Last year observed a global pandemic caused by SARS-CoV-2 (severe acute respiratory syndrome-coronavirus 2) infection affecting millions of individuals worldwide. There is an urgent unmet need to provide an easily producible and affordable medicine to prevent transmission and provide early treatment for this disease. Since the nasal cavity and the rhinopharynx are the sites of initial replication of SARS-CoV-2, a nasal spray may be an effective option to target SARS-CoV-2 infection. In this study, we tested the antiviral action of three candidate nasal spray formulations against SARS-CoV-2in vitro. We determined that iota-carrageenan in concentrations as low as 6 μg/mL inhibits SARS-CoV-2in vitro. The concentrations of iota-carrageenan with activity against SARS-CoV-2in vitromay be easily achieved through the application of nasal sprays as commonly used in several countries. Recently a double-blind, placebo-controlled study showed that iota-carrageenan in isotonic sodium chloride reduces ca. five times the risk of infection by SARS-CoV-2 in health care personnel. Further, xylitol at a concentration of 50 mg/mL (ca. 329 mM) was found to exert some antiviral action, though this preliminary finding needs further confirmation.

The impairment of the cystic fibrosis transmembrane conductance regulator (CFTR) activity induces intracellular chloride (Cl^–) accumulation. The anion Cl^–, acting as a second messenger, stimulates the secretion of interleukin‐1β (IL‐1β), which starts an autocrine positive feedback loop. Here, we show that NLR family pyrin domain containing 3 (NLRP3) and caspase 1 (CASP1) are indirectly modulated by the intracellular Cl^– concentration, showing maximal expression and activity at 75 mM Cl^–, in the presence of the ionophores nigericin and tributyltin. The expression of PYD and CARD domain containing (PYCARD/ASC) remained constant from 0 to 125 mM Cl^–. The CASP1 inhibitor VX‐765 and the NLRP3 inflammasome inhibitor MCC950 completely blocked the Cl^–‐stimulated IL‐1β mRNA expression and partially the IL‐1β secretion. DCF fluorescence (cellular reactive oxygen species, cROS) and MitoSOX fluorescence (mitochondrial ROS, mtROS) also showed maximal ROS levels at 75 mM Cl^–, a response strongly inhibited by the ROS scavenger N‐acetyl‐L‐cysteine (NAC) or the NADPH oxidase (NOX) inhibitor GKT137831. These inhibitors also affected CASP1 and NLRP3 mRNA and protein expression. More importantly, the serum/glucocorticoid regulated kinase 1 (SGK1) inhibitor GSK650394, or its shRNAs, completely abrogated the IL‐1β mRNA response to Cl^– and the IL‐1β secretion, interrupting the autocrine IL‐1β loop. The results suggest that Cl^– effects are mediated by SGK1, in which under Cl^– modulation stimulates the secretion of mature IL‐1β, in turn, responsible for the upregulation of ROS, CASP1, NLRP3 and IL‐1β itself, through autocrine signalling.

COVID-19 (coronavirus disease 2019) is a pandemic caused by SARS-CoV-2 (severe acute respiratory syndrome-coronavirus 2) infection affecting millions of persons around the world. There is an urgent unmet need to provide an easy-to-produce, affordable medicine to prevent transmission and provide early treatment for this disease. The nasal cavity and the rhinopharynx are the sites of initial replication of SARS-CoV-2. Therefore, a nasal spray may be a suitable dosage form for this purpose. The main objective of our study was to test the antiviral action of three candidate nasal spray formulations against SARS-CoV-2. We have found that iota-carrageenan in concentrations as low as 6 µg/ mL inhibits SARS-CoV-2 infection in Vero cell cultures. The concentrations found to be active in vitro against SARS-CoV-2 may be easily achieved by the application of nasal sprays already marketed in several countries. Xylitol at a concentration of 5 % m/V has proved to be viricidal on its own and the association with iota-carrageenan may be beneficial, as well.

There are, except for remdesivir, no approved antivirals for the treatment or prevention of SARS-CoV-2 infections. Iota-carrageenan formulated into a nasal spray has already been proven safe and effective in viral respiratory infections. We explored this antiviral activity in Calu-3, a human respiratory model cell line. A formula of iota-carrageenan and sodium chloride, as a nasal spray, already approved for human use, effectively inhibited SARS-CoV-2 infection in vitro, providing a more substantial reference for further clinical studies or developments.