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

Ductal plates in hepatic ductular reactions. Hypothesis and implications. II. Ontogenic liver growth in childhood

This article discusses the processes of bile duct growth and new lobule formation in the liver during childhood in the light of the ductal plate (DP) hypothesis. Unlike in other organs in which tubular elongation and branching ends with the creation of the organ-specific terminal differentiation products, in the liver a steadily enlarging parenchymal mass needs to establish continuity of its canalicular network with the existing bile duct system. The hypothesis suggests that this occurs by DP formation, like in the embryonic liver, and further assumes that pathological ductular reactions (DRs) induced by cholestasis or hypoxia are amplified equivalents of similar mechanisms operating at low level during liver growth. The concept is confronted with data on porcine liver growth, since swine and non-swine liver growth is thought to be comparable. Relative bile acid load may be the driving force for establishment of new canaliculo-ductular connections, supported in zones of relative hypoxia by hypoxia-inducible factor 1 alpha secreted by hepatocytes. The latter mechanism is at the base for induction of appropriate vascular changes in selected sinusoids, resulting in the development of portal inlet venules and additional draining central veins. The process gives rise to the formation of new single lobules by formation of new portal tracts or to the transformation of single lobules in compound lobules by development of new vascular septa. The concept of postnatal DP formation is important in the elucidation of several unexplained findings in adult liver diseases.

Experimental obstructive cholestasis: the wound-like inflammatory liver response

Obstructive cholestasis causes hepatic cirrhosis and portal hypertension. The pathophysiological mechanisms involved in the development of liver disease are multiple and linked. We propose grouping these mechanisms according to the three phenotypes mainly expressed in the interstitial space in order to integrate them.Experimental extrahepatic cholestasis is the model most frequently used to study obstructive cholestasis. The early liver interstitial alterations described in these experimental models would produce an ischemia/reperfusion phenotype with oxidative and nitrosative stress. Then, the hyperexpression of a leukocytic phenotype, in which Kupffer cells and neutrophils participate, would induce enzymatic stress. And finally, an angiogenic phenotype, responsible for peribiliary plexus development with sinusoidal arterialization, occurs. In addition, an intense cholangiocyte proliferation, which acquires neuroendocrine abilities, stands out. This histopathological finding is also associated with fibrosis.It is proposed that the sequence of these inflammatory phenotypes, perhaps with a trophic meaning, ultimately produces a benign tumoral biliary process - although it poses severe hepatocytic insufficiency. Moreover, the persistence of this benign tumor disease would induce a higher degree of dedifferentiation and autonomy and, therefore, its malign degeneration.

Epithelial expression of angiogenic growth factors modulate arterial vasculogenesis in human liver development

Intrahepatic bile ducts maintain a close anatomical relationship with hepatic arteries. During liver ontogenesis, the development of the hepatic artery appears to be modulated by unknown signals originating from the bile duct. Given the capability of cholangiocytes to produce angiogenic growth factors and influence peribiliary vascularization, we studied the immunohistochemical expression of vascular endothelial growth factor (VEGF), angiopoietin-1, angiopoietin-2, and their cognate receptors (VEGFR-1, VEGFR-2, Tie-2) in fetal human livers at different gestational ages and in mice characterized by defective biliary morphogenesis (Hnf6(-/-)). The results showed that throughout the different developmental stages, VEGF was expressed by developing bile ducts and angiopoietin-1 by hepatoblasts, whereas their cognate receptors were variably expressed by vascular cells according to the different maturational stages. Precursors of endothelial and mural cells expressed VEGFR-2 and Tie-2, respectively. In immature hepatic arteries, endothelial cells expressed VEGFR-1, whereas mural cells expressed both Tie-2 and Angiopoietin-2. In mature hepatic arteries, endothelial cells expressed Tie-2 along with VEGFR-1. In early postnatal Hnf6(-/-) mice, VEGF-expressing ductal plates failed to incorporate into the portal mesenchyma, resulting in severely altered arterial vasculogenesis.

CONCLUSION

The reciprocal expression of angiogenic growth factors and receptors during development supports their involvement in the cross talk between liver epithelial cells and the portal vasculature. Cholangiocytes generate a VEGF gradient that is crucial during the migratory stage, when it determines arterial vasculogenesis in their vicinity, whereas angiopoietin-1 signaling from hepatoblasts contributes to the remodeling of the hepatic artery necessary to meet the demands of the developing epithelium.

Vanishing bile duct syndrome

Perhaps no condition associated with chronic cholestasis is less understood than vanishing bile duct syndrome, a term that refers loosely to the group of acquired disorders associated with progressive destruction and disappearance of the intrahepatic bile ducts and, ultimately, cholestasis. Although the array of insults resulting in poor bile flow is vast, most adult patients who have chronic cholestasis have either primary biliary cirrhosis (or primary sclerosing cholangitis; in some cases, however, a cause cannot be identified. This article reviews the multiple causes, postulated pathophysiology, clinical features, and treatment options for this syndrome.

Human intrahepatic biliary epithelial cell as a possible modulator of hepatic regeneration: Potential role of biliary epithelial cell for hepatic remodeling in vivo

BACKGROUND

During liver regeneration, the process of hepatic wound healing, a complex cascade of inflammatory signals, recruit inflammatory cells, stimulate hepatobiliary cell proliferation, direct cell migration and induce vascularization to restore tissue integrity, irrespective of its etiology. This might also be the case in cholangiopathies, in which the initial target is the branch of the intrahepatic biliary tree; that is, primary biliary cirrhosis. Previous studies about biliary wound healing focused mainly on the inducers of compensatory biliary proliferation following bile duct insult. Nevertheless, the microenvironment around biliary wound healing responses, which in turn might affect hepatic remodeling, possibly by biliary epithelial cells themselves via paracrine manner, is still less known.

METHODS

In this study, we defined the humoral factors that are released from human intrahepatic biliary epithelial cell lines (HIBEC) with human cytokine array, and reviewed their relevance according to the previous published work.

RESULTS

Conditioned medium of HIBEC were revealed to be rich in multiple cytokines and chemokines, including ELR(+)CXC chemokines, such as interleukin-8/CXCL8, growth-related oncoprotein (GRO), epithelial neutrophil chemoattractant (ENA-78), known chemoattractants with a wide range of non-leukocytic activities. Subsequent enzyme-linked immunosorbent assay analyses confirmed that the secretion was commonly observed in various culture conditions and in both an apical and basolateral direction.

CONCLUSIONS

Considering that some of these factors had been already reported to have direct autocrine mitogenic influence on HIBEC, these findings could further strengthen an active role of HIBEC as a modulator of hepatic regeneration, through its biological reactivity on inflamed milieu.

Hepatobiliary pathology

PURPOSE OF REVIEW

Recent papers on disorders of the liver and biliary tract which clarify their pathogenesis and attendant morphologic changes are highlighted.

RECENT FINDINGS

The concept of 'bystander hepatitis' was cited in studies showing hepatic infiltration of CD8-positive T cells in the setting of extrahepatic infections such as influenza virus and severe acute respiratory syndrome. Diabetic liver lesions include glycogenic hepatopathy (in which poor diabetic control leads to swollen, glycogen-filled hepatocytes without fat, steatohepatitis or fibrosis) and diabetic hepatosclerosis in which there is diffuse perisinusoidal fibrosis (type IV collagen) without zonal predilection. Ground-glass hepatocellular inclusions (positive with periodic acid-Schiff stain for glycogen) were reported in three separate series of patients who were hepatitis B virus-negative, often transplant recipients, immunosuppressed and on multiple medications. A Banff consensus paper expertly compared and contrasted the histologic features which characterize the various causes of late liver allograft dysfunction.

SUMMARY

Informative papers emerged this past year concerning collateral damage to the liver in extrahepatic infections, diabetic lesions and causes of liver dysfunction after transplantation, among other topics.

Preservation of bile ductules mitigates bile duct loss

The finer branches of the biliary tree (FBBT) contain a regenerative compartment. We hypothesized that preservation of the FBBT together with its microvasculature will lead to recovery of biliary damage and prolonged preservation of bile ductules during the development of chronic liver allograft rejection. The interlobular bile ducts, portal bile ductules and extraportal biliary cells with and without microvessels were studied in sequential biopsies in five patients who fulfilled the Banff criteria of early chronic rejection (CR) (imminence group). Biopsies of CR patients (n = 12) served as controls. Biopsies were double immunostained with CD34 (microvessels) and cytokeratin 7 (biliary structures). Proliferation and proangiogenic activity were assessed with Ki67 and VEGF-A immunostaining. Severe damage of bile ducts in the imminence group did not progress to significant bile duct loss. This was associated with a high proliferative activity in all biliary structures and preservation of the microvascular compartment. VEGF-A expression was increased in all but the reperfusion biopsies. In conclusion, both regenerative activity of the FBBT and an intact microvascular compartment are associated with less damage of the biliary tree and could therefore be prerequisites for biliary regeneration.