An in vivo experimental model for effects of topical retinoic acid in human skin

Efficacy of Topical Hydroxypinacolone Retinoate-Peptide Product Versus Fractional CO2 Laser in Facial Aging

BACKGROUND

Many people are interested in addressing visible signs of aging with non-invasive cosmetic treatments. Development of effective topical products will provide options to delay or support cosmetic procedures.

AIMS

This study assessed and compared the efficacy and tolerance of a topical product used over the course of 16 weeks to a single ablative laser treatment on women with moderate global photodamage on the face.

METHODS

Subjects in Cell 1 (Laser Cell) were treated over the entire face with a fractional CO2 laser system. Subjects in Cell 2 (Topical Serum Cell) were treated with a topical serum containing hydroxypinacolone retinoate and peptides over the entire face, twice per day for 16 weeks. The study was composed of 71 women, with 29 in the Laser Cell (mean age 56.2) and 42 in the Topical Serum Cell (mean age 55.0), between 40 and 65 years old. Expert grading was used to determine efficacy parameters.

RESULTS

Participants in the Topical Serum Cell achieved more significant improvement (p < 0.05) in Marionette lines, fine lines (global face), wrinkles (global face), wrinkles (crow's feet), nasolabial folds, texture, smoothness (tactile), global hyperpigmentation, lift, and photodamage compared to participants in the Laser Cell. Participants in the Topical Serum Cell achieved parity in the look of fine lines (crow's feet), forehead lines, glabella, firmness/bounce (tactile), skin tone evenness, radiance.

CONCLUSIONS

While no statistically significant differences in tolerability were observed, treatment with the topical cosmetic product achieved parity or statistically better improvement in parameters compared to laser treatment at 16 weeks.

Cosmetic retinoid use in photoaged skin: A review of the compounds, their use and mechanisms of action

The inevitable attrition of skin due to ultraviolet radiation, termed photoaging, can be partially restored by treatment with retinoid compounds. Photoaged skin in lightly pigmented individuals, clinically presents with the appearance of wrinkles, increased laxity, and hyper- and hypopigmentation. Underlying these visible signs of ageing are histological features such as epidermal thinning, dermal-epidermal junction flattening, solar elastosis and loss of the dermal fibrillin microfibrillar network, fibrillar collagen and glycosaminoglycans. Retinoid compounds are comprised of three main generations with the first generation (all-trans retinoic acid, retinol, retinaldehyde and retinyl esters) primarily used for the clinical and cosmetic treatment of photoaging, with varying degrees of efficacy, tolerance and stability. All-trans retinoic acid is considered the 'gold standard' for skin rejuvenation; however, it is a prescription-only product largely confined to clinical use. Therefore, retinoid derivatives are readily incorporated into cosmeceutical formulations. The literature reported in this review suggests that retinol, retinyl esters and retinaldehyde that are used in many cosmeceutical products, are efficacious, safe and well-tolerated. Once in the skin, retinoids utilize a complex signalling pathway that promotes remodelling of photoaged epidermis and dermis and leads to the improvement of the cutaneous signs of photoaging.

Retinoids in the treatment of photoageing: A histological study of topical retinoid efficacy in black skin

BACKGROUND

Photoageing describes complex cutaneous changes that occur due to chronic exposure to solar ultraviolet radiation (UVR). The 'gold standard' for the treatment of photoaged white skin is all-trans retinoic acid (ATRA); however, cosmetic retinol (ROL) has also proven efficacious. Recent work has identified that black skin is susceptible to photoageing, characterized by disintegration of fibrillin-rich microfibrils (FRMs) at the dermal-epidermal junction (DEJ). However, the impact of topical retinoids for repair of black skin has not been well investigated.

OBJECTIVES

To determine the potential of retinoids to repair photoaged black skin.

METHODS

An exploratory intervention study was performed using an in vivo, short-term patch test protocol. Healthy but photoaged black volunteers (>45 years) were recruited to the study, and participant extensor forearms were occluded with either 0.025% ATRA (n = 6; 4-day application due to irritancy) or ROL (12-day treatment protocol for a cosmetic) at concentrations of 0.3% (n = 6) or 1% (n = 6). Punch biopsies from occluded but untreated control sites and retinoid-treated sites were processed for histological analyses of epidermal characteristics, melanin distribution and dermal remodelling.

RESULTS

Treatment with ATRA and ROL induced significant acanthosis (all p < 0.001) accompanied by a significant increase in keratinocyte proliferation (Ki67; all p < 0.01), dispersal of epidermal melanin and restoration of the FRMs at the DEJ (all p < 0.01), compared to untreated control.

CONCLUSIONS

This study confirms that topical ATRA has utility for the repair of photoaged black skin and that ROL induces comparable effects on epidermal and dermal remodelling, albeit over a longer timeframe. The effects of topical retinoids on black photoaged skin are similar to those reported for white photoaged skin and suggest conserved biology in relation to repair of UVR-induced damage. Further investigation of topical retinoid efficacy in daily use is warranted for black skin.

Skin ageing and topical rejuvenation strategies

Skin ageing is a complex process involving the additive effects of skin's interaction with its external environment, predominantly chronic sun exposure, upon a background of time-dependent intrinsic ageing. Skin health and beauty is considered one of the principal factors perceived to represent overall 'health and wellbeing'; thus, the demand for skin rejuvenation strategies has rapidly increased, with a worldwide annual expenditure expected to grow from $US24.6 billion to around $US44.5 billion by 2030 (https://www.databridgemarketresearch.com/reports/global-facial-rejuvenation-market). Skin rejuvenation can be achieved in several ways, ranging from laser and device-based treatments to chemical peels and injectables; however, topical skin care regimes are a mainstay treatment for ageing skin and all patients seeking skin rejuvenation can benefit from this relatively low-risk intervention. While the most efficacious topical rejuvenation treatment is application of tretinoin (all-trans retinoic acid) - a prescription-only medicine considered to be the clinical 'gold standard' - a hybrid category of 'cosmeceutical' products at the midpoint of the spectrum of cosmetics and pharmaceutical has emerged. This article reviews the clinical manifestations of skin ageing and the available topical treatments for skin rejuvenation, including retinoids, peptides and antioxidants.

Pirfenidone Protects from UVB-Induced Photodamage in Hairless Mice

Background: Ultraviolet radiation (UV) is the main environmental factor that causes histological degenerative changes of the skin giving rise to a chronic process called photodamage. Non-melanoma skin cancer induced by UVB radiation is a result of a cascade of molecular events caused by DNA damage in epidermis cells, including persistent inflammation, oxidative stress, and suppression of T cell-mediated immunity. Retinoids such as tretinoin have been widely used in skin to treat photoaging and photodamage, though its secondary adverse effects have been recognized. Pirfenidone (PFD) has emerged as an antifibrogenic, anti-inflammatory and antioxidant agent, and in this work its efficacy was evaluated in a model of UVB-induced photodamage. Methods: Epidermal, dermal, and inflammatory changes were measured by histomorphometric parameters. In addition, gene, and protein expression of key molecules in these processes were evaluated. Results: Our results revealed an anti-photodamage effect of topical PFD with absence of inflammatory skin lesions determined by dermoscopy. In addition, PFD reduced elastosis, improved organization, arrangement, and deposition of dermal collagens, downregulated several pro-inflammatory markers such as NF-kB, IL-1, IL-6 and TNFα, and decreased keratinocyte damage. Conclusion: Topical pirfenidone represents a promising agent for the treatment of cell photodamage in humans. Clinical trials need to be carried out to explore this premise.

Regulation of epidermal proliferation and hair follicle cycling by synthetic photostable retinoid EC23

BACKGROUND

Retinoid signaling is an important regulator of the epidermis and skin appendages. Therefore, synthetic retinoids have been developed for therapeutic use for skin disorders such as psoriasis and acne.

AIMS

In previous studies, we showed how the photostable retinoid EC23 induces neuronal differentiation in stem cell-like cell populations, and here, we aim to investigate its ability to influence epidermal and hair follicle growth.

METHODS

EC23 influence on skin biology was investigated initially in cultures of monolayer keratinocytes and three-dimentional in vitro models of skin, and finally in in vivo studies of mice back skin.

RESULTS

EC23 induces keratinocyte hyperproliferation in vitro and in vivo, and when applied to mouse skin increases the number of involucrin-positive suprabasal cell layers. These phenotypic changes are similar in skin treated with the natural retinoid all-trans retinoic acid (ATRA); however, EC23 is more potent; a tenfold lower dose of EC23 is sufficient to induce epidermal thickening, and resulting hyperproliferation is sustained for a longer time period after first dose. EC23 treatment resulted in a disorganized stratum corneum, reduced cell surface lipids and compromised barrier, similar to ATRA treatment. However, EC23 induces a rapid telogen to anagen transition and hair re-growth in 6-week-old mice with synchronously resting back skin follicles. The impact of EC23 on the hair cycle was surprising as similar results have not been seen with ATRA.

CONCLUSIONS

These data suggest that synthetic retinoid EC23 is a useful tool in exploring the turnover and differentiation of cells and has a potent effect on skin physiology.

Role of Vitamins in Skin Health: a Systematic Review

PURPOSE OF REVIEW

Skin is the main defense organ of the human body against external insults (ultraviolet radiations, infections by pathogenic microorganisms, and mechanical and chemical stress). The integrity and functions of the skin barrier are supported by an adequate supply of micronutrients, such as several vitamins. The purpose of this review was to analyze all vitamin-related skin problems.

RECENT FINDINGS

The World Health Organization has estimated that more than 2 billion people worldwide experience deficiencies in the intake of essential vitamins and minerals; the percentage of adults all over the world using daily vitamin supplements, for treatment or prevention of chronic disease, has increased very rapidly in recent years. In this review, 65 studies have been selected in order to examine the role of the main vitamins and their derivatives involved in maintaining the well-being of the skin and their use as prophylactic and therapeutic agents in the management of skin disorders.

Models for acne: A comprehensive study

Acne vulgaris (AV) is the familiar chronic skin ailment affecting most of the individuals. This multifarious, disease involves the bacterium gram-positive, anaerobic Propionibacterium acnes (P. acnes) which resides on skin microflora, and participated in acne inflammation and acne lesions. The object of this review is to discuss presently available in vitro, ex vivo, and in vivo models to evaluate the cosmetic formulations that are developed for dealing and prevention of acne formation. These various available models offer new chances for further research on biologically active materials, drugs & pharmaceutical as well as cosmetics for acne treatment.

All-trans-retinoic acid activated mast cells via Mas-related G-protein-coupled receptor-X2 in retinoid dermatitis

BACKGROUND

Retinoic acid (RA)-induced dermatitis is the most frequent side-effect limiting its widespread use. However, the exact mechanisms triggering dermatitis are not fully understood, including the role of skin mast cells. The newly discovered Mas-related G-protein-coupled receptor-X2 (MRGPRX2) in mast cells mediates pseudoallergic drug reactions in several types of dermatitis. A possible contribution of MRGPRX2 to contact dermatitis induced by RA has hitherto not been examined.

OBJECTIVES

To investigate whether all-trans-RA (ATRA) activates mast cells via MRGPRX2/MrgprB2 (the mouse orthologue), contributing to the pathogenesis of retinoid-induced dermatitis.

METHODS

Wild-type (WT) and MrgprB2^-/- mice were treated with topical ATRA to observe local inflammation and mast cell degranulation in vivo by the use of haematoxylin and eosin and immunofluorescence staining. Release of histamine and release of β-hexosaminidase were measured and calcium influx was detected in Laboratory of Allergic Disease 2 (LAD2) cells with specific knockdown targeting MRGPRX2 by small interfering RNA (siRNA) and in primary cells from MrgprB2^-/- mice.

RESULTS

As compared with WT mice, MrgprB2^-/- mice showed resistance to ATRA-triggered contact dermatitis and local inflammatory reactions in the paws. ATRA activated mast cells via the MrgprB2 pathway in murine cells, and via the MRGPRX2 pathway in human mast cells.

CONCLUSIONS

ATRA-induced dermatitis could be achieved by activating mast cells via MRGPRX2/MrgprB2, which may provide a potential therapy target to reduce the side-effect.

Practical management of acne for clinicians: An international consensus from the Global Alliance to Improve Outcomes in Acne

Scientific advances are continually improving the knowledge of acne and contributing to the refinement of treatment options; it is important for clinicians to regularly update their practice patterns to reflect current standards. The Global Alliance to Improve Outcomes in Acne is an international group of dermatologists with an interest in acne research and education that has been meeting regularly since 2001. As a group, we have continuously evaluated the literature on acne. This supplement focuses on providing relevant clinical guidance to health care practitioners managing patients with acne, with an emphasis on areas where the evidence base may be sparse or need interpretation for daily practice.

Why Topical Retinoids Are Mainstay of Therapy for Acne

Acne-focused dermatology expert groups have consistently recommended that most patients with acne be treated with a combination of topical retinoid and antimicrobial therapy. This is based on clinical data as well as evidence that these drug classes have different and complementary mechanisms of action that target multiple aspects of acne's complex pathophysiology. Recent evidence-based guidelines for acne, including those from the American Academy of Dermatology (AAD) and the European Dermatology Forum (EDF), have agreed that retinoids have an essential role in this widespread disease. The AAD states "retinoids are the core of topical therapy for acne because they are comedolytic, resolve the precursor microcomedone lesion, and are anti-inflammatory;" further, they "allow for maintenance of clearance." Despite uniform recommendation for use of topical retinoids, a recent study of prescribing practices from 2012 to 2014 indicated that dermatologists prescribed retinoids just 58.8% of the time while non-dermatologists prescribed them for only 32.4% of cases. In this article, we review the reasons supporting retinoids as the mainstay of acne therapy and discuss some of the perceived barriers that may be limiting use of this important drug class. Further, we discuss how and when titrating retinoid concentrations may be utilized in clinical practice.

FUNDING

Galderma International.

An integrative metabolomics and transcriptomics study to identify metabolic alterations in aged skin of humans in vivo

Background

Aging human skin undergoes significant morphological and functional changes such as wrinkle formation, reduced wound healing capacity, and altered epidermal barrier function. Besides known age-related alterations like DNA-methylation changes, metabolic adaptations have been recently linked to impaired skin function in elder humans. Understanding of these metabolic adaptations in aged skin is of special interest to devise topical treatments that potentially reverse or alleviate age-dependent skin deterioration and the occurrence of skin disorders.

Results

We investigated the global metabolic adaptions in human skin during aging with a combined transcriptomic and metabolomic approach applied to epidermal tissue samples of young and old human volunteers. Our analysis confirmed known age-dependent metabolic alterations, e.g. reduction of coenzyme Q10 levels, and also revealed novel age effects that are seemingly important for skin maintenance. Integration of donor-matched transcriptome and metabolome data highlighted transcriptionally-driven alterations of metabolism during aging such as altered activity in upper glycolysis and glycerolipid biosynthesis or decreased protein and polyamine biosynthesis. Together, we identified several age-dependent metabolic alterations that might affect cellular signaling, epidermal barrier function, and skin structure and morphology.

Conclusions

Our study provides a global resource on the metabolic adaptations and its transcriptional regulation during aging of human skin. Thus, it represents a first step towards an understanding of the impact of metabolism on impaired skin function in aged humans and therefore will potentially lead to improved treatments of age related skin disorders.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3547-3) contains supplementary material, which is available to authorized users.

Topical retinoids in the management of photodamaged skin: from theory to evidence-based practical approach

Skin, being exposed directly to the environment, represents a unique model for demonstrating the synergistic effects of intrinsic and extrinsic factors on the ageing process. Ultraviolet radiation (UVR) is the major factor among exogenous stressors responsible for premature skin ageing. The problem of skin ageing has captured public attention and has an important social impact. Different therapeutic approaches have been developed to treat cutaneous ageing and to diminish or prevent the negative effects of UVR. Topical retinoids represent an important and powerful class of molecules in the dermatologist's hands for the treatment of photodamaged skin. Since their introduction more than 20 years ago, topical retinoids have shown beneficial efficacy and good safety profiles in the management of photodamaged skin, and as therapeutic anti-ageing agents. This review provides a brief retrospective of the development of topical retinoids in the treatment of photodamaged skin, elucidates their mechanism of action, delineates their use and addresses clinical, pharmaceutical and regulatory issues in connection with their intended use.

Common cosmeceuticals

In the cosmetic arena, many materials are used commercially and claim to provide skin effects (eg, antiaging effects) when used topically. Considering there are so many such materials and many skin appearance effects are encompassed, this short contribution must, by necessity, be selective in terms of the number of materials discussed and the depth with which any particular material is overviewed. This presentation, therefore, focuses on only 10 types of cosmeceutical agents: five vitamins (A, B(3), C, E, panthenol), peptides, hydroxyl acids, sugar amines, ceramides, and metals. In particular, this contribution concentrates on those materials for which there are available clinical data that support a reported skin appearance improvement effect.

Retinoids in the treatment of skin aging: an overview of clinical efficacy and safety

Aging of skin is an intricate biological process consisting of two types. While intrinsic or chronological aging is an inevitable process, photoaging involves the premature aging of skin occurring due to cumulative exposure to ultraviolet radiation. Chronological and photoaging both have clinically differentiable manifestations. Various natural and synthetic retinoids have been explored for the treatment of aging and many of them have shown histological and clinical improvement, but most of the studies have been carried out in patients presenting with photoaged skin. Amongst the retinoids, tretinoin possibly is the most potent and certainly the most widely investigated retinoid for photoaging therapy. Although retinoids show promise in the treatment of skin aging, irritant reactions such as burning, scaling or dermatitis associated with retinoid therapy limit their acceptance by patients. This problem is more prominent with tretinoin and tazarotene whereas other retinoids mainly represented by retinaldehyde and retinol are considerably less irritating. In order to minimize these side effects, various novel drug delivery systems have been developed. In particular, nanoparticles have shown a good potential in improving the stability, tolerability and efficacy of retinoids like tretinoin and retinol. However, more elaborate clinical studies are required to confirm their advantage in the delivery of topical retinoids.

Retinoid therapy of pigmentary disorders

Topical retinoids such as all-trans-retinoic acid (RA), 13-cis-retinoic acid (isotretinoin), retinol, retinaldehyde, tazarotene, and adapalene have been shown to improve dyspigmentation of photodamaged skin including mottling and actinic lentigines. RA monotherapy has also been demonstrated to improve melasma and postinflammatory hypermelanosis. Furthermore, RA in combination with hydroquinone or 4-hydroxyanisole, or azelaic acid increases the potency of depigmenting agents for the treatment of melasma, actinic lentigines, and postinflammatory hypermelanosis. The basic mechanisms underlying these effects are not completely identified. Topical retinoids stimulate the cell turn-over of epidermal keratinocytes and promote a decrease in melanosome transfer and a rapid loss of melanins via epidermopoiesis. Topical retinoids are also involved in the control of cell differentiation. Retinoid-induced changes in the stratum corneum and the permeability barrier may also facilitate the penetration of depigmenting agents in the epidermis and increase their bioavailability, leading to increased depigmentation. In addition, several in vitro studies demonstrate that cis and trans-retinoic acid inhibit UV-B stimulated melanogenesis in term of tyrosinase activity and melanin synthesis. It is likely that topical retinoids modulate epidermal melanin count via a direct action on melanocytes and epidermal keratinocytes.

The use of retinoids in the treatment of photoaging

Photoaging describes the clinical and histologic consequences of chronic sun exposure, the key features of which--wrinkles and mottled hyperpigmentation--are frequently and erroneously attributed to the aging process. Although a number of surgical procedures can improve the clinical appearance of photoaged skin, the only medical therapy with proved benefit derived from randomized clinical trial evidence is the use of topical retinoids, particularly tretinoin, isotretinoin, and tazarotene. Retinoids are capable not only of repairing photoaged skin at both the clinical and biochemical levels but their use may prevent photoaging. There is in addition emerging evidence that topical retinoids could be beneficial in the treatment of intrinsically aged skin.

Co-localization of COX-2, CYP4F8, and mPGES-1 in epidermis with prominent expression of CYP4F8 mRNA in psoriatic lesions

Cyclooxygenase-2 (COX-2), cytochrome P450 4F8 (CYP4F8), and microsomal PGE synthase-1 (mPGES-1) form PGE and 19-hydroxy-PGE in human seminal vesicles. We have examined COX-2, CYP4F8, and mPGES-1 in normal skin and in psoriasis. All three enzymes were detected in epidermis by immunofluorescence and co-localized in the suprabasal cell layers. In lesional psoriasis the enzymes were also co-localized in the basal cell layers. Real-time RT-PCR analysis suggested that CYP4F8 mRNA was induced 15-fold in lesional compared to non-lesional epidermis. mRNA of all enzymes were present in cultured HEK and HaCaT cells, but the prominent induction of CYP4F8 mRNA in psoriasis could not be mimicked by treatment of these keratinocytes with a mixture of inflammatory cytokines or with phorbol 12-myristate-13-acetate. The function of CYP4F8 in epidermis might be related to lipid oxidation and keratinocyte proliferation.

Histological evaluation of a topically applied retinol-vitamin C combination

Two double-blind studies versus vehicle were carried out to investigate the effects of a topically applied retinol plus vitamin C combination on epidermal and dermal compartments of aged or photoaged human skin. The two studies were performed on postmenopausal women who were selected for treatment based on the mild level of elastosis of their facial skin. At completion of treatment, skin biopsies were collected and processed for classical histology and immunohistochemistry. In the first study (aged skin), 8 volunteers applied the retinol- and vitamin C-containing preparation on the ventral side of one elbow and the vehicle on the other elbow twice daily for 3 months. After the 3-month treatment we observed histological changes mainly within the epidermis. The stratum corneum was thinner with a compact pattern, whereas the epidermal proliferation increased, resulting in a thickening of the viable epidermis. Moreover, the interdigitation index was increased. In the second study (photoaged skin), 11 volunteers were divided in two groups; one applied the retinol- and vitamin C-containing preparation and the other one the vehicle on their face twice daily for 6 months. Facial skin samples presented histologic hallmarks of photoaging, i.e. accumulation of elastotic material in the papillary dermis. After the 6-month topical treatment, the observed histological changes were mainly concentrated at the dermal level. Both treated and control groups showed the same distribution pattern of type I procollagen, however, the high level of type III procollagen originally observed in photoaged skin was reduced in the retinol- and vitamin C-treated group, resulting in a lower type III-to-type I procollagen ratio. Furthermore, a wide band of eosinophilic material just beneath the epidermis, devoid of oxytalan fibers and forming the 'grenz zone', appeared more frequently and was larger in the retinol- and vitamin C-treated group. In conclusion, our results show that repeated topical application of a preparation containing both retinol and vitamin C is able to reverse, at least in part, skin changes induced by both chronologic aging and photoaging.

The role of topical retinoids in the treatment of photoaging

Aging of the skin is a complex biological process which is influenced by the interaction of several intrinsic and extrinsic factors. Intrinsic or chronological aging is an inevitable, genetically programmed process, of unclear underlying mechanism, for which no prevention or effective treatment is currently available. Photoaging refers to the gross and microscopic cutaneous changes that are induced by cumulative exposure to UV radiation and are superimposed on the background of chronological aging. Although primarily an aesthetic problem with significant psychological effects, photoaging constitutes the background for the development of precancerous and cancerous skin lesions.Overwhelming clinical and histological evidence indicate that certain structural changes induced by excessive sun exposure can be reversed, to some extent, by the use of topical retinoids. A number of retinoid compounds, for example tretinoin, isotretinoin, retinaldehyde and tazarotene, have been employed for the treatment of photoaged skin, and demonstrate beneficial clinical and histological effects. Adverse effects have been limited to an irritant reaction of variable intensity presenting with dryness, scaling and erythema. Ongoing research will enhance our understanding of the molecular mechanisms that determine the effects of retinoids on photodamaged skin and contribute to the employment of new, more effective and less irritating retinoid compounds.

Cumulative irritancy comparison of adapalene gel 0.1% versus other retinoid products when applied in combination with topical antimicrobial agents

This randomized, investigator-blinded study evaluated the level of skin tolerance to adapalene gel 0.1%, tretinoin cream 0.025%, or tretinoin microsphere gel 0.1% when applied in combination with clindamycin phosphate lotion 1%, erythromycin gel 2%, benzoyl peroxide gel 5%, or erythromycin-benzoyl peroxide gel. A total of 37 subjects underwent daily application of the topical antimicrobial and retinoid products to sites on their upper back under protective patches for approximately 16 hours each day; Friday patches were left in place over the weekend. Testing continued daily for 3 weeks or until discontinuation caused by a severe adverse reaction to any of the test products or to the patch. Adapalene gel 0.1% demonstrated statistically significantly (P <.001) less irritation after repeated application under occlusive conditions than tretinoin cream 0.025% or tretinoin microsphere gel 0.1%. Moreover, the application of adapalene gel 0.1% under these conditions, concomitantly with various antimicrobial agents, was safe and well tolerated in this subject population. In view of its low irritation potential and its efficacy, adapalene gel 0.1%, in combination with antimicrobial agents should be considered for the treatment of acne vulgaris.

Topical retinoic acid alters the expression of cellular retinoic acid-binding protein-I and cellular retinoic acid-binding protein-II in non-lesional but not lesional psoriatic skin

Therapeutic retinoids have profound effects on psoriatic skin pathology but their interactions with various retinoid-binding proteins in lesional vs non-lesional skin have not been investigated. Using quantitative real-time PCR the mRNA expression of cellular retinol-binding protein I (CRBPI) and retinoic acid-binding protein I/II (CRABPI/CRABPII) was studied in psoriatic and healthy control (=normal) skin after 4 days of occlusive RA/vehicle treatment (n=6). Untreated psoriatic lesions showed a markedly elevated CRABPII/CRABPI ratio, while the CRBPI level was reduced in lesional and non-lesional skin as compared to normal skin. In RA-treated normal and non-lesional skin, the mRNA expression of CRBPI was unaltered while that of CRABPI and CRABPII was reduced by approximately 80% and increased approximately 5-fold, respectively, as compared to vehicle-treated skin. In contrast, lesional skin exposed to RA showed an almost 90% increase in CRBPI transcripts but unaltered expression of CRABPI and CRABPII, yet, the mRNA expression of several inflammatory mediators, e.g. inducible nitric oxide synthase, interferon-gamma and interleukin-1beta, was clearly reduced. Immunohistochemistry localized CRABPII to suprabasal keratinocytes in normal skin and revealed markedly elevated levels in lesional skin. RA treatment induced CRABPII protein expression in normal and non-lesional skin, to similar levels as in untreated lesions. The results indicate that the effects of RA differ in normal/non-lesional psoriatic skin and lesional skin. Whether the high expression of CRABPII in psoriatic skin lesions is due to increased amounts of endogenous retinoids in lesional skin or reflects an abnormal regulation of the CRABPII gene in psoriasis remains to be studied.

A Short-Term Screening Protocol, Using Fibrillin-1 as a Reporter Molecule, for Photoaging Repair Agents

Photoaged skin is characterized by coarse and fine wrinkles. The mechanisms of wrinkle formation are undetermined, but appear to be due to changes within the matrix of the dermis and at the dermal-epidermal junction. Previous studies have identified marked reductions in procollagens I and III, collagen VII, and the fibrillin-rich microfibrillar apparatus in this area. Topically applied all-trans retinoic acid can repair photoaged dermal matrix, but this takes at least 6 mo of treatment. In this study, we have examined the abundance and distribution of fibrillin-1 prior to, and following, 192 wk of all-trans retinoic acid treatment. We have further developed a short-term protocol to determine the utility of potential repair agents, using fibrillin-1 as the marker for outcome. Individuals with clinically assessed severe photoaging were recruited to the study (n = 8). 0.025% all-trans retinoic acid, 5% sodium lauryl sulfate (irritant control), or vehicle were applied under occlusion to photoaged extensor forearm. A fourth control area was also occluded. After 96 h, punch biopsies were taken under local anesthesia and processed for either transmission electron microscopy or snap frozen. Frozen sections were prepared for immunohistochemistry and in situ hybridization immunohistochemistry. Electron microscopy revealed aberrant elastic fibers in the papillary dermis of photoaged forearm skin, with sparse microfibrillar apparatus and interstitial collagen. After application of 0.025% all-trans retinoic acid, there was increased deposition of both these dermal matrix components, with the aberrant elastic fibers no longer apparent. Significant increases (p < 0.05) were observed at the protein and mRNA levels for fibrillin-1 following all-trans retinoic acid and sodium lauryl sulfate treatments, with all-trans retinoic acid having a significantly greater effect than irritant control (p < 0.001); however, neither application had significant effect on the abundance of collagen VII or its mRNA. Investigation of collagen I synthesis revealed no difference following treatments. To ascertain the clinical relevance of using fibrillin-1 as a marker for photoaging, facial skin was biopsied at baseline and after long-term (192 wk) topical all-trans retinoic acid treatment (n = 5). Biopsies were wax-embedded and sections prepared for immunohistochemistry for fibrillin-1. Significant increases in the abundance of the microfibrillar apparatus was observed proximal to the dermal- epidermal junction (p < 0.001) following long-term all-trans retinoic acid application. This study indicates that all-trans retinoic acid can significantly affect fibrillin-1 content in photoaged skin. Furthermore, fibrillin-1 can be used as a "reporter" molecule in short-term protocols for testing the utility of topical agents in the repair of photoaged skin.

Keratin 4 upregulation by retinoic acid in vivo: a sensitive marker for retinoid bioactivity in human epidermis

Retinoids affect keratinocyte differentiation and modulate the expression of many epidermal proteins, among them cellular retinoic acid-binding protein II and the family of cytokeratins. The upregulation of the former protein is a well-known phenomenon, whereas the retinoid-induced regulation of epidermal keratin expression is more complex and only partially understood. We studied the effect of topical retinoids on the expression in healthy skin of cellular retinoic acid-binding protein II, tazarotene-induced genes 1 and 2, several epidermal keratins (K1, K2e, and K10), and two mucous keratins (K4 and K13) known to appear in epidermis under certain abnormal conditions. Reverse transcription-polymerase chain reaction experiments showed that the K4 expression was the one most overtly induced by 2 wk of open treatment with 0.05% of retinoic acid and tazarotene. Using real-time quantitative polymerase chain reaction (TaqMan) and normalization of the mRNA values to beta-actin, the increase in K4 was found to be 100-1000-fold. In comparison, the expression of K13 and cellular retinoic acid-binding protein II was increased 10-50-fold, the K1 and K10 mRNA levels remained unchanged, and the K2e level decreased by a factor of 100-1000. In parallel biopsies, immunohistochemistry showed no change in K1, K2e, or K10 staining, but a strong de novo appearance of K4 in the granular layer after retinoid treatment. In a separate study, occlusive application of 0.025% retinoic acid in four healthy subjects produced a maximal K4 mRNA signal after 48 h and strong K4 staining after 80 h. Finally, a dose-response study showed that the de novo appearance of K4 can be utilized as a sensitive test for retinoid bioactivity in epidermis in vivo.

Dowling Oration delivered at the Royal College of Physicians, London, Friday 5 June 1998. Retinoids: renaissance and reformation

There is confusion as to the cutaneous signs of ageing. For the most part the features of photoageing, namely actinic lentigines and wrinkling, are misinterpreted as features of ageing. Wrinkling is associated with a loss of collagens from the papillary dermis resulting from imperfect remodelling of the dermal extracellular matrix following sun exposure. Retinoids are either derivatives of vitamin A or synthetic ligands of nuclear retinoid receptors. Retinoid receptors, notably retinoic acid receptor gamma and retinoid X receptor alpha are present in human skin. Topically applied all-trans retinoic acid can repair and probably prevent photoageing of the skin by modulation of collagen synthesis in the dermis. There is emerging evidence that intrinsic ageing of the skin is also amenable to reversal by topical retinoids.

Drug treatment of photoaged skin

Although the prevention of skin aging is a holy grail of the cosmetic and pharmaceutical industries, this venture may be misplaced. The predominant clinical and biochemical features of aged skin are mostly attributable to photoaging rather than chronology. For instance chronic sun exposure is the major determinant of age spots (actinic lentigines) and wrinkles. Surgical approaches to the treatment of photoaging include face-lift, dermabrasion, chemical peeling, collagen and botulinum toxin injections, and laser re-surfacing. These approaches all have benefit and improve the clinical features of facial photoaging. Drug or pharmaceutical prevention and treatment of photoaged skin is still in its infancy. The main pharmaceutical approach to prevention of photoaging lies in the assiduous use of sunscreens. Recent evidence points to the importance of ultraviolet A (UVA) radiation as well as ultraviolet B (UVB) radiation in the aetiology of photoaging and thus the need for sunscreens that block both UVB and UVA. Drug treatment of photoaged skin can be categorised as antioxidants, alpha-hydroxy acids and topical retinoids. Of these 3 approaches only topical retinoids, particularly tretinoin (all-trans retinoic acid), have a well documented ability to repair photoaged skin at the clinical, histological and molecular level. Furthermore, the use of topical retinoids may actually prevent photoaging. The current interest in pharmaceutical modulation of the photoaging process has attracted considerable research into the mechanisms of photoaging and cutaneous aging. It is likely that treatment for, or prevention of, the chronological aging process may result from such research.

Adapalene 0.1% gel and adapalene 0.1% cream stimulate retinoic acid receptor mediated gene transcription without significant irritative effects in the skin of healthy human volunteers

A randomized, investigator masked, intra individual comparative study was conducted in 30 healthy volunteers to compare the cutaneous effects of adapalene 0.1% gel and adapalene 0.1% cream with their respective vehicles, using tretinoin 0.05% cream (n = 21) or tretinoin 0.1% cream (n = 9) and a tretinoin cream vehicle (n = 30) as controls. The products were applied to hip/buttock skin for 4 days under occlusive conditions. Cytosolic retinoic acid binding protein-II (CRABP-II) mRNA levels were measured using the RT-PCR technique in punch biopsies taken from 10 subjects. Epidermal thickness was assessed using image analysis of haematoxylin and eosin stained sections from another 11 subjects. Erythema was assessed in all subjects both by a visual scoring system and by chromameter. Adapalene 0.1% gel and adapalene 0.1% cream produced similar significant increases in CRABP-II mRNA levels compared to their vehicles (P < 0.01). The two tretinoin formulations also resulted in similar significant increases in CRABP-II compared to the cream vehicle (P < 0.001). However, only the two tretinoin formulations resulted in an increase in epidermal thickness and only the tretinoin 0.1% cream resulted in significant erythema. Adapalene 0.1% gel and adapalene 0.1% cream induce RAR-mediated gene expression to a similar degree in this model, without the irritant effects of tretinoin.

All-trans retinoic acid compromises desmosome expression in human epidermis

An undesirable side-effect of retinoid treatment is skin fragility. As desmosomes are important in maintaining the cohesion of epidermal keratinocytes, we investigated whether all-trans-retinoic acid (RA) compromises desmosome expression in human epidermis, thereby predisposing skin to fragility. Solutions containing 0.025% RA, 5% sodium dodecyl sulphate (SDS) as an irritant control, or vehicle alone were applied to three sites on the buttocks of normal volunteers (n = 9). Treated sites were occluded for 4 days, and biopsies taken under local anaesthesia. Cryostat sections were stained with a panel of antibodies to desmosomal proteins and visualized by immunofluorescence microscopy. Stained sections were randomized and assessed for intensity of staining. The epidermal thickness of each treated site was quantified by image analysis. Western blots of epidermal desmocollins were quantified by densitometry. RA and SDS treatments significantly, but equivalently, increased epidermal thickness compared with vehicle. Immunohistochemically, both RA and SDS were shown to reduce epidermal staining for desmoplakin, desmoglein 1, plakophilin 1 and desmocollin 3 equally compared with vehicle-treated skin (P < 0.001). RA produced a greater reduction in desmocollin 1 staining compared with SDS (P < 0.001). Similar reductions in desmocollins were found by Western blot analysis. Reduced desmocollin expression may indicate compromised desmosomal adhesion, leading to the skin fragility that results from retinoid treatment.

Photoaging therapy with topical tretinoin: an evidence-based analysis

Topical tretinoin is established as an effective treatment for photoaging. Yet some confusion still exists about the proper way to use this medication, confusion that can misguide physicians in their clinical approaches and patients in their treatment regimens. Most of the misinformation about tretinoin has been perpetuated from the early days of the drug, when its efficacy for treating the effects of photoaging was still in dispute. Significant advances in clinical and basic research in this area have dispelled much of the confusion, clearing the way for an evidence-based medical approach to tretinoin therapy for photoaging. This review summarizes recent relevant advances in tretinoin therapy to guide physicians in treating patients with this safe and effective hormone. To date, tretinoin remains the only therapeutic agent proved to repair photodamage.

Topical all-trans retinoic acid (RA) induces an early, coordinated increase in RA-inducible skin-specific gene/psoriasin and cellular RA-binding protein II mRNA levels which precedes skin erythema

Separation of specific and nonspecific "irritant" effects of topical all-trans retinoic acid (RA) is a key to understanding the mechanism of retinoid action in skin. Cellular RA-binding protein (CRABP) II has been found to be a marker of RA activity in human skin. We have also previously identified a skin-specific gene (RIS-1/psoriasin) which is rapidly induced in human skin treated with RA. Here we compared the kinetics and time-course of RIS-1 and CRABP II gene activation by RA, sodium lauryl sulfate (SLS), a classical irritant, and their vehicle (VH), using a quantitative reverse transcription polymerase chain reaction. RIS-1 and CRABP II were both expressed at very low levels in untreated normal human skin, and in RA-treated skin the kinetics and time course of RIS-1 and CRABP II mRNA induction were similar. Relative to VH-treated skin, RA induced RIS-1 mRNA levels within 6 h, which further increased to 6.4-fold by 24 h (n = 4). Similarly, CRABP II mRNA levels increased from 2.6-fold at 6 h to 7.8-fold after 24 h. At 48 h the relative mRNA levels for both genes decreased towards the steady-state levels. Relative to SLS-treated skin, RIS-1 mRNA increased by 3.2-fold after 6 h and by 5.1-fold after 12 h (n = 3). Also, a 2.6-fold higher CRABP II mRNA observed after 6 h increased to 6-fold after 12 h. After 24 and 48 h RA treatment the relative mRNA levels for both genes decreased towards the steady-state levels. RA-induced skin erythema was not obvious until 24 to 48 h. We conclude, therefore, that induction of RIS-1 and CRABP II mRNA levels by topical RA in human skin are early, coordinated molecular events which precede the clinical cutaneous erythematous response to RA.

Peeling agents and irritants, unlike tretinoin, do not stimulate collagen synthesis in the photoaged hairless mouse

Tretinoin has been shown to stimulate the synthesis of collagen in photo-aged human and hairless mouse skin. It has been suggested that this partial reversal of photodamage by tretinoin is a consequence of low-grade inflammation. The purpose of this study was to compare the effect of tretinoin with a number of irritants and peeling agents on collagen synthesis. Hairless mice were irradiated thrice weekly for 10 weeks with UVB. In the 10-week postirradiation period, the mice were treated topically five times per week with tretinoin (0.05%), glycolic acid (10%), benzalkonium chloride (1.0%), sodium lauryl sulfate (5%), croton oil (5%) and the water - propylene glycol vehicle. Microscopic measurements showed that the tretinoin-induced zone of new collagen was twice the depth of that induced by irritants or vehicle. The salt-soluble collagen content was determined by HPLC analysis of hydroxyproline levels. Type III procollagen was quantified by radioimmunoassay. Tretinoin-treated skin had increased amounts of collagen and type III procollagen whereas irritant- and peeling agent-treated skins were similar to vehicle-treated controls. Immunofluorescence studies were confirmatory. These results demonstrate that these agents, unlike tretinoin, do not have the capacity to enhance collagen synthesis. Therefore, it is likely that the effect of tretinoin does not depend upon irritation.

Liarozole inhibits human epidermal retinoic acid 4-hydroxylase activity and differentially augments human skin responses to retinoic acid and retinol in vivo

Metabolic inactivation of all-trans retinoic acid to 4-hydroxy retinoic acid occurs via a cytochrome P-450 enzyme. We investigated the effects of liarozole on the retinoic acid 4-hydroxylase activity of human epidermis and its ability to modify in vivo human skin responses to retinoic acid and all-trans retinol. Retinoic acid 4-hydroxylase activity induced in vivo by 4 d treatment with retinoic acid (0.1%) was inhibited in vitro by liarozole in a concentration-dependent manner. Comparable micromolar concentrations of liarozole were extracted from stratum corneum-free epidermis treated with 3% liarozole. Retinoic acid levels in liarozole-treated skin increased to 19 +/- 5 ng/g wet wt (mean +/- SEM, p < 0.002, n = 17) at 18 h and to 6 +/- 2 ng/g wet wt (p = 0.38, n = 17) at 48 h as compared to vehicle (not detectable). At 48 h, retinoic acid 4-hydroxylase activity was induced 9-fold over vehicle (p < 0.03, n = 8). At 96 h, no significant erythema or increased epidermal thickness was found when either retinoic acid (0.001%), all-trans retinol (0.0250%), or liarozole (3%) was applied individually, but when 0.001% retinoic acid and 3% liarozole were applied together, both erythema and increased epidermal thickness occurred. In contrast, 0.025% all-trans retinol and 3% liarozole together caused increased epidermal thickness but no erythema. These data demonstrate that, at doses used here, liarozole, although an effective inhibitor of retinoic acid 4-hydroxylase, cannot function alone like a retinoid in vivo, probably because of retinoic acid 4-hydroxylase induction. In the presence of a low dose retinoic acid or all-trans retinol, however, liarozole can amplify human skin responses to each retinoid in a manner characteristic of the retinoid at a higher dose (erythema and hyperplasia with retinoic acid; no erythema but hyperplasia with all-trans retinol).

Application of retinol to human skin in vivo induces epidermal hyperplasia and cellular retinoid binding proteins characteristic of retinoic acid but without measurable retinoic acid levels or irritation

We investigated the clinical, histologic, and molecular responses of normal human skin to all-trans-retinol (ROL) application, compared to those induced by topical all-trans-retinoic acid (RA), and measured ROL-derived metabolites. Up to 1.6% ROL, 0.025% RA in vehicle (70% ethanol/30% propylene glycol), or vehicle alone were applied in a double-blind fashion to normal buttock skin and occluded for 4 d. ROL produced from none to only trace erythema, which was clinically and statistically insignificant, whereas RA induced a significant 3.7-fold increase in erythema score compared to vehicle (n = 10, p < 0.01). However, ROL induced significant epidermal thickening (1.5-fold at 1.6% ROL, p < 0.01), similar to RA (1.6-fold at 0.025% RA, p < 0.01), relative to the vehicle. ROL, compared with vehicle, also increased mRNA levels of cellular retinoic acid binding protein (CRABP-II) and cellular retinol binding protein (CRBP) genes as determined by Northern analysis (5-6-fold and 6-7-fold, respectively) and riboprobe in situ hybridization. CRABP-II and CRBP protein levels were also higher following ROL than vehicle treatment, as measured by ligand binding (3.2-fold, p < 0.001; n = 7) and Western analysis (3.6-fold, p < 0.003; n = 6), respectively. Epidermal retinyl ester (RE) content, measured after removal of stratum corneum, rose 240-fold (p < 0.005, n = 5) by 24 h of ROL occlusion. RA content, however, was undetectable or detectable only at trace amounts in all samples obtained at 0, 6, 24, and 96 h after ROL occlusion. Detectability of RA was not correlated with ROL treatment (compared to untreated normal skin, p = 0.86) or baseline skin ROL levels (average r = -0.1, p > 0.3). These data demonstrate that ROL application 1) produces trace erythema not significantly different from vehicle, whereas RA causes erythema; 2) induces epidermal thickening and enhances expression of CRABP-II and CRBP mRNAs and proteins as does RA; 3) causes marked accumulation of retinyl ester; and 4) does not significantly increase RA levels. Taken together, the data are compatible with the idea that ROL may be a prohormone of RA, because it produces changes in skin similar to those produced by RA but without measurable RA or irritation.

Surfactants and experimental irritant contact dermatitis

Surface-active agents (surfactants) are characterized by the possession of 2 different moieties, both polar and non-polar regions on the same molecule. Surfactants are broadly classified as anionic, cationic, amphoteric, or non-ionic, according to the nature of the hydrophile yielded in aqueous solution. In currently marketed household, personal, and industrial cleaners, anionic surfactants are the most common class because of their relative ability to solubilize fats and oils, lower the surface tension of aqueous solutions, or form microemulsions. Many surfactants elicit irritant reactions when applied to the skin, partially due to their relative ability to solubilize lipid membranes. Hence, surfactants have become important implements in skin irritation investigations. In general, the physicochemical properties of surfactants are a crucial factor in eliciting skin irritation. Anionic surfactants are broadly accepted as potent irritants to human and animal skin. Cationic surfactants are reputedly at least equally irritating, but more cytotoxic than anionic, while the irritation potential of non-ionic surfactants is considered the lowest. Such classification of innumerable surfactants is convenient and held in high practical esteem. however, the categorization does not permit the exact determination of irritation and cytotoxicity potential of each surfactant. Ranking of surfactant skin irritancy and cytotoxicity obtained by both in vitro and in vivo assays provides a helpful orientation for future work.

Evaluation of topical retinoids for cutaneous pharmacological activity in Yucatan microswine

The pharmacological effects of retinoids on skin have been studied primarily in test systems using small animals, such as mice and rabbits. Because of potentially significant differences in skin permeation and metabolism between small animals and humans, we have used Yucatan microswine as an alternative model for testing topical retinoids. Microswine skin resembles human skin, functionally and anatomically, more closely than most other species. In these studies, microswine skin was treated topically with retinoids for 5 consecutive days per week for 5 weeks. We found microswine epidermis to be functionally responsive to retinoids in that it undergoes hyperplasia and shows an increase in transepidermal water loss (TEWL). All-trans-retinoic acid, and its analogs, 13-cis-retinoic acid, 4-hydroxy-retinoic acid and 4-oxo-retinoic acid all caused epidermal thickening and increased TEWL. The three analogs were less potent than all-trans-retinoic acid. A synthetic retinoid, TTNPB, potently induced epidermal hyperplasia and increased TEWL, but a close structural analog, m-carboxy-TTNPB, which is also inactive on nuclear retinoic acid receptors, was without effects on microswine epidermis. These findings show that microswine are useful for evaluating the cutaneous effects of topical retinoids. This model could be of value in identifying retinoids with potential clinical activity.

Down-regulation of Langerhans cell protein kinase C-beta isoenzyme expression in inflammatory and hyperplastic dermatoses

The family of protein kinase C (PKC) isoenzymes plays a fundamental part in signal transduction, and thereby regulates important cellular functions, including growth, differentiation, cytokine production and adhesion molecule expression. In lesional psoriatic skin, Ca(2+)-dependent PKC activity, PKC-beta protein and epidermal Langerhans cell (LC) PKC-beta immunostaining are significantly decreased, indicating activation and subsequent down-regulation of PKC. Whether these changes occur in other inflammatory/hyperplastic dermatoses is, however, unknown. We examined PKC-alpha and PKC-beta expression in normal skin, psoriasis, cutaneous T-cell lymphoma (CTCL), lamellar ichthyosis, non-bullous ichthyosiform erythroderma, atopic dermatitis, urushiol-induced allergic contact dermatitis, and sodium lauryl sulphate (SLS)-induced irritant contact dermatitis. Cryostat sections were stained for PKC-alpha and PKC-beta, and the LC marker CD1a, using an immunoperoxidase technique and specific monoclonal antibodies. Double-labelling studies, in normal skin, revealed co-expression of PKC-beta and CD1a by epidermal LCs. Analysis of the number of PKC-beta+ and CD1a+ epidermal LCs, in diseased compared with normal skin, revealed three categories: (i) in psoriasis and CTCL, the PKC-beta+ epidermal LC number was significantly reduced, whereas the CD1a+ epidermal LC number was unchanged; (ii) in allergic and irritant contact dermatitis, both PKC-beta+ and CD1a+ epidermal LCs were significantly reduced in number; and (iii) in atopic dermatitis, the PKC-beta+ epidermal LC number was normal, and CD1a+ epidermal LCs were significantly increased in number. Moreover, the ratio of epidermal LC PKC+/CD1a+ was reduced in all the dermatoses studied, suggesting activation of PKC-beta, with subsequent down-regulation. Within the dermis, increased PKC-beta staining of infiltrating cells was observed in all the conditions studied except lamellar ichthyosis and non-bullous ichthyosiform erythroderma. These data indicate that: (i) down-regulation of LC PKC-beta occurs in a variety of inflammatory and hyperplastic skin disorders, and is not unique to psoriasis, and (ii) the pattern of epidermal LC PKC-beta and CD1a expression varies among the diseases studied. In mice, PKC activation induces LC migration. Thus, down-regulation of epidermal LC PKC-beta associated with reduced CD1a+ epidermal LCs in allergic and irritant contact dermatitis suggests that PKC-beta may transduce the signal for migration of LCs from human epidermis.