Thermodynamic and physical interactions between novel polymeric surfactants and lipids: toward designing stable polymer-lipid complexes

Polyester-based particles to overcome the obstacles of mucus and biofilms in the lung for tobramycin application under static and dynamic fluidic conditions

Pulmonary infections with Pseudomonas aeruginosa and Burkholderia cepacia complex (Bcc) are difficult to treat and related with high mortality in some diseases like cystic fibrosis due to the recurrent formation of biofilms. The biofilm formation hinders efficient treatment with inhaled antibiotics due to a low penetration of the antibiotics through the polyanionic biofilm matrix and increased antimicrobial resistance of the biofilm-embedded bacteria. In this study, tobramycin (Tb) was encapsulated in particles based on poly(d,l,-lactide-co-glycolide) (PLGA) and poly(ethylene glycol)-co-poly(d,l,-lactide-co-glycolide) diblock (PEG-PLGA) to overcome the biofilm barrier with particle sizes of 225-231 nm (nanoparticles) and 896-902 nm (microparticles), spherical shape and negative zeta potentials. The effectiveness against biofilms of P. aeruginosa and B. cepacia was strongly enhanced by the encapsulation under fluidic experimental condition as well as under static conditions in artificial mucus. The biofilm-embedded bacteria were killed by less than 0.77 mg/l encapsulated Tb, whereas 1,000 mg/l of free Tb or the bulk mixtures of Tb and the particles were ineffective against the biofilms. Moreover, encapsulated Tb was even effective against biofilms of the intrinsically aminoglycoside-resistant B. cepacia, indicating a supportive effect of PEG and PLGA on Tb. No cytotoxicity was detected in vitro in human lung epithelial cells with any formulation.

Interaction of curcumin with 1,2-dioctadecanoyl-sn-glycero-3-phosphocholine liposomes: Intercalation of rhamnolipids enhances membrane fluidity, permeability and stability of drug molecule

Stability of curcumin in neutral and alkaline buffer conditions has been a serious concern for its medicinal applications. We demonstrate that the stability of curucmin can be improved in 1,2-Dioctadecanoyl-sn-glycero-3-phosphocholine (DSPC) liposomes. Curcumin strongly partition into liquid crystalline phase compared to solid gel phase of DSPC liposomes. Variation of fluorescence intensity of curcumin associated with liposomes with temperature successfully determines phase transition temperature of DSPC liposomes. However, at higher molar ratio curcumin can influence phase transition temperature by intercalating into deep hydrophobic layer of liposomes and facilitating fusion of two membrane phases. Rhamnolipids (RLs) are recently being applied for various biomedical applications. Here, we have explored new insight on intercalation of rhamnolipids with DSPC liposomes. Intercalation of rhamnolipids exceptionally increases partition of curcumin into solid gel phase of DSPC liposomes, whereas this increase is moderate in liquid crystalline phase. Fluorescence quenching study establishes that permeability and fluidity of the DSPC liposomes are enhanced in the presence of RLs. Membrane permeability and fluidity can be improved further by increasing the percentage of RLs in DSPC liposomes. The phase transition temperature of DSPC liposomes decreases with increase in percentage of RLs in DSPC liposomes by encouraging fusion between solid gel and liquid crystalline phases. Intercalation of RLs is found to further boost stability of drug, curcumin, in DSPC liposomes. Thus, mixing RLs with DSPC liposomes could potentially serve as a good candidate for drug delivery application.

Carbohydrate-derived amphiphilic macromolecules: a biophysical structural characterization and analysis of binding behaviors to model membranes

The design and synthesis of enhanced membrane-intercalating biomaterials for drug delivery or vascular membrane targeting is currently challenged by the lack of screening and prediction tools. The present work demonstrates the generation of a Quantitative Structural Activity Relationship model (QSAR) to make a priori predictions. Amphiphilic macromolecules (AMs) "stealth lipids" built on aldaric and uronic acids frameworks attached to poly(ethylene glycol) (PEG) polymer tails were developed to form self-assembling micelles. In the present study, a defined set of novel AM structures were investigated in terms of their binding to lipid membrane bilayers using Quartz Crystal Microbalance with Dissipation (QCM-D) experiments coupled with computational coarse-grained molecular dynamics (CG MD) and all-atom MD (AA MD) simulations. The CG MD simulations capture the insertion dynamics of the AM lipophilic backbones into the lipid bilayer with the PEGylated tail directed into bulk water. QCM-D measurements with Voigt viscoelastic model analysis enabled the quantitation of the mass gain and rate of interaction between the AM and the lipid bilayer surface. Thus, this study yielded insights about variations in the functional activity of AM materials with minute compositional or stereochemical differences based on membrane binding, which has translational potential for transplanting these materials in vivo. More broadly, it demonstrates an integrated computational-experimental approach, which can offer a promising strategy for the in silico design and screening of therapeutic candidate materials.

Sugar-based amphiphilic polymers for biomedical applications: from nanocarriers to therapeutics

Various therapeutics exhibit unfavorable physicochemical properties or stability issues that reduce their in vivo efficacy. Therefore, carriers able to overcome such challenges and deliver therapeutics to specific in vivo target sites are critically needed. For instance, anticancer drugs are hydrophobic and require carriers to solubilize them in aqueous environments, and gene-based therapies (e.g., siRNA or pDNA) require carriers to protect the anionic genes from enzymatic degradation during systemic circulation. Polymeric micelles, which are self-assemblies of amphiphilic polymers (APs), constitute one delivery vehicle class that has been investigated for many biomedical applications. Having a hydrophobic core and a hydrophilic shell, polymeric micelles have been used as drug carriers. While traditional APs are typically comprised of nondegradable block copolymers, sugar-based amphiphilic polymers (SBAPs) synthesized by us are comprised of branched, sugar-based hydrophobic segments and a hydrophilic poly(ethylene glycol) chain. Similar to many amphiphilic polymers, SBAPs self-assemble into polymeric micelles. These nanoscale micelles have extremely low critical micelle concentrations offering stability against dilution, which occurs with systemic administration. In this Account, we illustrate applications of SBAPs for anticancer drug delivery via physical encapsulation within SBAP micelles and chemical conjugation to form SBAP prodrugs capable of micellization. Additionally, we show that SBAPs are excellent at stabilizing liposomal delivery systems. These SBAP-lipid complexes were developed to deliver hydrophobic anticancer therapeutics, achieving preferential uptake in cancer cells over normal cells. Furthermore, these complexes can be designed to electrostatically complex with gene therapies capable of transfection. Aside from serving as a nanocarrier, SBAPs have also demonstrated unique bioactivity in managing atherosclerosis, a major cause of cardiovascular disease. The atherosclerotic cascade is usually triggered by the unregulated uptake of oxidized low-density lipoprotein, a cholesterol carrier, in macrophages of the blood vessel wall; SBAPs can significantly inhibit oxidized low-density lipoprotein uptake in macrophages and abrogate the atherosclerotic cascade. By modification of various functionalities (e.g., branching, stereochemistry, hydrophobicity, and charge) in the SBAP chemical structure, SBAP bioactivity was optimized, and influential structural components were identified. Despite the potential of SBAPs as atherosclerotic therapies, blood stability of the SBAP micelles was not ideal for in vivo applications, and means to stabilize them were pursued. Using kinetic entrapment via flash nanoprecipitation, SBAPs were formulated into nanoparticles with a hydrophobic solute core and SBAP shell. SBAP nanoparticles exhibited excellent physiological stability and enhanced bioactivity compared with SBAP micelles. Further, this method enables encapsulation of additional hydrophobic drugs (e.g., vitamin E) to yield a stable formulation that releases two bioactives. Both as nanoscale carriers and as polymer therapeutics, SBAPs are promising biomaterials for medical applications.

Liposomal stabilization using a sugar-based, PEGylated amphiphilic macromolecule

Liposomes are an important class of colloidal drug delivery systems, yet the clinical applications of conventional liposomes can be hampered by poor colloidal and biological stabilities. In this work, a sugar-based, PEGylated amphiphilic macromolecule (AM) was evaluated for its ability to stabilize dipalmitoyl phosphatidylcholine (DPPC)-based liposomes. Compared to unmodified liposomes, AM-stabilized liposomes exhibited enhanced colloidal stability, maintaining relatively constant particle sizes for 5 weeks without aggregation. AM-stabilized liposomes also showed significantly decreased membrane permeability, even in the presence of serum. Finally, AM-stabilized liposomes displayed improved biological stability, significantly inhibiting phagocytosis by macrophages. Overall, the effectiveness of AM to stabilize liposomes was comparable to a conventional stabilizing agent, PEG-modified phosphatidylethanolamine. Based upon these results, AM is a promising stabilizing agent for colloidal drug delivery applications and currently being optimized.

Prediction of micelle/water and liposome/water partition coefficients based on molecular dynamics simulations, COSMO-RS, and COSMOmic

Liposomes and micelles find various applications as potential solubilizers in extraction processes or in drug delivery systems. Thermodynamic and transport processes governing the interactions of different kinds of solutes in liposomes or micelles can be analyzed regarding the free energy profiles of the solutes in the system. However, free energy profiles in heterogeneous systems such as micelles are experimentally almost not accessible. Therefore, the development of predictive methods is desirable. Molecular dynamics (MD) simulations reliably simulate the structure and dynamics of lipid membranes and micelles, whereas COSMO-RS accurately reproduces solvation free energies in different solvents. For the first time, free energy profiles in micellar systems, as well as mixed lipid bilayers, are investigated, taking advantage of both methods: MD simulations and COSMO-RS, referred to as COSMOmic (Klamt, A.; Huniar, U.; Spycher, S.; Keldenich, J. COSMOmic: A Mechanistic Approach to the Calculation of Membrane-Water Partition Coefficients and Internal Distributions within Membranes and Micelles. J. Phys. Chem. B 2008, 112, 12148-12157). All-atom molecular dynamics simulations of the system SDS/water and CTAB/water have been applied in order to retrieve representative micelle structures for further analysis with COSMOmic. For the system CTAB/water, different surfactant concentrations were considered, which results in different micelle sizes. Free energy profiles of more than 200 solutes were predicted and validated by means of experimental partition coefficients. To our knowledge, these are the first quantitative predictions of micelle/water partition coefficients, which are based on whole free energy profiles from molecular methods. Further, the partitioning in lipid bilayer systems containing different hydrophobic tail groups (DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine), SOPC (stearoyl-oleoylphosphatidylcholine), DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine), and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine)) as well as mixed bilayers was calculated. Experimental partition coefficients (log P) were reproduced with a root-mean-square error (RMSE) of 0.62. To determine the influence of cholesterol as an important component of cellular membranes, free energy profiles in the presence of cholesterol were calculated and shown to be in good agreement with experimental data.