Immunologic protection afforded by sunscreens in vitro

Promoting sun safety among US Postal Service letter carriers: impact of a 2-year intervention

OBJECTIVES

We examined whether US Postal Service letter carriers who received a sun safety intervention would wear wide-brim hats and sunscreen significantly more often than those who did not receive the intervention.

METHODS

We used a 2-group randomized design with 2662 evaluation cohort participants from 70 US postal stations. Evaluations were conducted at baseline, 3 months, 1 year, and 2 years. Questionnaire items assessed occupational use of sun-screen and wide-brim hats. The 2-year sun safety intervention included the provision of wide-brim hats, accessible sunscreen, reminders, and 6 educational sessions.

RESULTS

At the 3-month follow-up evaluations, the odds ratio (OR) for regular sun-screen use was 2.8 times higher among the intervention group than among the control group (95% confidence interval [CI]=2.2, 3.5); at the 2-year follow-up evaluations, the rate was still significantly higher (OR=2.0; 95% CI=1.6, 2.6). Intervention group participants also had significantly higher rates of hat use, with the differences remaining consistent across all follow-ups (OR=2.9; 95% CI=2.3, 3.6).

CONCLUSIONS

The intervention should be disseminated to postal stations nationwide and possibly to other occupational groups that work outdoors.

Ethnoracial differences among outdoor workers in key sun-safety behaviors

BACKGROUND

Few sun-safety studies have included ethnoracially diverse groups. Comparison across such groups of sun-safety behaviors was the main objective of this analysis.

METHODS

Postal workers (n =2543) self-reported frequency of sunscreen, wide-brim hat, and sunglasses use during the last 5 workdays on 5-point Likert-type scales ranging from "never" to "always." Responses were dichotomized by "always" versus all other responses. Generalized estimating equations were used to assess the association between ethnicity/race and frequency of each sun safety behavior. The baseline data reported in this paper were collected in the summer of 2001, and the randomized trial was completed in the summer of 2004.

RESULTS

Ethnicity/race was significantly related to sunscreen and sunglasses use. For both sunscreen and sunglasses, the white group had significantly higher "always" rates than the other four groups (30% vs 14% to 23% and 63% vs 44% to 52%, respectively).

CONCLUSIONS

The results of this study indicated that although non-Latino white employees tended to have higher rates of sun-safety behaviors, the rates of adequate protection of all groups were low.

Sunburn Cell Formation, Dendritic Cell Migration, and Immunomodulatory Factor Production After Solar-Simulated Irradiation of Sunscreen-Treated Human Skin Explants In Vitro

Using human skin explants, we investigated the effects of two different sunscreen preparations containing a chemical UVB filter alone [sun protection factor (SPF) 5.2] or UVA+UVB filter [SPF 6.2] on sunburn cell formation, dendritic cell (DC) migration, CD86- and CD1a-positive cell number, and tumor necrosis factor alpha (TNFalpha) and interleukin (IL)-1, IL-10, and IL-12 production in the skin after irradiation with different doses of solar-simulated UV radiation. Sunscreen- or placebo-treated skin explants were irradiated with solar-simulated UV radiation at 0.5, 1, and 2 minimal erythematous dose equivalents (MEDE) (as determined in an in vivo human study) multiplied by the SPF of the placebo or sunscreens. After irradiation, skin explants were floated on RMPI medium for 48 h. Cells that had emigrated and the skin explants were histologically analyzed, and the soluble mediators were measured in the supernatants by ELISA. Exposure to UV radiation led to concentration-dependent increases in sunburn cell formation and TNFalpha production but a concentration-dependent decrease in DC migration and CD86- and CD1a-positive cell number in the epidermis. Both chemical sunscreens protected against those alterations. The immunoprotective capacity of the sunscreens correlated with their SPF but was independent of the sunscreens' UVA protection capacity, suggesting that UVA is not a major factor for immunosuppression under the conditions used in the model. UV irradiation did not significantly affect the vitality of emigrated DC; the expression of HLA, CD80, and lag on emigrated cells; the number of CD1a-positive cells in the dermis; or the production of IL-1, IL-10, and IL-12. We conclude that our model may be useful in determining the immunoprotective capacity of sunscreens.

Advantages of using hairless mice versus haired mice to test sunscreen efficacy against photoimmune suppressions

We tested the hypothesis that the strain of mice used in sunscreen protection experiments may influence immune protection. Ultraviolet (UV) dose-response curves were done in the presence or absence of a sun protection factor (SPF) 15 sunscreen using SKH1:hrBR or C3H/HeN mice. SKH1:hrBR mice showed a higher sensitivity to the suppressive effects of UV radiation (50% immune suppression equal to 5.2 kJ/m2 UVB in SKH1:hrBR mice versus 18.5 kJ/m2 in C3H mice). Immune protection factors (IPF) and an erythema protection factor (Ery-PF) for SKH1:hr mice were derived. The Ery-PF in hairless mice was 13.5, which was similar to the SPF of 15 measured in humans. When IPF were calculated as a ratio of minimal immune suppressive doses, the IPF for the SKH1:hrBR mice was 8.23 and the IFP for the C3H/HeN mice was 1.92. When IPF were estimated using the entire UV dose-response range, they were equal to 9.01 for SKH1:hrBR mice and 1.79 for the C3H/HeN mice. Because IPF and SPF can be measured directly in hairless mice, we suggest that the use of hairless mice may provide a better model to measure sunscreen efficacy, especially when the use of human volunteers is inappropriate, unethical or impossible.

Effects of low-dose ultraviolet radiation on in vivo human cutaneous recall responses

Relatively few studies have examined the effects of low-dose ultraviolet (UV) radiation on in vivo human cutaneous immunity, or the ability of sunscreens to prevent UV-induced immunosuppression. We have studied the effects of solar-simulated UV radiation on nickel contact hypersensitivity (CHS) in nickel-allergic volunteers, and on delayed type hypersensitivity responses in Mantoux-positive volunteers. Nickel CHS and Mantoux responses were significantly suppressed by acute, suberythemal UV exposures equivalent to less than 8 min summer sunlight. Both UVA and UVB wavebands were immunosuppressive, but UVA-induced immunosuppression was transient, whereas UVB had a more sustained effect. Dose-responses for UV immunosuppression were determined using the nickel method, enabling calculation of in vivo sunscreen immune protection factors in a manner analogous with sun protection factor measurement. Sunscreens were found to confer significantly less protection against UV-induced immunosuppression than against UV-induced erythema.

The effects of ultraviolet radiation on the human immune system

The adverse outcome of increased ultraviolet (UV) irradiation on human health is currently of concern. While many experiments have been carried out in rodent models, fewer have been designed to test the effects of UV exposure in human subjects. This review concentrates on the modulations induced in the human immune system by UV, and outlines changes in antigen presentation by Langerhans cells and macrophages, in the activities of natural killer cells and T cells, and in cytokine regulation. Precautionary measures which might be taken to help protect people against the immunosuppressive action of UV irradiation are considered.

p53 induction in normal human skin in vitro following exposure to solar simulated UV and UV-B irradiation

Exposure of normal human breast skin ex vivo to physiological levels of UV-B and solar simulated UV results in a UV dose- and time-dependent increase in epidermal p53, as determined by PAGE analysis. Peak p53 levels are detected 12 to 24 h post irradiation with UV-B (470-1410 mJ cm-2) and solar simulated UV (5-12 minimal erythema dose (MED) equivalents). Irradiation with an FS20 UV-B lamp, contaminated with UV-A and UV-C (74-1111 mJ cm-2), also induces peak levels after 12 h incubation at 37 degrees C but these levels persist to 36 h post UV irradiation. In all cases p53 levels start to return to normal by 48 h culture. A significant positive correlation is demonstrated between UV-B dose (47-1645 mJ cm-2) and p53 level (p < 0.01, R > 0.977) in explants cultured for 24 h at 37 degrees C post irradiation. The FS20 induces a 'UV-B' dose-dependent increase in p53 to a maximum from 370 to 1111 mJ cm-2. Similarly, solar simulated UV induces a plateau of peak p53 induction between 5 and 15 MED equivalents. Immunohistochemical analysis using microwave retrieval on 5 microns sections shows the same pattern of p53 staining with UV-B and solar UV insult, but proves unreliable as a method of quantification. These results suggest that the skin explant model may be a useful tool in the evaluation of UV-induced epidermal cell damage, providing a valuable alternative to in vivo studies.