A previous study assessing the environmental impact of Hurricane Katrina in New Orleans reported that a “powdery dust was aerosolized or resuspended via vehicular traffic disrupting sediments on previously flooded roadways and other hard surfaces” [16
]. The authors further reported the presence of numerous microbial and environmental contaminants present in sediment samples collected from the New Orleans area and suggested an “inhalational hazard” to residents and workers returning to the New Orleans area. While a much earlier study of soils and sediments from various urban sites around the New Orleans area clearly demonstrated that polycyclic aromatic hydrocarbons were a part of the soil mixture in 2001 [17
], a recent report suggests that this contamination (at least with arsenic) appears to have developed in post-flood spots after Hurricane Katrina (i.e. Lakeview, Gentilly, Lower Ninth) [18
]. Since we have no way of truly knowing what the soils in the New Orleans area contained immediately prior to the flooding, the present study makes no attempt to directly link the contaminants to the flooding.
In this study, we report our efforts to collect environmental samples and to conduct a preliminary assessment of the short-term and potentially long-term impact to public respiratory health in the New Orleans area due to Hurricane Katrina. Within a week of the hurricane, several investigations were conducted on soil and sediment samples to determine what, if any, biological and/or chemical contaminants were present. Interestingly, some reported only moderately elevated levels of metals [19
]; while others reported concentrations of aldrin, arsenic, lead, and seven SVOCs in sediments/soils exceeding EPA thresholds [16
]. Our chemical analysis, performed independent of the bio- and physio-logical analyses, showed that SS-12 contained significant levels of arsenic (approximately 30 times higher than USEPA screening levels) (). In addition, SS-12 contained high concentrations of SVOCs, including Benzo(b)fluoranthene, Benzo(a)anthracene, Benzo(a)pyrene, and Indeno(1,2,3-cd)pyrene ().
In vitro, SS-12 elicited marked cytotoxicity reducing the viability of HEp2 cells to less than 50% at the lowest exposure dose (30 μg/ml). We further demonstrated that acute exposure to SS-12 resulted in diminished pulmonary function. In particular SS-12 induced an abnormal increase in airflow limitation in response to MeCh provocation (i.e., increase airway resistance). Elevations in pulmonary resistance were accompanied by a moderate increase in the inflammatory response including the total number of leukocytes present in the BALF. Significant increases in the number of neutrophils seemed to account for the elevation in the total number of leukocytes observed. The analysis of BALF cellularity showed an increase in neutrophils in SS-12 treated mice, while histopathology demonstrated that exposure to SS-12 caused significant pulmonary inflammation with monocyte/macrophage infiltration of the alveolar ducts/alveoli and mild type II pneumocyte hyperplasia. Moreover, exposure to SS-12 resulted in a significant increase of TNF-α and IL-6 in the BALF. The lack of microbial presence in the lungs of SS-12treated mice suggested that viable microbes were most likely not responsible for these observed responses. Mice treated with SS-13 also developed significant neutrophilic inflammation and elevated IL-6 levels in their BALF. While IL-6 levels correlated well with neutrophilia in the BALF, airway resistance was most strongly correlated with levels of arsenic (common to both SS-12 and SS-13).
Both arsenic and SVOCs are associated with many adverse human health effects including cardiovascular, lung, hepatic, urinary, and renal diseases [20
]. While acute exposure to arsenic has been shown to induce bronchiolitis, SVOCs emitted from vehicles and instilled via the trachea have also been shown to elicit many of the same effects that were observed with short-term exposure to SS-12 including cytotoxicity, inflammation, and parenchymal changes in the lung [20
]. In fact, pneumocyte hyperplasia was the principal histopathological effect induced by exposure to SVOCs from gasoline and diesel engine exhaust. Although no correlations between SVOC content and the amount of parenchymal changes observed were presented by Seagrave and colleagues, their data compliment our data and suggest that exposure to samples containing greater than 50% SVOC results in significantly elevated levels of total BALF cell counts due to elevations mainly in neutrophils. Thus, it is possible that the cellular cytotoxicity and the acute lung damage observed in response to inhalation of SS-12 are due to the chemical constituents of this sample.
Arsenic and SVOCs have also been shown to elicit oxidative stress [22
]. In particular, arsenic has been shown to directly attack -SH groups of proteins and induce the generation of reactive oxygen species (ROS) in both cells and tissues [23
]. HO-1 is the rate limiting enzyme in the production of the bilirubin, an important anti-oxidant [14
]. In bronchial epithelial cells, expression of HO-1 has been shown to be a sensitive marker for oxidative stress [24
] and is often induced at very low levels of oxidative stress [26
]. Studies have suggested that HO-1 acts as an inducible defense, against oxidative stress in models of inflammation with the products of the HO-1 reaction potentially participating in cellular defense [27
]. The induction of HO-1 in lung tissue isolated from mice exposed to SS-12 suggests an escalating pulmonary response to oxidative stress. SS-12 showed significant oxidative ability in vitro and its ability to induce oxidative stress was confirmed by DCF staining of lung homogenates. The correlation between HO-1 expression, DCF staining, GSH/GSSG ratio, and redox activity of SS-12 as measured by DTT consumption provides evidence for the role of oxidative stress in HK-PM induced pulmonary dysfunction and toxicity.
Interestingly, epidemiological studies have shown that chronic exposure to arsenic-contaminated dust is associated with increased risks of lung cancer [29
]. Although it has been difficult to confirm the carcinogenicity of arsenic in animal models (probably due to the long latency period), intratracheal instillations of arsenic trioxide have been shown to induce pulmonary adenomas and papillomas [30
]. Although the mode of action of arsenic carcinogenicity has not been established, intracellular production of ROS may play a role in mediating DNA damage and initiating carcinogenic processes. Currently, chronic exposure studies using SS-12 are being developed to address the potential for SS-12 to induce pulmonary carcinogenesis and understand the role of ROS and oxidative stress in these processes.
TNF-α is known to play a critical role in the pathogenesis of airway inflammation and airway responsiveness in a number of pulmonary diseases often mediating cell differentiation, activation, apoptosis and release of pro-inflammatory mediators by specific binding to TNFR1 and TNFR2 [31
]. TNF-α is typically generated by macrophages, neutrophils, and epithelial cells in the airway [31
]. In SS-12 treated mice, an impressive increase of TNF-α in BALF was observed and suggests a role for TNF-α in SS-12 induced pulmonary inflammation and airways resistance. Although not statistically significant, a slight increase in TNF-α was also observed in mice exposed to silica particles alone (data not shown). This was not entirely unexpected, since TNF-α has been shown to be involved in the pathogenesis of silica induced lung disease [34
]. However, the inflammatory, pulmonary function, cytokine, and HO-1 data suggest that something inherent to the samples, and not just particulates such as silica, were responsible for the enhanced pulmonary pathophysiology observed in these mice. Although outside of the scope of the current studies, our data and that of others suggest that treatment with anti-oxidants may reduce pulmonary disease associated with SS-12 exposure.
The present study demonstrated that inhalation exposure to SS-12 leads to acute lung injury in mice, which is characterized by increased pulmonary inflammation and decrease lung function. The pathophysiological processes in the lung correlated to increases in TNF-α, IL-6, and biomarkers of oxidative stress. These results suggest that oxidative stress may, in part, be responsible for these observed respiratory effects. Studies are ongoing to determine the long-term effects of acute and chronic exposure to HK-PM and the precise role of oxidative stress and TNF-α in these events in animal models.