DNA liquid-crystalline gel as adsorbent of carcinogenic agent

Hydrogel composite of lanthanum and Halorubrum ejinoor sp. cell lysate as an adsorbing material

OBJECTIVES

Although halophilic archaea are rich in natural environments, their biotechnological applications are not as prevalent as those of other extremophiles, such as thermophiles and alkaliphiles. This study presents an simple method to prepare a hydrogel composite using crude cell lysate of a halophilic archaea, Halorubrum ejinoor sp. (H.e.) which was isolated from a saline lake in Inner Mongolia, China. Furthermore, formation mechanism and potential applications of the hydrogel as an adsorbing material are discussed.

RESULTS

Halorubrum ejinoor sp. (H.e.) cell lysate was firstly prepared by adding pure water onto the H.e. cell pellet, followed by a short incubation at 60 °C. The cell lysate was injected into different metal ion (or H⁺) solutions to obtain the hydrogel composite. It was observed that H⁺, Fe³⁺, La³⁺, Cu²⁺, and Ca²⁺ induced gelation of the cell lysate, while Fe²⁺, Co²⁺, Ni²⁺, Mg²⁺, Na⁺, and K⁺ did not. DNA and extracellular polysaccharides (EPS) in the H.e. cell lysate were found to be responsible for the gelation reaction. These results suggest that DNA and EPS should be crosslinked by metal ions (or H⁺) and form a networked structure in which the metal ion (or H⁺) serves as an anchor point. Potential application of the hydrogel as an adsorbing material was explored using La³⁺-induced H.e. hydrogel composite. The hydrogel composite can adsorb the fluoride, phosphate and DNA-binding carcinogenic agents, such as acridine orange.

CONCLUSIONS

The simplicity and cost effectiveness of the preparation method might make H.e. hydrogel a promising adsorbing material. This work is expected to expand the technical applications of haloarchaea.

Construction of ordered structure in polysaccharide hydrogel: A review

Hydrogels are three-dimensional, hydrophilic, polymeric networks, held together by a variety of physical or chemical crosslinks. Among the numerous polymers that can be employed to fabricate hydrogel, polysaccharides have attracted enormous attention due to their peculiar properties that make them suitable for various applications. Compared with homogeneous hydrogels, hydrogels with ordered structures on various length scales are endowed with excellent properties and promising applications in materials science. In the present review, a wide range of techniques were introduced and discussed, which had been utilized to construct ordered hierarchical structures in polysaccharide hydrogels. These techniques focused on the construction of multi-layered and orientated structure, which are two typical and very important forms of hierarchical structure.

Monodomain hydrogels prepared by shear-induced orientation and subsequent gelation

Shear-induced orientation of liquid crystalline hydroxypropylcellulose solution with reactants is frozen by subsequent polymerization and gelation process, resulting in monodomain hydrogel with anisotropic optical, swelling, and mechanical properties.

Swim bladder collagen forms hydrogel with macroscopic superstructure by diffusion induced fast gelation

Marine collagen has been attracting attention as a medical material in recent times due to the low risk of pathogen infection compared to animal collagen. Type I collagen extracted from the swim bladder of Bester sturgeon fish has excellent characteristics such as high denaturation temperature, high solubility, low viscosity and an extremely fast rate to form large bundle of fibers under certain conditions. These specific characteristics of swim bladder collagen (SBC) permit us to create stable, disk shaped hydrogels with concentric orientation of collagen fibers by the controlled diffusion of neutral buffer through collagen solution at room temperature. However, traditionally used animal collagens, e.g. calf skin collagen (CSC) and porcine skin collagen (PSC), could not form any stable and oriented structure by this method. The mechanism of the superstructure formation of SBC by a diffusion induced gelation process has been explored. The fast fibrillogenesis rate of SBC causes a quick squeezing out of the solvent from the gel phase to the sol phase during gelation, which builds an internal stress at the gel-sol interface. The tensile stress induces the collagen molecules of the gel phase to align along the gel-sol interface direction to give this concentric ring-shaped orientation pattern. On the other hand, the slow fibrillogenesis rate of animal collagens due to the high viscosity of the solution does not favor the ordered structure formation. The denaturation temperature of SBC increases significantly from 31 °C to 43 °C after gelation, whereas that of CSC and PSC were found to increase a little. Rheology experiment shows that the SBC gel has storage modulus larger than 15 kPa. The SBC hydrogels with thermal and mechanical stability have potential as bio-materials for tissue engineering applications.

Model carcinogen adsorption dynamics of DNA gel

We have derived theoretical equations describing the adsorption of carcinogen to gels in an immersion medium containing carcinogens. The theory was developed for a cylindrical boundary condition under the assumption of a carcinogen diffusion-limited process combined with the "moving boundary picture (Furusawa et al., 2007)". The time course of the adsorbed carcinogen layer thickness and that of the carcinogen concentration in an immersion medium were expressed by a set of scaled variables, and the asymptotic behavior in the initial stage was derived. Experiments based on the theory were performed using a DNA gel sandwiched between a set of coverglasses in a medium containing acridine orange (AO). The boundary between the AO-adsorbed gel layer and AO-nonadsorbed gel layer was traced during the immersion. The time courses of the AO-adsorbed gel layer thickness and the AO concentration in the immersion medium were well explained by the theory, and the number ratio of the total AO molecules to the adsorption sites in the DNA gel was determined.

Applied chemistry of natural DNA

Recently, natural DNA has emerged as an appealing biomacromolecule for functional materials. It is abundant and renewable, and possesses the well known double helix structure that promises many unique properties difficult to find in other polymers. Natural DNA has been applied in electronic, optical and biomaterials, as a catalyst for enantioselective reactions, and as a material for cleaning the environment. Most of the applications are based on combining DNA with other chemicals or nanoparticles by electrostatic binding, intercalation or groove binding. In this critical review article, recent developments in utilizing natural DNA are reviewed by focusing on three basic properties of DNA: the electrostatic property as a polyelectrolyte, selective affinity for small molecules, and biocompatibility (128 references).

Carcinogen adsorbent prepared from DNA complex by gamma-ray irradiation

The effects of gamma-ray irradiation on aqueous solutions of chub mackerel chromatin, salmon milt DNA with CoCl(2), mixtures of DNA with Type A gelatin, bovine serum albumin (BSA), CM-chitosan, carboxymethyl cellulose (CMC) and Catinal (hydroxyethyl-cellulose, O-[2-hydroxy-3-(trimethyl ammonio)-propyl], chloride) and DNA in the presence of polyfunctional monomers with the aim to insolubilize DNA for preparing a novel carcinogen adsorbent have been studied. Among those, precipitates or inhomogeneous gel consisting of cross-linked DNA were prepared from the samples of aqueous DNA in the presence of CoCl(2) at low irradiation dose, around 10 Gy, and bulk homogeneous gels were successfully prepared from aqueous mixtures of DNA with gelatin, BSA, CMC and Catinal in a limited range of irradiation doses. Gel fraction and swelling ratio of the gels were measured. Adsorption of a carcinogen, acridine orange, was also examined for the gels. From the experimental results, the optimum conditions for preparing insolubilized homogeneous DNA gels were determined.

Adsorption kinetics of carcinogens to DNA liquid crystalline gel beads

Adsorption behaviors of acridine orange (AO) and biphenyl (BP) to DNA liquid crystalline gel (LCG) beads in aqueous dispersing solution have been studied theoretically and experimentally. A theoretical consideration based on nonequilibrium thermodynamics predicted that the time course of the adsorption process is expressed with a scaled equation, and a scaled number of adsorbed carcinogen molecules ñ is expressed with the square root of a scaled immersion time t, ñ proportional, variant square root t at early stage, whereas it is expressed with a power law function 1 - ñ proportional, variant (te - t)3/2 for ñ0 > 1 and an exponential equation ñ0 - ñ proportional, variant e-t/alpha tau0 for ñ0 > 1 at later stages of adsorption. Here, ñ0 is the ratio of the initial number of carcinogen molecules in the dispersing solution to the number of the sites of adsorption of carcinogen molecules in the beads, te is the scaled equilibrium time of adsorption, tau0 is a time constant for adsorption, and alpha is a constant. Observed adsorption processes for AO were well expressed by the predicted ones, and the fitting parameters ñ0 and tau0 increased with increasing cobalt chloride concentration CCo used for preparation of the beads, and both saturated above CCo > or = 400 mM for the adsorption of AO, whereas the adsorption processes for BP were expressed with the square root function. These results indicate that (1) the adsorption process at early stage is explained by diffusion-limited binding of the carcinogen molecules to DNA beads, and the time range of the early stage depends on the solubility (the solubility of AO in water is high whereas that of BP is low); and (2) the process at later stages depends on the balance of the numbers of adsorption sites and carcinogen molecules.