15 May Development of a Heroin Vaccine
Vaccination is the general term doctors use to describe a process that protects the body from an infectious illness by preemptively introducing a weaker form of the illness in order to prepare and stimulate the immune system. The key to this process is the immune system’s ability to produce specialized proteins, called antibodies, which chemically “tag” the source of the illness for future reference and rapid response. Currently, researchers from several institutions are using the vaccine model to produce a treatment that blocks the effects of the illegal, addictive street drug heroin.
Heroin is one of several semi-synthetic drugs derived from psychoactive substances that occur naturally in the opium poppy. When it enters the bloodstream, it rapidly breaks down into two chemicals, called morphine and 6-acetylmorphine (commonly referred to as 6AM). Both of these chemicals migrate easily through the blood-brain barrier, a network of tiny, tightly structured blood vessels that stops many substances from passing from the bloodstream into the central nervous system (brain and spinal cord). Once they pass through this barrier, morphine and 6AM attach themselves to sites called opioid receptors, which form passageways into the interior of nerve cells inside the brain known as neurons. The presence of 6AM and morphine on the opioid receptors encourages a buildup of a neurotransmitting brain chemical called dopamine; in turn, the accumulation of dopamine produces the intense euphoria and pain relief that characterize the effects of heroin and a range of other narcotic or opioid drugs and medications.
As is true with many other opioid drugs/medications, heroin’s drastic effects on the brain’s dopamine levels create a high level of risk for addiction. Generally speaking, this process occurs gradually over time as users of the drug grow physically reliant on its dopamine-boosting effects and consciously or unconsciously starts to consider the new chemical environment in their brains as a normal situation. In the absence of heroin, people acclimated to its effects in this way will develop a variety of withdrawal symptoms, which can include such things as vomiting, diarrhea, bone pain, muscle aches, insomnia and agitation or restlessness.
In 2011, researchers from the Scripps Research Institute published the results of a study that explored the development of a vaccine designed to block the effects of heroin. During this study, the researchers created a specialized molecule called a heroin hapten, which has a very strong chemical resemblance to molecules of actual heroin. Critically, unlike heroin itself, heroin hapten is recognized as an invader by the immune system. When introduced into the body as part of a “vaccine cocktail,” heroin hapten breaks down slowly over time and releases small amounts of morphine and 6AM. In response, the immune system creates antibodies that “tag” heroin and its breakdown products just like they would tag an infectious microorganism. Theoretically, when actual heroin enters the body, these antibodies recognize the drug, as well as morphine and 6AM, and trigger an immune response that actively destroys molecules of these substances.
To test this theory, the Scripps Research Institute researchers vaccinated rats with heroin hapten in a laboratory setting, then later gave these animals access to heroin supplies that they could self-administer at their own discretion. As expected, vaccination with heroin hapten resulted in the formation of antibodies that specifically targeted heroin and its breakdown products. In addition, less than half of the vaccinated animals voluntarily used heroin when they had the opportunity to do so. For comparison’s sake, the researchers also made heroin available to a group of rats that did not receive heroin hapten; all of these animals voluntarily used the drug repeatedly.
The Scripps Research Institute researchers note that the heroin hapten vaccine is very specific in its effects and doesn’t interfere with the therapeutic actions of opioid-containing medications such as oxycodone and methadone. This finding means that, in the future, doctors may have the option to use the vaccine under a range of different circumstances without interfering with the usefulness of legitimate opioid-based medical treatments. Currently, a research team funded by the National Institute on Drug Abuse and the U.S. Military HIV Research Program is exploring the possibility of combining the heroin hapten vaccine with a vaccine designed to prevent transmission of the human immunodeficiency virus, which can ultimately produce the body-wide immune system collapse associated with AIDS (acquired immune deficiency syndrome). Before they become available to the general public, these vaccines must go through further stages of testing and refinement.
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