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There's no doubting that morphine is an extremely effective painkiller. The problem is that as an opioid, it can also be highly addictive – a fact that is particularly problematic in the US where more than 115 people die after overdosing on opioids every single day.
Now, researchers based in France have come up with an alternative that they say is far less addictive than morphine and synthetic opioids prescribed to relieve pain. What's more, the results of a study published in Science Advances suggest its pain-alleviating effects last longer than opiate equivalents.
As of yet, the drug has only been tested in rodents so we will have to wait to see if the same can be said for human patients.
The science behind the drug relies on peptides that naturally occur in the body, like enkephalin, that bind to our opioid receptors. In theory, they are less open to abuse than drugs like morphine because they target peripheral opioid receptors close to the location of the pain instead of the central opioid receptors found in the brain. However, in practice, they have not been adopted because of various difficulties, including problems crossing the blood-brain barrier.
To get around these obstacles, the researchers attached Leu-enkephalin (LENK) neuropeptides to a natural and biocompatible lipid called squalene. This could then be delivered directly to the source of the pain via injection.
To test its effectiveness as a painkiller, the team administered three different versions of their new drug to rats with inflamed paws. Using real-time imaging, they then were able to detect signs of reduced thermal sensitivity in the rats' paws four hours later. The pain-relieving benefits of the drug lasted longer than morphine, they say.
It's all extremely promising but right now, we only know that the drug seems to work in rodents. Before it can be prescribed by doctors, it must pass clinical trial – and even that could be a while off.
"Before starting a first phase clinical trial, it is necessary to be able to prepare a clinical sample of these nanoparticles," lead author Patrick Couvreur told IFLScience. This includes finding a way to sterilize the nanoparticles before intravenous injection and passing at least one more (non-rodent) animal study.
