By Colleen Bungard, staff writer
Most people know them for their peculiar appearances, but the platypus has more than just looks: a 2018 study conducted by the University of Adelaide revealed the presence of a protein in their venom and gut that could revolutionize the way we treat type 2 diabetes. It’s a fairly recent discovery, so even though further research is funded, clinical trials and a marketable drug are still a thing of the somewhat distant future.
The protein, called glucagon-like peptide-1 (GLP-1), is a slightly different version of a hormone found in the human intestinal tract. In the digestive systems of both people and platypuses, GLP-1 is part of a complex system of chemicals that regulates blood sugar. It’s released when glucose passes through the digestive tract and stimulates the pancreas to release insulin and lower blood sugar. However, male platypuses also use the hormone as a component of the venom they secrete during mating season. They use this venom and the spurs on their hind limbs that deliver it to fight for mates. Among other unsavory effects such as extreme pain, hyperventilation, and convulsions, the GLP-1 in platypus venom serves the same function as in the gut and lowers the blood sugar of the unfortunate creature on the receiving end of a sting.
So if GLP-1 serves the same function in human stomachs as it does in platypus venom, why is platypus GLP-1 so much better for treating diabetes than human GLP-1? The answer lies in the differing lifespans of the two kinds of hormones. Human GLP-1 is very short-lived, mostly because we also produce an enzyme called dipeptidyl peptidase-4 (DPP-4) that rapidly denatures GLP-1. Current diabetes treatments based around the blood sugar lowering properties of GLP-1 focus on inhibiting the production DPP-4 rather than increasing GLP-1.
However, platypus GLP-1 isn’t affected by DPP-4. This resistance to human enzyme stems from the massive biochemical differences platypuses have due to the sheer age of the species. The subgroup they belong to, monotremes, diverged from the main mammalian phylogenetic line over 160 million years ago. In comparison, primates split off only 55 million years ago. They’re still mammals, but they’ve been evolving separately from most mammals for a long time. Consequently, most of their organs work roughly the same way mammals’ do, but many of the biochemical systems used by their organs have evolved to be identical in function but composed of differently structured molecules. Platypus GLP-1 is no exception: it totally lacks the cleavage point that DPP-4 latches onto in human GLP-1. Platypuses developed a structurally different version of DDP-4 to denature their GLP-1, thus human DDP-4 does nothing to it. Yet, the platypus hormone is similar enough to its human counterpart that (at least according to preliminary testing) it activates the same receptors in the pancreas as normal human GLP-1
Platypuses are unique: they are similar enough to mammals that their biochemistry and features are mostly comparable to that of humans, yet they contain a multitude of key differences. GLP-1 structure is one such example, but there are others that are useful to humans. Platypuses and humans both produce milk to nurture their young, but only humans have nipples. Platypuses diverged from mammals before they evolved nipples to prevent bacterial contamination by reducing the surface area involved in feeding. As a result, platypuses developed an alternative way of preventing infection: a unique protein discovered in 2010 with highly antibacterial properties that could potentially help us fight bacterial resistance. Keep in mind, these two compounds are just the discoveries we’ve made since the platypus genome was sequenced in 2008. Who knows how many more amazing and unique compounds platypuses contain?
Unfortunately, we may never get the chance to explore this question. Playpuses are threatened by land development and predation by feral dogs and cats. They are especially vulnerable to droughts and bushfires like those recently plaguing Australia because of their water-dwelling nature. They have already disappeared from 40% of their former range, and a joint study conducted by the University of New South Wales and the University of Melbourne estimated that climate change could cause up to a 73% decline in the platypus population in the next 50 years.