Activating mGluR8 Attenuates Visceral Hypersensitivity in Neonatal Maternally Separated Rats / 胃肠病学

Activating metabolite glutamate receptor 8 (mGluR8) has anti-hyperpathia effect in central nervous system, however, studies of effects in gastrointestinal tract are rare. Visceral hypersensitivity is one of the pathogenesis factors of irritable bowel syndrome (IBS). Aims: To investigate the effect and potential mechanism of activating mGluR8 on visceral hypersensitivity in neonatal maternally separated (NMS) rats. Methods: Twenty-four male newborn SD rats were randomly divided into normal control (NC) group, NMS group and mGluR8 agonist (S)-3, 4-DCPG group (3, 10 mg/kg). Newborn rats were subjected to 3 hours daily maternal separation on postnatal day 2-14 to establish the NMS model; in (S)-3, 4-DCPG group, (S)-3, 4-DCPG (3 or 10 mg/kg) were administered 1 hour prior to the visceral sensitivity test in NMS rats. Abdominal withdrawal reflex (AWR) score and abdominal electromyography (EMG) activity were used to measure visceral sensitivity. mGluR8 mRNA and protein expressions in colon mucosa were measured by RT-PCR and Western blotting, respectively; TNF-α, IL-1β and IL-6 mRNA expressions in colon mucosa were measured by RT-PCR. The protein expression of myeloperoxidase (MPO) was measured by immunohistochemistry. Results: AWR score and EMG activity in NMS group were significantly higher than those in NC group under different colorectal distension (CRD) pressure. AWR score and EMG activity were significantly decreased in (S)-3, 4-DCPG group. mGluR8 mRNA and protein expressions in NMS group were significantly higher than those in NC group (P<0.05). Compared with NMS group, TNF-α mRNA expression was significantly decreased in 3 mg/kg (S)-3, 4-DCPG group (P<0.05), and MPO protein expression was significantly decreased in 10 mg/kg (S)-3, 4-DCPG group (P<0.05). Conclusions: Activating mGluR8 attenuates visceral hypersensitivity in NMS rats, the mechanism may be related to decrease of pro-inflammatory cytokine TNF-α.

Role of Principal Ionotropic and Metabotropic Receptors in Visceral Pain

Visceral pain is the most common form of pain caused by varied diseases and a major reason for patients to seek medical consultation. It also leads to a significant economic burden due to workdays lost and reduced productivity. Further, long-term use of non-specific medications is also associated with side effects affecting the quality of life. Despite years of extensive research and the availability of several therapeutic options, management of patients with chronic visceral pain is often inadequate, resulting in frustration for both patients and physicians. This is, most likely, because the mechanisms associated with chronic visceral pain are different from those of acute pain. Accumulating evidence from years of research implicates several receptors and ion channels in the induction and maintenance of central and peripheral sensitization during chronic pain states. Understanding the specific role of these receptors will facilitate to capitalize on their unique properties to augment the therapeutic efficacy while at the same time minimizing unwanted side effects. The aim of this review is to provide a concise review of the recent literature that reports on the role of principal ionotropic receptors and metabotropic receptors in the modulation visceral pain. We also include an overview of the possibility of these receptors as potential new targets for the treatment of chronic visceral pain conditions.

Targeting the cannabinoid system for pain relief?

Marijuana has been used to relieve pain for centuries, but its analgesic mechanism has only been understood during the past two decades. It is mainly mediated by its constituents, cannabinoids, through activating central cannabinoid 1 (CB1) receptors, as well as peripheral CB1 and CB2 receptors. CB2-selective agonists have the benefit of lacking CB1 receptor-mediated CNS side effects. Anandamide and 2-arachidonoylglycerol (2-AG) are two intensively studied endogenous lipid ligands of cannabinoid receptors, termed endocannabinoids, which are synthesized on demand and rapidly degraded. Thus, inhibitors of their degradation enzymes, fatty acid amide hydrolase and monoacylglycerol lipase (MAGL), respectively, may be superior to direct cannabinoid receptor ligands as a promising strategy for pain relief. In addition to the antinociceptive properties of exogenous cannabinoids and endocannabinoids, involving their biosynthesis and degradation processes, we also review recent studies that revealed a novel analgesic mechanism, involving 2-AG in the periaqueductal gray (PAG), a midbrain region for initiating descending pain inhibition. It is initiated by Gq-protein-coupled receptor (GqPCR) activation of the phospholipase C (PLC)-diacylglycerol lipase (DAGL) enzymatic cascade, generating 2-AG that produces inhibition of GABAergic transmission (disinhibition) in the PAG, thereby leading to analgesia. This GqPCR-PLC-DAGL-2-AG retrograde disinhibition mechanism in the PAG can be initiated by activating type 5 metabotropic glutamate receptor (mGluR5), muscarinic acetylcholine (M1/M3), and orexin (OX1) receptors. mGluR5-mediated disinhibition can be initiated by glutamate transporter inhibitors, or indirectly by substance P, neurotensin, cholecystokinin, capsaicin, and AM404, the bioactive metabolite of acetaminophen in the brain. The putative role of 2-AG generated after activating the above neurotransmitter receptors in stress-induced analgesia is also discussed.

Glutamate-mediated signaling pathway regulates the invasion and growth of malignant melanoma / 中华皮肤科杂志

Objective To investigate the action mechanism of glutamate-mediated signaling pathway in malignant melanoma. Methods WM451LU melanoma cells in log phase were classified into 6 groups, negative control group treated with PBS (100 μl), MK801 group treated with the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (100 μmol/L), CPCCOEt group treated with non-competitive metabotropic glutamate receptor 1 (mGluR1) antagonist CPCCOEt, MAP2 group transfected with adenovirus vector containing microtubule associated protein 2a (Ad-MAP2a), MK801 + MAP2 group treated with MK801 of 100 μmol/L and transfected with Ad-MAP2a, CPCCOEt + MAP2 group treated with CPCCOEt of 10 μmol/L and transfected with Ad-MAP2a. Western blot was performed to detect the expression of an ionotropic glutamate receptor, i.e., N-methyl-D-aspartate receptor type 2A (NMDAR2A) in WM451LU cells transfected with Ad-MAP2a. Scratch motility assay and cell invasion assay were conducted in vitro to detect the changes in migration and invasion ability of WM451LU cells after treated with Ad-MAP2a, MK-801, CPCCOEt alone or in combination. In vivo study was carried out to compare the inhibitory effect of the above treatments on melanoma. Results Western blot revealed a decrease in the expression of NMDAR2A in WM451LU cells after transfected with Ad-MAP2a. The scratch motility assay showed that the number of migrating cells per high power field was 117.04 ± 2.76 in MAP2 group,107.64 ± 6.50 in MK801 group,97.36 ± 4.79 in CPCCOEt group, 43.28 ± 3.02 in MK801 + MAP2 group,30.76 ± 3.97 in CPCCOEt + MAP2 group,significantly different from that in the negative control group (152.3 ± 5.75,all P ＜ 0.01 ). Cell invasion assay demonstrated that the average number of invading cells per high power field in the negative control was significantly higher than that in MAP2 group, MK801 group, CPCCOEt group, MK801+MAP2 group and CPCCOEt + MAP2 group (170.43 ±8.72 vs. 98.26 ± 3.84, 97.22 ± 5.54, 112.23 ± 7.21, 42.89 ± 5.06, 58.25 ± 6.68, P ＜ 0.05, 0.05, 0.05, 0.01and 0.01, respectively).A significant decrease was observed in the average volume of experimental melanoma in mice of MAP2 group, MK801 group, MK801 + MAP2 group, CPCCOEt group and CPCCOEt + MAP2 group compared with the negative control group (224.02 ± 46.19 mm3, 160.33 ± 33.91 mm3, 91.49 ± 21.48 mm3,202.30 ± 52.37 mm3, 111.13 ± 69.81 mm3 vs. 342.70 ± 60.92 mm3, all P ＜ 0.01 ). Conclusions To block the glutamate signaling pathway in vitro can inhibit the invasion and migration of melanoma cells, and to block the pathway in vivo can inhibit the growth of malignant melanoma and alter the morphology of melanoma cells.

Functional metabotropic glutamate receptor 1 and 5 expression in podocytes / 中华肾脏病杂志

Objective To investigate the expression of metabotropic glutamate receptor (mGluR) in murine podocytes.Methods Conditional immortalized podocytes were used in the research.RT-PCR was used to estimate the mRNA expression.Western blotting,immunofluorescence staining and immunoelectron microscopy were employed to determine the protein production.EIA,EMSA and Western blotting were used to examine the cAMP generation and cAMP response element-binding protein (CREB) activation.Intracellular calcium was investigated using confocal microscopy.Results mGluR1 and 5 mRNA and protein were expressed in murine brain and podocytes.In glomeruli,most of mGluR1 expression located in podocytes and was expressed in the submembrane space of the podocytes.Podocytes treated with (S)-3,5-dihydroxyphenylglycine (DHPG,an agonist for mGluR1/5) rapidly generated cAMP and activated CREB.(RS)-1-Aminoindan-1,5-dicarboxylic acid (AIDA,a selective antagonist of mGluR1/5) and SQ22536 (an adenylate cyclase inhibitor),but not 2-aminoethoxydiphenyl borate (2-APB an antagonist of canonical transient receptor potential) blocked DHPG-induced cAMP generation and CREB activation.Following DHPG treatment,intracellular calcium level rose and was prevented by pre-treatment with AIDA and 2-APB.DHPG-induced calcium influx was also prevented by incubation with calcium-free medium.Conclusion Podocytes express functional mGluR1 and mGluR5.