Influence of salt type and ionic strength on self-assembly of dextran sulfate-ciprofloxacin nanoplexes

Computational insights into fucoidan-receptor binding: Implications for fucoidan-based targeted drug delivery

Fucoidan, a polysaccharide from seaweed, holds promise as a drug delivery system and immune modulator; however, its exact mechanism of action remains unclear. As various carbohydrates play key roles in immune responses by binding to carbohydrate-binding proteins like lectins, fucoidan is hypothesized to interact with immune receptors, potentially driving its anticancer activities. However, structural variability, extraction-induced heterogeneity, and weak binding affinities pose challenges to research. Computational tools offer valuable insights into fucoidan-receptor interactions, addressing these challenges and enabling the design of more effective therapies. This review examines fucoidan's therapeutic activities, drug delivery potential, and receptor interactions, emphasizing computational approaches to advance immune modulation and anticancer applications using carbohydrate polymers.

Ionic Strength Dependence of the Complex Coacervation between Lactoferrin and β-Lactoglobulin

Heteroprotein complex coacervation is an assembly formed by oppositely charged proteins in aqueous solution that leads to liquid-liquid phase separation. The ability of lactoferrin and β-lactoglobulin to form complex coacervates at pH 5.5 under optimal protein stoichiometry has been studied in a previous work. The goal of the current study is to determine the influence of ionic strength on the complex coacervation between these two proteins using direct mixing and desalting protocols. The initial interaction between lactoferrin and β-lactoglobulin and subsequent coacervation process were highly sensitive to the ionic strength. No microscopic phase separation was observed beyond a salt concentration of 20 mM. The coacervate yield decreased drastically with increasing added NaCl from 0 to 60 mM. The charge-screening effect induced by increasing the ionic strength is attributed to a decrease of interaction between the two oppositely charged proteins throughout a decrease in Debye length. Interestingly, as shown by isothermal titration calorimetry, a small concentration of NaCl around 2.5 mM promoted the binding energy between the two proteins. These results shed new light on the electrostatically driven mechanism governing the complex coacervation in heteroprotein systems.

Non-intuitive Behavior of Polymer-Ciprofloxacin Nanoconjugate Suspensions: a Tool for Flexible Oral Drug Delivery

Ciprofloxacin (CPX) is prone to spontaneous self-aggregation and formation of supramolecular dimers (π - π stacking) due to its complicated surface chemistry which has been associated with its anomalous solubility and instability in aqueous systems particularly near neutral pH. The surface characteristic of ciprofloxacin was modified through non-intuitive counterion interaction between CPX and diethylaminoethyl dextran (DDEX) to form nanoconjugate assembly. The CPX-DDEX nanoconjugate was confirmed by FTIR, SEM, DSC, TGA, and ¹H-NMR. The DSC thermograms showed a remarkable 20% reduction in the melting temperature (T_m) of CPX from 268.57±1.11°C to 214.36±1.0211°C and 78% reduction in enthalpy of fusion (ΔH_f) from 59.84 kJ/mol (180.59 J/g) to 12.90 kJ/mol (38.92 J/g), indicating increased solubility and dissolution efficiency. DDEX polymer alone exhibited pseudoplastic characteristics however with more viscous rather than elastic response, while the CPX-DDEX nanoconjugate suspensions exhibited remarkable elastic behavior with significantly increased storage modulus (G') thus controlling and extending the release of CPX. The reconstituted freeze-dried CPX-DDEX nanoconjugate suspension was chemically stable throughout the 90-day study both in the refrigerator and at controlled room temperature, while the aqueous suspension of pure CPX without DDEX was only stable for 72 and 24 h, respectively. The dissolution efficiency of the CPX-DDEX nanoconjugate suspensions increased with increasing molar concentration of DDEX to a maximum of 100% at 50 μM of DDEX followed by a remarkable decrease within the 3-week study. It was apparent that the dissolution efficiency was governed by a critical balance between the CPX solubility and the viscoelastic characteristics of the polymeric nanoassembly. This study demonstrates the potential application of polymer-drug nanoconjugation formulation design to stabilization and flexible delivery of CPX from aqueous suspension systems. Graphical abstract.

Chitosan-induced Synergy for Extended Antimicrobial Potency and Enhanced In Vitro Drug Release of Free Base Ciprofloxacin Nanoplexes

BACKGROUND

Ciprofloxacin free base is practically insoluble in aqueous medium (0.0011 and 0.09 mg/mL at 25 and 37°C respectively). Its inorganic salt form (ciprofloxacin hydrochloride) is more soluble in water (1.35 mg/mL) however when administered orally, it exhibits decreased solubility in the stomach due to common ion effects. Ciprofloxacin free base was used in this study because of its greater hydrophobicity than its hydrochloride salt, which is required for effective permeability and potent antibacterial activity.

OBJECTIVE

The purpose of this study is to enhance oral solubility and bacterial cell permeability of the free base ciprofloxacin (CPX) using a single step CPX-chitosan (CT) selfassembly to form nanoplexes with organic counterions. It was envisioned that this would allow the delivery of larger amounts of active drug into the microorganisms.

METHODS

Ciprofloxacin-chitosan nanocomplex (nanoplex) was prepared using low energy electrostatic self-assembly technique previously described. Formation of eutectic nanoplex was confirmed using FTIR, DSC, TGA and SEM. The saturated solubility, in vitro release kinetics and mechanism of drug release were determined using mathematical models. Potency and synergism were determined from the inhibition zones, minimum inhibitory concentration (MIC) and Fractional Inhibitory Concentration (FIC) of the nanoplexes using Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus.

RESULTS

Formation of CPX-CT eutectic adduct polymeric nanoplexes was confirmed with FT-IR and DSC and SEM revealed the conversion of rod-like crystals of CPX (117 μm long) into spherical nanostructures (23-503 nm) dictated by pH, ionic strength and concentration of CT. The solubility of free base CPX increased to a maximum of 32.77 mg/mL compared to 0.0011-0.09 mg/mL reported in literature and dissolution efficiency increased to a maximum of 100% within 72 h. The synergistic effect of CT on antimicrobial activity of CPX was quantified, for the first time, using Fractional Inhibitory Concentration (FIC) of the nanoplexes. FIC was less than 0.5 in both Gram positive (0.031-0.250) and Gram negative (0.036-0.281) microorganisms used in this study, confirming synergistic enhancement of antimicrobial efficacy of CPX.

CONCLUSION

It is evident that the design of drug-polymer nanocomplex formulation provides a platform for the synergistic enhancement of therapeutic potency of antibiotics.

Delivery of novel vancomycin nanoplexes for combating methicillin resistant Staphylococcus aureus (MRSA) infections

The development of novel antibiotic systems is needed to address the methicillin-resistant Staphylococcus aureus (MRSA) infections. The aim of the study was to explore the novel nanoplex delivery method for vancomycin (VCM) against MRSA using dextran sulfate sodium salt (DXT) as a polyelectrolyte complexing agent. Nanoplexes were formulated by the self-assembling amphiphile polyelectrolyte complexation method and characterized. The size, polydispersity index (PDI), and zeta potential (ZP) of the optimized VCM nanoplexes were 84.6 ± 4.248 nm, 0.449 ± 0.024 and -33.0 ± 4.87 mV respectively, with 90.4 ± 0.77% complexation efficiency (CE %) and 62.3 ± 0.23% drug loading. The in vitro (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)tetrazolium (MTT) studies of the nanoplexes were found to be non-toxic against different mammalian cell lines tested and may confirm its biosafety. While the in vitro drug release studies demonstrated sustained slower release. The in silico study confirmed the spontaneous interaction of VCM with DXT in the presence of sodium chloride. A 6.24-fold enhancement was observed for VCM nanoplexes via in vitro antibacterial studies. Flow-cytometric analysis showed effective cell killing of 67% from VCM nanoplexes compared to 32.98% from the bare vancomycin at the minimum inhibitory concentration (MIC) of 1.25 μg/mL. The in vivo studies using BALB/c mouse skin infection model revealed that nanoplexes reduced MRSA burden by 2.3-folds compared to bare VCM. The novel nanoplexes have potential to be a promising delivery system to combat MRSA infections for improved treatment of bacterial infections.

Complexation of Polyelectrolytes with Hydrophobic Drug Molecules in Salt-Free Solution: Theory and Simulations

The delivery and dissolution of poorly soluble drugs is challenging in the pharmaceutical industry. One way to significantly improve the delivery efficiency is to incorporate these hydrophobic small molecules into a colloidal polyelectrolyes(PE)-drug complex in their ionized states. Despite its huge application value, the general mechanism of PE collapse and complex formation in this system has not been well understood. In this work, by combining a mean-field theory with extensive molecular simulations, we unveil the phase behaviors of the system under dilute and salt-free conditions. We find that the complexation is a first-order-like phase transition triggered by the hydrophobic attraction between the drug molecules. Importantly, the valence ratio between the drug molecule and PE monomer plays a crucial role in determining the stability and morphology of the complex. Moreover, the sign of the zeta potential and the net charge of the complex are found to be inverted as the hydrophobicity of the drug molecules increases. Both theory and simulation indicate that the complexation point and complex morphology and the electrostatic properties of the complex have a weak dependence on chain length. Finally, the dynamics aspect of PE-drug complexation is also explored, and it is found that the complex can be trapped into a nonequilibrium glasslike state when the hydropobicity of the drug molecule is too strong. Our work gives a clear physical picture behind the PE-drug complexation phenomenon and provides guidelines to fabricate the colloidal PE-drug complex with the desired physical characteristics.