Animal Study Links Missing Brain Enzyme With Addiction to Painkillers

The nature-nurture debate is alive and well in the world of drug addiction research. Scientists and addiction experts have long-speculated whether the biological factors—genetic variations and the resulting susceptibility—or the psycho-social factors—like depression, parental substance abuse, or socioeconomic disadvantage—are responsible for addiction. It’s generally agreed that both factors contribute to addiction, with at least 50 percent of addiction susceptibility being related to genes. The precise mechanisms by which genetic factors create a pre-disposition to addiction are an area of ongoing research, and a new study has uncovered that a specific enzyme could play an important role. The Cause of Drug Addiction Understanding the cause of addictions might seem like a purely academic pursuit, with researchers merely satisfying their curiosity by working out what leads to addiction, but it’s actually an extremely important area of research. Although addiction treatment is effective, if a precise set of biological markers is determined, there could be a vaccine developed to prevent drug addiction. Similarly, if a particular section of the population was determined to be at the most risk, or if a certain set of psycho-social circumstances had a very strong link to addiction, psychological intervention could be targeted to those at risk and even preemptively provided. Understanding Genetic Addiction Research The most confusing element of studies into the genetics of addiction is what it actually means. You may get the idea that scientists are looking for a specific “addiction gene” or that somebody with the gene will definitely become addicted, but neither of these is true. In fact, there are numerous genetic factors that are likely to contribute to addiction susceptibility, including the interactions between them. Having the biological markers for addiction doesn’t mean that you will definitely develop an addiction. It just makes it more likely that you will. New Research The new research looks at opiate addiction, which is essentially addiction to things like heroin or prescription medicines like Vicodin and OxyContin. Specifically, researchers using mice looked at the effects of removing a specific enzyme, called prohormone convertase 2 (or simply PC2). Enzymes serve as catalysts for chemical reactions within the body, making different enzymes vital for essentially all bodily processes. The brains of mice are studied because the brain’s reward pathways are essential to drug addiction. This means that mice make convenient tools to model the neurology of addiction, since doing things like removing enzymes from a human brain raises obvious ethical issues when the outcome is uncertain. In fact, research on mice provided one of the first clues to the genetic risk factors for addiction, according the University of Utah’s Genetic Science Learning Center. The Los Angeles researchers have previously implicated the PC2 enzyme in addiction, so the new study removed it entirely and monitored the numbers of opioid receptors in the brains of the mice. Receptors are like “collectors” of chemicals, and most drugs create their effect through their similarity to biological molecules. Opiates bind to the receptors to create their effects—like a key fitting perfectly into a lock. The scientists found that mice that didn’t have the PC2 enzyme had higher levels of a specific opioid receptor, and were therefore more susceptible to the effects of the drugs. It makes sense if you think of the receptors as “locks” and the influx of drugs as a stream of “keys.” The more locks there are, the more keys that will find their way to one of them and create an effect. Since the mice that lacked the enzyme responded with more opioid receptors, it could mean that the enzyme has some level of control over the susceptibility to addiction. The Future of Treatment The discovery of new biological markers for addiction always presents possibilities for the future of treatment. Previous advances in knowledge have led to proposed vaccines for drug abuse, and the possible influence of this enzyme may also increase the options for treatment. Although it probably won’t lead to a vaccine, it could prove to be a method of identifying individuals who are particularly at risk for addiction, allowing preventive action to be taken. If somebody has a genetic variation that causes him to produce less PC2, it could be identified and even rectified (by increasing PC2 levels, for example) in the future. However, just as the case for biological markers for addiction has strengthened, there is still an undeniable psychological component to addiction. This means that while genetic variations could be used to identify people who are at risk, the treatment offered will ultimately still need to be psychological. The face of addiction treatment isn’t set to change; it might just get some useful new tools.

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