Related Experiment Videos
Induction of microsomal epoxide hydrolase activity in inbred mice by chronic phenytoin exposure
J K Hartsfield1, S A Benford, D R Hilbelink
1Department of Oral Facial Development, Indiana University, Indianapolis 46202-5186, USA.
Abstract:
A lower microsomal epoxide hydrolase (mEH) activity has been associated with increased likelihood of fetal hydantoin syndrome. While phenytoin anticonvulsive regimens are long-term, there are no data regarding induction of mEH by chronic phenytoin exposure. Two inbred mouse strains which differ in their susceptibility (A/J > C57BL/6J) to phenytoin-induced oral clefting were treated with an oral gavage of phenytoin for 14 consecutive days. The mice were sacrificed on the 15th day, and hepatic microsomes were prepared. mEH activity was determined using benzo[a]pyrene-4,5-oxide. The dihydrodiol product was separated by HPLC and quantified. There was no significant difference (P = 0.15) in the phenytoin plasma level between the two strains on Day 15. There was no significant difference (P = 0.07) between control and sham control groups within each strain, so they were combined for further analysis. There was a significant strain difference (P = 0.0001) between the control and phenytoin-exposed group means, with the C57BL/6J strain having the greater activity before and after phenytoin exposure. The A/J phenytoin-exposed group activity was 51% higher (P = 0.01) than the A/J control, while the C57BL/6J phenytoin-exposed group activity was 78% higher (P = 0.001) than the C57BL/6J control. The greater mEH activity in the phenytoin-induced clefting resistant strain (C57BL/6J) before and after phenytoin exposure is consistent with a putative oxidative metabolism mechanism of phenytoin teratogenecity. Chronic phenytoin exposure induced mEH activity in both strains, although the strain with the greater enzyme activity prior to the exposure continued to have the greater activity following induction.
Insights
Chronic phenytoin exposure increases microsomal epoxide hydrolase (mEH) activity in mice. Higher baseline mEH activity correlates with resistance to phenytoin-induced birth defects, suggesting a protective metabolic pathway.
Area of Science:
- Pharmacology
- Toxicology
- Biochemistry
Background:
- Lower microsomal epoxide hydrolase (mEH) activity is linked to increased fetal hydantoin syndrome risk.
- Phenytoin is a long-term anticonvulsant, but its effect on mEH activity with chronic exposure is unknown.
Purpose of the Study:
- To investigate the induction of mEH activity by chronic phenytoin exposure in mice.
- To explore the relationship between mEH activity and phenytoin-induced teratogenicity.
Main Methods:
- Two inbred mouse strains (A/J and C57BL/6J) with differing phenytoin susceptibility were gavaged with phenytoin for 14 days.
- Hepatic microsomes were isolated on day 15, and mEH activity was measured using benzo[a]pyrene-4,5-oxide.
- Phenytoin plasma levels and mEH activity were quantified via HPLC.
Main Results:
- Phenytoin plasma levels did not differ significantly between strains on day 15.
- Both strains showed significantly increased mEH activity after chronic phenytoin exposure.
- The C57BL/6J strain, more resistant to phenytoin-induced clefting, exhibited higher mEH activity both before and after exposure compared to A/J mice.
Conclusions:
- Chronic phenytoin exposure induces mEH activity in mice.
- Higher baseline mEH activity is associated with resistance to phenytoin-induced oral clefting.
- These findings suggest that mEH-mediated oxidative metabolism plays a role in phenytoin teratogenicity.