Electron microscopic study on the hepatic sinusoidal wall and the fat-storing cells in the normal human liver

Blood defense system - Proposal for a new concept of an immune system against blood borne pathogens comprising the liver, spleen and bone marrow

Blood-borne pathogen (BBP) infections can rapidly progress to life-threatening sepsis and must therefore be promptly eliminated by the host's immune system. Intravascular macrophages of the liver sinusoid, splenic marginal zone and red pulp and perisinusoidal macrophage protrusions in the bone marrow (BM) directly phagocytose BBPs in the blood as an innate immune response. The liver, spleen and BM thereby work together as the blood defence system (BDS) in response to BBPs by exerting their different immunological roles. The liver removes the vast majority of these invading organisms via innate immunity, but their complete elimination is not possible without the actions of antibodies. Splenic marginal zone B cells promptly produce IgM and IgG antibodies against BBPs. The splenic marginal zone transports antigenic information from the innate to the adaptive immune systems. The white pulp of the spleen functions as adaptive immune tissue and produces specific and high-affinity antibodies with an immune memory against BBPs. The BM works to maintain immune memory by supporting the survival of memory B cells, memory T cells and long-lived plasma cells (LLPCs), all of which have dedicated niches. Furthermore, BM perisinusoidal naïve follicular B cells promptly produce IgM antibodies against BBPs in the BM sinusoid and the IgG memory B cells residing in the BM rapidly transform to plasma cells which produce high-affinity IgG antibodies upon reinfection. This review describes the complete immune defence characteristics of the BDS against BBPs through the collaboration of the liver, spleen and BM with combined different immunological roles.

Systematic profiling of the effective ingredients and mechanism of Scabiosa comosa and S. tschilliensis against hepatic fibrosis combined with network pharmacology

Scabiosa comosa and S. tschilliensis (SCST) are traditionally used for liver diseases in Mongolian medicine. However, their active ingredients and molecular mechanisms are unknown. The present study employed network pharmacology and experimental verification approaches to decipher the common pharmacological mechanisms of SCST on liver fibrosis, which is the key step in liver diseases. We predicted the targets of all available SCST ingredients with the SWISS and SuperPred servers and clustered the targets related to liver fibrosis from DrugBank, the OMIM database and the literature. We further evaluated the links between the herbal ingredients and pharmacological actions to explore the potential mechanism of action of SCST. We found that the PPARG signalling pathway could be regulated by SCST for liver fibrosis through enrichment analysis. The key targets included 8 co-targets, including HSP90AA1, PPARG, HSP90AB1, STAT1, etc., which play pivotal roles in the pathogenesis of liver fibrosis. Additionally, the top 15 key compounds included flavonoids and phenylpropanoids. Central to the pathogenesis of liver fibrosis is trans-differentiation or activation of hepatic stellate cells (HSCs). Therefore, LX2 cells, an immortalized human HSC line, were studied. Here, a total 37 components were isolated and identified from the inflorescences of SCST, including the new compound tschilliensisin, and the first separated components, β-sitosterol and luteolin, and these compounds were assessed against anti-hepatic fibrosis. An MTT assay and quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting analyses demonstrated that the flavonoids of SCST revealed anti-hepatic fibrosis effects via anti-proliferation and increases in the Stat1, Pparg, Hsp90aa1 genes and STAT1 and PPARG proteins in LX-2 cells. In conclusion, these results indicate that SCST has multi-targeted and multi-component synergistic anti-hepatic fibrosis effects.

Altered global microRNA expression in hepatic stellate cells LX-2 by angiotensin-(1-7) and miRNA-1914-5p identification as regulator of pro-fibrogenic elements and lipid metabolism

The development of new therapeutic strategies to control or reverse hepatic fibrosis requires thorough knowledge about its molecular and cellular basis. It is known that the heptapeptide angiotensin-(1-7) [ang-(1-7)] can reduce hepatic fibrosis and steatosis in vivo; therefore, it is important to uncover the mechanisms regulating its activity and cellular model of investigation. Ang-(1-7) is a peptide of the renin-angiotensin system (RAS), and here we investigated its modulatory effect on the expression pattern of microRNAs (miRNAs) in hepatic stellate cells (HSCs) LX-2, which transdifferentiate into fibrogenic and proliferative cells. We compared the miRNA profiles between quiesced, activated and ang-(1-7)-treated activated HSCs to identify miRNAs that may regulate their transdifferentiation. Thirteen miRNAs were pointed, and cellular and molecular analyses identified miRNA-1914-5p as a molecule that contributes to the effects of ang-(1-7) on lipid metabolism and on the pro-fibrotic environment control. In our cellular model, we also analyzed the regulators of fatty acid metabolism. Specifically, miRNA-1914-5p regulates the expression of malonyl-CoA decarboxylase (MLYCD) and phosphatidic acid phosphohydrolase (PAP or Lipin-1). Additionally, Lipin-1 was closely correlated with mRNA expression of peroxisome proliferator-activated receptors (PPAR)-α and -γ, which also contribute to lipid homeostasis and to the reduction of TGF-β1 expression. These findings provide a novel link between RAS and lipid metabolism in controlling HSCs activation.

Morphogen-related therapeutic targets for liver fibrosis

Recent research on hepatic stellate cells (HSCs) has spotlighted the involvement of morphogens in their cell fate determination in liver fibrosis. Temporally and spatially expressed during embryonic development, morphogens are involved in regulation of cell proliferation and differentiation, and tissue patterning. In normal adult liver, morphogens are generally expressed at low levels. However, in liver disease, myofibroblastic HSCs express morphogens such as Wnt, Shh, Necdin, DLK1, and Notch as part of their participation in fibrogenesis and wound healing. Liver regeneration involves cell proliferation and differentiation akin to embryonic liver development where the cells appear to undergo similar fates, and not surprisingly the morphogens are re-activated for the regenerative purpose in adult liver injury. Evidence also points to crosstalk of these morphogens in regulation of HSC fate determination. Genetic ablation or pharmacologic inhibition of morphogens reverts activated HSC to quiescent cells in culture and attenuates progression of hepatic fibrosis. However, positive regulation of liver regeneration by the morphogens needs to be spared. Therapeutically, manipulation of morphogen activities in a cell type and phase-specific manner should offer new modalities for chronic liver disease.

Role of intrahepatic innervation in regulating the activity of liver cells

Liver innervation comprises sympathetic, parasympathetic and peptidergic nerve fibers, organized as either afferent or efferent nerves with different origins and roles. Their anatomy and physiology have been studied in the past 30 years, with different results published over time. Hepatocytes are the main cell population of the liver, making up almost 80% of the total liver volume. The interaction between hepatocytes and nerve fibers is accomplished through a wealth of neurotransmitters and signaling pathways. In this short review, we have taken the task of condensing the most important data related to how the nervous system interacts with the liver and especially with the hepatocyte population, how it influences their metabolism and functions, and how different receptors and transmitters are involved in this complex process.

Human hepatic stellate cell line (LX-2) exhibits characteristics of bone marrow-derived mesenchymal stem cells

The LX-2 cell line has characteristics of hepatic stellate cells (HSCs), which are considered pericytes of the hepatic microcirculatory system. Recent studies have suggested that HSCs might have mesenchymal origin. We have performed an extensive characterization of the LX-2 cells and have compared their features with those of mesenchymal cells. Our data show that LX-2 cells have a phenotype resembling activated HSCs as well as bone marrow-derived mesenchymal stem cells (BM-MSCs). Our immunophenotypic analysis showed that LX-2 cells are positive for activated HSC markers (αSMA, GFAP, nestin and CD271) and classical mesenchymal makers (CD105, CD44, CD29, CD13, CD90, HLA class-I, CD73, CD49e, CD166 and CD146) but negative for the endothelial marker CD31 and endothelial progenitor cell marker CD133 as well as hematopoietic markers (CD45 and CD34). LX-2 cells also express the same transcripts found in immortalized and primary BM-MSCs (vimentin, annexin 5, collagen 1A, NG2 and CD140b), although at different levels. We show that LX-2 cells are capable to differentiate into multilineage mesenchymal cells in vitro and can stimulate new blood vessel formation in vivo. LX-2 cells appear not to possess tumorigenic potential. Thus, the LX-2 cell line behaves as a multipotent cell line with similarity to BM-MSCs. This line should be useful for further studies to elucidate liver regeneration mechanisms and be the foundation for development of hepatic cell-based therapies.

Innervation of the sinusoidal wall: regulation of the sinusoidal diameter

In the livers of humans, cats, guinea pigs, and tupaia, nerve endings are distributed all over the hepatic lobules. Nerve endings in the intralobular spaces are localized mainly in the Disse spaces and are oriented toward the hepatic stellate cells (HSCs), sinusoidal endothelial cells, and hepatocytes. They are especially closely related to HSCs. Various neurotransmitters such as substance P exist in the nerve endings. In addition, HSCs possess endothelin (ET) and adrenergic receptors and contract in response to the corresponding agonists. In contrast, nitric oxide (NO) inhibits the contraction of HSCs. HSCs thus appear to be involved in the regulation of hepatic sinusoidal microcirculation by contraction and relaxation. In the cirrhotic liver, intralobular innervation is decreased, but ET, ET receptors, and NO are overexpressed in the HSCs. These findings indicate that HSCs in cirrhotic liver may play an important role in the sinusoidal microcirculation through agents such as ET or NO rather than through intralobular innervation.

Biological activities of novel lipid mediator sphingosine 1-phosphate in rat hepatic stellate cells

Sphingosine 1-phosphate (S-1-P), a lipid mediator shown to be a ligand for aortic G protein-coupled receptor [corrected] (AGRs), endothelial differentiation gene (EDG)1, EDG3, and AGR16/EDG5, is stored in platelets and released on their activation. Platelet consumption occurs in acute liver injury. Hepatic stellate cells (HSCs) play an important role in wound healing. Effects of S-1-P on HSCs were investigated. S-1-P enhanced proliferation of culture-activated HSCs. The mitogenic effect was pertussis toxin sensitive, mitogen-activated protein kinase dependent, and more prominent at lower cell density. S-1-P increased contraction of collagen lattices containing HSCs, irrespective of activation state, in a C3 exotoxin-sensitive manner. mRNAs of EDG1 and AGR16, but not of EDG3, were detected in HSCs. In HSC activation, EDG1 mRNA levels were downregulated, whereas AGR16 mRNA levels were unchanged. Considering that HSCs are capable of production of extracellular matrices and modulation of blood flow in sinusoids, our results suggest that S-1-P may play a role in wound healing process in the liver.

Architectural pattern, tissue and cellular morphology in livers of fishes: relationship to experimentally-induced neoplastic responses

The teleost liver is one of the most sensitive organs to show alteration in biochemistry, physiology and structure following exposure to various types of environmental pollutants. Despite the importance of this organ to environmental toxicology and to ecotoxicology where biomarkers of exposure and of deleterious effect are found, the architectural pattern is not well known. This chapter reviews an architectural plan for teleost liver and compares that to the often cited mammalian pattern. Hepatic tubules composed principally of hepatocytes and biliary epithelial cells are in close proximity to lacunae which are of mesodermal origin. As is described, the tubule and lacunae concepts provide a means to better interpret morphologic alterations following exposure. These concepts are used to illustrate features of the chronic toxicity following exposure to proven carcinogens.

Zonal and regional differences identified from precision mapping of vitamin A-storing lipid droplets of the hepatic stellate cells in pig liver: a novel concept of addressing the intralobular area of heterogeneity

Knowledge of hepatic heterogeneity has been strikingly increased, while an accurate means for addressing intralobular positions is still lacking. We examined pig liver preparations of the gold impregnation method for vitamin A-storing lipid droplets in hepatic stellate cells. Droplet morphometry was performed under oil immersion, and the calculated volumes plotted on computerized maps. The heterogeneous results were assessed with five concentric zones and five radial regions; the latter were determined based on midseptum visualized by portal injection. Zonation and regionation thus subdivided lobules into 5-zone/5-region (5Z/5R) compartmentalization. Distribution of values exhibited a distinct zonal gradient, heightened at peripheral zones 1 and 2, decreased over intermediate zone 3 toward centrilobular zones 4 and 5; peak was always found at zone 2. Within a single zone, variations were obvious, forming a regional gradient. Values were significantly higher at periportal than midseptal regions. Digitized mapping showed that low values filled up centrilobular zones, whereas high values concentrated in periportal regions. Along the periphery, inlet venules were quantified, revealing an occurrence rate of 60% at periportal, and 5% at midseptal regions, closely compatible with the regional gradient of vitamin A-storing capacity. The interweaving between zonal and regional gradients results in a vitamin A-low territory, a compound area composed of centrilobular zones plus extensions into midseptal regions. Because the results could account for physiological and pathological events, we regard the 5Z/5R compartmentalization a model worth routine adoption for a precise description of any morphofunctionally demonstrable heterogeneity of the liver lobules.

Nonparenchymal cells in chronically hyperinsulinemic liver acini of diabetic rats, with special regard to hepatic stellate cells

BACKGROUND/AIMS

An increase in proliferative activity and other distinct hepatocellular alterations--resembling preneoplastic foci and progressing to hepatocellular tumors--have been shown to develop in liver acini draining the blood from islets of Langerhans, transplanted through the portal vein into the liver of streptozotocin-diabetic rats.

METHODS

Altered and unaltered liver acini were investigated for possible changes in hepatic stellate cells 4-76 days after islet transplantation.

RESULTS

Corresponding to a significant increase in the hepatocellular volume, the volume density of total nonparenchymal cells was significantly reduced in altered compared to unaltered liver acini. With regard to the total nonparenchymal cell volume, the hepatic stellate cell fraction was not different, whereas the fraction of Kupffer cells was significantly reduced and the fraction of sinusoidal endothelial cells was significantly increased in altered compared to unaltered liver acini, respectively. The volume density as well as the single volume of the hepatic stellate cell mitochondria increased significantly in altered compared to unaltered liver acini. Hepatic stellate cell lipid droplets did not show significant differences between altered and unaltered liver acini. In situ hybridization for hepatocyte growth factor mRNA showed no differences in intensity of the specific signals in hepatic stellate cells of altered versus unaltered liver acini. The transplanted islets were negative for hepatic growth factor mRNA.

CONCLUSIONS

The results suggest that hepatic growth factor production by hepatic stellate cells or by islet cells is not relevant to hepatocellular proliferative activity in altered liver acini.

Development of hepatic sinusoidal structure with special reference to the Ito cells

To elucidate sinusoidal cell structure and function under normal conditions and their behavior in diseased settings, an understanding of their developmental aspects is needed. At day 10 of gestation in mice and rats or at 5 weeks of gestation in humans, the hepatic cords grow into the mesenchymal tissue of the septum transversum, and the primitive sinusoidlike structure is simultaneously observed between the liver cell cords. In the margin of the growing liver primordium, mesenchymal cells in the septum transversum are trapped in the subendothelial space. These subendothelial cells are at the early stages of organogenesis and become progenitors of the Ito cells. By days 12-14 of gestation in mice and rats or 8 weeks of gestation in humans, the basic structure of the sinusoids has developed. Embryonic hepatic sinusoids are usually lined by a continuous endothelium without basement membranes, and an incompletely fenestrated sinusoid appears at the middle gestational stage. In the late gestational stages, the Ito cells exhibit myofibroblastlike features in humans, mice, and rats. In association with this event, perisinusoidal reticular networks are gradually intensified. After birth until days 4-5 in mice and rats, the sinusoidal and perisinusoidal structures are almost completely formed, although slight morphological differences from those in adult livers still exist. What happens to sinusoidal endothelial cells and Ito cells in hepatic fibrosis-cirrhosis of the adult may be a deviated or uncontrolled occurrence of what goes on during the fetal period, i.e., a continuous nonfenestrated sinusoidal lining in the early embryonic stage and a myofibroblastlike transformation of Ito cells in late fetal life.

Intralobular innervation and lipocyte contractility in the liver

In the liver of humans, guinea pigs, cats, and tupaia, nerve endings are distributed all over the hepatic lobules from the portal spaces to the centralobular spaces. Nerve endings in the intralobular spaces are located mainly in the space of Disse, and are closely related to lipocytes. In the human liver, various neurotransmitters such as substance P (SP) exist in the nerve endings. Lipocytes are believed to contract through these substances. In fact, the contraction of lipocytes is induced by SP. Moreover, lipocytes possess endothelin (ET) receptors (ETA, ETB), and the cells are contracted by ET-1 by way of ET receptors in the autocrine or paracrine mechanism. Contraction of lipocytes seems to be related to the enhancement of the intracellular Ca2+ and inositol phosphates. In addition, alpha-smooth muscle actin, which is a contractile protein, exists in the cytoplasm of lipocytes. Lipocyte contractility may be similar to that of vascular smooth muscle cells. On the other hand, prostaglandin E2, Iloprost, and adrenomedullin cause the elevation of c-AMP levels in lipocytes and relax the cells. In addition, lipocytes produce nitric oxide (NO) and inhibit contractility by an autocrine mechanism related to NO. In this way, lipocytes appear to be associated with the regulation of hepatic sinusoidal microcirculation by contraction and relaxation. In the cirrhotic liver, intralobular innervation is decreased or absent, but ET-1 and NO are overexpressed. These phenomena indicate that lipocytes may play an important role in the sinusoidal microcirculation through these agents rather than through intralobular innervation in liver cirrhosis.

Immunohistochemical identification of Ito cells and their myofibroblastic transformation in adult human liver

To identify Ito cells in normal and pathological adult human livers, immunohistochemical studies were performed by the avidin-biotin-peroxidase complex method using monoclonal antibodies for alpha-smooth muscle actin (ASMA), desmin, and vimentin. Fifty one needle biopsies, 7 surgically resected specimens, and 5 autopsy specimens were studied. In the normal adult liver vascular smooth muscle cells and pericytes, together with perisinusoidal cells with thin cytoplasmic processes were positive for ASMA. These latter cells formed a loose and discontinuous layer along the sinusoidal walls. Immunoelectron microscopy showed that the ASMA-positive perisinusoidal cells were Ito cells containing fat droplets. The other sinusoidal lining cells were negative for ASMA. In chronic liver disease, ASMA-positive Ito cells showed an increase in number, size, and the intensity of immunostaining in areas of piece-meal necrosis), and formed a continuous cellular network. These cells were dendritic in shape with irregularly elongated cytoplasmic processes and contained an increased amount of microfilaments, in association with loss of the characteristic fat droplets. Thus, their ultrastructural features corresponded to those of myofibroblastic cells. Ito cells showed no staining for desmin in both normal and pathological livers. These results indicate that immunohistochemistry using an anti-ASMA antibody is a sensitive and reliable method for the identification of both normal and transformed Ito cells in adult human livers.

Fat-storing cell abnormalities associated with endothelial cell damage after cold ischemic storage of rat liver in UW solution

Rat liver was stored at 1 degree C in University of Wisconsin solution, and morphological changes were observed after 12, 18, 24, and 36 hr by transmission electron microscopy. There were two types of endothelial cell damage in the hepatic sinusoids. One was disruption of the endothelial linings, and the other detachment of endothelial cells into the sinusoidal space accompanied by fat-storing cell abnormalities. The former damage was seen after storage longer than 12 hr, while the latter developed after 18 hr even in the hepatic sinusoids with no disruption of the linings. Considering that fat-storing cell damage can produce endothelial cell destruction, this damage should be given attention as one of factors of endothelial cell destruction in the hepatic sinusoids after cold storage of the liver.

"Lipomatous" lesions of unknown cellular origin in the liver of B6C3F1 mice

The gross, microscopic, and ultrastructural features of lipomatous lesions in the liver of B6C3F1 mice are described. The cases were selected from a database of 45,406 male and 45,674 female mice used as treated, control, or vehicle-control animals in the National Cancer Institute's Bioassays or the National Toxicology Program's 2-year carcinogenicity studies. Thirteen hepatic lesions identified from cases within the database were re-evaluated microscopically and selected for further study. These lesions were present in ten males and three females that were between 85 and 113 weeks of age at the time of death. Grossly, the liver lesions were described as white to yellow or red to brown nodules/masses or foci that ranged from 2.0 to 25 mm in diameter. The lesions commonly involved the median and left lateral hepatic lobes. Microscopically, many of the lesions closely resembled lipomas described in the liver of human beings, and they consisted of nonencapsulated mature adipose-like tissue with irregular margins. The majority of the cells that comprised the lipomatous lesions were signet-ring shaped. These cells were positive for lipid as evidenced with oil red-O. The lipid droplets were also present within the hepatocytes that comprised the hepatic plates trapped within or surrounding many of the lipomatous lesions. At the margins of many of the lesions there were spindle-shaped cells that contained small intracytoplasmic lipid vacuoles. These cells were often within a stromal matrix that had focal areas of collagen and mucopolysaccharides, as evidenced by weak staining with Masson's trichrome and periodic acid-Schiff's stains, respectively. There was also disruption of the reticulum fibers in many of the lesions, as noted with a Gomori's reticulum stain. Ultrastructurally, cytoplasmic organelles, such as rough endoplasmic reticulum, free ribosomes and small lipid vacuoles, were present in the spindle-shaped cells, whereas signet-ring-shaped cells had few discernible organelles due to peripheral compression of the cytoplasm by single large vacuoles occupying the cytoplasmic space. The spindle-shaped cells were free of lysosomes. Thin collagen fibers were seen in contact with some of the spindle-shaped cells and were located between these cells and adjacent hepatocytes, or endothelial cells lining sinusoidal capillaries. A distinct basal lamina was not associated with spindle- or signet-ring-shaped cells. Similar lipomatous lesions were not found in other visceral organs. The exact cellular origin of the hepatic lesions described here is not known.

Ultrastructure and function of hepatic fat-storing and pit cells

The present paper reviews the literature on the ultrastructure and function of sinusoidal fat-storing cells and pit cells in the mammalian liver. Ultrastructurally, fat-storing cells are characterized by the presence of cytoplasmic fat droplets, well developed rough endoplasmic reticulum; a Golgi complex; multivesicular bodies; one or two centrioles; and few, rather small, lysosomes. These lysosomes are sometimes associated with fat droplets. Fat-storing cells may bear a cilium and project characteristic cytoplasmic processes into the space of Disse. These processes contain microtubules and filaments. Fat-storing cells are the main storage site of retinol esters in the mammalian body. Moreover, these cells have the potential of synthesizing several connective tissue components including the collagens type I, III, and IV; fibronectin; laminin; heparan sulfate; chondroitin sulfate; and dermatan sulfate. Pit cells are polarized cells, with most organelles localized at one site of the nucleus near the cytocentre. They are characterized electron microscopically by the presence of dense cytoplasmic granules with a specific ultrastructure, by rod-cored vesicles, and by multivesicular bodies. It has recently been shown that pit cells have natural killer activity to certain tumor cells and have many features in common with large granular lymphocytes. They therefore may act in the liver as a first line of defense against neoplasia, metastasis, and viral infections.

A new method for three-dimensional reconstruction from serial sections by computer graphics using "meta-balls": reconstruction of "hepatoskeletal system" formed by Ito cells in the cod liver

A new method is described for three-dimensional reconstruction from serial ultrathin sections, using "meta-balls" as a primitive of object modeling in computer graphics (CG). We take advantage of the meta-ball's blobbiness characteristic and its rendering system for reconstructing images. The two-dimensional outline data from serial sections are converted into three-dimensional meta-ball data with a graphic editor, "Metack," by which we can check the correctness of the data conversion. Then the converted data are visualized on a color display with a CG rendering software, "Tracy". This reconstruction method is applied in studying the spatial distribution of Ito cells (fat storing cells) in the cod liver in relation to the blood capillary. By observing the reconstructed images, we can easily understand the three-dimensional relationship between the Ito cells and the blood capillary. The Ito cells surround the blood capillary and extend their cytoplasmic processes into the inter-parenchymal space to make a well-developed network system. These findings would support a concept of "hepatoskeletal system" formed by Ito cells in the cod liver. Therefore, we think that the meta-ball reconstruction method is useful in morphological study.

Hepatic sinusoidal cell destruction in the development of intravascular coagulation in acute liver failure of rats

Rats received a dose of dimethylnitrosamine (DMN) or carbon tetrachloride (CCl4). In the liver of rats given DMN, apoptosis of fat-storing cells occurred at 7.5 h, and sinusoidal endothelial cell degeneration followed, with parenchymal cell necrosis after 9 h. Fibrin thrombi appeared in the sinusoids as well as in these necrotic areas after 12 h. In contrast, in the liver of rats given CCl4, parenchymal cell degeneration was seen after 6 h and necrosis with fibrin thrombi developed after 9 h. Fat-storing cells and endothelial cells were almost intact, and fibrin thrombi were not present in the sinusoids. SGPT values increased with decreased plasma levels of fibrinogen and antithrombin III and prolonged prothrombin time after 3 and 6 h, in the CCl4 and DMN models, respectively. An extensive reduction in plasma factor VIIIC levels and peripheral platelets was seen after 18 and 24 h, respectively, only in the DMN model. These results suggest that endothelial cells destruction can cause fibrin formation in the hepatic sinusoids in acute liver injury. Fat-storing cell injury may contribute to the destruction.

Ultrastructure of cholinergic innervation in the cirrhotic liver in guinea pigs. Neurohistochemical and ultrastructural study

Hepatic cirrhosis was induced in guinea pigs by ligation of the common bile duct and innervation of the liver was studied by fluorescence histochemistry (glyoxylic acid method), acetylcholinesterase (AChE) neurohistochemistry (modified Karnovsky and Roots method), and transmission electron microscopy. In control animals the adrenergic terminals showed connections with endothelial cells, hepatocytes and fat-storing cells, but no cholinergic terminals were evident. Cirrhosis was present 6 weeks after the bile duct ligation and marked fibrosis, accompanied by bile duct proliferation, was evident in the portal areas. Numerous AChE-positive nerve fibers traversed the collagenous bundles in the fibrotic areas, and cholinergic terminals formed close contacts with fibroblasts. Each axon terminal was found to contain numerous small coreless vesicles and AChE-reaction products were confirmed in the space between a nerve terminal and a fibroblast. In contrast, fluorescence adrenergic nerve fibers and their terminals remained unchanged. This study demonstrates that parasympathetic cholinergic innervation participates in some stages in the development of hepatic cirrhosis.

Ontogeny of hepatic fatty acid-binding protein immunoreactivity in human liver and intestinal tract

Liver and intestinal tissues of human fetuses at gestational ages between 6 and 30 weeks were immunostained with rabbit antibody against fatty acid-binding protein (FABP) isolated from rat liver, since the antibody crossreacted with human FABP of the hepatic type. FABP-immunoreactive hepatocytes were found in the liver as early as the 7th week of gestation, but not at the 6th week. The frequency of immunoreactive cells was about 80% throughout the gestational period examined. No immunoreactive cells other than hepatocytes were found in liver tissue. In the intestinal tract, ileal, colonic and vermiform appendicular FABP immunoreactivity was demonstrated at the 23rd week of gestation, and duodenal and jejunal immunoreactivity at the 26th week. Positive cells in the jejunum were very few at this stage, but numerous at the 30th week of gestation. The immunoreactive cells were primitive absorptive cells in intestinal villi, and no cryptic epithelial cells were positively immunostained. Thus, FABP immunoreactivity was considered to be a marker for hepatocytes at the early to late fetal stage, and for intestinal absorptive cells at mid- to late fetal stage.

Localization of four phosphatases in rat liver sinusoidal cells. An enzyme cytochemical study

In the present study we have localized neutral phosphatase, acid phosphatase, alkaline phosphatase and 5' nucleotidase in the sinusoidal cells of rat liver using enzyme cytochemistry at light and electron microscopical level. Neutral phosphatase was present in the endoplasmic reticulum and nuclear envelope of parenchymal cells and of sinusoidal endothelial, Kupffer and fat-storing cells. The intensity of the neutral phosphatase reaction was stronger in sinusoidal than in parenchymal cells. Sinusoidal cells were devoid of cytochemically demonstrable alkaline phosphatase. Abundant acid phosphatase was present in the many lysosomes of endothelial and Kupffer cells. Substantially less acid phosphatase-positive lysosomes were found in fat-storing cells. 5' nucleotidase was present on the cell membrane of fat-storing cells, on 90% of all Kupffer cells and on the microvilli of parenchymal cells. We have further shown that combined staining for 5' nucleotidase and for endogenous peroxidase, offers a histochemical tool to discriminate between the three main sinusoidal cell types in normal rat liver.

Pulmonary intravascular macrophages in domestic animal species: review of structural and functional properties

In dogs, laboratory animals, and man, the clearance of bacteria and particulates from blood occurs predominantly in hepatic Kupffer cells and splenic macrophages. In contrast, removal of blood-borne particulates in calves, sheep, goats, cats, and pigs occurs predominantly in pulmonary intravascular macrophages (PIMs). Review of recent studies indicates that PIMs are a resident cell population, junctionally adherent to the capillary endothelium of lungs and morphologically similar to hepatic Kupffer cells. PIMs are a pulmonary constituent of the mononuclear phagocyte system with respect to secretory, endocytic, and functional properties. Differentiated PIMs are rare in newborn pigs, and the majority of cells closely apposed to capillary endothelium consists of monocytes, which are occasionally in mitosis. In 7-day-old and older pigs, most cells apposed to capillary endothelium have characteristics of differentiated PIMs. This suggests a monocytic origin of PIMs in pigs. Perinatal colonization of lung capillaries by monocytes and their subsequent differentiation into PIMs represent a component of postnatal lung development. Estimates of relative PIM numbers in ovine and porcine lung parenchyma suggest cell densities similar to that of rat hepatic Kupffer cells. Apart from phagocytic properties, PIMs participate in the removal and disintegration of aged and impaired blood cells. After phagocytic stimulation, isolated PIMs secrete oxygen radicals, which are essential for microbicidal function. Similarly, by secreting bioactive lipids, stimulated PIMs may contribute to regulation of pulmonary hemodynamics. After receiving minute amounts of bacterial endotoxin, pulmonary injury is pronounced in sheep, calves, pigs, and cats, but not in laboratory animals and dogs. This presumably is related to the secretion of bioactive lipids by PIMs.

Immunohistochemical studies on the distribution and frequency of fatty-acid-binding protein positive cells in human fetal, newborn and adult liver tissues

Human tissues from adult, newborn/infant, and fetal livers, and gall bladders were immunostained with rabbit antibodies against fatty-acid-binding protein (FABP) isolated from rat liver. These antibodies cross-reacted with FABP from human liver by a double immunodiffusion method. The antigenicity of FABP of human liver is well preserved in various fixatives including 10 per cent formaldehyde, 4 per cent paraformaldehyde, and Zamboni's and Bouin's solution. FABP immunoreactivities, moreover, could be detected similarly in both cryostat and paraffin sections. FABP of hepatic type was found in hepatocytes most frequently in the fetus (as early as the 7th week of gestation), moderately in the newborn/infant, and infrequently in adult liver tissues. The distribution pattern of the positive hepatocytes was uniform throughout the acini in fetuses, but periportal in adults. No immunoreactive cells were found in the gall bladder or in the extra- and intra-hepatic bile ducts. In this study, FABP was found in human hepatocytes in both fetal and postnatal livers. FABP, therefore, might be a useful marker substance in the investigation of the physiology and pathology of the human liver.

Resident sinusoidal macrophages in the liver of the brown bullhead (Ictalurus nebulosus): an ultrastructural, functional and cytochemical study

Ultrastructural, functional, and cytochemical characteristics of resident sinusoidal macrophages (RSM) in brown bullhead (Ictalurus nebulosus) liver were examined. Following perfusion fixation of the hepatic vascular bed, light micrographs revealed RSM that possessed multiple elongate cytoplasmic processes and frequently contained erythrocytes in various stages of degradation. Following brief perfusion fixation, light microscope examination of vibratome sections of bullhead liver reacted for peroxidase revealed intensely positive RSM. By transmission electron microscopy, peroxidase activity was localized to the nuclear envelope and cytoplasmic granules of RSM and in endothelial and perisinusoidal fat-storing cells. In cryostat sections of fresh-frozen liver, glucose-6-phosphate dehydrogenase (G-6-PDH) was uniformly distributed over hepatocytes, whereas intensely positive punctate staining for G-6-PDH was localized over RSM. To test for phagocytosis by RSM, latex beads (0.81 micron) were injected into a tributary of the hepatic portal vein 2 min prior to perfusion fixation. Latex beads appeared either singly or in dense aggregates within RSM. Ultrastructurally, RSM were characterized by an irregularly shaped, eccentrically located nucleus, electron-dense vacuoles, small patches of granular endoplasmic reticulum, a well-developed Golgi apparatus, elongated mitochondria, desmosomes or desmosome-like densities that served as a source of attachment to endothelial cells, and a centriole with radiating microtubules. Invaginations of the plasma membrane (vermiform processes) characteristic of mammalian Kupffer cells were not observed in bullhead RSM. The results indicated a resident cell population of sinusoidal macrophages in the bullhead liver with properties that partially resembled mammalian Kupffer cells. These results are important for the identification of the normal resident cells in the bullhead liver.

Stellate cells storing retinol in the liver of adult lamprey, Lampetra japonica

Distribution, localization and fine structure of the stellate cells in the liver of lamprey, Lampetra japonica, were studied during the spawning migration by use of Kupffer's gold-chloride method, fluorescence microscopy for vitamin A (retinol) and electron microscopy. The stellate cells in the lamprey liver differ in some of their properties from those in mammalian livers. Stellate cells which store abundant retinol in lipid droplets, occur not only in the hepatic parenchyma, but also in the dense perivascular and capsular connective tissue of the liver and in the interstitium of pancreatic tissue. In the hepatic parenchyma these cells are located perisinusoidally or along thick bundles of collagen fibrils. The stellate cells display a number of large retinol-containing lipid droplets, granular endoplasmic reticulum, tubular structures, dense bodies. Golgi complex, microtubules, and microfilaments. In the space of Disse, the stellate cells and extracellular fibrilar components such as collagen fibrils and microfibrils (11-12 nm in diameter) are intervened between the two layers of basal laminae. Differentiation and possible functions of the stellate cells in the lamprey liver are discussed.

Characterization of desmin-positive rat liver sinusoidal cells

Hepatic sinusoidal lining cells were isolated from mature male rats (12 months old) and cultured in order to clarify the characteristics of the Ito cells (fat-storing cells). Desmin staining was used as a marker in the isolation of the Ito cells, and a highly purified desmin-positive cell fraction was obtained. Less than 10% of the desmin-positive cells were positive for vitamin A auto-fluorescence. However, the number of vitamin A-positive cells increased with vitamin A treatment, and they extended to over half of the desmin-positive cells by the first week of vitamin A treatment. The cultured Ito cells were positive for both desmin and vimentin stainings. On the other hand, Kupffer and endothelial cells were positive only with vimentin staining. Ito cells lost their fat droplets after repeated subculturing. The electron microscopic features of the Ito cells became similar to those of myofibroblasts, except for the absence of dense bodies, indicating that the Ito cells may have possibly transformed into myofibroblasts. Collagen fibers were occasionally found in the extracellular space. These results indicate that Ito cells retain both their myogenic and fibrogenic properties, and that lipocytes or myofibroblasts may be desmin-positive cells which maintain specific functions. Furthermore, staining of the intermediate filaments is useful in the identification of Ito cells, and a highly purified Ito cell fraction can be easily obtained using desmin staining as a marker.

Alcoholic liver injury: defenestration in noncirrhotic livers--a scanning electron microscopic study

The fenestration of hepatic sinusoidal endothelial cells in 15 needle biopsies obtained from chronic alcoholics without cirrhosis was studied by scanning electron microscopy. As compared to nonalcoholics, a significant reduction in the number of fenestrae and porosity of the sinusoidal lining wall (fractional area of fenestrae) was observed in acinar Zone 3, both in biopsies with and without Zone 3 fibrosis as judged by light microscopy. A significant reduction of porosity as shown in this study may influence the blood hepatocytic exchange and contribute to the alcohol-induced liver injury.

The blood hepatocytic barrier: a light microscopical, transmission- and scanning electron microscopic study

The normal blood hepatocytic barrier (BHB), comprised by the endothelial lining cells and the perisinusoidal space, was investigated, and it was concluded that the BHB is a complex structure in which each individual part serves several functions. Immunohistochemical staining for factor VIII showed endothelial lining cells to be positive. By TEM and SEM the endothelial cells were seen to be fenestrated without a basal lamina. They possess numerous endocytotic vesicles. The perisinusoidal space contains the lipocytes and a matrix composed of fibrils, and a microfilamentous to granular material. The nature of these matrix components was poorly analyzable by conventional methods. Lipocytes were visualized by LM in: sections stained with oil red 0 after fixation in Baker's formol-calcium and following post-fixation in dichromate, and toluidine-blue-stained Epon-embedded sections. TEM revealed numerous cytoplasmic processes rich in microfilaments encircling the sinusoids.

Tridimensional observation of fluorescent granular perithelial (FGP) cells in rat cerebral blood vessels

The tridimensional appearance and distribution of FGP (fluorescent granular perithelial) cells was studied by means of light and scanning electron microscopy. In young rats they first appeared as hexagonal cells in that were closely associated; later they transformed into slender forms and were loosely arranged. Scanning electron microscope observation gave a general view of FGP cells, their globular vacuolated inclusions, and their hypertrophied protrusion into the luminal surface of blood vessels. The nodular protrusions may be related to the limitation of blood flow in small cerebral blood vessels.

Proliferation of Ito cells (fat-storing cells) in acute carbon tetrachloride liver injury. A light and electron microscopic autoradiographic study

The proliferative activity of Ito cells in acute liver injury induced by carbon tetrachloride (CCl4) was studied by light and electron microscopic autoradiography. At 48 hours after a single intraperitoneal injection of CCl4, the livers of the mice given vitamin A per os for preceding 9 days and those of the mice without vitamin A-pretreatment were removed. Small tissue blocks of each group were respectively incubated at 37 degrees C for 1 hour in culture medium containing 3H-thymidine. After CCl4 injection, perisinusoidal and sinusoidal cells adjacent to centrilobular necrotic liver cells increased in number and size. Some of them were labelled by 3H-thymidine. On the other hand, the perisinusoidal and sinusoidal cells in the peripheral zone in which liver cells are not markedly degenerated nor necrotic showed no noticeable increase in number. They contained very few or no silver grains after 3H-thymidine. In control mice the labelling of perisinusoidal cells was hardly observed. Electron microscopic autoradiography revealed that most of the labelled perisinusoidal cells in the centrilobular zone possess characteristics of Ito cells in their location and in the fine structures such as the presence of small fat droplets, well-developed rough endoplasmic reticulum, and Golgi complex in the cytoplasm. These findings indicate that Ito cells incorporate 3H-thymidine in DNA synthesis after hepatocellular necrosis resulting in cell proliferation.

The sinusoidal barrier in rats with portacaval anastomosis: a morphometric study

Shunting of portal blood in the rat leads to liver atrophy and to an increase in arterial blood flow with microcirculatory disturbances. The aim of this study was to investigate the effects of these disturbances on the liver sinusoidal barrier (endothelial and perisinusoidal cells) using morphometric techniques. Rats with portacaval anastomosis (PCA) and sham operated pair-fed controls were studied 3 months after the shunt. Sinusoidal volume density in PCA increased but not significantly and the volume density (Vv) of total endothelial (EC) and perisinusoidal cells (PSC) increased by 104.54% compared to sham operated pair-fed rats. The increase of EC Vv was not associated with an increase in surface density (Sv) suggesting a fall in the number of small fenestrations and an increase in cell thickness. This interpretation supports the morphological observations. The increase of PSC Vv was mainly related to the increase in their subendothelial processes Vv and not to that of the cell body Vv. Lipids Vv and RER Sv expressed per sinusoidal cells remained unchanged suggesting that the balance between the 2 hypothetical functions of the PSC, namely fibrogenesis and storage of vitamin A, was maintained. In conclusion, changes of EC and PSC after PCA result mainly in thickening of the sinusoidal barrier. This increase may impair exchanges between the sinusoidal lumen and Disse space and contribute to functional abnormalities.

Freeze-replica study of lipid droplets in the Ito cells of rat liver

The structure of lipid droplets in the Ito cells was studied by the freeze-replica method in vitamin A-treated rats. Most lipid droplets were fractured in planes through their lipid contents. Some of them were surrounded by a membrane structure that had intramembranous particles (IMP), which were more numerous on the protoplasmic face than the exoplasmic face. Those with the membrane containing IMP correspond to the membrane-bounded lipid droplets (lipid droplets surrounded by lysosomes) seen in the electron microscopic observation of conventional thin section preparations. There were no lipid droplets showing concave or convex multilayered structures in the Ito cells from properly fixed livers. Since these multilayered structures were observed only in the materials fixed by immersion with glutaraldehyde or fixed 40 minutes after the death of animals, it is likely that they represent an artifact, showing an autolytic change, caused by poor fixation or postmortem change.

Fine structure and cytochemistry of lysosomes in the Ito cells of the rat liver

Ultracytochemical studies of the performic acid-phosphotungstic acid (PFP) reaction and acid phosphatase (ACPase) activity in the Ito cells (fat-storing cells) of the rat liver revealed two kinds of lipid droplets: one surrounded by a structure giving PFP- and ACPase-positive reactions, recognized as a lysosome, the other without such a reactive structure displaying a limiting membrane. To elucidate the function of the lysosomes surrounding lipid droplets, experiments were carried out on the following groups of animals: (1) Vitamin A-deficient rats were fed a normal diet containing vitamin A, and (2) hypervitaminosis A was experimentally induced in previously untreated rats. Lipid droplets were studied in both groups. No lipid droplets reappearing in an early stage after restoration of the regular diet were either membrane-bounded or surrounded by lysosomes. Lipid droplets surrounded by lysosomes could be seen in rats fully restored from vitamin-A deficiency and more frequently in animals suffering from hypervitaminosis A. It seems likely that as a result of the lysosomal activity in the immediate vicinity of the lipid droplets a degradation of the vitamin A-containing lipid droplets takes place in the Ito cells. Therefore, the lysosome-surrounded lipid droplets can be regarded as a sort of autophagolysosome; these lysosomes may play a role in preventing an unrestricted increase in the number and volume of lipid droplets.

Peliosis hepatis-like lesion in aging rats

The incidence of peliosis hepatis-like lesions in two-year-old Charles River-CD Sprague-Dawley rats (Charles River Breeding Laboratories, Wilmington, MA) was almost twice as high in males as females. Blood lakes developed from progressive expansion of sinusoids with destruction of the hepatic cell cords. The endothelial processes of the blood lakes had edematous swelling, vesiculation, and denudation. The microvilli of hepatocytes became swollen, blunted, and sloughed where the endothelial processes were disrupted. Subsequently, the hepatocytes were exposed directly to circulating blood cells and had degenerative changes with accumulation of red blood cells in the cytoplasm. The membrane-bound cysts were observed with the blood lakes and were bounded with atrophic hepatocytes or membranous wall extending to the Disse's space of adjacent hepatocytes. The cysts were filled with proteinaceous fluid, fibrin, and a few red blood cells. The wall of membrane-bound cysts consisted of endothelial processes extending from the endothelial cells of adjacent hepatocytes. The wall appeared to develop from adhesion of endothelial processes surrounding sinusoidal spaces of the hepatocytes following lysis of atrophic hepatocytes.

Fine structure of hepatic sinusoids and their development in human embryos and fetuses

The fine structure of the hepatic sinusoids of 81 human embryos and fetuses and their development from 5 to 12 weeks gestation were studied. At 5 weeks gestation, sinusoid-like structures and Kupffer-like cells were observed between liver cell cords. Between 6 and 8 weeks gestation the sinusoids were completely developed. Definite Kupffer cells appear at this developmental stage, when the bone marrow has not yet formed. Floating macrophages form cell aggregates in the sinusoids which contact endothelial cells and settle as Kupffer cells. Erythroblastophagia is observed in Kupffer cells and macrophages. The endothelial linings are closed, with the attenuated cell processes and intercellular junctions between the adjoining endothelial cells. No transition was observed between Kupffer cells and endothelial cells. The findings suggest that Kupffer cells in the human embryo are extrahepatic in origin and that they reach the sinusoids via the circulatory system. Ito cells, which store fat, originate from mesenchymal cells in the septum transversum.

The perfused human liver wedge biopsy: a new in vitro model for morphological and functional studies

We developed a simple and inexpensive method of perfusing small specimens of human liver in vitro that maintains short-term tissue viability as judged by protein transport function and morphological features. The technique allows investigation of liver function at the cellular level in normal specimens and those with hepatobiliary disease. Electron microscopy of specimens perfused with this system demonstrates the presence of an incomplete basement membrane within the space of Disse and shows that human microbodies contain crystalline-like cores morphologically similar to those found in rat liver.

Peliosis of the female adrenal cortex of the aging rat

Foci of apparent peliosis are regularly observed in the mid-zone of the adrenal cortex in female rats older than 600 days. The changes present range from ectasis of the sinusoids to extensive cystic change of the whole organ. This lesion occurs almost exclusively in female animals and was seen in only one of 50 male animals older than 600 days examined. Experimental stimulation or inhibition did not influence adrenal peliosis. Electron microscopically, there was marked pericapillary edema with collapse of the capillaries, and erythrocytes and thrombocytes were seen infiltrating the edema. Fibrin accumulated in the larger foci. Degenerative alterations were not observed either in the epithelial cells of the cortex or in mesenchymal cells. The pathogenesis is unknown, but the possible role of constant estrus in aging female rats will be discussed.