New study shows long-assumed irreversible AGEs can be removed from aged human tissue ex vivo – opening a new chapter in damage repair.
For decades, researchers studying aging have largely viewed advanced glycation end products (AGEs) as part of biology’s accumulating baggage – chemical modifications that slowly build up on long-lived proteins and, once established, simply remain. While efforts have focused on slowing their formation or limiting their downstream effects, reversing them has remained an elusive goal.
Now, researchers from Revel Pharmaceuticals, working with collaborators at Calico and the University of Colorado Anschutz Medical Campus, report the development of an engineered enzyme capable of removing one of the most abundant AGE modifications, Nε-carboxymethyl-lysine (CML), from proteins in aged human tissues ex vivo. Published in Nature Communications, the study offers proof of principle that at least one form of molecular damage long considered effectively irreversible may, in fact, be repairable.
Longevity.Technology: For decades, advanced glycation end products such as CML have largely occupied the same mental category as wrinkles on a well-loved face or cracks in an old stone wall – the inevitable wear and tear of time; damage to be slowed, perhaps, but not repaired. This work challenges that assumption. It does not demonstrate age reversal, nor do the authors claim it does – the experiments were performed ex vivo, and considerable translational hurdles remain before anyone can begin talking seriously about therapies. Yet dismissing the study on those grounds would miss the point entirely. The real significance is conceptual: one abundant form of age-related molecular damage, long assumed to be effectively permanent, has now been shown to be enzymatically reversible. That shifts the conversation from prevention alone toward repair. Prevention remains the ideal, of course, but biology has an inconvenient habit of refusing to cooperate, and by the time aging announces itself much of the molecular damage has already been woven into our tissues. The ability to selectively remove even one component of that damage hints at a future in which aging is addressed not only by slowing its relentless advance, but also by undoing at least some of what has already been done. Equally intriguing is the platform behind the discovery – if directed evolution can be harnessed to engineer entirely new enzymatic activities against molecular lesions that nature itself never evolved to tackle, today’s CMLase may ultimately prove less important than the repair toolkit it foreshadows. There is, of course, a long road ahead, and aging will not yield to the removal of a single lesion; nevertheless, every field has moments that redefine what is considered possible. This could well prove to be one of them.
Repair rather than prevention
CML is one of the most prevalent advanced glycation end products found in aging tissues including skin, arterial walls and the lens of the eye. Beyond altering the chemistry of long-lived structural proteins, it also acts as a ligand for the receptor for advanced glycation end products (RAGE), contributing to chronic inflammatory signaling.
As the authors note, previous therapeutic strategies have largely focused on preventing AGE formation by targeting reactive intermediates [1]. Those approaches cannot address damage already accumulated over decades, nor restore the native structure of modified proteins. Their newly engineered enzyme, CMLase, instead oxidizes the CML modification itself, restoring the original lysine residue.
The route to that enzyme was itself notable. The researchers computationally screened almost 45,000 protein structures before applying five rounds of directed evolution to more than 500 million variants, ultimately creating what they describe as “a novel enzyme engineered… to specifically oxidize CML and restore the native lysine residue.” According to the authors, the work establishes “proof-of-concept that protein damage previously deemed irreversible is amenable to enzymatic repair [1].”
Reality bites
For Aaron Cravens, cofounder and CEO of Revel Pharmaceuticals and corresponding author on the paper, the turning point came not during enzyme engineering, but when the team first saw the results from aged human tissue.
“The first time we saw the enzyme working on human tissue, we were floored,” he told Longevity.Technology.
Cravens explained that an independent laboratory performed blinded testing using tissue from the aorta of a 75-year-old donor, heavily burdened with accumulated CML. “As they walked us through the data, they said they could tell which was the real one just by looking at the tissue. When an effect size is that large, you can see it with your own eyes – that’s when you get excited.”
He recalls the atmosphere inside Revel’s conference room as the results emerged.
“Our whole team was gathered in a conference room, and there was this collective sigh of relief, and honestly disbelief, that more than four years of work had paid off… A modification the whole field had written off as permanent was coming off, right there in front of us on tissue from a 75-year-old. That really reframes how you think about aging damage generally: not as a permanent sentence, but as a chemical reaction that can be undone.”
A careful proof of principle
The study deliberately stops short of claiming rejuvenation.
Experiments were performed on excised human tissues rather than living organisms, including arterial tissue from a 75-year-old donor, elderly skin and lens proteins from a 64-year-old donor. Treatment reduced CML levels by more than 70% in arterial tissue, more than 55% in skin and between 45% and 78% in lens proteins depending on the analytical method used.
Equally notable is what the authors acknowledge remains unknown. “While we demonstrated the chemical reversal of CML,” they write, “it remains to be determined if this translates to the recovery of tissue biomechanics or the silencing of pathogenic RAGE signaling in vivo [1].” Questions of tissue penetration, immunogenicity and delivery into intact extracellular matrix will also need to be addressed before therapeutic applications become realistic.
That candor strengthens rather than weakens the study, placing the findings firmly where they belong – as an important experimental advance rather than a clinical one.
More than one enzyme
Outside experts also see wider implications.
Aubrey de Grey, who has long championed damage-repair approaches to aging, described the work as “a really major breakthrough.”
“This is something that researchers have tried and failed to do for decades,” he told Longevity.Technology. “It’s a massive advance, and in arguably the single most neglected aspect of aging-damage repair.”
Wryly, he added: “Great also to see Calico being involved in something significant at last.”
Cravens, for his part, is already looking past CMLase, viewing it as a beginning rather than the destination.
“CMLase is a proof of principle for the platform, not the finish line,” he said. While CML represents a single chemical modification, glucosepane and related crosslinks present a more difficult engineering challenge because they join proteins together rather than modifying individual residues.
Even so, Revel has already turned its attention in that direction.
“The bigger point is that CMLase proves these targets are reachable by engineered enzymes – which was an open question until now,” Cravens said. “The vision is a systematic toolkit: one enzyme per type of damage, working through the whole catalog of gunk that builds up in our tissues as we age. Glucosepane is squarely on that roadmap, and CMLase is the first step towards that mission.”
From possibility to practice
Damage repair has always occupied an intriguing place within geroscience – compelling in theory, considerably harder in practice. Whether CMLase itself ultimately reaches the clinic remains to be seen, but the study offers something perhaps just as valuable at this stage: evidence that one class of molecular damage once regarded as biologically permanent can, with sufficient engineering, be chemically erased. That may not yet change medicine. It could, however, begin to change what researchers believe is possible.
