by Dan Ariely
Though AICAR is easy to buy, that doesn’t mean it’s safe. “The big problem with AICAR is the side effects,” says Laurie Goodyear, an associate professor of medicine at Harvard Medical School and a senior investigator at the Joslin Diabetes Center. “Athletes would get a huge increase in lactic acid. There’s also a molecular mutation in the heart that can lead to sudden death. Certainly there’s a possibility that drugs could be developed to increase endurance. But I don’t believe AICAR would improve performance in humans.” In 2008 Goodyear wrote an article for the New England Journal of Medicine that examined Evans’s claims. Her parting advice: “Don’t get too comfortable on that couch just yet.”
In addition, Evans’s mice were couch potatoes that had never exercised. With a fitness baseline of zero, there’s plenty of room to improve. “If you have a highly trained athlete that already has high levels of mitochondria,” Goodyear says, “it’s possible they may get some benefit, but I don’t think it would be really huge.”
Mark Davis, who directs the Exercise Biochemistry Laboratory at the University of South Carolina, believes that in elite athletes mitochondria hit a ceiling at some point, in part because “too many of them can actually be toxic to the cells.”
Evans isn’t dissuaded, but he’s also aware that the FDA won’t approve any drug unless it has a specific disease application. So his team is focusing its resources and funding on identifying legitimate therapeutic uses for AICAR and GW1516. He’s been talking with biotech firms about funding clinical trials that “target frailty, or people in wheelchairs who can’t exercise, or who’ve gone through surgery and are bedridden.” There’s also potential for treating diabetes, high cholesterol, obesity, metabolic disorders, and muscular dystrophy. Still, Evans isn’t bashful about admitting where the real money will be made.
“If approved, this can be prescribed by doctors for anything you want,” he says. “And very few people in this country get the recommended minimum of forty minutes a day of exercise. So when you ask me who would want a drug that confers some of the benefits of exercise without actually exercising, it would be the majority of the population.”
That’s the kind of market pharmaceutical companies love—and it’s why Evans isn’t the only one dreaming of riches. “We’re doing the same thing with resveratrol as Evans did with AICAR,” says Johan Auwerx, a professor of energy metabolism at École Polytechnique Fédérale de Lausanne, in Switzerland. “There is a healthy competition going on between us.” Resveratrol, in case you missed its being touted on Oprah, 60 Minutes, and Good Morning America, is a potent antioxidant found in the skin of red grapes. In mice given colossal doses—to match them, you’d have to chug something like 50,000 bottles of wine a day—it curbed aging, lowered blood sugar, slowed the spread of cancer, and spawned mitochondria.
“Our mice ran longer when we gave them resveratrol,” says Auwerx, who is now trying to identify other natural compounds more potent still, to be taken as over-the-counter supplements.
Evans is one of only a few scientists targeting endurance through genes—and that, he believes, gives him an edge. “A lot of people study the end result [of exercise] or study hormones,” he says. “But what controls everything is the genome. It’s the heart of the entire system, and it’s what I’m interested in changing.” First, though, he must test hordes of mice for every conceivable side effect, inject them with varying dosages of AICAR at different intervals to establish an optimal treatment program, and demonstrate that his compounds can do something other than just endow rodents (and ultimately humans) with superlative endurance. There’s also that minor little discrepancy between rodent and human physiology: after all, the list of prototype miracle drugs that performed spectacularly in mice and then failed catastrophically during human clinical trials is long and sordid.
In the basement lab at the Salk Institute, my escort—a bespectacled postdoc with a boyish smile, named Vihang Narkar—raises another concern. Athletes rely on mental stamina as much as on physical fortitude to push through pain, a phenomenon that could make it tricky to accurately assess the potency of AICAR or GW1516 in people. Our tendency to either persevere or succumb is inextricably tied to both brain and brawn. But according to Narkar, mice bonk for only one reason: their muscles are simply depleted of every last bit of ATP.
While chatting with Narkar, I sort of forget about the “wild” mice we’ve left on the treadmill, which he’d set up earlier to demonstrate a typical training session. Neither has been tainted with the magic jock-juice, and they appear identical—just two ordinary plump and furry rodents with no discerning features that might hint at physical prowess. They’ve been plodding along for twenty minutes or so without much fuss.
Then Narkar ups the belt speed to 18 meters per minute (roughly two-thirds of a mile per hour) and the mice burst into a gallop. He pushes it higher, to 22 meters per minute, and the mouse closest to me takes the lead—a born athlete, for sure—while the slower mouse languishes. Suddenly, the speedy mouse dashes right off the end of the belt, springs from the treadmill, plummets four feet to the floor, and is headed in a blind sprint for the door when Narkar nabs it with a lightning-fast lunge-and-swipe combo that he’s definitely performed more than once.
I insist that Narkar mistakenly grabbed an AICAR mouse for this demonstration. “Some wild mice are just inherently better runners,” he says. It’s apropos that he recognizes its natural athleticism—often the game-changing wild card integral to competitive sports—since he’s part of a team developing drugs that could give any beer-bellied schlub a fast-track ticket to the peloton.
BIJAL P. TRIVEDI
The Wipeout Gene
FROM Scientific American
OUTSIDE TAPACHULA, CHIAPAS, Mexico—ten miles from Guatemala. To reach the cages, we follow the main highway out of town, driving past soy, cocoa, banana, and lustrous dark green mango plantations thriving in the rich volcanic soil. Past the tiny village of Rio Florido the road degenerates into an undulating dirt track. We bump along on waves of baked mud until we reach a security checkpoint, guard at the ready. A sign posted on the barbed wire–enclosed compound pictures a mosquito flanked by a man and a woman: Estos mosquitos genéticamente modificados requieren un manejo especial, it reads. We play by the rules.
Inside, cashew trees frame a cluster of gauzy mesh cages perched on a platform. The cages hold thousands of Aedes aegypti mosquitoes—the local species, smaller and quieter than the typical buzzing specimens found in the States. At seven A.M., the scene looks ethereal: rays of sunlight filter through layers of mesh, creating a glowing, yellow hue. Inside the cages, however, genetically modified mosquitoes are waging a death match against the locals, an attempted genocide-by-mating that has the potential to wipe out dengue fever, one of the world’s most troublesome, aggressive diseases.
Throughout a swath of subtropical and tropical countries, four closely related dengue viruses infect about 100 million people annually, causing a spectrum of illness—from flulike aches to internal hemorrhaging, shock, and death. No vaccine or cure exists. As with other mosquito-borne diseases, the primary public health strategy is to prevent people from being bitten. To that end, authorities attempt to rid neighborhoods of standing water where the insects breed, spray with insecticides, and distribute bed nets and other low-tech mosquito blockers. They pursue containment, not conquest.
Anthony James, however, is mounting an offensive. James, a molecular biologist at the University of California, Irvine, and his colleagues have added genes to A. aegypti that block the development of flight muscles in females. When a genetically modified male mosquito mates with a wild female, he passes his engineered genes to the offspring. The females—the biters—don’t survive long. When they emerge from the pupal stage, they sit motionless on the water. They won’t fly, mate, or spread disease. The male progeny, in contrast, will live to spread their filicidal seed. In time, the absence of female offspring should lead to a population crash, which James’s collaborator has alre
ady demonstrated in the controlled environment of an indoor laboratory in Colorado. Now he has brought his bugs south.
Diagram by Emily Cooper
The technology marks the first time scientists have genetically engineered an organism to specifically wipe out a native population to block disease transmission. If the modified mosquitoes triumph, then releasing them in dengue-endemic zones worldwide could prevent tens of millions of people from suffering. Yet opponents of the plan warn of unintended consequences—even if mosquitoes are the intended victims.
Researchers also struggle with how to test their creations. No international laws or agencies exist to police trials of new transgenic organisms. For the most part, scientists and biotech companies can do what they want—even performing uncontrolled releases of test organisms in developing countries, neither warning the residents that their backyards are about to become a de facto biocolonialist field laboratory nor gaining their consent.
James has spent years attempting to play it straight. He has worked with community leaders in Tapachula, acquiring property through the traditional land-sharing program and building a secure test facility—all arduous, time-consuming, careful work. But he is not the only researcher testing modified mosquitoes outside the lab. James’s colleague Luke Alphey, founder of the UK-based biotechnology company Oxitec, has quietly pursued a more aggressive test strategy. In 2009 and 2010 his organization took advantage of the minimal regulations in the Caribbean’s Grand Cayman Island to release millions of genetically modified mosquitoes into the wild. James first learned of the experiments when Alphey described them publicly at a conference in Atlanta in 2010—fourteen months after the fact. Since then, Oxitec has continued the trials, releasing modified mosquitoes in Malaysia and Brazil.
Experts fear Oxitec’s actions could trigger a backlash against all genetically modified insects, reminiscent of Europe’s rejection of GM crops, a move that could snuff out the technology before scientists can fully understand both its promise and its potential consequences.
That would be a shame, because the technology has such promise. The Colorado lab test demonstrated that the modified mosquitoes work in a controlled environment, although a few indoor cages are not the wilds of Central America, Brazil, or Malaysia. To fight the sickness and death that ride inside the mosquito, the scientists’ creations must conquer the jungle.
Forced Sterilization
In 2001 James was already a pioneer of modern molecular mosquito genetics: the first researcher to genetically alter a mosquito and the first to clone a mosquito gene. That year he decided to apply his knowledge to the problems of disease transmission. He wondered if he could use a strategy designed to control agricultural pests on mosquitoes instead.
A year before, Alphey, then at the University of Oxford, had developed a technique for generating fruit flies harboring genes that selectively killed females. The population-control strategy is just a postgenomic riff on sterile insect technology (SIT), which has successfully controlled crop pests for sixty years. Technicians rear vast numbers of insects, sterilizing the males with blasts of radiation. When they mate with females in local fields, the union produces no offspring. The strategy is insecticide-free, targets only the pest species, and has been successfully applied many times—including a large-scale Mediterranean fruit fly (Medfly) eradication program in 1977 in Tapachula.
Unfortunately, sterile insect technology has never worked with mosquitoes. Radiation severely weakens adult males, and the processes of sorting and transport kill them before they can mate. Extending Alphey’s new fruit fly technique to mosquitoes, however, would enable researchers to design effectively sterile male mosquitoes from the genome up.
To kill female mosquitoes—the ones that suck blood and spread disease—James needed to hijack a genetic region that only females make use of. In 2002 James and Alphey identified a naturally occurring switch that controls flight-muscle development in females. Turn it off, and flight muscles won’t develop. Female mosquitoes emerging from the pupal stage just squat on the water’s surface, flightless, unable to attract mates. It was the perfect target.
Alphey founded Oxitec in 2002 to capitalize on the technology. In 2005 the Foundation for the National Institutes of Health, funded in large part by the Bill & Melinda Gates Foundation, granted James $20 million to test genetic strategies against dengue. James gave Oxitec $5 million to build the mosquitoes.
The collaborators designed a stretch of DNA that included a handful of genes and the regulatory switches needed to turn them on and off at the correct time. The system works like a relay team. During the mosquito’s metamorphosis from larva to adult, the female-specific switch flips on, activating the first gene, which produces a protein. This protein activates a second switch that kicks on gene number two, which then manufactures a toxin that destroys the female’s flight muscles. The researchers also added genes for fluorescent proteins that make modified larvae glow red and green, allowing them to monitor the spread of the genes through the population.
To breed large populations of a mosquito that they had explicitly programmed to die, Alphey and James needed a way to protect the females from the toxic gene cassette until after they reproduced. The trick was lacing the water with an antidote—the antibiotic tetracycline, which blocks production of the flight muscle–destroying protein. This design is also an emergency fail-safe: if a few of these genetically modified mosquitoes escape, they cannot reproduce without the drug.
The first tests of the new breed came in 2008 and 2009, when Megan Wise de Valdez, a colleague of James’s who at the time was based at Colorado State University, introduced modified males to a population of ordinary A. aegypti mosquitoes in the laboratory. Within five months the population crashed. The kill switch worked. The next step was to bring the modified mosquitoes into the field.
Breakbone Fever
In Tapachula, where James has set up his netted laboratory, dengue has long been a problem, as it has been in much of Mexico. “Dengue is my most important concern on a day-to-day basis,” said Hermilo Domínguez Zárate, undersecretary of health for Chiapas, when I visited the region last year. Dengue spreads explosively, causing the most hardship in densely populated areas.
During my trip to Chiapas I toured Pobres Unidos—Poor United—an impoverished neighborhood on Tapachula’s outskirts that suffered the most dengue cases in 2009 and 2010, along with Janine Ramsey, a parasitologist on James’s team who leads day-to-day work at the field site, and Rogelio Danis-Lozano, a medical epidemiologist.
One home we visited belonged to Maria, who asked that I not use her last name. As with most homes in Pobres Unidos, Maria’s house has only three walls, like a house on a movie set, so she has no way to keep mosquitoes out. The moist dirt floor creates a humid environment that lures the insects close. Piles of trash and dozens of containers collect rainwater, providing countless locations for mosquitoes to deposit eggs.
Danis-Lozano directed our attention to a large yellow tub brimming with fresh water and pointed to hundreds of skinny, black, threadlike mosquito larvae swimming vigorously in erratic zigzag patterns. Maria knows about dengue, of course, but Danis-Lozano discovered she had no idea that the larvae in her washtub morph into disease-spreading mosquitoes.
It is a scene that is mirrored in poor, crowded neighborhoods worldwide. More than one hundred countries suffer from dengue, from Asia to Africa to the Americas. Symptoms of dengue’s mild form—“breakbone fever”—mimic the flu: fever, joint and muscle pain, and crippling headaches that last about a week. A second infection can trigger potentially deadly dengue hemorrhagic fever, which induces vomiting, severe abdominal cramps, and internal hemorrhaging. Blood streams from the eyes, nose, mouth, and vagina. Without treatment, hemorrhagic dengue kills up to 20 percent of its victims; with costly expert care, mortality drops to 1 percent. The annual worldwide death toll exceeds that of all other viral hemorrhagic fevers—including Ebola and Marburg—combined.
In 2008 the epidemi
ologist David M. Morens and Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases, warned that dengue is “one of the world’s most aggressive reemerging infections.” The frequency and magnitude of outbreaks have been rising, spread by growing international travel and the exodus of people to cities. Caseloads have doubled every decade since the 1970s. In 2009 Florida public health officials reported the first dengue cases there in more than seven decades, raising fears among epidemiologists that the disease would soon take root in the continental United States.
One reason James decided to apply his genetic technology to the fight against dengue fever—instead of, say, malaria—is that the virus is primarily transmitted by a single species of mosquito. (Between thirty and forty species of mosquito carry malaria.) A. aegypti, the world’s main dengue vector, is an invasive, tree-dwelling African species that hitched a ride on slave ships some four hundred years ago. It is now an urbanite, breeding beside homes in anything that holds a few tablespoons of clean water. The mosquito bites during the day, so bed nets provide no protection. And it bites humans almost exclusively, drawing the nutrients that give it a life span of up to a month—plenty of time to bite and spread disease.
A. aegypti is stealthy, lacking the sharp, unnerving buzz that provokes a swift swat or panicked wave. Inside the secure insectary at the Regional Center for Public Health Research in Tapachula, I could barely hear a swarm of transgenic mosquitoes in a small cage. Laura Valerio, an entomologist at the University of California, Davis, stuck her gloved hand inside to point out a female. The intrusion scared the males, which took flight and zoomed around the cage. Females, however, just sat there or hopped away clumsily.