High-T(c) Superconductivity at the Interface between the CaCuO2 and SrTiO3 Insulating Oxides

At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low T(c). We report the occurrence of high T(c) superconductivity in the bilayer CaCuO(2)/SrTiO(3), where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO(2)/SrTiO(3) interface must be realized between the Ca plane of CaCuO(2) and the TiO(2) plane of SrTiO(3). Only in this case can oxygen ions be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO(2) planes. A detailed hole doping spatial profile can be obtained by scanning transmission electron microscopy and electron-energy-loss spectroscopy at the O K edge, clearly showing that the (super)conductivity is confined to about 1-2 CaCuO(2) unit cells close to the interface with SrTiO(3). The results obtained for the CaCuO(2)/SrTiO(3) interface can be extended to multilayered high T(c) cuprates, contributing to explaining the dependence of T(c) on the number of CuO(2) planes in these systems.

Contrast-enhanced ultrasound to evaluate the severity of chronic hepatitis C

BACKGROUND

Non-invasive techniques are being developed to assess the severity of liver disease. Haemodynamic changes in the hepatic circulation during the development of liver disease can be evaluated with contrast-enhanced ultrasound.

AIM

To evaluate the possible correlation between ultrasound contrast-agent transit times and different stages of chronic hepatitis C.

PATIENTS

Sixteen patients with clinically evident hepatitis C virus-related cirrhosis, 22 non-cirrhotic patients with chronic hepatitis C and 14 controls with no clinical evidence of liver disease were studied.

METHODS

Contrast-enhanced hepatic ultrasonography was performed with a sulphur hexafluoride-filled microbubble contrast agent, and time curves of hepatic vein signal intensity were analysed to determine the time of enhancement onset (hepatic vein arrival time) and peak enhancement (hepatic vein peak enhancement).

RESULTS

Hepatic vein arrival time in cirrhotic patients was significantly shorter (p<0.001) than in non-cirrhotic patients and controls. Within the group with chronic hepatitis C, METAVIR scores of fibrosis and necro-inflammatory changes had no significant effect on hepatic vein arrival times.

CONCLUSION

Analysis of the time of onset of ultrasound contrast enhancement of the hepatic vein appears to be a simple, non-invasive method for reliably excluding cirrhosis with signs of portal hypertension, but not for assessing the severity of either chronic hepatitis C or cirrhosis.

Post-load insulin resistance is an independent predictor of hepatic fibrosis in virus C chronic hepatitis and in non-alcoholic fatty liver disease

BACKGROUND

Insulin resistance is a significant risk factor for hepatic fibrosis in patients with both non-alcoholic fatty liver disease (NAFLD) and chronic hepatitis C (CHC), either directly or by favouring hepatic steatosis. Several methods are available to assess insulin resistance, but their impact on this issue has never been evaluated.

AIMS

To determine the relative contribution of steatosis, metabolic abnormalities and insulin resistance, measured by different basal and post-load parameters, to hepatic fibrosis in CHC and in NAFLD patients.

METHODS

In 90 patients with CHC and 90 pair-matched patients with NAFLD, the degree of basal insulin resistance (by the homeostasis model assessment, (HOMA)) and post-load insulin sensitivity (by the oral glucose insulin sensitivity (OGIS) index) was assessed, together with the features of the metabolic syndrome according to Adult Treatment Panel III definition. Data were correlated with hepatic histopathology.

RESULTS

The prevalence of basal insulin resistance (HOMA values >75th percentile of normal) was 23.3% in CHC patients and 57.8% in NAFLD, but it increased to 28.8 and 67.8% when measured by post-load insulin resistance (OGIS <25th percentile). In a multivariate model, after adjustment for age, gender and body mass index, OGIS was a predictor of severe fibrosis in CHC and in NAFLD patients, independently of steatosis. An OGIS value below the cut-off of the 25th percentile increased the likelihood ratio of severe fibrosis by a factor of 1.5-2 and proved to be a more sensitive and generally more specific test than HOMA-R for the identification of subjects with severe fibrosis both in NAFLD and in CHC.

CONCLUSIONS

Post-load insulin resistance (OGIS <9.8 mg/kg/min) is associated with severe hepatic fibrosis in both NAFLD and CHC patients, and may help identify subjects at risk of progressive disease.

Intracellular signaling pathways involved in acetaldehyde-induced collagen and fibronectin gene expression in human hepatic stellate cells

Ethanol induces liver fibrosis by several means that include, among others, the direct fibrogenic action of acetaldehyde on hepatic stellate cells (HSC). However the mechanisms responsible for this effect are not well understood. In this communication we investigated signal transduction pathways triggered by acetaldehyde leading to upregulation of alpha2(I) collagen and fibronectin gene expression in human HSC. Run-on assays showed that acetaldehyde-enhanced transcription of these 2 genes as early as 2 hours, via de novo protein synthesis-independent and -dependent mechanisms. It also stimulated a time-dependent induction in phosphorylation of pp70(S6K) and extracellular-regulated kinase (1/2) (ERK1/2). These effects were completely prevented by calphostin C, a protein kinase C inhibitor. As expected, acetaldehyde-elicited ERK1/2 phosphorylation was inhibited by PD98059, a MEK inhibitor, but not by wortmannin, a PI3K inhibitor. On the other hand, both of these inhibitors partially inhibited phosphorylation of pp70(S6K) induced by acetaldehyde suggesting that its activation is ERK1/2- and PI3K-dependent. Acetaldehyde-elicited fibronectin and alpha2(I) collagen upregulation was inhibited by calphostin C. However, while PD98059, wortmannin and rapamycin (a pp70(S6K) inhibitor) completely abrogated alpha2(I) collagen upregulation, they had no effect on fibronectin expression. Overall, these data suggest that protein kinase C is an upstream component from which acetaldehyde signals are transduced to other pathways such as PI3K and ERK1/2. In addition, differential activation of these pathways is needed for the increase in fibronectin and alpha2(I) collagen gene expression induced by acetaldehyde in human HSC.

Intracellular pH regulation and Na+/H+ exchange activity in human hepatic stellate cells: effect of platelet-derived growth factor, insulin-like growth factor 1 and insulin

BACKGROUND/AIMS

The Na+/H+ exchanger is involved in rat hepatic stellate cell (HSC) proliferation induced by platelet-derived growth factor (PDGF). We therefore evaluated in human HSC: (1) the mechanisms of intracellular pH regulation; (2) the relationship between Na+/H+ exchange activation and cell proliferation induced by PDGF, insulin-like growth factor 1 (IGF-1) and insulin.

METHODS/RESULTS

pH(i) regulation was mainly dependent on the activity of the Na+/H+ exchanger, which was evaluated by measuring pH(i) recovery from an acute acid load. PDGF (25 ng/ml) gradually increased the activity of the Na+/H+ exchanger which peaked at 18 h and remained stable until the 24th h. IGF-1 (10 nmol/l), but not insulin (100 nmol/l), slightly but significantly increased the activity of the Na+/H+ exchanger. Amiloride (100 micromol/l) and 20 micromol/l 5-N-ethyl-N-isopropyl-amiloride completely inhibited HSC proliferation (evaluated by measurement of bromodeoxyuridine incorporation) induced by PDGF and IGF-1, but did not affect proliferation of HSC induced by insulin. Finally, IGF-1 did not modify the activity of the Na+/Ca2+ exchanger.

CONCLUSIONS

The Na+/H+ exchanger is involved in HSC proliferation induced by PDGF and IGF-1, whereas the proliferative effect of insulin is mediated by intracellular pathways which are Na+/H+ exchange-independent.

Inhibition of the NA(+)/H(+) exchanger reduces rat hepatic stellate cell activity and liver fibrosis: an in vitro and in vivo study

BACKGROUND & AIMS

The Na(+)/H(+) exchanger is the main intracellular pH (pH(i)) regulator in hepatic stellate cells (HSCs) and plays a key role in regulating proliferation and gene expression. We evaluated the effect of specific inhibition of this exchanger on HSC proliferation and collagen synthesis in vivo and in vitro.

METHODS

Rat HSCs were incubated in the presence of platelet-derived growth factor (PDGF), transforming growth factor (TGF)-beta1, iron ascorbate (FeAsc), and ferric nitrilotriacetate solution (FeNTA) with or without the Na(+)/H(+) exchanger inhibitor 5-N-ethyl-N-isopropyl-amiloride (EIPA). pH(i) and Na(+)/H(+) exchanger activity, cell proliferation, and type I collagen accumulation were measured by using the fluorescent dye 2',7'-bis-(carboxyethyl)-5(6)-carboxyfluorescein, by immunohistochemistry for bromodeoxyuridine, and by enzyme-linked immunosorbent assay, respectively. In vivo liver fibrosis was induced by dimethylnitrosamine administration and bile duct ligation (BDL) in rats treated or not treated with amiloride.

RESULTS

PDGF, FeAsc, and FeNTA increased Na(+)/H(+) exchange activity and induced HSC proliferation. TGF-beta1 had no effect on the Na(+)/H(+) exchanger and was able, as for FeAsc and FeNTA, to induce type I collagen accumulation. EIPA inhibited all the effects determined by PDGF, FeAsc, and FeNTA and had no effect on TGF-beta1-induced collagen accumulation. In vivo, amiloride reduced HSC proliferation, activation, collagen deposition, and collagen synthesis.

CONCLUSIONS

The Na(+)/H(+) exchanger can play a key role in the development of liver fibrosis and in HSC activation in vivo.

Insulin and insulin-like growth factor-1 stimulate proliferation and type I collagen accumulation by human hepatic stellate cells: differential effects on signal transduction pathways

Insulin and insulin-like growth factor (IGF-1) are mitogenic for fibroblasts and smooth muscle cells. IGF-1 increases in inflamed and fibrotic tissues and induces proliferation of rat hepatic stellate cells (HSC). This study evaluates the potential roles of these hormones in the development of liver fibrosis. Insulin and IGF-1 receptor expression was evaluated by immunohistochemistry in both cultured human HSC and human liver tissue. Phosphorylation of both 70-kd S6 kinase and extracellular-regulated kinase (ERK), cell proliferation, type I collagen gene expression, and accumulation in HSC culture media were evaluated by Western blot, immunohistochemistry for bromodeoxyuridine (BrdU), Northern blot, and enzyme-linked immunosorbent assay, respectively. Insulin and IGF-1 receptors were detected in HSC in vitro and in liver sections from patients with chronic active hepatitis. Insulin and IGF-1 induced 70-kd S6 kinase phosphorylation in HSC, whereas IGF-1 only induced ERK phosphorylation. Insulin and IGF-1 stimulated HSC proliferation in a dose-dependent fashion, with IGF-1 being four to five times more potent than insulin. Cell exposure to specific inhibitors showed that both phosphatidylinositol 3-kinase (PI3-K) and ERK are involved in IGF-1-induced mitogenesis, whereas insulin stimulated mitogenesis through a PI3-K-dependent ERK-independent pathway. IGF-1 increased type I collagen gene expression and accumulation in HSC culture media through a PI3-K- and ERK-dependent mechanism. In conclusion, insulin and IGF-1, which stimulate HSC mitogenesis and collagen synthesis, may act in concert to promote liver fibrosis in vivo by a differential activation of PI3-K- and ERK1-dependent pathways.

Intracellular pathways mediating Na+/H+ exchange activation by platelet-derived growth factor in rat hepatic stellate cells

BACKGROUND & AIMS

The Na+/H+ exchanger is the main intracellular pH regulator in hepatic stellate cells (HSCs), and its activity is increased by platelet-derived growth factor (PDGF). Amiloride, an Na+/H+ exchange inhibitor, reduces PDGF-induced HSC proliferation, suggesting that the Na+/H+ exchanger plays a role in regulating HSC proliferative response. The aim of this study was to characterize the intracellular pathways mediating activation of the Na+/H+ exchanger by PDGF in HSCs.

METHODS

The activity of the Na+/H+ exchanger and HSC proliferation rate were evaluated under control condition and after incubation with PDGF in the absence or presence of specific inhibitors of the main intracellular pathways of signal transduction. Na+/H+ exchange protein expression was evaluated by means of Western blot.

RESULTS

PDGF induced a significant increase in the activity of the Na+/H+ exchanger without modifying protein expression. Inhibition of the calcium/calmodulin- and protein kinase C-dependent pathways resulted in a significant inhibition of both Na+/H+ exchange activity and of PDGF-induced HSC proliferation. The involvement of the two pathways was confirmed by showing that incubation of HSCs with both phorbol-12-myristate-13-acetate, a potent protein kinase C activator, and thapsigargin, which increases intracellular calcium levels, significantly increased both the Na+/H+ exchanger activity and HSC proliferation rate. Inhibition of the protein kinase A pathway did not modify either PDGF-induced Na+/H+ exchange activation or PDGF-induced HSC proliferation. On the contrary, inhibition of the mitogen-activated protein kinase- and of phosphatidylinositol 3-kinase-dependent pathways significantly reduced PDGF-induced HSC proliferation without affecting the activity of the Na+/H+ exchanger.

CONCLUSIONS

Activation of the Na+/H+ exchanger by PDGF in HSCs is mediated by calcium/calmodulin- and protein kinase C-dependent pathways. PDGF-induced HSC proliferation is mediated by Na+/H+ exchange-dependent and -independent pathways.

The Na+/H+ exchanger modulates the fibrogenic effect of oxidative stress in rat hepatic stellate cells

BACKGROUND/AIMS

Oxidative stress is associated with liver fibrosis in vivo and with hepatic stellate cell (HSC) activation in vitro, but the intracellular mechanisms mediating these effects are mostly unknown. The Na+/H+ exchanger plays a key role in regulating the cell cycle, and is involved in HSC proliferation. Its role in different HSC features, such as collagen accumulation, is still unknown. We thus evaluated if the Na+/H+ exchanger modulates the fibrogenic effect of oxidative stress in rat HSC.

METHODS

HSC were incubated with 0.1 mM ferric nitrilotriacetate complex (FeNTA). Intracellular hydroperoxides and malonildialdehyde (MDA) levels in the culture media were measured by the dichlorofluorescein and TBARS method, respectively. Intracellular pH and Na+/H+ exchanger activity were measured using the fluorescent dye BCECF. Cell proliferation was measured by immunohistochemistry for bromodeoxyuridine incorporation. Collagen type I accumulation in the culture media was measured by ELISA.

RESULTS

HSC incubation with FeNTA resulted in a significant production of intracellular hydroperoxides and MDA, associated with increased Na+/H+ exchange activity and baseline intracellular pH (pHi). Exposure of HSC to FeNTA significantly enhanced the number of proliferating HSC and collagen type I levels in the culture medium. All these effects were reversed by the antioxidant resveratrol and by the Na+/H+ exchanger inhibitor amiloride.

CONCLUSIONS

This study indicates that the Na+/H+ exchanger might represent a common mediator of the different effects induced by oxidative stress on HSC. The reduction in cell proliferation and collagen synthesis induced by amiloride could represent a new therapeutic challenge in liver fibrosis.

Fibrogenic effect of oxidative stress on rat hepatic stellate cells

Oxidative stress is associated with liver fibrosis and with hepatic stellate cell (HSC) activation in vivo. However, it remains controversial whether oxidative stress contributes to HSC activation either directly or through a paracrine stimulation by damaged hepatocytes. A medium containing products released from cells undergoing oxidative stress was obtained after incubation of hepatocytes with (HCM/Fe) or without (HCM) 0.1 mmol/L ferric nitrilotriacetate complex (FeNTA). Exposure of HSC to HCM/Fe for 24 hours significantly increased the number of proliferating HSC compared with HCM and to controls at all dilutions tested. The simultaneous coincubation of HSC with HCM/Fe and desferrioxamine (50 micromol/L) did not reduce the observed increase in cell proliferation, thus excluding a role for eventually contaminating iron in HCM/Fe. HCM/Fe induced also a significant increase in collagen type I accumulation in HSC culture media. To study the cellular mechanism underlying HCM/Fe effects, we evaluated the activity of the Na+/H+ exchanger, which plays a role in regulating HSC proliferation. The incubation of HSC for 24 hours with HCM/Fe significantly increased baseline intracellular pH (pHi) and Na+/H+ exchanger activity, indicating a plausible role of this antiport in mediating cell response. In conclusion, hepatocytes undergoing oxidative stress release factors which are fibrogenic for HSC, thereby, confirming what has been only hypothesized in vivo. In addition, HSC proliferation is associated with changes in the Na+/H+ exchanger activity, thus providing a useful target for the evaluation of inhibitors of this pathway for the treatment of hepatic fibrosis.

Characterization of ion transport mechanisms regulating intracellular pH in hepatic stellate cells

The aim of this study was to evaluate intracellular pH (pHi) regulation in nonactivated and activated rat hepatic stellate cells (HSC). The fluorescent pHi indicator 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein was used to measure pHi in the presence and absence of HCO3-. In the absence of HCO3-, baseline pHi was significantly higher (P < 0.001) in activated than in nonactivated HSC (7.1 +/- 0.1 vs. 6.9 +/- 0.2) and decreased, in both groups, after amiloride administration and after Na+ removal. After an acid-loading maneuver, pHi recovery was significantly higher (P < 0.03) in activated than in nonactivated HSC (H+ flux = 11.0 +/- 3.8 vs. 7.7 +/- 2.9 mM/min at pHi 6.6) and was inhibited by amiloride and Na+ removal. In the presence of HCO3-, baseline pHi was higher in both groups and decreased after amiloride administration. Amiloride and Na+ removal inhibited pHi recovery after an intracellular acid load by 77 and 93%, respectively, in nonactivated and by 82 and 92%, respectively, in activated HSC, whereas 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid inhibited pHi recovery by only 27%. Acute Cl- removal increased pHi by 0.07 +/- 0.01 pH unit/min in the absence but not in the presence of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid in nonactivated and activated HSC in an Na(+)-independent manner. In activated HSC, 24 h of incubation with 25 ng/ml platelet-derived growth factor (PDGF)-BB (in 0.5% serum) did not modify baseline pHi (7.07 +/- 0.1 vs. 7.08 +/- 0.1 in HSC cultured in 0.5% serum only) but significantly (P < 0.02) increased, with respect to controls, pHi recovery after an acute acid load. Incubation with PDGF for 24 h induced a fivefold increase in HSC proliferation expressed as percentage of bromodeoxyuridine-positive cells (30.8 +/- 6.7 vs. 6.1 +/- 1.9% in controls). When amiloride (0.1 mM) was present, PDGF-induced HSC proliferation was significantly inhibited (8.1 +/- 0.4%, P < 0.001). Our results show that 1) the Na+/H+ exchanger is the main pHi regulator in rat HSC, 2) activation of HSC is associated with an increase in pHi and in the activity of the Na+/H+ exchanger, 3) PDGF increases the activity of this exchanger, and 4) amiloride is able to inhibit HSC proliferation induced by PDGF.

The molecular basis of β-thalassemia in Turkey

By using oligonucleotide hybridization, restriction endonuclease analysis and direct sequencing of amplified genomic DNA, we have been able to characterize 18 different mutations in the beta-globin genes of 161 beta-thalassemia homozygotes and 107 beta-thalassemia heterozygotes from Turkey (429 beta-thalassemia chromosomes). Previous studies dealing with beta-thalassemia in Mediterranean countries have shown that, in most Mediterranean populations, only a few mutations are prevalent. In contrast, beta-thalassemia in Turkey does not seem to be associated with a few predominant mutations. The six most frequent alleles, IVS-I-110 (G----A), IVS-I-6(T----C), FSC-8 (-AA), IVS-I-1(G----A), -30(T----A) and FSC-5 (-CT), account for only 69.3% of the disease genes; indeed, all 26 mutations assayed represent 85.8% of the disease genes, confirming the considerable molecular heterogeneity of beta-thalassemia among Turks, and indicating the possible presence of rare, previously undefined, mutations in the population. Two mutations observed in this study, IVS-I-116 (T----G) and Cd44(-C), have not been reported in the Turkish population to date. Since preventive medical services, such as genetic counseling and prenatal diagnosis, are greatly improved by detailed knowledge of the molecular pathology of beta-thalassemia, we strongly believe that the presented data will facilitate the intended establishment of a prenatal diagnosis center, based on DNA analysis, in Turkey.

Molecular basis of beta-thalassemia in Turkey: detection of rare mutations by direct sequencing

Using restriction endonuclease analysis, oligonucleotide hybridization, and direct sequencing of amplified genomic DNA, we characterized 11 different mutations in the DNA of 26 patients from Turkey homozygous for beta-thalassemia. We found that mutations IVS-1 nt110, IVS-1 nt6, and the frameshift at codon 8 were the most frequent. By direct sequencing we characterized two very rare mutations not previously reported in the Turkish population: a frameshift +1 at codons 9/10 and a nonsense mutation at codon 15.