Zeta Potential Of Liposomes Research Articles

Charge boosting effect of cholesterol on cationic liposomes

Cationic liposomes that have been used as drug or gene delivery vehicles can be obtained by mixing cationic surfactants in phospholipid liposomes. Cytotoxicity of cationic molecules is one of the problems of the cationic nanocarriers. Therefore we aimed to formulate highly positively-charged cationic liposomes with low content of cationic surfactant, which have both higher cellular uptake ability and lower cytotoxicity. We have investigated the zeta potential behavior in water/soy bean lecithin/cationic surfactant/cholesterol systems by the changing composition as well as the molecular structure of the cationic surfactant. Mixing of monoalkyl (C12, C16 and C18) and dialkyl (C12 and C18) quaternary ammonium chlorides were increased the zeta potential of liposomes from negative to positive values (more than +50mV). Mixing the cholesterol into the cationic liposomes increased the maximum zeta potential further and also induced the large shift of the negative-positive transition point with respect to the cationic surfactant mixing fraction. It means much less cationic surfactant is needed to obtain highly positively-charged liposomes. The significant cholesterol effects on the zeta potential of liposomes were explained based on the lipid distribution inhomogeneity caused by the increased fluidity of liquid ordered phase membranes and the large critical packing parameter of the negatively-charged lipid.

Aggregation of PEGylated liposomes driven by hydrophobic forces

Polyethylene glycol (PEG) is widely used to sterically stabilize liposomes and improve the pharmacokinetic profile of drugs, peptides and nanoparticles. Here we report that ammonium sulfate (AS) can evoke the aggregation of PEGylated vesicles in a concentration-dependent manner. Liposomes with 5mol% PEG were colloidally stable at AS concentrations up to 0.7mM, above which they precipitated and formed micron-size aggregates with irregular shape. While aggregation was reversible up to 0.9M of AS, above 1M fusion occurred, which irreversibly distorted the size distribution. Zeta potential of liposomes markedly increased from −71±2.5mV to 2±0.5mV upon raising the AS concentration from 0 to 0.1M, but no considerable increase was seen during further AS addition, showing that the aggregation is independent of surface charge. There was no aggregation in the absence of the PEG chains, and increasing PEG molar% shifted the aggregation threshold to lower AS concentrations. Changes in the FTIR spectral features of PEGylated vesicles suggest that AS dehydrates PEG chains. Other kosmotropic salts also led to aggregation, while chaotropic salts did not, which indicates a general kosmotropic phenomenon. The driving force behind aggregation is likely to be the hydrophobic effect due to salting out the polymer similarly to what happens during protein purification or Hydrophobic Interaction Chromatography. Since liposome aggregation and fusion may result in difficulties during formulation and adverse reaction upon application, the phenomena detailed in this paper may have both technological and therapeutical consequences.

Zeta potential and surface charge of DPPC and DOPC liposomes in the presence of PLC enzyme

Zeta potential of liposomes is often measured in studies of their properties and/or applications. However, there are not many papers published in which zeta potential was determined during enzymatic reaction of a lipid. Therefore in this paper size, polydispersity index, and zeta potentials of 1,2-dipalmitoylsn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) liposomes were investigated in 1 mM NaCl (pH 6.2) and phosphate buffer (pH 8.1) during 60 min of phospholipase C action at 20 and 37 °C. The hydrocarbon chains saturation differ these two phospholipids what appears in some differences in the zeta potential changes during the hydrolysis reaction run. The polydispersity index of the liposomes indicates that they are relatively stable and monodisperse, except for DPPC in phosphate buffer where up to 30 % of the initial amount forms larger size moieties, possibly aggregates of the liposomes, enzyme and the hydrolysis products. However, in this buffer zeta potential of the liposomes practically does not change during PLC action. Also the changes of zeta potential of DOPC liposomes are minor, although their negative values are much smaller than those of DPPC at both temperatures. These small changes of the potential may be due to compression of the diffuse double layer by present phosphate buffer. However, distinct changes of the zeta potentials in the presence of PLC take place in NaCl solution. The observed changes can be explained by reorientation of the phospholipid polar heads and their different density on DPPC and DOPC surface of the liposomes. Although it appeared that the zeta potential is not a very sensitive parameter for tracking the hydrolysis reaction in phosphate buffer, generally zeta potential enables the characterization of such reactions through determination of electrokinetic properties of liposomes as well as the polydispersity and size distribution of the liposomes do.

Anti-Cancer Efficacy of Paclitaxel Loaded in pH Triggered Liposomes.

Smart liposomes that are responsive to the microenvironment of tumor tissue have been utilized to enhance chemotherapeutic efficiency. Here, we reported a novel liposome called Trojan horse liposome, which has a pH response, to enhance drug accumulation in tumor sites and intercellular uptake. L-lysine was used as a linker to connect 2,3-dimethylmaleic anhydride (DMA) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (DSPE) to yield a DSPE-Lys-DMA (DLD) lipid. The pH-responsive DLD was mixed with other commercially available lipids to form liposomes. The size, morphology and zeta potential of the DLD liposomes (DLD-Lip) were measured. Paclitaxel (PTX) was loaded in the liposomes. The release profile, cellular uptake, in vitro and in vivo anticancer activity of the PTX-loaded liposomes were investigated. The results showed that the mean diameter of the liposomes was less than 200 nm. The zeta potential of the liposomes was negative at pH 7.4. However, it was transferred to positive at weak acidic pH values with the cleavage of DMA amide. The charge reversion of DMA in acidic environments facilitated the cellular internalization and endosome escape of DLD-Lip, which inhibited the proliferation of 4T1 cancer cells in vitro. The pH-responsive "Trojan horse"-like liposomes also exhibited efficient anticancer activity in the xenograft breast cancer model in vivo.

Single-Tailed Lipidoids Enhance the Transfection Activity of Their Double-Tailed Counterparts.

Cationic lipid-like molecules (lipidoids) are widely used for in vitro and in vivo gene delivery. Nearly all lipidoids developed to date employ double-tail or multiple-tail structures for transfection. Single-tail lipidoids are seldom considered for transfection as they have low efficiency in gene delivery. So far, there is no detailed study on the contribution to transfection efficiency of single-tail lipidoids when combined with standard double-tail lipidoids. Here, we use combinatorial chemistry to synthesize 17 double-tail and 17 single-tail lipidoids using thiol-yne and thiol-ene click chemistry, respectively. HEK 293T cells were used to analyze transfection efficiency by fluorescence microscopy and calculated based on the percentage of cells transfected. The size and zeta potential of liposomes and lipoplexes were characterized by dynamic light scattering (DLS). Intracellular DNA delivery and trafficking was further examined using confocal microscopy. Our study shows that combining single with double-tail lipidoids increases uptake of lipoplexes, as well as cellular transfection efficiency.

DOTAP/DOPE ratio and cell type determine transfection efficiency with DOTAP-liposomes

The effects of lipid compositions on their physicochemical properties and transfection efficiencies were investigated. Four liposome formulations with different 1,2-dioleoyl-3-trimethylammoniumpropane (DOTAP) to dioleoylphosphatidylethanolamine (DOPE) weight ratios were investigated, that is, weight ratios 1:0 (T1P0), 3:1 (T3P1), 1:1 (T1P1), and 1:3 (T1P3). Mean sizes of liposomes were influenced by their lipid composition and the preparation concentration at the time of sonication. Zeta potentials of liposomes were inversely correlated with their liposome sizes. However, neither liposome sizes nor zeta potentials were correlated with transfection efficiency. The optimum composition of liposomes was cell-line dependent (T1P0 and T3P1 for Huh7 and AGS, T3P1 and T1P1 for COS7, and T1P1 and T1P3 for A549). The shape of lipoplexes was changed from lamellar to inverted hexagonal structure according to the increased ratio of DOPE, but there was no definite advantage of specific structure in transfection efficiency throughout all used cell lines. However, cellular internalization was consistently faster in T1P0, T3P1, T1P1 compared to T1P3 in all cell lines, suggesting the importance of endosomal escape. Our findings show that the transfection efficiency of DOTAP liposomes is mainly influenced by lipid composition and cell type, and not by size or zeta potential.

Preparation and characterization of liposomes coated with DEAE-Dextran

Abstract Liposomes as effective drug delivery vehicles have played significant role in therapeutics. However physicochemical instability of liposomes reduces its possibilities and potentials to be used in drug delivery systems. The present work describes the stabilization of liposome via electrostatic deposition of a polycationic derivative of dextran which is Diethylaminoethyl Dextran (DEAE-Dx) on soy lecithin liposome. Liposomes were prepared by thin film hydration method. The critical vesicular concentration (CVC) of lecithin was found at 0.1% (w/v) through surface tension analysis. Zeta potential and differential scanning calorimetry (DSC) measurements were obtained to study the interaction between DEAE-Dx and liposomes. The zeta potential of liposomes changed from negative value to increasingly positive after addition of DEAE-Dx. This confirmed the coating of liposomes by DEAE-Dx. Stability of the DEAE-Dx liposome suspension was studied through particle size and zeta potential measurements over a period of 35 days. DEAE-Dx liposome suspension was found more stable than the uncoated liposomes suspension. The optimum concentration of DEAE-Dx incorporated with liposome was observed at 0.02% (w/v) compared to other examined concentration of DEAE-Dx. Encapsulation efficiency of DEAE-Dx coated liposome loaded with curcumin shows slightly higher value compared to the uncoated ones.

The enhancement of gene silencing efficiency with chitosan-coated liposome formulations of siRNAs targeting HIF-1α and VEGF

RNA interference (RNAi) holds considerable promise as a novel therapeutic strategy in the silencing of disease-causing genes. The development of effective delivery systems is important for the use of small interfering RNA (siRNA) as therapy. In the present study, we investigated the effect on breast cancer cell lines and the co-delivery of liposomes containing siHIF1-α and siVEGF. In order to achieve the co-delivery of siHIF1-α and siVEGF and to obtain lower cytotoxicity, higher transfection and silencing efficiency, in this study, we used chitosan-coated liposomal formulation as the siRNA delivery system. The obtained particle size and zeta potential values show that the chitosan coating process is an effective parameter for particle size and the zeta potential of liposomes. The liposome formulations loaded with siHIF1-α and siVEGF showed good stability and protected siRNA from serum degradation after 24-h of incubation. The expression level of VEGF mRNA was markedly suppressed in MCF-7 and MDA-MB435 cells transfected with chitosan-coated liposomes containing HIF1-α and VEGF siRNA, respectively (95% and 94%). In vitro co-delivery of siVEGF and siHIF1-α using chitosan-coated liposome significantly inhibited VEGF (89%) and the HIF1-α (62%) protein expression when compared to other liposome formulations in the MDA-MB435 cell. The co-delivery of siVEGF and siHIF1-α was greatly enhanced in the vitro gene silencing efficiency. In addition, chitosan-coated liposomes showed 96% cell viability. Considering the role of VEGF and HIF1-α in breast cancer, siRNA-based therapies with chitosan coated liposomes may have some promises in cancer therapy.

Enhanced localization of anticancer drug in tumor tissue using polyethylenimine-conjugated cationic liposomes.

Liposome-based drug delivery systems hold great potential for cancer therapy. However, to enhance the localization of payloads, an efficient method of systemic delivery of liposomes to tumor tissues is required. In this study, we developed cationic liposomes composed of polyethylenimine (PEI)-conjugated distearoylglycerophosphoethanolamine (DSPE) as an enhanced local drug delivery system. The particle size of DSPE-PEI liposomes was 130 ± 10 nm and the zeta potential of liposomes was increased from -25 to 30 mV by the incorporation of cationic PEI onto the liposomal membrane. Intracellular uptake of DSPE-PEI liposomes by tumor cells was 14-fold higher than that of DSPE liposomes. After intratumoral injection of liposomes into tumor-bearing mice, DSPE-PEI liposomes showed higher and sustained localization in tumor tissue compared to DSPE liposomes. Taken together, our findings suggest that DSPE-PEI liposomes have the potential to be used as effective drug carriers for enhanced intracellular uptake and localization of anticancer drugs in tumor tissue through intratumoral injection.

Light- and temperature-responsive liposomes incorporating cinnamoyl Pluronic F127

Light- and temperature-responsive liposomes were prepared by immobilizing cinnamoyl Pluronic F127 (CP F127) on the surface of egg phosphatidylcholine liposomes. CP F127 was prepared by a condensation reaction, and the molar ratio of cinnamoyl group to Pluronic F127 was calculated to be 1:1.4 on (1)H NMR spectrum. The cinnamoyl group of CP F127 was readily dimerized under the irradiation of a UV light (254 nm, 6 W). CP F127 decreased the absolute value of the zeta potential of liposome possibly because it can shift the hydrodynamic plane away from the liposome surface. The size of liposome decorated with CP F127, measured on a dynamic light scattering machine and observed on a TEM, was larger than that of bare liposome. The liposome bearing CP F127 seemed to fuse and aggregate each other. The liposome released calcein, a fluorescence dye, in response to a UV irradiation, possibly because the photo-dimerization of cinnamoyl group perturbs the liposomal membrane. Moreover, the liposome released the dye in response to a temperature change, possible due to the phase transition of Pluronic F127 layer on the liposomal surface or the hydrophobic interaction of the polymer with liposomal membrane.

Mechanical and electrokinetic effects of polyamines/phospholipid interactions in model membranes.

The mechanical and electrical properties of phospholipids layers influenced by interaction with polyamines were determined by measuring surface pressure and compression modulus of monolayers and zeta potential of liposomes. The saturated derivative of phosphatidic acid (DPPA) formed layers of the organization varying with compression degree. Contact of DPPA layers with polyamines present in the subphase resulted in changing their mechanical properties and the conditions in which the layer reorganization appears. The parameters corresponding to the layer reorganization depended on the size and charge of polyamines’ molecules. The values of: area per DPPA molecule, surface pressure at the point of layer structure reorganization, and surface pressure at the point of collapse characterizing of DPPA layers in the studied systems were determined. It was found that polyamines influenced to a much lesser extent the mechanical properties of monolayers formed from unsaturated derivative of phosphatidic acid slightly increasing its mechanical resistance in the range of higher molecular packing. The results of electrokinetic measurements revealed that surface charge of phosphatidic acid liposomes was effectively neutralized in the presence of polyamines. A similar effect was observed for phosphatidyl glycerol and for negatively charged polystyrene latex particles used as a reference. The influence of polyamines on the mechanical properties of DPPA layers was interpreted assuming a possibility of penetration of the lipid layer by polyamines’ molecules. Comparison of action of putrescine and calcium ions and effects of polyamines on phosphatidyl glycerol provided additional justification for the proposed interpretation of the observed effects.Electronic supplementary materialThe online version of this article (doi:10.1007/s00232-013-9614-z) contains supplementary material, which is available to authorized users.

Investigation of parameters influencing incorporation, retention and cellular cytotoxicity in liposomal formulations of poorly soluble camptothecin

Improving tumor delivery of lipophilic drugs through identifying advanced drug carrier systems with efficient carrier potency is of high importance. We have performed an investigative approach to identify parameters that affect liposomes’ ability to effectively deliver lipophilic camptothecin (CPT) to target cells. CPT is a potent anticancer drug, but its undesired physiological properties are impairing its therapeutic use. In this study, we have identified parameters influencing incorporation and retention of lipophilic CPT in liposomes, evaluating the effect of lipid composition, lipid chemical structure (head and tail group variations, polymer inclusion), zeta potential and anisotropy. Polyethyleneglycol (PEG) surface decoration was included to avoid liposome fusing and increase the potential for prolonged in vivo circulation time. The in vitro effect of the different carrier formulations on cell cytotoxicity was compared and the effect of active targeting of one of the formulations was evaluated. We found that a combination of liposome surface charge, lipid headgroup and carbon chain unsaturation affect CPT incorporation. Retention in liposomes was highly dependent on the liposomal surroundings and liposome zeta potential. Inclusion of lipid tethered PEG provided stability and prevented liposome fusing. PEGylation negatively affected CPT incorporation while improving retention. In vitro cell culture testing demonstrated that all formulations increased CPT potency compared to free CPT, while cationic formulations proved significantly more toxic to cancer cells that healthy cells. Finally, antibody mediated targeting of one liposome formulation further enhanced the selectivity towards targeted cancer cells, rendering normal cells fully viable after 1 hour exposure to targeted liposomes.

Lipid composition of cationic nanoliposomes implicate on transfection efficiency

Cationic liposome (CL)-DNA complexes (lipoplexes) have appeared as leading nonviral gene carriers in worldwide gene therapy clinical trials. Arriving at therapeutic dosages requires the full understanding of the mechanism of transfection. However, using CLs to deliver therapeutic nucleic acids and drugs to target organs have some problems, including low transfection efficiency. The aim of this study was developing novel CLs containing four neutral lipids; cholesterol, 1,2-dioleoyl phosphatidylethanolamine, distearoylphosphatidylcholine and dipalmitoylphosphatidylcholine as a helper lipid and dimethyl dioctadecyl ammonium bromide as a cationic lipid to increase transfection efficiency. We have investigated the correlation between number of lipid composition and transfection efficiency. The morphology, size and zeta potential of liposomes and lipoplexes were measured and lipoplexes formation was monitored by gel retardation assay. Transfection efficiency was assessed using firefly luciferase reporter assay. It was found that transfection efficiency markedly depended on liposome to plasmid DNA (pDNA) weight ratio, lipid composition and efficiency of pDNA entrapment. High transfection efficiency of plasmid by four component lipoplexes was achieved. Moreover, lipoplexes showed lower transfection efficiency and less cytotoxicity compared to Lipofectamine™. These results suggest that lipid composition of nanoliposomes is an important factor in control of their physical properties and also yield of transfection.

Nanoencapsulation of quercetin and resveratrol into elastic liposomes

Based on the fact that quercetin (QUE) and resveratrol (RES) induce a synergic inhibition of the adipogenesis and increase apoptosis in adipocytes, and that sodium deoxycholate (SDC) has necrotic effects, the nanoencapsulation of QUE and RES into SDC-elastic liposomes is proposed as a new approach for dissolving the subcutaneous fat. The concentration of constituents and the effect of the drug incorporation into cyclodextrin inclusion complexes on the stability of QUE/RES-loaded liposomes were studied. The best liposomal formulation reduced the use of phosphatidylcholine and cholesterol in 17.7% and 68.4%, respectively. Liposomes presented a mean diameter of 149nm with a polydispersion index of 0.3. The zeta potential of liposomes was slightly negative (−13.3mV) due to the presence of SDC in the phospholipid bilayer. Encapsulation efficiency of QUE and RES into liposomes was almost 97%. To summarize, QUE/RES-loaded elastic liposomes are stable and suitable for subcutaneous injection, thereby providing a new strategy for reducing subcutaneous fat.

Electrophoretic mobility and zeta potential of liposomes due to arginine and polyarginine adsorption

Zeta potential determinations obtained from liposome electrophoretic mobilties provide direct evidence of the Arg orientation in the lipid interphase of phosphatidylcholine and phosphatidilethanolamine bilayers. In addition, the zeta potential of liposomes has also been used to determine the variations of the degree of coverage (θ) of individual liposomes of different lipids and to calculate the dissociation constants and the stoichiometry of the binding.The adsorption of positively charged aminoacids to these membranes deviates from a Langmuir type isotherm with the progressive demethylation of the phosphatidylcholine group suggesting that the adsorption takes place in non independent sites, probably producing surface rearrangements.The cooperative effect observed in dimirystoylphosphatidilethanolamines but not in phosphatidylcholines seems to be related to a reorganization of interfacial water as confirmed by fluorescence spectroscopy using Laurdan as an interphacial probe.It is concluded that that zeta potential measurements provide direct evidence of aminoacid orientation in a lipid interphase giving consistency of the findings suggested by MD and surface spectroscopic studies, congruent with the proposal that the guanidine group is buried in the membrane in a water environment.

Effect of quaternized chitosan on the fusion efficiency and cytocompatibility of liposomes

Liposomes of cholesterol and 1, 2-palmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) were prepared, followed by entrapping and/or coating with O-(2-hydroxyl) propyl-3-trimethyl ammonium chitosan chloride (O-HTCC). The appearance of liposome was examined using transmission electron microscope (TEM), and the loading of O-HTCC to the liposome was confirmed by infrared spectroscope. The zeta potential of liposome was measured. The antimicrobial activity of liposome against Staphylococcus aureus (ATCC 6538 P) was evaluated based on the MIC and MBC values. The results showed that the antimicrobial activity of O-HTCC loading liposome was higher than that of pure O-HTCC. The cytotoxicity of O-HTCC and O-HTCC-loading liposome was determined using L929 fibroblasts in vitro via MTT test and morphology of L-929 cells. The results showed that cytotoxicity was not observed when concentration of O-HTCC was below 100 μg/ml. By labeling with Dil, the fusion of liposome with the cell membrane of L929 was observed, and the efficiency of fusion was improved by the loading of O-HTCC.

Cholesterol-based anionic long-circulating cisplatin liposomes with reduced renal toxicity

Cholesterol anchored derivatives of 5-Cholestene-3-beta-ol 3-hemisuccinate (CHO-HS) and 1-cholesteryl-4-ω-methoxy-polyethylene glycol succinate (CHO-PEG) have been synthesized via esterification and employed at various ratios with di-stearoylphosphatidylcholine (DSPC) in the preparation of anionic long-circulating nanoliposmes for cisplatin (CDDP) delivery. In the present study, CHO-HS and CHO-PEG were characterized by FTIR and 1H NMR. The particle size and zeta potential of liposomes were determined by Dynamic lights scattering (DLS). The obtained liposomes have concentratedly distributed nanosizes around 100 nm and proper zeta potentials between −39.7 mV and −3.18 mV and good physical stability in test period of 28 days. Fine morphology of the liposomal vesicles can be observed via transmission electron microscopy (TEM). The CDDP encapsulating percentage of liposomes was 43–94% and loading efficiency was 7.5–29.3%, depending on the presence or absence of CHO-HS and CHO-PEG. In addition, the in vitro drug release behaviors, in vitro cytotoxicity against HeLa cells and 293T cells and in vivo CDDP distribution of CDDP loaded CHO-HS/CHO-PEG liposomes were evaluated. The results suggest that CHO-HS/CHO-PEG nanoliposomes represent a promising strategy for the CDDP delivery as an effective long-circulating drug carrier system which may reduce the acute renal toxicity.

The Effect of Cryoprotective Additives on the Zeta Potential of Liposomes

The Effect of Cryoprotective Additives on the Zeta Potential of Liposomes

염의 농도에 따른 DOPC 리포좀의 안정성에 관한 연구

In this study, DOPC liposomes were prepared with distilled water, phosphate buffer and phosphate buffered saline to evaluate the effects of salt on the stability of DOPC liposome. The changes in physical properties (like particle size and zeta potential) of liposome were measured after adding the salt. Liposomes were diluted 40 times and 80 times with hydration solvent to confirm the effect of dilution. Consequently, the stability of liposome was maintained up to 40 times dilution with hydration solvent. The liposome that prepared with distilled water was diluted with distilled water, phosphate buffer and phosphate buffered saline, and the liposome that prepared with phosphate buffer was diluted with phosphate buffer and phosphate buffered saline to evaluate the salt‐induced changes in particle size and zeta potentia. As results, the particle size increased slightly and zeta potential became closer to 0 when the salt concentration was increased. In conclusion, particle size and zeta potential of liposome could be reasonable factors to evaluate the stability of liposome. In addition, we suggest that salt concentration of hydration solvent has a significant effect on the stability of liposome.

Synthesis and DNA transfection properties of new head group modified malonic acid diamides

Malonic acid diamides with two long hydrophobic alkyl chains and a basic polar head group as a new class of non-viral gene transferring compounds have shown high transfection efficiency and moderate toxicity. Based on the results obtained with saturated and unsaturated alkyl residues new derivatives with a more complex head group structure have been synthesized. For this purpose, cationic respectively basic groups were introduced by one or two lysine residues bound via tris(aminoethyl)amine spacer to the malonic acid diamide backbone. By studying in vitro gene delivery an increase of transfection efficacy was observed when using lipids with at least one unsaturated alkyl chain. This leads to cationic lipids exhibiting comparable or even higher transfection efficacies compared to the commercially available transfection agents LipofectAmine™ and SuperFect™. Phase transitions and phase structures of selected compounds have been analyzed and discussed in terms of transfection abilities. Particle size and zeta potential of liposomes and lipoplexes were also determined.