Enzymatic quantification of polymorphonuclear leucocytes in normal and psoriatic skin following standardized injury

The evolution of the psoriatic lesion

Psoriasis comprises a host of abnormalities, and various aspects of the pathogenesis of psoriasis have been suggested to be of primary relevance. The aim of this review is to identity driving factors in the pathogenesis of psoriasis and to explore the dynamics of processes eventually resulting in a psoriatic lesion. In this review observations on the evolution from the symptomless skin to lesional skin in patients with psoriasis will be integrated with observations in various animal models of psoriasis.

Changes in keratinocyte differentiation following mild irritation by sodium dodecyl sulphate

Although the induction of acute irritant dermatitis by detergents has been studied extensively in recent years, our understanding of the cell biological events in the repair phase, and its relevance for the development of chronic irritant dermatitis is limited. Here we studied the reaction pattern of human skin to short-term application of sodium dodecyl sulphate (SDS) in a model that induced a minimal acute inflammatory reaction (absence of polymorphonuclear leucocytes, PMN) and did not have cytopathic effects on the epidermal keratinocytes as determined by histological investigation. All parameters were measured up to 14 days after exposure to SDS. Application of SDS caused disturbances of barrier function as measured by transepidermal water loss and had vascular effects as judged by erythema. Several cell biological markers for epidermal growth and differentiation were examined by immunohistochemistry. A rapid and strong induction of the cornified envelope precursor protein involucrin was seen in the stratum spinosum, with a peak at 24 h. Within 24 h a strong upregulation of epidermal fatty acid binding protein (E-FABP) was noted, with a peak at 7 days after injury. Cellular proliferation in the basal layer was increased fivefold as assessed by nuclear staining for the Ki-67 antigen, showing a peak at 48 h. Surprisingly, no significant induction of cytokeratin 16 and SKALP/elafin expression, two markers associated with epidermal hyper-proliferation and inflammation, was seen. These findings suggest that the cellular changes following exposure to detergent are distinct from those seen in other forms of skin injury. We would speculate that the epidermal response to detergent exposure is primarily directed at restoration of barrier function.

Multiparameter flow cytometric characterization of epidermal cell suspensions prepared from normal and hyperproliferative human skin using an optimized thermolysin-trypsin protocol

Reliable flow cytometric analysis of normal and diseased skin requires pure epidermal single-cell suspensions. Several methods to separate the dermis from the epidermis are available. The proteolytic enzyme thermolysin separates the epidermis from the dermis at the lamina lucida and therefore permits reliable dermoepidermal separation. In the present study an optimized cell isolation procedure using thermolysin and trypsin is described, which is particularly suitable for punch biopsies. A 16-20-h (overnight) incubation of biopsies taken from normal and hyperproliferative skin with thermolysin (0.5 mg/ml) at 4 degrees C produced a selective separation of the dermis and epidermis. After a 30-min trypsin incubation (0.25 mg/ml) at 37 degrees C a cell suspension was produced which was characterized by minimal cell damage (cellular debris and clumps), a high recovery of basal cells and high quality DNA histograms. Furthermore, dermal contamination was very low. The thermolysin-trypsin separation methodology followed by triple-labelling flow cytometry provided a precise quantification of the percentage of keratin 10-positive cells, vimentin-positive cells and cells in S and G2M phases. Proliferative activity was selectively measured in the basal, the suprabasal and the non-keratinocyte compartment at various time intervals during epidermal regeneration after adhesive tape stripping. In contrast to the non-keratinocytes, the percentage of cells in S and G2M phases in the basal keratinocytes and in the suprabasal compartment increased 44-48 h after stripping. The increased proliferation following tape stripping was paralleled by an increased invasion of vimentin-positive cells into the epidermis and preceded by a decreased number of keratin 10-positive cells. Thermolysin-trypsin separation followed by three-colour flow cytometry permits a highly selective characterization of normal and hyperproliferative epidermis.

Levels of skin-derived antileukoproteinase (SKALP)/elafin in serum correlate with disease activity during treatment of severe psoriasis with cyclosporin A

The epidermal serine proteinase inhibitor SKALP (also known as elafin), directed against human leukocyte elastase and proteinase 3, is strongly induced in suprabasal keratinocytes during inflammation. The presence of SKALP/elafin in urine has been demonstrated for several inflammatory skin disorders, such as psoriasis, erythroderma, and erysipelas. In this study we investigated whether SKALP/elafin levels in serum and urine of psoriatic patients can be used as a marker for disease activity during treatment. Patients with severe chronic disabling psoriasis were treated for 16 weeks with cyclosporin A, which resulted in a marked clinical improvement as measured with the PASI score. SKALP/elafin levels both in serum and urine were determined with an enzyme-linked immunosorbent assay (ELISA). Measurements were performed at the start of the cyclosporin A treatment, and after regular intervals up to 16 weeks. The results indicate that 1) SKALP/elafin determination in serum rather than in urine is the preferred method, because the decrease in serum SKALP levels during therapy is more pronounced and correlated better with the clinical course of the patients; 2) SKALP/elafin levels in serum decreased during cyclosporin A treatment (p < 0.05); and 3) SKALP/elafin levels in serum correlate with the PASI score (p < 0.01). We conclude that SKALP/elafin measurement in serum of patients with severe psoriasis provides a tool for monitoring disease activity.

Repeated tape stripping of normal skin: a histological assessment and comparison with events seen in psoriasis

The aim of the present study was to investigate the response of normal human skin to repeated courses of Sellotape stripping. The skin of healthy volunteers was stripped five times at 24-h intervals. Skin biopsies were taken before stripping (day 0) and on days 2, 4, 7 and 10. The responses were studied using H & E staining and an immunohistochemical analysis of several aspects of epidermal proliferation and keratinization. Although increased proliferation (nuclear binding to Ki-67 binding), acanthosis and parakeratosis were observed, the overall histological picture did not resemble psoriatic histology completely: no micropustules of Kogoj and no thinning of the suprapapillary plate were observed. Involucrin staining followed the recruitment of cycling epidermal cells showing a statistically significant elevation of positive cell layers from day 2 onwards. Filaggrin expression showed an increase from day 2 onwards, which was statistically significant on day 7 and day 10. Using the anti-keratin antibodies KS8.12 (K13 and K16) and RKSE60 (K10) we observed a fast induction of K13/K16 expression, while the staining of keratin 10 showed the same overall intensity at different time intervals. In conclusion, the response to repeated courses of tape stripping provides an adequate model for studies on epidermal proliferation, hypergranulosis and hyperkeratosis. This approach causes a more prolonged induction of these phenomena than a single course of stripping. In contrast to the situation following a single course of stripping, repeated tape stripping induced the expression of filagrin. Therefore the repeated tape stripping model is less compatible with psoriasis than a single course of stripping.

The inflammatory and proliferative response of normal skin in a model for acute chemical injury: ornithine decarboxylase induction as a common feature in various models for acute skin injury

Application of sodium dodecyl sulphate (SDS) on the skin of healthy volunteers was used as a model for acute chemical injury. The time course of the response with respect to cell proliferation was studied using ornithine decarboxylase (ODC) activity. Erythema, polymorphonuclear leucocyte (PMN) infiltration, and the induction of epidermal antiproteinase activity (SKALP/elafin) were used as markers for the inflammatory response. ODC induction was similar to that in other models of acute skin injury, such as tape-stripping and ultraviolet light radiation. The amount of PMN infiltration correlated with erythema, but not with ODC induction. In contrast with findings in the tape-stripping model, no induction of SKALP/elafin activity was found after SDS application. We conclude that cell proliferation as measured by ODC induction is a common feature in the various models for skin injury. Both the kinetics and the intensity of the inflammatory response, and the induction of epidermal antiproteinase activity, appear to vary, depending on the specific model.

Neuropeptides in psoriasis: possible role of beta-endorphin in the pathomechanism of the disease

BACKGROUND

An increased concentration of neuropeptides in psoriatic lesional skin may be responsible for alterations in the neurogenic erythematous response and transmission of stimuli through sensory nerve fibers (sensation of pruritus).

METHODS

Increasing doses of capsaicin from 0.125 to 4 micrograms/cm2 were applied to nonlesional psoriatic skin to establish the minimal dose that induced the substance P-mediated neurogenic response in 30 patients with psoriasis. Plasma beta-endorphin was quantitated in 71 psoriatics by radioimmunoassay using NEN 1251-RIA kit.

RESULTS

The mean beta-endorphin concentration was increased about 2-fold compared to normals, whereas doses of capsaicin needed to induce erythema were higher (1-4 micrograms/cm2) in psoriatics (mainly in patients with type II psoriasis) than in healthy subjects (0.125-0.25 microgram/cm2).

CONCLUSIONS

The data indicate that increased beta-endorphin in psoriatic skin might affect both substance P-mediated neurogenic inflammation and transmission of sensory stimuli due to local antinociceptive effects of this opioid. The differences in the neurogenic response in type I and II psoriasis may be related to the degradation of substance P and beta-endorphin by neutral proteinases in the lesional skin.

Demonstration of skin-derived antileukoproteinase (SKALP) in urine of psoriatic patients

Recently we described a new elastase inhibitor (skin-derived antileukoproteinase, SKALP) that is expressed in psoriatic epidermis and cultured keratinocytes, but is virtually absent in normal skin. In this study we investigated whether SKALP activity could be measured in urine of psoriatic patients and healthy controls. We found that urine of psoriatic patients contained considerable amounts of anti-elastase activity, whereas this activity in urine from normals was significantly lower. The properties of the urinary anti-elastase activity in psoriatic patients were indistinguishable from that of epidermal SKALP. It was found to be a cationic, heat-stable protein with an apparent molecular weight of 11 kDa on sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and a K(i) of approximately 2 x 10(-11) M. In addition, in Western blotting partially purified inhibitor from urine was found to react with a polyclonal anti-SKALP serum. SKALP in urine was either present in a free form or in a latent form, most likely complexed with elastase. We speculate that SKALP in urine of psoriatic patients is derived from the epidermis, and that it might serve as a marker for disease activity.

The effect of topical retinoids on the leukotriene-B4-induced migration of polymorphonuclear leukocytes into human skin

Systemic retinoids are effective in a variety of inflammatory dermatoses. Disorders in which polymorphonuclear leukocytes (PMN) are involved, such as psoriasis and acne, respond particularly well to various retinoids. However, side-effects restrict the use of systemic retinoids to severe manifestations. Topical application might provide the possibility of avoiding the systemic side-effects of these compounds. In this communication we report on the modulation of transepidermal migration of PMN by topical application of all-trans-retinoic acid, 13-cis-retinoic acid, arotinoid methyl sulphone and arotinoid ethyl sulphone. Test areas of healthy volunteers were pretreated with these retinoids in a cream base and with corresponding placebo creams, and intraepidermal accumulation of PMN was quantified 24 h after epicutaneous challenge with leukotriene B4 (LTB4), using elastase as a marker enzyme. Topical treatment with 13-cis-retinoic acid resulted in a marked and statistically significant inhibition of the LTB4-induced migration of PMN. All-trans-retinoic acid, arotinoid methyl sulphone and arotinoid ethyl sulphone reduced the accumulation of PMN slightly, but not statistically significantly. Topical treatment with arotinoid methyl sulphone had no effect.

Distribution of skin-derived antileucoproteases (SKALP) in the marginal zone of the spreading psoriatic lesion

Two new elastase inhibitors (SKALP, skin-derived antileucoproteases) were recently described in the lesional skin in psoriasis. The present study investigated the distribution of SKALP activity in the marginal zone of spreading psoriatic plaques. In a 4-mm zone immediately adjacent to the erythemato-squamous plaques, SKALP activity was slightly increased compared to distant uninvolved skin. Within the lesion the anti-elastase activity was pronounced, but was significantly higher in the central zone of the plaque compared to the periphery. The appearance of SKALP in the psoriatic lesion appears to be a late event compared to endothelial involvement, intraepidermal accumulation of PMNs, epidermal proliferation and abnormal keratinization. This observation lends further support for the hypothesis that the induction of anti-elastase activity is associated with the off-switch of cutaneous inflammation.

Skin-derived antileucoproteases (SKALPs): characterization of two new elastase inhibitors from psoriatic epidermis

Elastase inhibiting activity (EIA) was demonstrated in the epidermis from lesions and in psoriatic scale, whereas normal epidermis did not contain significant EIA. Two new elastase inhibitors were partially purified and characterized using psoriatic scale as a source. The two species (approximate molecular weights 10 and 20 kDa) were shown to be stable, and high-affinity inhibitors of human leucocyte elastase (Ki less than 10(-10) M). No activity against human cathepsin G could be demonstrated. Cultured human keratinocytes were shown to contain EIA activity similar to that found in psoriatic scale. EIA could also be demonstrated in human epidermis following the induction of an experimental inflammatory response by sellotape-stripping. We propose the acronym SKALP (skin-derived antileucoprotease) as a name for these new proteinase inhibitors.

Dithranol modulates the leukotriene B4-induced intraepidermal accumulation of polymorphonuclear leukocytes

Dithranol, with and without the addition of salicylic acid, was applied daily on normal skin according to a short contact protocol as used in the treatment of psoriasis. Sellotape stripping and epicutaneous application of leukotriene B4 (LTB4) were carried out within these pretreated areas. The challenged skin was subsequently biopsied and the intraepidermal accumulation of polymorphonuclear leukocytes (PMN) was quantified using the marker enzyme elastase. Dithranol pretreatment yielded a significant reduction of the LTB4-induced accumulation of PMN, whereas the tape stripping-induced accumulation of PMN was not affected by dithranol pretreatment. The addition of salicylic acid did not significantly enhance the effect of dithranol.

PUVA and UVB inhibit the intra-epidermal accumulation of polymorphonuclear leukocytes

Healthy volunteers were treated on test areas with UVB irradiation or topical PUVA therapy. The trauma-induced and leukotriene B4 (LTB4)-induced intra-epidermal accumulation of polymorphonuclear leukocytes (PMN) was quantified after these treatments, using elastase as a marker enzyme. Both UVB and PUVA treatment caused a profound inhibition of trauma- and LTB4-induced PMN accumulation. This observation indicates that reduction of the transepidermal migration of PMN might be part of the mechanism of action of UV therapies in psoriasis. Several possibilities are discussed to explain this hypothesis.