Hepatic collagen proline hydroxylase activity in primary biliary cirrhosis

Enzymes of Fibrosis in Chronic Liver Disease

Introduction: Liver fibrosis has been extensively studied at the cellular and molecular level, but very few data exist on the final enzymatic stages of collagen synthesis (prolyl hydroxylase, PH) and degradation (matrix metalloproteinases, MMPs), particularly in primary biliary cholangitis (PBC). Aim: We studied enzyme activities in liver tissue from patients with chronic liver diseases and compared them to normal livers. Patients: Eighteen patients with PBC of early and late stages (Ludwig’s classification) and seven on treatment with ursodeoxycholate (UDCA) were studied and compared to 34 patients with alcoholic liver disease (ALD), 25 patients with chronic viral liver disease and five normal biopsies. Sera were available from a total of 140 patients. Methods: The tritiated water released from the tritiated proline was measured in PH assessment. 14C intact and heat-denatured collagen substrates were used to measure collagenase and gelatinases, respectively. 3H Elastin was the substrate for elastase. In serum, ELISAs were used for MMP-1, TIMP-1, and TIMP-2 measurements while MMP-2 and MMP-9 were estimated by zymography. Results: PH was significantly increased in early and late PBC. Collagenase was reduced only in the late stages (p < 0.01), where the ratio PH/collagenase was increased. UDCA treatment restored values to almost normal. Gelatinases were reduced in late stages (p < 0.05). In contrast to PBC and ALD fibrosis, collagen synthesis is not increased in viral fibrosis. The balance shifted towards collagen deposition due to reduced degradation. Interestingly, gelatinolytic activity is not impaired in ALD. Elastase was similar to controls in all diseases studied. TIMP-1 was reduced in early PBC and viral and alcoholic hepatitis and cirrhosis (p < 0.001). Conclusions: (1) There is evidence that collagen synthesis increases in the early stages of PBC, but the collagenolytic mechanism may compensate for the increased synthesis. (2) In viral disease, fibrosis may be due to decreased degradation rather than increased synthesis. (3) The final biochemical stages of liver fibrosis may be quantitatively different according to underlying etiology.

Biochemical markers of hepatic fibrosis

Most liver diseases lead to a pathobiochemical reaction termed liver fibrosis. This is a dynamic process implying different rates of progression or regression. Thus, histological examination of a liver biopsy is essential for a diagnosis but biochemical tests are necessary for assessing the activity of the process and monitoring its evolution. We review the most important constituents of liver connective tissue and the biochemical tests developed for evaluating liver fibrosis. The aminopeptide of type III procollagen is the most widely used parameter: two different radioimmunoassays have been developed with different affinities for the two circulating forms of the molecule. The determination of serum P3P reveals an elevation of blood levels both in acute and chronic liver diseases. In the first, serum P3P is an index of hepatic necrosis and inflammation which correlates with other biochemical parameters. In the second it is an index of active fibrogenesis. Moreover, in primary biliary cirrhosis this parameter is an independent prognostic variable and an important predictor of survival. Other immunoassays exist for different collagen cleavage products, but their clinical value is not established. Laminin and fibronectin are the principal structural glycoproteins in liver. Fibronectin determination does not seem to be of clinical value in liver disease. In contrast, serum laminin correlates with the severity of portal venous pressure in advanced liver disease. Its concentration parallels the severity of varices and may indicate the risk of bleeding. Hyaluronate is a high molecular weight polysaccharide, raised serum concentrations reflect both its increased synthesis by activated fibroblasts and its impaired catabolism by the liver. Thus, it may be useful for evaluating and monitoring the progression of chronic liver disease. The measurement of the activity of prolyl 4-hydroxylase as well as that of lysine oxidase and other enzymes has been proposed, but their clinical value is not sufficiently demonstrated. A panel of tests (e.g., laminin, hyaluronate and the aminopeptide of type III procollagen) seems to be recommended for a biochemical assessment of liver fibrosis in clinical practice.

Changes in serum and hepatic levels of immunoreactive prolyl hydroxylase in two models of hepatic fibrosis in rats

Changes in serum and hepatic levels of immunoreactive prolyl hydroxylase (IRPH) as well as cellular localization of the enzyme were studied in 2 models of hepatic fibrosis, which was induced in male rats either by subcutaneous administration of CCl4 (Group A) or by intraperitoneal injection of porcine serum (Group B). Hepatic fibrosis appeared at the 8th week in Group A and at the 12th week in Group B, and liver cirrhosis developed at the 16th week in both models. Although tissue contents of hydroxyproline (HP) and IRPH increased in both models, only HP levels correlated with the degree of fibrosis. Serum IRPH levels and serum asparate aminotransferase (AST) activities increased, showing a significant positive correlation, in group A, whereas both remained in a control range in Group B. Moreover, in another model which received a single intraperitoneal injection of CCl4, serum IRPH showed a marked increase and then a rapid decrease in parallel with the change in serum AST. Immunohistochemical analysis also showed a difference between the two fibrosis models: in group A, IRPH was positive mainly in parenchymal cells in the peripheral zone of the pseudolobulus, while in group B the staining was diffuse. These results indicate that the elevation of serum IRPH is, at least in part, due to the parenchymal cell damage, and that IRPH levels should be carefully evaluated when being used as a parameter to estimate the activity of fibrogenesis in the liver.

Serum lysyl oxidase activity in patients with various liver diseases

Serum lysyl oxidase activity was examined in patients with various liver diseases. The activity of the enzyme was detected mainly in the serum fraction of the supernatant 80% saturated with (NH4)2SO4, and its molecular weight was estimated to be about 30,000 by Sephadex G-150 column filtration. Mean serum lysyl oxidase activity in 18 healthy controls was 129 +/- 50 (+/- SEM) cpm/ml and was significantly increased in patients with acute hepatitis, chronic active hepatitis, alcoholic liver disease and primary biliary cirrhosis, but not in those with chronic inactive hepatitis or liver cirrhosis. Serum lysyl oxidase activity was not correlated with the histological grade of hepatic fibrosis, but appeared to reflect active hepatic fibrogenesis in patients with liver diseases.

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.

Hepatic peptidyl prolyl hydroxylase activity and liver fibrosis--a prospective study of 94 infants and children with hepatobiliary disorders

To assess whether hepatic peptidyl prolyl hydroxylase (PPH) activity could serve as a practical quantitative indicator of hepatic fibrosis or aid in the categorization, diagnosis or prognosis of hepatobiliary disorders in infancy and childhood, the activity of this enzyme has been determined prospectively by a tritium release method in 97 biopsies from 94 infants and children with the following conditions: acute hepatitis of infancy, 10 patients; extrahepatic biliary atresia, 13; previous hepatitis of infancy, 8; alpha-1-antitrypsin deficiency, 6; chronic active hepatitis, 17; chronic persistent hepatitis, 5; glycogen storage disease, 5; and 25 patients with a miscellanea of other liver disorders. PPH activity was considered in relation to diagnosis, biochemical and histological abnormality and subsequent prognosis over a 4-year period. Five liver biopsies which showed no histological abnormality were considered as "controls" having PPH values of 0.72 +/- 0.47 (mean +/- S.D.). PPH activity was significantly elevated in acute hepatitis of infancy, 9 of the 10 infants having PPH greater than 1.66 units (i.e., mean +/- 2 S.D. of the "control" value). Nine infants (70%) with extrahepatic biliary atresia also had PPH activity above this value, as did two with alpha-1-antitrypsin deficiency and 12 patients all in different diagnostic categories. PPH activity did not correlate with hepatic fibrosis as indicated by hepatic hydroxyproline concentration or by histological assessment, or with biochemical tests of liver function within any diagnostic group or in the series as a whole. PPH activity was similar in biopsies with and without histological features of cirrhosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Liver procollagen prolyl hydroxylase in Opisthorchis viverrini infected hamsters after praziquantel administration

Infection of hamsters by the human liver fluke Opisthorchis viverrini elevated liver procollagen prolyl hydroxylase activity, reflecting increased collagen biosynthesis. The increase was proportional to the intensity of infection. However, the infected liver procollagen prolyl hydroxylase activity decreased after administration of praziquantel 300 mg kg-1 body weight, and approached normal levels two weeks after treatment. In the infected hamsters, praziquantel, at a curative dose, caused a transient increase in serum aminotransferase levels and a small but persistent rise in serum alkaline phosphatase. The drug, however, did not cause changes in these enzyme activities in the uninfected hamsters.

Increased liver prolyl hydroxylase activity in hamsters infected with the human liver fluke Opisthorchis viverrini

A parallel increase in liver collagen content and prolyl hydroxylase activity was observed in hamsters infected with the human liver fluke Opisthorchis viverrini. They were elevated at 2 weeks after infection, gradually increased to approximately 2-fold at 7-11 weeks of infection, and then declined as with duration of infection time increasing from 11 to 22 weeks.

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.

Hepatic prolyl hydroxylase and collagen synthesis in patients with alcoholic liver disease

Hepatic prolyl hydroxylase activity and collagen synthesis were measured in patients with alcoholic liver disease to determine the feasibility of using the enzyme prolyl hydroxylase as a marker of hepatic fibrogenesis. Alcoholic patients with liver histopathology consistent with normal, steatosis, alcoholic hepatitis, early cirrhosis, or advanced cirrhosis were analysed for liver prolyl hydroxylase activity and in vitro collagen synthesis. Prolyl hydroxylase activity and the rate of in vitro collagen synthesis were correlated when these parameters were measured in samples of the same liver biopsy. Mean prolyl hydroxylase activity was significantly raised in all groups of alcoholic patients with alcoholic liver disease, except those with steatosis, when compared with alcoholic patients with normal morphology. Alcoholic patients with early cirrhosis had enzyme activity (mean +/- SE: 1.367 +/-0.162 mU/mg protein) significantly raised over all other groups. Mean enzyme activity was less raised (0.985 +/- 0.097 mU/mg protein) in patients with advanced cirrhosis. The percentage of collagen synthesis in patients with early or advanced cirrhosis was also raised compared with alcoholic patients with normal morphology. Prolyl hydroxylase activity and the rate of collagen synthesis are significantly correlated (r=0.62). These findings suggest that hepatic prolyl hydroxylase activity is a useful indicator of hepatic fibrogenesis and its measurement on available liver biopsy tissue should be a potent diagnostic tool reflecting active fibrogenesis and predicting progression of alcoholic liverdisease.