High-Density Lipoprotein FacilitatesIn VivoDelivery of α-Tocopherol–Conjugated Short-Interfering RNA to the Brain

Abstract

We originally reported the use of vitamin E (a-tocopherol) as an in vivo vector of short-interfering RNA (siRNA) to the liver. Here, we apply our strategy to the brain. By combining high-density lipoprotein (HDL) as a second carrier with a-tocopherol-conjugated siRNA (Toc-siRNA) in the brain, we achieved dramatic improvement of siRNA delivery to neurons. After direct intracerebroventricular (ICV) infusion of Toc-siRNA/HDL for 7 days, extensive and specific knock-down of a target gene, b-site amyloid precursor protein cleaving enzyme 1 (BACE1), was observed in both mRNA and protein levels, especially in the cerebral cortex and hippocampus. This new delivery method achieved a much more prominent down-regulation effect than conventional silencing methods of the brain gene, i.e., ICV infusion of nonconjugated siRNA or oligonucleotides. With only 3 nmol Toc-siRNA with HDL, BACE1 mRNA in the parietal cortex could be reduced by *70%. We suppose that this dramatic improvement of siRNA delivery to the brain is due to the use of lipoprotein receptor-mediated endocytosis because the silencing efficiency was significantly increased by binding of Toc-siRNA to the lipoprotein, and in contrast, was clearly decreased in lipoprotein-receptor knockout mice. These results suggest exogenous siRNA could be used clinically for otherwise incurable neurological diseases.

Application of apolipoprotein E-modified liposomal nanoparticles as a carrier for delivering DNA and nucleic acid in the brain

“…16,17 However, in our system, no gene expression was detected in neuronal cells. This discrepancy can be explained by differences in the cargo.…”

“…16 In parallel with enhanced cellular uptake ( Figure 1B), the gene silencing effects increased with increasing ApoE concentration ( Figure 1C).…”

“…17 Uno et al also reported that α-tocopherol-conjugated siRNA accumulated efficiently in neuronal cells after incorporation into high-density lipoprotein after intracerebroventricular injection. 16 Even in this situation, premodification of ApoE significantly enhanced gene expression in the brain. Thus, binding of ApoE to YSK-MEND is a rate-limiting process for cellular uptake.…”

Short interfering RNA and the central nervous system: development of nonviral delivery systems

“…We reported efficient siRNA delivery by ICV administration when using lipoprotein as an in vivo carrier for the siRNA [13]. We used a-tocopherol-conjugated siRNA to bind serum HDL, and we achieved dramatic improvement in siRNA delivery to neurons.…”

“…Serum HDL and HDL-like particles have similar particle size and density and both use apolipoprotein E as a ligand for receptors. The dose of unconjugated siRNA needed for target suppression was as much as 3 µmol [9], whereas we found that only 3 nmol of a-tocopherol-conjugated siRNA with HDL could inhibit a target gene to a comparable degree [13].…”