REDUCTION OF INTRAFOLLICULAR APOPTOSIS IN CHEMOTHERAPY-INDUCED ALOPECIA BY TOPICAL CALCITRIOL-ANALOGS

Chemotherapy-induced alopecia is thought to result from cytotoxic and apoptosis-related damage to the hair follicle. This study was designed to confirm whether keratinocyte apoptosis is indeed induced in growin g (= anagen) hair follicles of C57 BL/6 mice after the injection of cy clophosphamide, using improved methods for histologic detection of apo ptotic cells in murine skin. More importantly, we asked whether topica l calcitriol-analogs are able to modulate cyclophosphamide-induced apo ptosis in vivo, because there are conflicting reports on the effects o f calcitriols on apoptosis in vitro, Anagen was induced in telogen mic e on day 0 by depilation. Starting on day 5 post-depilation, the back skin of mice was topically treated with either 0.2 mu g 1,25-dihydroxy vitamin D-3, 2.0 mu g calcipotriol, 0.02 mu g KH 1060, or vehicle (eth anol) only. On the last day of treatment (i.e., day 9 post-depilation) , all mice received 150 mg cyclophosphamide i.p. per kg as a single do se to induce alopecia, or vehicle (aqua dist.). Analysis of the treate d skin by in situ-end labeling (using a modified terminal UTP nucleoti de end labeling technique suitable for murine skin), by Hoechst 33342 stain, and by DNA electrophoresis on days 10 and 14, revealed the indu ction of massive apoptosis in cyclophosphamide-treated anagen hair bul bs, which was most prominent on day 10, whereas controls showed no fol licular apoptosis, The calcitriol-pretreated groups demonstrated a sig nificant reduction of apoptosis, with a maximal inhibition seen on day 14. This confirms that cyclophosphamide indeed induces massive kerati nocyte apoptosis in anagen hair follicles, and provides evidence that topical calcitriol-analogs can suppress epithelial cell apoptosis in v ivo. The mouse model employed here offers an excellent tool for dissec ting the as yet poorly understood controls of keratinocyte apoptosis i n situ and its pharmacologic manipulation.