CHRONIC EXPOSURE OF SK-1 HAIRLESS MICE TO NARROW-BAND ULTRAVIOLET-A (320-355 NM)

Several recent investigations collectively suggest that the role of ul traviolet A (UVA) in chronic actinic skin damage may be greater than o riginally thought. In the present work, the output of a xenon-are sola r-simulator passed through a Bausch & Lomb monochromator in conjunctio n with a 2-mm Schott WG-320 filter produced narrow-band UVA centered a t 338 nm, half-band width 24 nm, I-0=3.4+/-0.3 mW/cm(2). We chronicall y irradiated 10 Sk-l albino hairless mice 5 times per week for 18 week s, starting with 1.25 J/cm(2), for 33 irradiation days, sequentially f ollowed by 1.50 J/cm(2) (34 days), 1.8 J/cm(2) (10 days), 2.0 J/cm(2) (22 days) to afford a total WA dose of 154.3 J/cm(2) over 99 irradiati on days. Erythema was noted clinically by day 6, which persisted throu ghout the irradiation. During the irradiation period, some scaling, co nsistent with mild epidermal hyperplasia was noted during irradiation days 37-56. This response later regressed despite continued chronic ir radiation. Hematoxylin and eosin examination immediately after the fin al irradiation revealed a mild inflammatory response, with some dermal restructuring. At the end of the experiment, no significant signs of epidermal hyperplasia or (pre)malignant lesions were seen, although so me stratum corneum thickening was noted. Marked dermal collagen damage and moderate elastosis was also evident. We believe that the observed differences in results reported in previous studies are in large part due to differences in light sources and irradiation protocols.