Biologic effects of topical calcipotriol (MC 903) treatment in psoriatic skin

Abstract Background: The biologically active vitamin D analog calcipotriol is effective and safe in the topical treatment of psoriasis, but its exact mechanism of action is unknown. Objective: We investigated expression of 1,25-dihydroxyvitamin D 3 receptors, markers for inflammation (CD1a, CD4, CD8, CD11b, CD15; NAP-1/interleukin-8; 55 kd tumor necrosis factor–receptor; intercellular adhesion molecule–1; HLA-DR), proliferation (proliferating cell nuclear antigen, Ki-67), and differentiation (transglutaminase K; involucrin; cytokeratin 16) in psoriatic skin during topical calcipotriol treatment. Methods: For immunohistochemical staining we used the labeled avidin-biotin technique on cryostat-cut sections. Results: We found a significant increase of 1,25-dihydroxyvitamin D 3 receptor expression in epidermal basal keratinocytes of lesional psoriatic skin during calcipotriol treatment. In all patients analyzed, effects on proliferation and differentiation of epidermal keratinocytes were stronger than effects on dermal inflammation. Effects on inflammation were more pronounced in the epidermal than in the dermal compartment. Conclusion: Our findings indicate that analogs of 1,25-dihydroxyvitamin D 3 upregulate their corresponding receptor in human keratinocytes in vivo. This mechanism may be important in the therapeutic efficacy of vitamin D analogs in psoriasis. The differential therapeutic effects in the epidermal and dermal skin compartments may be due to a reduced bioavailability of calcipotriol in the dermal compartment. (J Am Acad Dermatol 1997;36:19-28.)