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The animal kingdom is diverse, fascinating, and even inspires the medical world!

Hosted by: Michael Aranda
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Antimicrobial peptides


[SciShow intro plays]

Michael: The animal kingdom is diverse, fascinating, and often downright amazing. Many people – including scientists – might even call it inspirational. Animals are currently inspiring a new generation of robots, but what about medicine?

We’re constantly facing new threats from viruses and antibiotic-resistant bacteria. So scientists are learning from animals’ natural disease-fighting abilities to make new antimicrobial drugs and materials.

One of these antimicrobials was first found in 1993, when researchers observed that dogfish sharks never seemed to get any sort of infection, even in unsterilized tanks. The scientists isolated a substance from the shark tissues that they named. And soon they were able to make it synthetically in the lab. More recent studies have shown that squalamine has the power to make human cells better at resisting viral infections.

Viruses have to use various tricks to get past our cell membranes and infect our cells -- like by recruiting help from our very own proteins! One of these proteins is called Rac1, which normally sits on the negatively-charged inside of the cell membrane, bound there by the protein’s positive charge. Rac1 helps regulate lots of different processes -- including what gets in and out of the cell, kind of like a bouncer. So, viruses can co-opt it to sneak inside our cells. But squalamine can put a stop to such treachery.

Squalamine is also positively charged, and certain cells have transporters to let it through their membranes. Then, squalamine latches onto the negatively-charged inside of the membrane, and displaces Rac1 and other proteins for a little while, which keeps the virus from coming in the cell. This means the immune system can kill off the exposed virus. And after a couple hours, any remaining squalamine is filtered right back out of the bloodstream by the liver. So squalamine may be what’s keeping the dogfish shark virus-free. And with a little more research, maybe it can protect us from some dangerous viral infections too.

We’re also learning about killing microbes from cicadas: those noisy, red-eyed bugs that spend most of their lives underground before coming out to scream for a few weeks, have sex, and then die. As annoying as they are, in 2012, researchers discovered that one species, the Clanger cicada, had an awesome antimicrobial power. Their wings are coated in tiny spikes that burst bacteria on contact!

Rather than straight-up popping the bacteria like a bubble, these nanopillars actually stretch the life out of them -- pulling the cell surfaces thinner and thinner until they rupture. This piqued the interest of a research group from Bristol, England, who wanted to see if these nanopillars could have medical applications. See, medical implants like hip replacements and pacemakers are often built with titanium.

This metal is strong, durable and relatively light, but not anti bacterial -- so bacteria tend to colonize the surface, which could lead to dangerous infections. And if standard antibiotics can’t kill the bacteria, the implant may need to be surgically replaced. But how can we make a metal surface with deadly spikes that kill bacteria without harming our own cells? Well, in this case, size matters.

The researchers created these titanium dioxide nanowires, which were a similar size to the cicada nanopillars and lethal to bacterial cells. Human cells, on the other hand, – which are about ten times larger – slid over the bumpy surface unharmed. So their calls may be annoying, but cicada wings can teach us a lot about medicine.

And so can molecules called antimicrobial peptides or AMPs -- which are just short chains of amino acids that many animals use as part of their defense strategies. Researchers have found potent AMPs in some pretty weird places... think cockroach brains and alligator blood! Peptides come in many shapes and sizes, but the best-known ones form a helix – kind of like a stretched Slinky – with an overall positive charge.

They’re attracted to the negative surface charge on bacterial cell membranes, and punch through the cell surface to make these gaping holes. Which isn’t so great for the bacteria, and they’re usually dead in seconds. Meanwhile our cells – which are mostly uncharged on the outside – are left unscathed. It would be amazing if we could use these natural AMPs in medicine, but it’s currently difficult -- some of them are toxic, while others get quickly destroyed by our bodies. So scientists are trying to bioengineer them to be safer and more effective.

For example, they tweaked an AMP that actually came from humans, making it shorter and more strongly charged. This new peptide successfully killed antibiotic-resistant MRSA bacteria when used as a nasal spray. So, who knows what some other modified AMPs could do for us? In a few years, we could be keeping harmful microbes at bay with science inspired by shark livers, cicada wings, locust brains and who-knows-what-else nature has to offer.

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