The Effect of Primary Drying Temperature on Freeze-dried Mesenchymal Stem Cell Secretome Composition

Abstract

Mesenchymal stem cells (MSC) are multipotent stromal cells capable of regenerating and differentiating into various tissues. MSCs can secrete over 200 different types of these bioactive molecules called secretomes, that contain chemokines, interleukins, growth factors, and extracellular matrix proteins. However, the bioactive molecules present in these can degrade over time due to temperature. This study compares different primary drying temperatures of the freeze-drying process and cryoprotectant choice towards protein content and purity. Freeze-drying of the secretome samples using 4% and 8% trehalose v/v was performed, where 8% showed a smaller decrease in the protein content. Furthermore, the secretome samples were freeze-dried at a primary drying temperature of -35°C, -30°C, and -25°C. The protein content and purity were then analyzed through pH measurement, BCA assay, and SDS-PAGE. There were no significant changes in the pH of the samples at different drying temperatures. In the BCA assay, there was no significant difference in the secretome decrease in protein as the temperatures were increased. However, SDS-PAGE results showed an increase in bands as the primary drying temperature. This indicates that although the proteins are broken down into smaller proteins, the total content was unaffected by the freeze-drying process.