EETs/sEHi alleviates nociception by blocking the crosslink between endoplasmic reticulum stress and neuroinflammation in a central poststroke pain model

Endoplasmic reticulum stress: The underlying mechanism of chronic pain

Chronic pain (CP) affects over 30 % of the global population, imposing significant financial burdens on individuals and society. However, existing treatments for CP offer limited efficacy and troublesome side effects, primarily owing to a lack of knowledge of its precise underlying mechanism. Pathological stimuli disrupt the intricate process of protein folding and endoplasmic reticulum (ER) homeostasis. This disruption leads to the accumulation of misfolded or unfolded proteins in the ER, generating a condition termed ER stress. Emerging data have indicated that ER stress, occurring in the peripheral and central nervous systems, contributes to the development and maintenance of CP. This review aimed to comprehensively explore the intersection of ER stress and CP within the lower and upper nervous systems and highlight the cell-specific contributions of the unfolded protein response in different CP types. We provide a comprehensive synthesis of evidence from animal models, examining neuronal and non-neuronal mechanisms and discuss the damaging ER stress-linked inflammation, autophagy, oxidative stress, and apoptosis, which collectively drive disease progression and contribute to a neurotoxic environment. However, the mechanisms through which ER stress influences the most advanced centre-of-pain projections in the brain remain unclear. Further investigation in this area is crucial to elucidate the relationship between ER stress and CP and facilitate the development of novel therapeutic drugs for this intractable dilemma.

Targeting the soluble epoxide hydrolase pathway as a novel therapeutic approach for the treatment of pain

Chronic pain is a major burden and the complexities of chronic pain pathophysiology, including both peripheral and central sensitisation mechanisms, involves multiple cell types (neuronal, immune, neuroimmune, and vascular) which substantially complicates the development of new effective analgesic treatments. The epoxy fatty acids (EpFAs), including the epoxyeicosatrienoic acids (EETs), are derived from the metabolism of polyunsaturated fatty acids (PUFAs) via the cytochrome P450 enzymatic pathway and act to shut-down inflammatory signalling and provide analgesia. The EpFAs are rapidly metabolised by the enzyme soluble epoxide hydrolase (sEH) into their corresponding diol metabolites, which recent studies suggest are pro-inflammatory and pro-nociceptive. This review discusses clinical and mechanistic evidence for targeting the sEH pathway for the treatment of pain.

Central post-stroke pain: advances in clinical and preclinical research

Central poststroke pain (CPSP) is a medical complication that arises poststroke and significantly impacts the quality of life and social functioning of affected individuals. Despite ongoing research, the exact pathomechanisms of CPSP remain unclear, and practical treatments are still unavailable. Our review aims to systematically analyse current clinical and preclinical studies on CPSP, which is critical for identifying gaps in knowledge and guiding the development of effective therapies. The review will clarify the clinical characteristics, evaluation scales and contemporary therapeutic approaches for CPSP based on clinical investigations. It will particularly emphasise the CPSP model initiated by stroke, shedding light on its underlying mechanisms and evaluating treatments validated in preclinical studies. Furthermore, the review will not only highlight methodological limitations in animal trials but also offer specific recommendations to researchers to improve the quality of future investigations and guide the development of effective therapies. This review is expected to provide valuable insights into the current knowledge regarding CPSP and can serve as a guide for future research and clinical practice. The review will contribute to the scientific understanding of CPSP and help develop effective clinical interventions.

Differential lipid signaling from CD4+ and CD8+ T cells contributes to type 1 diabetes development

Introduction

We reported that Ca2+-independent phospholipase A2β (iPLA2β)-derived lipids (iDLs) contribute to type 1 diabetes (T1D) onset. As CD4+ and CD8+ T cells are critical in promoting β-cell death, we tested the hypothesis that iDL signaling from these cells participates in T1D development.

Methods

CD4+ and CD8+ T cells from wild-type non-obese diabetic (NOD) and NOD.iPLA2β+/- (NOD.HET) mice were administered in different combinations to immunodeficient NOD.scid.

Results

In mice receiving only NOD T cells, T1D onset was rapid (5 weeks), incidence 100% by 20 weeks, and islets absent. In contrast, onset was delayed 1 week and incidence reduced 40%-50% in mice receiving combinations that included NOD.HET T cells. Consistently, islets from these non-diabetic mice were devoid of infiltrate and contained insulin-positive β-cells. Reduced iPLA2β led to decreased production of proinflammatory lipids from CD4+ T cells including prostaglandins and dihydroxyeicosatrienoic acids (DHETs), products of soluble epoxide hydrolase (sEH), and inhibition of their signaling decreased (by 82%) IFNγ+CD4+ cells abundance. However, only DHETs production was reduced from CD8+ T cells and was accompanied by decreases in sEH and granzyme B.

Discussion

These findings suggest that differential select iDL signaling in CD4+ and CD8+ T cells contributes to T1D development, and that therapeutics targeting such signaling might be considered to counter T1D.

Role of Brain Derived Neurotrophic Factor and Related Therapeutic Strategies in Central Post-Stroke Pain

Brain-derived neurotrophic factor (BDNF) is vital for synaptic plasticity, cell persistence, and neuronal development in peripheral and central nervous systems (CNS). Numerous intracellular signalling pathways involving BDNF are well recognized to affect neurogenesis, synaptic function, cell viability, and cognitive function, which in turn affects pathological and physiological aspects of neurons. Stroke has a significant psycho-socioeconomic impact globally. Central post-stroke pain (CPSP), also known as a type of chronic neuropathic pain, is caused by injury to the CNS following a stroke, specifically damage to the somatosensory system. BDNF regulates a broad range of functions directly or via its biologically active isoforms, regulating multiple signalling pathways through interactions with different types of receptors. BDNF has been shown to play a major role in facilitating neuroplasticity during post-stroke recovery and a pro-nociceptive role in pain development in the nervous system. BDNF-tyrosine kinase receptors B (TrkB) pathway promotes neurite outgrowth, neurogenesis, and the prevention of apoptosis, which helps in stroke recovery. Meanwhile, BDNF overexpression plays a role in CPSP via the activation of purinergic receptors P2X4R and P2X7R. The neuronal hyperexcitability that causes CPSP is linked with BDNF-TrkB interactions, changes in ion channels and inflammatory reactions. This review provides an overview of BDNF synthesis, interactions with certain receptors, and potential functions in regulating signalling pathways associated with stroke and CPSP. The pathophysiological mechanisms underlying CPSP, the role of BDNF in CPSP, and the challenges and current treatment strategies targeting BDNF are also discussed.

Potential Role of Endoplasmic Reticulum Stress in Modulating Protein Homeostasis in Oligodendrocytes to Improve White Matter Injury in Preterm Infants

Preterm white matter injury (WMI) is a demyelinating disease with high incidence and mortality in premature infants. Oligodendrocyte cells (OLs) are a specialized glial cell that produces myelin proteins and adheres to the axons providing energy and metabolic support which susceptible to endoplasmic reticulum protein quality control. Disruption of cellular protein homeostasis led to OLs dysfunction and cell death, immediately, the unfolded protein response (UPR) activated to attempt to restore the protein homeostasis via IRE1/XBP1s, PERK/eIF2α and ATF6 pathway that reduced protein translation, strengthen protein-folding capacity, and degraded unfolding/misfolded protein. Moreover, recent works have revealed the conspicuousness function of ER signaling pathways in regulating influenced factors such as calcium homeostasis, mitochondrial reactive oxygen generation, and autophagy activation to regulate protein hemostasis and improve the myelination function of OLs. Each of the regulation modes and their corresponding molecular mechanisms provides unique opportunities and distinct perspectives to obtain a deep understanding of different actions of ER stress in maintaining OLs' health and function. Therefore, our review focuses on summarizing the current understanding of ER stress on OLs' protein homeostasis micro-environment in myelination during white matter development, as well as the pathophysiology of WMI, and discussing the further potential experimental therapeutics targeting these factors that restore the function of the UPR in OLs myelination function.

Inhibition of soluble epoxide hydrolase as a therapeutic approach for blood-brain barrier dysfunction

The blood-brain barrier (BBB) is a protective semi-permeable structure that regulates the exchange of biomolecules between the peripheral blood and the central nervous system (CNS). Due to its specialized tight junctions and low vesicle trafficking, the BBB strictly limits the paracellular passage and transcellular transport of molecules to maintain the physiological condition of brain tissues. BBB breakdown is associated with many CNS disorders. Soluble epoxide hydrolase (sEH) is a hydrolase enzyme that converts epoxy-fatty acids (EpFAs) to their corresponding diols and is involved in the onset and progression of multiple diseases. EpFAs play a protective role in the central nervous system via preventing neuroinflammation, making sEH a potential therapeutic target for CNS diseases. Recent studies showed that sEH inhibition prevented BBB impairment caused by stroke, hemorrhage, traumatic brain injury, hyperglycemia and sepsis via regulating the expression of tight junctions. In this review, the protective actions of sEH inhibition on BBB and potential mechanisms are summarized, and some important questions that remain to be resolved are also addressed.

Unraveling the Connection: Pain and Endoplasmic Reticulum Stress

Pain is a complex and multifaceted experience. Recent research has increasingly focused on the role of endoplasmic reticulum (ER) stress in the induction and modulation of pain. The ER is an essential organelle for cells and plays a key role in protein folding and calcium dynamics. Various pathological conditions, such as ischemia, hypoxia, toxic substances, and increased protein production, may disturb protein folding, causing an increase in misfolding proteins in the ER. Such an overload of the folding process leads to ER stress and causes the unfolded protein response (UPR), which increases folding capacity in the ER. Uncompensated ER stress impairs intracellular signaling and cell function, resulting in various diseases, such as diabetes and degenerative neurological diseases. ER stress may be a critical universal mechanism underlying human diseases. Pain sensations involve the central as well as peripheral nervous systems. Several preclinical studies indicate that ER stress in the nervous system is enhanced in various painful states, especially in neuropathic pain conditions. The purpose of this narrative review is to uncover the intricate relationship between ER stress and pain, exploring molecular pathways, implications for various pain conditions, and potential therapeutic strategies.

Endoplasmic reticular stress as an emerging therapeutic target for chronic pain: a narrative review

Chronic pain is a severely debilitating condition with enormous socioeconomic costs. Current treatment regimens with nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, or opioids have been largely unsatisfactory with uncertain benefits or severe long-term side effects. This is mainly because chronic pain has a multifactorial aetiology. Although conventional pain medications can alleviate pain by keeping several dysfunctional pathways under control, they can mask other underlying pathological causes, ultimately worsening nerve pathologies and pain outcome. Recent preclinical studies have shown that endoplasmic reticulum (ER) stress could be a central hub for triggering multiple molecular cascades involved in the development of chronic pain. Several ER stress inhibitors and unfolded protein response modulators, which have been tested in randomised clinical trials or apprpoved by the US Food and Drug Administration for other chronic diseases, significantly alleviated hyperalgesia in multiple preclinical pain models. Although the role of ER stress in neurodegenerative disorders, metabolic disorders, and cancer has been well established, research on ER stress and chronic pain is still in its infancy. Here, we critically analyse preclinical studies and explore how ER stress can mechanistically act as a central node to drive development and progression of chronic pain. We also discuss therapeutic prospects, benefits, and pitfalls of using ER stress inhibitors and unfolded protein response modulators for managing intractable chronic pain. In the future, targeting ER stress to impact multiple molecular networks might be an attractive therapeutic strategy against chronic pain refractory to steroids, NSAIDs, or opioids. This novel therapeutic strategy could provide solutions for the opioid crisis and public health challenge.

Role of soluble epoxide hydrolase in pain and depression comorbidity

The coexistence of chronic pain and depression in clinical practice places a substantial social burden and profoundly impacts in patients. Although a clear correlation exists, the underlying mechanism of comorbidity between chronic pain and depression remains elusive. Research conducted in recent decades has uncovered that soluble epoxide hydrolase, a pivotal enzyme in the metabolism of polyunsaturated fatty acids, plays a crucial role in inflammation. Interestingly, this enzyme is intricately linked to the development of both pain and depression. With this understanding, this review aims to summarize the roles of soluble epoxide hydrolase in pain, depression, and their comorbidity. Simultaneously, we will also explore the underlying mechanisms, providing guidance for future research and drug development.

Sestrin2 can alleviate endoplasmic reticulum stress to improve traumatic brain injury by activating AMPK/mTORC1 signaling pathway

Traumatic brain injury (TBI), as a serious central nervous system disease, can result in severe neurological dysfunction or even disability and death of patients. The early and effective intervention of secondary brain injury can improve the prognosis of TBI. Endoplasmic reticulum (ER) stress is one of the main reasons to recover TBI. ER stress inhibition may be beneficial in treating TBI. Sestrin2 is a crucial regulator of ER stress, and its activation can significantly improve TBI. In this paper, we analyze the biological function of sestrin2, the latest findings on ER stress, and the relationship between ER stress and TBI. We elucidate the relationship of sestrin2 inhibiting ER stress via activating the AMP-activated protein kinase (AMPK)/mammalian target of rapamycin complex 1 (MTORC1) signaling. Finally, we elaborate on the possible role of sestrin2 in TBI and explain how its activation potentially improves TBI.

Protein tyrosine phosphatase 1B contributes to neuropathic pain by aggravating NF-κB and glial cells activation-mediated neuroinflammation via promoting endoplasmic reticulum stress

BACKGROUND

Neuropathic pain is a prevalent and highly debilitating condition that impacts millions of individuals globally. Neuroinflammation is considered a key factor in the development of neuropathic pain. Accumulating evidence suggests that protein tyrosine phosphatase 1B (PTP1B) plays a crucial role in regulating neuroinflammation. Nevertheless, the specific involvement of PTP1B in neuropathic pain remains largely unknown. This study aims to examine the impact of PTP1B on neuropathic pain and unravel the underlying molecular mechanisms implicated.

METHODS

In the current study, we evaluated the paw withdrawal threshold (PWT) of male rats following spared nerve injury (SNI) to assess the presence of neuropathic pain. To elucidate the underlying mechanisms, western blotting, immunofluorescence, and electron microscopy techniques were employed.

RESULTS

Our results showed that SNI significantly elevated PTP1B levels, which was accompanied by an increase in the expression of endoplasmic reticulum (ER) stress markers (BIP, p-PERK, p-IRE1α, and ATF6) and phosphorylated NF-κB in the spinal dorsal horn. SNI-induced mechanical allodynia was impaired by the treatment of intrathecal injection of PTP1B siRNA or PTP1B-IN-1, a specific inhibitor of PTP1B. Moreover, the intrathecal administration of PTP1B-IN-1 effectively suppressed the expression of ER stress markers (BIP, p-PERK/p-eIF2α, p-IRE1α, and ATF6), leading to the inhibition of NF-κB, microglia, and astrocytes activation, as well as a decrease in pro-inflammatory cytokines, including TNF-α, IL-6, and IL-1β. However, these effects were reversed by intrathecal administration of tunicamycin (Tm, an inducer of ER stress). Additionally, intrathecal administration of Tm in healthy rats resulted in the development of mechanical allodynia and the activation of NF-κB-mediated neuroinflammatory signaling.

CONCLUSIONS

The upregulation of PTP1B induced by SNI facilitates the activation of NF-κB and glial cells via ER stress in the spinal dorsal horn. This, in turn, leads to an increase in the production of pro-inflammatory cytokines, thereby contributing to the development and maintenance of neuropathic pain. Therefore, targeting PTP1B could be a promising therapeutic strategy for the treatment of neuropathic pain.

Role of arachidonic acid metabolism in intervertebral disc degeneration: identification of potential biomarkers and therapeutic targets via multi-omics analysis and artificial intelligence strategies

BACKGROUND

Intervertebral disc degeneration (IVDD) is widely recognized as the primary etiological factor underlying low back pain, often necessitating surgical intervention as the sole recourse in severe cases. The metabolic pathway of arachidonic acid (AA), a pivotal regulator of inflammatory responses, influences the development and progression of IVDD.

METHODS

Initially, a comparative analysis was conducted to investigate the relationship between AA expression patterns and different stages of IVDD using single-cell sequencing (scRNA-seq) data. Additionally, three machine learning methods (LASSO, random forest, and support vector machine recursive feature elimination) were employed to identify hub genes associated with IVDD. Subsequently, a novel artificial intelligence prediction model was developed for IVDD based on an artificial neural network algorithm and validated using an independent dataset. The identified hub genes were further subjected to functional enrichment, immune infiltration, and Connectivity Map analysis. Moreover, external validation was performed using flow cytometry and real-time reverse transcription polymerase chain reaction analysis.

RESULTS

Both scRNA-seq and bulk RNA-seq data revealed a positive correlation between the severity of IVDD and the AA metabolic pathway. They also revealed increased AA metabolic activity in macrophages and neutrophils, as well as enhanced intercellular communication with nucleus pulposus cells. Utilizing advanced machine learning algorithms, five hub genes (AKR1C3, ALOX5, CYP2B6, EPHX2, and PLB1) were identified, and an incipient diagnostic model was developed with an AUC of 0.961 in the training cohort and 0.72 in the validation cohort. An in-depth exploration of the functionality of these hub genes revealed their notable association with inflammatory responses and immune cell infiltration. Lastly, AH6809 was found to delay IVDD by inhibiting AKR1C3.

CONCLUSIONS

This study offers comprehensive insights into potential biomarkers and small molecules associated with the early pathogenesis of IVDD. The identified biomarkers and the developed integrated diagnostic model hold great promise in predicting the onset of early IVDD. AH6809 was established as a therapeutic target for AKR1C3 in the treatment of IVDD, as evidenced by computer simulations and biological experiments.

Soluble epoxide hydrolase deficiency attenuates airway inflammation in COPD via IRE1α/JNK/AP-1 signaling pathway

BACKGROUND

Soluble Epoxide Hydrolase (sEH) metabolizes anti-inflammatory epoxyeicosatrienoic acids and critically affects airway inflammation in chronic obstructive pulmonary disease (COPD). Considering the excessive endoplasmic reticulum stress is associated with the earlier onset of COPD. The role of sEH and endoplasmic reticulum stress in the pathogenesis of COPD remains unknown.

METHOD

16 weeks of cigarette-exposed mice were used to detect the relationship between sEH and endoplasmic reticulum stress in COPD. Human epithelial cells were used in vitro to determine the regulation mechanism of sEH in endoplasmic reticulum stress induced by cigarette smoke.

RESULTS

sEH deficiency helps reduce emphysema formation after smoke exposure by alleviating endoplasmic reticulum stress response. sEH deficiency effectively reverses the upregulation of phosphorylation IRE1α and JNK and the nuclear expression of AP-1, alleviating the secretion of inflammatory factors induced by cigarette smoke extract. Furthermore, the treatment with endoplasmic reticulum stress and IRE1α inhibitor downregulated cigarette smoke extract-induced sEH expression and the secretion of inflammatory factors.

CONCLUSION

sEH probably alleviates airway inflammatory response and endoplasmic reticulum stress via the IRE1α/JNK/AP-1 pathway, which might attenuate lung injury caused by long-term smoking and provide a new pharmacological target for preventing and treating COPD.

Research Progress on the Mechanisms of Central Post-Stroke Pain: A Review

Central Post-Stroke Pain (CPSP) is a primary sequelae of stroke that can develop in the body part corresponding to the cerebrovascular lesion after stroke, most typically after ischemic stroke but also after hemorrhagic stroke. The pathogenesis of CPSP is currently unknown, and research into its mechanism is ongoing. To summarize current research on the CPSP mechanism and provide guidance for future studies. Use "central post-stroke pain," "stroke AND thalamic pain," "stroke AND neuropathic pain," "post-stroke thalamic pain" as the search term. The search was conducted in the PubMed and China National Knowledge Infrastructure databases, summarizing and classifying the retrieved mechanism studies. The mechanistic studies on CPSP are extensive, and we categorized the included mechanistic studies and summarized them in terms of relevant pathway studies, relevant signals and receptors, relevant neural tissues, and described endoplasmic reticulum stress and other relevant studies, as well as summarized the mechanisms of acupuncture treatment. Studies have shown that the pathogenesis of CPSP involves the entire spinal-thalamo-cortical pathway and that multiple substances in the nervous system are involved in the formation and development of CPSP. Among them, the relevant receptors and signals are the hotspot of research, and the discovery and exploration of different receptors and signals have provided a wide range of therapeutic ideas for CPSP. As a very effective treatment, acupuncture is less studied regarding the analgesic mechanism of CPSP, and further experimental studies are still needed.

Soluble epoxide hydrolase inhibitor blockage microglial cell activation in subnucleus caudalis in a persistent model of arthritis

Rheumatoid arthritis (RA) is a chronic condition characterized by pain and infiltration of immune cells into the joint. Immune cells can be activated, producing inflammatory cytokines, leading to continuously degenerative and inflammatory reactions and the temporomandibular joint (TMJ) can be affected by RA. In this scenario, novel targets are needed to increase treatment efficacy with minimized side effects. The epoxy-eicosatrienoic acids (EETs), are endogenous signaling molecules, playing important roles in diminishing inflammation and pain but are promptly metabolized by soluble epoxide hydrolase (sEH), generating less-bioactive acids.Therefore, sEH inhibitors is an interest therapeutic target to enhance the beneficial effect of natural EETs. TPPU is a potent sEH inhibitor that is capable of dampening EETs hydrolysis. Thus, we aimed to assess the impact of pharmacological sEH inhibition on a persistent model of albumin-induced arthritis in the TMJ, in two scenarios: first, as post-treatment, in an installed arthritic condition, and second, the protective role, in preventing the development of an arthritic condition. In addition, we investigate the influence of sEH inhibition on microglia cell activation in the trigeminal subnucleus caudalis (TSC) and in vitro experiments. Finally, we examined the astrocyte phenotype. Oral administration of TPPU, acts in multiple pathways, in a protective and reparative post-treatment, ameliorating the preservation of the TMJ morphology, reducing the hypernociception, with an immunosuppressive action reducing neutrophil and lymphocytes and pro-inflammatory cytokines in the TMJ of rats. In TSC, TPPU reduces the cytokine storm and attenuates the microglia activated P2X7/Cathepsin S/Fractalkine pathway and reduces the astrocyte activation and glutamate levels. Collectively, our findings revealed that sEH inhibition mitigates hypersensitive nociception through the regulation of microglia activation and astrocyte modulation, demonstrating the potential use of sEH inhibitors as immunoresolvents in the treatment of autoimmune disorders.

Soluble epoxide hydrolase deficiency promotes liver regeneration and ameliorates liver injury in mice by regulating angiocrine factors and angiogenesis

BACKGROUND

Soluble epoxide hydrolase (sEH) is a key enzyme for the hydrolysis of epoxyeicosatrienoic acids (EETs) and has been implicated in the pathogenesis of hepatic inflammation, fibrosis, cancer, and nonalcoholic fatty liver disease. However, the role of sEH in liver regeneration and injury remains unclear.

METHODS

This study used sEH-deficient (sEH^-/-) mice and wild-type (WT) mice. Hepatocyte proliferation was assessed by immunohistochemical (IHC) staining for Ki67. Liver injury was evaluated by histological staining with hematoxylin and eosin (H&E), Masson's trichrome, and Sirius red, as well as IHC staining for α-SMA. Hepatic macrophage infiltration and angiogenesis were reflected by IHC staining for CD68 and CD31. Liver angiocrine levels were detected by ELISA. The mRNA levels of angiocrine or cell cycle-related genes were measured by quantitative real-time RT-PCR (qPCR). The protein levels of cell proliferation-related protein and phosphorylated signal transducer and activator of transcription 3 (STAT3) were detected by western blotting.

RESULTS

sEH mRNA and protein levels were significantly upregulated in mice after 2/3 partial hepatectomy (PHx). Compared with WT mice, sEH^-/- mice exhibited a higher liver/body weight ratio and more Ki67-positive cells on days 2 and 3 after PHx. The accelerated liver regeneration in sEH^-/- mice was attributed to angiogenesis and endothelial-derived angiocrine (HGF) production. Subsequently, hepatic protein expression of cyclinD1 (CYCD1) and the downstream direct targets of the STAT3 pathway, such as c-fos, c-jun, and c-myc, were also suppressed post-PHx in sEH^-/- compared to WT mice. Furthermore, sEH deficiency attenuated CCl₄-induced acute liver injury and reduced fibrosis in both CCl₄ and bile duct ligation (BDL)-induced liver fibrosis rodent models. Compared with WT mice, sEH^-/- mice had slightly decreased hepatic macrophage infiltration and angiogenesis. Meanwhile, sEH^-/- BDL mice had more Ki67-positive cells in the liver than WT BDL mice.

CONCLUSIONS

sEH deficiency alters the angiocrine profile of liver endothelial to accelerate hepatocyte proliferation and liver regeneration, and blunts acute liver injury and fibrosis by inhibiting inflammation and angiogenesis. sEH inhibition is a promising target for liver diseases to improve liver regeneration and damage.

Soluble epoxide hydrolase inhibitor promotes the healing of oral ulcers

OBJECTIVE

Oral ulcers are a lesion in the oral mucosa that impacts chewing or drinking. Epoxyeicosatrienoic Acids (EETs) have enhanced angiogenic, regenerative, anti-inflammatory, and analgesic effects. The present study aims to evaluate the effects of 1-Trifluoromethoxyphenyl-3-(1-Propionylpiperidin-4-yl) Urea (TPPU), a soluble epoxide hydrolase inhibitor for increasing EETs level, on the healing of oral ulcers.

METHODS

The chemically-induced oral ulcers were established in Sprague Dawley rats. The ulcer area was treated with TPPU to evaluate the healing time and pain threshold of ulcers. The expression of angiogenesis and cell proliferation-related protein in the ulcer area was detected using immunohistochemical staining. The effects of TPPU on migration and angiogenesis capability were measured with scratch assay and tube formation.

RESULTS

Compared with the control group, TPPU promoted wound healing of oral ulcers with a shorter healing time, and raised pain thresholds. Immunohistochemical staining showed that TPPU increased the expression of angiogenesis and cell proliferation-related protein with reduced inflammatory cell infiltration in the ulcer area. TPPU enhanced cell migration and tube-forming potential in vitro.

CONCLUSIONS

The present results support the potential of TPPU with multiple biological effects for the treatment of oral ulcers by targeting soluble epoxide hydrolase.

Spinal MCP-1 Contributes to Central Post-stroke Pain by Inducing Central Sensitization in Rats

Central post-stroke pain (CPSP) is a highly refractory form of central neuropathic pain that has been poorly studied mechanistically. Recent observations have emphasized the critical role of the spinal dorsal horn in CPSP. However, the underlying mechanisms remain unclear. In this study, rats were subjected to thalamic hemorrhage to investigate the role of spinal monocyte chemoattractant protein-1 (MCP-1) and C-C motif chemokine receptor 2 (CCR2) in the development of CPSP. Immunohistochemical staining and ELISA were used to assess the expression changes of c-Fos, Iba-1, GFAP, MCP-1, and CCR2 in the dorsal horn of the lumbar spinal cord following thalamic hemorrhage, and the involvement of spinal MCP-1 in CPSP was examined by performing intrathecal anti-MCP-1 mAb injection to neutralize the spinal extracellular MCP-1. We demonstrated that intra-thalamic collagenase microinjection induced persistent bilateral mechanical pain hypersensitivity and facilitated the spontaneous pain behaviors evoked by intraplantar bee venom injection. Accompanying CPSP, the expression of c-Fos, Iba-1, and GFAP in the lumbar spinal dorsal horn was significantly increased up to 28 days post-intra-thalamic collagenase microinjection. Intrathecal injection of minocycline and fluorocitrate dramatically reverses the bilateral mechanical pain hypersensitivity. Moreover, intra-thalamic collagenase microinjection dramatically induced the up-regulation of MCP-1 but had no effect on the expression of CCR2 in the bilateral lumbar spinal dorsal horn, and MCP-1 was primarily localized in the neuron. Intrathecal injection of anti-MCP-1 mAb was also able to reverse CPSP and reduce the expression of c-Fos, Iba-1, and GFAP in the lumbar spinal dorsal horn. These findings indicated that spinal MCP-1 contributes to CPSP by mediating the activation of spinal neurons and glial cells following thalamic hemorrhage stroke, which may provide insights into pharmacologic treatment for CPSP.

Stellate ganglion block ameliorated central post-stroke pain with comorbid anxiety and depression through inhibiting HIF-1α/NLRP3 signaling following thalamic hemorrhagic stroke

BACKGROUND

Central post-stroke pain (CPSP) is an intractable and disabling central neuropathic pain that severely affects patients' lives, well-being, and socialization abilities. However, CPSP has been poorly studied mechanistically and its treatment remains challenging. Here, we used a rat model of CPSP induced by thalamic hemorrhage to investigate its underlying mechanisms and the effect of stellate ganglion block (SGB) on CPSP and emotional comorbidities.

METHODS

Thalamic hemorrhage was produced by injecting collagenase IV into the ventral-posterolateral nucleus (VPL) of the right thalamus. The up-and-down method with von Frey hairs was used to measure the mechanical allodynia. Behavioral tests were carried out to examine depressive and anxiety-like behaviors including the open field test (OFT), elevated plus maze test (EPMT), novelty-suppressed feeding test (NSFT), and forced swim test (FST). The peri-thalamic lesion tissues were collected for immunofluorescence, western blotting, and enzyme-linked immunosorbent assay (ELISA). Genetic knockdown of thalamic hypoxia-inducible factor-1α (HIF-1α) and NOD-like receptor thermal protein domain associated protein 3 (NLRP3) with microinjection of HIF-1α siRNA and NLRP3 siRNA into the VPL of thalamus were performed 3 days before collagenase injection into the same regions. Microinjection of lificiguat (YC-1) and MCC950 into the VPL of thalamus were administrated 30 min before the collagenase injection in order to inhibited HIF-1α and NLRP3 pharmacologically. Repetitive right SGB was performed daily for 5 days and laser speckle contrast imaging (LSCI) was conducted to examine cerebral blood flow.

RESULTS

Thalamic hemorrhage caused persistent mechanical allodynia and anxiety- and depression-like behaviors. Accompanying the persistent mechanical allodynia, the expression of HIF-1α and NLRP3, as well as the activities of microglia and astrocytes in the peri-thalamic lesion sites, were significantly increased. Genetic knockdown of thalamic HIF-1α and NLRP3 significantly attenuated mechanical allodynia and anxiety- and depression-like behaviors following thalamic hemorrhage. Further studies revealed that intra-thalamic injection of YC-1, or MCC950 significantly suppressed the activation of microglia and astrocytes, the release of pro-inflammatory cytokines, the upregulation of malondialdehyde (MDA), and the downregulation of superoxide dismutase (SOD), as well as mechanical allodynia and anxiety- and depression-like behaviors following thalamic hemorrhage. In addition, repetitive ipsilateral SGB significantly restored the upregulated HIF-1α/NLRP3 signaling and the hyperactivated microglia and astrocytes following thalamic hemorrhage. The enhanced expression of pro-inflammatory cytokines and the oxidative stress in the peri-thalamic lesion sites were also reversed by SGB. Moreover, LSCI showed that repetitive SGB significantly increased cerebral blood flow following thalamic hemorrhage. Most strikingly, SGB not only prevented, but also reversed the development of mechanical allodynia and anxiety- and depression-like behaviors induced by thalamic hemorrhage. However, pharmacological activation of thalamic HIF-1α and NLRP3 with specific agonists significantly eliminated the therapeutic effects of SGB on mechanical allodynia and anxiety- and depression-like behaviors following thalamic hemorrhage.

CONCLUSION

This study demonstrated for the first time that SGB could improve CPSP with comorbid anxiety and depression by increasing cerebral blood flow and inhibiting HIF-1α/NLRP3 inflammatory signaling.

Soluble Epoxide Hydrolase Inhibitor TPPU Alleviates Nab-Paclitaxel-Induced Peripheral Neuropathic Pain via Suppressing NF-κB Signalling in the Spinal Cord of a Rat

Objective

Paclitaxel-induced peripheral neuropathy (PIPN) is a debilitating and difficult-to-treat side effect of paclitaxel. Soluble epoxide hydrolase (sEH) can rapidly metabolize the endogenous anti-inflammatory mediators' epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids. This study aimed to assess whether the sEH inhibitor N-(1-(1-oxopropy)-4-piperidinyl]-N'-(trifluoromethoxy) phenyl)-urea (TPPU) plays a critical role in PIPN of rats and provides a new target for treatment.

Methods

A Sprague-Dawley male rat model of PIPN induced by nab-paclitaxel was established. Rats were randomly divided into a control group, nab-paclitaxel group, and nab-paclitaxel + TPPU (sEH inhibitor) group, with 36 rats in each group. The effects of the sEH inhibitor TPPU on behavioural assays, apoptosis, glial activation, axonal injury, microstructure, and permeability of the blood-spinal cord barrier were detected, and the underlying mechanisms were explored by examining the expression of NF-κB signalling pathways, inflammatory cytokines, and oxidative stress.

Results

The results showed that the mechanical and thermal pain thresholds of rats were decreased after nab-paclitaxel treatment, accompanied by an increased expression of axonal injury-related proteins, enhanced cell apoptosis, aggravated destruction of vascular permeability, intense glial responses, and elevated inflammatory cytokines and oxidative stress in the L4-L6 spinal cord. TPPU restored the mechanical and thermal thresholds, decreased cell apoptosis, alleviated axonal injury and glial responses, and protected vascular permeability by increasing the expression of tight junction proteins. TPPU relieved PIPN by inhibiting the activation of the sEH and NF-κB signalling pathways by decreasing the levels of inflammatory cytokines and oxidative stress.

Conclusion

These findings support a role for sEH in PIPN and suggest that the inhibition of sEH represents a potential new therapeutic target for PIPN.

Targeting soluble epoxide hydrolase promotes osteogenic-angiogenic coupling via activating SLIT3/HIF-1α signalling pathway

Type H vessels have recently been identified to modulate osteogenesis. Epoxyeicostrioleic acids (EETs) have an essential contribution to vascular homeostasis. However, whether increased EETs with soluble epoxide hydrolase (sEH) inhibitor TPPU enhance the coupling of angiogenesis and osteogenesis remains largely unknown. The effects of TPPU on cross-talk between co-cultured human umbilical vein endothelial cells (HUVECs) and human dental pulp stem cells (hDPSCs), and on long bone growth and calvarial defect repair in mice were investigated in vitro and in vivo. TPPU enhanced osteogenic differentiation of co-cultured HUVECs and hDPSCs in vitro and increased type H vessels, and long bone growth and bone repair of calvarial defect. Mechanistically, TPPU promoted cell proliferation and angiogenesis, reclined cell apoptosis, and significantly increased CD31^hi EMCN^hi endothelial cells (ECs) and SLIT3 and HIF-1α expression levels in co-cultured HUVECs and hDPSCs. Knockdown of Slit3 in hDPSCs or Hif-1α in HUVECs impaired the formation of CD31^hi EMCN^hi ECs and reversed TPPU-induced osteogenesis. We defined a previously unidentified effect of TPPU coupling angiogenesis and osteogenesis. TPPU induced type H vessels by upregulating the expression of hDPSCs-derived SLIT3, which resulted in the activation of ROBO1/YAP1/HIF-1α signalling pathway in ECs. Targeting metabolic pathways of EETs represents a new strategy to couple osteogenesis and angiogenesis, sEH is a promising therapeutic target for bone regeneration and repair.

Soluble epoxide hydrolase inhibition alleviates chemotherapy induced neuropathic pain

Chemotherapy induced peripheral neuropathy (CIPN) is a particularly pernicious form of neuropathy and the associated pain is the primary dose-limiting factor of life-prolonging chemotherapy treatment. The prevalence of CIPN is high and can last long after treatment has been stopped. Currently, late in the COVID-19 pandemic, there are still increased psychological pressures on cancer patients as well as additional challenges in providing analgesia for them. These include the risks of nonsteroidal anti-inflammatory drug (NSAID) analgesics potentially masking early infection symptoms and the immunosuppression of steroidal and opiate based approaches. Even without these concerns, CIPN is often inadequately treated with few therapies that offer significant pain relief. The experiments we report use soluble epoxide hydrolase inhibitors (sEHI) which relieved this intractable pain in preclinical models. Doses of EC5026, an IND candidate intended to treat neuropathic pain, elicited dose dependent analgesic responses in multiple models including platinum-based, taxane, and vinca alkaloid-based CIPN pain in Sprague Dawley rats. At the same time as a class, the sEHI are known to result in fewer debilitating side effects of other analgesics, likely due to their novel mechanism of action. Overall, the observed dose-dependent analgesia in both male and female rats across multiple models of chemotherapy induced neuropathic pain holds promise as a useful tool when translated to the clinic.

Metabolomics Provides Insights into Renoprotective Effects of Semaglutide in Obese Mice

PURPOSE

Semaglutide, a new long-acting glucagon-like peptide-1 analogue, has shown benefits for renal diseases, but its direct role on kidney metabolism under obesity remains unclear. The study aims to elucidate the protective effect and metabolic modulation mechanism of semaglutide on obesity-related kidney injury.

METHODS

Male C57BL/6J mice were divided into control and obesity groups. Mice in the obesity group had a high-fat diet and were treated with or without semaglutide (30nmol/kg/day). The study assayed blood biochemistry and then evaluated renal pathological injury through Periodic Acid-Schiff staining and electron microscopy. Metabolomics was utilized to analyze obesity-related metabolites in kidney samples.

RESULTS

Semaglutide significantly improved glucose homeostasis, insulin resistance, and kidney injury in obese mice. We successfully identified 377 altered metabolites (P<0.05). It was suggested that semaglutide directly improved oxidative stress and inflammation-related metabolites such as nicotinamide adenine dinucleotide (NAD+) and adenosine in the kidney of obese mice, which have not been documented in obesity-related kidney injury. Relevant enriched pathways were included phospholipids and lysophospholipids metabolism, purine metabolism, NAD+ metabolism, and insulin resistance-related metabolism. They could serve as potential targets for intervention of obesity-related kidney injury.

CONCLUSION

Our study revealed the metabolomics-based renoprotective mechanism of semaglutide in obese mice for the first time. The innovation lied in the identified metabolites such as NAD+ and adenosine targeted by semaglutide, which have not been documented in obesity-related kidney injury. Semaglutide may be a promising therapy for obesity-related kidney diseases.

CYP450 Epoxygenase Metabolites, Epoxyeicosatrienoic Acids, as Novel Anti-Inflammatory Mediators

Inflammation plays a crucial role in the initiation and development of a wide range of systemic illnesses. Epoxyeicosatrienoic acids (EETs) are derived from arachidonic acid (AA) metabolized by CYP450 epoxygenase (CYP450) and are subsequently hydrolyzed by soluble epoxide hydrolase (sEH) to dihydroxyeicosatrienoic acids (DHETs), which are merely biologically active. EETs possess a wide range of established protective effects on many systems of which anti-inflammatory actions have gained great interest. EETs attenuate vascular inflammation and remodeling by inhibiting activation of endothelial cells and reducing cross-talk between inflammatory cells and blood vessels. EETs also process direct and indirect anti-inflammatory properties in the myocardium and therefore alleviate inflammatory cardiomyopathy and cardiac remodeling. Moreover, emerging studies show the substantial roles of EETs in relieving inflammation under other pathophysiological environments, such as diabetes, sepsis, lung injuries, neurodegenerative disease, hepatic diseases, kidney injury, and arthritis. Furthermore, pharmacological manipulations of the AA-CYP450-EETs-sEH pathway have demonstrated a contribution to the alleviation of numerous inflammatory diseases, which highlight a therapeutic potential of drugs targeting this pathway. This review summarizes the progress of AA-CYP450-EETs-sEH pathway in regulation of inflammation under different pathological conditions and discusses the existing challenges and future direction of this research field.

Epoxyeicosatrienoic acids and soluble epoxide hydrolase in physiology and diseases of the central nervous system

Epoxyeicosatrienoic acids (EETs) are fatty acid signaling molecules synthesized by cytochrome P450 epoxygenases from arachidonic acid. The biological activity of EETs is terminated when being metabolized by soluble epoxide hydrolase (sEH), a process that serves as a key regulator of tissue EETs levels. EETs act through several signaling pathways to mediate various beneficial effects, including anti-inflammation, anti-apoptosis, and anti-oxidation with relieve of endoplasmic reticulum stress, thereby sEH has become a potential therapeutic target in cardiovascular disease and cancer therapy. Enzymes for EET biosynthesis and metabolism are both widely detected in both neuron and glial cells in the central nervous system (CNS). Recent studies discovered that astrocyte-derived EETs not only mediate neurovascular coupling and neuronal excitability by maintaining glutamate homeostasis but also glia-dependent neuroprotection. Genetic ablation as well as pharmacologic inhibition of sEH has greatly helped to elucidate the physiologic actions of EETs, and maintaining or elevating brain EETs level has been demonstrated beneficial effects in CNS disease models. Here, we review the literature regarding the studies on the bioactivity of EETs and their metabolic enzyme sEH with special attention paid to their action mechanisms in the CNS, including their modulation of neuronal activity, attenuation of neuroinflammation, regulation of cerebral blood flow, and improvement of neuronal and glial cells survival. We further reviewed the recent advance on the potential application of sEH inhibition for treating cerebrovascular disease, epilepsy, and pain disorder.