The effect of delivery via narrow-bore needles on mesenchymal cells

Abstract

Aims: Recently, there have been numerous preclinical and human studies investigating the regenerative capacity of cell suspensions following their direct injection into a target organ: the fundamental parameters for successful (clinical) cell therapy. At present, limited data exist in the identification of factors important for the survival of these cells (i.e., morphology, viability and proliferation rates) during and following their ejection via narrow-bore needles. Materials & methods: Primary murine mesenchymal stem cells (mMSCs) were isolated, expanded and processed into a concentrated cell suspension consisting of either HBSS or HBSS supplemented with the antioxidant n-acetyl-cysteine. This suspension was then ejected from a 10 µl Hamilton syringe, via a variety of bore-sized needles, at different ejection rates. Cell characteristics including viability, spreading and attachment, apoptosis and proliferative ability were then assessed. Results: Following manipulation within a syringe, a decrease in the viability and cell spreading of mMSCs and a concurrent increase in the production of the caspase-3 protein, an early regulatory event in apoptosis, occurs. These detrimental effects were found to be increased when the cells were left in the syringe chamber for increased periods of time, and were similar at 5 µl/min and 1 µl/min ejection rates. However, on increasing the needle bore diameter, a significant reduction in these characteristics was observed. By comparison, mMSCs that were left to stand at room temperature (18–20°C), but were not manipulated within a syringe, showed a significantly greater viability compared with manipulated cells. However, cells kept at 4°C demonstrated a decreased viability compared with manipulated cells. When the mMSC were incubated with n-acetyl-cysteine, a known antioxidant, no significant change in caspase-3 production or cell spreading was observed. Conclusions: This study highlights potential parameters, such as minimizing the time period the cells are within the syringe and the use of wider-bore needles, involved in maintaining the high viable cell density required for the delivery of cell suspensions for cell therapy applications.