Document Detail


Effects of Toxicologically Relevant Xenobiotics and the Lipid-Derived Electrophile 4-Hydroxynonenal on Macrophage Cholesterol Efflux: Silencing Carboxylesterase 1 Has Paradoxical Effects on Cholesterol Uptake and Efflux.
MedLine Citation:
PMID:  25250848     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Cholesterol cycles between free cholesterol (unesterified) found predominantly in membranes and cholesteryl esters (CEs) stored in cytoplasmic lipid droplets. Only free cholesterol is effluxed from macrophages via ATP-binding cassette (ABC) transporters to extracellular acceptors. Carboxylesterase 1 (CES1), proposed to hydrolyze CEs, is inactivated by oxon metabolites of organophosphorus pesticides and by the lipid electrophile 4-hydroxynonenal (HNE). We assessed the ability of these compounds to reduce cholesterol efflux from foam cells. Human THP-1 macrophages were loaded with [3H]-cholesterol/acetylated LDL then allowed to equilibrate to enable [3H]-cholesterol to distribute into its various cellular pools. The cholesterol-engorged cells were then treated with toxicants in the absence of cholesterol acceptors for 24 h, followed by a 24 h efflux period in the presence of toxicant. A concentration-dependent reduction in [3H]-cholesterol efflux via ABCA1 (up to 50%) was found for paraoxon (0.1-10 M), whereas treatment with HNE had no effect. A modest reduction in [3H]-cholesterol efflux via ABCG1 (25%) was found after treatment with either paraoxon or chlorpyrifos oxon (10 M each), but not HNE. No difference in efflux rates were found after treatments with either paraoxon or HNE when the universal cholesterol acceptor 10% (v/v) fetal bovine serum was used. When the re-esterification arm of the CE cycle was disabled in foam cells, paraoxon treatment increased CE levels, suggesting the neutral CE hydrolysis arm of the cycle had been inhibited by the toxicant. However, paraoxon also partially inhibited lysosomal acid lipase, which generates cholesterol for efflux, and reduced the expression of ABCA1 protein. Paradoxically, silencing CES1 expression in macrophages did not affect % [3H]-cholesterol efflux. However, CES1 mRNA knockdown markedly reduced cholesterol uptake by macrophages, with SR-A and CD36 mRNA reduced 3- and 4-fold, respectively. Immunoblots confirmed SR-A and CD36 protein downregulation. Together, these results suggest that toxicants, e.g. oxons, may interfere with macrophage cholesterol homeostasis/metabolism.
Authors:
Matthew K Ross; Abdolsamad Borazjani; Lee Mangum; Ran Wang; J Allen Crow
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2014-9-24
Journal Detail:
Title:  Chemical research in toxicology     Volume:  -     ISSN:  1520-5010     ISO Abbreviation:  Chem. Res. Toxicol.     Publication Date:  2014 Sep 
Date Detail:
Created Date:  2014-9-24     Completed Date:  -     Revised Date:  2014-9-25    
Medline Journal Info:
Nlm Unique ID:  8807448     Medline TA:  Chem Res Toxicol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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