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Effect of dietary clofibrate on epoxide hydrolase activity in tissues of mice
Abstract:
The effects of dietary clofibrate on the epoxide-metabolizing enzymes of mouse liver, kidney, lung and testis were evaluated using trans-stilbene oxide as a selective substrate for the cytosolic epoxide hydrolase, cis-stilbene oxide and benzo[a]pyrene 4,5-oxide as substrates for the microsomal form, and cis-stilbene oxide as a substrate for glutathione S-transferase activity. The hydration of trans-stilbene oxide was greatest in liver followed by kidney greater than lung greater than testis. Its hydrolysis was increased significantly in the cytosolic fraction of liver and kidney of clofibrate-treated mice and in the microsomes from the liver. Isoelectric focusing indicates that the same enzyme is responsible for hydrolysis of trans-stilbene oxide in normal and induced liver and kidney. Clofibrate induced glutathione S-transferase activity on cis-stilbene oxide only in the liver. Hydrolysis of both cis-stilbene oxide and benzo[a]pyrene 4,5-oxide was highest in testis followed by liver greater than lung greater than kidney. Hydration of cis-stilbene oxide was induced significantly in both liver and kidney by clofibrate but that of benzo[a]pyrene 4,5-oxide was induced only in the liver. These and other data based on ratios of hydration of benzo[a]pyrene 4,5-oxide to cis-stilbene oxide in tissues of normal and induced animals indicate that there are one or more novel epoxide hydrolase activities which cannot be accounted for by either the classical cytosolic or microsomal hydrolases. These effects are notable in the microsomes of kidney and especially in the cytosol of testis.
Insights
Dietary clofibrate significantly impacts epoxide-metabolizing enzymes in mice, particularly affecting epoxide hydrolase and glutathione S-transferase activities in the liver, kidney, and testis. These changes suggest novel enzyme activities beyond classical hydrolases.
Area of Science:
- Biochemistry
- Toxicology
- Pharmacology
Background:
- Epoxide-metabolizing enzymes are crucial for xenobiotic detoxification.
- Clofibrate is a known inducer of various metabolic enzymes.
- Understanding clofibrate's effects on epoxide metabolism is vital for assessing its toxicological profile.
Purpose of the Study:
- To investigate the effects of dietary clofibrate on epoxide-metabolizing enzymes in mouse liver, kidney, lung, and testis.
- To characterize the specific enzymes and tissues affected by clofibrate treatment.
- To identify potential novel epoxide hydrolase activities induced by clofibrate.
Main Methods:
- Enzyme activity assays using specific substrates: trans-stilbene oxide, cis-stilbene oxide, and benzo[a]pyrene 4,5-oxide.
- Fractionation of tissues into cytosolic and microsomal components.
- Isoelectric focusing to identify enzyme characteristics.
- Comparative analysis of enzyme activity in normal versus clofibrate-treated mice.
Main Results:
- Clofibrate significantly increased cytosolic epoxide hydrolase activity in liver and kidney, and microsomal activity in the liver.
- Glutathione S-transferase activity towards cis-stilbene oxide was induced by clofibrate solely in the liver.
- Novel epoxide hydrolase activities were indicated, particularly in kidney microsomes and testis cytosol, not explained by classical enzymes.
Conclusions:
- Dietary clofibrate differentially affects epoxide-metabolizing enzymes across mouse tissues.
- The study identifies clofibrate-induced changes in epoxide hydrolase and glutathione S-transferase activities.
- Evidence suggests the presence of novel epoxide hydrolase activities responsive to clofibrate, especially in the kidney and testis.