Anja Thielitz

Frontiers in sebaceous gland biology and pathology.

Abstract:  The development of experimental models for the in vitro study of human sebaceous gland turned down the theory of a phylogenetic relict and led to the identification of several, unknown or disregarded functions of this organ. Such functions are the production of foetal vernix caseosa, the influence of three‐dimensional organization of the skin surface lipids and the integrity of skin barrier and the influence on follicular differentiation. In addition, the sebaceous gland contributes to the transport of fat‐soluble antioxidants from and to the skin surface, the natural photoprotection, the pro‐ and antiinflammatory skin properties and to the innate antimicrobial activity of the skin. It is mainly responsible for skin’s independent endocrine function, the hormonally induced skin ageing process, the steroidogenic function of the skin as well as its thermoregulatory and repelling properties and for selective control of the hormonal and xenobiotical actions of the skin. Interestingly, sebocytes, at least in vitro, preserve characteristics of stem‐like cells despite their programming for terminal differentiation. This review reports on various sebaceous gland functions, which are currently under investigation, including its role on the hypothalamus–pituitary–adrenal‐like axis of the skin, the impact of acetylcholine on sebocyte biology, the activity of ectopeptidases as new targets to regulate sebocyte function, the effects of vitamin D on human sebocytes, the expression of retinoid metabolizing cytochrome P450 enzymes and the possible role of sebum as vehicle of fragrances. These multiple homeostatic functions award the sebaceous gland the role ‘brain of the skin’ and the most important cutaneous endocrine gland.

Lipid analysis of follicular casts from cyanoacrylate strips as a new method for studying therapeutic effects of antiacne agents

Background The cyanoacrylate follicular biopsy is an established method for the examination of the horny layer and quantitative assessment of microcomedones. We have optimized the method by separating follicular casts mechanically from the cyanoacrylate strips.Objectives To use this method to analyse topical therapy‐induced changes of the lipid composition in the sebaceous follicular infundibulum.Methods Both the follicular casts and the residual skin surface strip, the last representing a mixture of stratum corneum and surface lipids, were extracted twice with n‐hexane–ethanol under ultrasonication, evaporated, redissolved in chloroform–methanol and separated by high‐performance thin layer chromatography, using cholesterol sulphate, cerebroside, ceramide types 3 and 4, cholesterol, oleic acid, triolein, cholesterol oleate and squalene as standards. Identification was performed by computer‐assisted densitometric analysis. Six patient groups receiving adapalene 0·1%, tretinoin 0·025%, clindamycin 1%, clindamycin 1% + tretinoin 0·025%, benzoyl peroxide 5% or benzoyl peroxide 5% + erythromycin 2% were investigated before and 12 weeks after application.Results A significant decrease in free fatty acid proportions combined with an increase in triglycerides was observed in the groups receiving antimicrobial therapy, supporting the hypothesis of lipolysis due to microbial colonization. The groups treated with topical retinoids showed an additional significant increase in ceramide subfractions, most probably reflecting their influence on epidermal keratinization.Conclusions Our method proved suitable for the detection of quantitative and qualitative changes in lipid profiles of both infundibulum cast content and surface lipids. It enabled simple, non‐invasive and objective assessment of the most relevant lipid classes in the sebaceous infundibulum, and efficient monitoring of drug effects on the follicular infundibulum.

Recent insights into the role of dipeptidyl aminopeptidase IV (DPIV) and aminopeptidase N (APN) families in immune functions

Abstract Background: In the past, different research groups could show that treatment of immune cells with inhibitors of post-proline splitting dipeptidyl aminopeptidases leads to functional changes in the immune system consistent with immunosuppression. This is due to the inhibition of proliferation of lymphocytes and the production of inflammatory cytokines of the TH1, TH2, and TH17 cells as well as the induction of immunosuppressive cytokines, such as transforming growth factor-β1 (TGF-β1) and interleukin (IL)-1RA. Until recently, most of the effects of these inhibitors on immune functions were attributed to the inhibition of dipeptidyl aminopeptidase IV (DPIV/CD26). With the identification of new peptidases of the DPIV family (DASH) with the same or similar substrate specificity [fibroblast activation protein (FAP), DP8/9], the question arose whether and to what extent the inhibition of intracellularly localized enzymes, DP8 and DP9, contribute to the observed immunosuppression. In addition, members of the aminopeptidase N (APN) family are also involved in the regulation of immune functions. Hence, the concept of a combined targeting of both families of peptidases for treatment of inflammatory diseases is a promising strategy. Results/Conclusions: Summarizing data obtained from the usage of different non-selective and selective inhibitors of DPIV, DP8/9, FAP, and DPII, this review provides evidence that in addition to DPIV, DP8/9 also regulate the immune response via modulation of cell cycle progression and cytokine production. The strongest and most consistent effects in vitro were, however, observed with non-selective inhibitors for the suppression of DNA synthesis and cytokine production. Similar effects were provoked by APN inhibitors, which were also found to suppress DNA synthesis and the production of inflammatory cytokines in vitro. However, different mechanisms and signaling pathways appear to mediate the cellular effects resulting from the inhibition of either APN or DPIV family members. In particular, members of the APN family uniquely influence the function of CD4+CD25+ regulatory T-cells. Consequently, the concomitant inhibition of both APN and DPIV enzyme families by means of two separate inhibitors or by binary inhibitors with specificity for both enzyme families (PETIR™, peptidase targeted immunoregulation) synergistically affects immune cells on the level of cell cycle regulation, suppression of TH1, TH2, and TH17 cytokines as well as the activation of regulatory T-cells. Besides leukocytes, dermal cells as sebocytes, keratinocytes, and fibroblasts are also targeted by these inhibitors. This strongly suggests a broad potential of the multiple anti-inflammatory effects of PETIR™ in treatment of chronic inflammatory diseases, such as autoimmune diseases, allergies, and transplant rejections, as well as of inflammatory skin diseases, such as acne, psoriasis, rosacea or atopic dermatitis. The first active dual inhibitor, IP10.C8, has been developed by IMTM for the treatment of inflammatory skin diseases and has just entered the first phase II study. Clin Chem Lab Med 2009;47:253–61.

Role of dipeptidyl peptidase IV (DP IV)-like enzymes in T lymphocyte activation: investigations in DP IV/CD26-knockout mice.

Abstract Background: Dipeptidyl peptidase IV (DP IV, CD26) and DP IV-like enzymes, such as dipeptidyl peptidase II (DP II), dipeptidyl peptidase 8 (DP8), and dipeptidyl peptidase 9 (DP9), have been recognized to regulate T lymphocyte activation. Lys[Z(NO2)]-thiazolidide (LZNT) and Lys[Z(NO2)]-pyrrolidide (LZNP), non-selective inhibitors of DP IV-like activity known to target DP IV as well as DP II, DP8, and DP9, suppress T lymphocyte proliferation in vitro. Moreover, these inhibitors are capable of attenuating the severity of autoimmune diseases, such as experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis, and experimental arthritis, a model of human rheumatoid arthritis, in vivo, particularly in combination with inhibitors of aminopeptidase N (APN, CD13) enzymatic activity. Methods: Here, we studied the influence of non-selective and selective inhibitors of DP IV-like enzymes on DNA synthesis in mitogen-stimulated splenocytes from wild-type C57BL/6 mice and DP IV/CD26-knockout (DP IV/CD26-KO) mice. Results: LZNT and LZNP, the non-selective inhibitors of DP IV-like activity, suppressed the DNA synthesis in stimulated splenocytes from wild-type and DP IV/CD26-KO mice to a comparable extent. Further, a selective inhibitor of DP8/DP9 activity was capable of suppressing DNA synthesis in mitogen-stimulated splenocytes of both wild-type and knockout mice to the same extent. In contrast, selective inhibitors of DP IV and DP II lacked this suppressive activity. Conclusions: Our data support the hypothesis that DP8 and/or DP9 represent additional pharmacological targets for the suppression of T cell proliferation and for anti-inflammatory therapy. Clin Chem Lab Med 2009;47:268–74.

Topical retinoids in acne vulgaris: update on efficacy and safety.

Topical retinoids represent a mainstay of acne treatment because they expel mature comedones, reduce microcomedone formation, and exert anti-inflammatory effects. The first-generation retinoid tretinoin (all-trans retinoic acid) and the synthetic third-generation polyaromatics adapalene and tazarotene are approved for acne treatment by the US FDA, whereas topical tretinoin, isotretinoin (13-cis retinoic acid), and adapalene are accredited in Canada and Europe. Topical retinoids have a favorable safety profile distinct from the toxicity of their systemic counterparts. Local adverse effects, including erythema, dryness, itching, and stinging, occur frequently during the early treatment phase. Their impact varies with the vehicle formation, skin type, frequency and mode of application, use of moisturizers, and environmental factors such as sun exposure or temperature. The broad anti-acne activity and safety profile of topical retinoids justifies their use as first-line treatment in most types of non-inflammatory and inflammatory acne. They are also suitable as long-term medications, with no risk of inducing bacterial resistance, for maintenance of remission after cessation of initial combination therapy.

Update in retinoid therapy of acne.

ABSTRACT:  The pathogenesis of acne, the most common skin disease, is complex and multifactorial. Clinical experience has demonstrated that parallel targeting of various pathogenetic factors, achieved either by mono‐ or combination therapy with appropriate drugs, represents the most effective approach to treating acne. Topical retinoids have been shown to expulse mature comedones, reduce microcomedone formation, and exert immunomodulatory effects. They have broad anti‐acne activity without the risk of inducing bacterial resistance, which justifies their use as first‐line treatment in most types of noninflammatory and inflammatory acne and makes them uniquely suitable as long‐term medication to maintain remission after cessation of initial combination therapy.

Topical retinoids in acne--an evidence-based overview.

Topical retinoids are important tools in the management of acne because they act against comedones and microcomedones and have direct anti‐inflammatory effects. The substances approved for acne treatment comprise tretinoin (all‐trans‐retinoic acid),isotretinoin (13‐cis retinoic acid) as well as the synthetic third‐generation polyaromatic retinoids adapalene and tazarotene,the latter being approved for acne treatment in the US only.Retinaldehyde is used in cosmetic preparations against acne.

Control of microcomedone formation throughout a maintenance treatment with adapalene gel, 0.1%.

Background  Microcomedones representing the clinically non‐visible central precursor lesions of acne are induced by sebaceous hyperplasia as well as altered follicular growth and differentiation, and evolve into both comedones and inflammatory lesions. Thus, targeting microcomedone formation is essential in the prevention and therapeutic control of acne.

Age and sex variation in lipid composition of human fingernail plates.

In contrast to epidermal lipid metabolism, the lipid biochemistry of nails has yet been poorly investigated. Our purpose was to define a reference population of healthy individuals as a base for the better understanding of nail diseases and age-induced changes. Therefore, we developed a method of processing and extracting the nail plates enabling us to assess the most relevant epidermal lipid classes by HPTLC. Our study revealed that nail plate lipid composition varies with age and sex: the lipid composition of the fertile years shows distinct profiles compared to that of childhood and old age, suggesting an influence of sex hormones on nail lipogenesis. Our results open the possibility in the future of an easier comparison between healthy and diseased nails and enable us to investigate factors influencing nail lipid composition such as drugs, metabolic diseases, toxic agents, cosmetics and nail therapeutics.

DP IV/CD26, APN/CD13 and related enzymes as regulators of T cell immunity: implications for experimental encephalomyelitis and multiple sclerosis.

Multiple sclerosis (MS) is the most frequent demyelinating disease of the central nervous system. Peptidases like dipeptidyl peptidase IV (DP IV, CD26) and aminopeptidase N (APN, CD13) play a regulatory role in T cell activation and represent potential targets for the treatment of inflammatory disorders. Synthetic inhibitors of DP IV and/or APN enzymatic activity induce production of the immunosuppressive cytokine TGF-beta1 and subsequently suppress DNA synthesis and Th1 cytokine production of activated human T cells. Compelling evidence has demonstrated that IL-17-producing CD4 cells (Th17) are a major contributor to the pathogenesis of autoimmune inflammation. Here, we report that inhibitors of DP IV-like activity as well as of APN activity inhibit IL-17 production in activated human and mouse T cells. Combining inhibitors of DP IV and APN increases the suppressive effect on T cell specific IL-17 production in vitro compared to a single peptidase inhibitor. In the following, we summarize the evidence for the role of both ectoenzymes in T cell activation in vitro and in vivo and provide a rationale for the use of combined or dual ectopeptidase inhibitors to treat autoimmune diseases like MS.