Posts tagged opioid receptors
Articles and news from the latest research reports.
A path to lower-risk painkillers: Newly-discovered drug target paves way for alternatives to morphine
New findings provide vital step towards exploring pain medications that may lower risks of prescription drug abuse and side effects of painkillers
For patients managing cancer and other chronic health issues, painkillers such as morphine and Vicodin are often essential for pain relief. The body’s natural tendency to develop tolerance to these medications, however, often requires patients to take higher doses – increasing risks of harmful side effects and dependency.
Now, new research from the University of Michigan Health System and a major pharmaceutical company has identified a novel approach to moderate and severe pain therapy that paves the way for lower dosage painkillers. The findings appear in Proceedings of the National Academy of Sciences of the United States of America.
Drugs such as hydrocodone (the main ingredient of Vicodin) and oxycodone (Oxycontin) are often the best options for the treatment of moderate to severe pain for patients facing medical conditions ranging from a wisdom tooth extraction to cancer. The drugs bind to specific molecules (opioid receptors) on nerve cells in the brain and spinal cord to prevent the feeling of pain.
“We have for the first time discovered compounds that bind to an alternative site on the nerve opioid receptors and that have significant potential to enhance the drug’s positive impact without increasing negative side effects,” says co-author John Traynor, Ph.D., professor of pharmacology at the U-M Medical School.
“We are still in the very early stages of this research with a long way to go, but we believe identifying these compounds is a key step in revolutionizing the treatment of pain. This opens the door to developing pain relief medications that require lower doses to be effective, helping address the serious issues of tolerance and dependence that we see with conventional pain therapy.”
Conventional drug treatments for pain work by targeting the so-called orthosteric site of the opioid receptor that provides pain relief. Targeting this site, however, is a double-edged sword because it is also responsible for all of the drug’s unwanted side effects, such as constipation and respiratory depression. Tolerance also limits chronic use of the drugs because higher doses are required to maintain the same effect.
Using cell systems and mouse brain membranes, researchers have identified compounds that bind to a physically distinct and previously unknown “allosteric” site on the opioid receptor- a site that fine-tunes the activity of the receptor. Not only do these compounds act at a location that hasn’t been studied as a drug target before but they bind to the receptor in a new way to enhance the actions of morphine – which means lower doses can have the same impact.
“The newly-discovered compounds bind to the same receptor as morphine but appear to act at a separate novel site on the receptor and therefore can produce different effects. What’s particularly exciting is that these compounds could potentially work with the body’s own natural painkillers to manage pain,” Traynor says.
“We know that conventional strong pain medications ultimately increase the risk of withdrawal symptoms and addiction, which is an especially serious issue with the current prescription drug abuse epidemic in our country. The implications of this work, if it translates to animal studies and then to humans, are highly significant to this area of study.”
(Source: uofmhealth.org)
Study stops stress-based drug relapse in rats
All too often, stress turns addiction recovery into relapse, but years of basic brain research have provided scientists with insight that might allow them develop a medicine to help. A new study in the journal Neuron pinpoints the neural basis for stress-related relapse in rat models to an unprecedented degree. The advance could accelerate progress toward a medicine that prevents stress from undermining addiction recovery.
In the paper published March 6, researchers at Brown University and the University of Pennsylvania demonstrated specific steps in the sequence of neural events underlying stress-related drug relapse and showed that they take place within a brain region called the ventral tegmental area (VTA), which helps reinforce behaviors related to fulfilling basic needs. They also showed that a closely related neural process believed to be crucial to stress-related relapse may not be involved after all.
Moreover, this new understanding allowed the researchers to prevent relapse to drug seeking in the animal model. When they treated rats that had recovered from cocaine addiction with a chemical that blocks the “kappa opioid receptors” that stress activates in the VTA, the rats did not relapse to cocaine use under stress. Untreated rats who had also recovered from addiction did relapse after the same stress.
The chemical that helped the rats, “nor-BNI,” may be one that would someday be tried in humans, said study senior author Julie Kauer, professor of biology in Brown’s Department of Molecular Pharmacology, Physiology, and Biotechnology. By deepening scientists’ understanding of the stress-related relapse mechanism, she and her co-authors hope to identify multiple possible targets for eventual patient treatments.
“If we understand how kappa opioid receptor antagonists are interfering with the reinstatement of drug seeking we can target that process,” Kauer said. “We’re at the point of coming to understand the processes and possible therapeutic targets. Remarkably, this has worked.”
The neural crux of relapse
Exactly how stress acts in the brain to trigger relapse is a complicated sequence that is still not fully understood, but the new study focuses on and elucidates three key players at the crux of the phenomenon in the VTA: GABA-releasing neurons, dopamine-releasing neurons, and the kappa opioid receptors that affect their connections.
Fulfilling natural needs such as hunger or thirst results in a rewarding release of dopamine from the VTA’s dopamine neurons, Kauer said. Unfortunately, so does using drugs of abuse.
In normal brain function, GABA applies the brakes on the rewarding dopamine release, slowing it back to a normal level. It achieves this by forging and then strengthening the connections, called synapses, with the dopamine neuron. The strengthening process is called long-term potentiation (LTP).
In the first of their experiments, the team at Brown, including lead author Nicholas Graziane, showed that stress interrupts the LTP process, hindering GABA’s ability to slam the brakes on dopamine release.
Previous research implicated kappa opioid receptors as one of many neural entities that could have a role in stress-related relapse. Kauer, Graziane, and co-author Abigail Polter investigated that directly by blocking the receptors in some rats with a treatment of nor-BNI in the VTA and leaving others untreated. Then they subjected the rats to a standardized five-minute stress exercise. After 24 hours they looked at the cells in the VTA and found that LTP was hindered in the untreated rats but still present and underway in the rats whose receptors had been blocked with nor-BNI.
With the role of stress and the receptors in the GABA-dopamine dynamic both confirmed and then mitigated, the question remained: Could this knowledge be used to prevent relapse?
To answer that, Penn co-authors Lisa Briand and Christopher Pierce performed the experiment demonstrating that nor-BNI delivered directly to the VTA prevented stressed rats from relapsing to cocaine seeking, while untreated rats subjected to the same stress did relapse.
“Our results indicate that the kappa receptors within the VTA critically control stress-induced drug seeking in animals,” the authors wrote in Neuron.
Along the way, the team also discovered evidence that another stress-affected synapse in the VTA – one that excites dopamine release rather than inhibits it – does not play a role in the stress-related relapse as many researchers have thought. The nor-BNI treatment that prevented stress-related relapse, for example, did not affect those synapses.
Kauer emphasized that her lab’s findings of therapeutic potential are the product of more than a decade of essential basic research on the importance of how changes in synapses relate to behaviors including addiction.
“If we can figure out how not only stress, but the whole system works, then we’ll potentially have a way to tune it down in a person who needs that,” she said.
Opioid Receptors as a Drug Target for Stopping Obesity
ScienceDaily (July 31, 2012) — New research demonstrates that blocking the delta opioid receptor in mice created resistance to weight gain and stimulated gene expression promoting non-shivering thermogenesis.
Imagine eating all of the sugar and fat that you want without gaining a pound. Thanks to new research published in The FASEB Journal, the day may come when this is not too far from reality. That’s because researchers from the United States and Europe have found that blocking one of three opioid receptors in your body could turn your penchant for sweets and fried treats into a weight loss strategy that actually works. By blocking the delta opioid receptor, or DOR, mice reduced their body weight despite being fed a diet high in fat and sugar. The scientists believe that the deletion of the DOR gene in mice stimulated the expression of other genes in brown adipose tissue that promoted thermogenesis.
"Our study provided further evidence that opioid receptors can control the metabolic response to diets high in fat and sugar, and raise the possibility that these gene products (or their respective pathways) can be targeted specifically to treat excess weight and obesity," said Traci A. Czyzyk, Ph.D., a researcher involved in the work from the Department of Physiology at the Mayo Clinic in Scottsdale, Arizona.
Scientists studied mice lacking the delta opioid receptor (DOR KO) and wild type (WT) control mice who were fed an energy dense diet (HED), high in fat and sugar, for three months. They found that DOR KO mice had a lean phenotype specifically when they were fed the HED. While WT mice gained significant weight and fat mass on this diet, DOR KO mice remained lean even though they consumed more food. Researchers then sought to determine how DOR might regulate energy balance and found that DOR KO mice were able to maintain their energy expenditure levels, in part, due to an increase in non-shivering thermogenesis. This was evidenced by an increase in thermogenesis-promoting genes in brown adipose tissue, an increase in body surface temperature near major brown adipose tissue depots, and the ability of DOR KO mice to maintain higher core body temperatures in response to being in a cold environment.
"Don’t reach for the ice cream and doughnuts just yet," said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. “We don’t know how all this works in humans, and of course, a diet of junk food causes other health problems. This exciting research identifies genes that activate brown adipose tissue to increase our burning of calories from any source. It may lead to a safe diet pill in the future.”
Source: Science Daily