Cholesterol 7 alpha-hydroxylase in isolated rat liver cells

Area of Science:

• Biochemistry
• Hepatology
• Enzymology

Background:

• Cholesterol 7 alpha-hydroxylase is a key enzyme in bile acid synthesis.
• Cholestyramine, a bile acid sequestrant, is known to upregulate this enzyme.
• Understanding enzyme stability in isolated cells is crucial for in vitro studies.

Purpose of the Study:

• To investigate the activity and stability of cholesterol 7 alpha-hydroxylase in isolated rat hepatocytes.
• To determine the effect of cholestyramine diet on enzyme activity in isolated cells.
• To explore factors influencing enzyme activity during in vitro incubation.

Main Methods:

• Isolated rat hepatocytes were prepared and incubated under various conditions.
• Enzyme activity was measured in the 10000 x g supernatant.
• Cytochrome P-450 content and cell viability were assessed.
• The effect of cholestyramine diet and incubation additives was evaluated.

Main Results:

• Cholesterol 7 alpha-hydroxylase activity was comparable in isolated cells and liver microsomes.
• Hepatocytes from cholestyramine-fed rats showed 2-3 fold higher enzyme activity.
• Enzyme activity decreased by 50% within 3 hours of incubation, independent of diet.
• Cycloheximide accelerated the decline, suggesting protein synthesis is involved.
• Cytochrome P-450 content also decreased during incubation.

Conclusions:

• Isolated rat hepatocytes retain significant cholesterol 7 alpha-hydroxylase activity, which is inducible by cholestyramine.
• In vitro incubation leads to a rapid loss of enzyme activity, partly due to reduced cytochrome P-450 and ongoing protein degradation.
• Further research is needed to stabilize enzyme activity in isolated hepatocytes for in vitro experiments.