Amyloïcide

The scientific community working on neurodegenerative diseases is in turmoil: Alzheimer’s disease would be transmissible after an inter-human contamination! This possibility had been considered for more than ten years, and this, for both Alzheimer’s and Parkinson’s disease. Indeed, these diseases have many points in common with another neurodegenerative disease: Creutzfeldt-Jakob disease, better known as prion disease. In addition to attacking the neurons of the brain, these three diseases have in common that they belong to the class of amyloïcidal proteinopathies or amyloidoses. That is, they result from abnormal folding of a protein leading to its accumulation in the form of amyloïcidal plaques (see box & video). This morphological change of a single protein (but different depending on the disease) has serious repercussions for the neurons which then enter a cycle of cell death. But above all, these proteins in their toxic abnormal conformation, are able, by themselves, to force the conformation change from the normal form of the protein to the abnormal form, and thus to spread and disseminate the disease to the whole tissue.

In the case of prion diseases, these protein clusters are even contagious! That is to say that they can contaminate a healthy human being after ingestion (as it was the case for the mad cow disease where the bovine prion spread to the brain of patients who developed the variant of the Creutzfeldt-Jakob disease), or after medical-surgical acts (electrode implant, cornea or dura mater graft, blood transfusion, growth hormone.)

But until 2017, evidence of transmission of Parkinson’s or Alzheimer’s disease had only been demonstrated in laboratory animals and in a context favorable to propagation (disease-susceptible animals, inoculation of high doses…). But very recently, scientific reports have reinforced the likelihood of human-to-human transmission of Alzheimer’s disease. Since then, no less than 8 independent studies worldwide have reported cases of iatrogenic transmission of Alzheimer’s disease in patients, causing them to develop amyloïcidal Cerebral Angiopathy nearly a decade after their exposure. These contaminations have occurred after injections of contaminated batches of growth hormones 1-4, dura mater transplants 5, or most likely after neurosurgical procedures6.

The alert is given! Amyloidosis, not just prion diseases, can present an iatrogenic risk! The question now arises as to how to manage this risk to protect the patient and the health care staff.

Amyloïcidal also involved in bacterial nosocomial diseases

Amyloïcidal fibers have mechanical characteristics comparable to those of steel, which makes these materials among the strongest observed in the living world: it is therefore impossible for an organism to get rid of them. The high resistance of these fibers makes them suitable for the construction of solid structures such as biofilms. Moreover, their biophysical properties represent a huge advantage for the bacteria in terms of biofilm architecture and adhesion (Fig.2). Thus, these pathogens take advantage of the difficulty of cleaning these amyloïcidal protein deposits, this is notably the case for pathogenic bacteria such as Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa, which together account for the majority of nosocomial infections (25% in the case of E. coli, 19% in the case of S. aureus and 10% for P. aeruginosa). The protective extracellular matrix produced by these organisms is composed mainly of an amyloïcidal architecture which gives them a very high resistance. In France, the prevalence of hospitalized patients having contracted a nosocomial disease is estimated at 5%. The statistics reach 23% in intensive care units: these figures are mainly due to the use of catheters and invasive probes. Hospital-acquired infections result in significant additional financial costs, mainly due to an increase in the length of hospitalization, i.e. an additional annual cost of 2.4 to 6 billion euros.

Scientists and industrialists are working hard to propose amyloïcidal procedures

Current prevention measures concerning infectious proteins and amyloïcidal in general only take into account the prion risk. However, given the very high prevalence of neurodegenerative diseases and their constant increase, it seems urgent to extend the management of this risk to all amyloidoses. This risk management includes the decontamination and sterilization of medical equipment and therefore the development of amyloïcidal processes (see box).

But the challenge is great! Indeed, to be considered amyloïcidal, the chemical formulation or the physical process must meet various criteria of the medical sector specifications:

– This process must, of course, denature, disaggregate and unhook, but above all inactivate all types of protein assemblies at the origin of amyloidosis. And the list is long: fibers, protofilaments, oligomers, monomers… these are all forms that these pathogenic proteins can adopt. The problem is that a change in shape, or conformation, alters the susceptibility of proteins to denaturing agents. The prion protein, at the origin of Creutzfeldt-Jakob disease and mad cow disease, is a perfect illustration of this problem: in its natural or “normal” form, the protein is sensitive to enzymes and classical protein degradation processes (heat, denaturants…); on the other hand, when it is in the pathogenic prion conformation, it adopts a whole range of conformations which give it physico-chemical properties, and capacities of adaptation to its host out of the ordinary. Among the biochemical changes, the most remarkable is its resistance to enzymes, but also to classical denaturation processes like heat. Prions are particularly resistant pathogenic entities: when amyloïcidal fibers are treated with a chaotrope, even at high concentrations (up to 6M urea), they do not denature but depolymerize into elementary subunits that retain all infectious properties once the denaturing pressure is lifted. These subunits are all released disease vectors. The amyloïcidal process must therefore take this reality into account. Simple depolymerization of the assemblies without inactivation could have a disastrous effect by releasing the elementary subunits and may be a factor favoring its dissemination7.

– Finally, to facilitate its use in hospitals, the amyloïcidal process must have a broad spectrum of action and be effective on the majority of amyloïcidals, whether they come from amyloidosis (Prion, Alzheimer’s disease, Parkinson’s disease, ALS, diabetes…) or from bacterial biofilms (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa…) So many different protein assemblies with various physicochemical properties and resistances must be taken into account.

Sources:

1. Cali, I. & al. Iatrogenic Creutzfeldt-Jakob disease with Amyloid-β pathology: an international study. Acta Neuropathol. Commun. 6, 5 (2018).
2. Duyckaerts, C. & al. Neuropathology of iatrogenic Creutzfeldt–Jakob disease and immunoassay of French cadaver-sourced growth hormone batches suggest possible transmission of tauopathy and long incubation periods for the transmission of Abeta pathology. Acta Neuropathol. 135, 201–212 (2018).
3. Jaunmuktane, Z. & al. Evidence for human transmission of amyloid-β pathology and cerebral amyloid angiopathy. Nature 525, 247–50 (2015).
4. Ritchie, D. L. & al. Amyloid-β accumulation in the CNS in human growth hormone recipients in the UK. Acta Neuropathol. (2017). doi:10.1007/s00401-017-1703-0
5. Kovacs, G. G. & al. Dura mater is a potential source of Aβ seeds. Acta Neuropathol. 131, 911–923 (2016).
6. Jaunmuktane, Z. & al. Evidence of amyloid-β cerebral amyloid angiopathy transmission through neurosurgery. Acta Neuropathol. 1–9 (2018). doi:10.1007/s00401-018-1822-2
7. Igel-Egalon, A. & al. Reversible unfolding of infectious prion assemblies reveals the existence of an oligomeric elementary brick. PLOS Pathog. 13, e1006557 (2017).