Collagen metabolism in the liver

Serum laminin P1 in chronic viral hepatitis: correlations with liver histological activity and diagnostic value

Laminin is a major basement membrane-associated, non-collagenous glycoprotein of the extracellular matrix and is deposited in the space of Disse during sinusoidal capillarisation. Laminin P1, a pepsin-resistant fragment originating from the central portion of the cross-shaped laminin molecule, is detectable in serum and has been related to liver fibrosis and portal hypertension. In this study we investigated the behaviour of serum laminin P1, measured by radioimmunoassay, in a homogeneous group of 95 patients suffering from chronic viral hepatitis, types C or B, in order to determine the relationships between serum laminin P1 and each of the main histological aspects of the disease process (i.e. portal-periportal activity, lobular activity and fibrosis), which were assigned numerical scores. Moreover, we computed, at several cut-off levels, the sensitivity, specificity and positive and negative predictive values of laminin P1 in detecting both necroinflammatory activity and fibrosis in the liver. The results show that serum laminin P1 levels parallel the severity of liver disease, the highest laminin concentrations being observed in cirrhotic patients. They suggest also that serum laminin P1 should be considered a marker of the liver disease process as a whole, rather than a marker exclusively linked to fibrosis. Nevertheless, the usefulness of serum laminin P1 measurement, as investigated in this study, seems too limited to be recommended for routine clinical practice.

Comparison between wedge and needle biopsies for evaluating the degree of cirrhosis

To examine whether the biopsy method could affect histological evaluation, the volumetric ratio of human liver parenchyma was estimated in specimens from subcapsular and intralobar areas, and also in specimens obtained by needle biopsy (Tru-Cut needle). A new method of morphometric analysis was performed using a computer-aided color image analyzer. Eighteen cirrhotic, 7 fibrotic, and 4 normal liver biopsies were taken during hepatic resection and analyzed. The parenchymal cell volume ratio in the intralobar area was significantly correlated with that in the subcapsular area, and less significantly with needle biopsy samples (r = 0.844, p < 0.001; r = 0.577, p < 0.01, respectively). Both showed one-to-one correspondence. These results suggest that both wedged and needle biopsy samples are appropriate for assessing the degree of fibrosis or cirrhosis, although the sampling variability of the latter is greater than the former.

A light microscopic and biochemical study of carbon tetrachloride-induced pulmonary fibrosis in rats: the preventive effect of malotilate

Orally administered malotilate was studied as a protective anti-fibrotic agent with respect to experimentally induced pulmonary fibrosis in rats. Intraperitoneally-injected carbon tetrachloride (CCI4) significantly increased the lung weight to body weight ratio, lung total protein and total hydroxyproline content, while the relative protein content of the lungs decreased. CCI4) induction caused diffuse alveolar damage and inflammatory changes mimicking usual interstitial pneumonia with interstitial fibrosis. The morphological findings suggest a primary toxic effect on the lungs. Treatment with malotilate completely normalized the lung weight to body weight ratio, lung total and relative protein content and total hydroxyproline content. Morphologically, malotilate seemed to prevent the exudative inflammatory changes and interstitial fibrosis, but not the primary toxic effect of CCI4 on the capillary endothelium or the alveolar epithelium, the result of which was diffuse alveolar damage. It is concluded that malotilate may be a useful drug for the prevention of pulmonary fibrosis.

Measurement of connective tissue parameters in serum for diagnosis and follow-up of liver fibrosis

Hepatic fibrogenesis, i.e. activated synthesis and excessive intercellular deposition of connective tissue molecules (collagens, adhesive glycoproteins, proteoglycans) occurs in chronic alcoholic and viral liver injury and, less frequently, in some other conditions. The process may be monitored biochemically by the radioimmunoassay of some connective tissue molecules or their fragments and by the measurement of the activity of certain enzymes in serum. Currently, the radioimmunoassay of the aminoterminal propeptide of type III procollagen in serum reflects best the activity of liver fibrogenesis. The serum level of laminin, a high molecular weight basement membrane glycoprotein, was found to be correlated with an elevated portal venous pressure.

Dynamics of collagen accumulation and activity of collagen-degrading enzymes in the liver of rats with carbon tetrachloride-induced hepatic fibrosis

Liver fibrosis in rats was induced by repeated subcutaneous injections of carbon tetrachloride. Total collagen, soluble and insoluble collagen fractions as well as type I and type III collagen content in the liver were subsequently measured over a 3-18 week period. Liver collagen was found to increase exponentially during this time. Insoluble collagen accumulated more rapidly than soluble forms, and the accumulation of type III collagen was relatively greater than type I collagen. Changes in specific liver enzymes were also observed. Collagenase, collagenolytic cathepsin and collagen peptidase activities all increased. Levels of collagen-degrading enzymes increased rapidly during the first weeks of fibrosis-induction, and were followed by a more gradual increase during the remainder of the study.

Inhibitors of collagenolytic enzymes in the serum of patients with chronic liver disorders

Inhibitory effect of serum on collagenolysis was studied in rat hepatic slices. Sera of patients with cirrhosis contained low concentrations of inhibitors. Higher concentrations were found in sera from patients with chronic active hepatitis and chronic persistent hepatitis, than in healthy individuals. It is suggested that changes of the serum inhibitory activity are responsible for the control of collagen degradation in the injured liver.

Measurement of fibrosis in needle liver biopsies: evaluation of a colorimetric method

Collagen content was measured in 38 needle liver biopsies (8 steatosis, 8 chronic hepatitis, 7 fibrosis and 15 cirrhosis) by a new colorimetric method based on the selective capacity of Sirius red and Fast green to bind to collagen and noncollagenous proteins, respectively. The values were compared with those obtained after determination of the degree of fibrosis by morphometry in the same tissue. In biopsies with cirrhosis and fibrosis, there was a higher amount of collagen than in biopsies with chronic hepatitis and steatosis. Furthermore, there was a highly significant direct correlation between the collagen content measured colorimetrically and the degree of fibrosis determined morphometrically (r = 0.77, p less than 0.001), suggesting that this new colorimetric method is useful in measuring the degree of fibrosis in needle liver biopsies.

Electron microscopic study of liver fibrosis associated with diabetes mellitus

Electron microscopic studies of 13 cases of liver fibrosis associated with longstanding diabetes mellitus are presented. Comparing the centrilobular and periportal areas of the lobules there appeared to be a difference in the amounts of glycogen, fat, collagen and the character of mesenchymal cells. Centrilobularly, collagenization of sinusoids and pericellular accumulation of fibres appeared with the destruction of hepatic cells. In the periportal regions there was an accumulation of Kupffer's cells with active phagocytosis and centrally of Ito's cells and fibroblasts. The presented alterations were similar to the central pericellular fibrosis described in connection with morbid obesity. Despite the large number of available data on liver fibrosis there is still no satisfactory explanation for the pathomechanism of centrilobularly developing fibrosis.

Diagnostic value of serum procollagen peptide measurements in alcoholic liver disease

Procollagen type I carboxyterminal and type III aminoterminal peptide concentrations were measured in sera of 60 patients with alcoholic and 14 with nonalcoholic liver disease to study whether these assays are useful as clinical tests to differentiate various stages of alcoholic liver injury. Both propeptides were markedly elevated in alcoholic hepatitis and cirrhosis: procollagen type III peptide in 90% and type I peptide in 60-80% of these patients. Moderately increased values were found less frequently in patients with fatty liver. These tests did not differentiate patients with simple fatty liver from those with fatty liver and early fibrosis. There was a significant difference in serum procollagen type III peptide between fatty liver and both alcoholic hepatitis and cirrhosis (p less than 0.001), and in type I peptide between fatty liver and alcoholic hepatitis (p less than 0.005). Although serum peptide values correlated with the degree of liver fibrosis, appreciable overlap of values was found between the various groups. The peptide concentrations also seemed to be related to the degree of hepatic inflammation, and the highest values were observed in a subgroup of patients with alcoholic hepatitis in whom numerous Mallory bodies were found. The data suggest that in alcoholic liver diseases, serum collagen propeptide determination may be useful in diagnosing severe alcoholic hepatitis.

Aminoterminal propeptides of type III procollagen in human cerebrospinal fluid

The concentrations of aminoterminal propeptides of procollagen type III were determined by radioimmunoassay in the cerebrospinal fluids of 64 patients with various neurological disorders, including 4 infant patients (less than 1 year). In cerebrospinal fluids of adult patients with normal composition (protein, glucose, cell count), adult patients with pathologic composition, and infant patients the peptide levels (mean value +/- S.D.) were 4.07 +/- 1.26 micrograms/l, 8.15 +/- 6.78 micrograms/l, and 56.9 +/- 31.0 micrograms/l, respectively. The concentrations ranged from 1.96 to 265 micrograms/l and were independent of the respective serum propeptide levels. No statistic correlation with other parameters was found. Gel chromatography revealed a high degree of molecular weight heterogeneity, a substantial portion of immunoreactive material was eluted even with the void volume of Sephacryl S 300. Different slopes of radioimmunoinhibition curves indicate heterogenous antigenicity among the propeptides from various patients. Interaction of the propeptides with fibronectin and/or heparin is probably not responsible for the heterogeneity. The diagnostic potential of cerebrospinal fluid propeptide levels for local connective tissue (collagen) turnover remains to be elucidated.

Tipos de colágeno na fibrose hepática esquistossomótica de Symmers

Os AA. estudaram o tipo de colágeno em cortes histológicos de fragmentos de fígado de 12 indivíduos portadores da forma hepatesplênica da esquistossomose mansoni, pela técnica de coloração pelo Sirius Supra Red F3BA. Como controle usaram cortes histológicos de 12 fragmentos de fígado de indivíduos sem doenças fibrosantes. As preparações coradas pelo Sirius Supra Red F3BA e examinadas em microscópio de polarização (Leitz) revelaram que a fibrose periportal é constituída por colágeno de tipos I e III, com predominância do primeiro.

Increased serum procollagen III aminoterminal peptide in myelofibrosis

Myelofibrosis has been shown to involve an increase in type III collagen in the marrow. The aminoterminal procollagen III (PC III) peptide fragment is released during the production of PC III by fibroblasts and its serum level is therefore a marker for type III collagen synthesis. Using a recently developed sensitive radioimmunoassay, serum levels of PC III peptide were measured in 30 patients with myeloproliferative disease and 23 normal volunteers. Levels were found to be elevated above normal values in patients with polycythemia vera, even more elevated in patients with polycythemia and evidence of secondary myelofibrosis with myeloid metaplasia, and most strikingly elevated in patients with agnogenic myeloid metaplasia and severe marrow fibrosis. There was a significant association between serum levels of PC III peptide and the extent of reticulin fibrosis in bone marrow biopsies. Serum PC III level appears to be a quantitative marker for myelofibrosis.

Levels of type I and type III collagen in the bile duct of rats infected with Fasciola hepatica

Collagen types and their levels were compared between bile ducts from Fasciola infected rats and bile ducts from uninfected animals. Both collagen types I and III were shown to be increased in infected animals but, levels of type I increased less than type III. These results indicate that fascioliasis produces changes in the collagen composition of the bile duct that are similar to those produced in cirrhosis of the liver and other pathologic conditions including wound healing. Such observations suggest that a study of the chronology of collagen deposition in fascioliasis might provide information on the sequence of molecular events which result in bile duct hyperplasia.

The diagnostic potential of the combined determination of serum monoamine oxidase and N-acetyl-beta-D-glucosaminidase for fibroproliferative liver diseases

The simultaneous determination of the catalytic activities in serum of monoamine oxidase (EC 1.4.3.4) and N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30) was performed in patients with various non-liver diseases, acute hepatitis and fibroproliferative liver disorders (cirrhosis and fibrosis) and the predictive values of the positive (both activities are pathologically elevated) and negative test results (normal activity of monoamine oxidase and/or N-acetyl-beta-D-glucosaminidase) were estimated. It was found that the incidence of the positive result is extremely low (0.024, 5/207) in patients suffering from a great variety of non-liver and liver diseases (except cirrhosis) but rather great in liver cirrhotic subjects (0.44, 18/41). A fraction of only 0.07 of liver fibrotic patients had a positive test result. Based on these data the estimated predictive value of the positive result for liver cirrhosis at a prevalence of 0.03 is 0.47. This value increases strongly with higher prevalence of cirrhosis (population preselected for chronic liver diseases). The negative predictive value for cirrhosis and the positive value for fibrosis are low. Thus, the probability of the presence of cirrhosis in patients with suspected chronic liver diseases is great in cases of abnormally high activities of both monoamine oxidase and N-acetyl-beta-D-glucosaminidase. Negative test results (normal catalytic activities of one or both enzymes), however, do not prove the absence of liver cirrhosis and/or liver fibrosis.

Intrahepatic synthesis of immunoglobulin in liver disease

Patterns of intrahepatic immunoglobulin production were investigated by an in vitro biosynthetic labelling technique which measured the rate of Ig production in liver biopsy fragments. This technique depends on the incorporation of 3H-leucine into proteins synthesized by cells in the biopsy fragment and subsequently released into the culture medium, and precipitation of Ig with monospecific antisera. Intrahepatic Ig production was expressed as counts of radioactivity precipitated/g of liver tissue/24 h. Mean values were high in various inflammatory diseases of the liver, including alcoholic hepatitis (AH) (17 cases), IgG, 87.8, IgA, 105.6 and IgM, 14.7, chronic active hepatitis (CAH) (19 cases), IgG, 86.0, IgA, 56.1 and IgM, 12.6, and acute viral hepatitis (3 cases), IgG, 116.0, IgA, 61.0 and IgM, 32.0, but low in histologically normal livers (6 cases), IgG, 4.5, IgA, 4.8 and IgM, 4.7, alcoholic fatty liver (11 cases), IgG, 9.4, IgA, 11.4 and IgM, 7.1, and miscellaneous non-inflammatory conditions (10 cases), IgG, 8.7, IgA, 11.1 and IgM, 5.0. Photomicrographs were used to measure the density of plasma cells, expressed as cells/mm2 of liver biopsy tissue: mean counts were for AH 5.1, CAH 16.2 and normal liver 0.0. Intrahepatic Ig production in vitro did not correlate with the density of plasma cells in biopsy samples from cases of AH or CAH, nor with serum Ig levels.

Prothrombin determination in plasma and in liver biopsies in chronic liver diseases

Following ribosomal synthesis of the protein moiety of prothrombin, postribosomal carboxylation in the liver is necessary to obtain prothrombin ready for physiologic activation. Both decarboxyprothrombin and carboxyprothrombin can be determined by means of specific activators. Using synthetic substrates for thrombin, a micro-prothrombin assay suitable for functional determinations of decarboxy- and carboxy-prothrombin in liver biopsies was evolved. Decarboxyprothrombin was not found in plasma, independent of the kind of liver disease. Prothrombin determination in 31 liver samples showed no relation between the absolute concentration of carboxyprothrombin and decarboxyprothrombin and the kind of disease. The carboxyprothrombin fraction of total prothrombin was correlated with the activity of histologically estimated fibrosis in the liver.

Connective tissue components of the normal and fibrotic human liver. II. Clinical aspects

In this second part, clinical aspects of connective tissue metabolism in the liver will be described and two main aspects considered. The first is the possibility to monitor the activity of fibrosis by the use of metabolites and enzymes of connective tissue metabolism. In recent studies the qualification for this purpose of enzymes such as procollagen prolyl hydroxylase and lysosomal N-Acetyl-beta-glucosaminidase and the N-terminal peptide of procollagen type III has been tested. The serum activities or concentrations of these substances in patients with chronic active liver diseases increase in due relation to the histologically estimated activity of liver fibrosis. The second aspect deals with therapeutic approaches to fibrosis in the liver by using connective tissue specific agents. So far none of the antifibrotic substances such as proline analogues, colchicine, lathyrogens and penicillamine has been used in longer-term antifibrotic treatment.

Nonparenchymal cells cultivated from explants of fibrotic liver resemble endothelial and smooth muscle cells from blood vessel walls

Tissue specimens from human fibrotic liver obtained by needle biopsy were cultured. Two cell types emerged from the tissue explants. From their morphology and biosynthetic products they resembled smooth muscle cells and endothelial cells from blood vessel walls. In the "endothelial" cells, factor VIII-associated protein was demonstrated by indirect immunofluorescence. Synthesis of collagen types I and III, basement membrane collagen types IV and V, and fibronectin by both cell types was observed by immunofluorescence microscopy. Homogeneous cultures of "smooth muscle cells" were observed in subcultures. After incubation with [14C]glycine, collagen was isolated and characterized by CM cellulose chromatography, and consisted mainly of types I and III. These data suggest involvement of mesenchymal cells in hepatic fibrosis; they presumably originate from blood vessel or sinusoidal walls.

Connective tissue components of the normal and fibrotic liver. I. Structure, local distribution and metabolism of connective tissue components in the normal liver and changes in chronic liver diseases

The first part of this review describes the chemistry, the occurrence and the metabolism of extracellular connective tissue components in the liver. The normal liver contains typical connective tissue proteins (collagens, structural glycoproteins and proteoglycans) not only in vessel walls, perivascular areas and in the capsule, but they occur also in small amounts in the parenchyma, mainly in the space of Disse along the sinusoidal walls. The "interstitial" collagens type I and III represent the major amount of collagen in the normal as well as in fibrotic liver, showing a relative increase of type III in fibrosis. Basement membrane collagens type IV and V as well as the cysteine-rich collagenous components "7 S collagen" and "short chain collagen" have been shown to occur in extracts prepared after limited pepsin digestion. In the normal liver, basement membrane collagen can hardly be detected within the parenchyma by immunofluorescence microscopy; increased occurrence, however, can be shown along the sinusoids even in early stages of chronic liver diseases. The glycoprotein fibronectin was shown to be distributed very similarly to collagens type I and III, whereas the basement membrane specific glycoprotein laminin is restricted to vessel walls and the epithelial layer of bile ductuli in the normal liver but is also found in the parenchyma in fibrosis. Occurrence of proteoglycans is increased in fibrosis: a change in the composition of glycosaminoglycans from mainly heparan sulfate in the normal to dermatan- and chondroitin sulfate in the fibrotic liver was observed. It is not yet clear which cell type is mainly responsible for increased connective tissue synthesis in fibrosis. The occurrence of cells resembling smooth muscle cells ("myofibroblasts") in connective tissue septa of fibrotic livers and the fact that similar cells which actively synthesize collagen grow from explants of fibrotic livers may indicate the significance of this cell type in the process of liver fibrosis.

Morphologic alterations in patients with alpha-methyldopa-induced liver damage after short- and long-term exposure

Alpha-methyldopa-induced histologic alterations were investigated in 21 patients with hepatic injury after short- and long-term exposure. Seven patients developed liver injury within 6 months and 24 after several years (mean, 5 years) of exposure. Histologic findings and clinical and biochemical data differed significantly in the two groups. Morphologic analysis of the short-term-treated group revealed marked parenchymatous degeneration, focal, confluent and massive necrosis, and inflammation. Fatty accumulation and increased fibrous trabeculae were characteristic for the patients treated for long term. All patients in the short-term-exposed group had acute and severe hepatitis. Four of them had icterus. Two patients died of hepatic coma. Patients in the long-term-treated group had for several months initially mild but increasing discomfort, dyspepsia, nausea, and colics. Liver function tests in these groups revealed differences in serum albumin, bilirubin, and transferase levels. No changes were observed in alkaline phosphatase and Thrombotest. Fat accumulation and fibrous trabeculae suggest that the alterations precede the clinical symptoms and biochemical signs of hepatitis. The findings show that alpha-methyldopa may induce hepatocellular injury after short- and long-term exposure.

Radioimmunoassay for type III procollagen peptide and its application to human liver disease

A sensitive and specific radioimmunoassay was developed for the precursor-specific peptide segment located at the amino end of bovine type III procollagen. Human material showed high cross-reactivity in this assay. Two forms of human procollagen peptides were detected in body fluids. The larger peptide (45K) was found in serum and ascites, and resembled the whole precursor-specific segment which is presumably released from human type III procollagen by a single enzymatic cleavage. The smaller peptide (10K) was found mainly in urine indicating that further degradation of circulating procollagen peptides is required prior to their passage through the kidney. Compared to peptide concentrations in normal human serum two to twenty-fold increases were observed in all patients with alcoholic liver disease, in fifteen of seventeen patients with acute hepatitis, and in ten of fourteen patients with chronic active hepatitis. Much higher levels were detected in ascites fluid. Patients with rheumatoid arthritis and other diseases showed far smaller elevations of the serum peptide. In alcoholic liver disease peptide levels correlated well with inflammation and necrosis observed in liver biopsies, but not with other laboratory parameters.

Studies of nucleic acid and collagen synthesis: current status in assessing liver repair

Much progress has been made in delineating biochemical, physiologic and morpholigic events in liver regeneration and collagen synthesis. Pharmacologic agents have been purported to be helpful in facilitating repair and preventing fibrosis. Objective indices are now available to monitor their effectiveness in man.