| The serine hydrolase superfamily is one of the largest and most diverse enzyme classes in mammals with key roles in nearly all biological systems. A large fraction of mammalian serine hydrolases remain uncharacterized in terms of their physiological or toxicological roles. The organophosphorus (OP) chemotype is an important chemical scaffold for inhibitor discovery of serine hydrolases. The OP chemotype includes insecticides and chemical warfare agents, for which off-targets constitute secondary toxicological sites. This thesis describes progress in annotating two serine hydrolases, KIAA1363 and monoacylglycerol lipase (MAGL), and their associated biological systems.;The first studies show that very surprisingly serine hydrolase KIAA1363 is the principal enzyme in brain hydrolyzing the OP insecticide metabolite chlorpyrifos oxon (CPO). KIAA1363 protects against OP inhibition of both acetylcholinesterase (AChE) and multiple secondary sites. Consistent with these findings, KIAA1363 gene-deficient (-/-) mice are more susceptible to toxicity of OP pesticides chlorpyrifos and parathion compared to the corresponding wild-type (+/+). Its physiological substrate acetyl monoalkylglycerol ether (AcMAGE) is a metabolic intermediate of the highly bioactive lipids platelet-activating factor (PAF) and alkyl lysophosphatidic acid and may therefore play a role in neurotransmission and carcinogenesis. KIAA1363 -/- mice have dramatically reduced AcMAGE hydrolytic activity in brain, lung, heart, and kidney compared to their +/+ counterparts. Inhibition or gene-deletion of KIAA1363 leads to increased conversion of metabolically stabilized AcMAGE to PAF in brain.;The second investigation used OP inhibitors of MAGL and fatty acid amide hydrolase (FAAH) that hydrolyze endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide, respectively, to study the physiology of this system in vivo. These studies show that dual blockade of MAGL and FAAH in mice leads to dramatic elevation of brain endocannabinoids and full-blown cannabinoid behavior. MAGL is the primary 2-AG hydrolase in vivo in brain. Surprisingly, 2-AG and MAGL also regulate the levels of free arachidonic acid levels in brain, spinal cord, spleen, liver and lung.;This dissertation establishes the utility of the OP chemotype to study the systems biology of serine hydrolases and novel toxic mechanisms of OP nerve poisons. The future of OP therapeutics depends on achieving appropriate specificity for the desired target. |
