Mimicking our eyes’ sun protection

US start-up Sóliome wants to produce a peptide-based sunscreen that can be entirely biodegraded by living organisms. Micah Nelp, Sóliome’s co-founder and chief executive, believes that the product could overcome some of the environmental and health-related problems of more traditional mineral and chemical sunscreens.

Various different chemicals in sunscreen are used to absorb ultraviolet (UV) light – both long wavelength (UVA) and short wavelength (UVB) – to protect us from its harmful effects. But some of these UV-filtering compounds can damage marine life, including corals, and have been banned in several countries.

This $18 billion (£14 billion) global market is dominated by chemical filters whose full effects on our health and environment are not well understood, says Nelp. ‘Some have been shown to penetrate our skin and accumulate in blood and breast milk – meaning there are hormone disruption concerns – and they kill coral,’ he explains. While mineral sunscreens containing titanium dioxide are considered safer, they can produce hydrogen peroxide in seawater and stress microplankton. ‘We looked for a solution that would complement our biochemistry and not interfere with it,’ he says.

‘In the lenses of our eyes, an amino acid called kynurenine can absorb UV light while allowing visible light to pass through transparently to our retinas,’ says Nelp. ‘We can get that same remarkable protection that our eyes have on our skin.’

When Nelp was working as a postdoc with John Groves at Princeton University in New Jersey, US, he had a light-bulb moment. ‘I was working on an enzyme called indoleamine 2,3-dioxygenase, which makes kynurenine,’ recalls Nelp. ‘I’d been studying for three years, doing kinetic assays, looking at the UV absorbance, and then it finally clicked: “Oh, that is the UV I’m trying to block with my sunscreen!”’

Inspired by this natural process, Nelp decided to experiment further with the help of co-founder Anthony Young, who he had met during his PhD at the University of Arizona, US. ‘My friend from grad school just jumped onto the project with me, we really didn’t think anything was going to happen but everything just kept working,’ he says. Sóliome spun out from Princeton University in 2021, backed up by venture capital firm SOSV’s biotechnology programme IndieBio. In 2022, Sóliome received a small business innovation research grant from the US National Science Foundation to further develop its sunscreen.

Initially Nelp and Young used peptides from plants and oxidised the amino acid tryptophan within those peptides to kynurenine. However, the kynurenine concentration in these preparations was not high enough to make an effective sunscreen. ‘So we moved to chemical synthesis,’ says Nelp. The peptides the team created have higher ratios of kynurenine, ‘but it is still a naturally-existing peptide, so every single cell in the body can quickly and safely break it down’, says Nelp, noting that kynurenine feeds in to the biosynthetic pathway to niacin (vitamin B3).

We looked for a solution that would complement our biochemistry and not interfere with it

The kynurenine-rich peptides are large enough to prevent them from penetrating through the skin. ‘The science is well known, as drug companies have tried to get peptides to cross the skin barrier, so we’re just taking those lessons and doing the opposite,’ says Nelp. He adds that while kynurenine has strong UVA protection on its own, it can be covalently modified to provide strong UVB protection as well. Sóliome has now patented the use of kynurenines or other UV-absorbing synthetic peptides in sunscreen ingredients.

But, whereas most countries treat sunscreens as cosmetics, the US considers them over-the-counter medications. That means the US Food and Drug Administration (FDA) regulates new UV filters to the same level of scrutiny as drugs. As a result, the approval process – which requires review of animal, clinical and marketing data – can be lengthy and expensive. Nelp points out that no new UV filters have been added to the FDA’s list of ingredients that can be used in sunscreens for over 20 years. Nevertheless, in recent years, updates to the FDA regulations on sunscreens have reduced the cost and burden of approval so Sóliome is hopeful.

Anti-aging serum

Given these regulatory differences between countries, Sóliome has decided to target the EU market first with an anti-aging daily serum. ‘We plan to launch our UVA protection filter in 2024, which is completely transparent, light and biocompatible, and can remain photo-stable well over 24 hours under UV light,’ says Nelp. Sóliome is now raising seed funds to scale up manufacturing and support further safety testing.

Together with a third co-founder, beauty care marketing expert Denise Koller, Nelp and Young want to introduce Sóliome’s technology to the market themselves. ‘We think the best way to get it out to consumers is through our own line of products. We’d love everybody to be able to use it, but we don’t want to wait for everybody to want it,’ says Nelp.