Restoration of Vitamin C Synthesis in Transgenic Gulo−/− Mice by Helper-Dependent Adenovirus-Based Expression of Gulonolactone Oxidase
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Inability to synthesize vitamin C, because of a deficiency in gulonolactone oxidase (GULO) expression, is a genetic deficiency shared by a small number of animals including humans. Although the most overt symptom of vitamin C deficiency, scurvy, can be readily corrected by modest consumption of vitamin C, there is increasing interest in the effect of high-level administration in treating human disease. Using a previously derived Gulo-expressing vector, which produces murine GULO under the control of the murine cytomegalovirus (mCMV) promoter, we constructed and validated a recombinant helper-dependent adenovirus (HDAd-mCMV-Gulo) that can be used to correct this genetic defect. A human liver cell line (Hep G2) infected with the HDAd-mCMV-Gulo vector expressed GULO in a time- and gene dose-dependent manner. These cells also produced ascorbic acid when exogenous gulonolactone was supplemented in the medium. Likewise, Gulo(-/-) mice treated with HDAd-mCMV-Gulo at 2 x 10(11) VP expressed GULO in the liver and produced ascorbic acid. Serum ascorbic acid concentrations in Gulo(-/-) mice injected with GULO-expressing HDAd were elevated to levels comparable to those of wild-type mice (62 +/- 15 microM) after 4 days of infection and were maintained at significantly higher levels compared with those in untreated Gulo(-/-) mice for at least 23 days. A similar elevation was observed in urine and tissue ascorbic acid concentrations in vector-treated animals. In conclusion, we demonstrate here that gene therapeutic HDAd-mCMV-Gulo vectors can mediate the expression of GULO and endogenous production of ascorbic acid in human cells and in Gulo(-/-) transgenic mice. Taken together, these data show that a gene therapy approach can be successfully employed in the treatment and further study of vitamin C deficiency in scurvy-prone mammals.
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