Caribbean frogs inspire drug delivery system

RESEARCHERS at the University of Strathclyde, UK have discovered that a foam made by a Caribbean frog can be used in a non-toxic delivery system for drugs such as antibiotics.

The Tungara frog (Engystomops pustulosus) produces a very stable foam nest to protect its eggs and tadpoles during development from disease, predators and adverse environmental conditions. Researcher Sarah Brozio found that the foam could take up model dyes and drugs and release them at a steady rate. Along with the foam’s stability, this makes it potentially useful for targeted drug delivery, particularly for delicate severe burns, which often become infected. Targeting the antibiotic therapy reduces side effects and can have more successful outcomes.

The researchers mixed samples of the foam with two model dyes, calcein and Nile red, and the antibiotic vancomycin, and measured the rates at which they were released again. The dyes were released steadily over a period of 72-168 hours. The team tested the vancomycin-laden foam in vitro on the bacterium Staphylococcus aureus, a common pathogen in burns and serious wounds. The foam prevented the growth of bacteria for 48 hours.

Obviously, one of the most important characteristics of a drug delivery system is its compatibility with living cells. Brozio and her colleagues exposed a type of human skin cell, keratinocytes, to the foam. After 48 hours, the cells were still alive and healthy, proving that the foam is safe.

“Foams are unusual in nature and are typically made of inactivated proteins. This foam is stable and importantly compatible with human cells, making it potentially ideal for pharmaceutical applications. While foams like these are a long way from hitting the clinic, they could help in burns and wound treatment, providing support and protection for healing tissue and delivering drugs at the same time - all from a humble little frog,” said research team leader Paul Hoskinsson.

The researchers are now working on producing a completely synthetic form of the foam. They have so far engineered Escherichia coli bacteria to produce two of the foam’s six protein constituents.

It is not the first time that the foam produced by Tungara frogs has proved useful to researchers. In 2010 researchers from the University of Cincinnati, US, found that it could be used to make a photosynthetic foam which can convert 96% of sunlight into sugars.

The latest research (see p80 for the abstract) was presented at the Microbiology Society's 2016 Annual Conference, held from 21-24 March in Liverpool, UK.