In vitro photoprotective evaluation in skin cells culture irradiated with UVA and UVB: phenolic compounds as a model of study

Abstract

Ultraviolet (UV) has detrimental effects on human skin and can result in clinical conditions such as burns, immunosuppression, premature aging and cancer. There are differences in the pattern of cellular damage from UVA and UVB waves. While UVA indirectly damage DNA by the formation of reactive oxygen species, UVB can directly reach the DNA, resulting in the formation of photo-products, such as cyclobutane dimers and formation of pyrimidine-pyrimidone photoproducts [(6-4) PD ]. Several mechanisms lead to elimination of damage caused by UV light resulting in apoptosis by mechanisms such as increased p53 expression, induction in delayed cell cycle via p21 gene transcription and subsequent activation of caspase-9 and caspase-3. UV radiation also leads to the formation of reactive oxygen species (ROS), which are removed by endogenous antioxidants. However, the overproduction of ROS can result in macromolecules damage, activation of enzymes such as matrix metalloproteinases, and dehydration of the skin, from the down-regulation of membrane protein aquaporin-3, characterizing the photoaging. Inflammatory mechanisms, such as release of cytokines and proinflammatory chemokines also occur in irradiated sites. Although the skin has an elaborate antioxidant system able to cope with oxidative stress, chronic and excessive exposure to UV rays can exceed the antioxidant capacity of the skin. Thus, the search for photoprotective agents such as those of vegetable origin may provide additional effects that aid the prevention of UV pathological consequences exposure. Evaluation of the sunscreens SPF value is currently carried out in vivo models of human exposure to radiation. This parameter, used by regulatory agencies to define the UVB protection capacity, only evaluates erythema that develops after sun exposure. This model, although internationally accepted, evaluates the early lesions that can induce the skin cancer development. Skin caner is a prevalent disease in our country, which has advanced greatly in recent years due to atmospheric phenomena such as the reduction of the ozone layer with increased population exposure to UVA and UVB. In vitro methodologies have been recommended for replacing or reducing the use of animals to evaluate the efficacy and safety of pharmaceuticals and cosmetics supplies. These methods may, in addition, reduce preparation time, elucidate the compounds activity in known sites of action, allowing to formulate products that interfere directly in the pathophysiological mechanisms under study. Thus, this project aims to assess by in vitro methodologies the photoquimioprotective activity of antioxidant compounds in human cell cultures exposed to UVA and UVB. Photoprotective activity of gallic acid, chlorogenic acid and rosmarinic acid will be benchmarked in order to know the possible mechanisms of action of these compounds in the proposed model and identify the compound that presents the best activity. These three compounds have antioxidant activity and structural similarities to substances with known photoprotective activity. (AU)