Neville Vassallo | University of Malta (original) (raw)

Papers by Neville Vassallo

Amyloid-(A) aggregation is a recognized key process in the pathogenesis of Alzheimer's disease (A... more Amyloid-(A) aggregation is a recognized key process in the pathogenesis of Alzheimer's disease (AD). Misfolded A peptides self-assemble into higher-order oligomers that compromise membrane integrity, leading to synaptic degeneration and neuronal cell death. The main aim of this study was to explore whether small-molecule compounds and black tea extract can protect phospholipid membranes from disruption by A aggregates. We first established a robust protocol for aggregating A 42 peptides into a range of oligomers that efficiently permeabilized small unilamellar liposomes. Next, 15 natural plant polyphenolic compounds, 8 N-benzylidene-benzohydrazide (NBB) compounds and black tea extract were assessed for their ability to antagonize liposome permeabilization by the A 42 oligomers. Our data indicates that black tea extract, the flavones apigenin and baicalein, and the stilbene nordihydroguaiaretic acid (NDGA) are indeed potent inhibitors. Taking into consideration the results of all the small-molecule polyphenols and NBB compounds, it can be proposed that a dihydroxyphenyl ring structure, alone or as part of a flavone scaffold, is particularly effective for protection against membrane damage by the A 42 oligomers. Given the critical role of membrane perforation in the neurodegenerative cascade, these conclusions may guide the design and development of novel therapeutic drugs in AD.

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“The black reaction, invented in 1873 by Camillo Golgi (1843-1926), was the first technique to re... more “The black reaction, invented in 1873 by Camillo Golgi (1843-1926), was the first technique to reveal neurons in their entirety, ie with all their processes. This important development passed unnoticed at first and only received wide international attention after a long delay. The Golgi stain was widely employed for almost thirty years and was directly responsible for major advances in our knowledge of the microscopic anatomy of the nervous system, as well as in other fields of study. In the hands of other researchers, the black reaction provided vital evidence that ...

Neurobiology of Disease, 2016

The neuromuscular disorder, spinal muscular atrophy (SMA), results from insufficient levels of th... more The neuromuscular disorder, spinal muscular atrophy (SMA), results from insufficient levels of the survival motor neuron (SMN) protein. Together with Gemins 2-8 and Unrip, SMN forms the large macromolecular SMN-Gemins complex, which is known to be indispensable for chaperoning the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs). It remains unclear whether disruption of this function is responsible for the selective neuromuscular degeneration in SMA. In the present study, we first show that loss of wmd, the Drosophila Unrip orthologue, has a negative impact on the motor system. However, due to lack of a functional relationship between wmd/Unrip and Gemin3, it is likely that Unrip joined the SMN-Gemins complex only recently in evolution. Second, we uncover that disruption of either Tgs1 or pICln, two cardinal players in snRNP biogenesis, results in viability and motor phenotypes that closely resemble those previously uncovered on loss of the constituent members of the SMN-Gemins complex. Interestingly, overexpression of both factors leads to motor dysfunction in Drosophila, a situation analogous to that of Gemin2. Toxicity is conserved in the yeast S. pombe where pICln overexpression induces a surplus of Sm proteins in the cytoplasm, indicating that a block in snRNP biogenesis is partly responsible for this phenotype. Importantly, we show a strong functional relationship and a physical interaction between Gemin3 and either Tgs1 or pICln. We propose that snRNP biogenesis is the pathway connecting the SMN-Gemins complex to a functional neuromuscular system, and its disturbance most likely leads to the motor dysfunction that is typical in SMA.

Aims: Parkinson’s disease (PD) is the most common motor disorder and the second most common neuro... more Aims: Parkinson’s disease (PD) is the most common motor disorder and the second most common neurodegenerative disease. Cumulative evidence now suggests that the aggregation of alpha- synuclein (aS) is critically involved in the pathogenesis of PD. The main aim of our research is to show that natural polyphenolic compounds are strong inhibitors of aS aggregation. Methods: Using confocal single-molecule fluorescence spectroscopy, we have studied the inhibitory and destabilizing effects of sixteen natural polyphenolic compounds on aS oligomer formation. The organic solvent DMSO, Fe3+ ions, and acidic phospholipids were used to trigger synucleinaggregation into oligomeric structures Results: We found that a select group of polyphenols, notably black tea extract, tannic acid, myricetin, baicalein, nordihydroguaiaretic acid and (–)-epigallocathecingallate, exhibited potent dose-dependent inhibitory activity at physiological (low μM and nM) concentrations. Moreover, they were capable of ro...

PLOS ONE, 2015

The SMN-Gemins complex is composed of Gemins 2-8, Unrip and the survival motor neuron (SMN) prote... more The SMN-Gemins complex is composed of Gemins 2-8, Unrip and the survival motor neuron (SMN) protein. Limiting levels of SMN result in the neuromuscular disorder, spinal muscular atrophy (SMA), which is presently untreatable. The most-documented function of the SMN-Gemins complex concerns the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs). Despite multiple genetic studies, the Gemin proteins have not been identified as prominent modifiers of SMN-associated mutant phenotypes. In the present report, we make use of the Drosophila model organism to investigate whether viability and motor phenotypes associated with a hypomorphic Gemin3 mutant are enhanced by changes in the levels of SMN, Gemin2 and Gemin5 brought about by various genetic manipulations. We show a modifier effect by all three members of the minimalistic fly SMN-Gemins complex within the muscle compartment of the motor unit. Interestingly, muscle-specific overexpression of Gemin2 was by itself sufficient to depress normal motor function and its enhanced upregulation in all tissues leads to a decline in fly viability. The toxicity associated with increased Gemin2 levels is conserved in the yeast S. pombe in which we find that the cytoplasmic retention of Sm proteins, likely reflecting a block in the snRNP assembly pathway, is a contributing factor. We propose that a disruption in the normal stoichiometry of the SMN-Gemins complex depresses its function with consequences that are detrimental to the motor system.

Current aging science, 2013

Dementia of the Alzheimer type is the most common form of dementia affecting mostly the elderly p... more Dementia of the Alzheimer type is the most common form of dementia affecting mostly the elderly population. It is a progressive and fatal neurodegenerative disorder with characteristic neuropathology and clinical symptomology. In the coming years, the number of individuals with Alzheimer's disease (AD) will increase as the elderly population worldwide is expected to grow significantly thus putting an added strain on national health care systems as well as caregivers who will inevitably carry most of the care burden. Thus it has been suggested that early intervention strategies which delay or halt the disease progression will have a strong impact on clinical outcomes. Changes in lifestyle habits such as diet modification or supplementation have been indicated as probable protective factors for a number of chronic conditions including AD. Particular attention has recently been devoted to the Mediterranean diet which is rich in the antioxidants Vitamins C and E, polyunsaturated fat...

In previous studies, we observed that aspirin, a promising cancer-preventive agent, induces apopt... more In previous studies, we observed that aspirin, a promising cancer-preventive agent, induces apoptosis in mitochondrial manganese superoxide dismutase (MnSOD)-deficient Saccharomyces cerevisiae cells grown aerobically in ethanol medium. In this study, we show that aspirin-induced apoptosis is associated with a significant increase in mitochondrial and cytosolic O ÁÀ 2 and oxidation of mitochondrial NAD(P)H. A concomitant rise in the level of cytosolic CuZn-SOD activity failed to compensate for mitochondrial MnSOD deficiency. However , an observed increase in activity of Escherichia coli FeSOD targeted to the mitochondrial matrix of the MnSOD-deficient yeast cells, markedly decreased aspirin-induced accumulation of mitochondrial O ÁÀ 2 , significantly increased the mitochondrial NAD(P)H level and rescued the apoptotic phenotype. Indeed, recombinant yeast cells expressing E. coli FeSOD behaved in a similar manner to the parent wild-type yeast cells with native mitochondrial MnSOD activity. Wild-type cells consistently showed a decrease in mitochondrial O ÁÀ 2 and an increase in mitochondrial NAD(P)H levels in the presence of aspirin in ethanol medium. In fact, in wild-type cells, our studies supported an antioxidant action of aspirin. Taken together, our results indicate that a pro-oxidant effect of aspirin occurring predominantly in cells with compromised mitochondrial redox balance may be enough to overcome antioxidant defences resulting in apopto-sis, as observed in MnSOD-deficient yeast cells.

Prion diseases are neurodegenerative disorders characterized by a hallmark event involving the po... more Prion diseases are neurodegenerative disorders characterized by a hallmark event involving the post-translational misfolding of the normal cellular prion protein (PrP C) into an infectious and toxic protease-resistant confor-mation (PrP Sc). Studies on identification of the pathological prion species and on the mechanisms involved in triggering neuronal death have been hampered by the heterogeneous nature of PrP Sc aggregates. The use of synthetic PrP-derived peptides has made possible exploration of the relationship between amino acid sequence, biophysical structure and biological effect. Indeed, most PrP-derived peptides replicate the fundamental aspects of full-length PrP Sc , including: a-sheet-rich structure; destabilization of lipid membranes; intracellular calcium dysregulation; increased oxidative stress; activation of pro-apoptotic signaling pathways; and, more contentiously, neurotoxicity dependent upon endogenous PrP C expression. Crucially, in vivo toxicity of the important PrP-peptides, e.g. PrP(106-126) and PrP(118-135), has additionally been established. Therefore, the use of prion-derived peptides facilitates the development of therapeutic strategies based on small-molecule inhibitors of aggregation and other pharmacological agents that protect against the lethal effect of these peptides in vivo.

Parkinson's disease (PD) is a common motor neurodegenerative disorder with multifactorial etiolog... more Parkinson's disease (PD) is a common motor neurodegenerative disorder with multifactorial etiology that is an increasing burden on our aging society. PD is characterized by nigrostriatal degeneration which might involve oxidative stress, '-synuclein ('S) aggregation, dysregulation of redox metal homeostasis and neurotoxicity. Although the exact cause remains unknown, both genetic and environmental factors have been implicated. Among the various environmental factors tea consumption has attracted increasing interest, as besides being one of the most consumed beverages in the world, tea contains specific polyphenols which can play an important role in delaying the onset or halting the progression of PD. Green and black teas are rich sources of polyphenols, the most abundant being epigallocatechin-3-gallate (EGCG) and theaflavins. There is now consistent mechanistic data on the neuroprotective and neuroregenerative effects of tea polyphenols, indicating that they do not just possess anti-oxidant or anti-chelating properties but may directly interfere with aggregation of the 'S protein and modulate intracellular signalling pathways, both in vitro and in animal models. EGCG in green tea has been by far the most studied compound and therefore future investigations should address more the effects of other polyphenols, especially theaflavins in black tea. Nevertheless, despite significant data on their potential neuroprotective effects, clinical studies are still very limited and to date only EGCG has

One of the key molecular events underlying the pathogenesis of Parkinson's disease (PD) is the ab... more One of the key molecular events underlying the pathogenesis of Parkinson's disease (PD) is the aberrant misfolding and aggregation of the α-synuclein (αS) protein into higher-order oligomers that play a key role in neuronal dysfunction and degeneration. A wealth of experimental data supports the hypothesis that the neuro-toxicity of αS oligomers is intrinsically linked with their ability to interact with, and disrupt, biological membranes; especially those membranes having negatively-charged surfaces and/or lipid packing defects. Consequences of αS–lipid interaction include increased membrane tension, permeation by pore formation, membrane lysis and/or leakage due to the extraction of lipids from the bilayer. Moreover, we assert that the interaction of αS with a liquid-disordering phospholipid uniquely enriched in mitochondrial membranes, namely cardiolipin (1,3-diphosphatidyl-sn-glycerol, CL), helps target the αS oligomeric complexes intracellularly to mitochondria. Binding mediated by CL may thus represent an important pathomechanism by which cytosolic αS could physically associate with mitochondrial membranes and disrupt their integrity. Impaired mitochondrial function culminates in a cellular bioenergetic crisis and apoptotic death. To conclude, we advocate the accelerated discovery of new drugs targeting this pathway in order to restore mitochondrial function in PD.

Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common age-related neurodegene... more Alzheimer's disease (AD) and Parkinson's disease (PD) are the most common age-related neurodegenerative disorders and hence pose remarkable socio-economical burdens to both families and state. Although AD and PD have different clinical and neuropathologi-cal features, they share common molecular mechanisms that appear to be triggered by multi-factorial events, such as protein aggregation, mitochondrial dysfunction, oxidative stress (OS), and neuroinflammation, ultimately leading to neuronal cell death. Currently, there are no established and validated disease-modifying strategies for either AD or PD. Among the various lifestyle factors that may prevent or slow age-related neurode-generative diseases, epidemiological studies on moderate consumption of red wine, especially as part of a holistic Mediterranean diet, have attracted increasing interest. Red wine is particularly rich in specific polyphenolic compounds that appear to affect the biological processes of AD and PD, such as quercetin, myricetin, catechins, tannins, anthocyanidins, resveratrol, and ferulic acid. Indeed, there is now a consistent body of in vitro and in vivo data on the neuroprotective effects of red wine polyphenols (RWP) showing that they do not merely possess antioxidant properties, but may additionally act upon, in a multi-target manner, the underlying key mechanisms featuring in both AD and PD. Furthermore, it is important that bioavailability issues are addressed in order for neuroprotection to be relevant in a clinical study scenario. This review summarizes the current knowledge about the major classes of RWP and places into perspective their potential to be considered as nutraceuticals to target neuropathology in AD and PD.

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Neurobiology of Disease, 2016

PLOS ONE, 2015

Current aging science, 2013

A prion protein is essentially a protein that can replicate itself. The mechanism of propagation ... more A prion protein is essentially a protein that can replicate itself. The mechanism of propagation is characterized by the ability of the protein in the prion-like state to catalytically convert the homologous natively-folded protein into a likeness of itself. This switch in conformation forms the basis for the infectious nature of prion proteins. The first such protein to be discovered was the cellular prion protein (PrP). Post-translational modification of native PrPC into its pathogenic isoform (PrPSc) is the molecular signature underlying a group of fatal mammalian neurodegenerative disorders (transmissible spongiform encephalopathies). Interestingly, recent studies on the physiological function of PrPC strongly indicate a critical role of the molecule in activation of signalling pathways linked to maintenance of mitochondrial integrity and cell survival. These include the phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways. Many interaction partners have been proposed for PrPC, but perhaps the most intriguing is its ability to bind copper(II) ions via the highly conserved N- terminal octapeptide repeat domains. Indeed, our studies were the first to suggest that copper enables triggering of PrP-dependent signalling to PI3K, which in turn acts as a modulator of neuroprotective signalling. Given that conversion of PrPC to PrPSc in prion diseases leads to PrPC deficiency, pharmacological stimulation of lost PrPC signals may provide a useful treatment approach for these fatal neurological illnesses. In addition, studies on the signalling aspect of PrP underscore the importance of the prion mechanism with respect to modulation of signalling pathways. Specifically, the self-sustaining conformational propagation of the prion-like state can induce a stable alteration in a signalling pathway. Such a novel mechanism of signalling is being proposed to play important roles in biological phenomena as diverse as adaptive growth, long-term memory, and cancer.

A large group of human diseases are characterised by the deposition of insoluble proteinaceous le... more A large group of human diseases are characterised by the deposition of insoluble proteinaceous lesions, termed amyloid. The underlying pathogenic process in these disorders involves the misfolding and self-assembly of native monomeric proteins into toxic, multimeric aggregates. Indeed, “protein misfolding” is one of the most researched topics in cell biology and sub- cellular biochemistry in recent years. To date, more than 20 amyloidogenic proteins have been identified, including amyloid-beta and tau in Alzheimer’s disease, alpha-synuclein in Parkinson’s disease, huntigtin in Huntington’s disease, superoxide dismutase in amyotrophic lateral sclerosis, prion protein in Creutzfeldt-Jakob disease and islet amyloid polypeptide in type 2 diabetes mellitus. Collectively, these disorders inflict an enormous economical burden on societies, whilst being devastating at a personal level. It is therefore of paramount importance to understand their origin and learn how to treat, or prevent, them. At present, there are no approved therapies that target amyloid formation directly, but a wealth of experimental and epidemiological evidence now indicates that various naturally derived compounds have beneficial anti- amyloid effects.
This book volume was written with the aim of disseminating the state- of-the-art and most recent knowledge of the field, highlighting the most promising nutra-therapeutics derived from natural compounds or extracts. The focus is mainly on Alzheimer’s disease and related dementias; how- ever, Parkinson’s disease and other forms of cerebral amyloidosis are also discussed. Evidence is presented based upon published studies that have undergone rigorous scientific peer review. Researches include a combination of in vitro (biophysics, biochemistry, molecular and cellular biology), in vivo (fruit fly, transgenic mice and rats) and epidemiological (human) studies, so as to provide the reader with a holistic scientific approach. Among the therapeutic agents that are discussed in detail, we find Mediterranean diet and olive oil polyphenols, teas and catechins, natural phenolic compounds and bioflavonoids. Given the recent surge of public interest in herbal medicines, a chapter is devoted to evidence-based traditional Chinese medicine in brain ageing. Individual chapters are written by established scientists in their relevant fields; sufficient background is given in each chapter by way of introduction to the non-expert reader. Hence, this book should be of interest to a wide audience, including academia, various health professionals, the nutraceutical industry and undergraduate students reading for pharmaceutical, medical, biology and chemistry degrees.

I conclude by stating that, on a personal level, the most noble goal of this book is that with our collective contributions to scientific progress, we aim to provide hope for the future and hope for the many people suffering from as yet incurable amyloid diseases. This book is, after all, dedicated to them.

Msida, Malta Neville Vassallo