Elsevier

Hepatology Research

Volume 23, Issue 3, July 2002, Pages 185-195
Hepatology Research

Expression of cyclooxygenase 2 and cytosolic phospholipase A2 in the liver tissue of patients with chronic hepatitis and liver cirrhosis

https://doi.org/10.1016/S1386-6346(01)00177-2Get rights and content

Abstract

Cyclooxgenase (COX) and phospholipase A2 (PLA2) are crucial rate-limiting enzymes involved in the conversion of arachidonic acid to prostaglandin H2, the precursor of various compounds including prostaglandins (PGs), prostacyclin, and thromboxanes in the process of PGs' synthesis. Recent studies have shown increased levels of COX2 in adjacent cirrhotic tissue of hepatocellular carcinoma. The relationship between the expression of COX2 or cytosolicPLA2 (cPLA2) and liver fibrosis has not been described previously. We used 45 formalin-fixed, paraffin-embedded liver tissue samples obtained by needle biopsies from patients with chronic hepatitis, consisting of 7 cases of F0, 10 cases of F1, 10 cases of F2, 9 cases of F3 and 9 cases of liver cirrhosis (LC) according to the New Inuyama Classification of the staging of liver fibrosis. The expression of COX2 and cPLA2 was investigated by immunohistochemistry, western blotting and image analysis. The positive signals for COX2 and cPLA2 were observed in the cytoplasm of hepatocytes. The signal intensity of COX2 increased significantly with the progression of liver fibrosis (P<0.001) and no significant difference was observed in the relative amount of cPLA2 from group F0 to group LC. According to the New Inuyama Classification of hepatitis activity grading, 45 samples were classified as group A1 (23 cases), group A2 (19 cases) and group A3 (3 cases). No significant differences were found in the relative amount of COX2 and cPLA2 between group A1 and group A2–3. Significant correlation was observed between the relative amount of COX2 and hyaluronan (P<0.01). Our findings suggested that COX2 may be involved in liver fibrogenesis.

Introduction

Cyclooxgenase (COX) and phospholipase A2 (PLA2) are crucial rate-limiting enzymes involved in the conversion of arachidonic acid to prostaglandin H2, the precursor of various compounds including prostaglandins (PGs), prostacyclin, and thromboxanes in the process of PGs' synthesis. PLA2 plays a key role in numerous cellular processes by regulating the release of arachidonic acid (AA) from membrane phospholipids. AA is then converted to a prostanoid by cyclooxygenase (COX). There are at least two isoforms of COX: COX1 and COX2. COX1 is constitutively expressed in a wide variety of tissues while COX2 is a highly inducible gene that is expressed in response to a variety of proinflammatory agents and cytokines [1], [2]. Over-expression of COX2 has been demonstrated in various chronic inflammatory diseases and tumor tissues such as rheumatoid arthritis, ulcerative colitis, colon cancer and pancreatic cancer [3], [4], [5], [6], [7]. Although several studies have shown the up-regulation of COX2 in adjacent cirrhotic tissue of hepatocellular carcinoma and well-differentiated hepatocellular carcinoma [8], [9], the precise role of COX2 in hepatopathology remains unclear. Previous reports have shown that COX2 and cPLA2 expression were involved in various pathologic course [10], [11], [12], [13], [14], but there is little evidence whether the expression of COX2 and cytosolic phospholipase A2 (cPLA2) coordinately regulate the process of liver fibrogenesis. In this study, we investigated the relationship between the expression of COX2 or cPLA2 and liver fibrosis using immunohistochemistry, western blotting and image analysis.

Section snippets

Tissue samples

We used 45 formalin-fixed, paraffin-embedded liver tissue samples for immunohistochemistry obtained by needle biopsies from patients with chronic hepatitis, consisting of 7 cases of F0, 10 cases of F1, 10 cases of F2, 9 cases of F3, and 9 cases of liver cirrhosis (LC) according to the New Inuyama Classification [15] of the staging of liver fibrosis. All paraffin-embedded liver tissue samples came from patients of the Third Department of Internal Medicine, Hyogo College of Medicine during

The expression of COX2 and cPLA2 in the progression of liver fibrosis

Cytoplasmic staining for COX2 in liver cell was observed (Fig. 1). The relative amount of COX2 was 1.24±0.11 D.U. (mean±SD) in group F0, 1.33±0.09 D.U. in group F1, 1.42±0.11 D.U in group F2, 1.44±0.09 D.U. in group F3 and 1.51±0.07 D.U. in group LC. The signal intensity of COX2 increased significantly with the progression of liver fibrosis (P<0.001) (Fig. 2). The positive signals of cPLA2 were observed in liver cytoplasm (Fig. 1). In some cells, cPLA2 staining was observed in the cytoplasm

Discussion

Prostaglandins have been recognized as important mediators of hepatic, renal, cardiovascular and pulmonary normal functions and their synthesis alters during the courses of several physiopathological situations [16], [17]. Biochemical and genetic studies have pointed out COX2 and cPLA2 expression as the main contributor of prostanoid synthesis under pathological circumstances [10], [11], [12], [13], [14]. COX2 and cPLA2 expression has not been described previously in relation to liver fibrosis.

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