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Ascorbic acid in nasal and tracheobronchial airway lining fluids
Bettina C Schock1, John Koostra, Sunye Kwack
1Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, and Center for Comparative Lung Biology and Medicine, School of Medicine, University of California, Davis, CA 95817, USA.
Free Radical Biology & Medicine
|September 30, 2004
Summary
Oral ascorbic acid (AA) supplementation increases antioxidant levels in nasal fluids but not in lower airways. Oxidative systems in saliva and sputum rapidly deplete AA, limiting its role in the lower respiratory tract.
Area of Science:
- Respiratory Medicine
- Biochemistry
- Antioxidant Research
Background:
- Ascorbic acid (AA) is a crucial antioxidant in the respiratory tract.
- The regulation of AA levels in respiratory tract lining fluids (RTLFs) is not fully understood.
Purpose of the Study:
- To determine if oral AA supplementation can increase AA concentrations in RTLFs.
- To investigate the stability and fate of AA in respiratory fluids.
Main Methods:
- Healthy subjects ingested 2g of AA.
- Plasma, nasal lavage fluids (NLFs), induced sputum (IS), and saliva were analyzed for AA before and 2 hours after ingestion.
- AA stability was assessed in fresh saliva and IS samples with and without inhibitors.
Main Results:
- Plasma and NLF AA levels significantly increased post-supplementation (2-fold and 3-fold, respectively).
- IS and saliva AA levels showed no significant increase after oral AA intake.
- AA was rapidly depleted in saliva and IS, a process inhibited by sodium azide or dithiothreitol, suggesting consumption by oxidants.
Conclusions:
- Oral AA supplementation effectively increases AA in nasal fluids but not in the lower airways (tracheobronchial lining fluid).
- Oxidant systems in saliva and sputum rapidly degrade AA, potentially limiting its antioxidant function in these compartments.
- AA's antioxidant role may be less significant in the lower respiratory tract compared to other extracellular compartments.