An evaluation of spraying as a delivery method for human mesenchymal stem cells suspended in low-methyl pectin solutions

BACKGROUND: Mesenchymal stem cells have shown promise in many areas of regenerative medicine due to the anti-inflammatory and pro-regenerative effects of the secreted factors. However, successful delivery remains problematic, particularly for delivery to areas such as the brain. Spray delivery is a method investigated in wound care and lung injury, which may be applicable for brain delivery to patients already requiring surgery. To retain therapeutic mesenchymal stem cells at the delivery site, biomaterials can be employed; pectin is a biocompatible, sprayable, and mucoadhesive material, which could prove suitable for spray delivery of cells for therapeutic uses. METHODS: The biocompatibility of four grades of low-methyl pectin gelled by addition of calcium was assessed using SH-SY5Y cells. After, mesenchymal stem cells were suspended within the four different grades of low-methyl pectin solutions and sprayed using a syringe-driven spray device. The suitability was then assessed by cell viability testing, flow cytometry to test for surface markers, and differential gene expression studies to understand the effects of both the pectin and the spraying process on the gene expression of the cells. RESULTS: All four grades of low-methyl pectin were biocompatible with SH-SY5Y cells. The syringe-driven spray device delivered human mesenchymal stem cells to well plates with high viability, and suspending these cells in pectin solutions for spraying did not negatively affect the viability. The grade of pectin named CU-701 was the best grade based on results of the flow cytometry, whereby the surface marker expression was not altered from the control cells. The RNA sequencing showing the differential expression showed that the process of spraying the cells did not alter gene expression compared to the control, however the pectin, and the presence of calcium used to induce gelation of the pectin, did lead to altered gene expression in cells. CONCLUSION: Spraying is a suitable delivery method for the mesenchymal stem cells, showing no detrimental effect on the cells. Pectin shows little effect on the viability of the cells, however the use of calcium to gel the pectin appears to affect the expression of several genes.