Autologous Transplantation Of Nucleus Pulposus Sensitizes Sodium Channels By Cystathionine β-synthetase Activation In A Rat Model Of Lumber Disc Herniation

Background and Aims: Lumbar disc herniation(LDH) is a common and frequently-occurring disease, lumbocrural pain and sciatica is the most common symptoms. Now there is three kinds of pathogenesis, but the exact mechanism of spinal nerve roots pain remains unclear. Lots of studies suggest that CBS play an important role in inflammatory and neuropathic pain,and that voltage-gated sodium channels(VGSCs) play an important role in the process of developing and maintaining in pain, Research on voltage dependent sodium channel in low back pain in the role is conducive to reveal the occurrence of the disease and maintenance mechanism, and provide a theoretical basis for the development of a new generation of analgesic drugs. Methods: 30 adult male SD rats were randomly divided into model group(15 rats) and sham operation group(15 rats), model group was induced by implantation of autologous nucleus pulposus(NP) harvested from rat tail to lumbar 5 and 6 spinal nerve roots) sham operation group only exposed the L5-L6 nerve root.Methods: L5-L6 dorsal root ganglion(DRG) neurons were labeled with Di I and acutely dissociated for measuring excitability and sodium channel current under whole-cell patch clamp configurations. The expression of Na V1.7 and Na V1.8 was analyzed by western blot and immunofluorescence study.Results: Compared with sham group, NP transplantation significantly reduced the PWT and PWL. Administration of CBS antagonist significantly reduced hyperexcitability of LDH model rats, and reversed the hypersensitivity in a dose dependent manner. NP transplantation also led to a significant reduction in rheobase and an increase in numbers of action potentials evoked by 2X and 3X rheobase current stimulation. Voltage-gated sodium current density was significantly enhanced in L5-L6 DRG neurons from LDH rats. Compared with sham controls, inactivation curve showed a leftward shift in LDH rats, evidenced by a marked hyperpolarization of the Vhalf(V1/2) of inactivation curve. NP transplantation did not significantly alter activation curve. However, NP transplantation remarkably enhanced expression of Na V1.7 and Na V1.8 of L5-L6 DRGs but not in T10-12 DRGs. We showed that CBS was colocalized with Na V1.8 in L5-L6 DRG neurons pre-labeled with Di I. Pretreatment of O-(Carboxymethyl) hydroxylamine hemi hydrochloride(AOAA), an inhibitor of CBS, significantly reduced expression of Na V1.7 and Na V1.8 in LDH rats when compared with NS treatment. AOAA treatment also inhibited the neurons’ excitability,reduced sodium current density and normalized the Vhalf of activation curve in L5-L6 DRG neurons in LDH rats. Compared with controls, inactivation curve showed a rightward shift and the inactivation curves significantly gave a leftward shift after injection of AOAA inhibitor. Conclusions: These data suggest that sensitization of sodium channel activity is most likely mediated by upregulation of CBS expression of L5-L6 DRG neurons in LDH rats, thus identifying a potential target for treatment for lumbocrural pain in patients with LDH.