Mechanism for Preventing and Treating Covid-19: NMN VS Paxlovid
With the epidemic control policies loosening worldwide, residents in China, India, Malaysia, Japan and Singapore have suffered a shortage of medicines to varying degrees. But on the other hand, the type of medicines available to the public is dynamically increasing, and at present the anti-Covid-19 stars available on the market include Paxlovid, NMN, etc. What are the similarities and differences between the two in terms of mechanism of preventing and treating the Coronavirus?
It is necessary to briefly make out the principle of Covid-19 infection in human cells before discussing the mechanism of action of Paxlovid and NMN.
How SARS-CoV-2 infect cells?
First, the mature Covid-19 (as shown in Figure 1) is mainly composed of structure proteins including spike (S) protein, nucleocapsid (N) protein, membrane (M) protein and envelope (E) protein and RNA viral gene.
Figure 1. SARS-Cov-2 structure
The SARS-CoV-2 opens a channel into the cell by its S protein through recognizing and binding to the ACE2 protein receptor of host cells in vivo. After entering the host cell, the SARS-CoV-2 initiates transcription and translation activities, replicating plenty of SARS-CoV-2, disrupting the cell structure and interfering with the normal cell function. Under this mechanism of action, the supplement of medicine directly comes into play on the sides of spike S protein of the Covid-19 and the ACE2 protein of host cells in human body.
Paxlovid prevents the synthesis of S proteins of SARS-CoV-2.
The mechanism of Paxlovid to treat Covid-19
Paxlovid was made up with two main ingredients, Nirmatrelvir and Ritonavir. Nirmatrelvir combats SARS-CoV-2 by blocking the synthesis of S proteins.The gene information of all SARS-CoV-2 proteins only take over 1/3 of the right side of RNA strand (as shown in Figure 2), and the remaining 2/3 of the RNA gene strand is used for transcription and translation for multiple proteins to synthesize the polyprotein. After the polyprotein is synthesized, it will be cleaved into several functional proteins likely S protein by virus proteases.
Figure 2. RNA structure
In short, when the SARS-CoV-2 replicates, the RNA initiates transcription and translation for proteins in bulk and then proteases cleave it to form structural proteins (S protein). The main proteases used when replicating is CL3. Nirmatrelvir of Paxlovid binds to the CL3 protease to prevent the cleavage of the SARS-CoV-2 polyprotein so as to interrupt the protein synthesis of viral. (As shown in Figure 3).
What’s more, another ingredient, Ritonavir, works by maintaining the concentration of Nirmatrelvir in the body, prolonging and enhancing its efficacy and maintaining the interruption strength for the replicating protease CL3.
Figure 3.CL3 in translation
The mechanism of NMN to prevent and treat Covid-19
NMN prevents Covid-19 infection by protecting DNA and reducing ACE2 expression, shutting down the pathway of ACE2 protein into human cells. The researchers found that DNA damages accumulates intracellular ACE2 receptor proteins. However, these two enzymes to repair DNA damage, sirtuins and PARP, need to be to motivated by NAD+. Studies showed that NMN supplementation is effective in increasing NAD+ levels and thus reducing ACE2 protein expression. As it demonstrates that experiment proved that a reduction in ACE2 expression after infected with the SARS-CoV-2, along with a reduction in viral load and tissue damage in the lungs (as shown in Figure 4) based on the situation that 200mg/kg of NMN fed to old mice aged 12 months for 7 days.
Figure 4. NMN performance in recuding viral loads
The study not only reaffirms the convincing for NMN to treat Covid-19 infection, but based on its proven ability to reduce lung pathological damage and even death in mice infected with neointima, NMN may be used in clinical trials to treat patients with Covid-19 infection.
It is clear from the above principles of action that both Paxlovid and NMN work on original source of infection to treat and prevent Covid-19. The difference between the two is that Paxlovid interferes with the replication of the virus while NMN closes the door to the entry of Covid-19 into human cells. Both different mechanisms of action are in principle effective in preventing the invasion of Covid-19.
1. FACT SHEET FOR HEALTHCARE PROVIDERS: EMERGENCY USE AUTHORIZATION FOR PAXLOVID, 2022
2. Jin R., Niu C.,et al. DNA damage contributes to age-associated differences in SARS-CoV-2 infection, Aging Cell, 2022