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Coordinate induction of peroxisomal beta-oxidation activity and cytosolic epoxide hydrolase activity
Abstract:
The effect of four hypolipidemic compounds (tiadenol, clofibrate, acetylsalicylic acid, 1-benzylimidazole) on the specific activities of peroxisomal beta-oxidation and cytosolic and microsomal epoxide hydrolase of rat liver was investigated. Since specific activity of cytosolic epoxide hydrolase from outbred Sprague-Dawley rats showed large interindividual variations (approximately 38-fold), induction studies were performed with inbred Fischer F-344 rats, which showed only low interindividual variations (approximately 2-fold). Clofibrate, tiadenol and acetylsalicylic acid caused a 8-, 13- and 4.5-fold induction of cEH and a 13-, 19- and 5-fold induction of peroxisomal beta-oxidation activity, respectively. Microsomal epoxide hydrolase activity was only slightly increased (less than 1.5-fold). 1-Benzylimidazole induced both cytosolic epoxide hydrolase and peroxisomal beta-oxidation activity about 2-fold, whereas microsomal epoxide hydrolase activity was increased about 4-fold. Increase in cytosolic epoxide hydrolase activity was not due to enzyme activation as demonstrated by in vitro studies. On the other hand, these in vitro studies showed that the increase in microsomal epoxide hydrolase activity by 1-benzylimidazole may partially be due to activation of the enzyme.
Insights
Four hypolipidemic compounds significantly induced peroxisomal beta-oxidation and cytosolic epoxide hydrolase (cEH) in rat liver. Clofibrate, tiadenol, and acetylsalicylic acid showed substantial induction, while 1-benzylimidazole had a moderate effect on cEH and a notable effect on microsomal epoxide hydrolase.
Area of Science:
- Biochemistry
- Pharmacology
- Toxicology
Background:
- Investigating the effects of hypolipidemic compounds on liver enzyme activity is crucial for understanding their metabolic impact.
- Cytosolic epoxide hydrolase (cEH) activity exhibits significant interindividual variations in Sprague-Dawley rats, necessitating the use of inbred Fischer F-344 rats for reliable induction studies.
Purpose of the Study:
- To determine the impact of four hypolipidemic compounds—tiadenol, clofibrate, acetylsalicylic acid, and 1-benzylimidazole—on the specific activities of rat liver peroxisomal beta-oxidation, cytosolic epoxide hydrolase (cEH), and microsomal epoxide hydrolase (mEH).
- To elucidate the mechanisms underlying changes in enzyme activity, distinguishing between enzyme induction and activation.
Main Methods:
- Enzyme activity assays were performed on rat liver homogenates to measure peroxisomal beta-oxidation, cEH, and mEH.
- Induction studies were conducted using inbred Fischer F-344 rats to minimize interindividual variations in cEH activity.
- In vitro studies were utilized to assess whether observed increases in enzyme activity were due to enzyme activation or de novo synthesis.
Main Results:
- Clofibrate, tiadenol, and acetylsalicylic acid significantly induced both cEH (8-, 13-, and 4.5-fold, respectively) and peroxisomal beta-oxidation (13-, 19-, and 5-fold, respectively).
- 1-Benzylimidazole moderately induced cEH and peroxisomal beta-oxidation (approximately 2-fold each) but significantly increased mEH activity (approximately 4-fold).
- In vitro studies confirmed that the increase in cEH activity was not due to enzyme activation, whereas the increase in mEH activity by 1-benzylimidazole may be partially attributed to activation.
Conclusions:
- Hypolipidemic compounds like clofibrate, tiadenol, and acetylsalicylic acid are potent inducers of peroxisomal beta-oxidation and cEH in rat liver.
- 1-Benzylimidazole exhibits a different activity profile, inducing mEH activity potentially through enzyme activation.
- These findings highlight the differential effects of hypolipidemic agents on key metabolic enzymes, with implications for drug metabolism and toxicity.