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    PCSK9 Inhibitors: A 5-Question Quiz

     

    Answer: C. Regulation of LDL receptor glycoprotein on hepatic membrane.

    PCSK9, is a part of a family of proprotein convertase enzymes that work to maintain homeostasis. PCSK9 directly regulates the cell-surface expression and degradation of low-density lipoprotein receptors (LDL-R) in the liver. When this enzyme is inhibited with a monoclonal antibody or siRNA (a PCSK9 inhibitor), the LDL-R does not bind PCSK9 and so can be recycled back to the cell surface to scavenge more circulating LDL-C. Hence, PCSK9 inhibition (or LOF mutations in PCSK9) leads to clinically lower levels of circulating cholesterol. Additional physiologic effects of PCSK9 have not yet been identified although animal studies have suggested a role in non-hepatic tissue, such as intestinal and adipocyte lipid metabolism, atherosclerotic plaque, apoptotic cell death, and regulation of glycemic control.

    Option A is the mechanism of action of statins, which competitively inhibit HMG-CoA reductase, which is the first and rate-limiting enzymatic step of the cholesterol biosynthetic pathway. Option B is the mechanism of action of ezetemibe (Zetia) and option D is the mechanism of action of niacin.

    In recent years, increasing attention has been turned towards familial lipid disorders, a risk factor that had previously been thought to not be readily modifiable.


    Question 3.

    Payal Kohli, MD
    Payal Kohli, MD, is an attending cardiologist for Kaiser Permanente in Denver, Colorado.

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