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The Role Of Transition Metals & Reactive Oxygen Species (ROS) In Alzheimer's Disease by Piril Erel
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The Role Of Transition Metals & Reactive Oxygen Species (ROS) In Alzheimer's Disease by Piril Erel

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This powerpoint discusses the role of transition metals and amyloid plaque formation in Alzheimer’s disease (AD) and how metal ion chelators may be employed as therapeutic agents for AD. It describes …

This powerpoint discusses the role of transition metals and amyloid plaque formation in Alzheimer’s disease (AD) and how metal ion chelators may be employed as therapeutic agents for AD. It describes the disorder, how it progresses and what happens to the brain tissue.
Furthermore, within the presentation I describe a drug which chelates metals including a description about the chemical formulation of these drugs and how the drug can be preventative of AD.


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  • Thank you so kindly. Very nice distillation of a complex topic, beautifully presented. Best of luck in your studies.
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  • It is now available to download, thank you ever so much for your interest

    Regards,
    Miss P Erel
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  • Piril this is an excellent presentation. Can you make it available for download? --thank you!
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  • Hi, my name is Piril Erel. I am in my first year Mpharm course. My SSA title is – The role of transition metals and reactive oxygen species(ROS) in AD. I decided to do my presentation in an area, in which, I wanted to work on a subject that was not yet mainstream and kind of out of the box. I got into Alzheimer’s Disease when I was working on Schizophrenia in A-Levels as a extended project and found it very interesting and intriguing information on AD too.
  • I will talk about the role of metals a s platform of pathophysiology for AD and other neurodegenerative disease My talk will focus on the metal hypothesis and a drug called PBT2 for AD and I will begin with an introduction to AD, quickly moving onto the Metal Hypothesis – role of transition metals.
  • So the objectives to my presentation are:Explaining the metal hypothesisProviding an insight in the dysfunction of an AD brain relating to the Metal HypothesisDescribing Reactive Oxygen Species (ROS)Discussing how the metal hypothesis integrates with ROS to cause ADDetails of how PBT2 could be an effective drug for AD patients
  • AD is a slow progressive and fatal neurodegenerative disease indicated by memory and cognitive dysfunction. Although there is an ever increasing knowledge in many medical areas, there still has not yet been a cure for AD. Current treatments are only temporary and try relieving symptoms not the actual underlying illness itself. Some figures for AD:Currently it affects eight hundred thousand in the UK alone. 36 million world wide. This figure is estimated to double every 20 years. Estimated to be 60 million in 2030 and 115 million in 2050. These figures compel researchers and scientists to find a cure as soon as possible.
  • AD is the most common form of dementia in the elderly, 1/5 people living today over the age of 65 will get AD if we live long enough and upto 50% over the age of 85 have AD. After Age the second greatest risk factor is family history and there is a very strong genetic component in this disease.Other risk factors include gender, females get it more then males and there is some though into whether menopause leads to some energy deprivation and the brain could be a risk factor. Most metabolic issues, obesity high cholesterol, stroke, diabetes. If you look at changes in selected causes of death 2000-2008 you can see that most of these diseases have a decreasing incidence rate apart from AD. Alzheimer’s is going up dramatically as there are no AD survivors as we do not have any drugs to stop this disease.
  • The brain is a specialized organ which has ‘special activities’ if you think about it, these activities require a high concentration of metal ions such as Zn and Cu. These metals are essential in neuronal activity, within synapses, due to this cells have a system which maintain metal-ion homeostasis. The interruption of these mechanisms alter the ionic balance and result in AD. Metal Ions have 2 roles:Aggregation of AB peptide plaquesProduction of ROS induced by AB
  • So what is the Metal Hypothesis? Essentially shows that zinc and copper are necessary for the aggregation of A-beta, now what will happen is that, when copper binds to a-beta you will also get a ROS being generated so you actually get a detrimental release of free radicals by the interaction of copper and a beta. But one of the points that we don’t consider is that when we get the excessive aggregates in the brain, the brain has a real tough time getting rid of these. As these aggregates accumulate, the excess a-beta actual trap these metals so zinc and copper no longer because bio-available
  • Transportation and utilization of anything within the body is maintained by their chemistry, making them physiologically useful and potentially able to give rise to pathological miracles. The concentrations within a health brain of metal ions are high however in AD these are increased even more and highest especially in amyloid plaque deposits. Zn released from the presynaptic terminal and Cu from the postsynaptic terminal are in free exchangeable form, when Abeta is within the synaptic cleft this results in a interaction.
  • A-beta is found in regions in the brain which govern memory, emotions and intellectual function of patients with AD. Studies have shown that Zn & Cu mediate the precipitation of AB deposits in AD-brain tissue, as a-beta plaques have a high concentration of Cu and Zn within however the three problems scientists has is that we do not know whether the increase in concentration is due to:Abnormal activity of Cu (or Zn) homeostasis which initiates Amyloid- β plaques.Amyloid plaques having a high affinity to metal ions.Amyloid plaques acting as metal sinks absorbing the ions into their core
  • In a diagram model: Monomers are basically neutral, but Zn & Cu then drive the formation of oligomers, these in excess cause synaptic dysfunction the lodge of Protofibril can then cause membrane disruption then a full blown B-amyloid fibril can cause inflammation and also as neurons start to die here, the neuronal debris will also drive inflammation.
  • AB and Cu binding forms oxidative crosslinks between monomers, these are then called oligomers. Oligomers are very difficult for the brain to clear and can eventually cause neuron death.The Image shows:Zn imaging in a mouse brain, it is a heat map so red is more and blue is less. Bottom is the AD mouse showing the entire cortex where Zn is bound to a-beta. This interaction between A-beta and metals gives a pathway which could be used as a therapeutic intervention which normalizes metal homeostasis and reduce levels of toxic A-beta oligomers in the brain. Cu binding to A-beta also generates ROS causing a detrimental release of free radicals.
  • Oxygen is require in the brain to maintain the synthesis of ATP, the brain accounts for 20% oxygen so has a high level of reactive oxygen species (ROS) generated. These exposures to free radicals damage neurons in the brain. Oxidative Stress is the imbalance between the amount of ROS being produced and the ability of the body to detect and remove these toxic substances, this happens because ROS overwhelms cellular antioxidant defense mechanisms causing macromolecular damage such as:Damage of DNAOxidation of polyunsaturated fatty acidsOxidation of amino acids in proteinsOxidatively inactivation of specific enzymes.
  • A drug must posses certain characteristics to be able to pass the blood brain barrier such as:Low molecular weightPoorly charged or not charged at allStableSelectivity of certain metal ions as we do not want a depletion of metal ions in wholeLow toxicityMinimum side effectsTherefore, scientists have found a newly developed drug called PBT2 which possess most of these characteristics.
  • So how do we fix this? PBT2 has firstly shown rapid improvement in cognition in mouse models in AD. The idea was that PBT2 would prevent the interactions of A-beta with the metals. It is a copper/zinc ionophore so essentially it competes for metals but also redistributes metals back into the cell as it transports ions across the lipid bilayer. It’s aim is to clear A-beta aggregates in the brain by targeting zinc and copper ions, effectively detoxifying the AB plaques. This type of drug has an affinity for the metal that is strong than a-beta. Metals are promiscuous, they will bind to which ever is stronger, the 10-4x greater force attracts metals to PBT2 more and how PBT2 redistributes metals back into the cell is due to an enzyme within the cell called SOD1 which has an even more stronger affinity to metals compared to a-beta and PBT2, so metals will then again leave PBT2 and bind to SOD1, further more being released back into the cell. Essentially PBT2 is like a bus transporting passengers, in our case metal ions from one place to another. After 2nd bullet point – therefore preventing the interaction of AB + ZN/CU
  • In an healthy synapse as we have discussed before, zinc is released pre-synaptically at around concentrations of 300um and copper is released post-synaptically at around concentrations of 15um both into the synaptic cleft.. A-beta is released into the synaptic cleft and it will aid in lowering the concentrations of the metal ions by acting as a sponge then A-beta is degraded into small monomer units by enzymes
  • However, in an AD synapse the decrease in ATP leads to a reduction of metal reuptake, causing the average concentration of metals to rise over time. This is why AD is a slowly progressive fatal neurodegenerative disease. As shown in my previous diagram, metal ions will react with A-beta forming oligomers then crucially to amyloid plaques. The higher the concentration of metals the more stronger and resistant it will be to degradation.
  • Now how PBT2 interacts within this synapse is again the fact that it has a high affinity for metals so chelates metals allowing copper and zinc to be removed from a-beta, the advantage lies in the chemical properties of PBT2, the ionophoric properties of the drug. PBT2 reduces these concentrations of the metal ions to normal so avoiding the binding between A-beta and the metals, furthermore decreasing precipitation and oligomers and toxic a-beta amyloid plaque forming.
  • The trail method for PBT2 was conducted by Prana Biotechnology who is the leading researchers in PBT2, their objective was to test the safety and efficacy of PBT2 in patients with mild AD. They also wanted to see changes in cognition after administration of PBT2 using the Neuro-psychological test battery which measures executive function. Executive function loss appears as: depression, apathy and personality changes. A 12-week trial was taken place where PBT2 was administered to 78 patients with mild AD in either one of the three doses:Placebo 50mg 250mg It was a double-blind, randomized, placebo-controlled trial.
  • 250mg dose in patients showed a significant increase in EF scores compared to placebo group. Also showed a significant decrease in a-beta protein plaques. This shows promising results for PBT2 as a therapeutic intervention to cure Alzheimer’s Disease. Phase Iib clinical trials are currently being tested where they’re evaluting the effect of PBT2 on many different aspects.
  • Finally, through thorough research into this area, current drug trials target memory deficit in early-moderate Alzheimer's however it is questionable whether this is too little too late and whether it is enough as the rising wave is coming over the next couple of years. The aim is to hit Alzheimer’s disease as early as possible, even though no cognitive symptoms pathology is starting and you are on your way maybe 15 years on average before there is any cognitive changes. This may establish a possible cure or at least the consequences will be more reversible at this stage where neuronal death has not yet occurred. The advantage of PBT2 is that it not only removes the toxic a-beta plaques but it also re-establishes homeostasis of metals. Clinical trials for PBT2 will hopefully provide promising result for curing AD.
  • Transcript

    • 1. The role of Transition Metals & Reactive Oxygen Species (ROS) in Alzheimer’s Disease(AD). By Piril Erel UoB: 12004723 Piril Erel - UoB: 12004723 1 Normal  Alzheimer’s
    • 2. Content Pages: Piril Erel - UoB: 12004723 2 10.Production Of ROS Induced By Aβ 11.Chelating Properties 12.PBT2 detoxifies Aβ Plaques 13.The Healthy Synapse – a glance into the synaptic cleft 14.Alzheimer’s Disease – a glance into the synaptic cleft 15.PBT2 – a glance into the synaptic cleft 16.Trial Method For PBT2 17.Results From PBT2 18.Conclusion 19.Ending 20.References 1. Aims & Objective 2. What Is Alzheimer’s Disease? 3. Risk Factors Associated With AD 4. Metal Homeostasis In Alzheimer’s Disease 5. Pathophysiology of AD 6. The Role Of Transition Metals 7. Amyloid- β(Aβ) Protein Plaque Formation And How It Links To Transition Metals 8. Aggregation Of Aβ Is Metal Dependent 9. Interactions Of Transition Metals With Amyloid – β Protein (AβPP)
    • 3. The main aim of this project is to investigate current research in Alzheimer’s Disease(AD) including novel ways to treat this illness which currently does not have any known cure. By doing this assignment I will introduce The Metal Hypothesis for AD and a novel drug called PBT2 which I will discuss in detail. Objectives: Explain ‘The Metal Hypothesis’ Provide an insight in the dysfunctions of an AD-brain relating to the Metal Hypothesis Describe Reduced Oxygen Species (ROS) Discuss how the Metal Hypothesis integrates with ROS to cause AD Detail of how PBT2 could be an effective drug for AD patients. Aims & Objective Piril Erel - UoB: 12004723 3
    • 4. Alzheimer’s Disease(AD) is a slow progressive and fatal neurodegenerative disease which is indicated by memory and cognitive dysfunction. Despite increasing knowledge of genetics, epidemiology and neuropathology AD is not treatable. Currently, disease modifying drugs or existing therapies only offer short-term symptomatic relief. It affects 800,000 people in the UK alone and 36 million people world wide, (data from 2010), this number approximately doubles every 20 years, and is estimated to reach 66 million in 2030 and 115 million in 2050.[1] This pressures scientists to make finding a long term pharmacotherapy a priority. What Is Alzheimer’s Disease? Piril Erel - UoB: 12004723 4
    • 5. Risk Factors: 1. Age: a. 1/5 people over 65 will get Alzheimer’s Disease b. Up to 50% over age 85 have AD 2. Family History: a. Strong genetic component in most cases of AD 3. Other: a. Gender (female; menopause?) b. Stroke, Obesity, High Cholesterol c. Diabetes Piril Erel - UoB: 12004723 5 Risk Factors Associated With AD
    • 6. The brain is a specialized organ which uses key cellular processes to work efficiently, these processes require a high concentration of transition metal ions such as zinc(Zn) and copper(Cu). Zn2+ & Cu2+ are required in neuronal activity within synapses Due to the necessity of these metal ions, cells have a sophisticated system to maintain metal-ion homeostasis. Breakdown of these mechanisms alter the ionic balance and can result in a disease state such as AD. These metal ions are suggested to have two distinct roles in the pathophysiology of AD: 1. Aggregation of Aβ peptide plaques 2. Production of reactive oxygen species induced by Aβ. Metal Homeostasis In Alzheimer’s Disease Piril Erel - UoB: 12004723 6
    • 7. Promotion of Aβ in the brain, which is collected over decades due to the presence of raised Zn2+ & Cu2+ concentrations. Sequestration of copper by Aβ, drives the generation of reactive oxygen species. Excessive aggregates of Aβ trap essential metals: Zinc & Copper. Piril Erel - UoB: 12004723 7 Pathophysiology Of AD
    • 8. Metals are involved in essential biological functions but the transport and utilization are generally controlled by their chemistry making them physiologically useful and potentially able to give rise to pathological miracles. The levels of transition metals such as Cu, Fe and Zn in a healthy brain neocortical parenchyma are still maintained at a high concentration, however within an AD-affected brain these concentrations are increased with the highest levels found within amyloid plaque deposits[2]. Kenche et al stated that both the Zn2+ released from the presynaptic terminals and Cu2+ released from the post-synaptic terminals, following synapse stimulation, are pre-dominantly in a ‘free’ exchangeable form. These ions, along with Aβ in the synaptic cleft results in an inevitable interaction. The Role Of Transition Metals Pic – Reference: Henryk Kozlowski, Marek Luczkowski, Maurizio Remelli, Daniel Valensin. (2012). Copper, Zinc and iron in neurodegenerative diseases (Alzheimer's, Parkinsons's and prion diseases). Metal Ion in Neurodegenerative Diseases. 256 (Fig. 3.), p1. Piril Erel - UoB: 12004723 8
    • 9. Aβ is the main component of deposits found in the regions of the brain involved with memory, emotions and intellectual function of patients with AD[3]. Cherny et al, 1999 found that the use of promoting chelation of metals in postmortem studies have shown that Zn2+ and Cu2+ mediate the precipitation of Aβ deposits in AD-brain tissue. Studies show that the neuropil and amyloid plaques in AD-brains have a high concentration of Cu and Zn, however we do not know whether this is due to: Abnormal activity of Cu (or Zn) homeostasis which initiates Amyloid- β plaques. Amyloid plaques having a high affinity to metal ions. Amyloid plaques acting as metal sinks absorbing the ions into their core [4]. Amyloid- β(Aβ) Protein Plaque Formation And How It Links To Transition Metals Pic2 - Reference: AHAF (American Health Assistance Foundation). (). Amyloid Plaques and Neurofibrillary Tangles.. Available: http://pakmed.net/academic/age/alz/alz030.htm. Last accessed 14th Apr 2013. Piril Erel - UoB: 12004723 9
    • 10. + Zn2+/Cu2+ Aβ Monomer Oligomer Protofibril β- Amyloid Fibril Aggregation Of Aβ Is Metal Dependent Non- Pathogenic Synaptic Dysfunction Membrane Disruption Inflammation Subsequently research showed that Zn2+ & Cu2+ are required for the aggregation of Aβ. Piril Erel - UoB: 12004723 10
    • 11. Aβ – Copper binding forms oxidative crosslinks between monomers. The resulting cross-linked species are called oligomers. Oligomers are very difficult for the brain to clear and can eventually cause neuron death Craddock et al, 2012 observed metal dyshomeostasis in a AD-affected mouse model. The interaction between Aβ and metals therefore represents a mechanism of therapeutic intervention that could both normalize metal homeostasis and reduce the levels of toxic Aβ oligomers in the brain. *5+ Furthermore, Copper binding to A also generates ROS, this binding causes a detrimental release of ROS. Piril Erel - UoB: 12004723 11 Interactions Of Transition Metals With Amyloid - β Protein (AβPP)
    • 12. The brain needs oxygen in order to synthesize the large quantities of ATP required. This accounts for 20% of the body’s total basal oxygen consumption therefore generates high levels of reactive oxygen species (ROS). Exposure to ROS damages neurons in the brain. Oxidative stress plays an important role in initiating AD through provoking cell signaling pathways. [4] It represents an imbalance between the amount of ROS being produced and the ability of the body to detect and remove these toxic substances. This is due to cellular antioxidant defense mechanisms becoming overwhelmed by ROS causing macromolecular damage. ROS may also result in harmful effects such as; Damage of DNA. Oxidation of polyunsaturated fatty acids. Oxidation of amino acids in proteins. Oxidatively inactivation of specific enzymes. [6] Production Of Reactive Oxygen Species Induced By Aβ Piril Erel - UoB: 12004723 12
    • 13. In order for a drug to be used as a potential treatment for brain disorders, it must possess certain characteristics which enable it to pass the blood brain barrier(BBB) such as: Low molecular weight Poorly charged or not charged at all Stable Selectivity of certain metal ions Low toxicity Minimum side effects.[7] Chelating Properties Piril Erel - UoB: 12004723 13
    • 14. This recently discovered treatment shows rapid improvement in cognition in mouse models of AD. A Copper/Zinc Ionophore – it competes for metals but also redistributes metals back into the cell as it transports ions across the lipid bilayer. PBT2 aids the clearance of Aβ aggregates in the brain by targeting zinc and copper ions effectively it detoxifies the Aβ plaques. PBT2 has a greater affinity for metal compared to Aβ’s affinity to metal: Aβ affinity for Zn is - Kd = 10-9 PBT2 affinity for Zn is - Kd =10-13 Metals are promiscuous, they can jump and bind to which ever is stronger, so if a metal is bound to an Aβ plaque and PBT2 is present, due to the 104x greater force, the metal will dissociate and bind to the drug. PBT2 provides a mechanism which shuttles metals away from Aβ PBT2 detoxifies A plaques Piril Erel - UoB: 12004723 14
    • 15. Zn2+ is exocytosed into the synaptic cleft in concentrations of around 300 μM Cu2+ is released post-synaptically following activation of NMDA with Cu2+ concentrations around 15 μM in the synaptic cleft. Once cleavage of APP takes place, Aβ is released into the synaptic cleft and it aids lowering of zinc concentration by acting as a sponge. Aβ is further degraded by enzymes into smaller monomers.[8] The Healthy Synapse – a glance into the synaptic cleft Piril Erel - UoB: 12004723 15
    • 16. The decrease in ATP leads to a reduction metal reuptake, causing the average concentration of metals to rise over time. Cu & Zn react with Aβ forming Aβ oligomers and then, crucially, to Aβ amyloid plaques Aβ can bind up to 2.5 moles of metal ions however the more metals it is bound to, the more aggregated it becomes Aβ oligomers are resistant to degradation. Alzheimer’s Disease – a glance into the synaptic cleft Piril Erel - UoB: 12004723 16
    • 17. PBT2: PBT2 taken orally crosses the blood brain barrier and can be detected in the synaptic cleft. PBT2 has a high affinity for metals Chelation by PBT2 allows Zu & Cu to be removed from Aβ The advantage of PBT2 lies in the ionophoric properties of the drug Concentrations of the metal ions are reduced to normal Thus diverted from binding to Aβ, This reduces precipitation, reduces covalent Aβ oligomer formation and reduces toxic redox activity. PBT2 – a glance into the synaptic cleft Piril Erel - UoB: 12004723 17
    • 18. Objectives For Phase IIa: To test the safety and efficacy of PBT2 in patients with mild AD. To monitor any changes in cognition after administration of PBT2 using the Neuro-psychological Test Battery (NTB) which measures Executive Function(EF). PBT2 has undergone a 12 week Phase II trial in which the drug was orally administered daily to 78 patients with mild AD who where randomly allocated into either one of the 3 groups below: Placebo 50mg and 250mg It was a double-blind, randomized, placebo-controlled trial Trial Method For PBT2 Piril Erel - UoB: 12004723 18
    • 19. Patients with a 250mg dose of PBT2 daily showed a significant increase in EF scores compared to the placebo group. 250mg dose of PBT2 also showed a significant decrease in Aβ protein plaques.*9+ This shows promising results for PBT2 as a treatment drug for Alzheimer’s Disease. Phase IIb clinical trials is currently underway this time scientists are evaluating the effect of PBT2 on: Safety and tolerability Brain metabolic activity Brain volumes Cognition Functional abilities[10] Results Piril Erel - UoB: 12004723 19
    • 20. Through thorough research into this area, current drug trials target memory deficit in early – moderate Alzheimer’s However it is questionable whether this is too late. Consideration of executive function and early treatment of AD; a cure may be possible or at least consequences are more reversible. PBT2 not only detoxifies the harmful Aβ plaques but also re-establishes homeostasis of metals at a stage where neuronal death hasn’t yet occurred. Clinical trials for PBT2 Phase IIb will hopefully provide promising results for curing AD. Conclusion Piril Erel - UoB: 12004723 20
    • 21. Thank You For Listening & Watching, Piril Erel 12004723 Piril Erel - UoB: 12004723 21
    • 22. 1. Nicole L Batsch, Mary S Mittelman. (2012). Overcoming The Stigma Of Dementia. Available: www.alz.co.uk/research/WorldAlzheimerReport2012.pdf. Last accessed 2th Apr 2013. 2. Craig S. Atwood, Richard C. Scarpa, Xudong Huang, Robert D. Moir, Walton D. Jones, David P. Fairlie, Rudolph E. Tanzi and Ashley I. Bush.. (2000). Characterization of Copper Interactions with Alzheimer Amyloid Beta Peptides: Identification of an Attomolar-Affinity Copper Binding Site on Amyloid Beta1–42. Journal of Neurochemistry. 75 (No.3), 1219. 3. Martini, FH (2012). Fundamentals of Anatomy & Physiology. 9th ed. San Francisco: Pearson Education. 542. 4. Xiongwei Zhu, Bo Su, Xinglong Wang, Akihiko Nunomura, Paula I. Moreira, Hyoung-gon Lee, George Perry, Mark A. Smith, . (2008). Oxidative Stress Signaling in Alzheimer's Disease. National Institute of Health. 5(6) (1), 525-532. 5. Daniel Kantor. (October 4, 2010). Alzheimer's Disease. Available: www.scripps.org/articles/3458-alzheimer-s-disease. Last accessed 15th Apr 2013. 6. Brooker, Robert J. (2011). Genetics: analysis and principles (4th ed.). McGraw-Hill Science. 7. Budimir, A. Metal Ions, Alzheimers Disease & Chelation Therapy. Acta Pharm.2011;61():1-14 8. Duce, JA et al. (2010). Biological Metals & Alzheimer's Disease: Implications for therapeutics and diagnostics. Progress in Neurobiology. 92 (1-18), 4. 9. Faux, N.A et al. (2010). PBT2 Rapidly Improves Cognition in Alzheimer's Disease: Additional Phase II Analyses. Journal of Alzheimer's Disease. 20 (1), 509-516. 10. Lannfelt, L and Prana Biotechnology. (2013). PBT2 Clinical Program. Available: www.pranabio.com/default.asp?contentID=625. Last accessed 20th Apr 2013. Piril Erel - UoB: 12004723 22 References