Nefopam downregulates autophagy and c-Jun N-terminal kinase activity in the regulation of neuropathic pain development following spinal nerve ligation

Abstract

BackgroundNeurodegeneration is associated with changes in basal cellular function due to the dysregulation of autophagy. A recent study introduced the involvement of autophagy during spinal nerve ligation (SNL). Nefopam has shown potential for reducing neuropathic pain, but the underlying mechanisms are unknown. Here, we investigated the effects of nefopam on neuropathic pain development following SNL, focusing on the involvement of autophagy.MethodsThe functional role of nefopam in capsaicin-induced autophagy was assessed by human glioblastoma M059 K cells. The neuropathic pain model was used to determine whether the effect of nefopam on pain control was mediated through autophagy control. Neuropathic pain was induced by L5 and L6 SNL in male rats randomized into three groups: Group S (sham-operated), Group C (received normal saline), and Group E (received nefopam). A behavioral test using a von Frey was examined. Expression changes of autophagy in response to nefopam was analyzed in spinal cord tissues (L4-L6) by immunoblotting and immunohistochemistry.ResultsThe paw withdrawal threshold examined on days 3, 5, 7, and 14 post-SNL was significantly higher in Group E than in Group C. SNL increased the levels of microtubule-associated protein 1 light chain 3B (LC3B-1), with concomitant reduction of sequestosome 1 (SQTSM1/p62), compared with Group S, indicating that SNL induced autophagy. These effects were reversed by nefopam injection, and the results were confirmed by immunohistochemistry for LC3-I/II. Furthermore, SNL-mediated JNK activation was markedly decreased following nefopam injection. Hematoxylin and eosin staining on Day 14 post-SNL revealed that SNL caused lymphocyte infiltration and oligodendrocyte localization in the substantia gelatinosa of the dorsal gray horn, which were reduced by nefopam injection.ConclusionCollectively, the mode of action of nefopam on neuropathic pain appears to be associated with downregulation of phospho-JNK and autophagy, as well as modulation of the immune response.

Sec-O-glucosylhamaudol mitigates inflammatory processes and autophagy via p38/JNK MAPK signaling in a rat neuropathic pain model

“…In terms of neuroinflammatory mechanisms, the development of neuropathic pain after peripheral nerve injury is associated with immense inflammatory cascades via the activation of glial cells and astrocytes in the DRG, which leads to the release of proinflammatory cytokines [ 1 , 27 - 29 ]. Such neuroinflammatory processes, after nerve injury, are regulated by various signaling pathways, such as p38 MAPK, JNK, and NF-κB, among others [ 4 - 7 ]. In stressful conditions such as spinal cord injury, the stress-activated protein kinase group of MAPKs, including JNK and p38 MAPK, which play an important role in the development of neuropathic pain via the production of IL-1β and TNF-α, are activated [ 30 ].…”

“…However, the excessive induction of autophagy might lead to type II programmed cell death. After SNL, increased activation of autophagy contributes to excessive inflammatory processes in the spinal cord via the activation of microglial cells and the aggravation of neuropathic pain [ 3 , 7 , 34 ].…”

“…After peripheral nerve injury, the activation of microglia leads to rapid inflammation within the spinal cord, facilitating the development and maintenance of neuropathic pain [ 3 ]. Neuroinflammatory processes are regulated by various signaling pathways such as mitogen-activated protein kinase (MAPK), including p38 and c-Jun N-terminal kinase (JNK), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), among others [ 4 - 7 ]. Signaling via the p38/JNK MAPK and NF-κB pathways is not only associated with the development of neuropathic pain but also the control of autophagy, which is essential for the balanced regulation of inflammation [ 6 - 8 ].…”

“…Neuroinflammatory processes are regulated by various signaling pathways such as mitogen-activated protein kinase (MAPK), including p38 and c-Jun N-terminal kinase (JNK), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), among others [ 4 - 7 ]. Signaling via the p38/JNK MAPK and NF-κB pathways is not only associated with the development of neuropathic pain but also the control of autophagy, which is essential for the balanced regulation of inflammation [ 6 - 8 ]. Autophagy is an ubiquitous cellular process required for homeostasis and survival, and initiated under stress conditions, such as malnutrition, organ damage, or inflammation [ 9 ].…”

“…For spinal nerve ligation (SNL), it is known that the dysregulation of autophagy is related to the development of neuropathic pain [ 10 ]. A previous study showed that the modulation of MAPK/JNK-mediated autophagic processes decreases the release of the proinflammatory cytokines and effectively alleviates neuropathic pain after SNL [ 7 ].…”