Dipotassium Glycyrrhizate Inhibits HMGB1-Dependent Inflammation and Ameliorates Colitis in Mice

Background

High mobility group box-1 (HMGB1) is a DNA-binding protein that is released from injured cells during inflammation. Advances in targeting HMGB1 represent a major challenge to improve the treatment of acute/chronic inflammation.

Aim

This study is aimed at verifying whether the inhibition of HMGB1 through dipotassium glycyrrhizate (DPG) is a good strategy to reduce intestinal inflammation.

Methods

Human colon adenocarcinoma cell line, HT29, human epithelial colorectal adenocarcinoma, Caco2, and murine macrophage cell line, RAW 264.7, were cultured to investigate the effect of DPG on the secretion of HMGB1. Acute colitis was induced in C57BL/6 mice through administration of 3% dextran sodium sulphate (DSS); a combined treatment with DSS and 3 or 8 mg/kg/day DPG was used to investigate the effects of DPG on intestinal inflammation. Animals were euthanized at seventh day and colonic samples underwent molecular and histological analyses.

Results

DPG significantly reduces in vitro the release of HMGB1 in the extracellular matrix as well as expression levels of pro-inflammatory cytokines, TNF-alpha, IL-1beta and IL-6, by inhibiting HMGB1. Moreover, DPG significantly decreases the severity of DSS-induced colitis in mice. Murine colonic samples show decreased mRNA levels of pro-inflammatory cytokines TNF-alpha, IL-1beta and IL-6, as well as HMGB1 receptors, RAGE and TLR4. Finally, HMGB1, abundantly present in the feces of mice with DSS-induced colitis, is strongly reduced by DPG.

Conclusions

HMGB1 is an early pro-inflammatory cytokine and an active protagonist of mucosal gut inflammation. DPG exerts inhibitory effects against HMGB1 activity, significantly reducing intestinal inflammation. Thus, we reason that DPG could represent an innovative tool for the management of human intestinal inflammation.     

Heme Oxygenase-1 Ameliorates Dextran Sulfate Sodium-induced Acute Murine Colitis by Regulating Th17/Treg Cell Balance

Inflammatory bowel disease (IBD), including ulcerative colitis and Crohn''s disease, is a group of autoimmune diseases characterized by nonspecific inflammation in the gastrointestinal tract. Recent investigations suggest that activation of Th17 cells and/or deficiency of regulatory T cells (Treg) is involved in the pathogenesis of IBD. Heme oxygenase (HO)-1 is a protein with a wide range of anti-inflammatory and immune regulatory function, which exerts significantly protective roles in various T cell-mediated diseases. In this study, we aim to explore the immunological regulation of HO-1 in the dextran sulfate sodium-induced model of experimental murine colitis. BALB/c mice were administered 4% dextran sulfate sodium orally; some mice were intraperitoneally pretreated with HO-1 inducer hemin or HO-1 inhibitor stannum protoporphyrin IX. The results show that hemin enhances the colonic expression of HO-1 and significantly ameliorates the symptoms of colitis with improved histological changes, accompanied by a decreased proportion of Th17 cells and increased number of Tregs in mesenteric lymph node and spleen. Moreover, induction of HO-1 down-regulates retinoic acid-related orphan receptor γt expression and IL-17A levels, while promoting Treg-related forkhead box p3 (Foxp3) expression and IL-10 levels in colon. Further study in vitro revealed that up-regulated HO-1 switched the naive T cells to Tregs when cultured under a Th17-inducing environment, which involved in IL-6R blockade. Therefore, HO-1 may exhibit anti-inflammatory activity in the murine model of acute experimental colitis via regulating the balance between Th17 and Treg cells, thus providing a possible novel therapeutic target in IBD.     

HMGB1 Mediates Anemia of Inflammation in Murine Sepsis Survivors

Patients surviving sepsis develop anemia, but the molecular mechanism is unknown. Here we observed that mice surviving polymicrobial gram-negative sepsis develop hypochromic, microcytic anemia with reticulocytosis. The bone marrow of sepsis survivors accumulates polychromatophilic and orthochromatic erythroblasts. Compensatory extramedullary erythropoiesis in the spleen is defective during terminal differentiation. Circulating tumor necrosis factor (TNF) and interleukin (IL)-6 are elevated for 5 d after the onset of sepsis, and serum high-mobility group box 1 (HMGB1) levels are increased from d 7 until at least d 28. Administration of recombinant HMGB1 to healthy mice mediates anemia with extramedullary erythropoiesis and significantly elevated reticulocyte counts. Moreover, administration of anti-HMGB1 monoclonal antibodies after sepsis significantly ameliorates the development of anemia (hematocrit 48.5 ± 9.0% versus 37.4 ± 6.1%, p < 0.01; hemoglobin 14.0 ± 1.7 versus 11.7 ± 1.2 g/dL, p < 0.01). Together, these results indicate that HMGB1 mediates anemia by interfering with erythropoiesis, suggesting a potential therapeutic strategy for anemia in sepsis.     

Fatty Acid Synthase Inhibitor C75 Ameliorates Experimental Colitis

Abnormalities of lipid metabolism through overexpression of fatty acid synthase (FASN), which catalyzes the formation of long-chain fatty acids, are associated with the development of inflammatory bowel disease (IBD). C75 is a synthetic α-methylene-γ-butyrolactone compound that inhibits FASN activity. We hypothesized that C75 treatment could effectively reduce the severity of experimental colitis. Male C57BL/6 mice were fed 4% dextran sodium sulfate (DSS) for 7 d. C75 (5 mg/kg body weight) or dimethyl sulfoxide (DMSO) (vehicle) was administered intraperitoneally from d 2 to 6. Clinical parameters were monitored daily. Mice were euthanized on d 8 for histological evaluation and measurements of colon length, chemokine, cytokine and inflammatory mediator expression. C75 significantly reduced body weight loss from 23% to 15% on d 8, compared with the vehicle group. The fecal bleeding, diarrhea and colon histological damage scores in the C75-treated group were significantly lower than scores in the vehicle animals. Colon shortening was significantly improved after C75 treatment. C75 protected colon tissues from DSS-induced apoptosis by inhibiting caspase-3 activity. Macrophage inflammatory protein 2, keratinocyte-derived chemokine, myeloperoxidase activity and proinflammatory cytokines (tumor necrosis factor-α, interleukin [IL]-1β and IL-6) in the colon were significantly downregulated in the C75-treated group, compared with the vehicle group. Treatment with C75 in colitis mice inhibited the elevation of FASN, cyclooxygenase-2 and inducible nitric oxide synthase expression as well as IκB degradation in colon tissues. C75 administration alleviates the severity of colon damage and inhibits the activation of inflammatory pathways in DSS-induced colitis. Thus, inhibition of FASN may represent an attractive therapeutic potential for treating IBD.     

Bifunctional Lipocalin Ameliorates Murine Immune Complex-induced Acute Lung Injury

Molecules that simultaneously inhibit independent or co-dependent proinflammatory pathways may have advantages over conventional monotherapeutics. OmCI is a bifunctional protein derived from blood-feeding ticks that specifically prevents complement (C)-mediated C5 activation and also sequesters leukotriene B4 (LTB₄) within an internal binding pocket. Here, we examined the effect of LTB₄ binding on OmCI structure and function and investigated the relative importance of C-mediated C5 activation and LTB₄ in a mouse model of immune complex-induced acute lung injury (IC-ALI). We describe two crystal structures of bacterially expressed OmCI: one binding a C16 fatty acid and the other binding LTB₄ (C20). We show that the C5 and LTB₄ binding activities of the molecule are independent of each other and that OmCI is a potent inhibitor of experimental IC-ALI, equally dependent on both C5 inhibition and LTB₄ binding for full activity. The data highlight the importance of LTB₄ in IC-ALI and activation of C5 by the complement pathway C5 convertase rather than by non-C proteases. The findings suggest that dual inhibition of C5 and LTB₄ may be useful for treatment of human immune complex-dependent diseases.     

Cellulose Supplementation Early in Life Ameliorates Colitis in Adult Mice

Decreased consumption of dietary fibers, such as cellulose, has been proposed to promote the emergence of inflammatory bowel diseases (IBD: Crohn disease [CD] and ulcerative colitis [UC]) where intestinal microbes are recognized to play an etiologic role. However, it is not known if transient fiber consumption during critical developmental periods may prevent consecutive intestinal inflammation. The incidence of IBD peaks in young adulthood indicating that pediatric environmental exposures may be important in the etiology of this disease group. We studied the effects of transient dietary cellulose supplementation on dextran sulfate sodium (DSS) colitis susceptibility during the pediatric period in mice. Cellulose supplementation stimulated substantial shifts in the colonic mucosal microbiome. Several bacterial taxa decreased in relative abundance (e.g., Coriobacteriaceae [p = 0.001]), and other taxa increased in abundance (e.g., Peptostreptococcaceae [p = 0.008] and Clostridiaceae [p = 0.048]). Some of these shifts persisted for 10 days following the cessation of cellulose supplementation. The changes in the gut microbiome were associated with transient trophic and anticolitic effects 10 days following the cessation of a cellulose-enriched diet, but these changes diminished by 40 days following reversal to a low cellulose diet. These findings emphasize the transient protective effect of dietary cellulose in the mammalian large bowel and highlight the potential role of dietary fibers in amelioration of intestinal inflammation.     

Abrogation of Plasminogen Activator Inhibitor-1-Vitronectin Interaction Ameliorates Acute Kidney Injury in Murine Endotoxemia

Sepsis-induced acute kidney injury (AKI) contributes to the high mortality and morbidity in patients. Although the pathogenesis of AKI during sepsis is poorly understood, it is well accepted that plasminogen activator inhibitor-1 (PAI-1) and vitronectin (Vn) are involved in AKI. However, the functional cooperation between PAI-1 and Vn in septic AKI has not been completely elucidated. To address this issue, mice were utilized lacking either PAI-1 (PAI-1^−/−) or expressing a PAI-1-mutant (PAI-1^R101A/Q123K) in which the interaction between PAI-1 and Vn is abrogated, while other functions of PAI-1 are retained. It was found that both PAI-1^−/− and PAI-1^R101A/Q123K mice are associated with decreased renal dysfunction, apoptosis, inflammation, and ERK activation as compared to wild-type (WT) mice after LPS challenge. Also, PAI-1^−/− mice showed attenuated fibrin deposition in the kidneys. Furthermore, a lack of PAI-1 or PAI-1-Vn interaction was found to be associated with an increase in activated Protein C (aPC) in plasma. These results demonstrate that PAI-1, through its interaction with Vn, exerts multiple deleterious mechanisms to induce AKI. Therefore, targeting of the PAI-1-Vn interaction in kidney represents an appealing therapeutic strategy for the treatment of septic AKI by not only altering the fibrinolytic capacity but also regulating PC activity.     

The Potential Protective Role of Caveolin-1 in Intestinal Inflammation in TNBS-Induced Murine Colitis

Background

Caveolin-1 (Cav-1) is a multifunctional scaffolding protein serving as a platform for the cell’s signal-transduction and playing an important role in inflammation. However, its role in inflammatory bowel disease is not clear. A recent study showed that Cav-1 is increased and mediates angiogenesis in dextran sodium sulphate-induced colitis, which are contradictory to our pilot findings in 2,4,6-trinitrobenzene sulphonic acid (TNBS)-induced colitis. In the present study, we further clarified the role of Cav-1 in TNBS-induced colitis.

Methods

In BALB/c mice, acute colitis was induced by intra-rectal administration of one dose TNBS, while chronic colitis was induced by administration of TNBS once a week for 7 weeks. To assess the effects of complete loss of Cav-1, Cav-1 knockout (Cav-1^−/−) and control wild-type C57 mice received one TNBS administration. Body weight and clinical scores were monitored. Colon Cav-1 and pro-inflammatory cytokine levels were quantified through ELISAs. Inflammation was evaluated through histological analysis.

Results

Colon Cav-1 levels were significantly decreased in TNBS-induced colitis mice when compared to normal mice and also inversely correlated with colon inflammation scores and proinflammatory cytokine levels (IL-17, IFN-γ and TNF) significantly. Furthermore, after administration of TNBS, Cav-1^−/− mice showed significantly increased clinical and colon inflammatory scores and body weight loss when compared with control mice.

Conclusions and Significance

Cav-1 may play a protective role in the development of TNBS-induced colitis. Our findings raise an important issue in the evaluation of specific molecules in animal models that different models may exhibit opposite results because of the different mechanisms involved.     

Beauvericin Ameliorates Experimental Colitis by Inhibiting Activated T Cells via Downregulation of the PI3K/Akt Signaling Pathway

Crohn''s disease is a common, chronic inflammatory bowel condition characterized by remission and relapse. Accumulating evidence indicates that activated T cells play an important role in this disease. In the present study, we aimed to examine the effect of beauvericin, a natural cyclic peptide, on 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis in mice, which mimics Crohn''s disease. Beauvericin significantly reduced weight loss, diarrhea and mortality, accompanied with notable alleviation of macroscopic and microscopic signs. In addition, this compound decreased serum levels of tumor necrosis factor (TNF)-α and interferon (IFN)- γ in a concentration-dependent manner in mice with experimental colitis. These effects of beauvericin are attributed to its inhibition on activated T cells. Flow cytometry and immunoblot assay data showed that beauvericin suppressed T-cell proliferation, activation and IFN-γ-STAT1-T-bet signaling and subsequently led to apoptosis of activated T cells by suppressing Bcl-2 and phosphorylated Bad as well as increasing cleavage of caspase-3, -9, -12 and PARP. Furthermore, inhibition of PI3K/Akt signaling, which was an upstream regulator of cell activation and survival in activated T cells, contributed to the effect of beauvericin. Overall, these results supported beauvericin as a novel drug candidate for the treatment of colonic inflammation mainly by targeting PI3K/Akt in activated T cells.     

Allyl Isothiocyanate Ameliorates Angiogenesis and Inflammation in Dextran Sulfate Sodium-Induced Acute Colitis

Allyl isothiocyanate (AITC) is a phytochemical found in cruciferous vegetables that has known chemopreventive and chemotherapeutic activities. Thus far, the antiangiogenic activity of AITC has not been reported in in vivo studies. Herein, we investigated the effect of AITC on angiogenesis and inflammation in a mouse model of colitis. Experimental colitis was induced in mice by administering 3% dextran sulfate sodium via drinking water. To monitor the activity of AITC in this model, we measured body weight, disease activity indices, histopathological scores, microvascular density, myeloperoxidase activity, F4/80 staining, inducible nitric oxide synthase (iNOS) expression, cyclooxygenase-2 (COX-2) expression, and vascular endothelial growth factor (VEGF)-A/VEGF receptor 2 (VEGFR2) expression in the mice. We found that AITC-treated mice showed less weight loss, fewer clinical signs of colitis, and longer colons than vehicle-treated mice. AITC treatment also significantly lessened the disruption of colonic architecture that is normally associated with colitis and repressed the microvascularization response. Further, AITC treatment reduced both leukocyte recruitment and macrophage infiltration into the inflamed colon, and the mechanism these activities involved repressing iNOS and COX-2 expression. Finally, AITC attenuated the expression of VEGF-A and VEGFR2. Thus, AITC may have potential application in treating conditions marked by inflammatory-driven angiogenesis and mucosal inflammation.     

Chlorogenic Acid Attenuates High Mobility Group Box 1 (HMGB1) and Enhances Host Defense Mechanisms in Murine Sepsis

Sepsis is a complex, multifactorial, rapidly progressive disease characterized by an overwhelming activation of the immune system and the countervailing antiinflammatory response. In the current study in murine peritoneal macrophages, chlorogenic acid suppressed endotoxin-induced high mobility group box 1 (HMGB1) release in a concentration-dependent manner. Administration of chlorogenic acid also attenuated systemic HMGB1 accumulation in vivo and prevented mortality induced by endotoxemia and polymicrobial sepsis. The mechanisms of action of chlorogenic acid included attenuation of the increase in toll-like receptor (TLR)-4 expression and suppression of sepsis-induced signaling pathways, such as c-Jun NH₂-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB, which are critical for cytokine release. The protection conferred by chlorogenic acid was achieved through modulation of cytokine and chemokine release, suppression of immune cell apoptosis and augmentation of bacterial elimination. Chlorogenic acid warrants further evaluation as a potential therapeutic agent for the treatment of sepsis and other potentially fatal systemic inflammatory disorders.     

Murine Colitis Modeling using Dextran Sulfate Sodium (DSS)

Colitis can occur from viral or bacterial infections, ischemic insult, or autoimmune disorders; most notably Ulcerative Colitis and the colonic variant of Crohn’s Disease - Crohn’s Colitis. Acute colitis may present with abdominal pain and distention, malabsorption, diarrhea, hematochezia and mucus in the stool. We are beginning to understand the complex interactions between the environment, genetics, and epithelial barrier dysfunction in Inflammatory Bowel Disease and animal models of colitis have been essential in advancing our understanding of this disease. One popular model involves supplementing the drinking water of mice with low-molecular weight Dextran Sodium Sulfate (DSS), resulting in epithelial damage and a robust inflammatory response in the colon lasting several days ¹.Variations of this approach can be used to model acute injury, acute injury followed by repair, and repeated cycles of DSS interspersed with recovery modeling chronic inflammatory diseases ². After a single four-day treatment of 3% DSS in drinking water, mice show signs of acute colitis including weight loss, bloody stools, and diarrhea. Mice are euthanized at the conclusion of the treatment course and at necropsy dissected colons are processed and can be ''Swiss rolled" ³ to allow microscopic analysis of the entire colon or infused with formalin as "sausages" to allow macroscopic analysis. Tissue is then embedded in paraffin, sectioned, and stained for histologic review.Open in a separate windowClick here to view.^{(49M, flv)}     

Lung endothelial barrier protection by resveratrol involves inhibition of HMGB1 release and HMGB1-induced mitochondrial oxidative damage via an Nrf2-dependent mechanism

High-mobility group box 1 (HMGB1) contributes to lung vascular hyperpermeability during ventilator-induced lung injury. We aimed to determine whether the natural antioxidant resveratrol protected against HMGB1-induced endothelial hyperpermeability both in vitro and in vivo. We found that HMGB1 decreased vascular endothelial (VE)-cadherin expression and increased endothelial permeability, leading to mitochondrial oxidative damage in primary cultured mouse lung vascular endothelial cells (MLVECs). Both the mitochondrial superoxide dismutase 2 mimetic MnTBAP and resveratrol blocked HMGB1-induced mitochondrial oxidative damage, VE-cadherin downregulation, and endothelial hyperpermeability. In in vivo studies, anesthetized male ICR mice were ventilated for 4 h using low tidal volume (6 ml/kg) or high tidal volume (HV_T; 30 ml/kg) ventilation. The mice were injected intraperitoneally with resveratrol immediately before the onset of ventilation. We found that resveratrol attenuated HV_T-associated lung vascular hyperpermeability and HMGB1 production. HV_T caused a significant increase in nuclear factor-erythroid 2-related factor 2 (Nrf2) nuclear translocation and Nrf2 target gene expression in lung tissues, which was further enhanced by resveratrol treatment. HMGB1 had no effect on Nrf2 activation, whereas resveratrol treatment activated the Nrf2 signaling pathway in HMGB1-treated MLVECs. Moreover, Nrf2 knockdown reversed the inhibitory effects of resveratrol on HMGB1-induced mitochondrial oxidative damage and endothelial hyperpermeability. The inhibitory effect of resveratrol on cyclic stretch-induced HMGB1 mRNA expression in primary cultured MLVECs was also abolished by Nrf2 knockdown. In summary, this study demonstrates that resveratrol protects against lung endothelial barrier dysfunction initiated by HV_T. Lung endothelial barrier protection by resveratrol involves inhibition of mechanical stretch-induced HMGB1 release and HMGB1-induced mitochondrial oxidative damage. These protective effects of resveratrol might be mediated through an Nrf2-dependent mechanism.     

Lipid Alterations in Experimental Murine Colitis: Role of Ceramide and Imipramine for Matrix Metalloproteinase-1 Expression

Background

Dietary lipids or pharmacologic modulation of lipid metabolism are potential therapeutic strategies in inflammatory bowel disease (IBD). Therefore, we analysed alterations of bioactive lipids in experimental models of colitis and examined the functional consequence of the second messenger ceramide in inflammatory pathways leading to tissue destruction.

Methodology/Principal Findings

Chronic colitis was induced by dextran-sulphate-sodium (DSS) or transfer of CD4⁺CD62L⁺ cells into RAG1^−/−-mice. Lipid content of isolated murine intestinal epithelial cells (IEC) was analysed by tandem mass spectrometry. Concentrations of MMP-1 in supernatants of Caco-2-IEC and human intestinal fibroblasts from patients with ulcerative colitis were determined by ELISA. Imipramine was used for pharmacologic inhibition of acid sphingomyelinase (ASM). Ceramide increased by 71% in chronic DSS–induced colitis and by 159% in the transfer model of colitis. Lysophosphatidylcholine (LPC) decreased by 22% in both models. No changes were detected for phosphatidylcholine. Generation of ceramide by exogenous SMase increased MMP-1-protein production of Caco-2-IEC up to 7-fold. Inhibition of ASM completely abolished the induction of MMP-1 by TNF or IL-1β in Caco-2-IEC and human intestinal fibroblasts.

Conclusions/Significance

Mucosal inflammation leads to accumulation of ceramide and decrease of LPC in the intestinal epithelium. One aspect of ceramide generation is an increase of MMP-1. Induction of MMP-1 by TNF or IL-1β is completely blocked by inhibition of ASM with imipramine. Therefore, inhibition of ASM may offer a treatment strategy to reduce MMP-1 expression and tissue destruction in inflammatory conditions.     

HMGB1 protein promotes glomerular mesangial matrix deposition via TLR2 in lupus nephritis

Lupus nephritis (LN) is the most common complication of systemic lupus erythematosus. Patients with LN mostly die of sclerosing glomerulonephritis and renal failure. The inhibition of glomerular mesangial matrix deposition is an efficient method to restrict the progress of renal injury. By recognizing and binding extracellular and intracellular ligands, Toll-like receptor 2 (TLR2) contributes to the pathogenesis of most immune diseases. However, the relationship between TLR2 and LN is still unknown. Our previous studies confirmed that high-mobility group box 1 (HMGB1), an important ligand of TLR2, promotes the progression of LN by inducing the proliferation of glomerular mesangial cells. However, whether or not HMGB1 participates in the pathogenesis of glomerular mesangial matrix deposition in LN remains unknown. In this study, we observed the upregulated expression of TLR2 in the glomeruli of LN patients and MRL/lpr mice. The inhibition of either TLR2 or HMGB1 inhibited the release of fibronectin and the activation of the MyD88/NF-κB pathway in mesangial cells cultured with LN plasma. In addition, both TLR2- and HMGB1-deficient mice showed reduced 24 hr urine protein levels and improved glomerular histological changes and sclerosis levels. These results indicate that TLR2 regulates glomerular mesangial matrix deposition in LN through the activation of the MyD88/NF-κB pathway by binding to HMGB1.     

Liraglutide Ameliorates Cerebral Ischemia in Mice via Antipyroptotic Pathways

Neurochemical Research - It was recently shown that pyroptosis, an inflammatory form of programmed cell death, is critically involved in the pathogenesis of ischemic stroke. Liraglutide (Lg) is a...