Effect of chelating agents and superoxide on human neutrophil NAD(P)H oxidation

Zinc accelerates respiratory burst termination in human PMN

The respiratory burst of phagocytes is essential for human survival. Innate immune defence against pathogens relies strongly on reactive oxygen species (ROS) production by the NADPH oxidase (NOX2). ROS kill pathogens while the translocation of electrons across the plasma membrane via NOX2 depolarizes the cell. Simultaneously, protons are released into the cytosol. Here, we compare freshly isolated human polymorphonuclear leukocytes (PMN) to the granulocytes-like cell line PLB 985. We are recording ROS production while inhibiting the charge compensating and pH regulating voltage-gated proton channel (H_V1). The data suggests that human PMN and the PLB 985 generate ROS via a general mechanism, consistent of NOX2 and H_V1. Additionally, we advanced a mathematical model based on the biophysical properties of NOX2 and H_V1. Our results strongly suggest the essential interconnection of H_V1 and NOX2 during the respiratory burst of phagocytes. Zinc chelation during the time course of the experiments postulates that zinc leads to an irreversible termination of the respiratory burst over time. Flow cytometry shows cell death triggered by high zinc concentrations and PMA. Our data might help to elucidate the complex interaction of proteins during the respiratory burst and contribute to decipher its termination.

Mechanism of dacron-activated monocytic cell oxidation of low density lipoprotein

PURPOSE

Oxidized lipids are believed to contribute to atherogenesis and may play a role in the development of anastomotic intimal hyperplasia in prosthetic vascular grafts. This study examines the hypothesis that clinically relevant graft material activates monocytes to oxidize low density lipoprotein (LDL).

METHODS

LDL and Dacron or expanded polytetrafluoroethylene (ePTFE) graft material were incubated in the presence of U937 cells, a monocytic cell line. LDL oxidation was measured by conjugated dienes, lipid peroxides, thiobarbituric acid-reacting substances, and electrophoretic mobility. Cell production of superoxide was measured by ferricytochrome c reduction. Metal ion requirement was assessed with the metal chelators, ethylenediaminetetra-acidic acid, deferoxamine, and bathocuproinedisulfonic acid. To determine whether human monocytes were capable of being activated by Dacron graft material to oxidize LDL, freshly isolated peripheral blood monocytes were also studied.

RESULTS

Incubation of LDL with U937 cells and Dacron increased LDL oxidation by 5- to 20-fold. LDL incubated with ePTFE or U937 cells alone resulted in minimal oxidation. Dacron graft increased U937 cell production of superoxide by 4-fold, whereas ePTFE had no effect. Superoxide dismutase inhibited Dacron-activated U937 cell oxidation of LDL by greater than 50%, which indicates a role for superoxide. Ethylenediaminetetra-acidic acid, deferoxamine, and bathocuproinedisulfonic acid each inhibited Dacron-activated U937 cell oxidation of LDL. Human peripheral blood monocytes were activated by Dacron graft material to oxidize LDL; superoxide dismutase inhibited Dacron-activated human monocytic oxidation of LDL, which suggests a role for superoxide.

CONCLUSION

These results suggest that Dacron graft material activates monocytes to oxidize LDL by a mechanism that involves superoxide and requires iron and copper ions. Our work suggests a mechanism by which lipids that have been deposited within implanted vascular grafts may become oxidized. Oxidized lipids may contribute to the cellular dysfunction that results in anastomotic intimal hyperplasia and graft failure.

Desferrioxamine enhances the reactivity of vanadium (IV) and vanadium (V) toward ferri- and ferrocytochrome c

Ligands, especially desferrioxamine, affect the rate at which vanadium reduces or oxidizes cytochrome c. Whether reduction or oxidation occurs, and how fast, depends on the nature of the ligand, the state of reduction of the vanadium, the pH (6.0, 7.0, or 7.4), and the availability of oxygen. In general, oxidation of ferrocytochrome c was favored by (1) low pH, (2) an oxidized state of the vanadium, (3) the presence of oxygen, and (4) more strongly binding ligands (desferrioxamine much greater than histidine = ATP greater than EDTA greater than albumin greater than aquo). Thus, at pH 6.0, desferrioxamine accelerated the V(V)-catalyzed ferrocytochrome c oxidation 160-fold aerobically, and 3500-fold anaerobically. In general, strongly binding ligands slowed oxidations, especially at higher pH. Desferrioxamine was unique among the five ligands in that it not only accelerated oxidation of ferrocytochrome c at pH 6.0, but at pH 7.4 the redox balance shifted to the point where it paradoxically reduced ferricytochrome c. V(V) is an improbable electron donor, but desferrioxamine will reduce cytochrome c, and V(V) accelerates this process. Oxidation of cytochrome c by V(V):desferrioxamine was faster anaerobically, and reduction by V(IV):desferrioxamine was faster aerobically. Although V(V) did not oxidize ferrocytochrome c at pH 7.4, V(IV) did, provided oxygen and desferrioxamine were both present. V(IV):desferrioxamine almost completely reduced ferricytochrome c, and this reduction was followed by a slow, progressive oxidation. This latter oxidation of cytochrome c is mediated by active species generated in the reaction between V(IV):desferrioxamine and oxygen, because none of these reagents alone can induce oxidation at a comparable rate. The mediating species were transient, and generated in reactions with oxygen.(ABSTRACT TRUNCATED AT 250 WORDS)

Superoxide-driven NAD(P)H oxidation induced by EDTA-manganese complex and mercaptoethanol

A purely chemical system for NAD(P)H oxidation to biologically active NAD(P)+ has been developed and characterized. Suitable amounts of EDTA, manganous ions and mercaptoethanol, combined at physiological pH, induce nucleotide oxidation through a chain length also involving molecular oxygen, which eventually undergoes quantitative reduction to hydrogen peroxide. Mn2+ is specifically required for activity, while both EDTA and mercaptoethanol can be replaced by analogs. Optimal molar ratios of chelator/metal ion (2:1) yield an active coordination compound which catalyzes thiol autoxidation to thiyl radical. The latter is further oxidized to disulfide by molecular oxygen whose one-electron reduction generates superoxide radical. Superoxide dismutase (SOD) inhibits both thiol oxidation and oxygen consumption as well as oxidation of NAD(P)H if present in the mixture. A tentative scheme for the chain length occurring in the system is proposed according to stoichiometry of reactions involved. Two steps appear of special importance in nucleotide oxidation: (a) the supposed transient formation of NAD(P). from the reaction between NAD(P)H and thiyl radicals; (b) the oxidation of the reduced complex by superoxide to keep thiol oxidation cycling.

Vanadate-stimulated NADH oxidation requires polymeric vanadate, phosphate and superoxide

NADH oxidation, catalyzed by the microsomal enzyme system is stimulated on addition of polymeric vanadate. Maximum stimulation by polymeric vanadate was obtained in the presence of phosphate buffer. The small stimulation obtained by metavanadate (500 microM) increased on acidification followed by neutralization, or on adding a trace amount of polymeric vanadate (1 microM).

Vanadate enhancement of the oxidation of NADH by O2-: effects of phosphate and chelating agents

Vanadate markedly stimulates the oxidation of NADH by O2-. Both phosphate and Tris are inhibitory, but phosphate diminishes the greater inhibitory effect of Tris and thus gives the appearance of stimulating when added to Tris-buffered reaction mixtures. Chelating agents moderately increased the oxidation of NADH but eliminated the much greater catalytic effect of vanadate. Desferal was the most effective of the chelating agents, and could be used to titrate vanadate spectrophotometrically or in terms of the diminution of its catalytic activity. This permitted the demonstration that metavanadate or orthovanadate could form 1:1 complexes with desferal and that orthovanadate was the catalytically active species.