Drug therapy in human and experimental transmissible spongiform encephalopathy

During the past 30 years, over 60 different chemical compounds have been used to treat experimental animals infected with transmissible spongiform encephalopathies (TSE), including a wide variety of anti-infectious agents, immunomodulating drugs, and chemicals interacting with the lympho-reticular system. Some compounds achieved a prolongation of the incubation period, but this effect decreased or disappeared when they were administered at or near the onset of symptomatic disease. Recent in vitro and tissue culture studies support earlier speculation about the importance of a chemical structure containing both water-soluble and lipid-soluble components, evidently as a means of interaction with the misfolded membrane-bound 'prion' protein. A number of compounds shown to eliminate the protein (or infectivity) in TSE-infected tissue cultures are the subject of ongoing studies in animals, and are under consideration for human drug trials. As with other recalcitrant infections, combinations of drugs with different modes of action are likely to be necessary for any effective therapy. Also, very recent work in developing antibodies that can neutralize in vitro infection (and, in conjunction with genetic engineering, in vivo infection) has renewed interest in the strategies of both active and passive immunization.

Creutzfeldt-Jakob disease and the eye. I. Background and patient management

This article attempts to summarise our current understanding of TSEs as they affect man. Specific aspects relevant to ophthalmological practice, in particular the management of patients in day-to-day clinical practice and with respect to corneal transplantation, have been discussed. In the companion article we discuss the specific ophthalmic and neuro-ophthalmic features of these diseases.

Reversion of prion protein conformational changes by synthetic beta-sheet breaker peptides

BACKGROUND

Transmissible spongiform encephalopathies are associated with a structural transition in the prion protein that results in the conversion of the physiological PrPc to pathological PrP(Sc). We investigated whether this conformational transition can be inhibited and reversed by peptides homologous to the PrP fragments implicated in the abnormal folding, which contain specific residues acting as beta-sheet blockers (beta-sheet breaker peptides).

METHODS

We studied the effect of a 13-residue beta-sheet breaker peptide (iPrP13) on the reversion of the abnormal structure and properties of PrP(Sc) purified from the brains of mice with experimental scrapie and from human beings affected by sporadic and variant Creutzfeldt-Jakob disease. In a cellular model of familial prion disease, we studied the effect of the peptide in the production of the abnormal form of PrP in intact cells. The influence of the peptide on prion infectivity was studied in vivo by incubation time assays in mice with experimental scrapie.

FINDINGS

The beta-sheet breaker peptide partly reversed in-vitro PrP(Sc) to a biochemical and structural state similar to that of PrPc. The effect of the peptide was also detected in intact cells. Treatment of prion infectious material with iPrP13 delayed the appearance of clinical symptoms and decreased infectivity by 90-95% in mice with experimental scrapie.

INTERPRETATION

Beta-sheet breaker peptides reverse PrP conformational changes implicated in the pathogenesis of spongiform encephalopathies. These peptides or their derivatives provide a useful tool to study the role of PrP conformation and might represent a novel therapeutic approach for prion-related disorders.

Creutzfeldt-Jakob disease, new variant creutzfeldt-jakob disease, and bovine spongiform encephalopathy

Creutzfeldt-Jakob disease (CJD) is a subacute spongiform encephalopathy (SSE) that is manifested by a variety of neurologic signs that usually include dementia, myoclonus, and an abnormal electroencephalogram (EEG). In 1996, a new variant of CJD (nvCJD) with a somewhat distinctive clinical presentation and neuropathology was reported in adolescents and young adults, a cohort of patients not normally affected with CJD. The appearance of nvCJD coincided temporally and geographically with the emergence of an SSE in cattle known as bovine spongiform encephalopathy (BSE), or mad cow disease. This article discusses the clinical syndrome, pathology, and pathogenesis of classical CJD, nvCJD, and other human SSEs, as well as the link between BSE and nvCJD.

Effectiveness of anthracycline against experimental prion disease in Syrian hamsters

Prion diseases are transmissible neurodegenerative conditions characterized by the accumulation of protease-resistant forms of the prion protein (PrP), termed PrPres, in the brain. Insoluble PrPres tends to aggregate into amyloid fibrils. The anthracycline 4'-iodo-4'-deoxy-doxorubicin (IDX) binds to amyloid fibrils and induces amyloid resorption in patients with systemic amyloidosis. To test IDX in an experimental model of prion disease, Syrian hamsters were inoculated intracerebrally either with scrapie-infected brain homogenate or with infected homogenate coincubated with IDX. In IDX-treated hamsters, clinical signs of disease were delayed and survival time was prolonged. Neuropathological examination showed a parallel delay in the appearance of brain changes and in the accumulation of PrPres and PrP amyloid.

Creutzfeldt-Jakob disease: therapeutic strategies

Creutzfeldt-Jakob disease (CJD) is a rare neurodegenerative illness which belongs to the group of transmissible subacute spongiform encephalopathies (TSSE). Today, no treatment is available for TSSE. The appearance of a new variant of CJD, which affects young people and could be linked to so-called ;mad cow disease', has stimulated researchers to develop new therapies against CJD. A few drugs have already been shown to delay the onset of experimental TSSE. They could contribute to the understanding of the pathogenic mechanisms involved in TSSE and, therefore, could be the basis for therapeutic strategies against CJD.

Differential effects of a new amphotericin B derivative, MS-8209, on mouse BSE and scrapie: implications for the mechanism of action of polyene antibiotics

Mice were infected intracerebrally with the bovine spongiform encephalopathy (BSE) or the scrapie agent and treated during 8 weeks postinfection to test the protective effect of a new amphotericin B (AmB) derivative, MS-8209, in experimental transmissible spongiform encephalopathies. The results show that (i) the treatment prolonged the incubation period of both BSE-infected and scrapie-infected mice, (ii) MS-8209 and AmB were much more efficient in delaying the onset of scrapie than that of BSE, and (iii) a delay in Prp-res (proteinase K-resistant prion protein) and GFAP (glial fibrillary acidic protein) accumulation was observed in the brains of scrapie-infected mice, but was not significant in BSE-infected mice. The analysis of the molecular and clinical results strongly suggests a common mechanism of action of this category of drugs on the different transmissible spongiform encephalopathy strains. This could be due to an interaction with the PrP transconformation process leading to the formation of PrP-res.

[Natural history of human transmissible subacute spongiform encephalopathies]

Transmissible spongiform subacute encephalopathies are rare fatal diseases which comprise in humans Creutzfeldt-Jakob disease (CJD), Kuru, Gerstmann Straüssler Scheinker, and Fatal Familial Insomnia (FFI). Their etiologic agents (Prions or TSA, for transmissible spongiform encephalopathy agents) are still unknown. TSA/prions resist all the physico-chemical procedures which are efficient against the other micro-organisms. These diseases are characterised by a long incubation period which may be as long as 40 years. Clinically, symptoms are only neurological, without any sign of immune response either in blood or cerebrospinal fluid. Neuropothalogy includes neuronal vacuolisation, neuronal death, spongiosis, gliosis with hyperastrocytosis. The biochemical hallmark is the post-translational accumulation of a host-encoded protein, the prion protein (PrP). In infected individuals, PrP accumulates under a proteinase K resistant isoform (PrP-res) which amino acid sequence does not differ from the normal isoform (PrP-c) PrP gene (PRNP) is located on chromosome 20 in humans, and is the major determinant of the susceptibility to TSA/prions. Several hypotheses have been raised to explain the uncommon biologic properties of these agents. The prion hypothesis postulates that the agent is only composed of proteins, mainly the PrP-res. Others support the presence of a host independent genetic information of which PrP could be the virulence factor.

The biology and molecular biology of scrapie-like diseases

The transmissible spongiform encephalopathies (TSE's) are degenerative diseases of the central nervous system which naturally affect man (Creutzfeldt-Jakob disease [CJD], Gerstmann-Sträussler syndrome [GSS], kuru), sheep and goats (scrapie), cattle (bovine spongiform encephalopathy [BSE]), mink (transmissible mink encephalopathy), mule deer, elk and antelope (chronic wasting disease). Spongiform encephalopathies have also been diagnosed in captive species of zoo antelope and in domestic cats. Much has been written about these maladies in the wake of the BSE outbreak, the tragic cases of CJD in recipients of cadaver-derived human growth hormone, sex hormones or dura mater and this has stimulated a continuing public health debate about the transmissibility, prevalence and clinical variability of scrapie, CJD and related ("prion") diseases. Prions (Weissmann, Liautard, this volume) and the human (Kretzschmar, this volume) and cattle (Wilesmith, Marsh, this volume) diseases are described in more detail elsewhere. This article presents a brief overview of the biology and molecular cell biology of scrapie and rodent models of these diseases.

Experimental drug treatment of scrapie: a pathogenetic basis for rationale therapeutics

Pharmacological treatment with polyanions or amphotericin B in hamsters with experimental scrapie reveals that it is possible to delay the appearance of the disease only when the drug is given before the invasion of the agent into the clinical target areas of the brain. We suggest such early treatment may be possible for individuals at high risk of acquiring the disease, such as healthy mutation-positive relatives of patients with familial Creutzfeldt-Jakob disease or Gerstmann-Sträussler syndrome, or recipients of potentially contaminated pituitary-extracted human growth hormone.