Interactions between xenoestrogens and ketoconazole on hepatic CYP1A and CYP3A, in juvenile Atlantic cod (Gadus morhua)

Abstract

BACKGROUND: Xenoestrogens and antifungal azoles probably share a common route of metabolism, through hepatic cytochrome P450 (CYP) enzymes. Chemical interactions with metabolic pathways may affect clearance of both xenobiotics and endobiotics. This study was carried out to identify possible chemical interactions by those substances on CYP1A and CYP3A, in Atlantic cod liver. We investigated effects of two xenoestrogens (nonylphenol and ethynylestradiol) and of the model imidazole ketoconazole, alone and in combination. RESULTS: Treatment with ketoconazole resulted in 60% increase in CYP1A-mediated ethoxyresorufin-O-deethylase (EROD) activity. Treatment with nonylphenol resulted in 40% reduction of CYP1A activity. Combined exposure to ketoconazole and nonylphenol resulted in 70% induction of CYP1A activities and 93% increase in CYP1A protein levels. Ketoconazole and nonylphenol alone or in combination had no effect on CYP3A expression, as analyzed by western blots. However, 2-dimensional (2D) gel electrophoresis revealed the presence of two CYP3A-immunoreactive proteins, with a more basic isoform induced by ketoconazole. Treatment with ketoconazole and nonylphenol alone resulted in 54% and 35% reduction of the CYP3A-mediated benzyloxy-4-[trifluoromethyl]-coumarin-O-debenzyloxylase (BFCOD) activity. Combined exposure of ketoconazole and nonylphenol resulted in 98% decrease in CYP3A activity. This decrease was greater than the additive effect of each compound alone. In vitro studies revealed that ketoconazole was a potent non-competitive inhibitor of both CYP1A and CYP3A activities and that nonylphenol selectively non-competitively inhibited CYP1A activity. Treatment with ethynylestradiol resulted in 46% decrease in CYP3A activity and 22% decrease in protein expression in vivo. In vitro inhibition studies in liver microsomes showed that ethynylestradiol acted as a non-competitive inhibitor of CYP1A activity and as an uncompetitive inhibitor of CYP3A activity. CONCLUSIONS: Ketoconazole, nonylphenol and ethynylestradiol all interacted with CYP1A and CYP3A activities and protein expression in Atlantic cod. However, mechanisms of interactions on CYP1A and CYP3A differ between theses substances and combined exposure had different effects than exposure to single compounds. Thus, CYP1A and CYP3A mediated clearance may be impaired in situations of mixed exposure to those types of compounds.

Figure 1

A) In vivo CYP1A enzyme activities (A) and in vivo CYP1A protein expression (B). CYP1A enzyme activities and protein expression in juvenile Atlantic cod exposed in vivo to vehicle (5 ml peanut oil/kg fish), ketoconazole (12 mg/kg fish), nonylphenol (25 mg/kg fish), ethynylestradiol (5 mg/kg fish) and ketoconazole + nonylphenol (12 + 25 mg/kg fish). A) EROD activities. B) CYP1A protein levels analyzed using PAb against rainbow trout CYP1A. Each bar represents mean values of eight to nine fish ± SD; ^aSignificantly different from vehicle treated fish; ^bSignificantly different from ketoconazole+nonylphenol treated fish; P < 0.05.

Figure 2

In vivo CYP3A enzyme activities (A) and in vivo CYP3A protein expression (B). CYP3A enzyme activities and protein expression in juvenile Atlantic cod exposed in vivo to vehicle (5 ml peanut oil/kg fish), ketoconazole (12 mg/kg fish), nonylphenol (25 mg/kg fish), ethynylestradiol (5 mg/kg fish) and ketoconazole + nonylphenol (12 + 25 mg/kg fish). A) BFCOD activities. B) CYP3A protein levels analyzed using PAb against rainbow trout CYP3A. Each bar represents mean values of eight to nine fish ± SD; ^aSignificantly different from vehicle treated fish; ^bSignificantly different from ketoconazole+nonylphenol treated fish; P < 0.05.

Figure 3

CYP3A Western blot (A) and CYP3A 2D-immunoblots (B). A) Western blot of hepatic microsomal CYP3A proteins in juvenile Atlantic cod treated with vehicle (5 ml peanut oil/kg fish) and ketoconazole (12 mg/kg fish) detected using PAb against rainbow trout CYP3A. B) 2D-gel electrophoresis followed by immunoblotting using PAb against rainbow trout CYP3A. Each blot represent pooled liver microsomes of eight to nine fish for each treatment; vehicle (5 ml peanut oil/kg fish), ketoconazole (12 mg/kg fish), nonylphenol (25 mg/kg fish), ethynylestradiol (5 mg/kg fish), ketoconazole + nonylphenol (12 + 25 mg/kg fish).

Figure 4

Non-competitive inhibition of CYP1A by ketoconazole (A) and non-competitive inhibition of CYP3A by ketoconazole (B). Dixon plots for ketoconazole on A) EROD activity (diamonds represent 8.2; squares represent 25 and triangles represent 677 pM ethoxyresorufin). B) BFCOD activity (diamonds represent 48; squares represent 84 and triangles represent 200 μM BFC).

Figure 5

Non-competitive inhibition of CYP1A by ethynylestradiol (A) and uncompetitive inhibition of CYP3A by ethynylestradiol (B). Dixon plots for ethynylestradiol on A) EROD activity (diamonds represent 8.2; squares represent 25 and triangles represents 677 pM ethoxyresorufin). B) BFCOD activity (diamonds represent 200; squares represent 267 and triangles represents 356 μM BFC).

Figure 6

CYP3A Western blot after in vivo incubation. Western blot of CYP3A proteins in pooled liver microsomes from Atlantic cod detected using PAb against rainbow trout CYP3A. The blot illustrates representative samples after in vitro incubation with 1.0 μM ketoconazole and 50 μM ethynylestradiol for 30 or 60 min.