Brazilian and U.S. researchers have developed a molecule called FRW that proved capable of binding to blood vessels; but in the brain but not in other organs when injected into the bloodstream in tests with mice. They used the technique to produce the first ever complete map of the vasculature of the brain; therefore paving the way for the creation of novel diagnostic imaging strategies; and therapies for diseases such as Alzheimer’s and Parkinson’s.
The research was supported by São Paulo Research Foundation; FAPESP and leding Ricardo José Giordano; a professor at the University of São Paulo’s Chemistry Institute (IQ-USP); which is in Brazil and head of its Vascular Biology Laboratory. The results are published in Proceedings of the National Academy of Sciences (PNAS).
As Giordano explained, the main obstacle to the development of drugs capable of binding to blood vessels; but in the brain is the blood-brain barrier, a selectively permeable cellular boundary; that protects the central nervous system from potentially toxic substances in the bloodstream. However, this research shows that FRW binds precisely to endothelial cell junctions in the blood-brain barrier.
In addition to producing a complete map of the brain’s vasculature; therefore, the new technique using to detect the kind of gap in the blood-brain barrier; but that may be one of the causes of neurodegenerative diseases such as Alzheimer’s and Parkinson’s.
“Theoretically speaking, if FRW does not bind to the cerebrovascular system; it’s a sign that the barrier is impairing,” Giordano told. To perform the study, the researchers used a library of bacteriophages, usually called phages; viruses that infect bacteria and can be used to deliver molecules because they are inoffensive to other organisms.
“Each of the phages in the library has been modifying genetic engineering; to have a different surface peptide [protein piece] from that of the original virus. This peptide carries a marker that’s detected when it binds to specific proteins, be they in the cerebrovascular system; in tumors, kidneys or other regions of the organism,” Giordano said.
The technique knowning as phage displaying winning; the 2018 Nobel Prize in Chemistry for its creators; George P. Smith and Gregory P. Winter. Smith first described phage display in 1985. In the following decade, the technique was adapting for application to living animals by Renata Pasqualini; a Brazilian-born researcher at Rutgers University in the U.S. and one of the authors of the article in PNAS.
The research led by Giordano began in 2011 as part of a project for which São Paulo Research Foundation FAPESP; awarded a scientific initiation scholarship to Fenny Hui Fen Tang, first author of the article. Tang continued to focus on this research interest for her master’s and again for her doctorate; recently completed at IQ-USP. FAPESP also provided funding to Giordano via a Young Investigator Grant and a Regular Research Grant.
The blood-brain barrier
To arrive at the molecule, the researchers injected mice with an entire library; comprising some 10 billion different phages. The modifying viruses circulating in the bloodstream; and although most were eliminating by the organism; but some bound to the vasculature of different organs and tissues, including the blood-brain barrier.
These phages were retrieved from the animals’ brains and cultured in bacteria so that they multiplied. The next-generation phages were injected into other mice to enhance selection. After three cycles, approximately 3,000 phages bound to blood vessels in the brain.
“The selection process was won by the peptides with the most affinity with the cerebrovascular system; because they multiplied the most,” Giordano explained. Out of the 3,000-odd peptides that bound to the blood-brain barrier, 1,021 contained a sequence of three amino acids: phenylalanine, arginine and tryptophan (FRW).