188 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS of chronic skin photodamage and/or neoplasia. The epidermal enzyme ornithine decar- boxylase (ODC) is potentially such a marker. ODC (EC 4.1.1.17) is the rate-limiting enzyme in the biosynthetic pathway of poly- amines, macromolecules essential for cell proliferation (10). In normal epidermis, basal ODC activity is relatively low. Acute exposure of skin to ultraviolet radiation (UVR) or chemical tumor promoters can cause transient induction of epidermal ODC activity. Repeated induction of epidermal ODC activity is thought to be essential, but not sufficient, for skin tumor promotion, the second stage of skin carcinogenesis (11,12). The association of ODC with neoplasia has led to the wide use of acute ODC induction as a short-term biochemical marker for long-term skin tumor promotion by chemicals and UVR in tissue culture models (13-15) and animal models (11,16-23). Recently, Hillebrand et al. (18) showed that chronic UVB radiation exposure leads to greatly elevated levels of basal epidermal ODC activity in hairless mice. Elevated levels of ODC activity have also been associated with hyperplastic skin disorders (17,24-26) and ma- lignant tumors (10,17,27) including squamous cell carcinomas. These studies support the potential of ODC as a biochemical marker for chronic skin photodamage and neo- plastic growth. The purpose of the present study was to determine if visible skin photodamage is asso- ciated with increased basal levels of epidermal ODC activity. Also, we wanted to know if photoprotective agents such as sunscreens, antioxidants, and iron chelators that in- hibit skin photodamage (28-30) might also affect basal ODC activity. While sun- screens and antioxidants protect skin from photodamage by direct UVR absorption (36) and scavenging of oxygen radicals (29), respectively, the photoprotective mechanism of iron chelators is less well known. Iron chelators are believed to be photoprotective by sequestering iron, thereby preventing the iron-catalyzed formation of damaging oxygen species. The following is the presumed mechanism: UVR damages blood vessels in the skin, resulting in increased permeability to iron-binding proteins such as transferrin. Iron then accumulates in the UVR-exposed skin. It is known that iron can act as a catalyst in the generation of damaging oxygen radicals (31), and evidence strongly suggests that oxygen radicals are involved in skin photodamage (32). Iron chelation may prevent generation of the damaging oxygen radicals. EXPERIMENTAL MATERIALS L-[1-14C]Ornithine hydrochloride (specific activity = 51.6 mCi/mmol) was purchased from New England Nuclear (Boston, MA). tx-Tocopherol was purchased from Sigma Chemical Co. (St. Louis, MO) and applied topically as a solution in 100% ethanol. 2,2'-Dipyridylamine was purchased from Aldrich Chemical Co. (Milwaukee, WI) and applied topically as a solution in simple vehicle (water:ethanol:propylene glycol, 1:2:1, v:v:v). Suncreen (containing p-methoxy cinnamate and 4-p-butyl-4'-methoxydibenzoyl methane) had a sun protection factor (SPF) of 8. All other chemicals were of analytical grade.

UV-INDUCED SKIN TUMORS 189 SUBJECTS Four normal healthy Caucasians between the ages of 55 and 81 with Fitzpatrick skin types of I, II, or III (33) and a past history of chronic solar exposure were included in the study. Subjects were selected on the basis of severe chronic photodamage to the dorsal neck, outer arm, or preauricular area of the face. Little photodamage existed on the upper back, buttock, or inner arm. None of the subjects showed signs nor had a history of skin cancer. Skin sites were graded subjectively on a 0-5 scale for photo- damage by an experienced grader. Extensively photodamaged skin (grade 5) was yel- lowish, wrinkled, and had poor elastic mechanical properties (determined by its resil- iency after extension). All subjects had refrained from taking antihistamines, antibi- otics, anti-inflammatory agents, and/or vitamins for at least two weeks prior to the study. None of the subjects had recently been exposed to either natural or artificial sunlight. An internal review board (Hill Top Research, Cincinnati, OH) approved all protocols used in this work, and all volunteers signed informed consent statements prior to the study. ANIMALS Female albino hairless mice (Skh:HR-1 from Charles River, Portage, MI) were used at 10- 15 weeks of age. Mice were housed five to a cage in a room with controlled temper- ature and humidity and with a 12-hour light/darkness cycle. Mice were then individu- ally identified by ink-colored tail markings and cage number throughout the course of the experiments (e.g., cage 1, red cage 1, green, etc.). They were given a standard diet and water ad libitum. UV IRRADIATION The UVR sources were either a solar simulator (Kratos, Ramsey, NJ) equipped with a 1000-W xenon arc lamp and dichroic filter or a bank of four Westinghouse FS-40 UVB sunlamps. Spectral emission of each UVR source was measured with an International Light 791 radiometer (Newburyport, MA) as previously described (18). For chronic UVB irradiation, mice were irradiated (3 X/week) in individual wire cage chambers (7.5 X 7.5 X 7.5 cm) in which their backs were 35 cm from the fluorescent tubes. UVB irradiance at this distance was 0.23 mW/cm 2 as measured with an International Light 700 radiometer total exposure dose was 55 mJ/cm 2 for each irradiation [•-0.8 mouse minimum erythemal dose (MED)]. For chronic simulated solar radiation (SSR), mice were individually irradiated (3 X/week) with their backs 10 cm from the dichroic filter, as previously described (28). SSR irradiance at this distance was 18 mW/cm2 total exposure dose was initially 540 mJ/cm 2 (•0.8 x MED) and was increased ap- proximately 30% every two weeks until a total daily dose of 900 mJ/cm 2 was reached, after which the dose remained constant for each irradiation. TOPICAL TREATMENTS There were 15-20 mice in each treatment group. Treatments [0.05 ml sunscreen 0.1 rnl 5% o•-tocopherol or 0.1 ml 5% iron chelators (w/v)] were applied topically to the