A medical device company in Minnesota has had a big win. It can now sell its weight-loss implant in the heaviest country on the planet. In the Lancet’s list of nations with the most obese people, the United States came out on top with 13 percent of the world’s 671 million. Now Enteromedics, the Minneapolis company, can offer those considering gastric-bypass surger—or similar drastic measures—a less radical alternative.
Enteromedics’ device, the Maestro System, is implanted under the skin of the torso just like a pacemaker. But instead of going to the heart, the device’s leads wrap around the vagus nerve near the stomach. That nerve connects the brain to the organs of the gut. Using periodic bursts of current at 5000 Hz, the Maestro temporarily blocks nerve traffic between the stomach and the brain. This reduces the feeling of hunger and enhances the feeling of fullness.
In the carefully controlled study that won approval for “VBLOC” therapy, patients had lost an average of about 24 percent of their excess weight after 12 months, and they maintained that weight loss at 18 months.
Gaining approval by the U.S. Food and Drug Administration is a big deal for medical device makers, because it gives them access to the biggest healthcare market in the world. But it requires an arduous and often costly effort. When I interviewed him last September, Enteromedics president and CEO Mark B. Knudson explained that one of the biggest difficulties was designing the trial so that any placebo effect could be eliminated. In the Enteromedics trial, control subjects underwent the exact same surgery, but had a dummy device implanted. The patients were then followed for 18 months or more with an eye to picking out the placebo. According to Knudson:
There’s data from multiple studies that make you think that a control surgery is almost as effective as the surgery itself, but over time that’s not how it actually works. Placebo is really strong especially if you have surgery, but the most it ever lasts is a year. So if you’re going to do something you have to follow patients for a long time.
With obesity under its belt, Enteromedics has its sights set on other conditions that might be ameliorated by modulating the signals that pass along the vagus nerve. “Our first target is obesity. But we’ve got interest in areas like pancreatitis, inflammatory bowel disease and other autoimmune disease like that,” Knudson told me in September. “In the literature there’s a great deal of support for the idea that changing how the vagus operates will in fact change how the course of those kind of diseases actually run.”
Two of the nearest term targets are diabetes and hypertension, both of which are associated with obesity. But new knowledge of what the vagus nerve can affect is coming out all the time. In August, a team that included an advisor to Enteromedics showed that stomach cancer growth in mice was suppressed—and the effectiveness of chemotherapy enhanced—by removing the vagus nerve connection.
(Vagus nerve stimulation, as opposed to blockade, is already used to ease epilepsy and severe depression. It’s also being explored as a treatment for tinnitis and heart failure.)
There will also be improvements to the implant and the software that runs it, Knudson said. “This is obviously in the early generations of the device.” On the hardware list are reducing the size of the pacemaker-like device and changing the configuration of the electrodes to achieve the nerve block using less current. On the software side there are number of levers Enteromedics can pull to achieve a more targeted effect, including changing how the energy of the blocking pulse is ramped up and down, altering the period between the pulses, and better matching the device’s activity to the body’s own metabolic clock.
But for now, Enteromedics can just savor its weighty win.
Samuel K. Moore is the senior editor at IEEE Spectrum in charge of semiconductors coverage. An IEEE member, he has a bachelor's degree in biomedical engineering from Brown University and a master's degree in journalism from New York University.