Factors stimulating collagen synthesis from the livers of hypercholesterolemic rats

Mild hepatic fibrosis in cholesterol and sodium cholate diet-fed rats

To date, the majority of research on hypercholesterolemia has focused on the effects of a high cholesterol diet on atherosclerosis and coronary heart disease. The toxic effects of cholesterol on the liver and the relationship between the intake of a high cholesterol diet and hepatic fibrosis, however, have not been investigated clearly or histopathologically. Male Wistar rats were fed a diet supplemented with 1.0% cholesterol and 0.3% sodium cholate for 12 weeks. Rats were sacrificed and analyzed via blood biochemistry, traditional microscopy and immunohistochemistry. Following the feeding of this diet, the rates of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase and total cholesterol in the rats were elevated consistently from week 3 and throughout the remainder of the experiment. From microscopic observation, hepatic necrosis, macrophage infiltration and steatosis increased markedly throughout the experiment. Hepatic fibrosis and myofibroblast proliferation were detected at weeks 9 and 12. Mast cell appearance was proportional to the degree of hepatic damage. These findings suggest that hepatic fibrosis is inducible by a high cholesterol diet and is likely the result of the interaction between several different cell types (i.e., macrophages, myofibroblasts, and mast cells) in an inflammatory milieu. Hypercholesterolemia should be considered as a risk factor for hepatic fibrosis as well as atherosclerosis and coronary artery disease.

Collagen stimulating factors in hepatic fibrogenesis

Four factors which stimulate collagen synthesis and prolyl hydroxylase activity in cultures of human and mouse fibroblasts have been isolated by molecular sieve chromatography from animal and human fibrotic and cirrhotic livers. These factors do not stimulate protein or DNA synthesis or total DNA in these cultures. It has also been shown that these factors, designated collagen stimulating factors F1-F4, do not owe their activity to ascorbate or glutamine. Collagen stimulating factors are heat stable, and F1 and F2 have apparent molecular weights of about 4000 and 1000 respectively. Since these factors are not present in normal animal or human liver it is suggested that they may be responsible for increased collagen production in vivo in hepatic fibrosis and cirrhosis.

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.

Dependence of collagen synthesis by embryonic chick tendon cells on the extracellular concentrations of glutamine

An agent in rheumatoid synovial fluid which stimulates collagen synthesis by embryonic chick tendon cells was identified as glutamine. The stimulating effect was observed only at a subnormal concentration of proline (0.02 mM). The concentration of glutamine in rheumatoid synovial fluid is about 2.5 mM but it falls rapidly during storage even at -20 degrees C. Collagen synthesis is shown to depend on the extracellular concentrations of glutamine and proline in addition to any connective tissue activating factors.

Identification of glutamine as a hepatic factor which influence the synthesis of collagen by freshly isolated fibroblasts

Earlier we have found that 35,000 g supernatants of liver homogenates from both normal and hypercholesterolaemic rats stimulate the synthesis of collagen by freshly isolated fibroblasts. Supernatants from the fatty livers of hypercholesterolaemic rats showed greater stimulation. In the present study we fractionated the 35,000 g supernatants using gel filtration, ion-exchange chromatography, paper electrophoresis and paper chromatography. One of the stimulating factors turned out to be glutamine. However, the concentration of glutamine was the same in normal and fatty livers suggesting that glutamine is not responsible for the greater stimulating activity found in the 35,000 g supernatants from fatty livers. Authentic glutamine increased the synthesis of collagen by 40% at a concentration of 40 mumol/l but inhibited it 80% at 4 mmol/l, which is widely used in cell culture media. There, the concentration of glutamine should be controlled carefully in tests for collagen synthesis in vitro.

Effect of serum and liver extracts from hypercholesterolemic rats on the synthesis of collagen by isolated aortas and cultured aortic smooth muscle cells

Rats were made hypercholesterolemic by feeding them a high-cholesterol, olive oil diet for one week. The effect of sera and 35,000 X g supernatants of liver homogenates on collagen synthesis was studied in isolated aortas, cultured arterial smooth muscle cells and the same cells in suspension. Compared to the preparations from normal rats, the liver preparations from hyperlipidemic rats stimulated collagen synthesis in both isolated aortas and cultured smooth muscle cells by about 25%. In these test systems hyperlipidemic serum was without effect but when added to smooth muscle cells incubated in suspension, produced a significant increase in the amount of collagen secreted. Hyperlipidemic serum caused an increase of about 50% in the incorporation of [3H]-thymidine by cultured smooth muscle cells.