Date Published: September 29, 2016
Publisher: Public Library of Science
Author(s): Andrew G. Hughson, Brent Race, Allison Kraus, Laura R. Sangaré, Lori Robins, Bradley R. Groveman, Eri Saijo, Katie Phillips, Luis Contreras, Virkamal Dhaliwal, Matteo Manca, Gianluigi Zanusso, Daniel Terry, Jeffrey F. Williams, Byron Caughey, David Westaway.
Hypochlorous acid (HOCl) is produced naturally by neutrophils and other cells to kill conventional microbes in vivo. Synthetic preparations containing HOCl can also be effective as microbial disinfectants. Here we have tested whether HOCl can also inactivate prions and other self-propagating protein amyloid seeds. Prions are deadly pathogens that are notoriously difficult to inactivate, and standard microbial disinfection protocols are often inadequate. Recommended treatments for prion decontamination include strongly basic (pH ≥~12) sodium hypochlorite bleach, ≥1 N sodium hydroxide, and/or prolonged autoclaving. These treatments are damaging and/or unsuitable for many clinical, agricultural and environmental applications. We have tested the anti-prion activity of a weakly acidic aqueous formulation of HOCl (BrioHOCl) that poses no apparent hazard to either users or many surfaces. For example, BrioHOCl can be applied directly to skin and mucous membranes and has been aerosolized to treat entire rooms without apparent deleterious effects. Here, we demonstrate that immersion in BrioHOCl can inactivate not only a range of target microbes, including spores of Bacillus subtilis, but also prions in tissue suspensions and on stainless steel. Real-time quaking-induced conversion (RT-QuIC) assays showed that BrioHOCl treatments eliminated all detectable prion seeding activity of human Creutzfeldt-Jakob disease, bovine spongiform encephalopathy, cervine chronic wasting disease, sheep scrapie and hamster scrapie; these findings indicated reductions of ≥103- to 106-fold. Transgenic mouse bioassays showed that all detectable hamster-adapted scrapie infectivity in brain homogenates or on steel wires was eliminated, representing reductions of ≥~105.75-fold and >104-fold, respectively. Inactivation of RT-QuIC seeding activity correlated with free chlorine concentration and higher order aggregation or destruction of proteins generally, including prion protein. BrioHOCl treatments had similar effects on amyloids composed of human α-synuclein and a fragment of human tau. These results indicate that HOCl can block the self-propagating activity of prions and other amyloids.
Prion diseases, or transmissible spongiform encephalopathies (TSEs), are fatal and untreatable neurodegenerative diseases. In humans, prion diseases include sporadic, variant and genetic forms of Creutzfeldt-Jakob disease (sCJD, vCJD and gCJD) as well as a number of other disorders [1–3]. Prion diseases of other species include classical bovine spongiform encephalopathy (C-BSE) , scrapie in sheep, goats  and rodents, and chronic wasting disease (CWD) of cervids [6, 7]. All mammalian prion diseases share an underlying molecular pathology that involves the conversion of the hosts’ normal form of prion protein, PrPC, to a misfolded, aggregated, infectious and pathological form, PrPSc [8, 9].
Numerous clinical and agricultural scenarios involving potential prion contamination would benefit from the availability of less harsh and more practical methods for inactivating prions. Here, we have demonstrated that weakly acidic BrioHOCl has strong anti-prion activity. In the case of hamster ScBH, we have shown a reduction in infectivity titer of ≥~105.75-fold by bioassay in mice (Table 1). This reduction is commensurate with the decrease in prion seeding activity measured by RT-QuIC. For sCJD, vCJD, C-BSE, CWD and sheep scrapie we have shown that BrioHOCl eliminates all detectable RT-QuIC seeding activity (Fig 2). Although we have not also done animal bioassays of BrioHOCl-treated brain homogenates containing these other strains, many prior studies have indicated that prion infection and RT-QuIC positivity in ex vivo samples are strongly correlated, and that RT-QuIC is at least as sensitive analytically as animal bioassays [32, 36, 37, 42, 43]. These results imply so far that if a disinfectant eliminates RT-QuIC seeding activity, it will likely also eliminate prion infectivity.