Over the last 30 years, many drugs have been tested both in cell culture and in vivo for their ability to prevent the generation of prions and the development of transmissible spongiform encephalopathies. Among the compounds tested, dendrimers are defined by their branched and repeating molecular structure. The anti-prion activity of new cationic phosphorus-containing dendrimers (P-dendrimers) with tertiary amine end-groups was tested. These molecules had a strong anti-prion activity, decreasing both PrP^Sc and infectivity in scrapie-infected cells at non-cytotoxic doses. They can bind PrP and decrease the amount of pre-existing PrP^Sc from several prion strains, including the BSE strain. More importantly, when tested in a murine scrapie model, the dendrimers were able to decrease PrP^Sc accumulation in the spleen by more than 80 %. These molecules have a high bio-availability and therefore exhibit relevant potential for prion therapeutics for at least post-exposure prophylaxis.

Recent progress determining the structure of the host-encoded prion protein (PrP^C) and the role of auxiliary molecules in prion replication permits a more rational approach in the development of therapeutic interventions. Our objective is to identify a new class of lead compounds that mimic the dominant negative PrP^Cmutants, which inhibit an abnormal isoform (PrP^Sc) formation. A computational search was conducted on the Available Chemicals Directory for molecules that mimic both the spatial orientation and basic polymorphism of PrP residues 168, 172, 215, and 219, which confer dominant negative inhibition. The search revealed 1,000 potential candidates that were visually analyzed with respect to the structure of this four-residue epitope on PrP^C. Sixty-three compounds were tested for inhibition of PrP^Scformation in scrapie-infected mouse neuroblastoma cells (ScN2a). Two compounds, Cp-60 (2-amino-6-[(2-aminophenyl)thio]-4-(2-furyl)pyridine-3,5-dicarbonitrile) and Cp-62 (N′1-({5-[(4,5-dichloro-1H-imidazol-1-yl)methyl]-2-furyl}carbonyl)-4 methoxybenzene-1-sulfonohydrazide), inhibited PrP^Scformation in a dose-dependent manner and demonstrated low levels of toxicity. A substructure search of the Available Chemicals Directory based on Cp-60 identified five related molecules, three of which exhibited activities comparable to Cp-60. Mimicking dominant negative inhibition in the design of drugs that inhibit prion replication may provide a more general approach to developing therapeutics for deleterious protein–protein interactions.

Our discovery of dominant-negative inhibition of prion formation in cultured cells provided an explanation for the resistance of some sheep to scrapie and humans to Creutzfeldt–Jakob disease. To determine whether dominant-negative inhibition occurs in vivo , we produced transgenic (Tg) mice expressing prion protein (PrP) with either the Q167R or Q218K mutation alone or in combination with wild-type (wt) PrP. Tg(MoPrP,Q167R) Prnp ^0/0 mice expressing mutant PrP at levels equal to non-Tg mice remained healthy for >550 days, indicating that inoculation with prions did not cause disease. Immunoblots of brain homogenates and histologic analysis did not reveal abnormalities. Tg(MoPrP,Q167R) Prnp ^+/+ mice expressing both mutant and wt PrP did not exhibit neurologic dysfunction, but their brains revealed low levels of the PrP pathogenic isoform (PrP ^Sc ), and sections showed numerous vacuoles and severe astrocytic gliosis at 300 days after inoculation. Both Tg(MoPrP,Q218K) Prnp ^0/0 and Tg(MoPrP,Q218K) Prnp ^+/+ mice expressing high levels of the transgene product remained healthy for >300 days after inoculation. Neither PrP ^Sc nor neuropathologic changes were found. Our studies demonstrate that although dominant-negative inhibition of wt PrP ^Sc formation occurs, expression of the dominant-negative PrP at the same level as wt PrP does not prevent prion formation completely. However, expression of dominant-negative PrP alone had no deleterious effects on the mice and did not support prion propagation.

The use of anti‐PrP antibodies represents one of the most promising strategies for the treatment of prion diseases. In the present study, we screened various anti‐PrP antibodies with the aim of identifying those that would block PrP^Sc replication in prion‐infected cell culture. Two antibodies, SAF34 recognizing the flexible octarepeats region on HuPrP protein, and SAF61 directed against PrP amino acid residues (144–152), not only inhibited PrP^Sc formation in prion‐infected neuroblastoma cells but also decreased the PrP^C levels in non‐infected N2a cells. In addition, treatment with both SAF34 and SAF61 antibodies decreased PrP^C and PrP^Sc levels in the cells synergistically. In the presence of both antibodies, our results showed that the mode of action which leads to the disappearance of PrP^Sc in cells is directly coupled to PrP^C degradation by reducing the half‐life of the PrP^C protein.

Environmental Health Perspectives is an Open Access journal published by the National Institute of Environmental Health Sciences. Environmental Health Perspectives is an Open Access journal published by the National Institute of Environmental Health Sciences.

Oxidative stress is recognized as one of the earliest and most intense pathological processes in Alzheimer’s disease (AD), and the antioxidant vitamin E has been shown to efficiently prevent amyloid plaque formation and neurodegeneration. Plasma phospholipid transfer protein (PLTP) has a major role in vitamin E transfers in vivo, and PLTP deficiency in mice is associated with reduced brain vitamin E levels. To determine the impact of PLTP on amyloid pathology in vivo, we analyzed the vulnerability of PLTP-deficient (PLTP-KO) mice to the toxic effects induced by intracerebroventricular injection of oligomeric amyloid-β_25–35 (Aβ_25–35) peptide, a non-transgenic model of AD. Under basal conditions, PLTP-KO mice showed increased cerebral oxidative stress, increased brain Aβ_1–42 levels, and a lower expression of the synaptic function marker synaptophysin, as compared with wild-type mice. This PLTP-KO phenotype was associated with increased memory impairment 1 week after Aβ_25–35 peptide injection. Restoration of brain vitamin E levels in PLTP-KO mice through a chronic dietary supplementation prevented Aβ_25–35-induced memory deficits and reduced cerebral oxidative stress and toxicity. We conclude that PLTP, through its ability to deliver vitamin E to the brain, constitutes an endogenous neuroprotective agent. Increasing PLTP activity may offer a new way to develop neuroprotective therapies.