Abnormal levels of stress hormones such as adrenaline and cortisol are linked to a variety of mental health disorders, including depression and posttraumatic stress disorder (PTSD). MIT researchers have now devised a way to remotely control the release of these hormones from the adrenal gland, using magnetic nanoparticles.
This approach could help scientists to learn more about how hormone release influences mental health, and could eventually offer a new way to treat hormone-linked disorders.
To achieve control over hormone release, the MIT team has developed specialized magnetic nanoparticles that can be injected into the adrenal gland. When exposed to a weak magnetic field, the particles heat up slightly, activating heat-responsive channels that trigger hormone release. This technique can be used to stimulate an organ deep in the body with minimal invasiveness.
The research team has previously devised several novel magnetic nanomaterials, including particles that can release drugs at precise times in specific locations in the body.
In the new study, they wanted to explore the idea of treating disorders of the brain by manipulating organs that are outside the central nervous system but influence it through hormone release. One well-known example is the hypothalamic-pituitary-adrenal (HPA) axis, which regulates stress response in mammals. Hormones secreted by the adrenal gland, including cortisol and adrenaline, play important roles in depression, stress, and anxiety.
As a target to stimulate hormone release, the researchers decided on ion channels that control the flow of calcium into adrenal cells. Those ion channels can be activated by a variety of stimuli, including heat. When calcium flows through the open channels into adrenal cells, the cells begin pumping out hormones.
To stimulate these heat-sensitive channels, which naturally occur in adrenal cells, the researchers designed nanoparticles made of magnetite, a type of iron oxide that forms tiny magnetic crystals about 1/5000 the thickness of a human hair. In rats, they found these particles could be injected directly into the adrenal glands and remain there for at least six months. When the rats were exposed to a weak magnetic field — about 50 millitesla, 100 times weaker than the fields used for magnetic resonance imaging (MRI) — the particles heated up by about 6 degrees Celsius, enough to trigger the calcium channels to open without damaging any surrounding tissue.
The heat-sensitive channel that they targeted, known as TRPV1, is found in many sensory neurons throughout the body, including pain receptors. TRPV1 channels can be activated by capsaicin, the organic compound that gives chili peppers their heat, as well as by temperature. They are found across mammalian species, and belong to a family of many other channels that are also sensitive to heat.
This stimulation triggered a hormone rush — doubling cortisol production and boosting noradrenaline by about 25 percent. That led to a measurable increase in the animals’ heart rates.
The researchers now plan to use this approach to study how hormone release affects PTSD and other disorders, and they say that eventually it could be adapted for treating such disorders. This method would offer a much less invasive alternative to potential treatments that involve implanting a medical device to electrically stimulate hormone release, which is not feasible in organs such as the adrenal glands that are soft and highly vascularized
Another area where this strategy could hold promise is in the treatment of pain, because heat-sensitive ion channels are often found in pain receptors.
News Source: MIT
