Enhancement of the dissolution rate and oral absorption of a poorly water soluble drug by formation of surfactant-containing microparticles.

The slow dissolution rate exhibited by poorly water-soluble drugs is a major challenge in the drug development process. Following oral administration, drugs with slow dissolution rates generally show erratic and incomplete absorption which may lead to therapeutic failure. The aim of this study was to improve the dissolution rate and subsequently the oral absorption and bioavailability of a model poorly water-soluble drug. Microparticles containing the model drug (griseofulvin) were produced by spray drying the drug in the absence/presence of a hydrophilic surfactant. Poloxamer 407 was chosen as the hydrophilic surfactant to improve the particle wetting and hence the dissolution rate. The spray dried particles were characterized and in vitro dissolution studies and in vivo absorption studies were carried out. The results obtained showed that the dissolution rate and absolute oral bioavailability of the spray dried griseofulvin/Poloxamer 407 particles were significantly increased compared to the control. Although spray drying griseofulvin alone increased the drug's in vitro dissolution rate, no significant improvement was seen in the absolute oral bioavailability when compared to the control. Therefore, it is believed that the better wetting characteristics conferred by the hydrophilic surfactant was responsible for the enhanced dissolution rate and absolute oral bioavailability of the model drug.

Fast-dissolving microparticles fail to show improved oral bioavailability.

Oral dosage forms are the preferred means of delivering drugs for systemic absorption. However, development problems occur for drugs with poor water solubility and/or gastrointestinal permeability. It is generally believed that the in-vivo bioavailability of poorly water-soluble drugs from Class II of the Biopharmaceutics Classification System can be improved by increasing the dissolution rate. We have attempted to increase the in-vivo oral bioavailability of a model Class II drug (griseofulvin) by preparing rapidly-dissolving particles. The solvent-diffusion method was used to prepare particles with hydrophilic surfactants (Brij 76/Tween 80 surfactant blend) and in-vivo studies were conducted in rats. The griseofulvin particles produced were bipyramidal in habit with a particle size of 2.18 +/- 0.12 microm; they contained crystalline drug and a relatively large proportion (12% w/w) of hydrophilic surfactant. The latter and the small particle size ensured rapid particle dispersion and dissolution in-vitro. Thus, within 30 min of the in-vitro dissolution test, the bipyramidal particles had released approximately 70% of drug compared with approximately 10% from the starting material (particle size 12.61 +/- 1.11 microm). However, the rapid and increased drug dissolution in-vitro was not translated to rapid and enhanced absorption in-vivo, and the oral bioavailability of the model drug was found to be the same from the control and from the bipyramidal particles. The poor in-vivo performance of the bipyramidal particles showed that although the dissolution rate of a Class II drug is thought to be a good indicator of its in-vivo bioavailability, this is not always the case.

Thermodynamics of steroid partitioning in dimyristoylphosphatidylcholine liposomes.

The thermodynamics of partitioning of some steroids into dimyristoylphosphatidylcholine (DMPC) liposomes determined above and below the phase-transition temperature (Tc) revealed that: (1) delta Gw leads to 1 for all steroids studied is negative. (2) The process is entropy dominated. (3) delta Hw leads to 1 and delta Sw leads to 1 is more positive below Tc than above it for C-21 steroids. (4) Partitioning occurs into areas slightly more hydrophilic than n-octanol. (5) Ketones substituted on the 11 position of a 21-OH steroid have greater hydrogen-bonding capability than 11-OH compounds. (6) Hydroxyl groups at different positions on the steroid nucleus are non-equivalent, and (7) The group contribution for 21-ester methylenes is greater than that reported for other solutes in DMPC liposome systems.

The solubilization of progesterone by mixed bile salt-phospholipid sols.

The solubility of progesterone was determined in several different bile salt-phospholipid mixtures, and it is concluded that: (1) The solubility in unconjugated bile salts is greater than in the conjugated analogues, and the solubility in deoxycholate solutions is twice that in cholate solutions. (2) Substitution of hydroxyl groups in the 11 and 21 positions of progesterone increases solubility, whilst substitution in the 17-position decreases solubility in bile salt solutions. (3) Progesterone solubility in mixed bile salt solutions is proportional to the mole ratio of the surfactant mixture. (4) Sodium deoxycholate (SDC)-phospholipid sols show no such linear solubilizing properties; a minimum occurring at a mole ratio of SDC to phospholipid of 1 : 4. (5) There is a break in the solubility curve of progesterone in lysophosphatidycholine (LPC)/phosphatidylcholine (PC) mixtures at a mole ratio of 65 : 35 coincident with maximum viscosity. (6) Introduction of SDC into LPC/PC mixtures results in decreased progesterone solubility.

The interaction of mequitazine with phospholipid model membranes.

The effect of increasing concentrations of mequitazine, a quinuclidinylmethyl-phenothiazine, on the phase transition temperature (Tc), the broadening of the transition peak, the enthalpy and entropy of transition of dimyristoyl-, dipalmitoyl- and distearoylphosphatidylcholine (DPPC) liposomes was studied. Pest critical micelle concentrations of mequitazine (CMC = 5.23 X 10(-2) M), caused broadening of the transition peak and lowering of the Tc of pure liposomes. The ratio of peak heights from the nuclear magnetic resonance (NMR) spectra of egg phosphatidycholine liposomes was used as a criterion for assessing the interaction of the drug with phsopholipid membranes. Mequitazine interacts with both the polar head groups and hydrophobic membrane interior.

The in vitro characterisation and biodistribution of some non-ionic surfactant coated liposomes in the rabbit.

The degree of adsorption of some novel silicone glycol copolymers onto polystyrene microspheres was studied and compared with the sorption onto small unilamellar vesicles (SUVs) composed of egg phosphatidylcholine (EPC) and prepared by the detergent dialysis technique. These non-ionic surfactants are 'comb' polymers of the ABn type where A is a silicone chain with n pendant polyglycol chains (B). Photon correlation spectroscopy was used to measure the adsorbed layer thickness (delta h) following polymer sorption from aqueous solutions. delta h on latex particles was a function of the length of the polymer hydrophilic chains. Upon incubation with SUVs, delta h of the different polymers was similar (3 nm) and significantly less (two sample t-test, p < 0.01) than the corresponding delta h on the polystyrene latex which could be attributed to the penetration of the polymers into the outer phospholipid bilayer. The glycol chains of the silicone polymers are assumed to be in a helical and planar position. Efflux of 5(6)-carboxyfluorescein from EPC liposomes was increased by the presence of these polymers. The highest retention (49% at 5 h) was obtained with SUVs coated with the silicone polymer possessing the highest glycol content and the longest ethylene oxide chains. Sterically stabilised vesicles were also formed by coating dipalmitoyl phosphatidyl-choline (DPPC)/cholesterol (Chol) (molar ratio 1:1) with two of these silicone glycol copolymers and Poloxamer 338. The liposomes were labelled with 67gallium-desferrioxamine (67Ga-DF). Incubation of radiolabelled Poloxamer 338-coated vesicles in saline or serum at 37 degrees C for 24 h resulted in less stable liposomes compared to the more stable non-coated or silicone coated vesicles. Following intravenous (i.v.) administration in rabbits, free 67Ga-DF rapidly disappeared from the circulation (half-life = 41.4 min) and accumulated in the bladder. Two populations of vesicles were prepared (136 +/- 2.9 nm and 100 +/- 1.4 nm). 24 h after i.v. injection of the different formulations of the 100 nm liposomes in rabbits, 20-27% of the activity was retained in blood. The silicone polymer with the highest glycol content and the longest ethylene oxide chains showed the longest half-life (21.4 h). Using gamma scintigraphy, the liver/spleen uptake of the 136 nm non-coated vesicles was 57% which was significantly reduced to 37% upon coating the liposomes with the silicone glycol copolymers. At 30 min post i.v. injection, approximately 10% of the activity was associated with the heart/lung region irrespective of liposome size or polymer coating.(ABSTRACT TRUNCATED AT 400 WORDS)

Absorption enhancers as tools to determine the route of nasal absorption of peptides.

The nasal absorption of a series of peptides was studied in order to examine the relationship between extent of absorption and lipophilicity and absorption enhancers were used to probe the mechanism of peptide absorption. An in situ rat nasal perfusion technique was employed to assess the nasal absorption of a series of peptides, D-FGGGGG (D-FG5), D-FD-FGGGG (D-F2G4) and D-FD-FD-FGGG (D-F3G3), [D-ala2, D-leu5]enkephalin (YD-AGFD-L) and thyrotrophin releasing hormone (TRH). The enhancers sodium tauro-24,25 dihydrofusidate (STDHF), ethylene diamine tetraacetic acid (EDTA and dimethyl-beta-cyclodextrin (DMbetaCD) were utilized to improve and elucidate the mechanisms of peptide absorption. There was no significant relationship between extent of peptide absorption and lipophilicity as determined by C log P values. STDHF was a potent absorption enhancer but demonstrated overt toxicity. Conversely, EDTA did not demonstrate extensive toxicity but was found to be a poor absorption enhancer. DMbetaCD displayed some toxicity and was also found to inhibit the absorption of D-FG5,D-F2G4 and D-F3G3. This reduction is likely to be a result of the peptide/DMbetaCD complex formation. The peptides studied appear to be predominantly absorbed by a passive paracellular mechanism.

Novel nanoparticles for pulmonary drug administration.

A novel one-step, low energy method, which avoids harsh processing conditions including potentially toxic and chemically reactive cross-linking agents, for the production of hydrophilic drug nanoparticles suitable for dispersion in the hydrofluoroalkane propellants was investigated. Reverse-phase microemulsions were used as the template for the production of nanoparticles. Two microemulsion systems were investigated: water/sodium bis(2-ethylhexyl) sulphosuccinate (AOT)/iso-octane and water/lecithin/propan-2-ol/iso-octane. Nanoparticles were captured by snap freezing with subsequent freeze-drying. Nanoparticles were dispersed in 1,1,1,2,3,3,3-heptafluoropropane (HFA-227) and the aerosol performance of the pressurised metered dose inhaler (pMDI) assessed by cascade impaction. Spherical nanoparticles less than 300 nm in size were produced. Nanoparticles produced using AOT as the surfactant could not be dispersed in HFA-227. However lecithin based nanoparticles could be dispersed in co-solvent modified HFA-227 and produced fine aerosols (Mass Median Aerodynamic Diameter < or = 1.5 microns, fine particle fraction > 58%). This data suggests that a high fraction of the nanoparticles would be deposited (targeted) within the lung with the deposition being mainly alveolar. That is the ideal deposition profile for the systemic delivery of drugs via the lungs.

Improved nasal bioavailability of FITC-dextran (Mw 4300) from mucoadhesive microspheres in rabbits.

The nasal bioavailability of fluorescein isothiocyanate-dextran (FITC-dextran) (Mw = 4300) encapsulated in non-mucoadhesive and mucoadhesive microspheres in New Zealand White rabbits was investigated. FITC-dextran was administered nasally encapsulated in carbopol 934P, chitosan and lactose microspheres and the bioavailability compared to intravenous administration of FITC-dextran solution. Administration of FITC-dextran as carbopol microspheres produced a significantly greater bioavailability (33%) than after administration as chitosan (13%) and non-mucoadhesive rapidly dissolving control lactose microspheres (9%). The FITC-dextran terminal plasma half-lives after carbopol 934P and chitosan microsphere administration were significantly longer than after intravenous administration of FITC-dextran. The FITC-dextran terminal plasma half-life after carbopol 934P microspheres administration was significantly longer than after lactose microsphere administration. This data suggested that the increase in FITC-dextran bioavailability after carbopol 934P microspheres administration was due to increased residence at the absorptive site via mucoadhesion and reduced mucociliary clearance. A change in mucosal permeability could not however be discounted especially for the chitosan microspheres.

Transport of a series of D-phenylalanine-glycine hexapeptides across rat alveolar epithelia in vitro.

The effect of lipophilicity on the absorption of peptides from the lungs was investigated. D-phenylalanine (F)-glycine (G) hexapeptides were synthesised to differ, predominantly, only in their lipophilicity. Rat alveolar type II cells were isolated and cultured on plastic, or polycarbonate filters; by day 6 they had de-differentiated to an alveolar type I-like epithelium. The permeability of the monolayers to the hexapeptides was determined. The hexapeptides were metabolically and chemically stable for greater than 24h in the presence of the cells. They did not adhere to the cell culture plastic and were associated only to a low extent with the cell monolayer. The apical to basolateral permeability coefficients for D-F1G5, D-F2G4, and D-F3G3 were 2.19+/-0.53, 1.75+/-0.42 and 2.20+/-0.56 x 10(-7) cm s(-1) respectively. The permeability of the monolayers to D-F1G5 and D-F2G4 was concentration and direction independent, however for D-F3G3 the monolayer was more permeable in the basolateral to apical direction. There was no correlation between the lipophilicity of the hexapeptides and permeability coefficients: other physicochemical parameters did not predict hexapeptide transport. Lipophilicity does not appear to control the transport of hexapeptides across the alveolar epithelium probably as a consequence of the peptides being transported via the paracellular route.

Rheological evaluation of hog gastric mucin as a model mucus system.

The rheological evaluation of preparations containing 10, 15, 20, and 25% powdered hog gastric mucin was carried out over the 13-48 degrees temperature range using rotational and creep viscometry. The preparations were almost viscous, and no elastic behavior was demonstrated. The addition of borate ions frequently produced a slight decrease in viscosity. Tetracycline hydrochloride decreased the viscosity of the 10 and 25% materials, although the addition of this compound to fresh gastric and bronchial mucous gels markedly increased viscosity. The model is, therefore, only suitable in limited circumstances as a basis for the evaluation of the effect of drugs on gastric mucus.

Correlations between physical and drug release characteristics of polyethylene glycol suppositories.

The mechanical strength and elastic moduli of blocks of polyethylene glycol with a range of molecular weights were determined. A rotating-basket dissolution test was used to measure the release characteristics of prednisolone from similar blocks. The effects of blending bases of different molecular weight and of the addition of water also were determined. Linear relationships were found for the mechanical strength, molecular weight, and release rate, but no simple relationship could be observed for the elastic moduli.

Putrescine uptake by alveolar epithelial cell monolayers exhibiting differing transepithelial electrical resistances.

Rat alveolar type II cells were isolated following elastase digestion and cultured on polycarbonate filters at various densities and in different media. Two days after seeding, the cells formed a monolayer on the filters which consisted predominantly of type II cells, these then de-differentiated to a alveolar type I-like cell monolayer by day 6. The seeding density and media utilized affected the transepithelial electrical resistance (TEER) generated by the monolayer. Only certain culture conditions allowed the production of a monolayer that mimics, putatively, the in vivo alveolar epithelium (TEER greater than 1000 omega cm2). Vmax and K(m) values for the uptake of putrescine by monolayers exhibiting low and high TEERs on day 6 were determined. The capacity of the putrescine uptake mechanisms was greater in cell monolayers exhibiting a high TEER than those exhibiting a low TEER, suggesting that the TEER does not only measure the "tightness" of the monolayer but contains an element representative of the viability of the cell monolayer. The selection of appropriate TEERs for cell culture investigations is discussed.

Combined effect of oleic acid and polyethylene glycol 200 on buccal permeation of [D-ala2, D-leu5]enkephalin from a cubic phase of glyceryl monooleate.

The combined use of the lipophilic permeation enhancer, oleic acid together with polyethylene glycol 200 (PEG 200) as a co-enhancer and incorporated into the cubic liquid crystalline phase of glyceryl monooleate was investigated in the ex vivo buccal permeation of [D-Ala2, D-Leu5]enkephalin (DADLE) through porcine buccal mucosa mounted in a Franz cell. The addition of oleic acid (1%) and PEG 200 (1-10%) did not change the intact appearance of the cubic phase. PEG 200 increased the aqueous solubility of oleic acid incorporated into the cubic phase and hence promoted the transport of oleic acid into the porcine buccal mucosa. The solubilising effect of PEG 200 on oleic acid incorporated into the cubic phase was dependent on the PEG 200 concentration but was non-linear. The buccal permeation flux of DADLE significantly increased when 5% (P<0.01) or 10% (P<0.001) of PEG 200 was co-administered with 1% oleic acid compared with the cubic phase containing 1% oleic acid alone. The present results suggest that PEG 200 enhances the action of the lipophilic permeation enhancer oleic acid and that the combination of oleic acid and PEG 200 as a co-enhancer can be a useful tool to improve the membrane permeability in the buccal delivery of peptide drugs using a cubic liquid crystalline phase of glyceryl monooleate and water.

Nebulisation of rehydrated freeze-dried beclomethasone dipropionate liposomes.

Beclomethasone dipropionate (BDP) liposomes were prepared from various lipids, dilauroyl phosphatidylcholine (DLPC), dimyristoyl phosphatidylcholine (DMPC), dipalmitoyl phosphatidylcholine (DPPC), and hydrogenated soybean phosphatidylcholine (Epikuron 200 SH). A lipid with a low transition temperature (T(m)) (DLPC) incorporated a higher amount of BDP than lipid with a high T(m). The nebulisation of rehydrated freeze-dried BDP liposomes was carried out using a Pari LC Plus nebuliser and the generated aerosol characterised by an Andersen Cascade Impactor operated at 28.3 l/min. The rehydrated BDP-DLPC liposomes showed a higher output (78.3%) and a higher fine particle fraction (FPF) (75.0%) and smaller mass median aerodynamic diameter (MMAD) (3.31 microm) than the other rehydrated liposome preparations. Liposomes containing lipid with a high T(m) (DPPC and Epikuron) underwent aggregation during nebulisation. This was shown by the large increase in size of the DPPC liposomes from 15.78 to 47.51 microm and the Epikuron liposomes from 5.84 to 46.70 microm.

In vitro peptide release from liquid crystalline buccal delivery systems.

Swelling and [D-Ala(2), D-Leu(5)]enkephalin (DADLE) release from the lamellar and cubic liquid crystalline phases of glyceryl monooleate (GMO) were studied using two in vitro methods, a total immersion method and a Franz cell method. The swelling of the lamellar phase and glyceryl monooleate (0% w/w water content) and DADLE release from the liquid crystalline phases were temperature dependent. The swelling ratio was greater at 20 degrees C than 37 degrees C while DADLE release increased at 37 degrees C compared to 20 degrees C for both the lamellar and cubic phases. The water uptake increased dramatically with decreasing initial water content of the liquid crystalline phases. However, DADLE release increased with increasing initial water content, which corresponded to increased viscosity. The swelling and DADLE release profiles obtained using a Franz cell method with a moist nylon membrane to mimic buccal drug release conditions were slower than the total immersion method. These results show that the swelling and DADLE release strongly depended on temperature, the initial water content of the liquid crystalline matrix and the methodology employed for determining the swelling and DADLE release.

Buccal permeation of [D-Ala(2), D-Leu(5)]enkephalin from liquid crystalline phases of glyceryl monooleate.

The ex vivo buccal permeability of a [D-Ala(2), D-Leu(5)]enkephalin (DADLE) and glyceryl monooleate (GMO) was examined from the cubic and lamellar liquid crystalline phases of GMO and aqueous phosphate-buffered saline (pH 7.4, PBS) solution across excised porcine buccal mucosa mounted in a Franz cell. GMO was released in vitro from the liquid crystalline phases indicating the erosion of the liquid crystal matrices. GMO released from the liquid crystalline matrices permeated the porcine buccal mucosa with fluxes of 0.10+/-0.03 and 0.07+/-0.00%/cm(2) per h for the cubic and lamellar phases, respectively. The flux of DADLE (1.21+/-0.32 and 1. 15+/-0.11%/cm(2) per h for the cubic and lamellar phases, respectively) from the liquid crystalline phases was significantly enhanced by the GMO compared with PBS solution (0.43+/-0.08%/cm(2) per h) during the initial permeation phase (t<3 h). Our results suggest that the cubic and lamellar liquid crystalline phases can be considered as promising buccal drug carriers for peptide drugs as well as acting as permeation enhancers.

Physical stability and in-vitro gene expression efficiency of nebulised lipid-peptide-DNA complexes.

The lower respiratory tract provides a number of disease targets for gene therapy. Nebulisation is the most practical system for the aerosolisation of non-viral gene delivery systems. The aerosolisation process represents a significant challenge to the maintenance of the physical stability and biological activity of the gene vector. In this study we investigate the role of a condensing polycationic peptide on the stability and efficiency of nebulised lipid-DNA complexes. Complexes prepared from the cationic lipid 1, 2-dioleoyl-3-trimethylammonium propane (DOTAP) and plasmid DNA (pDNA) at mass (w/w) ratios of 12:1, 6:1 and 3:1, and complexes prepared from DOTAP, the polycationic peptide, protamine, and pDNA (LPD) at 3:2:1 w/w ratio were nebulised using a Pari LC Plus jet nebuliser. Samples from the nebuliser reservoir (pre- and post-nebulisation) and from the aerosol mist were collected and investigated for changes, including: particle diameter, retention of in-vitro transfection activity and the relative concentration and nature of the complexed pDNA remaining after the nebulisation procedure. The process of jet nebulisation adversely affected the physical stability of lipid:pDNA complexes with only those formulated at 12:1 w/w DOTAP:pDNA able to maintain their pre-nebulisation particle size distribution (145+/-3 nm pre-nebulisation vs. 142+/-2 nm aerosol mist) and preserve significant pDNA integrity in the reservoir (35% of pre-nebulisation pDNA band intensity). The LPD complexes were smaller (102+/-1 nm pre-nebulisation vs. 113+/-2 nm aerosol mist) with considerably greater retention of pDNA integrity in the reservoir (90% of pre-nebulisation pDNA band intensity). In contrast the concentration of pDNA in the aerosol mist for both the 12:1 w/w DOTAP:pDNA and LPD complexes were significantly reduced (10 and 12% of pre-nebulised values, respectively). Despite reduced pDNA concentration the transfection (% cells transfected) mediated by aerosol mist for the nebulised complexes was comparatively efficient (LPD aerosol mist 26 vs. 40% for pre-nebulised complex; the respective values for 12: 1 w/w DOTAP:pDNA were 12 vs. 28%). The physical stability and biological activity of nebulised lipid:pDNA complexes can be improved by inclusion of a condensing polycationic peptide such as protamine. The incorporation of the peptide precludes the use of potentially toxic excesses of lipid and charge and may act as a platform for the covalent attachment of peptide signals mediating sub-cellular targetting.

The transport of polymeric microspheres across the ciliated epithelia of the bullfrog.

The influence of some hydrophilic polymers on the clearance of particles across the ciliated epithelium of the bullfrog palate has been examined. The polymers studied were Carbopol 907 cross-linked with maltose to provide microspheres of varying cross-link density, Carbopol 934P, hydroxypropylmethylcellulose, chitosan and poly(vinyl alcohol). Transport rates were determined relative to glass spheres. The polymers in dilute solution (0.1 and 0.5% w/v) resulted in a reduction in the transport rate of the glass spheres. For non-cross-linked microspheres, Carbopol 934P exhibited a lower transport rate than the more slowly hydrating chitosan. The cross-linked poly(acrylic acid) microspheres showed clearance rates which were dependent on the cross-link density. Incorporation of some preservatives (EDTA, methylhydroxybenzoate, chlorbutol and chlorocresol), known to reversibly retard clearance, into the cross-linked poly(acrylic acid) microspheres produced effects dependent on cross-link density: lightly cross-linked microspheres were cleared more slowly than the preservative-free microspheres whilst for more heavily cross-linked particles the converse was observed.

Physico-chemical characterisation and transfection efficiency of lipid-based gene delivery complexes.

Cationic liposomes spontaneously interact with negatively charged plasmid DNA to form a transfection competent complex capable of promoting the expression of a therapeutic gene. This work aims to improve the understanding of the poorly defined mechanisms and structural rearrangements associated with the lipid-DNA interaction. Specifically, dimethyl dioctadecylammonium bromide (DDAB):dioleoyl phosphatidylethanolamine (DOPE) and 1,2-dioleoyl-3-trimethylammonium propane (DOTAP) liposomes were mixed with a reporter plasmid (pADbeta or pCMVbeta) to form lipid-DNA complexes. The size and charge characteristics of the complexes as determined by photon correlation spectroscopy and microelectrophoresis were found to be dependent on the lipid:DNA ratio, with both DDAB:DOPE-DNA and DOTAP-DNA complexes aggregating at around neutral zeta potential. Negative stain transmission electron microscopy demonstrated at least three distinct complex structures being formed at the same DOTAP:DNA ratio. We postulate that two of these aggregates are structural moieties involved in the formation of the efficient transfection particle. Gel electrophoresis was used to determine the efficiency and extent of lipid-DNA complex formation. Results showed that only DOTAP liposomes were capable of preventing ethidium bromide intercalation with DNA and protecting the enclosed plasmid from nuclease digestion. When a range of lipid-DNA complexes were transfected into in vitro cell lines, the efficiency of reporter gene (beta-galactosidase) expression was found to depend on the type of liposome used in the complex, the ratio of lipid:DNA and the transfected cell line. Our results challenge the requirement for DOPE to be included in the formulation of cationic lipid vectors, especially in the case of DOTAP containing liposomes.