title: Redox-mediated mechanisms and biological responses of copper-catalyzed reduction of the nitrite ion in vitro.
abstract: During ischemia nitrite may be converted into nitric oxide (NO) by reaction with heme-carrying proteins or thiol-containing enzymes. NO acts as a regulator of vasodilation and protector against oxidative stress-induced tissue injuries. As a result of ischemia-induced oxidative stress, hypoxia and/or acidosis bivalent copper ions (Cu(2+)) can dissociate from their physiological carrier proteins. Reduced by the body's own antioxidants, the resultant Cu(1+) might represent an effective reductant of nitrite. Here we have evaluated in vitro copper-dissociation from copper/BSA (bovine serum albumin) complexes under ischemic conditions. Furthermore, using physiological concentrations, we have characterized the capacity of antioxidants and bivalent copper ions to serve as Cu(1+)-agitated catalytic sites for nitrite reduction and also the biological responses of this mechanism in vitro. We found that as a consequence of an acidic milieu and/or oxidative stress the copper-binding capacity of serum albumin strongly declined, leading to significant dissociation of copper ions into the ambient solution. At physiologically relevant pH-values Cu(2+) ions in combination with physiologically available copper reductants (i.e., ascorbate, glutathione, Fe(2+)) significantly enhanced nitrite reduction and subsequent non-enzymatic NO generation under hypoxic but also normoxic conditions. Our data demonstrate for the first time that upon ischemic conditions carrier protein-dissociated copper ions combined with appropriate reductants may serve as Cu(1+)-driven catalytic sites for nitrite reduction, leading to the formation of biologically relevant NO formation. Thus, in addition to the action of heme proteins, copper-catalyzed non-enzymatic NO formation from nitrite might represent a further physiologically relevant vasodilating and NO-dependent protective principle to ischemic stress.
authors.affiliation: Department of Plastic and Reconstructive Surgery, Hand Surgery, and Burn Center, Medical Faculty, RWTH Aachen University, Pauwelsstr. 30, D-52057 Aachen, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Opländer
authors.forename: Julian
authors.initials: J
authors.lastname: Rösner
authors.forename: Alexander
authors.initials: A
authors.lastname: Gombert
authors.forename: Alexander
authors.initials: A
authors.lastname: Brodski
authors.forename: Tatsiana
authors.initials: T
authors.lastname: Suvorava
authors.forename: Vera
authors.initials: V
authors.lastname: Grotheer
authors.forename: Ernst E
authors.initials: EE
authors.lastname: van Faassen
authors.forename: Klaus-Dietrich
authors.initials: KD
authors.lastname: Kröncke
authors.forename: Georg
authors.initials: G
authors.lastname: Kojda
authors.forename: Joachim
authors.initials: J
authors.lastname: Windolf
authors.forename: Christoph V
authors.initials: CV
authors.lastname: Suschek
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000737:chemistry; D001011:Aorta / Q000737:chemistry / Q000378:metabolism; D001205:Ascorbic Acid; D002417:Cattle; D002460:Cell Line; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009569:Nitric Oxide / Q000737:chemistry / Q000378:metabolism; D009573:Nitrites / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology; D010100:Oxygen / Q000032:analysis; D051381:Rats; D012710:Serum Albumin, Bovine / Q000737:chemistry / Q000378:metabolism; D013552:Swine
chemical_list: D000975:Antioxidants; D009573:Nitrites; D012710:Serum Albumin, Bovine; D009569:Nitric Oxide; D003300:Copper; D001205:Ascorbic Acid; D010100:Oxygen
keywords: Antioxidants; Copper; Nitric oxide; Nitrite; Reduction