Effect of penetration enhancers on the phase transition of multilamellar liposomes of dipalmitoylphosphatidylcholine. A study by differential scanning calorimetry

Permeation enhancer nanovesicles mediated topical delivery of curcumin for the treatment of hyperpigmentation

The main aim of the present study was to develop curcumin (CUR) loaded permeation enhancer-lipid vesicles for the treatment of hyperpigmentation. Hyperpigmentation is an acquired skin disorder characterized by uneven skin coloration, mainly in the regions of the facial skin, affecting millions of people worldwide. It often occurs in visible areas, hence causing significant negative psychological and social impacts. In the present study, curcumin-loaded permeation enhancer nanovesicles (PE-NVs) were developed by modified ethanol injection method and dimethyl sulfoxide was added as a penetration enhancer. PE-NVs were subjected to various physicochemical characterizations and drug permeation studies across the skin. The PE-NVs were tested for their efficacy in a sunlight-induced hyperpigmented rabbit skin model. Topical application of PE-NVs reduced symptoms of hyperpigmentation as compared with CUR methanolic solution because of higher accumulation because of better permeation into skin layers. Histopathological studies also confirmed the effectiveness of PE-NVs, since they reduced hyperpigmentation-induced lesions. Results confirmed that PE-NVs is a potential drug delivery system for topical administration drugs to treat skin-associated inflammatory disorders.

Accumulation of styrene oligomers alters lipid membrane phase order and miscibility

Growth of plastic waste in the natural environment, and in particular in the oceans, has raised the accumulation of polystyrene and other polymeric species in eukyarotic cells to the level of a credible and systemic threat. Oligomers, the smallest products of polymer degradation or incomplete polymerization reactions, are the first species to leach out of macroscopic or nanoscopic plastic materials. However, the fundamental mechanisms of interaction between oligomers and polymers with the different cell components are yet to be elucidated. Simulations performed on lipid bilayers showed changes in membrane mechanical properties induced by polystyrene, but experimental results performed on cell membranes or on cell membrane models are still missing. We focus here on understanding how embedded styrene oligomers affect the phase behavior of model membranes using a combination of scattering, fluorescence, and calorimetric techniques. Our results show that styrene oligomers disrupt the phase behavior of lipid membranes, modifying the thermodynamics of the transition through a spatial modulation of lipid composition.

Methods for evaluating penetration of drug into the skin: A review

BACKGROUND

Skin being the largest organ of the human body plays a very important role in the permeation and penetration of the drug. In addition, the transdermal drug delivery system (TDDS) plays a major role in managing dermal infections and attaining sustained plasma drug concentration. Thus, evaluation of percutaneous penetration of the drug through the skin is important in developing TDDS for human use.

MATERIAL AND METHODS

Various techniques are used for getting the desired drug penetration, permeation, and absorption through the skin in managing these dermal disorders. The development of novel pharmaceutical dosage forms for dermal use is much explored in the current era. However, it is very important to evaluate these methods to determine the bioequivalence and risk of these topically applied drugs, which ultimately penetrate and are absorbed through the skin.

RESULTS

Currently, numerous skin permeation models are being developed and persuasively used in studying dermatopharmacokinetic (DPK) profile and various models have been developed, to evaluate the TDD which include ex vivo human skin, ex vivo animal skin, and artificial or reconstructed skin models.

CONCLUSION

This review discusses the general physiology of the skin, the physiochemical characteristics affecting particle penetration, understand the models used for human skin permeation studies and understanding their advantages, and disadvantages.

Characterizations on the Stability and Release Properties of β-ionone Loaded Thermosensitive Liposomes (TSLs)

Liposomes with phase transition temperatures, T_m, near pathogenic site temperature are potential chemoprophylactic delivery vehicles. We prepared and characterized the thermal properties of liposomes composed of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) and hydrogenated soy phosphatidylcholine (HSPC) incorporating β-ionone with T_m at 42 °C. Liposomes with β-ionone/lipid ratio (w/w) of 1:20 and 1:8 had the necessary stability and released most of the β-ionone. The molecular architecture surrounding T_m was studied by fluorescent probes, Raman spectroscopy, and differential scanning calorimeter (DSC). β-Ionone was found to be preferentially located in the deep regions of the lipid bilayer (toward the long chain alkyl of the lipid) at moderate loading. The results showed that β-ionone encapsulated liposomes have a superior release at higher loading amount. Increasing β-ionone leads to disorder in the liquid crystalline state and accelerates the release rate. These studies provide information on the membrane structural properties of β-ionone loaded liposomes that guide rational bioactive molecular delivery systems design for health products.

Effects of various penetration enhancers on penetration of aminophylline through shed snake skin

BACKGROUND

Cellulite is the accumulation of subcutaneous fat and connective tissue in tights and buttocks. Xanthines, such as aminophylline, are used as phosphodiesterase inhibitors, and are also adenosine receptor antagonists.

OBJECTIVES

The aim of the present study was to characterize in vitro aminophylline transdermal absorption through shed snake skin, and to investigate the absorption enhancing effect of various enhancers.

MATERIALS AND METHODS

Aminophylline gels were prepared using theophylline and ethylenediamine as raw materials of aminophylline, hydroxypropyl methyl cellulose (HPMC) F4M as gelling agent, and propylene glycol as a co-solvent. Sodium tauroglycocholate (STGC) (100, 200, and 500 μg/mL), lauric acid (1.7 and 15%), and ethanol (60%) were added as enhancers. In vitro percutaneous absorption experiments were performed on snake skin using Franz diffusion cells. Flux (J), permeability coefficient (P), and enhancement factor (EF) for each formulation were calculated.

RESULTS

The results indicated that all of enhancers significantly enhanced drug permeability. This effect was decreased by increasing the concentration of STGC; in contrast, by increasing the concentration of lauric acid from 1.7 to 15%, EF was enhanced Although ethanol (60%) and STGC (100 μg/mL) showed the highest EFs, the effect of ethanol on drug permeability appeared with a lag time.

CONCLUSIONS

According to the findings, type and concentration of penetration enhancers can effect on transdermal permeation of drug.

Mechanisms of action of novel skin penetration enhancers: Phospholipid versus skin lipid liposomes

Employing thermal analysis, we investigated the mechanism of action of novel enhancers and probed phospholipid (PL) versus stratum corneum lipid (SCL) liposomes as model membranes. The enhancers included octyl salicylate (OS), padimate O (PADO) and 2-(1-nonyl)-1,3-dioxolane (ND). The negative controls were the empty liposomes. Positive controls employed dimethylsulfoxide (DMSO) and Azone (AZ). For PL liposomes, DMSO sharpened the transitions. AZ abolished the pre-transition, broadened the main transition and linearly reduced its transition temperature (T(m)). OS or PADO reduced T(m) and size of pre-transition, broadened the main transition and decreased its T(m) (non-linearly). ND abolished the pre-transition but increased T(m) of the main endotherm, suggesting retardation rather than enhancement. The results of SCL correlated with PL liposomes except for ND. In SCL liposomes, ND reduced T(m) and broadened the peaks indicating lipid disruption, which indicated its enhancing effects. In conclusion, OS, PADO and ND can enhance drugs by disrupting intercellular lipid domain but they differ from AZ in terms of the relationship between efficacy and concentration. Although PL liposomes are simple model membranes with sharp transitions which give detailed information about the effects of enhancers, they can provide misleading results. Simultaneous use of other models like SCL liposomes is recommended.

Mechanistic studies on percutaneous penetration enhancement by N-(4-halobenzoyl)-S,S-dimethyliminosulfuranes

Halogen-substituted iminosulfuranes are transdermal penetration enhancers (TPEs) in permeation studies using hairless mouse or human cadaver skin. The interaction of N--(4--R-benzoyl)-S,S-dimethyliminosulfuranes 1--4, where R=H, Cl, Br, and I, with l-alpha-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) has been studied using differential scanning calorimetry, isothermal titration calorimetry, nuclear Overhauser effect spectroscopy (NOESY), and NMR spectroscopy, and by calculation of the iminosulfurane polarizabilities in order to elucidate the molecular basis of the TPE activity. The active compounds reduce the melting temperature of the gel-to-liquid-crystal phase transition and induce multiple components in the transition excess heat capacity profile. The partitioning of the bromo derivative 3, the most active compound, into DMPC is unique in that 3 may be trapped in the bilayer, affording an enhanced residence time and a reason for its high TPE activity. The entropy decrease associated with the transfer of 3 to the bilayer is much lower than that for the other compounds, indicating that 3 occupies or induces sites that afford it considerable local motional freedom. Correlations between the iminosulfurane TPE activities, the partition coefficients, and NOESY crosspeak volume were observed. Molecular polarizabilities are not consistent with a TPE mode of action involving interaction of these agents with protein side chains.

Interaction of phloretin and 6-ketocholestanol with DPPC-liposomes as phospholipid model membranes

Phloretin and 6-ketocholestanol are penetration enhancers for percutaneous delivery of certain topically applied drugs. In the present study some physicochemical experiments have been performed to elucidate the mechanism of action of phloretin and 6-ketocholestanol. The penetration enhancing effect of phloretin and 6-ketocholestanol is believed to be due to their increase of the fluidity of the intercellular lipid bilayers of the stratum corneum. Phospholipid vesicles were chosen as a simple model to represent these bilayers. The effect of phloretin and 6-ketocholestanol on phase transition temperature and enthalpy was studied using differential scanning calorimetry. Beside of that the size of liposomes was monitored when the amount of penetration enhancer in the liposome preparation was changed. Addition of increasing amounts of phloretin and 6-ketocholestanol to the bilayer resulted in lowering of phase transition temperatures and increasing the enthalpy. Additionally the size of the liposomes was increased when penetration enhancer was added. The results suggest that phloretin as well as 6-ketocholestanol would interact with stratum corneum lipids in a similar manner, both reduce the diffusional resistance of the stratum corneum to drugs with balanced hydrophilic-lipophilic characteristics.

Drug interaction and location in liposomes: correlation with polar surface areas

An important step in liposome characterization is to determine the location of a drug within the liposome. This work thus investigated the interaction of dipalmitoylphosphatidylcholine liposomes with drugs of varied water solubility, polar surface area (PSA) and partition coefficient using high sensitivity differential scanning calorimetry. Lipophilic estradiol (ES) interacted strongest with the acyl chains of the lipid membrane, followed by the somewhat polar 5-fluorouracil (5-FU). Strongly hydrophilic mannitol (MAN) showed no evidence of interaction but water soluble polymers inulin (IN) and an antisense oligonucleotide (OLG), which have very high PSAs, interacted with the lipid head groups. Accordingly, the drugs could be classified as: hydrophilic ones situated in the aqueous core and which may interact with the head groups; those located at the water-bilayer interface with some degree of penetration into the lipid bilayer; those lipophilic drugs constrained within the bilayer.

Interactions of surfactants (edge activators) and skin penetration enhancers with liposomes

Incorporating edge activators (surfactants) into liposomes was shown previously to improve estradiol vesicular skin delivery; this phenomenon was concentration dependent with low or high concentrations being less effective. Replacing surfactants with limonene produced similar behaviour, but oleic acid effects were linear with concentration up to 16% (w/w), beyond which it was incompatible with the phospholipid. This present study thus employed high sensitivity differential scanning calorimetry to probe interactions of additives with dipalmitoylphosphatidylcholine (DPPC) membranes to explain such results. Cholesterol was included as an example of a membrane stabiliser that removed the DPPC pre-transition and produced vesicles with a higher transition temperature (T(m)). Surfactants also removed the lipid pre-transition but reduced T(m) and co-operativity of the main peak. At higher concentrations, surfactants also formed new species, possibly mixed micelles with a lower T(m). The formation of mixed micelles may explain reduced skin delivery from liposomes containing high concentrations of surfactants. Limonene did not remove the pre-transition but reduced T(m) and co-operativity of the main peak, apparently forming new species at high concentrations, again correlating with vesicular delivery of estradiol. Oleic acid obliterated the pre-transition. The T(m) and the co-operativity of the main peak were reduced with oleic acid concentrations up to 33.2mol%, above which there was no further change. At higher concentrations, phase separation was evident, confirming previous skin transport findings.

Valence Topological Charge-Transfer Indices for Dipole Moments

New valence topological charge-transfer indices are applied to the calculation of dipole moments. The algebraic and vector semisum charge-transfer indices are defined. The combination of the charge-transfer indices allows the estimation of the dipole moments. The model is generalized for molecules with heteroatoms. The ability of the indices for the description of the molecular charge distribution is established by comparing them with the dipole moments of a homologous series of phenyl alcohols. Linear and non-linear correlation models are obtained. The new charge-transfer indices improve the multivariable non-linear regression equations for the dipole moment. When comparing with previous results, the variance decreases 92%. No superposition of the corresponding G_k–J_k and – pairs is observed. This diminishes the risk of co-linearity. Inclusion of the oxygen atom in the π-electron system is beneficial for the description of the dipole moment, owing to either the role of the additional p orbitals provided by the heteroatom or the role of steric factors in the π-electron conjugation. Linear and non-linear correlations between the fractal dimension and various descriptors point not only to a homogeneous molecular structure but also to the ability to predict and tailor drug properties.

The influence of dilution of topical semisolid preparations on hydrocortisone permeation through excised human stratum corneum

Dilution of semisolid preparations, in order to tailor the formulations to the needs of the patients, was thought to be associated with a number of dangers, one of which is the unpredictable alteration of activity. In the present study the influence of dilution on hydrocortisone permeation through excised human stratum corneum was investigated. The permeation profiles of hydrocortisone from various cream bases (diluted and undiluted) were found to be very similar with no significant differences. This result was in accordance with the lack of interaction between the tested bases and the structure of stratum corneum as shown by differential scanning calorimetry experiments. Thus, the permeability of stratum corneum, which was not affected by the cream bases, is the rate limiting step for drug permeation. However, it could be shown that dilution of Soventol cream (placebo with 1% hydrocortisone) which is known to contain isopropyl myristate as permeation enhancer reduces drug permeation. The reduced hydrocortisone permeation is believed to be due to reduced enhancer concentration.

Oestradiol skin delivery from ultradeformable liposomes: refinement of surfactant concentration

The aims of this study were to refine ultradeformable liposomes for oestradiol skin delivery and to evaluate Span 80 and Tween 80 as edge activators compared with sodium cholate. Vesicles containing phosphatidylcholine (PC) mixed with edge activators and oestradiol were prepared. Entrapment efficiency and vesicle size were determined. Interactions between activators and vesicles were investigated using differential scanning calorimetry. Transepidermal permeation of oestradiol from vesicles was studied compared to saturated aqueous control in vitro. The maximum flux (J(max)) and its time (T(max)) were calculated from the flux curves and skin deposition was assessed. The compositions of refined formulations were predicted, liposomes prepared, and tested against control. Entrapment efficiency depended on PC concentration with some contribution from sodium cholate and Tween 80. Vesicle sizes ranged from 124 to 135 nm. Edge activators interacted with lipid bilayers and disrupted packing. The refined edge activator concentrations in PC vesicles were 14.0, 13.3 and 15.5% w/w for sodium cholate, Span 80 and Tween 80, respectively; they increased J(max) by 18, 16 and 15-fold and skin deposition by 8, 7 and 8-fold compared with control. Ultradeformable vesicles thus improved skin delivery of oestradiol compared to control and Span 80 and Tween 80 were equivalent to sodium cholate as edge-activators.

Liposomes, micelles and microemulsions as new delivery systems for cytotoxic alkaloids

This review describes the design and performance of specialized delivery systems, such as liposomes, micellar solutions and microemulsions, for the administration of cytotoxic alkaloids. Special attention is directed towards three types of compound, Vinca, Camptotheca and Taxus alkaloids, which have been previously indicated as of promise as antitumour agents but which still present serious drawbacks. In this respect, this review analyses different delivery strategies that are able to substantially improve the therapeutic applicability of such antitumour drugs.

Chemical enhancement of percutaneous absorption in relation to stratum corneum structural alterations

The outermost layer of the skin, stratum corneum (SC), provides an outstanding barrier against the external environment and is also responsible for skin impermeability toward most solutes. The barrier function is related to the unique composition of the SC lipids and their complex structural arrangement. The lipoidal matrix of the SC, therefore, is a target of penetration enhancer action. The literature on the skin barrier structure and function and on the mechanisms of action of some well established permeation promoters, with a focus on their impact on SC structural alterations, is reviewed. Data obtained from infrared, thermal, and fluorescence spectroscopic examinations of the SC and its components imply enhancer improved permeation of solutes through the SC is associated with alterations involving the hydrocarbon chains of the SC lipid components. Data obtained from electron microscopy and X-ray diffraction reveals that the disordering of the lamellar packing is also an important mechanism for increased permeation of drugs induced by penetration enhancers.

An attempt to clarify the mechanism of the penetration enhancing effects of lipophilic vehicles with differential scanning calorimetry (DSC)

In a previous in-vivo skin penetration study, it was observed that certain lipophilic liquid vehicles enhanced drug penetration, whilst others did not. To clarify the mechanism of skin penetration enhancement, isolated sheets of human stratum corneum were measured by differential scanning calorimetry (DSC), either untreated or after pretreatment with various lipophilic liquids (highly purified light mineral oil, isopropyl myristate, caprylic/capric acid triglycerides containing 5% phospholipids, dibutyl adipate, dimethicone 100, cetearyl iso-octanoate, caprylic/capric acid triglycerides), commonly used in ointment bases. All samples were analysed over a heating range of at least--10-130 degrees C. All DSC curves were evaluated with regard to the phase-transition enthalpies (peak areas) and peak maximum temperatures of the lipid-phase transitions at ca 75 and 85 degrees C. With the exception of dimethicone 100, cetearyl iso-octanoate and caprylic/capric acid triglycerides, all vehicles showed characteristic alterations of the phase-transition temperatures and enthalpies of the stratum corneum lipids. Mineral oil and isopropyl myristate caused a reduction of the enthalpy and a decrease of the phase-transition temperatures. These two vehicles are thought to fluidize the lamellar-gel phase of the stratum corneum lipids, and possibly partially dissolve the lipids. Dibutyl adipate and caprylic/capric acid triglycerides containing 5% phospholipids decreased the phase-transition enthalpy only, probably due to dissolution or extraction of the stratum corneum lipids. These DSC results provide an explanation for the in-vivo penetration-enhancing effects observed previously.

Spectroscopic studies of tin ethyl etiopurpurin in homogeneous and heterogeneous systems

Tin ethyl etiopurpurin is a promising second generation photosensitizer for photodynamic treatment of cancer. This compound is only poorly soluble in aqueous media and, therefore, needs a delivery system for administration to animals. Successful tumor eradication has previously been reported, following light exposure of rats previously administered with the purpurin formulated as a Cremophor El emulsion, in dipalmitoyl-phosphatidyl-choline liposomes or with gamma cyclodextrins. In this paper, we describe some absorbance and fluorescence studies of tin ethyl etiopurpurin in homogeneous and heterogeneous systems. In general, absorption and emission maxima were found to be red shifted as the environment changed from polar to non-polar. The viscosity and dielectric constant of the medium affected the purpurin fluorescence intensity. The liposome preparations were characterized by particle size determination, differential scanning calorimetry and by sensitizer fluorescence quenching studies. Photobleaching studies also showed variation owing to changes in the environment in which the dye was located.