Fig. 1

Optimization of ¹⁴C-TdR labeling concentration for PDB-MSCs. a In vitro cellular uptake of ¹⁴C-TdR in three different concentrations (0.2, 1 and 5μCi). Disintegration per minute (dpm) per cell was used to express the radioactivity. The radioactivity per cell increased in a concentration-dependent manner (n = 5). The radioactivity per cell increased in a concentration-dependent manner (n = 5). b ¹⁴C-TdR percentage uptake decreased with the concentration (n = 5). **P < 0.01 compared with the 0.2μCi group; ^ΔΔ P < 0.01 compared with the 1 μCi group. c The proliferation curve of the 4th passage of PDB-MSCs: 5μCi ¹⁴C-TdR labeled PDB-MSCs group showed a lower growth rate than any other groups. One μCi and 0.2μCi groups had the similar proliferation ability compared to the unlabeled group (n = 6). Data is shown as mean ± SD, N = 5 for ¹⁴C-TdR labeling study, N = 6 for cell proliferation analysis. ^** P < 0.01 1 μCi group compared with the control group; ^## P < 0.01 0.2μCi group compared with the control group; ^ΔΔ P < 0.01 5μCi group compared with the control group