Reanalysis of the testosterone displacement from its HSA binding site by DHEA using competitive Langmuir isotherm

In a previous manuscript [C. Andre, A. Berthelot, J.F. Robert, M. Thomassin, Y.C. Guillaume, J. Pharm. Bio. Med., in press], the Mg2+ effect on the testosterone displacement equilibrium from its human serum albumin (HSA) binding site by DHEA was investigated using a thermodynamic approach. In this paper, a novel concept based on the competitive Langmuir distribution isotherms was proposed to calculate the association constant of the HSA-hormone binding and to confirm the Mg2+ role on the testosterone displacement equilibrium from its HSA binding site by DHEA. Thus, both the HSA-hormone binding and the displacement equilibrium processes were reanalysed. The results obtained confirmed that: - DHEA and testosterone bound on the same HSA site; - DHEA displaced well testosterone to its HSA binding site; - Mg2+ cation led a change on both the HSA-hormone binding and the displacement equilibrium at a critical Mg2+ concentration x(c) around 1 mM. (C) 2004 Elsevier B.V. All rights reserved.