Evidence of different regulation of apolipoproteins A-I and B in human hepatoma HEPG2 cells under acute phase conditions

Abstract

Alterations in the release of acute phase proteins as one of the phenomena of an acute phase response are reportedly initiated by cytokines and glucocorticoids. To determine, whether apolipoproteins are similarly affected, human hepatoma HepG2 cells were exposed for up to 12 days to recombinant interleukin-6 (rhIL-6) either on its own or in combination 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 and α₂-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 glucocorticoid. A divergent effect of IL-6 and dexamethasone was also observed for α₂-macroglobulin, whereas they interacted synergistically in respect to fibrinogen, haptoglobin and albumin. Apparently, IL-6 and dexamethasone not only operate separately in the regulation of apolipoproteins but also of known acute phase proteins.