Cellular uptake of self-emulsifying drug-delivery systems: polyethylene glycol versus polyglycerol surface

Food emulsifiers aggravate inflammation and oxidative stress induced by food contaminants in zebrafish

Food emulsifiers like glycerol monostearate (G) and Tween 80 (TW) are commonly used to help formation and maintain stability of emulsions. However, certain food contaminants and emulsifiers often co-occur in the same food item due to food culture and cooking methods. For this reason, the present study investigated interaction of toxic effect of emulsifiers (G and TW) and process contaminants (acrylamide (AA) and benzo [a]pyrene (BAP)) on zebrafish. Adult zebrafish were exposed to emulsifiers, food contaminants, or the combination through diet for 2 h and 7 days. Oxidative stress and inflammation caused by food contaminants were increased when food emulsifiers were present. These combined treatments also induced more severe morphological changes than the contaminant alone treatments. In the gut, disruption of villi structure and increased number of goblet cells was observed and in the liver there were increased lipid deposition, infiltration of immune cells, glycogen depletion and focal necrosis. Increased accumulation of AA and BAP in the liver and gut were detected after addition of emulsifiers, suggesting that emulsifiers can enhance absorption of diet-borne contaminants. Our results showed food emulsifiers and contaminants can interact synergistically and increase risk.

Oral formulations for highly lipophilic drugs: Impact of surface decoration on the efficacy of self-emulsifying drug delivery systems

AIM

To evaluate the impact of the surface decoration of cannabidiol (CBD) loaded self-emulsifying drug delivery systems (SEDDS) on the efficacy of the formulations to cross the various barriers faced by orally administered drugs.

METHODS

Polyethylene glycol (PEG)-free polyglycerol (PG)-based SEDDS, mixed zwitterionic phosphatidyl choline (PC)/PEG-containing SEDDS and PEG-based SEDDS were compared regarding stability against lipid degrading enzymes, surface properties, permeation across porcine mucus, cellular uptake and cytocompatibility.

RESULTS

SEDDS with a size of about 200 nm with narrow size distributions were developed and loaded with 20-21 % of CBD. For PG containing PEG-free SEDDS increased degradation by lipid degrading enzymes was observed compared to PEG-containing formulations. The surface hydrophobicity of placebo SEDDS increased in the order of PG-based to mixed PC/PEG-based to PEG-based SEDDS. The influence of this surface hydrophobicity was also observed on the ability of the SEDDS to cross the mucus gel layer where highest mucus permeation was achieved for most hydrophobic PEG-based SEDDS. Highest cellular internalization was observed for PEG-based Lumogen Yellow (LY) loaded SEDDS with 92 % in Caco-2 cells compared to only 30 % for mixed PC/PEG-based SEDDS and 1 % for PG-based SEDDS, leading to a 100-fold improvement in cellular uptake for SEDDS having highest surface hydrophobicity. For cytocompatibility all developed placebo SEDDS showed similar results with a cell survival of above 75 % for concentrations below 0.05 % on Caco-2 cells.

CONCLUSION

Higher surface hydrophobicity of SEDDS to orally deliver lipophilic drugs as CBD seems to be a promising approach to increase the intracellular drug concentration by an enhanced permeation through the mucus layer and cellular internalization.

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.

Design of charge converting lipid nanoparticles via a microfluidic coating technique

It was the aim of this study to design charge converting lipid nanoparticles (LNP) via a microfluidic mixing technique used for the preparation and coating of LNP. LNP consisting of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), cholesterol, N-(carbonyl-methoxypolyethyleneglycol-2000)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (MPEG-2000-DSPE), and various cationic surfactants were prepared at diverging flow rate ratios (FRR) via microfluidic mixing. Utilizing a second chip in the microfluidic set-up, LNP were coated with polyoxyethylene (9) nonylphenol monophosphate ester (PNPP). LNP were examined for their stability in different physiologically relevant media as well as for hemolytic and cytotoxic effects. Finally, phosphate release and charge conversion of PNPP-coated LNP were evaluated after incubation with alkaline phosphatase and on Caco2-cells. LNP produced at an FRR of 5:1 exhibited a size between 80 and 150 nm and a positive zeta potential. Coating with PNPP within the second chip led to LNP exhibiting a negative zeta potential. After incubation with 1 U/ml alkaline phosphatase for 4 h, zeta potential of the LNP containing 1,2-dioleoyloxy-3-trimethylammonium-propane chloride (DOTAP) as cationic component shifted from - 35 mV to approximately + 5 mV. LNP prepared with other cationic surfactants remained slightly negative after enzymatic phosphate cleavage. Manufacturing of LNP containing PNPP and DOTAP via connection of two chips in a microfluidic instrument proves to show efficient change in zeta potential from negative to positive after incubation with alkaline phosphatase.

Overcoming intestinal barriers by heparanase-responsive charge-converting nanocarriers

In this study, we present a novel approach for overcoming intestinal barriers by utilizing heparanase-responsive charge-converting nanocarriers (NCs). These NCs are designed to undergo charge conversion in response to the activity of heparanase (HPSE), an enzyme commonly overexpressed in cancer cells. Nanostructured lipid carriers (NLCs) and solid lipid nanocarriers (SLNs) with a positively charged core were coated with heparin (Hep), resulting in a negative surface charge and a size between 195 and 220 nm. However, upon encountering heparanase, heparin undergoes enzymatic cleavage, resulting in zeta potential shift from -22.1 to +8.3 mV for NLC-Hep and from -19.8 to +5.1 mV for SLN-Hep. Heparin-coated NCs showed more than 6-fold higher mucus permeating properties compared to the uncoated NCs. In vitro experiments using the heparanase-expressing cancer cell line HT29 demonstrated an up to 4-fold improved cellular uptake of the heparin coated NCs compared to co-incubation with the HPSE inhibitor suramin. Furthermore, cellular uptake was investigated on Caco-2 cells and on a Caco-2/HT29-MTX co-culture. Overall, this study highlights the potential of heparanase-responsive charge-converting NCs as a promising strategy for overcoming intestinal barriers and enhancing cellular uptake.

PEG vs. zwitterions: How these surface decorations determine cellular uptake of lipid-based nanocarriers

AIM

To evaluate the impact of polyethylene glycol (PEG) and zwitterionic surface decoration of lipid-based nanocarriers (NC) on cellular uptake.

METHODS

Anionic, neutral and cationic zwitterionic lipid-based NCs based on lecithin were compared with conventional PEGylated lipid-based NCs regarding stability in biorelevant fluids, interaction with endosome mimicking membranes, cytocompatibility, cellular uptake and permeation across intestinal mucosa.

RESULTS

PEGylated and zwitterionic lipid-based NCs exhibited a droplet size between 100 and 125 nm with a narrow size distribution. For the PEGylated and zwitterionic lipid-based NCs only minor alterations in size and PDI in fasted state intestinal fluid and mucus containing buffer were observed, demonstrating similar bioinert properties. Erythrocytes interaction studies revealed enhanced endosomal escape properties for zwitterionic lipid-based NCs compared to PEGylated lipid-based NCs. For the zwitterionic lipid-based NCs negligible cytotoxicity on Caco-2 and HEK cells, even in the highest tested concentration of 1 % (v/v) was recorded. The PEGylated lipid-based NCs showed a cell survival of ≥75 % for concentrations ≤0.05 % on Caco-2 and HEK cells, which was considered as non-toxic. For the zwitterionic lipid-based NCs up to 60-fold higher cellular uptake on Caco-2 cells was determined compared to PEGylated lipid-based NCs. For the cationic zwitterionic lipid-based NCs the highest cellular uptake with 58.5 % and 40.0 % in Caco-2 and HEK cells, respectively, was determined. The results were confirmed visually by life cell imaging. Ex-vivo permeation experiments using rat intestinal mucosa demonstrated up to 8.6-fold enhanced permeation of the lipophilic marker coumarin-6 in zwitterionic lipid-based NCs compared to the control. Up to 6.9-fold enhanced permeation of coumarin-6 in neutral zwitterionic lipid-based NCs compared to the PEGylated counterpart was recorded.

CONCLUSION

The replacement of PEG surfactants with zwitterionic surfactants is a promising approach to overcome the drawbacks of conventional PEGylated lipid-based NCs regarding intracellular drug delivery.

Thiolated α-cyclodextrin: The likely smallest drug carrier providing enhanced cellular uptake and endosomal escape

This study aimed to evaluate the effect of thiolated α-cyclodextrin (α-CD-SH) on the cellular uptake of its payload. For this purpose, α-CD was thiolated using phosphorous pentasulfide. Thiolated α-CD was characterized by FT-IR and ¹H NMR spectroscopy, differential scanning calorimetry (DSC), and powder X-ray diffractometry (PXRD). Cytotoxicity of α-CD-SH was evaluated on Caco-2, HEK 293, and MC3T3 cells. Dilauryl fluorescein (DLF) and coumarin-6 (Cou) serving as surrogates for a pharmaceutical payload were incorporated in α-CD-SH, and cellular uptake was analyzed by flow cytometry and confocal microscopy. Endosomal escape was investigated by confocal microscopy and hemolysis assay. Results showed no cytotoxic effect within 3 h, while dose-dependent cytotoxicity was observed within 24 h. The cellular uptake of DLF and Cou was up to 20- and 11-fold enhanced by α-CD-SH compared to native α-CD, respectively. Furthermore, α-CD-SH provided an endosomal escape. According to these results, α-CD-SH is a promising carrier to shuttle drugs into the cytoplasm of target cells.

Bilosomes as Nanocarriers for the Drug and Vaccine Delivery against Gastrointestinal Infections: Opportunities and Challenges

The gastrointestinal tract (GIT) environment has an intricate and complex nature, limiting drugs' stability, oral bioavailability, and adsorption. Additionally, due to the drugs' toxicity and side effects, renders are continuously seeking novel delivery systems. Lipid-based drug delivery vesicles have shown various loading capacities and high stability levels within the GIT. Indeed, most vesicular platforms fail to efficiently deliver drugs toward this route. Notably, the stability of vesicular constructs is different based on the different ingredients added. A low GIT stability of liposomes and niosomes and a low loading capacity of exosomes in drug delivery have been described in the literature. Bilosomes are nonionic, amphiphilic, flexible surfactant vehicles that contain bile salts for the improvement of drug and vaccine delivery. The bilosomes' stability and plasticity in the GIT facilitate the efficient carriage of drugs (such as antimicrobial, antiparasitic, and antifungal drugs), vaccines, and bioactive compounds to treat infectious agents. Considering the intricate and harsh nature of the GIT, bilosomal formulations of oral substances have a remarkably enhanced delivery efficiency, overcoming these conditions. This review aimed to evaluate the potential of bilosomes as drug delivery platforms for antimicrobial, antiviral, antifungal, and antiparasitic GIT-associated drugs and vaccines.

Development of Environmentally Responsive Self-Emulsifying System Containing Copaiba Oil-Resin for Leishmaniasis Oral Treatment

Leishmaniasis is a disease caused by protozoa species of the Leishmania genus, and the current treatments face several difficulties and obstacles. Most anti-leishmanial drugs are administered intravenously, showing many side effects and drug resistance. The discovery of new anti-leishmanial compounds and the development of new pharmaceutical systems for more efficient and safer treatments are necessary. Copaiba oil-resin (CO) has been shown to be a promising natural compound against leishmaniasis. However, CO displays poor aqueous solubility and bioavailability. Self-emulsifying drug delivery systems (SEDDS) can provide platforms for release of hydrophobic compounds in the gastrointestinal tract, improving their aqueous solubilization, absorption and bioavailability. Therefore, the present work aimed to develop SEDDS containing CO and Soluplus® surfactant for the oral treatment of leishmaniasis. The design of the systems was accomplished using ternary phase diagrams. Emulsification and dispersion time tests were used to investigate the emulsification process in gastric and intestinal environments. The formulations were nanostructured and improved the CO solubilization. Their in vitro antiproliferative activity against promastigote forms of L. amazonensis and L. infantum, and low in vitro cytotoxicity against macrophages were also observed. More studies are necessary to determine effectiveness of SOL in these systems, which can be candidates for further pharmacokinetics and in vivo investigations.

Oral drug delivery: Influence of mucus on cellular interactions and uptake of lipid-based nanocarriers in Caco-2 cells

This study aimed to investigate the impact of the mucus gel barrier on intestinal mucosal uptake of lipid-based nanocarriers (NCs). Zwitterionic- (ZW), polyglycerol- (PG) and polyethylene glycol- (PEG) surfactant-based o/w nanoemulsions were developed. NCs were assessed regarding their size and zeta potential, stability in biorelevant media and mucus, mucus permeation behavior, cellular interactions and uptake by Caco-2 cells with and without mucus and by a Caco-2/HT29-MTX co-culture. All NCs were in the size range of 178 - 204 nm and exhibited a zeta potential between -4.2 and +1.2 mV. ZW- and PG-NCs demonstrated mucus permeating properties comparable to PEG-NCs. In contrast, ZW- and PG-NCs showed high cellular uptake, whereas limited cellular uptake was observed in case of PEG-NCs. Furthermore, mucus on Caco-2 cells as well as the mucus secreting co-culture had a significant impact on the cellular uptake of all tested NCs. According to these results, ZW- and PG-NCs are advantageous to overcome the mucus and epithelial barrier of the intestinal mucosa. STATEMENT OF SIGNIFICANCE: Within this study the impact of mucus on cellular uptake of lipid-based nanocarriers (NCs) with different surface decorations was investigated. The potential of NCs with zwitterionic-, polyglycerol- and polyethylene glycol-surfactants on their surface to overcome the mucus and epithelial barrier was evaluated. Zwitterionic- and polyglycerol-NCs showed mucus permeating properties similar to PEG-NCs. In contrast, zwitterionic- and polyglycerol-NCs substantially outperformed PEG-NCs in their cellular uptake properties. According to these findings, zwitterionic- and polyglycerol-NCs have the potential to overcome both the mucus and epithelial barrier of the mucosa.

Lipid-based nanoparticles: Enhanced cellular uptake via surface thiolation

The aim of this study was to evaluate the uptake mechanism of thiolated nanostructured lipid carriers (NLCs). NLCs were decorated with a short-chain polyoxyethylene(10)stearyl ether with a terminal thiol group (NLCs-PEG₁₀-SH) or without (NLCs-PEG₁₀-OH) as well as with a long-chain polyoxyethylene(100)stearyl ether with thiolation (NLCs-PEG₁₀₀-SH) or without (NLCs-PEG₁₀₀-OH). NLCs were evaluated for size, polydispersity index (PDI), surface morphology, zeta potential and storage stability over six months. Cytotoxicity, adhesion to the cell surface and internalization of these NLCs in increasing concentrations were evaluated on Caco-2 cells. The influence of NLCs on the paracellular permeability of lucifer yellow was determined. Furthermore, cellular uptake was examined with and without various endocytosis inhibitors as well as reducing and oxidizing agents. NLCs were obtained in a size ranging from 164 to 190 nm, a PDI of 0.2, a negative zeta potential < -33 mV and stability over six months. Cytotoxicity was shown to be concentration dependent and to be lower for NLCs with shorter PEG chains. Permeation of lucifer yellow was 2-fold increased by NLCs-PEG₁₀-SH. All NLCs displayed concentration dependent adhesion to the cell surface and internalization, which was in particular 9.5-fold higher for NLCs-PEG₁₀-SH compared to NLCs-PEG₁₀-OH. Short PEG chain NLCs and especially thiolated short PEG chain NLCs showed higher cellular uptake than NLCs with longer PEG chain. Cellular uptake of all NLCs was mainly clathrin-mediated endocytosis. Thiolated NLCs showed also caveolae-dependent and clathrin- and caveolae-independent uptake. Macropinocytosis was involved in NLCs with long PEG chains. NLCs-PEG₁₀-SH indicated thiol-dependent uptake, which was influenced by reducing and oxidizing agents. Due to thiol groups on the surface of NLCs their cellular uptake and paracellular permeation enhancing properties can be substantially improved.

Surface design of nanocarriers: Key to more efficient oral drug delivery systems

As nanocarriers (NCs) can improve the solubility of drugs, prevent their degradation by gastrointestinal (GI) enzymes and promote their transport across the mucus gel layer and absorption membrane, the oral bioavailability of these drugs can be substantially enhanced. All these properties of NCs including self-emulsifying drug delivery systems (SEDDS), solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs), liposomes, polymeric nanoparticles, inorganic nanoparticles and polymeric micelles depend mainly on their surface chemistry. In particular, interaction with food, digestive enzymes, bile salts and electrolytes, diffusion behaviour across the mucus gel layer and fate on the absorption membrane are determined by their surface. Bioinert surfaces limiting interactions with gastrointestinal fluid and content as well as with mucus, adhesive surfaces providing an intimate contact with the GI mucosa and absorption enhancing surfaces can be designed. Furthermore, charge converting surfaces shifting their zeta potential from negative to positive directly at the absorption membrane and surfaces providing a targeted drug release are advantageous. In addition to these passive surfaces, even active surfaces cleaving mucus glycoproteins on their way through the mucus gel layer can be created. Within this review, we provide an overview on these different surfaces and discuss their impact on the performance of NCs in the GI tract.

Nonviral delivery systems for antisense oligonucleotide therapeutics

Antisense oligonucleotides (ASOs) are an important tool for the treatment of many genetic disorders. However, similar to other gene drugs, vectors are often required to protect them from degradation and clearance, and to accomplish their transport in vivo. Compared with viral vectors, artificial nonviral nanoparticles have a variety of design, synthesis, and formulation possibilities that can be selected to accomplish protection and delivery for specific applications, and they have served critical therapeutic purposes in animal model research and clinical applications, allowing safe and efficient gene delivery processes into the target cells. We believe that as new ASO drugs develop, the exploration for corresponding nonviral vectors is inevitable. Intensive development of nonviral vectors with improved delivery strategies based on specific targets can continue to expand the value of ASO therapeutic approaches. Here, we provide an overview of current nonviral delivery strategies, including ASOs modifications, action mechanisms, and multi-carrier methods, which aim to address the irreplaceable role of nonviral vectors in the progressive development of ASOs delivery.

Development and In Vitro Characterization of Transferrin-Decorated Nanoemulsion Utilizing Hydrophobic Ion Pairing for Targeted Cellular Uptake

Purpose

The aim of this study was to develop transferrin-conjugated nanoemulsions utilizing hydrophobic ion pairing for a targeted cellular uptake.

Methods

In the lipophilic phase of nanoemulsion composed of 60% oleic acid, 30% Capmul MCM EP and 10% Span 85, 1% cetyltrimethylammonium bromide (CTAB) and 3% phosphatidic acid (PA) were incorporated. After emulsification, the resulting droplets were decorated with human protein transferrin via hydrophobic ion pairing with PA and characterized regarding droplet size and zeta potential. Subsequently, cellular uptake of transferrin-conjugated nanoemulsion was investigated on Caco-2 and HeLa cell lines and determined by flow cytometry, cell lysis method and live cell imaging using confocal laser scanning microscopy.

Results

The nanoemulsion showed a droplet size of 123.03 ± 2.1 nm and zeta potential of − 54.5 mV that changed because of the surface decoration with transferrin to 182.7 ± 0.2 and + 30.2 mV, respectively. Within the uptake studies utilizing flow cytometry, transferrin-conjugated nanoemulsion showed a 5.2-fold higher uptake in Caco-2 cells and twofold improvement in case of HeLa cells compared with unmodified formulation. The outcome was confirmed visually via live cell imaging.

Conclusion

According to the results, transferrin-conjugated nanoemulsion might be considered as a promising drug delivery system for a selective receptor-mediated drug delivery.

Thiolation of non-ionic surfactants for the development of lipid-based mucoadhesive drug delivery systems

The aim of this study was to develop thiolated self-emulsifying drug delivery systems (SEDDS) and nanostructured lipid carriers (NLCs) with improved mucoadhesive properties. Two non-ionic surfactants bearing a short and long PEG chain, namely polyoxyethylene (10) stearyl ether (PSE₁₀) and polyoxyethylene (100) stearyl ether (PSE₁₀₀), were thiolated for the first time by substituting the terminal hydroxyl group with a thiol group. The synthesis was confirmed by FT-IR, NMR and Ellman's test. SEDDS and NLCs containing these thiolated compounds were investigated for size, polydispersity index (PDI) and ζ potential. Subsequently, mucus diffusion studies, rheological evaluations after mixing the nanocarriers with mucus and mucoadhesion studies on porcine intestinal mucosa were performed. All nanocarriers had a size less than 250 nm, a maximum PDI of 0.3 and a ζ potential < -9.0 mV. Mucus diffusion studies resulted in the rank order of increasing diffusivity: PSE₁₀-SH < PSE₁₀₀-SH < PSE₁₀-OH < PSE₁₀₀-OH for NLCs and PSE₁₀-OH < PSE₁₀₀-OH < PSE₁₀₀-SH < PSE₁₀-SH for SEDDS. The mucoadhesive properties and increase in viscosity of SEDDS and NLCs ranked: PSE₁₀₀-OH < PSE₁₀-OH < PSE₁₀₀-SH < PSE₁₀-SH. In addition, the short chain PSE₁₀-SH showed higher mucus interactions than the long chain PSE₁₀₀-SH for both SEDDS and NLCs. The thiolated PSE surfactants appeared to be promising excipients for the design of highly mucoadhesive drug delivery systems.

Design of nanostructured lipid carriers and solid lipid nanoparticles for enhanced cellular uptake

In this study PEG-free and zeta potential changing lipid-based nanocarriers providing enhanced cellular uptake were developed. Nanostructured lipid carriers (NLC), consisting of paraffin wax, caprylic/ capric triglyceride, cetyltrimethylammoniumchloride and either soy lecithin or polyglycerol-4 laurate and solid lipid nanoparticles (SLN) with the same composition but without the liquid lipid content were developed. All formulations exposed a positive surface charge and were then coated with the polyphosphate Graham's salt. Phosphate release from these formulations was evaluated by incubation with intestinal alkaline phosphatase as well as on a Caco-2 monolayer and zeta potentials were measured. Additionally, cellular uptake studies were performed. Within 5 h, a remarkable amount of phosphate was released from all formulations incubated with intestinal alkaline phosphatase. Enzymatically induced phosphate release with intestinal alkaline phosphatase led to a zeta potential shift up to Δ 26 mV. Results of phosphate release and zeta potential change were confirmed on Caco-2 cells. Cellular uptake studies on Caco-2 cells showed an up to 5.6-times higher uptake compared to cells with inhibited phosphatase. According to these results, polyphosphate coating is a powerful tool to obtain lipid-based nanocarriers for enhanced cellular uptake.

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

Hydrophobic ion pairing is a promising strategy to raise the lipophilic character of therapeutic peptides and proteins. In past studies, docusate, an all-purpose surfactant with a dialkyl sulfosuccinate structure, showed highest potential as hydrophobic counterion. Being originally not purposed for hydrophobic ion pairing, it is likely still far away from the perfect counterion. Thus, within this study, docusate analogues with various linear and branched alkyl residues were synthesized to derive systematic insights into which hydrophobic tail is most advantageous for hydrophobic ion pairing, as well as to identify lead counterions that form complexes with superior hydrophobicity. The successful synthesis of the target compounds was confirmed by FT-IR, ¹H-NMR, and ¹³C-NMR. In a screening with the model protein hemoglobin, monostearyl sulfosuccinate, dioleyl sulfosuccinate, and bis(isotridecyl) sulfosuccinate were identified as lead counterions. Their potential was further evaluated with the peptides and proteins vancomycin, insulin, and horseradish peroxidase. Dioleyl sulfosuccinate and bis(isotridecyl) sulfosuccinate significantly increased the hydrophobicity of the tested peptides and proteins determined as logP or lipophilicity determined as solubility in 1-octanol, respectively, in comparison to the gold standard docusate. Dioleyl sulfosuccinate provided an up to 8.3-fold higher partition coefficient and up to 26.5-fold higher solubility in 1-octanol than docusate, whereas bis(isotridecyl) sulfosuccinate resulted in an up to 6.7-fold improvement in the partition coefficient and up to 44.0-fold higher solubility in 1-octanol. The conjugation of highly lipophilic alkyl tails to the polar sulfosuccinate head group allows the design of promising counterions for hydrophobic ion pairing. STATEMENT OF SIGNIFICANCE: Hydrophobic ion pairing enables efficient incorporation of hydrophilic molecules into lipid-based formulations by forming complexes with hydrophobic counterions. Docusate, a sulfosuccinate with two branched alkyl tails, has shown highest potential as anionic hydrophobic counterion. As it was originally not purposed for hydrophobic ion pairing, its structure is likely still far away from the perfect counterion. To improve its properties, analogues of docusate with various alkyl tails were synthesized in the present study. The investigation of different alkyl residues allowed to derive systematic insights into which tail structures are most favorable for hydrophobic ion pairing. Moreover, the lead counterions dioleyl sulfosuccinate and bis(isotridecyl) sulfosuccinate bearing highly lipophilic alkyl tails provided a significant improvement in the hydrophobicity of the resulting complexes.

Replacing PEG-surfactants in self-emulsifying drug delivery systems: Surfactants with polyhydroxy head groups for advanced cytosolic drug delivery

AIM

Evaluation of different polyhydroxy surfaces in SEDDS to overcome the limitations associated with conventional polyethylene glycol (PEG)-based SEDDS surfaces for intracellular drug delivery.

METHODS

Anionic, cationic and non-ionic polyglycerol- (PG-) and alkylpolyglucoside- (APG-) surfactant based SEDDS were developed and compared to conventional PEG-SEDDS. Particular emphasis was placed on the impact of SEDDS surface decoration on size and zeta potential, drug loading and protective effect, mucus diffusion, SEDDS-cell interaction and intracellular delivery of the model drug curcumin.

RESULTS

After self-emulsification, SEDDS droplets sizes were within the range of 35-190 nm. SEDDS formulated with high amounts of long PEG-chain surfactants (>10 monomers) a charge-shielding effect was observed. Replacing PEG-surfactants with PG- and an APG-surfactant did not detrimentally affect SEDDS self-emulsification, payloads or the protection of incorporated curcumin towards oxidation. PG- and APG-SEDDS bearing multiple hydroxy functions on the surface demonstrated mucus permeation comparable to PEG-SEDDS. Steric hinderance and charge-shielding of PEG-SEDDS surface substantially reduced cellular uptake up to 50-fold and impeded endosomal escape, yielding in a 20-fold higher association of PEG-SEDDS with lysosomes. In contrast, polyhydroxy-surfaces on SEDDS promoted pronounced cellular internalisation and no lysosomal co-localisation was observed. This improved uptake resulted in an over 3-fold higher inhibition of tumor cell proliferation after cytosolic curcumin delivery.

CONCLUSION

The replacement of PEG-surfactants by surfactants with polyhydroxy head groups in SEDDS is a promising approach to overcome the limitations for intracellular drug delivery associated with conventional PEGylated SEDDS surfaces.

Oral delivery of therapeutic peptides and proteins: Technology landscape of lipid-based nanocarriers

The oral administration of therapeutic peptides and proteins is favoured from a patient and commercial point of view. In order to reach the systemic circulation after oral administration, these drugs have to overcome numerous barriers including the enzymatic, sulfhydryl, mucus and epithelial barrier. The development of oral formulations for therapeutic peptides and proteins is therefore necessary. Among the most promising formulation approaches are lipid-based nanocarriers such as oil-in-water nanoemulsions, self-emulsifying drug delivery systems (SEDDS), solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), liposomes and micelles. As the lipophilic character of therapeutic peptides and proteins can be tremendously increased such as by the formation of hydrophobic ion pairs (HIP) with hydrophobic counter ions, they can be incorporated in the lipophilic phase of these carriers. Since gastrointestinal (GI) peptidases as well as sulfhydryl compounds such as glutathione and dietary proteins are too hydrophilic to enter the lipophilic phase of these carriers, the incorporated therapeutic peptide or protein is protected towards enzymatic degradation as well as unintended thiol/disulfide exchange reactions. Stability of lipid-based nanocarriers towards lipases can be provided by the use to excipients that are not or just poorly degraded by these enzymes. Nanocarriers with a size <200 nm and a mucoinert surface such as PEG or zwitterionic surfaces exhibit high mucus permeating properties. Having reached the underlying absorption membrane, lipid-based nanocarriers enable paracellular and lymphatic drug uptake, induce endocytosis and transcytosis or simply fuse with the cell membrane releasing their payload into the systemic circulation. Numerous in vivo studies provide evidence for the potential of these delivery systems. Within this review we provide an overview about the different barriers for oral peptide and protein delivery, highlight the progress made on lipid-based nanocarriers in order to overcome them and discuss strengths and weaknesses of these delivery systems in comparison to other technologies.

Charge-reversal nanoemulsions: A systematic investigation of phosphorylated PEG-based surfactants

Surfactants bearing monophosphate esters with PEG of increasing chain length and different lipophilic tail structures were investigated to improve the effectiveness of enzyme triggered charge-converting nanoemulsions. The surfactants PEG-8-stearate, PEG-22-tocopheryl succinate (TPGS), PEG-3-oleate, PEG-9-oleate and PEG-9-lauryl ether were phosphorylated and incorporated in a self-emulsifying drug delivery system (SEDDS) exhibiting a defined PEG corona. To provide a positive zeta potential increasing amounts of the cationic surfactant benzalkonium chloride (BA) were incorporated. The effect of these PEG monophosphate esters (P-PEG-surfactants) was evaluated based on enzyme induced phosphate release and change in zeta potential. Significant enzyme induced charge conversion was observed for all P-PEG-surfactants, showing shifts from Δ3 mV to Δ31 mV. Surfactants comprising the shortest and longest PEG chain showed similar amplitudes (P-PEG-3-oleate: Δ11.9 mV; P-PEG-22-TPGS Δ10.2 mV), whereas P-PEG-8-stearate, P-PEG-9-oleate and P-PEG-9-lauryl ether bearing similarly long PEG chains but different lipophilic tail structures resulted in pronounced differences in amplitudes of Δ10.3 mV, Δ14.5 mV and Δ18.1 mV, respectively. Furthermore, an indirect correlation between the lipophilicity of P-PEG-surfactants and the obtained charge-reversing effect was observed. With the exception of P-PEG-lauryl ether, this charge-reversal effect decreased with increasing BA concentrations. In conclusion, the enzyme induced amplitude of charge conversion of P-PEG-surfactants depends to a high extent on their lipophilic tail structure. Based on this knowledge potent charge-reversal nanoemulsions can be designed.

Charge reversal self-emulsifying drug delivery systems: A comparative study among various phosphorylated surfactants

HYPOTHESIS

Phosphorylated surfactants having ethoxylate spacer arms are promising excipients for charge reversal self-emulsifying drug delivery systems (SEDDS).

EXPERIMENTS

1,2-Dipalmitoyl-sn-glycero-3-phosphatidic acid disodium salt (PA), 2-((2,3-bis(oleoyloxy)propyl)dimethylammonio)ethyl hydrogen phosphate (DOCP), nonylphenol monophosphate ester (PNPP), C12-15 alcohol 3 ethoxylate phosphate ester (PME) and polyoxyethylene (9) dioctanoyl glycerol pyrophosphate (DGPP) loaded SEDDS were developed and characterized. Zeta potential of SEDDS was measured before and after incubation with intestinal alkaline phosphatase (IAP). Phosphate release was monitored by incubation of SEDDS with isolated as well as cell-associated IAP. Primary amine content on the surface of SEDDS was determined in parallel. Cytotoxicity was evaluated on Caco-2 cells and in vitro hemolysis test was performed. Cellular uptake studies were performed by confocal scanning microscopy.

FINDINGS

SEDDS formulations exhibited a size in the range of 17 and 193 nm and a polydispersity index (PDI) ≤ 0.5. Charge reversal from negative to positive values could be achieved in case of PNPP and PME loaded SEDDS with a zeta potential changing from -13 mV to +9 mV and from -7 to +2 mV, respectively, within 6 h. Significant amounts of phosphate were released from PNPP and PME loaded SEDDS incubated with isolated IAP and from all formulations incubated with cell-associated IAP in accordance with an increase in primary amines on the surface of oily droplets. SEDDS exhibited a concentration and time-dependent cytotoxicity. PNPP and PME SEDDS displayed an increased cellular uptake.

Polyphosphate coatings: A promising strategy to overcome the polycation dilemma

AIM

It was the aim of this study to develop a zeta potential changing drug delivery system by decorating lipid-based nanocarriers with a polycationic cell penetrating peptide (CPP) and subsequently masking these cationic substructures with polyphosphates.

METHODS

In order to anchor the CPP poly-l-lysine (PLL) on the surface of the oily droplets of an o/w nanoemulsion, stearic acid was covalently attached to the peptide. The resulting CPP-decorated oily droplets were coated with phytic acid and tripolyphosphate. The elimination of these polyphosphates due to cleavage by alkaline phosphatase was monitored by the release of monophosphate from the surface of the nanocarriers, by the change in zeta potential and by cellular uptake studies on Caco-2 cells.

RESULTS

Polyphosphate coated PLL-decorated nanocarriers exhibited a pronounced conversion of zeta potential from -14.1 mV to +4.2 mV in case of tripolyphosphate coated nanocarriers and from -9.9 mV to -2.6 mV in case of phytic acid coated nanocarriers. The cellular uptake on Caco-2 cells of the polyphosphate coated nanocarriers was 4-fold improved compared to the control nanocarriers. Furthermore, confocal images showed that the majority of nanodroplets distributed in cytoplasm not being internalized into lysosomes.

CONCLUSION

Polyphosphate coating of CPP-decorated nanocarriers seems to be a promising and simple strategy to overcome the polycation dilemma.