Direct impairment of vascular function by diesel exhaust particulate through reduced bioavailability of endothelium-derived nitric oxide induced by superoxide free radicals.

BACKGROUND: Diesel exhaust particulate (DEP) is a key arbiter of the adverse cardiovascular effects of air pollution. OBJECTIVES: We assessed the in vitro effects of DEP on vascular function, nitric oxide (NO) availability, and the generation of oxygen-centered free radicals. METHODS: We assessed the direct vascular effects of DEP (10-100 microg/mL) in isolated rat aortic rings using myography. We investigated NO scavenging and oxygen-centered free radical generation using an NO electrode and electron paramagnetic resonance (EPR) with the Tempone-H (1-hydroxyl-2,2,6,6-tetramethyl-4-oxo-piperidine) spin trap, respectively. RESULTS: Acetylcholine-induced relaxation was attenuated by DEP (maximum relaxation reduced from 91 +/- 4% to 49 +/- 6% with 100 microg/mL DEP; p < 0.001) but was restored by superoxide dismutase (SOD; maximum relaxation, 73 +/- 6%; p < 0.001). DEP caused a modest inhibition of relaxation to NO donor drugs, an effect that could be reversed by SOD (p < 0.01). At 10 microg/mL, DEP did not affect verapamil-induced relaxation (p = 0.73), but at 100 microg/mL DEP inhibited relaxation (p < 0.001) by a mechanism independent of SOD. NO concentrations generated by 2-(N,N-diethylamino)-diazenolate-2-oxide (DEA/NO; 10 microM) were reduced by DEP (100 microg/mL; from 5.2 +/- 0.4 to 3.3 +/- 0.4 microM; p = 0.002). Free radical generation was increased by DEP (10 microg/mL; 9-fold increase in EPR spectra; p = 0.004) in a manner that could be attenuated by SOD (p = 0.015). CONCLUSIONS: DEP caused oxidative stress through the generation of oxygen-centered free radicals that reduced the bioavailability of endothelium-derived NO without prior interaction with the lung or vascular tissue. These findings provide a mechanism for the adverse cardiovascular effects of particulate air pollution.