Passage
Depending on the active compound's specific method of action, sunscreens are broadly classified into two groups: organic and inorganic. Organic sunscreens typically contain aromatic compounds that absorb ultraviolet (UV) radiation. The absorbed energy from the UV radiation causes these compounds to enter electronically excited states which then relax back to the ground state and harmlessly re-emit the absorbed radiation as heat. Alternatively, inorganic sunscreens contain metallic nanoparticles that serve to reflect, scatter, and absorb incident radiation. The mechanism for UV protection of each group is shown in Figure 1.
Figure 1 Method of action for organic and inorganic sunscreensThe effectiveness of sunscreens is traditionally evaluated based on their ability to prevent reddening of the skin, as indicated by their sun protection factor (SPF) . However, studies have shown that additional deleterious effects, such as the suppression of T cell-mediated immune responses, can occur at lower UV doses than erythema, indicating the need for new metrics to judge sunscreen efficacy. For this reason, researchers conducted a study to compare the protective ability of six sunscreens against photo-isomerization of the photoreceptor trans-urocanic acid (UCA) to its cis form, a process believed to be linked to UV-induced immunosuppression. Table 1 lists the sunscreens tested and their relevant characteristics.Table 1 Results from Tested Sunscreens
In vivo experiments were conducted on two groups of human volunteers. Participants in the acute exposure group received a single UV dose of 100 mJ/cm² whereas participants in the chronic exposure group received the same dosage once daily over four consecutive days. Each sunscreen was applied to a different spot on the volunteers' back prior to irradiation. A portion of skin without sunscreen was also irradiated to serve as a control. After irradiation, the sunscreens were removed and the skin was wiped with filter papers. Filters were washed with potassium hydroxide, and the aqueous solution was analyzed for UCA using high-pressure liquid chromatography. Figure 2 shows the mean percentages of cis-UCA formed upon irradiation for each exposure type and sunscreen tested.
Figure 2 Percentage of UCA in cis configuration upon UV exposure with various sunscreens
Adapted from Van der molen RG, Out-luiting C, Driller H, Claas FH, Koerten HK, Mommaas AM. Broad-spectrum sunscreens offer protection against urocanic acid photoisomerization by artificial ultraviolet radiation in human skin. J Invest Dermatol. 2000;115(3) :421-6.
-Based on the results from the experiment in Figure 2, which of the following conclusions can be drawn?

Question

Passage
Depending on the active compound's specific method of action, sunscreens are broadly classified into two groups: organic and inorganic. Organic sunscreens typically contain aromatic compounds that absorb ultraviolet (UV) radiation. The absorbed energy from the UV radiation causes these compounds to enter electronically excited states which then relax back to the ground state and harmlessly re-emit the absorbed radiation as heat. Alternatively, inorganic sunscreens contain metallic nanoparticles that serve to reflect, scatter, and absorb incident radiation. The mechanism for UV protection of each group is shown in Figure 1.

Figure 1 Method of action for organic and inorganic sunscreensThe effectiveness of sunscreens is traditionally evaluated based on their ability to prevent reddening of the skin, as indicated by their sun protection factor (SPF) . However, studies have shown that additional deleterious effects, such as the suppression of T cell-mediated immune responses, can occur at lower UV doses than erythema, indicating the need for new metrics to judge sunscreen efficacy. For this reason, researchers conducted a study to compare the protective ability of six sunscreens against photo-isomerization of the photoreceptor trans-urocanic acid (UCA) to its cis form, a process believed to be linked to UV-induced immunosuppression. Table 1 lists the sunscreens tested and their relevant characteristics.Table 1 Results from Tested Sunscreens

In vivo experiments were conducted on two groups of human volunteers. Participants in the acute exposure group received a single UV dose of 100 mJ/cm² whereas participants in the chronic exposure group received the same dosage once daily over four consecutive days. Each sunscreen was applied to a different spot on the volunteers' back prior to irradiation. A portion of skin without sunscreen was also irradiated to serve as a control. After irradiation, the sunscreens were removed and the skin was wiped with filter papers. Filters were washed with potassium hydroxide, and the aqueous solution was analyzed for UCA using high-pressure liquid chromatography. Figure 2 shows the mean percentages of cis-UCA formed upon irradiation for each exposure type and sunscreen tested.

Figure 2 Percentage of UCA in cis configuration upon UV exposure with various sunscreens
Adapted from Van der molen RG, Out-luiting C, Driller H, Claas FH, Koerten HK, Mommaas AM. Broad-spectrum sunscreens offer protection against urocanic acid photoisomerization by artificial ultraviolet radiation in human skin. J Invest Dermatol. 2000;115(3) :421-6.
-Based on the results from the experiment in Figure 2, which of the following conclusions can be drawn?

Quizplus · Accepted Answer

11ecba2d_1197_5eac_a3bf_cbd095e721f8_MD0008_00 According to the passage, photo-isomerization of trans-UCA to cis-UCA is linked to UV-induced immunosuppression. Therefore, a sunscreen with a smaller percentage of cis-UCA provides better protection than a sunscreen that permits a greater percentage of cis-UCA formation. Figure 2 shows the mean percentages of cis-UCA formed during acute and chronic exposure for each sunscreen tested. The graph indicates that under acute exposure, skin treated with T10 sunscreen yields the least cis-UCA formation whereas under chronic exposure, skin treated with B19 sunscreen yields the least cis-UCA formation. Therefore, sunscreens T10 and B19 offer the best protection against acute and chronic UV exposure, respectively. (Choice A) Acute exposure leads to a smaller amount of cis-UCA formation than chronic exposure for all sunscreens tested in Figure 2. A smaller amount of cis-UCA indicates less immunosuppression. (Choice B) Exposure without sunscreen leads to 65% cis-UCA for acute exposure and 75% cis-UCA for chronic exposure. Therefore, UV radiation causes approximately two in three (acute exposure) and three in four (chronic exposure) UCA molecules to become the cis isomer. (Choice D) T5 provides the least protection from UV radiation because it leads to the highest percentage of cis-UCA formation for chronic exposure, which indicates a greater instance of UV-induced immunosuppression. Educational objective: Careful analysis of data and what it implies is important to form conclusions from experimental results. A correct understanding of what the data indicate is essential for drawing correct conclusions.

Passage Depending on the Active Compound's Specific Method of Action, Sunscreens