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Pan L, Xiao S, Xu Z, Li W, Zhao L, Zhang L, Qi R, Wang J, Cai Y. Orexin-A attenuated motion sickness through modulating neural activity in hypothalamus nuclei. Br J Pharmacol 2024; 181:1474-1493. [PMID: 38129941 DOI: 10.1111/bph.16307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Revised: 12/08/2023] [Accepted: 12/09/2023] [Indexed: 12/23/2023] Open
Abstract
BACKGROUND AND PURPOSE We evaluated the hypothesis that central orexin application could counteract motion sickness responses through regulating neural activity in target brain areas. EXPERIMENTAL APPROACH Thec effects of intracerebroventricular (i.c.v.) injection of orexin-A and SB-334867 (OX1 antagonist) on motion sickness-induced anorexia, nausea-like behaviour (conditioned gaping), hypoactivity and hypothermia were investigated in rats subjected to Ferris wheel-like rotation. Orexin-A responsive brain areas were identified using Fos immunolabelling and were verified via motion sickness responses after intranucleus injection of orexin-A, SB-334867 and TCS-OX2-29 (OX2 antagonist). The efficacy of intranasal application of orexin-A versus scopolamine on motion sickness symptoms in cats was also investigated. KEY RESULTS Orexin-A (i.c.v.) dose-dependently attenuated motion sickness-related behavioural responses and hypothermia. Fos expression was inhibited in the ventral part of the dorsomedial hypothalamus (DMV) and the paraventricular nucleus (PVN), but was enhanced in the ventral part of the premammillary nucleus ventral part (PMV) by orexin-A (20 μg) in rotated animals. Motion sickness responses were differentially inhibited by orexin-A injection into the DMV (anorexia and hypoactivity), the PVN (conditioned gaping) and the PMV (hypothermia). SB-334867 and TCS-OX2-29 (i.c.v. and intranucleus injection) inhibited behavioural and thermal effects of orexin-A. Orexin-A (60 μg·kg-1) and scopolamine inhibited rotation-induced emesis and non-retching/vomiting symptoms, while orexin-A also attenuated anorexia with mild salivation in motion sickness cats. CONCLUSION AND IMPLICATIONS Orexin-A might relieve motion sickness through acting on OX1 and OX2 receptors in various hypothalamus nuclei. Intranasal orexin-A could be a potential strategy against motion sickness.
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Affiliation(s)
- Leilei Pan
- Department of Nautical Injury Prevention, Faculty of Navy Medicine, Naval Medical University (Second Military Medical University), Shanghai, China
| | - Shuifeng Xiao
- Department of Nautical Injury Prevention, Faculty of Navy Medicine, Naval Medical University (Second Military Medical University), Shanghai, China
| | - Zichao Xu
- Department of Nautical Injury Prevention, Faculty of Navy Medicine, Naval Medical University (Second Military Medical University), Shanghai, China
| | - Wenping Li
- Department of Nautical Injury Prevention, Faculty of Navy Medicine, Naval Medical University (Second Military Medical University), Shanghai, China
| | - Long Zhao
- Department of Nautical Injury Prevention, Faculty of Navy Medicine, Naval Medical University (Second Military Medical University), Shanghai, China
| | - Ling Zhang
- Department of Nautical Injury Prevention, Faculty of Navy Medicine, Naval Medical University (Second Military Medical University), Shanghai, China
| | - Ruirui Qi
- Department of Nautical Injury Prevention, Faculty of Navy Medicine, Naval Medical University (Second Military Medical University), Shanghai, China
| | - Junqin Wang
- Department of Nautical Injury Prevention, Faculty of Navy Medicine, Naval Medical University (Second Military Medical University), Shanghai, China
| | - Yiling Cai
- Department of Nautical Injury Prevention, Faculty of Navy Medicine, Naval Medical University (Second Military Medical University), Shanghai, China
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Chen J, Finlay WH, Vehring R, Martin AR. Characterizing regional drug delivery within the nasal airways. Expert Opin Drug Deliv 2024; 21:537-551. [PMID: 38568159 DOI: 10.1080/17425247.2024.2336494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Accepted: 03/26/2024] [Indexed: 05/18/2024]
Abstract
INTRODUCTION The nose has been receiving increased attention as a route for drug delivery. As the site of deposition constitutes the first point of contact of the body with the drug, characterization of the regional deposition of intranasally delivered droplets or particles is paramount to formulation and device design of new products. AREAS COVERED This review article summarizes the recent literature on intranasal regional drug deposition evaluated in vivo, in vitro and in silico, with the aim of correlating parameters measured in vitro with formulation and device performance. We also highlight the relevance of regional deposition to two emerging applications: nose-to-brain drug delivery and intranasal vaccines. EXPERT OPINION As in vivo studies of deposition can be costly and time-consuming, researchers have often turned to predictive in vitro and in silico models. Variability in deposition is high due in part to individual differences in nasal geometry, and a complete predictive model of deposition based on spray characteristics remains elusive. Carefully selected or idealized geometries capturing population average deposition can be useful surrogates to in vivo measurements. Continued development of in vitro and in silico models may pave the way for development of less variable and more effective intranasal drug products.
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Affiliation(s)
- John Chen
- Access to Advanced Health Institute, Seattle, WA, USA
| | - Warren H Finlay
- Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada
| | - Reinhard Vehring
- Access to Advanced Health Institute, Seattle, WA, USA
- Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada
| | - Andrew R Martin
- Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta, Canada
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Li YY, Yu KY, Cui YJ, Wang ZJ, Cai HY, Cao JM, Wu MN. Orexin-A aggravates cognitive deficits in 3xTg-AD mice by exacerbating synaptic plasticity impairment and affecting amyloid β metabolism. Neurobiol Aging 2023; 124:71-84. [PMID: 36758468 DOI: 10.1016/j.neurobiolaging.2023.01.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 01/09/2023] [Accepted: 01/13/2023] [Indexed: 01/19/2023]
Abstract
Dementia is the main clinical feature of Alzheimer's disease (AD). Orexin has recently been linked to AD pathogenesis, and exogenous orexin-A (OXA) aggravates spatial memory impairment in APP/PS1 mice. However, the effects of OXA on other types of cognitive deficits, especially in 3xTg-AD mice exhibiting both plaque and tangle pathologies, have not been reported. Furthermore, the potential electrophysiological mechanism by which OXA affects cognitive deficits and the molecular mechanism by which OXA increases amyloid β (Aβ) levels are unknown. In the present study, the effects of OXA on cognitive functions, synaptic plasticity, Aβ levels, tau hyperphosphorylation, BACE1 and NEP expression, and circadian locomotor rhythm were evaluated. The results showed that OXA aggravated memory impairments and circadian rhythm disturbance, exacerbated hippocampal LTP depression, and increased Aβ and tau pathologies in 3xTg-AD mice by affecting BACE1 and NEP expression. These results indicated that OXA aggravates cognitive deficits and hippocampal synaptic plasticity impairment in 3xTg-AD mice by increasing Aβ production and decreasing Aβ clearance through disruption of the circadian rhythm and sleep-wake cycle.
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Affiliation(s)
- Yi-Ying Li
- Department of Physiology, Key Laboratory of Cellular Physiology, Ministry of Education; Key Laboratory of Cellular Physiology in Shanxi Province, Shanxi Medical University, Taiyuan, Shanxi, China
| | - Kai-Yue Yu
- Department of Physiology, Key Laboratory of Cellular Physiology, Ministry of Education; Key Laboratory of Cellular Physiology in Shanxi Province, Shanxi Medical University, Taiyuan, Shanxi, China
| | - Yu-Jia Cui
- Department of Physiology, Key Laboratory of Cellular Physiology, Ministry of Education; Key Laboratory of Cellular Physiology in Shanxi Province, Shanxi Medical University, Taiyuan, Shanxi, China
| | - Zhao-Jun Wang
- Department of Physiology, Key Laboratory of Cellular Physiology, Ministry of Education; Key Laboratory of Cellular Physiology in Shanxi Province, Shanxi Medical University, Taiyuan, Shanxi, China
| | - Hong-Yan Cai
- Department of Physiology, Key Laboratory of Cellular Physiology, Ministry of Education; Key Laboratory of Cellular Physiology in Shanxi Province, Shanxi Medical University, Taiyuan, Shanxi, China; Department of Microbiology and Immunology, Shanxi Medical University, Taiyuan, Shanxi, China
| | - Ji-Min Cao
- Department of Physiology, Key Laboratory of Cellular Physiology, Ministry of Education; Key Laboratory of Cellular Physiology in Shanxi Province, Shanxi Medical University, Taiyuan, Shanxi, China.
| | - Mei-Na Wu
- Department of Physiology, Key Laboratory of Cellular Physiology, Ministry of Education; Key Laboratory of Cellular Physiology in Shanxi Province, Shanxi Medical University, Taiyuan, Shanxi, China.
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Ramot Y, Rottenberg Y, Domb AJ, Kubek MJ, Williams KD, Nyska A. Preclinical In-Vivo Safety of a Novel Thyrotropin-Releasing Hormone-Loaded Biodegradable Nanoparticles After Intranasal Administration in Rats and Primates. Int J Toxicol 2023:10915818231152613. [PMID: 36634266 DOI: 10.1177/10915818231152613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Thyrotropin-releasing hormone (TRH) and TRH-like peptides carry a therapeutic potential for neurological conditions. Nanoparticles (NP) made of the biodegradable polymer, Poly(Sebacic Anhydride) (PSA), have been developed to carry TRH, intended for intranasal administration to patients. There is limited information on the safety of biodegradable polymers when given intranasally, and therefore, we have performed two preclinical safety and toxicity studies in cynomolgus monkeys and rats using TRH-PSA nanoparticles. The rats and monkeys were dosed intranasally for 42 days or 28 days, respectively, and several animals were followed for additional 14 days. Animals received either placebo, vehicle (PSA), or different concentrations of TRH-PSA. No systemic adverse effects were seen. Changes in T3 or T4 concentrations were observed in some TRH-PSA-treated animals, which did not have clinical or microscopic correlates. No effect was seen on TSH or prolactin concentrations. In the monkey study, microscopic changes in the nasal turbinates were observed, which were attributed to incidental mechanical trauma caused during administration. Taken together, the TRH-loaded PSA NPs have proven to be safe, with no local or systemic adverse effects attributed to the drug loaded nanoparticles. These findings provide additional support to the growing evidence of the safety of peptide-loaded NPs for intranasal delivery and pave the way for future clinical trials in humans.
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Affiliation(s)
- Yuval Ramot
- Faculty of Medicine, 54621Hebrew University of Jerusalem, Jerusalem, Israel.,Department of Dermatology, 58884Hadassah Medical Center, Jerusalem, Israel
| | - Yakir Rottenberg
- Faculty of Medicine, 54621Hebrew University of Jerusalem, Jerusalem, Israel.,Department of Oncology, Hadassah Medical Organization, Jerusalem, Israel
| | - Abraham J Domb
- School of Pharmacy-Faculty of Medicine, 54621The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Michael J Kubek
- 12250Indiana University School of Medicine, Indianapolis, IN, USA
| | - Kevin D Williams
- Consultant in Toxicology, WKM Consulting, LLC, Waunakee, WI, USA
| | - Abraham Nyska
- Consultant in Toxicologic Pathology, 26745Tel Aviv and Tel Aviv University, Tel Aviv, Israel
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Pardridge WM. A Historical Review of Brain Drug Delivery. Pharmaceutics 2022; 14:1283. [PMID: 35745855 PMCID: PMC9229021 DOI: 10.3390/pharmaceutics14061283] [Citation(s) in RCA: 63] [Impact Index Per Article: 31.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 06/01/2022] [Accepted: 06/07/2022] [Indexed: 12/13/2022] Open
Abstract
The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.
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Affiliation(s)
- William M Pardridge
- Department of Medicine, University of California, Los Angeles (UCLA), Los Angeles, CA 90095, USA
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Mizutani A, Kobayashi M, Ohuchi M, Sasaki K, Muranaka Y, Torikai Y, Fukakusa S, Suzuki C, Nishii R, Haruta S, Magata Y, Kawai K. Indirect SPECT Imaging Evaluation for Possible Nose-to-Brain Drug Delivery Using a Compound with Poor Blood–Brain Barrier Permeability in Mice. Pharmaceutics 2022; 14:pharmaceutics14051026. [PMID: 35631611 PMCID: PMC9145277 DOI: 10.3390/pharmaceutics14051026] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Revised: 04/22/2022] [Accepted: 05/07/2022] [Indexed: 02/01/2023] Open
Abstract
Single-photon emission computed tomography (SPECT) imaging using intravenous radioactive ligand administration to indirectly evaluate the time-dependent effect of intranasal drugs with poor blood-brain barrier permeability on brain drug distributions in mice was evaluated. The biodistribution was examined using domperidone, a dopamine D2 receptor ligand, as the model drug, with intranasal administration at 0, 15, or 30 min before intravenous [123I]IBZM administration. In the striatum, [123I]IBZM accumulation was significantly lower after intranasal (IN) domperidone administration than in controls 15 min after intravenous [125I]IBZM administration. [123I]IBZM SPECT was acquired with intravenous (IV) or IN domperidone administration 15 min before [123I]IBZM, and time–activity curves were obtained. In the striatum, [123I]IBZM accumulation was clearly lower in the IN group than in the control and IV groups. Time–activity curves showed no significant difference between the control and IV groups in the striatum, and values were significantly lowest during the first 10 min in the IN group. In the IN group, binding potential and % of receptor occupancy were significantly lower and higher, respectively, compared to the control and IV groups. Thus, brain-migrated domperidone inhibited D2R binding of [123I]IBZM. SPECT imaging is suitable for research to indirectly explore nose-to-brain drug delivery and locus-specific biological distribution.
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Affiliation(s)
- Asuka Mizutani
- Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa 920-1192, Japan; (A.M.); (M.K.); (M.O.); (Y.M.)
| | - Masato Kobayashi
- Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa 920-1192, Japan; (A.M.); (M.K.); (M.O.); (Y.M.)
| | - Makoto Ohuchi
- Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa 920-1192, Japan; (A.M.); (M.K.); (M.O.); (Y.M.)
| | - Keita Sasaki
- R&D Department, TR Company, Shin Nippon Biomedical Laboratories, Ltd., 2438 Miyanoura, Kagoshima 891-1394, Japan; (K.S.); (Y.T.); (S.F.); (S.H.)
| | - Yuka Muranaka
- Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa 920-1192, Japan; (A.M.); (M.K.); (M.O.); (Y.M.)
| | - Yusuke Torikai
- R&D Department, TR Company, Shin Nippon Biomedical Laboratories, Ltd., 2438 Miyanoura, Kagoshima 891-1394, Japan; (K.S.); (Y.T.); (S.F.); (S.H.)
| | - Shota Fukakusa
- R&D Department, TR Company, Shin Nippon Biomedical Laboratories, Ltd., 2438 Miyanoura, Kagoshima 891-1394, Japan; (K.S.); (Y.T.); (S.F.); (S.H.)
- Department of Molecular Imaging, Institute for Medical Photonics Research, Preeminent Medical Photonics Education & Research Center, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu 431-3192, Japan; (C.S.); (Y.M.)
| | - Chie Suzuki
- Department of Molecular Imaging, Institute for Medical Photonics Research, Preeminent Medical Photonics Education & Research Center, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu 431-3192, Japan; (C.S.); (Y.M.)
| | - Ryuichi Nishii
- Department of Molecular Imaging and Theranostics, Institute for Quantum Medical Science, Quantum Life and Medical Science Directorate, National Institutes for Quantum Science and Technology, 4-9-1 Anagawa, Inage, Chiba 263-8555, Japan;
| | - Shunji Haruta
- R&D Department, TR Company, Shin Nippon Biomedical Laboratories, Ltd., 2438 Miyanoura, Kagoshima 891-1394, Japan; (K.S.); (Y.T.); (S.F.); (S.H.)
| | - Yasuhiro Magata
- Department of Molecular Imaging, Institute for Medical Photonics Research, Preeminent Medical Photonics Education & Research Center, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu 431-3192, Japan; (C.S.); (Y.M.)
| | - Keiichi Kawai
- Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa 920-1192, Japan; (A.M.); (M.K.); (M.O.); (Y.M.)
- Biomedical Imaging Research Center, University of Fukui, 23-3 Matsuokashimoaizuki, Eiheiji, Yoshida-gun, Fukui 910-1193, Japan
- Correspondence: ; Tel.: +81-76-265-2527; Fax: +81-76-234-4366
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Pardridge WM. Blood-brain barrier delivery for lysosomal storage disorders with IgG-lysosomal enzyme fusion proteins. Adv Drug Deliv Rev 2022; 184:114234. [PMID: 35307484 DOI: 10.1016/j.addr.2022.114234] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 02/25/2022] [Accepted: 03/14/2022] [Indexed: 12/12/2022]
Abstract
The majority of lysosomal storage diseases affect the brain. Treatment of the brain with intravenous enzyme replacement therapy is not successful, because the recombinant lysosomal enzymes do not cross the blood-brain barrier (BBB). Biologic drugs, including lysosomal enzymes, can be re-engineered for BBB delivery as IgG-enzyme fusion proteins. The IgG domain of the fusion protein is a monoclonal antibody directed against an endogenous receptor-mediated transporter at the BBB, such as the insulin receptor or the transferrin receptor. This receptor transports the IgG across the BBB, in parallel with the endogenous receptor ligand, and the IgG acts as a molecular Trojan horse to ferry into brain the lysosomal enzyme genetically fused to the IgG. The IgG-enzyme fusion protein is bi-functional and retains both high affinity binding for the BBB receptor, and high lysosomal enzyme activity. IgG-lysosomal enzymes are presently in clinical trials for treatment of the brain in Mucopolysaccharidosis.
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Abstract
The hypocretins (Hcrts), also known as orexins, are two neuropeptides produced exclusively in the lateral hypothalamus. They act on two specific receptors that are widely distributed across the brain and involved in a myriad of neurophysiological functions that include sleep, arousal, feeding, reward, fear, anxiety and cognition. Hcrt cell loss in humans leads to narcolepsy with cataplexy (narcolepsy type 1), a disorder characterized by intrusions of sleep into wakefulness, demonstrating that the Hcrt system is nonredundant and essential for sleep/wake stability. The causal link between Hcrts and arousal/wakefulness stabilisation has led to the development of a new class of drugs, Hcrt receptor antagonists to treat insomnia, based on the assumption that blocking orexin-induced arousal will facilitate sleep. This has been clinically validated: currently, two Hcrt receptor antagonists are approved to treat insomnia (suvorexant and lemborexant), with a New Drug Application recently submitted to the US Food and Drug Administration for a third drug (daridorexant). Other therapeutic applications under investigation include reduction of cravings in substance-use disorders and prevention of neurodegenerative disorders such as Alzheimer's disease, given the apparent bidirectional relationship between poor sleep and worsening of the disease. Circuit neuroscience findings suggest that the Hcrt system is a hub that integrates diverse inputs modulating arousal (e.g., circadian rhythms, metabolic status, positive and negative emotions) and conveys this information to multiple output regions. This neuronal architecture explains the wealth of physiological functions associated with Hcrts and highlights the potential of the Hcrt system as a therapeutic target for a number of disorders. We discuss present and future possible applications of drugs targeting the Hcrt system for the treatment of circuit-related neuropsychiatric and neurodegenerative conditions.
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Affiliation(s)
- Laura H Jacobson
- The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia.,Department of Biochemistry and Pharmacology, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, Victoria, Australia.,Melbourne Dementia Research Centre, The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia
| | - Daniel Hoyer
- The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia.,Department of Biochemistry and Pharmacology, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, Victoria, Australia.,Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California, USA
| | - Luis de Lecea
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, California, USA
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Nance E, Pun SH, Saigal R, Sellers DL. Drug delivery to the central nervous system. NATURE REVIEWS. MATERIALS 2022; 7:314-331. [PMID: 38464996 PMCID: PMC10923597 DOI: 10.1038/s41578-021-00394-w] [Citation(s) in RCA: 84] [Impact Index Per Article: 42.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 10/05/2021] [Indexed: 03/12/2024]
Abstract
Despite the rising global incidence of central nervous system (CNS) disorders, CNS drug development remains challenging, with high costs, long pathways to clinical use and high failure rates. The CNS is highly protected by physiological barriers, in particular, the blood-brain barrier and the blood-cerebrospinal fluid barrier, which limit access of most drugs. Biomaterials can be designed to bypass or traverse these barriers, enabling the controlled delivery of drugs into the CNS. In this Review, we first examine the effects of normal and diseased CNS physiology on drug delivery to the brain and spinal cord. We then discuss CNS drug delivery designs and materials that are administered systemically, directly to the CNS, intranasally or peripherally through intramuscular injections. Finally, we highlight important challenges and opportunities for materials design for drug delivery to the CNS and the anticipated clinical impact of CNS drug delivery.
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Affiliation(s)
- Elizabeth Nance
- Department of Chemical Engineering, University of Washington, Seattle, WA, USA
- These authors contributed equally: Elizabeth Nance, Suzie H. Pun, Rajiv Saigal, Drew L. Sellers
| | - Suzie H. Pun
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- These authors contributed equally: Elizabeth Nance, Suzie H. Pun, Rajiv Saigal, Drew L. Sellers
| | - Rajiv Saigal
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- Department of Neurological Surgery, University of Washington, Seattle, WA, USA
- These authors contributed equally: Elizabeth Nance, Suzie H. Pun, Rajiv Saigal, Drew L. Sellers
| | - Drew L. Sellers
- Department of Bioengineering, University of Washington, Seattle, WA, USA
- These authors contributed equally: Elizabeth Nance, Suzie H. Pun, Rajiv Saigal, Drew L. Sellers
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Affiliation(s)
- Haiko Schlögl
- Division of Endocrinology, Department of Endocrinology, Nephrology, Rheumatology, University Hospital Leipzig, Leipzig, Germany.,Helmholtz Institute for Metabolic, Obesity, and Vascular Research (HI-MAG), Helmholtz Zentrum München, University of Leipzig and the University Hospital Leipzig, Leipzig, Germany
| | - Michael Stumvoll
- Division of Endocrinology, Department of Endocrinology, Nephrology, Rheumatology, University Hospital Leipzig, Leipzig, Germany
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Meusel M, Voß J, Krapalis A, Machleidt F, Vonthein R, Hallschmid M, Sayk F. Intranasal orexin A modulates sympathetic vascular tone - a pilot study in healthy male humans. J Neurophysiol 2022; 127:548-558. [PMID: 35044844 DOI: 10.1152/jn.00452.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
INTRODUCTION Previous research suggests that the neuropeptide orexin A contributes to sympathetic blood pressure (BP) control inasmuch as hypothalamic injection of orexin A increases sympathetic vasomotor tone and arterial BP in rodents. In humans with narcolepsy, a disorder associated with loss of orexin-producing neurons, vasoconstrictive muscle sympathetic nerve activity (MSNA) is reduced. Since intranasally administered oligopeptides like orexin are known to modulate brain function, we investigated the effect of intranasal orexin A on vascular sympathetic baroreflex function in healthy humans. METHODS In a balanced, double-blind cross-over study, orexin A (500 nmol) and placebo, respectively, were intranasally administered to 10 lean healthy males (age, 25.8±4.6 years). MSNA was assessed microneurographically before and 30-45 minutes after either substance administration. Additionally, baroreflex was challenged via graded infusions of vasoactive drugs before and after substance administration. Baroreflex function was defined as the correlation of BP with MSNA and heart rate. RESULTS Intranasal orexin A compared to placebo induced a significant increase in resting MSNA from prior to post administration (Δ-burst rate, orexin A vs. placebo: +5.8±0.8 vs. +2.1±0.6; p=0.007; total activity (169±11.5% vs. 115±5.0%; p=0.002). BP, heart rate and sympathovagal balance to the heart, as represented by HRV, as well as baroreflex sensitivity during the vasoactive challenge were not altered. CONCLUSION Intranasally administered orexin A acutely induced vasoconstrictory sympathoactivation in healthy male humans. This result suggests that orexin A mediates upward resetting of the vascular baroreflex setpoint at centers superordinate to the mere baroreflex-feedback-loop.
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Affiliation(s)
- Moritz Meusel
- Department of Internal Medicine II, University Heart Center Lübeck, University Hospital Schleswig-Holstein, Lübeck, Germany
| | - Jacqueline Voß
- Dept. of Internal Medicine I, University Hospital of Schleswig-Holstein, Luebeck, Germany
| | - Alexander Krapalis
- Dept. of Internal Medicine I, University Hospital of Schleswig-Holstein, Luebeck, Germany
| | - Felix Machleidt
- Department of Infectious Diseases and Respiratory Medicine, Charité, Universitätsmedizin Berlin, Berlin, Germany
| | - Reinhard Vonthein
- Institute for Medical Biometry and Statistics, University of Lübeck, Lübeck, Germany
| | - Manfred Hallschmid
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen, Germany.,German Center for Diabetes Research (DZD), München-Neuherberg, Germany.,Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the Eberhard Karls University Tübingen, Tübingen, Germany
| | - Friedhelm Sayk
- Dept. of Internal Medicine I, University Hospital of Schleswig-Holstein, Luebeck, Germany
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O'Doherty J, Mangini CD, Hamby DM, Boozer D, Singh N, Hippeläinen E. Estimation of absorbed radiation doses to skin and S-values for organs at risk due to nasal administration of PET agents using Monte Carlo simulations. Med Phys 2021; 48:871-880. [PMID: 33330987 DOI: 10.1002/mp.14669] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 10/29/2020] [Accepted: 12/08/2020] [Indexed: 11/11/2022] Open
Abstract
PURPOSE The intranasal (IN) administration of radiopharmaceuticals is of interest in being a viable route for the delivery of radiopharmaceuticals that do not ordinarily cross the blood-brain barrier (BBB). However, to be viable in a patient population, good image quality as well as safety of the administration should be demonstrated. This work provides radiation dosimetry calculations and simulations related to the radiation safety of performing such experiments in a human cohort. METHODS We performed Monte Carlo (MC) simulations to estimate radiation dose to the skin inside a cylindrical model of the nasal cavity assuming a homogenous distribution layer of 11 C and 18 F and calculated a geometry conversion factor (FP-C ) which can be used to convert from a planar geometry to a cylindrical geometry using more widely available software tools. We compared radiation doses from our simulated cylindrical geometry with the planar dose estimates employing our geometry conversion factor from VARSKIN 6.1 software and also from an analytical equation. Furthermore, in order to estimate radiation dosimetry to surrounding organs of interest, we performed a voxelized MC simulation of a fixed radioactivity inside the nasal cavity and calculated S-values to organs such as the eyes, thyroid, and brain. RESULTS MC simulations of contamination scenarios using planar absorbed doses of 15.50 and 8.60 mGy/MBq for 18 F and 11 C, respectively, and 35.70 and 19.80 mGy/MBq per hour for cylindrical geometries, leading to determination of an FP-C of 2.3. Planar absorbed doses (also in units of mGy/MBq) determined by the analytical equation were 16.96 and 8.68 (18 F and 11 C) and using VARSKIN were 16.60 and 9.26 (18 F and 11 C), respectively. Application of FP-C to these results demonstrates values with a maximum difference of 9.41% from the cylindrical geometry MC calculation, demonstrating that when accounting for geometry, more simplistic techniques can be utilized to estimate IN dosimetry. Voxelized MC simulations of radiation dosimetry from a fixed source of 1 MBq of activity confined to the nasal cavity resulted in S-values to the thyroid, eyes, and brain of 1.72 x 10-6 , 1.93 x 10-5 , and 3.51 x 10-6 mGy/MBq·s, respectively, for 18 F and 1.80 × 10-6 , 1.95 × 10-5 , and 3.54 × 10-6 mGy/MBq·s for 11 C. CONCLUSION Dosimetry concerns about IN administrations of PET radiotracers should be considered before clinical use. Values presented in the simulations such as the S-values can be further used for assessment of absorbed doses in cases of IN administration, and can be used to develop and adapt specific study protocols. All three presented methods provided similar results when considering the use of a geometry conversion factor for planar to cylindrical geometry, demonstrating that standard tools rather than dedicate MC simulations may be used to perform dose calculations in nasal administrations.
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Affiliation(s)
- Jim O'Doherty
- Clinical Imaging Research Centre, Centre for Translational Medicine, National University of Singapore, Singapore
| | | | - David M Hamby
- Renaissance Code Development LLC, Oregon, USA.,Department of Nuclear Science and Engineering, Oregon State University, Corvallis, USA
| | - David Boozer
- Department of Nuclear Engineering and Radiation Health Physics, Oregon State University, Corvallis, USA
| | - Nisha Singh
- Department of Psychiatry, University of Oxford, UK
| | - Eero Hippeläinen
- Department of Physics, University of Helsinki, Helsinki, Finland.,HUS Medical imaging Center, Clinical Physiology and Nuclear Medicine, University of Helsinki and Helsinki University Hospital, Finland
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13
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Abstract
Brain insulin signaling contributes to memory function and might be a viable target in the prevention and treatment of memory impairments including Alzheimer's disease. This short narrative review explores the potential of central nervous system (CNS) insulin administration via the intranasal pathway to improve memory performance in health and disease, with a focus on the most recent results. Proof-of-concept studies and (pilot) clinical trials in individuals with mild cognitive impairment or Alzheimer's disease indicate that acute and prolonged intranasal insulin administration enhances memory performance, and suggest that brain insulin resistance is a pathophysiological factor in Alzheimer's disease with or without concomitant metabolic dysfunction. Intranasally administered insulin is assumed to trigger improvements in synaptic plasticity and regional glucose uptake as well as alleviations of Alzheimer's disease neuropathology; additional contributions of changes in hypothalamus-pituitary-adrenocortical axis activity and sleep-related mechanisms are discussed. While intranasal insulin delivery has been conclusively demonstrated to be effective and safe, the recent outcomes of large-scale clinical studies underline the need for further investigations, which might also yield new insights into sex differences in the response to intranasal insulin and contribute to the optimization of delivery devices to grasp the full potential of intranasal insulin for Alzheimer's disease.
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Affiliation(s)
- Manfred Hallschmid
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Otfried-Müller-Str. 25, 72076, Tübingen, Germany.
- German Center for Diabetes Research (DZD), Tübingen, Germany.
- Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, Tübingen, Germany.
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14
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Pardridge WM. Treatment of Alzheimer's Disease and Blood-Brain Barrier Drug Delivery. Pharmaceuticals (Basel) 2020; 13:E394. [PMID: 33207605 PMCID: PMC7697739 DOI: 10.3390/ph13110394] [Citation(s) in RCA: 84] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2020] [Revised: 11/12/2020] [Accepted: 11/13/2020] [Indexed: 12/12/2022] Open
Abstract
Despite the enormity of the societal and health burdens caused by Alzheimer's disease (AD), there have been no FDA approvals for new therapeutics for AD since 2003. This profound lack of progress in treatment of AD is due to dual problems, both related to the blood-brain barrier (BBB). First, 98% of small molecule drugs do not cross the BBB, and ~100% of biologic drugs do not cross the BBB, so BBB drug delivery technology is needed in AD drug development. Second, the pharmaceutical industry has not developed BBB drug delivery technology, which would enable industry to invent new therapeutics for AD that actually penetrate into brain parenchyma from blood. In 2020, less than 1% of all AD drug development projects use a BBB drug delivery technology. The pathogenesis of AD involves chronic neuro-inflammation, the progressive deposition of insoluble amyloid-beta or tau aggregates, and neural degeneration. New drugs that both attack these multiple sites in AD, and that have been coupled with BBB drug delivery technology, can lead to new and effective treatments of this serious disorder.
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Affiliation(s)
- William M Pardridge
- Department of Medicine, University of California, Los Angeles, CA 90024, USA
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15
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Inoue D, Furubayashi T, Tanaka A, Sakane T, Sugano K. Effect of Cerebrospinal Fluid Circulation on Nose-to-Brain Direct Delivery and Distribution of Caffeine in Rats. Mol Pharm 2020; 17:4067-4076. [PMID: 32955898 DOI: 10.1021/acs.molpharmaceut.0c00495] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Direct drug delivery from nose to brain has drawn much attention as an effective strategy for the treatment of central nervous system diseases. After intranasal administration, drug molecules can be directly delivered from the nose to the brain. However, the detailed mechanism for this direct delivery to the brain has not been elucidated. In the present study, the effect of the activation of the cerebral fluid circulation (the glymphatic system) on the efficacy of direct delivery from nose to brain was investigated. Because the glymphatic system is activated by some anesthetic regimens, the differences in brain delivery and the pharmacokinetics under anesthetic and conscious conditions were compared in rats. Under urethane anesthesia, direct delivery from the nose to the brain was facilitated, whereas the brain uptake from the systemic circulation via the blood-brain barrier was decreased. In addition, both the brain uptake of caffeine injected into the subarachnoid cerebrospinal fluid (CSF) and the extracerebral clearance of caffeine after intrastriatal injection were enhanced under anesthesia. For intranasal administration, caffeine was transported directly from the nose to the CSF and then delivered into the brain parenchyma by the CSF circulation. The results obtained in the present study clarified that the direct delivery from nose to brain could be facilitated by anesthesia. These findings suggest that fluid circulation in the brain can contribute to a wider cerebral distribution of the drug after direct delivery from nose to brain.
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Affiliation(s)
- Daisuke Inoue
- Molecular Pharmaceutics Laboratory, College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga 525-8577, Japan.,Department of Pharmaceutics, School of Pharmacy, Shujitsu University, 1-6-1 Nishigawara, Naka-ku, Okayama 703-8516, Japan
| | - Tomoyuki Furubayashi
- Department of Pharmaceutics, School of Pharmacy, Shujitsu University, 1-6-1 Nishigawara, Naka-ku, Okayama 703-8516, Japan.,Laboratory of Pharmaceutical Technology, Kobe Pharmaceutical University, 4-19-1 Motoyamakita-machi, Higashinada, Kobe 658-8558, Japan
| | - Akiko Tanaka
- Laboratory of Pharmaceutical Technology, Kobe Pharmaceutical University, 4-19-1 Motoyamakita-machi, Higashinada, Kobe 658-8558, Japan
| | - Toshiyasu Sakane
- Laboratory of Pharmaceutical Technology, Kobe Pharmaceutical University, 4-19-1 Motoyamakita-machi, Higashinada, Kobe 658-8558, Japan
| | - Kiyohiko Sugano
- Molecular Pharmaceutics Laboratory, College of Pharmaceutical Sciences, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga 525-8577, Japan
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16
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Li T, Xu W, Ouyang J, Lu X, Sherchan P, Lenahan C, Irio G, Zhang JH, Zhao J, Zhang Y, Tang J. Orexin A alleviates neuroinflammation via OXR2/CaMKKβ/AMPK signaling pathway after ICH in mice. J Neuroinflammation 2020; 17:187. [PMID: 32539736 PMCID: PMC7294616 DOI: 10.1186/s12974-020-01841-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Accepted: 05/14/2020] [Indexed: 02/07/2023] Open
Abstract
Background Orexins are two neuropeptides (orexin A, OXA; orexin B, OXB) secreted mainly from the lateral hypothalamus, which exert a wide range of physiological effects by activating two types of receptors (orexin receptor 1, OXR1; orexin receptor 2, OXR2). OXA has equal affinity for OXR1 and OXR2, whereas OXB binds preferentially to OXR2. OXA rapidly crosses the blood-brain barrier by simple diffusion. Many studies have reported OXA’s protective effect on neurological diseases via regulating inflammatory response which is also a fundamental pathological process in intracerebral hemorrhage (ICH). However, neuroprotective mechanisms of OXA have not been explored in ICH. Methods ICH models were established using stereotactic injection of autologous arterial blood into the right basal ganglia of male CD-1 mice. Exogenous OXA was administered intranasally; CaMKKβ inhibitor (STO-609), OXR1 antagonist (SB-334867), and OXR2 antagonist (JNJ-10397049) were administered intraperitoneally. Neurobehavioral tests, hematoma volume, and brain water content were evaluated after ICH. Western blot and ELISA were utilized to evaluate downstream mechanisms. Results OXA, OXR1, and OXR2 were expressed moderately in microglia and astrocytes and abundantly in neurons. Expression of OXA decreased whereas OXR1 and OXR2 increased after ICH. OXA treatment significantly improved not only short-term but also long-term neurofunctional outcomes and reduced brain edema in ipsilateral hemisphere. OXA administration upregulated p-CaMKKβ, p-AMPK, and anti-inflammatory cytokines while downregulated p-NFκB and pro-inflammatory cytokines after ICH; this effect was reversed by STO-609 or JNJ-10397049 but not SB-334867. Conclusions OXA improved neurofunctional outcomes and mitigated brain edema after ICH, possibly through alleviating neuroinflammation via OXR2/CaMKKβ/AMPK pathway.
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Affiliation(s)
- Tao Li
- Department of Neurosurgery, The First People's Hospital of Yunnan Province (Kunhua Hospital/The Affiliated Hospital of Kunming University of Science and Technology), Yunnan, 650032, China.,Department of Physiology and Pharmacology, School of Medicine, Loma Linda University, 11041 Campus St, Loma Linda, CA, 92354, USA.,Department of Neurosurgery, The Second Affiliated Hospital of Zhejiang University School of Medicine, Zhejiang, 310009, Hangzhou, China
| | - Weilin Xu
- Department of Physiology and Pharmacology, School of Medicine, Loma Linda University, 11041 Campus St, Loma Linda, CA, 92354, USA.,Department of Neurosurgery, The Second Affiliated Hospital of Zhejiang University School of Medicine, Zhejiang, 310009, Hangzhou, China
| | - Jinsong Ouyang
- Department of Neurosurgery, The First People's Hospital of Yunnan Province (Kunhua Hospital/The Affiliated Hospital of Kunming University of Science and Technology), Yunnan, 650032, China
| | - Xiaoyang Lu
- Department of Neurosurgery, The Second Affiliated Hospital of Zhejiang University School of Medicine, Zhejiang, 310009, Hangzhou, China
| | - Prativa Sherchan
- Department of Physiology and Pharmacology, School of Medicine, Loma Linda University, 11041 Campus St, Loma Linda, CA, 92354, USA
| | - Cameron Lenahan
- Department of Physiology and Pharmacology, School of Medicine, Loma Linda University, 11041 Campus St, Loma Linda, CA, 92354, USA.,Burrell College of Osteopathic Medicine, 3501 Arrowhead Dr, Las Cruces, NM, 88001, USA
| | - Giselle Irio
- Department of Physiology and Pharmacology, School of Medicine, Loma Linda University, 11041 Campus St, Loma Linda, CA, 92354, USA.,Burrell College of Osteopathic Medicine, 3501 Arrowhead Dr, Las Cruces, NM, 88001, USA
| | - John H Zhang
- Department of Physiology and Pharmacology, School of Medicine, Loma Linda University, 11041 Campus St, Loma Linda, CA, 92354, USA
| | - Jianhua Zhao
- Department of Neurosurgery, The First People's Hospital of Yunnan Province (Kunhua Hospital/The Affiliated Hospital of Kunming University of Science and Technology), Yunnan, 650032, China
| | - Yongfa Zhang
- Department of Neurosurgery, The First People's Hospital of Yunnan Province (Kunhua Hospital/The Affiliated Hospital of Kunming University of Science and Technology), Yunnan, 650032, China.
| | - Jiping Tang
- Department of Physiology and Pharmacology, School of Medicine, Loma Linda University, 11041 Campus St, Loma Linda, CA, 92354, USA.
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17
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Santiago JCP, Hallschmid M. Outcomes and clinical implications of intranasal insulin administration to the central nervous system. Exp Neurol 2019; 317:180-190. [PMID: 30885653 DOI: 10.1016/j.expneurol.2019.03.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2018] [Revised: 02/12/2019] [Accepted: 03/13/2019] [Indexed: 12/20/2022]
Abstract
Insulin signaling in the brain plays a critical role in metabolic control and cognitive function. Targeting insulinergic pathways in the central nervous system via peripheral insulin administration is feasible, but associated with systemic effects that necessitate tight supervision or countermeasures. The intranasal route of insulin administration, which largely bypasses the circulation and thereby greatly reduces these obstacles, has now been repeatedly tested in proof-of-concept studies in humans as well as animals. It is routinely used in experimental settings to investigate the impact on eating behavior, peripheral metabolism, memory function and brain activation of acute or long-term enhancements in central nervous system insulin signaling. Epidemiological and experimental evidence linking deteriorations in metabolic control such as diabetes with neurodegenerative diseases imply pathophysiological relevance of dysfunctional brain insulin signaling or brain insulin resistance, and suggest that targeting insulin in the brain holds some promise as a therapy or adjunct therapy. This short narrative review gives an overview over recent findings on brain insulin signaling as derived from human studies deploying intranasal insulin, and evaluates the potential of therapeutic interventions that target brain insulin resistance.
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Affiliation(s)
- João C P Santiago
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, 72076 Tübingen, Germany; German Center for Diabetes Research (DZD), 72076 Tübingen, Germany; Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, 72076 Tübingen, Germany
| | - Manfred Hallschmid
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, 72076 Tübingen, Germany; German Center for Diabetes Research (DZD), 72076 Tübingen, Germany; Institute for Diabetes Research and Metabolic Diseases of the Helmholtz Center Munich at the University of Tübingen, 72076 Tübingen, Germany.
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18
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Orexin 2 receptor stimulation enhances resilience, while orexin 2 inhibition promotes susceptibility, to social stress, anxiety and depression. Neuropharmacology 2018; 143:79-94. [PMID: 30240784 DOI: 10.1016/j.neuropharm.2018.09.016] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2018] [Revised: 08/28/2018] [Accepted: 09/11/2018] [Indexed: 02/08/2023]
Abstract
Knockdown of orexin/hypocretin 2 receptor (Orx2) in the basolateral amygdala (BLA) affects anxious and depressive behavior. We use a new behavioral paradigm, the Stress Alternatives Model (SAM), designed to improve translational impact. The SAM induces social stress in adult male mice by aggression from larger mice, allowing for adaptive decision-making regarding escape. In this model, mice remain (Stay) in the oval SAM arena or escape from social aggression (Escape) via routes only large enough for the smaller mouse. We hypothesized intracerebroventricular (icv) stimulation of Orx2 receptors would be anxiolytic and antidepressive in SAM-related social behavior and the Social Interaction/Preference (SIP) test. Conversely, we predicted that icv antagonism of Orx2 receptors would promote anxious and depressive behavior in these same tests. Anxious behaviors such as freezing (both cued and conflict) and startle are exhibited more often in Stay compared with Escape phenotype mice. Time spent attentive to the escape route is more frequent in Escape mice. In Stay mice, stimulation of Orx2 receptors reduces fear conditioning, conflict freezing and startle, and promotes greater attention to the escape hole. This anxiolysis was accompanied by activation of a cluster of inhibitory neurons in the amygdala. A small percentage of those Stay mice also begin escaping; whereas Escape is reversed by the Orx2 antagonist. Escape mice were also Resilient, and Stay mice Susceptible to stress (SIP), with both conditions reversed by Orx2 antagonism or stimulation respectively. Together, these results suggest that the Orx2 receptor may be a useful potential target for anxiolytic or antidepressive therapeutics.
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