Aquaporin-1 and aquaporin-2 urinary excretion in cirrhosis: Relationship with ascites and hepatorenal syndrome

Aquaporins in Edema

One of the most prevalent indications of water-electrolyte imbalance is edema. Aquaporins (AQPs) are a protein family that can function as water channels. Osmoregulation and body water homeostasis are dependent on the regulation of AQPs. Human kidneys contain nine AQPs, five of which have been demonstrated to have a role in body water balance: AQP1, AQP2, AQP3, AQP4, and AQP7. Water imbalance is connected with AQP dysfunction. Hyponatremia with elevated AQP levels can accompany edema, which can be caused by disorders with low effective circulating blood volume and systemic vasodilation, such as congestive heart failure (CHF), hepatic cirrhosis, or the syndrome of incorrect antidiuretic hormone secretion (SIADH). In CHF, upregulation of AQP2 expression and targeting is critical for water retention. AQP2 is also involved in aberrant water retention and the formation of ascites in cirrhosis of the liver. Furthermore, water retention and hyponatremia in SIADH are caused by increased expression of AQP2 in the collecting duct. Fluid restriction, demeclocycline, and vasopressin type-2 receptor antagonists are widely utilized to treat edema. The relationship between AQPs and edema is discussed in this chapter.

Alleviation of liver cirrhosis and associated portal-hypertension by Astragalus species in relation to their UPLC-MS/MS metabolic profiles: a mechanistic study

Liver cirrhosis is a late-stage liver disease characterized by excessive fibrous deposition triggering portal-hypertension (PH); the prime restrainer for cirrhosis-related complications. Remedies that can dually oppose hepatic fibrosis and lower PH, may prevent progression into decompensated-cirrhosis. Different Astragalus-species members have shown antifibrotic and diuretic actions with possible subsequent PH reduction. However, A.spinosus and A.trigonus were poorly tested for eliciting these actions. Herein, A.spinosus and A.trigonus roots and aerial parts extracts were subjected to comprehensive metabolic-fingerprinting using UHPLC-MS/MS resulting in 56 identified phytoconstituents, followed by chemometric untargeted analysis that revealed variable metabolic profiles exemplified by different species and organ types. Consequently, tested extracts were in-vivo evaluated for potential antifibrotic/anticirrhotic activity by assessing specific markers. The mechanistic prospective to induce diuresis was investigated by analyzing plasma aldosterone and renal-transporters gene-expression. Serum apelin and dimethylarginine-dimethylaminohydrolase-1 were measured to indicate the overall effect on PH. All extracts amended cirrhosis and PH to varying extents and induced diuresis via different mechanisms. Further, An OPLS model was built to generate a comprehensive metabolic-profiling of A.spinosus and A.trigonus secondary-metabolites providing a chemical-based evidence for their efficacious consistency. In conclusion, A.spinosus and A.trigonus organs comprised myriad pharmacologically-active constituents that act synergistically to ameliorate cirrhosis and associated PH.

Clinical Implications, Evaluation, and Management of Hyponatremia in Cirrhosis

Hyponatremia is the most common electrolyte abnormality in patients with decompensated cirrhosis on Liver Transplantation (LT) waiting list. Most of these patients have dilutional or hypervolemic hyponatremia secondary to splanchnic vasodilatation. Excessive secretion of the antidiuretic hormone also plays an important role. Hypervolemic hyponatremia is commonly associated with refractory ascites, spontaneous bacterial peritonitis, and hepatic encephalopathy. Although uncommon, the use of diuretics and laxatives can cause hypovolemic hyponatremia that is characterized by the striking absence of ascites or pedal edema. Clinical features are often nonspecific and depend on the acuity of onset rather than the absolute value of serum sodium. Symptoms may be subtle, including nausea, lethargy, weakness, or anorexia. However, rarely patients may present with confusion, seizures, psychosis, or coma. Treatment includes discontinuation of diuretics, beta-blockers, and albumin infusion. Hypertonic saline (3%) infusion may be used in patients with very low serum sodium (<110 mmol/L) or when patients present with seizures or coma. Short-term use of Vasopressin (V₂) receptor antagonists may also be used to normalize sodium levels prior to LT. However, all these measures may be futile, and LT remains the definite treatment in these patients to improve survival. In this review, we describe the classification, pathogenesis of hyponatremia, and its clinical implications in patients with cirrhosis. Approach to these patients along with management will also be discussed briefly.

Anti-Malignant Ascites Effect of Total Diterpenoids from Euphorbiae Ebracteolatae Radix Is Attributable to Alterations of Aquaporins via Inhibiting PKC Activity in the Kidney

This study evaluated the anti-ascites effect of total diterpenoids extracted from Euphorbiae ebracteolatae Radix (TDEE) on malignant ascitic mice and elucidated its underlying mechanism. TDEE was extracted by dichloromethane and subjected to column chromatography. The purity of six diterpenoids isolated from TDEE was determined to be 77.18% by HPLC. TDEE (3 and 0.6 g raw herbs/kg, p.o.) reduced ascites and increased urine output. Meanwhile, analysis of tumor cell viability, cycle and apoptosis indicated that TDEE had no antitumor activity. In addition, the expression levels of aquaporins (AQPs) and the membrane translocation levels of protein kinase C (PKC) α and PKCβ in kidney and cells were measured. TDEE reduced the levels of AQP1–4, and inhibited PKCβ expression in membrane fraction. Four main diterpenoids, except compound 2, reduced AQP1 level in human kidney-2 cells. Compounds 4 and 5 inhibited AQP2–4 expression in murine inner medullary collecting duct cells. The diterpenoid-induced inhibition of AQP1–4 expression was blocked by phorbol-12-myristate-13-acetate (PMA; agonist of PKC). The diterpenoids from TDEE are the main anti-ascites components. The anti-ascites effect of diterpenoids may be associated with alterations in AQPs in the kidneys to promote diuresis. The inhibition of AQP1–4 expression by TDEE is related to the inhibition of PKCβ activation.

Tolvaptan treatment improves survival of cirrhotic patients with ascites and hyponatremia

Background

Although tolvaptan treatment improves hyponatremia, only few studies have investigated whether tolvaptan actually benefits the survival of cirrhotic patients. This study evaluated the impact of tolvaptan on six-month survival of decompensated cirrhotic patients with and without hyponatremia.

Methods

Two hundred forty-nine decompensated cirrhotic patients with or without hyponatremia were enrolled in a multicenter cohort study. Patients were divided into two groups according to receiving either tolvaptan or placebo treatment for 7-day. Subsequently, the patients were followed up for 6 months.

Results

Two hundred thirty patients, including 98 with hyponatremia (tolvaptan vs. placebo: 69 vs. 29) finished the study. Tolvaptan did not alter serum sodium levels and survival outcome of decompensated cirrhotic patients without hyponatremia. However, tolvaptan treatment remarkably improved serum sodium levels and six-month survival in patients with hyponatremia. Following tolvaptan treatment, serum sodium levels were restored to normal in 63.8% of patients, whereas in patients receiving placebo, only 36.2% showed the same effect (P < 0.05). Compared to a six-month survival rate of 68.97% in patients receiving placebo, the survival rate in tolvapatan-treated patients was 89.94% (P < 0.05). Furthermore, six-month survival rate in the tolvaptan-treated hyponatremia patients with resolved serum sodium was 81.32%, whereas the survival in those with unresolved serum sodium was only 24% (P < 0.05).

Conclusions

Tolvaptan improves short term survival in most decompensated cirrhotic hyponatremia patients with resolved serum sodium.

Trials registration

Clinical trial one: ClinicalTrials.gov ID:NCT00664014, Registered on April 14, 2008.

Clinical trial two: ClinicalTrials.gov ID:NCT01349335, Registered on March 5, 2010.

Clinical trial three: ClinicalTrials.gov ID:NCT01349348, Registered on May 4, 2011.

Terlipressin for variceal bleeding induces large plasma sodium fluctuations in patients without cirrhosis

Background

Terlipressin is used as pharmacological treatment for variceal bleeding. The drug's physiological effect favours hyponatremia, and rapid changes in plasma sodium (PNa) may cause brain injury. Cirrhosis patients seem to be largely protected against this effect but patients without cirrhosis may not be so.

Objective

The objective of this study was to examine whether terlipressin treatment of patients without cirrhosis leads to more serious fluctuations in PNa than in cirrhosis.

Methods

In a retrospective cohort design, during a 39-month period, 11 patients with prehepatic portal hypertension and no cirrhosis and 134 patients with cirrhosis received a minimum cumulative terlipressin dose of 4 mg during at least 24 hours for variceal bleeding. The groups' PNa changes were compared.

Results

During terlipressin, the non-cirrhotic patients developed a greater reduction in PNa [mean 8.3 (95% confidence interval (CI) 1.9-14.6) vs. 1.8 (1.0-2.7) mmol/l; p = 0.048], a lower nadir PNa [129 (123-135) vs. 133 (132-134) mmol/l; p = 0.06], and within 48 hours after terlipressin a greater increase in PNa [12.6 (3.4-21.7) vs. 2.3 (1.5-3.0) mmol/l; p = 0.03]. Severe (>10 mmol/l change) hyponatriemia or PNa rebound were seen in 27% of these patients but in only 4% of those with cirrhosis (p = 0.02). One non-cirrhotic patient developed permanent brain damage.

Conclusion

Terlipressin treatment of bleeding varices carries a high risk of potentially dangerous PNa fluctuations in patients with non-cirrhotic prehepatic portal hypertension.

Increased serum C-reactive protein and decreased urinary aquaporin 2 levels are predictive of the efficacy of tolvaptan in patients with liver cirrhosis

AIM

Water retention, hepatic ascites, and peripheral edema are significant problems in patients with liver cirrhosis (LC). Although furosemide and spironolactone are commonly used as treatment, they are often insufficient to treat hyponatremia and renal insufficiency in patients with LC. Tolvaptan (TVP) could provide an effective treatment alternative. However, predictive factors of a therapeutic response to TVP are unclear. Our aim was to examine clinical predictors of the response to TVP in patients with LC and water retention.

METHODS

Fifty-two patients were treated with TVP, with therapeutic effects judged by a decrease in body weight (≥2 kg) and increase in urinary volume (≥500 mL) within 7 days. Blood biochemical tests were carried out at baseline and post-treatment, including serum soluble CD14 (sCD14) and urinary aquaporin 2 (AQP2) levels. Clinical and laboratory predictive factors of a TVP response were evaluated by univariate and multivariate analyses.

RESULTS

The overall response to TVP was 55.8%. On univariate analyses, serum C-reactive protein (CRP) level, the neutrophil-to-lymphocyte ratio, urinary blood urea nitrogen, and urinary AQP2 were predictors of the TVP response, with only serum CRP retained on multivariate analysis. A higher serum sCD14 level was strongly associated with a non-response to TVP. A decrease in urinary AQP2 to undetectable level was associated with a response.

CONCLUSION

Tolvaptan provides a rapid and strong effect to improve water retention in patients with LC. Baseline serum sCD14 and CRP levels are useful predictors of a response to TVP, with a decrease in urinary AQP2 during treatment indicating an early response.

Transjugular intrahepatic portosystemic shunt: impact on systemic hemodynamics and renal and cardiac function in patients with cirrhosis

Transjugular intrahepatic portosystemic shunt (TIPS) alleviates portal hypertension and possibly increases central blood volume (CBV). Moreover, renal function often improves; however, its effects on cardiac function are unclear. The aims of our study were to examine the effects of TIPS on hemodynamics and renal and cardiac function in patients with cirrhosis. In 25 cirrhotic patients, we analyzed systemic, cardiac, and splanchnic hemodynamics by catheterization of the liver veins and right heart chambers before and 1 wk after TIPS. Additionally, we measured renal and cardiac markers and performed advanced echocardiography before, 1 wk after, and 4 mo after TIPS. CBV increased significantly after TIPS (+4.6%, P < 0.05). Cardiac output (CO) increased (+15.3%, P < 0.005) due to an increase in stroke volume (SV) (+11.1%, P < 0.005), whereas heart rate (HR) was initially unchanged. Cardiopulmonary pressures increased after TIPS, whereas copeptin, a marker of vasopressin, decreased (-18%, P < 0.005) and proatrial natriuretic peptide increased (+52%, P < 0.0005) 1 wk after TIPS and returned to baseline 4 mo after TIPS. Plasma neutrophil gelatinase-associated lipocalin, renin, aldosterone, and serum creatinine decreased after TIPS (-36%, P < 0.005; -65%, P < 0.05; -90%, P < 0.005; and -13%, P < 0.005, respectively). Echocardiography revealed subtle changes in cardiac function after TIPS, although these were within the normal range. TIPS increases CBV by increasing CO and SV, whereas HR is initially unaltered. These results indicate an inability to increase the heart rate in response to a hemodynamic challenge that only partially increases CBV after TIPS. These changes, however, are sufficient for improving renal function. NEW & NOTEWORTHY For the first time, we have combined advanced techniques to study the integrated effects of transjugular intrahepatic portosystemic shunt (TIPS) in cirrhosis. We showed that TIPS increases central blood volume (CBV) through improved cardiac inotropy. Advanced echocardiography demonstrated that myocardial function was unaffected by the dramatic increase in preload after TIPS. Finally, renal function improved due to the increase in CBV. Recognition of these physiological changes significantly contributes to our clinical understanding of TIPS.

Aquaporin-2 excretion in hospitalized patients with cirrhosis: Relation to development of renal insufficiency and mortality

BACKGROUND AND AIM

Urinary aquaporin-2 (AQP2) is a parameter of water transport in the principal cells in the distal part of the nephron and involved in water retention in cirrhosis and may be a marker of renal function. The aim of the study was to evaluate AQP2 as a predictor of renal insufficiency and death in patients with cirrhosis.

METHODS

Urine samples from 199 patients (90 patients without organ failure [Group 1], 58 patients with organ failure excluding renal failure [Group 2], and 51 patients with organ failure including renal failure [Group 3]) from the CANONIC study were analyzed for urine AQP2 and urine osmolality.

RESULTS

There was no difference in AQP2 between the three groups. Urine osmolality was significantly lower in patients in Group 3 versus Group 1 and Group 2 (P = 0.0004). No relation was found between AQP2 and glomerular filtration rate or creatinine; however, AQP2 was a significant predictor of the development of renal insufficiency (P = 0.0485). In a univariate analysis, AQP2 was a significant predictor of 14 and 28-day survival, but this was not confirmed in multivariate analysis.

CONCLUSIONS

Aquaporin-2 was not associated with disease severity or markers of renal function but was a predictor for the development of renal insufficiency and death. Therefore, its future use as marker of renal insufficiency could be promising, but further research is needed before it can be considered a clinical useful tool.

Limited Efficacy of Tolvaptan in Patients with Cirrhosis and Severe Hyponatremia: Real-Life Experience

BACKGROUND

Vaptans, vasopressin selective V2-receptor antagonists, represent the first pharmacologic approach to the treatment of hypervolemic hyponatremia in cirrhosis. However, information on the use of vaptans for patients with cirrhosis and hyponatremia in a real-life scenario is limited. Therefore, this study evaluated the effect of tolvaptan on serum sodium in patients with cirrhosis and severe hypervolemic hyponatremia.

METHODS

Nine patients with cirrhosis and serum sodium ≤125 mEq/L were included.

RESULTS

Only 2 of the 9 patients (22%) gained an increase in serum sodium >130 mEq/L that persisted throughout treatment. In the remaining patients, serum sodium did not change or increased during the first days but decreased thereafter despite continuation of treatment. Only 1 patient developed hyperkalemia as a side effect.

CONCLUSIONS

The efficacy of tolvaptan in patients with cirrhosis and severe hypervolemic hyponatremia seems to be limited.

Urinary excretion of the water channel aquaporin 2 correlated with the pharmacological effect of tolvaptan in cirrhotic patients with ascites

BACKGROUND

The water channel aquaporin 2 (AQP2) at the apical membrane of renal collecting duct cells mediates water reabsorption. The expression of AQP2 at the apical membrane is tightly regulated by vasopressin and was quantitated by measurement of the urinary form by a recently developed ELISA. Tolvaptan, an antagonist of vasopressin type 2 receptor, inhibits water reabsorption in cirrhosis. The aim of this study was to determine the correlation between the pharmacological effect of tolvaptan and the dynamics of urinary AQP2 levels.

METHODS

Tolvaptan was administered to 41 cirrhotic patients with ascites unresponsive to standard diuretic therapy. Urinary excretion of AQP2 and urinary osmolarity were measured at the baseline and at 4, 8, and 24 h after administration of tolvaptan.

RESULTS

At the baseline, urinary AQP2/creatinine ratios were significantly higher in cirrhotic patients with ascites than in healthy controls (P < 0.0001). After administration of tolvaptan, urinary AQP2/creatinine ratios decreased by 45.0 % at 4 h and 77.0 % at 8 h. Similarly, urinary osmolarity decreased by 42.0 % at 4 h and 41.5 % at 8 h. Urinary AQP2 levels and urinary osmolarity significantly correlated at the baseline and at all time points after tolvaptan administration. The degree of the decrease in urinary AQP2 levels and degree of the decrease in urinary osmolarity correlated significantly at 4 h (r = 0.452, P = 0.009) and 8 h (r = 0.384, P = 0.030) after tolvaptan administration.

CONCLUSIONS

These results indicate that the vasopressin-AQP2 system plays a major role in fluid retention in cirrhosis and that the pharmacological effect of tolvaptan to inhibit water reabsorption can be monitored by measurement of the dynamics of urinary AQP2 levels.

Do vasopressin V2 receptor antagonists benefit cirrhotics with refractory ascites?

Hyponatremia is a frequent complication of advanced cirrhosis with ascites associated with increased morbidity and mortality. It is caused by an impairment in the renal capacity to eliminate solute-free water and is considered to be related to persistent secretion of vasopressin despite low serum osmolality. This nonosmotic release of vasopressin is mediated by the autonomic nervous system, which senses the underfilling of arterial vascular component. This reduction of effective arterial blood volume is closely related to the development of ascites. Although the short-time effects of vasopressin V2 receptor antagonists (vaptans) on hyponatremia and ascites have been repeatedly reported, their effects on the long-term management of cirrhotic ascites have not been established yet. Considering that their effects on water diuresis and their safety are limited by severe underfilling state of patients, cautious approaches with adequate monitoring are needed to advanced cirrhosis. Proper indication, adequate doses and new possibility of combination therapy should be explored in the future controlled study. As hyponatremia is frequent obstacle to ascites management, judicious combination with low-dose diuretics may decrease the incidence of refractory ascites. Although vaptans show much promise in the treatment of advanced cirrhosis, the problem of high cost should be solved for the future.

Impact of hyponatremia on frequency of complications in patients with decompensated liver cirrhosis

Introduction

Hyponatremia is common in cirrhosis. The relationship between hyponatremia and severity of cirrhosis is evidenced by its close association with the occurrence of complications, the prevalence of hepatic encephalopathy, hepatorenal syndrome, spontaneous bacterial peritonitis, refectory ascites, and hepatic hydrothorax. The aim of this study was assess the impact of hyponatremia on the occurrence of both liver-related complications and the hemodynamic cardiovascular dysfunction.

Methods

This prospective study was conducted in 2015 on 74 patients with liver cirrhosis. The patients were from the Gastroenterology and Hepatology Department of Theodor Bilharz Research Institute in Giza, Egypt. The patients were divided into three groups according to their serum level of sodium. Group 1 included 30 patients with serum sodium >135 meq/L, group 2 included 24 patients with serum sodium between135 and 125 meq/L, and group 3 included 20 patients with serum sodium <125 meq/L. For each of the patients, we conducted aclinical examination, laboratory investigations, chest X-ray, ECG, abdominal sonar, and echocardiography.

Results

Hyponatremia was found in 59.46% of our cirrhotic patients, and they showed significantly increased Model for End-Stage Liver Disease (MELD) score, MELD-Na score, QTc interval, Pulmonary vascular resistance (PVR) and inferior vena cava (IVC) collapsibility, and decreased SVR and IVC diameter. Also hepatic encephalopathy, ascites, renal failure, infectious complications, and pleural effusion were significantly more common in hyponatremic cirrhotic patients.

Conclusion

In cirrhosis, hyponatremia is more common in severe cardiovascular dysfunction and associated with increased risk of hepatic encephalopathy, ascites, illness severity scores, renal failure, infectious complications, and pleural effusion. We recommend selective oral administration of vasopressin V2-receptor antagonist, tolvaptan, which acts to increase the excretion of free water, thereby resolving hypervolemic hyponatremia and may have the potential to improve outcomes in these patients.

Urinary aquaporin-2 excretion before and after transjugular intrahepatic portosystemic shunt insertion for refractory ascites

OBJECTIVE

The role of renal aquaporin-2 (AQP2) water channel turnover in patients with liver cirrhosis, portal hypertension and water retention remains unclear. Transjugular intrahepatic portosystemic shunt (TIPS) insertion reduces portal hypertension, improves water excretion and lowers plasma vasopressin. The aim of this study was to establish whether TIPS insertion decreases urinary AQP2 excretion (uAQP2) in parallel with improved water excretion.

MATERIAL AND METHODS

Fourteen cirrhosis patients with refractory ascites were studied before TIPS insertion and 4 and 12 weeks after insertion. A 24-h urine collection was followed by an oral water load (20 ml/kg body weight) with a 4-h blood and urine sampling.

RESULTS

TIPS reduced the portal pressure gradient from a median 18(4) (25-75% InterQuartile-range) to 7(2) mmHg, p < 0.05 and the need for diuretics (p < 0.05). TIPS increased plasma sodium from 136(6) mmol/l to 139(4), (p < 0.05) and diuresis from 1650(1043) ml/24 h to 2230(560) (p < 0.05), although the 24-h urinary sodium excretion did not change. There was no change in the baseline uAQP2 before 274(249) ng/(mmol creatinine/24 h) and 12 weeks after TIPS 242(201). There were no systematic changes in uAQP2, plasma vasopressin or other vasoactive substances during the water loads, before or after TIPS.

CONCLUSION

The effective amelioration of portal hypertension improved the patient's water excretion and plasma sodium, but there was no change in renal AQP2 trafficking or vasopressin. These findings do not support a primary role for renal AQP2 water channels in portal hypertensive water retention.

Hyponatremia in Patients with Cirrhosis of the Liver

Hyponatremia is common in cirrhosis. It mostly occurs in an advanced stage of the disease and is associated with complications and increased mortality. Either hypovolemic or, more commonly, hypervolemic hyponatremia can be seen in cirrhosis. Impaired renal sodium handling due to renal hypoperfusion and increased arginine-vasopressin secretion secondary to reduced effective volemia due to peripheral arterial vasodilation represent the main mechanisms leading to dilutional hyponatremia in this setting. Patients with cirrhosis usually develop slowly progressing hyponatremia. In different clinical contexts, it is associated with neurological manifestations due to increased brain water content, where the intensity is often magnified by concomitant hyperammonemia leading to hepatic encephalopathy. Severe hyponatremia requiring hypertonic saline infusion is rare in cirrhosis. The management of asymptomatic or mildly symptomatic hyponatremia mainly rely on the identification and treatment of precipitating factors. However, sustained resolution of hyponatremia is often difficult to achieve. V2 receptor blockade by Vaptans is certainly effective, but their long-term safety, especially when associated to diuretics given to control ascites, has not been established as yet. As in other conditions, a rapid correction of long-standing hyponatremia can lead to irreversible brain damage. The liver transplant setting represents a condition at high risk for the occurrence of such complications.

Renal sodium transporters are increased in urinary exosomes of cyclosporine-treated kidney transplant patients

BACKGROUND/AIMS

Cyclosporine (CsA) is a calcineurin inhibitor widely used as an immunosuppressant in organ transplantation. Previous studies demonstrated the relationship between CsA and renal sodium transporters such as the Na-K-2Cl cotransporter in the loop of Henle (NKCC2). Experimental models of CsA-induced hypertension have shown an increase in renal NKCC2.

METHODS

Using immunoblotting of urinary exosomes, we investigated in CsA-treated kidney transplant patients (n = 39) the excretion of NKCC2 and Na-Cl cotransporter (NCC) and its association with blood pressure (BP) level. We included 8 non-CsA-treated kidney transplant patients as a control group. Clinical data, immunosuppression and hypertension treatments, blood and 24-hour urine tests, and 24-hour ambulatory BP monitoring were recorded.

RESULTS

CsA-treated patients tended to excrete a higher amount of NKCC2 than non-CsA-treated patients (mean ± SD, 175 ± 98 DU and 90 ± 70.3 DU, respectively; p = 0.05) and showed higher BP values (24-hour systolic BP 138 ± 17 mm Hg and 112 ± 12 mm Hg, p = 0.003; 24-hour diastolic BP, 83.8 ± 9.8 mm Hg and 72.4 ± 5.2 mm Hg, p = 0.015, respectively). Within the CsA-treated group, there was no correlation between either NKCC2 or NCC excretion and BP levels. This was confirmed by a further analysis including potential confounding factors. On the other hand, a significant positive correlation was observed between CsA blood levels and the excretion of NKCC2 and NCC.

CONCLUSION

Overall, these results support the hypothesis that CsA induces an increase in NKCC2 and NCC in urinary exosomes of renal transplant patients. The fact that the increase in sodium transporters in urine did not correlate with the BP level suggests that in kidney transplant patients, other mechanisms could be implicated in CsA-induced hypertension.

Renal aquaporins and water balance disorders

BACKGROUND

Aquaporins (AQPs) are a family of proteins that can act as water channels. Regulation of AQPs is critical to osmoregulation and the maintenance of body water homeostasis. Eight AQPs are expressed in the kidney of which five have been shown to play a role in body water balance; AQP1, AQP2, AQP3, AQP4 and AQP7. AQP2 in particular is regulated by vasopressin.

SCOPE OF REVIEW

This review summarizes our current knowledge of the underlying mechanisms of various water balance disorders and their treatment strategies.

MAJOR CONCLUSIONS

Dysfunctions of AQPs are involved in disorders associated with disturbed water homeostasis. Hyponatremia with increased AQP levels can be caused by diseases with low effective circulating blood volume, such as congestive heart failure, or osmoregulation disorders such as the syndrome of inappropriate secretion of antidiuretic hormone. Treatment consists of fluid restriction, demeclocycline and vasopressin type-2 receptor antagonists. Decreased AQP levels can lead to diabetes insipidus (DI), characterized by polyuria and polydipsia. In central DI, vasopressin production is impaired, while in gestational DI, levels of the vasopressin-degrading enzyme vasopressinase are abnormally increased. Treatment consists of the vasopressin analogue dDAVP. Nephrogenic DI is caused by the inability of the kidney to respond to vasopressin and can be congenital, but is most commonly acquired, usually due to lithium therapy. Treatment consists of sufficient fluid supply, low-solute diet and diuretics.

GENERAL SIGNIFICANCE

In recent years, our understanding of the underlying mechanisms of water balance disorders has increased enormously, which has opened up several possible new treatment strategies. This article is part of a Special Issue entitled Aquaporins.

Water channel proteins in bile formation and flow in health and disease: when immiscible becomes miscible

An essential function of the liver is the formation and secretion of bile, a complex aqueous solution of organic and inorganic compounds essential as route for the elimination of body cholesterol as unesterified cholesterol or as bile acids. In bile, a considerable amount of otherwise insoluble cholesterol is solubilized by carriers including two other classes of lipids, namely phospholipid and bile acids. Formation of bile and generation of bile flow are driven by the active secretion of bile acids, lipids and electrolytes into the canalicular and bile duct lumens followed by the parallel movement of water. Thus, water has to cross rapidly into and out of the cell interior driven by osmotic forces. Bile as a fluid, results from complicated interplay of hepatocyte and cholangiocyte uptake and secretion, concentration, by involving a number of transporters of lipids, anions, cations, and water. The discovery of the aquaporin water channels, has clarified the mechanisms by which water, the major component of bile (more than 95%), moves across the hepatobiliary epithelia. This review is focusing on novel acquisitions in liver membrane lipidic and water transport and functional participation of aquaporin water channels in multiple aspects of hepatobiliary fluid balance. Involvement of aquaporins in a series of clinically relevant hepatobiliary disorders are also discussed.

Molecular biology of water and salt regulation in the kidney

The kidney plays a central role in the regulation of the salt and water balance, which depends upon an array of solute and water transporters in the renal tubules and upon vascular elements in the various regions of the kidney. Many recent studies have improved our understanding of this process. In this review, we summarize the current data on the molecules involved in sodium and water transport in the renal tubules, focusing in particular on aquaporins and renal sodium transporters and channels.

Aquaporin-1 associated with hepatic arterial capillary proliferation on hepatic sinusoid in human cirrhotic liver

BACKGROUND

Aquaporins (AQPs) are key regulators not only of water transport in the cytoplasm but also of angiogenesis. Although AQPs in the normal hepatobiliary system have been studied in mammals, little is known about the localization and changes of AQPs in the hepatic microvascular system including sinusoids in cirrhotic liver, which might contribute to portal hypertension.

AIMS

We designed this study to examine the localization of AQP1 in human cirrhotic liver.

METHODS

Surgical wedge biopsy specimens were obtained from non-cirrhotic portions of human livers (normal control) and from cirrhotic livers (LC) (Child A-LC and Child C-LC). Immunostaining, Western blotting, in situ hybridization (ISH) and laser-captured microdissection (LCM) were conducted.

RESULTS

In control liver tissue, AQP1 was localized mainly in the portal venules, hepatic arterioles and bile ducts in the portal tract, although AQP1 was detected only slightly in the sinusoids. In cirrhotic liver tissue, AQP1 expression was evident, aberrantly observed on periportal sinusoidal endothelial cells corresponding to the capillarized sinusoids, on the proliferated arterial capillaries opening into the sinusoid in the generating hepatic nodule and on proliferated bile ductules at the peripheral edge of nodules and fibrotic septa. In cirrhotic liver, overexpression of AQP1 at protein and mRNA levels was demonstrated, respectively, using Western blot and ISH. AQP-1 of mRNA level in sinusoid was confirmed using LCM.

CONCLUSIONS

Aberrant expressions of AQP1 in periportal sinusoidal regions in human cirrhotic liver indicate the proliferation of arterial capillaries directly connected to the sinusoids, contributing to microvascular resistance in cirrhosis.

Influence of aquaporin-1 gene polymorphism on water retention in liver cirrhosis

Water retention is a major clinical problem in patients with liver cirrhosis. The factors that predispose to water retention are poorly understood but may involve genetic factors. Recent research suggests that renal aquaporins may be a pathophysiological factor involved in this condition. Aquaporin-1 (AQP1) is expressed in the proximal tubule and aquaporin-2 (AQP2) in the renal collecting duct cells. The aim of our study was to investigate the distribution of single nucleotide polymorphisms (SNPs) of AQP1: rs1049305 (C/G) and AQP2: rs3741559 (A/G) and rs467323 (C/T) in 100 cirrhotic patients with ascites and to analyze their relationship with dilutional hyponatremia.

METHODS

Genomic DNA was extracted from peripheral blood. Genotyping for the presence of different polymorphisms was performed using the Custom Taqman SNP Genotyping Assays. The possible influence of rs1049305 (C/G) in AQP1 gene expression was evaluated by luciferase assays in vitro.

RESULTS

The allelic frequencies of the AQP1 gene were the following: CC = 15%; CG = 49%; GG = 36%. Patients with CC genotype had significantly lower plasma sodium concentration than those with CG or GG genotype. Luciferase assays showed that the rs1049305 (C/G) in the AQP1 gene functionally affected the expression level in vitro. In addition, we did not find any relationship between AQP2 SNPs observed and plasma sodium concentration.

CONCLUSIONS

Our results suggest that the rs1049305 (C/G, UTR3) AQP1 polymorphism could be involved in the genetic susceptibility to develop water retention in patients with liver cirrhosis.

Hepatorenal syndrome: beyond liver failure

Critical care nurses occasionally confront patient conditions that are not common. One such condition is hepatorenal syndrome (HRS). Three primary processes contribute to regional alterations in circulation in the renal and splanchnic beds. These processes include effective hypovolemia from the massive release of vasoactive mediators, thereby underfilling circulation, systemic and splanchnic vasodilation along with renal vasoconstriction, and hyperdynamic circulation. A "second-hit" hypothesis, whereby a triggering event causes intravascular volume depletion, likely initiates the development of HRS. The idea of a second hit focuses the attention of the health care team on surveillance strategies to prevent or limit HRS in patients with advanced cirrhosis and ascites. The treatment goal is to restore systemic and splanchnic vasoconstriction, while promoting renal vasodilation, balance sodium, and achieve euvolemia. The critical care nurse must maintain ongoing education to care for the patient with this complex syndrome in order to prevent complications and death.

Balancing volume resuscitation and ascites management in cirrhosis

PURPOSE OF REVIEW

Patients with cirrhosis have total extracellular fluid overload but central effective circulating hypovolaemia. The resulting neurohumoral compensatory response favours the accumulation of fluids into the peritoneal cavity (ascites) and may hinder renal perfusion (hepatorenal syndrome). Their deranged systemic haemodynamics (hyperdynamic circulatory syndrome) is characterized by elevated cardiac output with decreased systemic vascular resistance and low blood pressure.

RECENT FINDINGS

Molecular and biological mechanisms determining cirrhosis-induced haemodynamic alterations are progressively being elucidated. The need for a goal-directed assessment of volume resuscitation (especially with volumetric techniques) in patients with cirrhosis is becoming more and more evident. The role of fluid expansion with albumin and the use of splanchnic vasopressors in a variety of cirrhosis-related conditions has recently been investigated.

SUMMARY

The response to fluid loading in patients with advanced cirrhosis is abnormal, primarily resulting in expansion of their noncentral blood volume compartment. Colloid solutions, in particular albumin, are best used in these patients. Albumin may be effective in preventing the haemodynamic derangements associated with large-volume paracentesis (paracentesis-induced circulatory dysfunction), in preventing renal failure during spontaneous bacterial peritonitis and, in association with splanchnic vasopressors, in caring for patients with the hepatorenal syndrome.

The role of nitric oxide in the expression of renal aquaporin 2 in a cirrhotic rat model: does an AVP-independent mechanism exist for the regulation of AQP2 expression?

The aquaporin (AQP) water channel is expected to play a decisive role of hyponatremia and water retention in cirrhotic patients. Despite the importance of the water channel, however, previous findings vary widely when it concerns AQP2 of the kidneys in subjects with cirrhosis. The purpose of this study was to investigate the expression of AQP2 in the distal renal tubule in cirrhosis, and the presence of the nitric oxide-AQP2 signaling pathway as a possible vasopressin-aquaporin-independent pathway. Sixty male Wister rats were assigned to six groups: (1) control; (2) TAA (thioacetamide); (3) TAA with nitric oxide donor; (4) TAA with nitric oxide inhibitor; (5) TAA with HMG CoA reductase inhibitor; (6) TAA with tetrahydrobiopterin. Immunohistochemical staining for AQP2, real-time polymerase chain reaction (PCR) for AQP2 and 3, citrulline assay, and renal cGMP concentration were measured. The AQP2-positivity of cirrhotic rats were higher than the controls (P < 0.05). The AQP2-positivity decreased in the nitric oxide donor group, but the proportion rose back up when the subjects were injected with the nitric oxide inhibitor (P < 0.05). The expression of AQP2 and AQP3 mRNA was also found to show an increase in the cirrhotic group as compared with the normal controls (P < 0.05). The cirrhotic group administered with nitric oxide donor showed a significant decline in the expression of the mRNA. The control group's cGMP concentration was lower than that of the cirrhotic group (P < 0.05), but a comparison of the two groups injected with nitric oxide modulators, such as statin and BH4, did not show significant differences in the cGMP concentration level. The expression of AQP2 of the kidneys increased in the cirrhotic rats. AQP2 had relations to the activity changes of nitric oxide synthetase.

Aquaporin-2 urinary excretion in cirrhosis: relationship to vasopressin and nitric oxide

The aquaporin (AQP) water channel plays an important role in the regulation of water. AQP2 is expressed in the collection duct of the kidney, serving as the final channel that helps to regulate water excretion in the kidneys and affecting the regulation of water and hyponatremia in cirrhotic patients. So far, research on aquaporin expression in cirrhosis has had various results. The purpose of this study is to investigate the factors that affect the regulation of expression of AQP in patients with cirrhosis. The study comprised 81 cirrhosis patients and 18 control subjects. In each group, 24-h urine was collected and nitric oxide and vasopressin levels were measured in the blood. The amount of urinary AQP was measured by Western blot. In this study, the positivity rate and amount of expression of AQP was higher in the cirrhotic group than that of the control group. AQP expression in urine was also compared between the groups with use of diuretics and the groups with no use of diuretics. A 57.4% positivity was observed with the former, whereas a 51.5% was seen in the latter. No significance was found between the groups (P = 0.581). Expression of AQP in compensated cirrhotic patients is significantly higher than decompensated cirrhotic patients and is especially higher in cirrhotic patients with ascites than with no ascites. There is no relationship between the concentration of vasopressin and expression of AQP. Concentration of serum NOx is higher in cirrhotic patients than the control group and there is a positive association between the concentration of serum nitric oxide and AQP in urine. In conclusion, expression of AQP is increased in cirrhotic patients and is significantly higher in patients with ascites. There is a positive association between the expression of AQP and concentration of serum nitric oxide.

Ascites: pathogenesis and therapeutic principles

Ascites is a classic complication of advanced cirrhosis and it often marks the first sign of hepatic decompensation. Ascites occurs in more than 50% of patients with cirrhosis, worsens the course of the disease, and reduces survival substantially. Portal hypertension, splanchnic vasodilatation, liver insufficiency, and cardiovascular dysfunction are major pathophysiological hallmarks. Modern treatment of ascites is based on this recognition and includes modest salt restriction and stepwise diuretic therapy with spironolactone and loop-diuretics. Tense and refractory ascites should be treated with large volume paracentesis followed by plasma volume expansion or transjugular intrahepatic portosystemic shunt. Ascites complicated by spontaneous bacterial peritonitis requires adequate treatment with antibiotics. New potential treatment strategies include the use of vasopressin V(2)-receptor antagonists and vasoconstrictors. Since formation of ascites is associated with a poor prognosis, and treatment of fluid retention does not substantially improve survival, such patients should always be considered for liver transplantation.

Are sodium transporters in urinary exosomes reliable markers of tubular sodium reabsorption in hypertensive patients?

BACKGROUND

Altered renal sodium handling has a major pathogenic role in salt-sensitive hypertension. Renal sodium transporters are present in urinary exosomes. We hypothesized that sodium transporters would be excreted into the urine in different amounts in response to sodium intake in salt-sensitive versus salt-resistant patients.

METHODS

Urinary exosomes were isolated by ultracentrifugation, and their content of Na-K-2Cl cotransporter (NKCC2) and Na-Cl cotransporter (NCC) was analyzed by immunoblotting. Animal studies: NKCC2 and NCC excretion was measured in 2 rat models to test whether changes in sodium transporter excretion are indicative of regulated changes in the kidney tissue. Human studies: in hypertensive patients (n = 41), we investigated: (1) a possible correlation between sodium reabsorption and urinary exosomal excretion of sodium transporters, and (2) the profile of sodium transporter excretion related to blood pressure (BP) changes with salt intake. A 24-hour ambulatory BP monitoring and a 24-hour urine collection were performed after 1 week on a low- and 1 week on a high-salt diet.

RESULTS

Animal studies: urinary NKCC2 and NCC excretion rates correlated well with their abundance in the kidney. Human studies: 6 patients (15%) were classified as salt sensitive. The NKCC2 and NCC abundance did not decrease after the high-salt period, when the urinary sodium reabsorption decreased from 99.7 to 99.0%. In addition, the changes in BP with salt intake were not associated with a specific profile of exosomal excretion.

CONCLUSIONS

Our results do not support the idea that excretion levels of NKCC2 and NCC via urinary exosomes are markers of tubular sodium reabsorption in hypertensive patients.

Impact of pretransplant hyponatremia on outcome following liver transplantation

Hyponatremia is associated with reduced survival in patients with cirrhosis awaiting orthotopic liver transplantation (OLT). However, data are sparse regarding the impact of hyponatremia on outcome following OLT. We investigated the effect of hyponatremia at the time of OLT on mortality and morbidity following the procedure. The study included 2,175 primary OLT recipients between 1990 and 2000. Serum sodium concentrations obtained immediately prior to OLT were correlated with subsequent survival using proportional hazards analysis. Morbidity associated with hyponatremia was assessed, including length of hospitalization, length of intensive care unit (ICU) admission, and occurrence of central pontine myelinolysis (CPM). Out of 2,175 subjects, 1,495 (68.7%) had normal serum sodium (>135 mEq/L) at OLT, whereas mild hyponatremia (125-134 mEq/L) was present in 615 (28.3%) and severe hyponatremia (<125 mEq/L) in 65 (3.0%). Serum sodium had no impact on survival up to 90 days after OLT (multivariate hazard ratio = 1.00, P = 0.99). Patients with severe hyponatremia tended to have a longer stay in the ICU (median = 4.5 days) and hospital (17.0 days) compared to normonatremic recipients (median ICU stay = 3.0 days, hospital stay = 14.0 days; P = 0.02 and 0.08, respectively). There were 10 subjects that developed CPM, with an overall incidence of 0.5%. Although infrequent, the incidence of CPM did correlate with serum sodium levels (P < 0.01).

CONCLUSION

Pre-OLT serum sodium does not have a statistically significant impact on survival following OLT. The incidence of CPM correlates with hyponatremia, although its overall incidence is low. Incorporation of serum sodium in organ allocation may not adversely affect the overall post-OLT outcome.

Pathogenetic background for treatment of ascites and hepatorenal syndrome

Ascites and hepatorenal syndrome (HRS) are the major and challenging complications of cirrhosis and portal hypertension that significantly affect the course of the disease. Liver insufficiency, portal hypertension, arterial vasodilatation, and systemic cardiovascular dysfunction are major pathophysiological hallmarks. Modern treatment of ascites is based on this recognition and includes modest salt restriction and stepwise diuretic therapy with spironolactone and loop diuretics. Tense and refractory ascites should be treated with a large volume paracentesis, followed by volume expansion or transjugular intrahepatic portosystemic shunt. New treatment strategies include the use of vasopressin V(2)-receptor antagonists and vasoconstrictors. The HRS denotes a functional and reversible impairment of renal function in patients with severe cirrhosis with a poor prognosis. Attempts of treatment should seek to improve liver function, ameliorate arterial hypotension and central hypovolemia, and reduce renal vasoconstriction. Ample treatment of ascites and HRS is important to improve the quality of life and prevent further complications, but since treatment of fluid retention does not significantly improve survival, these patients should always be considered for liver transplantation.

Treatment of acute variceal bleeding

The management of variceal bleeding remains a clinical challenge with a high mortality. Standardisation in supportive and new therapeutic treatments seems to have improved survival within the last 25 years. Although overall survival has improved in recent years, mortality is still closely related to failure to control initial bleeding or early re-bleeding occurring in up to 30-40% of patients. Initial procedures are to secure and protect the airway, and administer volume replacement to stabilize the patient. Treatment with vasoactive drugs should be started as soon as possible, since a reduction in portal pressure is associated with a better control of bleeding and may facilitate later endoscopic procedures. Vasopressin and its analogues Terlipressin and somatostatin and analogues are the two types of medicine, which has been evaluated. In meta-analysis, only Terlipressin have demonstrated effects on control of bleeding and on mortality. Somatostatin and its analogues improve control of bleeding, but show in meta-analysis no effects on mortality. Approximately 20% of patients with variceal bleeding will suffer from an infection, when they are hospitalized. Invasive procedures will further increase the risk of bacterial infections. Meta-analysis of clinical trials comparing antibiotics with placebo demonstrates that antibiotic prophylaxis improves survival with 9% (p<0.004). Quinolones or intravenous cephalosporins should be preferred. Early endoscopy should be performed in patients with major bleeding. Endoscopic therapy increases control of bleeding and decreases the risks of rebleeding and mortality. Ligation is probably more effective than sclerotherapy with fewer complications and should therefore be preferred, if possible. In case of gastric variceal bleeding, tissue adhesives should be used.

IN CONCLUSION

Improvements in resuscitation and prevention of complications have together with introduction of vasoactive drugs and refinement of endoscopic therapy majorily changed the prognosis of the patient presenting with variceal bleeding.

AQP1 expression analysis in human diseases: implications for proteomic characterization

Aquaporin (AQP)1 belongs to a ubiquitous family of water channel proteins characterized by sequence similarity and the presence of two NPA (Asp-Pro-Ala) motifs existing in almost all organs and tissues. Currently, 13 human AQPs are known and they are divided into two subgroups according to their ability to transport only water molecules, such as AQP1, or also glycerol and other small solutes. The genomic, structural and functional aspects of AQP1 are briefly described. An in-depth discussion is devoted to proteomic approaches that are useful for identifying and characterizing AQP1, mainly through electrophoretic techniques combined with different extraction procedures followed by mass spectrometry analysis. Moreover, the relevance of AQP1 in human diseases is also explained. Its role in human tumors and, in particular, those of the kidney (e.g., clear cell renal carcinoma) is discussed.

Aquaporins in the hepatobiliary tract. Which, where and what they do in health and disease

The biological importance of the aquaporin family of water channels was recently acknowledged by the 2003 Nobel Prize for Chemistry awarded to the discovering scientist Peter Agre. Among the pleiotropic roles exerted by aquaporins in nature in both health and disease, the review addresses the latest acquisitions about the expression and regulation, as well as physiology and pathophysiology of aquaporins in the hepatobiliary tract. Of note, at least seven out of the thirteen mammalian aquaporins are expressed in the liver, bile ducts and gallbladder. Aquaporins are essential for bile water secretion and reabsorption, as well as for plasma glycerol uptake by the hepatocyte and its conversion to glucose during starvation. Novel data are emerging regarding the physio-pathological involvement of aquaporins in multiple diseases such as cholestases, liver cirrhosis, obesity and insulin resistance, fatty liver, gallstone formation and even microparasite invasion of intrahepatic bile ducts. This body of knowledge represents the mainstay of present and future research in a rapidly expanding field.

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.