Dissolution and partitioning behavior of hydrophobic ion-paired compounds

Cholesterol sulfate-mediated ion-pairing facilitates the self-nanoassembly of hydrophilic cationic mitoxantrone

HYPOTHESIS

Hydrophilic cationic drugs such as mitoxantrone hydrochloride (MTO) pose a significant delivery challenge to the development of nanodrug systems. Herein, we report the use of a hydrophobic ion-pairing strategy to enhance the nano-assembly of MTO.

EXPERIMENTS

We employed biocompatible sodium cholesteryl sulfate (SCS) as a modification module to form stable ion pairs with MTO, which balanced the intermolecular forces and facilitated nano-assembly. PEGylated MTO-SCS nanoassemblies (pMS NAs) were prepared via nanoprecipitation. We systematically evaluated the effect of the ratio of the drug module (MTO) to the modification module (SCS) on the nanoassemblies.

FINDINGS

The increased lipophilicity of MTO-SCS ion pair could significantly improve the encapsulation efficiency (∼97 %) and cellular uptake efficiency of MTO. The pMS NAs showed prolonged blood circulation, maintained the same level of tumor antiproliferative activity, and exhibited reduced toxicity compared with the free MTO solution. It is noteworthy that the stability, cellular uptake, cytotoxicity, and in vivo pharmacokinetic behavior of the pMS NAs increased in proportion to the molar ratio of SCS to MTO. This study presents a self-assembly strategy mediated by ion pairing to overcome the challenges commonly associated with the poor assembly ability of hydrophilic cationic drugs.

Salt-Triggered Release of Hydrophobic Agents from Polyelectrolyte Capsules Generated via One-Step Interfacial Multilevel and Multicomponent Assembly

Controlled release of hydrophobic agents from salt-responsive capsules is hindered by the hydrophilic shell and interfacial tension between inner oil and surrounding water. Rupturing shells in salt solution is another effective way. However, the densely entangled polyelectrolytes (PEs) in shells determined that the rupture requires extremely high ion-strength. Herein, salt-responsive capsules with double-network shells including a continuous PE-nanocrystal network and interfacial ion pairs are proposed and revealed via a one-step interfacial multilevel and multicomponent assembly (IMMA) method. Rigid nanocrystals can weaken the entanglements of PE chains and reduce the critical salt-concentration. Interfacial ion pairs are responsible for maintaining the stability of the shells. Such double networks enable the disintegration of capsules in an applicable salt-concentration without damaging the stability of capsules. In addition, hydrophobic domains assemblied by surfactants and PE-nanocrystal network supply transport pathway for oil to across hydrophilic shells and subsequently produce inverse micelle to carry oil into water. The mechanism of formation and release of capsules is systematically investigated, which further demonstrates IMMA to be a typical method for creation of sophisticated structures in a brief way.

Self-emulsifying drug delivery systems: Impact of stability of hydrophobic ion pairs on drug release

The aim of this study was to evaluate the impact of stability of hydrophobic ion pairs (HIPs) in gastrointestinal (GI) fluids on their release from self-emulsifying drug delivery systems (SEDDS). HIPs of leuprolide (LEU), insulin (INS) and bovine serum albumin (BSA) were formed using various mono- and di-carboxylate surfactants i.e. sodium deoxycholate (SDC), sodium dodecanoate (SDD), sodium stearoyl glutamate (SSG) and pamoic acid di-sodium salt (PAM). HIPs were evaluated regarding precipitation efficiency, log Pn-butanol/water and dissociation behavior at various pH and ionic strength. Solubility studies of these HIPs were accomplished to identify suitable solvents for the formulation of SEDDS. Subsequently, HIPs were incorporated into SEDDS followed by characterization regarding zeta potential, stability and log DSEDDS/release medium. Independent from the type of (poly)peptides, PAM showed most efficient HIP properties among tested surfactants. The highest encapsulation efficiency with PAM was achieved at molar ratios of 1:1 for LEU, 1:3 for INS and 1:50 for BSA and log Pn-butanol/water of HIPs were increased at least 2.5 units. Dissociation studies showed that LEU-PAM, INS-PAM, BSA-PAM complexes were dissociated within 6 h up to 25%, 60% and 85% in GI fluids, respectively. These HIPs were successfully incorporated into SEDDS exhibiting negative zeta potential and high stability for 4 h. Log DSEDDS/release medium of LEU-PAM, INS-PAM, BSA-PAM complexes were 2.4 ± 0.7, 2.1 ± 0.62 and 1.6 ± 0.45, respectively. Findings of this study showed that stability of HIPs has great impact on log DSEDDS/release medium and consequently on their release from SEDDS.

One-Step Generation of Salt-Responsive Polyelectrolyte Microcapsules via Surfactant-Organized Nanoscale Interfacial Complexation in Emulsions (SO NICE)

Polyelectrolyte microcapsules are versatile compartments for encapsulation, protection, and controlled/triggered release of active agents. Conventional methods of polyelectrolyte microcapsule preparation require multiple steps or do not allow for efficient encapsulation of active agents in the lumen of the microcapsule. In this work, we present the fabrication of hollow polyelectrolyte microcapsules with a salt-responsive property based on surfactant organized nanoscale interfacial complexation in emulsions (SO NICE). In SO NICE, polyelectrolyte microcapsules are templated by water-in-oil-in-water (W/O/W) double emulsions. One polyelectrolyte is dissolved in the inner water droplet of the W/O/W double emulsions, whereas the second polyelectrolyte is dissolved in the organic phase by hydrophobic ion paring with an oppositely charged hydrophobic surfactant. Interfacial complexation of the two polyelectrolytes generates a few hundred-nanometer thick film at the inner water-oil interface of the W/O/W double emulsions. SO NICE microcapsules can be triggered to release their cargo by increasing the ionic strength of the solution, which is a hallmark of polyelectrolyte-based microcapsules. By enabling dissolution and interfacial complexation of polyelectrolytes in organic solvents, SO NICE widens the pallet of polymers that can be used to generate functional polyelectrolyte microcapsules with high encapsulation efficiency for applications in encapsulation and controlled/triggered release.

An innovative method for preparation of hydrophobic ion-pairing colistin entrapped poly(lactic acid) nanoparticles: Loading and release mechanism study

Hydrophobic ion-pairing (HIP) complexation has emerged as an efficient approach to enhance the entrapment of therapeutic peptides in the biodegradable polymer matrix. In the present study, we developed an innovative extraction method for preparation of HIP-colistin (CST, a polycationic peptide) using various water-insoluble anionic lipids. To determine the loading mechanism of HIP-CST entrapped poly(lactic acid) (PLA) nanoparticles (HIP-CST-PLA-NPs), the effects of anionic lipids and PLA molecular weight (Mw) on the unentrapped fraction (uf) of CST in PLA-NPs were investigated. And CST release mechanism from HIP-CST-PLA-NPs was also investigated by evaluating their release behavior and NP swelling. It is showed that HIP-CST retention in the PLA-NPs was imposed by their physical localization in the networks of the PLA chains, rather than the electrostatic attraction between anionic lipid and CST in serum. And HIP-CST-PLA-NPs in serum exhibited the swelling-controlled release behavior with a substantially accelerated release and NP swelling observed in comparison with that in phosphate buffer. Our results can effectively guide the preparation of biodegradable polymer based modified drug release systems with desired properties for peptides delivery.

Recycling antibiotics into GUMBOS: a new combination strategy to combat multi-drug-resistant bacteria

The emergence of multi-drug-resistant bacteria, coupled with the lack of new antibiotics in development, is fast evolving into a global crisis. New strategies utilizing existing antibacterial agents are urgently needed. We propose one such strategy in which four outmoded β-lactam antibiotics (ampicillin, carbenicillin, cephalothin and oxacillin) and a well-known antiseptic (chlorhexidine di-acetate) were fashioned into a group of uniform materials based on organic salts (GUMBOS) as an alternative to conventional combination drug dosing strategies. The antibacterial activity of precursor ions (e.g., chlorhexidine diacetate and β-lactam antibiotics), GUMBOS and their unreacted mixtures were studied with 25 clinical isolates with varying antibiotic resistance using a micro-broth dilution method. Acute cytotoxicity and therapeutic indices were determined using fibroblasts, endothelial and cervical cell lines. Intestinal permeability was predicted using a parallel artificial membrane permeability assay. GUMBOS formed from ineffective β-lactam antibiotics and cytotoxic chlorhexidine diacetate exhibited unique pharmacological properties and profound antibacterial activity at lower concentrations than the unreacted mixture of precursor ions at equivalent stoichiometry. Reduced cytotoxicity to invasive cell types commonly found in superficial and chronic wounds was also observed using GUMBOS. GUMBOS show promise as an alternative combination drug strategy for treating wound infections caused by drug-resistant bacteria.

A novel approach for antibody nanocarriers development through hydrophobic ion-pairing complexation

IgG-Fab fragment, a model antibody protein was hydrophobically modified by a novel approach of ion-pairing complexation. Three different sulphated ion-pairing agents were utilised including sodium dodecyl sulphate, taurocholic acid and dextran sulphate (DS). The formations of hydrophobic ion-pairing (HIP) complexes were dependant on pH and molar ratio of ion-pairing agent to Fab. Aqueous solubilities of HIP complexes were very low compared to Fab alone. In particular, when dextran sulphate was added as ion-pairing agent, formed Fab:DS HIP complexes were least soluble in water. Further, nanoparticles (NPs) loaded with drug and Fab:DS HIP complex were prepared and characterised with respect to encapsulation efficiency and size. We observed significant improvement in encapsulation efficiency for Fab:DS HIP complex-loaded nanoparticles. This study demonstrates a novel approach of formulating antibody-loaded nanoparticles which can also be employed for delivery of large antibodies.

Formation of ion pairing as an alternative to improve encapsulation and anticancer activity of all-trans retinoic acid loaded in solid lipid nanoparticles

This work aims to develop solid lipid nanoparticles (SLNs) loaded with retinoic acid (RA) to evaluate the influence of two lipophilic amines, stearylamine (SA) and benethamine (BA), and one hydrophilic, triethylamine (TA), on drug-encapsulation efficiency (EE) and cytotoxicity in cancer cell lines. The SLNs were characterized for EE, size, and zeta potential. The mean particle size decreased from 155 ± 1 nm (SLNs without amine) to 104 ± 4, 95 ± 1, and 96 ± 1 nm for SLNs prepared with SA, BA, and TA, respectively. SA-RA-loaded SLNs resulted in positively charged particles, whereas those with TA and BA were negatively charged. The EEs were significantly improved with the addition of the amines, and they increased from 36% ± 6% (without amine) to 97% ± 2%, 90% ± 2%, and 100% ± 1% for SA, TA, and BA, respectively. However, stability studies showed higher EE for BA-RA-loaded SLNs than TA-RA-loaded SLNs after 30 days. The formulations containing SA loaded or unloaded (blank SLNs) with RA were cytotoxic in normal and cancer cell lines. In contrast, the blank SLNs containing TA or BA did not show cytotoxicity in human breast adenocarcinoma cells (MCF-7), while RA-loaded SLNs with the respective amines were significantly more cytotoxic than free RA. Furthermore, the cytotoxicity of BA-RA-loaded SLNs was significantly higher than TA-RA-loaded SLNs. These findings are in agreement with the data obtained in the evaluation of subdiploid DNA content and cell-cycle analysis, which showed better anticancer activity for BA-RA-loaded SLNs than TA-RA-loaded SLNs and free RA. Taken together, these findings suggest that the BA-RA-loaded SLN formulation is a promising alternative for the intravenous administration of RA in the treatment of cancer.

Enabling the intestinal absorption of highly polar antiviral agents: ion-pair facilitated membrane permeation of zanamivir heptyl ester and guanidino oseltamivir

Antiviral drugs often suffer from poor intestinal permeability, preventing their delivery via the oral route. The goal of this work was to enhance the intestinal absorption of the low-permeability antiviral agents zanamivir heptyl ester (ZHE) and guanidino oseltamivir (GO) utilizing an ion-pairing approach, as a critical step toward making them oral drugs. The counterion 1-hydroxy-2-naphthoic acid (HNAP) was utilized to enhance the lipophilicity and permeability of the highly polar drugs. HNAP substantially increased the log P of the drugs by up to 3.7 log units. Binding constants (K(11(aq))) of 388 M(-1) for ZHE-HNAP and 2.91 M(-1) for GO-HNAP were obtained by applying a quasi-equilibrium transport model to double-reciprocal plots of apparent octanol-buffer distribution coefficients versus HNAP concentration. HNAP enhanced the apparent permeability (P(app)) of both compounds across Caco-2 cell monolayers in a concentration-dependent manner, as substantial P(app) (0.8-3.0 x 10(-6) cm/s) was observed in the presence of 6-24 mM HNAP, whereas no detectable transport was observed without counterion. Consistent with a quasi-equilibrium transport model, a linear relationship with slope near 1 was obtained from a log-log plot of Caco-2 P(app) versus HNAP concentration, supporting the ion-pair mechanism behind the permeability enhancement. In the rat jejunal perfusion assay, the addition of HNAP failed to increase the effective permeability (P(eff)) of GO. However, the rat jejunal permeability of ZHE was significantly enhanced by the addition of HNAP in a concentration-dependent manner, from essentially zero without HNAP to 4.0 x 10(-5) cm/s with 10 mM HNAP, matching the P(eff) of the high-permeability standard metoprolol. The success of ZHE-HNAP was explained by its >100-fold stronger K(11(aq)) versus GO-HNAP, making ZHE-HNAP less prone to dissociation and ion-exchange with competing endogenous anions and able to remain intact during membrane permeation. Overall, this work presents a novel approach to enable the oral delivery of highly polar antiviral drugs, and provides new insights into the underlying mechanisms governing the success or failure of the ion-pairing strategy to increase oral absorption.

Characterization of physiochemical and biological properties of an insulin/lauryl sulfate complex formed by hydrophobic ion pairing

An insulin/lauryl sulfate complex was prepared by hydrophobic ion pairing (HIP). The physiochemical and biological properties of the HIP complex were characterized using octanol/water partition measurement, isothermal titration calorimetry (ITC), ultraviolet-circular dichroism (UV-CD) and Fourier transform infrared spectroscopy (FTIR). Sodium dodecyl sulfate (SDS) bound to the insulin in a stoichiometric manner. The formed complex exhibited lipophilicity, and its insulin retained its native structure integrity. The in vivo bioactivity of the complex insulin was evaluated in rats by monitoring the plasma glucose level after intravenous (i.v.) injection, and the glucose level was compared with that for free insulin. The pharmacodynamic study result in rats showed that the complex insulin had in vivo bioactivity comparable to free insulin.

Mechanism of permeability-enhancing effect of EDTA and boric acid on the corneal penetration of 4-[1-hydroxy-1-methylethyl]-2-propyl-1-[4-[2-[tetrazole-5-yl]phenyl]phenyl] methylimidazole-5-carboxylic acid monohydrate (CS-088)

This study was conducted to clarify the penetration properties of 4-[1-hydroxy-1-methylethyl]-2-propyl-1-[4-[2-[tetrazole-5-yl]phenyl]phenyl]methylimidazole-5-carboxylic acid monohydrate (CS-088), an ophthalmic agent, and the mechanism of the permeability-enhancing effect of EDTA and boric acid (EDTA/boric acid) on the corneal penetration of CS-088. In the absence of additives, corneal permeability decreased with increasing concentration of CS-088 as CS-088 monomers self-associate to form dimers. Presence of EDTA/boric acid caused no significant changes in the physicochemical properties of CS-088, the apparent partition coefficient or the mean particle size of CS-088. EDTA/boric acid induced only a slight change in the zeta potential of liposomes used as a model of the biological membrane. On the other hand, EDTA/boric acid significantly increased membrane fluidity of liposomes, whereas other buffering agents tested did not. This effect was synergistic and concentration-dependent for both EDTA and boric acid as was observed in in vitro corneal penetration of CS-088. In accordance with the result, the rate of CS-088 permeation into the liposomes significantly increased by the addition of EDTA/boric acid. Therefore, it was demonstrated that EDTA/boric acid promotes corneal penetration of CS-088 through the transcellular pathway by increasing membrane fluidity. Conversely, other buffering agents decreased corneal permeability of CS-088 by inducing further self-association of CS-088 aggregates.

Degradation kinetics of high molecular weight poly(L-lactide) microspheres and release mechanism of lipid:DNA complexes

Plasmid DNA encoding the green lantern protein was ion-paired with 1,2-dioleoyl, 3-trimethylammonium propane (DOTAP) at a (+/-) charge ratio of (1:1) to form a hydrophobic ion-pair (HIP) complex using the Bligh and Dyer method, and transferred into methylene chloride. Precipitation with a compressed antisolvent (PCA) was then employed to encapsulate plasmid DNA into poly(L-lactide) (PLLA) microspheres. The hydrophobicity of DOTAP:DNA complexes allowed consistently high encapsulation efficiencies (>70%) to be achieved. Release of the DOTAP:DNA complex from PLLA microspheres exhibited minimal burst and a short (ca. 1 week) lag phase, followed by sustained release over a 20 week period. Release kinetics were consistent with a simple Fickian diffusion model. No correlation was identified between release rate of soluble poly(L-lactide) species (< or =10 lactate units) from PLLA and the DNA release kinetics. Only approximately 12% of the polymer was degraded into soluble poly(L-lactide) over the time frame where approximately 90% of the plasmid load had been released.

Determination of Solvation Descriptors for Ionic Species: Hydrogen Bond Acidity and Basicity

Literature values of Gibbs energies of transfer of ions from water to other solvents have been used in conjunction with our solvation equation to obtain descriptors for univalent ions. It is suggested that descriptors used for nonelectrolytes are not adequate to describe transfers of single ions, and that two specific ionic descriptors (J(+) and J(-)) for cations and anions, respectively, are required. The ions studied include the alkali metal and tetraalkylammonium cations, halide and other anions, and the tetraphenylarsonium, tetraphenylphosphonium, and tetraphenylborate ions. It is shown that simple cations such as Na(+) act as very strong hydrogen bond acids and that the R(4)N(+) ions are only weak hydrogen bond acids. The halide anions are very strong hydrogen bond bases, as is also the acetate anion. Other anions, such as azide, cyanide, and nitrate, are again very strong hydrogen bond bases. The tetraphenylarsonium, tetraphenylphosphonium, and tetraphenylborate ions have no hydrogen bond acidity but are quite strong hydrogen bond bases. It is suggested that this is due to the basic properties of the phenyl groups.