The various aggregation states of beta-amyloid 1-42 mediate different effects on oxidative stress, neurodegeneration, and BACE-1 expression

Anthracene detoxification by Laccases from indigenous fungal strains Trichoderma lixii FLU1 and Talaromyces pinophilus FLU12

The persistence and ubiquity of polycyclic aromatic hydrocarbons (PAHs) in the environment necessitate effective remediation strategies. Hence, this study investigated the potential of purified Laccases, TlFLU1L and TpFLU12L, from two indigenous fungi Trichoderma lixii FLU1 (TlFLU1) and Talaromyces pinophilus FLU12 (TpFLU12), respectively for the oxidation and detoxification of anthracene. Anthracene was degraded with vmax values of 3.51 ± 0.06 mg/L/h and 3.44 ± 0.06 mg/L/h, and Km values of 173.2 ± 0.06 mg/L and 73.3 ± 0.07 mg/L by TlFLU1L and TpFLU12L, respectively. The addition of a mediator compound 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to the reaction system significantly increased the degradation of anthracene, with up to a 2.9-fold increase in vmax value and up to threefold decrease in Km values of TlFLU1L and TpFLU12L. The GC-MS analysis of the metabolites suggests that anthracene degradation follows one new pathway unique to the ABTS system-hydroxylation and carboxylation of C-1 and C-2 position of anthracene to form 3-hydroxy-2-naphthoic acid, before undergoing dioxygenation and side chain removal to form chromone which was later converted into benzoic acid and CO2. This pathway contrasts with the common dioxygenation route observed in the free Laccase system, which is observed in the second degradation pathways. Furthermore, toxicity tests using V. parahaemolyticus and HT-22 cells, respectively, demonstrated the non-toxic nature of Laccase-ABTS-mediated metabolites. Intriguingly, analysis of the expression level of Alzheimer's related genes in HT-22 cells exposed to degradation products revealed no induction of neurotoxicity unlike untreated cells. These findings propose a paradigm shift for bioremediation by highlighting the Laccase-ABTS system as a promising green technology due to its efficiency with the discovery of a potentially less harmful degradation pathway, and the production of non-toxic metabolites.

Myelin in Alzheimer's disease: culprit or bystander?

Alzheimer's disease (AD) is a neurodegenerative disorder with neuronal and synaptic losses due to the accumulation of toxic amyloid β (Αβ) peptide oligomers, plaques, and tangles containing tau (tubulin-associated unit) protein. While familial AD is caused by specific mutations, the sporadic disease is more common and appears to result from a complex chronic brain neuroinflammation with mitochondriopathies, inducing free radicals' accumulation. In aged brain, mutations in DNA and several unfolded proteins participate in a chronic amyloidosis response with a toxic effect on myelin sheath and axons, leading to cognitive deficits and dementia. Αβ peptides are the most frequent form of toxic amyloid oligomers. Accumulations of misfolded proteins during several years alters different metabolic mechanisms, induce chronic inflammatory and immune responses with toxic consequences on neuronal cells. Myelin composition and architecture may appear to be an early target for the toxic activity of Aβ peptides and others hydrophobic misfolded proteins. In this work, we describe the possible role of early myelin alterations in the genesis of neuronal alterations and the onset of symptomatology. We propose that some pathophysiological and clinical forms of the disease may arise from structural and metabolic disorders in the processes of myelination/demyelination of brain regions where the accumulation of non-functional toxic proteins is important. In these forms, the primacy of the deleterious role of amyloid peptides would be a matter of questioning and the initiating role of neuropathology would be primarily the fact of dysmyelination.

A Diet Containing Rutin Ameliorates Brain Intracellular Redox Homeostasis in a Mouse Model of Alzheimer's Disease

Quercetin has been studied extensively for its anti-Alzheimer's disease (AD) and anti-aging effects. Our previous studies have found that quercetin and in its glycoside form, rutin, can modulate the proteasome function in neuroblastoma cells. We aimed to explore the effects of quercetin and rutin on intracellular redox homeostasis of the brain (reduced glutathione/oxidized glutathione, GSH/GSSG), its correlation with β-site APP cleaving enzyme 1 (BACE1) activity, and amyloid precursor protein (APP) expression in transgenic TgAPP mice (bearing human Swedish mutation APP transgene, APPswe). On the basis that BACE1 protein and APP processing are regulated by the ubiquitin-proteasome pathway and that supplementation with GSH protects neurons from proteasome inhibition, we investigated whether a diet containing quercetin or rutin (30 mg/kg/day, 4 weeks) diminishes several early signs of AD. Genotyping analyses of animals were carried out by PCR. In order to determine intracellular redox homeostasis, spectrofluorometric methods were adopted to quantify GSH and GSSG levels using o-phthalaldehyde and the GSH/GSSG ratio was ascertained. Levels of TBARS were determined as a marker of lipid peroxidation. Enzyme activities of SOD, CAT, GR, and GPx were determined in the cortex and hippocampus. ΒACE1 activity was measured by a secretase-specific substrate conjugated to two reporter molecules (EDANS and DABCYL). Gene expression of the main antioxidant enzymes: APP, BACE1, a Disintegrin and metalloproteinase domain-containing protein 10 (ADAM10), caspase-3, caspase-6, and inflammatory cytokines were determined by RT-PCR. First, overexpression of APPswe in TgAPP mice decreased GSH/GSSG ratio, increased malonaldehyde (MDA) levels, and, overall, decreased the main antioxidant enzyme activities in comparison to wild-type (WT) mice. Treatment of TgAPP mice with quercetin or rutin increased GSH/GSSG, diminished MDA levels, and favored the enzyme antioxidant capacity, particularly with rutin. Secondly, both APP expression and BACE1 activity were diminished with quercetin or rutin in TgAPP mice. Regarding ADAM10, it tended to increase in TgAPP mice with rutin treatment. As for caspase-3 expression, TgAPP displayed an increase which was the opposite with rutin. Finally, the increase in expression of the inflammatory markers IL-1β and IFN-γ in TgAPP mice was lowered by both quercetin and rutin. Collectively, these findings suggest that, of the two flavonoids, rutin may be included in a day-to-day diet as a form of adjuvant therapy in AD.

Microglia and Cholesterol Handling: Implications for Alzheimer's Disease

Cholesterol is essential for brain function and structure, however altered cholesterol metabolism and transport are hallmarks of multiple neurodegenerative conditions, including Alzheimer's disease (AD). The well-established link between apolipoprotein E (APOE) genotype and increased AD risk highlights the importance of cholesterol and lipid transport in AD etiology. Whereas more is known about the regulation and dysregulation of cholesterol metabolism and transport in neurons and astrocytes, less is known about how microglia, the immune cells of the brain, handle cholesterol, and the subsequent implications for the ability of microglia to perform their essential functions. Evidence is emerging that a high-cholesterol environment, particularly in the context of defects in the ability to transport cholesterol (e.g., expression of the high-risk APOE4 isoform), can lead to chronic activation, increased inflammatory signaling, and reduced phagocytic capacity, which have been associated with AD pathology. In this narrative review we describe how cholesterol regulates microglia phenotype and function, and discuss what is known about the effects of statins on microglia, as well as highlighting areas of future research to advance knowledge that can lead to the development of novel therapies for the prevention and treatment of AD.

Potential of fluorescent nanoprobe in diagnosis and treatment of Alzheimer's disease

Alzheimer's disease (AD) is well known for its insidious nature, slow progression and high incidence as a neurodegenerative disease. In the past, diagnosis of AD mainly depended on analysis of a patient's cognitive ability and behavior. Without a unified standard for analysis methods, this is prone to produce incorrect diagnoses. Currently, definitive diagnosis mainly relies on histopathological examination. Because of the advantages of precision, noninvasiveness, low toxicity and high spatiotemporal resolution, fluorescent nanoprobes are suitable for the early diagnosis of AD. This review summarizes the research progress of different kinds of fluorescent nanoprobes for AD diagnosis and therapy in recent years and provides an outlook on the development prospects of fluorescent nanoprobes.

Resveratrol and neuroprotection: an insight into prospective therapeutic approaches against Alzheimer's disease from bench to bedside

Alzheimer's disease (AD) is the most common cause of dementia and cognitive impairment; yet, there is currently no treatment. A buildup of Aβ, tau protein phosphorylation, oxidative stress, and inflammation in AD is pathogenic. The accumulation of amyloid-beta (Aβ) peptides in these neurocognitive areas is a significant characteristic of the disease. Therefore, inhibiting Aβ peptide aggregation has been proposed as the critical therapeutic approach for AD treatment. Resveratrol has been demonstrated in multiple studies to have a neuroprotective, anti-inflammatory, and antioxidant characteristic and the ability to minimize Aβ peptides aggregation and toxicity in the hippocampus of Alzheimer's patients, stimulating neurogenesis and inhibiting hippocampal degeneration. Furthermore, resveratrol's antioxidant effect promotes neuronal development by activating the silent information regulator-1 (SIRT1), which can protect against the detrimental effects of oxidative stress. Resveratrol-induced SIRT1 activation is becoming more crucial in developing novel therapeutic options for AD and other diseases that have neurodegenerative characteristics. This review highlighted a better knowledge of resveratrol's mechanism of action and its promising therapeutic efficacy in treating AD. We also highlighted the therapeutic potential of resveratrol as an AD therapeutic agent, which is effective against neurodegenerative disorders.

Proteasome activity modulates amyloid toxicity

Alzheimer's disease (AD) is responsible for 60%-80% of identified cases of dementia. While the generation and accumulation of amyloid precursor protein (APP) fragments is accepted as a key step in AD pathogenesis, the precise role of these fragments remains poorly understood. To overcome this deficit, we induced the expression of the soluble C-terminal fragment of APP (C99), the rate-limiting peptide for the generation of amyloid fragments, in yeast that contain thermosensitive mutations in genes encoding proteasome subunits. Our previous work with this system demonstrated that these proteasome-deficient yeast cells, expressing C99 when proteasome activity was blunted, generated amyloid fragments similar to those observed in AD patients. We now report the phenotypic repercussions of inducing C99 expression in proteasome-deficient cells. We show increased levels of protein aggregates, cellular stress and chaperone expression, electron-dense accumulations in the nuclear envelope/ER, abnormal DNA condensation, and an induction of apoptosis. Taken together, these findings suggest that the generation of C99 and its associated fragments in yeast cells with compromised proteasomal activity results in phenotypes that may be relevant to the neuropathological processes observed in AD patients. These data also suggest that this yeast model should be useful for testing therapeutics that target AD-associated amyloid, since it allows for the assessment of the reversal of the perturbed cellular physiology observed when degradation pathways are dysfunctional.

Potential of Ramalin and Its Derivatives for the Treatment of Alzheimer's Disease

The pathogenesis of Alzheimer's disease (AD) is still unclear, and presently there is no cure for the disease that can be used for its treatment or to stop its progression. Here, we investigated the therapeutic potential of ramalin (isolated from the Antarctic lichen, Ramalina terebrata), which exhibits various physiological activities, in AD. Specifically, derivatives were synthesized based on the structure of ramalin, which has a strong antioxidant effect, BACE-1 inhibition activity, and anti-inflammatory effects. Therefore, ramalin and its derivatives exhibit activity against multiple targets associated with AD and can serve as potential therapeutic agents for the disease.

An Overview of β-Amyloid Cleaving Enzyme 1 (Bace1) in Alzheimer's Disease Therapy Elucidating its Exosite-Binding Antibody and Allosteric Inhibitor

Over decades of its identification, numerous past and ongoing researches have focused on the therapeutic roles of β-amyloid cleaving enzyme 1 (BACE1) as a target in treating Alzheimer's disease (AD). Although the initial BACE1 inhibitors at phase-3 clinical trials tremendously reduced β-amyloid-associated plaques in patients with AD, the researchers eventually discontinued the tests due to the lack of potency. This discontinuation has resulted in limited drug development and discovery targeted at BACE1, despite the high demand for dementia and AD therapies. It is, therefore, imperative to describe the detailed underlying biological basis of the BACE1 therapeutic option in neurological diseases. Herein, we highlight BACE1 bioactivity, genetic properties, and role in neurodegenerative therapy. We review research contributions to BACE1 exosite-binding antibody and allosteric inhibitor development as AD therapies. The review also covers BACE1 biological function, the disease-associated mechanisms, and the enzyme conditions for amyloid precursor protein sites splitting. Based on the present review, we suggest further studies on anti-BACE1 exosite antibodies and BACE1 allosteric inhibitors. Non-active site inhibition might be the way forward to BACE1 therapy in Alzheimer's neurological disorder.

Molecular Mechanisms and Genetics of Oxidative Stress in Alzheimer's Disease

Alzheimer’s disease is the most common neurodegenerative disorder that can cause dementia in elderly over 60 years of age. One of the disease hallmarks is oxidative stress which interconnects with other processes such as amyloid-β deposition, tau hyperphosphorylation, and tangle formation. This review discusses current thoughts on molecular mechanisms that may relate oxidative stress to Alzheimer’s disease and identifies genetic factors observed from in vitro, in vivo, and clinical studies that may be associated with Alzheimer’s disease-related oxidative stress.

The Role of Mitochondrial Calcium Homeostasis in Alzheimer's and Related Diseases

Calcium signaling is essential for neuronal function, and its dysregulation has been implicated across neurodegenerative diseases, including Alzheimer’s disease (AD). A close reciprocal relationship exists between calcium signaling and mitochondrial function. Growing evidence in a variety of AD models indicates that calcium dyshomeostasis drastically alters mitochondrial activity which, in turn, drives neurodegeneration. This review discusses the potential pathogenic mechanisms by which calcium impairs mitochondrial function in AD, focusing on the impact of calcium in endoplasmic reticulum (ER)–mitochondrial communication, mitochondrial transport, oxidative stress, and protein homeostasis. This review also summarizes recent data that highlight the need for exploring the mechanisms underlying calcium-mediated mitochondrial dysfunction while suggesting potential targets for modulating mitochondrial calcium levels to treat neurodegenerative diseases such as AD.

Early administration of galantamine from preplaque phase suppresses oxidative stress and improves cognitive behavior in APPswe/PS1dE9 mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a common neurodegenerative disease that progressively impairs memory and cognition. Deposition of amyloid-β (Aβ) peptides is the most important pathophysiological hallmark of AD. Oxidative stress induced by generation of reactive oxygen species (ROS) is a prominent phenomenon in AD and known to occur early in the course of AD. Several reports suggest a relationship between change in redox status and AD pathology including progressive Aβ deposition, glial cell activation, and inflammation. Galantamine is an acetylcholinesterase inhibitor and has been reported to have an oxidative stress inhibitory function. In the present study, galantamine was administered orally to AD model mice from before the appearance of Aβ plaques (preplaque phase), and in vivo change in redox status of the brain was measured using electron paramagnetic resonance (EPR) imaging. Administration of galantamine from the preplaque phase ameliorated memory decline in Morris water maze test and novel object recognition test. Monitoring of the redox status of the brain using EPR imaging showed that galantamine treatment improved the unbalanced redox state. Additionally, galantamine administration enhanced microglial function to promote Aβ clearance, reducing the Aβ-positive area in the cortex and amount of insoluble Aβ in the brain. In contrast, galantamine treatment from the preplaque phase suppressed the production of proinflammatory cytokines through neurotoxic microglial activity. Therefore, galantamine administration from the preplaque phase may have the potential of clinical application for the prevention of AD. In addition, our results demonstrate the usefulness of EPR imaging for speedy and quantitative evaluation of the efficacy of disease-modifying drugs for AD.

Early Alterations of Hippocampal Neuronal Firing Induced by Abeta42

We studied the effect of Amyloid β 1-42 oligomers (Abeta42) on Ca2+ dependent excitability profile of hippocampal neurons. Abeta42 is one of the Amyloid beta peptides produced by the proteolytic processing of the amyloid precursor protein and participates in the initiating event triggering the progressive dismantling of synapses and neuronal circuits. Our experiments on cultured hippocampal network reveal that Abeta42 increases intracellular Ca2+ concentration by 46% and inhibits firing discharge by 19%. More precisely, Abeta42 differently regulates ryanodine (RyRs), NMDA receptors (NMDARs), and voltage gated calcium channels (VGCCs) by increasing Ca2+ release through RyRs and inhibiting Ca2+ influx through NMDARs and VGCCs. The overall increased intracellular Ca2+ concentration causes stimulation of K+ current carried by big conductance Ca2+ activated potassium (BK) channels and hippocampal network firing inhibition. We conclude that Abeta42 alters neuronal function by means of at least 4 main targets: RyRs, NMDARs, VGCCs, and BK channels. The development of selective modulators of these channels may in turn be useful for developing effective therapies that could enhance the quality of life of AD patients during the early onset of the pathology.

Quantum dots-based sandwich immunoassay for sensitive detection of Alzheimer's disease-related Aβ1-42

Amyloid-beta peptide 1-42 (Aβ_1-42) is known as a component of amyloid plaques in association with Alzheimer's disease. Herein, we developed a reliable and remarkably sensitive sandwich immunoassay to detect the Aβ_1-42 using quantum dots (QDs) as fluorescent label. In the presence of Aβ_1-42, the biotinylated Anti-beta Amyloid 1-16 (N-Ab) recognized the target and formed C-Ab-Aβ_1-42-N-Ab sandwich immunocomplexes. Then Streptavidin-QDs conjugated to biotinylated N-Ab and the concentration of Aβ_1-42 was determined by detecting the fluorescence intensity in the supernatant. This method is faster and more efficient than the previous approach we reported. It also has reasonable sensitivity and selectivity. Under the optimized conditions, the linear range is 5.0 to 100 pM (0.023-0.45 ng/mL) and the detection limit is 1.7 pM (7.6 pg/ mL). In addition, this method has been successfully applied to detect the Aβ_1-42 in human cerebrospinal fluid sample.

Betaine reduces β-amyloid-induced paralysis through activation of cystathionine-β-synthase in an Alzheimer model of Caenorhabditis elegans

BACKGROUND

The neurodegenerative disorder Alzheimer's disease is caused by the accumulation of toxic aggregates of β-amyloid in the human brain. On the one hand, hyperhomocysteinemia has been shown to be a risk factor for cognitive decline in Alzheimer's disease. On the other hand, betaine has been demonstrated to attenuate Alzheimer-like pathological changes induced by homocysteine. It is reasonable to conclude that this is due to triggering the remethylation pathway mediated by betaine-homocysteine-methyltransferase. In the present study, we used the transgenic Caenorhabditis elegans strain CL2006, to test whether betaine is able to reduce β-amyloid-induced paralysis in C. elegans. This model expresses human β-amyloid 1-42 under control of a muscle-specific promoter that leads to progressive, age-dependent paralysis in the nematodes.

RESULTS

Betaine at a concentration of 100 μM was able to reduce homocysteine levels in the presence and absence of 1 mM homocysteine. Simultaneously, betaine both reduced normal paralysis rates in the absence of homocysteine and increased paralysis rates triggered by addition of homocysteine. Knockdown of cystathionine-β-synthase using RNA interference both increased homocysteine levels and paralysis. Additionally, it prevented the reducing effects of betaine on homocysteine levels and paralysis.

CONCLUSION

Our studies show that betaine is able to reduce homocysteine levels and β-amyloid-induced toxicity in a C. elegans model for Alzheimer's disease. This effect is independent of the remethylation pathway but requires the transsulfuration pathway mediated by cystathionine-β-synthase.

The Unexpected Role of Aβ1-42 Monomers in the Pathogenesis of Alzheimer's Disease

Amyloid-β (Aβ) has been proposed as a biomarker and a drug target for the therapy of Alzheimer's disease (AD). The neurotoxic entity and relevance of each conformational form of Aβ to AD pathology is still under debate; Aβ oligomers are considered the major killer form of the peptide whereas monomers have been proposed to be involved in physiological process. Here we reviewed some different effects mediated by monomers and oligomers on mechanisms involved in AD pathogenesis such as autophagy and tau aggregation. Data reported in this review demonstrate that Aβ monomers could have a major role in sustaining the pathogenesis of AD and that AD therapy should be focused not only in the removal of oligomers but also of monomers.

Role of Vitamin E in the Treatment of Alzheimer's Disease: Evidence from Animal Models

Alzheimer's disease (AD) is a neurodegenerative disorder representing the major cause of dementia. It is characterized by memory loss, and cognitive and behavioral decline. In particular, the hallmarks of the pathology are amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs), formed by aggregated hyperphosphorylated tau protein. Oxidative stress plays a main role in AD, and it is involved in initiation and progression of AD. It is well known that Aβ induced oxidative stress, promoting reactive oxygen species (ROS) production and consequently lipid peroxidation, protein oxidation, tau hyperphosphorylation, results in toxic effects on synapses and neurons. In turn, oxidative stress can increase Aβ production. For these reasons, the administration of an antioxidant therapy in AD patients was suggested. The term vitamin E includes different fat-soluble compounds, divided into tocopherols and tocotrienols, that possess antioxidant action. α-Tocopherol is the most studied, but some studies suggested that tocotrienols may have different health promoting capacities. In this review, we focused our attention on the effects of vitamin E supplementation in AD animal models and AD patients or older population. Experimental models showed that vitamin E supplementation, by decreasing oxidative stress, may be a good strategy to improve cognitive and memory deficits. Furthermore, the combination of vitamin E with other antioxidant or anti-inflammatory compounds may increase its efficacy. However, even if some trials have evidenced some benefits, the effects of vitamin E in AD patients are still under debate.

Forging our understanding of lncRNAs in the brain

During both development and adulthood, the human brain expresses many thousands of long noncoding RNAs (lncRNAs), and aberrant lncRNA expression has been associated with a wide range of neurological diseases. Although the biological significance of most lncRNAs remains to be discovered, it is now clear that certain lncRNAs carry out important functions in neurodevelopment, neural cell function, and perhaps even diseases of the human brain. Given the relatively inclusive definition of lncRNAs-transcripts longer than 200 nucleotides with essentially no protein coding potential-this class of noncoding transcript is both large and very diverse. Furthermore, emerging data indicate that lncRNA genes can act via multiple, non-mutually exclusive molecular mechanisms, and specific functions are difficult to predict from lncRNA expression or sequence alone. Thus, the different experimental approaches used to explore the role of a lncRNA might each shed light upon distinct facets of its overall molecular mechanism, and combining multiple approaches may be necessary to fully illuminate the function of any particular lncRNA. To understand how lncRNAs affect brain development and neurological disease, in vivo studies of lncRNA function are required. Thus, in this review, we focus our discussion upon a small set of neural lncRNAs that have been experimentally manipulated in mice. Together, these examples illustrate how studies of individual lncRNAs using multiple experimental approaches can help reveal the richness and complexity of lncRNA function in both neurodevelopment and diseases of the brain.

Resveratrol and Amyloid-Beta: Mechanistic Insights

The amyloid-beta (Aβ) hypothesis that dyshomeostasis between Aβ production and clearance is a very early, key molecular factor in the etiology of Alzheimer’s disease (AD) has been proposed and examined in the AD research field. Scientists have focused on seeking natural products or drugs to influence the dynamic equilibrium of Aβ, targeting production and clearance of Aβ. There is emerging evidence that resveratrol (Res), a naturally occurring polyphenol mainly found in grapes and red wine, acts on AD in numerous in vivo and in vitro models. Res decreases the amyloidogenic cleavage of the amyloid precursor protein (APP), enhances clearance of amyloid beta-peptides, and reduces Aβ aggregation. Moreover, Res also protects neuronal functions through its antioxidant properties. This review discusses the action of Res on Aβ production, clearance and aggregation and multiple potential mechanisms, providing evidence of the useful of Res for AD treatment.

Cannabidiol: State of the art and new challenges for therapeutic applications

Over the past years, several lines of evidence support a therapeutic potential of Cannabis derivatives and in particular phytocannabinoids. Δ⁹-THC and cannabidiol (CBD) are the most abundant phytocannabinoids in Cannabis plants and therapeutic application for both compounds have been suggested. However, CBD is recently emerging as a therapeutic agent in numerous pathological conditions since devoid of the psychoactive side effects exhibited instead by Δ⁹-THC. In this review, we highlight the pharmacological activities of CBD, its cannabinoid receptor-dependent and -independent action, its biological effects focusing on immunomodulation, angiogenetic properties, and modulation of neuronal and cardiovascular function. Furthermore, the therapeutic potential of cannabidiol is also highlighted, in particular in nuerological diseases and cancer.

Statins Inhibit Fibrillary β-Amyloid Induced Inflammation in a Model of the Human Blood Brain Barrier

Background

Astrocytes and cerebral endothelial cells are important components of the blood-brain barrier (BBB). Disruption to this barrier through inflammation is a major contributor to Alzheimer’s disease (AD) pathology. The amyloid beta (Aβ) protein is known to exist in several forms and is a key modulator of AD that is known to cause inflammation and changes to BBB function. While one of these forms, fibrillary Aβ (fAβ), is known to cause endothelial cell death at the BBB, no studies have looked specifically at its role on inflammation in a model of the human BBB.

Aims

To determine if fAβ is inflammatory to the human BBB. As statins have been shown to be anti-inflammatory and protective in AD, we also tested if these could inhibit the inflammatory effect of fAβ.

Methods

Using cultured cerebral endothelial cells and astrocytes we determined changes in cytokine release, cell toxicity and barrier function in response to fibrillary β-amyloid_1–42 (fAβ_1–42) alone and in combination with statins.

Results

fAβ_1–42 induced inflammatory cytokine release from endothelial cells in the absence of cell toxicity. It also induced astrocyte cytokine release and cell death and caused a loss of barrier integrity. Statin treatment inhibited all of these effects.

Conclusions

We conclude that fAβ_1–42 has both inflammatory and cytotoxic effects on the BBB and the protective effect of statins in AD may in part be through inhibiting these effects.

Bamboo leaf extract improves spatial learning ability in a rat model with senile dementia

Senile dementia (SD) is a syndrome characterized by progressive neurological deterioration. Treatment for the disease is still under investigation. Bamboo leaf extract (B-extract) has been known for its biological efficacy in anti-oxidant and anti-cancer activities. However, study on B-extract for its protection against dementia is very limited. The effect of B-extract on a rat model with SD was examined. B-extract improved spatial learning ability of the dementia rats. The hippocampus of dementia model rats showed reduced levels of acetylcholine (ACh), epinephrine (E), norepinephrine (NE), and dopamine (DA), and increased activities of acetylcholine esterase (AChE) and monoamine oxidase (MAO). Treatment with B-extract 20 mg/(kg·d) for 7 weeks significantly inhibited the enzyme activity compared with untreated dementia rats, and raised the levels of ACh, E, and DA in the hippocampus. In addition, treatment with B-extract elevated the level of γ-aminobutyric acid (GABA), but reduced the level of glutamate (Glu) in the brain. These data suggest that B-extract might be a potential drug in treating impairment of spatial memory in dementia rats by regulating the central neurotransmitter function.

Biological and computational evaluation of resveratrol inhibitors against Alzheimer's disease

It has been reported that beta amyloid induces production of radical oxygen species and oxidative stress in neuronal cells, which in turn upregulates β-secretase (BACE-1) expression and beta amyloid levels, thereby propagating oxidative stress and increasing neuronal injury. A series of resveratrol derivatives, known to be inhibitors of oxidative stress-induced neuronal cell death (oxytosis) were biologically evaluated against BACE-1 using homogeneous time-resolved fluorescence (TRF) assay. Correlation between oxytosis inhibitory and BACE-1 inhibitory activity of resveratrol derivatives was statistically significant, supporting the notion that BACE-1 may act as pivotal mediator of neuronal cell oxytosis. Four of the biologically evaluated resveratrol analogs demonstrated considerably higher activity than resveratrol in either assay. The discovery of some "hits" led us to initiate detailed docking studies associated with Molecular Dynamics in order to provide a plausible explanation for the experimental results and understand their molecular basis of action.

Oxidized cholesterol as the driving force behind the development of Alzheimer's disease

Alzheimer’s disease (AD), the most common neurodegenerative disorder associated with dementia, is typified by the pathological accumulation of amyloid Aβ peptides and neurofibrillary tangles (NFT) within the brain. Considerable evidence indicates that many events contribute to AD progression, including oxidative stress, inflammation, and altered cholesterol metabolism. The brain’s high lipid content makes it particularly vulnerable to oxidative species, with the consequent enhancement of lipid peroxidation and cholesterol oxidation, and the subsequent formation of end products, mainly 4-hydroxynonenal and oxysterols, respectively from the two processes. The chronic inflammatory events observed in the AD brain include activation of microglia and astrocytes, together with enhancement of inflammatory molecule and free radical release. Along with glial cells, neurons themselves have been found to contribute to neuroinflammation in the AD brain, by serving as sources of inflammatory mediators. Oxidative stress is intimately associated with neuroinflammation, and a vicious circle has been found to connect oxidative stress and inflammation in AD. Alongside oxidative stress and inflammation, altered cholesterol metabolism and hypercholesterolemia also significantly contribute to neuronal damage and to progression of AD. Increasing evidence is now consolidating the hypothesis that oxidized cholesterol is the driving force behind the development of AD, and that oxysterols are the link connecting the disease to altered cholesterol metabolism in the brain and hypercholesterolemia; this is because of the ability of oxysterols, unlike cholesterol, to cross the blood brain barrier (BBB). The key role of oxysterols in AD pathogenesis has been strongly supported by research pointing to their involvement in modulating neuroinflammation, Aβ accumulation, and cell death. This review highlights the key role played by cholesterol and oxysterols in the brain in AD pathogenesis.

NADH fluorescence lifetime is an endogenous reporter of α-synuclein aggregation in live cells

α-Synuclein (aS) aggregation has been amply investigated for its involvement in Parkinson's disease because its amyloid fibrils are the main constituent of Lewy bodies, one of the hallmarks of the disease. aS aggregation was studied here in vitro and in cellular models to correlate aggregation products with toxicity mechanisms. Independent results published elsewhere suggested that aS overexpression and/or aggregation may impair cellular metabolism and cause mitochondrial damage. In this context, we report the characterization of changes in NADH fluorescence properties in vitro and in human embryonic kidney 293 cells upon aS aggregation. The application of the phasor approach to study NADH fluorescence lifetime and emission allowed us to identify changes that correlate with aS aggregation. In particular, the fraction of bound NADH, characterized by longer lifetimes in comparison to free NADH, is increased, and the maximum of the NADH emission is shifted toward shorter wavelengths in the presence of aggregating aS both in vitro and in cells. These data suggest that NADH binds to aggregated aS. NMR experiments in vitro substantiate such binding, which occurs during aggregation. NADH fluorescence is thus useful to detect aS aggregation and by extension the associated oxidative stress.

Can BACE1 inhibition mitigate early axonal pathology in neurological diseases?

β-Secretase-1 (BACE1) is the rate-limiting enzyme for the genesis of amyloid-β (Aβ) peptides, the main constituents of the amyloid plaques in the brains of Alzheimer's disease (AD) patients. BACE1 is being evaluated as an anti-Aβ target for AD therapy. Recent studies indicate that BACE1 elevation is associated with axonal and presynaptic pathology during plaque development. Evidence also points to a biological role for BACE1 in axonal outgrowth and synapse formation during development. Axonal, including presynaptic, pathology exists in AD as well as many other neurological disorders such as Parkinson's disease, epilepsy, stroke, and trauma. In this review, we discuss pharmaceutical BACE1 inhibition as a therapeutic option for axonal pathogenesis, in addition to amyloid pathology. We first introduce the amyloidogenic processing of amyloid-β protein precursor and describe the normal expression pattern of the amyloidogenic proteins in the brain, with an emphasis on BACE1. We then address BACE1 elevation relative to amyloid plaque development, followed by updating recent understanding of a neurotrophic role of BACE1 in axon and synapse development. We further elaborate the occurrence of axonal pathology in some other neurological conditions. Finally, we propose pharmacological inhibition of excessive BACE1 activity as an option to mitigate early axonal pathology occurring in AD and other neurological disorders.

Aβ1-42 monomers or oligomers have different effects on autophagy and apoptosis

The role of autophagy and its relationship with apoptosis in Alzheimer disease (AD) pathogenesis is poorly understood. Disruption of autophagy leads to buildup of incompletely digested substrates, amyloid-β (Aβ) peptide accumulation in vacuoles and cell death. Aβ, in turn, has been found to affect autophagy. Thus, Aβ might be part of a loop in which it is both the substrate of altered autophagy and its cause. Given the relevance of different soluble forms of Aβ1-42 in AD, we have investigated whether monomers and oligomers of the peptide have a differential role in causing altered autophagy and cell death. Using differentiated SK-N-BE neuroblastoma cells, we found that monomers hamper the formation of the autophagic BCL2-BECN1/Beclin 1 complex and activate the MAPK8/JNK1-MAPK9/JNK2 pathway phosphorylating BCL2. Monomers also inhibit apoptosis and allow autophagy with intracellular accumulation of autophagosomes and elevation of levels of BECN1 and LC3-II, resulting in an inhibition of substrate degradation due to an inhibitory action on lysosomal activity. Oligomers, in turn, favor the formation of the BCL2-BECN1 complex favoring apoptosis. In addition, they cause a less profound increase in BECN1 and LC3-II levels than monomers without affecting the autophagic flux. Thus, data presented in this work show a link for autophagy and apoptosis with monomers and oligomers, respectively. These studies are likely to help the design of novel disease modifying therapies.

p53 functional inhibitors behaving like pifithrin-β counteract the Alzheimer peptide non-β-amyloid component effects in human SH-SY5Y cells

Alzheimer's disease (AD) develops from a complex setting of genetic and biochemical alterations, including an increased level of p53 in the brain. Here, the robust and specific activation of p53 by the fibrillar non-β-amyloid component (NAC) of AD was demonstrated in human neuroblastoma SH-SY5Y cells. For the first time, the increase in the level of p53 target gene transcription, the cell cycle arrest, and the induction of apoptosis elicited by NAC were evidenced. These effects were counterbalanced by pifithrin-β, a small molecule interfering with the p53 functions. Using the structure of a pifithrin-β analogue as a reference, a pharmacophore-based virtual screening of the ZINC database was performed. Among the resulting hits, 20 druglike heterocyclic compounds were selected and evaluated for their neuroprotective activity against fibrillar NAC in the human SH-SY5Y cellular model. Three compounds exhibited neuroprotective effects. In particular, 2-(4-methoxyphenyl)-7-methyl-7H-pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine resulted in a promising lead compound for further development of anti-AD agents in terms of neuroprotection, reducing the rate of NAC-induced cell death with an activity higher than that of pifithrin-β, as a result of a more effective functional inhibition of p53 target gene transcription.

Pre-moxibustion and moxibustion prevent Alzheimer's disease

The Alzheimer's disease model in Wistar rats was established by injection of amyloid β-peptide (Aβ1-42) into the hippocampal CA1 region. Rats were treated with suspended moxibustion on Baihui (GV20) and Shenshu (BL23) acupoints. Prior to and post Aβ1-42 exposure. Results showed no evidence of apoptosis in hippocampal neurons, a significantly reduced apoptosis rate of neurons and improved learning and memory abilities were observed in the Alzheimer's disease model. In particular, moxibustion prior to Aβ1-42 exposure was more effective than moxibustion after Aβ1-42 exposure in protecting the neuronal structure and lowering the apoptosis rate. Our findings indicate that a combination of preventive and therapeutic moxibustion has a beneficial effect for the prevention of Alzheimer's disease development.

Monoclonal antibodies against large oval aggregates of Aβ1-42

Abnormal cerebral accumulation of amyloid beta protein(1-42) (Aβ(1-42)) is one of the hallmarks of Alzheimer's disease (AD). Aβ(1-42) aggregates exist in two distinct forms: fibrils that are composed of highly ordered β-sheets and amorphous aggregates that differ in size and toxicity. Here, we generated large oval aggregates (LOA) 369 ± 81 nm and 224 ± 92 nm in size on their major and minor axes, respectively, as measured by tapping-mode atomic force microscopy. LOA were produced by slow rotation of high concentrations (0.22 mM, 1.0 mg/mL) of Aβ(1-42) for 16 h at 37°C in the presence of 2.2 mM Aβ(16-20), which prevents the fibril formation, and purified with 0.22-μm filters. Analysis with thioflavin T showed that LOA have little β-sheet structure on their surfaces. Monoclonal antibodies that react with LOA, but not the fibril forms, were screened from 960 mouse hybridoma cell lines, and seven antibodies consisting of four IgG and three IgM antibodies were obtained. Four IgG monoclonal antibodies showed cross-reactivity of <10% against the monomer and fibril forms and amorphous aggregates that passed through 0.22-μm filters. Among the four antibodies, the antibody that was designated as 31-2 exhibited the highest reactivity against LOA and showed the lowest reactivity against the fibril forms. On the basis of these results, a unique epitope on the surface of LOA was suggested. The 31-2 antibody may be useful for future basic research and therapeutic applications for AD.

BACE1 is at the crossroad of a toxic vicious cycle involving cellular stress and β-amyloid production in Alzheimer's disease

Alzheimer’s disease (AD) is a complex age-related pathology, the etiology of which has not been firmly delineated. Among various histological stigmata, AD-affected brains display several cellular dysfunctions reflecting enhanced oxidative stress, inflammation process and calcium homeostasis disturbance. Most of these alterations are directly or indirectly linked to amyloid β-peptides (Aβ), the production, molecular nature and biophysical properties of which likely conditions the degenerative process. It is particularly noticeable that, in a reverse control process, the above-described cellular dysfunctions alter Aβ peptides levels. β-secretase βAPP-cleaving enzyme 1 (BACE1) is a key molecular contributor of this cross-talk. This enzyme is responsible for the primary cleavage generating the N-terminus of “full length” Aβ peptides and is also transcriptionally induced by several cellular stresses. This review summarizes data linking brain insults to AD-like pathology and documents the key role of BACE1 at the cross-road of a vicious cycle contributing to Aβ production.

Aβ1-42-mediated down-regulation of Uch-L1 is dependent on NF-κB activation and impaired BACE1 lysosomal degradation

Amyloid-β 1-42 accumulation is the major pathogenetic event in Alzheimer's disease (AD), believed to be responsible for synaptic dysfunction and neuronal cell death. However, the physiologic activity of Aβ peptides remains elusive: Aβ might not only play a toxic role, but also act as a functional signaling intermediate. We recently reported that Aβ1-42 promotes BACE1 transcription through the activation of the JNK-c-jun pathway. Here, we show that the Aβ1-42-mediated increase in BACE1 expression is accompanied by a decrease in ubiquitin C-terminal hydrolase L1 (Uch-L1) expression and activity in different cellular models such as neuroblastoma SH-SY5Y as well as NT(2) neuronal cells. We also found that the increase in BACE1 and the decrease in Uch-L1 are related events and depend on NF-κB pathway; thus, Aβ1-42 is able to activate NF-κB pathway and the pretreatment with a pharmacological inhibitor, able to block the nuclear translocation of the transactivating unit p65, almost completely prevents both the decrease in Uch-L1 and the increase in BACE1 expression. In addition, the decrease in Uch-L1 activity interferes with the lysosomal degradation of BACE1, as demonstrated by the decrease in Cathepsin D activity and the partial accumulation of BACE1 in lysosomes after Aβ1-42 treatment as well after Uch-L1 inhibition. In support of the in vitro data, we observed low protein levels of Uch-L1 associated with high protein levels of BACE1 in sporadic AD brains. Our data suggest that Uch-L1 could be an attractive target for the development of new therapeutic approaches for AD.

Amyloid generation and dysfunctional immunoproteasome activation with disease progression in animal model of familial Alzheimer's disease

Double-transgenic amyloid precursor protein/presenilin 1 (APP/PS1) mice express a chimeric mouse/human APP bearing the Swedish mutation (Mo/HuAPP695swe) and a mutant human PS1-dE9 both causative of familial Alzheimer's disease (FAD). Transgenic mice show impaired memory and learning performance from the age of 6 months onwards. Double-transgenic APP/PS1 mice express altered APP and PS1 mRNAs and proteins, reduced β-secretase 1 (BACE1) mRNA and normal BACE1 protein, all of which suggest a particular mechanism of amyloidogenesis when compared with sporadic AD. The first β-amyloid plaques in APP/PS1 mice appear at 3 months, and they increase in number and distribution with disease progression in parallel with increased levels of brain soluble β-amyloid 1-42 and 1-40, but also with reduced 1-42/1-40 ratio with age. Amyloid deposition in plaques is accompanied by altered mitochondria and increased oxidative damage, post-translational modifications and accumulation of altered proteins at the dystrophic neurites surrounding plaques. Degradation pathways are also modified with disease progression including activation of the immunoproteasome together with variable alterations of the different protease activities of the ubiquitin-proteasome system. Present observations show modifications in the production of β-amyloid and activation and malfunction of the subcellular degradation pathways that have general implications in the pathogenesis of AD and more particularly in specificities of FAD amyloidogenesis.

Proteomic changes in cerebrospinal fluid of presymptomatic and affected persons carrying familial Alzheimer disease mutations

OBJECTIVE

To identify cerebrospinal fluid (CSF) protein changes in persons who will develop familial Alzheimer disease (FAD) due to PSEN1 and APP mutations, using unbiased proteomics.

DESIGN

We compared proteomic profiles of CSF from individuals with FAD who were mutation carriers (MCs) and related noncarriers (NCs). Abundant proteins were depleted and samples were analyzed using liquid chromatography-electrospray ionization-mass spectrometry on a high-resolution time-of-flight instrument. Tryptic peptides were identified by tandem mass spectrometry. Proteins differing in concentration between the MCs and NCs were identified.

SETTING

A tertiary dementia referral center and a proteomic biomarker discovery laboratory.

PARTICIPANTS

Fourteen FAD MCs (mean age, 34.2 years; 10 are asymptomatic, 12 have presenilin-1 [PSEN1 ] gene mutations, and 2 have amyloid precursor protein [APP ] gene mutations) and 5 related NCs (mean age, 37.6 years).

RESULTS

Fifty-six proteins were identified, represented by multiple tryptic peptides showing significant differences between MCs and NCs (46 upregulated and 10 downregulated); 40 of these proteins differed when the analysis was restricted to asymptomatic individuals. Fourteen proteins have been reported in prior proteomic studies in late-onset AD, including amyloid precursor protein, transferrin, α(1)β-glycoprotein, complement components, afamin precursor, spondin 1, plasminogen, hemopexin, and neuronal pentraxin receptor. Many other proteins were unique to our study, including calsyntenin 3, AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) 4 glutamate receptor, CD99 antigen, di- N-acetyl-chitobiase, and secreted phosphoprotein 1.

CONCLUSIONS

We found much overlap in CSF protein changes between individuals with presymptomatic and symptomatic FAD and those with late-onset AD. Our results are consistent with inflammation and synaptic loss early in FAD and suggest new presymptomatic biomarkers of potential usefulness in drug development.

Cannabidiol as an emergent therapeutic strategy for lessening the impact of inflammation on oxidative stress

Oxidative stress with reactive oxygen species generation is a key weapon in the arsenal of the immune system for fighting invading pathogens and initiating tissue repair. If excessive or unresolved, however, immune-related oxidative stress can initiate further increasing levels of oxidative stress that cause organ damage and dysfunction. Targeting oxidative stress in various diseases therapeutically has proven more problematic than first anticipated given the complexities and perversity of both the underlying disease and the immune response. However, growing evidence suggests that the endocannabinoid system, which includes the CB₁ and CB₂ G-protein-coupled receptors and their endogenous lipid ligands, may be an area that is ripe for therapeutic exploitation. In this context, the related nonpsychotropic cannabinoid cannabidiol, which may interact with the endocannabinoid system but has actions that are distinct, offers promise as a prototype for anti-inflammatory drug development. This review discusses recent studies suggesting that cannabidiol may have utility in treating a number of human diseases and disorders now known to involve activation of the immune system and associated oxidative stress, as a contributor to their etiology and progression. These include rheumatoid arthritis, types 1 and 2 diabetes, atherosclerosis, Alzheimer disease, hypertension, the metabolic syndrome, ischemia-reperfusion injury, depression, and neuropathic pain.

The Basic Biology of BACE1: A Key Therapeutic Target for Alzheimer's Disease

Alzheimer’s disease (AD) is an intractable, neurodegenerative disease that appears to be brought about by both genetic and non-genetic factors. The neuropathology associated with AD is complex, although amyloid plaques composed of the β-amyloid peptide (Aβ) are hallmark neuropathological lesions of AD brain. Indeed, Aβ plays an early and central role in this disease. β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the initiating enzyme in Aβ genesis and BACE1 levels are elevated under a variety of conditions. Given the strong correlation between Aβ and AD, and the elevation of BACE1 in this disease, this enzyme is a prime drug target for inhibiting Aβ production in AD. However, nine years on from the initial identification of BACE1, and despite intense research, a number of key questions regarding BACE1 remain unanswered. Indeed, drug discovery and development for AD continues to be challenging. While current AD therapies temporarily slow cognitive decline, treatments that address the underlying pathologic mechanisms of AD are completely lacking. Here we review the basic biology of BACE1. We pay special attention to recent research that has provided some answers to questions such as those involving the identification of novel BACE1 substrates, the potential causes of BACE1 elevation and the putative function of BACE1 in health and disease. Our increasing understanding of BACE1 biology should aid the development of compounds that interfere with BACE1 expression and activity and may lead to the generation of novel therapeutics for AD.

The lipid peroxidation products 4-oxo-2-nonenal and 4-hydroxy-2-nonenal promote the formation of α-synuclein oligomers with distinct biochemical, morphological, and functional properties

Oxidative stress has been implicated in the etiology of neurodegenerative disorders with α-synuclein pathology. Lipid peroxidation products such as 4-oxo-2-nonenal (ONE) and 4-hydroxy-2-nonenal (HNE) can covalently modify and structurally alter proteins. Herein, we have characterized ONE- or HNE-induced α-synuclein oligomers. Our results demonstrate that both oligomers are rich in β-sheet structure and have a molecular weight of about 2000 kDa. Atomic force microscopy analysis revealed that ONE-induced α-synuclein oligomers were relatively amorphous, with a diameter of 40-80 nm and a height of 4-8 nm. In contrast, the HNE-induced α-synuclein oligomers had a protofibril-like morphology with a width of 100-200 nm and a height of 2-4 nm. Furthermore, neither oligomer type polymerized into amyloid-like fibrils despite prolonged incubation. Although more SDS and urea stable, because of a higher degree of cross-linking, ONE-induced α-synuclein oligomers were less compact and more sensitive to proteinase K treatment. Finally, both ONE- and HNE-induced α-synuclein oligomers were cytotoxic when added exogenously to a neuroblastoma cell line, but HNE-induced α-synuclein oligomers were taken up by the cells to a significantly higher degree. Despite nearly identical chemical structures, ONE and HNE induce the formation of off-pathway α-synuclein oligomers with distinct biochemical, morphological, and functional properties.

Lipid Rafts: Linking Alzheimer's Amyloid-β Production, Aggregation, and Toxicity at Neuronal Membranes

Lipid rafts are membrane microdomains, enriched in cholesterol and sphingolipids, into which specific subsets of proteins and lipids partition, creating cell-signalling platforms that are vital for neuronal functions. Lipid rafts play at least three crucial roles in Alzheimer's Disease (AD), namely, in promoting the generation of the amyloid-β (Aβ) peptide, facilitating its aggregation upon neuronal membranes to form toxic oligomers and hosting specific neuronal receptors through which the AD-related neurotoxicity and memory impairments of the Aβ oligomers are transduced. Recent evidence suggests that Aβ oligomers may exert their deleterious effects through binding to, and causing the aberrant clustering of, lipid raft proteins including the cellular prion protein and glutamate receptors. The formation of these pathogenic lipid raft-based platforms may be critical for the toxic signalling mechanisms that underlie synaptic dysfunction and neuropathology in AD.

The inhibitory effects of different curcuminoids on β-amyloid protein, β-amyloid precursor protein and β-site amyloid precursor protein cleaving enzyme 1 in swAPP HEK293 cells

The hallmark of Alzheimer's disease (AD) is the accumulation of β-amyloid protein (Aβ). Aβ is generated from the β-amyloid precursor protein (APP) through the proteolysis of β-site APP cleaving enzyme 1 (BACE1) and γ-secretase. Aβ(42) isoform is more easily aggregate and more toxic to neurons than any other Aβ isoforms, thus being regarded as the primary toxic specie in AD. Curcumin mix has potent anti-amyloidogenic effect and shows great promise for AD treatment and prevention. The present study was conducted to examine the effects of curcumin mix and its different curcuminoids including curcumin (Cur), demethoxycurcumin (DMC) and bisdemethoxycurcumin (BDMC) on Aβ(42), APP and BACE1. We found that Cur was the most active curcuminoid fraction in suppressing Aβ(42) production and the order of inhibitory potency of other curcuminoids was DMC>curcumin mix>BDMC. Cur, but not other curcuminoids, could reduce APP protein expression and none of curcuminoids affected APP mRNA level. BDMC could reduce BACE1 mRNA and protein levels, while DMC only affected BACE1 mRNA expression. Our data indicate that the anti-amyloidogenic effect of Cur may be mediated through the modulation of APP, while the anti-amyloidogenic effect of BDMC may be mediated through the modulation of BACE1.

Reconvene and reconnect the antioxidant hypothesis in human health and disease

The antioxidants are essential molecules in human system but are not miracle molecules. They are neither performance enhancers nor can prevent or cure diseases when taken in excess. Their supplemental value is debateable. In fact, many high quality clinical trials on antioxidant supplement have shown no effect or adverse outcomes ranging from morbidity to all cause mortality. Several Chochrane Meta-analysis and Markov Model techniques, which are presently best available statistical models to derive conclusive answers for comparing large number of trials, support these claims. Nevertheless none of these statistical techniques are flawless. Hence, more efforts are needed to develop perfect statistical model to analyze the pooled data and further double blind, placebo controlled interventional clinical trials, which are gold standard, should be implicitly conducted to get explicit answers. Superoxide dismutase (SOD), glutathione peroxidase and catalase are termed as primary antioxidants as these scavenge superoxide anion and hydrogen peroxide. All these three enzymes are inducible enzymes, thereby inherently meaning that body increases or decreases their activity as per requirement. Hence there is no need to attempt to manipulate their activity nor have such efforts been clinically useful. SOD administration has been tried in some conditions especially in cancer and myocardial infarction but has largely failed, probably because SOD is a large molecule and can not cross cell membrane. The dietary antioxidants, including nutrient antioxidants are chain breaking antioxidants and in tandem with enzyme antioxidants temper the reactive oxygen species (ROS) and reactive nitrogen species (RNS) within physiological limits. Since body is able to regulate its own requirements of enzyme antioxidants, the diet must provide adequate quantity of non-enzymic antioxidants to meet the normal requirements and provide protection in exigent condition. So far, there is no evidence that human tissues ever experience the torrent of reactive species and that in chronic conditions with mildly enhanced generation of reactive species, the body can meet them squarely if antioxidants defense system in tissues is biochemically optimized. We are not yet certain about optimal levels of antioxidants in tissues. Two ways have been used to assess them: first by dietary intake and second by measuring plasma levels. Lately determination of plasma/serum level of antioxidants is considered better index for diagnostic and prognostic purposes. The recommended levels for vitamin A, E and C and beta carotene are 2.2-2.8 μmol/l; 27.5-30 μmol/l; 40-50 μmol/l and 0.4-0.5 μmol/l, respectively. The requirement and recommended blood levels of other dietary antioxidants are not established. The resolved issues are (1) essential to scavenge excess of radical species (2) participants in redox homeostasis (3) selective antioxidants activity against radical species (4) there is no universal antioxidant and 5) therapeutic value in case of deficiency. The overarching issues are (1) therapeutic value as adjuvant therapy in management of diseases (2) supplemental value in developing population (3) selective interactivity of antioxidant in different tissues and on different substrates (4) quantitative contribution in redox balance (5) mechanisms of adverse action on excess supplementation (6) advantages and disadvantages of prooxidant behavior of antioxidants (7) behavior in cohorts with polymorphic differences (8) interaction and intervention in radiotherapy, diabetes and diabetic complications and cardiovascular diseases (9) preventive behavior in neurological disorders (10) benefits of non-nutrient dietary antioxidants (11) markers to assess optimized antioxidants status (12) assessment of benefits of supplementation in alcoholics and heavy smokers. The unresolved and intriguing issues are (1) many compounds such as vitamin A and many others possessing both antioxidant and non-antioxidant properties contribute to both the activities in vivo or exclusively only to non-antioxidant activity and (2) since human tissues do not experience the surge of FR, whether there is any need to develop stronger synthetic antioxidants. Theoretically such antioxidants may do more harm than good.