Abstract
Macrophages are an essential component of unstable atherosclerotic plaques and play a pivotal role in the destabilization process. We have demonstrated previously that local delivery of the mammalian target of rapamycin (mTOR) inhibitor everolimus selectively clears macrophages in rabbit plaques. Because mTOR controls mRNA translation, inhibition of protein synthesis might induce selective macrophage cell death. We therefore investigated in the present study the effect of the protein synthesis inhibitor cycloheximide on macrophage and smooth muscle cell (SMC) viability. In vitro studies with cultured macrophages and SMCs showed that cycloheximide induced selective apoptosis of macrophages in a concentration- and time-dependent manner. Moreover, macrophages could be selectively depleted in rabbit carotid artery rings with collar-induced atherosclerotic plaques after in vitro treatment with cycloheximide. Local in vivo administration of cycloheximide via osmotic minipumps to rabbit carotid arteries with collar-induced atherosclerotic plaques significantly reduced the macrophage but not the SMC content. Cycloheximide-treated plaques showed signs of apoptosis (increased terminal deoxynucleotidyl transferase end labeling and fluorescein isothiocyanate-Val-Ala-dl-Asp(O-methyl)-fluoromethylketone labeling) that did not colocalize with SMCs. Organ chamber studies demonstrated that the functionality of SMCs and the endothelium were not influenced by cycloheximide treatment. All together, these findings demonstrate that cycloheximide decreases the macrophage load in atherosclerotic plaques by induction of apoptosis without changing SMC content or contractility.
Footnotes
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Research was supported by funding from the Fonds voor Wetenschappelijk Onderzoek (FWO) (projects G.0308.04 and G.0113.06), Special Research Fund of the University of Antwerp (Nieuwe Onderzoeksinitiatieven-Bijzonder Onderzoeksfonds) and the Bekales Foundation. Wim Martinet is a postdoctoral fellow of the Fund for Scientific Research-Flanders (Belgium, FWO).
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.106.113944.
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ABBREVIATIONS: SMC, smooth muscle cell; mTOR, mammalian target of rapamycin; Erk, extracellular signal-regulated kinase; SAPK, stress-activated protein kinase; JNK, c-Jun NH2-terminal kinase; MAPK, mitogen-activated protein kinase; FITC, fluorescein isothiocyanate; TUNEL, terminal deoxynucleotidyl transferase dUTP nick-end labeling; FITC-VAD-fmk, FITC-labeled Val-Ala-dl-Asp(O-methyl)-fluoromethylketone; CHOP, CCAAT/enhancer-binding protein homologous protein; eIF2α, eukaryotic initiation factor 2α; z-VAD-fmk, benzyloxycarbonyl-Val-Ala-dl-Asp(O-methyl)-fluoromethylketone; TNFα, tumor necrosis factor-α.
- Received September 14, 2006.
- Accepted November 27, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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