Heme oxygenase-1 induction may explain the antioxidant profile of aspirin

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Abstract

Aspirin is known to exert antioxidant effects by as yet unidentified mechanisms. In cultured endothelial cells derived from human umbilical vein, aspirin (30–300 μM) increased heme oxygenase-1 (HO-1) protein levels in a concentration-dependent fashion up to fivefold over basal levels. HO-1 induction was accompanied by a marked increase in catalytic activity of the enzyme as reflected by enhanced formation of both carbon monoxide and bilirubin. Pretreatment with aspirin or bilirubin at low micromolar concentrations protected endothelial cells from hydrogen peroxide-mediated toxicity. HO-1 induction and endothelial protection by aspirin were not mimicked by indomethacin, another inhibitor of cyclooxygenase. The nitric oxide (NO) synthase blocker L-NAME prevented aspirin-dependent HO-1 induction. These findings demonstrate that aspirin targets HO-1, presumably via NO-dependent pathways. Induction of HO-1 expression and activity may be a novel mechanism by which aspirin prevents cellular injury under inflammatory conditions and in cardiovascular disease.

Section snippets

Methods

Materials. Fetal bovine serum, cell culture media, and penicillin–streptomycin were obtained from Gibco (Eggenstein, FRG). Tin protoporphyrin-IX (SnPP) was purchased from Alexis Deutschland GmbH (Grünberg, FRG). The Chemiluminescence Western blotting kit and anti-rabbit peroxidase-conjugated secondary antibody were from Boehringer Mannheim (Mannheim, FRG). All other chemicals were bought from Sigma (Deisenhofen, FRG).

Cell culture. Human endothelial cells derived from umbilical cord were

Endothelial cell viability

A 12-h pretreatment with aspirin protected endothelial cells from hydrogen peroxide-mediated toxicity, whereas indomethacin failed to exert a cytoprotective action (Fig. 1). Endothelial protection by aspirin was mimicked by exogenous bilirubin which led to an almost complete reversal of hydrogen peroxide-induced toxicity (Fig. 2). In order to explore a potential involvement of HO products such as bilirubin in the observed protection by aspirin, the HO inhibitor SnPP was used. At a concentration

Discussion

The beneficial cardiovascular effects of aspirin are generally attributed to its immediate platelet inhibitory function. However, accumulating evidence suggests that aspirin may have additional biological properties on the vasculature that contributes to the reduction of ischemic cardiovascular events in patients with hypertension and atherosclerosis [27], [28]. These possible nonplatelet-mediated effects include the attenuation of atherosclerosis due to inhibition of vascular smooth muscle

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    Abbreviations: CO, carbon monoxide; HO, heme oxygenase; NO, nitric oxide; L-NAME, NG-nitro-l-arginine-methyl-ester; SnPP, tin protoporphyrin-IX.

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