Cholinesterase in fibroblasts grown in the presence of hypercholesterolaemic serum [proceedings].

Cholinesterase is widely distributed in the animal kingdom, but its function apart from its involvement in the process of cholinergic transmission is unknown. Recent evidence indicates a close association between lipids and cholinesterase. Hyperlipaemia in humans.(Cucuinau etal., 1968)andrabbits (Kutty etal., 1973) is associated with increased serum cholinesterase activity. Cholinesterase has been suggested to be involved in the removal of toxic esters during fatty acid metabolism in the liver (Clitherow et al., 1963) and reticuloendothelial cells (Ballantyne, 1967). Cholinesterase activity is high in adipocytes (Ballantyne, 1968). The development of artherosclerosis is associated with smooth-muscle-cell proliferation (Ross & Glomset, 1973) and cholesterol ester accumulation (Jackson & Gotto, 1976). In tissue culture, atherosclerotic changes, such as increased cholesterol ester synthesis and lipid accumulation, have been mimicked when both the smooth-muscle cells and fibroblasts are incubated in the presence of hypercholesterolaemic serum (Pearson, 1976). We grew rat (Sprague-Dawley) skeletal-muscle fibroblasts (Stein et al., 1976), and after six passages incubated them in the presence of media containing 10% of hypercholesterolaemic (test) and normal (control) serum from rabbits for 48 h in the presence of 2pCi of [“Clacetate per flask. At the end of the incubation, the cells were harvested after trypsin treatment, washed three times in 0.9% NaCl and extracted with distilled water containing 1 % Triton X-100. Cholinesterase activity in the extract was measured with acetylthiocholine as substrate (Kutty et al., 1977) and protein by the method of Lowry et al. (1951). Lipids were extracted with chloroform/methanol(2: 1 , v/v) (Folch et a[., 1957) and separated by t.1.c. (Gloster & Fletcher, 1966). Cholesterol and cholesterol ester spots were removed from the plate directly into scintillation fluid (PCS; Amersham/Searle, Don Mills, Ont., Canada) for radioactivity counting. The results in Table 1 show a significant increase in cholinesterase specific activity in the fibroblasts grown in the presence of hypercholesterolaemic serum. Under the same conditions there were also significant increases in synthesis of cholesterol ester and in the ratio of cholesterol ester to cholesterol. These results indicate increased synthesis of cholinesterase by the cultured cells. Such an increased synthesis of the enzyme may be necessary to remove toxic esters formed during accelerated lipid metabolism. Further studies should show whether similar changes in cholinesterase synthesis occur in the atherosclerotic initma.