Thymoquinone protects DRG neurons from axotomy-induced cell death

Thymoquinone Alleviates Paclitaxel-Induced Peripheral Neuropathy through Regulation of the TLR4-MyD88 Inflammatory Pathway

Paclitaxel-induced peripheral neuropathy (PIPN) is one of the common adverse effects during the paclitaxel (PTX) treatment of cancer. In this study, we investigated the neuroprotective effects and mechanisms of thymoquinone (TQ) in the PIPN model. Through pain behavioral assays and histological assessment, we demonstrated that TQ significantly alleviated the nociceptive behavior, modulated the pathological changes in peripheral nerves, and decreased the expression of inflammatory factors TNF-α, IL-1β, and IL-6 induced by PIPN in mice. In addition, TQ significantly reversed the reduced viability and inflammatory response of primary DRG neurons caused by PTX. Moreover, the gene expression of related pathways was detected by Western blot, qPCR, and immunofluorescence, and the results showed that TQ exerts neuroprotective effects by regulating TLR4/MyD88 and its downstream NF-κB and MAPKs inflammatory pathways in vivo and in vitro. The treatment with TLR4 antagonist TAK-242 further indicated the important role of the TLR4/MyD88 signaling pathway in PIPN. Furthermore, molecular docking and a cellular thermal shift assay were used to confirm the interaction of TQ with TLR4. In summary, our study shows that TQ can inhibit inflammatory responses against PIPN by regulating TLR4 and MyD88 and its downstream inflammatory pathways.

Neuron-Schwann cell interactions in peripheral nervous system homeostasis, disease, and preclinical treatment

Schwann cells (SCs) have a critical role in the peripheral nervous system. These cells are able to support axons during homeostasis and after injury. However, mutations in genes associated with the SCs repair program or myelination result in dysfunctional SCs. Several neuropathies such as Charcot-Marie-Tooth (CMT) disease, diabetic neuropathy and Guillain-Barré syndrome show abnormal SC functions and an impaired regeneration process. Thus, understanding SCs-axon interaction and the nerve environment in the context of homeostasis as well as post-injury and disease onset is necessary. Several neurotrophic factors, cytokines, and regulators of signaling pathways associated with proliferation, survival and regeneration are involved in this process. Preclinical studies have focused on the discovery of therapeutic targets for peripheral neuropathies and injuries. To study the effect of new therapeutic targets, modeling neuropathies and peripheral nerve injuries (PNIs) in vitro and in vivo are useful tools. Furthermore, several in vitro protocols have been designed using SCs and neuron cell lines to evaluate these targets in the regeneration process. SCs lines have been used to generate effective myelinating SCs without success. Alternative options have been investigated using direct conversion from somatic cells to SCs or SCs derived from pluripotent stem cells to generate functional SCs. This review will go over the advantages of these systems and the problems associated with them. In addition, there have been challenges in establishing adequate and reproducible protocols in vitro to recapitulate repair SC-neuron interactions observed in vivo. So, we also discuss the mechanisms of repair SCs-axon interactions in the context of peripheral neuropathies and nerve injury (PNI) in vitro and in vivo. Finally, we summarize current preclinical studies evaluating transgenes, drug, and novel compounds with translational potential into clinical studies.

A Brief Review of In Vitro Models for Injury and Regeneration in the Peripheral Nervous System

Nerve axonal injury and associated cellular mechanisms leading to peripheral nerve damage are important topics of research necessary for reducing disability and enhancing quality of life. Model systems that mimic the biological changes that occur during human nerve injury are crucial for the identification of cellular responses, screening of novel therapeutic molecules, and design of neural regeneration strategies. In addition to in vivo and mathematical models, in vitro axonal injury models provide a simple, robust, and reductionist platform to partially understand nerve injury pathogenesis and regeneration. In recent years, there have been several advances related to in vitro techniques that focus on the utilization of custom-fabricated cell culture chambers, microfluidic chamber systems, and injury techniques such as laser ablation and axonal stretching. These developments seem to reflect a gradual and natural progression towards understanding molecular and signaling events at an individual axon and neuronal-soma level. In this review, we attempt to categorize and discuss various in vitro models of injury relevant to the peripheral nervous system and highlight their strengths, weaknesses, and opportunities. Such models will help to recreate the post-injury microenvironment and aid in the development of therapeutic strategies that can accelerate nerve repair.

Revisiting the Role of Biologically Active Natural and Synthetic Compounds as an Intervention to Treat Injured Nerves

Traumatic lesions in nerves present high incidence and may culminate in sensorimotor and/or autonomic dysfunctions or a total loss of function, affecting the patient's quality of life. Although the microenvironment favors peripheral nerve regeneration, the regenerative process is not always successful. Some herbs, natural products, and synthetic drugs have been studied as potential pro-regenerative interventions. We reviewed and discussed the most recent articles published over the last ten years in high impact factor journals. Even though most of the articles contemplated in this review were in vitro and animal model studies, those with herbs showed promising results. Most of them presented antioxidant and anti-inflammatory effects. Drugs of several pharmacological classes also showed optimistic outcomes in nerve functional recovery, including clinical trials. The results are hopeful; however, mechanisms of action need to be elucidated, and there is a need for more high-quality clinical studies. The study presents careful compilation of findings of dozens of compounds with consistent pro-regenerative evidence published in respected scientific journals. It may be valuable for health professionals and researchers in the field.

Thymoquinone and Curcumin Defeat Aging-Associated Oxidative Alterations Induced by D-Galactose in Rats' Brain and Heart

D-galactose (D-gal) administration causes oxidative disorder and is widely utilized in aging animal models. Therefore, we subcutaneously injected D-gal at 200 mg/kg BW dose to assess the potential preventive effect of thymoquinone (TQ) and curcumin (Cur) against the oxidative alterations induced by D-gal. Other than the control, vehicle, and D-gal groups, the TQ and Cur treated groups were orally supplemented at 20 mg/kg BW of each alone or combined. TQ and Cur effectively suppressed the oxidative alterations induced by D-gal in brain and heart tissues. The TQ and Cur combination significantly decreased the elevated necrosis in the brain and heart by D-gal. It significantly reduced brain caspase 3, calbindin, and calcium-binding adapter molecule 1 (IBA1), heart caspase 3, and BCL2. Expression of mRNA of the brain and heart TP53, p21, Bax, and CASP-3 were significantly downregulated in the TQ and Cur combination group along with upregulation of BCL2 in comparison with the D-gal group. Data suggested that the TQ and Cur combination is a promising approach in aging prevention.

Sinomenine alleviates dorsal root ganglia inflammation to inhibit neuropathic pain via the p38 MAPK/CREB signalling pathway

The objective of study was to investigate the inhibitory effect of sinomenine on neuropathic pain on dorsal root ganglia (DRG). The DRG cell line and spinal nerve ligation (SNL) model were used in this study. The effect of sinomenine on the cell viability was examined by MTT assay. The expression of p38 MAPK, NF-κB, c-fos, SP and TNF-α was detected by using immunofluorescence and immunohistochemistry assay. We also assessed the level of p-CaMKII, COX-2, p-CREB, IL-17A, TLR4 and IL-1β via western blotting and RT-qPCR. Compared to the controls, sinomenine showed a protective effect on TNF-α-induced apoptosis on DRG cells in a dose-dependent manner, with an increase of cell viability and a decrease of reactive oxygen species level as well as LDH release. Parallelly, sinomenine treatment significantly reduced the expression of various factors related to stress and inflammation, including p38 MAPK, NF-κB, c-fos, p-CAMKII, COX-2, p-CREB, TLR4 and IL-17A in DRG cells in vitro. Furthermore, we found that administration of sinomenine significantly reduced mechanical withdrawal threshold and thermal withdrawal latency and inhibited the inflammation and activation of p38 signaling in SNL rats. It is noting that combined therapy of sinomenine and pulsed radiofrequency exhibited higher efficacy of dorsal root ganglia inflammation than single treatment as well as the combination of oxycodone and pulsed radiofrequency. Sinomenine inhibited the apoptosis of DRG cell by regulating p38 MAPK/CREB signalling pathway, which provides evidence to alleviate neuropathic pain in clinic.