title: 5-Methyltetrahydrofolate inhibits photosensitization reactions and strand breaks in DNA.
abstract: The known functions of folate are to support one-carbon metabolism and to serve as photoreceptors for cryptochromes and photolyases. We demonstrate that 5-methyltetrahydrofolate (5-MTHF, the predominant folate in plasma) is also a potent, near diffusion limited, scavenger of singlet oxygen and quencher of excited photosensitizers. Both pathways result in decomposition of 5-MTHF, although ascorbate can protect against this loss. In the absence of photosensitizers, 5-MTHF is directly decomposed only very slowly by UVA or UVB. Although synthetic folic acid can promote DNA damage by UVA, submicromolar 5-MTHF inhibits photosensitization-induced strand breaks. These observations suggest a new role for reduced folate in protection from ultraviolet damage and have bearing on the hypothesis that folate photodegradation influenced the evolution of human skin color.
authors.affiliation: Nutrition and Metabolism Center, CHORI, Oakland, California, USA.
authors.forename: Tal
authors.initials: T
authors.lastname: Offer
authors.forename: Bruce N
authors.initials: BN
authors.lastname: Ames
authors.forename: Steven W
authors.initials: SW
authors.lastname: Bailey
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Sabens
authors.forename: Mamoru
authors.initials: M
authors.lastname: Nozawa
authors.forename: June E
authors.initials: JE
authors.lastname: Ayling
mesh_terms: D001205:Ascorbic Acid / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D053960:DNA Breaks; D004249:DNA Damage / Q000187:drug effects*; D004278:DNA, Superhelical / Q000187:drug effects / Q000528:radiation effects; D003864:Depression, Chemical; D005492:Folic Acid / Q000138:chemical synthesis / Q000494:pharmacology / Q000502:physiology*; D016166:Free Radical Scavengers / Q000494:pharmacology*; D010084:Oxidation-Reduction; D004369:Pentetic Acid / Q000494:pharmacology; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D011621:Pteridines / Q000037:antagonists & inhibitors / Q000494:pharmacology; D012395:Rose Bengal / Q000494:pharmacology / Q000528:radiation effects; D026082:Singlet Oxygen / Q000378:metabolism; D019810:Sodium Azide / Q000494:pharmacology; D013482:Superoxide Dismutase / Q000378:metabolism; D013763:Tetrahydrofolates / Q000494:pharmacology*; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D004278:DNA, Superhelical; D016166:Free Radical Scavengers; D017319:Photosensitizing Agents; D011621:Pteridines; D013763:Tetrahydrofolates; C405202:pterine-6-carboxylic acid; D026082:Singlet Oxygen; D012395:Rose Bengal; D004369:Pentetic Acid; D005492:Folic Acid; D019810:Sodium Azide; D013482:Superoxide Dismutase; D001205:Ascorbic Acid; C005984:5-methyltetrahydrofolate