Introduction: Adipose aspirates from a conventional liposuction can be an excellent source of human stem cells but whether these tissues can be processed later to produce possible human stem cells after long-term preservation remains unknown. The purpose of this study was to test our hypothesis that previously cryopreserved adipose aspirates would still be a potential source of human stem cells.

Methods: Samples of adipose aspirates were obtained from 12 adult female patients who underwent a conventional liposuction of the abdomen. Each specimen was collected from the middle layer after centrifugation. In the cryopreserved group, adipose tissues were preserved by an optimal cryopreservation method where cryoprotective agents, a combination of 0.5 M dimethyl sulfoxide and 0.2 M trehalose, were added to the tissues. Cryopreservation of the tissues was subsequently conducted with controlled slow cooling and then stored in liquid nitrogen (-196 °C). One gram of fresh or cryopreserved (after fast rewarming)adipose aspirates was digested with collagenase and centrifuged. The resulting cell pellet, consisting of so-called processed lipoaspirate (PLA) cells, was suspended in culture medium supplemented with fetal bovine serum and antibiotics. The adherent PLA cells after a two-week standard cell culture were detached from the culture plate with trypsin and then suspended for cell counts.

Results: Flat, spindle-shape PLA cells from the cryopreserved group became adherent to the plate within 48 to 72 hours after culture compared to the control group where the cells became adherent by 24 hours. After a two-week culture, the cryopreserved adipose aspirates yielded an average of 3.7±1.4 x 100000(mean±SEM)/ml PLA cells, equal to 90% of the yielded number of cells obtained from the fresh adipose aspirates (4.1±1.4 x 100000 PLA cells/ml).

Conclusions: Our results, for the first time, indicate that although there is a latency of cell growth after an optimal cryopreservation, cryopreserved adipose aspirates can yield a significant number of PLA cells compared to fresh aspirates. Cryopreserved adipose aspirates can be a potential source of human stem cells because they can still be processed later for PLA cells after long-term preservation.