HYPERTONIC SALINE SOLUTION INHIBITS SARS-COV-2 REPLICATION IN VITRO
A recent Brazilian study by Machado et.al presented data in a not yet peer certified reviewed preprint report that suggested hypertonic saline solution (HS) may have a possible role as a prophylactic and as an alternative therapeutic option for COVID-19.
In vitro, the potential antiviral activity of sodium chloride (NaCl) has been already studied for RNA viruses such as mengovirus13, respiratory syncytial virus (RSV) and others. Furthermore, a randomized controlled clinical trial studying the effectiveness of treatment of viral upper respiratory tract infection, using hypertonic saline nasal irrigation and gargle (HSNIG)15, observed a decrease in the duration of illness, over-the-counter medication use, transmission within household contacts and viral shedding15.
Furthermore, findings from a post-hoc analysis of NCT02438579 clinical trial suggest that hypertonic saline nasal irrigation and gargling may play a role in reducing symptoms and duration of illness caused by COVID-1949.
The experiments were performed to test if hypertonic saline solution is able to inhibit SARS-CoV-2 virus replication in vitro.
The SARS-CoV-2 inhibition assays were performed using monkey kidney Vero cells and as lung epithelial cells, may be heavily infected by SARS-CoV-216 and are capable of undergoing endo- and exocytosis, being therefore a good model cell to study the SARS-CoV-2 life cycle.
Machado et.al measured the effects of increasing concentrations of NaCl (135, 160,185, 210, 235, 260 and 285mM equivalent to 0.8, 0.9, 1.1, 1.2, 1.4, 1.5, 1.7%, respectively) on cell viability and their antiviral activity on SARS-CoV-2 at 0hr, 1hr, 24hrs and 72hrs after the NaCl challenge.
The authors show (a) that 210mM NaCl (1.2% saline) was sufficient to inhibit the virus replication by 90% (Fig. 1a), achieving 100% of inhibition on 260mM (1.5% saline), (b) the efficacy of hypertonic NaCl solutions in blocking SARS-CoV-2 replication in Vero cells and (c) that SARS-CoV-2 inhibition effects occur at the onset of hypertonic stress.
NaCl seems to depolarize the plasma membrane supposedly associated with the inhibition of the SARS-CoV-2 life cycle. The results show that the increase of NaCl concentration causes an immediate membrane depolarization, probably through the activation of an extracellular Na+ sensitive channel called Nax32.
Since NaCl decreases viral replication by more than 90%, probably due to a mechanism associated with the effect of membrane depolarization, the authors suggest that tests on humans should be carried out to validate the effectiveness of hypertonic saline solution treatment in patients with COVID-19.
The authors suggest that hypertonic saline solution can be used as prophylaxis and an alternative treatment for Covid-19 patients and mention as well that this procedure is already used to improve lung function in cystic fibrosis patients45 and nebulized 3% hypertonic saline treatments for infants with moderate to severe bronchiolitis is safe without adverse events such as bronchospasm, cough or wheezing aggravation 46-48.
Rafael R. G. Machado et.al, Hypertonic saline solution inhibits SARS-CoV-2 in vitro assay, BioRxiv Preprint doi: https://doi.org/10.1101/2020.08.04.235549