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Nigel H Greig

Publications and source records attributed to Nigel H Greig.

16 recordsLinked to original sources
PubMed2003

The importance of the nine-amino acid C-terminal sequence of exendin-4 for binding to the GLP-1 receptor and for biological activity.

Exendin-4, a 39-amino acid (AA) peptide, is a long-acting agonist at the glucagon-like peptide-1 (GLP-1) receptor. Consequently, it may be preferable to GLP-1 as a long-term treatment for type 2 diabetes mellitus. Exendin-4 (Ex-4), unlike GLP-1, is not degraded by dipeptidyl peptidase IV (DPP IV), is less susceptible to degradation by neutral endopeptidase, and possesses a nine-AA C-terminal sequence absent from GLP-1. Here we examine the importance of these nine AAs for biological activity of Ex-4, a sequence of truncated Ex-4 analogs, and native GLP-1 and GLP-1 analogs to which all or parts of the C-terminal sequence have been added. We found that removing these AAs from Ex-4 to produce Ex (1-30) reduced the affinity for the GLP-1 receptor (GLP-1R) relative to Ex-4 (IC50: Ex-4, 3.22+/-0.9 nM; Ex (1-30), 32+/-5.8 nM) but made it comparable to that of GLP-1 (IC50: 44.9+/-3.2 nM). The addition of this nine-AA sequence to GLP-1 improved the affinity of both GLP-1 and the DPP IV resistant analog GLP-1 8-glycine for the GLP-1 receptor (IC50: GLP-1 Gly8 [GG], 220+/-23 nM; GLP-1 Gly8 Ex (31-39), 74+/-11 nM). Observations of the cAMP response in an insulinoma cell line show a similar trend for biological activity.

Amino Acid Sequence↗
PubMed2003

Glucagon-like peptide-1 decreases endogenous amyloid-beta peptide (Abeta) levels and protects hippocampal neurons from death induced by Abeta and iron.

Glucagon-like peptide-1(7-36)-amide (GLP-1) is an endogenous insulinotropic peptide that is secreted from the gastrointestinal tract in response to food. It enhances pancreatic islet beta-cell proliferation and glucose-dependent insulin secretion and lowers blood glucose and food intake in patients with type 2 diabetes mellitus. GLP-1 receptors, which are coupled to the cyclic AMP second messenger pathway, are expressed throughout the brains of rodents and humans. It was recently reported that GLP-1 and exendin-4, a naturally occurring, more stable analogue of GLP-1 that binds at the GLP-1 receptor, possess neurotrophic properties and can protect neurons against glutamate-induced apoptosis. We report here that GLP-1 can reduce the levels of amyloid-beta peptide (Abeta) in the brain in vivo and can reduce levels of amyloid precursor protein (APP) in cultured neuronal cells. Moreover, GLP-1 and exendin-4 protect cultured hippocampal neurons against death induced by Abeta and iron, an oxidative insult. Collectively, these data suggest that GLP-1 can modify APP processing and protect against oxidative injury, two actions that suggest a novel therapeutic target for intervention in Alzheimer's disease.

Alzheimer Disease↗
PubMed2003

A critical analysis of new molecular targets and strategies for drug developments in Alzheimer's disease.

Alzheimer's disease (AD), a progressive, degenerative disorder of the brain, is believed to be the most common cause of dementia amongst the elderly. AD is characterized by the presence of amyloid deposits and neurofibrillary tangles in the brain of afflicted individuals. AD is associated with a loss of the presynaptic markers of the cholinergic system in the brain areas related to memory and learning. AD appears to have a heterogeneous etiology with a large percentage termed sporadic AD arising from unknown causes and a smaller fraction of early onset familial AD (FAD) caused by mutations in one of several genes, such as the beta-amyloid precursor protein (APP) and presenilins (PS1, PS2). These proteins along with tau, secretases, such as beta-amyloid cleaving enzyme (BACE), and apolipoprotein E play important roles in the pathology of AD. On therapeutic fronts, there is significant research underway in the development of new inhibitors for BACE, PS-1 and gamma-secretase as targets for treatment of AD. There is also a remarkable advancement in understanding the function of cholinesterase (ChE) in the brain and the use of ChE-inhibitors in AD. A new generation of acetyl- and butyryl cholinesterase inhibitors is being studied and tested in human clinical trials for AD. The development of vaccination strategies, anti-inflammatory agents, cholesterol-lowering agents, anti-oxidants and hormone therapy are examples of new approaches for treating or slowing the progression of AD. In addition, nutritional, genetic and environmental factors highlight more effective preventive strategies for AD. Developments of early diagnostic tools and of quantitative markers are critical to better follow the course of the disease and to evaluate different therapeutic strategies. In this review, we attempt to critically examine recent trends in AD research from molecular, genetic to clinical areas. We discuss various neurobiological mechanisms that provide the basis of new targets for AD drug development. All these current research efforts should lead to a deeper understanding of the pathobiochemical processes that occur in the AD brain in order to effectively diagnose and prevent their occurrence.

Alzheimer Disease↗
PubMed2002

Novel p53 inactivators with neuroprotective action: syntheses and pharmacological evaluation of 2-imino-2,3,4,5,6,7-hexahydrobenzothiazole and 2-imino-2,3,4,5,6,7-hexahydrobenzoxazole derivatives.

Tumor suppressor protein, p53, is an intracellular protein that is critical within the biochemical cascade that leads to cell death via apoptosis. Recent studies identified the tetrahydrobenzothiazole analogue, pifithrin-alpha (2), as a p53 inhibitor that was effective in protecting neuronal cells against a variety of lethal insults and reducing the side effects of anticancer drugs. As up-regulation of p53 has been described as a common feature of several neurodegenerative disorders, including Alzheimer's disease, 2 and novel analogues (3-16) were synthesized to (i) assess the value of tetrahydrobenzothiazole analogues as neuroprotective agents and (ii) define the structural requirements for p53 inactivation. Not only did 2 exhibit neuroprotective activity in both tissue culture and in vivo stroke models but also compounds 6, 7, 10, 13, 15, and 16 proved to be highly potent in protecting PC12 cells and compounds 3, 4, and 6 were highly potent in protecting primary hippocampal cells against death induced by the DNA-damaging agent, camptothecin.

Animals↗
PubMed2002

An iron-responsive element type II in the 5'-untranslated region of the Alzheimer's amyloid precursor protein transcript.

Iron-responsive elements (IREs) are the RNA stem loops that control cellular iron homeostasis by regulating ferritin translation and transferrin receptor mRNA stability. We mapped a novel iron-responsive element (IRE-Type II) within the 5'-untranslated region (5'-UTR) of the Alzheimer's amyloid precursor protein (APP) transcript (+51 to +94 from the 5'-cap site). The APP mRNA IRE is located immediately upstream of an interleukin-1 responsive acute box domain (+101 to +146). APP 5'-UTR conferred translation was selectively down-regulated in response to intracellular iron chelation using three separate reporter assays (chloramphenicol acetyltransferase, luciferase, and red fluorescent protein reflecting an inhibition of APP holoprotein translation in response to iron chelation. Iron influx reversed this inhibition. As an internal control to ensure specificity, a viral internal ribosome entry sequence was unresponsive to intracellular iron chelation with desferrioxamine. Using RNA mobility shift assays, the APP 5'-UTRs, encompassing the IRE, bind specifically to recombinant iron-regulatory proteins (IRP) and to IRP from neuroblastoma cell lysates. IRP binding to the APP 5'-UTR is reduced after treatment of cells with desferrioxamine and increased after interleukin-1 stimulation. IRP binding is abrogated when APP cRNA probe is mutated in the core IRE domain (Delta4 bases:Delta83AGAG86). Iron regulation of APP mRNA through the APP 5'-UTR points to a role for iron in the metabolism of APP and confirms that this RNA structure can be a target for the selection of small molecule drugs, such as desferrioxamine (Fe chelator) and clioquinol (Fe, Cu, and Zn chelator), which reduce Abeta peptide burden during Alzheimer's disease.

5' Untranslated Regions↗
PubMed2002

Anticholinesterase activity of compounds related to geneserine tautomers. N-Oxides and 1,2-oxazines.

A series of phenylcarbamate analogues of geneserine (8, 10, 12, 14) were synthesized from their counterparts, the phenylcarbamate analogues of physostigmine (2-5), by oxidation. The geneserine analogues can undergo tautomerism between N-oxide and 1,2-oxazine structures in a pH- and time-dependent manner. Assessment by (1)H NMR indicated that the N-oxide structure is adopted at neutral pH and that the compound exists in an equilibrium between several epimers. Evaluation of their biological action to inhibit human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), ex vivo, demonstrated that the N-oxide (7, 9, 11, 13, 15) and 1,2-oxazine (6, 8, 10, 12, 14) structures possessed similar potencies against AChE, but the latter structures were more potent against BChE. With the exception of the BChE selective inhibitor, 12, none of the geneserine analogues were as potent or enzyme subtype selective as their physostigmine analogue counterparts.

Acetylcholinesterase↗
PubMed2002

p53 inhibitors preserve dopamine neurons and motor function in experimental parkinsonism.

Drugs currently used for patients with Parkinson's disease provide temporary relief of symptoms but do not halt or slow the underlying neurodegenerative disease process. Increasing evidence suggests that neurons die in Parkinson's disease by a process called apoptosis, which may be triggered by mitochondrial impairment and oxidative stress. We report that two novel synthetic inhibitors of the tumor suppressor protein p53, pifithrin-alpha (PFT-alpha) and Z-1-117, are highly effective in protecting midbrain dopaminergic neurons and improving behavioral outcome in a mouse model of Parkinson's disease. Mice given intraperitoneal injections of PFT-alpha or Z-1-117 exhibited improved motor function, reduced damage to nigrostriatal dopaminergic neurons and reduced depletion of dopamine and its metabolites after exposure to the toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP caused an increase in the level of the proapoptotic protein Bax, which was prevented by giving mice PFT-alpha and Z-1-117. PFT-alpha and Z-1-117 also suppressed Bax production and apoptosis in cultured dopaminergic cells exposed to MPP(+). Our findings demonstrate a pivotal role for p53 in experimental parkinsonism and identify a novel class of synthetic p53 inhibitors with clinical potential.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2002

Butyrylcholinesterase: an important new target in Alzheimer's disease therapy.

Acetylcholinesterase (AChE) predominates in the healthy brain, with butyrylcholinesterase (BuChE) considered to play a minor role in regulating brain acetylcholine (ACh) levels. However, BuChE activity progressively increases in patients with Alzheimer's disease (AD), while AChE activity remains unchanged or declines. Both enzymes therefore represent legitimate therapeutic targets for ameliorating the cholinergic deficit considered to be responsible for the declines in cognitive, behavioral and global functioning characteristic of AD. The two enzymes differ in substrate specificity, kinetics and activity in different brain regions. Experimental evidence from the use of agents with enhanced selectivity for BuChE (cymserine analogues, MF-8622) and the dual inhibitor of both AChE and BuChE, rivastigmine, indicates potential therapeutic benefits of inhibiting both AChE and BuChE in AD and related dementias. Recent evidence suggests that both AChE and BuChE may have roles in the aetiology and progression of AD beyond regulation of synaptic ACh levels. The development of specific BuChE inhibitors and further experience with the dual enzyme inhibitor rivastigmine will improve understanding of the aetiology of AD and should lead to a wider variety of potent treatment options.

Acetylcholine↗
PubMed2002

Protection and reversal of excitotoxic neuronal damage by glucagon-like peptide-1 and exendin-4.

Glucagon-like peptide-1 (7-36)-amide (GLP-1) is an endogenous insulinotropic peptide that is secreted from the L cells of the gastrointestinal tract in response to food. It has potent effects on glucose-dependent insulin secretion, insulin gene expression, and pancreatic islet cell formation. In type 2 diabetes, GLP-1, by continuous infusion, can normalize blood glucose and is presently being tested in clinical trials as a therapy for this disease. More recently, GLP-1 has been found to have central nervous system (CNS) effects and to stimulate neurite outgrowth in cultured cells. We now report that GLP-1, and its longer-acting analog exendin-4, can completely protect cultured rat hippocampal neurons against glutamate-induced apoptosis. Extrapolating these effects to a well defined rodent model of neurodegeneration, GLP-1 and exendin-4 greatly reduced ibotenic acid-induced depletion of choline acetyltransferase immunoreactivity in basal forebrain cholinergic neurons. These findings identify a novel neuroprotective/neurotrophic function of GLP-1 and suggest that such peptides may have potential for halting or reversing neurodegenerative processes in CNS disorders, such as Alzheimer's disease, and in neuropathies associated with type 2 diabetes mellitus.

Animals↗
PubMed2002

A novel neurotrophic property of glucagon-like peptide 1: a promoter of nerve growth factor-mediated differentiation in PC12 cells.

The insulinotropic hormone glucagon-like peptide-1 (7-36)-amide (GLP-1) has potent effects on glucose-dependent insulin secretion, insulin gene expression, and pancreatic islet cell formation and is presently in clinical trials as a therapy for type 2 diabetes mellitus. We report on the effects of GLP-1 and two of its long-acting analogs, exendin-4 and exendin-4 WOT, on neuronal proliferation and differentiation, and on the metabolism of two neuronal proteins in the rat pheochromocytoma (PC12) cell line, which has been shown to express the GLP-1 receptor. We observed that GLP-1 and exendin-4 induced neurite outgrowth in a manner similar to nerve growth factor (NGF), which was reversed by coincubation with the selective GLP-1 receptor antagonist exendin (9-39). Furthermore, exendin-4 could promote NGF-initiated differentiation and may rescue degenerating cells after NGF-mediated withdrawal. These effects were induced in the absence of cellular dysfunction and toxicity as quantitatively measured by 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and lactate dehydrogenase assays, respectively. Our findings suggest that such peptides may be used in reversing or halting the neurodegenerative process observed in neurodegenerative diseases, such as the peripheral neuropathy associated with type 2 diabetes mellitus and Alzheimer's and Parkinson's diseases. Due to its novel twin action, GLP-1 and exendin-4 have therapeutic potential for the treatment of diabetic peripheral neuropathy and these central nervous system disorders.

Amino Acid Sequence↗
PubMed2002

Advances in the cellular and molecular biology of the beta-amyloid protein in Alzheimer's disease.

Alzheimer's disease (AD) is a progressive senile dementia characterized by deposition of a 4 kDa peptide of 39-42 residues known as amyloid beta-peptide (Abeta) in the form of senile plaques and the microtubule associated protein tau as paired helical filaments. Genetic studies have identified mutations in the Abeta precursor protein (APP) as the key triggers for the pathogenesis of AD. Other genes such as presenilins 1 and 2 (PS1/2) and apolipoprotein E (APOE) also play a critical role in increased Abeta deposition. Several biochemical and molecular studies using transfected cells and transgenic animals point to mechanisms by which Abeta is generated and aggregated to trigger the neurodegeneration that may cause AD. Three important enzymes collectively known as "secretases" participate in APP processing. An enzymatic activity, beta-secretase, cleaves APP on the amino side of Abeta producing a large secreted derivative, sAPPbeta, and an Abeta-bearing membrane-associated C-terminal derivative, CTFbeta, which is subsequently cleaved by the second activity, gamma-secretase, to release Abeta. Alternatively, a third activity, alpha-secretase, cleaves APP within Abeta to the secreted derivative sAPPalpha and membrane-associated CTFalpha. The predominant secreted APP derivative is sAPPalpha in most cell-types. Most of the secreted Abeta is 40 residues long (Abeta40) although a small percentage is 42 residues in length (Abeta42). However, the longer Abeta42 aggregates more readily and was therefore considered to be the pathologically important form. Advances in our understanding of APP processing, trafficking, and turnover will pave the way for better drug discovery for the eventual treatment of AD. In addition, APP gene regulation and its interaction with other proteins may provide useful drug targets for AD. The emerging knowledge related to the normal function of APP will help in determining whether or not the AD associated changes in APP metabolism affect its function. The present review summarizes our current understanding of APP metabolism and function and their relationship to other proteins involved in AD.

Aged↗
PubMed2002

Nicotine lowers the secretion of the Alzheimer's amyloid beta-protein precursor that contains amyloid beta-peptide in rat.

Reports of an inverse relationship between nicotine intake, due to cigarette smoking, and the incidence of Alzheimer's disease (AD) prompted us to investigate the effects of nicotine on amyloid beta-protein precursor (AbetaPP) processing in rat. Over-production and/or altered metabolism of AbetaPP, resulting in increased amyloid beta-peptide (Abeta), appear pivotal in the pathogenesis of AD. Abeta is generated proteolytically from betaPP by a group of secretases. AbetaPP cleavage by gamma-secretase results in the secretion of a truncated soluble betaPP (sAPPgamma) that contains intact Abeta. Nicotine, 1 and 8 mg/kg/day, doses commensurate with cigarette smoking and a higher but well tolerated dose, respectively, was administered over 14 days and Western blot analysis was performed on sAPP fragments. Both doses significantly reduced sAPPgamma. These actions were blocked by nicotinic receptor antagonism. Whereas nicotinic antagonists alone had no effect on either total sAPP or sAPPgammalevels in CSF, muscarinic antagonism significantly elevated them; suggesting that muscarinic rather than nicotinic receptor silence alters processing of AbetaPP to favor a potentially amyloidogenic route. Combined nicotine and muscarinic antagonism attenuated the action of the latter to elevate sAPPgamma, indicating that nicotine modifies AbetaPP processing away from potentially amyloidogenic products. These results suggest that within the brain, levels of total sAPP, sAPPgamma and, accordingly, Abeta are subject to cholinergic manipulation, offering therapeutic potential at the level of AbetaPP processing to decrease Abetadeposition.

Alzheimer Disease↗
PubMed2002

The glucagon-like peptides: a new genre in therapeutic targets for intervention in Alzheimer's disease.

Glucagon-like peptide-1 (7-36)-amide (GLP-1) is an insulinotropic hormone, secreted from the enteroendocrine L cells of the intestinal tract in response to nutrient ingestion. It enhances pancreatic islet beta-cell proliferation and glucose-dependent insulin secretion, and lowers blood glucose in patients with type 2 diabetes mellitus. GLP-1 receptors, which are coupled to the cyclic AMP second messenger pathway, are expressed throughout the brains of rodents and humans. The chemoarchitecture of receptor distribution in the brain correlates well with a central role for GLP-1 in the regulation of food intake and response to aversive stress. We have recently reported that GLP-1 and several longer acting analogs that bind at the GLP-1 receptor, possess neurotrophic properties, and offer protection against glutamate-induced apoptosis and oxidative injury in cultured neuronal cells. Furthermore, GLP-1 can modify processing of the amyloid beta- protein precursor in cell culture and dose-dependently reduces amyloid beta-peptide levels in the brain in vivo. As such, this review discusses the known role of GLP-1 within the central nervous system, and considers the potential of GLP-1 and analogs as novel therapeutic targets for intervention in Alzheimer's disease (AD) and potentially other central and peripheral neurodegenerative conditions.

Alzheimer Disease↗
PubMedDate not supplied

Worsening of motor function and mood in a patient with Parkinson's disease after pharmacologic challenge with oral rivastigmine.

Patients with Parkinson's disease (PD) can experience cognitive impairment. There are currently no medications indicated for the treatment of cognitive impairment in PD. Clinicians are faced with the dilemma as to whether or not to treat patients with PD with the acetylcholinesterase inhibitors that are currently approved for use in Alzheimer's disease (AD) and that have shown promise in clinical trials of Dementia with Lewy bodies (DLB). Although these medications may help cognition, there is a theoretical concern that by increasing acetylcholine relative to dopamine, they might worsen motor function. We report the case of a patient with PD and cognitive impairment who developed a marked worsening of motor function, mood, and anxiety in the setting of a pharmacologic challenge study using a 3-mg oral dose of the acetylcholinesterase inhibitor, rivastigmine. We believe that the mechanism of the motor and perhaps psychiatric worsening was increased central cholinergic tone. We conclude that further studies should be done to evaluate the efficacy and tolerability of these agents in this illness but that caution should be exercised when using acetylcholinesterase inhibitors in patients with PD.

Administration, Oral↗