Short-term retinoic acid treatment increases in vivo, but decreases in vitro, epidermal transglutaminase-K enzyme activity and immunoreactivity

Molecular Basis of Transglutaminase-2 and Muscarinic Cholinergic Receptors in Experimental Myopia: A Target for Myopia Treatment

Myopia, a prevalent refractive error disorder worldwide, is characterized by the elongation of the eye, leading to visual abnormalities. Understanding the genetic factors involved in myopia is crucial for developing therapeutic and preventive measures. Unfortunately, only a limited number of genes with well-defined functionality have been associated with myopia. In this study, we found that the homozygous TGM2-deleted gene in mice protected against the development of myopia by slowing down the elongation of the eye. The effectiveness of gene knockdown was confirmed by achieving a 60 percent reduction in TGM-2 transcript levels through the use of TGM-2-specific small interfering RNA (siRNA) in human scleral fibroblasts (SFs). Furthermore, treating normal mouse SFs with various transglutaminase inhibitors led to the down-regulation of TGM-2 expression, with the most significant reduction observed with specific TGM-2 inhibitors. Additionally, the study found that the pharmacological blockade of muscarinic receptors also slowed the progression of myopia in mice, and this effect was accompanied by a decrease in TGM-2 enzyme expression. Specifically, mice with homozygous mAChR5, mAChR1, and/or mAChR4 and knockout mice exhibited higher levels of TGM-2 mRNA compared to mice with homozygous mAChR2 and three knockout mice (fold changes of 5.8, 2.9, 2.4, -2.2, and -4.7, respectively; p < 0.05). These findings strongly suggest that both TGM-2 and muscarinic receptors play central roles in the development of myopia, and blocking these factors could potentially be useful in interfering with the progression of this condition. In conclusion, targeting TGM-2 may have a beneficial effect regarding myopia, and this may also be at least partially be the mechanism of anti-muscarinic drugs in myopia. Further studies should investigate the interaction between TGM-2 and muscarinic receptors, as well as the changes in other extracellular matrix genes associated with growth during the development of myopia.

Main effects of retinol palmitate on skin structures and the technology of its use in dermatological practice

Vitamin A and its synthetic analogues are used in the treatment of numerous skin diseases. The main genomic effects of the natural form of vitamin A (retinol palmitate) are associated with its active metabolite all-trans-retinoic acid and are compensated by several restrictive mechanisms. Numerous studies have proved that retinol stimulates the proliferation of keratinocytes of the basal layer of the epidermis and endothelial cells, and also activates dermal fibroblasts to synthesize proteins of the extracellular matrix of the dermis. As a result, the thickening the epidermis, increases the mechanical strength of the skin and the hydrating ability of the dermis, angiogenesis increase. The ability of retinol to enhance the adhesion of endothelial cells and leukocytes, regulate the processes of keratinization and sebum secretion was found. Vitamin A is also a powerful antioxidant. Retinol palmitate is used as the main or auxiliary drug for the treatment of a wide range of dermatoses. The principle of application is based on clinical studies and confirmed by existing experimental data. In the treatment, the following algorithm is followed. If retinol palmitate is necessary to improve epithelialization and strengthen the epidermal barrier, medium therapeutic doses should be used. For the treatment of disorders of keratinization processes, depending on the severity of the pathological condition, medium and high therapeutic doses of the drug are used. Violation of the processes of sebum secretion and severe hyperkeratosis respond better to treatment at high therapeutic doses. It should be noted that many skins clinical manifestations mostly regress under the action of vitamin A in doses that do not lead to the appearance of signs of toxicity of the drug.

Current Strategies for the Gene Therapy of Autosomal Recessive Congenital Ichthyosis and Other Types of Inherited Ichthyosis

Mutations in genes such as transglutaminase-1 (TGM1), which are responsible for the formation and normal functioning of a lipid barrier, lead to the development of autosomal recessive congenital ichthyosis (ARCI). ARCIs are characterized by varying degrees of hyperkeratosis and the presence of scales on the body surface since birth. The quality of life of patients is often significantly affected, and in order to alleviate the manifestations of the disease, symptomatic therapy with moisturizers, keratolytics, retinoids and other cosmetic substances is often used to improve the condition of the patients' skin. Graft transplantation is commonly used to correct defects of the eye. However, these approaches offer symptomatic treatment that does not restore the lost protein function or provide a long-term skin barrier. Gene and cell therapies are evolving as promising therapy for ARCIs that can correct the functional activity of altered proteins. However, these approaches are still at an early stage of development. This review discusses current studies of gene and cell therapy approaches for various types of ichthyosis and their further prospects for patient treatment.

Retinoic acid and hydroquinone induce inverse expression patterns on cornified envelope-associated proteins: implication in skin irritation

BACKGROUND

Hydroquinone (HQ) with or without retinoic acid (RA) is routinely used for the treatment of hyperpigmented conditions. Skin irritation is a major problem with popular depigmenting agents, resulting in postinflammatory hyperpigmentation.

OBJECTIVE

To examine the molecular mechanism associated with skin irritation by RA or HQ.

METHODS

A genome-wide transcriptional profiling analysis was performed using monolayer cultures of human keratinocytes treated with or without irritant doses of RA, HQ, or sodium lauryl sulfate (SLS), a representative irritant. Differentially expressed genes (DEGs) were mapped on human chromosomes using a Manhattan plot. For the validation of candidate DEGs, the chemicals with different concentrations of varying irritation intensities were applied in vitro and in vivo and analyzed using real time-PCR and Western blotting.

RESULTS

DEGs mapped to the 1q21 locus, which is composed of a cluster of genes encoding the cornified envelope precursors, showed an inverse expression pattern in response to HQ and RA. Concentrations of RA and HQ that induced a broad range of irritant responses in cultured cells or mice skin also induced inverse effects on the expression of cornified envelope-associated proteins.

CONCLUSIONS

Genetic modulation on cornified envelope-associated proteins by RA-induced irritation, which may be involved in physiological skin barrier disturbance, could be inverse to that by HQ- or SLS-induced irritation.

The effect of two endogenous retinoids on the mRNA expression profile in human primary keratinocytes, focusing on genes causing autosomal recessive congenital ichthyosis

Retinoids (natural forms and synthetic derivatives of vitamin A) are used as therapeutic agents for numerous skin diseases such as keratinization disorders (e.g. ichthyoses) and psoriasis. Two endogenous ligands for retinoic acid receptors exist, retinoic acid (atRA) and 3,4-didehydroretinoic acid (ddRA). In primary human epidermal keratinocytes many transcriptional targets for atRA are known, whereas the targets for ddRA are unknown. In an attempt to determine the targets, we compared the effect of atRA and ddRA on transcriptional profiles in undifferentiated and differentiating human primary keratinocytes. First, as expected, many genes were induced or suppressed in response to keratinocyte differentiation. Furthermore, the two retinoids affected substantially more genes in differentiated keratinocytes (>350) than in proliferating keratinocytes (≈20). In differentiating keratinocytes markers of cornification were suppressed suggesting a de-differentiating effect by the two retinoids. When comparing the expression profile of atRA to that of ddRA, no differently regulated genes were found. The array analysis also found that a minor number of miRNAs and a large number of non-coding transcripts were changed during differentiation and in response to the two retinoids. Furthermore, the expression of all, except one, genes known to cause autosomal recessive congenital ichthyosis (ARCI) were found to be induced by differentiation. These results comprehensively document that atRA and ddRA exert similar transcriptional changes in keratinocytes and also add new insights into the molecular mechanism influenced by retinoids in the epidermis. Furthermore, it suggests which ARCI patients could benefit from therapy with retinoids.

The thyroid hormone receptors modulate the skin response to retinoids

Background

Retinoids play an important role in skin homeostasis and when administered topically cause skin hyperplasia, abnormal epidermal differentiation and inflammation. Thyroidal status in humans also influences skin morphology and function and we have recently shown that the thyroid hormone receptors (TRs) are required for a normal proliferative response to 12-O-tetradecanolyphorbol-13-acetate (TPA) in mice.

Methodology/Principal findings

We have compared the epidermal response of mice lacking the thyroid hormone receptor binding isoforms TRα1 and TRβ to retinoids and TPA. Reduced hyperplasia and a decreased number of proliferating cells in the basal layer in response to 9-cis-RA and TPA were found in the epidermis of TR-deficient mice. Nuclear levels of proteins important for cell proliferation were altered, and expression of keratins 5 and 6 was also reduced, concomitantly with the decreased number of epidermal cell layers. In control mice the retinoid (but not TPA) induced parakeratosis and diminished expression of keratin 10 and loricrin, markers of early and terminal epidermal differentiation, respectively. This reduction was more accentuated in the TR deficient animals, whereas they did not present parakeratosis. Therefore, TRs modulate both the proliferative response to retinoids and their inhibitory effects on skin differentiation. Reduced proliferation, which was reversed upon thyroxine treatment, was also found in hypothyroid mice, demonstrating that thyroid hormone binding to TRs is required for the normal response to retinoids. In addition, the mRNA levels of the pro-inflammatory cytokines TNFα and IL-6 and the chemotactic proteins S1008A and S1008B were significantly elevated in the skin of TR knock-out mice after TPA or 9-cis-RA treatment and immune cell infiltration was also enhanced.

Conclusions/significance

Since retinoids are commonly used for the treatment of skin disorders, these results demonstrating that TRs regulate skin proliferation, differentiation and inflammation in response to these compounds could have not only physiological but also therapeutic implications.

Epidermal Hyperplasia and Elevated HB-EGF are More Prominent in Retinoid Dermatitis Compared with Irritant Contact Dermatitis Induced by Benzalkonium Chloride

BACKGROUND

'Retinoid dermatitis' is a retinoid-induced irritant contact dermatitis (ICD). The mechanism of retinoid dermatitis may be different from that of other ICDs. However, it remains uncertain how topical retinoid induce ICD.

OBJECTIVE

We compared several aspects of contact dermatitis induced by topical retinol and benzalkonium chloride (BKC) on hairless mice skin.

METHODS

2% retinol or 2.5% BKC was applied to hairless mice and transepidermal water loss (TEWL), ear thickness, histologic and immunohistochemical findings were compared. We also compared mRNA expression of inflammatory cytokines, epidermal differential markers, cyclooxygenases (COXs) and heparin binding epidermal growth factor like growth factor (HB-EGF).

RESULTS

Topical application of 2% retinol and 2.5% BKC increased TEWL and ear thickness in similar intensity. Epidermal hyperplasia was more prominent in retinol treated skin. Proliferating cell nuclear antigen, involucrin and loricrin expression were higher in retinol-treated skin than in BKC-treated skin. Filaggrin, however, was more expressed in BKC-treated skin. The mRNA expression of IL-8, TNF-alpha, COX-2, involucrin, loricrin and filaggrin were increased in both retinol- and BKC-treated skin in similar intensity. HB-EGF was more significantly increased in retinol-treated skin.

CONCLUSION

Elevated HB-EGF and epidermal hyperplasia are more prominent features of retinoid dermatitis than in BKC-induced ICD.

Silybin from Silybum Marianum Seeds Inhibits Confluent-Induced Keratinocytes Differentiation as Effectively as Retinoic Acid without Inducing Inflammatory Cytokine

Retinoic acid (RA) has been effective for improving wrinkles. However, it has also been reported that RA induces skin irritation. In this study, we explored new botanical compounds that show RA-like activity, but do not induce inflammation in vitro. Keratinocytes were maintained in a confluent condition and induced differentiation. Under this condition keratinocytes were treated with many botanical extracts and their morphological change were observed and compared with RA-treated. We found that silybin, which is a major flavonolignan from Silybum Marianum seeds, induced RA-like morphological change and prevented differentiation. We showed that silybin, like RA, reduced the expression of keratinocyte terminal differentiation markers and stimulated the expression of basement membrane component proteins. In contrast, silybin, unlike RA, did not stimulate the secretion of IL-1α, which is a skin irritation mediator. These results suggest that silybin has RA-like activity on keratinocytes and has the potential to improve winkle without inducing skin irritation.

A comparative trial of two retinoids commonly used in the treatment of acne vulgaris

BACKGROUND

Topical retinoids are highly effective treatments for acne vulgaris. The various formulations and concentrations available allow physicians to tailor therapies to individual patient's needs and minimize the cutaneous irritation that is often observed with the use of these drugs.

OBJECTIVE

To compare the efficacy and safety of tretinoin gel microsphere 0.1% with adapalene gel 0.1% in the treatment of acne vulgaris.

METHODS

A 12-week double-blind study was conducted, and patients were evaluated at baseline and at weeks 2, 3, 4, 6, 8, 10, and 12.

RESULTS

Although the two drugs displayed similar efficacy in the resolution of acne lesions at 12 weeks, a significantly greater reduction in the number of comedones was seen at week 4 among patients treated with tretinoin gel microsphere (p = 0.047). Patients receiving tretinoin gel microsphere had an increased incidence of dryness (weeks 8 and 10) and peeling (weeks 3, 6, 8, and 10) compared with those patients treated with adapalene gel, but the two groups were comparable with respect to erythema, burning/stinging, and itching.

CONCLUSION

Both drugs have similar efficacy in the resolution of acne lesions but tretinoin gel microsphere may result in a faster onset of action in the reduction of comedones compared to adapalene.

The expression of differentiation markers in aquaporin-3 deficient epidermis

Aquaporin-3 (AQP3) is a water/glycerol transporting protein expressed strongly at the plasma membrane of keratinocytes. There is evidence for involvement of AQP3-facilitated water and glycerol transport in keratinocyte migration and proliferation, respectively. Here, we investigated the involvement of AQP3 in keratinocyte differentiation. Studies were done using AQP3 knockout mice, primary cultures of mouse keratinocytes (AQP3 knockout), neonatal human keratinocytes (AQP3 knockdown), and human skin. Cells were cultured with high Ca(2+) or 1alpha,25-dihydroxyvitamin D(3) (VD(3)) to induce differentiation. The expression of differentiation marker proteins and differentiating responses were comparable in control and AQP3-knockout or knockdown keratinocytes. Topical application of all-trans retinoic acid (RA), a known regulator of keratinocyte differentiation and proliferation, induced comparable expression of differentiation marker proteins in wildtype and AQP3 null epidermis, though with impaired RA-induced proliferation in AQP3 null mice. Immunostaining of human and mouse epidermis showed greater AQP3 expression in cells undergoing proliferation than differentiation. Our results showed little influence of AQP3 on keratinocyte differentiation, and provide further support for the proposed involvement of AQP3-facilitated cell proliferation.

Expression of keratin K2e in cutaneous and oral lesions: association with keratinocyte activation, proliferation, and keratinization

The cytoskeleton in keratinocytes is a complex of highly homologous structural proteins derived from two families of type I and type II polypeptides. Keratin K2e is a type II polypeptide that is expressed in epidermis late in differentiation. Here we report the influence of keratinocyte activation, proliferation, and keratinization on K2e expression in samples of cutaneous and oral lesions. The normal expression of K2e in the upper spinous and granular layers of interfollicular epidermis is increased in keloid scars but showed distinct down-regulation in psoriasis and hypertrophic scars where keratinocytes are known to undergo activation. Unlike normal and psoriatic skin, K2e expression in hypertrophic and keloid scars began in the deepest suprabasal layer. In cutaneous basal and squamous cell carcinomas, K2e was absent in most tumor islands but the overlying epidermis showed strong expression. No significant K2e expression in nonkeratinized or keratinized oral epithelia, including buccal mucosa, lateral border of tongue and gingiva was detected. In oral lichen planus K2e expression was undetectable, but in benign keratoses of lingual mucosa induction of K2e along with K1 and K10 was observed. In mild-to-moderate oral dysplasia with orthokeratinization, K2e was highly expressed compared with parakeratinized areas but in severe dysplasia as well as in oral squamous cell carcinoma, K2e expression was undetectable. Taken together, the data suggest that K2e expression in skin is sensitive to keratinocyte activation but its up-regulation in oral lesions is a reflection of the degree of orthokeratinization.

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).

Retinoid receptors and keratinocytes

In 1987, a tremendous boost in our understanding of the action of dietary vitamin A occurred with the discovery and characterization of nuclear receptors for retinoic acid, the active form of the vitamin, in the laboratories of P. Chambon and R. Evans. They have shown that the nuclear receptors are ligand-activated transcription factors capable of specific gene regulation. Since that discovery, it has been determined that there are at least six retinoic acid receptors belonging to two families, RARs and RXRs, that they are differentially expressed in various mammalian tissues, and that they act as homo- and heterodimers interacting with other ligand-activated nuclear receptors. The domain structure of the receptors has been described, and their DNA-binding, ligand-binding, dimerization, and transcriptional activation regions characterized. Among the most important retinoid-regulated genes are the homeobox proteins, regulatory transcription factors which are responsible for body axis formation, patterning, limb formation, and other crucial processes during development. Retinoic acid and its receptors also regulate many differentiation markers which are particularly important in stratified epithelia, such as skin and oral epithelia. Our increased understanding led to improved therapy of a large number of skin disorders, ranging from acne to wrinkles and including epidermal and oral carcinomas.

All-trans retinoic acid induces cellular retinol-binding protein in human skin in vivo

We examined the regulation of cellular retinol-binding protein (CRBP) mRNA and protein expression in human skin in vivo by all-trans retinoic acid and all-trans retinol. Treatment of human skin for 24 h with all-trans retinoic acid (0.1%) or all-trans retinol (1.6%) induced CRBP mRNA 5.5-fold (p < 0.01, n = 10) and 5.7-fold (p < 0.01, n = 5), respectively, compared with skin treated with vehicle or sodium lauryl sulfate (used as an irritant control). In vitro translation of poly A+ RNA from all-trans retinoic acid, all-trans retinol, sodium lauryl sulfate, and vehicle-treated human skin demonstrated that the observed increased CRBP mRNA in all-trans retinoic acid- and all-trans retinol-treated skin was able to direct increased (2.3-2.9-fold) CRBP protein synthesis. Riboprobe in situ hybridization revealed that CRBP mRNA was uniformly elevated throughout the epidermis and in dermal cells after all-trans retinoic acid treatment of human skin. Western analysis revealed that CRBP protein was elevated 3.2-fold (p < 0.01, n = 6) and 3.0-fold (p < 0.01, n = 6) after all-trans retinoic acid treatment of human skin in vivo for 24 and 96 h, respectively, compared with vehicle- and sodium lauryl sulfate-treated skin. In addition, functional CRBP levels measured by [3H]all-trans retinol binding were elevated 1.9-fold (p < 0.01, n = 6) and 3.5-fold (p < 0.01, n = 6) at 24 and 94 h, respectively, after all-trans retinoic acid treatment, compared with vehicle- or sodium lauryl sulfate-treated skin. Gel mobility shift analysis revealed that retinoid receptors in nuclear extracts from human skin formed a specific complex with a DNA probe containing the retinoic acid response element in the mouse CRBP gene. Monoclonal antibodies to nuclear retinoid receptors demonstrated that predominantly retinoic acid receptor-alpha/retinoid X receptor-alpha heterodimers bound to the CRBP retinoic acid response element. These data demonstrate that CRBP expression in human skin in vivo is regulated by exogenous all-trans retinoic acid and all-trans retinol.

Human in vivo pharmacology of topical retinoids

All-trans retinoic acid is used topically for treating a variety of dermatologic conditions ranging from acne to photoaged skin. Although the clinical effects of retinoic acid treatment are often considerable, relatively little is known about the basic mechanisms underlying such effects. With the development of an in vivo human assay we have investigated the pleiotypic effects of topical retinoids from the histologic to the molecular. Histologically, retinoic acid induces epidermal proliferation and differentiation coupled with dermal fibroblast production of collagen. Immunologic effects include stimulation of the antigen-presenting capacity of Langerhans cells and induction of keratinocyte ICAM-1 expression. At the biochemical level, retinoic acid regulates transglutaminase and tyrosinase activities and activates protein kinase C. Both polar metabolites and stereoisomers of all-trans retinoic acid are also biologically active. Molecular biologic techniques have revealed that elevation of mRNA for cellular retinoic acid binding protein II is a retinoid-related event and that nuclear receptors such as retinoic acid receptors and retinoid X-receptors may transduce the retinoid response.

Programmed expression of cholesterol sulfotransferase and transglutaminase during epidermal differentiation of murine skin development

To clarify the role of cholesterol sulfate (CS) in the process of epidermal differentiation in vivo, we investigated the concentration of CS and the specific activities of cholesterol sulfotransferase (CST), cholesterol sulfate sulfatase (CS sulfatase) and epidermal transglutaminase (ETG) in murine skin in the pre- and postnatal periods. In the skin at day 14 of gestation, CS was not detected with TLC and the specific activities of all the enzymes were low. However, concomitant with the formation of the multilayered structure of the epidermis (at day 16), the specific activities of CST steeply increased. Although the insoluble CS sulfatase in the microsomal fraction remained at a relatively constant level, the soluble CST in the cytosol fraction showed a 6-fold increase from day 14 to day 16, and the activity decreased continuously in the following period, reaching one forty-sixth of the maximum level at 4-months-old mice. Reflected by the increase in activity, CS was detected in fetal skin at day 15, and the concentration in epidermis significantly increased during the gestation period, reaching maximum level at day 17. Furthermore, the changes in the concentration of cholesterol sulfate were identical with those of N-(O-linoleoyl)-omega-hydroxy fatty acyl sphingosine and its glucosyl derivative in the epidermis. On the other hand, the specific activity of ETG increased after birth. Thus, the activation of CST and ETG was shown to occur separately in association with the formation of the multilayered structure and thickening of the stratum corneum, respectively.

Differential effects of topical retinoic acid application on keratin K1 and filaggrin expression in mouse epidermis

Retinoic acid (RA) modulates epidermal homeostasis and affects differentiation-associated proteins such as keratin K1 and filaggrin. Because results from in vitro and in vivo studies have been conflicting with respect to RA effects on keratinization, we examined the terminal differentiation of epidermal cell cohorts after RA stimulation in vivo. Pulse-labelling with 5-bromo-2-deoxyuridine (BrdU) was performed by intraperitoneal injection of mice immediately or at 16 h after a single topical application of 100 nmol RA. The cell cohort labelled at the time of RA application consisted of previously unperturbed cells exposed to RA after initiation of S-phase, whereas the cohort labelled 16 h after RA application consisted of cells stimulated into the S-phase by RA. These two cohorts of partially synchronized cells were followed for up to 72 h after BrdU labelling. Such labelling combined with keratin K1 or filaggrin expression was scored by paired immunofluorescence staining of skin sections. The onset of keratin K1 expression was unchanged in both series after RA treatment, while filaggrin appeared earlier than in controls. The differential effect of RA on the maturation markers was related to the proliferative activity, the increased cell turnover, and the shortened epidermal transit time. The onset of keratin expression appeared to be regulated before the postmitotic period, whereas filaggrin expression appeared to be regulated during the late phase of the maturation process, thus being influenced by the actual epidermal kinetics and structural alterations. These results suggested that the effect of RA on epidermal differentiation is secondary to its effect on proliferation, as determined by the altered cellular age distribution following regenerative proliferation.

Use of a human skin-grafted nude mouse model for the evaluation of topical retinoic acid treatment

Cultured human keratinocytes and artificial dermal equivalents maintained in vitro do not perfectly mimic the terminal differentiation patterns and response to drugs observed in intact human skin. We have made use of human skin grafted onto nude mice to demonstrate that such grafts maintain the pattern of pharmacologic responsiveness to all-trans retinoic acid previously reported in human subjects. The use of a quantitative polymerase chain reaction method to measure induction of a retinoic acid responsive gene, cytoplasmic retinoic acid binding protein II, has made it possible to generate objective data suitable for investigations of drug efficacy. This method of using grafted human skin has potential broad applicability for investigation of topical drugs in a number of therapeutic fields.

Response of psoriasis to a new topical retinoid, AGN 190168

BACKGROUND

Oral retinoids have been widely used in psoriasis, but topical forms have been ineffective or irritating.

OBJECTIVE

Our purpose was to determine the clinical and molecular effects of a new topical retinoid, AGN 190168, on psoriasis.

METHODS

Seven patients with psoriasis were treated for 2 weeks with topical retinoid and 2 weeks with vehicle. Two control subjects with psoriasis were treated for 2 weeks with vehicle alone. Biopsy specimens from normal skin as well as from untreated and treated psoriatic lesions were compared by immunohistochemical analysis. Differentiation and inflammatory markers were studied.

RESULTS

Clinical improvement was seen in all seven patients after 2 weeks of treatment. Improvement was still present, but not significant, after 2 additional weeks of vehicle application. Histologic examination showed a return to a more normal morphology in four of seven biopsy specimens, which correlated with filaggrin expression. There was a diminution in the precocious expression of keratinocyte transglutaminase, keratin 16, and involucrin, as well as a decrease in epidermal growth factor receptor and in the number of cells expressing intercellular adhesion molecule type 1 and HLA-DR.

CONCLUSION

Clinical and histologic improvements were seen in psoriasis in association with the topical application of AGN 190168 at 2 weeks, including decreased inflammation and restoration of normal epidermal differentiation. Small patient numbers and the possibility that the changes were related to clinical improvement alone and not the topical agent preclude definitive conclusions.

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

An occlusive patch-test assay has been developed for assessment of topical retinoid action in human epidermis. Previous work with this assay has demonstrated marked epidermal hyperplasia in skin treated with topical all-trans-retinoic acid for 4 days and similar effects with the local irritant, sodium lauryl sulphate. To investigate the capabilities of this assay further, a time-course and dose-response were performed with all-trans-retinoic acid, and a comparison made with sodium lauryl sulphate. At no time, between 1 and 4 days, could the clinical or histological effects of 0.1% and 0.025% cream formulations of all-trans-retinoic acid be distinguished from each other. Epidermal hyperplasia was used to generate a 4-day dose-response for all-trans-retinoic acid at concentrations from 0.001 to 0.025% dissolved in a 70% ethanol/30% propylene glycol vehicle. All-trans-retinoic acid could be successfully differentiated from sodium lauryl sulphate at 2 days by virtue of its greater ability to increase epidermal thickness, spongiosis and glycosaminoglycan deposition. It appears that although all-trans-retinoic acid and sodium lauryl sulphate produce similar epidermal histological changes at 4 days, significant differences at earlier time-points suggest differing mechanisms of action. In addition, this in vivo human assay is able to provide potency ranking for doses of all-trans-retinoic acid, and may predict clinical efficacy of retinoids in improvement of acne and/or photodamage.

Comparison of CD271 (adapalene) and all-trans retinoic acid in human skin: dissociation of epidermal effects and CRABP-II mRNA expression

A new synthetic retinoid analogue, adapalene (6-[3-(1-adamantyl)-4-methoxyphenyl]-2-naphthoic acid, CD271), which is relatively selective for retinoic acid receptor beta, was noted to be an effective comedolytic agent in the rhino mouse model and to have clinical efficacy against acne. In pursuit of this observation, we studied the effects of CD271 on the development of erythema, spongiosis, and epidermal hyperplasia as well as other well-characterized markers of in vivo retinoid action after 4 d of occluded topical treatment. The objective of the study was to elucidate further those parameters associated with potential clinical efficacy. Twenty-five subjects were treated with 0.1% all-trans retinoic acid cream, all-trans retinoic acid vehicle, 0.1% CD271 gel, or CD271 vehicle under occlusion for 4 d. Only all-trans retinoic acid induced erythema (p < 0.01 versus all other treatments). Similarly, histologic analysis revealed that epidermal hyperplasia and spongiosis were induced only by all-trans retinoic acid (p < 0.01 versus all other treatments). By immunohistochemical analysis: all-trans retinoic acid increased expression of epidermal transglutaminase, involucrin, and calgranulin (p < 0.05 versus all other treatments). In contrast to these data, both CD271 and all-trans retinoic acid caused marked and significant (p < 0.05) elevation of cellular retinoic acid-binding protein-II (CRABP-II) messenger ribonucleic acid steady-state levels as judged by quantitative RNA blot analysis. Although CD271 treatment did not lead to erythema or affect epidermal morphology, its ability to induce a marker of retinoid action (i.e., CRABP-II) was 70% the potency of all-trans retinoic acid. This study suggests that CRABP-II gene expression may be a more sensitive indicator of retinoid biologic activity in skin than are erythema or changes in epidermal morphology and differentiation.

Squamous cell differentiation markers in normal, premalignant, and malignant epithelium: effects of retinoids

Vitamin A and some of its analogs (retinoids) maintain normal differentiation of epithelial tissues by preventing aberrant squamous differentiation of cells in nonkeratinizing epithelia. They can also reverse squamous metaplasia, which develops in vivo during vitamin A deficiency. These effects are the result of the ability of retinoids to suppress the expression of genes associated with squamous differentiation (e.g., transglutaminase type I, loricrin, involucrin, filaggrin, and keratin K1). In addition, retinoids reverse keratinizing premalignant lesions in the oral cavity, and inhibit the growth and squamous differentiation of head and neck squamous cell carcinomas (HNSCCs) in vitro. Nuclear retinoic acid receptors, which function as DNA-binding, trans-acting, transcription-modulating factors, are considered to be the proximate mediators of the effects of retinoids on gene expression and may mediate the re-regulation of aberrant differentiation and growth of premalignant and some malignant cells, thereby suppressing the development of head and neck cancer.

Mechanisms of action of retinoic acid in skin repair

The ability of topically applied retinoic acid to improve photoaged skin has stimulated research interest into its mechanism of action. Currently available assay systems are either in-vitro or mouse models, neither of which are truly representative of the in-vivo situation in man. Another drawback is that skin biopsies available from studies using retinoic acid to treat photoageing are of insufficient size to accomplish biochemical and molecular assays. In order to address these problems, a 4-day in-vivo retinoid assay has been developed which serves as a good predictive model for the chronic effects of retinoic acid on skin and helps to characterize the mechanism of action of retinoic acid.