TOPICAL CALCITRIOL ENHANCES NORMAL HAIR REGROWTH BUT DOES NOT PREVENTCHEMOTHERAPY-INDUEED ALOPECIA IN MICE

Using a murine model that mimics chemotherapy-induced alopecia (CIA) i n humans particularly well, we show here that in contrast to previousl y reported CIA-protective effects in neonatal rats, topical calcitriol does not prevent CIA in adolescent mice hut enhances the regrowth of normally pigmented hair shafts. When, prior to injecting 1 x 120 mg/kg cyclophosphamide i.p., 0.2 mu g calcitriol or vehicle alone were admi nistered topically to the back skin of C57BL/6 mice with all hair foll icles in anagen, no significant macroscopic differences in the onset a nd severity of CIA were seen. However, hair shaft regrowth after CIA, which is often retarded and patchy, thus displaying severe and sometim es persistent pigmentation disorders, was significantly accelerated, e nhanced, and qualitatively improved in test compared with control mice . Histomorphometric analysis suggests that this is related to the fact that calritriol-pretreated follicles favor the ''dystrophic catagen p athway'' of response to chemical injury, i.e., a follicular repair str ategy allowing for the unusually fast reconstruction of a new, undamag ed anagen hair bulb. Thus, it may be unrealistic to expect that topica l calcitriol can prevent human CIA, but topical calcitriols may well e nhance the regrowth of a normal hair coat.