Development of self-assembling supramolecular peptide gel: road to cell-free regenerative therapy in brain regeneration

In collaboration with researchers from Kitasato University, National Yang Ming Chiao Tung University in Taiwan, Nagoya City University, and others, the research group comprising Associate Professor Itsuki Ajioka of the Center for Brain Integration Research at Tokyo Medical and Dental University, Professor Takahiro Muraoka of the Graduate School of Engineering at Tokyo University of Agriculture and Technology, and colleagues announced that they had developed a peptide "JigSAP", that forms a supramolecular peptide gel, allowing sustained release of proteins at the site of administration in the body. They demonstrated that the walking capabilities of stroke model mice was improved by the administration of the gel that allowed sustained release of VEGF protein, which shows revascularization action 1 week after the onset of cerebral infarction. This result is expected to advance studies on cell-free regenerative therapy for subacute cerebral infarction. The findings were published in November in the 19th issue of the international scientific journal Nature Communications.

In Japan, 200,000 patients develop cerebral infarction annually, and approximately 5% of them recover after receiving thrombolytic treatment and thrombus aspiration within 4.5 and 8 hours of onset, respectively. The other 95% have sequelae requiring nursing care levels 1-5. It is important that the medical and nursing care costs for these patients be reduced by the healthcare industry and government. However, there is no effective treatment for patients with subacute and severe cerebral infarction 1 week after its onset.

Despite high expectations from autologous stem cell transplantation that utilizes the potential regenerative ability of the brain and the technology of gradually releasing cell growth factors using a peptide gel as a scaffold, the method of stem cell transplantation is complicated, and there had been no peptide gel that could incorporate cell growth factors and allow their sustained release in the body.

The research group developed "JigSAP", a novel, clinically applicable, and highly safe supramolecular peptide gel that allows sustained release of an incorporated cellular growth factor at the site of administration in the brain.

While developing the peptide gel, the research group found that amphiphilic peptides form a gel by self-assembly and that the hydrophobic group of the amino acid side chain was planar with strong cohesive force owing to its hydrophobic interaction. However, although proteins with an amphiphilic tag were easily incorporated into the gel, their efficient sustained release in the body was still a challenge.

Then, they designed the hydrophobic group of an amphiphilic peptide to have an uneven shape like a jigsaw puzzle piece and synthesized the peptide "JigSAP". It consists of 11 amino acids, which form a gel in the ecological environment. The peptide forms a gel at neutral pH and hardens over time. Its capability was shown to be comparable to that of fibronectin, a natural cell scaffold.

Furthermore, its sustained release of proteins was examined. The research group demonstrated that enhanced green fluorescent protein (EGFP) tagged with JigSAP at the C-terminus (EGFP-JigSAP) self-assembled when mixed with an excess amount of JigSAP. When tested in an environment comparable to a that in the living body, the sustained release by EGFP-JigSAP had a high efficiency of approximately 40% in 1 week.

Next, based on previous reports, vascular endothelial growth factor (VEGF) was selected as a target for sustained release. VEGF tagged with JigSAP (VEGF-JigSAP) was prepared and mixed with JigSAP, which was then administered to the infarct site in cerebral infarction model mice to examine its efficacy.

Specifically, gait analysis was performed 7 days after the onset of cerebral infarction in the mice. Then, the gel was administered under different conditions, and gait and histological analyses were performed again 7 days later. Five administration conditions were compared: phosphate-buffered saline (PBS: control), JigSAP only, VEGF-JigSAP only, VEGF and VEGF-JigSAP, and a mixture of VEGF-JigSAP and JigSAP.

Walking function was improved in the mice only under mixed administration of VEGF-JigSAP and JigSAP. Histological analysis confirmed the promotion of angiogenesis and suppression of neuronal cell death around the injury site under this mixed administration. These effects likely contributed to the improvement of the walking function in the cerebral infarction model mice.

The research group are now working on the medical application and commercialization of JigSAP. They have been working actively by initiating the "Regeneration Project for Cerebral Infarction using Supramolecular Peptides" at the Kanagawa Institute of Industrial Science and Technology in April this year.

Associate Professor Ajioka says, "These results will not only facilitate the development of technology to exploit, but also advance research to elucidate the potential regenerative ability of the brain. In fact, we have obtained interesting data, and we hope that they will contribute to the development of neuroregenerative science."