FASEB Journal 2007-07-01

5-Methyltetrahydrofolate inhibits photosensitization reactions and strand breaks in DNA.

Tal Offer, Bruce N Ames, Steven W Bailey, Elizabeth A Sabens, Mamoru Nozawa, June E Ayling

Index: FASEB J. 21 , 2101-2107, (2007)

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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.