Bladder pain relief by HMGB1 neutralization and soluble thrombomodulin in mice with cyclophosphamide-induced cystitis

Methylglyoxal and Advanced Glycation End Products (AGEs): Targets for the Prevention and Treatment of Diabetes-Associated Bladder Dysfunction?

Methylglyoxal (MGO) is a highly reactive α-dicarbonyl compound formed endogenously from 3-carbon glycolytic intermediates. Methylglyoxal accumulated in plasma and urine of hyperglycemic and diabetic individuals acts as a potent peptide glycation molecule, giving rise to advanced glycation end products (AGEs) like arginine-derived hydroimidazolone (MG-H1) and carboxyethyl-lysine (CEL). Methylglyoxal-derived AGEs exert their effects mostly via activation of RAGE, a cell surface receptor that initiates multiple intracellular signaling pathways, favoring a pro-oxidant environment through NADPH oxidase activation and generation of high levels of reactive oxygen species (ROS). Diabetic bladder dysfunction is a bothersome urological complication in patients with poorly controlled diabetes mellitus and may comprise overactive bladder, urge incontinence, poor emptying, dribbling, incomplete emptying of the bladder, and urinary retention. Preclinical models of type 1 and type 2 diabetes have further confirmed the relationship between diabetes and voiding dysfunction. Interestingly, healthy mice supplemented with MGO for prolonged periods exhibit in vivo and in vitro bladder dysfunction, which is accompanied by increased AGE formation and RAGE expression, as well as by ROS overproduction in bladder tissues. Drugs reported to scavenge MGO and to inactivate AGEs like metformin, polyphenols, and alagebrium (ALT-711) have shown favorable outcomes on bladder dysfunction in diabetic obese leptin-deficient and MGO-exposed mice. Therefore, MGO, AGEs, and RAGE levels may be critically involved in the pathogenesis of bladder dysfunction in diabetic individuals. However, there are no clinical trials designed to test drugs that selectively inhibit the MGO-AGEs-RAGE signaling, aiming to reduce the manifestations of diabetes-associated bladder dysfunction. This review summarizes the current literature on the role of MGO-AGEs-RAGE-ROS axis in diabetes-associated bladder dysfunction. Drugs that directly inactivate MGO and ameliorate bladder dysfunction are also reviewed here.

High mobility group box-1: A therapeutic target for analgesia and associated symptoms in chronic pain

The number of patients with chronic pain continues to increase against the background of an ageing society and a high incidence of various epidemics and disasters. One factor contributing to this situation is the absence of truly effective analgesics. Chronic pain is a persistent stress for the organism and can trigger a variety of neuropsychiatric symptoms. Hence, the search for useful analgesic targets is currently being intensified worldwide, and it is anticipated that the key to success may be molecules involved in emotional as well as sensory systems. High mobility group box-1 (HMGB1) has attracted attention as a therapeutic target for a variety of diseases. It is a very unique molecule having a dual role as a nuclear protein while also functioning as an inflammatory agent outside the cell. In recent years, numerous studies have shown that HMGB1 acts as a pain inducer in primary sensory nerves and the spinal dorsal horn. In addition, HMGB1 can function in the brain, and is involved in the symptoms of depression, anxiety and cognitive dysfunction that accompany chronic pain. In this review, we will summarize recent research and discuss the potential of HMGB1 as a useful drug target for chronic pain.

Hmgb1 Silencing in the Amygdala Inhibits Pain-Related Behaviors in a Rat Model of Neuropathic Pain

Chronic pain presents a therapeutic challenge due to the highly complex interplay of sensory, emotional-affective and cognitive factors. The mechanisms of the transition from acute to chronic pain are not well understood. We hypothesized that neuroimmune mechanisms in the amygdala, a brain region involved in the emotional-affective component of pain and pain modulation, play an important role through high motility group box 1 (Hmgb1), a pro-inflammatory molecule that has been linked to neuroimmune signaling in spinal nociception. Transcriptomic analysis revealed an upregulation of Hmgb1 mRNA in the right but not left central nucleus of the amygdala (CeA) at the chronic stage of a spinal nerve ligation (SNL) rat model of neuropathic pain. Hmgb1 silencing with a stereotaxic injection of siRNA for Hmgb1 into the right CeA of adult male and female rats 1 week after (post-treatment), but not 2 weeks before (pre-treatment) SNL induction decreased mechanical hypersensitivity and emotional-affective responses, but not anxiety-like behaviors, measured 4 weeks after SNL. Immunohistochemical data suggest that neurons are a major source of Hmgb1 in the CeA. Therefore, Hmgb1 in the amygdala may contribute to the transition from acute to chronic neuropathic pain, and the inhibition of Hmgb1 at a subacute time point can mitigate neuropathic pain.

Urothelial Oxidative Stress and ERK Activation Mediate HMGB1-Induced Bladder Pain

Activation of intravesical protease activated receptors-4 (PAR4) results in bladder pain through the release of urothelial macrophage migration inhibitory factor (MIF) and high mobility group box-1 (HMGB1). We aimed to identify HMGB1 downstream signaling events at the bladder that mediate HMGB1-induced bladder pain in MIF-deficient mice to exclude any MIF-related effects. We studied whether oxidative stress and ERK activation are involved by examining bladder tissue in mice treated with intravesical disulfide HMGB1 for 1 h and analyzed with Western blot and immunohistochemistry. HMGB1 intravesical treatment increased urothelium 4HNE and phospho-ERK1/2 staining, suggesting that HMGB1 increased urothelial oxidative stress and ERK activation. Furthermore, we examined the functional roles of these events. We evaluated lower abdominal mechanical thresholds (an index of bladder pain) before and 24 h after intravesical PAR4 or disulfide HMGB1. Intravesical pre-treatments (10 min prior) included: N-acetylcysteine amide (NACA, reactive oxygen species scavenger) and FR180204 (FR, selective ERK1/2 inhibitor). Awake micturition parameters (voided volume; frequency) were assessed at 24 h after treatment. Bladders were collected for histology at the end of the experiment. Pre-treatment with NACA or FR significantly prevented HMGB1-induced bladder pain. No significant effects were noted on micturition volume, frequency, inflammation, or edema. Thus, HMGB1 activates downstream urothelial oxidative stress production and ERK1/2 activation to mediate bladder pain. Further dissection of HMGB1 downstream signaling pathway may lead to novel potential therapeutic strategies to treat bladder pain.

Bladder Oxidative Stress and HMGB1 Release Contribute to PAR4-Mediated Bladder Pain in Mice

Activation of intravesical PAR4 receptors leads to bladder hyperalgesia (BHA) through release of urothelial macrophage migration inhibitory factor (MIF) and urothelial high mobility group box-1 (HMGB1). MIF deficiency and/or MIF antagonism at the bladder block BHA in mice yet the mechanisms are not clear. Since oxidative stress and ERK phosphorylation are involved in MIF signaling we hypothesized that oxidative stress and/or ERK signaling, activated by MIF release, promote intravesical HMGB1 release to induce BHA. We induced BHA by intravesical PAR4 infusion in female C57BL/6 mice. Mechanical sensitivity was evaluated by measuring abdominal von Frey (VF) 50% thresholds before (baseline) and 24 h post-infusion. Intravesical pre-treatment (10 min infusion prior to PAR4) with N-acetylcysteine amide (NACA; reactive-oxygen species scavenger; 3 mg in 50 μl), FR180204 (selective ERK1/2 inhibitor; 200 μg in 50 μl), ethyl pyruvate (EP; HMGB1 release inhibitor; 600 μg in 50 μl), or diluent controls (50 μl) tested the effects of pre-treatment on PAR4-induced BHA. Intravesical fluid was collected after each treatment and HMGB1 concentration was measured using ELISA. Awake micturition parameters (volume and frequency) were assessed at the end of the experiments. Bladders were collected and examined for histological signs of edema and inflammation. Pre-treatment with PBS followed by PAR4 induced BHA in mice but PBS followed by scrambled peptide did not. Pre-treatment with NACA or EP partially blocked PAR4-induced BHA while FR180204 had no effect. A significant correlation between intravesical HMGB1 levels and 50% VF thresholds was observed. All PAR4 treated groups had increased levels of HMGB1 in the intravesical fluid compared to PBS-Scrambled group although not statistically significant. No significant effects were noted on awake micturition volume, micturition frequency or histological evidence of bladder edema or inflammation. Our results show that intravesical antagonism of bladder reactive-oxygen species accumulation was effective in reducing PAR4-induced bladder pain. The correlation between intravesical levels of HMGB1 and bladder pain indicates that released HMGB1 is pivotal to bladder pain. Thus, modulating events in the MIF signaling cascade triggered by PAR4 activation (including bladder oxidative stress and HMGB1 release) warrant further investigation as possible therapeutic strategies.

Macrophage as a Peripheral Pain Regulator

A neuroimmune crosstalk is involved in somatic and visceral pathological pain including inflammatory and neuropathic components. Apart from microglia essential for spinal and supraspinal pain processing, the interaction of bone marrow-derived infiltrating macrophages and/or tissue-resident macrophages with the primary afferent neurons regulates pain signals in the peripheral tissue. Recent studies have uncovered previously unknown characteristics of tissue-resident macrophages, such as their origins and association with regulation of pain signals. Peripheral nerve macrophages and intestinal resident macrophages, in addition to adult monocyte-derived infiltrating macrophages, secrete a variety of mediators, such as tumor necrosis factor-α, interleukin (IL)-1β, IL-6, high mobility group box 1 and bone morphogenic protein 2 (BMP2), that regulate the excitability of the primary afferents. Neuron-derived mediators including neuropeptides, ATP and macrophage-colony stimulating factor regulate the activity or polarization of diverse macrophages. Thus, macrophages have multitasks in homeostatic conditions and participate in somatic and visceral pathological pain by interacting with neurons.

A Systematic Review of Therapeutic Approaches Used in Experimental Models of Interstitial Cystitis/Bladder Pain Syndrome

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a multifactorial, chronic bladder disorder with limited therapeutic options currently available. The present review provides an extensive overview of therapeutic approaches used in in vitro, ex vivo, and in vivo experimental models of IC/BPS. Publications were identified by electronic search of three online databases. Data were extracted for study design, type of treatment, main findings, and outcome, as well as for methodological quality and the reporting of measures to avoid bias. A total of 100 full-text articles were included. The majority of identified articles evaluated therapeutic agents currently recommended to treat IC/BPS by the American Urological Association guidelines (21%) and therapeutic agents currently approved to treat other diseases (11%). More recently published articles assessed therapeutic approaches using stem cells (11%) and plant-derived agents (10%), while novel potential drug targets identified were proteinase-activated (6%) and purinergic (4%) receptors, transient receptor potential channels (3%), microRNAs (2%), and activation of the cannabinoid system (7%). Our results show that the reported methodological quality of animal studies could be substantially improved, and measures to avoid bias should be more consistently reported in order to increase the value of preclinical research in IC/BPS for potential translation to a clinical setting.

Sesamol Alleviates the Cytotoxic Effect of Cyclophosphamide on Normal Human Lung WI-38 Cells via Suppressing RAGE/NF-κB/Autophagy Signaling

Cyclophosphamide (CYL) is a chemotherapeutic medication commonly used in managing various malignancies like breast cancer or leukemia. Though, CYL has been documented to induce lung toxicity. Mechanism of CYL toxicity is through oxidative stress and the release of damage-associated molecular patterns (DAMPs). Sesamol (SES) is a natural antioxidant isolated from Sesamum indicum and its effect against CYL-induced lung toxicity is not studied yet. This study aims to investigate whether SES could prevent any deleterious effects induced by CYL on lung using normal human lung cells, WI-38 cell line, without suppressing its efficacy. Cells were pretreated with SES and/or CYL for 24 h, then cell viability was estimated by MTS and trypan blue assays. The mode of cell death was determined by AO/EB staining. Additionally, caspase-3 level, oxidative stress, and inflammatory markers were evaluated by colorimetric and ELISA techniques. qRT-PCR was performed to evaluate RAGE, NF-κB, and Beclin-1 mRNA-expression. CYL-treated WI-38 cells developed a significantly increased cell death with enhanced oxidative and RAGE/NF-κb/Autophagy signaling, which were all attenuated after pretreatment with SES. Thus, we concluded that SES offered a protective role against CYL-induced lung injury via suppressing oxidative stress and RAGE/NF-κB/Autophagy signaling, which is a natural safe therapeutic option against CYL toxicities.

Estrogen decline is a risk factor for paclitaxel-induced peripheral neuropathy: Clinical evidence supported by a preclinical study

We performed clinical retrospective study in female cancer patients and fundamental experiments in mice, in order to clarify risk factors for paclitaxel-induced peripheral neuropathy (PIPN). In the clinical study, 131 of 189 female outpatients with cancer undergoing paclitaxel-based chemotherapy met inclusion criteria. Breast cancer survivors (n = 40) showed significantly higher overall PIPN (grades 1-4) incidence than non-breast cancer survivors (n = 91). Multivariate sub-analyses of breast cancer survivors showed that 57 years of age or older and endocrine therapy before paclitaxel treatment were significantly associated with severe PIPN (grades 2-4). The age limit was also significantly correlated with overall development of severe PIPN. In the preclinical study, female mice subjected to ovariectomy received repeated administration of paclitaxel, and mechanical nociceptive threshold was assessed by von Frey test. Ovariectomy aggravated PIPN in the mice, an effect prevented by repeated treatment with 17β-estradiol. Repeated administration of thrombomodulin alfa (TMα), known to prevent chemotherapy-induced peripheral neuropathy in rats and mice, also prevented the development of PIPN in the ovariectomized mice. Collectively, breast cancer survivors, particularly with postmenopausal estrogen decline and/or undergoing endocrine therapy, are considered a PIPN-prone subpopulation, and may require non-hormonal pharmacological intervention for PIPN in which TMα may serve as a major candidate.

Role of HMGB1 in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN), one of major dose-limiting side effects of first-line chemotherapeutic agents such as paclitaxel, oxaliplatin, vincristine, and bortezomib is resistant to most of existing medicines. The molecular mechanisms of CIPN have not been fully understood. High mobility group box 1 (HMGB1), a nuclear protein, is a damage-associated molecular pattern protein now considered to function as a pro-nociceptive mediator once released to the extracellular space. Most interestingly, HMGB1 plays a key role in the development of CIPN. Soluble thrombomodulin (TMα), known to degrade HMGB1 in a thrombin-dependent manner, prevents CIPN in rodents treated with paclitaxel, oxaliplatin, or vincristine and in patients with colorectal cancer undergoing oxaliplatin-based chemotherapy. In this review, we describe the role of HMGB1 and its upstream/downstream mechanisms in the development of CIPN and show drug candidates that inhibit the HMGB1 pathway, possibly useful for prevention of CIPN.

Cystitis-Related Bladder Pain Involves ATP-Dependent HMGB1 Release from Macrophages and Its Downstream H2S/Cav3.2 Signaling in Mice

Cystitis-related bladder pain involves RAGE activation by HMGB1, and increased Ca_v3.2 T-type Ca²⁺ channel activity by H₂S, generated by upregulated cystathionine-γ-lyase (CSE) in mice treated with cyclophosphamide (CPA). We, thus, investigated possible crosstalk between the HMGB1/RAGE and CSE/H₂S/Ca_v3.2 pathways in the bladder pain development. Bladder pain (nociceptive behavior/referred hyperalgesia) and immuno-reactive CSE expression in the bladder were determined in CPA-treated female mice. Cell signaling was analyzed in urothelial T24 and macrophage-like RAW264.7 cells. The CPA-induced bladder pain was abolished by pharmacological inhibition of T-type Ca²⁺ channels or CSE, and genetic deletion of Ca_v3.2. The CPA-induced CSE upregulation, as well as bladder pain was prevented by HMGB1 inactivation, inhibition of HMGB1 release from macrophages, antagonists of RAGE or P2X₄/P2X₇ receptors, and N-acetylcysteine, an antioxidant. Acrolein, a metabolite of CPA, triggered ATP release from T24 cells. Adenosine triphosphate (ATP) stimulated cell migration via P2X₇/P2X₄, and caused HMGB1 release via P2X₇ in RAW264.7 cells, which was dependent on p38MAPK/NF-κB signaling and reactive oxygen species (ROS) accumulation. Together, our data suggest that CPA, once metabolized to acrolein, causes urothelial ATP-mediated, redox-dependent HMGB1 release from macrophages, which in turn causes RAGE-mediated CSE upregulation and subsequent H₂S-targeted Ca_v3.2-dependent nociceptor excitation, resulting in bladder pain.

Role of high-mobility group box 1 and its modulation by thrombomodulin/thrombin axis in neuropathic and inflammatory pain

High-mobility group box 1 (HMGB1), a nuclear protein, once released to the extracellular space, facilitates pain signals as well as inflammation. Intraplantar or intraspinal application of HMGB1 elicits hyperalgesia/allodynia in rodents by activating the advanced glycosylation end-product specific receptor (receptor for advanced glycation end-products; RAGE) or Toll-like receptor 4 (TLR4). Endogenous HMGB1 derived from neurons, perineuronal cells or immune cells accumulating in the dorsal root ganglion or sensory nerves participates in somatic and visceral pain consisting of neuropathic and/or inflammatory components. Endothelial thrombomodulin (TM) and recombinant human soluble TM, TMα, markedly increase thrombin-dependent degradation of HMGB1, and systemic administration of TMα prevents and reverses various HMGB1-dependent pathological pain. Low MW compounds that directly inactivate HMGB1 or antagonize HMGB1-targeted receptors would be useful to reduce various forms of intractable pain. Thus, HMGB1 and its receptors are considered to serve as promising targets in developing novel agents to prevent or treat pathological pain. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.4/issuetoc.

HMGB1 and its membrane receptors as therapeutic targets in an intravesical substance P-induced bladder pain syndrome mouse model

HMGB1, a nuclear protein, once released to the extracellular space, promotes somatic and visceral pain signals. We thus analyzed the role of HMGB1 in an intravesical substance P-induced bladder pain syndrome (BPS) mouse model. Intravesical administration of substance P caused referred hyperalgesia/allodynia in the lower abdomen and hindpaw without producing severe urothelial damage, which was prevented by an anti-HMGB1-neutralizing antibody, thrombomodulin α capable of inactivating HMGB1 and antagonists of RAGE or CXCR4. The HMGB1 inactivation or RAGE blockade also reversed the established bladder pain symptoms. HMGB1 and RAGE are thus considered to serve as therapeutic targets for BPS.

Enhanced effect of recombinant human soluble thrombomodulin by ultrasound irradiation in acute liver failure

The administration of recombinant human soluble thrombomodulin (rhsTM) significantly improves liver inflammation and increases the survival rate of patients with acute liver failure (ALF). However, rhsTM is dose-dependently correlated to the risk of bleeding. Recently, ultrasound (US) was found to enhance the effect of various drugs. Thus, the present study aimed to determine the enhancement effect of US irradiation on rhsTM in ALF. rhsTM (1 mg/kg) and US (1 MHz, 0.3 W/cm²) were irradiated to the liver of lipopolysaccharide/D-galactosamine-induced ALF mice model. The post-treatment aspartate aminotransferase, alanine aminotransferase, and high-mobility group box 1 levels were significantly lower in the rhsTM + US group than in the rhsTM alone group. Histopathological findings revealed significantly reduced liver injury and apoptosis in the rhsTM + US group. By contrast, US irradiation had no effect on rhsTM and TNF-α concentration in the liver tissue. In conclusion, US irradiation enhanced the effect of rhsTM in the ALF mice model. However, further studies must be conducted to determine the exact mechanism of such enhancement effect.

High-Mobility Group Box 1 Protein Signaling in Painful Diabetic Neuropathy

Diabetes is a global epidemic and more than 50% diabetic patients are also diagnosed with neuropathy, which greatly affects the quality of life of the patients. Available treatments are not always successful due to the limited efficacy and complications, such as addiction and dependency. Studies have implicated that high mobility group box1 (HMGB1) protein plays a crucial role in neuroinflammation and the development of neuropathic conditions. HMGB1 is a proinflammatory cytokine that can be released from necrotic cells in passive form or in response to inflammatory signals as an active form. HMGB1 is the ligand for the receptor for advanced glycation end products (RAGE), and toll-like receptors, (TLR)-2 and TLR4, which also indirectly activates C-X-C chemokine receptor type 4 (CXCR4). We investigated whether blocking of HMGB1 can reduce pain and inflammation in diabetic neuropathic animals to further understand the role of HMGB1 in diabetic neuropathy. Type 2 diabetic rats and mice were treated with natural inhibitor of HMGB1, glycyrrhizin (GLC) for five days/week for four weeks at a dose of 50 mg/kg per day by intraperitoneal injection. The animals were divided into three categories: naïve control, diabetic alone, diabetic with GLC treatment. All of the behavioral analyses were conducted before and after the treatment. The expression of inflammatory markers and changes in histone acetylation in the peripheral nervous system were measured by immunohistochemistry and Western blot analysis after the completion of the treatment. Our study revealed that TLR4, HMGB1, CXCR4, and Nod-like receptor protein 3 (NLRP3) levels were increased in the spinal and dorsal root ganglia (DRG) neurons of Type 2 diabetic mice and rats with painful neuropathy. GLC treatment inhibited the increases in TLR4, NLRP3, and CXCR4 expressions and improved the mechanical and thermal pain threshold in these animals. Immunohistochemical studies revealed that hyperglycemia mediated inflammation influenced HMGB1 acetylation and its release from the neurons. It also altered histone 3 acetylation in the microglial cells. The inhibition of HMGB1 by GLC prevented the release of HMGB1 as well as H3K9 acetylation. These findings indicate that the interruption of HMGB1 mediated inflammation could ameliorate diabetic neuropathy and might exhibit a unique target for the treatment.

[HMGB1 as a target for prevention of chemotherapy-induced peripheral neuropathy]

Chemotherapy-induced peripheral neuropathy (CIPN) considerably impairs cancer patients' QOL, and may lead to discontinuation of drug treatment of cancer. Currently, there is no effective strategy against CIPN. Therefore, it is an urgent issue to develop clinically available drugs that prevent or treat CIPN. We have shown that high mobility group box 1 (HMGB1), a damage-associated molecular pattern (DAMP) molecule, plays an essential role in the development of CIPN. Most interestingly, thrombomodulin α, approved as a medicine for treatment of disseminated intravascular coagulation (DIC) in Japan, causes thrombin-dependent degradation of extracellular HMGB1 that is released in response to chemotherapeutics, and prevents CIPN. Thus, we expect that targeting HMGB1 or its receptors would lead to prevention of CIPN in cancer patients in near future.

Attenuated lipopolysaccharide-induced inflammatory bladder hypersensitivity in mice deficient of transient receptor potential ankilin1

Transient receptor potential ankyrin 1 (TRPA1) channel expressed by urothelial cells and bladder sensory nerve fibers might act as a bladder mechanosensor and nociceptive transducer. To disclose the role of TRPA1 in bladder function and inflammation-associated hypersensitivity, we evaluated in vitro and in vivo bladder function and inflammatory mechanosensory and nociceptive responses to intravesical lipopolysaccharide (LPS)-instillation in wild type (WT) and TRPA1-knock out (KO) mice. At baseline before treatment, no significant differences were observed in frequency volume variables, in vitro detrusor contractility, and cystometric parameters between the two groups in either sex. LPS-instillation significantly increased voiding frequency and decreased mean voided volume at 24-48 hours after instillation in WT but not in TRPA1-KO mice. LPS-instillation also significantly increased the number of pain-like behavior at 24 hours after instillation in WT mice, but not in TRPA1-KO mice. Cystometry 24 hours after LPS-instillation revealed shorter inter-contraction intervals in the WT mice compared with TRPA1-KO mice. In contrast, inflammatory cell infiltration in the bladder suburothelial layer was not significantly different between the two groups. These results indicate that TRPA1 channels are involved in bladder mechanosensory and nociceptive hypersensitivity accompanied with inflammation but not in physiological bladder function or development of bladder inflammation.

Paclitaxel-induced HMGB1 release from macrophages and its implication for peripheral neuropathy in mice: Evidence for a neuroimmune crosstalk

Given our recent evidence for the role of high mobility group box 1 (HMGB1) in chemotherapy-induced peripheral neuropathy (CIPN) in rats, we examined the origin of HMGB1 and the upstream and downstream mechanisms of HMGB1 release involved in paclitaxel-induced neuropathy in mice. Paclitaxel treatment developed mechanical allodynia in mice, as assessed by von Frey test, which was prevented by an anti-HMGB1-neutralizing antibody or thrombomodulin alfa capable of inactivating HMGB1. RAGE or CXCR4 antagonists, ethyl pyruvate or minocycline, known to inhibit HMGB1 release from macrophages, and liposomal clodronate, a macrophage depletor, prevented the paclitaxel-induced allodynia. Paclitaxel caused upregulation of RAGE and CXCR4 in the dorsal root ganglia and macrophage accumulation in the sciatic nerve. In macrophage-like RAW264.7 cells, paclitaxel evoked cytoplasmic translocation of nuclear HMGB1 followed by its extracellular release, and overexpression of CBP and PCAF, histone acetyltransferases (HATs), known to cause acetylation and cytoplasmic translocation of HMGB1, which were suppressed by ethyl pyruvate, N-acetyl-l-cysteine, an anti-oxidant, and SB203580 and PDTC, inhibitors of p38 MAP kinase (p38MAPK) and NF-κB, respectively. Paclitaxel increased accumulation of reactive oxygen species (ROS) and phosphorylation of p38MAPK, NF-κB p65 and I-κB in RAW264.7 cells. In mice, N-acetyl-l-cysteine or PDTC prevented the paclitaxel-induced allodynia. Co-culture of neuron-like NG108-15 cells or stimulation with their conditioned medium promoted paclitaxel-induced HMGB1 release from RAW264.7 cells. Our data indicate that HMGB1 released from macrophages through the ROS/p38MAPK/NF-κB/HAT pathway participates in the paclitaxel-induced peripheral neuropathy in mice, and unveils an emerging therapeutic avenue targeting a neuroimmune crosstalk in CIPN.

Extracellular HMGB1 as a therapeutic target in inflammatory diseases

INTRODUCTION

High-mobility group box 1 (HMGB1) is a ubiquitous nuclear protein that promotes inflammation when released extracellularly after cellular activation, stress, damage or death. HMGB1 operates as one of the most intriguing molecules in inflammatory disorders via recently elucidated signal and molecular transport mechanisms. Treatments based on antagonists specifically targeting extracellular HMGB1 have generated encouraging results in a wide number of experimental models of infectious and sterile inflammation. Clinical studies are still to come. Areas covered: We here summarize recent advances regarding pathways for extracellular HMGB1 release, receptor usage, and functional consequences of post-translational modifications. The review also addresses results of preclinical HMGB1-targeted therapy studies in multiple inflammatory conditions and outlines the current status of emerging clinical HMGB1-specific antagonists. Expert opinion: Blocking excessive amounts of extracellular HMGB1, particularly the disulfide isoform, offers an attractive clinical opportunity to ameliorate systemic inflammatory diseases. Therapeutic interventions to regulate intracellular HMGB1 biology must still await a deeper understanding of intracellular HMGB1 functions. Future work is needed to create more robust assays to evaluate functional bioactivity of HMGB1 antagonists. Forthcoming clinical studies would also greatly benefit from a development of antibody-based assays to quantify HMGB1 redox isoforms, presently assessed by mass spectrometry methods.

Involvement of the cystathionine-γ-lyase/Cav3.2 pathway in substance P-induced bladder pain in the mouse, a model for nonulcerative bladder pain syndrome

Hydrogen sulfide (H₂S) formed by cystathionine-γ-lyase (CSE) enhances the activity of Ca_v3.2 T-type Ca²⁺ channels, contributing to the bladder pain accompanying hemorrhagic cystitis caused by systemic administration of cyclophosphamide (CPA) in mice. Given clinical and fundamental evidence for the involvement of the substance P/NK₁ receptor systems in bladder pain syndrome (BPS)/interstitial cystitis (IC), we created an intravesical substance P-induced bladder pain model in mice and analyzed the possible involvement of the CSE/Ca_v3.2 pathway. Bladder pain/cystitis was induced by i.p. CPA or intravesical substance P in female mice. Bladder pain was evaluated by counting nociceptive behavior and by detecting referred hyperalgesia in the lower abdomen and hindpaw. The isolated bladder tissue was weighed to estimate bladder swelling and subjected to histological observation and Western blotting. Intravesical substance P caused profound referred hyperalgesia accompanied by little bladder swelling or edema 6-24 h after the administration, in contrast to i.p. CPA-induced nociceptive behavior/referred hyperalgesia with remarkable bladder swelling/edema and urothelial damage. The bladder pain and/or cystitis symptoms caused by substance P or CPA were prevented by the NK₁ receptor antagonist. CSE in the bladder was upregulated by substance P or CPA, and the NK₁ antagonist prevented the CPA-induced CSE upregulation. A CSE inhibitor, a T-type Ca²⁺ channel blocker and gene silencing of Ca_v3.2 abolished the intravesical substance P-induced referred hyperalgesia. The intravesical substance P-induced pain in mice is useful as a model for nonulcerative BPS, and involves the activation of the NK₁ receptor/CSE/H₂S/Ca_v3.2 cascade.

Cutaneous Burn Injury Modulates Urinary Antimicrobial Peptide Responses and the Urinary Microbiome

OBJECTIVES

Characterization of urinary bacterial microbiome and antimicrobial peptides after burn injury to identify potential mechanisms leading to urinary tract infections and associated morbidities in burn patients.

DESIGN

Retrospective cohort study using human urine from control and burn subjects.

SETTING

University research laboratory.

PATIENTS

Burn patients.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Urine samples from catheterized burn patients were collected hourly for up to 40 hours. Control urine was collected from "healthy" volunteers. The urinary bacterial microbiome and antimicrobial peptide levels and activity were compared with patient outcomes. We observed a significant increase in urinary microbial diversity in burn patients versus controls, which positively correlated with a larger percent burn and with the development of urinary tract infection and sepsis postadmission, regardless of age or gender. Urinary psoriasin and β-defensin antimicrobial peptide levels were significantly reduced in burn patients at 1 and 40 hours postadmission. We observed a shift in antimicrobial peptide hydrophobicity and activity between control and burn patients when urinary fractions were tested against Escherichia coli and Enterococcus faecalis urinary tract infection isolates. Furthermore, the antimicrobial peptide activity in burn patients was more effective against E. coli than E. faecalis. Urinary tract infection-positive burn patients with altered urinary antimicrobial peptide activity developed either an E. faecalis or Pseudomonas aeruginosa urinary tract infection, suggesting a role for urinary antimicrobial peptides in susceptibility to select uropathogens.

CONCLUSIONS

Our data reveal potential links for urinary tract infection development and several morbidities in burn patients through alterations in the urinary microbiome and antimicrobial peptides. Overall, this study supports the concept that early assessment of urinary antimicrobial peptide responses and the bacterial microbiome may be used to predict susceptibility to urinary tract infections and sepsis in burn patients.

Disulfide high mobility group box-1 causes bladder pain through bladder Toll-like receptor 4

BACKGROUND

Bladder pain is a prominent symptom in several urological conditions (e.g. infection, painful bladder syndrome/interstitial cystitis, cancer). Understanding the mechanism of bladder pain is important, particularly when the pain is not accompanied by bladder pathology. Stimulation of protease activated receptor 4 (PAR4) in the urothelium results in bladder pain through release of urothelial high mobility group box-1 (HMGB1). HGMB1 has two functionally active redox states (disulfide and all-thiol) and it is not known which form elicits bladder pain. Therefore, we investigated whether intravesical administration of specific HMGB1 redox forms caused abdominal mechanical hypersensitivity, micturition changes, and bladder inflammation in female C57BL/6 mice 24 hours post-administration. Moreover, we determined which of the specific HMGB1 receptors, Toll-like receptor 4 (TLR4) or receptor for advanced glycation end products (RAGE), mediate HMGB1-induced changes.

RESULTS

Disulfide HMGB1 elicited abdominal mechanical hypersensitivity 24 hours after intravesical (5, 10, 20 μg/150 μl) instillation. In contrast, all-thiol HMGB1 did not produce abdominal mechanical hypersensitivity in any of the doses tested (1, 2, 5, 10, 20 μg/150 μl). Both HMGB1 redox forms caused micturition changes only at the highest dose tested (20 μg/150 μl) while eliciting mild bladder edema and reactive changes at all doses. We subsequently tested whether the effects of intravesical disulfide HMGB1 (10 μg/150 μl; a dose that did not produce inflammation) were prevented by systemic (i.p.) or local (intravesical) administration of either a TLR4 antagonist (TAK-242) or a RAGE antagonist (FPS-ZM1). Systemic administration of either TAK-242 (3 mg/kg) or FPS-ZM1 (10 mg/kg) prevented HMGB1 induced abdominal mechanical hypersensitivity while only intravesical TLR4 antagonist pretreatment (1.5 mg/ml; not RAGE) had this effect.

CONCLUSIONS

The disulfide form of HMGB1 mediates bladder pain directly (not secondary to inflammation or injury) through activation of TLR4 receptors in the bladder. Thus, TLR4 receptors are a specific local target for bladder pain.

Inhibiting HMGB1 Reduces Cerebral Ischemia Reperfusion Injury in Diabetic Mice

High mobility group box1 (HMGB1) promotes inflammatory injury, and accumulating evidence suggests that it plays a key role in brain ischemia reperfusion (I/R), as well as the development of diabetes mellitus (DM). The purpose of this study was to investigate whether HMGB1 plays a role in brain I/R in a DM mouse model. Diabetes mellitus was induced by a high-calorie diet and streptozotocin treatment, and cerebral ischemia was induced by middle cerebral artery occlusion. We examined HMGB1 levels following cerebral I/R injury in DM and non-DM mice and evaluated the influence of altered HMGB1 levels on the severity of cerebral injury. Serum HMGB1 levels and the inflammatory factors IL-1β, IL-6, and inflammation-related enzyme iNOS were significantly elevated in DM mice with brain I/R compared with non-DM mice with brain I/R. Blocking HMGB1 function by intraperitoneal injection of anti-HMGB1 neutralizing antibodies reversed the inflammatory response and the extent of brain damage, suggesting that HMGB1 plays an important role in cerebral ischemic stroke in diabetic mice.

Repeated Cold Stress Reduces Cyclophosphamide-Induced Cystitis/Bladder Pain and Macrophage Activity in Mice

We examined the effect of repeated cold (RC) stress on cyclophosphamide (CPA)-induced cystitis/bladder pain in mice, in relation to macrophage activity. CPA, given i.p. at 400 mg/kg, caused bladder pain symptoms accompanying cystitis in both unstressed and RC-stressed mice, which were prevented by the macrophage inhibitor minocycline. A low dose, that is, 200 mg/kg, of CPA still produced bladder pain symptoms in unstressed but not RC-stressed mice. Lipopolysaccharide-induced cytokine production in peritoneal macrophages from RC-stressed mice was less than that from unstressed mice. Thus, RC stress appears to reduce CPA-induced bladder pain in mice, which may be associated with the decreased macrophage activity.

Involvement of high mobility group box 1 in the development and maintenance of chemotherapy-induced peripheral neuropathy in rats

Given that high mobility group box 1 (HMGB1), a nuclear protein, once released to the extracellular space, promotes nociception, we asked if inactivation of HMGB1 prevents or reverses chemotherapy-induced painful neuropathy in rats and also examined possible involvement of Toll-like receptor 4 (TLR4) and the receptor for advanced glycation endproduct (RAGE), known as targets for HMGB1. Painful neuropathy was produced by repeated i.p. administration of paclitaxel or vincristine in rats. Nociceptive threshold was determined by the paw pressure method and/or von Frey test in the hindpaw. Tissue protein levels were determined by immunoblotting. Repeated i.p. administration of the anti-HMGB1-neutralizing antibody or recombinant human soluble thrombomodulin (rhsTM), known to inactivate HMGB1, prevented the development of hyperalgesia and/or allodynia induced by paclitaxel or vincristine in rats. A single i.p. or intraplantar (i.pl.) administration of the antibody or rhsTM reversed the chemotherapy-induced neuropathy. A single i.pl. administration of a TLR4 antagonist or low molecular weight heparin, known to inhibit RAGE, attenuated the hyperalgesia caused by i.pl. HMGB1 and also the chemotherapy-induced painful neuropathy. Paclitaxel or vincristine treatment significantly decreased protein levels of HMGB1 in the dorsal root ganglia, but not sciatic nerves. HMGB1 thus participates in both development and maintenance of chemotherapy-induced painful neuropathy, in part through RAGE and TLR4. HMGB1 inactivation is considered useful to prevent and treat the chemotherapy-induced painful neuropathy.

Pattern recognition receptors in chronic pain: Mechanisms and therapeutic implications

For the individual, it is vital to promptly detect and recognize a danger that threatens the integrity of the body. Pattern recognition receptors (PRRs) are several classes of protein families originally classified as receptors detecting exogenous pathogens. PRRs are also capable of recognizing molecules released from damaged tissues (damage-associated molecular pattern molecules; DAMPs) and thereby contribute to danger recognition. Importantly, it is now evident that PRRs, such as toll-like receptors (TLRs) and receptors for advanced glycation end products (RAGE), are not only expressed in peripheral immune cells but also present in neurons and glial cells in the nervous system. These PRR-expressing cells work in concert, enabling highly sensitive danger recognition. However, this sensitiveness can act as a double-edged sword. Accumulated evidence has led to the hypothesis that aberrant activation of PRRs may play a crucial role in the pathogenesis of pathological pain. Indeed, numerous studies employing gene deletion or pharmacological inhibition of PRRs successfully reversed or prevented pathological pain in experimental animal models. Furthermore, a number of preclinical studies have shown the therapeutic potential of targeting PRRs for chronic pain. Here, we review the current knowledge regarding the role of PRRs in chronic pain and discuss the promise and challenges of targeting PRRs as a novel therapeutic approach for chronic pain.

The Emerging Role of HMGB1 in Neuropathic Pain: A Potential Therapeutic Target for Neuroinflammation

Neuropathic pain (NPP) is intolerable, persistent, and specific type of long-term pain. It is considered to be a direct consequence of pathological changes affecting the somatosensory system and can be debilitating for affected patients. Despite recent progress and growing interest in understanding the pathogenesis of the disease, NPP still presents a major diagnostic and therapeutic challenge. High mobility group box 1 (HMGB1) mediates inflammatory and immune reactions in nervous system and emerging evidence reveals that HMGB1 plays an essential role in neuroinflammation through receptors such as Toll-like receptors (TLR), receptor for advanced glycation end products (RAGE), C-X-X motif chemokines receptor 4 (CXCR4), and N-methyl-D-aspartate (NMDA) receptor. In this review, we present evidence from studies that address the role of HMGB1 in NPP. First, we review studies aimed at determining the role of HMGB1 in NPP and discuss the possible mechanisms underlying HMGB1-mediated NPP progression where receptors for HMGB1 are involved. Then we review studies that address HMGB1 as a potential therapeutic target for NPP.

Protease-Activated Receptor 4 Induces Bladder Pain through High Mobility Group Box-1

Pain is the significant presenting symptom in Interstitial Cystitis/Painful Bladder Syndrome (IC/PBS). Activation of urothelial protease activated receptor 4 (PAR4) causes pain through release of urothelial macrophage migration inhibitory factor (MIF). High Mobility Group Box-1 (HMGB1), a chromatin-binding protein, mediates bladder pain (but not inflammation) in an experimental model (cyclophosphamide) of cystitis. To determine if PAR4-induced bladder hypersensitivity depends on HMGB1 downstream, we tested whether: 1) bladder PAR4 stimulation affected urothelial HMGB1 release; 2) blocking MIF inhibited urothelial HMGB1 release; and 3) blocking HMGB1 prevented PAR4-induced bladder hypersensitivity. HMGB1 release was examined in immortalized human urothelial cultures (UROtsa) exposed to PAR4-activating peptide (PAR4-AP; 100 μM; 2 hours) or scrambled control peptide. Female C57BL/6 mice, pretreated with a HMGB1 inhibitor (glycyrrhizin: 50 mg/kg; ip) or vehicle, received intravesical PAR4-AP or a control peptide (100 μM; 1 hour) to determine 1) HMGB1 levels at 1 hour in the intravesical fluid (released HMGB1) and urothelium, and 2) abdominal hypersensitivity to von Frey filament stimulation 24 hours later. We also tested mice pretreated with a MIF blocker (ISO-1: 20 mg/kg; ip) to determine whether MIF mediated PAR4-induced urothelial HMGB1 release. PAR4-AP triggered HMGB1 release from human (in vitro) and mice (in vivo) urothelial cells. Intravesical PAR4 activation elicited abdominal hypersensitivity in mice that was prevented by blocking HMGB1. MIF inhibition prevented PAR4-mediated HMGB1 release from mouse urothelium. Urothelial MIF and HGMB1 represent novel targets for therapeutic intervention in bladder pain conditions.

Recombinant human soluble thrombomodulin ameliorates cerebral ischemic injury through a high-mobility group box 1 inhibitory mechanism without hemorrhagic complications in mice

BACKGROUND

It has been reported that recombinant human soluble thrombomodulin (rhsTM) has a high-mobility group box (HMGB)1 inhibitory effect. Some investigators reported that HMGB1 is associated with ischemic stroke. However, there have been no previous studies to determine whether rhsTM can ameliorate cerebral ischemic injury through its HMGB1 inhibitory mechanism in ischemic stroke. We investigated the effects of rhsTM on cerebral ischemic injury in a 4-h middle cerebral artery occlusion (MCAO) murine model.

METHODS

rhsTM (1 or 5mg/kg, i.v.) was administered immediately after 4-h MCAO. Infarct volume, motor coordination, plasma HMGB1 level, and hemorrhage volume were evaluated 24h after 4-h MCAO.

RESULTS

The infarct volume (P<0.05) was reduced by rhsTM in mice subjected to 4-h MCAO in a dose-dependent manner. Moreover, rhsTM (5mg/kg) significantly improved motor coordination determined by the rotarod test (P<0.05), and significantly decreased plasma HMGB1 level compared with vehicle-treated controls (P<0.001). In addition, there was no difference in hemorrhage volume between vehicle-treated controls and the rhsTM treatment group.

CONCLUSIONS

This represents the first report that rhsTM ameliorates cerebral ischemic injury through an HMGB1 inhibitory mechanism without hemorrhagic complications in mice. Taken together, these observations indicate a palliative effect of rhsTM and suggest new therapeutic possibilities for treatment of ischemic stroke via inhibition of HMGB1.

PK2/PKR1 Signaling Regulates Bladder Function and Sensation in Rats with Cyclophosphamide-Induced Cystitis

Prokineticin 2 (PK2) is a novel chemokine-like peptide with multiple proinflammatory and nociception-related activities. This study aimed to explore the potential role of PK2 in modulating bladder activity and sensation in rats with cyclophosphamide- (CYP-) induced cystitis. Changes of PK2 and prokineticin receptors (PKRs) in normal and inflamed urinary bladders were determined at several time points (4 h, 48 h, and 8 d) after CYP treatment. Combining a nonselective antagonist of prokineticin receptors (PKRA), we further evaluated the regulatory role of PK2 in modulating bladder function and visceral pain sensation via conscious cystometry and pain behavioral scoring. PK2 and prokineticin receptor 1 (PKR1), but not prokineticin receptor 2, were detected in normal and upregulated in CYP-treated rat bladders at several levels. Immunohistochemistry staining localized PKR1 primarily in the urothelium. Blocking PKRs with PKRA showed no effect on micturition reflex activity and bladder sensation in control rats while it increased the voiding volume, prolonged voiding interval, and ameliorated visceral hyperalgesia in rats suffering from CYP-induced cystitis. In conclusion, PK2/PKR1 signaling pathway contributes to the modulation of inflammation-mediated voiding dysfunction and spontaneous visceral pain. Local blockade of PKRs may represent a novel and promising therapeutic strategy for the clinical management of inflammation-related bladder diseases.

Animal models of gastrointestinal and liver diseases. Animal models of visceral pain: pathophysiology, translational relevance, and challenges

Visceral pain describes pain emanating from the thoracic, pelvic, or abdominal organs. In contrast to somatic pain, visceral pain is generally vague, poorly localized, and characterized by hypersensitivity to a stimulus such as organ distension. Animal models have played a pivotal role in our understanding of the mechanisms underlying the pathophysiology of visceral pain. This review focuses on animal models of visceral pain and their translational relevance. In addition, the challenges of using animal models to develop novel therapeutic approaches to treat visceral pain will be discussed.

Extracellular high-mobility group box 1 protein (HMGB1) as a mediator of persistent pain

Although originally described as a highly conserved nuclear protein, high-mobility group box 1 protein (HMGB1) has emerged as a danger-associated molecular pattern molecule protein (DAMP) and is a mediator of innate and specific immune responses. HMGB1 is passively or actively released in response to infection, injury and cellular stress, providing chemotactic and cytokine-like functions in the extracellular environment, where it interacts with receptors such as receptor for advanced glycation end products (RAGE) and several Toll-like receptors (TLRs). Although HMGB1 was first revealed as a key mediator of sepsis, it also contributes to a number of other conditions and disease processes. Chronic pain arises as a direct consequence of injury, inflammation or diseases affecting the somatosensory system and can be devastating for the affected patients. Emerging data indicate that HMGB1 is also involved in the pathology of persistent pain. Here, we give an overview of HMGB1 as a proinflammatory mediator, focusing particularly on the role of HMGB1 in the induction and maintenance of hypersensitivity in experimental models of pain and discuss the therapeutic potential of targeting HMGB1 in conditions of chronic pain.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.