Animal Study Links Missing Brain Enzyme with Addiction to Painkillers

A new animal study suggests a missing brain enzyme increases concentrations of a protein related to opioid addiction, Science Daily reports.

The study, presented this week at the Endocrine Society Annual Meeting, involved mice bred so they did not produce a brain enzyme called prohormone convertase 2 (PC2). This hormone converts pre-hormonal substances into active hormones in the brain. In a previous study, the researchers from Charles R. Drew University of Medicine and Science in Los Angeles found PC2 levels in the brain are raised after long-term treatment with morphine.

In the new study, the researchers evaluated the effects of morphine on the brains of mice without the PC2 enzyme. Morphine binds to a protein on cells called the mu opioid receptor (MOR). In mice without PC2, MOR concentrations were higher in brain regions related to drug addiction, compared with mice that did produce PC2.

The researchers concluded PC2 regulates naturally produced opioids in the brain involved in the addiction response. In the absence of PC2, an increase in MOR occurs in key brain areas related to drug addiction.