P.C.M. Kerkhof

Simultaneous assessment of inflammation and epidermal proliferation in psoriatic plaques during long-term treatment with the vitamin D3 analogue MC903: modulations and interrelations

The influence of topical application of MC903, an analogue of 1α, 25‐dihydroxyvitamin D3, on psoriatic plaques was investigated during a long‐term treatment study. The parameters for epidermal growth and for inflammation were assessed on frozen sections using immunohistochemical methods to elucidate their modulations in time and the interrelations between the different cell types involved during treatment with MC903. Biopsies were taken before and after 1, 2, 4 and 12 weeks of treatment. Monoclonal antibodies against the hyperproliferation‐associated keratin 16, against cycling nuclei, and against T lymphocytes, B lymphocytes, Langerhans cells and CD14‐positive cells were used in combination with a polyclonal antibody against polymorphonuclear leucocyte (PMN)‐elastase.

Topical treatment of psoriatic plaques with 1,25‐dihydroxyvitamin D3: a cell biological study

Calcitriol, 1α,25 dihydroxycholecalciferol (α.25 (OH)2 D2) is a natural active vitamin D3 metabolite, which has been shown to have antipsoriatic efficacy. In vitro studies have demonstrated that calcitriol influences various aspects of inflammation, epidermal proliferation and keratinization. The aim of the present study was to determine to what extent caicitriol (3 μ/g in white petrolatum) affects these parameters in vivo.

Calmodulin levels are grossly elevated in the psoriatic lesion.

Levels of the intracellular calcium receptor, calmodulin, in the psoriatic lesion are more than thirty times higher than normal. By contrast, values in the clinically uninvolved psoriatic skin are unchanged.

Epidermal hyperproliferation following the induction of microabscesses by leukotriene B4

The percentage of non‐diploid epidermal cells was determined by flow cytometry following application of leukotriene B4 (LTB4) to human skin. Doses in the range 35–500 ng were shown to cause a marked increase in proliferation, the non‐diploid cells reaching a maximum between 72 and 96 h after LTB4 application. No difference was observed between the response of healthy controls and the uninvolved skin of psoriatic patients. We suggest, therefore, that the hyperproliferation is a consequence of the physical disruption of the stratum corneum accompanying the rupture of microabscesses.

A double-blind study of topical 1α,25-dihydroxyvitamin D3 in psoriasis

Several open studies with active forms of vitamin D3 have been reported to be effective in the treatment of psoriasis. We report a double‐blind study of 1α,25‐dihydroxycholecalciferol in psoriasis using 0.5 μg of active substance applied topically twice daily. In contrast to previous studies, the present investigation does not provide evidence of clinical efficacy for the drug at that dosage and with the vehicle that was used.

Elastase, a marker for neutrophils in skin infiltrates

The enzyme elastase (EC 3.4.21.37) has proved to be a convenient and extremely sensitive marker for the quantification of neutrophils in cutaneous infiltrates. Fluorometric assay using the synthetic substrate MeOSuc‐Ala‐Ala‐Pro‐Val‐N‐methylcoumarin permitted the measurement of this enzyme in as few as five cells and was linear up to about 1000 cells per sample. The mean activity of lysates of human blood‐derived neutrophils was 0.57 ± 0.08 pmol of 7‐amino‐4‐methyl‐coumarin released per hour per neutrophil. Extracts of normal human skin contained no measurable elastase activity but resulted in a slight inhibition of the neutrophil enzyme (mean 12%).

Methotrexate inhibits the leukotriene B4 induced intraepidermal accumulation of polymorphonuclear leukocytes.

The penetration of polymorphonuclear leukocytes (PMNs) into the epidermis following topical application of leukotriene B4 was assessed in the clinically uninvolved skin of psoriatic patients treated with methotrexate and of psoriatic patients without treatment, and in normal controls. Inhibition of PMN infiltration was observed in those patients treated with methotrexate while there was no significant difference between untreated psoriatic patients and normal controls.

Markers for proliferation and keratinization in the margin of the active psoriatic lesion.

To study the development of the psoriatic lesion, biopsies were taken from the margin of spreading plaques and acute pinpoint papules. Consecutive sections across the margin were stained using different monoclonal antibodies to characterize epidermal growth (Ki‐67) and abnormal keratinization (Ks8.12, RKSE60). All three immunohistochemical markers showed pronounced changes in the lesional skin with a clear transition to the uninvolved skin. The suprabasal Ks8.12 binding was the earliest change found in the epidermis, and its localization high in the suprabasal compartment indicates that metabolic dysregulation in this cell population was not a consequence of the recruitment process in the basal layer.

The inter-relation between inflammation and epidermal proliferation in normal skin following epicutaneous application of leukotriene-B4—an immunohistochemical study

Topical application of leukotriene‐B4 (LTB4) on normal skin has been used as an in‐vivo model to investigate cutaneous inflammation and epidermal proliferation, which are important phenomena in the pathogenesis of psoriasis. The aim of the present investigation is to further elucidate the interrelation between inflammation and epidermal proliferation, using specific monoclonal antibodies as markers for the different cell types involved.

Confirmation of raised phospholipase A2 activity in the uninvolved skin of psoriasis

Phospholipase A2 has been measured in the lesions and the ‘uninvolved’ skin of patiens with psoriasis. We confirm a previous report that there is a generalized increase in the activity of this enzyme in psoriatic skin.