Renal sodium retention in cirrhotic rats depends on glucocorticoid-mediated activation of mineralocorticoid receptor due to decreased renal 11β-HSD-2 activity

Decaying kidney function during cirrhosis correlates with remodeling of distal colon aldosterone target gene expression

Liver cirrhosis is associated to circulatory abnormalities leading to hypovolemia and stimulation of the renin-angiotensin-aldosterone system (RAAS). Advanced stages of the disease cause renal failure, impairing K+ and Na+ homeostasis. It has been proposed that the distal colon undergoes functional remodeling during renal failure, in particular by aldosterone-driven increased K+ excretion. In this study, we compared the transcriptional response of aldosterone target genes in the rat distal colon under two models of increased circulating aldosterone (one with concomitant RAAS activation) and in a model of secondary hyperaldosteronism induced by cirrhosis. The expression of a subset of these genes was also tested in distal colon biopsies from control subjects or patients with cirrhosis with varying levels of disease progression and treated or not with mineralocorticoid receptor inhibitor spironolactone. We examined known aldosterone-regulated transcripts involved in corticosteroid signaling and transepithelial ion transport. In addition, we included aldosterone-regulated genes related to cell proliferation. Our comparison revealed multiple aldosterone target genes upregulated in the rat distal colon during decompensated cirrhosis. Epithelial Na+ channel β and γ subunit expression correlated positively with plasma aldosterone concentration and negatively with glomerular filtration rate. Patients with cirrhosis showed increased expression of 11-β-hydroxysteroid-dehydrogenase 2 (11βHSD2), which was reverted by spironolactone treatment, suggesting a sensitization of the distal colon to aldosterone action. In summary, our data show that decaying kidney function during cirrhosis progression toward a decompensated state with hypovolemia correlates with remodeling of distal colon ion transporter expression, supporting a role for aldosterone in the process.NEW & NOTEWORTHY Liver cirrhosis progression significantly alters ion transporter subunit expression in the rat distal colon, a change that correlated well with declining kidney function and the severity of the disease. Our data suggest that the steroid hormone aldosterone participates in this homeostatic response to maintain electrolyte balance.

A mouse model of subacute liver failure with ascites induced by step-wise increased doses of (-)-epigallocatechin-3-gallate

Acute liver failure is divided into hyperacute, acute and subacute liver failure. Ascites is a common complication of subacute liver failure. Although animal models of acute liver failure have been established, the study of the pathogenesis of subacute liver failure with ascites complication is hampered by the lack of experimental animal model. The present study aimed at providing a mouse model of subacute liver failure with ascites complication. Kunming mice were intraperitoneally injected with (-)-epigallocatechin-3-gallate (EGCG), a redox-active polyphenol from green tea, for 32 consecutive days with step-wise increased dosage. The EGCG treatment resulted in liver failure as evidenced by extensive hepatocyte necrosis observed histologically along with significant elevation of serum alanine aminotransferase, aspartate aminotransferase, total bilirubin and direct bilirubin levels as well as significant reduction of serum albumin. Liver fibrosis was not observed by Masson staining and fibrosis-associated proteins were not increased. The mortality was less than 12% and the survival mice developed noticeable ascites. Hepatic thioredoxin and glutathione systems were activated by the EGCG. These adaptive responses might render most mice tolerable to the EGCG treatment. The EGCG treatment significantly up-regulated renal urea transporter A1 and promoted its trafficking to apical membrane. These alterations, known to increase water reabsorption, may be responsible, at least in part, for the formation of the ascites. Overall, the mice treated with gradually elevated doses of EGCG exhibits some of the features observed in patients with subacute liver failure, especially ascites. This mouse model is a useful tool for investigating the pathogenesis of subacute liver failure with ascites complication.

Activation of RAAS in a rat model of liver cirrhosis: no effect of losartan on renal sodium excretion

Background

Liver cirrhosis is characterized by avid sodium retention where the activation of the renin angiotensin aldosterone system (RAAS) is considered to be the hallmark of the sodium retaining mechanisms. The direct effect of angiotensin II (ANGII) on the AT-1 receptor in the proximal tubules is partly responsible for the sodium retention. The aim was to estimate the natriuretic and neurohumoral effects of an ANGII receptor antagonist (losartan) in the late phase of the disease in a rat model of liver cirrhosis.

Methods

Bile duct ligated (BDL) and sham operated rats received 2 weeks of treatment with losartan 4 mg/kg/day or placebo, given by gastric gavage 5 weeks after surgery. Daily sodium and potassium intakes and renal excretions were measured.

Results

The renal sodium excretion decreased in the BDL animals and this was not affected by losartan treatment. At baseline the plasma renin concentration (PRC) was similar in sham and BDL animals, but increased urinary excretion of ANGII and an increase P-Aldosterone was observed in the placebo treated BDL animals. The PRC was more than 150 times higher in the losartan treated BDL animals (p < 0.001) which indicated hemodynamic impairment.

Conclusions

Losartan 4 mg/kg/day did not increase renal sodium excretion in this model of liver cirrhosis, although the urinary ANGII excretion was increased. The BDL animals tolerated Losartan poorly, and the treatment induced a 150 times higher PRC.

DNA methylation and hypertension: emerging evidence and challenges

Hypertension is a multifactorial disease influenced by an interaction of environmental and genetic factors. The exact molecular mechanism of hypertension remains unknown. Aberrant DNA methylation is the most well-defined epigenetic modification that regulates gene transcription. However, studies on the association between DNA methylation and hypertension are still in their infancy. This review summarizes the latest evidence and challenges regarding the role of DNA methylation on hypertension.

Differential Sympathetic Vasomotor Activation Induced by Liver Cirrhosis in Rats

We tested the hypothesis that there is a topographical sympathetic activation in rats submitted to experimental cirrhosis. Baseline renal (rSNA) and splanchnic (sSNA) sympathetic nerve activities were evaluated in anesthetized rats. In addition, we evaluated main arterial pressure (MAP), heart rate (HR), and baroreceptor reflex sensitivity (BRS). Cirrhotic Wistar rats were obtained by bile duct ligation (BDL). MAP and HR were measured in conscious rats, and cardiac BRS was assessed by changes in blood pressure induced by increasing doses of phenylephrine or sodium nitroprusside. The BRS and baseline for the control of sSNA and rSNA were also evaluated in urethane-anesthetized rats. Cirrhotic rats had increased baseline sSNA (BDL, 102 vs control, 58 spikes/s; p<0.05), but no baseline changes in the rSNA compared to controls. These data were accompanied by increased splanchnic BRS (p<0.05) and decreased cardiac (p<0.05) and renal BRS (p<0.05). Furthermore, BDL rats had reduced basal MAP (BDL, 93 vs control, 101 mmHg; p<0.05) accompanied by increased HR (BDL, 378 vs control, 356; p<0.05). Our data have shown topographical sympathetic activation in rats submitted to experimental cirrhosis. The BDL group had increased baseline sSNA, independent of dysfunction in the BRS and no changes in baseline rSNA. However, an impairment of rSNA and HR control by arterial baroreceptor was noted. We suggest that arterial baroreceptor impairment of rSNA and HR is an early marker of cardiovascular dysfunction related to liver cirrhosis and probably a major mechanism leading to sympathoexcitation in decompensated phase.

17β-Estradiol in the systemic circulation derives mainly from the parietal cells in cholestatic female rats

PURPOSE

Estrogenic symptoms of liver disease patients including biliary tract disorder with high frequency is observed in clinical cases. However, the origin of 17β-estradiol which is abundant enough to cause symptoms remains uncertain. In male rats, it has been reported that the parietal cells which have an abundance of aromatase-synthesized 17β-estradiol, and a part of 17β-estradiol secreted into the portal vein, may flow into the systemic circulation under a pathophysiological condition of the liver including bile duct ligation (BDL). The aim of this study is to reveal the origin of 17β-estradiol increment in female rats and to investigate the effect of BDL on the ovary during the estrus cycle.

METHODS

Wistar female rats were used, and the common bile duct was ligated twice and transected completely at 7 days before termination. Serum portal venous and arterial 17β-estradiol levels, Cyp19a1 expressions, aromatase protein levels, and estrogen receptor (ER) α levels in the liver were measured during the estrus cycle.

RESULTS

Both arterial and portal venous 17β-estradiol levels increased 2.9 times at proestrus and maintained constant levels during the cycle. The expression of Cyp19a1 and aromatase protein in the stomach maintained constant levels, and significantly decreased during the estrus cycle in the ovary. Hepatic ERα protein and Esr1 expressions decrease by BDL in all stages.

CONCLUSIONS

These results suggest that the increment of serum 17β-estradiol levels in obstructive cholestasis induced by BDL is derived from 17β-estradiol secreted from the parietal cells in females as well as males.

The role of glucocorticoids in sodium retention in cirrhotic patients: a double blind, randomized, crossover study

OBJECTIVE

Cirrhotic patients have an increased ratio of urinary cortisol to cortisone metabolites, indicating decreased renal 11-β-hydroxysteroid dehydrogenase type-2 activity. This suggests that cortisol--by activation of the mineralocorticoid receptor--may contribute to the abnormal sodium retention evident in cirrhosis. The aim was to elucidate the role of glucocorticoids in sodium retention in decompensated cirrhotic patients.

METHODS

A randomized, double-blind, placebo-controlled, crossover study was performed in nine patients with alcoholic cirrhosis of the liver. A washout interval of 14 days separated the two periods. After a basal period of 36 h, dexamethasone (0.5 mg every 6 h) or placebo was given for two days. Urine was collected for 12 h periods, and the concentrations of sodium, potassium, creatinine, cortisol and cortisol metabolites were determined. Blood samples for hemoglobin, glucose, sodium, potassium, creatinine, aldosterone and cortisol were obtained daily.

RESULTS

Dexamethasone treatment decreased S-cortisol 92.3% (82.9-93.4%) (median and range) compared with that in the basal period. Natriuresis (dexamethasone--placebo) increased 55.1 (-26.4-168.7) mmol/day (median and range). No statistically significant differences (dexamethasone--placebo) were found in changes in body weight (0.00 (-0.45-2.20) kg/day), diuresis (0.56 (-0.35-1.43) L/day) or mean arterial pressure (8.33 (-16.0-41.3) mmHg) (median and range) in reference to the preceding 24 h basal period.

CONCLUSION

These results indicate that endogenous glucocorticoids contribute to the sodium retention in patients with alcoholic cirrhosis of the liver.

Bile acids modulate glucocorticoid metabolism and the hypothalamic-pituitary-adrenal axis in obstructive jaundice

BACKGROUND & AIMS

Suppression of the hypothalamic-pituitary-adrenal axis occurs in cirrhosis and cholestasis and is associated with increased concentrations of bile acids. We investigated whether this was mediated through bile acids acting to impair steroid clearance by inhibiting glucocorticoid metabolism by 5beta-reductase.

METHODS

The effect of bile acids on glucocorticoid metabolism was studied in vitro in hepatic subcellular fractions and hepatoma cells, allowing quantitation of the kinetics and transcript abundance of 5beta-reductase. Metabolism was subsequently examined in vivo in rats following dietary manipulation or bile duct ligation. Finally, glucocorticoid metabolism was assessed in humans with obstructive jaundice.

RESULTS

In rat hepatic cytosol, chenodeoxycholic acid competitively inhibited 5beta-reductase (K(i) 9.19+/-0.40 microM) and reduced its transcript abundance (in H4iiE cells) and promoter activity (reporter system, HepG2 cells). In Wistar rats, dietary chenodeoxycholic acid (1% w/w chow) inhibited hepatic 5beta-reductase activity, reduced urinary excretion of 3alpha,5beta-tetrahydrocorticosterone and reduced adrenal weight. Conversely, a fat-free diet suppressed bile acid levels and increased hepatic 5beta-reductase activity, supplementation of the fat-free diet with CDCA reduced 5beta-reductase activity, and urinary 3alpha,5beta-reduced corticosterone. Cholestasis in rats suppressed hepatic 5beta-reductase activity and transcript abundance. In eight women with obstructive jaundice, relative urinary excretion of 3alpha,5beta-tetrahydrocortisol was significantly lower than in healthy controls.

CONCLUSION

These data suggest a novel role for bile acids in inhibiting hepatic glucocorticoid clearance, of sufficient magnitude to suppress hypothalamic-pituitary-adrenal axis activity. Elevated hepatic bile acids may account for adrenal insufficiency in liver disease.

Plasmin in nephrotic urine activates the epithelial sodium channel

Proteinuria and increased renal reabsorption of NaCl characterize the nephrotic syndrome. Here, we show that protein-rich urine from nephrotic rats and from patients with nephrotic syndrome activate the epithelial sodium channel (ENaC) in cultured M-1 mouse collecting duct cells and in Xenopus laevis oocytes heterologously expressing ENaC. The activation depended on urinary serine protease activity. We identified plasmin as a urinary serine protease by matrix-assisted laser desorption/ionization time of-flight mass spectrometry. Purified plasmin activated ENaC currents, and inhibitors of plasmin abolished urinary protease activity and the ability to activate ENaC. In nephrotic syndrome, tubular urokinase-type plasminogen activator likely converts filtered plasminogen to plasmin. Consistent with this, the combined application of urokinase-type plasminogen activator and plasminogen stimulated amiloride-sensitive transepithelial sodium transport in M-1 cells and increased amiloride-sensitive whole-cell currents in Xenopus laevis oocytes heterologously expressing ENaC. Activation of ENaC by plasmin involved cleavage and release of an inhibitory peptide from the ENaC gamma subunit ectodomain. These data suggest that a defective glomerular filtration barrier allows passage of proteolytic enzymes that have the ability to activate ENaC.

Plasmin in nephrotic urine activates the epithelial sodium channel

Proteinuria and increased renal reabsorption of NaCl characterize the nephrotic syndrome. Here, we show that protein-rich urine from nephrotic rats and from patients with nephrotic syndrome activate the epithelial sodium channel (ENaC) in cultured M-1 mouse collecting duct cells and in Xenopus laevis oocytes heterologously expressing ENaC. The activation depended on urinary serine protease activity. We identified plasmin as a urinary serine protease by matrix-assisted laser desorption/ionization time of-flight mass spectrometry. Purified plasmin activated ENaC currents, and inhibitors of plasmin abolished urinary protease activity and the ability to activate ENaC. In nephrotic syndrome, tubular urokinase-type plasminogen activator likely converts filtered plasminogen to plasmin. Consistent with this, the combined application of urokinase-type plasminogen activator and plasminogen stimulated amiloride-sensitive transepithelial sodium transport in M-1 cells and increased amiloride-sensitive whole-cell currents in Xenopus laevis oocytes heterologously expressing ENaC. Activation of ENaC by plasmin involved cleavage and release of an inhibitory peptide from the ENaC gamma subunit ectodomain. These data suggest that a defective glomerular filtration barrier allows passage of proteolytic enzymes that have the ability to activate ENaC.

Renal nerves and nNOS: roles in natriuresis of acute isovolumetric sodium loading in conscious rats

It was hypothesized that renal sympathetic nerve activity (RSNA) and neuronal nitric oxide synthase (nNOS) are involved in the acute inhibition of renin secretion and the natriuresis following slow NaCl loading (NaLoad) and that RSNA participates in the regulation of arterial blood pressure (MABP). This was tested by NaLoad after chronic renal denervation with and without inhibition of nNOS by S-methyl-thiocitrulline (SMTC). In addition, the acute effects of renal denervation on MABP and sodium balance were assessed. Rats were investigated in the conscious, catheterized state, in metabolic cages, and acutely during anesthesia. NaLoad was performed over 2 h by intravenous infusion of hypertonic solution (50 μmol·min−1·kg body mass−1) at constant body volume conditions. SMTC was coinfused in amounts (20 μg·min−1·kg−1) reported to selectively inhibit nNOS. Directly measured MABPs of acutely and chronically denervated rats were less than control (15% and 9%, respectively, P < 0.005). Plasma renin concentration (PRC) was reduced by renal denervation (14.5 ± 0.2 vs. 19.3 ± 1.3 mIU/l, P < 0.005) and by nNOS inhibition (12.4 ± 2.3 vs. 19.6 ± 1.6 mlU/l, P < 0.005). NaLoad reduced PRC ( P < 0.05) and elevated MABP modestly ( P < 0.05) and increased sodium excretion six-fold, irrespective of renal denervation and SMTC. The metabolic data demonstrated that renal denervation lowered sodium balance during the first days after denervation ( P < 0.001). These data show that renal denervation decreases MABP and renin secretion. However, neither renal denervation nor nNOS inhibition affects either the renin down-regulation or the natriuretic response to acute sodium loading. Acute sodium-driven renin regulation seems independent of RSNA and nNOS under the present conditions.

DHEA induces 11 -HSD2 by acting on CCAAT/enhancer-binding proteins

11beta-Hydroxysteroid dehydrogenase (11beta-HSD) type 1 and type 2 catalyze the interconversion of inactive and active glucocorticoids. Impaired regulation of these enzymes has been associated with obesity, diabetes, hypertension, and cardiovascular disease. Previous studies in animals and humans suggested that dehydroepiandrosterone (DHEA) has antiglucocorticoid effects, but the underlying mechanisms are unknown. In this study, DHEA treatment markedly increased mRNA expression and activity of 11beta-HSD2 in a rat cortical collecting duct cell line and in kidneys of C57BL/6J mice and Sprague-Dawley rats. DHEA-treated rats tended to have reduced urinary corticosterone to 11-dehydrocorticosterone ratios. It was found that CCAAT/enhancer-binding protein-alpha (C/EBP-alpha) and C/EBP-beta regulated HSD11B2 transcription and that DHEA likely modulated the transcription of 11beta-HSD2 in a phosphatidylinositol-3 kinase/Akt-dependent manner by increasing C/EBP-beta mRNA and protein expression. Moreover, it is shown that C/EBP-alpha and C/EBP-beta differentially regulate the expression of 11beta-HSD1 and 11beta-HSD2. In conclusion, DHEA induces a shift from 11beta-HSD1 to 11beta-HSD2 expression, increasing conversion from active to inactive glucocorticoids. This provides a possible explanation for the antiglucocorticoid effects of DHEA.

Sodium retention and ascites formation in a cholestatic mice model: role of aldosterone and mineralocorticoid receptor?

Renal sodium retention in experimental liver cirrhosis originates from the distal nephron sensitive to aldosterone. The aims of this study were to (1) determine the exact site of sodium retention along the aldosterone-sensitive distal nephron, and (2) to evaluate the role of aldosterone and mineralocorticoid receptor activation in this process. Liver cirrhosis was induced by bile duct ligation in either adrenal-intact or corticosteroid-clamped mice. Corticosteroid-clamp was achieved through adrenalectomy and corticosteroid supplementation with aldosterone and dexamethasone via osmotic minipumps. 24-hours renal sodium balance was evaluated in metabolic cages. Activity and expression of sodium- and potassium-dependent adenosine triphosphatase were determined in microdissected segments of nephron. Within 4-5 weeks, cirrhosis induced sodium retention in adrenal-intact mice and formation of ascites in 50% of mice. At that time, sodium- and potassium-dependent adenosine triphosphatase activity increased specifically in cortical collecting ducts. Hyperaldosteronemia was indicated by increases in urinary aldosterone excretion and in sgk1 (serum- and glucocorticoid-regulated kinase 1) mRNA expression in collecting ducts. Corticosteroid-clamp prevented induction of sgk1 but not cirrhosis-induced sodium retention, formation of ascites and stimulation of sodium- and potassium-dependent adenosine triphosphatase activity and expression (mRNA and protein) in collecting duct. These findings demonstrate that sodium retention in cirrhosis is independent of hyperaldosteronemia and of the activation of mineralocorticoid receptor.

CONCLUSION

Bile duct ligation in mice induces cirrhosis which, within 4-5 weeks, leads to the induction of sodium- and potassium-dependent adenosine triphosphatase in cortical collecting ducts, to renal sodium retention and to the formation of ascites. Sodium retention, ascites formation and induction of sodium- and potassium-dependent adenosine triphosphatase are independent of the activation of mineralocorticoid receptors by either aldosterone or glucocorticoids.

Portal hypertension and its complications

PURPOSE OF REVIEW

Portal hypertension is responsible for most of the complications associated with cirrhosis, specifically variceal hemorrhage, ascites and hepatic encephalopathy. Progress in understanding the pathophysiology of portal hypertension and improvements in the diagnosis and management of its complications that have occurred over the last year are discussed.

RECENT FINDINGS

Endothelial dysfunction contributes to the pathogenesis of portal hypertension and may represent a novel therapeutic target. Hepatic venous pressure gradient measurements, when properly performed, are useful in the management of patients with cirrhosis. Hyponatremia in cirrhosis has prognostic value and novel aquaretic and other agents may provide alternative approaches to the management of chronic liver disease. The mechanisms for bacterial translocation in cirrhosis that predisposes patients to infectious complications, such as spontaneous bacterial peritionitis, are being explored. Adrenal insufficiency is common in septic patients with advanced cirrhosis and corticosteroids may provide a survival benefit. Pulmonary disease complicates the management of patients with advanced liver disease.

SUMMARY

Significant advances continue to be made in the diagnosis and management of the complications of portal hypertension in the face of an increasing burden of chronic liver disease.