New research shows that opioid drugs, such as morphine, may activate an immune response that boosts addictiveness and that blocking a specific receptor may eliminate this immune-addiction response. The New Scientist reports:
[Australian researcher Mark Hutchinson, PhD, and colleagues] previously observed that opioids bind to TLR-4 – immune system receptors in the cell membrane – which are responsible for identifying foreign bodies. However, the team did not know how this binding affected the body.
In their latest study, the team found that the receptor acts as an amplifier of reward when opioids are bound to it. The team did a series of experiments looking at addictive behaviour in rats and mice that had been given either morphine alone, or a drug called plus-naloxone – which blocks the TLR-4 receptor – followed by morphine.
Rats given plus-naloxone before receiving morphine did not exhibit behaviour linked to addiction. Their brains also showed a significantly lower release of dopamine than in rats that only received morphine. Using a heat sensitivity test, the team also showed that the rodents given plus-naloxone still experienced pain relief from the morphine, despite lacking signs of addiction.
The researchers say clinical trials could begin within the next 18 months.
Previously: Patients’ genetics may play a role in determining side effects of commonly prescribed painkillers, Addiction: All in the mind? and Sucrose-craving rats shed light on neural pathways responsible for addiction