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Cholesterol Efflux Assay
07:54

Cholesterol Efflux Assay

Published on: March 6, 2012

Inhibition of cellular cholesterol esterification can decrease low density lipoprotein receptor number in human

B Middleton

    Biochemical and Biophysical Research Communications
    |May 29, 1987
    PubMed

    Insights

    Cholesterol esterification inhibition affects low density lipoprotein (LDL) receptors. Reversible inhibitors cause LDL receptor downregulation by accumulating intracellular cholesterol, while irreversible inhibitors do not.

    Area of Science:

    • Cell Biology
    • Biochemistry
    • Molecular Biology

    Background:

    • Fibroblasts normally regulate low density lipoprotein (LDL) receptors in response to cholesterol levels.
    • Cholesterol esterification is a continuous process in cells, even when cholesterol-deprived.
    • Acyl-CoA: cholesterol acyl-transferase (ACAT) is a key enzyme in cholesterol esterification.

    Purpose of the Study:

    • To investigate the role of cholesterol esterification in regulating LDL receptor expression.
    • To determine if inhibition of cholesterol esterification affects LDL receptor binding and metabolism.
    • To differentiate the effects of reversible versus irreversible ACAT inhibitors on LDL receptors.

    Main Methods:

    • Utilized cholesterol-deprived fibroblasts to induce LDL receptors.
    • Administered structurally unrelated ACAT inhibitors: progesterone, trimethylcyclohexanyl mandelate, and 58035.
    • Measured basal cholesterol esterification rates.
    • Assessed specific binding and metabolism of LDL after inhibitor exposure.
    • Examined the time-dependent effects of inhibitors on LDL receptor function.

    Main Results:

    • Progesterone, trimethylcyclohexanyl mandelate, and 58035 all inhibited basal cholesterol esterification within 1 hour.
    • Progesterone and trimethylcyclohexanyl mandelate (reversible inhibitors) caused decreased LDL binding and metabolism after 17 hours.
    • This downregulation was time-dependent and linked to reversible inhibition of esterification.
    • The irreversible inhibitor 58035 did not affect LDL receptor number.
    • Reversible ACAT inhibition leads to intracellular cholesterol accumulation, triggering LDL receptor downregulation.

    Conclusions:

    • Downregulation of LDL receptors is initiated by the accumulation of cholesterol in a specific intracellular pool.
    • Reversible inhibition of cholesterol esterification by compounds like progesterone and trimethylcyclohexanyl mandelate causes this accumulation.
    • Irreversible inhibition of esterification by 58035 does not lead to the same intracellular cholesterol accumulation or receptor downregulation.

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