Ascorbate recycling in human neutrophils: induction by bacteria.
Ascorbate (vitamin C) recycling occurs when extracellular ascorbate is oxidized, transported as dehydroascorbic acid, and reduced intracellularly to ascorbate. We investigated microorganism induction of ascorbate recycling in human neutrophils and in microorganisms themselves. Ascorbate recycling was determined by measuring intracellular ascorbate accumulation. Ascorbate recycling in neutrophils was induced by both Gram-positive and Gram-negative pathogenic bacteria, and the fungal pathogen Candida albicans. Induction of recycling resulted in as high as a 30-fold increase in intracellular ascorbate compared with neutrophils not exposed to microorganisms. Recycling occurred at physiologic concentrations of extracellular ascorbate within 20 min, occurred over a 100-fold range of effector/target ratios, and depended on oxidation of extracellular ascorbate to dehydroascorbic acid. Ascorbate recycling did not occur in bacteria nor in C. albicans. Ascorbate did not enter microorganisms, and dehydroascorbic acid entry was less than could be accounted for by diffusion. Because microorganism lysates reduced dehydroascorbic acid to ascorbate, ascorbate recycling was absent because of negligible entry of the substrate dehydroascorbic acid. Because ascorbate recycling occurs in human neutrophils but not in microorganisms, it may represent a eukaryotic defense mechanism against oxidants with possible clinical implications.
Wang
Y
Y
Molecular and Clinical Nutrition Section, Building 10, Room 4D52, MSC 1372, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda MD 20892-1372, USA.
Russo
T A
TA
Kwon
O
O
Chanock
S
S
Rumsey
S C
SC
Levine
M
M
D001205:Ascorbic Acid / Q000008:administration & dosage / Q000378:metabolism*; D001419:Bacteria / Q000378:metabolism / Q000472:pathogenicity*; D001693:Biological Transport, Active; D002176:Candida albicans / Q000472:pathogenicity; D004926:Escherichia coli / Q000378:metabolism / Q000472:pathogenicity; D006090:Gram-Negative Bacteria / Q000472:pathogenicity; D006094:Gram-Positive Bacteria / Q000472:pathogenicity; D006801:Humans; D066298:In Vitro Techniques; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism* / Q000382:microbiology*; D010084:Oxidation-Reduction
D001205:Ascorbic Acid