EVIDENCE OF DIFFERENT REGULATION OF APOLIPOPROTEIN-A-I AND APOLIPOPROTEIN-B IN HUMAN HEPATOMA HEPG2 CELLS UNDER ACUTE-PHASE CONDITIONS

Alterations in the release of acute phase proteins as one of the pheno mena of an acute phase response are reportedly initiated by cytokines and glucocorticoids. To determine, whether apolipoproteins are similar ly affected, human hepatoma HepG2 cells were exposed for up to 12 days to recombinant interleukin-6 (rhIL-6) either on its own or in combina tion with dexamethasone. The quantities of the apolipoproteins A-I and B secreted daily were determined, and were compared with those of the known acute phase plasma proteins albumin, fibrinogen, haptoglobin an d alpha(2)-macroglobulin. The apolipoproteins responded differently to the mediators: while apo B was down-regulated by both mediators, apo A-I was not affected by the cytokine but stimulated by the glucocortic oid. A divergent effect of IL-6 and dexamethasone was also observed fo r alpha 2-macroglobulin, whereas they interacted synergistically in re spect to fibrinogen, haptoglobin and albumin. Apparently, IL-6 and dex amethasone not only operate separately in the regulation of apolipopro teins but also of known acute phase proteins.