The effects of bile acids on beta-adrenoceptors, fluidity, and the extent of lipid peroxidation in rat cardiac membranes

Coronary Microvascular Dysfunction in Acute Cholestasis-Induced Liver Injury

BACKGROUND

Previous studies have shown cardiac abnormalities in acute liver injury, suggesting a potential role in the associated high mortality.

METHODS

We designed an experimental study exploring the short-term effects of acute cholestasis-induced liver injury on cardiac function and structure in a rodent bile duct ligation (BDL) model to elucidate the potential interplay. Thirty-seven male Sprague-Dawley rats were subjected to BDL surgery (n = 28) or served as sham-operated (n = 9) controls. Transthoracic echocardiography, Doppler evaluation of the left anterior descending coronary artery, and myocardial contrast echocardiography were performed at rest and during adenosine and dobutamine stress 5 days after BDL. Immunohistochemical staining of myocardial tissue samples for hypoxia and inflammation as well as serum analysis were performed.

RESULTS

BDL animals exhibited acute liver injury with elevated transaminases, bilirubin, and total circulating bile acids (TBA) 5 days after BDL (TBA control: 0.81 ± 2.54 µmol/L vs. BDL: 127.52 ± 57.03 µmol/L; p < 0.001). Concurrently, cardiac function was significantly impaired, characterized by reduced cardiac output (CO) and global longitudinal strain (GLS) in the echocardiography at rest and under pharmacological stress (CO rest control: 120.6 ± 24.3 mL/min vs. BDL 102.5 ± 16.6 mL/min, p = 0.041; GLS rest control: -24.05 ± 3.8% vs. BDL: -18.5 ± 5.1%, p = 0.01). Myocardial perfusion analysis revealed a reduced myocardial blood flow at rest and a decreased coronary flow velocity reserve (CFVR) under dobutamine stress in the BDL animals (CFVR control: 2.1 ± 0.6 vs. BDL: 1.7 ± 0.5 p = 0.047). Immunofluorescence staining indicated myocardial hypoxia and increased neutrophil infiltration.

CONCLUSIONS

In summary, acute cholestasis-induced liver injury can lead to impaired cardiac function mediated by coronary microvascular dysfunction, suggesting that major adverse cardiac events may contribute to the mortality of acute liver failure. This may be due to endothelial dysfunction and direct bile acid signaling.

Human Gut Microbiota in Heart Failure: Trying to Unmask an Emerging Organ

There is a bidirectional relationship between the heart and the gut. The gut microbiota, the community of gut micro-organisms themselves, is an excellent gut-homeostasis keeper since it controls the growth of potentially harmful bacteria and protects the microbiota environment. There is evidence suggesting that a diet rich in fatty acids can be metabolized and converted by gut microbiota and hepatic enzymes to trimethyl-amine N-oxide (TMAO), a product that is associated with atherogenesis, platelet dysfunction, thrombotic events, coronary artery disease, stroke, heart failure (HF), and, ultimately, death. HF, by inducing gut ischemia, congestion, and, consequently, gut barrier dysfunction, promotes the intestinal leaking of micro-organisms and their products, facilitating their entrance into circulation and thus stimulating a low-grade inflammation associated with an immune response. Drugs used for HF may alter the gut microbiota, and, conversely, gut microbiota may modify the pharmacokinetic properties of the drugs. The modification of lifestyle based mainly on exercise and a Mediterranean diet, along with the use of pre- or probiotics, may be beneficial for the gut microbiota environment. The potential role of gut microbiota in HF development and progression is the subject of this review.

The clinical impact of paroxysmal arrhythmias on the hospital outcomes of patients admitted with cirrhosis: propensity score matched analysis of 2011-2017 US hospitals

BACKGROUND

We evaluate the effects of paroxysmal arrhythmia on the hospital outcomes of patients admitted with cirrhosis.

RESEARCH DESIGN AND METHODS

2011-2017 National Inpatient Sample was used to isolate patients with decompensated/compensated cirrhosis, stratified by paroxysmal arrhythmia (supraventricular: PSVT and ventricular: PVT). The cohorts were matched using propensity-score matching and compared to mortality, length of stay, cost, and cardiac complications (cardioversion, cardiogenic shock, cardiac arrest, and ventricular fibrillation).

RESULTS

In compensated cirrhosis, 2,453 had PSVT with matched controls; 5,274 had PVT with matched controls. Those with PSVT had higher mortality (aOR 1.55 95%CI 1.23-1.95) and higher rates of cardioversion and cardiogenic shock; likewise, those with PVT had higher mortality (aOR 2.41 95%CI 2.09-2.78) and higher rates of all complications. In decompensated cirrhosis, 1,598 had PSVT with matched controls; 4,178 had PVT with matched controls. Those with PSVT had higher mortality (aOR 1.57 95%CI 1.28-1.93) and higher rates of cardioversion, cardiogenic shock, cardiac arrest; those with PVT had higher mortality (aOR 2.25 95%CI 1.98-2.56) and higher rates of all complications.

CONCLUSION

The findings from this study show that in either decompensated or compensated cohort, those with paroxysmal arrhythmias are at a higher risk of in-hospital mortality and adverse cardiac outcomes.

Redox-Dependent Effects in the Physiopathological Role of Bile Acids

Bile acids (BA) are recognized by their role in nutrient absorption. However, there is growing evidence that BA also have endocrine and metabolic functions. Besides, the steroidal-derived structure gives BA a toxic potential over the biological membrane. Thus, cholestatic disorders, characterized by elevated BA on the liver and serum, are a significant cause of liver transplant and extrahepatic complications, such as skeletal muscle, central nervous system (CNS), heart, and placenta. Further, the BA have an essential role in cellular damage, mediating processes such as membrane disruption, mitochondrial dysfunction, and the generation of reactive oxygen species (ROS) and oxidative stress. The purpose of this review is to describe the BA and their role on hepatic and extrahepatic complications in cholestatic diseases, focusing on the association between BA and the generation of oxidative stress that mediates tissue damage.

Cirrhotic Cardiomyopathy

Cirrhotic cardiomyopathy (CCM), cardiac dysfunction in end-stage liver disease in the absence of prior heart disease, is an important clinical entity that contributes significantly to morbidity and mortality. The original definition for CCM, established in 2005 at the World Congress of Gastroenterology (WCG), was based upon known echocardiographic parameters to identify subclinical cardiac dysfunction in the absence of overt structural abnormalities. Subsequent advances in cardiovascular imaging and in particular myocardial deformation imaging have rendered the WCG criteria outdated. A number of investigations have explored other factors relevant to CCM, including serum markers, electrocardiography, and magnetic resonance imaging. CCM characteristics include a hyperdynamic circulatory state, impaired contractility, altered diastolic relaxation, and electrophysiological abnormalities, particularly QT interval prolongation. It is now known that cardiac dysfunction worsens with the progression of cirrhosis. Treatment for CCM has traditionally been limited to supportive efforts, but new pharmacological studies appear promising. Left ventricular diastolic dysfunction in CCM can be improved by targeted heart rate reduction. Ivabradine combined with carvedilol improves left ventricular diastolic dysfunction through targeted heart rate reduction, and this regimen can improve survival in patients with cirrhosis. Orthotopic liver transplantation also appears to improve CCM. Here, we canvass diagnostic challenges associated with CCM, introduce cardiac physiology principles and the application of echocardiographic techniques, and discuss the evidence behind therapeutic interventions in CCM.

Gut microbiome - A potential mediator of pathogenesis in heart failure and its comorbidities: State-of-the-art review

Gut microbiome (GMB) has been increasingly recognized as a contributor to development and progression of heart failure (HF), immune-mediated subtypes of cardiomyopathy (myocarditis and anthracycline-induced cardiotoxicity), response to certain cardiovascular drugs, and HF-related comorbidities, such as chronic kidney disease, cardiorenal syndrome, insulin resistance, malnutrition, and cardiac cachexia. Gut microbiome is also responsible for the "gut hypothesis" of HF, which explains the adverse effects of gut barrier dysfunction and translocation of GMB on the progression of HF. Furthermore, accumulating evidence has suggested that gut microbial metabolites, including short chain fatty acids, trimethylamine N-oxide (TMAO), amino acid metabolites, and bile acids, are mechanistically linked to pathogenesis of HF, and could, therefore, serve as potential therapeutic targets for HF. Even though there are a variety of proposed therapeutic approaches, such as dietary modifications, prebiotics, probiotics, TMAO synthesis inhibitors, and fecal microbial transplant, targeting GMB in HF is still in its infancy and, indeed, requires further preclinical and clinical evidence. In this review, we aim to highlight the role gut microbiome plays in HF pathophysiology and its potential as a novel therapeutic target in HF.

Dietary metabolism, the gut microbiome, and heart failure

Advances in our understanding of how the gut microbiota contributes to human health and diseases have expanded our insight into how microbial composition and function affect the human host. Heart failure is associated with splanchnic circulation congestion, leading to bowel wall oedema and impaired intestinal barrier function. This situation is thought to heighten the overall inflammatory state via increased bacterial translocation and the presence of bacterial products in the systemic blood circulation. Several metabolites produced by gut microorganisms from dietary metabolism have been linked to pathologies such as atherosclerosis, hypertension, heart failure, chronic kidney disease, obesity, and type 2 diabetes mellitus. These findings suggest that the gut microbiome functions like an endocrine organ by generating bioactive metabolites that can directly or indirectly affect host physiology. In this Review, we discuss several newly discovered gut microbial metabolic pathways, including the production of trimethylamine and trimethylamine N-oxide, short-chain fatty acids, and secondary bile acids, that seem to participate in the development and progression of cardiovascular diseases, including heart failure. We also discuss the gut microbiome as a novel therapeutic target for the treatment of cardiovascular disease, and potential strategies for targeting intestinal microbial processes.

What Every Intensivist should Know about Impairment of Cardiac Function and Arrhythmias in Liver Disease Patients: A Review

Objectives

Impairment of cardiac function and arrhythmias often coexist in patients with liver diseases. Many studies have proved this coexistence and put forward various theories toward its pathophysiology. This narrative review tries to find the answers with supporting evidence on five main questions:

Materials and methods

Clinical evidence was obtained by using search engines, namely, Cochrane Library, PubMed, and Google Scholar. Studies published in journals in the English language, between January 1969 and December 2019, which mentioned the relationship between cardiac arrhythmia and liver disease, were included. We used the keywords: jaundice, bilirubin, arrhythmia, ECG, QTc interval, QT dispersion, liver, and cirrhosis. Relevant animal or human studies answering the five main questions were extracted and reviewed.

Conclusion

The evidence included in our review sheds light on the fact that approximately 50% of liver cirrhosis cases develop cirrhotic cardiomyopathy (CC) and there has been an association between liver abnormalities and cardiac pathology. The present review also supports that there exists a strong association between high levels of serum bilirubin levels and cardiac arrhythmias, QTc value can be relied upon as a risk factor for predicting imminent arrhythmias, and that it is associated with mortality. Its basic pathophysiology can be explained by the potential action of bile acids in prolonging the QT interval. It also causes cardiac hypertrophy and apoptosis of cardiomyocytes leading to cardiac dysfunction.

How to cite this article

Arya S, Kumar P, Tiwari B, Belwal S, Saxena S, Abbas H. What Every Intensivist should Know about Impairment of Cardiac Function and Arrhythmias in Liver Disease Patients: A Review. Indian J Crit Care Med 2020;24(12):1251–1255.

Bile acids and cardiovascular function in cirrhosis

Cirrhotic cardiomyopathy and the hyperdynamic syndrome are clinically important complications of cirrhosis, but their exact pathogenesis is still partly unknown. Experimental models have proven the cardiotoxic effects of bile acids and recent studies of their varied receptor-mediated functions offer new insight into their involvement in cardiovascular dysfunction in cirrhosis. Bile acid receptors such as farnesoid X-activated receptor and TGR5 are currently under investigation as potential therapeutic targets in a variety of pathological conditions. These receptors have also recently been identified in cardiomyocytes, vascular endothelial cells and smooth muscle cells where they seem to play an important role in cellular metabolism. Chronic cholestasis leading to abnormal levels of circulating bile acids alters the normal signalling pathways and contributes to the development of profound cardiovascular disturbances. This review summarizes the evidence regarding the role of bile acids and their receptors in the generation of cardiovascular dysfunction in cirrhosis.

Cirrhotic cardiomyopathy: review of pathophysiology and treatment

Cirrhotic cardiomyopathy is a cardiac condition observed in patients with cirrhotic regardless of the etiologies. It is characterized by the impaired systolic response to physical stress, diastolic dysfunction, and electrophysiological abnormalities, especially QT interval prolongation. Its pathophysiology and clinical significance has been a focus of various researchers for the past decades. The impairment of β-adrenergic receptor, the increase in endogenous cannabinoids, the presence of cardiosuppressants such as nitric oxide and inflammatory cytokines are the proposed mechanisms of systolic dysfunction. The activation of cardiac renin-angiotensin system and salt retention play the role in the development of cardiac hypertrophy and impaired diastolic function. QT interval prolongation, which is observed in 40-50 % of cirrhotic patients, occurs as a result of the derangement in membrane fluidity and ion channel defect. The increased recognition of this disease will prevent the complications of overt heart failure after procedures such as transjugular intrahepatic portosystemic shunt (TIPS) and liver transplantation. Better understandings of the pathogenesis and pathology of cirrhotic cardiomyopathy is crucial in developing more accurate diagnostic tools and specific treatments of this condition.

Cirrhotic cardiomyopathy: review of pathophysiology and treatment

Cirrhotic cardiomyopathy is a cardiac condition observed in patients with cirrhotic regardless of the etiologies. It is characterized by the impaired systolic response to physical stress, diastolic dysfunction, and electrophysiological abnormalities, especially QT interval prolongation. Its pathophysiology and clinical significance has been a focus of various researchers for the past decades. The impairment of β-adrenergic receptor, the increase in endogenous cannabinoids, the presence of cardiosuppressants such as nitric oxide and inflammatory cytokines are the proposed mechanisms of systolic dysfunction. The activation of cardiac renin-angiotensin system and salt retention play the role in the development of cardiac hypertrophy and impaired diastolic function. QT interval prolongation, which is observed in 40-50 % of cirrhotic patients, occurs as a result of the derangement in membrane fluidity and ion channel defect. The increased recognition of this disease will prevent the complications of overt heart failure after procedures such as transjugular intrahepatic portosystemic shunt (TIPS) and liver transplantation. Better understandings of the pathogenesis and pathology of cirrhotic cardiomyopathy is crucial in developing more accurate diagnostic tools and specific treatments of this condition.

Cardiomyopathy reverses with recovery of liver injury, cholestasis and cholanemia in mouse model of biliary fibrosis

BACKGROUND

Triggers and exacerbants of cirrhotic cardiomyopathy (CC) are poorly understood, limiting treatment options in patients with chronic liver diseases. Liver transplantation alone reverses some features of CC, but the physiology behind this effect has never been studied.

AIMS

We aimed to determine whether reversal of liver injury and fibrosis in mouse affects cardiac parameters. The second aim was to determine whether cardiomyopathy can be induced by specifically increasing systemic bile acid (BA) levels.

METHODS

6-8 week old male C57BL6J mice were fed either chow (n = 5) or 3,5-diethoxycarbonyl-1,4-dihydroxychollidine (DDC) (n = 10) for 3 weeks. At the end of 3 weeks, half the mice in the DDC fed group were randomized to chow (the reversed [REV] group). Serial ECHOs and electrocardiographic analysis was conducted weekly for 6 weeks followed by liver tissue and serum studies. Hearts were analysed for key components of function and cell signalling. Cardiac physiological and molecular parameters were similarly analysed in Abcb11(-/-) mice (n = 5/grp) fed 0.5% cholic acid supplemented diet for 1 week.

RESULTS

Mice in the REV group showed normalization of biochemical markers of liver injury with resolution of electrocardiographic and ECHO aberrations. Catecholamine resistance seen in DDC group resolved in the REV group. Cardiac recovery was accompanied by normalization of cardiac troponin-T2 as well as resolution of cardiac stress response at RNA level. Cardiovascular physiological and molecular parameters correlated with degree of cholanemia. Cardiomyopathy was reproduced in cholanemic BA fed Abcb11(-/-) mice.

CONCLUSIONS

Cardiomyopathy resolves with resolution of liver injury, is associated with cholanaemia, and can be induced by BA feeding.

Cardiovascular abnormalities in obstructive cholestasis: the possible mechanisms

Cholestatic liver disease is associated with widespread derangements in the cardiovascular system, such as bradycardia, hypotension, QT prolongation and peripheral vasodilation; it is also associated with increased susceptibility to postoperative renal failure and haemorrhagic shock. A number of cellular signalling pathways have been shown to contribute to these abnormalities. In this article, we briefly review recent in vivo and in vitro findings in the field in an attempt to highlight the areas of agreement and areas of controversy. In this review, we will summarize pathogenic mechanisms underlying cardiac and vascular abnormalities in obstructive cholestasis. It seems that cardiovascular dysfunction is likely because of bile acids as one of the predominant factors. Other important factors which might play roles in these abnormalities are increased nitric oxide, endogenous opioids and endocannabinoids. These three factors interact with each other to exert vasodilation and impaired cardiovascular responses to sympathetic stimulation.

In vivo and ex vivo effects of propofol on myocardial performance in rats with obstructive jaundice

BACKGROUND

Responsiveness of the "jaundiced heart" to propofol is not completely understood. The purpose of this study was to evaluate the effect of propofol on myocardial performance in rats with obstructive jaundice.

METHODS

Male Sprague-Dawley rats (n = 40) were randomly allocated into two groups, twenty underwent bile duct ligation (BDL), and 20 underwent a sham operation. Seven days after the surgery, propofol was administered in vivo and ex vivo (Langendorff preparations). Heart rate, left ventricular end-systolic pressure (LVESP) left ventricular end-diastolic pressure (LVEDP), and maximal rate for left ventricular pressure rise and decline (± dP/dtmax ) were measured to determine the influence of propofol on the cardiac function of rats.

RESULTS

Impaired basal cardiac function was observed in the isolated BDL hearts, whereas in vivo indices of basal cardiac function (LVESP and ± dP/dt) in vivo were significantly higher in rats that underwent BDL compared with controls. With low or intermediate concentrations of propofol, these indices of cardiac function were within the normal physiologic range in both groups, and responsiveness to propofol was unaffected by BDL. When the highest concentration of propofol was administrated, a significant decline in cardiac function was observed in the BDL group.

CONCLUSIONS

In rats that underwent BDL, basal cardiac performance was better in vivo and worse ex vivo compared with controls. Low and intermediate concentrations of propofol did not appear to impair cardiac function in rats with obstructive jaundice.

Cardiac structural and functional alterations in infants and children with biliary atresia, listed for liver transplantation

BACKGROUND & AIMS

Cirrhotic liver diseases are associated with abnormalities in cardiac geometry and function in adults (cirrhotic cardiomyopathy) but rarely explored in cirrhotic infants or children. We proposed that features of cirrhotic cardiomyopathy are present in infants with cirrhosis due to biliary atresia (BA) as early as the time of evaluation for liver transplant and will correlate with mortality and postoperative morbidity.

METHODS

Two-dimensional echocardiography (2DE) of infants with BA (n=40; median age, 8 months), listed for transplantation at the Texas Children's Hospital from 2004 to 2010, were reviewed and compared with age- and sex-matched infants without cardiac or liver disease (controls). Length of stay and correlation with 2DE results were assessed.

RESULTS

Compared with controls, children with BA had significant increases in multiple 2DE parameters, notably left ventricle wall thickness (23% increase), left ventricular (LV) mass indexed to body surface area (51% increase), and LV shortening fraction (8% increase). Overall, features of cirrhotic cardiomyopathy were observed in most infants (29/40; 72%); 17 had hyperdynamic contractility, and 24 had altered LV geometry. After liver transplantation (33), infants with abnormal 2DE results had longer stays in the intensive care unit (median, 6 vs 4 days) and the hospital (21 vs 11 days) compared with infants who had normal 2DE reports. On univariate analysis, the length of hospital stay correlated with LV mass index.

CONCLUSIONS

Cardiomyopathy is a prevalent condition in infants with end-stage cirrhotic liver disease due to BA (>70%). This underrecognized condition likely contributes to the prolongation of posttransplant hospitalization.

The interactivities with lipid membranes differentially characterize selective and nonselective beta1-blockers

BACKGROUND AND OBJECTIVE

beta-Adrenoceptor-blocking agents have been used for perioperative management during anaesthesia, in which selective beta1-blockers are advantageous over nonselective beta-blockers. Apart from the different affinity for beta-adrenoceptors, beta1-blockers were differentially characterized in light of their different interaction with lipid membranes.

METHODS

Selective (atenolol, metoprolol and esmolol) and nonselective (alprenolol, oxprenolol and propranolol) beta1-blockers were reacted at 0.2-1 mmol l with 1,2-dipalmitoylphosphatidylcholine liposomes and biomimetic membranes consisting of phospholipids, sphingolipid and cholesterol. Their membrane interactivities were comparatively determined using the potency to modify membrane fluidity by measuring fluorescence polarization. Their relative hydrophobicities were evaluated by reversed-phase liquid chromatography.

RESULTS

The chromatographic evaluation divided the tested drugs into more hydrophobic ones containing nonselective beta-blockers and less hydrophobic ones containing selective beta1-blockers. Nonselective beta-blockers, but not selective beta1-blockers, fluidized liposomal membranes, with the potency being oxprenolol < alprenolol < propranolol. Membrane-active alprenolol preferentially acted on the hydrophobic deeper regions of phospholipid bilayers. The potency of nonselective beta-blockers to fluidize biomimetic membranes was greatest in propranolol, followed by alprenolol and oxprenolol, whereas all selective beta1-blockers were inactive.

CONCLUSION

The membrane-fluidizing effects of beta-blockers are correlated with their relative hydrophobicities and their respective conformations to perturb the alignment of phospholipid acyl chains. The membrane-interacting characteristics differentiate beta-blockers as nonselective propranolol, alprenolol and oxprenolol vs. beta1-selective atenolol, metoprolol and esmolol. Such differentiation reflects not only the structural difference but also the beta-adrenoceptor-blocking difference. The membrane fluidization may be partly responsible for the nonselective blockade of beta-adrenoceptors.

The role of lipophilic bile acids in the development of cirrhotic cardiomyopathy

Marked hemodynamic changes occur in humans and experimental animals with cirrhotic liver disease. In the heart, basal contractility, responsiveness to beta-adrenoceptor activation, and excitation-contraction coupling (ECC) are negatively affected in models of cirrhosis and portal hypertension with portosystemic shunting (PVS), and comprise what has been called cirrhotic cardiomyopathy. These effects are accompanied by elevated circulating levels of bile acids. We investigated whether elevated bile acids act as a myocardial toxicant by exposing cardiac muscle in vitro to bile acids and compared these results with two models of cirrhotic cardiomyopathy with elevated bile acids: CCl4-induced cirrhosis and PVS. Cholic acid, a lipophilic bile acid, produced a decrease in basal cardiac contractility and responsiveness to beta-adrenoceptor activation, both of which appeared to result from altered ECC. beta-Adrenoceptor density and signaling were unaffected. Acutely, ursodeoxycholic acid, a more hydrophilic bile acid, had no effect. Cirrhosis produced a decrease in basal force, depressed beta-adrenoceptor responsiveness, and altered ECC similar to cholic acid. However, cirrhosis also altered beta-adrenoceptor signaling including decreases in cyclic AMP formation, expression of the stimulatory G protein, GS, and beta-adrenoceptor density. Displacement of lipophilic bile acids by chronic administration of ursodeoxycholic acid to rats during the development of cirrhotic cardiomyopathy produced by PVS produced attenuation of the effect on ECC. These results suggest a possible role for lipophilic bile acids in some, but not all of the myocardial consequences of chronic portal vein stenosis and CCl4-induced cirrhosis.

Cirrhotic cardiomyopathy

Cirrhotic cardiomyopathy is a clinical syndrome in patients with liver cirrhosis characterized by an abnormal and blunted response to physiologic, pathologic, or pharmacologic stress but normal to increased cardiac output and contractility at rest. As many as 50% of cirrhotic patients undergoing liver transplantation show signs of cardiac dysfunction, and 7% to 21% of deaths after orthotopic liver transplantation result from overt heart failure. In this review, we critically evaluate the existing literature on the pathophysiology and clinical implications of cirrhotic cardiomyopathy.

Hypertrophic cardiomyopathy and dysregulation of cardiac energetics in a mouse model of biliary fibrosis

Cardiac dysfunction is a major cause of morbidity and mortality in patients with end-stage liver disease; yet the mechanisms remain largely unknown. We hypothesized that the complex interrelated impairments in cardiac structure and function secondary to progression of liver diseases involve alterations in signaling pathways engaged in cardiac energy metabolism and hypertrophy, augmented by direct effects of high circulating levels of bile acids. Biliary fibrosis was induced in male C57BL/6J mice by feeding a 0.1% 3,5-diethoxycarbonyl-1,4-dihydroxychollidine (DDC) supplemented diet. After 3 weeks, mice underwent live imaging (dual energy x-ray absorptiometry [DEXA] scanning, two-dimensional echocardiography [2DE], electrocardiography, cardiac magnetic resonance imaging), exercise treadmill testing, and histological and biochemical analyses of livers and hearts. Compared with chow-fed mice, DDC-fed mice fatigued earlier on the treadmill, with reduced VO(2). Marked changes were identified electrophysiologically (bradycardia and prolonged QT interval) and functionally (hyperdynamic left ventricular [LV] contractility along with increased LV thickness). Hearts of DDC-fed mice showed hypertrophic signaling (activation of v-akt murine thymoma viral oncogene/protein kinase B [AKT], inhibition of glycogen synthase kinase-3beta [GSK3beta], a 20-fold up-regulation of beta myosin heavy chain RNA and elevated G(s)alpha/G(i)alpha ratio. Genes regulating cardiac fatty acid oxidation pathways were suppressed, along with a threefold increase in myocardial glycogen content. Treatment of mouse cardiomyocytes (which express the membrane bile acid receptor TGR5) with potent natural TGR5 agonists, taurochenodeoxycholic acid and lithocholic acid, activated AKT and inhibited GSK3beta, similar to the changes seen in DDC-fed mouse hearts. This provides support for a novel mechanism whereby circulating natural bile acids can induce signaling pathways in heart associated with hypertrophy.

CONCLUSION

Three weeks of DDC feeding-induced biliary fibrosis leads to multiple functional, metabolic, electrophysiological, and hypertrophic adaptations in the mouse heart, recapitulating some of the features of human cirrhotic cardiomyopathy.

Superoxide radical formation in diverse organs of rats with experimentally induced obstructive jaundice

Oxidative stress seems to be a cardinal feature of cholestasis, implicated in the pathophysiology of organ injury not only in the liver, but also in several extrahepatic tissues. The present study was designed to assess directly oxidative stress in vital organs of experimentally jaundiced rats by measuring the key oxidative stress marker superoxide radical (O2(*-)). Twelve male Wistar rats underwent laparotomy and were divided into two groups - group I (n = 6) sham operated, and group II (n = 6) bile-duct ligated. Ten days later, the O2(*-) formation rate was quantified in liver, intestine, kidney and heart of all animals. These measurements were done by application of a new ultrasensitive fluorescent assay for the in vivo quantification of O2(*-), which is based on the 1:1 molar stoichiometric reaction of O2(*-) with dihydroethidine (DHE, an O2(*-) trap) that results in the formation of the specific product 2-OH-ethidium. 2-OH-Ethidium was measured by fluorescence in rats' organs and its formation rate was converted to O2(*-) production rate. As compared to sham-operated rats, in jaundiced rats there was a significant increase of O2(*-) in the intestine (136%, P < 0.01), liver (104%, P < 0.01), and kidney (95%, P < 0.01), whereas there was no significant difference in heart O2(*-) levels. Superoxide radical may play an important role in the pathophysiology of cholestatic liver injury, intestinal barrier failure and renal failure, associated with postoperative morbidity and mortality in obstructive jaundice. On the contrary, O2(*-) and oxidative stress are possibly not implicated in the pathophysiology of hepatic cardiomyopathy.

Cirrhotic cardiomyopathy

Cirrhotic cardiomyopathy is a recently recognized condition in cirrhosis consisting of systolic incompetence under condition of stress, diastolic dysfunction related to altered diastolic relaxation, and electrophysiological abnormalities in the absence of any known cardiac disease. It can be diagnosed by using a combination of electrocardiograph, 2-dimensional echocardiography, and various serum markers such as brain natriuretic factor. The underlying pathogenetic mechanisms include abnormalities in the beta-adrenergic signaling pathway, altered cardiomyocyte membrane fluidity, increased myocardial fibrosis, cardiomyocyte hypertrophy, and ion channel defects. Various compounds for which levels are elevated in cirrhosis such as nitric oxide and carbon monoxide can also exert a negative inotropic effect on the myocardium, whereas excess sodium and volume retention can lead to myocardial hypertrophy. Various toxins can also aggravate the ion channel defects, thereby widening the QRS complex causing prolonged QT intervals. Clinically, systolic incompetence is most evident when cirrhotic patients are placed under stress, whether physical or pharmacological, or when the extent of peripheral arterial vasodilatation demands an increased cardiac output as in the case of bacterial infections. Acute volume overload such as immediately after insertion of a transjugular intrahepatic portosystemic shunt or after liver transplantation can also tip these cirrhotic patients into cardiac failure. Treatment of cirrhotic cardiomyopathy is unsatisfactory. There is some evidence that beta-blockade may help some cirrhotic patients with baseline prolonged QT interval. Long-term aldosterone antagonism may help reduce myocardial hypertrophy. Future studies should include further elucidation of pathogenetic mechanisms so as to develop effective treatment strategies.

Mitochondrially-mediated toxicity of bile acids

In the healthy hepatocyte, uptake of bile acids across the basolateral membrane and export via the canalicular export pump, are tightly coupled. Impairment of bile formation or excretion results in cholestasis, characterized by accumulation of bile acids in systemic blood and within the hepatocyte. When the concentration of bile acids exceeds the binding capacity of the binding protein located in the cytosol of the hepatocyte, bile acids induce apoptosis and necrosis, by damage to mitochondria. Mitochondria play a central role on the toxicity of bile acids. In this article, we review the published literature regarding bile acid effects on cell function, especially at the mitochondrial level. In patients with cholestatic liver disease, the extent of hepatocyte damage caused by intracellular accumulation of bile acids appears to be delayed by ingesting a hydrophilic bile acid. However, its effects on disease progression are not completely clarified. Therefore, identification of the mechanisms of cell injury will be of clinical utility, helping in the development of new therapeutic strategies. The goal of this review is to include a fresh consideration of all possible targets and integrating pathways that are involved in cholestasis, as well as in the benefits of bile acid therapy.

Resistance of cholestatic rats against epinephrine-induced arrhythmia: the role of nitric oxide and endogenous opioids

Short-term ligation of bile duct has been used as a model to study acute cholestasis and is associated with various cardiovascular abnormalities. We examined the role of nitric oxide (NO) and endogenous opioids on epinephrine-induced arrhythmia in 7-day bile duct-ligated (BDL) rats. Six groups of rats, each of which was subdivided into two subgroups (sham-operated and BDL), were examined. First group of animals were chronically treated with normal saline. In the second and third groups, single intraperitoneal administration of N(omega)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg) or naltrexone (20 mg/kg) was performed 30 min before evaluation of epinephrine-induced arrhythmia. Two groups received chronic administration of low dose (3 mg/kg/day) or high dose (10 mg/kg/day) L-NAME; and the last group was treated chronically with naltrexone (20 mg/kg/day). Chronic drug administration was performed subcutaneously for 6 consecutive days following BDL or sham operation. After induction of arrhythmia by intravenous injection of 10 microg/kg epinephrine, mean arterial pressure and electrocardiogram were recorded for 1 min. Heart rate and mean arterial pressure were significantly lower in BDL rats (P<0.01). Chronic injection of naltrexone increased heart rate and mean arterial pressure in BDL (P<0.05). Chronic low dose L-NAME administration had no effect on baseline hemodynamic parameters. High dose L-NAME injection corrected hypotension in BDL rats, but not bradycardia (P<0.05). Epinephrine induced less arrhythmia in BDL rats (P<0.05). Acute and chronic injection of naltrexone had no effect on the resistance of BDL rats against epinephrine-induced arrhythmia. Although acute L-NAME administration enhanced arrhythmias in sham-operated rats (P<0.001), it had no effect on BDL animals. Chronic injection of low dose or high dose L-NAME, without having any effect on sham-operated animals, increased arrhythmias in BDL rats (P<0.01). This study showed that BDL animals are resistant against epinephrine-induced arrhythmia and this resistance depends on long-term NO overproduction.

Cardiac Mitochondrial Calcium Loading Capacity is Severely Affected after Chronic Cholestasis in Wistar Rats

Background

Cardiovascular changes correlated with some forms of hepatic disease are being reported in the literature. Objectives: The aim of this work was to characterize cardiac mitochondrial bioenergetics and calcium buffering capacity in Wistar rats injected with six weekly doses of α-naphthylisothio-cyanate (ANIT), a compound known to induce cholestasis in animal models.

Methods

Isolated heart mitochondria were obtained from both injected and control animals and bioenergetic parameters were measured, as well as the capacity to buffer externally added calcium and the mitochondrial content of reduced protein thiol groups. Blood biochemistry analyses were obtained at the initial and end points of treatment. The in vitro ANIT effect on isolated heart mitochondria was also studied.

Results and Discussion

Our results showed that the respiratory control ratio was the only parameter affected in injected animals ( p < .05, n = 5). Nevertheless, heart mitochondria from injected animals showed an inability to accumulate added calcium owing to an increased susceptibility to the calcium-dependent mitochondrial permeability transition ( p < .0001, n = 5). The effects were still present 1 week after ending ANIT administration, when serum markers for liver injury and hyperbilirubinemia were already abated (although in the presence of bile duct proliferation). To our knowledge, this is the first time that cardiac mitochondrial calcium homeostasis and mitochondrial respiratory ratio are seen affected during ANIT-induced cholestasis, prevailing even in the absence of hepatic damage serum markers.

Reduction in cardiac mitochondrial calcium loading capacity is observable during alpha-naphthylisothiocyanate-induced acute cholestasis: a clue for hepatic-derived cardiomyopathies?

Cardiovascular changes of still obscure origin are sometimes correlated with co-existing liver diseases, as cholestasis. The aim of this work was to examine and compare cardiac mitochondrial bioenergetics and calcium loading capacity from rats injected with a single dose of alpha-naphthylisothiocyanate (ANIT), a cholestasis-inducing compound. Forty-eight hours after ANIT administration, blood samples were collected and markers for hepatic disease were determined. Heart mitochondria from both control and ANIT-injected rats were isolated and subjected to biochemical characterization, including the susceptibility to the calcium-dependent permeability transition. The results showed that cardiac mitochondria from cholestatic animals did not have significant changes in respiratory parameters or in the basal levels of adenine nucleotide. The most impressive result from this work was that cardiac mitochondria from ANIT-injected animals had a lower calcium loading capacity. The prevention of this property by cyclosporin-A, a specific inhibitor of the mitochondrial permeability transition, showed that this phenomenon was reason for the reduced calcium loading capacity in ANIT-injected animals. The results suggest that, during the development of ANIT-induced cholestasis, heart mitochondria loose their default ability to buffer calcium. Our results may contribute to explain the occurrence of cardiomyopathies sometimes associated with cholestatic disease.

Protective effect of carvedilol on chenodeoxycholate induction of the permeability transition pore

Intracellular accumulation of toxic, hydrophobic bile acids has been proposed as one of the putative final common pathways leading to cholestatic liver injury. Furthermore, bile acids have been proposed as a causative factor for hepatic cardiomyopathy. Hepatic tissue concentrations of chenodeoxycholic acid (CDCA) during cholestasis are greater than those of other toxic bile acids. In the presence of calcium and phosphate, CDCA induced the permeability transition pore (PTP) in freshly isolated rat liver mitochondria. In this study, we evaluated the effects of carvedilol, a multirole cardioprotective compound, on CDCA-induced PTP. Mitochondrial membrane potential, osmotic swelling, and calcium fluxes were monitored. CDCA-induced PTP, characterized by membrane depolarization, release of matrix calcium, and osmotic swelling, was prevented by carvedilol. Under the same conditions, its hydroxylated analog BM-910228 did not reveal any protective effect. This finding reinforces carvedilol's therapeutic interest, because it may potentially prevent mitochondrial dysfunction associated with cardiomyopathy in the pathophysiology of cholestatic liver disease

Oxidative stress and vascular smooth muscle cell function in liver disease

Reactive oxygen species and reactive nitroxy species are now being recognized as regulatory molecules in signaling pathways influencing contractile and noncontractile functions of healthy vascular smooth muscle cells. In liver disease, oxidative stress is a systemic phenomenon, whose extent correlates with the severity of disease. A role for oxidative stress in the development of the hyperdynamic circulation in portal hypertension has been proposed. Evaluation of the limited available data indicates that it is premature to conclude that oxidative stress per se impacts on vascular smooth muscle cell function in liver disease.

Cirrhosis of the liver and receptor-mediated function in vascular smooth muscle

Altered regulation of receptors on the vascular smooth muscle has been proposed as one of the mechanisms that may account for the vascular abnormalities in patients with cirrhosis of the liver. Impaired contractility and down-regulation of contractile receptors have been demonstrated in cirrhotic patients and animal models, although interpretation of the literature is hampered by methodological variation and conflicting results. There is little evidence, however, that receptor down-regulation is the cause of contractile dysfunction in either patients or animal models. Receptor desensitisation may contribute to impaired contraction in human arteries, but further investigation is required to confirm this possibility.

Role of heme oxygenase-carbon monoxide pathway in pathogenesis of cirrhotic cardiomyopathy in the rat

The enzyme heme oxygenase (HO), which exists in inducible (HO-1) and constitutive (HO-2) isoforms, degrades heme to biliverdin and CO. CO depresses cardiac contraction via cGMP. We aimed to clarify a possible role for the HO-CO pathway in the pathogenesis of cirrhotic cardiomyopathy in bile duct-ligated rats. Four weeks after bile duct ligation or sham operation, rat ventricles were examined for HO-1 and HO-2 mRNA by RT-PCR and for protein expression by Western blotting. Total HO enzyme activity and cGMP levels were also measured. The effects of a HO inhibitor, zinc protoporphyrin IX (ZnPP), on ventricular cGMP levels and isolated papillary muscle contractility were studied. We found that HO-1 mRNA transcription and protein expression were significantly augmented in cirrhotic hearts compared with sham-operated controls, whereas there was no difference in HO-2 mRNA or protein levels. Total HO activity and cGMP levels were significantly increased in cirrhotic ventricles vs. controls. In cirrhotic ventricles, treatment with ZnPP significantly decreased cGMP production and improved the blunted papillary muscle contractility, whereas it had no effect on control muscles. CO perfusion inhibited papillary muscle contractility, an effect completely blocked by methylene blue and partially blocked by ZnPP. These results indicate that activation of the HO-CO-cGMP pathway is involved in the pathogenesis of cirrhotic cardiomyopathy.

On the in vitro vasoactivity of bile acids

We compared the vasorelaxant action of nine different bile acids and correlated their vasorelaxant activity with their individual indices for hydrophobicity or lipophilicity. Vasorelaxant activity correlated with the relative lipid solubility of bile acids with lipophilic bile acids exhibiting the greatest vasorelaxant activity with modest to no vasorelaxant activity exhibited by hydrophilic bile acids. We also investigated whether bile acid-induced vasorelaxation is mediated by antagonism of a prototypal contractile receptor, the alpha(1)-adrenoceptor, by stimulation of a bile acid surface membrane receptor, by the release of endothelium-derived relaxant factors, by promoting the generation of reactive oxygen species and increasing the extent of lipid peroxidation, or by modifying membrane fluidity. Lipophilic bile acids induce vasorelaxation possibly by antagonizing alpha(1)-adrenoceptors, a phenomenon that manifests itself as a lowering of the affinity of vascular alpha(1)-adrenoceptors. Bile acid-induced vasorelaxation was not dependent upon stimulation of a bile acid surface membrane receptor or the release of endothelium-derived relaxant factors. Lipophilic bile acids can also increase the extent of lipid peroxidation with a subtle reduction in the fluidity of rat vascular smooth muscle membranes not associated with loss of membrane cholesterol or phospholipid. We have concluded that lipophilic bile acids are non-selective vasorelaxants whose mechanism of action is a multifaceted process involving antagonism of contractile surface membrane receptors possibly effected by an increased extent of lipid peroxidation and/or membrane fluidity but occurs independent of the release of endothelial-derived relaxant factors or stimulation of a surface membrane bile acid binding site.