Redistribution of renal blood flow in patients with liver cirrhosis. The role of renal PGE2

Hepatorenal Syndrome in Cirrhosis

Hepatorenal syndrome (HRS) is a form of kidney dysfunction that characteristically occurs in liver cirrhosis. It is characterized by a marked impairment of kidney function in response to circulatory and hemodynamic alterations that occur in advanced stages of liver cirrhosis, aggravated by systemic inflammation and bacterial translocation. The classical definitions of the types of HRS have been recently revisited and 2 forms of HRS have been redefined: the acute form, referred to as acute kidney injury (HRS-AKI), and the chronic form, referred to as chronic kidney disease. HRS-AKI is one of the most severe forms of AKI in patients with cirrhosis and it consists of an abrupt impairment of kidney function, frequently triggered by an infection, appearing in the setting of advanced decompensated cirrhosis. Differential diagnosis with other causes of AKI is crucial because HRS-AKI requires a specific treatment. Differential diagnosis with AKI-acute tubular necrosis may be challenging and kidney biomarkers may be useful in this setting. Treatment of HRS-AKI is based on the administration of vasoconstrictor drugs in combination with volume expansion with albumin. Prognosis of HRS-AKI is poor, and the ideal definitive treatment consists of liver transplantation or simultaneous liver-kidney transplantation. HRS-AKI has a big impact on patients' quality of life. Management of HRS-AKI remains challenging in specific situations such as alcohol-associated hepatitis or metabolic-associated steatotic liver disease cirrhosis. Developing preventive measures for HRS-AKI, improving its early identification, discovering new biomarkers for differential diagnosis, and improving the response to therapy are some of the unmet needs in the field of HRS-AKI.

Pathophysiology of Hepatorenal Syndrome

Hepatorenal syndrome type 1 (HRS-1) is a unique form of acute kidney injury that affects individuals with decompensated cirrhosis with ascites. The primary mechanism leading to reduction of kidney function in HRS-1 is hemodynamic in nature. Cumulative evidence points to a cascade of events that led to a profound reduction in kidney perfusion. A state of increased intrahepatic vascular resistance characteristic of advanced cirrhosis and portal hypertension is accompanied by maladaptive peripheral arterial vasodilation and reduction in systemic vascular resistance and mean arterial pressure. As a result of a fall in effective arterial blood volume, there is a compensatory activation of the sympathetic nervous system and the renin-angiotensin system, local renal vasoconstriction, loss of renal autoregulation, decrease in renal blood flow, and ultimately a fall in glomerular filtration rate. Systemic release of nitric oxide stimulated by the fibrotic liver, bacterial translocation, and inflammation constitute key components of the pathogenesis. While angiotensin II and noradrenaline remain the critical mediators of renal arterial and arteriolar vasoconstriction, other novel molecules have been recently implicated. Although the above-described mechanistic pathway remains the backbone of the pathogenesis of HRS-1, other noxious elements may be present in advanced cirrhosis and likely contribute to the renal impairment. Direct liver-kidney crosstalk via the hepatorenal sympathetic reflex can further reduce renal blood flow independently of the systemic derangements. Tense ascites may lead to intraabdominal hypertension and abdominal compartment syndrome. Cardio-hemodynamic processes have also been increasingly recognized. Porto-pulmonary hypertension, cirrhotic cardiomyopathy, and abdominal compartment syndrome may lead to renal congestion and complicate the course of HRS-1. In addition, a degree of ischemic or toxic (cholemic) tubular injury may overlap with the underlying circulatory dysfunction and further exacerbate the course of acute kidney injury. Improving our understanding of the pathogenesis of HRS-1 may lead to improvements in therapeutic options for this seriously ill population.

Metamizole-Associated Risks in Decompensated Hepatic Cirrhosis

BACKGROUND

Because of the increased risk of acute renal failure (ARF), the use of cyclooxygenase (COX) inhibitors is not recommended in patients with decompensated hepatic cirrhosis. Metamizole is not a classic COX inhibitor, but there are insufficient data to support its safe use. In this study, we investigate the effect of metamizole on the risk of ARF in these patients.

METHODS

Metamizole use, ARF incidence, and patient mortality were examined in a large, retrospective, exploratory cohort and validated with data from a prospective registry.

RESULTS

523 patients were evaluated in the exploratory cohort. Metamizole use at baseline was documented in 110 cases (21%) and was independently associated with the development of ARF, severe (grade 3) ARF, and lower survival without liver transplantation at follow-up on day 28 (HR: 2.2, p < 0.001; HR: 2.8, p < 0.001; and HR: 2.6, p < 0.001, respectively). Interestingly, the risk of ARF depended on the dose of metamizole administered (HR: 1.038, p < 0.001). Compared to patients who were treated with opioids, the rate of ARF was higher in the metamizole group (49% vs. 79%, p = 0.014). An increased risk of ARF with metamizole use was also demonstrated in the independent validation cohort (p < 0.001).

CONCLUSION

Metamizole therapy, especially at high doses, should only be used with a high level of caution in patients with decompensated cirrhosis.

Role of the cytochrome P-450/ epoxyeicosatrienoic acids pathway in the pathogenesis of renal dysfunction in cirrhosis

Background

Hepatorenal syndrome (HRS) is a life-threatening complication of advanced liver cirrhosis that is characterized by hemodynamic alterations in the kidney and other vascular beds. Cytochrome P(CYP)-450 enzymes metabolize arachidonic acid to epoxyeicosatrienoic acids (EETs) and 20-hydroxyeicosatetraenoic acids. These eicosanoids regulate blood pressure, vascular tone and renal tubular sodium transport under both physiological and pathophysiological states.

Methods

Experiments were performed to investigate the role of the CYP system in the pathogenesis of renal dysfunction during cirrhosis. Rats underwent bile duct ligation (BDL) or sham surgery and were studied at 2, 4 and 5 weeks post-surgery. In additional experiments, post-BDL rats were treated with three daily intraperitoneal doses of either the selective epoxygenase inhibitor N-(methylsulfonyl)-2-(2-propynyloxy)-benzenehexanamide (MSPPOH) or a vehicle, starting on Day 22 after surgery.

Results

BDL led to progressive renal dysfunction that was associated with reduced renal cortical perfusion but without any overt histologic changes, consistent with HRS. CYP isoform enzyme expression was significantly altered in BDL rats. In the kidney, CYP2C23 expression was upregulated at both the mRNA and protein levels in BDL rats, while CYP2C11 was downregulated. Histologically, the changes in CYP2C23 and CYP2C11 expression were localized to the renal tubules. EET production was increased in the kidneys of BDL rats as assessed by urinary eicosanoid levels. Finally, treatment with the selective epoxygenase inhibitor MSPPOH significantly reduced renal function and renal cortical perfusion in BDL rats, suggesting a homeostatic role for epoxygenase-derived eicosanoids.

Conclusions

The CYP/EET pathway might represent a novel therapeutic target for modulating renal dysfunction in advanced cirrhosis.

Hepatorenal syndrome

Hepatorenal syndrome (HRS) is a form of kidney function impairment that characteristically occurs in cirrhosis. Recent changes in terminology have led to acute HRS being referred to as acute kidney injury (AKI)-HRS and chronic HRS as chronic kidney disease (CKD)-HRS. AKI-HRS is characterized by a severe impairment of kidney function owing to vasoconstriction of the renal arteries in the absence of substantial abnormalities in kidney histology. Pathogenetic mechanisms involve disturbances in circulatory function due to a marked splanchnic arterial vasodilation, which triggers the activation of vasoconstrictor factors. An intense systemic inflammatory reaction that is characteristic of advanced cirrhosis may also be involved. The main triggering factors of AKI-HRS are bacterial infections, particularly spontaneous bacterial peritonitis. The diagnosis of AKI-HRS is a challenge because of a lack of specific diagnostic tools and mainly involves the differential diagnosis from other forms of AKI, particularly acute tubular necrosis. The prognosis of patients with AKI-HRS is poor, with a median survival of ≤3 months. The ideal treatment for AKI-HRS is liver transplantation in patients without contraindications. Medical therapy consists of vasoconstrictor drugs to counteract splanchnic arterial vasodilation together with volume expansion with albumin. Effective measures to prevent AKI-HRS include early identification and treatment of bacterial infections and the administration of albumin in patients with spontaneous bacterial peritonitis.

Renal Hemodynamic Changes Assessed by Color Doppler Sonography in Children With Liver Cirrhosis

Detection of early renal affection before proceeding to hepatorenal failure as a complication of liver cirrhosis in children will be helpful in the prognosis of the disease. The objective of this study was to detect early hemodynamic changes in children with liver cirrhosis who had normal kidney function tests to measure the pulsatility index (PI) and resistance index (RI) and their correlation to some risk factors (severity of cirrhosis, renal infection, blood hemoglobin level, and the presence of portal hypertension). Thirty children with different stages of liver cirrhosis (with normal kidney function tests) and 10 apparently healthy children were included. RI and PI were measured by Doppler spectral wave analysis for patients and control. Both PI and RI indices were significantly higher in all children with liver cirrhosis compared with the control group. Both indices showed highest values with class C compared with classes B and A. Each was significantly higher in the presence of anemia, renal infection and portal hypertension. Monitoring of resistance indices (PI and RI) measured noninvasively by Doppler sonography is an effective and easy method for detection of very early renal hemodynamic alternation in childhood cirrhosis and consequently early proper management.

Vasoactive factors and hemodynamic mechanisms in the pathophysiology of portal hypertension in cirrhosis

Portal hypertension is primarily caused by the increase in resistance to portal outflow and secondly by an increase in splanchnic blood flow, which worsens and maintains the increased portal pressure. Increased portal inflow plays a role in the hyperdynamic circulatory syndrome, a characteristic feature of portal hypertensive patients. Almost all the known vasoactive systems/substances are activated in portal hypertension, but most authors stress the pathogenetic role of endothelial factors, such as COX-derivatives, nitric oxide, carbon monoxide. Endothelial dysfunction is differentially involved in different vascular beds and consists in alteration in response both to vasodilators and to vasoconstrictors. Understanding the pathogenesis of portal hypertension could be of great utility in preventing and curing the complications of portal hypertension, such as esophageal varices, hepatic encephalopathy, ascites.

Hemodynamic features of advanced cirrhosis due to chronic bile duct ligation

AIM

The aim of the present study was to compare the hemodynamic features of portal hypertension in rats with early cirrhosis with those of rats with advanced cirrhosis following common bile duct ligation (CBDL).

METHODS

A total of 53 male Sprague-Dawley rats were used. Hemodynamics were evaluated under conscious and unrestrained conditions 4 weeks and 8 weeks after CBDL, and 4 weeks after a sham operation. Arterial pressure and portal pressure were measured directly via catheters placed in the right femoral artery and main portal vein, respectively. The cardiac index and organ (splanchninc organs, brain, kidneys and lungs) blood flow were determined by the reference sample method using (141)Ce-labeled microspheres (15 mum in diameter). Arterial levels of endothelin-1 and nitrate/nitrite, as well as liver function variables, were also determined.

RESULTS

Portal pressure was significantly higher 8 weeks after CBDL (15.8+/-2.1, n=8) than 4 weeks after CBDL (13.9+/-2.1 mmHg, n=12, p<0.05), and the hyperdynamic circulation of the early period was attenuated (p<0.05). Although hepatic artery blood flow 4 and 8 weeks after CBDL was higher than that after sham operation (p<0.05), portal territory blood flow was not increased. There was a significant positive correlation between portal pressure and portal territory blood flow 8 weeks after CBDL (r=0.822, n=8, p=0.012). In rats with anemia 4 weeks after CBDL, the hemoglobin concentration was negatively correlated with portal territory blood flow (r=-0.597, n=12, p=0.040).

CONCLUSION

Portal pressure was higher 8 weeks after CBDL than 4 weeks after CBDL and increased with portal territory blood flow, suggesting that portal hypertension is maintained by a mechanism consistent with the forward flow theory. Anemia might exacerbate the hyperdynamic systemic circulation 4 weeks after CBDL.

Renal resistive indexes and some renal functions in liver cirrhotic children

BACKGROUND

The aim of the present study was to investigate renal vascular resistive changes in children with different stages of liver cirrhosis without obvious renal failure.

METHODS

Twenty-nine children (14 girls, 15 boys, mean age 11.6 years) with cirrhosis and 20 healthy children (mean age 10.3 years) were investigated for renal vascular resistance with Doppler ultrasonography, urinary sodium, N-acetyl-beta-D glucosaminidase (NAG) and microalbuminuria excretion.

RESULTS

The measurements of renal resistive indexes (RRI) were significantly higher in cirrhotic patients than the control group (0.69 +/- 0.07 vs 0.62 +/- 0.02, P < 0.0001). RRI measurement was found to be increased in decompensated cirrhotic patients than in compensated cirrhotic patients (0.73 +/- 0.05 vs 0.67 +/- 0.08, P < 0.0001). A significant positive relationship was observed between RRI and child score (r = 0.53). Urine NAG/Cr ratio was significantly higher in cirrhotic patients than in the control subjects (P < 0.001). Microalbumin concentrations were increased in the patients with decompensated cirrhosis than in the controls (P = 0.02). Patients with ascites and portal hypertension showed increased RRI values.

CONCLUSIONS

We conclude that patients with cirrhosis are at risk of renal deterioration, which can not be detected by serum urea, creatinine, and glomerular filtration rate. The increase of RRI is associated with the progress of hepatocellular disease, and also the development of ascites and portal hypertension. Elevated urinary sodium excretion, elevated urinary NAG/Cr ratio and microalbuminuria might have a prognostic value especially in patients with Child scores> 6. Hence, monitoring RRI is a non-invasive means of studying early renal hemodynamic alteration in childhood cirrhosis.

Vitamin E prevents renal dysfunction induced by experimental chronic bile duct ligation

BACKGROUND

The mechanisms by which prolonged cholestasis alters renal hemodynamics and excretory function are unknown but may be related to increased oxidative stress, with subsequent formation of lipid peroxidation-derived products (e.g., F2-isoprostanes) and endothelin (ET). We investigated whether antioxidant therapy prevents chronic bile duct ligation (CBDL)-induced alterations in systemic and renal hemodynamics, and reduces F2-isoprostane and ET levels.

METHODS

Sprague-Dawley rats were placed on either a normal or a high vitamin E diet for 7 days and then underwent either CBDL or sham surgery. They were then maintained on their respective diets for 21 more days, at which time the physiologic studies were performed.

RESULTS

Thirty-three percent of the CBDL rats died by day 21. The remaining rats had a lower mean arterial pressure (MAP), renal blood flow (RBF), glomerular filtration rate (GFR), and sodium and water excretion than control rats. CBDL rats had higher portal pressure, renal venous pressure, and renal vascular resistance (RVR). These changes were associated with increased levels of systemic and renal venous F2-isoprostanes and ET. Vitamin E normalized MAP, RBF, GFR, RVR, and sodium and water excretion, and improved the 21-day survival without altering portal or renal venous pressures. Surprisingly, vitamin E did not alter the systemic levels of F2-isoprostanes but markedly reduced their levels in the renal venous circulation.

CONCLUSION

Vitamin E improves MAP and renal function in CBDL rats, and selectively decreases renal levels of oxidative stress and ET, suggesting that local redox balance is implicated in CBDL-induced renal dysfunction.

The use of microcomputed tomography to study microvasculature in small rodents

Appropriate nephron function is dependent on the intrarenal arrangement of blood vessels. The preferred and primary means to study the architecture of intrarenal circulation has been by filling it with opaque substances such as india ink, radio-opaque contrast material, or various polymers for study by light or scanning electron microscopy. With such methodologies, superficial vessels may obscure deep vessels and little quantitative information may be obtained. Serial-section microtomy has not been practical because of problems relating to alignment and registration of adjacent sections, lost sections, and preparation time and effort. Microcomputed tomography (micro-CT) overcomes such limitations and provides a means to study the three-dimensional architecture of filled vessels within an intact rodent kidney and to obtain more quantitative information. As an example of micro-CT's capabilities, we review the use of micro-CT to study the alterations in renal microvasculature caused by the development of liver cirrhosis after chronic bile duct ligation. In this example, micro-CT evidence shows a selective decrease in cortical vascular filling in the kidney, with a maintenance of medullary vascular filling. These changes may contribute to the salt and water retention that accompanies cirrhosis. These results indicate that micro-CT is a promising method to evaluate renal vascular architecture in the intact rodent kidney relative to physiological and pathological function.

Microcomputed tomography of kidneys following chronic bile duct ligation

BACKGROUND

In hepatic cirrhosis, renal sodium and water retention can occur prior to decreases in renal blood flow (RBF). This may be explained in part by redistribution of the intrarenal microcirculation toward the juxtamedullary nephrons. To appreciate this three-dimensional spatial redistribution better, we examined the intrarenal microcirculatory changes using microcomputed tomography (micro-CT) in rats subjected to chronic bile duct ligation (CBDL).

METHODS

Six kidneys from control rats and eight kidneys from rats that had undergone CBDL for 21 days were perfusion fixed in situ at physiological pressure, perfused with silicon-based Microfil containing lead chromate, embedded in plastic, and scanned by micro-CT. The microvasculature in the reconstructed three-dimensional renal images was studied using computerized image-analysis techniques. To determine the physiological condition of the rats, parallel experiments were conducted on six control and six CBDL rats to measure mean arterial pressure (MAP), RBF, glomerular filtration rate (GFR), urine flow (UF) rate, and sodium excretion by conventional methods.

RESULTS

The percentage of vasculature in the renal cortex from CBDL rats was significantly decreased (10.8 +/- 0.4% vs. 16.8 +/- 2.7% control values). However, the vascular volume fractions of the medullary tissues were not significantly altered. There were no significant differences in the number of glomeruli between groups (36,430 +/- 1908 CBDLs, 36,609 +/- 3167 controls). The CBDL rats had a similar GFR than the controls but a reduced MAP, RBF, UF, and sodium excretion.

CONCLUSIONS

The results indicate that after CBDL, there is a selective decrease in cortical vascular filling, which may contribute to the salt and water retention that accompanies cirrhosis.

Eicosanoid excretion in hepatic cirrhosis. Predominance of 20-HETE

The cytochrome P450 system transforms AA to hydroxyeicosatetraenoic acid (HETE) metabolites that are vasoactive and affect transport in several nephron segments. A principal product of this system, 20-HETE, participates in key mechanisms that regulate the renal circulation and extracellular fluid volume. We hypothesized that excess production of 20-HETE, which constricts the renal vasculature, contributes to the renal functional disturbances in patients with hepatic cirrhosis, particularly the depression of renal hemodynamics. The development of a precise and sensitive gas chromatographic/mass spectrometric method makes it possible to measure 20-HETE and the subterminal HETEs (16-,17-,18-, and 19-HETEs) in biological fluids. As 20-HETE was excreted as the glucuronide conjugate, measurement of 20-HETE required treatment of urine with glucuronidase. We measured HETEs in the urine of patients with cirrhosis, and compared these values to those of normal subjects. Urinary excretion rate of 20-HETE was highest in patients with ascites; 12.5+/-3.2 ng/min vs. 5.0+/-1.5 and 1.6+/-0.2 ng/min in cirrhotic patients without ascites and in normal subjects, respectively. Excretion of 16-, 17-, and 18-HETEs was not increased. In patients with cirrhosis, the excretory rate of 20-HETE was several-fold higher than those of prostaglandins and thromboxane, whereas in normal subjects 20-HETE and prostaglandins were excreted at similar rates. Of the eicosanoids, only increased excretion of 20-HETE in subjects with cirrhosis was correlated (r = -0.61; P < 0.01) with reduction of renal plasma flow (RPF).

Renal cytochrome P-450-dependent metabolism of arachidonic acid in cirrhotic rats

Cirrhosis was induced in Wistar-Kyoto rats by intragastric administration of carbon tetrachloride. Microsomes were obtained from the renal cortex and outer medulla and incubated with [14C]arachidonic acid (AA) (0.2-0.4 microCi) in the presence or absence of indomethacin, NADPH, and SKF-525A. Cytochrome P-450-dependent AA metabolites (those whose formation required NADPH, were inhibited by SKF-525A, but not by indomethacin) were separated by thin-layer chromatography and high-pressure liquid chromatography (HPLC). Compared to controls, total synthesis of cytochrome P-450-dependent AA metabolites was reduced in cirrhotic rats (renal cortex: cirrhotics 380 +/- 52 vs. controls 493 +/- 68 pg/mg protein per 30 min; p less than 0.05; renal outer medulla: cirrhotics 304 +/- 57 vs. controls 387 +/- 53 pg/mg protein per 30 min; p less than 0.05). The cytochrome P-450-dependent AA metabolites were composed of three peaks separated by HPLC. Peak I, which had a retention time of 16.3 +/- 0.3 min and comigrated with 11,12-dihydroxyeicosatrienoic acid, and peak II, which had a retention time of 18.7 +/- 0.4 min and comigrated with 19- and 20-hydroxyeicosatetraenoic acid, were not different in cirrhotics and controls. Peak III, which had a retention time of 26.8 +/- 0.3 min, and comigrated with 11,12-epoxyeicosatrienoic acid, was significantly decreased in the renal cortex of cirrhotic rats compared to controls (cirrhotics 316 +/- 40 vs. controls 473 +/- 89 pg/mg protein per 30 min; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Renal effects of nadolol in cirrhosis

The effects of nadolol on renal haemodynamics and function, and on the renin-angiotensin-aldosterone system and on renal prostaglandin production were studied in eighteen cirrhotics. After 1 month of treatment, nadolol had significantly decreased cardiac output by 25% without affecting arterial pressure, renal plasma flow or renal vascular resistance. Glomerular filtration rate, filtration fraction and the proportion of the cardiac output delivered to the kidneys were significantly increased. The renin-angiotensin-aldosterone system was suppressed and urinary PGE2 excretion was slightly increased. The latter effects were not correlated with those on renal haemodynamics and function.