Altered cellular calcium regulatory systems in a rat model of cirrhotic cardiomyopathy

Cardiac dysfunction in cirrhosis

Cirrhosis is known to be associated with numerous cardiovascular abnormalities. These include increased cardiac output and decreased arterial pressure and total peripheral resistance. Despite this increased baseline cardiac output, patients with cirrhosis show an attenuated systolic and diastolic function in the face of pharmacological, physiological and surgical stresses, as well as cardiac electrical abnormalities such as QT prolongation. These abnormalities have been termed cirrhotic cardiomyopathy. The pathogenic mechanisms that underlie this syndrome include impairment of the beta-adrenergic receptor signalling, cardiomyocyte plasma membrane function, intracellular calcium kinetics, and humoral factors such as endogenous cannabinoids, nitric oxide and carbon monoxide. Cirrhotic cardiomyopathy is believed to contribute to the cardiac dysfunction that can be observed in patients with transjugular intrahepatic portosystemic stent-shunt insertion and liver transplantation. Insufficient cardiac contractile function may also play a role in the pathogenesis of hepatorenal syndrome precipitated by spontaneous bacterial peritonitis. In this review, the clinical features, pathogenic mechanisms, clinical consequences and management options for cirrhotic cardiomyopathy are discussed.

Therapy insight: Cirrhotic cardiomyopathy

Liver cirrhosis is associated with several cardiovascular disturbances. These disturbances include hyperdynamic systemic circulation, manifested by an increased cardiac output and decreased peripheral vascular resistance and arterial pressure. Despite the baseline increase in cardiac output, cardiac function in patients with cirrhosis is abnormal in several respects. Patients show attenuated systolic and diastolic contractile responses to stress stimuli, electrophysiological repolarization changes, including prolonged QT interval, and enlargement or hypertrophy of cardiac chambers. This constellation of cardiac abnormalities is termed cirrhotic cardiomyopathy. It has been suggested that cirrhotic cardiomyopathy has a role in the pathogenesis of cardiac dysfunction and even overt heart failure after transjugular intrahepatic portosystemic shunt placement, major surgery and liver transplantation. Cardiac dysfunction contributes to morbidity and mortality after liver transplantation, even in many patients who have no prior history of cardiac disease. Depressed cardiac contractility contributes to the pathogenesis of hepatorenal syndrome, especially in patients with spontaneous bacterial peritonitis. Pathogenic mechanisms underlying cirrhotic cardiomyopathy include cardiomyocyte-membrane biophysical changes, attenuation of the stimulatory beta-adrenergic system and overactivity of negative inotropic systems mediated via cyclic GMP. The clinical features, general diagnostic criteria, pathogenesis and treatment of cirrhotic cardiomyopathy are discussed in this review.

Nonischemic cardiomyopathy after orthotopic liver transplantation: a report of three cases and a review of the literature

In 2002 there were more than 5,000 liver transplantations performed in the United States. As of February 2004 there were more than 17,000 registrations for liver transplantation. As more organs are transplanted and surgical techniques improve, unique causes of morbidity and mortality will become apparent. We describe three cases of postoperative nonischemic dilated cardiomyopathy in patients who underwent orthotopic liver transplantation (OLT), one of whom underwent diagnostic myocardial biopsy. This paper will discuss the three patients, including biopsy results, and briefly review the relevant literature.

IgG from patients with liver diseases inhibit mitochondrial respiration in permeabilized oxidative muscle cells: impaired function of intracellular energetic units?

The effect of IgG purified from the sera of healthy persons and patients with primary biliary cirrhosis (PBC) and chronic hepatitis (CH) on ADP dependent respiration (oxidative phosphorylation) in skinned muscle fibers from rat oxidative muscles (heart and M. soleus) and glycolytic skeletal muscle (M. gastrocnemius) was studied. The results show that IgG from three different sources inhibited the rate of respiration by 13, 44 and 42%, respectively, these effects being equally expressed in both types of oxidative muscles, whereas no inhibition was observed in glycolytic muscle. The following washout of unbound IgG did not abolish the inhibition of respiration suggesting that the specific interaction of IgG with antigens had taken place. Laser confocal analysis revealed binding of IgG predominantly to the sarcomeric structures such as Z-disk and M-lines in the cardiomyocytes. The staining of IgG within Z-disks and intermitochondrial space coincided throughout the muscle cells so that transversally serial spaces, each containing mitochondria and adjacent sarcomere, became clearly visible. When the IgG from a CH patient was incubated with the skinned myocardial fibers of the desmin knockout mice, its binding to Z-disks and the sarcomeric area was found to be similar to that in normal cardiac muscle. However, the transversal staining pattern was disintegrated, because of the slippage of the myofibrils in relation to each other and accumulation of mitochondria between them. These observations support the recent hypothesis that in oxidative muscles the mitochondria and adjacent sarcomeres form complexes, termed as the intracellular energetic units, ICEUs. Moreover, they indicate that human autoantibodies can be useful tools for localizing the proteins responsible for formation of ICEUs and modulation of their function. Thus, it appears that the proteins associated with the Z-disks and M-lines may participate in formation of ICEUs and that binding of IgG to these proteins decreases the access of exogenous adenine nucleotides to mitochondria, which manifests as decreased rate of ADP-dependent respiration.

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.

Cholestatic syndromes

Further insights into the molecular regulation of bile acid transport and metabolism have provided the basis for a better understanding of the pathogenesis of cholestatic liver diseases. Novel insights into the mechanisms of action of ursodeoxycholic acid should advance our understanding of the treatment of cholestatic liver diseases. Mutations of transporter genes can cause hereditary cholestatic syndromes in both infants and adults as well as cholesterol gallstone disease. Important studies have been published on the pathogenesis, clinical features, and treatment of primary biliary cirrhosis, drug-induced cholestasis, and cholestasis of pregnancy.