In the near future, it could be possible to give a 75-year-old the vitality and health of a 50-year-old. It could be possible, even, to reverse the effects of diabetes, kidney failure and other age-related diseases, all thanks to a drug that has the potential to slow the aging process.
Developed by Japanese scientists and tested in animal models in collaboration with Northwestern Medicine scientists, this drug blocks the activity of a protein called plasminogen activator inhibitor-1 (PAI-1), which is overexpressed in many diseases including metabolic syndromes, blood disorders and cardiovascular diseases.
“We are particularly interested in applying drugs to groups of patients that age rapidly, such as people with chronic kidney disease,” says Douglas Vaughan, MD, chair of the Department of Medicine. “A 25-year-old that goes on dialysis has the cardiovascular risk of a 75-year-old. We really don’t have any good therapies to slow down cardiovascular disease in that population.”
Other patients, including those with HIV infections and diabetes, also suffer from accelerated aging and could benefit from a drug like the PAI-1 antagonist.
Vaughan and his group have studied PAI-1 and its role in cardiovascular disease for nearly 30 years. Through their experiments, they observed that PAI-1 is created as cells age, during a biological process called senescence.
Before joining Northwestern in 2008, Vaughan’s lab at Vanderbilt University Medical Center created a transgenic mouse model that overexpressed human PAI-1. The mice expressed an accelerated aging phenotype with features such as baldness and were prone to heart attacks at an early age.
“Surprising to us, the mouse not only had clogged arteries but also a number of other phenotypes,” said Mesut Eren, PhD, research assistant professor of Medicine in the Division of Cardiology, who developed the mouse model. “The most striking was hair loss; as the mice grow old, they become almost totally nude. They also develop huge spleens and livers and build up amyloid, which is the same protein that can cause Alzheimer’s disease. These are all characteristics of mammals as they age.”
“It made us think PAI-1 might be related to aging,” sums up Vaughan.
With a variety of mouse lines available with rapid aging phenotypes, Vaughan decided to test another hypothesis: that PAI-1 contributes to the aging of a mouse model with a deficiency in another protein known as Klotho. These mice have a short lifespan, arteriosclerosis and emphysema.
“We asked the question: If you take PAI-1 out of the Klotho-deficient mice, what happens?” Vaughan recounts.
The study found that when PAI-1 was either completely or partially taken out of the Klotho-deficient mice, the mice had a prolonged lifespan. In addition, their cells had delayed senescence and their organs were protected. The results, published in a paper in the Proceedings of the National Academy of Sciences, also showed that Klotho-deficient mice treated with the protein antagonist drug had the same results as the genetically deficient PAI-1 mice.
Meanwhile, collaborator Toshio Miyata, a professor at Tohoku University in Japan, was interested as a nephrologist in PAI-1 because of its role in diabetic kidney disease. Miyata screened potential inhibitors of PAI-1 and came up with a group of compounds that block PAI-1 but leave other proteins alone. When he heard about Vaughan’s mouse model that overexpressed the human form of PAI-1, he asked to test it.
Vaughan admits, “I wasn’t overly enthusiastic to test the drug because we had tested other inhibitors developed by pharmaceutical companies over the years and nothing had worked very well. But he sent us the drug, we fed it to the mice and they started growing hair — it reversed their baldness phenotype. The drug really worked.”
“We were always interested in a molecule that can inhibit PAI-1, but because of the structure of PAI-1 it’s difficult to effectively inhibit it,” Eren said. “We’ve worked with several inhibitors and the best so far was the one discovered by Dr. Miyata at Tohoku University. When I feed the inhibitor to the Klotho mice, they live longer and their blood chemistry improves significantly. This has been a starting point for the lab to focus on various aspects of senescence and aging.”
To date, the team has published more than a dozen papers testing the drug in a variety of ways, creating a clinical portfolio to test in human populations.
“We hope that taking a drug like this will prolong the health span of people, make them functionally healthy for longer,” Vaughan says.
A MUTATION IN A SMALL POPULATION
An Amish population in Berne, Indiana, is the only known human population in the world that has a PAI-1 deficiency. Intrigued to learn if the carriers of this mutation are protected from biological aging, Vaughan partnered with Amy Shapiro, MD, a pediatric hematologist-oncologist who has studied this community since the early 1990s.
While studying blood coagulation disorders, Shapiro discovered the PAI-1 deficiency in a young woman in this Amish population. With collaborators from the University of Michigan, she found the gene mutation involved an insertion of two base pairs, creating a premature stop codon in the PAI-1 gene. Originally from Switzerland, this group of Amish people has a mutation in PAI-1 that’s been handed down through generations.
“I read about this Amish population in 1992 in the New England Journal of Medicine and dreamed for a long time of studying them,” Vaughan says. “But I didn’t have a hypothesis to test. Then as we developed the aging study more, we found the effects of PAI-1 deficiency on aging in the Klotho-deficient mice and wanted to learn if these Amish people would be protected from aging.”
Funded by a National Institutes of Health grant, Vaughan and Shapiro visited members of this Amish community and assessed them over two days. They measured blood pressure, did echocardiograms and took blood samples. Vaughan estimates there are at least 115 carriers of the mutant gene and at least 10 that are homozygous (have two copies) for the PAI-1 deficiency.
The results of the study, to be published in an upcoming paper, suggest that Vaughan’s hypothesis is correct. The carriers of the mutant gene exhibit protection from aging and don’t have the bleeding disorder.
Other aging studies — working with everything from worm to mouse models — have also found that insulin and insulin-like growth factors have a role in the aging process. The carriers of the mutant PAI-1 gene also have a significantly lower level of insulin, just as one would predict if they are protected from aging, Vaughan added.
“We have data at the cellular level that PAI-1 is involved in senescence and data from mouse models that PAI-1 contributes to age-related changes, and now we have data from human beings that are PAI-1 deficient,” Vaughan.
NEW CLASS OF DRUGS AND THE FUTURE
Interest in longevity research continues to grow. A program at the National Institute on Aging is currently testing the PAI-1 antagonist drug to see if it will prolong the lifespan of healthy “normal” mice. Two other drugs that appear to have an effect on lifespan that have gone through the program include metformin, a diabetes drug, and rapamycin, an immunosuppressant. This past spring, metformin was FDA approved to undergo clinical trials in humans to find out if it can protect against aging diseases.
“There are a lot of people thinking about ways to prolong lifespan in people,” Vaughan says. “We think eventually a PAI-1 antagonist will be part of a group of interventions that a healthy person might have as part of a combined therapy to slow the aging process.”
As part of this surge in research, Vaughan is competing for $1 million against nearly 30 teams for the Palo Alto Longevity Prize, founded by Joon Yun, MD, a radiologist and president of Palo Alto Investors. While the teams are taking different approaches to delay aging, they have a common goal to identify a therapy intervention that either increases the lifespan of mice or reverses cardiovascular aging in mice. Vaughan believes his chances to win are good, if the results from the National Institute on Aging program are positive.
Vaughan and his team have plans for future studies exploring how the PAI-1 antagonist drug could work as a topical treatment for hair growth, to help people with diabetes and obesity, and even to prolong the lifespan of dogs.
“We are continuing to discover new functions for PAI-1,” Eren says. “Aging and hair loss are exciting new frontiers in the PAI-1 field.”
In Japan, the drug has gone through phase I clinical trials and is starting phase II studies. Vaughan says his group is working to facilitate early-phase testing in the United States.
“There isn’t a lot of enthusiasm for living longer if you are ravaged by diseases, but I think a lot of people would be interested in living longer if they could maintain their vitality and vigor,” he says. “If we can extend that healthy lifespan, it could have positive effects on our culture, economy and way of life.”