| Abstract |
Apolipoprotein (apo) A-I generates high-density lipoprotein (HDL) by removing cellular cholesterol and phospholipid on the interaction with cells as a main source of plasma HDL. The reaction is induced by dibutylyl cyclic (dbc) adenosine monophosphate (AMP) in RAW 264, mouse macrophage cell line cells, and we investigated its pharmacologic modulation using this cell model. Release of cellular cholesterol and choline phospholipid by apoA-I was increased 9.9 and 4.2 times, respectively, by pretreatment of the cells with 300 microM dbcAMP for 24 h. Calmodulin inhibitors, W7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide) and W5 (N(6-aminohexyl)-1-naphthalenesulfonamide), increased the apoA-I-mediated lipid release by 3 times from the dbcAMP-treated cells. The optimal drug concentrations (80 and 160 microM for W7 and W5, respectively) were not parallel with those reported for in vitro calmodulin inhibition (IC50, 28 and 240 microM for W7 and W5, respectively, toward phosphodiesterase activity), and in fact 40 microM W7 showed much stronger intracellular calmodulin inhibition than did 300 microM W5 using S7AAS2, a fluorescent peptide probe. Other calmodulin inhibitors such as amitriptyline, chlorpromazine, and trifluoperazine showed no effect on the apoA-I-mediated cholesterol release. In contrast to these results, neither dbcAMP nor W7 influenced the diffusion-mediated nonspecific cholesterol efflux to lipid microemulsion. We concluded that W7 and W5 increased the interaction of apoA-I with RAW 264 cells to generate more HDL. The effect did not seem directly correlated to their cal modulin inhibition or modulation of cAMP and protein kinase C.
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