Antioxidant protection against hypochlorous acid in human plasma.
Hypochlorous acid (HOCI) is a powerful oxidizing and chlorinating agent produced by the neutrophil enzyme myeloperoxidase. The antioxidant defenses of freshly prepared human plasma against HOCI/OCI- were explored. Addition of HOCI/OCI- to plasma caused rapid oxidation of ascorbic acid and thiol (-SH) groups but not of uric acid. Plasma -SH groups (which are known to be largely located on albumin) were quantitatively the most important scavenger of HOCI/OCI-, but adding extra ascorbate to plasma caused this molecule to have a more important scavenging role against HOCI/OCI-. Added HOCI/OCI- produced no detectable lipid peroxidation in plasma or depletion of lipid-soluble antioxidants (alpha-tocopherol or ubiquinol-10). No evidence of oxidative damage to protein amino acid residues (other than -SH) was detected by the carbonyl assay. It seems that -SH groups are a major target of attack by HOCI/OCI- in vivo, and plasma albumin may be an important protective antioxidant. Ascorbic acid might also play a protective role, especially in individuals supplemented with this vitamin. Ascorbate might also be important in extracellular fluids with low albumin concentrations such as synovial, respiratory tract lining, and cerebrospinal fluids.
Department of Pulmonary-Critical Care Medicine, University of California-Davis Medical Center, Sacramento 95817.
M L
ML
Hu
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S
Louie
C E
CE
Cross
P
P
Motchnik
B
B
Halliwell
D000975:Antioxidants / Q000737:chemistry; D001205:Ascorbic Acid / Q000737:chemistry; D006801:Humans; D006997:Hypochlorous Acid / Q000037:antagonists & inhibitors* / Q000737:chemistry; D066298:In Vitro Techniques; D010084:Oxidation-Reduction; D012710:Serum Albumin, Bovine / Q000737:chemistry
D000975:Antioxidants; D012710:Serum Albumin, Bovine; D006997:Hypochlorous Acid; D001205:Ascorbic Acid