Tolvaptan, an orally active non-peptide arginine vasopressin V2 receptor antagonist, reduces ascites in rats with chronic liver injury

Urea Transporter Inhibitor 25a Reduces Ascites in Cirrhotic Rats

Ascites is a typical symptom of liver cirrhosis that is caused by a variety of liver diseases. Ascites severely affects the life quality of patients and needs long-term treatment. 25a is a specific urea transporter inhibitor with a diuretic effect that does not disturb the electrolyte balance. In this study, we aimed to determine the therapeutic effect of 25a on ascites with a dimethylnitrosamine (DMN)-induced cirrhotic rat model. It was found that 100 mg/kg of 25a significantly increased the daily urine output by 60% to 97% and reduced the daily abdominal circumference change by 220% to 260% in cirrhotic rats with a water intake limitation. The 25a treatment kept the serum electrolyte levels within normal ranges in cirrhotic rats. The H&E and Masson staining of liver tissue showed that 25a did not change the cirrhotic degree. A serum biochemical examination showed that 25a did not improve the liver function in cirrhotic rats. A Western blot analysis showed that 25a did not change the expression of fibrosis-related marker protein α-SMA, but significantly decreased the expressions of type I collagen in the liver of cirrhotic rats, indicating that 25a did not reverse cirrhosis, but could slow the cirrhotic progression. These data indicated that 25a significantly reduced ascites via diuresis without an electrolyte imbalance in cirrhotic rats. Our study provides a proof of concept that urea transporter inhibitors might be developed as novel diuretics to treat cirrhotic ascites.

Arginine vasopressin modulates electrical activity and calcium homeostasis in pulmonary vein cardiomyocytes

Background

Atrial fibrillation (AF) frequently coexists with congestive heart failure (HF) and arginine vasopressin (AVP) V1 receptor antagonists are used to treat hyponatremia in HF. However, the role of AVP in HF-induced AF still remains unclear. Pulmonary veins (PVs) are central in the genesis of AF. The purpose of this study was to determine if AVP is directly involved in the regulation of PV electrophysiological properties and calcium (Ca²⁺) homeostasis as well as the identification of the underlying mechanisms.

Methods

Patch clamp, confocal microscopy with Fluo-3 fluorescence, and Western blot analyses were used to evaluate the electrophysiological characteristics, Ca²⁺ homeostasis, and Ca²⁺ regulatory proteins in isolated rabbit single PV cardiomyocytes incubated with and without AVP (1 μM), OPC 21268 (0.1 μM, AVP V1 antagonist), or OPC 41061 (10 nM, AVP V2 antagonist) for 4–6 h.

Results

AVP (0.1 and 1 μM)-treated PV cardiomyocytes had a faster beating rate (108 to 152%) than the control cells. AVP (1 μM) treated PV cardiomyocytes had higher late sodium (Na⁺) and Na⁺/Ca²⁺ exchanger (NCX) currents than control PV cardiomyocytes. AVP (1 μM) treated PV cardiomyocytes had smaller Ca²⁺_i transients, and sarcoplasmic reticulum (SR) Ca²⁺ content as well as higher Ca²⁺ leak. However, combined AVP (1 μM) and OPC 21268 (0.1 μM) treated PV cardiomyocytes had a slower PV beating rate, larger Ca²⁺_i transients and SR Ca²⁺ content, smaller late Na⁺ and NCX currents than AVP (1 μM)-treated PV cardiomyocytes. Western blot experiments showed that AVP (1 μM) treated PV cardiomyocytes had higher expression of NCX and p-CaMKII, and a higher ratio of p-CaMKII/CaMKII.

Conclusions

AVP increases PV arrhythmogenesis with dysregulated Ca²⁺ homeostasis through vasopressin V1 signaling.

Tolvaptan regulates aquaporin-2 and fecal water in cirrhotic rats with ascites

AIM: To investigate the role of tolvaptan in regulating aquaporin (AQP)-2 expression and fecal water content in cirrhotic rats with ascites.

METHODS: Cirrhosis with ascites was induced in rats by repetitive dorsal injection of CCl₄ for 14 wk. In total, 84 cirrhotic rats with ascites divided into three groups (vehicle, 3 mg/kg and 5 mg/kg tolvaptan), and then further divided into five subgroups (days 1, 2, 3, 4, and 5). Blood samples were obtained to measure vasopressin and sodium concentrations. Rats were killed and colonic mucosa was scraped for analysis of protein expression and AQP-2 transcriptional level. The whole layer was fixed for hematoxylin&eosin (HE) staining and feces were collected for determination of fecal water content.

CONCLUSION: Compared with vehicle, vasopressin decreased significantly in the tolvaptan groups from day 2 to a similar level in each treatment group. AQP-2 showed significant upregulation in cirrhotic rats with ascites compared with an untreated control group (100% ± 22.9% vs 22.2% ± 10.23%, P < 0.01). After administration of tolvaptan, AQP-2 expression began to decrease significantly from day 2 in each treatment group, but no significant difference was finally found between the treatment groups. Fecal water content in the distal colon was increased by 5 mg/kg tolvaptan on day 1 (66.8% ± 9.3% vs 41.4% ± 6.3%, in the vehicle group, P < 0.05). Fecal water content returned to baseline at day 4 at the latest in both treatment groups, and did not correspond to the change in AQP-2 expression. HE staining of the colonic mucosa showed no mucosal damage related to tolvaptan.

CONCLUSION: Upregulation of AQP-2 in the distal colon is found in cirrhotic rats with ascites. Tolvaptan inhibits its expression and may decrease water reabsorption and induce diarrhea.

Clinical efficacy of tolvaptan for treatment of refractory ascites in liver cirrhosis patients

AIM

To evaluate the efficacy and safety of tolvaptan to treat refractory ascites in decompensated liver cirrhosis patients with or without further complications, such as hepatorenal syndrome and/or hepatocellular carcinoma.

METHODS

Thirty-nine patients (mean age 55 years, males: 32) with decompensated liver cirrhosis and refractory ascites were enrolled. All patients received a combination of tolvaptan (15 mg/d for 5-14 d) and diuretics (40-80 mg/d of furosemide and 80-160 mg/d of spironolactone). The etiology of cirrhosis included hepatitis B (69.2%), hepatitis C (7.7%) and alcohol-induced (23.1%). Changes in the urine excretion volume, abdominal circumference and edema were assessed. The serum sodium levels were also measured, and adverse events were recorded. A follow-up assessment was conducted 1 mo after treatment with tolvaptan.

RESULTS

Tolvaptan increased the mean urine excretion volume (1969.2 ± 355.55 mL vs 3410.3 ± 974.1 mL, P < 0.001), and 89.7% of patients showed improvements in their ascites, 46.2% of whom showed significant improvements. The overall efficacy of tolvaptan in all patients was 89.7%; the efficacies in patients with hepatocellular carcinoma and hepatorenal syndrome were 84.2% and 77.8%, respectively. The incidence of hyponatremia was 53.8%. In patients with hyponatremia, the serum sodium levels increased after tolvaptan treatment (from 128.1 ± 4.22 mEq/L vs 133.1 ± 3.8 mEq/L, P < 0.001). Only mild drug-related adverse events, including thirst and dry mouth, were observed.

CONCLUSION

Tolvaptan is a promising aquaretic for the treatment of refractory ascites in patients with decompensated liver cirrhosis.