Nuclear and Urinary Measurements Show the Efficacy of Sun-Protection Factor 50+ Sunscreen against DNA Photoproducts upon Real-Life Recreational Exposure

Abstract

Sunscreens have been shown to protect against UVR-induced DNA damage in human skin under laboratory conditions. We presently extended these observations to real-life conditions in volunteers after their ordinary exposure habits during summer holidays. Volunteers were randomly assigned to a control group and an educated group supplied with a SPF ≥50 sunscreen and receiving instructions for use. A questionnaire was used to determine the extent of exposure. No difference in average solar UVR exposure was found between the two groups. DNA photoprotection was first assessed by, to our knowledge, a previously unreported noninvasive assay on the basis of the quantification of pyrimidine dimers released by DNA repair in urine. Damage was also quantified in the nuclear DNA extracted from the roof of suction blisters collected after recreational exposure. The urinary concentration of photoproducts was significantly higher in the control than in the educated group. The same trend was observed for the level of photoproducts in the DNA from suction blisters. The unambiguous observation of an efficient photoprotection against DNA damage afforded by sunscreen under real-life conditions provides strong support for the efficiency of the sunscreens. In addition, the results validate the use of urinary DNA photoproducts as a noninvasive assay applicable to photoprotection.

Figure 1

Exposition scores determined in the two investigated groups (control group and educated group). The graph is presented with the median and 25th–75th percentiles range. The difference is not statistically significant.

Figure 2

HPLC-MS/MS detection of TT-CPD in the urine of volunteers after summer recreational exposure. The color code corresponds to the three different fragmentation reactions monitored during the analysis (- m/z 545 → 79, - m/z 545 → 195, - m/z 545 → 447). The vertical axis represents the intensity of the signals expressed in cps. Oligonucleotides produced by DNA repair were isolated and hydrolyzed, and the samples were analyzed by HPLC-MS/MS. The chromatograms correspond to the sample with the lowest (min) and largest (max) concentrations in (a) the control and (b) the educated groups. The corresponding volunteers are number 5, 16, 17, and 21. cps, count per second; HPLC-MS/MS, high-performance liquid chromatography–tandem mass spectrometry; max, maximum; min, minimum; TT CPD, thymine–thymine cyclobutane pyrimidine dimer.

Figure 3

The concentration of TT CPDs in the urine of the control and educated groups before and after recreational exposure to solar UVR. Data are median with 25th–75th percentiles range (n = 12 for control, and n = 11 for educated). A covariance analysis on the change between V1 (before) and V2 (after) with group as a fixed factor and baseline as a covariate was made. Comparisons between LSMeans were realized to perform intragroup and intergroup analyses. ns denotes nonsignificant difference. ∗P < 0.050 and ∗∗P < 0.010. TT CPD, thymine–thymine cyclobutene pyrimidine dimer; V1, visit 1; V2, visit 2.

Figure 4

Level of TT and TC CPDs in the DNA extracted from suction blisters in control and educated groups after recreational exposure to solar UVR. Data are median with 25th–75th percentiles range (n = 12 for control, and n = 11 for educated). ∗P < 0.050 (TT CPD P = 0.047; TC CPD P = 0.047). CPD, cyclobutene pyrimidine dimer; TC, thymine–cytosine; TT, thymine–thymine.