Role of hydrogen peroxide in the neutrophil-mediated release of prostacyclin from cultured endothelial cells.

398

148

Oxidant-induced damage to the intima of pulmonary and systemic vessels is thought to be an important mechanism of injury in a variety of syndromes of vascular damage. Hydrogen peroxide (H202) is an active oxygen metabolite that may induce intimal injury by cytolytic attack or by inducing biochemical and functional alterations in the endothelial cells (EC); however, mechanisms involved in noncytolytic perturbation of EC are largely unknown. We found that H202 stimulated the synthesis of platelet-activating factor (PAF) by primary cultures of bovine pulmonary artery endothelium (BPAEC) and by human umbilical vein endothelium (HUVEC). In each cell type the incorporation of I3Hlacetate into 13H-acetylIPAF was concentration-and time-dependent and was temporally dissociated from severe plasma membrane disruption and cytolytic cell injury; the newly synthesized PAF remained associated with the EC. H202 caused permeabilization of EC to 45Ca2+ and an increase in intracellular Ca2+, suggesting that a transmembrane Ca2+ flux is the signal that initiates PAF synthesis.H202 also induced the endothelial cell-dependent adhesion of neutrophils to HUVEC monolayers. This response was rapid, with an onset within minutes and a subsequent time course that paralleled the time course of PAF accumulation, and was dependent on extracellular Ca2' but not on de novo protein synthesis. These studies demonstrate that H202 can induce two rapid activation responses of endothelium, PAF synthesis and EC-dependent neutrophil adhesion, events that may be important in physiologic and pathologic inflammation.

Section: Discussionsupporting

confidence: 91%

“…), we considered the possibility that the activity was H202. H202 is generated by neutrophils activated by IoA or PMA, and can alter membrane phospholipids in EC (7,43 Table I). Inactivation of catalase by boiling prevented the inhibition (Table I).…”

Section: Measurements Ofec Injury and Cytotoxicitymentioning

confidence: 99%

Hydrogen peroxide stimulates the synthesis of platelet-activating factor by endothelium and induces endothelial cell-dependent neutrophil adhesion.

Lewis¹,

Whatley²,

Cain³

et al. 1988

398

148

“…6 would appear to be due to the progressively increasing levels of H202. (31,32,35) or in inhibition of this enzyme as our present data indicate. The ambient peroxide level in a cell is determined by a number of factors including the glutathione redox cycle (3, 30).…”

Section: Resultssupporting

confidence: 83%

Effect of hydrogen peroxide on prostaglandin production and cellular integrity in cultured porcine aortic endothelial cells.

Whorton¹,

Montgomery²,

Kent³

1985

156

Oxidative damage to the vascular endothelium may play an important role in the pathogenesis of atherosclerosis and aging, and may account in part for reduced vascular prostacyclin (PGI2) synthesis associated with both conditions. Using H202 to induce injury, we investigated the effects of oxidative damage on PGI2 synthesis in cultured endothelial cells (EC). Preincubation of EC with H202 produced a dose-dependent inhibition (inhibitory concentration [ICso1 = 35 gM) of PGI2 formation from arachidonate. The maximum dose-related effect occurred within 1 min after exposure although appreciable H202 remained after 30 min (30% of original). In addition, H202 produced both a time-and dose-dependent injury leading to cell disruption, lactate dehydrogenase release, and 51Cr release from prelabeled cells. However, in dramatic contrast to H202 effects on PGI2 synthesis, loss of cellular integrity required doses in excess of 0.5 mM and incubation times in excess of 1 h. The superoxide-generating system, xanthine plus xanthine oxidase, produced a similar inhibition of PGI2 formation. Such inhibition was dependent on the generation of H202 but not superoxide in that catalase was completely protective whereas superoxide dismutase was not. H202 (50 gM) also effectively inhibited basal and ionophore A23187 (0.5 1M)-stimulated PGI2 formation. However, H202 had no effect on phospholipase A2 activity, because ionophore A23187-induced arachidonate release was unimpaired. To determine the effects on cyclooxygenase and PGI2 synthase, prostaglandin products from cells prelabeled with IHlarachidonate and stimulated with ionophore A23187, or products formed from exogenous arachidonate were examined. Inhibition of cyclooxygenase but not PGI2 synthase was observed. Incubation of H202-treated cells with prostaglandin cyclic endoperoxide indicated no inhibition of PGI2 synthase. Thus, in EC low doses of H202 potently inhibit cyclooxygenase after brief exposure whereas larger doses and prolonged exposure are required for classical cytolytic effects. Surprisingly, PGI2 synthase, which is known to be extremely sensitive to a variety of lipid peroxides, is not inhibited by H202. Lipid solubility, enzyme location within the EC mem-

“…These experiments suggest a second possible mechanism for peroxide stimulation of prostaglandin production: the activation of inflammatory or mesenchymal cells. H202, myeloperoxidase, and eosinophilic peroxidase will stimulate PGE2 and/ or PGO2 production in mast cells (30-33), fibroblasts (34,35), renal gomerular mesangial cells (36), and cultured endothelial cells (37,38). The mechanism of this stimulation is unclear, but in the endothelial cells it seems to involve gating of Ca2+ across the cell membrane either as the result of a receptor-mediated event or secondary to lipid peroxidation of the cell membrane, making it more permeable to Ca2+ with subsequent liberation of AA from membrane stores (38 (4,39).…”

Section: Discussionmentioning

confidence: 99%

Hydrogen peroxide stimulates rat colonic prostaglandin production and alters electrolyte transport.

Karayalçın

Sturbaum²,

Wachsman³

et al. 1990

The changes in short circuit current (electrogenic a-secretion) of rat colon brought about by xanthine/xanthine oxidase in the Ussing chamber were inhibited by catalase and diethyldithiocarbamate, but not by superoxide dismutase. These results, the reproduction of the response with glucose/glucose oxidase and with exogenous H202, and the lack of effect of preincubation with deferoxamine or thiourea implicate H202, and not 02 or OH, as the important reactive oxygen metabolite altering intestinal electrolyte transport. 1 mM H202 stimulated colonic PGE2 and PGI2 production 8-and 15-fold, respectively, inhibited neutral NaCl absorption, and stimulated biphasic electrogenic a secretion with little effect on enterocyte lactic dehydrogenase release, epithelial conductance, or histology. a-secretion was reduced by cyclooxygenase inhibition. Also, the Cl-secretion, but not the increase in prostaglandin production, was reduced by enteric nervous system blockade with tetrodotoxin, hexamethonium, or atropine. Thus, H202 appears to alter electrolyte transport by releasing prostaglandins that activate the enteric nervous system. The change in short circuit current in response to Iloprost, but not PGE2, was blocked by tetrodotoxin. Therefore, PGI2 may be the mediator of the H202 response. H202 produced in nontoxic concentrations in the inflamed gut could have significant physiologic effects on intestinal water and electrolyte transport. (J.