Arsenic is recognized as a carcinogen for human skin, bladder, and lung, following either ingestion or inhalation; however the exact mode of action of environmentally relevant exposure has not been determined. Because arsenic in the environment exists in several oxidative states and can interact with thiols, it is thought that arsenic toxicity is mediated through oxidative stress. Production of oxygen radicals following acute in vitro exposures has been demonstrated. However, our research has chosen to focus on the role of oxidative stress following whole animal exposure to environmentally relevant doses of arsenic. Following a 28-d inhalation of arsenic or cigarette smoke or both, there was a significant decrease in both the reduced and total glutathione levels in the combined arsenic and smoke group compared to groups exposed to arsenic or smoke alone. This correlated with a 5-fold increase in DNA oxidation. Lungs processed for immunohistochemistry localization of 8-oxo-dG showed increased staining in nuclei of airway epithelium and subadjacent interstitial cells. Increases in DNA oxidation were not due to increased inflammation. Although inhalation of arsenic is an important occupational exposure, the majority of human exposures occurs through ingestion of arsenic. Our recent work has been devoted to the identification of altered pulmonary gene and protein expression following ingestion of environmentally relevant levels of arsenic in drinking water. We have found that, following chronic exposure, arsenic leads to misregulation of a number of genes and proteins in the lung. A large percentage of the altered genes and proteins are known to be regulated by redox-sensitive transcription factors, (SP1, NF kappaB, AP-1), suggesting that, at environmentally relevant levels of chronic exposure, arsenic may be acting through alteration of cellular redox status. Validation of the alterations seen in animal models of exposure is being carried out in humans.

In a simulated military flight-line exposure protocol, the effects of JP-8 jet fuel exposure on lung epithelial permeability were evaluated in male Fischer 344 rats (F344). Exposures were nose-only and for one hour daily. Groups were exposed for 7, 28, and 56 days. A protocol for administering a low dose (500mg/m3/hr) and a high dose (813-1094mg/m3/hr) of JP-8 jet fuel was used. Longitudinal sham-exposure groups (no jet fuel) for 7, 28, and 56 days were included in the protocol. Lung epithelial permeability was measured by clearance of technetium-labeled diethylenetriamine pentaacetate (99mTcDTPA, molecular weight = 492 daltons, physical half-life = 6.02 hours). The percent clearance of 99mTcDTPA per minute was calculated. Alveolar epithelial clearance for JP-8-exposed rats was dependent on both exposure concentration and duration. It was noted that at low-dose exposure concentrations alveolar epithelial clearance of 99mTcDTPA returned to low levels (LD56 = 1.09% per min; LC56 = 0.98% per min), suggesting recovery as evidenced by microscopic exam. The corresponding 56-day high-dose group (n = 10) had a significantly higher (p < 0.05) value of 2.25% per minute. The 28-day low-dose (n = 15) and high-dose (n = 20) groups had clearance values that were significantly increased from their longitudinal control group (n = 17). The alveolar epithelial permeability values were 2.51, 1.95, and 1.20, respectively. The seven-day longitudinal control, low-dose, and high-dose groups had alveolar permeability values of 1.57, 2.16, and 2.07, respectively. The lung histology correlated with the clearance values. Electron micrographs showed that all groups had interstitial edema resulting from endothelial damage. There was apparent thickening of the alveolar septa, and alveolar macrophages were activated in all groups. Lung permeability data, as determined by 99mTcDTPA alveolar clearance, indicated that lung injuries peaked at 28 days of jet fuel exposure, and this finding corresponded with the histology data. There was a discrepancy in the seven-day group between the number of cells and the 99mTcDTPA clearance values. The HD7 group had a total cell count significantly higher than all other groups, but the 99mTcDTPA clearance values in that group were not significantly different from that of any other group.

In a simulated military flightline exposure protocol, Fischer 344 rats (F344) were used to investigate the pulmonary effects of JP-8 jet fuel inhalation. Exposures were nose only and for 1 h daily. Groups were exposed for 7 days (7D) or 28 days (28D). Each exposure group had a matched longitudinal control group (LC7 and LC28). Exposure concentrations of 520 mg m-3 caused an increase in dynamic compliance after 7 days of exposure, but compliance changes were not seen with continued exposure (28D, 495 mg m-3). Pulmonary resistance was increased in both 7- and 28-day JP-8-exposed groups. Changes in pulmonary function were accompanied by a decrease in substance P concentrations from the bronchoalveolar lavage fluid (BALF). No significant change was observed in BALF levels of 6-keto-PGF1 alpha, the stable metabolite of prostacyclin, which is a marker of endothelial cell function. The JP-8-exposed rats gained significantly less weight during the study period than the LC7 and LC28 groups, and the lungs of the 7D group were heavier by wet lung/body weight ratio (WtL/WtB). Alveolar clearance of technetium-labelled diethylenetriamine pentaacetate ([99mTc]DTPA) was increased in jet fuel-exposed groups. Light microscopy showed no pathological evidence of lung injury. Recovery from the early pulmonary effects of JP-8 inhalation occurred with continued exposure, as seen by recovery of pulmonary compliance and WtL/WtB.

Epidemiological evidence has indicated that arsenic and cigarette smoking exposure act synergistically to increase the incidence of lung cancer. Since oxidative damage of DNA has been linked to cancer, our hypothesis is that aerosolized arsenic and cigarette smoke work synergistically to increase oxidative stress and increase DNA oxidation in the lung. To test this hypothesis male Syrian golden hamsters were exposed to room air (control), aerosolized arsenic compounds (3.2 mg/m 3 for 30 minutes), cigarette smoke (5 mg/m 3 for 30 minutes), or both smoke and arsenic. Exposures were for 5 days/week for 5 or 28-days. Animals were sacrificed one day after the last exposure. In the 28-day group, glutathione levels and DNA oxidation (8-oxo-2 -deoxyguanosine (8-oxo-dG)) were determined. Our results show that in the 28-day arsenic/smoke group there was a significant decrease in both the reduced and total glutathione levels compared with arsenic or smoke alone. This correlated with a 5-fold increase in DNA oxidation as shown by HPLC. Immunohistochemical localization of 8-oxo-dG showed increase staining in nuclei of airway epithelium and subadjacent interstitial cells. These results show that dual exposure of arsenic and cigarette smoke at environmentally relevant levels can act synergistically to cause DNA damage.