Cell Toxicity Induced by Inhibition of Acyl Coenzyme A:Cholesterol Acyltransferase and Accumulation of Unesterified Cholesterol

Abstract

Considerable evidence supports the involvement of acyl-CoA:cholesterol acyltransferase (ACAT) in the maintenance of intracellular cholesterol homeostasis. A number of recently developed ACAT inhibitors may have potential use as pharmacological agents to reduce the development of atherosclerosis. Recently, however, reports arose describing cytotoxic effects following administration of a specific ACAT inhibitor to experimental animals. In order to address the specific intracellular mechanisms involved with the cytotoxic effect, we examined the consequences of ACAT inhibition in cholesterol-enriched mouse peritoneal macrophages. Mouse peritoneal macrophages were cholesterol-enriched by incubation with acetylated low density lipoprotein and free cholesterol:phospholipid dispersions prior to the addition of an ACAT inhibitor, either Sandoz 58-035 or Pfizer CP-113,818. The adenine pool of the macrophages was radiolabeled prior to addition of the ACAT inhibitors, in order to monitor the release of radiolabeled adenine, a technique shown to be a sensitive method to monitor drug-induced toxicity. The ACAT inhibitors were added for up to 48 h and at concentrations up to 2 micrograms/ml. These conditions resulted in an approximately 2-fold increase in adenine release. The increase in cell toxicity paralleled an increase in the cellular free cholesterol content. Reducing the cellular free cholesterol content, by the addition of extracellular acceptors, decreased the cytotoxic effects of the ACAT inhibitors. Addition of an intracellular cholesterol transport inhibitor, either progesterone or U18666A, together with CP-113,818 blocked the toxic effect of CP-113,818. These results suggest that ACAT inhibition of cholesterol-enriched macrophages increases cell toxicity due to the buildup of cellular free cholesterol. Removal of free cholesterol by the addition of extracellular cholesterol acceptors or by blocking intracellular sterol transport relieves the ACAT inhibitor-induced toxicity.

Novel Large Apolipoprotein E‐Containing Lipoproteins of Density 1.006–1.060 g/ml in Human Cerebrospinal Fluid

“…These particles may be generated by apoE in regulating cholesterol content and perhaps removing excess cholesterol from regions of cell injury. Recently excess cholesterol has been shown to be toxic for cells (Warner et al, 1995;Tabas et al, 1996). The importance of controlling cellular cholesterol content is suggested by the large number of mechanisms for such control, including intracellular esterification and deesterification, regulated expression of LDL receptors, delivery of excess cell cholesterol to extracellular acceptor particles such as apoA-I-containing lipoproteins, and synthesis and secretion of apoE-HDL from certain cells (Brown and Goldstein, 1986;Johnson et al, 1991).…”

ACAT1 gene ablation increases 24(S)-hydroxycholesterol content in the brain and ameliorates amyloid pathology in mice with AD

“…S4): in neurons, cholesterol trafficking in and out of the ER occurs. The unnecessary buildup of unesterified cholesterol at the ER (and other membranes) is toxic (50,51). To minimize cholesterol accumulation, A1 located at the ER removes a portion of ER cholesterol by converting it to CE.…”

Combinatorial pattern recognition receptor signaling alters the balance of life and death in macrophages

“…5 A-C]. Of note, very prolonged FC loading causes necrosis of macrophages (27), which is independent of TLR4 (unpublished observations). TLR4 activation by LPS requires two additional components, CD14 and MD2 (25), and these molecules also were found to be essential for SRA/ER stress-induced macrophage apoptosis ( Fig.…”