Introduction: Human platelet lysate (hPL) part of the growth factor cocktail derived from human platelets, which has been applied as a cell growth supplement. The production process is easier in comparison to platelet-rich plasma; thus, hPL is now considered for use in wound healing therapy. However, methods for preserving hPL for more than several months that maintain its bioactivity must be considered, especially for chronic wound treatment. The present study compared the effects of preservation for 9 months using a refrigerator or deep freezer.
Methods: We investigated three preservation conditions. In the C-hPL group, hPL was stored at -80 °C in a deep freezer for 9 months; in the CL-hPL group, hPL was cryopreserved for 9 months at -80 °C in a deep freezer then lyophilized; in the L-hPL group, lyophilized hPL was refrigerated at 4 °C for 9 months. The quantity and quality of growth factors in these three groups were measured by an ELISA and in fibroblast cell cultures. Then, gelatin hydrogel discs were impregnated with hPL and its effects with regard to the promotion of wound healing in mice were evaluated by histologic examinations.
Results: The PDGF-BB concentration in C-hPL, CL-hPL and L-hPL was 18,363 ± 370 pg/ml, 11,325 ± 171 pg/ml, and 12,307 ± 348 pg/ml, respectively; the VEGF concentration was 655 ± 23 pg/ml, 454 ± 27 pg/ml, and 499 ± 23 pg/ml, respectively; and the TGF-β1 concentration was 97,363 ± 5418 pg/ml, 73,198 ± 2442 pg/ml, and 78,034 ± 3885 pg/ml, respectively. In cell culture medium, fibroblast cell cultures were better supported in the hPL groups than in the fetal bovine serum group. In the histologic examination of the wound healing process, no differences were observed among the three preserved hPL groups with regard to epithelialization, or granulation tissue or capillary formation. The wounds in all groups had almost healed by day 14.
Conclusions: The stability of growth factors contained in lyophilized hPL is maintained at 4 °C for up to 9 months. This was a versatile preservation method that can be applied in clinical practice.
Keywords: Cryopreservation; Gelatin hydrogel; Long-term preservation; Lyophilization; Platelet lysate; Wound healing.