Frogs Regrow Limb With New Treatment

The African clawed frog. (Photo: Smithsonian’s National Zoo & Conservation Biology Institute) Biological engineers have found a way to help African clawed frogs regrow lost limbs. According to a new study published in the journal Cell Reports, scientists applied topical drugs to amputation sites, resulting in the growth of a “leg-like limb.”  

The African clawed frog is predisposed to regeneration, able to regrow severed limbs throughout much of its youth. But this ability dwindles as the frog reaches adulthood; at a certain level of maturity, attempts to regrow limbs result in cartilaginous spikes with little practical value. Biological engineers at Tufts University, Harvard, and the University of Florida saw this shift as a valuable opportunity to learn how regeneration could be manually encouraged using topical steroids. 

The team got to work applying wearable bioreactors (in this case, small caps) to several frogs’ amputation sites. Each bioreactor contained progesterone, a naturally-occurring steroid hormone, suspended in a protein-based hydrogel. Despite only remaining on the frogs’ bodies for 24 hours, the progesterone cocktail induced “robust” bone growth, resulting in the production of “paddle-like” appendages across the span of 18 months. 

“It’s not a full limb that’s regrown, but it’s certainly a robust response,” scientists unrelated to the research have said. “It is particularly promising that only a daylong treatment can have such a positive effect on an adult animal.”

(Image: Celia Herrera-Rincon et. al)

Though the frogs’ new limbs can’t quite be considered legs, they’re certainly more leg-like than the spikes they would have otherwise developed. The study indicates that frogs that didn’t receive progesterone treatment produced growth mainly made up of cartilage, with any new bone mass appearing beneath the amputation plane. In contrast, the treated frogs produced appendages containing “complex, patterned structures” made up of non-ossified and weakly ossified bone. The scientists also found that the administered progesterone remained local to the amputation site instead of dissipating among the frog’s system, thus preventing any impact on the rest of the frog’s physiology. 

Beyond being impressive in their own right, the study’s results show promise for the future of regeneration research as it relates to amputated limbs. Its authors note that around 2 million Americans have experienced limb amputations. Lost limbs are currently replaced with prosthetics (if anything at all), which are incredibly expensive and must be fitted to the patient’s exact measurements.  It will be challenging to reproduce the frogs’ exciting results in humans or most other mammals, though; after all, African clawed frogs already have regenerative qualities, a privilege we humans unfortunately don’t share. 

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