Synthesis and evaluation of sulfosuccinate-based surfactants as counterions for hydrophobic ion pairing

Comparative Analysis of PEG-Free and PEG-Based Self-Emulsifying Drug Delivery Systems for Enhanced Oral Bioavailability of Therapeutic (Poly) Peptides

This study aims to compare the potential of Polyethylene glycol (PEG-free and PEG-based self-emulsifying drug delivery systems (SEDDS) for the oral administration of insulin glargine (IG). Hydrophobic ion pairs (HIPs) of IG are formed using various counterions. HIPs are assessed for log P octanol/water and dissociation behavior. They are incorporated into SEDDS based on polyglycerol (PG) and zwitterionic surfactant (ZW) using response surface methodology and compared to conventional PEG-SEDDS in size, stability, and log D SEDDS/release medium. Oral IG bioavailability in PG/ZW-SEDDS and PEG-SEDDS is evaluated in rats. Among the various counterions studied, IG-BIS (bis(isotridecyl)sulfosuccinate) HIPs demonstrated the highest log P and an improved dissociation profile. PG/ZW-SEDDS and PEG-SEDDS have similar ≈40 nm sizes and are stable over 24 h. Both formulations have log D > 4 in water and >2 in 50 mM phosphate buffer pH 6.8. PG/ZW-SEDDS yielded an oral bioavailability of 2.13 ± 0.66% for IG, while the employment of PEG-SEDDS resulted in an oral bioavailability of 1.15 ± 0.35%. This study highlights the prospective utilization of PEG-free SEDDS involving the concurrent application of PG and ZW surfactants, an alternative to conventional PEG surfactants, for improved oral therapeutic (poly) peptide delivery.

Green Synthesis of Cation Exchange Membranes: A Review

Cation exchange membranes (CEMs) play a significant role in the transition to a more sustainable/green society. They are important components for applications such as water electrolysis, artificial photosynthesis, electrodialysis and fuel cells. Their synthesis, however, is far from being sustainable, affecting safety, health and the environment. This review discusses and evaluates the possibilities of synthesizing CEMs that are more sustainable and green. First, the concepts of green and sustainable chemistry are discussed. Subsequently, this review discusses the fabrication of conventional perfluorinated CEMs and how they violate the green/sustainability principles, eventually leading to environmental and health incidents. Furthermore, the synthesis of green CEMs is presented by dividing the synthesis into three parts: sulfonation, material selection and solvent selection. Innovations in using gaseous SO3 or gas-liquid interfacial plasma technology can make the sulfonation process more sustainable. Regarding the selection of polymers, chitosan, cellulose, polylactic acid, alginate, carrageenan and cellulose are promising alternatives to fossil fuel-based polymers. Finally, water is the most sustainable solvent and many biopolymers are soluble in it. For other polymers, there are a limited number of studies using green solvents. Promising solvents are found back in other membrane, such as dimethyl sulfoxide, Cyrene™, Rhodiasolv® PolarClean, TamiSolve NxG and γ-valerolactone.

Power-Up for Mucoadhesiveness: Two Generations of Thiolated Surfactants for Enhanced Sticky Nanoemulsions

Nanoemulsions can be tuned toward enhanced gastro-intestinal retention time by incorporating thiolated surfactants into their surface. Tailoring the chemical reactivity of the thiol headgroup has major influence on mucoadhesive features of the nanoemulsion. Two generations of thiolated surfactants were synthetically derived from PEG-40-stearate featuring either a free thiol group or an S-protected thiol group. The surfactants were characterized regarding critical micelle concentration (CMC), hemolytic activity, and cytotoxicity. Subsequently, they were incorporated into nanoemulsions and the resulting nanoemulsions were characterized regarding particle size, polydispersity index (PDI), zeta potential, and time-dependent stability. Afterward, mucosal interactions as well as mucoadhesion on porcine intestinal mucosa were investigated. Successful synthesis of Cysteine-PEG-40-stearate (CYS-PEG-40-stearate) and MNA-Cysteine-PEG-40-stearate (MNA-CYS-PEG-40-stearate) was confirmed by 1H NMR spectroscopy. Both chemical modifications led to slightly elevated CMC values while preserving low cytotoxicity and hemotoxicity. Incorporation into nanoemulsions had minor influence on overall physical particle characteristics, while interactions with mucus and mucoadhesiveness of the nanoemulsions were drastically improved resulting in the rank order PEG-40-stearate < CYS-PEG-40-stearate < MNA-CYS-PEG-40-stearate. Accordingly, thiolated surfactants, especially S-protected derivatives, are versatile tools to generate highly mucoadhesive nanoemulsions.

Counterion optimization for hydrophobic ion pairing (HIP): Unraveling the key factors

In the present study, various surfactants were combined with insulin (INS), bovine serum albumin (BSA) and horseradish peroxidase (HRP) via hydrophobic ion pairing to increase lipophilicity and facilitate incorporation into self-emulsifying drug delivery systems (SEDDS). Lipophilicity of model proteins was successfully increased, achieving log Dn-butanol/water values up to 3.5 (INS), 3.2 (BSA) and 1.2 (HRP). Hereby, key factors responsible for complex formation were identified. In particular, surfactants with branched alkyl chains or chain lengths greater than C12 showed favorable properties for hydrophobic ion pairs (HIP). Furthermore, flexibility of the carbon chain resulted in higher lipophilicity and suitability of polar head groups of surfactants for HIP decreased in the rank order sulfonate > sulfosuccinate > phosphate = sulfate > carbonate > phosphonic acids = sulfobetaines. Stability studies of formed HIP complexes were performed in various gastrointestinal fluids and their solubility was determined in commonly used SEDDS excipients. Formed complexes were stable in simulated gastrointestinal fluids and could be incorporated into SEDDS formulations (C1: 10% caprylocaproyl polyoxyl-8 glycerides, 20% PEG-40 hydrogenated castor oil, 20% medium-chain triglycerides, 50% n-butanol; C2: 10% caprylocaproyl polyoxyl-8 glycerides, 20% PEG-40 hydrogenated castor oil, 20% medium-chain triglycerides, 40% n-butanol, 10% 1,2-butanediol), resulting in suitable payloads of up to 11.9 mg/ml for INS, 1.0 mg/ml for BSA and 1.6 mg/ml for HRP.

Biodegradable Cationic and Ionizable Cationic Lipids: A Roadmap for Safer Pharmaceutical Excipients

Cationic and ionizable cationic lipids are broadly applied as auxiliary agents, but their use is associated with adverse effects. If these excipients are rapidly degraded to endogenously occurring metabolites such as amino acids and fatty acids, their toxic potential can be minimized. So far, synthesized and evaluated biodegradable cationic and ionizable cationic lipids already showed promising results in terms of functionality and safety. Within this review, an overview about the different types of such biodegradable lipids, the available building blocks, their synthesis and cleavage by endogenous enzymes is provided. Moreover, the relationship between the structure of the lipids and their toxicity is described. Their application in drug delivery systems is critically discussed and placed in context with the lead compounds used in mRNA vaccines. Moreover, their use as preservatives is reviewed, guidance for their design is provided, and an outlook on future developments is given.

Hydrophobic Ion Pairing of Small Molecules: How to Minimize Premature Drug Release from SEDDS and Reach the Absorption Membrane in Intact Form

The present work aimed to form hydrophobic ion pairs (HIPs) of a small molecule remaining inside the oily droplets of SEDDS to a high extent. HIPs of ethacridine and various surfactants classified by functional groups of phosphates, sulfates, and sulfonates were formed and precipitation efficiency, log D_{n-octanol/water}, and solubility in different excipients were investigated. Most lipophilic HIPs were incorporated into SEDDS and evaluated regarding drug release. Docusate HIPs showed the highest increase in lipophilicity with a precipitation efficiency of 100%, a log D_{n-octanol/water} of 2.66 and a solubility of 132 mg/mL in n-octanol, 123 mg/mL in oleyl alcohol, and 40 mg/mL in medium chain triglycerides. Docusate HIPs were incorporated into three SEDDS of increasing lipophilicity (F1 < F2 < F3) based on medium chain triglycerides, oleyl alcohol, Kolliphor EL, and Tween 80 (F1: 1 + 5 + 2 + 2; F2: 3 + 3 + 2 + 2; F3: 5 + 1 + 4 + 0). Highest achievable payloads ranged from 74.49 mg/mL (F3) to 97.13 mg/mL (F1) and log D_SEDDS/RM increased by at least 7.5 units (4.99, F1). Drug release studies via the diffusion membrane method confirmed minor release of docusate HIPs from all SEDDS (<2.7% within 4 h). In conclusion, highly lipophilic HIPs remain inside the oily phase of SEDDS and likely reach the absorption membrane in intact form.

Oral delivery of calcitonin-ion pairs: In vivo proof of concept for a highly lipophilic counterion

Hydrophobic ion pairing and subsequent incorporation into self-emulsifying drug delivery systems (SEDDS) is a promising strategy to orally deliver hydrophilic macromolecular drugs. Within this study, hydrophobic ion pairs (HIP) between salmon calcitonin (sCT) and highly lipophilic sulfosuccinate counterions were formed and compared to frequently applied commercially available counterions. Bis(isotridecyl) sulfosuccinate resulted in HIPs of the highest lipophilicity and in significantly higher solubility in lipophilic co-solvents. Thus, bis(isotridecyl) sulfosuccinate allowed efficient solubilization of sCT in a SEDDS preconcentrate based on a lipophilic co-solvent and an indigestible lipid, but omitting hydrophilic co-solvents. In addition to the increased solubility in the lipidic matrix, markedly reduced dissociation in biorelevant media resulted in high distribution coefficients between oil droplet and FaSSGF or FaSSIF (logD) of 2.98 ± 0.12 or 2.77 ± 0.14, respectively. The composition of the lipidic matrix preserved integrity of the oil droplets after emulsification and subsequent lipolysis, allowing to fully exploit the potential of the HIP attributed to the high logD. Oral administration of the HIP-loaded SEDDS resulted in an excellent relative pharmacological activity of 13.8 ± 5.6 % measured as hypocalcaemic effect in rats.

Biodegradable arginine based steroid-surfactants: Cationic green agents for hydrophobic ion-pairing

The aim of this study was to evaluate the safety and efficacy for hydrophobic ion-pairing of surfactants based on arginine (Arg). The prepared Arg-cholesteryl ester (ACE) and Arg-diosgenyl ester (ADE) were characterized regarding solubility, pKa, critical micellar concentration (CMC), biodegradability as well as membrane- and aquatic toxicity using DOTAP as reference. The ability for hydrophobic ion-pairing was evaluated and the lipophilicity of formed complexes was determined. NMR, FT-IR and MS confirmed successful synthesis of Arg-surfactants. The slightly soluble single-charged Arg-surfactants (pH < pKa₃ (ACE = 10.42 ± 0.52; ADE = 10.38 ± 0.27)) showed CMCs of 27.17 µM for ACE and 35.67 µM for ADE. CMCs of the sparingly soluble double-charged species (pH < pKa₂ (ACE = 5.30 ± 0.20; ADE = 5.55 ± 0.06)) were determined at concentrations of ≥ 250 µM for ACE and ≥ 850 µM for ADE. The enzymatic- and environmental biodegradability was proven by an entire cleavage of Arg-surfactants within 24 h, whereas DOTAP remained stable. Arg-surfactants exhibited lower membrane- (> 2-fold) and aquatic toxicity (> 15-fold) than DOTAP. The complexes formed with Arg-surfactants and insulin showed higher lipophilicity than the DOTAP-complex. According to these results, Arg-surfactants might be a promising safe tool for the delivery of peptide drugs.