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Walters AS, Li Y, Koo BB, Ondo WG, Weinstock LB, Champion D, Afrin LB, Karroum EG, Bagai K, Spruyt K. Review of the role of the endogenous opioid and melanocortin systems in the restless legs syndrome. Brain 2024; 147:26-38. [PMID: 37633259 PMCID: PMC10796165 DOI: 10.1093/brain/awad283] [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: 03/07/2023] [Revised: 07/23/2023] [Accepted: 08/01/2023] [Indexed: 08/28/2023] Open
Abstract
Restless legs syndrome (RLS) is responsive to opioid, dopaminergic and iron-based treatments. Receptor blocker studies in RLS patients suggest that the therapeutic efficacy of opioids is specific to the opioid receptor and mediated indirectly through the dopaminergic system. An RLS autopsy study reveals decreases in endogenous opioids, β-endorphin and perhaps Met-enkephalin in the thalamus of RLS patients. A total opioid receptor knock-out (mu, delta and kappa) and a mu-opioid receptor knock-out mouse model of RLS show circadian motor changes akin to RLS and, although both models show sensory changes, the mu-opioid receptor knock mouse shows circadian sensory changes closest to those seen in idiopathic RLS. Both models show changes in striatal dopamine, anaemia and low serum iron. However, only in the total receptor knock-out mouse do we see the decreases in serum ferritin that are normally found in RLS. There are also decreases in serum iron when wild-type mice are administered a mu-opioid receptor blocker. In addition, the mu-opioid receptor knock-out mouse also shows increases in striatal zinc paralleling similar changes in RLS. Adrenocorticotropic hormone and α-melanocyte stimulating hormone are derived from pro-opiomelanocortin as is β-endorphin. However, they cause RLS-like symptoms and periodic limb movements when injected intraventricularly into rats. These results collectively suggest that an endogenous opioid deficiency is pathogenetic to RLS and that an altered melanocortin system may be causal to RLS as well.
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Affiliation(s)
- Arthur S Walters
- Sleep Division, Department of Neurology, Vanderbilt University Medical Center, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Yuqing Li
- Norman Fixel Institute for Neurological Diseases, Department of Neurology, College of Medicine, University of Florida, Gainesville, FL 32610, USA
| | - Brian B Koo
- Sleep Medicine Laboratory, VA Connecticut Health Care System, West Haven, CT 06516, USA
- Yale Center for Restless Legs Syndrome, Yale School of Medicine, New Haven, CT 06520, USA
| | - William G Ondo
- Department of Neurology, Methodist Hospital, Weill Cornell Medical School, Houston, TX 77030, USA
| | - Leonard B Weinstock
- Department of Internal Medicine, Washington University School of Medicine, St.Louis, MO 63130, USA
| | - David Champion
- Sydney Children's Hospital, Department of Pain Medicine, Randwick, NSW 2031, Australia
| | - Lawrence B Afrin
- Hematology/Oncology, AIM Center for Personalized Medicine, Purchase, NY 10577, USA
| | - Elias G Karroum
- Department of Neurology and Rehabilitation Medicine, The George Washington University School of Medicine and Health Sciences, George Washington University, Washington, D.C. 20052, USA
| | - Kanika Bagai
- Sleep Division, Department of Neurology, Vanderbilt University Medical Center, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
| | - Karen Spruyt
- Université Paris Cité, NeuroDiderot Inserm, Paris 75019, France
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Walters AS, Li Y, Karroum EG, Champion D, Weinstock LB, Bagai K, Afrin LB, Spruyt K. Exploring the role of the endogenous opiate system in the pathogenesis of anemia in an opiate receptor knock-out model of Restless Legs Syndrome. Med Hypotheses 2022; 167:110941. [PMID: 36505961 PMCID: PMC9731170 DOI: 10.1016/j.mehy.2022.110941] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Restless Legs Syndrome (RLS) is characterized by bothersome leg discomfort accompanied by an urge to move to obtain relief and symptoms are worse at night and on lying down. There is at least partial and temporary relief with activity. It is also an opioid responsive disorder, often accompanied by iron deficiency with or without anemia, and inflammation may be a precipitating factor in some cases. We created two in-vivo opiate receptor knock out mouse models of RLS - a triple opiate receptor knock-out mouse and a mu opiate receptor knock-out mouse. Both sets of animals were restless during the sleep period as is also true of RLS. Both of our knockout models showed statistically significantly decreased Hemoglobin and Hematocrit indicating anemia and both models showed statistically significant decreases in serum iron suggestive of either iron deficiency anemia or inflammatory anemia. The rest of the hematologic studies were not consistent enough to determine which of these two types of anemia was present in either model. An additional experiment in normal wild type mice showed a statistically significant decrease in serum iron when an opiate receptor blocker was used. To our knowledge this is the first demonstration that deficiency of endogenous opioids might play a role in the production of anemia. Our hypothesis is that an intact endogenous opiate system is necessary for red cell homeostasis. The presence of opioid receptors both on red blood cells and on various immunologically based white blood cells suggest mechanisms by which deficiency in the endogenous opiate system could cause anemia of either the iron deficiency or inflammatory types. The administration of opioid agonists or antagonists to iron deficient cultures of red blood cell precursors is a next step in determining the role of the endogenous opiate system in the maintenance of red cell homeostasis and in the possible prevention of iron deficiency or inflammatory anemia where iron dysregulation is key.
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Affiliation(s)
- Arthur S. Walters
- Sleep Division, Dept of Neurology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Yuqing Li
- Norman Fixel Institute for Neurological Diseases, Dept of Neurology, College of Medicine, University of Florida, Gainesville, FL, USA
| | - Elias G. Karroum
- Department of Neurology & Rehabilitation Medicine, The George Washington University School of Medicine and Health Sciences, Washington, DC., USA
| | - David Champion
- Sydney Children’s Hospital, Randwick, NSW 2031, Australia
| | - Leonard B. Weinstock
- Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Kanika Bagai
- Sleep Division, Dept of Neurology, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Lawrence B. Afrin
- Hematology/Oncology, AIM Center for Personalized Medicine, Purchase, New York
| | - Karen Spruyt
- Université de Paris, NeuroDiderot Inserm, France
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Youdim MBH. Brain iron deficiency and excess; cognitive impairment and neurodegeneration with involvement of striatum and hippocampus. Neurotox Res 2009; 14:45-56. [PMID: 18790724 DOI: 10.1007/bf03033574] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
While iron deficiency is not perceived as a life threatening disorder, it is the most prevalent nutritional abnormality in the world, and a better understanding of modes and sites of action, can help devise better treatment programs for those who suffer from it. Nowhere is this more important than in infants and children that make up the bulk of iron deficiency in society. Although the effects of iron deficiency have been extensively studied in systemic organs, until very recently little attention was paid to its effects on brain function. The studies of Oski at Johns Hopkin Medical School in 1974, demonstrating the impairment of learning in young school children with iron deficiency, prompted us to study its relevance to brain biochemistry and function in an animal model of iron deficiency. Indeed, rats made iron deficient have lowered brain iron and impaired behaviours including learning. This can become irreversible especially in newborns, even after long-term iron supplementation. We have shown that in this condition it is the brain striatal dopaminergic-opiate system which becomes defective, resulting in alterations in circadian behaviours, cognitive impairment and neurochemical changes closely associated with them. More recently we have extended these studies and have established that cognitive impairment may be closely associated with neuroanatomical damage and zinc metabolism in the hippocampus due to iron deficiency, and which may result from abnormal cholinergic function. The hippocampus is the focus of many studies today, since this brain structure has high zinc concentration and is highly involved in many forms of cognitive deficits as a consequence of cholinergic deficiency and has achieved prominence because of dementia in ageing and Alzheimer's disease. Thus, it is now apparent that cognitive impairment may not be attributed to a single neurotransmitter, but rather, alterations and interactions of several systems in different brain regions. In animal models of iron deficiency it is apparent that dopaminergic interaction with the opiate system and cholinergic neurotransmission may be defective.
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Affiliation(s)
- M B H Youdim
- Eve Topf and USA National Parkinson Foundation, Centers of Excellence for Neurodegenerative Diseases Research and Department of Pharmacology, Rappaport Family Research Institute, Technion-Faculty of Medicine, Haifa, Israel.
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Focusing on symptoms rather than diagnoses in brain dysfunction: Conscious and nonconscious expression in impulsiveness and decision-making. Neurotox Res 2008; 14:1-20. [DOI: 10.1007/bf03033572] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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