What Humans Can Learn From the Sea Cucumber’s Toxic Arsenal

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However, this chemical defense poses a major problem for sea cukes: They need to prevent themselves from being killed by their own toxins. And that means their own cells can’t contain cholesterol, the target that the saponins bind to and pierce. Instead, they have developed two cholesterol alternatives: lathosterol (the target that the saponins pierce) and 9(11), which likely fulfill the same function in maintaining cell membrane stability. The scientists believe that the sea cucumbers’ ability to make saponins—and these saponin-resistant sterols—evolved concurrently. “We think it’s a self-defense strategy,” Osbourn says. “If you can produce these toxic compounds, you have to be able to not poison yourself.”

These unique evolutionary abilities were based on a single point, it turns out. Along with sea stars, sea urchins and sea cucumbers, the echinoderms family includes sea cucumbers. They all share a common ancestor, but sea urchins don’t have the same saponin defense superpowers. Osbourn, Thimmappa, now an assistant professor of genomic engineering at Amity University, compared the genomes of sea cucumbers with their echinoderm cousins to find out why they had evolved genetically differently. Researchers were specifically interested in studying lanosterol synthesise, a highly evolutionary conserved enzyme that is crucial for sterol or saponin biosynthesis. It transforms the precursor molecules into complex origami-like forms.

The team discovered that sea cucumbers just don’t have it. They instead have two enzymes of the same family that are fundamentally different in biological function. The one gives rise to the saponins present in juvenile sea cucumbers. The other creates their cholesterol alternative, and generates saponins for their outer walls. One change from the traditional lanosterol synthase sequence in the amino acid chain was all it took to create these two sea cucumber-specific enzymes with completely different functions—an evolutionary adaptation that was “simple, but very elegant,” says Thimmappa.

This work of characterizing and determining the functions of single chemical compounds in sea cucumbers is “super cool,” says Leah Dann, a PhD student at the University of Queensland who studies island conservation and was unaffiliated with the study. For sea cucumbers, which don’t have adaptive immunity (the ability to generate antibodies that can prevent future diseases), these saponins might help protect against harmful microbes or fungi. And, since they don’t have a spiny outer shell, these chemical defenses may explain why many organisms leave them alone. “They look so yummy,” Dann says. “But most fish will not touch them.”

“They explained why sea cucumbers have triterpenoid saponins,” says Lina Sun, a professor at the Institute of Oceanology at the Chinese Academy of Sciences. Sun is not affiliated with the study and her comments were translated from Chinese. Discovering and characterizing the two synthase pathways that generate these saponins and special sterols is “very important,” she adds. Sun is curious to learn how the genes involved in saponin biosynthesis might be different in other species of echinoderms.

The compound that reduces cholesterol has interesting implications for human health care. “Sea cucumbers are highly valued both for food and for health,” Osbourn says. “Sea cucumber extracts, which are rich in saponins, are very valuable.” They have long been harvested as a culinary delicacy—and revered for their antioxidant and anti-inflammatory health benefits. Although certain sea cucumbers can sometimes be fatal to small animals like fish, the saponins in them can be eaten and even used for human health. Sea cucumber saponins have been shown to reduce cholesterol and inflame the symptoms of inflammation. Atherosclerotic plaquesIn mice, and have been linked with Anti-tumor activityAgainst cancer

Saponins are also useful for personal care and home use, such as soap making. Saponins were originally named for their presence in the roots the soapwort plant.SaponariaSaponins can be dissolved in water to make a frothy soup. “Nature is so good at making chemicals,” Osbourn says admiringly.

In the future, she and her team are interested in learning how to synthesize more of these naturally derived compounds—to recreate them on a larger scale without having to harm any sea cucumbers, and to “harness all of the triterpene diversity that’s out there in nature.” Ultimately, she thinks, such molecules could be designed and made on demand, to be used as medicines, or commercialized as foaming agents or emulsifiers.

In the meantime, though, one of the most likely places you’ll find sea cucumbers and their compounds is in soup—something Osbourn was once served for lunch when attending a conference in China. “It was quite chewy,” she says. “I’m sure it was good for me.”

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