Selenium Protects a Specific Type of Interneurons in The Brain
Exactly 200 years ago, the Swedish scientist Jöns Jacob Berzelius discovered the trace element selenium, which he named after the goddess of the moon, Selene. Besides its industrial applications (chemical industry, production of semiconductors and toners), selenium is an essential trace element and indispensable for humans, many animals and some bacteria. A team led by Dr. Marcus Conrad, research group leader at the Institute of Developmental Genetics (IDG) at Helmholtz Zentrum München, showed for the first time why selenium is a limiting factor for mammals.
Scientific ‘by-catch’ solves decades-old mystery
The scientists have been investigating for years the processes of a novel type of cell death, known as ferroptosis. In this context, the enzyme GPX4, which normally contains selenium in the form of the amino acid selenocysteine, plays an important role.
In order to better understand the role of GPX4 in this death process, we established and studied mouse models in which the enzyme was modified,” said study leader Conrad. “In one of these models, we observed that mice with a replacement of selenium to sulfur in GPX4 did not survive for longer than three weeks due to neurological complications.”
In their search for the underlying reasons, the researchers identified a distinct subpopulation of specialized neurons in the brain, which were absent when selenium-containing GPX4 was lacking. “In further studies, we were able to show that these neurons were lost during postnatal development, when sulfur- instead of selenium-containing GPX4 was present,” stated first author of the study, Irina Ingold.
Furthermore, the scientists were able to show that ferroptosis is triggered by oxidative stress, which is known to occur for instance during high metabolic activity of cells and high neuronal activity. “Our study demonstrates for the first time that selenium is an essential factor for the postnatal development of a specific type of interneurons,” said Dr. José Pedro Friedmann Angeli, a scientist at the IDG, describing the results. “Selenium-containing GPX4 protects these specialized neurons from oxidative stress and from ferroptotic cell death.”
Thus, the study explains why certain selenoenzymes are essential in some organisms, including mammals, whereas they are dispensable in other organisms, such as fungi and higher plants. In future investigations, study leader Marcus Conrad and his team aim to investigate how ferroptosis is triggered in cells. As a long-term goal, he wants to elucidate the role of ferroptosis in various disease conditions in order to be able to alleviate diseases, such as cancer or neurodegeneration, which are currently difficult to tackle.
Irina Ingold, Carsten Berndt, Sabine Schmitt, Sebastian Doll, Gereon Poschmann, Katalin Buday, Antonella Roveri, Xiaoxiao Peng, Florencio Porto Freitas, Tobias Seibt, Lisa Mehr, Michaela Aichler, Axel Walch, Daniel Lamp, Martin Jastroch, Sayuri Miyamoto, Wolfgang Wurst, Fulvio Ursini, Elias S.J. Arnér, Noelia Fradejas-Villar, Ulrich Schweizer, Hans Zischka, José Pedro Friedmann Angeli, Marcus Conrad. Selenium Utilization by GPX4 Is Required to Prevent Hydroperoxide-Induced Ferroptosis. Cell, 2017; DOI: 10.1016/j.cell.2017.11.048
10 Foods Rich in Selenium
This important nutrient is vital to immune system function. Selenium works in conjunction with vitamin E, vitamin C, glutathione and vitamin B3 as an antioxidant to prevent free radical damage in the body. It’s thought to help prevent cancer by affecting oxidative stress, inflammation and DNA repair. Selenium has been found to be important to male fertility; increasing selenium levels leads to improved sperm motility. There is preliminary research that suggests that selenium supplementation may also help with asthma symptoms, but more studies are needed.
Deficiencies of selenium can occur in areas where soil content of this mineral is low. Diets high in refined foods may also lead to deficiency, as selenium can be destroyed by food processing. Taking anti-inflammatory drugs may reduce the body’s supply of selenium.
Low selenium levels can contribute to autoimmune problems, such as psoriasis and thyroid disease. Low levels have also been tied to stomach, throat and prostate cancers, although more research is needed to determine if this is a cause or a result of the disease. Some studies suggest that selenium deficiency is linked to mood disorders. There’s indication that deficiencies in selenium may contribute to the progression of viral infections.
10 Selenium Food Sources
The selenium content in foods depends on the concentration of selenium in the soil where the crops were grown. The following foods are generally considered good sources of selenium:
- Brazil Nuts
- Sunflower Seeds
- Fish (tuna, halibut, sardines, flounder, salmon)
- Shellfish (oysters, mussels, shrimp, clams, scallops)
- Meat (Beef, liver, lamb, pork)
- Poultry (chicken, turkey)
- Mushrooms (button, crimini, shiitake)
- Grains (wheat germ, barley, brown rice, oats)
Recommended Daily Allowance
- Children (under 3): 20 mcg
- Children (4-8): 30 mcg
- Children (9-13): 40 mcg
- Adolescents (14-18): 55 mcg
- Adults 19 and older: 55 mcg
- Pregnant women: 60 mcg
- Lactating women: 70 mcg
Exceeding 400 mcg per day can lead to selenium toxicity. Side effects may include hair loss, white spots on fingernails, fatigue, dizziness, nausea and nerve damage. There’s some evidence that high selenium levels may increase the risk of squamous cell skin cancer. Another well controlled study found a correlation between higher levels of selenium and an increased risk of developing type-2 diabetes.
Because of the possibility of toxicity, selenium supplements are controversial. The safest way to ensure a sufficient level of selenium in the diet is by eating a variety of selenium rich foods, like those listed above. Brazil nuts can be very high in selenium and should only be eaten occasionally. One Brazil nut can supply a whole day’s requirement of selenium, although this can vary depending on soil conditions. A multivitamin that contains some selenium is safe for most people to take and can help to fill the gap in a diet that is lacking.