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Prion diseases are fatal transmissible neurodegenerative disorders. Among known anti-prions, hydroxypropyl methylcellulose compounds (HPMCs) are unique in their chemical structure and action. They have several excellent anti-prion properties but the effectiveness depends on the prion-infected mouse model. In the present study, we investigated the effects of stearoxy-modified HPMCs on prion-infected cells and mice. Stearoxy modification improved the anti-prion efficacy of HPMCs in prion-infected cells and significantly prolonged the incubation period in a lower HPMC-responding mouse model. However, stearoxy modification showed no improvement over nonmodified HPMCs in an HPMC-responding mouse model. These results offer a new line of inquiry for use with prion-infected mice that do not respond well to HPMCs., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Kenta Teruya reports financial support was provided by the Japan Society for the Promotion of Science [grant numbers 19K22479 and 23K05036]. Kenta Teruya has patent #P2017-93414 issued to Tohoku University. Katsumi Doh-ura has patent #P2017-93414 issued to Tohoku University. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Prion diseases are fatal transmissible neurodegenerative disorders. Tremendous efforts have been made for prion diseases; however, no effective treatment is available. Several anti-prion compounds have a preference for which prion strains or prion-infected animal models to target. Styrylbenzoazole compound called cpd-B is effective in RML prion-infected mice but less so in 263K prion-infected mice, whereas hydroxypropyl methylcellulose is effective in 263K prion-infected mice but less so in RML prion-infected mice. In the present study, we developed a combination therapy of cpd-B and hydroxypropyl methylcellulose expecting synergistic effects in both RML prion-infected mice and 263K prion-infected mice. A single subcutaneous administration of this combination had substantially a synergistic effect in RML prion-infected mice but had no additive effect in 263K prion-infected mice. These results showed that the effect of cpd-B was enhanced by hydroxypropyl methylcellulose. The complementary nature of the two compounds in efficacy against prion strains, chemical properties, pharmacokinetics, and physical properties appears to have contributed to the effective combination therapy. Our results pave the way for the strategy of new anti-prion agents., (© 2023. The Author(s).)

Prion diseases, also known as transmissible spongiform encephalopathies, are caused by the accumulation of abnormal isoforms of the prion protein (scrapie isoform of the prion protein, PrPSc) in the central nervous system. Many compounds with anti-prion activities have been found using in silico screening, in vitro models, persistently prion-infected cell models, and prion-infected rodent models. Some of these compounds include several types of polymers. Although the inhibition or removal of PrPSc production is the main target of therapy, the unique features of prions, namely protein aggregation and assembly accompanied by steric structural transformation, may require different strategies for the development of anti-prion drugs than those for conventional therapeutics targeting enzyme inhibition, agonist ligands, or modulation of signaling. In this paper, we first overview the history of the application of polymers to prion disease research. Next, we describe the characteristics of each type of polymer with anti-prion activity. Finally, we discuss the common features of these polymers. Although drug delivery of these polymers to the brain is a challenge, they are useful not only as leads for therapeutic drugs but also as tools to explore the structure of PrPSc and are indispensable for prion disease research., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Previous studies have revealed that the infectious scrapie isoform of prion protein (PrP Sc ) harbored in the skin tissue of patients or animals with prion diseases can be amplified and detected through the serial protein misfolding cyclic amplification (sPMCA) or real-time quaking-induced conversion (RT-QuIC) assays. These findings suggest that skin PrP Sc -seeding activity may serve as a biomarker for the diagnosis of prion diseases; however, its utility as a biomarker for prion therapeutics remains largely unknown. Cellulose ethers (CEs, such as TC-5RW), widely used as food and pharmaceutical additives, have recently been shown to prolong the lifespan of prion-infected mice and hamsters. Here we report that in transgenic (Tg) mice expressing hamster cellular prion protein (PrP C ) infected with the 263K prion, the prion-seeding activity becomes undetectable in the skin tissues of TC-5RW-treated Tg mice by both sPMCA and RT-QuIC assays, whereas such prion-seeding activity is readily detectable in the skin of untreated mice. Notably, TC-5RW exhibits an inhibitory effect on the in vitro amplification of PrP Sc in both skin and brain tissues by sPMCA and RT-QuIC. Moreover, we reveal that TC-5RW is able to directly decrease protease-resistant PrP Sc and inhibit the seeding activity of PrP Sc from chronic wasting disease and various human prion diseases. Our results suggest that the level of prion-seeding activity in the skin may serve as a useful biomarker for assessing the therapeutic efficacy of compounds in a clinical trial of prion diseases and that TC-5RW may have the potential for the prevention/treatment of human prion diseases., (© 2021. The Author(s).)

Anti-prion effects of cellulose ether (CE) are reported in rodents, but the molecular mechanism is fully unknown. Here, we investigated the genetic background of CE effectiveness by proteomic and genetic analysis in mice. Proteomic analysis in the two mouse lines showing a dramatic difference in CE effectiveness revealed a distinct polymorphism in the glia maturation factor β gene. This polymorphism was significantly associated with the CE effectiveness in various prion-infected mouse lines. Sequencing of this gene and its vicinity genes also revealed several other polymorphisms that were significantly related to the CE effectiveness. These polymorphisms are useful as genetic markers for finding more suitable mouse lines and exploring the genetic factors of CE effectiveness., Competing Interests: Declaration of competing interest The authors have declared that no competing interests exist., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Lowering of prion protein (PrP) expression in the brain is a genetically validated therapeutic hypothesis in prion disease. We recently showed that antisense oligonucleotide (ASO)-mediated PrP suppression extends survival and delays disease onset in intracerebrally prion-infected mice in both prophylactic and delayed dosing paradigms. Here, we examine the efficacy of this therapeutic approach across diverse paradigms, varying the dose and dosing regimen, prion strain, treatment timepoint, and examining symptomatic, survival, and biomarker readouts. We recapitulate our previous findings with additional PrP-targeting ASOs, and demonstrate therapeutic benefit against four additional prion strains. We demonstrate that <25% PrP suppression is sufficient to extend survival and delay symptoms in a prophylactic paradigm. Rise in both neuroinflammation and neuronal injury markers can be reversed by a single dose of PrP-lowering ASO administered after the detection of pathological change. Chronic ASO-mediated suppression of PrP beginning at any time up to early signs of neuropathology confers benefit similar to constitutive heterozygous PrP knockout. Remarkably, even after emergence of frank symptoms including weight loss, a single treatment prolongs survival by months in a subset of animals. These results support ASO-mediated PrP lowering, and PrP-lowering therapeutics in general, as a promising path forward against prion disease., (© The Author(s) 2020. Published by Oxford University Press on behalf of Nucleic Acids Research.)

In prion diseases, infectious pathogenic particles that are composed of abnormal prion proteins (PrP Sc ) accumulate in the brain. PrP Sc is biochemically characterized by its protease-resistance core (PrP res ), but its structural features have not been fully elucidated. Here, we report that primuline, a fluorescent dye with photosensitization activity, dramatically enhances UV-irradiation-induced SDS-resistant PrP Sc/res oligomer formation that can be detected by immunoblot analysis of prion-infected materials. This oligomer formation occurs specifically with PrP Sc/res but not with normal prion protein, and it was demonstrated using purified PrP Sc/res as well as unpurified materials. The oligomer formation proceeded in both primuline-dose- and UV irradiation time-dependent manners. Treatment with urea or formic acid did not break oligomers into monomers. Neither did the presence of aromatic amino acids modify oligomer formation. Analysis with a panel of anti-prion protein antibodies showed that the antibodies against the N-terminal region of PrP res were less reactive in the dimer than the monomer. These findings suggest that the primuline-sensitized photoreaction enhances intermolecular crosslinking of PrP Sc/res molecules at a hydrophobic area of the N-terminal region of PrP res . In the screening of other compounds, photoreactive compounds such as luciferin exhibited a similar but lower activity with respect to oligomer formation than primuline. The enhanced photoreaction with these compounds will be useful for evaluating the structural features of PrP Sc/res , especially the interactions between PrP Sc/res molecules., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Prion diseases are fatal transmissible neurodegenerative disorders that affect animals and humans. Prions are proteinaceous infectious particles consisting of a misfolded isoform of the cellular prion protein PrP C , termed PrP Sc . PrP Sc accumulates in infected neurons due to partial resistance to proteolytic digestion. Using compounds that interfere with the production of PrP Sc or enhance its degradation cure prion infection in vitro , but most drugs failed when used to treat prion-infected rodents. In order to synergize the effect of anti-prion drugs, we combined drugs interfering with the generation of PrP Sc with compounds inducing PrP Sc degradation. Here, we tested autophagy stimulators (rapamycin or AR12) and cellulose ether compounds (TC-5RW or 60SH-50) either as single or combination treatment of mice infected with RML prions. Single drug treatments significantly extended the survival compared to the untreated group. As anticipated, also all the combination therapy groups showed extended survival compared to the untreated group, but no combination treatment showed superior effects to 60SH-50 or TC-5RW treatment alone. Unexpectedly, we later found that combining autophagy stimulator and cellulose ether treatment in cultured neuronal cells mitigated the pro-autophagic activity of AR12 and rapamycin, which can in part explain the in vivo results. Overall, we show that it is critical to exclude antagonizing drug effects when attempting combination therapy. In addition, we identified AR-12 as a pro-autophagic drug that significantly extends survival of prion-infected mice, has no adverse side effects on the animals used in this study, and can be useful in future studies.

Prion diseases are progressive fatal neurodegenerative illnesses caused by the accumulation of transmissible abnormal prion protein (PrP). To find treatments for prion diseases, we searched for substances from natural resources that inhibit abnormal PrP formation in prion-infected cells. We found that high-molecular-weight components from insect cuticle extracts reduced abnormal PrP levels. The chemical nature of these components was consistent with that of melanin. In fact, synthetic melanin produced from tyrosine or 3-hydroxy-l-tyrosine inhibited abnormal PrP formation. Melanin did not modify cellular or cell surface PrP levels, nor did it modify lipid raft or cellular cholesterol levels. Neither did it enhance autophagy or lysosomal function. Melanin was capable of interacting with PrP at two N-terminal domains. Specifically, it strongly interacted with the PrP region of amino acids 23 to 50 including a positively charged amino acid cluster and weakly interacted with the PrP octarepeat peptide region of residues 51 to 90. However, the in vitro and in vivo data were inconsistent with those of prion-infected cells. Abnormal PrP formation in protein misfolding cyclic amplification was not inhibited by melanin. Survival after prion infection was not significantly altered in albino mice or exogenously melanin-injected mice compared with that of control mice. These data suggest that melanin, a main determinant of skin color, is not likely to modify prion disease pathogenesis, even though racial differences in the incidence of human prion diseases have been reported. Thus, the findings identify an interaction between melanin and the N terminus of PrP, but the pathophysiological roles of the PrP-melanin interaction remain unclear. IMPORTANCE The N-terminal region of PrP is reportedly important for neuroprotection, neurotoxicity, and abnormal PrP formation, as this region is bound by many factors, such as metal ions, lipids, nucleic acids, antiprion compounds, and several proteins, including abnormal PrP in prion disease and the Aβ oligomer in Alzheimer's disease. In the present study, melanin, a main determinant of skin color, was newly found to interact with this N-terminal region and inhibits abnormal PrP formation in prion-infected cells. However, the data for prion infection in mice lacking melanin production suggest that melanin is not associated with the prion disease mechanism, although the incidence of prion disease is reportedly much higher in white people than in black people. Thus, the roles of the PrP-melanin interaction remain to be further elucidated, but melanin might be a useful competitive tool for evaluating the functions of other ligands at the N-terminal region., (Copyright © 2017 American Society for Microbiology.)

Prion diseases are fatal, progressive, neurodegenerative diseases caused by prion accumulation in the brain and lymphoreticular system. Here we report that a single subcutaneous injection of cellulose ethers (CEs), which are commonly used as inactive ingredients in foods and pharmaceuticals, markedly prolonged the lives of mice and hamsters intracerebrally or intraperitoneally infected with the 263K hamster prion. CEs provided sustained protection even when a single injection was given as long as one year before infection. These effects were linked with persistent residues of CEs in various tissues. More effective CEs had less macrophage uptake ratios and hydrophobic modification of CEs abolished the effectiveness. CEs were significantly effective in other prion disease animal models; however, the effects were less remarkable than those observed in the 263K prion-infected animals. The genetic background of the animal model was suggested to influence the effects of CEs. CEs did not modify prion protein expression but inhibited abnormal prion protein formation in vitro and in prion-infected cells. Although the mechanism of CEs in vivo remains to be solved, these findings suggest that they aid in elucidating disease susceptibility and preventing prion diseases., Competing Interests: I have read the journal's policy and the authors of this manuscript have the following competing interests: Itoham Foods Inc. and Tohoku University hold a patent (WO2007123187 A1) on medicinal chemicals associated with cellulose ethers, and KD is the inventor of the patent.

The cellular mechanisms behind prion biosynthesis and metabolism remain unclear. Here we show that secretin signaling via the secretin receptor regulates abnormal prion protein formation in prion-infected cells. Animal studies demonstrate that secretin receptor deficiency slightly, but significantly, prolongs incubation time in female but not male mice. This gender-specificity is consistent with our finding that prion-infected cells are derived from females. Therefore, our results provide initial insights into the reasons why age of disease onset in certain prion diseases is reported to occur slightly earlier in females than males., (Copyright © 2015 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.)

Unlabelled: A new type of antiprion compound, Gly-9, was found to inhibit abnormal prion protein formation in prion-infected neuroblastoma cells, in a prion strain-independent manner, when the cells were treated for more than 1 day. It reduced the intracellular prion protein level and significantly modified mRNA expression levels of genes of two types: interferon-stimulated genes were downregulated after more than 2 days of treatment, and the phosphodiesterase 4D-interacting protein gene, a gene involved in microtubule growth, was upregulated after more than 1 day of treatment. A supplement of interferon given to the cells partly restored the abnormal prion protein level but did not alter the normal prion protein level. This interferon action was independent of the Janus activated kinase-signal transducer and activator of transcription signaling pathway. Therefore, the changes in interferon-stimulated genes might be a secondary effect of Gly-9 treatment. However, gene knockdown of phosphodiesterase 4D-interacting protein restored or increased both the abnormal prion protein level and the normal prion protein level, without transcriptional alteration of the prion protein gene. It also altered the localization of abnormal prion protein accumulation in the cells, indicating that phosphodiesterase 4D-interacting protein might affect prion protein levels by altering the trafficking of prion protein-containing structures. Interferon and phosphodiesterase 4D-interacting protein had no direct mutual link, demonstrating that they regulate abnormal prion protein levels independently. Although the in vivo efficacy of Gly-9 was limited, the findings for Gly-9 provide insights into the regulation of abnormal prion protein in cells and suggest new targets for antiprion compounds., Importance: This report describes our study of the efficacy and potential mechanism underlying the antiprion action of a new antiprion compound with a glycoside structure in prion-infected cells, as well as the efficacy of the compound in prion-infected animals. The study revealed involvements of two factors in the compound's mechanism of action: interferon and a microtubule nucleation activator, phosphodiesterase 4D-interacting protein. In particular, phosphodiesterase 4D-interacting protein was suggested to be important in regulating the trafficking or fusion of prion protein-containing vesicles or structures in cells. The findings of the study are expected to be useful not only for the elucidation of cellular regulatory mechanisms of prion protein but also for the implication of new targets for therapeutic development.

Prion diseases, or transmissible spongiform encephalopathies, are characterized by abnormal prion protein accumulation in the brain. Abnormal prion proteins, having properties of amyloids when extracted from the brain, are observed as amyloid plaque deposits in the brain in some prion diseases such as variant Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker syndrome. This article reviews amyloid-binding compounds from the perspective of their usefulness for diagnosis and therapy of prion diseases. Styrylbenzoazole derivatives and phenylhydrazine derivatives are recently developed amyloid binding compounds that present benefits for prion-disease-related medicinal applications. For instance, styrylbenzoazole derivative BF-227, currently used as an amyloid imaging probe of positron emission tomography in Alzheimer disease, is useful also for the diagnosis of Gerstmann-Sträussler-Scheinker syndrome. A phenylhydrazine derivative, compB, has remarkable prophylactic effects on intracerebrally infected animals with certain prion strains, even when administered orally. These amyloid-binding compounds, however, are not applicable to prion strains or prion diseases of all types. For example, amyloid-binding compounds are ineffective for inhibiting prion strains such as 263K. They are not feasible for detecting abnormal prion protein accumulation in the brain for prion diseases having no amyloid plaques. To elucidate the limitations of amyloid-binding compounds, further investigation is necessary to clarify the binding mode of the compounds to abnormal prion protein structures at an atomic level.

Intraventricular infusion of pentosan polysulfate (PPS) as a treatment for various human prion diseases has been applied in Japan. To evaluate the influence of PPS treatment we performed pathological examination and biochemical analyses of PrP molecules in autopsied brains treated with PPS (one case of sporadic Creutzfeldt-Jakob disease (sCJD, case 1), two cases of dura mater graft-associated CJD (dCJD, cases 2 and 4), and one case of Gerstmann-Sträussler-Scheinker disease (GSS, case 3). Six cases of sCJD without PPS treatment were examined for comparison. Protease-resistant PrP (PrP(res) ) in the frontal lobe was evaluated by Western blotting after proteinase K digestion. Further, the degree of polymerization of PrP molecules was examined by the size-exclusion gel chromatography assay. PPS infusions were started 3-10 months after disease onset, but the treatment did not achieve any clinical improvements. Postmortem examinations of the treated cases revealed symmetrical brain lesions, including neuronal loss, spongiform change and gliosis. Noteworthy was GFAP in the cortical astrocytes reduced in all treated cases despite astrogliosis. Immunohistochemistry for PrP revealed abnormal synaptic deposits in all treated cases and further plaque-type PrP deposition in case 3 of GSS and case 4 of dCJD. Western blotting showed relatively low ratios of PrP(res) in case 2 of dCJD and case 3 of GSS, while in the treated sCJD (case 1), the ratio of PrP(res) was comparable with untreated cases. The indices of oligomeric PrP were reduced in one sCJD (case 1) and one dCJD (case 2). Although intraventricular PPS infusion might modify the accumulation of PrP oligomers in the brains of patients with prion diseases, the therapeutic effects are still uncertain., (© 2011 Japanese Society of Neuropathology.)

Protein-bound polysaccharide K (PSK) is a clinical immunotherapeutic agent that exhibits various biological activities, including anti-tumor and anti-microbial effects. In the present study, we report on the anti-prion activity of PSK. It inhibited the formation of protease-resistant abnormal prion protein in prion-infected cells without any apparent alterations in either the normal prion protein turnover or the autophagic function in the cells. Its anti-prion activity was predominantly composed of the high molecular weight component(s) of the protein portion of PSK. A single subcutaneous dose of PSK slightly but significantly prolonged the survival time of peritoneally prion-infected mice, but PSK-treated mice produced neutralizing antibodies against the anti-prion activity of PSK. These findings suggest that PSK is a new anti-prion substance that may be useful in elucidating the mechanism of prion replication, although the structure of the anti-prion component(s) of PSK requires further evaluation., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Gamma-aminobutyric acid type A (GABAA) receptor beta1 (gabrb1), a subunit of GABAA receptors involved in inhibitory effects on neurotransmission, was found to associate with the formation of protease-resistant prion protein in prion-infected neuroblastoma cells. Silencing of gabrb1 gene expression significantly decreased the abnormal prion protein level but paradoxically increased the normal prion protein level. Treatment with a gabrb1-specific inhibitor, salicylidene salicylhydrazide, dose-dependently decreased the abnormal prion protein level, but silencing of other GABAA receptor subunits' gene expression and treatments with the receptor antagonists and agonists did not. Therefore, gabrb1 involvement in abnormal prion protein formation is independent of GABAA receptors., (Copyright 2010 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.)

There is no established treatment for prion diseases; however, recently several drug candidates, including pentosan polysulfate and doxycycline, have been clinically used on a trial basis to prevent accumulation of abnormal prion protein in the brain. So far the outcome of the trials is still very far from the goal where a complete cure of the diseases is expected. In order to bridge the gap between the reality and the ideal, the followings are suggested. First, combination therapy needs to be developed against multi-targets: inhibition of prion replication; degradation and scavengery of prion; inhibition of prion-related neurodegeneration. Secondly, preclinical diagnostic means, by which healthy prion-carriers can be revealed before the onset of the diseases, should be explored for earlier therapeutic interventions. The last is to disclose intrinsic disease susceptibility factors and environmental factors, both of which could solely or jointly facilitate in suppressing prion replication and disease progress. Exploitation of these items should be tough but will be deserved for overcoming the fatal diseases.

Prion diseases are progressive neurological disorders due to abnormal prion protein (PrP(Sc)) deposition in the central nervous system. At present, there is no effective treatment available for any form of prion disease. Pentosan polysulfate (PPS) has been shown to prolong significantly the incubation period in mice with PrP(Sc) infection when administered to the cerebral ventricles in preclinical trials. In human studies conducted in European countries and Japan, intraventricular PPS was administered to patients with different forms of prion disease and was well tolerated. We report 11 patients with prion disease treated with intraventricular PPS at Fukuoka University from 2004. Cases included three familial CJD (two with V180I mutation, one GSS with P102L mutation), two iatrogenic CJD, and six sporadic CJD cases. At present, average survival period after treatment was 24.2 months (range, 4-49). Seven cases died of sepsis and pneumonia. Subdural effusion with various degrees was seen on CT scan in most cases. Except for these, adverse effects did not occur in the treatment period. Although our preliminary study of the new treatment with PPS by continuous intraventricular infusion showed no apparent improvement of clinical features in patients with prion disease, the possibility of extended survival in some patients receiving long-term PPS was suggested.

Recent outbreaks of variant Creutzfeldt-Jakob disease and iatrogenic Creutzfeldt-Jakob disease have aroused great concern in many countries and have necessitated the development of suitable therapies. We have demonstrated that sulfated glycans such as pentosan polysulfate and fucoidan, and amyloidophilic compounds such as amyloid dye derivatives, styrylbenzoazole derivatives, and phenylhydrazine derivatives have efficacies in prion-infected animals. Amyloidophilic compounds present potentialities not only as therapeutic candidates but also as prion amyloid imaging probes for use in nuclear medicine technology such as positron emission tomography. A representative of styrylbenzoazole compounds has been used recently for clinical trials of brain prion amyloid imaging in patients. On the other hand, a representative of phenylhydrazine compounds, compB, displays excellent effectiveness in prolonging the incubation times of infected animals when given orally. However, both its anti-prion effectiveness in vitro and its therapeutic efficacy in vivo are consistently dependent on the prion strain. This prion-strain-dependency is similarly observed in other amyloidophilic compounds. Therefore, aside from further improvement of the safety profiles and pharmacokinetic properties of such compounds, elucidation and management in the mechanism of the prion strain-dependent effectiveness is necessary. Nevertheless, because compB studies suggest that amyloidophilic compounds are also therapeutic candidates for Alzheimer's disease, amyloidophilic compounds might be attractive as drug candidates for various conformational diseases and hasten development of therapeutic drugs for prion diseases.

The establishment of effective therapeutic interventions for prion diseases is necessary. We report on a newly developed amyloidophilic compound that displays therapeutic efficacy when administered orally. This compound inhibited abnormal prion protein formation in prion-infected neuroblastoma cells in a prion strain-dependent manner: effectively for RML prion and marginally for 22L prion and Fukuoka-1 prion. When the highest dose (0.2% [wt/wt] in feed) was given orally to cerebrally RML prion-inoculated mice from inoculation until the terminal stage of disease, it extended the incubation periods by 2.3 times compared to the control. The compound exerted therapeutic efficacy in a prion strain-dependent manner such as that observed in the cell culture study: most effective for RML prion, less effective for 22L prion or Fukuoka-1 prion, and marginally effective for 263K prion. Its effectiveness depended on an earlier start of administration. The glycoform pattern of the abnormal prion protein in the treated mice was modified and showed predominance of the diglycosylated form, which resembled that of 263K prion, suggesting that diglycosylated forms of abnormal prion protein might be least sensitive or resistant to the compound. The mechanism of the prion strain-dependent effectiveness needs to be elucidated and managed. Nevertheless, the identification of an orally available amyloidophilic chemical encourages the pursuit of chemotherapy for prion diseases.

Prion diseases, or transmissible spongiform encephalopathies, are fatal, neurodegenerative disorders associated with the accumulation of a misfolded infectious prion protein which is made by a posttranslational conformational change of the host-encoded cellular prion protein. A large number of studies to reveal the pathogenesis of prion diseases have been done using such experimental models as animals, cell cultures and cell-free systems over the past 30 years. The prion pathogenesis is still enigmatic, but current explosion of the knowledge about prion biology has led to the discovery of either more reliable diagnostic measurements or more beneficial therapeutic candidates. Here, the recent advances are reviewed in the diagnostics and the therapeutics for prion diseases.

Dietary seaweed fucoidan delays the onset of disease of enterally infected mice with scrapie when given orally for 6 days after infection, but not when given before the infection. This effect was not modified at a tested fucoidan dose range and appeared to reach the maximum level at a concentration of 2.5% or less in feed. Daily uptake of fucoidan might be prophylactic against prion diseases caused by ingestion of prion-contaminated materials, although further evaluation of its pharmacology remains to be done.

Human transmissible spongiform encephalopathies (TSEs), also known as prion diseases, are caused by the accumulation of an abnormal isoform of the prion protein in the CNS. Creutzfeldt-Jakob disease in its sporadic form is the most frequent type of human TSE. At present, there is no proven specific or effective treatment available for any form of TSE. Pentosan polysulfate (PPS) has been shown to prolong the incubation period when administered to the cerebral ventricles in a rodent TSE model. Cerebroventricular administration of PPS has been carried out in 26 patients with TSEs and has been shown to be well tolerated in doses < or = 220 microg/kg/day. Proof of efficacy has been difficult because the specific and objective criteria for measurement of response have not been established yet. Preliminary clinical experience confirms extended survival in patients with variant Creutzfeldt-Jakob disease receiving intraventricular PPS; however, it is still not clear if this is due to PPS itself. Further prospective investigations of long-term intraventricular PPS administration are essential for the assessment of its effects.

Prion diseases, or transmissible spongiform encephalopathies, are fatal, neurodegenerative diseases that include Creutzfeldt-Jacob disease (CJD) in humans, bovine spongiform encephalopathy (BSE) and scrapie in animals. Prion diseases are characterized by the accumulation of a misfolded prion protein, PrPSc, which is made by a posttranslational conformational change of the host-encoded cellular prion protein, PrPC. The process of the conformational change remains enigmatic, but a large number of researches on the therapeutic intervention have been done in experimental models over the past 30 years. Against the background of the occurrence of variant CJD in the UK in the 1990s, which is considered to occur by transmission of the BSE agent and to possibly spread through secondary infection via blood transfusion, the research on the development of therapeutic agents has been accelerated using an increasing number of disease models in animals, cells and in vitro system. Candidate therapeutic targets for prion diseases include the following four factors: the PrPC; the PrPSc; the cellular factors associated with the conversion of PrPC into PrPSc; the cellular factors responsible for the neurodegenerative processes. In this article, recent advances in the therapeutic development for prion diseases on the basis of molecular targeting are reviewed, and its future perspectives are discussed.

Recent prevalence of acquired forms of transmissible spongiform encephalopathies (TSEs) has urged the development of early diagnostic measures as well as therapeutic interventions. To extend our previous findings on the value of amyloid imaging probes for these purposes, styrylbenzoazole derivatives with better permeability of blood-brain barrier (BBB) were developed and analyzed in this study. The new styrylbenzoazole compounds clearly labeled prion protein (PrP) plaques in brain specimens from human TSE in a manner irrespective of pathogen strain, and a representative compound BF-168 detected abnormal PrP aggregates in the brain of TSE-infected mice when the probe was injected intravenously. On the other hand, most of the compounds inhibited abnormal PrP formation in TSE-infected cells with IC50 values in the nanomolar range, indicating that they represent one of the most potent classes of inhibitor ever reported. BF-168 prolonged the lives of mice infected intracerebrally with TSE when the compound was given intravenously at the preclinical stage. The new compounds, however, failed to detect synaptic PrP deposition and to show pathogen-independent therapeutic efficacy, similar to the amyloid imaging probes we previously reported. The compounds were BBB permeable and non-toxic at doses for imaging and treatment; therefore, they are expected to be of practical use in human TSE.

More than one hundred victims of iatrogenic CJD with cadaveric dura mater grafting have been recognized in Japan, and the people have been also exposed to a risk of outbreaks of variant CJD. These diseases are distinct from other forms of prion diseases as well as other neuropsychiatric disorders, but on an early clinical stage, their differential diagnoses from other atypical forms of prion diseases are not necessarily easy. Thus, atypical forms of prion diseases were overviewed and discussed here. In addition, data on recent clinical trials of enteral antimalarial drug (quinacrine or quinine) treatment or intracerebroventricular pentosan polysulfate treatment were presented and discussed, because research progress in the therapeutics for prion diseases has been remarkably made on the basis of the prevalence of those acquired forms of prion diseases.

Diagnostic imaging probes have been developed to monitor cerebral amyloid lesions in patients with neurodegenerative disorders. A thioflavin derivative, 2-[4'-(methylamino)phenyl] benzothiazole (BTA-1) and a Congo red derivative, (trans, trans),-1-bromo-2,5-bis-(3-hydroxycarbonyl-4-hydroxy)styrylbenzene (BSB) are representative chemicals of these probes. In this report, the two chemicals were studied in transmissible spongiform encephalopathies (TSE). Both BTA-1 and BSB selectively bound to compact plaques of prion protein (PrP), not only in the brain specimens of certain types of human TSE, but also in the brains of TSE-infected mice when the probes were injected intravenously. The chemicals bound to plaques in the brains were stable and could be detected for more than 42 h post-injection. In addition, the chemicals inhibited abnormal PrP formation in a cellular model of TSE with IC(50) values of 4 nM for BTA-1 and 1.4 micro M for BSB. In an experimental mouse model, the intravenous injection of 1 mg BSB prolonged the incubation period by 14 %. This efficacy was only observed against the RML strain and not the other strains examined. These observations suggest that these chemicals bind directly to PrP aggregates and inhibit new formation of abnormal PrP in a strain-dependent manner. Both BTA-1 and BSB can be expected to be lead chemicals not only for imaging probes but also for therapeutic drugs for TSEs caused by certain strains.

Because a definite diagnosis of prion diseases relies on the detection of the abnormal isoform of prion protein (PrPSc), it has been urgently necessary to establish a non-invasive diagnostic test to detect PrPSc in human prion diseases. To evaluate diagnostic usefulness and reliability of the detection of protease-resistant prion protein in urine, we extensively analyzed proteinase K (PK)-resistant proteins in patients affected with prion diseases and control subjects by Western blot, a coupled liquid chromatography and mass spectrometry analysis, and N-terminal sequence analysis. The PK-resistant signal migrating around 32 kDa previously reported by Shaked et al. (Shaked, G. M., Shaked, Y., Kariv-Inbal, Z., Halimi, M., Avraham, I., and Gabizon, R. (2001) J. Biol. Chem. 276, 31479-31482) was not observed in this study. Instead, discrete protein bands with an apparent molecular mass of approximately 37 kDa were detected in the urine of many patients affected with prion diseases and two diseased controls. Although these proteins also gave strong signals in the Western blot using a variety of anti-PrP antibodies as a primary antibody, we found that the signals were still detectable by incubation of secondary antibodies alone, i.e. in the absence of the primary anti-PrP antibodies. Mass spectrometry and N-terminal protein sequencing analysis revealed that the majority of the PK-resistant 37-kDa proteins in the urine of patients were outer membrane proteins (OMPs) of the Enterobacterial species. OMPs isolated from these bacteria were resistant to PK and the PK-resistant OMPs from the Enterobacterial species migrated around 37 kDa on SDS-PAGE. Furthermore, nonspecific binding of OMPs to antibodies could be mistaken for PrPSc. These findings caution that bacterial contamination can affect the immunological detection of prion protein. Therefore, the presence of Enterobacterial species should be excluded in the immunological tests for PrPSc in clinical samples, in particular, urine.

The therapeutic efficacy of direct drug infusion into the brain, the target organ of transmissible spongiform encephalopathies, was assessed in transgenic mice intracerebrally infected with 263K scrapie agent. Pentosan polysulfate (PPS) gave the most dramatic prolongation of the incubation period, and amphotericin B had intermediate effects, but antimalarial drugs such as quinacrine gave no significant prolongation. Treatment with the highest dose of PPS at an early or late stage of the infection prolonged the incubation time by 2.4 or 1.7 times that of the control mice, respectively. PPS infusion decreased not only abnormal prion protein deposition but also neurodegenerative changes and infectivity. These alterations were observed within the brain hemisphere fitted with an intraventricular infusion cannula but not within the contralateral hemisphere, even at the terminal disease stage long after the infusion had ended. Therapeutic effects of PPS were also demonstrated in mice infected with either RML agent or Fukuoka-1 agent. However, at doses higher than that providing the maximal effects, intraventricular PPS infusion caused adverse effects such as hematoma formation in the experimental animals. These findings indicate that intraventricular PPS infusion might be useful for the treatment of transmissible spongiform encephalopathies in humans, providing that the therapeutic dosage is carefully evaluated.

We previously reported that quinacrine inhibited the formation of an abnormal prion protein (PrPres), a key molecule in the pathogenesis of transmissible spongiform encephalopathy, or prion disease, in scrapie-infected neuroblastoma cells. To elucidate the structural aspects of its inhibiting action, various chemicals with a quinoline ring were screened in the present study. Assays of the scrapie-infected neuroblastoma cells revealed that chemicals with a side chain containing a quinuclidine ring at the 4 position of a quinoline ring (represented by quinine) inhibited the PrPres formation at a 50% inhibitory dose ranging from 10(-1) to 10(1) micro M. On the other hand, chemicals with a side chain at the 2 position of a quinoline ring (represented by 2,2'-biquinoline) more effectively inhibited the PrPres formation at a 50% inhibitory dose ranging from 10(-3) to 10(-1) micro M. A metabolic labeling study revealed that the action of quinine or biquinoline was not due to any alteration in the biosynthesis or turnover of normal prion protein, whereas surface plasmon resonance analysis showed a strong binding affinity of biquinoline with a recombinant prion protein. In vivo studies revealed that 4-week intraventricular infusion of quinine or biquinoline was effective in prolonging the incubation period in experimental mouse models of intracerebral infection. The findings suggest that quinoline derivatives with a nitrogen-containing side chain have the potential of both inhibiting PrPres formation in vitro and prolonging the incubation period of infected animals. These chemicals are new candidates for therapeutic drugs for use in the treatment of transmissible spongiform encephalopathies.

Recent outbreaks of acquired forms of human prion diseases in younger people are promoting the development of prophylaxis and therapeutics. One possible target for therapeutic interventions is to inhibit the biosynthesis and accumulation of an abnormal isoform of prion protein, which is supposed to be a pathogen itself. Here, our current in-vitro and in-vivo data on anti-prion chemicals with amyloid binding capacity, represented by pentosan polysulfate and thioflavin-related chemicals, are presented, and structural aspects on the interaction between prion protein molecules and anti-prion chemicals including quinacrine are discussed. The current status of clinical trials using quinacrine or pentosan polysulfate is also reviewed. Finally, key structure(s) in the prion protein molecules, important to inhibit the conversion into abnormal prion protein molecules, are discussed in terms of pharmacology, and possibility of the in-silico rational drug design is also referred. Exploitation of anti-prion drugs should facilitate to solve the enigma of "prion" which can be the only creature against the central dogma, in addition to its contributing to the people with the illness or the people in high risks.

Clusterin (apolipoprotein J), a multifunctional protein involved in amyloidogenesis in Alzheimer's disease, was studied immunohistochemically in both human transmissible spongiform encephalopathies (TSEs) and a mouse model of human TSE. Clusterin immunoreactivity was co-localized with plaque-type deposits but not with punctate-type prion protein (PrP) deposits in human TSEs. On the other hand, clusterin-positive astrocytes were readily demonstrated in the regions of punctate PrP deposits, but not around plaque PrP deposits despite the presence of surrounding astrocytes. Clusterin expression in astrocytes was not disease specific, but the punctate immunoreactivity for clusterin was more prominently demonstrated in TSEs with punctate PrP deposits. Serial analysis in the mouse model of human TSE revealed that clusterin expression in astrocytes was enhanced in the lesions with punctate-type PrP deposits during the disease progression. Thus, the induction of clusterin expression in astrocytes could be more enhanced by punctate-type PrP deposits than by plaque-type deposits. The clusterin molecules co-localized in plaque PrP deposits might be derived not from surrounding astrocytes but from other resources such as cerebrospinal fluid and blood plasma, both of which contain clusterin in significant amounts. Taken together with previously reported findings of the anti-amyloidogenic property in clusterin, our findings suggest that clusterin may be induced as one of the important molecules participating in the neurodegeneration caused by abnormally deposited PrP.

A tetraspan protein CD9, normally expressed in the myelin sheath of the central and peripheral nervous system, was identified to be up-regulated in mouse brains infected with transmissible spongiform encephalopathy (TSE), by mRNA differential display screening. To elucidate its role in the neurodegeneration process observed in TSE, CD9 expression was examined in the murine disease model and in the human disease materials. Up-regulation of CD9 gene expression in the TSE-infected mouse brains was detected as early as a preclinical stage, when abnormal prion protein deposition and vacuolation were obviously manifested in the internal capsule and thalamus. In contrast, other myelin protein genes showed a reverse pattern of CD9 gene expression. Enhanced CD9 expression was immunohistochemically detected in the astrocytes of such pathological regions. In human specimens of TSE, enhanced CD9 immunoreactivity was observed in the astrocytes and some oligodendrocytes in the brains, but no relevant alteration in CD9 immunoreactivity was observed in the other organs or tissues. Positive CD9 immunoreactivity in astrocytes was also manifest in other neurological disorders in a less prominent manner. The findings indicate that up-regulated CD9 plays a role in glial cells in pathological conditions, especially in such a devastating condition as TSE.

We herein report an immunohistochemical and a Western blot analysis on metal/free radical chelating proteins, metallothioneins (MTs; MT-I/II and MT-III), in the brains of human prion disease patients with or without prion protein gene mutation and polymorphism. Irrespective of the isoforms of MTs, the immunoreaction was detected in the cytoplasm and processes of the astrocytes in the cerebral cortex and white matter in normal controls and prion disease brains. Although the immunoreactivities for MTs in Creutzfeldt-Jakob disease (CJD) brains varied from case to case, they were generally dependent upon the disease duration. In CJD patients with a relatively long disease course, the immunoreaction for both MT-I/II and MT-III in the astrocytes was significantly reduced, and this finding was not modified by the genotypes of the patients. On the other hand, in patients with Gerstmann-Sträussler-Scheinker syndrome, MT-I/II immunoreactivity in the astrocytes was exclusively reduced, while the immunoreaction for MT-III was relatively well preserved. Especially the astrocytes in the vicinities of the kuru plaques exhibited a weak or no immunoreaction even for MTs but a strong immunoreaction for glial fibrillary acidic protein. A quantitative Western blot analysis also revealed that MT-I/II protein accumulated in CJD brain with a short disease duration, whereas MT-III in CJD brain with a long disease duration was statistically significantly reduced in comparison to the normal brains. These findings suggest that the protein expression of MTs in the astrocytes is thus regulated differentially among human prion diseases and modified locally by such abnormal prion protein depositions as kuru plaques., (Copyright 2000 S. Karger AG, Basel)

The pathogenesis of neuroinvasion in Creutzfeldt-Jakob disease and other transmissible spongiform encephalopathies following the peripheral uptake of a disease agent is still not fully understood. The possibility of neuroinvasion either being established or being accelerated by an insult to the brain has not previously been tested. The experiment described herein was designed to examine this possibility by wounding the brain following an intraperitoneal challenge with a mouse-adapted strain of human transmissible spongiform encephalopathy, Fukuoka-1 strain. The results showed that brain injury introduced in any period before the appearance of cerebral abnormal prion protein deposition modified neither the clinical features, including the incubation period, nor the histopathology of the mice. Our findings suggest that neurovirulence of the agent may not be sufficiently promoted by brain injury.

The causal link of a new variant of CJD (v-CJD) with bovine spongiform encephalopathy (BSE) has led to world-wide panic. BSE emerged in 1986 through dietary products contaminated with scrapie pathogen, BSE case reports increased in number up to 37,000/year in 1993, then declined in 1994 when the first case of v-CJD emerged. There is a 3-year gap between the emergence of BSE and the introduction of a ban on the use of specified bovine offal in human food. People might have consumed dietary products contaminated with BSE pathogen for the period. Species barrier which has protected human from being transmitted with sheep scrapie pathogen might not work so well in cow-to-human transmission as in sheep-to-human. There are familial forms and sporadic forms of human prion diseases. The familial prion diseases are always related to prion protein (PrP) gene mutations. Sporadic forms of prion diseases are composed of sporadic CJD, iatrogenic CJD and kuru. Sporadic CJD occurs in elder people and shows cortical signs and periodic synchronous discharges (PSD) in short clinical course and pathologically spongiform degeneration and abnormal PrP deposition in synapse structures, but no amyloid plaque deposition in the brain is observed. Since the v-CJD patients had no mutations in PrP gene, v-CJD belongs to sporadic forms of prion diseases. v-CJD shows quite different clinicopathological features from those of sporadic CJD, rather shows similar features to iatrogenic CJD of pituitary hormone and kuru. These three diseases share several features, which are younger patient age, main clinical manifestation of cerebellar signs, negative or rare record of PSD, and PrP amyloid plaque deposition in the brain. The patients of v-CJD, however, had no history of exposure to iatrogenic factors and of cannibalism. Also they did not have a valine polymorphism at PrP codon 129 which is frequently observed in the patients with iatrogenic CJD and kuru. Thus, v-CJD is a quite novel entity in human prion diseases.

K. Sasaki, K. Doh-ura, Y. Wakisaka, H. Tomoda and T. Iwaki (2004)Neuropathology and Applied Neurobiology, doi: 10.1111/j.1365-2990.2004.00592.xFatal familial insomnia with an unusual prion protein deposition pattern: an autopsy report with an experimental transmission studyWe recently performed apost-mortemexamination on a Japanese patient who had a prion protein gene mutation responsible for fatal familial insomnia (FFI). The patient initially developed cerebellar ataxia, but finally demonstrated insomnia, hyperkinetic delirium, autonomic signs and myoclonus in the late stage of the illness. Histological examination revealed marked neuronal loss in the thalamus and inferior olivary nucleus; however, prion protein (PrP) deposition was not proved in these lesions by immunohistochemistry. Instead, PrP deposition and spongiform change were both conspicuous within the cerebral cortex, whereas particular PrP deposition was also observed within the cerebellar cortex. The abnormal protease-resistant PrP (PrPres) molecules in the cerebral cortex of this case revealed PrPres type 2 pattern and were compatible with those of FFI cases, but the transmission study demonstrated that a pathogen in this case was different from that in a case with classical FFI. By inoculation with homogenate made from the cerebral cortex, the disease was transmitted to mice, and neuropathological features that were distinguishable from those previously reported were noted. These findings indicate the possibility that a discrete pathogen was involved in the disease in this case. We suggest that not only the genotype of the PrP gene and some other as yet unknown genetic factors, but also the variation in pathogen strains might be responsible for the varying clinical and pathological features of this disease. [ABSTRACT FROM AUTHOR]