The Research On Protective Effect Of Lycium Barbarum Polysaccharide And Its Mechanism Involved In MTOR/p70S6K/Autophagy Signaling Pathway On Diabetic Peripheral Neuropathy In Streptozotocin-induced Diabetic Rats

Objective We evaluated the protective effect of Lycium barbarum polysaccharide(LBP)through the induction of autophagy by inhibiting the activation of the m TOR/p70S6 K pathways in diabetic peripheral neuropathy(DPN).Methods After overnight fasting,the rats were intraperitoneally(i.p.)injected with streptozotocin(STZ,50 mg/kg body weight)in a sodium citrate buffer(0.1 mol/L of citrate,p H 4.5)one time.Their blood glucose was measured from the tail vein 72 hours after the STZ injection.Diabetes mellitus(DM)was defined as a serum glucose level above 16.8 mmol/L.Diabetic rats were randomly assigned into diabetes mellitus(DM),Lycium barbarum pol ysaccharide(LBP),lipoic acid(LA)and metformin groups.Animals in the control group w ere randomly selected from normal rats.Each group contained 15 rats.The blood glucose levels were measured every four weeks.The protective effects of the LBP were assessed in Von Frey filaments test and hot plate test.To further evaluate the positive effects of LBP treatment on sciatic nerve function,electrophysiological parameters were tested.The ultrastructural changes of sciatic nerves after treatment with LBP were evaluated by electron microscopy in DM rats.The expression of the myelin-related proteins,tracing myelin protein zero(P0)and myelin basic protein(MBP),was further examined by Western blot.The expression of the autophagy-related proteins,microtubule-associated protein light chain 3-?(LC3-?),Beclin1,P62,mammalian target of rapamycin(m TOR),p-m TOR,p70 ribosomal protein S6 kinase(p70S6K)and p-p70S6 K in the sciatic nerve of the rats was examined by Western blot and immunohistochemical staining.Results LBP mildly decreased blood glucose levels and partially rescued allodynia and hyperalgesia in the diabetes mellitus(DM)rats.For the electrophysiological function of the sciatic nerve,the decrease in sensory nerve conduction velocity(SNCV)and sensory nerve action potential(SNA P)amplitudes in DM rats were partiall y rescued.Moreover,DM-induced structural damage to the nerve fiber myelination showed great improvement by 12 weeks of LBP treatment.The decreased expression of the myelin-related proteins,myelin protein zero(P0)and myelin basic protein(MBP),in the DM sciatic nerve was also markedly rescued after 12 weeks of LBP treatment.Furthermore,the possible role of mammalian target of rapam ycin(m TOR)-mediated autophagy during these protective processes was examined.The expression of microtubule-associated protein light chain 3-?(LC3-?)and Beclin1 in the sciatic nerve was significantl y decreased while the expression of P62 increased in DM rats,demonstrating an decreased activation of autophagy.As expected,the LC3-? and Beclin1 protein levels were markedl y increased,and P62 was markedly decreased after LBP treatment.The expression of m TOR,p-m TOR,p70 ribosomal protein S6 kinase(p70S6K)and p-p70S6 K in the DM group were markedl y increased,while all of these proteins decreased in LBP group.Conclusions LBP exerts protective effects on DPN,which is likely to be mediated through the induction of autophagy by inhibiting the activation of the m TOR/p70S6 K pathways.