Polyoxyethylated nonionic surfactants and their applications in topical ocular drug delivery

Molecular conformation and bilayer pores in a nonionic surfactant lamellar phase studied with 1H-13C solid-state NMR and molecular dynamics simulations

The structure of the lamellar phase of aqueous pentaethylene glycol mono-n-dodecyl ether (C12E5) surfactant at various temperatures and molar fractions is studied by using united atom molecular dynamics simulations and nuclear magnetic resonance measurements. Namely, the simulation model is used to interpret the magnitude and temperature dependence of experimental C-H order parameter profiles in terms of the molecular conformation and orientation. Our simulations suggest that the low order parameters that are generally measured in poly(ethylene oxide) surfactant bilayers are due to the presence of bilayer pores throughout the entire lamellar phase region.

A critical appraisal of microemulsions for drug delivery: part II

Microemulsions are thermodynamically stable, optically transparent isotropic solutions of oil and water successfully formulated by using a combination of suitable surfactant and cosurfactant. The solubilization power of microemulsions for lipophilic, hydrophilic and amphiphilic solutes form a viable approach for enhancing the bioavailability of hydrophobic drugs and percutaneous permeation of poorly permeable drugs, mainly due to the large area per volume ratio available for mass transfer. Microemulsions have emerged as novel vehicles for drug delivery due to their versatile applications. They allow sustained release for topical, oral, nasal, intravenous, ocular, parenteral and other administration routes of drugs. They also offer a relevant application platform for improving target specificity, therapeutic activity, and reducing toxicity of drugs.

Aqueous nanomicellar formulation for topical delivery of biotinylated lipid prodrug of acyclovir: formulation development and ocular biocompatibility

PURPOSE

The objective of this study was to develop a clear, aqueous nanomicellar formulation and evaluate its in vitro ocular biocompatibility as a novel carrier for topical ocular delivery of biotinylated lipid prodrug for the treatment of herpetic keratitis.

METHODS

Micellar formulation of Biotin-12Hydroxystearic acid-acyclovir (B-12HS-ACV) was prepared by solvent evaporation/film hydration method with two nonionic surfactants, vitamin E TPGS and octoxynol-40. The optimized formulation was characterized for various parameters including micelle size, polydispersity index (PDI), and zeta-potential and in vitro prodrug release. Human corneal epithelial cells (HCECs) were employed for studying the cytotoxicity of the formulation. Further, mRNA expression levels of various cytokines were also studied with quantitative real-time PCR (qPCR).

RESULTS

Average size was 10.46±0.05 nm with a PDI of 0.086 for blank nanomicelles, and 10.78±0.09 nm with a PDI of 0.075 for prodrug-loaded nanomicelles. Both unloaded and prodrug-loaded nanomicelles had low negative zeta potential. Prodrug encapsulation efficiency of mixed nanomicelles was calculated to be ∼90%. Transmission electron microscopy analysis revealed that nanomicelles were spherical, homogenous, and devoid of aggregates. B-12HS-ACV release from nanomicelles was slow with no significant burst effect. Results show a sustained release of the prodrug from nanomicelles over a period of 4 days. Neither the blank formulation nor the prodrug-loaded micellar formulation demonstrated any cytotoxic effects. Further, incubation of HCECs with blank and prodrug-loaded nanomicellar groups did not significantly alter the expression levels of IL-1β, IL-6, IL-8, IL-17, TNF-α, and IFN-γ.

CONCLUSIONS

In summary, a topical clear, aqueous nanomicellar formulation comprised of vitamin E TPGS and octoxynol-40 loaded with 0.1% B-12HS-ACV was successfully developed. B-12HS-ACV-loaded nanomicelles are small in size, spherical, and homogenous, without any aggregates. The micellar formulations were perfectly transparent similar to pure water. Ocular biocompatibility studies indicated that mixed nanomicelles were nontoxic and noninflammatory to corneal epithelial cells. Therefore, nanomicellar technology represents a promising strategy for the delivery of biotinylated lipid prodrugs of ACV.

Expand classical drug administration ways by emerging routes using dendrimer drug delivery systems: a concise overview

Drugs are introduced into the body by numerous routes such as enteral (oral, sublingual and rectum administration), parenteral (intravascular, intramuscular, subcutaneous and inhalation administration), or topical (skin and mucosal membranes). Each route has specific purposes, advantages and disadvantages. Today, the oral route remains the preferred one for different reasons such as ease and compliance by patients. Several nanoformulated drugs have been already approved by the FDA, such as Abelcet®, Doxil®, Abraxane® or Vivagel®(Starpharma) which is an anionic G4-poly(L-lysine)-type dendrimer showing potent topical vaginal microbicide activity. Numerous biochemical studies, as well as biological and pharmacological applications of both dendrimer based products (dendrimers as therapeutic compounds per se, like Vivagel®) and dendrimers as drug carriers (covalent conjugation or noncovalent encapsulation of drugs) were described. It is widely known that due to their outstanding physical and chemical properties, dendrimers afforded improvement of corresponding carried-drugs as dendrimer-drug complexes or conjugates (versus plain drug) such as biodistribution and pharmacokinetic behaviors. The purpose of this manuscript is to review the recent progresses of dendrimers as nanoscale drug delivery systems for the delivery of drugs using enteral, parenteral and topical routes. In particular, we focus our attention on the emerging and promising routes such as oral, transdermal, ocular and transmucosal routes using dendrimers as delivery systems.

Topical delivery of ocular therapeutics: carrier systems and physical methods

OBJECTIVE

The basic concepts, major mechanisms, technological developments and advantages of the topical application of lipid-based systems (microemulsions, nanoemulsions, liposomes and solid lipid nanoparticles), polymeric systems (hydrogels, contact lenses, polymeric nanoparticles and dendrimers) and physical methods (iontophoresis and sonophoresis) will be reviewed.

KEY FINDINGS

Although very convenient for patients, topical administration of conventional drug formulations for the treatment of eye diseases requires high drug doses, frequent administration and rarely provides high drug bioavailability. Thus, strategies to improve the efficacy of topical treatments have been extensively investigated. In general, the majority of the successful delivery systems are present on the ocular surface over an extended period of time, and these systems typically improve drug bioavailability in the anterior chamber whereas the physical methods facilitate drug penetration over a very short period of time through ocular barriers, such as the cornea and sclera.

SUMMARY

Although in the early stages, the combination of these delivery systems with physical methods would appear to be a promising tool to decrease the dose and frequency of administration; thereby, patient compliance and treatment efficacy will be improved.

Enhancement of oral bioavailability of E804 by self-nanoemulsifying drug delivery system (SNEDDS) in rats

Indirubin and its derivatives have been shown to interrupt the cell cycle by inhibiting cyclin-dependent kinases, explaining their long-time use in traditional Chinese medicine for the treatment of chronic myelocytic leukemia. A potent derivative of indirubin, indirubin-3'-oxime 2,3-dihydroxypropyl ether (E804), has been shown to block the Src-Stat3 and Src-Stat5 signaling pathway in human cancer cells, inducing apoptosis. The anticancer effects of E804, however, cannot be easily examined in vivo because of its poor water solubility and low absorption. The aim of this study was to develop and evaluate a self-nanoemulsifying drug delivery system (SNEDDS) containing E804 for enhancing its solubility and bioavailability. Solubility of E804 was determined in various vehicles, and pseudoternary phase diagram was used to evaluate the self-emulsifying existence area. The SNEDDS composed of Capmul MCM (oil), Solutol HS 15 (surfactant), and polyethylene glycol 400 (cosurfactant) on the ratio of 20.5:62.5:16 loaded 1.5% of E804. The particle size of droplets was found to be 16.8 and 140 nm, and SNEDDS was stable after freeze-thaw cycles and upon dilution in HCl 0.1 N and pH 7.4 HBSS++. The ability of formulation for absorption enhancement was studied in rats in vivo after oral administration. The results showed that the developed SNEDDS increased the E804 bioavailability 984.23% compared with the aqueous suspension. Our studies for the first time show that the developed SNEDDS can be used as a possible formulation for E804 to improve its solubility and oral bioavailability.

Ocular disposition of the hemiglutarate ester prodrug of ∆⁹-Tetrahydrocannabinol from various ophthalmic formulations

PURPOSE

The overall goal of this project is to enhance ocular delivery of ∆(9)-Tetrahydrocannabinol (THC) through the topical route.

METHODS

Solubility, stability and in vitro transcorneal permeability of the relatively hydrophilic hemiglutarate ester derivative, THC-HG, was studied in the presence of surfactants. The solutions were characterized with respect to micelle size, zeta potential and solution viscosity. In vivo studies were carried out in New Zealand albino rabbits. A previously reported promising THC-HG ion-pair formulation was also studied in vivo.

RESULTS

Aqueous solubility and stability and in vitro transcorneal permeability of THC-HG was enhanced significantly in the presence of surfactants. THC levels in the ocular tissues (except cornea) were found to be below detection limits from mineral oil, surfactant or emulsion based formulations containing THC. In contrast, micellar and ion pair based THC-HG formulations produced significantly higher total THC concentrations in the anterior ocular chamber.

CONCLUSION

In this study, although delivery of THC to the anterior chamber ocular tissues could be significantly increased through the prodrug and formulation approaches tested, further studies are needed to increase penetration to the back-of-the eye.

Drug delivery to the ocular posterior segment using lipid emulsion via eye drop administration: effect of emulsion formulations and surface modification

This work explored submicron-sized lipid emulsion as potential carriers for intraocular drug delivery to the posterior segment via eye drops. The effects of physicochemical properties of lipid emulsion on drug delivery were evaluated in vivo using mice. Different formulations of submicron-sized lipid emulsions were prepared using a high pressure homogenization system. Using coumairn-6 as a model drug and fluorescent marker, fluorescence could be observed in the retina after administration of the lipid emulsion. The fluorescence intensity observed after administration of medium chain triglycerides containing the same amount of coumarin-6 was much lower than that observed after administration of lipid emulsions. The inner oil property and phospholipid emulsifier did not affect the drug delivery efficiency to the retina. However, compared with unmodified emulsions, the fluorescence intensity in the retina increased by surface modification using a positive charge inducer and the functional polymers chitosan (CS) and poloxamer 407 (P407). CS-modified lipid emulsions could be electrostatically interacted with the eye surface. By its adhesive property, poloxamer 407, a surface modifier, possibly increased the lipid emulsion retention time on the eye surface. In conclusion, we suggested that surface-modified lipid emulsions could be promising vehicles of hydrophobic drug delivery to the ocular posterior segment.

Niosomes: novel sustained release nonionic stable vesicular systems--an overview

Vesicular systems are novel means of delivering drug in controlled manner to enhance bioavailability and get therapeutic effect over a longer period of time. Niosomes are such hydrated vesicular systems containing nonionic surfactants along with cholesterol or other lipids delivering drug to targeted site which are non toxic, requiring less production cost, stable over a longer period of time in different conditions, so overcomes drawbacks of liposome. Present review describes history, all factors affecting niosome formulation, manufacturing conditions, characterization, stability, administration routes and also their comparison with liposome. This review also gives relevant information regarding various applications of niosomes in gene delivery, vaccine delivery, anticancer drug delivery, etc.

Recent advances in topical ophthalmic drug delivery with lipid-based nanocarriers

Ocular barriers and the poor water solubility of drug candidates present a number of problems for the development of ocular drug delivery systems. Recently, the emergence of lipid-based nanocarriers has provided a viable means of enhancing the bioavailability of ophthalmic formulations. A number of these formulations have been found to be clinically active and several others are currently undergoing clinical trials. In this review, the advantages of lipid-based nanocarriers as non-invasive topical ocular drug delivery systems are presented. Many systems, including emulsions, liposomes, cubosomes, niosomes and other lipid-based nanocarriers, are reviewed.

Enhancement of corneal permeation of riboflavin-5'-phosphate through vitamin E TPGS: a promising approach in corneal trans-epithelial cross linking treatment

Corneal accumulation of riboflavin-5'-phosphate (riboflavin) is an essential step in the so called corneal cross-linking (CXL), an elective therapy for the treatment of progressive keratoconus, corneal ectasia and irregular astigmatism. CXL is usually performed after surgical debridement of corneal epithelium, since it impedes the stromal penetration of riboflavin in a relatively short time. d-Alpha-tocopheryl poly(ethylene glycol) 1000 succinate (VE-TPGS) is an effective permeation enhancer used to increase adsorption of drugs trough different biological barriers. Moreover, belonging to the group of tocopherol pro-drugs, VE-TPGS exerts a protective effect on biological membrane against free-radical damage. The aim of this work is the evaluation of VE-TPGS effects on riboflavin corneal permeability, and the assessment of its protective effect against free-radicals generated during CXL procedures. Different solutions containing riboflavin (0.125% w/w), dextran (20.0% w/w) and increasing concentration of VE-TPGS were tested. Corneal permeation was evaluated in vitro by the use of modified Franz-cell type diffusion cells and freshly excised porcine corneas as barrier. The effect of VE-TPGS on riboflavin corneal penetration was compared with a standard commercial solution of riboflavin in dextran at different times. Accumulation experiments were conducted both on epithelized and non-epithelized corneas. Moreover, epithelized porcine corneas, treated with the tested solutions, were subjected to an in vitro CXL procedure versus non-epithelized corneas, treated with a commercial solution of riboflavin. Differences were measured by means of corneal rigidity using Young's modulus. The photo-protective effect of tested solutions on corneal epithelium was, finally, evaluated. CXL treatment was applied, in vitro, on human explanted corneas and resulting morphology of corneal epithelium was investigated by scanning electron microscopy.

Light and neutron scattering study of PEG-oleate and its use in emulsion polymerization

Steric stabilization of colloids forms a robust mechanism to obtain colloids that are stable in a variety of environments, and that can be used to study the phase behavior of hard or soft spheres. We report the synthesis of sterically stabilized colloids in an aqueous environment using readily dissolvable surfactants, with an unsaturated hydrophobic tail. We synthesized a new surfactant by esterification of a poly(ethylene glycol) (PEG) chain of 4.1 kg/mol with oleic acid, called PEG4OA. The micellization of PEG4OA was characterized by light and neutron scattering, which yielded values for the aggregation number and the overall size that are in excellent agreement with a comparable surfactant with a saturated octadecane chain, Brij 700. We successfully used PEG4OA in the emulsion polymerization of polystyrene colloids. In comparison with the smaller surfactant Tween 80, PEG4OA yielded smaller colloids with radii around 50 nm, and the addition of 1-dodecanethiol reduced the formation of aggregates during the synthesis. A contrast variation study with small angle neutron scattering (SANS) showed that a dense PEG layer was grafted to the colloid surface.

High-throughput discovery of novel steric stabilizers for cubic lyotropic liquid crystal nanoparticle dispersions

High-throughput methodologies have been employed to establish structure-property relationships and assess the effectiveness of nonionic steric stabilizers for inverse bicontinuous cubic lyotropic liquid crystalline nanoparticulate dispersions of monoolein and phytantriol. The ability of the stabilizers to disperse the lipids was compared with that of the commonly employed triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) copolymer Pluronic F127, which was used as a positive control. The poly(ethylene oxide) stearate class of stabilizers (commercially known as Myrj) were discovered to be effective as steric stabilizers for cubosomes, while retaining the internal nanostructure of the "parent" bulk phase. In particular, Myrj 59, with an average of 100 poly(ethylene oxide) units, was more effective than F127 at dispersing phytantriol, forming stable phytantriol cubosome dispersions at a concentration of 0.1 wt %, 5-fold lower than that achievable with Pluronic F127. The discovery of this new effective class of stabilizers for cubosomes, specifically enabled by high-throughput approaches, broadens the versatility of components from which to construct these interesting potential drug delivery and medical imaging nanoparticles.

Design of cationic nanostructured heterolipid matrices for ocular delivery of methazolamide

Solid lipid nanoparticles (SLNs) formulated from one type of lipid (homolipid) suffer from low drug encapsulation and drug bursting due to crystallization of the lipid into the more ordered β modification, which leads to decreased drug entrapment and faster drug release. This study assessed the feasibility of using nanostructured lipid matrices (NLMs) for ocular delivery of methazolamide-(MZA) adopting heterolipids composed of novel mixtures of Compritol (®) and cetostearyl alcohol (CSA), and stabilized by Tween 80(®). The systems were prepared using the modified high shear homogenization followed by ultrasonication method, which avoids the use of organic solvents. A 3(2) full factorial design was constructed to study the influence of two independent variables, namely the ratio of CSA:Compritol and the concentration of Tween 80, each in three levels. The dependent variables were the entrapment efficiency percentages (EE%), mean particle size (PS), polydispersity index (PDI), and zeta potential (ZP). In vivo intraocular pressure (IOP) lowering activity for the selected formulae was compared to that of MZA solution. The results showed that increasing the ratio of CSA to Compritol increased the EE% and PS, while increasing the concentration of Tween 80, decreased PS with no significant effect on EE%. The ZP values of all formulae were positive, and greater than 30 mV. The best formula, composed of 4% CSA, 2% Compritol, 0.15% stearylamine, and 2% Tween 80, with EE% of 25.62%, PS of 207.1 nm, PDI of 0.243, and ZP of 41.50 mV, showed in vitro sustained release properties for 8 hours and lowered the intraocular pressure by 8.3 mmHg within 3 hours, with this drop in pressure lasting for 12 hours.

Pseudomonas aeruginosa exopolysaccharide Psl promotes resistance to the biofilm inhibitor polysorbate 80

Polysorbate 80 (PS80) is a nonionic surfactant and detergent that inhibits biofilm formation by Pseudomonas aeruginosa at concentrations as low as 0.001% and is well tolerated in human tissues. However, certain clinical and laboratory strains (PAO1) of P. aeruginosa are able to form biofilms in the presence of PS80. To better understand this resistance, we performed transposon mutagenesis with a PS80-resistant clinical isolate, PA738. This revealed that mutation of algC rendered PA738 sensitive to PS80 biofilm inhibition. AlgC contributes to the biosynthesis of the exopolysaccharides Psl and alginate, as well as lipopolysaccharide and rhamnolipid. Analysis of mutations downstream of AlgC in these biosynthetic pathways established that disruption of the psl operon was sufficient to render the PA738 and PAO1 strains sensitive to PS80-mediated biofilm inhibition. Increased levels of Psl production in the presence of arabinose in a strain with an arabinose-inducible psl promoter were correlated with increased biofilm formation in PS80. In P. aeruginosa strains MJK8 and ZK2870, known to produce both Pel and Psl, disruption of genes in the psl but not the pel operon conferred susceptibility to PS80-mediated biofilm inhibition. The laboratory strain PA14 does not produce Psl and does not form biofilms in PS80. However, when PA14 was transformed with a cosmid containing the psl operon, it formed biofilms in the presence of PS80. Taken together, these data suggest that production of the exopolysaccharide Psl by P. aeruginosa promotes resistance to the biofilm inhibitor PS80.

Mucoadhesive nanoparticles for prolonged ocular delivery of natamycin: In vitro and pharmacokinetics studies

The aim of this study was to prepare natamycin encapsulated lecithin/chitosan mucoadhesive nanoparticles (NPs) for prolonged ocular application. These NPs were characterized by their mean particle size 213nm, encapsulation efficiency 73.57%, with a theoretical drug loading 5.09% and zeta potential +43. In vitro release exhibited a biphasic drug release profile with initial burst followed by a very slow drug release. The MIC(90) and zone of inhibition of NPs showed similar antifungal activity as compared to marketed suspension and free natamycin against Candida albicans and Aspergillus fumigates. The ocular pharmacokinetics of NPs and marketed formulation were evaluated in NZ rabbits. The NPs exhibit significant mucin adhesion. The AUC((0-∞)) was increased up to 1.47 fold and clearance was decreased up to 7.4-fold as compared to marketed suspension. The PK-PD and pharmacokinetic simulation was carried out to estimate optimum dosing regimen for good efficacy. Thus, lecithin/chitosan NPs could be considered useful approach aiming to prolong ocular residence and reduce dosing frequency.

Lecithin-linker microemulsion gelatin gels for extended drug delivery

This article introduces the formulation of alcohol-free, lecithin microemulsion-based gels (MBGs) prepared with gelatin as gelling agent. The influence of oil, water, lecithin and hydrophilic and lipophilic additives (linkers) on the rheological properties and appearance of these gels was systematically explored using ternary phase diagrams. Clear MBGs were obtained in regions of single phase microemulsions (μEs) at room temperature. Increasing the water content in the formulation increased the elastic modulus of the gels, while increasing the oil content had the opposite effect. The hydrophilic additive (PEG-6-caprylic/capric glycerides) was shown to reduce the elastic modulus of gelatin gels, particularly at high temperatures. In contrast to anionic (AOT) μEs, the results suggest that in lecithin (nonionic) μEs, the introduction of gelatin “dehydrates” the μE. Finally, when the transdermal transport of lidocaine formulated in the parent μE and the resulting MBG were compared, only a minor retardation in the loading and release of lidocaine was observed.

Gelucire44/14 as a novel absorption enhancer for drugs with different hydrophilicities: in vitro and in vivo improvement on transcorneal permeation

The objective of this study was to investigate the application of Gelucire44/14 as a novel absorption enhancer in ophthalmic drug delivery system. Six compounds, namely ribavirin, puerarin, mangiferin, berberin hydrochloride, baicalin, and curcumin in the order of increasing lipophilicity were selected as model drugs. The effect of Gelucire44/14 on transcorneal permeation was evaluated across excised rabbit cornea. Ocular irritation and precorneal retention time were assessed. Additionally, aqueous humor pharmacokinetic test was performed by microdialysis. The results indicated that Gelucire44/14, at a concentration of 0.05% or 0.1% (w/v), was found to maximally increase the apparent permeability coefficient by 6.47-, 4.14-, 3.50-, 3.97-, 2.92-, and 1.86-fold for ribavirin, puerarin, mangiferin, berberin hydrochloride, baicalin, and curcumin, respectively (p < 0.05). Moreover, Gelucire44/14 was nonirritant at broad concentrations of 0.025%-0.4% (w/v). Pharmacokinetic tests showed that Gelucire44/14 promoted ocular bioavailability of the compounds as indicated by 5.40-, 4.03-, 3.46-, 3.57-, 2.77-, and 1.77-fold maximal increase in the area under the curve for the drugs aforementioned, respectively (p < 0.01). Therefore, Gelucire44/14 exerted a significant improvement on the permeation of both hydrophilic and lipophilic compounds, especially hydrophilic ones. Hence, Gelucire44/14 can be considered as a safe and effective absorption enhancer for ophthalmic drug delivery system.

Food protein-stabilized nanoemulsions as potential delivery systems for poorly water-soluble drugs: preparation, in vitro characterization, and pharmacokinetics in rats

Nanoemulsions stabilized by traditional emulsifiers raise toxicological concerns for long-term treatment. The present work investigates the potential of food proteins as safer stabilizers for nanoemulsions to deliver hydrophobic drugs. Nanoemulsions stabilized by food proteins (soybean protein isolate, whey protein isolate, β-lactoglobulin) were prepared by high-pressure homogenization. The toxicity of the nanoemulsions was tested in Caco-2 cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide viability assay. In vivo absorption in rats was also evaluated. Food protein-stabilized nanoemulsions, with small particle size and good size distribution, exhibited better stability and biocompatibility compared with nanoemulsions stabilized by traditional emulsifiers. Moreover, β-lactoglobulin had a better emulsifying capacity and biocompatibility than the other two food proteins. The pancreatic degradation of the proteins accelerated drug release. It is concluded that an oil/water nanoemulsion system with good biocompatibility can be prepared by using food proteins as emulsifiers, allowing better and more rapid absorption of lipophilic drugs.

Optimizing flurbiprofen-loaded NLC by central composite factorial design for ocular delivery

The purpose of this study was to design and optimize a new topical delivery system for ocular administration of flurbiprofen (FB), based on lipid nanoparticles. These particles, called nanostructured lipid carriers (NLC), were composed of a fatty acid (stearic acid (SA)) as the solid lipid and a mixture of Miglyol(®) 812 and castor oil (CO) as the liquid lipids, prepared by the hot high pressure homogenization method. After selecting the critical variables influencing the physicochemical characteristics of the NLC (the liquid lipid (i.e. oil) concentration with respect to the total lipid (cOil/L (wt%)), the surfactant and the flurbiprofen concentration, on particle size, polydispersity index and encapsulation efficiency), a three-factor five-level central rotatable composite design was employed to plan and perform the experiments. Morphological examination, crystallinity and stability studies were also performed to accomplish the optimization study. The results showed that increasing cOil/L (wt%) was followed by an enhanced tendency to produce smaller particles, but the liquid to solid lipid proportion should not exceed 30 wt% due to destabilization problems. Therefore, a 70:30 ratio of SA to oil (miglyol + CO) was selected to develop an optimal NLC formulation. The smaller particles obtained when increasing surfactant concentration led to the selection of 3.2 wt% of Tween(®) 80 (non-ionic surfactant). The positive effect of the increase in FB concentration on the encapsulation efficiency (EE) and its total solubilization in the lipid matrix led to the selection of 0.25 wt% of FB in the formulation. The optimal NLC showed an appropriate average size for ophthalmic administration (228.3 nm) with a narrow size distribution (0.156), negatively charged surface (-33.3 mV) and high EE (∼90%). The in vitro experiments proved that sustained release FB was achieved using NLC as drug carriers. Optimal NLC formulation did not show toxicity on ocular tissues.

Design and ocular tolerance of flurbiprofen loaded ultrasound-engineered NLC

Packaging small drug molecules, such as non-steroidal anti-inflammatory drugs (NSAIDs) into nanoparticulate systems has been reported as a promising approach to improve the drug's bioavailability, biocompatibility and safety profiles. In the last 20 years, lipid nanoparticles (lipid dispersions) entered the nanoparticulate library as novel carrier systems due to their great potential as an alternative to other systems such as polymeric nanoparticles and liposomes for several administration routes. For ocular instillation nanoparticulate carriers are required to have a low mean particle size, with the lowest polydispersity as possible. The purpose of this work was to study the combined influence of 2-level, 4-factor variables on the formulation of flurbiprofen (FB), a lipophilic NSAID, in lipid carriers currently named as nanostructured lipid carriers (NLC). NLC were produced with stearic acid (SA) and castor oil (CO) stabilized by Tween® 80 (non-ionic surfactant) in aqueous dispersion. A 2(4) full factorial design based on 4 independent variables was used to plan the experiments, namely, the percentage of SA with regard to the total lipid, the FB concentration, the stabilizer concentration, and the storage conditions (i.e., storage temperature). The effects of these parameters on the mean particle size, polydispersity index (PI) and zeta potential (ZP) were investigated as dependent variables. The optimization process was achieved and the best formulation corresponded to the NLC formulation composed of 0.05 (wt%) FB, 1.6 (wt%) Tween® 80 and a 50:50 ratio of SA to CO, with an average diameter of 288 nm, PI 0.245 of and ZP of -29 mV. This factorial design study has proven to be a useful tool in optimizing FB-loaded NLC formulations. Stability of the optimized NLC was predicted using a TurbiScanLab® and the ocular tolerance was assessed in vitro and in vivo by the Eytex® and Draize test, respectively. The developed systems were shown physico-chemically stable with high tolerance for eye instillation.

Cationic lipids: molecular structure/ transfection activity relationships and interactions with biomembranes

Abstract Synthetic cationic lipids, which form complexes (lipoplexes) with polyanionic DNA, are presently the most widely used constituents of nonviral gene carriers. A large number of cationic amphiphiles have been synthesized and tested in transfection studies. However, due to the complexity of the transfection pathway, no general schemes have emerged for correlating the cationic lipid chemistry with their transfection efficacy and the approaches for optimizing their molecular structures are still largely empirical. Here we summarize data on the relationships between transfection activity and cationic lipid molecular structure and demonstrate that the transfection activity depends in a systematic way on the lipid hydrocarbon chain structure. A number of examples, including a large series of cationic phosphatidylcholine derivatives, show that optimum transfection is displayed by lipids with chain length of approximately 14 carbon atoms and that the transfection efficiency strongly increases with increase of chain unsaturation, specifically upon replacement of saturated with monounsaturated chains.