Submitted on March 28, 2003
Revised on August 25, 2003
Accepted on August 26, 2003
Inactive hepatic lipase in rat plasma
Xavier Galan, Julia Peinado-Onsurbe, Josep Julve, David Ricart-Jané, Monique Q. Robert, Miquel Lobera, and Ignasi Ramírez
Biochemistry and Molecular Biology, University of Barcelona, Faculty of Biology, Barcelona 08071
Corresponding Author: iramirez{at}ub.edu
Hepatic lipase is located in the space of Disse of the liver but also in capillaries of adrenal glands and ovaries. In addition, a small amount of hepatic lipase activity is reported in plasma. The relationship between hepatic lipase activity in liver, adrenal glands and plasma was examined in several physiological situations, with a highly significant correlation between activity in liver and adrenal glands. There is no agreement on subunit size of hepatic lipase in liver and adrenal glands, but this has not been studied in non-heparin plasma. Therefore, the subunit size of hepatic lipase in liver, adrenal glands and non-heparin plasma was compared. After 7.5% polyacrylamide gel electrophoresis, hepatic lipase in liver and adrenal glands appeared as a 55 kDa band. In liver, a faint band of lower size was also detected. In non-heparin plasma, hepatic lipase appeared as a doublet of 57 and 59 kDa. When activity/mass ratio was calculated, similar values were obtained for liver and adrenal glands. However, in non-heparin plasma, the activity/mass ratio was 1/240 of that in liver. After heparin administration in vivo, hepatic lipase activity in plasma increased nearly 100-fold with appearance of an additional 55 kDa band in post-heparin plasma. This band co-eluted with activity after preparative polyacrylamide gel electrophoresis. The difference in size was not due to alteration of the carbohydrate moiety, because the difference persisted after digestion with peptide-N-glycosidase F. A progressive increase in 57 and 59 kDa in post-heparin plasma followed disappearance of the 55 kDa band, suggesting that these larger bands originate from the smaller form. In plasma, both smaller and larger forms were associated with HDL, but not with LDL or VLDL. We conclude that rat plasma contains a larger form of hepatic lipase that is inactive in in vitro assay.
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