STUDIO DEI MECCANISMI DI DANNO DA RAGGI UVA E UVB E DEGLI EFFETTI PROTETTIVI DA PARTE DI COMPOSTI POLIFENOLICI IN SISTEMI CELLULARI E MODELLI EX VIVO DI CUTE UMANA
Tesi di Dottorato
Data di Pubblicazione:
2014
Citazione:
STUDIO DEI MECCANISMI DI DANNO DA RAGGI UVA E UVB E DEGLI EFFETTI PROTETTIVI DA PARTE DI COMPOSTI POLIFENOLICI IN SISTEMI CELLULARI E MODELLI EX VIVO DI CUTE UMANA / R. Calo' ; tutor: L. Marabini ; coordinatore: A. Panerai. Università degli Studi di Milano, 2014 Dec 15. 27. ciclo, Anno Accademico 2014. [10.13130/calo-rossella_phd2014-12-15].
Abstract:
Sun radiation consists of several spectrum regions, depending on the wavelengths, such as ultraviolet, visible and infrared portions. The ultraviolet rays (UV) are associated with both positive and negative effects on humans’ health. Ultraviolet light is used in the process of disinfection, it shows immunoregolatory activity and it stimulates vitamin D and serotonin production. It is well known that artificial sources of UVR are employed in the health field for sterilization procedures and for therapeutical purposes, such as treatment of dermatological pathologies like psoriasis, vitiligo and icterus neonatorum, as well as for aesthetic purposes (sunbed). In the last decade, besides these positive effects, UV side effects on skin have been demonstrated by different studies which correlated the intense and prolonged exposure to UV light with skin cancer development.
Based on wavelength, UV spectrum can be divided into three segments: UVA (320-400 nm), UVB (280-320 nm) and UVC (100-280 nm). Radiation in the UVC range, considered to be the most cytotoxic and harmful, is largely absorbed by the stratospheric ozone layer, so UV regions mainly involved in photocancerogenesis development are considered to be ultraviolet radiation A (UVA) and ultraviolet radiation B (UVB). The amount and the UVA/UVB ratio that reach the Earth’s surface is influenced by a lot of environmental factors as latitude, seasons, weather/atmospheric conditions and the time of day.
UVA is by far the most abundant solar UV radiation that reaches the Earth (about 90-95% of total UV radiation), penetrates the human epidermis down to the proliferative basal cells and even further to the derma and mediate biological events generating reactive oxygen species (ROS) in cells. ROS oxide other cellular constituents, particularly carbohydrates, lipids, proteins and DNA. Interactions between ROS and DNA induce formation of single strand breaks (SSBs), DNA-proteins crosslink and oxidized bases. The most abundant oxidized base is the guanine that produces the 8-oxoguanine, considered as promoter of carcinogenesis.
UVB represents only 5% of total UV radiation that reaches the Earth. Besides it acts mainly at the epidermis basal layer of the skin, it is considered extremely damaging because of its high energy. UVB photons are directly absorbed by DNA and cause the formation of cyclobutane pyrimide dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts (6-4PPs), which in turn can lead to apoptotic events or carcinogenesis development. Also tryptophan and tyrosine are modified by UVB inducing the alteration of structure and function of proteins. Moreover, UVB is able to produce reactive oxygen species (ROS) and reactive nitric species (RNS).
Cells have developed defense mechanisms and endogenous repair systems in order to reduce genotoxic damage UV-induced: complexes of antioxidant enzymes which take advantage of the presence of a metal to inactivate reactive oxygen species, and DNA repair systems like the base excision repair system (BER), used for oxidized bases, and the nucleotide excision repair (NER), used to repair photolesions like CPD and 6-4 PP. Recently, several molecules have been studied for their ability to give a contribution to these antioxidant defenses. For these reasons, there is a considerable interest in the concept of the use of phytochemicals and micronutrients present in the diet such as carotenoids, vitamin E and C, and polyphenols. This last group of compounds are well known for their several biological properties, such as their antioxidant activity, their ability to enhance the activity of DNA repair systems and also their skills in inflammatory and apoptotic events modulations.
Several epidemiological studies have demonstrated their biologi
Tipologia IRIS:
Tesi di dottorato
Keywords:
cheratinociti; radiazioni ultraviolette; Vaccinium Myrtillus; Timolo; Thymus Vulgaris L.; biopsie cute umana
Elenco autori:
R. Calo'
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