Transcriptional changes in innate immunity genes in head kidneys from Aeromonas salmonicida-challenged rainbow trout fed a mixture of polycyclic aromatic hydrocarbons.

We previously observed that exposure to a complex mixture of high molecular weight polycyclic aromatic hydrocarbons (PAHs) increased sensitivity of rainbow trout (Oncorhynchus mykiss) to subsequent challenge with Aeromonas salmonicida, the causative agent of furunculosis. In this study, we evaluate potential mechanisms associated with disease susceptibility from combined environmental factors of dietary PAH exposure and pathogen challenge. Rainbow trout were fed a mixture of ten high molecular weight PAHs at an environmentally relevant concentration (7.82µg PAH mixture/g fish/day) or control diet for 50 days. After 50 days of PAH exposure, fish were challenged with either Aeromonas salmonicida at a lethal concentration 30 (LC30) or growth media without the pathogen (mock challenge). Head kidneys were collected 2, 4, 10 and 20 days after challenge and gene expression (q<0.05) was evaluated among treatments. In animals fed the PAH contaminated diet, we observed down-regulation of expression for innate immune system genes in pathways (p<0.05) for the terminal steps of the complement cascade (complement component C6) and other bacteriolytic processes (lysozyme type II) potentially underlying increased disease susceptibility after pathogen challenge. Increased expression of genes associated with hemorrhage/tissue remodeling/inflammation pathways (p<0.05) was likely related to more severe head kidney damage due to infection in PAH-fed compared to control-fed fish. This study is the first to evaluate transcriptional signatures associated with the impact of chronic exposure to an environmentally relevant mixture of PAHs in disease susceptibility and immunity.

Using fluorescent aromatic compounds in bile from juvenile salmonids to predict exposure to polycyclic aromatic hydrocarbons.

We provide data from four different studies in which fish were fed polycyclic aromatic hydrocarbons (PAHs) that were used to develop a predictive relationship between dose (mug/g fish/d) and metabolites of PAHs in bile. Juvenile salmonids were fed various doses of total PAH that were applied as a mixture to fish pellets. The number of PAHs in each mixture ranged from 10 to 21 different low- and high-molecular-weight compounds, and their relative proportions and abundance were based on stomach concentrations observed for field-collected fish. Although we examined both the phenanthrene (PHN) and benzo[a]pyrene signals for the fluorescent aromatic compounds (FACs) in bile, the PHN signal exhibited the highest correlation and was considered to be the better choice for predicting exposure. A large database of PHN FAC values for field-collected fish was examined and used to predict dose by the method of inverse prediction. The goal of the present study was to develop a predictive relationship that would allow estimation of an exposure dose for an observed value of PHN FACs from juvenile salmonids sampled in the field. This dose would then be used to estimate adverse effects based on toxicity results from laboratory studies. Additional analyses were performed to determine ventilation doses from water concentrations of total PAH and then relate those to PHN FAC values.

Dibenzo[a,l]pyrene induced DNA adduct formation in lung tissue in vivo.

Polycyclic aromatic hydrocarbons (PAHs) are environmental carcinogens present in the atmosphere from combustion sources such as cigarette smoke, diesel exhaust, residential heating processes, and industrial coke production. To date, dibenzo[a,l]pyrene (DBP) has been found to be the strongest tumor-initiating PAH ever tested in rodent skin and mammary tumor models. Here we show for the first time that systemic exposure to DBP causes DNA damage in mouse lung tissue. C57BL/6 mice were gavaged with 1, 5 or 20 mg DBP/kg body weight, daily for 10 days. Toxicity of DBP was revealed by a decrease in body and organ weight of mice while no apparent cell death was observed on P815 mastocytoma cells (allograft model) in vitro. However, treatment of P815 cells in vitro with the ultimate carcinogenic metabolite of DBP, the fjord region (-)-anti-11,12-diol 13,14-epoxide [(-)-anti-DBPDE], resulted in the total loss of cell viability. Lungs from the animals were removed and subjected to DBP-DNA adduct analysis. A dose dependent adduct formation was revealed by 33P-postlabeling analysis of DNA from lung tissue. The majority of DNA adducts formed in lungs of mice after systemic exposure to DBP were contributed by (-)-anti-DBPDE. The data from this in vivo model are consistent with previous metabolic activation results obtained with DBP in human cells in culture.

An evaluation of the influence of stock origin and out-migration history on the disease susceptibility and survival of juvenile Chinook salmon.

Various methods have been developed to mitigate the adverse effects of the Federal Columbia River Power System on juvenile Pacific salmon out-migrating through the Columbia River basin. In this study, we found that hatchery-reared spring Chinook salmon Oncorhynchus tshawytscha in the river are in varying degrees of health, which may affect delayed mortality and the assessment of the effectiveness of management actions to recover listed stocks (e.g., barging fish downstream versus leaving fish in the river). A laboratory disease challenge with Listonella anguillarum was completed on fish from Rapid River Hatchery and Dworshak National Fish Hatchery (NFH) with different out-migration histories: (1) transported by barge, (2) removed from the river before barging, or (3) left to travel in-river. Barged fish from Rapid River Hatchery experienced less mortality than fish from Dworshak NFH. No statistical differences were found between the hatcheries with fish that had in-river out-migration histories. We suggest that the stressors and low survival associated with out-migration through the hydropower system eliminated any differences that could have been present. However, 18-25% of the fish that were barged or collected before barging died in the laboratory before the disease challenge, compared with less than 2% of those that traveled in-river. Owing to disproportionate prechallenge mortality, the disease-challenged populations may have been biased; thus, they were also considered together with the prechallenge mortalities. The synthesis of prechallenge and disease-challenged mortalities and health characteristics evaluated during out-migration indicated that the benefit of barging was not consistent between the hatcheries. This finding agrees with adult survival and delayed mortality estimates for the individual hatcheries determined from adult returns. The results suggest that the health status of fish and their history before entering the hydropower system (hatchery of origin and out-migration path) are critical variables affecting the conclusions drawn from studies that evaluate mitigation strategies.

Disease susceptibility of salmon exposed to polybrominated diphenyl ethers (PBDEs).

The health effects of the flame retardant polybrominated diphenyl ethers (PBDEs) in fish are not well understood. To determine the potential effects of this ubiquitous contaminant class on fish health, juvenile subyearling Chinook salmon (Oncorhynchus tshawytscha) were fed a diet that reflected the PBDE congeners found in the stomach contents of subyearling Chinook salmon collected from the highly urbanized and industrialized lower Willamette River in the Columbia River Basin of North America. The diet, consisting of five PBDE congeners (BDE-47, BDE-99, BDE-100, BDE-153 and BDE-154), was fed to the salmon at 2% of their body weight in food per day for 40 days. Two concentrations of the diet (1x and 10x PBDE) were fed to the salmon. The 1x PBDE diet reflected the concentration of PBDEs (190 ng PBDEs/g food) found in the stomach contents of juvenile subyearling Chinook salmon; the 10x diet was prepared at 10 times that concentration. The fish were then exposed to the marine bacterial pathogen Listonella anguillarum to assess susceptibility to infectious disease. Juvenile Chinook salmon fed the 1x PBDE diet were more susceptible to L. anguillarum than salmon fed the control diet. This suggests that juvenile salmonids in the lower Willamette River exposed to PBDEs may be at greater risk for disease than nonexposed juvenile salmonids. In contrast, salmon that consumed the 10x PBDE diet were not more susceptible to the pathogen than salmon fed the control diet. The mechanisms for the dichotomous results observed in disease susceptibility between salmon fed the 1x and 10x PBDE diets are currently not known but have also been observed in other species exposed to PBDEs with respect to immune function.