Gender-specific induction of cytochrome P450s in nonylphenol-treated FVB/NJ mice

Abstract

Nonylphenol (NP) is a breakdown product of nonylphenol ethoxylates, which are used in a variety of industrial, agricultural, household cleaning, and beauty products. NP is one of the most commonly found toxicants in the United States and Europe and is considered a toxicant of concern because of its long half-life. NP is an environmental estrogen that also activates the pregnane X-receptor (PXR) and in turn induces P450s. No study to date has examined the gender-specific effects of NP on hepatic P450 expression. We provided NP at 0, 50 or 75 mg/kg/day for 7 days to male and female FVB/NJ mice and compared their P450 expression profiles. Q-PCR was performed on hepatic cDNA using primers to several CYP isoforms regulated by PXR or its relative, the constitutive androstane receptor (CAR). In female mice, NP induced Cyp2b10 and Cyp2b13, and downregulated the female-specific P450s, Cyp3a41 and Cyp3a44. In contrast, male mice treated with NP showed increased expression of Cyp2a4, Cyp2b9, and Cyp2b10. Western blots confirmed induction of Cyp2b subfamily members in both males and females. Consistent with the Q-PCR data, Western blots showed dose-dependent downregulation of Cyp3a only in females and induction of Cyp2a only in males. The overall increase in female-predominant P450s in males (Cyp2a4, 2b9) and the decrease in female-predominant P450s in females (Cyp3a41, 3a44) suggest that NP is in part feminizing the P450 profile in males and masculinizing the P450 profile in females. Testosterone hydroxylation was also altered in a gender-specific manner, as testosterone 16alpha-hydroxylase activity was only induced in NP-treated males. In contrast, NP-treated females demonstrated a greater propensity for metabolizing zoxazolamine probably due to greater Cyp2b induction in females. In conclusion, NP causes gender-specific P450 induction and therefore exposure to NP may cause distinct pharmacological and toxicological effects in males compared to females.

Fig. 1

FVB/NJ female and male mice treated with NP showed sexually dimorphic changes in P450 expression as determined by Q-PCR. Q-PCR was performed as described in the Materials and methods. Data are expressed as mean ± SD (n = 4–5) for each of the different P450s in males and females (a–i). Relative mean differential expression compared to the controls is reported above the columns in each graph. An asterisk indicates a significant difference from the untreated mice by ANOVA followed with Fisher's PLSD as the post hoc test (P < 0.05).

Fig. 2

Western blots of hepatic microsomes from NP treated FVB/NJ male and female mice. Western blots were performed and visualized as described in the Materials and methods. Blots were quantified densitometrically and the relative mean differential expression as compared to the controls is reported above the blots. An asterisk indicates a significant difference from the untreated mice by ANOVA followed with Fisher's PLSD as the post hoc test (P < 0.05).

Fig. 3

Relative testosterone hydroxylase activities in male (A) and female (B) hepatic mouse microsomes following in vivo treatment with nonylphenol. Data are presented as mean ± SD. An asterisk indicates a significant difference from the untreated mice by ANOVA followed with Fisher's PLSD as the post hoc test (P < 0.05).

Fig. 4

Zox-induced paralysis in treated mice. NP significantly decreased paralysis time in male and female mice. The graph shows the paralysis time for each mouse. The individual mice in each treatment group are shown from left-to-right with increasing paralysis time, with d indicating the mouse remained paralyzed for more than 8 h (females) or 6 h (males) and was euthanized. The statistical analysis for Fig. 4 is shown in Table 4.