The experiments in this thesis tested <i>in vitro</i> and <i>in vivo</i> the proposal that zinc-deficient superoxide dismutase, resulting from mutations or oxidative damage to the enzyme, gains ascorbate oxidase activity that contributes to the pathology of amyotrophic lateral sclerosis (ALS). They also tested whether flavonoids can help protect against this activity.<p>The <i>in vitro</i> experiments showed that zinc-extracted Cu/Zn-SOD (Cu-SOD) as well as SOD treated with H2O2 or H2O2 plus ascorbate accelerated ascorbate oxidation 100 to 300 %, while native SOD had no effect. With Cu-SOD, the activity was unaffected by EDTA, EGTA, or catalase, showing that the catalytic copper was firmly bound and that the H2O2 product of SOD activity was not responsible. Catechin and uric acid slowed ascorbate oxidation by Cu-SOD by 72% and 67%, respectively.<p>The <i>in vivo</i> study investigated tissue levels of ascorbate and biomarkers of oxidative stress in a transgenic mice bearing a mutation in Cu/Zn-SOD as a model of familial ALS (FALS mice), and the effects of dietary ascorbate and quercetin. In FALS mice on control modified AIN93G diet for 10 weeks compared to the wild-type, liver thiobarbituric acid reactive substances (TBARS) were 47% higher and liver oxidized vitamin C was 2800% higher. These results support, in liver, that mutant SOD acquired ascorbate oxidase activity and increased oxidative stress. The only difference in other tissues was a 136% increase in GSH/GSSG ratio in thigh muscle of FALS mice.<p>In dietary treatments of FALS mice, spinal cord TBARS was 93 % higher with ascorbate-supplemented diet compared to control diet, suggesting that dietary ascorbate increased oxidative stress. Also in spinal cord, oxidized-vitamin C was 250% higher in ascorbate + quercetin-fed FALS mice, which suggests there is no protection by quercetin against ascorbate oxidation. In brain, protein thiols were 56% and 58% lower in quercetin-fed and ascorbate + quercetin-fed FALS mice, suggesting that quercetin worsened oxidative damage. In liver, quercetin feeding produced a 40% decrease in vitamin C, total vitamin C and oxidized-vitamin C, perhaps by down-regulating ascorbate biosynthesis.
Overall the results support a gain of ascorbate oxidase activity of mutant SOD in ALS, but do not support protection by dietary treatment with ascorbate or quercetin.
| Identifer | oai:union.ndltd.org:USASK/oai:usask.ca:etd-10312007-235840 |
| Date | 03 December 2007 |
| Creators | ElRody, Nehad Mohammed |
| Contributors | Bandy, Brian |
| Publisher | University of Saskatchewan |
| Source Sets | University of Saskatchewan Library |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://library.usask.ca/theses/available/etd-10312007-235840/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Saskatchewan or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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