Co-Delivery of mRNA and pDNA Using Thermally Stabilized Coacervate-Based Core-Shell Nanosystems

Co-delivery of different species of protein-encoding polynucleotides, e.g., messenger RNA (mRNA) and plasmid DNA (pDNA), using the same nanocarrier is an interesting topic that remains scarcely researched in the field of nucleic acid delivery. The current study hence aims to explore the possibility of the simultaneous delivery of mRNA (mCherry) and pDNA (pAmCyan) using a single nanocarrier. The latter is based on gelatin type A, a biocompatible, and biodegradable biopolymer of broad pharmaceutical application. A core-shell nanostructure is designed with a thermally stabilized gelatin-pDNA coacervate in its center. Thermal stabilization enhances the core's colloidal stability and pDNA shielding effect against nucleases as confirmed by nanoparticle tracking analysis and gel electrophoresis, respectively. The stabilized, pDNA-loaded core is coated with the cationic peptide protamine sulfate to enable additional surface-loading with mRNA. The dual-loaded core-shell system transfects murine dendritic cell line DC2.4 with both fluorescent reporter mRNA and pDNA simultaneously, showing a transfection efficiency of 61.4 ± 21.6% for mRNA and 37.6 ± 19.45% for pDNA, 48 h post-treatment, whereas established commercial, experimental, and clinical transfection reagents fail. Hence, the unique co-transfectional capacity and the negligible cytotoxicity of the reported system may hold prospects for vaccination among other downstream applications.

Effect of organic and inorganic salt environment on the complex coacervation of in situ formed protein nanoparticles and DNA

Complex coacervation was noticed between in situ formed protein (a primarily hydrophobic Zein protein with pI = 6.2) nanoparticles (size 80-120 nm) and ds-DNA (a high charge density polyanion), in the ionic liquid (IL) solutions of 1-ethyl-3-methyl imidazolium chloride [C2mim][Cl], and 1-octyl-3-methyl imidazolium chloride [C8mim][Cl], in the studied ionic strength range of I = 10^-4 to 6 × 10^-1 M, which was extended to strong monovalent 1:1 electrolyte (NaCl) to explore the commonality between the organic and inorganic salt (ionic) environment on coacervation. The salt dependent coacervation profile was monitored from the measured turbidity of the interacting solution, and zeta potential, (ζ) and apparent hydrodynamic radius (R_h) of interpolymer complexes, which depicted the following three discernible interaction regimes common to all the salts: (i) Region-I: I = 0.0001-0.01 M, primary binding, (ii) Region-II, I = 0.01-0.1 M, secondary binding, and (iii) Region-III, I = 0.1-0.6 M, saturation binding. The free-energy and the network density calculations favored preferential coacervation in [C2mim][Cl] samples. Nonetheless, commonality in the overall ionic strength dependent coacervation profiles could still be observed.

DNA ionogel: Structure and self-assembly

DNA dissolved in ionic liquid (IL) solution (1-ethyl-3-methylimidazolium chloride, [C2mim][Cl]) showed a transition to the gel phase ([DNA] ≥ 1% (w/v)). The gelation time was 400 s for the 1% [IL] sample which reduced to 260 s for 5% [IL] concentration. Gelation times, obtained from the viscosity and ergodicity breaking from the dynamic structure factor data, were remarkably identical to each other. Correspondingly, the gelation temperature which was ∼60 °C increased to 67 °C with [IL] content. The small angle neutron scattering (SANS) structure factor profile revealed the presence of the following three distinct length scales: (a) mesh size, ξ ≈ 3 ± 0.5 nm for ionogels, and ≈0.73 ± 0.06 nm, for sol; (b) cross-sectional radius of DNA strand, R_c ≈ 1.6 ± 0.1 nm; and (c) the characteristic inter-cluster distance ≈33 ± 5 nm. Physical conformation of the DNA-IL complexes remained close to the Gaussian coil definition. It was observed that without IL, in the sol phase, the system was completely ergodic and did not gel, while on addition of IL a sudden transition to the non-ergodic (arrested) gel phase occurred. This was due to the formation of an amorphous network of DNA-IL complexes preceding gelation. In summary, it is shown that the DNA ionogels can be prepared with a tunable gel strength (27-70 Pa) and gelation temperature (60-67 °C). Further, the relaxation dynamics was found to be hierarchical in IL content of the gel, revealing considerable self-organization.

Complex coacervation in charge complementary biopolymers: Electrostatic versus surface patch binding

In this review, a number of systems are described to demonstrate the effect of polyelectrolyte chain stiffness (persistence length) on the coacervation phenomena, after we briefly review the field. We consider two specific types of complexation/coacervation: in the first type, DNA is used as a fixed substrate binding to flexible polyions such as gelatin A, bovine serum albumin and chitosan (large persistence length polyelectrolyte binding to low persistence length biopolymer), and in the second case, different substrates such as gelatin A, bovine serum albumin, and chitosan were made to bind to a polyion gelatin B (low persistence length substrate binding to comparable persistence length polyion). Polyelectrolyte chain flexibility was found to have remarkable effect on the polyelectrolyte-protein complex coacervation. The competitive interplay of electrostatic versus surface patch binding (SPB) leading to associative interaction followed by complex coacervation between these biopolymers is elucidated. We modelled the SPB interaction in terms of linear combination of attractive and repulsive Coulombic forces with respect to the solution ionic strength. The aforesaid interactions were established via a universal phase diagram, considering the persistence length of polyion as the sole independent variable.

Mimicking mechanical response of natural tissues. Strain hardening induced by transient reticulation in lactose-modified chitosan (chitlac)

The effect of transient cross-links has been explored on a lactose-modified chitosan, which previously had shown interesting biological features. The presence of galactose side chains and of the polyol spacer resulted particularly appealing for the reticulation by borate ions. The interaction between chitlac and borax was investigated by means of ¹¹B NMR while rheology pointed to a marked non-linear behavior depending on the amount of borax added to the system. The presence of limited amount of cross-linking ion led to dilatant behavior when the steady flow curve was measured. In addition, strain stiffening was noticed on elastic response upon exceeding a critical stress, indicating a transient nature in the formation of the cross-links. The non-linear response of chitlac in the presence of borax compared surprisingly well with the one showed by proteins composing the natural ECM pointing at a possible role of mechanotransduction in the biological significance of the modified chitosan.

Surface behavior and bulk properties of aqueous chitosan and type-B gelatin solutions for effective emulsion formulation

The behavior of aqueous chitosan (CH), type-B gelatin (GB) and CH-GB coacervate was studied on oil-in-water emulsion formulation at various pH and concentration ratio. The coacervate was formed by phase separation at ratios CH:GB, 1:10 to 1:1 with total biopolymer concentrations of 0.55%-1.0% (w/v) at pH 4.0-5.5. Soluble complexes were formed below pH 5.0 and coacervate formation was confirmed at pH 5.0 and above by zeta potential and UV-spectroscopy measurements. The coacervate formation was found maximum at the CH-GB ratios of 1:10 and 1:5 at pH 5.5. Formulated emulsions (>10μm droplets) using 1% (w/v) chitosan and GB were found stable (+52.5mv and creaming index 86%) and unstable respectively. Emulsion stabilized by mixed CH:GB 1:5 (3%w/v) had no creaming effect. The instability was attributed to the lower surface activity (K=5.0Lg^-1) of pure GB compared to CH (K=14.3Lg^-1). The formulation and methods can successfully tune the stability of the emulsions.

Surface active ionic liquid induced conformational transition in aqueous medium of hemoglobin

The molecular interactions and effect of SAILs on the conformation of human hemoglobin (Hb) has been studied using various techniques.

Hierarchical surface charge dependent phase states of gelatin-bovine serum albumin dispersions close to their common pI

We report interaction between bovine serum albumin ([BSA] = 1% (w/v)) and gelatin B ([GB] = 0.25-3.5% (w/v)) occurring close to their common isoelectric pH (pI). This interaction generated distinguishable multiple soft matter phases like opaque coacervates (phase I) and transparent gels (phase II), where the former are composed of partially charge neutralized intermolecular complexes (zeta potential, ζ ≤ 0) and the latter of overcharged complexes (ζ ≥ 0) that organized into a network pervading the entire sample volume. These phase states were completely governed by the protein mixing ratio r = [GB]:[BSA]. Coacervates, when heated above 32 °C, produced thermoirreversible turbid gels (phase III), stable in the region 32 ≥ T ≤ 50 °C. When the transparent gels were heated to T ≥ 34 °C, these turned into turbid solutions that did form a turbid fragile gel (phase IV) upon cooling. Mechanical and thermal behaviors of aforesaid coacervates (phase I) and gels (phase II) were examined; coacervates had lower storage modulus and melting temperature compared to gels. Cole-Cole plots attributed considerable heterogeneity to coacervate phase, but gels were relatively homogeneous. Raman spectroscopy data suggested differential microenvironment for these phases. Coacervates were mostly hydrated by partially structured water with degree of hydration dependent on gelatin concentration whereas for gels hydration was invariant of [GB]. Small-angle neutron scattering (SANS) data gave static structure factor profiles, I(q), versus wavevector q, that were remarkably different. For transparent gels, data could be split into two distinct regions: (i) 0.01 < q < 0.1 Å(-1), I(q) = IOZ(0)/(1 + q(2)ζgel(2))(2) (Debye-Bueche function) with ζgel = 9-13 nm, and (ii) 0.1 < q < 0.35 Å(-1), I(q) = IOZ(0)/(1 + q(2)ξgel(2)) (Ornstein-Zernike function) with ξgel = 3.1 ± 0.6 nm. Similarly, for coacervate, the aforesaid two q-regions were described by (i) I(q) = IPL(0)q(-α) with α = 1.7 ± 0.1 and (ii) I(q) = IOZ(0)/(1 + q(2)ξcoac(2)) with ξcoac = 1.6 ± 0.2 nm, a value close to the persistence length of gelatin chain (lp ≈ 2 nm). Phase transition from one equilibrium state to another, i.e., phase I to II, was hierarchical in the charge state of the protein-protein complex. Within the same charge state, transition from phase I to III and from phase II to IV was thermally activated. The aforesaid mechanisms are captured in a unique ζ-T phase diagram.

Biofunctionalization of α-zirconium phosphate nanosheets: toward rational control of enzyme loading, affinities, activities and structure retention

Controlling the properties of enzymes bound to solid surfaces in a rational manner is a grand challenge. Here we show that preadsorption of cationized bovine serum albumin (cBSA) to α-Zr(IV) phosphate (α-ZrP) nanosheets promotes enzyme binding in a predictable manner, and surprisingly, the enzyme binding is linearly proportional to the number of residues present in the enzyme or its volume, providing a powerful, new predictable tool. The cBSA loaded α-ZrP (denoted as bZrP) was tested for the binding of pepsin, glucose oxidase (GOX), tyrosinase, catalase, myoglobin and laccase where the number of residues increased from the lowest value of ∼153 to the highest value of 2024. Loading depended linearly on the number of residues, rather than enzyme charge or its isoelectric point. No such correlation was seen for the binding of these enzymes to α-ZrP nanosheets without the preadsorption of cBSA, under similar conditions of pH and buffer. Enzyme binding to bZrP was supported by centrifugation studies, powder X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray spectroscopy. All the bound enzymes retained their secondary structure and the extent of structure retention depended directly on the amount of cBSA preadsorbed on α-ZrP, prior to enzyme loading. Except for tyrosinase, all enzyme/bZrP biocatalysts retained their enzymatic activities nearly 90-100%, and biofunctionalization enhanced the loading, improved structure retention and supported higher enzymatic activities. This approach of using a chemically modified protein to serve as a glue, with a predictable affinity/loading of the enzymes, could be useful to rationally control enzyme binding for applications in advanced biocatalysis and biomedical applications.