Hepatic response to right ventricular pressure overload

Chronic heart failure induces early defenestration of liver sinusoidal endothelial cells (LSECs) in mice

AIM

Chronic heart failure (CHF) is often linked to liver malfunction and systemic endothelial dysfunction. However, whether cardio-hepatic interactions in heart failure involve dysfunction of liver sinusoidal endothelial cells (LSECs) is not known. Here we characterize LSECs phenotype in early and end stages of chronic heart failure in a murine model.

METHODS

Right ventricle (RV) function, features of congestive hepatopathy, and the phenotype of primary LSECs were characterized in Tgαq*44 mice, with cardiomyocyte-specific overexpression of the Gαq protein, at the age of 4- and 12-month representative for early and end-stage phases of CHF, respectively.

RESULTS

4- and 12-month-old Tgαq*44 mice displayed progressive impairment of RV function and alterations in hepatic blood flow velocity resulting in hepatic congestion with elevated GGT and bilirubin plasma levels and decreased albumin concentration without gross liver pathology. LSECs isolated from 4- and 12-month-old Tgαq*44 mice displayed significant loss of fenestrae with impaired functional response to cytochalasin B, significant changes in proteome related to cytoskeleton remodeling, and altered vasoprotective function. However, LSECs barrier function and bioenergetics were largely preserved. In 4- and 12-month-old Tgαq*44 mice, LSECs defenestration was associated with prolonged postprandial hypertriglyceridemia and in 12-month-old Tgαq*44 mice with proteomic changes of hepatocytes indicative of altered lipid metabolism.

CONCLUSION

Tgαq*44 mice displayed right-sided HF and altered hepatic blood flow leading to LSECs dysfunction involving defenestration, shift in eicosanoid profile, and proteomic changes. LSECs dysfunction appears as an early and persistent event in CHF, preceding congestive hepatopathy and contributing to alterations in lipoprotein transport and CHF pathophysiology.

Histology and Glutamine Synthetase Immunoreactivity in Liver Biopsies From Patients With Congestive Heart Failure

Background

Long-standing congestive heart failure can induce a constellation of histopathology changes in the liver that can range from mild sinusoidal dilation to advanced fibrosis and loss of normal perivenular expression of glutamine synthetase (GS). Liver biopsies might be performed to assess the perioperative risk of these patients or to determine the need of synchronous liver transplant. We aimed to assess interobserver agreement in recognizing these liver histologic features in patients undergoing evaluation for heart transplantation and to examine whether immunohistochemistry of GS will aid the diagnosis of cardiac hepatopathy (CH).

Methods

Hematoxylin-eosin and trichrome-stained slides from 36 liver biopsies from patients undergoing evaluation for heart transplantation were reviewed by four liver pathologists. Histologic features of CH were reviewed and an overall fibrosis (stage) was assessed according to a recently proposed congestive hepatic fibrosis score (CHFS). In addition, 24 liver biopsies with a consensus diagnosis of CH and eight liver biopsies with no significant pathological changes were subjected to immunohistochemistry for GS. The Fleiss’ kappa coefficient (K) analysis was performed to determine the interobserver agreement. Further, histologic features of CH were correlated with the staining pattern of GS.

Results

Sinusoidal dilation, centrilobular hepatocyte atrophy, centrilobular fibrosis and hemorrhage were the most common findings in this cohort with a substantial-to-fair level of interobserver agreement among four reviewers. The overall agreement on the diagnosis of CH and CHFS was moderate (K = 0.55, 95% confidence interval (CI): 0.32 - 0.73) and fair (K = 0.35, 95% CI: 0.24 - 0.49), respectively. Twelve (of 24, 50%) cases of CH showed loss of the normal perivenular GS staining, while the remaining 12 cases of CH and all eight controls showed retained GS expression. Histologic features of CH (presence of sinusoidal dilation, centrilobular hepatocyte atrophy, hemorrhage, and centrilobular fibrosis) and the stage of fibrosis (CHFS) were not correlated with the loss of GS staining.

Conclusion

Most common features of CH can be interpreted with fair-to-substantial level of agreement by liver pathologists, with an overall moderate level agreement for the diagnosis and fair agreement for CHFS. Loss of normal perivenular expression of GS only occurs in 50% CH and thus is not a sensitive marker for CH.

Extracardiac Signs of Fluid Overload in the Critically Ill Cardiac Patient: A Focused Evaluation Using Bedside Ultrasound

Fluid balance management is of great importance in the critically ill cardiac patient. Although intravenous fluids are a cornerstone therapy in the management of unstable patients, excessive administration coupled with cardiac dysfunction leads to elevation in central venous pressure and end-organ venous congestion. Fluid overload is known to have a detrimental effect on organ function and is responsible for significant morbidity in critically ill patients. Multisystem bedside point of care ultrasound imaging can be used to assess signs of fluid overload and venous congestion in critically ill patients. In this review we describe the ultrasonographic extracardiac signs of fluid overload and how they can be used to complement clinical evaluation to individualize patient management.

Fluid Overload

Most critically ill patients experience external or internal fluid shifts and hemodynamic instability. In response to these changes, intravenous fluids are frequently administered. However, rapid losses of administered fluids from circulation and the indirect link between the short-lived plasma volume expansion and end points frequently result in transient responses to fluid therapy. Therefore, fluid overload is a common finding in intensive care units. The authors consider the evidence of harm associated with fluid overload and the physiologic processes that lead to fluid accumulation in critical illness. The authors then consider methods to prevent fluid accumulation and/or manage its resolution.

Liver fibrosis in an extremely small infant for gestational age

Premature infants with intrauterine growth restriction (IUGR) are at greater risk for an adverse perinatal outcome. IUGR affects hepatocyte function, but the histopathological changes in the postnatal liver are not well known. We report a male infant with severe IUGR. His mother was transferred to our hospital at 26 weeks of gestation because of preterm labor and severe IUGR. An emergency cesarean section was carried out because of a non-reassuring fetal status. The birth weight of the infant was 332 g. He showed congestive heart failure and marked hepatomegaly from birth. After 1 week, blood examinations showed hyperbilirubinemia with high direct bilirubin. Because of liver dysfunction, he received the minimal total parenteral nutrition for 7 days. After 1 month, he progressively developed ascites and coagulopathy, and died 3 months after birth. Liver autopsy showed diffuse perisinusoidal fibrosis. Fibrosis was also prominent around the central vein. Immunohistochemical study revealed many alpha-smooth muscle actin-positive cells, which represent activated hepatic stellate cells, and a few transforming growth factor-beta1-positive cells in the perisinusoidal fibrotic area. These results indicate that the infant developed chronic (end stage) liver failure by 3 months of age. We excluded congenital infection, metabolic syndrome and citrin deficiency. It is therefore conceivable that intrauterine cardiac failure may be responsible for liver fibrosis. Early detection of liver dysfunction soon after birth is a key to predict the prognosis of severe IUGR in preterm infants.

Hepatocellular expression of glutamine synthetase: an indicator of morphogen actions as master regulators of zonation in adult liver

Glutamine synthetase (GS) has long been known to be expressed exclusively in pericentral hepatocytes most proximal to the central veins of liver lobuli. This enzyme as well as its peculiar distribution complementary to the periportal compartment for ureogenesis plays an important role in nitrogen metabolism, particularly in homeostasis of blood levels of ammonium ions and glutamine. Despite this fact and intensive studies in vivo and in vitro, many aspects of the regulation of its activity on the protein and on the genetic level remained enigmatic. Recent experimental advances using transgenic mice and new analytic tools have revealed the fundamental role of morphogens such as wingless-type MMTV integration site family member signals (Wnt), beta-catenin, and adenomatous polyposis coli in the regulation of this particular enzyme. In addition, novel information concerning the structure of transcription factor binding sites within regulatory regions of the GS gene and their interactions with signalling pathways could be collected. In this review we focus on all aspects of the regulation of GS in the liver and demonstrate how the new findings have changed our view of the determinants of liver zonation. What appeared as a simple response of hepatocytes to blood-derived factors and local cellular interactions must now be perceived as a fundamental mechanism of adult tissue patterning by morphogens that were considered mainly as regulators of developmental processes. Though GS may be the most obvious indicator of morphogen action among many other targets, elucidation of the complex regulation of the expression of the GS gene could pave the road for a better understanding of the mechanisms involved in patterning of liver parenchyma. Based on current knowledge we propose a new concept of how morphogens, hormones and other factors may act in concert, in order to restrict gene expression to small subpopulations of one differentiated cell type, the hepatocyte, in different anatomical locations. Although many details of this regulatory network are still missing, and an era of exciting new discoveries is still about to come, it can already be envisioned that similar mechanisms may well be active in other organs contributing to the fine-tuning of organ-specific functions.

Liver-specific loss of beta-catenin blocks glutamine synthesis pathway activity and cytochrome p450 expression in mice

There is accumulating evidence that Wnt/beta-catenin signaling is involved in the regulation of liver development and physiology. The presence of genetic alterations resulting in constitutive beta-catenin stabilization in human and murine liver tumors also implicates this pathway in hepatocyte proliferation. In the present study, we generated hepatocyte-specific beta-catenin knockout mice to explore the role of beta-catenin in liver function. Conditional knockout mice were born at the expected Mendelian ratio and developed normally to adulthood, indicating beta-catenin is dispensable for essential liver function under normal breeding conditions. However, the liver mass of knockout mice was 20% less than those of mice in the control groups. Expression analysis revealed loss of genes required for glutamine synthesis in knockout mice. Loss of the liver glutamine synthesis pathway did not affect the blood ammonia level in mice fed a standard diet, yet, knockout mice showed significantly elevated blood ammonia levels with high-protein dietary feeding. Furthermore, the expression of two cytochrome P450 enzymes, CYP1A2 and CYP2E1, was almost completely abolished in livers from hepatocyte-specific beta-catenin knockout mice. Consequently, these mice were resistant to acetaminophen challenge, confirming the requirement of these cytochrome P450 enzymes for metabolism of xenobiotic substances. In conclusion, in addition to regulating hepatocyte proliferation, beta-catenin may also control multiple aspects of normal liver function.

Hepatobiliary pathology

PURPOSE OF REVIEW

This review highlights recent publications on hepatobiliary pathology concerning several unusual types of hepatitis, fatty liver disease, disorders of the biliary tree and other topics that have a substantial impact on liver biopsy interpretation.

RECENT FINDINGS

In the outbreak of severe acute respiratory syndrome (SARS), many patients had abnormalities in liver function tests. Liver biopsy findings in three cases were reported that showed a generic picture of hepatitis, with exceptionally increased mitotic activity. The role of portal myofibroblasts in cirrhosis was examined in several studies. A newly described lesion, isolated ductular hyperplasia (IDH) was found in patients with prolonged abnormalities of liver function tests of uncertain origin. Hyperplastic, well-differentiated bile ductules were seen on liver biopsy in the absence of any identifiable biliary disease. Hereditary hemochromatosis is now a complex entity with various clinicopathological forms based on mutations in the HFE gene and other iron-homeostatic genes such as transferrin receptor 2 and ferroportin 1. In some of these heritable forms of primary iron overload, stainable iron is present in both hepatocytes and Kupffer cells. After liver transplantation, differentiating recurrent HCV infection from acute rejection on liver biopsy is problematic, with exceptionally low inter- and intra-observer reliability shown in one study.

SUMMARY

The hepatitis associated with the SARS coronavirus, Isolated Ductular Hyperplasia in patients with liver function test abnormalities and other topics with pathologic relevance are reviewed.