A study in mice found that a certain composition of amino acids in peptides can inhibit the protein associated with Alzheimer's, thus diagnosing the disease before symptoms appear and preventing its development.
Many diseases, especially neurodegenerative diseases, are associated with protein aggregation – a condition in which their three-dimensional structure is damaged, causing them to stick together and eventually accumulate and settle on brain cells as insoluble particles (amyloids) and damage them. Before that, in the initial stage of the disease, processes occur in which soluble initial particles called oligomers are formed (which, if untreated, become amyloids). One of the common diseases associated with aggregation is Alzheimer’s – a degenerative brain disease characterized by decreased cortical function and cognitive and mental deterioration.
“There are over 35 diseases in which a single protein or a series of proteins lose their three-dimensional structure and undergo aggregation. Until about 30 years ago, it was thought that amyloids, the insoluble particles, were toxic to cells and caused disease. But more recent studies have revealed that there is no correlation between the amount of these deposits and the severity of the disease. Furthermore, attempts to reduce insoluble amyloids in Alzheimer’s did not lead to an improvement in the patients’ condition (the disease continued even after their reduction). Therefore, researchers began to suspect that the development of the disease lies in the transitional state before deposition, in which oligomers are formed, unstable particles that do not settle because they are soluble. Over time, they realized that oligomers are the initial stage of the disease, in their development into amyloids,” says Prof. Shai Rahimipour from the Department of Chemistry at Bar-Ilan University, who specializes in amyloid proteins that cause diseases.
In their research, Prof. Rahimipour and his team are trying to influence the amount of oligomers formed in the brain in order to contribute to the prevention and treatment of diseases such as Alzheimer's. They rely on studies that have shown that amyloids, which are formed from different proteins and cause different diseases, form similar three-dimensional structures, which can perforate the cell membrane and destroy them. They also found that amyloids can form molecular interactions with each other, probably due to the great similarity in their structure and function, and thus can sink together.
According to Prof. Rahimipour, “We discovered in the professional literature several types of proteins that aggregate together in various diseases. In Alzheimer’s, for example, it is known that several types of amyloids can accumulate together in the brain. Therefore, we hypothesized that they have a common chemical language that can be used to influence aggregation; we decided to build a simple synthetic chemical system with a structure similar to these proteins, which would speak the language of amyloids, interfere with aggregation, reduce it, and reduce their toxicity.”
The researchers prepared peptides (short chains of amino acids that make up proteins) from natural L-amino acids (which exist in the body's proteins) and unnatural, synthetic D-amino acids (which are not recognized by the body). This is because previous studies found that this compound can produce a structure very similar to that found in amyloids (Cross-beta-sheet) – like the amyloid beta protein that accumulates in the brain in Alzheimer's – and can therefore communicate with them in their "language". It was later found that these peptides can indeed bind the initial structure of two or three amyloid beta proteins, thus preventing the aggregation and production of oligomers and amyloids. "We put human beta amyloid in a test tube together with the peptides we prepared and saw that they inhibit the entire early process of the formation of toxic oligomers in Alzheimer's," notes Prof. Rahimipour.
The latest research by Prof. Rahimipour and his team, which won a grant from the National Science Foundation, was based on this discovery and in which they sought to know whether these peptides could be used both as markers for the early detection of Alzheimer's, even before the symptoms of the disease appear, and as a drug to prevent it. In collaboration with researchers from Canada, they labeled the peptides with a radioactive material and injected them into Alzheimer's disease mice (whose brains had been injected with human beta amyloid), young and old. They then performed PET-CT brain imaging on the mice and monitored the amount and location of the oligomers that developed in their brains.
Amyloid deposits (marked in red) and the peptides that prevent their development (marked in green) in mouse brain cells
In another experiment, the mice were treated with peptides three times a week for three to four months, at a very early stage of the disease, before symptoms appeared. They then underwent three cognitive, behavioral, and memory tests (in collaboration with Prof. Eitan Okun of the Multidisciplinary Center for Brain Research at Bar-Ilan University). Finally, the mice's brains were examined using biochemical and histopathological methods to check the amount of oligomers before and after peptide treatment.
In one cognitive test, mice were placed on a circular surface with several sealed holes and one open hole through which they could escape. For about a week, the mice learned where the open hole was located (for example, by placing food on it). After this week, the mice were returned to the surface and the researchers tested how long it took them to find the open hole. A group of healthy mice (without Alzheimer's) and a group of mice with Alzheimer's that were not treated with peptides also underwent the same tests, brain imaging, and brain surgery.
The researchers discovered that after a week of practice, the diseased mice treated with the peptides needed less than 20 seconds to find the open hole, similar to the healthy mice. In contrast, the untreated diseased mice needed about 40 seconds. Using brain imaging and in the brain itself, the researchers analyzed the level of oligomers and discovered that in the mice treated with the peptides it was much lower, significantly and distinctly, than in the untreated mice. “We discovered that the treated mice succeeded in the task similarly to healthy mice and that their brains had a very small amount of oligomers compared to the untreated mice. In other words, their disease did not progress significantly during the treatment,” explains Prof. Rahimipour.
The researchers also discovered that the accumulation of oligomers began in a brain region that had not previously been linked to Alzheimer’s – the thalamus (which, among other things, is responsible for sleep quality) – and from there spread to the cerebral cortex and hippocampus. According to Prof. Rahimipour, “this finding is consistent with the sleep disturbances that appear in the early stages of Alzheimer’s.”
The researchers then tried to improve the effectiveness of the peptides by attaching them to liposomes (microscopic spherical structures consisting of a lipid bilayer shell and used as delivery systems for a variety of drugs). They discovered that, together with liposomes, the peptides were more active and effective in reducing oligomers, possibly due to the increased number of molecules in a smaller area. “These findings raise great hope for the development of a new drug for the treatment of Alzheimer’s and even for its early diagnosis, and we are now planning clinical trials in humans to test its efficacy and safety,” concludes Prof. Rahimipour.
