Alzheimer Disease: Lockridge O

Duysen EG, Li B, Lockridge O. · Researcher Eppley Institute, University of Nebraska Medical Center, Omaha, NE 68198 6805, USA. · Expert Opin Drug Metab Toxicol. · Pubmed #19416087 No free full text.

Abstract: Butyrylcholinesterase (BChE) mutations common in the human population may result in complete or partial BChE deficiency, making the BChE knockout (KO) mouse a model for human deficiencies. The BChE KO mouse cannot tolerate standard doses of the muscle relaxant succinylcholine or the Alzheimer's disease drugs huperzine A and donepezil. It is resistant to the asthma drug bambuterol. The importance of BChE in detoxication of cocaine has been demonstrated by hepatotoxicity and cardiotoxicity in cocaine-challenged BChE KO mice. The BChE KO mouse becomes obese on a high-fat diet, suggesting a role for BChE in fat metabolism. BChE serves as a backup for acetylcholinesterase by hydrolyzing the neurotransmitter acetylcholine in acetylcholinesterase knockout mice. Imaging studies show that BChE injected intrathecally crosses the blood-brain barrier. Mice, but not humans, have carboxylesterase in their blood. Carboxylesterase obscures the role of BChE in detoxication of organophosphorus pesticides. Future studies will make a double knockout that has neither BChE nor carboxylesterase. The double knockout is expected to be unusually sensitive to the toxicity of organophosphorus pesticides. Knowledge of drug sensitivities in the mouse model of human BChE deficiency will aid in understanding adverse drug effects in humans.

Naik RS, Hartmann J, Kiewert C, Duysen EG, Lockridge O, Klein J. · Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Science Center, 1300 Coulter Dr, Amarillo, TX 79106, USA. · J Pharm Pharm Sci. · Pubmed #19470293 links to  free full text

Abstract: PURPOSE: Alzheimer s disease is characterized by a dysfunction of central cholinergic systems and is treated by inhibitors of acetylcholinesterase (AChE). This study tests the effect of two AChE inhibitors in therapeutic use, rivastigmine and donepezil, in mice that are devoid of AChE (AChE-/- mice). Rivastigmine is an inhibitor of both AChE and butyrylcholinesterase (BChE) whereas donepezil is a selective inhibitor of AChE. METHODS: We have used in vivo microdialysis to investigate the effects of the two drugs on the extracellular concentration of acetylcholine (ACh) in the hippocampus of AChE-/- mice. RESULTS: Extracellular ACh levels in the hippocampus were 30-fold elevated in AChE-/- mice compared to wild-type (AChE+/+) animals. Infusion of rivastigmine (1 and 10 microM) caused a further doubling of ACh levels in AChE-/- mice within 90-120 min. In contrast, infusion of donepezil (1 microM) did not affect hippocampal ACh levels in AChE-/- mice although it increased ACh levels more than twofold in wild-type mice. CONCLUSIONS: In the absence of AChE, rivastigmine enhances the levels of extracellular ACh by inhibiting BChE. This finding may be of therapeutic relevance because BChE activity is preserved, but AChE activity is strongly decreased, in late-stage Alzheimer s disease.

Mikami LR, Wieseler S, Souza RL, Schopfer LM, Lockridge O, Chautard-Freire-Maia EA. · aDepartment of Genetics, Federal University of Paraná, Curitiba, Paraná, Brasil bEppley Institute, University of Nebraska Medical Center, Omaha, Nebraska, USA. · Pharmacogenet Genomics. · Pubmed #17700357 No free full text.

Abstract: The present paper examined the effects of three non synonymous BCHE mutations (G75R, E90D and /99M) on enzyme kinetic parameters obtained after the expression of the respective recombinant BChEs. The respective nucleotide substitution that characterizes each of the three variants was introduced into BCHE cDNA by site directed mutagenesis and transfected into human embryonic kidney 293 T cells and Chinese hamster ovary cells (for E90D). BChE catalysed hydrolysis of butyrylthiocoline (BTC) was measured by Ellman method. The expression results showed that: (1) the activity of the G75R enzyme represents approximately 45% of the wild-type activity, whereas that of the I99M enzyme does not differ from the wild-type; (2) the E90D enzyme presents a silent phenotype; disruption of the salt bridge between E90 and R42 may cause the enzyme to be rapidly degraded inside the cells. In homozygous form the E90D enzyme may confer increased susceptibility to succinylcholine, but may delay cognitive impairment in aged individuals. BChE genotyping may become important for estimating prognosis, and the knowledge of the genetic variants of BChE in a particular population may be useful for carrying out the genotyping assays.

Rice SG, Nowak L, Duysen EG, Lockridge O, Lahiri DK, Reyes PF. · Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ, USA. · J Alzheimers Dis. · Pubmed #17656828 No free full text.

Abstract: The 'cholinergic hypothesis', based on the correlation of the reduction of cholinergic activity in Alzheimer's disease (AD) with cognition and memory, is currently the most widely-held view for AD. Drug treatments for AD focus mainly on inhibition of acetylcholinesterase (AChE), and to some extent butyrylcholinesterase (BChE). In addition to changes in AChE in AD, there is a rise in the level of the sister enzyme BChE. However, the role of the two cholinesterases is poorly understood in vivo. We characterized several proteins immunohistochemically in brain sections from AChE nullizygote (AChE-/-) and wild type AChE+/+ mice. Previous studies had shown that AChE-/- mouse tissues are devoid of AChE activity and that the overall cholinesterase activity is significantly decreased in the knockout group [16]. Despite the differences of cholinesterase activity, we found no significant structural alterations between the experimental groups. Immunohistochemical examination revealed no neuronal, dendritic, astrocytic, synaptic, microglial, and endothelial differences between AChE-/- and AChE+/+ mice. Similarly, the histochemical examination showed no morphologic alterations between AChE-/- and AChE+/+ mice. Our studies show that neither the absence of AChE nor the presence exclusively of BChE is associated with neuroglial and vascular pathology.

Duysen EG, Li B, Darvesh S, Lockridge O. · Eppley Institute, University of Nebraska Medical Center, Omaha, NE 68198-6805, USA. · Toxicology. · Pubmed #17194517 No free full text.

Abstract: Butyrylcholinesterase (EC 3.1.1.8 BChE) is present in all human and mouse tissues, and is more abundant than acetylcholinesterase (EC 3.1.1.7 AChE) in all tissues except brain. People who have no BChE activity due to a genetic variation are healthy. This has led to the hypothesis that BChE has no physiological function. We tested this hypothesis by challenging BChE and AChE knockout mice, as well as wild-type mice, with the AChE specific inhibitors, (--)-huperzine A and donepezil, and with serine hydrolase inhibitors, echothiophate and chlorpyrifos oxon. (--)-Huperzine A and donepezil caused mortality and significant toxicity in the BChE-/- animals. The BChE heterozygote (BCHE+/-) mice with approximately one-half the BChE activity of the BChE wild type (BChE+/+) exhibited intermediate toxic symptoms, and survived a longer period. The BChE+/+ animals displayed comparatively minor toxic symptoms and recovered by 24h post-dosing. Plasma AChE activity was inhibited to the same extent in BChE-/-, +/-, and +/+ mice, whereas BChE activity was not inhibited. This indicated that the protective effect of BChE was not due to scavenging (--)-huperzine A. AChE-/- mice were unaffected by (--)-huperzine A and donepezil, demonstrating the specificity of these inhibitors for AChE. AChE-/- mice treated with chlorpyrifos oxon lost all BChE activity, had severe cholinergic symptoms and died of convulsions. This showed that BChE activity was essential for survival of AChE-/- mice. In conclusion, we propose that the protective effect of BChE is explained by hydrolysis of excess acetylcholine in physiologically relevant regions such as diaphragm, cardiac muscle, and brain. Thus, BChE has a function in neurotransmission. People with BChE deficiency are expected to be intolerant of standard doses of the anti-Alzheimer's drugs, (--)-huperzine A and donepezil.

Volpicelli-Daley LA, Duysen EG, Lockridge O, Levey AI. · Center for Neurodegenerative Disease and Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322, USA. · Ann Neurol. · Pubmed #12783426 No free full text.

Abstract: A primary therapeutic strategy for Alzheimer's disease includes acetylcholinesterase (AChE) inhibitors with the goal of enhancing cholinergic transmission. Stimulation of muscarinic acetylcholine receptors (mAChRs) by elevated levels of ACh plays a role in the effects of AChE inhibitors on cognition and behavior. However, AChE inhibitors only demonstrate modest symptomatic improvements. Chronic treatment with these drugs may cause mAChR downregulation and consequently limit the treatment efficacy. AChE knockout (-/-) mice were utilized in this study as a model for investigating the effects of selective, complete, and chronic diminished AChE activity on mAChR expression and function. In AChE -/- mice, the M(1), M(2), and M(4) mAChRs showed strikingly 50 to 80% decreased expression in brain regions associated with memory. In addition, mAChRs showed decreased presynaptic, cell surface, and dendritic distributions and increased localization to intracellular puncta. Furthermore, mAChR agonist-induced activation of extracellular signal-regulated kinase, a signaling pathway associated with synaptic plasticity and amyloidogenesis, is diminished in the hippocampus and cortex of AChE -/- mice. Therefore, chronic diminished ACh metabolism produces profound effects on mAChR expression and function. The alterations of mAChRs in AChE -/- mice suggest that mAChR downregulation may contribute to the limited efficacy of AChE inhibitors in Alzheimer's disease treatment.