Anti-SARS-CoV-2 Activity of Rhamnan Sulfate from Monostroma nitidum.

The COVID-19 pandemic is a major human health concern. The pathogen responsible for COVID-19, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), invades its host through the interaction of its spike (S) protein with a host cell receptor, angiotensin-converting enzyme 2 (ACE2). In addition to ACE2, heparan sulfate (HS) on the surface of host cells also plays a significant role as a co-receptor. Our previous studies demonstrated that sulfated glycans, such as heparin and fucoidans, show anti-COVID-19 activities. In the current study, rhamnan sulfate (RS), a polysaccharide with a rhamnose backbone from a green seaweed, Monostroma nitidum, was evaluated for binding to the S-protein from SARS-CoV-2 and inhibition of viral infectivity in vitro. The structural characteristics of RS were investigated by determining its monosaccharide composition and performing two-dimensional nuclear magnetic resonance. RS inhibition of the interaction of heparin, a highly sulfated HS, with the SARS-CoV-2 spike protein (from wild type and different mutant variants) was studied using surface plasmon resonance (SPR). In competitive binding studies, the IC50 of RS against the S-protein receptor binding domain (RBD) binding to immobilized heparin was 1.6 ng/mL, which is much lower than the IC50 for heparin (~750 ng/mL). RS showed stronger inhibition than heparin on the S-protein RBD or pseudoviral particles binding to immobilized heparin. Finally, in an in vitro cell-based assay, RS showed strong antiviral activities against wild type SARS-CoV-2 and the delta variant.

Strategies for decreasing contamination of homemade nasal saline irrigation solutions.

BACKGROUND: Saline nasal irrigations (SNI) are an important adjunct in the treatment of rhinosinusitis, and many patients prepare and store these solutions in their homes without an awareness of the potential for contamination. The objectives of this study were to determine if such contamination occurs and the effect of preparation methods on contamination. METHODS: Stock solutions of various tonicities and pHs were prepared using boiled, bottled, and distilled water (n = 57). The solutions were stored at ambient temperature or refrigerated for 1 week. Each day, 50 mL of the solutions were decanted to simulate transferring the stock solution into an irrigation vector. Cultures of the stock solutions were taken on days 1, 3, and 7. RESULTS: Overall contamination rate was 35.1%. The boiled water solutions were more likely to demonstrate bacterial growth (p < 0.001), as were those that were hypotonic (p = 0.046). pH had no significant effect (p = 0.127). Growth occurred as early as 24 hours after solution preparation. Pathogenic species isolated were Staphylococcus aureus, Moraxella sp, Sphingomonas paucimobilis, Acinetobacter junii, Methylobacterium sp, and Brevundimonas diminuta. No bacterial growth occurred in refrigerated solutions (p = 0.008). CONCLUSION: Pathogenic bacterial growth can occur in a short period of time in homemade SNI solutions with routine handling. Solutions should be refrigerated if possible. If solutions are to be stored at ambient temperature, they should be either isotonic or hypertonic and prepared from bottled or distilled water.