Drug-induced zeta potential changes in liposomes studied by laser Doppler spectroscopy

Potential of liposomes and lipid membranes for the separation of β-blockers by capillary electromigration and liquid chromatographic techniques

β-Blockers belong to a frequently used class of drugs primarily used to treat heart and circulatory conditions. Here we describe the use of lipid vesicles and liposomes as cell membrane biomimicking models in capillary electromigration (CE) and liquid chromatography (LC) techniques for the investigation of interactions between lipid membranes and β-blockers. In addition to liposomes, the use of commercial intravenous lipid emulsions, and their interactions with β-blockers are also discussed. Different CE and LC instrumental techniques designed for these purposes are introduced. Other methodologies for studying interactions between β-blockers and lipid membranes are also briefly discussed, and the different methodologies are compared. The aim is to give the reader a good overview on the status of the use of liposomes and lipids in CE and LC for studying β-blocker interactions.

Lipidated Peptidomimetic Ligand-Functionalized HER2 Targeted Liposome as Nano-Carrier Designed for Doxorubicin Delivery in Cancer Therapy

The therapeutic index of chemotherapeutic agents can be improved by the use of nano-carrier-mediated chemotherapeutic delivery. Ligand-targeted drug delivery can be used to achieve selective and specific delivery of chemotherapeutic agents to cancer cells. In this study, we prepared a peptidomimetic conjugate (SA-5)-tagged doxorubicin (Dox) incorporated liposome (LP) formulation (SA-5-Dox-LP) to evaluate the targeted delivery potential of SA-5 in human epidermal growth factor receptor-2 (HER2) overexpressed non-small-cell lung cancer (NSCLC) and breast cancer cell lines. The liposome was prepared using thin lipid film hydration and was characterized for particle size, encapsulation efficiency, cell viability, and targeted cellular uptake. In vivo evaluation of the liposomal formulation was performed in a mice model of NSCLC. The cell viability studies revealed that targeted SA-5-Dox-LP showed better antiproliferative activity than non-targeted Dox liposomes (Dox-LP). HER2-targeted liposome delivery showed selective cellular uptake compared to non-targeted liposomes on cancer cells. In vitro drug release studies indicated that Dox was released slowly from the formulations over 24 h, and there was no difference in Dox release between Dox-LP formulation and SA-5-Dox-LP formulation. In vivo studies in an NSCLC model of mice indicated that SA-5-Dox-LP could reduce the lung tumors significantly compared to vehicle control and Dox. In conclusion, this study demonstrated that the SA-5-Dox-LP liposome has the potential to increase therapeutic efficiency and targeted delivery of Dox in HER2 overexpressing cancer.

Computational and Experimental Approaches to Investigate Lipid Nanoparticles as Drug and Gene Delivery Systems

Lipid nanoparticles (LNPs) have been widely applied in drug and gene delivery. More than twenty years ago, DoxilTM was the first LNPs-based drug approved by the US Food and Drug Administration (FDA). Since then, with decades of research and development, more and more LNP-based therapeutics have been used to treat diverse diseases, which often offer the benefits of reduced toxicity and/or enhanced efficacy compared to the active ingredients alone. Here, we provide a review of recent advances in the development of efficient and robust LNPs for drug/gene delivery. We emphasize the importance of rationally combining experimental and computational approaches, especially those providing multiscale structural and functional information of LNPs, to the design of novel and powerful LNP-based delivery systems.

Bilosomes as Promising Nanovesicular Carriers for Improved Transdermal Delivery: Construction, in vitro Optimization, ex vivo Permeation and in vivo Evaluation

Purpose

The goal of this research was to enhance the transdermal delivery of lornoxicam (LX), using nanovesicular carriers composed of the bile salt sodium deoxycholate (SDC), soybean phosphatidyl choline (SPC) and a permeation enhancer limonene.

Methods

Thin-film hydration was the technique employed for the fabrication using a Box–Behnken design with three central points. The investigated factors were SPC molar concentration, SDC amount in mg and limonene percentage (%). The studied responses were percent entrapment efficiency (%EE), particle size (PS), polydispersity index (PDI), zeta potential (ZP), and in vitro drug release (after 2, 10 h). In order to obtain the optimum formula, numerical optimization by Design-Expert® software was used. Electing the optimized bilosomal formula was based on boosting %EE, ZP (as absolute value) and in vitro drug release, taking in consideration diminishing PS and PDI. Further assessment of the selected formula was achieved by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), stability testing, ex vivo skin permeation and deposition. The in vivo pharmacodynamics activities of the optimized formula were examined on male rats and mice and compared to that of the oral market product.

Results

The optimized bilosomal formula demonstrated to be nonirritant, with noticeably enhanced anti-inflammatory and antinociceptive activities. Superior in vivo permeation was proved by confocal laser scanning microscopy (CLSM).

Conclusion

The outcomes demonstrated that bilosomes could improve transdermal delivery of lornoxicam.

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Dynamic Light Scattering Based Microelectrophoresis: Main Prospects and Limitations

Microelectrophoresis based on the dynamic light scattering (DLS) effect has been a major tool for assessing and controlling the conditions for stability of colloidal systems. However, both the DLS methods for characterization of the hydrodynamic size of dispersed submicron particles and the theory behind the electrokinetic phenomena are associated with fundamental and practical approximations that limit their sensitivity and information output. Some of these fundamental limitations, including the spherical approximation of DLS measurements and an inability of microelectrophoretic analyses of colloidal systems to detect discrete charges and differ between differently charged particle surfaces due to rotational diffusion and particle orientation averaging, are revisited in this work. Along with that, the main prospects of these two analytical methods are mentioned. A detailed review of the role of zeta potential in processes of biochemical nature is given too. It is argued that although zeta potential has been used as one of the main parameters in controlling the stability of colloidal dispersions, its application potentials are much broader. Manipulating surface charges of interacting species in designing complex soft matter morphologies using the concept of zeta potential, intensively investigated recently, is given as one of the examples. Branching out from the field of colloid chemistry, DLS and zeta potential analyses are now increasingly finding application in drug delivery, biotechnologies, physical chemistry of nanoscale phenomena and other research fields that stand on the frontier of the contemporary science. Coupling the DLS-based microelectrophoretic systems with complementary characterization methods is mentioned as one of the prosperous paths for increasing the information output of these two analytical techniques.

Effect of Amphiphilic Drugs on the Stability and Zeta-Potential of Their Liposome Formulations: A Study with Prednisolone, Diazepam, and Griseofulvin

Multilamellar liposomes consisting of phosphatidylcholine and incorporating prednisolone (PZ), diazepam (DZ), or griseofulvin (GF) were prepared and characterized. Liposome size, surface charge, and stability (in buffer and serum proteins) were measured for drug-incorporating liposomes and empty liposomes for comparison. The results reveal that for all drugs studied drug incorporation has a substantial effect on the vesicle zeta-potential and stability. Drug-incorporating liposomes have a negative surface charge, while their membrane integrity is significantly higher when compared with that of empty liposomes. Release of DZ from liposomes is induced by dilution. Summarizing, the results of this study demonstrate that the presence of PZ, DZ, or GF in liposome membranes has a significant effect on main vesicle properties and correlates well with those obtained previously for hydrochlorothiazide and chlorothiazide. Thereby, we may conclude that the previously demonstrated effects of the thiazides on liposome properties are not solely related to their structure.

Physicochemical properties of liposomes incorporating hydrochlorothiazide and chlorothiazide

In an attempt to study the effect of hydrophobic drugs on liposome properties, multilamellar liposomes (MLV) consisting of phosphatidylcholine (PC) and incorporating chlorothiazide (CT) or hydrochlorothiazide (HCT), were prepared and characterized. Liposome size, surface charge, stability (in buffer, plasma and sodium cholate) and calcium-induced aggregation were studied for drug-incorporating liposomes and empty liposomes for comparison. Results show that drug incorporation affects liposome size, z-potential and stability in presence of buffer and plasma proteins. Indeed, drug-incorporating liposomes are slightly larger and have a negative surface charge, which increases with the amount of drug incorporated in the lipid membrane. The membrane integrity of drug incorporating liposomes (in absence and presence of plasma proteins) is significantly higher when compared with that of empty liposomes (for both drugs studied). On the contrary, vesicle membrane integrity in presence of sodium cholate and calcium induced vesicle aggregation, are not affected by drug incorporation. Leakage of thiazides from liposomes was demonstrated to be induced by dilution. Low amounts of thiazides (around 10-15%) are released when lipid concentration is over 0.1 mM, while further dilution increased drug leakage exponentially. Concluding, results demonstrate that the presence of HCT or CT in liposome membranes has a significant effect on main vesicle properties, which are known to influence vesicle targeting ability. Thereby, it is very interesting to continue studies in this respect, especially with more lipophilic drugs.

Electrophysiological study with oxonol VI of passive NO3- transport by isolated plant root plasma membrane

In contrast to animal cells, plant cells contain approximately 5-50 mM nitrate in cytosol and vacuole. The lack of specific spectroscopic probes, or suitable isotopes, impedes in vitro studies of NO3- transport. Reconstitution of root cell plasma membrane (PM) proteins in mixed soybean lipid:egg phosphatidylcholine allowed for the generation of large K+-valinomycin diffusion potentials (Em), monitored with the oxonol VI dye. Nevertheless, Em was restricted to approximately 130 mV by capacitor properties of biological membranes. This caused an increasing discrepancy at higher K+-Nernst potentials used for calibration. Therefore, Em was determined directly from the fluorescence of the dye free in buffer, bound at zero Em, and bound upon Em generation. Then, an electrophysiological analysis of the NO3--dependent dissipation rate of Em gave the net passive flux (JN) and the permeability coefficient to NO3- (PN). The plant root cell PM exhibited a strikingly large PN (higher than 10(-9) m s-1) at high Em (90-100 mV) and pH 6.5. At low Em (50-60 mV) and pH 7.4, PN decreased by 70-fold and became similar to that of the lipid bilayer. This agreed with the previous observation that 15 mM NO3- short-circuits the plant root PM H+-ATPase at its optimal pH of 6.5.

Cationic cholesterol with a hydroxyethylamino head group promotes significantly liposome-mediated gene transfection

A novel cationic cholesterol derivative with a hydroxyethylamino head group, cholesteryl-3beta-carboxyamidoethylene-N-hydroxyethylamine (II), has been synthesized and used for liposome-mediated gene transfection. The cationic liposomes containing the derivative (II) facilitated greatly pSV2CAT gene transfection into mouse NIH3T3 and L929 cells in the absence of serum. The transfection efficiency was much higher than those by the cationic liposomes containing cationic derivatives with a dialkylamino head group (I, III or IV). Further, the efficiency by the cationic liposomes with the derivative (II) was not so much decreased in the presence of serum. This suggested that a novel cationic cholesterol derivative (II) should be very promising in liposome-mediated gene transfection of plasmid and antisense DNA into target cells.

Effect of zeta potential of cationic liposomes containing cationic cholesterol derivatives on gene transfection

Cationic liposomes are known to be useful tools for gene transfection. However, the relation between transfection efficiency and physicochemical properties of liposomes has not been well understood. Here, we synthesized eight cationic derivatives of cholesterol which contain a tertiary amino head group with a different spacer arm. Transfection of plasmid pSV2CAT DNA into cells was done by cationic liposomes made of a mixture of dioleoylphosphatidylethanolamine (DOPE) and each cationic cholesterol derivative. At the same time we measured zeta potential of cationic liposomes by laser Doppler spectroscopy. The present results indicated that zeta potentials of cationic liposomes were well related to transfection activity of pSV2CAT DNA. This suggested that zeta potential of cationic liposomes is one of important factors which control gene transfection.

Probing biomembrane interfacial potential and pH profiles with a new type of float-like fluorophores positioned at varying distance from the membrane surface

Fluorophores of a new type were synthesized to probe the electrostatic potential or pH profiles in the external interface of biomembranes. The probes consist of the pH-sensitive fluorophore 7-hydroxycoumarin, coupled to a tetradecyl (myristyl) tail by a spacer group of varying length. A positively charged group is included between the tetradecyl and spacer groups to encourage a float-like alignment in the membrane head-group region. Three probes of this type were compared with 4-heptadecyl-7-hydroxycoumarin the fluorophore of which is embedded in the lipid head-group domain. Thus, a ruler-type positioning of the fluorophores was obtained at about 0.2, 0.6, 1.0, and 1.3 nm from the surface. The membrane-bound probes were tested in well-defined liposomes prepared by extrusion with different surface charge densities and size. The predicted positioning of the float-like probes is supported by their binding behavior in liposomes and by steady-state and nanosecond time-resolved fluorescence anisotropy, as well as by their accessibility to different quenchers. The interfacial electrostatic potential (psi d) and pH (pHd) values were derived from the observed apparent pKa shifts of the probes. The obtained psi d and pHd profiles as function of the surface potential (psi 0) and distance from the membrane surface are in good harmony with predictions from nonlinear Gouy-Chapman theory. The electrokinetic potentials (zeta) of the liposome series, measured by Doppler-electrophoretic frequency shift of laser light scattering, are in good proportion to the probe data. When bound to yeast cells, these probes monitor interfacial changes in parallel with glucose-induced medium acidification.(ABSTRACT TRUNCATED AT 250 WORDS)

Sterically stabilized liposomes. Reduction in electrophoretic mobility but not electrostatic surface potential

The electrophoretic mobility of liposomes containing a negatively charged derivative of phosphatidylethanolamine with a large headgroup composed of the hydrophilic polymer polyethylene glycol (PEG-PE) was determined by Doppler electrophoretic light scattering. The results show that this method is improved by the use of measurements at multiple angles to eliminate artifacts and that very small mobilities can be measured. The electrophoretic mobility of liposomes with 5 to 10 mol% PEG-PE is approximately -0.5 mu ms-1/Vcm-1 regardless of PEG-PE content compared with approximately -2 mu ms-1/Vcm-1 for similar liposomes but containing 7.5% phosphatidylglycerol (PG) instead of PEG-PE. Measurements of surface potential by distribution of an anionic fluorescent probe show that the PEG-PE imparts a negative charge identical to that by PG, consistent with the expectation of similar locations of the ionized phosphate responsible for the charge. The reduced mobility imparted by the surface bound PEG is attributed to a mechanism similar to that described for colloidal steric stabilization: hydrodynamic drag moves the hydrodynamic plane of shear, or the hydrodynamic radius, away from the charge-bearing plane, that of the phosphate moities. An extended length of approximately 50 A for the 2,000 molecular weight PEG is estimated from the reduction in electrophoretic mobility.

Characterization of distribution behavior of 2-imidazolines into multilamellar liposomes

The distribution of 2-imidazolines in neutral dimyristoylphosphatidylcholine (DMPC) liposomes, in negatively charged liposomes containing dicetylphosphate (DCP) or phosphatidylserine (PS), and in positively charged liposomes containing stearylamine (STA), has been investigated. Electrophoretic mobilities of multilamellar liposomes have also been measured as a function of drug concentration. Apparent equilibrium partition coefficients (log K'm) increased as a function of the DCP or PS concentration in DMPC liposomes whereas log K'm decreased with STA concentration, except for lofexidine and clonidine. Similarly, the electrokinetic parameters increased in DMPC liposomes that exhibited a small, positive surface charge, decreased in DMPC/cholesterol/DCP (7:1:2 mole ratio) liposomes, and increased in DMPC/STA (3:1 mole ratio) liposomes, except for clonidine which showed a decrease, as a function of the 2-imidazoline concentration. Surface potential change (delta psi o) due to drug inclusion in the liposomes obtained from theoretical considerations exhibited a positive linear relationship with log K'm. Values of delta psi o were greater but less sensitive to log K'm in negatively charged than in neutral or positively charged liposomes at 1 mM drug concentration. Likewise, surface charge densities varied in the same order as the surface potentials as a function of log K'm of the 2-imidazolines, except for clonidine and lofexidine. These data indicate the relative importance of the membrane surface characteristics on the partitioning behavior, and also possibly the membrane transport behavior, of the 2-imidazoline drugs.

Partition coefficients of dopamine antagonists in brain membranes and liposomes

Partition coefficients, Kp of dopamine antagonists, spiperone, haloperidol, domperidone and pimozide were determined in caudate nucleus microsomal membranes and in liposomes from membrane lipids. Kp values were measured as a function of temperature and the thermodynamics parameters for the transfer of the drugs from the aqueous medium to the lipid bilayer were evaluated. Partition in native membranes or in liposomes formed from the membrane lipids is not strongly dependent on temperature over the range from 8 to 37 degrees. The Kp values for spiperone, haloperidol and domperidone in membrane are 32 +/- 6, 192 +/- 11 and 308 +/- 40 respectively, whereas the equivalent values in liposomes are much higher: 195 +/- 12, 558 +/- 16 and 316 +/- 16. In contrast, for pimozide, the Kp values in membranes are higher than in liposomes: 1097 +/- 11 for microsomes and 662 +/- 10 for liposomes. Partition values in natural membranes decrease sequentially as follows: pimozide greater than domperidone greater than haloperidol greater than spiperone. Membranes rich in cholesterol show lower partition coefficients for haloperidol. The interaction of the antagonists with the bilayer is associated with small enthalpy changes and large increases in entropy, as expected for hydrophobic interactions. We conclude that the partition coefficients of the drugs studied for membranes and membranes lipids are very different from those reported for octanol/water and the latter values should not be used to estimate drug partition into membranes.

Interaction of electrically charged drug molecules with phospholipid membranes

Model membranes (egg-yolk PC liposomes) were exposed to the cationic form of amphiphilic drugs. Microelectrophoresis was used to measure the change of the electrokinetic potential as a function of the drug concentration. By use of the Gouy-Chapman theory the surface potential and surface charge density were calculated. A theoretical model postulating a simple partition equilibrium of the charged drug molecules between the membrane and the aqueous phase in the vicinity of the membrane failed to describe the experimental results. Modification of the partition law by introducing a mechanism of saturation at high drug concentrations, however, resulted in concordance of model and experiment. Some parameters of the model can be used as a means of evaluating the efficiency of neuroactive drugs.

Electrokinetic and hydrodynamic properties of sarcoplasmic reticulum vesicles: a study by laser Doppler electrophoresis and quasi-elastic light scattering

The electrical properties of sarcoplasmic reticulum vesicles were studied using electrophoretic mobility measurements by laser Doppler velocimetry. Combined with quasi-elastic light scattering analysis, this method enabled us to monitor changes in membrane surface charge density upon addition of NaCl, CaCl2, and MgCl2 solutions. At low ionic strength (4.7 mM), and in the absence of divalent salts, sarcoplasmic reticulum vesicles displayed a zeta potential value of -32.6 mV and a surface charge density of 5.4 10(-3) C/m2, corresponding to one elementary negative charge per 30 nm2 or about 2900 negative charges per vesicle. Upon addition of NaCl (up to 100 mM) vesicles became more negative (from 2900 to 6200 negative charges per vesicle), suggesting chloride binding or adsorption on the membrane. A noticeable increase of the vesicular size was observed upon addition of calcium or magnesium (25 to 30% increase of the hydrodynamic radius for 2.5 mM CaCl2 or MgCl2). This effect was prevented or suppressed by addition of relatively low concentrations of NaCl (50 mM). At low divalent cation concentrations one-third of the total net charge of the vesicles was neutralized suggesting a specific binding of cation on the membrane. At higher salt concentrations no modification of this parameter was observed. These results support the Gouy and Chapman theory about the electrical properties of sarcoplasmic reticulum vesicles.

The effect of different surface chemical groups on drug binding to liposomes

The binding of four secondary and tertiary amine drugs with local anesthetic activity (propranolol, tetracaine, lidocaine, procaine) to liposomes containing charged surface groups of different chemical composition has been investigated. Binding is determined by measurement of partition coefficients and of drug induced zeta potential changes of the liposomes. For propranolol 30% of the total amount of drug dissolved in phosphatidylcholine is located as protonated form in the liposome surface. Fifty percent of tetracaine and 13% of procaine contribute to the surface charges. Negative surface charges (phosphatidylserine) facilitate drug binding and drug protonization in the liposome surface. Positive surface charges (hexadecyltrimethylammonium) prevent the protonization of the drugs. Different chemical groups of single negatively charged phospholipids or of electrostatically neutral lipids have no significant effect on drug binding which proves that binding is not influenced by steric and bulky head group configurations. The drugs interact hydrophobically with the lipid phase in such a way that the drug amine protonizes in the presence of the negatively charged phosphate oxygen of the phospholipid. Hexadecanoic acid is located deeper within the liposome surface than other negatively charged phospholipids. Correspondingly the drug action is weaker and drug protonization is prevented.

Influence of various cationic amphiphilic drugs on the phase-transition temperature of phosphatidylcholine liposomes

The influence of 16 cationic amphiphilic compounds from various pharmacological groups on the phase-transition temperature (Tt) of dipalmitoyl-phosphatidylcholine (DPPC) liposomes was investigated using the method of differential scanning calorimetry. All drugs, the hydrophobicity of which varied in a wide range, depressed Tt. Biphasic dose-effect curves were obtained when the reduction of Tt (delta Tt) was plotted vs the molar ratio of drug/DPPC; beyond a plateau, Tt could again be reduced markedly by increasing the molar ratio. Concomitantly with the depression of Tt, the width of the transition peak changed in a characteristic way: it broadened during the (first) steep part of the dose-effect curves and became narrow like a control transition when the plateau of the dose-effect curves was reached. At still higher ratios the peak broadened again and eventually vanished, probably due to a detergent-like effect of the drug. Increasing hydrophobicity of the compounds shifted the dose-effect curves to lower molar ratios and enhanced the delta Tt attained at the plateau phase. It is proposed that the different potencies of the drugs to depress Tt result from different binding equilibria between the compounds and DPPC membranes, the individual equilibrium being determined by hydrophobic attraction and electrostatic repulsion.

Drug-induced surface potential changes of lipid vesicles and the role of calcium

The effects of four different drugs with local anesthetic properties were investigated on the surface potential of phospholipid vesicles composed of electrostatically neutral lipids (phosphatidylcholine), negatively charged lipids (phosphatidylserine) and a mixture of acidic and neutral lipids (soy bean lipids). Propranolol, tetracaine, lidocaine and procaine decrease the negative surface potential of phosphatidylserine and soy bean liposomes and increase that of phosphatidylcholine liposomes. The drugs interact with the liposomes in such a way that the protonated amine groups point towards the polar head groups of the phospholipids and the rest of the molecule is probably incorporated into the hydrophobic core of the lipid bilayer. The same sequence in drug activity normally measured in biological tissues (propranolol greater than tetracaine greater than lidocaine greater than procaine) is found for the surface potential change of the phospholipids. Calcium prevents the binding of the drugs to phosphatidylserine, especially the binding of lidocaine and procaine. Because of its high affinity for negative surface charges, Ca2+ chelates with phosphatidylserine and blocks the incorporation of the drug molecule. Vice versa, when incorporated into the liposomal bilayer, the drug blocks the interaction of calcium. These antagonistic effects are only observed in liposomes made from acidic phospholipids and not in those made from pure electrostatically neutral lipids like phosphatidylcholine.