Oxidative stress and neurodegeneration in prion diseases

Reactive oxygen species in biological systems: Pathways, associated diseases, and potential inhibitors-A review

Reactive oxygen species (ROS) are produced under normal physiological conditions and may have beneficial and harmful effects on biological systems. ROS are involved in many physiological processes such as differentiation, proliferation, necrosis, autophagy, and apoptosis by acting as signaling molecules or regulators of transcription factors. In this case, maintaining proper cellular ROS levels is known as redox homeostasis. Oxidative stress occurs because of the imbalance between the production of ROS and antioxidant defenses. Sources of ROS include the mitochondria, auto-oxidation of glucose, and enzymatic pathways such as nicotinamide adenine dinucleotide phosphate reduced (NAD[P]H) oxidase. The possible ROS pathways are NF-κB, MAPKs, PI3K-Akt, and the Keap1-Nrf2-ARE signaling pathway. This review covers the literature pertaining to the possible ROS pathways and strategies to inhibit them. Additionally, this review summarizes the literature related to finding ROS inhibitors.

Carnosic Acid and Carnosol Display Antioxidant and Anti-Prion Properties in In Vitro and Cell-Free Models of Prion Diseases

Prion diseases are transmissible encephalopathies associated with the conversion of the physiological form of the prion protein (PrP^C) to the disease-associated (PrP^Sc). Despite intense research, no therapeutic or prophylactic agent is available. The catechol-type diterpene Carnosic acid (CA) and its metabolite Carnosol (CS) from Rosmarinus officinalis have well-documented anti-oxidative and neuroprotective effects. Since oxidative stress plays an important role in the pathogenesis of prion diseases, we investigated the potential beneficial role of CA and CS in a cellular model of prion diseases (N2a22L cells) and in a cell-free prion amplification assay (RT-QuIC). The antioxidant effects of the compounds were confirmed when N2a22L were incubated with CA or CS. Furthermore, CA and CS reduced the accumulation of the disease-associated form of PrP, detected by Western Blotting, in N2a22L cells. This effect was validated in RT-QuIC assays, indicating that it is not associated with the antioxidant effects of CA and CS. Importantly, cell-free assays revealed that these natural products not only prevent the formation of PrP aggregates but can also disrupt already formed aggregates. Our results indicate that CA and CS have pleiotropic effects against prion diseases and could evolve into useful prophylactic and/or therapeutic agents against prion and other neurodegenerative diseases.

Melatonin: Regulation of Prion Protein Phase Separation in Cancer Multidrug Resistance

The unique ability to adapt and thrive in inhospitable, stressful tumor microenvironments (TME) also renders cancer cells resistant to traditional chemotherapeutic treatments and/or novel pharmaceuticals. Cancer cells exhibit extensive metabolic alterations involving hypoxia, accelerated glycolysis, oxidative stress, and increased extracellular ATP that may activate ancient, conserved prion adaptive response strategies that exacerbate multidrug resistance (MDR) by exploiting cellular stress to increase cancer metastatic potential and stemness, balance proliferation and differentiation, and amplify resistance to apoptosis. The regulation of prions in MDR is further complicated by important, putative physiological functions of ligand-binding and signal transduction. Melatonin is capable of both enhancing physiological functions and inhibiting oncogenic properties of prion proteins. Through regulation of phase separation of the prion N-terminal domain which targets and interacts with lipid rafts, melatonin may prevent conformational changes that can result in aggregation and/or conversion to pathological, infectious isoforms. As a cancer therapy adjuvant, melatonin could modulate TME oxidative stress levels and hypoxia, reverse pH gradient changes, reduce lipid peroxidation, and protect lipid raft compositions to suppress prion-mediated, non-Mendelian, heritable, but often reversible epigenetic adaptations that facilitate cancer heterogeneity, stemness, metastasis, and drug resistance. This review examines some of the mechanisms that may balance physiological and pathological effects of prions and prion-like proteins achieved through the synergistic use of melatonin to ameliorate MDR, which remains a challenge in cancer treatment.

Applied Proteomics in 'One Health'

‘One Health’ summarises the idea that human health and animal health are interdependent and bound to the health of ecosystems. The purpose of proteomics methodologies and studies is to determine proteins present in samples of interest and to quantify changes in protein expression during pathological conditions. The objectives of this paper are to review the application of proteomics technologies within the One Health concept and to appraise their role in the elucidation of diseases and situations relevant to One Health. The paper develops in three sections. Proteomics Applications in Zoonotic Infections part discusses proteomics applications in zoonotic infections and explores the use of proteomics for studying pathogenetic pathways, transmission dynamics, diagnostic biomarkers and novel vaccines in prion, viral, bacterial, protozoan and metazoan zoonotic infections. Proteomics Applications in Antibiotic Resistance part discusses proteomics applications in mechanisms of resistance development and discovery of novel treatments for antibiotic resistance. Proteomics Applications in Food Safety part discusses the detection of allergens, exposure of adulteration, identification of pathogens and toxins, study of product traits and characterisation of proteins in food safety. Sensitive analysis of proteins, including low-abundant ones in complex biological samples, will be achieved in the future, thus enabling implementation of targeted proteomics in clinical settings, shedding light on biomarker research and promoting the One Health concept.

Interplay between reactive oxygen species and autophagy in the course of age-related macular degeneration

Pathological biomolecules such as lipofuscin, methylglyoxal-modified proteins (the major precursors of advanced glycationend products), misfolding protein deposits and dysfunctional mitochondria are source of oxidative stress and act as strong autophagic stimulators in age-related macular degeneration. Disturbed autophagy accelerates progression of the disease, since it leads to retinal cells' death and activates inflammation by the interplay with the NLRP3 inflammasome complex. Vascular dysfunction and hypoxia, as well as circulating autoantibodies against autophagy regulators (anti-S100A9, anti-ANXA5, and anti-HSPA8, A9 and B4) compromise an autophagy-mediated mechanism as well. Metformin, the autophagic stimulator, may act as a senostatic drug to inhibit the senescent phenotype in the age-related macular degeneration. PGC-1α , Sirt1 and AMPK represent new therapeutic targets for interventions in this disease.

Phytochemical Constituents, Antioxidant Activity, and Toxicity Assessment of the Seed of Spondias mombin L. (Anacardiaceae)

Objectives

Increased generation of free radicals exceeding the antioxidant capacity of the host is deleterious. Thus new, potent, and safe antioxidants will be a valuable addition to the limited antioxidant arsenals available. Therefore, the antioxidant activity, cytotoxicity potential, and phytochemical constituents of the methanol extract of Spondias mombin seed (MESSM) were investigated.

Materials and Methods

2,2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO), and hydrogen peroxide (H₂O₂) were the antioxidant assays used. The cytotoxicity of MESSM was evaluated against a rhabdomyosarcoma (RD) cell line in a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide based assay. The phytochemical constituents of MESSM were identified using gas chromatography-mass spectrometry.

Results

MESSM produced better antioxidant activity in the DPPH (IC₅₀=58.64±1.49 μg/mL) and H₂O₂ (IC₅₀=44.03±5.57 μg/mL) assays than in the NO (IC₅₀=494.55±12.68 μg/mL, p<0.0001) assay. Moreover, MESSM was nontoxic (CC50=139.6±0.54 μg/mL) in comparison to cyclophosphamide (CC50=0.97±0.03 μg/mL) against the RD cell line. The major compounds in MESSM were dodecanoic acid (22.48%), tetradecanoic acid (17.95%), n-hexadecanoic acid (15.35%), capsaicin (12.11%), and dihydrocapsaicin (5.23%).

Conclusion

The seed extract of Spondias mombin contains nontoxic antioxidant compounds that could be explored in the pharmaceutical and cosmetics industries for the development of antioxidant agents.

Cellular Stress and General Pathological Processes

From the viewpoint of the general pathology, most of the human diseases are associated with a limited number of pathogenic processes such as inflammation, tumor growth, thrombosis, necrosis, fibrosis, atrophy, pathological hypertrophy, dysplasia and metaplasia. The phenomenon of chronic low-grade inflammation could be attributed to non-classical forms of inflammation, which include many neurodegenerative processes, pathological variants of insulin resistance, atherosclerosis, and other manifestations of the endothelial dysfunction. Individual and universal manifestations of cellular stress could be considered as a basic element of all these pathologies, which has both physiological and pathophysiological significance. The review examines the causes, main phenomena, developmental directions and outcomes of cellular stress using a phylogenetically conservative set of genes and their activation pathways, as well as tissue stress and its role in inflammatory and para-inflammatory processes. The main ways towards the realization of cellular stress and its functional blocks were outlined. The main stages of tissue stress and the classification of its typical manifestations, as well as its participation in the development of the classical and non-classical variants of the inflammatory process, were also described. The mechanisms of cellular and tissue stress are structured into the complex systems, which include networks that enable the exchange of information with multidirectional signaling pathways which together make these systems internally contradictory, and the result of their effects is often unpredictable. However, the possible solutions require new theoretical and methodological approaches, one of which includes the transition to integral criteria, which plausibly reflect the holistic image of these processes.

Aberrant Decrease of the Endogenous SIRT3 and Increases of Acetylated Proteins in Scrapie-Infected Cell Line SMB-S15 and in the Brains of Experimental Mice

The linkage between mitochondrial dysfunction and neurodegenerative diseases including prion diseases has been frequently reported. As the major deacetylase in mitochondria, SIRT3 plays a crucial part in regulating the function of many mitochondrial proteins. Although SIRT3 was reported to be linked to several neurodegenerative diseases, it is still unknown if SIRT3 is involved in prion diseases. In this study, we have presented a substantially declined status of mitochondrial SIRT3 in both the levels of cultured cells and an experimental rodent model during scrapie prion replication and infection. Such decreased SIRT3 activity led to a decreased deacetylating activity, resulting in increases of the acetylated forms of some substrates of SIRT3 in cells, such as SOD2 and ATP5β. Declined SOD2 and ATP5β activities subsequently caused an increase of intracellular ROS and a reduction of ATP. Furthermore, we have also proposed evidence that the activity of cellular SIRT3 is partially recovered when abnormal prion propagation in the cultured cells is removed by resveratrol. Those data emphasize a close connection between the prion replication and mitochondrial deacetylation due to SIRT3, thereby partially explaining mitochondrial dysfunction in prion diseases.

Dietary magnesium and copper affect survival time and neuroinflammation in chronic wasting disease

Chronic wasting disease (CWD), the only known wildlife prion disease, affects deer, elk and moose. The disease is an ongoing and expanding problem in both wild and captive North American cervid populations and is difficult to control in part due to the extreme environmental persistence of prions, which can transmit disease years after initial contamination. The role of exogenous factors in CWD transmission and progression is largely unexplored. In an effort to understand the influence of environmental and dietary constituents on CWD, we collected and analyzed water and soil samples from CWD-negative and positive captive cervid facilities, as well as from wild CWD-endozootic areas. Our analysis revealed that, when compared with CWD-positive sites, CWD-negative sites had a significantly higher concentration of magnesium, and a higher magnesium/copper (Mg/Cu) ratio in the water than that from CWD-positive sites. When cevidized transgenic mice were fed a custom diet devoid of Mg and Cu and drinking water with varied Mg/Cu ratios, we found that higher Mg/Cu ratio resulted in significantly longer survival times after intracerebral CWD inoculation. We also detected reduced levels of inflammatory cytokine gene expression in mice fed a modified diet with a higher Mg/Cu ratio compared to those on a standard rodent diet. These findings indicate a role for dietary Mg and Cu in CWD pathogenesis through modulating inflammation in the brain.

The Role of the Reactive Oxygen Species and Oxidative Stress in the Pathomechanism of the Age-Related Ocular Diseases and Other Pathologies of the Anterior and Posterior Eye Segments in Adults

The reactive oxygen species (ROS) form under normal physiological conditions and may have both beneficial and harmful role. We search the literature and current knowledge in the aspect of ROS participation in the pathogenesis of anterior and posterior eye segment diseases in adults. ROS take part in the pathogenesis of keratoconus, Fuchs endothelial corneal dystrophy, and granular corneal dystrophy type 2, stimulating apoptosis of corneal cells. ROS play a role in the pathogenesis of glaucoma stimulating apoptotic and inflammatory pathways on the level of the trabecular meshwork and promoting retinal ganglion cells apoptosis and glial dysfunction in the posterior eye segment. ROS play a role in the pathogenesis of Leber's hereditary optic neuropathy and traumatic optic neuropathy. ROS induce apoptosis of human lens epithelial cells. ROS promote apoptosis of vascular and neuronal cells and stimulate inflammation and pathological angiogenesis in the course of diabetic retinopathy. ROS are associated with the pathophysiological parainflammation and autophagy process in the course of the age-related macular degeneration.

Treatment of SMB-S15 Cells with Resveratrol Efficiently Removes the PrP(Sc) Accumulation In Vitro and Prion Infectivity In Vivo

Prion diseases are transmissible and invariably fatal neurodegenerative disorders, which still lack of efficacious prophylactic and therapeutic tools. Our previous study has proposed that the natural phytoalexin, resveratrol, can reduce the amounts of PrP(Sc) in a scrapie-infected cell line SMB-S15. To address its anti-prion efficacy, the inhibitive activity of resveratrol on prion accumulation in vitro and prion infectivity in vivo was analyzed in the present study. Exposure of SMB-S15 cells to various concentrations of resveratrol (0.25 to 200 μM) reduced and even removed cellular PrP(Sc) in a dose-dependent manner, with EC50 0.61 μM. Meanwhile, PrP(Sc) signals in SMB-S15 cells treated with 5 and 10 μM resveratrol maintained undetectable after drug withdrawal, indicating that the removal of PrP(Sc) in SMB-S15 cells by resveratrol is irreversible. Furthermore, the lysates of SMB-S15 cells exposed to 10 μM resveratrol for 2 and 7 days were intracerebrally inoculated into CD1 mice. All mice (n = 9) infected with SMB-S15 cells without treatment of resveratrol appeared typical experimental scrapie symptoms from 155 to 228 day post inoculation (dpi), while all mice (n = 9) inoculated with SMB-S15 cells treated with resveratrol for 7 days maintained healthy by the end of observations (284 dpi). PrP-specific Western blots and neuropathological tests did not identify PrP(Sc) or prion disease-associated pathological abnormality in the brains of mice inoculated with 7-day resveratrol-treated SMB-S15 cells. It indicates that the prion infectivity of SMB-S15 onto CD1 mice is eradicated by 1-week resveratrol treatment. Sensitivity of PrP(Sc) to resveratrol highlights its potential role in prion therapeutics.

Role of proteolytic activation of protein kinase Cδ in the pathogenesis of prion disease

Prion diseases are infectious and inevitably fatal neurodegenerative diseases characterized by prion replication, widespread protein aggregation and spongiform degeneration of major brain regions controlling motor function. Oxidative stress has been implicated in prion-related neuronal degeneration, but the molecular mechanisms underlying prion-induced oxidative damage are not well understood. In this study, we evaluated the role of oxidative stress-sensitive, pro-apoptotic protein kinase Cδ (PKCδ) in prion-induced neuronal cell death using cerebellar organotypic slice cultures (COSC) and mouse models of prion diseases. We found a significant upregulation of PKCδ in RML scrapie-infected COSC, as evidenced by increased levels of both PKCδ protein and its mRNA. We also found an enhanced regulatory phosphorylation of PKCδ at its two regulatory sites, Thr505 in the activation loop and Tyr311 at the caspase-3 cleavage site. The prion infection also induced proteolytic activation of PKCδ in our COSC model. Immunohistochemical analysis of scrapie-infected COSC revealed loss of PKCδ positive Purkinje cells and enhanced astrocyte proliferation. Further examination of PKCδ signaling in the RML scrapie adopted in vivo mouse model showed increased proteolytic cleavage and Tyr 311 phosphorylation of the kinase. Notably, we observed a delayed onset of scrapie-induced motor symptoms in PKCδ knockout (PKCδ(-/-)) mice as compared with wild-type (PKCδ(+/+)) mice, further substantiating the role of PKCδ in prion disease. Collectively, these data suggest that PKCδ signaling likely plays a role in the neurodegenerative processes associated with prion diseases.

Methionine oxidation accelerates the aggregation and enhances the neurotoxicity of the D178N variant of the human prion protein

The D178N mutation of the prion protein (PrP) results in the hereditary prion disease fatal familial insomnia (FFI). Little is known regarding the effects of methionine oxidation on the pathogenesis of D178N-associated FFI. In the present study, we found that the D178N variant was more susceptible to oxidation than wild-type PrP, as indicated by reverse-phase high performance liquid chromatography (RP-HPLC) and mass spectrometry (MS) analysis. Circular dichroism (CD), differential scanning calorimetry (DSC), thioflavin T (ThT) binding assay studies demonstrated that methionine oxidation decreased the structural stability of the D178N variant, and the oxidized D178N variant exhibited a greater propensity to form β-sheet-rich oligomers and aggregates. Moreover, these aggregates of oxidized D178N PrP were more resistant to proteinase K (PK) digestion. Additionally, using fluorescence confocal microscopy, we detected a high degree of aggregation in D178N-transfected Neuro-2a (N2a) cells after treatment with hydrogen peroxide (H2O2). Furthermore, the oxidation and consequent aggregation of the D178N variant induced greater apoptosis of N2a cells, as monitored using flow cytometry. Collectively, these observations suggest that methionine oxidation accelerates the aggregation and enhances the neurotoxicity of the D178N variant, possibly providing direct evidence to link the pathogenesis of D178N-associated FFI with methionine oxidation.

Regulation of proteasomes in prion disease

The hallmark of prion disease is the accumulation of misfolded protein PrP(Sc), which is toxic to neuronal cells. The proteasome system is responsible for the rapid, precise, and timely degradation of proteins and plays an important role in cellular protein quality control. Increasing evidence indicates impaired activity of proteasomes in prion diseases. Accumulated PrP(Sc) can directly or indirectly affect proteasome activity. Misfolded protein may influence the assembly and activity of 19S regulatory particle, or post-translational modification of 20S proteasome, which may adversely affect the protein degradation activity of proteasomes. In this review, we summarized the recent findings concerning the possible regulation of proteasomes in prion and other neurodegenerative diseases. The proteasome system may enhance its degradation activity by changing its structure, and this activity can also be increased by related chaperones when neuronal cells are subject to stress. When the proteasome system is inhibited, degradation of protein aggregates via autophagy may increase as a compensatory system. It is possible that a balance exists between the proteasome and autophagy in vivo; when one is impaired, the activity of the other may increase to maintain homeostasis. However, more studies are needed to elucidate the relationship between the proteasome system and autophagy.

Oxidative stress impairs autophagic flux in prion protein-deficient hippocampal cells

We previously reported that autophagy is upregulated in Prnp-deficient (Prnp ( 0/0) ) hippocampal neuronal cells in comparison to cellular prion protein (PrP (C) )-expressing (Prnp (+/+) ) control cells under conditions of serum deprivation. In this study, we determined whether a protective mechanism of PrP (C) is associated with autophagy using Prnp ( 0/0) hippocampal neuronal cells under hydrogen peroxide (H 2O 2)-induced oxidative stress. We found that Prnp ( 0/0) cells were more susceptible to oxidative stress than Prnp (+/+) cells in a dose- and time-dependent manner. In addition, we observed enhanced autophagy by immunoblotting, which detected the conversion of microtubule-associated protein 1 light chain 3 β (LC3B)-I to LC3B-II, and we observed increased punctate LC3B immunostaining in H 2O 2-treated Prnp ( 0/0) cells compared with H 2O 2-treated control cells. Interestingly, this enhanced autophagy was due to impaired autophagic flux in the H 2O 2-treated Prnp ( 0/0) cells, while the H 2O 2-treated Prnp (+/+) cells showed enhanced autophagic flux. Furthermore, caspase-dependent and independent apoptosis was observed when both cell lines were exposed to H 2O 2. Moreover, the inhibition of autophagosome formation by Atg7 siRNA revealed that increased autophagic flux in Prnp (+/+) cells contributes to the prosurvival effect of autophagy against H 2O 2 cytotoxicity. Taken together, our results provide the first experimental evidence that the deficiency of PrP (C) may impair autophagic flux via H 2O 2-induced oxidative stress.

Methionine oxidation perturbs the structural core of the prion protein and suggests a generic misfolding pathway

Oxidative stress and misfolding of the prion protein (PrP^C) are fundamental to prion diseases. We have therefore probed the effect of oxidation on the structure and stability of PrP^C. Urea unfolding studies indicate that H₂O₂ oxidation reduces the thermodynamic stability of PrP^C by as much as 9 kJ/mol. ¹H-¹⁵N NMR studies indicate methionine oxidation perturbs key hydrophobic residues on one face of helix-C as follows: Met-205, Val-209, and Met-212 together with residues Val-160 and Tyr-156. These hydrophobic residues pack together and form the structured core of the protein, stabilizing its ternary structure. Copper-catalyzed oxidation of PrP^C causes a more significant alteration of the structure, generating a monomeric molten globule species that retains its native helical content. Further copper-catalyzed oxidation promotes extended β-strand structures that lack a cooperative fold. This transition from the helical molten globule to β-conformation has striking similarities to a misfolding intermediate generated at low pH. PrP may therefore share a generic misfolding pathway to amyloid fibers, irrespective of the conditions promoting misfolding. Our observations support the hypothesis that oxidation of PrP destabilizes the native fold of PrP^C, facilitating the transition to PrP^Sc. This study gives a structural and thermodynamic explanation for the high levels of oxidized methionine in scrapie isolates.

Association of endothelial nitric oxide synthase and mitochondrial dysfunction in the hippocampus of scrapie-infected mice

The elevation of nitric oxide (NO) within the central nervous system (CNS) is known to be associated with the pathogenesis of neurodegenerative diseases such as HIV-associated dementia (HAD), brain ischemia, Parkinson's disease, and Alzheimer's disease. NO is enzymatically formed by the enzyme nitric oxide synthase (NOS). There are two forms of NOS, the constitutive and the inducible form. The constitutive form is present in endothelial cells (eNOS) and neurons (nNOS). The inducible form (iNOS) is expressed in various cell types including astroglia and microglia of the CNS. Using an animal model, we investigated the involvement of eNOS in the pathology of prion disease. We showed dramatic upregulation of eNOS immunoreactivity in reactive astroglial cells in the hippocampus in the prion disease animal model, scrapie in mice. Expression of eNOS was upregulated in cytosolic and mitochondrial fractions of whole brain. In the hippocampal region, eNOS was widely overexpressed in various components of the cell. We found that eNOS dramatically accumulated in hippocampal mitochondria and was particularly prevalent in structurally dysfunctional mitochondria. In association with the accumulation of eNOS in mitochondria, we showed that mitochondrial superoxide dismutase (Mn-SOD or SOD2), cytochrome c, and ATP activity were downregulated both in whole brain and in the hippocampal region. These results indicate that eNOS plays a role in the development of dysfunctional mitochondria and this, in turn, could induce some of the histopathological changes seen in prion diseases.

Gene expression profiling and association with prion-related lesions in the medulla oblongata of symptomatic natural scrapie animals

The pathogenesis of natural scrapie and other prion diseases remains unclear. Examining transcriptome variations in infected versus control animals may highlight new genes potentially involved in some of the molecular mechanisms of prion-induced pathology. The aim of this work was to identify disease-associated alterations in the gene expression profiles of the caudal medulla oblongata (MO) in sheep presenting the symptomatic phase of natural scrapie. The gene expression patterns in the MO from 7 sheep that had been naturally infected with scrapie were compared with 6 controls using a Central Veterinary Institute (CVI) custom designed 4×44K microarray. The microarray consisted of a probe set on the previously sequenced ovine tissue library by CVI and was supplemented with all of the Ovis aries transcripts that are currently publicly available. Over 350 probe sets displayed greater than 2-fold changes in expression. We identified 148 genes from these probes, many of which encode proteins that are involved in the immune response, ion transport, cell adhesion, and transcription. Our results confirm previously published gene expression changes that were observed in murine models with induced scrapie. Moreover, we have identified new genes that exhibit differential expression in scrapie and could be involved in prion neuropathology. Finally, we have investigated the relationship between gene expression profiles and the appearance of the main scrapie-related lesions, including prion protein deposition, gliosis and spongiosis. In this context, the potential impacts of these gene expression changes in the MO on scrapie development are discussed.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

Redox control of prion and disease pathogenesis

Imbalance of brain metal homeostasis and associated oxidative stress by redox-active metals like iron and copper is an important trigger of neurotoxicity in several neurodegenerative conditions, including prion disorders. Whereas some reports attribute this to end-stage disease, others provide evidence for specific mechanisms leading to brain metal dyshomeostasis during disease progression. In prion disorders, imbalance of brain-iron homeostasis is observed before end-stage disease and worsens with disease progression, implicating iron-induced oxidative stress in disease pathogenesis. This is an unexpected observation, because the underlying cause of brain pathology in all prion disorders is PrP-scrapie (PrP(Sc)), a beta-sheet-rich conformation of a normal glycoprotein, the prion protein (PrP(C)). Whether brain-iron dyshomeostasis occurs because of gain of toxic function by PrP(Sc) or loss of normal function of PrP(C) remains unclear. In this review, we summarize available evidence suggesting the involvement of oxidative stress in prion-disease pathogenesis. Subsequently, we review the biology of PrP(C) to highlight its possible role in maintaining brain metal homeostasis during health and the contribution of PrP(Sc) in inducing brain metal imbalance with disease progression. Finally, we discuss possible therapeutic avenues directed at restoring brain metal homeostasis and alleviating metal-induced oxidative stress in prion disorders.

Consequences of dietary manganese and copper imbalance on neuronal apoptosis in a murine model of scrapie

AIMS

Copper and manganese levels are altered in mice both lacking PrPc and prion-infected brains. The aim of this study was to analyse the effects of manganese and copper imbalance on neuronal apoptosis in a scrapie-infected Tga20 mouse model.

METHODS

Immunoreactivities for the apoptotic proteins Bax and active caspase-3 were evaluated in nine regions of the brain of scrapie-infected and control Tga20 mice treated with one of several diets: depleted cooper (-Cu), loaded manganese (+Mn), depleted copper/loaded manganese (-Cu+Mn) and regular diet. Immunohistochemical determination of NeuN was used to detect possible neuronal loss.

RESULTS

Intracellular Bax detection was significantly decreased in animals fed with modified diets, particularly in those treated with copper-depleted diets. A decrease in active caspase-3 was primarily observed in animals fed with enhanced manganese diets. Our results show that the -Cu, -Cu+Mn and +Mn diets protected against apoptosis in scrapie-infected mice. However, NeuN immunolabelling quantification revealed that no diet was sufficient to arrest neuronal death.

CONCLUSIONS

With regard to apoptosis induction, the response of Tga20 mice to prion infection was similar to that reported for other mice models. Our results demonstrate the neuroprotective effects of -Cu, -Cu+Mn and +Mn diets in a murine model of scrapie. However, neuronal death induced by infection with prions seems to be independent of apoptosis marker signalling. Moreover, copper-modified diets were neuroprotective against the possible toxicity of the prion transgene in Tga20 control and infected mice even though manganese supplementation could not counteract this toxicity.

Decreased catalase expression and increased susceptibility to oxidative stress in primary cultured corneal fibroblasts from patients with granular corneal dystrophy type II

Granular corneal dystrophy type II (GCD II) is an autosomal dominant disorder characterized by age-dependent progressive accumulation of transforming growth factor-beta-induced protein (TGFBIp) deposits in the corneal stroma. Several studies have suggested that corneal fibroblasts may decline with age in response to oxidative stress. To investigate whether oxidative stress is involved in the pathogenesis of GCD II, we assayed antioxidant enzymes, oxidative damage, and susceptibility to reactive oxygen species-induced cell death in primary cultured corneal fibroblasts (PCFs) from GCD II patients and healthy subjects. We found elevated protein levels of Mn-superoxide dismutase, Cu/Zn-superoxide dismutase, glutathione peroxidase, and glutathione reductase, as well as increased CAT mRNA and decreased catalase protein in GCD II PCFs. Furthermore, catalase is down-regulated in normal PCFs transfected with transforming growth factor-beta-induced gene-h3. We also observed an increase in not only intracellular reactive oxygen species and H(2)O(2) levels, but also malondialdehyde, 4-hydroxynonenal, and protein carbonyls levels in GCD II PCFs. Greater immunoreactivity for malondialdehyde was observed in the corneal tissue of GCD II patients. In addition, we observed a decrease in Bcl-2 and Bcl-xL levels and an increase in Bax and Bok levels in GCD II PCFs. Finally, GCD II PCFs are more susceptible to H(2)O(2)-induced cell death. Together, these results suggest that oxidative damage induced by decreased catalase is involved in GCD II pathogenesis, and antioxidant agents represent a possible treatment strategy.

Opposing roles of prion protein in oxidative stress- and ER stress-induced apoptotic signaling

Although the prion protein is abundantly expressed in the CNS, its biological functions remain unclear. To determine the endogenous function of the cellular prion protein (PrP(c)), we compared the effects of oxidative stress and endoplasmic reticulum (ER) stress inducers on apoptotic signaling in PrP(c)-expressing and PrP(ko) (knockout) neural cells. H(2)O(2), brefeldin A (BFA), and tunicamycin (TUN) induced increases in caspase-9 and caspase-3, PKCdelta proteolytic activation, and DNA fragmentation in PrP(c) and PrP(ko) cells. Interestingly, ER stress-induced activation of caspases, PKCdelta, and apoptosis was significantly exacerbated in PrP(c) cells, whereas H(2)O(2)-induced proapoptotic changes were suppressed in PrP(c) compared to PrP(ko) cells. Additionally, caspase-12 and caspase-8 were activated only in the BFA and TUN treatments. Inhibitors of caspase-9, caspase-3, and PKCdelta significantly blocked H(2)O(2)-, BFA-, and TUN-induced apoptosis, whereas the caspase-8 inhibitor attenuated only BFA- and TUN-induced cell death, and the antioxidant MnTBAP blocked only H(2)O(2)-induced apoptosis. Overexpression of the kinase-inactive PKCdelta(K376R) or the cleavage site-resistant PKCdelta(D327A) mutant suppressed both ER and oxidative stress-induced apoptosis. Thus, PrP(c) plays a proapoptotic role during ER stress and an antiapoptotic role during oxidative stress-induced cell death. Together, these results suggest that cellular PrP enhances the susceptibility of neural cells to impairment of protein processing and trafficking, but decreases the vulnerability to oxidative insults, and that PKCdelta is a key downstream mediator of cellular stress-induced neuronal apoptosis.

The ubiquitin-proteasome system in spongiform degenerative disorders

Spongiform degeneration is characterized by vacuolation in nervous tissue accompanied by neuronal death and gliosis. Although spongiform degeneration is a hallmark of prion diseases, this pathology is also present in the brains of patients suffering from Alzheimer’s disease, diffuse Lewy body disease, human immunodeficiency virus (HIV) infection, and Canavan’s spongiform leukodystrophy. The shared outcome of spongiform degeneration in these diverse diseases suggests that common cellular mechanisms must underlie the processes of spongiform change and neurodegeneration in the central nervous system. Immunohistochemical analysis of brain tissues reveals increased ubiquitin immunoreactivity in and around areas of spongiform change, suggesting the involvement of ubiquitin–proteasome system dysfunction in the pathogenesis of spongiform neurodegeneration. The link between aberrant ubiquitination and spongiform neurodegeneration has been strengthened by the discovery that a null mutation in the E3 ubiquitin–protein ligase mahogunin ring finger-1 (Mgrn1) causes an autosomal recessively inherited form of spongiform neurodegeneration in animals. Recent studies have begun to suggest that abnormal ubiquitination may alter intracellular signaling and cell functions via proteasome-dependent and proteasome-independent mechanisms, leading to spongiform degeneration and neuronal cell death. Further elucidation of the pathogenic pathways involved in spongiform neurodegeneration should facilitate the development of novel rational therapies for treating prion diseases, HIV infection, and other spongiform degenerative disorders.

Infection of metallothionein 1+2 knockout mice with Rocky Mountain Laboratory scrapie

Metallothioneins (MT) are heavy metal-binding, antioxidant proteins with relevant roles described in many pathological conditions affecting the central nervous system (CNS). Regarding prion diseases, a number of publications demonstrate an up-regulation of MT-1+2 in the brains of TSE affected cattle, humans and experimentally inoculated rodents. Since the prion protein also binds copper, and oxidative stress is one of the events presumably triggered by PrPsc deposition, it seems plausible that MTs have a relevant role in the outcome of these neurodegenerative processes. To gain knowledge of the role of MTs in TSE pathogeny, and particularly of that of MT-1+2, a transgenic MT-1+2 knockout mouse model (MT-1+2 KO) was intracerebrally inoculated with the mouse-adapted Rocky Mountain Laboratory (RML) strain of scrapie; 129SvJ mice were used as controls (WT). Clinical signs were monitored and animals were humanely sacrificed when they scored positive clinically. Brains were fixed following intracardiac perfusion with 4% formaldehyde, paraffin embedded, and processed for histological, histochemical and immunohistochemical evaluation. The incubation period did not show significant differences between MT-1+2 KO and WT mice, nor did the evolution of neurological signs. Upon neuropathological characterisation of the brains, moderate differences were observed in astroglial and microglial response, spongiosis score and PrPsc deposition, particularly in brain regions to which the studied strain showed a stronger tropism (i.e. hippocampus). Results showed that the brain defence mechanisms against PrPsc deposition involve, aside from MT-1+2, other molecules, such as HSP25, which are capable of compensating for the lack of MT-1+2.

Oxidative stress and neurodegeneration in the ischemic overactive bladder

PURPOSE

The central and peripheral nervous systems are highly sensitive to ischemia and oxidative stress. We searched for markers of oxidative injury and examined neural density in the rabbit ischemic overactive bladder.

MATERIALS AND METHODS

Blood flow and oxygenation were recorded during cystometrogram in overactive and control rabbit bladders at weeks 8 and 16 after the induction of ischemia. Oxidative products and neural density were assessed by enzyme immunoassay and immunohistochemical staining, respectively. Reverse transcriptase-polymerase chain reaction was done to determine the gene expression of nerve growth factor and its receptor p75. The effect of acute oxidative stress was examined in tissue culture medium containing H(2)O(2).

RESULTS

Overactivity produced repeating cycles of ischemia/reperfusion and hypoxia/reoxygenation in the ischemic bladder, leading to oxidative and nitrosative products. Neural density in the 8-week ischemic bladder was similar to that in controls, while neurodegeneration was evident after 16 weeks of ischemia. Nerve growth factor gene levels initially increased at week 8 but significantly decreased at week 16 after the induction of ischemia. Gene levels of p75 decreased after 8 weeks and remained lower than in controls after 16 weeks of ischemia. Acute oxidative stress decreased nerve growth factor protein release in culture medium. The antioxidant enzyme catalase had no significant effect on control tissues but it partially protected nerve growth factor from H(2)O(2) injury.

CONCLUSIONS

Ischemia may have a role in bladder neuropathy. Overactivity under ischemic conditions produces noxious oxidative products in the bladder. Neurodegeneration in bladder ischemia may involve a lack of nutrients, hypoxia and overactivity induced free radicals. Nerve growth factor and its receptors may regulate neural reactions to oxidative injury.

Alteration of iron regulatory proteins (IRP1 and IRP2) and ferritin in the brains of scrapie-infected mice

Considerable evidence suggests that oxidative stress may be involved in the pathogenesis of Transmissible Spongiform Encephalopathies (TSEs). To investigate the involvement of iron metabolism in TSEs, we examined the expression levels of iron regulatory proteins (IRPs), ferritins, and binding activities of IRPs to iron-responsive element (IRE) in scrapie-infected mice. We found that the IRPs-IRE-binding activities and ferritins were increased in the astrocytes of hippocampus and cerebral cortex in the brains of scrapie-infected mice. These results suggest that alteration of iron metabolism contributes to development of neurodegeneration and that some protective mechanisms against iron-induced oxidative damage may occur during the pathogenesis of TSEs.

Application of nicotine enantiomers, derivatives and analogues in therapy of neurodegenerative disorders

This review gives a brief overview over the major aspects of application of the nicotine alkaloid and its close derivatives in the therapy of some neurodegenerative disorders and diseases (e.g. Alzheimer's disease, Parkinson's disease, Tourette's syndrome, schizophrenia etc.). The issues concerning methods of nicotine analysis and isolation, and some molecular aspects of nicotine pharmacology are included. The natural and synthetic analogues of nicotine that are considered for medical practice are also mentioned. The molecular properties of two naturally occurring nicotine enantiomers are compared--the less-common but less-toxic (R)-nicotine is suggested as a natural compound that may find its place in pharmaceutical practice.

Protein oxidation and lipid peroxidation in brain of subjects with Alzheimer's disease: insights into mechanism of neurodegeneration from redox proteomics

Alzheimer's disease (AD), the leading cause of dementia, involves regionalized neuronal death, synaptic loss, and an accumulation of intraneuronal, neurofibrillary tangles and extracellular senile plaques. Although the initiating causes leading to AD are unknown, a number of previous studies reported the role of oxidative stress in AD brain. Postmortem analysis of AD brain showed elevated markers of oxidative stress including protein nitrotyrosine, carbonyls in proteins, lipid oxidation products, and oxidized DNA bases. In this review, we focus our attention on the role of protein oxidation and lipid peroxidation in the pathogenesis of AD. Particular attention is given to the current knowledge about the redox proteomics identification of oxidatively modified proteins in AD brain.

Oxidative stress in the brain at early preclinical stages of mouse scrapie

Oxidative stress has been shown to be involved in the pathogenesis of neurodegenerative diseases including prion diseases. Although a growing body of evidence suggests direct involvement of oxidative stress in the pathogenesis of prion diseases, it is still not clear whether oxidative stress is a causative early event in these conditions or a secondary phenomenon commonly found in the progression of neurodegenerative diseases. Using a mouse scrapie model, we assessed oxidative stress in the brain at various stages of the disease progression and observed significantly increased concentration of lipid peroxidation markers, malondialdehyde and 4-hydroxyalkenals, and mRNA level of an oxidative stress response enzyme, heme oxygenase-1, at early preclinical stages of scrapie. The changes preceded dramatic synaptic loss demonstrated by immunohistochemical staining of a synaptic protein, synaptophysin. These findings imply that the brain undergoes oxidative stress even from an early stage of prion invasion into the brain. Given the well-known deleterious effects of reactive-oxygen-species-mediated damage in the brain, it is considered that the oxidative stress at the preclinical stage of prion diseases may predispose the brain to neurodegenerative mechanisms that characterize the diseases.

Green fluorescent protein as a reporter of prion protein folding

Background

The amino terminal half of the cellular prion protein PrP^c is implicated in both the binding of copper ions and the conformational changes that lead to disease but has no defined structure. However, as some structure is likely to exist we have investigated the use of an established protein refolding technology, fusion to green fluorescence protein (GFP), as a method to examine the refolding of the amino terminal domain of mouse prion protein.

Results

Fusion proteins of PrP^c and GFP were expressed at high level in E.coli and could be purified to near homogeneity as insoluble inclusion bodies. Following denaturation, proteins were diluted into a refolding buffer whereupon GFP fluorescence recovered with time. Using several truncations of PrP^c the rate of refolding was shown to depend on the prion sequence expressed. In a variation of the format, direct observation in E.coli, mutations introduced randomly in the PrP^c protein sequence that affected folding could be selected directly by recovery of GFP fluorescence.

Conclusion

Use of GFP as a measure of refolding of PrP^c fusion proteins in vitro and in vivo proved informative. Refolding in vitro suggested a local structure within the amino terminal domain while direct selection via fluorescence showed that as little as one amino acid change could significantly alter folding. These assay formats, not previously used to study PrP folding, may be generally useful for investigating PrP^c structure and PrP^c-ligand interaction.

Prion proteins with insertion mutations have altered N-terminal conformation and increased ligand binding activity and are more susceptible to oxidative attack

We compared the biochemical properties of a wild type recombinant normal human cellular prion protein, rPrP(c), with a recombinant mutant human prion protein that has three additional octapeptide repeats, rPrP(8OR). Monoclonal antibodies that are specific for the N terminus of rPrP(c) react much better with rPrP(8OR) than rPrP(c), suggesting that the N terminus of rPrP(8OR) is more exposed and hence more available for antibody binding. The N terminus of PrP(c) contains a glycosaminoglycan binding motif. Accordingly, rPrP(8OR) also binds more glycosaminoglycan than rPrP(c). In addition, the divalent cation copper modulates the conformations of rPrP(c) and rPrP(8OR) differently. When compared with rPrP(c), rPrP(8OR) is also more susceptible to oxidative damage. Furthermore, the abnormalities associated with rPrP(8OR) are recapitulated, but even more profoundly, in another insertion mutant, which has five extra octapeptide repeats, rPrP(10OR). Therefore, insertion mutants appear to share common features, and the degree of abnormality is proportional to the number of insertions. Any of these anomalies may contribute to the pathogenesis of inherited human prion disease.

Oxidation, glycoxidation, lipoxidation, nitration, and responses to oxidative stress in the cerebral cortex in Creutzfeldt-Jakob disease

Gel electrophoresis and Western blotting of frontal cortex homogenates have been carried out in sporadic Creutzfeldt-Jakob disease (CJD) cases and age-matched controls to gain understanding of the expression of glycation-end products (AGEs). N-Carboxymethyl-lysine (CML) and N-carboxyethyl-lysine (CEL) were used as markers of glycoxidation; 4-hydroxynonenal (4-HNE) and malondialdehyde-lysine (MDAL) as markers of lipoxidation; and nitrotyrosine (N-tyr) and neuronal, endothelial and inducible nitric oxide synthase (nNOS, eNos and iNos) as markers of protein nitration and as sources of NO production, respectively. Age receptor (RAGE) and Cu/Zn superoxide dismutase (SOD1) and Mn superoxide dismutase (SOD2) expression levels were also examined. The results showed a significant increase in the expression levels of AGE (p<0.05), CEL (p<0.001), RAGE (p<0.05), HNE-modified proteins (p<0.01), nNOS, iNOS and eNOS (p<0.01 and p<0.05, respectively), N-tyr (p<0.05), and SOD1 (p<0.05) and SOD2 (p<0.05). No relationship was observed between PrP genotype, PrP type, PrP burden, and expression levels of oxidative stress markers. The present findings demonstrate oxidative, glycoxidative, lipoxidative and nitrative protein damage, accompanied by increased oxidative responses, in the cerebral cortex in sporadic CJD. These results provide support for the concept that oxidative stress may have important implications in the pathogenesis of prion diseases.

Effect of transition metals (Mn, Cu, Fe) and deoxycholic acid (DA) on the conversion of PrPCto PrPres

The PMCA (protein misfolding cyclic amplification) technique has been shown to drive the amplification of misfolded prion protein by PrP(Sc) seeds during several cycles of incubation-sonication. Here, we report that cyclic amplification of normal hamster brain homogenates treated with a number of transition metals (manganese [Mn], copper [Cu], and iron [Fe]) leads to conversion of PrP(C) into protease-resistant PrP(res). The efficiency of PrP(res) formation and the glycoforms induced by Mn were different from those obtained by Cu and Fe. Previous results have shown higher Mn and lower Cu levels in the affinity-purified PrP(Sc) from the brain of prion diseases compared with normal hamster brain homogenates. We focused on Mn because we observed higher levels of Mn in whole brain, mitochondria, and scrapie-associated fibril-enriched fractions from the brains of animals with prion disease. In the presence of minute quantities of Mn-induced PrP(res) template with a large amount of PrP(C), PrP(res) amplification is observed. A metal chelater, EDTA reverses the effect of Mn on PrP(res) amplification, suggesting that Mn may play a role in the formation of PrP(res). It has been proposed that metal-catalyzed oxidation of PrP leads to the oxidation of amino acids and extensive aggregation of oxidized PrP. Carboxyl acids such as deoxycholic acid (DA) are oxidized molecules produced by 3' oxidation pathway. In in vitro studies, the potent effect of Mn on PrP(res) amplification is augmented by DA in a dose-dependent manner. On the basis of the evidence of the elevated Mn levels in scrapie-associated fibril (SAF)-enriched preparations from the brains of animals with prion disease, Mn-loaded PrP and oxidized molecules such as carboxyl acids may contribute to the formation of the scrapie isoform of PrP in prion diseases.

Oligodendrocytes are susceptible to apoptotic cell death induced by prion protein-derived peptides

Neurodegenerative prion diseases, characterized by a progressive dementia, are associated with the accumulation of abnormal forms of the prion (PrPc) protein, potentially due to an aberrant regulation of PrPc biogenesis and/or topology. One of these forms, termed ctmPrP, displays a transmembrane conformation and might trigger neuronal cell death in Gerstmann-Straüssler-Scheinker (GSS) syndrome and other prion-associated diseases in humans. Although the primary target cells involved in the progression of prion diseases remain unidentified, it was recently suggested that modifications of the oligodendroglial cells occur early in prion diseases. In the present study, we demonstrate that a putative transmembrane domain of the human PrPc, i.e., amino acids 118-135, induces oligodendrocyte (OLG) death in vitro in a time- and dose-dependent manner. The process leading to OLG death and induced by the PrP[118-135] peptide was characterized by DNA fragmentation, cytoskeletal disruption, and caspase activation. Protection against the PrP[118-135] peptide-induced OLG apoptosis by several antioxidant molecules, such as probucol, propylgallate, and promethazine, suggests that oxidative injuries contribute to the PrP[118-135] cytotoxicity to OLGs. These results suggest a potential pathophysiological role of the ctmPrP- and/or PrP fragment-mediated OLG cytotoxicity in spongiform encephalopathies.

Amino terminal interaction in the prion protein identified using fusion to green fluorescent protein

In contrast to the well-characterized carboxyl domain, the amino terminal half of the mature cellular prion protein has no defined structure. Here, following fusion of mouse prion protein fragments to green fluorescence protein as a reporter of protein stability, we report extreme variability in fluorescence level that is dependent on the prion fragment expressed. In particular, exposure of the extreme amino terminus in the context of a truncated prion protein molecule led to rapid degradation, whereas the loss of only six amino terminal residues rescued high level fluorescence. Study of the precise endpoints and residue identity associated with high fluorescence suggested a domain within the amino terminal half of the molecule defined by a long-range intramolecular interaction between 23KKRPKP28 and 143DWED146 and dependent upon the anti-parallel beta-sheet ending at residue 169 and normally associated with the structurally defined carboxyl terminal domain. This previously unreported interaction may be significant for understanding prion bioactivity and for structural studies aimed at the complete prion structure.

Regulation of intrinsic prion protein by growth factors and TNF-alpha: the role of intracellular reactive oxygen species

Function and regulation of the intrinsic prion protein (PrPc) are largely unknown. In the present study the regulation of PrPc expression by growth factors and cytokines that increase intracellular reactive oxygen species (ROS) levels was studied in glioma and neuroblastoma cells grown as multicellular tumor spheroids. PrPc protein was significantly increased when glioma spheroids were treated with either ATP, nerve growth factor (NGF), epidermal growth factor (EGF), or tumor necrosis factor alpha (TNF-alpha), whereas mRNA levels as evaluated by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) remained unchanged. ATP, NGF, EGF, and TNF-alpha raised intracellular ROS levels as evaluated using the redox-sensitive fluorescence dye 2'7'-dichlorodihydrofluorescein diacetate (H2DCFDA). The observed elevation in PrPc was completely abolished in the presence of the free radical scavengers vitamin E and ebselen, as well as following pretreatment with the NADPH-oxidase inhibitor diphenylen iodonium chloride (DPI), indicating that PrPc levels are regulated by intracellular ROS. The correlation of PrPc expression to the intracellular ROS levels was investigated by the use of neuroblastoma cells overexpressing either mutant V210I PrP, or wild-type PrPc. It was observed that the intracellular redox state was significantly reduced in PrPc as well as V210I PrP overexpressing cells as compared to non-transfected cells. Consequently, the observed elevation of ROS following treatment with ATP was completely abolished in PrP overexpressing cells. Our data are in line with the assumption that PrPc plays a role as free radical scavenger and/or sensor molecule for oxidative stress.

Approaches to prophylaxis and therapy

Despite important progress in experimental treatment of neurodegenerative diseases, no therapeutic strategy has today proven its capability to cure or even to stabilise human TSEs. Pathogenesis experiments performed in rodent TSE models have shown that central nervous system damages are detectable long before the appearance of the clinical symptoms. At the time of disease onset, PrP(Sc) accumulation has almost reached its highest level, and the neuropathological lesions (spongiosis, gliosis) are as intense as they are at the time of death. Therefore, the neurodegeneration that is present at the onset of the disease is beyond therapy, and, in theory, only a preclinical diagnosis of TSEs would permit the prevention (or delay) of neurodegeneration. Unfortunately, there are no diagnostic tests that can be used to show TSE agent infection during the preclinical phase of the disease. Nevertheless, since the appearance of variant Creutzfeldt-Jakob disease (vCJD), those in the scientific community working on experimental therapy have increased their efforts. Tens of drugs have been tested in several experimental models, and there are some high-output screening platforms being used in Europe and in the US. Any rational therapeutic strategy needs to be based on pathogenesis data and/or knowledge on the nature of the causative agent. Therefore, progress in therapy is tightly linked to a better understanding of the basic science of TSE.