Researchers from the University of Medicine and Science in Los Angeles have found that a missing enzyme in the body could be responsible for a person's addiction to pain killers.

Pain killers are essentially synthetic opioids derived from the opium plant. They work by sending blocking pain signals between nerves. This way a person doesn't feel any pain. Opioids are found in prescription medications like morphine and codeine as well as in illegal drugs like heroin.

Opioids are also produced naturally in the body by various body organs during physical activities. However, addiction occurs when the synthetic opioids alter the chemical balance of natural producing opioids .

Since drug abuse has become a growing concern nationwide, researchers from the University of Medicine and Science in Los Angeles did a study to see why some people are more vulnerable to drug addiction than others.

For the study, they used an animal model and eliminated an enzyme called prohormone convertase 2 (PC2), which is responsible for converting pre-hormonal substances into active hormones in certain parts of the brain.

Lead author Theodore C. Friedman, MD, PhD, chairman of the internal medicine department at Charles R. Drew University of Medicine and Science in Los Angeles stated in a press release that previous studies conducted by him and his team had established that after long morphine use, the PC2 levels in the body increase. This discovery led the authors to speculate whether PC2-derived peptides may be involved in some of the addiction parameters related to morphine.

In the study when the enzyme was eliminated from mice, researchers found that the mu opioid receptor (MOR) concentration level was higher than in mice that had PC2. MOR is a protein in cells that molecules of morphine usually attach themselves to. Researchers then analyzed the MOR concentration levels in certain parts of the brain that were related to pain relief and found that mice lacking the enzyme PC2 were found to have higher MOR concentration levels in parts of the brain that were related to pain relief.

"We conclude that PC2 regulates endogenous opioids involved in the addiction response and in its absence, up-regulation of MOR expression occurs in key brain areas related to drug addiction," said Friedman.