This study revealed that by binding to lipoproteins, cholesterol-binding heteroduplex oligonucleotides (chol-hdos) can stay in the bloodstream for longer and reach brain tissue much more effectively than the counterpart of antisense oligonucleotides (ASOs). These findings pave the way for the development of brain-targeted gene regulatory drugs. Credit: Tokyo University of Science, Nishikawa, Japan
Taking medications past the blood-brain barrier has been one of the most challenging medical challenges that limits our ability to treat conditions such as Alzheimer’s disease, Parkinson’s disease, and brain cancer. Manipulating gene expression in brain cells holds a huge promise to treat these conditions, but effectively providing gene targeting drugs to the brain remains an elusive goal.
Contrary to this background, a research team at the University of Tokyo Science (TUS), led by Professor Nishikawa Makiya, is looking for ways to improve delivery of antisense oligonucleotides (ASOS), a promising class of gene targeting drugs, to the brain and other organs. With an emphasis on the UN Sustainable Development Goals (SDGS), the team set out to improve health and well-being (SDG 3) and promote industry, innovation and infrastructure (SDG 9).
In the latest study published online in the Journal of Controlled Release on February 18, 2025, researchers delved into the mechanisms that govern how long these compounds remain in the bloodstream, what they are restrained, and which tissues they can enter. This study was co-authored by Yukitake Yoshioka of TUS and Yunsuke Yunsuke of Takeda Pharmaceutical Company Limited.
Given its ability to regulate genetic expression within cells, ASOS has become a hot topic in medical research. These compounds are made up of single-stranded DNA with a nucleotide sequence complementary to the target messenger RNA (mRNA). ASOS can prevent the production of specific proteins within cells by binding to targets. Despite this possibility, ASOS is unable to effectively reach the brain and tends to be cleared quickly from the bloodstream.
To address this issue, researchers focused on a new type of gene target compound called heteroduplex oligonucleotides (HDOs). HDO behaves similarly to ASOS, but has additional complementary RNA strands that increase stability and specificity.
Microscopic image analysis of Alexa Fluor 647-labeled ASO and Chol-HDO. C57BL/6 mice were injected intravenously with Alexa Fluor 647-labeled ASO and CHOL-HDO. Four hours after injection, brain samples were collected. The Alexa Fluor 647 signal was visualized using a light sheet fluorescence microscope. (A) Alexa Fluor 647-labeled ASO, (b) Alexa Fluor 647-labeled ASO and blood vessels (fluorescein isothiocyanate-labeled anti-alpha muscle actin antibody and Alexa Flur 488-labeled anti-CD31 antibody) Alexa Fluor 647-labeled chol-hdo and blood vessels (fluorescein isothiocyanate-labeled anti-alpha smooth muscle antibody and Alexa fluorescence 488-labeled anti-CD31 antibody). Credit: Journal of Controlled Release (2025). doi: 10.1016/j.jconrel.2025.02.025
Interestingly, this extra RNA strand can be further modified by attaching cholesterol (CHOL) molecules to create Chol-HDO. It is built on recent reports on the improvement in Chol-hdo’s ability to reach various organs within the body. Nishikawa’s team tried to clarify the pharmacokinetics of these compounds compared to ASOS and HDO, shedding light on how they are distributed in the body.
To this end, the researchers conducted several experiments in rats and mice using techniques such as liquid chromatography, tandem mass spectrometry, photosheet fluorescence microscopy, and polyacrylamide gel electrophoresis. After a detailed analysis, the team demonstrated that unlike HDO and ASOS, Chol-HDO can penetrate the cerebral cortex across blood vessels.
The key to this success lies in how chol-hdos interact with proteins in the blood. “We found that HDOS binds electrostatically to serum proteins with low binding affinity and is collected in cells, but CHOL-HDO binds firmly to serum proteins, including lipoproteins, via hydrophobic interactions,” explains Professor Nishikawa. “The strong binding of CHOL-HDOS to serum proteins leads to slower clearance from the bloodstream.”
Interestingly, the researchers also showed that inhibiting intracellular scavenger receptors reduces both liver and kidney ASOS and Chol-HDO uptake, shedding light on how these compounds are harvested by different organs.
Taken together, the results of this study provide valuable insight into how brain-targeted drugs can be designed based on Chol-hdos. “The possibility of efficiently delivering ASOS and other nucleic acid-based drugs to the brain can lead to the development of treatment for brain diseases with unmet medical needs,” says Professor Nishikawa.
Today, more than 55 million people live with dementia caused by a curable, or at least preventable, disease, if they can deliver the right compounds beyond the blood-brain barrier. The same applies to brain cancer, with 300,000 cases reported worldwide each year. Continuing research has enabled revised HDO to pave the way for a new generation of drugs that effectively target brain diseases, providing hope to millions of patients and their families around the world.
Details: Yukitake Yoshioka et al, Pharmacokinetics and Protein Binding of Cholesterol-Binding Heteroduple Oligonucleotides, Journal of Controlled Release (2025). doi: 10.1016/j.jconrel.2025.02.025
Provided by Tokyo University of Science
Citation: Cholesterol-modified oligonucleotides indicate potential treatment for brain diseases recovered from https://phys.org/2025-04 from April 17, 2025 (April 16, 2025)
This document is subject to copyright. Apart from fair transactions for private research or research purposes, there is no part that is reproduced without written permission. Content is provided with information only.
