The protective action of ketanserin against lipopolysaccharide-induced shock in mice is mediated by inhibiting inducible NO synthase expression via the MEK/ERK pathway

Serotonin Receptors in Myocardial Infarction: Friend or Foe?

Acute myocardial infarction (AMI) is one of the leading causes of death worldwide and treatment costs pose a major burden on the global health care system. Despite the variety of treatment options, individual recovery can be still poor and the mortality rate, especially in the first few years after the event, remains high. Therefore, intense research is currently focused on identifying novel target molecules to improve the outcome following AMI. One of the potentially interesting targets is the serotonergic system (5-HT system), not at least because of its connection to mental disorders. It is known that patients suffering from AMI have an increased risk of developing depression and vice versa. This implicates that the 5-HT system can be affected in response to AMI and might thus represent a target structure for patients' treatment. This review aims to highlight the importance of the 5-HT system after AMI by describing the role of individual serotonin receptors (5-HTR) in the regulation of physiological and pathophysiological responses. It particularly focuses on the signaling pathways of the serotonin receptors 1, 2, 4, and 7, which are expressed in the cardiovascular system, during disease onset, and the following remodeling process. This overview also emphasizes the importance of the 5-HT system in AMI etiology and highlights 5-HTRs as potential treatment targets.

Psilocybin and Eugenol Reduce Inflammation in Human 3D EpiIntestinal Tissue

Inflammation plays a pivotal role in the development and progression of inflammatory bowel disease (IBD), by contributing to tissue damage and exacerbating the immune response. The investigation of serotonin receptor 2A (5-HT2A) ligands and transient receptor potential (TRP) channel ligands is of significant interest due to their potential to modulate key inflammatory pathways, mitigate the pathological effects of inflammation, and offer new avenues for therapeutic interventions in IBD. This study investigates the anti-inflammatory effects of 5-HT2A ligands, including psilocybin, 4-AcO-DMT, and ketanserin, in combination with TRP channel ligands, including capsaicin, curcumin, and eugenol, on the inflammatory response induced by tumor necrosis factor (TNF)-α and interferon (IFN)-γ in human 3D EpiIntestinal tissue. Enzyme-linked immunosorbent assay was used to assess the expression of pro-inflammatory markers TNF-α, IFN-γ, IL-6, IL-8, MCP-1, and GM-CSF. Our results show that psilocybin, 4-AcO-DMT, and eugenol significantly reduce TNF-α and IFN-γ levels, while capsaicin and curcumin decrease these markers to a lesser extent. Psilocybin effectively lowers IL-6 and IL-8 levels, but curcumin, capsaicin, and 4-AcO-DMT have limited effects on these markers. In addition, psilocybin can significantly decrease MCP-1 and GM-CSF levels. While ketanserin lowers IL-6 and GM-CSF levels, there are no effects seen on TNF-α, IFN-γ, IL-8, or MCP-1. Although synergistic effects between 5-HT2A and TRP channel ligands are minimal in this study, the results provide further evidence of the anti-inflammatory effects of psilocybin and eugenol. Further research is needed to understand the mechanisms of action and the feasibility of using these compounds as anti-inflammatory therapies for conditions like IBD.

Anti-Inflammatory Effects of Serotonin Receptor and Transient Receptor Potential Channel Ligands in Human Small Intestinal Epithelial Cells

Intestinal inflammation and dysbiosis can lead to inflammatory bowel diseases (IBD) and systemic inflammation, affecting multiple organs. Developing novel anti-inflammatory therapeutics is crucial for preventing IBD progression. Serotonin receptor type 2A (5-HT2A) ligands, including psilocybin (Psi), 4-Acetoxy-N,N-dimethyltryptamine (4-AcO-DMT), and ketanserin (Ket), along with transient receptor potential (TRP) channel ligands like capsaicin (Cap), curcumin (Cur), and eugenol (Eug), show promise as anti-inflammatory agents. In this study, we investigated the cytotoxic and anti-inflammatory effects of Psi, 4-AcO-DMT, Ket, Cap, Cur, and Eug on human small intestinal epithelial cells (HSEIC). HSEIC were exposed to tumor necrosis factor (TNF)-α and interferon (IFN)-γ for 24 h to induce an inflammatory response, followed by treatment with each compound at varying doses (0-800 μM) for 24 to 96 h. The cytotoxicity was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and protein expression by Western blot (WB) analysis. As single treatments, Psi (40 μM), Cur (0.5 μM), and Eug (50 μM) significantly reduced COX-2 levels without cytotoxic effects. When combined, Psi (40 μM) and Cur (0.5 μM) exhibited synergy, resulting in a substantial decrease in COX-2 protein levels (-28× fold change), although the reduction in IL-6 was less pronounced (-1.6× fold change). Psi (20 μM) and Eug (25 μM) demonstrated the most favorable outcomes, with significant decreases in COX-2 (-19× fold change) and IL-6 (-10× fold change) protein levels. Moreover, the combination of Psi and Eug did not induce cytotoxic effects in vitro at any tested doses. This study is the first to explore the anti-inflammatory potential of psilocybin and 4-AcO-DMT in the intestines while highlighting the potential for synergy between the 5-HT2A and TRP channel ligands, specifically Psi and Eug, in alleviating the TNF-α/IFN-γ-induced inflammatory response in HSEIC. Further investigations should evaluate if the Psi and Eug combination has the therapeutic potential to treat IBD in vivo.

PD184352 exerts anti-inflammatory and antioxidant effects by promoting activation of the Nrf2/HO-1 axis

Osteoarthritis (OA) is a disabling joint disease characterized by cartilage degeneration. Reactive oxygen species (ROS)-induced oxidative stress is an important cause of early chondrocyte death. For this reason, we investigated PD184352, a small molecule inhibitor with potential anti-inflammatory and antioxidant activity. We evaluated the protective effect of PD184352 against destabilized medial meniscus (DMM)-induced OA in mice. The knee joints of the PD184352-treated group had higher Nrf2 expression and milder cartilage damage. Moreover, in in vitro experiments, PD184352 suppressed IL-1β-induced NO, iNOS, PGE2 production, and attenuated pyroptosis. PD184352 treatment promoted antioxidant protein expression and reduced the accumulation of ROS by activating the Nrf2/HO-1 axis. Finally, the anti-inflammatory and antioxidant effects of PD184352 were shown to be partially dependent on Nrf2 activation. Our study reveals the potential role of PD184352 as an antioxidant and provides a new strategy for OA treatment.

Influence of 5-HT2A receptor function on anxiety-like behavior induced by a combination treatment with doxorubicin and cyclophosphamide in rats

Anxiety-like behavior induced by a combination of doxorubicin and cyclophosphamide may be mediated by serotonin (5-HT)_2A receptor hyperactivity. The anxiolytic effects of fluoxetine may be inhibited by this combination. The present study examined the mechanisms underlying anxiety-like behavior induced by the combination doxorubicin and cyclophosphamide in rats. Anxiety-like behavior was induced during a light-dark test by the doxorubicin and cyclophosphamide treatment (once a week for 2 weeks). 5-HT_2A receptor and 5-HT_2A receptor-mediated extracellular signal-related kinase (ERK)1/2 levels were measured using Western blotting. 5-HT reuptake activity in fluoxetine-treated rats was also examined using microdialysis. ( ±)-1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane, a 5-HT_2A receptor agonist, induced anxiety-like behavior. The fluoxetine treatment increased extracellular 5-HT concentrations in the hippocampus of vehicle- and doxorubicin and cyclophosphamide-treated rats. 5-HT transporter levels in the hippocampus were not affected by chemotherapy. The doxorubicin and cyclophosphamide treatment did not alter 5-HT_2A receptor levels in the frontal cortex. However, chemotherapy increased 5-HT_2A receptor-mediated ERK1/2 phosphorylation levels significantly more than the vehicle treatment. The present results suggest that anxiety-like behavior induced by the combination of doxorubicin and cyclophosphamide is mediated by 5-HT_2A receptor hyperactivity without an increase in 5-HT_2A receptor levels in rats.

Cannabidiol and the corticoraphe circuit in post-traumatic stress disorder

Post-Traumatic Stress Disorder (PTSD), characterized by re-experiencing, avoidance, negative affect, and impaired memory processing, may develop after traumatic events. PTSD is complicated by impaired plasticity and medial prefrontal cortex (mPFC) activity, hyperactivity of the amygdala, and impaired fear extinction. Cannabidiol (CBD) is a promising candidate for treatment due to its multimodal action that enhances plasticity and calms hyperexcitability. CBD’s mechanism in the mPFC of PTSD patients has been explored extensively, but literature on the mechanism in the dorsal raphe nucleus (DRN) is lacking. Following the PRISMA guidelines, we examined current literature regarding CBD in PTSD and overlapping symptomologies to propose a mechanism by which CBD treats PTSD via corticoraphe circuit. Acute CBD inhibits excess 5-HT release from DRN to amygdala and releases anandamide (AEA) onto amygdala inputs. By first reducing amygdala and DRN hyperactivity, CBD begins to ameliorate activity disparity between mPFC and amygdala. Chronic CBD recruits the mPFC, creating harmonious corticoraphe signaling. DRN releases enough 5-HT to ameliorate mPFC hypoactivity, while the mPFC continuously excites DRN 5-HT neurons via glutamate. Meanwhile, AEA regulates corticoraphe activity to stabilize signaling. AEA prevents DRN GABAergic interneurons from inhibiting 5-HT release so the DRN can assist the mPFC in overcoming its hypoactivity. DRN-mediated restoration of mPFC activity underlies CBD’s mechanism on fear extinction and learning of stress coping.

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CBD reduces PTSD symptoms via the DRN and corticoraphe circuit.

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Acute effects of CBD reduce DRN-amygdala excitatory signaling to lessen the activity disparity between amygdala and mPFC.

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Chronic CBD officially resolves mPFC hypoactivity by facilitating 5-HT release from DRN to mPFC.

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CBD-facilitated endocannabinoid signaling stabilizes DRN activity and restores mPFC inhibitory control.

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Chronically administered CBD acts via the corticoraphe circuit to favor fear extinction over fear memory reconsolidation.

Dehydroepiandrosterone alleviates intestinal inflammatory damage via GPR30-mediated Nrf2 activation and NLRP3 inflammasome inhibition in colitis mice

Dehydroepiandrosterone (DHEA) is a popular dietary supplement that has anti-inflammatory, anti-oxidant and immune-regulating role; meanwhile, it also can effective in the protection of inflammation diseases such as inflammatory bowel disease (IBD), but the underlying mechanisms remain elusive. Here, we demonstrated that DHEA inhibits excessive inflammation response and enhances gut barrier function via activating the G protein-coupled receptor 30 (GPR30). GPR30-induced the ERK phosphorylation and p62 accumulation led to the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, which subsequently inhibited the reactive oxygen species (ROS) overproduction and finally alleviated the intestinal barrier dysfunction. Furthermore, DHEA blocked the p38-induced NLRP3 inflammasome activation in both LPS-stimulated colon epithelial cells and macrophages. In addition, in vivo results showed that DHEA and GPR30 agonist G1 attenuated inflammatory responses and gut barrier dysfunction in colitis mice, while the GPR30 specific inhibitor G15 abrogated these beneficial effects of DHEA. Cumulatively, our study unveiled that DHEA is an effective anti-inflammatory agent and suggested that GPR30 could as a potential target for the treatment of IBD.

Dehydroepiandrosterone attenuates LPS-induced inflammatory responses via activation of Nrf2 in RAW264.7 macrophages

Dehydroepiandrosterone (DHEA) is the major steroid hormone in humans and animals, which can regulate the body's inflammatory responses. However, the detail mechanism of this beneficial function is still poorly understood. The present study aimed to explore the anti-inflammation effect of DHEA and its underlying molecular mechanism in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. The findings showed that DHEA significantly inhibited the inflammation-related mediators production and pro-inflammatory cytokines expression level. Further research found that DHEA obviously blocked the LPS-stimulated PI3K/AKT, MAPK and NF-κB activation in RAW 264.7 cells. Meanwhile, DHEA enhanced the autophagy-dependent Keap1 protein degradation, subsequently activated the Nrf2 pathway to alleviate the redox imbalance and inflammatory responses. In conclusion, our data demonstrated that DHEA suppresses inflammatory responses through the activation of Nrf2 and inhibition of NF-κB in LPS-stimulated macrophages.

Soybean protein-derived peptides inhibit inflammation in LPS-induced RAW264.7 macrophages via the suppression of TLR4-mediated MAPK-JNK and NF-kappa B activation

This study aimed to determine the effect of soybean protein-derived peptides (SBP) on the inhibition of lipopolysaccharide (LPS)-induced RAW264.7 cell inflammation. The mRNA of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β), Lymphocyte Antigen 96 (LY96), and nuclear factor-κB (NF-κB) were detected with RT-qPCR. The concentrations of cytokines (TNF-α, IL-6, and IL-1β) secreted were detected by ELISA Kit. The results indicated that SBP inhibited the inflammatory stress induced by LPS in RAW264.7 cells. Western blot analysis was used to examine this anti-inflammatory molecular mechanism. The findings showed that SBP impeded the increase of toll-like receptor 4 activity by restricting LY96, while also inhibiting the mitogen-activated protein kinase-c-Jun N-terminal kinase pathway in cells, as well as LPS-induced NF-κB activation caused by the degradation of nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (IκBα). Consequently, the release of pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) was inhibited, preventing LPS-induced inflammation of RAW 264.7 cells. Therefore, this research highlighted the potential application of SBP in the development of anti-inflammatory foods that prevented inflammatory-immune diseases. PRACTICAL APPLICATIONS: Inflammation is the root cause of almost all pathology and is related to many human diseases, including arthritis, obesity, cancer and atherosclerosis. Therefore, the development of products that can regulate and intervene inflammation has a broad application prospect. Soybean protein and soybean peptide have many functional properties, including immunoregulation, anti-inflammatory, anti-oxidation and so on. However, there are still some shortcomings in the development of soy protein supplements, such as solubility and absorption. Compared with soybean protein, derived peptide is easy to digest, and has high solubility. As a good nutritional supplement, the nutritional support of soybean protein-derived peptides may help to reduce inflammation and improve the level of cytokines combined with drugs.

MEK2 Negatively Regulates Lipopolysaccharide-Mediated IL-1β Production through HIF-1α Expression

LPS-activated macrophages require metabolic reprogramming and glucose uptake mediated by hypoxia-inducible factor (HIF)-1 α and glucose transporter 1 (Glut1) expression for proinflammatory cytokine production, especially IL-1β. This process is tightly regulated through activation of MAPK kinases, including the MEK/ERK pathway as well as several transcription factors including HIF-1α. Although MAPK kinase (MEK) 2 deficiency had no significant effect on NO, TNF-α, or IL-12 production in response to LPS challenge, MEK2-deficient murine bone marrow-derived macrophages (BMDMs) exhibited lower IL-10 production. Importantly, MEK2-deficient BMDMs exhibited a preserved ERK1/2 phosphorylation, higher HIF-1α and Glut1 levels, and substantially increased IL-1β as well as IL-6 production in response to LPS stimulation. Knockdown of HIF-1α expression via short interference RNA decreased the level of HIF-1α expression in MEK2-deficient BMDMs and decreased IL-1β production in response to LPS treatment. Furthermore, we performed gain of function experiments by overexpressing MEK2 protein in RAW264.7 cells. LPS stimulation of MEK2 overexpressed in RAW264.7 cells led to a marked decreased IL-1β production. Finally, we investigated the role of Mek1 and Mek2 double and triple mutation on ERK phosphorylation, HIF-1α expression, and IL-1β production. We found that MEK2 is the major kinase, which inversely proportionally regulates HIF-1α and IL-1β expression independent of ERK activation. Our findings demonstrate a novel regulatory function for MEK2 in response to TLR4 activation in IL-1β production through modulating HIF-1α expression.

Role of Oxidative Stress and Mitochondrial Dysfunction in Sepsis and Potential Therapies

Sepsis is one of the most important causes of death in intensive care units. Despite the fact that sepsis pathogenesis remains obscure, there is increasing evidence that oxidants and antioxidants play a key role. The imbalance of the abovementioned substances in favor of oxidants is called oxidative stress, and it contributes to sepsis process. The most important consequences are vascular permeability impairment, decreased cardiac performance, and mitochondrial malfunction leading to impaired respiration. Nitric oxide is perhaps the most important and well-studied oxidant. Selenium, vitamin C, and 3N-acetylcysteine among others are potential therapies for the restoration of redox balance in sepsis. Results from recent studies are promising, but there is a need for more human studies in a clinical setting for safety and efficiency evaluation.

Activation of Cannabinoid Receptor 2 Ameliorates DSS-Induced Colitis through Inhibiting NLRP3 Inflammasome in Macrophages

Activation of cannabinoid receptor 2 (CB2R) ameliorates inflammation, but the underlying mechanism remains unclear. In the present study, we examined whether activation of CB2R could suppress the nucleotide-binding domain and leucine-rich repeat protein 3 (NLRP3) inflammasome. In peritoneal macrophages isolated from C57BL/6 mice, LPS/DSS challenge for 24 h increased the expression of the components of NLRP3 inflammasome NLRP3, Casp-1 p20/Casp-1 p45 ratio, proIL-1β and IL-1β and also enhanced autophagy (LC3-II/LC3-I ratio, Beclin-1 and SQSTM1). Pretreatment of peritoneal macrophages with HU 308, a selective CB2R agonist, attenuated LPS/DSS-induced NLRP3 inflammasome activation, but further enhanced autophagy. In comparison with wild-type (WT) control, peritoneal macrophages from CB2R knockout (KO) mice had more robust NLRP3 inflammasome activation and attenuated autophagy upon LPS/DSS challenge. Knockdown autophagy-related gene 5 (Atg5) with a siRNA in peritoneal macrophages attenuated the inhibitory effects of HU 308 on LPS/DSS-induced NLRP3 inflammasome activation in vitro. In vivo, HU308 treatment attenuated DSS-induced colitis mice associated with reduced colon inflammation and inhibited NLRP3 inflammasome activation in wild-type mice. In CB2R KO mice, DSS-induced inflammation and NLRP3 inflammasome activation were more pronounced than those in WT control. Finally, we demonstrated that AMPK-mTOR-P70S6K signaling pathway was involved in this CB2R-mediated process. We conclude that activation of CB2R ameliorates DSS-induced colitis through enhancing autophagy that may inhibit NLRP3 inflammasome activation in macrophages.

Effects of ketanserin on experimental colitis in mice and macrophage function

Ketanserin is a selective 5-hydroxytryptamine (serotonin)-2A receptor (5-HT_2AR) antagonist. Studies have suggested that ketanserin exerts anti-inflammatory effects independent of the baroreflex; however, the mechanisms involved remain unclear. Thus, in the present study, we aimed to evaluate the effects of ketanserin in colitis and the possible underlying mechanisms. The expression of 5-HT_2AR was assessed in the colon tissues of patients with inflammatory bowel disease (IBD) and in mice with dextran sodium sulfate (DSS)-induced colitis. The therapeutic potential of ketanserin was investigated in the mice with colitis. In the colon tissue samples from the patients with IBD, a high expression level of 5-HT_2AR was observed. Treatment with ketanserin attenuated the progression of experimental colitis in the mice, as indicated by body weight assessment, colon length, histological scores and cytokine release. The colonic macrophages from the ketanserin-treated mice with colitis exhibited a decreased production of inflammatory cytokines, with M2 polarization and impaired migration. The knockdown of 5-HT_2AR using siRNA partly abolished the inhibitory effects of ketanserin on the release of pro-inflammatory cytokines in bone marrow derived-macrophages (BMDMs), thus demonstrating that the inhibitory effects of ketanserin on the production of inflammatory cytokines are partly dependent on 5-HT_2AR. Ketanserin also inhibited the activation of nuclear factor-κB (NF-κB) in BMDMs. In conclusion, the findings of the present study demonstrate that ketanserin alleviates colitis. Its anti-inflammatory effects may be due to the promotion of the anti-inflammatory function of macrophages through 5-HT_2AR/NF-κB.

Bakkenolide-IIIa Protects Against Cerebral Damage Via Inhibiting NF-κB Activation

AIMS

This study was designed to examine the neuroprotective effects of bakkenolide-IIIa, a major novel compound extracted from the rhizome of P. trichinous.

METHODS

Transient focal cerebral damage model in rats and oxygen-glucose deprivation (OGD) in cultured hippocampal neurons were performed. The amount of apoptotic neurons was determined using TUNEL assay. The expressions of Bcl-2, Bax, Akt, ERK1/2, IKKβ, IκBα were measured using Western blot. The nuclear translocation and activation of NF-κB was measured using a fluorescence microscope and electrophoretic mobility shift assay (EMSA).

RESULTS

Bakkenolide-IIIa (4, 8, 16 mg/kg; i.g.) was administered immediately after reperfusion could reduce the brain infarct volume, and the neurological deficit, as well as a high dose of bakkenolide-IIIa, increases the 72 h survival rate in cerebrally damaged rats. In vitro data demonstrated that bakkenolide-IIIa could increase cell viability and decrease the amount of apoptotic cells in cultured primary hippocampal neurons exposed to OGD. Bakkenolide-IIIa also dose-dependently increased the ratio of Bcl-2 to Bax. These results indicated that inhibition of apoptosis partly mediated the neuroprotection of bakkenolide-IIIa. Furthermore, bakkenolide-IIIa inhibited the phosphorylation of Akt, ERK1/2, IKKβ, IκBα, and p65 in cultured hippocampal neurons exposed to OGD. Bakkenolide-IIIa not only inhibited the nuclear translocation of NF-κB in cultured neurons exposed to OGD, but also inhibited the activation of NF-κB in peri-infarct area in cerebrally damaged rats.

CONCLUSION

Collectively, our findings indicated that bakkenolide-IIIa protects against cerebral damage by inhibiting AKT and ERK1/2 activation and inactivated NF-κB signaling.

Punicalagin inhibits inflammation in LPS-induced RAW264.7 macrophages via the suppression of TLR4-mediated MAPKs and NF-κB activation

Punicalagin (2,3,hexahydroxydiphenoyl-gallagyl-D-glucose and referred to as PUN) is a bioactive ellagitannin isolated from pomegranate, which is widely used for the treatment of inflammatory bowel disease (IBD), diarrhea, and ulcers in Chinese traditional medicine. In this study, we detected the anti-inflammation potentials of PUN in lipopolysaccharide (LPS)-induced macrophages and tried to uncover the underlying mechanism. Results demonstrated that PUN (25, 50, or 100 μM) treatment could significantly decrease the LPS-induced production of nitric oxide), prostaglandin E2 (PGE2), interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α in RAW264.7 cells. Molecular research showed that PUN inhibited the activation of upstream mediator nuclear factor-κB by suppressing the phosphorylation of IκBα and p65. Results also indicated that PUN could suppress the phosphorylation of mitogen-activated protein kinase including p38, c-Jun N-terminal kinase, and extracellular signal-regulated kinase. In conclusion, we observed that PUN could inhibit LPS-induced inflammation, and it may be a potential choice for the treatment of inflammation diseases.

The role of serotonin and its receptors in activation of immune responses and inflammation

Serotonin or 5-hydroxytryptamine (5-HT) is a neurotransmitter and hormone that contributes to the regulation of various physiological functions by its actions in the central nervous system (CNS) and in the respective organ systems. Peripheral 5-HT is predominantly produced by enterochromaffin (EC) cells of the gastrointestinal (GI) tract. These gut-resident cells produce much more 5-HT than all neuronal and other sources combined, establishing EC cells as the main source of this biogenic amine in the human body. Peripheral 5-HT is also a potent immune modulator and affects various immune cells through its receptors and via the recently identified process of serotonylation. Alterations in 5-HT signalling have been described in inflammatory conditions of the gut, such as inflammatory bowel disease. The association between 5-HT and inflammation, however, is not limited to the gut, as changes in 5-HT levels have also been reported in patients with allergic airway inflammation and rheumatoid arthritis. Based on searches for terms such as '5-HT', 'EC cell', 'immune cells' and 'inflammation' in pubmed.gov as well as by utilizing pertinent reviews, the current review aims to provide an update on the role of 5-HT in biological functions with a particular focus on immune activation and inflammation.

Anandamide rescues retinal barrier properties in Müller glia through nitric oxide regulation

The blood retinal barrier (BRB) can mitigate deleterious immune response. Dysfunction at the BRB can affect disease progression. Under inflammatory conditions Müller glia produce increased pro-inflammatory factors, like nitric oxide (NO). In this study we describe molecular events at the Müller glia during inflammation which could affect inner BRB properties. Griess assay and 4,5-diaminofluorescein diacetate (DAF-2DA) time-lapse fluorescence were used to measure NO production. Western blot was used to analyze the expression of inducible nitric oxide synthase (iNOS) and mitogen-activated protein kinases (MAPK) components. Lucifer Yellow was used to measure permeability. Griess assay and DAF-2DA time-lapse fluorescence images revealed that lipopolysaccharide (LPS) induced inflammation and increased NO production. In parallel, changes were observed in tight junction proteins, zona occludens 1 (ZO-1), connexin 43 (Cx43), and permeability. This was mediated through activation of iNOS and mitogen-activated protein kinase phosphatase-1 (MKP-1), implicated in immune response. Endocannabinoids can exert a protective and anti-inflammatory effect. Exogenous arachidonoyl ethanolamide (AEA) inhibited NO generation and also abolished LPS-induced increase in permeability. Our work suggests that subtle changes in Müller glia function, which act as part of the BRB, could contribute to retinal health. AEA which can reduce inflammatory cytotoxicity has potential as treatment in several ocular manifestations where the integrity of the BRB is crucial.