Quantum dots increase the efficiency of RNA interference
For more than 15 years, scientists have been using short fragments of RNA (miRNA) to block the production of a certain protein encoded in the target gene, which allows us to study the effects of the activity of individual genes. In the conditions of the body, RNA interference can be used to treat various diseases, ranging from cancer to vision loss. The principle of RNA interference, the developers of which received the Nobel Prize, has great potential for medical science, but the application of this technology to living cells is complicated by many difficulties.
Scientists at the University of Washington (Seattle) and Emory University (Georgia) have successfully used nanotechnological material – the so–called quantum dots - to solve two problems at once: increasing the efficiency of protein synthesis suppression and improving the visualization of the RNA interference process. Their proposed technique is not only much less toxic, but also 10-20 times more effective than existing methods of blocking gene activity by introducing miRNAs (small interfering RNAs) into cells.
The authors used quantum dots in experiments – fluorescent spheres made of semiconductor material with a diameter of no more than 6 nm. Due to their unique optical properties – the ability to emit light from different parts of the spectrum depending on the size – these particles are used to visualize cells and produce solar panels and LEDs.
The negative charge of miRNAs prevents their penetration into cells, so the researchers attached quantum dots to them, covered with a positive charge-bearing "proton sponge". The resulting complex successfully penetrates into the cell by endocytosis (penetration of the membrane into the cell and the formation of membrane vesicles – endosomes), is released from the endosomes and enters the cytoplasm, where it performs its functions, consisting in disruption of the synthesis of a protein.
The key point of this approach is that scientists can select the chemical composition of the proton sponge, which allows them to control the bond strength of the complex with a high degree of accuracy.
The new approach led to a decrease in the synthesis of the protein of interest to scientists to 2% of the normal value, while for traditional methods of using RNA interference, this indicator is 13-51%.
It is also important that the fluorescent quantum dots allow you to track the movement of miRNA in the cell. (The figure shows a fluorescent image of a cell obtained 15 minutes after the introduction of a complex of quantum dots and miRNA. At this stage, the particles are inside the cell membrane.)
Existing miRNA tracking tags glow for no more than a minute, while quantum dots emit light for many hours. Moreover, the new approach is 5-10 times less toxic to living cells than the chemical compounds currently used to monitor the course of RNA interference.
The reason for the higher efficiency of quantum dots compared to earlier techniques is unclear. The authors suggest that it is based on the ability of the complex to be released from endosomes, and quantum dots to separate from miRNA.
Quantum dots have not yet been approved for introduction into the human body, so at the moment the authors are trying to replace them with iron oxide nanoparticles, several types of which are approved by the US Food and Drug Administration. They are also working on methods of targeting tumor cells by labeling the cell surface with specific markers.
Portal "Eternal youth" www.vechnayamolodost.ru based on the materials of ScienceDaily
26.06.2008