Hypothiocyanite Explained

Hypothiocyanite is the anion [OSCN]⁻ and the conjugate base of hypothiocyanous acid (HOSCN). It is an organic compound part of the thiocyanates as it contains the functional group SCN. It is formed when an oxygen is singly bonded to the thiocyanate group. Hypothiocyanous acid is a fairly weak acid; its acid dissociation constant (pK_a) is 5.3.

Hypothiocyanite is formed by peroxidase^[1] catalysis of hydrogen peroxide and thiocyanate:

H₂O₂ + SCN⁻ → OSCN⁻ + H₂O

As a bactericide

Hypothiocyanite occurs naturally in the antimicrobial immune system of the human respiratory tract^[2] in a redox reaction catalyzed by the enzyme lactoperoxidase.^[3] It has been researched extensively for its capabilities as an alternative antibiotic as it is harmless to human body cells while being cytotoxic to bacteria.^[4] The exact processes for making hypothiocyanite have been patented as such an effective antimicrobial has many commercial applications.^[5]

Mechanism of action

Lactoperoxidase-catalysed reactions yield short-lived intermediary oxidation products of SCN⁻, providing antibacterial activity.^[6]

The major intermediary oxidation product is hypothiocyanite OSCN⁻, which is produced in an amount of about 1 mole per mole of hydrogen peroxide. At the pH optimum of 5.3, the OSCN⁻ is in equilibrium with HOSCN. The uncharged HOSCN is considered to be the greater bactericidal of the two forms.^[7] At pH 7, it was evaluated that HOSCN represents 2% compare to OSCN⁻ 98%.^[8]

The action of OSCN⁻ against bacteria is reported to be caused by sulfhydryl (SH) oxidation.^[9]

The oxidation of -SH groups in the bacterial cytoplasmic membrane results in loss of the ability to transport glucose and also in leaking of potassium ions, amino acids and peptide.

OSCN⁻ has also been identified as an antimicrobial agent in milk, saliva,^[10] tears, and mucus.

OSCN⁻ is considered as a safe product as it is not mutagenic.^[11]

Relation to cystic fibrosis

Initially, this particular lactoperoxidase-catalyzed compound was originally discovered while viewing the specific environment of cystic fibrosis patients' weakened respiratory immune system against bacterial infection.^[12]

Symptoms of cystic fibrosis include an inability to secrete sufficient quantities of SCN⁻ which results in a shortage of necessary hypothiocyanite, resulting in increasing mucous viscosity, inflammation and bacterial infection in the respiratory tract.

Lactoferrin with hypothiocyanite has been granted orphan drug status by the EMEA^[13] and the FDA.^[14]

Naturally, the discovery correlated with studies exploring different methods seeking to further gain alternative antibiotics, understanding that most older antibiotics are decreasing in effectiveness against bacteria with antibiotic resistance.

OSCN⁻, which is not an antibiotic, has proved efficacy on superbugs including MRSA reference strains, BCC, Mucoid PA

Schema of LPO/SCN⁻/H₂O₂ in human lung:

Efficacy range

Non exhaustive list of microorganisms.

Bacteria (Gram-positive and -negative)

• Acinetobacter spp.
• Aeromonas hydrophila
• Bacillus brevis
• Bacillus cereus
• Bacillus megaterium
• Bacillus subtilis
• Burkholderia cepacia
• Campylobacter jejuni
• Capnocytophaga ochracea
• Corynebacterium xerosis
• Enterobacter cloacae
• Escherichia coli
• Haemophilus influenzae
• Helicobacter pylori
• Klebsiella oxytoca
• Klebsiella pneumoniae
• Legionella spp.
• Listeria monocytogenes
• Micrococcus luteus
• Mycobacterium smegmatis
• Mycobacterium abscessus
• Neisseria spp.
• Pseudomonas aeruginosa
• Pseudomonas pyocyanea
• Salmonella spp.
• Selenomonas sputigena
• Shigella sonnei
• Staphylococcus aerogenes
• Staphylococcus aureus
• Streptococcus agalactiae
• Streptococcus faecalis
• Streptococcus mutans
• Wolinella recta
• Xanthomonas campestris
• Yersinia enterocolitica

Viruses^[15]

• Echovirus 11
• Herpes simplex virus, HSV
• Influenza virus
• Human immunodeficiency virus, HIV
• Respiratory syncytial virus, RSV

Yeasts and moulds

• Aspergillus niger
• Botryodiplodia theobromae
• Byssochlamys fulva
• Candida albicans
• Colletotrichum gloeosporioide
• Colletotrichum musae
• Fusarium monoliforme
• Fusarium oxysporum
• Rhodotula rubra
• Sclerotinia spp.

See also

• Respiratory tract antimicrobial defense system

Further reading

• Conner GE, Salathe M, Forteza R . Lactoperoxidase and hydrogen peroxide metabolism in the airway . Am. J. Respir. Crit. Care Med. . 166 . 12 Pt 2 . S57–61 . December 2002 . 12471090 . 10.1164/rccm.2206018 .
• Conner GE, Wijkstrom-Frei C, Randell SH, Fernandez VE, Salathe M . The Lactoperoxidase System Links Anion Transport To Host Defense in Cystic Fibrosis . FEBS Lett. . 581 . 2 . 271–8 . January 2007 . 17204267 . 1851694 . 10.1016/j.febslet.2006.12.025 .
• Eastvold JS . 2005 . Hypothiocyanous Acid: An Overview . Free Radical Biology and Medicine .
• Minarowski Ł, Sands D, Minarowska A, Karwowska A, Sulewska A, Gacko M, Chyczewska E . Thiocyanate concentration in saliva of cystic fibrosis patients . Folia Histochem. Cytobiol. . 46 . 2 . 245–6 . 2008 . 18519245 . 10.2478/v10042-008-0037-0 . free .
• Rada B, Leto TL . Redox warfare between airway epithelial cells and Pseudomonas: Dual oxidase versus pyocyanin . Immunol. Res. . 43 . 1–3 . 198–209 . 2009 . 18979077 . 2776630 . 10.1007/s12026-008-8071-8 .
• Conner GE, Salathe M, Forteza R . Lactoperoxidase and hydrogen peroxide metabolism in the airway . Am. J. Respir. Crit. Care Med. . 166 . 12 Pt 2 . S57–61 . December 2002 . 12471090 . 10.1164/rccm.2206018 .
• Fischer H . Mechanisms and Function of DUOX in Epithelia of the Lung . Antioxid. Redox Signal. . 11 . 10 . 2453–65 . October 2009 . 19358684 . 2823369 . 10.1089/ARS.2009.2558 .
• Kussendrager KD, van Hooijdonk AC . Lactoperoxidase: physico-chemical properties, occurrence, mechanism of action and applications . Br. J. Nutr. . 84 . S19–25 . November 2000 . Suppl 1 . 11242442 . 10.1017/S0007114500002208. free .
• Pedemonte N, Caci E, Sondo E, Caputo A, Rhoden K, Pfeffer U, Di Candia M, Bandettini R, Ravazzolo R, Zegarra-Moran O, Galietta LJ . Thiocyanate transport in resting and IL-4-stimulated human bronchial epithelial cells: role of pendrin and anion channels . J. Immunol. . 178 . 8 . 5144–53 . April 2007 . 17404297 . 10.4049/jimmunol.178.8.5144. free .
• Rada B, Leto TL . Redox warfare between airway epithelial cells and Pseudomonas: Dual oxidase versus pyocyanin . Immunol. Res. . 43 . 1–3 . 198–209 . 2009 . 18979077 . 2776630 . 10.1007/s12026-008-8071-8 .
• Book: Rada B, Leto TL . Trends in Innate Immunity . Oxidative innate immune defenses by Nox/Duox family NADPH Oxidases . Contrib Microbiol . 15 . 164–87 . 2008 . 18511861 . 2776633 . 10.1159/000136357 . Contributions to Microbiology . 978-3-8055-8548-4 .
• Reiter B, Härnulv G . 1984 . Lactoperoxidase antibacterial system natural occurrence, biological functions and practical applications . J Food Prot . 47 . 9 . 724–732 . 10.4315/0362-028X-47.9.724 . 30934451 . free .
• Shin K, Wakabayashi H, Yamauchi K, Teraguchi S, Tamura Y, Kurokawa M, Shiraki K . Effects of orally administered bovine lactoferrin and lactoperoxidase on influenza virus infection in mice . J. Med. Microbiol. . 54 . Pt 8 . 717–23 . August 2005 . 16014423 . 10.1099/jmm.0.46018-0 . free .
• Thomas EL, Bates KP, Jefferson MM . Hypothiocyanite ion: detection of the antimicrobial agent in human saliva . J. Dent. Res. . 59 . 9 . 1466–72 . September 1980 . 6931123 . 10.1177/00220345800590090201. 7717994 .
• Wijkstrom-Frei C, El-Chemaly S, Ali-Rachedi R, Gerson C, Cobas MA, Forteza R, Salathe M, Conner GE . Lactoperoxidase and human airway host defense . Am. J. Respir. Cell Mol. Biol. . 29 . 2 . 206–12 . August 2003 . 12626341 . 10.1165/rcmb.2002-0152OC . 10.1.1.325.1962 .
• Xu Y, Szép S, Lu Z . The antioxidant role of thiocyanate in the pathogenesis of cystic fibrosis and other inflammation-related diseases . Proc. Natl. Acad. Sci. U.S.A. . 106 . 48 . 20515–9 . December 2009 . 19918082 . 2777967 . 10.1073/pnas.0911412106 . 2009PNAS..10620515X . free .

Notes and References

1. Furtmüller PG, Zederbauer M, Jantschko W, Helm J, Bogner M, Jakopitsch C, Obinger C . Active site structure and catalytic mechanisms of human peroxidases . Arch. Biochem. Biophys. . 445 . 2 . 199–213 . January 2006 . 16288970 . 10.1016/j.abb.2005.09.017 .
2. Al Obaidi AH . Role of airway lactoperoxidase in scavenging of hydrogen peroxide damage in asthma . Ann Thorac Med . 2 . 3 . 107–10 . July 2007 . 19727356 . 2732085 . 10.4103/1817-1737.33698 . free .
3. Moskwa P, Lorentzen D, Excoffon KJ, Zabner J, McCray PB, Nauseef WM, Dupuy C, Bánfi B . A Novel Host Defense System of Airways Is Defective in Cystic Fibrosis . Am. J. Respir. Crit. Care Med. . 175 . 2 . 174–83 . January 2007 . 17082494 . 2720149 . 10.1164/rccm.200607-1029OC .
4. Carlsson J, Edlund MB, Hänström L . Bactericidal and cytotoxic effects of hypothiocyanite-hydrogen peroxide mixtures . Infect. Immun. . 44 . 3 . 581–6 . June 1984 . 6724690 . 263633 . 10.1128/IAI.44.3.581-586.1984.
5. Mansson-Rahemtulla B, Pruitt KM, Tenovuo J, Le TM . A mouthrinse which optimizes in vivo generation of hypothiocyanite . J. Dent. Res. . 62 . 10 . 1062–6 . October 1983 . 6578235 . 10.1177/00220345830620101101. 19490884 .
6. Pruitt KM, Tenovuo J, Andrews RW, McKane T . Lactoperoxidase-catalyzed oxidation of thiocyanate: polarographic study of the oxidation products . Biochemistry . 21 . 3 . 562–7 . February 1982 . 7066307 . 10.1021/bi00532a023.
7. Thomas EL, Pera KA, Smith KW, Chwang AK . Inhibition of Streptococcus mutans by the lactoperoxidase antimicrobial system . Infect. Immun. . 39 . 2 . 767–78 . February 1983 . 6832819 . 348016 . 10.1128/IAI.39.2.767-778.1983.
8. Thomas EL . Lactoperoxidase-catalyzed oxidation of thiocyanate: equilibria between oxidized forms of thiocyanate . Biochemistry . 20 . 11 . 3273–80 . May 1981 . 7248282 . 10.1021/bi00514a045.
9. Thomas EL, Aune TM . Lactoperoxidase, peroxide, thiocyanate antimicrobial system: correlation of sulfhydryl oxidation with antimicrobial action . Infect. Immun. . 20 . 2 . 456–63 . May 1978 . 352945 . 421877 . 10.1128/IAI.20.2.456-463.1978.
10. Tenovuo J . Clinical applications of antimicrobial host proteins lactoperoxidase, lysozyme and lactoferrin in xerostomia: efficacy and safety . Oral Dis . 8 . 1 . 23–9 . January 2002 . 11936452 . 10.1034/j.1601-0825.2002.1o781.x.
11. White WE, Pruitt KM, Mansson-Rahemtulla B . Peroxidase-Thiocyanate-Peroxide Antibacterial System Does Not Damage DNA . Antimicrob. Agents Chemother. . 23 . 2 . 267–72 . February 1983 . 6340603 . 186035 . 10.1128/aac.23.2.267.
12. Gattas MV, Forteza R, Fragoso MA, Fregien N, Salas P, Salathe M, Conner GE . Oxidative epithelial host defense is regulated by infectious and inflammatory stimuli . Free Radic. Biol. Med. . 47 . 10 . 1450–8 . November 2009 . 19703552 . 2767478 . 10.1016/j.freeradbiomed.2009.08.017 .
13. Web site: Public summary of positive opinion for orphan designation of hypothiocyanite / lactoferrin for the treatment of cystic fibrosis. 2009-09-07. Pre-authorisation Evaluation of Medicines for Human Use. European Medicines Agency. https://web.archive.org/web/20100530100046/http://www.ema.europa.eu/pdfs/human/comp/opinion/39298409en.pdf. 2010-05-30. 2010-01-23. dead.
14. Web site: Meveol: orphan drug status granted by the FDA for the treatment of cystic fibrosis. 2009-11-05. United States Food and Drug Administration. https://web.archive.org/web/20091224145219/http://www.bioalaxia.eu/content/meveol-orphan-drug-status-granted-fda-treatment-cystic-fibrosis. 2009-12-24. 2010-01-23. dead.
15. Mikola H, Waris M, Tenovuo J . Mar 1995 . Inhibition of herpes simplex virus type 1, respiratory syncytial virus and echovirus type 11 by peroxidase-generated hypothiocyanite . Antiviral Res. . 26 . 2. 161–71 . 10.1016/0166-3542(94)00073-h. 7605114 .