Long-term cryopreserved allogeneic nervous and vascular tissue transfers in monkeys

Plunge-Freezing Cryopreservation of Tendons

Allograft transplantation is an important method for tendon reconstruction after injury, and its clinical success highly relies on the storage and transportation of the grafts. Cryopreservation is a promising strategy for tendon storage. In this study, we report a novel cryopreservation agent (CPA) formulation with a high biocompatibility for tendon cryopreservation. Mainly composed of natural zwitterionic betaine and the biocompatible polymer poly(vinylpyrrolidone) (PVP), it exhibited ideal abilities to depress the freezing point and inhibit ice growth and recrystallization. Notably, after cryopreservation via plunge-freezing for 1 month, Young's modulus (144 MPa, 98% of fresh tendons) and ultimate stress (46.7 MPa, 99% of fresh tendons) remained stable, and the cross-linking of collagen microfibers, protein structures, and glycosaminoglycan (GAG) contents changed slightly. These results indicate that the formulation (5 wt % betaine and 5 wt % PVP in phosphate-buffered saline, PBS solution) effectively maintains the biomechanical properties and tissue structure. This work offers a novel cryopreservation method for tendons and may also provide insights into the long-term preservation of various other tissues.

Nerve regeneration in rat peripheral nerve allografts: Evaluation of cold-inducible RNA-binding protein in nerve storage and regeneration

The prevalence of peripheral nerve injury has attracted increased attention. Allografting has been proposed as a potential treatment strategy for peripheral nerve injury. Moreover, cryopreservation may provide almost unlimited graft material. We investigated whether cold-inducible RNA-binding protein (CIRP) could protect peripheral nerves during cryopreservation to promote regeneration postoperation. First, CIRP was highly expressed after pretreatment at 32°C. After 4 weeks of cryopreservation, the increased live cells, low Bax/Bcl-2 ratio and high nerve growth factor and glial cell-derived neurotrophic factor levels in the 32°C group demonstrated high nerve graft viability. At 4 weeks postoperation, 32°C-Allo group demonstrated low plasma levels of interleukin-6 and interferon-gamma and a diminished cellular immune response. At 20 weeks postoperation, nerve regeneration in the 32°C-Allo group was similar to that in the fresh isograft group and superior to that in the 4°C-Allo and 15°C-Allo groups. Moreover, the compound muscle action potential and the motor nerve conduction velocity of the 32°C-Allo group were equal to those of the fresh isograft group. In conclusion, CIRP induction increased Schwann cell biological activity, inhibited cell apoptosis, reduced immune rejection, and promoted recipient nerve regeneration. Thus, CIRP could exert protective effects during nerve storage and stimulate regeneration in peripheral nerve reconstruction.

Successful storage of peripheral nerves using University of Wisconsin solution with polyphenol

We have previously reported that green tea polyphenol can preserve peripheral nerve segments for up to 1 month. In this study, we investigated the effect on peripheral nerve preservation of adding polyphenol to the conventional University of Wisconsin solution (UW solution), which has been widely used for organ storage. Twenty millimeter-long sciatic nerve segments, harvested from Lewis rats, were immersed in UW solution containing polyphenol (1 mg/mL) for 1 week and then in UW solution alone at 4 degrees C for 3 additional weeks before transplantation into recipient Lewis rats. Neural cell viability of the preserved nerve segments was confirmed by vital staining (calcein-AM/ethidium homodimer), electron microscopy, and genomic studies. Morphologically, nerve regeneration was similar to that of fresh isografts and superior to that of grafts stored with UW solution alone. Moreover, the electrophysiological results were equal to those of fresh isografts. Polyphenol has the potential to be used for peripheral nerve storage and could be useful for routine peripheral nerve banking.

Successful storage of peripheral nerve before transplantation using green tea polyphenol: an experimental study in rats

Green tea polyphenol is known to act as a buffer, reducing biological responses to oxidative stress. Several effects of polyphenol have been reported, such as protection of tissue from ischemia, antineoplasmic and anti-inflammatory effects, and suppression of arteriosclerosis. In this study, we investigated whether peripheral nerve segments could be kept viable in a polyphenol solution for 1 month. Sciatic nerve segments, 20 mm long, were harvested from Lewis rats and treated in three different ways before transplanting to recipient Lewis rats to bridge sciatic nerve gaps created by removal of 15-mm-long nerve segments. Group F: nerve segments were transplanted immediately after harvesting. Group P: nerve segments were transplanted after they had been stored in Dulbecco's Modified Eagle's Medium (DMEM) containing polyphenol for 7 days at 4 degrees C and then in DMEM for 21 days at 4 degrees C. Group M: nerve segments were stored in DMEM solution alone for 28 days at 4 degrees C. Viability of the nerve segments was assessed by vital staining (calcein-AM/ethidium homodimer), by electron microscopy and by genomic studies before transplantation. Nerve regeneration was evaluated using electrophysiological and morphological studies 12 and 24 weeks after transplantation. Neural cell viability of the preserved nerve segments was confirmed in group P, in which the nerve regeneration was similar to that in group F and superior to that in group M. Peripheral nerve segments can be successfully preserved for 1 month using green tea polyphenol.