Prion strain discrimination based on rapid in vivo amplification and analysis by the cell panel assay

Prion strain identification has been hitherto achieved using time-consuming incubation time determinations in one or more mouse lines and elaborate neuropathological assessment. In the present work, we make a detailed study of the properties of PrP-overproducing Tga20 mice. We show that in these mice the four prion strains examined are rapidly and faithfully amplified and can subsequently be discriminated by a cell-based procedure, the Cell Panel Assay.

In vitro and in vivo neurotoxicity of prion protein oligomers

The mechanisms underlying prion-linked neurodegeneration remain to be elucidated, despite several recent advances in this field. Herein, we show that soluble, low molecular weight oligomers of the full-length prion protein (PrP), which possess characteristics of PrP to PrPsc conversion intermediates such as partial protease resistance, are neurotoxic in vitro on primary cultures of neurons and in vivo after subcortical stereotaxic injection. Monomeric PrP was not toxic. Insoluble, fibrillar forms of PrP exhibited no toxicity in vitro and were less toxic than their oligomeric counterparts in vivo. The toxicity was independent of PrP expression in the neurons both in vitro and in vivo for the PrP oligomers and in vivo for the PrP fibrils. Rescue experiments with antibodies showed that the exposure of the hydrophobic stretch of PrP at the oligomeric surface was necessary for toxicity. This study identifies toxic PrP species in vivo. It shows that PrP-induced neurodegeneration shares common mechanisms with other brain amyloidoses like Alzheimer disease and opens new avenues for neuroprotective intervention strategies of prion diseases targeting PrP oligomers.

Toxic effects of intracerebral PrP antibody administration during the course of BSE infection in mice

The absence of specific immune response is a hallmark of prion diseases. However, in vitro and in vivo experiments have provided evidence that an anti-PrP humoral response could have beneficial effects. Prophylactic passive immunization performed at the time of infection delayed or prevented disease. Nonetheless, the potential therapeutic effect of PrP antibodies administered shortly before the clinical signs has never been tested in vivo. Moreover, a recent study showed the potential toxicity of PrP antibodies administered intracerebrally. We aimed at evaluating the effect of a prolonged intracerebral anti-PrP antibody administration at the time of neuroinvasion in BSE infected Tg20 mice. Unexpectedly, despite a good penetration of the antibodies in the brain parenchyma, the treatment was not protective against the development of BSE. Instead, it led to an extensive neuronal loss, strong astrogliosis and microglial activation. Since this effect was observed after injection of anti-PrP antibodies as whole IgGs, F(ab')(2) or Fab fragments, the toxicity was directly related to the ability of the antibodies to recognize native PrP and to the intracerebral concentration achieved, and not to the Fc portion or the divalence of the antibodies. This experiment shows that a prolonged treatment with anti-PrP antibodies by the intracerebral route can induce severe side-effects and calls for caution with regard to the use of similar approaches for late therapeutic interventions in humans.

PrPTSE distribution in a primate model of variant, sporadic, and iatrogenic Creutzfeldt-Jakob disease

Human prion diseases, such as Creutzfeldt-Jakob disease (CJD), are neurodegenerative and fatal. Sporadic CJD (sCJD) can be transmitted between humans through medical procedures involving highly infected organs, such as the central nervous system. However, in variant CJD (vCJD), which is due to human contamination with the bovine spongiform encephalopathy (BSE) agent, lymphoreticular tissue also harbors the transmissible spongiform encephalopathy-associated prion protein (PrP(TSE)), which poses a particularly acute risk for iatrogenic transmission. Two blood transfusion-related cases are already documented. In addition, the recent observation of PrP(TSE) in spleen and muscle in sCJD raised the possibility that peripheral PrP(TSE) is not limited to vCJD cases. We aimed to clarify the peripheral pathogenesis of human TSEs by using a nonhuman primate model which mimics human diseases. A highly sensitive enzyme-linked immunosorbent assay was adapted to the detection of extraneural PrP(TSE). We show that affected organs can be divided into two groups. The first is peripheral organs accumulating large amounts of PrP(TSE), which represent a high risk of iatrogenic transmission. This category comprises only lymphoreticular organs in the vCJD/BSE model. The second is organs with small amounts of PrP(TSE) associated with nervous structures. These are the muscles, adrenal glands, and enteric nervous system in the sporadic, iatrogenic, and variant CJD models. In contrast to the first set of organs, this low level of tissue contamination is not strain restricted and seems to be linked to secondary centrifugal spread of the agent through nerves. It might represent a risk for iatrogenic transmission, formerly underestimated despite previous reports of low rates of transmission from peripheral organs of humans to nonhuman primates (5, 10). This study provides an additional experimental basis for the classification of human organs into different risk categories and a rational re-evaluation of current risk management measures.

Role of gut macrophages in mice orally contaminated with scrapie or BSE

While there is a growing consensus on the understanding of the propagation pathways after oral infection of transmissible spongiform encephalopathy (TSE) agents and even if the central role of follicular dendritic cells is identified, little is known about the key players in the first steps of the infection and about the site of the disease development. We investigated the role of gut macrophages, which are capable of capturing aggregates of the prion protein. PLGA particles containing clodronate were designed in order to be orally administered and to target Peyer's patches for inducing gut-associated macrophages suicide in mice. Mice were subsequently infected with scrapie or BSE by the oral route. It was found that the efficacy of macrophage suppression in the Peyer's patches correlated well with an earlier appearance of PrPres in these formations and with a higher amount of PrPres at a later stage of the infection. Thus, the capture of infectious particles that have crossed the epithelial gut barrier and their elimination by macrophages seems to be a key event to restrict the amount of agent initiating the infection.

Risk of oral infection with bovine spongiform encephalopathy agent in primates

The uncertain extent of human exposure to bovine spongiform encephalopathy (BSE)--which can lead to variant Creutzfeldt-Jakob disease (vCJD)--is compounded by incomplete knowledge about the efficiency of oral infection and the magnitude of any bovine-to-human biological barrier to transmission. We therefore investigated oral transmission of BSE to non-human primates. We gave two macaques a 5 g oral dose of brain homogenate from a BSE-infected cow. One macaque developed vCJD-like neurological disease 60 months after exposure, whereas the other remained free of disease at 76 months. On the basis of these findings and data from other studies, we made a preliminary estimate of the food exposure risk for man, which provides additional assurance that existing public health measures can prevent transmission of BSE to man.

Tissue distribution of bovine spongiform encephalopathy agent in primates after intravenous or oral infection

BACKGROUND

The disease-associated form of prion protein (PrP(res)) has been noted in lymphoreticular tissues in patients with variant Creutzfeldt-Jakob disease (vCJD). Thus, the disease could be transmitted iatrogenically by surgery or use of blood products. We aimed to assess transmissibility of the bovine spongiform encephalopathy (BSE) agent to primates by the intravenous route and study its tissue distribution compared with infection by the oral route.

METHODS

Cynomolgus macaques were infected either intravenously or orally with brain homogenates from first-passage animals with BSE. They were clinically monitored for occurrence of neurological signs and killed humanely at the terminal stage of the disease. Brain, lymphoreticular tissues, digestive tract, and peripheral nerves were obtained and analysed by sandwich ELISA and immunohistochemistry for quantitative and qualitative assessment of their PrP(res) content.

FINDINGS

Incubation periods after intravenous transmission of BSE were much shorter than after oral infection. We noted that PrP(res) was present in lymphoreticular tissues such as spleen and tonsils and in the entire gut from the duodenum to the rectum. In the gut, PrP(res) was present in Peyer's patches and in the enteric nervous system and nerve fibres of intestinal mucosa. Furthermore, PrP(res) was found in locomotor peripheral nerves and the autonomic nervous system. Amount of PrP(res) ranged from 0.02% to more than 10% of that recorded in brain. Distribution of PrP(res) was similar in animals infected by the intravenous or oral route.

INTERPRETATION

Our findings suggest that the possible risk of vCJD linked to endoscopic procedures might be currently underestimated. Human iatrogenic vCJD cases infected intravenously raise the same public-health concerns as primary cases and need the same precautionary measures with respect to blood and tissue donations and surgical procedures.

A novel generation of heparan sulfate mimetics for the treatment of prion diseases

The accumulation of PrP(res), the protease-resistant abnormal form of the host-encoded cellular prion protein, PrP(C), plays a central role in transmissible spongiform encephalopathies. Human contamination by bovine spongiform encephalopathy (BSE) has propelled many scientific teams on a highway for anti-prion drug development. This study reports that heparan sulfate mimetics (HMs), developed originally for their effect on tissue regeneration, abolish prion propagation in scrapie-infected GT1 cells. PrP(res) does not reappear for up to 50 days post-treatment. When tested in vivo, one of these compounds, HM2602, hampered PrP(res) accumulation in scrapie- and BSE-infected mice and prolonged significantly the survival time of 263K scrapie-infected hamsters. Interestingly, HM2602 is an apparently less toxic and more potent inhibitor of PrP(res) accumulation than dextran sulfate 500, a molecule known to exhibit anti-prion properties in vivo. Kinetics of PrP(res) disappearance in vitro and unaffected PrP(C) levels during treatment suggest that HMs are able to block the conversion of PrP(C) into PrP(res). It is speculated that HMs act as competitors of endogenous heparan sulfates known to act as co-receptors for the prion protein. Since these molecules are particularly amenable to drug design, their anti-prion potential could be developed further and optimized for the treatment of prion diseases.

Evaluation of quinacrine treatment for prion diseases

Based on in vitro observations in scrapie-infected neuroblastoma cells, quinacrine has recently been proposed as a treatment for Creutzfeldt-Jakob disease (CJD), including a new variant CJD which is linked to contamination of food by the bovine spongiform encephalopathy (BSE) agent. The present study investigated possible mechanisms of action of quinacrine on prions. The ability of quinacrine to interact with and to reduce the protease resistance of PrP peptide aggregates and PrPres of human and animal origin were analyzed, together with its ability to inhibit the in vitro conversion of the normal prion protein (PrPc) to the abnormal form (PrPres). Furthermore, the efficiencies of quinacrine and chlorpromazine, another tricyclic compound, were examined in different in vitro models and in an experimental murine model of BSE. Quinacrine efficiently hampered de novo generation of fibrillogenic prion protein and PrPres accumulation in ScN2a cells. However, it was unable to affect the protease resistance of preexisting PrP fibrils and PrPres from brain homogenates, and a "curing" effect was obtained in ScGT1 cells only after lengthy treatment. In vivo, no detectable effect was observed in the animal model used, consistent with other recent studies and preliminary observations in humans. Despite its ability to cross the blood-brain barrier, the use of quinacrine for the treatment of CJD is questionable, at least as a monotherapy. The multistep experimental approach employed here could be used to test new therapeutic regimes before their use in human trials.

Effects of the polyene antibiotic derivative MS-8209 on the astrocyte lysosomal system of scrapie-infected hamsters

Amphotericine B (AmB), a macrolide polyene antibiotic, is one of a few drugs that has shown therapeutic properties in scrapie-infected hamster. Its beneficial effect on survival time is mostly marked when animals are treated with its derivative MS-8209. To explore the MS-8209 effect at the cellular level, we investigated at the light and electron microscopy levels, the sequential appearance and distribution of PrP concurrently with histopathological changes in hamsters that were infected intracerebrally with the 263 K scrapie strain and treated or not with the drug. The first histopathological modifications and PrP immunostaining were observed in the thalamus and at the inoculation site where the drug caused a delay in the appearance of lesions and PrP accumulation. Using immunoelectron microscopy, at 70 d postinfection, the inoculation site of untreated animals showed an accumulation of PrP in plaque areas constitued by filaments mixed with alterated membrane structures and in developed lysosomal system of reactive astrocytes. Most of the numerous lysosomes containing PrP showed intra-organelle filaments. In contrast, in MS-8209 treated animals, the number of lysosomes was significantly lower (p < 0.0038), with very few organelles harboring PrP. Our results suggest that in this scrapie model, MS-8209 treatment delays the disease by preventing the replication of the scrapie agent at the inoculation site where the astrocytes appear to be the first cells producing abnormal PrP. The lysosomal system of these astrocytes could constitute a privileged target for MS-8209.

Developmental expression of the cellular prion protein in elongating axons

PrPc, a sialoglycoprotein present in the normal adult hamster brain, is particularly abundant in plastic brain regions but little is known about the level of expression and the localization of the protein during development. Western blot analysis of whole brain homogenates with mab3F4 show very low levels of the three main molecular weight forms of the protein at birth, in contrast to the strong and wide expression of mRNA transcripts. The PrPc levels increase sharply through P14 and are diminished somewhat in the adult. Regional analysis showed that in structures with ongoing growth or plasticity such as the olfactory bulb and hippocampus, PrPc remains high in the adult, while in areas where structural and functional relationships stabilize during development, such as the cortex and the thalamus, PrPc levels decline after the third postnatal week. In the neonate brain PrPc was prominent along fiber tracts similar to markers of axon elongation and in vitro experiments showed that the protein was present on the surface of elongating axons. PrPc is then localized to the synaptic neuropil in close spatio-temporal association with synapse formation. The localization of PrPc on elongating axons suggests a role for the protein in axon growth. In addition, the relative abundance of the protein in developing axon pathways and during synaptogenesis may provide a basis for the age-dependent susceptibility to transmissible spongiform encephalopathies.

Immunolocalization of the cellular prion protein in normal brain

We examined the localization of PrP(c) in normal brain using free-floating section immunohistochemistry and monclonal antibody 3F4. In the mature hamster and baboon brain, PrP(c) is localized to the neuropil with a synaptic distribution and the PrP(c) immunoreactivity is denser in regions known for ongoing plasticity. Cell bodies and major fiber tracts have little or no PrP(c) immunoreactivity. At the electron microscopic level, PrP(c) immunoreactivity decorates synaptic profiles, both pre- and postsynaptically. Results obtained with two additional antibodies, 3B5 and Pri-304, showed similar patterns of PrP(c) bands on Western blots, although Pri-304 was less sensitive. On sections through the adult hamster hippocampus, 3B5 and Pri-304 both stained the synaptic neuropil while cell bodies in the pyramidal and dentate granule cell layers were not immunoreactive. Pri-304 differentiated between synaptic layers in the hippocampus and closely resembled the pattern of staining obtained with 3F4. Preliminary results of developing brain showed that PrP(c) is initially localized along fiber tracts in the neonate brain. These results show that PrP(c) has a synaptic distribution in the adult brain and suggest that there are important changes in its distribution during brain development. These results also characterize two additional reagents for studies of PrP(c) localization.

Cellular prion protein localization in rodent and primate brain

The presence of an abnormal, protease-resistant form of the prion protein (PrP) is the hallmark of various forms of transmissible spongiform encephalopathies (TSE) which can affect a number of mammalian species, including humans. The normal, cellular form of this protein, PrPc, while abundant in brain is also present in many tissues and a number of species. In order to address the unresolved question of the precise localization of normal cerebral PrPc, we used a free-floating immunohistochemistry procedure to localize the protein at both the light and the electron microscopic levels in the brain of three TSE-sensitive species: hamster, macaque and humans. This method shows that PrPc is abundant in synaptic terminal fields in olfactory bulb, limbic-associated structures and in the striato-nigral complex, whereas many other regions of the hamster brain are essentially devoid of immunoreactivity. With the striking exception of the olfactory nerve, in which axons are continually growing throughout life, PrPc is not abundant in fibre pathways. PrPc distribution in the primate hippocampus and cortex is very similar to the distribution observed in hamster. PrPc was present at synaptic profiles as shown by immunoelectron microscopy, but was not detectable in neuronal perikaryon either by light or electron microscopy. Our results show that PrPc is abundant in a number of brain structures known for ongoing plasticity, and are consistent with the hypothesis that the protein also plays a role in synaptic function.

Autoradiographic localisation of NMDA binding sites in brainstem cardiorespiratory areas of adult and newborn cats

Quantitative autoradiography was used to determine the distribution of [3H]1-[1-(2-thienyl)cyclohexyl] piperidine ([3H]TCP) binding sites in the brainstem in order to localize the possible targets activated by excitatory amino acids in adult and newborn cats during autonomic rhythmic functions. Medium to high densities of binding sites were found in the nucleus tractus solitarius complex and the laterodorsal part of the pontine tegmentum. In the kitten, there was an apparent higher density in cranial motor nuclei proximal to these structures. It is concluded that there is an overlapping between the high density of NMDA receptors and the localization of cardiorespiratory neurons in cat as well as in kitten.

Pre- and post-natal ontogeny of neutral endopeptidase 24-11 ('enkephalinase') studied by in vitro autoradiography in the rat

Neutral endopeptidase (NEP, enkephalinase, CALLA) which is present in various neural and non-neural tissues, is able to cleave a variety of regulatory peptides. The distribution of NEP has been studied during rat pre- and post-natal development by autoradiography after in vitro binding of the tritiated inhibitor [3H]HACBO-Gly to whole-body and organ sections. In the central nervous system (CNS), where the presence of NEP has been related to the termination of the action of enkephalins, the external layer of the olfactory bulbs is the only structure prominently labeled before birth. Other CNS structures rich in NEP in the adult, such as the nigrostriatal tract, are progressively labeled after birth. Outside the CNS, the progressive appearance of NEP in the kidney, the lungs and the salivary glands suggests its concomitant involvement in adult physiological functions, including fluid balance control, possibly by cleaving the atrial natriuretic peptide (ANP) and other peptides. On the other hand, transient or enhanced expression of NEP is observed during the development of several organs such as the sensory organs, the heart and the major blood vessels, the intestine, the bones and the genital tubercle. In addition to the still incompletely known physiological functions of the enzyme, the developmental pattern of its expression in several tissues strongly suggests a modulatory role for NEP in the ontogeny of a large number of organs.

Ontogeny of mu and delta opioid receptors and of neutral endopeptidase in human spinal cord: an autoradiographic study

The distributions of the neutral endopeptidase 24.11 (NEP; enkephalinase) and of mu and delta opioid receptors have been studied by autoradiography in the human spinal cord during ontogenesis, mu and delta sites were assessed by using [3H]DAGO and [3H]DTLET respectively and NEP was labelled by [3H]HACBO-Gly, a NEP inhibitor. Labelling by the three markers was found at an early stage of development of the central nervous system (14 weeks) and was mainly localized in the gray matter, with highest densities in the superficial layers of the dorsal horn. Moreover [3H]DAGO also diffusely labelled the ventral motor areas. NEP and delta binding sites were localized transiently in the fasciculus gracilis at the cervical level at a fetal age of 24 weeks, an area where no enkephalin-like immunoreactivity (ELI) has been found. Conversely no opioid binding sites or NEP were observed at a fetal age of 18 weeks in the intermediolateral region where ELI fibres and cells were detected transiently. In general, a better correlation between the distribution of NEP and that of delta opioid sites was observed. Meninges contained a very high density of [3H]HACBO-Gly sites. This labelling appeared almost simultaneously with that in the spinal cord tissue and increased with maturation. An increase in labelling by the three markers appeared slightly earlier than the clustering of ELI fibres in the substantia gelatinosa. Our data show that in the human spinal cord, structural and biochemical elements involved in enkephalinergic transmission appear almost simultaneously and early in ontogeny.

Cytochemical and autoradiographic study of the early nuclear lesions induced by an ellipticine derivative in isolated rat hepatocytes

Isolated rat liver cells maintained in primary culture were treated with 9-OH ellipticinium (9-OH E+). The effects of this drug on the nuclear ultrastructure and on the chromatin transcriptional activity were studied by the combination of cytochemistry with hgih resolution autoradiography. At a low concentration (1 microgram/ml) for periods ranging from 10 min to 3 hr, 9-OH E+ induced chromatin clumping, nucleolar microsegregation and a diminution in the number of perichromatin and interchromatin fibrils. Autoradiography revealed that this compound inhibited rapidly the incorporation of [5-3H]-uridine in the nucleus, preferentially but not exclusively in the nucleolar area. In addition, the distribution of the radioactivity in the nucleoli proved that the processing of the pre-ribosomal ribonucleic acids (pre-rRNA) synthesized in the presence of the drug was blocked while the processing during 9-OH E+ treatment of normally synthesized pre-rRNA was not altered. These findings suggest that the inhibition of pre-rRNA processing might result from an impairment of factors controlling this processing rather than from a direct action of 9-OH E+ on pre-rRNA molecules.