Role of hydroxyl radicals in the activation of human platelets

Abstract

Platelets primed by exposure to subthreshold concentrations of arachidonic acid or collagen are known to be activated by nanomolar levels of hydrogen peroxide. We here demonstrate that this effect is mediated by hydroxyl radicals (OH") formed in an extracellular Fenton-like reaction. H,O,-induced platelet aggregation, serotonin release and thromboxane A, productions were inhibited by OH" scavengers and by the iron chelator desferrioxamine ; hydroxyl radicals were detected directly by ESR measurements of the spin-trapped OH" adduct. The role of OH" was confirmed in experiments with exogenously added iron; free or EDTA-bound ferrous iron activated platelets in a process blocked by deoxyribose, mannitol or catalase, whereas ferric iron was without effect unless reductants were included. The activation by OH" depended on concomitant release of arachidonic acid and was blocked by the phospholipase A, inhibitors mepacrine and aristolochic acid, and by the Na+/K+ antiporter inhibitor ethylisopropylamiloride. In contrast, neomycin and staurosporin were without effects, indicating that phospholipase C and protein kinase C were not involved in the initial phase of activation. Neither radical formation nor arachidonic acid release was blocked by aspirin. In whole blood aggregation of platelets could be induced by H,O, generated upon specific stimulation of neutrophils by N-formyl-methionyl-leucyl-phenylalanine ; platelet activation and radical formation were blocked by the NADPH oxidase inhibitor diphenyliodonium as well as by catalase and mannitol. These results suggest that reactive oxygen species act as 'second messengers' during the initial phase of the platelet activation process.

Microarray analysis reveals the inhibition of nuclear factor-kappa B signaling by aristolochic acid in normal human kidney (HK-2) cells

“…AAI inhibits the growth of bacteria, including Escherichia coli, Pseudomonas aeruginosa, Streptococcus faecalis, Staphylococcus aureus, and Staphylococcus epidermidis [5] . AA can block H 2 O 2 -induced platelet aggregation and suppress hydroxyl radicalinduced platelet activation through the arachidonic acid pathMicroarray analysis reveals the inhibition of nuclear factor-kappa B signaling by aristolochic acid in normal human kidney (HK-2) cells Ya-yin CHEN 1, 2 , Su-yin CHIANG 1 , Hsiu-ching WU 3 , Shung-te KAO 1, 2 , Chien-yun HSIANG 4, # , Tin-yun HO 1, # , Jaung-geng LIN 1, #, * www.nature.com/aps Chen YY et al Acta Pharmacologica Sinica npg way [7,8] . AA was found to possess anti-inflammation effects as demonstrated by its ability to inhibit phospholipase A 2 (PLA 2 ) when administered by intramuscular or intraperitoneal injection [9,10] .…”

“…* To whom correspondence should be addressed. [7,8] . AA was found to possess anti-inflammation effects as demonstrated by its ability to inhibit phospholipase A 2 (PLA 2 ) when administered by intramuscular or intraperitoneal injection [9,10] .…”

Do iron and vitamin C co-supplementation influence platelet function or LDL oxidizability in healthy volunteers?

“…This study addresses the question as to whether dietary co-supplementation of iron with vitamin C in normal healthy subjects can lead to deleterious effects in biochemical markers of oxidative stress related to cardiovascular disease. Since previous studies have shown a link between antioxidant levels and oxidative stress in platelet function (Salvemini et al, 1989;Salonen et al, 1992;Iuliano et al, 1992Iuliano et al, , 1994Violi et al, 1993;Calzada et al, 1997) and in the susceptibility of isolated plasma LDL to oxidation ex vivo (Esterbauer, 1989), we have examined parameters of both platelet function, aggregability and ATP release, and LDL oxidation.…”

Tetrahydrobiopterin impairs the action of endothelial nitric oxide via superoxide derived from platelets

“…The present experimental model might be applicable for the investigation of the interaction between O 2 7 (generated by platelets) and endothelial NO (induced by shear stress). It is known that platelets produce reactive oxygen species (Iuliano et al, 1994;Leoncini et al, 1991;Marcus et al, 1977). The inhibitory eect of BH 4 was suppressed by diphenyleneiodonium (a speci®c inhibitor of NADPH oxidase) (Cross & Jones, 1986), diclofenac sodium and SOD, but not by allopurinol (a xanthine oxidase inhibitor).…”