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.     

Isotretinoin increases skin-surface levels of neutrophil gelatinase-associated lipocalin in patients treated for severe acne

Background A clear‐cut need exists for safe and effective alternatives to the use of isotretinoin in severe acne. Lack of data regarding the specifics of isotretinoin’s mechanism of action has hampered progress in this area. Recently, the protein neutrophil gelatinase‐associated lipocalin (NGAL) has been identified as a mediator of the apoptotic effect of isotretinoin on sebocytes. Objectives To establish further the clinical relevance of NGAL and to elucidate the factors that induce NGAL expression in sebocytes. Methods Methods were developed to isolate and quantify skin‐surface levels of NGAL from normal subjects and patients with acne undergoing treatment with isotretinoin. Results Patients with acne were found to have higher skin levels of NGAL compared with normal subjects. Studies in SEB‐1 sebocytes indicate that NGAL expression is increased in response to Propionibacterium acnes and interleukin (IL)‐1β. In patients, isotretinoin increases NGAL levels by 2·4‐fold on the skin surface and this increase precedes decreases in sebum and P. acnes counts. Conclusions These data support the hypothesis that NGAL is an important mediator of the early effects of isotretinoin on the sebaceous glands and provide insights into the mechanisms that regulate NGAL expression in the skin.     

TRAIL contributes to the apoptotic effect of 13-cis retinoic acid in human sebaceous gland cells

Background The full mechanism of action of isotretinoin [13‐cis retinoic acid (13‐cis RA)] in treating acne is unknown. 13‐cis RA induces key genes in sebocytes that are involved in apoptosis, including Tumor necrosis factor Related Apoptosis Inducing Ligand (TRAIL). Objectives In this study, we investigated the role of 13‐cis RA‐induced TRAIL within SEB‐1 sebocytes. Methods Using 13‐cis RA and recombinant human TRAIL (rhTRAIL) protein, we assessed induction of TRAIL and apoptosis in SEB‐1 sebocytes, normal keratinocytes and patient skin biopsies. Results Treatment with rhTRAIL protein increased TUNEL‐positive staining in SEB‐1 sebocytes. TRAIL siRNA significantly decreased the percentage of TUNEL‐positive SEB‐1 sebocytes in response to 13‐cis RA treatment. Furthermore, TRAIL expression increased in the skin of patients with acne after 1 week of isotretinoin therapy compared with baseline. TRAIL expression localized within sebaceous glands. Unlike sebocytes, TRAIL protein expression was not increased in normal human epidermal keratinocytes in response to 13‐cis RA, nor did rhTRAIL induce apoptosis in keratinocytes, suggesting that TRAIL is key in the sebocyte‐specific apoptotic effects of 13‐cis RA. Conclusions Taken together, our data suggest that TRAIL, like the neutrophil gelatinase‐associated lipocalin, is involved in mediating 13‐cis RA apoptosis of sebocytes.     

Effect of dihydrotestosterone on the upregulation of inflammatory cytokines in cultured sebocytes

Acne is a complex, chronic and common skin disorder of pilosebaceous units. Hyperkeratinization of keratinocytes, increased sebum excretion from sebocytes via androgen stimulation and inflammatory cytokines are the major factors involved in the pathophysiology of acne. In addition, it is known that keratinocytes play an important role in acne synthesizing a number of inflammatory cytokines. However, the nature of the association between inflammatory cytokines and sebocytes in acne remains unclear. Culture of sebocytes provides a new insight into the participation of dihydrotestosterone (DHT) in the production of inflammatory cytokines in acne. To examine the possible involvement of DHT in the production of inflammatory cytokines in the cultured sebocytes, we used immunohistochemistry and RT-PCR to compare the expression of interleukin-1 (IL-1), IL-6, tumor necrosis factor-α (TNF-α). Upregulation of IL-6 and TNF-α in immunohistochemistry, and increase in RNA amplification for IL-6 and TNF-α were observed after addition of DHT compared with the control. This study suggests that DHT may not only be involved in sebum production but also in production of proinflammatory cytokines in acne.     

All-trans retinoic acid shifts Propionibacterium acnes-induced matrix degradation expression profile toward matrix preservation in human monocytes

Propionibacterium acnes is a critical component in the pathogenesis of acne vulgaris, stimulating the production of various inflammatory mediators, such as cytokines and chemokines, important in the local inflammatory response found in acne. This study explored the role of P. acnes and its ability to induce matrix metalloproteinases (MMPs) in primary human monocytes and how this induction is regulated by retinoids. MMP-1- and MMP-9-expressing cells were present in perifollicular and dermal inflammatory infiltrates within acne lesions, suggesting their role in acne pathogenesis. In vitro, we found that P. acnes induced MMP-9 and MMP-1 mRNA, and the expression of MMP-9, but not of MMP-1, was found to be Toll-like receptor 2-dependent. P. acnes induced the mRNA expression of tissue inhibitors of metalloproteinase (TIMP)-1, the main regulator of MMP-9 and MMP-1. Treatment of monocytes with all-trans retinoic acid (ATRA) significantly decreased baseline MMP-9 expression. Furthermore, co-treatment of monocytes with ATRA and P. acnes inhibited MMP-9 and MMP-1 induction, while augmenting TIMP-1 expression. These data indicate that P. acnes-induced MMPs and TIMPs may be involved in acne pathogenesis and that retinoic acid modulates MMP and TIMP expression, shifting from a matrix-degradative phenotype to a matrix-preserving phenotype.     

Skin expression of metalloproteinases and tissue inhibitor of metalloproteinases in sibling patients with recessive dystrophic epidermolysis and intrafamilial phenotypic variation

A number of COL7A1 mutations have now been reported in recessive dystrophic epidermolysis bullosa patients, and the analysis of phenotype-genotype correlations showed evidence for interfamilial and intrafamilial phenotypic variability, occurring for the same mutation. Collagenase and stromelysin activities have been found to be overexpressed in skin cultures of some recessive dystrophic epidermolysis bullosa patients, and tissue destruction in the disease process might result from an imbalance of metalloproteinases (MMP) over tissueinhibitor of metalloproteinases (TIMP). So we suspected that the phenotypic variability for the same mutation could be linked to other genetic or environmental factors, as a particular balance between MMP and TIMP. Organ cultures were performed using explants from the skin of three patients from the same family with recessive dystrophic epidermolysis bullosa to reveal and quantify the expression of MMP-1 (collagenase 1), MMP-2 and MMP-9 (gelatinases A and B), MMP-3 (stromelysin 1), TIMP-1, and TIMP-2, and to compare the results with those obtained with two human control skins, with the same experimental conditions. Increased amounts of all metalloproteinases investigated were observed in the skin of the three recessive dystrophic epidermolysis bullosa affected sibling brothers, both in lesioned and in apparently nonlesioned skin, compared with controls. The amounts of MMP-1, MMP-2, MMP-3, and MMP-9 increased particularly in the skin of the more clinically affected patient. Furthermore for this patient we evidenced higher amounts of MMP-1 and also a lower TIMP-1 amount in his unlesioned and lesioned skin compared with the other two affected patients and with healthy control donors. So we can suspect that recessive dystrophic epidermolysis bullosa phenotypic variability could be related to patients' collagenase activity heterogeneity, linked to imbalance between MMP-1 and TIMP-1.     

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.     

中波紫外线对角质形成细胞MMP-1及TIMP-1的影响

目的：研究中波紫外线照射对永生化人角质形成细胞的影响。方法：绘制细胞生长曲线,用不同剂量UVB（30、60、90 mJ/cm2）照射永生化人角质形成细胞,用MTT方法测定UVB照射后细胞的增殖活性,用RT-PCR方法测定HaCaT细胞中MMP-1mRNA和TIMP-1mRNA的表达。结果：UVB照射后,HaCaT细胞的增殖活性受到抑制,MMP-1 mRNA表达增强,TIMP-1 mRNA表达下降,90 mJ/cm2照光组与未照光组比较,差异均有统计学意义。结论：UVB照射可诱导HaCaT细胞损伤和细胞凋亡,促使MMP-1mRNA表达增加,TIMP-1 mRNA表达减少,二者比例失调,这可能与光老化的发生有一定的关系。     

皮肤恶性黑素瘤中基质金属蛋白酶-9及其组织抑制物-1的表达及意义

目的:探讨基质金属蛋白酶-9(MMP-9)及其组织抑制物-1(TIMP-1)在皮肤恶性黑素瘤中的表达及其临床、病理学意义。方法:采用免疫组织化学S-P方法观察MMP-9和TIMP-1在51例皮肤黑素瘤及15例色素痣石蜡切片中的表达,使用图像分析技术对免疫组化结果进行定量分析。结果:与色素痣比较,皮肤恶性黑素瘤中MMP-9表达较强(P<0.05),MMP-9/TIMP-1比值较高(P<0.05)。MMP-9和TIMP-1的表达及MMP-9/TIMP-1比值与黑素瘤浸润深度有关(P<0.05)。有淋巴结转移者MMP-9表达较强(P<0.05),MMP-9/TIMP-1比值较高(P<0.05)。结论:MMP-9、TIMP-1蛋白的表达与皮肤恶性黑素瘤的侵袭性有关,MMP-9/TIMP-1比值增高提示肿瘤具有较高侵袭转移能力。     

Arotinoid Ro 13-6298 and etretin: two new retinoids inferior to isotretinoin in sebum suppression and acne treatment

Thirty patients have been treated with either etretin, the main derivative of etretinate, or arotinoid Ro 13-6298, a polyaromatic retinoid, or isotretinoin. Sebum production was measured before and during the treatments. While no change was observed in the patients treated with etretin, a reduction of 33% of the sebum excretion rate was observed for those treated with arotinoid Ro 13-6298 but only after long treatment periods of 20 to 30 weeks. The sebum excretion rate decreased by 92% in the patients treated with isotretinoin. Four patients suffering from severe nodulocystic acne were treated with arotinoid Ro 13-6298 for 2-5 months without improvement. Substantial improvement, however, resulted after a subsequent treatment with isotretinoin; sebum production decreased markedly as well. This study suggests that neither etretin nor arotinoid Ro 13-6298 will replace isotretinoin in the treatment of severe nodulocystic acne.     

Sebocytes differentially express and secrete adipokines

In addition to producing sebum, sebocytes link lipid metabolism with inflammation at a cellular level and hence, greatly resemble adipocytes. However, so far no analysis was performed to identify and characterize the adipocyte‐associated inflammatory proteins, the members of the adipokine family in sebocytes. Therefore, we determined the expression profile of adipokines [adiponectin, interleukin (IL) 6, resistin, leptin, serpin E1, visfatin, apelin, chemerin, retinol‐binding protein 4 (RBP4) and monocyte chemoattractant protein 1 (MCP1)] in sebaceous glands of healthy and various disease‐affected (acne, rosacea, melanoma and psoriasis) skin samples. Sebaceous glands in all examined samples expressed adiponectin, IL6, resistin, leptin, serpin E1 and visfatin, but not apelin, chemerin, RBP4 and MCP1. Confirming the presence of the detected adipokines in the human SZ95 sebaceous gland cell line we further characterized their expression and secretion patterns under different stimuli mimicking bacterial invasion [by using Toll‐like receptor (TLR)2 and 4 activators], or by 13‐cis retinoic acid (13CRA; also known as isotretinoin), a key anti‐acne agent. With the exception of resistin, the expression of all of the detected adipokines (adiponectin, IL6, leptin, serpin E1 and visfatin) could be further regulated at the level of gene expression, showing a close correlation with the secreted protein levels. Besides providing further evidence on similarities between adipocytes and sebocytes, our results strongly suggest that sebocytes are not simply targets of inflammation but may exhibit initiatory and modulatory roles in the inflammatory processes of the skin through the expression and secretion of adipokines.     

Novel anti-acne actions of nadifloxacin and clindamycin that inhibit the production of sebum, prostaglandin E(2) and promatrix metalloproteinase-2 in hamster sebocytes

Acne vulgaris is characteristic of excess sebum production and the induction of inflammatory reactions, for example, the augmentation of cytokine, prostaglandin (PG) and matrix metalloproteinase (MMP) production in sebaceous glands and pilosebaceous units. As Propionibacterium acnes is considered to be involved in the aggravation of acne vulgaris, antimicrobial agents have been found to be effective for treating acne leading to the remission of inflammation. However, it is not fully understood whether antimicrobial agents influence sebum production and/or the inflammatory reactions in sebaceous gland cells (sebocytes). In the present study, topical antimicrobial agents such as nadifloxacin (NDFX) and clindamycin (CLDM) decreased the production of triacylglycerols (TG), which are a major component of sebum in insulin-differentiated hamster sebocytes. These antibiotics also suppressed insulin-augmented gene expression and the production of perilipin, by which intracellular lipid droplet formation was concomitantly inhibited. On the other hand, peptidoglycan (PGN) from Gram-positive bacteria dose-dependently increased TG production in hamster sebocytes. The augmented TG production was decreased by treating NDFX or CLDM. Furthermore, NDFX and CLDM inhibited the PGN-augmented PGE(2) production in the sebocytes. Moreover, NDFX, but not CLDM, suppressed the PGN-augmented gene expression and production of pro-MMP-2/progelatinase A in hamster sebocytes. Therefore, these results provide novel evidence that NDFX and CLDM exhibit anti-lipogenesis and anti-inflammatory activities against insulin- or PGN-activated sebocytes which at least partly mimic acne pathology in vitro. Moreover, NDFX for acne therapy is likely to be effective in not only inhibiting microbial proliferation but also in preventing the onset of acne scar formation.     

Zileuton, an oral 5-lipoxygenase inhibitor, directly reduces sebum production

BACKGROUND: Zileuton, a 5-lipoxygenase inhibitor, reduces the number of inflammatory lesions in moderate acne and inhibits the synthesis of sebaceous lipids. OBJECTIVE: To detect whether zileuton directly reduces sebum synthesis. METHODS: A 40-year-old female with mild disseminated sebaceous gland hyperplasia and seborrhea was treated with zileuton 4 x 600 mg/day over 2 weeks, was followed-up for 6 weeks after discontinuation of zileuton and was re-treated with low-dose isotretinoin 10 mg/2nd day over 5 weeks. Casual skin surface lipids and sebum synthesis were determined. RESULTS: Under treatment with zileuton increased casual skin surface lipids were normalized and synthesis of facial sebum was decreased. Six weeks after discontinuation of treatment casual skin surface lipids were increased again and synthesis of sebum returned to baseline. Subsequent low-dose isotretinoin treatment led to similar changes of casual skin surface lipids and sebum synthesis with zileuton already after 2 weeks. CONCLUSION: Zileuton directly inhibits sebum synthesis in a transient manner with a potency similar to low-dose isotretinoin at least in our patient.     

Polyphenol‐rich apple extract inhibits dexamethasone‐induced sebaceous lipids production by regulating SREBP1 expression

Sebum production and excretion is a primary function of the sebaceous glands, but abnormally increased sebum production is a major cause of acne vulgaris. To identify a new candidate that regulates sebum production, we investigated the possible inhibitory effects of apple polyphenols (APP) purified from unripe apples on primary cultured human sebocytes and in patients with acne vulgaris. Dexamethasone (Dex) increased lipid synthesis and expression of the sterol response element‐binding protein 1 (SREBP 1) and its target enzymes, acetyl‐CoA carboxylase (ACC) and fatty acid synthase (FAS), in the sebocytes. However, APP inhibited Dex‐induced lipid production and expression of SREBP‐1, ACC and FAS. APP also inhibited the increase in the expression and activation of glucocorticoid receptor in the sebocytes. Taken together, these results suggest that APP may be useful to regulate sebum production and may alleviate sebum‐involved skin disease, such as acne vulgaris.     

Basement membrane alterations in psoriasis are accompanied by epidermal overexpression of MMP-2 and its inhibitor TIMP-2

Psoriasis is most probably an inherited disease characterized by cell proliferation, angiogenesis, and an inflammatory process. The pathophysiology remains unknown, although an alteration in cell-cell and cell-matrix adhesion versus an autoimmune process has been proposed as the primary defect. Here, we show evidence of a new mechanism involving basement membrane alterations accompanied by keratinocyte overexpression of matrix metalloproteinase (MMP) 2 and tissue inhibitor of MMP-2 (TIMP-2) in both uninvolved and involved psoriatic skin. Immunocytochemistry with antibodies against collagen IV (alpha1, alpha2 chains) and laminins (alpha2, alpha5, beta1, gamma1 chains) revealed gaps, folding, and reduplication of the epidermo-dermal basement membrane. There was overexpression of MMP-2 in the cytoplasm of suprabasal keratinocytes. Gelatin zymography revealed pro-MMP-2 and its activated form, a-MMP-2, in both uninvolved and involved psoriatic skin, whereas pro-MMP-9 was only present in involved skin. TIMP-2 was expressed at the cell surface of psoriatic involved suprabasal keratinocytes whereas it was restricted to basal keratinocytes in uninvolved areas. Western blots showed a marked increase in a-MMP-2 and TIMP-2 in uninvolved and involved psoriatic skin although it was more pronounced in the latter. MT1-MP, known to activate pro-MMP-2, was increased in involved areas. In situ hybridization revealed strong signals of MMP-2 mRNA in both uninvolved and involved psoriatic epidermis. The overexpression of MMP-2 in uninvolved and involved psoriatic epidermis supports the concept that the primary alteration may reside in the keratinocyte. In addition, the presence of the activated form of MMP-2 could be responsible for cell-cell and cell-matrix changes noted in psoriatic epidermis.     

基质金属蛋白酶-9及其组织抑制物-1在皮肤鳞状细胞癌中的表达

目的探讨基质金属蛋白酶-9(MMP-9)及其组织抑制物-1(TIMP-1)在皮肤鳞状细胞癌(SCC)中的表达及其与肿瘤浸润转移的关系。方法免疫组化SP法检测MMP-9和TIMP-1蛋白在65例皮肤SCC(Bowen病17例,SCC48例)和5例正常表皮石蜡切片的表达,采用图像分析技术对免疫组化结果进行定量分析。结果MMP-9和TIMP-1蛋白均弥漫表达于皮肤SCC,分布于SCC癌巢及癌巢周围间质细胞,而在正常人皮肤仅见MMP-9和TIMP-1的弱阳性表达。SCC组MMP-9蛋白的表达水平及MMP-9/TIMP1比值高于Bowen病组(t值分别为2.33、2.36,P<0.05),SCC中淋巴结转移组MMP-9/TIMP1的比值高于无淋巴结转移组(t=2.46,P<0.05)。结论MMP-9、TIMP-1蛋白的表达与SCC的侵袭性有关,MMP-9/TIMP1比值升高(MMP-TIMP失衡)预示了SCC肿瘤细胞较高的侵袭转移潜能。     

Acne as an altered dermato-endocrine response problem

Acne is the most common skin disease in adolescent Westernized populations. Several data support the involvement of the mammalian target of rapamycin complex 1 (mTORC1) signalling in the interplay between androgens, insulin, insulin-like growth factor (IGF1) and high-glycaemic index diet in acne. The peroxisome proliferator–activated receptor γ (PPARγ) is involved in both differentiation and anti-inflammatory response. Low differentiated sebocytes showed decreased expression of PPARγ and increased level of insulin and IGF-1 receptors, resulting in the production of acne-like sebum and inflammatory mediators. In this viewpoint, we discuss how in acne the dysregulation of proliferation and differentiation processes in sebocytes and keratinocytes may be associated with altered response to androgens and other hormones, such as insulin or IGF-1. Moreover, we propose PPARγ modulation as an innovative therapeutic approach to normalize sebocyte differentiation process, interfering with the different mechanisms involved in altered pilosebaceous unit.     

Acne vulgaris

Peripherally active androgens control cellular functions by binding to androgen receptors. Follicular keratinocytes and sebocytes are target cells for androgens, which, directly or indirectly, stimulate keratinocyte proliferation and the volume of sebaceous glands as well as the sebum secretion rate. Acne often begins with the adrenarche, namely with the up- regulation of adrenal synthesis of dehydroepiandrosterone sulfate, a hormone that is upstream to testosterone. The majority of acne patients exhibit normal levels of circulating androgens, while sebaceous glands from acne regions exhibit a stronger sensitivity to androgens than the sebaceous glands from other parts of the body. Hormone-like active lipids, hormones in diet and neuropeptides may also play a role in the development of acne lesions. The target of antiandrogen treatment of the skin is mainly the sebaceous gland and the primary effect is sebostasis.