Design, synthesis and evaluation of novel ferulic acid-memoquin hybrids as potential multifunctional agents for the treatment of Alzheimer's disease

Novel neuroprotective pyromeconic acid derivatives with concurrent anti-Aβ deposition, anti-inflammatory, and anti-oxidation properties for treatment of Alzheimer's disease

We synthesized a series of novel pyromeconic acid-styrene hybrid compounds and measured their activities in inhibiting Aβ_1-42 self-aggregation and promoting disaggregation, and their anti-inflammatory and antioxidant properties. The most potent compound, compound 30, had IC₅₀ values of 11.15 μM and 6.87 μM for inhibition of fibril aggregation and promotion of fibril disaggregation, respectively. Because of its redox metal chelating property, 30 also inhibited Cu²⁺-induced Aβ_1-42 fibril aggregation and promoted fibril disaggregation with IC₅₀ of 3.69 μM and 3.35 μM, respectively. Molecular docking demonstrated that 30 interacted with key amino acids of Aβ_1-42, and the reliability of the complex was confirmed by molecular dynamics. In addition, 30 displayed excellent antioxidative activity (oxygen radical absorbance capacity = 2.65 Trolox equivalents) and moderate anti-inflammatory activity and neuroprotection in cell culture assays. Compound 30 was safe in acute toxicity test in mice, and it exhibited favorable pharmacokinetic properties, particularly, accumulation in the hippocampus (maximum ratio of hippocampus to plasma = 7.12). Compound 30 alleviated cognitive deficits in scopolamine-induced amnesia mice; this property may have been attributed to reducing neuroinflammation by inhibiting ionized calcium binding adapter molecule 1 and glial fibrillary acidic protein expression and reducing oxidative stress by activating the Nrf2/HO-1 signaling pathway. In view of its many properties, we envision that 30 is a promising lead for the treatment of Alzheimer's disease.

Curcumin, Resveratrol and Cannabidiol as Natural Key Prototypes in Drug Design for Neuroprotective Agents

Nowadays, neurodegenerative diseases (NDs), such as Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS), represent a great challenge in different scientific fields, such as neuropharmacology, medicinal chemistry, molecular biology and medicine, as all these pathologies remain incurable, with high socioeconomic impacts and high costs for governmental health services. Due to their severity and multifactorial pathophysiological complexity, the available approved drugs for clinic have not yet shown adequate effectiveness and exhibited very restricted options in the therapeutic arsenal; this highlights the need for continued drug discovery efforts in the academia and industry. In this context, natural products, such as curcumin (1), resveratrol (2) and cannabidiol (CBD, 3) have been recognized as important sources, with promising chemical entities, prototype models and starting materials for medicinal organic chemistry, as their molecular architecture, multifunctional properties and single chemical diversity could facilitate the discovery, optimization and development of innovative drug candidates with improved pharmacodynamics and pharmacokinetics compared to the known drugs and, perhaps, provide a chance for discovering novel effective drugs to combat NDs. In this review, we report the most recent efforts of medicinal chemists worldwide devoted to the exploration of curcumin (1), resveratrol (2) and cannabidiol (CBD, 3) as starting materials or privileged scaffolds in the design of multi-target directed ligands (MTDLs) with potential therapeutic properties against NDs, which have been published in the scientific literature during the last 10 years of research and are available in PubMed, SCOPUS and Web of Science databases.

Molecular Insights into Therapeutic Potentials of Hybrid Compounds Targeting Alzheimer's Disease

Alzheimer's disease (AD) is one of the most complex progressive neurological disorders involving degeneration of neuronal connections in brain cells leading to cell death. AD is predominantly detected among elder people (> 65 years), mostly diagnosed with the symptoms of memory loss and cognitive dysfunctions. The multifarious pathogenesis of AD comprises the accumulation of pathogenic proteins, decreased neurotransmission, oxidative stress, and neuroinflammation. The conventional therapeutic approaches are limited to symptomatic benefits and are ineffective against disease progression. In recent years, researchers have shown immense interest in the designing and fabrication of various novel therapeutics comprised of naturally isolated hybrid molecules. Hybrid therapeutic compounds are developed from the combination of pharmacophores isolated from bioactive moieties which specifically target and block various AD-associated pathogenic pathways. The method of designing hybrid molecules has numerous advantages over conventional multitarget drug development methods. In comparison to in silico high throughput screening, hybrid molecules generate quicker results and are also less expensive than fragment-based drug development. Designing hybrid-multitargeted therapeutic compounds is thus a prospective approach in developing an effective treatment for AD. Nevertheless, several issues must be addressed, and additional researches should be conducted to develop hybrid therapeutic compounds for clinical usage while keeping other off-target adverse effects in mind. In this review, we have summarized the recent progress on synthesis of hybrid compounds, their molecular mechanism, and therapeutic potential in AD. Using synoptic tables, figures, and schemes, the review presents therapeutic promise and potential for the development of many disease-modifying hybrids into next-generation medicines for AD.

Natural Products as Sources of Multitarget Compounds: Advances in the Development of Ferulic Acid as Multitarget Therapeutic

Nature has provided therapeutic substances for millennia, with many valuable medications derived from plant sources. Multitarget drugs become essential in the management of various disorders including hepatic disorders, neurological disorders, diabetes, and carcinomas. Ferulic acid is a significant potential therapeutic agent, which is easily available at low cost, possesses a low toxicity profile, and has minimum side effects. Ferulic acid exhibits various therapeutic actions by modulation of various signal transduction pathways such as Nrf2, p38, and mTOR. The actions exhibited by ferulic acid include anti-apoptosis, antioxidant, anti-inflammatory, antidiabetic, anticarcinogenic, hepatoprotection, cardioprotection, activation of transcriptional factors, expression of genes, regulation of enzyme activity, and neuroprotection, which further help in treating various pathophysiological conditions such as cancer, skin diseases, brain disorders, diabetes, Parkinson's disease, Alzheimer's disease, hypoxia, hepatic disorders, H1N1 flu, and viral infections. The current review focuses on the significance of natural products as sources of multitarget compounds and a primary focus has been made on ferulic acid and its mechanism, role, and protective action in various ailments.

Therapeutic Potential of Ferulic Acid in Alzheimer's Disease

Alzheimer's Disease (AD) is one of the most important neurodegenerative diseases and it covers 60% of whole dementia cases. AD is a constantly progressing neurodegenerative disease as a result of the production of β-amyloid (Aβ) protein and the accumulation of hyper-phosphorylated Tau protein; it causes breakages in the synaptic bonds and neuronal deaths to a large extent. Millions of people worldwide suffer from AD because there is no definitive drug for disease prevention, treatment or slowdown. Over the last decade, multiple target applications have been developed for AD treatments. These targets include Aβ accumulations, hyper-phosphorylated Tau proteins, mitochondrial dysfunction, and oxidative stress resulting in toxicity. Various natural or semisynthetic antioxidant formulations have been shown to protect brain cells from Aβ induced toxicity and provide promising potentials for AD treatment. Ferulic acid (FA), a high-capacity antioxidant molecule, is naturally synthesized from certain plants. FA has been shown to have different substantial biological properties, such as anticancer, antidiabetic, antimicrobial, anti-inflammatory, hepatoprotective, and cardioprotective actions, etc. Furthermore, FA exerted neuroprotection via preventing Aβ-fibril formation, acting as an anti-inflammatory agent, and inhibiting free radical generation and acetylcholinesterase (AChE) enzyme activity. In this review, we present key biological roles of FA and several FA derivatives in Aβ-induced neurotoxicity, protection against free radical attacks, and enzyme inhibitions and describe them as possible therapeutic agents for the treatment of AD.

Synthesis of highly substituted fluorenones via metal-free TBHP-promoted oxidative cyclization of 2-(aminomethyl)biphenyls. Application to the total synthesis of nobilone

Highly substituted fluorenones are readily prepared in mostly fair to good yields via metal- and additive-free TBHP-promoted cross-dehydrogenative coupling (CDC) of readily accessible N-methyl-2-(aminomethyl)biphenyls and 2-(aminomethyl)biphenyls. This methodology is compatible with numerous functional groups (methoxy, cyano, nitro, chloro, and SEM and TBS-protective groups for phenols) and was further utilized in the first total synthesis of the natural product nobilone.

Beyond Antioxidant Effects: Nature-Based Templates Unveil New Strategies for Neurodegenerative Diseases

The complex network of malfunctioning pathways occurring in the pathogenesis of neurodegenerative diseases (NDDs) represents a huge hurdle in the development of new effective drugs to be used in therapy. In this context, redox reactions act as crucial regulators in the maintenance of neuronal microenvironment homeostasis. Particularly, their imbalance results in the severe compromising of organism’s natural defense systems and subsequently, in the instauration of deleterious OS, that plays a fundamental role in the insurgence and progress of NDDs. Despite the huge efforts in drug discovery programs, the identification process of new therapeutic agents able to counteract the relentless progress of neurodegenerative processes has produced low or no effective therapies. Consequently, a paradigm-shift in the drug discovery approach for these diseases is gradually occurring, paving the way for innovative therapeutical approaches, such as polypharmacology. The aim of this review is to provide an overview of the main pharmacological features of most promising nature-based scaffolds for a possible application in drug discovery, especially for NDDs, highlighting their multifaceted effects against OS and neuronal disorders.

A review on ferulic acid and analogs based scaffolds for the management of Alzheimer's disease

Alzheimer's disease (AD) is an age-related multifactorial neurodegenerative disorder characterized by severe central cholinergic neuronal loss, gradually contributing to cognitive dysfunction and impaired motor activity, resulting in the brain's cell death at the later stages of AD. Although the etiology of AD is not well understood, however, several factors such as oxidative stress, deposition of amyloid-β (Aβ) peptides to form Aβ plaques, intraneuronal accumulation of hyperphosphorylated tau protein, and low level of acetylcholine are thought to play a major role in the pathogenesis of AD. There is practically no drug for AD treatment that can address the basic factors responsible for the neurodegeneration and slow down the disease progression. The currently available therapies for AD in the market focus on providing only symptomatic relief without addressing the aforesaid basic factors responsible for the neurodegeneration. Ferulic acid (FA) is a phenol derivative from natural sources and serves as a potential pharmacophore that exerts multiple pharmacological properties such as antioxidant, neuroprotection, Aβ aggregation modulation, and anti-inflammatory. Several FA based hybrid analogs are under investigation as a multi-target directed ligand (MTDLs) to develop novel hybrid compounds for the treatment of AD. In the present review article, we are focused on the critical pathogenic factors responsible for the onset of AD followed by the developments of FA pharmacophore-based hybrids compounds as a novel multifunctional therapeutic agent to address the limitations associated with available treatment for AD. The rationale behind the development of these compounds and their pharmacological activities in particular to their ChE inhibition (ChEI), neuroprotection, antioxidant property, Aβ aggregation modulation, and metal chelation ability, are discussed in detail. We have also discussed the discovery of caffeic and cinnamic acids based MTDLs for AD. This review paper provides an in-depth insight into the research progress and current status of these novel therapeutics in AD and prospects for developing a druggable molecule with desired pharmacological affinity and reduced toxicity for the management of AD.

Molecular Hybridization as a Tool in the Design of Multi-target Directed Drug Candidates for Neurodegenerative Diseases

Neurodegenerative Diseases (NDs) are progressive multifactorial neurological pathologies related to neuronal impairment and functional loss from different brain regions. Currently, no effective treatments are available for any NDs, and this lack of efficacy has been attributed to the multitude of interconnected factors involved in their pathophysiology. In the last two decades, a new approach for the rational design of new drug candidates, also called multitarget-directed ligands (MTDLs) strategy, has emerged and has been used in the design and for the development of a variety of hybrid compounds capable to act simultaneously in diverse biological targets. Based on the polypharmacology concept, this new paradigm has been thought as a more secure and effective way for modulating concomitantly two or more biochemical pathways responsible for the onset and progress of NDs, trying to overcome low therapeutical effectiveness. As a complement to our previous review article (Curr. Med. Chem. 2007, 14 (17), 1829-1852. https://doi.org/10.2174/092986707781058805), herein we aimed to cover the period from 2008 to 2019 and highlight the most recent advances of the exploitation of Molecular Hybridization (MH) as a tool in the rational design of innovative multifunctional drug candidate prototypes for the treatment of NDs, specially focused on AD, PD, HD and ALS.

Perspectives for New and More Efficient Multifunctional Ligands for Alzheimer's Disease Therapy

Despite tremendous research efforts at every level, globally, there is still a lack of effective drugs for the treatment of Alzheimer's disease (AD). The biochemical mechanisms of this devastating neurodegenerative disease are not yet clearly understood. This review analyses the relevance of multiple ligands in drug discovery for AD as a versatile toolbox for a polypharmacological approach to AD. Herein, we highlight major targets associated with AD, ranging from acetylcholine esterase (AChE), beta-site amyloid precursor protein cleaving enzyme 1 (BACE-1), glycogen synthase kinase 3 beta (GSK-3β), N-methyl-d-aspartate (NMDA) receptor, monoamine oxidases (MAOs), metal ions in the brain, 5-hydroxytryptamine (5-HT) receptors, the third subtype of histamine receptor (H3 receptor), to phosphodiesterases (PDEs), along with a summary of their respective relationship to the disease network. In addition, a multitarget strategy for AD is presented, based on reported milestones in this area and the recent progress that has been achieved with multitargeted-directed ligands (MTDLs). Finally, the latest publications referencing the enlarged panel of new biological targets for AD related to the microglia are highlighted. However, the question of how to find meaningful combinations of targets for an MTDLs approach remains unanswered.

Ferulic Acid Attenuates Hypoxia/Reoxygenation Injury by Suppressing Mitophagy Through the PINK1/Parkin Signaling Pathway in H9c2 Cells

Ferulic acid protects against cardiac injury by scavenging free radicals. However, the role of mitophagy in ferulic acid-induced cardioprotection remains obscure. In the present study, H9c2 cells were exposed to hypoxia/reoxygenation and ferulic acid treatment during hypoxia. We illustrated the impact of ferulic acid on oxidative damage in H9c2 cells. Our results showed that ferulic acid significantly attenuated apoptosis induced by hypoxia/reoxygenation injury and reduced mitochondrial dysfunction, evidenced by a decline in the overproduction of reactive oxygen species and ATP depletion and recovery of the membrane potential. We also found that mitophagy, a selective form of autophagy, was excessively activated in H9c2 cells subjected to hypoxia/reoxygenation. Ferulic acid reduced the binding of mitochondria to lysosomes, down-regulated the PINK1/Parkin pathway, and was accompanied by increased p62 and decreased LC3-II/LC3-I levels. Ferulic acid also antagonistically reduced the activation of mitophagy by rapamycin. These findings suggest that ferulic acid may protect H9c2 cells against ischemia/reperfusion injury by suppressing PINK1/Parkin-dependent mitophagy. Accordingly, our findings may provide a potential target and powerful reference for ferulic acid in clinical prevention and treatment of hypoxia/reoxygenation injury.

Mitochondria in Neuroprotection by Phytochemicals: Bioactive Polyphenols Modulate Mitochondrial Apoptosis System, Function and Structure

In aging and neurodegenerative diseases, loss of distinct type of neurons characterizes disease-specific pathological and clinical features, and mitochondria play a pivotal role in neuronal survival and death. Mitochondria are now considered as the organelle to modulate cellular signal pathways and functions, not only to produce energy and reactive oxygen species. Oxidative stress, deficit of neurotrophic factors, and multiple other factors impair mitochondrial function and induce cell death. Multi-functional plant polyphenols, major groups of phytochemicals, are proposed as one of most promising mitochondria-targeting medicine to preserve the activity and structure of mitochondria and neurons. Polyphenols can scavenge reactive oxygen and nitrogen species and activate redox-responsible transcription factors to regulate expression of genes, coding antioxidants, anti-apoptotic Bcl-2 protein family, and pro-survival neurotrophic factors. In mitochondria, polyphenols can directly regulate the mitochondrial apoptosis system either in preventing or promoting way. Polyphenols also modulate mitochondrial biogenesis, dynamics (fission and fusion), and autophagic degradation to keep the quality and number. This review presents the role of polyphenols in regulation of mitochondrial redox state, death signal system, and homeostasis. The dualistic redox properties of polyphenols are associated with controversial regulation of mitochondrial apoptosis system involved in the neuroprotective and anti-carcinogenic functions. Mitochondria-targeted phytochemical derivatives were synthesized based on the phenolic structure to develop a novel series of neuroprotective and anticancer compounds, which promote the bioavailability and effectiveness. Phytochemicals have shown the multiple beneficial effects in mitochondria, but further investigation is required for the clinical application.

Advancement of multi-target drug discoveries and promising applications in the field of Alzheimer's disease

Complex diseases (e.g., Alzheimer's disease) or infectious diseases are usually caused by complicated and varied factors, including environmental and genetic factors. Multi-target (polypharmacology) drugs have been suggested and have emerged as powerful and promising alternative paradigms in modern medicinal chemistry for the development of versatile chemotherapeutic agents to solve these medical challenges. The multifunctional agents capable of modulating multiple biological targets simultaneously display great advantages of higher efficacy, improved safety profile, and simpler administration compared to single-targeted agents. Therefore, multifunctional agents would certainly open novel avenues to rationally design the next generation of more effective but less toxic therapeutic agents. Herein, the authors review the recent progress made in the discovery and design processes of selective multi-targeted agents, especially the successful application of multi-target drugs for the treatment of Alzheimer's disease.

Incorporation of an intramolecular hydrogen bonding motif in the side chain of antimalarial benzimidazoles

Analogues of a novel class of benzimidazoles with an intramolecular hydrogen bonding motif have been synthesized and evaluated in vitro for their antiplasmodium activity against chloroquine-sensitive (NF54) and multi-drug resistant (K1) strains of the human malaria parasite Plasmodium falciparum. Compounds were also screened for their cytotoxicity towards a mammalian Chinese hamster ovarian (CHO) cell line. Most of the compounds exhibited good antiplasmodium activity (PfNF54 IC₅₀ <1 μM) and were relatively noncytotoxic. Moreover, towards establishing the possible mode of action of these molecules, inhibition of beta-hematin formation was investigated and two compounds were found to be inhibitors. Single crystal X-ray data confirmed the existence of an intramolecular hydrogen bond.

Design, synthesis and evaluation of novel cinnamic acid derivatives bearing N-benzyl pyridinium moiety as multifunctional cholinesterase inhibitors for Alzheimer's disease

A novel family of cinnamic acid derivatives has been developed to be multifunctional cholinesterase inhibitors against AD by fusing N-benzyl pyridinium moiety and different substituted cinnamic acids. In vitro studies showed that most compounds were endowed with a noteworthy ability to inhibit cholinesterase, self-induced Aβ (1–42) aggregation, and to chelate metal ions. Especially, compound 5l showed potent cholinesterase inhibitory activity (IC₅₀, 12.1 nM for eeAChE, 8.6 nM for hAChE, 2.6 μM for eqBuChE and 4.4 μM for hBuChE) and the highest selectivity toward AChE over BuChE. It also showed good inhibition of Aβ (1–42) aggregation (64.7% at 20 μM) and good neuroprotection on PC12 cells against amyloid-induced cell toxicity. Finally, compound 5l could penetrate the BBB, as forecasted by the PAMPA-BBB assay and proved in OF1 mice by ex vivo experiments. Overall, compound 5l seems to be a promising lead compound for the treatment of Alzheimer’s diseases.