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. The most potent inhibitors of total LysoPLA in mouse brain are isopropyl dodecylphosphonofluoridate (also for LysoPLA of Vibrio bacteria), ethyl octylphosphonofluoridate (EOPF), and two alkyl-benzodioxaphosphorin 2-oxides (BDPOs)[(S)-octyl and dodecyl] (IC50 2-8 nM). OP inhibitors acting in vitro and in vivo differentiate a more sensitive portion but not a distinct NTE-LysoPLA compared with total LysoPLA activity. For 10 active inhibitors, NTE-LysoPLA is 17-fold more sensitive than total LysoPLA, but structure-activity comparisons give a good correlation (r(2) = 0.94) of IC50 values, suggesting active site structural similarity or identity. In mice 4 h after intraperitoneal treatment with discriminating doses, EOPF, tribufos (a plant defoliant), and dodecanesulfonyl fluoride inhibit 41-57% of the total brain LysoPLA and 85-99% of the NTE-LysoPLA activity. Total LysoPLA as well as NTE-LysoPLA is decreased in activity in Nte(+/-)-haploinsufficient mice compared to their Nte(+/+) littermates. The lysolecithin level of spinal cord but not brain is elevated significantly following EOPF treatment (3 mg/kg), thereby focusing attention on localized rather than general alterations in lysophospholipid metabolism in OP-induced hyperactivity and toxicity.
Novel inhibitors of human digestive lipases, lipophilic trifluoromethyl ketones, were developed. These analogues of the natural triacylglycerol substrates of lipases were designed to contain the carbonyl group of the trifluoromethyl ketone functionality in place of the carbonyl group of the scissile ester bond at the sn-1 position. The ester bond at the sn-3 position was replaced by an ether bond, while the secondary hydroxy group was either esterified or etherified. The inhibitors were prepared starting from solketal. The inhibition of human pancreatic and gastric lipases by the trifluoromethyl ketones was studied by the monolayer technique. 5,5,5-Trifluoro-1-(dodecyloxymethyl)-4-oxopentyl decanoate is the best synthetic inhibitor of human gastric lipase ever reported (inhibition constant alpha(50)=0.003).
Title: Toxicological and structural features of organophosphorus and organosulfur cannabinoid CB1 receptor ligands Segall Y, Quistad GB, Sparks SE, Nomura DK, Casida JE Ref: Toxicol Sci, 76:131, 2003 : PubMed
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. Compounds 2 and 14 are also effectivein vivo, with 84% inhibition of mouse brain CB1 binding 4 h after intraperitoneal dosage at 30 mg/kg. Compound 14-inhibited CB1 in mouse brain requires about 3-4 days for recovery of 50% activity, suggesting covalent derivatization. Delayed toxicity (mortality in 0.3-5 days) from compounds 2, 14, and octanesulfonyl fluoride (18) is more closely associated with in vivo inhibition of brain neuropathy target esterase-lysophospholipase (NTE-LysoPLA) than with that of CB1 or acetylcholinesterase. NTE-LysoPLA inhibited by sulfonyl fluorides 14 and 18 cannot "age," a proposed requirement for NTE phosphorylated by organophosphorus-delayed neurotoxicants. Several octane- and dodecanesulfonamides with N-(2-hydroxyethyl) and other substituents based on anandamide give depressed mobility and recumbent posture in mice, but the effects do not correlate with potency for CB1 inhibition in vitro. Specific toxicological responses are not clearly associated with organophosphorus- or organosulfur-induced inhibition of the proposed CB1 nucleophilic site in mouse brain. On the other hand, the most potent CB1 inhibitors examined here are also NTE-LysoPLA inhibitors and cause delayed toxicity in mice.
