Sci. Aging Knowl. Environ., 26 March 2003
Vol. 2003, Issue 12, p. nf6
[DOI: 10.1126/sageke.2003.12.nf6]


Mindful of Metal

Footballer, neuroscientist, and former stand-up comic, Ashley Bush keeps hammering at the idea that a glut of metals in elderly brains galvanizes Alzheimer's disease

Mitch Leslie;2003/12/nf6 This article comes to you through a collaboration between SAGE KE and Science's career development Web site, Next Wave. The joint venture is supported by the AARP Andrus Foundation. A basketball game starts with a jump ball, a hockey game with a face-off. But these opening rituals are as tame as afternoon tea on the verandah compared with the beginning of an Australian-rules football match. When the referee bounces the ball off the ground in the center of the field, "the two biggest guys on the teams run at each other, jump on each other, and try to punch the ball in the direction that the team is going," says Ashley Bush, who took many of these "center bounces" for the Boston Demons, the 1998 and 1999 Aussie-rules champions of the United States. The mutual mugging can be punishing, particularly because Aussie footballers wear about as much body protection as ice skaters do. "You usually wind up with somebody's boot in your abdomen," says Bush, but he enjoyed the challenge "because I'm fond of throwing my weight around."

For more than a decade, the Harvard Medical School neuroscientist has thrown his weight behind the notion that Alzheimer's disease (AD) stems from what he calls the "metallically befouled milieu of the aging brain." He argues that rising amounts of metals set off the disease's devastating neural damage by corrupting {beta} amyloid, the protein that jams the brains of AD patients (see "Detangling Alzheimer's Disease"), and spurring production of harmful oxidants. Science can be a full-contact sport too, and as Bush has tried to convince fellow AD researchers that his hypothesis is valid, he's absorbed a few kicks to the ego. "I was told more than once I was wasting my time," he recalls. Despite the discouragement, Bush persevered, and now he and his colleagues in the United States and Australia can claim a coup. They have begun clinical trials of a drug that sops up extra metals in the brain. "This story has built incrementally from an observation that could have disappeared to a plausible candidate for treating Alzheimer's disease," says neuroscientist John Trojanowski of the University of Pennsylvania in Philadelphia.

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Australian export. Bush tried surgery and psychiatry before settling on neuroscience. [Credit: Tiffany Cowie]

Friends and researchers laud his scientific acumen, zeal, and hard-headed pursuit of AD's dark secrets. "He's got a voracious appetite for data," says fellow Aussie expatriate and molecular gerontologist Simon Melov of the Buck Institute for Age Research in Novato, California. According to cell biologist Charles Glabe of the University of California, Irvine, "It probably goes back to his football days; he's fearless about taking on new challenges." Taking on those challenges meant recasting himself more than once, from would-be surgeon to fledgling psychiatrist to metal biologist. Along the way, he's performed stand-up comedy, served as scriptwriter for the Australian Broadcasting Corporation, and even co-written a song for the Olympics. "He can be a bit exhausting," says Melov. "He's always thinking."

Two Generations of �migr�s Back to Top

Bush, now 44, says he loves the people and landscape of Australia but considers himself an exile from the country's egalitarian ethos: "Australia, culturally, has a chip on its shoulder about highly educated, successful people." The upshot of that attitude, he says, is that Australian governments dole out scant funding for science. "I've had postdocs in my lab who earn more than a tenured Australian professor of neuroscience," says Bush. The problem goes beyond low salaries: Money for basic research is scarce, compared with what's available in the United States, he says. Australia's loss has been the United States' gain, as flocks of Australia's best scientific minds have boarded planes to cross the Pacific. Although Bush works over here, he doesn't want to sever connections to the country where he was born. His two daughters, Sarah, 11, and Miriam, 12, live in Australia with his ex-wife, and he still works closely with Colin Masters, his Ph.D. adviser at the University of Melbourne. So he's become an intercontinental commuter, shuttling between his two countries 10 or more times a year.

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Family life Down Under. Bush clowns with daughters Miriam (left) and Sarah, who attend school in Melbourne. [Credit: Tiffany Cowie]

His path to a tenure-track job at Harvard Medical School has twisted and turned. His parents were Jewish refugees who fled from the Nazis to Australia. His mother bolted Warsaw, Poland, before the German invasion. His father's family raised fruit in what was then the British protectorate of Palestine. In the summer of 1939, they feared that Hitler's storm troopers would soon be goose-stepping through the streets of Jerusalem. It was a reasonable worry: During World War II, Germany's army in North Africa advanced to within 600 kilometers of the city. So Bush's grandparents dispatched their son "to the end of the world as a kind of human message in a bottle," Bush says.

Bush grew up in Melbourne, Australia's second-largest city and a hotbed of "footy," as the Aussies call their unique brand of football. From early childhood he aspired to be a surgeon, but his plan foundered during a surgical internship at the University of Melbourne. "I'm not a morning person, and all other surgeons are," he says. "To turn up late for an operation is a very, very bad thing." When he did, his advisers encouraged a shift from surgery to psychiatry. The field taught him self-discipline, he says, and he found it so stimulating that he made plans to venture overseas for further clinical training. But a nagging feeling held him back--too often, all the psychiatrist could offer was a hopeless diagnosis. "You can't do a lot for people with Alzheimer's disease or schizophrenia without chemistry," he says. Convinced he could be more helpful as a researcher, Bush remained at the university to do his Ph.D. with Masters, one of two scientists who had recently uncovered the sequence of {beta} amyloid.

Comic Interludes Back to Top

For much of his time in science, Bush also dabbled in comedy. He began performing stand-up in clubs as a starving student; it was the quickest way to earn good money, he says. Amateur theater is a tradition for Australian students, says Melov, who did some stand-up during his undergraduate days in Sydney, but Bush went further than most by trying to make a living at it. He supported himself during his last 3 years of medical school by poking fun at politicians and singing silly songs "about the weird women I would date." In grad school, he wrote episodes of comedy shows for the Australian Broadcasting Corporation, work he continued after moving to Harvard for a postdoc with neuroscientist Rudy Tanzi. "I used to annoy the hell out of Tanzi by sitting at my desk in the lab writing TV scripts," says Bush. "And I used to threaten him by saying, 'If you don't back off, I'll put you into a script.' " Bush made good on his threat, borrowing Tanzi's character for a homicidal ethicist in his unproduced screenplay, a sci-fi thriller about parthenogenesis.

He picked up his pen again when a wealthy acquaintance commissioned a song about the 2000 Olympics. Tanzi, who plays keyboard and distributes his recordings on the Internet, wrote the music, and Bush supplied the lyrics. Their backer wanted a satirical piece, and that's what they gave him, mocking the hallowed Olympic virtue of competition. "We shouldn't be competing/It's just self-defeating" go the first two lines. The two scientist-songwriters recorded the piece, and Bush heard that it even got some airplay--although not at Olympic Stadium.

Bush has left the stage for the last time, he says, but performing before a live audience has benefited his science: "It prepared me to stand up at [the Society for] Neuroscience [meeting] and get laughed at" for his ideas. He's given up scriptwriting too, although when he's suffering through somebody's tedious seminar, he says he can't help thinking, "Who writes your material, mate?"

Nearly Canned by Aluminum Back to Top

Bush arrived in Boston for his postdoc in 1992. Getting used to the United States took effort on his part. Nobody played footy--the Boston Demons were born years later--and the winters brought prodigious amounts of snow, which never falls in Melbourne. Boston logged a total of nearly 3 meters during his first year there, and even more the next, he recalls. Adding deprivation to discomfort, stores in the United States didn't stock his favorite brew, Victoria Bitter, known to millions of thirsty Aussies as VB. The beer packs too much alcohol to be imported into the United States. "If VB came to this country, it would evolve the civilization of the United States," he says. "It's liquid gold." But in one way, Bush fit in well with Bostonians. At home he had cheered for his local footy team, the St Kilda Saints, which holds many Australian Football League records for ineptitude, including the fewest points scored in a game. Boston, too, fields a team that excels at failure--the Red Sox--and Bush became a fan. "I like lost causes," he says.

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Whose round is it? Bush faces the tragedy of a nearly empty glass. [Credit: Tiffany Cowie]

The notion that metals might have anything to do with AD seemed like a lost cause when Bush started his graduate work in the late 1980s. Earlier in the decade, exaggerated stories that aluminum might cause the illness had scared thousands of Americans into tossing out their aluminum cookware, Tanzi remembers, but the idea was losing credibility. Bush got his first inkling of a metallic link during his Ph.D. research on {beta}-amyloid precursor protein (APP), which enzymes snip apart to produce {beta} amyloid. The prevailing wisdom has been that these free {beta}-amyloid snippets bunch to form plaques. Cells all over the body make APP and {beta} amyloid, even though trouble occurs only in the brain, and Bush was hunting for enzymes that might dismember APP in the blood. He found one and discovered that it required zinc to cleave APP. While mining the literature on that metal, he unearthed an article by Christopher Frederickson of the University of Texas Medical Branch in Galveston, who later became Bush's friend and collaborator. Looking at an illustration in the paper, Bush noticed that the distribution of zinc in the brain matched the location of {beta}-amyloid deposits.

Bush and colleagues provided stronger evidence in a 1994 Science paper. They showed that adding zinc to a test tube of dissolved {beta}-amyloid molecules incited the proteins to clump. The logjams closely resembled {beta}-amyloid plaques, suggesting that zinc somehow causes the brain scars characteristic of AD.

The idea clanged. Almost nobody bought it, Bush recalls, probably because they thought it was an attempt to revive the moribund aluminum hypothesis. Whatever the cause, the next few years were frustrating, he says. He tallied morbid statistics of rejection: 39 papers and grant applications spurned between 1995 and 1999. After finishing his postdoc, Bush stayed at Harvard Medical School as a new assistant professor and continued collaborating with Tanzi, who remembers scraping together money to pay for research on metals after grant proposals failed. This fallow period crimped his career just as he was establishing his own lab. "There's a dip in my CV for those years," he says. But Bush kept banging away at the metal hypothesis. "What kept me going on copper and zinc was Ashley's infectious enthusiasm, perseverance, and belief in the idea," says Tanzi. And by this time, Bush's responsibilities also included keeping his postdocs revved up. "The most common word that came out of my mouth in the lab was 'patience,' " he says.

Patience paid off. Starting in 1999, Bush, Tanzi, Masters, and colleagues forged a series of papers that hardened the metal hypothesis. To measure the durability of plaques, they doused brain samples from patients who had died of AD with molecules that snap up metals. Some plaques began to break down, a big surprise to many experts in the field. "Everyone thought that amyloid was made out of titanium, that you couldn't dissolve it," says Bush. The researchers' findings also cast suspicion on other metals. They discovered that the reaction between copper and {beta} amyloid spawns the fierce oxidant hydrogen peroxide, which can assault DNA, proteins, and other molecules (see "The Two Faces of Oxygen").

To determine whether they could reduce {beta}-amyloid concentrations in a living brain, the researchers needed a drug that chelates, or abducts, metals. Not just any chelator would do, Masters points out. It had to pass through the blood-brain barrier that keeps many molecules from entering the sensitive organ. Instead of designing a new drug, they pulled one out of retirement: the antibiotic clioquinol, which for decades had been used to treat traveler's diarrhea and been known to cross the blood-brain barrier. Then, they dosed old mice that were genetically engineered to develop AD-like plaques with the compound. Compared with control rodents, the treated mice showed nearly 50% less congealed {beta} amyloid, and a rise in dissolved {beta} amyloid in the brain suggested that the drug might be dissolving the protein knots. "It's a remarkable study," says Trojanowski, because it showed that clioquinol could curtail plaques in a living animal.

AD Heading for Defeat? Back to Top

As Bush now sees it, AD results from dangerous liaisons between metals and {beta} amyloid. The amounts of copper and iron in the brain climb by 50% or more as people age. Excess metals in older brains pervert {beta} amyloid, which is presumably a wholesome, hardworking protein, Bush says. First, they glom onto the protein. Then, this decorated form of {beta} amyloid reacts with copper to produce destructive hydrogen peroxide. Further dalliances with copper or hydrogen peroxide wound the protein, transforming it into a "rogue" form that slips out of the cell membrane and diffuses into synapses between brain cells. Zinc leaking from firing neurons stimulates lone {beta}-amyloid fibers to congregate into plaques, which block the body's trash collectors from sweeping up the damaged {beta} amyloid. Plaques might cause damage because they leak oxidants, although they don't produce as much hydrogen peroxide as free-floating {beta} amyloid does. What wrecks the brain in AD, Bush argues, are these oxidants, although not all AD researchers agree. Some parts of the hypothesis still need polishing, he says. No one knows what {beta} amyloid normally does--its function somehow involves metals--or why iron and copper accumulate in older brains.

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The road to Alzheimer's disease is paved with metal. Excess metals in the brain touch off chemical reactions that injure brain cells, according to Bush's hypothesis. [Source: Mitch Leslie; Illustration: Julie White]

Bush predicts that clioquinol works in two ways. By snatching up zinc that makes the proteins clingy, it helps dissolve plaques and allows cleanup of rogue {beta} amyloid. By incarcerating copper, it thwarts the chemical reactions that produce hydrogen peroxide. The drug might blunt other neurodegenerative diseases, such as Parkinson's disease (PD), in which protein pileups pollute the brain. Tests on brain tissue from patients who have died from PD found large amounts of iron in the substantia nigra, a region that deteriorates as the disease worsens. In a study reported this month, Julie Andersen of the Buck Institute and her colleagues deployed clioquinol against an artificial form of PD. Mice treated with MPTP, a drug that provokes Parkinson-like symptoms, lose large numbers of neurons in the substantia nigra and become uncoordinated. However, clioquinol spared more than half of those neurons and helped the animals maintain their poise (see "Turn Off the Iron").

"He's been very diligent in pursuing [the metal hypothesis and clioquinol]. I think he's made a very strong basic science case," says dementia neuroscientist David Knopman of the Mayo Clinic in Rochester, Minnesota, who treats AD patients. "But the proof is in the clinical trials."

Those trials have already started. At the Alzheimer's conference in Stockholm, Sweden, last summer, Masters presented results of treating 18 patients with clioquinol for 9 months. Compared with 18 patients who received a placebo, the clioquinol group showed a slight slowing of AD progression, as measured by standard tests of cognition, and reduced amounts of {beta} amyloid in the blood. A paper reporting a more extensive study is under review. Bush dubs the results promising, but clioquinol might just provide a template for safer, more effective drugs, he says. Developing such drugs might be necessary, because clioquinol can cause deadly side effects under certain conditions. The manufacturer shelved it after approximately 10,000 people, mostly in Japan, developed a sometimes-fatal neurodegeneration. Supplemental vitamin B-12 might forestall the problem, Bush says, but it's still worrisome. Ironically, clioquinol's long history in the clinic and documented side effects give it an advantage, says William Thies, vice president for medical and scientific affairs at the Alzheimer's Association in Chicago. Many pharmaceutical companies are reluctant to test putative anti-AD compounds because of fear of possible harm. Although clioquinol can cause trouble, "we pretty much know what to expect," he says. An anti-AD drug can be a stopgap, Glabe adds: "It's not a disease you need to cure; you need to slow it down by 5 years, and then people will be dying of something else."

Bush's years of work put a shine on the metal hypothesis. Reflecting the idea's increased luster, this year he shared the Potamkin Prize with David Holtzman of Washington University in St. Louis. The award, sponsored by the American Academy of Neurology and the Potamkin Foundation, is one of the two top prizes in Alzheimer's research. Previous winners include Tanzi, Masters, and Trojanowski, along with Nobel laureate Stanley Prusiner of the University of California, San Francisco, whose studies implicated rogue proteins called prions in brain illnesses such as Creutzfeldt-Jakob disease.

Although he still takes to the football field, Bush finds that he has to try harder to keep up with the young bruisers. The Demons finished fourth in last year's national competition, and Bush missed the final games, although he doesn't think his absence hampered the team. He says he sees his role as mentoring the younger players: "teaching them to be violent." The creativity he used to channel into stand-up routines or comic songs now flows into his science, he says: "The papers I write are like science fiction." The results aren't invented, he clarifies, but the work he's accomplished in the last decade "was risky, creative stuff; the ideas were different." Like a good Aussie-rules player, Bush moved forward through nimble shifts and stubborn plodding. Although he and his colleagues haven't beaten AD, they have scored a goal.

March 26, 2003

Mitch Leslie, a writer in Albuquerque, New Mexico, would rather handle cobras than play footy.

Suggested ReadingBack to Top

  1. A. I. Bush, Metal complexing agents as therapies for Alzheimer's disease. Neurobiol. Aging 23, 1031-1038 (2002). [CrossRef][Medline]
  2. A. I. Bush and R. E. Tanzi, The galvanization of {beta}-amyloid in Alzheimer's disease. Proc. Natl. Acad. Sci. U.S.A. 99, 7317-7319 (2002). [Free Full Text]
  3. A. I. Bush et al., Rapid induction of Alzheimer A{beta} amyloid formation by zinc. Science 265, 1464-1467 (1994). [Abstract/Free Full Text]
  4. R. A. Cherny et al., Aqueous dissolution of Alzheimer's disease A{beta} amyloid deposits by biometal depletion. J. Biol. Chem. 274, 23223-23228 (1999). [Abstract/Free Full Text]
  5. R. A. Cherny et al., Treatment with a copper-zinc chelator markedly and rapidly inhibits {beta}-amyloid accumulation in Alzheimer's disease transgenic mice. Neuron 30, 665-676 (2001). [CrossRef][Medline]
  6. C. J. Frederickson and A. I. Bush, Synaptically released zinc: Physiological functions and pathological effects. Biometals 14, 353-366 (2001). [CrossRef][Medline]
  7. X. Huang et al., Cu (II) potentiation of Alzheimer A{beta} neurotoxicity. J. Biol. Chem. 274, 37111-37116 (1999). [Abstract/Free Full Text]
  8. X. Huang et al., The A{beta} peptide of Alzheimer's disease directly produces hydrogen peroxide through metal ion reduction. Biochemistry 38, 7609-7616 (1999). [CrossRef][Medline]
  9. D. Kaur et al., Genetic or pharmacological iron chelation prevents MPTP-induced neurotoxicity in vivo: A novel therapy for Parkinson's disease. Neuron 37, 899-909 (2003). [Abstract] [Full Text] [CrossRef][Medline]
  10. C. J. Maynard et al., Overexpression of Alzheimer's disease amyloid-{beta} opposes the age dependent elevations of brain copper and iron. J. Biol. Chem. 277, 44670-44676 (2002). [Abstract/Free Full Text]
  11. C. A. McLean et al., Soluble pool of A{beta} amyloid as a determinant of severity of neurodegeneration in Alzheimer's disease. Ann. Neurol. 46, 860-866 (1999). [CrossRef][Medline]
  12. A. R. White et al., The Alzheimer's disease amyloid precursor protein modulates copper-induced toxicity and oxidative stress in primary neuronal cultures. J. Neurosci. 19, 9170-9179 (1999). [Abstract/Free Full Text]
Citation: M. Leslie, Mindful of Metal. Sci. SAGE KE 2003, nf6 (26 March 2003);2003/12/nf6

Science of Aging Knowledge Environment. ISSN 1539-6150