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

Reduced collagenolytic activity of matrix metalloproteinases and development of liver fibrosis in the aging rat

Although moderate fibrosis is a histological hallmark of the aging liver, the molecular mechanisms underlying this phenomenon are little known. Here, we provide a comprehensive description of hepatic collagen expression and metabolism during natural aging in rats. Interstitial collagen accumulated significantly in the oldest animals, mainly in the periportal area (P<0.05, 19- vs. 2-month-old rats). This was ascribed to COL-III protein deposition (P<0.05 vs. 2-month-old rats), rather than COL-I. Conversely, the transcription activity of COL-III gene decreased (P<0.05) during the considered lifespan (2-19-months), whereas COL-I and transforming growth fator-beta1 (TGF-beta1) mRNA content was substantially unchanged. In the aged rats, hepatic matrix metalloproteinases (MMP) activity, (both MMP-1 and MMP-2) dropped significantly (P<0.05), with a concomitant increase of the inactive tissue inhibitor of MMP (TIMP-1)/MMP-1 complex (P<0.05). MMP-2 and TIMP-1 levels were weakly affected. All together, these results suggest that during natural aging, (i) COL III is the protein that accumulates preferentially in the liver; (ii) liver fibrosclerosis is mainly explained by a reduced proteolytic activity of matrix MMP, in which TIMP-1 seems to be a major regulating factor.

Molecular characteristics of dimethylnitrosamine induced fibrotic liver collagen

The molecular characteristics of purified pepsin solubilized collagen from rat liver was studied in control and dimethylnitrosamine administered animals. The alpha- and beta-chains of purified pepsin solubilized liver collagen were separated by subjecting the denatured collagen to SDS-polyacrylamide gel electrophoresis. The alpha 1(III) chains were resolved from the alpha 1(I) chains by interrupted electrophoresis with delayed reduction of the disulfide bonds of type III collagen. The aldehyde content of the purified pepsin solubilized collagen was estimated in control and experimental samples in order to assess the extent of collagen cross-links. Fibril formation curves were studied with purified pepsin solubilized collagen to see the rate of formation of cross-links within the fibrillar mesh. The results of the unreduced electrophoretic studies revealed a significant increase in the beta-subunit of type I collagen with a remarkable decrease of alpha/beta ratio in DMN treated animals. Reduction with beta-mercaptoethanol indicated the presence of type III collagen in the electrophoretic field with a proportionate increase on the 21st day. A significant increase in the aldehyde content and an increased rate of fibril formation were noticed in DMN induced fibrotic liver collagen. The data of the present investigation revealed that the DMN induced fibrotic liver collagen is more cross-linked than normal liver collagen and the deposition of type III collagen in more prominent than type I collagen in early fibrosis.

Serum collagenase activity in chronic liver diseases

To examine whether serum collagenase activity reflects the amount of hepatic collagenase in the fibrotic liver, we measured serum collagenase activity in 67 patients with chronic liver disease and in 26 healthy controls. Collagenase activity in serum was measured after reactivation by denaturing and dissociating the inhibitors with 3 M KSCN and 1 mM aminophenylmercuric acetate. Serum collagenase activity was 35% lower than control in chronic persistent hepatitis, 48% lower in chronic active hepatitis, 56% lower in liver cirrhosis and 68% lower in hepatocellular carcinoma. To interpret this finding of low serum collagenase activity, we measured serum concentration of TIMP (Tissue Inhibitor of Metallo-Proteinases). Serum TIMP concentration was increased as liver disease developed, and it was inversely correlated with serum collagenase activity. These results suggest that in this assay condition serum collagenase activity is influenced by TIMP, and thus may not reflect the amount of hepatic collagenase in patients with chronic liver disease.

Collagenase activity and collagenase-inhibitory factors of serum and bone marrow fibroblast-conditioned medium in chronic myelogenous leukaemia

Chronic myelogenous leukaemia (CML) is frequently accompanied by progressive myelofibrosis that is probably largely due to increased collagen production by bone marrow fibroblasts or decreased collagen degradation by collagenase. We investigated the activity of collagenase and collagenase-inhibitory factors (CIF) in serum and bone marrow fibroblast-conditioned medium obtained from patients with CML and healthy volunteers. The activity of both collagenase and CIF was significantly higher in the CML patients than in the normal volunteers. Our previous study showed that bone marrow fibroblasts from CML patients produce significantly more collagen than fibroblasts from normal subjects. Therefore, it appears that the in vitro production of collagenase and CIF by bone marrow fibroblasts is related to the degree of in vivo collagen production. and that both the increased collagenase and CIF activities are reflections of collagen overproduction in CML.

Serum collagenase activity in patients with chronic liver disease

To examine the clinical significance of serum collagenase activity in chronic liver disease, serum collagenase activity was determined in 50 patients with chronic liver disease and in 24 healthy controls. Collagenase activity was measured after reactivation by denaturing and dissociating the inhibitors with potassium thiocyanate and aminophenylmercuric acetate. In patients with chronic persistent hepatitis, serum collagenase activity was 37% lower than controls, 50% lower in those with chronic active hepatitis, 66% lower in those with cirrhosis and 68% lower in those with hepatocellular carcinoma. Serum collagenase activity was significantly and inversely correlated with serum levels of the aminoterminal propeptide of type III procollagen and type IV collagen 7S domain, indicating that serum collagenase activity decreased as liver active fibrogenesis and/or fibrosis occurred. In contrast, serum levels of the metalloproteinase inhibitor was 30% higher than controls in patients with chronic active hepatitis, 50% higher in those with cirrhosis and 80% higher in those with hepatocellular carcinoma and was inversely correlated with serum collagenase activity. These results suggest that in this assay condition serum collagenase activity is influenced by the metallo-proteinase tissue inhibitor and thus does not reflect the amount of collagenase in the fibrotic liver.

Ito cell expression of a nuclear retinoic acid receptor

Although it has been suggested that retinoids regulate Ito cell proliferation and collagen synthesis, little is known about the ability of Ito cells to respond to retinoids in vivo. Because retinoids may mediate their molecular effects through nuclear receptors, Ito cells were examined for the presence of one of these receptors, nuclear retinoic acid receptor-beta. The modulation of nuclear retinoic acid receptor-beta expression was also studied during cell culture and hepatic fibrogenesis. Northern hybridization analysis revealed that Ito cells freshly isolated from normal rat liver contained nuclear retinoic acid receptor-beta messenger RNA at levels significantly higher than those found in other hepatic cell types. Ito cells also contained messenger RNA for two other nuclear retinoic acid receptors, nuclear retinoic acid receptor-alpha and nuclear retinoic acid receptor-gamma. Using an antibody to human nuclear retinoic acid receptor-beta, the nuclear presence of this receptor was demonstrated in normal Ito cells. In contrast, Ito cells cultured for at least 7 days had no detectable messenger RNA or nuclear staining for nuclear retinoic acid receptor-beta despite a 20 +/- 5-fold increase in the messenger RNA level of another retinoid binding protein, cellular retinol binding protein. Analysis of Ito cells isolated from rats with carbon tetrachloride-induced hepatic fibrosis revealed an 81% +/- 3% decrease in nuclear retinoic acid receptor-beta messenger RNA levels in these cells when compared with normal Ito cells. No difference in the messenger RNA levels of cellular retinol binding protein was found in Ito cells isolated from either normal or fibrotic liver.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of hepatic fibrosis on Ito cell gene expression

While Ito cells appear to be a major source of increased matrix synthesis during hepatic fibrogenesis, the cellular changes that occur in these cells during liver fibrosis have not been well delineated. In this study we examined Ito cell gene expression in isolated cells from normal rats, and rats with carbon tetrachloride-induced fibrosis, in order to better define the changes occurring in these cells during this pathologic process. Specifically, we addressed three questions: (1) which matrix genes are over expressed in Ito cells in fibrotic liver; (2) do these cells increase their expression of the fibrogenic cytokine transforming growth factor-beta 1 (TGF-beta 1); and (3) do Ito cells change their phenotype during hepatic fibrogenesis as reflected by alterations in the expression of their intermediate filament genes? Northern hybridization analysis revealed that Ito cells isolated from fibrotic livers had significant increases in mRNA levels of types I, III and IV procollagen compared to normal cells, while no increases were found in hepatocytes, and Kupffer/endothelial cells had only an increase in type I procollagen mRNA. Analysis of other matrix proteins which increase during hepatic fibrogenesis revealed elevations in laminin B and fibronectin mRNA levels only in Ito cells. Increased Ito cell matrix gene expression was also associated with a 4-fold increase in TGF-beta 1 levels in these cells. No increase in TGF-beta 1 mRNA was found in hepatocytes, and less than a 2-fold increase was found in Kupffer/endothelial cells isolated from fibrotic livers.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagenase of hepatocytes and sinusoidal liver cells in the reversibility of experimental cirrhosis of the liver

In order to explore the cellular source(s) and the behaviour of the collagenolytic activity previously described in rat liver homogenates, in the reversibility of experimental cirrhosis of the liver, enriched suspensions of hepatocytes and of sinusoidal liver cells were obtained by a procedure which employs low EDTA concentrations and no bacterial collagenase. Cell suspensions were prepared from three different groups of animals: 1) normal controls, 2) rats with CCl4-induced cirrhosis of the liver, and 3) rats with swine serum-induced cirrhosis of the liver. Animals were sacrificed in each group upon completion of treatment and also after 3, 6 and 12 months. In each liver wet weight and collagen concentration were determined, and collagenolytic activity of both enriched cell suspensions was measured separately. In addition, histological studies of liver tissue and ultrastructural examination of cell suspensions were performed by standard procedures. Enriched suspensions of both normal hepatocytes and sinusoidal liver cells display Ca2(+)-dependent collagenolytic activities. Both cell suspensions obtained from each of the two types of cirrhotic livers show normal or slightly increased average levels of collagenase activity at the time of treatment discontinuation, when average liver collagen content ranges from 6 to 10-fold over normal, suggesting that the normal collagenase/collagen ratio is disturbed and that collagenolytic activity is deeply decreased in relation to the actual liver collagen load.(ABSTRACT TRUNCATED AT 250 WORDS)