Synthesis, structural characterization, and prospects for new cobalt (II) complexes with thiocarbamoyl-pyrazoline ligands as promising antifungal agents

doi:10.1016/j.jinorgbio.2020.111277

Journal of Inorganic Biochemistry

Volume 213, December 2020, 111277

https://doi.org/10.1016/j.jinorgbio.2020.111277 Get rights and content

Highlights

•
Two new Co(II) complexes with thiocarbamoyl-pyrazoline ligands were synthesized.
•
Both complexes showed greater potential against Candida glabrata.
•
The complexes inhibited and degraded biofilms by up to 90%.
•
Both complexes can be considered safe in terms of mutagenic and cytotoxic potential.
•
The complexes suggest promising alternatives for the development of new antifungal drugs.

Abstract

Candida spp. cause invasive fungal infections. One species, Candida glabrata, may present intrinsic resistance to conventional antifungal agents, thereby increasing mortality rates in hospitalized patients. In this context, metal complexes present an alternative for the development of new antifungal drugs owing to their biological and pharmacological activities demonstrated in studies in the last decades. Accordingly, in this study we have synthesized and characterized two new Co(II) complexes with thiocarbamoyl-pyrazoline ligands to assess their antimicrobial, mutagenic, and cytotoxic potential. For antimicrobial activity, the broth microdilution method was performed against ATCC strains of Candida spp. and fluconazole dose-dependent isolates of C. glabrata obtained from urine samples. The Ames test was used to assess mutagenic potential. The reduction method of the MTS reagent (3 [4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium) was performed with HeLa, SiHa, and Vero cells to determine cytotoxicity. Both complexes exhibited fungistatic and fungicidal activity for the yeasts used in the study, demonstrating greater potential for C. glabrata ATCC 2001 and the C. glabrata CG66 isolate with a Minimum Inhibitory Concentration MIC from 3.90 to 7.81 μg mL⁻¹ and fungicidal action from 7.81 to 15.62 μg mL⁻¹. The complexes inhibited and degraded biofilms by up to 90% and did not present mutagenic and cytotoxic potential at the concentrations evaluated for MIC. Thus, the complexes examined herein suggest promising alternatives for the development of new antifungal drugs.

Graphical abstract

Two new Co(II) complexes with thiocarbamoyl-pyrazoline ligands were synthesized and showed remarkable antifungal and antibiofilm activity against isolates of Candida species.

Introduction

Opportunistic infections caused by yeasts belonging to Candida have become an aggravating factor in public health as some species have presented an intrinsic resistance or acquired some resistance mechanism to conventional treatments [1,2]. Candida species are part of the normal microbiota of human beings; they colonize the respiratory, gastrointestinal, and reproductive systems as well as the skin and oral cavity. However, an imbalance of this microbiota can favor the multiplication of these opportunistic pathogens and lead to the development of invasive fungal infections [3,4].

Candida glabrata is one of the main Candida species which is most frequently isolated in hospitalized patients with urinary tract infections and is normally associated with candidemia and candiduria [5]. This yeast is capable of developing biofilms in cellular tissues or in abiotic environments, such as those in the urinary tubes of hospitalized patients, through adhesion in multilayers [6]. In addition, C. glabrata has haploid genome characteristics, unlike C. albicans and other species of the genus that have a diploid genome [7]. This genomic characteristic can promote a secondary resistance system which demonstrates a large, rapid ability to develop tolerance and resistance to antifungal drugs, such as the overexpression of several resistance genes [[8], [9], [10]].

Resistant C. glabrata can cause invasive fungal infections (IFIs), which are correlated with high rates of morbidity and mortality in hospitalized patients and patients with immunological diseases [11]. Treatment for IFIs is strictly limited to four classes of drugs: triazoles, polyenes, echinocandins, and pyrimidine analogs, with the last class not commercialized in Brazil [12]. Surveillance studies have reported the resistance of C. glabrata isolates to triazoles, and more recently, to echinocandins, thus characterizing this species as resistant to multiple drugs [13]. The difficulty in finding new antifungal agents is related to the yeast's cellular structure. As it is a eukaryote, it presents a lower number of targets for antifungal agents, in addition to hindering the diffusion of compounds through the cytoplasmic membrane [14].

Heterocycles of the pyrazole family have antifungal activity [15]; however, they can also present toxicity and low solubility [16]. The use of metal complexes combined with a bioactive ligand can enhance pharmacological activities, such as improving bioavailability or reinforcing the action of an existing drug [17]. Recently, cobalt(II) complexes containing pyrazole ligands were tested against C. glabrata strains and were shown to be more effective than their free ligands [18]. Cobalt complexes containing arylhydrazones also shown to be effective compounds against the fungus Penicillium chrysogenum [19].

In the search for new antifungal agents, the coordination of metal complexes to heterocyclic ligands is a promising alternative as it allows the replacement of organic groups in order to improve liposolubility [20]. In order to contribute to the scientific advance and aiming to explore new promising metallodrugs for facing fungal resistance and fungal infection, we describe in this paper the synthesis and structural characterization of two new Co(II) complexes containing thiocarbamoyl-pyrazoline ligands and their biological activity against yeast species of Candida and resistant isolates of C. glabrata. Furthermore, we also examined cytotoxic and mutagenic activities of such Co(II) compounds.

Section snippets

General procedures

Ligands L1 (1-thiocarbamoyl-5-(4-chlorophenyl)-3-phenyl-4,5-dihydro-1H-pyrazole) and L2 (1-thiocarbamoyl-5-(4-bromophenyl)-3-phenyl-4,5-dihydro-1H-pyrazole) were prepared based on the methods reported in the literature [21]. The solvents (grade AR) were obtained commercially and used in the synthesis without further purification. Elemental analyses (CHN) were conducted using a PerkinElmer 2400 analyzer. The FTIR spectra were acquired on a JASCO-4100 spectrophotometer using KBr pellets. Uv–Vis

Synthesis and structural characterization

The Co(II) complexes were obtained through the direct reaction between cobalt(II) chloride hexahydrate and the respective ligands, based on the methodology published in the literature [31], as shown below in Fig. 1:

The prepared complexes 1 and 2 have been presented as isostructural neutral complexes of the general formula [Co(L)₂Cl₂], where two molecules of the thiocarbamoyl-pyrazoline ligand are coordinated to the Co(II) atom. Fig. 2, Fig. 3 show the crystalline and molecular structures of

Discussion

The fungal and invasive infections caused by Candida have increased worldwide, becoming a global health challenge [15]. Candida species are opportunistic pathogens that are commonly related to urinary tract infections affecting mainly women and children [5]. However, the treatment of these infections still poses a challenge owing to the limited number of antifungal drugs and the increased resistance of microorganisms to conventional antimicrobial drugs [2]. Therefore, the synthesis and

Conclusion

The two new cobalt(II) complexes 1 and 2 containing thiocarbamoyl-pyrazoline ligands were evaluated for their pharmacological potential. Both showed antifungal and antibiofilm activity and stood out in the control of Candida glabrata ATCC 2001 and the resistant clinical isolate C. glabrata CG66 obtained from a urine sample. None of the complexes exhibited mutagenic or cytotoxic activity at the concentrations applied in the assays. In this context, the present study indicates cobalt(II)

Declaration of Competing Interest

None.

Acknowledgements

The author G.A.C thanks to CNPq (302532/2017), B.B.D, P.P.R, K.V.T thank to CAPES (001) for the scholarships. The authors thank to UFGD for financial support.

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Synthesis, structural characterization, and prospects for new cobalt (II) complexes with thiocarbamoyl-pyrazoline ligands as promising antifungal agents

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

General procedures

Synthesis and structural characterization

Discussion

Conclusion

Declaration of Competing Interest

Acknowledgements

Int. J. Antimicrob. Agents

Infect. Dis. Clin. N. Am.

Clin. Microbiol. Infect.

J. Mol. Struct.

Eur. J. Med. Chem.

Polyhedron.

Food Chem.

Microb. Pathog.

Mutat. Res.

Inorg. Chim. Acta

Polyhedron

J. Mycol. Med.

Int. J. Antimicrob. Agents

Phytomedicine

Mutat. Res.

Azole-resistant aspergillosis: epidemiology, molecular mechanisms and treatment

J Infect Dis.

Prevalent mutator genotype identified in fungal pathogen Candida glabrata promotes multi-drug resistance

Nat. Commun.

Avaliação da atividade antifúngica do óleo essencial de Pogostemon cablin (Blanco) Benth. (Lamiaceae) contra cepas de Candida glabrata

Scientia Plena

Prevalence, virulence factors and antifungal susceptibility of Candida spp. isolated from bloodstream infections in a tertiary care hospital in Brazil

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Biofilms of non-Candida albicans Candida species: quantification, structure and matrix composition

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