“The Sinusoid” in the Liver: Lessons Learned from the Original Definition by Charles Sedgwick Minot (1900)

The hepatic sinusoid with its associated sinusoidal cells is a multifunctional cell‐complex in the liver. Despite recent advances in research on the hepatic sinusoid, no investigator has played a more basic role in its characterization than Charles Sedgwick Minot (1852–1914), a pioneer who distinguished the sinusoid from the blood‐capillary as early as 1900. According to Minot, sinusoids are typically larger in diameter than capillaries, particularly at the early embryonic stage. They closely approach the parenchymal tissue, are formed passively by the adjacent parenchymal tissue, and are on rare occasion surrounded with connective tissue. Sinusoids (sinus‐like) are small blood‐channels formed by subdivision of the lumen of large blood vessels (sinuses) by the invasion of developing parenchymal cell‐cords. Although some of Minot's definitions may no longer be accepted, he described some fundamental and interesting characteristics of sinusoids, to which we have not paid much attention. Here, we have attempted to illustrate lessons we have learned from Minot's view point of sinusoids at this occasion of centenary of his death. Anat Rec, 298:2071–2080, 2015. © 2015 Wiley Periodicals, Inc.     

Experimental Adenovirus Infection of the Mouse Adrenal Gland: II. Electron Microscopic Observations

A strain of mouse adenovirus, found to have a striking tropism for the weanling mouse adrenal gland, enabled electron microscopic examination of adrenals in various stages of infection. Nucleolar hypertrophy and the successive formation of three types of inclusion bodies in association with nucleoli preceded virion production. Angular crystals of virions formed in the affected nuclei. Virus was released by lysis of nuclear membranes; rapid degeneration of cytoplasmic organelles followed. Rupture of external cell membranes released virus into the extracellular spaces where virions crossed vascular basement membranes to enter endothelial cells. Virions were also phagocytized by inflammatory cells which reentered vascular sinusoids, and by adrenal parenchymal cells. Disruption of virus-laden phagocytic vacuoles in parenchymal cells released virions into the cytoplasm. Typical viral inclusion bodies also formed in vascular endothelial cells and in inflammatory cells, but virion replication was not detected. The possibility that virus directly entered parenchymal cells through the external cell membrane without phagocytosis is discussed.     

Dynamic microscopic anatomy of the fetal liver III. Erythropoiesis

Erythropoiesis was studied in the living fetal and neonatal rabbit liver in situ by in vivo microscopic and routine histologic methods. The results demonstrated in life: (1) that fetal hepatic erythropoiesis occurs extravascularly; (2) that individual erythroid cells late in their development pass by diapedesis from the extravascular compartment into the sinusoids; (3) that diapedesis occurs through the sinusoid wall in all parts of the hepatic lobule and possibly may be through the cytoplasm of the endothelial cells; and (4) that the sinusoid sphincters, the flow of blood through the sinusoids, and the intravascular adhesion of maturing erythroid cells to the endothelium affect the length of time that the erythroid cells remain in the sinusoids prior to their release into the peripheral circulating blood.     

A histochemical study of the liver lesion induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) in rats.

A histochemical study of plasma-membrane associated enzymes in rat liver demonstrated a significant lesion 3 days after a single oral dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin). The complete loss of canalicular ATPase reaction in the parenchymal cells of the centrilobular zone remained the prominent feature of the liver throughout the 6-wk period studied. Involvement of the periportal and midzonal regions occurred in moribund animals and improvement in the health of two surviving animals at 9 mth was associated with a normal distribution of ATPase in the liver. Qualitative changes in 5-nucleotidase and acid phosphatase were secondary to the parenchymal cell damage. This lesion supports the morphological evidence, reported previously, that the parenchymal cell plasma-membrane is a specific subcellular site of the toxic action of dioxin.     

Pathology of the liver sinusoids

The hepatic sinusoids comprise a complex of vascular conduits to transport blood from the porta hepatis to the inferior vena cava through the liver. Under normal conditions, portal venous and hepatic artery pressures are equalized within the sinusoids, oxygen and nutrients from the systemic circulation are delivered to the parenchymal cells and differentially distributed throughout the liver acini, and proteins of liver derivation are carried into the cardiac/systemic circulation. Liver sinusoid structures are lined by endothelial cells unique to their location, and Kupffer cells. Multifunctional hepatic stellate cells and various immune active cells are localized within the space of Disse between the sinusoid and the adjacent hepatocytes. Flow within the sinusoids can be compromised by physical or pressure blockage in their lumina as well as obstructive processes within the space of Disse. The intimate relationship of the liver sinusoids to neighbouring hepatocytes is a significant factor affecting the health of hepatocytes, or transmission of the effects of injury within the sinusoidal space. Pathologists should recognize several patterns of injury involving the sinusoids and surrounding hepatocytes. In this review, injury, alterations and accumulations within the liver sinusoids are illustrated and discussed.     

Pathologie entlang der sinusoidalen Wegstrecke: sinusendotheliale und perisinusoidale Befunde

Sinusoidal alterations unrelated to primary hepatocellular damage present without characteristic clinical findings and in these cases the liver biopsy is particularly important. Capillarization of sinusoids is characterized by closing of fenestration, formation of a basal membrane and by the expression of CD34 and is typical for active cirrhosis. In nodular regeneratory hyperplasia, capillarization indicates a local or general disturbance of perfusion. In large regenerative nodules, focal nodular hyperplasia and liver cell adenoma CD34-positive capillaries reflect afferent parts and CD34-negative sinusoids the efferent parts of the parenchymal vascular bed. HCC generally have a completely capillarized CD34-positive vascular bed. Hepatic angiosarcomas and epithelioid hemangioendotheliomas can be easily overseen in liver biopsies, if they spread along the sinusoids without detoriation of the acinar architecture and without significant alteration of the surrounding liver cell plates. Toxic damage of endothelial cells, post-sinusoidal stasis and sinusoidal hyperperfusion are the underlying pathogenetic principles of sinusoidal injury. Rupture and loss of the perisinusoidal reticulin fibres lead to peliosis hepatis. In these cases liver biopsy might disclose occlusion of the terminal liver veins (VOD). Perisinusoidal fibrosis can be caused by intrasinusoidal accumulation of pathologic cells, advanced intrasinusoidal macrophagocytic storage diseases and by activation of the vitamin A-storing hepatic stellate cells. Perisinusoidal amyloidosis can be the first sign of an underlying B-cell neoplasia.     

The Hepatic Microvascular System in Health and Its Response to Toxicants

This review briefly summarizes what is known about the dynamic morphology of the hepatic microvascular system that includes all vessels in the liver with a diameter less than 300 μm and various morphological sites within these vessels that regulate the distribution of blood flow. The latter include the various segments of the afferent portal venules and hepatic arterioles, the sinusoids, and central and hepatic venules. Sinusoids are unique exchange vessels lined by fenestrated endothelial cells which have important endocytotic functions and phagocytic Kupffer cells which are important for host defense. These are encircled by extraluminal stellate cells that are specialized pericytes containing fat droplets that store vitamin A. The principle sites for regulating blood flow are in the sinusoidal network with stellate and endothelial cells playing a major role in regulating the diameters of sinusoids and the distribution of blood flow in individual sinusoids, lobules, or segments of lobules. The sinusoidal endothelial cells are a sensitive and early target for several toxicants. For example, as early as 30 minutes after the administration of acetaminophen, the endothelial cells become swollen and begin to lose the ability to endocytose ligands. Within 2 hr, gaps through the cytoplasm appear formed by the destruction and/or coalescence of fenestrae which permit red blood cells to penetrate into the space of Disse. Subsequently, the sinusoid may collapse or disintegrate reducing blood flow. Anat Rec, 291:661–671, 2008. © 2008 Wiley‐Liss, Inc.     

Cellular and matrix changes in drug abuser liver sinusoids: A semiquantitative and morphometric ultrastructural study

The aim of the present work was to analyse, at the ultrastructural level, the action of heroin of 150 centrilobular sinusoids from liver biopsies of five intravenous drug abusers, who presented clinical and biological manifestations of hepatic impairment. A comparative study of 90 sinusoids from liver biopsies of three control patients was performed. Electron microscopic observations showed a thickening of the sinusoidal wall related to endothelial cell hypertrophy and to fibrosis of the space of Disse. This was generally associated with basement-membrane-like material and hepatocyte microvilli flattening. In addicts, hepatic vascular pole changes were a constant finding, accompanied by interhepatocyte space disjunction and perisinusoidal collagenization. Morphometric assessment confirmed a significant increase of sinusoidal wall surface, endothelial cell body and processes and Ito cell process surface was significantly different between the patient groups. This cellular hypertrophy may represent hyperactivation of the sinusoidal cell functional capacity, triggering the fibrogenesis in the space of Disse. While this mechanical barrier might hinder the free exchange through the space of Disse, it may equally well protect the liver against heroin toxicity.     

肝窦内皮细胞的窗孔调控与脂肪肝形成的研究进展

衬贴于肝血窦的肝窦内皮细胞具有无隔膜的窗孔,并汇聚成肝筛。窗孔相当于可选择超滤系统,有利于调控肝细胞与肝窦血液的物质交换,尤其是在脂质代谢方面,窗孔结构异常是脂质代谢紊乱的重要因素。本文就窗孔的超微结构、开窗机制和调控因素以及与脂肪肝相关联系的进展做一综述。     

Helicobacter pylori induces lymphocyte activation in peripheral blood cultures.

Immunohistological assessment of Kupffer cells was made using the antibody MAC387 and an antibody to lysozyme. Autopsy liver samples from 13 fetuses aged from 17 weeks gestation to term, and from 10 neonates and children aged 1 day to 18 months, were studied. For comparison, 10 normal adult autopsy liver specimens were included. The number of positively staining cells per unit area was counted for periportal sinusoids (zone 1) and centrilobular sinusoids (zone 3). No difference was found between zone 1 and zone 3 macrophage numbers with either antibody at any stage of development. Hepatic sinusoidal macrophage numbers were low during early gestation but increased during intra-uterine life to reach approximately normal adult values in the neonatal period. The numbers of cells staining with MAC387 or lysozyme were similar in each case except for hepatic sinusoidal macrophages in fetuses of less than 30 weeks gestation. Here anti-lysozyme stained significantly fewer cells, suggesting that lysozyme production may be low in immature fetuses. No difference was found between infants of similar maturity who had died immediately or had lived for more than 48 h and hence been exposed to gut antigens.     

Alcohol-associated capillarization of sinusoids: A critique since the discovery by Schaffner and Popper in 1963

This article reviews the literature on capillarization of hepatic sinusoids since its discovery in 1963. Liver sinusoidal endothelial cells are uniquely fenestrated and lack an underlying basement membrane. In chronic liver disease, the sinusoids capillarize and transform into systemic capillaries, a process termed capillarization of sinusoids. The histopathology is marked by defenestration, basement membrane formation, and space of Disse fibrogenesis. Capillarized sinusoids compromise the bidirectional exchange of materials between sinusoids and hepatocytes, leading to hepatocellular dysfunction. Sinusoidal capillarization was first described in active cirrhosis of alcoholics in 1963. Since then, it has been found in early and progressive stages of alcoholic hepatic fibrosis before the onset of cirrhosis. The sinusoidal structure is not altered in alcoholic steatosis without fibrosis. Defenestration impairs the ability of the endothelium to filter chylomicron remnants from sinusoids into the Disse's space, contributing to alcohol-induced postprandial hyperlipidemia and possibly atherosclerosis. Ethanol also modulates the fenestration dynamics in animals. In baboons, chronic alcohol consumption diminishes endothelial porosity in concomitance with hepatic fibrogenesis and in rats defenestrates the endothelium in the absence of fibrosis, and sometimes capillarizes the sinusoids. Acute ethanol ingestion enlarges fenestrations in rats and contracts fenestrations in rabbits. In sinusoidal endothelial cell culture, ethanol elicits fenestration dilation, which is likely related to its interaction with fenestration-associated cytoskeleton. Ethanol potentiates sinusoidal injury caused by cocaine, acetaminophen or lipopolysaccharide in mice and rats. Understanding ethanol's mechanisms on pathogenesis of sinusoidal capillarization and fenestration dynamics will lead to development of methods to prevent risks for atherosclerosis in alcoholism.     

Haemodynamic and ultrastructural observations on the rat liver after two-thirds partial hepatectomy*

Rat liver ultrastructure was investigated after partial hepatectomy (PH), by scanning and transmission electron microscopy. Portal pressure was monitored before and after PH and, after killing performed at 6, 12, 24, 48 h and 10 d, regenerating livers were fixed by portal vein perfusion under haemodynamic conditions identical to those existing in vivo. An early and persistent increase in portal pressure after PH was found (P<0.01 for normal vs sham-operated controls). Ultrastructural study showed sinusoid dilatation and disappearance of the sieve-plate arrangement of small endothelial pores, thus leaving the parenchymal liver cell surface directly exposed to portal blood. Widening of sinusoids, endothelial fenestrations, intercellular spaces and spaces of Disse, was accompanied by dilatation of bile canaliculi. At 10 d, liver ultrastructure had returned to normal. Our observations suggest that a rise in portal pressure, as a consequence of PH, may be related to the observed ultrastructural changes in the liver.     

Effect of hepatic venous outflow obstruction on pores and fenestration in sinusoidal endothelium.

The ultrastructure of pores and fenestrations in hepatic sinusoidal endothelial cells was examined following partial surgical occlusion of the suprahepatic portion of the inferior vena cava. Within 12 h after partial obstruction of hepatic venous outflow, endothelial pores (less than 0-1 mum in diameter) and sieve plates in the distal halves of sinusoids were greatly reduced in number or were totally absent, and they were replaced by large fenestration (less than 1-0 mum in diameter). These results suggest that pores forming sieve plates may fuse to form large fenestrations. The findings also indicate that sinusoidal hypertension and hypoxia associated with obstruction of hepatic venous outflow alter the distribution of pores and fenestrations in sinusoidal endothelium     

Benign Recurrent Cholestasis: A Light and Electron Microscopic Study with Emphasis on Sinusoidal Cells

A liver biopsy was performed on a patient with benign recurrent cholestasis. Cholestasis was mainly centrolobular with infiltration by sinusoidal macrophages. There was no necrosis. All the classic and specific ultrastructural criteria of cholestasis were observed in hepatocytes under electron microscopy. Perfusion-fixation of the biopsy allowed in addition a good visualization of sinusoids and sinusoidal cells. Numerous macrophages (Kupffer cells) with intense phagocytic activity were present in the lumen; some formed the sinusoidal barrier or were infiltrated in the Disse space. Endothelial cells contained numerous dense bodies and had few fenestrae. Cellular debris of hepatocytic origin which were not phagocytized in the Disse space were extruded in the lumen either through enlarged endothelial pores or by progressive invagination in the endothelial wall followed by outpouching in the sinusoid. In an enlarged Disse space containing amorphous material and collagen fibrils some perisinusoidal cells were transitional cells. These results indicate that pure cholestasis leads not only to hepatocyte injury with intense phagocytic activity but also to some degree of sinusoidal cell damage and extracellular matrix changes.     

An ultrastructural comparison of sinusoids in hepatocellular carcinoma, adenomatous hyperplasia, and fetal liver.

Transmission and scanning electron microscopic examinations were performed to evaluate the fine-structural differences in sinusoids of hepatocellular carcinoma, adenomatous hyperplasia of the liver, and fetal livers. In cancerous sinusoids, thickened endothelial cells with loss of sieve plates were conspicuous features. In the sinusoids of adenomatous hyperplasia, scanning electron microscopy showed apparent sieve plates, and basement membrane formation (capillarization) was less conspicuous than in carcinoma. In fetal livers, occasional large gaps as well as small fenestrations in the endothelium were noted. Basement membrane materials were not seen. It was concluded that the sinusoids of hepatocellular carcinoma lost the fine-structural nature of normal sinusoids and showed much more prominent capillarizations than the sinusoids of adenomatous hyperplasia, and that the fine structures of cancerous sinusoids were also different from those of the sinusoids in fetal livers.     

Development of ultrastructural heterogeneity among hepatocytes in the mouse

Ultrastructural stereological analyses of periportal and centrilobular hepatocytes of newborn, 5- and 10-day-old, and adult male ddY mice were carried out to study the postnatal development of the morphologic heterogeneity among hepatocytes. In newborn animals, the periportal and centrilobular cells did not differ in the volume densities of the smooth and rough endoplasmic reticulum; in the volume and numerical densities of the mitochondria, lysosomes, peroxisomes, and lipid droplets; or in the shape (the axial ratio) of the mitochondria. In 5-day-old animals, the volume densities of the mitochondria and rough endoplasmic reticulum were greater in periportal cells than centrilobular cells, and the volume density of the smooth endoplasmic reticulum was greater in centrilobular cells than periportal cells. In 10-day-old animals, a further difference was seen in the numerical density of the mitochondria, which was greater in centribular cells than periportal cells. Adult hepatocytes showed also a difference in the axial ratio of the mitochondria, which was greater in centrilobular than periportal cells; there was no difference in the volume density of the rough endoplasmic reticulum. When the data were expressed as volume and number per hepatocyte, the patterns of sublobular distributions of these organelles differed from the patterns seen in the volume and numerical density data, mainly in adult animals. This difference was caused by the marked increase in hepatocyte volume between 10 days of age and adulthood, especially in centrilobular cells. The results show that, in general, the ultrastructural heterogeneity among hepatocytes, evident in adult animals, is not present in newborn animals but arises during postnatal development, and suggest the occurrence of a lobular gradient in postnatal development of hepatocyte functions.     

Pathology of dietary carbonyl iron overload in rats

Serial light microscopic and ultrastructural studies were performed in rats with experimental iron overload produced by dietary supplementation with carbonyl (elemental) iron over a 12-month period. Hepatic iron increased rapidly to concentrations approximately 40 to 90 times those of control rats by 3 months. Within the liver, iron deposition was initially confined to periportal (zone 1) hepatocytes but subsequently extended to midzonal (zone 2) and centrilobular (zone 3) hepatocytes. Reticuloendothelial cell deposits of iron increased gradually and became prominent after 3 months. At this time, morphologic evidence of hepatocellular injury was mild and subtle with occasional foci of spotty necrosis and ultrastructural subcellular organelle damage. By 8 months, iron deposition was massive. Portal areas were enlarged with collections of iron-loaded macrophages and increased collagenous tissue. This portal fibrous tissue extended between periportal (zone 1) hepatocytes at sites of maximal iron deposition and around iron-loaded Kupffer cells and macrophages. At 12 months, the periportal (zone 1) fibrosis was more pronounced. These serial morphologic studies are the first to demonstrate the production of hepatic fibrosis by chronic dietary iron overload. This experimental model may reproduce important components of the pathophysiologic sequence of chronic liver damage seen in iron overload states in humans.     

Liver reconstruction on the chorioallantoic membrane of the chick embryo

The liver from a 6-day-old chick embryo was transplanted on the chorioallantoic membrane of a 9-day-old chick embryo to observe the process of liver regeneration histologically. When a piece of the liver was implanted on the chorioallantoic membrane, only cells in the superficial zone of the graft adhering to the chorioallantoic membrane survived. Eventually, these surviving cells in the superficial zone proliferated with hematopoiesis, resulting in the formation of clusters of blood cells surrounded by the hepatocytes (or hepatic parenchymal cells). Semi-thin serial sections showed that these clusters of blood cells were confined to the space formed by hepatocytes. Furthermore, structures similar to the hepatic cord, sinusoid, central vein, and bile duct appeared in the reconstructed liver eleven days after transplantation. Meanwhile, when a pellet of the dissociated liver cells was transplanted onto the chorioallantoic membrane, two types of liver like structures were reconstructed: one was clusters of hepatocytes accompanied by sinusoids after hematopoiesis, and the other was a simple accumulation of hepatocytes without any sinusoids or hematopoiesis. The sinusoids found in the former type became clear following the connection between the space in the transplant and vessels of the chorioallantoic membrane. These findings indicated that the reconstructed liver was primarily produced by the accumulation of hepatocytes accompanied by hematopoietic cells, followed by the formation of sinusoidal spaces. We therefore consider that hematopoiesis is important for liver regeneration with a normal structure. Transplantation of the liver in the chorioallantoic membrane could be also useful for research into liver regeneration.     

Expression of hepatocyte growth factor mRNA during oval cell activation in the rat liver

The customary wave of hepatocyte regeneration which occurs in the rat liver after two-thirds partial hepatectomy can be abolished by oral administration of the carcinogen 2-acetylaminofluorene. Instead, regeneration is achieved through the proliferation and differentiation of potential stem cells (oval cells) which appear to emanate from the portal space. Ultrastructural studies have illustrated the undifferentiated nature of these cells in the first 3 days after resection, but very rapidly they acquire features of small hepatocytes or biliary epithelia. Oval cell progeny can form either cohesive columns of cells within sinusoids which may later differentiate into new hepatic plates, or single cells that can insinuate within existing plates. Using a ³⁵S antisense riboprobe to hepatocyte growth factor (HGF) mRNA, the synthesis of HGF mRNA was observed in sinusoid-lining cells. There were few HGF mRNA-expressing cells in the liver removed at resection, but numbers steadily increased in the remnant over the next 7 days. In particular, an almost nine-fold increase in the density of HGF mRNA-producing cells occurred in the periportal areas, resulting in approximately double the density present within the centrilobular parenchyma. The superabundance of HGF-producing cells in the immediate vicinity of oval cell proliferation and differentiation strongly suggests that this growth factor is involved in all aspects of stem cell behaviour—proliferation, migration, and differentiation, through a paracrine mechanism.     

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.