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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/02/28 21:04:14」(JST)

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Photoprotection is a group of mechanisms that nature has developed to minimize the damage that the human body suffers when exposed to UV radiation. This damage mostly occurs in the skin, but the rest of the body can be affected by the oxidative stress caused by UV light.

Photoprotection of the human skin is achieved by extremely efficient internal conversion of DNA, proteins and melanin. Internal conversion is a photochemical process that converts the energy of the UV photon into small, harmless amounts of heat. If the energy of the UV photon were not transformed into heat, then it would lead to the generation of free radicals or other harmful reactive chemical species (e.g. singlet oxygen, or hydroxyl radical).

In DNA this photoprotective mechanism evolved four billion years ago at the dawn of life.^[1] The purpose of this extremely efficient photoprotective mechanism is to prevent direct DNA damage and indirect DNA damage. The ultrafast internal conversion of DNA reduces the excited state lifetime of DNA to only a few femtoseconds (10⁻¹⁵s)—this way the excited DNA does not have enough time to react with other molecules.

For melanin this mechanism has developed later in the course of evolution. Melanin is such an efficient photoprotective substance that it dissipates more than 99.9% of the absorbed UV radiation as heat. ^[2] This means that less than 0.1% of the excited melanin molecules will undergo harmful chemical reactions or produce free radicals.

Artificial melanin

The cosmetic industry claims that the UV filter acts as an "artificial melanin". But those artificial substances used in sunscreens do not efficiently dissipate the energy of the UV photon as heat. Instead these substances have a very long excited state lifetime. ^[3]
In fact, the substances used in sunscreens are often used as photosensitizers in chemical reactions. (see Benzophenone).

This discrepancy between melanin and sunscreen ingredients is one of the reasons for the increased melanoma risk that can be found in sunscreen users compared to non-users. (see sunscreen) Oxybenzone, titanium oxide and octyl methoxycinnamate are photoprotective agents used in many sunscreens, providing broad-spectrum UV coverage, including UVB and short-wave UVA rays.^[4]^[5]

UV-absorber	other names	percentage of molecules that dissipate the photon energy (quantum yield: Φ ) ^[3]	molecules not dissipating the energy quickly
DNA		> 99.9%	< 0.1%
natural melanin		> 99.9%	< 0.1%
2-phenylbenzimidazole-5-sulfonic acid	PBSA, Eusolex 232, Parsol HS,
2-ethylhexyl 4-dimethylaminobenzoate	Padimate-O, oxtyldimethyl PABA, OD-PABA	0.1 = 10%	90%
4-Methylbenzylidene camphor	(4-MBC), (MBC), Parsol 5000, Eusolex 6300	0.3 = 30%	70%
4-tert-butyl-4-methoxydibenzoyl-methane	(BM-DBM), Avobenzone, Parsol 1789, Eusolex 9020
Menthyl Anthranilate	(MA), Menthyl-2-aminobenzoate, meradimate	0.6 = 60%	40%
Ethylhexyl methoxycinnamate	(2-EHMC), (EHMC), EMC, Octyl methoxycinnamate, OMC, Eusolex 2292, Parsol	0.81 = 81%	19%

References

^ "ultrafast internal conversion of DNA". Retrieved 2008-02-13.
^ Meredith, Paul; Riesz, Jennifer (2004). "Radiative Relaxation Quantum Yields for Synthetic Eumelanin". Photochemistry and photobiology 79 (2): 211–216. doi:10.1111/j.1751-1097.2004.tb00012.x. ISSN 0031-8655. PMID 15068035.
^ ^a ^b Cantrell, Ann; McGarvey, David J; (2001). "3(Sun Protection in Man)". Comprehensive Series in Photosciences 495: 497–519. CAN 137:43484.
^ Burnett, M. E. and Wang, S. Q. (2011), Current sunscreen controversies: a critical review. Photodermatology, Photoimmunology & Photomedicine, 27: 58–67
^ Serpone N, Salinaro A, Emeline AV, Horikoshi S, Hidaka H, Zhao JC. 2002. An in vitro systematic spectroscopic examination of the photostabilities of a random set of commercial sunscreen lotions and their chemical UVB/UVA active agents. Photochemical & Photobiological Sciences 1(12): 970-981.

UpToDate Contents

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English Journal

Photoprotective effects of cranberry juice and its various fractions against blue light-induced impairment in human retinal pigment epithelial cells.

Chang CH1, Chiu HF2, Han YC3, Chen IH3, Shen YC4, Venkatakrishnan K3, Wang CK3.
Pharmaceutical biology.Pharm Biol.2017 Dec;55(1):571-580.
CONTEXT: Cranberry has numerous biological activities, including antioxidation, anticancer, cardioprotection, as well as treatment of urinary tract infection (UTI), attributed to abundant phenolic contents.OBJECTIVE: The current study focused on the effect of cranberry juice (CJ) on blue light expos
PMID 27937080

Ultrasound-assisted extraction of bioactive compounds from palm pressed fiber with high antioxidant and photoprotective activities.

Dal Prá V1, Lunelli FC2, Vendruscolo RG3, Martins R2, Wagner R3, Lazzaretti AP Jr1, Freire DM4, Alexandri M5, Koutinas A5, Mazutti MA6, da Rosa MB7.
Ultrasonics sonochemistry.Ultrason Sonochem.2017 May;36:362-366. doi: 10.1016/j.ultsonch.2016.12.021. Epub 2016 Dec 18.
This work is focused on the optimization of the ultrasound-assisted extraction of antioxidant compounds with photoprotective effect from palm pressed fiber. The influence of ultrasound intensity and pulse cycle was investigated by means of a central composite rotational design. The optimized conditi
PMID 28069222

Carotenoid:β-cyclodextrin stability is independent of pigment structure.

Fernández-García E1, Pérez-Gálvez A2.
Food chemistry.Food Chem.2017 Apr 15;221:1317-1321. doi: 10.1016/j.foodchem.2016.11.024. Epub 2016 Nov 5.
Carotenoids refer to a wide class of lipophilic pigments synthesized by plants, exert photoprotective and antioxidant properties that are lost upon carotenoid degradation. Their inclusion into hydrophilic host-molecules could improve their stability. Cyclodextrins, provide a hydrophobic cavity in th
PMID 27979095

Japanese Journal

Fluorescent protein content and stress tolerance of two color morphs of the coral Galaxea fascicularis

NAKAEMA Sho,HIDAKA Michio
Galaxea, Journal of Coral Reef Studies 17(1), 1-11, 2015
… Fluorescent proteins in corals have been re-ported to have photoprotective function for algal sym-bionts, though it remains controversial whether the coral fluorescent proteins are actually photoprotective. …
NAID 130005087650

Regulation of xanthophyll cycle pool size in response to high light irradiance in Arabidopsis

Kawabata Yuiko,Takeda Satomi
Plant Biotechnology 31(3), 229-240, 2014
… The xanthophyll cycle is known to play a key photoprotective role in plants. …
NAID 130004677758

Photoprotective effect of Undaria crenata against ultraviolet B-induced damage to keratinocytes(MISCELLANEOUS)

Hyun Yu Jae,Piao Mei Jing,Ko Mi Hee [他],Lee Nam Ho,Kang Hee Kyoung,Yoo Eun Sook,Koh Young Sang,Hyun Jin Won
Journal of bioscience and bioengineering 116(2), 256-264, 2013-08
… The aim of this study was to investigate the photoprotective properties of an U. …
NAID 110009657212

「光防護」

　　[★]

英: photoprotection、photoprotective

[DNA_IC-1] "ultrafast internal conversion of DNA". Retrieved 2008-02-13.

[Meredith-2] Meredith, Paul; Riesz, Jennifer (2004). "Radiative Relaxation Quantum Yields for Synthetic Eumelanin". Photochemistry and photobiology 79 (2): 211–216. doi:10.1111/j.1751-1097.2004.tb00012.x. ISSN 0031-8655. PMID 15068035.

[Cantrell-3] Cantrell, Ann; McGarvey, David J; (2001). "3(Sun Protection in Man)". Comprehensive Series in Photosciences 495: 497–519. CAN 137:43484.

[4] Burnett, M. E. and Wang, S. Q. (2011), Current sunscreen controversies: a critical review. Photodermatology, Photoimmunology & Photomedicine, 27: 58–67

[5] Serpone N, Salinaro A, Emeline AV, Horikoshi S, Hidaka H, Zhao JC. 2002. An in vitro systematic spectroscopic examination of the photostabilities of a random set of commercial sunscreen lotions and their chemical UVB/UVA active agents. Photochemical & Photobiological Sciences 1(12): 970-981.

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photoprotective