Prions

Prions are proteinaceous infectious agents that cause fatal, neurodegenerative diseases in animals and humans. During prion diseases, a cellular protein, PrPC, is converted into a pathogenic form, PrPSc, that invariably leads to toxic protein aggregates and apoptosis. The exact mechanisms for prion replication and transmissibility are currently unclear.

The robust persistence of this infectious agent requires specific biomedical and research procedures and decontamination protocols. Indirect transmission of prion diseases (i.e., not directly from organism to organism) is a particular concern among biomedical and research personnel. There are two main issues. First, the prion contamination of medical equipment has led to iatrogenic transmission of these diseases, which makes it difficult to work directly with the infectious agent. For example, iatrogenic Creutzfeldt-Jakob Disease (CJD; an acquired human prion disease) has been observed when tissue transplants or medical equipment has been collected/used on CJD patients and then subsequently given/applied to an individual who does not have prion disease (these naïve individuals have acquired CJD through medical procedures, e.g., dura mater grafts and growth hormone injections). Additionally, laboratory personnel have acquired iCJD through prion research, and there has been evidence for iatrogenic transmissions of other protein misfolding diseases. Second, the persistence of animal prions in water, soil, plants, and other fomites have increased the uncertainty of prion laboratory spaces. For example, there are several environmental sources of chronic wasting disease (CWD; an infectious cervid prion disease). A particular pathogenic phenotype of CWD is its accumulation in lymphoid and other peripheral tissues, especially during the latter stages of disease. This prion peripheralization leads to shedding infectious material into the environment to transmit to naïve organisms. The lymphoreticular properties of CWD have been recapitulated in novel laboratory models that are used for prion research at CSU.

These two issues illustrate the challenge of prion decontamination. Prions are resistant to most normal infectious disease sterilization protocols. For example, formaldehyde, ethanol, household detergents, and acetic acid have all been proven ineffective as prion decontaminates. Also, there is no (minimally destructive) method shown to be fully effective against prions, partly due to the presence of innumerable prion strains that have unique biochemical properties. This has led to no uniform standard to decontaminate prions in biomedical or research facilities. Currently, the CSU Prion Research Center does not have a set standard of biosafety, and every laboratory that researches prions is responsible for establishing its own standard operating procedures. Nevertheless, there are some universal criteria that inhibit prion laboratories from adopting certain sustainability practices:

• Everything that enters and contacts a prion-positive space must stay in the prion-positive space. Ideally, any infectious prion material should be in a closed container or neutralized/removed as soon as possible. Prion-positive items and articles are neutralized/removed via:
  • Biohazard bag – waste bags are autoclaved at 134 degrees for a 70-minute cycle.
  • Bleach bucket – liquid waste that is permitted to enter bleach is deposited in bleach to make a final concentration of 40% bleach. Bleach bucket must sit for an hour before it is dumped down the sink and diluted with water.
  • Bleach wash – 40% bleach is used to wash large equipment before disposal outside of the laboratory
  • Hazardous waste – hazardous waste is placed into containers for EHS removal
• Any piece of labware/plastic ware that contacts prions is not reused unless it is washed with 40% bleach and undergone sterilization

Thus, prion-positive spaces cannot (1) recycle or reuse and (2) limit autoclave use. However, prion positive labs can look for ways to reduce energy and resource use:

• Electricity and light use – this includes turning off lights in areas not in use.
• Energy usage – keeping electronic devices turned off when not in use and/or placing frequently used electronics on outlet timers when appropriate.
• Water usage – using waterspout aerators to reduce water consumption.
• Limiting the number of items that enter prion-positive spaces – this can include (but is not limited to) packaging materials that can be recycled. Additionally, be conscious of consumable material usage.
• Sustainable ordering practices – ordering in larger qualities and from companies that incorporate sustainability to reduce packaging waste and shipping pollution.
• Reusing prion positive sterilized surgical tools for necropsies when appropriate.
• Switching ULT freezers from –80°C to -70°C for energy saving.
• Using microchemistry practices when optimizing protocols.

Prion-negative work spaces should implement all the aforementioned sustainability practices and additionally incorporate the following when possible:

• Recycle and reuse procedures of consumables.
• Limiting autoclave usage.

As research advances to determine less harmful means to decontaminate prions, it will be easier to implement sustainability practices. We recommend creating a uniform standard operating procedure for the CSU Prion Research Center to standardize the biosafety of prion work and considerations of sustainability that can be started now and adapted as technology advances.

For future consideration, there is growing use of gas plasma sterilization in the clinical field for surgical instrumentsthat could potentially be incorporated into future PRC sustainable waste protocols. This form of prion decontamination with the BLP-TES and STERRAD® systems is done with the use of nitrogen or hydrogen gas that is excited via UV rays and/or high voltage energy. With a current growing study into prions and prion decontamination as a more Enviromental friendly decontamination method, this decontamination is seen to be very effective and comparable to autoclaving and can be used for temperature sensitive materials.  Current limitations for implementation include growing research of efficacy as well as safety with usage of treated materials. Overall, development of standard prion materials and waste protocols for the PRC and rolling incorporation of newer technologies that are on the horizon can help to increase research sustainability efforts in our prion research laboratories.

Authors: Dev Aldaz, Joe DeFranco, and Nick Heyer

References:

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