Inhibition of Ku70 in a high-glucose environment aggravates bupivacaine-induced dorsal root ganglion neurotoxicity

Long-term sensorimotor changes after a sciatic nerve block with bupivacaine and liposomal bupivacaine in a high-fat diet/low-dose streptozotocin rodent model of diabetes

Introduction

It is unclear whether patients with diabetes are more susceptible to nerve toxicity of local anesthetics or whether nerve blocks can accelerate the progression of diabetic peripheral neuropathy. Bupivacaine is one of the most widely used local anesthetics for regional anesthesia despite many pre-clinical studies demonstrating neurotoxicity. Herein, we report the long-term functional consequences of sciatic nerve block with bupivacaine and liposomal bupivacaine (Exparel®) in an animal model of diabetes.

Methods

Male Sprague Dawley rats were subject to standard chow/vehicle or high-fat diet/low-dose streptozotocin to induce a diabetic phenotype. Animals were then subdivided into groups that received repeated sciatic nerve blocks of saline, bupivacaine, or liposomal bupivacaine. Mechanical allodynia and thermal hyperalgesia were assessed prior to and 12 weeks following nerve blocks utilizing the von Frey and Hargreaves tests, respectively. Exploratory and locomotor activity were assessed with open field testing, and nerve conduction velocity testing was conducted prior to the termination of the study at 28 weeks.

Results

Animals in the diabetic group developed sustained hyperglycemia >200 mg/dl and signs of peripheral neuropathy six weeks after treatment with streptozotocin, which persisted until the end of the study. Twelve weeks after a repeated sciatic nerve block with saline, bupivacaine, or liposomal bupivacaine, results indicate significant interaction effects of the disease group (control vs. diabetic) and local anesthetic treatment. Overall, diabetic status resulted in worse sensorimotor function compared to control animals. Treatment with perineural bupivacaine resulted in worse sensorimotor functions in both control and diabetic animals. Furthermore, bupivacaine treatment in diabetic animals with pre-existing neuropathy exacerbated sensorimotor function in some measures. In contrast, liposomal bupivacaine did not appear to cause any negative effects on functional outcomes for control or diabetic animals.

Conclusion

Our data indicate that bupivacaine, and not liposomal bupivacaine, causes long-term changes in tactile allodynia, thermal hyperalgesia, locomotor behaviors, and nerve conduction velocity in control as well as a high-fat diet/low-dose streptozotocin rodent model of diabetes. These results highlight the necessity to investigate safe peripheral nerve block strategies to preserve long-term functional independence in patients with or at risk for diabetic peripheral neuropathy.

P53 and taurine upregulated gene 1 promotes the repair of the DeoxyriboNucleic Acid damage induced by bupivacaine in murine primary sensory neurons

The research aimed to explore the biological role of p53 protein and long non-coding RNA (lncRNA) taurine upregulated gene 1 (TUG1) in bupivacaine (bup)-induced neurotoxicity. Our work treated dorsal root ganglion (DRG) cells with bup, detected cell viability through CCK-8, apoptosis through TUNEL assays, DeoxyriboNucleic Acid (DNA) damage through γ-H2AX protein and comet assay, including p53 mRNA, protein and TUG1 expression through q-PCR and western blot, furthermore, cell viability and DNA damage were determined after the silencing of p53 and TUG1, biological information and TUG1 FISH combined with p53 protein immunofluorescence (IF) was performed to determine the cellular localization of these molecule. In vivo experiments, we explored the impact of intrathecal injection of bup on p53 mRNA and protein, TUG1, γ-H2AX protein expression. The results showed that bup was available to signally decreased cell viability, promoted apoptosis rate and DNA damage, additionally, bup increased p53 mRNA and protein and TUG1 expression. P53 siRNA and TUG1 siRNA significantly increased DNA damage. Furthermore, bioinformatics analysis and colocalization experiments revealed that the p53 protein is a transcription factor of TUG1, in vivo experiment, intrathecal injection of bup increased the p53 mRNA, p53 protein, TUG1 and γ-H2AX protein in the murine DRG. In this study, it was found p53 and TUG1 promote the repair of the DNA damage induced by bup in murine dorsal root ganglion cells, suggesting a new strategy for the amelioration of bup-induced neurotoxicity.

MiR-1224 downregulation inhibits OGD/R-induced hippocampal neuron apoptosis through targeting Ku protein

Ischemic cerebrovascular disease is the main cause of disability due to stroke. This study aimed to investigate the function of miR-1224 in OGD/R-induced hippocampal neuron apoptosis, as well as the regulatory mechanism of miR-1224 in ischemic cerebrovascular disease. The oxygen-glucose deprivation/reperfusion (OGD/R) model of primary mouse hippocampal neurons was established. RT-qPCR detected miR-1224, Ku70 and Ku86 levels. Western blotting was applied to measure the expression of Ku70/86 and apoptosis related proteins. Flow cytometry was used to assess apoptosis. JC-1 fluorescence was performed to test the mitochondrial membrane potential (MMP) in neurons. The double luciferase reporter assay was performed to investigate the relationship between miR-1224 and Ku70/86. OGD/R induced the apoptosis and mitochondrial injury in neuronal cells, while miR-1224 downregulation or Ku70/86 upregulation reversed this phenomenon. Meanwhile, miR-1224 negatively regulated the expression of Ku70/86 in neuronal cells through directly targeting Ku70/86. Furthermore, knockdown of Ku70/86 significantly reversed the inhibitory effect of miR-1224 silencing on apoptosis and mitochondrial injury in OGD/R-treated neuronal cells. Our findings indicated that miR-1224 downregulation suppressed OGD/R-induced hippocampal neuron apoptosis by targeting Ku protein, suggesting that miR-1224 could serve as a new target for ischemic cerebrovascular disease treatment.

Bupivacaine Induces ROS-Dependent Autophagic Damage in DRG Neurons via TUG1/mTOR in a High-Glucose Environment

Bupivacaine (BP) is a commonly clinically used local anesthetic (LA). Current studies suggest that neurological complications are increased in diabetic patients after LA application, but the molecular mechanism is poorly understood. LA-induced autophagy and neuronal injury have been reported. We hypothesized that a high-glucose environment aggravates BP-induced autophagic damage. Mouse dorsal root ganglion (DRG) neurons were treated with BP in a high-glucose environment, and the results showed that reactive oxygen species (ROS) levels increased, autophagy was activated, autophagy flux was blocked, and cell viability decreased. Pretreatment with the ROS scavenger N-acetyl-cysteine (NAC) attenuated ROS-mediated autophagy regulation. Moreover, the expression of the long noncoding RNA (lncRNA) taurine upregulated gene 1 (TUG1) increased, and NAC and TUG1 siRNA inhibited the expression of TUG1/mammalian target of rapamycin (mTOR) in DRGs treated with BP in a high-glucose environment. Intriguingly, contrary to previous reports on a positive effect on neurons, we found that rapamycin, an autophagy activator, and chloroquine, an autophagy and lysosome inhibitor, both exacerbated autophagic damage. These data suggest that a high-glucose environment exacerbated BP induced ROS-dependent autophagic damage in DRG neurons through the TUG1/mTOR signaling pathway, which provides a theoretical basis and target for the clinical prevention and treatment of BP neurotoxicity in diabeties.

P53 inhibitor pifithrin-α inhibits ropivacaine-induced neuronal apoptosis via the mitochondrial apoptosis pathway

The neurotoxicity of local anesthetics (LAs) has attracted more and more attention, However, they lack preventive and therapeutic measures. Many studies have shown that apoptosis plays an important role in the process of LA-induced neurotoxicity. As an important signaling molecule to activate apoptosis, p53 has been proved to be involved in the neurotoxicity induced by LAs, but the mechanism is unclear. In this study, we explored the effect of pifithrin-α (PFT-α), a p53 inhibitor, on apoptosis by ropivacaine (Rop) in vivo and in vitro. Cell viability and apoptosis detected by CCK-8 and a JC-1 apoptosis detection kit, the changes of spinal cord structure observed after hematoxylin and eosin staining, apoptosis of the spinal cord measured by terminal deoxynucleotidyl transferase dUTP nick end labeling staining, behavioral assessment of the nerve Injury evaluated by the detection of sciatic nerve conduction velocity (SNCV) andmechanical withdrawal threshold (MWT), the expression of p53 and many apoptosis-related genes included Bax, Bcl-2, and caspase-3 detected by quantitative real-time polymerase chain reaction, Western blot analysis, immunofluorescence, and immunohistochemistry. Results showed that PC12 cell viability decreased because of Rop, but the pretreatment of PFT-α could protect it. And PFT-α reduced the injuries in the spinal cord by Rop included vacuoles or edema. The results of immunofluorescence and immunohistochemistry testing showed that PFT-α inhibited the p53 protein upregulated by Rop. Apoptosis rate and many proapoptotic genes include p53, Bax, caspase-3 messenger RNA, and proteins were increased by Rop, but PFT-α could decrease it. In conclusion, PFT-α inhibited cell apoptosis and spinal cord injuries induced by Rop.