MIT researchers find that in mice and human cell cultures, lipid nanoparticles can deliver a potential therapy for inflammation in the brain, a prominent symptom in Alzheimer’s.
Some Covid-19 vaccines safely and effectively used lipid nanoparticles (LNPs) to deliver messenger RNA to cells. A new MIT study shows that different nanoparticles could be used for a potential Alzheimer’s disease (AD) therapy. In tests in multiple mouse models and with cultured human cells, a newly tailored LNP formulation effectively delivered small interfering RNA (siRNA) to the brain’s microglia immune cells to suppress expression of a protein linked to excessive inflammation in Alzheimer’s disease.
Credits:Image courtesy of the Tsai and Langer labs.
In a prior study, the researchers showed that blocking the consequences of PU.1 protein activity helps to reduce Alzheimer’s disease-related neuroinflammation and pathology. The new open-access results, reported in the journal Advanced Materials, achieves a reduction in inflammation by directly tamping down expression of the Spi1 gene that encodes PU.1. More generally, the new study also demonstrates a new way to deliver RNA to microglia, which have been difficult to target so far.
The simplest way to test whether siRNA could therapeutically suppress PU.1 expression would have been to make use of an already available delivery device, but one of the first discoveries in the study is that none of eight commercially available reagents could safely and effectively transfect cultured human microglia-like cells in the lab.
Instead, the team had to optimize an LNP to do the job. LNPs have four main components; by changing the structures of two of them, and by varying the ratio of lipids to RNA, the researchers were able to come up with seven formulations to try. Importantly, their testing included trying their formulations on cultured microglia that they had induced into an inflammatory state. That state, after all, is the one in which the proposed treatment is needed.
Among the seven candidates, one the team named “MG-LNP” stood out for its especially high delivery efficiency and safety of a test RNA cargo.
What works in a dish sometimes doesn’t work in a living organism, so the team next tested their LNP formulations’ effectiveness and safety in mice. Testing two different methods of injection, into the body or into the cerebrospinal fluid (CSF), they found that injection into the CSF ensured much greater efficacy in targeting microglia without affecting cells in other organs. Among the seven formulations, MG-LNP again proved the most effective at transfecting microglia. Langer said he believes this could potentially open new ways of treating certain brain diseases with nanoparticles someday.
Once they knew MG-LNP could deliver a test cargo to microglia both in human cell cultures and mice, the scientists then tested whether using it to deliver a PU.1-suppressing siRNA could reduce inflammation in microglia. In the cell cultures, a relatively low dose achieved a 42 percent reduction of PU.1 expression (which is good because microglia need at least some PU.1 to live). Indeed, MG-LNP transfection did not cause the cells any harm. It also significantly reduced the transcription of the genes that PU.1 expression increases in microglia, indicating that it can reduce multiple inflammatory markers.
In all these measures, and others, MG-LNP outperformed a commercially available reagent called RNAiMAX that the scientists tested in parallel.
“These findings support the use of MG-LNP-mediated anti-PU.1 siRNA delivery as a potential therapy for neuroinflammatory diseases,” the researchers wrote.
The final set of tests evaluated MG-LNP’s performance delivering the siRNA in two mouse models of inflammation in the brain. In one, mice were exposed to LPS, a molecule that simulates infection and stimulates a systemic inflammation response. In the other model, mice exhibit severe neurodegeneration and inflammation when an enzyme called CDK5 becomes hyperactivated by a protein called p25.
In both models, injection of MG-LNPs carrying the anti-PU.1 siRNA reduced expression of PU.1 and inflammatory markers, much like in the cultured human cells.
News Source: MIT
