Different Roles of Peripheral Mitogen-Activated Protein Kinases in Carrageenan-Induced Arthritic Pain and Arthritis in Rats

The Anti-Inflammatory Activities of Benzylideneacetophenone Derivatives in LPS Stimulated BV2 Microglia Cells and Mice

A previously reported study highlighted the neuroprotective potential of the novel benzylideneacetophenone derivative, JC3, in mice. In pursuit of compounds with even more robust neuroprotective and anti-inflammatory properties compared to JC3, we synthesized substituted 1,3-diphenyl-2-propen-1-ones based on chalcones. Molecular modeling studies aimed at discerning the chemical structural features conducive to heightened biological activity revealed that JCII-8,10,11 exhibited the widest HOMOLUMO gap within this category, indicating facile electron and radical transfer between HOMO and LUMO in model assessments. From the pool of synthesized compounds, JCII-8,10,11 were selected for the present investigation. The biological assays involving JCII-8,10,11 demonstrated their concentration-dependent suppression of iNOS and COX-2 protein levels, alongside various cytokine mRNA expressions in LPS-induced murine microglial BV2 cells. Furthermore, western blot analyses were conducted to investigate the MAPK pathways and NF-κB/p65 nuclear translocation. These evaluations conclusively confirmed the inflammatory inhibition effects in both in vitro and in vivo inflammation models. These findings establish JCII-8,10,11 as potent anti-inflammatory agents, hindering inflammatory mediators and impeding NF-κB/p65 nuclear translocation via JNK and ERK MAPK phosphorylation in BV2 cells. The study positions them as potential therapeutics for inflammation-related conditions. Additionally, JCII-11 exhibited greater activity compared to other tested JCII compounds.

Magnetic targeting of lornoxicam/SPION bilosomes loaded in a thermosensitive in situ hydrogel system for the management of osteoarthritis: Optimization, in vitro, ex vivo, and in vivo studies in rat model via modulation of RANKL/OPG

Osteoarthritis is a bone and joint condition characterized pathologically by articular cartilage degenerative damage and can develop into a devastating and permanently disabling disorder. This investigation aimed to formulate the anti-inflammatory drug lornoxicam (LOR) into bile salt-enriched vesicles loaded in an in situ forming hydrogel as a potential local treatment of osteoarthritis. This was achieved by formulating LOR-loaded bilosomes that are also loaded with superparamagnetic iron oxide nanoparticles (SPIONs) for intra-muscular (IM) administration to improve joint targeting and localization by applying an external magnet to the joint. A 31.22 full factorial design was employed to develop the bilosomal dispersions and the optimized formula including SPION (LSB) was loaded into a thermosensitive hydrogel. Moreover, in vivo evaluation revealed that the IM administration of LSB combined with the application of an external magnet to the joint reversed carrageen-induced suppression in motor activity and osteoprotegerin by significantly reducing the elevations in mitogen-activated protein kinases, extracellular signal-regulated kinase, and receptor activator of nuclear factor kappa beta/osteoprotegerin expressions. In addition, the histopathological evaluation of knee joint tissues showed a remarkable improvement in the injured joint tissues. The results proved that the developed LSB could be a promising IM drug delivery system for osteoarthritis management.

Role of EPAC1 in chronic pain

Chronic pain usually lasts over three months and commonly occurs in chronic diseases (cancer, arthritis, and diabetes), injuries (herniated discs, torn ligaments), and many major pain disorders (neuropathic pain, fibromyalgia, chronic headaches). Unfortunately, there is currently a lack of effective treatments to help people with chronic pain to achieve complete relief. Therefore,it is particularly important to understand the mechanism of chronic pain and find new therapeutic targets. The exchange protein directly activated by cyclic adenosine monophosphate(cAMP) (EPAC) has been recognized for its functions in nerve regeneration, stimulating insulin release, controlling vascular pressure, and controlling other metabolic activities. In recent years, many studies have found that the subtype of EPAC, EPAC1 is involved in the regulation of neuroinflammation and plays a crucial role in the regulation of pain, which is expected to become a new therapeutic target for chronic pain. This article reviews the major contributions of EPAC1 in chronic pain.

Therapeutic Effects of Tryptanthrin and Tryptanthrin-6-Oxime in Models of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease involving joint and bone damage that is mediated in part by proteases and cytokines produced by synovial macrophages and fibroblast-like synoviocytes (FLS). Although current biological therapeutic strategies for RA have been effective in many cases, new classes of therapeutics are needed. We investigated anti-inflammatory properties of the natural alkaloid tryptanthrin (TRYP) and its synthetic derivative tryptanthrin-6-oxime (TRYP-Ox). Both TRYP and TRYP-Ox inhibited matrix metalloproteinase (MMP)-3 gene expression in interleukin (IL)-1β-stimulated primary human FLS, as well as IL-1β–induced secretion of MMP-1/3 by FLS and synovial SW982 cells and IL-6 by FLS, SW982 cells, human umbilical vein endothelial cells (HUVECs), and monocytic THP-1 cells, although TRYP-Ox was generally more effective and had no cytotoxicity in vitro. Evaluation of the therapeutic potential of TRYP and TRYP-Ox in vivo in murine arthritis models showed that both compounds significantly attenuated the development of collagen-induced arthritis (CIA) and collagen-antibody–induced arthritis (CAIA), with comparable efficacy. Collagen II (CII)-specific antibody levels were similarly reduced in TRYP- and TRYP-Ox-treated CIA mice. TRYP and TRYP-Ox also suppressed proinflammatory cytokine production by lymph node cells from CIA mice, with TRYP-Ox being more effective in inhibiting IL-17A, granulocyte-macrophage colony-stimulating factor (GM-CSF), and receptor activator of nuclear factor-κB ligand (RANKL). Thus, even though TRYP-Ox generally had a better in vitro profile, possibly due to its ability to inhibit c-Jun N-terminal kinase (JNK), both TRYP and TRYP-Ox were equally effective in inhibiting the clinical symptoms and damage associated with RA. Overall, TRYP and/or TRYP-Ox may represent potential new directions for the pursuit of novel treatments for RA.

Gabapentin regulates expression of FGF2 and FGFR1 in dorsal root ganglia via microRNA-15a in the arthritis rat model

BACKGROUND

Arthritis is an inflammatory disease with a prevalence rate of approximately 10% in China, which commonly manifests as pain. The aim of the current study was to investigate the function of gabapentin in the dorsal root ganglion in an arthritis rat model, and assess the effect of gabapentin on the expression of fibroblast growth factor 2 (FGF2) and FGF receptor 1 (FGFR1).

METHODS

A total of 30 healthy male Sprague-Dawley rats were randomly divided into the following three groups: Untreated group, control group and gabapentin group. Rats in the control and the gabapentin groups were injected with Freund's complete adjuvant to induce arthritis. A total of 7 days subsequent to model establishment, the gabapentin group was administered intraperitoneally gabapentin for 8 days. The alterations in thickness of paw pad and paw withdrawal mechanical threshold (PWMT) were detected, which indicated that the rats in the control and gabapentin groups presented with the symptoms of arthritis.

RESULTS

In the control group, the PWMT value was significantly reduced (P < 0.05), whereas the PWMT value was significantly increased in the gabapentin group. Immunohistochemistry demonstrated that the expression levels of FGF2 and FGFR1 were increased in the control group compared with the untreated group, while the expression levels of FGF2 and FGFR1 were reduced in the gabapentin group. Moreover, the FGF2 antagonist PD173074 partially improved the plantar thickness and PWMT of the arthritic rats. Bioinformatics analysis predicted microRNA-15a binding sites in the 3'untranslated regions (UTR) of FGF2 and FGFR1. Furthermore, the expression of microRNA-15a was reduced in the control group compared with untreated rats, whereas microRNA-15a in the gabapentin group was upregulated compared with the control. Additionally, the luciferase reporter assay confirmed that microRNA-15a could inhibit the protein expression through pairing with the 3'UTR of FGF2 and FGFR1 mRNAs.

CONCLUSION

Gabapentin may relieve arthritis pain and reduce the expression of FGF2 and FGFR1 in dorsal root ganglia. Furthermore, microRNA-15a may be involved in the regulatory process.

Redox-sensitive transcription factors play a significant role in the development of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease which is associated with significant morbidity. Redox sensitive transcription factors including NF-κB, HIF, AP-1, and Nrf2 are intimately involved in the pathogenesis of RA. The treatment of this disease is limited by the elusive nature of the pathogenesis of RA. NF-κB is crucial for the maturation of immune cells as well as production of TNFα and MMPs, which escalate RA. HIF is essential for activation of inflammatory cells, angiogenesis and pannus formation in RA. AP-1 regulates cytokine and MMP production as well as synovial hyperplasia which are key processes in RA. Nrf2 is involved with chondrogenesis, osteoblastogenesis, prostaglandin secretion and ROS production in RA. Targeting two or more of these transcription factors may result in increased efficacy than either therapy in isolation. This review will highlight the control specific mediators on these transcription factors, the subsequent effect of these transcription factors once activated, and then mesh this with the pathogenesis of RA. The elucidation of key transcription factor regulation in the pathogenesis of RA may highlight the novel therapy interventions which may prove to have a greater efficacy than those therapies currently available.

Mitogen-activated protein kinase phosphatase-3 (MKP-3) in the surgical wound is necessary for the resolution of postoperative pain in mice

Mitogen-activated protein kinase (MAPK) phosphatase-3 (MKP-3) and its substrates (extracellular signal-regulated kinase [ERK] and p38) play an important role in pathophysiological mechanisms of acute postoperative and chronic neuropathic pain in the spinal cord. This study aimed to understand the role of MKP-3 and its target MAPKs at the site of surgical incision in nociceptive behavior. Wild-type (WT) and MKP-3 knockout (KO) mice underwent unilateral plantar hind paw incision. Mechanical allodynia was assessed by using von Frey filaments. Peripheral ERK-1/2 and p38 phosphorylation were measured by Western blot. Cell infiltration was determined using hematoxylin and eosin histological staining. Peripheral phosphorylated ERK-1/2 (p-ERK-1/2) inhibition was performed in MKP-3 KO mice. In WT mice, mechanical hypersensitivity was observed on postoperative day 1 (0.69±0.17 g baseline vs 0.13±0.08 g day 1), which resolved normally by postoperative day 12 (0.46±0.08 g, N=6). In MKP-3 KO mice, this hypersensitivity persisted at least 12 days after surgery (0.19±0.06 g; N=6). KO mice displayed higher numbers of infiltrating cells (51.4±6 cells/0.1 mm²) than WT mice (8.7±1.2 cells/0.1 mm²) on postoperative day 1 (vs 5–6 cells/0.1 mm² at baseline) that returned to baseline 12 days after surgery (10–12 cells/0.1 mm²). In WT mice, peripheral p-p38 and p-ERK-1/2 expression increased (5- and 3-fold, respectively) on postoperative days 1 and 5, and returned to basal levels 7–12 days after surgery (N=3 per group). Peripheral p-p38 levels in MKP-3 KO mice followed a similar expression pattern as WT mice. Peripheral p-ERK-1/2 levels in MKP-3 KO mice remained elevated 12 days after surgery (2.5-fold, N=3 per group). Administration of PD98059 (MEK inhibitor, N=8, vehicle N=9) reduced p-ERK-1/2 expression in the incised tissue and blocked hypersensitivity in MKP-3 KO mice (N=6). The findings of this study suggest that MKP-3 is pivotal for normal resolution of acute postoperative allodynia, through the regulation of peripheral p-ERK-1/2.

Antihyperalgesic effect of tetrodotoxin in rat models of persistent muscle pain

Persistent muscle pain is a common and disabling symptom for which available treatments have limited efficacy. Since tetrodotoxin (TTX) displays a marked antinociceptive effect in models of persistent cutaneous pain, we tested its local antinociceptive effect in rat models of muscle pain induced by inflammation, ergonomic injury and chemotherapy-induced neuropathy. While local injection of TTX (0.03-1 μg) into the gastrocnemius muscle did not affect the mechanical nociceptive threshold in naïve rats, exposure to the inflammogen carrageenan produced a marked muscle mechanical hyperalgesia, which was dose-dependently inhibited by TTX. This antihyperalgesic effect was still significant at 24h. TTX also displayed a robust antinociceptive effect on eccentric exercise-induced mechanical hyperalgesia in the gastrocnemius muscle, a model of ergonomic pain. Finally, TTX produced a small but significant inhibition of neuropathic muscle pain induced by systemic administration of the cancer chemotherapeutic agent oxaliplatin. These results indicate that TTX-sensitive sodium currents in nociceptors play a central role in diverse states of skeletal muscle nociceptive sensitization, supporting the suggestion that therapeutic interventions based on TTX may prove useful in the treatment of muscle pain.

Glial activation in the periaqueductal gray promotes descending facilitation of neuropathic pain through the p38 MAPK signaling pathway

The midbrain ventrolateral periaqueductal gray (VL-PAG) is a key component that mediates pain modulation. Although spinal cord glial cells appear to play an important role in chronic pain development, the precise mechanisms involving descending facilitation pathways from the PAG following nerve injury are poorly understood. This study shows that cellular events that occur during glial activation in the VL-PAG may promote descending facilitation from the PAG during neuropathic pain. Chronic constriction nerve injury (CCI) was induced by ligature construction of the sciatic nerve in male Sprague-Dawley rats. Behavioral responses to noxious mechanical (paw withdrawal threshold; PWT) and thermal (paw withdrawal latency; PWL) stimuli were evaluated. After CCI, immunohistochemical and Western blot analysis of microglia and astrocytes in the VL-PAG showed morphological and quantitative changes indicative of activation in microglia and astrocytes. Intra-VL-PAG injection of microglial or astrocytic inhibitors attenuated PWT and PWL at days 7 and 14, respectively, following CCI. We also evaluated the effects of intra-VL-PAG administration of the phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK) inhibitor SB 203580 at day 7 after CCI. This treatment abolished microglial activation and produced a significant time-dependent attenuation of PWT and PWL. Western blot analysis showed localized expression of p-p38 in the VL-PAG after CCI. P-p38 was expressed in labeled microglia of the VL-PAG but was not present in astrocytes and neurons on day 7 after CCI. These results demonstrate that CCI-induced neuropathic pain is associated with glial activation in the VL-PAG, which likely participates in descending pain facilitation through the p38 MAPK signaling pathway.

ERK1/2: Function, signaling and implication in pain and pain-related anxio-depressive disorders

Despite the increasing knowledge regarding pain modulation, the understanding of the mechanisms behind a complex and pathologic chronic pain condition is still insufficient. These knowledge gaps might result in ineffective therapeutic approaches to relieve painful sensations. As a result, severe untreated chronic pain frequently triggers the onset of new disorders such as depression and/or anxiety, and therefore, both the diagnosis and treatment of patients suffering from chronic pain become seriously compromised, prompting a self-perpetuating cycle of symptomatology. The extracellular signal-regulated kinases 1 and 2 (ERK1/2) are molecules strongly implicated in the somatic component of pain at the spinal cord level and have been emerging as mediators of the emotional-affective component as well. Although these molecules might represent good biomarkers, their use as pharmacological targets is still open to discussion as paradoxical information has been obtained. Here we review the current scientific literature regarding ERK1/2 signaling in the modulation of pain, depression and anxiety, including the emotional-affective spheres of the pain experience.

Tolerance to the antinociceptive effects of chronic morphine requires c-Jun N-terminal kinase

BACKGROUND

Morphine and fentanyl are opioid analgesics in wide clinical use that act through the μ-opioid receptor (MOR). However, one limitation of their long-term effectiveness is the development of tolerance. Receptor desensitization has been proposed as a putative mechanism driving tolerance to G protein-coupled receptor (GPCR) agonists. Recent studies have found that tolerance to morphine is mediated by the c-Jun N-terminal Kinase (JNK) signaling pathway. The goal of the present study was to test the hypotheses that: 1) JNK inhibition will be antinociceptive on its own; 2) JNK inhibition will augment morphine antinociception and; 3) JNK mediates chronic tolerance for the antinociceptive effects of morphine using acute (hotplate and tail-flick), inflammatory (10 μl of formalin 2.5%) and chemotherapy (cisplatin 5 mg/kg ip once weekly)-induced neuropathic pain assays.

RESULTS

We found that JNK inhibition by SP600125 (3 mg/kg) produces a greater antinociceptive effect than morphine (6 mg/kg) alone in the formalin test. Moreover, co-administration of morphine (6 mg/kg) with SP600125 (3 mg/kg) produced a sub-additive antinociceptive effect in the formalin test. We also show that pre-treatment with SP600125 (3 or 10 mg/kg), attenuates tolerance to the antinociceptive effects of morphine (10 mg/kg), but not fentanyl (0.3 mg/kg), in the tail-flick and hotplate tests. Pre-treatment with SP600125 also attenuates tolerance to the hypothermic effects of both morphine and fentanyl. We also examined the role of JNK in morphine tolerance in a cisplatin-induced model of neuropathic pain. Interestingly, treatment with SP600125 (3 mg/kg) alone attenuated mechanical and cold allodynia in a chemotherapy-induced pain model using cisplatin. Strikingly, SP600125 (3 mg/kg) pre-treatment prolonged the anti-allodynic effect of morphine by several days (5 and 7 days for mechanical and cold, respectively).

CONCLUSIONS

These results demonstrate that JNK signaling plays a crucial role in mediating antinociception as well as chronic tolerance to the antinociceptive effects of morphine in acute, inflammatory, and neuropathic pain states. Thus, inhibition of JNK signaling pathway, via SP600125, represents an efficacious pharmacological approach to delay tolerance to the antinociceptive effects of chronic morphine in diverse pain models.

Cdk5 contributes to inflammation-induced thermal hyperalgesia mediated by the p38 MAPK pathway in microglia

BACKGROUND

The mechanisms underlying cyclin-dependent kinase 5 (Cdk5)-mediated thermal hyperalgesia induced by inflammation remain poorly understood. In the present study, we examined thermal hyperalgesia provoked by peripheral injection of complete Freund׳s adjuvant (CFA) to test for Cdk5 signaling in the spinal dorsal horns of rats through the p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway, which is known to function in mediating inflammatory pain.

METHODS

We induced the inflammatory pain model by plantar injection of CFA and compared the inhibitory effects of roscovitine and SB203580 on thermal hyperalgesia. We measured localization of Cdk5, p35, OX-42, and glial fibrillary acidic protein (GFAP) in the dorsal horn at 1 and 3 days after CFA injection using immunohistochemistry, and we measured protein levels of OX-42 and phosphorylated-p38 (p-p38) using Western blot analysis. Tumor necrosis factor-a (TNF-a) was measured by ELISA.

RESULTS

The maximum thermal hyperalgesia induced by CFA occurred at 1d following injection and decreased until 5 d. We found colocalization of the Cdk5 activator p35, the microglial marker OX-42 and p-p38 in the same microglial cells and neurons of the spinal cord at day 1 after CFA injection; however, we saw no colocalization of p35 and GFAP, a marker of activated astrocytes. The thermal hyperalgesia induced by CFA was inhibited by intrathecal administration of the Cdk5 inhibitor roscovitine and by the p38 inhibitor SB203580. Furthermore, the expression of OX-42, p-p38, and TNF-a was remarkably increased from days 1 to 5 post-CFA injection and were significantly reversed by roscovitine between 1 and 3 days.

CONCLUSIONS

Cdk5, an upstream regulator of p38 and TNF-a, mediates CFA-induced thermal hyperalgesia. As such, pharmacological blocking of the generation of p-p38 mediated by Cdk5 may present a novel approach for diminishing inflammatory pain. This article is part of a Special Issue entitled SI: Spinal cord injury.

Anti-Inflammatory Effects and Joint Protection in Collagen-Induced Arthritis after Treatment with IQ-1S, a Selective c-Jun N-Terminal Kinase Inhibitor

c-Jun N-terminal kinases (JNKs) participate in many physiologic and pathologic processes, including inflammatory diseases. We recently synthesized the sodium salt of IQ-1S (11H-indeno[1,2-b]quinoxalin-11-one oxime) and demonstrated that it is a high-affinity JNK inhibitor and inhibits murine delayed-type hypersensitivity. Here we show that IQ-1S is highly specific for JNK and that its neutral form is the most abundant species at physiologic pH. Molecular docking of the IQ-1S syn isomer into the JNK1 binding site gave the best pose, which corresponded to the position of cocrystallized JNK inhibitor SP600125 (1,9-pyrazoloanthrone). Evaluation of the therapeutic potential of IQ-1S showed that it inhibited matrix metalloproteinase 1 and 3 gene expression induced by interleukin-1β in human fibroblast-like synoviocytes and significantly attenuated development of murine collagen-induced arthritis (CIA). Treatment with IQ-1S either before or after induction of CIA resulted in decreased clinical scores, and joint sections from IQ-1S-treated CIA mice exhibited only mild signs of inflammation and minimal cartilage loss compared with those from control mice. Collagen II-specific antibody responses were also reduced by IQ-1S treatment. By contrast, the inactive ketone derivative 11H-indeno[1,2-b]quinoxalin-11-one had no effect on CIA clinical scores or collagen II-specific antibody titers. IQ-1S treatment also suppressed proinflammatory cytokine and chemokine levels in joints and lymph node cells. Finally, treatment with IQ-1S increased the number of Foxp3(+)CD4(+)CD25(+) regulatory T cells in lymph nodes. Thus, IQ-1S can reduce inflammation and cartilage loss associated with CIA and can serve as a small-molecule modulator for mechanistic studies of JNK function in rheumatoid arthritis.