Title of Project: Examination of the photoprotective effects of 1,25-dihydroxycholecalciferol Brief Abstract of Project: 1,25-dihydroxycholecalciferol (1,25(OH)2D3 or calcitriol) has been found to inhibit UV induced apoptosis in keratinocytes, melanocytes and fibroblasts. Most studies have been conducted in cell culture and apoptosis measured indirectly via cell loss following irradiation. It has also been found that 1,25(OH)2D3 upregulates Bcl2 family members and inhibits cytochrome C release from mitochondria. The cell survival raises the possibility that cells with DNA damage are being preserved. There have been two further studies specifically investigating the effect of 1,25(OH)2D3 on DNA repair. Again this was done in vitro as above (in human keratinocytes, melanocytes and fibroblasts) but also in vivo, using mice and was concerned with repair of cyclobutane pyrimidine dimers, more specifically thymine dimers (T<>T). In this latter study, 1,25(OH)2D3 applied after UVB +UVA irradiation reduced dimer persistence. However there are no reports of protection from other forms of UV induced DNA damage. The aim of this project is to investigate whether 1,25(OH)2D3 has a protective effect on total DNA damage, T<>T and oxidative damage, using the comet assay. This will be done in cell culture using human keratinocytes and a solar simulator. Also, investigation of postirradiation apoptosis and cell survival will be examined. write about previous work in the same topic write about comet assay write about the hypothesis write about the objectives and aims of the project u.k english must be used provide diagrams and illustration fully referenced bibliography is needed min number of references: 40