Organ distribution of prion proteins in variant Creutzfeldt-Jakob disease

Optimization of the photodynamic inactivation of prions by a phthalocyanine photosensitizer: The crucial involvement of singlet oxygen

Prion disorders are fatal neurodegenerative diseases caused by the autocatalytic conversion of a natively occurring prion protein (PrP^C ) into its misfolded infectious form (PrP^TSE ). The proven resistance of PrP^TSE to common disinfection procedures increases the risk of prion transmission in medical settings. Herein, we present the effective photodynamic inactivation (PDI) of prions by disulfonated hydroxyaluminum phthalocyanine (AlPcOH(SO₃ )₂ ) utilizing two custom-built red light sources. The treatment eliminates PrP^TSE signal in infectious mouse brain homogenate with efficiency that depends on light intensity but has a low effect on the overall protein content. Importantly, singlet oxygen (O₂ (¹ Δ_g )) is the only species significantly photogenerated by AlPcOH(SO₃ )₂ , and it is responsible for the PDI of prions. More intensive light conditions show not only higher O₂ (¹ Δ_g ) production but also decreases in AlPcOH(SO₃ )₂ photostability. Our findings suggest that PDI by AlPcOH(SO₃ )₂ -generated O₂ (¹ Δ_g ) represents a promising approach for prion inactivation that may be useful in future decontamination strategies for delicate medical tools.

Biosafety of Prions

Prions are the infectious agents that cause devastating and untreatable disorders known as Transmissible Spongiform Encephalopathies (TSEs). The pathologic events and the infectious nature of these transmissible agents are not completely understood yet. Due to the difficulties in inactivating prions, working with them requires specific recommendations and precautions. Moreover, with the advent of innovative technologies, such as the Protein Misfolding Cyclic Amplification (PMCA) and the Real Time Quaking-Induced Conversion (RT-QuIC), prions could be amplified in vitro and the infectious features of the amplified products need to be carefully assessed.

Evaluating the Species Barrier

A Transmissible Spongiform Encephalopathy (TSE) agent from one species generally transmits poorly to a new species, a phenomenon known as the species barrier. However once in the new species it generally but not always adapts and then more readily transmits within the new host. No single test is available to determine accurately the ability of a prion strain to transmit between species. Evaluating the species barrier for any prion strain has to take into consideration as much information as can be gathered for that strain from surveillance and research. The interactions of the agent with a particular host can be measured by in vivo and in vitro methods and assessing the species barrier needs to make full use of all the tools available. This review will identify the important considerations that need to be made when evaluating the species barrier.

Nerve regeneration techniques respecting the special characteristics of the inferior alveolar nerve

PURPOSE

The aim of this study was to examine the in situ regeneration of the inferior alveolar nerve (IAN) in its bony channel, using autologous tissue in combination with a recombinant human nerve growth factor (rhNGF).

MATERIALS AND METHODS

A total of 20 New Zealand rabbits were randomly divided into five groups. Following dissection of the IAN, the animals underwent reconstruction either with muscle tissue (groups 1 and 2) or with fat tissue (groups 3 and 4). In group 5 (control), the dissected nerve was resected and reconstructed by placement of the reversed autologous segment. After 2 and 4 weeks, 1 mL rhNGF was locally injected in groups 1 and 3. Nerve function was monitored by measuring the jaw-opening reflex using electromyography for a period of 24 weeks.

RESULTS

Regeneration of the nerve was achieved in all groups, but preoperative threshold values were not achieved. Comparing the experimental groups to the control, there was a significant difference in favor of the autologous nerve reconstruction. Differences between the experimental groups remained statistically not significant.

CONCLUSION

Regeneration of the IAN with autologous tissue is possible, but without achieving preoperative thresholds. Additional injection of a growth factor seems to improve the speed of regeneration for fat and muscle grafts.

Re-assessment of PrP(Sc) distribution in sporadic and variant CJD

Human prion diseases are fatal neurodegenerative disorders associated with an accumulation of PrP^Sc in the central nervous system (CNS). Of the human prion diseases, sporadic Creutzfeldt-Jakob disease (sCJD), which has no known origin, is the most common form while variant CJD (vCJD) is an acquired human prion disease reported to differ from other human prion diseases in its neurological, neuropathological, and biochemical phenotype. Peripheral tissue involvement in prion disease, as judged by PrP^Sc accumulation in the tonsil, spleen, and lymph node has been reported in vCJD as well as several animal models of prion diseases. However, this distribution of PrP^Sc has not been consistently reported for sCJD. We reexamined CNS and non-CNS tissue distribution and levels of PrP^Sc in both sCJD and vCJD. Using a sensitive immunoassay, termed SOFIA, we also assessed PrP^Sc levels in human body fluids from sCJD as well as in vCJD-infected humanized transgenic mice (Tg666). Unexpectedly, the levels of PrP^Sc in non-CNS human tissues (spleens, lymph nodes, tonsils) from both sCJD and vCJD did not differ significantly and, as expected, were several logs lower than in the brain. Using protein misfolding cyclic amplification (PMCA) followed by SOFIA, PrP^Sc was detected in cerebrospinal fluid (CSF), but not in urine or blood, in sCJD patients. In addition, using PMCA and SOFIA, we demonstrated that blood from vCJD-infected Tg666 mice showing clinical disease contained prion disease-associated seeding activity although the data was not statistically significant likely due to the limited number of samples examined. These studies provide a comparison of PrP^Sc in sCJD vs. vCJD as well as analysis of body fluids. Further, these studies also provide circumstantial evidence that in human prion diseases, as in the animal prion diseases, a direct comparison and intraspecies correlation cannot be made between the levels of PrP^Sc and infectivity.

THE SPREAD OF PRION DISEASES IN THE BRAIN — MODELS OF REACTION AND TRANSPORT ON NETWORKS

In this paper we will present a modeling approach to describe the progression and the spread of prion diseases in the brain. Although there exist a number of mathematical models for the interaction of prions with their native counterpart, prion transport and spread is usually neglected. The concentration dynamics of prions, and thus the dynamics of the disease progression, however, are influenced by prion transport, especially in a medium as complex as the brain. Therefore, we focus here on the interaction between prion concentration dynamics and prion transport. The model is constructed by combining a model of prion-prion interaction with transport on networks. The approach leads to a system of reaction-diffusion equations, whereby the diffusion term is discrete. The equations are solved numerically on domains given as large networks. We show that the prion concentration grows faster on networks characterized by a higher degree heterogeneity. Furthermore, we introduce cell death as a consequence of increasing prion concentration, leading to network decomposition. We show that infectious diseases destroy networks similarly to targeted attacks, namely by affecting the nodes with the highest degree first. Relating the incubation period and disease progression to the process of network decomposition, we find that, interestingly, a long incubation time followed by sudden onset and fast progression of the disease does not need to be reflected in the overall concentration dynamics of the infective agent.

Prion proteins in subpopulations of white blood cells from patients with sporadic Creutzfeldt-Jakob disease

Recent cases of prion transmission in humans following transfusions using blood donated by patients with asymptomatic variant Creutzfeldt-Jakob disease (CJD) implicate the presence of prion infectivity in peripheral blood. In this study, we examined the levels of the normal, cellular prion protein (PrPC), and the disease-causing isoform (PrPSc) in subpopulations of circulating white blood cells (WBCs) from patients with sporadic (s) CJD, age-matched neurological controls and healthy donors. Though widely distributed, the highest levels of PrPC were found in a subpopulation of T lymphocytes: approximately 12,000 PrPC molecules were found per CD4+CD45RA-CD62L- effector memory T helper cell. Although platelets expressed low levels of PrPC on their surface, their high abundance in circulation resulted in the majority of PrPC being platelet associated. Using quantitative fluorescence-activated cell sorting analysis, we found that neither WBC composition nor the amount of cell-surface PrPC molecules was altered in patients with sCJD. Eight different WBC fraction types from the peripheral blood of patients with sCJD were assessed for PrPSc. We were unable to find any evidence for PrPSc in purified granulocytes, monocytes, B cells, CD4+ T cells, CD8+ T cells, natural killer cells, nonclassical gamma delta T cells, or platelets. If human WBCs harbor prion infectivity in patients with sCJD, then the levels are likely to be low.

Use of cold-preserved allografts seeded with autologous Schwann cells in the treatment of a long-gap peripheral nerve injury

BACKGROUND

Limitations in autogenous tissue have inspired the study of alternative materials for repair of complex peripheral nerve injuries. Cadaveric allografts are one potential reconstructive material, but their use requires systemic immunosuppression. Cold preservation (> or =7 weeks) renders allografts devoid of antigens, but these acellular substrates generally fail in supporting regeneration beyond 3 cm. In this study, the authors evaluated the reconstruction of extensive nonhuman primate peripheral nerve defects using 7-week cold-preserved allografts repopulated with cultured autologous Schwann cells.

METHODS

Ten outbred Macaca fascicularis primates were paired based on maximal genetic disparity as measured by similarity index assay. A total of 14 ulnar nerve defects measuring 6 cm were successfully reconstructed using autografts (n = 5), fresh allografts (n = 2), cold-preserved allografts (n = 3), or cold-preserved allografts seeded with autogenous Schwann cells (n = 4). Recipient immunoreactivity was evaluated by means of enzyme-linked immunosorbent spot assay, and nerves were harvested at 6 months for histologic and histomorphometric analysis.

RESULTS

Cytokine production in response to cold-preserved allografts and cold-preserved allografts seeded with autologous Schwann cells was similar to that observed for autografts. Schwann cell-repopulated cold-preserved grafts demonstrated significantly enhanced fiber counts, nerve density, and percentage nerve (p < 0.05) compared with unseeded cold-preserved grafts at 6 months after reconstruction.

CONCLUSIONS

Cold-preserved allografts seeded with autologous Schwann cells were well-tolerated in unrelated recipients and supported significant regeneration across 6-cm peripheral nerve defects. Use of cold-preserved allogeneic nerve tissue supplemented with autogenous Schwann cells poses a potentially safe and effective alternative to the use of autologous tissue in the reconstruction of extensive nerve injuries.

Recent Developments in Prion Disease Research: Diagnostic Tools and In Vitro Cell Culture Models

After prion infection, an abnormal isoform of prion protein (PrP(Sc)) converts the cellular isoform of prion protein (PrP(C)) into PrP(Sc). PrP(C)-to-PrP(Sc) conversion leads to PrP(Sc) accumulation and PrP(C) deficiency, contributing etiologically to induction of prion diseases. Presently, most of the diagnostic methods for prion diseases are dependent on PrP(Sc) detection. Highly sensitive/accurate specific detection of PrP(Sc) in many different samples is a prerequisite for attempts to develop reliable detection methods. Towards this goal, several methods have recently been developed to facilitate sensitive and precise detection of PrP(Sc), namely, protein misfolding cyclic amplification, conformation-dependent immunoassay, dissociation-enhanced lanthanide fluorescent immunoassay, capillary gel electrophoresis, fluorescence correlation spectroscopy, flow microbead immunoassay, etc. Additionally, functionally relevant prion-susceptible cell culture models that recognize the complexity of the mechanisms of prion infection have also been pursued, not only in relation to diagnosis, but also in relation to prion biology. Prion protein (PrP) gene-deficient neuronal cell lines that can clearly elucidate PrP(C) functions would contribute to understanding of the prion infection mechanism. In this review, we describe the trend in recent development of diagnostic methods and cell culture models for prion diseases and their potential applications in prion biology.

Pathological findings in retina and visual pathways associated to natural Scrapie in sheep

This work represents a comprehensive pathological description of the retina and visual pathways in naturally affected Scrapie sheep. Twenty naturally affected Scrapie sheep and 6 matched controls were used. Eyes, optic nerves and brain from each animal were fixed and histologically processed using hematoxylin-eosin, followed by immunohistochemical staining for prion protein (PrPsc) and glial fibrillar acidic protein (GFAP). Retinal histopathological changes were observed in only 7 clinically affected animals and mainly consisted of loss of outer limitant layer definition, outer plexiform layer atrophy, disorganization and loss of nuclei in both nuclear layers, and Müller glia hypertrophy. PrPsc was detected in the retina of 19 of the 20 sheep and characterized by a disseminated granular deposit across layers and intraneuronally in ganglion cells. The inner plexiform and the ganglion cell layers were the structures most severely affected by PrPsc deposits. PrPsc exhibited a tendency to spread from these two layers to the others. A marked increase in the number and intensity of GFAP-expressing Müller cells was observed in the clinical stage, especially at the terminal stage of the disease. Spongiosis and PrPsc were detected within the visual pathways at the preclinical stage, their values increasing during the course of the disease but varying between the areas examined. PrPsc was detected in only 3 optic nerves. The results suggest that the presence of PrPsc in the retina correlates with disease progression during the preclinical and clinical stages, perhaps using the inner plexiform layer as a first entry site and diffusing from the brain using a centrifugal model.

Diffusion versus network models as descriptions for the spread of prion diseases in the brain

In this paper we will discuss different modeling approaches for the spread of prion diseases in the brain. Firstly, we will compare reaction-diffusion models with models of epidemic diseases on networks. The solutions of the resulting reaction-diffusion equations exhibit traveling wave behavior on a one-dimensional domain, and the wave speed can be estimated. The models can be tested for diffusion-driven (Turing) instability, which could present a possible mechanism for the formation of plaques. We also show that the reaction-diffusion systems are capable of reproducing experimental data on prion spread in the mouse visual system. Secondly, we study classical epidemic models on networks, and use these models to study the influence of the network topology on the disease progression.

Ensuring the biologic safety of plasma-derived therapeutic proteins: detection, inactivation, and removal of pathogens

Human plasma-derived proteins, such as immunoglobulins, coagulation factors, α₁-antitrypsin, fibrin sealants, and albumin, are widely used as therapeutics for many serious and life-threatening medical conditions. The human origin of these proteins ensures excellent efficacy and compatibility but may also introduce the risk of unintentional disease transmission. Historically, only viruses, particularly hepatitis and HIV, have posed serious threats to the safety of these therapeutics. Fortunately, between 1970 and 1990, the molecular biology of each of the major viruses was elucidated. These advances led to the development and implementation of effective donor screening tests, mainly based on immunoassays and nucleic acid testing, which resulted in a significant reduction of disease transmission risk. In addition, viral inactivation and removal steps were implemented and validated by manufacturers, further reducing the risk associated with known, as well as unidentified, viruses. Since the late 1990s, a different class of transmissible agent, referred to as prions, has been identified as a new risk for disease transmission. However, prion diseases are very rare, and prion transmission through plasma-derived proteins has not been reported to date. The prion-related risk is minimized by deferring donors with certain key risk factors, and by the manufacturing processes that are capable of removing prions. Advances in science and pathogen safety-related technology, compliance with good manufacturing practices by manufacturers, and increasingly stringent regulatory oversight, has meant that plasma-derived proteins have been developed into today’s highly effective therapeutics with very low risk of disease transmission.

Tissue Safety in View of CJD and Variant CJD

Epidemiological studies on human transmissible spongiform encephalopathies (Creutzfeldt-Jakob Disease, CJD) have shown that the agent could be transmitted by highly infectious tissues like brain, spinal cord or retina and medicinal products derived from these tissues (i.e. human growth hormone, dura mater). A few cases of transmission of CJD by neurosurgical instruments have been reported. The transmission of the agent of variant CJD, which is suspected to be transmitted by BSE-contaminated food, by blood transfusion implies that in contrast to the agent of classical CJD this agent can also be transmitted by organs and tissues other than nerve tissues. Health authorities have implemented guidelines to reduce the risk of transmission of human and animal TSE by human and veterinary medicinal products. The high resistance of TSE agents against physical or chemical treatment hamper the development of highly efficient inactivation steps in the production of medicinal products. Donor selection is considered as an efficient measure to reduce the risk of TSE transmission. However, the development of rapid, sensitive and specific diagnostic test systems is urgently required to test blood, organs and tissue of donors.

Genetic risk factors associated with Creutzfeld-Jakob disease in Slovenians and a rapid typing for PRNP codon 129 single nucleotide polymorphism

PRNP has been the most informative marker for the predisposition to variant Creutzfeld-Jakob disease (vCJD). All victims of the vCJD carried methionine (M) at the position 129 of the PrP. Prions could travel through the immune system to get from the gut to the brain, and human leucocyte antigens (HLAs) could be involved in this carriage, with HLA-DQ7 being less efficient. Contradictory reports have raised the question of the influence of sampling in population studies. We developed a fast and reliable real-time polymerase chain reaction for codon 129 single nucleotide polymorphism (SNP) using TaqMan technology, which overcomes the main drawbacks of other methods and analysed Slovenian population (n = 97). The comparison with other populations served for the estimation of the genetic risk for the development of vCJD in Slovenians. The frequencies at the codon 129 SNP in the Slovenian population were 43.3% M, 45.4% M/V 11.3% V. Considerable differences between the DQ7 frequencies in diverse samples from the same population can be seen, especially when compared to Slovenian population. This could be because of the diverse criteria for including subjects into the study and the sampling of geographically distinct subpopulations. Analysing the adequacy of HLA-DQ7 as a possible predictive factor for developing Creutzfeld-Jakob disease (CJD) by case - control studies could be improved with exact and equal sampling of groups of patients and controls. CJD genetic risk factors in the Slovenians were not found significantly different than those in British.

Prevalence of risk factors of prion-related disease according to the French circular 138 (DGS/DH/5C/DHOS/E2/2001/138) among patients referred for gastrointestinal endoscopy

AIM OF THE STUDY

To assess the prevalence of risk factors of prion-related disease transmission in a gastrointestinal endoscopy unit.

METHODS

Clinical evaluation of the risk of transmission of prion-related diseases using the criteria defined by the French circular 138 in patients referred for digestive endoscopy without anesthesia.

RESULTS

1017 patients were included in this study. According to circular 138, 7 patients (0.68%) were at high risk of transmitting prion-related disease. According to these criteria, a high index of suspicion of prion-related disease was detected in 26 patients (2.55%). Clinical evaluation of risk was not possible for 56 patients (5.51%), due to coma or sedation (38 patients) or communication impairment (18 patients).

CONCLUSIONS

Application of circular 138 led us to consider that 2.55% of patients in this study had a high risk of prion-related disease. The circular criteria cannot be assessed in patients with sedation for mechanical ventilation, coma or communication impairment.

Variant Creutzfeldt-Jakob disease: a cause for concern. Review of the evidence for risk of transmission through abdominal lymphoreticular tissue surgery

BACKGROUND

Concern has long existed regarding the possible iatrogenic spread of variant Creutzfeldt-Jakob disease (v-CJD) through surgery. This had been fueled by recent reports of bovine spongiform encephalopathy in U.S. cattle and the first probable case of blood transmission of v-CJD in the UK.

METHODS

Systematic review of experimental and nonexperimental studies. Studies identified from searches of Medline, Embase, Cochrane Library, Science Citation Index medical databases, searching bibliographies of retrieved papers, and personal communication with international experts in the field.

RESULTS

Six articles satisfied our search criteria. Evidence stems from case reports, case series, and cross-sectional studies. There are no published cases of surgically transmitted v-CJD.

CONCLUSION

We found evidence of v-CJD prion agents in the spleen, appendix, rectum, and adrenal glands of affected patients and evidence of v-CJD prion in the appendix of patients in the preclinical stage of the disease. The risk of transmission of v-CJD prion during abdominal surgery is currently unquantifiable.

[Hospital practice and prion risks]

Procedures applicable in France for the prevention of prion diseases were first implemented in 1995, resulting from the threat of an epidemic extension of Creutzfeldt-Jakob Disease (CJD) following contamination resulting from the use of extracted growth hormone. It was found later that the bovine disease could infect humans via foodstuffs, and the human variant of the disease (v-CJD) transmissible through lymphoid formations was described in 1996. This led to generalizing precautions to a larger number of medical interventions, taking into account the risk for a population more broadly exposed to contamination. The principles for managing these new risks are described, as well for the use of medical devices or in patient as pathology laboratories.

Simple and specific detection of abnormal prion protein by a magnetic bead-based immunoassay coupled with laser-induced fluorescence spectrofluorometry

Transmissible spongiform encephalopathies (TSEs), also termed prion diseases, are fatal neurodegenerative conditions that affect both humans and animals. The transmissibility and fatal nature of TSEs necessitate their rapid and accurate diagnosis. Laser-induced fluorescence (LIF) spectrofluorometry is useful for obtaining measurements on fluorescence-labeled targets with a high degree of sensitivity. In the present study, we applied this technology to the immunological detection of abnormal prion protein, PrPSc, which is a universal diagnostic marker for TSEs. The assay format consists of a magnetic bead-based sandwich immunoassay utilizing a biotin-conjugated capture antibody and a fluorophore-labeled detector antibody. By using one pair of anti-PrP monoclonal antibodies (MAbs), PrPSc in brain homogenates from various experimental and natural TSEs can be easily detected with high specificity. Furthermore, the assay proved to be applicable for the detection of PrPSc in the lymph nodes from deer with TSE. The sensitivity of the assay was shown to be comparable to standard immunoblotting, but has several advantages over conventional tests, in terms of flexibility, simplicity, specificity, and run time. These results provide an important basis for the development of an early diagnostic test with potential for multi-sample analysis.

Decontamination of surgical instruments from prion proteins: in vitro studies on the detachment, destabilization and degradation of PrPSc bound to steel surfaces

Effective reprocessing of surgical instruments ensuring elimination of inadvertent contamination with infectious agents causing transmissible spongiform encephalopathies (TSEs) is essential for the prevention of iatrogenic transmission of Creutzfeldt-Jakob disease (CJD) or its new variant (vCJD) from asymptomatic carriers. In a search for effective yet instrument-friendly and routinely applicable reprocessing procedures, we used an in vitro carrier assay to assess the decontamination activity exerted by different reagents on pathological prion protein (PrP(Sc)), the biochemical marker for TSE infectivity, attached to steel surfaces. In this assay, steel wires were contaminated with 263K scrapie brain homogenate and reprocessed for decontamination by exposure to several different test reagents. Residual contamination with PrP(Sc) and its protease-resistant core PrP27-30, still present after reprocessing on the wire surface or in the cleaning solution, was monitored by sensitive Western blot detection without or after proteinase K digestion. Using this approach, various reagents and processing conditions were screened for both their efficacy of decontamination and their active principles, such as detachment, destabilization or degradation of surface-bound prion protein. This revealed that, under appropriate conditions, relatively mild reagents such as 0.2 % SDS/0.3 % NaOH (pH 12.8), a commercially available alkaline cleaner (pH 11.9-12.2), a disinfectant containing 0.2 % peracetic acid and low concentrations of NaOH (pH 8.9) or 5 % SDS (pH 7.1) exert potent decontaminating activities on PrP(Sc)/PrP27-30 attached to steel surfaces. For in vivo validation, wires reprocessed in these reagents have been implanted into reporter animals in ongoing experiments.

The risk of accidental transmission of transmissible spongiform encephalopathy: identification of emerging issues

The transmissible spongiform encephalopathies (TSEs), thought to be caused by prions, are fatal neurodegenerative disorders of humans and animals. Despite their rarity, human prion diseases have received prominence because the consumption of prion-contaminated meat from cattle with bovine spongiform encephalopathy (BSE) is thought to be responsible for the emergence of variant Creutzfeldt-Jakob disease (vCJD) in humans. Clinical criteria for the diagnosis of vCJD is now available. Recent, more startling evidence suggests that the clinical presentation of vCJD may vary and that patients may present as classical (sporadic) CJD or may have subclinical infection and be apparently healthy. These patients may still pose a risk of iatrogenic transmission through surgical or medical (blood transfusion) procedures. The aim of future work is to develop preclinical screening tests for the identification of infected but still healthy individuals. The future course of vCJD is still uncertain. Modelling studies to predict the cases of vCJD depend on the date of origin of BSE and time of infection, which is, at best, only approximated. As the number of cases of BSE in the UK declines, the risk of BSE in other countries from imported cattle or meat and bone meal from the UK has been increasing. It is also recognized that other animal species (farmed, domestic and wild animals) other than cows are susceptible to TSEs. The possibility of interspecies transmission of TSEs and the global presence of the disease suggests a need for a co-ordinated worldwide risk management approach to eradicate TSEs.