Vitamin D analogues and psoriasis

Topical application of imatinib mesylate ameliorated psoriasis-like skin lesions in imiquimod-induced murine model via angiogenesis inhibition

Psoriasis is a chronic skin disorder characterized by a skin rash with scaly patches. Microvascular abnormalities are a characteristic feature of psoriasis and play a crucial role in the pathogenesis of psoriatic lesions. Angiogenic factors are upregulated in psoriatic skin lesions and are thought to induce angiogenesis. Platelet-derived growth factor (PDGF) induces vascular endothelial growth factor (VEGF), and PDGF is upregulated in keratinocytes in psoriatic skin lesions. The present study aimed to investigate the effect of topical imatinib mesylate (IMT) in inhibiting the activation of PDGF signalling in the pathogenesis of psoriasis. When topically applied to the skin of mice with imiquimod (IMQ)-induced psoriasis, IMT ameliorated skin symptoms similar to those of human psoriasis. Hyperproliferation of keratinocytes, hyperkeratosis, inflammatory cell infiltration and hypervascularity were histologically suppressed by topical IMT. The expression of angiogenic factors including fibroblast growth factor (FGF) and VEGF was decreased. The expression of FGF and VEGF in a PDGF-stimulated fibroblast cell line was inhibited by IMT. PDGF is required for the signalling pathway producing angiogenic factors in fibroblast. Thus, topically applied IMT inhibits PDGFR activation in fibroblast and suppresses the production of angiogenic factors, thereby mitigating the symptoms of psoriasis. The inhibitory effect of IMT on angiogenesis suggests that topical application IMT may be a viable treatment option for psoriasis.

Therapeutic options in the treatment of psoriasis and atopic dermatitis

A variety of therapeutic options are available to treat psoriasis and atopic dermatitis (AD). Local agents typically are used to treat localized and milder forms of disease, whereas phototherapy and systemic agents are used for more generalized and severe disease. Various combinations and sequences of topical or systemic therapies, or both, have been utilized in the treatment of psoriasis and, less frequently, of AD. Conventional systemic therapies for psoriasis, such as corticosteroids, oral calcineurin inhibitors, antimetabolites, and retinoids, are limited by their propensity to cause serious side effects. More recently, a number of immunobiologic agents, such as monoclonal antibodies, recombinant cytokines, and fusion proteins, have been approved by the Food and Drug Administration or are undergoing development as systemic antipsoriatic treatments. In many of these categories, a number of exciting new therapies are in development that may augment the existing armamentarium available to clinicians for the treatment of inflammatory skin diseases.

A clinician's paradigm in the treatment of psoriasis

Psoriasis is a chronically recurring inflammatory disease that affects the skin, scalp, and joints. It ranges in severity from mild to severe, and patients with moderate to severe disease experience significant deterioration in quality of life. The goals of psoriasis treatment are to gain initial and rapid control of the disease process, decrease the percentage of body surface area involved, decrease plaque lesions, achieve and maintain long-term remission, minimize adverse events, and improve patient quality of life. Therapy varies depending on disease severity and spread and will shift from control of acute flares to long-term maintenance. Topical treatment for mild psoriasis includes the use of topical corticosteroids, calcipotriene, tazarotene, topical tars, anthralin, and keratolytics. Treatment of moderate to severe psoriasis includes systemic therapies, such as methotrexate, acitretin, cyclosporine, and biologic agents. Treatment can be effected using combination, rotational, or sequential regimens. Treatment algorithms developed by a 2002 consensus conference are described. Because some degree of therapy will always be necessary, ranging from maintenance of long-term remission to control of acute psoriasis flares, each patient requires an individualized plan.

Mechanisms of action of topical therapies and the rationale for combination therapy

The advent of new topical agents such as topical calcineurin inhibitors, as well as the reformulations of older agents in new vehicles, has broadened the treatment approaches to psoriasis and atopic dermatitis. The clinician must now consider additional novel physiologic pathways and mechanisms of action as well as expanding options for combination therapy. Combination therapy is especially beneficial when the selected agents possess differing mechanisms of action that provide additive or synergistic efficacy, reducing the required doses of the individual agents compared with monotherapy and potentially limiting side effects. Therapeutic approaches also can be rotated or used in various sequences for maintenance therapy. In psoriasis, a number of trials have demonstrated the effectiveness of combination therapy. Although combination therapy has not been extensively studied in atopic dermatitis, many practitioners combine topical corticosteroids and topical calcineurin inhibitors in their clinical practice because the two drug classes have different and possibly complementary mechanisms of action. For both diseases, the decision as to what agents are combined must also be tempered by patient type, disease presentation or severity, and patient preferences.

Melanin pigmentation in mammalian skin and its hormonal regulation

Cutaneous melanin pigment plays a critical role in camouflage, mimicry, social communication, and protection against harmful effects of solar radiation. Melanogenesis is under complex regulatory control by multiple agents interacting via pathways activated by receptor-dependent and -independent mechanisms, in hormonal, auto-, para-, or intracrine fashion. Because of the multidirectional nature and heterogeneous character of the melanogenesis modifying agents, its controlling factors are not organized into simple linear sequences, but they interphase instead in a multidimensional network, with extensive functional overlapping with connections arranged both in series and in parallel. The most important positive regulator of melanogenesis is the MC1 receptor with its ligands melanocortins and ACTH, whereas among the negative regulators agouti protein stands out, determining intensity of melanogenesis and also the type of melanin synthesized. Within the context of the skin as a stress organ, melanogenic activity serves as a unique molecular sensor and transducer of noxious signals and as regulator of local homeostasis. In keeping with these multiple roles, melanogenesis is controlled by a highly structured system, active since early embryogenesis and capable of superselective functional regulation that may reach down to the cellular level represented by single melanocytes. Indeed, the significance of melanogenesis extends beyond the mere assignment of a color trait.

1,25-dihydroxyvitamin D3 regulates estrogen metabolism in cultured keratinocytes

Local estrogen metabolism may play an important role in modulating cell development in peripheral tissues such as breast, adipose, and bone. C19 androgens are converted to C18 estrogens by the enzyme aromatase, overexpression of which is associated with breast cancer. Interconversion of active estradiol (E2) to inactive estrone is controlled by various isoforms of the enzyme 17beta-hydroxysteroid dehydrogenase (17betaHSD). We have studied the expression of these two enzymes in human keratinocytes and report rapid changes in 17betaHSD activity in response to treatment with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Keratinocytes cultured in serum-free medium showed aromatase activity of 2.5 fmol/h x mg cell protein, which was unaffected by any culture treatment. A much higher level of 17betaHSD activity was observed in the keratinocytes, predominantly conversion of E2 to estrone (approximately 120 pmol/h x mg cell protein). This inactivation of E2 increased in a dose-dependent fashion after treatment of the cells with antiproliferative doses of 1,25-(OH)2D3 (0.1-200 nM). The effect of 1,25-(OH)2D3 on 17betaHSD activity was enhanced by simultaneous treatment with dexamethasone, which also increased the antiproliferative action of 1,25-(OH)2D3. Reverse transcription-PCR and Northern analysis showed that keratinocytes expressed messenger RNA for three 17betaHSD isoenzymes (types I, II, and IV). Treatment with 1,25-(OH)2D3 (10 nM for 20 h) resulted in the up-regulation of messenger RNA levels for type 2 17betaHSD. Further RNA studies combined with E2 binding experiments demonstrated the presence of estrogen receptors in the cultured keratinocytes. These data indicate that keratinocytes are potential targets for systemically or locally produced estrogens, which may, in turn, play a key role in the development of normal skin. In particular, we propose that 17betaHSD isoenzymes are key target genes for 1,25-(OH)2D3 in keratinocytes and may be an important feature of the antipsoriatic effects of vitamin D and its analogs.