Altered lipid composition and differential changes in activities of membrane-bound enzymes of erythrocytes in hepatic cirrhosis

Abstract

Lipid composition, fluidity, and Na +,K +—adenosine triphosphatase (ATPase), Mg 2+-ATPase, and acetylcholinesterase (AChE) activities of erythrocyte membranes were examined in comparison to plasma lipid composition and lecithin:cholesterol acyltransferase (LCAT) activities in 39 patients with hepatic cirrhosis due to viral hepatitis (Child-Pugh class A, n = 12; class B, n = 13; and class C, n = 14). Plasma LCAT activities decreased and the plasma free—cholesterol to phospholipid molar ratio ( C PL ) increased with progressive severity of hepatic cirrhosis. C PL and fluorescence polarization (inverse of fluidity) of erythrocyte membranes also increased with disease progression ( C PL : Child-Pugh A, 0.911 ± 0.010; B, 0.941 ± 0.011; C, 0.979 ± 0.028; and normal, 0.798 ± 0.010; fluorescence polarization: Child-Pugh A, 0.348 ± 0.002; B, 0.351 ± 0.002; C, 0.355 ± 0.002; and normal, 0.340 ± 0.002). There was a correlation between C PL and fluorescence polarization of erythrocyte membranes ( r = .629, P < .001). Na +,K +-ATPase activity of erythrocyte membranes did not differ between cirrhotic patients and normal subjects. On the other hand, Mg 2+-ATPase activity decreased in Child-Pugh C cirrhosis. AChE activity was decreased in Child-Pugh A cirrhosis, and decreased further in Child-Pugh B and C cirrhosis. AChE and Mg 2+-ATPase activities correlated inversely with fluorescence polarization ( r = −.652, P < .001 and r = −.381, P < .01, respectively). These results suggest that the free-cholesterol content of erythrocyte membranes increased in parallel with a decrease in plasma LCAT activity with progression of severity of hepatic cirrhosis, and that a resultant decrease in membrane fluidity affected Mg 2+-ATPase and AChE activities but not Na +,K +-ATPase activity. These membrane-bound enzyme activities may show different dependencies on membrane fluidity.