Three-dimensional observations of the human hepatic artery (Arterial system in the liver)

Ultrasound-Targeted Microbubble Cavitation During Machine Perfusion Reduces Microvascular Thrombi and Graft Injury in a Rat Liver Model of Donation After Circulatory Death

BACKGROUND

Ischemic cholangiopathy is a process of bile duct injury that might result from peribiliary vascular plexus (PBP) thrombosis and remains a dreaded complication in liver transplantation from donors after circulatory death (DCD). The aim of this study was to propose a mechanical method of clot destruction to clear microvascular thrombi in DCD livers before transplantation.

METHODS

Sonothrombolysis (STL) is a process by which inertial cavitation of circulating microbubbles entering an ultrasound field create a high-energy shockwave at a microbubble-thrombus interface, causing mechanical clot destruction. The effectiveness of STL in DCD liver treatment remains unclear. We carried out STL treatment during normothermic, oxygenated, ex vivo machine perfusion (NMP), introducing microbubbles into the perfusate with the liver enveloped in an ultrasound field.

RESULTS

The STL livers showed reduction in hepatic arterial and PBP thrombus and decreases in hepatic arterial and portal venous flow resistance, reduced parenchymal injury as measured by aspartate transaminase release and oxygen consumption, and improved cholangiocyte function. Light and electron microscopy showed reduction of hepatic arterial and PBP thrombus in STL livers compared with controls and preserved hepatocyte structure, sinusoid endothelial morphology, and biliary epithelial microvilli.

CONCLUSION

In this model, STL improved flow and functional measures in DCD livers undergoing NMP. These data suggest a novel therapeutic approach to treat PBP injury in DCD livers, which may ultimately increase the pool of grafts available to patients awaiting liver transplantation.

Gastroduodenal artery disconnection during liver transplantation decreases non-anastomotic stricture incidence

BACKGROUND

The hepatic artery is the only blood source nourishing the biliary duct and associated with biliary complication after liver transplantation (LT). Gastroduodenal artery (GDA) disconnection increased proper hepatic artery flow. Whether this procedure attenuates biliary non-anastomotic stricture (NAS) is not clear.

METHODS

A total of 241 patients with LT were retrospectively analyzed. The patients were divided into the GDA disconnection (GDA-) and GDA preservation (GDA+) groups. Propensity score matching (PSM) was administrated to reduce bias. Logistic regression was conducted to analyze risk factors for biliary NAS before and after PSM. Postoperative complications were compared. Kaplan-Meier survival analysis and log-rank tests were performed to compare overall survival.

RESULTS

In all, 99 patients (41.1%) underwent GDA disconnection, and 49 (20.3%) developed NAS. Multivariate logistic regression revealed that GDA preservation (OR = 2.24, 95% CI: 1.11-4.53; P = 0.025) and model for end-stage liver disease (MELD) score > 15 (OR = 2.14, 95% CI: 1.12-4.11; P = 0.022) were risk factors for biliary NAS. PSM provided 66 pairs using 1:2 matching method, including 66 GDA disconnection and 99 GDA preservation patients. Multivariate logistic regression after PSM also showed that GDA preservation (OR = 3.15, 95% CI: 1.26-7.89; P = 0.014) and MELD score > 15 (OR = 2.41, 95% CI: 1.08-5.36; P = 0.031) were risk factors for NAS. When comparing complications between the two groups, GDA preservation was associated with a higher incidence of biliary NAS before and after PSM (P = 0.031 and 0.017, respectively). In contrast, other complications including early allograft dysfunction (P = 0.620), small-for-size graft syndrome (P = 0.441), abdominal hemorrhage (P = 1.000), major complications (Clavien-Dindo grade ≥ 3, P = 0.318), and overall survival (P = 0.088) were not significantly different between the two groups.

CONCLUSIONS

GDA disconnection during LT ameliorates biliary NAS incidence and may be recommended for application in clinical practice.

Contrast-Enhanced Ultrasound for Biliary Ischemia: A Possible New Clinical Indication

OBJECTIVES

Biliary perfusion is considered to contribute to biliary diseases, but routine imaging methods are insufficient to show it. This research investigated the ability of contrast-enhanced ultrasound (CEUS) for biliary perfusion in a biliary ischemia model.

METHODS

This research consisted of 2 parts. First, to determine whether CEUS enhancement of the tiny biliary wall represents biliary perfusion, a vascular tracer was used as a reference to evaluate the consistency with the enhancement of the biliary wall on CEUS and the staining by the vascular tracer under the conditions of occluded and recovered biliary perfusion. In the second part, the ability of CEUS for biliary ischemia was further evaluated with microvascular density measurement as a reference. The enhancement patterns were assigned CEUS scores, in which higher scores meant more decreased enhancement, and the diagnostic ability of CEUS was assessed by a receiver operating characteristic curve analysis.

RESULTS

The biliary wall was unstained by the vascular tracer and nonenhanced on CEUS when biliary perfusion was interrupted and was stained blue and enhanced after recovery. The biliary wall in the ischemia surgery group showed lower microvascular density measurements (P < .001), decreased enhancement levels (P < .001), and higher CEUS scores (P < .001). When a CEUS score of 3 or higher (obvious decrease of the biliary wall to hypoenhancement or nonenhancement in the arterial phase or rapid wash-out to nonenhancement in the portal venous phase) was applied, CEUS had sensitivity of 87.8%, specificity of 98.3%, accuracy of 93.8%, and an area under the receiver operating characteristic curve of 0.98.

CONCLUSIONS

Contrast enhancement of the biliary wall on CEUS represents biliary perfusion and has reasonably good diagnostic performance for biliary ischemia in an experimental animal setting.

Pathophysiology and Imaging Findings of Bile Duct Necrosis: A Rare but Serious Complication of Transarterial Therapy for Liver Tumors

Simple Summary

Bile duct necrosis (BDN) is rare but serious complication of transarterial therapy for liver tumors. During development of BDN, ischemia of the peribiliary vascular plexus (PBP) induces the disruption of the bile duct epithelial protection mechanism, causing necrosis of the surrounding tissue by the detergent action of exuded bile acids, and eventually a biloma forms. Once BDN starts, persistent tissue damage to the surrounding bile duct is induced by imbibed bile acids, and portal vein thrombosis may also be observed. On CT images, BDN shows similar findings to intrahepatic bile duct dilatation, and, therefore, it is sometimes misdiagnosed. Clinicians should be aware that although BDN and biloma can usually be treated conservatively, in the presence of symptoms such as moderate or severe infection or interval growth of the biloma, prompt treatment is essential to avoid lethal abscess formation and sepsis.

Abstract

Bile duct necrosis (BDN) with biloma formation is a type of ischemic bile duct injury that is one of the serious complications associated with transarterial therapies, such as transcatheter chemoembolization therapy (TACE), and radioembolization for hepatocellular carcinoma (HCC) and hepatic arterial infusion chemotherapy (HAIC) for metastatic liver cancer from colorectal carcinoma. In terms of the occurrence of BDN and subsequent biloma formation, ischemic injury to the peribiliary vascular plexus (PBP), the supporting vessel of bile duct epithelium, is thought to be intimately associated. In this paper, we first describe the anatomy, blood supply, and function of the intrahepatic bile duct, and then illustrate the pathophysiology of BDN, and finally present the imaging findings of BDN. Under the process of BDN formation, ischemia of the PBP induces the disruption of the bile duct epithelial protection mechanism that causes coagulation and fibrinoid necrosis of the surrounding tissue by the detergent action of exuded bile acids, and eventually a biloma forms. Once BDN occurs, persistent tissue damage to the surrounding bile duct is induced by imbibed bile acids, and portal vein thrombosis may also be observed. On pre-contrast and contrast-enhanced computed tomography (CT), BDN shows similar findings to intrahepatic bile duct dilatation, and, therefore, it is sometimes misdiagnosed. Differentiation of imaging findings on CT and ultrasound (US)/magnetic resonance (MR) imaging/MR cholangiopancreatography (MRCP) is important for correct diagnosis of BDN.

Hepatic artery classification based on three-dimensional CT

BACKGROUND

Precise classification of the hepatic artery is helpful for preoperative surgical planning in hepatobiliary-pancreatic surgery. However, the anatomy of hepatic arteries is variable. This study investigated anatomical variation using three-dimensional visualization and evaluation (3DVE) to develop a nomenclature system.

METHODS

The origin and course of the hepatic artery were tracked and analysed by using three-dimensional visualization of CT images acquired between 2013 and 2017. The new classification and nomenclature system, named CRL, was developed based on the origins of the common, right and left hepatic arteries.

RESULTS

Scans from 770 adults were evaluated. Preoperative 3DVE correlated better with surgical findings than the original CT images alone. Using the CRL classification system, hepatic arteries were divided into nine subtypes. Only 87·4-89·2 per cent of the hepatic arteries of 610 living-donor liver transplant donors were depicted in Michels', Hiatt's or Varotti's classification, compared with 100 per cent identified by the CRL classification. The CRL classification was validated against external data sets from previous studies, with 99·6-100·0 per cent of patients classified by the CRL system.

CONCLUSION

The CRL classification covers hepatic artery variants and may be used for planning liver surgery.

Immunofluorescence identifies distinct subsets of endothelial cells in the human liver

As well as systemic vascular endothelial cells, the liver has specialised sinusoidal endothelial cells (LSEC). LSEC dysfunction has been documented in many diseased states yet their phenotype in normal human liver has not been comprehensively assessed. Our aim was to improve characterisation of subsets of endothelial cells and associated pericytes in the human liver. Immunofluorescence microscopy was performed on normal human liver tissue samples to assess endothelial and structural proteins in a minimum of three donors. LSEC are distributed in an acinar pattern and universally express CD36, but two distinctive subsets of LSEC can be identified in different acinar zones. Type 1 LSEC are CD36^hiCD32⁻CD14⁻LYVE-1⁻ and are located in acinar zone 1 of the lobule, while Type 2 LSEC are LYVE-1⁺CD32^hiCD14⁺CD54⁺CD36^mid-lo and are located in acinar zones 2 and 3 of the lobule. Portal tracts and central veins can be identified using markers for systemic vascular endothelia and pericytes, none of which are expressed by LSEC. In areas of low hydrostatic pressure LSEC are lined by stellate cells that express the pericyte marker CD146. Our findings identify distinctive populations of LSEC and distinguish these cells from adjacent stellate cells, systemic vasculature and pericytes in different zones of the liver acinus.

Importance Rat Liver Morphology and Vasculature in Surgical Research

BACKGROUND The laboratory rat is one of the most popular experimental models for the experimental surgery of the liver. The objective of this study was to investigate the morphometric parameters, physiological data, differences in configuration of liver lobes, biliary system, and vasculature (arteries, veins, and lymphatic vessels) of the liver in laboratory rats. In addition, this study supports the anatomic literature and identified similarities and differences with human and other mammals. MATERIAL AND METHODS Forty laboratory rats were dissected to prepare corrosion casts of vascular system specimens (n=20), determine the lymph vessels and lymph nodes (n=10), and for macroscopic anatomical dissection (n=10) of the rat liver. The results are listed in percentages. The anatomical nomenclature of the liver morphology, its arteries, veins, lymph nodes, and lymphatic vessels are in accordance with Nomina Anatomica Veterinaria. RESULTS We found many variations in origin, direction, and division of the arterial, venous, and lymphatic systems in rat livers, and found differences in morphometric parameters compared to results reported by other authors. The portal vein was formed by 4 tributaries in 23%, by 3 branches in 64%, and by 2 tributaries in 13%. The liver lymph was drained to the 2 different lymph nodes. The nomenclature and morphological characteristics of the rat liver vary among authors. CONCLUSIONS Our results may be useful for the planing of experimental surgery and for cooperation with other investigation methods to help fight liver diseases in human populations.

Functional Immune Anatomy of the Liver-As an Allograft

The liver is an immunoregulatory organ in which a tolerogenic microenvironment mitigates the relative "strength" of local immune responses. Paradoxically, necro-inflammatory diseases create the need for most liver transplants. Treatment of hepatitis B virus, hepatitis C virus, and acute T cell-mediated rejection have redirected focus on long-term allograft structural integrity. Understanding of insults should enable decades of morbidity-free survival after liver replacement because of these tolerogenic properties. Studies of long-term survivors show low-grade chronic inflammatory, fibrotic, and microvascular lesions, likely related to some combination of environment insults (i.e. abnormal physiology), donor-specific antibodies, and T cell-mediated immunity. The resultant conundrum is familiar in transplantation: adequate immunosuppression produces chronic toxicities, while lightened immunosuppression leads to sensitization, immunological injury, and structural deterioration. The "balance" is more favorable for liver than other solid organ allografts. This occurs because of unique hepatic immune physiology and provides unintended benefits for allografts by modulating various afferent and efferent limbs of allogenic immune responses. This review is intended to provide a better understanding of liver immune microanatomy and physiology and thereby (a) the potential structural consequences of low-level, including allo-antibody-mediated injury; and (b) how liver allografts modulate immune reactions. Special attention is given to the microvasculature and hepatic mononuclear phagocytic system.

Application of contrast-enhanced ultrasound after liver transplantation: Current status and perspectives

Liver transplantation is an effective treatment for patients with end-stage liver disease. Accurate imaging evaluation of the transplanted patient is critical for ensuring that the limited donor liver is functioning appropriately. Ultrasound contrast agents (UCAs), in combination with contrast-specific imaging techniques, are increasingly accepted in clinical use for the assessment of the hepatic vasculature, bile ducts and liver parenchyma in pre-, intra- and post-transplant patients. We describe UCAs, their technical requirements, the recommended clinical indications, image interpretation and the limitations for contrast-enhanced ultrasound applications in liver transplantation.

Ratio of hepatic arterial flow to recipient body weight predicts biliary complications after deceased donor liver transplantation

OBJECTIVES

Adequate hepatic arterial (HA) flow to the bile duct is essential in liver transplantation. This study was conducted to determine if the ratio of directly measured HA flow to weight is related to the occurrence of biliary complications after deceased donor liver transplantation.

METHODS

A retrospective review of 2684 liver transplants carried out over a 25-year period was performed using data sourced from a prospectively maintained database. Rates of biliary complications (biliary leaks, anastomotic and non-anastomotic strictures) were compared between two groups of patients with HA flow by body weight of, respectively, <5 ml/min/kg (n = 884) and ≥5 ml/min/kg (n = 1800).

RESULTS

Patients with a lower ratio of HA flow to weight had higher body weight (92 kg versus 76 kg; P < 0.001) and lower HA flow (350 ml/min versus 550 ml/min; P < 0.001). A lower ratio of HA flow to weight was associated with higher rates of biliary complications at 2 months, 6 months and 12 months (19.8%, 28.2% and 31.9% versus 14.8%, 22.4% and 25.8%, respectively; P < 0.001).

CONCLUSIONS

A ratio of HA flow to weight of < 5 ml/min/kg is associated with higher rates of biliary complications. This ratio may be a useful parameter for application in the prevention and early detection of biliary complications.

New diagnosis and therapy model for ischemic-type biliary lesions following liver transplantation--a retrospective cohort study

Ischemic-type biliary lesions (ITBLs) are a major cause of graft loss and mortality after orthotopic liver transplantation (OLT). Impaired blood supply to the bile ducts may cause focal or extensive damage, resulting in intra- or extrahepatic bile duct strictures or dilatations that can be detected by ultrasonography, computed tomography, magnetic resonance cholangiopancreatography, and cholangiography. However, the radiographic changes occur at an advanced stage, after the optimal period for therapeutic intervention. Endoscopic retrograde cholangio-pancreatography (ERCP) and percutaneous transhepatic cholangiodrainage (PTCD) are the gold standard methods of detecting ITBLs, but these procedures cannot be used for continuous monitoring. Traditional methods of follow-up and diagnosis result in delayed diagnosis and treatment of ITBLs. Our center has used the early diagnosis and intervention model (EDIM) for the diagnosis and treatment of ITBLs since February 2008. This model mainly involves preventive medication to protect the epithelial cellular membrane of the bile ducts, regular testing of liver function, and weekly monitor of contrast-enhanced ultrasonography (CEUS) to detect ischemic changes to the bile ducts. If the liver enzyme levels become abnormal or CEUS shows low or no enhancement of the wall of the hilar bile duct during the arterial phase, early ERCP and PTCD are performed to confirm the diagnosis and to maintain biliary drainage. Compared with patients treated by the traditional model used prior to February 2008, patients in the EDIM group had a lower incidence of biliary tract infection (28.6% vs. 48.6%, P = 0.04), longer survival time of liver grafts (24±9.6 months vs. 17±12.3 months, P = 0.02), and better outcomes after treatment of ITBLs.

Pathogenesis of Portal Cavernoma Cholangiopathy: Is it Compression by Collaterals or Ischemic Injury to Bile Ducts During Portal Vein Thrombosis?

The pathogenesis of portal cavernoma cholangiopathy (PCC) is important as it can impact the choice of treatment modalities. PCC consists of a reversible component, which resolves by decompression of collaterals as well as a fixed component, which persists despite the decompression of collaterals. The reversible component is due to compression by large collaterals located adjacent to the bile duct as well as possibly intracholedochal varices. The fixed component is likely to be due to ischemia at the time of portal vein thrombosis, local ischemia by compression as well as encasement by a solid tumor-like cavernoma comprising of fibrous hilar mass containing multiple tiny collateral veins rather than markedly enlarged portal collaterals. Although cholangiographic abnormalities in portal hypertension are common, the prevalence of symptomatic PCC is low. This is likely to be related to the cause of portal hypertension, the duration of portal hypertension and possibly the pattern of occlusion of the splenoportal axis. There may possibly be higher prevalence of symptomatic PCC in extension of the thrombosis to the splenomesentric veins.

Experiences of microsurgical reconstruction for variant hepatic artery in living donor liver transplantation

There is an emergent need for improving the microsurgical technique of variant arterial anastomosis to reduce the often seen surgery-related complications. We describe in this article our experience in improving this technique, in 73 living donor liver grafts (64 right lobes, 9 left lobes) in patients with end-stage liver disease during living donor liver transplantation. The hepatic arteries were evaluated preoperatively with computed tomography and magnetic resonance angiography. In this series, 13 grafts (17.80 %) with variant hepatic artery were conducted arterioplasty on a back-table under a loupe or a high-power microscope, which included one recipient in situ interposition vessel graft of recipient proper hepatic artery for artery reconstruction. The back-table reconstruction time was 16 ± 5.6 min. No arterial thrombosis was found in these cases during the 6-month postoperative follow-up. On the basis of our experience, we suggest that back-table microsurgical plasty for graft with arterial variation should be applied to minimize operative difficulties and to avoid arterial complications in living donor liver transplantation.

Revealing impaired blood supply to the bile ducts on contrast-enhanced ultrasound: a novel diagnosis method to ischemic-type biliary lesions after orthotropic liver transplantation

Ischemic-type biliary lesions (ITBLs) are a major source of morbidity and mortality after orthotropic liver transplantation (OLT). The study determines diagnostic accuracy of contrast-enhanced ultrasound (CEUS) in diagnosing ITBLs. Nine healthy volunteers, six OLT recipients without complications, 36 OLT patients with complications (12 without ITBLs and 24 with ITBLs) underwent CEUS. Two radiologists reviewed the sonograms of the hilar bile duct wall and established specific criteria used to detect ITBLs. Next, the sonograms of six OLT recipients without complications and 36 patients with complications (12 without ITBLs and 24 with ITBLs) were retrospectively reviewed by two other independent, blinded radiologists. The sensitivity, specificity and accuracy of CEUS were evaluated. The main feature differentiating ITBLs from three other groups was non- or hypo-enhancement of the hilar bile duct wall in arterial phase (all p < 0.05), which was selected as the primary criterion for subsequent study. The sensitivity, specificity and accuracy were 66.7%, 88.9% and 76.2% for reader 1 and 62.5%, 88.9% and 73.8% for reader 2, respectively. A good interobserver agreement (κ = 0.85) was achieved. In this study, CEUS shows promise of detection of ITBLs by revealing impaired blood supply to the bile ducts, but more studies will be needed to establish its usefulness.

Hepatic sinusoidal endothelium avidly binds platelets in an integrin-dependent manner, leading to platelet and endothelial activation and leukocyte recruitment

Platelets have recently been shown to drive liver injury in murine models of viral hepatitis and promote liver regeneration through the release of serotonin. Despite their emerging role in inflammatory liver disease, little is known about the mechanisms by which platelets bind to the hepatic vasculature. Therefore, we referenced public expression data to determine the profile of potential adhesive receptors expressed by hepatic endothelium. We then used a combination of tissue-binding and flow-based endothelial-binding adhesion assays to show that resting platelets bind to human hepatic sinusoidal endothelial cells and that the magnitude of adhesion is greatly enhanced by thrombin-induced platelet activation. Adhesion was mediated by the integrins Gp1b, αIIbβIII, and αvβ3, as well as immobilized fibrinogen. Platelet binding to hepatic endothelial cells resulted in NF-κB activation and increased chemokine secretion. The functional relevance of platelet binding was confirmed by experiments that showed markedly increased binding of neutrophils and lymphocytes to hepatic endothelial cells under shear conditions replicating those found in the hepatic sinusoid, which was in part dependent on P-selectin expression. Thus the ability of platelets to activate endothelium and promote leukocyte adhesion may reflect an additional mechanism through which they promote liver injury.

Quantitative modeling of the physiology of ascites in portal hypertension

Although the factors involved in cirrhotic ascites have been studied for a century, a number of observations are not understood, including the action of diuretics in the treatment of ascites and the ability of the plasma-ascitic albumin gradient to diagnose portal hypertension. This communication presents an explanation of ascites based solely on pathophysiological alterations within the peritoneal cavity. A quantitative model is described based on experimental vascular and intraperitoneal pressures, lymph flow, and peritoneal space compliance. The model's predictions accurately mimic clinical observations in ascites, including the magnitude and time course of changes observed following paracentesis or diuretic therapy.

Vascular disorders of the liver

Hepatic vascular disorders are a set of conditions that may be acute, or may be insidious and subclinical for many years. They can be organized into 3 categories: obstruction to hepatic vascular inflow, obstruction to blood flow through the liver, and obstruction to hepatic vascular outflow. In the first category are portal vein thrombosis, hepatic artery thrombosis, and presinusoidal causes of vascular obstruction. In the second category are sickle cell disease, disseminated intravascular coagulation, intrasinusoidal malignancy, and infection. In the third category are macroscopic hepatic venous thrombosis, thrombosis of the retrohepatic inferior vena cava, and venoocclusive disease. There are 2 nodular conditions of the liver that are not neoplastic but the result of occlusion of hepatic vasculature with compensatory hyperplasia of well-vascularized parenchyma. Hepatic vascular disorders constitute a heterogeneous group of conditions that must be considered in the differential diagnosis of any patient with hepatic compromise.

A distinct nitric oxide and adenosine A1 receptor dependent hepatic artery vasodilatatory response in the CCl-cirrhotic liver

Increase of portal venous vascular resistance is counteracted by decrease of hepatic arterial vascular resistance (hepatic arterial buffer response). This process is mediated by adenosine in normal livers. In cirrhosis, hepatic arterial vascular resistance is decreased but the involvement of adenosine in this process is unknown. The aim of our study was to identify the signalling pathway responsible for the decreased hepatic arterial resistance in cirrhotic livers.

METHODS

Cirrhosis was induced by CCl(4). Using a bivascular liver perfusion dose-response curves to adenosine of the HA were performed in the presence and the absence of pan-adenosine blocker (8-SPT), A1 blocker (caffeine) or nitric oxide synthase-blocker (l-NMMA) after preconstriction with an alpha1-agonist (methoxamine). Western blot of the HA were used to measure the density of the A1 and A2a receptors.

RESULTS

Adenosine caused a dose dependent relaxation of the hepatic artery of both cirrhotic and control animals that were blocked in both groups by 8-SPT (P<0.02). The response to adenosine was greater in cirrhotic rats (P=0.016). Both l-NMMA (P=0.003) and caffeine reduced the response to adenosine in cirrhotic but not in control animals. Western blot analysis showed a higher density of A1 and a lower density of A2a receptor in cirrhotic animals (P<0.05).

CONCLUSION

The adenosine-induced vasodilatation of the HA is increased in cirrhotic rats suggesting a role for adenosine-NO in the decreased hepatic arterial vascular resistance found in cirrhosis. This significantly greater response in cirrhosis by the A1 receptor follows the same pathway that is seen in hypoxic conditions in extra-hepatic tissues.

Evaluation of the microcirculatory disturbance of biliary ischemia after liver transplantation with contrast-enhanced ultrasound: preliminary experience

The aim of this study was to determine the efficacy of contrast-enhanced ultrasound for depicting the perfusion of hilar bile ducts in ischemic-type biliary lesions after orthotopic liver transplantation. Thirteen transplant recipients with ischemic-type biliary lesions and 12 patients without ischemic-type biliary lesions underwent ultrasound examinations after the injection of 1.5 mL of an intravenous contrast agent. The enhancement of the hilar bile duct wall in the arterial, portal venous, and late phases was qualitatively graded as higher, equal, lower, or none with respect to that of the adjacent liver parenchyma. No or low contrast enhancement was seen in 10 of 13 patients (76.90%) with biliary ischemia, whereas increased contrast enhancement with respect to the normal liver parenchyma was found in all 12 patients without biliary ischemia. The difference in the enhancement patterns between the 2 groups was significant (P = 0.0001). In conclusion, contrast-enhanced ultrasound is a new imaging modality to depict perfusion of the hilar bile duct. No or low contrast enhancement of the bile duct wall in the arterial phase may reflect the microcirculatory disturbance of biliary ischemia and may contribute to its early diagnosis.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

Portal venous arterialization resulting in increased portal inflow and portal vein wall thickness in rats

AIM: To explore the influence of portal vein hemo-dynamic changes after portal venous arterialization (PVA) on peribiliary vascular plexus (PVP) morphological structure and hepatic pathology, and to establish a theoretical basis for the clinical application of PVA.

METHODS: Sprague-Dawley rats were randomly divided into control and PVA groups. After PVA, hemodynamic changes of the portal vein and morphological structure of hepatohilar PVP were observed using Doppler ultrasound, liver function tests, ink perfusion transparency management and three-dimensional reconstruction of computer microvisualization, and pathological examination was performed on tissue from the bile duct wall and the liver.

RESULTS: After PVA, the cross-sectional area and blood flow of the portal vein were increased, and the increase became more significant over time, in a certain range. If the measure to limit the flow in PVA was not adopted, the high blood flow would lead to dilatation of intrahepatic portal vein and its branches, increase in collagen and fiber degeneration in tunica intima. Except glutamic pyruvic transaminase (GPT), other liver function tests were normal.

CONCLUSION: Blood with a certain flow and oxygen content is important for filling the PVP and meeting the oxygen requirement of the bile duct wall. After PVA, It is the anatomic basis to maintain normal morphology of hepatohilar bile duct wall that the blood with high oxygen content and high flow in arterialized portal vein may fill PVP by collateral vessel reflux. A adequate measure to limit blood flow is necessary in PVA.

Nitric oxide and vascular remodeling modulate hepatic arterial vascular resistance in the isolated perfused cirrhotic rat liver

BACKGROUND/AIMS

Hepatic arterial resistance is modulated by the hepatic arterioles but the role of NO and vascular remodeling in hepatic arterial resistance in cirrhosis is unknown.

METHODS

Cirrhosis was induced by CCl(4) or BDL. Using a bivascular liver perfusion dose-responses curves to methoxamine were obtained from the hepatic artery in absence and presence of L-NMMA. Lumen-diameter, wall thickness and number of smooth muscle nuclei were quantitated in the arteries using image analysis.

RESULTS

Hepatic arterial resistance and the response to methoxamine were lower in cirrhosis compared to controls (p< or = 0.04) and lower in BDL compared to CCl(4) (p< or = 0.01). L-NMMA increased the response to methoxamine in CCl(4) (p=0.002) and BDL (p=0.05) but corrected the response only in CCl(4) (p=n.s. vs. control). Wall thickness and the number of smooth muscle nuclei were significantly smaller in cirrhosis compared to controls (p<0.05) and the number of nuclei was also lower in BDL compared to CCl(4) (p=0.005).

CONCLUSIONS

NO is the main modulator of hepatic arterial resistance in CCl(4) but not in BDL. Intrahepatic arterial remodeling is present in both cirrhotic models but is greater in BDL. This indicates a larger role of structural changes in the control of hepatic arterial resistance in BDL.

Immune interactions in hepatic fibrosis

Liver cirrhosis is caused by iterative cycles of tissue injury, inflammation, and repair. Although most causes of acute hepatitis resolve without scarring, chronic hepatitis is associated with persistent inflammation and matrix remodeling, which leads to fibrosis and, eventually, cirrhosis. The mechanisms that govern wound healing involve interactions between the innate and adaptive immune systems and stromal cells within a microenvironment composed of cytokines, growth factors, and modified matricellular proteins. The immune system plays a central role in the regulation of fibrosis, tissue repair, and recovery that is vital for the maintenance of tissue homeostasis. Chronic inflammation and fibrosis are inextricably linked and the cellular interactions between immune effector cells, local fibroblasts, and tissue macrophages at sites of scar formation determine the outcome of liver injury and the development of scarring.

Vascular development and differentiation during human liver organogenesis

The vascular architecture of the human liver is established at the end of a complex embryological history. The hepatic primordium emerges at the 4th week and is in contact with two major venous systems of the fetal circulation: the vitelline veins and the umbilical veins. The fetal architecture of the afferent venous circulation of the liver is acquired between the 4th and the 6th week. At the end of this process, the portal vein is formed from several distinct segments of the vitelline veins; the portal sinus, deriving from the subhepatic intervitelline anastomosis, connects the umbilical vein, which is the predominant vessel of the fetal liver, to the portal system; the ductus venosus connects the portal sinus to the vena cava inferior. At birth, the umbilical vein and the ductus venosus collapse; the portal vein becomes the only afferent vein of the liver. The efferent venous vessels of the liver derive from the vitelline veins and are formed between the 4th and the 6th week. The hepatic artery forms at the 8th week; intrahepatic arterial branches progressively extend from the central to the peripheral areas of the liver between the 10th and the 15th week. Hepatic sinusoids appear very early, as soon as hepatic cords invade the septum transversum at the 4th week. They then progressively acquire their distinctive structural and functional characters, through a multistage process. Vascular development and differentiation during liver organogenesis is, therefore, a unique process; many of the cellular and molecular mechanisms involved remain poorly understood.

Hemodynamics in the isolated cirrhotic liver

Increased intrahepatic resistance is the initial event to the increased portal pressure and development portal hypertension in cirrhosis. Narrowing of the sinusoids due to anatomic changes is the main component of the increased intrahepatic resistance. However, a dynamic component is also involved in the increased vascular tone in cirrhosis. The imbalance between the hyperresponsiveness and overproduction of vasoconstrictors (mainly endothelin-1 and cyclooxygenase-derived prostaglandins) and the hyporesponsiveness and impaired production of vasodilators [mainly nitric oxide (NO)] are the mechanisms responsible of the increased vascular tone in the sinusoidal/postsinusoidal area. In contrast, the vascular resistance in the hepatic artery, which is determined in the presinusoidal area, is decreased due to increased vasodilators (NO and adenosine). This suggests different availabilities of NO in the intrahepatic circulation with preserved production in the presinusoidal area and impaired production in the sinusoidal/postsinusoidal area.

An integrated approach to model hepatic drug clearance

It has been well accepted that hepatic drug extraction depends on the blood flow, vascular binding, transmembrane barriers, transporters, enzymes and cosubstrate and their zonal heterogeneity. Models of hepatic drug clearances have been appraised with respect to their utility in predicting drug removal by the liver. Among these models, the "well-stirred" model is the simplest since it assumes venous equilibration, with drug emerging from the outflow being in equilibrium with drug within the liver, and the concentration is the same throughout. The "parallel tube" and dispersion models, and distributed model of Goresky and co-workers have been used to account for the observed sinusoidal concentration gradient from the inlet and outlet. Departure from these models exists to include heterogeneity in flow, enzymes, and transporters. This article utilized the physiologically based pharmacokinetic (PBPK) liver model and its extension that include heterogeneity in enzymes and transporters to illustrate how in vitro uptake and metabolic data from zonal hepatocytes on transport and enzymes may be used to predict the kinetics of removal in the intact liver; binding data were also necessary. In doing so, an integrative platform was provided to examine determinants of hepatic drug clearance. We used enalapril and digoxin as examples, and described a simple liver PBPK model that included transmembrane transport and metabolism occurring behind the membrane, and a zonal model in which the PBPK model was expanded three sets of sub-compartments that are arranged sequentially to represent zones 1, 2, and 3 along the flow path. The latter model readily accommodated the heterogeneous distribution of hepatic enzymes and transporters. Transport and metabolic data, piecewise information that served as initial estimates, allowed for the unknown efflux and other intrinsic clearances to be estimated. The simple or zonal PBPK model provides predictive views on the hepatic removal of drugs and metabolites.

Human hepatic sinusoidal endothelial cells can be distinguished by expression of phenotypic markers related to their specialised functions in vivo

The hepatic sinusoids are lined by a unique population of hepatic sinusoidal endothelial cells (HSEC), which is one of the first hepatic cell populations to come into contact with blood components. However, HSEC are not simply barrier cells that restrict the access of blood-borne compounds to the parenchyma. They are functionally specialised endothelial cells that have complex roles, including not only receptor-mediated clearance of endotoxin, bacteria and other compounds, but also the regulation of inflammation, leukocyte recruitment and host immune responses to pathogens. Thus understanding the differentiation and function of HSEC is critical for the elucidation of liver biology and pathophysiology. This article reviews methods for isolating and studying human hepatic endothelial cell populations using in vitro models. We also discuss the expression and functions of phenotypic markers, such as the presence of fenestrations and expression of VAP-1, Stabilin-1, L-SIGN, which can be used to identify sinusoidal endothelium and to permit discrimination from vascular and lymphatic endothelial cells.

Dynamics of the vascular profile of the finer branches of the biliary tree in normal and diseased human livers

BACKGROUND/AIMS

Results of our previous studies supported the concept that in the human liver, the smallest ramification of the biliary tree, the bile ductules, might contain hepatic progenitor cells. An insufficient proliferative response and loss of bile ductules preceded bile duct loss whereas preservation of bile ductules mitigated bile duct loss.

METHODS

Presently we investigated the vascular profile of the bile ductules in diseased human livers and livers showing normal histological features as controls, using CD34, CK7 and alphaSMA antibodies in a double immunolabeling technique. VEGF-A expression was also studied. In control livers bile ductules traversed the boundaries of the portal tract into the lobule as ductular-vascular units, in a pattern outlining the classic hexagonal lobule, following the vascular septa. The latter are thought to be extensions of portal veins. In diseased states the two structures reacted in unison. Increased or decreased numbers of ductules were consistently accompanied by similar changes of accompanying microvessels. Increased numbers of ductules and microvessels were paralleled by increased ductular expression of VEGF-A.

RESULTS

Our data support the concept that the smallest branches of the biliary tree might have their own vascular supply and that the ductules might in turn maintain their vasculature during regenerative processes.

The finest branches of the biliary tree might induce biliary vascularization necessary for biliary regeneration

BACKGROUND/AIMS

The finer branches of the biliary tree play an important role in biliary regeneration. They are consistently escorted by microvessels. Defects in the vascularization of these structures could impair bile duct regeneration. Therefore, we investigated the pattern of the escorting microvessels during the development of bile duct loss in the human liver, using chronic rejection as a model.

METHODS

The number of interlobular bile ducts, bile ductules and extraportal biliary cells with and without escorting microvessels and the expression of VEGF-A were studied in follow-up biopsies of 12 patients with chronic rejection and 16 control patients with acute rejection without progression to chronic rejection.

RESULTS

The controls showed a proliferation of bile ductules at 1-week and 1-month. Proliferation of bile ductules without microvessels preceded proliferation of bile ductules with microvessels. Proliferation of the microvascular compartment followed biliary proliferation. This sequence of events was not observed in the chronic rejection group, in which all biliary structures decreased in time. VEGF-A expression was increased at 1-week and 1-month in both groups.

CONCLUSIONS

An immediate proliferative response of the finer branches of the biliary tree followed by proliferation of the microvascular compartment after biliary injury seems to be a prerequisite for bile duct regeneration.

Medial thickening of hepatic artery branches in biliary atresia. A morphometric study

BACKGROUND/PURPOSE

Medial layer hypertrophy of hepatic arterial branches may be associated with biliary atresia (BA) pathogenesis. This study aimed at evaluating medial layer thickness in hepatic arterial branches at portoenterostomy and liver transplantation.

METHODS

The authors evaluated 1274 arterial branches both in BA cases and in control subjects involving a total of 1108 arterioles and 166 arteries. Arterial branch characteristics were morphometrically evaluated in 47 BA patients at the time of portoenterostomy. Controls were patients with intrahepatic cholestasis (n = 3), immature neonates (n = 7), and infants (n = 7) without liver disease. Progression of medial layer thickening between the time of portoenterostomy and transplantation was evaluated in 7 BA patients. Biliary atresia patients at the time of transplantation were compared with non-BA-transplanted patients (n = 4).

RESULTS

The arterial medial layer of BA cases at portoenterostomy was thicker than that of infants without liver disease ( P = .03). The arterial medial thickness increased during the interval between portoenterostomy and transplantation ( P = .05). Arterioles and arteries with thickened medial layers were found in transplanted BA patients but not in patients transplanted for other liver diseases (P = .05 and P = .01). Thickening of the medial layer of the hepatic arteries was associated with focal distribution of interlobular bile ducts in portal spaces in BA ( P = .02).

CONCLUSIONS

In BA, there is a progressive thickening of the arterial medial layer, suggestive of vascular remodeling, which is associated to the disappearance of interlobular bile ducts.

Hepatic microcirculation assessed by positron emission tomography of first-pass ammonia metabolism in porcine liver

AIMS/BACKGROUND

Intrahepatic branching of the hepatic artery (HA) to liver microcirculatory units, the acini, is more heterogeneous than that of the portal vein (PV). Furthermore, part of HA blood enters the sinusoid partially downstream between the in- and outlets. We examined the effects of these vascular variations on porcine hepatic first-pass ammonia metabolism, which is characterised by high uptake and separate periportal urea and perivenous glutamine formations.

METHODS

(13)NH(3) was given via the PV, HA or caval vein, followed by 22 min dynamic liver positron emission tomography (PET) recordings in six pigs. Heterogeneity of liver (13)N-metabolism was quantified by the coefficient of variation of tissue (13)N-radioactivity measured 10 min after tracer infusion. Sinusoidal zonal clearances of (13)NH(3) into (13)N-urea and (13)N-glutamine were calculated by kinetic PET modelling.

RESULTS

Liver metabolic heterogeneity was 0.65+/-0.20 (mean+/-SD, n=6) following (13)NH(3)-infusion into HA, 0.34+/-0.17 into PV and 0.10+/-0.02 into the caval vein. Clearance of (13)NH(3) to (13)N-urea was of similar magnitude following (13)NH(3) administration into HA and PV: 0.27+/-0.11 ml/min/g (mean+/-SD) and 0.29+/-0.09 ml/min/g, respectively. Clearances of (13)NH(3) to (13)N-glutamine when (13)NH(3) was given into HA and PV were also similar: 0.47+/-0.18 and 0.50+/-0.13 ml/min/g, respectively.

CONCLUSIONS

The present measurements of the hepatic metabolism of (13)NH(3) showed metabolic heterogeneity compatible with variation of the HA supply of the acini. Second, results of PET modelling of the sinusoidal zonation metabolism of (13)NH(3) to (13)N-urea and to (13)N-glutamine did not indicate metabolically important partial downstream arterial entry into the sinusoids.

Microsurgical reconstruction of hepatic artery during living donor liver transplantation

Living donor liver transplantation (LDLT) has become a well-recognized treatment modality for patients with end-stage liver disease. Arterial reconstruction during LDLT is perhaps the most important aspect of the grafting procedure. Although microsurgical hepatic artery reconstruction has become the essential technique in LDLT, it poses significant challenges even to experienced microsurgeons. In this report, the experiences of 155 microsurgical reconstructions of the hepatic artery in 150 LDLTs were reviewed, and the problems that were encountered and the solutions are discussed. From June 1999-March 2004 150 LDLTs were performed on 148 recipients at Ege University Organ Transplantation and Research Center. Hepatic arterial thrombosis was encountered in 3 patients. Microsurgical technique has overcome the difficulties in LDLT. This has increased liver transplantations in the presence of limited cadaver grafts and has decreased the patient mortality in the waiting list.

Lymphocyte recruitment to the liver in alcoholic liver disease

The normal liver contains a large number of lymphocytes, which include not only specialized natural killer (NK) and NKT cells but also CD4 and CD8 T cells. Whereas some of these cells are terminally differentiated effector cells that are destined to die by apoptosis, many of them are not and include immunocompetent cells that traffic through the liver to provide continuing immune surveillance as well as epithelial-associated effector T cells. In alcoholic liver disease the number of lymphocytes in the liver increases and the type and distribution of these infiltrating cells will determine the nature of the inflammation. For instance, a predominance of parenchymal inflammation is a feature of alcoholic hepatitis, whereas a predominantly portal infiltrate is a feature of cirrhosis. In this article we discuss the molecular mechanisms that regulate the entry of lymphocytes to the inflamed liver in alcoholic hepatitis. Lymphocytes play a critical role in regulating the immune/inflammatory response to alcohol, and understanding how these cells are recruited to the liver has important implications for understanding the pathogenesis of alcoholic liver disease in which parenchymal infiltration is a critical determinant of disease progression. Aberrant recruitment and retention of lymphocytes in the liver may explain why some patients with alcoholic liver disease show progressive inflammatory damage whereas in others the disease takes a more indolent course. Similarly, leukocyte recruitment may present new therapeutic targets in which lymphocyte recruitment to the specific liver compartments can be inhibited, thereby minimizing tissue damage whilst leaving generalized lymphocyte recirculation intact. Potentially the most exciting potential is to modulate the nature of the lymphocyte subsets recruited to the liver, so that harmful cells are excluded and beneficial subsets are preferentially recruited.

Hepatobiliary pathology

Technologic advances using cDNA microarray hybridization, liver diseases characterized by mitochondrial DNA depletion, and new work characterizing bile salt transport problems in familial intrahepatic cholestasis syndromes were some of the major highlights of this past year. Analysis of normal livers by cDNA microarrays disclosed 2418 unique gene transcripts encoding a host of cellular structural and functional proteins. This technique was also applied to hepatocellular carcinoma, where enhanced expression of a number of genes involved in antiapoptosis and cell transformation may shed additional light on the process of hepatocarcinogenesis. Mitochondrial DNA depletion seen in Navajo neurohepatopathy and in respiratory chain disorders of infancy was associated with cholestasis and cirrhosis in the former and microvesicular steatosis and oncocytic transformation (mitochondrial hyperplasia) in the latter. Pathologists who routinely examine liver biopsies after liver or bone marrow transplantation should be aware of unusual biopsy features that mimic other diseases, such as the autoimmune hepatitis-like syndrome that may follow liver transplantation and chronic graft-versus-host disease that clinically and pathologically resembles acute hepatitis.