Lack of toxic effects of F 12511, a novel potent inhibitor of acylcoenzymeA: cholesterol O-acyltransferase, on human adrenocortical cells in culture

Inhibition of acyl-coenzyme A: cholesterol O-acyltransferase (EC 2.3.1.26; ACAT) reduces intracellular cholesteryl esters that are substrates for ster oidogenesis in adrenal cells. The adrenal side effects of ACAT inhibitors r emain a key point for their development as antiatherosclerotic agents. The aim of this study was to characterize the effects of a novel and powerful A CAT inhibitor, F 12511 (S)-2',3',5 '-trimethyl-4' -hydroxy-alpha -dodecylth io-phenylacetanilide, on the NCI-H295R cell line, which has functional prop erties comparable to those of normal human adrenal cells. F 12511 incubated with cultured cells for 4-72 hr strongly inhibited cholesteryl oleate form ation. The concentrations required to produce 50% inhibition (IC50 values) ranged from 20 to 50 nM; in the presence of low-density lipoproteins (LDL), this effect was paralleled by a decrease in cholesteryl ester mass and an increase in intracellular free cholesterol. At concentrations 100-fold larg er than the IC50 value for up to 48 hr, F 12511 reduced neither the basal r elease of cortisol and aldosterone nor the production of cortisol stimulate d by forskolin. F 12511 did not modify the mRNA levels of the steroidogenic enzyme genes cytochrome P450 cholesterol side-chain cleavage (P450scc), cy tochrome P450 17 alpha -hydroxylase (P450c17), or cytochrome P450 21-hydrox ylase (P450c21) or those of the LDL receptor and high-density lipoprotein s cavenger receptor class B, type I (SR-BI) genes, either in the presence or absence of adenosine 3',5'-cyclic monophosphate stimulation for 24 hr. Expo sure to F 12511 at up to 3 mum for 24 or 48 hr did not result in significan t change in morphological and ultrastructural characteristics; the cytoplas m contained large numbers of mitochondria with intact crystae, and the same typical features of secretory activity were observed in NCI-H295R control cells. Exposure to 3 muM of F 12511 for 96 hr also did not affect cell viab ility. These data demonstrate that reduction of the substrate for steroidog enesis by the ACAT inhibitor F 12511 impairs neither steroid production nor transcription of genes involved in steroidogenesis and lipoprotein uptake in the pluripotent human adrenal cell line NCI-H295R. (C) 2001 Elsevier Sci ence Inc. All rights reserved.