Selenium: childhood poisoning and cystic fibrosis

Toxicity of repeated oral intake of organic selenium, inorganic selenium, and selenium nanoparticles: A review

BACKGROUND

To protect from toxicity at supra-essential doses of selenium, it is important to determine dose levels at which adverse effects occur.

METHODS

We identified relevant literature on the repeated dosage of selenium and extracted dose descriptors on reported endpoints, except on genotoxicity/carcinogenicity.

RESULTS

Selenium forms with toxicological data were organic ones: selenomethionine, selenocystine/selenocysteine; and inorganic ones, including selenite (SeO₃^2-), selenate (SeO₄^2-), selenium sulphide (SeS₂), selenide (Se^2-) and selenium nanoparticles. Clinical signs of selenium toxicity in humans include a garlicky-smelling breath, hair loss, and nail changes. One human study showed increased mortality following daily ingestion of 300 µg Se per day for 5 years, equal to a lowest-observed-adverse-effect level (LOAEL) of ∼4.3 µg/kg bw/days. The corresponding no-observed-adverse-effect level (NOAEL) was ∼2.9 µg Se/kg bw/day. One study reported an increased risk of type 2 diabetes after ∼2.9 µg Se/kg bw/day, but other studies with similar doses found no increases in mortality or incidence of type 2 diabetes. NOAELs on affected body weight in animal studies were 0.24-1.2 mg Se/kg bw/day. Other endpoints of selenium toxicity in animals include hepatotoxicity with a NOAEL as low as 2 µg/kg bw/day in rats, as well as gastrointestinal, cardiovascular, and reproductive toxicities with NOAELs of 0.6 (gastrointestinal), 0.08, and 0.4 (cardiovascular) and ≥ 0.04 mg Se/kg bw/day (reproductive), respectively.

CONCLUSIONS

Dose descriptors describing selenium toxicity were as low as 2-3 µg Se/kg bw/day.

Global survey of urinary selenium in children: A systematic review

BACKGROUND

Selenium (Se) is an essential element in the human body that plays an important role in numerous fundamental physiological functions. However, the distribution of Se in the environment varies widely resulting in this element being available in a large concentration range in the ecosystem, and thus, in the human body. Urinary Se is a biomarker considered to be involved in adaptive mechanisms that help prevent health problems.

OBJECTIVES

The purpose of the present study was to conduct a systematic review to identify studies reporting the status of urinary Se in healthy children and create a global map.

METHODS

A literature search was conducted using MEDLINE (United States National Library of Medicine), Web of Science, Toxicology Bibliographic Information (TOXLINE), Latin-American and Caribbean Literature on Health Sciences (LILACS), and the grey literature. This study was registered in PROSPERO (international prospective register of systematic reviews) and was conducted in accordance with the PRISMA guidelines.

RESULTS

We identified 322 relevant articles, out of which 15 were included in this systematic review. The study identified a total of 4038 healthy children worldwide with urinary Se concentrations from 7.7 to 145.0 μg/L.

CONCLUSION

This is a pioneering study that provides evidence for the presence of Se in the urine of healthy children; we have shown that the available data is restricted to a small number of individuals and specific groups. Furthermore, there is a lack of information on urinary Se, especially in Latin America, Africa, and Asia.

Etiologic factors and pathologic alterations in selenium-vitamin E deficiency and excess in animals and humans

The etiology of selenium-vitamin E (Se-E) deficiency diseases may be complex. Many of the syndromes involve combined deficiency of selenium and vitamin E. Selenium moves into the animal and human food chain from soil and plants, which may contain inadequate amounts of the nutrient in many areas of the world. Vitamin E may be in low concentration in many animal feeds unless supplements are added. Some syndromes, such as steatitis in cats, result from an increased requirement of vitamin E in diets that contain large amounts of polyunsaturated fatty acids, and these diseases will only respond to vitamin E administration. Deficiency syndromes in animals owing to pure Se deficiency are infrequent and have been produced mainly by laboratory studies utilizing extreme deficiency conditions. Other factors that may affect the occurrence of these deficiency diseases are concurrent dietary deficiency of S-containing amino acids, bioavailability of different forms of dietary Se, intake of compounds that antagonize Se (e.g., silver salts), and exposure to various prooxidant substances (e.g., iron compounds, oxygen, ozone, and various drugs).

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.

Hydrogen selenide poisoning: an illustrative case with review of the literature

Hydrogen selenide is a non-metallic compound currently receiving attention in both medicine and electronics. Toxicity results in multiple symptoms, the most characteristic of which is a garlicky odor of the breath. A young woman exposed repeatedly to hydrogen selenide gas developed gastrointestinal complaints, dental caries, conjunctivitis, nail deformities, and garlicky breath. Other reported cases are discussed along with various proposed treatments.

Fatal poisoning with selenium dioxide

Two hours after suicidal ingestion of an unknown amount of selenium dioxide, a 17-year-old male was admitted to hospital with asystolia and apnea. Attempts at resuscitation failed and the patient was pronounced dead. Findings at autopsy included congestion of lungs and kidneys, diffuse swelling of the heart, and brain edema. The most impressive finding was an orange-brown discoloration of the skin and all viscera, probably due to hemolysis and/or pigmentation related to ingestion of selenium dioxide. Selenium blood and tissue levels were increased by a factor of 100-1000 as compared to normal. The highest concentrations were found in pancreas, spleen, liver, and adipose tissue. For elucidation of the chemical nature of selenium in tissues, a new analytical method which was based on carbon disulfide extraction was developed. Carbon disulfide is a good solvent for non-polar selenium compounds like elemental selenium and selenium disulfide, but not for polar compounds like selenite and selenoproteins. A major fraction of selenium in tissues was extractable by carbon disulfide, which seems to indicate the presence of elemental selenium and/or selenium disulfide. The color of these substances is red and orange, respectively. This might explain at least part of the discoloration of skin and tissues. In vitro experiments suggested that trace amounts of hydrogen selenide, which is an intermediate of selenite metabolism, probably induced hemolysis. For evaluation of the therapeutic value of hemoperfusion in selenium poisoning in vitro hemoperfusion experiments were performed, which revealed only a moderate effect on selenium blood levels.

Involvement of glutathione reductase in selenite metabolism and toxicity, studied in isolated rat hepatocytes

Cellular lysis in freshly isolated hepatocytes incubated with varying concentrations of selenite could be related to the reductive metabolism of selenite. A decrease in intracellular GSH levels was observed concomitant with an increased rate of accumulation of oxidized glutathione in the incubation medium. Pretreatment of hepatocytes with an inhibitor of GSSG-reductase (1,3-bis(2-chloroethyl)-1-nitrosourea), prior to the addition of 50 microM selenite, resulted in substantially lower GSH-levels. The rate of GSSG reductase-catalyzed metabolism of selenite (50 microM) could be estimated to approximately 7 nmoles reduced/h per 10(6) cells. The results indicate that this was the major metabolic pathway for toxic concentrations of selenite in isolated hepatocytes. Furthermore, selenite considerably decreased cellular NADPH levels. In hepatocytes isolated from starved rats, the presence of alanine and glucose in the incubation medium protected against selenite-mediated cellular lysis. These observations suggest that an insufficient NADPH generation could be critical for selenite reduction and toxicity in isolated hepatocytes.