A common antibiotic could be used to treat – or even prevent – post-traumatic stress disorder (PTSD), according to new research.
Scientists at UCL, England, and the University of Zurich, Switzerland, say that their placebo-controlled, double-blind randomised controlled trial found that doxycycline can disrupt the formation of negative associations in the brain.
The study, published in Molecular Psychiatry, involved 76 healthy volunteers, who were given either doxycycline or a placebo and learned to associate a certain colour with an electric shock in the first session in the trial.
The following week, they were shown the colours again, but this time it was accompanied by a loud sound but no shocks.
Their fear responses were measured and the researchers found that the fear response was 60% lower in participants who had doxycycline in the first session compared to those who had the placebo.
This suggested that the drug significantly suppressed fear memory. Other cognitive measures including sensory memory and attention were not affected.
Lead author Professor Dominik Bach said: “When we talk about reducing fear memory, we are not talking about deleting the memory of what actually happened.
"The participants may not forget that they received a shock when the screen was red, but they ‘forget’ to be instinctively scared when they next see a red screen. Learning to fear threats is an important ability for any organism, helping us to avoid dangers such as predators. Over-prediction of threat, however, can cause tremendous suffering and distress in anxiety disorders such as PTSD."
Professor Bach said the team had demonstrated a proof-of-principle for a new treatment strategy for PTSD.
"The theory is based on the recent discovery that our brains need proteins outside nerve cells, called matrix enzymes, to form memories,” he said.
“Matrix enzymes are found throughout the body, and their over-activity is involved in certain immune diseases and cancers. To treat such diseases, we already have clinically approved drugs that block these enzymes, including the antibiotic doxycycline, so we wanted to see if they could help to prevent fear memories from forming in the brain.
“Our results support this theory, opening up an exciting avenue of research that might help us to find treatments for PTSD.”
He admitted that using drugs to prevent PTSD would be challenging, but growing evidence of ‘reconsolidation’ – a change of people’s memories and associations after the event when they experience or imagine similar situations – offers an avenue for the testing of doxycycline.
Bach et al. Blocking human fear memory with the matrix metalloproteinase inhibitor doxycycline. Molecular Psychiatry. April 2017; doi: 10.1038/mp.2017.65. [abstract]
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