DNA compaction to multi-molecular DNA condensation induced by cationic imidazolium gemini surfactants

https://doi.org/10.1016/j.colsurfa.2012.08.060Get rights and content

Abstract

The compaction and condensation of DNA induced by cationic imidazolium gemini surfactants ([Cn-4-Cnim]Br2, n = 10, 12, 14) at different charge ratios have been investigated by dynamic light scattering (DLS), zeta potential, circular dichroism (CD), and ethidium bromide exclusion assay. Upon addition of [Cn-4-Cnim]Br2, DNA molecules undergo the process from compaction to multi-molecular condensation accompanied by conformation change, which could be proved by the DLS and CD results. The charge density changes in zeta potential measurements indicated the impact of the electrostatic interaction in DNA–surfactant complex. The comparison between DNA compaction and condensation by [Cn-4-Cnim]Br2 with different tail lengths demonstrated the important contribution of the hydrophobic interaction. The EtBr exclusion assay indicates the π–π interaction between imidazolium groups of [Cn-4-Cnim]Br2 and DNA aromatic rings also plays a role in the DNA/[Cn-4-Cnim]Br2 complex formation. The impact of the different interactions on the DNA compaction and condensation by gemini surfactants would shed light on their potential applications in gene delivery.

Highlights

► An evolution from DNA compaction to multi-molecular DNA condensation induced by [Cn-4-Cnim]Br2 is identified and its mechanism is discussed. ► [Cn-4-Cnim]Br2 as novel imidazolium gemini surfactants can interact with DNA via electrostatic, hydrophobic and π–π interaction. ► The stronger interaction between DNA and [Cn-4-Cnim]Br2 with longer tails demonstrates the important contribution of the hydrophobic interaction.

Introduction

Gene therapy has been demonstrated as a potential treatment of both genetic and acquired diseases, while the effective delivery of the therapeutic genes into target cells in vitro and in vivo is still one of the greatest challenges in gene therapy. It has been confirmed that the key parameters for achieving effective gene therapy is the size of the DNA condensates [1], [2]. It is also necessary to neutralize the negative charges of DNA, because an overall positive charge significantly improves the docking of the DNA condensate on the primarily negatively charged cell membranes [3]. As an anionic polyelectrolyte, due to the highly negative charge of phosphate backbone, DNA can bind a variety of cationic agents, such as simple lipid-like cations [4], [5], cationic surfactants [6], [7], [8], [9], polycations [10], dendrimers [11], nanoparticles [12], and peptides [13]. These cationic agents demonstrated their capabilities to compact, condense, and transfect DNA across the cell membrane for gene delivery application.

In recent years, DNA compaction and condensation by cationic surfactants have been investigated intensively due to their multifunctional structures including positive charges to neutralize charges of DNA phosphate backbone and the hydrophobic tails to interact with DNA bases and cell membrane [14], [15], [16], [17], [18]. A clear understanding of these driving forces could be very important for exploring and predicting cationic surfactants’ biological applications. Matulis et al. [19] studied the lipid–DNA binding by using isothermal titration calorimetry, which indicated that lipids with longer aliphatic chains bind to DNA stronger than short ones mostly due to highly positive hydrophobic entropy. Zhu and Evans [20] employed various independent methods to investigate the interactions of plasmid DNA and cationic surfactants, and the results indicated the hydrophobic interactions between surfactant molecules and DNA play important roles. The binding isotherm results reported by Jadhav et al. [21] showed that hydrophobic forces were important for 14mer oligonucleotide and cationic surfactants systems. In other aspects, to better comprehend the factors governing the gene delivery abilities of cationic surfactants, detailed biophysical characterization of DNA/surfactants have been performed extensively, using fluorescence microscopy [1], dynamic light scattering [2], [6], and isothermal titration calorimetry [7], [19], etc. These studies shed light on the application and design of novel surfactants as DNA condensation agents, such as gemini surfactants. As a relatively new class of amphiphilic molecules, gemini surfactants show greatly enhanced surfactant properties relative to the corresponding monovalent (single chain, single head-group) compounds such as surface activity, which have shown potential as DNA transfection agents [22]. Bacteriophage T4 DNA underwent a transition from random coil to globule with an intermediate coexistence region by using cationic gemini surfactant from a series of alkanediyl-α,ω-bis-(dimethylalkylammonium bromide) surfactants, and the influence of spacer length, valency, head-group size and tail length on the aggregation behavior of DNA/gemini surfactant system was determined [23]. With more and more gemini surfactants with superior properties synthesized and characterized, a majority of the new cationic surfactants are shown to condense DNA efficiently and to present very good transfection activity in vitro [22].

Most of the new gemini surfactants studied for DNA binding are based on dicationic quaternary ammonium compounds [23], [24], [25], [26]. While, including aromatic functional groups similar to DNA bases could enrich the chemistry of the gemini surfactants and would also bring new thoughts into the DNA-condensing agent interactions, such as π–π interaction and hydrogen bonds. Recently, our group has explored the synthesis and physicochemical properties of a series of imidazolium gemini surfactants [Cn-4-Cnim]Br2 [27], [28], [29], [30]. Imidazolium gemini surfactants are a new generation of amphiphilic molecules exhibiting many promising features. They are made up of two lipophilic chains and two polar imidazolium head-groups covalently linked by a spacer. Owing to the inherent ionic nature of imidazolium ionic liquids [31], [32] and the properties of conventional gemini surfactants, they display stronger self-aggregation tendency and stronger π–π interaction with aromatic rings. Meanwhile, imidazolium gemini surfactants have lower critical aggregation concentrations (CACs) than conventional single-chain surfactants with equivalent tail length due to the hydrophobic contribution [27]. The lower CACs would result in the decrease of agent amount needed for most applications especially biological applications, which is highly desirable for optimization of the safety profile in vivo. Moreover, the introduction of histidine residues into DNA condensing agent was reported to promote gene transfection through the enhancement of “proton-sponge” effect [33]. The side chain of histidine, imidazole group, has a pK  6.0, can absorb protons in an endosomal environment to induce endolysosomal escape following endocytosis of the DNA condensates for intracellular delivery of DNA. Thus the two imidazolium head-groups in an amphiphilic molecule could increase the gene transfection efficiency by extra π–π interaction with DNA bases and the “proton-sponge” effect.

The understanding of the interaction between the imidazolium gemini surfactants [Cn-4-Cnim]Br2 and DNA is of genuine importance for their application in gene delivery and other biological and medical applications. Herring sperm DNA is chosen here as a model gene system for short DNA, microRNA (miRNA), small interfering RNA (siRNA), and so on, which have shown promising gene therapy in clinical trials. In the present work, we investigate the interactions between herring sperm DNA and imidazolium gemini surfactants with a four-methylene spacer group ([Cn-4-Cnim]Br2, n = 10, 12, and 14) by dynamic light scattering (DLS), zeta potential circular dichroism (CD), and ethidium bromide (EtBr) displacement assay. The aim of this study is to characterize the physicochemical properties of DNA/[Cn-4-Cnim]Br2, and to understand the effect of the hydrophobic chain lengths of [Cn-4-Cnim]Br2 on the DNA condensation, which could be beneficial for their potential gene delivery applications.

Section snippets

Materials

The imidazolium gemini surfactants with a four-methylene spacer group ([Cn-4-Cnim]Br2, n = 10, 12, 14) were prepared and characterized according to the procedure reported previously [27]. The chemical structures of [Cn-4-Cnim]Br2 are shown in Scheme 1. Deoxyribonucleic acid from herring sperm (sodium salt) was purchased from Sigma and used as received. The ratio of the absorbance of the DNA stock solution at 260 nm to that at 280 nm was found to be 1.9, suggesting that the DNA solution was

Hydrodynamic radius of DNA/[C12-4-C12im]Br2

Hydrodynamic radii (RH) of DNA/[Cn-4-Cnim]Br2 were obtained by DLS measurement for investigating the size changes of DNA and DNA/[Cn-4-Cnim]Br2 complexes. For all the [Cn-4-Cnim]Br2 with different hydrophobic tail lengths, similar trends have been observed showing the initial decrease of RH to a minimum value followed by an increase. Typical results for [C12-4-C12im]Br2 show the intensity-weighted size distribution of DNA and DNA/[C12-4-C12im]Br2 solutions with Z+/− increasing (Fig. 1). The

Conclusions

Cationic imidazolium gemini surfactants ([Cn-4-Cnim]Br2, n = 10, 12, 14) as novel amphiphilic molecules can interact with DNA via attractive electrostatic interaction, strong hydrophobic force and π–π interaction. Upon addition of [Cn-4-Cnim]Br2, DNA molecules undergo the process from compaction to multi-molecular condensation accompanied by conformation change, which could be evidenced by the DLS and CD results. The impact of the electrostatic interaction can be deduced from the charge density

Acknowledgments

We acknowledge financial support from the Natural Science Foundation of China (20833010, 20973043). Financial support from the National Basic Research Program of China (2009CB9301000) is also gratefully acknowledged. The authors thank Prof. Xia Wu from Shandong University for providing herring sperm DNA.

References (44)

  • C.H. Spink et al.

    Thermodynamics of the binding of a cationic lipid to DNA

    J. Am. Chem. Soc.

    (1997)
  • F.M.P. Wong et al.

    Cationic lipid binding to DNA: characterization of complex formation

    Biochemistry

    (1996)
  • S. Marchetti et al.

    DNA condensation induced by cationic surfactant: a viscosimetry and dynamic light scattering study

    J. Phys. Chem.

    (2005)
  • V. Jadhav et al.

    Effect of the head-group geometry of amino acid-based cationic surfactants on interaction with plasmid DNA

    Biomacromolecules

    (2008)
  • X. Guo et al.

    Facilitation effect of oligonucleotide on vesicle formation from single-chained cationic surfactant-dependences of oligonucleotide sequence and size and surfactant structure

    J. Polym. Sci. Polym. Chem.

    (2009)
  • M.C. Morán et al.

    DNA gel particles from single and double-tail surfactants: supramolecular assemblies and release characteristics

    Soft Matter

    (2011)
  • T.M. Reineke

    Poly(glycoamidoamine)s: cationic glycopolymers for DNA delivery

    J. Polym. Sci. Polym. Chem.

    (2006)
  • M.L. Ainalem et al.

    DNA condensation using cationic dendrimers-morphology and supramolecular structure of formed aggregates

    Soft Matter

    (2011)
  • H. Chen et al.

    Study on interaction between cationic polystyrene nanoparticles and DNA, and the detection of DNA by resonance light scattering technology

    Microchim. Acta

    (2010)
  • M. Tecle et al.

    Kinetic study of DNA condensation by cationic peptides used in nonviral gene therapy: analogy of DNA condensation to protein folding

    Biochemistry

    (2003)
  • D. Llères et al.

    Investigation of the stability of dimeric cationic surfactant/DNA complexes and their interaction with model membrane systems

    Langmuir

    (2002)
  • C. Leal et al.

    Electrostatic attraction between DNA and a cationic surfactant aggregate. The screening effect of salt

    J. Phys. Chem.

    (2007)
  • Cited by (53)

    • Metallosurfactant based synthetic liposomes as a substitute for phospholipids to safely store curcumin

      2022, Colloids and Surfaces B: Biointerfaces
      Citation Excerpt :

      Although, when cationic agents are introduced to the saturated DNA-EtBr complex, they will condense the DNA chains and hence expel the intercalated EtBr molecules. This would lead to decreased fluorescence intensity as EtBr molecules are now forced to reside in aqueous bulk [48]. When we gradually added DNA to the EtBr solution, a sharp increase in fluorescence intensity was observed (Fig. 7(i)) till the saturation level where all the free EtBr molecules have been anticipated to be attached to DNA.

    • Interactions with ctDNA of novel sugar-based gemini cationic surfactants

      2020, International Journal of Biological Macromolecules
      Citation Excerpt :

      From Fig. 5B, with the addition of 1c, the zeta potential values first decreased remarkably till a minimum value was reached, which were inconsistent with previous reports of DNA compression by CTAB, during which the zeta potential values increased continuously with the increase of the concentration of CTAB [6,35]. This variation tendency could be a consequence of the concentrated negative charges due to the compression of DNA folding induced by 1c [38]. It may be also attributed to the increasing negative charges aroused by exposing the original hidden negative charges because of DNA conformation change [39].

    View all citing articles on Scopus
    View full text