01 Jun Potential RNA-Based Treatment for Drug Addiction
RNA is the common abbreviation for ribonucleic acid, a generalized term that describes a particular group of specialized substances in the body’s cells called nucleic acids. Along with another type of nucleic acid, called deoxyribonucleic acid or DNA, the various forms of RNA perform a wide variety of tasks absolutely essential to human life. In the 1990s, researchers uncovered the existence of a previously unknown form of RNA, called microRNA. Current evidence indicates that a specific type of microRNA strongly influences a person’s risks for drug addiction. As a result of this fact, future researchers may be able to develop microRNA-based therapies that serve as highly effective drug addiction treatments.
Both RNA and DNA are made from mostly identical building blocks that belong to a group of substances called nucleotides. The four nucleotides used to build DNA include guanine, adenine, cytosine and thymine; in RNA, the nucleotide uracil takes the place of thymine. While DNA molecules contain double-stranded pairs of nucleotides, RNA usually exists in a single-stranded form. As indicated previously, there are several different types of RNA, each of which plays a particular role inside the body’s cells.
One type of molecule, called messenger RNA or mRNA, transcribes the genetic information encoded in DNA and uses that information to create a vast assortment of proteins. Another type of molecule, called transfer RNA or tRNA, transports the amino acid building blocks required for protein production. A third type of molecule, called ribosomal RNA or rRNA, actually links amino acid building blocks together inside cellular structures called ribosomes. Other types of RNA play additional roles in vital areas such as cellular communication and regulation of the biochemical reactions that sustain the body’s internal processes.
As is true with the term RNA itself, scientists use microRNA as a collective term to describe a range of structurally similar molecules, each of which possesses certain defining characteristics. Molecules in this category get their name because they contain far fewer nucleotide building blocks than molecules of messenger RNA. This comparison with messenger RNA is relevant because the various microRNAs act as a counterbalance to the protein-building actions of mRNA. While mRNA transcribes the genetic instructions for protein construction, microRNAs interfere with the transmission of those instructions, and therefore prevent mRNA from doing its job. The human body’s cells contain roughly 1000 distinct types of microRNA; each of these molecules achieves it effects by attaching itself to specific, identifying nucleotide segments only found on certain strands of messenger RNA.
Relevance to Drug Addiction
According to the results of two separate studies reported in 2011 by the National Institute on Drug Abuse, one particular type of microRNA—called miR-212—plays a clear role in determining risks for drug addiction. Each of these studies involved rats, not human beings; however, the human body contains a form of the miR-212 molecule that’s structurally identical to the molecule found in rats. Also, it’s worth noting that the two studies focused specifically on the effects of miR-212 in cocaine addicts; however, the molecule likely plays the same function in the risks for other forms of drug addiction.
In one of the studies, researchers from the Scripps Research Institute exposed a group of rats to cocaine in sessions that lasted for a relatively short amount of time (one hour); a second group of rats was exposed to the drug in sessions that lasted for a much longer amount of time (six hours). At the end of these cocaine sessions, the researchers measured the amount of microRNA contained in key areas of the brain. They concluded that the rats exposed to cocaine for six hours at a time had twice the amount of miR-212 in their brains than the amount of the molecule found in rats that were only exposed to cocaine for an hour at a time.
Critically, they also concluded that the heightened presence of miR-212 in the brains of heavily cocaine-exposed rats actually decreased the animals’ involvement in addiction-related behaviors. For instance, when compared to rats that did not have increased brain levels of miR-212, those with heightened levels of the molecule significantly lowered their overall voluntary cocaine intake. Additionally, rats with increased levels of miR-212 showed a marked preference for relatively small individual doses of cocaine, while rats with normal levels of the molecule showed a preference for relatively large individual doses of the drug. When all of these factors are taken into account, the Scripps Research Institute researchers note, rats (and people) with only a modest ability to naturally boost their miR-212 production likely have higher overall risks for drug addiction than rats and people with a stronger ability to naturally boost their miR-212 production.
At some point in the future, researchers and pharmaceutical companies may be able to use these recent findings regarding miR-212 as a linchpin for the development of new targeted treatments that directly decrease the chances for drug addiction or a drug relapse during addiction recovery. However, the National Institute on Drug Abuse notes, much more research must be done in order to make the current laboratory findings relevant to real-world use in human populations.
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