Formulation induces direct DNA UV-A photooxidation. Part II. Pro-oxidant effect of formulated Vitamin E via generation of singlet oxygen

The study focuses on the photosensitization of DNA in nanoemulsion-type systems containing Vitamin E under UVA radiation. Cetyltriethylammonium bromide (CTEAB) surfactant was first combined with Vitamin E to form a CTEAB-Vitamin E nanoemulsion to complex the plasmid pBR322, in TRIS/HCl buffer. The self-organization properties of the CTEAB-Vitamin E system were studied by complementary physico-chemical characterizations (tensiometry, pyrene fluorimetry and scattering experiments). It formed a nanoemulsion composed of CTEAB micelles (that can incorporate Vitamin E) as well as larger Vitamin E droplets. This nanoemulsion was then contacted with DNA and the resulting formulated CTEAB-Vitamin E-DNA lipoplex was irradiated under UVA radiation (λ ≥ 335 nm). The presence of Vitamin E generated a significant enhancement of the DNA photodamage as shown by agarose gel electrophoresis and quantified by photodensitometry. It underlines the pro-oxidant role of the Vitamin E in this self-assembled system. A mechanistic study based on the use of specific scavengers reveals that the singlet oxygen is responsible for the UVA DNA photooxidation in the CTEAB-Vitamin E-DNA lipoplex.