Optimal conditions for peripheral nerve storage in green tea polyphenol: an experimental study in animals

Our previous study demonstrated successful peripheral nerve storage for 1 month using polyphenol solution. We here report two studies to solve residual problems in using polyphenols as a storage solution for peripheral nerves. Study 1 was designed to determine the optimal concentration of the polyphenol solution and the optimal immersion period for nerve storage. Rat sciatic nerve segments were immersed in polyphenol solution at three different concentrations (2.5, 1.0, and 0.5 mg/ml) for three different periods (1, 7, and 26 days). Electrophysiological and morphological studies demonstrated that nerve regeneration from nerve segments that had been immersed in 1 mg/ml polyphenol solution for 1 week and in Dulbecco's modified Eagle's medium (DMEM) for the subsequent 3 weeks was superior to the regeneration in other treatment groups. In study 2, the permeability of nerve tissue to polyphenol solution was investigated using canine sciatic nerve segments stored in 1.0 mg/ml polyphenol solution for 1 week and in DMEM for the subsequent 3 weeks. Electron microscopy revealed that the Schwann cell structure within 500-700 μm of the perineurium was preserved, but cells deeper than 500-700 μm were badly damaged or had disappeared. The infiltration limit for polyphenol solution into neural tissue is inferred to be 500-700 μm.