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Dec. 6 (UPI) -- The erectile dysfunction drug sildenafil -- better known as the brand name Viagra -- may help prevent and treat Alzheimer's disease, a study published Monday by Nature Aging found. In addition, a separate study, also published Monday, indicated that cataract surgery may lower the risk for developing dementia, researchers said.
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Taken collectively, the findings offer positive insight into the potential prevention and treatment of the condition, for which there is no cure, they said.
In an analysis on data for more than 7 million patients, sildenafil, which also is used to resolve high blood pressure in the arteries of the lungs, appears to reduce the risk for the most common form of dementia by 69% compared with other drugs, the data showed.
However, because the results come from computational modeling based on cases of Alzheimer's disease among users of the drug, they will need to be confirmed in clinical trials to test its effectiveness, according to the study authors.
"We found that sildenafil use reduced the likelihood of Alzheimer's in individuals with coronary artery disease, hypertension and Type 2 diabetes," study co-author Feixiong Cheng said in a press release.
"All of [these conditions] are comorbidities significantly associated with risk of the diseases," said Cheng, a researcher in the Cleveland Clinic Genomic Medicine Institute in Ohio.
Sildenafil also reduced the risk for Alzheimer's in people without these comorbidities, which are underlying health conditions that are often associated with other diseases, he said.
More than 6 million people in the United States have been diagnosed with dementia, of which Alzheimer's disease is the most common form, according to data from the Alzheimer's Association.
Alzheimer's is expected to be more than twice as common nationally by 2050, affecting nearly 14 million people, the association estimates.
Drug repurposing -- or using existing drugs currently approved by the Food and Drug Administration for other purposes -- offers a less expensive alternative to the costly and time-consuming process of research and development, Cheng and his colleagues said.
Alzheimer's is caused by the buildup of beta amyloid and tau proteins in the brain, research suggests.
However, no FDA-approved, anti-amyloid or anti-tau drugs are approved for use in the prevention or treatment of Alzheimer's, and many clinical trials for such treatments have failed to produce positive results.
For this study, Cheng and his colleagues hypothesized that drugs that target the "interplay" between these two proteins, such as sildenafil, might "have the greatest potential for success" in preventing the disease.
The researchers analyzed insurance claims data for more than 7 million people in the United States to examine the relationship between sildenafil and Alzheimer's disease outcomes by comparing sildenafil users to non-users in rates of dementia diagnosis, they said.
The analysis included patients who used comparator drugs the either were in an active Alzheimer's clinical trial, such as losartan or metformin, or not yet reported as relevant to the disease, including diltiazem or glimepiride, the researchers said.
Sildenafil users were 69% less likely to develop Alzheimer's disease compared to non-users of the drug, the data showed.
Taking the drug also reduced a person's risk for the disease by 55% compared to losartan, 63% compared to metformin, 65% compared to diltiazem and 64% compared to glimepiride, the researchers said.
To further explore sildenafil's effect on Alzheimer's disease, the researchers said they developed a patient-derived brain cell model of the disease using stem cells.
In the model, sildenafil increased brain cell growth and decreased the activity of tau proteins, which may be how the drug influences disease-related brain changes, according to the researchers.
"Sildenafil, which has been shown to significantly improve cognition and memory in preclinical models, presented as the best drug candidate," Cheng said in a press release.
However, "because our findings only establish an association between sildenafil use and reduced incidence of Alzheimer's disease, we are now planning a mechanistic trial and a phase II randomized clinical trial to test causality and confirm [the drug's] clinical benefits," he said.
"This sildenafil research is an exciting illustration of the promise of repurposing existing drugs to treat Alzheimer's," Dr. Howard Fillit, founding executive director of the Alzheimer's Drug Discovery Foundation, said in a statement.
"Exploring FDA-approved drugs, which have already been proved safe, can fast-track the development of Alzheimer's drugs, [and] we will conquer Alzheimer's through the kind of combination therapies and precision medicine that has been effective in treating cancer," he said.
Meanwhile, a separate analysis, published Monday by JAMA Internal Medicine, found that surgery to repair cataracts, an eye condition that is common in older adults, may reduce a person's risk for all forms of dementia, including Alzheimer's.
In the study, researchers tracked participants diagnosed with a cataract or glaucoma, both of which cause vision loss, but who did not have dementia at the time they volunteered for the study, they said.
Participants were evaluated every two years for cognitive abilities based on the Cognitive Abilities Screening Instrument, a commonly used test for cognitive function, and those who achieved lower scores underwent neurological exams, the researchers said.
In more than 3,000 participants 65 years old and older, 853 developed dementia, with 709 cases of Alzheimer's disease, the data showed.
Approximately half of the participants had cataract surgery, and those who had the procedure in either eye were about 30% less likely to develop any form of dementia over at least the next 10 years, the researchers said.
Vision loss has been associated with an increased risk for all forms of dementia, due at least in part to its effect on independence and quality of life, so surgery to correct it may help keep older adults active and mentally engaged, according to the researchers.
In addition, "cells in the retina are associated with cognition and regulate sleep cycles, and these cells respond well to blue light," which is blocked by cataracts, study co-author Dr. Cecilia S Lee said in a press release.
Still, the way in which cataract surgery lowers dementia risk was not determined in this study, said Lee, chair of the department of ophthalmology at the University of Washington in Seattle.
"Innovative research like this cataract study is helping to uncover how age-related changes in our senses contribute to dementia," said the Alzheimer's Drug Discovery Foundation's Fillit, who was not part of either study.
"In this case, we believe post-cataract surgery patients benefit from a higher quantity of sensory input, or an increase in blue light that may stimulate cells in the retina associated with cognition and sleep cycles," he said.
