concentration levels in these biological fluids, found by this technique, are discussed and compared to values found by other techniques for the same healthy population group in the same area. XRS analysis of blood from patients with various pathological conditions is reviewed, with special attention to the relation of Se with the concentration level of other essential or nonessential trace elements.

Selenium: clinical significance and analytical concepts

Selenium is an essential trace element in humans and animals. Its only established function in humans is the antioxidant activity of glutathione peroxidase, a selenoenzyme. Severe prolonged deficiency may cause a fatal cardiomyopathy. Iatrogenic causes of selenium deficiency include parenteral and enteral nutrition. Low plasma selenium is also found in malabsorption, cystic fibrosis, rheumatoid arthritis, neoplasia, and other varied clinical disorders. Death has resulted from a single massive ingestion of selenium, while chronic excessive intake causes skin, nail, and hair pathology. Extreme geographical variation in population blood and urine selenium levels and a marked age-specific variation in population reference intervals are important factors in understanding selenium nutrition. Nutritional requirements, biological availability, and metabolism are discussed in relation to geographical, age, and method variability. Sampling, processing procedures, and methods for selenium quantitation are reviewed. Selenium content in different biological matrices and reference values for pediatric, adult, and obstetric populations are provided.