G. Pott

Distribution of collagen type I and type III and of two collagenous components of basement membranes in the human liver.

The distribution of collagen type I and III and of the basement membrane collagens type IV and alphaA (alphaB)2 in normal and fibrotic human livers has been studied by indirect immunofluorescence using type specific antibodies. Collagens type I as well as type III are present in normal livers in the blood vessel walls and the wall of biliary ducts of the portal tracts. In the parenchyma both types are visible along the sinusoids. Basement membrane collagens are only present in the connective tissue of portal canals and of central veins whereas in the parenchyma both type IV and alphaA (alphaB)2-collagen are nearly absent. In the tissue of fibrotic livers basement membrane collagens are also found in the parenchyma in similar distribution as type I and III.

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.

SummaryThe 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 the 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.ZusammenfassungIm ersten Teil dieser Übersicht werden die Chemie, das Vorkommen im Gewebe und der Stoffwechsel bindegewebstypischer extrazellulärer Komponenten in der Leber beschrieben. Die normale Leber enthält Proteine des Bindegewebes (Kollagene, Struktur-Glykoproteine, Proteoglykane) nicht nur in den Gefäßwänden, den perivasculären Bereichen und in der Kapsel, sondern sie sind auch im Parenchym in geringer Menge, vor allem im Disseschen Raum entlang den Sinusoiden nachweisbar.Die „interstitiellen“ Kollagentypen I und III bilden die Hauptmenge des Kollagens sowohl in der normalen als auch in der fibrotischen Leber; dabei ist der relative Anteil an Typ III in der fibrotischen gegenüber der normalen Leber erhöht. Die „Basalmembrankollagene“ Type IV und V sowie die cysteinreichen kollagenen Komponenten 7 S und das Kurzkettenkollagen (Intimenkollagen) konnten aus nach limitiertem Pepsinabbau gewonnenen Extrakten isoliert werden. In der normalen Leber sind die Basalmembrankollagene im Parenchym immunhistologisch kaum nachzuweisen; ein verstärktes Auftreten entlang der Sinusoide ist jedoch schon in frühen Stadien chronischer Lebererkrankungen sichtbar.Das extrazelluläre Glykoprotein Fibronectin tritt in der Leber in einer dem Typ I und III Kollagen sehr ähnlichen Verteilung auf, während das basalmembranspezifische Glykoprotein Laminin in der nicht-fibrotischen Leber auf Gefäßwände und Gallengangepithelien beschränkt ist und erst bei Fibrose auch in parenchymalen Bereichen nachgewiesen werden kann.Proteoglykane treten in der fibrotischen Leber ebenfalls vermehrt auf, eine Veränderung der Zusammensetzung der Glykosaminoglykane von überwiegend Heparansulfat in der normalen zu Dermatan-und Chondroitinsulfat in der fibrotischen Leber wurde beobachtet.Unklarheit besteht noch über den Zelltyp, der hauptsächlich zur vermehrten Bindegewebsbildung in der Leber beiträgt. Vermehrtes Auftreten von Zellen, die glatten Muskelzellen ähneln (Myofibroblasten) in den Septen fibrotischer Lebern und der Befund, daß aus Explantaten fibrotischer Lebern hauptsächlich ähnliche Zellen auswachsen, die eine aktive Kollagensynthese zeigen, können auf die Bedeutung dieses Zelltyps für die Fibrose hindeuten.

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

SummaryIn 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-β-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.ZusammenfassungIm zweiten Teil dieser Übersicht werden die klinischen Aspekte des Bindegewebsstoffwechsels in der fibrotischen Leber dargestellt. Besonders eingegangen wird auf die Möglichkeit, die Aktivität der Leberfibrose durch neuere Laborproben zur Erfassung von Enzymen und Metaboliten des Bindegewebsstoffwechsels zu verfolgen. Für diesen Zweck geeignet erscheinen die Enzyme Prokollagen-Prolyl-Hydroxylase, die lysosomale N-Acetyl-β-Glucosaminidase und das N-terminale Peptid vom Prokollagen Typ III. Die Aktivitäten bzw. Konzentrationen im Serum von Patienten mit chronisch aktiven Leberkrankheiten korrelieren gut mit der histologisch geschätzten Aktivität der Fibrose im punktierten Lebergewebe der gleichen Patienten. Weiterhin werden die therapeutischen Versuche zur Behandlung der Leberfibrose mit bindegewebsspezifischen Substanzen besprochen.

7 S Collagen: A method for the measurement of serum concentrations in man

A radioimmunoassay was developed for the detection of 7 S collagen, a basement membrane component derived from type IV collagen, in sera of patients. Two forms of 7 S collagen were isolated by limited collagenase digestion of type IV collagen from bovine placenta. Antisera against both forms were raised in rabbits. The antigens were labeled by conjugation with the Bolton Hunter reagent or by the Chloramine T method. Free and bound antigen were separated using a second antibody directed against rabbit-IgG. Serum concentrations of 7 S collagen ranged from 5-14 micrograms/l. Serum levels of 7 S collagen were increased in diabetic patients as compared to normal subjects.

Drug intoxication: influence of hemoperfusion on human plasma fibronectin.

SummaryFibronectin is a glycoprotein belonging to the opsonic system and able to mediate phagocytosis by the reticuloendothelial system (RES). Severe intoxications are often followed by a diminished capacity of RES-clearance. Patients with severe drug intoxications have lower concentrations of fibronectin in plasma than healthy persons. Charcoal hemoperfusion lowers plasma fibronectin by an average of 4.7 mg/dl. Initial values below 15 mg/dl did not undergo a significant decrease in the case of hemoperfusion. Regarding these findings, determination of plasma fibronectin seems a useful parameter for monitoring RES function during treatment of drug-intoxicated patients by hemoperfusion.

Collagen peptidase and type III procollagen peptide serum levels in chronic liver diseases

The concentration of the N-terminal peptide of procollagen III and the activity of collagen peptidase (PZ-peptidase) were measured in sera from 92 patients with chronic liver disease. In patients with liver cirrhosis and chronic hepatitis with transformation of liver structure, high values were found for both variables compared with hepatoses and chronic hepatitis without transformation. The concentration of procollagen III peptide and the activity of collagen peptidase in serum increased with increasing degrees of fibrosis and, even more markedly, with increasing degrees of mesenchymal activity in the liver.

Biochemical characteristics and cellular mechanisms of fibrotic processes

Fibrosis can occur as systemic disease or restricted to single organs; it is characterized by pathologic new-formation of connective tissue. Most fibrotic processes are characterized not only by proliferation but also by changes in the composition of the extracellular matrix and by qualitative changes of single components. There is no general tendency concerning the properties of the newly formed tissue, but there are considerable organ-specific differences. One reason for this diversity may be the participation of different cell types. In addition to typical connective tissue cells (fibroblasts, smooth muscle cells, “myofibroblasts”), cell types may be involved which have been shown to take up synthesis of connective tissue components under cell culture conditions.

Extracellular Matrix Proteins of the Vessel Wall: Are they Possible Markers of Atherosclerotic Processes?

Some of the main functions of the arterial wall are fulfilled by the extracellular matrix of this tissue: tensile strength and elasticity to withstand the pulsating blood stream and filtration functions in regulating the transport between blood and tissues. This extracellular matrix is composed of a variety of different macromolecular components. They can be grouped into several chemically defined classes such as collagens and proteoglycans (Table 1).