A joint research group of Osaka Metropolitan University Graduate School of Medicine, Veterinary Medicine, and Cosmo Bio Co., Ltd. has revealed that proteins in saliva inhibit infection with the new coronavirus.
There is a clear age-dependent relationship between the onset and aggravation of the new coronavirus infection (COVID-19), and the aggravation and mortality rates of the elderly are significantly higher than those of young people and children.On the other hand, the scientific basis that can fully explain this age dependence has not been clarified.
This group focused on the fact that saliva secretion, which is one of the innate immune systems in the body, is significantly reduced in the elderly.We hypothesized that saliva contributed to the prevention of infection with the new coronavirus, and investigated this possibility experimentally.
Infection is established when the spike protein S1 on the virus envelope binds to the angiotensin converting enzyme 2 (ACE2) receptor present in the human cell membrane.As a result of the experiment, saliva of healthy subjects showed an effect of inhibiting the binding of S1 and ACE2 in a concentration-dependent manner.
Among them, we found that neutrophil-related positively charged (cationic) proteins, histone H2A and elastase, present in saliva significantly inhibit S1-ACE2 binding.The mechanism is that neutrophil-related cationic proteins cover the surface of negatively charged ACE2, providing a barrier to the invasion of the new coronavirus and protecting it from infection.
In addition, a similar S1-ACE2 binding inhibitory effect was confirmed with other cationic substances, and in particular, ε-poly-L-lysine, which is also known as a food preservative in bacterial fermentation products, showed strong inhibitory activity. This suggests the usefulness of cationic natural substances.
Based on this result, not only the development of COVID-19 infection prevention method and treatment method is expected, but also the development of a method to prevent unknown virus infection that will attack human beings in the future at the innate immune level. Expectations are high.
Paper information:[The Journal of Biochemistry] Cloaking the ACE2 receptor with salivary unsubstituted proteins inhibits SARS-CoV-2 entry
