Immunohistochemical localization of the cytochrome P450 isozymes LMC2 and LM4B (P4501A1) in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated zebrafish (Brachydanio rerio).

Dibenzo-p-dioxins are persistent pollutants in our environment that exert a variety of biological and toxic effects in various species, in particular developmental toxicity in fish. Using zebrafish (Brachydanio rerio) as a model system, we analyzed the expression and inducibility of a constitutive isozyme (LMC2) and a dioxin-inducible isozyme (LM4B or P4501A1) of cytochrome (cyt.) P450 in different organs by immunohistochemical techniques. In untreated zebrafish, LMC2 was constitutively expressed at high levels in the liver, kidney, skin, and oral mucosa, while moderate expression was detected in gills, pseudobranch, intestine, and ovaries. LM4B was either not expressed in these organs or was found at comparatively low levels. After treatment of zebrafish with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; total dose of 15 ng per fish), LM4B expression was strongly induced in livers and kidneys and less pronounced in gills and pseudobranches, whereas no or only marginal induction was seen in skin, intestine, oral mucosa, and ovaries. In addition, cyt. P450 catalyzed 7-ethoxyresorufin-O-deethylation and phenol UDP-glucuronosyltransferase activity were also found to be inducible in liver and kidney. Our results demonstrate that zebrafish respond to inducing stimuli of TCDD in a fashion similar to that observed with related compounds in other fish species, suggesting that zebrafish may be a useful experimental model for studying biological and toxic effects of TCDD and other environmental pollutants in fish.