Neutral endopeptidase (EC 3.4.24.11) in cirrhotic liver: a new target to treat portal hypertension?

Dual angiotensin receptor and neprilysin inhibitor reduced portal pressure through peripheral vasodilatation and decreasing systemic arterial pressure in cirrhotic rats

BACKGROUND

Portal hypertension develops along with the progression of liver cirrhosis. Natriuretic peptides have been shown to reduce portal pressure but concomitantly activate the renin-angiotensin-aldosterone system (RAAS). Angiotensin receptor-neprilysin inhibitors (ARNIs) upregulate natriuretic peptides and avoid the adverse effects of RAAS activation. ARNIs have been shown to reduce portal pressure in rats with pre-hepatic portal hypertension, which involves relatively little liver injury. This study aimed to evaluate the relevant effects of an ARNI in rats with both liver cirrhosis and portal hypertension.

METHODS

Male Sprague-Dawley rats received common bile duct ligation to induce liver cirrhosis and portal hypertension. Sham-operated rats served as surgical controls. All rats were randomly allocated into three groups to receive distilled water (vehicle), LCZ696 (an ARNI), or valsartan for 4 weeks. Portal hypertension and relevant derangements were assessed after treatment.

RESULTS

Portal hypertension and hyperdynamic circulation developed in the cirrhotic rats. In the rats with cirrhosis and portal hypertension, both LCZ696 and valsartan reduced portal hypertension, mean arterial pressure, and systemic vascular resistance. The decrease in portal pressure was highly associated with the reduction in arterial pressure and systemic vascular resistance. Blood flow in hepatic, splanchnic, and portosystemic collateral systems was not altered. LCZ696 did not significantly influence liver injury or plasma cytokine levels. Liver fibrosis and splanchnic angiogenesis were not affected.

CONCLUSION

ARNI treatment exerted portal pressure lowering effects via peripheral vasodilatation and decreasing systemic arterial pressure in the rats with liver cirrhosis and portal hypertension. Caution should be taken when using ARNIs in liver cirrhosis.

New Viral Diseases and New Possible Remedies by Means of the Pharmacology of the Renin-Angiotensin System

All strains of SARS-CoV-2, as well as previously described SARS-CoV and MERS-CoV, bind to ACE2, the cell membrane receptor of β-coronaviruses. Monocarboxypeptidase ACE2 activity stops upon viral entry into cells, leading to inadequate tissue production of angiotensin 1-7 (Ang1-7). Acute lung injury due to the human respiratory syncytial virus (hRSV) or avian influenza A H7N9 and H5N1 viruses is also characterized by significant downregulation of lung ACE2 and increased systemic levels of angiotensin II (Ang II). Restoration of Ang1-7 anti-inflammatory, antifibrotic, vasodilating, and natriuretic properties was attempted at least in some COVID-19 patients through i.v. infusion of recombinant human ACE2 or intranasal administration of the modified ACE2 protein, with inconsistent clinical results. Conversely, use of ACE inhibitors (ACEis), which increase ACE2 cell expression, seemed to improve the prognosis of hypertensive patients with COVID-19. To restore Ang1-7 tissue levels in all these viral diseases and avoid the untoward effects frequently seen with ACE2 systemic administration, a different strategy may be hypothesized. Experimentally, when metallopeptidase inhibitors block ACE2, neprilysin (NEP), highly expressed in higher and lower airways, starts cleaving angiotensin I (Ang I) into Ang1-7. We suggest a discerning use of ACEis in normohypertensive patients with β-coronavirus disease as well as in atypical pneumonia caused by avian influenza viruses or hRSV to block the main ACE-dependent effects: Ang II synthesis and Ang1-7 degradation into angiotensin 1-5. At the same time, i.v.-infused Ang I, which is not hypertensive provided ACE is inhibited, may become the primary substrate for local Ang1-7 synthesis via ubiquitous NEP; i.e., NEP could replace inadequate ACE2 function if Ang I was freely available. Moreover, inhibitors of chymase, a serine endopeptidase responsible for 80% of Ang II-forming activity in tissues and vessel walls, could protect patients with atypical pneumonia from Ang II-mediated microvascular damage without reducing arterial blood pressure.

The systemic and hepatic alternative renin-angiotensin system is activated in liver cirrhosis, linked to endothelial dysfunction and inflammation

We aimed to assess the systemic and hepatic renin-angiotensin-system (RAS) fingerprint in advanced chronic liver disease (ACLD). This prospective study included 13 compensated (cACLD) and 12 decompensated ACLD (dACLD) patients undergoing hepatic venous pressure gradient (HVPG) measurement. Plasma components (all patients) and liver-local enzymes (n = 5) of the RAS were analyzed using liquid chromatography-tandem mass spectrometry. Patients with dACLD had significantly higher angiotensin (Ang) I, Ang II and aldosterone plasma levels. Ang 1-7, a major mediator of the alternative RAS, was almost exclusively detectable in dACLD (n = 12/13; vs. n = 1/13 in cACLD). Also, dACLD patients had higher Ang 1-5 (33.5 pmol/L versus cACLD: 6.6 pmol/L, p < 0.001) and numerically higher Ang III and Ang IV levels. Ang 1-7 correlated with HVPG (ρ = 0.655; p < 0.001), von Willebrand Factor (ρ = 0.681; p < 0.001), MELD (ρ = 0.593; p = 0.002) and interleukin-6 (ρ = 0.418; p = 0.047). Considerable activity of ACE, chymase, ACE2, and neprilysin was detectable in all liver biopsies, with highest chymase and ACE2 activity in cACLD patients. While liver-local classical and alternative RAS activity was already observed in cACLD, systemic activation of alternative RAS components occurred only in dACLD. Increased Ang 1-7 was linked to severe liver disease, portal hypertension, endothelial dysfunction and inflammation.

Update on New Aspects of the Renin-Angiotensin System in Hepatic Fibrosis and Portal Hypertension: Implications for Novel Therapeutic Options

There is considerable experimental evidence that the renin angiotensin system (RAS) plays a central role in both hepatic fibrogenesis and portal hypertension. Angiotensin converting enzyme (ACE), a key enzyme of the classical RAS, converts angiotensin I (Ang I) to angiotensin II (Ang II), which acts via the Ang II type 1 receptor (AT1R) to stimulate hepatic fibrosis and increase intrahepatic vascular tone and portal pressure. Inhibitors of the classical RAS, drugs which are widely used in clinical practice in patients with hypertension, have been shown to inhibit liver fibrosis in animal models but their efficacy in human liver disease is yet to be tested in adequately powered clinical trials. Small trials in cirrhotic patients have demonstrated that these drugs may lower portal pressure but produce off-target complications such as systemic hypotension and renal failure. More recently, the alternate RAS, comprising its key enzyme, ACE2, the effector peptide angiotensin-(1–7) (Ang-(1–7)) which mediates its effects via the putative receptor Mas (MasR), has also been implicated in the pathogenesis of liver fibrosis and portal hypertension. This system is activated in both preclinical animal models and human chronic liver disease and it is now well established that the alternate RAS counter-regulates many of the deleterious effects of the ACE-dependent classical RAS. Work from our laboratory has demonstrated that liver-specific ACE2 overexpression reduces hepatic fibrosis and liver perfusion pressure without producing off-target effects. In addition, recent studies suggest that the blockers of the receptors of alternate RAS, such as the MasR and Mas related G protein-coupled receptor type-D (MrgD), increase splanchnic vascular resistance in cirrhotic animals, and thus drugs targeting the alternate RAS may be useful in the treatment of portal hypertension. This review outlines the role of the RAS in liver fibrosis and portal hypertension with a special emphasis on the possible new therapeutic approaches targeting the ACE2-driven alternate RAS.

Plasma Neprilysin Displays No Relevant Association With Neurohumoral Activation in Chronic HFrEF

Background

Neprilysin is a transmembrane endopeptidase involved in the breakdown of a variety of vasoactive peptides and serves as a therapeutic target in heart failure with reduced ejection fraction (HFrEF). This study aimed to investigate the relationship of circulating neprilysin with neurohumoral activation and the impact of plasma neprilysin activity on prognosis in HFrEF.

Methods and Results

A total of 369 chronic HFrEF patients were enrolled prospectively. Plasma neprilysin concentration and activity were determined by a specific ELISA and a fluorometric method. The association between plasma neprilysin and heart failure (HF) severity, neurohumoral activation, ie norepinephrine and absolute renin concentration, as well as all‐cause mortality was assessed. Median plasma neprilysin concentrations and activity levels were 413 pg/mL (interquartile range 0–4111) and 2.36 nmol/mL per minute (interquartile range 1.16–4.59). No correlation could be shown between plasma neprilysin concentrations and activity (r_s=0.09, P=0.088). Plasma neprilysin activity correlated with HF severity reflected by New York Heart Association stage (P=0.003) and tertiles of N‐terminal pro‐B‐type natriuretic peptide (P<0.001), whereas neprilysin concentrations did not (P=0.220; P=0.849). There was no relevant relationship between plasma neprilysin concentrations and activity, with neurohumoral activation reflected by absolute renin concentration (r_s=−0.02, P=0.648; r_s=0.03, P=0.574) or norepinephrine levels (r_s=−0.06, P=0.248; r_s=0.20, P<0.001). Neither circulating neprilysin concentrations nor activity were associated with outcome.

Conclusions

Plasma neprilysin concentrations and activity are not directly related to neurohumoral activation, indicating that neprilysin regulation is either more complex or not correctly mirrored by circulating neprilysin as a biomarker. Circulating neprilysin concentrations and activity were not associated with overall survival, implicating limited prognostic value of plasma neprilysin measurements in HFrEF patients.

Dual Angiotensin Receptor and Neprilysin Inhibitor Ameliorates Portal Hypertension in Portal Hypertensive Rats

Background: Portal hypertension is characterized by exaggerated activation of the renin-angiotensin-aldosterone axis. Natriuretic peptide system plays a counter-regulatory role, which is modulated by neprilysin. LCZ696 (sacubitril/valsartan) is a dual angiotensin receptor and neprilysin inhibitor. This study evaluated the effect of LCZ696 on portal hypertensive rats. Methods: Portal hypertension was induced by partial portal vein ligation (PVL) in rats. LCZ696, valsartan (angiotensin receptor blocker), or normal saline (control) was administered in PVL rats for 10 days. Then, hemodynamic and biochemistry data were obtained. The hepatic histology and protein expressions were surveyed. On the parallel groups, the portal-systemic shunting degrees were determined. Results: LCZ696 and valsartan reduced mean arterial pressure and systemic vascular resistance. LCZ696, but not valsartan, reduced portal pressure in portal hypertensive rats (control vs. valsartan vs. LCZ696: 15.4 ± 1.6 vs. 14.0 ± 2.3 vs. 12.0 ± 2.0 mmHg, control vs. LCZ696: P < 0.05). LCZ696 and valsartan improved liver biochemistry data and reduced intrahepatic Cluster of Differentiation 68 (CD68)-stained macrophages infiltration. Hepatic endothelin-1 (ET-1) protein expression was downregulated by LCZ696. The portal-systemic shunting was not affected by LCZ696 and valsartan. Conclusion: LCZ696 and valsartan reduced mean arterial pressure through peripheral vasodilation. Furthermore, LCZ696 significantly reduced portal pressure in PVL rats via hepatic ET-1 downregulation.

Pathways of hepatic and renal damage through non-classical activation of the renin-angiotensin system in chronic liver disease

In liver cirrhosis, renin-angiotensin system (RAS) activation sustains renal sodium retention and hepatic fibrogenesis. New information has recently enlivened the traditional concept of RAS. For instance, renin and prorenin bind their ubiquitous receptors, resulting in the local production of angiotensin (Ang) II; increased serum calcium and calcimimetic agents, through stimulation of extracellular calcium-sensing receptors (CaSR), blunt renin production and lead to natriuretic effects in human and experimental cirrhosis. Alongside systemic production, there is Ang II tissue production within various organs through RAS enzymes different from angiotensin-converting enzyme (ACE), that is chymase, tissue plasminogen activator and several cathepsins. In experimental cirrhosis, inhibition of chymase leads to natriuretic and hepatic antifibrotic effects, without changes in systemic haemodynamics. In the kidney, local RAS coordinates proximal and distal tubular sodium reabsorption. However, renalase, whose plasma and tissue levels are severely altered in experimental cirrhosis, degrades systemic and renal tubule catecholamines, antagonizing the effects of renal RAS. Angiotensinogen-derived natriuretic and vasodilating peptides (Ang1-9, Ang1-7, Ang3-8) and their receptors have been described. Receptor agonists or antagonists are available to affect portal hypertension and sodium retention in cirrhosis. ACE2-dependent generation of Ang1-7 may inhibit experimental liver fibrosis. inhibition of Ang1-7 clearance by means of neprilysin blockade has portal hypotensive and natriuretic effects. Ang1-12, whose production renin does not regulate, is converted to several different angiotensin peptides via chymase. Finally, Ang II behaves as either an antinatriuretic or a natriuretic agent, based on the tissue content of AT₁ R and AT₂ R receptors, their ratio being prone to pharmacological modulation.

Animal models of portal hypertension

Chronic liver diseases ultimately lead to cirrhosis and portal hypertension (PHT). Indeed, PHT is a major cause of severe complications, while medical treatment is limited to non-selective beta blockers. Sophisticated animal models are needed to investigate novel treatment options for different etiologies of liver disease, effective anti-fibrotic agents as well as vasoactive drugs against PHT. In this review, we present some of the most common animal models of liver disease and PHT - including pre-hepatic, intra-hepatic and post-hepatic PHT in rodents. Methodology for induction, considerations for disease etiology, advantages and limitations and practical issues of these animal models are discussed. The appropriate and sensible use of animal models in preclinical research supporting the 3R concept of replacement, reduction and refinement is highlighted.

Role of Chymase in the Development of Liver Cirrhosis and Its Complications: Experimental and Human Data

Background

Tissue Angiotensin II (Ang-II), produced through local non ACE-dependent pathways, stimulates liver fibrogenesis, renal vasoconstriction and sodium retention.

Aim

To highlight chymase-dependent pathway of Ang-II production in liver and kidney during cirrhosis development.

Methods

Liver histology, portal pressure, liver and kidney function, and hormonal status were investigated in rat liver cirrhosis induced through 13 weeks of CCl₄, with or without chymase inhibitor SF2809E, administered between 4^th and 13^th CCl₄ weeks; liver and kidney chymase immunolocation and Ang-II content were assessed. Chymase immunohistochemistry was also assessed in normal and cirrhotic human liver, and chymase mRNA transcripts were measured in human HepG2 cells and activated hepatic stellate cells (HSC/MFs) in vitro.

Results

Rats receiving both CCl₄ and SF2809E showed liver fibrotic septa focally linking portal tracts but no cirrhosis, as compared to ascitic cirrhotic rats receiving CCl₄. SF2809E reduced portal pressure, plasma bilirubin, tissue content of Ang-II, plasma renin activity, norepinephrine and vasopressin, and increased glomerular filtration rate, water clearance, urinary sodium excretion. Chymase tissue content was increased and detected in α-SMA-positive liver myofibroblasts and in kidney tubular cells of cirrhotic rats. In human cirrhosis, chymase was located in hepatocytes of regenerative nodules. Human HepG2 cells and HSC/MFs responded to TGF-β1 by up-regulating chymase mRNA transcription.

Conclusions

Chymase, through synthesis of Ang-II and other mediators, plays a role in the derangement of liver and kidney function in chronic liver diseases. In human cirrhosis, chymase is well-represented and apt to become a future target of pharmacological treatment.

Alpha-2A Adrenoceptor Agonist Guanfacine Restores Diuretic Efficiency in Experimental Cirrhotic Ascites: Comparison with Clonidine

BACKGROUND

In human cirrhosis, adrenergic hyperfunction causes proximal tubular fluid retention and contributes to diuretic-resistant ascites, and clonidine, a sympatholytic drug, improves natriuresis in difficult-to-treat ascites.

AIM

To compare clonidine (aspecific α2-adrenoceptor agonist) to SSP-002021R (prodrug of guanfacine, specific α2A-receptor agonist), both associated with diuretics, in experimental cirrhotic ascites.

METHODS AND RESULTS

Six groups of 12 rats were studied: controls (G1); controls receiving furosemide and potassium canrenoate (G2); rats with ascitic cirrhosis due to 14-week CCl4 treatment (G3); cirrhotic rats treated (over the 11th-14th CCl4 weeks) with furosemide and canrenoate (G4), furosemide, canrenoate and clonidine (G5), or diuretics and SSP002021R (G6). Three rats of each group had their hormonal status and renal function assessed at the end of 11th, 12th, 13th, and 14th weeks of respective treatments.Cirrhotic rats in G3 and G4 gained weight over the 12th-14th CCl4 weeks. In G4, brief increase in sodium excretion over the 11th-12th weeks preceded worsening of inulin clearance and natriuresis (diuretic resistance). In comparison with G4, the addition of clonidine (G5) or guanfacine (G6) to diuretics improved, respectively, sodium excretion over the 11th-12th CCl4 weeks, or GFR and electrolytes excretion over the 13th-14th CCl4 weeks. Natriuretic responses in G5 and G6 were accompanied by reduced catecholamine serum levels.

CONCLUSIONS

α2A-receptor agonists restore glomerular filtration rate and natriuresis, and delay diuretic-resistant ascites in experimental advanced cirrhosis. Clonidine ameliorates diuretic-dependent natriuresis just for a short time.

Dose-dependency of clonidine's effects in ascitic cirrhotic rats: comparison with α1-adrenergic agonist midodrine

BACKGROUND & AIMS

Sympathetic nervous system (SNS) activation decreases response to diuretics, but both α1-adrenoceptor agonists and sympatholytic α2-adrenoceptor agonists are recommended in the management of ascitic cirrhosis. We intend to compare the effects of increasing doses of clonidine (α2-agonist) vs. midodrine (α1-agonist) in advanced cirrhosis.

METHODS

Renal function, mean arterial pressure (MAP), and hormonal status were measured in rats with ascitic cirrhosis due to 13-week CCl(4) administration (groups G1-G5), in control rats (Gc), and in rats with ascitic cirrhosis untreated (G6) or treated with daily diuretics (0.5 mg/kg furosemide plus 2 mg/kg K(+) -canrenoate during the 11(th) -13(th) weeks of CCl(4)) (G7). G1-G5 cirrhotic rats received daily, during the 11(th)-13(th) CCl(4) weeks: clonidine 0.3 μg only (G1), diuretics + clonidine 0.2 (G2), 0.5 (G3) or 1 μg (G4), and diuretics + midodrine 1 mg/kg b.w. (G5).

RESULTS

Cirrhotic rats in G1 or G2 had higher glomerular filtration rate, renal plasma flow and natriuresis than cirrhotic rats treated with diuretics (G7) (all P < 0.05). The addition of clonidine 0.2 μg to diuretics (G2 vs. G7) reduced serum norepinephrine (169 ± 71 ng/L vs. 523 ± 88 ng/L) and plasma renin activity (12 ± 3 ng/ml/h vs. 25 ± 5 ng/ml/h) (all P < 0.05). Midodrine did not improve the renal performance in ascitic rats treated with diuretics. In comparison to absolute cirrhotic controls (G6), MAP was lower in G4 and higher in G5 (all P < 0.05).

CONCLUSION

Low-dose α2-agonists improve natriuresis and reduce SNS function and hyper-aldosteronism without affecting arterial pressure in experimental ascitic cirrhosis treated with diuretics.

Pathogenesis of solute-free water retention in experimental ascitic cirrhosis: is vasopressin the only culprit?

Catecholamines trigger proximal tubular fluid retention and reduce renal excretion of solute-free water. In advanced cirrhosis, non-osmotic hypersecretion of vasopressin (antidiuretic hormone or ADH) is considered the cause of dilutional hyponatraemia, but ADH V2 receptor antagonists are not beneficial in long-term treatment of ascites. To test the hypothesis that water retention in experimental ascitic cirrhosis might depend primarily on adrenergic hyper-function, hormonal status, renal function and tubular free-water reabsorption (TFWR) were assessed in six groups of rats with ascitic cirrhosis: rats with cirrhosis due to 13-week CCl4 (carbon tetrachloride) administration (group G1); cirrhotic rats receiving daily diuretics (0.5 mg/kg furosemide plus 2 mg/kg K(+)-canrenoate) from the 11th to the 13th week of CCl4 (G2), diuretics associated with guanfacine oral prodrug (α2A-adrenergic receptor agonist and sympatholytic agent) at 2 (G3), 7 (G4) or 10 (G5) mg/kg, or with SSP-004240F1 (V2 receptor antagonist) at 1 mg/kg (G6). Natriuresis was lower in G1 than in G2, G4 and G6 (all P<0.05). Guanfacine, added to diuretics (i.e. G3 compared with G2), reduced serum noradrenaline from 423±22 to 211±41 ng/l (P<0.05), plasma renin activity (PRA) from 35±8 to 9±2 ng/ml/h (P<0.05) and TFWR from 45±8 to 20±6 μl/min (P<0.01). TFWR correlated with plasma aldosterone (r=0.51, P<0.01) and urinary potassium excretion (r=0.90, P<0.001). In ascitic cirrhosis, reduced volaemia, use of diuretics (especially furosemide) and adrenergic hyper-function cause tubular retention of water. Suitable doses of sympatholytic agents are effective aquaretics.

Calcium receptors located in fibrotic septa: a new target to reduce portal pressure in liver cirrhosis

In rats with experimental liver cirrhosis, the kidney contains reduced amounts of membrane-bound CaRs (calcium-sensing receptors), and the specific stimulation of CaRs causes the generation of PGE2 (prostaglandin E2), renal vasodilation and increased natriuresis. CaR content and function in the liver of cirrhotic rats are unknown. To assess the activity of this Ca2+-dependent vasomotor system, we evaluated the effects of intravenous administration of PolyAg (poly-L-arginine), a selective CaR agonist, on hormonal status, portal haemodynamics, MAP (mean arterial pressure) in rats with liver cirrhosis induced by chronic CCl4 (carbon tetrachloride) administration. Two groups of eight control rats received intravenously 1 ml of 5% (w/v) glucose solution alone or containing 0.5 mg of PolyAg; two groups of ten cirrhotic rats were administered vehicle or PolyAg. Compared with controls, at baseline cirrhotic rats showed higher portal pressure (P<0.01), lower estimated functional liver plasma flow, measured as CICG (Indocyanine Green clearance) (P<0.03) and reduced hepatic protein content of CaRs (P<0.03), which were located mainly in sub-endothelial layers of portal venules and in myofibroblasts of fibrotic septa (immunohistochemistry and indirect immunofluorescence staining of liver sections). In cirrhotic animals, 0.5 mg of PolyAg decreased portal pressure (P<0.01) and increased CICG (P<0.05), without effects on arterial pressure and hormonal status. In conclusion, the present study provides evidence that in experimental cirrhosis agonists of liver CaRs elicit beneficial portal hypotensive effects by reducing intrahepatic resistance to portal flow. Moreover, these drugs are devoid of effects on systemic haemodynamics.

Dual endothelin-converting enzyme/neutral endopeptidase blockade in rats with D-galactosamine-induced liver failure

Secondary activation of the endothelin system is thought to be involved in toxic liver injury. This study tested the hypothesis that dual endothelin-converting enzyme / neutral endopeptidase blockade might be able to attenuate acute toxic liver injury.

Male Sprague-Dawley rats were implanted with subcutaneous minipumps to deliver the novel compound SLV338 (10 mg/kg*d) or vehicle. Four days later they received two intraperitoneal injections of D-galactosamine (1.3 g/kg each) or vehicle at an interval of 12 hours. The animals were sacrificed 48 hours after the first injection.

Injection of D-galactosamine resulted in very severe liver injury, reflected by strongly elevated plasma liver enzymes, hepatic necrosis and inflammation, and a mortality rate of 42.9 %. SLV338 treatment did not show any significant effect on the extent of acute liver injury as judged from plasma parameters, hepatic histology and mortality. Plasma measurements of SLV338 confirmed adequate drug delivery. Plasma concentrations of big endothelin-1 and endothelin-1 were significantly elevated in animals with liver injury (5-fold and 62-fold, respectively). Plasma endothelin-1 was significantly correlated with several markers of liver injury. SLV338 completely prevented the rise of plasma big endothelin-1 (p < 0.05) and markedly attenuated the rise of endothelin-1 (p = 0.055).

In conclusion, dual endothelin-converting enzyme / neutral endopeptidase blockade by SLV338 did not significantly attenuate D-galactosamine-induced acute liver injury, although it largely prevented the activation of the endothelin system. An evaluation of SLV338 in a less severe model of liver injury would be of interest, since very severe intoxication might not be relevantly amenable to pharmacological interventions.

Calcium-dependent diuretic system in preascitic liver cirrhosis

BACKGROUND & AIMS

Extracellular Ca(++) activates cell membrane calcium-sensing receptors (CaRs), leading to renal tubule production of prostaglandins E(2) (PGE(2)), which decrease both sodium reabsorption in the thick ascending limb of Henle's loop and free-water reabsorption in collecting ducts.

AIMS & METHODS

To assess the activity of this diuretic system in experimental cirrhosis, we evaluated renal function, hormonal status, PGE(2) urinary excretion, and renal tissue concentrations of Na(+)-K(+)-2Cl(-) co-transporters (BSC-1) and CaRs in three groups of rats: one group of controls receiving 5% glucose solution (vehicle) intravenously and two groups of rats with CCl(4)-induced preascitic cirrhosis receiving either vehicle or 0.5mg i.v. Poly-l-Arginine (PolyAg), a CaR-selective agonist.

RESULTS

Compared to controls, cirrhotic rats showed reduced urine volume and sodium excretion (p<0.05). Western blot analysis revealed reduced CaRs and increased BSC-1 protein content in kidneys of cirrhotic rats compared with controls (all p<0.01). PolyAg-treated cirrhotic rats had their urine and sodium excretion returned to normal; PolyAg also increased renal plasma flow, PGE(2) urinary excretion, and free-water clearance in cirrhotic rats (all p<0.01 v. untreated cirrhotic animals).

CONCLUSIONS

In preascitic cirrhosis, sodium retention may be linked to down-regulation of renal CaRs and up-regulation of tubular sodium-retaining channels. Calcimimetic drugs normalize preascitic sodium retention.

Continuos intravenous infusion of atrial natriuretic peptide (ANP) prevented liver fibrosis in rat

The atrial natriuretic peptide (ANP) are used as the acute heart failure treatment in clinical and reported the suppression of fibrosis in the heart, lung recently. The aim of this study was to analyze the suppressive effect of liver fibrosis about ANP. In vitro, rat hepatic stellate cell line (HSC-T6) were treated with ANP. In vivo, Wister rats were injected with dimethylnitrosamine (DMN) twice a week via intra-peritoneal for 4 weeks. ANP group was given by continuance intravenous dosage system used 24h infusion pump for 3 weeks after 1 week of DMN administration. In vitro, ANP suppressed alpha-SMA expression and was inhibited the growth of HSC, and reduced the expression of type 1 procollagen, TIMP-1, -2 expression. In vivo, The ANP group showed lower serum AST, ALT, HA level. Liver fibrosis was suppressed by ANP. ANP also decreased gene expression of type 1 procollagen, TIMP-1, -2 and alpha-SMA, TGF-beta1 expression. Our results showed that continuous ANP infusion has the specific capacity of inhibiting HSC activation and protecting hepatocytes and the useful capacity to suppress the liver fibrosis.

Atrial natriuretic peptide attenuates elevations in Ca2+ and protects hepatocytes by stimulating net plasma membrane Ca2+ efflux

Elevations in intracellular Ca(2+) concentration and calpain activity are common early events in cellular injury, including that of hepatocytes. Atrial natriuretic peptide is a circulating hormone that has been shown to be hepatoprotective. The aim of this study was to examine the effects of atrial natriuretic peptide on potentially harmful elevations in cytosolic free Ca(2+) and calpain activity induced by extracellular ATP in rat hepatocytes. We show that atrial natriuretic peptide, through protein kinase G, attenuated both the amplitude and duration of ATP-induced cytosolic Ca(2+) rises in single hepatocytes. Atrial natriuretic peptide also prevented stimulation of calpain activity by ATP, taurolithocholate, or Ca(2+) mobilization by thapsigargin and ionomycin. We therefore investigated the cellular Ca(2+) handling mechanisms through which ANP attenuates this sustained elevation in cytosolic Ca(2+). We show that atrial natriuretic peptide does not modulate the release from or re-uptake of Ca(2+) into intracellular stores but, through protein kinase G, both stimulates plasma membrane Ca(2+) efflux from and inhibits ATP-stimulated Ca(2+) influx into hepatocytes. These findings suggest that stimulation of net plasma membrane Ca(2+) efflux (to which both Ca(2+) efflux stimulation and Ca(2+) influx inhibition contribute) is the key process through which atrial natriuretic peptide attenuates elevations in cytosolic Ca(2+) and calpain activity. Moreover we propose that plasma membrane Ca(2+) efflux is a valuable, previously undiscovered, mechanism through which atrial natriuretic peptide protects rat hepatocytes, and perhaps other cell types, against Ca(2+)-dependent injury.

Proangiogenic cytokines as hypoxia-dependent factors stimulating migration of human hepatic stellate cells

Pathological angiogenesis is associated with the fibrogenic progression of chronic liver diseases. Experimental data suggest that hypoxia and vascular endothelial growth factor (VEGF) may stimulate proliferation and synthesis of type I collagen in activated, myofibroblast-like rat hepatic stellate cells (HSC/MFs). In this study, we investigated whether hypoxia, recombinant VEGF, or angiopoietin 1 (Ang-1) may affect other crucial profibrogenic features. In human HSC/MFs, which constitutively express VEGF receptor-1 and -2 (VEGFR-1, VEGFR-2) and the Ang-1 receptor Tie-2, exposure to hypoxia, VEGF, or Ang-1 resulted in a Ras/Erk-dependent stimulation of chemokinesis and chemotaxis. Migration of human HSC/MFs under hypoxic conditions involved up-regulation of VEGF-A, Ang-1, and related receptors and was mainly dependent on VEGFR-2 (Flk-1). In specimens from either cirrhotic rat livers or from patients with hepatitis C virus-related cirrhosis, HSC/MFs expressed proangiogenic factors and related receptors in areas of active fibrogenesis (ie, at the leading or lateral edge of developing incomplete fibrotic septa). Data presented herein suggest that VEGF and Ang-1 may contribute to fibrogenesis by acting as hypoxia-inducible, autocrine, and paracrine factors able to recruit myofibroblast-like cells. Moreover, HSC/MFs, in addition to their established profibrogenic role, may also contribute to neoangiogenesis during chronic hepatic wound healing.

Splenic artery ligation improves remnant liver function in partially hepatectomized rats with ischemia/reperfusion injury

BACKGROUND

In liver resection, the temporary occlusion of the hepatoduodenal ligament (Pringle maneuver) is often used. However, the maneuver causes severe ischemia/reperfusion injury in the remnant liver. Our aim was to investigate the effects of splenic artery ligation on the liver function in partially hepatectomized rat with the Pringle maneuver.

METHODS

The Pringle maneuver was conducted for 30 min just before a two-thirds partial hepatectomy. Splenic artery ligation was performed before the Pringle maneuver. The efficacy of splenic artery ligation was assessed by survival, serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), recovery of remnant liver weight, and portal pressure.

RESULTS

On day 3, animal survival was four rats of 12 in partially hepatectomized rats with the Pringle maneuver and 10 rats of 12 in the splenic artery ligation-treated partially hepatectomized rats with the Pringle maneuver. A two-thirds partial hepatectomy alone or splenic artery ligation itself did not show any effects on the survival. Compared with partially hepatectomized rats with the Pringle maneuver, splenic artery-ligated animals had lower serum AST and ALT levels, and higher recovery of remnant liver weight. Splenic artery ligation significantly reduced the portal pressure and also decreased the fatality in excessively hepatectomized rats.

CONCLUSIONS

Splenic artery ligation ameliorated the remnant liver function in partially hepatectomized rats with the Pringle maneuver and excessively hepatectomized rats. The amelioration may be mediated at least by decreasing portal pressure.

Portal hypertension

PURPOSE OF REVIEW

Significant advances in the pathophysiology, diagnosis and management of the complications of portal hypertension that have occurred in the last year are reported.

RECENT FINDINGS

The specific areas reviewed are those that refer to experimental studies aimed at modifying the factors that lead to portal hypertension (increased intrahepatic vascular resistance and splanchnic vasodilatation) and recent advances in the diagnosis and management of the complications of portal hypertension. The specific complications reviewed in this paper are varices and variceal bleeding (primary prophylaxis, treatment of the acute episode and secondary prophylaxis), ascites and hepatorenal syndrome, spontaneous bacterial peritonitis and hepatic encephalopathy, as well as recent studies of predictors of death in cirrhosis.

SUMMARY

Important studies, mostly prospective, regarding the management of the complications of portal hypertension are reviewed, including a trial of beta-blockers in the prevention of varices, a randomized trial of endoscopic variceal ligation plus nadolol in preventing recurrent variceal bleeding and several meta-analyses on trials comparing large-volume paracentesis with transjugular intrahepatic portosystemic shunt in the management of refractory ascites.