Ultrastructure of oval cells in children with chronic hepatitis B, with special emphasis on the stage of liver fibrosis: The first pediatric study

Liver fibrosis in children: a comprehensive review of mechanisms, diagnosis, and therapy

Chronic liver disease incidence is increasing among children worldwide due to a multitude of epidemiological changes. Most of these chronic insults to the pediatric liver progress to fibrosis and cirrhosis to different degrees. Liver and immune physiology differs significantly in children from adults. Because most of pediatric liver diseases have no definitive therapy, a better understanding of population and disease-specific fibrogenesis is mandatory. Furthermore, fibrosis development has prognostic significance and often guide treatment. Evaluation of liver fibrosis continues to rely on the gold-standard liver biopsy. However, many high-quality studies put forward the high diagnostic accuracy of numerous diagnostic modalities in this setting. Herein, we summarize and discuss the recent literature on fibrogenesis with an emphasis on pediatric physiology along with a detailed outline of disease-specific signatures, noninvasive diagnostic modalities, and the potential for antifibrotic therapies.

The Ultrastructure of Hepatic Stellate Cell-Macrophage Intercellular Crosstalk as a New Morphological Insight into Phenomenon of Fibrogenesis in Pediatric Autoimmune Hepatitis

The aim of the study was the pioneering retrospective ultrastructural evaluation of respective forms of hepatic stellate cells (HSCs) and analysis of their crosstalk with other adjacent nonparenchymal cells (NPCs), especially Kupffer cells/macrophages (KCs/MPs), in pediatric autoimmune hepatitis (AIH).

METHODS

Ultrastructural assessment of the HSC population and NPCs was performed in transmission electron microscopy (TEM) using pretreatment liver biopsies from 25 children (8 boys and 17 girls) aged 4-17 with clinic-pathologically diagnosed untreated AIH.

RESULTS

Submicroscopic evaluation allowed easy identification of numerous HSCs in the form of transitory cells, i.e., T-HSCs, accompanied by signs of fibrosis. T-HSCs included cells with features of activation initiation (iHSCs) and activation perpetuation (pHSCs), indicating high HSC activation plasticity. The pHSCs were markedly elongated and mainly showed a distinct loss of lipid cytoplasmic material, expanded and dilated channels of granular endoplasmic reticulum, and linear bundles of microfilaments beneath the cell membrane. They were surrounded by usually mature collagen fibers. Frequently activated KCs/MPs adhered directly to T-HSCs. Between them, tight intercellular junctions were formed by means of point desmosomes.

CONCLUSIONS

Our qualitative TEM observations indicate a key role of T-HSCs in liver fibrogenesis in pediatric AIH, with the essential involvement of activated KCs/MPs that directly adhere to them. Tight intercellular junctions, being the ultrastructural exponent of the specific cellular mechanisms of the crosstalk between NPCs, can play a vital role in hepatic collagen fibroplasia. A better understanding of HSC population morphology at the ultrastructural level in AIH seems important not only to improve the disease morphological diagnostics but to also provide new insights into therapeutic interventions for the phenomenon of liver fibrogenesis.

Ultrastructural Profile Combined with Immunohistochemistry of a Hepatic Progenitor Cell Line in Pediatric Autoimmune Hepatitis: New Insights into the Morphological Pattern of the Disease

Considering that the heterogenic population of a hepatic progenitor cell line (HPCL) can play a vital role in autoimmune hepatitis (AIH), we decided to conduct pioneering retrospective evaluation of these cells in pediatric AIH by means of transmission electron microscopy (TEM). The aim of the study was to assess the ultrastructure of the HPCL in children with untreated AIH. Ultrastructural analysis of the HPCL population, preceded by immunohistochemical staining for cytokeratin 7 (CK7), was performed using pretreatment liver biopsies from 23 children with clinicopathologically diagnosed AIH. Immunohistochemical assessment for CK7 allowed detection of proliferating immature epithelial cells differentiating towards periportal and intralobular intermediate hepatocytes without marked formation of ductular reactions in AIH children. Using TEM, we distinguished three morphological types of HPCs: I—the most undifferentiated progenitor cells; III—intermediate hepatocyte-like cells; II—intermediate bile duct cells. Most frequent were the cells differentiating towards hepatocytes, most rare—those differentiating towards cholangiocytes. The results indicate that an HPCL may be an important source of hepatocyte regeneration. Ultrastructural analyses of the HPCL population, combined with immunohistochemistry for CK7, might be a useful tool to evaluate liver cell regeneration, including fibrogenesis, and may help better understand the morphological pattern of the disease, in pediatric AIH. Frequent appearance of an HPCL in the vicinity of fibrotic foci, often accompanied by hyperactive Kupffer cells and transitional hepatic stellate cells, may indicate their significant involvement in liver fibrogenesis.

Ultrastructural characteristics of the respective forms of hepatic stellate cells in chronic hepatitis B as an example of high fibroblastic cell plasticity. The first assessment in children

PURPOSE

Activation of hepatic stellate cells (HSCs), mainly responsible for extracellular matrix synthesis, is assumed to be central event in the process of liver fibrogenesis. The major objective of the research was to analyze the ultrastructural profile of activated HSCs in children with chronic hepatitis B (chB), with respect to fibrosis intensity.

MATERIALS/METHODS

Ultrastructural investigations of HSCs were conducted on liver bioptates from 70 children with clinicopathologically diagnosed chB before antiviral treatment. Biopsy material, fixed in paraformaldehyde and glutaraldehyde solution, was routinely processed for electron-microscopic analysis.

RESULTS

In children with intensive liver fibrosis (S-2 and S-3), the ultrastructural picture showed almost total replacement of quiescent HSCs (Q-HSCs) by activated, i.e. transitional HSCs (T-HSCs). Among T-HSCs, two types of cells were distinguished: cells exhibiting initiation of HSC activation (Ti-HSCs), never before described in chB, that were frequently accompanied by activated Kupffer cells, and cells with features of perpetuation of activation (Tp-HSCs). Tp-HSCs were elongated and characterized by substantial loss of cytoplasmic lipid material; they contained an increased number of cytoskeletal components, extremely dilated channels of granular endoplasmic reticulum and activated Golgi apparatus, which indicated their marked involvement in intensive synthesis of extracellular matrix proteins. Many collagen fibers were found to adhere directly to Tp-HSCs.

CONCLUSIONS

The current study showed T-HSCs to be an important link between Q-HSCs and myofibroblastic HSCs (Mf-HSCs). Transformation of HSCs into new morphological variations (Ti-HSCs; Tp-HSCs and Mf-HSCs), observed along with growing fibrosis, indicates their high plasticity and a key role in fibrogenesis in pediatric chB.

Glassy droplet inclusions within the cytoplasm of Kupffer cells: A novel ultrastructural feature for the diagnosis of pediatric autoimmune hepatitis

Since Kupffer cells/macrophages (KCs/MPs) may be involved in the pathogenesis of autoimmune hepatitis (AIH), this pioneer study was undertaken to evaluate KCs/MPs in pediatric AIH in transmission-electron microscope.

METHODS

Ultrastructural analyses were performed using liver biopsies from 14 children with clinicopathologically diagnosed AIH.

RESULTS

In all AIH children, ultrastructural findings revealed changes in the cells lining sinusoidal vessels, especially KCs/MPs and endothelial cells. KCs/MPs showed increased phagocytic activity and damaged mitochondria, frequently with accompanying intense fibrosis. In 10/14 AIH patients, the cytoplasm of sinusoidal KCs/MPs contained characteristic glassy droplet inclusions. They were round, sharply circumscribed, and contained homogeneous material and distinct translucent fields. Their ultrastructure was identical with the Russel bodies of plasma cells, which were also found in liver biopsies in the same patients.

CONCLUSION

Ultrastructural identification of characteristic cytoplasmic droplets with glassy appearance in KCs/MPs, never before described in AIH, provides a useful novel morphological feature in the diagnosis of this disease.

Ultrastructural Characteristics of Rat Hepatic Oval Cells and Their Intercellular Contacts in the Model of Biliary Fibrosis: New Insights into Experimental Liver Fibrogenesis

PURPOSE

Recently, it has been emphasized that hepatic progenitor/oval cells (HPCs) are significantly involved in liver fibrogenesis. We evaluated the multipotential population of HPCs by transmission electron microscope (TEM), including relations with adherent hepatic nonparenchymal cells (NPCs) in rats with biliary fibrosis induced by bile duct ligation (BDL).

METHODS

The study used 6-week-old Wistar Crl: WI(Han) rats after BDL for 1, 6, and 8 weeks.

RESULTS

Current ultrastructural analysis showed considerable proliferation of HPCs in experimental intensive biliary fibrosis. HPCs formed proliferating bile ductules and were scattered in periportal connective tissue. We distinguished 4 main types of HPCs: 0, I, II (bile duct-like cells; most common), and III (hepatocyte-like cells). We observed, very seldom presented in literature, cellular interactions between HPCs and adjacent NPCs, especially commonly found transitional hepatic stellate cells (T-HSCs) and Kupffer cells/macrophages. We showed the phenomenon of penetration of the basement membrane of proliferating bile ductules by cytoplasmic processes sent by T-HSCs and the formation of direct cell-cell contact with ductular epithelial cells related to HPCs.

CONCLUSIONS

HPC proliferation induced by BDL evidently promotes portal fibrogenesis. Better understanding of the complex cellular interactions between HPCs and adjacent NPCs, especially T-HSCs, may help develop antifibrotic therapies in the future.

Potential ultrastructure predicting factors for hepatocellular carcinoma in HCV infected patients

Hepatitis C virus represents one of the rising causes of hepatocellular carcinoma (HCC). Although the early diagnosis of HCC is vital for successful curative treatment, the majority of lesions are diagnosed in an irredeemable phase. This work deals with a comparative ultrastructural study of experimentally gradually induced HCC, surgically resected HCC, and potential premalignant lesions from HCV-infected patients, with the prospect to detect cellular criteria denoting premalignant transformation. Among the main detected pathological changes which are postulated to precede frank HCC: failure of normal hepatocyte regeneration with star shape clonal fragmentation, frequent elucidation of hepatic progenitor cells and Hering canals, hepatocytes of different electron density loaded with small sized rounded monotonous mitochondria, increase junctional complexes bordering bile canaliculi and in between hepatocyte membranes, abundant cellular proteinaceous material with hypertrophied or vesiculated rough endoplasmic reticulum (RER), sequestrated nucleus with proteinaceous granular material or hypertrophied RER, formation of lipolysosomes, large autophagosomes, and micro-vesicular fat deposition. In conclusion, the present work has visualized new hepatocytic division or regenerative process that mimic splitting or clonal fragmentation that occurs in primitive creature. Also, new observations that may be of value or assist in predicting HCC and identifying the appropriate patient for surveillance have been reported. Moreover, it has pointed to the possible malignant potentiality of liver stem/progenitor cells. For reliability, the results can be subjected to cohort longitudinal study.

Hepatic oval cells and liver diseases

In recent years, hepatic oval cells (HOC) have gradually become a research hotspot, and their participation in the reconstruction of liver structure and function has been preliminarily confirmed. This provides a new direction for the study of the pathogenesis and treatment of liver injury, hepatitis, liver fibrosis, cirrhosis, liver neoplasms and other liver diseases. This paper will discuss the relationship between hepatic oval cells and liver diseases.

Advances in mesenchymal stem cells combined with traditional Chinese medicine therapy for liver fibrosis

Liver fibrosis is a primary cause of liver cirrhosis, and even hepatocarcinoma. Recently, the usage of mesenchymal stem cells (MSCs) has been investigated to improve liver fibrosis. It has been reported that the differentiation, proliferation and migration of MSCs can be regulated by traditional Chinese medicine treatment; however, the mechanisms are still unclear. In this article, the authors review the characteristics of MSCs such as multidirectional differentiation and homing, and its application in animal experiments and clinical trials. The authors also list areas that need further investigation, andlook at the future prospects of clinical application of MSCs.

TWEAK and LTβ Signaling during Chronic Liver Disease

Chronic liver diseases (CLD) such as hepatitis B and C virus infection, alcoholic liver disease, and non-alcoholic steatohepatitis are associated with hepatocellular necrosis, continual inflammation, and hepatic fibrosis. The induced microenvironment triggers the activation of liver-resident progenitor cells (LPCs) while hepatocyte replication is inhibited. In the early injury stages, LPCs regenerate the liver by proliferation, migration to sites of injury, and differentiation into functional biliary epithelial cells or hepatocytes. However, when this process becomes dysregulated, wound healing can progress to pathological fibrosis, cirrhosis, and eventually hepatocellular carcinoma. The other key mediators in the pathogenesis of progressive CLD are fibrosis-driving, activated hepatic stellate cells (HSCs) that usually proliferate in very close spatial association with LPCs. Recent studies from our group and others have suggested the potential for cytokine and chemokine cross-talk between LPCs and HSCs, which is mainly driven by the tumor necrosis factor (TNF) family members, TNF-like weak inducer of apoptosis (TWEAK) and lymphotoxin-β, potentially dictating the pathological outcomes of chronic liver injury.

Immunohistochemical characterization of the hepatic progenitor cell compartment in medaka (Oryzias latipes) following hepatic injury

Laboratory fish species are used increasingly in biomedical research and are considered robust models for the study of regenerative processes. Studies investigating the response of the fish liver to injury have demonstrated the presence of a ductular reaction and oval-like cells in injured and regenerating liver. To date, however, it is unclear if this cell population is the piscine equivalent of oval cells (OCs) or intermediate hepatobiliary cells (IHBCs) identified in rodents and man, respectively. The present study defines the process of OC differentiation in fish liver using histopathology, immunohistochemistry and transmission electron microscopy. To generate OC proliferation in Japanese medaka (Oryzias latipes), hepatic injury was induced by exposure of adult fish to either microcystin LR or dimethylnitrosamine. A transgenic strain of medaka expressing a red fluorescent protein (RFP) exclusively in hepatocytes was used. The morphological response to injury was characterized by a ductular reaction comprised of cytokeratin (CK) AE1/AE3(+) OCs progressing to IHBCs variably positive for CK and RFP and finally mature RFP(+) hepatocytes and CK(+) cholangiocytes. These observations support a bipotential differentiation pathway of fish OCs towards hepatocytes and cholangiocytes. Ultrastructural morphology confirmed the presence of OCs and differentiation towards hepatocytes. These results demonstrated clear similarities between patterns of reaction to injury in fish and mammalian livers. They also confirm the presence of, and support the putative bipotential lineage capabilities of, the fish OC.

Ultrastructure of liver progenitor/oval cells in children with nonalcoholic steatohepatitis

PURPOSE

Very interesting reports have appeared lately on the role of liver progenitor/oval cells in the morphogenesis and development of nonalcoholic steatohepatits (NASH) in adult patients and experimental animals. However, no literature data concerning pediatric patients have been available. Therefore, the purpose of the study was to evaluate the ultrastructure of the population of liver progenitor/oval cells in the biopsy material from children with previously clinocopathologically diagnosed NASH.

MATERIAL/METHODS

Electron-microscopic examinations were conducted on fresh tissue samples collected from 10 children with NASH (aged 2-14 years), which were fixed with a solution of 2% paraformaldehyde and 2.5% glutaraldehyde in 0.1 M cacodylate buffer.

RESULTS

Ultrastructural examinations of the liver progenitor/oval cells in children with NASH show a quite prominent number of these cells, especially their two types, hepatic progenitor cells (HPCs) and intermediate hepatocyte-like cells (IHCs), with intermediate bile-like cells being the least frequent. They were found to occur single or in clusters of two, seldom of three, and frequently in the areas of advanced liver fibrosis or close to them. Many times, these cells were accompanied by hepatocytes showing a varying degree of death, to total cell disintegration. Interesting was the presence of activated nonparenchymal liver cells, i.e. Kupffer cells/macrophages and hepatic stellate cells, frequently found to adhere to the hepatic oval cells.

CONCLUSIONS

The current study suggests a marked involvement of the population of liver progenitor/oval cells, mainly HPCs and IHCs, in the development of nonalcoholic steatohepatitis in pediatric patients, especially in fibrosis progression.

Electron microscopic alterations in intermediate hepatocyte-like cells in children with chronic hepatitis B: the first report in pediatric patients

OBJECTIVE

The study objective was an in-depth ultrastructural analysis of intermediate hepatocyte-like cells (IHCs), constituting a subpopulation of liver progenitor/oval cells, in children with chronic hepatitis B viral (HBV) infection.

METHODS

Ultrastructural investigations were conducted on liver biopsy material, fixed in a solution of 2.5% glutaraldehyde, 2% paraformaldehyde, and 0.1 mol/l cacodylate buffer, obtained from 40 children, aged 3-16 years, with chronic hepatitis B.

RESULTS

Transmission-electron microscopic analysis of liver progenitor/oval cells showed, apart from a morphologically unchanged population of oval cells, the presence of IHCs displaying variously pronounced ultrastructural changes, including degeneration. Interesting was that damaged IHCs were mainly observed in patients with a coexisting advanced liver fibrosis, where they frequently adhered to bundles of collagen fibers. Submicroscopic abnormalities in these cells referred mainly to mitochondria and granular endoplasmic reticulum. The most pronounced mitochondrial alterations observed in degenerating IHCs in the course of chronic HBV infection were characterized by distinct swelling, loss of mitochondrial crests, and the presence of myelin structures within the matrix. In granular endoplasmic reticulum, shortening and segmental degranulation of the reticulum were observed. The above changes were accompanied by the appearance of primitive phagosome-like structures with absorbed biliary pigment. In the vicinity of altered IHCs, transitional hepatic stellate cells could be found.

CONCLUSION

Our study seems to suggest that chronic HBV infection, lasting from childhood and coexisting with intensive fibrosis may, with the involvement of other carcinogenic factors, promote degenerating IHCs towards neoplastic transformation in adulthood.

Expression and localization of aquaporin-1 in human cirrhotic liver

We investigated the expression and localization of aquaporin-1 (AQP-1) in hepatitis B virus (HBV)-associated cirrhotic human liver tissues. The expression of AQP-1 at the protein and mRNA levels was analyzed by immunohistochemistry, quantitative real-time polymerase chain reaction (qPCR) and Western blotting in normal and HBV-associated cirrhotic human liver tissues. The correlation with the expression of CK19, CK7 and AQP-1 was also compared. AQP-1 staining was strongly and uniformly positive in mature bile ducts, isolated hepatic progenitor cells (HPCs) and ductular reactions. Scattered intermediate hepatocyte-like cells expressed AQP-1, which are often intimately associated with CK7 positive hepatocytes. However, the number of AQP-1+ intermediate hepatocyte-like cells was lower than that of CK7+ cells, and such positivity was rarely seen on stains for CK19. When compared with normal liver tissues, AQP-1 was overexpressed at both the mRNA and protein levels in the cirrhotic liver tissues. AQP-1 was overexpressed in the cirrhotic liver tissues. AQP-1, similar to CK19, might be a more specific and more sensitive marker than CK7 for the identification of HPCs.