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 treat ed with tazarotene gel (0.1%, 0.05%), dithranol ointment (1.0%), tretinoin cream (0.05%) and methylcellulose (5%) hydrogel (vehicle control) for 2 wee ks. Longitudinal histological sections were prepared from the tail skin, an d the degree of orthokeratosis was determined by measuring the horizontal l ength of the fully developed granular layer within an individual scale in r elation to its total length according to a method originally described by B osman and co-authors. The degree of orthokeratosis was significantly (p les s than or equal to 0.05) increased by 0.1% tazarotene (87 +/- 20%), 1.0% di thranol (75 +/- 26%), 0.05% tazarotene (59 +/- 27%), and 0.05% tretinoin (2 3 +/- 13%) as compared to untreated (11 +/- 6%) and methylcellulose hydroge l-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. Copyright (C) 2000 S. Karger AG, Basel.