Selenoproteins have the 21st amino acid, selenocysteine incorporated into their polypeptide chain. This is the primary mechanism by which selenium can aid biological functions. There are at least 25 genes that encode selenoproteins in humans, some of which are essential in development.
They are also known to play important roles in disease pathogenesis. GPX 1-4, for example, are highly involved in antioxidants, while TXNRD 1-3, methionine sulfoxide reductase B (MSRB) 1, selenoproteins (SELENO) H, M and W are important for redox regulation. Iodothyronine deiodinase (DIO) 1-3 is used in thyroid hormone metabolism and SELENOP for selenium transport and storage.
Researchers from Florida International University have reviewed research into the role that selenium may play in protecting individuals against coronavirus disease 2019 (COVID-19) and have published their findings in International Journal of Molecular Sciences.
Selenium can act on the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus by restoring GPX and TXNRD, which would reduce oxidative stress, reduce virus-induced cell apoptosis, protect endothelial cells, and reduce platelet aggregation. The increased level of oxidative stress and inflammation typically seen in patients with severe COVID-19 is implicated in the pathogenesis of lung disease. GSH is known to protect the epithelial barrier in the lungs.
Much of the inflammation of severe COVID-19 occurs when SARS-CoV-2 attempts to infect endothelial cells, which quickly die and spread cell remnants widely, triggering inflammatory signals. Improving GSH levels could protect against this.
In a study examining the effect of supplementing sodium selenite levels in patients with ARDS – often seen in severe COVID-19 cases – it was found that this reduced inflammation, improved respiratory mechanics and restored the antioxidant capacity of the lungs. It is also possible that selenium status may affect the function of B and T cells in COVID-19 patients, as severe COVID-19 patients often show lower levels of lymphocytes, CD4 +, CD8 +, B and NK cells compared with people with a milder form of the disease.
Unfortunately, there is little concrete data on the relationship between selenium and COVID-19. However, China naturally has a wide range of selenium levels in the soil and a similar level of levels in the population. It has been reported that there is a linear relationship between COVID-19 cure rates and selenium levels in hair, with higher selenium levels corresponding to a significant increase in cure rates.
A similar relationship can be seen with risk of death. This could be seen most in Wuhan, Suizhou and Xiaogan. Another study in Wuhan revealed that the severity of COVID-19 was associated with higher selenium levels in the urine, possibly due to liver abnormalities due to the disease.
A South Korean study took a narrower focus on selenium and COVID-19, specifically examining the levels of selenium in hospitalized COVID-19 patients. While they found that 42% of COVID-19 patients had selenium deficiency and that selenium levels decreased as the severity of the disease increased, they also showed several other nutritional deficiencies. Similar studies in India, Iran and Russia all showed lower plasma selenium levels in COVID-19 patients compared to healthy patients.
A study examining serum selenium levels in Germany found that patients who had survived COVID-19 were less likely to have selenium deficiency than those who died. A similar study in Belgium, which examined individuals with COVID-19 pneumonia, found both lower GSH and GPX compared to references, as well as higher markers of oxidative stress and lower antioxidant status.
There is currently a study investigating the efficacy of selenic acid infusion therapy in moderately, severely and critically ill COVID-19 patients and no clinical trials are under way. Sodium selenite is readily available, mostly non-toxic in the short term, and can cross the blood-brain barrier. It also has the potential effect of oxidizing thiol groups, which can prevent the virus from entering the cells.
The authors conclude that selenium is important for protecting the host from viruses such as SARS-CoV-2, and when individuals are deficient in selenium, important functions such as redox homeostasis, antioxidant stress, and reduction of oxidative stress are significantly impaired. The reduction in serum and plasma selenium levels from severe COVID-19 patients is likely to indicate a lack of functional selenoproteins. This information can be very valuable to drug development manufacturers and COVID-19 researchers and can help develop selenium-based therapies.