An Experimental Study On Enhancing Peripheral Nerve Regeneration Of Glycyrrhizin In Mice

Objective: To observe the effect of Glycyrrhizin on immune function ofBalb/c mice with sciatic nerve injury, and explore the mechanism of improvedperipheral nerve regeneration induced by Glycyrrhizin.Methods and Results:1. The effect of Glycyrrhizin on immune function of Balb/c mice80mice with sciatic nerve injury were randomly divided into4groups, andthe Glycyrrhizin were injected intraperitioneally according to the dose of20mg/kg/d，10mg/kg/d,5mg/kg/d, respectively. The mice of control group wereinjected with normal saline. The day before the molding, the start ofadministration,Continuous administration to death，After3days,5days,7days,14days administration, respectively, the mice were killed by spinal separation, andthe spleen lymphocytes were isolated and cultured in RPMI1640medium.Thenthe transformation capability of T and B lymphocytes were tested by MTT method.At the same time, the T and B lymphocytes of normal mice were stimulated bydifferent concentrations of Glycyrrhizin and Cyclosporine A in vitro, and thetransformation capability of T and B lymphocyte were also tested by MTT method.The results show that: Glycyrrhizin can significantly inhibit T and B lymphocytes’proliferation and transformation in vitro and in vivo by dose-dependent method.2. The effect of Glycyrrhizin on expression of GAP-43and p75NTR in Balb/C mice with sciatic nerve injuryBalb/c mice with sciatic nerve injury were interved by different dose ofGlycyrrhizin for1day,3days,5days,1week,2weeks,4weeks,8weeks,12weeks,respectively, and the expression of GAP-43and in spinal cord were testedby immunohistochemical assay, Real-time PCR and western-blot. The resultsshow that:(1) the expression of GAP-43in the spinal cord segment wasincreased,and GAP-43mainly occur in the cytoplasm of anterior horn cells;(2) theexpression of GAP-43in high and middle dose of Glycyrrhizin groups weresignificantly higher than that of low dose and control groups;(3) the expression ofp75NTR in spinal cord start to increase and reach to peak after1day to2weeks ofsciatic nerve injury, and the expression of p75NTR mainly occur in the cytoplasmof anterior horn cells;(4) the expression of p75NTR in high and middle dose ofGlycyrrhizin groups were significantly lower than that of low dose and controlgroups.3. The effect of Glycyrrhizin on nerve regeneration after injuryAfter intervention by different dose of Glycyrrhizin, the spinal cord segmentof Balb/c mice with sciatic nerve injury were stained by HE, double stain ofimproved Marsland and LFB method and observed under the microscope. Theapoptosis of spinal cord segment of mice with sciatic nerve injury were also testedby TUNEL method. And nerve conduction velocity and amplitude were tested byMedtronic Keypoint machine.The results showed that:(1) Glycyrrhizin decreasedthe secondary never injury and demyelination level;(2) the number of myelinated nerve fibers of Glycyrrhizin treated groups with uniform distribution and lessdemyelination level are more than that of control group;(3) Glycyrrhizin canimprove the structure, function, distribution of the muscle cells, and the musclecells treated by Glycyrrhizin arranged closely and has the larger cross-sectionalarea of muscle fibers with low proliferation of connective tissue;(4) the nervefunction improvement of Glycyrrhizin treated groups are better than control group;(5) Glycyrrhizin decreased the apoptosis of spinal cord segment of mice withsciatic nerve injury.Conclusion:1. Glycyrrhizin inhibited immune function and decrease the immune responseintensity of Balb/c mice in a dose dependent manner.2. Glycyrrhizin increased the expression of GAP-43and decreased theexpression of p75NTR.3. Glycyrrhizin improved the regeneration of injured peripheral nerve, whichis related to the inhibition of immune system and reduction of expression ofp75NTR by decreasing the secondary immune injury and uploading the expressionof GAP-43.