Susceptibility of influenza viruses to hypothiocyanite and hypoiodite produced by lactoperoxidase in a cell-free system

The therapeutic potential of thiocyanate and hypothiocyanous acid against pulmonary infections

Hypothiocyanous acid (HOSCN) is an endogenous oxidant produced by peroxidase oxidation of thiocyanate (SCN-), an ubiquitous sulfur-containing pseudohalide synthesized from cyanide. HOSCN serves as a potent microbicidal agent against pathogenic bacteria, viruses, and fungi, functioning through thiol-targeting mechanisms, independent of currently approved antimicrobials. Additionally, SCN- reacts with hypochlorous acid (HOCl), a highly reactive oxidant produced by myeloperoxidase (MPO) at sites of inflammation, also producing HOSCN. This imparts both antioxidant and antimicrobial potential to SCN-. In this review, we discuss roles of HOSCN/SCN- in immunity and potential therapeutic implications for combating infections.

High dietary iodine intake may contribute to the low death rate from COVID-19 infection in Japan with activation by the lactoperoxidase system

We draw the attention of readers and governments to the death rate from coronavirus disease 2019 in Japan, continuing as a fraction of that experienced by many other developed nations. We think this is due to the activity of the powerful, protective lactoperoxidase system (LPO) which prevents serious airborne infections. The LPO system requires iodine, which is liberally provided by the typical Japanese diet but lacking in many others. One might consider the Japanese experience an incredibly large, open-label study exhibiting the preventative power of a high-iodine diet. We predict this favourable trend will continue for Japan because deadly variants of the severe, acute respiratory syndrome coronavirus 2 will be with us, forever.

A Bacterial Myeloperoxidase with Antimicrobial Properties

The four mammalian peroxidases (myeloperoxidase, eosinophilperoxidase, lactoperoxidase, and thyroid peroxidase) are widely studied in the literature. They catalyze the formation of antimicrobial compounds and participate in innate immunity. Owing to their properties, they are used in many biomedical, biotechnological, and agro-food applications. We decided to look for an enzyme that is easiest to produce and much more stable at 37 °C than mammalian peroxidases. To address this question, a peroxidase from Rhodopirellula baltica, identified by bioinformatics tools, was fully characterized in this study. In particular, a production and purification protocol including the study of heme reconstitution was developed. Several activity tests were also performed to validate the hypothesis that this peroxidase is a new homolog of mammalian myeloperoxidase. It has the same substrate specificities as the human one and accepts I^-, SCN^-, Br^-, and Cl^- as (pseudo-) halides. It also exhibits other auxiliary activities such as catalase and classical peroxidase activities, and it is very stable at 37 °C. Finally, this bacterial myeloperoxidase can kill the Escherichia coli strain ATCC25922, which is usually used to perform antibiograms.

Supporting the Aspecific Physiological Defenses of Upper Airways against Emerging SARS-CoV-2 Variants

The rapid rollout of COVID-19 vaccines in 2021 sparked general optimism toward controlling the severe form of the disease, preventing hospitalizations and COVID-19-associated mortality, and the transmissibility of SARS-CoV-2 infection [...].

Preventing Respiratory Viral Diseases with Antimicrobial Peptide Master Regulators in the Lung Airway Habitat

The vast surface area of the respiratory system acts as an initial site of contact for microbes and foreign particles. The whole respiratory epithelium is covered with a thin layer of the airway and alveolar secretions. Respiratory secretions contain host defense peptides (HDPs), such as defensins and cathelicidins, which are the best-studied antimicrobial components expressed in the respiratory tract. HDPs have an important role in the human body's initial line of defense against pathogenic microbes. Epithelial and immunological cells produce HDPs in the surface fluids of the lungs, which act as endogenous antibiotics in the respiratory tract. The production and action of these antimicrobial peptides (AMPs) are critical in the host's defense against respiratory infections. In this study, we have described all the HDPs secreted in the respiratory tract as well as how their expression is regulated during respiratory disorders. We focused on the transcriptional expression and regulation mechanisms of respiratory tract HDPs. Understanding how HDPs are controlled throughout infections might provide an alternative to relying on the host's innate immunity to combat respiratory viral infections.

Excess iodine exposure acutely increases salivary iodide and antimicrobial hypoiodous acid concentrations in humans

The lactoperoxidase (LPO)-hydrogen peroxide-halides reaction (LPO system) converts iodide and thiocyanate (SCN^-) into hypoiodous acid (HOI) and hypothiocyanite (OSCN^-), respectively. Since this system has been implicated in defense of the airways and oropharynx from microbial invasion, in this proof-of-concept study we measured the concentrations of these analytes in human saliva from a convenience clinical sample of 40 qualifying subjects before and after acute iodine administration via the iodinated contrast medium used in coronary angiography to test the hypothesis that an iodide load increases salivary iodide and HOI concentrations. Saliva was collected and salivary iodide, SCN^-, HOI and OSCN^- were measured using standard methodology. The large iodine load delivered by the angiographic dye, several 100-fold in excess of the U.S. Recommended Daily Allowance for iodine (150 µg/day), significantly increased salivary iodide and HOI levels compared with baseline levels, whereas there was no significant change in salivary SCN^- and OSCN^- levels. Iodine load and changes of salivary iodide and HOI levels were positively correlated, suggesting that higher iodide in the circulation increases iodide output and salivary HOI production. This first of its kind study suggests that a sufficient but safe iodide supplementation less than the Tolerable Upper Limit for iodine set by the U.S. Institute of Medicine (1,100 µg/day) may augment the generation of antimicrobial HOI by the salivary LPO system in concentrations sufficient to at least in theory protect the host against susceptible airborne microbial pathogens, including enveloped viruses such as coronaviruses and influenza viruses.

Iodine contrast exposure and incident COVID-19 infection

Background

Iodine and particularly its oxidated forms have long been recognized for its effective antiseptic properties. Limited in vitro and in vivo data suggest that iodine exposure may rapidly inactivate, reduce transmission, and reduce infectivity of SARS-CoV-2. We hypothesized that iodine exposure may be associated with decreased incident COVID-19 infection.

Methods

A retrospective population-level cohort analysis was performed of the U.S. Veterans Health Administration between 1 March 2020 and 31 December 2020, before the widespread availability of vaccines against SARS-CoV-2. Multivariable logistic regression models estimated the adjusted odds ratios (OR) and 95% confidence intervals (CI) of the associations between iodinated contrast exposure and incident COVID-19 infection, adjusting for age, sex, race/ethnicity, place of residence, socioeconomic status, and insurance status.

Results

530,942 COVID-19 tests from 333,841 Veterans (mean ± SD age, 62.7 ± 15.2 years; 90.2% men; 61.9% non-Hispanic Whites) were analyzed, of whom 9% had received iodinated contrast ≤60 days of a COVID-19 test. Iodine exposure was associated with decreased incident COVID-19 test positivity (OR, 0.75 95% CI, 0.71–0.78). In stratified analyses, the associations between iodinated contrast use and decreased COVID-19 infection risk did not differ by age, sex, and race/ethnicity.

Conclusion

Iodine exposure may be protective against incident COVID-19 infection. Weighed against the risks of supraphysiologic iodine intake, dietary, and supplemental iodine nutrition not to exceed its Tolerable Upper Limit may confer an antimicrobial benefit against SARS-CoV-2. A safe but antimicrobial level of iodine supplementation may be considered in susceptible individuals, particularly in geographic regions where effective COVID-19 vaccines are not yet readily available.

Thyroidal and Extrathyroidal Requirements for Iodine and Selenium: A Combined Evolutionary and (Patho)Physiological Approach

Iodide is an antioxidant, oxidant and thyroid hormone constituent. Selenoproteins are needed for triiodothyronine synthesis, its deactivation and iodine release. They also protect thyroidal and extrathyroidal tissues from hydrogen peroxide used in the ‘peroxidase partner system’. This system produces thyroid hormone and reactive iodine in exocrine glands to kill microbes. Exocrine glands recycle iodine and with high urinary clearance require constant dietary supply, unlike the thyroid. Disbalanced iodine-selenium explains relations between thyroid autoimmune disease (TAD) and cancer of thyroid and exocrine organs, notably stomach, breast, and prostate. Seafood is iodine unconstrained, but selenium constrained. Terrestrial food contains little iodine while selenium ranges from highly deficient to highly toxic. Iodine vs. TAD is U-shaped, but only low selenium relates to TAD. Oxidative stress from low selenium, and infection from disbalanced iodine-selenium, may generate cancer of thyroid and exocrine glands. Traditional Japanese diet resembles our ancient seashore-based diet and relates to aforementioned diseases. Adequate iodine might be in the milligram range but is toxic at low selenium. Optimal selenoprotein-P at 105 µg selenium/day agrees with Japanese intakes. Selenium upper limit may remain at 300–400 µg/day. Seafood combines iodine, selenium and other critical nutrients. It brings us back to the seashore diet that made us what we currently still are.

The Hypothiocyanite and Amantadine Combination Treatment Prevents Lethal Influenza A Virus Infection in Mice

The influenza virus has a large clinical burden and is associated with significant mortality and morbidity. The development of effective drugs for the treatment or prevention of influenza is important in order to reduce its impact. Adamantanes and neuraminidase inhibitors are two classes of anti-influenza drugs in which resistance has developed; thus, there is an urgent need to explore new therapeutic options. Boosting antiviral innate immune mechanisms in the airways represents an attractive approach. Hypothiocyanite (OSCN⁻) is produced by the airway epithelium and is effective in reducing the replication of several influenza A virus strains in vitro. It remains, however, largely unexplored whether OSCN⁻ has such an antiviral effect in vivo. Here we determined the therapeutic potential of OSCN⁻, alone or in combination with amantadine (AMT), in preventing lethal influenza A virus replication in mice and in vitro. Mice intranasally infected with a lethal dose of A/Puerto Rico/8/1934 (H1N1) or A/Hong Kong/8/1968 (H3N2) were cured by the combination treatment of OSCN⁻ and AMT. Monotherapy with OSCN⁻ or AMT alone did not substantially improve survival outcomes. However, AMT+OSCN⁻ treatment significantly inhibited viral replication, and in vitro treatment inhibited viral entry and nuclear transport of different influenza A virus strains (H1N1 and H3N2) including the AMT-resistant strain A/WSN/33 (H1N1). A triple combination treatment consisting of AMT, oseltamivir, and OSCN⁻ was also tested and further inhibited in vitro viral replication of the AMT-resistant A/WSN/33 strain. These results suggest that OSCN⁻ is a promising anti-influenza treatment option when combined with other antiviral drugs.

Structural evidence of the oxidation of iodide ion into hyper-reactive hypoiodite ion by mammalian heme lactoperoxidase

Lactoperoxidase (1.11.1.7, LPO) is a mammalian heme peroxidase found in the extracellular fluids of mammals including plasma, saliva, airway epithelial lining fluids, nasal lining fluid, milk, tears, gastric juices, and intestinal mucosa. To perform its innate immune action against invading microbes, LPO utilizes hydrogen peroxide (H₂ O₂ ) to convert thiocyanate (SCN^- ) and iodide (I^- ) ions into the oxidizing compounds hypothiocyanite (OSCN^- ) and hypoiodite (IO^- ). Previously determined structures of the complexes of LPO with SCN^- , OSCN^- , and I^- show that SCN^- and I^- occupy appropriate positions in the distal heme cavity as substrates while OSCN^- binds in the distal heme cavity as a product inhibitor. We report here the structure of the complex of LPO with IO^- as the first structural evidence of the conversion of iodide into hypoiodite by LPO. To obtain this complex, a solution of LPO was first incubated with H₂ O₂ , then mixed with ammonium iodide solution and the complex crystallized by the addition of PEG-3350, 20% (wt/vol). These crystals were used for X-ray intensity data collection and structure analysis. The structure determination revealed the presence of four hypoiodite ions in the substrate binding channel of LPO. In addition to these, six other hypoiodite ions were observed at different exterior sites. We surmise that the presence of hypoiodite ions in the distal heme cavity blocks the substrate binding site and inhibits catalysis. This was confirmed by activity experiments with the colorimetric substrate, ABTS (2,2'-azino-bis(3-ethylbenzthiazoline-sulfonic acid)), in the presence of hypoiodite and iodide ions.

[Atmospheric reactive oxygen species and some aspects of the antiviral protection of the respiratory epithelium]

The review focuses on molecular and biochemical mechanisms of nonspecific protection of respiratory epithelium. The authors provide a comprehensive analysis of up-to-date data on the activity of the lactoperoxidase system expressed on the surface of the respiratory epithelium which provides the generation of hypothiocyanate and hypoiodite in the presence of locally produced or inhaled hydrogen peroxide. Molecular mechanisms of production of active compounds with antiviral and antibacterial effects, expression profiles of enzymes, transporters and ion channels involved in the generation of hypothiocyanite and hypoiodate in the mucous membrane of the respiratory system in physiological and pathological conditions (inflammation) are discussed. In the context of antibacterial and antiviral defense special attention is paid to recent data confirming the effects of atmospheric air composition on the efficiency of hypothiocyanite and hypoiodate synthesis in the respiratory epithelium. The causes and outcomes of lactoperoxidase system impairment due to the action of atmospheric factors are discussed in the context of controlling the sensitivity of the epithelium to the action of bacterial agents and viruses. Restoration of the lactoperoxidase system activity can be achieved by application of pharmacological agents aimed to compensate for the lack of halides in tissues, and by the control of chemical composition of the inhaled air.

Microbicidal Activity of Hypothiocyanite against Pneumococcus

Infections caused by Streptococcus pneumoniae (pneumococcus, Spn) manifest in several forms such as pneumonia, meningitis, sinusitis or otitis media and are associated with severe morbidity and mortality worldwide. While current vaccines and antibiotics are available to treat Spn infections, the rise of antibiotic resistance and limitations of the vaccines to only certain Spn serotypes urge the development of novel treatments against Spn. Hypothiocyanite (OSCN-) is a natural antimicrobial product produced by the body's own innate immune system to fight a variety of pathogens. We recently showed that OSCN- is also capable of killing Spn in vitro. OSCN- is an oxidative agent attacking microbes in a nonspecific manner, is safe for the host and also has anti-inflammatory effects that make it an ideal candidate to treat a variety of infections in humans. However, OSCN- has a short life span that makes its use, dosage and administration more problematic. This minireview discusses the antimicrobial mechanism of action of OSCN- against Spn and elaborates on the potential therapeutic use of OSCN- against Spn and other infectious agents, either alone or in combination with other therapeutic approaches.

Comments on the Discussion Forum: Oromucosal immunomodulation as clinical spectrum mitigating factor in SARS-CoV-2 infection

The mammalian lactoperoxidase system, consisting of lactoperoxidase and the H₂O₂‐producing enzyme duox, is our first line of defence against airborne microbes. This system catalyses the production of hypoiodite and hypoiodous acid in the presence of sufficient iodine. These products are highly efficient at destroying the H1N1 virus and the respiratory syncytial virus (RSV). Japan has not been affected as much as other nations during the COVID‐19 pandemic (death rate about 10% of the United States), and we think this is due to a diet high in iodine. With this in mind, we suggest four actions to prevent SARS‐CoV‐2 infections. First, health professionals should study the preventative effect of increasing iodine in the diets of the aged, institutionalized, diabetics andsmokers. Second, the recommended daily intake (RDI) for iodine should be significantly increased, to at least double, the current RDI. Governments should encourage the use and distribution of cheap iodized salts, kelp and seaweed. Third, more research should be done around the physiology and the protective effects of the lactoperoxidase system. Finally, the degradation products of the SARS‐CoV‐2 viral particle by hypoiodite and hypoiodous acid should be characterized; portions of the damaged particle are likely to elicit stronger immunity and better vaccines.

Clustering of catalytic nanocompartments for enhancing an extracellular non-native cascade reaction

Compartmentalization is fundamental in nature, where the spatial segregation of biochemical reactions within and between cells ensures optimal conditions for the regulation of cascade reactions. While the distance between compartments or their interaction are essential parameters supporting the efficiency of bio-reactions, so far they have not been exploited to regulate cascade reactions between bioinspired catalytic nanocompartments. Here, we generate individual catalytic nanocompartments (CNCs) by encapsulating within polymersomes or attaching to their surface enzymes involved in a cascade reaction and then, tether the polymersomes together into clusters. By conjugating complementary DNA strands to the polymersomes' surface, DNA hybridization drove the clusterization process of enzyme-loaded polymersomes and controlled the distance between the respective catalytic nanocompartments. Owing to the close proximity of CNCs within clusters and the overall stability of the cluster architecture, the cascade reaction between spatially segregated enzymes was significantly more efficient than when the catalytic nanocompartments were not linked together by DNA duplexes. Additionally, residual DNA single strands that were not engaged in clustering, allowed for an interaction of the clusters with the cell surface as evidenced by A549 cells, where clusters decorating the surface endowed the cells with a non-native enzymatic cascade. The self-organization into clusters of catalytic nanocompartments confining different enzymes of a cascade reaction allows for a distance control of the reaction spaces which opens new avenues for highly efficient applications in domains such as catalysis or nanomedicine.

Dual oxidase 1 promotes antiviral innate immunity

Dual oxidase 1 (DUOX1) is an NADPH oxidase that is highly expre-ssed in respiratory epithelial cells and produces H₂O₂ in the airway lumen. While a line of prior in vitro observations suggested that DUOX1 works in partnership with an airway peroxidase, lactoperoxidase (LPO), to produce antimicrobial hypothiocyanite (OSCN^-) in the airways, the in vivo role of DUOX1 in mammalian organisms has remained unproven to date. Here, we show that Duox1 promotes antiviral innate immunity in vivo. Upon influenza airway challenge, Duox1 ^-/- mice have enhanced mortality, morbidity, and impaired lung viral clearance. Duox1 increases the airway levels of several cytokines (IL-1β, IL-2, CCL1, CCL3, CCL11, CCL19, CCL20, CCL27, CXCL5, and CXCL11), contributes to innate immune cell recruitment, and affects epithelial apoptosis in the airways. In primary human tracheobronchial epithelial cells, OSCN^- is generated by LPO using DUOX1-derived H₂O₂ and inactivates several influenza strains in vitro. We also show that OSCN^- diminishes influenza replication and viral RNA synthesis in infected host cells that is inhibited by the H₂O₂ scavenger catalase. Binding of the influenza virus to host cells and viral entry are both reduced by OSCN^- in an H₂O₂-dependent manner in vitro. OSCN^- does not affect the neuraminidase activity or morphology of the influenza virus. Overall, this antiviral function of Duox1 identifies an in vivo role of this gene, defines the steps in the infection cycle targeted by OSCN^-, and proposes that boosting this mechanism in vivo can have therapeutic potential in treating viral infections.

Oral peroxidases: From antimicrobial agents to ecological actors (Review)

Sialoperoxidase and myeloperoxidase are the two main peroxidase enzymes found in the oral cavity. Sialoperoxidase is present in salivary secretions and in the biofilms that line the oral surfaces, while myeloperoxidase is abundant in the dento-gingival sulcus area. In the presence of hydrogen peroxide (H₂O₂), oral peroxidases catalyze the oxidation of the pseudohalide anion thiocyanate (SCN⁻) to hypothiocyanite (OSCN⁻), a strong oxidant that serves an antimicrobial role. Furthermore, oral peroxidases consume bacteria-produced H₂O₂ and could help inactivate toxic carcinogenic and genotoxic substances. Numerous in vitro studies have reported the antibacterial, antimycotic and antiviral role of peroxidases, suggesting possible applications in oral therapy. However, the use of oral hygiene products incorporating peroxidase systems has not yet been shown to be beneficial for the treatment or prevention of oral infections. This paradox reflects our incomplete knowledge of the physiological role of peroxidases in a complex environment, such as the oral region. While hygiene is crucial for restoring oral microbiota to a symbiotic state, there are no data to suggest that the addition of a peroxidase per se can create a dysbiotic state. Recent investigations have associated the presence of peroxidase activity with gram-positive cocci microbial flora, and its insufficiency with dysbiosis has been linked to pathologies, such as caries, periodontitis or infections of the oral mucosa. Therefore, oxidants generated by oral peroxidases appear to be an essential ecological determinant for oral health through the selection of a symbiotic microbiota capable of resisting oxidative stress. The objective of the present review was to update the current knowledge of the physiological aspects and applications of oral peroxidases in clinical practice.

Supplementation of Bovine Colostrum in Inflammatory Bowel Disease: Benefits and Contraindications

Inflammatory bowel disease (IBD) is a group of chronic relapsing disorders whose etiology has not been fully explained. Therefore, available therapeutic approaches for IBD patients are still insufficient. Current treatment strategies are targeted to immune system dysfunctions, often associated with alternations in the microbiota, which contribute to the development of chronic intestinal inflammation. Therapeutics include anti-inflammatory drugs such as aminosalicylates and corticosteroids, immunosuppressive agents, antibiotics, and biological agents such as infliximab and vedolizumab. Auxiliary therapies involve a balanced and personalized diet, healthy lifestyle, avoiding stress, as well as dietary supplements. In this review, we discuss the use of bovine colostrum (BC) as a therapeutic agent, including its advantages and contraindications. We summarize our knowledge on well-researched BC constituents and their effects on the gastrointestinal tract as evidenced in in vitro and in vivo studies.

DUOX1 in mammalian disease pathophysiology

Dual oxidase 1 (DUOX1) is a member of the protein family of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases. DUOX1 has several normal physiological, immunological, and biochemical functions in different parts of the body. Dysregulated oxidative metabolism interferes with various disease pathologies and numerous therapeutic options are based on targeting cellular redox pathways. DUOX1 forms an important enzymatic source of biological oxidants, and DUOX1 expression is frequently dysregulated in various diseases. While this review shortly addresses the biochemical and cellular properties and proposed physiological roles of DUOX1, its main purpose is to summarize the current knowledge with respect to the potential role of DUOX1 enzyme in disease pathology, especially in mammalian organisms. Although DUOX1 is normally prominently expressed in epithelial lineages, it is frequently silenced in epithelial-derived cancers by epigenetic mechanisms. While an abundance of information is available on DUOX1 transcription in different diseases, an increasing number of mechanistic studies indicate a causative relationship between DUOX1 function and disease pathophysiology. Additionally, specific functions of the DUOX1 maturation factor, DUOXA1, will also be addressed. Lastly, urgent and outstanding questions on the field of DUOX1 will be discussed that could provide valuable new diagnostic tools and novel therapeutic options.

Hypothiocyanite and Hypothiocyanite/Lactoferrin Mixture Exhibit Virucidal Activity In Vitro against SARS-CoV-2

SARS-CoV-2 replicates efficiently in the upper airways during the prodromal stage, resulting in environmental viral shedding from patients with active COVID-19 as well as from asymptomatic individuals. There is a need to find pharmacological interventions to mitigate the spread of COVID-19. Hypothiocyanite and lactoferrin are molecules of the innate immune system with a large spectrum cidal activity. The Food and Drug Administration and the European Medicines Agency designated the hypothiocyanite and lactoferrin combination as an orphan drug. We report an in vitro study showing that micromolar concentrations of hypothiocyanite exhibit dose- and time-dependent virucidal activity against SARS-CoV-2 and that the latter is slightly enhanced by the simultaneous presence of lactoferrin.

Reactive oxygen and nitrogen species and innate immune response

The innate immune system is the first line of defense against pathogens and is characterized by its fast but nonspecific response. One important mechanism of this system is the production of the biocidal reactive oxygen and nitrogen species, which are widely distributed within biological systems, including phagocytes and secretions. Reactive oxygen and nitrogen species are short-lived intermediates that are biochemically synthesized by various enzymatic reactions in aerobic organisms and are regulated by antioxidants. The physiological levels of reactive species play important roles in cellular signaling and proliferation. However, higher concentrations and prolonged exposure can fight infections by damaging important microbial biomolecules. One feature of the reactive species generation system is the interaction between its components to produce more biocidal agents. For example, the phagocytic NADPH oxidase complex generates superoxide, which functions as a precursor for antimicrobial hydrogen peroxide synthesis. Peroxide is then used by myeloperoxidase in the same cells to generate hypochlorous acid, a highly microbicidal agent. Studies on animal models and microorganisms have shown that deficiency of these antimicrobial agents is associated with severe recurrent infections and immunocompromised diseases, such as chronic granulomatous disease. There is accumulating evidence that reactive species have important positive aspects on human health and immunity; however, some important promising features of this system remain obscure.

The Role of Thiocyanate in Modulating Myeloperoxidase Activity during Disease

Thiocyanate (SCN⁻) is a pseudohalide anion omnipresent across mammals and is particularly concentrated in secretions within the oral cavity, digestive tract and airway. Thiocyanate can outcompete chlorine anions and other halides (F⁻, Br⁻, I⁻) as substrates for myeloperoxidase by undergoing two-electron oxidation with hydrogen peroxide. This forms their respective hypohalous acids (HOX where X⁻ = halides) and in the case of thiocyanate, hypothiocyanous acid (HOSCN), which is also a bactericidal oxidative species involved in the regulation of commensal and pathogenic microflora. Disease may dysregulate redox processes and cause imbalances in the oxidative profile, where typically favoured oxidative species, such as hypochlorous acid (HOCl), result in an overabundance of chlorinated protein residues. As such, the pharmacological capacity of thiocyanate has been recently investigated for its ability to modulate myeloperoxidase activity for HOSCN, a less potent species relative to HOCl, although outcomes vary significantly across different disease models. To date, most studies have focused on therapeutic effects in respiratory and cardiovascular animal models. However, we note other conditions such as rheumatic arthritis where SCN⁻ administration may worsen patient outcomes. Here, we discuss the pathophysiological role of SCN⁻ in diseases where MPO is implicated.

Nasal disinfection for the prevention and control of COVID-19: A scoping review on potential chemo-preventive agents

BACKGROUND

Neither pre-exposure nor post-exposure chemo-prophylaxis agents are currently available to prevent COVID-19. On the other hand, high loads of SARS-CoV-2 are shed from the nasal cavity before and after symptoms onset.

OBJECTIVE

To conduct a scoping review on the available evidence on tolerable nasal disinfectants with encouraging health outcomes against SARS-CoV-2, i.e., agents effective against at least two different viruses beyond SARS-CoV-2.

METHODS

Online databases were searched to identify papers published during 2010-2020. Publications were selected if they were relevant to the scoping review. The review was narrative, describing for each treatment the mechanism(s) of action, tolerability, in vitro and in vivo evidence of the effects against SARS-CoV-2 and whether the product had been marketed.

RESULTS

Eight treatments were scrutinized: hypothiocyanite, lactoferrin, N-chlorotaurine, interferon-alpha, povidone-iodine, quaternary ammonium compounds, alcohol-based nasal antiseptics and hydroxychloroquine. In vitro viricidal effect against SARS-CoV-2 was reported for ethanol, alcohol-based hand sanitizers and povidone-iodine. Inhibition of other coronaviruses was described for lactoferrin, ethanol, hydroxychloroquine and quaternary ammonium compound. No treatment has been tested against SARS-CoV-2 in randomized controlled clinical trials thus far. However, interferon-alpha, lactoferrin and hydroxychloroquine were tested in one-arm open label uncontrolled clinical trial. Oxidant activity (hypothiocyanite, N-chlorotaurine and povidone-iodine), enhancement of endocytic and lysosomal pH (quaternary ammonium compounds and hydroxychloroquine) and destruction of the viral capsid (quaternary ammonium compounds, alcohol-based nasal antiseptics) were the main mechanisms of action. Lactoferrin and interferon-alpha have subtle biological mechanisms. With the exception of N-chlorotaurine, all other products available on the market.

CONCLUSIONS

Effective and safe chemo-prophylactic drugs against SARS-CoV-2 do not exist yet but most eligible candidates are already in the market. Whilst the human nasal cavity is the port of entry for SARS-CoV-2, the mouth is involved as exit site through emission of respiratory droplets. The well-known hand-to-nose-to-hand cycle of contamination requires appropriate additional strategies for infection control. To narrow down the subsequent laboratory and clinical investigations, a case-control approach could be employed to compare the use of candidate drugs among individuals testing positive and negative to COVID-19 swabs.

Oxidative killing of encapsulated and nonencapsulated Streptococcus pneumoniae by lactoperoxidase-generated hypothiocyanite

Streptococcus pneumoniae (Pneumococcus) infections affect millions of people worldwide, cause serious mortality and represent a major economic burden. Despite recent successes due to pneumococcal vaccination and antibiotic use, Pneumococcus remains a significant medical problem. Airway epithelial cells, the primary responders to pneumococcal infection, orchestrate an extracellular antimicrobial system consisting of lactoperoxidase (LPO), thiocyanate anion and hydrogen peroxide (H₂O₂). LPO oxidizes thiocyanate using H₂O₂ into the final product hypothiocyanite that has antimicrobial effects against a wide range of microorganisms. However, hypothiocyanite’s effect on Pneumococcus has never been studied. Our aim was to determine whether hypothiocyanite can kill S. pneumoniae. Bactericidal activity was measured in a cell-free in vitro system by determining the number of surviving pneumococci via colony forming units on agar plates, while bacteriostatic activity was assessed by measuring optical density of bacteria in liquid cultures. Our results indicate that hypothiocyanite generated by LPO exerted robust killing of both encapsulated and nonencapsulated pneumococcal strains. Killing of S. pneumoniae by a commercially available hypothiocyanite-generating product was even more pronounced than that achieved with laboratory reagents. Catalase, an H₂O₂ scavenger, inhibited killing of pneumococcal by hypothiocyanite under all circumstances. Furthermore, the presence of the bacterial capsule or lytA-dependent autolysis had no effect on hypothiocyanite-mediated killing of pneumococci. On the contrary, a pneumococcal mutant deficient in pyruvate oxidase (main bacterial H₂O₂ source) had enhanced susceptibility to hypothiocyanite compared to its wild-type strain. Overall, results shown here indicate that numerous pneumococcal strains are susceptible to LPO-generated hypothiocyanite.