Regulation of activated microglia and macrophages by systemically administered DNA/RNA heteroduplex oligonucleotides

Unlocking the future: Precision oligonucleotide therapy for targeted treatment of neurodegenerative disorders

Neurodegenerative disorders are complex and devastating conditions of the central nervous system that profoundly impact quality of life. Given the limited treatment options available, there is a pressing need to develop novel therapeutic strategies. Oligonucleotides have emerged as key players in precision medicine for these disorders, but their potential is hindered by poor translocation across the blood-brain barrier. This review focuses on neurodegenerative disorders other than Alzheimer's and Parkinson's, which are widely reported in the literature, and aims to address the significant hurdles in oligonucleotide delivery for neurodegenerative diseases. It highlights recent advancements in CNS-targeting approaches, such as chemical conjugation, antibody-oligonucleotide conjugates, focused ultrasound, and viral and nanocarrier-based delivery systems. Each strategy's strengths and limitations are discussed, with potential solutions proposed for more effective treatments. Additionally, the review offers valuable insights into regulatory requirements and prospects for clinical translation, which are crucial for shaping the future of neurodegenerative therapies. By exploring these innovative approaches, the goal is to surmount challenges posed by the blood-brain barrier and develop more effective treatments, thereby enhancing the quality of life of the patients suffering from these debilitating conditions.

Pharmacokinetics and protein binding of cholesterol-conjugated heteroduplex oligonucleotide

Heteroduplex oligonucleotide (HDO) is a novel oligonucleotide therapeutic consisting of an antisense oligonucleotide (ASO) and its complementary RNA. A recent report showed that cholesterol-conjugated HDO (Chol-HDO) exhibited antisense activity in various tissues, including the brain; however, little information is available on the pharmacokinetic and plasma protein-binding properties of HDO and Chol-HDO. In the present study, we investigated the tissue distributions of an ASO, HDO, and Chol-HDO in mice and rats after intravenous injection. Tissue distribution was evaluated by measuring the concentration of ASO in tissue samples using liquid chromatography and tandem mass spectroscopy. ASO and HDO disappeared rapidly from the plasma, whereas Chol-HDO showed prolonged retention in the systemic circulation. The amount of ASO in the brain tissue was highest after injection of Chol-HDO, confirming its efficient delivery to the brain. The tissue distribution of oligonucleotides differed less in rats than in mice. Hepatic uptake of ASO and HDO, but not of Chol-HDO, was significantly inhibited by co-administration with the scavenger receptor inhibitor dextran sulfate sodium. The binding to plasma proteins was evaluated. Compared to ASO, HDO showed lower protein binding, but Chol-HDO showed much higher binding, with remarkable differences in binding to high-density and low-density lipoproteins. The binding of Chol-HDO to these proteins was also confirmed in mouse plasma after injection. These results indicate that the binding of Chol-HDO to plasma proteins, especially lipoproteins, is critical for determining tissue distribution and brain delivery after intravenous injection.

Frontiers of Neurodegenerative Disease Treatment: Targeting Immune Cells in Brain Border Regions

Neurodegenerative diseases (NDs) demonstrate a complex interaction with the immune system, challenging the traditional view of the brain as an "immune-privileged" organ. Microglia were once considered the sole guardians of the brain's immune response. However, recent research has revealed the critical role of peripheral immune cells located in key brain regions like the meninges, choroid plexus, and perivascular spaces. These previously overlooked cells are now recognized as contributors to the development and progression of NDs. This newfound understanding opens doors for pioneering therapeutic strategies. By targeting these peripheral immune cells, we may be able to modulate the brain's immune environment, offering an alternative approach to treat NDs and circumvent the challenges posed by the blood-brain barrier. This comprehensive review will scrutinize the latest findings on the complex interactions between these peripheral immune cells and NDs. It will also critically assess the prospects of targeting these cells as a ground-breaking therapeutic avenue for these debilitating disorders.

Temporal changes of spinal microglia in murine models of neuropathic pain: a scoping review

Neuropathic pain (NP) is an ineffectively treated, debilitating chronic pain disorder that is associated with maladaptive changes in the central nervous system, particularly in the spinal cord. Murine models of NP looking at the mechanisms underlying these changes suggest an important role of microglia, the resident immune cells of the central nervous system, in various stages of disease progression. However, given the number of different NP models and the resource limitations that come with tracking longitudinal changes in NP animals, many studies fail to truly recapitulate the patterns that exist between pain conditions and temporal microglial changes. This review integrates how NP studies are being carried out in murine models and how microglia changes over time can affect pain behavior in order to inform better study design and highlight knowledge gaps in the field. 258 peer-reviewed, primary source articles looking at spinal microglia in murine models of NP were selected using Covidence. Trends in the type of mice, statistical tests, pain models, interventions, microglial markers and temporal pain behavior and microglia changes were recorded and analyzed. Studies were primarily conducted in inbred, young adult, male mice having peripheral nerve injury which highlights the lack of generalizability in the data currently being collected. Changes in microglia and pain behavior, which were both increased, were tested most commonly up to 2 weeks after pain initiation despite aberrant microglia activity also being recorded at later time points in NP conditions. Studies using treatments that decrease microglia show decreased pain behavior primarily at the 1- and 2-week time point with many studies not recording pain behavior despite the involvement of spinal microglia dysfunction in their development. These results show the need for not only studying spinal microglia dynamics in a variety of NP conditions at longer time points but also for better clinically relevant study design considerations.

Regulation of human microglial gene expression and function via RNAase-H active antisense oligonucleotides in vivo in Alzheimer's disease

BACKGROUND

Microglia play important roles in maintaining brain homeostasis and neurodegeneration. The discovery of genetic variants in genes predominately or exclusively expressed in myeloid cells, such as Apolipoprotein E (APOE) and triggering receptor expressed on myeloid cells 2 (TREM2), as the strongest risk factors for Alzheimer's disease (AD) highlights the importance of microglial biology in the brain. The sequence, structure and function of several microglial proteins are poorly conserved across species, which has hampered the development of strategies aiming to modulate the expression of specific microglial genes. One way to target APOE and TREM2 is to modulate their expression using antisense oligonucleotides (ASOs).

METHODS

In this study, we identified, produced, and tested novel, selective and potent ASOs for human APOE and TREM2. We used a combination of in vitro iPSC-microglia models, as well as microglial xenotransplanted mice to provide proof of activity in human microglial in vivo.

RESULTS

We proved their efficacy in human iPSC microglia in vitro, as well as their pharmacological activity in vivo in a xenografted microglia model. We demonstrate ASOs targeting human microglia can modify their transcriptional profile and their response to amyloid-β plaques in vivo in a model of AD.

CONCLUSIONS

This study is the first proof-of-concept that human microglial can be modulated using ASOs in a dose-dependent manner to manipulate microglia phenotypes and response to neurodegeneration in vivo.

Nanomedicine based strategies for oligonucleotide traversion across the blood-brain barrier

Neurological disorders are considered the most prominent cause of disability worldwide. The major hurdle in the management of neurological disorders is the existence of the blood-brain barrier (BBB), which hinders the entry of several therapeutic moieties. In recent years, oligonucleotides have gained tremendous attention for their target specificity, diminished dose and adverse effects, thereby halting disease progression. However, enzymatic degradation, rapid clearance, limited circulation and availability at the bio-active site, etc., limit its clinical translation. Nanomedicine has opened up a breadth of opportunities in the delivery of oligonucleotides across the BBB. This review addresses the pitfalls associated with oligonucleotide delivery in traversing the BBB via nanotherapeutics for the management of brain disorders. Regulatory perspectives pertaining to hastening the clinical translation of oligonucleotide-loaded nanocarriers for brain delivery have been highlighted.

Nonviral delivery systems for antisense oligonucleotide therapeutics

Antisense oligonucleotides (ASOs) are an important tool for the treatment of many genetic disorders. However, similar to other gene drugs, vectors are often required to protect them from degradation and clearance, and to accomplish their transport in vivo. Compared with viral vectors, artificial nonviral nanoparticles have a variety of design, synthesis, and formulation possibilities that can be selected to accomplish protection and delivery for specific applications, and they have served critical therapeutic purposes in animal model research and clinical applications, allowing safe and efficient gene delivery processes into the target cells. We believe that as new ASO drugs develop, the exploration for corresponding nonviral vectors is inevitable. Intensive development of nonviral vectors with improved delivery strategies based on specific targets can continue to expand the value of ASO therapeutic approaches. Here, we provide an overview of current nonviral delivery strategies, including ASOs modifications, action mechanisms, and multi-carrier methods, which aim to address the irreplaceable role of nonviral vectors in the progressive development of ASOs delivery.