Exposure of rats to diesel exhaust particle (DEP) has been shown to induce the formation of inducible nitric oxide synthase (iNOS) and elevate nitric oxide (NO) production by alveolar macrophages (AM). DEP are known to induce pulmonary inflammation and increase pulmonary susceptibility to infection through altered metabolic function and secretion of pro- and anti-inflammatory cytokines. The present study examines the role of NO in DEP-altered P450 activities which mediate genotoxic and mutagenic effects in the lung. Male Sprague-Dawley rats were intratracheally (IT) instilled with saline, DEP (35 mg/kg) or the DEP organic extract (DEPE). To illustrate the role of iNOS, another group of rats was treated with an iNOS inhibitor, aminoguanidine (AG, 100 mg/kg), by i.p. injection 30 min prior to and 3, 6 and 9 h after IT exposure. At 1 day post exposure, DEP-induced genotoxicity and lung-S9 dependent mutagenicity were monitored via comet assay and the Ames test with S. typhimurium YG1024, respectively. The results show that AG treatment markedly inhibited DEP-induced NO production by AM without affecting iNOS levels. DEP-exposed AM exhibited significant DNA damage compared to controls. Both DEP and DEPE induced CYP1A1 activity, which was significantly reduced by AG. However, DEP and DEPE attenuated CYP2B1 activity that was not altered by AG. CYP1A1 and CYP2B1 supersomes activated 2-aminoanthracene (2-AA) mutagenicity in the Ames test, suggesting that both CYP isoforms were involved in 2-AA activation. DEP- and DEPE-S9, although containing less CYP2B1, activated 2-AA to a similar extent as the control. AG treatment significantly lowered DEP- and DEPE-S9, but not control-S9, dependent activation of 2-AA mutagenicity. These results demonstrate that DEP exposure induces genotoxicity and mutagenicity in the lung. The organic component of the particle is responsible for DEP-induced CYP1A1, while NO plays a major role in DEP-induced mutagenic effects in the lung by regulating CYP1A1 activity.
The Toxicologist. Society of Toxicology 44th Annual Meeting and ToxExpo, March 6-10, 2005, New Orleans, Louisiana