Systemic Injection of Thalidomide Prevent and Attenuate Neuropathic Pain and Alleviate Neuroinflammatory Response in the Spinal Dorsal Horn

Thalidomide alleviates neuropathic pain through microglial IL-10/β-endorphin signaling pathway

Thalidomide is an antiinflammatory, antiangiogenic and immunomodulatory agent which has been used for the treatment of erythema nodosum leprosum and multiple myeloma. It has also been employed in treating complex regional pain syndromes. The current study aimed to reveal the molecular mechanisms underlying thalidomide-induced pain antihypersensitive effects in neuropathic pain. Thalidomide gavage, but not its more potent analogs lenalidomide and pomalidomide, inhibited mechanical allodynia and thermal hyperalgesia in neuropathic pain rats induced by tight ligation of spinal nerves, with ED₅₀ values of 44.9 and 23.5 mg/kg, and E_max values of 74% and 84% MPE respectively. Intrathecal injection of thalidomide also inhibited mechanical allodynia and thermal hyperalgesia in neuropathic pain. Treatment with thalidomide, lenalidomide and pomalidomide reduced peripheral nerve injury-induced proinflammatory cytokines (TNFα, IL-1β and IL-6) in the ipsilateral spinal cords of neuropathic rats and LPS-treated primary microglial cells. In contrast, treatment with thalidomide, but not lenalidomide or pomalidomide, stimulated spinal expressions of IL-10 and β-endorphin in neuropathic rats. Particularly, thalidomide specifically stimulated IL-10 and β-endorphin expressions in microglia but not astrocytes or neurons. Furthermore, pretreatment with the IL-10 antibody blocked upregulation of β-endorphin in neuropathic rats and cultured microglial cells, whereas it did not restore thalidomide-induced downregulation of proinflammatory cytokine expression. Importantly, pretreatment with intrathecal injection of the microglial metabolic inhibitor minocycline, IL-10 antibody, β-endorphin antiserum, and preferred or selective μ-opioid receptor antagonist naloxone or CTAP entirely blocked thalidomide gavage-induced mechanical antiallodynia. Our results demonstrate that thalidomide, but not lenalidomide or pomalidomide, alleviates neuropathic pain, which is mediated by upregulation of spinal microglial IL-10/β-endorphin expression, rather than downregulation of TNFα expression.

Electroacupuncture improves neuronal plasticity through the A2AR/cAMP/PKA signaling pathway in SNL rats

Improvements in neuronal plasticity are considered to be conducive to recovery from neuropathic pain. Electroacupuncture (EA) is regarded as an effective rehabilitation method for neuropathic pain. However, the effects and potential mechanism associated with EA-induced repair of hyperesthesia are not fully understood. Evidence has suggested that the adenosine A2A receptor (A2AR) and the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway play an important role in improving neuropathic pain. Here, we examined the function of EA in promoting neuronal plasticity in spinal nerve ligation (SNL) rats. The A2AR antagonist SCH58261, A2AR agonist 2-p-(2-carboxyethyl)phenethylamino-50-N-ethylcarboxamido adenosine HCl (CGS21680) and A2AR siRNA were used to confirm the relationship between A2AR and the cAMP/PKA pathway as well as the effects of A2AR on EA-induced improvements in neurobehavioral state and neuronal plasticity. Mechanical withdrawal threshold (MWT), thermal withdrawal latency (TWL), HE staining, Western blotting, RT-PCR, immunofluorescence, enzyme-linked immunosorbent assay, Nissl staining, silver staining, Golgi-Cox staining and transmission electron microscopy were used to evaluate the changes in neurobehavioral performance, protein expression, neuronal structure and dendrites/synapses. The results showed that EA and CGS21680 improved the behavioral performance, neuronal structure and dendritic/synaptic morphology of SNL rats, consistent with higher expression levels of A2AR, cAMP and PKA. In contrast to the positive effects of EA, SCH58261 inhibited dendritic growth and promoted dendritic spine/synaptic remodeling. In addition, the EA-induced improvement in neuronal plasticity was inhibited by SCH58261 and A2AR siRNA, consistent with lower expression levels of A2AR, cAMP and PKA, and worse behavioral performance. These results indicate that EA suppresses SNL-induced neuropathic pain by improving neuronal plasticity via upregulating the A2AR/cAMP/PKA signaling pathway.

Electroacupuncture may alleviate neuropathic pain via suppressing P2X7R expression

Neuropathic pain is a severe problem that is difficult to treat clinically. Reducing abnormal remodeling of dendritic spines/synapses and increasing the anti-inflammatory effects in the spinal cord dorsal horn are potential methods to treat this disease. Previous studies have reported that electroacupuncture (EA) could increase the pain threshold after peripheral nerve injury. However, the underlying mechanism is unclear. P2X7 receptors (P2X7R) mediate the activation of microglia and participate in the occurrence and development of neuropathic pain. We hypothesized that the effects of EA on relieving pain may be related to the downregulation of the P2X7R. Spinal nerve ligation (SNL) rats were used as a model in this experiment, and 2'(3')-O-(4-benzoyl)benzoyl ATP (BzATP) was used as a P2X7R agonist. We found that EA treatment decreased dendritic spine density, inhibited synaptic reconstruction and reduced inflammatory response, which is consistent with the decrease in P2X7R expression as well as the improved neurobehavioral performance. In contrast to the beneficial effects of EA, BzATP enhanced abnormal remodeling of dendritic spines/synapses and inflammation. Furthermore, the EA-mediated positive effects were reversed by BzATP, which is consistent with the increased P2X7R expression. These findings indicated that EA improves neuropathic pain by reducing abnormal dendritic spine/synaptic reconstruction and inflammation via suppressing P2X7R expression.

Oxidative stress mediates thalidomide-induced pain by targeting peripheral TRPA1 and central TRPV4

Background

The mechanism underlying the pain symptoms associated with chemotherapeutic-induced peripheral neuropathy (CIPN) is poorly understood. Transient receptor potential ankyrin 1 (TRPA1), TRP vanilloid 4 (TRPV4), TRPV1, and oxidative stress have been implicated in several rodent models of CIPN-evoked allodynia. Thalidomide causes a painful CIPN in patients via an unknown mechanism. Surprisingly, the pathway responsible for such proalgesic response has not yet been investigated in animal models.

Results

Here, we reveal that a single systemic administration of thalidomide and its derivatives, lenalidomide and pomalidomide, elicits prolonged (~ 35 days) mechanical and cold hypersensitivity in C57BL/6J mouse hind paw. Pharmacological antagonism or genetic deletion studies indicated that both TRPA1 and TRPV4, but not TRPV1, contribute to mechanical allodynia, whereas cold hypersensitivity was entirely due to TRPA1. Thalidomide per se did not stimulate recombinant and constitutive TRPA1 and TRPV4 channels in vitro, which, however, were activated by the oxidative stress byproduct, hydrogen peroxide. Systemic treatment with an antioxidant attenuated mechanical and cold hypersensitivity, and the increase in oxidative stress in hind paw, sciatic nerve, and lumbar spinal cord produced by thalidomide. Notably, central (intrathecal) or peripheral (intraplantar) treatments with channel antagonists or an antioxidant revealed that oxidative stress-dependent activation of peripheral TRPA1 mediates cold allodynia and part of mechanical allodynia. However, oxidative stress-induced activation of central TRPV4 mediated the residual TRPA1-resistant component of mechanical allodynia.

Conclusions

Targeting of peripheral TRPA1 and central TRPV4 may be required to attenuate pain associated with CIPN elicited by thalidomide and related drugs.

Pharmacological treatments of COVID-19

The viral infection due to the new coronavirus or coronavirus disease 2019 (COVID-19), which was reported for the first time in December 2019, was named by the World Health Organization (WHO) as Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV2), because of the very similar genome and also its related symptoms to SARS-CoV1. The ongoing COVID-19 pandemic with significant mortality, morbidity, and socioeconomic impact is considered by the WHO as a global public health emergency. Since there is no specific treatment available for SARS-CoV2 infection, and or COVID-19, several clinical and sub-clinical studies are currently undertaken to find a gold-standard therapeutic regimen with high efficacy and low side effect. Based on the published scientific evidence published to date, we summarized herein the effects of different potential therapies and up-to-date clinical trials. The review is intended to help readers aware of potentially effective COVID-19 treatment and provide useful references for future studies.

[Effects of different materials for partial sciatic nerve ligation on glial cell activation in rat models of chronic constriction injury]

OBJECTIVE

To compare the effects of different materials for partial sciatic nerve ligation on glial cell activation in the spinal cord in a rat model of chronic constriction injury (CCI).

METHODS

SD rats were randomly divided into the sham group (n=15), silk suture CCI group (n=15) and chromic catgut CCI group (n=14). The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) of the rats were detected at 3, 7, 11 and 15 days after the operation. The changes in the sciatic nerve, the activation of spinal cord glial cells and the expression of inflammatory factors were observed using Western blotting and RT-PCR.

RESULTS

At 3 to 15 days after the surgery, MWT and TWL of the rats were significantly lower in silk suture group and chromic catgut group than in the control group (P < 0.05), and was significantly lower in chromic catgut group than in the silk suture group (P < 0.05) at 3 days after the surgery. The results of sciatic nerve myelin staining showed that the sciatic nerve was damaged and demyelinated in both the ligation groups. The expressions of CD11b, GFAP, IL-1β and TNF-α in the two ligation groups were similar and all significantly higher than those in the control group (P < 0.05). IL-6 mRNA level was significantly higher in chromic catgut group than in the silk suture group (P < 0.05).

CONCLUSIONS

The CCI models established by partial sciatic nerve ligation with silk suture and chromic catgut all show glial activation, and the inflammatory response is stronger in chromic catgut group.

Bioinformatic Analysis of Neuroimmune Mechanism of Neuropathic Pain

Background

Neuropathic pain (NP) is a devastating complication following nerve injury, and it can be alleviated by regulating neuroimmune direction. We aimed to explore the neuroimmune mechanism and identify some new diagnostic or therapeutic targets for NP treatment via bioinformatic analysis.

Methods

The microarray GSE18803 was downloaded and analyzed using R. The Venn diagram was drawn to find neuroimmune-related differentially expressed genes (DEGs) in neuropathic pain. Gene Ontology (GO), pathway enrichment, and protein-protein interaction (PPI) network were used to analyze DEGs, respectively. Besides, the identified hub genes were submitted to the DGIdb database to find relevant therapeutic drugs.

Results

A total of 91 neuroimmune-related DEGs were identified. The results of GO and pathway enrichment analyses were closely related to immune and inflammatory responses. PPI analysis showed two important modules and 8 hub genes: PTPRC, CD68, CTSS, RAC2, LAPTM5, FCGR3A, CD53, and HCK. The drug-hub gene interaction network was constructed by Cytoscape, and it included 24 candidate drugs and 3 hub genes.

Conclusion

The present study helps us better understand the neuroimmune mechanism of neuropathic pain and provides some novel insights on NP treatment, such as modulation of microglia polarization and targeting bone resorption. Besides, CD68, CTSS, LAPTM5, FCGR3A, and CD53 may be used as early diagnostic biomarkers and the gene HCK can be a therapeutic target.