Impact of pyridine-2-carboxaldehyde-derived aroylhydrazones on the copper-catalyzed oxidation of the M112A PrP103–112 mutant fragment

Cardiotoxicity and ROS Protection Assessment of three Structure-Related N-Acylhydrazones with Potential for the Treatment of Neurodegenerative Diseases

The senescence process is associated with accumulated oxidative damage and increased metal concentration in the heart and brain. Besides, abnormal metal-protein interactions have also been linked with the development of several conditions, including Alzheimer's and Parkinson's diseases. Over the years we have described a series of structure-related compounds with different activities towards models of such diseases. In this work, we evaluated the potential of three N-acylhydrazones (INHHQ: 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone, HPCIH: pyridine-2-carboxaldehyde isonicotinoyl hydrazone and X1INH: 1-methyl-1H-imidazole-2-carboxaldehyde isonicotinoyl hydrazone) to prevent oxidative stress in cellular models, with the dual intent of being active on this pathway and also to confirm their lack of cardiotoxicity as an important step in the drug development process, especially considering that the target population often presents cardiovascular comorbidity. The 8-hydroxyquinoline-contaning compound, INHHQ, exhibits a significant cardioprotective effect against hydrogen peroxide and a robust antioxidant activity. However, this compound is the most toxic to the studied cell models and seems to induce oxidative damage on its own. Interestingly, although not possessing a phenol group in its structure, the new-generation 1-methylimidazole derivative X1INH showed a cardioprotective tendency towards H9c2 cells, demonstrating the importance of attaining a compromise between activity and intrinsic cytotoxicity when developing a drug candidate.

Effects of the aldehyde-derived ring substituent on the properties of two new bioinspired trimethoxybenzoylhydrazones: methyl vs nitro groups

N-Acylhydrazones are a versatile class of organic compounds with a diversity of potential applications. In this study, two new structure-related 3,4,5-trimethoxybenzoyl-containing N-acylhydrazones were synthesized and fully characterized, both in solution and in the solid state. The compounds differ with respect to the carbonyl precursors, i.e., 3-substituted salicylaldehydes with either a methyl or a nitro group. Single crystals of both compounds were isolated from the respective mother liquors and, in both cases, XRD confirmed the obtention of the (E)-isomer, in an anti-conformation. Computational calculations (gas and water phases) were performed in order to confirm some of the structural and vibrational aspects of the compounds. An important intramolecular H bond involving the phenolic hydroxy group and the azomethine nitrogen was identified in the solid state and seems to be maintained in solution. Moreover, the presence of the electron-withdrawing nitro substituent makes this interaction stronger. However, the contact should probably not subsist for the nitro compound under physiological conditions since the presence of this substituent significantly affects the pKa of the phenol: an apparent value of 5.68 ± 0.02 was obtained. This also impacts the basicity of the azomethine nitrogen and, as a consequence, increases the hydrazone's susceptibility to hydrolysis. Nevertheless, both compounds are stable at physiological-like conditions, especially the methyl-derived one, which qualifies them for further toxicological and activity studies, such as those involving trivalent metal ions sequestering in the context of neurodegenerative diseases.

Unscrambling the Role of Redox-Active Biometals in Dopaminergic Neuronal Death and Promising Metal Chelation-Based Therapy for Parkinson's Disease

Biometals are all metal ions that are essential for all living organisms. About 40% of all enzymes with known structures require biometals to function correctly. The main target of damage by biometals is the central nervous system (CNS). Biometal dysregulation (metal deficiency or overload) is related to pathological processes. Chronic occupational and environmental exposure to biometals, including iron and copper, is related to an increased risk of developing Parkinson's disease (PD). Indeed, biometals have been shown to induce a dopaminergic neuronal loss in the substantia nigra. Although the etiology of PD is still unknown, oxidative stress dysregulation, mitochondrial dysfunction, and inhibition of both the ubiquitin-proteasome system (UPS) and autophagy are related to dopaminergic neuronal death. Herein, we addressed the involvement of redox-active biometals, iron, and copper, as oxidative stress and neuronal death inducers, as well as the current metal chelation-based therapy in PD.

New mescaline-related N-acylhydrazone and its unsubstituted benzoyl derivative: Promising metallophores for copper-associated deleterious effects relief in Alzheimer's disease

Alzheimer's disease (AD) is related to the presence of extracellular aggregated amyloid-β peptide (Aβ), which binds copper(II) with high affinity in its N-terminal region. In this sense, two new 1-methylimidazole-containing N-acylhydrazonic metallophores, namely, X1TMP and X1Benz, were synthesized as hydrochlorides and characterized. The compound X1TMP contains the 3,4,5-trimethoxybenzoyl moiety present in the structure of mescaline, a natural hallucinogenic protoalkaloid that occurs in some species of cacti. Single crystals of X1Benz, the unsubstituted derivative of X1TMP, were obtained. The experimental partition coefficients of both compounds were determined, as well as their apparent affinity for Cu²⁺ in aqueous solution. Ascorbate consumption assays showed that these N-acylhydrazones are able to lessen the production of ROS by the Cu(Aβ)-system, and a short-time scale aggregation study, measured through turbidity and confirmed by TEM images, revealed their capacity in preventing Aβ fibrillation at equimolar conditions in the presence and absence of copper. ¹H¹⁵N HSQC NMR experiments demonstrated a direct interaction between Aβ and X1Benz, the most soluble of the compounds. The Cu²⁺ sequestering potential of this hydrazone towards Aβ was explored by ¹H NMR. Although increasing amounts of X1Benz were unexpectedly not efficient at removing the metal-induced perturbations in Aβ backbone amides, the broadening effects observed on the compound's signals indicate the formation of a ternary Aβ‑copper-X1Benz species, which can be responsible for the observed ROS-lessening and aggregation-preventing activities. Overall, the N-acylhydrazones X1TMP and X1Benz have shown promising prospects as agents for the treatment of AD.

Full Equilibrium Picture in Aqueous Binary and Ternary Systems Involving Copper(II), 1-Methylimidazole-Containing Hydrazonic Ligands, and the 103-112 Human Prion Protein Fragment

In this work, we describe two novel 1-methylimidazole N-acylhydyrazonic ligands and their interaction with copper(II) in solution. Binary systems constituted by each of these hydrazones and the metal ion were studied by potentiometric titrations. The magnitude of their affinities for zinc(II) was also determined for the sake of comparison. Additionally, a full evaluation of the copper(II) chelation profile of the new ligands in ternary systems containing a human prion protein fragment was performed. Mixed ligand complexes comprising the HuPrP103-112 fragment, copper(II) ions, and an N-acylhydrazone were characterized by potentiometry, ultraviolet-visible spectroscopy, and circular dichroism. Some of these species were also identified by electrospray ionization mass spectrometry and unequivocally assigned through their isotopic distribution pattern. To the best of our knowledge, this is the first report concerning the stability of ternary complexes involving a hydrazonic metal-protein interaction modulator, copper, and a peptide. The ability of N-acylhydrazones to prevent peptide oxidation was also examined. Both ligands can partially prevent the formation of the doubly oxidized product, a process mediated by copper(II) ions. Oxidative stress is considered an important hallmark of neurodegenerative diseases such as prion-related spongiform encephalopathies. In this context, active intervention with respect to the deleterious copper-catalyzed methionine oxidation could represent an interesting therapeutic approach.

X1INH, an improved next-generation affinity-optimized hydrazonic ligand, attenuates abnormal copper(I)/copper(II)-α-Syn interactions and affects protein aggregation in a cellular model of synucleinopathy

Although normal aging presents an accumulation of copper and iron in the brain, this becomes more relevant in neurodegeneration. α-Synuclein (α-Syn) misfolding has long been linked with the development of Parkinson's disease (PD). Copper binding promotes aggregation of α-Syn, as well as generalized oxidative stress. In this sense, the use of therapies that target metal dyshomeostasis has been in focus in the past years. Metal-Protein Attenuating Compounds (MPACs) are moderate chelators that aim at disrupting specific, abnormal metal-protein interactions. Our research group has now established that N-acylhydrazones compose a set of truly encouraging MPACs for the bioinorganic management of metal-enhanced aggregopathies. In the present work, a novel ligand, namely 1-methyl-1H-imidazole-2-carboxaldehyde isonicotinoyl hydrazone (X1INH), is reported. We describe solution studies on the interaction and affinity of this compound for copper(ii) ions showing that a fine tuning of metal-affinity was achieved. A series of in vitro biophysical NMR experiments were performed in order to assess the X1INH ability to compete with α-Syn monomers for the binding of both copper(i) and copper(ii) ions, which are central in PD pathology. A preference for copper(i) has been observed. X1INH is less toxic to human neuroglioma (H4) cells in comparison to structure-related compounds. Finally, we show that treatment with X1INH results in a higher number of smaller, less compact inclusions in a well-established model of α-Syn aggregation. Thus, X1INH constitutes a promising MPAC for the treatment of Parkinson's disease.