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This presentation explores the peripheral and central mechanisms of methamphetamine neurotoxicity and the potential role of liver damage and ammonia toxicity. It discusses the impact of methamphetamine on dopamine and serotonin levels and the contribution of excitotoxicity, oxidative stress, and metabolic compromise. Additionally, it examines the effects of local administration of methamphetamine and the protective function of the blood-brain barrier.
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Addiction Therapy-2014Chicago, USAAugust 4 - 6, 2014 Bryan Yamamoto
Peripheral and Central Mechanisms of Methamphetamine Neurotoxicity: Connecting the Dots Bryan Yamamoto, Ph.D. Department of Neurosciences University of Toledo College of Medicine and Life Sciences August 4, 2014
Methamphetamine Neurotoxicity in Humans Volkow et al, Am. J. Psychiatry, 2001 Callaghan et al., Drug and Alcohol Dependence, 2011 Meth abuse increases risk of Parkinson’s Disease by 76% compared to age-matched controls and cocaine-abusers
Overarching Hypothesis Excitotoxicity and oxidation of proteins and lipids are mechanisms underlying the neurotoxicity of Methamphetamine
Identified Events Leading to a Loss of Dopamine and 5HT X X Glutamate Release Dopamine Release X Glu Receptor Activation Calcium MAO X NOS X H2O2 Calpain NO Fe++ X ONOO- (peroxynitrite) OH* O2- Protein oxidation, Mitochondrial Dysfunction Lipid Peroxidation Proteolysis
But, there are caveats to the proposition that the neurotoxicity/excitotoxicity of METH is a result of its direct action on the brain……..
Systemic and Local Administration of METH: Local administration of METH does not increase glutamate Glutamate (pg/20 ml Glutamate (pg/20 ml) Perfusion -1 0 1 2 3 4 5 6 7 8 Burrows
Glutamate Synergizes with Local METH To Deplete Dopamine Content * Dopamine (pg/mg protein) # Meth No Meth Meth/Heat No Meth Meth Meth/Heat Without Glutamate With Glutamate Burrows
Thinking Outside the Brain…… • If it is not the direct effect of METH alone on the brain (striatum), what other systems could be responsible for the neurotoxicity? • Another target of METH is the liver • Liver damage can produce encephalopathy (i.e. hepatic encephalopathy) • Tremor, movement disorders • Delirium, stupor, confusion, and coma
Methamphetamine Increases Liver Enzymes in Plasma * Alanine Aminotransferase Aspartate Aminotransferase ALT (IU/L) * AST (IU/L) Saline METH Saline METH Halpin
Liver Damage and Ammonia • The liver normally removes excess ammonia from the blood via the urea cycle. • This is important because ammonia is a neurotoxic byproduct of protein metabolism and other metabolic reactions. • If the liver damaged, there is an accumulation of ammonia that is thought to cause hepatic encephalopathy
Ammonia Toxicity • Excitotoxicity(Fan and Szerb, 1993, Hermenegildo et al., 1996) • Oxidative stress (Kosenko et al., 1997 and Kosenko et al., 1995) • Metabolic compromise (Hawkins et al., 1973, McCandless and Schenker, 1981) \Similar mechanisms that mediate the toxicity to ammonia and the neurotoxicity to METH • Unknown whether peripheral organ (e.g. liver) damage is produced by METH and if it contributes to METH neurotoxicity
Overarching Hypothesis Methamphetamine Liver Damage Hyperammonemia X Lactulose Neurotoxicity
Methamphetamine Increases Ammonia in Plasma * # Plasma Ammonia (mM) Saline Lactulose METH METH + Lactulose Halpin
Methamphetamine Increases Ammonia in Striatum: Blocked by Lactulose 500 400 300 200 100 Halpin
Lactulose Does Not Affect METH Concentrations in the Brain 3 2 1 0 METH METH + Lactulose Halpin
Lactulose Attenuates METH-induced Long-term Depletions of Dopamine and 5HT Content Dopamine Serotonin * # # (pg/mg protein) (pg/mg protein) * * Vehicle Lactulose Vehicle Lactulose Vehicle Lactulose Vehicle Lactulose Saline Saline METH METH Saline Saline METH METH Halpin
Lactulose Blocks METH-induced Decreases in Dopamine Transporter Immmunoreactivity Dopamine Transporter Immunoreactivity 1.2 1.0 0.8 * % Control 0.6 0.4 0.2 Vehicle Lactulose Vehicle Lactulose Saline METH Saline METH Halpin
METH-Induced Increases in Striatal Extracellular Glutamate: Blocked by Lactulose 600 500 Vehicle-METH 400 Glutamate (% Baseline) 300 200 Vehicle-Saline 100 Lac-METH Lac-Saline B Time (hrs) Halpin, Northrop
Lactulose Blocks METH-Induced Increases in Striatal Spectrin Proteolysis 180 * 160 140 120 Percent Control 100 80 60 40 20 Vehicle Lactulose Vehicle Lactulose Saline Saline METH METH Halpin, Northrop
METH-Induced Astroglyosis (GFAP) is Blocked by Lactulose * Percent Control Vehicle Lactulose Vehicle Lactulose Saline Saline METH METH Halpin, Northrop
Local Perfusion of Ammonia on Glutamate: Efflux Through Reversal of the Glutamate Transporter 300 250 200 Glutamate (% Baseline) * 150 100 50 NH3 or aCSF TBOA or aCSF Time (hrs) Halpin, Northrop
Combined Local Perfusions of Ammonia and METH Dopamine and 5HT Content in the Striatum 5HT Dopamine * * (pg/mg protein) (pg/mg protein) NH3 Vehicle NH3 Vehicle NH3 Vehicle Vehicle NH3 NH3 NH3 METH GYKI Saline Saline METH METH Saline Saline METH METH METH GYKI Halpin, Northrop
The Blood-Brain Barrier: A Protective Barrier of the Brain Amphetamines
BBB Function in Cortex After Meth Vehicle+Saline Lactulose+Saline Vehicle+Meth Lactulose+Meth Quantification of FITC-Dextran Extravasation * # Vehicle Saline Lactulose Saline Vehicle Meth Lactulose Meth Northrop
Blood-Brain Barrier Tight Junctions Occludin Claudin 3, 5, 12 JAM
Meth-Induced Disruption of BBB Structure in Cortex Isolated Brain Capillaries Occludin Claudin-5 # # * * * * Vehicle Saline Lactulose Saline Vehicle Meth Lactulose Meth Vehicle Saline Lactulose Saline Vehicle Meth Lactulose Meth Northrop
Ammonia as a Pro-Oxidant? Representative Blot for Tight Junction Proteins Representative Blot for Nitrotyrosine Isolated Brain Capillaries from Cortex Northrop
Ammonia as a Pro-Inflammatory Agent? Cyclooxygenase-2 * COX-2 Immunoreactivity (% Vehicle + Saline) & Vehicle Saline Lactulose Saline Vehicle Meth Lactulose Meth Northrop
Summary and Conclusions Effects of METH: • Increases in extracellular glutamate and evidence of excitotoxicity and oxidative degradation of proteins • Causes hepatotoxicity and increases ammonia concentrations in peripheral plasma and brain to mediate excitotoxicity • Damages the BBB via ammonia, oxidative stress, and inflammation (COX2-dependent prostaglandin synthesis?) • Opening of the BBB can render the brain vulnerable to toxins by that would otherwise by restricted to the periphery. • Peripheral organ effects should be considered as possible causes of the neurotoxicity associated with psychostimulant drug use
Collaborators Methamphetamine Project Past and Current Other Current Lab Members • Jeffrey Brown, Ph.D. • Kristan Burrows Cline, Ph.D. • David Eyerman, Ph.D. • Amy Ferng, M.S. • Laura Halpin, Ph.D. • John Irlam, D.O. • J. F. Nash, Ph.D. • Arunan Nadarajah, Ph.D. • Nicole Northrop, Ph.D. • Robert Staszewski, M.S. • Despina Tata, Ph.D • Amanda Blaker • Veronica Chiu, Ph.D. • Stuart Collins • Nicole Harless • Katelyn Marchal • Carmen Mitchell • Reka Natarajan, Ph.D. • Allen Schroering, M.S. • Erin Semple • Branden Stansley NIH grants DA007606, DA016866, DA035499
Meet the eminent gathering once again atAddiction Therapy-2015Florida, USAAugust 3 - 5, 2015 Addiction Therapy – 2015 Website: addictiontherapy.conferenceseries.com