Clinically tested drugs for Alzheimer's disease

Anti-Neurodegenerating Activity: Structure-Activity Relationship Analysis of Flavonoids

An anti-neurodegeneration activity study was carried out for 80 flavonoid compounds. The structure-activity analysis of the structures was carried out by performing three different anti-neurodegeneration screening tests, showing that in these structures, the presence of a hydroxy substituent group at position C3' as well as C5' of ring B and a methoxy substituent group at the C7 position of ring A play a vital role in neuroprotective and antioxidant as well as anti-inflammatory activity. Further, we found structure (5) was the top-performing active structure out of 80 structures. Subsequently, a molecular docking study was carried out for the 3 lead flavonoid compounds (4), (5), and (23) and 21 similar hypothetical proposed structures to estimate the binding strength between the tested compounds and proteins potentially involved in disease causation. Ligand-based pharmacophores were generated to guide future drug design studies.

Pathophysiological Association of Alzheimer's Disease and Hypertension: A Clinical Concern for Elderly Population

Alzheimer's disease (AD), the most common cause of dementia and the fifth leading cause of death in the adult population has a complex pathophysiological link with hypertension (HTN). A growing volume of published literature on a parallel elevation of blood pressure (BP), amyloid plaques, and neurofibrillary tangles formation in post-middle of human brain cells has developed new, widely accepting foundations on this association. In particular, HTN in elderly life mediates cerebral blood flow dysfunction, neuronal dysfunction, and significant decline in cognitive impairment, primarily in the late-life populace, governing the onset of AD. Thus, HTN is an established risk factor for AD. Considering the impact of AD, 1.89 million deaths annually, and the failure of palliative therapies to cure AD, the scientific research community is looking to adopt integrated approaches to target early modified risk factors like HTN to reduce AD burden. The current review highlights the significance and impact of HTN-based prevention in lowering the AD burden in the elderly by providing a comprehensive overview of the physiological relationship between AD and HTN with an in-detail explanation of the role and applications of pathological biomarkers in this clinical association. The review will gain worth in presenting new insights and providing inclusive discussion on the correlation between HTN and cognitive impairment. It will increase across a wider scientific audience to expand understanding of this pathophysiological association.

Repurposing Antihypertensive Drugs for the Management of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder that has affected millions of people worldwide. However, currently, there is no treatment to cure the disease. The AD drugs available in the market only manage the disease symptomatically and the effects are usually short-term. Thus, there is a need to look at alternatives AD therapies. This literature review aims to shed some light on the potential of repurposing antihypertensives to treat AD. Mid-life hypertension has not only been recognised as a risk factor for AD, but its relation with AD has also been well established. Hence, antihypertensives were postulated to be beneficial in managing AD. Four classes of antihypertensives, as well as their potential limitations and prospects in being utilised as AD therapeutics, were discussed in this review.

Bojungikgi-Tang, a Traditional Herbal Formula, Exerts Neuroprotective Effects and Ameliorates Memory Impairments in Alzheimer's Disease-Like Experimental Models

Bojungikgi-tang (BJIGT; Bu Zhong Yi Qi Tang in China, Hochuekkito in Japan) is a traditional Oriental herbal formula comprised of eight medicinal herbs that has long been used for the treatment of digestive disorders. A recent clinical study from South Korea reported that BJIGT-gamibang administration may be effective in treating dementia. We aimed to establish scientific evidence for the anti-dementia effects of BJIGT using in vitro and in vivo experimental models. We measured amyloid- β (Aβ) aggregation, β-secretase (BACE), and antioxidant activity in a cell free system. Neuroprotective effects were assessed using CCK-8. Imprinting control region (ICR) mice were divided into the following six groups: Normal control, Aβ-injected, Aβ-injection + oral BJIGT gavage (200, 400, or 800 mg/kg/day), and Aβ-injection + oral morin administration (10 mg/kg/day). Subsequently, behavioral evaluations were conducted and brain samples were collected from all the animals and assessed. BJIGT enhanced inhibition of Aβ aggregation and BACE activity in vivo, as well as antioxidant activity in in vitro, cell-free systems. BJIGT also exerted neuroprotective effects in a hydroperoxide (H₂O₂)-induced damaged HT22 hippocampal cell line model. In addition, BJIGT administration significantly ameliorated cognitive impairments in Aβ-injected mice, as assessed by the passive avoidance and Y-maze tests. Furthermore, BJIGT treatment suppressed Aβ aggregation and expression, as well as expression of Aβ, NeuN, and brain-derived neurotrophic factor (BDNF) in the hippocampi of Aβ-injected mice. Overall, our results demonstrate that, with further testing in clinical populations, BJIGT may have great utility for the treatment of dementia and especially Alzheimer's disease.

Coumarin derivatives bearing benzoheterocycle moiety: synthesis, cholinesterase inhibitory, and docking simulation study

Objective(s):

To investigate the efficiency of a novel series of coumarin derivatives bearing benzoheterocycle moiety as novel cholinesterase inhibitors.

Materials and Methods:

Different 7-hydroxycoumarin derivatives were synthesized via Pechmann or Knoevenagel condensation and conjugated to different benzoheterocycle (8-hydroxyquinoline, 2-mercaptobenzoxazole or 2-mercaptobenzimidazole) using dibromoalkanes 3a-m: Final compounds were evaluated against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) by Ellman’s method. Kinetic study of AChE inhibition and ligand-protein docking simulation were also carried out for the most potent compound 3b.

Results:

Some of the compounds revealed potent and selective activity against AChE. Compound 3b containing the quinoline group showed the best activity with an IC₅₀ value of 8.80 μM against AChE. Kinetic study of AChE inhibition revealed the mixed-type inhibition of the enzyme by compound 3b. Ligand-protein docking simulation also showed that the flexibility of the hydrophobic five carbons linker allows the quinoline ring to form π-π interaction with Trp279 in the PAS.

Conclusion:

We suggest these synthesized compounds could become potential leads for AChE inhibition and prevention of AD symptoms.

The position of fluorine in CP-118,954 affects AChE inhibition potency and PET imaging quantification for AChE expression in the rat brain

The in vitro inhibition potency against acetylcholinesterase (AChE) of fluorinated derivatives of CP-118,954 (1) has been shown to depend upon the position of aromatic fluorine (F) substitution on the N-benzyl moiety. Indeed, the meta-F-substituted compound 3 (IC₅₀=1.4nM) shows similar potency with the parent compound 1 (IC₅₀=1.2nM), whereas the ortho-F derivative 2 (IC₅₀=3.2nM) and para-F derivative 4 (IC₅₀=10.8nM) were found to be less potent AChE inhibitors. A comparative in vivo microdialysis study in rats showed that 3 has the strongest effect on the neuropharmacological properties as AChE inhibitor. For PET imaging studies, a radiolabeled ligand ([¹⁸F]3) was synthesized through nucleophilic aromatic substitution reaction of diaryliodonium salt-based aldehyde precursor followed by reductive alkylation in a two-step radiolabeling procedure with 11.5 ± 1.2% (n=24, non-decay corrected) radiochemical yield and over 99% radiochemical purity. In a comparative PET imaging study of the three ¹⁸F-containing derivatives of CP-118,954 ([¹⁸F]2-4), [¹⁸F]3 showed the highest radioactivity in the AChE-rich region of normal rat brain which visually reflected the in vitro AChE-binding affinity of 3. These findings support [¹⁸F]3 as a promising AChE-targeted PET imaging ligand for the assessment of cholinergic activity into the brain, providing also insights into the AChE ligand disposition, which depends upon the position of the aromatic fluorine in the benzyl moiety.

Effect of Donepezil, Tacrine, Galantamine and Rivastigmine on Acetylcholinesterase Inhibition in Dugesia tigrina

Dugesia tigrina is a non-parasitic platyhelminth, which has been recently utilized in pharmacological models, regarding the nervous system, as it presents a wide sensitivity to drugs. Our trials aimed to propose a model for an in vivo screening of substances with inhibitory activity of the enzyme acetylcholinesterase. Trials were performed with four drugs commercialized in Brazil: donepezil, tacrine, galantamine and rivastigmine, utilized in the control of Alzheimer's disease, to inhibit the activity of acetylcholinesterase. We tested five concentrations of the drugs, with an exposure of 24 h, and the mortality and the inhibition of acetylcholinesterase planarian seizure-like activity (pSLA) and planarian locomotor velocity (pLMV) were measured. Galantamine showed high anticholinesterasic activity when compared to the other drugs, with a reduction of 0.05 μmol·min(-1) and 63% of convulsant activity, presenting screw-like movement and hypokinesia, with pLMV of 65 crossed lines during 5 min. Our results showed for the first time the anticholinesterasic and convulsant effect, in addition to the decrease in locomotion induced by those drugs in a model of invertebrates. The experimental model proposed is simple and low cost and could be utilized in the screening of substances with anticholinesterasic action.

Lessons from Microglia Aging for the Link between Inflammatory Bone Disorders and Alzheimer's Disease

Bone is sensitive to overactive immune responses, which initiate the onset of inflammatory bone disorders, such as rheumatoid arthritis and periodontitis, resulting in a significant systemic inflammatory response. On the other hand, neuroinflammation is strongly implicated in Alzheimer's disease (AD), which can be enhanced by systemic inflammation, such as that due to cardiovascular disease and diabetes. There is growing clinical evidence supporting the concept that rheumatoid arthritis and periodontitis are positively linked to AD, suggesting that inflammatory bone disorders are risk factors for this condition. Recent studies have suggested that leptomeningeal cells play an important role in transducing systemic inflammatory signals to brain-resident microglia. More importantly, senescent-type, but not juvenile-type, microglia provoke neuroinflammation in response to systemic inflammation. Because the prevalence of rheumatoid arthritis and periodontitis increases with age, inflammatory bone disorders may be significant sources of covert systemic inflammation among elderly people. The present review article highlights our current understanding of the link between inflammatory bone disorders and AD with a special focus on microglia aging.

The Neuroprotective Effects of Ratanasampil on Oxidative Stress-Mediated Neuronal Damage in Human Neuronal SH-SY5Y Cells

We previously found that Ratanasampil (RNSP), a traditional Tibetan medicine, improves the cognitive function of mild-to-moderate AD patients living at high altitude, as well as learning and memory in an AD mouse model (Tg2576); however, mechanism underlying the effects of RNSP is unknown. In the present study, we investigated the effects and molecular mechanisms of RNSP on oxidative stress-induced neuronal toxicity using human neuroblastoma SH-SY5Y cells. Pretreatment with RNSP significantly ameliorated the hydrogen peroxide- (H2O2-) induced cytotoxicity of SH-SY5Y cells in a dose-dependent manner (up to 60 μg/mL). Furthermore, RNSP significantly reduced the H2O2-induced upregulation of 8-oxo-2'-deoxyguanosine (8-oxo-dG, the oxidative DNA damage marker) but significantly reversed the expression of repressor element-1 silencing transcription factor (REST) from H2O2 associated (100 μM) downregulation. Moreover, RNSP significantly attenuated the H2O2-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase 1/2 (ERK 1/2) in SH-SY5Y cells. These observations strongly suggest that RNSP may protect the oxidative stress-induced neuronal damage that occurs through the properties of various antioxidants and inhibit the activation of MAPKs. We thus provide the principle molecular mechanisms of the effects of RNSP and indicate its role in the prevention and clinical management of AD.

A review on coumarins as acetylcholinesterase inhibitors for Alzheimer's disease

Acetylcholinesterase (AChE) enzyme inhibition is an important target for the management of Alzheimer disease (AD) and AChE inhibitors are the main stay drugs for its management. Coumarins are the phytochemicals with wide range of biological activities including AChE inhibition. The scientists have attempted to explore the coumarin template for synthesizing novel AChE inhibitors with additional pharmacological activities including decrease in beta-amyloid (Aβ) deposition and beta-secretase inhibition that are also important for AD management. Most of the designed schemes have involved incorporation of a catalytic site interacting moiety at 3- and 4-positions of the coumarin ring. The present review describes these differently synthesized coumarin derivatives as AChE inhibitors for management of AD.

Novel cholinesterase inhibitors as future effective drugs for the treatment of Alzheimer's disease

Current pharmacotherapy for Alzheimer's disease involves compounds that are aimed at increasing the levels of acetylcholine in the brain by facilitating cholinergic neurotransmission through inhibition of cholinesterase. These drugs, known as acetylcholinesterase inhibitors, have been shown to improve cognition and global functions but have little impact on improving the eventual progression of the disease; however, there is evidence that other cholinesterases such as butyrylcholinesterase can play an important role in cholinergic function in the brain, and the long-suspected non-cholinergic actions of acetylcholinesterase, mainly the interference with the beta-amyloid protein cascade, have recently driven a profound revolution in cholinesterase drug research. Several disease-modifying agents are under development that target these enzymes and have hope of becoming the next generation of effective drugs in the treatment of Alzheimer's disease.

Pharmacological characterization of DM232 (unifiram) and DM235 (sunifiram), new potent cognition enhancers

DM232 (unifiram) and DM235 (sunifiram) are potent cognition-enhancers, which are four order of magnitude more potent than piracetam. These compounds, although not showing affinity in binding studies for the most important central receptors or channels, are able to prevent amnesia induced by modulation of several neurotransmission systems. These compounds are able to increase the release of acetylcholine from rat cerebral cortex, and, as far as unifiram is concerned, to increase the amplitude of fEPSP in rat hippocampal slices. In vitro experiments, performed on hippocampal slices, also supported the hypothesis of a role of the AMPA receptors for the cognition-enhancing properties of unifiram and sunifiram.

Huperzia saururus, activity on synaptic transmission in the hippocampus

Huperzia saururus (Lam.) Trevis. (Lycopodiaceae) known as cola de quirquincho is used in folk medicine to improve memory. The cholinergic neurons of the basal forebrain, including those in the medial septum, and in the vertical limbs of the diagonal band of Broca and the nucleus basalis of Meynert, provide a major source of cholinergic enervation of the cortex and hippocampus. These neurons have also been shown to play an important role in learning and memory processes. Thus, the effects of this traditional Argentinean species were studied in relation to its activity on synaptic transmission in the hippocampus. The alkaloid extract obtained first by decoction of the aerial parts and by subsequent alkaline extraction, was purified by using a Sephadex LH 20 packed column. Electrophysiological experiments were developed with the purified extract (E(2)) on rat hippocampus slices, thus eliciting long-term potentiation (LTP). Results show a marked increase in the hippocampal synaptic plasticity. The threshold value for generation of LTP was 22 +/- 1.01 Hz on average for E(2), while for controls it was 86 +/- 0.92 Hz. All of these factors could explain the use of Huperzia saururus as a memory improver as is reported in the ethnomedicine.

High cholesterol diet results in increased expression of interleukin-6 and caspase-1 in the brain of apolipoprotein E knockout and wild type mice

Inflammation in the central nervous system is an early hallmark of many neurodegenerative diseases including Alzheimer's disease (AD). Recently, increasing evidence suggests that hypercholesterolemia during midlife and abnormalities in the cholesterol metabolism could have an important role in the pathogenesis of AD. In the present study, we have evaluated the effect of high cholesterol (HC) diet on the expression of interleukin-6 (IL-6), a cytokine involved in neurodegeneration, and caspase-1, that is responsible for the cleavage of the precursors of interleukin-1 beta (IL-1 beta) and interleukin-18 (IL-18) in the brain of apolipoprotein E (Apo E) knock-out (KO) and wild type (WT) mice. The density of IL-6-positive cells was increased in the hippocampus (p<0.0001) and the dorsal part of the cortex (p<0.001) of KO and WT mice on HC diet (KOHC and WTHC mice, respectively) compared to KO and WT mice on ND (KOND and WTND mice, respectively). KOHC mice had increased caspase-1 positive cells and staining intensity in the hippocampus in comparison with WTHC mice (p<0.01). In the hippocampus, the density of caspase-1 positive cells was also higher in KOHC compared to KOND mice (p<0.05) and KOHC compared with WTHC mice (p<0.01). There was a major increase in caspase-1 immunoreactivity and cell density in both the dosal part of the cortex (p<0.001) and the lateral part of the cortex (p<0.005) in KO and WT mice on HC diet compared to ND. The findings of the present study indicate that chronic exposure to HC diet increases the expression of the two important inflammatory mediators IL-6 and caspase-1 in the brain of KO and WT mice. In the case of caspase-1, we report a major difference in the effect of HC diet on the KO mice compared to WT mice in the hippocampus. Increased expression of inflammatory mediators involved in neurodegeneration could be a potential mechanism by which hypercholesterolemia and HC diet increase the risk of AD.

Microglial responses to amyloid beta peptide opsonization and indomethacin treatment

Background

Recent studies have suggested that passive or active immunization with anti-amyloid β peptide (Aβ) antibodies may enhance microglial clearance of Aβ deposits from the brain. However, in a human clinical trial, several patients developed secondary inflammatory responses in brain that were sufficient to halt the study.

Methods

We have used an in vitro culture system to model the responses of microglia, derived from rapid autopsies of Alzheimer's disease patients, to Aβ deposits.

Results

Opsonization of the deposits with anti-Aβ IgG 6E10 enhanced microglial chemotaxis to and phagocytosis of Aβ, as well as exacerbated microglial secretion of the pro-inflammatory cytokines TNF-α and IL-6. Indomethacin, a common nonsteroidal anti-inflammatory drug (NSAID), had no effect on microglial chemotaxis or phagocytosis, but did significantly inhibit the enhanced production of IL-6 after Aβ opsonization.

Conclusion

These results are consistent with well known, differential NSAID actions on immune cell functions, and suggest that concurrent NSAID administration might serve as a useful adjunct to Aβ immunization, permitting unfettered clearance of Aβ while dampening secondary, inflammation-related adverse events.

Antioxidant potential of vitamins A, E and C in modulating oxidative stress in rat brain

BACKGROUND

Stress is known to affect synaptic plasticity, dendritic morphology and induces neurotoxic damage in humans, probably through generation of free radicals. Both ex vivo antioxidant vitamins and in vivo free radical scavenging enzymes exist. In the present study, restraint stress induced pro-oxidant status of rat brain was evaluated in terms of measurement of glutathione (GSH), lipid peroxidation (thiobarbituric acid reactive substances, TBARS) and free radical scavenging enzymes activities. The efficacy of antioxidant vitamins A, E and C alone and in combination was also evaluated in modulating inherent antioxidant system in stressed rats.

METHODS

Rats were treated with vit A, E and C alone (15 mg/kg of body weight) and in combination vitamins (E and C) prior to and after 6 h of restraint stress exposure. Both nonstressed and stressed rats were handled simultaneously. Pro-oxidant status of brain tissue was evaluated by determining the levels of GSH, TBARS and activities of superoxide dismutase (SOD), glutathione-S-transferase (GST) and catalase (CAT).

RESULTS

Restraint stress induced a decrease in the level of GSH and the activities of SOD, GST and catalase, while the levels of TBARS were found elevated. Both pre-stress and post-stress vitamin treatments (either alone or combined) resulted in alteration of these parameters towards their controls values with a relative dominance by latter. Vitamin E was found most effective in restoring inherent antioxidant system, no additive effect was observed in combined vitamin treatment as expected.

CONCLUSION

Immobilization of rats generated oxidative stress in rat brain, by decreasing the activities of SOD, GST, catalase and glutathione levels, while increasing the lipid peroxidation. Post stress vitamin E treatment was found most effective than vitamins A and C in enhancing the levels of glutathione and activities of SOD, GST and catalase and decreasing lipid peroxidation. Thus vitamin E can be given as a nutritional supplement for scavenging free radical generated in the brain tissues in order to reduce oxidative stress.