Hepatic fibrosis. Correlation of biochemical and morphologic investigations

Fat-storing cells in the liver of rats kept on a low-magnesium diet

While studying the effect of low-magnesium diet on the rat liver considerable proliferation and enlargement of cells, identified as the Ito cells, has been observed. These events were accompanied by the accumulation of lipid substances in the cells. It is the authors' opinion that the lipid accumulation in the Ito cells is due to the deficiency in the lipid metabolising and transporting enzymes. Disturbances in the production of enzymatic proteins may result from the considerable and longlasting magnesium deficiency. The contribution of the fat-storing cells to the collagen biosynthesis is also discussed.

The synthesis of total and specific glycosaminoglycans during development of experimental liver cirrhosis

During hepatic fibrogenesis induced by long-term administration of thioacetamide, the synthesis of chondroitin 4,6-sulfate and hyaluronic acid was strongly enhanced; the formation of heparan sulfate comprising at least 70% of total liver GAG synthesis and of a keratan-sulfate-like fraction was stimulated 1.7 fold. Formation of dermatan-sulfate in liver could not be detected.

Abnormal liver function in chronic hypervitaminosis A

A case of chronic hypervitaminosis A is reported in a 57-year-old woman who took vitamin preparations for alopecia. Liver biopsy of the patient showed both an increase in the number and size of fat-storing cells on light microscopy and rapidly fading green autofluorescence of vitamin A. Electron microscopy confirmed the presence of engorged fat-storing cells in the space of Disse and minor toxic changes in hepatocytes. This case illustrates the early hepatic changes of chronic hypervitaminosis A and indicates a need for restriction of sales of vitamin preparations.

Liver collagen synthesis in murine schistosomiasis

Collagen synthesis was measured in liver slices obtained from mice with hepatosplenic schistosomiasis. Enlarged fibrotic livers from these mice contained 20 times more collagen than normal. This model of hepatic fibrosis results from an inflammatory granulomatous host response to Schistosoma mansoni ova in portal tracts, rather than from direct lover cell injury as with carbon tetrachloride-induced liver fibrosis. Collagen synthesis, as measured by the formation of labeled protein-bound hydroxyproline, occurred in granulomas isolated from fibrotic livers. Labeled collagen that cochromatographed with type I collagen was extracted with neutral salt solution from liver slices incubated with labeled proline. The free proline pool of the liver was doubled in infected mice; coordinately, liver slices from these animals showed maximal collagen production when the concentration of free proline in the medium was raised to 0.4 mM, the same level measured in the fibrotic livers. Under such conditions, collagen synthesis was at a rate equivalent to the formation of 5.4 nmol of protein-bound hydroxyproline per g liver in 6 h. In comparative incubations in medium containing 0.2 mM proline, fibrotic liver slices produced 16-fold more collagen than normal slices. The proline analogue, L-azetidine 2-carboxylic acid, effectively inhibited synthesis of labeled collagen by fibrotic liver slices. These studies show the synthesis of collagen in a reproducible animal model of the most prevalent form of human liver fibrosis. Difinitition of the controlling factors in this system is of interest for the general problem of fibrosis produced by immunological responses.

Collagen polymorphism in normal and cirrhotic human liver

Collagens in normal human liver and in alcoholic cirrhotic liver were investigated. Collagens were solubilized by limited proteolysis with pepsin under nondenaturing conditions, and after purification, were fractionated into types I and III by selective precipitation with NaCl. After carboxymethyl cellulose and agarose chromatography, the resulting alpha-chains from each of the collagen types were analyzed with respect to their amino acid and carbohydrate compositions. A comparison of the results obtained from normal liver with those from the diseases organ revealed no significant differences. The isolated human liver alpha1(I) and alpha1(III) chains were digested with CNBr and the generated peptides were separated and purified by a combination of ion-exchange and molecular sieve chromatography. The molecular weight and the amino acid and the carbohydrate compositions of each of the peptides were identical to those of the corresponding human skin peptides except for the slightly higher content of hydroxylysine in some of the peptides. The relative content of type III in relation to type I collagen in both normal anc cirrhotic liver was determined by digesting washed liver homogenates directly with CNBr and quantitating the resultant alpha1(I) and alpha 1(III) peptides after chromatographic separation. The relative quantities of these peptides indicated that normal human liver contained an average of 47% type III, with the remainder being type I. Cirrhotic liver, on the other hand, contained a significantly smaller proportion of type III, ranging from 18 to 34% in different samples, with a corresponding increase in type I. These findings indicate that although the amino acid and carbohydrate compositions of collagens deposited in cirrhotic liver are normal, the fibrotic process of alcoholic liver disease in humans is accompanied by an alteration in tissue collagen polymorphism, and suggest that the observed alterations may have pathogenetic implications.

Electron microscopic study of alcoholic liver disease with special attention to the changes of mesenchymal cells of the liver

The authors investigated electron microscopically the biopsy material of 48 chronic alcoholic liver patients. On the basis of clinical and histological criteria 5 stages were differentiated: fatty liver, fatty liver with increased mesenchymal activity, acute alcoholic hepatitis, chronic alcoholic hepatitis, alcoholic cirrhosis. In each group changes of liver cell organelles and mesenchymal cells were compared. In this investigation it was demonstrated that liver cell damage--except for acute alcoholic hepatitis was not parallel with the severity of the clinical picture. On the contrary, the proliveration of mesenchymal cells, signs of its secretory activity and fibre forming, were in correlation with the progression of liver disease. The authors suggest that an intermediate stage must be taken into account between acute alcoholic hepatitis and alcoholic cirrhosis: the chronic progressive alcoholic hepatitis. It reminds morphologically to a great extent of the active chronic hepatitis and it is characterized not by severity of the injury of liver cell organelles, but by great proliferation of mesenchymal cells and lymphoid infiltration.

Vitamin A-containing lipocytes and formation of type III collagen in liver injury

Hepatocellular necrosis in carbon tetracholride-induced injury of rats is associated with an accumulation of lipocytes (perisinusoidal cells or Ito cells) containing fat droplets and giving vitamin A fluorescence. In the subsequent formation of connective tissue septa, transitional cells having morphologic characteristics of lipocytes and fibroblasts are abundant and are associated with the appearance of type III collage-. The features suggest that the lipocyte is the precursor of the fibroblasts responsible for parenchymal fibrillogenesis and under these conditions forms type III collagen. The process is a postulated link between hepatocellular necrosis and fibrosis.

Enzyme histochemical study on fat-storing cells (so-called Ito's cell) of liver

Inorder to gain a foothold in clarifying the functional significance of fatstoring cells, an enzyme histochemical study on these cells was carried out. Fat-storing cells showed no alkaline phosphatase, acid phosphatase or esterase activity but demonstrated a marked gamma-glutamyl transpeptidase activity suggesting the possibility of its participation in the synthesis of fiber protein. This possibility was further heightened by its remarkable activity noted at the site of progressive fibrosis. Fat-storing cells under a normal condition partake in the formation of fibers supporting the sinusoidal wall, and under an abnormal condition gradually change their shape with loss of fat droplets and then transform into fibroblast-like cells closely related to the progress of fibrosis.

Factors stimulating collagen synthesis from the livers of hypercholesterolemic rats

Hypercholesterolemia was induced in rats by feeding them a high cholesterol olive oil diet. The livers were homogenized in modified Krebs-Ringer medium and centrifuged at 35,000 x g. The supernatants from livers of both hypercholesterolemic and normal rats were found to stimulate collagen synthesis in freshly isolated embryonic chick-tendon fibroblasts. However, this was significantly greater in the supernatants from fatty livers. The stimulating principle proceed to be dialyzable, non-lipid and heat-stable. There were at least two factors involved, the more effective of which was trypsin-sensitive, with a molecular weight below 2,000. The results suggest that a mediator is formed in the livers of hypercholesterolemic rats which might be responsible for the enhanced collagen synthesis of fibrotic processes vivo, e.g., in atherosclerosis and liver cirrhosis.

Hepatic collagen proline hydroxylase activity in alcoholic liver disease

The activity of hepatic collagen proline hydroxylase was examined in biopsy samples as a factor in collagen synthesis in 77 patients with alcoholic liver disease. The urinary excretion of peptide bound hydroxyproline was also measured in most of the patients, as an index of collagen degradation. The highest activities of collagen proline hydroxylase were found in the patients with alcoholic hepatitis. Enzyme activity was markedly increased in patients with non-specific changes on liver biopsy, whereas, patients with fatty infiltration had only mild elevations, and those with inactive cirrhosis had normal enzyme activity. Urinary hydroxyproline was elevated only in patients with alcoholic hepatitis and inactive cirrhosis. Follow-up determinations in 16 patients with alcoholic hepatitis, after 4 to 5 weeks, revealed a decrease in enzyme activity, but no change in urinary hydroxyproline. We conclude that among the types of alcohol-related liver diseases, alcoholic hepatitis is associated with the greatest turnover of hepatic collagen.

The heterogeneity of dermatan sulfate and heparan sulfate in rat liver and a shift in the glycosaminoglycan contents in carbon tetrachloride-damaged liver

The glycosaminoglycan of rat liver can be separated into five distinct fractions; a hyaluronic acid fraction, a heparan sulfate fraction with a molar ratio of sulfate to hexosamine (S/HexN) around 0.7, a heparan sulfate fraction with a S/HexN ratio around 1.4, a dermatan sulfate fraction with a S/HexN ratio near unity, and a dermatan sulfate fraction with a S/HexN ratio around 1.3. Enzymatic analysis of the two dermatan sulfate fractions indicates that they differ significantly in that the high sulfated fraction contains relatively more N-acetylgalactosamine 4,6-bissulfate units (about 26% of the total hexosamine). In experimental injury produced by carbon tetrachloride, the low sulfated fraction increases as much as 9-fold on a dry weight basis, bearing no linear relationship to the amount of the high sulfated fraction which increases only 2-fold. A significant shift is also observed in the levels of the two heparan sulfate fractions. In this case, however, the high sulfated fraction shows a much more pronounced increase than does the low sulfated fraction. On the basis of these observations, it is suggested that for each of the dermatan sulfate and heparan sulfate classes there are at least two pools, distinguished by sulfation degree and perhaps by turnover rate and physiological function.

Increase in type I and type III collagens in human alcoholic liver cirrhosis

Collagen in bulk was isolated in about 30% yield from the livers of normal human beings and from livers of persons with alcholic cirrhosis. Analyzed chemically and examined by electron microscopy, the collagen in each case was shown to consist of two types identical with, or resembling closely, type I and type III collagens of skin. The collagen from normal liver was predominantly type I, whereas, that from cirrhotic livers consisted or approximately equal amounts of the two types. By chromatography on carboxymethyl-cellulose, the type I collagen from the cirrhotic livers showed one alpha2chain and two alpha1 chains. The alpha1 chains were separable from one another, but gel electrophoretic patterns of peptides obtained from them after treatment with CNBr were almost identical, and resembled the pattern obtained with CNBr peptides of the alpha1 chain of rat skin type I collagen. The increased collagen of both types was responsible in part for the observed distortion of the architecture of the cirrhotic livers associated with increased rigidity of the stroma. The predominance of type III collagen in the areas of collapse of architecture where, as shown by others, few fibroblasts are present, suggests that hepatocytes might have an important function in fibrogenesis during the course of liver cirrhosis.

Effect of long-term administration of ethanol to the rat: lipids, collagen and other proteins, and Mallory bodies in the liver

Rats drank ethanol, on the average 1.20 g/100 g body weight, for various periods up to nearly 300 days. Experimental variables included a high-fat, low-protein diet, administration of additional ethanol by stomach tube, and CCl4 injections instead of ethanol. Growth was retarded by all the variables, especially by the high-fat, low-protein diet. The specific histological finding in the ethanol groups was the presence of Mallory bodies. Significant increase in total liver lipids was caused by ethanol, and rapid fat accumulation, inflammatory changes, and even fibrosis and cirrhosis by the high-fat, low-protein diet and the CCl4 injections. Ethanol raised the concentrations of collagen and soluble protein in the liver; the collagen content was increased also by the high-fat, low-protein diet and the CCl4 injections. The incorporation of proline to collagen was stimulated in incubated liver slices from both ethanol-treated and high-fat, low-protein-fed rats. These treatments also increased the concentration of free proline in the liver, thus augmenting the protein synthesis in fibroblasts.

[Immunohistochemical characterization of collagen in liver cirrhosis (author's transl)]

Using indirect immunofluorescence technique, 21 cases of hepatic cirrhosis of differing etiology were studied with type-specific antibodies to collagen type I, II, and III. In all cases the fibrous septa and portal tracts showed an increase in type III collagen. No fluorescence could be observed with antibodies to collagen type I and II. Thus, biochemical studies are supported which show, in addition to type III collagen, a new, as yet undescribed type of collagen in liver cirrhosis that is similar to type I collagen electronmicroscopically, but differs from type I collagen biochemically and immunologically. No correlation between the etiology of cirrhosis and the pattern of different collagen types could be found. The origin of different collagen types in liver cirrhosis is briefly discussed.

Liver cirrhosis: immunofluorescence and biochemical studies demonstrate two types of collagen

Pepsin solubilization of small and large noduled liver cirrhosis yielded two types of collagen (precipitated at 1.7 and 2.5 M NaCl concentrations) as demonstrated by electronmicroscopy. The 1.7 M NaCl precipitate was identified as type III collagen using an immunofluorescence technique. The 2.5 M NaCl precipitate appeared to be type I in the electronmicroscope. However, immunofluorescent and biochemical studies indicated that it was not type I but a type of collagen not yet described.

Activities of prolyl hydroxylase, lysyl hydroxylase, collagen galactosyltransferase and collagen glucosyltransferase in the liver of rats with hepatic injury

The activities of four enzymes catalysing post-translational modifications of the collagen polypeptide chains were assayed in the livers of rats with experimental hepatic injury. The liver injury was induced by injecting carbon tetrachloride twice weekly, and assays of the enzymic activities were carried out 2 and 4 weeks after commencement of administration of carbon tetrachloride. The liver homogenates were preincubated with Triton X-100 before the assays, because such treatment was found to increase the activities of all four enzymes in the supernatants of liver homogenates. The activities of all four enzymes had increased by 2 weeks after commencement of carbon tetrachloride administration. No increase was found in the collagen content of the livers at this stage and thus an increase in all four enzyme activities preceded an increase in the collagen content of the liver. A further slight increase was found in three of the enzyme activities during the subsequent 2 weeks of the experiment, whereas no further increase was found in the collagen galactosyltransferase activity. A statistically significant correlation was found between all four enzyme activities, but the magnitude of the increases varied considerably. The largest increase was found in lysyl hydroxylase activity, and at 4 weeks the magnitude of this was about three times that of the collagen galactosyltransferase activity. The results thus indicate that the increased enzyme activities cannot be explained simply by an increase in the number of collagen-producing cells having similar enzyme activity patterns to those of the cells initially present in the liver.

Collagen proline hydroxylase activity and 35S sulphate uptake in human liver biopsies

In an effort to assess connective tissue biosynthetic activity in human liver disease, collagen proline hydroxylase (a key enzyme in collagen biosynthesis) and the uptake of (35)S sulphate (a precursor of sulphated mucopolysaccharides) were measured in hepatic tissue obtained mainly by percutaneous biopsy.A procedure is described for the quantitation of collagen proline hydroxylase in cryostat sections which allows for the simultaneous histopathological examination of the liver specimen. A three to eightfold increase in the activity of this enzyme was found in four cirrhotic livers compared with the mean value of four normal livers and two biopsies from patients with Gilbert's syndrome. Elevated hydroxylase levels were found also in five patients with hepatic dysfunction but without cirrhosis (four alcoholics and one patient with persistent hepatitis associated with serum smooth muscle antibody). It is suggested that the hepatic level of collagen proline hydroxylase may be a useful quantitative index of fibroblastic activity in human liver disease. Autoradiographic studies of radioactive sulphate uptake in biopsy specimens from patients with chronic liver disease showed an exaggerated incorporation of isotope not only at sites of established fibrogenesis but also in the walls of sinusoids throughout the liver.

Types of 'reticulin' antibodies detected in human sera by immunofluorescence

Reticulin antibodies have been classified by immunofluorescence into five types reacting with distinct antigens of intra- and extracellular components in mesenchyme. Two types of fibrillar antigens can be distinguished on the basis of the staining patterns, anatomical distribution, and species specificity. A third antibody reacts with either small fibres, amorphous proteins, or mucopolysaccharides lining the hepatic sinusoids (ground substance antigens). In addition, at least two kinds of intrasinusoidal cells show cytoplasmic fluorescence, ie, Kupffer cells and glass-adherent, blood-borne cells antigenically related to peritoneal macrophages. Some sera may contain antibodies reacting with sinusoidal endothelial cells though this has not yet been proven. It has been confirmed that all these distinct antibodies related to reticulin antigens are most frequent in dermatitis herpetiformis and coeliac disease, but they are also found with increased frequency in chronic heroin addicts and in rheumatoid and Sjögren's syndromes. About 5% of normal individuals had such antibodies and no significant increase could be demonstrated in autoimmune disorders or in liver cirrhosis. The antibodies appear to be stimulated by bacterial or nutritional antigens and are likely to represent anamnestic responses rather than direct cross reactions with a multiplicity of foreign antigens.

Natural history of alcoholic hepatitis. IV. Glycosaminoglycuronans and collagen in the hepatic connective tissue

The extractable and nonextractable collagen and glycosaminoglycuronans (GAG) were estimated and characterized in 32 dried, defatted human livers obtained at necropsy. 10 had normal livers. 22 of the 32 livers were from patients who drank in excess: 5 had fatty livers, 7 had alcholic hepatitis, and 10 had cirrhosis. Livers with alcoholic hepatitis or cirrhosis had significantly increased total and 1 N NaCl-extractable collagen. Only alcoholic hepatitis livers had significantly increased Tris-buffer-extractable GAG, but the amino acid composition of these GAG (proteoglycans) was no different from that of normal livers. The major fraction of these GAG had isoelectric pH (pI) </= 3.1 in all livers. Livers with alcoholic hepatitis or cirrhosis had significantly increased nonextractable GAG. The major GAG fraction of all livers was chondroitin-4 or -6-SO(4). Alcoholic hepatitis livers had a significant increase of hyaluronic acid and an unidentified hyaluronidase-resistant GAG. Fatty livers showed no differences from normal ones. The data indicates that alcoholic hepatitis is associated with a significantly increased fibroblast activity, but fatty livers of alcoholics are not. The changes in histologically "inactive" micronodular cirrhosis of alcoholic patients indicate continued activity of fibroblasts in the connective tissue of these cirrhotic livers.

Inhibition of liver fibrosis by 1-azetidine-2-carboxylic acid in rats treated with carbon tetrachloride

L-Azetidine-2-carboxylic acid (AZC), an analogue of proline, has been shown to partially ameliorate hepatic cirrhosis induced in rats by CCl(4). AZC caused a diminution in formation of collagen in the liver accompanied by a relative decrease in the pool of free proline. The synthesis of noncollagenous proteins in the livers of treated rats did not appear to be affected.