Prevention of endotoxin-induced monokine release by human low- and high-density lipoproteins and by apolipoprotein A-I.

Interaction of endotoxin (lipopolysaccharide [LPS]) with human lipoproteins is known to prevent the LPS-induced activation of human monocytes and release of cytokines (monokines). LPS was exposed to lipoprotein classes separated by ultracentrifugation and to apolipoprotein A-I. Then monocytes were added, and the LPS activation of monocytes was determined by measuring the induced monokines. Failure of LPS to induce monokine release was called LPS inactivation caused by lipoproteins or apolipoproteins. The LPS inactivation is shown to be a function of low-density lipoproteins. High-density lipoproteins inactivate LPS to a much lesser extent. The very-low-density lipoproteins cannot inactivate LPS. Lipid components seemed not absolutely required for LPS inactivation, because purified human apolipoprotein A-I without its physiological lipid complement also inhibits LPS-induced monokine release.