By age 60 almost all adults carry herpes simplex virus 1, and more than a quarter of the population is infected with herpes simplex 2 by the time they are 40. One special feature of herpes viruses is their ability to maintain a persistent infection. During a persistent infection, the body’s immune system wasn’t able to completely clear the virus during the primary infection, and the virus continues to exist with, without, or with sporadic symptoms. For most viruses that can cause persistent infection, there are no cures, and while antiviral treatments can help, persistent infections are good at persisting.
A recent study identified a new way to treat HSV-1 in mice. For the herpes virus to go from its latent or hiding phase to its active phase, a few changes need to occur in the genome. The DNA encoding important genes needed to reactivate the virus must be made available for transcription. This usually happen via epigenetic changes meaning that the genome must be unpackaged and made easily accessible to transcription factors. This study wanted to evaluate the effects of tranylcypromine, an antidepressant. Tranylcypromine blocks the enzyme, LSD1, which is an important enzyme involved in opening up the genome. By blocking the activity of LSD1, you are keeping the genome closely packaged and unavailable for transcription. The study determined that by blocking the activity of a key enzyme you are epigenetically inhibiting the reactivation of the herpes simplex virus.
The paper reports that the drug is effective in different animals and at different stages of infection. In herpes keratitis virus infected rabbits, there were less reoccurrences and decreased viral shedding. In guinea pigs infected with genital herpes, there were also less lesion reoccurrences. And in mice that were used as models for herpes transmission at birth, fewer mice died. If this herpes treatment were to carry over to humans, the treatment would be a pure LSD1 blocker as opposed to an antidepressant drug. While this study only looked at animals, its easy to see how this therapy could be applied to humans.