Metabolic reprogramming of the intestinal microbiome with functional bile acid changes underlie the development of NAFLD

BACKGROUND AND AIMS

Bile acids are hepatic metabolites and have many properties considered to be relevant to the pathophysiology of NAFLD. Circulating levels of the intestinal microbiome-modified bile acid deoxycholate are increased in cirrhosis.

APPROACH AND RESULTS

To further elucidate the role of bile acids and intestinal microbiota linked to bile acids in progressively severe NAFLD, a multiomic study of feces including 16S rRNA sequencing, microbial transcriptomics and metabolomics was performed in a cohort with varying phenotypes of NAFLD. Several bile acids of microbial origin derived from deoxycholic acid (DCA) (glycodeoxycholate, 7-ketodeoxycholic acid, dehydrocholic acid) increased with disease activity and fibrosis stage. These were linked to increased expression of microbial bile salt hydrolase, bile acid operon (BaiCD) and hydroxysteroid dehydrogenases (hdhA) required for DCA and downstream metabolite synthesis providing a mechanistic basis for altered bile acid profiles with disease progression. Bacteroidetes and several genera of Lachnospiraceae family containing DCA generating genes increased with increasing disease severity, whereas several potentially beneficial microbes sensitive to antibacterial effects of DCA e.g., Ruminococcaceae were decreased. The clinical relevance of these data was confirmed in an independent cohort enrolled in a clinical trial for NASH where at entry DCA and its conjugates were associated with advanced fibrosis. In patients treated with placebo, DCA declined in those with fibrosis regression and increased in those with fibrosis progression. DCA rose further in those with compensated cirrhosis when they experienced decompensation.

CONCLUSIONS

These findings demonstrate a role for bile acids and the bile acid dependent microbiome in the development and progression of NAFLD and set the stage to leverage these findings for NASH biomarker development and for therapeutics.

Gene Expression and DNA Methylation Alterations in the Glycine N-Methyltransferase Gene in Diet-Induced Nonalcoholic Fatty Liver Disease-Associated Carcinogenesis

Nonalcoholic fatty liver disease (NAFLD) is becoming a major etiological risk factor for hepatocellular carcinoma (HCC) in the United States and other Western countries. In this study, we investigated the role of gene-specific promoter cytosine DNA methylation and gene expression alterations in the development of NAFLD-associated HCC in mice using (1) a diet-induced animal model of NAFLD, (2) a Stelic Animal Model of nonalcoholic steatohepatitis-derived HCC, and (3) a choline- and folate-deficient (CFD) diet (CFD model). We found that the development of NAFLD and its progression to HCC was characterized by down-regulation of glycine N-methyltransferase (Gnmt) and this was mediated by progressive Gnmt promoter cytosine DNA hypermethylation. Using a panel of genetically diverse inbred mice, we observed that Gnmt down-regulation was an early event in the pathogenesis of NAFLD and correlated with the extent of the NAFLD-like liver injury. Reduced GNMT expression was also found in human HCC tissue and liver cancer cell lines. In in vitro experiments, we demonstrated that one of the consequences of GNMT inhibition was an increase in genome methylation facilitated by an elevated level of S-adenosyl-L-methionine. Overall, our findings suggest that reduced Gnmt expression caused by promoter hypermethylation is one of the key molecular events in the development of NAFLD-derived HCC and that assessing Gnmt methylation level may be useful for disease stratification.

Abstract 5323: Gene-specific DNA methylation alterations in non-alcoholic fatty liver disease (NAFLD)-derived hepatocellular carcinoma in mice

Hepatocellular carcinoma (HCC) ranks as one of the most aggressive human cancers, with a steadily increasing incidence in the United States and worldwide. HCC is a disease characterized by the presence of multiple heritable cellular, molecular, and metabolic abnormalities driven by genetic and epigenetic alterations. Among these abnormalities, cancer-related gene-specific cytosine DNA methylation alterations, which are potentially reversible, are of special interest. In the vast majority of patients, HCC develops in association with an underlying chronic liver disease, such as non-alcoholic fatty liver disease (NAFLD). In the present study, we investigated the role of gene-specific DNA methylation alterations in the transcriptomic deregulation in HCC and adjacent liver tissue samples from mice subjected to a diet-induced animal model of non-alcoholic fatty liver disease (DIAMOND)-derived liver carcinogenesis. A combined transcriptomic and gene-specific methylation analysis showed that the number of differentially expressed protein-coding genes, which can be regulated by epigenetic mechanisms, was 2.6-times greater in full-fledged HCC than in adjacent liver tissue, 181 and 69, respectively. This indicates that the development of HCC is characterized by a progressive accumulation of epigenetic abnormalities in tumor tissue. The extent of gene-specific DNA methylation varied among epigenetically-regulated differentially expressed genes; however, the number of down-regulated genes was markedly greater in full-fledged HCC. This was evidenced by the fact that only eight epigenetically down-regulated genes in adjacent tissue were in common with HCC. In contrast, in addition to these eight common genes, the expression of additional 35 genes was reduced in HCC. Analysis of gene-specific DNA methylation demonstrated an increase in DNA methylation of several carcinogenesis-related genes down-regulated in HCC, including Gnmt, Cbs, Egfr, Fgfr2, and Esr1. These genes were hypermethylated also in adjacent liver tissue. The hypermethylation and down-regulation of these genes in HCC were confirmed independently in the Stelic Animal Model (STAM) of derived liver carcinogenesis, another mouse model of NAFLD-associated hepatocarcinogenesis. These results demonstrate that the altered expression of key genes is mediated through aberrant DNA methylation and can be a mechanism contributing to the development of NAFLD-related HCC.

Citation Format: Barbara Borowa-Mazgaj, Aline de Conti, Mulugeta Seneshaw, Faridodin Mirshahi, Frederick A. Beland, Arun J. Sanyal, Igor P. Pogribny. Gene-specific DNA methylation alterations in non-alcoholic fatty liver disease (NAFLD)-derived hepatocellular carcinoma in mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5323.

Nonalcoholic steatohepatitis is associated with a state of betaine-insufficiency

BACKGROUND AND AIMS

Nonalcoholic fatty liver disease (NAFLD) develops from a complex process, which includes changes in the liver methylome. Betaine plays a pivotal role in the regulation of methylogenesis. We performed a two-stage case-control study, which included patients with biopsy-proven NAFLD to explore circulating levels of betaine and its association with the histological spectrum. We also explored the association between a missense rs1805074, p.Ser646Pro variant in DMGDH (dimethylglycine dehydrogenase mitochondrial) and NAFLD severity (n=390).

RESULTS

In the discovery phase (n=48), betaine levels were associated with the disease severity (P=.0030), including liver inflammation (Spearman R:-0.51, P=.001), ballooning degeneration (R: -0.50, P=.01) and fibrosis (R: -0.54, P=.0008). Betaine levels were significantly decreased in nonalcoholic steatohepatitis (NASH) in comparison with nonalcoholic fatty liver (NAFL). Further replication (n=51) showed that betaine levels were associated with advanced NAFLD (P=.0085), and patients with NASH had a 1.26-fold decrease in betaine levels compared with those with NAFL. The rs1805074 was significantly associated with the disease severity (P=.011).

CONCLUSION

NAFLD severity is associated with a state of betaine-insufficiency.

Circulating microRNA signature in non-alcoholic fatty liver disease: from serum non-coding RNAs to liver histology and disease pathogenesis

OBJECTIVES

We used a screening strategy of global serum microRNA (miRNA) profiling, followed by a second stage of independent replication and exploration of liver expression of selected miRNAs to study: (1) the circulating miRNA signature associated with non-alcoholic fatty liver disease (NAFLD) progression and predictive power, (2) the role of miRNAs in disease biology and (3) the association between circulating miRNAs and features of the metabolic syndrome.

METHODS

The study used a case-control design and included patients with NAFLD proven through biopsy and healthy controls.

RESULTS

Among 84 circulating miRNAs analysed, miR-122, miR-192, miR-19a and miR-19b, miR-125b, and miR-375 were upregulated >2-fold (p<0.05) either in simple steatosis (SS) or non-alcoholic steatohepatitis (NASH). The most dramatic and significant fold changes were observed in the serum levels of miR-122 (7.2-fold change in NASH vs controls and 3.1-fold change in NASH vs SS) and miR-192 (4.4-fold change in NASH vs controls); these results were replicated in the validation set. The majority of serum miR-122 circulate in argonaute2-free forms. Circulating miR-19a/b and miR-125b were correlated with biomarkers of atherosclerosis. Liver miR-122 expression was 10-fold (p<0.03) downregulated in NASH compared with SS and was preferentially expressed at the edge of lipid-laden hepatocytes. In vitro exploration showed that overexpression of miR-122 enhances alanine aminotransferase activity.

CONCLUSIONS

miR-122 plays a role of physiological significance in the biology of NAFLD; circulating miRNAs mirror the histological and molecular events occurring in the liver. NAFLD has a distinguishing circulating miRNA profile associated with a global dysmetabolic disease state and cardiovascular risk.

[Thalidomide inhibits the angiogenic activity of culture supernatants of multiple myeloma cell line]

OBJECTIVE

To investigate the pro-angiogenic effects of several multiple myeloma (MM) cell line culture supernatants on human bone marrow endothelial cell (HBMEC) proliferation, migration, and capillary formation, and the anti-angiogenic effects of thalidomide.

METHODS

HBMEC was cultured in the presence of MM cell lines (IM9, XG1, U266 and MOLP-5) supernatants. Proliferation and migration of HBMEC were determined, capillary-like tubule formation of HBMEC was examined in fibrin and Matrigel. The inhibiting effect of thalidomide was investigated by adding it into myeloma cell line culture supernatants. Vascular endothelial growth factor (VEGF) was measured by ELISA.

RESULTS

(1) MM cell lines culture supernatants promoted HBMEC proliferation and migration. (2) In fibrin and Matrigel, capillary-like tubule network formation promoted by the supernatants. (3) All of these effects could be inhibited by thalidomide. (4) This effect was not related to VEGF in the supernatants.

CONCLUSIONS

MM cell line promote proliferation, migration and tubule formation by secreting VEGF or other several cytokines. Thalidomide can inhibit these effects.

Oncostatin M induces procoagulant activity in human vascular smooth muscle cells by modulating the balance between tissue factor and tissue factor pathway inhibitor

Oncostatin M (OSM) is a cytokine of the interleukin-6 (IL-6) family secreted by activated monocytes, and is expressed in atherosclerotic plaque. Smooth muscle cells (SMC), by expressing tissue factor (TF) and tissue factor pathway inhibitor (TFPI) can contribute to the thrombogenicity of atherosclerotic plaque. Consequently, the aim of this study was to evaluate the effects of OSM on the procoagulant activity of SMC. We observed that OSM induced in a concentration-dependent manner a potent procoagulant activity (PCA) that was related in part to an increased synthesis of TF, both at the cell membrane and in SMC lysates. The increased expression of TF on SMC membrane induced by OSM was sustained and was still observed 24 h after stimulation by OSM. IL-6 and leukaemia inhibitory factor (LIF), two OSM-related cytokines, did not significantly modify TF expression at the surface of SMC. In addition to its effects on TF, OSM decreased the secretion of TFPI in the supernatants of SMC, as well as in the lysates, but was devoid of effect on TFPI bound at the membrane of SMC. IL-6 and LIF reduced also TFPI secretion, which could explain why the PCA of SMC lysates treated by IL-6 or LIF was increased, despite an absence of effect on TF expression. In conclusion, these data support the hypothesis that by increasing the PCA of SMC, OSM might be involved in the thrombotic complications associated with plaque rupture.

Fibrinogen: a vascular risk factor, why? Contributing effect of oncostatin M on both fibrinogen biosynthesis by hepatocytes and participation in atherothrombotic risk related to modifications of endothelial cells

Fibrinogen is a vascular risk factor. We suggest that it is a marker of cytokine secretion that simultaneously stimulates fibrinogen biosynthesis and vascular modifications responsible for atherothrombosis. Among these cytokines, oncostatin M (OSM) is the most potent cytokine for inducing fibrinogen biosynthesis by hepatocytes, and it could contribute to endothelial cell anomalies involved in the atherothrombotic process. Here we show that OSM acts (1) by inducing the secretion involved in invasion of the vessel wall by monocytes; (2) by inducing angiogenesis it promotes plaque destabilization, rupture, and consequently thrombosis; and (3) by decreasing fibrinolysis on macrovascular endothelial cells.

Endocannabinoids acting at vascular CB1 receptors mediate the vasodilated state in advanced liver cirrhosis

Advanced cirrhosis is associated with generalized vasodilation of unknown origin, which contributes to mortality. Cirrhotic patients are endotoxemic, and activation of vascular cannabinoid CB1 receptors has been implicated in endotoxin-induced hypotension. Here we show that rats with biliary cirrhosis have low blood pressure, which is elevated by the CB1 receptor antagonist SR141716A. The low blood pressure of rats with CCl4-induced cirrhosis was similarly reversed by SR141716A, which also reduced the elevated mesenteric blood flow and portal pressure. Monocytes from cirrhotic but not control patients or rats elicited SR141716A-sensitive hypotension in normal recipient rats and showed significantly elevated levels of anandamide. Compared with non-cirrhotic controls, in cirrhotic human livers there was a three-fold increase in CB1 receptors on isolated vascular endothelial cells. These results implicate anandamide and vascular CB1 receptors in the vasodilated state in advanced cirrhosis and indicate a novel approach for its management.

Inhibition of endothelial cell migration by cerivastatin, an HMG-CoA reductase inhibitor: contribution to its anti-angiogenic effect

Recent studies have suggested that inhibitors of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (statins) can play a role in protection against vascular risk, which is independent of cholesterol reduction. It could act by inhibiting the synthesis of isoprenoids (farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP)), which are respectively essential for membrane attachment and biological activity of GTPases Ras and RhoA. This study demonstrates that a statin (cerivastatin) inhibits angiogenesis. This effect was due to a decrease in endothelial cell locomotion which was reversed by GGPP. It was mainly related to delocalization of RhoA from cell membrane to cytoplasm, responsible for the disorganization of actin stress fibers. Furthermore, a decrease in MMP-2 secretion, involved in cell invasion, was also observed. This effect is rather due to Ras inhibition as it was reversed by FPP. This anti-angiogenic activity could explain the beneficial effect of statins on atherosclerosis and on cancer prevention as shown by clinical studies.

Nonalcoholic steatohepatitis: association of insulin resistance and mitochondrial abnormalities

BACKGROUND AND AIMS

The pathogenesis of nonalcoholic steatohepatitis (NASH) is unknown. We tested the hypothesis that NASH is associated with 2 defects: (1) peripheral insulin resistance, which increases lipolysis, delivery of free fatty acids (FFA) to the liver, and hepatic fatty acid beta oxidation, thereby creating oxidative stress; and (2) an abnormality within the hepatocytes that might render them more susceptible to injury from oxidative stress.

METHODS

The hypothesis was tested by evaluation of (1) insulin resistance by a 2-step hyperinsulinemic (10 and 40 mU. m(-2). min(-1)) euglycemic clamp; (2) insulin effects on lipolysis by enrichment of [U-(13)C]glycerol; (3) frequency and severity of structural defects in hepatocyte mitochondria in vivo; (4) fatty acid beta oxidation from serum [beta-OH butyrate], release of water-soluble radioactivity from (3)H-palmitate by cultured fibroblasts and urinary dicarboxylic acid excretion; and (5) hepatic lipid peroxidation by immunohistochemical staining for 3-nitrotyrosine (3-NT). Subjects with NASH (n = 6-10 for different studies) were compared with those with fatty liver (n = 6) or normal controls (n = 6).

RESULTS

NASH and fatty liver were both associated with insulin resistance, with mean glucose infusion rates (normal/fatty liver/NASH) of step 1, 4.5/1.6/0.9; step 2, 9.5/7.7/4.5 (P < 0.03 for both steps). Although baseline rates of glycerol appearance were higher in those with NASH than in those with fatty liver (means, 14.6 vs. 21.6 micromol. kg(-1). min(-1); P < 0.05), neither group significantly suppressed glycerol appearance at insulin infusion rates of 10 mU. m(-2). min(-1). NASH was associated with loss of mitochondrial cristae and paracrystalline inclusions in 9 of 10 subjects, compared with 0 of 6 subjects with fatty liver. However, no evidence of a generalized defect in fatty acid beta oxidation was noted in any group. Also, mean [beta-OH butyrate] was highest in those with NASH (means, 90 vs. 110 vs. 160 micromol/L; P < 0.04). Increased staining for 3-NT was present in fatty liver, and even greater staining was seen in NASH.

CONCLUSIONS

These data indicate that peripheral insulin resistance, increased fatty acid beta oxidation, and hepatic oxidative stress are present in both fatty liver and NASH, but NASH alone is associated with mitochondrial structural defects.

Systemic and portal hemodynamic effects of anandamide

The endogenous cannabinoid anandamide causes hypotension and mesenteric arteriolar dilation. A detailed analysis of its effects on systemic and portal venous hemodynamics had not yet been performed. We assessed the effects of anandamide (0.4-10 mg/kg) on systemic and portal hemodynamics with and without prior treatment with various antagonists. The specific antagonists used included SR-141716A, N(omega)-nitro-L-arginine methyl ester, indomethacin, and nordihydroguaiaretic acid. Anandamide produced a dose-dependent decrease in mean arterial pressure due to a drop in systemic vascular resistance (SVR) that was accompanied by a compensatory rise in cardiac output. Anandamide also elicited an increase in both portal venous flow and pressure, along with a decline in mesenteric vascular resistance (MVR). Pretreatment with 3 mg/kg SR-141716A, a CB(1) antagonist, prevented the decline of SVR and MVR from the lower dose of anandamide. Antagonism of nitric oxide synthetase, cyclooxygenase, or 5-lipoxygenase did not prevent the systemic nor the portal hemodynamic effects of anandamide. Furthermore, the use of R-methanandamide, a stable analog of anandamide, produced similar hemodynamic effects on the mesenteric vasculature, thereby implying that the effects of anandamide are not related to its breakdown products. Anandamide produced profound, dose-dependent alterations in both the systemic and portal circulations that could be at least partially blocked by pretreatment with SR-141716A.

SDF-1 activity on microvascular endothelial cells: consequences on angiogenesis in in vitro and in vivo models

The chemokine stromal cell-derived factor-1 (SDF-1) has been shown to be involved in cell migration. As the receptor CXCR-4 is expressed on endothelial cells and upregulated by angiogenic factors, we were prompted to study the effect of SDF-1 on angiogenesis in endothelial cells from microvasculature. This study demonstrates that SDF-1 induces an angiogenic effect in vitro, primarily in a tridimensional fibrin gel. The increase in capillary tube formation was evident after a 10-day incubation with SDF-1. This was associated with a mild increase in VEGF production by microvascular endothelial cells (ELISA and rt-PCR) and a potent chemotactic effect. SDF-1 also induced an in vivo angiogenic activity as shown in the model of the rabbit corneal pocket. However, the angiogenesis was located in an area rich in inflammatory cells. The results of our study suggest that these data underline the potential role of SDF-1 in angiogenesis as the microvascular endothelial cells were greatly involved in this process.

Functional CB1 cannabinoid receptors in human vascular endothelial cells

Cannabinoid CB1 receptor mRNA was detected using reverse transcription-polymerase chain reaction (RT-PCR) in endothelial cells from human aorta and hepatic artery and in the ECV304 cell line derived from human umbilical vein endothelial cells. CB1 receptor-binding sites were detected by the high-affinity antagonist radioligand [(125)I]AM-251. In ECV304 cells, both the highly potent synthetic cannabinoid agonist HU-210 and the endogenous ligand anandamide induce activation of mitogen-activated protein (MAP) kinase, and the effect of HU-210 was completely blocked, whereas the effect of anandamide was partially inhibited by SR141716A, a selective CB1 receptor antagonist. Transfection of ECV304 cells with CB1 receptor antisense, but not sense, oligonucleotides caused the same pattern of inhibition as SR141716A. This provides more definitive evidence for the involvement of CB1 receptors in MAP kinase activation and suggests that anandamide may also activate MAP kinase via an additional, CB1 receptor-independent, SR141716A-resistant mechanism. The MAP kinase activation by anandamide in ECV304 cells requires genistein-sensitive tyrosine kinases and protein kinase C (PKC), and anandamide also activates p38 kinase and c-Jun kinase. These findings indicate that CB1 receptors located in human vascular endothelium are functionally coupled to the MAP kinase cascade. Activation of protein kinase cascades by anandamide may be involved in the modulation of endothelial cell growth and proliferation.

Cyclooxygenase-2 activity is necessary for the angiogenic properties of oncostatin M

Macrophages play a major role in angiogenesis. We recently reported that oncostatin M (OSM), a cytokine of the interleukin (IL)-6 family secreted by macrophages, has a potent angiogenic activity on human microvascular endothelial cells (HMEC-1), but has no effect on macrovascular cells (human umbilical vein endothelial cells (HUVECs)). In this work, we show that in HMEC-1, OSM (0.5-2.5 ng/ml), leukemia inhibitory factor (LIF) (25 ng/ml), bFGF (25 ng/ml) and IL-1beta (5 ng/ml) induced production of cyclooxygenase (COX)-2. In contrast, in HUVECs, neither OSM nor LIF induced COX-2 mRNA, suggesting that COX-2 might be implicated in the angiogenic activity of OSM. This was confirmed by the inhibiting effect on OSM-induced HMEC-1 proliferation of specific COX-2 inhibitors. In vivo studies confirmed this findings. We conclude that induction of COX-2 by OSM is necessary for its angiogenic activity, but is not sufficient since IL-1beta, which also induces COX-2 in HMEC-1, has only a poor proliferative effect.

Endothelial cells lining transjugular intrahepatic portasystemic shunts originate in hepatic sinusoids: implications for pseudointimal hyperplasia

The phenotype of the endothelial cells (ECs) in the pseudointima of transjugular intrahepatic portasystemic shunts (TIPS) and the mechanisms of pseudointima formation after TIPS were unknown. We hypothesized that TIPS were lined by hepatic sinusoidal ECs, which stimulated the migration of smooth muscle cells (SMCs) into the pseudointima and their proliferation. Studies were done with the following specific aims: (1) isolation of ECs from TIPS pseudointima and comparison of their phenotype with human cirrhotic sinusoidal and vascular ECs derived from hepatic and portal veins as well as aorta, and (2) testing of the effects of TIPS ECs on TIPS-derived SMC migration and proliferation. ECs were isolated from eight TIPS retrieved from liver explants by immunomagnetic separation using monodispersed magnetizable polystyrene beads (Dynabeads M-450) coated with Ulex Europeus 1. EC phenotypes were examined by transmission electron microscopy, factor VIII-related antigen, CD31, CD14, and CD34 expression, uptake of acetylated LDL and secretion of type IV collagen. The effects of EC-conditioned media on SMC migration and proliferation were tested in multiwell chemotaxis chambers and by cell counting, respectively. ECs were obtained from TIPS pseudointima with >95% purity. The phenotype of TIPS-derived ECs matched that of cirrhotic sinusoidal endothelium (both expressed CD14) and differed from that of vascular endothelium (CD14 negative, Weibel-Palade positive). Conditioned media from both stenosed (n = 3) and nonstenosed (n = 3) TIPS-derived endothelial cells produced a marked (>100%) P <.001 increase in migration as well as (up to 88%) P <.01 proliferation of SMCs from both stenosed (n = 3) as well as nonstenosed TIPS (n = 3). These data indicate that TIPS pseudointima are lined by hepatic sinusoidal endothelial cells, which stimulate pseudointima formation by increasing SMC migration and proliferation.

Omeprazole may exert both a bacteriostatic and a bacteriocidal effect on the growth of Helicobacter pylori (NCTC 11637) in vitro by inhibiting bacterial urease activity

AIMS

To assess the potential antibacterial effect of omeprazole, a benzimidazole proton pump inhibitor, on the growth of Helicobacter pylori in vitro and to evaluate the effect of this compound on bacterial urease activity.

METHODS

The growth of H pylori was observed in liquid culture in the presence and absence of omeprazole (0.8 mg/ml). Urease activity was evaluated in aliquots removed from two hour cultures by monitoring the initial change in absorbency at 560 nm in the presence of 0.02% phenol red.

RESULTS

The minimum inhibitory concentration of omeprazole against H pylori was 0.8 mg/ml. The concentration of omeprazole required to inhibit growth was dependent on inoculum density: omeprazole (0.8 mg/ml) prevented growth from a 1 x 10(6) cfu/ml inoculum, but not from the higher inocula of 10(7) or 10(8) cfu/ml. This is the first study to demonstrate that omeprazole exerts a bacteriocidal effect against low bacterial densities and a bacteriostatic effect when bacterial density is high. When used at the onset of growth, this concentration of omeprazole has a bacteriocidal effect after four hours, although it exerts a bacteriostatic effect when added to cultures after the exponential phase. Bacterial urease activity is competitively inhibited by omeprazole in a dose dependent manner.

CONCLUSION

The results suggest that omeprazole exerts both a bacteriocidal and a bacteriostatic effect against H pylori and competitively inhibits bacterial extracellular urease activity.

Evidence for receptor-mediated mineralocorticoid action in rat osteoblastic cells

Aldosterone significantly enhanced the proliferation of osteoblastic cells from rat calvaria, and this effect was inhibited by RU 26752 and ZK 91587, two antagonists specific to the mineralocorticoid receptor (MCR). In addition, aldosterone inhibited the activity of alkaline phosphatase, a marker of the osteoblastic phenotype, and this effect was also reversed by RU 26752. Cytoplasmic staining of MCR was observed in rat calvaria osteoblasts incubated with a specific polyclonal antiserum raised against rat kidney MCR. This anti-MCR immunoglobulin G immunoprecipitated and macroaggregated the MCR-[3H]RU 26752 complex in osteoblastic cytosol. A single 98-kDa band was observed when osteoblastic cytosol was analyzed by Western blotting with anti-MCR serum. The 98-kDa band was also obtained after autoradiography of irradiated osteoblastic cytosol-[3H]R 5020 complex, and this was abolished in the presence of RU 26752. A p26MR probe, specific to COOH-terminal end of MCR, hybridized with the predicted product after amplification of total cell RNA by polymerase chain reaction technique. Furthermore, hybridization of poly(A)+ mRNA from at calvaria osteoblastic cells with the p26MR probe revealed a major band of approximately 4.2 kb. Collectively, our studies demonstrate the existence of a functional MCR in rat calvaria osteoblasts.

Properties of the mineralocorticoid receptor immunopurified from bovine kidney

The mineralocorticoid receptor (MCR) from bovine kidney was purified on an affinity column containing covalently linked polyclonal IgG raised in the rabbit against rat kidney protein purified in the presence of RU 26752 that is specific to the MCR. The immuno-affinity eluate was excluded as a single peak during gel permeation chromatography and could be resolved as a single band of approximately 98 kDa by western blot and gel electrophoresis. Immunohistochemistry revealed MCR-specific staining in both the cortical and glomerular regions of bovine kidney. Interestingly, the purified MCR could not be activated in the presence of the specific ligand RU 26752 whereas binding to DNA-cellulose increased by 100% when crude cytosol was left at room temperature for 45 min. The binding of calcium to the MCR resulted in an increase in the fluorescence signal that could be partially reversed by EDTA. By a calcium-specific fluorescence dye technique, 1.13 nM of ionized Ca2+ was bound per 0.01 nM MCR. The binding of ATP32 to the immunopurified receptor was observed following chromatography on P-10 columns. The fluorescence signal of etheno-ATP was maximally attenuated by the receptor at 1/1 stoichiometry of the ATP-MCR complex. Asparagine-linked complex chain N-glycosylation of the purified MCR was also observed. Analysis by far-UV circular dichroism spectra showed that MCR contains 33% alpha helices and 30% beta sheets, compatible with a relatively flat conformation of the native protein. These data provide experimental proof for the predicted computer simulation regarding the structural features of the steroid receptor superfamily and suggest crosstalk between several protein families.

Immunochemical detection of the mineralocorticoid receptor in rat brain

The mineralocorticoid receptor (MCR) in the brain of adult male rats was analyzed with the aid of an antiserum generated by immunizing rabbits with this protein purified biochemically from rat kidney. In Western blots, the antibody recognized a single band of protein of about 98 kD from all target tissues studied to date. The granular cells in the cerebellum appeared to be the richest region of the central nervous system in the MCR analyzed by dot blots and by immunoperoxidase staining. High immunoreactivity was also observed in the dorsal and ventral hippocampus, as well as the anterior, mediobasal and posterior hypothalamus. In contrast, midbrain, septum and striatum were MCR-negative. The antibody macroaggregated and precipitated brain MCR labelled with 3H-aldosterone but did not recognize 3H-RU 26752 bound nonspecifically to non-MCR proteins in whole brain cytosol. Thus, MCR function and expression in the adult rat brain need to be reassessed.

The role of fibroblasts in organization and degradation of a fibrin clot

Older clots become less sensitive to fibrin degradation than newly formed ones. A possible role for fibroblasts in this defective thrombus lysis was studied. A system has been developed in which different clones of fibroblasts were incorporated into a floating whole blood clot. The effect of the incorporated fibroblasts on clot lysis has been analyzed in relation to their basic characteristics: clot retraction, production of plasminogen activators (PAs) and their inhibitors (PAIs), and secretion of collagen. In neoplastic fibroblast-enriched clots, secretion of PA was associated with spontaneous lysis of a whole blood clot. Normal fibroblasts, secreting levels of PA and PAI similar to those of the cancer cells, did not induce spontaneous lysis of the clot. Moreover, these cells protected whole blood clot from thrombolysis by added PA. Our data show that the resistance to fibrin clot degradation induced by normal fibroblasts was mainly mediated by collagen secretion and deposition rather than PAI secretion or retraction of the clot. We suggest a key role for normal fibroblasts in the acquisition of resistance to proteolytic fibrin degradation of whole blood clots through the secretion of collagen.