Serine hydrolase KIAA1363: toxicological and structural features with emphasis on organophosphate interactions.

Serine hydrolase KIAA1363 is highly expressed in invasive cancer cells and is the major protein in mouse brain diethylphosphorylated by and hydrolyzing low levels of chlorpyrifos oxon (CPO) (the activated metabolite of a major insecticide). It is also the primary CPO-hydrolyzing enzyme in spinal cord, kidney, heart, lung, testis, and muscle but not liver, a pattern of tissue expression confirmed by fluorophosphonate-rhodamine labeling. KIAA1363 gene deletion using homologous recombination reduces CPO binding, hydrolysis, and metabolism 3-29-fold on incubation with brain membranes and homogenates determined with 1 nM [(3)H-ethyl]CPO and the inhibitory potency for residual CPO with butyrylcholinesterase as a biomarker.

Each lipase has a unique sensitivity profile for organophosphorus inhibitors.

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 degrees 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.

Monoacylglycerol lipase inhibition by organophosphorus compounds leads to elevation of brain 2-arachidonoylglycerol and the associated hypomotility in mice.

Three components of the cannabinoid system are sensitive to selected organophosphorus (OP) compounds: monoacylglycerol (MAG) lipase that hydrolyzes the major endogenous agonist 2-arachidonoylglycerol (2-AG); fatty acid amide hydrolase (FAAH) that cleaves the agonist anandamide present in smaller amounts; the CB1 receptor itself. This investigation considers which component of the cannabinoid system is the most likely contributor to OP-induced hypomotility in mice. Structure-activity studies by our laboratory and others rule against major involvement of a direct toxicant-CB1 receptor interaction for selected OPs.

Serine hydrolase targets of organophosphorus toxicants.

Acetylcholinesterase (AChE) is one of several hundred serine hydrolases in people potentially exposed to about 80 organophosphorus (OP) compounds important as insecticides or chemical warfare agents. The toxicology of OPs was interpreted until recently almost solely on the basis of AChE inhibition. It is assumed that each serine hydrolase has a specific function and proposed that every OP compound has a unique inhibitory profile.

Platelet-activating factor acetylhydrolase: selective inhibition by potent n-alkyl methylphosphonofluoridates.

Platelet-activating factor (PAF) is a potent endogenous phospholipid modulator of diverse biological activities, including inflammation and shock. PAF levels are primarily regulated by PAF acetylhydrolases (PAF-AHs). These enzymes are candidate secondary targets of organophosphorus (OP) pesticides and related toxicants.

Blood acylpeptide hydrolase activity is a sensitive marker for exposure to some organophosphate toxicants.

Acylpeptide hydrolase (APH) unblocks N-acetyl peptides. It is a major serine hydrolase in rat blood, brain, and liver detected by derivatization with (3)H-diisopropyl fluorophosphate (DFP) or a biotinylated fluorophosphonate. Although APH does not appear to be a primary target of acute poisoning by organophosphorus (OP) compounds, the inhibitor specificity of this secondary target is largely unknown.

A brain detoxifying enzyme for organophosphorus nerve poisons.

Organophosphorus (OP) insecticides and chemical warfare agents act primarily by inhibiting acetylcholinesterase. There are many secondary targets for OP toxicants as observed for example with the major insecticide chlorpyrifos and its bioactivated metabolite chlorpyrifos oxon (CPO). Therefore, it was surprising that the predominant mouse brain protein labeled in vitro by [(3)H-ethyl]CPO (1 nM) (designated CPO-binding protein or CPO-BP) is not one of these known OP toxicant targets.

Lysophospholipase inhibition by organophosphorus toxicants.

Lysophospholipases (LysoPLAs) are a large family of enzymes for removing lysophospholipids from cell membranes. Potent inhibitors are needed to define the importance of LysoPLAs as targets for toxicants and potential therapeutics. This study considers organophosphorus (OP) inhibitors with emphasis on mouse brain total LysoPLA activity relative to the mipafox-sensitive neuropathy target esterase (NTE)-LysoPLA recently established as 17% of the total activity and important in the action of OP delayed toxicants.

Arachidonylsulfonyl derivatives as cannabinoid CB1 receptor and fatty acid amide hydrolase inhibitors.

Arachidonylsulfonyl fluoride (3), reported here for the first time, is similar in potency to its known methyl arachidonylfluorophosphonate (2) analogue as an inhibitor of mouse brain fatty acid amide hydrolase activity (IC(50) 0.1 nM) and cannabinoid CB1 agonist [3H]CP 55,940 binding (IC(50) 304-530 nM). Interestingly, 3 is much more selective than 2 as an inhibitor for fatty acid amide hydrolase relative to acetylcholinesterase, butyrylcholinesterase and neuropathy target esterase.

Toxicological and structural features of organophosphorus and organosulfur cannabinoid CB1 receptor ligands.

Potent cannabinoid CB1 receptor ligands include anandamide [N-(2-hydroxyethyl)arachidonamide], Delta9-tetrahydrocannabinol, and 3H-CP 55,940 at the agonist site and selected organophosphorus esters (including some pesticides) and organosulfur compounds at a proposed closely coupled "nucleophilic" site. This study considers the toxicological and structural features of alkylfluorophosphonates, benzodioxaphosphorin oxides, alkanesulfonyl fluorides, and analogs acting at the nucleophilic site. Binding at the agonist site, using3H-CP 55,940 in assays with mouse brain membranes, is inhibited byO-isopropyl dodecylfluorophosphonate (compound 2), dodecanesulfonyl fluoride (compound 14) and dodecylbenzodioxaphosphorin oxide with IC50 values of 2-11 nM.

Evidence that mouse brain neuropathy target esterase is a lysophospholipase.

Neuropathy target esterase (NTE) is inhibited by several organophosphorus (OP) pesticides, chemical warfare agents, lubricants, and plasticizers, leading to OP-induced delayed neuropathy in people (>30,000 cases of human paralysis) and hens (the best animal model for this demyelinating disease). The active site region of NTE as a recombinant protein preferentially hydrolyzes lysolecithin, suggesting that this enzyme may be a type of lysophospholipase (LysoPLA) with lysolecithin as its physiological substrate. This hypothesis is tested here in mouse brain by replacing the phenyl valerate substrate of the standard NTE assay with lysolecithin for an "NTE-LysoPLA" assay with four important findings.

Major intermediates in organophosphate synthesis (PCl3, POCl3, PSCl3, and their diethyl esters) are anticholinesterase agents directly or on activation.

Three phosphotrichlorides [phosphorus trichloride (PCl(3)), phosphorus oxychloride (POCl(3)), and thiophosphoryl chloride (PSCl(3))] with an annual U.S. production of >500,000,000 pounds and their diethyl esters are intermediates in the production of organophosphorus pesticides, plastics, flame retardants, and hydraulic fluids.

Loss of neuropathy target esterase in mice links organophosphate exposure to hyperactivity.

Neuropathy target esterase (NTE) is involved in neural development and is the target for neurodegeneration induced by selected organophosphorus pesticides and chemical warfare agents. We generated mice with disruptions in Nte, the gene encoding NTE. Nte(-/-) mice die after embryonic day 8, and Nte(+/-) mice have lower activity of Nte in the brain and higher mortality when exposed to the Nte-inhibiting compound ethyl octylphosphonofluoridate (EOPF) than do wild-type mice.

Cannabinoid CB1 receptor as a target for chlorpyrifos oxon and other organophosphorus pesticides.

Binding of the endocannabinoid anandamide or of Delta(9)-tetrahydrocannabinol to the agonist site of the cannabinoid receptor (CB1) is commonly assayed with [3H]CP 55,940. Potent long-chain alkylfluorophosphonate inhibitors of agonist binding suggest an additional, important and closely-coupled nucleophilic site, possibly undergoing phosphorylation. We find that the CB1 receptor is also sensitive to inhibition in vitro and in vivo by several organophosphorus pesticides and analogs.

Selective inhibitors of fatty acid amide hydrolase relative to neuropathy target esterase and acetylcholinesterase: toxicological implications.

Fatty acid amide hydrolase (FAAH) plays an important role in nerve function by regulating the action of endocannabinoids (e.g., anandamide) and hydrolyzing a sleep-inducing factor (oleamide).

Chlorpyrifos oxon potentiates diacylglycerol-induced extracellular signal-regulated kinase (ERK 44/42) activation, possibly by diacylglycerol lipase inhibition.

Chlorpyrifos oxon (CPO) activates extracellular signal-regulated kinase (ERK 44/42) in Chinese hamster ovary (CHOK1) cells but the mechanism is not defined. This study tests the hypothesis that diacylglycerol (DAG) is the secondary messenger responsible for CPO-induced ERK 44/42 activation. It is known that DAG is sequentially hydrolyzed by DAG lipase and monoacylglycerol (MAG) lipase, both of which are organophosphate sensitive.