alexa The protective effect of ascorbic acid in retinal light damage of rats exposed to intermittent light.


Vitamins & Minerals

Author(s): Organisciak DT, Jiang YL, Wang HM, Bicknell I

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Abstract Retinal light damage in dark-reared rats supplemented with ascorbic acid and exposed to multiple doses of intermittent light was studied and compared with damage in unsupplemented dark-reared and cyclic-light-reared rats. The extent of photoreceptor cell loss from intense light exposure was determined by whole-eye rhodopsin levels and retinal DNA measurements two weeks after light treatment. Two weeks after 3 or 8 hr of intermittent light, ascorbate-supplemented animals had rhodopsin and retinal DNA levels that were two to three times higher than in unsupplemented dark-reared rats. In both types of rats rhodopsin levels were influenced by the number of light doses, the duration of light exposure, and to a lesser extent, by the length of the dark period between exposures. Rhodopsin levels in the dark-reared ascorbate-supplemented rats were significantly higher than in unsupplemented dark-reared rats, and were similar to the levels in unsupplemented cyclic-light-reared animals. Ascorbate treatment had no effect on the rate of rhodopsin bleaching. However, regeneration was greater in supplemented rats after multiple 1-hr light exposures. Intermittent light also resulted in lower ascorbate levels in the retinas of supplemented and unsupplemented rats, with dramatic losses from the retinal pigment epithelium (RPE)-choroid in both types of animals. We conclude that ascorbic acid protects the eye by reducing the irreversible Type I form of light damage in dark-reared rats. Ascorbate appears to shift light damage to the Type II form typical of cyclic-light-reared animals.
This article was published in Invest Ophthalmol Vis Sci and referenced in Vitamins & Minerals

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  • Yosef Yarden
    Classically, the 3’untranslated region (3’UTR) is that region in eukaryotic protein-coding genes from the translation termination codon to the polyA signal. It is transcribed as an integral part of the mRNA encoded by the gene. However, there exists another kind of RNA, which consists of the 3’UTR alone, without all other elements in mRNA such as 5’UTR and coding region. The importance of independent 3’UTR RNA (referred as I3’UTR) was prompted by results of artificially introducing such RNA species into malignant mammalian cells. Since 1991, we found that the middle part of the 3’UTR of the human nuclear factor for interleukin-6 (NF-IL6) or C/EBP gene exerted tumor suppression effect in vivo. Our subsequent studies showed that transfection of C/EBP 3’UTR led to down-regulation of several genes favorable for malignancy and to up-regulation of some genes favorable for phenotypic reversion. Also, it was shown that the sequences near the termini of the C/EBP 3’UTR were important for its tumor suppression activity. Then, the C/EBP 3’UTR was found to directly inhibit the phosphorylation activity of protein kinase CPKC in SMMC-7721, a hepatocarcinoma cell line. Recently, an AU-rich region in the C/EBP 3’UTR was found also to be responsible for its tumor suppression. Recently we have also found evidence that the independent C/EBP 3’UTR RNA is actually exists in human tissues, such as fetal liver and heart, pregnant uterus, senescent fibroblasts etc. Through 1990’s to 2000’s, world scientists found several 3’UTR RNAs that functioned as artificial independent RNAs in cancer cells and resulted in tumor suppression. Interestingly, majority of genes for these RNAs have promoter-like structures in their 3’UTR regions, although the existence of their transcribed products as independent 3’UTR RNAs is still to be confirmed. Our studies indicate that the independent 3’UTR RNA is a novel non-coding RNA species whose function should be the regulation not of the expression of their original mRNA, but of some essential life activities of the cell as a whole.
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