Superoxide production and reducing activity in human platelets.

Abstract

A B S T R A C T Human platelets contain the cuprozinc (cytoplasmic) and manganese (mitochondrial) forms of superoxide dismutase. Nevertheless, superoxide radicals were detectable in the surrounding medium of metabolically viable platelet suspensions by using two assay systems: cytochrome c and nitroblue tetrazolium. The quantity of superoxide generated by platelets (5 x 105 superoxide radicals/platelet per 10 min) was constant and did not increase after aggregation by agents such as collagen and thrombin. The superoxide-generating system was present in the supernate of both aggregated and resting platelets and therefore was not platelet-bound. Platelet superoxide production was unaffected by prior ingestion of aspirin, indicating that the prostaglandin and thromboxane pathways were not involved. Both resting and aggregated platelets exhibited a reductive capacity toward cytochrome c and nitroblue tetrazolium which was unrelated to superoxide production. Furthermore, the aggregation process always resulted in a marked increase in this reduction. The nonsuperoxide reduction associated with aggregation was found to be membrane bound and to decrease with an apparent first order reaction rate (k1 = 0.067 min-'). In addition, accumulative, time-dependent nonsuperoxide-related cytochrome c reduction was also detected. Since there is no superoxide dismutase in plasma, the presence of superoxide radicals in the surrounding medium of platelets may have in vitro significance for platelet and leukocyte concentration and storage and in vivo significance for hemostasis, coagulation, and thrombosis. The nonsuperoxiderelated reducing activities may represent a biochemical basis for platelet-blood vessel interactions, with particular reference to blood vessel integrity.

Metabolic aspects of the secretion of stored compounds from blood platelets. The effect of NaF at different pH on nucleotide metabolism and function of washed platelets

“…However, fluoride is not believed to activate adenylate cyclase in intact cells (Vigdahl et al, 1969). In leucocytes (Curnutte & Babior, 1975) and in platelets (Marcus et al, 1977) fluoride causes production of superoxide, which may activate platelets in synergism with other inducers, but such secondary activation is unlikely to be the main mechanism of fluoride-induced secretion. One might postulate that fluoride could act via an activation of the production of thromboxane A2; but no malonaldehyde production (E. H. Miirer & M. H. Fukami, unpublished work) or 02 burst (Miirer, 1968) accompanies fluoride-induced secretion, which argues against this suggestion.…”

Aluminum induces lipid peroxidation and aggregation of human blood platelets

“…Gutteridge and co-workers (24) demonstrated that Al 3+ salts do not directly stimulate lipid peroxidation, but instead accelerate iron-and hydrogen peroxide-dependent lipid peroxidation in phospholipid liposomes and human erythrocyte membranes. On the other hand, superoxide and hydrogen peroxide are known to induce platelet aggregation and they can be produced by these cells (8). Although Al 3+ has no redox capacity, the metal can cause alterations at the membrane level facilitating iron-initiated lipid peroxidation.…”

“…The end products of lipid peroxidation are cytotoxic and may cause platelet dysfunction. Nevertheless, reactive oxygen species (ROS) such as the superoxide anion, hydrogen peroxide and the hydroxyl radical, well-known stimulators of lipid peroxidation, are generated by platelets (7,8). These species have been shown to be modulators of platelet adhesion and aggregation, directly or through effects on vascular endothelial cells which generate prostacyclin and nitric oxide (9).…”

Comparative pharmacology of endothelium‐derived relaxing factor, nitric oxide and prostacyclin in platelets

“…Since catalase did not affect the activity of NO or of EDRF, it is likely that superoxide anions (02), rather than another oxygen-derived radical, play a role in the destruction of these compounds (Gryglewski et al, 1986b). Superoxide anions are present in the medium of platelet suspensions (Marcus et al, 1977), although the amount of 02-present does not increase during aggregation and SOD does not affect platelet function directly (Marcus et al, 1977;Clemmons et al, 1985). These findings suggest that although 2-are not involved in platelet aggregation per se they may contribute to the inactivation of NO.…”