The treatment of depression faces two main challenges. The first is that almost 50% of patients do not respond well to existing antidepressants. The second is that conventional drugs take relatively long – about three to five weeks – to have the desired effect. A group of researchers affiliated with the University of São Paulo (USP) in Brazil set out to address the second problem using epigenetic modulators to try to “erase” the consequences of stress. Epigenetic mechanisms are part of a complex system that controls how and when genes are turned on or off.
Exposure to stress, a key factor in depression, alters certain epigenetic markers in the brain. Many of these changes occur in genes associated with neuroplasticity, the brain’s ability to change in response to experience. Stress increases DNA methylation in these genes.
DNA methylation is a chromatin remodeling process that regulates gene expression by recruiting proteins involved in gene repression or by inhibiting the binding of transcription factors to DNA. Most existing antidepressants are designed to reduce this process.
The team led by Sâmia Joca, a professor at USP and the University of Aarhus in Denmark, decided to conduct an in-depth investigation into the action of BDNF (brain-derived neurotrophic factor), a nervous system protein with well-documented effects on regulating neuronal plasticity.
“Stress reduces BDNF expression and, as shown in the literature, antidepressants have no effect if BDNF signaling is blocked. That’s why we focused on BDNF,” said Joca, who is affiliated with the School’s Biomolecular Sciences Department. of Pharmaceutical Ribeirão Preto of USP. Sciences (FCFRP).
The group tested the hypothesis that stress increases the methylation of the BDNF gene, reducing its expression, and that this reduction is related to depressive behavior. “Our starting point was this: if we administered a genetic modulator that inhibits DNA methylation, the process would not happen, BDNF levels would be normal and there would be an antidepressant effect,” Joca said. “If the antidepressant effect is really related to the normalization of the methylation profile, so conventional drugs need time to function, because it takes time to eliminate stress-induced changes, we imagined that the direct modulation of these mechanisms epigenetics would produce the rapid effect. I found that to be the case. “
They report the results in a journal article Molecular neurobiology. The first author is Amanda Juliana Sales, who was supported by FAPESP. The other authors are Izaque S. Maciel and Angélica Suavinha, researchers supervised by the last author Joca and also supported by FAPESP.
We tested two drugs, one of which is used to treat cancer (gliomas). The other is completely experimental. It is important to note that these drugs cannot be used to treat depression, because if they reduce DNA methylation without restrictions, they will increase the expression of more genes than just the gene we are interested in. So there will be side effects. The findings do not point to prospects for new antidepressants, but to an interesting angle from which to develop new treatments. “
Sâmia Joca, professor at USP and the University of Aarhus
Behavior
According to Joca, in order to test the hypothesis that direct modulation of epigenetic mechanisms would work faster, it was necessary to use (and validate) a model that clearly distinguishes between chronic and acute treatment. The scientists first validated a model of stress-induced depression in rats treated with well-known conventional drugs. In this model, called “learning disability”, the rats were exposed to inevitable stress, followed seven days later by a situation in which it was possible to avoid stress by moving to the other side of the room where they were.
The results showed a greater number of failures in learning this avoidance behavior in stressed animals than in non-stressed animals, which was to be expected. This trend was attenuated by chronic treatment with conventional antidepressants and acute treatment with epigenetic modulators.
“What we call learning disability in this model is similar to depression in people, with the feeling that the person can do nothing to improve the situation,” said Joca. “The model was validated and showed that when treated continuously with antidepressants, the animals returned to normal and resembled animals not stressed in behavioral terms. However, this only happened if they were treated repeatedly. The same is true. also applies to depressed people who need to take the medicine continuously. There is no acute effect of a single dose. “
The forced swimming test was also used to stress rats, whose behavior was observed after 24 hours. And in this case, conventional drugs have reduced the level of stress-induced depression. After validating the model, the researchers performed another series of experiments in which it was found that epigenetic modulators have an antidepressant effect.
Check the reliability again
The team tested two different drugs as modulators, 5-AzaD and RG108. Both inhibit the enzyme responsible for DNA methylation, “but are not chemically bound,” Joca explained. “We wanted to avoid the possibility that the effect was due to a non-specific mechanism of one of the drugs. So I used completely different drugs and got the same result. We measured the effect at two different times, shortly after the inevitable stress in one group and before the impotence test in the other. We noticed a rapid antidepressant effect in both cases. “
The next step was a molecular analysis of 5-AzaD to produce a methylation profile of the gene of interest. “We found that stress did indeed increase the methylation of BDNF, as well as TrkB, another protein in the nervous system, and this was moderately attenuated by our treatments,” Joca said.
Because the change was very subtle, the researchers decided to analyze the reliability of the retest. “Using a different model, we reproduced the results of the forced swimming test and injected the drug systemically, while administering a BDNF signaling inhibitor to the cortex. This had no antidepressant effect,” Joca said.
The study was a continuation of the work that Joca and her team have been carrying out for several years. “In 2010, I published an article showing that these drugs had an antidepressant effect. Not long after, I published another article showing that antidepressant treatment modulated DNA methylation. The interesting point in this latest study was the production of “This is the first time that epigenetic modulators have been shown to have a rapid antidepressant effect,” said Joca.
Sales continued his postdoctoral research with a FAPESP scholarship and is currently working under the leadership of Francisco Silveira Guimarães, a professor at USP’s Ribeirão Preto Medical School (FMRP).