Early Changes in Dermal Collagen of Mice Exposed to Chronic UVB Irradiation and the Effects of a UVB Sunscreen

Our previous studies have shown that hairless albino mice receiving chronic UVB irradiation show an increase in type III collagen, in the irradiated skin, after 12–36 weeks treatment. In this study we wished to find the earliest time at which such collagen changes were detectable and also to ascertain whether a topically applied UV-B sunscreen could prevent such changes.Groups of 10 hairless albino mice were irradiated, dorsally, with a daily dose of 62 mJcm-2 UVB for 3, 6, 9, and 12 weeks. Three parallel groups were used. They received a) no topical treatment, b) sunscreen vehicle alone, and c) sunscreen (containing 2-ethylhexyl 4'-methoxy-cinnamate) applied dorsally at 2 μlcm-2. Dorsal and ventral (non-irradiated) skin samples were taken and the types I and III collagen quantified densitometrically after cyanogen bromide digestion and polyacrylamide gel electrophoresis. The ratio of dorsal/ventral type III collagen (D/V III) was determined for each mouse.The topical treatments caused no change in D/V III in the non-irradiated animals. In the non-topically treated group the irradiated animals showed a considerable increase in D/V III, compared with controls, at 12 weeks (P < 0.001). The group treated with sunscreen vehicle alone also showed a significant increase in D/V III at week 12 (P < 0.01). Both these groups showed a slight elevation in D/V III at week 6. The group treated with sunscreen showed no significant difference in D/V III between irradiated and control animals at any time