Clinical trials have shown that ketamine can lift depression in hours, or even minutes - much faster than the most commonly used antidepressant medications now available, which often require weeks to take effect. Further, the antidepressant effects of a single dose can last for a week or longer. However, despite legitimate medical uses, ketamine also has dissociative, euphoric, and addictive properties, making it a potential drug of abuse and limiting its usefulness as a depression medication.
In hopes of finding leads to a more practical treatment, the research team sought to pinpoint the exact mechanism by which ketamine relieves depression. Ketamine belongs to a class of drugs that block cellular receptors for glutamate, the brain's chief excitatory chemical messenger. Until now, the prevailing view was that ketamine produced its antidepressant effects by blocking N-methyl-D-aspartic acid (NMDA) glutamate receptors.
However, human trials of other NMDA-receptor blockers failed to produce ketamine's robust and sustained antidepressant effects. So the team explored the effects of ketamine on antidepressant-responsive behaviors in mice. Ketamine harbors two chemical forms that are mirror images of each other, denoted (S)- and (R)-ketamine. The investigators found that while (S)-ketamine is more potent at blocking NMDA receptors, it is less effective in reducing depression-like behaviors than the (R) form.
The team then looked at the effects of the metabolites created as the body breaks down (S)- and (R)-ketamine. It was known that ketamine's antidepressant effects are greater in female mice. NIA researchers identified a key metabolite (2S,6S;2R,6R)-HNK (hydroxynorketamine) and showed that it is pharmacologically active. The team then discovered that levels of this metabolite were three times higher in female mice, hinting that it might be responsible for the sex difference in the antidepressant-like effect. To find out, the researchers chemically blocked the metabolism of ketamine. This prevented formation of the metabolite, which blocked the drug's antidepressant-like effects.
Like ketamine, this metabolite includes two forms that mirror each other. By testing both forms, they found that one - (2R,6R)-HNK - had antidepressant-like effects similar to ketamine, lasting for at least three days in mice. Notably, unlike ketamine, the compound does not inhibit NMDA receptors. It instead activates, possibly indirectly, another type of glutamate receptor, α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA). Blocking AMPA receptors prevented the antidepressant-like effects of (2R,6R)-HNK in mice. The experiments confirmed that the rapid antidepressant-like effects require activation of AMPA receptors, not inhibition of NMDA receptors.
Ketamine also has effects in mice that mimic its dissociative, euphoric effects in humans and underlie its abuse and addictive potential; however, these effects were not observed with (2R,6R)-HNK. (2R,6R)-HNK did not cause the changes in physical activity, sensory processing, and coordination in mice that occur with ketamine. In an experimental situation where mice were able to self-administer medication, they did so with ketamine but not the (2R,6R)-HNK metabolite, indicating that (2R, 6R)-HNK is not addictive.
"Pending confirmation in humans, this line of studies exemplifies the power of mouse translational experiments for teasing out brain mechanisms that hold promise for future treatment breakthroughs," added NIMH acting director.
The researchers are now following up on their discovery with safety and toxicity studies of the metabolite as part of a drug development plan in advance of a NIMH clinical trial in humans for the treatment of depression.
http://www.nimh.nih.gov/news/science-news/2016/ketamine-lifts-depression-via-a-byproduct-of-its-metabolism.shtml
Ketamine Lifts Depression via a Byproduct of its Metabolism
- 5,625 views
- Added
Edited
Latest News
Metabolic rewiring promotes…
By newseditor
Posted 18 Apr
A drug to prevent flu-induc…
By newseditor
Posted 18 Apr
New origin of deep brain waves
By newseditor
Posted 17 Apr
Starving cells hijack prote…
By newseditor
Posted 17 Apr
Miniature battery-free epid…
By newseditor
Posted 17 Apr
Other Top Stories
Mechanism of FGF21 mediated decrease in triglycerides
Read more
Intestinal Phospholipid Remodeling Is Required for Dietary-Lipid Up…
Read more
Cells found in mouse brain that signal 'stop eating'
Read more
MicroRNA deletion prevents diet-induced obesity
Read more
Genetic cause found for loss of beta cells during diabetes development
Read more
Protocols
MemPrep, a new technology f…
By newseditor
Posted 08 Apr
A tangible method to assess…
By newseditor
Posted 08 Apr
Stem cell-derived vessels-o…
By newseditor
Posted 06 Apr
Single-cell biclustering fo…
By newseditor
Posted 01 Apr
Modular dual-color BiAD sen…
By newseditor
Posted 31 Mar
Publications
How does the microbiota con…
By newseditor
Posted 18 Apr
The integrated stress respo…
By newseditor
Posted 18 Apr
The immunobiology of herpes…
By newseditor
Posted 17 Apr
Circulating microbiome DNA…
By newseditor
Posted 17 Apr
Spindle oscillations in com…
By newseditor
Posted 17 Apr
Presentations
Hydrogels in Drug Delivery
By newseditor
Posted 12 Apr
Lipids
By newseditor
Posted 31 Dec
Cell biology of carbohydrat…
By newseditor
Posted 29 Nov
RNA interference (RNAi)
By newseditor
Posted 23 Oct
RNA structure and functions
By newseditor
Posted 19 Oct
Posters
A chemical biology/modular…
By newseditor
Posted 22 Aug
Single-molecule covalent ma…
By newseditor
Posted 04 Jul
ASCO-2020-HEALTH SERVICES R…
By newseditor
Posted 23 Mar
ASCO-2020-HEAD AND NECK CANCER
By newseditor
Posted 23 Mar
ASCO-2020-GENITOURINARY CAN…
By newseditor
Posted 23 Mar