Researchers from the University of Tennessee Health Science Center-USA and Instituto de Ciencia y Tecnología-Argentina have in a new study demonstrated that a combination of iota-carrageenan and xylitol inhibit SARS-CoV-2 in Vero cell culture, paving the way for the development of a prophylactic and therapeutic nasal spray for COVID-19.
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.
The COVID-19 Prophylactics-Therapeutics study team tested the antiviral action of three candidate nasal spray formulations against SARS-CoV-2 in vitro.
The team determined that iota-carrageenan in concentrations as low as 6 μg/mL inhibits SARS-CoV-2 in vitro. The concentrations of iota-carrageenan with activity against SARS-CoV-2 in vitro may 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 study findings were published in the peer reviewed journal: PLOS ONE.
SARS-CoV-2 is the single-stranded positive-sense RNA virus responsible for COVID-19, causing one of the most significant pandemics of our time, with more than 244,980,203 confirmed cases and more than 4,971,409 deaths worldwide as of October 27th, 2021 . In most cases, COVID-19 manifests with flu-like symptoms and results in manageable symptoms that resolve without intervention.
However, 15% of patients develop severe pneumonia that requires hospitalization and oxygen support. This includes 5% requiring admission to an intensive care unit (ICU), and among these cases, half result in death . Older adults and those with pre-existing conditions are most susceptible to adverse outcomes. Children are also affected but display milder symptoms than adults, nonetheless, they remain active transmitters of COVID-19 .
Currently, there are no adequate therapeutic or preventive medicines available for COVID-19, except for vaccines. However, by the time of this publication, only 3.1% of people in low-income countries have received at least one dose .
Therefore, effective approaches are urgently needed to reduce the spread of the virus and its death toll. Recent data have shown that a high viral load and a long virus-shedding period were associated with severe COVID-19 [5, 6].
Furthermore, in the early stage of pathogenesis, the virus is localized mainly in the nasal cavity and the nasopharynx [7, 8]. Therefore, the use of antiviral nasal sprays may help reduce nasal and nasopharyngeal viral load, thereby slowing down disease progression and transmission.
Iota-carrageenan formulated into a nasal spray has proven to be safe and effective against coronavirus virus causing common cold [9–11]. Moreover, iota-carrageenan-containing nasal sprays are currently available in several countries in the world. Carrageenans are linear sulfated polysaccharides that are often extracted from red seaweeds, and commercially available in the form of kappa (κ), iota (ι), or lambda (λ).
They have been used for years as thickening agents and stabilizers for food and in the cosmetic and pharmaceutical industry as suspension and emulsion stabilizers. Their antiviral capacity was discovered decades ago and has been experimentally confirmed on herpes virus type 1 and 2, human papilloma virus, H1N1 influenza virus, dengue virus, rhinovirus, hepatitis A virus, enteroviruses, and coronaviruses. Iota-carrageenan inhibits several viruses based on its interaction with the surface of viral particles, thus preventing viral entry and viral budding. [12–17].
In vitro studies examining HeLa cells and primary respiratory epithelial cells have shown inhibition of rhinovirus and influenza. Further, in one study, iota-carrageenan spray reduced mortality by at least 50% in mice infected with lethal doses of the H1N1 influenza virus . In all cases, the antiviral action of iota-carrageenan is more effective, when administrated prophylactically or in the early stages of disease and has shown synergy with other antiviral agents.
Studies performed on adults and children with a common cold demonstrate the effectiveness of an iota-carrageenan nasal spray to alleviate clinical symptoms and shorten their duration, as well as to decrease the viral load of nasopharyngeal specimens and relapses during the follow-up period [9–11, 19–21].
In addition, xylitol is a polyol (formula (CHOH)3(CH2OH)2) that has been used as a sugar substitute in Finland since the 1960s. Obtained from xylan, which is first extracted from hardwood, xylitol has demonstrated multiple health benefits . It has been extensively used in oral health care to prevent cavities because of its antibacterial capacity.
It is already being used in otorhinolaryngology as a nasal spray and irrigation for the treatment of rhinosinusitis and the prevention of otitis media [23, 24]. Both in vitro and animal model studies have demonstrated the antiviral properties of xylitol against the human respiratory syncytial virus .
Both iota-carrageenan and xylitol are safe for humans, being used in much larger amounts as food additives than what may be used for nasal delivery. The safety of iota-carrageenan has already been tested intranasally in New Zealand rabbits in daily doses up to 448 μg/kg/day for up to 28 days and by inhalation in F344 rats for seven days in doses up to 1.2 mg/kg/day .
These studies showed neither local nor systemic toxicity. No immunotoxicity or immunogenicity was observed either. On the other hand, a 50 mg/mL xylitol aqueous solution was well tolerated when administered as a nasal irrigation to chronic rhinosinusitis patients  and when administered by inhalation to naïve and atopic mice, as well as to healthy human volunteers . Both are included in nasal formulations currently available for use in children and adults.
Based on the above knowledge, an experiment was designed and carried out in a Biosafety Level 3 (BSL3) laboratory to investigate the SARS-CoV-2 inhibition capacity of three different candidate preservative-free formulations. It is postulated that the antiviral pathways of iota-carrageenan are due to the electrostatic attraction between its negatively charged molecules and positively charged viral particles . Therefore, by increasing the ionic strength of the medium, the in vitro antiviral action of iota-carrageenan should decrease, as has been previously observed . For this reason, we tested formulations with two different concentrations of sodium chloride (9 and 5 mg/mL) and one that contains xylitol (50 mg/mL) with almost no addition of electrolytes.
reference link: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0259943