The dark side of melanin exposed: Sun worshippers may have more to worry about than the DNA damage that occurs while they're relaxing on the beach. It seems that the DNA photoproducts responsible for cancer-causing mutations in skin cells continue to be generated for hours after sunlight exposure. Premi et al. find that a key mediator of this delayed damage is melanin, a pigment thought to protect against cancer (see the Perspective by Taylor). They propose a “chemiexcitation” model in which reactive oxygen and nitrogen species induced by ultraviolet light excite an electron in melanin fragments. This energy is then transferred to DNA, inducing the same damage as ultraviolet light, but in the dark. Conceivably, this energy could be dissipated by adding quenchers to sunscreens. Science , this issue p. 842 ; see also p. 824

To spin trap hydroxyl radical (HO*) with in vivo detection of the resultant radical adducts, the use of two spin traps, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) (10 mmol/kg) has been compared. In mice treatment with 5-aminolevulinic acid and Fe3+ resulted in detection of adducts of hydroxyl radicals (HO*), but only with use of DEPMPO. Similarly, 'HO* adducts' generated via nucleophilic substitution of SO4*- adducts formed in vivo could be observed only when using DEPMPO as the spin trap. The reasons for the differences observed between DEPMPO and DMPO are likely due to different in vivo lifetimes of their hydroxyl radical adducts. These results seem to be the first direct in vivo EPR detection of hydroxyl radical adducts.

Polymeric nanoparticles (PLGA) have been developed for the encapsulation and controlled release of quercetin and catechin. Nanoparticles were fabricated using a solvent displacement method. Physicochemical properties were measured by light scattering, scanning electron microscopy and ζ‐potential, X‐ray diffraction, infrared spectroscopy and differential scanning calorimetry. Encapsulation efficiency and in vitro release profiles were obtained from differential pulse voltammetry experiments. Antioxidant properties of free and encapsulated flavonoids were determined by TBARS, fluorescence spectroscopy and standard chelating activity methods. Relatively small (d≈ 400 nm) polymeric nanoparticles were obtained containing quercetin or catechin in a non‐crystalline form (EE ≈ 79%) and the main interactions between the polymer and each flavonoid were found to consist of hydrogen bonds. In vitro release profiles were pH‐dependant, the more acidic pH, the faster release of each flavonoid from the polymeric nanoparticles. The inhibition of the action of free radicals and chelating properties, were also enhanced when quercetin and catechin were encapsulated within PLGA nanoparticles. The information obtained from this study will facilitate the design and fabrication of polymeric nanoparticles as possible oral delivery systems for encapsulation, protection and controlled release of flavonoids aimed to prevent oxidative stress in human body or food products.