Alzheimer's: Glaucoma drug may help fight dementia

A drug commonly used to treat eye diseases could soon be used to protect against dementia, new research shows. The drug could also hold promise in treating other neurodegenerative diseases, including Huntington's and Parkinson's.

According to the U.S. Centers for Disease Control and Prevention, dementia affects more than 5 million Americans over 65. Dementia comes in different forms – the most common form is Alzheimer's disease – and is characterized by an impairment in the ability to remember, think and make decisions.

Today, there is no known cure for Alzheimer's, although scientists believe the disease is caused by the abnormal buildup of proteins in and around brain cells. A key protein known to accumulate in the brain cells of Alzheimer's patients is called tau.

Now new research from the UK Dementia Research Institute at the University of Cambridge has shown that a drug commonly used to treat glaucoma – an eye disease that causes damage to the optic nerve – can also clear these tau protein clumps.

The drug, called methazolamide, was one of 1,437 clinically approved compounds the researchers tested in zebrafish that were genetically engineered to mimic these protein assemblies.

“Zebrafish offer a much more effective and realistic way to screen drug compounds than using cell cultures, which function very differently than living organisms,” said study co-author Ana Lopez Ramirez of the Cambridge Institute for Medical Research, Department of Physiology, Development and Neuroscience and the UK Dementia Research Institute at the University of Cambridge said in a statement. “They also allow us to do this on a large scale, which is neither feasible nor ethical for larger animals like mice.”

After promising results in zebrafish models, the team tested methazolamide in mice that had in turn been genetically engineered to mimic these tau protein assemblies. “We were excited to see in our mouse studies that methazolamide lowers tau levels in the brain and protects against its further accumulation,” said co-author Dr. Farah Siddiqi, also from the Cambridge Institute for Medical Research and the UK Dementia Research Institute, said in a statement.

How could this drug eliminate these protein clumps?

Methazolamide is a drug known as a carbonic anhydrase inhibitor that stops the activity of an important enzyme involved in regulating acid levels in our cells. This, in turn, forces the cells to “spit out” the tau proteins, almost as if their stomachs were being pumped out.

“Methazolamide is a promising drug that is urgently needed to prevent the formation of dangerous tau proteins in the brain,” Professor David Rubinsztein, another co-author of the study, said in a statement. “Although we have only studied its effects in zebrafish and mice so far, so it is still early days, we at least know the safety profile of this drug in patients. This will allow us to begin clinical trials much more quickly than we would normally expect if we were starting from scratch with an unknown drug substance.”

The study also demonstrates the use of zebrafish to test existing drugs for their ability to clear Alzheimer's-related protein clumps. “This shows how we can use zebrafish to test whether existing drugs could be used to combat various diseases, potentially significantly speeding up the drug development process,” Rubinsztein said.

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Lopez, A & Siddiqi, FH et al. Inhibition of carbonic anhydrase improves tau toxicity by increasing tau secretion. Nat Chem Bio; Oct. 31, 2024; DOI: 10.1038/s41589-024-01762-7