SOD activity of new copper II complexes with ligands derived from pyridoxal and toxicity in Caenorhabditis elegans

doi:10.1016/j.jinorgbio.2019.110950

Journal of Inorganic Biochemistry

Volume 204, March 2020, 110950

https://doi.org/10.1016/j.jinorgbio.2019.110950 Get rights and content

Highlights

•
Copper(II) pyridoxal-based complexes exhibit superoxide dismutase (SOD) mimetic activity.
•
Antioxidant activity parameters were determined via photoreduction methodology.
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In vivo SOD inhibition rates were evaluated using the Caenorhabditis elegans nematode.

Abstract

This work presents the synthesis, characterization of copper(II) complexes (C1-C6) and the potential of these compounds to mimic the catalytic activity of the enzyme superoxide dismutase (SOD). The copper(II)complexes were obtained by reaction between the aldol condensation between substituted aromatic hydrazides and aromatic aldehydes (salicylic aldehyde and pyridoxal hydrochloride), forming two new ligands (L1 to L6), resulting in new dimeric dicopper (II) complexes (C1 and C2), new three monomeric Cu^II derivatives (C3, C4 and C6) and a polymeric complex (C5). The Cu^II complexes were fully characterized by X-ray diffraction, spectroscopic and electrochemical analysis. Subsequently, Cu^II derivatives were evaluated for their antioxidant activities, using the NBT (Nitro blue tetrazolium chloride) photoreduction methodology.

After evaluating the antioxidant activity in vitro, it was observed that the best inhibition rates of the superoxide ion are associated to the C4 and C5 complexes. Computational analysis via molecular docking and quantum chemical calculation (Fukui map) offered a molecular level explanation on the biological activity of Cu^II complexes. Additionally, cytotoxicity of C1-C6 was tested in the first time in vivo in nematodes Caenorhabditis elegans, corroborating with the results identified for C4 and C5.

Graphical abstract

Pyridoxal copper complexes were evaluated by in vitro antioxidant activity, by the nitrotetrazolium photoreduction and in vivo using the nematode Caenorhabditis elegans.

Introduction

Hydrazide derivatives present wide pharmacological potential with functionality in antibacterial [1], anti-inflammatory [2], antiviral activities [3], as well as anti-tuberculosis agents [4]. Moreover, when coordinated to transition metals, they significantly expand the lipophilic character that contributes to increasing potential biological complexes [5]. In order to obtain complexes, it is necessary to use active metals (redox potential) that have low toxicity to organisms. For example, copper species has antitumor, antioxidant, antimicrobial, and anti-inflammatory activities in several compounds [6,7].

Another potential contributor to obtaining mimetics [8,9] is one of the variations of vitamin B6, which is pyridoxal unit. This molecule plays a fundamental role in the biological system by acting as an enzymatic cofactor in transamination reactions, decarboxylation, dehydration, and racemization processes [10,11]. In addition to its role in biological processes, pyridoxal is interesting due to the presence of different coordination sites with hard and intermediate centers that allow the synthesis of metal complexes [12].

The compounds obtained to carry out the study of antioxidant potential were synthesized through aldol condensation reactions. This process formed imines, where benzoic hydrazides were initially synthesized and substituted with different organic functions. Thus, effective correlations between antioxidant activities of the complexes and molecular structure were performed.

In this study, evaluations of mimetic catalytic activities for SOD were performed through in vitro tests using NBT (nitro blue tetrazolium) and in vivo tests evaluating the reduction of oxidative damage in the nematode species Caenorhabditis elegans. Despite the simple body scheme of Caenorhabditis elegans, this nematode has been shown to share many vital biological pathways in mammals. Some advantages in relation to conventional models include low cost, rapid generation time, and a simple nervous system, which allows high-throughput screening of compounds [13]. In order to offer a molecular level explanation on the biological activity of copper(II) complexes computational calculations were also carried out.

Section snippets

Materials and instruments - general instrumentation

All synthetic manipulations were conducted by use of standard N₂ atmosphere. CHN% elemental analyses were performed at a Shimadzu EA112 microanalysis instrument. ¹H and ¹³C NMR spectra were recorded on a Bruker DPX-400 spectrometer. DMSO‑d₆ and CDCl₃ were used as the solvent and TMS as the internal reference. Chemical shifts are reported in parts per million (δ, ppm) and were referenced to residual solvent peak. With the multiplicities expressed as: s, singlet; t, triplet; q, quartet; quintet;

Crystal structures of complexes C1 and C3

An ORTEP representation of C1 complex structure is shown in Fig. 1. It is possible to observe that the L1 ligand acts in a polydentate coordinated form to the metallic center by an oxygen O2 (carbonyl), a nitrogen N1 (imine), and an oxygen O1 (phenolate) atom [30,31]. The coordination sphere is filled with another phenolate oxygen bridge from a second molecule of the L1 ligand. The copper ion has a distorted quadratic geometry. Coordination involving the donor atoms and the metal center

Conclusion

The copper (II) complexes obtained by the condensation of aldehydes and hydrazides revealed the monomeric and dimeric structure formation, as well as coordination polymers. All complexes presented mimetic catalytic activity to superoxide dismutase. However, the C4 and C5 complexes presented dismutation indexes considered promising for future applications, since IC₅₀ values were below 0.2. The characterization of cyclic voltammetry, DFT and molecular docking corroborated with in vitro test

Acknowledgments

We would like to thanks the financial agencies: Brazilian Research Councils: CNPq – Edital CMCTIC/CNPq N° 28/2018; Proc. 424514/2018-4; Edital N^o 12/2016/Proc. Num. 303011/2016-5; CNPq N° 28/2018; Proc. 409150/2018-5 and FAPERGS (Edital 02/2017 – PqG) and CAPES-PROEX - Finance Code 001.

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SOD activity of new copper II complexes with ligands derived from pyridoxal and toxicity in Caenorhabditis elegans

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials and instruments - general instrumentation

Crystal structures of complexes C1 and C3

Conclusion

Acknowledgments

Bioorg. Med. Chem. Lett.

Eur. J. Med. Chem.

Bioorg. Chem.

Journal Inorganic Biochemistry

Coord. Chem. Rev.

Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics

Coordenation Chemistry Reviews

Inorg. Chim. Acta

J. Biol. Chem.

Dev. Biol.

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Toxicology

Polyhedron

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Bioorg. Med. Chem. Lett.

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Polyhedron

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Spectrochim. Acta A Mol. Biomol. Spectrosc.

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