Lipoxins and aspirin-triggered lipoxin alleviate bone cancer pain in association with suppressing expression of spinal proinflammatory cytokines

Influence of physico-chemical properties of two lipoxin emulsion-loaded hydrogels on pre-polarized macrophages: a comparative analysis

Inflammation, a crucial defense mechanism, must be rigorously regulated to prevent the onset of chronic inflammation and subsequent tissue damage. Specialized pro resolving mediators (SPMs) such as lipoxin A4 (LXA4) have demonstrated their ability to facilitate the resolution of inflammation by orchestrating a transition of M1 pro-inflammatory macrophages towards an anti-inflammatory M2 phenotype. However, the hydrophobic and chemically labile nature of LXA4 necessitates the development of a delivery system capable of preserving its integrity for clinical applications. In this study, two types of emulsion were formulated using different homogenization processes:mechanical overhead stirrer (MEB for blank Emulsion and MELX for LXA4 loaded-Emulsion) or Luer-lock syringes (SEB for blank Emulsion and SELX for LXA4 loaded-Emulsion)). Following characterization, including size and droplet morphology assessment by microscopy, the encapsulation efficiency (EE) was determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). To exert control over LXA4 release, these emulsions were embedded within silanized hyaluronic acid hydrogels. A comprehensive evaluation, encompassing gel time, swelling, and degradation profiles under acidic, basic, and neutral conditions, preceded the assessment of LXA4 cumulative release using LC-MS/MS. Physicochemical results indicate that H-MELX (Mechanical overhead stirrer LXA4 Emulsion loaded-Hydrogel) exhibits superior efficiency over H-SELX (Luer-lock syringes LXA4 Emulsion loaded-Hydrogel). While both formulations stimulated pro-inflammatory cytokine secretion and promoted a pro-inflammatory macrophage phenotype, LXA4 emulsion-loaded hydrogels displayed a diminished pro-inflammatory activity compared to blank emulsion-loaded hydrogels. These findings highlight the biological efficacy of LXA4 within both systems, with H-SELX outperforming H-MELX in terms of efficiency. To the best of our knowledge, this is the first successful demonstration of the biological efficacy of LXA4 emulsion-loaded hydrogel systems on macrophage polarization. These versatile H-MELX and H-SELX formulations can be customized to enhance their biological activity making them promising tools to promote the resolution of inflammation in diverse clinical applications.

Protective Effects of Lipoxin A4 and B4 Signaling on the Inner Retina in a Mouse Model of Experimental Glaucoma

Glaucoma is a common neurodegenerative disease characterized by progressive degeneration of retinal ganglion cells (RGCs) and the retinal nerve fiber layer (RNFL), resulting in a gradual decline of vision. A recent study by our groups indicated that the levels of lipoxins A4 (LXA4) and B4 (LXB4) in the retina and optic nerve decrease following acute injury, and that restoring their function is neuroprotective. Lipoxins are members of the specialized pro-resolving mediator (SPM) family and play key roles to mitigate and resolve chronic inflammation and tissue damage. Yet, knowledge about lipoxin neuroprotective activity remains limited. Here we investigate the in vivo efficacy of exogenous LXA4 and LXB4 administration on the inner retina in a mouse model of chronic experimental glaucoma. To investigate the contribution of LXA4 signaling we used transgenic knockout (KO) mice lacking the two mouse LXA4 receptors (Fpr2/Fpr3-/-). Functional and structural changes of inner retinal neurons were assessed longitudinally using electroretinogram (ERG) and optical coherence tomography (OCT). At the end of the experiment, retinal samples were harvested for immunohistological assessment. While both lipoxins generated protective trends, only LXB4 treatment was significant, and consistently more efficacious than LXA4 in all endpoints. Both lipoxins also appeared to dramatically reduce Müller glial reactivity following injury. In comparison, Fpr2/Fpr3 deletion significantly worsened inner retinal injury and function, consistent with an essential protective role for endogenous LXA4. Together, these results support further exploration of lipoxin signaling as a treatment for glaucomatous neurodegeneration.

LncRNA NONRATT014888.2 contributes to cancer-induced bone pain through downregulation of natriuretic peptide receptor 3 in rats

Long noncoding RNA (lncRNA) is implicated in both cancer development and pain process. However, the role of lncRNA in the development of cancer-induced bone pain (CIBP) is unclear. LncRNA NONRATT014888.2 is highly expressed in tibia related dorsal root ganglions (DRGs) in CIBP rats which function is unknown. CIBP was induced by injection of Walker 256 mammary gland tumor cells into the tibia canal of female SD rats. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) of rats were measured. Down-regulation of NONRATT014888.2 by siRNA in CIBP rats markedly attenuated hind-paw mechanical pain hypersensitivity. LncRNA-predicted target mRNAs analysis and mRNA sequencing results cued Socs3, Npr3 were related with NONRATT014888.2. Intrathecal injection of NONRATT014888.2-siR206 upregulated Npr3 both in mRNA and protein level. Npr3 was co-expressed in NONRATT014888.2-positive DRGs neurons and mainly located in cytoplasm, but not in Glial fibrillary acidic protein (GFAP)-positive cells. Intrathecal injection of ADV-Npr3 upregulated Npr3 expression and enhanced the PWT of CIBP rats. Our results suggest that upregulated lncRNA NONRATT014888.2 contributed to hyperalgesia in CIBP rats, and the mechanism may through downregulation of Npr3.

Regulation of inflammation in cancer by dietary eicosanoids

BACKGROUND

Cancer is a major burden of disease worldwide and increasing evidence shows that inflammation contributes to cancer development and progression. Eicosanoids are derived from dietary polyunsaturated fatty acids, such as arachidonic acid (AA), and are mainly produced by a series of enzymatic pathways that include cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P-450 epoxygenase (CYP). Eicosanoids consist of at least several hundred individual molecules and play important roles in the inflammatory response and inflammation-related cancers.

SCOPE AND APPROACH

Dietary sources of AA and biosynthesis of eicosanoids from AA through different metabolic pathways are summarized. The bioactivities of eicosanoids and their potential molecular mechanisms on inflammation and cancer are revealed. Additionally, current challenges and limitations in eicosanoid research on inflammation-related cancer are discussed.

KEY FINDINGS AND CONCLUSIONS

Dietary AA generates a large variety of eicosanoids, including prostaglandins, thromboxane A2, leukotrienes, cysteinyl leukotrienes, lipoxins, hydroxyeicosatetraenoic acids (HETEs), and epoxyeicosatrienoic acids (EETs). Eicosanoids exert different bioactivities and mechanisms involved in the inflammation and related cancer developments. A deeper understanding of eicosanoid biology may be advantageous in cancer treatment and help to define cellular targets for further therapeutic development.

Behavioral Voluntary and Social Bioassays Enabling Identification of Complex and Sex-Dependent Pain-(-Related) Phenotypes in Rats with Bone Cancer

Cancer-induced bone pain (CIBP) is a common and devastating symptom with limited treatment options in patients, significantly affecting their quality of life. The use of rodent models is the most common approach to uncovering the mechanisms underlying CIBP; however, the translation of results to the clinic may be hindered because the assessment of pain-related behavior is often based exclusively on reflexive-based methods, which are only partially indicative of relevant pain in patients. To improve the accuracy and strength of the preclinical, experimental model of CIBP in rodents, we used a battery of multimodal behavioral tests that were also aimed at identifying rodent-specific behavioral components by using a home-cage monitoring assay (HCM). Rats of all sexes received an injection with either heat-deactivated (sham-group) or potent mammary gland carcinoma Walker 256 cells into the tibia. By integrating multimodal datasets, we assessed pain-related behavioral trajectories of the CIBP-phenotype, including evoked and non-evoked based assays and HCM. Using principal component analysis (PCA), we discovered sex-specific differences in establishing the CIBP-phenotype, which occurred earlier (and differently) in males. Additionally, HCM phenotyping revealed the occurrence of sensory-affective states manifested by mechanical hypersensitivity in sham when housed with a tumor-bearing cagemate (CIBP) of the same sex. This multimodal battery allows for an in-depth characterization of the CIBP-phenotype under social aspects in rats. The detailed, sex-specific, and rat-specific social phenotyping of CIBP enabled by PCA provides the basis for mechanism-driven studies to ensure robustness and generalizability of results and provide information for targeted drug development in the future.

Possibility of averting cytokine storm in SARS-COV 2 patients using specialized pro-resolving lipid mediators

Fatal "cytokine storms (CS)" observed in critically ill COVID-19 patients are consequences of dysregulated host immune system and over-exuberant inflammatory response. Acute respiratory distress syndrome (ARDS), multi-system organ failure, and eventual death are distinctive symptoms, attributed to higher morbidity and mortality rates among these patients. Consequent efforts to save critical COVID-19 patients via the usage of several novel therapeutic options are put in force. Strategically, drugs being used in such patients are dexamethasone, remdesivir, hydroxychloroquine, etc. along with the approved vaccines. Moreover, it is certain that activation of the resolution process is important for the prevention of chronic diseases. Until recently Inflammation resolution was considered a passive process, rather it's an active biochemical process that can be achieved by the use of specialized pro-resolving mediators (SPMs). These endogenous mediators are an array of atypical lipid metabolites that include Resolvins, lipoxins, maresins, protectins, considered as immunoresolvents, but their role in COVID-19 is ambiguous. Recent evidence from studies such as the randomized clinical trial, in which omega 3 fatty acid was used as supplement to resolve inflammation in COVID-19, suggests that direct supplementation of SPMs or the use of synthetic SPM mimetics (which are still being explored) could enhance the process of resolution by regulating the aberrant inflammatory process and can be useful in pain relief and tissue remodeling. Here we discussed the biosynthesis of SPMs, & their mechanistic pathways contributing to inflammation resolution along with sequence of events leading to CS in COVID-19, with a focus on therapeutic potential of SPMs.

Lipoxins in the Nervous System: Brighter Prospects for Neuroprotection

Lipoxins (LXs) are generated from arachidonic acid and are involved in the resolution of inflammation and confer protection in a variety of pathological processes. In the nervous system, LXs exert an array of protective effects against neurological diseases, including ischemic or hemorrhagic stroke, neonatal hypoxia-ischemia encephalopathy, brain and spinal cord injury, Alzheimer's disease, multiple sclerosis, and neuropathic pain. Lipoxin administration is a potential therapeutic strategy in neurological diseases due to its notable efficiency and unique superiority regarding safety. Here, we provide an overview of LXs in terms of their synthesis, signaling pathways and neuroprotective evidence. Overall, we believe that, along with advances in lipoxin-related drug design, LXs will bring brighter prospects for neuroprotection.

Specialized Pro-Resolving Lipid Mediators: The Future of Chronic Pain Therapy?

Chronic pain (CP) is a severe clinical entity with devastating physical and emotional consequences for patients, which can occur in a myriad of diseases. Often, conventional treatment approaches appear to be insufficient for its management. Moreover, considering the adverse effects of traditional analgesic treatments, specialized pro-resolving lipid mediators (SPMs) have emerged as a promising alternative for CP. These include various bioactive molecules such as resolvins, maresins, and protectins, derived from ω-3 polyunsaturated fatty acids (PUFAs); and lipoxins, produced from ω-6 PUFAs. Indeed, SPMs have been demonstrated to play a central role in the regulation and resolution of the inflammation associated with CP. Furthermore, these molecules can modulate neuroinflammation and thus inhibit central and peripheral sensitizations, as well as long-term potentiation, via immunomodulation and regulation of nociceptor activity and neuronal pathways. In this context, preclinical and clinical studies have evidenced that the use of SPMs is beneficial in CP-related disorders, including rheumatic diseases, migraine, neuropathies, and others. This review integrates current preclinical and clinical knowledge on the role of SPMs as a potential therapeutic tool for the management of patients with CP.

Role of Specialized Pro-Resolving Mediators in Neuropathic Pain

Inflammation and neuroinflammation are critical mechanisms in the generation of neuropathic pain that is experienced in several chronic diseases. The aberrant inflammation that triggers this pathophysiologic process can be tracked down to an exacerbated immune response, which establishes a vicious cycle and continuously recruits inflammatory cells by inducing chronic tissue damage. Recently, impairment of the cellular and molecular machinery orchestrated by specialized pro-resolving mediators (SPMs)-i.e., endogenous lipids termed resolvins, protectins, maresins, and lipoxins that confine the inflammatory cascades in space and time during the "resolution of inflammation"-has emerged as a crucial event in the derangement of the inflammatory homeostasis and the onset of chronic inflammation and pain. Indeed, a deviant inflammatory response that is not adequately controlled by the resolution network leads to the overproduction of pro-inflammatory eicosanoids that, opposite to SPMs, lead to neuropathic pain. Interestingly, in the last two decades convincing evidence has demonstrated that SPMs antagonize the in vivo activity of pro-inflammatory eicosanoids and, overall, exert potent anti-hyperalgesic effects in a number of pain-associated paradigms of disease, such as arthritis and chemotherapy-induced peripheral neuropathy, as well as in many experimental models of pain like mechanical allodynia, chemical pain, heat hypersensitivity and phase 1 and 2 inflammatory pain. Of note, accumulated evidence supports a synergy between SPMs and other signalling pathways, such as those mediated by transient receptor potential (TRP) channels and those triggered by opioid receptors, suggesting that the cascade of events where inflammation and pain perception take part might be ways more intricated than originally expected. Here, we aim at presenting a state-of-the-art view of SPMs, their metabolism and signalling, in the context of cellular and molecular pathways associated to neuropathic pain.

Carcinogenesis: Failure of resolution of inflammation?

Inflammation in the tumor microenvironment is a hallmark of cancer and is recognized as a key characteristic of carcinogens. However, the failure of resolution of inflammation in cancer is only recently being understood. Products of arachidonic acid and related fatty acid metabolism called eicosanoids, including prostaglandins, leukotrienes, lipoxins, and epoxyeicosanoids, critically regulate inflammation, as well as its resolution. The resolution of inflammation is now appreciated to be an active biochemical process regulated by endogenous specialized pro-resolving lipid autacoid mediators which combat infections and stimulate tissue repair/regeneration. Environmental and chemical human carcinogens, including aflatoxins, asbestos, nitrosamines, alcohol, and tobacco, induce tumor-promoting inflammation and can disrupt the resolution of inflammation contributing to a devastating global cancer burden. While mechanisms of carcinogenesis have focused on genotoxic activity to induce mutations, nongenotoxic mechanisms such as inflammation and oxidative stress promote genotoxicity, proliferation, and mutations. Moreover, carcinogens initiate oxidative stress to synergize with inflammation and DNA damage to fuel a vicious feedback loop of cell death, tissue damage, and carcinogenesis. In contrast, stimulation of resolution of inflammation may prevent carcinogenesis by clearance of cellular debris via macrophage phagocytosis and inhibition of an eicosanoid/cytokine storm of pro-inflammatory mediators. Controlling the host inflammatory response and its resolution in carcinogen-induced cancers will be critical to reducing carcinogen-induced morbidity and mortality. Here we review the recent evidence that stimulation of resolution of inflammation, including pro-resolution lipid mediators and soluble epoxide hydrolase inhibitors, may be a new chemopreventive approach to prevent carcinogen-induced cancer that should be evaluated in humans.

Neuroinflammation, oxidative stress and their interplay in neuropathic pain: Focus on specialized pro-resolving mediators and NADPH oxidase inhibitors as potential therapeutic strategies

Neuropathic pain (NP) is a chronic condition that results from a lesion or disease of the nervous system, greatly impacting patients' quality of life. Current pharmacotherapy options deliver inadequate and/or insufficient responses and thus a significant unmet clinical need remains for alternative treatments in NP. Neuroinflammation, oxidative stress and their reciprocal relationship are critically involved in NP pathophysiology. In this context, new pharmacological approaches, aiming at enhancing the resolution phase of inflammation and/or restoring redox balance by targeting specific reactive oxygen species (ROS) sources, are emerging as potential therapeutic strategies for NP, with improved efficacy and safety profiles. Several reports have demonstrated that administration of exogenous specialized pro-resolving mediators (SPMs) ameliorates NP pathophysiology. Likewise, deletion or inhibition of the ROS-generating enzyme NADPH oxidase (NOX), particularly its isoforms 2 and 4, results in beneficial effects in NP models. Notably, SPMs also modulate oxidative stress and NOX also regulates neuroinflammation. By targeting neuroinflammatory and oxidative pathways, both SPMs analogues and isoform-specific NOX inhibitors are promising therapeutic strategies for NP.

The Perspective of Diagnostic and Prognostic Values of Lipoxygenases mRNA Expression in Colon Adenocarcinoma

Background

This study was mainly to explore and study the potential application of lipoxygenases (ALOX) family genes in the diagnostic and prognostic values of colon adenocarcinoma (COAD).

Methods

Data sets related to the ALOX genes of COAD were obtained from The Cancer Genome Atlas and the University of California, Santa Cruz Xena browser. Then, the relevant biological information was downloaded from the public data platform. Finally, the bioinformatics technologies and clinical verification were employed to comprehensively analyze the potential values of ALOX genes.

Results

The Pearson correlation analysis indicated that there were correlations among ALOXE3, ALOX5, ALOX12, and ALOX12B. The diagnostic receiver operating characteristic (ROC) curves suggested that ALOXE3 and ALOX12 had significant diagnosis in COAD: ALOXE3; P<0.001, area under curve (AUC) 95%CI:=0.818 (0.773–0.862) and ALOX12; P<0.001, AUC 95%CI=0.774 (0.682–0.807). Besides, the verification study indicated that ALOX12 had a diagnostic value in COAD. Finally, our multivariate survival analysis and comprehensive prognosis of ALOX genes in COAD suggested that the ALOXE3 and ALOX12 were associated with COAD overall survival: ALOXE3; P=0.025, HR 95%CI=1.765 (1.074–2.901), ALOX12; P=0.046, HR 95%CI=1.680 (1.009–2.796), and the low expression of ALOXE3 and ALOX12 had a favorable prognosis of COAD (all P<0.05); on the contrary, the high regulation of them increased the risk of death.

Conclusion

In our study, we observed that the mRNA expressions of ALOX genes were associated with the diagnosis and prognosis of COAD. The results of the diagnostic analysis suggested that ALOX12 might have a diagnosis value in COAD. Besides, our comprehensive prognosis analysis indicated that ALOXE3 combined ALOX12 might serve as potential prognosis biomarkers for COAD.

Intrathecal administration of Resolvin D1 and E1 decreases hyperalgesia in mice with bone cancer pain: Involvement of endocannabinoid signaling

Pain produced by bone cancer is often severe and difficult to treat. Here we examined effects of Resolvin D1 (RvD1) or E1 (RvE1), antinociceptive products of ω-3 polyunsaturated fatty acids, on cancer-induced mechanical allodynia and heat hyperalgesia. Experiments were performed using a mouse model of bone cancer produced by implantation of osteolytic ficrosarcoma into and around the calcaneus bone. Mechanical allodynia and heat hyperalgesia in the tumor-bearing paw were assessed by measuring withdrawal responses to a von Frey monofilament and to radiant heat applied on the plantar hind paw. RvD1, RvE1, and cannabinoid receptor antagonists were injected intrathecally. Spinal content of endocannabinoids was evaluated using UPLC-MS/MS analysis. RvD1 and RvE1 had similar antinociceptive potencies. ED_50s for RvD1 and RvE1 in reducing mechanical allodynia were 0.2 pg (0.53 fmol) and 0.6 pg (1.71 fmol), respectively, and were 0.3 pg (0.8 fmol) and 0.2 pg (0.57 fmol) for reducing heat hyperalgesia. Comparisons of dose-response relationships showed equal efficacy for reducing mechanical allodynia, however, efficacy for reducing heat hyperalgesia was greater for of RvD1. Using UPLC-MS/MS we determined that RvD1, but not RvE1, increased levels of the endocannabinoids Anandamide and 2-Arachidonoylglycerol in the spinal cord. Importantly, Resolvins did not alter acute nociception or motor function in naïve mice. Our data indicate, that RvD1 and RvE1 produce potent antiallodynia and antihyperalgesia in a model of bone cancer pain. RvD1 also triggers spinal upregulation of endocannabinoids that produce additional antinociception predominantly through CB2 receptors.

Fatty Acid Mediators in the Tumor Microenvironment

Patients with cancer frequently overexpress inflammatory cytokines with an associated neutrophilia both of which may be downregulated by diets with high omega-3 polyunsaturated fatty acids (ω-3 PUFA). The anti-inflammatory activity of dietary ω-3 PUFA has been suggested to have anticancer properties and to improve survival of cancer patients. Currently, the majority of dietary research efforts do not differentiate between obesity and dietary fatty acid consumption as mediators of inflammatory cell expansion and tumor microenvironmental infiltration, initiation, and progression. In this chapter, we discuss the relationships between dietary lipids, inflammation, neoplasia and strategies to regulate these relationships. We posit that dietary composition, notably the ratio of ω-3 vs. ω-6 PUFA, regulates tumor initiation and progression and the frequency and sites of metastasis that, together, impact overall survival (OS). We focus on three broad topics: first, the role of dietary lipids in chronic inflammation and tumor initiation, progression, and regression; second, lipid mediators linking inflammation and cancer; and third, dietary lipid regulation of murine and human tumor initiation, progression, and metastasis.

Amitriptyline influences the mechanical withdrawal threshold in bone cancer pain rats by regulating glutamate transporter GLAST

Patients with cancer, especially breast, prostate, and lung cancer, commonly experience bone metastases that are difficult to manage and are associated with bone cancer pain. Amitriptyline is often used to treat chronic pain, such as neuropathic pain. In this study, the effects of amitriptyline on the mechanical withdrawal threshold and its underlying mechanisms were evaluated in rat models of bone cancer pain. Walker 256 rat mammary gland carcinoma cells were injected into the bone marrow cavity of the right tibia of rats to provoke bone cancer pain. Then, amitriptyline was intraperitoneally administered twice daily from fifth day after the operation. Rats with bone cancer showed an apparent decline in the mechanical withdrawal threshold at day 11 after Walker 256 cells inoculation. The levels of the glutamate-aspartate transporter in the spinal cord dorsal horn decreased remarkably, and the concentration of the excitatory amino acid glutamate in the cerebrospinal fluid increased substantially. Amitriptyline injection could prevent the decline of mechanical withdrawal threshold in bone cancer pain rats. In addition, glutamate-aspartate transporter was upregulated on the glial cell surface, and glutamate levels were reduced in the cerebrospinal fluid. However, amitriptyline injection could not prevent the bone cancer pain-induced reduction in glutamate-aspartate transporter in the glial cell cytosol, it further downregulated cytosolic glutamate-aspartate transporter. Amitriptyline had no significant effect on GLAST messenger RNA expression, and bone cancer pain-invoked protein kinase A/protein kinase C upregulation was prevented. Taken together, these results suggest that the intraperitoneal injection of amitriptyline can prevent the decrease of mechanical withdrawal threshold in bone cancer pain rats, the underlying mechanisms may be associated with the inhibition of protein kinase A/protein kinase C expression, thus promoting glutamate-aspartate transporter trafficking onto the glial cell surface and reducing excitatory amino acid concentrations in the cerebrospinal fluid.

Specialized pro-resolving lipid mediators: A new class of non-immunosuppressive and non-opioid analgesic drugs

We now appreciate that the mechanism of resolution depends on an active and time-dependent biosynthetic shift from pro-inflammatory to pro-resolution mediators, the so-called specialized pro-resolving lipid mediators (SPMs). These SPMs are biosynthesized from the omega-3 fatty acids arachidonic acid (AA), eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), or docosahexaenoic acid (DHA). Despite effective for a fraction of patients with rheumatic diseases and neuropathic pain, current analgesic therapies such as biological agents, opioids, corticoids, and gabapentinoids cause unwanted side effects, such as immunosuppression, addiction, or induce analgesic tolerance. A growing body of evidence demonstrates that isolated SPMs show efficacy at very low doses and have been successively used as therapeutic drugs to treat pain and infection in experimental models showing no side effects. Moreover, SPMs work as immunoresolvents and some of them present long-lasting analgesic and anti-inflammatory effects (i.e. block pain without immunosuppressive effects). In this review, we focus on how SPMs block pain, infection and neuro-immune interactions and, therefore, emerge as a new class of non-immunosuppressive and non-opioid analgesic drugs.

Antinociceptive effects of Ginsenoside Rb1 in a rat model of cancer-induced bone pain

Ginsenoside Rb1 (GRb1) is a major ingredient of ginseng, a traditional medicine that has been used for thousands of years. Previous studies have reported that GRb1 had anti-inflammatory, antioxidant and neuroprotective effects. The current study aimed to evaluate the antinociceptive effects of GRb1 in a rat model of cancer-induced bone pain (CIBP) established by intratibial injection of Walker 256 cells. Intraperitoneal injection (i.p.) of GRb1 (5 and 10 mg/kg, but not 1 mg/kg) partially and transiently reversed the mechanical allodynia and thermal hyperalgesia in CIBP rats at 14 days following surgery when the pain behavior is established. Furthermore, repeated administration of GRb1 demonstrated persistent analgesic effect. Additionally, the protein expression and immunoreactivity of iba1, which is the maker of microglia, was significantly suppressed in CIBP rats treated with GRb1 (i.p., 10 mg/kg) from day 12 for three consecutive days compared with CIBP rats treated with a vehicle. Furthermore, upregulation of spinal interleukin (IL)-1β, IL-6 and tumor necrosis factor-α were also significantly inhibited by the treatment of GRb1 (i.p., 10 mg/kg) from day 12 for three consecutive days. Together, these results indicated that GRb1 may attenuate CIBP via inhibiting the activation of microglia and glial-derived proinflammatory cytokines.

Aspirin-triggered proresolving mediators stimulate resolution in cancer

Inflammation in the tumor microenvironment is a strong promoter of tumor growth. Substantial epidemiologic evidence suggests that aspirin, which suppresses inflammation, reduces the risk of cancer. The mechanism by which aspirin inhibits cancer has remained unclear, and toxicity has limited its clinical use. Aspirin not only blocks the biosynthesis of prostaglandins, but also stimulates the endogenous production of anti-inflammatory and proresolving mediators termed aspirin-triggered specialized proresolving mediators (AT-SPMs), such as aspirin-triggered resolvins (AT-RvDs) and lipoxins (AT-LXs). Using genetic and pharmacologic manipulation of a proresolving receptor, we demonstrate that AT-RvDs mediate the antitumor activity of aspirin. Moreover, treatment of mice with AT-RvDs (e.g., AT-RvD1 and AT-RvD3) or AT-LXA₄ inhibited primary tumor growth by enhancing macrophage phagocytosis of tumor cell debris and counter-regulating macrophage-secreted proinflammatory cytokines, including migration inhibitory factor, plasminogen activator inhibitor-1, and C-C motif chemokine ligand 2/monocyte chemoattractant protein 1. Thus, the pro-resolution activity of AT-resolvins and AT-lipoxins may explain some of aspirin's broad anticancer activity. These AT-SPMs are active at considerably lower concentrations than aspirin, and thus may provide a nontoxic approach to harnessing aspirin's anticancer activity.

The roles of special proresolving mediators in pain relief

The resolution of acute inflammation, once thought to be a passive process, is now recognized as an active one. The productions of endogenous special proresolving mediators (SPMs) are involved in this process. SPMs, including lipoxins, resolvins, protectins, and maresins, are endogenous lipid mediators generated from ω-6 arachidonic acid or ω-3 poly-unsaturated fatty acids during the resolution phase of acute inflammation. They have potent anti-inflammatory and proresolving actions in various inflammatory disorders. Due to the potent proresolving and anti-inflammatory effects, SPMs are also used for pain relief. This review focuses on the mechanisms by which SPMs act on their respective G-protein-coupled receptors in immune cells and nerve cells to normalize pain via regulating inflammatory mediators, transient receptor potential ion channels, and central sensitization. SPMs may offer novel therapeutic approaches for preventing and treating pain conditions associated with inflammation.

Can inflammation be resolved in Alzheimer's disease?

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive memory loss and dementia. Accumulating evidence suggests that inflammation is involved in the pathogenesis of AD. Epidemiological studies suggest that use of anti-inflammatory drugs is associated with a lower incidence of AD. However, clinical trials with anti-inflammatory drugs have not been successful. Recent studies have shown that inflammation is resolved by a process that is mediated by a group of lipid mediators, so called specialized pro-resolving lipid mediators (SPMs). Unlike anti-inflammatory strategies, which usually involve inhibition of the synthesis of inflammatory mediators, stimulating the resolution of inflammation is aimed at ending inflammation in a similar fashion as under normal physiological conditions. We have previously shown that pathways of resolution are impaired in AD. Moreover, we found that SPMs can improve neuronal survival and increase microglial phagocytosis of amyloid beta (Aβ) in in vitro studies, indicating that stimulating resolution of inflammation may be a potential therapeutic target in AD. In this review, we summarize recent findings regarding resolution of inflammation in AD. We also discuss possible strategies to stimulate the resolution of inflammation in AD, specifically focusing on signaling pathways, including SPMs, their receptors and enzymes involved in their formation.

Optimization and In Vivo Profiling of a Refined Rat Model of Walker 256 Breast Cancer Cell-Induced Bone Pain Using Behavioral, Radiological, Histological, Immunohistochemical and Pharmacological Methods

In the majority of patients with advanced breast cancer, there is metastatic spread to bones resulting in pain. Clinically available drug treatments for alleviation of breast cancer-induced bone pain (BCIBP) often produce inadequate pain relief due to dose-limiting side-effects. A major impediment to the discovery of novel well-tolerated analgesic agents for the relief of pain due to bony metastases is the fact that most cancer-induced bone pain models in rodents relied on the systemic injection of cancer cells, causing widespread formation of cancer metastases and poor general animal health. Herein, we have established an optimized, clinically relevant Wistar Han female rat model of breast cancer induced bone pain which was characterized using behavioral assessments, radiology, histology, immunohistochemistry and pharmacological methods. In this model that is based on unilateral intra-tibial injection (ITI) of Walker 256 carcinoma cells, animals maintained good health for at least 66 days post-ITI. The temporal development of hindpaw hypersensitivity depended on the initial number of Walker 256 cells inoculated in the tibiae. Hindpaw hypersensitivity resolved after approximately 25 days, in the continued presence of bone tumors as evidenced by ex vivo histology, micro-computed tomography scans and immunohistochemical assessments of tibiae. A possible role for the endogenous opioid system as an internal factor mediating the self-resolving nature of BCIBP was identified based upon the observation that naloxone, a non-selective opioid antagonist, caused the re-emergence of hindpaw hypersensitivity. Bolus dose injections of morphine, gabapentin, amitriptyline and meloxicam all alleviated hindpaw hypersensitivity in a dose-dependent manner. This is a first systematic pharmacological profiling of this model by testing standard analgesic drugs from four important diverse classes, which are used to treat cancer induced bone pain in the clinical setting. Our refined rat model more closely mimics the pathophysiology of this condition in humans and hence is well-suited for probing the mechanisms underpinning breast cancer induced bone pain. In addition, the model may be suitable for efficacy profiling of new molecules from drug discovery programs with potential to be developed as novel agents for alleviation of intractable pain associated with disseminated breast cancer induced bony metastases.

Levo-Corydalmine Alleviates Neuropathic Cancer Pain Induced by Tumor Compression via the CCL2/CCR2 Pathway

Background: Tumor compression-induced pain (TCIP) is a complex pathological cancer pain. Spinal glial cells play a critical role in maintenance of cancer pain by releasing proinflammatory cytokines and chemokines. In this study, we verified the role of levo-corydalmine (l-CDL) on TCIP. Methods: Spontaneous pain, paw withdrawal threshold and latency were assessed using TCIP mouse model. Immunofluorescence was used to identify the reactions of glia. RT-PCR and western blot or ELISA were used to determine mRNA or protein expression of tumor necrosis factor-α (TNF-α), interlukin-1β (IL-1β), CC chemokine ligand 2 (CCL2) and chemotactic cytokine receptor 2 (CCR2) in vivo and in vitro. Results: l-CDL significantly attenuated TCIP hypersensitivity, accompanying with downregulation of TNF-α and IL-1β expression levels and declined astrocytes and microglial activation. It also significantly decreased the expression of the mRNA and protein level for CCL2 and CCR2. Further, l-CDL could suppress TNF-α-induced astrocytes activation and IL-1β expression through downregulating the CCL2/CCR2. Besides, CCL2-induced BV-microglia activation and inflammatory factors secretion were suppressed by l-CDL via CCR2. Conclusions: Suppression of CCL2/CCR2 by l-CDL may contribute to alleviate TCIP, offering an alternative medication for TCIP.

Hydroalcoholic crude extract of Casearia sylvestris Sw. reduces chronic post-ischemic pain by activation of pro-resolving pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Casearia sylvestris Sw. is widely used in popular medicine to treat conditions associated with pain.

AIM OF THE STUDY

The present study investigated the influence of hydroalcoholic crude extract of Casearia sylvestris (HCE-CS) and contribution of pro-resolving mediators on mechanical hyperalgesia in a mouse model of chronic post-ischemia pain (CPIP).

METHODS AND RESULTS

Male Swiss mice were subjected to ischemia of the right hind paw (3h), then reperfusion was allowed. At 10min, 24h or 48h post-ischemia/reperfusion (I/R), different groups of animals were treated with HCE-CS (30mg/Kg, orally [p.o]), selected agonists at the pro-resolving receptor ALX/FPR2 (natural molecules like resolvin D1 and lipoxin A4 or the synthetic compound BML-111; 0.1-1µg/animal) or vehicle (saline, 10mL/Kg, s.c.), in the absence or presence of the antagonist WRW4 (10µg, s.c.). Mechanical hyperalgesia (paw withdrawal to von Frey filament) was asseseed together with histological and immunostainning analyses. In these settings, pro-resolving mediators reduced mechanical hyperalgesia and HCE-CS or BML-111 displayed anti-hyperalgesic effects which was markedly attenuated in animals treated with WRW4. ALX/FPR2 expression was raised in skeletal muscle or neutrophils after treatment with HCE-CS or BML-111.

CONCLUSION

These results reveal significant antihyperalgesic effect of HCE-CS on CPIP, mediated at least in part, by the pathway of resolution of inflammation centred on the axis modulated by ALX/FPR2.

The Walker 256 Breast Cancer Cell- Induced Bone Pain Model in Rats

The majority of patients with terminal breast cancer show signs of bone metastasis, the most common cause of pain in cancer. Clinically available drug treatment options for the relief of cancer-associated bone pain are limited due to either inadequate pain relief and/or dose-limiting side-effects. One of the major hurdles in understanding the mechanism by which breast cancer causes pain after metastasis to the bones is the lack of suitable preclinical models. Until the late twentieth century, all animal models of cancer induced bone pain involved systemic injection of cancer cells into animals, which caused severe deterioration of animal health due to widespread metastasis. In this mini-review we have discussed details of a recently developed and highly efficient preclinical model of breast cancer induced bone pain: Walker 256 cancer cell- induced bone pain in rats. The model involves direct localized injection of cancer cells into a single tibia in rats, which avoids widespread metastasis of cancer cells and hence animals maintain good health throughout the experimental period. This model closely mimics the human pathophysiology of breast cancer induced bone pain and has great potential to aid in the process of drug discovery for treating this intractable pain condition.

Structural and functional basis of phospholipid oxygenase activity of bacterial lipoxygenase from Pseudomonas aeruginosa

Pseudomonas aeruginosa expresses a secreted LOX-isoform (PA-LOX, LoxA) capable of oxidizing polyenoic fatty acids to hydroperoxy derivatives. Here we report high-level expression of this enzyme in E. coli and its structural and functional characterization. Recombinant PA-LOX oxygenates polyenoic fatty acids including eicosapentaenoic acid and docosahexaenoic acid to the corresponding (n-6)S-hydroperoxy derivatives. This reaction involves abstraction of the proS-hydrogen from the n-8 bisallylic methylene. PA-LOX lacks major leukotriene synthase activity but converts 5S-HETE and 5S,6R/S-DiHETE to anti-inflammatory and pro-resolving lipoxins. It also exhibits phospholipid oxygenase activity as indicated by the formation of a specific pattern of oxygenation products from different phospholipid subspecies. Multiple mutagenesis studies revealed that PA-LOX does not follow classical concepts explaining the reaction specificity of mammalian LOXs. The crystal structure of PA-LOX was solved with resolutions of up to 1.48Å and its polypeptide chain is folded as single domain. The substrate-binding pocket consists of two fatty acid binding subcavities and lobby. Subcavity-1 contains the catalytic non-heme iron. A phosphatidylethanolamine molecule occupies the substrate-binding pocket and its sn1 fatty acid is located close to the catalytic non-heme iron. His377, His382, His555, Asn559 and the C-terminal Ile685 function as direct iron ligands and a water molecule (hydroxyl) completes the octahedral ligand sphere. Although the biological relevance of PA-LOX is still unknown its functional characteristics (lipoxin synthase activity) implicate this enzyme in a bacterial evasion strategy aimed at downregulating the hosts' immune system.

Targeting glia for bone cancer pain

INTRODUCTION

Bone cancer pain (BCP) remains to be a clinical challenge with limited pharmaceutical interventions. Therefore, novel therapeutic targets for the management of BCP are in desperate need. Recently, a growing body of evidence has suggested that glial cells may play a pivotal role in the pathogenesis of BCP. Areas covered: This review summarizes the recent progress in the understanding of glia in BCP and reveals the potential therapeutic targets in glia for BCP treatment. Expert opinion: Pharmacological interventions inhibiting the activation of glial cells, suppressing glia-derived proinflammatory cytokines, cell surface receptors, and the intracellular signaling pathways may be beneficial for the pain management of advanced cancer patients. However, these pharmacological interventions should not disrupt the normal function of glia cells since they play a vital supportive and protective role in the central nervous system.

Walker 256 Tumor Growth Suppression by Crotoxin Involves Formyl Peptide Receptors and Lipoxin A₄

We investigated the effects of Crotoxin (CTX), the main toxin of South American rattlesnake (Crotalus durissus terrificus) venom, on Walker 256 tumor growth, the pain symptoms associated (hyperalgesia and allodynia), and participation of endogenous lipoxin A₄. Treatment with CTX (s.c.), daily, for 5 days reduced tumor growth at the 5th day after injection of Walker 256 carcinoma cells into the plantar surface of adult rat hind paw. This observation was associated with inhibition of new blood vessel formation and decrease in blood vessel diameter. The treatment with CTX raised plasma concentrations of lipoxin A₄ and its natural analogue 15-epi-LXA₄, an effect mediated by formyl peptide receptors (FPRs). In fact, the treatment with Boc-2, an inhibitor of FPRs, abolished the increase in plasma levels of these mediators triggered by CTX. The blockage of these receptors also abolished the inhibitory action of CTX on tumor growth and blood vessel formation and the decrease in blood vessel diameter. Together, the results herein presented demonstrate that CTX increases plasma concentrations of lipoxin A₄ and 15-epi-LXA₄, which might inhibit both tumor growth and formation of new vessels via FPRs.

Lipoxin A4 inhibits microglial activation and reduces neuroinflammation and neuropathic pain after spinal cord hemisection

BACKGROUND

Spinal cord injury (SCI) is a severe neurological disorder with many disabling consequences, including persistent neuropathic pain, which develops in about 40 % of SCI patients and is induced and sustained by excessive and uncontrolled spinal neuroinflammation. Here, we have evaluated the effects of lipoxin A4 (LXA4), a member of a unique class of endogenous lipid mediators with both anti-inflammatory and analgesic properties, on spinal neuroinflammation and chronic pain in an experimental model of SCI.

METHODS

Spinal hemisection at T10 was carried out in adult male CD1 mice and Wistar rats. To test if LXA4 can reduce neuroinflammation and neuropathic pain, each animal received two intrathecal injections of LXA4 (300 pmol) or vehicle at 4 and 24 h after SCI. Sensitivity to mechanical stimulation of the hind paws was evaluated using von Frey monofilaments, and neuroinflammation was tested by measuring the mRNA and/or protein expression levels of glial markers and cytokines in the spinal cord samples after SCI. Also, microglia cultures prepared from murine cortical tissue were used to assess the direct effects of LXA4 on microglial activation and release of pro-inflammatory TNF-α.

RESULTS

LXA4 treatment caused significant reductions in the intensity of mechanical pain hypersensitivity and spinal expression levels of microglial markers and pro-inflammatory cytokines induced by SCI, when compared to rodents receiving control vehicle injections. Notably, the increased expressions of the microglial marker IBA-1 and of the pro-inflammatory cytokine TNF-α were the most affected by the LXA4 treatment. Furthermore, cortical microglial cultures expressed ALX/FPR2 receptors for LXA4 and displayed potentially anti-inflammatory responses upon challenge with LXA4.

CONCLUSIONS

Collectively, our results suggest that LXA4 can effectively modulate microglial activation and TNF-α release through ALX/FPR2 receptors, ultimately reducing neuropathic pain in rodents after spinal cord hemisection. The dual anti-inflammatory and analgesic properties of LXA4, allied to its endogenous nature and safety profile, may render this lipid mediator as new therapeutic approach for treating various neuroinflammatory disorders and chronic pain with only limited side effects.

The Analgesic and Antineuroinflammatory Effect of Baicalein in Cancer-Induced Bone Pain

Cancer-induced bone pain (CIBP) is a severe type of chronic pain. It is imperative to explore safe and effective analgesic drugs for CIBP treatment. Baicalein (BE), isolated from the traditional Chinese herbal medicine Scutellaria baicalensis Georgi (or Huang Qin), has been demonstrated to have anti-inflammatory and neuroprotective effects. In this study, we examined the effect of BE on CIBP and the mechanism of this effect. Intrathecal and oral administration of BE at different doses could alleviate the mechanical allodynia in CIBP rats. Intrathecal 100 μg BE could inhibit the production of IL-6 and TNF-α in the spinal cord of CIBP rats. Moreover, intrathecal 100 μg BE could effectively inhibit the activation of p-p38 and p-JNK MAPK signals in CIBP rats. The analgesic effect of BE may be associated with the inhibition of the expression of the inflammatory cytokines IL-6 and TNF-α and through the activation of p-p38 and p-JNK MAPK signals in the spinal cord. These findings suggest that BE is a promising novel analgesic agent for CIBP.

Early single Aspirin-triggered Lipoxin blocked morphine anti-nociception tolerance through inhibiting NALP1 inflammasome: Involvement of PI3k/Akt signaling pathway

Clinical usage of opioids in pain relief is dampened by analgesic tolerance after chronic exposure, which is related to opioid-associated neuroinflammation. In the current study, which is based on a chronic morphine tolerance rat model and sustained morphine treatment on primary neuron culture, it was observed that Akt phosphorylation, cleaved-Caspase-1-dependent NALP1 inflammasome activation and IL-1β maturation in spinal cord neurons were significantly enhanced by morphine. Moreover, treatment with LY294002, a specific inhibitor of PI3k/Akt signaling, significantly reduced Caspase-1 cleavage, NALP1 inflammasome activation and attenuated morphine tolerance. Tail-flick tests demonstrated that pharmacological inhibition on Caspase-1 activation or antagonizing IL-1β dramatically blocked the development of morphine tolerance. The administration of an exogenous analogue of lipoxin, Aspirin-triggered Lipoxin (ATL), caused a decline in Caspase-1 cleavage, inflammasome activation and mature IL-1β production and thus attenuated the development of morphine tolerance by inhibiting upstream Akt phosphorylation. Additionally, treatment with DAMGO, a selective μ-opioid receptor peptide, significantly induced Akt phosphorylation, Caspase-1 cleavage and anti-nociception tolerance, all of which were attenuated by ATL treatment. Taken together, the present study revealed the involvement of spinal NALP1 inflammasome activation in the development of morphine tolerance and the role of the μ-receptor/PI3k-Akt signaling/NALP1 inflammasome cascade in this process. By inhibiting this signaling cascade, ATL blocked the development of morphine tolerance.

Lipoxins: nature's way to resolve inflammation

An effective host defense mechanism involves inflammation to eliminate pathogens from the site of infection, followed by the resolution of inflammation and the restoration of tissue homeostasis. Lipoxins are endogenous anti-inflammatory, pro-resolving molecules that play a vital role in reducing excessive tissue injury and chronic inflammation. In this review, the mechanisms of action of lipoxins at the site of inflammation and their interaction with other cellular signaling molecules and transcription factors are discussed. Emphasis has also been placed on immune modulatory role(s) of lipoxins. Lipoxins regulate components of both the innate and adaptive immune systems including neutrophils, macrophages, T-, and B-cells. Lipoxins also modulate levels of various transcription factors such as nuclear factor κB, activator protein-1, nerve growth factor-regulated factor 1A binding protein 1, and peroxisome proliferator activated receptor γ and control the expression of many inflammatory genes. Since lipoxins and aspirin-triggered lipoxins have clinical relevance, we discuss their important role in clinical research to treat a wide range of diseases like inflammatory disorders, renal fibrosis, cerebral ischemia, and cancer. A brief overview of lipoxins in viral malignancies and viral pathogenesis especially the unexplored role of lipoxins in Kaposi’s sarcoma-associated herpes virus biology is also presented.

Ticagrelor Protects the Heart Against Reperfusion Injury and Improves Remodeling After Myocardial Infarction

Objective—

In addition to P2Y 12 receptor antagonism, ticagrelor inhibits adenosine cell uptake. Prior data show that 7-day pretreatment with ticagrelor limits infarct size. We explored the acute effects of ticagrelor and clopidogrel on infarct size and potential long-term effects on heart function.

Approach and Results—

Rats underwent 30-minute ischemia per 24-hour reperfusion. (1) Ticagrelor (10 or 30 mg/kg) or clopidogrel (12.5 mg/kg) was given via intraperitoneal injection 5 minutes before reperfusion. (2) Rats received ticagrelor acute (intraperitoneal; 30 mg/kg), chronic (oral; 300 mg/kg per day) for 4 weeks starting 1 day after reperfusion or the combination (acute+chronic). Another group received clopidogrel (intraperitoneal [12.5 mg/kg]+oral [62.5 mg/kg per day]) for 4 weeks. (1) Ticagrelor dose-dependently reduced infarct size, 10 mg/kg (31.5%±1.8%; P <0.001) and 30 mg/kg (21.4%±2.6%; P <0.001) versus control (45.3±1.7%), whereas clopidogrel had no effect (42.4%±2.6%). Ticagrelor, but not clopidogrel, increased myocardial adenosine levels, increased phosphorylation of Akt, endothelial NO synthase, and extracellular-signal-regulated kinase 1/2 4 hours after reperfusion and decreased apoptosis. (2) After 4 weeks, left ventricular ejection fraction was reduced in the vehicle-treated group (44.8%±3.5%) versus sham (77.6%±0.9%). All ticagrelor treatments improved left ventricular ejection fraction, acute (69.5%±1.6%), chronic (69.2%±1.0%), and acute+chronic (76.3%±1.2%), whereas clopidogrel had no effect (37.4%±3.7%). Ticagrelor, but not clopidogrel, attenuated fibrosis and decreased collagen-III mRNA levels 4 weeks after ischemia/reperfusion. Ticagrelor, but not clopidogrel, attenuated the increase in proinflammatory tumor necrosis factor-α, interleukin-1β, and interleukin-18, and increased anti-inflammatory 15-epi-lipoxin-A 4 levels.

Conclusions—

Ticagrelor, but not clopidogrel, administered just before reperfusion protects against reperfusion injury. This acute treatment or chronic ticagrelor for 4 weeks or their combination improved heart function, whereas clopidogrel, despite achieving a similar degree of platelet inhibition, had no effect.

Structural and functional biology of arachidonic acid 15-lipoxygenase-1 (ALOX15)

Lipoxygenases (LOX) form a family of lipid peroxidizing enzymes, which have been implicated in a number of physiological processes and in the pathogenesis of inflammatory, hyperproliferative and neurodegenerative diseases. They occur in two of the three domains of terrestrial life (bacteria, eucarya) and the human genome involves six functional LOX genes, which encode for six different LOX isoforms. One of these isoforms is ALOX15, which has first been described in rabbits in 1974 as enzyme capable of oxidizing membrane phospholipids during the maturational breakdown of mitochondria in immature red blood cells. During the following decades ALOX15 has extensively been characterized and its biological functions have been studied in a number of cellular in vitro systems as well as in various whole animal disease models. This review is aimed at summarizing the current knowledge on the protein-chemical, molecular biological and enzymatic properties of ALOX15 in various species (human, mouse, rabbit, rat) as well as its implication in cellular physiology and in the pathogenesis of various diseases.

Lipoxin A4 attenuates radicular pain possibly by inhibiting spinal ERK, JNK and NF-κB/p65 and cytokine signals, but not p38, in a rat model of non-compressive lumbar disc herniation

Inflammatory response induced by protrused nucleus pulposus (NP) has been shown to play a crucial role in the process of radicular pain. Lipoxins represent a unique class of lipid mediators that have anti-inflammatory and pro-resolving action. The present study was undertaken to investigate if intrathecal lipoxin A4 (LXA4) could alleviate mechanical allodynia in the rat models of application of NP to the L5 dorsal root ganglion (DRG). Non-compressive models of application of NP to L5 DRG were established and intrathecal catheterization for drug administration was performed in rats. Daily intrathecal injection of vehicle or LXA4 (10ng or 100ng) was performed for three successive days post-operation. Mechanical thresholds were tested and the ipsilateral lumbar (L4-L6) segment of spinal dorsal horns were removed for the determination of tumor necrosis factor-α (TNF-α), IL-1β, transforming growth factor-β1 (TGF-β1) and IL-10 expression and NF-κB/p65, extracellular signal-regulated kinase (ERK), C-Jun N-terminal kinase (JNK) and P38 expression. Application of NP to DRG in rats induced mechanical allodynia, increased the expression of pro-inflammatory factors (TNF-α and IL-1β), NF-κB/p65, the phosphorylated-ERK (p-ERK), -JNK (p-JNK) and -P38 (p-p38) and decreased the expression of anti-inflammatory cytokines (TGF-β1 and IL-10) in the ipsilateral lumbar (L4-L6) segment of spinal dorsal horns. Intrathecal injection of LXA4 alleviated the development of neuropathic pain, inhibited the upregulation of pro-inflammatory cytokines (TNF-α and IL-1β), upregulated the expression of anti-inflammatory cytokines (TGF-β1 and IL-10) and attenuated the activation of NF-κB/p65, p-ERK, p-JNK, but not p-p38, in a dose-dependent manner. In this study, we have demonstrated that LXA4 potently alleviate radicular pain in a rat model of non-compressive lumbar disc herniation. The anti-inflammatory and pro-resolution properties of LXA4 have shown a great promise for the management of radicular pain caused by intervertebral disc herniation.

Intrathecal injection of lentivirus-mediated glial cell line-derived neurotrophic factor RNA interference relieves bone cancer-induced pain in rats

Bone cancer pain is a common symptom in cancer patients with bone metastases and the underlying mechanisms are largely unknown. The aim of this study is to explore the endogenous analgesic mechanisms to develop new therapeutic strategies for bone-cancer induced pain (BCIP) as a result of metastases. MRMT-1 tumor cells were injected into bilateral tibia of rats and X-rays showed that the area suffered from bone destruction, accompanied by an increase in osteoclast numbers. In addition, rats with bone cancer showed apparent mechanical and thermal hyperalgesia at day 28 after intratibial MRMT-1 inoculation. However, intrathecal injection of morphine or lentivirus-mediated glial cell line-derived neurotrophic factor RNAi (Lvs-siGDNF) significantly attenuated mechanical and thermal hyperalgesia, as shown by increases in paw withdrawal thresholds and tail-flick latencies, respectively. Furthermore, Lvs-siGDNF interference not only substantially downregulated GDNF protein levels, but also reduced substance P immunoreactivity and downregulated the ratio of pERK/ERK, where its activation is crucial for pain signaling, in the spinal dorsal horn of this model of bone-cancer induced pain. In this study, Lvs-siGDNF gene therapy appeared to be a beneficial method for the treatment of bone cancer pain. As the effect of Lvs-siGDNF to relieve pain was similar to morphine, but it is not a narcotic, the use of GDNF RNA interference may be considered as a new therapeutic strategy for the treatment of bone cancer pain in the future.

Interleukin-10 limits intense acute swimming-induced muscle mechanical hyperalgesia in mice

NEW FINDINGS

What is the central question of this study? This study investigated the role of the endogenous anti-inflammatory cytokine interleukin-10 in intense acute swimming-induced muscle mechanical hyperalgesia in mice. What is the main finding and its importance? Endogenous interleukin-10 has a key role in limiting exercise-induced muscle pain in a model presenting similarities to delayed-onset muscle soreness in mice. Interleukin-10 reduced muscle pain by diminishing leucocyte recruitment, hyperalgesic cytokine production, oxidative stress and myocyte damage. Interleukin-10 (IL-10) is an antihyperalgesic cytokine. In this study, IL-10-deficient (IL-10(-/-) ) mice were used to investigate the role of endogenous IL-10 in intense acute swimming-induced muscle mechanical hyperalgesia, which presents similarities with delayed-onset muscle soreness. An intense acute swimming session of 1 or 2 h induced significant muscle mechanical hyperalgesia in a time-dependent manner in wild-type mice compared with the sham group 24 h after the session, which was further increased in IL-10(-/-) mice (P ˂ 0.05). Intraperitoneal treatment of wild-type mice with IL-10 (1-10 ng) reduced muscle mechanical hyperalgesia in a dose-dependent manner and reversed the enhanced muscle hyperalgesia in IL-10(-/-) mice (P ˂ 0.05). The 2 h swimming session induced increases in tumour necrosis factor-α, interleukin-1β and IL-10 production in the soleus muscle. However, tumour necrosis factor-α and interleukin-1β production in the soleus muscle were even higher in IL-10(-/-) mice between 2 and 6 h after the stimulus (P ˂ 0.05). There was no statistical difference in the levels of the antihyperalgesic cytokines interleukin-4, interleukin-5, interleukin-13 and transforming growth factor-β between wild-type and IL-10(-/-) mice (P ˃ 0.05). Interleukin-10 deficiency also resulted in increased myeloperoxidase activity, greater depletion of reduced glutathione levels, increased superoxide anion production and the maintenance of high plasma concentrations of creatine kinase (until 24 h after the swimming session) in soleus muscle (P ˂ 0.05). These results demonstrate that endogenous IL-10 controls intense acute swimming-induced muscle mechanical hyperalgesia by limiting oxidative stress and cytokine production.

Current studies of acupuncture in cancer-induced bone pain animal models

Acupuncture is generally accepted as a safe and harmless treatment option for alleviating pain. To explore the pain mechanism, numerous animal models have been developed to simulate specific human pain conditions, including cancer-induced bone pain (CIBP). In this study, we analyzed the current research methodology of acupuncture for the treatment of CIBP. We electronically searched the PubMed database for animal studies published from 2000 onward using these search terms: (bone cancer OR cancer) AND (pain OR analgesia) AND (acupuncture OR pharmacopuncture OR bee venom). We selected articles that described cancer pain in animal models. We analyzed the methods used to induce cancer pain and the outcome measures used to assess the effects of acupuncture on CIBP in animal models. We reviewed articles that met our inclusion criteria. Injection of mammary cancer cells into the cavity of the tibia was the most frequently used method for inducing CIBP in the animal models. Among the eight selected studies, five studies demonstrated the effects of electroacupuncture on CIBP. The effects of acupuncture were assessed by measuring pain-related behavior. Future researches will be needed to ascertain the effectiveness of acupuncture for treating CIBP and to explore the specific mechanism of CIBP in animal models.

Mammalian lipoxygenases and their biological relevance

Lipoxygenases (LOXs) form a heterogeneous class of lipid peroxidizing enzymes, which have been implicated not only in cell proliferation and differentiation but also in the pathogenesis of various diseases with major public health relevance. As other fatty acid dioxygenases LOXs oxidize polyunsaturated fatty acids to their corresponding hydroperoxy derivatives, which are further transformed to bioactive lipid mediators (eicosanoids and related substances). On the other hand, lipoxygenases are key players in the regulation of the cellular redox homeostasis, which is an important element in gene expression regulation. Although the first mammalian lipoxygenases were discovered 40 years ago and although the enzymes have been well characterized with respect to their structural and functional properties the biological roles of the different lipoxygenase isoforms are not completely understood. This review is aimed at summarizing the current knowledge on the physiological roles of different mammalian LOX-isoforms and their patho-physiological function in inflammatory, metabolic, hyperproliferative, neurodegenerative and infectious disorders. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Evidence for involvement of spinal RANTES in the antinociceptive effects of triptolide, a diterpene triepoxide, in a rat model of bone cancer pain

It has been shown that triptolide has beneficial effects in the treatment of neuropathic pain, but its effects on bone cancer pain (BCP) remain unclear. In this study, we aimed to explore the potential role of spinal regulated activation of normal T cell expressed and secreted (RANTES) in the antinociceptive effects of triptolide on BCP. A BCP model was induced by injecting Walker 256 mammary gland carcinoma cells into the intramedullary space of rat tibia. Intrathecal administration of triptolide (0.5, 1, 2 μg) could dose-dependently alleviate mechanical hyperalgesia and spontaneous pain. In addition, there were also concomitant decreases in RANTES mRNA and protein expression levels in spinal dorsal horn. These results suggest that the antinociceptive effects of triptolide are related with inhibition of spinal RANTES expression in BCP rats. The findings of this study may provide a promising drug for the treatment of BCP.

Aspirin-triggered Lipoxin A4 attenuates mechanical allodynia in association with inhibiting spinal JAK2/STAT3 signaling in neuropathic pain in rats

Aspirin-triggered Lipoxin A4 (ATL), as a Lipoxin A4 (LXA4) epimer, is endogenously produced by aspirin-acetylated cycloxygenase-2 (COX-2) and plays a vital role in endogenous anti-inflammation via the LXA4 receptor (ALX). Recent investigations have indicated that spinal neuroinflammation and the activation of the Janus Kinase 2 (JAK2)/Signal Transducers and Transcription Activators 3 (STAT3) signaling pathway are involved in neuropathic pain states. However, the effect of ATL on neuroinflammation and JAK2/STAT3 signaling in chronic constriction injury (CCI)-induced neuropathic pain in rats has not been well-studied. The present study demonstrated the anti-inflammatory and analgesic effect of ATL on neuropathic pain and assessed the role of spinal JAK2/STAT3 signaling on the effect of ATL. Intrathecal administration of ATL significantly attenuated mechanical allodynia via spinal ALX and inhibited the upregulation of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) on day 7 of CCI surgery. In addition, ATL markedly suppressed the upregulation of p-STAT3 induced by the neuropathic pain. Blockade of JAK2-STAT3 signaling with intrathecal administration of the JAK2 inhibitor AG490 or the STAT3 inhibitor S3I-201 clearly reduced mechanical allodynia and the upregulation of pro-inflammatory cytokines in CCI rats. Interestingly, inhibition of JAK2/STAT3 signaling via ATL or the specific signaling inhibitor (AG49, S3I-201) further promoted the increased expression of suppressor of cytokine signaling 3 (SOCS3) mRNA in the spinal cord induced by CCI surgery. Taken together, our results suggested that the analgesic effect of ATL was mediated by inhibiting spinal JAK2/STAT3 signaling and hence the spinal neuroinflammation in CCI rats.

Involvement of the spinal NALP1 inflammasome in neuropathic pain and aspirin-triggered-15-epi-lipoxin A4 induced analgesia

Neuroinflammation plays an important role in nerve-injury-induced neuropathic pain, but the explicit molecular mechanisms of neuroinflammation in neuropathic pain remain unclear. As one of the most critical inflammatory cytokines, interleukin-1β (IL-1β) has been regarded as broadly involved in the pathology of neuropathic pain. The inflammasome caspase-1 platform is one primary mechanism responsible for the maturation of IL-1β. Lipoxins, a type of endogenous anti-inflammatory lipid, have proved to be effective in relieving neuropathic pain behaviors. The present study was designed to examine whether the inflammasome caspase-1 IL-1β platform is involved in chronic constriction injury (CCI)-induced neuropathic pain and in lipoxin-induced analgesia. After rats were subjected to the CCI surgery, mature IL-1β was significantly increased in the ipsilateral spinal cord, and the inflammasome platform consisting of NALP1 (NAcht leucine-rich-repeat protein 1), caspase-1 and ASC (apoptosis-associated speck-like protein containing a caspase-activating recruitment domain) was also activated in spinal astrocytes and neurons, especially at the superficial laminae of the spinal dorsal horn; The aspirin-triggered-15-epi-lipoxin A4 (ATL), which shares the potent actions of the endogenous lipoxins, was administered to the CCI rats. Repeated intrathecal injection with ATL markedly attenuated the CCI-induced thermal hyperalgesia and significantly inhibited NALP1 inflammasome activation, caspase-1 cleavage, and IL-1β maturation. These results suggested that spinal NALP1 inflammasome was involved in the CCI-induced neuropathic pain and that the analgesic effect of ATL was associated with suppressing NALP1 inflammasome activation.

Spinal actions of lipoxin A4 and 17(R)-resolvin D1 attenuate inflammation-induced mechanical hypersensitivity and spinal TNF release

Lipoxins and resolvins have anti-inflammatory and pro-resolving actions and accumulating evidence indicates that these lipid mediators also attenuate pain-like behavior in a number of experimental models of inflammation and tissue injury-induced pain. The present study was undertaken to assess if spinal administration of lipoxin A4 (LXA4) or 17 (R)-resolvin D1 (17(R)-RvD1) attenuates mechanical hypersensitivity in the carrageenan model of peripheral inflammation in the rat. Given the emerging role of spinal cytokines in the generation and maintenance of inflammatory pain we measured cytokine levels in the cerebrospinal fluid (CSF) after LXA4 or 17(R)-RvD1 administration, and the ability of these lipid metabolites to prevent stimuli-induced release of cytokines from cultured primary spinal astrocytes. We found that intrathecal bolus injection of LXA4 and17(R)-RvD1 attenuated inflammation-induced mechanical hypersensitivity without reducing the local inflammation. Furthermore, both LXA4 and 17(R)-RvD1 reduced carrageenan-induced tumor necrosis factor (TNF) release in the CSF, while only 17(R)-RvD1attenuated LPS and IFN-γ-induced TNF release in astrocyte cell culture. In conclusion, this study demonstrates that lipoxins and resolvins potently suppress inflammation-induced mechanical hypersensitivity, possibly by attenuating cytokine release from spinal astrocytes. The inhibitory effect of lipoxins and resolvins on spinal nociceptive processing puts them in an intriguing position in the search for novel pain therapeutics.

Painful boney metastases

Boney metastasis may lead to terrible suffering from debilitating pain. The most likely malignancies that spread to bone are prostate, breast, and lung. Painful osseous metastases are typically associated with multiple episodes of breakthrough pain which may occur with activities of daily living, weight bearing, lifting, coughing, and sneezing. Almost half of these breakthrough pain episodes are rapid in onset and short in duration and 44% of episodes are unpredictable. Treatment strategies include: analgesic approaches with "triple opioid therapy", bisphosphonates, chemotherapeutic agents, hormonal therapy, interventional and surgical approaches, steroids, radiation (external beam radiation, radiopharmaceuticals), ablative techniques (radiofrequency ablation, cryoablation), and intrathecal analgesics.