Allopregnanolone (Allo) is an experimental treatment for Alzheimer’s disease that is being developed by Roberta Diaz Brinton, PhD, of the University of Arizona, the University of Southern California, and the National Institute on Aging. Allopregnanolone is a neurosteroid that may help generate new brain cells.

How allopregnanolone works

The exact cause of Alzheimer’s disease is unknown, but the disease leads to the death of brain cells and decreased connectivity between them. It is believed that this may be due to the accumulation of certain proteins in the brain. One of these proteins is beta-amyloid, which forms clumps called plaques.

Allopregnanolone is formed naturally in the brain when the hormone progesterone is broken down. Both women and men produce progesterone and allopregnanolone. A study has shown that Alzheimer’s patients have lower levels of allopregnanolone in their brains compared to people with healthy brains.

In mice, allopregnanolone has been shown to increase the generation of new brain cells from neural stem cells, reduce the formation of beta-amyloid plaques, and improve cognitive function. It is hoped that allopregnanolone can also help reverse the effects of Alzheimer’s.

Allopregnanolone in clinical trials

A small Phase 1 clinical trial (NCT02221622) evaluated the safety and tolerability of allopregnanolone in mild cognitive impairment and early Alzheimer’s disease. The primary goal of the study was to determine the maximum tolerated dose of allopregnanolone. Twenty-four participants received one of three intravenous doses of allopregnanolone or a placebo. Vital signs, adverse events, and brain MRI were measured over 16 weeks. The trial finished in February of 2018 but results have not been posted.

Brinton is preparing to start a larger, Phase 2 clinical trial with the support of the Alzheimer’s Drug Discovery Foundation (ADDF).

Another Phase 1 clinical trial (NCT03748303) has been listed but is not currently recruiting participants. The study is designed to test the safety, tolerability, and pharmacokinetics (how the drug moves through the body) of intramuscular administration of allopregnanolone as opposed to the intravenous method that was used in the prior study. When the trial begins, it will enroll 12 participants with mild Alzheimer’s disease (half male and half female) who will receive allopregnanolone intramuscularly instead of intravenously. Participant dosages will be adjusted for the first 4 weeks of the study to determine a maintenance dosage and then will continue for a total of 12 weeks. The primary outcomes of the study are related to the safety and tolerability of the treatment. Additional outcomes are the pharmacokinetics and changes in cognitive score tests.


Last updated: Aug. 28, 2019


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