Adapalene biochemistry and the evolution of a new topical retinoid for treatment of acne.

The emergence of oral and topical retinoids was a major advance in the clinical management of acne vulgaris. However, the benefits of these agents were somewhat limited by the degree of side effects caused by these drugs. Over the last 15 years, researchers have sought compounds that can provide the manifold therapeutic benefits obtained with tretinoin and isotretinoin while minimizing the potential for irritation and other unwanted effects. Adapalene, a naphthoic-acid derivative, is one result of this search, and it serves as an example of rational drug development: the formulation of a novel substance with specific pharmacological properties and clinical objectives in mind. These goals included enhancing stability, enhancing anti-inflammatory effects, maintaining effectiveness and minimizing cutaneous irritation. This paper reviews the history of the development of adapalene, its unique physical and biochemical properties, and the pharmacological studies that demonstrate a wide range of retinoid-receptor, genetic and anti-inflammatory effects, all of which contribute to the therapeutic efficacy and improved tolerability of adapalene observed in the clinical use of this agent for the treatment of acne.

Laser skin resurfacing using a frequency doubled Nd:YAG laser after topical application of an exogenous chromophore.

BACKGROUND AND OBJECTIVES: Although laser skin resurfacing performed with CO(2) or Er:YAG lasers is efficient, side effects such as prolonged postoperative erythema, delayed healing, scarring, and pigmentation, have been reported. These side effects are due to skin characteristics but also to variations of the thermal effects associated with laser skin resurfacing. The study aimed to evaluate a new laser resurfacing method based on a previous topical application of an exogenous chromophore in order to have reproducible thermal effects. MATERIALS AND METHODS: Exogenous chromophore consisted in carbon dispersed and mixed with film-forming polymers and water. The resultant solution was applied to the skin surface using an airbrush. Experimental evaluation was performed in vivo on hairless rat skin using the following parameters (532 nm, 2.7 W, 1 mm, 50-200 ms, 17.2-68.8 J/cm(2), single pass). Skin biopsies were taken to evaluate histological changes and to quantify epidermis ablation and dermal coagulation depth. Wound healing was followed up during 10 days. RESULTS: Total epidermis ablation was achieved with all pulse durations used. Dermal coagulation depth increased as a function of exposure time. Scar formation was correlated with dermal coagulation depth. CONCLUSION: The concept of applying a carbon-based solution onto skin in order to obtain laser light conversion into heat followed by heat transfer to the tissue is valid for laser skin resurfacing. By selecting exposure time, the thermal effects are predictable and dermal coagulation depth can be either that observed with a Er:YAG laser or that obtained with a CO(2) laser. Moreover, frequency doubled Nd:YAG laser, already used in dermatology for angiodysplasias treatment, could be easily used for resurfacing of periorbital or perioral zones.

A new method to improve penetration depth of dyes into the follicular duct: potential application for laser hair removal.

BACKGROUND: Many persons seek to decrease hair growth and hair density. Although a variety of epilating methods are available, a practical and permanent hair removal treatment is needed. OBJECTIVE: The purpose of this study was to evaluate a new method of obtaining a better penetration depth of dyes into the follicular duct. By increasing both the quantity and the penetration depth of dye into the follicular duct, the efficacy of laser hair removal could be improved. METHODS: Dye penetration depth was assessed histologically after the use of formulations containing rhodamine-6G-loaded microspheres dispersed into two different silicones. Each formulation was tested on two hairless rats. After formulation application, dye diffusion was realized by applying ethanol on the skin to extract rhodamine-6G from microspheres. RESULTS: In all our experimental conditions follicular targeting occurred. No difference in the penetration depth of rhodamine-loaded microspheres was seen between our different silicone formulations. After ethanol application, the penetration of rhodamine-6G into the hair follicle was considerably increased by the fluid silicone vehicle (vs volatile silicone). CONCLUSION: This new galenical approach aims to transport a dye into the hair follicle specifically and deeply. By using adequate laser, the efficiency of laser hair removal could be increased.

A preliminary clinical and histopathological study of laser skin resurfacing using a frequency-doubled Nd:YAG laser after application of Chromofilm.

BACKGROUND AND OBJECTIVES: Carbon dioxide (CO2) and Er:YAG lasers are commonly used for laser skin resurfacing. In demonstrating their efficacy, intra- and interoperator variability may be important. In attempting to solve this problem, a new concept was developed which combines a previous application of an exogenous chromophore onto the skin in a standardized way (Chromofilm) and irradiation with a millisecond, low-power pulsed laser. MATERIALS AND METHODS: This study aimed to evaluate this new concept in vivo in human skin using a 532-nm Nd:YAG laser connected to a scanner using the following parameters: 532 nm, 2W, 1-mm spot size, 30-mm2 hexagonal surface irradiation and 50-120-ms pulse duration. The laser irradiation was performed both 15 h and 1 h prior to the facelift procedure. Tissue samples were examined histologically to determine the injury depth using nitroblue-tetrazolium chloride (NBTC) staining, haematoxylin-eosin staining and Masson's staining. RESULTS: Morphometric analysis of histological preparations showed that the depth of injury was dose-dependent: 50-ms pulse duration induced total epidermis ablation and fine dermal coagulation; 120-ms pulse duration induced dermal coagulation down to 120 microns. No residual carbon film was observed on histologic sections. CONCLUSION: Laser skin resurfacing using a 532-nm laser irradiation after application of a carbon film transfer is an effective method for skin resurfacing. With this new galenic approach (Chromofilm), the control of all parameters (thickness, chromophore concentration and distribution) can be achieved to predict the thermal injury obtained after laser irradiation.

A novel in vitro model for the study of human keratinocyte/leucocyte interactions under autologous conditions.

Keratinocyte/leucocyte interactions have become an area of intense investigations in the last decade. However, few convenient in vitro models are available at present. We have therefore designed a novel in vitro system for autologous human keratinocyte/leucocyte co-culture. Non-invasive epidermal cell sampling was achieved by using outer root sheath cells from hair follicles. After one passage, pure keratinocyte cultures (no Langerhans cells or melanocytes) were obtained. Co-culture experiments were performed on a Transwell system: keratinocytes were grown on the porous cupula, and then laid on to wells containing leucocytes. Alternatively, leucocytes can be added to the cupula when contact interactions between the two cell types are to be investigated. Using this system, we demonstrated that Phaesolus vulgaris phytohaemagglutinin-activated T lymphocytes (with 10% monocytes) in the lower compartment induced intercellular adhesion molecule 1 (ICAM-1) and HLA-DR expression, and inhibited methyl-3H-thymidine incorporation in normal human autologous keratinocytes cultured on the cupula. These changes were mediated by soluble factors (no cell contacts between keratinocytes and leucocytes), and required lymphocyte activation. This is the first direct in vitro evidence for leucocyte-induced ICAM-1 and HLA-DR expression on keratinocytes. This system is a potential tool for the study of keratinocyte/leucocyte interactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Topical retinoids. Their uses in dermatology.

The retinoids provide an important new way of treating dermatologic disorders. They have also proved to have a role in the prevention of new lesion formation. New retinoids, of which adapalene is one, have recently been synthesized in order to obtain similar or better efficacy while reducing skin irritation potential. These new molecules are currently under clinical investigation. Preliminary results are encouraging. In the near future, an expanded range of topical retinoids should be available.

Repeated application of dinitrochlorobenzene to the ears of sensitized guinea pigs: a preliminary characterization of a potential new animal model for contact eczema in humans.

We have evaluated a subchronic model of contact hypersensitivity in the guinea pig to mimic human chronic/recurrent eczema. Repeated challenges of the ears of previously sensitized guinea pigs with 0.1% dinitrochlorobenzene (once a week for 4 weeks) induced a typical oedema response, which increased during the first 48 h after each challenge. Crusts were detectable (48 h after challenge) and histological observations (72 h after challenge) revealed hyperplasia, papillomatosis, hyperkeratosis and some mononuclear cell infiltrates in the dermis. In agreement with clinical observations in humans, topical treatment of challenged animals with corticosteroid (1% hydrocortisone) reduced the oedema, hyperplasia, papillomatosis, and leucocyte infiltrates, while application of 5% bufexamac (a non-steroidal drug) was associated with a slight enhancement of the inflammatory response. Thus, this model presents clinical and histological similarities with human eczema. Its pharmacological relevance is also suggested, although further investigations are required to better define its selectivity.

The rhino mouse model: the effects of topically applied all-trans retinoic acid and CD271 on the fine structure of the epidermis and utricle wall of pseudocomedones.

The histological and ultrastructural effects following 3 weeks' topical treatment with two agents (all-trans retinoic acid and a new synthetic retinoid-like substance, CD271) were evaluated on the epidermis and the epithelial wall of the pseudocomedones in rhino mouse skin. The comedolytic effects of these drugs were similar, and consisted of a reduction of the utricular diameter, with normalization of follicular units. Morphological examinations revealed a hyperplastic response with an increase in the number of cell layers of both epidermis and follicular epithelium, and modifications in keratinocyte differentiation. Ultrastructural changes in the epidermis and epithelial wall were observed mainly in the granular and horny layers, with increased desquamation, and a decrease in the cohesiveness of corneocytes. During the first week of treatment, some cutaneous toxic effects were noticed, but they normalized within two weeks. On the other hand, a fine granular material persisted in the intercellular spaces. It is confirmed that the skin of the rhino mouse is a good model for the evaluation of the comedolytic effects of drugs. Moreover, it reveals the specific effects of retinoids on epidermal differentiation. We have demonstrated that topically applied CD271 induces modifications similar to those obtained with all-trans retinoic acid. It is thus concluded that CD271 is a potentially effective anti-acne agent.

Quantification of epidermal histological changes induced by topical retinoids and CD271 in the rhino mouse model using a standardized image analysis technique.

The rhino mouse has been used as an experimental model to screen topically active comedolytic agents. Adult rhino mice were treated on the back once daily for 5 consecutive days per week during 3 weeks. Skin histological preparations were analyzed by image analysis techniques to quantify the number of epidermal comedones, comedo profile and epidermal thickness. Using both a negative (treated with acetone) and a positive (treated with Aberel gel 0.025%) control group of animals in all experiments conducted over a period of about 3 years, we defined the upper and lower limit of acceptability of the results. Topical treatment with an acetone solution of all-trans retinoic acid (0.01, 0.03, 0.1%) and 13-cis-retinoic acid (0.1%) induced comedolysis and a marked increase in epidermal thickness. Commercial preparations of all-trans retinoic acid (Aberel lotion, gel and cream, Retin A cream, Retacnyl cream) presented a similar comedolytic activity. However, the epidermal thickening was higher with Retin A and weaker with Retacnyl. CD271, a new modulator of cell differentiation, applied either in acetone solution (0.01, 0.1%) or in lotion, gel or cream formulations (0.1%) also demonstrated a marked activity (i.e. comedolysis and epidermal thickening). These data confirm that the rhino mouse model can be used to assay drugs applied either in solvent or in topical formulations. Activity in this model compares favorably with published clinical observations in the treatment of acne.

Hexadecane-induced skin hyperplasia in the hairless rat: time course of histological and biochemical events related to the synthesis of polyamines and DNA.

Several biochemical parameters including ornithine decarboxylase activity (ODC) and tissue polyamine levels were measured during the hexadecane-induced epidermal hyperplasia of hairless rat skin. Animals received three applications of 200 microliters pure n-hexadecane on day 1. ODC activity and polyamine levels (putrescine, spermidine and spermine) in the epidermis were significantly increased and reached maximum elevations at 12 h after the start of n-hexadecane treatment with DNA synthesis peaking at 24 h. Histological studies confirmed a significant cellular edema at 24 h after the beginning of the treatment followed at 48 h by an epidermal hyperplasia which was maximum at 72 h. These data support the view that ODC activation, increased biosynthesis of polyamines and DNA are early events in epidermal cell hyperproliferation.

Induction of ornithine decarboxylase activity in hairless rat epidermis as a pharmacological model: validation of the animal model.

We use a mutant hairless Sprague Dawley rat to evaluate the capacity of retinoids to inhibit the epidermal ornithine decarboxylase activity induced by sellotape stripping. In order to minimize the variability introduced by the animals in our model we decided to validate the hairless rats used. A number of animal parameters were examined using a single lot of 50 males and 50 females aged from 4 to 11 weeks and acclimatized to laboratory conditions. The body weight growth curves were established. Nude animals present two periods of hair growth, the first at 6-7 weeks and the second at about 10-11 weeks. Hair development is more pronounced in males. No histological change was observed in the stratum corneum but an increase in epidermal thickness was noted in males aged 9 weeks. Removal of the stratum corneum by sellotape stripping was more effective and reproducible in the females, as determined histologically. Sellotape-stripping induction of ornithine decarboxylase in the epidermis was higher in rats aged 5-6 weeks and reached a plateau in animals aged 6-12 weeks. Individual variations obtained were lower in females (about 5%-10% in females and 10%-20% in males). The present research suggests that female rats aged about 8 weeks provide maximum reproducibility of response and ease of use.

A rapid and simple test system for the evaluation of the inhibitory activity of retinoids on induced ornithine decarboxylase activity in the hairless rat epidermis.

In mouse skin, antiproliferative agents including retinoids inhibit induction of ornithine decarboxylase activity by a variety of hyperproliferative stimuli. In the hairless rat skin, ornithine decarboxylase activity was induced by ten successive strippings with cellotape and by topical application of 12-O-tetradecanoyl-phorbol-13-acetate. Topical application of all trans-retinoic acid (25 nmol/cm2) immediately after the tape stripping of the skin significantly inhibited the induction of ornithine decarboxylase activity at all time points measured. The inhibition by all trans-retinoic acid of ornithine decarboxylase induced by cellotape stripping was dose dependent as was found to be the case for arotinoid, retinol, Ro-10-1670, motretinid, 13-cis-retinoic acid, etretinate, and vitamin A. Oral administration of all trans-retinoic acid also inhibited the ornithine decarboxylase activity induced by cellotape stripping. We propose the assay of ornithine decarboxylase activity in the hairless rat epidermis after tape stripping for a rapid evaluation of new retinoids.