Author: ketaveradev

Ketamine was once used mainly as an anesthetic on battlefields and in operating rooms. Now this medication is gaining ground as a promising treatment for some cases of major depression, which is the leading cause of disability worldwide. In the US, recent estimates show 16 million adults had an episode of major depression in the course of a year. Suicide rates rose substantially between 1999 and 2016, increasing by more than 30% in 25 states. Because of its rapid action, ketamine could have a role to play in helping to prevent suicide.

Why is ketamine exciting for treating depression?

If a person responds to ketamine, it can rapidly reduce suicidality (life-threatening thoughts and acts) and relieve other serious symptoms of depression. Ketamine also can be effective for treating depression combined with anxiety.

Other treatments for suicidal thoughts and depression often take weeks or even months to take effect, and some people need to try several medications or approaches to gain relief. This is true for talk therapies, antidepressant medicines, transcranial magnetic stimulation (TMS), and electroconvulsive therapy (ECT), which is currently the most effective treatment for major depression that fails to respond to other therapies.

Are there different types of ketamine?

Two main types of ketamine are used to treat major depression that hasn’t responded to two or more medications (treatment-resistant depression).

• Racemic ketamine, which is most often given as an infusion into the bloodstream. This is sometimes called intravenous, or IV, ketamine. It is a mixture of two mirror-image molecules: “R” and “S” ketamine. While it was approved decades ago as an anesthetic by the FDA, it is used off-label to treat depression.
• Esketamine (Spravato), which the FDA approved in March, is given as a nasal spray. It uses only the “S” molecule.

The Food and Drug Administration’s approval in March of a depression treatment based on ketamine generated headlines, in part, because the drug represents a completely new approach for dealing with a condition the World Health Organization has labeled the leading cause of disability worldwide. The FDA’s approval marks the first genuinely new type of psychiatric drug—for any condition—to be brought to market in more than 30 years.

Although better known as a party drug, the anesthetic ketamine has spurred excitement in psychiatry for almost 20 years, since researchers first showed that it alleviated depression in a matter of hours. The rapid reversal of symptoms contrasted sharply with the existing set of antidepressants, which take weeks to begin working. Subsequent studies have shown ketamine works for patients who have failed to respond to multiple other treatments, and so are deemed “treatment-resistant.”

Despite this excitement, researchers still don’t know exactly how ketamine exerts its effects. A leading theory proposes that it stimulates regrowth of synapses (connections between neurons), effectively rewiring the brain. Researchers have seen these effects in animals’ brains, but the exact details and timing are elusive.

A new study, from a team led by neuroscientist and psychiatrist Conor Liston at Weill Cornell Medicine, has confirmed that synapse growth is involved, but not in the way many researchers were expecting. Using cutting-edge technology to visualize and manipulate the brains of stressed mice, the study reveals how ketamine first induces changes in brain circuit function, improving “depressed” mice’s behavior within three hours, and only later stimulating regrowth of synapses.

As well as shedding new light on the biology underlying depression, the work suggests new avenues for exploring how to sustain antidepressant effects over the long term. “It’s a remarkable engineering feat, where they were able to visualize changes in neural circuits over time, corresponding with behavioral effects of ketamine,” says Carlos Zarate, chief of the Experimental Therapeutics and Pathophysiology Branch at the National Institute of Mental Health, who was not involved in the study. “This work will likely set a path for what treatments should be doing before we move them into the clinic.”

Another reason ketamine has researchers excited is that it works differently than existing antidepressants. Rather than affecting one of the “monoamine” neurotransmitters (serotonin, norepinephrine and dopamine), as standard antidepressants do, it acts on glutamate, the most common chemical messenger in the brain. Glutamate plays an important role in the changes synapses undergo in response to experiences that underlie learning and memory. That is why researchers suspected such “neuroplasticity” would lie at the heart of ketamine’s antidepressant effects.

Ketamine’s main drawback is its side effects, which include out-of-body experiences, addiction and bladder problems. It is also not a “cure.” The majority of recipients who have severe, difficult-to-treat depression will ultimately relapse. A course of multiple doses typically wears off within a few weeks to months. Little is known about the biology underlying depressive states, remission and relapse. “A big question in the field concerns the mechanisms that mediate transitions between depression states over time,” Liston says. “We were trying to get a better handle on that in the hopes we might be able to figure out better ways of preventing depression and sustaining recovery.”

Chronic stress depletes synapses in certain brain regions, notably the medial prefrontal cortex (mPFC), an area implicated in multiple aspects of depression. Mice subjected to stress display depressionlike behaviors, and with antidepressant treatment, they often improve. In the new study, the researchers used light microscopes to observe tiny structures called spines located on dendrites (a neuron’s “input” wires) in the mPFC of stressed mice. Spines play a key role because they form synapses if they survive for more than a few days.

For the experiment, some mice became stressed when repeatedly restrained, others became so after they were administered the stress hormone corticosterone. “That’s a strength of this study,” says neuroscientist Anna Beyeler, of the University of Bordeaux, France, who was not involved in the work, but wrote an accompanying commentary article in Science. “If you’re able to observe the same effects in two different models, this really strengthens the findings.” The team first observed the effects of subjecting mice to stress for 21 days, confirming that this resulted in lost spines. The losses were not random, but clustered on certain dendrite branches, suggesting the damage targets specific brain circuits.

The researchers then looked a day after administering ketamine and found that the number of spines increased. Just over half appeared in the same location as spines that were previously lost, suggesting a partial reversal of stress-induced damage. Depressionlike behaviors caused by the stress also improved. The team measured brain circuit function in the mPFC, also impaired by stress, by calculating the degree to which activity in cells was coordinated, a measure researchers term “functional connectivity.” This too improved with ketamine.

When the team looked closely at the timing of all this, they found that improvements in behavior and circuit function both occurred within three hours, but new spines were not seen until 12 to 24 hours after treatment. This suggests that the formation of new synapses is a consequence, rather than cause, of improved circuit function. Yet they also saw that mice who regrew more spines after treatment performed better two to seven days later. “These findings suggest that increased ensemble activity contributes to the rapid effects of ketamine, while increased spine formation contributes to the sustained antidepressant actions of ketamine,” says neuroscientist Ronald Duman, of the Yale School of Medicine, who was not involved in the study. Although the molecular details of what happens in the first hours are not yet fully understood, it seems a restoration of coordinated circuit activity occurs first; this is then entrenched by neuroplasticity effects in synapses, which then maintain behavioral benefits over time.

To prove that new synapses were a cause of antidepressant effects, rather than just coinciding with the improved behaviors, the team used a newly developed optogenetic technique, which allowed them to eliminate newly formed spines using light. Optogenetics works by introducing viruses that genetically target cells, causing them to produce light-sensitive proteins. In this case, the protein is expressed in newly formed synapses, and exposure to blue light causes the synapse to collapse. The researchers found that eliminating newly formed synapses in ketamine-treated mice abolished some of the drug’s positive effects, two days after treatment, confirming that new synapses are needed to maintain benefits. “Many mechanisms are surely involved in determining why some people relapse and some don’t,” Liston says, “ but we think our work shows that one of those involves the durability of these new synapses that form.”

And Liston adds: “Our findings open up new avenues for research, suggesting that interventions aimed at enhancing the survival of these new synapses might be useful for extending ketamine’s antidepressant effects.” The implication is that targeting newly formed spines might be useful for maintaining remission after ketamine treatment. “This is a great question and one the field has been considering,” Duman says. “This could include other drugs that target stabilization of spines, or behavioral therapies designed to engage the new synapses and circuits, thereby strengthening them.”

The study used three behavioral tests: one involving exploration, a second a struggle to escape, and a third an assessment of how keen the mice are on a sugar solution. This last test is designed to measure anhedonia—a symptom of depression in which the ability to experience pleasure is lost. This test was unaffected by deleting newly formed spines, suggesting that the formation of new synapses in the mPFC is important for some symptoms, such as apathy, but not others (anhedonia)—and that different aspects of depression involve a variety of brain circuits.

These results could relate to a study published last year that found activity in another brain region, the lateral habenula, is crucially involved in anhedonia, and injecting ketamine directly into this region improves anhedonia-related behavior in mice. “We’re slowly identifying specific regions associated with specific behaviors,” Beyeler says. “The factors leading to depression might be different depending on the individual, so these different models might provide information regarding the causes of depression.”

One caveat is that the study looked at only a single dose, rather than the multiple doses involved in a course of human treatment, Zarate says. After weeks of repeated treatments, might the spines remain, despite a relapse, or might they dwindle, despite the mice still doing well? “Ongoing effects with repeated administration, we don’t know,” Zarate says. “Some of that work will start taking off now, and we’ll learn a lot more.” Of course, the main caution is that stressed mice are quite far from humans with depression. “There’s no real way to measure synaptic plasticity in people, so it’s going to be hard to confirm these findings in humans,” Beyeler says.

On March 5, the Food and Drug Administration (FDA) approved the first truly new medication for major depression in decades. The drug is a nasal spray called esketamine, derived from ketamine—an anesthetic that has made waves for its surprising antidepressant effect.  

Because treatment with esketamine might be so helpful to patients with treatment-resistant depression (meaning standard treatments had not helped them), the FDA expedited the approval process to make it more quickly available. In one study, 70 percent of patients with treatment-resistant depression who were started on an oral antidepressant and intranasal esketamine improved, compared to just over half in the group that did not receive the medication (called the placebo group).  

“This is a game changer,” says John Krystal, MD, chief psychiatrist at Yale Medicine and one of the pioneers of ketamine research in the country. The drug works differently than those used previously, he notes, calling ketamine “the anti-medication” medication. “With most medications, like valium, the anti-anxiety effect you get only lasts when it is in your system. When the valium goes away, you can get rebound anxiety. When you take ketamine, it triggers reactions in your cortex that enable brain connections to regrow. It’s the reaction to ketamine, not the presence of ketamine in the body that constitutes its effects,” he says.  

And this is exactly what makes ketamine unique as an antidepressant, says Dr. Krystal.  

However, as the nasal spray becomes available via prescription, patients have questions: How does it work? Is it safe? And who should get it? Read on for answers.  

How do antidepressants work?

Research into ketamine as an antidepressant began in the 1990s with Dr. Krystal and his colleagues Dennis Charney, MD, and Ronald Duman, PhD, at the Yale School of Medicine. At the time (as is still mostly true today) depression was considered a “black box” disease, meaning that little was known about its cause.  

One popular theory was the serotonin hypothesis, which asserted that people with depression had low levels of a neurotransmitter called serotonin. This hypothesis came about by accident—certain drugs given to treat other diseases like high blood pressure and tuberculosis seemed to drastically affect people’s moods. Those that lowered serotonin levels caused depression-like symptoms; others that raised serotonin levels created euphoric-like feelings in depressed patients. This discovery ushered in a new class of drugs meant to treat depression, known as selective serotonin reuptake inhibitors (SSRIs). The first one developed for the mass market was Prozac.  

But eventually it became clear that the serotonin hypothesis didn’t fully explain depression. Not only were SSRIs of limited help to more than one-third of people given them for depression, but growing research showed that the neurotransmitters these drugs target (like serotonin) account for less than 20 percent of the neurotransmitters in a person’s brain. The other 80 percent are neurotransmitters called GABA and glutamate.  

GABA and glutamate were known to play a role in seizure disorders and schizophrenia. Together, the two neurotransmitters form a complex push-and-pull response, sparking and stopping electrical activity in the brain. Researchers believe they may be responsible for regulating the majority of brain activity, including mood.  

What’s more, intense stress can alter glutamate signaling in the brain and have effects on the neurons that make them less adaptable and less able to communicate with other neurons.

This means stress and depression themselves make it harder to deal with negative events, a cycle that can make matters even worse for people struggling with difficult life events.  

Ketamine—from anesthetic to depression “miracle drug”

Interestingly, studies from Yale research labs showed that the drug ketamine, which was widely used as anesthesia during surgeries, triggers glutamate production, which, in a complex, cascading series of events, prompts the brain to form new neural connections. This makes the brain more adaptable and able to create new pathways, and gives patients the opportunity to develop more positive thoughts and behaviors. This was an effect that had not been seen before, even with traditional antidepressants.  

“I think the interesting and exciting part of this discovery is that it came largely out of basic neuroscience research, instead of by chance,” says Gerard Sanacora, MD, PhD, a psychiatrist at Yale Medicine who was also involved in many of the ketamine studies. “It wasn’t just, ‘let’s try this drug and see what happens.’ There was increasing evidence suggesting that there was some abnormality within the glutamatergic system in the brains of people suffering from depression, and this prompted the idea of using a drug that targets this system.”  

For the last two decades, researchers at Yale have led ketamine research by experimenting with using subanesthetic doses of ketamine delivered intravenously in controlled clinic settings for patients with severe depression who have not improved with standard antidepressant treatments. The results have been dramatic: In several studies, more than half of participants show a significant decrease in depression symptoms after just 24 hours. These are patients who felt no meaningful improvement on other antidepressant medications.  

Most important for people to know, however, is that ketamine needs to be part of a more comprehensive treatment plan for depression. “Patients will call me up and say they don’t want any other medication or psychotherapy, they just want ketamine, and I have to explain to them that it is very unlikely that a single dose, or even several doses of ketamine alone, will cure their depression,” says Dr. Sanacora. Instead, he explains, “I tell them it may provide rapid benefits that can be sustained with comprehensive treatment plans that could include ongoing treatments with ketamine.  Additionally, it appears to help facilitate the creation new neural pathways that can help them develop resiliency and protect against the return of the depression.”  

This is why Dr. Sanacora believes that ketamine may be most effective when combined with cognitive behavioral therapy (CBT). CBT is a type of psychotherapy that helps patients learn more productive attitudes and behaviors. Ongoing research, including clinical trials, addressing this idea are currently underway here at Yale.     

A more patient-friendly version

The FDA-approved drug esketamine is one version of the ketamine molecule, and makes up half of what is found in the commonly used anesthetic form of the drug. It works similarly, but its chemical makeup allows it to bind more tightly to the NMDA glutamate receptors, making it two to five times more potent. This means that patients need a lower dose of esketamine than they do ketamine. The nasal spray allows the drug to be taken more easily in an outpatient treatment setting (under the supervision of a doctor), making it more accessible for patients than the IV treatments currently required to deliver ketamine.  

But like any new drug, this one comes with its cautions. Side effects, including dizziness, a rise in blood pressure, and feelings of detachment or disconnection from reality may arise. In addition, the research is still relatively new. Studies have only followed patients for one year, which means doctors don’t yet know how it might affect patients over longer periods of time. Others worry that since ketamine is sometimes abused (as a club drug called Special K), there may be a downside to making it more readily available—it might increase the likelihood that it will end up in the wrong hands.  

Also, esketamine is only part of the treatment for a person with depression. To date, it has only been shown to be effective when taken in combination with an oral antidepressant. For these reasons, esketamine is not considered a first-line treatment option for depression. It’s only prescribed for people with moderate to severe major depressive disorder who haven’t been helped by at least two other depression medications.  

In the end, though, the FDA approval of esketamine gives doctors another valuable tool in their arsenal against depression—and offers new hope for patients no one had been able to help before.