PPAR and Pain

Oxymatrine and Gut Microbiota Modulation: A Potential Therapeutic Strategy for Bone Cancer Pain Management

Chronic pain often coincides with changes in gut microbiota composition. Yet, the role of gut microbiota in bone cancer pain (BCP) is still not fully understood. This study investigated the role of gut microbiota in BCP and the effect of oxymatrine (OMT) on gut microbiota in BCP. A BCP mice model was developed to assess gut microbiota composition, serum and brain tissue butyric acid levels, and blood-brain barrier (BBB) permeability. Microbiota transplantation was used to restore gut microbiota, and the effect of Clostridium butyricum or sodium butyrate (NaB) supplementation on pain-related behaviors and BBB integrity was evaluated. The potential benefits of OMT on gut microbiota composition, peroxisome proliferator-activated receptor gamma (PPARγ)/cyclooxygenase-2 (COX-2) signaling, BBB integrity, and pain-related behaviors were also explored. BCP significantly altered gut microbiota composition and reduced serum and brain tissue butyric acid levels. Additionally, BBB permeability increased considerably in the BCP group compared with sham and control mice. Microbiota transplantation, as well as C butyricum or NaB supplementation, ameliorated pain-related behaviors and BBB integrity; the supplementation of C butyricum or NaB boosted brain-tight-junction protein expression, potentially through modulating PPARγ/COX-2 signaling. OMT influenced gut microbiota composition and regulated PPARγ/COX-2 signaling in the BCP model, improving pain-related behaviors and BBB integrity. BCP affects gut microbiota composition and butyric acid levels. Modulating gut microbiota and butyric acid levels through transplantation or supplementation may alleviate BCP. OMT shows potential as a treatment by altering gut microbiota composition and regulating PPARγ/COX-2 signaling. These findings provide new insights into BCP pathophysiology and possible treatments. PERSPECTIVE: This study explores the impact of gut microbiota on BCP. Microbiota transplantation alleviates BCP and enhances BBB integrity. Also, C butyricum or NaB improves BBB via PPARγ/COX-2. OMT, a BCP treatment, modifies microbiota by regulating PPARγ/COX-2, in turn improving pain and BBB integrity. These findings suggest a therapeutic approach, emphasizing clinical relevance in targeting gut microbiota and restoring butyric acid levels.

Gut Microbiota and Probiotics in Perioperative Management: A Narrative Review

The human gut is the abode of several complex and diverse microbes. It is a fact that the human brain is interconnected with the spinal cord and sense organs; however, there is also a possibility of a connection between the brain and the gut microbiome. The human gut can be altered in various ways, the principal method being the intake of prebiotics, probiotics and synbiotics. Can this alteration in the gut microbiome be clinically utilised in the perioperative period? We conducted a literature search related to this topic using databases and search engines (Medical Literature Analysis and Retrieval System Online {MEDLINE}, Embase, Scopus, PubMed and Google Scholar). The search revealed some preclinical and clinical studies in animals and humans that demonstrate the alteration of the gut microbiome with the use of anxiolysis, probiotics/prebiotics and other perioperative factors including opioids, anaesthetics and perioperative stress. The significant effects of this alteration have been seen on preoperative anxiety and postoperative delirium/cognitive dysfunction/pain. These effects are described in this narrative review, which opens up newer vistas for high-quality research related to the gut microbiome, gut-brain axis, the related signaling pathways and their clinical application in the perioperative period.

Peroxisome proliferator activated receptor-gamma (PPAR-γ) ligand, pioglitazone, increases analgesic and anti-inflammatory effects of naproxen

The aim of this study was the investigation of analgesic and anti-inflammatory activity of naproxen and pioglitazone following intra-plantar injection of carrageenan and assessment of the PPAR-γ receptor involvement in these effects. Rats were intra-plantarly injected with carrageenan (1%, 100 μl) to induce thermal hyperalgesia and paw inflammation. Different groups of rats were pre-treated intraperitoneally with naproxen (1 and 10 mg/kg) or pioglitazone (3 and 10 mg/kg) or GW9662 (a selective PPAR-γ antagonist, 100 μl/paw). The volume of the paw was evaluated using a plethysmometer, and the hot plate test was employed to assess the pain threshold in the animals. Finally, TNF-α, IL-1ß, IL-6, and myeloperoxidase (MPO) activity status were evaluated in the hind paw tissue. Naproxen and pioglitazone demonstrated analgesic and anti-inflammatory activity. Concurrent injection of an ineffective dose of naproxen (1 mg/kg) with an ineffective dose of pioglitazone (3 mg/kg) caused augmented analgesic and anti-inflammatory activity, significantly (p≤0.001 and p≤0.01, respectively). Additionally, intra-plantar injection of GW-9662 before naproxen or pioglitazone significantly suppressed their analgesic (p≤0.001) and anti-inflammatory activity (p≤0.01). Also, naproxen and pioglitazone (10 mg/kg) significantly (p≤0.001) reduced carrageenan-induced MPO activity and TNF-α, IL-6, and IL-1ß releasing. Furthermore, PPAR-γ blockade significantly prevented suppressive effects of naproxen and pioglitazone on the MPO activity and inflammatory cytokines. Pioglitazone significantly increased analgesic and anti-inflammatory effects of naproxen. This study proposes that concurrent treatment with naproxen and pioglitazone may be a substitute for overcome pain and inflammation clinically, in the future, particularly in patients with cardiovascular disorders and diabetes.

Virtual screening combined with experimental verification reveals the potential mechanism of Fuzitang decoction against Gouty Arthritis

Background

and Purpose: Fuzitang decoction (FZT), a classic prescription of traditional Chinese medicine (TCM), has excellent efficacy in treating gouty arthritis (GA). However, the underlying molecular mechanism remains obscure. In the present study, we aimed to explore the underlying mechanisms of FZT in treating GA by virtual screening combined with experimental verification.

Methods

In this study, the active components of FZT and their corresponding targets were screened from the TCMSP database and TargetNet database. Then, the potential targets of FZT against GA were retrieved from multiple databases to generate a network. Protein-protein interaction, herbal-component-target, Gene Ontology (GO) enrichment, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were applied to identify potential targets and related signaling pathways. Furthermore, molecular docking simulation was applied to identify the interactions between the drug and targets. Finally, in vitro experiments were conducted to validate the potential targets and signaling pathways.

Results

In the present study, several crucial components, including kaempferol, luteolin, catechin, deoxyandrographolide, and perlolyrine in FZT, were obtained through network pharmacology, and several potential targets to treat GA were developed, such as PPARG, CYP3A4, PTGS2 (known as COX2), VEGFA, and CYP1A1. Experimental validation suggested that deoxyandrographolide significantly suppressed the expression of IL-1β, COX2, NLRP3 and IL-6 in inflammatory monocyte cells.

Conclusions

Our results identified a novel anti-inflammatory compound, deoxyandrographolide, which helps to explain the potential mechanism of FZT in treating GA and provides evidence to support FZT's clinical use.

Probiotics in Postoperative Pain Management

Postoperative pain is the unpleasant sensory and emotional experience after surgery, its origin being both the inflammatory reaction induced by the surgical trauma on the abdominal wall and the splanchnic pain induced by the activation of nociceptors of the viscera, which are highly sensitive to distension, ischemia, and inflammation. Nowadays, it is well recognized that there is a close relationship between the gut microbiome and pain perception, and that microbiome is highly affected by both anesthesia and surgical manipulation. Thus, efforts to restore the disturbed microbiome via supplementation with beneficial bacteria, namely probiotics, seem to be effective. In this article, the knowledge gained mainly from experimental research on this topic is analyzed, the concluding message being that each probiotic strain works in its own way towards pain relief.

Expression of Cannabinoid Receptors in the Trigeminal Ganglion of the Horse

Cannabinoid receptors are expressed in human and animal trigeminal sensory neurons; however, the expression in the equine trigeminal ganglion is unknown. Ten trigeminal ganglia from five horses were collected post-mortem from an abattoir. The expression of cannabinoid receptors type 1 (CB1R) and type 2 (CB2R), and the cannabinoid-related receptors like transient receptor potential vanilloid type 1 (TRPV1), peroxisome proliferator-activated receptor gamma (PPARɣ), and G protein-related receptor 55 (GPR55) in the trigeminal ganglia (TG) of the horse were studied, using immunofluorescence on cryosections and formalin-fixed paraffin-embedded (FFPE) sections. Neurons and glial cells were identified using fluorescent Nissl staining NeuroTrace® and an antibody directed against the glial marker glial fibrillary acidic protein (GFAP), respectively. Macrophages were identified by means of an antibody directed against the macrophages/microglia marker ionized calcium-binding adapter molecule 1 (IBA1). The protein expression of CB1R, CB2R, TRPV1, and PPARɣ was found in the majority of TG neurons in both cryosections and FFPE sections. The expression of GPR55 immunoreactivity was mainly detectable in FFPE sections, with expression in the majority of sensory neurons. Some receptors were also observed in glial cells (CB2R, TRPV1, PPARγ, and GPR55) and inflammatory cells (PPARγ and GPR55). These results support further investigation of such receptors in disorders of equine trigeminal neuronal excitability.

A cholinergic circuit that relieves pain despite opioid tolerance

Chronic pain is a tremendous burden for afflicted individuals and society. Although opioids effectively relieve pain, significant adverse outcomes limit their utility and efficacy. To investigate alternate pain control mechanisms, we explored cholinergic signaling in the ventrolateral periaqueductal gray (vlPAG), a critical nexus for descending pain modulation. Biosensor assays revealed that pain states decreased acetylcholine release in vlPAG. Activation of cholinergic projections from the pedunculopontine tegmentum to vlPAG relieved pain, even in opioid-tolerant conditions, through ⍺7 nicotinic acetylcholine receptors (nAChRs). Activating ⍺7 nAChRs with agonists or stimulating endogenous acetylcholine inhibited vlPAG neuronal activity through Ca2+ and peroxisome proliferator-activated receptor α (PPAR⍺)-dependent signaling. In vivo 2-photon imaging revealed that chronic pain induces aberrant excitability of vlPAG neuronal ensembles and that ⍺7 nAChR-mediated inhibition of these cells relieves pain, even after opioid tolerance. Finally, pain relief through these cholinergic mechanisms was not associated with tolerance, reward, or withdrawal symptoms, highlighting its potential clinical relevance.

Characterization of pain-related behaviors and gene expression profiling of peripheral sensory ganglia in a mouse model of acute ankle sprain

Introduction

Lateral ankle sprain (LAS) is a very common type of joint injury. It occurred with high incidence among general population and especially among individuals participating sports and outdoor activities. A certain proportion of individuals who once developed LAS may suffer persistent ankle pain that affects daily activities. However, the mechanisms underlying LAS-induced pain still remained largely unknown.

Methods

We established a LAS mouse model and systematically evaluated the pain-related behaviors in this mouse model. RNA sequencing (RNA-Seq), combined with bioinformatics analysis, was undertaken to explore gene expression profiles. Immunostaining was used to study glial cell and neuron activation in ipsilateral spinal cord dorsal horn (SCDH) of LAS model mice. Ibuprofen was used to treat LAS model mice.

Results

The LAS model mice developed obvious signs of mechanical and heat hypersensitivities as well as gait impairments in ipsilateral hind paws. Besides, LAS model mice developed signs of pain-related emotional disorder, including pain-induced aversion. By RNA-Seq, we were able to identify certain differentially expressed genes and signaling pathways that might contribute to pain mechanisms of LAS mouse model. In addition, LAS model mice showed increased c-Fos and p-ERK immunoreactivity as well as astrocyte and microglia overactivation in ipsilateral spinal cord dorsal horn, indicating central sensitization might occur. Finally, LAS model mice respond to ibuprofen, a drug clinically used to treat ankle sprain pain.

Conclusion

Our study found LAS model mice may be used as a preclinical animal model for screening novel targets or therapies for ankle sprain. Thus, the study may further help to understand molecular mechanisms contributing to ankle sprain-induced pain.

The Efficacy of Camelina sativa Defatted Seed Meal against Colitis-Induced Persistent Visceral Hypersensitivity: The Relevance of PPAR α Receptor Activation in Pain Relief

Brassicaceae are natural sources of bioactive compounds able to promote gut health. Belonging to this plant family, Camelina sativa is an ancient oil crop rich in glucosinolates, polyunsaturated fatty acids, and antioxidants that is attracting renewed attention for its nutraceutical potential. This work aimed at investigating the therapeutic effects of a defatted seed meal (DSM) of Camelina sativa on the colon damage and the persistent visceral hypersensitivity associated with colitis in rats. Inflammation was induced by the intrarectal injection of 2,4-dinitrobenzenesulfonic acid (DNBS). The acute administration of Camelina sativa DSM (0.1–1 g kg⁻¹) showed a dose-dependent pain-relieving effect in DNBS-treated rats. The efficacy of the meal was slightly enhanced after bioactivation with myrosinase, which increased isothiocyanate availability, and drastically decreased by pre-treating the animals with the selective peroxisome proliferator-activated receptor alpha (PPAR α) receptor antagonist GW6471. Repeated treatments with Camelina sativa DSM (1 g kg⁻¹) meal counteracted the development, as well as the persistence, of visceral hyperalgesia in DNBS-treated animals by reducing the intestinal inflammatory damage and preventing enteric neuron damage. In conclusion, Camelina sativa meal might be employed as a nutraceutical tool to manage persistent abdominal pain in patients and to promote gut healing.

Transcriptomic Analysis Revealed an Important Role of Peroxisome-Proliferator-Activated Receptor Alpha Signaling in Src Homology Region 2 Domain-Containing Phosphatase-1 Insufficiency Leading to the Development of Renal Ischemia-Reperfusion Injury

In kidney transplantation, the donor kidney inevitably undergoes ischemia-reperfusion injury (IRI). It is of great importance to study the pathogenesis of IRI and find effective measures to attenuate acute injury of renal tubules after ischemia-reperfusion. Our previous study found that Src homology region 2 domain-containing phosphatase-1 (SHP-1) insufficiency aggravates renal IRI. In this study, we systematically analyzed differences in the expression profiles of SHP-1 (encoded by Ptpn6)-insufficient mice and wild-type mice by RNA-seq. We found that a total of 161 genes showed at least a twofold change, with a false discovery rate <0.05 in Ptpn6 +/mev mice after IRI and 42 genes showing more than a fourfold change. Of the eight genes encoding proteins with immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that bind to Ptpn6, three were upregulated, and five were downregulated. We found that for the differentially expressed genes (DEGs) with a fold change >2, the most significantly enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were the cell division pathway and peroxisome-proliferator activated receptor PPARα signaling pathways. Furthermore, the downregulated genes of the PPARα signaling pathway were mainly related to fatty acid absorption and degradation. Using an agonist of the PPARα signaling pathway, fenofibrate, we found that renal IRI was significantly attenuated in Ptpn6 +/mev mice. In summary, our results show that insufficiency of SHP-1 inhibits the expression of genes in the PPARα signaling pathway, thereby leading to increased reactive oxygen species (ROS) and exacerbating the renal IRI. The PPARα signaling agonist fenofibrate partially attenuates renal IRI induced by SHP-1 insufficiency.

Gut Microbiome in Anesthesiology and Pain Medicine

The gut microbiome plays critical roles in human health and disease. Recent studies suggest it may also be associated with chronic pain and postoperative pain outcomes. In animal models, the composition of the gut microbiome changes after general anesthesia and affects the host response to medications, including anesthetics and opioids. In humans, the gut microbiome is associated with the development of postoperative pain and neurocognitive disorders. Additionally, the composition of the gut microbiome has been associated with pain conditions including visceral pain, nociplastic pain, complex regional pain syndrome, and headaches, partly through altered concentration of circulating bacterial-derived metabolites. Furthermore, animal studies demonstrate the critical role of the gut microbiome in neuropathic pain via immunomodulatory mechanisms. This article reviews basic concepts of the human gut microbiome and its interactions with the host and provide a comprehensive overview of the evidence linking the gut microbiome to anesthesiology, critical care, and pain medicine.

Cellular distribution of cannabinoid-related receptors TRPV1, PPAR-gamma, GPR55 and GPR3 in the equine cervical dorsal root ganglia

BACKGROUND

The activation of cannabinoid and cannabinoid-related receptors by endogenous, plant-derived or synthetic cannabinoids may exert beneficial effects on pain perception. Of the cannabinoids contained in Cannabis sativa, cannabidiol (CBD) does not produce psychotropic effects and seems to represent a molecule having great therapeutic potential. Cannabidiol acts on a great number of cannabinoid and cannabinoid-related G-protein-coupled receptors and ionotropic receptors which have, to date, been understudied in veterinary medicine particularly in equine medicine.

OBJECTIVES

To localise the cellular distribution of four putative cannabinoid-related receptors in the equine cervical dorsal root ganglia (DRG).

STUDY DESIGN

A qualitative and quantitative immunohistochemical study.

METHODS

The cervical (C6-C8) DRG of six slaughtered horses were obtained from a local slaughterhouse. The tissues were fixed and processed for immunohistochemistry, and the resulting cryosections were used to investigate immunoreactivity for the following putative CBD receptors: Transient receptor potential vanilloid type 1 (TRPV1), nuclear peroxisome proliferator-activated receptor gamma (PPARγ), and G protein-coupled receptors 55 (GPR55) and 3 (GPR3).

RESULTS

Large percentages of neuronal cell bodies showed immunoreactivity for TRPV1 (80 ± 20%), PPARγ (100%), GPR55 (64 ± 15%) and GPR3 (63 ± 11%). The satellite glial cells (SGCs) were immunoreactive for TRPV1, PPARγ and GPR55. In addition, GPR55 immunoreactivity was expressed by DRG interneuronal macrophages. In addition, microglia cells were observed surrounding the neuron-SGC complex.

MAIN LIMITATIONS

The limited number of horses included in the study.

CONCLUSIONS

Cannabinoid-related receptors were distributed in the sensory neurons (TRPV1, PPARγ, GPR55 and GPR3), SGCs (TRPV1, PPARγ and GPR55), macrophages (GPR55) and other interneuronal cells (PPARγ and GPR55) of the equine DRG. Given the key role of DRG cellular elements and cannabinoid receptors in the pathophysiology of pain, the present findings provided an anatomical basis for additional studies aimed at exploring the therapeutic uses of non-psychotropic cannabinoid agonists for the management of pain in horses.

Zerumbone Ameliorates Neuropathic Pain Symptoms via Cannabinoid and PPAR Receptors Using In Vivo and In Silico Models

Neuropathic pain is a chronic pain condition persisting past the presence of any noxious stimulus or inflammation. Zerumbone, of the Zingiber zerumbet ginger plant, has exhibited anti-allodynic and antihyperalgesic effects in a neuropathic pain animal model, amongst other pharmacological properties. This study was conducted to further elucidate the mechanisms underlying zerumbone's antineuropathic actions. Research on therapeutic agents involving cannabinoid (CB) and peroxisome proliferator-activated receptors (PPARs) is rising. These receptor systems have shown importance in causing a synergistic effect in suppressing nociceptive processing. Behavioural responses were assessed using the von Frey filament test (mechanical allodynia) and Hargreaves plantar test (thermal hyperalgesia), in chronic constriction injury (CCI) neuropathic pain mice. Antagonists SR141716 (CB1 receptor), SR144528 (CB2 receptor), GW6471 (PPARα receptor) and GW9662 (PPARγ receptor) were pre-administered before the zerumbone treatment. Our findings indicated the involvement of CB1, PPARα and PPARγ in zerumbone's action against mechanical allodynia, whereas only CB1 and PPARα were involved against thermal hyperalgesia. Molecular docking studies also suggest that zerumbone has a comparable and favourable binding affinity against the respective agonist on the CB and PPAR receptors studied. This finding will contribute to advance our knowledge on zerumbone and its significance in treating neuropathic pain.

Role of PPARs in Progression of Anxiety: Literature Analysis and Signaling Pathways Reconstruction

Peroxisome proliferator-activated receptor (PPAR) group includes three isoforms encoded by PPARG, PPARA, and PPARD genes. High concentrations of PPARs are found in parts of the brain linked to anxiety development, including hippocampus and amygdala. Among three PPAR isoforms, PPARG demonstrates the highest expression in CNS, where it can be found in neurons, astrocytes, and glial cells. Herein, the highest PPARG expression occurs in amygdala. However, little is known considering possible connections between PPARs and anxiety behavior. We reviewed possible connections between PPARs and anxiety. We used the Pathway Studio software (Elsevier). Signal pathways were created according to previously developed algorithms. SNEA was performed in Pathway Studio. Current study revealed 14 PPAR-regulated proteins linked to anxiety. Possible mechanism of PPAR involvement in neuroinflammation protection is proposed. Signal pathway reconstruction and reviewing aimed to reveal possible connection between PPARG and CCK-ergic system was conducted. Said analysis revealed that PPARG-dependent regulation of MME and ACE peptidase expression may affect levels of nonhydrolysed, i.e., active CCK-4. Impairments in PPARG regulation and following MME and ACE peptidase expression impairments in amygdala may be the possible mechanism leading to pathological anxiety development, with brain CCK-4 accumulation being a key link. Literature data analysis and signal pathway reconstruction and reviewing revealed two possible mechanisms of peroxisome proliferator-activated receptors involvement in pathological anxiety: (1) cytokine expression and neuroinflammation mechanism and (2) regulation of peptidases targeted to anxiety-associated neuropeptides, primarily CCK-4, mechanism.

Hyphenated chromatography detection and compound-target-disease investigation on herb-pair Chuanxiong Rhizoma - Xiangfu Rhizoma

ETHNOPHARMACOLOGY RELEVANCE

The combination of Chuanxiong Rhizoma (Ligusticum chuanxiong Hort., umbelliferae) with Xiangfu Rhizoma (the rhizoma of Cyperus rotundus L., Cyperaceae), is deemed as CR-XR herb-pair (Yaodui) in China. Their compatible mechanism needs a further research using modern analytical techniques and bioinformatic tool.

METHODS

Head Space- Solid Phase Micro Extraction coupled with Gas Chromatography/Mass Spectrometer detection (HS-SPME-GC/MS) and Liquid Chromatography coupled to quadrupole Time of Flight - Mass Spectrometry (LC-qTOF-MS) were applied in an accurate identification of the absorbed phytochemicals in mice serum; Their potential targets were available after compound-protein interaction (CPI) prediction and molecular docking verification; Then the corresponding disease types, as well as the relevant Traditional Chinese Medicine (Zhongyi) syndromes (Zheng), were matched from databases and references.

RESULTS

Resolution from hyphenated chromatographic datasets, thirty-eight phytochemicals were detected in serum samples from mice. Seventy potential target proteins were thereby found through a bioinformatic calculation, which mainly focused on circulatory, endocrine and nervous diseases in Western medicine, also related with Qizhi and Xueyu Zheng from the perspective of Zhongyi. Part of the relationships among compound-Target-Disease have been confirmed by literatures. These virtual data were sketched out as 'The active Compound - potential Target' network, 'Target - Disease' network and 'Target - Zhongyi Disease' network, in which the network topology was used to analyze them.

CONCLUSIONS

Our work successfully explained the compatible mechanism of CR-XR Yaodui, which exert 'multi-components, multi targets' in treating Qizhi and Xueyu Zheng.

Crosstalk between Cdk5/p35 and ERK1/2 signalling mediates spinal astrocyte activity via the PPARγ pathway in a rat model of chronic constriction injury

The specific mechanisms underlying cyclin-dependent kinase 5 (Cdk5)-mediated neuropathic pain at the spinal cord level remain elusive. The aim of the present study was to explore the role of crosstalk between Cdk5/p35 and extracellular signal-regulated kinase 1/2 (ERK1/2) signalling in mediating spinal astrocyte activity via the PPARγ pathway in a rat model of chronic constriction injury (CCI). Here, we quantified pain behaviour after CCI; detected the localization of p35, Cdk5, phosphorylated ERK1/2 (pERK1/2), phosphorylated peroxisome proliferator-activated receptor γ (pPPARγ), neuronal nuclei (a neuronal marker), glial fibrillary acidic protein (GFAP, an activated astrocyte marker) and ionized calcium binding adaptor molecule 1 (a microglial marker) in the dorsal horn using immunofluorescence; measured the protein levels of Cdk5, p35, pERK1/2, pPPARγ and GFAP using western blot analysis; and gauged the enzyme activity of Cdk5/p35 kinase using a Cdk5/p35 kinase activity assay kit. Tumour necrosis factor-α, interleukin (IL)-1β and IL-6 levels were measured using enzyme-linked immunosorbent assay (ELISA). Ligation of the right sciatic nerve induced mechanical allodynia; thermal hyperalgesia; and the time-dependent upregulation of p35, pERK1/2 and GFAP and downregulation of pPPARγ. p35 colocalized with Cdk5, pERK1/2, pPPARγ, neurons and astrocytes but not microglia. Meanwhile, intrathecal injection of the Cdk5 inhibitor roscovitine, the mitogen-activated ERK kinase (MEK) inhibitor U0126 and the PPARγ agonist pioglitazone prevented or reversed behavioural allodynia, increased pPPARγ expression, inhibited astrocyte activation and alleviated proinflammatory cytokine (tumour necrosis factor-α, IL-1β, and IL-6) release from activated astrocytes. Furthermore, crosstalk between the Cdk5/p35 and ERK1/2 pathways was observed with CCI. Blockade of either Cdk5/p35 or ERK1/2 inhibited Cdk5 activity. These findings indicate that spinal crosstalk between the Cdk5/p35 and ERK1/2 pathways mediates astrocyte activity via the PPARγ pathway in CCI rats and that targeting this crosstalk could be an effective strategy to attenuate CCI and astrocyte-derived neuroinflammation.

Pharmacological Treatment of Chemotherapy-Induced Neuropathic Pain: PPARγ Agonists as a Promising Tool

Chemotherapy-induced neuropathic pain (CINP) is one of the most severe side effects of anticancer agents, such as platinum- and taxanes-derived drugs (oxaliplatin, cisplatin, carboplatin and paclitaxel). CINP may even be a factor of interruption of treatment and consequently increasing the risk of death. Besides that, it is important to take into consideration that the incidence of cancer is increasing worldwide, including colorectal, gastric, lung, cervical, ovary and breast cancers, all treated with the aforementioned drugs, justifying the concern of the medical community about the patient’s quality of life. Several physiopathological mechanisms have already been described for CINP, such as changes in axonal transport, mitochondrial damage, increased ion channel activity and inflammation in the central nervous system (CNS). Another less frequent event that may occur after chemotherapy, particularly under oxaliplatin treatment, is the central neurotoxicity leading to disorders such as mental confusion, catatonia, hyporeflexia, etc. To date, no pharmacological therapy has shown satisfactory effect in these cases. In this scenario, duloxetine is the only drug currently in clinical use. Peroxisome proliferator-activated receptors (PPARs) belong to the class of nuclear receptors and are present in several tissues, mainly participating in lipid and glucose metabolism and inflammatory response. There are three PPAR isoforms: α, β/δ and γ. PPARγ, the protagonist of this review, is expressed in adipose tissue, large intestine, spleen and neutrophils. This subtype also plays important role in energy balance, lipid biosynthesis and adipogenesis. The effects of PPARγ agonists, known for their positive activity on type II diabetes mellitus, have been explored and present promising effects in the control of neuropathic pain, including CINP, and also cancer. This review focuses largely on the mechanisms involved in chemotherapy-induced neuropathy and the effects of the activation of PPARγ to treat CINP. It is the aim of this review to help understanding and developing novel CINP therapeutic strategies integrating PPARγ signalling.

15d-PGJ2-loaded nanocapsules ameliorate experimental gout arthritis by reducing pain and inflammation in a PPAR-gamma-sensitive manner in mice

Gout arthritis (GA) is a painful inflammatory disease in response to monosodium urate (MSU) crystals in the joints. 15deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is a natural activator of PPAR-γ with analgesic, anti-inflammatory, and pro-resolution properties. Thus, we aimed to evaluate the effect and mechanisms of action of 15d-PGJ₂ nanocapsules (NC) in the model of GA in mice, since a reduction of 33-fold in the dose of 15d-PGJ₂ has been reported. Mice were treated with 15d-PGJ₂-loaded NC, inert NC, free 15d-PGJ₂ (without NC), or 15d-PGJ₂-loaded NC+ GW9662, a PPAR-γ inhibitor. We show that 15d-PGJ₂-loaded NC provided analgesic effect in a dose that the free 15d-PGJ₂ failed to inhibiting pain and inflammation. Hence, 15d-PGJ₂-loaded NC reduced MSU-induced IL-1β, TNF-α, IL-6, IL-17, and IL-33 release and oxidative stress. Also, 15d-PGJ₂-loaded NC decreased the maturation of IL-1β in LPS-primed BMDM triggered by MSU. Further, 15d-PGJ₂-loaded NC decreased the expression of the components of the inflammasome Nlrp3, Asc, and Pro-caspase-1, as consequence of inhibiting NF-κB activation. All effects were PPAR-γ-sensitive. Therefore, we demonstrated that 15d-PGJ₂-loaded NC present analgesic and anti-inflammatory properties in a PPAR-γ-dependent manner inhibiting IL-1β release and NF-κB activation in GA. Concluding, 15d-PGJ₂-loaded NC ameliorates MSU-induced GA in a PPAR-γ-sensitive manner.

PPARγ Agonists Attenuate Trigeminal Neuropathic Pain

OBJECTIVES

The aim of this study is to investigate the role of peroxisome proliferator-activated receptor-gamma isoform (PPARγ), in trigeminal neuropathic pain utilizing a novel mouse trigeminal inflammatory compression (TIC) injury model.

RESULTS

The study determined that the PPARγ nuclear receptor plays a significant role in trigeminal nociception transmission, evidenced by: 1) Intense PPARγ immunoreactivity is expressed 3 weeks after TIC nerve injury in the spinal trigeminal caudalis, the termination site of trigeminal nociceptive nerve fibers. 2) Systemic administration of a PPARγ agonist, pioglitazone (PIO), attenuates whisker pad mechanical allodynia at doses of 300 mg/kg i.p. and 600 mg/kg p.o. 3) Administration of a PPARγ antagonist, GW9662 (30 mg/kg i.p.), prior to providing the optimal dose of PIO (300 mg/kg i.p.) blocked the analgesic effect of PIO.

DISCUSSION

This is the first study localizing PPARγ immunoreactivity throughout the brainstem trigeminal sensory spinal nucleus (spV) and its increase three weeks after TIC nerve injury. This is also the first study to demonstrate that activation of PPARγ attenuates trigeminal hypersensitivity in the mouse TIC nerve injury model. The findings presented here suggest the possibility of utilizing the FDA approved diabetic treatment drug, PIO, as a new therapeutic that targets PPARγ for treatment of patients suffering from orofacial neuropathic pain.

Neuroprotective Potential of Gentongping in Rat Model of Cervical Spondylotic Radiculopathy Targeting PPAR-γ Pathway

Cervical spondylotic radiculopathy (CSR) is the most general form of spinal degenerative disease and is characterized by pain and numbness of the neck and arm. Gentongping (GTP) granule, as a classical Chinese patent medicine, has been widely used in curing CSR, whereas the underlying mechanism remains unclear. Therefore, the aim of this study is to explore the pharmacological mechanisms of GTP on CSR. The rat model of CSR was induced by spinal cord injury (SCI). Our results showed that GTP could significantly alleviate spontaneous pain as well as ameliorate gait. The HE staining and Western blot results showed that GTP could increase the quantity of motoneuron and enhance the activation of peroxisome proliferator-activated receptor gamma (PPAR-γ) in the spinal cord tissues. Meanwhile, immunofluorescence staining analysis indicated that GTP could reduce the expression of TNF-α in the spinal cord tissues. Furthermore, the protein level of Bax was decreased whereas the protein levels of Bcl-2 and NF200 were increased after the GTP treatment. These findings demonstrated that GTP might modulate the PPAR-γ pathway by inhibiting the inflammatory response and apoptosis as well as by protecting the cytoskeletal integrity of the spinal cord, ultimately play a neuroprotective role in CSR.

Pioglitazone rapidly reduces neuropathic pain through astrocyte and nongenomic PPARγ mechanisms

Repeated administration of peroxisome proliferator-activated receptor gamma (PPARγ) agonists reduces neuropathic pain-like behavior and associated changes in glial activation in the spinal cord dorsal horn. As PPARγ is a nuclear receptor, sustained changes in gene expression are widely believed to be the mechanism of pain reduction. However, we recently reported that a single intrathecal (i.t.) injection of pioglitazone, a PPARγ agonist, reduced hyperalgesia within 30 minutes, a time frame that is typically less than that required for genomic mechanisms. To determine the very rapid antihyperalgesic actions of PPARγ activation, we administered pioglitazone to rats with spared nerve injury and evaluated hyperalgesia. Pioglitazone inhibited hyperalgesia within 5 minutes of injection, consistent with a nongenomic mechanism. Systemic or i.t. administration of GW9662, a PPARγ antagonist, inhibited the antihyperalgesic actions of intraperitoneal or i.t. pioglitazone, suggesting a spinal PPARγ-dependent mechanism. To further address the contribution of nongenomic mechanisms, we blocked new protein synthesis in the spinal cord with anisomycin. When coadministered intrathecally, anisomycin did not change pioglitazone antihyperalgesia at an early 7.5-minute time point, further supporting a rapid nongenomic mechanism. At later time points, anisomycin reduced pioglitazone antihyperalgesia, suggesting delayed recruitment of genomic mechanisms. Pioglitazone reduction of spared nerve injury-induced increases in GFAP expression occurred more rapidly than expected, within 60 minutes. We are the first to show that activation of spinal PPARγ rapidly reduces neuropathic pain independent of canonical genomic activity. We conclude that acute pioglitazone inhibits neuropathic pain in part by reducing astrocyte activation and through both genomic and nongenomic PPARγ mechanisms.

A multimodal disease modifying approach to treat neuropathic pain--inhibition of soluble epoxide hydrolase (sEH)

Both neuronal and non-neuronal mechanisms have been proposed to contribute to neuropathic pain (NP). All currently approved treatments for NP modulate neuronal targets and provide only symptomatic relief. Here we review evidence that inhibition of soluble epoxide hydrolase (sEH), the enzyme that degrades epoxyeicosatrienoic acids (EETs), has potential to be a multimodal, disease modifying approach to treat NP: (1) EET actions involve both endogenous opioid system and the GABAergic systems thus provide superior pain relief compared to morphine or gabapentin, (2) EETs are directly anti-inflammatory and inhibit expression of inflammatory cytokines and adhesion molecules thus can prevent continued nerve damage; and (3) EETs promote nerve regeneration in cultured neurons. Thus, an sEH inhibitor will not only provide effective pain relief, but would also block further nerve damage and promote healing.

Ameliorative potential of pioglitazone and ceftriaxone alone and in combination in rat model of neuropathic pain: Targeting PPARγ and GLT-1 pathways

BACKGROUND

The relation between glutamate homeostasis and PPAR gamma has got tremendous importance in nerve trauma and pain. Present study has been designed to elucidate the interaction between the GLT-1 activator (ceftriaxone) and PPAR gamma agonist (pioglitazone) in the spinal nerve ligation induced neuropathic pain.

METHODS

Male SD rats were subjected to spinal nerve ligation to induce neuropathic pain. Pioglitazone, ceftriaxone and their combination treatments were given for 28 days. Various behavioral, biochemical, neuroinflammatory and apoptotic mediators were assessed subsequently.

RESULTS

In the present study, ligation of L5 and L6 spinal nerves resulted in marked hyperalgesia and allodynia to different mechanical and thermal stimuli. In addition there is marked increase in oxidative-nitrosative stress parameters, inflammatory and apoptotic markers in spinal cord of spinal nerve ligated rats. Treatment with pioglitazone and ceftriaxone significantly prevented these behavioral, biochemical, mitochondrial and cellular alterations in rats. Further, combination of pioglitazone (10mg/kg, ip) with ceftriaxone (100mg/kg, ip) significantly potentiated the protective effects as compared to their effects per se.

CONCLUSION

Based on these results we propose that possible interplay between the neuroprotective effects of pioglitazone and ceftriaxone exists in suppressing the behavioral, biochemical, mitochondrial, neuroinflammatory and apoptotic cascades in spinal nerve ligation induced neuropathic pain in rats.

Role of PPAR γ in the Differentiation and Function of Neurons

Neuronal processes (neurites and axons) have an important role in brain cells communication and, generally, they are damaged in neurodegenerative diseases. Recent evidence has showed that the activation of PPARγ pathway promoted neuronal differentiation and axon polarity. In addition, activation of PPARγ using thiazolidinediones (TZDs) prevented neurodegeneration by reducing neuronal death, improving mitochondrial function, and decreasing neuroinflammation in neuropathic pain. In this review, we will discuss important evidence that supports a possible role of PPARγ in neuronal development, improvement of neuronal health, and pain signaling. Therefore, activation of PPARγ is a potential target with therapeutic applications against neurodegenerative disorders, brain injury, and pain regulation.

Antioxidant Stress and Anti-Inflammation of PPARα on Warm Hepatic Ischemia-Reperfusion Injury

Hepatic ischemia-reperfusion (IR) injury is a serious clinical problem. Minimizing the adverse effect of ischemia-reperfusion injury after liver surgery or trauma is an urgent need. It has been proved that besides the effect of regulating the lipid and lipoprotein metabolism, PPARα also undertakes the task of organ protection. In this paper, related literature has been summarized and we come to the conclusion that administration of PPARα agonists can strengthen the antioxidant and anti-inflammation defense system by the upregulation of the expression of antioxidant enzymes and inhibition of NF-κB activity. This may provide a potential clinical treatment for hepatic ischemia-reperfusion injury.

Alteration of neuropathic and visceral pain in female C57BL/6J mice lacking the PPAR-α gene

RATIONALE

Peroxisome proliferator-activated receptors (PPARs) participate in the control of chronic neuropathic and inflammatory pain, and these receptors could play a role on acute pain.

OBJECTIVES

We used null (PPAR-α -/-) and wild-type female mice and the PPAR-α blocker GW6471 to evaluate (1) the role of PPAR-α on neuropathic pain, (2) the involvement of PPAR-α on visceral and acute thermal nociception, and (3) tissue levels of pro-inflammatory factors.

METHODS

Neuropathic pain was induced by sciatic nerve ligature. Acute thermal nociception was evaluated through hot-plate, tail-immersion, and writhing tests. The pro-inflammatory factors nitric oxide, TNF-α, and interleukins-1β and -3 were measured.

RESULTS

Regarding neuropathic pain, higher sensitivity to thermal and mechanical non-noxious and noxious stimuli was observed in mice lacking PPAR-α. Cold and mechanical allodynia and heat hyperalgesia were augmented in null mice. With respect to visceral nociception, writhes after acetic acid were enhanced in mutant mice. Although basal thermal sensitivity was enhanced in PPAR-α -/- mice, cutaneous thermal nociception did not differ between genotypes. Blockade of PPAR-α was devoid of effects on acute thermal and writhing tests. Finally, nerve ligature enhanced pro-inflammatory factors in plantar tissue, levels being higher in null mice. No changes in pro-inflammatory factors were observed in the hot-plate test.

CONCLUSIONS

Genetic ablation of PPAR-α is involved in neuropathic and visceral nociception. Lack of PPAR-α is not involved in acute thermal pain, but it is involved in basal thermal reaction. Changes are biological adaptations to receptor deletion because blockade of PPAR-α does not affect inflammatory pain or thermal reactions.

Ligand-dependent nucleo-cytoplasmic shuttling of peroxisome proliferator-activated receptors, PPARα and PPARγ

Peroxisome proliferator-activated receptors (PPARs) play important roles in diverse biological processes including metabolisms of sugars and lipids and differentiation of cells such as adipocytes. PPARs are transcription factors belonging to the ligand-dependent hormone receptor group. To function as transcription factors, PPARs translocate into nucleus where they associate with transcription apparatus. However, mechanisms underlying nuclear transport of PPARs remain enigmatic. We show here that PPARα and PPARγ dynamically shuttle between nucleus and cytoplasm, although they constitutively and predominantly appear in nucleus. With a series of truncation mutants, we identify that PPAR nuclear transport is mediated by at least two nuclear localization signals (NLSs) in DNA-binding domain (DBD)-hinge and activation function 1 (AF1) regions and their respective receptors including importinα/β, importin 7, and an unidentified receptor. PPARs also harbor two nuclear export signals in DBD and ligand-binding domain regions that are recognized by distinct export receptors, calreticulin and CRM1. Moreover, we show that nuclear-cytoplasmic shuttling of PPARs is regulated by respective PPAR ligands and Ca2+ concentration. Taken together, we suggest that the multiple pathways for the nuclear-cytoplasmic transport of PPARs regulate the biological functions of PPARs in response to external signals.

Role of Peroxisome Proliferator-Activated Receptor α in Diabetic Nephropathy

With a developing worldwide epidemic of diabetes mellitus, the renal complications associated with diabetes have become a serious health concern. Primary therapy for treating diabetic nephropathy is a multifactorial process. Peroxisome proliferator-activated receptor alpha (PPARα) agonists have been used primarily in clinical practice for the treatment of dyslipidemia and insulin resistance. Given that PPARα expression and regulation of metabolic pathways are involved in oxidative stress, inflammation, blood pressure regulation, and the renin-angiotensin aldosterone system, PPARα likely influences the development and pathogenesis of diabetic nephropathy via indirect effects on glucose and lipid homeostasis and also by direct action on the kidneys. These findings suggest that PPARα may become an important therapeutic target for treating diabetic renal complications.

Peroxisome proliferator activating receptor (PPAR) in cerebral malaria (CM): a novel target for an additional therapy

Cerebral malaria (CM) is a global life-threatening complication of Plasmodium infection and represents a major cause of morbidity and mortality among severe forms of malaria. Despite developing knowledge in understanding mechanisms of pathogenesis, the current anti-malarial agents are not sufficient due to drug resistance and various adverse effects. Therefore, there is an urgent need for the novel target and additional therapy. Recently, peroxisome proliferator-activated receptor (PPAR) a nuclear receptors (NR) and agonists of its isoforms (PPARγ, PPARα and PPARβ/δ) have been demonstrated to exhibit anti-inflammatory and immunomodulatory properties, which are driven to a new approach of research on inflammatory diseases. Although many studies on PPARs have confirmed their diverse biological role, there is a lack of knowledge of its therapeutic use in CM. The major objective of this review is to explore the possible experimental studies to link these two areas of research. We focus on the data describing the beneficial effects of this receptor in inflammation, which is observed as a basic pathology in CM. In conclusion, PPARs could be a novel target in treating inflammatory diseases, and continued work with the available and additional agonists screened from various sources may result in a potential new treatment for CM.