Heparin penetration into and permeation through human skin from aqueous and liposomal formulations in vitro

Development and evaluation of a heparin gel for transdermal delivery via laser-generated micropores

Aim: Our study investigated the feasibility of transdermal delivery of heparin, an anticoagulant used against venous thromboembolism, as an alternative to intravenous administration. Materials & methods: Skin was pretreated using ablative laser (Precise Laser Epidermal System [P.L.E.A.S.E.^®] technology) for enhanced delivery of heparin. In vitro permeation studies using static Franz diffusion cells provided a comparison between delivery from 0.3% w/v heparin-loaded poloxamer gel and solution across untreated and laser-treated dermatomed porcine ear skin. Results: No passive delivery of heparin was observed. Laser-assisted delivery from solution (26.07 ± 1.82 μg/cm²) was higher (p < 0.05) than delivery from heparin gel (11.28 ± 5.32 μg/cm²). However, gel is likely to sustain the delivery over prolonged periods like a maintenance dose via continuous intravenous infusion. Conclusion: Thus, ablative laser pretreatment successfully delivered heparin, establishing the feasibility of delivering hydrophilic macromolecules using the transdermal route.

A human skin high-throughput formulation screening method using a model hydrophilic drug

Franz cell (FC) experiments in topical and transdermal drug development represent the gold standard in vitro method but require a relatively high quantity of human skin, are low-throughput, and are time-consuming to perform. To address these issues, we studied a micro-well plate-based screening method for permeability and retention that could enable the direct screening of large numbers of formulations simultaneously across human skin. Using freshly excised dermatomed human skin modified to reflect poor barrier function and a model hydrophilic compound, Sulforhodamine B (SRB), FC permeation and retention quantification was compared to the 96-well high-throughput system (HTS). The skin was analyzed using 2-photon microscopy to determine the drug distribution within the skin. A screen of 15 different formulations in triplicate in a single piece of human skin, using full factorial design was then conducted. Permeability of SRB across the skin as well as the drug distribution profile of SRB retained in the skin were similar for the FC and HTS system. The influence of different excipients on drug retention was observed in the full factorial formulation screen. The HTS method is promising for the investigation of large numbers of formulations and the influence of formulations changes in skin retention of drug.

Production of LMWH-conjugated core/shell hydrogels encapsulating paclitaxel for transdermal delivery: In vitro and in vivo assessment

Topical applications that reduce systemic toxic effects while increasing therapeutic efficacy are a promising alternative strategy. The aim of this study was to provide an enhanced transdermal delivery of low molecular weight heparin (LMWH) through the stratum corneum by using cationic carrier as a novel permeation enhancer. Recent studies have shown that heparin-conjugated biomaterials can be effective in inhibiting tumor growth during cancer treatment due to their high ability to bind growth factors. Paclitaxel (PCL) was co-encapsulated into the same cationic carrier for the purpose of improving of therapeutic efficacy for a combined cancer treatment with LMWH. In vitro and in vivo studies showed that the LMWH and PCL release was significantly affected by polymer molecular weight and block composition. Skin penetration tests have indicated that larger amounts of LMWH were absorbed from LMWH-gel conjugate through SC, than aqueous formula. However, it was found that the plasma transition of LMWH released from gel conjugate was lower compared to the plasma concentration of LMWH released from aqueous solution. It is recommended that PCL-loaded LMWH-conjugated core/shell hydrogels can be used as promising drug release systems for transdermal applications that can improve therapeutic efficacy and reduce side effects in a combined cancer treatment.

Nanocrystal: a novel approach to overcome skin barriers for improved topical drug delivery

INTRODUCTION

Skin is an important route of drug delivery for the treatment of various dermatological conditions. The advent of nanotechnology is paving the roadmaps for topical drug delivery by providing sustained release as well as maintaining a localized effect, outweighing the toxicity concern.

AREAS COVERED

This review highlighted the morphology of skin, its barrier nature as well as drug penetration pathways after topical application of formulations. The existing methods to improve topical drug delivery, by infringing or permeating the skin barriers, are discussed. This context concretes the foundation to accentuate the need for the development of nanocrystal-based topical formulation. The mechanism of drug release, immediate as well as sustained release, after topical administration of drug nanocrystals is also elaborated. The special emphasis is given on the breakthrough achieved, in topical drug delivery using drug nanocrystals, so far in the plethora of literature, patents, and products, under clinical trial as well as in the market.

EXPERT OPINION

The current research on nanocrystals for topical drug delivery is highlighting the breakthroughs achieved so far. The output of these research envisages that topical nanocrystals based formulations can be a novel strategy for the drugs which are facing solubility, bioavailability and toxicity concerns.

Ultradeformable Liposomes: a Novel Vesicular Carrier For Enhanced Transdermal Delivery of Procyanidins: Effect of Surfactants on the Formation, Stability, and Transdermal Delivery

The aims of this work were to develop a novel vesicular carrier, procyanidins, ultradeformable liposomes (PUDLs), to expand the applications for procyanidins, and increase their stability and transdermal delivery. In this study, we prepared procyanidins ultradeformable liposomes using thin film hydration method and evaluated their encapsulation efficiency, vesicle deformability, storage stability, and skin permeation in vitro. The influence of different surfactants on the properties of PUDLs was also investigated. The results obtained showed that the PUDLs containing Tween 80 had a high entrapment efficiency (80.27 ± 0.99%), a small particle size (140.6 ± 19 nm), high elasticity, and prolonged drug release. Compared with procyanidins solution, the stability of procyanidins in PUDLs improved significantly when stored at 4, 25, and 30°C. The penetration rate of PUDLs was 6.25-fold greater than that of procyanidins solution. Finally, the results of our study suggested that PUDLs could increase the transdermal flux, prolong the release and improve the stability of procyanidins, and could serve as an effective dermal delivery system for procyanidins.

Liposomal Heparin Spray: A New Formula in Adjunctive Treatment of Superficial Venous Thrombosis

The objective of this study was to assess the efficacy and safety of liposomal heparin spray—a new formula of topical heparin delivery. This was a randomized, multicenter, controlled open clinical trial with 2 parallel groups. Forty-six outpatients with clinical signs of superficial venous thrombosis (SVT) were treated with either topical liposomal heparin spraygel (LHSG) (Lipohep Forte Spraygel, 4 puffs of 458 IU tid (n=22) or with low-molecular-weight heparin (LMWH) (Clexane 40 mg once a day (n=24), administered subcutaneously (sc). Main outcome measures were efficacy parameters (improvement of local symptoms—pain control and planimetric evaluation of erythema size, duplex Doppler assessment of thrombus regression) and safety parameters (documentation of adverse events, with particular reference to deep vein thrombosis [DVT] by duplex sonography, and patients’ and investigators’ assessment of drug tolerance). Patients’ and investigators’ subjective assessment of efficacy of treatment and change in basic biochemical parameters were defined as secondary outcome measures. Statistical analysis was performed with use of Wilcoxon test, Mann-Whitney U-test and Chi-square test. Regression of SVT-related symptoms, including pain, erythema, and thrombus presence, was shown as comparable in LHSG and LMWH groups. These results were corroborated by efficacy assessment by investigators and patients. Three cases of deep venous thrombosis in heparin spraygel and 1 in heparin sc group were reported. No significant adverse reactions were observed in the spraygel group, but 1 serious allergic reaction was observed in the LMWH group. Tolerance of new formula heparin was assessed as good. Heparin spraygel—a new topical mode of heparin application, seems a promising method of heparin delivery. This initial study has demonstrated comparable efficacy and safety of LHSG and LMWH in local treatment of SVT. These findings should be confirmed by further extensive study that will reach appropriate statistical power to support such conclusion, for despite heparin treatment, significant risk of DVT was demonstrated in both groups.

Strategies to Overcome Heparins' Low Oral Bioavailability

Even after a century, heparin is still the most effective anticoagulant available with few side effects. The poor oral absorption of heparins triggered the search for strategies to achieve oral bioavailability since this route has evident advantages over parenteral administration. Several approaches emerged, such as conjugation of heparins with bile acids and lipids, formulation with penetration enhancers, and encapsulation of heparins in micro and nanoparticles. Some of these strategies appear to have potential as good delivery systems to overcome heparin’s low oral bioavailability. Nevertheless, none have reached the market yet. Overall, this review aims to provide insights regarding the oral bioavailability of heparin.

Effect of enoxaparin and onion extract on human skin fibroblast cell line - therapeutic implications for the treatment of keloids

CONTEXT

Keloids and hypertrophic scars are hyperproliferative skin disorders resulting in abnormal wound healing. In the prevention and treatment of keloids and hypertrophic scars, ointments containing heparin and onion extract are very popular. Their therapeutic effects, however, are still controversial and the mechanism of action is not fully understood.

OBJECTIVE

The aim of this study was to assess the effect of enoxaparin and dry onion extract on proliferation, apoptosis and β1 integrin expression in human fibroblasts.

MATERIALS AND METHODS

Fibroblast human cell lines (46 BR.1 N) were treated for 48 h with various concentrations of enoxaparin sodium (20, 100, 500 µg/mL) and/or onion [Allium cepa L. (Alliaceae)] extract (50, 250, 1000 µg/mL). The cell proliferation was evaluated by [(3)H]-thymidine incorporation assay. Furthermore, the expression of β1 integrin and apoptosis was determined by flow cytometry.

RESULTS AND DISCUSSION

The results demonstrate that enoxaparin and onion extract inhibited the proliferation of human fibroblasts. Almost complete inhibition of cell proliferation was achieved by enoxaparin in 500 µg/mL concentration (91.5% reduction). The onion extract at a concentration of 250 µg/mL also strongly inhibited the proliferation of cells (50.8% reduction). Depending on concentration, enoxaparin and onion extract induced apoptosis (500 and 1000 µg/mL, respectively) and, depending on concentration, downregulated the expression of β1 integrin on human fibroblasts.

CONCLUSION

This work points at possible mechanism of action of enoxaparin and onion extract, when administered in the treatment of patients with keloids and hypertrophic scars.

Laser-engineered dissolving microneedles for active transdermal delivery of nadroparin calcium

There is an urgent need to replace the injection currently used for low molecular weight heparin (LMWH) multidose therapy with a non- or minimally invasive delivery approach. In this study, laser-engineered dissolving microneedle (DMN) arrays fabricated from aqueous blends of 15% w/w poly(methylvinylether-co-maleic anhydride) were used for the first time in active transdermal delivery of the LMWH nadroparin calcium (NC). Importantly, an array loading of 630IU of NC was achieved without compromising the array mechanical strength or drug bioactivity. Application of NC-DMNs to dermatomed human skin (DHS) using the single-step 'poke and release' approach allowed permeation of approximately 10.6% of the total NC load over a 48-h study period. The cumulative amount of NC that permeated DHS at 24h and 48h attained 12.28±4.23IU/cm(2) and 164.84±8.47IU/cm(2), respectively. Skin permeation of NC could be modulated by controlling the DMN array variables, such as MN length and array density as well as application force to meet various clinical requirements including adjustment for body mass and renal function. NC-loaded DMN offers great potential as a relatively low-cost functional delivery system for enhanced transdermal delivery of LMWH and other macromolecules.

Influence of intracellular Ca2+ release modulating drugs on bupivacaine infiltration anesthesia in mice

The endoplasmic reticulum inside neurons can provide enormous amounts of releasable Ca2+ to increase cytosolic Ca2+ levels through the activation of endoplasmic membrane ion channels. Ryanodine (RyR) channels release Ca2+ into the cytosol when activated by Ca2+ influx through voltage-gated channels, or by cyclicADP ribose. Inositol tris-phosphate (IP3) channels are stimulated by phospolipid metabolism and the release of IP3. The hypothesis was tested that drugs that bind RyR or IP3 channels would affect the anesthetic potency of bupivacaine. The radiant heat tail-flick test was used to assess for anesthesia following subcutaneous infiltration of bupivacaine and Ca2+ modulating drugs in the tails of mice. No musculature is contained in the tail that could result in motor block. The RyR channel agonists 4-chloro-m-cresol and poly-L-lysine significantly reduced the anesthetic potency of bupivacaine. The plant alkaloid ryanodine elicited a bi-phasic effect, with low concentrations blocking bupivacaine anesthesia, and a high concentration enhancing anesthesia. Alternatively, the RyR channel antagonist dantrolene sodium dose-dependently increased bupivacaine's potency. However, the IP3 channel drugs were inactive. The IP3 agonist adenophostin A failed to affect bupivacaine anesthesia. Furthermore, bupivacaine was unaffected by the IP3 channel antagonists xestospongin C or low molecular weight heparin. Our results indicate that only the RyR channel drugs modulated the anesthetic effects of bupivacaine. Electrophysiological and molecular studies of sensory dorsal root ganglia neurons, the source of Adelta and C-fiber nociceptors, have demonstrated the presence of RyR3 Ca2+ release channels. This provides the first evidence that RyR channels might affect bupivacaine anesthesia in some fashion.

Retained topical delivery of 5-aminolevulinic acid using cationic ultradeformable liposomes for photodynamic therapy

5-Aminolevulinic acid (5-ALA), inducing photodynamic protoporphyrin (PpIX), is a hydrophilic molecule, resulting in leashing the capacity to cross tissue barriers like stratum corneum (SC) of skin. Here, we aimed to develop 5-ALA loaded ultradeformable liposomes (UDL) with different surface charges, and to investigate their physicochemical characteristics and capability for the skin penetration and retention of 5-ALA for topical photodynamic therapy (PDT). The effects of surface charges of UDL on in vitro permeation of 5-ALA and in vivo accumulation of 5-ALA-induced PpIX in viable skin were determined and then compared with conventional neutral liposomes (nLiposome). All UDL showed smaller particle size and better deformability than nLiposome. However, entrapment efficiency of 5-ALA was similar to each vesicle. Among vesicles, the cationic UDL (cUDL) demonstrated higher stability and permeability, and could deliver 5-ALA into deep skin tissue by topical application. Moreover, the 5-ALA loaded in cUDL was long retained, and induced more amount of PpIX in viable skin than those in other UDL and nLiposome. Considering that the conversion of 5-ALA into PpIX occurs preferentially in epidermis, these results suggested that topical delivery of 5-ALA loaded in cUDL could be an interesting proposal to optimize PDT related to 5-ALA.

Novel sulfated polysaccharides disrupt cathelicidins, inhibit RAGE and reduce cutaneous inflammation in a mouse model of rosacea

BACKGROUND

Rosacea is a common disfiguring skin disease of primarily Caucasians characterized by central erythema of the face, with telangiectatic blood vessels, papules and pustules, and can produce skin thickening, especially on the nose of men, creating rhinophyma. Rosacea can also produce dry, itchy eyes with irritation of the lids, keratitis and corneal scarring. The cause of rosacea has been proposed as over-production of the cationic cathelicidin peptide LL-37.

METHODOLOGY/PRINCIPAL FINDINGS

We tested a new class of non-anticoagulant sulfated anionic polysaccharides, semi-synthetic glycosaminoglycan ethers (SAGEs) on key elements of the pathogenic pathway leading to rosacea. SAGEs were anti-inflammatory at ng/ml, including inhibition of polymorphonuclear leukocyte (PMN) proteases, P-selectin, and interaction of the receptor for advanced glycation end-products (RAGE) with four representative ligands. SAGEs bound LL-37 and inhibited interleukin-8 production induced by LL-37 in cultured human keratinocytes. When mixed with LL-37 before injection, SAGEs prevented the erythema and PMN infiltration produced by direct intradermal injection of LL-37 into mouse skin. Topical application of a 1% (w/w) SAGE emollient to overlying injected skin also reduced erythema and PMN infiltration from intradermal LL-37.

CONCLUSIONS

Anionic polysaccharides, exemplified by SAGEs, offer potential as novel mechanism-based therapies for rosacea and by extension other LL-37-mediated and RAGE-ligand driven skin diseases.

A plaster containing DHEP and heparin for mild to moderate contusions and sprains with haematoma: a double-blind randomized study

OBJECTIVE

This prospective, randomized, double-blind, three-arm study was performed to investigate the efficacy of a medicated plaster containing the combination of diclofenac epolamine (DHEP) 180 mg and heparin 5600 IU in the treatment of unilateral blunt soft tissue injuries involving the upper or lower limb, complicated by severe local haematoma.

RESEARCH DESIGN AND METHODS

Patients with mild-to-moderate injuries complicated by local haematoma (< or =140 cm(2)) were included and randomly treated once daily with plasters containing DHEP/heparin, DHEP only, or placebo. Plasters were applied for at least 12 hours daily for 10 consecutive days.

MAIN OUTCOME MEASURES

The time to complete haematoma dissolution was the primary efficacy endpoint; secondary endpoints were spontaneous pain reduction, pain on movement, muscle swelling and use of rescue analgesia.

RESULTS

A total of 185 patients (90 males and 95 females, aged 18-80 years) were evaluated for efficacy. Baseline clinical and demographic characteristics were similar across the treatment groups. The time to complete haematoma dissolution was significantly shorter with the DHEP/heparin plaster compared with both the DHEP and placebo plasters (p < 0.05). Patients in the DHEP/heparin group had a 60% probability of achieving complete haematoma dissolution within the 10-day treatment period compared with patients receiving either DHEP or placebo plasters. Patient-rated reductions in pain on movement were significantly (p < 0.05) greater in the two active treatment groups compared with placebo. Overall, the DHEP/heparin, DHEP and placebo plasters were well-tolerated. While a reliance on patient self-reporting had the potential to limit the usefulness of some data obtained in this study, the investigators accounted for this accordingly.

CONCLUSIONS

The plaster formulation combining DHEP and heparin relieves pain and induces faster dissolution of superficial haematomas, and may therefore contribute to a more rapid and complete recovery.

Dermal delivery of selected hydrophilic drugs from elastic liposomes: effect of phospholipid formulation and surfactants

The effect of phospholipid formulation and choice of surfactant on skin permeation of selected hydrophilic drugs from elastic liposomes across human epidermal membrane has been studied. Sodium cholate and various concentrations of phosphatidylcholine were used for the preparation of liposomes namely hydrogenated phosphatidylcholine 90% (Phospholipon 90H), phosphatidylcholine 95% (Phospholipon 90G), phosphatidylcholine 78.6% (Phospholipon 80), and phosphatidylcholine 50% (Phosal PG). To investigate the effect of the surfactant, liposomes were prepared from 95% phosphatidylcholine (Phospholipon 90G) and various surfactants (sodium cholate, sodium deoxycholate, Span 20 (sorbitan monolaurate), Span 40 (sorbitan monopalmitate), Span 60 (sorbitan stearate) and Span 80 (sorbitan monooleate)). The vesicles were prepared by the conventional rotary evaporation technique. The film was hydrated with phosphate-buffered saline (10 mL) containing 9, 2 and 2.5 mg mL−1 of methotrexate, idoxuridine and aciclovir, respectively. All formulations contained 7% ethanol. Homogenously-sized liposomes were produced following extrusion through 100-nm polycarbonate filters using Lipex Extruder. Particle size was characterized by transmission electron microscopy. Vertical Franz diffusion cells were used for the study of drug delivery through human epidermal membrane. For the three drugs, the highest transcutaneous fluxes were from elastic liposomes containing 95% phosphatidylcholine. In general, a higher flux value was obtained for liposomes containing sodium cholate compared with sodium deoxycholate. For the liposomes containing sorbitan monoesters, there was no clearly defined trend between alkyl chain length and flux values. Overall, transcutaneous fluxes of liposomal preparations of hydrophilic drugs were comparable with those from saturated aqueous solutions (P &gt; 0.05).

Anti-herpes simplex virus activities of two novel disulphated cyclitols

By screening a library of sulphated compounds of low molecular weight, we have found that several cyclitol derivatives, each modified with two sulphate groups in addition to pyrrole and various aromatic moieties, inhibited infectivity of herpes simplex virus (HSV) at concentrations approximately 100 times lower than those toxic for cultured cells. These disulphated cyclitols interfered with HSV-1 attachment to cells, and efficiently reduced the cell-to-cell spread of the virus. This effect is most likely due to their low molecular weight and associated with the compounds' capability to access the narrow intercellular spaces. Furthermore, these disulphated cyclitols also inactivated infectivity of HSV. However, the virus-inactivating activities of these compounds were to some extent diminished in the presence of human cervical secretions or other protein-rich solutions suggesting that disulphated cyclitols may have some features of surfactant-type virucides. In conclusion, this new class of anti-HSV compounds offers potential for further development.

The quest for non-invasive delivery of bioactive macromolecules: a focus on heparins

The development of a non-invasive drug delivery system for unfractionated heparin (UFH) and low molecular weight heparins (LMWHs) has been the elusive goal of several research groups since the initial discovery of this glycosaminogylcan by McLean in 1916. After a brief update on current parenteral formulations of UFH and LMWHs, this review revisits past and current strategies intended to identify alternative routes of administration (e.g. oral, sublingual, rectal, nasal, pulmonary and transdermal). The following strategies have been used to improve the bioavailability of this bioactive macromolecule by various routes: (i) enhancement in cell-membrane permeabilization, (ii) modification of the tight-junctions, (iii) increase in lipophilicity and (iv) protection against acidic pH of the stomach. Regardless of the route of administration, a simplified unifying principle for successful non-invasive macromolecular drug delivery may be: "to reversibly overcome the biological, biophysical and biochemical barriers and to safely and efficiently improve the in vivo spatial and temporal control of the drug in order to achieve a clinically acceptable therapeutic advantage". Future macromolecular drug delivery research should embrace a more systemic approach taking into account recent advances in genomics/proteomics and nanotechnology.

Experimental design for in vitro skin penetration study of liposomal superoxide dismutase

A computer-based technique using a 2((5-2)) fractional factorial design was applied for screening the factors affecting the penetration effectiveness of liposomal recombinant human-Cu/Zn-superoxide dismutase. Unilamellar liposomes, containing recombinant rh-Cu/Zn-SOD in the aqueous core, are aimed at enhancing the penetration of the drug applied topically. Factors that mainly influence the chemical and physical characteristics of liposomes such as charge, molar content of cholesterol, size, surfactant and lipid were evaluated at two levels. In vitro skin penetration studies with pigskin were carried out in Franz-type diffusion cells over a period of 4 and 8h. The response variables, namely the amounts of rh-Cu/Zn-SOD penetrated into the different skin layers, were analyzed by ELISA (enzyme linked immunosorbent assay). Analysis of variance showed that the size and the cholesterol content of liposomes as well as the duration of the penetration studies have a statistically significant influence on the amount of protein found in deeper skin layers.

Synthesis, Biological Activity, and Preliminary Pharmacokinetic Evaluation of Analogues of a Phosphosulfomannan Angiogenesis Inhibitor (PI-88)

The phosphosulfomannan 1 (PI-88) is a mixture of highly sulfated oligosaccharides that is currently undergoing clinical evaluation in cancer patients. As well as its anticancer properties, 1 displays a number of other interesting biological activities. A series of analogues of 1 were synthesized with a single carbon (pentasaccharide) backbone to facilitate structural characterization and interpretation of biological results. In a fashion similar to 1, all compounds were able to inhibit heparanase and to bind tightly to the proangiogenic growth factors FGF-1, FGF-2, and VEGF. The compounds also inhibited the infection of cells and cell-to-cell spread of herpes simplex virus (HSV-1). Preliminary pharmacokinetic data indicated that the compounds displayed different pharmacokinetic behavior compared with 1. Of particular note was the n-octyl derivative, which was cleared 3 times less rapidly than 1 and may provide increased systemic exposure.

Liposomes and niosomes as topical drug delivery systems

The skin acts as a major target as well as a principle barrier for topical/transdermal (TT) drug delivery. The stratum corneum plays a crucial role in barrier function for TT drug delivery. Despite major research and development efforts in TT systems and the advantages of these routes, low stratum corneum permeability limits the usefulness of topical drug delivery. To overcome this, methods have been assessed to increase permeation. One controversial method is the use of vesicular systems, such as liposomes and niosomes, whose effectiveness depends on their physicochemical properties. This review focuses on the effect of liposomes and niosomes on enhancing drug penetration, and defines the effect of composition, size and type of the vesicular system on TT delivery.

Lipid vesicles and other colloids as drug carriers on the skin

Colloids from an aqueous suspension can cross the skin barrier only through hydrophilic pathways. Various colloids have a different ability to do this by penetrating narrow pores of fixed size in the skin, or the relevant nano-pores in barriers modelling the skin. Such ability is governed by colloid adaptability, which must be high enough to allow penetrant deformation to the size of a pore in such barrier: for a 100 nm colloid trespassing the skin this means at least 5-fold deformation/elongation. (Lipid) Bilayer vesicles are normally more adaptable than the comparably large (lipid coated) fluid droplets. One of the reasons for this, and an essential condition for achieving a high bilayer adaptability and pore penetration, is a high bilayer membrane elasticity. The other reason is the relaxation of changing colloid's volume-to-surface constraint during pore penetration; it stands to reason that such relaxation requires a concurrent, but only transient and local, bilayer permeabilisation. Both these phenomena are reflected in bilayer composition sensitivity, which implies non-linear pressure dependency of the apparent barrier penetrability, for example. Amphipats that acceptably weaken a membrane (surfactants, (co)solvents, such as certain alcohols, etc.) consequently facilitate controlled, local bilayer destabilisation and increase lipid bilayer flexibility. When used in the right quantity, such additives thus lower the energetic expense for elastic bilayer deformation, associated with pore penetration. Another prerequisite for aggregate transport through the skin is the colloid-induced opening of the originally very narrow ( approximately 0.4 nm) gaps between cells in the barrier to pores with diameter above 30 nm. Colloids incapable of enforcing such widening-and simultaneously of self-adapting to the size of 20-30 nm without destruction-are confined to the skin surface. All relatively compact colloids seem to fall in this latter category. This includes mixed lipid micelles, solid (nano)particles, nano-droplets, biphasic vesicles, etc. Such colloids, therefore, merely enter the skin through the rare wide gaps between groups of skin cells near the organ surface. Transdermal drug delivery systems based on corresponding drug formulations, therefore, rely on simple drug diffusion through the skin; the colloid then, at best, can modulate drug transport through the barrier. In contrast, the adaptability-and stability-optimised mixed lipid vesicles (Transfersomes, a trademark of IDEA AG) can trespass much narrower pathways between most cells in the skin; such highly adaptable colloids thus mediate drug transport through the skin. Sufficiently stable ultra-adaptable carriers, therefore, can ensure targeted drug delivery deep below the application site. This has already been shown in numerous preclinical tests and several phase I and phase II clinical studies. Drug delivery by means of highly adaptable drug carriers, moreover, allows highly efficient and well-tolerated drug targeting into the skin proper. Sustained drug release through the skin into systemic blood circulation is another field of ultradeformable drug carrier application.

Interactions of heparin with human skin cells: Binding, location, and transdermal penetration

The development of new materials for tissue engineering of skin substitutes requires an increasing knowledge of their interactions with human skin cells. Since carbohydrate recognition is involved in numerous biologic processes, including skin regeneration, the aim of this study was to identify sugar receptors expressed at the surface of human dermic and epidermic cells. Binding of fluorescent sugar-polyhydroxyethylacrylamide derivatives was analyzed by flow cytofluorimetry on cultured human skin fibroblasts, keratinocytes, and melanocytes. We observed that these three cell types express a membrane receptor specific for GlcNAc6S. Since the polysaccharide heparin contains this sugar moiety, we further investigated the interactions of heparin with skin cells. We analyzed the in vitro cell binding and ex vivo diffusion with the Franz cell of heparin and of two other polysaccharides of similar molecular weight, dextran and chondroitin sulfate. We found evidence of the preferential binding of heparin on keratinocytes and its high transcutaneous penetration of skin. Altogether, our results describe the affinity of heparin for human skin cells and suggest it may be an excellent candidate for use in the skin delivery of drugs or cosmetics and also as an active component in engineered skin.

Permeation, metabolism and site of action concentration of nicotinic acid derivatives in human skin

A novel methodology for establishing a pharmacological dose-effect relationship of methyl nicotinate, hexyl nicotinate and nicotinic acid acting as peripheral vasodilators in the skin following topical application is investigated. This methodology involves the estimation of the unbound drug concentration in the aqueous compartment at the site of action in tissue, termed C(*), which was evaluated as the pertinent concentration responsible for the pharmacological effect. Blood capillaries next to the epidermis-dermis boundary were postulated to be the relevant site of action. C(*) was estimated from drug transport parameters for different layers of human cadaver skin determined in vitro. Immunohistochemical studies showed that the plane of separation of skin achieved by heat treatment was between the basal cells of the epidermis and the lamina lucida, confirming the integrity of the epidermis and the dermis used in the experiments. The permeation rate for epidermis increased drastically with increasing lipophilicity of the drug. Dermis permeability was roughly the same for all three compounds. The epidermis represented the major transport barrier in vitro for methyl nicotinate and nicotinic acid but not for hexyl nicotinate. The esters were metabolised to nicotinic acid during tissue permeation to an extent that was rather limited for the epidermis but very pronounced for the dermis. Nonspecific alpha-naphthylacetate-esterase activity was predominantly located in the dermis, which was in agreement with the metabolism results. The drugs were applied each at three different concentrations in vivo to the ventral forearm of healthy human volunteers and vasodilation was evaluated based on skin erythema which was quantified by measuring colour change of reflected light. Area under the curve of the change of colour co-ordinates as a function of time was used as a measure of pharmacological effect. The pharmacological effect of all three drugs was comparable when similar C(*) values were considered, even though the concentrations applied to the skin differed by orders of magnitude. The effect showed a strong positive dependence on C(*). Methyl and hexyl nicotinate showed identical, nearly sigmoidal effect/C(*)-profiles, while the profile for nicotinic acid was linear, suggesting a possible difference in the intrinsic pharmacological potency between the esters and the acid. These results demonstrate the validity of C(*) as the relevant drug concentration for the cutaneous pharmacological effect of the topically applied drugs and underline the usefulness of the presented methodology for establishing dose-response relationships in dermal therapy and expressing bioavailability.

Interaction of liposome formulations with human skin in vitro

The interaction of liposome formulations consisting of Phospholipon 80 and sphingomyelin with human skin was investigated. These formulations were shown previously to have a composition-dependent effect on the penetration of Heparin into the skin. Fluorescence labelled phosphatidylethanolamine (PE-NBD) was incorporated in the liposomes and the depth in which the fluorescent phospholipid label enters into epidermal membrane and full thickness skin was studied by confocal laser scanning microscopy (CLSM). Confocal sections parallel to the surface of the skin were recorded in heat separated epidermis. An even distribution of phospholipid in the lipid matrix of the stratum corneum surrounding the corneocytes was observed with Phospholipon 80 but not when sphingomyelin was included in the formulation. The addition of Heparin which formed a coating around the liposomes, caused a strong localization of fluorescence within the epidermis. For full thickness skin, mechanical cross sections of skin were made and optical sections were recorded parallel to the plane of cut. Phospholipid penetrated and was distributed fairly homogeneously in the lower dermis layers within 30 min of application regardless of liposome composition and the presence of Heparin. This rather quick penetration process seemed to follow distinct pathways along the epidermis and the upper dermis, notably the hair follicle route. Thus, a strong and in some respects composition-dependent interaction of phospholipids with skin is evident. These observations, however, are limited to the level of phospholipid molecules, rather than of entire liposomes interacting with skin.