Revolutionizing Psoriasis Topical Treatment: Enhanced Efficacy Through Ceramide/Phospholipid Composite Cerosomes Co-Delivery of Cyclosporine and Dithranol: In-Vitro, Ex-Vivo, and in-Vivo Studies

Purpose

Improving the treatment of psoriasis is a serious challenge today. Psoriasis is an immune-mediated skin condition affecting 125 million people worldwide. It is commonly treated with cyclosporine-A (CsA) and dithranol (DTH). CsA suppresses the activation of T-cells, immune cells involved in forming psoriatic lesions. Meanwhile, DTH is a potent anti-inflammatory and anti-proliferative drug that effectively reduces the severity of psoriasis symptoms such as redness, scaling, and skin thickness. CsA and DTH belong to BCS class II with limited oral bioavailability. We aim to develop a drug delivery system for topical co-delivery of CsA and DTH, exploring its therapeutic potential.

Methods

Firstly, we developed a niosomal drug delivery system based on ceramide IIIB to form Cerosomes. Cerosomes were prepared from a mixture of Ceramide, hyaluronic acid, and edge activator using a thin-film hydration technique. To co-deliver CsA and DTH topically for the treatment of psoriasis. These two hydrophobic drugs encapsulated into our synthesized positively charged particle cerosomes.

Results

 Cerosomes had an average particle size of (222.36 nm± 0.36), polydispersity index of (0.415±0.04), Entrapment Efficiency of (96.91%± 0.56), and zeta potential of (29.36±0.38mV) for selected formula. In vitro, In silico, in vivo, permeation, and histopathology experiments have shown that cerosomes enhanced the skin penetration of both hydrophobic drugs by 66.7% compared to the CsA/DTH solution. Imiquimod (IMQ) induced psoriatic mice model was topically treated with our CsA/DTH cerosomes. We found that our formulation enhances the skin penetration of both drugs and reduces psoriasis area and severity index (PASI score) by 2.73 times and 42.85%, respectively, compared to the CsA/DTH solution. Moreover, it reduces the levels of proinflammatory cytokines, TNF-α, IL-10, and IL-6 compared to CsA/DTH solution administration.

Conclusion

The Cerosomes nano-vesicle-containing CsA/DTH represents a more promising topical treatment for psoriasis, giving new hope to individuals with psoriasis, compared to commercial and other conventional alternatives.

Induction of IL-1β and antimicrobial peptides as a potential mechanism for topical dithranol

Topical dithranol is effective in autoimmune conditions like alopecia areata, inducing hair regrowth in a high percentage of cases. Exact mechanisms of dithranol in alopecia areata, with seemingly healthy epidermis besides altered hair follicles, are not well understood. To better understand dithranol's mechanisms on healthy skin, we analysed its effect on normal murine as well as xenografted human skin. We found a strong increase in mRNA expression of anti-microbial peptides (AMPs) (eg Lcn2, Defb1, Defb3, S100a8, S100a9), keratinocyte differentiation markers (eg Serpinb3a, Flg, Krt16, Lce3e) and inflammatory cytokines (eg Il1b and Il17) in healthy murine skin. This effect was paralleled by inflammation and disturbed skin barrier, as well as an injury response resulting in epidermal hyperproliferation, as observed in murine and xenografted adult human skin. This contact response and disturbed barrier induced by dithranol might lead via a vicious loop between AMPs such as S100a8/a9 (that led to skin swelling itself after topical application) and cytokines such as IL-1β to an immune suppressive environment in the skin. A better understanding of the skin's physiologic response to dithranol may open up new avenues for the establishment of novel therapeutics (including AMP-related/interfering molecules) for certain skin conditions, such as alopecia areata.

Dithranol targets keratinocytes, their crosstalk with neutrophils and inhibits the IL-36 inflammatory loop in psoriasis

Despite the introduction of biologics, topical dithranol (anthralin) has remained one of the most effective anti-psoriatic agents. Serial biopsies from human psoriatic lesions and both the c-Jun/JunB and imiquimod psoriasis mouse model allowed us to study the therapeutic mechanism of this drug. Top differentially expressed genes in the early response to dithranol belonged to keratinocyte and epidermal differentiation pathways and IL-1 family members (i.e. IL36RN) but not elements of the IL-17/IL-23 axis. In human psoriatic response to dithranol, rapid decrease in expression of keratinocyte differentiation regulators (e.g. involucrin, SERPINB7 and SERPINB13), antimicrobial peptides (e.g. ß-defensins like DEFB4A, DEFB4B, DEFB103A, S100 proteins like S100A7, S100A12), chemotactic factors for neutrophils (e.g. CXCL5, CXCL8) and neutrophilic infiltration was followed with much delay by reduction in T cell infiltration. Targeting keratinocytes rather than immune cells may be an alternative approach in particular for topical anti-psoriatic treatment, an area with high need for new drugs.

Potent inhibitors of equine steroid isomerase EcaGST A3-3

Equine glutathione transferase A3-3 (EcaGST A3-3) belongs to the superfamily of detoxication enzymes found in all higher organisms. However, it is also the most efficient steroid double-bond isomerase known in mammals. Equus ferus caballus shares the steroidogenic pathway with Homo sapiens, which makes the horse a suitable animal model for investigations of human steroidogenesis. Inhibition of the enzyme has potential for treatment of steroid-hormone-dependent disorders. Screening of a library of FDA-approved drugs identified 16 out of 1040 compounds, which at 10 μM concentration afforded at least 50% inhibition of EcaGST A3-3. The most potent inhibitors, anthralin, sennoside A, tannic acid, and ethacrynic acid, were characterized by IC₅₀ values in the submicromolar range when assayed with the natural substrate Δ⁵-androstene-3,17-dione.

Anthralin modulates the expression pattern of cytokeratins and antimicrobial peptides by psoriatic keratinocytes

BACKGROUND

Psoriasis is an inflammatory skin disease with aberrant keratinocyte proliferation, presumably as a result of immune cell activation. Th17 cytokines like IL-17A and IL-22 are critically implicated in epidermal thickening, altered keratinocyte differentiation and production of innate factors such as antimicrobial peptides. Psoriasis treatment options include modern targeted therapies using anti-cytokine antibodies and traditional non-targeted treatments like anthralin (dithranol). While the mode of action of anti-cytokine antibodies is defined, the effects of topical anthralin on psoriatic skin are not fully understood.

OBJECTIVE

This study aims to unravel the direct effects of anthralin on keratinocyte proliferation, differentiation and production of psoriasis-associated factors.

METHODS

We tested the effects of anthralin on cell proliferation, cytokeratin expression and changes in the expression of antimicrobial peptides using primary keratinocytes and 3D psoriasis tissue models with and without stimulation of the psoriasis-promoting cytokines IL-17A and IL-22. Moreover, we compared the findings derived from monolayer and multilayer cultures to data derived from lesional skin of patients with psoriasis before and under treatment with anthralin.

RESULTS

Our study shows that anthralin directly induces cell apoptosis in vitro in monolayer cultures but not in 3D psoriasis tissue models treated with IL-17A and IL-22. Yet, keratinocyte proliferation as determined by Ki-67 staining is impaired by anthralin in vivo. In lesional skin but not in 3D psoriasis tissue models anthralin rapidly normalizes cytokeratin (CK)16 expression. Furthermore, anthralin directly inhibits DEFB4 expression in vitro and in vivo, while other antimicrobial peptides and cytokines studied like IL-6 and IL-8 are regulated differently in vitro and in vivo.

CONCLUSIONS

Our results show that anthralin directly regulates DEFB4A expression. However, its beneficial effects on psoriasis cannot be explained by direct effects on keratinocyte differentiation or cytokine expression.

Dithranol treatment of plaque-type psoriasis increases serum TNF-like weak inducer of apoptosis (TWEAK)

PURPOSE

TNF-like weak inducer of apoptosis (TWEAK) mediates not only apoptosis, but also inflammation, cell growth and angiogenesis. The role of TWEAK in psoriasis remains unknown. The aim of the study was to assess serum levels of TWEAK in psoriatic patients before and after topical treatment with dithranol in relation to the clinical activity of the disease.

MATERIAL AND METHODS

Serum samples were collected from 40 patients with plaque type psoriasis before and after topical treatment with dithranol. The concentrations of serum TWEAK were measured by ELISA and next compared with 16 healthy controls. The data were analyzed with respect to Psoriasis Area and Severity Index (PASI).

RESULTS

Baseline serum TWEAK concentrations of psoriatic patients (685±166pg/ml) were significantly greater compared to healthy controls (565±110pg/ml). Topical treatment resulted in further increase in serum TWEAK (749±179pg/ml; p<0.01). In case of patients with initial serum TWEAK concentrations above the median, PASI after topical treatment was lower compared to the individuals with initial TWEAK below the median.

CONCLUSION

According to the study, serum Tweak was increased in psoriasis patients compared with controls. Moreover, dithranol topical treatment caused further increase in serum TWEAK. Also, a higher effectiveness of topical treatment was observed in case of patients with higher initial TWEAK concentrations. The results suggest a potential role of TWEAK in psoriasis therapy.

Antibacterial activities of the methanol extracts, fractions and compounds from Harungana madagascariensis Lam. ex Poir. (Hypericaceae)

ETHNOPHARMACOLOGICAL RELEVANCE

Harungana madagascariensis Lam. ex Poir. (Hypericaceae) is used in folk medicine to treat a variety of human ailments, mainly antibacterial, antifungal, antiviral and viral infections. In the present study, the methanol extract from the leaves (HML) and bark (HMB) of this plant as well as fractions (HMBa-c), sub-fractions (HMBa1-5) and compounds isolated from HMBa and HMBb namely betulinic acid (1), madagascin (2), ferruginin A (3) and Kaempferol-3-O-β-d-glucopyranoside (4) were tested for their antimicrobial activities against a panel of 28 g-negative bacteria including multidrug resistant (MDR) phenotypes.

MATERIALS AND METHODS

The broth microdilution method was used to determine the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of the above samples; column chromatography was used for the fractionation and purification of the bark extract whilst the chemical structures of compounds were determined using spectroscopic techniques.

RESULTS

Crude extract HMB together with fraction HMBa and sub-fraction HMBa3 were active on the 28 tested bacterial strains. HML as well as fractions HMBb, HMBc and sub-fractions HMBa1, HMBa2, HMBa4 and HMBa5 were selectively active. MIC values below or equal to 1024µg/mL were recorded with these samples on 92.9% (for HML and HMBa 4), 82.1% (for HMBb), 78.6% (for HMBa2), 50.0% (for HMBa5) and 42.9% (for HMBc) tested bacteria. For crude material, the lowest MIC value below 8µg/mL was obtained with HMB against Escherichia coli ATCC10536 and W3110 strains, and with sub-fraction HMBa3 against Klebsiella pneumoniae K2 strains. MIC values below 10µg/mL were recorded with compound 3 against E. coli ATCC10536, Enterobacter aerogenes ATCC13048 and EA294, Pseudomonas aeruginosa PA01, K. pneumoniae K2 and Kp55 and Enterobacter cloacae BM67.

CONCLUSIONS

Harungana madagascariensis is a potential source of antimicrobial drugs to fight against MDR bacteria. The anthranol 3 is the main antibacterial constituents of the bark of the plant. HMB and compound 3 deserve further investigations to develop natural drug to combat Gram-negative bacteria and otherwise MDR phenotypes.

α-Glucosidase Inhibitory Prenylated Anthranols from Harungana madagascariensis

Four new prenylated anthranols, harunganols C-F (1-4), along with kenganthranol A (5), harunganin (6), and ferruginin A (7), were identified from the leaves of Harungana madagascariensis. The structures of compounds 2, 5, and 7 were confirmed by single-crystal X-ray diffraction analysis. Compound 1 is a unique symmetrical anthranol dimer connected via a CH2 group. Compound 4 possesses a unique C-10 hemiketal group. All anthranols were evaluated for their α-glucosidase inhibitory activities. They displayed a higher potency compared to acarbose except for 3 and 4. In particular, harunganol C (1) showed an IC50 value of 1.2 μM.

Synthesis and biological evaluation of new C-10 substituted dithranol pleiotropic hybrids

Selective alkylation of the antipsoriatic drug dithranol (DTR) at C-10 with tert-butyl bromoacetate, followed by acid-mediated deprotection, produced the corresponding carboxylic acid 4 which was coupled with selectively protected polyamines (PAs), such as putrescine (PUT), spermidine (SPD) and spermine (SPM), dopamine and aliphatic amines and substituted benzylamines producing a series of DTR-PA hybrids, after acid-mediated deprotection, as well as simple amides. The compounds were tested as antioxidants and inhibitors of lipoxygenase (LOX). The amides 4,4'-dimethoxybenzhydrylamide 13 (86% and 95%), 2,4-dimethoxybenzylamide 12 (87% and 81%) and dodecylamide 9 (98% and 74%), and the hybrid DTR-SPM (7) (93% and 87%), showed the highest antioxidant activity in the DPPH and AAPH assays, whereas the most potent inhibitors of LOX were amide 13 (IC50=7 μM), the benzylamide 10 (IC50=7.9 μM) and the butylamide 8 (IC50=10 μM). Molecular binding studies showed that binding of these derivatives into the hydrophobic domain blocks approach of substrate to the active site, inhibiting soybean LOX. Amide 13 presented the highest anti-inflammatory activity (79.7%). The DTR moiety was absolutely necessary for securing high anti-inflammatory potency. Ethyl ester 3 (IC50=0.357 μM) and the amides 9 (IC50=0.022 μM) and 13 (IC50=0.56 μM) exhibited higher antiproliferative activity than DTR (IC50=0.945 μM) on HaCaT keratinocytes whereas amide 13 generally presented better cytocompatibility. Amide 13 is a very promising lead compound for further development as an anti-inflammatory and antiproliferative agent.

The cutaneous epidermal growth factor network: Can it be translated clinically to stimulate hair growth?

The influences exerted by the epidermal growth factor receptor (EGFR) on the skin act at multiple levels, which involve compartments that normally express EGFR. These include the basal and suprabasal layers of the epidermis, sebaceous glands, and the outer root sheath of the hair follicles. The physiological roles of EGFR ensure epidermal renewal and integrity, along with a gatekeeping and function and hair growth stimulation functions. Important cellular functions that are altered during EGF receptor blocking therapy consist of epidermal differentiation, proliferation, apoptosis, and migration, with an overall dominating effect of inducing growth arrest and terminal differentiation of the keratinocytes in the basal layers. The effects of EGFR blockage on the hair cycle include terminal differentiation of the hair follicle, which in certain cases may be associated with trichomegaly. Trichomegaly of the eyelashes may occur as an isolated occurrence or, frequently, as part of a generalized phenomenon that may be associated with the use of the EGFR inhibitors. Molecular changes associated with EGFR blockage are discussed, relevant to their association with hair growth. Modulation of Akt, AP2alpha, CDK4, Notch-1, p27KIP1, and Hedgehog expression are involved in the initiation of the hair cycle and inducement of the anagen phase, followed by proliferation and differentiation of the hair follicles. Epidermal growth factor receptor inhibitors have been developed as therapeutic molecules directed against cancer; in these regimens the knowledge of EGF receptor signaling functions has been translated into significant clinical results. However, among their various collateral effects on the skin, hair growth is observed to occur in certain patients. A particular "wavy" hair phenotype is observed during the pharmacological EGFR receptor blockade, just as in murine transgenic models that carry loss of function of TGF-alpha or EGFR genes. A better characterization of the individual roles pertaining to the EGF family ligands and receptors, has the potential provide new strategies for the management of hair loss.

The effect of cyclooxygenase-2 overexpression on skin carcinogenesis is context dependent

The up-regulation of the inducible form of cyclooxygenase (COX-2), a central enzyme in the prostaglandin (PG) biosynthetic pathway, occurs in many epithelial tumors and has been associated with tumor cell proliferation and angiogenesis. To better understand the role of COX-2 in skin tumor development, we generated transgenic mice that overexpress COX-2 under the control of the keratin 14 promoter. We previously reported (Cancer Res. 62: 2516, 2002) that these mice, referred to as keratin 14 (K14).COX2 mice, were unexpectedly very resistant to 12-O-tetradecanoylphorbol 13-acetate (TPA) tumor promotion. The current studies were undertaken to determine the mechanism of this resistance and determine if it was restricted to TPA promotion. Transgenic and wild-type mice were subjected to a complete carcinogenesis protocol using 7,12-dimethylbenz[a]anthracene (DMBA) only, as well as a two-stage protocol using DMBA plus an unrelated tumor promoter, anthralin. In addition, the responses of transgenic and wild-type mice to TPA in terms of induction of proliferation and various down-stream mediators were examined. The TPA resistance phenotype correlated with a reduced ability to induce ornithine decarboxylase, interleukin-1alpha, and tumor necrosis factor-alpha and a reduced proliferation response. This resistance phenotype appears to be restricted to phorbol ester promotion because K14.COX2 mice developed six times more tumors than wild-type mice when anthralin was used as the tumor promoter. Additionally, K14.COX2 mice treated only with DMBA developed approximately 3.5 times more tumors than wild-type mice, suggesting that PGs have intrinsic tumor promoting activity. We conclude that the role of PGs in skin tumorigenesis is context dependent.

Altered expression of prohibitin in psoriatic lesions and its cellular implication

Psoriasis is characterized by excessive proliferation of keratinocytes accompanying acanthosis and incomplete differentiation. Prohibitin was investigated by examining its function of HaCaT as well as psoriasis. Psoriatic involved skin revealed high level of prohibitin in the basal layer. Prohibitin was analyzed by applying RNAi (PHBi) with HaCaT, which demonstrated increased S-phase. PHBi showed enhanced sensitivity to anthralin-mediated cell death due to enhanced loss of mitochondrial membrane potential, suggesting a protective role of prohibitin against apoptosis. Collectively, prohibitin plays a role both in cell cycle regulation and in maintaining mitochondrial integrity, implying its association with pathogenesis of psoriasis.

The expression of keratinocyte growth factor receptor (FGFR2-IIIb) correlates with the high proliferative rate of HaCaT keratinocytes

Keratinocyte growth factor receptor (KGFR = FGFR2-IIIb) is a tyrosine kinase receptor expressed by keratinocytes, which mediates the effects of fibroblast growth factors (FGF). There are contradictory data in the literature regarding the role of FGFR2-IIIb during the proliferation/differentiation programme of keratinocytes. In this study, we aimed to investigate whether overexpression of FGFR2-IIIb may have a role in the regulation of keratinocyte proliferation. We analysed the expression of FGFR2-IIIb in an in vitro HaCaT model system representing different stages of proliferation and differentiation of keratinocytes. Real-time RT-PCR and Western blot analyses demonstrated a correlation between FGFR2-IIIb mRNA and protein expression and the proportion of cells in S/G2/M phase in synchronized HaCaT keratinocytes and thus with proliferation activity (r = 0.96). After treatment with the antipsoriatic drug, dithranol, FGFR2-IIIb is downregulated dose dependently both at mRNA and protein levels. Moreover, when the rate of proliferation is decreased by the lack of cell attachment to the culturing surface, FGFR2-IIIb mRNA (P = 0.0315) and protein expressions were also reduced (P = 0.0242), while a differentiation marker, keratin 10, mRNA (P = 0.0003) and protein levels (P = 0.001) were increased (r = -0.92). Based on our results we conclude that FGFR2-IIIb expression in HaCaT keratinocytes corresponds with the proliferative activation of the cells and is not related to the differentiation programme.

Dithranol abolishes UCH-L1 immunoreactivity in the nerve fibers of the rat orofacial skin

Dithranol has been used to treat psoriasis for decades. Although its beneficial effect may involve the induction of cutaneous inflammation, and inflammation often leads to damages in nerve fibers, these alterations are not well documented. Therefore, we investigated the effects of dithranol on the immunohistochemical characteristics of the cutaneous nerve fibers in the rat skin. Epidermal nerve fiber staining was achieved with ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) immunohistochemistry in the orofacial skin of control rats, rats treated with (a) dithranol for 5 days, (b) corticosteroid for 5 days following dithranol treatment for 5 days, and (c) corticosteroid for 5 days. The results revealed a complete loss of UCH-L1 immunoreactivity in the dithranol-treated animals. Topical application of corticosteroid onto the inflamed skin for 5 days reversed this effect: the UCH-L1 immunoreactivity was almost completely restored. Steroid treatment for 5 days did not change the appearance of the UCH-L1-immunoreactive nerve fibers. These findings were supported by Western blot analyses. We conclude that dithranol, incidentally similarly to psoriasis, causes inflammation and abolishes UCH-L1 immunoreactivity in the rat orofacial skin in a corticosteroid-reversible manner. This phenomenon may be due to the ability of dithranol to cause oxidative damage to the UCH-L1 protein, and to the antioxidant activity of the corticosteroids countering this effect.

Alpha-glucosidase inhibitory anthranols, kenganthranols A-C, from the stem bark of Harungana madagascariensis

One new prenylated 1,4-anthraquinone and three new prenylated anthranols, named kengaquinone (1) and kenganthranols A (2), B (3), and C (4), were isolated from a hexane extract of the stem bark of Harungana madagascariensis. Six known compounds including anthraquinones, anthrones, and xanthones were also isolated and identified. The structures of the new compounds were determined by analysis of spectroscopic data and comparison with data of previously known analogues. Some isolated compounds (3-5, 7-11) were evaluated for their alpha-glucosidase inhibition activity. Compounds 3, 4, 8, and 11 showed significant activity, whereas compounds 7, 9, and 10 were inactive in this test.

RNase P: a promising molecular target for the development of new drugs

RNase P is an ubiquitous and essential endonuclease in tRNA biogenesis, which generates the mature 5'-termini of tRNAs. RNase P activities have been identified in all three kingdoms of life (Bacteria, Archaea, Eukarya). Most forms of RNase P are ribonucleoproteins, i.e., they consist of an essential RNA and protein subunits. In bacteria and in some archaea, the catalytic function of this enzyme resides entirely in its RNA subunit, which is one of firstly identified ribozymes. Its high structural and functional diversity among representatives of a vast variety of phylogenetic domains indicates that RNase P could also serve as a molecular target of and a useful screening system for the biological activity of different compounds and give more insight into the molecular mechanisms of their action inside the cell. The emerged information from recent studies on the mechanism and structural idiosyncrasies of RNase P provides a convenient platform for designing specific inhibitors for this ribozyme and potential areas of its application in gene therapy. This review summarises the current information on the effect of several protein synthesis inhibitors, retinoids and arotinoids, vitamin D analogues and anthalin on the activity of RNase P.

The antipsoriatic drug anthralin accumulates in keratinocyte mitochondria, dissipates mitochondrial membrane potential, and induces apoptosis through a pathway dependent on respiratory competent mitochondria

Anthralin is a potent topical drug, inducing clearance of psoriatic plaques. Anthralin disrupts mitochondrial function and structure, but its mechanism of action remains undefined. This study aimed to determine whether anthralin induced keratinocyte apoptosis as well as to investigate molecular mechanisms and the role of mitochondria. We studied human keratinocytes and human 143B rho(0) cells, which lack mitochondrial DNA and a functional respiratory chain. We show that anthralin disrupts mitochondrial membrane potential (DeltaPsim) and causes endogenous cytochrome c release, resulting in the activation of caspase-3 and characteristic morphological changes of apoptosis. Disruption of DeltaPsim and cytochrome c release were independent of mitochondrial permeability transition or caspase activation. Human 143B rho(0) cells were resistant to anthralin-induced cell death, disruption of DeltaPsim, and cytochrome c release compared with the isogenic 143B rho+ cell line. Using the intrinsic fluorescence of anthralin, rapid accumulation within mitochondria was observed independent of DeltaPsim. Using assays that measure individual respiratory chain complexes, we show that anthralin specifically interacts with ubiquinone pool. These data indicate that anthralin induces apoptosis through a novel mitochondrial pathway dependent on oxidative respiration and involving electron transfer with the ubiquinone pool. These studies identify keratinocyte apoptosis as a potentially important mechanism involved in the clearance of psoriasis.

Antipsoriatic drug anthralin induces EGF receptor phosphorylation in keratinocytes: requirement for H(2)O(2) generation

Even though anthralin is a well-established topical therapeutic agent for psoriasis, little is known about its effects and biochemical mechanisms of signal transduction. In contrast to a previous report, we found that anthralin induced time- and concentration-dependent phosphorylation of epidermal growth factor receptor in primary human keratinocytes. Four lines of evidence show that this process is mediated by reactive oxygen species. First, we found that anthralin induces time-dependent generation of H(2)O(2). Second, there is a correlation between a time-dependent increase in anthralin-induced epidermal growth factor receptor phosphorylation and H(2)O(2) generation. Third, the structurally different antioxidants n-propyl gallate and N-acetylcysteine inhibited epidermal growth factor receptor phosphorylation induced by anthralin. Fourth, overexpression of catalase inhibited this process. The epidermal growth factor receptor-specific tyrosine kinase inhibitor PD153035 abrogated anthralin-induced epidermal growth factor receptor phosphorylation and activation of extracellular-regulated kinase 1/2. These findings establish the following sequence of events: (1) H(2)O(2) generation, (2) epidermal growth factor receptor phosphorylation, and (3) extracellular-regulated kinase activation. Our data identify anthralin-induced reactive oxygen species and, more specifically, H(2)O(2) as an important upstream mediator required for ligand-independent epidermal growth factor receptor phosphorylation and downstream signaling.

Dithranol in an Emulsifying Oil Base (Bio-Wash-Oil) for the Treatment of Psoriasis of the Scalp

On the scalp, dithranol has been studied in only a few trials. The dithranol molecule that contains both hydrophilic and lipophilic centers can be incorporated into detergents and allows easy removal from hair. This property has led to the incorporation of dithranol in an emulsifying oil base (bio-wash-oil). The formulation has been used routinely for more than two decades in East Germany. We reexamined the efficacy and safety of dithranol in bio-wash-oil and compared it to dithranol embedded in crystalline monoglycerides (Micanol) in patients with psoriasis of the scalp. In a prospective, parallel group study, 64 patients attending a day-care clinic were randomly allocated to 3 treatment groups: (1) dithranol in bio-wash-oil; (2) Micanol cream, and (3) Micanol cream in bio-wash-oil. Treatment was carried out for 3 weeks and results assessed using a modified Psoriasis Area and Severity Index score. Dithranol in bio-wash-oil resulted in a reduction in the score of 34% on day 7 and 57% on day 14. This was significantly better than in groups 2 and 3, as were the overall response and patients' assessment at the end of treatment (p < 0.05). Dithranol in a bio-wash-oil is an effective, well-tolerated and low-priced treatment in psoriasis of the scalp.

Cytokines and signal transduction pathways mediated by anthralin in alopecia areata-affected Dundee experimental balding rats

Although many therapeutic modalities have been tested on alopecia areata, patient outcomes have been disappointing. Use of animal models would help to develop more efficient therapies as well as understanding therapeutic mechanisms. We have demonstrated that 0.1% topical anthralin ointment is 100% effective in restoring follicular activity in Dundee experimental balding rats. This is the most promising topical treatment for Dundee experimental balding rats among the therapeutic agents tested on this model. Various cytokines have been shown to be associated with the pathogenesis of alopecia areata. To test whether any of these cytokines might be modulated by anthralin, an RNase protection assay and the real-time polymerase chain reaction were performed to compare their expression between anthralin-treated and control skins. These experiments showed that expression of tumor necrosis factor-alpha and interferon-gamma was inhibited by anthralin, whereas expression of interleukin-1alpha/beta and their receptor antagonist, interleukin-1Ra, and interleukin-10 was stimulated by anthralin. In addition, using an antibody-based multi-immunoblotting technique, we found that certain signaling regulatory proteins were modulated by anthralin. Their potential roles in reversing the autoimmune-arrested follicular activity in Dundee experimental balding rats are discussed.

The topical treatment of psoriasis

According to the patients, improvement of efficacy, long-term safety and improvement of compliance are needed. The topical treatment has been innovated during the last decade. Most important are the introduction of two new classes of treatments: topical vitamin D(3) analogues and the retinoid tazarotene. To what extent, however, have we achieved developments which are in line with the needs as expressed by the patients? Improved efficacy has been realized by successful combinations of topical treatments. In particular, the combinations of dithranol, vitamin D(3) and tazarotene with a topical corticosteroid proved to be very effective with a reduced profile of side-effects. The efficacy of vitamin D(3) analogues and tazarotene is such that the efficacy of a potent corticosteroid (betamethasone-17-valerate) is approached; calcipotriol even showed an efficacy which is at least as good as this corticosteroid. The long-term safety of new compounds has been evaluated for at least 12 months in large studies. Remarkably for corticosteroids such information is available for only 12 weeks. However, intermittent applications of a topical corticosteroid in combination with another topical treatment provide an effective and safe long-term control of psoriasis. Compliance is a conditio sine qua non for an effective topical treatment. Important progress has been made to increase compliance. Short-contact dithranol has been popularized as an ambulatory treatment which is a highly effective approach as a care instruction programme. Formulations which are better from a cosmetical point of view have been developed for various topical treatments. Reduction of the frequency of applications proved to be possible for most treatments. Once daily applications for corticosteroids, vitamin D(3) analogues and retinoids have been developed, and intermittent applications, a few times per week, are possible for corticosteroids, which proved to be very effective with a reduced profile of side-effects, and are also developed for dithranol.

Comparison of antiproliferative effects of experimental and established antipsoriatic drugs on human keratinocytes, using a simple 96-well-plate assay

Pharmacological treatments for psoriasis are generally based on antiproliferative, anti-inflammatory, or differentiation-modifying activity, or a combination of two or more of these actions. Potentially new drugs for treatment of psoriasis, which act on proliferation, can be identified by screening large compound libraries in a cell proliferation model that allows for characterization of drug effects on in vitro growth of normal human keratinocytes. High-throughput programs based on biological testing of diverse collections of compounds can rapidly identify leads for potential drug candidates in the treatment of psoriasis. In this study, we describe nonradioactive measurement of keratinocyte proliferation in the exponential growth phase in a 96-well format, using a sensitive deoxyribonucleic acid-binding dye to analyze drugs that are pharmacologically active in growth inhibition. Release of lactate dehydrogenase was used to exclude cytotoxic effects. We examined a number of compounds in a test range of 10(-7) to 10(-5) M, including known antipsoriatic drugs, and experimental drugs that are potentially useful in the treatment of psoriasis. We found strong concentration-dependent growth inhibition by dithranol, an antipsoriatic compound that is presumed to target the epidermal compartment. Methotrexate, cyclosporin A, and all-trans retinoic acid did not significantly affect proliferation at therapeutically relevant concentrations. The p38 mitogen-activated protein kinase inhibitor, SB220025, and curcumin, a natural phytochemical, inhibited keratinocyte proliferation at 10(-5) M. We conclude that this assay, in combination with the previously developed assays for psoriatic differentiation, provides a useful tool for identification of antipsoriatic drugs.

[Influence of dithranol therapy on clinical status and serum calcitonin concentrations in patients with common psoriasis]

The aim of this work was to study the effects of external dithranol therapy of psoriatic patients on the clinical status and serum calcitonin concentrations. This was done on 19 patients with common psoriasis using Cignoderm in the short contact therapy. Calcitonin concentration in serum samples was determined before and after a 14-day therapy. Results obtained before were compared with concentrations after dithranol treatment and with results in control group. Serum TSH was also measured in serum samples from both groups at the very beginning time. The determinations showed statistically significant lower serum TSH level in psoriatic patients before therapy vs. control and significant, negative correlation with calcitonin concentration in those patients. After a 14-day dithranol therapy a significant calcitonin concentration decrease as well as clinical effects were observed in the investigated group.

The potential of the essential fatty acid-deficient hairless rat as a psoriasis screening model for topical anti-proliferative drugs

The objective of this study was to establish essential fatty acid deficiency (EFAD) in hairless rats and investigate the potential of this model as a psoriasis screening model by testing the effects of calcipotriol and dithranol on differentiation and proliferation in the epidermis. Hairless rats were fed with a fat-free diet lacking linoleic acid. The EFAD condition was established within 8 weeks. In order to ensure that this condition had been established, several parameters were measured and observed, i.e. animal weight, water consumption, transepidermal water loss, clinical skin symptoms, histology of the epidermis and fatty acid analysis of serum and skin. Immediately after the EFAD condition had been established, the animals were treated with dithranol ointment or different concentrations of calcipotriol solution. A reduction in epidermal thickness of 15-20% was seen after the treatment with calcipotriol. Dithranol and its coal tar-containing vehicle also showed a reductive effect on epidermal thickness. EFAD hairless rats possess various histological changes resembling psoriasis. These histological changes normalise during treatment with anti-psoriatic drugs as calcipotriol, dithranol and coal tar. The results of the present study indicate that the EFAD rat may be a useful model for studies of anti-psoriatic drugs affecting cell proliferation.

A simple technique for high-throughput screening of drugs that modulate normal and psoriasis-like differentiation in cultured human keratinocytes

Established treatments for psoriasis act ei-ther on hyperproliferation, inflammation, aberrant epidermal differentiation or a combination of these aspects of the disease. Potential new drugs for treatment of psoriasis or other disorders with abnormalities in epidermal differentiation can be identified by high-throughput screening of large compound libraries using surrogate markers for the disease. Here we describe a screening model to detect pharmacologically active drugs in two keratinocyte-based, 96-well culture models that use expression of cytokeratin 10 (CK10) and skin-derived antileucoprotease (SKALP)/elafin as markers for normal and psoriatic differentiation, respectively, and allow multiple parameters to be determined from a single well. In this model we tested a number of compounds in a pharmacological range from 10(-7) to 10(-5) M, including known antipsoriatic drugs, and experimental drugs that are potentially useful in the treatment of psoriasis. All-trans-retinoic acid, dithranol and the p38 mitogen-activated protein (MAP) kinase inhibitor SB220025 displayed a strong inhibitory effect on SKALP expression while cyclosporin A, dexamethasone, the vitamin D(3) derivative calcipotriol and the p38 MAP kinase inhibitor SB203580 showed only moderate inhibition. Methotrexate and dimethylfumarate did not affect the expression of SKALP. With respect to CK10 expression, all-trans-retinoic acid, calcipotriol, SB203580 and SB220025 exhibited strong inhibition while dithranol showed only moderate suppression of this normal differentiation marker. Expression levels of CK10 were not significantly affected by dexamethasone, methotrexate, cyclosporin A or dimethylfumarate. This model system parallels most, but not all, findings on the in vitro effect of known antipsoriatic drugs on keratinocytes. In addition, the model identifies p38 MAP kinase inhibitors as potent suppressors of differentiation-associated gene expression. Although further delineation and validation of this model is required, we conclude that the system is amenable to down-scaling and application as a high-throughput screen for differentiation-modifying compounds.

The response of normal human skin to single and repeated applications of dithranol cream: an immunohistochemical assessment

The irritative response of uninvolved skin is a serious limitation of dithranol therapy in psoriasis. A characterisation in cell biological terms may be helpful in finding an effective counteraction to this well-known irritation. Therefore, we studied the effect of single and repeated applications of dithranol on normal human skin. Besides a clinical evaluation, we studied aspects of epidermal proliferation, differentiation and inflammation. On day 2, after single dithranol challenge, we observed an induction of both the cornified envelope precursor protein involucrin and the cross-linking enzyme transglutaminase I. Subsequently, epidermal hyperproliferation was observed with a maximum on day 8. The epidermal response to dithranol appears to be a reinforcement of the barrier function. Remarkably, however, filaggrin was found to be decreased. Profilaggrin breakdown might be an attempt to compensate for xerosis of uninvolved skin that accompanies dithranol therapy. T lymphocytes and to a lesser extent polymorphonucleocytes were found to be significantly increased. The reduction of Langerhans cells suggests a dose-dependent toxic effect of dithranol or one of its metabolites on Langerhans cells. The dynamics in the induction of changes after repeated challenge are comparable with those after single challenge. However, the induction of hyperproliferation following repeated application appeared to continue between day 8 and 12. Based on the dynamics of dithranol-induced irritation, it may be of interest to study the efficacy of intermittent dithranol treatment. Our results indicate that an optimal timing for biopsies in future dithranol irritation studies lies between 4 and 8 days after the first dithranol challenge.

Dithranol and dimethylfumarate suppress the interferon-gamma-induced up-regulation of cytokeratin 17 as a putative psoriasis autoantigen in vitro

In psoriasis an etiopathogenetic vicious circle has been hypothesized in which disease manifestation is triggered by skin-specific autoantigen structures. Autoreactive T cells are supposed to mediate inflammation and hyperproliferation in the epidermopapillary compartment, positively feeding back the expression and accessibility of decisive antigen structures. Recently an epitope within cytokeratin 17 (K17) has been described as such a putative psoriasis autoantigen, which is moreover known to be up-regulated under the influence of proinflammatory interferon-gamma (IFN-gamma), which is abundantly detected in psoriatic plaques. The present study proposes an in vitro model for this presumptive IFN-gamma/K17 autoimmune loop, i.e. the incubation of hyperproliferative human HaCaT keratinocytes with 25 U IFN-gamma/ml for 72 h. This treatment led to a significant up-regulation of K17 protein expression (> or =300%) measured by flow immunocytometry as compared to the untreated control (100%, p < or = 0.05). Preincubation with a subcytotoxic and antiproliferative dithranol concentration as low as 0.3 microM for 2 h prior to the IFN-gamma exposure resulted in a K17 expression that was significantly lower than the IFN-gamma-induced K17 expression reference level. The IFN-gamma-induced K17 expression was also significantly lowered by coincubation with a subcytotoxic and nonantiproliferative concentration of 3 microM dimethylfumarate. The data indicate for dithranol and dimethylfumarate that a part of their antipsoriatic mode of action may be related to a direct down-regulation of putative psoriasis autoantigen structures.

Cornified envelope formation by anthralin, simple analogues, and related anthracenones

The ability of the antipsoriatic anthralin to induce HaCaT keratinocyte differentiation was investigated and correlated with its potency to inhibit proliferation of keratinocytes. To determine the structural requirements for this effect, anthralin and seventeen simple analogues or related anthracenones were examined for their ability to induce the formation of cornified envelope as a marker of terminal differentiation. Covalently cross-linked protein was measured as a key feature of this process. Induction of keratinocyte differentiation was significant at a concentration of 0.5 microM anthralin after 48 h exposure. The presence of the 1,8-dihydroxy groups is a critical determinant of cross-linking activity, since removing or exchanging these groups prevented the induction of keratinocyte differentiation. Furthermore, at least one hydrogen atom at the 10-position of anthralin is required. Moreover, anthralin, anthralin dimer, and anthralin triacetate exhibited antiproliferative and antirespiratory activity at concentrations required to induce keratinocyte differentiation, suggesting a causality between these effects. In addition, cornified envelope formation was observed for a number of related anthracenones at concentrations as low as 1-5 microM. In general, compounds containing benzoyl substituents, independent of the position in the anthralin nucleus, were more potent than those having benzyl substituents. Only marginal differences in cross-linking potency were observed within a number of phenylpropionyl substituted analogues, suggesting that the ability to induce keratinocyte differentiation is independent of the nature of substituents at the side chain.

Heterocyclic substituted anthralin derivatives as inhibitors of keratinocyte growth and inducers of differentiation

Heterocyclic substituted derivatives of the antipsoriatic anthralin were synthesized and evaluated in vitro for their antiproliferative action against keratinocytes and their ability to induce keratinocyte differentiation. The indole-2-carboxylic acid analogue 2e exhibited the same excellent antiproliferative activity as anthralin and also induced terminal differentiation of keratinocytes. As a benefit of its strongly diminished potential to generate oxygen radicals, 2e did not induce damage of keratinocyte membranes.

Dithranol upregulates IL-10 receptors on the cultured human keratinocyte cell line HaCaT

OBJECTIVE

Dithranol is highly effective in the treatment of psoriasis, however its mode of action is still not well known. Since interleukin-8 and interleukin-10 are involved in the pathogenesis of psoriasis, the aim of our study was to investigate the effect of dithranol on interleukin-8, interleukin-10 mRNA production and interleukin-10 receptor expression of the HaCaT keratinocyte cell line which is commonly used in experiments examining the effects of therapeutic drugs on keratinocytes.

MATERIALS AND METHODS

Cultured HaCaT cells were treated with 0.1-0.5 microg/ml dithranol for 30 minutes. After 2 and 4 h total cellular RNA isolated from HaCaT cells was reverse transcribed (RT) to cDNA which was subjected to polymerase chain reaction (PCR) with specific primer pairs for interleukin-8, interleukin-10 and interleukin-10 receptor. For immunohistochemistry cultured HaCaT cells were stained with a monoclonal antibody against the human interleukin-10 receptor.

RESULTS

Our results showed that dithranol treatment did not change the highly elevated level of interleukin-8 mRNA of HaCaT cells. Interleukin-10 mRNA signal with RT-PCR could not be detected in HaCaT cells. Depending on the concentration dithranol increased the mRNA production of interleukin-10 receptors in HaCaT cells. This dithranol induced dose dependent upregulation of IL-10 receptors in HaCaT cells was also observed on the protein level using immunohistochemistry.

CONCLUSIONS

Since the interleukin-10 receptor expression of keratinocytes in psoriatic lesional skin is downregulated, the dithranol induced upregulation of the receptor in our model system might help to reveal the therapeutic action of the drug.

Tazarotene induces epidermal cell differentiation in the mouse tail test used as an animal model for psoriasis

Disturbed epidermal proliferation and keratinization are major features of psoriatic skin lesions. The so-called mouse tail test is known as an animal model to evaluate the antipsoriatic efficacy of topical drugs with regard to the induction of orthokeratosis. The purpose of the present study was to investigate the effect of tazarotene, a novel, receptor-specific retinoid, by the mouse tail test in a direct comparison to dithranol representing a classical topical antipsoriatic compound. The tails of CFLP mice were treated with tazarotene gel (0.1%, 0.05%), dithranol ointment (1.0%), tretinoin cream (0.05%) and methylcellulose (5%) hydrogel (vehicle control) for 2 weeks. Longitudinal histological sections were prepared from the tail skin, and the degree of orthokeratosis was determined by measuring the horizontal length of the fully developed granular layer within an individual scale in relation to its total length according to a method originally described by Bosman and co-authors. The degree of orthokeratosis was significantly (p < or = 0.05) increased by 0.1% tazarotene (87+/-20%), 1.0% dithranol (75+/-26%), 0.05% tazarotene (59+/-27%), and 0.05% tretinoin (23+/-13%) as compared to untreated (11+/-6%) and methylcellulose hydrogel-treated (13+/-6%) controls. Under the conditions of the mouse tail test, tazarotene showed a strong potency to induce orthokeratosis. With regard to clinically relevant concentrations this effect was even more pronounced than that observed for dithranol.

Additive inhibitory effect of calcipotriol and anthralin on ribonuclease P activity

The effects of two antipsoriatic compounds, calcipotriol and anthralin, separately or in combination on ribonuclease P (RNase P), were investigated using a cell-free system from the slime mold Dictyostelium discoideum. RNase P is an ubiquitous and essential enzyme which endonucleolytically cleaves all tRNA precursors to produce the mature 5' end. The substrate for RNase P assays was an in vitro (32)P-labeled transcript of the Schizosaccharomyces pombe tRNA(Ser) gene supS1. Enzyme assays were carried out at 37 degrees in 20 microL 50 mM Tris-HCL 7.6 buffer, containing 10 mM NH(4)Cl, 5 mM MgCl(2), and 10% isopropanol. Calcipotriol or anthralin alone exerted a dose-dependent inhibitory effect on RNase P activity, with the former being more active than the latter in this respect. Simultaneous exposure of the enzyme to both drugs resulted in an enhancement of RNase P inhibition, which was additive. Considering the lack of structural similarities between the substrate (precursor tRNA) of RNase P and the tested drugs, it seems reasonable to suggest that their effects may be due to binding to allosteric inhibition sites of the enzyme. Although our in vitro findings cannot be directly extrapolated to the in vivo human condition, they do suggest that the inhibitory effects of calcipotriol and anthralin on tRNA biogenesis may be implicated in the mechanisms of their antipsoriatic action. Moreover, the additive inhibitory effect of these compounds on RNase P activity provides an experimental basis for their possible combined therapeutic application in the management of psoriasis.

Anti-psoriatic drug anthralin activates JNK via lipid peroxidation: mononuclear cells are more sensitive than keratinocytes

Anthralin is a widely used, topical therapy for psoriasis. Anti-proliferative and anti-inflammatory properties of anthralin have been identified. Little is known, however, about differential sensitivities of targeted cell types and specific mechanisms of signaling pathway activation. We demonstrate that anthralin exerts potent effects on keratinocytes and mononuclear cells through strong induction of lipid peroxidation and JNK activation, a stress-induced signal transduction pathway. Lipid peroxidation was observed rapidly and half-maximal levels of lipid peroxidation were reached at a 10-fold lower concentration of anthralin for peripheral blood mononuclear cells vs normal keratinocytes. JNK activation was detected in peripheral blood mononuclear cells at a 40-fold lower anthralin dose compared with keratinocytes. For both cell types, selected inhibitors of lipid peroxidation prevented JNK activation. This study demonstrates that mononuclear leukocytes are markedly more sensitive than keratinocytes to anthralin-induced lipid peroxidation and JNK activation. We identify anthralin as a novel and potent inducer of JNK activation and demonstrate that this process is mediated, at least in part, by lipid peroxidation which is among the earliest and most proximate, membrane-related responses to anthralin yet described.

Dose-dependent inhibition of ribonuclease P activity by anthralin

The effect of five different anthralin concentrations on tRNA biogenesis was investigated employing the ribonuclease P (RNase P) of the slime mold Dictyostelium discoideum as an in vitro cell-free experimental system. RNase P is an ubiquitous and essential enzyme that endonucleolytically cleaves all tRNA precursors to produce the mature 5' end. Anthralin revealed a dose-dependent inhibition of RNase P activity indicating that this compound may have a direct effect on tRNA biogenesis. Taking into account that anthralin has no structural similarities to the substrate (pre-tRNA) of RNase P, it seems reasonable to suggest that this compound may bind to allosteric inhibition sites of the enzyme.

Potential antipsoriatic agents: lapacho compounds as potent inhibitors of HaCaT cell growth

A number of lapacho compounds, representing the most common constituents of the inner bark of Tabebuia impetiginosa, together with some synthetic analogues, were evaluated in vitro against the growth of the human keratinocyte cell line HaCaT. With an IC(50) value of 0.7 microM, beta-lapachone (4) displayed activity comparable to that of the antipsoriatic drug anthralin. 2-Acetyl-8-hydroxynaphtho[2,3-b]furan-4,9-dione (7), which was prepared in a four-step synthesis from 2,8-dihydroxy-1, 4-naphthoquinone, was the most potent inhibitor among the known lapacho-derived compounds and inhibited cell growth with an IC(50) value of 0.35 microM. Furthermore, other active constituents of lapacho inhibited keratinocyte growth, with IC(50) values in the range of 0.5-3.0 microM. However, as already observed with anthralin, treatment of HaCaT cells with these potent lapacho compounds also caused remarkable damage to the plasma membrane. This was documented by leakage of lactate dehydrogenase into the culture medium, which significantly exceeded that of the vehicle control. Because of their potent activity against the growth of human keratinocytes, some lapacho-derived compounds appear to be promising as effective antipsoriatic agents.

Induction of hair growth by skin irritants and its relation to skin protein kinase C isoforms

Induction of hair growth by skin irritants and its relation to skin protein kinase C (PKC) isoforms were evaluated. Dorsal skin of BALB/c mice was shaved and anthralin (0.1% in corn oil) was applied on one side of the shaved backs in 20 mice daily for 5 days. The corresponding opposite side treated with corn oil served as a control. In another 20 mice, sodium dodecyl sulphate (SDS, 10% in water) was applied on one side of the shaved backs for 5 days by the same procedure as above and the corresponding opposite side treated with water served as control. Visible acceleration of hair growth on anthralin-treated skin was observed as early as 14 days after the application of anthralin and significant hair growth was observed at about 17-20 days. Enhancement of hair growth on SDS-treated skin was observed at about 3 weeks from the beginning of the treatment. None of the mice showed remarkable hair growth on the control side in either group. Mouse skin PKC isoforms levels detected by Western blot showed a similar pattern in both treatment groups. PKC alpha was downregulated initially, and was then elevated from 3 days after anthralin treatment and 14 days after SDS application. PKC beta was unchanged initially, decreased at 8 and 14 days after anthralin and SDS treatment, respectively, and reverted to the control level at 25 days after anthralin treatment, when it was still lower than the control in SDS-treated skin. PKC delta was also unchanged at first, but was elevated from 3 days after anthralin treatment and 14 days after SDS application. These results suggest that involvement of PKC may be a general phenomenon in irritant-induced hair growth in mice. Considering the stimulatory effect of PKC alpha and inhibitory effect of PKC delta on cell growth, we postulate that PKC alpha may be responsible for enhancement of hair growth while PKC delta may inhibit hair growth to keep the hair growth in balance.

Effects of cinnarizine on different experimentally induced oedemas

Experiments with male mice (28-32 g) of the CFLP strain showed that cinnarizine in doses of 2.5, 5.0 or 10.0 mg kg-1 significantly inhibited the extent of ear oedema induced by croton oil, capsaicin or dithranol, in a dose-dependent manner. In rats of the Wistar strain, oedema was induced in the hind paw by subplantar injection of carrageenin, and simultaneously by the application of croton oil to the inner surface of the ear. Preliminary cinnarizine treatment (5, 10 or 20 mg kg-1) inhibited the development of both types of oedema, to a statistically significant extent, in a dose-dependent manner.

Optimized visualization and PCR reamplification of differentially displayed cDNA bands detected by silver staining in polyacrylamide gels as established in the model of dithranol-treated keratinocytes

The differential display of cDNA species defined by a combination of so-called anchored and arbitrary primers has been acknowledged as a powerful complex strategy to identify differences in gene expression, and depends in its original version, inaugurated by P. Liang and A. B. Pardee in 1992, on the use of radioactive-labelled nucleotides. As a non-radioactive methodological alternative, we established the use of polyesterfilm-backed 10% polyacrylamide gels for horizontal differential-display electrophoresis under non-denaturing conditions, with subsequent detection of cDNA bands by an optimized, semi-automated silver staining omitting any fixation step. Polyacrylamide gel slices carrying the silvered cDNA species of interest were cut out, chopped, squashed and incubated in an ammonium acetate/EDTA solution at 37 degrees C overnight under vigorous shaking. This procedure resulted in a 70% average success rate for subsequent PCR reamplification with regard to the number of cDNAs harvested from the differential-display gel. Novel sequence data of three cDNA clones are communicated, which under these methodological conditions were selected to be up- or down-regulated, respectively, by antipsoriatic dithranol in cultured HaCaT keratinocytes.

Anthralin stimulates keratinocyte-derived proinflammatory cytokines via generation of reactive oxygen species

OBJECTIVE AND DESIGN

Topical application of anthralin, used in the treatment of psoriasis, is often accompanied by severe skin inflammation, presumably due to free radical products of the drug. The role of inflammatory cytokines and their induction by anthralin-derived reactive oxygen species were studied in cultures of normal human keratinocytes (NHKs).

MATERIALS AND METHODS

Anthralin was added to cultures of NHKs in the presence or absence of various antioxidants, including superoxide dismutase, tetramethylthiourea, N-acetylcysteine and vitamin E and relative changes in cytokine secretion and in the number of mRNA transcripts were examined. In addition, NHKs were either treated with neutralizing antibodies to tumor necrosis factor (TNF)-alpha or transfected with a CAT-linked IL-8 promoter to establish the direct effects of anthralin on chemokine synthesis.

RESULTS

Anthralin, at concentrations between 5 microM and 25 microM, caused a marked increase in granulocyte macrophage-colony stimulating factor (GM-CSF), interleukin (IL)-6, IL-8 and TNFalpha synthesis that was selectively inhibited by specific antioxidants. Furthermore, anthralin induced chemokine secretion without the need of primary cytokines.

CONCLUSIONS

Taken together, these studies suggest that oxygen radicals generated from anthralin are responsible for the induction of inflammatory cytokines which, in turn contributes to their dermal toxicity.

Simple analogues of anthralin: unusual specificity of structure and antiproliferative activity

Fifty-nine simple analogues of the antipsoriatic agent, anthralin, have been prepared by modifying the positions of the 1,8-hydroxyl groups, replacement of the hydroxyl groups, substitution at the oxygen functions, introduction of additional functional groups into various positions of the anthracenone nucleus, or removal of particular structural elements. The compounds were evaluated for their antiproliferative action against human keratinocytes and inhibition of the generation of leukotriene B4 in polymorphonuclear leukocytes, which may be useful to resolve the proliferative and inflammatory aspects of psoriasis, respectively. Even though many anthracenones were more potent inhibitors of leukotriene biosynthesis than anthralin, none of the compounds was substantially more effective as this drug in suppressing keratinocyte cell growth. There is an absolute requirement for two hydroxyl groups peri to a hydrogen bond acceptor such as a keto or an imino group for high potency. In addition to further delineating the nature of the pharmacophore for this class of compounds, also naphthalenedione with a peri hydroxyl group was identified as a pharmacophore with antiproliferative activity against keratinocyte growth.

Antipsoriatic and proinflammatory action of anthralin. Implications for the role of oxygen radicals

Anthralin is among the most effective agents for the topical treatment of psoriasis. However, this drug causes unpleasant side-effects such as inflammation and staining of the nonaffected skin surrounding a psoriatic lesion. The biochemical basis for the induction of an inflammatory response in the skin and the antipsoriatic effectiveness are uncertain, although several cellular targets of anthralin action have been identified. Because no single mechanism is operative, the view was taken that all the effects exerted by anthralin are caused by its redox activity leading to the generation of anthralin free radicals and oxygen radicals. Clear relationships between oxygen-radical production by anthralin and biological response are evident with respect to chemical lesions in cellular macromolecules such as DNA, lipid membranes, and enzymes, indicating that these species account for the antipsoriatic and proinflammatory effects elicited by anthralin. This poses new challenges for the medicinal chemist and provides impetus for identifying novel compounds having potential for an improved therapeutic index.

Anthralin (dithranol) in vitro inhibits human monocytes to secrete IL-6, IL-8 and TNF-alpha, but not IL-1

Anthralin is a most widely used compound for topical treatment of psoriasis. Whereas numerous studies have ascertained anthralin as a safe and effective drug its mode of action still remains unclear. Previous studies demonstrated dose-dependent inhibition of a number of pro-inflammatory functions in human neutrophils and monocytes (MO). The aim of the present study was to investigate in stimulated MO the effect of anthralin on the secretion of cytokines which are of known importance for the psoriatic tissue reaction. Highly purified MO were incubated with anthralin (0.01-1.0 microgram/ml), its clinically inactive derivative danthrone (0.1 and 10 micrograms/ml), the solvent acetone, or medium alone. Culture supernatants were analysed for immunoreactivity for interleukin-1 beta, and -8 (IL-1 beta, IL-8), and tumour necrosis factor alpha (TNF-alpha) by specific ELISA. IL-6 bioactivity was determined using the B9-bioassay. Additionally, IL-1 bioactivity was measured by the D10[N4]M-bioassay. The results show a dose-dependent inhibition of MO IL-6, IL-8, and TNF-alpha release with a half-maximal inhibitory concentration of 0.25-0.6 microgram/ml of anthralin. There was no effect of danthrone or acetone on the secretion of these cytokines from MO. Secretion of IL-1 beta immunoreactivity measured by ELISA as well as determination of biological activity of IL-1 using the D10[N4]M-bioassay revealed a slight increase in IL-1 secretion with a maximum at an anthralin concentration of 0.1 microgram/ml. Danthrone at a concentration of 10 micrograms/ml and acetone (0.1%) similarly enhanced IL-1 secretion from human MO measured by both methods. Our results demonstrate a differential, dose-dependent inhibition of cytokine secretion from human MO by anthralin. The present data provide evidence that the anti-inflammatory and anti-proliferative activity of anthralin may at least in part be due to its inhibitory effect on pro-inflammatory cytokine secretion by MO.

Effects of reactive oxygen species on the biosynthesis of 12 (S)-hydroxyeicosatetraenoic acid in mouse epidermal homogenate

Arachidonic acid is converted to 12-hydroxyeicosatetraenoic acid (12-HETE) in a homogenate of mouse epidermal cells. When the epidermal homogenate was preincubated with scavengers of reactive oxygen species (ROS), catalase or superoxide dismutase, significantly larger amounts of 12-HETE were produced as compared to untreated controls, suggesting that 12-lipoxygenase is quite prone to inactivation by ROS and peroxides. Mouse epidermal homogenate was then exposed to nine different ROS-generating systems to study the effects of superoxide, hydrogen peroxide, singlet oxygen, hypochlorite, peroxyl radicals, and alkyl hydroperoxides on the enzyme activity. Analysis by chiral phase high performance liquid chromatography demonstrated that the 12-HETE biosynthesized from arachidonic acid by mouse epidermal homogenate was the 12 (S)-enantiomer and excludes oxidation of arachidonic acid by ROS in a nonspecific free radical mechanism which leads to racemic 12-HETE. ROS generated by the interaction of xanthine with xanthine oxidase strongly inhibited epidermal 12 (S)-HETE biosynthesis. A flux of 0.7 nmol of superoxide/min/ml of reaction medium resulted in more than 50% inhibition of epidermal 12-lipoxygenase activity. The decrease in 12 (S)-HETE biosynthesis appeared to involve both superoxide and hydrogen peroxide. The efficacy of the latter species was also documented by exposure of mouse epidermal 12-lipoxygenase to glucose and glucose oxidase, which resulted in similar inhibitory effects on 12 (S)-HETE biosynthesis. The presence of the iron chelator diethylenetriaminepentaacetic acid during incubation of epidermal 12-lipoxygenase with both the xanthine/xanthine oxidase or the glucose/glucose oxidase systems partially protected the enzyme against inhibition, indicating that hydroxyl radical contributes to the overall inhibitory effect. Also, organic hydroperoxides inhibited epidermal 12-lipoxygenase, whereas singlet oxygen, hypochlorite, and peroxyl radicals were not effective. The results of this study lead to the proposal that 12-lipoxygenase activity may be regulated by ROS such as hydrogen peroxides, superoxide, and hydroxyl radicals.

Antipsoriatic anthrones: aspects of oxygen radical formation, challenges and prospects

1. Antipsoriatic anthrones are among the most commonly used topical agents for the treatment of psoriasis. 2. These drugs generate reactive oxygen species during their auto-oxidation under physiological conditions. 3. Recent studies have indicated that activation of molecular oxygen by anthrones may play a critical role in their mechanism of action at the molecular level. 4. This article summarizes the evidence pointing toward the significance of oxygen activation and radical formation in the antipsoriatic action and induction of skin inflammation of anthrones. 5. Also, the role of oxygen radical formation in the development of novel anthrones devoid of inflammatory and staining properties is discussed.

Induction of apoptosis in human HaCaT keratinocytes

Although cell death by apoptosis has been recognized as an important control mechanism in the maintenance of tissue homeostasis and in the elimination of cells with damaged DNA, information on the induction and characteristics of apoptosis in keratinocytes is rather scarce. Apoptotic mechanisms may play an important role in normal and disturbed homeostasis of the skin. In the present study, we therefore investigated the effects of several potential inducers of apoptosis in the human keratinocyte cell line HaCaT. Apoptosis was assessed with respect to morphological changes by light and electron microscopic examinations and to DNA integrity by a specific ELISA. UVB irradiation induced the morphology and internucleosomal DNA fragmentation characteristic of apoptosis in a dose- and time-dependent manner. Interferon-gamma caused DNA cleavage at the linker regions without producing morphological features consistent with apoptotic cell death. In contrast, treatment with dithranol and NP-40 resulted in necrotic alterations in the keratinocytes. Treatment with the calcium ionophore A23187 caused morphological changes which were similar to the characteristics of 'nonapoptotic programmed cell death'. Dexamethasone, tumor necrosis factor-alpha, transforming growth factor-beta, TPA, retinoic acid, the podophyllin derivative etoposide, the thromboxane A2 analogue U46619, cycloheximide, and the nitric oxide donors sodium nitroprusside and S-nitroso-glutathione, which are all known to induce apoptosis in other cell types, did not affect HaCaT keratinocytes. These results demonstrate that apoptosis can be induced in keratinocytes in vitro but the apoptosis differs from that in other cell types, such as haematopoietic cells, with regard to the type of inducer and/or the sensitivity of the target cells. Since keratinocytes are affected by numerous external and internal stimuli, they might posses several protective mechanisms to prevent apoptosis and to ensure the structural integrity of the outermost barrier of the body.

Antipsoriatic anthrones with modulated redox properties. 3. 10-thio-substituted 1,8-dihydroxy-9(10H)-anthracenones as inhibitors of keratinocyte growth, 5-lipoxygenase, and the formation of 12(S)-HETE in mouse epidermis

The synthesis of a series of 1,8-dihydroxy-9(10H)-anthracenones bearing sulfur-linked substituents in the 10-position is described. These compounds were evaluated for their ability to inhibit the growth of the human keratinocyte cell line HaCaT and the 5- and 12-lipoxygenase enzymes in bovine polymorphonuclear leukocytes and mouse epidermal homogenate, respectively. In addition, the following redox properties of the compounds were determined: reactivity against 2,2-diphenyl-1-picrylhydrazyl, generation of hydroxyl radicals as measured by deoxyribose degradation, and inhibition of lipid peroxidation in model membranes. Compounds 4e and 4h of this series compare favorably in the cellular assays with the antipsoriatic anthralin. They have the combined inhibitory action against leukotriene B4 and 12(S)-HETE formation and are highly potent antiproliferative agents against keratinocyte growth. In contrast to anthralin, 4h, 1,8-dihydroxy-10-[(4-hydroxyphenyl)thio]-9(10H)-anthracenone, is not cytotoxic as documented by the LDH activity released from cytoplasm of keratinocytes and does not enhance lipid peroxidation in model membranes.

Anti-psoriatic drug anthralin activates transcription factor NF-kappa B in murine keratinocytes

Anthralin is one of the most effective and safest therapeutic agents for the treatment of psoriasis, a skin disease characterized by epidermal hyperproliferation and hyperkeratosis. The drug induces and inflammatory response in the skin involving the expression of cytokine and cell adhesion molecule genes that is thought to be essential for its therapeutic efficacy. Reactive oxygen intermediates (ROIs) generated in vivo during the auto-oxidation of anthralin were discussed as mediators of the inflammatory response, but it is not yet understood how this is translated into novel inflammatory gene expression. In this study, we show that at little as 10 microM anthralin can activate a prototypic form of transcription factor NF-(kappa)B, a central transcriptional regulator of inflammatory and immune responses. Two different lines of evidence show that ROIs, in particular H2O2, are second messengers for the anthralin-induced NF-(kappa)B activation. Firstly, the activation could be inhibited by the structurally unrelated antioxidants N-acetyl-L-cysteine and pyrrolidinedithiocarbamate. Secondly, keratinocytes stably overexpressing catalase showed a significant reduction of NF-(kappa)B activation, while stable overexpression of Cu/Zn-superoxide dismutase augmented the anthralin effect. Our data suggest that ROI-induced NF-(kappa)B plays a role in the anti-psoriatic activity of the drug anthralin.