Modification by metals, sulphydryl reagents and cyanide of the particle stimulated enhancement of oxygen consumption in bovine granulocytes

In vitro inhibition of superoxide anion production and superoxide dismutase activity by zinc in human spermatozoa

The in vitro effect of zinc on superoxide anion (O2-) generation and on SOD-like activity in spermatozoa of infertile men was investigated. The formation of superoxide anion was stimulated by NADPH and the level of superoxide anion was measured by the reduction of ferricytochrome c. Both Percoll-isolated (n = 14) and washed spermatozoa (n = 14) exposed to 1 mmol/L zinc (60 min, 37 degrees C), released less (p < 0.002 and p < 0.04, respectively) superoxide anions than did zinc-untreated spermatozoa. These results implicate a possible role for zinc as a scavenger of excessive superoxide anions produced by defective spermatozoa in semen after ejaculation. Additionally, zinc was found to dose-dependently inhibit superoxide dismutase (SOD)-like activity of spermatozoa in vitro. The inhibition of SOD-like activity by an equal concentration of zinc (1 mmol/L) was less pronounced in oligospermic (p < 0.002; n = 16) and asthenozoospermic (p < 0.0005; n = 20) than in normozoospermic samples (p < 0.0001; n = 20). This differential ability of zinc to inhibit SOD-like activity may be relevant to the physiological function of spermatozoa in fertilization. The evidence that zinc may elicit an inhibition of both superoxide anion production and SOD-like activity in human spermatozoa, indicate the existence of novel, zinc-related mechanism(s) involved in the oxidative events occurring after ejaculation, with a possible modulatory effect on germ cell function.

The activation of gold complexes by cyanide produced by polymorphonuclear leukocytes. III. The formation of aurocyanide by myeloperoxidase

There is considerable evidence that the anti-rheumatic gold complexes are activated by their conversion to aurocyanide. In order to understand the mechanism of production of aurocyanide, we investigated the involvement of myeloperoxidase in the reaction. This haem enzyme of neutrophils and monocytes uses hydrogen peroxide to oxidise chloride and thiocyanate to hypochlorous acid and hypothiocyanite, respectively. When aurothiomalate (10 microM) was incubated with thiocyanate (200 microM), hydrogen peroxide (100 microM) and myeloperoxidase (20 nM), it was transformed to a product that was spectrally identical to authentic aurocyanide. Aurothiomalate was quantitatively converted to aurocyanide in about 10 min at pH 6.0 and in 40 min at pH 7.4. Aurocyanide formation occurred after myeloperoxidase had used all the hydrogen peroxide available to produce hypothiocyanite. Thus, the cyanide must have formed from the slow decomposition of hypothiocyanite. The rate of aurocyanide production was increased in the presence of 100 mM chloride, which indicates that hypochlorous acid accelerates the formation of cyanide. Hypochlorous acid (100 to 400 microM) reacted non-enzymatically with thiocyanate (200 microM) and aurothiomalate (10 microM) to produce aurocyanide. Thus, aurocyanide is produced by two processes, involving both the formation of hypothiocyanite and hypochlorous acid. Aurocyanide is an effective inhibitor of the respiratory burst of neutrophils and monocytes and the proliferation of lymphocytes. Therefore, aurothiomalate may attenuate inflammation by acting as a pro-drug which is reliant on neutrophils and monocytes to produce hypothiocyanite. When the hypothiocyanite decays to hydrogen cyanide, the pro-drug is converted to aurocyanide which then suppresses further oxidant production by these inflammatory cells.

Effect of captopril, enalaprilat and mercaptopropionyl glycine (MPG) on the oxidative activity of human isolated neutrophils

1. Neutrophil NADPH oxidase produces the superoxide anion (O2-) anion radical from oxygen. The thiol containing ACE inhibitor, captopril has been reported to inhibit isolated NADPH oxidase. The above effect of captopril, if present in intact cells, could contribute to the ability of this drug to alleviate neutrophil-mediated tissue damage. We have, therefore, investigated the effect of captopril on the oxidative activity of intact human isolated neutrophils. 2. The effects of captopril on neutrophil oxidative activity were compared with those of enalaprilat (a non-thiol ACE inhibitor) and N-mercaptopropionyl glycine (MPG) (a simple thiol). 3. The oxidative response of PMA-stimulated neutrophils measured by lucigenin chemiluminescence was not affected by any of these test agents. The thiol captopril and MPG (but not enalaprilat) caused an initial delay in luminol chemiluminescence production by PMA-stimulated neutrophils. 4. Captopril and MPG (but not enalaprilat) increased, rather than decreased oxygen uptake, when added to PMA-stimulated neutrophils. Thiol oxidation was determined to be, at least partly, responsible for the excess oxygen uptake observed. 5. NADPH oxidase activity in intact neutrophils was not affected by captopril, MPG or enalaprilat. The inhibition of NADPH oxidase activity is unlikely to contribute to the therapeutic effects of captopril and other thiols.

Scavenging by alginate of free radicals released by macrophages

Failure to eradicate mucoid forms of P. aeruginosa has implicated bacterial alginate in a local evasion of host defence mechanisms within the lung of Cystic Fibrosis (CF) patients. We have found that purified bacterial alginate scavenges free radicals released by triggered macrophages as detected by lucigenin amplified chemiluminescence (CL) and reduction of cytochrome c. In agreement with this, alginate was also able to scavenge radicals generated by a chemical system (hydrogen peroxide and copper; detected by benzoate hydroxylation and chemiluminescence), and by an enzymatic system (hypoxanthine and xanthine oxidase; detected by chemiluminescence). All inhibitions were dose-related. Oxygen consumption by neutrophils (unlike that of macrophages) could be detected in a Clark electrode, and was not reduced by alginate, confirming that scavenging of radicals was responsible for the earlier observations. These data suggest that bacterial alginate by scavenging free radicals, may favour the survival of mucoid forms of P. aeruginosa, particularly in the CF lung.

A comparison of the oxidative reactions of neutrophils from a variety of species when stimulated by opsonized zymosan and F-met-leu-phe

Bovine, ovine and porcine blood neutrophils produced less superoxide and consumed less oxygen than human neutrophils when they were challenged with serum-treated zymosan. These differences were not related to methodological considerations or the origin of the serum used to treat the zymosan. When the two main methods of neutrophil isolation were applied to human neutrophils, no differences in the particle stimulated respiratory bursts were observed. The bacterial chemotactic peptide, F-met-leu-phe, which enhances superoxide production of human neutrophils whether or not they are challenged with serum-treated zymosan, did not increase superoxide production of neutrophils from cattle, sheep or pigs under either of these conditions. We conclude that, if our understanding of these host defence mechanisms in domesticated animals is to match that of man, further detailed studies of animal neutrophils are necessary.

Formation of HCN and its chlorination to ClCN by stimulated human neutrophils--2. Oxidation of thiocyanate as a source of HCN

Leucocytes challenged by Staphylococcus epidermidis or stimulated by phorbol myristate acetate (PMA) produce cyanide from thiocyanate. The amount of H14CN formed depends on KS14CN concentration and is enhanced by pretreatment of phagocytosed bacteria with penicillin or by adding amine-taurine to the medium of PMA-stimulated neutrophils. The reaction of taurine chloramine or chlorinated Staphylococcus epidermidis (containing N-Cl groups) with thiocyanate results in HCN formation. At higher concentration of chloramine cyanogen chloride is formed. Cyanide is chlorinated by PMA-stimulated neutrophils and this process is significantly enhanced by exogenous taurine and inhibited by 3-amino 1,2,4-triazole. It is conceivable that oxidation of thiocyanate to HCN and chlorination of HCN to ClCN is mediated by the chlorinating species (taurine chloramine) produced by stimulated neutrophils.