Retinoids and psoriasis: novel issues in retinoid pharmacology and implications for psoriasis treatment

Lazy neutrophils - a lack of DGAT1 reduces the chemotactic activity of mouse neutrophils

BACKGROUND

Neutrophils are key players in the innate immune system, actively migrating to sites of inflammation in the highly energetic process of chemotaxis. In this study, we focus on the role of acyl-CoA: diacylglycerol acyltransferase 1 (DGAT1), an enzyme that catalyzes the synthesis of triglycerides, the major form of stored energy, in neutrophil chemotaxis.

METHODS AND RESULTS

Using a mouse model of psoriasis, we show that DGAT1-deficiency reduces energy-demanding neutrophil infiltration to the site of inflammation, but this inhibition is not caused by decreased glycolysis and reduced ATP production by neutrophils lacking DGAT1. Flow cytometry and immunohistochemistry analysis demonstrate that DGAT1 also does not influence lipid accumulation in lipid droplets during inflammation. Interestingly, as has been shown previously, a lack of DGAT1 leads to an increase in the concentration of retinoic acid, and here, using real-time PCR and publicly-available next-generation RNA sequencing datasets, we show the upregulation of retinoic acid-responsive genes in Dgat1KO neutrophils. Furthermore, supplementation of WT neutrophils with exogenous retinoic acid mimics DGAT1-deficiency in the inhibition of neutrophil chemotaxis in in vitro transwell assay.

CONCLUSIONS

These results suggest that impaired skin infiltration by neutrophils in Dgat1KO mice is a result of the inhibitory action of an increased concentration of retinoic acid, rather than impaired lipid metabolism in DGAT1-deficient mice.

Effect of Allergen-Specific Immunotherapy on Transcriptomic Changes in Canine Atopic Dermatitis

Canine atopic dermatitis (cAD) is a genetic, chronic, and recurrent inflammatory and pruritic skin disorder. Allergen-specific immunotherapy (ASIT) is presently recognized as the only clinically effective disease-modifying treatment for allergies. The aim of our study was to analyze the changes in gene expression observed in the peripheral blood nuclear cells of cAD patients subjected to ASIT. Blood samples designated for transcriptomic analyses were collected from AD dogs twice, before and six months after ASIT, and also from healthy dogs. Statistical analysis revealed 521 differentially expressed transcripts, among which 241 transcripts represented genes with well-described functions. Based on the available literature, we chose nine differentially expressed genes (RARRES2, DPP10, SLPI, PLSCR4, MMP9, NTSR1, CBD103, DEFB122, and IL36G) which may be important in the context of the dysregulated immune response observed in cAD patients. The expressions of five out of the nine described genes (DPP10, PLSCR4, NTSR1, DEFB122, and IL36G) changed after the application of ASIT. The expressions of three of these genes returned to the level observed in the healthy control group. The genes listed above need further investigation to determine details of their role in the molecular mechanism of immune tolerance induction in response to allergen-specific immunotherapy.

Cellular retinol-binding protein 1: a therapeutic and diagnostic tumor marker

Cellular Retinol Binding Protein 1 (CRBP1) gene is a protein coding gene located on human chromosome 3q21, which codifies a protein named CRBP1. CRBP1 is widely expressed in many tissues as a chaperone protein to regulate the uptake, subsequent esterification and bioavailability of retinol. CRBP1 combines retinol and retinaldehyde with high affinity to protect retinoids from non-specific oxidation, and transports retinoids to specific enzymes to promote the biosynthesis of retinoic acid. The vital role of CRBP1 in retinoids metabolism has been gradually discovered, which has been implicated in tumorigenesis. However, the precise functions of CRBP1 in different diseases are still poorly understood. The purpose of this review is to provide an overview of the role of CRBP1 in various diseases, especially in both the promotion and inhibition of cancers, which may also offer a novel biomarker and potential therapeutic target for human diseases.

Mechanism of acitretin-induced relaxations in isolated rat thoracic aorta preparations

Acitretin is a member of vitamin A-derived retinoids, and its effect on vascular smooth muscle had not yet been studied. The aim of this study is to investigate the effect of acitretin, a retinoid, on vascular smooth muscle contractility. Thoracic aorta preparations obtained from 34 male Sprague-Dawley rats (355 ± 15 g) were studied in isolated organ baths containing Krebs-Henseleit solution. The relaxation responses were obtained with acitretin (10-12-10-4 M) in endothelium-preserved and endothelium-denuded aorta preparations precontracted with submaximal concentration of phenylephrine (10-6 M). The role of retinoic acid receptors (RARs), nitric oxide, adenylyl, and guanylyl cyclase enzymes, and potassium channels in these relaxation responses were investigated. Acitretin produced concentration-dependent relaxations, which were independent of its solvent dimethylsulfoxide (DMSO), in endothelium-denuded phenylephrine-precontracted thoracic aorta preparations. While incubation with the RAR antagonist (AGN193109, 10-5 M) had no effect on these relaxations; nitric oxide synthase inhibitor (L-NG-Nitro arginine methyl ester (L-NAME), 10-4 M), adenylyl cyclase inhibitor (SQ2253, 10-5 M), guanylyl cyclase inhibitor (oxadiazolo [4,3-a] quinoxalin-1-one (ODQ), 10-6 M), and potassium channel blocker (tetraethylammonium (TEA), 10-2 M) significantly eliminated the relaxation responses induced by acitretin. Acitretin induces relaxation in rat isolated thoracic aorta preparations without endothelium, which may be mediated by nitric oxide, cyclic adenosine monophosphate, and cyclic guanosine monophosphate-dependent kinases and potassium channels.

Treatment Strategies Against Psoriasis: Principle, Perspectives and Practices

BACKGROUND

Psoriasis is a genetically predisposed autoimmune disease mediated by cytokines released by the activated immune cells. It manifests inflammatory, scaly red or white silvery flaky skin which may be a fluid-filled lesion with soreness and itchiness. The prevalence rate of psoriasis is increasing day by day. Despite having such a high prevalence rate, the treatment of psoriasis is still limited. Hence, there is a need to rethink the various treatment strategies available in the allopathic as well as in the alternative systems of medicine.

METHODS

Various bibliographic databases of previously published peer-reviewed research papers were explored and systematic data culminated in terms of various treatment strategies used for the management of psoriasis. The prime focus is given towards modern as well as alternative systems of medicine such as phototherapy, a combination of phototherapy with pharmacotherapy such as Ayurveda, Yoga and naturopathy, Unani, Siddha, and Homeopathy to treat psoriasis.

RESULTS

A comprehensive review of 161 papers, including both research and review articles, was carried out to make the article readily understandable. The pathogenesis including inflammatory mediators and type of psoriasis is discussed before the treatment strategies to understand the pathophysiology of the disease. The uniqueness, procedure, advantages, and limitations of conventional, advanced, and traditional systems of medicine to treat psoriasis are discussed in detail. Emphasis has also been given towards marine sources such as fish oil, marine sponges, and algae.

CONCLUSION

Although there are many modern and alternative treatment strategies available to treat psoriasis, none of them have been proven to provide complete relief to patients. Moreover, they are associated with certain side effects. In order to overcome them, novel drug delivery systems have been utilized and found effective; however, their stability and safety become the major impediments towards their successful positioning. Traditional and alternative treatment strategies have found to be safe and effective but their use is localized to certain areas. In a nutshell, to achieve successful treatment of psoriasis, there is a need to focus on the development of stable and non-toxic novel drug delivery systems or the promotion of traditional systems to treat psoriasis.

Tackling the various classes of nano-therapeutics employed in topical therapy of psoriasis

Psoriasis is a dermatological chronic skin condition with underlying autoimmune etiology. It deeply affects patients' quality of life. Therefore, it was an interesting target for researchers throughout the past years. Conventionally, the treatment options include anti-inflammatory agents, immune suppressants, biologic treatment, and phototherapy. Nanotechnology offers promising characteristics that allow for tailoring a drug carrier to achieve dermal targeting, improved efficacy and minimize undesirable effects. Being the safest route, the first line of treatment and a targeted approach, we solely discussed the use of the topical route, combined with advanced drug delivery systems for the management of psoriasis in this article. Advanced systems include polymeric, metallic, lipidic and hybrid nanocarriers incorporating different active agents. All formerly mentioned types of drug delivery systems were investigated through the past decades for the purpose of topical application on psoriatic plaques. Scientists' efforts are promising to reach an optimized formula with a convenient dosage form to improve efficacy, safety, and compliance for the treatment of psoriasis. Accordingly, it will offer a better quality of life for patients.

Retinol and vitamin A metabolites accumulate through RBP4 and STRA6 changes in a psoriasis murine model

Background

Psoriasis is a common chronic inflammatory skin disease that features the abnormal proliferation of keratinocytes. This proliferation could partly result from disturbances in vitamin A metabolism. Changes in psoriasis patients of the levels of retinol-binding protein 4 (RBP4), a carrier of retinol (vitamin A); transmembrane protein stimulated by retinoic acid 6 (STRA6); and other retinol metabolic molecules have not yet been fully established. Therefore, we investigated vitamin A-related proteins in mice with imiquimod (IMQ)-induced psoriasis.

Methods

Thirty mice were divided into four study groups: two groups underwent IMQ application for 3 or 6 days (groups A and B, respectively), and two groups underwent Vaseline application for 3 or 6 days (groups C and D, respectively). Blood and skin samples from both lesional and non-lesional areas of the mice were analyzed using enzyme-linked immunosorbent assays, hematoxylin and eosin staining, immunochemistry, real-time reverse transcription polymerase chain reaction, and RNA sequencing.

Results

IMQ-treated mice developed erythema, scales, and skin thickening. Compared with the control groups, IMQ-treated groups had the following changes: 1) interleukin (IL)-17A, IL-23, and tumor necrosis factor (TNF)-α levels were raised significantly in both serum and lesional skin (all p < 0.001); 2) retinol levels in lesional skin increased slightly (p = 0.364), but no change was evident in serum retinol levels; 3) STRA6 was upregulated in both lesional skin (p = 0.021) and serum (p = 0.034); 4) RBP4 levels were elevated in serum (p = 0.042), but exhibited only an increasing trend (p = 0.273) in lesional skin; and 5) proteins and enzymes that mediate retinoic acid formation and transformation were upregulated in lesional skin.

Conclusions

As the demand for vitamin A in psoriatic mice increased, retinol underwent relocation from the circulation to target tissues. RBP4, STRA6, and the transformation from retinol to retinoic acid were upregulated, which may be part of the mechanism of psoriasis skin lesion formation. We propose that a positive feedback mechanism was formed that maintained the severity of psoriasis.

Resistin-like Molecule α Provides Vitamin-A-Dependent Antimicrobial Protection in the Skin

Vitamin A deficiency increases susceptibility to skin infection. However, the mechanisms by which vitamin A regulates skin immunity remain unclear. Here, we show that resistin-like molecule α (RELMα), a small secreted cysteine-rich protein, is expressed by epidermal keratinocytes and sebocytes and serves as an antimicrobial protein that is required for vitamin-A-dependent resistance to skin infection. RELMα was induced by microbiota colonization of the murine skin, was bactericidal in vitro, and was protected against bacterial infection of the skin in vivo. RELMα expression required dietary vitamin A and was induced by the therapeutic vitamin A analog isotretinoin, which protected against skin infection in a RELMα-dependent manner. The RELM family member Resistin was expressed in human skin, was induced by vitamin A analogs, and killed skin bacteria, indicating a conserved function for RELM proteins in skin innate immunity. Our findings provide insight into how vitamin A promotes resistance to skin infection.

Transcriptome analysis of comb and testis from Rose-comb Silky chicken (R1/R1) and Beijing Fatty wild type chicken (r/r)

Rose-comb was one of the chicken comb-variants first used by Bateson and Punnet in 1902 to demonstrate Mendelian inheritance in animals. Rose-comb is a monogenic trait that has been widely described in chickens. It is caused by a large structural rearrangement that leads to mis-expression of transcription factor MNR2 on chromosome 7. Rose-comb has pleiotropic effects in homozygous roosters, which is associated with poor sperm mobility. It was postulated that this is caused by the disruption of the CCDC108 gene located at the distal inversion breakpoint. In this study, we did the transcriptional profiling of combs and testes from Rose-comb Silky (RS) (R1/R1) and Beijing Fatty (BF) wild type chickens (r/r) using RNA-seq. We obtained 68,694,797 unique mapped reads and over 80% of the chicken genes were covered for each sample. In combs, we found that differentially expressed genes (DEGs) were significantly enriched in the retinol metabolism (RPE65, CYP26A1, and CYP26C1) and hedgehog-signaling pathway (PTCH1, GLI1, and HHIP), while genes related to cell differentiation and morphogenesis were down-regulated in R1/R1 chickens, suggesting that the transient expression of MNR2 might affect the expression of these genes and influence the development of comb tissue. For testes, DEGs were significantly enriched in the GO terms of binding activates and mitochondrial oxidation-reduction reactions. Our results suggested that the CCDC108 might be functionally related with mitochondrial oxidation-reduction reactions and caused subfertility of roosters. Compared with the genome average, the degree of expression variations within the inversion region did not show significant differences. However, DEGs near the breakpoints showed greater expression variance. Our results demonstrated that the large-scale rearrangements affected the gene expression only around the breakpoint in this case.

Pivotal role of Acitretin nanovesicular gel for effective treatment of psoriasis: ex vivo-in vivo evaluation study

The goal of the current study was to explore the potential benefits of Acitretin (Act) nanovesicular gel as a prospective antipsoriatic topical delivery system counteracting the drug challenges in terms of its extremely low aqueous solubility, instability, skin irritation, and serious systemic adverse effects. Act-loaded niosomes were successfully developed, entirely characterized, and optimized. Further evaluation of the optimized formula was conducted regarding its stability and ex vivo cytotoxicity on different cell lines. The optimized niosomal vesicles were then incorporated in gel base matrix and investigated by sequential ex vivo (skin permeation and deposition) and in vivo (skin irritation and antipsoriatic activity using mouse tail model) experiments. The optimized Act-loaded niosomes (span 60:cholesterol molar ratio 1:1) were spherical in shape and exhibited the highest entrapment efficiency (90.32±3.80%) with appropriate nanosize and zeta potential of 369.73±45.45 nm and -36.33±1.80 mV, respectively. Encapsulation of the drug in the nanovesicles was further emphasized by differential scanning calorimetric and powder X-ray diffraction studies. After 3 months storage at 4±1°C, the optimized formula preserved its stability. Act nano niosomal gel produced a remarkable enhanced ex vivo permeation profile up to 30 h and significant drug deposition in the viable epidermal-dermal layers compared with those of Act gel. The pronounced antipsoriatic activity of the medicated nano niosomes was proved ex vivo in HaCaT cells (a keratinocyte cell line). Topical application of Act nano niosomal gel to mouse tail model further established its distinct in vivo antipsoriatic superiority in terms of significantly higher orthokeratosis, drug activity, and reduction in epidermal thickness compared with the control and other gel formulations. Also, negligible skin irritation and better skin tolerability of Act nanovesicular gel were revealed by primary irritation index and histopathologic examination.

Synthesis and activity of the salicylic acid ester of bakuchiol in psoriasis-surrogate keratinocytes and skin substitutes

BACKGROUND

Topical retinoids are effective in retarding skin ageing and restoring homeostasis in skin conditions such as psoriasis. However their adverse effects (AEs), which include irritation (retinoid dermatitis), photosensitivity and teratogenicity, limit their use and patient compliance. Development of retinoid analogues with minimal AEs would allow a broader and more compliant use.

AIM

To synthesise a novel molecule, bakuchiol salicylate (bakusylan), with a modulatory gene expression profile similar to retinoids, using as reference three prescription retinoids: tretinoin, tazarotene and adapalene.

METHODS

We hypothesized that because bakuchiol salicylate has a structure entirely different from existing retinoids, there would be at least a partial uncoupling of AEs from the skin-normalizing activity of this retinoid. This hypothesis was tested at the transcriptional level in psoriatic cytokine-treated cultures of keratinocytes and organotypic skin substitutes, using DNA microarrays and custom PCR arrays.

RESULTS

Evaluation of the gene expression profile of bakuchiol salicylate revealed elimination of several components of the retinoid-like proinflammatory response and teratogenic signature, without a substantial loss of normalizing potential. A possible mechanism of action, consisting of keratinocyte desensitization to psoriatic cytokine signalling through inhibition of the signal transducer and regulator of transcription (STAT)1/3/interferon inflammatory signal transduction axis was also identified.

CONCLUSION

Bipartite materials obtained by merging two skin-active entities with specific, complementary bioactivities, such as bakuchiol and salicylic acid, may yield a new class of functional retinoids.

Peroxisomes in Dermatology. Part II

Background:

Peroxisomes are small cellular organelles that were almost ignored for years because they were believed to play only a minor role in cellular functions. However, it is now known that peroxisomes play an important role in regulating cellular proliferation and differentiation as well as in the modulation of inflammatory mediators. In addition, peroxisomes have broad effects on the metabolism of lipids, hormones, and xenobiotics. Through their effects on lipid metabolism, peroxisomes also affect cellular membranes and adipocyte formation, as well as insulin sensitivity, and peroxisomes play a role in aging and tumorigenesis through their effects on oxidative stress.

Objective:

To review genetically determined peroxisomal disorders, especially those that particularly affect the skin, and some recent information on the specific genetic defects that lead to some of these disorders. In addition, we present some of the emerging knowledge of peroxisomal proliferator activator receptors (PPARs) and how ligands for these receptors modulate different peroxisomal functions. We also present information on how the discovery of PPARs, and the broad and diverse group of ligands that activate these members of the superfamily of nuclear binding transcription factors, has led to development of new drugs that modulate the function of peroxisomes.

Conclusion:

PPAR expression and ligand modulation within the skin have shown potential uses for these ligands in a number of inflammatory cutaneous disorders, including acne vulgaris, cutaneous disorders with barrier dysfunction, cutaneous effects of aging, and poor wound healing associated with altered signal transduction, as well as for side effects induced by the metabolic dysregulation of other drugs.

Retinoid X Receptor Agonists Upregulate Genes Responsible for the Biosynthesis of All-Trans-Retinoic Acid in Human Epidermis

UAB30 is an RXR selective agonist that has been shown to have potential cancer chemopreventive properties. Due to high efficacy and low toxicity, it is currently being evaluated in human Phase I clinical trials by the National Cancer Institute. While UAB30 shows promise as a low toxicity chemopreventive drug, the mechanism of its action is not well understood. In this study, we investigated the effects of UAB30 on gene expression in human organotypic skin raft cultures and mouse epidermis. The results of this study indicate that treatment with UAB30 results in upregulation of genes responsible for the uptake and metabolism of all-trans-retinol to all-trans-retinoic acid (ATRA), the natural agonist of RAR nuclear receptors. Consistent with the increased expression of these genes, the steady-state levels of ATRA are elevated in human skin rafts. In ultraviolet B (UVB) irradiated mouse skin, the expression of ATRA target genes is found to be reduced. A reduced expression of ATRA sensitive genes is also observed in epidermis of mouse models of UVB-induced squamous cell carcinoma and basal cell carcinomas. However, treatment of mouse skin with UAB30 prior to UVB irradiation prevents the UVB-induced decrease in expression of some of the ATRA-responsive genes. Considering its positive effects on ATRA signaling in the epidermis and its low toxicity, UAB30 could be used as a chemoprophylactic agent in the treatment of non-melanoma skin cancer, particularly in organ transplant recipients and other high risk populations.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Serum concentrations of interleukin-2 and tumour necrosis factor-α under cyclosporine versus acitretin treatment in plaque-type psoriasis

Objective

A prospective, randomized clinical study to compare the short-term effects of cyclosporin and acitretin on psoriasis severity, and serum interleukin (IL)-2 and tumour necrosis factor (TNF)-α concentrations.

Methods

Patients with moderate-to-severe plaque-type psoriasis were randomly assigned to receive either 3 mg/kg per day cyclosporine or 0.3–0.5 mg/kg per day acitretin for 8 weeks. Disease severity (psoriasis area severity index [PASI] score) and serum IL-2 and TNF-α concentrations were determined before and after treatment.

Results

PASI scores and serum IL-2 and TNF-α concentrations were significantly decreased after treatment with either cyclosporine ( n = 21) or acitretin ( n = 25). There were no statistically significant between-group differences in any parameter.

Conclusions

Acitretin and cyclosporine are equally effective in the treatment of moderate-to-severe plaque-type psoriasis.

Cystoid macular edema associated with acitretin

Cystoid macular edema represents a "final common pathway" response of the retina to a variety of insults. It has been reported in association with vascular problems, inflammatory conditions, inherited diseases, tractional problems, intraocular surgery and medications. We report a case of cystoid macular edema associated with acitretin in a 65-year-old woman and document its resolution with optical coherence tomography (OCT).

Narrow-band ultraviolet B phototherapy versus broad-band ultraviolet B or psoralen-ultraviolet A photochemotherapy for psoriasis

BACKGROUND

The most commonly used types of phototherapy for treating psoriasis are narrow-band ultraviolet B (NB-UVB); broad-band ultraviolet B (BB-UVB), which includes selective (delivering radiation with a wavelength range of 305 to 325 nm) and conventional BB-UVB (280 to 320 nm); and psoralen ultraviolet A photochemotherapy (oral or bath PUVA). There is substantial controversy regarding their efficacy when compared with each other.

OBJECTIVES

To assess the effects of narrow-band ultraviolet B phototherapy versus broad-band ultraviolet B or psoralen ultraviolet A photochemotherapy for psoriasis.

SEARCH METHODS

We searched the following databases up to August 2013: the Cochrane Skin Group Specialised Register, CENTRAL in The Cochrane Library (2013, Issue 7), MEDLINE (from 1946), and EMBASE (from 1974). We searched the following databases up to November 2012: CNKI (from 1974) and CBM (from 1978). We also searched trials registers and the OpenGrey database.

SELECTION CRITERIA

We included all randomised controlled trials (RCTs) that compared NB-UVB phototherapy with BB-UVB or PUVA for treating psoriasis, which included chronic plaque psoriasis (CPP), guttate psoriasis (GP), and palmoplantar psoriasis (PPP).

DATA COLLECTION AND ANALYSIS

Two review authors independently conducted the study selection, 'Risk of bias' assessment, and data extraction.

MAIN RESULTS

We included 13 RCTs, with a total of 662 participants. We report the results of intention-to-treat analyses (ITT) here. Our primary outcomes of interest were as follows: Participant-rated global improvement, Percentage of participants reaching Psoriasis Area and Severity Index (PASI) 75 (which meant equal to or more than 75% reduction in PASI score), Withdrawal due to side-effects, and Clearance rate.In one RCT of NB-UVB compared with oral PUVA in participants with CPP, the difference in PASI 75 was not statistically significant (risk ratio (RR) 0.91, 95% confidence interval (CI) 0.63 to 1.32; N = 51; low quality). In three other RCTs of CPP, the clearance rates were inconsistent because in one, there was no difference between the groups (RR 1.01, 95% CI 0.91 to 1.12; N = 54), and in the other two, the clearance rates were statistically significantly in favour of oral PUVA: RR 0.66, 95% CI 0.47 to 0.93; N = 93 and RR 0.75, 95% CI 0.59 to 0.96; N = 100, respectively. Pooled data from these three studies indicated that withdrawals due to adverse events were not significantly different between either group (RR 0.71, 95% CI 0.20 to 2.54; N = 247; low quality).The evidence from the comparison of NB-UVB with bath PUVA in terms of clearance rate for CPP was also inconsistent: Pooled data from two left-right body comparison RCTs found no significant difference between the NB-UVB and bath PUVA groups (RR 1.79, 95% CI 0.46 to 6.91; N = 92; low quality), while a parallel RCT favoured bath PUVA (RR 0.18, 95% CI 0.05 to 0.71; N = 36; low quality).In participants with PPP, one RCT found there were no significant differences between NB-UVB treated sides and topical PUVA treated sides in terms of clearance rate (RR 0.09, 95% CI 0.01 to 1.56; N = 50; low quality).Two RCTs found NB-UVB plus retinoid (re-NB-UVB) and PUVA plus retinoid (re-PUVA) had similar effects for treating people with CPP or GP in terms of clearance rate (RR 0.93, 95% CI 0.79 to 1.10; N = 90; low quality).One RCT in people with CPP found no significant differences between NB-UVB and selective BB-UVB in terms of clearance rate (RR 1.40, 95% CI 0.92 to 2.13; N = 100; low quality) and withdrawals due to adverse events (RR 3.00, 95% CI 0.32 to 27.87; N = 100; low quality).No studies reported our primary outcomes for NB-UVB compared with conventional BB-UVB.

AUTHORS' CONCLUSIONS

Current evidence is very heterogeneous and needs to be interpreted with caution. The clearance rate between oral PUVA and NB-UVB is inconsistent among the included studies. Evidence regarding NB-UVB versus bath PUVA is also inconsistent. Re-NB-UVB and re-PUVA are similarly effective for treating people with CPP or GP. In practice, NB-UVB may be more convenient to use since exogenous photosensitiser is not required before phototherapy.NB-UVB is considered ineffective for PPP in clinical practice, and a small RCT did not detect a statistically significant difference between NB-UVB and topical PUVA for clearing PPP. NB-UVB seemed to be similar to selective BB-UVB for clearing CPP.Larger prospective studies are needed to confirm the long-term safety of NB-UVB.

Allergen-induced dermatitis causes alterations in cutaneous retinoid-mediated signaling in mice

Nuclear receptor-mediated signaling via RARs and PPARδ is involved in the regulation of skin homeostasis. Moreover, activation of both RAR and PPARδ was shown to alter skin inflammation. Endogenous all-trans retinoic acid (ATRA) can activate both receptors depending on specific transport proteins: Fabp5 initiates PPARδ signaling whereas Crabp2 promotes RAR signaling. Repetitive topical applications of ovalbumin (OVA) in combination with intraperitoneal injections of OVA or only intraperitoneal OVA applications were used to induce allergic dermatitis. In our mouse model, expression of IL-4, and Hbegf increased whereas expression of involucrin, Abca12 and Spink5 decreased in inflamed skin, demonstrating altered immune response and epidermal barrier homeostasis. Comprehensive gene expression analysis showed alterations of the cutaneous retinoid metabolism and retinoid-mediated signaling in allergic skin immune response. Notably, ATRA synthesis was increased as indicated by the elevated expression of retinaldehyde dehydrogenases and increased levels of ATRA. Consequently, the expression pattern of genes downstream to RAR was altered. Furthermore, the increased ratio of Fabp5 vs. Crabp2 may indicate an up-regulation of the PPARδ pathway in allergen-induced dermatitis in addition to the altered RAR signaling. Thus, our findings suggest that ATRA levels, RAR-mediated signaling and signaling involved in PPARδ pathways are mainly increased in allergen-induced dermatitis and may contribute to the development and/or maintenance of allergic skin diseases.

Guidelines for the use of acitretin in psoriasis. Psoriasis Group of the Spanish Academy of Dermatology and Venereology

Phototherapy, classic systemic treatments (methotrexate, acitretin, and ciclosporin), and biologic agents (etanercept, infliximab, adalimumab, and ustekinumab) constitute a broad therapeutic arsenal that increases the likelihood of achieving control of severe and extensive disease in patients with psoriasis. Acitretin continues to be a very valuable tool in both monotherapy, in which it is combined with other systemic treatments (classic or biologic), and in sequential therapy. Thanks to its lack of a direct immunosuppressive effect and its ability to achieve a long-term response, acitretin has an important role in the treatment of psoriasis, although this has not always been acknowledged in relevant treatment guidelines. We present consensus guidelines for the use of acitretin in psoriasis drawn up by the Psoriasis Group of the Spanish Academy of Dermatology and Venereology. These guidelines provide a detailed account of acitretin, including pharmacological properties, indications and contraindications, adverse effects, and factors that should be taken into account to enhance the safe use of this drug. They also propose treatment strategies for use in routine clinical practice. The overall aim of these guidelines is to define the criteria for the use and management of acetretin in psoriasis.

Regulation of retinoid-mediated signaling involved in skin homeostasis by RAR and RXR agonists/antagonists in mouse skin

Endogenous retinoids like all-trans retinoic acid (ATRA) play important roles in skin homeostasis and skin-based immune responses. Moreover, retinoid signaling was found to be dysregulated in various skin diseases. The present study used topical application of selective agonists and antagonists for retinoic acid receptors (RARs) α and γ and retinoid-X receptors (RXRs) for two weeks on mouse skin in order to determine the role of retinoid receptor subtypes in the gene regulation in skin. We observed pronounced epidermal hyperproliferation upon application of ATRA and synthetic agonists for RARγ and RXR. ATRA and the RARγ agonist further increased retinoid target gene expression (Rbp1, Crabp2, Krt4, Cyp26a1, Cyp26b1) and the chemokines Ccl17 and Ccl22. In contrast, a RARα agonist strongly decreased the expression of ATRA-synthesis enzymes, of retinoid target genes, markers of skin homeostasis, and various cytokines in the skin, thereby markedly resembling the expression profile induced by RXR and RAR antagonists. Our results indicate that RARα and RARγ subtypes possess different roles in the skin and may be of relevance for the auto-regulation of endogenous retinoid signaling in skin. We suggest that dysregulated retinoid signaling in the skin mediated by RXR, RARα and/or RARγ may promote skin-based inflammation and dysregulation of skin barrier properties.

Evaluation of plasma vitamin A and E levels and tear film changes in patients with psoriasis vulgaris

Purpose

To evaluate whether alterations in plasma vitamin A and E levels in patients with psoriasis have an effect on tear film changes.

Methods

Sixty-two eyes of 31 patients with psoriasis vulgaris (Group A) and 74 eyes of 37 age- and gender-matched control subjects (Group B) were included in the study. Ocular and medical histories and dietary habits were obtained from each patient. The tear film break-up time (TBUT), the Schirmer 1 test results and plasma vitamin A and E levels were evaluated.

Results

The mean Schirmer 1 test score was 14.76 ± 6.12 mm/5 min in Group A and 15.69 ± 3.10 mm/5 min in Group B. The mean plasma levels of vitamins A and E in Groups A and B were 1.86 ± 0.62 µmol/L and 1.88 ± 0.65 µmol/L vs. 26.21 ± 5.13 µmol/L and 27.19 ± 8.89 µmol/L, respectively. The Schirmer 1 test results and plasma vitamin A and E levels were not found to be significantly different between the groups (p > 0.05). The mean TBUT was 9.94 ± 6.18 seconds in Group A and 14.47 ± 5.65 seconds in Group B, a significant difference (p < 0.05). No correlation existed between plasma vitamin A and E levels, TBUT or the severity and duration of the disease (p > 0.05).

Conclusions

Plasma vitamin A and E levels do not seem to be related to tear film changes in patients with psoriasis vulgaris.

Pharmacologically active drug metabolites: impact on drug discovery and pharmacotherapy

Metabolism represents the most prevalent mechanism for drug clearance. Many drugs are converted to metabolites that can retain the intrinsic affinity of the parent drug for the pharmacological target. Drug metabolism redox reactions such as heteroatom dealkylations, hydroxylations, heteroatom oxygenations, reductions, and dehydrogenations can yield active metabolites, and in rare cases even conjugation reactions can yield an active metabolite. To understand the contribution of an active metabolite to efficacy relative to the contribution of the parent drug, the target affinity, functional activity, plasma protein binding, membrane permeability, and pharmacokinetics of the active metabolite and parent drug must be known. Underlying pharmacokinetic principles and clearance concepts are used to describe the dispositional behavior of metabolites in vivo. A method to rapidly identify active metabolites in drug research is described. Finally, over 100 examples of drugs with active metabolites are discussed with regard to the importance of the metabolite(s) in efficacy and safety.

Retinyl palmitate–loaded poly(lactide-co-glycolide) nanoparticles for the topical treatment of skin diseases

Nanoparticles were prepared with poly(lactide- co-glycolide), Pluronic F127, and phospholipids and loaded with retinyl palmitate. Morphology and physicochemical properties of these nanoparticles were determined by atomic force microscopy, light scattering, and zeta potential. The elasticity and deformability of the nanoparticles were correlated to Tg values measured by differential scanning calorimetry. The in vitro cytotoxicity and genotoxicity of the nanosystems were determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, cell membrane asymmetry, and Ames tests with BALB/3T3 mouse embryo fibroblasts and HaCaT human keratinocytes cell lines. The reactive oxygen species levels and cytokine production in response to the exposure of cells to these nanoparticles were investigated, as well as the penetration in human skin culture.

The use of retinoids in ovarian cancer: a review of the literature

Ovarian cancer is the deadliest of all gynecologic malignancies. The search for novel treatment modalities to augment traditional chemotherapy and improve quality of life is ongoing. Retinoids, a class of compounds composed of vitamin A, its natural derivatives, and synthetic analogs, have been studied extensively in both the prevention and treatment of gynecologic malignancies. In this article, we reviewed preclinical studies and clinical trials conducted using retinoids in ovarian cancer.

Keratins 2 and 4/13 in reconstituted human skin are reciprocally regulated by retinoids binding to nuclear receptor RARalpha

Disorders of keratinization are often treated with vitamin A derivatives (retinoids) which affect keratinocyte differentiation, including keratin (KRT) gene expression. In vivo, suprabasal keratinocytes normally express only keratin (K) 1, K2 and K10, but after topical application of all-trans retinoic acid (ATRA), the granular cells will additionally express K4 and K13, i.e. keratins normally present in oral mucosa and in cultured epidermal keratinocytes. To learn more about the retinoid regulation of keratin expression under in vivo-like conditions, we cultured keratinocytes on de-epidermized dermis in only 0.5% serum. These cells produce a normal-looking epidermis that expresses high mRNA levels of KRT1, KRT2 and KRT10, but minimal amounts of KRT4 and KRT13. Addition of ATRA to the medium for 48 h caused a dose-dependent increase in KRT4/KRT13 and a down-regulation of KRT2 mRNA. An increase in K4 protein was also found. The response was greater than the up-regulation of another retinoid-regulated gene, CRABPII. By studying 10 retinoids with different affinities for the retinoic acid receptors (RAR) and retinoid X receptors (RXR) isoforms, the reciprocal expression of KRT2 and KRT4/KRT13 could be connected with agonists for RARalpha. Two of these agonists, CD336/Am580 and CD2081, altered the expression profile with similar potency as the pan-RAR agonists ATRA and CD367. Co-addition of a pan-RAR antagonist (CD3106/AGN193109) markedly inhibited the induction of KRT4/KRT13 expression, whereas the down-regulation of KRT2 was less affected. In conclusion, RARalpha agonists elicit a reciprocal modulation of KRT2 and KRT4/KRT13 expression in human epidermis, but whether or not the keratin genes also possess RARalpha-specific regulatory elements is still unclear.

Management of psoriasis: the position of retinoid drugs

Oral synthetic retinoids have been established as effective systemic therapy for psoriasis since their introduction for clinical use in the 1970s; a compound for topical use, tazarotene has been recently marketed. Despite the demonstrated clinical success of retinoid therapy in psoriasis, its mechanism of action has not been fully elucidated, and investigators are confronted with two paradoxes. One is that the binding of retinoids to nuclear retinoic acid receptors (RARs) does not match their therapeutic efficacy: acitretin activates the three receptor subtypes, RAR-alpha, -beta and -gamma, without measurable receptor binding, whereas tazarotene preferentially binds to and activates RAR-beta and -gamma in preference to RAR-alpha. The other is that there is already increased formation of retinoic acid in the psoriatic lesion. Answering these questions should result in better use of these drugs in the treatment of psoriasis. Oral administration of acitretin remains one of the first therapeutic choices for severe psoriasis, particularly in association with ultraviolet light therapy, of which it may decrease the carcinogenic risk. Topical tazarotene is suitable for moderate plaque psoriasis. Its efficacy and tolerability can be enhanced by the addition of topical corticosteroids; its irritative potential is counterbalanced by a sustained therapeutic effect after the treatment is stopped.

Psoriasis: evolution of pathogenic concepts and new therapies through phases of translational research

Psoriasis is perhaps unique for a disease studied through translational science in that there is not an accepted animal model, yet many rounds of bidirectional translation have taken place that have helped to define disease pathogenesis and to advance therapy. In this review, we illustrate the evolution of new pathogenic concepts and the testing of new therapeutic agents through translational research in humans. We present a current view of disease pathogenesis that stems from research in patients and animal models, but with the perspectives (i) that disease models can advance or hinder the overall translational enterprise and (ii) that the research process must be firmly grounded in the pathophysiology of the actual human condition.

Systemic retinoid therapy: a status report on optimal use and safety of long-term therapy

Systemic retinoids are an important component of the dermatology treatment armamentarium offering unique therapeutic properties, and are widely used to treat a large spectrum of skin disorders. Rational selection of candidates for treatment, knowledge regarding appropriate and optimal use, awareness of common and uncommon potential adverse reactions, and proper use of clinical and laboratory monitoring can result in effective and safe treatment of several severe skin disorders that impact poorly on the overall health and quality of life of affected patients.

Topical immunomodulation: modes of action with clinical correlation

Many classes and preparations of immunomodulators are available to the clinician, serving as stimulatory or inhibitory influences on a variety of disease states. To maximize their efficacy, it is important for the clinician to take a step back from the usual routine of treating symptoms and consider the immune processes that took place to create inflammation, tumors, or responses to infections. From there, after considering the short-term and long-term consequences of the treatment, one can match the immune profile of the disease to the treatment. Most importantly, immunomodulators provide the opportunity to do what is best for the patient at that time, as well as for control of the future of the disease, whether it is acute or chronic.

The evaluation of psoriasis therapy with biologics leads to a revision of the current view of the pathogenesis of this disorder

Psoriasis is a common chronic, recurring skin disease that is characterised by typical macroscopic and microscopic skin alterations. It is widely accepted that the immune system plays an important role in the pathogenesis of this disorder. Since the early 1990s, the dominant role of a subpopulation of T cells, so-called T1 cells, and their prominent cytokine IFN-gamma has been assumed in the pathogenesis of psoriasis. Surprisingly, the comparison of the therapeutic success of treatments with recombinant proteins directed against defined immunological structures shows that those that directly affect T cells (alefacept, efalizumab, Hu-max-CD4, OKTcdr4a) were clearly less effective than those targeting TNF-alpha (etanercept, adalimumab, infliximab). For this reason, the authors critically re-evaluated the view of psoriasis pathogenesis and postulate that in the majority of patients the T1 cells do not play a dominant role in the clinical, visible stage of this disease.

The effect of various methods of psoriasis treatment on somatotrophin axis hormones in serum

OBJECTIVE

To investigate the effect of pharmacotherapy and phototherapy on the concentration of hormones of the somatotrophin axis [growth hormone (GH), insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3)] in the serum of patients with psoriasis in exacerbation and remission.

METHODS

GH and IGFBP-3 in serum were determined by immunoradiometric assay (IRMA), and IGF-I concentrations - by radioimmunological assay (RIA). The dermatological state was assessed by the psoriasis area and severity index (PASI).

RESULTS

There was no significant difference in the GH concentrations in patients both in exacerbation and remission, irrespective of therapy applied. However, in the group treated by phototherapy a significant increase in IGFBP-3 secretion was observed, whereas in the group treated with cyclosporin A - a significant increase in IGF-I secretion was observed in remission.

CONCLUSION

Different methods of treatment have different effects on the secretion of somatotrophin axis hormones, but generally the hormone concentrations do not return to the values observed in healthy people. The therapeutic actions of the drugs concerned are not fully known and require further investigations.

Carbazole Is a Naturally Occurring Inhibitor of Angiogenesis and Inflammation Isolated from Antipsoriatic Coal Tar

Coal tar is one of the oldest and an effective treatment for psoriasis. Coal tar has been directly applied to the skin, or used in combination with UV light as part of the Goeckerman treatment. The use of coal tar has caused long-term remissions in psoriasis, but has fallen out of favor because the treatment requires hospitalization and coal tar is poorly acceptable aesthetically to patients. Thus, determining the active antipsoriatic component of coal tar is of considerable therapeutic interest. We fractionated coal tar into its components, and tested them using the SVR angiogenesis inhibitor assay. Treatment of SVR endothelial cells with coal tar fractions resulted in the isolation of a single fraction with antiangiogenic activity. The active antiangiogenic compound in coal tar is carbazole. In addition to antiangiogenic activity, carbazole inhibited the production of inflammatory IL-15 by human mononuclear cells. IL-15 is elevated in psoriasis and is thought to contribute to psoriatic inflammation. Carbazole treatment also reduced activity of inducible nitric oxide synthase (iNOS), which is proinflammatory and elevated in psoriasis. The effect of carbazole on upstream pathways in human psoriasis was determined, and carbazole was shown to inhibit signal transducer and activator of transcription (stat)3-mediated transcription, which has been shown to be relevant in human psoriasis. IL-15, iNOS, and stat3 activation require the activation of the small GTPase rac for optimal activity. Carbazole was found to inhibit rac activation as a mechanism for its inhibition of downstream inflammatory and angiogenic pathways. Given its antiangiogenic and anti-inflammatory activities, carbazole is likely a major component of the antipsoriatic activity of coal tar. Carbazole and derivatives may be useful in the therapy of human psoriasis.

Single Crystal and Powder Diffraction Characterization of Three Polymorphic Forms of Acitretin

Acitretin [all-trans-9-(4-methoxy-2,3,6-trimethylphenyl)-3,7-dimethyl-2,4,6,8-nonatetraenoic acid or 3-methoxy-2-methyl-17-nor-1,2,3,4-tetradehydroretinoic acid], a widely marketed oral synthetic retinoid, introduced for clinical use as effective therapy against psoriasis, was found to crystallize in three polymorphic modifications (hereafter, I, II, and III), the crystal structures of which have been determined by single-crystal diffractometry (form I) or X-ray powder diffraction methods (form II and III) from conventional laboratory data only. In these latter cases, real space techniques (simulated annealing and whole-profile pattern matching) have been employed. Polymorph I crystallizes in space group P2(1), Z = 8, with unit cell parameters a = 7.894(1), b = 58.454(6), c = 8.161(1) angstroms, beta = 102.04(1) degrees, and V = 3682.9(8) angstroms3. Polymorph II crystallizes in space group P2(1)/n, Z = 4, with unit cell parameters a = 13.999(2), b = 10.714(1), c = 12.465(2) angstroms, beta = 98.76(5) degrees, and V = 1847.9(3) angstroms3. Polymorph III crystallizes in space group P2(1)/c, Z = 4, with unit cell parameters a = 3.0751(4), b = 4.0487(4), c = 14.956(2) angstroms, beta = 100.41(7) degrees, and V = 1831.3(4) angstroms3. Polymorph I, found to be identical with that deposited in the European Pharmacopeia, shows four crystallographically independent Acitretin molecules, arranged in pairs through conventional hydrogen-bonded carboxylic dimers; also in form II, carboxylic dimers are observed, located on crystallographic inversion centres, while in form III, a catameric arrangement of the carboxylic residues, winding up about the rather short monoclinic axis, generates one-dimensional chains of hydrogen-bonded Acitretin molecules. Thermal analysis showed that form I can be quantitatively transformed into form II by moderate heating near 200 degrees C, under vacuum. These results show that ab initio structural studies from conventional laboratory X-ray powder diffraction (XRPD) data are fully providing the opportunity to investigate the structural aspects of moderately complex substances also in the absence of single crystals, disclosing the crystal chemistry of a few polymorphs of pharmaceutically relevant species.

Increasing the intracellular availability of all-trans retinoic acid in neuroblastoma cells

Recent data indicate that isomerisation to all-trans retinoic acid (ATRA) is the key mechanism underlying the favourable clinical properties of 13-cis retinoic acid (13cisRA) in the treatment of neuroblastoma. Retinoic acid (RA) metabolism is thought to contribute to resistance, and strategies to modulate this may increase the clinical efficacy of 13cisRA. The aim of this study was to test the hypothesis that retinoids, such as acitretin, which bind preferentially to cellular retinoic acid binding proteins (CRABPs), or specific inhibitors of the RA hydroxylase CYP26, such as R116010, can increase the intracellular availability of ATRA. Incubation of SH-SY5Y cells with acitretin (50 μM) or R116010 (1 or 10 μM) in combination with either 10 μM ATRA or 13cisRA induced a selective increase in intracellular levels of ATRA, while 13cisRA levels were unaffected. CRABP was induced in SH-SY5Y cells in response to RA. In contrast, acitretin had no significant effect on intracellular retinoid concentrations in those neuroblastoma cell lines that showed little or no induction of CRABP after RA treatment. Both ATRA and 13cisRA dramatically induced the expression of CYP26A1 in SH-SY5Y cells, and treatment with R116010, but not acitretin, potentiated the RA-induced expression of a reporter gene and CYP26A1. The response of neuroblastoma cells to R116010 was consistent with inhibition of CYP26, indicating that inhibition of RA metabolism may further optimise retinoid treatment in neuroblastoma.

Differential regulation of Cu, Zn- and Mn-superoxide dismutases by retinoic acid in normal and psoriatic human fibroblasts

Superoxide dismutases' (SODs) expression is altered in several diseases including Alzheimer, atherosclerosis, cancer and psoriasis. Previously, we reported a marked increase in Mn-SOD and Cu,Zn-SOD functional activity in human dermal psoriatic fibroblasts. As retinoic acid (RA) has been used in the treatment of psoriasis and a mechanism for its beneficial effects is not understood, we investigated the effects of RA on SOD mRNA and protein expression levels in human normal and psoriatic fibroblasts. Prior to RA exposure, Cu,Zn-SOD protein and mRNA levels were similar in normal compared to psoriatic fibroblasts while Mn-SOD protein and mRNA levels were increased in psoriatic cells. However, in contrast to normal fibroblasts, exposure of psoriatic fibroblasts to 1 microM RA down-regulated Mn-SOD mRNA, and also decreased Mn-SOD activity by approximately 80% with no change in Mn-SOD protein levels. In contrast, Cu,Zn-SOD protein and enzymatic activity were modestly reduced by RA treatment in both normal and psoriatic fibroblasts. Furthermore, RA treatment of psoriatic fibroblasts also caused a decrease in Cu,Zn-SOD steady-state mRNA levels. These results indicate that RA can serve as a regulatory agent to down-regulate the steady-state levels of both Mn-SOD and Cu,Zn-SOD in psoriatic cells. These findings offer a new model for the antiinflammatory activity of RA when used in the treatment of psoriasis.

Novel pharmacological approaches in the treatment of psoriasis

Progress in the understanding of psoriasis as a T-cell mediated inflammatory disease has led to the development of new immunomodulatory therapies. Currently the main focus is on the so-called biologics (or biological agents), including fusion proteins, monoclonal antibodies, cytokines and selective receptors. They mainly target single steps in the complex cascade of humoral and cellular inflammatory immuno-mechanisms that finally lead to the accelerated growth of epidermal and vascular cells in the psoriatic lesions. The most promising and advanced biological agents are discussed along with their influence on the critical pathophysiological steps in psoriasis, including depletion of T cells, blockade of initial T-cell activation and T-cell receptor (TCR) stimulation, blockade of costimulatory signals and T-cell proliferative signals as well as restoration of the T helper type 1 (Th1)/Th2 balance by diminishing type 1 cytokines and administration of type 2 cytokines. In addition to the biological agents, further development of 'classical' dermatological therapies, such as retinoids, or the discovery of new indications for non-dermatological agents contribute to the novel pharmacological approaches in the treatment of psoriasis.

Retinoid therapy for psoriasis

This article focuses on the treatment of psoriasis with acitretin, the only systemic retinoid approved for psoriasis, and also briefly discusses its predecessor, etretinate, which was replaced by acitretin in 1997 and is no longer available. The use of topical tazarotene is also discussed in detail. Combination therapy of retinoids, both topical and systemic,with phototherapy and other therapeutic agents is described. In addition, new retinoid analogues that are undergoing clinical investigation are mentioned. Finally, potential toxicities and adverse effects associated with retinoids are discussed.

Vitamin D3 induces caspase-14 expression in psoriatic lesions and enhances caspase-14 processing in organotypic skin cultures

Caspase-14 is a nonapoptotic caspase family member whose expression in the epidermis is confined to the suprabasal layers, which consist of differentiating keratinocytes. Proteolytic activation of this caspase is observed in the later stages of epidermal differentiation. In psoriatic skin, a dramatic decrease in caspase-14 expression in the parakeratotic plugs was observed. Topical treatment of psoriatic lesions with a vitamin D3 analogue resulted in a decrease of the psoriatic phenotype and an increase in caspase-14 expression in the parakeratotic plugs. To investigate whether vitamin D3 directly affects caspase-14 expression levels, we used keratinocyte cell cultures. 1alpha,25-Dihydroxycholecalciferol, the biologically active form of vitamin D3, increased caspase-14 expression, whereas retinoic acid inhibited it. Moreover, retinoic acid repressed the vitamin D3-induced caspase-14 expression level. In addition, the use of organotypic skin cultures demonstrated that 1alpha,25-dihydroxycholecalciferol enhanced epidermal differentiation and caspase-14 activation, whereas retinoic acid completely blocked caspase-14 processing. Our data indicate that caspase-14 plays an important role in terminal epidermal differentiation, and its absence may contribute to the psoriatic phenotype.

Systemic treatment of psoriatic patients with bexarotene decreases epidermal proliferation and parameters for inflammation, and improves differentiation in lesional skin

BACKGROUND

Bexarotene, a novel synthetic retinoid X receptor (RXR)-selective retinoid, has been reported to have antiproliferative and apoptotic stimulating effects in cutaneous T-cell lymphoma. In benign, hyperproliferative, and retinoid sensitive disorders, such as psoriasis, bexarotene has not been evaluated so far and no information on these parameters is available.

OBJECTIVE

In the present study, immunohistochemical parameters for proliferation, differentiation, inflammation, and apoptosis were investigated in a group of bexarotene-treated psoriatic patients.

METHODS

Twenty-nine patients with plaque-type psoriasis were treated for 12 weeks with oral bexarotene in four dose-defined treatment panels. Treatment was initiated in the following consecutive order: 1.0 mg/kg/day, 2.0 mg/kg/day, 0.5 mg/kg/day, and 3.0 mg/kg/day. Biopsies for immunohistochemical analysis were taken at the baseline and after 12 weeks of treatment.

RESULTS

Significant reductions in Ki-67, keratin 16, transglutaminase, dermal CD4, epidermal CD8, and inflammation scores were seen after bexarotene treatment in combination with a significant increase in keratin 10. No induction of keratin 13 and 19 and no alterations in apoptosis associated p53 expression were observed. Apart from a weak significant dose-response effect for Ki-67, no other significant dose-response effects were seen.

CONCLUSION

We have demonstrated efficacy of oral bexarotene in psoriasis in doses up to 3.0 mg/kg/day during 12 weeks of treatment for proliferation, differentiation, and inflammation parameters. Studies investigating higher doses of bexarotene in a larger number of patients are necessary to reveal potentially dose-related immunohistochemical effects of this new rexinoid and to elucidate the role of RXR-signaling in retinoid-associated keratin expression.

Peroxisome proliferator-activated receptor (PPAR)-beta/delta stimulates differentiation and lipid accumulation in keratinocytes

Peroxisome proliferator-activated receptor (PPAR) are nuclear hormone receptors that are activated by endogenous lipid metabolites. Previous studies have demonstrated that PPAR-alpha activation stimulates keratinocyte differentiation in vitro and in vivo, is anti-inflammatory, and improves barrier homeostasis. Recent studies have shown that PPAR-beta/delta activation induces keratinocyte differentiation in vitro. This study demonstrated that topical treatment of mice with a selective PPAR-beta/delta agonist (GW1514) in vivo had pro-differentiating effects, was anti-inflammatory, improved barrier homeostasis, and stimulated differentiation in a disease model of epidermal hyperproliferation [corrected]. In contrast to PPAR-alpha activation, PPAR-beta/deltain vivo did not display anti-proliferative or pro-apoptotic effects. The pro-differentiating effects persisted in mice lacking PPAR-alpha, but were decreased in mice deficient in retinoid X receptor-alpha, the major heterodimerization partner of PPAR. Furthermore, in vitro PPAR-beta/delta activation, aside from stimulating differentiation-related genes, additionally induced adipose differentiation-related protein (ADRP) and fasting induced adipose factor (FIAF) mRNA in cultures keratinocytes, which was paralleled by increased oil red O staining indicative of lipid accumulation, the bulk of which were triglycerides (TG). Comparison of differentially expressed genes between PPAR-beta/delta and PPAR-alpha activation revealed distinct profiles. Together, these studies indicate that PPAR-beta/delta activation stimulates keratinocyte differentiation, is anti-inflammatory, improves barrier homeostasis, and stimulates TG accumulation in keratinocytes.