Studies were made on why glycyrrhizin injection decreases the plasma aspartate aminotransferase (AST) and alanine aminotransferase activities in patients with chronic hepatitis. For this, rat hepatocytes were isolated, and incubated with antibody raised against rat liver cell membranes, and the effect of glycyrrhizin on their release of transaminase was investigated. Isolated rat hepatocytes released AST on incubation with anti-liver cell antibody in the presence of complement. At this time, their endogenous phospholipase A2 activity was increased. Cultured hepatocytes also released the transaminase in the presence of venom phospholipase A2. Glycyrrhizin suppressed the release of transaminase in the presence of either anti-liver cell membrane antibody or phospholipase A2. These results suggest that antibody treatment raised the phospholipase A2 activity in liver cell membranes, resulting in release of transaminases, and that glycyrrhizin suppressed this increase in phospholipase A2 activity and so inhibited the release of transaminase.
The influence of glycyrrhizin on the effect of phospholipase A2 on lysosomes was studied. Treatment of rat liver lysosomes with venom phospholipase A2 caused release of acid phosphatase. This release of acid phosphatase was inhibited by 0.1 mM glycyrrhizin. Glycyrrhizin also inhibited acid phospholipase A2 with pH optimum of 4.5, which is thought to be present in the lysosomal membrane. These results suggest that glycyrrhizin stabilizes lysosomes by inhibiting phospholipase A2 activity in the lysosomal membrane.
Studies were made on the effect of phospholipase A2 on the stability of arterial wall lysosomes, and the influence of glycyrrhizin on this effect. Lysosomal phospholipase A2 activity was found to be increased in the aorta of hypercholesterolemic rats. Treatment of the lysosomal fraction of the arterial wall with venom phospholipase A2 resulted in release of acid phosphatase, and addition of glycyrrhizin (0.1 mM) inhibited this release. Lysosomal phospholipase A2 in the arterial wall was also inhibited dose-dependently by glycyrrhizin. These results suggest that lysis of lysosomes was due to increase in phospholipase A2 activity, and that glycyrrhizin stabilized the lysosomes by inhibiting phospholipase A2 activity.
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