Constantin E. Orfanos

Other Functions, Other Genes: Alternative Activation of Antigen-Presenting Cells

We would like to thank Drs. C. C. Geilen, S. Runkel, and N. Runkel for providing comments on this review.

Alternative versus Classical Activation of Macrophages

In parallel to the Th1/Th2 paradigm, antigen-presenting cells (APC) are divided into classically activated APC (dendritic cells/effector macrophages) and alternatively activated APC (IL-4-induced, alternatively activated macrophages/IL-10-induced, immature dendritic cells). Alternatively activated APC share a special molecular repertoire including receptors of innate immunity with broad specificity for foreign antigen and anti-inflammatory cytokines such as IL-1Ra and alternative macrophage activation-associated CC-chemokine-1. Alternatively activated APC mediated tolerance and downregulated inflammation. Abuse of alternatively activated APC in support of infectious susceptibility or tumor immune escape is counteracted by the classical pathway. Thus, classically and alternatively activated APC secure the balance between proinflammatory and anti-inflammatory immune reactions.

What is the pathogenesis of acne

Abstract:  For a long time, the mantra of acne pathogenesis debates has been that acne vulgaris lesions develop when (supposedly largely androgen‐mediated) increased sebum production, ductal hypercornification, and propionibacteria come together with local inflammatory process in the unlucky affected individual. And yet, the exact sequence, precise interdependence, and choreography of pathogenic events in acne, especially the ‘match that lights the fire’ have remained surprisingly unclear, despite the venerable tradition of acne research over the past century.

Current Use and Future Potential Role of Retinoids in Dermatology

SummarySince their introduction 15 years ago, retinoids have been increasingly used for topical and systemic treatment of psoriasis and other hyperkeratotic and parakeratotic skin disorders, keratotic genodermatoses, severe acne and acne-related dermatoses, and also for therapy and/or chemoprevention of skin cancer and other neoplasia. Oxidative metabolites of vitamin A (retinol) are natural retinoids present at low levels in the peripheral blood. Synthetic retinoids are classified into 3 generations including nonaromatic, monoaromatic and polyaromatic compounds. They are detectable in plasma 30–60 minutes after systemic administration, and reach maximum concentrations 2 to 4 hours later. Elimination half-life is 10 to 20 hours for isotretinoin, 80 to 175 days for etretinate and 2 to 4 days for trans-acitretin; the latter, however, partially converts into etretinate. Retinoid concentrations in skin are rather low in contrast to subcutaneous fat tissue.Intracellularly, retinoids interact with cytosolic proteins and specific nuclear receptors. Two classes of nuclear receptors have been suggested to mediate retinoid activity at the molecular level, RARs and RXRs. The expression of retinoid receptors is tissue specific; skin mainly espresses RARγ and RXRα. Retinoids affect epidermal cell growth and differentiation as well as sebaceous gland activity and exhibit immunomodulatory and anti-inflammatory properties.Current retinoid research targets the development of receptor-selective retinoids for tailoring and/or improving their therapeutic profile. Currently, tretinoin is used systemically for acute promyelocytic leukaemia, etretinate and acitretin for psoriasis and related disorders, as well as other disorders of keratinisation, and isotretinoin for seborrhoea, severe acne, rosacea and acneiform dermatoses. Systemic retinoids are also applied for chemoprevention of epithelial skin cancer and cutaneous T cell lymphoma. The major adverse effect of retinoids is teratogenicity; all other adverse effects are dose-dependent and controllable. Contraception is, therefore, essential during retinoid treatment in women of child-bearing age. Clinical monitoring requires physical examination for adverse effects every 3 to 4 weeks and proper laboratory investigations, also including analysis of retinoid bioavailability in selected cases. Topical retinoids are rapidly developing at present and seem promising for the future; their clinical application includes acne, aging, photodamage, precanceroses, skin cancer and disorders of skin pigmentation. The development of receptor-specific retinoids for topical treatment of psoriasis and/or acne may lead to interesting new compounds based on our current concepts of retinoid function.

Alternatively activated macrophages differentially express fibronectin and its splice variants and the extracellular matrix protein betaIG-H3.

Alternative activation of macrophages, induced by Th2 cytokines and glucocorticoids, is essential for the proper functioning of anti‐inflammatory immune reactions. To this end, alternatively activated macrophages (aaMΦ) express a not yet fully unravelled set of genes including cytokines such as alternative macrophage activation‐associated CC‐chemokine (AMAC)‐1 and pattern recognition molecules such as the scavenger receptor CD163. In order to further characterize the molecular repertoire of aaMΦ, differential gene expression was analyzed by combining subtractive suppression cloning and differential hybridization. We show here that aaMΦ induced by interleukin (IL)‐4 overexpress the prototype extracellular matrix (ECM) protein fibronectin on the mRNA and protein level. This overall increase is accompanied by a shift in fibronectin splice variants from an embryonic to a mature pattern. In addition, the expression of another ECM protein, βIG‐H3, is also upregulated by IL‐4 in aaMΦ. In contrast to IL‐4 and in line with its inhibitory effect on wound healing, dexamethasone exerts a strongly suppressive effect on fibronectin and βIG‐H3 expression. In conclusion, overexpression of ECM proteins induced by IL‐4 in macrophages suggests that aaMΦ may be involved in ECM deposition and tissue remodelling during the healing phase of acute inflammatory reactions and in chronic inflammatory diseases.

Corticotropin-releasing hormone: An autocrine hormone that promotes lipogenesis in human sebocytes

Sebaceous glands may be involved in a pathway conceptually similar to that of the hypothalamic-pituitary-adrenal (HPA) axis. Such a pathway has been described and may occur in human skin and lately in the sebaceous glands because they express neuropeptide receptors. Corticotropin-releasing hormone (CRH) is the most proximal element of the HPA axis, and it acts as central coordinator for neuroendocrine and behavioral responses to stress. To further examine the probability of an HPA equivalent pathway, we investigated the expression of CRH, CRH-binding protein (CRH-BP), and CRH receptors (CRH-R) in SZ95 sebocytes in vitro and their regulation by CRH and several other hormones. CRH, CRH-BP, CRH-R1, and CRH-R2 were detectable in SZ95 sebocytes at the mRNA and protein levels: CRH-R1 was the predominant type (CRH-R1/CRH-R2 = 2). CRH was biologically active on human sebocytes: it induced biphasic increase in synthesis of sebaceous lipids with a maximum stimulation at 10−7 M and up-regulated mRNA levels of 3β- hydroxysteroid dehydrogenase/Δ5–4 isomerase, although it did not affect cell viability, cell proliferation, or IL-1β-induced IL-8 release. CRH, dehydroepiandrosterone, and 17β-estradiol did not modulate CRH-R expression, whereas testosterone at 10−7 M down-regulated CRH-R1 and CRH-R2 mRNA expression at 6 to 24 h, and growth hormone (GH) switched CRH-R1 mRNA expression to CRH-R2 at 24 h. Based on these findings, CRH may be an autocrine hormone for human sebocytes that exerts homeostatic lipogenic activity, whereas testosterone and growth hormone induce CRH negative feedback. The findings implicate CRH in the clinical development of acne, seborrhea, androgenetic alopecia, skin aging, xerosis, and other skin disorders associated with alterations in lipid formation of sebaceous origin.

The retinoids. A review of their clinical pharmacology and therapeutic use.

SummaryWith the introduction of the synthetic retinoids, oral therapy with an acceptable risk/ benefit ratio became possible for a variety of skin diseases including severe acne, psoriasis and numerous genodermatoses. This article reviews the clinical pharmacology, mechanisms of action and therapeutic use of the retinoids, particularly isotretinoin (13-cis-retinoic acid) and etretinate. The free aromatic acid of etretinate, etretin, and the new polyaromatic retinoid compounds (arotinoids) are also discussed.Isotretinoin is used clinically for oral therapy of severe acne, but is also recommended for severe Gram- negative folliculitis and rosacea not responding to traditional therapy. The results of several studies have established that acne therapy should be started with 1.0 mg/kg/day for 2 to 3 months after which the daily dosage should be lowered to 0.2 to 0.5 mg/kg/day for another 2 to 3 months. This therapeutic regimen of isotretinoin has proven to be the most successful in preventing relapses.Etretinate is particularly useful for oral therapy of widespread plaque- like, pustular and erythrodermic psoriasis, and of generalised lichen planus, Darier’s disease and severe congenital ichthyoses. Whereas pustular forms of psoriasis require a high daily dosage of 1.0 mg/kg/day, erythrodermic psoriasis should be treated with a lower dosage of 0.25 to 0.35 mg/kg/day. In chronic plaque- like psoriasis, a mean daily dosage of 0.5 mg/kg/day over several weeks to months, usually combined with photo(chemo)therapy, tar or dithranol, is recommended. Other indications for oral etretinate therapy are adequately treated with a moderate dosage of 0.4 to 0.75 mg/kg/day.Etretin differs from etretinate in having a much shorter elimination half- life of 2 to 3 days, in contrast to 80 to 100 days after long term administration of etretinate. Moreover, it has not been shown to increase serum cholesterol levels. However, its clinical efficacy is not yet clearly established.Among the arotinoids, arotinoid ethylester (Ro 13- 6298) has revealed the best anti- psoriatic and anti- inflammatory effects at extremely low dose levels. Furthermore, no significant elevations of serum lipids have been observed. Taking its prolonged elimination half- life and its efficacy/side effect ratio into account, the drug is comparable to etretinate. The free arotinoid carboxylic acid (Ro 13- 7410) is currently undergoing clinical investigation.Another arotinoid, the parent compound Ro 15- 0778, has not demonstrated any convincing clinical efficacy in acne or psoriasis, but topical anti- inflammatory effects were evident in some models. Experimental studies in animals have not demonstrated any bone toxicity, suggesting that arotinoid sulphone (Ro 15- 1570) may be the first polyaromatic retinoid with the potential for not causing adverse effects on the skeletal system. Preliminary results have demonstrated some antipsoriatic efficacy when applied topically.Among other synthetic retinoids tested clinically for topical use, only motretinide has shown similar therapeutic results in acne when compared with tretinoin. Due to its chemical instability to ultraviolet light, the topical application of isotretinoin in acne was therapeutically not clearly successful.Oral therapy with the retinoids causes a variety of mostly tolerable and reversible mucocutaneous side effects; however, their use requires careful laboratory and clinical monitoring of each patient. In particular, bone toxicity, serum lipid elevations, dysmorphogenicity and embryotoxicity are the most unacceptable adverse effects of the synthetic retinoids.

Borrelia burgdorferi—associated cutaneous B cell lymphoma: Clinical and immunohistologic characterization of four cases

Four patients with low-grade malignant B cell lymphoma of the skin in association with chronic Borrelia burgdorferi infection are presented. Plaque-shaped or nodular erythematous lesions with ill-defined borders were seen. Clinical progression was slow; the skin tumors occurred for up to 7 to 15 years. Extracutaneous involvement was found in only one case. Immunohistologic investigations showed an expression of B cell markers with restriction to only one light chain type and absence of T cell antigens. The growth fraction was 5% to 30%, as shown with the monoclonal antibody Ki-67. The immunoarchitecture of the tumors in three patients was unusual compared with established criteria for cutaneous B cell lymphoma and revealed similarities to mucosa-associated B cell lymphoma. Some immunohistologic heterogeneity may indicate the development of monoclonal proliferation that originated from different phases of B lymphocytic differentiation. In three cases no clinical signs of B. burgdorferi infection were found; in one patient acrodermatitis chronica atrophicans was present. The occurrence of acrodermatitis chronica atrophicans and malignant lymphomas was frequently reported in the European literature before B. burgdorferi was recognized. These findings suggest a relation between B. burgdorferi infection and cutaneous B cell lymphoma. In geographic regions where infected ticks are present, borreliosis should be considered in patients with cutaneous B cell lymphoma.

The Human Sebocyte Culture Model Provides New Insights into Development and Management of Seborrhoea and Acne

Seborrhoea and acne are exclusively human diseases and sebaceous gland differentiation is species specific. Therefore, fundamental research on human sebaceous cell function and control requires human in vitro models. The human sebocyte culture model, introduced in 1989, has been used in several studies to elucidate sebaceous gland activity and its regulation at the cellular level. Cultured human sebocytes have been shown to preserve important sebocytic characteristics, although they undergo an incomplete terminal differentiation in vitro. In vitro synthesis of free fatty acids without bacterial involvement and marked interleukin 1α expression at the mRNA and protein levels with no further induction by lipopolysaccharides lead to the assumption that human sebocytes may initiate acne lesions by an intrinsic mechanism. Androgens affected sebocyte activity in vitro in a manner dependent on the localization of the sebaceous glands. In vitro stimulation of sebocyte proliferation by androgens could be completely abolished by spironolactone. Cultured sebocytes strongly expressed type 1 5α-reductase and metabolized testosterone to androstenedione, 5α-androstanedione, 5α-dihydrotestosterone, androsterone and 5α-androstanediol, whereas the levels of 5α-reductase activity were probably not feedback regulated. 4,7β-Dimethyl-4-aza-5αcholestan-3-one, a type 1 5α-reductase inhibitor, induced an early, marked down-regulation of 5α-reductase activity in human sebocytes in vitro, while hydrofinasteride, a type 2 inhibitor, required 103-fold higher concentrations to induce similar effects. Stimulation of sebocyte proliferation by insulin, thyroid-stimulating hormone and hydrocortisone indicates that the hormonal control of the sebaceous gland could be a complex mechanism. Retinoids inhibited sebocyte proliferation in a dose-dependent manner and down-regulated lipid synthesis and sebocyte differentiation in vitro. Isotretinoin was the most potent compound. On the other hand, vitamin A was found essential for sebocyte activity and differentiation in vitro and could be partially substituted by synthetic retinoids. The inhibitory effect of isotretinoin on sebocyte proliferation was barely affected by the presence of vitamin A. The low persistent isotretinoin levels or, more likely, the considerably elevated tretinoin concentrations detected in human sebocytes after treatment with isotretinoin in vitro may be responsible for the inhibitory effect of this compound on sebocyte activity.

DIFFERENCES IN ANGIOGENIC POTENTIAL OF CLASSICALLY VS ALTERNATIVELY ACTIVATED MACROPHAGES

Macrophages (M phi) are important for angiogenesis during inflammation, wound repair, and tumor growth. However, well-characterized M phi subsets such as IFN-gamma-induced, classically activated (ca) M phi or IL-4/glucocorticoid-induced, alternatively activated (aa) M phi have not been thoroughly examined for a positive or negative association with angiogenesis. While caM phi populate early inflammatory reactions and high-turnover granulomas, aaM phi occur in healing wounds and chronic inflammation. In contrast to caM phi-dominated lesions, aaM phi-rich lesions are highly vascularized. In order to determine their angiogenic potential in vitro, these M phi subsets as well as unstimulated control macrophages (coM phi) were analyzed by RT-PCR for mRNA expression of 10 angiogenic factors after 3 and 6 days of culture. Early during activation, caM phi and coM phi expressed equal levels of 8 of 10 angiogenic factors (PDGF-A, MK, TNF-alpha, TGF-beta 1, PDGF-B, HGF, TGF-alpha, IGF-1), while aaM phi showed expression of only 4 of these factors (TGF-beta 1, PDGF-B, HGF, GF-1). After maturation, TGF-alpha and IGF-1 showed a shift in mRNA expression from caM phi to aaM phi resulting in a considerably enhanced expression of these factors in day-6 aaM phi as compared to day-6 caM phi and coM phi while PDGF-A, MK, and TNF-alpha remained suppressed in day 6 aaM phi. In all M phi subsets including controls, mRNA expression of aFGF and bFGF was minimal or absent while TGFG-beta 1, HGF, and ODGF-B were constitutively expressed. In order to functionally integrate angiogenic factor mRNA expression profiles, mitogenic activity of M phi subsets towards microvascular endothelium was assessed by cocultivation. Coculture experiments revealed that endothelial proliferation induced by aaM phi was 3.0-3.5x higher than induced by caM phi. In conclusion, mature aaM phi are well equipped to play an important role in protracted M phi-associated angiogenic processes. Presumably due to expression of predominantly angio-inhibitory cytokines such as TNF-alpha by caM phi but much less by aaM phi, caM phi exhibit only a low angiogenic potential in vitro and in vivo despite considerable expression of angiogenic factor mRNA.