Barbara Renga

The third gas: H2S regulates perfusion pressure in both the isolated and perfused normal rat liver and in cirrhosis

The regulation of sinusoidal resistance is dependent on the contraction of hepatic stellate cells (HSC) around sinusoidal endothelial cell (SEC) through paracrine cross‐talk of vasoconstrictor and vasodilator agents. Hydrogen sulfide (H2S), a recently discovered gas neurotransmitter, is a putative vasodilator whose role in hepatic vascular regulation and portal hypertension is unexplored. Four‐week bile duct–ligated (BDL) rats with cirrhosis and control rats were treated daily with NaHS (56 μmol/kg) for 5 days. Isolated livers were perfused first with NaHS for 20 minutes and then with norepinephrine (NE) and the intrahepatic resistance studied. In normal rats and animals with cirrhosis, administration of NE resulted in a dose‐dependent increase of portal pressure. This effect was attenuated by H2S treatment (P < .05). The H2S‐induced relaxation of hepatic microcirculation was attenuated by glibenclamide, an adenosine triphosphate (ATP)‐sensitive K+ channel inhibitor. L‐Cysteine, a substrate of cystathionine‐gamma‐lyase (CSE), decreased vasoconstriction in normal rat livers (P < .05) but failed to do so in livers with cirrhosis. BDL resulted in a downregulation of CSE mRNA/protein levels and activity (P < .05). Our in vitro data demonstrate that CSE is expressed in hepatocytes, HSCs, but not in sinusoidal endothelial cells (SEC). HSC activation downregulates CSE mRNA expression, resulting in a defective production of H2S and abrogation of relaxation induced by L‐cysteine. In conclusion, CSE‐derived H2S is involved in the maintenance of portal venous pressure. The reduction of CSE expression in the liver with cirrhosis contributes to the development of increased intrahepatic resistance and portal hypertension. (HEPATOLOGY 2005.)

The Bile Acid Receptor FXR Is a Modulator of Intestinal Innate Immunity

The farnesoid X receptor (FXR) is a bile acid-regulated nuclear receptor expressed in enterohepatic tissues. In this study we investigated whether FXR is expressed by cells of innate immunity and regulates inflammation in animal models of colitis. Acute (7 days) and chronic (8 wk) colitis were induced in wild-type and FXR−/− mice by intrarectal administration of trinitrobenzensulfonic acid or by 7-day administration of 5% dextran sulfate in drinking water. The results of this experiment demonstrate that FXR is expressed by and exerts counterregulatory effects on cells of innate immunity. Exposure of LPS-activated macrophages to 6-ethyl chenodeoxycholic acid (6E-CDCA; INT-747) a synthetic FXR ligand, results in a reciprocal regulation of NF-κB dependent-genes (TNF-α, IL-1β, IL-6, COX-1, COX-2, and iNOS) and induction of SHP, a FXR-regulated gene. FXR activation stabilizes the nuclear corepressor NCoR on the NF-κB responsive element on the IL-1β promoter. Colon inflammation in Crohn’s disease patients and in rodent models of colitis is associated with a reduced expression of FXR mRNA. Using two rodent models of colon inflammation, we show that progression of these immune-mediated disorders is exacerbated in FXR−/− mice (p < 0.01). In vivo treatment with INT-747 attenuates organ injury and immune cell activation. FXR activation increased the colon expression of I-BABP, FXR, and SHP while reducing IL-1β, IL-2, IL-6, TNF-α, and IFN-γ mRNA expression and attenuating disease severity. In aggregate, these findings provide evidence that FXR is an essential component of a network of nuclear receptors that regulate intestinal innate immunity and homeostasis.

5-Amino-2-hydroxybenzoic Acid 4-(5-Thioxo-5H-[1,2]dithiol-3yl)-phenyl Ester (ATB-429), a Hydrogen Sulfide-Releasing Derivative of Mesalamine, Exerts Antinociceptive Effects in a Model of Postinflammatory Hypersensitivity

H2S functions as a neuromodulator and exerts anti-inflammatory activities. Recent data indicate that irritable bowel syndrome (IBS) is linked to inflammation of the gastrointestinal tract. In this study, we have investigated the role of a novel H2S-releasing derivative of mesalamine (5-amino-2-hydroxybenzoic acid 4-(5-thioxo-5H-[1,2]dithiol-3yl)-phenyl ester, ATB-429) in modulating nociception to colorectal distension (CRD), a model that mimics some features of IBS, in healthy and postcolitic rats. Four graded (0.4-1.6 ml of water) CRDs were produced in conscious rats, and colorectal sensitivity and pain were assessed by measuring the abdominal withdrawal response and spinal c-Fos expression. In healthy rats, ATB-429 dose dependently (25, 50, or 100 mg/kg) attenuated CRD-induced hypersensitivity and significantly inhibited CRD-induced overexpression of spinal c-FOS mRNA, whereas mesalamine had no effect. ATB-429-induced antinociception was reversed by glibenclamide, a ATP-sensitive K+ (KATP) channel inhibitor. The antinociceptive effect of ATB-429 was maintained in a rodent model of postinflammatory hypersensitivity (4 weeks after colitis induction). At a dose of 100 mg/kg, ATB-429 reversed the allodynic response caused by CRD in postcolitic rats. Colonic cyclooxygenase-2 and interkeukin-1β mRNA and spinal c-FOS mRNA expression were significantly down-regulated by ATB-429, but not by mesalamine. ATB-429, but not mesalamine, increased blood concentrations of H2S in both healthy and postcolitic rats. Taken together, these data suggest that ATB-429 inhibits hypersensitivity induced by CRD in both healthy and postcolitic, allodynic rats by a KATP channel-mediated mechanism. This study provides evidence that H2S-releasing drugs might have beneficial effects in the treatment of painful intestinal disorders.

The bile acid receptor GPBAR-1 (TGR5) modulates integrity of intestinal barrier and immune response to experimental colitis

Background GP-BAR1, a member G protein coupled receptor superfamily, is a cell surface bile acid-activated receptor highly expressed in the ileum and colon. In monocytes, ligation of GP-BAR1 by secondary bile acids results in a cAMP-dependent attenuation of cytokine generation. Aims To investigate the role GP-BAR1 in regulating intestinal homeostasis and inflammation-driven immune dysfunction in rodent models of colitis. Methods Colitis was induced in wild type and GP-BAR1−/− mice by DSS and TNBS administration. Potential GP-BAR1 agonists were identified by in silico screening and computational docking studies. Results GP-BAR1−/− mice develop an abnormal morphology of colonic mucous cells and an altered molecular architecture of epithelial tight junctions with increased expression and abnormal subcellular distribution of zonulin 1 resulting in increased intestinal permeability and susceptibility to develop severe colitis in response to DSS at early stage of life. By in silico screening and docking studies we identified ciprofloxacin as a GP-BAR1 ligand. In monocytes, ciprofloxacin increases cAMP concentrations and attenuates TNFα release induced by TLR4 ligation in a GP-BAR1 dependent manner. Treating mice rendered colitic by TNBS with ciprofloxacin and oleanolic acid, a well characterized GP-BAR1 ligand, abrogates signs and symptoms of colitis. Colonic expression of GP-BAR1 mRNA increases in rodent models of colitis and tissues from Crohns disease patients. Flow cytometry analysis demonstrates that ≈90% of CD14+ cells isolated from the lamina propria of TNBS-treated mice stained positively for GP-BAR1. Conclusions GP-BAR1 regulates intestinal barrier structure. Its expression increases in rodent models of colitis and Crohns disease. Ciprofloxacin is a GP-BAR1 ligand.

The Farnesoid X Receptor Promotes Adipocyte Differentiation and Regulates Adipose Cell Function in Vivo

The differentiation of a preadipocyte into a mature adipocyte is a highly regulated process that requires a scripted program of transcriptional events leading to changes in gene expression. Several genes are associated with adipogenesis, including the CAAT/enhancer-binding protein (C/EBPs) and peroxisome proliferator-activated receptor (PPAR) families of transcription factors. In this study, we have investigated the role of the farnesoid X receptor (FXR), a bile acid-activated nuclear receptor, in regulating adipogenesis in a preadipocyte cell line (3T3-L1 cells). Our results show that FXR is expressed in the white adipose tissue of adult mice and in differentiated 3T3-L1 cells but not in undifferentiated preadipocytes. Exposure of 3T3-L1 cells to INT-747 (6-ethyl cheno-deoxycholic acid), a potent and selective FXR ligand, increases preadipocyte differentiation induced by a differentiating mixture containing insulin. Augmentation of differentiating mixture-induced differentiation of 3T3-L1 cells by INT-747 associated with induction of aP2, C/EBPα, and PPARγ2 mRNAs along with other adipocyte-related genes. This effect was reversed by guggulsterone, an FXR antagonist, and partially reverted by GW9662 (2-chloro-5-nitro-N-phenylbenzamide), a selective PPARγ antagonist, indicating that FXR modulates adipocyte-related genes by PPARγ-dependent and -independent pathways. Regulation of adipocyte-related genes by INT-747 was lost in FXR-/- mice, indicating that modulation of these genes by INT-747 requires an intact FXR. In addition, INT-747 enhances both insulin-induced serine phosphorylation of Akt and glucose uptake by 3T3-L1 cells. Taken together, these results suggest that activation of FXR plays a critical role in regulating adipogenesis and insulin signaling.

Antiatherosclerotic effect of farnesoid X receptor

The farnesoid X receptor (FXR) is a member of the nuclear receptor superfamily that functions as an endogenous sensor for bile acids and regulates cholesterol and fatty acid metabolism. The effect of FXR activation on aortic plaque formation was assessed by feeding apolipoprotein E-deficient (ApoE-/-) mice with the synthetic FXR ligand INT-747, a cheno-deoxycholic acid derivative, at doses of 3 and 10 mg x kg(-1) x day(-1), or with rosiglitazone, a peroxisome proliferator-activated receptor-gamma ligand, at the dose of 10 mg x kg(-1) x day(-1) for 12 wk. Administration of INT-747 reduced formation of aortic plaque area by 95% (P < 0.01), and a similar antiplaque activity was exerted by administration of rosiglitazone. INT-747 administration to ApoE-/- mice reduced aortic expression of IL-1beta, IL-6, and CD11b mRNA, while it upregulated the expression of FXR and its target gene, the small heterodimer partner (SHP). FXR activation reduced the liver expression of sterol regulatory element binding protein 1c, resulting in reduced triglyceride and cholesterol content in the liver and amelioration of hyperlipidemia. FXR expression, mRNA and protein, was detected in human macrophages and macrophage cell lines. FXR activation by natural and synthetic ligands in these cell types attenuated IL-1beta, IL-6, and TNF-alpha gene induction in response to Toll-like receptor 4 activation by LPS. Using spleen monocytes from wild-type and FXR-/- mice, we demonstrated that FXR gene ablation exacerbates IL-6 and TNF-alpha generation by LPS-stimulated macrophages. FXR was also able to reduce cholesterol uptake on macrophages by regulation of CD36 and ABCA1 expression. We found that FXR and SHP are expressed in the aorta and macrophages and that FXR ligands might have utility in prevention and treatment of atherosclerotic lesions.

The bile acid sensor FXR regulates insulin transcription and secretion.

Farnesoid X Receptor plays an important role in maintaining bile acid, cholesterol homeostasis and glucose metabolism. Here we investigated whether FXR is expressed by pancreatic beta-cells and regulates insulin signaling in pancreatic beta-cell line and human islets. We found that FXR activation induces positive regulatory effects on glucose-induced insulin transcription and secretion by genomic and non-genomic activities. Genomic effects of FXR activation relay on the induction of the glucose regulated transcription factor KLF11. Indeed, results from silencing experiments of KLF11 demonstrate that this transcription factor is essential for FXR activity on glucose-induced insulin gene transcription. In addition FXR regulates insulin secretion by non-genomic effects. Thus, activation of FXR in betaTC6 cells increases Akt phosphorylation and translocation of the glucose transporter GLUT2 at plasma membrane, increasing the glucose uptake by these cells. In vivo experiments on Non Obese Diabetic (NOD) mice demonstrated that FXR activation delays development of signs of diabetes, hyperglycemia and glycosuria, by enhancing insulin secretion and by stimulating glucose uptake by the liver. These data established that an FXR-KLF11 regulated pathway has an essential role in the regulation of insulin transcription and secretion induced by glucose.

Modulation of intestinal microbiota by the probiotic VSL#3 resets brain gene expression and ameliorates the age-related deficit in LTP.

The intestinal microbiota is increasingly recognized as a complex signaling network that impacts on many systems beyond the enteric system modulating, among others, cognitive functions including learning, memory and decision-making processes. This has led to the concept of a microbiota-driven gut–brain axis, reflecting a bidirectional interaction between the central nervous system and the intestine. A deficit in synaptic plasticity is one of the many changes that occurs with age. Specifically, the archetypal model of plasticity, long-term potentiation (LTP), is reduced in hippocampus of middle-aged and aged rats. Because the intestinal microbiota might change with age, we have investigated whether the age-related deficit in LTP might be attenuated by changing the composition of intestinal microbiota with VSL#3, a probiotic mixture comprising 8 Gram-positive bacterial strains. Here, we report that treatment of aged rats with VSL#3 induced a robust change in the composition of intestinal microbiota with an increase in the abundance of Actinobacteria and Bacterioidetes, which was reduced in control-treated aged rats. VSL#3 administration modulated the expression of a large group of genes in brain tissue as assessed by whole gene expression, with evidence of a change in genes that impact on inflammatory and neuronal plasticity processes. The age-related deficit in LTP was attenuated in VSL#3-treated aged rats and this was accompanied by a modest decrease in markers of microglial activation and an increase in expression of BDNF and synapsin. The data support the notion that intestinal microbiota can be manipulated to positively impact on neuronal function.

The Bile Acid Sensor Farnesoid X Receptor Is a Modulator of Liver Immunity in a Rodent Model of Acute Hepatitis

Immune-mediated liver diseases including autoimmune and viral hepatitis are a major health problem worldwide. In this study, we report that activation of the farnesoid X receptor (FXR), a member of the ligand-activated nuclear receptor superfamily and bile sensor highly expressed in the liver, attenuates liver injury in a model of autoimmune hepatitis induced by Con A. We found that FXR gene ablation results in a time-dependent increase of liver expression (up to 20-fold in a 9-mo-old mouse) of osteopontin, a NKT cell-derived extracellular matrix protein and immunoregulatory cytokine. In comparison to wild-type, FXR−/− mice are more susceptible to Con A-induced hepatitis and react to Con A administration by an unregulated production of osteopontin. Administering wild-type mice with a synthetic FXR agonist attenuated Con A-induced liver damage and liver expression of the osteopontin gene. By in vitro studies, we found that FXR is expressed by primarily isolated NKT cells and its ablation favors ostepontin production in response to Con A. Chromatin immunoprecipitation assay and coimmunoprecipitation experiments demonstrate that the short heterodimer partner (SHP), a nuclear receptor and FXR target, was expressed by NKT cell hybridomas and increased in response to FXR activation. FXR activates SHP that interacts with and inhibits c-Jun binding to the osteopontin promoter. These data indicate that in NKT cells, FXR activation causes a SHP-mediated inhibition of osteopontin production. These data support the notion that the bile acid sensor FXR regulates the activation of liver NKT cells.

Pregnane-X-receptor mediates the anti-inflammatory activities of rifaximin on detoxification pathways in intestinal epithelial cells.

The pregnane-X-receptor (PXR) is master gene overseeing detoxification of wide number of xenobiotics and is critical for maintenance of intestinal integrity. The intestinal expression of genes involved in cellular detoxification is down-regulated in patients with inflammatory bowel diseases (IBD). Rifaximin is a non-absorbable antibiotic endowed with a PXR agonistic activity. In the present study we have investigated whether rifaximin activates PXR in primary human colon epithelial cells and human colon biopsies and assessed whether this antibiotic antagonizes the effect of tumor necrosis factor (TNF)-α on expression of PXR and PXR-related genes. Present results demonstrate that primary colon epithelial cells express PXR and that their exposure to rifaximin induces the expression of genes involved in cellular detoxification. Exposure to TNFα reduces the expression of PXR mRNA as well as expression of its target genes. This inhibitory effect was prevented by that co-treatment with rifaximin. Knocking down the expression of PXR in colon epithelial cells by an anti-PXR siRNA, abrogated the counter-regulatory effects exerted by rifaximin on cell exposed to TNFα. Finally, ex vivo exposure of colon biopsies obtained from ulcerative colitis patients to rifaximin increased the expression of genes involved in xenobiotics metabolism. In aggregate, these data illustrate that rifaximin increases the expression of PXR and PXR-regulated genes involved in the metabolism and excretion of xenobiotics and antagonizes the effects of TNFα in intestinal epithelial cells and colon biopsies. These non-antibiotic effects of rifaximin could contribute to the maintenance of the intestinal barrier integrity against xenobiotics and products generated by luminal bacteria.