From anti-Parkinson's drug rasagiline to novel multitarget iron chelators with acetylcholinesterase and monoamine oxidase inhibitory and neuroprotective properties for Alzheimer's disease

Protective Mechanisms of Nootropic Herb Shankhpushpi (Convolvulus pluricaulis) against Dementia: Network Pharmacology and Computational Approach

Convolvulus pluricaulis (CP), a Medhya Rasayana (nootropic) herb, is a major ingredient in Ayurvedic and Traditional Chinese formulae indicated for neurological conditions, namely, dementia, anxiety, depression, insanity, and epilepsy. Experimental evidence suggests various neuroactive potentials of CP such as memory-enhancing, neuroprotective, and antiepileptic. However, precise mechanisms underlying the neuropharmacological effects of CP remain unclear. The study, therefore, aimed at deciphering the molecular basis of neuroprotective effects of CP phytochemicals against the pathology of dementia disorders such as Alzheimer's (AD) and Parkinson's (PD) disease. The study exploited bioinformatics tools and resources, such as Cytoscape, DAVID (Database for annotation, visualization, and integrated discovery), NetworkAnalyst, and KEGG (Kyoto Encyclopedia of Genes and Genomes) database to investigate the interaction between CP compounds and molecular targets. An in silico analysis was also employed to screen druglike compounds and validate some selective interactions. ADME (absorption, distribution, metabolism, and excretion) analysis predicted a total of five druglike phytochemicals from CP constituents, namely, scopoletin, 4-hydroxycinnamic acid, kaempferol, quercetin, and ayapanin. In network analysis, these compounds were found to interact with some molecular targets such as prostaglandin G/H synthase 1 and 2 (PTGS1 and PTGS2), endothelial nitric oxide synthase (NOS3), insulin receptor (INSR), heme oxygenase 1 (HMOX1), acetylcholinesterase (ACHE), peroxisome proliferator-activated receptor-gamma (PPARG), and monoamine oxidase A and B (MAOA and MAOB) that are associated with neuronal growth, survival, and activity. Docking simulation further confirmed interaction patterns and binding affinity of selected CP compounds with those molecular targets. Notably, scopoletin showed the highest binding affinity with PTGS1, NOS3, PPARG, ACHE, MAOA, MAOB, and TRKB, quercetin with PTGS2, 4-hydroxycinnamic acid with INSR, and ayapanin with HMOX1. The findings indicate that scopoletin, kaempferol, quercetin, 4-hydroxycinnamic acid, and ayapanin are the main active constituents of CP which might account for its memory enhancement and neuroprotective effects and that target proteins such as PTGS1, PTGS2, NOS3, PPARG, ACHE, MAOA, MAOB, INSR, HMOX1, and TRKB could be druggable targets against dementia.

Sources and triggers of oxidative damage in neurodegeneration

Neurodegeneration describes a group of more than 300 neurological diseases, characterised by neuronal loss and intra- or extracellular protein depositions, as key neuropathological features. Multiple factors play role in the pathogenesis of these group of disorders: mitochondrial dysfunction, membrane damage, calcium dyshomeostasis, metallostasis, defect clearance and renewal mechanisms, to name a few. All these factors, without exceptions, have in common the involvement of immensely increased generation of free radicals and occurrence of oxidative stress, and as a result - exhaustion of the scavenging potency of the cellular redox defence mechanisms. Besides genetic predisposition and environmental exposure to toxins, the main risk factor for developing neurodegeneration is age. And although the "Free radical theory of ageing" was declared dead, it is undisputable that accumulation of damage occurs with age, especially in systems that are regulated by free radical messengers and those that oppose oxidative stress, protein oxidation and the accuracy in protein synthesis and degradation machinery has difficulties to be maintained. This brief review provides a comprehensive summary on the main sources of free radical damage, occurring in the setting of neurodegeneration.

Insights into the Mechanism of the Therapeutic Potential of Herbal Monoamine Oxidase Inhibitors in Neurological Diseases

Monoamine oxidase (MAO) is an enzyme that catalyzes the deamination of monoamines and other proteins. MAO's hyperactivation results in the massive generation of reactive oxygen species, which leads to a variety of neurological diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and depression-like disorders. Although synthetic MAO inhibitors are clinically available, they are associated with side effects such as hepatotoxicity, cheese reaction, hypertensive crisis, and so on, necessitating the investigation of alternative MAO inhibitors from a natural source with a safe profile. Herbal medications have a significant impact on the prevention of many diseases; additionally, they have fewer side effects and serve as a precursor for drug development. This review discusses the potential of herbal MAO inhibitors as well as their associated mechanism of action, with an aim to foster future research on herbal MAO inhibitors as potential treatment for neurological diseases.

Role of Monoamine Oxidase Activity in Alzheimer's Disease: An Insight into the Therapeutic Potential of Inhibitors

Despite not being utilized as considerably as other antidepressants in the therapy of depression, the monoamine oxidase inhibitors (MAOIs) proceed to hold a place in neurodegeneration and to have a somewhat broad spectrum in respect of the treatment of neurological and psychiatric conditions. Preclinical and clinical studies on MAOIs have been developing in recent times, especially on account of rousing discoveries manifesting that these drugs possess neuroprotective activities. The altered brain levels of monoamine neurotransmitters due to monoamine oxidase (MAO) are directly associated with various neuropsychiatric conditions like Alzheimer’s disease (AD). Activated MAO induces the amyloid-beta (Aβ) deposition via abnormal cleavage of the amyloid precursor protein (APP). Additionally, activated MAO contributes to the generation of neurofibrillary tangles and cognitive impairment due to neuronal loss. No matter the attention of researchers on the participation of MAOIs in neuroprotection has been on monoamine oxidase-B (MAO-B) inhibitors, there is a developing frame of proof indicating that monoamine oxidase-A (MAO-A) inhibitors may also play a role in neuroprotection. The therapeutic potential of MAOIs alongside the complete understanding of the enzyme’s physiology may lead to the future advancement of these drugs.

Exploring the Role of Monoamine Oxidase Activity in Aging and Alzheimer's Disease

Monoamine oxidases (MAOs) are a family of flavin adenine dinucleotide-dependent enzymes that exert a crucial role in the metabolism of neurotransmitters of the central nervous system. The impaired function of MAOs is associated with copious brain diseases. The alteration of monoamine metabolism is a characteristics feature of aging. MAO plays a crucial role in the pathogenesis of Alzheimer's disease (AD) - a progressive neurodegenerative disorder associated with an excessive accumulation of amyloid-beta (Aβ) peptide and neurofibrillary tangles (NFTs). Activated MAO has played a critical role in the development of amyloid plaques from Aβ, as well as the formation of the NFTs. In the brain, MAO mediated metabolism of monoamines is the foremost source of reactive oxygen species formation. The elevated level of MAO-B expression in astroglia has been reported in the AD brains adjacent to amyloid plaques. Increased MAO-B activity in the cortical and hippocampal regions is associated with AD. This review describes the pathogenic mechanism of MAOs in aging as well as the development and propagation of Alzheimer's pathology.

Multi-Target-Directed Ligands as an Effective Strategy for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurological disorder, and multiple pathological factors are believed to be involved in the genesis and progression of the disease. A number of hypotheses, including Acetylcholinesterase, Monoamine oxidase, β-Amyloid, Tau protein, etc., have been proposed for the initiation and progression of the disease. At present, acetylcholine esterase inhibitors and memantine (NMDAR antagonist) are the only approved therapies for the symptomatic management of AD. Most of these single-target drugs have miserably failed in the treatment or halting the progression of the disease. Multi-factorial diseases like AD require complex treatment strategies that involve simultaneous modulation of a network of interacting targets. Since the last few years, Multi-Target-Directed Ligands (MTDLs) strategy, drugs that can simultaneously hit multiple targets, is being explored as an effective therapeutic approach for the treatment of AD. In the current review article, the authors have briefly described various pathogenic pathways associated with AD. The importance of Multi-Target-Directed Ligands and their design strategies in recently reported articles have been discussed in detail. Potent leads are identified through various structure-activity relationship studies, and their drug-like characteristics are described. Recently developed promising compounds have been summarized in the article. Some of these MTDLs with balanced activity profiles against different targets have the potential to be developed as drug candidates for the treatment of AD.

Design, synthesis, and in vitro evaluation of 4-aminoalkyl-1(2H)-phthalazinones as potential multifunctional anti-Alzheimer's disease agents

A series of 4-aminoalkyl-1(2H)-phthalazinone derivatives was designed and synthesized as potential multifunctional agents for Alzheimer's disease (AD) treatment. In vitro biological assay results demonstrated that most synthesized compounds exhibited significant AChE inhibition, moderate to high MAOs inhibitory potencies and good anti-platelet aggregation abilities. Among them, compound 15b exhibited the highest inhibitory potencies towards MAO-B and MAO-A (IC₅₀ = 0.7 µM and 6.4 µM respectively), moderate inhibition towards AChE (IC₅₀ = 8.2 µM), and good activities against self- and Cu²⁺-induced Aβ_1-42 aggregation and platelet aggregation. Moreover, 15b also displayed antioxidant capacity, neuroprotective potency, anti-neuroinflammation and BBB permeability. These excellent results indicated that compound 15b could be worthy of further studies to be considered as a promising multifunctional candidate for the treatment of AD.

Effects of novel 17β-hydroxysteroid dehydrogenase type 10 inhibitors on mitochondrial respiration

Mitochondrial enzymes are targets of newly synthesized drugs being tested for the treatment of neurodegenerative disorders, such as Alzheimer's disease (AD). The enzyme 17β-hydroxysteroid dehydrogenase type 10 (HSD10) is a multifunctional mitochondrial protein that is thought to play a role in the pathophysiology of AD and is one of the targets of new potential AD drugs. The in vitro effects of frentizole, riluzole, AG18051, and 42 novel modulators of HSD10 (potential AD drugs) on citrate synthase (CS) activity, monoamine oxidase (MAO) activity, complex I- or complex II-linked mitochondrial respiratory rate, and complex I activity were measured in isolated pig brain mitochondria. Based on their minimal inhibitory effects on the respiratory rate of mitochondria and CS and complex I activity, six novel compounds were selected for further testing. Assuming that inhibition of MAO-B could be a desirable effect of AD drugs, only AG18051 and one new compound met the criteria for MAO-B inhibition with minimal drug-induced effects on mitochondrial respiration. In conclusion, our in vitro screening of mitochondrial effect of novel potential AD drugs has enabled the selection of the most promising molecules for further testing that are relatively safe in terms of drug-induced mitochondrial toxicity.

Multi-Target Drug Candidates for Multifactorial Alzheimer's Disease: AChE and NMDAR as Molecular Targets

Alzheimer's disease (AD) is one of the most common forms of dementia among elder people, which is a progressive neurodegenerative disease that results from a chronic loss of cognitive activities. It has been observed that AD is multifactorial, hence diverse pharmacological targets that could be followed for the treatment of AD. The Food and Drug Administration has approved two types of medications for AD treatment such as cholinesterase inhibitors (ChEIs) and N-methyl-D-aspartic acid receptor (NMDAR) antagonists. Rivastigmine, donepezil, and galantamine are the ChEIs that have been approved to treat AD. On the other hand, memantine is the only non-competitive NMDAR antagonist approved in AD treatment. As compared with placebo, it has been revealed through clinical studies that many single-target therapies are unsuccessful to treat multifactorial Alzheimer's symptoms or disease progression. Therefore, due to the complex nature of AD pathophysiology, diverse pharmacological targets can be hunted. In this article, based on the entwined link of acetylcholinesterase (AChE) and NMDAR, we represent several multifunctional compounds in the rational design of new potential AD medications. This review focus on the significance of privileged scaffolds in the generation of the multi-target lead compound for treating AD, investigating the idea and challenges of multi-target drug design. Furthermore, the most auspicious elementary units for designing as well as synthesizing hybrid drugs are demonstrated as pharmacological probes in the rational design of new potential AD therapeutics.

Is 1,8-Cineole-Rich Extract of Small Cardamom Seeds More Effective in Preventing Alzheimer's Disease than 1,8-Cineole Alone?

The present study demonstrates the efficacies of synthetic 1,8-cineole and an 1,8-cineole-rich supercritical carbon dioxide (SC-CO₂) extract of small cardamom seeds in preventing oligomerization of amyloid beta peptide (Aβ42) and inhibiting iron-dependent oxyradical production in vitro. The oligomerization of Aβ42 was monitored by thioflavin T assay and MALDI-TOF analysis of the oligomers. The iron-dependent production of oxygen free radicals was detected by fluorometric benzoate hydroxylation assay. We observed that both pure 1,8-cineole and 1,8-cineole-rich extract of small cardamom seeds at concentrations of 50 µM and 100 µM prevented the production of reactive hydroxyl radicals from a mixture of Fe²⁺ and ascorbate. However, the 1,8-cineole-rich extract of small cardamom seeds prevented in vitro Aβ42 oligomerization more effectively vis-à-vis the synthetic (99% pure) 1,8-cineole. Additional study on SHSY5Y cells indicated that both pure 1,8-cineole and 1,8-cineole-rich SC-CO₂ extract of small cardamom seeds prevented iron-dependent cell death. Since oxidative damage, Aβ42 aggregation and loss of cell viability (iron-induced) are characteristics of onset of Alzheimer's disease pathology, our results suggest a putative therapeutic role of 1,8-cineole-rich extract of small cardamom seeds over pure 1,8-cineole in preventing this neurodegenerative disease.

Design, Synthesis, and Evaluation of Novel Ferulic Acid Derivatives as Multi-Target-Directed Ligands for the Treatment of Alzheimer's Disease

A novel series of ferulic acid derivatives was designed and synthesized on the basis of the multi-target-directed ligands strategy for the treatment of Alzheimer's disease (AD). In vitro results revealed that all the target compounds were highly effective and selective butyrylcholinesterase (BuChE) inhibitors. In particular, compound TM-10 showed the best BuChE inhibitory activity, with IC₅₀ = 8.9 nM, and remarkable monoamine oxidase A and B inhibitory potency, with IC₅₀ = 6.3 and 8.6 μM, respectively. TM-10 could inhibit (53.9%) and disaggregate (43.8%) self-induced amyloid-β peptide (Aβ) aggregation. In addition, TM-10 exhibited potent antioxidant activity (ORAC = 0.52 equiv) and neuroprotective effect against Aβ_1-42-mediated SH-SY5Y neurotoxicity, and it acted as an autophagic activator. TM-10 also showed good blood-brain barrier penetration. Furthermore, TM-10 exhibited a favorable dyskinesia recovery rate and response efficiency on an AlCl₃-induced zebrafish AD model and a potent neuroprotective effect on Aβ_1-40-induced zebrafish vascular injury. Further, in vivo assays demonstrated that TM-10 showed low acute toxicity, and the step-down passive avoidance test indicated that this compound could improve scopolamine-induced memory deficit in mice. Therefore, the present study displays evidence that TM-10 is a potent, multi-functional agent against AD and could be a promising lead candidate for anti-Alzheimer's disease drug development.

Comprehensive review of mechanisms of pathogenesis involved in Alzheimer's disease and potential therapeutic strategies

AD is a progressive neurodegenerative disorder and a leading cause of dementia in an aging population worldwide. The enormous challenge which AD possesses to global healthcare makes it as urgent as ever for the researchers to develop innovative treatment strategies to fight this disease. An in-depth analysis of the extensive available data associated with the AD is needed for a more comprehensive understanding of underlying molecular mechanisms and pathophysiological pathways associated with the onset and progression of the AD. The currently understood pathological and biochemical manifestations include cholinergic, Aβ, tau, excitotoxicity, oxidative stress, ApoE, CREB signaling pathways, insulin resistance, etc. However, these hypotheses have been criticized with several conflicting reports for their involvement in the disease progression. Several issues need to be addressed such as benefits to cost ratio with cholinesterase therapy, the dilemma of AChE selectivity over BChE, BBB permeability of peptidic BACE-1 inhibitors, hurdles related to the implementation of vaccination and immunization therapy, and clinical failure of candidates related to newly available targets. The present review provides an insight to the different molecular mechanisms involved in the development and progression of the AD and potential therapeutic strategies, enlightening perceptions into structural information of conventional and novel targets along with the successful applications of computational approaches for the design of target-specific inhibitors.

Monoamine oxidase inhibitors, and iron chelators in depressive illness and neurodegenerative diseases

In early 1920s, tyramine oxidase was discovered that metabolized tyramine and in 1933 Blaschko demonstrated that this enzyme also metabolized adrenaline, noradrenaline and dopamine. Zeller gave it the name monoamine oxidase (MAO) to distinguish it from the enzyme that oxidatively deaminated diamines. MAO was recognized as an enzyme of crucial interest to pharmacologists because it catalyzed the major inactivation pathway for the catecholamines (and, later, 5-hydroxytryptamine, as well). Within the few decade, the inhibitors of MAO were discovered and introduced for the treatment of depressive illness which was established clinically. However, the first clinical use exposed serious side effects, pharmacological interest in, and investigation of, MAO continued, resulting in the characterization of two forms, distinct forms, MAO-A and -B, and selective inhibitors for them. Selective inhibitors of MAO-B (selegiline, rasagiline and safinamide) have found a therapeutic role in the treatment of Parkinson's disease and reversible inhibitors of MAO-A offered antidepressant activity without the serious side effects of the earlier nonselective MAO inhibitors. Subsequent molecular pharmacological have also generated the concept of neuroprotection, reflecting the possibility of slowing, halting and maybe reversing, neurodegeneration in Parkinson's or Alzheimer's diseases. Increased levels of oxidative stress through the accumulation of iron in the Parkinsonian and Alzheimer brains has been suggested to be critical for the initiation and progress of neurodegeneration. Selective inhibition of brain MAO could contribute importantly to lowering such stress, preventing the formation of hydrogen peroxide. Interaction of Iron with hydrogen peroxide and lead to Fenton reaction and production of the most reactive radical, namely hydroxyl radical. There are complex interactions between free iron levels in brain and MAO, and cascade of neurotoxic events may have practical outcomes for depressive disorders and neurodegenerative diseases. As consequence recent novel therapeutic drugs for neurodegenerative diseases has led to the development of multi target drugs, that possess selective brain MAO A and B inhibitory moiety, iron chelating and antioxidant activities and the ability to increase brain levels of endogenous neurotrophins, such as BDNF, GDNF VEGF and erythropoietin and induce mitochondrial biogenesis.

Oxidative stress and neurodegeneration: the involvement of iron

Many evidences indicate that oxidative stress plays a significant role in a variety of human disease states, including neurodegenerative diseases. Iron is an essential metal for almost all living organisms due to its involvement in a large number of iron-containing proteins and enzymes, though it could be also toxic. Actually, free iron excess generates oxidative stress, particularly in brain, where anti-oxidative defences are relatively low. Its accumulation in specific regions is associated with pathogenesis in a variety of neurodegenerative diseases (i.e., Parkinson's disease, Alzheimer's disease, Huntington's chorea, Amyotrophic Lateral Sclerosis and Neurodegeneration with Brain Iron Accumulation). Anyway, the extent of toxicity is dictated, in part, by the localization of the iron complex within the cell (cytosolic, lysosomal and mitochondrial), its biochemical form, i.e., ferritin or hemosiderin, as well as the ability of the cell to prevent the generation and propagation of free radical by the wide range of antioxidants and cytoprotective enzymes in the cell. Particularly, ferrous iron can act as a catalyst in the Fenton reaction that potentiates oxygen toxicity by generating a wide range of free radical species, including hydroxyl radicals (·OH). The observation that patients with neurodegenerative diseases show a dramatic increase in their brain iron content, correlated with the production of reactive oxigen species in these areas of the brain, conceivably suggests that disturbances in brain iron homeostasis may contribute to the pathogenesis of these disorders. The aim of this review is to describe the chemical features of iron in human beings and iron induced toxicity in neurodegenerative diseases. Furthermore, the attention is focused on metal chelating drugs therapeutic strategies.

Slowly progressive behavioral frontotemporal dementia with C9orf72 mutation. Case report and review of the literature

We present a 86-year-old woman without relevant medical history and two brothers who died by dementia, who started at 55 years with depression and personality changes with ongoing worsening (>30 years) and functional decline. Screening dementia blood test and brain magnetic resonance imaging did not show results that pointed to a secondary cause. The patient met the diagnostic criteria for possible behavioral frontotemporal dementia with a slow progression (bvFTD-SP), suggesting a benign variant. A genetic study confirmed a C9ORF72 hexanucleotide expansion, making this the sixth case mentioned in the literature. We review and discuss the other cases described previously.

Dual inhibitors of cholinesterases and monoamine oxidases for Alzheimer’s disease

Accumulating evidence indicates a solid relationship between several enzymes and Alzheimer’s disease. Cholinesterases and monoamine oxidases are closely associated with the disease symptomatology and progression and have been tackled simultaneously using several multifunctional ligands. This design strategy offers great chances to alter the course of Alzheimer’s disease, in addition to alleviation of the symptoms. More than 15 years of research has led to the identification of various dual cholinesterase/monoamine oxidase inhibitors, while some showing positive outcomes in clinical trials, thus giving rise to additional research efforts in the field. The aim of this review is to provide an update on the novel dual inhibitors identified recently and to shed light on their therapeutic potential.

The proof-of-concept of ASS234: Peripherally administered ASS234 enters the central nervous system and reduces pathology in a male mouse model of Alzheimer disease

BACKGROUND

The heterogeneity of Alzheimer disease requires the development of multitarget drugs for treating the symptoms of the disease and its progression. Both cholinergic and monoamine oxidase dysfunctions are involved in the pathological process. Thus, we hypothesized that the development of therapies focused on these targets might be effective. We have developed and assessed a new product, coded ASS234, a multipotent acetyl and butyrylcholinesterase/monoamine oxidase A-B inhibitor with a potent inhibitory effect on amyloid-β aggregation as well as antioxidant and antiapoptotic properties. But there is a need to reliably correlate in vitro and in vivo drug release data.

METHODS

We examined the effect of ASS234 on cognition in healthy adult C57BL/6J mice in a model of scopolamine-induced cognitive impairment that often accompanies normal and pathological aging. Also, in a characterized transgenic APPswe/PS1ΔE9 mouse model of Alzheimer disease, we examined the effects of short-term ASS234 treatment on plaque deposition and gliosis using immunohistochemistry. Toxicology of ASS234 was assessed using a quantitative high-throughput in vitro cytotoxicity screening assay following the MTT assay method in HepG2 liver cells.

RESULTS

In vivo, ASS234 significantly decreased scopolamine-induced learning deficits in C57BL/6J mice. Also, reduction of amyloid plaque burden and gliosis in the cortex and hippocampus was assessed. In vitro, ASS234 exhibited lesser toxicity than donepezil and tacrine.

LIMITATIONS

The study was conducted in male mice only. Although the Alzheimer disease model does not recapitulate all features of the human disease, it exhibits progressive monoaminergic neurodegeneration.

CONCLUSION

ASS234 is a promising alternative drug of choice to treat the cognitive decline and neurodegeneration underlying Alzheimer disease.

Interactions between heme and tau-derived R1 peptides: binding and oxidative reactivity

The interaction of hemin with the first 18-amino acid repeat in tau protein has been investigated at both the N-terminal free-amine (R1τ) and N-acetylated (AcR1τ) forms for its potential relevance in traumatic brain injury and possibly other neurodegenerative diseases. The binding properties of hemin-R1τ and hemin-AcR1τ were compared with those of the hemin complex with amyloid-β peptide fragment 1-16 (Aβ16) and synthetic hemins. AcR1τ and R1τ bind with moderate affinity to both monomeric and dimeric hemin to form 1 : 1 complexes, but for the acetylated peptide, the affinity is one order of magnitude larger (K1 = 3.3 × 10(6) M(-1)). The binding constants were similar to that of Aβ16 for hemin, but unlike the latter, neither of the two R1τ peptides forms a 2 : 1 complex with hemin. This is mostly due to electrostatic repulsion between R1τ chains, and in particular the C-terminal proline-15 kink, while structural features of the hemin-R1τ complexes do not seem to play a role. In fact, the same features are observed for the interaction between ferric heme and peptide R1τ*, where the P15 residue is replaced by an alanine. Imidazole neither binds to [hemin(R1τ)] nor [hemin(AcR1τ)], whereas small ligands such as CN and CO easily bind to the ferric and ferrous forms of the complexes, respectively. A detailed comparative study of the peroxidase activity of [hemin(R1τ)] and [hemin(AcR1τ)] shows that such activity is very low. Thus, the association between heme and unfolded neuronal peptides does not, per se, involve a significant gain of toxic pseudo-enzymatic activity. However, under conditions of heavy heme release occurring on traumatic brain injury or when this activity is prolonged for long time, it can contribute to neuronal oxidative stress. In addition, the presence of hemin increases the aggregation propensity of R1τ.

Molecular aspects of monoamine oxidase B

Monoamine oxidases (MAO) influence the monoamine levels in brain by virtue of their role in neurotransmitter breakdown. MAO B is the predominant form in glial cells and in platelets. MAO B structure, function and kinetics are described as a background for the effect of alterations in its activity on behavior. The need to inhibit MAO B to combat decreased brain amines continues to drive the search for new drugs. Reversible and irreversible inhibitors are now designed using data-mining, computational screening, docking and molecular dynamics. Multi-target ligands designed to combat the elevated activity of MAO B in Alzheimer's and Parkinson's Diseases incorporate MAO inhibition (usually irreversible) as well as iron chelation, antioxidant or neuroprotective properties. The main focus of drug design is the catalytic activity of MAO, but the imidazoline I2 site in the entrance cavity of MAO B is also a pharmacological target. Endogenous regulation of MAO B expression is discussed briefly in light of new studies measuring mRNA, protein, or activity in healthy and degenerative samples, including the effect of DNA methylation on the expression. Overall, this review focuses on examples of recent research on the molecular aspects of the expression, activity, and inhibition of MAO B.

Drugs related to monoamine oxidase activity

Progress in understanding the role of monoamine neurotransmission in pathophysiology of neuropsychiatric disorders was made after the discovery of the mechanisms of action of psychoactive drugs, including monoamine oxidase (MAO) inhibitors. The increase in monoamine neurotransmitter availability, decrease in hydrogen peroxide production, and neuroprotective effects evoked by MAO inhibitors represent an important approach in the development of new drugs for the treatment of mental disorders and neurodegenerative diseases. New drugs are synthesized by acting as multitarget-directed ligands, with MAO, acetylcholinesterase, and iron chelation as targets. Basic information is summarized in this paper about the drug-induced regulation of monoaminergic systems in the brain, with a focus on MAO inhibition. Desirable effects of MAO inhibition include increased availability of monoamine neurotransmitters, decreased oxidative stress, decreased formation of neurotoxins, induction of pro-survival genes and antiapoptotic factors, and improved mitochondrial functions.

Multitarget strategies in Alzheimer's disease: benefits and challenges on the road to therapeutics

Alzheimer's disease is a multifactorial syndrome, for which effective cures are urgently needed. Seeking for enhanced therapeutic efficacy, multitarget drugs have been increasingly sought after over the last decades. They offer the attractive prospect of tackling intricate network effects, but with the benefits of a single-molecule therapy. Herein, we highlight relevant progress in the field, focusing on acetylcholinesterase inhibition and amyloid pathways as two pivotal features in multitarget design strategies. We also discuss the intertwined relationship between selected molecular targets and give a brief glimpse into the power of multitarget agents as pharmacological probes of Alzheimer's disease molecular mechanisms.

Tacrine-allyl/propargylcysteine–benzothiazole trihybrids as potential anti-Alzheimer's drug candidates

Eight novel trihybrids as potential anti-Alzheimer's drugs showed high AChEI and anti-Aβ aggregation capacity, moderate anti-ROS activity and low MAO inhibition.

Catecholamine-Based Treatment in AD Patients: Expectations and Delusions

In Alzheimer disease, the gap between excellence of diagnostics and efficacy of therapy is wide. Despite sophisticated imaging and biochemical markers, the efficacy of available therapeutic options is limited. Here we examine the possibility that assessment of endogenous catecholamine levels in cerebrospinal fluid (CSF) may fuel new therapeutic strategies. In reviewing the available literature, we consider the effects of levodopa, monoamine oxidase inhibitors, and noradrenaline (NE) modulators, showing disparate results. We present a preliminary assessment of CSF concentrations of dopamine (DA) and NE, determined by HPLC, in a small dementia cohort of either Alzheimer’s disease (AD) or frontotemporal dementia patients, compared to control subjects. Our data reveal detectable levels of DA, NE in CSF, though we found no significant alterations in the dementia population as a whole. AD patients exhibit a small impairment of the DA axis and a larger increase of NE concentration, likely to represent a compensatory mechanism. While waiting for preventive strategies, a pragmatic approach to AD may re-evaluate catecholamine modulation, possibly stratified to dementia subtypes, as part of the therapeutic armamentarium.

Synthesis and evaluation of selegiline derivatives as monoamine oxidase inhibitor, antioxidant and metal chelator against Alzheimer's disease

A series of compounds with monoamine oxidase inhibition and biometal chelation activities were designed, synthesised and evaluated as agents against Alzheimer's disease. The in vitro assay shows that most target compounds exhibit good MAO-B activities with submicromolar IC50 values and antioxidant activity (1.49-5.67 ORAC-FL values). The selected compounds were used to determine the biometal chelating ability using UV-vis spectrometry and high-resolution mass spectrometry, which confirm that they can effectively interact with copper(II), iron(II) and zinc(II). The ThT fluorescence binding assay indicates that the synthetic compounds can inhibit Cu(II)-induced Aβ1-42 aggregation. The parallel artificial membrane permeation assay shows that most target compounds can cross the BBB. Based on these results, compound 8a was selected as a potential multifunctional agent for the treatment of AD.

Catecholamine autotoxicity. Implications for pharmacology and therapeutics of Parkinson disease and related disorders

Several neurodegenerative diseases involve loss of catecholamine neurons-Parkinson disease is a prototypical example. Catecholamine neurons are rare in the nervous system, and why they are vulnerable in PD and related disorders has been mysterious. Accumulating evidence supports the concept of "autotoxicity"-inherent cytotoxicity of catecholamines and their metabolites in the cells in which they are produced. According to the "catecholaldehyde hypothesis" for the pathogenesis of Parkinson disease, long-term increased build-up of 3,4-dihydroxyphenylacetaldehyde (DOPAL), the catecholaldehyde metabolite of dopamine, causes or contributes to the eventual death of dopaminergic neurons. Lewy bodies, a neuropathologic hallmark of PD, contain precipitated alpha-synuclein. Bases for the tendency of alpha-synuclein to precipitate in the cytoplasm of catecholaminergic neurons have also been mysterious. Since DOPAL potently oligomerizes and aggregates alpha-synuclein, the catecholaldehyde hypothesis provides a link between alpha-synucleinopathy and catecholamine neuron loss in Lewy body diseases. The concept developed here is that DOPAL and alpha-synuclein are nodes in a complex nexus of interacting homeostatic systems. Dysfunctions of several processes, including decreased vesicular sequestration of cytoplasmic catecholamines, decreased aldehyde dehydrogenase activity, and oligomerization of alpha-synuclein, lead to conversion from the stability afforded by negative feedback regulation to the instability, degeneration, and system failure caused by induction of positive feedback loops. These dysfunctions result from diverse combinations of genetic predispositions, environmental exposures, stress, and time. The notion of catecholamine autotoxicity has several implications for treatment, disease modification, and prevention. Conversely, disease modification clinical trials would provide key tests of the catecholaldehyde hypothesis.

Interneurons, tau and amyloid-β in the piriform cortex in Alzheimer's disease

Impaired olfaction has been described as an early symptom of Alzheimer's disease. Neuroanatomical changes underlying this deficit in the olfactory system are largely unknown. Interestingly, neuropathology begins in the transentorhinal cortex and extends to the neighboring limbic system and basal telencephalic structures that mediate olfactory processing, including the anterior olfactory nucleus and olfactory bulb. The human piriform cortex has been described as a crucial area in odor quality coding; disruption of this region mediates early olfactory deficits in Alzheimer's disease. Most neuropathological investigations have focused on the entorhinal cortex and hippocampus, whereas the piriform cortex has largely been neglected. This work aims to characterize the expression of the neuropathological amyloid-β peptide, tau protein and interneuron population markers (calretinin, parvalbumin and somatostatin) in the piriform cortex of ten Alzheimer-diagnosed (80.4 ± 8.3 years old) and five control (69.6 ± 11.1) cases. Here, we examined the distribution of different interneuronal markers as well as co-localization of interneurons and pathological markers. Results indicated preferential vulnerability of somatostatin- (p = 0.0001 < α = 0.05) and calretinin-positive (p = 0.013 < α = 0.05) cells that colocalized with amyloid-β peptide, while the prevalence of parvalbumin-positive cells was increased (p = 0.045 < α = 0.05) in the Alzheimer's cases. These data may help to reveal the neural basis of olfactory deficits linked to Alzheimer's disease as well as to characterize neuronal populations preferentially vulnerable to neuropathology in regions critically involved in early stages of the disease.

Monoamine oxidase inhibitors: promising therapeutic agents for Alzheimer's disease (Review)

Activated monoamine oxidase (MAO) has a critical role in the pathogenesis of Alzheimer's disease (AD), including the formation of amyloid plaques from amyloid β peptide (Aβ) production and accumulation, formation of neurofibrillary tangles, and cognitive impairment via the destruction of cholinergic neurons and disorder of the cholinergic system. Several studies have indicated that MAO inhibitors improve cognitive deficits and reverse Aβ pathology by modulating proteolytic cleavage of amyloid precursor protein and decreasing Aβ protein fragments. Thus, MAO inhibitors may be considered as promising therapeutic agents for AD.

Multitarget-directed resveratrol derivatives: anti-cholinesterases, anti-β-amyloid aggregation and monoamine oxidase inhibition properties against Alzheimer's disease

Resveratrol derivatives were designed and synthesized as multitarget-directed agents for treating AD, and 6r was a balanced inhibitor toward all the tested targets.

Where, when, and in what form does sporadic Alzheimer's disease begin?

PURPOSE OF REVIEW

Intraneuronal lesions consisting of abnormal tau protein are seen to develop from the beginning until the end-phase of the pathological process underlying Alzheimer's disease. This review highlights the earliest phase of this process.

RECENT FINDINGS

Development of abnormal tau frequently begins during childhood or puberty in nuclei of the lower brainstem sending diffuse projections to the cerebral cortex. Nonfibrillar abnormal tau material first occurs in the proximal axon of projection neurons in the locus coeruleus. Subsequently, a similar material (pretangle material) fills the somatodendritic compartment. In contrast with the pretangle material in cell bodies and dendrites, the nonfibrillar material in the axon normally does not convert into stable fibrillary inclusions.

SUMMARY

Projection neurons (not only those of the locus coeruleus) are sturdy and can survive for a lifetime despite the existence of Alzheimer-related abnormal tau. Currently, little understood mechanisms most probably exist that enable neurons to fulfill their general functions even when severe tau pathology is present. The proclivity of predisposed neuronal types to develop abnormal tau may be intrinsic to the human brain. However, the tempo of disease progression reveals considerable individual differences, thereby offering opportunities to study conditions that may modify disease progression.

Synthesis and biological evaluation of novel styryl benzimidazole derivatives as probes for imaging of neurofibrillary tangles in Alzheimer's disease

This paper describes the synthesis and biological evaluation of styrylbenzimidazole (SBIM) derivatives as agents for imaging neurofibrillary tangles (NFT) in patients with Alzheimer's disease (AD). SBIM derivatives were prepared with 4-iodobenzene-1,2-diamine and substituted cinnamaldehydes. In binding experiments using recombinant tau and Aβ(1-42) aggregates, SBIM-3 showed higher affinity for the tau aggregates than Aβ(1-42) aggregates (ratio of K(d) values was 2.73). In in vitro autoradiography and fluorescent staining, [(125)I]SBIM-3 (or SBIM-3) bound NFT in sections of AD brain tissue. In biodistribution experiments using normal mice, all [(125)I]SBIM derivatives showed high initial uptake into (3.20-4.11%ID/g at 2 min after the injection) and rapid clearance from (0.12-0.33%ID/g at 60 min after the injection) the brain. In conclusion, appropriate structural modifications of SBIM derivatives could lead to more useful agents for the in vivo imaging of NFT in AD brains.

7-Methoxytacrine-adamantylamine heterodimers as cholinesterase inhibitors in Alzheimer's disease treatment--synthesis, biological evaluation and molecular modeling studies

A structural series of 7-MEOTA-adamantylamine thioureas was designed, synthesized and evaluated as inhibitors of human acetylcholinesterase (hAChE) and human butyrylcholinesterase (hBChE). The compounds were prepared based on the multi-target-directed ligand strategy with different linker lengths (n = 2-8) joining the well-known NMDA antagonist adamantine and the hAChE inhibitor 7-methoxytacrine (7-MEOTA). Based on in silico studies, these inhibitors proved dual binding site character capable of simultaneous interaction with the peripheral anionic site (PAS) of hAChE and the catalytic active site (CAS). Clearly, these structural derivatives exhibited very good inhibitory activity towards hBChE resulting in more selective inhibitors of this enzyme. The most potent cholinesterase inhibitor was found to be thiourea analogue 14 (with an IC₅₀ value of 0.47 µM for hAChE and an IC₅₀ value of 0.11 µM for hBChE, respectively). Molecule 14 is a suitable novel lead compound for further evaluation proving that the strategy of dual binding site inhibitors might be a promising direction for development of novel AD drugs.

Recommendations to standardize preanalytical confounding factors in Alzheimer's and Parkinson's disease cerebrospinal fluid biomarkers: an update

Early diagnosis of neurodegenerative disorders such as Alzheimer's (AD) or Parkinson's disease (PD) is needed to slow down or halt the disease at the earliest stage. Cerebrospinal fluid (CSF) biomarkers can be a good tool for early diagnosis. However, their use in clinical practice is challenging due to the high variability found between centers in the concentrations of both AD CSF biomarkers (Aβ42, total tau and phosphorylated tau) and PD CSF biomarker (α-synuclein). Such a variability has been partially attributed to different preanalytical procedures between laboratories, thus highlighting the need to establish standardized operating procedures. Here, we merge two previous consensus guidelines for preanalytical confounding factors in order to achieve one exhaustive guideline updated with new evidence for Aβ42, total tau and phosphorylated tau, and α-synuclein. The proposed standardized operating procedures are applicable not only to novel CSF biomarkers in AD and PD, but also to biomarkers for other neurodegenerative disorders.

Role of ABC transporters in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of age-related dementia that begins with memory loss and progresses to include severe cognitive impairment. A major pathological hallmark of AD is the accumulation of beta amyloid peptide (Aβ) in senile plaques in the brain of AD patients. The exact mechanism by which AD takes place remains unknown. However, an increasing number of studies suggests that ATP-binding cassette (ABC) transporters, which are localized on the surface of brain endothelial cells of the blood-brain barrier (BBB) and brain parenchyma, may contribute to the pathogenesis of AD. Recent studies have unraveled important roles of ABC transporters including ABCB1 (P-glycoprotein, P-gp), ABCG2 (breast cancer resistant protein, BCRP), ABCC1 (multidrug resistance protein 1, MRP1), and the cholesterol transporter ABCA1 in the pathogenesis of AD and Aβ peptides deposition inside the brain. Therefore, understanding the mechanisms by which these transporters contribute to Aβ deposition in the brain is important for the development of new therapeutic strategies against AD. This review summarizes and highlights the accumulating evidence in the literature which describe the role of altered function of various ABC transporters in the pathogenesis and progression of AD and the implications of modulating their functions for the treatment of AD.

Neurochemical correlates of cognitive dysfunction in patients with leukoaraiosis: a proton magnetic resonance spectroscopy study

OBJECTIVES

Leukoaraiosis (LA) is a common radiological finding in the elderly and may reflect cerebral small vessel disease (SVD). Although SVD has been identified as a major cause of vascular cognitive impairment or vascular dementia, the mechanisms for this association remain unclear. We therefore aimed to measure brain metabolites in LA using proton magnetic resonance spectroscopy ((1)H-MRS) as to determine the relationship between cognitive function and neurochemical white matter profile.

METHODS

We recruited 23 patients with LA and 23 age- and sex-matched healthy controls consecutively. Multi-voxel (1)H-MRS was performed with a volume of interest located in centrum semiovale that contained mainly white matter voxels. Three main ratios of N-acetyl aspartate (NAA)/Cr, choline (Cho)/Cr and NAA/Cho were obtained. Spearman rank correlation coefficients were calculated between the cognitive function and the measured metabolite ratios.

RESULTS

We found significantly lower levels of NAA/Cho and NAA/Cr ratios in lesioned white matter in patients with LA than healthy controls (P<0.05). The ratios of NAA/Cho and NAA/Cr in normal appearing white matter (NAWM) were higher than lesioned white matter and lower than controls, but this difference was not significant (P>0.05). There was a positive relationship between Mini-Mental State Examination (MMSE) and NAA/Cho in NAWM (r = 0.417, P = 0.048), and also a positive relationship between MMSE and NAA/Cr in lesioned white matter (r = 0.551, P = 0.006) in patients with LA. A positive relationship between the Z scores of the executive function and NAA/Cho in lesioned white matter (r = 0.557, P = 0.006) was also found.

CONCLUSION

The main finding of this study was a significant reduction in the ratios of NAA/Cr and NAA/Cho in lesioned white matter, which indicates a marker of neuronal loss or dysfunction in patients with LA, which was correlated with cognitive function. This relationship between cognitive function and metabolic changes suggests that (1)H-MRS can be explored as a marker for cognitive dysfunction in patients with LA.

The War (on Terror) on Alzheimer's

In the decade following the tragedies of 9/11, a US-led "War on Terror" has coincided with a US-led "War on Alzheimer's disease". Not only has the rhetoric from these two wars overlapped and produced similar practical and conceptual problems, the campaigns have also become interwoven through the emerging public health issue of war-related head injuries, as well as a shared neglect for environmental contributions to human suffering. This article first explores similarities in the framing and prosecution of both wars, and then considers the long-term consequences of traumatic brain injuries (TBI) and traumatic environmental injuries (TEI) in the context of a society facing the increased prevalence of dementia. Ultimately, it is argued that addressing the challenges of cognitive aging and preventing violent social conflict both require a vernacular of higher ideals and values--as well as new language patterns rising out of the ecological movement--to trump the more expedient war rhetoric that has disproportionately marked public discourse around terrorism and Alzheimer's disease during the past decade.

Multi-target drugs: the trend of drug research and development

Summarizing the status of drugs in the market and examining the trend of drug research and development is important in drug discovery. In this study, we compared the drug targets and the market sales of the new molecular entities approved by the U.S. Food and Drug Administration from January 2000 to December 2009. Two networks, namely, the target–target and drug–drug networks, have been set up using the network analysis tools. The multi-target drugs have much more potential, as shown by the network visualization and the market trends. We discussed the possible reasons and proposed the rational strategies for drug research and development in the future.