Yuan Guo

All-trans retinoic acid down-regulates inflammatory responses by shifting the Treg/Th17 profile in human ulcerative and murine colitis

IBD is characterized by uncontrolled immune responses in inflamed mucosa, with dominance of IL‐17‐producing cells and deficiency of Treg cells. The aim of this study was to explore the effect and mechanisms of RA, the ligand of RARα, on immune responses in human and murine colitis. Colonic biopsies from patients with UC were cultured and treated with RA as the agonist of RARα or LE135 as the antagonist of RARα. Expressions of IL‐17 and FOXP3 were detected by immunohistochemistry. Murine colitis was induced by intrarectal administration with TNBS at Day 1. Mice were then i.p.‐treated with RA or LE135 daily for 7 days. Cytokine levels in the cultures of mouse LPMCs were measured. Expressions of FOXP3 and IL‐17 in colon tissues or MLN were detected by immunohistological analysis. Body weight and colon inflammation were evaluated. RA treatment up‐regulated FOXP3 expression and down‐regulated IL‐17 expression in colon biopsies of patients and in colon tissues and MLN of mice with colitis compared with controls. LPMCs from RA‐treated mice produced lower levels of proinflammatory cytokines (TNF‐α, IL‐1β, IL‐17) but more regulatory cytokines (IL‐10, TGF‐β) compared with that of untreated mice. LE135 showed the opposite effect of RA. Furthermore, RA ameliorated TNBS‐induced colitis in a dose‐dependent manner, as seen by improved body weight and colon inflammation. RA down‐regulates colon inflammatory responses in patients with IBD in vitro and in murine colitis in vivo, representing a potential therapeutic approach in IBD treatment.

Modulation of inflammatory response via α2-adrenoceptor blockade in acute murine colitis

Inflammatory bowel disease (IBD) is characterized by heavy production of proinflammatory cytokines such as tumour necrosis factor (TNF)‐α and interleukin (IL)‐1β. Interactions of the autonomic nervous system with local immune cells play an important role in the development of IBD, and the balance of autonomic nerve function is broken in IBD patients with sympathetic overactivity. However, the function of catecholamines in the progress of colitis is unclear. In this study, we examined the role of catecholamines via α2‐adrenoreceptor in acute murine colitis. The expression of tyrosine hydroxylase (TH) and dopamine b‐hydroxylase (DBH), two rate‐limiting enzymes in catecholamine synthesis, was detected by immunohistochemistry in murine colitis. Murine colitis was induced by dextran sodium sulphate or trinitrobenzene sulphonic acid (TNBS), and the mice were administered RX821002 or UK14304, α2‐adrenoceptor antagonists or agonists. Colitis was evaluated by clinical symptoms, myeloperoxidase assay, TNF‐α and IL‐1β production and histology. Lamina propria mononuclear cells (LPMCs) from mice with TNBS colitis were cultured in the absence or presence of RX821002 or UK14304, and stimulated further by lipopolysaccharide. TH and DBH are induced in LPMCs of inflamed colon, the evidence of catecholamine synthesis during the process of colitis. RX821002 down‐regulates the production of proinflammatory cytokines from LPMCs, while UK14304 leads to exacerbation of colitis. Together, our data show a critical role of catecholamines via α2‐adrenoreceptors in the progress of acute colitis, and suggest that use of the α2‐adrenoceptor antagonist represents a novel therapeutic approach for the management of colitis.

The Effect of the Cholinergic Anti-Inflammatory Pathway on Experimental Colitis

Inflammatory bowel diseases (IBD) are characterized by proinflammatory cytokines, tissue damage and loss of neuron in inflamed mucosa, which implies the cholinergic anti‐inflammatory pathway may be destroyed during the process of inflammatory response. In the study, we identified the effect of cholinergic agonist as anabaseine (AN) and nicotinic receptor antagonist as chlorisondamine diiodide (CHD) on trinitrobenzene sulfonic acid (TNBS)‐induced colitis, to investigate the potential therapeutic effect of the cholinergic anti‐inflammatory pathway on IBD. Experimental colitis was induced by TNBS at day 1, 10 μg AN or 1.5 μg CHD was injected i.p. to mouse right after the induction of colitis, and repeated on interval day till the mice were sacrificed at day 8. Colonic inflammation was examined by histological analysis, myeloperoxidase (MPO) activity, and the production of tumour necrosis factor (TNF)‐α in tissue. Lamina propria mononuclear cells (LPMC) were isolated, and NF‐κB activation was detected by western blot. The mice with colitis treated by AN showed less tissue damage, less MPO activity, less TNF‐α production in colon, and inhibited NF‐κB activation in LPMC, compared with those mice with colitis untreated, whereas the mice with colitis treated by CHD showed the worst tissue damage, the highest MPO activity, the highest TNF‐α level, and enlarged NF‐κB activation in LPMC. Agonist of the cholinergic anti‐inflammatory pathway inhibits colonic inflammatory response by downregulating the production of TNF‐α, and inhibiting NF‐κB activation, which suggests that modulating the cholinergic anti‐inflammatory pathway may be a new potential management for IBD.

All-Trans Retinoic Acid Ameliorates Trinitrobenzene Sulfonic Acid-Induced Colitis by Shifting Th1 to Th2 Profile

Inflammatory bowel disease is characterized with uncontrolled immune response in inflamed mucosa, with dominance of Th1 cells. Recently, all-trans retinoic acid has been shown that can lead T-cell response by suppressing Th17 development via retinoic acid receptor (RAR), but it is still unknown whether all-trans retinoic acid can modulate Th1 response of inflammatory bowel disease. In the experiment, we investigated the effect of all-trans retinoic acid on trinitrobenzene sulfonic acid (TNBS)-induced murine colitis, and the possible mechanism. Mice were intraperitoneally treated daily with all-trans retinoic acid (the agonist of RAR-alpha) or LE135 (the antagonist of RAR-alpha) or medium, and sacrificed 6 days later. Colon was collected for histological analysis and myeloperoxidase (MPO) activity measurement. Lamina propria mononuclear cells (LPMCs) were isolated, cultured, and assayed for the expressions of T-bet and GATA-3 by the use of Western blot and for cytokine levels by the use of ELISA. All-trans retinoic acid treatment inhibited inflammatory responses as shown by lower histological inflammatory scores and MPO activity, compared with LE135 and medium groups. Furthermore, in LPMCs culture supernatants, the levels of Th1 cytokines (INF-gamma, IL-12, and TNF-alpha) were decreased while those of Th2 cytokines (IL-4 and IL-10) were increased significantly in all-trans retinoic acid-treated mice. In addition, T-bet expression in LPMCs was inhibited and GATA-3 expression was up-regulated in all-trans retinoic acidtreated mice. On the contrary, LE135 showed the reverse effects in colon inflammation and cytokine profile. By shifting Th1 to Th2 profile in inflamed mucosa, all-trans retinoic acid down-regulates inflammatory response and ameliorates acute TNBS-induced colitis, which suggests the ligand of RAR-alpha-based pharmaceutical strategies for managing inflammatory bowel disease.

AMPK Inhibition Blocks ROS-NFκB Signaling and Attenuates Endotoxemia-Induced Liver Injury

Background AMP-activated protein kinase (AMPK) is an important enzyme in regulation of cellular energy homeostasis. We have previously shown that AMPK activation by 5-aminoimidazole-4-carboxamide (AICAR) results in suppression of immune responses, indicating the pivotal role of AMPK in immune regulation. However, the cellular mechanism underpinning AMPK inhibition on immune response remains largely to be elucidated. The study aimed to investigate the effects of AMPK inhibition on reactive oxygen species (ROS)-nuclear factor κB (NFκB) signaling and endotoxemia-induced liver injury. Methodology/Principal Findings RAW 264.7 cells were pretreated with AMPK activator or inhibitor, followed by LPS challenge. In addition, LPS was injected intraperitoneally into mice to induce systemic inflammation. The parameters of liver injury and immune responses were determined, and survival of mice was monitored respectively. LPS challenge in RAW 264.7 cells resulted in AMPK activation which was then inhibited by compound C treatment. Both AMPK activation by AICAR or inhibition by compound C diminished LPS-induced ROS generation, inhibited phosphorylation of IKK, IκB, and NFκB p65, and consequently, decreased TNF production of RAW 264.7 cells. AICAR or compound C treatment decreased ALT, AST, and TNF levels in serum, reduced CD68 expression and MPO activity in liver tissue of mice with endotoxemia. Moreover, AICAR or compound C treatment improved survival of endotoxemic mice. Conclusions AICAR or compound C treatment attenuates LPS-induced ROS-NFκB signaling, immune responses and liver injury. Strategies to activate or inhibit AMPK signaling may provide alternatives to the current clinical approaches to inhibit immune responses of endotoxemia.

All-trans retinoic acid attenuates experimental colitis through inhibition of NF-κB signaling

Inflammatory bowel disease (IBD) is characterized by excessive innate immune cell activation, which is responsible for tissue damage and induction of adaptive immune responses. All-trans retinoic acid (ATRA), the ligand of retinoic acid receptors (RAR), has been previously shown to regulate adaptive immune responses and restore Th17/Treg balance, while its role in regulation of innate immune cell function such as macrophages remains to be elucidated. The study was performed to explore the effect of ATRA on regulation of innate immune responses during dextran sulfate sodium (DSS) induced murine colitis. The mice with DSS colitis were administered with vehicle, ATRA, or LE135. Colitis was evaluated by clinical symptoms, tissue myeloperoxidase (MPO) activity, and the expressions of CD68 and nuclear factor (NF) κB p65, and tumor necrosis factor (TNF) level in inflamed colon. RAW 264.7 cells were pretreated with vehicle, ATRA, or LE135, followed by LPS challenge in vitro. ATRA administration ameliorates DSS-induced colitis evidenced with decreased TNF level and CD68 expression, while LE135 leads to exacerbation of colitis. ATRA treatment in vitro dampens LPS induced NF-κB activation and TNF production of RAW 264.7 cells. Together, our data show a crucial role of ATRA in the progress of acute colitis through inhibiting NF-κB activation, and suggest that ATRA represents a novel therapeutic approach for the management of IBD.

Clinical Use and Mechanisms of Infliximab Treatment on Inflammatory Bowel Disease: A Recent Update

The pathogenesis and treatment of inflammatory bowel disease (IBD) have been recently advanced, while it is still challenged with high morbidity and poor prognosis. Infliximab, a monoclonal antibody of tumor necrosis factor (TNF), has emerged as an efficient treatment with many clinical benefits such as quick disease activity reduction and IBD patient life quality improvement. However, the biological effects of infliximab on IBD need to be elucidated. This paper reviewed the clinical use and recently advanced biological action of infliximab on IBD. By forming the stable complex with the soluble or the membrane form of TNF in fluid environment or on cell surface of immune cell, fibroblast, endothelium, and epithelium, infliximab quenches TNF activity and performs the important biological actions which lead to amelioration and remission of immune responses. The mechanisms of infliximab treatment for IBD were intensively discussed. The recent advances on two topics including predictors and side effects of infliximab treatment were also reviewed.

Treatment of inflammatory bowel disease with neural stem cells expressing choline acetyltransferase.

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder, with increasing incidence and prevalence in the last one-half century. IBD patients suffer from autonomic vagal neuropathy and nerve dysfunction, with deficiency of acetylcholine in inflamed mucosa. Recent studies showed that death of enteric neuron in local tissue was induced during the process of IBD, which also played a crucial role in the pathogenesis of disease. Stem cells have been demonstrated a new biological treatment for IBD, therefore, we proposal that neural stem cells expressing choline acetyltransferase may enhance enteric neural cell regeneration, restore acetylcholine production in intestinal mucosa, and thus inhibit immune responses of IBD.

M1671 All-Trans Retinoic Acid Downregulates Inflammatory Responses By Shifting the Treg/TH17 Profile in Human Ulcerative and Murine Colitis

IBD is characterized by uncontrolled immune responses in inflamed mucosa, with dominance of IL-17-producing cells and deficiency of Treg cells. The aim of this study was to explore the effect and mechanisms of RA, the ligand of RAR, on immune responses in human and murine colitis. Colonic biopsies from patients with UC were cultured and treated with RA as the agonist of RAR or LE135 as the antagonist of RAR. Expressions of IL-17 and FOXP3 were detected by immunohistochemistry. Murine colitis was induced by intrarectal administration with TNBS at Day 1. Mice were then i.p.-treated with RA or LE135 daily for 7 days. Cytokine levels in the cultures of mouse LPMCs were measured. Expressions of FOXP3 and IL-17 in colon tissues or MLN were detected by immunohistological analysis. Body weight and colon inflammation were evaluated. RA treatment up-regulated FOXP3 expression and downregulated IL-17 expression in colon biopsies of patients and in colon tissues and MLN of mice with colitis compared with controls. LPMCs from RA-treated mice produced lower levels of proinflammatory cytokines (TNF-, IL-1, IL-17) but more regulatory cytokines (IL-10, TGF-) compared with that of untreated mice. LE135 showed the opposite effect of RA. Furthermore, RA ameliorated TNBS-induced colitis in a dose-dependent manner, as seen by improved body weight and colon inflammation. RA down-regulates colon inflammatory responses in patients with IBD in vitro and in murine colitis in vivo, representing a potential therapeutic approach in IBD treatment. J. Leukoc. Biol. 86: 959–969; 2009.