Demonstration and functional analysis of IL-10 receptors in human epidermal cells: decreased expression in psoriatic skin, down-modulation by IL-8, and up-regulation by an antipsoriatic glucocorticosteroid in normal cultured keratinocytes

The chronic skin disease psoriasis is characterized by epidermal hyperproliferation and inflammation. The exact etiology of the disease is still unknown. At the molecular level, overexpression of growth factors and proinflammatory cytokines such as IL-8 and the corresponding receptor has been described in psoriatic plaques. On the other hand, the loss of inhibitory control mechanisms is involved in the pathogenesis of the disease, as exemplified by the reduced mRNA levels for the cell cycle inhibitor p53 found in lesional skin. Here we extend these findings to a cytokine with negative regulatory functions, IL-10. Only under certain conditions are human keratinocytes able to synthesize IL-10. In skin, pathological overexpression of IL-10 was described om atopic dermatitis. IL-10 exerts its effects via a specific receptor (IL-10R). We show here for the first time the presence and functionality of IL-10R in epidermal cells and its dramatically decreased expression in acute exanthematic psoriatic epidermis by in vitro and in situ binding studies. These results were substantiated using semiquantitative reverse transcriptase-PCR, demonstrating decreased expression of the IL-10R gene in psoriatic skin, its down-modulation by the proinflammatory cytokine IL-8, and its pharmacological induction in cultured cells. Biological responsiveness of epidermal cells toward IL-10 could also be demonstrated by a reduction of the growth rate and inhibition of IFN-gamma-induced HLA-DR expression. Our results provide the first evidence for a role of the IL-10R gene in the homeostasis of the epidermis and substantiate the concept of a loss of negative regulatory peptides as a step in the eruption of psoriasis.

Demonstration and functional analysis of IL-10 receptors in human epidermal cells: decreased expression in psoriatic skin, down-modulation by IL-8, and up-regulation by an antipsoriatic glucocorticosteroid in normal cultured keratinocytes

The chronic skin disease psoriasis is characterized by epidermal hyperproliferation and inflammation. The exact etiology of the disease is still unknown. At the molecular level, overexpression of growth factors and proinflammatory cytokines such as IL-8 and the corresponding receptor has been described in psoriatic plaques. On the other hand, the loss of inhibitory control mechanisms is involved in the pathogenesis of the disease, as exemplified by the reduced mRNA levels for the cell cycle inhibitor p53 found in lesional skin. Here we extend these findings to a cytokine with negative regulatory functions, IL-10. Only under certain conditions are human keratinocytes able to synthesize IL-10. In skin, pathological overexpression of IL-10 was described om atopic dermatitis. IL-10 exerts its effects via a specific receptor (IL-10R). We show here for the first time the presence and functionality of IL-10R in epidermal cells and its dramatically decreased expression in acute exanthematic psoriatic epidermis by in vitro and in situ binding studies. These results were substantiated using semiquantitative reverse transcriptase-PCR, demonstrating decreased expression of the IL-10R gene in psoriatic skin, its down-modulation by the proinflammatory cytokine IL-8, and its pharmacological induction in cultured cells. Biological responsiveness of epidermal cells toward IL-10 could also be demonstrated by a reduction of the growth rate and inhibition of IFN-gamma-induced HLA-DR expression. Our results provide the first evidence for a role of the IL-10R gene in the homeostasis of the epidermis and substantiate the concept of a loss of negative regulatory peptides as a step in the eruption of psoriasis.

Pyodermatitis-pyostomatitis vegetans

A 43-year-old woman developed annular and pustular cutaneous lesions preceded by tiny yellow pustules coating the surface of the oral mucosa. The clinical, histological and immunopathological evidence clearly showed that the patient had pyodermatitis-pyostomatitis vegetans. It is suggested that this disease is a distinct entity which should be differentiated from pemphigus vegetans.

Kaposi's sarcoma-associated herpesvirus/human herpesvirus-8: a new virus in human pathology

The discovery of a new human herpesvirus in Kaposi's sarcoma (KS) tissue of patients with AIDS has opened up new vistas in virology and oncology. This herpesvirus was first descriptively named KS-associated herpesvirus (KSHV), but was recently renamed human herpesvirus 8 (HHV8). KSHV/HHV8 DNA has been found in all forms of KS, suggesting that it might be involved in the pathogenesis of KS. In addition, KSHV/HHV8 can be detected in both malignant and benign lymphoproliferative disease. KSHV/HHV8 was also found in patients with angiosarcoma of the face and angiolymphoid hyperplasia with eosinophilia. Although only a limited portion of the virus has been sequenced, KSHV/HHV8 is equipped with genes that could confer oncogenic potential. The virus can now be cultured, providing the possibility for studies of viral replication and the mode of transmission. The recently developed serologic assays for antiviral antibodies suggest that infection with KSHV/HHV8 is not ubiquitous because KSHV/HHV8 seropositivity is limited to a small proportion of the population.

[Kaposi sarcoma-associated herpesvirus; human herpesvirus 8]

The discovery of a new human herpesvirus in Kaposi's sarcoma tissues of AIDS patients has opened up new facts in virology and oncology. This herpesvirus was first descriptively named Kaposi's sarcoma-associated herpesvirus, but was recently renamed human herpesvirus 8. Human herpesvirus 8 DNA has been consequently found in all forms of Kaposi's sarcoma, suggesting that it might be involved in the pathogenesis of the disease. Additionally, human herpesvirus 8 can be detected in both malignant and benign lymphoproliferative diseases, such as body-cavity-based B-cell lymphomas and multicentric Castleman disease. The virus was also recently found in rare vascular tumors in patients with angiosarcoma of the face and angiolymphoid hyperplasia with eosinophilia. Although only a limited portion of the viral DNA has been sequenced, it has become evident that the new herpesvirus is equipped with genes that could confer oncogenic potential. The virus can now be cultured, providing the possibility for studies of viral replication and the mode of transmission, and also for the development of serologic tests.

Antioncogene P53 and mitogenic cytokine interleukin-8 aberrantly expressed in psoriatic skin are inversely regulated by the antipsoriatic drug tacrolimus (FK506)

Uncontrolled proliferation of epidermal cells is the most prominent characteristic of psoriasis. This widespread skin disease can be effectively treated with the microbial substance FK506, which acts by modulating gene expression. We, therefore, asked if the drug changes the expression of genes involved in growth regulation (the mitogenic cytokine interleukin-8 (IL-8) and p53, a negative cell cycle regulator) and signal transduction (protooncogenes c-ras, c-raf, and HER-2). Gene expression was monitored by semiquantitative mRNA-PCR and for p53 by immunocytochemistry in cultured primary keratinocytes (KC). In addition, p53 expression was analysed in skin biopsies of psoriatic patients. After 1-3 hr, IL-8 mRNA levels were dose-dependently decreased in tacrolimus (FK506)-treated cells. Protooncogene expression was not significantly altered. Interestingly, p53 transcription was clearly induced by FK506 treatment. This tendency could be verified on the protein level by immunocytochemistry. In contrast, p53 expression was decreased in lesional psoriatic as compared to normal skin, providing evidence that not only posttranslational modification of the p53 protein, but also transcriptional modulation of the p53 gene, are involved in pathological processes and pharmacological drug action in skin. Together with earlier results showing downmodulation for IL-8 receptor type A expression in cultured KC treated with FK506, these results suggest that both the mitogenic IL-8/IL-8R system and the cell cycle inhibitor p53 represent potential targets for the antipsoriatic action of the drug, whereas protooncogenes acting downstream in mitogenic signal transduction cascades are unaffected. The differential modulation of an entire set of genes provides evidence for the specificity of the drug effects and rules out nonspecific toxic effects on KC.

Human herpesvirus 8 in classic Kaposi sarcoma

Recent studies suggest the role of a new human herpesvirus (HHV8) in the pathogenesis of different forms of Kaposi sarcoma (KS). In the present work we investigated the presence of HHV8 sequences in KS tumour tissues from patient with classic KS. Since clear evidences point to the role of immune suppression in the development of AIDS-associated KS or patients receiving immunosuppressive therapy, immunological investigations were also performed. We could show a highly consequent association of HHV8 sequences with classic KS in the large series of patients supporting our previous findings that this virus might be in some way involved in the pathogenesis of this tumour. In addition immunological examination of the patients revealed a mild decrease in the CD4 positive cell number, a significantly reduced CD4/CD8 ratio, a diminished PHA reactivity and leukocyte migration factor production of lymphocytes. The changes observed in the present study are similar, but much less pronounced than those may be observed in HIV infection.

Interleukin-8 induces HLA-DR expression on cultured human keratinocytes via specific receptors

Recent studies suggest that interleukin (IL)-8 exerts a direct influence on several functions such as the chemotaxis or proliferation of human keratinocytes (HK). Since the effects of IL-8 in skin are mediated through specific receptors, we have studied the characteristics of the keratinocyte IL-8 receptor. We could identify specific binding sites for IL-8 in cultured HKs by flow cytometry. Pretreatment of the cells with tumor necrosis factor (TNF)-alpha or IL-1 alpha resulted in a significant increase in IL-8 binding. IL-8 selectively induced expression of HLA-DR antigen, but had no effect on the expression of other cell surface antigens (CD11a, CD18, CD36 and CD54).

Novel steroid derivative modulates gene expression of cytokines and growth regulators

Topical steroid treatment is a common therapy for psoriasis. Steroids are known to bind to specific cytoplasmic receptors and to influence gene expression. We investigated the effects of the novel steroid derivative mometasone furoate on the expression of putative target genes in normal human epidermal cells (KC). Gene expression was measured by semiquantitative mRNA-PCR. In addition, cytokine receptor characteristics were assessed by ligand binding studies. We found a dose-dependent downregulation of proinflammatory mediators (IL-8, TNF alpha). Genes involved in growth regulation (HER-2, p53) were also modulated. IL-8 binding to KC was inhibited. We conclude that modulation of the expression of cytokine, cytokine receptor and growth factor genes may contribute to the antipsoriatic action of steroids.

Role of interleukin-8 receptor in skin

Interleukin-8 (IL-8) is a potent chemotactic and proinflammatory cytokine, produced in the skin by a variety of cells in response to inflammatory stimuli. Recent studies suggest that in addition to its potent actions on leukocytes, IL-8 exerts a direct influence on several functions of human epidermal cells such as chemotaxis, Candida albicans killing activity or proliferation. The effects of IL-8 are mediated by binding to two types of specific high-affinity receptors which contain seven transmembrane domains typical of guanine nucleotide binding protein (G protein)-coupled receptors. In the skin, a broad spectrum of cells such as neutrophils, T lymphocytes, mast cells, dermal macrophages, endothelial cells and keratinocytes possess binding sites for IL-8. Recently, increased expression of epidermal IL-8 receptors has been observed in psoriasis an inflammatory and hyperproliferative skin disease. Since the effects of IL-8 may be modulated at the receptor level, the pharmacological manipulation of the IL-8 receptor may prove an important target for the therapy of skin diseases with increased IL-8 levels.

Chemotaxis of freshly separated and cultured human keratinocytes

It is generally accepted that keratinocyte migration plays a critical role in the process of wound healing. A study was therefore made of the migratory response of freshly separated and cultured human keratinocytes to factors with chemotactic properties for a variety of cells. Interleukin-1 alpha (IL-1 alpha), interferon-gamma (IFN-gamma), interleukin-8 (IL-8), and tumour necrosis factor alpha (TNF-alpha) were tested for their chemotactic effectiveness in a modified Boyden chamber assay. IFN-gamma, IL-1 alpha and IL-8 were demonstrated to serve as chemoattractants for freshly separated keratinocytes. For cultured cells, however, only IFN-gamma was found to display chemotactic properties. The findings demonstrate that there is significant difference between the chemotactic behaviour of freshly separated and cultured cells.

The interleukin-8 receptor: a potential target for antipsoriatic therapy?

Interleukin-8 is assumed to play a central role in the pathogenesis of psoriasis. Since an increased expression of the interleukin-8 receptor has been observed both in polymorphonuclear leukocytes and in affected psoriatic epidermis, we were interested in whether the interleukin-8 receptor could be a molecular target of antipsoriatic compounds. Cyclosporine, calcitriol, calcipotriol or dithranol caused a dose-dependent decrease in interleukin-8 binding to cultured human keratinocytes, while interleukin-8 binding to granulocytes was not affected. In addition, the interleukin-8-induced human leukocyte antigen-DR (HLA-DR) expression of keratinocytes was nearly completely blocked by treatment of the cells with these substances. The inhibition of the keratinocyte interleukin-8 receptor and its function by antipsoriatic drugs may contribute to their therapeutic action.

Cytokine system as potential target for antipsoriatic therapy

Cytokines are produced by a variety of cells and have numerous of overlapping activities. There is increasing evidence that cytokines play a crucial role in the pathogenesis of psoriasis and of other dermatologic diseases. This review summarizes current knowledge as to how the altered cytokine network is involved in the accumulation of inflammatory cells in lesional skin, and how the cytokines are involved in epidermal hyperproliferation. The actions of the most important therapeutic compounds, such as corticosteroids, dithranol, cyclosporine, retinoids, vitamin D3 analogues and ultraviolet radiation, on the cytokine system are also discussed. Consideration is given as to how the effects on the production of cytokines and/or cytokine receptors contribute to their therapeutic action.

Increased expression of epidermal IL-8 receptor in psoriasis. Down-regulation by FK-506 in vitro

IL-8 is a chemotactic cytokine with proinflammatory and growth-promoting activities. Recently it has been shown to influence several functions of keratinocytes, including HLA-DR expression, chemotaxis, and proliferation by binding to a specific receptor. Because psoriasis vulgaris is characterized by epidermal hyperproliferation and infiltration of inflammatory cells, we investigated the expression of IL-8 and its receptor in normal and psoriatic epidermis using semiquantitative reverse-transcriptase-polymerase chain reaction. In addition the mRNA levels of the proto-oncogenes c-ras, c-raf, c-myc, and HER-2 were also investigated as potential growth-promoting stimuli in psoriatic epidermis. IL-8 mRNA was only detected in lesional psoriatic epidermis, and IL-8R-specific mRNA was found to be 10 times increased in lesional psoriatic epidermis. There was no significant difference in the protooncogene mRNA levels. In order to test the relevance of the massively increased IL-8R levels in psoriatic epidermis, we investigated the effect of the antipsoriatic drug FK-506 on specific IL-8 and IL-8R mRNA expression. FK-506 dose dependently inhibited IL-8R expression and function. Our data suggest that in psoriatic skin, elevated IL-8 levels and markedly increased IL-8R expression may act in concert to induce the cardinal signs of psoriasis--epidermal hyperproliferation and leukocyte infiltration. IL-8R may prove a molecular target for antipsoriatic drugs such as FK-506.

Increased expression of epidermal IL-8 receptor in psoriasis. Down-regulation by FK-506 in vitro

IL-8 is a chemotactic cytokine with proinflammatory and growth-promoting activities. Recently it has been shown to influence several functions of keratinocytes, including HLA-DR expression, chemotaxis, and proliferation by binding to a specific receptor. Because psoriasis vulgaris is characterized by epidermal hyperproliferation and infiltration of inflammatory cells, we investigated the expression of IL-8 and its receptor in normal and psoriatic epidermis using semiquantitative reverse-transcriptase-polymerase chain reaction. In addition the mRNA levels of the proto-oncogenes c-ras, c-raf, c-myc, and HER-2 were also investigated as potential growth-promoting stimuli in psoriatic epidermis. IL-8 mRNA was only detected in lesional psoriatic epidermis, and IL-8R-specific mRNA was found to be 10 times increased in lesional psoriatic epidermis. There was no significant difference in the protooncogene mRNA levels. In order to test the relevance of the massively increased IL-8R levels in psoriatic epidermis, we investigated the effect of the antipsoriatic drug FK-506 on specific IL-8 and IL-8R mRNA expression. FK-506 dose dependently inhibited IL-8R expression and function. Our data suggest that in psoriatic skin, elevated IL-8 levels and markedly increased IL-8R expression may act in concert to induce the cardinal signs of psoriasis--epidermal hyperproliferation and leukocyte infiltration. IL-8R may prove a molecular target for antipsoriatic drugs such as FK-506.

Down-regulation of epidermal growth factor receptors by dithranol

Dithranol is highly effective in the treatment of psoriasis, but the exact mechanism of action is not known. Since persistent expression of epidermal growth factor (EGF) receptors in psoriatic epidermis is assumed to have pathogenetic significance, we have studied the effects of dithranol on EGF binding to the human epidermal cell line SCL-II. After treatment of cells with dithranol or its therapeutically inactive oxidation product, danthrone, radioligand binding assays were performed with 125I-EGF. In therapeutically active concentrations (0.25-1 micrograms/ml) dithranol induced a decrease in EGF binding in a dose dependent manner. Danthrone was inactive. The inhibition occurred after a latency period of 6 h and reached its maximum at 24 h. At the concentration of 1 microgram/ml, the drug led to approximately a 70% decrease in the number of specific high-affinity EGF receptors (Bmax), whereas receptor affinity (Kd) showed no change. The down-regulation of EGF receptors on epidermal cells by dithranol may contribute to its antipsoriatic action.

Interleukin-8 receptors in normal and psoriatic polymorphonuclear leukocytes

Polymorphonuclear leukocyte (PMNL) infiltration is an important characteristic in psoriatic lesions. The proinflammatory 8-kD peptide interleukin-8 (IL-8) is present in psoriatic scales and possesses a high chemotactic activity on human neutrophils, which may relate to its role in psoriasis. Its chemotactic activity is mediated via specific receptors on PMNL. The goal of our work was to ascertain whether PMNL infiltration in psoriasis can be accounted for by functional abnormalities of the circulating PMNL due to alterations in the IL-8 receptor density or affinity (or both). Results of radioligand binding studies performed in 10 psoriatic patients, 10 patients with atopic eczema and 11 normal controls showed no difference in receptor affinity (Kd) between the groups. However, a slight but significant elevation in IL-8 receptor density was seen on PMNL from psoriatic individuals (31,230 +/- 3,237 binding sites per cell) compared to those from normal volunteers (24,152 +/- 2,643) and atopic eczema patients (24,092 +/- 2,743). Increased number of IL-8 receptors may, besides elevated cutaneous IL-8 concentrations, contribute to the intraepidermal accumulation of PMNL in psoriasis.

Characterization of high-affinity 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) binding sites on normal human keratinocytes

Eicosanoids are thought to play an important role in the pathogenesis of inflammatory skin diseases. The object of the present study was the detection and characterization of putative 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) binding sites in normal human keratinocytes. Keratinocytes were obtained from foreskin and dermatome-shaved normal human skin. Radioligand binding assays were performed with 12(S)-[3H]HETE on cultured cells. Analysis of saturation curves suggested a one-site model for 12(S)-HETE binding with a KD of 3.84 +/- 0.18 nM and receptor number Bmax of 2.32 +/- 0.12 x 10(5) per cell. Ligand binding was reversible. The rank order of potency in competition for 12(S)-[3H]HETE was 12(S)-HETE > 12(R)- HETE > or = leukotriene B4. Preincubation of cells with 12(S)-HETE (2 x 10(-6) M) resulted in down-regulation of the binding site by approximately 50%. The identification and characterization of specific 12(S)-HETE binding sites on normal human keratinocytes should enable further elucidation of the role of 12-HETE in cutaneous biology and in the pathophysiology of psoriasis and other inflammatory and hyperproliferative dermatoses.

The lipoxygenase inhibitor 2-phenylmethyl-1-naphthol (DuP 654) is a 12(S)-hydroxyeicosatetraenoic acid receptor antagonist in the human epidermal cell line SCL-II

The lipoxygenase inhibitor 2-phenylmethyl-1-naphthol (DuP 654) has been shown to be an active anti-inflammatory drug in a murine skin inflammation model. Since 12-HETE is assumed to have a pathophysiological role in inflammatory skin diseases, and epidermal cells possess high affinity binding sites for 12(S)-HETE, we studied the effect of DuP 654 on 12(S)-HETE binding to the human epidermal cell line SCL-II. DuP 654 antagonized 12(S)-HETE binding in a dose-dependent manner with a Ki of 3.41 +/- 0.23 nM. The antagonistic effect was reversible. After 1- and 24-hour preincubation, the drug had no more significant inhibitory effect at concentrations between 10(-10) and 10(-5) M on specific 12(S)-HETE binding (Bmax of 215,000 +/- 21,000 receptors per cell) or on receptor affinity (Kd of 3.25 +/- 0.42 nM). Our results show that DuP 654, in addition to its 5-lipoxygenase inhibitory activity, exhibits 12-HETE receptor antagonist effect, and therefore may be of benefit in skin diseases with elevated 12-HETE levels.

Langerhans cells of the human skin possess high-affinity 12(S)-hydroxyeicosa tetraenoic acid receptors

The arachidonic acid metabolite 12-hydroxyeicosatetraenoic acid (12-HETE) is the main eicosanoid formed by epidermal cells and is assumed to play an important role in skin physiology and pathophysiology. Our aim was to find out whether epidermal Langerhans cells possess specific receptors for 12-HETE which would mediate the effects of this eicosanoid in their skin microenvironment. By radioligand binding studies on isolated human Langerhans cells, we could identify specific binding sites for 12(S)-HETE. The analysis of binding data revealed a single class of binding sites with a Kd of 3.32 +/- 0.45 nM and a Bmax of 691,000 +/- 58,000 receptors per cell. The binding was saturable, readily reversible, and specific for 12(S)-HETE. The receptor is likely to mediate the potent chemotactic response of human Langerhans cells towards 12(S)-HETE, which we previously described. Our results strongly suggest that extremely low concentrations of 12-HETE which is formed by epidermal keratinocytes may dramatically influence the biology of Langerhans cells by receptor-mediated effects.

Interleukin-8 receptor-mediated chemotaxis of normal human epidermal cells

Normal human keratinocytes show chemotactic behavior towards interleukin-8 (IL-8). Under physiological conditions this cytokine seems to be present in an equilibrium between monomeric and dimeric forms, as indicated by Western blotting data. Radioligand binding studies suggest that keratinocyte chemotaxis is mediated by receptors specific for IL-8 dimers. IL-8 receptor-specific mRNA can be detected in a keratinocyte cell line by polymerase chain reaction.

Defect of epidermal 12(S)-hydroxyeicosatetraenoic acid receptors in psoriasis

12-hydroxyeicosatetraenoic acid (12-HETE) is assumed to play a central role in the pathophysiology of psoriasis. Since its effects in skin are mediated by specific high-affinity receptors, we studied the receptor characteristics in cultured epidermal cells from involved and apparently healthy skin of psoriasis patients by radioligand binding assay. Involved and uninvolved psoriatic epidermal cells showed a fourfold decrease in the number of 12-HETE binding sites as compared with normal healthy individuals and patients with atopic dermatitis, while receptor affinity remained unchanged. The decrease in receptor number was evident in psoriatic cells even in long-term culture and was not due to receptor down-regulation, defective response to interferon gamma or to protease degradation of receptor protein. The decrease in the number of 12-HETE receptors detectable even in clinically normal psoriatic skin functionally leads to diminished 12-HETE uptake and may thus represent a primary central molecular defect in the pathophysiology of the disease.

Inhibition of 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] binding to epidermal cells by ultraviolet-B

12-hydroxyeicosatetraenoic acid (12-HETE), the main eicosanoid in skin, is assumed to have both pathophysiologic effects in inflammatory skin diseases such as psoriasis and atopic eczema and a physiologic role in the biology of cutaneous reparative processes. Because 12-HETE exerts its effects via specific high-affinity epidermal receptors, and ultraviolet-B (UV-B) is capable of modulating various cell-surface molecules, the effects of single and repeated UV-B irradiations on the 12(S)-HETE binding sites in a human epidermal cell line, SCL-II, were studied. UV-B (100-300 J/m2) induced a large decrease in 12(S)-HETE binding in a dose-dependent manner. The inhibition occurred after a latency period of 6 h, reached its maximum at 18 h and slowly declined thereafter. A single UV-B dose of 300 J/m2 or repeated irradiation with 50 J/m2 of UV-B resulted in a 70% decrease in the number of binding sites (Bmax), whereas receptor affinity remained unaffected. The modulation of epidermal 12-HETE receptors by UV-B may partly explain the therapeutic effects of UV-B, but possibly also contribute to photodamage to skin.

Dithranol-induced down-regulation of 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] receptors in a human epidermal cell line

The effects of dithranol and its therapeutically inactive oxidation product, danthrone, on 12(S)-HETE binding to the human epidermal cell line SCL-II were studied. Dithranol (0.25-1 microgram/ml), in contrast to danthrone, induced a substantial decrease in 12(S)-HETE binding in a dose-dependent manner. The inhibition occurred after a latency period of 6 h, reached its maximum at 18-24 h and slowly declined thereafter. At a concentration of 1 microgram/ml, the drug led to an approximately 50% decrease in the number of specific high-affinity 12(S)-HEFE receptors (Bmax), whereas receptor affinity (Kd) showed no change. The down-regulation of 12(S)-HETE receptors on epidermal cells by dithranol may contribute to its antipsoriatic action.

SC-41930, a leukotriene B4 receptor antagonist, inhibits 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) binding to epidermal cells

SC-41930, 7-[3-(4-acetyl-3-methoxy-2-propylphenoxy)-propoxyl]-3, 4-dihydro-8-propyl-2H-1-benzopyran-2-carboxylic acid, a potent leukotriene-B4 (LTB4) receptor antagonist, inhibits in vivo 12-hydroxyeicosatetraenoic acid (12-HETE)-induced neutrophil infiltration, suggesting a potential 12-HETE receptor antagonist effect, as well. Since 12-HETE is assumed to have a pathophysiological role in inflammatory skin diseases, and epidermal cells possess high affinity binding sites for 12(S)-HETE, we studied the effect of SC-41930 on 12(S)-HETE binding to the human epidermal cell line, SCL-II. SC-41930 antagonized the 12(S)-HETE binding to SCL-II cells with a Ki of 480 nM. This Ki value is similar to that obtained for the inhibition of LTB4 binding to human neutrophils. Our results show that SC-41930, in addition to its LTB4 receptor antagonist effect, exhibits 12-HETE receptor antagonist effect as well, and therefore may be of benefit in skin diseases with elevated 12-HETE levels.

Effect of ciclosporin on epidermal 12(S)-hydroxyeicosatetraenoic acid binding sites

12-Hydroxyeicosatetraenoic acid (12-HETE) is assumed to play an important role in the pathogenesis of inflammatory skin diseases. Recently, high-affinity binding sites for this eicosanoid have been identified on human keratinocytes by our group. Since ciclosporin exerts therapeutic effects in chronic inflammatory dermatoses such as psoriasis or atopic eczema, the influence of the drug on 12(S)-HETE binding to human keratinocytes was studied. No competitive inhibition of 12(S)-HETE binding was observed in ciclosporin concentrations between 10(-10) and 10(-6) M. In contrast, pretreatment of epidermal cells for 24 h resulted in a dose-dependent decrease of specific 12(S)-HETE binding. The analysis of saturation curves showed that the inhibition of 12(S)-HETE binding by ciclosporin was due to the decrease of 12-HETE binding sites, while receptor affinity remained unchanged. In addition, ciclosporin blocked the interferon-gamma-induced increase in epidermal 12(S)-HETE binding. These findings suggest that the effects of ciclosporin in cutaneous disorders could be partly mediated via an influence on epidermal 12(S)-HETE binding.

Effect of BN 52021, a platelet activating factor antagonist, on dithranol-induced inflammation

The effect of BN 52021, a selective platelet activating factor (PAF) antagonist was studied on dithranol-induced irritant dermatitis. Pretreatment of the skin with 0.45% BN 52021 ointment significantly suppressed the decrease in capillary resistance, rise in skin temperature and increase in skin-fold thickness produced by dithranol.

Dithranol: a review of the mechanism of action in the treatment of psoriasis vulgaris

Dithranol is highly effective in the treatment of psoriasis. The drug inhibits keratinocyte hyperproliferation, granulocyte function and, in addition, may exert an immunosuppressive effect. Free radicals, histamine, eicosanoids and platelet-activating factor have been shown to be involved in dithranol-induced dermatitis, and the oxidation products of the drug are responsible for the staining. Our experimental data suggest that extracellularly generated oxygen free radicals are responsible for both the antipsoriatic and irritative effect of the drug. Furthermore, we could recently provide evidence that extracellularly generated superoxide anion radical also induces an active adaptation mechanism resulting in increased tolerance to dithranol upon repeated application. This adaptive process may explain the requirement for increasing dithranol concentrations to maintain the antipsoriatic efficacy, and also the beneficial effect of other antipsoriatic modalities such as UV-B on dithranol-induced dermatitis. The recognition of this adaptive mechanism may open future prospects to overcome some limitations concerning the practical use of dithranol.

Pharmacological studies on dithranol-induced irritative dermatitis in mice

The effects of different pharmacological substances on dithranol-induced irritative dermatitis were studied in mice. Pretreatment of the animals with a specific platelet activating factor (PAF) antagonist, BN 52021, significantly reduced the ear swelling in a dose-dependent manner. The cyclooxygenase inhibitor indomethacin, the antihistamine clemastine, and the anti-oxidant superoxide dismutase also proved to be effective in the reduction of the dermatitis. The results provide evidence of the coinvolvement of PAF, prostaglandins, histamine, and reactive oxygen radicals in dithranol-induced irritative dermatitis in mice.

[The irritant effect of dithranol using capillary resistance measurement]

The effect of topically applied dithranol on the capillary resistance (CR) was studied both in healthy volunteers and in clinically unaffected skin of psoriatic patients. The CR of the psoriatic patients was significantly lower than that of the healthy persons. O.10% and 0.25% dithranol ointment induced a significant decrease of CR in the skin of both groups. This decrease was prevented or at least reduced, if the patients had previously been treated with either the antihistamine clemastine or the cyclooxygenase-inhibitor indomethacin. The effect of dithranol on the CR was also moderated, if 5% coal tar had been added to the dithranol preparation.

The effect of mouse erythrocyte rosette forming lymphocytes on lymphokine production in T-cell cultures

An enhancement effect of mouse erythrocyte rosette forming (MERF) cells on the production of migration inhibitory factor, chemotactic factor for neutrophils and skin reactive factor in T-lymphocyte cultures stimulated with the purified protein derivative of tuberculin was observed. We consider it likely that the MERF cells, possessing the appropriate cell surface constituents to construct an immunogenic moiety, present antigen on their surfaces to elicit lymphokine production.

Regulation of lymphokine production in peripheral blood mononuclear cell cultures

An increase in the production of macrophage migration inhibitory factor, chemotactic factor for neutrophils, and skin reactive factor, was observed in lymphocyte cultures if the cells were allowed to age in culture for 24 h. The increased lymphokine production was reduced by adding concanavalin A-stimulated and mitomycin C-treated suppressor cells. It is suggested that the lymphokine production could be regulated by suppressive mononuclear cells.