British zyxwvutsrqponm ]ournu/ zyxwvutsrqpon of Dermatology 1995: 132: 841-852. The effects of KH 1060, a potent 20-epi analogue of the vitamin D3 hormone, on hairless mouse skin in vivo R.GNIADECKI,* M.GNIADECKAt AND J.SERUP* *Department o/ Dermatological Research (2 1 zyxwvutsrqp ), Leo Pharmaceutical Products, Industriparken 55. DK-27SO Ballerup. Denmark tDepurtrnent oj Dermatology. University of Copenhagen. Bispebjerg Hospital. Copenhagen. Denmark Accepted for publication 15 August 1994 Summary Dermal effects of KH 1060, a novel, highly potent 20-epi analogue of la,25dihyroxyvitamin D3. were investigated in a hairless mouse model. During daily topical applications of a zy 0.4~~ solution of KH 1060 for zyxwvu 4 weeks, epidermal hyperplasia and an increase of dermal thickness and mass were observed. KH 1060 upregulated glycosaminoglycan and collagen synthesis in the skin, and increased glycosaminoglycan deposition in the subepidermal region. Reverse transcription-polymerase chain reaction amplification of the transforming growth factor (TGF) pl-specific mRNA revealed that KH 1060 stimulated expression of this growth factor in the epidermis, but not in the dermis. Changes observed after application of la,25-dihydroxyvitamin D3 were much less pronounced but qualitatively similar to the effects of KH 1060, whereas structurally related but receptor inactive compounds, vitamin D3 and lp,2 5-dihydroxyvitamin D3. did not produce any effects. Furthermore, we were unable to demonstrate the involvement of the non-genomic. receptor-independent vitamin D signalling in the skin, using a specific stimulator (Ro 24-2090) and a blocker (lp,25-dihydroxyvitamin D3) of this pathway. Our findings provide the first evidence that a strong vitamin D3 analogue triggers synthesis of skin connective tissue, possibly via vitamin epidermisderived TGF-Pl, The recent demonstration of receptor-mediated effects of la,25-dihydroxyvitamin D3( 1~~25-(0H)~D~) in non-classical target tissues (other than bone, kidney and intestine) has led to the development of the concept that this hormone is a general regulator of cell growth and differentiation.’ Skin not only pro- duces vitamin D3. but is also a target organ for the vitamin D3 hormone. 10.2 5-(OH)2D3 suppresses pro- liferation and induces differentiation of cultured kera- tin~cytes.’.~ and inhibits epidermal hyperproliferation in psoriasi~.~.~ In contrast, 1a,2 5-(OH)2D3 Stimulates proliferation of normal epidermis after topical applica- tion zyxwvutsr in vivo6 (()&endsen unpubl. obs.). In addition to the epidermis. the receptor for 10,25-(OH)zD3 (VDR) is expressed in the connective tissue of the dermis, in fibroblasts and endothelio~ytes.~-’~ However. there are few data on the dermal effects of la,25-(OH)2D3 in either humans or experimental animals. In the latter, studying dermal changes in Small animals such as mice or rats may be impeded by the development of hypercalcaemia which. compared with humans, D receptor activation and the paracrine action of becomes evident after topical application of much lower concentrations of the vitamin D com- p~und.~.~ 1*12 Therefore, it is conceivable that non- toxic doses of lo,25-(OH)2D3 are not sufficient to induce distinct dermal alterations. The availability of the novel series of 20-epi analogues of la,25-(0H)zD3 may provide a solution to this problem. One of the most potent of these compounds, the 20-epi-22-oxa- 24a-homo-26,2 7-dimethyl analogue (Leo Pharmaceu- tical Products code KH 1060: Fig. 1) has been shown to be 104-105 times more active than lcr.25-(OH)$3 in its cell regulating effects in vitro. but without a concomitant increase in the calcaemic effects in vi~o.~’’~~ The mechanism of action of 20-epi analo- gues is considered to be the same as that of the natural hormone,’*’4 although the reason for the increased potency remains speculative. One possibility is that the 20-epi compound is metabolized less rapidly in target In the present study, KH 1060 was used as a Pharmacological tool to investigate the cutaneous effects of the vitamin D endocrine system. cm 1995 British Association of*matologists 84 1