Weekly, Michael Levin receives phone calls and letters from people who have lost limbs.
How this happened varies — industrial accidents, military injuries, birth defects, the list goes on — but they approach Levin, a professor and director of the Center for Regenerative and Developmental Biology at Tufts University, with the same question: When can they get their limb back? ?
Scientists project that by 2050, approximately 3.6 million Americans will live with the loss of a limb. Although technologies such as prosthetics have advanced, doctors are still unable to induce regeneration of human limbs.
But scientists are one step closer. In an investigation published Wednesday in the journal Science Advances, Levin and his colleagues announced they could induce leg regrowth in adult frogs.
“They weren’t perfect cosmetically, but they were damn good legs,” he said.
The regrowth was made possible by a combination of a five-drug cocktail and a portable silicone bioreactor called a BioDome. The cocktail was developed by Levin and the study’s first author Nirosha Murugannow an assistant professor at Algoma University in Ontario, and designed to contain ingredients that spur various actions, including inhibiting collagen production, which causes scarring, stimulating nerve fibers, blood vessels and muscle growth, and suppressing inflammation.
This cocktail was also the first the team tried — the first attempt at getting the right combination of ingredients and doses.
“This makes me really happy because if this is our first guess and it’s so good, just imagine what the optimized version will look like in the future,” Levin said.
In the experiment, 115 female African Clawed Frogs were assigned to one of three treatment conditions after a hind limb was amputated: the BioDome with the cocktail treatment, the BioDome only, or a control experience without intervention. As tadpoles, these types of frogs can regenerate legs, but lose the ability to do so once they reach adulthood.
The BioDiome was used within the first 24 hours of amputation – and in the case of one group of frogs, it was loaded with the five pro-regenerative compounds. This short treatment activated an 18-month regrowth period, resulting in nearly fully functional legs. The new limbs contain bones, muscles and nerves. The frogs could use them to stand and swim.
The legs did not have the same tissue and long toes that these frogs usually have. However, Levin doesn’t know if that’s because the team hasn’t come up with the right cocktail yet, or because they haven’t waited long enough to develop.
There was also some variation. “Some animals responded great, and some animals not as great as others, but everyone got better,” he said.
Even the drug-free BioDome had a beneficial effect on some frogs, facilitating partial limb regrowth, likely because it still provided a protected environment. While animals such as flatworms, starfish and crabs regenerate limbs, injury in mammals often leads to scar tissue, which prevents blood loss and infection. This allows for survival and is partly the result of injuries exposed to air — but it may also explain why humans don’t grow back arms the way a salamander can.
A hydrated, protected environment, such as a predator-free pond or, in this case, a BioDome, allowed the frogs’ bodies to do their best to regenerate, Levin said.
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Levin’s lab investigates how cells make decisions and how they can use this process to initiate regeneration. Other approaches in regenerative medicine focus more on tissue engineering and the actual construction of new body parts. Levin endorses a different school of thought that approaches regenerative medicine by harnessing the capabilities of cells and driving them into action. He likens it to focusing on software instead of making hardware.
“Cells already know how to make all the organs in your body — they did it once during embryonic development and that information hasn’t gone anywhere, it’s still there,” he said. “What we need to do is try to find out which triggers will convince the cells to do what we want them to do.”
In the case of this experiment, the trigger is the combination of the BioDome and the drug cocktail. The BioDome is important because it provides a localized, controlled environment in which the drugs can do their work. The drug cocktail, meanwhile, contained nothing leg-specific — which Levin says is critical. Zero percent of the time, the experiment resulted in anything but leg creation.
“This technology isn’t necessarily about limbs; it’s a way of looking at all kinds of body organs and repairing them — anything that’s missing, damaged, degenerating, carcinogenic, aging,” he said.
This strategy relies on activating the information cells contain about making body parts and triggering natural regenerative abilities. After applying the BioDome containing the drug cocktail, the research team saw the activation of molecular pathways typically used when an embryo begins to take on the shape of a body.
This activation isn’t necessary because frogs are unique in their ability to regenerate limbs as juveniles, Levin said. Humans and many different animals have regenerative abilities. For example, children can regenerate lost fingertipswhile adults experience constant regeneration on a smaller scale through the replacement of functions such as skin, hair and intestinal mucosa.
The idea that mammals can regenerate through this procedure is being tested on mice by Levin and his colleagues. Him and co-author David Kaplana professor of biomedical engineering at Tufts University, are also co-founders of a company, Morphoceuticals, with the aim of bringing these technologies to clinical application. While people are calling to volunteer, the scientists are still a long way from human trials — Levin said it’s not possible to estimate when this will happen.
“I think it’s going to get there and I’m very optimistic about it all,” he said. “But we’re not there yet. There’s a very important basic science that has to happen before it’s ready to move on to a person.”
But in the distant future, he can envision the BioDome and its cocktail being applied to individuals in the hospital, and the concepts behind the work informing organ creation. If we know how to stimulate cells, “we should be able to build what we want them to build,” Levin said.
The question is already there. “People don’t realize the depth of biomedical suffering,” he said. “The need is great.”