Selenium as an antioxidant and protector of brain

Selenium (Se) is a trace element, a powerful antioxidant and an important micronutrient that’s absolutely essential for human health. Selenium plays an important role in human cell function - it strengthens and protects cell structure and supports cellular metabolism. As an antioxidant, selenium helps fight free radical damage and moderates reactive oxygen species (ROS), which cause cellular oxidative stress. In addition to acting as an essential nutrient for the immune system and overall body function, selenium also plays a critical role in the operation of the nervous system and in human brain function.The functions of selenium are carried out by selenoproteins, in which selenium is specifically incorporated as the amino acid, selenocysteine (21st amino acid).

Human beings have 25 selenoproteins in their genome and majority of these are relative to the antioxidant defence of the body. The three well-studied subfamilies of selenoproteins include thioredoxin reductase (TrxR), glutathione peroxidase (GPx), and iodothyronine deiodinases (DIO). Three of these TrxR selenoproteins have been identified in mammals that includes TrxR1, which functions in the cytosol and nucleus, TrxR2, which functions in the mitochondria, and TrxR3, which functions in testis. The TrxRs are also important components of the mechanism to reduce peroxide. This group of selenoproteins is required for reduction of thioredoxin (Trx), which uses a cysteine thiol-disulfide exchange for reduction of thiol groups in protein residues. Trx can inhibit apoptosis signaling regulating kinase1 (ASK1) and prevent apoptosis to control cell division, longevity, and cell death. The Trx–TrxR systems are also important for reducing proteins that have cysteine in DNA-binding domains, which include NF-kB, AP-1, p53, and glucocorticoid receptors [1]. Also Selenoprotein P has been reported to possess antioxidant activities and the ability to promote neuronal cell survival according to recent research. Selenium and selenoproteins are also involved in brain metabolism and brain signalling pathways. Selenoproteins have special importance to the neuronal cells, which utilise γ-aminobutyric acid (GABA) as their signalling molecule (GABAergic neurons). In both selenium deficient organisms and organism with genetic impairment of selenoprotein biosynthesis this kind of neurons are affected most heavily [2]. Severe selenium deficiency or malfunction of selenium transporting protein, selenoprotein P, causes degeneration of special group of GABAergic neurons leading to impaired neuronal function that results in motor function disorders, including seizures, and cognitive impairments like affected learning. This is because of the abundance of the GABA-utilising neurons in the corresponding brain regions – hippocampus, cerebral cortex and cerebellum.

Through selenoproteins selenium is involved in the diverse functions of the brain including motor performance, coordination, memory and cognition. Selenoproteins are important for normal brain function, and decreased function of selenoproteins can lead to impaired cognitive function and neurological disorders such as Alzheimer's disease, Parkinson's disease (impaired function of glutathione peroxidase selenoenzymes), Huntington's disease (here selenium deters lipid peroxidation by increasing specific glutathione peroxidases/GPX), amyotrophic lateral sclerosis and epilepsy [3]. Since the human body cannot produce selenium, it must be consumed from an external source and generally an adult human requires a minimum of 55 micrograms per day. Women who are pregnant or breastfeeding require slightly more.

References:

1. Pillai, R., Uyehara-Lock, J. H. and Bellinger, F. P. (2014), Selenium and selenoprotein function in brain disorders. IUBMB Life, 66: 229–239. doi:10.1002/iub.1262
2. https://atlasofscience.org/importance-of-selenium-for-brain-function/
3. https://www.ncbi.nlm.nih.gov/pubmed/12807419