The aim of this study was to evaluate biodegradable cationic surfactants based on lysine. Methods: Lysine was esterified with cholesterol, oleyl alcohol and 1-decanol resulting in cholesteryl lysinate (CL), oleyl lysinate (OL) and decyl lysinate (DL). Esters were investigated regarding their log D noctanol/water , critical micelle concentration (CMC) and biodegradability. Hemolytic potential of CL, OL, DL and the already established hexadecyl lysinate (HL) was determined and complexes with insulin (INS) were formed by hydrophobic ion pairing (HIP). Lipophilic characteristics of ion-pairs were examined by analyzing their log P n-butanol/water. Results: Successful synthesis of CL, OL and DL was confirmed by IR, NMR and MS. Log D analysis revealed amphiphilic properties for the esters and a CMC of 0.01 mM, 2.0 mM and 6.0 mM was found for CL, OL and DL, respectively. Biodegradability was proven, as over 99% of OL and DL were degraded by isolated enzymes within 30 min and after 3 h 97% of CL was cleaved by membrane bound enzymes. OL as well as DL displayed no hemolytic effect and for CL cytotoxicity was significantly reduced in comparison to HL. INS/CL complex exhibited highest lipophilicity. Conclusion: Cholesterol-amino acid based surfactants seem to be promising agents for HIP.
In the present study, chitosan (CS) was thiolated by introducing l -cysteine via amide bond formation. Free thiol groups were protected with highly reactive 6-mercaptonicotinic acid (6-MNA) and less-reactive l -cysteine, respectively, via thiol/disulfide-exchange reactions. Unmodified CS, l -cysteine-modified thiolated CS (CS-Cys), 6-MNA-S-protected thiolated CS (CS-Cys-MNA), and l -cysteine-S-protected thiolated CS (CS-Cys-Cys) were applied as coating materials to solid lipid nanoparticles (SLN). The strength of mucus interaction followed the rank order plain < CS < CS-Cys-Cys < CS-Cys < CS-Cys-MNA, whereas mucus diffusion followed the rank order CS-Cys < CS-Cys-Cys < CS < CS-Cys-MNA < plain. In accordance with lower reactivity, CS-Cys-Cys-coated SLN were immobilized to a lower extent than CS-Cys-coated SLN, while CS-Cys-MNA-coated SLN dissociated from their coating material resulting in a similar diffusion behavior as plain SLN. Consequently, CS-Cys-Cys-coated SLN and CS-Cys-MNA-coated SLN showed the highest retention on porcine intestinal mucosa by enabling a synergism of efficient mucus diffusion and strong mucoadhesion.
The use of cationic and ionizable cationic lipids in pharmaceutical products, however, is a double-edged sword, as these excipients are of considerable safety concerns. Because of their permanent or pHdependent cationic nature, they perturbate cellular and nuclear membranes, trigger the release of degrading enzymes from lysosomes, cause mitochondrial permeabilization and dysfunction, generate reactive oxygen species (ROS), alter cytoplasmatic enzyme functions, and damage DNA. [3] To address this substantial shortcoming of cationic and ionizable cationic lipids, biodegradable alternatives have been introduced that are rapidly degraded in vivo to preferably endogenous metabolites. The design of such lipids is inspired by natural cationic or ionizable cationic compounds like arginine, lysine or betaine that are generally regarded as safe. Their conjugation to endogenous lipids like fatty acids or cholesterol results in amphiphilic lipids. As ester and amide bonds are cleaved in vivo by numerous enzymes such as lipases, esterases, and proteases, they are the preferred linkages between these natural building blocks.Since the FDA approved ethyl Nα-lauroyl-l-arginate as biodegradable food preservative being effective against a broad range of Gram-positive and Gram-negative bacteria, yeasts, and molds in 2005, [4] the potential use of biodegradable cationic and ionizable cationic lipids as pharmaceutical excipients has been evaluated by numerous research groups. As these excipients exhibit the same properties as their non-biodegradable counterparts but causing relatively low adverse effects, they will likely substitute currently used non-biodegradable lipids in the future. Within this review, we provide an overview on the different types of biodegradable cationic and ionizable cationic lipids, their synthesis and cleavage by endogenous enzymes. Applications in drug delivery systems and as antimicrobial agents are discussed. A guideline on their design and application is provided and an outlook on future developments is given. Building Blocks and Formation of Cationic and Ionizable Cationic LipidsGenerally, biodegradable cationic and ionizable cationic lipids are composed of biocompatible building blocks that are conjugated via a linkage such as an ester or amide bond. [5] Representative building blocks and linkages are depicted in Figure 1. Endogenous enzymes can break these linkages and degrade 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 aim of this study was to investigate the fate and the impact of cosolvents in self-emulsifying drug delivery systems (SEDDS). Three different SEDDS comprising the cosolvents DMSO (F D ), ethanol (F E ), and benzyl alcohol (F BA ) as well as the corresponding formulations without these cosolvents (F D0 , F E0 , and F BA0 ) were developed. Mean droplet size, polydispersity index (PDI), ζ potential, stability, and emulsification time were determined. Cosolvent release studies were performed via the dialysis membrane method and Taylor dispersion analysis (TDA). Furthermore, the impact of cosolvent utilization on payloads in SEDDS was examined using quinine as a model drug. SEDDS with and without a cosolvent showed no significant differences in droplet size, PDI, and ζ potential. The emulsification time was 3-fold (F D0 ), 80-fold (F E0 ), and 7-fold (F BA0 ) longer due to the absence of the cosolvents. Release studies in demineralized water provided evidence for an immediate and complete release of DMSO, ethanol, and benzyl alcohol. TDA confirmed this result. Moreover, a 1.4-fold (F D ), 2.91-fold (F E ), and 2.17-fold (F BA ) improved payload of the model drug quinine in the selected SEDDS preconcentrates was observed that dropped after emulsification within 1–5 h due to drug precipitation. In parallel, the quinine concentrations decreased until reaching the same levels of the corresponding SEDDS without cosolvents. Due to the addition of hydrophilic cosolvents, the emulsifying properties of SEDDS are strongly improved. As hydrophilic cosolvents are immediately released from SEDDS during the emulsification process, however, their drug solubilizing properties in the resulting oily droplets are very limited.
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