In vitro and ex-vivo evaluation of topical formulations designed to minimize transdermal absorption of Vitamin K1

Topical application of Vitamin K1 has been demonstrated to effectively treat papulopustular skin rash, a serious and frequently encountered side effect of Epidermal Growth Factor Inhibitors (EGFRIs). Systemic absorption of vitamin K1 from skin and the resultant consequence of antagonizing EGFRIs anticancer effects jeopardizes the clinical acceptability of this rather effective treatment. The purpose of the present study was to rationally formulate and evaluate the release rate and transdermal absorption of a wide range of Vitamin K1 dermal preparations with a variety of physiochemical properties. A library of 33 formulations with were compounded and tested for Vitamin K1 permeation using hydrophobic membranes and porcine skin mounted in a Fran diffusion cells. Our results demonstrate the lowest diffusion for water-in-oil emulsions, which also demonstrated a negligible transdermal absorption. The statistical analysis showed a significant correlation between in vitro and ex vivo results. While viscosity did not have a significant impact on the diffusion or absorption of vitamin K1, an increase in the lipid content was correlated with an increase in transmembrane diffusion (not with transdermal absorption). Overall, formulation design significantly impacts the release rate and transdermal absorption of vitamin K1, and confirms the possibility of minimal systemic distribution of this vitamin for this specific purpose.

Methylation and Esterification of Magnolol for Ameliorating Cutaneous Targeting and Therapeutic Index by Topical Application

PURPOSE

As a continuing effort to elucidate the impact of structure modification upon cutaneous absorption behavior, we attempted to assess the skin permeation of magnolol by methylation and acetylation.

METHODS

Diacetylmagnolol and 2-O-acetyl-2'-O-methylmagnolol (AMM) were designed and synthesized in this study. The anti-inflammatory activity against stimulated neutrophils and keratinocytes was evaluated to check the bioactivity of the analogues. In vitro skin absorption was investigated using nude mouse and pig skin models at both equimolar and saturated doses.

RESULTS

Magnolol generally showed the strongest anti-inflammatory potential, followed by diacetylmagnolol and AMM. The antibacterial activity was observed for magnolol and diacetylmagnolol but not AMM. Diacetylmagnolol and AMM could be partly hydrolyzed to magnolol and 2-O-methylmagnolol after entering the skin. The hydrolysis rate of diacetylmagnolol was faster than that of AMM. The lipophilicity played a crucial role in cutaneous absorption, with AMM exhibiting the highest skin deposition. AMM accumulation within nude mouse skin was about 2.5-fold greater than that of magnolol and diacetylmagnolol. On the other hand, the transdermal penetration across the skin was lessened by methylation and esterification. This led to a superior skin targeting of AMM. Although the pharmacological activity of AMM was low, the high skin uptake and bioconversion into 2-O-methylmagnolol in the skin contributed to a greater therapeutic index (TI, skin deposition x inflammatory inhibition percentage) compared to the others. The accumulation of AMM in the hair follicles was 77.12 nmol/cm(2), which was significantly greater than that with magnolol (44.84 nmol/cm(2)) and diacetylmagnolol (26.96 nmol/cm(2)). The synthetic analogues were tolerable to the nude mouse skin.

CONCLUSIONS

Based on the experimental results, we may suggest topically applied AMM as a potent and safe candidate for the treatment of cutaneous inflammation.

In vitro evaluation of bioactive potential of Bacillus methylotrophicus YML008 against Propionibacterium acnes

Acne vulgaris is the most common skin diseases that people experience during their lives. Thirteen rhizosphere isolates were screened against Propionibacterium acnes. The bacterium exhibited the highest activity against P. acnes was identified as Bacillus methylotrophicus YML008 by 16S rRNA gene sequencing. Scanning electron microscopy was used to assess the changes in morphology of P. acnes. Preliminary studies on the antimicrobial substance demonstrated the hydrophilic nature of compound with MIC of 0.17mg/ml and MBC of 0.3mg/ml. The cytotoxic effect of the extract was least (80% survival) as compared to benzyperoxide (40% survival). These results suggest YML008 as a promising bioresource and may be useful as a lead bacterium to develop a new type of anti-acne skin care prep to cure or prevent acne. Further, mechanism of action and proper clinical trials may be promising for this research.

Protective effects of equol and their polyphenolic isomers against dermal aging: microarray/protein evidence with clinical implications and unique delivery into human skin

CONTEXT

Equol is a polyphenolic/isoflavonoid molecule that can be expressed as isomers. However, the characteristics of the equol isomers on dermal gene/protein expression and human skin percutaneous absorption remain unknown.

OBJECTIVE

Perform a comprehensive investigation on equol as: R-equol, racemic equol or S-equol to determine their differential expression of skin-related genes, quantify collagen expression and determine percutaneous absorption in human skin.

METHODS

Quantified: (i) gene expression/mRNA levels via gene array technology using human skin equivalents with equol exposure at 1.2% in qPCR experiments, (ii) in vitro collagen expression in human fibroblasts, and (iii) percutaneous absorption by Franz cell techniques.

RESULTS

In the qPCR studies, only three genes displayed the greatest significant expression by S-equol, whereas 16 genes displayed the greatest significant levels (either stimulation or inhibition) by R-equol and/or racemic equol, such as extracellular matrix proteins (i.e., collagen and elastin), nerve growth factor, aging genes [FOS, 100 A8 and A9 calcium-binding proteins, 5α-reductase type 1, and matrix metalloproteinases (1, 3, and 9)], and inflammatory genes (e.g., interleukin-1 alpha, interleukin-6, and cyclooxygenase-1). Collagen type I expression in fibroblasts was greater with racemic versus S-equol treatment at 1 and 10 nM. Percutaneous absorption demonstrated high sequestering in keratinocytes with subsequent accumulation/release over time.

DISCUSSION AND CONCLUSION

Overall, these results illustrate the significant differences in mirror-image molecules or isomers of equol where R-equol and/or racemic equol are better molecules for skin gene expression compared to S-equol and the percutaneous absorption of equol represents a unique epidermal reservoir delivery mechanism.

Biological importance and applications of squalene and squalane

Squalene is a polyunsaturated hydrocarbon with a formula of C₃₀H₅₀. Squalene can be found in certain fish oils, especially shark liver oil, in high amounts and some vegetable oils in relatively smaller amounts. Human sebum also contains 13% squalene as one of its major constituents. Squalane is a saturated derivative of squalene and also found in these sources. Interest in squalene has been raised after its characterization in shark liver oil which is used as a traditional medicine for decades. Several studies exhibited results that prove certain bioactivities for squalene and squalane. Up to date, anticancer, antioxidant, drug carrier, detoxifier, skin hydrating, and emollient activities of these substances have been reported both in animal models and in vitro environments. According to promising results from recent studies, squalene and squalane are considered important substances in practical and clinical uses with a huge potential in nutraceutical and pharmaceutical industries.

Physicochemical Characterisation of a Novel Thermogelling Formulation for Percutaneous Penetration of 5-Aminolevulinic Acid

The present contribution was dedicated to the development and characterisation of a semisolid formulation of 5-aminolevulinic acid (5-ALA), appropriate for the diagnosis and treatment of actinic keratosis in photodynamic therapy. To achieve sufficiently high concentrations of the polar substance within the living epithelium after topical application, the semisolid base was enriched with penetration enhancers. A semisolid liquid crystalline system for drug delivering was the formulation of choice. It was composed of isopropyl alcohol, dimethyl isosorbide, medium chain triglycerides, water, and Pluronic F 127 as a polyoxyethylene-polyoxypropylene surface-active block copolymer. Rheometrical investigations were performed in the oscillatory mode and showed a thermo reversible gelification behaviour of the formulation, which therefore was denoted Thermogel. Permeation studies through human stratum corneum revealed higher permeation coefficients for 5-ALA from the Thermogel than from different German Pharmacopoeia creams. For example a 7.5-fold increase in comparison with Basiscreme DAC, and a 19.5-fold increase compared to water containing hydrophilic ointment. With respect to Dolgit(R) Mikrogel, the permeation coefficient from the Thermogel was 6.4-fold higher. These results were in accordance with those of differential scanning calorimetry measurements. Thermogel disclosed the strongest interactions with stratum corneum lipids.

Evaluation of in vivo efficacy of topical formulations containing soybean extract

In the present study it was evaluated the: (i) functional stability of the soybean extract as a raw material and dispersed in two different topical formulations, (ii) skin retention using modified Franz diffusion cells, and (iii) in vivo activity of these formulations to inhibit 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced hydrogen peroxide (H(2)O(2)) and malondialdehyde (MDA) increases in the skin of hairless mice. The physico-chemical stability was evaluated by pH, globule size and centrifugation test. Furthermore, functional stability was also evaluated by antilipoperoxidative activity. The two topical formulations were stored at 4 degrees C, 30 degrees C/60% RH and 40 degrees C/70% RH for 6 months. The evaluation of the antiperoxidative stability of soybean extract itself and incorporated in formulations did not demonstrate loss of activity by storage at 4 degrees C/6 months. During 6 months of the study in different storage conditions the formulations 1 and 2 added or not with soybean extract were stable to physico-chemical tests. The effect of antioxidant compounds detected by the inhibition of MDA formation was time-dependent for formulation 2 as detected in the skin retention study. Pretreatment with formulation 1 or 2 significantly diminished TPA-induced H(2)O(2) and MDA generation. In conclusion, the present results suggest for the first time that formulations containing soybean extract may be a topical source of antioxidant compounds that decrease oxidative damages of the skin.

Dermal and transdermal delivery of an anti-psoriatic agent via ethanolic liposomes

The aim of the current investigation is to evaluate the transdermal potential of novel vesicular carrier, ethosomes, bearing methotrexate (MTX), an anti-psoriatic, anti-neoplastic, highly hydrosoluble agent having limited transdermal permeation. MTX loaded ethosomes were prepared, optimized and characterized for vesicular shape and surface morphology, vesicular size, entrapment efficiency, stability, in vitro human skin permeation and vesicle-skin interaction. The formulation (EE(9)) having 3% phospholipid content and 45% ethanol showing the greatest entrapment (68.71+/-1.4%) and optimal nanometric size range (143+/-16 nm) was selected for further transdermal permeation studies. Stability profile of prepared system assessed for 120 days revealed very low aggregation and growth in vesicular size (8.8+/-1.2%). MTX loaded ethosomal carriers also provided an enhanced transdermal flux of 57.2+/-4.34 microg/cm(2)/h and decreased lag time of 0.9 h across human cadaver skin. Skin permeation profile of the developed formulation further assessed by confocal laser scanning microscopy (CLSM) revealed an enhanced permeation of Rhodamine Red (RR) loaded formulations to the deeper layers of the skin (170 microm). Also, the formulation retained its penetration power after storage. Vesicle skin interaction study also highlighted the penetration enhancing effect of ethosomes with some visual penetration pathways and corneocytes swelling, a measure of retentive nature of formulation. Our results suggests that ethosomes are an efficient carrier for dermal and transdermal delivery of MTX.

Enhancement of skin penetration of vitamin K using monoolein-based liquid crystalline systems

Application of vitamin K (vitK) to the skin has been used for suppression of pigmentation and resolution of bruising. However, there is no report concerning the extent of its penetration in the skin. In this study, we investigated the in vitro skin penetration and transdermal delivery of vitK, and whether these parameters may be enhanced by lipid-based drug delivery systems. The lipid formulation used in this study contains monoolein (MO), which is structured as a liquid crystalline phase, named hexagonal phase. The skin penetration of vitK was assessed in vitro using porcine ear skin mounted in a Franz diffusion cell. VitK (2.5%, w/w) was incorporated in either of three formulations: liquid vaseline, MO-based hexagonal phase gel (MO-vitK-water at 77.5/2.5/20, w/w/w) and MO-based nanodispersion of hexagonal phase (MO-vitK-poloxamer-water at 15/2.5/0.9/81.6, w/w/w/w). When vaseline was used, vitK was delivered mainly to the stratum corneum (SC): 9.50+/-0.97 microg/cm(2) of vitK was delivered to the SC at 12 h post-application, whereas 4.90 +/- 1.28 microg/cm(2) of vitK was delivered to the epidermis (E)+dermis (D) at the same time point. The hexagonal phase gel and the nanodispersion delivered approximately 2 times more vitK to the SC and 2.0-3.7 times more vitK to the [E+D] than the vaseline solution. The nanodispersion (but not the gel) also increased the transdermal delivery of vitK at 9 h ( approximately 3-fold increase). These results demonstrate that the topical delivery of vitK incorporated in a lipophilic vehicle is small, but it may be enhanced by MO-based systems, which might be useful to increase the effectiveness of topical vitK therapy.

Evaluation of nanoparticles loaded with benzopsoralen in rat peritoneal exudate cells

Psoralens are widely used for the treatment of hyperproliferative skin disease. In this work, we prepared nanoparticles (NP) containing a benzopsoralen (3-ethoxy carbonyl-2H-benzofuro[3,2-f]-1-benzopiran-2-one) by the solvent evaporation technique. We evaluated important NP parameters such as particle size, drug encapsulation efficiency, effect of the encapsulation process over the drug's photochemistry, zeta potential, external morphology, and in vitro release behavior. We also investigated the nanoparticle as a drug delivery system (DDS), as well as its target delivery to the action site, which is a very important parameter to increase the therapeutic use of psoralens and to reduce their side effects. The uptake of benzopsoralen-loaded PLGA nanoparticles by different kinds of cells found in rat peritoneal exudates was also studied. The photodamage promoted by irradiation with UV light revealed morphological characteristics of cell damage such as cytoplasmic vesiculation, mitochondrial damage, and swelling of both the granular endoplasmatic reticulum and nuclear membrane. This encapsulation method maintained the drug's properties and improved drug delivery to the target cell.

Effect of DC/mDC iontophoresis and terpenes on transdermal permeation of methotrexate: In vitro study

The systemic toxicity caused by methotrexate limits its use and transdermal delivery would be a possible alternative. Transdermal permeation of methotrexate loaded into polyacrylamide-based hydrogel patch, across mice skin was studied in vitro after pretreatment with terpenes and ethanol, alone or in combination with iontophoresis (DC/mDC). Polyacrylamide patches gave the maximum flux as compared to the copolymers of acrylamide and acrylic acid. Of the terpenes used, pure menthol showed maximum enhancement (38%), whereas pure limonene elicited a minimum of 9.9% enhancement. Binary combination of menthol and ethanol increased the permeation to 54.9%, which was further enhanced to 93.69% and 117% when used in combination with DC and square wave (mDC) iontophoresis, respectively. ATR-FTIR of the stratum corneum treated with terpenes showed a split in the asymmetric C-H stretching vibrations along with decrease in peak heights and areas of asymmetric, symmetric C-H stretching, C=O stretching and amide bands. A split in amide II band was observed with iontophoresis. ATR-FTIR studies suggest conformational changes in the lipid-protein domains thereby increasing permeation. Histopathological studies on treated skin samples, gave an insight about the anatomical changes brought by the application of various enhancers. Binary mixture of menthol and ethanol in combination with square wave gave best results.

Isotretinoin-loaded solid lipid nanoparticles with skin targeting for topical delivery

The purpose of this study was to construct isotretinoin-loaded SLN (IT-SLN) formulation with skin targeting for topical delivery of isotretinoin. PRECIROL ATO 5 was selected as the lipid of SLN. Tween 80 and soybean lecithin were used as the surfactants to stabilize SLN. The hot homogenization method was performed to prepare the drug-loaded SLN. The various formulations were characterized by photon correlation spectroscopy and all the SLN formulations had low average size between 30 and 50 nm. Transmission electron microscopy studies showed that the IT-SLN formulation had a spherical shape. All the formulations had high entrapment efficiency ranging from 80% to 100%. The penetration of isotretinoin from the IT-SLN formulations through skins and into skins were evaluated in vitro using Franz diffusion cells fitted with rat skins. The in vitro permeation data showed that all the IT-SLN formulations can avoid the systemic uptake of isotretinoin in skins, however the control tincture had a permeation rate of 0.76+/-0.30 microg cm(-2)h(-1) through skins. The IT-SLN consisting of 3.0% PRECIROL ATO 5, 4.0% soybean lecithin and 4.5% Tween 80 could significantly increased the accumulative uptake of isotretinoin in skin and showed a significantly enhanced skin targeting effect. The studied IT-SLN showed a good stability. These results indicate that the studied IT-SLN formulation with skin targeting may be a promising carrier for topical delivery of isotretinoin.

Dermatological drug dosage in the elderly

The elderly population is increasing and drug dosing requires special considerations for efficacy and decreasing toxicity. This overview provides algorithms for adjusting drug and dosage based on current evidence-based knowledge with emphasis on drugs prescribed in dermatological practice.

Reverse hexagonal phase nanodispersion of monoolein and oleic acid for topical delivery of peptides: in vitro and in vivo skin penetration of cyclosporin A

PURPOSE

To obtain and characterize reverse hexagonal phase nanodispersions of monoolein and oleic acid, and to evaluate the ability of such system to improve the skin penetration of a model peptide (cyclosporin A, CysA) without causing skin irritation.

METHODS

The nanodispersion was prepared by mixing monoolein, oleic acid, poloxamer, and water. CysA was added to the lipid mixture to obtain a final concentration of 0.6% (w/w). The nanodispersion was characterized; the skin penetration of CysA was assessed in vitro (using porcine ear skin mounted in a Franz diffusion cell) and in vivo (using hairless mice).

RESULTS

The obtainment of the hexagonal phase nanodispersion was demonstrated by polarized light microscopy, cryo-TEM and small angle X-ray diffraction. Particle diameter was 181.77 +/- 1.08 nm. At 0.6%, CysA did not change the liquid crystalline structure of the particles. The nanodispersion promoted the skin penetration of CysA both in vitro and in vivo. In vitro, the maximal concentrations (after 12 h) of CysA obtained in the stratum corneum (SC) and in the epidermis without stratum corneum (E) + dermis (D) were approximately 2 fold higher when CysA was incorporated in the nanodispersion than when it was incorporated in the control formulation (olive oil). In vivo, 1.5- and 2.8-times higher concentrations were achieved in the SC and [E+D], respectively, when the nanodispersion was employed. No histopathological alterations were observed in the skin of animals treated with the nanodispersion.

CONCLUSION

These results demonstrate that the hexagonal phase nanodispersion is effective in improving the topical delivery of peptides without causing skin irritation.

Analysis of in Vitro Skin Permeation of 22-Oxacalcitriol Having a Complicated Metabolic Pathway

PURPOSE

The purpose of this study is to analyze simultaneous skin permeation and metabolism of 22-oxacalcitriol (OCT) having several metabolites in skin by observing skin permeation of only unchanged OCT through excised rat skin.

METHODS

A diffusion model including metabolic processes was employed to express simultaneous skin permeation and metabolism of OCT. In vitro permeation experiments of OCT from Oxarol ointment through full-thickness and stripped rat skin were carried out using Franz-type diffusion cells. Time courses of unchanged OCT amounts in ointment, skin, and receptor fluid were determined and fitted to diffusion equations to obtain permeation parameters and a metabolic rate.

RESULTS

Fitting curves of the skin permeation profile obtained by the model were sufficiently close to observed data of unchanged OCT amounts in ointment, skin, and receptor fluid. The following parameters were obtained: metabolic rate of 1.37 x 10(-1) h(-1), and diffusion constants of OCT in stratum corneum (SC) (D(SC)) and viable epidermis and dermis (VED) (D(VED)) of 1.50 x 10(-7) and 2.96 x 10(-4) cm2/h, respectively. The partition coefficient of OCT for SC/ointment (K(SC/D)) was 7 times greater than that of VED/ointment (K(VED/D)).

CONCLUSIONS

The present analysis made it possible to calculate skin permeation parameters (partitioning, diffusivity, and metabolic rate) of OCT without requiring metabolic information, e.g., quantification of metabolites or identification of metabolic pathways. This would be widely applicable for drugs that are not suitable for conventional methods due to complicated metabolic pathways.

Mechanisms of the comedolytic and anti-inflammatory properties of topical retinoids

Retinoids comprise a family of compounds with structures and mechanisms of action that resemble those of vitamin A (retinol), an essential nutrient which plays a role in cell growth and differentiation. The retinoids, which interact with nuclear receptors and affect gene transcription, have enormous therapeutic potential, particularly if they are receptor- and function-selective. Tretinoin was the first topical retinoid employed for the treatment of acne. In recent years, other topical retinoids for the treatment of acne have been designed from a disease-specific approach, with enhanced receptor and function selectivity, which translates to improved therapeutic effects and more favorable tolerability. The properties that differentiate the topical retinoids tretinoin, adapalene, and tazarotene have permitted clinicians to tailor acne treatment regimens for maximum therapeutic outcomes. Tretinoin (all-trans-retinoic acid), considered a first-generation retinoid, acts by altering the milieu of the microcomedo and influences desquamation of abnormal epithelium. Two receptor-selective synthetic retinoids, adapalene and tazarotene, may be classified as third-generation retinoids. Adapalene, a derivative of naphthoic acid, has comedolytic, antiproliferative, and anti-inflammatory properties. Tazarotene is a prodrug metabolized to tazarotenic acid that modulates cellular differentiation, desquamation, and inflammation.

Tazarotene: therapeutic strategies in the treatment of psoriasis, acne and photoaging

Tazarotene is a member of the new generation of receptor-selective, synthetic retinoids for the topical treatment of mild to moderate plaque psoriasis, acne vulgaris and photoaging. Though they are effective in monotherapy, clinical studies with a focus on novel combination treatments and a comparison of different agents for these skin disorders are accumulating. The concomitant use of tazarotene with a mid-potency or high-potency corticosteroid enhances the efficacy in psoriatic plaques and reduces the risk of steroid-induced skin atrophy. Combining phototherapy with adjunctive tazarotene accelerates the clinical response and reduces the cumulative UVB or PUVA exposure load. Tazarotene applied once daily is superior to adapalene monotherapy in acne vulgaris and is efficacious in the treatment of photodamage. Novel therapeutic regimens such as short-contact therapy have been developed for both acne and psoriasis in order to diminish the major adverse events like pruritus, burning, local skin irritation and erythema.

In vitro pharmacokinetics of anti-psoriatic fumaric acid esters

BACKGROUND

Psoriasis is a chronic inflammatory skin disease that can be successfully treated with a mixture of fumaric acid esters (FAE) formulated as enteric-coated tablets for oral use. These tablets consist of dimethylfumarate (DMF) and salts of monoethylfumarate (MEF) and its main bioactive metabolite is monomethylfumarate (MMF). Little is known about the pharmacokinetics of these FAE. The aim of the present study was to investigate the hydrolysis of DMF to MMF and the stability of MMF, DMF and MEF at in vitro conditions representing different body compartments.

RESULTS

DMF is hydrolyzed to MMF in an alkaline environment (pH 8), but not in an acidic environment (pH 1). In these conditions MMF and MEF remained intact during the period of analysis (6 h). Interestingly, DMF was hardly hydrolyzed to MMF in a buffer of pH 7.4, but was rapidly hydrolyzed in human serum having the same pH. Moreover, in whole blood the half-life of DMF was dramatically reduced as compared to serum. The concentrations of MMF and MEF in serum and whole blood decreased with increasing time. These data indicate that the majority of the FAE in the circulation are metabolized by one or more types of blood cells. Additional experiments with purified blood cell fractions resuspended in phosphate buffered saline (pH 7.4) revealed that at concentrations present in whole blood monocytes/lymphocytes, but not granulocytes and erythrocytes, effectively hydrolyzed DMF to MMF. Furthermore, in agreement with the data obtained with the pure components of the tablet, the enteric-coated tablet remained intact at pH 1, but rapidly dissolved at pH 8.

CONCLUSION

Together, these in vitro data indicate that hydrolysis of DMF to MMF rapidly occurs at pH 8, resembling that within the small intestines, but not at pH 1 resembling the pH in the stomach. At both pHs MMF and MEF remained intact. These data explain the observation that after oral FAE intake MMF and MEF, but not DMF, can be readily detected in the circulation of human healthy volunteers and psoriasis patients.

In situ FTIR ATR spectroscopic study of the interaction of immobilized human tumor necrosis factor-alpha with a monoclonal antibody in aqueous environment

By in situ FTIR ATR measurements, the antibody (AB) recognition of human tumor necrosis factor-alpha (TNFalpha) immobilized on the Ge surface of a multiple internal reflection element (MIRE) was investigated. The experiments were performed in aqueous environment in a flow-through cell. After immobilization of TNFalpha on the Ge-MIRE by direct adsorption from aqueous solution, the immobilisate reached stability after about 1 h under flow-through conditions. The remaining sites of the Ge surface were saturated by bovine serum albumin (BSA) in order to prevent unspecific binding of anti-TNFalpha AB which was then added. The obtained FTIR ATR spectra were shown to result exclusively from AB specifically interacting with TNFalpha, since the absence of immunoglobulin binding to BSA adsorbed to the Ge MIRE was verified by a reference experiment. Finally, the stability of all adsorbed protein immobilisates was monitored under flow-through conditions for 10.5 h. The TNFalpha-AB complex showed a decrease of 7.4%, whereas the BSA adsorbate remained stable. IR measurements were performed with polarized light in order to study orientational effects of the immobilized proteins. The dichroic ratios and surface concentrations of all used proteins are available after quantitative analysis of the amide II bands.

Oral tazarotene and oral pimecrolimus: novel oral therapies in development for psoriasis

Psoriasis is a chronic skin disorder that affects approximately 2% of the US and European population. Over the last several years, one of the major focuses in psoriasis research has been the development of novel biologic therapies for this disease. The aim of these therapies is to provide selective, immunologically directed intervention, with the hope that such specificity will result in fewer side effects than traditional therapies. In addition to these therapies, there are also oral medications in development for psoriasis. The goal of this article is to review oral tazarotene, a novel retinoid, and oral pimecrolimus, a novel macrolactam therapy, for the treatment of moderate to severe psoriasis.

Factors influencing sunless tanning with dihydroxyacetone

BACKGROUND

Sunless tanning preparations have been used for more than 50 years and are still very popular because they provide temporary pigmentation resembling an ultraviolet-induced tan. The pigment is the product of reactions between dihydroxyacetone (DHA) and amino acids in the stratum corneum.

OBJECTIVES

To understand the factors that influence the reactions of DHA with amino acids in the stratum corneum with the ultimate goal of producing pigmentation with greater photoprotection.

METHODS

The influence of hydration and/or oxygen on the development of DHA-induced pigment was assessed in vivo using an occlusive dressing and ex vitro on human epidermal preparations. Two spectroscopic techniques, diffuse reflectance and fluorescence emission, were used to monitor the extent of pigment development. The optimal relative humidity for DHA-induced pigmentation was assessed on the epidermal preparations. The formation of products from reactions between DHA and nine amino acids was studied in solutions buffered at pH 5 and 7.

RESULTS

Development of DHA-induced pigmentation was inhibited by a 24-h occlusive dressing but appeared after its removal, indicating that DHA was still present. High hydration but not the absence of oxygen inhibited coloration of occluded skin. The extent of pigmentation did not vary in a simple manner with hydration, as pigment formation was positively correlated with humidity from 0 to 75% but negatively correlated from 75 to 100%. Lysine, glycine and histidine reacted most rapidly with DHA, with reaction rates greater at pH 7 than at pH 5. The products absorbed with maxima at wavelengths up to 340 nm.

CONCLUSIONS

These results indicate that extent of hydration, pH and availability of certain amino acids influence the development of DHA-induced pigmentation in the stratum corneum and suggest that manipulation of these factors might produce pigmentation with greater photoprotection.

Important drug interactions and reactions in dermatology

A constantly expanding pharmacological armamentarium increases the concern for serious drug interactions. This article discusses drug metabolism and how the cytochrome P-450 family facilitates drug biotransformation. Clinically significant drug interactions involving antifungal drugs, antibiotics, retinoids, and immunosuppressive agents, as well as topical anesthetics and various foods, are included.

Biologic therapy for psoriasis--the first wave: infliximab, etanercept, efalizumab, and alefacept

Over the last several years, a new generation of therapies for psoriasis has been in development. These biologic therapies target the activity of T lymphocytes and cytokines responsible for the inflammatory nature of this disease. In this review, we present an update on the progress of the four biologic agents in the forefront: infliximab, etanercept, efalizumab, and alefacept. The mechanism of each drug will be reviewed, as well as the most recent efficacy and safety data.

Teratogenicity of isotretinoin revisited: species variation and the role of all-trans-retinoic acid

This paper reviews the teratogenicity of isotretinoin in regard to aspects of species variation, toxicokinetics, and metabolism. Particular emphasis is given to the hypothesis that most effects of isotretinoin (13-cis-retinoic acid) are mediated by isomerization to the all-trans-retinoic acid. This mechanism of action would provide a basis for the understanding of species differences and the extrapolation of experimental results to the human situation and thus improve drug development. The insensitive species (rat, mouse) eliminate the drug rapidly through detoxification to the beta-glucuronide; also, placental transfer is limited in these species. On the other hand, in sensitive species (primates), the drug is predominantly metabolized to the active 13-cis-4-oxo-retinoic acid; placental transfer is more extensive here. The beta-glucuronides showed limited placental transfer in all species examined; these metabolites exhibited very low, if any, measurable concentrations in the human. The 13-cis-retinoic acid is not appreciably bound to cellular retinoid-binding proteins or nuclear receptors and exhibits low tissue distribution and placental transfer. Its access to the nucleus may be extensive. Because of the long half life of 13-cis-retinoic acid, continuous isomerization results in significant area under the concentration-time curve levels of all-trans-retinoic acid in the mouse, monkey and the human; the all-trans-retinoic acid formed is extensively distributed across the placenta and may be an important factor that contributes to the teratogenic potency of 13-cis-retinoic acid. Isomerization cannot explain the teratogenic effects of 13-cis-retinoic acid in the rat and rabbit. It is concluded that the high teratogenic activity of isotretinoin in sensitive species (human, monkey) is related to slow elimination of the 13-cis-isomer, to metabolism to the 4-oxo-derivative, to increased placental transfer, to continuous isomerization and significant exposure of the target tissue to all-trans-retinoic acid; and to lack of binding to cytoplasmic retinoid binding proteins that could possibly result in ready access to the nucleus.

Cellular metabolism and actions of 13-cis-retinoic acid

Retinoids (vitamin A and its derivatives) are potent substances for regulating the expression of many different genes within the body. The gene regulatory activities of retinoids are mediated primarily by the all-trans and 9-cis isomers of retinoic acid. Although 13-cis-retinoic acid (isotretinoin) does not have the potent gene regulatory activity of the other two isomers, it is an effective pharmacologic agent for treating a variety of dermatologic conditions. Because 13-cis-retinoic acid is also a naturally occurring retinoid that is present in the circulation, question is raised as to the biochemical mechanism(s) responsible for its pharmacologic efficacy. Some of this efficacy likely arises from the ability of 13-cis-retinoic acid to undergo isomerization to the significantly more active all-trans and 9-cis isomers; however, this does not account for all of the pharmacologic effects observed upon use of this retinoid. Some recent studies suggest that 13-cis-retinoic acid may act by inhibiting the actions of enzymes that are needed to metabolize steroids, while other recent studies indicate that 13-cis-retinoic acid acts through membrane receptors present on the surface of cells. At the present, it is not possible to rule out still other possible biochemical actions of 13-cis-retinoic acid in the body. It is clear, however, that if we are to fully understand the basis for the clinical efficacy of 13-cis-retinoic acid, a better understanding of such biochemical actions is needed.

Correlation of the local distribution of topically applied substances inside the stratum corneum determined by tape-stripping to differences in bioavailability

Tape-stripping and optical spectroscopy are used as a suitable combined method to determine the horny layer profile. Firstly, typical ultraviolet filter substances are used as active substances which are fixed inside the horny layer. Secondly, clobetasol propionate was applied topically in two formulations, Temovate Cream and Temovate and Emollient. The measured changes in the local distribution of the drug inside stratum corneum reflect the observed differences in the biological response visualized as blanching. The concentration of the drug in deeper parts of the horny layer proposes the existence of a small channel available for the percutaneous absorption. The observed low intensity blanching is correlated to the follicle orifices of the skin. After application of Temovate and Emollient, a lateral spreading of the drug must be taken into account.

Reversed‐phase high‐performance liquid chromatography (RP‐HPLC) determination of lipophilicity of furocoumarins: Relationship with DNA interaction

The partition coefficient (P) of 82 furocoumarins and analogs (psoralens, angelicins, allopsoralens, 8-azapsoralens, angular furoquinolin-2-ones, sulfur and selenium isosters of psoralen and angelicin) has been determined by reversed-phase HPLC. The chromatographic behavior correlates well with the in vitro affinity of the compounds toward DNA.

Corticosteroid cross-reactions: an alternative view

An alternative view of corticosteroid cross-reactivity is proposed, based on 2 immune recognition sites on the corticosteroid molecule, 1 influenced by C 6/9 substitution and 1 by C 16/17 substitution. A case report is adduced in support of such a hypothesis.

Isolation and identification of 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3: metabolites of 1alpha,24(R)-dihydroxyvitamin D3 produced in rat kidney

1alpha,24(R)-Dihydroxyvitamin D3 [1alpha,24(R)(OH)2D3], a synthetic vitamin D3 analog, has been developed as a drug for topical use in the treatment of psoriasis. At present, the target tissue metabolism of 1alpha,24(R)(OH)2D3 is not understood completely. In our present study, we investigated the metabolism of 1alpha,24(R)(OH)2D3 in the isolated perfused rat kidney. The results indicated that 1alpha,24(R)(OH)2D3 is metabolized in rat kidney into several metabolites, of which 1alpha,24(R),25-trihydroxyvitamin D3, 1alpha,25-dihydroxy-24-oxovitamin D3, 1alpha,23(S),25-trihydroxy-24-oxovitamin D3, and 1alpha,23-dihydroxy-24,25,26,27-tetranorvitamin D3 are similar to the previously known metabolites of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3]. In addition to these aforementioned metabolites, we also identified two new metabolites, namely 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3. The two new metabolites do not possess the C-25 hydroxyl group. Thus, the metabolism of 1alpha,24(R)(OH)2D3 into both 25-hydroxylated and non-25-hydroxylated metabolites suggests that 1alpha,24(R)(OH)2D3 is metabolized in the rat kidney through two pathways. The first pathway is initiated by C-25 hydroxylation and proceeds further via the C-24 oxidation pathway. The second pathway directly proceeds via the C-24 oxidation pathway without prior hydroxylation at the C-25 position. Furthermore, we demonstrated that rat kidney did not convert 1alpha-hydroxyvitamin D3 [1alpha(OH)D3] into 1alpha,25(OH)2D3. This finding indicates that the rat kidney does not possess the classical vitamin D3-25-hydroxylase (CYP27) activity. However, from our present study it is apparent that prior hydroxylation of 1alpha(OH)D3 at the C-24 position in the 'R' orientation allows 25-hydroxylation to occur. At present, the enzyme responsible for the C-25 hydroxylation of 1alpha,24(R)(OH)2D3 is unknown. Our observation that the side chain of 1alpha,24(R)(OH)2D3 underwent 24-ketonization and 23-hydroxylation even in the absence of the C-25 hydroxyl group suggests that 1alpha,25(OH)2D3-24-hydroxylase (CYP24) can perform some steps of the C-24 oxidation pathway without prior C-25 hydroxylation. Thus, we speculate that CYP24 may be playing a dual role in the metabolism of 1alpha,24(R)(OH)2D3.

Clinical pharmacokinetics and drug metabolism of tazarotene: a novel topical treatment for acne and psoriasis

Tazarotene (AGN 190168) is a new acetylenic retinoid which is effective for the topical treatment of patients with stable plaque psoriasis and mild to moderate acne vulgaris. Topical gel application provides direct delivery of tazarotene into the skin. At 10 hours after a topical application of 0.1% tazarotene gel to the skin of healthy individuals and patients with psoriasis, approximately 4 to 6% of the dose resided in the stratum corneum and 2% of the dose distributed to the viable epidermis and dermis. Tazarotene is rapidly hydrolysed by esterases to its active metabolite, tazarotenic acid. Tazarotenic acid does not accumulate in adipose tissue, but undergoes further metabolism to its sulfoxide and to other polar metabolites and is rapidly eliminated via both urinary and faecal pathways with a terminal half-life of about 18 hours. Percutaneous absorption is similar between healthy individuals and patients with facial acne, leading to plasma concentrations below 1 microg/L. The systemic bioavailability of tazarotene (measured as tazarotenic acid) is low, approximately 1% after single and multiple topical applications to healthy skin. In patients with psoriasis under typical conditions of use, systemic bioavailability increased during the initial 2 weeks of treatment from 1% (single dose) to 5% or less (steady state). The increased bioavailability is probably related to decreases in plaque elevation and scaling due to successful treatment, resulting in a less effective skin penetration barrier to tazarotene. Steady-state concentrations of tazarotenic acid are achieved within 2 weeks of topical treatment in both healthy and psoriatic skin types. The large variability in plasma concentrations observed in patients with psoriasis is probably because of the large differences in lesional skin condition, the amount of drug applied and the surface area of application. There was no significant drug accumulation in the body with long term treatment of patients with psoriasis. Topical administration of tazarotene requires dosages much smaller than those usually required for oral retinoids, such as isotretinoin, acitretin and etretinate, and it delivers the drug directly into the target skin tissues. The low systemic absorption and rapid systemic elimination of tazarotene and tazarotenic acid results in limited systemic exposure. Thus, topical tazarotene has a low potential for systemic adverse effects and is effective in the treatment of patients with acne and psoriasis.

A novel anti-inflammatory drug, SDZ ASM 981, for the treatment of skin diseases: in vitro pharmacology

SDZ ASM 981, a novel ascomycin macrolactam derivative, has high anti-inflammatory activity in animal models of allergic contact dermatitis and shows clinical efficacy in atopic dermatitis, allergic contact dermatitis and psoriasis, after topical application. Here we report on the in vitro activities of this promising new drug. SDZ ASM 981 inhibits the proliferation of human T cells after antigen-specific or non-specific stimulation. It downregulates the production of Th1 [interleukin (IL)-2, interferon-gamma] and Th2 (IL-4, IL-10) type cytokines after antigen-specific stimulation of a human T-helper cell clone isolated from the skin of an atopic dermatitis patient. SDZ ASM 981 inhibits the phorbol myristate acetate/phytohaemagglutinin-stimulated transcription of a reporter gene coupled to the human IL-2 promoter in the human T-cell line Jurkat and the IgE/antigen-mediated transcription of a reporter gene coupled to the human tumour necrosis factor (TNF)-alpha promoter in the murine mast-cell line CPII. It does not, however, affect the human TNF-alpha promoter controlled transcription of a reporter gene in a murine dendritic cell line (DC18 RGA) after stimulation via the FcgammaRIII receptor. SDZ ASM 981 also prevents the release of preformed pro-inflammatory mediators from mast cells, as shown in the murine cell line CPII after stimulation with IgE/antigen. In summary, these results demonstrate that SDZ ASM 981 is a specific inhibitor of the production of pro-inflammatory cytokines from T cells and mast cells in vitro.

Effects of oral supplementation with evening primrose oil for six weeks on plasma essential fatty acids and uremic skin symptoms in hemodialysis patients

Abnormalities in plasma composition of essential fatty acids (EFAs) may be associated with the etiology of pruritus and other skin problems in patients undergoing hemodialysis. To study whether an oral supplementation with omega-6 (n-6) EFAs would restore deranged plasma EFAs and ameliorate skin symptoms, 9 and 7 dialysis patients were randomly assigned to receive either gamma-linolenic acid (GLA)-rich evening primrose oil (EPO) or linoleic acid (LA) (2 g/day each) for 6 weeks. Plasma concentrations of EFA were analyzed by gas chromatography and uremic skin symptoms were assessed for dryness, pruritus and erythema by questionnaire and visual inspection in a double-blind manner. The patients given EPO exhibited a significant (p < 0.05) increase in plasma dihomo-gamma-linolenic acid (a precursor of anti-inflammatory prostaglandin E1) with no concomitant change in plasma arachidonic acid (a precursor of pro-inflammatory prostaglandin E2 and leukotriene B4). In contrast, those given LA exhibited a significant (p < 0.05) increase in LA but not in any other n-6 EFAs, whereas they exhibited a significant (p < 0.05) decrease in plasma docosahexaenoic acid. The patients given EPO showed a significant (p < 0.05) improvement in the skin scores for the three different uremic skin symptoms over the baseline values and a trend toward a greater improvement (0.05 < p < 0.1) in pruritus scores than those given LA. Results indicate that GLA-rich EPO would be a more favorable supplemental source than LA in terms of shifting eicosanoid metabolism toward a less inflammation status through modifying plasma concentrations of their precursor n-6 EFAs. Further studies are required to confirm the efficacy and safety of EPO therapy for the treatment of uremic pruritus.

Effect of tazarotene, an acetylenic retinoid, on human dermal fibroblast

The inhibitory effect of tazarotene, an acetylenic retinoid, on human dermal fibroblast in vitro was compared to that of all-trans-retinoic acid. The proliferation of fibroblasts was inhibited by both retinoids at the concentration of 1 microM after 5 days of culture. Synthesis of DNA and collagen was inhibited by both retinoids concentration-dependently up to 10 microM, although tazarotene was weaker in the inhibition of collagen synthesis. These results suggest the possible usefulness of tazarotene in the treatment of fibrotic diseases.

Toxicology and pharmacology of the chemical warfare agent sulfur mustard

There have been reports of chemical attacks in which sulfur mustard might have been used (a) on Iranian soldiers and civilians during the Gulf War in 1984 and 1985 and (b) in an Iraqi chemical attack on the Iranian-occupied village of Halbja in 1988, resulting in many civilian casualties. Heavy use of chemical warfare in Afghanistan by the Soviet military is a recent innovation in military tactics that has been highly successful and may ensure further use of chemical agents in future military conflicts and terrorist attacks as a profitable adjunct to conventional military arms. Mustard is a poisonous chemical agent that exerts a local action on the eyes, skin, and respiratory tissue, with subsequent systemic action on the nervous, cardiac, and digestive systems in humans and laboratory animals, causing lacrimation, malaise, anorexia, salivation, respiratory distress, vomiting, hyperexcitability, and cardiac distress. Under extreme circumstances, dependent upon the dose and length of exposure to the agent, necrosis of the skin and mucous membranes of the respiratory system, bronchitis, bronchopneumonia, intestinal lesions, hemoconcentration, leucopenia, convulsions with systemic distress, and death occur. Severe mustard poisoning in humans is associated with systemic injury, which is manifested as headache, epigastric distresses, anorexia, diarrhea, and cachexia and is usually observed at mustard doses of 1000 mg/min/m3 with damage to hematopoietic tissues and progressive leucopenia. Sulfur mustard is a cell poison that causes disruption and impairment of a variety of cellular activities that are dependent upon a very specific integral relationship. These cytotoxic effects are manifested in widespread metabolic disturbances whose variable characteristics are observed in enzymatic deficiencies, vesicant action, abnormal mitotic activity and cell division, bone marrow disruption, disturbances in hematopoietic activity, and systemic poisoning. Indeed, mustard gas readily combines with various components of the cell such as amino acids, amines, and proteins. Although evidence of an association between lung cancer and mustard gas encountered on the battlefields of World War I is at best suggestive if not problematical (Case and Lea, 1955; Beebe, 1960; Norman, 1975), the epidemiological data accumulated from the poison gas factories in Japan (Yamada et al., 1953; Wada et al., 1968; Inada et al., 1978; Shigenobu, 1980; Nishimoto et al., 1983; Hirono et al., 1984; Takuoka et al., 1986), in Germany (Weiss, 1958; Hellmann, 1970a; Weiss and Weiss, 1975; Klehr, 1984) and in England (Manning et al., 1981; Easton et al., 1988) are substantial (International Agency for Research on Cancer, 1975). Unfortunately, attempts to seek confirmatory and substantial evidence in laboratory animals such as mice (Boyland and Horning, 1949; Heston, 1950; Heston, 1953a; McNamara et al., 1975) and rats (Griffin et al., 1951; McNamara et al., 1975; Sasser et al., 1996) have not been consistent. Sulfur mustard has been shown to be mutagenic in a variety of different species using many different laboratory techniques from fruit flies, microorganisms and mammalian cell cultures (Fox and Scott, 1980). Evidence is slowly accumulating from human data (Hellmann, 1970a; Lohs, 1975; Wulf et al., 1985). Evidence for the teratogenicity of mustard has been negative in assessment of fetotoxicity and adverse effects of mustard on the reproductive potential of both human and animal studies. Indeed, investigations of women adversely affected by mustard are minimal because most of the studies have been performed on former men employees of poison gas factories and have been negative or questionable. We have recently emphasized the need to assess the affect of a suspected teratogen on maternal toxicity in laboratory animals before any conclusions can be made.(ABSTRACT TRUNCATED)

Thalidomide-induced neuropathy and genetic differences in drug metabolism

A pharmacogenetic predisposition to thalidomide-induced neuropathy has been investigated. Differences of drug metabolism were examined in 16 patients with severe orogenital ulceration, who were treated with thalidomide (< or = 200 mg/day) for 0.3-5.0 years. Eight had evidence of early peripheral neuropathy according to nerve conduction studies. Rates of C-hydroxylation, N-acetylation, and conjugation reactions with sulphate, glucuronide and glycine, were tested with the probe compounds debrisoquine, sulphadimidine, paracetamol and aspirin, respectively. Urinary drug metabolites were analysed by high pressure liquid chromatography. Results were compared with 16 healthy age- and sex-matched volunteers. Of the patients 6.25% and 13.3% of the controls had a poor Debrisoquine Hydroxylator Ratio (DMR); none of the patients with neuropathy had a poor DMR as compared to 12.5% without neuropathy. Of the patients 40.0% and 35.7% of the controls were slow acetylators; 28.6% with neuropathy were slow acetylators as opposed to 50% without neuropathy. Similarly, there were no significant differences in rates of conjugation between groups. All unaffected patients were active smokers, whereas only two of those with neuropathy smoked. Cumulative dose or duration of therapy were unrelated to risk of neuropathy. In conclusion, changes of nerve conductivity are a frequent and unpredictable adverse effect of thalidomide (< or = 200 mg/day), although smoking may have a protective action against their development. Nerve conduction studies are required before and during treatment, irrespective of the prescribed dose.

In vitro metabolism of the anti-psoriatic vitamin D analog, calcipotriol, in two cultured human keratinocyte models

Calcipotriol (MC903) is a side chain analog of the vitamin D hormone calcitriol, containing a 22-23 double bond, a 24(S)-hydroxyl function, and carbons 25, 26, and 27 incorporated into a cyclopropane ring which has been developed for treating psoriasis. The in vitro metabolism of calcipotriol was studied in two keratinocyte cell models, HPK1A and HPK1A-ras. Calcipotriol was initially converted into the 24-ketone (MC1046) and its 22,23-hydrogenated derivative (MC1080), metabolites observed in osteosarcoma, kidney, and hepatoma cell lines. We also observed the formation of further metabolites, identified as the two 23-hydroxylated derivatives of MC1080 (MC1439 and MC1441), the two 23,24-dihydroxylated compounds (MC1575 and 1577), and the side chain-cleaved compounds, tetranor-1,23-(OH)2D3 and calcitroic acid, the end products of catabolism of calcitriol. These findings suggest that calcitriol and calcipotriol may share catabolic enzymes. The biological activity of each of the principal metabolites of calcipotriol, assessed using a growth hormone reporter gene transcriptional activation system and a vitamin D receptor assay, was found to be lower than that of calcipotriol. If the extensive in vitro metabolism of calcipotriol is also found in normal and psoriatic keratinocytes in vivo, then this may explain the lack of systemic calcemic activity of topically applied drug.

Efficacy of vitamin D3 derivatives in the treatment of psoriasis vulgaris: a preliminary report

The efficacy of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and the new analogue calcipotriene (MC 903) in the treatment of psoriasis was investigated. Eight patients with psoriasis were enrolled in a pilot study with systemically administered vitamin D3 and were given 1,25(OH)2D3 (Rocaltrol; Hoffmann-La Roche) in dosages from 0.5 microgram to 2 micrograms/day for a 6-month trial. In one patient, the psoriatic plaques resolved within 2 months after treatment (0.5 microgram/day) was initiated. Moderate improvement was noted in one other patient (1 microgram/day). The serum level of 1,25(OH)2D before treatment was not less than the normal range of the adult population. Side effects of systemically administered 1,25(OH)2D3 included a dose-dependent increase in the 24-hour urinary calcium excretion and a decrease in the total number of platelets. Seven patients with symmetric plaque-type psoriasis were treated topically with 2 micrograms/g of 1,25(OH)2D3 in petrolatum. During 3 months of follow-up, mild improvement was noted in three patients. Five patients in the calcipotriene study were part of a nationwide double-blind placebo-controlled trial by Bristol-Myers Squibb. Moderate to marked improvement was noted in the two patients who received 50 micrograms/g of calcipotriene topically. The three patients who received placebo showed no response. We conclude that a subset of patients with psoriasis responds well to 1,25(OH)2D3. Calcipotriene is efficacious and an excellent alternative to topically applied corticosteroids.

Comparison of calcipotriol with selected metabolites and analogues of vitamin D3: effects on cell growth regulation in vitro and calcium metabolism in vivo

Calcipotriol is a novel vitamin D3 analogue developed for topical treatment of psoriasis. Calcipotriol is believed to act via regulation of cell proliferation and differentiation. In this respect calcipotriol is as potent as 1 alpha, 25(OH)2D3, the physiologically active form of vitamin D3, but its calcaemic activity in vivo is 100 to 200 times lower. In the present investigation, the effects of calcipotriol on cell growth regulation in vitro and on calcium metabolism in vivo were compared to those exerted by a number of metabolites and analogues of vitamin D3. Besides 1 alpha, 25(OH)2D3, these included the two physiologically occurring metabolites 25(OH)D3 and 24,25(OH)2D3, and the two synthetic analogues 1 alpha (OH)D3 and 1 alpha, 24(OH)2D3. 25(OH)D3 and 24,25(OH)2D3 were shown to be inactive both in vitro and in vivo. 1 alpha (OH)D3 was found to have a low biological activity in vitro, but was highly calcaemic in vivo after biotransformation to 1 alpha, 25(OH)2D3. Calcipotriol, 1 alpha, 24(OH)2D3 and 1 alpha, 25(OH)2D3 were all three potent regulators of cell proliferation and differentiation in vitro. In vivo, only calcipotriol showed a greatly reduced calcaemic activity after both oral and intravenous administration. It is concluded that calcipotriol, with a reduced risk of inducing calcaemic side-effects upon absorption from the skin, possesses a favourable therapeutic profile for topical treatment of hyperproliferative diseases.

Liposomes. A perspective for dermatologists

We believe that it is unlikely that intact liposomes can cross the stratum corneum and act as carriers of drugs through the skin. However, it is probable that liposomes have the potential to modify the cutaneous biodistribution of applied chemicals (e.g., drugs, toxins, humectants) and thus modify their activity. Liposomal lipids can also penetrate the skin barrier. The effect of this is likely to be varied and lipid dependent, but this phenomenon could hold the most potential for the application of liposomes to topical therapy.