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.

Neurotoxicity of the putative transmembrane domain of the prion protein

It has been shown recently that the generation of an abnormal transmembrane form of the prion protein ((Ctm)PrP) is involved in the neurodegeneration process during inherited and infectious prion diseases but a causative relationship has never been established. We wanted to know if and how the proposed transmembrane domain of PrP could induce neuronal dysfunction. Thus, we investigated the neurotoxic properties of two peptides whose sequences are encompassed within this domain. We show that PrP peptides 118-135 and 105-132 as well as an amidated more soluble peptide 105-132 induce the death of pure cortical neurons originating from normal and PrP knockout mice. This can be correlated with the high propensity of these peptides to insert stably into and to destabilize cell membranes. Through this study, we have identified a novel mechanism of neurotoxicity for PrP, which directly involves membrane perturbation; this mechanism is independent of fibril formation and probably corresponds to the effect of the transmembrane insertion of (Ctm)PrP.

New insight into abnormal prion protein using monoclonal antibodies

Studies of abnormal prion protein (PrPres) are hindered by the lack of specific monoclonal antibodies (mAbs), and the relationships between PrPres, infectivity, and strain specificity in prion diseases are still subject to debate. We have studied PrPres with new mAbs produced against PrP in mice using various immunization strategies. PrPres was analyzed by Western blot with different prion strains in various hosts. Differences in the electrophoretic pattern of human PrPres revealed by these antibodies provide new insight into PrPres cleavage by proteases and interpretation of strain typing. This study confirms that the N-terminal extremity of PrPres is differentially sensitive to proteases. Conversely, the C-terminal extremity, which resists proteolysis, seems to be abnormally detectable by antibodies in ultrastructural studies. This work confirms the highly complex role of PrPres in prion diseases and provides new tools which will be made available to facilitate progress in qualitative and quantitative studies of PrP.

Gene expression in scrapie. Cloning of a new scrapie-responsive gene and the identification of increased levels of seven other mRNA transcripts

To define genes associated with or responsible for the neurodegenerative changes observed in transmissible spongiform encephalopathies, we analyzed gene expression in scrapie-infected mouse brain using "mRNA differential display." The RNA transcripts of eight genes were increased 3-8-fold in the brains of scrapie-infected animals. Five of these genes have not previously been reported to exhibit increased expression in this disease: cathepsin S, the C1q B-chain of complement, apolipoprotein D, and two previously unidentified genes denominated scrapie-responsive gene (ScRG)-1 and ScRG-2, which are preferentially expressed in brain tissue. Increased expression of the three remaining genes, beta2 microglobulin, F4/80, and metallothionein II, has previously been reported to occur in experimental scrapie. Kinetic analysis revealed a concomitant increase in the levels of ScRG-1, cathepsin S, the C1q B-chain of complement, and beta2 microglobulin mRNA as well as glial fibrillary acidic protein and F4/80 transcripts, markers of astrocytosis and microglial activation, respectively. In contrast, the level of ScRG-2, apolipoprotein D, and metallothionein II mRNA was only increased at the terminal stage of the disease. ScRG-1 mRNA was found to be preferentially expressed in glial cells and to code for a short protein of 47 amino acids with a strong hydrophobic N-terminal region.

[Bovine spongiform encephalopathy. Second update of data collected since the report of February 6, 1996]

The observation in 1995 and 1996 of 12 cases of a new variant of Creutzfeldt-Jakob disease (V-CJD) in U.K. suggested a possible relation between this human cases and bovine spongiform encephalopathy (BSE). Recent papers about this topic are reviewed: BSE transmission to macaques, transmission of scrapie with embryo transfer, incidence of maternal transmission, PrP protein released by platelets, diagnostic test by detection of PrP protein in tissues of sheep, epidemiology of BSE, french regulations, identification of cattle in U.K.

Pharmacological studies of a new derivative of amphotericin B, MS-8209, in mouse and hamster scrapie

Transmissible subacute spongiform encephalopathies (TSSE) are neurodegenerative diseases characterized by the presence of a modified, partially proteinase-resistant host protein, PrPSc, which accumulates in the brains of infected individuals. Recently it has been reported that amphotericin B (AmB) treatment of hamsters infected with scrapie strain 263K prolongs the incubation period of the disease, and dissociates in vivo replication of the scrapie agent from PrPSc accumulation. We report here on data obtained after treatment with AmB and one of its derivatives, MS-8209, in experimental scrapie of mouse and hamster. Treatment was carried out by the intraperitoneal route 6 days per week, at three different dosages initiated at the time of infection. Two regimens were used: during the early time of infection or throughout the experimental infection. Results indicate that MS-8209 was as efficient as AmB in prolonging the incubation time and decreasing PrPSc accumulation in the hamster scrapie model. A dose-dependent response was observed in mice treated early after experimental infection. At a dose of 2.5 mg/kg, MS-8209 significantly prolonged the incubation period (by 11.9%). In long-term treatment of mice, MS-8209 and AmB markedly reduced PrPSc levels in the preclinical stage of the disease. These data demonstrate that the effect of AmB is not restricted to one model (hamster-263K). This regimen leads to an inversion of the PrPSc to proteinase-sensitive protein (PrPSens) ratio, suggesting PrPSens (presumably cellular PrPC) accumulation occurs before its conversion into PrPSc. As it has been shown that AmB does not modify the infectivity titre, we conclude that the drugs could act by inhibiting either the interaction of the scrapie agent with PrPSens during the early times of infection or the conversion of PrPSens into PrPSc.

Recombinant human growth hormone and insulin-like growth factor I induce PrP gene expression in PC12 cells

Growth factors like NGF are known to increase the expression of PrP gene, a housekeeping gene which is responsible for susceptibility to transmissible spongiform encephalopathies. We evaluated in vitro the effect of recombinant human growth hormone (hGH) and one of its in vivo effectors, the insulin-like growth factor I (IGF-I), on PrP gene expression in PC12 cells. We observed a 30% increase of PrP mRNA level after 7 day treatment by hGH at 10 micrograms/ml and potentiation of NGF effect (reaching four times baseline expression as opposed to three times baseline with NGF alone). IGF-I induced a dose-dependent increase of PrP mRNA up to twice baseline at a dose of 100 ng/ml and had an additive effect with NGF at 10 ng/ml. These preliminary results indicate that growth promoting factors may play a role in the PrP gene regulation within neuron-like cells.