Dietary intervention using (1,3)/(1,6)-ß-glucan, a fungus-derived soluble prebiotic ameliorates high-fat diet-induced metabolic distress and alters beneficially the gut microbiota in mice model.

PURPOSE: Western diet, rich in carbohydrates and fat, is said to be a major factor underlying metabolic syndrome. Interventions with prebiotics, the key modulators of the gut microbiota, have paramount impact on host-associated metabolic disorders. Herein, we investigated the effect of fungus-derived (1,3)/(1,6)-ß-glucan, a highly soluble dietary fiber, on high-fat diet (HFD)-induced metabolic distress. METHODS: Male C57BL/6 J mice were fed with different diet groups (n = 11): control diet, HFD, 3 g/kg or 5 g/kg of ß-glucan-incorporated HFD. At the end of experimental study period (12th week), body weight, feces weight and fecal moisture content were observed. Further, colonic motility was measured using activated charcoal meal study. Proteins extracted from liver and intestine tissues were subjected to western blot technique. Paraffin-embedded intestinal tissues were sectioned for histochemical [Periodic acid-Schiff (PAS) and Alcian blue (AB) staining] analysis. Fecal microbiota analysis was performed using MOTHUR bioinformatic software. RESULTS: ß-glucan consumption exhibited anti-obesity property in mice groups fed with HFD. In addition, ß-glucan ameliorated HFD-induced hepatic stress, colonic motility and intestinal atrophy (reduction in colon length, goblet cells, and mucosal layer thickness). Further, ß-glucan incorporation shifted bacterial community by increasing butyrate-producing bacteria such as Anaerostipes, Coprobacillus, and Roseburia and decreasing reportedly obesity-associated bacteria such as Parabacteroides and Lactococcus. CONCLUSION: Altogether, the outcomes of this present pre-clinical animal study show ß-glucan to be a promising therapeutic candidate in the treatment of HFD-induced metabolic distress. Further comprehensive research has to be conducted to brace its clinical relevance, reproducibility and efficacy for aiding human health.

Emerging Role of Spinal Cord TRPV1 in Pain Exacerbation.

TRPV1 is well known as a sensor ion channel that transduces a potentially harmful environment into electrical depolarization of the peripheral terminal of the nociceptive primary afferents. Although TRPV1 is also expressed in central regions of the nervous system, its roles in the area remain unclear. A series of recent reports on the spinal cord synapses have provided evidence that TRPV1 plays an important role in synaptic transmission in the pain pathway. Particularly, in pathologic pain states, TRPV1 in the central terminal of sensory neurons and interneurons is suggested to commonly contribute to pain exacerbation. These observations may lead to insights regarding novel synaptic mechanisms revealing veiled roles of spinal cord TRPV1 and may offer another opportunity to modulate pathological pain by controlling TRPV1. In this review, we introduce historical perspectives of this view and details of the recent promising results. We also focus on extended issues and unsolved problems to fully understand the role of TRPV1 in pathological pain. Together with recent findings, further efforts for fine analysis of TRPV1's plastic roles in pain synapses at different levels in the central nervous system will promote a better understanding of pathologic pain mechanisms and assist in developing novel analgesic strategies.

Are sensory TRP channels biological alarms for lipid peroxidation?

Oxidative stress induces numerous biological problems. Lipid oxidation and peroxidation appear to be important steps by which exposure to oxidative stress leads the body to a disease state. For its protection, the body has evolved to respond to and eliminate peroxidation products through the acquisition of binding proteins, reducing and conjugating enzymes, and excretion systems. During the past decade, researchers have identified a group of ion channel molecules that are activated by oxidized lipids: transient receptor potential (TRP) channels expressed in sensory neurons. These ion channels are fundamentally detectors and signal converters for body-damaging environments such as heat and cold temperatures, mechanical attacks, and potentially toxic substances. When messages initiated by TRP activation arrive at the brain, we perceive pain, which results in our preparing defensive responses. Excessive activation of the sensory neuronal TRP channels upon prolonged stimulations sometimes deteriorates the inflammatory state of damaged tissues by promoting neuropeptide release from expresser neurons. These same paradigms may also work for pathologic changes in the internal lipid environment upon exposure to oxidative stress. Here, we provide an overview of the role of TRP channels and oxidized lipid connections during abnormally increased oxidative signaling, and consider the sensory mechanism of TRP detection as an alert system.

GPR171 Activation Modulates Nociceptor Functions, Alleviating Pathologic Pain.

Modulation of the function of somatosensory neurons is an important analgesic strategy, requiring the proposal of novel molecular targets. Many G-protein-coupled receptors (GPRs) have been deorphanized, but the receptor locations, outcomes due to their activations, and their signal transductions remain to be elucidated, regarding the somatosensory nociceptor function. Here we report that GPR171, expressed in a nociceptor subpopulation, attenuated pain signals via Gi/o-coupled modulation of the activities of nociceptive ion channels when activated by its newly found ligands. Administration of its natural peptide ligand and a synthetic chemical ligand alleviated nociceptor-mediated acute pain aggravations and also relieved pathologic pain at nanomolar and micromolar ranges. This study suggests that functional alteration of the nociceptor neurons by GPR171 signaling results in pain alleviation and indicates that GPR171 is a promising molecular target for peripheral pain modulation.

ß-Glucan-Based Wet Dressing for Cutaneous Wound Healing.

Objective: Recognized as pathogen-associated molecular patterns (PAMPs), ß-glucans, a naturally occurring heterogeneous group of polysaccharides, were investigated for their ability to accelerate wound healing in the form of high water-retaining hydrogel dressing. Approach: Full-thickness wounds on the dorsal side of mice created using a 5-mm biopsy punch were treated with ß-glucan-based hydrogel for 2 weeks. Standardized photographs of the wound site were taken at regular time intervals to calculate the percentage of wound closure. Tissues isolated from the wound area were subjected to histological examination and immunoblot analysis. Results: ß-Glucan-based hydrogel significantly accelerated the duration of wound healing and enhanced the development of skin appendages in the regenerated skin tissue. Increased expression of transforming growth factor-ß3 in the skin tissue isolated from the healed wound site indicated that skin regeneration rather than skin repair occurred, thereby minimizing cutaneous scarring. The expression level of cytokeratin 10 and cytokeratin 14 in the isolated skin tissue revealed that the wounds treated with hydrogel showed proper differentiation and proliferation of keratinocytes in the epidermal layer. Innovation: Immunomodulating ß-glucan (responsible for fighting infections at the wound site, and enhancing the migration and proliferation of keratinocytes and fibroblasts) in the form of a three-dimensional hydrogel membrane that retains a high water content (responsible for cooling and soothing effect around the wound site, thereby reducing pain) was prepared and analyzed for its effects on the cutaneous wound healing mechanism. Conclusion: ß-Glucan-based hydrogels are promising as wet wound dressings in the health care industry.

TRPV4-Mediated Anti-nociceptive Effect of Suberanilohydroxamic Acid on Mechanical Pain.

Biological effects of suberanilohydroxamic acid (SAHA) have mainly been observed in the context of tumor suppression via epigenetic mechanisms, but other potential outcomes from its use have also been proposed in different fields such as pain modulation. Here, we tried to understand whether SAHA modulates specific pain modalities by a non-epigenetic unknown mechanism. From 24 h Complete Freund's Adjuvant (CFA)-inflamed hind paws of mice, mechanical and thermal inflammatory pain indices were collected with or without immediate intraplantar injection of SAHA. To examine the action of SAHA on sensory receptor-specific pain, transient receptor potential (TRP) ion channel-mediated pain indices were collected in the same manner of intraplantar treatment. Activities of primarily cultured sensory neurons and heterologous cells transfected with TRP channels were monitored to determine the molecular mechanism underlying the pain-modulating effect of SAHA. As a result, immediate and localized pretreatment with SAHA, avoiding an epigenetic intervention, acutely attenuated mechanical inflammatory pain and receptor-specific pain evoked by injection of a TRP channel agonist in animal models. We show that a component of the mechanisms involves TRPV4 inhibition based on in vitro intracellular Ca2+ imaging and electrophysiological assessments with heterologous expression systems and cultured sensory neurons. Taken together, the present study provides evidence of a novel off-target action and its mechanism of SAHA in its modality-specific anti-nociceptive effect and suggests the utility of this compound for pharmacological modulation of pain.

Impairment of proprioceptive movement and mechanical nociception in Drosophila melanogaster larvae lacking Ppk30, a Drosophila member of the Degenerin/Epithelial Sodium Channel family.

The mechanosensory neurons of Drosophila larvae are demonstrably activated by diverse mechanical stimuli, but the mechanisms underlying this function are not completely understood. Here we report a genetic, immunohistochemical, and electrophysiological analysis of the Ppk30 ion channel, a member of the Drosophila pickpocket (ppk) family, counterpart of the mammalian Degenerin/Epithelial Na+ Channel family. Ppk30 mutant larvae displayed deficits in proprioceptive movement and mechanical nociception, which are detected by class IV sensory (mdIV) neurons. The same neurons also detect heat nociception, which was not impaired in ppk30 mutant larvae. Similarly, Ppk30 mutation did not alter gentle touch mechanosensation, a distinct mechanosensation detected by other neurons, suggesting that Ppk30 has a functional role in mechanosensation in mdIV neurons. Consistently, Ppk30 was expressed in class IV neurons, but was not detectable in other larval skin sensory neurons. Mutant phenotypes were rescued by expressing Ppk30 in mdIV neurons. Electrophysiological analysis of heterologous cells expressing Ppk30 did not detect mechanosensitive channel activities, but did detect acid-induced currents. These data show that Ppk30 has a role in mechanosensation, but not in thermosensation, in class IV neurons, and possibly has other functions related to acid response.

Depolarizing Effectors of Bradykinin Signaling in Nociceptor Excitation in Pain Perception.

Inflammation is one of the main causes of pathologic pain. Knowledge of the molecular links between inflammatory signals and pain-mediating neuronal signals is essential for understanding the mechanisms behind pain exacerbation. Some inflammatory mediators directly modulate the excitability of pain-mediating neurons by contacting the receptor molecules expressed in those neurons. For decades, many discoveries have accumulated regarding intraneuronal signals from receptor activation through electrical depolarization for bradykinin, a major inflammatory mediator that is able to both excite and sensitize pain-mediating nociceptor neurons. Here, we focus on the final effectors of depolarization, the neuronal ion channels, whose functionalities are specifically affected by bradykinin stimulation. Particular G-protein coupled signaling cascades specialized for each specific depolarizer ion channels are summarized. Some of these ion channels not only serve as downstream effectors but also play critical roles in relaying specific pain modalities such as thermal or mechanical pain. Accordingly, specific pain phenotypes altered by bradykinin stimulation are also discussed. Some members of the effector ion channels are both activated and sensitized by bradykinin-induced neuronal signaling, while others only sensitized or inhibited, which are also introduced. The present overview of the effect of bradykinin on nociceptor neuronal excitability at the molecular level may contribute to better understanding of an important aspect of inflammatory pain and help future design of further research on the components involved and pain modulating strategies.

Endogenous TRPV4 Expression of a Hybrid Neuronal Cell Line N18D3 and Its Utilization to Find a Novel Synthetic Ligand.

Primary sensory afferent neurons detect environmental and painful stimuli at their peripheral termini. A group of transient receptor potential ion channels (TRPs) are expressed in these neurons and constitute sensor molecules for the stimuli such as thermal, mechanical, and chemical insults. We examined whether a mouse sensory neuronal line, N18D3, shows the sensory TRP expressions and their functionality. In Ca2+ imaging and electrophysiology with these cells, putative TRPV4-mediated responses were observed. TRPV4-specific sensory modalities including sensitivity to a specific agonist, hypotonicity, or an elevated temperature were reproduced in N18D3 cells. Electrophysiological and pharmacological profiles conformed to those from native TRPV4 of primarily cultured neurons. The TRPV4 expression in N18D3 was also confirmed by RT-PCR and Western blot analyses. Thus, N18D3 cells may represent TRPV4-expressing sensory neurons. Further, using this cell lines, we discovered a novel synthetic TRPV4-specific agonist, MLV-0901. These results suggest that N18D3 is a reliable cell line for functional and pharmacological TRPV4 assays. The chemical information from the novel agonist will contribute to TRPV4-targeting drug design.

Atypical sensors for direct and rapid neuronal detection of bacterial pathogens.

Bacterial infection can threaten the normal biological functions of a host, often leading to a disease. Hosts have developed complex immune systems to cope with the danger. Preceding the elimination of pathogens, selective recognition of the non-self invaders is necessary. At the forefront of the body's defenses are the innate immune cells, which are equipped with particular sensor molecules that can detect common exterior patterns of invading pathogens and their secreting toxins as well as with phagocytic machinery. Inflammatory mediators and cytokines released from these innate immune cells and infected tissues can boost the inflammatory cascade and further recruit adaptive immune cells to maximize the elimination and resolution. The nervous system also seems to interact with this process, mostly known to be affected by the inflammatory mediators through the binding of neuronal receptors, consequently activating neural circuits that tune the local and systemic inflammatory states. Recent research has suggested new contact points: direct interactions of sensory neurons with pathogens. Latest findings demonstrated that the sensory neurons not only share pattern recognition mechanisms with innate immune cells, but also utilize endogenous and exogenous electrogenic components for bacterial pathogen detection, by which the electrical firing prompts faster information flow than what could be achieved when the immune system is solely involved. As a result, rapid pain generation and active accommodation of the immune status occur. Here we introduced the sensory neuron-specific detector molecules for directly responding to bacterial pathogens and their signaling mechanisms. We also discussed extended issues that need to be explored in the future.