Role of intercellular lipids in stratum corneum in the percutaneous permeation of drugs

Assessing Barrier Function in Psoriasis and Cornification Models of Artificial Skin Using Non-Invasive Impedance Spectroscopy

Reconstructed epidermal equivalents (REEs) consist of two distinct cell layers - the stratum corneum (SC) and the keratinocyte layer (KL). The interplay of these layers is particularly crucial in pruritic inflammatory disorders, like psoriasis, where a defective SC barrier is associated with immune dysregulation. However, independent evaluation of the skin barrier function of the SC and KL in REEs is highly challenging because of the lack of quantitative methodologies that do not disrupt the counter layer. Here, a non-invasive impedance spectroscopy technique is introduced for dissecting the distinct contributions of the SC and KL to overall skin barrier function without disrupting the structure. These findings, inferred from the impedance spectra, highlight the individual barrier resistances and maturation levels of each layer. Using an equivalent circuit model, a correlation between impedance parameters and specific skin layers, offering insights beyond traditional impedance methods that address full-thickness skin only is established. This approach successfully detects subtle changes, such as increased paracellular permeability due to mild irritants and the characterization of an immature SC in psoriatic models. This research has significant implications, paving the way for detailed mechanistic investigations and fostering the development of therapies for skin irritation and inflammatory disorders.

Dehydrated Biomimetic Membranes with Skinlike Structure and Function

Novel vapor-permeable materials are sought after for applications in protective wear, energy generation, and water treatment. Current impermeable protective materials effectively block harmful agents but trap heat due to poor water vapor transfer. Here we present a new class of materials, vapor permeable dehydrated nanoporous biomimetic membranes (DBMs), based on channel proteins. This application for biomimetic membranes is unexpected as channel proteins and biomimetic membranes were assumed to be unstable under dry conditions. DBMs mimic human skin's structure to offer both high vapor transport and small molecule exclusion under dry conditions. DBMs feature highly organized pores resembling sweat pores in human skin, but at super high densities (>1012 pores/cm2). These DBMs achieved exceptional water vapor transport rates, surpassing commercial breathable fabrics by up to 6.2 times, despite containing >2 orders of magnitude smaller pores (1 nm vs >700 nm). These DBMs effectively excluded model biological agents and harmful chemicals both in liquid and vapor phases, again in contrast with the commercial breathable fabrics. Remarkably, while hydrated biomimetic membranes were highly permeable to liquid water, they exhibited higher water resistances after dehydration at values >38 times that of commercial breathable fabrics. Molecular dynamics simulations support our hypothesis that dehydration induced protein hydrophobicity increases which enhanced DBM performance. DBMs hold promise for various applications, including membrane distillation, dehumidification, and protective barriers for atmospheric water harvesting materials.

Development of Ultradeformable Liposomes with Fatty Acids for Enhanced Dermal Rosmarinic Acid Delivery

This study aimed to develop ultradeformable liposomes (ULs) with fatty acids, namely, oleic, linoleic, and linolenic acid, to improve the skin penetration of rosmarinic acid. This study also investigated the vesicle-skin interaction and skin penetration pathway of ULs with fatty acids using the co-localization technique of multifluorescently labeled particles. The prepared ULs were characterized in terms of size, surface charge, size distribution, shape, % entrapment efficiency (% EE), and % loading efficiency (% LE). The prepared ULs with fatty acids had an average particle size between 50.37 ± 0.3 and 59.82 ± 17.3 nm with a size distribution within an acceptable range and exhibited a negative surface charge. The average % EE and % LE were 9 and 24.02, respectively. The in vitro skin penetration study found that ULs with oleic acid could significantly increase the skin penetration of rosmarinic acid compared to ULs. According to confocal laser scanning microscopy observations, this study suggested that UL vesicles attach to the skin before releasing the entrapped drug to penetrate the skin. These findings suggested that ULs with oleic acid penetrated the skin via the transfollicular pathway as a major penetration pathway.

Inorganic ions in the skin: Allies or enemies?

Skin constitutes a barrier protecting the organism against physical and chemical factors. Therefore, it is constantly exposed to the xenobiotics, including inorganic ions that are ubiquitous in the environment. Some of them play important roles in homeostasis and regulatory functions of the body, also in the skin, while others can be considered dangerous. Many authors have shown that inorganic ions could penetrate inside the skin and possibly induce local effects. In this review, we give an account of the current knowledge on the effects of skin exposure to inorganic ions. Beneficial effects on skin conditions related to the use of thermal spring waters are discussed together with the application of aluminium in underarm hygiene products and silver salts in treatment of difficult wounds. Finally, the potential consequences of dermal exposure to topical sensitizers and harmful heavy ions including radionuclides are discussed.

Evaluation of the analgesic and pharmacokinetic properties of transdermally administered fentanyl in goats

OBJECTIVE

Evaluate the analgesic properties and pharmacokinetics of transdermal fentanyl patches (TFPs) in goats.

DESIGN

Prospective, randomized study.

SETTING

Preclinical Testing Facility at a University Teaching Hospital.

ANIMALS

Thirty-four adult female Boer-cross goats.

INTERVENTIONS

Goats underwent surgery as part of a concurrent orthopedic research study. Twelve hours prior to surgery, each goat received a TFP (target dosage of 2.5 μg/kg/h), or a placebo patch with analgesia provided by buprenorphine (0.01 mg/kg, IM, q 6 h). Patches were removed after 72 hours. Blood was sampled at specified intervals, up to 84 hours following TFP placement. Plasma concentrations of fentanyl (FEN) were determined using liquid chromatography-mass spectrometry. Postoperative pain assessments were performed by two independent blinded observers.

MEASUREMENTS AND MAIN RESULTS

TFPs were applied at a mean (± standard deviation, SD) dose of 2.54 ± 0.36 μg/kg/h. No adverse events occurred. Pain scores between TFP and BUP groups were not significantly different at any time point. Mean plasma FEN concentration (± SD) 2 hours following patch application was 1.06 ± 0.85 ng/mL, and remained above 0.5 ng/mL for 40 hours. Maximum mean plasma FEN concentration (C_max ) was 1.84 (ranging from 0.81 to 3.35) ng/mL with average time to maximum concentration (T_max ) of 12 hours after patch application.

CONCLUSIONS

TFP resulted in consistent FEN absorption and plasma concentrations within the human and ovine therapeutic ranges. Pain scores for goats administered TFP were not different than those administered buprenorphine. Ease of administration, duration of analgesia, and decreased dosing frequency make TFPs an attractive option for pain management in goats.

Effect of compositions in nanostructured lipid carriers (NLC) on skin hydration and occlusion

Purpose

To study the effects of varying lipid concentrations, lipid and oil ratio, and the addition of propylene glycol and lecithin on the long-term physical stability of nanostructured lipid nanocarriers (NLC), skin hydration, and transepidermal water loss.

Methods

The various NLC formulations (A1–A5) were prepared and their particle size, zeta potential, viscosity, and stability were analyzed. The formulations were applied on the forearms of the 20 female volunteers (one forearm of each volunteer was left untreated as a control). The subjects stayed for 30 minutes in a conditioned room with their forearms uncovered to let the skin adapt to the temperature (22°C ± 2°C) and humidity (50% ± 2%) of the room. Skin hydration and skin occlusion were recorded at day one (before treatment) and day seven (after treatment). Three measurements for skin hydration and skin occlusion were performed in each testing area.

Results

NLC formulations with the highest lipid concentration, highest solid lipid concentration, and additional propylene glycol (formulations A1, A2, and A5) showed higher physical stability than other formulations. The addition of propylene glycol into an NLC system helped to reduce the particle size of the NLC and enhanced its long-term physical stability. All the NLC formulations were found to significantly increase skin hydration compared to the untreated controls within 7 days. All NLC formulations exhibited occlusive properties as they reduced the transepidermal water loss within 7 days. This effect was more pronounced with the addition of propylene glycol or lecithin into an NLC formulation, whereby at least 60% reduction in transepidermal water loss was observed.

Conclusion

NLCs with high lipid content, solid lipid content, phospholipid, and lecithin are a highly effective cosmetic delivery system for cosmetic topical applications that are designed to boost skin hydration.

Percutaneous absorption in diseased skin: an overview

The stratum corneum's (SC) functions include protection from external hazardous environments, prevention of water loss and regulation of body temperature. While intact skin absorption studies are abundant, studies on compromised skin permeability are less common, although products are often used to treat affected skin. We reviewed literature on percutaneous absorption through abnormal skin models. Tape stripping is used to disrupt water barrier function. Studies demonstrated that physicochemical properties influence the stripping effect: water-soluble drugs are more affected. Abrasion did not affect absorption as much. Freezing is commonly used to preserve skin. It does not seem to modify water absorption, but still increases the penetration of compounds. Comparatively, heating the skin consistently increased percutaneous absorption. Removing SC lipids may increase percutaneous absorption of drugs. Many organic solvents are employed to delipidize. Delipidization with chloroform-methanol increased hydrophilic compound permeability, but not lipophilic. Acetone pre-treatment enhanced hydrophilic compound penetration. More data is needed to determine influence on highly lipophilic compound penetration. Sodium lauryl sulfate (SLS) induces irritant dermatitis and is frequently used as a model. Studies revealed that SLS increases hydrophilic compound absorption, but not lipophilic. However, skin irritation with other chemicals increases lipophilic penetration as much as hydrophilic. Animal studies show that UV exposure increases percutaneous absorption whereas human studies do not. Human studies show increased penetration in psoriatic and atopic dermatitis skin. The data summarized here begin to characterize flux alteration associated with damaged skin. Understanding the degree of alteration requires interpretation of involved conditions and the enlarging of our database to a more complete physicochemical spectrum.

Damage/recovery by additive on lipid membrane as a mimicry of human stratum corneum

The effects of sodium dodecyl sulfate (SDS) on the model lipid membrane of human stratum corneum, composed of three main lipids of ceramide III, palmitic acid, and cholesterol, have been examined as a function of exposure period. Cholesterol first got to elute, palmitic acid followed it late, and the remaining solid was mainly ceramide III. The removal of lipids influenced the configurational structure of remaining lipid and the intralayer structure of lamellae. Monitoring of structural reorganization in the damaged membrane was carried out on the recovering procedure of palmitic acid and cholesterol. Both lipids were penetrated in the damaged membrane and recovered mostly the configurational lipid structure and the lamellar structure. Especially, it can be noted that cholesterol is more effective than palmitic acid on recovery.

Noninvasive characterization of human stratum corneum of undiseased skin of patients with atopic dermatitis and psoriasis as studied by Fourier transform Raman spectroscopy

Etiopathogenetic regulatory disorders of epidermal metabolism and the subsequent changes in the molecular pattern of the stratum corneum play an important role in the clinical differentiation of particular dermatoses (e.g., psoriasis, atopic dermatitis). In this study we present in vitro Fourier transform Raman spectra of the stratum corneum from healthy skin, as well as from clinically undiseased skin of the right heel of atopic and psoriatic volunteers. Differences in the averaged spectra were detected, particularly in the spectral ranges of 1112-1142 (lipid band), 1185-1220, and 1394-1429 cm(-1). By using the first derivative of the averaged spectra and/or a statistical evaluation of the spectroscopic data it was possible to distinguish the skin types examined.

Non-invasive administration of drugs through the skin: challenges in delivery system design

Vehicles designed to enhance drug delivery through the skin must incorporate specific elements that improve the ability of the delivery system to overcome the barrier posed by the stratum corneum. This review discusses several chemical penetration enhancers that have been investigated as potential tools to increase drug flux. In addition, lipid-based delivery systems offer an attractive alternative to traditional drug vehicles. The relationship between liposome composition and drug permeation is discussed, in addition to the possible mechanism of action of lipid vesicle-mediated drug delivery.

Different stratum corneum lipid liposomes as models to evaluate the effect of the sodium dodecyl sulfate

The stability of stratum corneum (SC) liposomes against the action of surfactants has been revised. To this end, two types of vesicles were used; vesicles formed with the lipid and protein material extracted from SC, and lipid mixtures approximating the SC composition. In this case, the proportion of ceramides (Cer) and cholesteryl sulfate (Chol-sulf) was varied and the relative proportion of the other lipids remained constant. The increasing presence of these two lipids increased the resistance of liposomes against the action of the anionic surfactant sodium dodecyl sulfate (SDS). The rise in the cell-to-cell cohesion that occurred in recessive X-linked ichthyosis due to the accumulation of Chol-sulf could be associated in part to the enhanced stability of (Chol-sulf)-enriched bilayers. It is noteworthy that the surfactant partitioning between bilayers and the aqueous phase increased and decreased, respectively, as the proportion of Cer and Chol-sulf increased. This effect may be attributed to the variations in both the electrostatic interactions lipid-surfactant (electrostatic repulsion between the sulfate groups of both Chol-sulf and SDS), and the hydrophilic lipophilic balance of the lipid mixtures, in which Cer is replaced by the major polar lipid of the mixture (Chol-sulf). The fact that the free surfactant concentration was always smaller than its critical micelle concentration indicates that the permeability alterations were mainly ruled by the action of surfactant monomers, in agreement with the results reported for sublytic interactions of this surfactant with PC liposomes.

Local cutaneous water barrier in cold- and heat-acclimated pigeons (Columba livia) in relation to cutaneous water evaporation

The thermoregulatory function of the skin differs in adult cold-acclimated and heat-acclimated rock pigeons (Columba livia). In general, the cutaneous evaporative cooling mechanism is not activated by appropriate stimuli in cold-acclimated pigeons in contrast to heat-acclimated pigeons. We studied with electron microscopy whether the differences in the function of the skin are reflected in the structure of the epidermal water barrier of these two extreme acclimation states. The epidermis of cold-acclimated pigeons is attenuated, and the underlying dermis lacks any intimate vascularization. Both the extracellular and the intracellular domains in the stratum corneum contain organized lamellar lipids. At the stratum transitivum-stratum corneum interface, multigranular body secretion is indicated by the highly convoluted cell membranes and membraneous sacculae enclosing the multigranular bodies. Alternatively, multigranular bodies retain in the corneocytes, and the lipoid material originated from them is reprocessed to broad lamellae. The keratohyalin (KH) granules are spotlike and oriented as cortical bands beneath the plasma membrane. In heat-acclimated pigeons, the epidermis displays modified patches side by side with basic structural type of epidermis. The modified areas are characterized by hypertrophy and abundance of dermal capillaries adjacent to the hypertrophied patch. No lamellar lipids are discerned in the dilated extracellular space. The structure of multigranular bodies is abnormal, and the numbers of lipid droplets in the outer viable epidermis and stratum corneum are decreased. The transitional cells contain stellate KH granules, which form a network throughout the cell. It is concluded that cold-acclimated pigeons have a lamellar, extracellular water barrier, the cutaneous water evaporation is minimized, and heat is stored in the body core. Acclimation to heat leads to formation of structurally heterogeneous skin. The structurally modified skin patches show disruption of the barrier-forming machinery in the multigranular bodies and marked reorganization of fibrillar proteins and electron-dense KH masses in the transitional layer. Thus water barrier adjustments in cold- and heat-acclimated pigeons manifest the dynamic function of avian skin as a thermoregulatory organ.

Enhancement of topical delivery of a lipophilic drug from charged multilamellar liposomes

To enhance the topical delivery of rhodamine B base (Rho), a model lipophilic compound, the electrostatic interaction between the positive and negative components incorporated in the liposomal bilayer was utilized. The higher in vitro permeability to Rho in rat skin was observed with positive and neutral multilamellar liposomal preparations, the former was prepared with phosphatidylcholine (PC) and stearylamine (SA) and the latter with PC alone, than that given as a solution. Negative liposome composed of PC and dicetyl phosphate (DCP) showed lower skin permeability to Rho. To enhance the Rho retention in the skin, the electrostatic interaction between SA and DCP, which was confirmed by in vitro partition study, was utilized. By pretreating the skin surface with SA solution or empty SA liposome, the skin distribution of Rho given as DCP liposome was substantially enhanced, with increase in the PC distribution into the skin. The pretreatment effect of empty SA liposome was also observed in rats in vivo. In conclusion, it was found that negative DCP liposome provides better drug retention in the skin with lower skin permeability, and the topical drug delivery from DCP liposome was further enhanced by the pretreatment of the skin surface with empty SA liposome.

The skin permeation mechanism of ketotifen: evaluation of permeation pathways and barrier components in the stratum corneum

To evaluate the pathways and barrier components in the stratum corneum (SC) for the permeation of ketotifen, the effect of delipidization on the permeation and partition was examined under several donor pHs. Assuming that ionized ketotifen (KTH+) and un-ionized ketotifen (KT) contribute independently in both permeation and partition, the intrinsic permeability coefficients and SC/water partition coefficients of both species were estimated. Delipidization enlarged the permeability of KTH+ 100 times. This suggested that the lipid phase functions as the barrier against KTH+. KT has an intrinsic permeability 100 times larger than that of KTH+. Delipidization did not result in a significant change in permeability of KT. This suggested that the permeability of KT through the lipid phase is comparable to that through the aqueous phase in delipidized SC; that is, the lipid phase functions as a highly permeable pathway for KT. On the other hand, the permeability coefficient of KT through delipidized SC was 1/34 of that through the pure aqueous layer, which had a thickness equivalent to SC. Since this suggests that the permeability of KT through the proteinaceous phase is much lower than that through the aqueous phase, the proteinaceous phase can be assumed to function as a barrier against the permeation of KT. From these results, it is concluded that the predominant permeation pathway for KT is through the lipid phase. The SC/water partition coefficient of KT was cut in half by delipidization, but the value was still more than 100. These results show that the proteinaceous phase functions not only as the barrier, but also as the depot for KT. The knowledge obtained here will be useful for formulation design and for the selection of enhancers in a transdermal therapeutic system of ketotifen.

Influence of ceramides in the solubilization of stratum corneum lipid liposomes by C(12)-betaine/sodium dodecyl sulfate mixtures

The solubilization of liposomes modeling the stratum corneum (SC) lipid composition and those obtained varying the proportion of ceramides by means of dodecyl betaine (C(12)-Bet)/sodium dodecyl sulfate (SDS) mixtures was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the static light scattering of the system during solubilization. The fact that the free surfactant concentration was always similar to its critical micelle concentration (CMC) indicates that the liposome solubilization was mainly ruled by the formation of mixed micelles. The mole fraction of the zwitterionic component (X(zwitter)) of 0.4 showed the lowest ability to saturate or solubilize liposomes, although exhibiting the highest degree of partitioning into liposomes. This X(zwitter) corresponded to the highest derivation of the CMCs of these mixtures (negative synergism) and to the highest reduction in the skin irritation with respect to the anionic component. Higher and lower proportion of ceramides in the mixture led to a fall and to a rise in both the activity and the partitioning of a specific surfactant mixture (X(zwitter)=0.4). This finding could be related to the recently reported dependences of the level of ceramides in skin and function barrier abnormalities. Comparison of the present Re and K values with those reported for phosphatidylcholine (PC) liposomes shows that, although SC liposomes were more resistant to the action of surfactant mixtures, the surfactant partitioning into SC bilayers was similar to that reported for PC ones in all cases.

Influence of the Level of Cholesteryl Sulfate Present in Stratum Corneum Lipid Liposomes on Their Stability Against Triton X-100

The interaction of Triton X-100 (TX-100) with stratum corneum (SC) lipid liposomes varying the proportion of cholesteryl sulfate (Chol-sulf) was investigated. The surfactant/lipid molar ratios and the bilayer/aqueous phase partition coefficients were determined at sublytic level by monitoring the changes in the fluorescence intensity of liposomes due to the 5(6) carboxyfluorescein released from the interior of vesicles. The fact that the free surfactant concentration was always lower than the surfactant CMC indicates that permeability changes were mainly ruled by the action of surfactant monomers in all cases. The lowest surfactant ability to alter the permeability of SC liposomes and highest surfactant affinity with these bilayer structures was reached when the proportion of Chol-sulf in bilayers was 10%. Futhermore, the highest resistance of SC liposomes to be solubilized by TX-100 (via mixed micelle formation) also occurred at this Chol-sulf proportion, which corresponds to that existing in the intercellular SC lipids. These surfactant effects may be related to the reported dependencies between the level of Chol-sulf in the intercellular lipids and the abnormalities in the skin properties as the barrier function. Copyright 1999 Academic Press.

Influence of the level of ceramides on the permeability of stratum corneum lipid liposomes caused by a C12-betaine/sodium dodecyl sulfate mixture

The sublytic interactions of a mixture of N-dodecyl-N, N-dimethylbetaine dodecyl betaine (C12-Bet)/sodium dodecyl sulfate (SDS) (mole fraction of the zwitterionic surfactant=0.6) with stratum corneum (SC) lipid liposomes varying the proportion of ceramides type III (Cer) were investigated. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the fluorescence intensity of liposomes due to the 5(6) carboxyfluorescein (CF) released from the interior of vesicles. The fact that the free surfactant mixture concentration was always lower than its critical micelle concentration indicates that permeability changes were ruled by the action of surfactant monomers in all cases. Higher and lower Cer proportions than that of the SC lipids led to a fall and to a rise in the activity of the surfactant mixture on these bilayer structures. However, the surfactant partitioning into liposomes (or affinity with these bilayer structures) increased as the proportion of Cer increased up to the highest value was achieved for a Cer proportion similar to that in the SC lipids (about 40-45%). Thus, at low Cer proportions the ability of the surfactant mixture to alter the permeability of these bilayer structures was higher than that for liposomes approximating the SC lipid composition despite their reduced partitioning into liposomes. These findings are in agreement with the recently reported dependencies of the level of ceramides in skin lipids and function barrier abnormalities and could explain in part these dependencies.

Influence of the level of ceramides in the permeability of stratum corneum lipid liposomes caused by sodium dodecyl sulfate

The role played by the ceramides in the sublytic interactions of sodium dodecyl sulfate (SDS) with liposomes modeling the stratum corneum (SC) lipid composition was studied. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (k) were determined by monitoring the changes in the fluorescence intensity of liposomes due to the 5(6) carboxyfluorescein (CF) released from the interior of vesicles. The presence in liposomes of higher and lower ceramide proportions than that existing in the SC lipids led to a fall and to a rise in the sublytic activity of SDS on these structures. However, the SDS partitioning into liposomes (or affinity with these bilayer structures) increased as the proportion of Cer increased up to achieve almost a constant value for a Cer proportion similar to that in the SC lipids (about 40%). Thus, at low Cer proportions the ability of SDS molecules to alter these bilayer structures was higher than that for liposomes approximating the SC lipid composition despite their reduced partitioning into liposomes. These findings are in agreement with the recently reported dependencies of the level of ceramides in skin lipids and function barrier abnormalities and could explain in part these dependencies. The fact that the free surfactant concentration needed to achieve the two interaction levels investigated was lower than the surfactant critical micellar concentration (CMC) indicates that permeability alterations were mainly ruled by the action of surfactant monomers, regardless of the liposome lipid composition.

Effect of ointment bases on topical and transdermal delivery of salicylic acid in rats: evaluation by skin microdialysis

Microdialysis has been used to determine the concentration of salicylic acid in skin tissue and plasma periodically for 4 h to evaluate the effect of ointment bases on topical and transdermal delivery of salicylic acid. The ointment bases examined were solbase (water-soluble), poloid and white petrolatum (oleaginous), hydrophilic poloid (water in oil (w/o) type emulsion lacking water) and absorptive ointment (w/o-type emulsion containing water). The ointments (0.1 g) containing 25 micromol salicylic acid were applied for 2 h to the surface of rat skin (1 cm2) with (intact) or without the stratum corneum. For intact skin, the extent of topical delivery from different ointments, evaluated by the area under the concentration-time curve (AUC) of salicylic acid in the skin tissue (AUCskin), increased in the order solbase << white petrolatum, poloid, hydrophilic poloid << absorptive ointment. The ratio of AUCskin (topical delivery) to the AUC of salicylic acid in plasma (AUCplasma, transdermal delivery) varied remarkably among the different bases, the greatest ratio being observed for absorptive ointment. When the ointments were applied to skin surface without stratum corneum, AUCskin for solbase was much higher (about 45 times that for intact skin), whereas only a small (two-fold) increase was observed for poloid and hydrophilic poloid and the increase was negligible for white petrolatum and absorptive ointment. For skin without the stratum corneum, the ratio AUCskin/AUCplasma for the different ointments was comparable, although the magnitudes of AUCskin and AUCplasma still varied substantially. The variance of AUC values arises as a result of the different rates of release of salicylic acid from the bases. These results indicate that: the topical and transdermal delivery of salicylic acid in intact skin varies substantially among different ointment bases, and the greatest topical delivery is observed for absorptive ointment; use of absorptive ointment increases the retention of salicylic acid in the stratum corneum; and the stratum corneum functions strongly as a penetration barrier for solbase, moderately for poloid and hydrophilic poloid, and less for absorptive ointment and white petrolatum.

Percutaneous penetration of octyl salicylate from representative sunscreen formulations through human skin in vitro

The human skin penetration of [14C]octyl salicylate from two representative sunscreen vehicles was determined in vitro. 3H-sucrose was incorporated into all formulations and provided a marker for membrane integrity. When applied as a finite dose in an oil-in-water emulsion vehicle containing 5% (w/w) octyl salicylate, the average total absorption of 14C over 48 hr was 0.65+/-0.16% of the applied dose (representing a total amount permeated of 1.58+/-0.36 microg/cm2). When applied as an infinite dose in the oil-in-water emulsion vehicle the average total absorption of 14C over 48 hr was 0.47+/-0.22% of the applied dose (representing a total amount permeated of 27.54+/-13.91 microg/cm2). When applied as a finite dose in a representative hydroalcoholic formulation containing 5% (w/w) octyl salicylate, the average total absorption of 14C over 48 hr was 0.59+/-0.09% of the applied dose (representing a total amount permeated of 1.58+/-0.25 microg/cm2). When applied as an infinite dose in the hydroalcoholic formulation the average total absorption of 14C over 48 hr was 0.23+/-0.05% of the applied dose (representing a total amount permeated of 11.28+/-2.55 microg/cm2). The penetration of [14C]salicylic acid [applied at a concentration of 2.7% (w/w), in the oil-in-water emulsion] was also determined. When applied as a finite dose the average total absorption of 14C over 48 hr was 1.14+/-0.23% of the applied dose (representing a total amount permeated of 1.65+/-0.39 microg/cm2). These results suggest that the in vitro human skin permeation of octyl salicylate is relatively low. The amounts of octyl salicylate and salicylic acid permeated when applied in similar vehicles were remarkably similar over 48 hr (1.58 microg/cm2 and 1.65 microg/cm2, respectively). This suggests the possibility that the 14C label appearing in the receptor fluid may, in both cases, represent salicylic acid. If this is the case, then it is possible that the amount of octyl salicylate permeating through the skin is much less than that suggested by the data obtained here. This supposition is, however, entirely speculative and has yet to be confirmed experimentally.

Transdermal iontophoretic delivery of triamcinolone acetonide: a preliminary study in hairless rats

Transdermal iontophoretic delivery of triamcinolone acetonide was examined using a commercially available iontophoretic system (Phoresor, Iomed) in hairless rats. A drug electrode containing triamcinolone acetonide 10 mg dissolved in 1 ml of N,N-dimethylacetamide and water (7/3 v/v) was connected to the positive pole of a Phoresor (set at 4 mA) and direct current was applied for 10, 30, or 90 minutes. The amount delivered to the skin tissues increased with time at a constant rate. Even after the drug electrode had been removed, triamcinolone acetonide was retained in the local skin tissues beneath where it had been for about 24 hours after 30 minutes iontophoresis. These results suggest that the iontophoresis with an organic solvent used as a drug vehicle is useful to increase transdermal absorption of compounds that do not dissolve completely in water.

Percutaneous absorption of biologically-active interferon-gamma in a human skin graft-nude mouse model

PURPOSE

Topical delivery has been suggested to reduce systemic side effects while targeting cytokines for the treatment of certain skin conditions. Liposomes have been proposed as an enhancing agent for such a delivery. We have tested the potential of liposomes to augment the uptake of biologically active recombinant human interferon-gamma (rhIFN-gamma) into human skin lacking adnexa in an in vivo model.

METHODS

Stable grafts of human skin on nude mice were used to test aqueous formulations of rhIFN-gamma containing or lacking liposomes composed of phosphatidylcholine and cholesterol. Transport of rhIFN-gamma was assessed by monitoring the stimulated expression of intercellular adhesion molecule-1 (ICAM-1) by keratinocytes by light-level immunomicroscopy and ELISA.

RESULTS

A single application of liposomal rhIFN-gamma increased ICAM-1 levels in the epidermal basal and suprabasal cell layers of grafts. Continued application maintained this response. An aqueous formulation of rhIFN-gamma or liposomes alone applied to grafts failed to induce an ICAM-1 response. Preliminary studies suggested that at least some of the lipids applied in the liposomal formulation also entered the epidermis.

CONCLUSIONS

Using a nude mouse-human skin graft model lacking adnexa, we have demonstrated that a liposomal formulation can augment the uptake of a biologically-active human cytokine, rhIFN-gamma, into the epidermis of viable human skin. The therapeutic application of topical IFN-gamma delivery remains to be evaluated.

Transport of biologically active interferon-gamma across human skin in vitro

PURPOSE

Several studies have suggested epidermal uptake of cytokines, such as interferons, can be facilitated using topical liposomal formulations. We have evaluated the in vitro transport of biologically active recombinant human interferon-gamma (rhIFN-gamma) into and through split-thickness human skin to assess this possibility.

METHODS

Skin samples were exposed to rhIFN-gamma under various conditions involving hydrated and dry surface conditions in the presence and absence of liposomes. A new low-level ELISA and an anti-viral bioassay were used to quantitate transported rhIFN-gamma. Immunohistochemical staining for ICAM-1 expression by keratinocytes was used to visualize the extent and distribution of rhIFN-gamma transport.

RESULTS

Apparent steady-state transport of rhIFN-gamma occurred within the first 5 hours of exposure with approximately 10% of transported rhIFN-gamma demonstrating bioactivity. While the permeability of rhIFN-gamma across human skin under drying conditions was enhanced by the presence of liposomes, no augmentation of permeability was observed when the skin was kept hydrated. Liposomal formulations of rhIFN-gamma had greater transport rates than aqueous formulations when the applied formulations were allowed to dry after dosing.

CONCLUSIONS

Our results demonstrate the transport of biologically active rhIFN-gamma across human skin in vitro and suggest a role for stratum corneum hydration as one possibility for the augmented cytokine transport.