THURSDAY, August 16, 2012 — It may be possible to block addiction to opioids — like addiction to heroin and morphine — while not interfering with how opioids effectively relieve pain, newly published research asserts.
The process of addiction can be halted, say researchers from the University of Adelaide, Australia, and the University of Colorado, by blocking a specific immune system receptor, known as Toll-Like receptor 4 (TLR4). Not only does blocking the receptor halt addiction, it increases the effectiveness of pain medications. Previous research had overlooked the immune system's role in addiction, the researchers say in their study, which was published in the Journal of Neuroscience.
"Both the central nervous system and the immune system play important roles in creating addiction, but our studies have shown we only need to block the immune response in the brain to prevent cravings for opioid drugs,” lead study author Mark Hutchinson, PhD, of the University of Adelaide’s School of Medical Sciences said in a statement.
The researchers say they were able to block the addiction-driving immune response in rats and mice by administering the drug Narcan ((+)-naloxone), a narcotic drug that is commonly used to counteract the effects of opioid overdoses and the effects of other narcotics. But they also found that while Narcan halts the addiction response, it enhances the pain-relieving effect of opioids.
"If you block Toll-Like Receptor 4, you make opiates work better for pain, but at the same time you make them have less abuse potential — they're less rewarding," says study co-author Linda Watkins, PhD, of the Center for Neuroscience at the University of Colorado-Boulder.
"For 60 years we've tried to separate the effects of opiates in terms of their very potent analgesic effects from their ability to be abused, and that's been very unsuccessful up to this point, says Theodore Cicero, PhD., a professor of neuropharmacology in psychiatry at Washington University, who was not involved in the research on Narcan. "The exciting part of these data, if they can be repeated, is that it may be possible that you can block the reinforcing effects of opiates. If this were true, then you would have the long-sought-after drug that relieves pain and doesn't get abused."
Dr. Cicero also notes it would be wise to wait and see the Australian and Colorado research team's results replicated in other laboratories.