Tissue specificity of aryl hydrocarbon receptor (AhR) mediated responses and relative sensitivity of white sturgeon (Acipenser transmontanus) to an AhR agonist

Sturgeons are endangered in some parts of the world. Due to their benthic nature and longevity sturgeon are at greater risk of exposure to bioaccumulative contaminants such as dioxin-like compounds that are associated with sediments. Despite their endangered status, little research has been conducted to characterize the relative responsiveness of sturgeon to dioxin-like compounds. In an attempt to study the biological effects and possible associated risks of exposure to dioxin-like compounds in sturgeon, the molecular and biochemical responses of white sturgeon (Acipenser transmontanus) to a model aryl hydrocarbon receptor (AhR) agonist, β-naphthoflavone (βNF) were investigated. White sturgeon were injected intraperitoneally with one of three doses of βNF (0, 50, or 500 mg/kg, bw). Rainbow trout (Oncorhynchus mykiss) were used as a reference species since their responses have been well characterized in the past. Three days following injection with βNF, fish were euthanized and livers, gills, and intestines collected for biochemical and molecular analyses. White sturgeon exposed to βNF had significantly greater ethoxyresorufin O-deethylase (EROD) activity in liver (up to 37-fold), gill (up to 41-fold), and intestine (up to 36-fold) than did unexposed controls. Rainbow trout injected with βNF exhibited EROD activity that was significantly greater in liver (88-fold), than that of controls, but was undetectable in gills or intestine. Abundance of CYP1A transcript displayed a comparable pattern of tissue-specific induction with intestine (up to 189-fold), gills (up to 53-fold), and liver (up to 21-fold). Methoxyresorufin O-deethylase (MROD) and pentoxyresorufin O-deethylase (PROD) activities were undetectable in unexposed white sturgeon tissues while exposed tissues displayed MROD activity that was only moderately greater than the activity that could be detected. Differential inducibility among liver, gill, and intestine following exposure to an AhR agonist is likely associated with tissue-specific regulation of the AhR signalling pathway. Liver and gill of white sturgeon had significantly greater AhR transcript abundance than did the intestine, however following exposure to βNF, significantly greater induction in AhR transcript abundance was detected in intestine (up to 35-fold) compared to liver (up to 5-fold) or gills (up to 11-fold). It was shown that white sturgeon are responsive to AhR agonists in the liver, gill, and intestine and could be among the more sensitive fish species with regard to inducibility of CYP1A.

► Induction of EROD activity was observed in liver, intestine, and gills of white sturgeon, however EROD activity was not observed in intestine or gills of rainbow trout.
► Basal EROD activity and abundance of CYP1A transcript was greatest in the liver, however the intestine and gills had greater induction.
► Basal abundance of AhR transcript was greatest in the liver, however the intestine and gills had greater induction.
► White sturgeon are among the most responsive of studied fish species outside of the salmonids with regards to inducibility of CYP1A.