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ToxSci Advance Access published online on January 31, 2006
Toxicological Sciences, doi:10.1093/toxsci/kfj124
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© The Author 2006. Published by Oxford University Press on behalf of the Society of Toxicology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received December 21, 2005
Accepted January 27, 2006

In Vitro Toxicology

Each Lipase has a Unique Sensitivity Profile for Organophosphorus Inhibitors

Gary B. Quistad 1, Shannon N. Liang 1, Karl J. Fisher 1, Daniel K. Nomura 1, and John E. Casida 1 *

1 Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720-3112, USA

* To whom correspondence should be addressed.
John E. Casida, E-mail: ectl{at}nature.berkeley.edu


  Abstract

Lipases sensitive to organophosphorus (OP) inhibitors play critical roles in cell regulation, nutrition and disease, but little is known on the toxicological aspects in mammals. To help fill this gap, six lipases or lipase-like proteins are assayed for OP sensitivity in vitro under standard conditions (25°C, 15 min incubation). Postheparin serum lipase, lipoprotein lipase (LPL) (two sources), pancreatic lipase, monoacylglycerol (MAG) lipase, cholesterol esterase and KIAA1363 are considered with 32 OP pesticides and related compounds. Postheparin lipolytic activity in rat serum is inhibited by 14 OPs, including chlorpyrifos oxon (IC50 50-97 nM). LPL (bovine milk and Pseudomonas) generally is less inhibited by the insecticides or activated oxons, but the milk enzyme is very sensitive to six fluorophosphonates and benzodioxaphosphorin oxides (IC50 7-20 nM). Porcine pancreatic lipase is very sensitive to dioctyl 4-nitrophenyl phosphate (IC50 8 nM), MAG lipase of mouse brain to O-4-nitrophenyl methyldodecylphosphinate (IC50 0.6 nM) and cholesterol esterase (bovine pancreas) to all of the classes of OPs tested (IC50 <10 nM for 17 compounds). KIAA1363 is sensitive to numerous OPs, including two O-4-nitrophenyl compounds (IC50 3-4 nM). In an overview, inhibition of 28 serine hydrolases (including lipases) by 8 OPs (chlorpyrifos oxon, diazoxon, paraoxon, dichlorvos and four nonpesticides) showed that brain acetylcholinesterase is usually less sensitive than butyrylcholinesterase, liver esterase, cholesterol esterase, and KIAA1363. In general, each lipase (like each serine hydrolase) has a different spectrum of OP sensitivity and individual OPs have unique ranking of potency for inhibition of serine hydrolases.

Keywords: chlorpyrifos oxon; cholesterol esterase; lipase; lipoprotein; organophosphorus.
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