The structure – Activity correlation in the family of dicationic imidazolium surfactants: Antimicrobial properties and cytotoxic effect

https://doi.org/10.1016/j.bbagen.2020.129728Get rights and content

Highlights

  • Antimicrobial, hemolytic, cytotoxic activities of m-s-m(Im) surfactants were studied.

  • The highest antimicrobial activity was observed for surfactants of 10-s-10(Im) series.

  • 10-s-10 (Im) show high bactericidal activity against methicillin-resistant strains.

  • 10-4-10 (Im) demonstrates IC50 at the level of doxorubicin (HuTu 80 cell line).

  • Сytotoxic effect is associated with induction of apoptosis via mitochondrial pathway

Abstract

Background

The development of new effective microbicide surfactants and the search for the structure–biological activity relationship is an important and promising problem. Surfactants containing imidazolium fragment attract attention of researchers in the field of chemotherapy, because these compounds often exhibit high antimicrobial activity. The aim of this work is to identify the newly synthesized surfactants from the viewpoint of their potential usefulness in pharmacology and medicine. For this purpose, a detailed study of antimicrobial, hemolytic and cytotoxic activity of dicationic alkylimidazolium surfactants of the m-s-m (Im) series with a variable length of a hydrocarbon tail (m = 10, 12) and a spacer fragment (s = 2, 3, 4) was carried out.

Methods

Aggregation of surfactants in solutions was estimated by tensiometry and conductivity. Antimicrobial activity was determined by the serial dilution technique. Cytotoxic effects of the test compounds on human cancer and normal cells were estimated by means of the multifunctional Cytell Cell Imaging system. Cell Apoptosis Analysis was made by flow cytometry.

Results

The test compounds show high antimicrobial activity against a wide range of test microorganisms and do not possess high hemolytic activity. Importantly, some of them display a bactericidal activity comparable to ciprofloxacin fluoroquinolone antibiotic against Gram-positive bacteria, including methicillin-resistant strains of S. aureus (MRSA). The cytotoxicity of the compounds against normal and tumor human cell lines has been tested as well, with cytotoxic effect and selectivity strongly controlled by structural factor and kind of cell line. Superior results were revealed for compound 10–4-10 (Im) in the case of HuTu 80 cell line (duodenal adenocarcinoma), for which IC50 value at the level of doxorubicin and a markedly higher selectivity index (SI 7.5) were demonstrated. Flow cytometry assay shows apoptosis-inducing effect of this compound on HuTu 80 cells, through significant changes in the potential of mitochondrial membrane.

Major conclusions

Antibacterial properties are shown to be controlled by alkyl chain length, with the highest activity demonstrated by surfactants with decyl tail, with the length of the spacer fragment showing practically no effect. The results indicate that the mechanism of cytotoxic effect of the compounds can be associated with the induction of apoptosis via the mitochondrial pathway.

General significance

Selectivity against pathogenic microorganisms and low toxicity against eukaryotic cells allow considering dicationic imidazolium surfactants as new effective antimicrobial agents. At the same time, high selectivity against some cancer cell lines indicates the prospect of their using as components of new anticancer drugs.

Introduction

Due to the widespread occurrence of multidrug-resistant infectious agents, there is a demand to search for safe chemical compounds, which will form the basis of new drugs. Surfactants containing imidazolium fragment attract attention of researchers in the field of chemotherapy, because these compounds often exhibit high antimicrobial activity [[1], [2], [3], [4], [5], [6]]. Functionalization of imidazolium surfactants with various substituents makes it possible to modify their hydrophilic-lipophilic balance and aggregation properties, as well as to tune their biological activity. Dicationic imidazolium surfactants are of a particular interest [[7], [8], [9]]. They represent a large class of geminal surfactants with two hydrophobic tails and two positively charged head groups covalently linked by a spacer fragment. Gemini surfactants display superior properties to corresponding monocationic analogues: they more effectively reduce the surface tension at the phase boundary, have an order of magnitude lower critical micelle concentration (CMC), possess high solubility, and high wetting and solubilization effects [[10], [11], [12], [13], [14], [15]]. These properties of dicationic surfactants predetermine their broad application as solubilizers and adjuvants, nanocontainers and nanoreactors, as well as non-viral vectors for gene delivery into cells of a living organism. Dicationic surfactants also show antimicrobial effect, which is maximum in compounds with a tail length C10-C12 [16,17]. In contrast, monocationic amphiphiles, whose antimicrobial activity shows a positive trend with an increasing the carbon chain length, reach maximum activity in case of tetra- or hexadecyl compounds, above which a so-called ‘cut off effect’ is observed [3,4,18,19].

The structure of head group and spacer fragment plays an important role in the aggregation behavior and properties of gemini surfactants [[20], [21], [22]]. There is a large body of recent literature data on the aggregation behavior of imidazolium dicationic surfactants in solutions, in which CMC values and adsorption parameters are determined [1,23,24]. There is a few information about their solubilization effect and complexation with proteins and DNA [1,[25], [26], [27], [28], [29]]. By contrast, an information on the antimicrobial properties of such compounds is fragmentary. However, some data on dicationic imidazolium surfactants indicate their significant potential. Thus, the study of 3,3′(α,ω-dioxaalkyl)-bis(1-alkylimidazolium) chlorides showed the high efficiency of this surfactants against Staphylococcus aureus, Enterococcus faecalis, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Pseudomonas aeruginosa, Candida krusei, and Candida albicans [30,31]. In addition, antimicrobial effect was demonstrated for a series of new dicationic imidazolium surfactants containing amide group in the spacer fragment, which depends on the length of hydrophobic tail. High antifungal activity of these compounds against Candida albicans, one of the main opportunistic pathogens that cause a wide range of human diseases, should particularly be noted [32].

In this regard, the development of new effective microbicides based on dicationic imidazolium surfactants and the search of structure–biological activity relationship is an important and promising problem. Taking into account the wide use of amphiphilic compounds in cancer chemotherapy for the preparation of nanoparticles with target agents and antitumor drugs [[33], [34], [35], [36]], the investigation of antimicrobial properties of imidazolium surfactants should be extended by their cytotoxicity study.

The aim of this work is to identify new bioactive surfactants that can be used in pharmacology and medicine. For this purpose, a detailed study of antimicrobial, hemolytic and cytotoxic activity of a number of dicationic alkylimidazolium surfactants of the m-s-m (Im) series with a variable length of the hydrophobic radical and a varying distance between the head groups was carried out (Fig. 1).

Section snippets

Alkylimidazoles and bis-imidazolium salts. General remarks

Alkylimidazoles and bis-imidazolium salts were made according to Scheme 1.

This scheme is known from literature [37,38], but some details look incomplete or controversial. That is why detailed synthetic description provided for representative examples. Structure and purity of final and intermediary compounds were confirmed by 1H NMR and IR spectra, and appropriate results of elemental analysis.

Step 1. N-Dodecylimidazole.

In a high form beaker (250 ml), imidazole (8.19 g; 0.120 M) was dissolved in

Antimicrobial activity of test compounds

Table 1 summarizes results on the antibacterial activity of geminis under study. The compounds were tested for antibacterial (bacteriostatic and bactericidal) activity against a number of Gram-positive S. aureus 209P (Sa), B. сereus 8035 (Вс) and Gram-negative bacteria E. coli F-50 (Ec), Pseudomonas aeruginosa 9027 (Ра) including methicillin-resistant strains of S. aureus (MRSA-Sa). Antifungal activity was studied on Trichophyton mentagrophytes var. gypseum 1773, Aspergillus niger 1119 and

Conclusion

The antimicrobial, hemolytic and cytotoxic activities of dicationic imidazolium surfactants with a variable length of a hydrophobic group and spacer fragment have been studied. It has been shown that the nature of a hydrophobic tail is the main structural factor affecting the antimicrobial activity of the compounds, while the length of the spacer fragment has practically no effect on their biological properties. The compounds have displayed high antimicrobial activity against a wide range of

Declaration of Competing Interest

The authors declare that they have no conflict of interest.

Acknowledgements

This work is supported by the Russian Science Foundation (grant № 19-73-30012).

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