Smad3 loss confers resistance to the development of trinitrobenzene sulfonic acid-induced colorectal fibrosis.

BACKGROUND: Transforming growth factor-beta (TGF-beta)/Smad3 signalling plays a central role in tissue fibrogenesis, acting as a potent stimulus of extracellular matrix (ECM) protein accumulation. The aim of this study was to evaluate the potential role of Smad3 in the pathogenesis of colonic fibrosis induced by trinitrobenzene sulfonic acid (TNBS) in Smad3 null mice. MATERIALS AND METHODS: Chronic colitis-associated fibrosis was induced in 15 Smad3 null and 13 wild-type mice by intra-rectal administration of TNBS. Each mouse received an incremental dose of TNBS (0.5-1.0 mg per week) over a 6-week period. The colon was excised for macroscopic examination and histological, morphometric and immunohistochemical analyses. For immunohistochemistry, alpha-smooth muscle actin (alpha-SMA), collagen types I-III, TGF-beta1, connective tissue growth factor (CTGF), Smad3, Smad7, and CD3 antibodies were used. RESULTS: At macroscopic examination, the colon of Smad3 wild-type mice appeared significantly harder, thicker and shorter than that of the Smad3 null mice. Of the wild-type mice, 50% presented colonic adhesions and strictures. Histological and morphometric evaluation revealed a significantly higher degree of colonic fibrosis and accumulation of collagen in the Smad3 wild-type compared to null mice, whereas the degree of colonic inflammation did not differ between the two groups of mice. Immunohistochemical evaluation showed a marked increase in CTGF, collagen I-III, TGF-beta and Smad3 staining in the colon of Smad3 wild-type compared to null mice, whereas Smad7 was increased only in null mice. CONCLUSIONS: These results indicate that Smad3 loss confers resistance to the development of TNBS-induced colonic fibrosis. The reduced fibrotic response appears to be due to a reduction in fibrogenic mesenchymal cell activation and ECM production and accumulation. Smad3 could be a novel target for potential treatment of intestinal fibrosis, especially in inflammatory bowel disease.

Prevention of colonic fibrosis by Boswellia and Scutellaria extracts in rats with colitis induced by 2,4,5-trinitrobenzene sulphonic acid.

BACKGROUND: Currently, no effective preventive measures or medical therapies are available for intestinal fibrosis and, thus, surgery remains the only available strategy in the management of fibrostenotic enteropathies, especially Crohn's disease. The aim of this study was to evaluate the efficacy of a combined therapy of anti-inflammatory Boswellia and antifibrotic Scutellaria extracts on the development of colonic fibrosis in rats. MATERIALS AND METHODS: Chronic colonic inflammation-associated fibrosis was induced in rats by intracolonic administration of 2,4,5-trinitrobenzene sulphonic acid (TNBS). Sixty-four healthy male Sprague-Dawley rats were assigned to five groups: 8 controls, 14 TNBS, 14 TNBS orally treated with Boswellia extracts (50 mg kg(-1) day(-1)), 14 TNBS orally treated with Scutellaria extracts (150 mg kg(-1) day(-1)), and 14 TNBS orally treated with both Boswellia (50 mg kg(-1) day(-1)) and Scutellaria extracts (150 mg kg(-1) day(-1)). The colon was removed after 21 days of treatment and assessed by macroscopic, histological, morphometric and immunohistochemical analyses. For immunohistochemical analysis, alpha-smooth muscle actin (alpha-SMA), collagen types I-III, connective tissue growth factor (CTGF), transforming growth factor-beta1 (TGF-beta1), Smad3, Smad7 and CD3 antibodies were used. RESULTS: Combined oral administration of Boswellia and Scutellaria significantly improved the course and macroscopic findings of TNBS-induced chronic colitis assessed by disease activity index, colon weight, length, adhesions, strictures, dilatation, thickness, oedema, ulcerations and extension of damage. The histological severity of the colonic fibrosis was also notably improved by the treatment and associated with a significant reduction in the colonic expression of alpha-SMA, collagen I-III, CTGF, TGF-beta1, Smad3, and Smad7. CONCLUSIONS: These data demonstrate that the prophylactic administration of anti-inflammatory Boswellia and antifibrotic Scutellaria extracts is effective in preventing colonic fibrosis in TNBS-induced colitis. Their antifibrotic mechanism of action seems to be mediated by the inhibition of TGF-beta1/Smad3 pathway.

Smad3-null mice lack interstitial cells of Cajal in the colonic wall.

BACKGROUND: Transforming growth factor-beta (TGF-beta)/Smad's signalling pathway plays a pivotal role in organogenesis, oncogenesis, inflammation, repair and fibrosis. The aim of this study was to evaluate the morphology of muscle layers and the density and distribution of interstitial cells of Cajal (ICC) in the colon of Smad3 knockout mice. MATERIALS AND METHODS: Eighteen Smad3 wild-type mice and 12 null mice were sacrificed at age 4 months and the colons were collected for histology (Haematoxilin-Eosin, Masson thrichrome and Gomori silver staining), morphometry and immunohistochemistry (IHC) analysis. For IHC we used the c-Kit, alpha-smooth muscle actine (alpha-SMA), vimentin, desmin and neuronal cocktail (S-100, NSE, neurofilament 200) antibodies. RESULTS: When sacrificed, 40% of the null mice showed different degrees of colon dilatation when compared with the wild-type. Histological and morphometric evaluation revealed a significant reduction in muscle layer thickness of the colon in all the null mice when compared with the wild-type. Immunohistochemistry evaluation showed a marked reduction, or even absence, of c-Kit immunoreactivity, which identifies ICC, in the colon of all the null mice, compared with the wild-type. CONCLUSIONS: Smad3 null mice showed a marked reduction, or even absence, of ICC in the colon together with a concomitant reduction of intestinal smooth muscle layer thickness. This data could account for the colonic dilation observed in approximately 40% of the Smad3 null mice. Alteration of intestinal smooth muscle layers and ICC could also be involved in the resistance of the Smad3 null mice to develop colonic fibrosis.

LPI-labile plasma iron in iron overload.

Labile plasma iron (LPI) represents a component of non-transferrin-bound iron (NTBI) that is both redox-active and chelatable, capable of permeating into organs and inducing tissue iron overload. It appears in various types of hemosiderosis (transfusional and non-transfusional) and in other iron-overload conditions. Sustained levels of LPI could over time compromise organ (e.g. heart) function and patient survival. With the advent of methods for measuring LPI in the clinical setting, it has become possible to assess the implications of LPI in the management of iron overload based on regimens of iron chelation. As LPI is detected primarily in patients with transfusional iron overload and other forms of hemosiderosis, we review here regimens of iron chelation with deferrioxamine and deferiprone (separately or combined) in terms of their efficacy in minimizing daily exposure to LPI in thalassemia major and thalassemia intermedia patients.

[Current data on iron metabolism]. / Données actuelles sur le métabolisme du fer.

Iron is required for cellular life. However, abnormalities of its metabolism may lead to iron deficiency or iron overload, both conditions which are deleterious. Therefore, stock and distribution of iron in the body must be very stable. Classically, four major proteins are involved in iron metabolism: (a) transferrin which is implicated in its plasmatic transport, (b) transferrin receptor which regulates iron-transferrin uptake, (c) ferritin, the major iron storage protein, and (d) IRP (Iron Regulatory Protein) which regulates both the entry and storage of iron by linking to the IRE (Iron Responsive Element), a nucleotidic sequence found on transferrin receptor and ferritin mRNA. Thus, IRP adapts gene expression to the iron cellular status. Recent data give informations about new proteins involved in iron metabolism: HFE whose gene is mutated in genetic hemochromatosis, ceruloplasmin which permits cellular iron egress and frataxin which is implicated in the exit of iron from mitochondria.

The mitogen-activated protein kinase kinase/extracellular signal-regulated kinase cascade activation is a key signalling pathway involved in the regulation of G(1) phase progression in proliferating hepatocytes.

In this study, activation of the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signalling pathway was analyzed in proliferating rat hepatocytes both in vivo after partial hepatectomy and in vitro following epidermal growth factor (EGF)-pyruvate stimulation. First, a biphasic MEK/ERK activation was evidenced in G(1) phase of hepatocytes from regenerating liver but not from sham-operated control animals. One occurred in early G(1) (30 min to 4 h), and the other occurred in mid-late G(1), peaking at around 10.5 h. Interestingly, the mid-late G(1) activation peak was located just before cyclin D1 induction in both in vivo and in vitro models. Second, the biological role of the MEK/ERK cascade activation in hepatocyte progression through the G(1)/S transition was assessed by adding a MEK inhibitor (PD 98059) to EGF-pyruvate-stimulated hepatocytes in primary culture. In the presence of MEK inhibitor, cyclin D1 mRNA accumulation was inhibited, DNA replication was totally abolished, and the MEK1 isoform was preferentially targeted by this inhibition. This effect was dose dependent and completely reversed by removing the MEK inhibitor. Furthermore, transient transfection of hepatocytes with activated MEK1 construct resulted in increased cyclin D1 mRNA accumulation. Third, a correlation between the mid-late G(1) MEK/ERK activation in hepatocytes in vivo after partial hepatectomy and the mitogen-independent proliferation capacity of these cells in vitro was established. Among hepatocytes isolated either 5, 7, 9, 12 or 15 h after partial hepatectomy, only those isolated from 12- and 15-h regenerating livers were able to replicate DNA without additional growth stimulation in vitro. In addition, PD 98059 intravenous administration in vivo, before MEK activation, was able to inhibit DNA replication in hepatocytes from regenerating livers. Taken together, these results show that (i) early induction of the MEK/ERK cascade is restricted to hepatocytes from hepatectomized animals, allowing an early distinction of primed hepatocytes from those returning to quiescence, and (ii) mid-late G(1) MEK/ERK activation is mainly associated with cyclin D1 accumulation which leads to mitogen-independent progression of hepatocytes to S phase. These results allow us to point to a growth factor dependency in mid-late G(1) phase of proliferating hepatocytes in vivo as observed in vitro in proliferating hepatocytes and argue for a crucial role of the MEK/ERK cascade signalling pathway.

Novel orally active iron chelators (3-hydroxypyridin-4-ones) enhance the biliary excretion of plasma non-transferrin-bound iron in rats.

BACKGROUND/AIMS: It is well documented that levels of plasma non-transferrin-bound iron (NTBI), a particularly toxic form of iron, are increased in iron overload disorders. In light of the pathogenetic importance of NTBI in chronic iron overload, we have studied the ability of new orally active iron chelators to promote the biliary excretion of iron originating as plasma 55Fe-NTBI. METHODS: Biliary iron kinetics of plasma 55Fe-labeled NTBI and cumulative recoveries of 55Fe in bile were determined in normal and carbonyl iron-loaded rats receiving a single intragastric dose of iron chelator. These chelators were the novel hydroxypyridin-4-one compounds CP102, CP41, and their respective pro-drugs CP117 and CP165. RESULTS: The cumulative recovery of 55Fe in bile of normal rats was increased by 5.2-, 7.9-, 11.5-, and 9.2-fold with CP102, CP117, CP41 and CP165, respectively. In iron overloaded rats, these compounds increased the cumulative recovery by 28.6-, 48.6-, 72.6-, and 32-fold, respectively. All the chelators had a choleretic effect, were metabolized by the liver as demonstrated by HPLC study of bile, and were not cytotoxic since normal plasma transaminase levels were maintained at the end of the experiments. CONCLUSIONS: These chelators have potential interest for the treatment of iron overload conditions and may offer advantages over simple N-alkyl-hydroxypyridinones such as deferiprone (CP20, L1).

Chelation and mobilization of cellular iron by different classes of chelators.

Iron chelators belonging to three distinct chemical families were assessed in terms of their physicochemical properties and the kinetics of iron chelation in solution and in two biological systems. Several hydroxypyridinones, reversed siderophores, and desferrioxamine derivatives were selected to cover agents with different iron-binding stoichiometry and geometry and a wide range of lipophilicity, as determined by the octanol-water partition coefficients. The selection also included highly lipophilic chelators with potentially cell-cleavable ester groups that can serve as precursors of hydrophilic and membrane-impermeant chelators. Iron binding was determined by the chelator capacity for restoring the fluorescence of iron-quenched calcein (CA), a dynamic fluorescent metallosensor. The iron-scavenging properties of the chelators were assessed under three different conditions: (a) in solution, by mixing iron salts with free CA; (b) in resealed red cell ghosts, by encapsulation of CA followed by loading with iron; and (c) in human erythroleukemia K562 cells, by loading with the permeant CA-acetomethoxy ester, in situ formation of free CA, and binding of cytosolic labile iron. The time-dependent recovery of fluorescence in the presence of a given chelator provided a continuous measure for the capacity of the chelator to access the iron/CA-containing compartment. The resulting rate constants of fluorescence recovery indicated that chelation in solution was comparable for the members of each family of chelators, whereas chelation in either biological system was largely dictated by the lipophilicity of the free chelator. For example, desferrioxamine was among the fastest and most efficient iron scavengers in solution but was essentially ineffective in either biological system when used at < or = 200 microM over a 2-hr period at 37 degrees. On the other hand, the highly lipophilic and potentially cell-cleavable hydroxypyridinones and reversed siderophores were highly efficient in all biological systems tested. It is implied that in K562 cells, hydrolysis of these chelators is relatively slower than their ingress and binding of intracellular iron. The chelator-mediated translocation of iron from cells to medium was assessed in 55Fe-transferrin-loaded K562 cells. The speed of iron mobilization by members of the three families of chelators correlated with the lipophilicity of the free ligand or the iron-complexed chelator. The acquired information is of relevance for the design of chelators with improved biological performance.

Biliary excretion of plasma non-transferrin-bound iron in rats: pathogenetic importance in iron-overload disorders.

Plasma non-transferrin-bound iron (NTB-iron) is a potentially toxic form of iron, which is efficiently taken up by the normal, as well as the chronically iron-overloaded liver. In fact, NTB-iron may represent the major source of iron gaining access to hepatocytes in the iron-loaded state. We postulated that efficient biliary excretion of this form of iron could protect against iron-related hepatocellular injury. To characterize the biliary excretion of NTB-iron in intact normal and iron-loaded rats, the plasma disappearance and biliary excretion kinetics of plasma 55Fe-labeled NTB-iron were determined. In normal rats, prompt biliary excretion of plasma NTB-iron was evident, with peak radioactivity approximately 10 min after 55Fe injection (4.1% mean recovery at 3 h). In contrast, biliary iron excretion in iron-loaded rats was minimal (0.1%). In normal rats, a marked increase in biliary excretion of plasma NTB-iron was observed after intravenous desferrioxamine (mean recovery 20.9%) and the new oral iron chelator 1,2-dimethyl-3-hydroxypyrid-4-one administered intravenously (mean recovery 16.1%) or orally (11.4%). In iron-loaded rats, the cumulative recoveries of 55Fe in bile achieved by chelators were lower than in controls (7.6, 3.9, and 3.7%, respectively). Collectively, these findings demonstrate that 1) the normal liver rapidly excretes significant amounts of plasma NTB-iron in bile; 2) the iron-loaded liver exhibits a marked decrease in the capacity to excrete plasma NTB-iron into bile; and 3) chelating agents greatly enhance the biliary excretion of plasma NTB-iron, although the response in terms of cumulative recoveries is less pronounced in the iron-loaded state.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the terpenic compound epomediol on biliary secretion and bile composition in the rat.

The aim of the present investigation was to define the role of the synthetic terpenoid epomediol on biliary secretion in rats recovered from anaesthesia, in stabilized conditions and receiving an intravenous infusion of Na+ taurocholate (120 or 240 nmol.min-1 per 100 g body wt.) or physiologic saline (NaCl 0.16 M). Epomediol was administered at the rate of 20 and 50 mg.kg-1 per h, through a second syringe connected to the same vein catheter. Bile flow was increased up to 67% according to the model. The effect of epomediol is dose-dependent, associated with enhanced Na+ transport into bile and with an increased anionic gap. The extent of epomediol action also changes according to the different rates of bile acid secretion. At low secretory rates a greater choleretic action was observed with epomediol. The effect was negligible for a secretion of bile acids above 350 nmol.min-1 per 100 g body wt. Excretion into bile of the epomediol glucuronide was not hampered by high Na+ taurocholate output. This suggests that there is no competition of the two anions for a common excretory pathway at the studied rates. The effect of epomediol seems due to a mechanism of action both independent and additive to the mechanism for bile acids. The presence of additivity of the two choleretic mechanisms at low flow and bile acid secretion and the loss of action at high secretory rates, suggests that the maximal capacity of passage for water into bile was reached.

Lymphocyte function tests in cirrhotic patients under treatment with spironolactone and potassium canrenoate.

This controlled study in cirrhotic patients investigated whether two antialdosteronic steroids, spironolactone (100-200 mg/day; n = 12 patient pairs) and potassium canrenoate (50-100 mg/day, n = 32 patient pairs) which are reported to bind to intracellular membranes and modify cytochrome P-450, could also produce nuclear changes. The model used was the response of peripheral lymphocytes to blastogenic agents by studying lymphocyte sub-populations. No changes occurred in the B- and T-lymphocyte sub-populations or in the helper and suppressor sub-types. The response to the blastogenic agents, phytohaemagglutinin and purified protein derived from mycobacteria, did not change significantly from before entry into the study to the follow-up (18.1 +/- 2.9 months). All control patients (n = 44 patient pairs) had slightly greater mitogenic activity compared with patients treated with spironolactone; no difference was found when control patients were compared with patients given potassium canrenoate. The difference between spironolactone and potassium canrenoate might be due to toxicity caused by the thio group of spironolactone. Overall, however, both drugs may be regarded as safe, in terms of effects on lymphatic tissue, occurring during the course of cirrhosis.

Changes in bilirubin transport across the liver by the flavonoids (+)-cyanidanol-3 and palmitoyl-catechin.

The apparent maximal transport capacity (Tm) of the liver for bilirubin was studied in rats after oral treatment for two weeks with the two flavonoids (+)-cyanidanol-3 and palmitoyl-catechin in order to investigate a possible mechanism of action on jaundice described in humans. (+)-Cyanidanol-3 produces no changes in bilirubin-Tm, and the analysis of bilirubin and its conjugates in the different compartments reveals a decreased amount of the whole bilirubin taken up by the liver. Palmitoyl-catechin, a more lipophilic derivative of catechin, produces a slight increase in bilirubin-Tm. This appears related to the increased conjugation rate demonstrated in vitro for bilirubin. A multicompartimental analysis shows a different distribution of bilirubins as compared to controls. It is likely that physicochemical changes of the membrane environment, where the enzyme is buried, have modified the capacity of the hepatocyte to dispose bilirubin.