siRNAs are small double-stranded RNAs which can control the expression of specific genes, and the process is done by degrading mRNA after transcription. siRNAs are perfect therapeutic agents for the disease-causing gene-silencing expression due to their high degree of specificity. In addition, as they are hydrophilic and with large size, there are several problems that should be overcome to deliver siRNA through membrane. At last, siRNA is immediately degraded by RNase while circulating in the blood. As a result, a perfect delivery system is important for the transportation of the highly specific therapeutic agents to cells.
In a recent study, the researchers found that by intravenously injecting chondroitin sulfate (CS), cationic lipoplexes allow the siRNA to be delivered to liver cells efficiently. The original study did not demonstrate whether the cationic lipid used in the cationic lipoplexes could affect the biodistribution and gene-silencing effects of the encapsulated siRNA. In order to answer the questions, the researchers investigated the effect of the different cationic lipids on the factors. They chose 6 kinds of cationic lipids derived from cholesterol and 11 di- or tri-alkyl cationic lipids to prepare 17 cationic liposomes containing DOPE. The reason why they chose DOPE is that it could promote the endosomal release of cationic lipoplexes by increasing the interaction between liposomal and endosomal membranes.
Using a Cy5.5 labelled siRNA, researchers can evaluate the biodistribution of siRNA after injection. The type of cationic lipid used in the liposomal formula has been proven to play a key role in the lungs, kidneys or livers where the siRNA were accumulated. In addition, they proved that the cationic lipid used in the lipoplexes affected the gene-silencing results of the therapeutic agents. After several experiments, they found that DC-1-16 and DC-1-18 induced the accumulation of siRNA in the liver after sequential injection of CS. The combination of these cationaic lipids and DOPE creates an excellent siRNA delivery tool.