Transmissible spongiform encephalopathies: a family of etiologically complex diseases--a review

Insights Into the Role of Copper in Neurodegenerative Diseases and the Therapeutic Potential of Natural Compounds

Neurodegenerative diseases encompass a collection of neurological disorders originating from the progressive degeneration of neurons, resulting in the dysfunction of neurons. Unfortunately, effective therapeutic interventions for these diseases are presently lacking. Copper (Cu), a crucial trace element within the human body, assumes a pivotal role in various biological metabolic processes, including energy metabolism, antioxidant defense, and neurotransmission. These processes are vital for the sustenance, growth, and development of organisms. Mounting evidence suggests that disrupted copper homeostasis contributes to numerous age-related neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), Wilson's disease (WD), Menkes disease (MD), prion diseases, and multiple sclerosis (MS). This comprehensive review investigates the connection between the imbalance of copper homeostasis and neurodegenerative diseases, summarizing pertinent drugs and therapies that ameliorate neuropathological changes, motor deficits, and cognitive impairments in these conditions through the modulation of copper metabolism. These interventions include Metal-Protein Attenuating Compounds (MPACs), copper chelators, copper supplements, and zinc salts. Moreover, this review highlights the potential of active compounds derived from natural plant medicines to enhance neurodegenerative disease outcomes by regulating copper homeostasis. Among these compounds, polyphenols are particularly abundant. Consequently, this review holds significant implications for the future development of innovative drugs targeting the treatment of neurodegenerative diseases.

A study on the analytical sensitivity of 6 BSE tests used by the Canadian BSE reference laboratory

Bovine spongiform encephalopathy (BSE) surveillance programs have been employed in numerous countries to monitor BSE prevalence and to protect animal and human health. Since 1999, the European Commission (EC) authorized the evaluation and approval of 20 molecular based tests for the rapid detection of the pathological prion protein (PrP^sc) in BSE infection. The diagnostic sensitivity, convenience, and speed of these tests have made molecular diagnostics the preferred method for BSE surveillance. The aim of this study was to determine the analytical sensitivity of 4 commercially available BSE rapid-test kits, including the Prionics®-Check WESTERN, the Prionics® Check-PrioSTRIP™, the BioRad® TeSeE™ ELISA, and the IDEXX® HerdChek™ EIA. Performances of these tests were then compared to 2 confirmatory tests, including the BioRad® TeSeE™ Western Blot and the modified Scrapie Associated Fibrils (SAF)/OIE Immunoblot. One 50% w/v homogenate was made from experimentally generated C-type BSE brain tissues in ddH₂O. Homogenates were diluted through a background of BSE-negative brainstem homogenate. Masses of both positive and negative tissues in each dilution were calculated to maintain the appropriate tissue amounts for each test platform. Specific concentrated homogenization buffer was added accordingly to maintain the correct buffer condition for each test. ELISA-based tests were evaluated using their respective software/detection platforms. Blot-protocols were evaluated by manual measurements of blot signal density. Detection limitations were determined by fitted curves intersecting the manufacturers' positive/negative criteria. The confirmatory SAF Immunoblot displayed the highest analytical sensitivity, followed by the IDEXX® HerdChek™ EIA, Bio-Rad® TeSeE™ Western Blot, the Bio-Rad® TeSeE™ ELISA, Prionics®-Check PrioSTRIP™, and Prionics®-Check WESTERN™, respectively. Although the tests performed at different levels of sensitivity, the most sensitive and least sensitive of the rapid tests were separated by 2 logs in analytical sensitivity, meeting European performance requirements. All rapid tests appear suitable for targeted BSE surveillance programs, as implemented in Canada.

Metal complexes with superoxide dismutase-like activity as candidates for anti-prion drug

Various compounds were evaluated for ability to inhibit the formation of the abnormal protease-resistant form of prion protein (PrP-res) in two cell lines infected with different prion strains. Examination of the structure-activity relationships indicated that compounds with copper-selective chelating ability and whose copper complexes have high SOD-like activity are candidates for anti-prion drug.

Cellular Prion Protein in the Bovine Mammary Gland Is Selectively Expressed in Active Lactocytes

The cellular prion protein (PrPc) is a highly conserved glycoprotein with a still enigmatic physiological function. It is mainly expressed in the central nervous system but accumulating data suggest that PrPc is also found in a broad spectrum of non-neuronal tissue. Here we investigated the cell-type-related PrPc expression in the bovine mammary gland by using immunohistochemistry (IHC), ELISA, Western blot, and real-time RT-PCR. Specific immunostaining of serial sections revealed that PrPc is selectively localized in mammary gland epithelial cells. Particularly strong expression was found at the basolateral surface of those cells showing active secretion. Results obtained by RT-PCR and ELISA complemented IHC findings. No correlation was found between the level of PrPc expression and other parameters such as age of the animals under study or stage of lactation.

Scrapie infection alters the distribution of plasma metabolites in diseased Cheviot sheep indicating a change in energy metabolism

Nuclear magnetic resonance (NMR) spectroscopy has been used to profile the metabolic status of plasma from; sheep showing clinical signs of scrapie, those known to be infected with scrapie but yet to show clinical signs, and control animals. The NMR measurements have shown that energy metabolism in scrapie infected animals is altered before the onset of clinical symptoms. These metabolic changes may provide the foundation for a pre-clinical diagnostic test for scrapie in sheep.

Prion protein expression in bovine podocytes and extraglomerular mesangial cells

The cellular form of the prion protein (PrP(c)) is thought to be a substrate for an abnormal isoform of the prion protein (PrP(sc)). One emerging hypothesis is that the proposed conversion phenomenon takes place at the site at which the infectious agent meets PrP(c). PrP(c) is abundant in the central nervous system, but little is known about the cell-type-specific distribution of PrP(c) in non-neuronal tissues of cattle. We have studied whether PrP(c), a protein found predominantly in neurons, also exists in bovine podocytes, since neurons and podocytes share a large number of similarities. We have therefore examined the expression of PrP(c) by immunohistochemistry, reverse transcription/polymerase chain reaction and enzyme-linked immunosorbent analysis. Immunostained serial sections and specific antibodies against PrP(c) have revealed that PrP(c) is selectively localized in podocytes and is particularly strongly expressed in extraglomerular mesangial cells but not in endothelial or intraglomerular mesangial cells. The selective expression of PrP(c) in podocytes is of special importance, as it suggests that these cells represent possible targets for peripheral infection with prions and demonstrates that PrP(c) can be added to the list of neuronal factors expressed in mammalian podocytes.

Intracellular distribution of copper and zinc in the liver of copper-exposed cattle from northwest Spain

The intracellular distribution of copper (Cu) and zinc (Zn) in the livers of normal and moderately Cu-exposed cattle was investigated with the aim of improving understanding of the pathophysiology of Cu accumulation in cattle. At total liver Cu concentrations within the generally accepted normal range (25-100 mg/kg fresh weight) the large-granule fraction was the main subcellular compartment for Cu accumulation, followed by the cytosol and the nucleus, whereas in the microsomal fraction Cu accumulation was very low. With increasing Cu exposure, the capacity of the large-granule fraction to accumulate Cu decreased, proceeding towards a plateau (estimated at about 80 mg/kg at a projected total liver Cu concentrations of 450 mg/kg), accompanied by progressively greater Cu accumulation in the nucleus and cytosol. Total liver Cu concentration had little influence on subcellular Zn distribution, with hepatic Cu concentrations being only moderately correlated with Zn concentration in the large-granule fraction. There was a strong association between the proportion of total Cu bound to metallothionein (MT) and the proportion of total Zn in the large-granule fraction, suggesting that Zn displaced from MT is taken up by the lysosomes for excretion. This pattern of Cu accumulation, as in sheep, may be due to the limited capacity for metallothionein binding of Cu and excretion in bile.

The normal cellular prion protein (PrPc) is strongly expressed in bovine endocrine pancreas

Expression of the cellular prion protein (PrP(c)) has been shown to be crucial for the development of transmissible spongiform encephalopathies and for the accumulation of the disease-associated conformer (PrP(sc)) in the brain and other tissues. One of the emerging hypotheses is that the conversion phenomenon could take place at the site where the infectious agent meets PrP(c). In this work we have studied whether PrP(c), a protein found predominantly in neurons, could also exist in pancreatic endocrine cells since neuroectoderm-derived cells and pancreatic islet cells share a large number of similarities. For this purpose we have examined the expression of PrP(c) in a series of fetal and postnatal bovine pancreatic tissue by immunohistochemistry and RT-PCR. Using immunostained serial sections and specific antibodies against bovine PrP(c), insulin, glucagon, somatostatin, chromogranin A and chromogranin B we found that PrP(c) is highly expressed in all endocrine cells of fetal and adult pancreatic islets with a particular strong expression in A-cells. Moreover it became evident that the PrP(c) gene-neighbour chromogranin B as well as chromogranin A are coexpressed together with PrP(c). The selective expression of PrP(c) in the bovine endocrine pancreas is of particular importance regarding possible iatrogenic transmission routes and demonstrates also that bovine pancreatic islet cells could represent an interesting model to study the control of PrP-gene expression.

Synthesis of Analogues of Congo Red and Evaluation of Their Anti-Prion Activity

No cure as of yet exists for any of the transmissible spongiform encephalopathies. In this paper, we describe the synthesis of analogues of Congo red and evaluation against a cellular model of infection, the SMB (scrapie mouse brain) persistently infected cell line, for their ability to inhibit the infectivity of the abnormal form of prion protein (PrP-res). The compounds have also been tested for their ability to inhibit the polymerization of PrPC by PrP-res. A number of analogues showed inhibition of PrP-res infectivity at nanomolar concentrations. Several analogues show promise; the most active compound, 2a, inhibits the formation of PrP-res in SMB cells with an EC50 of 25-50 nM.

Investigation of trace elements in soil as risk factors in the epidemiology of scrapie

Scrapie is a fatal transmissible spongiform encephalopathy (TSE) of sheep and goats which is thought to be caused by a conformational change of the normal prion protein to its pathological isoform. It has been speculated that this change may be mediated by an interaction between the prion protein and various trace elements, in particular manganese and copper, and that the levels of trace elements in soils may therefore be risk factors for TSEs. This hypothesis was tested by comparing the level of trace elements in the soils on farms with and without scrapie and on those with a higher and lower incidence of the disease. The levels of trace elements were obtained from the UK's National Soil Inventory and deficiencies reported by farmers. The results provide no evidence that trace elements are risk factors for scrapie on farms, and the variations in the levels of trace elements in soils at regional scales do not account for the regional differences in the prevalence of scrapie.