VITAMINS

Direct attack to genomic DNA by reactive oxygen species causes various types of lesions. The most significant lesion is considered to be an unrepaired double-strand break that can lead to fatal cell damage. Using fluorescence microscopy, we directly observed double-strand breaks of DNA in reconstituted chromatin stained by a fluorescent cyanine dye, YOYO, in solution. YOYO is known to have the ability to photo-cleave DNAs by generating reactive oxygen species. We also investigated the effect of an antioxidant vitamin, vitamin C, on preventing double-strand breaks in a quantitative manner. We showed that doublestrand breaks can be monitored at the level of individual DNA molecules, and that the kinetics of the breakage reaction can be deduced from such single-molecule observation. We found that DNA is protected against double-strand breaks by the addition of vitamin C.

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Senescence Marker Protein-30 (SMP30) was originally identified as a novel protein in the rat liver, the expression of which decreases androgen-independently with aging. To examine the physiological function of SMP30, we established SMP30 knockout mice and found that they were viable and fertile although lower in body weight and shorter in life span than the wild type when fed autoclaved mouse chow. The mean survival time of these SMP30 knockout mice was approximately 6 months. On the other hand, wild type mice was approximately 24 months. Although phenotypical analysis during the survival interval of SMP30 knockout mice uncovered no obvious abnormalities, immediate postmortem examination revealed atrophy in almost all their abdominal organs. Recently, we identified SMP30 as the lactone-hydrolyzing enzyme gluconolactonases (GNL) of animal species. GNL was a key enzyme which involve in vitamin C biosynthesis, and the essential role of SMP30 in this synthetic process was verified by a nutritional study. These knockout mice fed a vitamin C-deficient diet did not thrive; i.e., they displayed symptoms of scurvy such as bone fracture and rachitic rosary, then died by 136 days after the start of receiving the deficient diet. Thus SMP30 knockout mice developed symptoms of scurvy when fed a vitamin C-deficient diet, verifying the pivotal role of SMP30 in vitamin C biosynthesis. As mentioned above, these mice were shorter in life span than the wild type when fed autoclaved mouse chow contained 〜55mg/kg of vitamin C, which we now know contains too little vitamin C to maintain normal levels of vitamin C in tissues. However, never before did we observe scurvy symptoms in the knockout mice when fed autoclaved mouse chow. Collectively, these results demonstrate that vitamin C deficiency accelerates aging.

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