Photoprotective properties of new derivatives of kinetin.

The chronic exposure of skin to ultraviolet (UV) radiation causes adverse dermal reactions, such as erythema, sunburn, photoaging, and cancer, by altering several signalling pathways associated with oxidative stress, inflammation, and DNA damage. One of the possible UV light protection strategies is the use of dermal photoprotective preparations. The plant hormone kinetin (N6-furfuryladenine; KIN) exhibits antioxidant and anti-senescent effects in human cells. Topically applied KIN also reduced some of the clinical signs of photodamaged skin. To improve the biological activities of KIN, several derivatives have been recently prepared and their beneficial effects on cell viability of skin cells exposed to UVA and UVB light were screened. Two potent candidates, 6-(tetrahydrofuran-2-yl)methylamino-9-(tetrahydrofuran-2-yl)purine (HEO) and 6-(thiophen-2-yl)methylamino-9-(tetrahydrofuran-2-yl)purine (HEO6), were identified. Here the effects of KIN, its N9-substituted derivatives the tetrahydropyran-2-yl derivative of KIN (THP), tetrahydrofuran-2-yl KIN (THF), HEO and HEO6 (both THF derivatives) on oxidative stress, apoptosis and inflammation in UVA- or UVB-exposed skin cell was investigated. Human primary dermal fibroblasts and human keratinocytes HaCaT pre-treated with the tested compounds were then exposed to UVA/UVB light using a solar simulator. All compounds effectively prevented UVA-induced ROS generation and glutathione depletion in both cells. HEO6 was found to be the most potent. All compounds also reduced UVB-induced caspase-3 activity and interleukin-6 release. THP and THF exhibited the best UVB protection. In conclusion, our results demonstrated the UVA- and UVB-photoprotective potential of KIN and its derivatives. From this point of view, they seem to be useful agents for full UV spectrum protective dermatological preparations.