Wu-tou decoction inhibits chronic inflammatory pain in mice: participation of TRPV1 and TRPA1 ion channels

The analgesic effects of Yu-Xue-Bi tablet (YXB) on mice with inflammatory pain by regulating LXA4-FPR2-TRPA1 pathway

BACKGROUND

Oxylipins including lipoxin A4 (LXA4) facilitate the resolution of inflammation and possess analgesic properties by inhibiting macrophage infiltration and transient receptor potential (TRP) protein expression. Yu-Xue-Bi Tablet (YXB) is a traditional Chinese patent medicine used to relieve inflammatory pain. Our previous research has shown that the analgesic effect of YXB is related to inhibiting peripheral inflammation and regulating macrophage infiltration, but the mechanism is not yet clear. The purpose of this study is to explore the mechanisms of YXB on mice models with Complete Freund's Adjuvant (CFA)-induced inflammatory pain from the perspective at the resolution of inflammation.

METHODS

Mechanical allodynia thresholds and heat hypersensitivity were measured using the Von Frey test and the hot plate test respectively. The open field test and the tail suspension test were employed to measure anxiety and depressive behaviors respectively. The expression of CD68+ and the proportion of F4/80+CD11b+ cells were measured by immunofluorescence staining and flow cytometry. The expression of transient receptor potential ankyrin 1(TRPA1) was measured by immunofluorescence staining and western blotting. Oxylipins omics analysis provided quantitative data on oxylipins in the paws, and enzyme linked immunosorbent assay (ELISA) was used to measure the levels of LXA4 there. Immunofluorescence staining was used to perform the expression of Leukotriene A4 hydroxylase (LTA4H) in the paws of mice. The impact of injecting the formyl peptide receptor 2(FPR2) antagonist WRW4 and the TRPA1 agonist AITC into the left paws was observed, focusing on the expression of mechanical allodynia thresholds, the expression of CD68+, TRPA1 in the paws, and Calcitonin gene-related peptide (CGRP) in the L5 spinal dorsal horn.

RESULTS

YXB elevated mechanical allodynia thresholds, alleviated heat hypersensitivity and anxiety and depressive behaviors in CFA mice. It significantly reduced the number of CD68+ and proportion of F4/80+CD11b+ within the paws, thereby decreasing macrophage infiltration. Additionally, it diminished the expression of TRPA1 in the paws and TRPV1 in the DRG, leading to an inhibition of peripheral sensitization. Through quantitative analysis, it was found that YXB could modulate DHA-derived oxylipins and LXA4. ELISA results indicated that YXB elevated the levels of LXA4 and inhibited the expression of LAT4H in the paws. Furthermore, the pro-resolution and analgesic effects of YXB were hindered after administration of the FPR2 antagonist. Compared with the AITC group, YXB showed no significant improvement in anti-inflammatory and analgesic effects.

CONCLUSIONS

YXB can regulate the oxylipins of paws in CFA mice to promote the resolution of inflammation. The LXA4-FPR2-TRPA1 pathway is a key mechanism for the resolution of inflammation and analgesic effects.

Disease-Modifying Anti-rheumatic Drug Prescription Baihu-Guizhi Decoction Attenuates Rheumatoid Arthritis via Suppressing Toll-Like Receptor 4-mediated NLRP3 Inflammasome Activation

As a traditional Chinese medicine-originated disease-modifying anti-rheumatic drug prescription, Baihu-Guizhi decoction (BHGZD) is extensively used for the treatment of rheumatoid arthritis (RA) with a satisfying therapeutic efficacy. Mechanically, our previous data indicated that BHGZD may ameliorate RA partially by restoring the balance of the “inflammation-immune” system through regulating the TLR4-c-Fos-IL2-TNF-alpha axis. Toll-like receptor 4 (TLR4) has been revealed to be involved in the activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome complex. Thus, the aim of the current study was to determine the regulatory effects of BHGZD on the TLR4–mediated inflammasome activation during RA progression based on the modified adjuvant-induced arthritis model (AIA-M) and the lipopolysaccharide/adenosine triphosphate (LPS/ATP)–induced pyroptosis cellular models. As a result, oral administration of BHGZD exhibited prominent improvement in the disease severity of AIA-M rats, such as reducing the redness and swelling of joints, arthritis incidence, arthritic scores, and diameter of the limb and increasing pain thresholds. In line with the in vivo findings, BHGZD treatment effectively inhibited the LPS/ATP–induced pyroptosis of both Raw264.7 macrophage and MH7A cells in vitro by reducing pyroptotic cell death morphology (swollen cells) and decreasing propidium iodide–positive and terminal deoxynucleotidyl transferase–mediated dUTP-fluorescein nick end labeling (TUNEL)–positive cells. Notably, the increased expression levels of TLR4, NLRP3, interleukin 1β, and interleukin 18 proteins and the elevated activities of caspase-1 and lactic dehydrogenase in in vivo and in vitro disease models were markedly reversed by the treatment with BHGZD. In conclusion, the above findings proved the immunomodulatory and anti-inflammatory activities of BHGZD, especially in pyroptosis, which may be attributed to the activation of TLR4–mediated NLRP3 inflammasome signaling.

The PAR2 inhibitor I-287 selectively targets Gαq and Gα12/13 signaling and has anti-inflammatory effects

Protease-activated receptor-2 (PAR2) is involved in inflammatory responses and pain, therefore representing a promising therapeutic target for the treatment of immune-mediated inflammatory diseases. However, as for other GPCRs, PAR2 can activate multiple signaling pathways and those involved in inflammatory responses remain poorly defined. Here, we describe a new selective and potent PAR2 inhibitor (I-287) that shows functional selectivity by acting as a negative allosteric regulator on Gα_q and Gα_12/13 activity and their downstream effectors, while having no effect on G_i/o signaling and βarrestin2 engagement. Such selective inhibition of only a subset of the pathways engaged by PAR2 was found to be sufficient to block inflammation in vivo. In addition to unraveling the PAR2 signaling pathways involved in the pro-inflammatory response, our study opens the path toward the development of new functionally selective drugs with reduced liabilities that could arise from blocking all the signaling activities controlled by the receptor.

Avet et al. characterize I-287, an inhibitor to protease-activated receptor 2 using BRET-assays. They find that I-287 selectively inhibits Gα_q and Gα_12/13 without affecting the activation of G_i/o or the recruitment of βarrestin2 and that it blocks inflammation in vitro and in vivo.

Analgesic Effects of Triterpenoid Saponins From Stauntonia chinensis via Selective Increase in Inhibitory Synaptic Response in Mouse Cortical Neurons

Triterpenoid saponins from Stauntonia chinensis (TSS) are potential therapeutic agents because of its analgesic properties. However, the underlying mechanisms of the anti-nociceptive activity of TSS are largely unclear, especially in CNS. The present study confirmed the analgesic effect of TSS using four models of acute pain based on thermal or chemical stimuli. TSS treatment specifically impaired the threshold of thermal- and chemical-stimulated acute pain. Naloxone did not block the anti-nociceptive effects of TSS, which showed no participation of the opioid system. We investigated the electrical signal in cultured cortical neurons to explore whether TSS treatment directly affected synaptic transmission. TSS treatment selectively increased spontaneous inhibitory synaptic release and GABA induced charge transfer in mouse cortical neurons. The effects of TSS were maintained for at least 8 h in cultured neurons and in injected mice. Taken together, our results suggest that the analgesic role of TSS in cortex occurs via a particular increase in the inhibitory synaptic response at resting state, which supports TSS as a potential candidate for inflammatory pain relief.

The Chinese Medicine Wu-Tou Decoction Relieves Neuropathic Pain by Inhibiting Hippocampal Microglia Activation

The comorbidity between the nociceptive and mental syndromes adds to the refractoriness of neuropathic pain (NP). Wu-Tou decoction (WTD) has been prescribed for chronic pain for thousands of years in China. Recently, we reported that WTD was helpful for hippocampus and co-curative for the nociceptive, depressive and anxiety behaviors in the spinal cord ligation (SNL) mice. However, the mechanism underlying the rescue of hippocampus, as well as the roles hippocampus assumed in co-curation remain unexplored. In this study, we validated that in SNL mice, the long-lasting damages to limbic system were mainly limited to hippocampus. In addition, hippocampal neurons were proven sensitive to harms induced by microglia and rescued by WTD, which in sum indicated hippocampal microglia as the critical modulator of co-curation. To validate this hypothesis the hippocampal microglia were mal-activated in shamed mice, in which the atrophy of hippocampus and the development of NP syndromes were consolidated and proven rescued by WTD. On the contrary, in the SNL mice, the failure to control hippocampal microglia was sufficient to void all the rescues mediated by WTD. In sum, our study points out that the effective modulation of microglia in hippocampus is of pivotal importance for the co-curation by WTD.

Molecular mechanisms of the analgesic action of Wu-tou Decoction on neuropathic pain in mice revealed using microarray and network analysis

Wu-tou Decoction (WTD) is a classic herbal formula in traditional Chinese medicine for the treatment of joint diseases, neuropathic pain (NP) and inflammatory pain. In this study we investigated whether WTD produced analgesic action in a mouse spinal nerve ligation (SNL) model and elucidated the underlying molecular mechanisms. Mice were subjected to SNL and orally treated with WTD (3.15, 6.30 or 12.60 g·kg^-1·d^-1) for 21 d. SNL induced mechanical hyperalgesia and heat hyperalgesia characterized by rapid and persistent pain hypersensitivity. In addition, the expression levels of IL-1β, TNF-α, CCL2 and CXCL1 in the spinal cord dorsal horn were dramatically increased on the 10^th d post-surgery. Oral administration of WTD dose-dependently suppressed both mechanical and heat hyperalgesia as well as the expression levels of inflammatory cytokines in the spinal cord dorsal horn on the 21^st d post-surgery. Then whole-genome microarray analyses were conducted to detect the gene expression profiles of spinal cord dorsal horn in SNL mice with or without WTD treatment. After construction of the WTD-SNL-network and topological analysis, a list of candidate target genes of WTD acting on SNL-induced NP was identified and found to be functionally enriched in several glial cell activation-related pathways and neuroinflammatory pathways. Our data have clarified the gene expression patterns in the mouse spinal cord under the NP condition. We also demonstrate the analgesic action of WTD through suppression of glial cell activation and neuroinflammation, which suggest the potential of WTD as a promising candidate for the treatment of NP.

Wu-tou decoction attenuates neuropathic pain via suppressing spinal astrocytic IL-1R1/TRAF6/JNK signaling

Neuropathic pain (NP) caused by nerve injuries continues to be an intractable challenge due to inadequate therapeutic strategies. Recent study demonstrated glia-induced neuro-inflammation in the spinal cord, especially the activation of astrocytes, plays an essential role in the development of NP, which opens new avenues for NP treatment. In this study, we explored the anti-hyperalgesia properties of Wu-tou decoction (WTD) and showed that WTD potently attenuates mechanical allodynia and heat hyperalgesia in lumbar 5 (L5) spinal nerve ligation (SNL)-induced NP without noticeable side effect or affecting basal pain perception of mice. Mechanistically, initial targets screening tests indicated WTD's analgesic action may be centrally mediated within the spinal cord, which further verified by its inhibitory actions on glia-releasing factors of IL-1β, CCL2 and CXCL1. Meanwhile, WTD significantly reduced spinal IL-1R1, TRAF6 expressions, p-JNK levels, and number of GFAP/IL-1R1, GFAP/TRAF6, GFAP/p-JNK positive astrocytes in the superficial lamina of spinal cord. Additionally, co-administration of IL-1Ra increased the anti-hyperalgesia effects of WTD and further decreased CCL2 and CXCL1 expressions, while no synergistic effects were detected when TRAF6 or JNK inhibitors were co-administrated with WTD. Thus, our data suggested that the effective inhibition of spinal astrocytic IL-1R1/TRAF6/JNK signaling (especially IL-1R1) contributes, at least in part, to WTD's anti-hyperalgesia action. It also indicates that WTD might be a promising candidate for the treatments of chronic pain, especially under NP-related neurological disorders.

Evidence that CA3 is Underling the Comorbidity Between Pain and Depression and the Co-curation by Wu-Tou decoction in Neuropathic Pain

In neuropathic pain (NP), the atrophy of hippocampus contributes to the comorbidity between pain, depression and the cognitive deficits. However, the exact mechanism underling the comorbidity, the effective control of the degenerations in hippocampus and the remission of the accompanied depressive symptoms are still lacking. Wu-Tou decoction (WTD) has been prescribed for inflammatory pain for thousands of years. In this study, we manifested the effects of WTD on the pain, depression and anxiety co-curative symptoms of NP. Moreover, we reported that WTD rescued the mal-regulated BDNF and TNF-α in hippocampal CA3 alone, which is proven contributing to the pain and induced psychiatric symptoms. Finally, analysis of biochemistry, morphology and electrophysiology exhibited the potential mechanism of WTD in CA3. We found that, in the late stage of SNL condition, WTD mediated the rescue of the down-regulated glutamate as well as its pre-synaptic vesicular glutamate transporters (VGLuT1) and the post-synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in CA3. In sum, the targeted mediation of glutamatergic system in CA3 suggest that WTD may be responsible for the remission of the hypo-functioned CA3 glutamatergic neurons and further contribute to the co-curative effects of WTD.

Mother root of Aconitum carmichaelii Debeaux exerts antinociceptive effect in Complet Freund's Adjuvant-induced mice: roles of dynorpin/kappa-opioid system and transient receptor potential vanilloid type-1 ion channel

BACKGROUND

Processed Chuanwu (PCW), the mother root of Aconitum carmichaelii Debeauxv, has been widely used as a classic Traditional Chinese Medicine for pain relieve for over two millennia clinically. However, its action on chronic inflammatory pain has not been clarified. Here, we investigated the antinociceptive effect of PCW in complete freund's adjuvant (CFA)-induced mice and its possible mechanisms associated with opioid system and TRPV1 ion channel.

METHODS

Male ICR mice were intraplantarly injected with CFA. PCW (0.34, 0.68 and 1.35 g/kg) was orally given to mice once a day for 7 days. Von frey hairs and planter test were assessed to evaluate the antinociceptive effect of PCW. To investigate the participation of dynorphin/opioid system in PCW antinociception, subtype-specific opioid receptor antagonists or anti-dynorphin A antiserum were used. To eliminate other central mechanisms that contribute to PCW antinociception, hot plate (50 °C) test were performed. Further, involvements of TRPV1 in PCW antinociception were evaluated in CFA-induced TRPV1(-/-) and TRPV1(+/+) C57BL/6 male mice, and in capsaicin-induced nociception ICR naive mice pretreated with nor-BNI. Meanwhile, calcium imaging was performed in HEK293T-TRPV1 cells. Finally, rotarod, open-field tests and body temperature measurement were carried out to assess side effects of PCW.

RESULTS

PCW dose-dependently attenuated mechanical and heat hypersensitivities with no tolerance, which could be partially attenuated by coadministration of k-opioid receptor antagonist nor-binaltorphimine (nor-BNI) or anti-dynorphin A (1-13) antiserum. And PCW antinociception was totally erased by pretreatment with nor-BNI in the hot plate test. In addition, PCW antinociception was decreased in TRPV1(-/-) mice compared to TRPV1(+/+) group. And PCW still manifested inhibitory effects in capsaicin-induced nociception with nor-BNI pretreatment. PCW significantly inhibited capsaicin-induced calcium influx in HEK293T-TRPV1 cells. Finally, no detectable side effects were found in naive mice treated with PCW.

CONCLUSIONS

This study shows PCW's potent antinociceptive effect in inflammatory conditions without obvious side effects. This effect may result from the activation of κ-opioid receptor via dynorpin release and the inhibition of TRPV1. These findings indicate that PCW might be a potential agent for the management of chronic inflammatory pain.

A study on the effective substance of the Wu-tou formula based on the metabonomic method using UPLC-Q-TOF-HDMS

To elucidate the mechanisms of five single herbs in the Wu-tou Formula, the treatment effects were evaluated on AIA rats based on the pathological variation, serum biochemical parameters and using a metabonomic method.