Effects of 13-cis-retinoic acid, all-trans-retinoic acid, and acitretin on the proliferation, lipid synthesis and keratin expression of cultured human sebocytes in vitro

Thymic stromal lymphopoietin induces IL-4/IL-13 from T cells to promote sebum secretion and adipose loss

BACKGROUND

The cytokine TSLP promotes type 2 immune responses and can induce adipose loss by stimulating lipid loss from the skin through sebum secretion by sebaceous glands, which enhances the skin barrier. However, the mechanism by which TSLP upregulates sebaceous gland function is unknown.

OBJECTIVES

This study investigated the mechanism by which TSLP stimulates sebum secretion and adipose loss.

METHODS

RNA-sequencing analysis was performed on sebaceous glands isolated by laser capture microdissection and single-cell RNA-sequencing analysis was performed on sorted skin T cells. Sebocyte function was analyzed by histological analysis and sebum secretion in vivo and by measuring lipogenesis and proliferation in vitro.

RESULTS

This study found that TSLP sequentially stimulated the expression of lipogenesis genes followed by cell death genes in sebaceous glands to induce holocrine secretion of sebum. TSLP did not affect sebaceous gland activity directly. Rather, single-cell RNA-sequencing revealed that TSLP recruited distinct T-cell clusters that produce IL-4 and IL-13, which were necessary for TSLP-induced adipose loss and sebum secretion. Moreover, IL-13 was sufficient to cause sebum secretion and adipose loss in vivo and to induce lipogenesis and proliferation of a human sebocyte cell line in vitro.

CONCLUSIONS

This study proposes that TSLP stimulates T cells to deliver IL-4 and IL-13 to sebaceous glands, which enhances sebaceous gland function, turnover, and subsequent adipose loss.

Galectin-12 Regulates Immune Responses in the Skin through Sebaceous Glands

Sebaceous glands (SGs) are holocrine glands that produce sebum, which primarily contains lipids that help to maintain the barrier function of the skin. Dysregulated lipid production contributes to the progression of some diseases characterized by dry skin, including atopic dermatitis. Although the lipid production of SGs has been well-studied, few studies have assessed their role in skin immune responses. We found that SGs and sebocytes expressed IL-4 receptor and produced high levels of T helper 2-associated inflammatory mediators after IL-4 treatment, suggesting immunomodulatory effects. Galectin-12 is a lipogenic factor expressed in sebocytes that affects their differentiation and proliferation. Using galectin-12-knockdown sebocytes, we showed that galectin-12 regulated the immune response in cells exposed to IL-4 and promoted CCL26 expression by upregulating peroxisome proliferator-activated receptor-γ. Moreover, galectin-12 suppressed the expression of endoplasmic reticulum stress-response molecules, and CCL26 upregulation by IL-4 was reversed after sebocyte treatment with inducers of endoplasmic reticulum stress, suggesting that galectin-12 controls IL-4 signaling by suppressing endoplasmic reticulum stress. Using galectin-12-knockout mice, we showed that galectin-12 positively regulated the IL-4-induced enlargement of SGs and the development of an atopic dermatitis-like phenotype. Thus, galectin-12 regulates the skin immune response by promoting peroxisome proliferator-activated receptor-γ expression and suppressing endoplasmic reticulum stress in SGs.

β-1,4-Galactan suppresses lipid synthesis in sebaceous gland cells via TLR4

Sebum is a lipid mixture secreted from sebaceous glands of the skin. The excessive secretion of sebum causes acne vulgaris and seborrheic dermatitis, while its deficiency causes xerosis. Therefore, the appropriate control of sebum secretion is crucially important to keep the skin healthy. In the present study, we evaluated the effects of naturally occurring polysaccharides on lipid biosynthesis in hamster sebaceous gland cells. Among the tested polysaccharides, β-1,4-galactan, the main chain of type I arabinogalactan, most potently suppressed lipid synthesis in the sebaceous gland cells as analysed by oil red O staining. Toll-like receptor (TLR)4 inhibitors counteracted this suppressive effect and lipopolysaccharide, a TLR4 ligand, mimicked this effect, suggesting the involvement of the TLR4 signalling pathway. In the cells β-1,4-galactan significantly decreased mRNA levels of lipogenesis-related transcription factors (peroxisomeGraphical Abstract$\includegraphics{\bwartpath }$ proliferator-activated receptor γ and sterol regulatory element-binding protein 1) and enzymes (acetyl-CoA carboxylase and fatty acid synthase) as well as the glucose transporter GLUT4. Furthermore, β-1,4-galactan increased the production of lactic acid serving as a natural moisturizing factor and enhanced the proliferation of sebaceous gland cells. These results suggest potential of β-1,4-galactan as a material with therapeutic and cosmetic values for the skin.

Skin as an endocrine organ: A narrative review

Skin being the largest organ of the body, is equipped with numerous functional properties. Over the past few years, intricate research into the biology of skin has led to a gamut of discoveries. Skin is now regarded as one of the most vital endocrine organs. The skin contains equivalents of the hypothalamo-pituitary-adrenal axis, hypothalamo-pituitary-thyroid axis and the appendages produce multiple hormones such as Vitamin D, sex steroids, retinoids and opioids. In this article, we will explore the role of skin as a target and source of some of the hormones of the human body, and briefly touch on the clinical applications.

Effect of Genetic Polymorphisms of Human SLC22A3 in the 5'-flanking Region on OCT3 Expression and Sebum Levels in Human Skin

BACKGROUND

Human organic cation transporter 3 (OCT3,SLC22A3) mediates the uptake of many important endogenous substances and basic drugs, and has been identified as one of the transporters that are highly expressed in human skin. However, the mechanisms responsible for variability in mRNA expression, and the role of SLC22A3 in human skin is not clear.

OBJECTIVE

We examined the effects of the single nucleotide polymorphisms ofSLC22A3 on the variability in SLC22A3 expression and sebum levels in humans.

METHODS

Immunostaining of OCT3 in human skin was performed. We analyzed the association of promoter variants with the SLC22A3 mRNA expression levels in human skins. Luciferase, knockdown, chromatin immunoprecipitation (ChIP), electrophoretic mobility shift assay were employed to investigate transcriptional regulation of SLC22A3 expression. Effects of the identified variant on sebum levels were evaluated in healthy volunteers.

RESULTS

Immunohistochemistry revealed marked expressions of OCT3 in the basal epidermis, sebaceous glands, hair follicles, and sweat glands of human skin. SLC22A3 mRNA levels were significantly lower in skin samples with homozygotes for -1603A/A than in those for -1603 G/G. The analysis of p53 binding to -1603 G > A in the promoter ofSLC22A3 suggested that -1603 G > A down-regulates SLC22A3 gene expression by decreased p53 binding in the vicinity of the -1603 site. In humans, squalene levels in samples from the back at the baseline were significantly lower in homozygotes for -1603A/A than in those for -1603 G/G.

CONCLUSION

These results suggest that the genetic variant contributes to the variability of expression and activities of OCT3 in human skin.

[Nodulocystic eruption induced by sorafenib]

INTRODUCTION

Sorafenib is a multikinase inhibitor used in the treatment of hepatocellular carcinoma, advanced renal cell carcinoma, and differentiated thyroid carcinoma. Cutaneous adverse events are numerous and occur frequently.

PATIENTS AND METHODS

We present two cases of nodulocystic lesions associated with comedones in patients treated with sorafenib for hepatocellular carcinoma. In the first patient, a 64-year-old man, lesions appeared on the trunk one year after beginning sorafenib. Histopathological examination revealed a non-granulomatous, perivascular and perisudoral polymorphic cellular infiltrate associated with comedones and microcysts. These lesions progressed via inflammatory episodes interrupted by long periods of spontaneous remission without any specific treatment. In the second patient, a 53-year-old woman, a rash appeared on the buttocks three months after starting sorafenib and then spread to the lumbar region and thighs. Histopathological examination was consistent with granulomatous acne lesions. The initial treatment (oral tetracycline and zinc) given for 3 months proved ineffective. Patient follow-up over 3 years showed gradual regression without the appearance of any further lesions.

DISCUSSION

In the literature, several reports discuss acneiform rashes in patients treated with targeted therapy. In most cases, these lesions were papulopustular without retentional lesions. There are few reports of nodulocystic eruptions associated with comedones following sorafenib therapy. The mechanisms of emergence of these lesions seem to involve inhibition of the RAF pathway, C-KIT, and the PDGF signaling pathway.

Alterations in IL-4, IL-10 and IFN-γ levels synergistically decrease lipid content and protein expression of FAS and mature SREBP-1 in human sebocytes

When anti-acne alternatives from dietary and plant sources are ingested, systemic alterations of interleukin (IL)-4, IL-10, IL-12 and interferon (IFN)-γ, individually or simultaneously, are induced at a 0.1-10.0-fold (×) range of normal physiological concentrations (1×). However, little is known about the effects of these cytokines on excess sebum, a pathophysiological factor of acne development. In this study, human sebocytes were treated with 0.1-10.0× of IL-4, IL-10, IL-12 and IFN-γ for 3 or 5 days to elucidate the effects on lipid content. Treatment with individual cytokines decreased the lipid content at specific concentrations rather than in a concentration-dependent manner. Specifically, 5.0× of IL-4, 5.0× of IFN-γ (5.0IFN), and 0.5×, 5.0× and 10.0× of IL-10 for 3 days, and 0.5× of IL-4 (0.5IL4) for 5 days decreased lipid content to 87.6-93.0% of the control. Treatment with other concentrations of IL-4, IL-10 and IFN-γ, and 0.1-10.0× of IL-12 did not alter lipid content. Combined treatment with 0.5IL4, 5.0IFN and 0.5× of IL-10 for 3 or 5 days decreased the lipid content more than each individual treatment. However, this effect was more evident after 3 days, in parallel with decreased levels of triglycerides, cholesterol esters and free fatty acids, the major lipid compositions of sebocytes, and decreased protein expression of fatty acid synthase (FAS) and mature sterol response element-binding protein-1 (SREBP-1), the lipogenesis-related factors, without altered cell proliferation. We demonstrated that suppressed IL-4 and IL-10 with enhanced IFN-γ synergistically decreased lipid content and protein expression of FAS and mature SREBP-1 in human sebocytes.

Sebaceous-immunobiology is orchestrated by sebum lipids

The major role of sebaceous glands in mammals is to produce sebum, which coats the epidermis and the hair providing waterproofing, thermoregulation and photoprotection. However, as the need for these functions decreased along the evolutionary changes in humans, a relevant question has been raised: are sebaceous glands and sebum the remnants of our mammalian heritage or do they have overtaken a far more complex role in human skin biology? Trying to provide answers to this question, this review introduces the evolving field of sebaceous immunobiology and puts into the focus the pathways that sebum lipids use to influence the immune milieu of the skin. By introducing possible modifiers of sebaceous lipogenesis and discussing the – human-specific – alterations in composition and amount of sebum, the attribute of sebum as a sensitive tool, which is capable of translating multiple signalling pathways into the dermal micro environment is presented. Further their interaction with macrophages and keratinocytes involves sebum lipid fractions into disease pathogenesis, which could lead – on the other side – to the development of novel sebum-based therapeutic strategies.

Beyond acne: Current aspects of sebaceous gland biology and function

The sebaceous gland is most commonly found in association with a hair follicle. Its traditional function is the holocrine production of sebum, a complex mixture of lipids, cell debris, and other rather poorly characterized substances. Due to the gland's central role in acne pathogenesis, early research had focused on its lipogenic activity. Less studied aspects of the sebaceous gland, such as stem cell biology, the regulation of cellular differentiation by transcription factors, the significance of specific lipid fractions, the endocrine and specially the neuroendocrine role of the sebaceous gland, and its contribution to the innate immunity, the detoxification of the skin, and skin aging have only recently attracted the attention of researchers from different disciplines. Here, we summarize recent multidisciplinary progress in sebaceous gland research and discuss how sebaceous gland research may stimulate the development of novel therapeutic strategies targeting specific molecular pathways of the pathogenesis of skin diseases.

Acitretin

Background:

Hidradenitis suppurativa (HS) is a chronic, recurrent inflammatory disease of the pilosebaceous follicle that severely affects patients’ quality of life and can be challenging for clinicians to manage. A few case series have reported on the efficacy of acitretin monotherapy in the treatment of intractable HS.

Objective:

To assess the efficacy of acitretin for the treatment of intractable HS.

Methods:

A retrospective review was conducted involving all patients with HS who received acitretin between January 2011 and January 2015 in a tertiary academic medical center. All patients with HS who received acitretin, either as a monotherapy or as an adjuvant to other systemic medications, were included, and clinical response was assessed using the physician global scale.

Results:

Fourteen patients with HS (mean age 48 years [range 32-64 years]; 9 [64%] were men) received acitretin. Most patients (86%) had Hurley stage II or III disease. All patients had failed other standard systemic medications prior to initiating acitretin. Six patients (43%) received acitretin monotherapy, and 8 patients (57%) received acitretin as an adjuvant to other standard systemic medications. None of the patients who received acitretin monotherapy exhibited clinical improvements. Clinical improvements were observed in 7 of the 8 (87.5%) patients who received acitretin as an adjuvant to other systemic medications, with 3 patients (37.5%) exhibiting partial response and 4 patients (50%) exhibiting good response.

Conclusions and Relevance:

Acitretin monotherapy was ineffective for the treatment of intractable HS. Acitretin may be effective when used as an adjuvant to other systemic medications.

Hidradenitis Suppurativa: A Frequently Missed Diagnosis, Part 2: Treatment Options

Hidradenitis suppurativa (HS) is a chronic inflammatory disorder of the intertriginous area. Patients with HS have several challenges to their quality of life and activities of everyday living, including malodor, purulent discharge, and discomfort. There is often a delay in diagnosis and appropriate treatment. The need for cosmetically acceptable local treatments and dressing application makes this disease an important challenge for wound care specialists. The choice of optimal treatment varies depending on the disease severity, expert knowledge, the availability of an interprofessional team, and patient factors.

The P450 system and mTORC1 signalling in acne

In this issue, Hellmann-Regen et al. suggested that anti-acne effects of erythromycin and tetracyclines may be related to their inhibitory effect of cytochrome P450-mediated degradation of all-trans-retinoic acid (ATRA). We have recently proposed that all anti-acne agents function by attenuation of increased mTORC1 signalling. This commentary links the P450 system to mTORC1 regulation in acne. Drug-mediated induction of P450 activity or P450 mutants with increased catabolic activity may reduce cellular ATRA levels and FoxO1 expression, thus reducing FoxO-mediated mTORC1 inhibition. In contrast, agents blocking ATRA degradation such as erythromycin and tetracyclines may improve acne by increasing FoxO1 expression with consecutive inhibition of mTORC1 signalling.

Recent advances in acne pathogenesis: implications for therapy

Acne pathogenesis is a multifactorial process that occurs at the level of the pilosebaceous unit. While acne was previously perceived as an infectious disease, recent data have clarified it as an inflammatory process in which Propionibacterium acnes and innate immunity play critical roles in propagating abnormal hyperkeratinization and inflammation. Alterations in sebum composition, and increased sensitivity to androgens, also play roles in the inflammatory process. A stepwise approach to acne management utilizes topical agents for mild to moderate acne (topical retinoid as mainstay ± topical antibiotics) and escalation to oral agents for more resistant cases (oral antibiotics or hormonal agents in conjunction with a topical retinoid or oral isotretinoin alone for severe acne). Concerns over antibiotic resistance and the safety issues associated with isotretinoin have prompted further research into alternative medications and devices for the treatment of acne. Radiofrequency, laser, and light treatments have demonstrated modest improvement for inflammatory acne (with blue-light photodynamic therapy being the only US FDA-approved treatment). However, limitations in study design and patient follow-up render these modalities as adjuncts rather than standalone options. This review will update readers on the latest advancements in our understanding of acne pathogenesis and treatment, with emphasis on emerging treatment options that can help improve patient outcomes.

Downregulation of STRA6 expression in epidermal keratinocytes leads to hyperproliferation-associated differentiation in both in vitro and in vivo skin models

Retinoids are known to affect skin cell proliferation and differentiation and are key molecules that target retinoid and retinoic acid receptors (RXRs and RARs), leading to physiological and pharmacologic effects. Our aim was to elucidate the role of the retinol-binding protein receptor STRA6, mediating cellular uptake of retinol, on skin structure and function. Our results indicate that STRA6 is constitutively expressed in human epidermal keratinocytes and dermal fibroblasts and is regulated via RAR/RXR-mediated pathways. HaCaT (Human adult low Calcium high Temperature) cells with stable STRA6 knockdown (STRA6KD) showed increased proliferation. Consistently, human organotypic 3D skin models using stable STRA6KD HaCaT cells showed a significantly thicker epidermis and enhanced expression of activation, differentiation, and proliferation markers. The effects were reversible after treatment with free retinol. Human skin reconstitution employing STRA6KD HaCaT cells leads to massive epithelial thickening under in vivo conditions in SCID mice. We propose that STRA6KD could lead to cellular vitamin A deficiency in keratinocytes. Consequently, STRA6 has a role for regulating retinoid homeostasis and in helping to program signaling that drives proliferation and differentiation of human skin cells. By its influence on hyperproliferation-associated differentiation, STRA6 could also have a role in skin regeneration and could be a target for pharmacological approaches to improve wound healing.

Acne is an inflammatory disease and alterations of sebum composition initiate acne lesions

Hyperseborrhoea has been considered as a major aetiopathogenetic factor of acne. However, changes in sebaceous gland activity not only correlate with seborrhoea but also with alterations in sebum fatty acid composition. Current findings indicate that sebum lipid fractions with proinflammatory properties and inflammatory tissue cascades are associated in the process of the development of acne lesions. The oxidant/antioxidant ratio of the skin surface lipids and alterations of lipid composition are the main players in the induction of acne inflammation. Nutrition may influence the development of seborrhoea, the fractions of sebum lipids and acne. Acne is an inflammatory disease probably triggered, among others, by proinflammatory sebum lipid fractions.

Endogenous retinoids in the hair follicle and sebaceous gland

Vitamin A and its derivatives (retinoids) are critically important in the development and maintenance of multiple epithelial tissues, including skin, hair, and sebaceous glands, as shown by the detrimental effects of either vitamin A deficiency or toxicity. Thus, precise levels of retinoic acid (RA, active metabolite) are needed. These precise levels of RA are achieved by regulating several steps in the conversion of dietary vitamin A (retinol) to RA and RA catabolism. This review discusses the localization of RA synthesis to specific sites within the hair follicle and sebaceous gland, including their stem cells, during both homeostasis and disease states. It also discusses what is known about the specific roles of RA within the hair follicle and sebaceous gland. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.

Functional properties and substrate characterization of human CYP26A1, CYP26B1, and CYP26C1 expressed by recombinant baculovirus in insect cells

INTRODUCTION

The cytochrome P450 CYP26 family of retinoic acid (RA) metabolizing enzymes, comprising CYP26A1, CYP26B1, and CYP26C1 is critical for establishing patterns of RA distribution during embryonic development and retinoid homeostasis in the adult. All three members of this family can metabolize all trans-RA. CYP26C1 has also been shown to efficiently metabolize the 9-cis isomer of RA.

METHODS

We have co-expressed each of the CYP26 enzymes along with the NADPH-cytochrome P450 oxidoreductase using a baculovirus/Sf9 insect cell expression system to determine the enzymatic activities of these enzymes in cell free preparations and have established an in vitro binding assay to permit comparison of binding affinities of the three CYP26 enzymes.

RESULTS

We demonstrated that the expressed enzymes can efficiently coordinate heme, as verified by spectral-difference analysis. All CYP26s efficiently metabolized all-trans-RA to polar aqueous-soluble metabolites, and in competition experiments exhibited IC(50) values of 16, 27, and 15nM for CYP26A1, B1, and C1 respectively for all-trans-RA. Furthermore, this metabolism was blocked with the CYP inhibitor ketoconazole. CYP26C1 metabolism of all trans-RA could also be effectively competed with 9-cis RA, with IC(50) of 62nM, and was sensitive to ketoconazole inhibition.

DISCUSSION

CYP26 enzymes are functionally expressed in microsomal fractions of insect cells and stably bind radiolabeled RA isomers with affinities respecting their substrate specificities. We demonstrated that compared to CYP26A and CYP26B, only CYP26C1 was able to bind with high affinity to 9-cis-RA. These assays will be useful for the screening of synthetic substrates and inhibitors of CYP26 enzymes and may be applicable to other cytochrome P450s and their respective substrates.

An update on the role of the sebaceous gland in the pathogenesis of acne

The pathogenesis of acne, a disease of the pilosebaceous follicle and one of the most common chronic skin disorders, is attributed to multiple factors such as increased sebum production, alteration of the quality of sebum lipids, inflammatory processes, dysregulation of the hormone microenvironment, interaction with neuropeptides, follicular hyperkeratinisation and the proliferation of Propionibacterium acnes within the follicle. In particular, the sebaceous gland plays an exquisite role in the initiation of the disease as it possesses all the enzyme machinery for the production of hormones and cytokines. In addition, in response to the altered tissue environment in the pilosebaceous follicle as well as in answer to emotional fret, stress response system mechanisms with induction of central and local expression of neuropeptides, are also initiated. This review summarises the latest advances in understanding the role of sebaceous gland cells in the pathomechanism of acne.

Isotretinoin and FoxO1: A scientific hypothesis

Oral isotretinoin (13-cis retinoic acid) is the most effective drug in the treatment of acne and restores all major pathogenetic factors of acne vulgaris. isotretinoin is regarded as a prodrug which after isomerizisation to all-trans-retinoic acid (ATRA) induces apoptosis in cells cultured from human sebaceous glands, meibomian glands, neuroblastoma cells, hypothalamic cells, hippocampus cells, Dalton's lymphoma ascites cells, B16F-10 melanoma cells, and neuronal crest cells and others. By means of translational research this paper provides substantial indirect evidence for isotretinoin's mode of action by upregulation of forkhead box class O (FoxO) transcription factors. FoxOs play a pivotal role in the regulation of androgen receptor transactivation, insulin/insulin like growth factor-1 (IGF-1)-signaling, peroxisome proliferator-activated receptor-γ (PPArγ)- and liver X receptor-α (LXrα)-mediated lipogenesis, β-catenin signaling, cell proliferation, apoptosis, reactive oxygene homeostasis, innate and acquired immunity, stem cell homeostasis, as well as anti-cancer effects. An accumulating body of evidence suggests that the therapeutic, adverse, teratogenic and chemopreventive effecs of isotretinoin are all mediated by upregulation of FoxO-mediated gene transcription. These FoxO-driven transcriptional changes of the second response of retinoic acid receptor (RAR)-mediated signaling counterbalance gene expression of acne due to increased growth factor signaling with downregulated nuclear FoxO proteins. The proposed isotretinoin→ATRA→RAR→FoxO interaction offers intriguing new insights into the mode of isotretinoin action and explains most therapeutic, adverse and teratogenic effects of isotretinoin in the treatment of acne by a common mode of FoxO-mediated transcriptional regulation.

Studying the genetic predisposing factors in the pathogenesis of acne vulgaris

Acne is one of the most common dermatologic diseases in the developed regions of the world, affecting a large percentage of the population. Despite the great improvement in the number and quality of studies of the molecular etiology of this disease in the past 3 decades, the detailed molecular pathogenesis and the cause of the large individual variations in severity of skin symptoms remain unknown. The roles of genetic inheritance and special genetic susceptibility and protective factors have been suggested for over 100 years, but their identification and determination started only in the 1990s. To date, only a small number of genetic polymorphisms affecting the expression and/or function of a handful of genes have been investigated. This review surveys the major findings of the classic and molecular genetic studies that have been conducted in this field, draws conclusions, and indicates how the available data help our current understanding of the pathogenesis of this common skin disease.

Treating acne with antibiotic-resistant bacterial colonization

INTRODUCTION

Acne is a chronic skin disorder of the pilosebaceous unit; it has a multifactorial pathogenesis. Propionibacterium acnes within the follicle is considered to be a triggering factor of inflammation in acne. Antibiotics have been the primary treatment against P. acnes for more than 40 years. However, a gradual increase in the prevalence of antibiotic-resistant strains of P. acnes has been observed.

AREAS COVERED

This review discusses the pathophysiology of antibiotic-resistant acne development. It focuses on strategies to minimize the development of resistance and, most importantly, confront the development of antibiotic-resistant acne. The literature search was conducted up to August 2010, using the search terms 'acne', 'antibiotic-resistant acne' and 'bacterial resistance'.

EXPERT OPINION

Antibiotic-resistant acne is a real phenomenon. Strategies to prevent and confront it should include not only the use of certain treatment regimens but also rational prescribing policies, combination therapies, use of antibacterial non-antibiotic agents and treatment options targeting all the pathogenetic components of acne. Benzoyl-peroxide-based treatment is the most evidence-based approach. Oral isotretinoin remains the most efficacious option for severe acne.

Characterization of the vitamin D endocrine system in human sebocytes in vitro

Sebocytes are sebum-producing cells that form the sebaceous glands. We investigated the role of sebocytes as target cells for vitamin D metabolites and the existence of an enzymatic machinery for the local synthesis and metabolism of 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3), calcitriol], the biologically active vitamin D metabolite, in these cell types. Expression of vitamin D receptor (VDR), vitamin D-25-hydroxylase (25 OHase), 25-hydroxyvitamin D-1alpha-hydroxylase (1 alphaOHase), and 1,25-dihydroxyvitamin D-24-hydroxylase (24 OHase) was detected in SZ95 sebocytes in vitro using real time quantitative polymerase chain reaction. Splice variants of 1alphaOHase were identified by nested touchdown polymerase chain reaction. We demonstrated that incubation of SZ95 sebocytes with 1,25(OH)(2)D(3) resulted in a cell culture condition-, time-, and dose-dependent modulation of cell proliferation, cell cycle regulation, lipid content and interleukin-6/interleukin-8 secretion in vitro. RNA expression of VDR and 24 OHase was upregulated along with vitamin D analogue treatment. Although several other splice variants of 1alphaOHase were detected, our findings indicate that the full length product represents the major 1 alphaOHase gene product in SZ95 cells. In conclusion, SZ95 sebocytes express VDR and the enzymatic machinery to synthesize and metabolize biologically active vitamin D analogues. Sebocytes represent target cells for biologically active metabolites. Our findings indicate that the vitamin D endocrine system is of high importance for sebocyte function and physiology. We conclude that sebaceous glands represent potential targets for therapy with vitamin D analogues or for pharmacological modulation of 1,25(OH)(2)D(3) synthesis/metabolism.

Thematic review series: glycerolipids. DGAT enzymes and triacylglycerol biosynthesis

Triacylglycerols (triglycerides) (TGs) are the major storage molecules of metabolic energy and FAs in most living organisms. Excessive accumulation of TGs, however, is associated with human diseases, such as obesity, diabetes mellitus, and steatohepatitis. The final and the only committed step in the biosynthesis of TGs is catalyzed by acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes. The genes encoding two DGAT enzymes, DGAT1 and DGAT2, were identified in the past decade, and the use of molecular tools, including mice deficient in either enzyme, has shed light on their functions. Although DGAT enzymes are involved in TG synthesis, they have distinct protein sequences and differ in their biochemical, cellular, and physiological functions. Both enzymes may be useful as therapeutic targets for diseases. Here we review the current knowledge of DGAT enzymes, focusing on new advances since the cloning of their genes, including possible roles in human health and diseases.

Neutrophil gelatinase-associated lipocalin mediates 13-cis retinoic acid-induced apoptosis of human sebaceous gland cells

13-cis retinoic acid (13-cis RA; also known as isotretinoin) is the most potent agent available for treatment of acne. It is known that the drug induces apoptosis in cells cultured from human sebaceous glands, but its mechanism of action has not been determined. In this study, skin biopsies were taken from 7 patients with acne prior to and at 1 week of treatment with 13-cis RA. TUNEL staining confirmed that 13-cis RA induced apoptosis in sebaceous glands. Transcriptional profiling of patient skin and cultured human sebaceous gland cells (SEB-1 sebocytes) indicated that lipocalin 2 was among the genes most highly upregulated by 13-cis RA. Lipocalin 2 encodes neutrophil gelatinase-associated lipocalin (NGAL), which functions in innate immune defense and induces apoptosis of murine B lymphocytes. Increased immunolocalization of NGAL was noted in patients' sebaceous glands following treatment with 13-cis RA, and recombinant NGAL induced apoptosis in SEB-1 sebocytes. Furthermore, apoptosis in response to 13-cis RA was inhibited in the presence of siRNA to lipocalin 2. These data indicate that NGAL mediates the apoptotic effect of 13-cis RA and suggest that agents that selectively induce NGAL expression in sebaceous glands might represent therapeutic alternatives to the use of 13-cis RA to treat individuals with acne.

Use of oral isotretinoin in photoaging therapy

BACKGROUND

Many drugs are being used for prevention and treatment of photoaging, especially topical retinoids. The use of systemic retinoids, more specifically, isotretinoin, for this purpose has not been properly addressed to date. Our study was designed to assess the systemic use of isotretinoin used alone for the therapy of cutaneous photoaging.

OBJECTIVE

To demonstrate that isotretinoin is converted into retinoid and improves the appearance of the photoaged skin.

METHODS

Fifty women aged 40 to 60 years, phototype I, II, or III according Fitzpatrick, were selected to receive 20 mg of isotretinoin orally 3 times a week for a 3-month period. Patients underwent clinical and laboratory evaluation. Two biopsies and photographic control were performed. Patients were requested to use only topical photoprotecting agents during the treatment. Improvement in photoaging clinical parameters were evaluated through pictures taken and also through an evaluation form. Anatomopathologic parameters were obtained by comparing collagen degeneration and skin trophism. Results. Thirty patients fully complied with study requirements and were adequately analyzed. From the anatomopathologic data, an improvement of photoaging in 20 patients was observed.

CONCLUSIONS

Isotretinoin improves photoaging with few adverse events because of the low dose used and to the short treatment duration.

A Citrus Polymethoxy Flavonoid, Nobiletin Inhibits Sebum Production and Sebocyte Proliferation, and Augments Sebum Excretion in Hamsters

Acne vulgaris is characterized by excess sebum production, and apart from all-trans retinoic acid (atRA) or 13-cis retinoic acid (13-cisRA), there are few effective agents for acne therapy that directly suppresses sebaceous lipogenesis. In this study, we demonstrated that topical application of a citrus polymethoxy flavonoid, nobiletin, to hamster auricles decreased skin surface triacylglycerols (TG) level and the size of sebaceous glands along with inhibition of diacylglycerol acyltransferase (DGAT)-dependent TG synthesis and sebocyte proliferation. The inhibitory actions were similar to that observed with atRA and 13-cisRA in hamster sebocytes. The antilipogenic and antiproliferative actions of nobiletin were also reproduced in UVB (5.4 kJ/m2)-irradiated hamsters, which showed aberrant enhancement of sebum accumulation and sebaceous enlargement. Furthermore, nobiletin, but not 13-cisRA, augmented sebum excretion along with increases in intracellular cAMP level, protein kinase A (PKA) activation, and apoptosis-independent phosphatidylserine (PS) externalization in cell membrane. These phenomena were reproduced by forskolin and inhibited by a PKA inhibitor, H-89. These results provide early evidence that nobiletin is an effective candidate for acne therapy through mechanisms that include the inhibition of DGAT-dependent TG synthesis and sebocyte proliferation, and the progression of apoptosis-independent and PS-externalization-dependent sebum excretion by PKA activation.

Identification of histamine receptors and reduction of squalene levels by an antihistamine in sebocytes

Overproduction of sebum, especially during adolescence, is causally related to acne and inflammation. As a way to reduce sebum and its interference with the process of follicular keratinization in the pilosebaceous unit leading to inflammatory acne lesions, antihistamines were investigated for their effect on sebocytes, the major cell of the sebaceous gland responsible for producing sebum. Reverse transcriptase-PCR analysis and immunofluorescence of an immortalized sebocyte cell line (SZ95) revealed the presence of histamine-1 receptor (H-1 receptor), and thus indicated that histamines and, conversely, antihistamines could potentially modulate sebocyte function directly. When sebocytes were incubated with an H-1 receptor antagonist, diphenhydramine (DPH), at non-cytotoxic doses, a significant decrease in squalene levels, a biomarker for sebum, was observed. As determined by high-performance liquid chromatography, untreated sebocytes contained 6.27 (+/-0.73) nmol squalene per 10(6) cells, whereas for DPH-treated cells, the levels were 2.37 (+/-0.24) and 2.03 (+/-0.97) nmol squalene per 10(6) cells at 50 and 100 microM, respectively. These data were further substantiated by the identification of histamine receptors in human sebaceous glands. In conclusion, our data show the presence of histamine receptors on sebocytes, demonstrate how an antagonist to these receptors modulated cellular function, and may indicate a new paradigm for acne therapy involving an H-1 receptor-mediated pathway.

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.

Isotretinoin revisited: pluripotent effects on human sebaceous gland cells

Nelson et al. confirmed the previously described antiproliferative effect of isotretinoin on human sebocytes. They attributed a portion of this decrease to cell cycle arrest and detected sebocyte apoptosis, which was not recapitulated by alitretinoin or tretinoin. These events were specific to sebocytes, as isotretinoin failed to induce apoptosis in keratinocytes. Isotretinoin-induced apoptosis was shown to be an RAR-independent mechanism.

Peroxisome Proliferator-Activated Receptors Increase Human Sebum Production

Sebum production is key in the pathophysiology of acne, an extremely common condition, which when severe, may require treatment with isotretinoin, a known teratogen. Apart from isotretinoin and hormonal therapy, no agents are available to reduce sebum. Increasing our understanding of the regulation of sebum production is a milestone in identifying alternative therapeutic targets. Studies in sebocytes and human sebaceous glands indicate that agonists of peroxisome proliferator-activated receptors (PPARs) alter sebaceous lipid production. The goal of this study is to verify the expression and activity of PPARs in human skin and SEB-1 sebocytes and to assess the effects of PPAR ligands on sebum production in patients. To investigate the contribution of each receptor subtype to sebum production, lipogenesis assays were performed in SEB-1 sebocytes that were treated with PPAR ligands and isotretinoin. Isotretinoin significantly decreased lipogenesis, while the PPARalpha agonist-GW7647, PPARdelta agonist-GW0742, PPARalpha/delta agonist-GW2433, PPARgamma agonist rosiglitazone, and the pan-agonist-GW4148, increased lipogenesis. Patients treated with thiazolidinediones or fibrates had significant increases in sebum production (37 and 77%, respectively) when compared to age-, disease-, and sex-matched controls. These data indicate that PPARs play a role in regulating sebum production and that selective modulation of their activity may represent a novel therapeutic strategy for the treatment of acne.

13-cis Retinoic acid induces apoptosis and cell cycle arrest in human SEB-1 sebocytes

Isotretinoin (13-cis retinoic acid (13-cis RA)) is the most potent inhibitor of sebum production, a key component in the pathophysiology of acne, yet its mechanism of action remains largely unknown. The effects of 13-cis RA, 9-cis retinoic acid (9-cis RA), and all-trans retinoic acid (ATRA) on cell proliferation, apoptosis, and cell cycle proteins were examined in SEB-1 sebocytes and keratinocytes. 13-cis RA causes significant dose-dependent and time-dependent decreases in viable SEB-1 sebocytes. A portion of this decrease can be attributed to cell cycle arrest as evidenced by decreased DNA synthesis, increased p21 protein expression, and decreased cyclin D1. Although not previously demonstrated in sebocytes, we report that 13-cis RA induces apoptosis in SEB-1 sebocytes as shown by increased Annexin V-FITC staining, increased TUNEL staining, and increased cleaved caspase 3 protein. Furthermore, the ability of 13-cis RA to induce apoptosis cannot be recapitulated by 9-cis RA or ATRA, and it is not inhibited by the presence of a retinoid acid receptor (RAR) pan-antagonist AGN 193109. Taken together these data indicate that 13-cis RA causes cell cycle arrest and induces apoptosis in SEB-1 sebocytes by a RAR-independent mechanism, which contributes to its sebosuppressive effect and the resolution of acne.

Expression of retinoid receptors in sebaceous cell carcinoma

PURPOSE

The aim of this study is to investigate whether there are any abnormalities in the in vivo expression of retinoid acid receptors (RAR-alpha, RAR-beta and RAR-gamma) and retinoid X receptors (RXR-alpha, RXR-beta and RXR-gamma) in sebaceous cell carcinoma.

METHODS

Expression of retinoid receptors in paired specimens of cancerous tissues (n = 10) and adjacent normal tissues (n = 10) from 10 patients with sebaceous cell carcinoma was studied immunohistochemically by using anti-retinoid receptor antibodies.

RESULTS

In eight of the 10 normal tissue samples, all six receptors were expressed. In the other two samples, all receptors were expressed except RAR-gamma (one sample) or RXR-gamma (two samples). Five tumours (50%) lacked RAR-alpha; RAR-alpha expression was lower in tumours than in normal tissues in eight of 10 cases. RAR-beta was expressed in the cytoplasm of nine of 10 tumours; RAR-beta expression was at least as high in tumours as in normal tissue in eight of 10 cases. Two tumours lacked RAR-gamma; three tumours had lower RAR-gamma expression than paired normal epithelium; four had the same RAR-gamma expression, and one had higher RAR-gamma expression. RXR-alpha expression was strong in all normal tissues and tumour samples. Ten tumours lacked RXR-beta and all 10 tumours lacked RXR-gamma expression.

CONCLUSIONS

Diminished RXR-beta and RXR-gamma expression might be related to the development of sebaceous cell carcinoma. Additional studies are required to establish whether the defects in RAR expression in sebaceous cell carcinoma might affect the potential response of this tumour to treatment with retinoids.

The triacylglycerol synthesis enzyme DGAT1 also catalyzes the synthesis of diacylglycerols, waxes, and retinyl esters

The final step of triacylglycerol biosynthesis is catalyzed by acyl CoA:diacylglycerol acyltransferase (DGAT) enzymes. The two known DGATs, DGAT1 and DGAT2, are encoded by unrelated genes. Although both DGAT1 and DGAT2 knockout mice have reduced tissue triacylglycerol contents, they have disparate phenotypes, prompting us to investigate whether the two enzymes have unrecognized functional differences. We now report that DGAT1 exhibits additional acyltransferase activities in vitro, including those of acyl CoA:monoacylglycerol acyltransferase (MGAT), wax monoester and wax diester synthases, and acyl CoA:retinol acyltransferase (ARAT), which catalyze the synthesis of diacylglycerols, wax esters, and retinyl esters, respectively. These activities were demonstrated in in vitro assays with membranes from insect cells or homogenates from COS7 cells overexpressing DGAT1. Wax synthase and ARAT activities were also demonstrated in intact COS7 cells expressing DGAT1. Additionally, cells and tissues from DGAT1-deficient mice exhibited reduced ARAT activity, and the mice had increased levels of unesterified retinol in their livers on a high-retinol diet. Our findings indicate that DGAT1 can utilize a variety of acyl acceptors as substrates in vitro and suggest that these activities may be relevant to the in vivo functions of DGAT1.