They then administered a single low dose of Klotho under the skin to each monkey, increasing protein levels to levels normally present in the animals at birth. Four hours later, the researchers had them complete foraging in groups of 20 trials, and the team then tested the monkeys again over the next two weeks. Overall, the animals made correct decisions more often than before the injection. The team tested monkeys with two versions of the task: an easier one with fewer subjects to choose from, and a more difficult one with more of them. According to Dubal, Klotho improved his performance by about 6 percent on the easier task and about 20 percent on the harder variant.
“This is very encouraging,” says Moe, who was not involved with the new study.
The researchers had the monkeys perform this task multiple times over the course of two weeks, and the team found that the cognition-enhancing effect lasted the entire time, even though Klotho was cleared from the body within days of the injection. “The fact that it can be administered once and lasts for two weeks seems great, although at this point we don’t know if repeated administration would work again,” says Eric Verdin, CEO of the Buck Institute for Research on Aging I AM not involved in the study.
In fact, in earlier studies with miceBoth low and high doses of Klotho increased cognition and helped them perform better on several maze tasks that challenge learning and memory. But when Dubal’s team administered doses of 10, 20, and 30 micrograms per kilogram to monkeys, the benefits at the 10-microgram dose plateaued. This is an important signal for researchers as they consider testing Klotho injections in humans one day. Verdin says about the dosage: “More is not always better.”
Humans are born with about five times as much Klotho as in adulthood – and in the monkey experiment, the low Klotho dose was equivalent to infancy levels. Dubal surmises that dosing within a range that the body has previously experienced, without exceeding it, may be more important for primates than mice. The next step will be testing even lower doses in human clinical trials to find the “therapeutic sweet spot for humans,” says Dubal. “Perhaps brain health needs a boost rather than a superdose.”
But Klotho is a big mystery: Nobody knows exactly how it affects the brain. “It’s a complete black box,” says Verdin. Researchers think the protein must protect the brain in some way — but how? It does not appear to cross the blood-brain barrier, the semi-permeable barrier of blood vessels and tissues that keeps many harmful substances out of the brain.
Given that Klotho’s cognitive effects long outlive its presence in the body, Dubal suspects that it must be affecting the connections between neurons in the brain, possibly “remodeling the synapse to better receive and retain memories.” she says. Her research group is currently working to understand how Klotho gets into the brain and what it does once it gets there.