Early in atherosclerosis endothelium-dependent relaxation is impaired. The underlying endothelial dysfunction is thought to involve inadequate bioavailability of nitric oxide (NO). Mechanisms that underlie this effect remain uncertain but may include reaction of NO with free radicals and depletion of substrate. Since NO plays a crucial role in atherogenesis, it is important to determine if NO bioavailability can be enhanced. Recent clinical studies suggest that vitamin C (ascorbate) can reverse endothelial dysfunction by enhancing endogenous NO-mediated vasorelaxation. However, the molecular mechanisms underlying this effect are not clearly understood. The current concepts are that ascorbate acts as an antioxidant by either sparing intracellular thiols or by scavenging superoxide radicals produced during an enhanced oxidative stress. Preliminary data presented in this application suggest an alternative hypothesis that encompasses both aforementioned concepts. We propose a unique role for ascorbate in the vasculature based on the finding that, in addition to eliciting vasorelaxation, part of the NO produced from endothelial NO-synthase (eNOS) is stored in the tissue in the form of stable NO adducts. While the existence of such tissue stores of NO has been recognized earlier, its potential physiological and clinical implications have not yet been examined. We have observed that ascorbate relaxes vascular aortic rings in vitro by redox-activating tissue stores to release NO. Our preliminary data suggest that NO is bound in endothelial and smooth muscle cells in the form of S-nitrosothiols, which are cleaved by an increase in intracellular reduced glutathione. The intriguing and novel hypothesis built on these observations is that vitamin C reverses endothelial dysfunction by allowing the release of NO from a preformed vascular pooi. Using a combined biochemical/functional approach, the following three specific aims are proposed to address the above hypothesis: 1. To investigate the mechanism of ascorbate induced vasorelaxation and its relationship to the cellular redox status; 2. To identify the chemical nature and localization of NO stores in the vasculature and determine the factors that govern their stability and bioactivation to yield NO; and 3. To investigate the role of ascorbate in the maintenance of vascular homeostasis using different animal models of endothelial dysfunction. Results from these investigations are expected to significantly enhance our understanding of the role of NOS dependent and -independent NO production in endothelial dysfunction. Moreover, they should provide new insight into the actions of ascorbate beyond those of mere antioxidant nature and a rationale for vitamin C supplementation in disease states associated with an enhanced oxidative stress such as hypertension, hypercholesterolemia, and diabetes.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL069029-02
Application #
6620920
Study Section
Nutrition Study Section (NTN)
Program Officer
Srinivas, Pothur R
Project Start
2002-01-01
Project End
2003-07-31
Budget Start
2003-01-01
Budget End
2003-07-31
Support Year
2
Fiscal Year
2003
Total Cost
$94,250
Indirect Cost
Name
Louisiana State University Hsc Shreveport
Department
Physiology
Type
Schools of Medicine
DUNS #
095439774
City
Shreveport
State
LA
Country
United States
Zip Code
71103
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Garcia-Saura, Maria-Francisca; Saijo, Fumito; Bryan, Nathan S et al. (2012) Nitroso-redox status and vascular function in marginal and severe ascorbate deficiency. Antioxid Redox Signal 17:937-50
Dyson, Alex; Bryan, Nathan S; Fernandez, Bernadette O et al. (2011) An integrated approach to assessing nitroso-redox balance in systemic inflammation. Free Radic Biol Med 51:1137-45
Garcia-Saura, Maria Francisca; Fernandez, Bernadette O; McAllister, Brian P et al. (2010) Dermal nitrite application enhances global nitric oxide availability: new therapeutic potential for immunomodulation? J Invest Dermatol 130:608-11
Saijo, Fumito; Milsom, Alexandra B; Bryan, Nathan S et al. (2010) On the dynamics of nitrite, nitrate and other biomarkers of nitric oxide production in inflammatory bowel disease. Nitric Oxide 22:155-67
Jourd'heuil, Frances L; Lowery, Anthony M; Melton, Elaina M et al. (2010) Redox-sensitivity and site-specificity of S- and N- denitrosation in proteins. PLoS One 5:e14400
Lim, Chee Chew; Bryan, Nathan S; Jain, Mohit et al. (2009) Glutathione peroxidase deficiency exacerbates ischemia-reperfusion injury in male but not female myocardium: insights into antioxidant compensatory mechanisms. Am J Physiol Heart Circ Physiol 297:H2144-53
Perlman, David H; Bauer, Selena M; Ashrafian, Houman et al. (2009) Mechanistic insights into nitrite-induced cardioprotection using an integrated metabolomic/proteomic approach. Circ Res 104:796-804
Feelisch, Martin; Fernandez, Bernadette O; Bryan, Nathan S et al. (2008) Tissue processing of nitrite in hypoxia: an intricate interplay of nitric oxide-generating and -scavenging systems. J Biol Chem 283:33927-34
Erzurum, S C; Ghosh, S; Janocha, A J et al. (2007) Higher blood flow and circulating NO products offset high-altitude hypoxia among Tibetans. Proc Natl Acad Sci U S A 104:17593-8

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