A new study published in the journal Nature Aging has identified an association between using Viagra, a popular erectile dysfunction drug, and reduced instances of Alzheimer’s disease. This is not the first time a beneficial link between Viagra and Alzheimer’s has been proposed but clinical trials will be necessary to explore causality.
The new research, led by Feixong Cheng from the Cleveland Clinic’s Genomic Medicine Unit, didn’t set out to investigate Viagra specifically. Instead, the primary purpose of the work was to establish a new methodology for screening pre-existing drugs to treat Alzheimer’s disease. Cheng’s team focused not solely on a drug’s potential to interact with the toxic amyloid and tau proteins generally associated with Alzheimer’s but the larger networks of genes and proteins known to be linked with the disease.
“Recent studies show that the interplay between amyloid and tau is a greater contributor to Alzheimer’s than either by itself,” says Cheng. “Therefore, we hypothesized that drugs targeting the molecular network intersection of amyloid and tau endophenotypes should have the greatest potential for success.”
Over 1,600 FDA-approved drugs were screened and sildenafil (commonly known as Viagra) stood out as the best potential candidate. The researchers then looked at health insurance data from over seven million people to determine any real-world association between Viagra use and lower rates of Alzheimer’s disease.
Strikingly, the analysis revealed Viagra users were 69 percent less likely to develop Alzheimer’s disease compared to those not taking Viagra. In subsequent stem cell lab studies the researchers found Viagra can increase brain cell growth and reduce certain pathological signs of Alzheimer’s.
This research is not the first to indicate Viagra could be repurposed as a treatment for Alzheimer’s. A compelling study last year from Harvard University researchers offered plausible evidence indicating the drug can reduce accumulation of the toxic proteins associated with the disease.
Catherine Hall, from the University of Sussex, says this new study is certainly interesting but it is unclear how Viagra could specifically become an Alzheimer’s treatment in its current form. Hall suggests these research findings may be better utilized as inspiration for developing new treatments since it seems unlikely Viagra could be deployed as a daily Alzheimer’s preventative medication.
“Is it feasible to treat everyone with sildenafil for years before they are likely to develop Alzheimer’s disease, or would this cause more problems than it solves?” Hall asks. “It might it be better to study the pathway by which these beneficial effects of sildenafil are being mediated and then encourage lifestyle factors (e.g. exercise) that can be shown to reduce risk in the same way.”
Other researchers question whether this study is detecting a real causal link between Viagra use and Alzheimer’s. Tara Spires-Jones, from the University of Edinburgh, says Alzheimer’s disease is known to reduce a person’s sex drive. So it is possible in the early stages of disease, with a waning libido, one would be less likely to even seek out prescriptions for erectile dysfunction.
Jack Auty from the University of Tasmania, echoes this limitation, pointing out a large array of lifestyle variables could explain the link between Viagra and lower rates of Alzheimers, despite the hypothetical mechanism proposed by the new study.
“For example, walking slower has been associated with increased risk of a dementia diagnosis,” says Auty. “Not because walking faster prevents dementia, it is because walking speed correlates with health. Now replace walking with sex life. Previous research has shown that people with the early signs of Alzheimer’s disease are, on average, less sexually active. So sildenafil use could be a spurious correlation – aka a red herring.”
Cheng is realistic about the limitations in his team’s study. He proposes further clinical work will better investigate whether there is a causal relationship between Viagra and Alzheimer’s. But also, the novel methodology for screening pre-existing drugs developed in the research will be applied to other brain diseases.
“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 sildenafil’s clinical benefits for Alzheimer’s patients,” adds Cheng. “We also foresee our approach being applied to other neurodegenerative diseases, including Parkinson’s disease and amyotrophic lateral sclerosis, to accelerate the drug discovery process.”
The new study was published in the journal Nature Aging.
Source: Cleveland Clinic
