Cholesterol Synthesis Inhibitor U18666A and the Role of Sterol Metabolism and Trafficking in Numerous Pathophysiological Processes

Abstract

The multiple actions of U18666A have enabled major discoveries in lipid research and contributed to understanding the pathophysiology of multiple diseases. This review describes these advances and the utility of U18666A as a tool in lipid research. Harry Rudney's recognition that U18666A inhibited oxidosqualene cyclase led him to discover a pathway for formation of polar sterols that he proved to be important regulators of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase. Laura Liscum's recognition that U18666A inhibited the egress of cholesterol from late endosomes and lysosomes led to greatly improved perspective on the major pathways of intracellular cholesterol trafficking. The inhibition of cholesterol trafficking by U18666A mimicked the loss of functional Niemann-Pick type C protein responsible for NPC disease and thus provided a model for this disorder. U18666A subsequently became a tool for assessing the importance of molecular trafficking through the lysosomal pathway in other conditions such as atherosclerosis, Alzheimer's disease, and prion infections. U18666A also provided animal models for two important disorders: petite mal (absence) epilepsy and cataracts. This was the first chronic model of absence epilepsy. U18666A is also being used to address the role of oxidative stress in apoptosis. How can one molecule have so many effects? Perhaps because of its structure as an amphipathic cationic amine it can interact and inhibit diverse proteins. Restricting the availability of cholesterol for membrane formation through inhibition of cholesterol synthesis and intracellular trafficking could also be a mechanism for broadly affecting many processes. Another possibility is that through intercalation into membrane U18666A can alter membrane order and therefore the function of resident proteins. The similarity of the effects of natural and enantiomeric U18666A on cells and the capacity of intercalated U18666A to increase membrane order are arguments in favor of this possibility.

Endoplasmic Reticulum Stress and Ca2+ Depletion Differentially Modulate the Sterol Regulatory Protein PCSK9 to Control Lipid Metabolism

“…2, B and C, treatment of cells with siRNA knockdown of SREBP2 blocked TG-mediated PCSK9 induction to a similar extent as that observed for U18666A (U18), a known activator of SREBP2 ( Fig. 2D) (43).…”

“…13778030, Thermo Fisher Scientific) and incubated in the transfection mixture for 48 h. Cells were then either untreated or treated with TG (100 nM) or U18 (1 g/ml, Sigma) for 24 h following initiation of the transfection. In addition to TG, U18 was used as an activator of SREBP2 due to its ability to promote intracellular sterol starvation (43).…”

Endocytosis of beta-cyclodextrins is responsible for cholesterol reduction in Niemann-Pick type C mutant cells

“…To test whether the apparent EC 50 for clearance of cholesterol from LSO depended on cholesterol levels accumulated and to examine this in an isogenic background, we used apparently normal human fibroblasts (GM05659) treated with various concentrations of the NPC phenotype-inducing compound U18666A (3-β-[(2-diethyl-amino) ethoxy]androst-5-en-17-one). U18666A is a class II amphipathic amine that has been reported to impair cholesterol efflux from LE/ LY and create an NPC-like phenotype in treated cells (23). The extent of cholesterol accumulation in LSOs of U18666A-treated cells is dose dependent (Fig.…”

Plasma Membrane Origin of the Steroidogenic Pool of Cholesterol Used in Hormone-induced Acute Steroid Formation in Leydig Cells

“…To ensure that Bt 2 cAMP did not negatively affect D4 binding, we employed the inhibitor U18666A, which efficiently blocks cholesterol trafficking and interferes in cholesterol synthesis in the cell (55). In the presence of U18666A, cholesterol was trapped at the plasma membrane even after treatment with Bt 2 cAMP, and steroid formation was inhibited.…”