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Abstract
Substances cross the blood-brain barrier (BBB) by a variety of mechanisms. These include transmembrane diffusion, saturable transporters, adsorptive endocytosis, and the extracellular pathways. Here, we focus on the chief characteristics of two mechanisms especially important in drug delivery: transmembrane diffusion and transporters. Transmembrane diffusion is non-saturable and depends, on first analysis, on the physicochemical characteristics of the substance. However, brain-to-blood efflux systems, enzymatic activity, plasma protein binding, and cerebral blood flow can greatly alter the amount of the substance crossing the BBB. Transport systems increase uptake of ligands by roughly 10-fold and are modified by physiological events and disease states. Most drugs in clinical use to date are small, lipid soluble molecules that cross the BBB by transmembrane diffusion. However, many drug delivery strategies in development target peptides, regulatory proteins, oligonucleotides, glycoproteins, and enzymes for which transporters have been described in recent years. We discuss two examples of drug delivery for newly discovered transporters: that for phosphorothioate oligonucleotides and for enzymes.
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Affiliation(s)
- William A Banks
- Veterans Affairs Medical Center-St Louis, 915 N, Grand Blvd, St, Louis, MO 63106, USA.
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552
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Abstract
Impaired insulin secretion plays a major role in the pathogenesis of type 2 diabetes mellitus, and progressive loss of beta-cell function is a pathophysiologic hallmark of type 2 diabetes. Recent science has elaborated on the role of the incretin hormones on beta-cell function and insulin secretion, as well as the role that incretin-based pharmacotherapies may have on glycemic control and beta-cell function, possibly altering the progressive loss of beta-cell function and possibly reversing/halting disease progression. However, incretin-based therapies may also have benefits extending beyond glycemic control and insulin secretion. In this review we examine some of those "beyond-glycemic" benefits, including presentation of data on weight reduction, blood pressure lowering, beneficial changes in the lipid profile, and improvements in myocardial and endothelial function. We investigate how those effects may help ameliorate the cardiovascular burden in patients with diabetes.
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Affiliation(s)
- Sunder Mudaliar
- Section of Diabetes/Metabolism, VA San Diego HealthCare System, San Diego California 92161, USA.
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553
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Noyan-Ashraf MH, Momen MA, Ban K, Sadi AM, Zhou YQ, Riazi AM, Baggio LL, Henkelman RM, Husain M, Drucker DJ. GLP-1R agonist liraglutide activates cytoprotective pathways and improves outcomes after experimental myocardial infarction in mice. Diabetes 2009; 58:975-83. [PMID: 19151200 PMCID: PMC2661586 DOI: 10.2337/db08-1193] [Citation(s) in RCA: 427] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
OBJECTIVE Glucagon-like peptide-1 receptor (GLP-1R) agonists are used to treat type 2 diabetes, and transient GLP-1 administration improved cardiac function in humans after acute myocardial infarction (MI) and percutaneous revascularization. However, the consequences of GLP-1R activation before ischemic myocardial injury remain unclear. RESEARCH DESIGN AND METHODS We assessed the pathophysiology and outcome of coronary artery occlusion in normal and diabetic mice pretreated with the GLP-1R agonist liraglutide. RESULTS Male C57BL/6 mice were treated twice daily for 7 days with liraglutide or saline followed by induction of MI. Survival was significantly higher in liraglutide-treated mice. Liraglutide reduced cardiac rupture (12 of 60 versus 46 of 60; P = 0.0001) and infarct size (21 +/- 2% versus 29 +/- 3%, P = 0.02) and improved cardiac output (12.4 +/- 0.6 versus 9.7 +/- 0.6 ml/min; P = 0.002). Liraglutide also modulated the expression and activity of cardioprotective genes in the mouse heart, including Akt, GSK3beta, PPARbeta-delta, Nrf-2, and HO-1. The effects of liraglutide on survival were independent of weight loss. Moreover, liraglutide conferred cardioprotection and survival advantages over metformin, despite equivalent glycemic control, in diabetic mice with experimental MI. The cardioprotective effects of liraglutide remained detectable 4 days after cessation of therapy and may be partly direct, because liraglutide increased cyclic AMP formation and reduced the extent of caspase-3 activation in cardiomyocytes in a GLP-1R-dependent manner in vitro. CONCLUSIONS These findings demonstrate that GLP-1R activation engages prosurvival pathways in the normal and diabetic mouse heart, leading to improved outcomes and enhanced survival after MI in vivo.
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Affiliation(s)
| | | | - Kiwon Ban
- Toronto General Hospital, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | | | - Yu-Qing Zhou
- Mouse Imaging Centre, Department of Medical Biophysics, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Ali M. Riazi
- Mouse Imaging Centre, Department of Medical Biophysics, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Laurie L. Baggio
- Samuel Lunenfeld Research Institute, Mt. Sinai Hospital, Toronto, Ontario, Canada
| | - R. Mark Henkelman
- Mouse Imaging Centre, Department of Medical Biophysics, Hospital for Sick Children, Toronto, Ontario, Canada
| | - Mansoor Husain
- Toronto General Hospital, Toronto, Ontario, Canada
- Heart and Stroke Richard Lewar Centre of Excellence in Cardiovascular Research, Toronto, Ontario, Canada
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada
| | - Daniel J. Drucker
- Samuel Lunenfeld Research Institute, Mt. Sinai Hospital, Toronto, Ontario, Canada
- Department of Medicine, University of Toronto, Toronto, Ontario, Canada
- Corresponding author: Daniel J. Drucker,
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554
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Walther T, Albrecht D, Becker M, Schubert M, Kouznetsova E, Wiesner B, Maul B, Schliebs R, Grecksch G, Furkert J, Sterner-Kock A, Schultheiss HP, Becker A, Siems WE. Improved learning and memory in aged mice deficient in amyloid beta-degrading neutral endopeptidase. PLoS One 2009; 4:e4590. [PMID: 19240795 PMCID: PMC2643003 DOI: 10.1371/journal.pone.0004590] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2008] [Accepted: 01/17/2009] [Indexed: 12/03/2022] Open
Abstract
Background Neutral endopeptidase, also known as neprilysin and abbreviated NEP, is considered to be one of the key enzymes in initial human amyloid-β (Aβ) degradation. The aim of our study was to explore the impact of NEP deficiency on the initial development of dementia-like symptoms in mice. Methodology/Principal Findings We found that while endogenous Aβ concentrations were elevated in the brains of NEP-knockout mice at all investigated age groups, immunohistochemical analysis using monoclonal antibodies did not detect any Aβ deposits even in old NEP knockout mice. Surprisingly, tests of learning and memory revealed that the ability to learn was not reduced in old NEP-deficient mice but instead had significantly improved, and sustained learning and memory in the aged mice was congruent with improved long-term potentiation (LTP) in brain slices of the hippocampus and lateral amygdala. Our data suggests a beneficial effect of pharmacological inhibition of cerebral NEP on learning and memory in mice due to the accumulation of peptides other than Aβ degradable by NEP. By conducting degradation studies and peptide measurements in the brain of both genotypes, we identified two neuropeptide candidates, glucagon-like peptide 1 and galanin, as first potential candidates to be involved in the improved learning in aged NEP-deficient mice. Conclusions/Significance Thus, the existence of peptides targeted by NEP that improve learning and memory in older individuals may represent a promising avenue for the treatment of neurodegenerative diseases.
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Affiliation(s)
- Thomas Walther
- Department of Cardiology, Charité-University Medicine Berlin, Campus Benjamin Franklin, Berlin, Germany.
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555
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Iwai T, Suzuki M, Kobayashi K, Mori K, Mogi Y, Oka JI. The influences of juvenile diabetes on memory and hippocampal plasticity in rats: improving effects of glucagon-like peptide-1. Neurosci Res 2009; 64:67-74. [PMID: 19321133 DOI: 10.1016/j.neures.2009.01.013] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2008] [Revised: 01/22/2009] [Accepted: 01/26/2009] [Indexed: 10/21/2022]
Abstract
Previous studies in children with diabetes found that hyperglycemia induces memory dysfunction. In this study, we investigated memory and synaptic plasticity in streptozotocine (STZ)-induced diabetic rats during the juvenile period. We further investigated the effects of glucagon-like peptide-1 (GLP-1) on the diabetes-induced profiles. STZ (85 mg/kg, i.p.) was administered to 17-day-old Wistar rats to induce type-1 juvenile diabetes mellitus (JDM). In the Y-maze test, JDM rats showed significant impairment of learning and memory, which were improved by GLP-1 (7-36) amide (1 microg/5 microl/rat, i.c.v.). Extracellular recording at Schaffer collateral synapses in the CA1 region of hippocampal slices showed that long-term potentiation and paired-pulse facilitation in JDM rats were similar to age-matched control rats. However, the input-output relation was strengthened, and long-term depression (LTD) and responses of N-methyl d-aspartic acid through NR2B subunits were weakened in the JDM rats. GLP-1 (7-36) amide (100 nM) increased the magnitude of LTD and the responses through NR2B in the JDM rats. These results indicate that the lack of LTD and NR2B responses may contribute to impairment of memory associated with JDM, suggesting the potential usefulness of GLP-1 in the treatment of memory dysfunction in JDM.
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Affiliation(s)
- Takashi Iwai
- Laboratory of Pharmacology, Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
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556
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Martin B, Golden E, Carlson OD, Pistell P, Zhou J, Kim W, Frank BP, Thomas S, Chadwick WA, Greig NH, Bates GP, Sathasivam K, Bernier M, Maudsley S, Mattson MP, Egan JM. Exendin-4 improves glycemic control, ameliorates brain and pancreatic pathologies, and extends survival in a mouse model of Huntington's disease. Diabetes 2009; 58:318-28. [PMID: 18984744 PMCID: PMC2628604 DOI: 10.2337/db08-0799] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
OBJECTIVE The aim of this study was to find an effective treatment for the genetic form of diabetes that is present in some Huntington's disease patients and in Huntington's disease mouse models. Huntington's disease is a neurodegenerative disorder caused by a polyglutamine expansion within the huntingtin protein. Huntington's disease patients exhibit neuronal dysfunction/degeneration, chorea, and progressive weight loss. Additionally, they suffer from abnormalities in energy metabolism affecting both the brain and periphery. Similarly to Huntington's disease patients, mice expressing the mutated human huntingtin protein also exhibit neurodegenerative changes, motor dysfunction, perturbed energy metabolism, and elevated blood glucose levels. RESEARCH DESIGN AND METHODS Huntington's disease mice were treated with an FDA-approved antidiabetic glucagon-like peptide 1 receptor agonist, exendin-4 (Ex-4), to test whether euglycemia could be achieved, whether pancreatic dysfunction could be alleviated, and whether the mice showed any neurological benefit. Blood glucose and insulin levels and various appetite hormone concentrations were measured during the study. Additionally, motor performance and life span were quantified and mutant huntingtin (mhtt) aggregates were measured in both the pancreas and brain. RESULTS Ex-4 treatment ameliorated abnormalities in peripheral glucose regulation and suppressed cellular pathology in both brain and pancreas in a mouse model of Huntington's disease. The treatment also improved motor function and extended the survival time of the Huntington's disease mice. These clinical improvements were correlated with reduced accumulation of mhtt protein aggregates in both islet and brain cells. CONCLUSIONS Targeting both peripheral and neuronal deficits, Ex-4 is an attractive agent for therapeutic intervention in Huntington's disease patients suffering from diabetes.
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Affiliation(s)
- Bronwen Martin
- Laboratory of Neurosciences, National Institute on Aging Intramural Research Program, Baltimore, Maryland, USA
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557
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Neuroprotection of geniposide against hydrogen peroxide induced PC12 cells injury: involvement of PI3 kinase signal pathway. Acta Pharmacol Sin 2009; 30:159-65. [PMID: 19151742 DOI: 10.1038/aps.2008.25] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
AIM Oxidative stress plays a critical role in the pathogenic cascade leading to neuronal degeneration in AD. Consequently, the induction of endogenous antioxidative proteins by antioxidants seems to be a very reasonable strategy for delaying the disease's progression. In previous work, we identified the neurotrophic and neuroprotective effects of geniposide, which result from the activation of glucagon-like peptide 1 receptor (GLP-1R). In this study, we explore the role of PI3 kinase signaling pathway in the neuroprotection of geniposide in PC12 cells. METHODS Cell viability was determined by MTT assay. Apoptosis was detected by Hoechst and PI double staining. The protein expression of Bcl-2 and phosphorylation of Akt308, Akt473, GSK-3beta, and PDK1 was measured by Western blot. RESULTS Geniposide induced the expression of the antiapoptotic protein Bcl-2, which inhibited apoptosis in PC12 cells induced by H(2)O(2), and this effect could be inhibited by preincubation with LY294002, a selective inhibitor of PI3K. Furthermore, geniposide enhanced the phosphorylation of Akt308, Akt473, GSK-3beta and PDK1 under conditions of oxidative stress. CONCLUSION These results demonstrate that the PI3K signaling pathway is involved in the neuroprotection of geniposide in PC12 cells against the oxidative damage induced by H(2)O(2) in PC12 cells.
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558
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Abbatecola AM, Maggi S, Paolisso G. New approaches to treating type 2 diabetes mellitus in the elderly: role of incretin therapies. Drugs Aging 2009; 25:913-25. [PMID: 18947259 DOI: 10.2165/0002512-200825110-00002] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The increasing proportion of elderly persons in the global population, and the implications of this trend in terms of increasing rates of chronic diseases such as type 2 diabetes mellitus, continue to be a cause for concern for clinicians and healthcare policy makers. The diagnosis and treatment of type 2 diabetes in the elderly is challenging, as age-related changes alter the clinical presentation of diabetic symptoms. Once type 2 diabetes is diagnosed, the principles of its management are similar to those in younger patients, but with special considerations linked to the increased prevalence of co-morbidities and relative inability to tolerate the adverse effects of medication and hypoglycaemia. In addition, there are many underappreciated factors complicating diabetes care in the elderly, including cognitive disorders, physical disability and geriatric syndromes, such as frailty, urinary incontinence and pain. Available oral antihyperglycaemic drugs include insulin secretagogues (meglitinides and sulfonylureas), biguanides (metformin), alpha-glucosidase inhibitors and thiazolidinediones. Unfortunately, as type 2 diabetes progresses in older persons, polypharmacy intensification is required to achieve adequate glycaemic control with the attendant increased risk of adverse effects as a result of age-related changes in drug metabolism. The recent introduction of the incretins, a group of intestinal peptides that enhance insulin secretion after ingestion of food, as novel oral antihyperglycaemic treatments may prove significant in older persons. The two main categories of incretin therapy currently available are: glucagon-like peptide-1 (GLP-1) analogues and inhibitors of GLP-1 degrading enzyme dipeptidyl peptidase-4 (DPP-4). The present review discusses the effect of aging on metabolic control in elderly patients with type 2 diabetes, the current treatments used to treat this population and some of the more recent advances in the field of geriatric type 2 diabetes. In particular, we highlight the efficacy and safety of GLP-1 and DPP-4 inhibitors, administered as monotherapy or in combination with other oral antihyperglycaemic agents, especially when the relevant clinical trials included older persons. There is strong evidence that use of incretin therapy, in particular, the DPP-4 inhibitors, could offer significant advantages in older persons. Clinical evidence suggests that the DPP-4 inhibitors vildagliptin and sitagliptin are particularly suitable for frail and debilitated elderly patients because of their excellent tolerability profiles. Importantly, these agents lack the gastrointestinal effects seen with metformin and alpha-glucosidase inhibitors taken alone, and have a low risk of the hypoglycaemic events commonly seen with agents that directly lower blood glucose levels.
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Affiliation(s)
- Angela M Abbatecola
- Department of Geriatric Medicine and Metabolic Diseases, Second University of Naples, Naples, Italy
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559
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GLP-1 receptor stimulation preserves primary cortical and dopaminergic neurons in cellular and rodent models of stroke and Parkinsonism. Proc Natl Acad Sci U S A 2009; 106:1285-90. [PMID: 19164583 DOI: 10.1073/pnas.0806720106] [Citation(s) in RCA: 434] [Impact Index Per Article: 28.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Glucagon-like peptide-1 (GLP-1) is an endogenous insulinotropic peptide secreted from the gastrointestinal tract in response to food intake. 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 (T2DM). A long-acting GLP-1 receptor (GLP-1R) agonist, exendin-4 (Ex-4), is the first of this new class of antihyperglycemia drugs approved to treat T2DM. GLP-1Rs are coupled to the cAMP second messenger pathway and, along with pancreatic cells, are expressed within the nervous system of rodents and humans, where receptor activation elicits neurotrophic actions. We detected GLP-1R mRNA expression in both cultured embryonic primary cerebral cortical and ventral mesencephalic (dopaminergic) neurons. These cells are vulnerable to hypoxia- and 6-hydroxydopamine-induced cell death, respectively. We found that GLP-1 and Ex-4 conferred protection in these cells, but not in cells from Glp1r knockout (-/-) mice. Administration of Ex-4 reduced brain damage and improved functional outcome in a transient middle cerebral artery occlusion stroke model. Ex-4 treatment also protected dopaminergic neurons against degeneration, preserved dopamine levels, and improved motor function in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD). Our findings demonstrate that Ex-4 can protect neurons against metabolic and oxidative insults, and they provide preclinical support for the therapeutic potential for Ex-4 in the treatment of stroke and PD.
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560
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Banks WA, Morley JE, Niehoff ML, Mattern C. Delivery of testosterone to the brain by intranasal administration: Comparison to intravenous testosterone. J Drug Target 2009; 17:91-7. [DOI: 10.1080/10611860802382777] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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561
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Rossetti P, Porcellati F, Lucidi P, Busciantella Ricci N, Candeloro P, Cioli P, Santeusanio F, Bolli GB, Fanelli CG. Portal vein glucose sensors do not play a major role in modulating physiological responses to insulin-induced hypoglycemia in humans. Diabetes 2009; 58:194-202. [PMID: 18852332 PMCID: PMC2606871 DOI: 10.2337/db08-0641] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
OBJECTIVE Experimental data from animal studies indicate that portal vein glucose sensors play a key role in the responses to slow-fall hypoglycemia. However, their role in modulating these responses in humans is not well understood. The aim of the present study was to examine in humans the potential role of portal vein glucose sensors in physiological responses to insulin-induced hypoglycemia mimicking the slow fall of insulin-treated diabetic subjects. RESEARCH DESIGN AND METHODS Ten nondiabetic subjects were studied on two different occasions during intravenous insulin (2 mU . kg(-1) . min(-1)) plus variable glucose for 160 minutes. In both studies, after 60 min of normal plasma glucose concentrations, hypoglycemia (47 mg/dl) was induced slowly (60 min) and maintained for 60 min. Hypoglycemia was preceded by the ingestion of either oral placebo or glucose (28 g) given at 30 min. RESULTS Plasma glucose and insulin were not different with either placebo or glucose (P > 0.2). Similarly, counterregulatory hormones, substrates, and symptoms were not different with either placebo or glucose. The Stroop color and colored words subtest of the Stroop test deteriorated less (P < 0.05) with glucose than placebo. CONCLUSIONS In contrast to animals, in humans, prevention of portal hypoglycemia with oral glucose from the beginning of insulin-induced slow-fall hypoglycemia has no effect on sympathoadrenal and symptomatic responses to hypoglycemia.
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Affiliation(s)
- Paolo Rossetti
- Department of Internal Medicine, University of Perugia, Perugia, Italy
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562
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Zhang Y, Wang Q, Zhang J, Lei X, Xu GT, Ye W. Protection of exendin-4 analogue in early experimental diabetic retinopathy. Graefes Arch Clin Exp Ophthalmol 2008; 247:699-706. [DOI: 10.1007/s00417-008-1004-3] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Revised: 10/30/2008] [Accepted: 11/05/2008] [Indexed: 12/13/2022] Open
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563
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Takamoto I, Terauchi Y, Kubota N, Ohsugi M, Ueki K, Kadowaki T. Crucial role of insulin receptor substrate-2 in compensatory beta-cell hyperplasia in response to high fat diet-induced insulin resistance. Diabetes Obes Metab 2008; 10 Suppl 4:147-56. [PMID: 18834442 DOI: 10.1111/j.1463-1326.2008.00951.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
In type 2 diabetes, there is a defect in the regulation of functional beta-cell mass to overcome high-fat (HF) diet-induced insulin resistance. Many signals and pathways have been implicated in beta-cell function, proliferation and apoptosis. The co-ordinated regulation of functional beta-cell mass by insulin signalling and glucose metabolism under HF diet-induced insulin-resistant conditions is discussed in this article. Insulin receptor substrate (IRS)-2 is one of the two major substrates for the insulin signalling. Interestingly, IRS-2 is involved in the regulation of beta-cell proliferation, as has been demonstrated using knockout mice models. On the other hand, in an animal model for human type 2 diabetes with impaired insulin secretion because of insufficiency of glucose metabolism, decreased beta-cell proliferation was observed in mice with beta-cell-specific glucokinase haploinsufficiency (Gck(+/) (-)) fed a HF diet without upregulation of IRS-2 in beta-cells, which was reversed by overexpression of IRS-2 in beta-cells. As to the mechanism underlying the upregulation of IRS-2 in beta-cells, glucose metabolism plays an important role independently of insulin, and phosphorylation of cAMP response element-binding protein triggered by calcium-dependent signalling is the critical pathway. Downstream from insulin signalling via IRS-2 in beta-cells, a reduction in FoxO1 nuclear exclusion contributes to the insufficient proliferative response of beta-cells to insulin resistance. These findings suggest that IRS-2 is critical for beta-cell hyperplasia in response to HF diet-induced insulin resistance.
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Affiliation(s)
- I Takamoto
- Department of Metabolic Diseases, Graduate School of Medicine, University of Tokyo, Japan
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564
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New roles for insulin-like hormones in neuronal signalling and protection: new hopes for novel treatments of Alzheimer's disease? Neurobiol Aging 2008; 31:1495-502. [PMID: 18930564 DOI: 10.1016/j.neurobiolaging.2008.08.023] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2008] [Revised: 06/21/2008] [Accepted: 08/30/2008] [Indexed: 01/06/2023]
Abstract
Type 2 diabetes has been identified as a risk factor for Alzheimer's disease (AD). This is most likely due to the desensitisation of insulin receptors in the brain. Insulin acts as a growth factor and supports neuronal repair, dendritic sprouting, and differentiation. This review discusses the potential role that insulin-like hormones could play in ameliorating the reduced growth factor signalling in the brains of people with AD. The incretins glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) have very similar properties in protecting neurons from toxic effects, and are capable of reversing the detrimental effects that beta-amyloid fragments have on synaptic plasticity. Therefore, incretins show great promise as a novel treatment for reducing degenerative processes in AD.
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565
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Riley DE, Krieger JN. Embryonic nervous system genes predominate in searches for dinucleotide simple sequence repeats flanked by conserved sequences. Gene 2008; 429:74-9. [PMID: 18952158 DOI: 10.1016/j.gene.2008.09.025] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2008] [Revised: 09/18/2008] [Accepted: 09/23/2008] [Indexed: 12/15/2022]
Abstract
To study evolution of dinucleotide simple sequence repeats (diSSRs) we searched recently available mammalian genomes for UTR-localized diSSRs with conserved upstream flanking sequences (CFS). There were 252 reported Homo sapiens genes containing the repeats (AC)n, (GT)n, (AG)n or (CT)n in their UTRs including 22 (8.7%) with diSSR-upstream flanking sequences conserved comparing divergent mammalian lineages represented by Homo sapiens and the marsupial, Monodelphis domestica. Of these 22 genes, 19 had known functions including 18 (95%) that proved critical for mammalian nervous systems (Fishers exact test, P<0.0001). The remaining gene, Cd2ap, proved critical for development of kidney podocytes, cells that have multiple similarities to neurons. Gene functions included voltage and chloride channels, synapse-associated proteins, neurotransmitter receptors, axon and dendrite pathfinders, a NeuroD potentiator and other neuronal activities. Repeat length polymorphism was confirmed for 68% of CFS diSSRs even though these repeats were nestled among highly conserved sequences. This finding supports a hypothesis that SSR polymorphism has functional implications. A parallel study was performed on the self-complementary diSSRs (AT)n and (GC)n. When flanked by conserved sequences, the self-complementary diSSR (AT)n was also associated with genes expressed in the developing nervous system. Our findings implicate functional roles for diSSRs in nervous system development.
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Affiliation(s)
- Donald E Riley
- Department of Urology, University of Washington, Seattle, WA 98195, USA.
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566
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Knauf C, Cani PD, Kim DH, Iglesias MA, Chabo C, Waget A, Colom A, Rastrelli S, Delzenne NM, Drucker DJ, Seeley RJ, Burcelin R. Role of central nervous system glucagon-like Peptide-1 receptors in enteric glucose sensing. Diabetes 2008; 57:2603-12. [PMID: 18519802 PMCID: PMC2551668 DOI: 10.2337/db07-1788] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2007] [Accepted: 05/28/2008] [Indexed: 12/17/2022]
Abstract
OBJECTIVE Ingested glucose is detected by specialized sensors in the enteric/hepatoportal vein, which send neural signals to the brain, which in turn regulates key peripheral tissues. Hence, impairment in the control of enteric-neural glucose sensing could contribute to disordered glucose homeostasis. The aim of this study was to determine the cells in the brain targeted by the activation of the enteric glucose-sensing system. RESEARCH DESIGN AND METHODS We selectively activated the axis in mice using a low-rate intragastric glucose infusion in wild-type and glucagon-like peptide-1 (GLP-1) receptor knockout mice, neuropeptide Y-and proopiomelanocortin-green fluorescent protein-expressing mice, and high-fat diet diabetic mice. We quantified the whole-body glucose utilization rate and the pattern of c-Fos positive in the brain. RESULTS Enteric glucose increased muscle glycogen synthesis by 30% and regulates c-Fos expression in the brainstem and the hypothalamus. Moreover, the synthesis of muscle glycogen was diminished after central infusion of the GLP-1 receptor (GLP-1Rc) antagonist Exendin 9-39 and abolished in GLP-1Rc knockout mice. Gut-glucose-sensitive c-Fos-positive cells of the arcuate nucleus colocalized with neuropeptide Y-positive neurons but not with proopiomelanocortin-positive neurons. Furthermore, high-fat feeding prevented the enteric activation of c-Fos expression. CONCLUSIONS We conclude that the gut-glucose sensor modulates peripheral glucose metabolism through a nutrient-sensitive mechanism, which requires brain GLP-1Rc signaling and is impaired during diabetes.
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Affiliation(s)
- Claude Knauf
- Institut de Medecine Moleculaire de Rangueil, Institut National de la Santé et de la Recherche Médicale U858, IFR31, Centre Hospitalier Universitaire Rangueil, Toulouse, France
| | - Patrice D. Cani
- Institut de Medecine Moleculaire de Rangueil, Institut National de la Santé et de la Recherche Médicale U858, IFR31, Centre Hospitalier Universitaire Rangueil, Toulouse, France
- Unit of Pharmacokinetics, Metabolism, Nutrition, and Toxicology, Université Catholique de Louvain, Brussels, Belgium
| | - Dong-Hoon Kim
- Department of Psychiatry, Genome Research Institute, University of Cincinnati, Cincinnati, Ohio
| | - Miguel A. Iglesias
- Institut de Medecine Moleculaire de Rangueil, Institut National de la Santé et de la Recherche Médicale U858, IFR31, Centre Hospitalier Universitaire Rangueil, Toulouse, France
| | - Chantal Chabo
- Institut de Medecine Moleculaire de Rangueil, Institut National de la Santé et de la Recherche Médicale U858, IFR31, Centre Hospitalier Universitaire Rangueil, Toulouse, France
| | - Aurélie Waget
- Institut de Medecine Moleculaire de Rangueil, Institut National de la Santé et de la Recherche Médicale U858, IFR31, Centre Hospitalier Universitaire Rangueil, Toulouse, France
| | - André Colom
- Institut de Medecine Moleculaire de Rangueil, Institut National de la Santé et de la Recherche Médicale U858, IFR31, Centre Hospitalier Universitaire Rangueil, Toulouse, France
| | - Sophie Rastrelli
- Institut de Medecine Moleculaire de Rangueil, Institut National de la Santé et de la Recherche Médicale U858, IFR31, Centre Hospitalier Universitaire Rangueil, Toulouse, France
| | - Nathalie M. Delzenne
- Unit of Pharmacokinetics, Metabolism, Nutrition, and Toxicology, Université Catholique de Louvain, Brussels, Belgium
| | - Daniel J. Drucker
- Banting and Best Diabetes Centre, Samuel Lunenfeld Research Institute, Mt. Sinai Hospital, University of Toronto, Canada
| | - Randy J. Seeley
- Department of Psychiatry, Genome Research Institute, University of Cincinnati, Cincinnati, Ohio
| | - Remy Burcelin
- Institut de Medecine Moleculaire de Rangueil, Institut National de la Santé et de la Recherche Médicale U858, IFR31, Centre Hospitalier Universitaire Rangueil, Toulouse, France
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567
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McIntyre RS, Vagic D, Swartz SA, Soczynska JK, Woldeyohannes HO, Voruganti LP, Konarski JZ. Insulin, insulin-like growth factors and incretins: neural homeostatic regulators and treatment opportunities. CNS Drugs 2008; 22:443-53. [PMID: 18484789 DOI: 10.2165/00023210-200822060-00001] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Mood disorders may be conceptualized as progressive neurodegenerative disorders associated with cognitive decline. Novel treatments capable of preserving and/or enhancing cognitive function represent an area of priority for research in the future. Insulin, insulin-like growth factor (IGF)-1 and incretins may play a critical role in both physiological and pathophysiological processes of the CNS. An emerging paradigm regarding the pathophysiology of mood disorders posits that alterations in biological networks that mediate stress compromise optimal neuronal and glial function. A growing body of evidence indicates that central administration of insulin may enhance cognitive function in both healthy and cognitively impaired individuals. The neuroactive peptides, insulin, IGF-1 and incretins, or agents that facilitate their central effects (e.g. insulin-sensitizing agents), may constitute novel and possibly disease-modifying neurocognitive treatments.
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Affiliation(s)
- Roger S McIntyre
- Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada.
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568
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Lin L. Commonality between diabetes and Alzheimer's disease and a new strategy for the therapy. CLINICAL MEDICINE. PATHOLOGY 2008; 1:83-91. [PMID: 21876656 PMCID: PMC3160008 DOI: 10.4137/cpath.s667] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Li Lin
- Key laboratory of cellular physiology, Shanxi Medical University, China
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569
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Abstract
It has long been suspected that the relative abundance of specific nutrients can affect cognitive processes and emotions. Newly described influences of dietary factors on neuronal function and synaptic plasticity have revealed some of the vital mechanisms that are responsible for the action of diet on brain health and mental function. Several gut hormones that can enter the brain, or that are produced in the brain itself, influence cognitive ability. In addition, well-established regulators of synaptic plasticity, such as brain-derived neurotrophic factor, can function as metabolic modulators, responding to peripheral signals such as food intake. Understanding the molecular basis of the effects of food on cognition will help us to determine how best to manipulate diet in order to increase the resistance of neurons to insults and promote mental fitness.
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570
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Gault VA, Hölscher C. GLP-1 agonists facilitate hippocampal LTP and reverse the impairment of LTP induced by beta-amyloid. Eur J Pharmacol 2008; 587:112-7. [DOI: 10.1016/j.ejphar.2008.03.025] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2007] [Revised: 02/28/2008] [Accepted: 03/13/2008] [Indexed: 01/21/2023]
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571
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Abstract
There is growing evidence that receptors that respond to orexigenic and anorexigenic signals of respective neuropeptides are also implicated in cognitive, emotional, sensory and motor functions. How do these signals trigger a particular appetitive function while also acting in so different contexts in controlling non-appetitive behaviours? This perspective seeks an answer in their peculiar modular organization when each module planted in complex networks controlling appetite is also engaged in different domains. Network analysis may be essential in considering pharmacotherapeutic interventions and, in particular, when anticipating untoward central effects of agents explored from a therapeutic point of view.
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Affiliation(s)
- M Myslobodsky
- Howard University Graduate School, Washington, DC and Clinical Brain Disorders Branch, NIMH/National Institutes of Health, Bethesda, MD 20892-1379, USA.
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572
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Ban K, Noyan-Ashraf MH, Hoefer J, Bolz SS, Drucker DJ, Husain M. Cardioprotective and vasodilatory actions of glucagon-like peptide 1 receptor are mediated through both glucagon-like peptide 1 receptor-dependent and -independent pathways. Circulation 2008; 117:2340-50. [PMID: 18427132 DOI: 10.1161/circulationaha.107.739938] [Citation(s) in RCA: 783] [Impact Index Per Article: 48.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
BACKGROUND The glucagon-like peptide 1 receptor (GLP-1R) is believed to mediate glucoregulatory and cardiovascular effects of the incretin hormone GLP-1(7-36) (GLP-1), which is rapidly degraded by dipeptidyl peptidase-4 (DPP-4) to GLP-1(9-36), a truncated metabolite generally thought to be inactive. Novel drugs for the treatment of diabetes include analogues of GLP-1 and inhibitors of DPP-4; however, the cardiovascular effects of distinct GLP-1 peptides have received limited attention. METHODS AND RESULTS Here, we show that endothelium and cardiac and vascular myocytes express a functional GLP-1R as GLP-1 administration increased glucose uptake, cAMP and cGMP release, left ventricular developed pressure, and coronary flow in isolated mouse hearts. GLP-1 also increased functional recovery and cardiomyocyte viability after ischemia-reperfusion injury of isolated hearts and dilated preconstricted arteries from wild-type mice. Unexpectedly, many of these actions of GLP-1 were preserved in Glp1r(-/-) mice. Furthermore, GLP-1(9-36) administration during reperfusion reduced ischemic damage after ischemia-reperfusion and increased cGMP release, vasodilatation, and coronary flow in wild-type and Glp1r(-/-) mice, with modest effects on glucose uptake. Studies using a DPP-4-resistant GLP-1R agonist and inhibitors of DPP-4 and nitric oxide synthase showed that the effects of GLP-1(7-36) were partly mediated by GLP-1(9-36) through a nitric oxide synthase-requiring mechanism that is independent of the known GLP-1R. CONCLUSIONS These data describe cardioprotective actions of GLP-1(7-36) mediated through the known GLP-1R and novel cardiac and vascular actions of GLP-1(7-36) and its metabolite GLP-1(9-36) independent of the known GLP-1R. Our data suggest that the extent to which GLP-1 is metabolized to GLP-1(9-36) may have functional implications in the cardiovascular system.
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Affiliation(s)
- Kiwon Ban
- Heart and Stroke Richard Lewar Centre of Excellence for Cardiovascular Research, University of Toronto, Ontario, Canada M5G-1C4
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573
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Edmondson SD, Wei L, Xu J, Shang J, Xu S, Pang J, Chaudhary A, Dean DC, He H, Leiting B, Lyons KA, Patel RA, Patel SB, Scapin G, Wu JK, Beconi MG, Thornberry NA, Weber AE. Fluoroolefins as amide bond mimics in dipeptidyl peptidase IV inhibitors. Bioorg Med Chem Lett 2008; 18:2409-13. [DOI: 10.1016/j.bmcl.2008.02.050] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2008] [Revised: 02/18/2008] [Accepted: 02/21/2008] [Indexed: 10/22/2022]
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574
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Biswas SC, Buteau J, Greene LA. Glucagon-like Peptide-1 (GLP-1) Diminishes Neuronal Degeneration and Death Caused by NGF Deprivation by Suppressing Bim Induction. Neurochem Res 2008; 33:1845-51. [DOI: 10.1007/s11064-008-9646-4] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2007] [Accepted: 02/28/2008] [Indexed: 10/22/2022]
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575
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Banks WA. Delivery of peptides to the brain: Emphasis on therapeutic development. Biopolymers 2008; 90:589-94. [DOI: 10.1002/bip.20980] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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576
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Nonaka N, Farr SA, Kageyama H, Shioda S, Banks WA. Delivery of galanin-like peptide to the brain: targeting with intranasal delivery and cyclodextrins. J Pharmacol Exp Ther 2008; 325:513-9. [PMID: 18270319 DOI: 10.1124/jpet.107.132381] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Galanin-like peptide (GALP) shows potential as a therapeutic in the treatment of obesity and related conditions. In this study, we compared the uptake by brain regions and peripheral tissues of radioactively iodinated GALP (I-GALP) after intranasal (i.n.), i.v., and i.c.v. administration. I-GALP was stable in blood and brain during the 10-min study time regardless of route of administration, and similar levels were achieved in cerebrospinal fluid after i.v. and i.n. administration. However, levels in most brain regions were approximately 4 to 10 times higher and uptake by spleen, representative of peripheral tissues, approximately 10% as high after i.n. than i.v. administration. Thus, i.n. administration provided about a 40- to 100 fold improvement in targeting brain versus peripheral tissues compared with i.v. administration. Uptake of I-GALP by whole brain after i.n. administration was inhibited by approximately 50% by 1 mug/mouse of unlabeled GALP, thus demonstrating a saturable component to uptake. Combining I-GALP with cyclodextrins increased brain uptake approximately 3-fold. Selectivity for brain region uptake was also seen with route of administration and with use of cyclodextrins. The hippocampus had the greatest uptake after i.c.v. administration, the cerebellum after i.v. administration, the hypothalamus with i.n. administration without cyclodextrins, the hypothalamus and olfactory bulb (OB) after i.n. administration with alpha-cyclodextrin, and the OB after i.n. administration with dimethyl-beta cyclodextrin. These studies show that intranasal administration is an effective route of administration for the delivery of GALP to the brain and that targeting among brain regions may be possible with the use of various cyclodextrins.
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Affiliation(s)
- Naoko Nonaka
- Geriatric Research, Education, and Clinical Center, Veterans Affairs Medical Center, John Cochran Division, 915 N. Grand Blvd., St. Louis, MO 63106, USA.
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577
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Schmitz O. The GLP-1 concept in the treatment of type 2 diabetes--still standing at the gate of dawn? J Clin Endocrinol Metab 2008; 93:375-7. [PMID: 18258781 DOI: 10.1210/jc.2007-2750] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
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578
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Park S, Hong SM, Sung SR. Exendin-4 and exercise promotes β-cell function and mass through IRS2 induction in islets of diabetic rats. Life Sci 2008; 82:503-11. [PMID: 18237751 DOI: 10.1016/j.lfs.2007.12.018] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2007] [Revised: 11/21/2007] [Accepted: 12/08/2007] [Indexed: 12/19/2022]
Affiliation(s)
- Sunmin Park
- Department of Food & Nutrition, College of Natural Science, Hoseo University, Asan-Si, South Korea.
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579
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Lerche S, Brock B, Rungby J, Bøtker HE, Møller N, Rodell A, Bibby BM, Holst JJ, Schmitz O, Gjedde A. Glucagon-like peptide-1 inhibits blood-brain glucose transfer in humans. Diabetes 2008; 57:325-31. [PMID: 17991759 DOI: 10.2337/db07-1162] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Glucagon-like peptide-1 (GLP-1) has many effects on glucose homeostasis, and GLP-1 receptors are broadly represented in many tissues including the brain. Recent research in rodents suggests a protective effect of GLP-1 on brain tissue. The mechanism is unknown. We therefore tested whether these neuroprotective effects could relate to changes of glucose transport and consumption. RESEARCH DESIGN AND METHODS We studied 10 healthy men in a randomized, double-blinded, placebo-controlled cross-over experiment. We used positron emission tomography to determine the acute insulin-independent effect of GLP-1 on unidirectional glucose transport into the brain during a pituitary-pancreatic normoglycemic (plasma glucose approximately 4.5 mmol/l) clamp with 18-fluoro-deoxy-glucose as tracer. RESULTS On average, GLP-1 reduced cerebral glucose transport by 27% in total cerebral gray matter (P = 0.05) and by 25-30% in individual gray matter regions (P = 0.02-0.06). The same regions revealed a uniform trend toward similarly reduced cerebral glucose metabolism. Consequently, the intracerebral glucose concentration remained constant in all regions, with and without GLP-1. CONCLUSIONS We have demonstrated that a hormone involved in postprandial glucose regulation also limits glucose delivery to brain tissue and hence provides a possible regulatory mechanism for the link between plasma glucose and brain glucose. Because GLP-1 reduces glucose uptake across the intact blood-brain barrier at normal glycemia, GLP-1 may also protect the brain by limiting intracerebral glucose fluctuation when plasma glucose is increased.
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Affiliation(s)
- Susanne Lerche
- Institute of Pharmacology, University of Aarhus, The Bartholin Building, University Park 1240, 8000 Aarhus C, Denmark.
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580
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Delivery of interferon-beta to the monkey nervous system following intranasal administration. Neuroscience 2008; 152:785-97. [PMID: 18304744 DOI: 10.1016/j.neuroscience.2008.01.013] [Citation(s) in RCA: 161] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2007] [Revised: 12/12/2007] [Accepted: 02/01/2008] [Indexed: 12/25/2022]
Abstract
We determined the nervous system targeting of interferon-beta1b (IFN-beta1b), a 20 kDa protein used to treat the relapsing-remitting form of multiple sclerosis, following intranasal administration in anesthetized, adult cynomolgus monkeys. Five animals received an intranasal bolus of [(125)I]-labeled IFN-beta1b, applied bilaterally to the upper nasal passages. Serial blood samples were collected for 45 min, after which the animals were euthanized by transcardial perfusion-fixation. High resolution phosphor imaging of tissue sections and gamma counting of microdissected tissue were used to obtain the distribution and concentration profiles of [(125)I]-IFN-beta1b in central and peripheral tissues. Intranasal administration resulted in rapid, widespread targeting of nervous tissue. The olfactory bulbs and trigeminal nerve exhibited [(125)I]-IFN-beta1b levels significantly greater than in peripheral organs and at least one order of magnitude higher than any other nervous tissue area sampled. The basal ganglia exhibited highest [(125)I]-IFN-beta1b levels among CNS regions other than the olfactory bulbs. Preferential IFN-beta1b distribution to the primate basal ganglia is a new finding of possible clinical importance. Our study suggests both IFN-beta and IFN-alpha, which share the same receptor, may be bound with relatively high affinity in these structures, possibly offering new insight into a neurovegetative syndrome induced by IFN-alpha therapy and suspected to involve altered dopamine neurotransmission in the basal ganglia. Most importantly, our results suggest intranasally applied macromolecules may bypass the blood-brain barrier and rapidly enter the primate CNS along olfactory- and trigeminal-associated extracellular pathways, as shown previously in the rat. This is the first study to finely detail the central distribution of a labeled protein after intranasal administration in non-human primates.
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581
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582
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Bertilsson G, Patrone C, Zachrisson O, Andersson A, Dannaeus K, Heidrich J, Kortesmaa J, Mercer A, Nielsen E, Rönnholm H, Wikström L. Peptide hormone exendin-4 stimulates subventricular zone neurogenesis in the adult rodent brain and induces recovery in an animal model of parkinson's disease. J Neurosci Res 2008; 86:326-38. [PMID: 17803225 DOI: 10.1002/jnr.21483] [Citation(s) in RCA: 252] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
We investigated the effects of exendin-4 on neural stem/progenitor cells in the subventricular zone of the adult rodent brain and its functional effects in an animal model of Parkinson's disease. Our results showed expression of GLP-1 receptor mRNA or protein in the subventricular zone and cultured neural stem/progenitor cells isolated from this region. In vitro, exendin-4 increased the number of neural stem/progenitor cells, and the number of cells expressing the neuronal markers microtubule-associated protein 2, beta-III-tubulin, and neuron-specific enolase. When exendin-4 was given intraperitoneally to naïve rodents together with bromodeoxyuridine, a marker for DNA synthesis, both the number of bromodeoxyuridine-positive cells and the number of neuronal precursor cells expressing doublecortin were increased. Exendin-4 was tested in the 6-hydroxydopamine model of Parkinson's disease to investigate its possible functional effects in an animal model with neuronal loss. After unilateral lesion and a 5-week stabilization period, the rats were treated for 3 weeks with exendin-4. We found a reduction of amphetamine-induced rotations in animals receiving exendin-4 that persisted for several weeks after drug administration had been terminated. Histological analysis showed that exendin-4 significantly increased the number of both tyrosine hydroxylase- and vesicular monoamine transporter 2-positive neurons in the substantia nigra. In conclusion, our results show that exendin-4 is able to promote adult neurogenesis in vitro and in vivo, normalize dopamine imbalance, and increase the number of cells positive for markers of dopaminergic neurons in the substantia nigra in a model of Parkinson's disease.
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583
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Abstract
Glucagon-like peptide 1 (GLP-1) is a 30-amino acid peptide hormone produced in the intestinal epithelial endocrine L-cells by differential processing of proglucagon, the gene which is expressed in these cells. The current knowledge regarding regulation of proglucagon gene expression in the gut and in the brain and mechanisms responsible for the posttranslational processing are reviewed. GLP-1 is released in response to meal intake, and the stimuli and molecular mechanisms involved are discussed. GLP-1 is extremely rapidly metabolized and inactivated by the enzyme dipeptidyl peptidase IV even before the hormone has left the gut, raising the possibility that the actions of GLP-1 are transmitted via sensory neurons in the intestine and the liver expressing the GLP-1 receptor. Because of this, it is important to distinguish between measurements of the intact hormone (responsible for endocrine actions) or the sum of the intact hormone and its metabolites, reflecting the total L-cell secretion and therefore also the possible neural actions. The main actions of GLP-1 are to stimulate insulin secretion (i.e., to act as an incretin hormone) and to inhibit glucagon secretion, thereby contributing to limit postprandial glucose excursions. It also inhibits gastrointestinal motility and secretion and thus acts as an enterogastrone and part of the "ileal brake" mechanism. GLP-1 also appears to be a physiological regulator of appetite and food intake. Because of these actions, GLP-1 or GLP-1 receptor agonists are currently being evaluated for the therapy of type 2 diabetes. Decreased secretion of GLP-1 may contribute to the development of obesity, and exaggerated secretion may be responsible for postprandial reactive hypoglycemia.
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Affiliation(s)
- Jens Juul Holst
- Department of Medical Physiology, The Panum Institute, University of Copenhagen, Copenhagen, Denmark.
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584
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Abstract
Apoptosis mediates the precise and programmed natural death of neurons and is a physiologically important process in neurogenesis during maturation of the central nervous system. However, premature apoptosis and/or an aberration in apoptosis regulation is implicated in the pathogenesis of neurodegeneration, a multifaceted process that leads to various chronic disease states, such as Alzheimer's (AD), Parkinson's (PD), Huntington's (HD) diseases, amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and diabetic encephalopathy. The current review focuses on two major areas (a) the fundamentals of apoptosis, which includes elements of the apoptotic machinery, apoptosis inducers, and emerging concepts in apoptosis research, and (b) apoptotic involvement in neurodegenerative disorders, neuroprotective treatment strategies/modalities, and the mechanisms of, and signaling in, neuronal apoptosis. Current and new experimental models for apoptosis research in neurodegenerative diseases are also discussed.
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Affiliation(s)
- Masahiro Okouchi
- Department of Internal Medicine and Bioregulation, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan
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585
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Abstract
This review focuses on the mechanisms regulating the synthesis, secretion, biological actions, and therapeutic relevance of the incretin peptides glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). The published literature was reviewed, with emphasis on recent advances in our understanding of the biology of GIP and GLP-1. GIP and GLP-1 are both secreted within minutes of nutrient ingestion and facilitate the rapid disposal of ingested nutrients. Both peptides share common actions on islet beta-cells acting through structurally distinct yet related receptors. Incretin-receptor activation leads to glucose-dependent insulin secretion, induction of beta-cell proliferation, and enhanced resistance to apoptosis. GIP also promotes energy storage via direct actions on adipose tissue, and enhances bone formation via stimulation of osteoblast proliferation and inhibition of apoptosis. In contrast, GLP-1 exerts glucoregulatory actions via slowing of gastric emptying and glucose-dependent inhibition of glucagon secretion. GLP-1 also promotes satiety and sustained GLP-1-receptor activation is associated with weight loss in both preclinical and clinical studies. The rapid degradation of both GIP and GLP-1 by the enzyme dipeptidyl peptidase-4 has led to the development of degradation-resistant GLP-1-receptor agonists and dipeptidyl peptidase-4 inhibitors for the treatment of type 2 diabetes. These agents decrease hemoglobin A1c (HbA1c) safely without weight gain in subjects with type 2 diabetes. GLP-1 and GIP integrate nutrient-derived signals to control food intake, energy absorption, and assimilation. Recently approved therapeutic agents based on potentiation of incretin action provide new physiologically based approaches for the treatment of type 2 diabetes.
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Affiliation(s)
- Laurie L Baggio
- Department of Medicine, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Banting and Best Diabetes Centre, University of Toronto, Toronto, Ontario, Canada
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586
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Brouillette J, Young D, During MJ, Quirion R. Hippocampal gene expression profiling reveals the possible involvement ofHomer1andGABABreceptors in scopolamine-induced amnesia. J Neurochem 2007; 102:1978-1989. [PMID: 17540011 DOI: 10.1111/j.1471-4159.2007.04666.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Scopolamine-treated rats are commonly used as a psychopharmacological model of memory dysfunction and have been extensively studied to establish the effectiveness of acetylcholinesterase inhibitors in the treatment of Alzheimer's disease. Scopolamine is a muscarinic acetylcholine receptor antagonist that induces memory deficits in young subjects similar to those occurring during aging. The amnesic effect of scopolamine is well established but the molecular and cellular mechanisms that sustain its neuropharmacological action are still unclear. The present genome wide study investigates hippocampal gene expression profiling in scopolamine-treated adult rats following stimulation in a spatial memory task. Using microarray and quantitative real-time RT-PCR approaches, we identified several genes previously known to be associated with memory processes (Homer1, GABA(B) receptor, early growth response 1, prodynorphin, VGF nerve growth factor inducible) and multiple novel candidate genes possibly involved in cognition (including calcium/calmodulin-dependent protein kinase kinase 2, dual specificity phosphatase 5 and 6, glycophorin C) that were altered following scopolamine treatment. Moreover, we found that stable over-expression of glutamatergic components Homer1a and 1c in the hippocampus of adult rats induced by recombinant adeno-associated virus vector abolished memory improvement produced by the GABA(B) receptor antagonist SGS742 in scopolamine-treated rats. Taken together, these results reveal novel genes and mechanisms involved in scopolamine-induced amnesia, and demonstrate the involvement of both GABA and glutamate neurotransmission in this animal model of cognitive dysfunctions.
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Affiliation(s)
- Jonathan Brouillette
- Department of Neurology & Neurosurgery, Douglas Mental Health University Institute, McGill University, Montréal, Quebec, CanadaDepartment of Molecular Medicine and Pathology, University of Auckland, Auckland, New ZealandDepartment of Psychiatry, Douglas Mental Health University Institute, McGill University, Montréal, Quebec, Canada
| | - Deborah Young
- Department of Neurology & Neurosurgery, Douglas Mental Health University Institute, McGill University, Montréal, Quebec, CanadaDepartment of Molecular Medicine and Pathology, University of Auckland, Auckland, New ZealandDepartment of Psychiatry, Douglas Mental Health University Institute, McGill University, Montréal, Quebec, Canada
| | - Matthew J During
- Department of Neurology & Neurosurgery, Douglas Mental Health University Institute, McGill University, Montréal, Quebec, CanadaDepartment of Molecular Medicine and Pathology, University of Auckland, Auckland, New ZealandDepartment of Psychiatry, Douglas Mental Health University Institute, McGill University, Montréal, Quebec, Canada
| | - Rémi Quirion
- Department of Neurology & Neurosurgery, Douglas Mental Health University Institute, McGill University, Montréal, Quebec, CanadaDepartment of Molecular Medicine and Pathology, University of Auckland, Auckland, New ZealandDepartment of Psychiatry, Douglas Mental Health University Institute, McGill University, Montréal, Quebec, Canada
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587
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Abstract
The glucoincretins, glucagon-like peptide-1 (GLP-1) and gastric inhibitory peptide (GIP), are intestinal peptides secreted in response to glucose or lipid intake. Data on isolated intestinal tissues, dietary treatments and knockout mice strongly suggest that GIP and GLP-1 secretion requires glucose and lipid metabolism by intestinal cells. However, incretin secretion can also be induced by non-digestible carbohydrates and involves the autonomic nervous system and endocrine factors such as GIP itself and cholecystokinin. The classical pharmacological approach and the recent use of knockout mice for the incretin receptors have shown that a remarkable feature of incretins is the ability to stimulate insulin secretion in the presence of hyperglycaemia only, hence avoiding any hypoglycaemic episode. This important role is the basis of ongoing clinical trials using GLP-1 analogues. Since most of the data concern GLP-1, we will focus on this incretin. In addition, GLP-1 is involved in glucose sensing by the autonomic nervous system of the hepato-portal vein controlling muscle glucose utilization and indirectly insulin secretion. GLP-1 has been shown to decrease glucagon secretion, food intake and gastric emptying, preventing excessive hyperglycaemia and overfeeding. Another remarkable feature of GLP-1 is its secretion by the brain. Recently, elegant data showed that cerebral GLP-1 is involved in cognition and memory. Experiments using knockout mice suggest that the lack of the GIP receptor prevents diet-induced obesity. Consequently, macronutrients controlling intestinal glucose and lipid metabolism would control incretin secretion and would consequently be beneficial for health. The control of incretin secretion represents a major goal for new therapeutic as well as nutrition strategies for treating and/or reducing the risk of hyperglycaemic syndromes, excessive body weight and thus improvement of well-being.
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Affiliation(s)
- Rémy Burcelin
- UMR 5018 CNRS-UPS and IFR 31, Rangueil Hospital, Toulouse, France.
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588
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Abstract
Admission hyperglycemia complicates approximately one-third of acute ischemic strokes and is associated with a worse clinical outcome. Both human and animal studies have showed that hyperglycemia is particularly detrimental in ischemia/reperfusion. Decreased reperfusion blood flow has been observed after middle cerebral artery occlusion in acutely hyperglycemic animals, suggesting the vasculature as an important site of hyperglycemic reperfusion injury. This paper reviews biochemical and molecular pathways in the vasculature that are rapidly affected by hyperglycemia and concludes that these changes result in a pro-vasoconstrictive, pro-thrombotic and pro-inflammatory phenotype that renders the vasculature vulnerable to reperfusion injury. Understanding these pathways should lead to the development of rational therapies that reduce hyperglycemic reperfusion injury and thus improve outcome in this large subset of acute ischemic stroke patients.
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Affiliation(s)
- Sharyl R Martini
- Department of Neurology, Baylor College of Medicine and the Michael E DeBakey Veterans Affairs Medical Center Stroke Program, Houston, TX 77030, USA
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589
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Knudsen LB, Kiel D, Teng M, Behrens C, Bhumralkar D, Kodra JT, Holst JJ, Jeppesen CB, Johnson MD, de Jong JC, Jorgensen AS, Kercher T, Kostrowicki J, Madsen P, Olesen PH, Petersen JS, Poulsen F, Sidelmann UG, Sturis J, Truesdale L, May J, Lau J. Small-molecule agonists for the glucagon-like peptide 1 receptor. Proc Natl Acad Sci U S A 2007; 104:937-42. [PMID: 17213325 PMCID: PMC1783418 DOI: 10.1073/pnas.0605701104] [Citation(s) in RCA: 175] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The peptide hormone glucagon-like peptide (GLP)-1 has important actions resulting in glucose lowering along with weight loss in patients with type 2 diabetes. As a peptide hormone, GLP-1 has to be administered by injection. Only a few small-molecule agonists to peptide hormone receptors have been described and none in the B family of the G protein coupled receptors to which the GLP-1 receptor belongs. We have discovered a series of small molecules known as ago-allosteric modulators selective for the human GLP-1 receptor. These compounds act as both allosteric activators of the receptor and independent agonists. Potency of GLP-1 was not changed by the allosteric agonists, but affinity of GLP-1 for the receptor was increased. The most potent compound identified stimulates glucose-dependent insulin release from normal mouse islets but, importantly, not from GLP-1 receptor knockout mice. Also, the compound stimulates insulin release from perfused rat pancreas in a manner additive with GLP-1 itself. These compounds may lead to the identification or design of orally active GLP-1 agonists.
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Affiliation(s)
- Lotte Bjerre Knudsen
- Department of Discovery Biology, Novo Nordisk Als, Novo Nordisk Park, DK-2760 Maaloev, Denmark.
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590
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Abstract
Peptides hold great potential as CNS drugs, but their delivery to the CNS is problematic. However, actual roadblocks to peptide delivery are different from those often perceived. Many peptides cross the blood-brain barrier by saturable and non-saturable mechanisms, and accumulate in brain in amounts sufficient to produce physiological effects. Peripheral factors (e.g., short half-life in blood) can be dominant factors limiting therapeutic use. Production of therapeutics that are enzymatically resistant and have long circulation times, even when the blood-brain barrier penetration is low, can result in substances with significant CNS accumulation. Surprisingly low amounts of peptide in brain can result in CNS effects, and so the dose needed for brain delivery is generally much smaller than for peripheral tissues. Brain-to-blood transporters can greatly limit CNS accumulation of a potential therapeutic. Finally, intranasal and intrathecal routes may be especially useful for substances that are rapidly degraded in blood or are large and hydrophobic, respectively.
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Affiliation(s)
- William A Banks
- Veterans Affairs Medical Center - St. Louis and Saint Louis University School of Medicine, Geriatric Research, Education and Clinical Center, Division of Geriatrics, Department of Internal Medicine, St. Louis, MO 63106, USA.
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591
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Perry T, Holloway HW, Weerasuriya A, Mouton PR, Duffy K, Mattison JA, Greig NH. Evidence of GLP-1-mediated neuroprotection in an animal model of pyridoxine-induced peripheral sensory neuropathy. Exp Neurol 2006; 203:293-301. [PMID: 17125767 PMCID: PMC1850958 DOI: 10.1016/j.expneurol.2006.09.028] [Citation(s) in RCA: 150] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2006] [Revised: 09/14/2006] [Accepted: 09/19/2006] [Indexed: 12/22/2022]
Abstract
Pyridoxine (vitamin B6) intoxicated rodents develop a peripheral neuropathy characterized by sensory nerve conduction deficits associated with disturbances of nerve fiber geometry and axonal atrophy. To investigate the possibility that glucagon-like peptide-1 (7-36)-amide (GLP-1) receptor agonism may influence axonal structure and function through neuroprotection neurotrophic support, effects of GLP-1 and its long acting analog, Exendin-4 (Ex4) treatment on pyridoxine-induced peripheral neuropathy were examined in rats using behavioral and morphometric techniques. GLP-1 is an endogenous insulinotropic peptide secreted from the gut in response to the presence of food. GLP-1 receptors (GLP-1R) are coupled to the cAMP second messenger pathway, and are expressed widely throughout neural tissues of humans and rodents. Recent studies have established that GLP-1 and Ex4, have multiple synergistic effects on glucose-dependent insulin secretion pathways of pancreatic beta-cells and on neural plasticity. Data reported here suggest that clinically relevant doses of GLP-1 and Ex4 may offer some protection against the sensory peripheral neuropathy induced by pyridoxine. Our findings suggest a potential role for these peptides in the treatment of neuropathies, including that associated with type II diabetes mellitus.
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Affiliation(s)
- TracyAnn Perry
- Drug Design and Development Section, Laboratory of Neurosciences, Intramural Research Program, National Institute on Aging, National Institutes of Health, Room 2C13, Gerontology Research Center, 5600 Nathan Shock Dr., Baltimore, MD 21224, USA
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592
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Bavec A, Jiang Y, Langel U, Zorko M. Role of cysteine 341 and arginine 348 of GLP-1 receptor in G-protein coupling. Mol Biol Rep 2006; 34:53-60. [PMID: 17103235 DOI: 10.1007/s11033-006-9015-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2006] [Accepted: 08/21/2006] [Indexed: 10/23/2022]
Abstract
We have demonstrated the ability of peptides derived from the third intracellular loop of GLP-1 receptor to differently modulate activity of four different types of G-proteins overexpressed in sf9 cells. In this respect, the involvement of Cys(341) in inhibition of G(s) and Cys(341) in activation of G(s) and in inhibition of G(i1,) G(o), and G(11), respectively, indicates their potential role in discrimination between different types of G-proteins. Moreover, these two amino acids from the third intracellular loop might represent an important novel targets for covalent modification by downstream regulators in signaling through GLP-1 receptor.
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Affiliation(s)
- Aljosa Bavec
- Institute of Biochemistry, Medical Faculty, University of Ljubljana, Vrazov trg 2, 1000, Ljubljana, Slovenia.
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593
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Liu J, Zheng X, Yin F, Hu Y, Guo L, Deng X, Chen G, Jiajia J, Zhang H. Neurotrophic property of geniposide for inducing the neuronal differentiation of PC12 cells. Int J Dev Neurosci 2006; 24:419-24. [PMID: 17045447 DOI: 10.1016/j.ijdevneu.2006.08.009] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2006] [Revised: 08/12/2006] [Accepted: 08/22/2006] [Indexed: 11/26/2022] Open
Abstract
The emerging data show that the insulinotrophic hormone glucagon-like peptide-1(GLP-1) and its agonist extendin-4 have neurotrophic function to inducing neuronal differentiation of PC12 cells and prevent neurons damage challenged by oxidative stress. Here, with the model of high throughput screen for GLP-1 receptor agonists, we screen and identify that geniposide is a novel agonist for GLP-1 receptor. Furthermore, geniposide induces the neuronal differentiation of PC12 cells with resulting neurites outgrowth; we also observe an increase in expression of growth-associated protein-43. U0126, a selective MEK inhibitor, prevents neurites out growth and phosphorylation of mitogen-activated kinase proteins in PC12 cells induced by geniposide. All these results show that activation of GLP-1 receptor by geniposide to induce the neuronal differentiation of PC12 cells involves in MAPK signaling cascade.
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Affiliation(s)
- Jianhui Liu
- Research Center of Pharmaceutical Chemistry & Chemobiology, Chongqing Technology and Business University, Chongqing 400067, China.
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594
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Hanson LR, Frey WH. Strategies for intranasal delivery of therapeutics for the prevention and treatment of neuroAIDS. J Neuroimmune Pharmacol 2006; 2:81-6. [PMID: 18040829 DOI: 10.1007/s11481-006-9039-x] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2006] [Accepted: 08/14/2006] [Indexed: 11/29/2022]
Abstract
Intranasal drug administration is a noninvasive method of bypassing the blood-brain barrier (BBB) to deliver neurotrophins and other therapeutic agents to the brain and spinal cord. This method allows drugs that do not cross the BBB to be delivered to the central nervous system (CNS) and eliminates the need for systemic delivery, thereby reducing unwanted systemic side effects. Delivery from the nose to the CNS occurs within minutes along both the olfactory and trigeminal neural pathways. Intranasal delivery occurs by an extracellular route and does not require that drugs bind to any receptor or undergo axonal transport. Intranasal delivery also targets the nasal associated lymphatic tissues (NALT) and deep cervical lymph nodes. In addition, intranasally administered therapeutics are observed at high levels in the blood vessel walls and perivascular spaces of the cerebrovasculature. Using this intranasal method in animal models, researchers have successfully reduced stroke damage, reversed Alzheimer's neurodegeneration, reduced anxiety, improved memory, stimulated cerebral neurogenesis, and treated brain tumors. In humans, intranasal insulin has been shown to improve memory in normal adults and patients with Alzheimer's disease. Intranasal delivery strategies that can be employed to treat and prevent NeuroAIDS include: (1) target antiretrovirals to reach HIV that harbors in the CNS; (2) target therapeutics to protect neurons in the CNS; (3) modulate the neuroimmune function of moncyte/macrophages by targeting the lymphatics, perivascular spaces of the cerebrovasculature, and the CNS; and (4) improve memory and cognitive function by targeting therapeutics to the CNS.
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Affiliation(s)
- Leah R Hanson
- Alzheimer's Research Center at Regions Hospital, HealthPartners Research Foundation, 640 Jackson Street, Mailstop 11203A, St. Paul, Minnesota, MN, USA
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595
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Vellai T, McCulloch D, Gems D, Kovács AL. Effects of sex and insulin/insulin-like growth factor-1 signaling on performance in an associative learning paradigm in Caenorhabditis elegans. Genetics 2006; 174:309-16. [PMID: 16849598 PMCID: PMC1569791 DOI: 10.1534/genetics.106.061499] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2006] [Accepted: 07/04/2006] [Indexed: 12/21/2022] Open
Abstract
Learning is an adaptive change in behavior in response to environmental stimuli. In mammals, there is a distinct female bias to learn skills that is still unprecedented in other animal taxa. Here we have investigated the biological determinants of performance in an associative learning paradigm in the nematode Caenorhabditis elegans. Using an assay of chemotactic reactions associated with food deprivation, wild-type male worms show inferior learning ability relative to hermaphrodites. Sex-based learning difference is therefore an ancient evolutionary feature appearing even in relatively simple animals. C. elegans mutants with reduced insulin/IGF-1 signaling also exhibit a greatly reduced learning ability in this assay. In addition, hyperactivation of insulin/IGF-1 signaling through loss-of-function mutations in the PTEN phosphatase daf-18, a negative regulator of insulin/IGF-1 signaling, enhances learning ability beyond that of wild type. According to our epistasis analysis, the effect of DAF-2 on learning acts via phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) production, but not the DAF-16 FOXO transcription factor. This implies that the signaling pathway from DAF-2 affecting this learning paradigm branches between PIP(3) production and DAF-16. However, learning capacity of nematodes is lowered by loss-of-function mutations in daf-16, suggesting involvement of noninsulin/IGF-1 signaling-dependent DAF-16 activation in learning. Potentially, sex and insulin/IGF-1 signaling affect performance in this learning assay via effects on the neurobiology of learning.
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Affiliation(s)
- Tibor Vellai
- Department of Genetics, Eötvös Loránd University, Budapest, H-1117, Hungary.
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596
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Kumar KG, Poole AC, York B, Volaufova J, Zuberi A, Richards BKS. Quantitative trait loci for carbohydrate and total energy intake on mouse chromosome 17: congenic strain confirmation and candidate gene analyses (Glo1, Glp1r). Am J Physiol Regul Integr Comp Physiol 2006; 292:R207-16. [PMID: 16946080 DOI: 10.1152/ajpregu.00491.2006] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Quantitative trait loci (QTL) for carbohydrate (Mnic1) and total energy (Kcal2) intake on proximal mouse chromosome 17 were identified previously from a C57BL/6J (B6) X CAST/Ei (CAST) intercross. Here we report that a new congenic strain developed in our laboratory has confirmed this complex locus by recapitulating the original linked phenotypes: B6.CAST-17 homozygous congenic mice consumed more carbohydrate (27%) and total energy (17%) compared with littermate wild-type mice. Positional gene candidates with relevance to carbohydrate metabolism, glyoxalase I (Glo1) and glucagon-like peptide-1 receptor (Glp1r), were evaluated. Glo1 expression was upregulated in liver and hypothalamus of congenic mice when compared with B6 mice. Analyses of Glp1r mRNA and protein expression revealed tissue-specific strain differences in pancreas (congenic>B6) and stomach (B6>congenic). These results suggest the possibility of separate mechanisms for enhanced insulin synthesis and gastric accommodation in the presence of high carbohydrate intake and larger food volume, respectively. Sequence analysis of Glp1r found a G insert at nt position 1349, which results in earlier termination of the open reading frame, thus revealing an error in the public sequence. Consequently, the predicted length of GLP-1R is 463 aa compared with 489 aa, as previously reported. Also, we found a polymorphism in Glp1r between parental strains that alters the amino acid sequence. Variation in Glp1r could influence nutrient intake in this model through changes in the regulatory or protein coding regions of the gene. These congenic mice offer a powerful tool for investigating gene interactions in the control of food intake.
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Affiliation(s)
- K Ganesh Kumar
- Division of Experimental Obesity, Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, LA 70808-4124, USA
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597
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Yehuda S, Rabinovitz S, Mostofsky DI. Mediation of cognitive function by high fat diet following stress and inflammation. Nutr Neurosci 2006; 8:309-15. [PMID: 16669601 DOI: 10.1080/00268970500509972] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
In addition to commonly advertised hazards of obesity contributed by excess dietary fat, evidence of alterations in brain chemistry and structure are well documented. This brief review examines the role of nutrients, minerals and certain lipids, primarily the essential fatty acids (FA), that are beneficial to the maintenance of good health and that may offer therapeutic options by dietary supplementation. The review also considers the damaging effects of stress, especially in pre-existing conditions of obesity and diabetes, as studied in both animals and humans. The main focus of this brief review is to examine the effects of a high fat diet on stress and the immune system with particular emphasis on brain and cognitive function.
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Affiliation(s)
- S Yehuda
- Psychopharmacology Laboratory, Department of Psychology and Brain Research Institute, Bar Ilan University, Ramat Gan 52900, Israel.
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598
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Gallwitz B. Glucagon-like peptide-1-based therapies for the treatment of type 2 diabetes mellitus. ACTA ACUST UNITED AC 2006; 4:361-70. [PMID: 16318402 DOI: 10.2165/00024677-200504060-00005] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The 'incretin effect' describes the phenomenon of an enhanced insulin response following oral ingestion of glucose compared with that after intravenous administration of glucose, leading to identical postprandial plasma glucose excursions. It accounts for up to 60% of the postprandial insulin secretion, but is diminished in patients with type 2 diabetes mellitus. Gastrointestinal hormones that promote the incretin effect are called incretins. Glucagon-like peptide-1 (GLP-1) is an important incretin. Under hyperglycemic conditions in humans, it stimulates insulin secretion and normalizes blood glucose levels. GLP-1 does not stimulate insulin secretion at normal glucose levels; therefore, it does not cause hypoglycemia. Furthermore, it inhibits glucagon secretion and delays gastric emptying. In vitro and animal data have demonstrated that GLP-1 increases beta-cell mass by stimulating islet cell neogenesis and by inhibiting the apoptosis of islet cells. The improvement of beta-cell function due to GLP-1 can be indirectly observed from the increased insulin secretory capacity of humans receiving such treatment. GLP-1 may represent an attractive therapeutic method for patients with type 2 diabetes because of its multiple effects, including the simulation of satiety in the CNS by acting as a transmitter or by crossing the blood brain barrier. Native GLP-1 is degraded rapidly upon intravenous or subcutaneous administration and is therefore not feasible for routine therapy. Long-acting GLP-1 analogs (e.g. liraglutide) and exendin-4 (exenatide) that are resistant to degradation, called 'incretin mimetics', are being investigated in clinical trials. Dipeptidyl peptidase-IV inhibitors (e.g. vildagliptin, sitagliptin, and saxagliptin) that inhibit the enzyme responsible for incretin degradation are also being studied.
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Affiliation(s)
- Baptist Gallwitz
- Department of Medicine, Eberhard-Karls-University, Tübingen, Germany.
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599
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Abstract
Gut peptides, exemplified by glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are secreted in a nutrient-dependent manner and stimulate glucose-dependent insulin secretion. Both GIP and GLP-1 also promote beta cell proliferation and inhibit apoptosis, leading to expansion of beta cell mass. GLP-1, but not GIP, controls glycemia via additional actions on glucose sensors, inhibition of gastric emptying, food intake and glucagon secretion. Furthermore, GLP-1, unlike GIP, potently stimulates insulin secretion and reduces blood glucose in human subjects with type 2 diabetes. This article summarizes current concepts of incretin action and highlights the potential therapeutic utility of GLP-1 receptor agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors for the treatment of type 2 diabetes.
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Affiliation(s)
- Daniel J Drucker
- Department of Medicine, The Banting and Best Diabetes Centre, Toronto General Hospital, University of Toronto, Ontario M5G 2C4, Canada.
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600
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Affiliation(s)
- Matthew C Riddle
- Section of Diabetes, Division of Endocrinology, Diabetes, and Clinical Nutrition, Oregon Health and Science University, Portland, Oregon, USA
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