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March 2001
Vol. 4, No. 3, p 12.
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Oil and sunlight
Olive me. Topically applying olive oil to mice after UV exposure reduces levels of the DNA mutagen 8-hydroxy-2'-deoxyguanosine.
UV radiation, particularly UVB, has been shown to cause nonmelanoma skin cancers (NMSCs) by damaging DNA and inducing immunosuppression. Direct absorption of UVB energy causes the formation of cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts at dipyrimidine sites in DNA, a mutational hotspot in the p53 tumor suppressor gene. Reactive oxygen species alter DNA under conditions of high UV stress. One such product, 8-hydroxy-2'-deoxyguanosine (8-OHdG), induces C–G to T–A transversions during DNA replication. These transversions occur in the ras and p53 genes of human NMSCs.

Thus, compounds containing antioxidant and free radical scavenging capabilities are potential cancer preventive agents. Studies have shown that a diet rich in natural antioxidants, including vegetable and plant extracts, reduces the risk of skin cancer. Furthermore, topical application of the polyphenol fractions in green tea also suppresses UV-induced carcinogenesis.

Arief Budiyanto and colleagues investigated the effects of topical application of olive and camellia oil on skin tumor formation in mice (Carcinogenesis 2000, 21, 2085–2090). The anti-inflammatory effects of camellia oil, the antioxidant properties of olive oil, and the lower incidence of certain cancers in Mediterranean areas where olive oil consumption is high make these products good therapeutic candidates.

Hairless mice received topical camellia or olive oil applications before or after UVB irradiation performed 3 times a week for up to 32 weeks, while a control group received only irradiation. Tumor onset was delayed in treated mice and, although the percentage of mice with tumors at 32 weeks was similar in all 3 groups, fewer tumors per mouse were seen in the group treated with olive oil after irradiation. This effect was not seen with camellia oil. There was no difference in tumor histopathology, p53 protein production, or levels of CPD and (6-4) photoproducts between the groups. There was less 8-OHdG in tumors from mice treated with olive oil after UVB irradiation, but this effect was abolished if UV-irradiated olive oil was used. Thus, olive oil has no sunscreen effect, as its antioxidant factor is UV-labile.

The reduction in 8-OHdG seen when olive oil is applied after UVB irradiation is attributed to its ability to scavenge reactive oxygen species. The identity of the antioxidant factor and its oral efficacy need to be determined. If parallels with green tea can be made, olive oil and other foods may be candidates for cancer preventive agents.


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