Ashley Bush

Ashley Bush led this live discussion on 15 January 2004. Readers are invited to submit additional comments by using our Comments form at the bottom of the page.

View Transcript of Live Discussion — Posted 23 August 2006

Background Text
By Ashley Bush, Massachusetts General Hospital, Boston, Massachusetts

Long considered a fringe approach in the field of Alzheimerology, the attempt to treat AD by targeting specific metal-Aβ complexes reached a clinical milestone last year when a phase 2 trial was completed, (see ARF related news story). The historical timeline below, by Ashley Bush, lays out how this approach developed over the past 20 years.

1984: Zn2+ is released in an exchangeable ionic form in neocortical glutamatergic. synapses. This pool of zinc represents about 15-30 percent of brain zinc.(1,2)

1988: Cu2+ released by synaptic transmission.(3)

1992: Proteolytic processing of APP by a zinc metalloenzyme.(4) Subsequently, zinc-metalloproteinases have been identified as α-secretases,(5) and of these activities, tumor necrosis factor α converting enzyme (TACE) and ADAM-10(6) appear to be responsible for the majority of α-secretase activity in cell culture. Also, occupation of Aβ by Zn(II) protects the substrate from α-secretase-like cleavage,(7) hence the effects of Zn2+ upon APP processing are pleiotropic.

1993: Zinc binding site on cysteine-rich ectodomain of APP and APLP1 and 2.(8,9) Promotes heparin binding, and inhibits oxidation induced by Cu2+ in the ectodomain binding site.(10,11)

1994: Zinc forms amyloid from human but not rat Aβ in vitro.(7,12)
1994: Cu2+ binding site in the cysteine-rich N-terminus of APP.(13)

1996: Cu2+ binding site in the cysteine-rich N-terminus of APP reduces to Cu+.(10)

1997: Zn2+-induced amyloid aggregation is dependent upon -helical structure, and is reversible with chelation.(14)

1998: Copper and iron precipitate Aβ (Aβ42>Aβ40>>ratAβ) under conditions representing mild acidosis; Co induces precipitation analogous to Zn, Ni analogous to Cu in vitro. Only Cu and Zn are released in an exchangeable form at the synapse.(15)

1998: Zinc, iron and copper are highly enriched in Aβ plaques,(16) later found to actually bind to Aβ.(17,18)

1999: Aβ is highly redox active (Aβ42>Aβ40>>ratAβ) reduces copper and iron, generates hydrogen peroxide from oxygen, which mediates toxicity in cell culture.(19,20)
1999: Amyloid can be resolubilized from human brain using zinc and copper: selective chelators. (21)
1999: APP knockouts have increased copper levels.(22)

2000: The copper binding site on Aβ42 has attomolar affinity (Aβ40 has pM affinity), making it among the strongest affinity copper binding sites in nature, akin to superoxide dismutase 1.(23)
2000: Trace metal contamination is responsible for initiating Aβ nucleation in the seeding of Aβ fibril formation. Aβ fibrils do not form in the absence of metals.(23)
2000: Cu2+ selectively oxidizes Aβ leading to oligomeric species,(23) and other modifications such as methionine sulfoxide Aβ, which becomes released from lipid membranes.(24)

2001: Aβ may act as a physiological antioxidant in CSF and plasma lipoproteins, functioning by chelating transition metal ions.(25,26)
2001: The copper/zinc binding site on Aβ resembles that of SOD, confirming the possibility that Aβ might be an antioxidant. The structure is a membrane-embedded hexamer with histidine/metal bridges.(27)
2001: 50 percent decrease in amyloid accumulation in APP transgenic mice treated orally with clioquinol, a USP antibiotic with copper/zinc binding properties. No effect of TETA, a traditional chelator that does not cross the BBB(28) (see ARF related news story).

2002: Genetic ablation of ZnT3, the ionic transporter that loads Zn2+ into synaptic vesicles, decreases brain zinc concentrations by approx. 20 percent, but markedly (>80 percent) inhibits amyloid deposition in Tg2576 mice(29) (see ARF related news story).
2002: Tg2576 and CT100 transgenic mice have decreased brain copper levels. Brain copper and iron levels rise with age in mice, and this increase is opposed by the expression of these transgenes.(30)
2002: Biological reducing agents, such as cholesterol, fuel the Cu2+-dependent generation of H2O2 and neurotoxicity of Aβ, which can be rescued with Cu2+ chelation.(17)

2003: Raising brain copper levels by genetic(31) or dietary(32) means decreases Aβ accumulation in two strains of transgenic mice, and restores diminished SOD1 activity. This possibly is compatible with Aβ being situated on the export side of copper homeostasis (see ARF related news story).
2003: Promising double-blind, placebo-controlled, phase 2 pilot clinical trial of clioquinol in patients with Alzheimer's disease (arrest in cognitive decline, lowering of plasma Aβ levels)(33) (see ARF related news story).

2004: Estrogen decreases zinc transporter 3 expression and synaptic vesicle zinc levels in mouse brain.(34)

References:
1. Assaf SY, Chung S-H. Release of endogenous Zn2+ from brain tissue during activity. Nature. 1984 Apr 19-25;308(5961):734-6. Abstract

2. Howell GA, Welch MG, Frederickson CJ. Stimulation-induced uptake and release of zinc in hippocampal slices. Nature. 1984 Apr 19-25;308(5961):736-8. Abstract

3. Hartter DE, Barnea A Evidence for release of copper in the brain: depolarization-induced release of newly taken-up 67copper. Synapse. 1988;2(4):412-5. Abstract

4. Bush AI, Whyte S, Thomas LD, Williamson TG, Van Tiggelen CJ, Currie J, Small DH, Moir RD, Li QX, Rumble B, et al. An abnormality of plasma amyloid protein precursor in Alzheimer's disease. Ann Neurol. 1992 Jul;32(1):57-65. Abstract

5. Roberts SB, Ripellino JA, Ingalls KM, Robakis NK, Felsenstein KM. Non-amyloidogenic cleavage of the beta-amyloid precursor protein by an integral membrane metalloendopeptidase. J Biol Chem. 1994 Jan 28;269(4):3111-6. Abstract

6. Buxbaum JD, Liu KN, Luo Y, Slack JL, Stocking KL, Peschon JJ, Johnson RS, Castner BJ, Cerretti DP, Black RA. Evidence that tumor necrosis factor alpha converting enzyme is involved in regulated alpha-secretase cleavage of the Alzheimer amyloid protein precursor. J Biol Chem. 1998 Oct 23;273(43):27765-7. Abstract

7. Bush AI, Pettingell W.H, Jr., Paradis MD, Tanzi RE. Modulation of A beta adhesiveness and secretase site cleavage by zinc. J Biol Chem. 1994 Apr 22;269(16):12152-8. Abstract

8. Bush AI, Multhaup G, Moir RD, Williamson TG, Small DH, Rumble B, Pollwein P, Beyreuther K, Masters CL. A novel zinc(II) binding site modulates the function of the beta A4 amyloid protein precursor of Alzheimer's disease. J Biol Chem. 1993 Aug 5;268(22):16109-12. Abstract

9. Bush AI, Pettingell WH, de Paradis M, Tanzi RE, Wasco W. The amyloid beta-protein precursor and its mammalian homologues. Evidence for a zinc-modulated heparin-binding superfamily. J Biol Chem. 1994 Oct 28;269(43):26618-21. Abstract

10. Multhaup G, Schlicksupp A, Hesse L, Beher D, Ruppert T, Masters CL, Beyreuther K. The amyloid precursor protein of Alzheimer's disease in the reduction of copper(II) to copper(I). Science. 1996 Mar 8;271(5254):1406-9. Abstract

11. Multhaup G, Ruppert T, Schlicksupp A, Hesse L, Bill E, Pipkorn R, Masters CL, Beyreuther K. Copper-binding amyloid precursor protein undergoes a site-specific fragmentation in the reduction of hydrogen peroxide. Biochemistry. 1998 May 19;37(20):7224-30. Abstract

12. Bush AI, Pettingell WH, Multhaup G, Paradis Md, Vonsattel JP, Gusella JF, Beyreuther K, Masters CL, Tanzi RE. Rapid induction of Alzheimer A beta amyloid formation by zinc. Science. 1994 Sep 2;265(5177):1464-7. Abstract

13. Hesse L, Beher D, Masters CL, Multhaup G. The beta A4 amyloid precursor protein binding to copper. FEBS Lett. 1994 Jul 25;349(1):109-16. Abstract

14. Huang X, Atwood CS, Moir RD, Hartshorn MA, Vonsattel J-P, Tanzi RE, Bush AI. Zinc-induced Alzheimer's Abeta1-40 aggregation is mediated by conformational factors. J Biol Chem. 1997 Oct 17;272(42):26464-70. Abstract

15. Atwood CS, Moir RD, Huang X, Bacarra NME, Scarpa RC, Romano DM, Hartshorn MA, Tanzi RE, Bush AI. Dramatic aggregation of Alzheimer abeta by Cu(II) is induced by conditions representing physiological acidosis. J Biol Chem. 1998 May 22;273(21):12817-26. Abstract

16. Lovell MA, Robertson JD, Teesdale WJ, Campbell JL, Markesbery WR. Copper, iron and zinc in Alzheimer's disease senile plaques. J Neurol Sci. 1998 Jun 11;158(1):47-52. Abstract

17. Opazo C, Huang X, Cherny R, Moir R, Roher A, White A, Cappai R, Masters C, Tanzi R, Inestrosa N, Bush A. Metalloenzyme-like activity of Alzheimer's disease beta-amyloid. Cu-dependent catalytic conversion of dopamine, cholesterol, and biological reducing agents to neurotoxic H(2)O(2). J Biol Chem. 2002 Oct 25;277(43):40302-8. Epub 2002 Aug 20. Abstract

18. Dong J, Atwood CS, Anderson VE, Siedlak SL, Smith MA, Perry G, Carey PR. Metal binding and oxidation of amyloid-beta within isolated senile plaque cores: Raman microscopic evidence. Biochemistry. 2003 Mar 18;42(10):2768-73. Abstract

19. Huang X, Atwood CS, Hartshorn MA, Multhaup G, Goldstein LE, Scarpa RC, Cuajungco MP, Gray DN, Lim J, Moir RD, Tanzi RE, Bush AI. The A beta peptide of Alzheimer's disease directly produces hydrogen peroxide through metal ion reduction. Biochemistry. 1999 Jun 15;38(24):7609-16. Abstract

20. Huang X, Cuajungco MP, Atwood CS, Hartshorn MA, Tyndall J, Hanson GR, Stokes KC, Leopold M, Multhaup G, Goldstein LE, Scarpa RC, Saunders AJ, Lim J, Moir RD, Glabe C, Bowden EF, Masters CL, Fairlie DP, Tanzi RE, Bush AI. Cu(II) potentiation of alzheimer abeta neurotoxicity. Correlation with cell-free hydrogen peroxide production and metal reduction. J Biol Chem. 1999 Dec 24;274(52):37111-6. Abstract

21. Cherny RA, Legg JT, McLean CA, Fairlie D, Huang X, Atwood CS, Beyreuther K, Tanzi RE, Masters CL, Bush AI. Aqueous dissolution of Alzheimer's disease Abeta amyloid deposits by biometal depletion. J Biol Chem. 1999 Aug 13;274(33):23223-8. Abstract

22. White AR, Reyes R, Mercer JF, Camakaris J, Zheng H, Bush AI, Multhaup G, Beyreuther K, Masters CL, Cappai R (1999) Copper levels are increased in the cerebral cortex and liver of APP and APLP2 knockout mice. Brain Res 842, 439-44. Abstract

23. Atwood CS, Scarpa RC, Huang X, Moir RD, Jones WD, Fairlie DP, Tanzi RE, Bush AI. Characterization of copper interactions with alzheimer amyloid beta peptides: identification of an attomolar-affinity copper binding site on amyloid beta1-42. J Neurochem. 2000 Sep;75(3):1219-33. Abstract

24. Barnham KJ, Ciccotosto GD, Tickler AK, Ali FA, Smith DG, Williamson NA, Lam Y-H, Carrington D, Tew D, Kocak G, Volitakis I, Separovic F, Barrow CJ, Wade JD, Masters CL, Cherny RA, Curtain CC, Bush AI, Cappai R. Neurotoxic, redox-competent Alzheimer's beta-amyloid is released from lipid membrane by methionine oxidation. J Biol Chem. 2003 Oct 31;278(44):42959-65. Epub 2003 Aug 18. Abstract

25. Kontush A, Berndt C, Weber W, Akopyan V, Arlt S, Schippling S, Beisiegel U (2001) Amyloid-beta is an antioxidant for lipoproteins in cerebrospinal fluid and plasma. Free Radic Biol Med. 2001 Jan 1;30(1):119-28. Abstract

26. Kontush A, Donarski N, Beisiegel U. Resistance of human cerebrospinal fluid to in vitro oxidation is directly related to its amyloid-beta content. Free Radic Res. 2001 Nov;35(5):507-17. Abstract

27. Curtain C, Ali F, Volitakis I, Cherny R, Norton R, Beyreuther K, Barrow C, Masters C, Bush A, Barnham K. Alzheimer's disease amyloid-beta binds copper and zinc to generate an allosterically ordered membrane-penetrating structure containing superoxide dismutase-like subunits. J Biol Chem. 2001 Jun 8;276(23):20466-73. Epub 2001 Mar 27. Abstract

28. Cherny RA, Atwood CS, Xilinas ME, Gray DN, Jones WD, McLean CA, Barnham KJ, Volitakis I, Fraser FW, Kim Y-S, Huang X, Goldstein LE, Moir RD, Lim JT, Beyreuther K, Zheng H, Tanzi RE, Masters CL, Bush AI. Treatment with a copper-zinc chelator markedly and rapidly inhibits beta-amyloid accumulation in Alzheimer's disease transgenic mice. Neuron. 2001 Jun;30(3):665-76. Abstract

29. Lee J-Y, Cole TB, Palmiter RD, Suh SW, Koh J-Y. Contribution by synaptic zinc to the gender-disparate plaque formation in human Swedish mutant APP transgenic mice. Proc Natl Acad Sci U S A. 2002 May 28;99(11):7705-10. Abstract

30. Maynard CJ, Cappai R, Volitakis I, Cherny RA, White AR, Beyreuther K, Masters CL, Bush AI, Li Q-X. Overexpression of Alzheimer's disease amyloid-beta opposes the age-dependent elevations of brain copper and iron. J Biol Chem. 2002 Nov 22;277(47):44670-6. Epub 2002 Sep 04. Abstract

31. Phinney AL, Drisaldi B, Schmidt SD, Lugowski S, Coronado V, Liang Y, Horne P, Yang J, Sekoulidis J, Coomaraswamy J, Chishti MA, Cox DW, Mathews PM, Nixon RA, Carlson GA, George-Hyslop PS, Westaway D. In vivo reduction of amyloid-beta by a mutant copper transporter. Proc Natl Acad Sci U S A. 2003 Nov 25;100(24):14193-8. Epub 2003 Nov 14. Abstract

32. Bayer TA, Schafer S, Simons A, Kemmling A, Kamer T, Tepests R, Eckert A, Schussel K, Eikenberg O, Sturchler-Pierrat C, Abramowski D, Staufenbiel M, Multhaup G. Dietary Cu stabilizes brain superoxide dismutase 1 activity and reduces amyloid Abeta production in APP23 transgenic mice. Proc Natl Acad Sci U S A. 2003 Nov 25;100(24):14187-92. Epub 2003 Nov 14. Abstract

33. Ritchie CW, Bush AI, Mackinnon A, Macfarlane S, Mastwyk M, MacGregor L, Kiers L, Cherny RA, Li QX, Tammer A, Carrington D, Mavros C, Volitakis I, Xilinas M, Ames D, Davis S, Beyreuther K, Tanzi RE, Masters CL. Metal-protein attenuation with iodochlorhydroxyquin (clioquinol) targeting Abeta amyloid deposition and toxicity in Alzheimer disease: a pilot phase 2 clinical trial. Arch Neurol. 2003 Dec;60(12):1685-91. Abstract

34. Lee J-Y, Kim J-H, Hong SH, Lee JY, Cherny RA, Bush AI, Palmiter RD, Koh J-Y. Estrogen decreases zinc transporter 3 expression and synaptic vesicle zinc levels in mouse brain. J Biol Chem. 2003 Dec 17 [Epub ahead of print] Abstract

RELATED LINKS
Pilot Study Suggests Clioquinol Benefits AD Patients

Ironing out the Role of Metals in Neurodegenerative Diseases

Two Ways to Attack Amyloid: Metal Chelator and Antibody

Coping with Copper—Minute Amount of Metal Plagues Rabbit Brain

Copper to the Rescue?

CNDR 2nd Annual Retreat: Metal Complexing Agents as Therapies for AD

Synaptic Zinc Fingered As Critical In Plaque Formation

Maverick Scientist Is Winning Converts On Alzheimer's (A .pdf is available for free download from the Wall Street Journal)

	Submit a Comment on this Live Discussion
	Cast your vote and/or make a comment on this live discussion.  If you already are a member, please login. Not sure if you are a member? Search our member database. *First Name   *Last Name   Country or Territory: USA Canada Afghanistan Albania Algeria American Samoa Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia Bosnia and Herzegovina Botswana Bouvet Island Brazil British Indian Ocean Territory British Virgin Islands Brunei Bulgaria Burkina Faso Burma Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos Islands Colombia Comoros Congo Cook Islands Corte d'lvoire (formerly Ivory Coast) Costa Rica Croatia Cuba Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic East Timor Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands Faroe Islands Fiji Finland France French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guam Guatemala Guinea Guinea-Bissau Guyana Haiti Heard and McDonald Islands Honduras Hong Kong Hungary Iceland India Indonesia Iran Iraq Ireland Israel Italy Ivory Coast (now known as Corte d'lvoire) Jamaica Japan Jordan Kazakhstan Kenya Kiribati Korea, North Korea, South Kuwait Kyrgyzstan Laos Latvia Lebanon Lesotho Liberia Libya Liechtenstein Lithuania Luxembourg Macau Macedonia ( Former Yugoslav Republic of) Madagascar Malawi Malaysia Maldives Mali Malta Marshall Islands Martinique Mauritania Mauritius Mayotte Mexico Micronesia ( Federated States of) Moldova Monaco Mongolia Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands Netherlands Antilles New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Northern Mariana Islands Norway Oman Pakistan Palau Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Island Poland Portugal Puerto Rico Qatar Reunion Romania Russia Rwanda S. Georgia and S. Sandwich Isls. Saint Kitts & Nevis Saint Lucia Saint Vincent and The Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Seychelles Sierra Leone Singapore Slovakia Slovenia Somalia South Africa Spain Sri Lanka St. Helena St. Pierre and Miquelon Sudan Suriname Svalbard and Jan Mayen Islands Swaziland Sweden Switzerland Syria Taiwan Tajikistan Tanzania Thailand Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu U.S. Minor Outlying Islands U.S.A. Uganda Ukraine United Arab Emirates United Kingdom Uruguay Uzbekistan Vanuatu Vatican City Venezuela Vietnam Virgin Islands Wallis and Futuna Islands Western Sahara Yemen Yugoslavia (Former) Zaire Zambia Zimbabwe *Login Email Address   *Password    Minimum of 8 characters *Confirm Password   Stay signed in?   Comment: (If coauthors exist for this comment, please enter their names and email addresses at the end of the comment.) References: *Enter the verification code you see in the picture below: This helps Alzforum prevent automated registrations. Terms and Conditions of Use: Printable Version By clicking on the 'I accept' below, you are agreeing to the Terms and Conditions of Use above.