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Species-specific regulation of PXR/CAR/ER-target genes in the mouse and rat liver elicited by o, p'-DDT.

Kiyosawa N, Kwekel JC, Burgoon LD, Dere E, Williams KJ, Tashiro C, Chittim B, Zacharewski TR - BMC Genomics (2008)

Bottom Line: In addition, o, p'-DDT induced Gadd45a, Gadd45b and Cdkn1, suggesting DNA damage may be an additional risk factor.Although DDT is known to cause rodent hepatic tumors, the marked species differences in PXR/CAR structure, expression patterns and ligand preference as well as significant species-specific differences in steroidogenesis, especially CYP17A1 expression and activity, confound the extrapolation of these results to humans.Nevertheless, the identification of potential modes of action as well as species-specific responses may assist in the selection and further development of more appropriate models for assessing the toxicity of DDT to humans and wildlife.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan, USA. kiyosawa.naoki.wr@daiichisankyo.co.jp

ABSTRACT

Background: Dichlorodiphenyltrichloroethane (DDT) is a persistent estrogenic organochlorine pesticide that is a rodent hepatic tumor promoter, with inconclusive carcinogenicity in humans. We have previously reported that o, p'-DDT elicits primarily PXR/CAR-mediated activity, rather than ER-mediated hepatic responses, and suggested that CAR-mediated effects, as opposed to ER-mediated effects, may be more important in tumor promotion in the rat liver. To further characterize species-specific hepatic responses, gene expression analysis, with complementary histopathology and tissue level analyses were investigated in immature, ovariectomized C57BL/6 mice treated with 300 mg/kg o, p'-DDT, and compared to Sprague-Dawley rat data.

Results: Rats and mice exhibited negligible histopathology with rapid o, p'-DDT metabolism. Gene expression profiles were also similar, exhibiting PXR/CAR regulation with the characteristic induction of Cyp2b10 and Cyp3a11. However, PXR-specific target genes such as Apoa4 or Insig2 exhibited more pronounced induction compared to CAR-specific genes in the mouse. In addition, mouse Car mRNA levels decreased, possibly contributing to the preferential activation of mouse PXR. ER-regulated genes Cyp17a1 and Cyp7b1 were also induced, suggesting o, p'-DDT also elicits ER-mediated gene expression in the mouse, while ER-mediated effects were negligible in the rat, possibly due to the inhibitory effects of CAR on ER activities. In addition, o, p'-DDT induced Gadd45a, Gadd45b and Cdkn1, suggesting DNA damage may be an additional risk factor. Furthermore, elevated blood DHEA-S levels at 12 h after treatment in the mouse may also contribute to the endocrine-related effects of o, p'-DDT.

Conclusion: Although DDT is known to cause rodent hepatic tumors, the marked species differences in PXR/CAR structure, expression patterns and ligand preference as well as significant species-specific differences in steroidogenesis, especially CYP17A1 expression and activity, confound the extrapolation of these results to humans. Nevertheless, the identification of potential modes of action as well as species-specific responses may assist in the selection and further development of more appropriate models for assessing the toxicity of DDT to humans and wildlife.

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Species-specific regulation of steroid hormone metabolism elicited by o, p'-DDT. (A) Overview of the role of CYP17A1 and CYP7B1 in steroid metabolism. CYP17A1 metabolizes pregnenolone and progesterone to produce DHEA and androstenedione, respectively. Hepatic CYP7B1 is involved in bile acid biosynthesis, and also responsible for 7α-hydroxylation of DHEA. (B) Hepatic Cyp17a1 and (C) Cyp7b1 mRNA levels in the o, p'-DDT-treated mouse and rat. QRT-PCR results relative to time-matched vehicle controls are shown as bars and presented as mean ± SE. Microarray results are represented as lines. o, p'-DDT induced Cyp17a1 and Cyp7b1 mRNAs in the mouse liver, while it did not affect in the rat liver [11]. The dashed line indicates the expression level of the time-matched vehicle control. The asterisk (*) indicates a significant (p < 0.05) difference from the time-matched vehicle controls for QRT-PCR, n = 5. (C) Representative Western analysis result for hepatic CYP17A1 protein in o, p'-DDT-treated mouse liver. CYP17A1 protein levels were induced at 18 and 24 h. Western analyses were performed on 3 independent biological replicates to verify the consistency of the results. C, control; T, 300 mg/kg o, p'-DDT. (D) Blood DHEA-S levels. DHEA-S level was significantly higher at 12 h following o, p'-DDT treatment compared to time-matched controls in the mouse, while it did not change in rats.
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Figure 4: Species-specific regulation of steroid hormone metabolism elicited by o, p'-DDT. (A) Overview of the role of CYP17A1 and CYP7B1 in steroid metabolism. CYP17A1 metabolizes pregnenolone and progesterone to produce DHEA and androstenedione, respectively. Hepatic CYP7B1 is involved in bile acid biosynthesis, and also responsible for 7α-hydroxylation of DHEA. (B) Hepatic Cyp17a1 and (C) Cyp7b1 mRNA levels in the o, p'-DDT-treated mouse and rat. QRT-PCR results relative to time-matched vehicle controls are shown as bars and presented as mean ± SE. Microarray results are represented as lines. o, p'-DDT induced Cyp17a1 and Cyp7b1 mRNAs in the mouse liver, while it did not affect in the rat liver [11]. The dashed line indicates the expression level of the time-matched vehicle control. The asterisk (*) indicates a significant (p < 0.05) difference from the time-matched vehicle controls for QRT-PCR, n = 5. (C) Representative Western analysis result for hepatic CYP17A1 protein in o, p'-DDT-treated mouse liver. CYP17A1 protein levels were induced at 18 and 24 h. Western analyses were performed on 3 independent biological replicates to verify the consistency of the results. C, control; T, 300 mg/kg o, p'-DDT. (D) Blood DHEA-S levels. DHEA-S level was significantly higher at 12 h following o, p'-DDT treatment compared to time-matched controls in the mouse, while it did not change in rats.

Mentions: For example, Cyp17a1, a key enzyme gene for steroidogenesis (Fig. 4A) fell into the lower left quadrant (Fig. 3C) suggesting divergent gene expression profiles in the mouse and rat. Fig. 4B clearly demonstrates that Cyp17a1 is significantly induced in the mouse and is non-responsive in the rat in both microarray and QRT-PCR data. Cyp7b1, another steroid metabolism gene, exhibited a similar species-specific gene expression profile (Fig 4B). Moreover, hepatic CYP17A1 protein induction was evident at 18 and 24 h in the mouse liver (Fig. 4C).


Species-specific regulation of PXR/CAR/ER-target genes in the mouse and rat liver elicited by o, p'-DDT.

Kiyosawa N, Kwekel JC, Burgoon LD, Dere E, Williams KJ, Tashiro C, Chittim B, Zacharewski TR - BMC Genomics (2008)

Species-specific regulation of steroid hormone metabolism elicited by o, p'-DDT. (A) Overview of the role of CYP17A1 and CYP7B1 in steroid metabolism. CYP17A1 metabolizes pregnenolone and progesterone to produce DHEA and androstenedione, respectively. Hepatic CYP7B1 is involved in bile acid biosynthesis, and also responsible for 7α-hydroxylation of DHEA. (B) Hepatic Cyp17a1 and (C) Cyp7b1 mRNA levels in the o, p'-DDT-treated mouse and rat. QRT-PCR results relative to time-matched vehicle controls are shown as bars and presented as mean ± SE. Microarray results are represented as lines. o, p'-DDT induced Cyp17a1 and Cyp7b1 mRNAs in the mouse liver, while it did not affect in the rat liver [11]. The dashed line indicates the expression level of the time-matched vehicle control. The asterisk (*) indicates a significant (p < 0.05) difference from the time-matched vehicle controls for QRT-PCR, n = 5. (C) Representative Western analysis result for hepatic CYP17A1 protein in o, p'-DDT-treated mouse liver. CYP17A1 protein levels were induced at 18 and 24 h. Western analyses were performed on 3 independent biological replicates to verify the consistency of the results. C, control; T, 300 mg/kg o, p'-DDT. (D) Blood DHEA-S levels. DHEA-S level was significantly higher at 12 h following o, p'-DDT treatment compared to time-matched controls in the mouse, while it did not change in rats.
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Figure 4: Species-specific regulation of steroid hormone metabolism elicited by o, p'-DDT. (A) Overview of the role of CYP17A1 and CYP7B1 in steroid metabolism. CYP17A1 metabolizes pregnenolone and progesterone to produce DHEA and androstenedione, respectively. Hepatic CYP7B1 is involved in bile acid biosynthesis, and also responsible for 7α-hydroxylation of DHEA. (B) Hepatic Cyp17a1 and (C) Cyp7b1 mRNA levels in the o, p'-DDT-treated mouse and rat. QRT-PCR results relative to time-matched vehicle controls are shown as bars and presented as mean ± SE. Microarray results are represented as lines. o, p'-DDT induced Cyp17a1 and Cyp7b1 mRNAs in the mouse liver, while it did not affect in the rat liver [11]. The dashed line indicates the expression level of the time-matched vehicle control. The asterisk (*) indicates a significant (p < 0.05) difference from the time-matched vehicle controls for QRT-PCR, n = 5. (C) Representative Western analysis result for hepatic CYP17A1 protein in o, p'-DDT-treated mouse liver. CYP17A1 protein levels were induced at 18 and 24 h. Western analyses were performed on 3 independent biological replicates to verify the consistency of the results. C, control; T, 300 mg/kg o, p'-DDT. (D) Blood DHEA-S levels. DHEA-S level was significantly higher at 12 h following o, p'-DDT treatment compared to time-matched controls in the mouse, while it did not change in rats.
Mentions: For example, Cyp17a1, a key enzyme gene for steroidogenesis (Fig. 4A) fell into the lower left quadrant (Fig. 3C) suggesting divergent gene expression profiles in the mouse and rat. Fig. 4B clearly demonstrates that Cyp17a1 is significantly induced in the mouse and is non-responsive in the rat in both microarray and QRT-PCR data. Cyp7b1, another steroid metabolism gene, exhibited a similar species-specific gene expression profile (Fig 4B). Moreover, hepatic CYP17A1 protein induction was evident at 18 and 24 h in the mouse liver (Fig. 4C).

Bottom Line: In addition, o, p'-DDT induced Gadd45a, Gadd45b and Cdkn1, suggesting DNA damage may be an additional risk factor.Although DDT is known to cause rodent hepatic tumors, the marked species differences in PXR/CAR structure, expression patterns and ligand preference as well as significant species-specific differences in steroidogenesis, especially CYP17A1 expression and activity, confound the extrapolation of these results to humans.Nevertheless, the identification of potential modes of action as well as species-specific responses may assist in the selection and further development of more appropriate models for assessing the toxicity of DDT to humans and wildlife.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan, USA. kiyosawa.naoki.wr@daiichisankyo.co.jp

ABSTRACT

Background: Dichlorodiphenyltrichloroethane (DDT) is a persistent estrogenic organochlorine pesticide that is a rodent hepatic tumor promoter, with inconclusive carcinogenicity in humans. We have previously reported that o, p'-DDT elicits primarily PXR/CAR-mediated activity, rather than ER-mediated hepatic responses, and suggested that CAR-mediated effects, as opposed to ER-mediated effects, may be more important in tumor promotion in the rat liver. To further characterize species-specific hepatic responses, gene expression analysis, with complementary histopathology and tissue level analyses were investigated in immature, ovariectomized C57BL/6 mice treated with 300 mg/kg o, p'-DDT, and compared to Sprague-Dawley rat data.

Results: Rats and mice exhibited negligible histopathology with rapid o, p'-DDT metabolism. Gene expression profiles were also similar, exhibiting PXR/CAR regulation with the characteristic induction of Cyp2b10 and Cyp3a11. However, PXR-specific target genes such as Apoa4 or Insig2 exhibited more pronounced induction compared to CAR-specific genes in the mouse. In addition, mouse Car mRNA levels decreased, possibly contributing to the preferential activation of mouse PXR. ER-regulated genes Cyp17a1 and Cyp7b1 were also induced, suggesting o, p'-DDT also elicits ER-mediated gene expression in the mouse, while ER-mediated effects were negligible in the rat, possibly due to the inhibitory effects of CAR on ER activities. In addition, o, p'-DDT induced Gadd45a, Gadd45b and Cdkn1, suggesting DNA damage may be an additional risk factor. Furthermore, elevated blood DHEA-S levels at 12 h after treatment in the mouse may also contribute to the endocrine-related effects of o, p'-DDT.

Conclusion: Although DDT is known to cause rodent hepatic tumors, the marked species differences in PXR/CAR structure, expression patterns and ligand preference as well as significant species-specific differences in steroidogenesis, especially CYP17A1 expression and activity, confound the extrapolation of these results to humans. Nevertheless, the identification of potential modes of action as well as species-specific responses may assist in the selection and further development of more appropriate models for assessing the toxicity of DDT to humans and wildlife.

Show MeSH
Related in: MedlinePlus