Causes of oxidative stress in Alzheimer disease

Changes in Chemokines and Chemokine Receptors Expression in a Mouse Model of Alzheimer's Disease

The amyloid precursor protein plus presenilin-1 (APP/PS1) mice are a frequently-used model for Alzheimer's disease studies (AD). However, the data relevant to which proteins are involved in inflammatory mechanism are not sufficiently well-studied using the AD mouse model. Using behavioral studies, quantitative RT-PCR and Western-blot techniques, significant findings were determined by the expression of proteins involved in inflammation comparing APP/PS1 and Wild type mice. Increased GFAP expression could be associated with the elevation in number of reactive astrocytes. IL-3 is involved in inflammation and ABDF1 intervenes normally in the transport across cell membranes and both were found up-regulated in APP/PS1 mice compared to Wild type mice. Furthermore, CCR5 expression was decreased and both CCL3 and CCL4 chemokines were highly expressed indicating a possible gliosis and probably an increase in chemotaxis from lymphocytes and T cell generation. We also noted for the first time, a CCR8 increase expression with diminution of its CCL1 chemokine, both normally involved in protection from bacterial infection and demyelination. Control of inflammatory proteins will be the next step in understanding the progression of AD and also in determining the mechanisms that can develop in this disease.

Cu and Zn interactions with Aβ peptides: consequence of coordination on aggregation and formation of neurotoxic soluble Aβ oligomers

The coordination chemistry of transition metal ions (Fe, Cu, Zn) with the amyloid-β (Aβ) peptides has attracted a lot of attention in recent years due to its repercussions in Alzheimer's disease (AD).

Brain Iron Homeostasis: A Focus on Microglial Iron

Iron is an essential trace element required for important brain functions including oxidative metabolism, synaptic plasticity, myelination, and the synthesis of neurotransmitters. Disruptions in brain iron homeostasis underlie many neurodegenerative diseases. Increasing evidence suggests that accumulation of brain iron and chronic neuroinflammation, characterized by microglia activation and secretion of proinflammatory cytokines, are hallmarks of neurodegenerative disorders including Alzheimer’ s disease. While substantial efforts have led to an increased understanding of iron metabolism and the role of microglial cells in neuroinflammation, important questions still remain unanswered. Whether or not increased brain iron augments the inflammatory responses of microglial cells, including the molecular cues that guide such responses, is still unclear. How these brain macrophages accumulate, store, and utilize intracellular iron to carry out their various functions under normal and disease conditions is incompletely understood. Here, we describe the known and emerging mechanisms involved in microglial cell iron transport and metabolism as well as inflammatory responses in the brain, with a focus on AD.

A Unified View of Assessing the Pro-oxidant versus Antioxidant Nature of Amyloid Beta Conformers

Transition-metal-catalyzed oxidative stress is a widespread concern in the pathogenesis of Alzheimer's disease. However, the exact role of amyloid beta oligomers towards oxidative stress is widely debated. Assessing the oxidative nature of the oligomers in vitro is complicated by the different experimental conditions under which they are prepared. We have investigated Cu²⁺ -catalyzed reactive oxygen species (ROS) generation by using oligomers prepared in phosphate-buffered saline (Aβ^O-PBS ) and in cell culture medium (Aβ^O-CCM ), and compared their activities with respect to the monomers and fibrils prepared at neutral and acidic pH. Although both are deca- to dodecamers, the Aβ^O-PBS oligomers have a spherical morphology and are smaller than the Aβ^O-CCM . The Aβ^O-PBS behaved as pro-oxidants; in contrast, Aβ^O-CCM quench OH^. generation attributed to CCM itself. Although the pro-oxidant oligomers showed oxidation, they also partially protect themselves from radical damage and maintain their overall spherical arrangement. The monomers and fibrils manifested antioxidant properties: radical scavenging as opposed to redox silencing. A dual role of Aβ species depending on the stage of the disease is proposed. In the earlier stages, the monomers can act as antioxidants, whereas at the later stages, the oligomers take on a pro-oxidant role. Kaempferol, a natural flavonoid, bound Cu²⁺ in 2:1 ratio and abolished ROS production in all Aβ species. It also distinctly modified the folding landscape of Aβ species into new or altered morphologies.

Protective effects of silibinin on insulin amyloid fibrillation, cytotoxicity and mitochondrial membrane damage

A growing body of evidence suggests that secretion and assembly of insulin to amyloid fibrils reduce its efficacy in treating type II diabetes and may lead to dysfunctioning of several organs. The research presented here explores the effects of silibinin on the in vitro amyloid fibrillation and cytotoxicity of bovine insulin fibrils on SH-SY5Y human neuroblastoma cells. Interaction of the resulting structures with rat brain mitochondria was also investigated. Using a range of methods for amyloid detection we showed that insulin fibrillation was significantly inhibited by silibinin in a dose-dependent fashion. Moreover, we found that silibinin was very effective in attenuating insulin fibril-induced neuronal toxicity characterized by decrease of cell viability, the release of lactate dehydrogenase, intracellular reactive oxygen species enhancement, morphological alterations, and apoptotic cell death induction. While insulin fibrillation products showed the capacity to damage mitochondria, the resultant structures produced in the presence of silibinin were totally ineffective. Together, results demonstrate the capacity of insulin fibrils to cause SH-SY5Y cell death by inducing necrosis/apoptosis changes and suggest how silibinin may afford protection. It is concluded that elucidation of such protection may provide important insights into the development of preventive and therapeutic agents for amyloid-related diseases.

Design and characterization of bivalent compounds as potential neuroprotectants for Alzheimer's disease: Impact of the spacer on biological activity

In our continuing efforts to develop bivalent compounds as potential neuroprotectants for Alzheimer's disease, a series of bivalent compounds that contain cholesterylamine and an extended spacer were synthesized and biologically characterized. Our results demonstrated that incorporation of a piperazine ring into the spacer composition significantly improved the protective potency in MC65 cell models. Our results also suggested that the optimal spacer length for such bivalent compounds ranges from 17 to 21 atoms, and further spacer extension beyond 21 atoms results no further optimization. Notably, incorporation of a piperazine ring into the spacer diminished the biometal chelating capacity for these bivalent compounds, thus suggesting structural flexibility of these compounds in interactions with metals. Collectively, the results provided valuable guidance to develop new bivalent compounds as neuroprotectants for Alzheimer's disease.

The Relationship Between Copper, Iron, and Selenium Levels and Alzheimer Disease

This study aimed to evaluate the concentrations of copper, iron, and selenium in elderly people with Alzheimer disease (AD), comparing the same parameters in a paired group of healthy people, in order to verify if the amount of these metals may influence the cognitive impairment progression. Patients' cognitive impairment was evaluated by Clinical Dementia Rating (CDR). The elementary quantification of erythrocytes was performed by inductively coupled plasma mass spectrometry technique. The statistical analyses were carried out by SPSS software 20.0 version, employing Shapiro-Wilk, Wilcoxon, Kruskall-Wallis, and Spearman correlation tests, considering significant results of p < 0.05. The sample was composed of 34% (n = 11) of women and 66% (n = 21) of men in each group. The AD group was characterized by a higher concentration of copper (p < 0.0001) and iron (p < 0.0001); however, there is no significant difference in selenium level. The analyses of the metal levels in different stages of AD were not significant in CDR-1, however in CDR-2 and CDR-3, elevated levels of copper and iron were observed; in CDR-3 patients, the level of selenium was lower (p < 0.008) compared to that of healthy controls. Patients with Alzheimer disease studied present increase in biometal blood levels, especially of copper and iron, and such increase can be different according to the disease stage and can cause more impairment cognitive functions in AD.

Impairment of Several Immune Functions and Redox State in Blood Cells of Alzheimer's Disease Patients. Relevant Role of Neutrophils in Oxidative Stress

Since aging is considered the most risk factor for sporadic Alzheimer’s Disease (AD), the age-related impairment of the immune system (immunosenescence), based on a chronic oxidative-inflammatory stress situation, could play a key role in the development and progression of AD. Although AD is accompanied by systemic disturbance, reflecting the damage in the brain, the changes in immune response and redox-state in different types of blood cells in AD patients have been scarcely studied. The aim was to analyze the variations in several immune functions and oxidative-inflammatory stress and damage parameters in both isolated peripheral neutrophils and mononuclear blood cells, as well as in whole blood cells, from patients diagnosed with mild (mAD) and severe AD, and of age-matched controls (elderly healthy subjects) as well as of adult controls. The cognitive decline of all subjects was determined by Mini-Mental State Examination (MMSE) test (mAD stage was established at 20 ≤ MMSE ≤ 23 score; AD stage at <18 MMSE; elderly subjects >27 MMSE). The results showed an impairment of the immune functions of human peripheral blood neutrophils and mononuclear cells of mAD and AD patients in relation to healthy elderly subjects, who showed the typical immunosenescence in comparison with the adult individuals. However, several alterations were only observed in severe AD patients (lower chemotaxis, lipopolysaccharide lymphoproliferation, and interleukin (IL)-10 release; higher basal proliferation, tumor necrosis factor (TNF)-α release, and IL-10/TNF-α ratio), others only in mAD subjects (higher adherence), meanwhile others appeared in both mAD and AD patients (lower phytohemaglutinin lymphoproliferation and higher IL-6 release). This impairment of immune functions could be mediated by: (1) the higher oxidative stress and damage also observed in blood cells from mAD and AD patients and in isolated neutrophils [lower glutathione (GSH) levels, high oxidized glutathione (GSSG)/GSH ratio, and GSSG and malondialdehyde contents], and (2) the higher release of basal pro-inflammatory cytokines (IL-6 and TNF-α) found in AD patients. Because the immune system parameters studied are markers of health and rate of aging, our results supported an accelerated immunosenescence in AD patients. We suggest the assessment of oxidative stress and function parameters in peripheral blood cells as well as in isolated neutrophils and mononuclear cells, respectively, as possible markers of AD progression.

Insights into the Impact of a Membrane-Anchoring Moiety on the Biological Activities of Bivalent Compounds As Potential Neuroprotectants for Alzheimer's Disease

Bivalent compounds anchoring in different manners to the membrane were designed and biologically characterized to understand the contribution of the anchor moiety to their biological activity as neuroprotectants for Alzheimer's disease. Our results established that the anchor moiety is essential, and we identified a preference for diosgenin, as evidenced by 17MD. Studies in primary neurons and mouse brain mitochondria also identified 17MD as exhibiting activity on neuritic outgrowth and the state 3 oxidative rate of glutamate while preserving the coupling capacity of the mitochondria. Significantly, our studies demonstrated that the integrated bivalent structure is essential to the observed biological activities. Further studies employing bivalent compounds as probes in a model membrane also revealed the influence of the anchor moiety on how they interact with the membrane. Collectively, our results suggest diosgenin to be an optimal anchor moiety, providing bivalent compounds with promising pharmacology that have potential applications for Alzheimer's disease.

Copper binding and redox chemistry of the Aβ16 peptide and its variants: insights into determinants of copper-dependent reactivity

The metal-binding sites of Aβ peptides are dictated primarily by the coordination preferences of the metal ion. Consequently, Cu(i) is typically bound with two His ligands in a linear mode while Cu(ii) forms a pseudo-square planar stereochemistry with the N-terminal amine nitrogen acting as an anchoring ligand. Several distinct combinations of other groups can act as co-ligands for Cu(ii). A population of multiple binding modes is possible with the equilibrium position shifting sensitively with solution pH and the nature of the residues in the N-terminal region. This work examined the Cu(ii) chemistry of the Aβ16 peptide and several variants that targeted these binding modes. The results are consistent with: (i) at pH < 7.8, the square planar site in Cu^II-Aβ16 consists primarily of a bidentate ligand provided by the carboxylate sidechain of Asp1 and the N-terminal amine supported by the imidazole sidechains of two His residues (designated here as component IA); it is in equilibrium with a less stable component IB in which the carboxylate ligand is substituted by the Asp1-Ala2 carbonyl oxygen. (ii) Both IA and IB convert to a common component II (apparent transition pK_a ∼7.8 for IA and ∼6.5 for IB, respectively) featuring a tridentate ligand consisting of the N-terminal amine, the Asp1-Ala2 amide and the Ala2-Pro3 carbonyl; this stereochemistry is stabilized by two five-membered chelate rings. (iii) Component IA is stabilized for variant Aβ16-D1H, components I (both IA and IB) are imposed on Aβ16-A2P while the less stable IB is enforced on Aβ16-D1A (which is converted to component II at pH ∼6.5); (iv) components IA and IB share two His ligands with Cu(i) and are more reactive in redox catalysis than component II that features a highly covalent and less reactive amide N^- ligand. The redox activity of IA is further enhanced for peptides with a His1 N-terminus that may act as a ligand for either Cu(i) or Cu(ii) with lower re-organization energy required for redox-shuttling. This study provided insights into the determinants that regulate the reactivity of Cu-Aβ complexes.

p47Phox/CDK5/DRP1-Mediated Mitochondrial Fission Evokes PV Cell Degeneration in the Rat Dentate Gyrus Following Status Epilepticus

Parvalbumin (PV) is one of the calcium-binding proteins, which plays an important role in the responsiveness of inhibitory neurons to an adaptation to repetitive spikes. Furthermore, PV neurons are highly vulnerable to status epilepticus (SE, prolonged seizure activity), although the underlining mechanism remains to be clarified. In the present study, we found that p47Phox expression was transiently and selectively increased in PV neurons 6 h after SE. This up-regulated p47Phox expression was accompanied by excessive mitochondrial fission. In this time point, CDK5-tyrosine 15 and dynamin-related protein 1 (DRP1)-serine 616 phosphorylations were also increased in PV cells. Apocynin (a p47Phox inhibitor) effectively mitigated PV cell loss via inhibition of CDK5/DRP1 phosphorylations and mitochondrial fragmentation induced by SE. Roscovitine (a CDK5 inhibitor) and Mdivi-1 (a DRP1 inhibitor) attenuated SE-induced PV cell loss by inhibiting aberrant mitochondrial fission. These findings suggest that p47Phox/CDK5/DRP1 may be one of the important upstream signaling pathways in PV cell degeneration induced by SE via excessive mitochondrial fragmentation.

Novel cinnamamide-dibenzylamine hybrids: Potent neurogenic agents with antioxidant, cholinergic, and neuroprotective properties as innovative drugs for Alzheimer's disease

By using fragments endowed with interesting and complementary properties for the treatment of Alzheimer's disease (AD), a novel series of cinnamamide-dibenzylamine hybrids have been designed, synthesized, and evaluated biologically. In vitro assay indicated that most of the target compounds exhibited a significant ability to inhibit ChEs, strong potency inhibitory of self-induced β-amyloid (Aβ) aggregation and to act as potential antioxidants and biometal chelators. A Lineweaver-Burk plot and molecular modeling study showed that compound 7f targeted both the CAS and PAS of AChE. In addition, compound 7f could chelate metal ions, reduce PC12 cells death induced by oxidative stress and penetrate the blood-brain barrier (BBB). Overall, all of these outstanding in vitro results in combination with promising in vivo outcomes highlighted derivative 7f as the lead structure worthy of further investigation.

Quercetin protects neuronal cells from oxidative stress and cognitive degradation induced by amyloid β-peptide treatment

The present study aimed to investigate the effect of quercetin on cytotoxicity and cognitive degradation induced by amyloid β(Aβ)‑peptide in mice. Using the 1,1-diphenyl-2‑picrylhydrazyl (DPPH) method and a Y‑maze assay, the radical quenching ability and effect on working memory were determined, respectively, of quercetin treatment following 4 days of Aβ administration. The acute oral toxicity was assessed used to determine the concentration of quercetin at which 50% lethality of the neuronal cells was induced. For determination of the effect of quercetin on degradation of learning and memory loss induced by Aβ, a passive avoidance test was used. The results revealed that quercetin was involved in the inhibition of DPPH radical activity and was found to reduce radical activity by 76.5%. Quercetin significantly protected PC12 neuronal cells from death induced by Aβ treatment. Treatment of mice with daily doses of 100 mg/kg body weight quercetin for 30 days significantly improved the degradation of learning and memory loss induced by Aβ. The acute oral dose of quercetin in mice was determined to be 575 mg/kg body weight. Therefore, quercetin was found to be of therapeutic value for the treatment of neurological disorders, including AD, although further investigations are required.

Metabolic inhibitors accentuate the anti-tumoral effect of HDAC5 inhibition

The US FDA approval of broad-spectrum histone deacetylase (HDAC) inhibitors has firmly laid the cancer community to explore HDAC inhibition as a therapeutic approach for cancer treatment. Hitting one HDAC member could yield clinical benefit but this required a complete understanding of the functions of the different HDAC members. Here we explored the consequences of specific HDAC5 inhibition in cancer cells. We demonstrated that HDAC5 inhibition induces an iron-dependent reactive oxygen species (ROS) production, ultimately leading to apoptotic cell death as well as mechanisms of mitochondria quality control (mitophagy and mitobiogenesis). Interestingly, adaptation of HDAC5-depleted cells to oxidative stress passes through reprogramming of metabolic pathways towards glucose and glutamine. Therefore, interference with both glucose and glutamine supply in HDAC5-inhibited cancer cells significantly increases apoptotic cell death and reduces tumour growth in vivo; providing insight into a valuable clinical strategy combining the selective inhibition of HDAC5 with various inhibitors of metabolism as a new therapy to kill cancer cells.

Discovery of the first dual GSK3β inhibitor/Nrf2 inducer. A new multitarget therapeutic strategy for Alzheimer's disease

The formation of neurofibrillary tangles (NFTs), oxidative stress and neuroinflammation have emerged as key targets for the treatment of Alzheimer’s disease (AD), the most prevalent neurodegenerative disorder. These pathological hallmarks are closely related to the over-activity of the enzyme GSK3β and the downregulation of the defense pathway Nrf2-EpRE observed in AD patients. Herein, we report the synthesis and pharmacological evaluation of a new family of multitarget 2,4-dihydropyrano[2,3-c]pyrazoles as dual GSK3β inhibitors and Nrf2 inducers. These compounds are able to inhibit GSK3β and induce the Nrf2 phase II antioxidant and anti-inflammatory pathway at micromolar concentrations, showing interesting structure-activity relationships. The association of both activities has resulted in a remarkable anti-inflammatory ability with an interesting neuroprotective profile on in vitro models of neuronal death induced by oxidative stress and energy depletion and AD. Furthermore, none of the compounds exhibited in vitro neurotoxicity or hepatotoxicity and hence they had improved safety profiles compared to the known electrophilic Nrf2 inducers. In conclusion, the combination of both activities in this family of multitarget compounds confers them a notable interest for the development of lead compounds for the treatment of AD.

Role of enzymatic free radical scavengers in management of oxidative stress in autoimmune disorders

Autoimmune disorders are distinct with over production and accumulation of free radicals due to its undisclosed genesis. The cause of numerous disorders as cancer, arthritis, psoriasis, diabetes, alzheimer's, cardiovascular disease, Parkinson's, respiratory distress syndrome, colitis, crohn's, pulmonary fibrosis, obesity and ageing have been associated with immune dysfunction and oxidative stress. In an oxidative stress, reactive oxygen species generally provoke the series of oxidation at cellular level. The buildup of free radicals in turn triggers various inflammatory cells causing release of various inflammatory interleukins, cytokines, chemokines, and tumor necrosis factors which mediate signal transduction and transcription pathways as nuclear factor- kappa B (NF-κB), signal transducer and activator of transcription 3 (STAT3), hypoxia-inducible factor-1 (HIF-1α) and nuclear factor-erythroid 2-related factor (Nrf2). The imbalance could only be combat by supplementing natural defensive antioxidant enzymes such as superoxide dismutase and catalase. The efficiency of these enzymes is enhanced by use of colloidal carriers which include cellular carriers, vesicular and particulate systems like erythrocytes, leukocytes, platelets, liposomes, transferosomes, solid lipid nanoparticles, microspheres, emulsions. Thus this review provides a platform for understanding importance of antioxidant enzymes and its therapeutic applications in treatment of various autoimmune disorders.

Neuro-Preventive Effect and Elevation of Cellular Adenosine Triphosphate by PUFAs from Pteleiosis suberosa Stem Bark on Mercury Sub-Acute Exposed Rats

OBJECTIVES

Occupational/industrial exposure and experimental intoxication of mercury can produce neurological effects but Pteleiosis suberosa stem bark extract (PTSSBE) might be useful in the treatment of brain disorders because it's anti-ulcer, anti-inflammatory and antioxidant effects had been documented.

METHODS

The present study was therefore designed to investigate some phenolic constituents, evaluate its antioxidant properties and examine its reversal effects of PTSSBE on sub-acute mercury-induced brain toxicity. Rats were divided into five groups of 10 animals each. Group I was given distilled water; group II, III, IV and V was orally administered with mercury at a dose of 3.75 mg/kg body weight. Group III, IV and V were co-treated with PTSSBE of 25, 50 and 100 mg/ kg body weight respectively, for 10 days.

RESULTS

The results revealed that the stem bark extract exhibited high presence of antioxidants. Experimental exposure of rats to mercury significantly decreased the activities of catalase (CAT), lactate dehydrogenase (LDH), and the level of reduced glutathione (GSH), while the activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and the formation of malondialdehyde (MDA) were increased. These effects were reversed by co-administration with PTSSBE in mercury-induced brain toxicity in rats.

CONCLUSION

The protective effects of Pteleiosis suberosa, during mercury exposure suggest that these phenolics and PUFAs may be helpful in treating neurological disorders and other related cerebral toxicity implicated in depleted cellular ATP and oxidative stress.

Design, synthesis and evaluation of 2-arylethenyl-N-methylquinolinium derivatives as effective multifunctional agents for Alzheimer's disease treatment

A series of 2-arylethenyl-N-methylquinolinium derivatives were designed and synthesized based on our previous research of 2-arylethenylquinoline analogues as multifunctional agents for the treatment of Alzheimer's disease (AD) (Eur. J. Med. Chem. 2015, 89, 349-361). The results of in vitro biological activity evaluation, including β-amyloid (Aβ) aggregation inhibition, cholinesterase inhibition, and antioxidant activity, showed that introduction of N-methyl in quinoline ring significantly improved the anti-AD potential of compounds. The optimal compound, compound a12, dramatically attenuated the cell death of glutamate-induced HT22 cells by preventing the generation of ROS and increasing the level of GSH. Most importantly, intragastric administration of a12•HAc was well tolerated at doses up to 2000 mg/kg and could traverse blood-brain barrier.

A Peroxynitrite Dicopper Complex: Formation via Cu-NO and Cu-O2 Intermediates and Reactivity via O-O Cleavage Chemistry

A mixed-valent Cu(I)Cu(II) complex, [Cu^I,II₂(UN-O^-)]²⁺ (1), reacts with NO_(g) at -80 °C to form [Cu^I,II₂(UN-O^-)(NO)]²⁺ (2), best described as a mixed-valent nitrosyl complex that has a ν(N-O) band at 1670 cm^-1 in its infrared (IR) spectrum. Complex 2 undertakes a one-electron oxidation via the addition of O_2(g) to generate a new intermediate, best described as a superoxide and nitrosyl adduct, [Cu^II₂(UN-O^-)(NO)(O₂^-)]²⁺ (3), based on its distinctively blue-shifted ν(N-O) band at 1853 cm^-1. Over the course of 20 min at -80 °C, 3 is converted to the peroxynitrite (PN) complex [Cu^II₂(UN-O^-)(^-OON═O)]²⁺ (4), which was characterized by low-temperature electrospray ionization mass spectrometry (ESI-MS) and IR spectroscopy; ν(N-O) absorptions at 1520 and 1640 cm^-1 have been assigned as cis- and trans-conformers of the PN ligand in 4. Alternatively, the superoxide complex [Cu^II₂(UN-O^-)(O₂^•-)]²⁺ (5) is found to react with NO_(g) to generate the same intermediate superoxide and nitrosyl adduct 3 (based on IR criteria), which likewise converts to the same PN complex 4. The O-O bond in 4 undergoes heterolysis in dichloromethane solvent and is postulated to produce nitronium ion, leading to ortho-nitration of 2,4-di-tert-butylphenol (DTBP). However, in 2-methyltetrahydrofuran as solvent, the O-O bond undergoes homolysis to generate ^•NO₂ (detected spectrophotometrically) and a putative higher-valent complex, [Cu^II,III₂(UN-O^-)(O^2-)]²⁺, that abstracts a H-atom from DTBP to give [Cu^II₂(UN-O^-)(OH)]²⁺ and a phenoxyl radical. The latter may dimerize to form the bis-phenol observed experimentally or couple with the ^•NO₂ present, leading to o-phenol nitration.

Humulus japonicus inhibits the progression of Alzheimer's disease in a APP/PS1 transgenic mouse model

Humulus japonicus Siebold & Zucc. (HJ) has traditionally been administered to patients with pulmonary disease, skin disease and hypertension in Korea, and it is considered to exert anti-inflammatory, antioxidant, antimicrobial and anti-mycobacterial effects. However, its effects against Alzheimer's disease (AD) have yet to be explored. Thus, this study was carried out to investigate whether HJ has a beneficial effect on the progression of AD in an animal model. A methanolic extract of HJ (500 mg/kg/day) was intragastrically administered to 5-month-old APP/PS1 transgenic (Tg-APP/PS1) mice for 2.5 months. Novel object recognition and Y-maze alteration tests were used to assess cognitive function, and an immunohistochemical assay was performed to assess amyloid β (Aβ) deposition, tau phosphorylation and gliosis. An in vitro assay using a microglial cell line was also performed to investigate the anti-inflammatory effects of HJ. Our results revealed that HJ significantly decreased the mRNA and protein expression levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6 and inducible nitric oxide synthase (iNOS) induced by lipopolysaccharide in the microglial cell line. The administration of HJ for 2 months improved the cognitive function of Tg-APP/PS1 mice. HJ notably reduced the area occupied by Aβ and neurofibrillary tangles, and the number of activated astrocytes and microglia in the cortex of Tg-APP/PS1 mice. The findings of our study suggest that HJ has the therapeutic potential to inhibit the progression of AD and to improve cognitive deterioration in Tg-APP/PS1 mice.

Recent progress in repositioning Alzheimer's disease drugs based on a multitarget strategy

Alzheimer's disease (AD) is a serious progressive neurological disorder, characterized by impaired cognition and profound irreversible memory loss. The multifactorial nature of AD and the absence of a cure so far have stimulated medicinal chemists worldwide to follow multitarget drug-design strategies based on repositioning approved drugs. This review describes a summary of recently published works focused on tailoring new derivatives of US FDA-approved acetylcholinesterase inhibitors, in addition to huperzine (a drug approved in China), either by hybridization with other pharmacophore elements (to hit more AD targets), or by combination of two FDA-approved drugs. Besides the capacity for improving the cholinergic activity, these polyfunctional derivatives are also able to tackle other important neuroprotective properties, such as anti-β-amyloid aggregation, scavenging of radical oxygen species, modulation of redox-active metals or inhibition of monoamine oxidase, thereby resulting in potentially novel and more effective therapeutics for the treatment of AD.

Bivalent Compound 17MN Exerts Neuroprotection through Interaction at Multiple Sites in a Cellular Model of Alzheimer's Disease

Multiple pathogenic factors have been suggested to play a role in the development of Alzheimer's disease (AD). The multifactorial nature of AD also suggests the potential use of compounds with polypharmacology as effective disease-modifying agents. Recently, we have developed a bivalent strategy to include cell membrane anchorage into the molecular design. Our results demonstrated that the bivalent compounds exhibited multifunctional properties and potent neuroprotection in a cellular AD model. Herein, we report the mechanistic exploration of one of the representative bivalent compounds, 17MN, in MC65 cells. Our results established that MC65 cells die through a necroptotic mechanism upon the removal of tetracycline (TC). Furthermore, we have shown that mitochondrial membrane potential and cytosolic Ca2+ levels are increased upon removal of TC. Our bivalent compound 17MN can reverse such changes and protect MC65 cells from TC removal induced cytotoxicity. The results also suggest that 17MN may function between the Aβ species and RIPK1 in producing its neuroprotection. Colocalization studies employing a fluorescent analog of 17MN and confocal microscopy demonstrated the interactions of 17MN with both mitochondria and endoplasmic reticulum, thus suggesting that 17MN exerts its neuroprotection via a multiple-site mechanism in MC65 cells. Collectively, these results strongly support our original design rationale of bivalent compounds and encourage further optimization of this bivalent strategy to develop more potent analogs as novel disease-modifying agents for AD.

Mechanistic Insight of Bivalent Compound 21MO as Potential Neuroprotectant for Alzheimer's Disease

We have recently developed a bivalent strategy to provide novel compounds that potentially target multiple risk factors involved in the development of Alzheimer’s disease (AD). Our previous studies employing a bivalent compound with a shorter spacer (17MN) implicated that this compound can localize into mitochondria and endoplasmic reticulum (ER), thus interfering with the change of mitochondria membrane potential (MMP) and Ca²⁺ levels in MC65 cells upon removal of tetracycline (TC). In this report, we examined the effects by a bivalent compound with a longer spacer (21MO) in MC65 cells. Our results demonstrated that 21MO suppressed the change of MMP, possibly via interaction with the mitochondrial complex I in MC65 cells. Interestingly, 21MO did not show any effects on the Ca²⁺ level upon TC removal in MC65 cells. Our previous studies suggested that the mobilization of Ca²⁺ in MC65 cells, upon withdraw of TC, originated from ER, so the results implicated that 21MO may preferentially interact with mitochondria in MC65 cells under the current experimental conditions. Collectively, the results suggest that bivalent compounds with varied spacer length and cell membrane anchor moiety may exhibit neuroprotective activities via different mechanisms of action.

Inhibition of myeloperoxidase-mediated oxidative damage by nitrite in SH-SY5Y cells: Relevance to neuroprotection in neurodegenerative diseases

Myeloperoxidase (MPO) and MPO-catalyzed hypochlorous acid (HOCl) is elevated in many neurodegenerative diseases, and lead to severe tissue injuries. Nitrite (NO2(-)) is a widespread inorganic molecule that has recently been proposed as a direct NO donor to exert antioxidant properties in vivo and vitro. Since NO2(-) and MPO (and/or HOCl) were important mediators in brain function and disease, we investigated the effects of NO2(-) on MPO-mediated damage to human neuroblastoma SH-SY5Y cells. Here, we showed that exposure of SH-SY5Y cells to MPO (or HOCl) resulted in a significant loss in viability, ATP and glutathione levels, and treatment of neuronal cells with NO2(-) substantially attenuated MPO (or HOCl)-dependent cellular toxicity. The protective effects of NO2(-) on MPO (or HOCl)-induced cytotoxicity were because that (1) NO2(-) at high concentrations competed effectively with Cl(-) for MPO, thus limiting OCl(-) production by the enzyme; (2) HOCl was removed by reacting with NO2(-), forming less damaging compound; (3) NO2(-) significantly inhibited MPO-mediated inactivation of brain protein (enolase) and protein oxidation. Therefore, NO2(-) could show novel protective effects in some neurodegenerative diseases by preventing MPO-mediated oxidative damage.

Versatility of the Curcumin Scaffold: Discovery of Potent and Balanced Dual BACE-1 and GSK-3β Inhibitors

The multitarget approach has gained increasing acceptance as a useful tool to address complex and multifactorial maladies such as Alzheimer's disease (AD). The concurrent inhibition of the validated AD targets β-secretase (BACE-1) and glycogen synthase kinase-3β (GSK-3β) by attacking both β-amyloid and tau protein cascades has been identified as a promising AD therapeutic strategy. In our study, curcumin was identified as a lead compound for the simultaneous inhibition of both targets; therefore, synthetic efforts were dedicated to obtaining a small library of novel curcumin-based analogues, and a number of potent and balanced dual-target inhibitors were obtained. In particular, 2, 6, and 7 emerged as promising drug candidates endowed with neuroprotective potential and brain permeability. Notably, for some new compounds the symmetrical diketo and the β-keto-enol tautomeric forms were purposely isolated and tested in vitro, allowing us to gain insight into the key requirements for BACE-1 and GSK-3β inhibition.

HNK-1 Carrier Glycoproteins Are Decreased in the Alzheimer's Disease Brain

The human natural killer-1 (HNK-1), 3-sulfonated glucuronic acid, is a glycoepitope marker of cell adhesion that participates in cell-cell and cell-extracellular matrix interactions and in neurite growth. Very little is known about the regulation of the HNK-1 glycan in neurodegenerative disease, particularly in Alzheimer's disease (AD). In this study, we investigate changes in the levels of HNK-1 carrier glycoproteins in AD. We demonstrate an overall decrease in HNK-1 immunoreactivity in glycoproteins extracted from the frontal cortex of AD subjects, compared with levels from non-demented controls (NDC). Immunoblotting of ventricular post-mortem and lumbar ante-mortem cerebrospinal fluid with HNK-1 antibodies indicate similar levels of carrier glycoproteins in AD and NDC samples. Decrease in HNK-1 carrier glycoproteins were not paralleled by changes in messenger RNA (mRNA) levels of the enzymes involved in the synthesis of the glycoepitope, β-1,4-galactosyltransferase (β4GalT), glucuronyltransferases GlcAT-P and GlcAT-S, or sulfotransferase HNK-1ST. Over-expression of amyloid precursor protein in Tg2576 transgenic mice and in vitro treatment of SH-SY5Y neuroblastoma cells with the amyloidogenic Aβ42 peptide resulted in a decrease in HNK-1 immunoreactivity levels in brain and cellular extracts, whereas the levels of soluble HNK-1 glycoproteins detected in culture media were not affected by Aβ treatment. HNK-1 levels remain unaffected in the brain extracts of Tg-VLW mice, a model of mutant hyperphosphorylated tau, and in SH-SY5Y cells over-expressing hyperphosphorylated wild-type tau. These results provide evidence that cellular levels of HNK-1 carrier glycoforms are decreased in the brain of AD subjects, probably influenced by the β-amyloid protein.

Oxidative stress in oral diseases

Oxidative species, including reactive oxygen species (ROS), are components of normal cellular metabolism and are required for intracellular processes as varied as proliferation, signal transduction, and apoptosis. In the situation of chronic oxidative stress, however, ROS contribute to various pathophysiologies and are involved in multiple stages of carcinogenesis. In head and neck cancers specifically, many common risk factors contribute to carcinogenesis via ROS-based mechanisms, including tobacco, areca quid, alcohol, and viruses. Given their widespread influence on the process of carcinogenesis, ROS and their related pathways are attractive targets for intervention. The effects of radiation therapy, a central component of treatment for nearly all head and neck cancers, can also be altered via interfering with oxidative pathways. These pathways are also relevant to the development of many benign oral diseases. In this review, we outline how ROS contribute to pathophysiology with a focus toward head and neck cancers and benign oral diseases, describing potential targets and pathways for intervention that exploit the role of oxidative species in these pathologic processes.

Free Superoxide is an Intermediate in the Production of H2O2 by Copper(I)-Aβ Peptide and O2

Oxidative stress is considered as an important factor and an early event in the etiology of Alzheimer's disease (AD). Cu bound to the peptide amyloid-β (Aβ) is found in AD brains, and Cu-Aβ could contribute to this oxidative stress, as it is able to produce in vitro H2O2 and HO˙ in the presence of oxygen and biological reducing agents such as ascorbate. The mechanism of Cu-Aβ-catalyzed H2O2 production is however not known, although it was proposed that H2O2 is directly formed from O2 via a 2-electron process. Here, we implement an electrochemical setup and use the specificity of superoxide dismutase-1 (SOD1) to show, for the first time, that H2O2 production by Cu-Aβ in the presence of ascorbate occurs mainly via a free O2˙(-) intermediate. This finding radically changes the view on the catalytic mechanism of H2O2 production by Cu-Aβ, and opens the possibility that Cu-Aβ-catalyzed O2˙(-) contributes to oxidative stress in AD, and hence may be of interest.

Association of the C47T Polymorphism in SOD2 with Amnestic Mild Cognitive Impairment and Alzheimer's Disease in Carriers of the APOEε4 Allele

Oxidative stress plays an important part in amnestic mild cognitive impairment (aMCI), the prodromal phase of Alzheimer's disease (AD). Recent evidence shows that polymorphisms in the SOD2 gene affect the elimination of the reactive oxygen species (ROS) generated in mitochondria. The aim of this study was to determine whether the functional rs4880 SNP in the SOD2 gene is a risk factor associated with aMCI and sporadic AD. 216 subjects with aMCI, 355 with AD, and 245 controls have been studied. The SNP rs4880 of the SOD2 gene was genotyped by RT-PCR and the APOE genotype was determined by PCR and RFLPs. Different multinomial logistic regression models were used to determine the risk levels for aMCI and AD. Although the T allele of the SOD2 rs4880 SNP gene (rs4880-T) is not an independent risk for aMCI or AD, this allele increases the risk to aMCI patients carrying at least one APOEε4 allele. Moreover, rs4880-T allele and APOEε4 allele combination has been found to produce an increased risk for AD compared to aMCI reference patients. These results suggest that APOEε4 and rs4880-T genotype may be a risk for aMCI and a predictor of progression from aMCI to AD.

Multiple function fluorescein probe performs metal chelation, disaggregation, and modulation of aggregated Aβ and Aβ-Cu complex

An exceptional probe comprising indole-3-carboxaldehyde fluorescein hydrazone (FI) performs multiple tasks, namely, disaggregating amyloid β (Aβ) aggregates in different biomarker environments such as cerebrospinal fluid (CSF), Aβ1-40 fibrils, β-amyloid lysozyme aggregates (LA), and U87 MG human astrocyte cells. Additionally, the probe FI binds with Cu(2+) ions selectively, disrupts the Aβ aggregates that vary from few nanometers to micrometers, and prevents their reaggregation, thereby performing disaggregation and modulation of amyloid-β in the presence as well as absence of Cu(2+) ion. The excellent selectivity of probe FI for Cu(2+) was effectively utilized to modulate the assembly of metal-induced Aβ aggregates by metal chelation with the "turn-on" fluorescence via spirolactam ring opening of FI as well as the metal-free Aβ fibrils by noncovalent interactions. These results confirm that FI has exceptional ability to perform multifaceted tasks such as metal chelation in intracellular conditions using Aβ lysozyme aggregates in cellular environments by the disruption of β-sheet rich Aβ fibrils into disaggregated forms. Subsequently, it was confirmed that FI had the ability to cross the blood-brain barrier and it also modulated the metal induced Aβ fibrils in cellular environments by "turn-on" fluorescence, which are the most vital properties of a probe or a therapeutic agent. Furthermore, the morphology changes were examined by atomic force microscopy (AFM), polarizable optical microscopy (POM), fluorescence microscopy, and dynamic light scattering (DLS) studies. These results provide very valuable clues on the Aβ (CSF Aβ fibrils, Aβ1-40 fibrils, β-amyloid lysozyme aggregates) disaggregation behavior via in vitro studies, which constitute the first insights into intracellular disaggregation of Aβ by "turn-on" method thereby influencing amyloidogenesis.

Bivalent ligands incorporating curcumin and diosgenin as multifunctional compounds against Alzheimer's disease

In an effort to combat the multifaceted nature of Alzheimer's disease (AD) progression, a series of multifunctional, bivalent compounds containing curcumin and diosgenin were designed, synthesized, and biologically characterized. Screening results in MC65 neuroblastoma cells established that compound 38 with a spacer length of 17 atoms exhibited the highest protective potency with an EC50 of 111.7 ± 9.0 nM. A reduction in protective activity was observed as spacer length was increased up to 28 atoms and there is a clear structural preference for attachment to the methylene carbon between the two carbonyl moieties of curcumin. Further study suggested that antioxidative ability and inhibitory effects on amyloid-β oligomer (AβO) formation may contribute to the neuroprotective outcomes. Additionally, compound 38 was found to bind directly to Aβ, similar to curcumin, but did not form complexes with the common biometals Cu, Fe, and Zn. Altogether, these results give strong evidence to support the bivalent design strategy in developing novel compounds with multifunctional ability for the treatment of AD.

Inhibitory effect of human serum albumin on Cu-induced Aβ(40) aggregation and toxicity

It has been suggested that the aggregation and cytotoxicity of amyloid-β (Aβ) peptide with transition-metal ions in neuronal cells is involved in the development and progression of Alzheimer's disease (AD). As the most abundant protein in blood plasma and in cerebrospinal fluid, human serum albumin (HSA) can bind Aβ in vivo and subsequently inhibit Aβ fibril growth. However, the roles of albumin in Cu-induced Aβ aggregation and toxicity, and its potential biological relevance to AD therapy, were not stressed enough. Here, we showed that HSA was capable of binding Cu (I) with much higher affinity than Aβ, competitively inhibiting the interaction of Aβ and Cu ions. In the presence of biological reducing agent ascorbate, HSA inhibited Cu (II)/Cu (I)-mediated Aβ40 aggregation, reactive oxygen species production, and neurotoxicity. However, in the absence of Cu (II)/Cu (I), HSA could not effectively inhibit Aβ40 aggregation and neurotoxicity at 24 h (or less) incubation time, but decreased Aβ40 aggregation at much longer incubation (120 h). Our data suggested that through competitively decreasing Cu-Aβ interaction, HSA could effectively inhibit Cu (II)/Cu (I)-induced Aβ40 aggregation and neurotoxicity, and play important roles in regulating redox balance as well as metal homeostasis in AD prevention and therapy.

Inhibition of amyloid fibrillation and cytotoxicity of lysozyme fibrillation products by polyphenols

An increasing number of studies conducted under in vitro and in vivo conditions, have concluded that polyphenols, compounds frequently occurring in many herbs with antioxidant properties, prevent and reverse amyloid fibril formation. However, the mechanisms by which these natural products modulate the protein aggregation process are poorly understood. Herein, a range of techniques including thioflavin T (ThT) and ANS fluorescence assays, electron microscopy and circular dichroism have been employed to determine the efficacy of rosmarinic acid (RA) and resveratrol (Res) on the inhibition/reversion of fibrillogenesis and hindering cytotoxicity induced by protofibrils and amyloid fibrils of hen egg white lysozyme (HEWL). Results demonstrated that both polyphenols effectively inhibit fibrillogenesis and destabilize preformed fibrils of HEWL in a concentration-dependent manner. Cytotoxicity protection on PC12 cells was also observed using the MTT assay, ROS production assay, and phase-contrast microscopy. It is suggested that the mechanism underlying the inhibitory effects of RA and Res is to prevent hydrophobic interactions between HEWL amyloidogenic prefibrillar species, although additional studies is needed to elucidate the detailed mechanisms involved. A combination of antioxidative and anti-amyloidogenic properties of these molecules may provide them with the described neuroprotective capacities.

Naringin ameliorates cognitive deficits via oxidative stress, proinflammatory factors and the PPARγ signaling pathway in a type 2 diabetic rat model

Naringenin is a flavonoid polyphenolic compound, which facilitates the removal of free radicals, oxidative stress and inflammation. The present study aimed to obtain a better understanding of the effects of curcumin on the regulation of diabetes‑associated cognitive decline, and its underlying mechanisms. An experimental diabetes mellitus (DM) rat model was induced by streptozoticin (50 mg/kg). Following treatment with naringin (100 and 200 mg/kg) for 16 weeks, the body weight and blood glucose levels of the DM rats were measured. A morris water maze test was used to analyze the effects of naringin on the cognitive deficit of the DM rats. The levels of oxidative stress, proinflammatory factors, caspase‑3 and caspase‑9, and the protein expression of peroxisome proliferator‑activated receptor γ (PPARγ) were quantified in the DM rats using a commercially‑available kit and western blot assay, respectively. In addition, a GW9662 PPARγ inhibitor (0.3 mg/kg) was administered to the DM rats to determine whether PPARγ affected the effects of naringin on the cognitive deficit of the DM rats. The results demonstrated that naringin increased the body weight, blood glucose levels, and cognitive deficits of the DM rats. The levels of oxidative stress and proinflammatory factors in the naringin‑treated rats were significantly lower, compared with those of the DM rats. In addition, naringin activated the protein expression of PPARγ, and administration of the PPARγ inhibitor decreased the protein expression of PPARγ, and attenuated the effects of naringin on cognitive deficit. The results also demonstrated that naringin decreased the expression levels of caspase‑3 and caspase‑9 in the DM rats. These results suggested that naringin ameliorated cognitive deficits via oxidative stress, proinflammatory factors and the PPARγ signaling pathway in the type 2 diabetic rat model. Furthermore, oxidative stress, proinflammatory factors and PPARγ signaling may be involved in mediating these effects.

Curcumin/melatonin hybrid 5-(4-hydroxy-phenyl)-3-oxo-pentanoic acid [2-(5-methoxy-1H-indol-3-yl)-ethyl]-amide ameliorates AD-like pathology in the APP/PS1 mouse model

In our efforts to develop hybrid compounds of curcumin and melatonin as potential disease-modifying agents for Alzheimer's disease (AD), a potent lead hybrid compound, Z-CM-I-1, has been recently identified and biologically characterized in vitro. In this work, we report the in vivo effects of Z-CM-I-1 on AD pathologies in an APP/PS1 transgenic AD model. Our studies demonstrated that Z-CM-I-1 significantly decreased the accumulation of Aβ in the hippocampus and cortex regions of the brain and reduced inflammatory responses and oxidative stress after treatment for 12 weeks at 50 mg/kg per dose via oral administration. Furthermore, Z-CM-I-1 significantly improved synaptic dysfunction evidenced by the increased expression of synaptic marker proteins, PSD95 and synaptophysin, indicating its protective effects on synaptic degeneration. Lastly, we demonstrated that Z-CM-I-1 significantly increased the expression level of complexes I, II, and IV of the mitochondria electron transport chain in the brain tissue of APP/PS1 mice. Collectively, these results clearly suggest that Z-CM-I-1 is orally available and exhibits multifunctional properties in vivo on AD pathologies, thus strongly encouraging further development of this lead compound as a potential disease-modifying agent for AD patients.

Highly Efficient Synthesis of 1,3-Dihydroxy-2-carboxycarbazole and Its Neuroprotective Effects

Carbazoles represent a family of tricyclic compounds that widely appeared in nature. Numerous studies have revealed a diverse array of bioactivity associated with this scaffold. In the present study, a novel and highly efficient methodology for preparing 1,3-dihydroxy-2-carboxycarbazole from indole-3-acetic acid and Meldrum's acid was developed. Furthermore, biological characterization demonstrated that this multisubstituted carbazole analogue exhibited inhibitory activity on Aβ aggregation, antioxidative properties, and promising neuroprotective activities in a cellular model of Alzheimer's disease, thus further supporting the valuable application of this synthetic methodology in search for effective neuroprotectants.